Method for producing fluoropolymer powder

文档序号：260963 发布日期：2021-11-16 浏览：33次中文

阅读说明：本技术 含氟聚合物粉末的制造方法 (Method for producing fluoropolymer powder ) 是由奥井千亚纪吉田裕俊佐藤洋之市川贤治加藤丈人山中拓于 2020-04-16 设计创作，主要内容包括：一种含氟聚合物粉末的制造方法,其特征在于,包括下述工序：工序(A1),在通过使用羧酸型烃系表面活性剂的聚合得到的含氟聚合物水性分散液中添加酸,将pH调整到4.0以下而进行凝析,得到包含下述通式(1A)所示的含氟化合物的湿润含氟聚合物粉末；和工序(B1),在超过150℃且小于240℃的条件下对上述湿润含氟聚合物粉末进行热处理。通式(1A)：H-(CF-(2))-(m)-COOH(式中,m为3～19)。(A method for producing a fluoropolymer powder, comprising the steps of: a step (A1) in which an acid is added to an aqueous fluoropolymer dispersion obtained by polymerization using a carboxylic acid type hydrocarbon surfactant, the pH is adjusted to 4.0 or less, and coagulation is carried out, thereby obtaining a wet fluoropolymer powder containing a fluorine-containing compound represented by the following general formula (1A); and a step (B1) of heat-treating the wet fluoropolymer powder at a temperature exceeding 150 ℃ and below 240 ℃. General formula (1A): h- (CF) 2 ) m -COOH (wherein m is 3 to 19).)

1. A method for producing a fluoropolymer powder, comprising the steps of:

a step (A1) in which an acid is added to an aqueous fluoropolymer dispersion obtained by polymerization using a carboxylic acid type hydrocarbon surfactant, the pH is adjusted to 4.0 or less, and coagulation is carried out, thereby obtaining a wet fluoropolymer powder containing a fluorine-containing compound represented by the following general formula (1A); and

a step (B1) of heat-treating the wet fluoropolymer powder at a temperature exceeding 150 ℃ and below 240 ℃,

general formula (1A): h- (CF)₂)_m-COOH

Wherein m is 3 to 19.

2. The production method according to claim 1, wherein the wet fluoropolymer powder contains 2 or more kinds of fluorine-containing compounds represented by general formula (1A).

3. The production method according to claim 1 or 2, wherein the wet fluoropolymer powder contains substantially no salt of the fluorine-containing compound represented by general formula (1A).

4. The production process according to any one of claims 1 to 3, wherein the fluorine-containing polymer is polytetrafluoroethylene.

5. A method for producing a fluoropolymer powder, comprising the steps of:

a step (A2) in which an acid is added to an aqueous fluoropolymer dispersion obtained by polymerization using an aliphatic carboxylic acid type hydrocarbon surfactant, the pH is adjusted to 4.0 or less, and coagulation is carried out to obtain a wet fluoropolymer powder containing a fluorine-containing compound represented by the following general formula (1A); and

a step (B2) of heat-treating the wet fluoropolymer powder at a temperature exceeding 100 ℃,

general formula (1A): h- (CF)₂)_m-COOH

Wherein m is 3 to 19.

6. The manufacturing method according to claim 5, wherein the temperature of the heat treatment exceeds 150 ℃ and is less than 240 ℃.

7. The production method according to claim 5 or 6, wherein the wet fluoropolymer powder contains 2 or more kinds of fluorine-containing compounds represented by general formula (1A).

8. The production method according to any one of claims 5 to 7, wherein the wet fluoropolymer powder contains substantially no salt of the fluorine-containing compound represented by general formula (1A).

9. The production process according to any one of claims 5 to 8, wherein the fluorine-containing polymer is polytetrafluoroethylene.

Technical Field

The present invention relates to a method for producing a fluoropolymer powder.

Background

In the case of producing a fluoropolymer by emulsion polymerization, a fluorine-containing anionic surfactant is used. Recently, the use of hydrocarbon surfactants instead of fluorine-containing anionic surfactants has been proposed and various studies have been made.

Patent document 1 describes a method for producing a modified polytetrafluoroethylene powder, which is characterized by comprising a step of removing or reducing a compound represented by the following general formula (1) or (2) from a polytetrafluoroethylene powder obtained by using a hydrocarbon-based surfactant.

General formula (1): (H- (CF)₂)_m-COO)_pM¹

(wherein M is 3 to 19, M¹Is H, a metal atom, NR⁵ ₄(R⁵The same or different, H or an organic group having 1 to 10 carbon atoms), optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium. p is 1 or 2. )

General formula (2): (H- (CF)₂)_n-SO₃)_qM²

(wherein n is 4 to 20. M)²Is H, a metal atom, NR⁵ ₄(R⁵May be the same or different, and is H or an organic group having 1 to 10 carbon atoms), an imidazolium having or not having a substituent, a salt thereof, a hydrate thereof, a solid thereof, a pharmaceutical composition containing the solid, a pharmaceutical composition comprising the solid, a carrier, and a pharmaceutical composition,Pyridinium with or without substituents, or phosphonium with or without substituents. q is 1 or 2. )

Patent document 2 describes a method for reducing thermochromism of a fluorinated polymer resin, wherein the fluorinated polymer resin is produced by the following steps: a step of polymerizing a fluorine-containing monomer in an aqueous dispersion medium to form an aqueous fluorinated polymer dispersion; separating the fluorinated polymer resin in a wet form from the aqueous medium to thereby separate the fluorinated polymer from the aqueous medium; and drying to produce a fluorinated polymer resin in dry form, said method comprising the step of exposing said fluorinated polymer resin in wet or dry form to an oxidizing agent.

Documents of the prior art

Patent document

Patent document 1: international publication No. 2019/031617

Patent document 2: japanese laid-open publication No. 516029 (Japanese Kokai) No. 2015-

Disclosure of Invention

Problems to be solved by the invention

The present invention provides a method for producing a fluoropolymer powder having a reduced content of a specific fluorine-containing compound by a simple method.

Means for solving the problems

The present invention provides a method for producing a fluoropolymer powder (hereinafter also referred to as "production method 1 of the present invention"), comprising the steps of: a step (A1) in which an acid is added to an aqueous fluoropolymer dispersion obtained by polymerization using a carboxylic acid type hydrocarbon surfactant, the pH is adjusted to 4.0 or less, and coagulation is carried out, thereby obtaining a wet fluoropolymer powder containing a fluorine-containing compound represented by the following general formula (1A); and a step (B1) of heat-treating the wet fluoropolymer powder at a temperature exceeding 150 ℃ and below 240 ℃.

General formula (1A): h- (CF)₂)_m-COOH

(wherein m is 3 to 19.)

The wet fluoropolymer powder preferably contains 2 or more kinds of the fluorine-containing compounds represented by the general formula (1A).

The wet fluoropolymer powder preferably contains substantially no salt of the fluorine-containing compound represented by the general formula (1A).

The fluoropolymer is preferably polytetrafluoroethylene.

The present invention also provides a method for producing a fluoropolymer powder (hereinafter also referred to as "production method 2 of the present invention"), comprising the steps of:

and (B2) heat-treating the wet fluoropolymer powder at a temperature exceeding 100 ℃.

General formula (1A): h- (CF)₂)_m-COOH

(wherein m is 3 to 19.)

The temperature of the above heat treatment is preferably more than 150 ℃ and less than 240 ℃.

The wet fluoropolymer powder preferably contains 2 or more kinds of the fluorine-containing compounds represented by the general formula (1A).

The wet fluoropolymer powder preferably contains substantially no salt of the fluorine-containing compound represented by the general formula (1A).

The fluoropolymer is preferably polytetrafluoroethylene.

Hereinafter, the term "production method of the present invention" refers to a concept including both the production method 1 and the production method 2 of the present invention.

ADVANTAGEOUS EFFECTS OF INVENTION

The production method of the present invention can produce a fluoropolymer powder having a reduced content of a specific fluorine-containing compound by a simple method.

Detailed Description

Before the present invention is explained in detail, some terms used in the present specification are defined or explained.

In the present specification, unless otherwise specified, "organic group" means a group containing 1 or more carbon atoms or a group formed by removing 1 hydrogen atom from an organic compound.

Examples of the "organic group" include:

an alkyl group which may have 1 or more substituents,

An alkenyl group which may have 1 or more substituents,

An alkynyl group which may have 1 or more substituents,

Cycloalkyl which may have 1 or more substituents,

Cycloalkenyl group which may have 1 or more substituents,

A cycloalkadienyl group which may have 1 or more substituents,

An aryl group which may have 1 or more substituents,

An aralkyl group which may have 1 or more substituents,

A non-aromatic heterocyclic group which may have 1 or more substituents,

A heteroaryl group which may have 1 or more substituents,

A cyano group,

Formyl, methyl,

RaO-、

RaCO-、

RaSO₂-、

RaCOO-、

RaNRaCO-、

RaCONRa-、

RaOCO-, and

RaOSO₂-

(in the formulae, Ra is independently

An alkyl group which may have 1 or more substituents,

An alkenyl group which may have 1 or more substituents,

An alkynyl group which may have 1 or more substituents,

Cycloalkyl which may have 1 or more substituents,

Cycloalkenyl group which may have 1 or more substituents,

A cycloalkadienyl group which may have 1 or more substituents,

An aryl group which may have 1 or more substituents,

An aralkyl group which may have 1 or more substituents,

A non-aromatic heterocyclic group which may have 1 or more substituents, or

A heteroaryl group which may have 1 or more substituents).

The organic group is preferably an alkyl group which may have 1 or more substituents.

In the present specification, unless otherwise specified, "substituent" means a group that can be substituted. Examples of the "substituent" include: aliphatic group, aromatic group, heterocyclic group, acyl group, acyloxy group, acylamino group, aliphatic oxy group, aromatic oxy group, heterocyclic oxy group, aliphatic oxycarbonyl group, aromatic oxycarbonyl group, heterocyclic oxycarbonyl group, carbamoyl group, aliphatic sulfonyl group, aromatic sulfonyl group, heterocyclic sulfonyl group, aliphatic sulfonyloxy group, aromatic sulfonyloxy group, heterocyclic sulfonyloxy group, sulfamoyl group, aliphatic sulfonamide group, aromatic sulfonamide group, heterocyclic sulfonamide group, amino group, aliphatic amino group, aromatic amino group, heterocyclic amino group, aliphatic oxycarbonylamino group, aromatic oxycarbonylamino group, heterocyclic oxycarbonylamino group, aliphatic sulfinyl group, aromatic sulfinyl group, aliphatic thio group, aromatic thio group, hydroxyl group, cyano group, sulfo group, carboxyl group, aliphatic oxyamino group, aromatic oxyamino group, carbamoyl aminocarbonyl group, amino group, heterocyclic oxycarbonyl amino group, heterocyclic oxycarbonylamino group, aliphatic sulfinyl group, aromatic sulfinyl group, aliphatic thio group, aromatic sulfenyl group, hydroxyl group, cyano group, sulfo group, carboxyl group, aliphatic oxyamino group, aromatic oxyamino group, carbamoyl amino group, and the like, Sulfamoylamino, a halogen atom, sulfamoylcarbamoyl, carbamoylsulfamoyl, dialiphatic oxyphosphinyl or diaromatic oxyphosphinyl.

The aliphatic group may be saturated or unsaturated, and may have a hydroxyl group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an amido group, a carbamoylamino group, or the like. Examples of the aliphatic group include alkyl groups having 1 to 8, preferably 1 to 4, total carbon atoms, such as methyl, ethyl, vinyl, cyclohexyl, and carbamoylmethyl.

The aromatic group may have, for example, a nitro group, a halogen atom, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, or the like. Examples of the aromatic group include aryl groups having 6 to 12 carbon atoms, preferably 6 to 10 carbon atoms in total, such as phenyl, 4-nitrophenyl, 4-acetylaminophenyl, 4-methanesulfonylphenyl and the like.

The heterocyclic group may have a halogen atom, a hydroxyl group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group or the like. Examples of the heterocyclic group include 5-to 6-membered heterocyclic rings having 2 to 12, preferably 2 to 10, total carbon atoms, for example, 2-tetrahydrofuranyl group, 2-pyrimidinyl group and the like.

The acyl group may have an aliphatic carbonyl group, an arylcarbonyl group, a heterocyclic carbonyl group, a hydroxyl group, a halogen atom, an aromatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, or the like. Examples of the acyl group include acyl groups having 2 to 8, preferably 2 to 4, total carbon atoms, such as acetyl, propionyl, benzoyl, and 3-pyridinecarbonyl.

The acylamino group may have an aliphatic group, an aromatic group, a heterocyclic group, etc., and may have, for example, an acetylamino group, a benzoylamino group, a 2-pyridinecarbonylamino group, a propionylamino group, etc. Examples of the acylamino group include acylamino groups having 2 to 12, preferably 2 to 8, total carbon atoms, alkylcarbonylamino groups having 2 to 8 total carbon atoms, for example, acetylamino group, benzoylamino group, 2-pyridinecarbonylamino group, propionylamino group and the like.

The aliphatic oxycarbonyl group may be saturated or unsaturated, and may have a hydroxyl group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an amido group, a carbamoylamino group, or the like. Examples of the aliphatic oxycarbonyl group include an alkoxycarbonyl group having 2 to 8, preferably 2 to 4, total carbon atoms, such as a methoxycarbonyl group, an ethoxycarbonyl group, and a tert-butoxycarbonyl group.

The carbamoyl group may have an aliphatic group, an aromatic group, a heterocyclic group, or the like. Examples of the carbamoyl group include an unsubstituted carbamoyl group and an alkylcarbamoyl group having 2 to 9 total carbon atoms, preferably an unsubstituted carbamoyl group and an alkylcarbamoyl group having 2 to 5 total carbon atoms, for example, an N-methylcarbamoyl group, an N, N-dimethylcarbamoyl group, an N-phenylcarbamoyl group and the like.

The aliphatic sulfonyl group may be saturated or unsaturated, and may have a hydroxyl group, an aromatic group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group, or the like. Examples of the aliphatic sulfonyl group include alkylsulfonyl groups having 1 to 6, preferably 1 to 4, total carbon atoms, for example, methylsulfonyl group.

The aromatic sulfonyl group may have a hydroxyl group, an aliphatic oxy group, a carbamoyl group, an aliphatic oxycarbonyl group, an aliphatic thio group, an amino group, an aliphatic amino group, an acylamino group, a carbamoylamino group or the like. Examples of the aromatic sulfonyl group include arylsulfonyl groups having 6 to 10 total carbon atoms, for example, benzenesulfonyl groups.

The amino group may have an aliphatic group, an aromatic group, a heterocyclic group, or the like.

The acylamino group may have, for example, acetylamino, benzoylamino, 2-pyridinecarbonylamino, propionylamino and the like. Examples of the acylamino group include acylamino groups having 2 to 12 total carbon atoms, preferably 2 to 8 total carbon atoms, more preferably alkylcarbonylamino groups having 2 to 8 total carbon atoms, for example acetylamino group, benzoylamino group, 2-pyridinecarbonylamino group, propionylamino group and the like.

The aliphatic sulfonamide group, the aromatic sulfonamide group and the heterocyclic sulfonamide group may be, for example, a methylsulfonamide group, a benzenesulfonamide group, a 2-pyridinesulfonamide group or the like.

The sulfamoyl group may have an aliphatic group, an aromatic group, a heterocyclic group, or the like. Examples of the sulfamoyl group include a sulfamoyl group, an alkylsulfamoyl group having 1 to 9 total carbon atoms, a dialkylsulfamoyl group having 2 to 10 total carbon atoms, an arylsulfamoyl group having 7 to 13 total carbon atoms, and a heterocyclic sulfamoyl group having 2 to 12 total carbon atoms, and more preferably include a sulfamoyl group, an alkylsulfamoyl group having 1 to 7 total carbon atoms, a dialkylsulfamoyl group having 3 to 6 total carbon atoms, an arylsulfamoyl group having 6 to 11 total carbon atoms, and a heterocyclic sulfamoyl group having 2 to 10 total carbon atoms, such as a sulfamoyl group, a methylsulfamoyl group, an N, N-dimethylsulfamoyl group, a phenylsulfamoyl group, and a 4-pyridinesulfamoyl group.

The aliphatic oxy group may be saturated or unsaturated, and may have methoxy, ethoxy, isopropoxy, cyclohexyloxy, methoxyethoxy, or the like. Examples of the aliphatic oxy group include alkoxy groups having 1 to 8, preferably 1 to 6, total carbon atoms, for example, methoxy, ethoxy, isopropoxy, cyclohexyloxy, methoxyethoxy, and the like.

The aromatic amino group and the heterocyclic amino group may have an aliphatic group, an aliphatic oxy group, a halogen atom, a carbamoyl group, a heterocyclic group fused to the aryl group, or an aliphatic oxycarbonyl group, and preferably may have an aliphatic group having 1 to 4 total carbon atoms, an aliphatic oxy group having 1 to 4 total carbon atoms, a halogen atom, a carbamoyl group having 1 to 4 total carbon atoms, a nitro group, or an aliphatic oxycarbonyl group having 2 to 4 total carbon atoms.

The aliphatic thio group may be saturated or unsaturated, and examples thereof include alkylthio groups having 1 to 8 total carbon atoms, more preferably 1 to 6 total carbon atoms, such as methylthio, ethylthio, carbamoylmethylthio, and tert-butylthio.

The carbamoylamino group may have an aliphatic group, an aryl group, a heterocyclic group or the like. Examples of the carbamoylamino group include a carbamoylamino group, an alkylcarbamoylamino group having 2 to 9 total carbon atoms, a dialkylcarbamoylamino group having 3 to 10 total carbon atoms, an arylcarbamoylamino group having 7 to 13 total carbon atoms, a heterocyclic carbamoylamino group having 3 to 12 total carbon atoms, preferably a carbamoylamino group, an alkylcarbamoylamino group having 2 to 7 total carbon atoms, a dialkylcarbamoylamino group having 3 to 6 total carbon atoms, arylcarbamoylamino group having 7 to 11 total carbon atoms, heterocyclic carbamoylamino group having 3 to 10 total carbon atoms, for example, carbamoylamino group, methylcarbamoylamino group, N-dimethylcarbamoylamino group, phenylcarbamoylamino group, 4-pyridinecarbamoylamino group and the like.

The production method of the present invention will be described in detail below.

When a fluoropolymer powder is obtained by polymerization using a hydrocarbon surfactant, the fluoropolymer powder may contain specific fluorine-containing compounds represented by the following general formulae (1) and (2).

General formula (1): (H- (CF)₂)_m-COO)_pM¹

General formula (2): (H- (CF)₂)_n-SO₃)_qM²

(wherein n is 4 to 20. M)²Is H, a metal atom, NR⁵ ₄An imidazolium with or without a substituent, a pyridinium with or without a substituent, or a phosphonium with or without a substituent. q is 1 or 2. )

The specific fluorine-containing compounds represented by the above general formulae (1) and (2) are preferably removed from the fluorine-containing polymer powder, and an additional step such as a fluorination treatment is required for removing the specific fluorine-containing compounds.

The production method of the present invention is completed by the following findings: a wet fluoropolymer powder obtained from an aqueous fluoropolymer dispersion obtained by polymerization using a carboxylic acid type hydrocarbon surfactant, wherein the wet fluoropolymer powder contains-COOM of a fluorine-containing compound represented by the general formula (1) ¹By performing a specific heat treatment in the state of-COOH, a fluoropolymer powder reduced in the above-mentioned fluorine-containing compound can be obtained without performing complicated steps.

The first production method of the present invention comprises the steps of: a step (A1) in which an acid is added to an aqueous fluoropolymer dispersion obtained by polymerization using a carboxylic acid type hydrocarbon surfactant, the pH is adjusted to 4.0 or less, and coagulation is carried out, thereby obtaining a wet fluoropolymer powder containing a fluorine-containing compound represented by the following general formula (1A); and a step (B1) of heat-treating the wet fluoropolymer powder at a temperature exceeding 150 ℃ and below 240 ℃.

The production method 1 of the present invention has the above-described configuration, and can obtain a fluoropolymer powder reduced in the specific fluorine-containing compounds represented by the general formulae (1) and (2) in spite of its simple method. Further, since the specific fluorine-containing compounds represented by the general formulae (1) and (2) can be reduced at a relatively low temperature, the fluorine-containing compounds represented by the general formulae (1) and (2) can be reduced and the resulting fluoropolymer powder can be inhibited from being thermally adhered.

The step (a1) is a step of: an acid is added to an aqueous fluoropolymer dispersion obtained by polymerization using a carboxylic acid type hydrocarbon surfactant, and the pH is adjusted to 4.0 or less to coagulate the dispersion, thereby obtaining a wet fluoropolymer powder containing a fluorine-containing compound represented by the following general formula (1A).

By a method of adding an acid to the aqueous fluoropolymer dispersion to adjust the pH to 4.0 or less and thereby conducting coagulation, a wet fluoropolymer powder containing the fluorine-containing compound represented by the general formula (1A) can be obtained.

The fluorine-containing compound represented by the general formula (1) contained in the aqueous fluoropolymer dispersion can be changed to a fluorine-containing compound represented by the general formula (1A) by adjusting the pH of the aqueous dispersion to 4.0 or less, more preferably 3.5 or less, further preferably 3.0 or less, further more preferably 2.5 or less, and particularly preferably 2.0 or less. Thus, a wet fluoropolymer powder containing the fluorine-containing compound represented by general formula (1A) is obtained, and the content of the fluorine-containing compound represented by general formulae (1) and (2) can be reduced by the heat treatment performed in step (B1).

The acid may be an organic acid or an inorganic acid, and is preferably an inorganic acid in view of being difficult to remain during heat treatment, and particularly preferably at least one selected from the group consisting of nitric acid, sulfuric acid, fuming sulfuric acid, perchloric acid, and hydrochloric acid, and more preferably at least one selected from the group consisting of nitric acid, sulfuric acid, and hydrochloric acid. As the organic acid, succinic acid, oxalic acid, citric acid, trifluoroacetic acid, and the like can be used. The amount of the acid to be added is not limited, and may be appropriately set in accordance with the pH of the aqueous fluoropolymer dispersion.

As a method of adding an acid to perform coagulation, for example, a method of stirring an aqueous dispersion while adding an acid is exemplified. More specifically, the wet fluoropolymer powder containing the fluorine-containing compound represented by the general formula (1A) can be obtained by coagulating the fluoropolymer by stirring in a vessel equipped with a stirrer. The condensation may be continuously performed using an in-line mixer or the like.

In the step (a1), the condensation temperature is not limited, and may be, for example, 3 to 80 ℃. From the viewpoint of stability of the dispersion, it is preferably 5 ℃ or higher, more preferably 10 ℃ or higher. In addition, from the viewpoint of suppressing granulation of secondary particles, 60 ℃ or lower is preferable.

The step (B1) is a step of: the wet fluoropolymer powder containing the fluorine-containing compound represented by the above general formula (1A) is subjected to a heat treatment at a temperature exceeding 150 ℃ and below 240 ℃. By changing the fluorine-containing compound represented by the above general formula (1) to a fluorine-containing compound represented by the general formula (1A) and then performing heat treatment, the amount of the fluorine-containing compound represented by the general formula (1) contained in the fluorine-containing polymer powder can be efficiently reduced while suppressing the thermal adhesion of the resulting fluorine-containing polymer powder.

In the step (B1), the heat treatment temperature is more than 150 ℃ and less than 240 ℃. Since the specific fluorine-containing compound can be reduced more efficiently, the temperature of the heat treatment is preferably 155 ℃ or more, more preferably 160 ℃ or more, further preferably 165 ℃ or more, further preferably 170 ℃ or more, particularly preferably 175 ℃ or more, and particularly preferably 180 ℃ or more.

From the viewpoint of suppressing the thermal sticking of the fluoropolymer powder, the temperature is more preferably 235 ℃ or lower, still more preferably 230 ℃ or lower, still more preferably 225 ℃ or lower, particularly preferably 220 ℃ or lower, particularly preferably 215 ℃ or lower, and most preferably 210 ℃ or lower.

The heat treatment is preferably performed by drying the wet fluoropolymer powder. The term "dry" as used herein means a heat treatment for making the water content of the wet fluoropolymer powder 0.01% by mass or less.

The drying temperature is more than 150 ℃ and less than 240 ℃. Since the specific fluorine-containing compound can be reduced more efficiently, the drying temperature is preferably 155 ℃ or higher, more preferably 160 ℃ or higher, further preferably 165 ℃ or higher, further preferably 170 ℃ or higher, particularly preferably 175 ℃ or higher, and particularly preferably 180 ℃ or higher.

In the production method 1 of the present invention, even when the temperature of the heat treatment or the drying is relatively low, the specific fluorine-containing compound can be efficiently reduced, and therefore, the thermal adhesion can be suppressed.

In the present specification, the term "hot tack" means that the average particle diameter greatly changes before and after drying, and particularly means that the average particle diameter after drying becomes large. The degree of thermal adhesion can be evaluated, for example, by the ratio of the percent rejects when a 10-mesh screen is used.

Retention on sieve ═ amount remaining on 10 mesh (g))/(total amount of fluoropolymer sieved (g)) × 100

According to the production method 1 of the present invention, the thermal adhesion can be suppressed, the oversize fraction is preferably 5% or less, and preferably 3% or less, and the productivity can be improved.

The method of measuring the average particle diameter may be appropriately selected depending on the kind of the fluoropolymer. For example, in the case of low molecular weight PTFE, the average particle diameter is a particle diameter corresponding to 50% of the integral of the obtained particle size distribution, which is measured under a pressure of 0.1MPa for a measurement time of 3 seconds without using a cascade using a laser diffraction particle size distribution measuring apparatus (manufactured by japan laser corporation).

In the case of high molecular weight PTFE, the average particle diameter is a value measured according to JIS K6891.

From the viewpoint of efficiently removing or reducing the fluorine-containing compound represented by the general formula (1A), the heat treatment or drying time is preferably 120 minutes or more, more preferably 180 minutes or more, further preferably 240 minutes or more, and further preferably 300 minutes or more.

The upper limit of the heat treatment or drying time is not particularly limited, and may be, for example, 1500 minutes or less, or 1200 minutes or less.

In the heat treatment or drying, the temperature is preferably controlled to be less than 240 ℃ or not more than 240 ℃, but may be 240 ℃ or more than 240 ℃ as long as the effect of the present invention is not impaired. In the heat treatment or drying, the time for the temperature to reach 240 ℃ or more or the time for the temperature to exceed 240 ℃ is preferably 120 minutes or less from the viewpoint of suppressing the powder from being thermally stuck. More preferably 90 minutes or less, further preferably 60 minutes or less, and further preferably 30 minutes or less. In the heat treatment or drying, the time when the temperature reaches 240 ℃ or more or the time when the temperature exceeds 240 ℃ is preferably 40% or less of the total drying time from the viewpoint of suppressing the powder from being thermally bonded, as long as the effect of the present invention is not impaired. More preferably 30% or less, further preferably 20% or less, further preferably 10% or less, particularly preferably 5% or less, and particularly preferably 3% or less.

The 2 nd production method of the present invention comprises the steps of: a step (A2) in which an acid is added to an aqueous fluoropolymer dispersion obtained by polymerization using an aliphatic carboxylic acid type hydrocarbon surfactant, the pH is adjusted to 4.0 or less, and coagulation is carried out to obtain a wet fluoropolymer powder containing a fluorine-containing compound represented by the following general formula (1A); and a step (B2) of heat-treating the wet fluoropolymer powder at a temperature exceeding 100 ℃.

General formula (1A): h- (CF)₂)_m-COOH

(wherein m is 3 to 19.)

The production method 2 of the present invention has the above-described configuration, and can obtain a fluoropolymer powder reduced in the specific fluorine-containing compounds represented by the general formulae (1) and (2) in spite of a simple method.

The step (a2) is a step of: an acid is added to an aqueous fluoropolymer dispersion obtained by polymerization using an aliphatic carboxylic acid type hydrocarbon surfactant, and the pH is adjusted to 4.0 or less to coagulate the dispersion, thereby obtaining a wet fluoropolymer powder containing a fluorine-containing compound represented by the following general formula (1A).

By adjusting the pH of the aqueous dispersion to 4.0 or less, more preferably 3.5 or less, further preferably 3.0 or less, further more preferably 2.5 or less, and particularly preferably 2.0 or less, the fluorine-containing compound represented by the general formula (1) contained in the aqueous fluoropolymer dispersion can be changed to the fluorine-containing compound represented by the general formula (1A). Thus, a wet fluoropolymer powder containing the fluorine-containing compound represented by general formula (1A) is obtained, and the content of the fluorine-containing compound represented by general formulae (1) and (2) can be reduced by the heat treatment in step (B2).

As a method of adding an acid to perform coagulation, for example, a method of stirring an aqueous dispersion while adding an acid is exemplified. The wet fluoropolymer powder containing the fluorine-containing compound represented by the general formula (1A) can be obtained by coagulating the fluoropolymer by stirring in a vessel equipped with a stirrer. The condensation may be continuously performed using an in-line mixer or the like.

In the step (a2), the condensation temperature is not limited, and may be, for example, 3 to 80 ℃. From the viewpoint of stability of the dispersion, it is preferably 5 ℃ or higher, more preferably 10 ℃ or higher. In addition, from the viewpoint of suppressing granulation of secondary particles, 60 ℃ or lower is preferable.

In the step (B2), the heat treatment temperature is more than 100 ℃. Since the specific fluorine-containing compound can be reduced more efficiently, the temperature of the heat treatment is preferably 110 ℃ or higher, more preferably 120 ℃ or higher, further preferably 130 ℃ or higher, and particularly preferably 140 ℃ or higher.

Further, since the specific fluorine-containing compound can be further efficiently reduced, it is preferably more than 150 ℃, more preferably 155 ℃ or more, further preferably 160 ℃ or more, further preferably 165 ℃ or more, particularly preferably 170 ℃ or more, particularly preferably 175 ℃ or more, and most preferably 180 ℃ or more.

From the viewpoint of suppressing the thermal sticking of the fluoropolymer powder, it is preferably 240 ℃ or lower, more preferably less than 240 ℃, more preferably 235 ℃ or lower, further preferably 230 ℃ or lower, further preferably 225 ℃ or lower, particularly preferably 220 ℃ or lower, particularly preferably 215 ℃ or lower, and most preferably 210 ℃ or lower.

In the step (B2), the heat treatment is preferably performed to dry the wet fluoropolymer powder.

The term "dry" means a heat treatment for making the water content of the wet fluoropolymer powder 0.010 mass% or less.

The drying temperature is above 100 ℃. Since the specific fluorine-containing compound can be reduced more efficiently, the drying temperature is preferably 110 ℃ or higher, more preferably 120 ℃ or higher, further preferably 130 ℃ or higher, and particularly preferably 140 ℃ or higher.

Further, since the specific fluorine-containing compound can be further efficiently reduced, the drying temperature is preferably more than 150 ℃, more preferably 155 ℃ or more, further preferably 160 ℃ or more, further preferably 165 ℃ or more, particularly preferably 170 ℃ or more, particularly preferably 175 ℃ or more, and most preferably 180 ℃ or more.

In the production method 2 of the present invention, even when the temperature of the heat treatment or the drying is relatively low, the specific fluorine-containing compound can be efficiently reduced, and therefore, the thermal adhesion can be suppressed.

Retention on sieve ═ amount remaining on 10 mesh (g))/(total amount of fluoropolymer sieved (g)) × 100

According to the production method of the present invention, the thermal adhesion can be suppressed, the oversize fraction is preferably 5% or less, and preferably 3% or less, and the productivity can be improved.

In the case of high molecular weight PTFE, the average particle diameter is a value measured according to JIS K6891.

From the viewpoint of efficiently removing or reducing the fluorine-containing compound represented by the general formula (1A), the time for the heat treatment or drying is preferably 120 minutes or longer, more preferably 180 minutes or longer, still more preferably 240 minutes or longer, and still more preferably 300 minutes or longer.

The upper limit of the time for the heat treatment or drying is not particularly limited, and may be, for example, 1500 minutes or less, or 1200 minutes or less.

In the production method of the present invention, the wet powder obtained by condensing the fluoropolymer is dried by means of vacuum, high frequency, hot air or the like while keeping the wet powder in a state where the wet powder is hardly fluidized, preferably in a state where the wet powder is left to stand.

For example, in the case where the fluoropolymer is PTFE, friction between the powders, particularly at high temperatures, often adversely affects the fine powder type PTFE. This is because such particles composed of PTFE have a property that they simply fibrillate even when subjected to a small shear force, losing the state of the original stable particle structure.

In the present specification, the presence or absence of fibrillation can be judged by "paste extrusion", which is a typical method of molding "high molecular weight PTFE powder" as powder (fine powder) made from emulsion polymer of TFE. This is because, in general, high molecular weight PTFE powder has fibrillating properties when paste extrusion is possible. When the green molded product obtained by paste extrusion does not have substantial strength or elongation, for example, when the elongation is 0% and the green molded product is broken by stretching, it is considered that the green molded product does not have fibrillation.

In the production method of the present invention, the solid content concentration of the aqueous fluoropolymer dispersion is not limited, and may be, for example, 1.0 to 70.0 mass%. The solid content concentration is preferably 8.0% by mass or more, more preferably 10.0% by mass or more, and is preferably 60.0% by mass or less, more preferably 50.0% by mass or less. The solid content concentration is also preferably 10.0 to 25.0% by mass, more preferably 10.0 to 22.0% by mass, and still more preferably 10.0 to 20.0% by mass, from the viewpoint of reducing the non-condensable components.

The production method of the present invention may comprise a step of diluting the aqueous fluoropolymer dispersion with water. For example, the solid content concentration can be diluted to 10.0 to 25.0 mass% by the dilution.

The content of the fluorine-containing compound represented by the general formula (1) in the aqueous fluoropolymer dispersion is not particularly limited. For example, the content of the fluorine-containing compound represented by the general formula (1) contained in the wet fluoropolymer powder obtained after coagulation is preferably in the range described below.

In order to increase the bulk density of the fluoropolymer powder, it is preferable that the fluoropolymer solid content concentration in the aqueous fluoropolymer dispersion is high. When the concentration of the fluoropolymer solid content in the aqueous fluoropolymer dispersion for condensation is high, the degree of association of the primary particles of the fluoropolymer increases, and the primary particles of the fluoropolymer densely associate and aggregate to form particles. When the fluoropolymer solid content concentration of the aqueous fluoropolymer dispersion is less than 8% by mass, the agglomeration density of the primary fluoropolymer particles tends to be low, and it is difficult to obtain a fluoropolymer powder having a high bulk density. On the other hand, when the fluoropolymer solid content concentration in the aqueous fluoropolymer dispersion is too high, the unagglomerated fluoropolymer increases, and the unagglomerated fluoropolymer solid content concentration in the coagulation waste water increases. If the concentration of the unagglomerated fluoropolymer solids in the condensate drain is high, the cost and labor for pipe clogging and drain treatment are incurred. In addition, the yield of the fluoropolymer powder decreases. From the viewpoint of productivity of the fluoropolymer powder, the concentration of non-coagulated fluoropolymer solids in the condensate water is preferably low, more preferably less than 0.4 mass%, even more preferably less than 0.3 mass%, and particularly preferably less than 0.2 mass%. When the fluoropolymer solid content concentration of the aqueous fluoropolymer dispersion exceeds 25 mass%, it becomes difficult to make the unagglomerated fluoropolymer solid content concentration of the condensate drain less than 0.4 mass%.

Since the fluoropolymer solid content concentration in the aqueous fluoropolymer dispersion obtained in the polymerization step described later is about 8 to 45% by mass, when the fluoropolymer solid content concentration is high, a diluting solvent such as water is added to adjust the concentration to 8 to 25% by mass. When the fluoropolymer solid content concentration in the aqueous fluoropolymer dispersion after emulsion polymerization is from 8 to 25% by mass, the aqueous fluoropolymer dispersion may be used as it is.

In the production method of the present invention, the content of the fluorine-containing compound represented by the general formula (1) contained in the aqueous fluoropolymer dispersion is not limited, and is, for example, about 1ppb to 10000ppm, preferably 100ppb or more, more preferably 1ppm or more, further preferably 10ppm or more, and particularly preferably 100ppm or more, relative to the fluoropolymer.

The aqueous dispersion to be subjected to the above-mentioned heat treatment may contain 1 kind of fluorine-containing compound represented by the general formula (1), or may contain 2 or more kinds, and in the case of containing 2 or more kinds, the production method of the present invention is particularly effective.

Examples thereof include a mode comprising a fluorine-containing compound having m of 7 and a fluorine-containing compound having m of 13 in the general formula (1). When the fluorine-containing compound is contained in 2 or more species, the fluorine-containing compound may be contained in 3 or more species, or may be contained in 4 or more species, and the whole fluorine-containing compound contained in the general formula (1) may be contained. The aqueous dispersion to be subjected to the heat treatment may contain, as the fluorine-containing compound, a fluorine-containing compound having m of the general formula (1) of 7 or less and a fluorine-containing compound having m of the general formula (1A) of 8 or more, or may contain, as the fluorine-containing compound, a fluorine-containing compound having m of the general formula (1A) of 8 or less and a fluorine-containing compound having m of the general formula (1A) of 9 or more.

The aqueous fluoropolymer dispersion may be one containing a fluorochemical compound having m of 3, 5, 7, 9, 11, 13, 15, 17 and 19 and not containing a fluorochemical compound having m of 4, 6, 8, 10, 12, 14, 16 and 18 among fluorochemical compounds contained in the general formula (1), one containing a fluorochemical compound having m of 4, 6, 8, 10, 12, 14, 16, 18 and 20 and not containing a fluorochemical compound having m of 3, 5, 7, 9, 11, 13, 15, 17 and 19, or one containing all fluorochemical compounds having m of 3 to 19.

In the production method of the present invention, the concentration of the fluorine-containing compound represented by the general formula (1) in the aqueous fluoropolymer dispersion is not particularly limited, and an aqueous fluoropolymer dispersion having an arbitrary concentration can be coagulated. In the aqueous fluoropolymer dispersion to be condensed, the total amount of the fluorine-containing compound represented by the above general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, 10ppm or more, or 100ppm or more based on the fluoropolymer. The total amount may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more with respect to the total amount of water. When the concentration of the fluorine-containing compound represented by the general formula (1) in the aqueous fluoropolymer dispersion is not less than a certain value as described above, the production method of the present invention exhibits higher removal efficiency.

In addition, in the aqueous fluoropolymer dispersion to be treated, the fluorine-containing compound represented by the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the total amount of the fluorine-containing compound in water to the above range, the removal efficiency can be further improved. In the present specification, ppm and ppb refer to values obtained in terms of mass unless otherwise specified.

The amount of at least one kind of fluorine-containing compound having m of the above general formula (1) of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19 may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, 10ppm or more, or 100ppm or more, respectively, based on the total amount of water.

When the concentration of the fluorine-containing compound represented by the general formula (1) in the aqueous fluoropolymer dispersion is not less than a certain value as described above, the production method of the present invention exhibits higher removal efficiency.

Further, the amount of at least one kind of fluorine-containing compound having m of the above general formula (1) of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19 may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less, respectively, relative to the total amount of water. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 3 in the above general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 3 in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m 4 in the general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 4 in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 5 in the general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 5 in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 6 in the general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 6 in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 7 in the general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 7 in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 8 in the above general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 8 in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 9 in the general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m 9 of the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 10 in the general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 10 in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 11 in the above general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 11 in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 12 in the above general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 12 in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m 13 of the general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having 13 m in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 14 in the above general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having 14 m in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 15 in the above general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having 15 m in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 16 in the above general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 16 in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 17 in the above general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having 17 m in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 18 in the above general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 18 in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 19 in the general formula (1) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 19 in the general formula (1) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The fluorine-containing compound represented by the general formula (1) contained in the aqueous fluoropolymer dispersion is a fluorine-containing compound represented by the general formula (1), wherein M in the general formula (1)¹Preferably a metal atom, NR⁵ ₄(R⁵May be the same or different, and is H or an organic group having 1 to 10 carbon atoms), optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted pyridiniumA substituted phosphonium.

Such a fluorine-containing compound can be changed to a fluorine-containing compound represented by the general formula (1A) by adding an acid to the aqueous fluoropolymer dispersion to adjust the pH to 4.0 or less.

Therefore, according to the production method of the present invention, it is possible to obtain a fluorine-containing polymer powder containing no or substantially no fluorine-containing compound represented by the general formula (1) wherein M is represented by the general formula (1) ¹Is H, a metal atom, NR⁵ ₄(R⁵The same or different, H or an organic group having 1 to 10 carbon atoms), optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium.

The aqueous fluoropolymer dispersion after the addition of the acid preferably contains substantially no salt of the fluorine-containing compound represented by the general formula (1A) (preferably, the fluorine-containing compound represented by the general formula (1) wherein M is M¹Is a metal atom, NR⁵ ₄(R⁵H or an organic group having 1 to 10 carbon atoms), optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium). The aqueous dispersion liquid substantially not containing the salt of the fluorine-containing compound represented by the general formula (1A) means that the salt of the fluorine-containing compound represented by the general formula (1A) is contained in an amount of 500ppb or less, respectively, with respect to all m. For example, the salt of the fluorine-containing compound having m of 3 in the general formula (1A) may be 400ppb or less, the salt of the fluorine-containing compound having m of 9 may be 400ppb or less, or the total amount of the salts of the fluorine-containing compounds having m of 3 to 19 may be 500ppb or less.

The content of the salt of the fluorine-containing compound represented by the general formula (1A) may be 400ppb or less, 300ppb or less, 200ppb or less, 100ppb or less, 50ppb or less, or 10ppb or less, respectively, for all m.

By adjusting the pH to 4.0 or less by adding an acid, an aqueous fluoropolymer dispersion substantially not containing a salt of the fluorine-containing compound represented by the general formula (1A) can be obtained as described above.

The content of the salt of the fluorine-containing compound represented by the general formula (1A) in the aqueous fluoropolymer dispersion can be measured, for example, by ion chromatography (ion chromatography).

The wet fluoropolymer powder in the above-mentioned step (a1) and step (a2) may be any powder obtained by condensing the aqueous fluoropolymer dispersion obtained by polymerization, and examples thereof include water, fluoropolymer powder, and a fluorine-containing compound represented by the general formula (1A).

The water content in the wet fluoropolymer powder is not limited, and is, for example, about 0.01 to 1000 mass% based on the wet fluoropolymer powder.

The water content in the wet fluoropolymer powder is a value determined by the following equation.

(water content in wet fluoropolymer powder) ((mass of wet fluoropolymer powder) - (mass of fluoropolymer powder obtained by freeze-drying))/(mass of wet fluoropolymer powder) × 100

The wet fluoropolymer powder in the steps (a1) and (a2) contains a fluorine-containing compound represented by the general formula (1A). The content of the fluorine-containing compound represented by the general formula (1A) is not limited. For example, the amount of the fluorine-containing polymer may be 1ppb or more, 10ppb or more, 100ppb or more, 1ppm or more, 10ppm or more, or 100ppm or more. Further, the amount of the fluorine-containing polymer may be 10000ppm or less, or may be 1000ppm or less.

In the step (a1) and the step (a2), an acid is added to adjust the pH to 4.0 or less, and the coagulation is performed, whereby a wet fluoropolymer powder containing a fluorine-containing compound represented by the general formula (1A) can be obtained.

The wet fluoropolymer powder in the steps (B1) and (B2) may contain 1 kind of the fluorochemical represented by the general formula (1A), or may contain 2 or more kinds, and when 2 or more kinds are contained, the production method of the present invention is particularly effective.

Examples thereof include a mode comprising a fluorine-containing compound having m of 7 and a fluorine-containing compound having m of 13 in the general formula (1A). When the fluorine-containing compound is contained in 2 or more species, the fluorine-containing compound may be contained in 3 or more species, or 4 or more species, and the whole fluorine-containing compound contained in the general formula (1A) may be contained.

The wet fluoropolymer powder in steps (B1) and (B2) may contain, as the above-mentioned fluorochemical, a fluorochemical having m of general formula (1A) of 7 or less and a fluorochemical having m of general formula (1A) of 8 or more, or may contain, as the above-mentioned fluorochemical, a fluorochemical having m of general formula (1A) of 8 or less and a fluorochemical having m of general formula (1A) of 9 or more.

The wet fluoropolymer powder in steps (B1) and (B2) may be a form containing a fluorochemical in which m is 3, 5, 7, 9, 11, 13, 15, 17, and 19 and not containing a fluorochemical in which m is 4, 6, 8, 10, 12, 14, 16, and 18 among the fluorochemicals contained in general formula (1A), a form containing a fluorochemical in which m is 4, 6, 8, 10, 12, 14, 16, 18, and 20 and not containing a fluorochemical in which m is 3, 5, 7, 9, 11, 13, 15, 17, and 19, or a form containing all fluorochemical in which m is 3 to 19.

In the production method of the present invention, the concentration of the fluorine-containing compound represented by the general formula (1A) in the wet fluoropolymer powder subjected to heat treatment is not particularly limited, and the wet fluoropolymer powder having an arbitrary concentration can be treated. In the wet fluoropolymer powder, the total amount of the compound represented by the above general formula (1A) may be 0.01ppm or more, 0.1ppm or more, or 0.5ppm or more based on the fluoropolymer. The total amount may be 1ppm or more, 5ppm or more, 10ppm or more, or 100ppm or more based on the fluoropolymer. When the concentration of the fluorine-containing compound represented by the general formula (1A) in the wet fluoropolymer powder is not less than a certain value as described above, the production method of the present invention exhibits higher removal efficiency.

In the wet fluoropolymer powder, the fluorine-containing compound represented by the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the total amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

In the present specification, ppm and ppb refer to values obtained in terms of mass unless otherwise specified.

The amount of at least one kind of fluorine-containing compound having m of the above general formula (1A) of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19 may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more, based on the fluoropolymer.

When the concentration of the fluorine-containing compound represented by the general formula (1A) in the wet fluoropolymer powder is not less than a certain value as described above, the removal method of the present invention exhibits higher removal efficiency.

Further, the amount of at least one kind of fluorine-containing compound having m of the above general formula (1A) of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19 may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less, respectively, relative to the fluorine-containing polymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 3 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 3 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m 4 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

When the concentration of the fluorine-containing compound represented by the general formula (1A) in the wet fluoropolymer powder is not less than a certain value as described above, the production method of the present invention exhibits higher removal efficiency.

The amount of the fluorine-containing compound having m of 4 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 5 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 5 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 6 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 6 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 7 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 7 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 8 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 8 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m 9 of the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m 9 of the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 10 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 10 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 11 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m 11 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 12 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 12 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m 13 of the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m 13 of the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 14 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having 14 m in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 15 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having 15 m in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 16 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 16 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 17 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having 17 m in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 18 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m of 18 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 19 in the general formula (1A) may be 0.01ppm or more, 0.1ppm or more, 0.5ppm or more, 1ppm or more, 5ppm or more, or 10ppm or more based on the fluoropolymer.

The amount of the fluorine-containing compound having m 19 of the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the amount of the fluorine-containing compound in the wet fluoropolymer powder to the above range, the removal efficiency can be further improved.

The wet fluoropolymer powder preferably contains substantially no salt of the fluorine-containing compound represented by the general formula (1A) (preferably, the fluorine-containing compound represented by the general formula (1) wherein M is represented by the general formula (1))¹Is a metal atom, NR⁵ ₄(R⁵H or an organic group having 1 to 10 carbon atoms), optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium). The wet fluoropolymer powder described above, which does not substantially contain a salt of the fluorine-containing compound represented by the general formula (1A), means that the content of the salt of the fluorine-containing compound represented by the general formula (1A) is 500ppb or less, respectively, for all m. For example, a fluorinated compound of the formula (1A) wherein m is 3The salt content of the compound is 400ppb, the salt content of the fluorine-containing compound having m of 9 is 400ppb or less, and the total amount of the salt content of the fluorine-containing compound having m of 3 to 19 may be 500ppb or less.

The content of the salt of the fluorine-containing compound represented by the general formula (1A) may be 500ppb or less, 400ppb or less, 300ppb or less, 200ppb or less, 100ppb or less, 50ppb or less, 10ppb or less, or less than 10ppb in all m.

The content of the salt of the fluorine-containing compound represented by the general formula (1A) in the wet fluoropolymer powder can be measured, for example, by ion chromatography (ion chromatography).

Before or during the above-mentioned coagulation, a pigment for coloring or various fillers for improving mechanical properties are added to obtain a pigment-or filler-containing fluoropolymer powder in which a pigment or a filler is uniformly mixed.

The production method 1 of the present invention may further comprise a step of recovering the condensed wet fluoropolymer powder after the step (a1) and before the step (B1).

The production method 2 of the present invention may further comprise a step of recovering the condensed wet fluoropolymer powder after the step (a2) and before the step (B2).

The aqueous fluoropolymer dispersion of step (a1) is obtained by polymerization of a fluoromonomer using a carboxylic acid type hydrocarbon surfactant. The production method 1 of the present invention also preferably includes the following polymerization steps: an aqueous fluoropolymer dispersion is obtained by polymerizing a fluorine-containing monomer in an aqueous medium in the presence of a carboxylic acid type hydrocarbon surfactant.

The aqueous fluoropolymer dispersion of step (a2) is obtained by polymerization of a fluoromonomer using an aliphatic carboxylic acid type hydrocarbon surfactant. The production method 2 of the present invention also preferably includes the following polymerization steps: an aqueous fluoropolymer dispersion is obtained by polymerizing a fluorine-containing monomer in an aqueous medium in the presence of an aliphatic carboxylic acid type hydrocarbon surfactant.

In the production method of the present invention, an aqueous fluoropolymer dispersion containing a fluorine-containing compound represented by the general formula (1) and substantially no compound represented by the general formula (2) can be obtained by a polymerization step described later using a carboxylic acid type hydrocarbon surfactant or an aliphatic carboxylic acid type hydrocarbon surfactant.

In the following description, only the portion referred to as "carboxylic acid type hydrocarbon surfactant" is applied to the "aliphatic carboxylic acid type hydrocarbon surfactant" in the production method 2 of the present invention.

The fluorine-containing monomer preferably has at least 1 double bond.

The fluorine-containing monomer is preferably selected from the group consisting of tetrafluoroethylene [ TFE ]]Hexafluoropropylene [ HFP ]]Chlorotrifluoroethylene [ CTFE ]]Vinyl fluoride, vinylidene fluoride [ VDF ]]Trifluoroethylene, fluoroalkyl vinyl ether, fluoroalkyl ethylene, fluoroalkyl allyl ether, trifluoropropene, pentafluoropropene, trifluorobutene, tetrafluoroisobutylene, hexafluoroisobutylene, general formula (100): CHX ¹⁰¹＝CX¹⁰²Rf¹⁰¹(in the formula, X¹⁰¹And X¹⁰²One of them is H, the other is F, Rf¹⁰¹A linear or branched fluoroalkyl group having 1 to 12 carbon atoms), a fluorovinyl heterocyclic compound, and a monomer providing a crosslinking site.

The fluorinated alkyl vinyl ether is preferably at least one selected from the group consisting of the following fluorine-containing monomers:

general formula (110): CF (compact flash)₂＝CF-ORf¹¹¹

(wherein Rf¹¹¹Represents a perfluoroorganic group), a fluorine-containing monomer represented by,

General formula (120): CF (compact flash)₂＝CF-OCH₂-Rf¹²¹

(wherein Rf¹²¹A perfluoroalkyl group having 1 to 5 carbon atoms) and a fluorine-containing monomer,

General formula (130): CF (compact flash)₂＝CFOCF₂ORf¹³¹

(wherein Rf¹³¹Is a linear or branched perfluoroalkyl group having 1 to 6 carbon atoms,A cyclic perfluoroalkyl group having 5 to 6 carbon atoms, a linear or branched perfluorooxyalkyl group having 2 to 6 carbon atoms and containing 1 to 3 oxygen atoms) and a fluorine-containing monomer,

General formula (140): CF (compact flash)₂＝CFO(CF₂CF(Y¹⁴¹)O)_m(CF₂)_nF

(in the formula, Y¹⁴¹Represents a fluorine atom or a trifluoromethyl group. m is an integer of 1 to 4. n is an integer of 1 to 4), and

general formula (150): CF (compact flash)₂＝CF-O-(CF₂CFY¹⁵¹-O)n-(CFY¹⁵²)_m-A¹⁵¹

(in the formula, Y¹⁵¹Represents a fluorine atom, a chlorine atom or-SO₂F groups or perfluoroalkyl groups. The perfluoroalkyl group may contain etheric oxygen and-SO ₂And F group. n represents an integer of 0 to 3. n number of Y¹⁵¹May be the same or different. Y is¹⁵²Represents a fluorine atom, a chlorine atom or-SO₂And F group. m represents an integer of 1 to 5. m number of Y¹⁵²May be the same or different. A. the¹⁵¹represents-SO₂X¹⁵¹、-COZ¹⁵¹or-POZ¹⁵²Z¹⁵³。X¹⁵¹Represents F, Cl, Br, I, -OR¹⁵¹or-NR¹⁵²R¹⁵³。Z¹⁵¹、Z¹⁵²And Z¹⁵³Same or different, represent-NR¹⁵⁴R¹⁵⁵OR-OR¹⁵⁶。R¹⁵¹、R¹⁵²、R¹⁵³、R¹⁵⁴、R¹⁵⁵And R¹⁵⁶The same or different, represents H, ammonium, an alkali metal, an alkyl group which may or may not contain a fluorine atom, an aryl group, or a sulfonyl group-containing group).

In the present specification, the "perfluoro organic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. The aforementioned perfluoroorganic group may have an ether oxygen.

Rf is an example of the fluorine-containing monomer represented by the general formula (110)¹¹¹Is a fluorine-containing monomer of perfluoroalkyl group with 1-10 carbon atoms. The perfluoroalkyl group preferably has 1 to 5 carbon atoms.

Examples of the perfluoroorganic group in the general formula (110) include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

The fluorine-containing monomer represented by the general formula (110) may further include Rf in the general formula (110)¹¹¹Is a C4-9 perfluoro (alkoxyalkyl) monomer, Rf ¹¹¹Is of the formula:

[ solution 1]

(wherein m represents 0 or an integer of 1 to 4), and Rf¹¹¹Is of the formula:

[ solution 2]

(wherein n represents an integer of 1 to 4) or the like.

As the fluorine-containing monomer represented by the general formula (110), among them, preferred are

General formula (160): CF (compact flash)₂＝CF-ORf¹⁶¹

(wherein Rf¹⁶¹A perfluoroalkyl group having 1 to 10 carbon atoms). Rf¹⁶¹Preferably, the perfluoroalkyl group has 1 to 5 carbon atoms.

The fluorinated alkyl vinyl ether is preferably at least one selected from the group consisting of fluorine-containing monomers represented by the general formulae (160), (130) and (140).

The fluorine-containing monomer represented by the general formula (160) is preferably at least one selected from the group consisting of perfluoro (methyl vinyl ether), perfluoro (ethyl vinyl ether), and perfluoro (propyl vinyl ether), and more preferably at least one selected from the group consisting of perfluoro (methyl vinyl ether) and perfluoro (propyl vinyl ether).

The fluorine-containing monomer represented by the general formula (130) is preferably selected from the group consisting of CF₂＝CFOCF₂OCF₃、CF₂＝CFOCF₂OCF₂CF₃And CF₂＝CFOCF₂OCF₂CF₂OCF₃At least one of the group consisting of.

The fluorine-containing monomer represented by the general formula (140) is preferably selected from the group consisting of CF₂＝CFOCF₂CF(CF₃)O(CF₂)₃F、CF₂＝CFO(CF₂CF(CF₃)O)₂(CF₂)₃F and CF₂＝CFO(CF₂CF(CF₃)O)₂(CF₂)₂F.

The fluorine-containing monomer represented by the general formula (150) is preferably selected from the group consisting of CF ₂＝CFOCF₂CF₂SO₂F、CF₂＝CFOCF₂CF(CF₃)OCF₂CF₂SO₂F、CF₂＝CFOCF₂CF(CF₂CF₂SO₂F)OCF₂CF₂SO₂F and CF₂＝CFOCF₂CF(SO₂F)₂At least one of the group consisting of.

As the fluorine-containing monomer represented by the general formula (100), Rf is preferable¹⁰¹A fluorine-containing monomer which is a linear fluoroalkyl group, more preferably Rf¹⁰¹A fluoromonomer that is a linear perfluoroalkyl group. Rf¹⁰¹The number of carbon atoms of (C) is preferably 1 to 6. Examples of the fluorine-containing monomer represented by the general formula (100) include CH₂＝CFCF₃、CH₂＝CFCF₂CF₃、CH₂＝CFCF₂CF₂CF₃、CH₂＝CFCF₂CF₂CF₂H、CH₂＝CFCF₂CF₂CF₂CF₃、CHF＝CHCF₃(E-form), CHF ═ CHCF₃(Z form), etc., wherein CH is preferred₂＝CFCF₃2,3,3, 3-tetrafluoropropene is shown.

The fluoroalkylethylene is preferably a fluoroalkylethylene

General formula (170): CH (CH)₂＝CH-(CF₂)_n-X¹⁷¹

(in the formula, X¹⁷¹H or F, n is an integer of 3 to 10), more preferably selected from the group consisting of CH₂＝CH-C₄F₉And CH₂＝CH-C₆F₁₃At least one of the group consisting of.

Examples of the fluoroalkyl allyl ether include

General formula (240): CF (compact flash)₂＝CF-CF₂-ORf¹¹¹

(wherein Rf¹¹¹Represents a perfluoroorganic group).

Rf of the general formula (240)¹¹¹And Rf of the formula (110)¹¹¹The same is true. As Rf¹¹¹Preferably, a C1-10 perfluoroalkyl group or a C1-10 perfluoroalkoxyalkyl group. The fluoroalkyl allyl ether represented by the general formula (240) is preferably selected from the group consisting of CF₂＝CF-CF₂-O-CF₃、CF₂＝CF-CF₂-O-C₂F₅、CF₂＝CF-CF₂-O-C₃F₇And CF₂＝CF-CF₂-O-C₄F₉At least one selected from the group consisting of CF, more preferably CF₂＝CF-CF₂-O-C₂F₅、CF₂＝CF-CF₂-O-C₃F₇And CF₂＝CF-CF₂-O-C₄F₉At least one of the group consisting of, more preferably CF ₂＝CF-CF₂-O-CF₂CF₂CF₃。

Examples of the fluorovinyl heterocyclic compound include compounds represented by the general formula (230):

[ solution 3]

(in the formula, X²³¹And X²³²Independently F, Cl, methoxy or fluoromethoxy, Y²³¹Is of the formula Y²³²Or formula Y²³³。

[ solution 4]

(in the formula, Z²³¹And Z²³²Independently F or a fluoroalkyl group having 1 to 3 carbon atoms)).

As the monomer providing the crosslinking site, at least one selected from the group consisting of:

general formula (180): CX¹⁸¹ ₂＝CX¹⁸²-R_f ¹⁸¹CHR¹⁸¹X¹⁸³

(in the formula, X¹⁸¹And X¹⁸²Independently a hydrogen atom, a fluorine atom or CH₃，R_f ¹⁸¹Is a fluoroalkylene, perfluoroalkylene, fluoro (poly) oxyalkylene or perfluoro (poly) oxyalkylene radical, R¹⁸¹Is a hydrogen atom or CH₃，X¹⁸³Is an iodine atom or a bromine atom), a fluorine-containing monomer,

General formula (190): CX¹⁹¹ ₂＝CX¹⁹²-R_f ¹⁹¹X¹⁹³

(in the formula, X¹⁹¹And X¹⁹²Independently a hydrogen atom, a fluorine atom or CH₃，R_f ¹⁹¹Is a fluoroalkylene, perfluoroalkylene, fluoropolyoxyalkylene or perfluoropolyoxyalkylene radical, X¹⁹³Is an iodine atom or a bromine atom), a fluorine-containing monomer,

General formula (200): CF (compact flash)₂＝CFO(CF₂CF(CF₃)O)_m(CF₂)_n-X²⁰¹

(wherein m is an integer of 0 to 5, n is an integer of 1 to 3, and X is²⁰¹Is cyano, carboxyl, alkoxycarbonyl, an iodine atom, a bromine atom or-CH₂I) The fluorine-containing monomer, and

general formula (210): CH (CH) ₂＝CFCF₂O(CF(CF₃)CF₂O)_m(CF(CF₃))_n-X²¹¹

(wherein m is an integer of 0 to 5, n is an integer of 1 to 3, and X is²¹¹Is cyano, carboxyl, alkoxycarbonyl, an iodine atom, a bromine atom or-CH₂OH) and a fluorine-containing monomer, and

general formula (220): CR²²¹R²²²＝CR²²³-Z²²¹-CR²²⁴＝CR²²⁵R²²⁶

(in the formula, R²²¹、R²²²、R²²³、R²²⁴、R²²⁵And R²²⁶The same or different, and is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. Z²²¹Is a linear or branched alkylene group having 1 to 18 carbon atoms, a cycloalkylene group having 3 to 18 carbon atoms, an alkylene group or oxyalkylene group having 1 to 10 carbon atoms, which is at least partially fluorinated, having or not having an oxygen atom

-(Q)_p-CF₂O-(CF₂CF₂O)_m(CF₂O)_n-CF₂-(Q)_p-

(wherein Q is an alkylene group or an oxyalkylene group, p is 0 or 1. m/n is 0.2 to 5) and a (per) fluoropolyoxyalkylene group having a molecular weight of 500 to 10000).

X¹⁸³And X¹⁹³Preferably an iodine atom. R_f ¹⁸¹And R_f ¹⁹¹Preferably a C1-5 perfluoroalkylene group. R¹⁸¹Preferably a hydrogen atom. X²⁰¹Preferably a cyano group, an alkoxycarbonyl group, an iodine atom, a bromine atom or-CH₂I。X²¹¹Preferably a cyano group, an alkoxycarbonyl group, an iodine atom, a bromine atom or-CH₂OH。

As the monomer providing the crosslinking site, it is preferably selected from the group consisting of CF₂＝CFOCF₂CF(CF₃)OCF₂CF₂CN、CF₂＝CFOCF₂CF(CF₃)OCF₂CF₂COOH、CF₂＝CFOCF₂CF(CF₃)OCF₂CF₂CH₂I、CF₂＝CFOCF₂CF₂CH₂I、CH₂＝CFCF₂OCF(CF₃)CF₂OCF(CF₃)CN、CH₂＝CFCF₂OCF(CF₃)CF₂OCF(CF₃)COOH、CH₂＝CFCF₂OCF(CF₃)CF₂OCF(CF₃)CH₂OH、CH₂＝CHCF₂CF₂I、CH₂＝CH(CF₂)₂CH＝CH₂、CH₂＝CH(CF₂)₆CH＝CH₂And CF₂＝CFO(CF₂)₅CN, more preferably selected from the group consisting of CF₂＝CFOCF₂CF(CF₃)OCF₂CF₂CN and CF₂＝CFOCF₂CF₂CH₂I.

In the step, the fluorine-containing monomer may be polymerized with a non-fluorine-containing monomer. Examples of the non-fluorine-containing monomer include hydrocarbon monomers reactive with the fluorine-containing monomer. Examples of the hydrocarbon-based monomer include: olefins such as ethylene, propylene, butylene, and isobutylene; alkyl vinyl ethers such as ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether, and cyclohexyl vinyl ether; vinyl esters such as vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyl isobutyrate, vinyl valerate, vinyl pivalate, vinyl hexanoate, vinyl octanoate, vinyl decanoate, vinyl versatate, vinyl laurate, vinyl tetradecanoate, vinyl palmitate, vinyl stearate, vinyl benzoate, vinyl p-tert-butylbenzoate, vinyl cyclohexanecarboxylate, vinyl monochloroacetate, vinyl adipate, vinyl acrylate, vinyl methacrylate, vinyl crotonate, vinyl sorbate, vinyl cinnamate, vinyl undecylenate, vinyl hydroxyacetate, vinyl hydroxypropionate, vinyl hydroxybutyrate, vinyl hydroxyvalerate, vinyl hydroxyisobutyrate, and vinyl hydroxycyclohexanecarboxylate; alkylallyl ethers such as ethylallyl ether, propylallyl ether, butylallyl ether, isobutylallyl ether, and cyclohexylallyl ether; alkyl allyl esters such as ethyl allyl ester, propyl allyl ester, butyl allyl ester, isobutyl allyl ester, and cyclohexyl allyl ester; and so on.

The non-fluorine-containing monomer may be a hydrocarbon monomer having a functional group (excluding a monomer providing a crosslinking site). Examples of the functional group-containing hydrocarbon monomer include: hydroxyalkyl vinyl ethers such as hydroxyethyl vinyl ether, hydroxypropyl vinyl ether, hydroxybutyl vinyl ether, hydroxyisobutyl vinyl ether and hydroxycyclohexyl vinyl ether; non-fluorine-containing monomers having a carboxyl group such as itaconic acid, succinic anhydride, fumaric acid, fumaric anhydride, crotonic acid, maleic anhydride, and perfluorocrotonic acid; non-fluorine-containing monomers having a glycidyl group such as glycidyl vinyl ether and glycidyl allyl ether; non-fluorine-containing monomers having an amino group such as aminoalkyl vinyl ether and aminoalkyl allyl ether; non-fluorine-containing monomers having amide groups such as (meth) acrylamide and methylolacrylamide; and so on.

In the polymerization step, particles of the desired fluoropolymer can be obtained by polymerizing 1 or 2 or more kinds of the above-mentioned fluoromonomers.

The polymerization temperature and polymerization pressure in the above polymerization step are appropriately determined depending on the kind of the monomer to be used, the molecular weight of the target fluoropolymer, and the reaction rate.

For example, the polymerization temperature is preferably 10 ℃ to 150 ℃. The polymerization temperature is more preferably 30 ℃ or higher, and still more preferably 50 ℃ or higher. Further, it is more preferably 120 ℃ or lower, and still more preferably 100 ℃ or lower.

The polymerization pressure is preferably 0.05MPaG to 10 MPaG. The polymerization pressure is more preferably 0.3MPaG or more, and still more preferably 0.5MPaG or more. Further, it is more preferably 5.0MPaG or less, and still more preferably 3.0MPaG or less. In particular, from the viewpoint of increasing the amount of the fluoropolymer to be obtained, it is preferably 1.0MPaG or more, more preferably 1.2MPaG or more, still more preferably 1.5MPaG or more, particularly preferably 1.8MPaG or more, and particularly preferably 2.0MPaG or more.

In the polymerization step, the amount of the carboxylic acid type hydrocarbon surfactant at the start of polymerization is preferably more than 50ppm with respect to the aqueous medium. The amount of the hydrocarbon surfactant at the start of polymerization is preferably 60ppm or more, more preferably 70ppm or more, further preferably 80ppm or more, further preferably 100ppm or more, particularly preferably 150ppm or more, particularly preferably 200ppm or more, and most preferably 300ppm or more. The upper limit is not particularly limited, but is preferably 10000ppm, more preferably 5000ppm, for example. When the amount of the carboxylic acid type hydrocarbon surfactant at the start of polymerization is in the above range, an aqueous dispersion having a smaller average primary particle diameter and more excellent stability can be obtained.

The polymerization can be started when the gaseous fluoromonomer in the reactor becomes a fluoropolymer and a pressure drop occurs in the reactor. U.S. Pat. No. 3,391,099 (Punderson) discloses a dispersion polymerization of tetrafluoroethylene in an aqueous medium, which includes 2 different stages of the polymerization process, first the formation of polymer nuclei as nucleation sites, and second the growth stage of the polymerization, which contains the established particles. Note that the polymerization is usually started when both the monomer to be polymerized and the polymerization initiator are charged into the reactor. In the present invention, an additive involved in the formation of a nucleation site is used as a nucleating agent.

The polymerization step is a step of polymerizing a fluorine-containing monomer such as tetrafluoroethylene in an aqueous medium in the presence of a carboxylic acid type hydrocarbon surfactant, and preferably includes a step of continuously adding a carboxylic acid type hydrocarbon surfactant.

The continuous addition of the carboxylic acid type hydrocarbon surfactant means, for example, that the carboxylic acid type hydrocarbon surfactant is not added all at once but is added over time or in portions.

In the step of continuously adding the carboxylic acid type hydrocarbon surfactant in the polymerization step, it is preferable that the addition of the carboxylic acid type hydrocarbon surfactant to the aqueous medium is started when the concentration of the fluoropolymer formed in the aqueous medium is less than 0.60% by mass. The addition of the carboxylic acid type hydrocarbon surfactant is started more preferably at the concentration of 0.50% by mass or less, still more preferably at the concentration of 0.36% by mass or less, yet more preferably at the concentration of 0.30% by mass or less, particularly preferably at the concentration of 0.20% by mass or less, particularly preferably at the concentration of 0.10% by mass or less, and most preferably at the same time as the start of polymerization. The concentration is a concentration based on the total of the aqueous medium and the fluoropolymer.

By including the above steps, an aqueous dispersion having a smaller average primary particle size and more excellent stability can be obtained.

In the step of continuously adding the carboxylic acid type hydrocarbon surfactant, the amount of the carboxylic acid type hydrocarbon surfactant added is preferably 0.01 to 10% by mass with respect to 100% by mass of the aqueous medium. The lower limit is more preferably 0.05% by mass, the lower limit is still more preferably 0.1% by mass, the upper limit is still more preferably 5% by mass, and the upper limit is still more preferably 1% by mass.

In the step of emulsion polymerization of the fluorine-containing monomer in the aqueous medium in the presence of the carboxylic acid type hydrocarbon surfactant, the amount of the carboxylic acid type hydrocarbon surfactant is preferably large, and is preferably 0.01 to 10% by mass based on 100% by mass of the aqueous medium. The lower limit is more preferably 0.1% by mass, and the upper limit is more preferably 1% by mass.

The above-mentioned carboxylic acid type hydrocarbon surfactant is usually an anionic surfactant having a hydrophilic portion of a carboxylic acid salt and a hydrophobic portion which is a long-chain hydrocarbon portion such as an alkyl group.

The carboxylic acid type hydrocarbon surfactant may be an aliphatic carboxylic acid type hydrocarbon surfactant, or a carboxylic acid type hydrocarbon other than an aliphatic type.

In the present specification, the "aliphatic carboxylic acid type hydrocarbon surfactant" refers to a carboxylic acid type hydrocarbon surfactant containing no carbonyl group (excluding a carboxyl group and a carbonyl group in an ester group). The ester group means a group represented by-COO-or-OCO-.

Examples of the carboxylic acid type hydrocarbon surfactant include the following formulas:

R¹⁰-COOM

(in the formula, R¹⁰Is a 1-valent organic group containing 1 or more carbon atoms. M is H, a metal atom, NR¹¹ ₄Imidazolium with or without substituents, pyridinium with or without substituents or phosphonium with or without substituents, R¹¹H or an organic group, which may be the same or different). As R¹¹Preferably H or C_1-10More preferably H or C_1-4An organic group of (2).

From the aspect of surface-active ability, R¹⁰The number of carbon atoms of (b) is preferably 2 or more, more preferably 3 or more. In addition, from the aspect of water solubility, R¹⁰The number of carbon atoms of (b) is preferably 29 or less, more preferably 23 or less.

Examples of the metal atom of M include alkali metals (group 1), alkaline earth metals (group 2), and the like, and Na, K, and Li are preferable. M is preferably H, a metal atom or NR ¹¹ ₄More preferably H, alkali metal (group 1), alkaline earth metal (group 2) or NR¹¹ ₄Further, H, Na, K, Li or NH is preferable₄Further more preferably Na, K or NH₄Particularly preferred is Na or NH₄Most preferably NH₄。

The carboxylic acid type hydrocarbon surfactant may further include a surfactant represented by the formula R¹²-COOM (wherein R¹²The alkyl group may be a linear or branched alkyl, alkenyl, alkylene or alkenylene group having 1 or more carbon atoms which may have a substituent, or a cyclic alkyl, alkenyl, alkylene or alkenylene group having 3 or more carbon atoms which may have a substituent, and may contain an ether bond. When the number of carbon atoms is 3 or more, a heterocyclic ring having a valence of 1 or 2 may be included, or a ring may be formed. M is the same as above).

Specifically, the group consisting of CH₃-(CH₂)_n-COOM (wherein n is an integer of 2 to 28, and M is the same as above).

From the viewpoint of emulsion stability, the carboxylic acid type hydrocarbon surfactant may not contain a carbonyl group (excluding a carbonyl group in a carboxyl group).

The surfactant used in the polymerization is preferably only a carboxylic acid type hydrocarbon surfactant containing no carbonyl group.

As the carboxylic acid type hydrocarbon surfactant not containing a carbonyl group, for example, the following formula (α) is preferably exemplified:

R-COO-M (α)

(wherein R is an alkyl group, an alkenyl group, an alkylene group or an alkenylene group, which may contain an ether bond; M is H, a metal atom, NR¹¹ ₄An imidazolium with or without a substituent, a pyridinium with or without a substituent, or a phosphonium with or without a substituent. R¹¹The same or different, H or an organic group having 1 to 10 carbon atoms).

In the above formula (. alpha.), R is preferably an alkyl group or an alkenyl group (which may contain an ether group). The alkyl group or alkenyl group in the above-mentioned R may be linear or branched. The number of carbon atoms of R is not limited, and is, for example, 2 to 29. The alkyl or alkenyl group in R preferably does not contain a carbonyl group (excluding the carbonyl group in the ester group).

When the alkyl group is linear, the number of carbon atoms of R is preferably 3 to 29, more preferably 5 to 23. When the alkyl group is branched, the number of carbon atoms in R is preferably 5 to 35, more preferably 11 to 23.

When the alkenyl group is linear, the number of carbon atoms of R is preferably 2 to 29, more preferably 9 to 23. When the alkenyl group is branched, the number of carbon atoms in R is preferably 2 to 29, more preferably 3 to 29, and still more preferably 9 to 23.

Examples of the alkyl group and the alkenyl group include a methyl group, an ethyl group, an isobutyl group, a tert-butyl group, and a vinyl group.

Examples of the carboxylic acid type hydrocarbon surfactant include butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, pentadecanoic acid, palmitic acid, palmitoleic acid, heptadecanoic acid, stearic acid, oleic acid, vaccenic acid, linoleic acid, (9,12,15) -linolenic acid, (6,9,12) linolenic acid, eleostearic acid, arachidic acid, 8, 11-eicosadienoic acid, eicosatrienoic acid, arachidonic acid, behenic acid, lignoceric acid, nervonic acid, cerotic acid, montanic acid, melissic acid, crotonic acid, myristoleic acid, palmitoleic acid, cis-6-hexadecenoic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, eicosenoic acid, erucic acid, nervonic acid, linoleic acid, eicosadienoic acid, docosenoic acid, pinolenic acid, alpha-eleostearic acid, Beta-eleostearic acid, eicosatrienoic acid, dihomo-gamma-linolenic acid, eicosatrienoic acid, stearidonic acid, arachidonic acid, eicosatetraenoic acid, docosatetraenoic acid, octadecapentaenoic acid, eicosapentaenoic acid, docosapentaenoic acid, sardine acid, tetracosapentaenoic acid, docosahexaenoic acid, herring acid, and salts thereof.

Particularly, at least one selected from the group consisting of lauric acid, capric acid, myristic acid, pentadecanoic acid, palmitic acid, and salts thereof is preferable, lauric acid and salts thereof are more preferable, salts of lauric acid are particularly preferable, and sodium laurate or ammonium laurate is most preferable.

Examples of the salt include a metal atom having a carboxyl group and a hydrogen atom of the formula M, NR¹¹ ₄The salt of imidazolium, pyridinium, or phosphonium is not particularly limited.

Examples of the carboxylic acid type hydrocarbon surfactant include those selected from the following formulas (a):

[ solution 5]

(in the formula, R^1aIs a linear or branched alkyl group having 1 or more carbon atoms or a cyclic alkyl group having 3 or more carbon atoms, the hydrogen atom bonded to the carbon atom may be substituted with a hydroxyl group or a 1-valent organic group containing an ester bond, the carbon atom may contain a carbonyl group when the carbon atom number is 2 or more, and the carbon atom may contain a 1-valent or 2-valent organic group when the carbon atom number is 3 or moreThe heterocyclic ring may form a ring. R^2aAnd R^3aIndependently a single bond or a 2-valent linking group. R^1a、R^2aAnd R^3aThe total number of carbon atoms of (2) is 5 or more. A. the^ais-COOX^a(X^aIs H, a metal atom, NR^4a ₄Imidazolium with or without substituents, pyridinium with or without substituents or phosphonium with or without substituents, R^4aAre H or organic radicals, which may be identical or different. ). R^1a、R^2aAnd R^3aAny two of which may be bonded to each other to form a ring), and the following formula (b):

[ solution 6]

(in the formula, R^1bThe alkyl group may be a linear or branched alkyl group having 1 or more carbon atoms, which may have a substituent, or a cyclic alkyl group having 3 or more carbon atoms, which may have a substituent, and may contain a heterocyclic ring having 1 or 2 valences or may form a ring when the number of carbon atoms is 3 or more. R^2bAnd R^4bIndependently is H or a substituent. R^3bIs an alkylene group having 1 to 10 carbon atoms, which may have a substituent. n is an integer of 1 or more. p and q are independently integers of 0 or more. A. the^bis-COOX^b(X^bIs H, a metal atom, NR^5b ₄Imidazolium with or without substituents, pyridinium with or without substituents or phosphonium with or without substituents, R^5bAre H or organic radicals, which may be identical or different. ). R^1b、R^2b、R^3bAnd R^4bAny two of which may be bonded to each other to form a ring. L is a single bond, -CO₂-B-*、-OCO-B-*、-CONR^6b-B-*、-NR^6bCO-B-, or-CO- (excluding-CO)₂-B-、-OCO-B-、-CONR^6b-B-、-NR^6bCarbonyl group contained in CO-B-), B is a single bond or the number of carbon atoms having a substituent(s) of 1 toAlkylene of 10, R^6bH or an alkyl group having 1 to 4 carbon atoms, which may have a substituent. Is represented by A in the formula^bOne side of the bond. ) At least one member of the group consisting of the surfactants (b) shown.

The surfactant (a) will be explained.

In the formula (a), R^1aIs a linear or branched alkyl group having 1 or more carbon atoms or a cyclic alkyl group having 3 or more carbon atoms.

When the number of carbon atoms of the alkyl group is 3 or more, a carbonyl group (-C (═ O) -) may be contained between 2 carbon atoms. When the alkyl group has 2 or more carbon atoms, the carbonyl group may be contained at the end of the alkyl group. I.e. CH₃Acyl groups such as an acetyl group represented by — C (═ O) -, are also included in the above alkyl groups.

When the number of carbon atoms of the alkyl group is 3 or more, the alkyl group may contain a heterocyclic ring having a valence of 1 or 2, or may form a ring. The heterocyclic ring is preferably an unsaturated heterocyclic ring, more preferably an oxygen-containing unsaturated heterocyclic ring, and examples thereof include furan rings and the like. R^1aIn the above formula, a 2-valent heterocyclic ring may be inserted between 2 carbon atoms, a 2-valent heterocyclic ring may be located at the terminal and bonded to — C (═ O) -, and a 1-valent heterocyclic ring may be located at the terminal of the alkyl group.

In the present specification, the "number of carbon atoms" of the alkyl group also includes the number of carbon atoms constituting the carbonyl group and the number of carbon atoms constituting the heterocycle. E.g. CH₃-C(＝O)-CH₂-the number of carbon atoms of the group represented is 3, CH ₃-C(＝O)-C₂H₄-C(＝O)-C₂H₄-the number of carbon atoms of the group represented is 7, CH₃The number of carbon atoms of the group represented by — C (═ O) — is 2.

In the above alkyl group, the hydrogen atom bonded to the carbon atom may be substituted with a functional group, for example, a hydroxyl group (-OH) or a 1-valent organic group containing an ester bond, but is preferably not substituted with any functional group.

Examples of the 1-valent organic group containing an ester bond include the following: -O-C (═ O) -R^101a(in the formula, R^101aIs an alkyl group).

In the above alkyl groups, 75% or less of hydrogen atoms bonded to carbon atoms may be substituted with a halogen atom, 50% or less may be substituted with a halogen atom, and 25% or less may be substituted with a halogen atom, but a non-halogenated alkyl group containing no halogen atom such as a fluorine atom or a chlorine atom is preferable.

In the formula, R^2aAnd R^3aIndependently a single bond or a 2-valent linking group.

R^2aAnd R^3aPreferably a single bond, a linear or branched alkylene group having 1 or more carbon atoms, or a cyclic alkylene group having 3 or more carbon atoms.

Form R^2aAnd R^3aThe above alkylene group of (a) preferably does not contain a carbonyl group.

In the above alkylene group, the hydrogen atom bonded to the carbon atom may be substituted with a functional group, for example, a hydroxyl group (-OH) or a 1-valent organic group containing an ester bond, but is preferably not substituted with any functional group.

Examples of the 1-valent organic group containing an ester bond include the following: -O-C (═ O) -R^102a(in the formula, R^102aIs an alkyl group).

Of the above alkylene groups, 75% or less of hydrogen atoms bonded to carbon atoms may be substituted with halogen atoms, 50% or less may be substituted with halogen atoms, and 25% or less may be substituted with halogen atoms, but a non-halogenated alkylene group containing no halogen atom such as a fluorine atom or chlorine atom is preferable.

R^1a、R^2aAnd R^3aThe total number of carbon atoms of (2) is 5 or more. The total number of carbon atoms is preferably 7 or more, more preferably 9 or more, preferably 20 or less, more preferably 18 or less, and further preferably 15 or less.

R^1a、R^2aAnd R^3aAny two of which may be bonded to each other to form a ring.

In the formula (a), A^ais-COOX^a(X^aIs H, a metal atom, NR^4a ₄Imidazolium with or without substituents, with or withoutPyridinium with substituents or phosphonium with or without substituents, R^4aAre H or an organic group, and may be the same or different. ). As R^4aPreferably, the organic group has 1 to 10 carbon atoms, and more preferably 1 to 4 carbon atoms. Examples of the metal atom include alkali metals (group 1), alkaline earth metals (group 2), and the like, and Na, K, and Li are preferable.

As X^aPreferably H, alkali metal (group 1), alkaline earth metal (group 2) or NR^4a ₄For reasons of easy solubility in water, H, Na, K, Li or NH are more preferred₄Further, Na, K or NH is preferable for the reason of being more soluble in water₄Particularly preferred is Na or NH₄For reasons of easy removal, NH is most preferred₄。X^aIs NH₄In the case of the above surfactant, the surfactant is excellent in solubility in an aqueous medium, and the metal component is not likely to remain in the fluoropolymer or in the final product.

As R^1aPreferably, the alkyl group is a linear or branched alkyl group having 1 to 8 carbon atoms, which does not include a carbonyl group, a cyclic alkyl group having 3 to 8 carbon atoms, which does not include a carbonyl group, a linear or branched alkyl group having 2 to 45 carbon atoms, which includes 1 to 10 carbonyl groups, a cyclic alkyl group having 3 to 45 carbon atoms, which includes a carbonyl group, or an alkyl group having 3 to 45 carbon atoms, which includes a heterocyclic ring having 1 or 2 valences.

In addition, as R^1aMore preferably, the following formula:

[ solution 7]

(in the formula, n^11aIs an integer of 0 to 10, R^11aIs a linear or branched alkyl group having 1 to 5 carbon atoms or a cyclic alkyl group having 3 to 5 carbon atoms, R^12aIs an alkylene group having 0 to 3 carbon atoms. n is^11aWhen R is an integer of 2 to 10 ^12aEach may be the same or different).

As n^11aPreferably an integer of 0 to 5, more preferably an integer of 0 to 3, and further preferably an integer of 1 to 3.

As R^11aThe above alkyl group of (a) preferably does not contain a carbonyl group.

As R^11aIn the above alkyl group, the hydrogen atom bonded to the carbon atom may be substituted with a functional group, for example, a hydroxyl group (-OH) or a 1-valent organic group containing an ester bond, but is preferably not substituted with any functional group.

Examples of the 1-valent organic group containing an ester bond include the following: -O-C (═ O) -R^103a(in the formula, R^103aIs an alkyl group).

As R^11aIn the above alkyl groups, 75% or less of the hydrogen atoms bonded to the carbon atoms may be substituted with a halogen atom, 50% or less may be substituted with a halogen atom, and 25% or less may be substituted with a halogen atom, but a non-halogenated alkyl group containing no halogen atom such as a fluorine atom or a chlorine atom is preferable.

R^12aIs an alkylene group having 0 to 3 carbon atoms. The number of carbon atoms is preferably 1 to 3.

As R^12aThe alkylene group in (b) may be linear or branched.

As R^12aThe above alkylene group of (a) preferably does not contain a carbonyl group. As R^12aMore preferably an ethylene group (-C)₂H₄-) or propylene (-C)₃H₆-)。

As R^12aIn the above alkylene group, the hydrogen atom bonded to the carbon atom may be substituted with a functional group, for example, a hydroxyl group (-OH) or a 1-valent organic group containing an ester bond, but is preferably not substituted with any functional group.

Examples of the 1-valent organic group containing an ester bond include the following: -O-C (═ O) -R^104a(in the formula, R^104aIs an alkyl group).

As R^12aIn the above alkylene group, 75% or less of the hydrogen atoms bonded to the carbon atoms may be substituted with halogen atoms, 50% or less may be substituted with halogen atoms, and 25% or less may be substituted with halogen atoms, butThe non-halogenated alkylene group is preferably one containing no halogen atom such as a fluorine atom or a chlorine atom.

As R^2aAnd R^3aThe alkylene group having 1 or more carbon atoms and not containing a carbonyl group is preferable, the alkylene group having 1 to 3 carbon atoms and not containing a carbonyl group is more preferable, and the ethylene group (-C) is further preferable₂H₄-) or propylene (-C)₃H₆-)。

Next, the surfactant (b) will be described.

In the formula (b), R^1bIs a linear or branched alkyl group having 1 or more carbon atoms, which may have a substituent, or a cyclic alkyl group having 3 or more carbon atoms, which may have a substituent.

When the number of carbon atoms of the alkyl group is 3 or more, the alkyl group may contain a heterocyclic ring having a valence of 1 or 2, or may form a ring. The heterocyclic ring is preferably an unsaturated heterocyclic ring, more preferably an oxygen-containing unsaturated heterocyclic ring, and examples thereof include furan rings and the like. R^1bIn the above formula, a 2-valent heterocyclic ring may be inserted between 2 carbon atoms, a 2-valent heterocyclic ring may be located at the terminal and bonded to — C (═ O) -, and a 1-valent heterocyclic ring may be located at the terminal of the alkyl group.

In the present specification, the "number of carbon atoms" of the alkyl group also includes the number of carbon atoms constituting the heterocyclic ring.

With respect to as R^1bThe substituent which the alkyl group may have is preferably a halogen atom, a linear or branched alkyl group having 1 to 10 carbon atoms, a cyclic alkyl group having 3 to 10 carbon atoms or a hydroxyl group, and particularly preferably a methyl group or an ethyl group.

As R^1bThe above alkyl group of (a) preferably does not contain a carbonyl group.

The above alkyl group preferably does not have any substituent.

As R^1bThe alkyl group is preferably a linear or branched alkyl group having 1 to 10 carbon atoms, which may or may not have a substituent, or a cyclic alkyl group having 3 to 10 carbon atoms, more preferably a linear or branched alkyl group having 1 to 10 carbon atoms, which may or may not include a carbonyl group, or a cyclic alkyl group having 3 to 10 carbon atoms, which may not include a carbonyl group, further preferably a linear or branched alkyl group having 1 to 10 carbon atoms, which may not have a substituent, further more preferably a linear or branched alkyl group having 1 to 3 carbon atoms, which may not have a substituent, and particularly preferably a methyl group (-CH) ₃) Or ethyl (-C)₂H₅) Most preferred is methyl (-CH)₃)。

In the formula (b), R^2bAnd R^4bIndependently is H or a substituent. More than 2R^2bAnd R^4bEach may be the same or different.

With respect to as R^2bAnd R^4bThe substituent(s) is preferably a halogen atom, a linear or branched alkyl group having 1 to 10 carbon atoms, a cyclic alkyl group having 3 to 10 carbon atoms, or a hydroxyl group, and particularly preferably a methyl group or an ethyl group.

As R^2bAnd R^4bThe above alkyl group of (a) preferably does not contain a carbonyl group. In the above alkyl groups, 75% or less of hydrogen atoms bonded to carbon atoms may be substituted with a halogen atom, 50% or less may be substituted with a halogen atom, and 25% or less may be substituted with a halogen atom, but a non-halogenated alkyl group containing no halogen atom such as a fluorine atom or a chlorine atom is preferable.

The above alkyl group preferably does not have any substituent.

With respect to as R^2bAnd R^4bThe alkyl group (C) is preferably a linear or branched alkyl group having 1 to 10 carbon atoms and not containing a carbonyl group or a cyclic alkyl group having 3 to 10 carbon atoms and not containing a carbonyl group, more preferably a linear or branched alkyl group having 1 to 10 carbon atoms and not containing a carbonyl group, further preferably a linear or branched alkyl group having 1 to 3 carbon atoms and not containing a substituent, and particularly preferably a methyl group (-CH) ₃) Or ethyl (-C)₂H₅)。

As R^2bAnd R^4bPreferably independently H or a linear or branched alkyl group having 1 to 10 carbon atoms and not containing a carbonyl group, more preferably H or a linear or branched alkyl group having 1 to 3 carbon atoms and not containing a substituent, and still more preferably H or a methyl group (-CH)₃) Or ethyl (-C)₂H₅) H is particularly preferred.

In the formula (b), R^3bIs an alkylene group having 1 to 10 carbon atoms, which may have a substituent. R^3bWhen there are 2 or more, they may be the same or different.

The alkylene group preferably does not contain a carbonyl group.

In the above alkylene group, 75% or less of hydrogen atoms bonded to carbon atoms may be substituted with a halogen atom, 50% or less may be substituted with a halogen atom, and 25% or less may be substituted with a halogen atom, but a non-halogenated alkyl group containing no halogen atom such as a fluorine atom or a chlorine atom is preferable.

The above alkylene group preferably does not have any substituent.

The alkylene group is preferably a linear or branched alkylene group having 1 to 10 carbon atoms which may have a substituent or may not have a substituent or a cyclic alkylene group having 3 to 10 carbon atoms which may have a substituent or not, more preferably a linear or branched alkylene group having 1 to 10 carbon atoms which may not contain a carbonyl group or a cyclic alkylene group having 3 to 10 carbon atoms which may not contain a carbonyl group, more preferably a linear or branched alkylene group having 1 to 10 carbon atoms which may not have a substituent, and still more preferably methylene (-CH) ₂-) ethylene (-C), ethylene (-C)₂H₄-) isopropylidene (-CH (CH)₃)CH₂-) or propylene (-C)₃H₆-)。

R^1b、R^2b、R^3bAnd R^4bAny two of which may be bonded to each other to form a ring.

In the formula (b), n is an integer of 1 or more. The number n is preferably an integer of 1 to 40, more preferably an integer of 1 to 30, and still more preferably an integer of 5 to 25.

In the formula (b), p and q are independently integers of 0 or more. P is preferably an integer of 0 to 10, more preferably 0 or 1. Q is preferably an integer of 0 to 10, more preferably an integer of 0 to 5.

The sum of n, p and q is preferably an integer of 6 or more. The sum of n, p and q is more preferably an integer of 8 or more. The total of n, p and q is preferably an integer of 60 or less, more preferably an integer of 50 or less, and still more preferably an integer of 40 or less.

In the formula (b), A^bis-COOX^b(X^bIs H, a metal atom, NR^5b ₄Imidazolium with or without substituents, pyridinium with or without substituents or phosphonium with or without substituents, R^5bAre H or an organic group, and may be the same or different. ). As R^5bPreferably, H or an organic group having 1 to 10 carbon atoms, and more preferably H or an organic group having 1 to 4 carbon atoms. Examples of the metal atom include alkali metals (group 1), alkaline earth metals (group 2), and the like, and Na, K, and Li are preferable. X ^bMay be a metal atom or NR^5b ₄(R^5bAs described above).

As X^bPreferably H, alkali metal (group 1), alkaline earth metal (group 2) or NR^5b ₄For reasons of easy solubility in water, H, Na, K, Li or NH are more preferred₄Further, Na, K or NH is preferable for the reason of being more soluble in water₄Particularly preferred is Na or NH₄For reasons of easy removal, NH is most preferred₄。X^bIs NH₄In the case of the above surfactant, the surfactant is excellent in solubility in an aqueous medium, and the metal component is not likely to remain in the fluoropolymer or in the final product.

In the formula (b), L is a single bond, -CO₂-B-*、-OCO-B-*、-CONR^6b-B-*、-NR^6bCO-B-, or-CO- (excluding-CO)₂-B-、-OCO-B-、-CONR^6b-B-、-NR^6bA carbonyl group contained in CO-B-), B is a single bond or an alkylene group having 1 to 10 carbon atoms and having or not having a substituent, R^6bH or an alkyl group having 1 to 4 carbon atoms, which may have a substituent. The number of carbon atoms of the alkylene group is more preferably 1 to 5. In addition, the above R^6bMore preferably H or methyl. Means thatAnd A in the formula^bOne side of the bond.

L is preferably a single bond.

The above surfactant is in¹The integral value of all peak intensities observed in the region of chemical shifts 2.0ppm to 5.0ppm in the H-NMR spectrum is preferably 10% or more.

The above surfactant is in¹The integral value of all peak intensities observed in the region of chemical shifts 2.0ppm to 5.0ppm in the H-NMR spectrum is preferably within the above range. In this case, the surfactant preferably has a ketone structure in the molecule.

In the surfactant, the integrated value is more preferably 15 or more, preferably 95 or less, more preferably 80 or less, and still more preferably 70 or less.

The integral value was measured at room temperature using a heavy water solvent. The amount of heavy water was 4.79 ppm.

Further, as the carboxylic acid type hydrocarbon surfactant in the present invention, a compound represented by the general formula (1-0) (hereinafter also referred to as "surfactant (1-0)") can also be used.

General formula (1-0):

[ solution 8]

(in the formula, R¹～R⁵Represents H or a monovalent substituent, wherein R¹And R³At least 1 of which represents the general formula: -Y-R⁶A group shown, R²And R⁵At least 1 of which represents the general formula: -X-A or a group of formula: -Y-R⁶The groups shown.

Further, X, which is the same or different at each occurrence, is a 2-valent linking group or bond;

a is the same or different at each occurrence and represents-COOM (M is H, a metal atom, NR)⁷ ₄Imidazolium with or without substituents, pyridinium with or without substituents or phosphonium with or without substituents, R⁷Is H or hasAn organic group);

y is the same or different at each occurrence and represents a group selected from-S (═ O)₂-、-O-、-COO-、-OCO-、-CONR⁸-and-NR⁸2-valent linking groups or bonds in the group consisting of CO-, R ⁸Is H or an organic group;

R⁶each occurrence, which may be the same or different, represents an alkyl group having 1 or more carbon atoms which may contain at least one selected from the group consisting of a carbonyl group, an ester group, an amide group and a sulfonyl group between carbon-carbon atoms.

R¹～R⁵Any two of which may be bonded to each other to form a ring.

Wherein R is⁶In the case where any one of the carbonyl group, the ester group, the amide group, and the sulfonyl group is not included, X is a 2-valent linking group including at least one selected from the group consisting of a carbonyl group, an ester group, an amide group, and a sulfonyl group. )

In the formula, R¹～R⁵Represents H or a monovalent substituent, wherein R¹And R³At least one of them represents the general formula: -Y-R⁶A group shown, R²And R⁵At least one of them represents the general formula: -X-A or a group of formula: -Y-R⁶The groups shown. R¹～R⁵Any two of which may be bonded to each other to form a ring.

As R¹The substituent which the alkyl group may have is preferably a halogen atom, a linear or branched alkyl group having 1 to 10 carbon atoms, or a cyclic alkyl group having 3 to 10 carbon atoms, or a hydroxyl group, and particularly preferably a methyl group or an ethyl group.

As R¹The above alkyl group of (a) preferably does not contain a carbonyl group.

The above alkyl group preferably does not have any substituent.

As R¹The alkyl group is preferably a linear or branched alkyl group having 1 to 10 carbon atoms, which may or may not have a substituent, or a cyclic alkyl group having 3 to 10 carbon atoms, more preferably a linear or branched alkyl group having 1 to 10 carbon atoms, which may or may not include a carbonyl group, or a cyclic alkyl group having 3 to 10 carbon atoms, which may not include a carbonyl group, further preferably a linear or branched alkyl group having 1 to 10 carbon atoms, which may not have a substituent, further more preferably a linear or branched alkyl group having 1 to 3 carbon atoms, which may not have a substituent, and particularly preferably a methyl group (-CH)₃) Or ethyl (-C)₂H₅) Most preferred is methyl (-CH)₃)。

As monovalent substituents, preference is given to those of the formula: -Y-R⁶A group represented by the general formula: a group represented by-X-A, -H, C with or without a substituent_1-20Alkyl, -NH of₂、-NHR⁹(R⁹Is an organic radical), -OH, -COOR⁹(R⁹Is an organic group) OR-OR⁹(R⁹Is an organic group). The number of carbon atoms of the alkyl group is preferably 1 to 10.

As R⁹Preferably C_1-10Alkyl or C_1-10Alkylcarbonyl of (a), more preferably C_1-4Alkyl or C_1-4An alkylcarbonyl group of (a).

Wherein X, which is the same or different at each occurrence, represents a 2-valent linking group or bond.

R⁶In the case where any one of a carbonyl group, an ester group, an amide group, and a sulfonyl group is not included, X is preferably a 2-valent linking group including at least one selected from the group consisting of a carbonyl group, an ester group, an amide group, and a sulfonyl group.

X preferably contains a substituent selected from the group consisting of-CO-, -S (═ O)₂-、-O-、-COO-、-OCO-、-S(＝O)₂-O-、-O-S(＝O)₂-、-CONR⁸-and-NR⁸A 2-valent linking group of at least one bond of the group consisting of CO-, C_1-10Alkylene groups, or a bond. R⁸Represents H or an organic group.

As R⁸Preferably H or C_1-10Organic group of (2), more preferablyH or C_1-4The organic group of (3), is more preferably H.

Wherein A is the same or different at each occurrence and represents-COOM (M is H, a metal atom, NR)⁷ ₄Imidazolium with or without substituents, pyridinium with or without substituents or phosphonium with or without substituents, R⁷Is H or an organic group. 4R⁷May be the same or different).

As R⁷Preferably H or C_1-10More preferably H or C_1-4An organic group of (2).

Examples of the metal atom include alkali metals (group 1), alkaline earth metals (group 2), and the like, and Na, K, and Li are preferable.

M is preferably H, a metal atom or NR⁷ ₄More preferably H, alkali metal (group 1), alkaline earth metal (group 2) or NR⁷ ₄Further, H, Na, K, Li or NH is preferable ₄Further more preferably Na, K or NH₄Particularly preferred is Na or NH₄Most preferably NH₄。

Wherein each occurrence of Y, which may be the same or different, is selected from the group consisting of-S (═ O)₂-、-O-、-COO-、-OCO-、-CONR⁸-and-NR⁸2-valent linking groups or bonds in the group consisting of CO-, R⁸Represents H or an organic group.

Y is preferably selected from the group consisting of a bond, -O-, -COO-, -OCO-, -CONR⁸-and-NR⁸The 2-valent linking group in the group consisting of CO-, more preferably a 2-valent linking group selected from the group consisting of a bond, -COO-, and-OCO-.

As R⁸Preferably H or C_1-10More preferably H or C_1-4The organic group of (3), is more preferably H.

In the formula, R⁶The alkyl group having 1 or more carbon atoms, which may be the same or different at each occurrence, may or may not contain at least one selected from the group consisting of a carbonyl group, an ester group, an amide group and a sulfonyl group between carbon-carbon atoms. R is as defined above⁶The number of carbon atoms of the organic group (2) is preferably 2 or more, preferably 20 or less, more preferably 2 to 20, and still more preferably 2 to 10.

R⁶The alkyl group of (2) may contain 1 or 2 or more carbon-carbon atoms selected from the group consisting of a carbonyl group, an ester group, an amide group and a sulfonyl group, but these groups are not contained at the terminal of the alkyl group. R is as defined above ⁶In the alkyl group (b), 75% or less of hydrogen atoms bonded to carbon atoms may be substituted with a halogen atom, 50% or less may be substituted with a halogen atom, and 25% or less may be substituted with a halogen atom, but a non-halogenated alkyl group containing no halogen atom such as a fluorine atom or a chlorine atom is preferable.

As R⁶Preference is given to

A compound of the general formula: -R¹⁰-CO-R¹¹The group shown,

A compound of the general formula: -R¹⁰-COO-R¹¹The group shown,

A compound of the general formula: -R¹¹The group shown,

A compound of the general formula: -R¹⁰-NR⁸CO-R¹¹The group shown, or

A compound of the general formula: -R¹⁰-CONR⁸-R¹¹The group shown,

(in the formula, R⁸Represents H or an organic group. R¹⁰Is alkylene, R¹¹Alkyl with or without substituents).

As R⁶More preferred is the general formula: -R¹⁰-CO-R¹¹The groups shown.

As R⁸Preferably H or C_1-10More preferably H or C_1-4The organic group of (3), is more preferably H.

R¹⁰The number of carbon atoms of the alkylene group(s) is preferably 1 or more, more preferably 3 or more, preferably 20 or less, more preferably 12 or less, further preferably 10 or less, and particularly preferably 8 or less. In addition, R¹⁰The alkylene group (B) preferably has 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms, and further preferably 3 to 10 carbon atoms.

R¹¹The alkyl group (C) may have 1 to 20 carbon atoms, preferably 1 to 1 carbon atom5. More preferably 1 to 12, further preferably 1 to 10, further preferably 1 to 8, particularly preferably 1 to 6, further preferably 1 to 3, particularly preferably 1 or 2, and most preferably 1. In addition, the above R ¹¹The alkyl group (b) preferably consists only of a primary carbon, a secondary carbon and a tertiary carbon, and particularly preferably consists only of a primary carbon and a secondary carbon. I.e. as R¹¹Methyl, ethyl, n-propyl and isopropyl are preferred, and methyl is particularly preferred.

As the surfactant (1), a compound represented by the general formula (1-2) or a compound represented by the general formula (1-3) is preferable, and a compound represented by the general formula (1-1) or a compound represented by the general formula (1-2) is more preferable.

General formula (1-1):

[ solution 9]

(in the formula, R³～R⁶X, A and Y are as described above. )

General formula (1-2):

[ solution 10]

(in the formula, R⁴～R⁶X, A and Y are as described above. )

General formula (1-3):

[ solution 11]

(in the formula, R²、R⁴～R⁶X, A and Y are as described above. )

As a general formula: a group represented by-X-A, preferably

-COOM、

-R¹²COOM、

-OCO-R¹²-COOM、

-COO-R¹²-COOM、

-CONR⁸-R¹²-COOM、

-NR⁸CO-R¹²-COOM、

-OS(＝O)₂-R¹²-COOM

(in the formula, R⁸And M is as described above. R¹²Is C_1-10Alkylene groups of (ii).

R is as defined above¹²The alkylene group of (2) may have 75% or less of hydrogen atoms bonded to carbon atoms substituted with halogen atoms, 50% or less of hydrogen atoms substituted with halogen atoms, and 25% or less of hydrogen atoms substituted with halogen atoms, but is preferably a non-halogenated alkylene group containing no halogen atom such as a fluorine atom or chlorine atom.

As a general formula: -Y-R⁶The radicals indicated are preferred

A compound of the general formula: -R¹⁰-CO-R¹¹The group shown,

A compound of the general formula: -OCO-R¹⁰-CO-R¹¹The group shown,

A compound of the general formula: -COO-R¹⁰-CO-R¹¹The group shown,

A compound of the general formula: -OCO-R¹⁰-COO-R¹¹The group shown,

A compound of the general formula: -COO-R¹¹The group shown,

A compound of the general formula: -NR⁸CO-R¹⁰-CO-R¹¹The group shown, or

A compound of the general formula: -CONR⁸-R¹⁰-NR⁸CO-R¹¹A group shown

(in the formula, R⁸、R¹⁰And R¹¹As described above).

In the formula, as R⁴And R⁵Independently, H or C is preferred_1-4Alkyl group of (1).

R is as defined above⁴And R⁵In the alkyl group (b), 75% or less of hydrogen atoms bonded to carbon atoms may be substituted with halogen atoms, 50% or less may be substituted with halogen atoms, and 25% or less may be substituted with halogen atoms, but it is preferably free from fluorine atoms, chlorine atoms and the likeA non-halogenated alkyl group of a halogen atom.

As R in the general formula (1-1)³Preferably H or C with or without substituents_1-20More preferably H or C having no substituent_1-20The alkyl group of (3) is more preferably H.

R is as defined above³In the alkyl group (b), 75% or less of hydrogen atoms bonded to carbon atoms may be substituted with a halogen atom, 50% or less may be substituted with a halogen atom, and 25% or less may be substituted with a halogen atom, but a non-halogenated alkyl group containing no halogen atom such as a fluorine atom or a chlorine atom is preferable.

As R in the general formula (1-3)²Preferably H, OH or C with or without substituents_1-20More preferably H, OH or C having no substituent _1-20Further, the alkyl group of (1) is preferably H or OH.

R is as defined above²In the alkyl group (b), 75% or less of hydrogen atoms bonded to carbon atoms may be substituted with a halogen atom, 50% or less may be substituted with a halogen atom, and 25% or less may be substituted with a halogen atom, but a non-halogenated alkyl group containing no halogen atom such as a fluorine atom or a chlorine atom is preferable.

Among the above carboxylic acid type hydrocarbon surfactants, the aliphatic carboxylic acid type hydrocarbon surfactants include the surfactant represented by the above formula (α), the following formula (1-0A):

[ solution 12]

(in the formula, R^1A～R^5AIs H, a 1-valent hydrocarbyl group that may contain an ester group between carbon-carbon atoms, or a compound of the formula: -X^A-A is a group represented by. However, R^2AAnd R^5ARepresents the general formula: -X^A-A is a group represented by.

X^AIdentical or different at each occurrence and is a 2-valent hydrocarbyl group or a bond;

a is identical or different on each occurrence and is-COOM (M is H, a metal atom, NR)⁷ ₄Imidazolium with or without substituents, pyridinium with or without substituents or phosphonium with or without substituents, R⁷Is H or an organic group);

R^1A～R^5Aany two of which may be bonded to each other to form a ring), and the like.

In the general formula (1-0A), in R ^1A～R^5AIn the above formula, the number of carbon atoms of the 1-valent hydrocarbon group which may contain an ester group between carbon-carbon atoms is preferably 1 to 50, more preferably 5 to 20. R^1A～R^5AThe hydrocarbon group in (1) does not contain a carbonyl group (excluding a carboxyl group and a carbonyl group in an ester group). R^1A～R^5AAny two of which may be bonded to each other to form a ring. The 1-valent hydrocarbon group which may contain an ester group between carbon and carbon atoms is preferably an alkyl group.

In the formula, X^AIn the (2) -valent hydrocarbon group, the number of carbon atoms is preferably 1 to 50, more preferably 5 to 20. X^AThe hydrocarbon group in (1) does not contain a carbonyl group. Examples of the 2-valent hydrocarbon group include an alkylene group and an alkanediyl group, and an alkylene group is preferable.

In the general formula (1-0A), R^2AAnd R^5AAny of the above is preferably of the general formula: -X^AA group represented by-A, more preferably R^2AIs represented by the general formula: -X^A-A is a group represented by.

In the general formula (1-0A), R is a preferable embodiment^2AIs represented by the general formula: -X^AA group represented by-A, R^1A、R^3A、R^4AAnd R^5AIn the form of H. In this case, X^APreferably a bond or an alkylene group having 1 to 5 carbon atoms.

In the general formula (1-0A), the following is also preferable: r^2AIs represented by the general formula: -X^AA group represented by-A, R^1AAnd R^3Ais-Y^A-R⁶A group shown, Y^AIs the same or different at each occurrence and is-COO-, -OCO-, or a bond, R ⁶Each occurrence of the alkyl group is the same or different and is an alkyl group having 1 or more carbon atoms. In this case, R^4AAnd R^5APreferably, it isH。

Examples of the aliphatic carboxylic acid type hydrocarbon surfactant represented by the general formula (1-0A) include glutaric acid or a salt thereof, adipic acid or a salt thereof, pimelic acid or a salt thereof, suberic acid or a salt thereof, azelaic acid or a salt thereof, sebacic acid or a salt thereof, and the like.

The aliphatic carboxylic acid type hydrocarbon surfactant represented by the general formula (1-0A) may be a double-chain double hydrophilic group type synthetic surfactant, and examples of the Gemini type surfactant include Gemini Surf (kyoto fat and oil co., ltd.), gemmurf α 142 (c 12 lauryl), gemmurf α 102 (c 10), and gemmurf α 182 (c 14).

The production process of the present invention may include, before the polymerization step, a step of subjecting a carboxylic acid type hydrocarbon surfactant (aliphatic carboxylic acid type hydrocarbon surfactant in the production process 2) to radical treatment or oxidation treatment.

The radical treatment may be a treatment for generating radicals in the carboxylic acid type hydrocarbon surfactant, and examples of the radical treatment include the following treatments: adding deionized water and a carboxylic acid type hydrocarbon surfactant into a reactor, sealing the reactor, replacing the system with nitrogen, heating and pressurizing the reactor, adding a polymerization initiator, stirring for a certain time, releasing the pressure of the reactor until the pressure reaches atmospheric pressure, and cooling. The oxidation treatment is a treatment in which an oxidizing agent is added to a carboxylic acid type hydrocarbon surfactant. Examples of the oxidizing agent include oxygen, ozone, hydrogen peroxide, manganese (IV) oxide, potassium permanganate, potassium dichromate, nitric acid, and sulfur dioxide. In order to promote the radical treatment or the oxidation treatment, the radical treatment or the oxidation treatment may be performed in an aqueous solution having a pH adjusted. The pH of the aqueous solution for the radical treatment or the oxidation treatment is preferably less than 7, and for example, the pH of the aqueous solution can be adjusted using sulfuric acid, nitric acid, hydrochloric acid, or the like.

In the production method of the present invention, the polymerization step may further include a step of adjusting the pH of an aqueous medium containing a carboxylic acid type hydrocarbon surfactant (aliphatic carboxylic acid type hydrocarbon surfactant in the production method 2) to be alkaline. The basic is a pH of preferably 7.1 or more, more preferably 7.5 or more, further preferably 8.0 or more, particularly preferably 8.5 or more, and further preferably 9.0 or more. By adjusting the pH to be alkaline, the surface active ability can be improved. The step of adjusting the pH may be performed before the step of subjecting the carboxylic acid type hydrocarbon surfactant to radical treatment or oxidation treatment, or may be performed after the step, and is preferably performed after the step. The method of adjusting the pH is not particularly limited, and a method of adding a pH adjuster to the aqueous medium may be mentioned. As the pH adjuster, ammonia, NaOH, potassium hydroxide, sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, ammonium hydrogen carbonate, sodium phosphate, potassium phosphate, sodium citrate, potassium citrate, ammonium citrate, sodium gluconate, potassium gluconate, ammonium gluconate, or the like can be used. The pH can be measured by a pH meter manufactured by orion.

In the production method of the present invention, the polymerization may be carried out using at least one carboxylic acid type hydrocarbon surfactant. In the production method of the present invention, 2 or more kinds of the above-mentioned carboxylic acid type hydrocarbon surfactants may be used together as the surfactant, and any surfactant other than the above-mentioned carboxylic acid type hydrocarbon surfactants may be used together as long as it is a volatile surfactant or a surfactant which can remain in a molded article or the like made of a fluoropolymer.

Examples of the other surfactants include nonionic surfactants and silicone surfactants.

The nonionic surfactant is preferably at least one selected from the group consisting of:

general formula (240): rf²⁴¹-(X²⁴¹)_n-Y²⁴¹

(wherein Rf²⁴¹Is a partially or fully fluorinated alkyl group having 1 to 12 carbon atoms, n is 0 or 1, X²⁴¹is-O-, -COO-or-OCO-, Y²⁴¹Is- (CH)₂)_pH、-(CH₂)_pOH OR- (OR)²⁴¹)_q(OR²⁴²)_rOH, p is an integer of 1 to 12, q is an integer of 1 to 12, R is an integer of 0 to 12, R²⁴¹And R²⁴²Is an alkylene group having 2 to 4 carbon atoms. Wherein R is²⁴¹And R²⁴²Different from each other) of the compounds represented by (a) above,

general formula (250): h (OR)²⁵¹)_u(OR²⁵²)_vOH

(in the formula, R ²⁵¹And R²⁵²Is an alkylene group having 1 to 4 carbon atoms, and u and v are integers of 1 to 5. Wherein R is²⁵¹And R²⁵²Different from each other) of the block polymers shown in (a),

a nonionic polymer having a hydrophobic group comprising a hydrocarbon group having 8 to 20 carbon atoms and a hydrophilic group comprising a polyalkylene oxide in the molecule, and

general formula (260): r²⁶¹ _m-Si-(OR²⁶²)_4-m

(in the formula, R²⁶¹Is an alkyl group having 1 to 12 carbon atoms, R²⁶²An alkyl group having 1 to 4 carbon atoms, and m is an integer of 1 to 3).

Specific examples of the block polymer represented by the general formula (250) include block polymers composed of at least 2 segments selected from the group consisting of polyoxyethylene, polyoxypropylene, and polyoxybutylene. Among them, polyoxyethylene-polyoxypropylene block polymers and polyoxyethylene-polyoxybutylene block polymers can be exemplified, and not only A-B type block polymers but also A-B-A type block polymers are preferably exemplified. It is further preferable that a stable fluoropolymer dispersion can be prepared at a high concentration by using a polyoxyethylene-polyoxypropylene block polymer or a polyoxypropylene-polyoxyethylene-polyoxypropylene block polymer. Further, when the content of the polyoxyethylene segment is 10% to 50%, it is considered that generation of aggregates due to re-aggregation is small, and therefore it is preferable; further, when the content is 20% to 40%, a low-viscosity fluoropolymer dispersion can be prepared, which is preferable. The molecular weight is not particularly limited as long as it is 1000g/mol to 7000 g/mol; further, particularly when the molecular weight is 2500g/mol to 6500g/mol, a dispersion having a low viscosity and excellent dispersibility can be prepared.

Examples of the Silicone surfactant include those described in Silicone Surfactants, R.M. Hill, Marcel Dekker, Inc., ISBN: 0-8247-00104. The structure of silicone-based surfactants contains well-defined hydrophobic and hydrophilic moieties. The hydrophobic moiety comprises 1 or more dihydrocarbylsiloxane units, where the substituents on the silicon atoms are entirely hydrocarbons.

These silicone surfactants can also be considered as hydrocarbon surfactants in the sense that, when the carbon atom of the hydrocarbon group can be substituted with a halogen such as fluorine, the monovalent substituent on the carbon atom of the hydrocarbon group is hydrogen, in which case the siloxane surfactant is completely substituted with a hydrogen atom.

The hydrophilic moiety of the silicone surfactant may include 1 or more polar moieties containing ionic groups, such as phosphonate, phosphate, carboxylate, carbonate, taurate (in the form of a free acid, salt, or ester), phosphine oxide, betaine polyol, and quaternary ammonium salt. The ionic hydrophobic moiety may also comprise ionically functionalized siloxane grafts.

Examples of such silicone surfactants include polydimethylsiloxane-graft- (meth) acrylate, polydimethylsiloxane-graft-polyacrylate, and polydimethylsiloxane-grafted quaternary amine.

The polar portion of the hydrophilic portion of the silicone-based surfactant may comprise: polyethers such as Polyoxyethylene (PEO) and mixed polyoxyethylene/oxypropylene polyethers (PEO/PPO); monosaccharides and disaccharides; and a nonionic group formed from a water-soluble heterocyclic ring such as pyrrolidone. The ratio of ethylene oxide to propylene oxide (EO/PO) can be varied in the mixed polyoxyethylene/oxypropylene polyethers.

The hydrophilic portion of the silicone-based surfactant may also comprise a combination of ionic and nonionic moieties. Examples of such moieties include polyethers or polyols functionalized with ionic ends or randomly. In the practice of the present invention, silicone-based surfactants having a nonionic moiety, i.e., nonionic silicone-based surfactants, are preferred.

The arrangement of the hydrophobic and hydrophilic portions of the structure of the silicone surfactant may take the form of a diblock polymer (AB), a triblock polymer (ABA) (here, "B" represents the siloxane portion of the molecule), or a multiblock polymer. Alternatively, the silicone-based surfactant may comprise a graft polymer.

Silicone surfactants are also disclosed in U.S. Pat. No. 6,841,616.

Examples of the anionic hydrocarbon surfactant for the silicone-based matrix include Noveon (registered trademark) available from Lubrizol Advanced Materials, Inc., and SilSense available from Consumer Specialties^TMPE-100Silicone、SilSense^TMCA-1Silicone, and the like.

Examples of the anionic hydrocarbon surfactant include a sulfosuccinate surfactant Lankropol (registered trademark) K8300 of Akzo Nobel Surface Chemistry LLC.

Examples of the sulfosuccinate hydrocarbon surfactant include diisodecyl sulfosuccinate Na salt, (Emulsogen (registered trademark) SB10 from Clariant), and diisotridecyl sulfosuccinate Na salt (Polirol (registered trademark) TR/LNA from Cesapini Chemicals).

As the hydrocarbon-based surfactant, a PolyFox (registered trademark) surfactant (PolyFox) by Omnova Solutions, inc^TMPF-156A、PolyFox^TMPF-136A, etc.).

When the above-mentioned carboxylic acid type hydrocarbon surfactant (aliphatic carboxylic acid type hydrocarbon surfactant in the production process 2) and another surfactant are used in combination, the content of the carboxylic acid type hydrocarbon surfactant is preferably 50% by mass or more, more preferably 60% by mass or more, further preferably 70% by mass or more, particularly preferably 80% by mass or more, and particularly preferably 90% by mass or more, based on the total amount of the surfactants. In the polymerization step, the carboxylic acid type hydrocarbon surfactant and the other surfactant are not substantially used, and the content of the other surfactant is preferably 1% by mass or less, more preferably 0.5% by mass or less, and further preferably 0.1% by mass or less of the total amount of the surfactants.

The carboxylic acid type hydrocarbon surfactant is preferably at least one selected from the group consisting of a surfactant represented by the formula (α), a surfactant (1-0) represented by the general formula (1-0), a surfactant (a) represented by the formula (a), a surfactant (b) represented by the formula (b), and a surfactant obtained by subjecting the above surfactants to radical treatment or oxidation treatment.

The aliphatic carboxylic acid type hydrocarbon surfactant is preferably at least one selected from the group consisting of a surfactant represented by the formula (α), a surfactant represented by the general formula (1-0A), and a surfactant obtained by subjecting the surfactant to radical treatment or oxidation treatment, and particularly preferably at least one selected from the group consisting of a surfactant represented by the formula (α) and a surfactant obtained by subjecting the surfactant represented by the formula (α) to radical treatment or oxidation treatment.

The polymerization step is preferably a step of polymerizing the fluorine-containing monomer in the substantial absence of a fluorine-containing surfactant.

Conventionally, a fluorine-containing surfactant has been used for polymerization of a fluorine-containing polymer, but the production method of the present invention can obtain a fluorine-containing polymer powder having a reduced content of the specific fluorine-containing compound without using a fluorine-containing surfactant.

In the present specification, "under the condition that the fluorosurfactant is substantially not present" means that the fluorosurfactant is 10ppm or less, preferably 1ppm or less, more preferably 100ppb or less, further preferably 10ppb or less, and further more preferably 1ppb or less with respect to the aqueous medium.

Examples of the fluorinated surfactant include anionic fluorinated surfactants.

The anionic fluorosurfactant may be a surfactant containing fluorine atoms, for example, in which the total carbon number of the portion excluding the anionic groups is 20 or less.

The above-mentioned fluorine-containing surfactant may be a surfactant containing fluorine, the molecular weight of the anionic moiety of which is 1000 or less, more preferably 800 or less, and still more preferably 600 or less.

The "anionic moiety" refers to a moiety of the above-mentioned fluorosurfactant other than cations. For example, F (CF) represented by the following formula (I)₂)_n1COOM is "F (CF)₂)_n1COO'.

The above-mentioned fluorosurfactant includes a fluorosurfactant having a LogPOW of 3.5 or less. The LogPOW is a partition coefficient between 1-octanol and water and is represented by LogP [ where P represents a ratio of a concentration of a fluorosurfactant in octanol/a concentration of the fluorosurfactant in water when a mixed solution of octanol/water (1: 1) containing the fluorosurfactant is phase-separated ].

The LogPOW is calculated as follows: in the column: TOSOH ODS-120T columnManufactured by tokyo corporation), eluent: acetonitrile/0.6 mass% HClO₄Water 1/1 (vol/vol%), flow rate: 1.0 ml/min, sample size: 300. mu.L, column temperature: detection at 40 ℃ light: HPLC was performed under UV210nm conditions on standard substances (heptanoic acid, octanoic acid, nonanoic acid, and decanoic acid) having known octanol/water partition coefficients, calibration curves were prepared for each elution time and the known octanol/water partition coefficients, and the elution time of HPLC in the sample solution was calculated based on the calibration curves.

Specific examples of the above-mentioned fluorosurfactant include U.S. patent application publication No. 2007/0015864, U.S. patent application publication No. 2007/0015865, U.S. patent application publication No. 2007/0015866, U.S. patent application publication No. 2007/0276103, U.S. patent application publication No. 2007/0117914, U.S. patent application publication No. 2007/142541, U.S. patent application publication No. 2008/0015319, U.S. patent application publication No. 3250808, U.S. patent application publication No. 3271341, Japanese patent laid-open No. 2003-119204, International publication No. 2005/042593, International publication No. 2008/060461, International publication No. 2007/046377, International publication No. 2007/119526, International publication No. 2007/046482, International publication No. 2007/046345, And fluorosurfactants described in U.S. patent application publication No. 2014/0228531, international publication No. 2013/189824, and international publication No. 2013/189826.

Examples of the anionic fluorosurfactant include those represented by the following general formula (N)⁰)：

Xⁿ⁰-Rfⁿ⁰-Y⁰ (N⁰)

(in the formula, Xⁿ⁰H, Cl or F. Rfⁿ⁰The alkylene group may contain 1 or more ether bonds and may have 3 to 20 carbon atoms in a chain, branched or cyclic manner, wherein part or all of H is substituted by F, and part of H may be substituted by Cl. Y is⁰Is an anionic group).

Y⁰The anionic group of (A) may be-COOM, -SO₂M or-SO₃M, may also be-COOM or-SO₃M。

M is H, a metal atom, NR^y ₄Imidazolium with or without substituents, pyridinium with or without substituents or phosphonium with or without substituents, R^yIs H or an organic group.

Examples of the metal atom include alkali metals (group 1), alkaline earth metals (group 2), and the like, and examples thereof include Na, K, and Li.

As R⁷May be H or C_1-10May also be H or C_1-4May also be H or C_1-4Alkyl group of (1).

M may be H, a metal atom or NR^y ₄It may be H, an alkali metal (group 1), an alkaline earth metal (group 2) or NR^y ₄And may also be H, Na, K, Li or NH₄。

Rf aboveⁿ⁰In (b), 50% or more of H may be substituted by fluorine.

As the above general formula (N)⁰) Examples of the compounds include ：

The following general formula (N)¹)：

Xⁿ⁰-(CF₂)_m1-Y⁰ (N¹)

(in the formula, Xⁿ⁰H, Cl and F, m1 is an integer of 3-15, Y⁰Is a substance defined above); the following general formula (N)²)：

Rfⁿ¹-O-(CF(CF₃)CF₂O)_m2CFXⁿ¹-Y⁰ (N²)

(wherein Rfⁿ¹Is a perfluoroalkyl group having 1 to 5 carbon atoms, m2 is an integer of 0 to 3, Xⁿ¹Is F or CF₃，Y⁰Is a substance defined above); the following general formula (N)³)：

Rfⁿ²(CH₂)_m3-(Rfⁿ³)_q-Y⁰ (N³)

(wherein Rfⁿ²Is a partially or fully fluorinated alkyl group having 1 to 13 carbon atoms and containing an ether bond, m3 is an integer of 1 to 3, and Rfⁿ³Is a linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, q is 0 or 1, Y⁰Is a substance defined above); the following general formula (N)⁴)：

Rfⁿ⁴-O-(CYⁿ¹Yⁿ²)_pCF₂-Y⁰ (N⁴)

(wherein Rfⁿ⁴Is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms and containing an ether bond, Yⁿ¹And Yⁿ²Identical or different, is H or F, p is 0 or 1, Y⁰Is a substance defined above); and the following general formula (N)⁵)：

[ solution 13]

(in the formula, Xⁿ²、Xⁿ³And Xⁿ⁴H, F or a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms and optionally containing an ether bond. Rfⁿ⁵Is a linear or branched partially or fully fluorinated alkylene group having 1 to 3 carbon atoms and containing an ether bond, L is a linking group, Y is ⁰Are defined above. Wherein, Xⁿ²、Xⁿ³、Xⁿ⁴And Rfⁿ⁵The total number of carbon atoms of (2) is 18 or less).

As the above general formula (N)⁰) More specifically, the compound(s) include a perfluorocarboxylic acid (I) represented by the following general formula (I), an ω -H perfluorocarboxylic acid (II) represented by the following general formula (II), a perfluoropolyether carboxylic acid (III) represented by the following general formula (III), a perfluoroalkylalkylalkylene carboxylic acid (IV) represented by the following general formula (IV), a perfluoroalkoxyfluorocarboxylic acid (V) represented by the following general formula (V), a perfluoroalkylsulfonic acid (VI) represented by the following general formula (VI), an ω -H perfluorosulfonic acid (VII) represented by the following general formula (VII), a perfluoroalkylalkylalkylene sulfonic acid (VIII) represented by the following general formula (VIII), an alkylalkylalkylene carboxylic acid (IX) represented by the following general formula (IX), a fluorocarboxylic acid (X) represented by the following general formula (X), an alkoxyfluorosulfonic acid (XI) represented by the following general formula (XI), a compound (XII) represented by the following general formula (XII), and a compound (XII) represented by the following general formula (XII), A compound (XIII) represented by the following general formula (XIII), and the like.

The above-mentioned perfluorocarboxylic acid (I) is represented by the following general formula (I)

F(CF₂)_n1COOM (I)

(wherein n1 is an integer of 3 to 14, M is H, a metal atom, NR⁷ ₄Imidazolium with or without substituents, pyridinium with or without substituents or phosphonium with or without substituents, R ⁷Is H or an organic group).

The above-mentioned omega-H perfluorocarboxylic acid (II) is represented by the following general formula (II)

H(CF₂)_n2COOM (II)

(wherein n2 is an integer of 4 to 15, and M is as defined above).

The above perfluoropolyether carboxylic acid (III) is represented by the following general formula (III)

Rf¹-O-(CF(CF₃)CF₂O)_n3CF(CF₃)COOM (III)

(wherein Rf¹A perfluoroalkyl group having 1 to 5 carbon atoms, n3 is an integer of 0 to 3, and M is as defined above).

The above perfluoroalkyl alkylene carboxylic acid (IV) is represented by the following general formula (IV)

Rf²(CH₂)_n4Rf³COOM (IV)

(wherein Rf²Is a perfluoroalkyl group having 1 to 5 carbon atoms, Rf³A linear or branched perfluoroalkylene group having 1 to 3 carbon atoms, n4 is an integer of 1 to 3, and M is as defined above).

The alkoxy fluorocarboxylic acid (V) is represented by the following general formula (V)

Rf⁴-O-CY¹Y²CF₂-COOM (V)

(wherein Rf⁴Is a linear or branched partially or fully fluorinated alkyl group having 1 to 12 carbon atoms and containing an ether bond, Y¹And Y²Identical or different, H or F, M being a substance as defined above).

The above perfluoroalkylsulfonic acid (VI) is represented by the following general formula (VI)

F(CF₂)_n5SO₃M (VI)

(wherein n5 is an integer of 3 to 14, and M is as defined above).

The omega-H perfluorosulfonic acid (VII) is represented by the following general formula (VII)

H(CF₂)_n6SO₃M (VII)

(wherein n6 is an integer of 4 to 14, and M is as defined above).

The above perfluoroalkyl alkylene sulfonic acid (VIII) is represented by the following general formula (VIII)

Rf⁵(CH₂)_n7SO₃M (VIII)

(wherein Rf⁵Is a perfluoroalkyl group having 1 to 13 carbon atoms, n7 is an integer of 1 to 3, and M is as defined aboveSubstance) is shown.

The above-mentioned alkyl alkylene carboxylic acid (IX) is represented by the following general formula (IX)

Rf⁶(CH₂)_n8COOM (IX)

(wherein Rf⁶A linear or branched partially or fully fluorinated alkyl group having 1 to 13 carbon atoms and containing an ether bond, n8 is an integer of 1 to 3, and M is defined as above).

The fluorocarboxylic acid (X) is represented by the following general formula (X)

Rf⁷-O-Rf⁸-O-CF₂-COOM (X)

(wherein Rf⁷Is a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms and containing an ether bond, and Rf⁸A linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms, wherein M is as defined above).

The above alkoxy fluorosulfonic acid (XI) is represented by the following general formula (XI)

Rf⁹-O-CY¹Y²CF₂-SO₃M (XI)

(wherein Rf⁹Is a linear or branched C1-12 alkyl group which may contain an ether bond and may be partially or fully fluorinated and may contain chlorine, and Y is¹And Y²Identical or different, H or F, M being a substance as defined above).

The above compound (XII) is represented by the following general formula (XII):

[ solution 14]

In the formula, X¹、X²And X³H, F and a linear or branched partially or fully fluorinated alkyl group having 1 to 6 carbon atoms and containing an ether bond, and Rf ¹⁰Is a C1-3 perfluoroalkylene group, L is a linking group, Y⁰Anionic group).

Y⁰Can be-COOM, -SO₂M or-SO₃M, may also be-SO₃M or COOM (wherein M is defined above).

Examples of L include a single bond, a partially or fully fluorinated alkylene group having 1 to 10 carbon atoms and containing an ether bond.

The above compound (XIII) is represented by the following general formula (XIII):

Rf¹¹-O-(CF₂CF(CF₃)O)_n9(CF₂O)_n10CF₂COOM (XIII)

(wherein Rf¹¹A fluorinated alkyl group containing 1 to 5 carbon atoms and containing chlorine, n9 is an integer of 0 to 3, n10 is an integer of 0 to 3, and M is defined as above). As the compound (XIII), CF is mentioned₂ClO(CF₂CF(CF₃)O)_n9(CF₂O)_n10CF₂COONH₄(mixture of average molecular weights 750, where n9 and n10 are numbers as defined above).

Examples of the anionic fluorosurfactant include a carboxylic acid surfactant and a sulfonic acid surfactant.

The polymerization step may further comprise polymerizing the fluorine-containing monomer in the presence of a nucleating agent.

The nucleating agent is preferably at least one selected from the group consisting of fluoropolyethers, nonionic surfactants, and chain transfer agents.

In this case, the polymerization step is preferably a step of: the fluorine-containing monomer is polymerized in an aqueous medium in the presence of a carboxylic acid type hydrocarbon surfactant and the above-mentioned nucleating agent, thereby obtaining a fluorine-containing polymer.

The fluoropolyether is preferably a perfluoropolyether.

The fluoropolyether preferably has repeating units represented by the formulae (1a) to (1 d).

(-CFCF₃-CF₂-O-)_n (1a)

(-CF₂-CF₂-CF₂-O-)_n (1b)

(-CF₂-CF₂-O-)n-(-CF₂-O-)_m (1c)

(-CF₂-CFCF₃-O-)n-(-CF₂-O-)_m (1d)

(in the formulae (1a) to (1d), m and n are integers of 1 or more.)

The fluoropolyether is preferably a fluoropolyether acid or a salt thereof, and the fluoropolyether acid is preferably a carboxylic acid, a sulfonic acid, a sulfonamide, or a phosphonic acid, and more preferably a carboxylic acid. Among fluoropolyether acids or salts thereof, preferred are salts of fluoropolyether acids, more preferred are ammonium salts of fluoropolyether acids, and still more preferred are ammonium salts of fluoropolyether carboxylic acids.

The fluoropolyether acid or salt thereof may have: an arbitrary chain structure in which oxygen atoms in the main chain of the molecule are separated by saturated fluorocarbon groups having 1 to 3 carbon atoms. More than 2 fluorocarbon groups may be present in the molecule.

The fluoropolyether acid or salt thereof is preferably represented by the formula:

CF₃-CF₂-CF₂-O(-CFCF₃-CF₂-O-)_nCFCF₃-COOH、

CF₃-CF₂-CF₂-O(-CF₂-CF₂-CF₂-O-)_n-CF₂-CF₂COOH, or

HOOC-CF₂-O(-CF₂-CF₂-O-)n-(-CF₂-O-)_mCF₂COOH

(wherein m and n are the same as described above)

The compounds shown or their salts.

These structures were studied by Kasai in j.appl.polymer sci.57,797 (1995). Such fluoropolyethers may have a carboxylic acid group or salt thereof at one or both ends, as disclosed herein. Likewise, such fluoropolyethers may have sulfonic or phosphonic acid groups or salts thereof at one or both ends. In addition to this, fluoropolyethers having acid functional groups at both ends may have different groups at each end. With regard to monofunctional fluoropolyethers, the other end of the molecule is typically perfluorinated and may also contain a hydrogen or chlorine atom.

The fluoropolyether having an acid group at one or both ends has at least 2 ether oxygens, preferably at least 4 ether oxygens, and even more preferably at least 6 ether oxygens. Preferably at least one of the fluorocarbon groups separating the ether oxygens, more preferably at least two of such fluorocarbon groups, has 2 or 3 carbon atoms. Even more preferably at least 50% of the fluorocarbon groups separating the ether oxygens have 2 or 3 carbon atoms. In addition, it is preferred that the fluoropolyethers have at least 15 carbon atoms in total, e.g., a preferred minimum value of n or n + m in the above repeating unit structure is at least 5. More than 2 fluoropolyethers having acid groups at one or both ends may be used in the process of the present invention. Typically, in the manufacture of a single species of a particular fluoropolyether compound, unless otherwise noted, the fluoropolyether can contain two or more compounds in various proportions within the molecular weight range relative to the average molecular weight.

The fluoropolyether preferably has a number average molecular weight of 800g/mol or more. The fluoropolyether acid or salt thereof preferably has a number average molecular weight of less than 6000g/mol, since dispersion in aqueous media can be difficult. The number average molecular weight of the fluoropolyether acid or salt thereof is more preferably 800g/mol to 3500g/mol, and still more preferably 1000g/mol to 2500 g/mol.

The amount of the fluoropolyether is preferably 5ppm to 3000ppm, more preferably 5ppm to 2000ppm, with a more preferred lower limit of 10ppm and a more preferred upper limit of 100ppm with respect to the aqueous medium.

The nonionic surfactant of the nucleating agent may be the nonionic surfactant described above, and preferably a nonionic surfactant containing no fluorine. Examples thereof include the following general formula (i)

R³-O-A¹-H (i)

(in the formula, R³Is a linear or branched primary or secondary alkyl group having 8 to 18 carbon atoms, A¹Is a polyoxyalkylene chain). R³The number of carbon atoms of (A) is preferably 10 to 16, more preferably 12 to 16. If R is³When the number of carbon atoms of (2) is 18 or less, good dispersion stability of the aqueous dispersion can be easily obtainedAnd (4) sex. In addition if R³If the number of carbon atoms exceeds 18, the flow temperature is high, and therefore, handling is difficult. If R is³When the number of carbon atoms of (2) is less than 8, the surface tension of the aqueous dispersion increases, and the permeability and wettability tend to decrease.

The polyoxyalkylene chain may be composed of ethylene oxide and propylene oxide. Is a polyoxyalkylene chain having 5 to 20 average repeating numbers of oxyethylene groups and 0 to 2 average repeating numbers of oxypropylene groups, and is a hydrophilic group. The ethylene oxide unit number may comprise any of a broad or narrow monomodal distribution, as typically provided, or a broader or bimodal distribution obtained by blending. When the average repeating number of the oxypropylene group exceeds 0, the oxyethylene group and the oxypropylene group in the polyoxyalkylene chain may be arranged in a block form or in a random form.

From the viewpoint of viscosity and stability of the aqueous dispersion, a polyoxyalkylene chain comprising an average repeating number of oxyethylene groups of 7 to 12 and an average repeating number of oxypropylene groups of 0 to 2 is preferred. Especially if A¹It is preferable that the acrylic resin composition has an oxypropylene group of 0.5 to 1.5 on average because low foaming property is good.

More preferably R³Is (R ') (R') HC-, wherein R 'and R' are the same or different linear, branched or cyclic alkyl groups, and the total number of carbon atoms is at least 5, preferably 7 to 17. Preferably, at least one of R 'or R' is a branched or cyclic hydrocarbon group.

Specific examples of the nonionic surfactant include C₁₃H₂₇-O-(C₂H₄O)₁₀-H、C₁₂H₂₅-O-(C₂H₄O)₁₀-H、C₁₀H₂₁CH(CH₃)CH₂-O-(C₂H₄O)₉-H、C₁₃H₂₇-O-(C₂H₄O)₉-(CH(CH₃)CH₂O)-H、C₁₆H₃₃-O-(C₂H₄O)₁₀-H、HC(C₅H₁₁)(C₇H₁₅)-O-(C₂H₄O)₉-H, etc. As the above nonionic surfactantExamples of the commercially available products include Genapol X080 (product name, manufactured by Clariant corporation), Noigen TDS series (first Industrial pharmaceutical Co., Ltd.) such as Noigen TDS-80 (trade name), Leocol TD series (LION corporation) such as Leocol TD-90 (trade name), LIONOL (registered trademark) TD series (manufactured by LION corporation), T-Det A series (manufactured by Harcross Chemicals) such as T-Det A138 (trade name), and GITOL (registered trademark) 15S series (manufactured by Takara).

The above nonionic surfactants are also preferably ethoxylates of 2,6, 8-trimethyl-4-nonanol having an average of about 4 to about 18 ethylene oxide units, ethoxylates of 2,6, 8-trimethyl-4-nonanol having an average of about 6 to about 12 ethylene oxide units, or mixtures thereof. Nonionic surfactants of this type are also commercially available, for example, as TERGITOL TMN-6, TERGITOL TMN-10, and TERGITOL TMN-100X (both product names, manufactured by the Dow chemical company).

In addition, the hydrophobic group of the nonionic surfactant may be any of an alkylphenol group, a straight-chain alkyl group, and a branched-chain alkyl group.

Examples of the nonionic surfactant include, for example, those represented by the following general formula (ii)

R⁴-C₆H₄-O-A²-H (ii)

(in the formula, R⁴Is a linear or branched primary or secondary alkyl group having 4 to 12 carbon atoms, A²Polyoxyalkylene chain) and a polyoxyethylene alkylphenyl ether-based nonionic compound. Specific examples of the polyoxyethylene alkylphenyl ether nonionic compound include TRITON (registered trademark) X-100 (trade name, manufactured by Dow chemical Co., Ltd.).

Examples of the nonionic surfactant include a bifunctional block copolymer supplied as Pluronic (registered trademark) R series by BASF corporation, and a tridecanol alkoxylate supplied as Iconol (registered trademark) TDA series by BASF corporation

The amount of the nonionic surfactant is preferably 0.1 to 0.0000001% by mass, more preferably 0.01 to 0.000001% by mass, based on the aqueous medium.

Examples of the chain transfer agent include esters such as dimethyl malonate, diethyl malonate, methyl acetate, ethyl acetate, butyl acetate, and dimethyl succinate, and halogenated hydrocarbons such as isopentane, methane, ethane, propane, isobutane, methanol, ethanol, isopropanol, acetone, various mercaptans, and carbon tetrachloride, and cyclohexane.

As the chain transfer agent, a bromine compound or an iodine compound can be used. Examples of the polymerization method using a bromine compound or an iodine compound include a method of polymerizing a fluorine-containing monomer in an aqueous medium in the substantial absence of oxygen in the presence of a bromine compound or an iodine compound (iodine transfer polymerization method). Representative examples of the bromine compound or iodine compound to be used include compounds represented by the general formula:

R^aI_xBr_y

(wherein x and y are each an integer of 0 to 2 and satisfy 1. ltoreq. x + y. ltoreq.2, R^aIs a saturated or unsaturated fluorocarbon group or chlorofluorocarbon group having 1 to 16 carbon atoms or a hydrocarbon group having 1 to 3 carbon atoms, wherein R is ^aWith or without an oxygen atom). By using a bromine compound or an iodine compound, iodine or bromine is introduced into the polymer to function as a crosslinking point.

Examples of the iodine compound include 1, 3-diiodoperfluoropropane, 2-iodoperfluoropropane, 1, 3-diiodo-2-chloroperfluoropropane, 1, 4-diiodoperfluorobutane, 1, 5-diiodo-2, 4-dichloroperfluoropentane, 1, 6-diiodoperfluorohexane, 1, 8-diiodoperfluorooctane, 1, 12-diiodoperfluorododecane, 1, 16-diiodoperfluorohexadecane, diiodomethane, 1, 2-diiodoethane, 1, 3-diiodon-propane, CF₂Br₂、BrCF₂CF₂Br、CF₃CFBrCF₂Br、CFClBr₂、BrCF₂CFClBr、CFBrClCFClBr、BrCF₂CF₂CF₂Br、BrCF₂CFBrOCF₃1-bromo-2-iodoperfluoroethane, 1-bromo-3-iodoperfluoropropane, 1-bromo-4-iodoperfluorobutane, 2-bromo-3-iodoperfluorobutane, 3-bromo-4-iodoperfluoro-1-butene, 2-bromo-4-iodoperfluorobutane1-butene, monoiodomonobromo-substituted benzene, diiodomonobromo-substituted benzene, and (2-iodoethyl) and (2-bromoethyl) substituted benzene, which may be used alone or in combination with each other.

Among these, at least one selected from the group consisting of alkanes and alcohols is preferable from the viewpoints of polymerization reactivity, crosslinking reactivity, availability, and the like. The number of carbon atoms of the alkane is preferably 1 to 6, more preferably 1 to 5. The carbon number of the alcohol is preferably 1 to 5, more preferably 1 to 4. As the chain transfer agent, at least one selected from the group consisting of methane, ethane, propane, isobutane, methanol, ethanol, and isopropanol is particularly preferable.

The amount of the chain transfer agent is preferably 0.001ppm to 10000ppm relative to the aqueous medium. The amount of the chain transfer agent is more preferably 0.01ppm or more, still more preferably 0.05ppm or more, and particularly preferably 0.1ppm or more, based on the aqueous medium. Further, the concentration is more preferably 1000ppm or less, still more preferably 500ppm or less, and particularly preferably 100ppm or less with respect to the aqueous medium.

The chain transfer agent may be added to the reaction vessel at a time before the start of polymerization, may be added at a time after the start of polymerization, may be added in several portions during polymerization, or may be continuously added during polymerization.

In the production method of the present invention, in addition to the above-mentioned hydrocarbon-based surfactant and other compounds having a surface-active ability used as desired, an additive for stabilizing each compound may be used. Examples of the additives include a buffer, a pH adjuster, a stabilizing aid, and a dispersion stabilizer.

The stabilizing aid is preferably paraffin, a fluorine-based oil, a fluorine-based solvent, silicone oil, or the like. The stabilizing aids may be used singly or in combination of 1 or more. As the stabilizing aid, paraffin wax is more preferable. The paraffin wax may be liquid, semisolid, or solid at room temperature, but is preferably a saturated hydrocarbon having 12 or more carbon atoms. The melting point of the paraffin wax is usually preferably 40 to 65 ℃ and more preferably 50 to 65 ℃.

The amount of the stabilizing aid used is preferably 0.1 to 12% by mass, more preferably 0.1 to 8% by mass, based on the mass of the aqueous medium used. The stabilizing aid is preferably sufficiently hydrophobic to be completely separated from the aqueous fluoropolymer emulsion after emulsion polymerization of the fluoromonomer and not to become a contaminating component.

The polymerization in the above-mentioned production method may be carried out as follows: the aqueous medium, the hydrocarbon surfactant, the monomer, and other additives as needed are charged into a polymerization reactor, the contents of the reactor are stirred, the reactor is maintained at a predetermined polymerization temperature, and a predetermined amount of a polymerization initiator is added to initiate a polymerization reaction, thereby allowing polymerization to proceed. After the polymerization reaction is started, a monomer, a polymerization initiator, a chain transfer agent, the surfactant, and the like may be added thereto according to the purpose. The hydrocarbon surfactant may be added after the polymerization reaction is started.

The polymerization initiator is not particularly limited as long as it can generate radicals in the above polymerization temperature range, and known oil-soluble and/or water-soluble polymerization initiators can be used. Further, the polymerization may be initiated in a redox form in combination with a reducing agent or the like. The concentration of the polymerization initiator is appropriately determined depending on the kind of the monomer, the molecular weight of the target fluoropolymer, and the reaction rate.

As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator can be used.

The oil-soluble radical polymerization initiator may be a known oil-soluble peroxide, and examples thereof include the following peroxides as representative: dialkyl peroxycarbonates such as diisopropyl peroxydicarbonate and di-sec-butyl peroxydicarbonate; peroxyesters such as tert-butyl peroxyisobutyrate and tert-butyl peroxypivalate; dialkyl peroxides such as di-tert-butyl peroxide; and di (omega-hydro-dodecafluorohexanoyl) peroxide, di (omega-hydro-tetradecafluoroheptanoyl) peroxide, di (omega-hydro-hexadecafluorononoyl) peroxide, di (perfluorobutanoyl) peroxide, di (perfluoropentanoyl) peroxide, di (perfluorohexanoyl) peroxide, di (perfluoroheptanoyl) peroxide, di (perfluorooctanoyl) peroxide, di (perfluorononanoyl) peroxide, di (omega-chloro-hexafluorobutanoyl) peroxide, di (omega-chloro-decafluorohexanoyl) peroxide, di (omega-chloro-tetradecafluorooctanoyl) peroxide, omega-hydro-dodecafluoroheptanoyl-omega-hydroxyhexadecafluorononoyl-peroxide, omega-chloro-hexafluorobutanoyl-omega-chloro-decafluorohexanoyl-peroxide, di (omega-chloro-tetradecafluorooctanoyl) peroxide, omega-hydro-dodecafluoroheptanoyl-omega-hydroxyhexanoyl-peroxide, di (omega-hydro-tetradecafluorohexanoyl) peroxide, di (omega-chlorohexanoyl-perfluorohexanoyl-peroxide, di (omega-chlorohexafluorohexanoyl-perfluorohexanoyl-peroxide, di (perfluoroheptanoyl) peroxide, di (omega-chlorohexanoyl) peroxide, di (omega-chlorohexafluorohexanoyl) peroxide, di (perfluoroheptanoyl) peroxide, di (omega-perfluorooctanoyl) peroxide, di (omega-chlorohexanoyl) peroxide, di (omega-perfluorooctanoyl) peroxide, and (omega-perfluorooctanoyl) peroxide, Di [ perfluoro (or fluorochloro) acyl ] peroxides such as ω -hydroxydodecafluoroheptanoyl-perfluorobutanoyl-peroxide, di (dichloropentafluorobutanoyl) peroxide, di (trichlorooctafluorohexanoyl) peroxide, di (tetrachloroundecanooctanoyl) peroxide, di (pentachlorotridecanoyl) peroxide, and di (undecanoyl-triacontadoxodidodecanoyl) peroxide; and so on.

For example, when the polymerization is carried out at a low temperature of 30 ℃ or lower, a redox initiator comprising a combination of an oxidizing agent and a reducing agent is preferably used as the polymerization initiator. Examples of the oxidizing agent include persulfates, organic peroxides, potassium permanganate, manganese triacetate, cerium ammonium nitrate, and the like. Examples of the reducing agent include bromate, diimine, and oxalic acid. Examples of the persulfate include ammonium persulfate and potassium persulfate. In order to increase the decomposition rate of the initiator, it is also preferable to add a copper salt or an iron salt to the combination of the redox initiators. Copper salt may be copper (II) sulfate, and iron salt may be iron (II) sulfate.

Examples of the redox initiator include potassium permanganate/oxalic acid, potassium permanganate/ammonium oxalate, manganese triacetate/oxalic acid, manganese triacetate/ammonium oxalate, cerium ammonium nitrate/oxalic acid, cerium ammonium nitrate/ammonium oxalate and the like, and potassium permanganate/oxalic acid is preferred. In the case of using a redox initiator, either an oxidizing agent or a reducing agent may be charged into a polymerization vessel in advance, and then the other may be continuously or intermittently added to initiate polymerization. For example, in the case of using potassium permanganate/oxalic acid, it is preferable to charge oxalic acid to the polymerization vessel and continuously add potassium permanganate thereto.

The amount of the polymerization initiator to be added is not particularly limited, and may be added at once, or sequentially, or continuously in the initial stage of polymerization in an amount (for example, several ppm with respect to the concentration of water) or more to such an extent that the polymerization rate does not significantly decrease. The upper limit is a range in which the heat of polymerization reaction can be removed from the apparatus surface and the reaction temperature can be increased, and the more preferable upper limit is a range in which the heat of polymerization reaction can be removed from the apparatus surface.

As the polymerization initiator, a radical polymerization initiator may be used. As the radical polymerization initiator, peroxides are preferable. Examples of the radical polymerization initiator include the above-mentioned oil-soluble radical polymerization initiator and water-soluble radical polymerization initiator, and the above-mentioned water-soluble radical polymerization initiator is preferable. The water-soluble radical polymerization initiator is more preferably a peroxide, and still more preferably a persulfate, an organic peroxide, or a mixture thereof. Examples of the persulfate include ammonium persulfate and potassium persulfate. Examples of the organic peroxide include disuccinic acid peroxide and dipentanedioic acid peroxide. More preferably ammonium persulfate and disuccinic acid peroxide. In the polymerization step, for example, ammonium persulfate is preferably added in an amount of 5ppm or more, more preferably 10ppm or more, further preferably 20ppm or more, further preferably 30ppm or more, particularly preferably 40ppm or more, particularly preferably 50ppm or more, particularly preferably 80ppm or more, and particularly preferably 100ppm or more, to the aqueous medium. In the polymerization step, a radical polymerization initiator may be continuously or intermittently added after the start of polymerization.

The aqueous medium is a reaction medium for carrying out the polymerization and is a liquid containing water. The aqueous medium is not particularly limited as long as it contains water, and may contain water and a non-fluorine-containing organic solvent such as an alcohol, an ether, or a ketone and/or a fluorine-containing organic solvent having a boiling point of 40 ℃ or lower.

In the aqueous dispersion obtained by the above polymerization, the average primary particle diameter of the fluoropolymer is, for example, 50nm to 500 nm. The lower limit of the average primary particle diameter is preferably 100nm, more preferably 150 nm. The upper limit of the average primary particle diameter is preferably 400nm, more preferably 350 nm.

The average primary particle diameter can be measured by a dynamic light scattering method. The average primary particle size can be measured by a dynamic light scattering method under conditions of 25 ℃, 1.3328 for the refractive index of the solvent (water), 0.8878mPa · s for the viscosity of the solvent (water), and 70 times of accumulation, to prepare an aqueous fluoropolymer dispersion in which the fluoropolymer solid content concentration is adjusted to about 1.0 mass%. As the dynamic light scattering method, for example, ELSZ-1000S (manufactured by Otsuka electronics Co., Ltd.) can be used.

The carboxylic acid type hydrocarbon surfactant can be suitably used as a dispersant for dispersing the fluoropolymer obtained by polymerization in an aqueous medium.

In the above polymerization, an aqueous dispersion containing particles composed of the above fluoropolymer, the above surfactant, and the above aqueous medium is usually obtained. The aqueous dispersion is obtained by dispersing particles made of a fluoropolymer in an aqueous medium in the presence of the surfactant.

The lower limit of the content of the carboxylic acid type hydrocarbon surfactant in the aqueous dispersion is preferably 10ppb, more preferably 100ppb, further preferably 1ppm, further more preferably 10ppm, and particularly preferably 50ppm with respect to the fluoropolymer. The upper limit value is preferably 100000ppm, more preferably 50000ppm, further preferably 10000ppm, further preferably 5000ppm to the fluoropolymer.

The aqueous dispersion may be any of an aqueous dispersion obtained by the polymerization, a dispersion obtained by concentrating or performing dispersion stabilization treatment on the aqueous dispersion, and an aqueous dispersion obtained by dispersing a powder composed of a fluoropolymer in an aqueous medium in the presence of the surfactant.

As a method for producing the aqueous dispersion, an aqueous dispersion obtained by the polymerization may be subjected to the following steps: (I) a step (I) of contacting the resulting product with an anion exchange resin or a mixed bed comprising an anion exchange resin and a cation exchange resin in the presence of a nonionic surfactant; and/or (II) a step (II) of concentrating the aqueous dispersion so that the solid content concentration is 30 to 70 mass% with respect to 100 mass% of the aqueous dispersion.

The nonionic surfactant is not particularly limited, and those described later can be used. The anion exchange resin is not particularly limited, and a known one can be used. In addition, the above-mentioned method of contacting with the anion exchange resin may employ a known method.

As a method for producing the aqueous dispersion, a purified aqueous dispersion can be produced by subjecting the aqueous dispersion obtained by the polymerization to the step (I) and subjecting the aqueous dispersion obtained by the step (I) to the step (II). Alternatively, the purified aqueous dispersion may be produced by performing the step (II) without performing the step (I). The steps (I) and (II) may be repeated, or may be combined.

Examples of the anion exchange resin include resins having a functional group of-N⁺X^-(CH₃)₃Strongly basic anion exchange resin of group (X represents Cl or OH), having-N⁺X^-(CH₃)₃(C₂H₄OH) group (X is the same as above). Specifically, examples thereof include those described in International publication No. 99/62858, International publication No. 03/020836, International publication No. 2004/078836, International publication No. 2013/027850 and International publication No. 2014/084399.

The cation exchange resin is not particularly limited, and examples thereof include those having a functional group of-SO₃ ^-Strongly acidic cation exchange resin having-COO as a functional group^-Among them, a strongly acidic cation exchange resin is preferable, and H is more preferable from the viewpoint of removal efficiency⁺Strong acid cation exchange resins of the type.

The "mixed bed containing a cation exchange resin and an anion exchange resin" is not particularly limited, and includes a case where both are packed in the same column, a case where both are packed in different columns, a case where both are dispersed in an aqueous dispersion, and the like.

As the above concentration method, a known method is used. Specifically, there are methods described in International publication No. 2007/046482 and International publication No. 2014/084399. Examples thereof include phase separation, centrifugal sedimentation, cloud point concentration, electric concentration, electrophoresis, filtration treatment using ultrafiltration, filtration treatment using a reverse osmosis membrane (RO membrane), nanofiltration treatment, and the like. The concentration may be such that the fluoropolymer concentration is 30 to 70% by mass depending on the application. The stability of the dispersion may be impaired by concentration, but in this case a dispersion stabilizer may be further added.

The dispersion stabilizer may be added with the nonionic surfactant or various other surfactants.

As the nonionic surfactant, the nonionic surfactant can be suitably used in the same manner as the nonionic surfactant exemplified as the nucleating agent. The nonionic surfactant preferably does not contain an aromatic moiety.

In addition, the cloud point of a nonionic surfactant is a measure of the solubility of the surfactant in water. The surfactant used in the aqueous dispersion of the present invention has a cloud point of from about 30 ℃ to about 90 ℃, preferably from about 35 ℃ to about 85 ℃.

The total amount of the dispersion stabilizer is 0.5 to 20 mass% with respect to the solid content of the dispersion. If less than 0.5 mass%, dispersion stability may be deteriorated; if the amount exceeds 20% by mass, the dispersion effect is not obtained in accordance with the amount of the polymer, and the method is not practical. A more preferable lower limit of the dispersion stabilizer is 2% by mass, and a more preferable upper limit is 12% by mass.

The method for producing a fluoropolymer powder of the present invention may comprise a step of recovering the aqueous fluoropolymer dispersion obtained in the polymerization step.

The method for producing a fluoropolymer powder of the present invention may further comprise a step of recovering the coagulated wet fluoropolymer powder.

Examples of the fluoropolymer include a TFE polymer in which TFE is the monomer having the largest mole fraction of the monomer (hereinafter referred to as the "largest monomer"), a VDF polymer in which VDF is the largest monomer, and a CTFE polymer in which CTFE is the largest monomer in the polymer. Hereinafter, more preferred embodiments of each fluoropolymer are described.

The TFE polymer may be suitably a TFE homopolymer, or a copolymer composed of: (1) TFE; (2) 1 or 2 or more fluorine-containing monomers other than TFE having 2 to 8 carbon atoms, particularly VDF, HFP or CTFE; and (3) other monomers. Examples of the other monomer (3) include fluoro (alkyl vinyl ether) having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms; fluoro dioxole; a perfluoroalkylethylene; omega-hydrogenated perfluoroolefins; a perfluoroallyl ether; and so on.

The TFE polymer may be a copolymer of TFE and 1 or 2 or more kinds of non-fluorine-containing monomers. Examples of the non-fluorine-containing monomer include olefins such as ethylene and propylene; vinyl esters; vinyl ethers. The TFE polymer may be a copolymer of TFE, 1 or 2 or more fluorine-containing monomers having 2 to 8 carbon atoms, and 1 or 2 or more non-fluorine-containing monomers.

As the VDF polymer, a copolymer composed of: (1) VDF; (2) 1 or 2 or more fluoroolefins other than VDF having 2 to 8 carbon atoms, particularly TFE, HFP or CTFE; and (3) perfluoro (alkyl vinyl ether) having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms; and so on.

As the CTFE polymer, a copolymer composed of: (1) CTFE; (2) 1 or 2 or more fluoroolefins other than CTFE having 2 to 8 carbon atoms, particularly TFE or HFP; and (3) perfluoro (alkyl vinyl ether) having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms.

The CTFE polymer may be a copolymer of CTFE and 1 or 2 or more types of non-fluorine-containing monomers, and examples of the non-fluorine-containing monomers include olefins such as ethylene and propylene; vinyl esters; vinyl ethers, and the like.

The fluoropolymer produced by the production method of the present invention may be glassy, plastic or elastomeric. These materials are amorphous or partially crystalline and can be subjected to compression firing processing, melt processing or non-melt processing.

The production method of the present invention can suitably produce, for example, the following: (I) tetrafluoroethylene polymer [ TFE Polymer (PTFE) ] as a non-melt-processable fluororesin, (II) ethylene/TFE copolymer [ ETFE ], TFE/HFP copolymer [ FEP ], TFE/perfluoro (alkyl vinyl ether) copolymer [ PFA, MFA, etc. ], TFE/perfluoroallyl ether copolymer, electrolyte polymer precursor, etc. as a melt-processable fluororesin.

The fluorine-containing polymer is preferably a fluororesin, more preferably a fluororesin having a fluorine substitution rate of 50% or more, further preferably a fluororesin having a fluorine substitution rate of more than 50%, still more preferably a fluororesin having a fluorine substitution rate of 55% or more, still more preferably a fluororesin having a fluorine substitution rate of 60% or more, still further preferably a fluororesin having a fluorine substitution rate of 75% or more, particularly preferably a fluororesin having a fluorine substitution rate of 80% or more, and most preferably a perfluororesin that is a fluororesin having a fluorine substitution rate of 90% to 100%, among the above-mentioned fluoropolymers.

(formula (II))

The fluorine substitution rate (%)/((the number of hydrogen atoms bonded to carbon atoms constituting the fluoropolymer) + (the number of fluorine atoms and chlorine atoms bonded to carbon atoms constituting the fluoropolymer)) × 100

The perfluoro resin is more preferably a fluororesin having a fluorine substitution rate of 95% to 100%, even more preferably PTFE, FEP, PFA, particularly preferably PTFE, and particularly preferably high molecular weight PTFE.

The fluoropolymer may have a core-shell structure. Examples of the fluoropolymer having a core-shell structure include modified PTFE in which particles contain a core of high molecular weight PTFE and a shell of lower molecular weight PTFE or modified PTFE. Examples of such modified PTFE include PTFE described in JP-A-2005-527652.

As the core-shell structure, the following structure can be adopted.

And (3) nucleus: TFE homopolymer shell: TFE homopolymers

And (3) nucleus: modified PTFE shell: TFE homopolymers

And (3) nucleus: modified PTFE shell: modified PTFE

And (3) nucleus: TFE homopolymer shell: modified PTFE

And (3) nucleus: low molecular weight PTFE shell: high molecular weight PTFE

And (3) nucleus: high molecular weight PTFE shell: low molecular weight PTFE

In the fluoropolymer having a core-shell structure, the lower limit of the proportion of the core is preferably 0.5% by mass, more preferably 1.0% by mass, even more preferably 3.0% by mass, particularly preferably 5.0% by mass, and most preferably 10.0% by mass. The upper limit of the proportion of the core is preferably 99.5% by mass, more preferably 99.0% by mass, still more preferably 98.0% by mass, even more preferably 97.0% by mass, particularly preferably 95.0% by mass, and most preferably 90.0% by mass.

In the fluoropolymer having a core-shell structure, the lower limit of the proportion of the shell is preferably 0.5% by mass, more preferably 1.0% by mass, even more preferably 3.0% by mass, particularly preferably 5.0% by mass, and most preferably 10.0% by mass. The upper limit of the proportion of the shell is preferably 99.5 mass%, more preferably 99.0 mass%, still more preferably 98.0 mass%, even more preferably 97.0 mass%, particularly preferably 95.0 mass%, most preferably 90.0 mass%.

In the fluoropolymer having a core-shell structure, the core or the shell may have a structure of 2 or more layers. For example, the fluoropolymer may have a 3-layer structure (the 3-layer structure has a core center portion of modified PTFE, a core outer layer portion of TFE homopolymer, and a shell of modified PTFE). Examples of such a fluoropolymer having a 3-layer structure include PTFE described in international publication No. 2006/054612.

The above-mentioned (I) non-melt-processable fluororesin and (II) melt-processable fluororesin suitably produced by the production method of the present invention are preferably produced as follows.

(I) Non-melt-processable fluororesin

In the production method of the present invention, polymerization of TFE is usually carried out at a polymerization temperature of 10 to 150 ℃ and a polymerization pressure of 0.05 to 5 MPaG. For example, the polymerization temperature is more preferably 30 ℃ or higher, and still more preferably 50 ℃ or higher. Further, it is more preferably 120 ℃ or lower, and still more preferably 100 ℃ or lower. The polymerization pressure is more preferably 0.3MPaG or more, further preferably 0.5MPaG or more, and still more preferably 5.0MPaG or less, further preferably 3.0MPaG or less. In particular, from the viewpoint of increasing the amount of the fluoropolymer to be obtained, it is preferably 1.0MPaG or more, more preferably 1.2MPaG or more, still more preferably 1.5MPaG or more, and still more preferably 2.0MPaG or more.

In one embodiment, the polymerization is initiated by charging pure water into a pressure-resistant reaction vessel equipped with a stirrer, deoxidizing, charging TFE to a predetermined temperature, and adding a polymerization initiator. When the pressure decreases as the reaction proceeds, additional TFE is continuously or intermittently additionally supplied to maintain the initial pressure. When a predetermined amount of TFE was supplied, the supply was stopped, and TFE in the reaction vessel was purged to return the temperature to room temperature, thereby terminating the reaction. Additional TFE may be continuously or intermittently additionally supplied so as not to decrease the pressure.

In the production of the above-mentioned TFE Polymer (PTFE), various known modified monomers may be used in combination. In the present specification, the PTFE is a concept including not only a homopolymer of TFE but also a non-melt-processable material (hereinafter referred to as "modified PTFE") which is a copolymer of TFE and a modified monomer.

The PTFE may be a TFE homopolymer, or may be modified PTFE containing 99.0 mass% or more of polymerized units based on TFE and 1.0 mass% or less of polymerized units based on a modified monomer.

In the modified PTFE, the content of polymerized units based on the modified monomer (hereinafter also referred to as "modified monomer units") is preferably in the range of 0.00001 to 1.0 mass% relative to the total polymerized units of the modified PTFE. The lower limit of the modifying monomer unit is more preferably 0.0001% by mass, still more preferably 0.001% by mass, and yet more preferably 0.005% by mass. The upper limit of the modified monomer unit is 0.90 mass%, 0.50 mass%, 0.40 mass%, 0.30 mass%, 0.20 mass%, 0.15 mass%, 0.10 mass%, 0.05 mass%.

In the present specification, the modified monomer unit refers to a portion derived from a modified monomer as a part of the molecular structure of PTFE.

In the present specification, the content of each monomer constituting PTFE can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis depending on the type of the monomer. The content of each monomer constituting PTFE can also be determined by calculating the amount of the modifying monomer used in the polymerization.

The modifying monomer is not particularly limited as long as it is copolymerizable with TFE, and examples thereof include fluorine-containing monomers and non-fluorine-containing monomers.

The non-fluorine-containing monomer is not particularly limited, and examples thereof include those of the general formula:

CH₂＝CR^Q1-LR^Q2

(in the formula, R^Q1Represents a hydrogen atom or an alkyl group. L represents a single bond, -CO-O-, -O-CO-, or-O-. Is represented by the formula^Q2The bonding position of (2). R^Q2Represents a hydrogen atom, an alkyl group or a nitrile group).

Examples of the non-fluorine-containing monomer include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, ethyl vinyl ether, cyclohexyl vinyl ether, and the like. Among the non-fluorine-containing monomers, butyl methacrylate, vinyl acetate and acrylic acid are preferable.

The fluorine-containing monomer is not particularly limited as long as it can be copolymerized with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene [ HFP ]; hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride [ VDF ]; perhaloolefins such as chlorotrifluoroethylene; a fluorovinyl ether; (perfluoroalkyl) ethylene; perfluoroallyl ether, and the like. The number of the modifying monomers used may be 1, or 2 or more.

The fluorovinyl ether is not particularly limited, and examples thereof include the following general formula (A):

CF₂＝CF-ORf (A)

and (wherein Rf represents a perfluoroorganic group). In the present specification, the "perfluoro organic group" refers to an organic group in which all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. The aforementioned perfluoroorganic group may have an ether oxygen.

Examples of the fluorovinyl ether include perfluoro (alkyl vinyl ether) [ PAVE ] in which Rf in the general formula (A) is a perfluoroalkyl group having 1 to 10 carbon atoms. The perfluoroalkyl group preferably has 1 to 5 carbon atoms.

Examples of the perfluoroalkyl group in PAVE include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.

The perfluorovinyl ether may further include a monomer represented by the general formula (A) wherein Rf is a C4-9 perfluoro (alkoxyalkyl) group, and Rf is represented by the following formula:

[ solution 15]

(wherein m represents 0 or an integer of 1 to 4), and Rf is represented by the following formula:

[ solution 16]

(wherein n represents an integer of 1 to 4) or the like.

As the hydrogen-containing fluoroolefin, CH may be mentioned₂＝CF₂、CFH＝CH₂、CFH＝CF₂、CF₂＝CFCF₃、CH₂＝CFCF₃、CH₂＝CHCF₃、CHF＝CHCF₃(E-form), CHF ═ CHCF₃(Z body), etc.

As the perfluorovinyl ether, at least one selected from the group consisting of perfluoro (methyl vinyl ether) (PMVE), perfluoro (ethyl vinyl ether) (PEVE) and perfluoro (propyl vinyl ether) (PPVE) is preferable, and PMVE is more preferable.

The (perfluoroalkyl) ethylene (PFAE) is not particularly limited, and examples thereof include (perfluorobutyl) ethylene (PFBE), and (perfluorohexyl) ethylene.

Examples of the perfluoroallyl ether include

A compound of the general formula: CF (compact flash)₂＝CF-CF₂-ORf

(wherein Rf represents a perfluoroorganic group).

Rf in the above formula is the same as Rf in the formula (A). Rf is preferably a C1-10 perfluoroalkyl group or a C1-10 perfluoroalkoxyalkyl group. The perfluoroallyl ether is preferably selected from the group consisting of CF ₂＝CF-CF₂-O-CF₃、CF₂＝CF-CF₂-O-C₂F₅、CF₂＝CF-CF₂-O-C₃F₇And CF₂＝CF-CF₂-O-C₄F₉At least one selected from the group consisting of CF, more preferably CF₂＝CF-CF₂-O-C₂F₅、CF₂＝CF-CF₂-O-C₃F₇And CF₂＝CF-CF₂-O-C₄F₉At least one of the group consisting of, more preferably CF₂＝CF-CF₂-O-CF₂CF₂CF₃。

The above-mentioned modified monomer is also preferably exemplified by a comonomer (3) having a monomer reactivity ratio of 0.1 to 8. By the presence of the comonomer (3), PTFE particles having a small particle diameter can be obtained, and an aqueous dispersion having high dispersion stability can be obtained.

Here, the monomer reactivity ratio in copolymerization with TFE is a value obtained as follows: when the growth radical is smaller than the repeating unit based on TFE, the rate constant at the time when the growth radical reacts with TFE is divided by the rate constant at the time when the growth radical reacts with the comonomer, and the obtained value is the monomer reactivity ratio. The lower the value, the higher the reactivity of the comonomer with TFE. The monomer reactivity ratio can be calculated as follows: the composition of the resulting polymer immediately after the initiation of copolymerization of TFE and a comonomer was determined and calculated from Fineman-Ross formula.

The copolymerization was carried out in a stainless steel autoclave having an internal volume of 6.0L using 3600g of deionized and degassed water, 1000ppm of ammonium perfluorooctanoate relative to the water, and 100g of paraffin wax under a pressure of 0.78MPa and a temperature of 70 ℃. 0.05g, 0.1g, 0.2g, 0.5g and 1.0g of a comonomer were fed into the reactor, respectively, and 0.072g of ammonium persulfate (20 ppm relative to water) was fed thereto, and TFE was continuously fed so as to maintain a polymerization pressure of 0.78 MPa. When the TFE charge reached 1000g, stirring was stopped and the pressure was released until the reactor reached atmospheric pressure. After cooling, the paraffin wax was separated, thereby obtaining an aqueous dispersion containing the resulting polymer. The resulting aqueous dispersion was stirred to coagulate the polymer, and dried at 150 ℃. The composition of the resulting polymer was calculated by appropriately combining NMR, FT-IR, elemental analysis, and fluorescent X-ray analysis depending on the type of the monomer.

The comonomer (3) having a monomer reactivity ratio of 0.1 to 8 is preferably at least one selected from the group consisting of comonomers represented by formulae (3a) to (3 d).

CH₂＝CH-Rf¹ (3a)

(wherein Rf¹Is a perfluoroalkyl group having 1 to 10 carbon atoms. )

CF₂＝CF-O-Rf² (3b)

(wherein Rf²Is a perfluoroalkyl group having 1 to 2 carbon atoms. )

CF₂＝CF-O-(CF₂)_nCF＝CF₂ (3c)

(wherein n is 1 or 2.)

[ solution 17]

(in the formula, X³And X⁴F, Cl or methoxy, Y is of formula Y1 or Y2. )

[ solution 18]

(in the formula Y2, Z and Z' are F or a fluoroalkyl group having 1 to 3 carbon atoms.)

The content of the comonomer (3) unit is preferably in the range of 0.00001 to 1.0 mass% based on the total polymerized units of PTFE. The lower limit is more preferably 0.0001% by mass, still more preferably 0.001% by mass, and yet more preferably 0.005% by mass. The upper limit is preferably 0.90 mass%, 0.50 mass%, 0.40 mass%, 0.30 mass%, 0.20 mass%, 0.15 mass%, 0.10 mass%, 0.08 mass%, 0.05 mass%, 0.01 mass% in this order.

The modified monomer is preferably at least one selected from the group consisting of hexafluoropropylene, chlorotrifluoroethylene, vinylidene fluoride, fluoro (alkyl vinyl ether), (perfluoroalkyl) ethylene, and a modified monomer having a functional group reactive in radical polymerization and a hydrophilic group, because an aqueous dispersion having a small average primary particle diameter, a small aspect ratio of the primary particles, and excellent stability can be obtained. By using the modified monomer, an aqueous dispersion of PTFE having a smaller average primary particle diameter, a smaller aspect ratio of primary particles, and excellent dispersion stability can be obtained. In addition, an aqueous dispersion with less non-condensable polymer can be obtained.

From the viewpoint of reactivity with TFE, the above-mentioned modifying monomer preferably contains at least one selected from the group consisting of hexafluoropropylene, perfluoro (alkyl vinyl ether), and (perfluoroalkyl) ethylene.

More preferably, at least one selected from the group consisting of hexafluoropropylene, perfluoro (methyl vinyl ether), perfluoro (propyl vinyl ether), (perfluorobutyl) ethylene, (perfluorohexyl) ethylene, and (perfluorooctyl) ethylene.

The total amount of the above hexafluoropropylene unit, perfluoro (alkyl vinyl ether) unit and (perfluoroalkyl) ethylene unit is preferably in the range of 0.00001 to 1 mass% with respect to the total polymerized units of PTFE. The lower limit of the total amount is more preferably 0.0001% by mass, still more preferably 0.001% by mass, and yet more preferably 0.005% by mass. The upper limit is preferably 0.90 mass%, 0.50 mass%, 0.40 mass%, 0.30 mass%, 0.20 mass%, 0.15 mass%, 0.10 mass%, 0.08 mass%, 0.05 mass%, 0.01 mass% in this order.

The above-mentioned modifying monomer also preferably contains a modifying monomer having a functional group capable of reacting in radical polymerization and a hydrophilic group (hereinafter referred to as "modifying monomer (a)").

The presence of the modified monomer (a) can provide PTFE particles having a small primary particle diameter, and can provide an aqueous dispersion having high dispersion stability. In addition, the amount of non-condensable polymer can be reduced. Further, the aspect ratio of the primary particles can be reduced.

The amount of the modifying monomer (A) used is preferably an amount exceeding 0.1ppm, more preferably an amount exceeding 0.5ppm, still more preferably an amount exceeding 1.0ppm, even more preferably 5ppm or more, and particularly preferably 10ppm or more based on the aqueous medium. If the amount of the modifying monomer (a) used is too small, the average primary particle diameter of the PTFE obtained may not be small.

The amount of the modifying monomer (A) may be in the above range, and for example, the upper limit can be set to 5000 ppm. In the above production method, the modifying monomer (a) may be added to the system during the reaction in order to improve the stability of the aqueous dispersion during or after the reaction.

Since the modified monomer (a) has high water solubility, even if unreacted modified monomer (a) remains in the aqueous dispersion, it can be easily removed in the concentration step or the condensation/washing step.

The modified monomer (A) is incorporated into the resulting polymer during the polymerization, but the concentration of the modified monomer (A) in the polymerization system is low, and the amount of the modified monomer (A) incorporated into the polymer is small, so that there is no problem that the heat resistance of PTFE is lowered or coloring after firing is caused.

Examples of the hydrophilic group in the modified monomer (A) include-NH₂、-PO₃M、-PO(OM)₂、-OPO₃M、-OPO(OM)₂、-SO₃M、-OSO₃M and-COOM (in the formula, M is H, metal atom, NR)⁷ ₄Imidazolium with or without substituents, pyridinium with or without substituents or phosphonium with or without substituents, R⁷Are H or an organic group, which may be the same or different. Any 2 of which may be bonded to each other to form a ring). As the above hydrophilic group, -SO is preferable₃M or-COOM. As R⁷The organic group of (2) is preferably an alkyl group. As R⁷Preferably H or C_1-10More preferably H or C_1-4Further preferably H or C_1-4Alkyl group of (1).

Examples of the metal atom include a metal atom having a valence of 1 and a metal atom having a valence of 2, and examples thereof include an alkali metal (group 1), an alkaline earth metal (group 2), and the like, and preferably include Na, K, and Li.

Examples of the "functional group capable of reacting in radical polymerization" in the modified monomer (a) include groups having an ethylenically unsaturated bond such as a vinyl group and an allyl group. The group having an ethylenically unsaturated bond may be represented by the formula:

CX^eX^g＝CX^fR-

(in the formula, X^e、X^fAnd X^gEach independently of the other is F, Cl, H, CF₃、CF₂H、CFH₂Or CH₃(ii) a R is a linking group). Examples of the linking group of R include the following R ^aA linking group of (a). Preferably, the group-CH ═ CH₂、-CF＝CH₂、-CH＝CF₂、-CF＝CF₂、-CH₂-CH＝CH₂、-CF₂-CF＝CH₂、-CF₂-CF＝CF₂、-(C＝O)-CH＝CH₂、-(C＝O)-CF＝CH₂、-(C＝O)-CH＝CF₂、-(C＝O)-CF＝CF₂、-(C＝O)-C(CH₃)＝CH₂、-(C＝O)-C(CF₃)＝CH₂、-(C＝O)-C(CH₃)＝CF₂、-(C＝O)-C(CF₃)＝CF₂、-O-CH₂-CH＝CH₂、-O-CF₂-CF＝CH₂、-O-CH₂-CH＝CF₂、-O-CF₂-CF＝CF₂And the like having an unsaturated bond.

Since the modified monomer (a) has a functional group reactive in radical polymerization, it is presumed that when used in the above polymerization, TFE reacts at the initial stage of the polymerization reaction, and the modified monomer (a) has a hydrophilic group derived from the modified monomer (a), and particles having high stability can be formed. Therefore, it is considered that when the polymerization is carried out in the presence of the modified monomer (a), the number of particles increases.

In the above polymerization, the modified monomer (a) may be present in 1 kind, or may be present in 2 or more kinds.

In the above polymerization, as the modifying monomer (a), a compound having an unsaturated bond can be used.

The modifying monomer (A) is preferably of the general formula (4):

CXⁱX^k＝CX^jR^a-(CZ¹Z²)_k-Y³ (4)

(in the formula, Xⁱ、X^jAnd X^kEach independently of the others being F, Cl, H or CF₃；Y³Is a hydrophilic group; r^aIs a linking group; z¹And Z²Each independently H, F or CF₃And k is 0 or 1).

Examples of the hydrophilic group include-NH₂、-PO₃M、-PO(OM)₂、-OPO₃M、-OPO(OM)₂、-SO₃M、-OSO₃M and-COOM (in each formula, M isH. Metal atom, NR⁷ ₄Imidazolium with or without substituents, pyridinium with or without substituents or phosphonium with or without substituents, R ⁷Are H or an organic group, which may be the same or different. Any 2 of which may be bonded to each other to form a ring). As the above hydrophilic group, -SO is preferable₃M or-COOM. As R⁷The organic group of (2) is preferably an alkyl group. As R⁷Preferably H or C_1-10More preferably H or C_1-4Further preferably H or C_1-4Alkyl group of (1).

By using the modified monomer (a), an aqueous dispersion having a smaller average primary particle diameter and more excellent stability can be obtained. In addition, the aspect ratio of the primary particles can be further reduced.

R is as defined above^aIs a linking group. In the present specification, "linking group" means a divalent linking group. The linking group may be a single bond, preferably contains at least 1 carbon atom, and the number of carbon atoms may be 2 or more, may be 4 or more, may be 8 or more, may be 10 or more, and may be 20 or more. The upper limit is not limited, and may be, for example, 100 or less or 50 or less.

The linking group may have a chain or branched structure, a cyclic or acyclic structure, a saturated or unsaturated structure, a substituted or unsubstituted structure, and may contain 1 or more heteroatoms selected from the group consisting of sulfur, oxygen, and nitrogen, and may contain 1 or more functional groups selected from the group consisting of esters, amides, sulfonamides, carbonyls, carbonates, carbamates, ureas, and carbamates, as desired. The linking group does not contain a carbon atom, and may be a chain hetero atom such as oxygen, sulfur or nitrogen.

R is as defined above^aPreferred is a chain hetero atom such as oxygen, sulfur, and nitrogen, or a 2-valent organic group.

R^aIn the case of a 2-valent organic group, bonded to a carbon atomThe hydrogen atom(s) of (3) may be substituted with a halogen other than fluorine, for example, chlorine, and may or may not contain a double bond. In addition, R^aThe polymer may be either a linear or branched one, or a cyclic or acyclic one. In addition, R^aFunctional groups (e.g., esters, ethers, ketones, amines, halides, etc.) may be included.

In addition, R^aMay be a non-fluorinated 2-valent organic group, or may be a partially fluorinated or perfluorinated 2-valent organic group.

As R^aThis may be, for example: a hydrocarbon group having no fluorine atom bonded to a carbon atom; a hydrocarbon group in which a part of hydrogen atoms bonded to carbon atoms is substituted with fluorine atoms; a hydrocarbon group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms; the hydrocarbon group containing- (C ═ O) -, - (C ═ O) -O-or- (C ═ O) -, may contain an oxygen atom, may contain a double bond, and may contain a functional group.

R^aThe hydrocarbon group may preferably contain a carbon number of 1 to 100, optionally a carbonyl group, and optionally an ether bond, and may contain fluorine in part or all of the hydrogen atoms bonded to the carbon atoms.

As R^aPreferably selected from- (CH)₂)_a-、-(CF₂)_a-、-O-(CF₂)_a-、-(CF₂)_a-O-(CF₂)_b-、-O(CF₂)_a-O-(CF₂)_b-、-(CF₂)_a-[O-(CF₂)_b]_c-、-O(CF₂)_a-[O-(CF₂)_b]_c-、-[(CF₂)_a-O]_b-[(CF₂)_c-O]_d-、-O[(CF₂)_a-O]_b-[(CF₂)_c-O]_d-、-O-[CF₂CF(CF₃)O]_a-(CF₂)_b-、-(C＝O)-、-(C＝O)-O-、-(C＝O)-(CH₂)_a-、-(C＝O)-(CF₂)_a-、-(C＝O)-O-(CH₂)_a-、-(C＝O)-O-(CF₂)_a-、-(C＝O)-[(CH₂)_a-O]_b-、-(C＝O)-[(CF₂)_a-O]_b-、-(C＝O)-O[(CH₂)_a-O]_b-、-(C＝O)-O[(CF₂)_a-O]_b-、-(C＝O)-O[(CH₂)_a-O]_b-(CH₂)_c-、-(C＝O)-O[(CF₂)_a-O]_b-(CF₂)_c-、-(C＝O)-(CH₂)_a-O-(CH₂)_b-、-(C＝O)-(CF₂)_a-O-(CF₂)_b-、-(C＝O)-O-(CH₂)_a-O-(CH₂)_b-、-(C＝O)-O-(CF₂)_a-O-(CF₂)_b-、-(C＝O)-O-C₆H₄-and combinations thereof.

Wherein a, b, c and d are independently at least 1 or more. a. b, c and d independently may be 2 or more, 3 or more, 4 or more, 10 or more, or 20 or more. a. The upper limit of b, c and d is, for example, 100.

As R^aA preferable specific example thereof is-CF₂-O-、-CF₂-O-CF₂-、-CF₂-O-CH₂-、-CF₂-O-CH₂CF₂-、-CF₂-O-CF₂CF₂-、-CF₂-O-CF₂CH₂-、-CF₂-O-CF₂CF₂CH₂-、-CF₂-O-CF(CF₃)-、-CF₂-O-CF(CF₃)CF₂-、-CF₂-O-CF(CF₃)CF₂-O-、-CF₂-O-CF(CF₃)CH₂-、-(C＝O)-、-(C＝O)-O-、-(C＝O)-(CH₂)-、-(C＝O)-(CF₂)-、-(C＝O)-O-(CH₂)-、-(C＝O)-O-(CF₂)-、-(C＝O)-[(CH₂)₂-O]_n-、-(C＝O)-[(CF₂)₂-O]_n-、-(C＝O)-O[(CH₂)₂-O]_n-、-(C＝O)-O[(CF₂)₂-O]_n-、-(C＝O)-O[(CH₂)₂-O]_n-(CH₂)-、-(C＝O)-O[(CF₂)₂-O]_n-(CF₂)-、-(C＝O)-(CH₂)₂-O-(CH₂)-、-(C＝O)-(CF₂)₂-O-(CF₂)-、-(C＝O)-O-(CH₂)₂-O-(CH₂)-、-(C＝O)-O-(CF₂)₂-O-(CF₂)-、-(C＝O)-O-C₆H₄-and the like. Wherein, specifically, R is as defined above^apreferably-CF₂-O-、-CF₂-O-CF₂-、-CF₂-O-CF₂CF₂-、-CF₂-O-CF(CF₃)-、-CF₂-O-CF(CF₃)CF₂-、-CF₂-O-CF(CF₃)CF₂-O-、-(C＝O)-、-(C＝O)-O-、-(C＝O)-(CH₂)-、-(C＝O)-O-(CH₂)-、-(C＝O)-O[(CH₂)₂-O]_n-、-(C＝O)-O[(CH₂)₂-O]_n-(CH₂)-、-(C＝O)-(CH₂)₂-O-(CH₂) -, or- (C ═ O) -O-C₆H₄-。

In the above formula, n is an integer of 1 to 10.

as-R in the above general formula (4)^a-(CZ¹Z²)_k-, preferably-CF₂-O-CF₂-、-CF₂-O-CF(CF₃)-、-CF₂-O-C(CF₃)₂-、-CF₂-O-CF₂-CF₂-、-CF₂-O-CF₂-CF(CF₃)-、-CF₂-O-CF₂-C(CF₃)₂-、-CF₂-O-CF₂CF₂-CF₂-、-CF₂-O-CF₂CF₂-CF(CF₃)-、-CF₂-O-CF₂CF₂-C(CF₃)₂-、-CF₂-O-CF(CF₃)-CF₂-、-CF₂-O-CF(CF₃)-CF(CF₃)-、-CF₂-O-CF(CF₃)-C(CF₃)₂-、-CF₂-O-CF(CF₃)-CF₂-、-CF₂-O-CF(CF₃)-CF(CF₃)-、-CF₂-O-CF(CF₃)-C(CF₃)₂-、-CF₂-O-CF(CF₃)CF₂-CF₂-、-CF₂-O-CF(CF₃)CF₂-CF(CF₃)-、-CF₂-O-CF(CF₃)CF₂-C(CF₃)₂-、-CF₂-O-CF(CF₃)CF₂-O-CF₂-、-CF₂-O-CF(CF₃)CF₂-O-CF(CF₃)-、-CF₂-O-CF(CF₃)CF₂-O-C(CF₃)₂-、-(C＝O)-、-(C＝O)-O-、-(C＝O)-(CH₂)-、-(C＝O)-(CF₂)-、-(C＝O)-O-(CH₂)-、-(C＝O)-O-(CF₂)-、-(C＝O)-[(CH₂)₂-O]_n-(CH₂)-、-(C＝O)-[(CF₂)₂-O]_n-(CF₂)-、-(C＝O)-[(CH₂)₂-O]_n-(CH₂)-(CH₂)-、-(C＝O)-[(CF₂)₂-O]_n-(CF₂)-(CF₂)-、-(C＝O)-O[(CH₂)₂-O]_n-(CF₂)-、-(C＝O)-O[(CH₂)₂-O]_n-(CH₂)-(CH₂)-、-(C＝O)-O[(CF₂)₂-O]_n-(CF₂)-、-(C＝O)-O[(CF₂)₂-O]_n-(CF₂)-(CF₂)-、-(C＝O)-(CH₂)₂-O-(CH₂)-(CH₂)-、-(C＝O)-(CF₂)₂-O-(CF₂)-(CF₂)-、-(C＝O)-O-(CH₂)₂-O-(CH₂)-(CH₂)-、-(C＝O)-O-(CF₂)₂-O-(CF₂)-(CF₂)-、-(C＝O)-O-(CH₂)₂-O-(CH₂)-C(CF₃)₂-、-(C＝O)-O-(CF₂)₂-O-(CF₂)-C(CF₃)₂-, or- (C ═ O) -O-C₆H₄-C(CF₃)₂-, more preferably-CF₂-O-CF(CF₃)-、-CF₂-O-CF₂-CF(CF₃)-、-CF₂-O-CF₂CF₂-CF(CF₃)-、-CF₂-O-CF(CF₃)-CF(CF₃)-、-CF₂-O-CF(CF₃)CF₂-CF(CF₃)-、-CF₂-O-CF(CF₃)CF₂-O-CF(CF₃)-、-(C＝O)-、-(C＝O)-O-(CH₂)-、-(C＝O)-O-(CH₂)-(CH₂)-、-(C＝O)-O[(CH₂)₂-O]_n-(CH₂)-(CH₂)-、-(C＝O)-O-(CH₂)₂-O-(CH₂)-C(CF₃)₂-, or- (C ═ O) -O-C₆H₄-C(CF₃)₂-。

In the above formula, n is an integer of 1 to 10.

Specific examples of the compound represented by the general formula (4) include

[ solution 19]

(in the formula, X^jAnd Y³As described above. n is an integer of 1 to 10), and the like.

As R^aPreferably, the following general formula (r 1):

-(C＝O)_h-(O)_i-CF₂-O-(CX⁶ ₂)_e-{O-CF(CF₃)}_f-(O)_g- (r1)

(in the formula, X⁶Each independently H, F or CF₃E is an integer of 0 to 3, f is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, i is 0 or 1), and the following general formula (r2) is also preferable:

-(C＝O)_h-(O)_i-CF₂-O-(CX⁷ ₂)_e-(O)_g- (r2)

(in the formula, X⁷Each independently H, F or CF₃E is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, and i is a 2-valent group represented by 0 or 1).

as-R of the above general formula (4)^a-(CZ¹Z²)_kThe following formula (t1) is also preferred:

-(C＝O)_h-(O)_i-CF₂-O-(CX⁶ ₂)_e-{O-CF(CF₃)}_f-(O)_g-CZ¹Z²- (t1)

(in the formula, X⁶Each independently H, F or CF₃E is an integer of 0 to 3, f is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, i is 0 or 1, Z¹And Z²Each independently is F or CF₃) The 2-valent group shown in the formula (t1), Z¹And Z²More preferably, one is F and the other is CF₃。

In the above general formula (4), the group represented by the formula-R^a-(CZ¹Z²)_kThe following formula (t2) is also preferred:

-(C＝O)_h-(O)_i-CF₂-O-(CX⁷ ₂)_e-(O)_g-CZ¹Z²- (t2)

(in the formula, X⁷Each independently H, F or CF₃E is an integer of 0 to 3, g is 0 or 1, h is 0 or 1, i is 0 or 1, Z¹And Z²Each independently is F or CF₃) The 2-valent group shown in the formula (t2), Z¹And Z²More preferably, one is F and the other is CF₃。

The compound represented by the formula (4) is also preferably selected in addition to the hydrophilic group (Y)³) And has no C-H bond and a C-F bond. That is, in the general formula (4), X is preferableⁱ、X^jAnd X^kAll are F, R^aThe perfluoroalkylene group may be any of a chain and a branched chain, may be any of a cyclic and an acyclic, and may contain at least 1 chain hetero atom. The number of carbon atoms of the perfluoroalkylene group may be 2 to 20, or 4 to 18.

The compounds of formula (4) may also be partially fluorinated. That is, the compound represented by the general formula (4) is also preferably selected from hydrophilic groups (Y) ³) And has at least 1 hydrogen atom bonded to a carbon atom and has at least 1 fluorine atom bonded to a carbon atom.

The compound represented by the general formula (4) is also preferably a compound represented by the following formula (4 a).

CF₂＝CF-O-Rf⁰-Y³ (4a)

(in the formula, Y³Is a hydrophilic group, Rf⁰The perfluorinated compound is a perfluorinated divalent linking group which is perfluorinated, may have a chain or branched chain structure, a cyclic or acyclic structure, a saturated or unsaturated structure, a substituted or unsubstituted structure, and optionally additionally contains 1 or more heteroatoms selected from the group consisting of sulfur, oxygen, and nitrogen. )

The compound represented by the general formula (4) is also preferably a compound represented by the following formula (4 b).

CH₂＝CH-O-Rf⁰-Y³ (4b)

(in the formula, Y³Is a hydrophilic group, Rf⁰A per-fluorinated divalent linking group as defined for formula (4 a). )

In the general formula (4), Y³is-OSO₃M is one of the preferred modes. At Y³is-OSO₃In the case of M, CF is exemplified as the compound represented by the general formula (4)₂＝CF(OCF₂CF₂CH₂OSO₃M)、CH₂＝CH((CF₂)₄CH₂OSO₃M)、CF₂＝CF(O(CF₂)₄CH₂OSO₃M)、CF₂＝CF(OCF₂CF(CF₃)CH₂OSO₃M)、CF₂＝CF(OCF₂CF(CF₃)OCF₂CF₂CH₂OSO₃M)、CH₂＝CH((CF₂)₄CH₂OSO₃M)、CF₂＝CF(OCF₂CF₂SO₂N(CH₃)CH₂CH₂OSO₃M)、CH₂＝CH(CF₂CF₂CH₂OSO₃M)、CF₂＝CF(OCF₂CF₂CF₂CF₂SO₂N(CH₃)CH₂CH₂OSO₃M)、CH₂＝CH(CF₂CF₂CH₂OSO₃M), and the like.In the above formula, M is the same as described above.

In the general formula (4), Y³is-SO₃M is also one of the preferred modes. At Y³is-SO₃In the case of M, CF is exemplified as the compound represented by the general formula (4)₂＝CF(OCF₂CF₂SO₃M)、CF₂＝CF(O(CF₂)₄SO₃M)、CF₂＝CF(OCF₂CF(CF₃)SO₃M)、CF₂＝CF(OCF₂CF(CF₃)OCF₂CF₂SO₃M)、CH₂＝CH(CF₂CF₂SO₃M)、CF₂＝CF(OCF₂CF(CF₃)OCF₂CF₂CF₂CF₂SO₃M)、CH₂＝CH((CF₂)₄SO₃M)、CH₂＝CH(CF₂CF₂SO₃M)、CH₂＝CH((CF₂)₃SO₃M), and the like. In the above formula, M is the same as described above.

In the general formula (4), Y³It is also one of the preferred modes to be-COOM. At Y³In the case of-COOM, CF is mentioned as the compound represented by the general formula (4) ₂＝CF(OCF₂CF₂COOM)、CF₂＝CF(OCF₂CF₂CF₂COOM)、CF₂＝CF(O(CF₂)₅COOM)、CF₂＝CF(OCF₂CF(CF₃)COOM)、CF₂＝CF(OCF₂CF(CF₃)O(CF₂)_nCOOM) (n is more than 1), CH₂＝CH(CF₂CF₂COOM)、CH₂＝CH((CF₂)₄COOM)、CH₂＝CH(CF₂CF₂COOM)、CH₂＝CH((CF₂)₃COOM)、CF₂＝CF(OCF₂CF₂SO₂NR’CH₂COOM)、CF₂＝CF(O(CF₂)₄SO₂NR’CH₂COOM)、CF₂＝CF(OCF₂CF(CF₃)SO₂NR’CH₂COOM)、CF₂＝CF(OCF₂CF(CF₃)OCF₂CF₂SO₂NR’CH₂COOM)、CH₂＝CH(CF₂CF₂SO₂NR’CH₂COOM)、CF₂＝CF(OCF₂CF(CF₃)OCF₂CF₂CF₂CF₂SO₂NR’CH₂COOM)、CH₂＝CH((CF₂)₄SO₂NR’CH₂COOM)、CH₂＝CH(CF₂CF₂SO₂NR’CH₂COOM)、CH₂＝CH((CF₂)₃SO₂NR’CH₂COOM), and the like. In the above formula, R' is H or C_1-4Alkyl, M are the same as described above.

In the general formula (4), Y³is-OPO₃M or-OP (O) (OM)₂Is also one of the preferred modes. At Y³is-OPO₃M or-OP (O) (OM)₂In the case (4), CF is an example of the compound represented by the general formula₂＝CF(OCF₂CF₂CH₂OP(O)(OM)₂)、CF₂＝CF(O(CF₂)₄CH₂OP(O)(OM)₂)、CF₂＝CF(OCF₂CF(CF₃)CH₂OP(O)(OM)₂)、CF₂＝CF(OCF₂CF(CF₃)OCF₂CF₂CH₂OP(O)(OM)₂)、CF₂＝CF(OCF₂CF₂SO₂N(CH₃)CH₂CH₂OP(O)(OM)₂)、CF₂＝CF(OCF₂CF₂CF₂CF₂SO₂N(CH₃)CH₂CH₂OP(O)(OM)₂)、CH₂＝CH(CF₂CF₂CH₂OP(O)(OM)₂、CH₂＝CH((CF₂)₄CH₂OP(O)(OM)₂)、CH₂＝CH(CF₂CF₂CH₂OP(O)(OM)₂)、CH₂＝CH((CF₂)₃CH₂OP(O)(OM)₂) -and the like. In the above formula, M is the same as described above.

In the general formula (4), Y³is-PO₃M or-P (O) (OM)₂Is also one of the preferred modes. At Y³is-PO₃M or-P (O) (OM)₂In the case (4), CF is an example of the compound represented by the general formula₂＝CF(OCF₂CF₂P(O)(OM)₂)、CF₂＝CF(O(CF₂)₄P(O)(OM)₂)、CF₂＝CF(OCF₂CF(CF₃)P(O)(OM)₂)、CF₂＝CF(OCF₂CF(CF₃)OCF₂CF₂P(O)(OM)₂)、CH₂＝CH(CF₂CF₂P(O)(OM)₂)、CH₂＝CH((CF₂)₄P(O)(OM)₂)、CH₂＝CH(CF₂CF₂P(O)(OM)₂)、CH₂＝CH((CF₂)₃P(O)(OM)₂) Wherein M is the same as described above.

The compound represented by the above general formula (4) is preferably at least one selected from the group consisting of the following monomers, the monomers being represented by the following general formula (5):

CX₂＝CY(-CZ₂-O-Rf-Y³) (5)

(wherein X is the same or different and is-H or-F, Y is-H, -F, alkyl or fluoroalkyl, and Z is the same or different and is-H, -F, alkyl or fluoroalkyl Rf is a fluoroalkylene group having 1 to 40 carbon atoms or a fluoroalkylene group having 2 to 100 carbon atoms and having an ether bond.Y³The same as described above). ) A monomer as shown; the following general formula (6):

CX₂＝CY(-O-Rf-Y³) (6)

(wherein X is-H or-F, Y is-H, -F, alkyl or fluoroalkyl, and Rf is a C1-40 fluoroalkylene group or a C2-100 fluoroalkylene group having an ether bond.) Y ³The same as above); and the following general formula (7):

CX₂＝CY(-Rf-Y³) (7)

(wherein X is the same or different and is-H or-F, Y is-H, -F, alkyl or fluoroalkyl group, and Rf is a carbon atomA fluorinated alkylene group having 1 to 40 carbon atoms or a fluorinated alkylene group having 2 to 100 carbon atoms and an ether bond. Y is³The same as described above).

The fluorine-containing alkylene group having an ether bond and having 2 to 100 carbon atoms is an alkylene group having an ether bond between carbon and carbon atoms, which does not have an oxygen atom as a terminal structure.

In the general formula (5), X is-H or-F. X may be both-F or at least one of-H. For example, one may be-F and the other may be-H, or both may be-H.

In the general formula (5), Y is-H, -F, alkyl or fluoroalkyl.

The alkyl group may be an alkyl group containing no fluorine atom and having 1 or more carbon atoms. The number of carbon atoms of the alkyl group is preferably 6 or less, more preferably 4 or less, and still more preferably 3 or less.

The fluoroalkyl group may be an alkyl group containing at least 1 fluorine atom and having 1 or more carbon atoms. The number of carbon atoms of the fluoroalkyl group is preferably 6 or less, more preferably 4 or less, and still more preferably 3 or less.

As Y, preferred is-H, -F or-CF₃And more preferably-F.

In the above general formula (5), Z, which may be the same or different, is-H, -F, alkyl or fluoroalkyl.

As the above Z, preferred is-H, -F or-CF₃And more preferably-F.

In the above general formula (5), at least one of X, Y and Z preferably contains a fluorine atom. For example, X may be-H, and Y and Z may be-F.

In the general formula (5), Rf is a C1-40 fluoroalkylene group or a C2-100 fluoroalkylene group having an ether bond.

The number of carbon atoms of the fluorinated alkylene group is preferably 2 or more. Further, it is preferably 30 or less, more preferably 20 or less, and still more preferably 10 or less. Examples of the fluoroalkylene group include-CF₂-、-CH₂CF₂-、-CF₂CF₂-、-CF₂CH₂-、-CF₂CF₂CH₂-、-CF(CF₃)-、-CF(CF₃)CF₂-、-CF(CF₃)CH₂-and the like. The above-mentioned fluoroalkylene group is preferably a perfluoroalkylene group.

The number of carbon atoms of the fluorinated alkylene group having an ether bond is preferably 3 or more. The number of carbon atoms of the fluorinated alkylene group having an ether bond is preferably 60 or less, more preferably 30 or less, and still more preferably 12 or less.

As the fluorine-containing alkylene group having an ether bond, for example, also preferred is the following formula:

[ solution 20]

(in the formula, Z¹Is F or CF₃；Z²And Z³Are H or F respectively; z⁴Is H, F or CF₃(ii) a p1+ q1+ r1 is an integer of 1-10; s1 is 0 or 1; t1 is an integer of 0 to 5).

Specific examples of the fluorinated alkylene group having an ether bond include-CF (CF)₃)CF₂-O-CF(CF₃)-、-(CF(CF₃)CF₂-O)_n-CF(CF₃) - (wherein n is an integer of 1 to 10), -CF (CF)₃)CF₂-O-CF(CF₃)CH₂-、-(CF(CF₃)CF₂-O)_n-CF(CF₃)CH₂- (wherein n is an integer of 1 to 10), -CH₂CF₂CF₂O-CH₂CF₂CH₂-、-CF₂CF₂CF₂O-CF₂CF₂-、-CF₂CF₂CF₂O-CF₂CF₂CH₂-、-CF₂CF₂O-CF₂-、-CF₂CF₂O-CF₂CH₂-and the like. The fluorine-containing alkylene group having an ether bond is preferably a perfluoroalkylene group.

In the above general formula (5), Y³preferably-COOM, -SO₃M or-OSO₃M (M is H, a metal atom, NR)⁷ ₄Imidazolium with or without substituents, pyridinium with or without substituents or phosphonium with or without substituents, R⁷Are H or an organic group, which may be the same or different. Any 2 of which may be bonded to each other to form a ring).

As R⁷The organic group of (2) is preferably an alkyl group. As R⁷Preferably H or C_1-10More preferably H or C _1-4Further preferably H or C_1-4Alkyl group of (1).

Examples of the metal atom include alkali metals (group 1), alkaline earth metals (group 2), and the like, and Na, K, and Li are preferable.

As the above M, preferred is-H, a metal atom or-NR⁷ ₄More preferably-H, alkali metal (group 1), alkaline earth metal (group 2) or-NR⁷ ₄Further, it is preferably-H, -Na, -K, -Li or-NH₄Further more preferably-Na, -K or-NH₄Particularly preferred is-Na or-NH₄Most preferably-NH₄。

As the above Y³preferably-COOM or-SO₃M, more preferably-COOM.

The monomer represented by the general formula (5) is preferably a monomer (5a) represented by the following general formula (5 a).

CH₂＝CF(-CF₂-O-Rf-Y³) (5a)

(wherein Rf and Y³As described above. )

Specific examples of the monomer represented by the general formula (5a) include the following formulae:

[ solution 21]

(in the formula, Z¹Is F or CF₃；Z²And Z³Are H or F respectively; z⁴Is H, F or CF₃(ii) a p1+ q1+ r1 is an integer of 0-10; s1 is 0 or 1; t1 is an integer of 0 to 5, Y³As described above. Wherein Z is³And Z⁴P1+ q1+ r1+ s1 is not 0) in all cases. More specifically, preferred examples thereof include

[ solution 22]

Etc., among them, preferred are

[ solution 23]

As the monomer represented by the above general formula (5a), Y in the formula (5a) is preferable³is-COOM, particularly preferably selected from the group consisting of CH₂＝CFCF₂OCF(CF₃) COOM and CH₂＝CFCF₂OCF(CF₃)CF₂OCF(CF₃) COOM (wherein M is as defined above), more preferably CH ₂＝CFCF₂OCF(CF₃)COOM。

The monomer represented by the general formula (5) is preferably a monomer (5b) represented by the following general formula (5 b).

CX² ₂＝CFCF₂-O-(CF(CF₃)CF₂O)_n5-CF(CF₃)-Y³(5b)

(in the formula, each X²The same indicates F or H. n5 represents 0 or an integer of 1 to 10, Y³As defined above. )

In the formula (5b), n5 is preferably 0 or an integer of 1 to 5, more preferably n5 in view of stability of the aqueous dispersion obtainedIs 0, 1 or 2, and more preferably 0 or 1. The above Y is a group of compounds having a suitable water solubility and stability of the aqueous dispersion³preferably-COOM, and M is preferably H or NH, from the viewpoint of being less likely to remain as an impurity and improving the heat resistance of the resulting molded article₄。

Examples of the monomer represented by the formula (5b) include CH₂＝CFCF₂OCF(CF₃)COOM、CH₂＝CFCF₂OCF(CF₃)CF₂OCF(CF₃) COOM (wherein M is as defined above).

Further, examples of the monomer represented by the general formula (5) include a monomer represented by the following general formula (5 c).

CF₂＝CFCF₂-O-Rf-Y³ (5c)

(wherein Rf and Y³As described above. )

More specifically, there may be mentioned

[ solution 24]

And the like.

In the above general formula (6), X is-H or-F. X may be both-F or at least one of-H. For example, one may be-F and the other may be-H, or both may be-H.

In the general formula (6), Y is-H, -F, alkyl or fluoroalkyl.

As Y, preferred is-H, -F or-CF₃And more preferably-F.

In the general formula (6), it is preferable that at least one of X and Y contains a fluorine atom. For example, X may be-H, and Y and Z may be-F.

In the general formula (6), Rf is a C1-40 fluoroalkylene group or a C2-100 fluoroalkylene group having an ether bond.

The number of carbon atoms of the fluorinated alkylene group is preferably 2 or more. The number of carbon atoms of the fluorinated alkylene group is preferably 30 or less, more preferably 20 or less, and still more preferably 10 or less. Examples of the fluoroalkylene group include-CF₂-、-CH₂CF₂-、-CF₂CF₂-、-CF₂CH₂-、-CF₂CF₂CH₂-、-CF(CF₃)-、-CF(CF₃)CF₂-、-CF(CF₃)CH₂-and the like. The above-mentioned fluoroalkylene group is preferably a perfluoroalkylene group.

In the above general formula (6), Y³preferably-COOM, -SO₃M or-OSO₃M (M is H, metal atom, NR)⁷ ₄Imidazolium with or without substituents, pyridinium with or without substituents or phosphonium with or without substituents, R ⁷Are H or an organic group, which may be the same or different. Any 2 of which may be bonded to each other to form a ring).

As R⁷The organic group of (2) is preferably an alkyl group. As R⁷Preferably H or C_1-10More preferably H or C_1-4Further preferably H or C_1-4Alkyl group of (1).

Examples of the metal atom include alkali metals (group 1), alkaline earth metals (group 2), and the like, and Na, K, and Li are preferable.

As the above Y³preferably-COOM or-SO₃M, more preferably-COOM。

The monomer represented by the above general formula (6) is preferably at least one selected from the group consisting of monomers represented by the following general formulae (6a), (6b), (6c), (6d) and (6 e).

CF₂＝CF-O-(CF₂)_n1-Y³ (6a)

(wherein n1 represents an integer of 1 to 10, and is as defined above.)

CF₂＝CF-O-(CF₂C(CF₃)F)_n2-Y³ (6b)

(wherein n2 represents an integer of 1 to 5, and Y represents³As defined above. )

CF₂＝CF-O-(CFX¹)_n3-Y³ (6c)

(in the formula, X¹Represents F or CF₃N3 represents an integer of 1 to 10, Y³As defined above. )

CF₂＝CF-O-(CF₂CFX¹O)_n4-(CF₂)_n6-Y³ (6d)

(wherein n4 represents an integer of 1 to 10, n6 represents an integer of 1 to 3, and Y represents ³And X¹As defined above. )

CF₂＝CF-O-(CF₂CF₂CFX¹O)_n5-CF₂CF₂CF₂-Y³ (6e)

(wherein n5 represents an integer of 0 to 10, and Y represents³And X¹As defined above. )

In the formula (6a), n1 is preferably an integer of 5 or less, more preferably an integer of 2 or less. The above Y is a group of compounds having a suitable water solubility and stability of the aqueous dispersion³preferably-COOM, and M is preferably H or NH from the viewpoint of being less likely to remain as an impurity and improving the heat resistance of the resulting molded article₄。

Examples of the monomer represented by the formula (6a) include CF₂＝CF-O-CF₂COOM、CF₂＝CF(OCF₂CF₂COOM)、CF₂＝CF(OCF₂CF₂CF₂COOM) (wherein M is as defined above).

In the above formula (6b), n2 is preferably an integer of 3 or less from the viewpoint of stability of the aqueous dispersion to be obtained, and Y is an integer of appropriate water solubility and stability of the aqueous dispersion to be obtained³preferably-COOM, and M is preferably H or NH from the viewpoint of being less likely to remain as an impurity and improving the heat resistance of the resulting molded article₄。

In the formula (6c), n3 is preferably an integer of 5 or less from the viewpoint of water solubility, and Y is preferably an integer of 5 or less from the viewpoint of obtaining appropriate water solubility and stability of the aqueous dispersion³preferably-COOM, and M is preferably H or NH from the viewpoint of improving dispersion stability ₄。

In the above formula (6d), the X is a group represented by the formula¹preferably-CF₃In terms of water solubility, n4 is preferably an integer of 5 or less, and Y is an integer of 5 or less in terms of obtaining appropriate water solubility and stability of the aqueous dispersion³preferably-COOM, and the above M is preferably H or NH₄。

Examples of the monomer represented by the formula (6d) include CF₂＝CFOCF₂CF(CF₃)OCF₂CF₂COOM、CF₂＝CFOCF₂CF(CF₃)OCF₂COOM、CF₂＝CFOCF₂CF(CF₃)OCF₂CF₂CF₂OOM (wherein M represents H, NH₄Or an alkali metal).

In the general formula (6e), n5 is preferably an integer of 5 or less from the viewpoint of water solubility, and Y is an integer of 5 or less from the viewpoint of obtaining appropriate water solubility and excellent sedimentation stability of the composition³preferably-COOM, and the above M is preferably H or NH₄。

Examples of the monomer represented by the general formula (6e) include CF₂＝CFOCF₂CF₂CF₂COOM (wherein M represents H, NH)₄Or an alkali metal).

In the general formula (7), Rf is preferably a C1-40 fluoroalkylene group. In the general formula (7), at least one of X and Y preferably contains a fluorine atom.

The monomer represented by the above general formula (7) is preferably selected from the group consisting of the following general formula (7 a):

CF₂＝CF-(CF₂)_n1-Y³ (7a)

(wherein n1 represents an integer of 1 to 10, and Y represents³The same as defined above), and the following general formula (7 b):

CF₂＝CF-(CF₂C(CF₃)F)_n2-Y³ (7b)

(wherein n2 represents an integer of 1 to 5, and Y represents ³Same as defined above) of the above-mentioned monomers.

Y is above³preferably-SO₃M or-COOM, M preferably being H, a metal atom, NR⁷ ₄An imidazolium with or without substituents, a pyridinium with or without substituents or a phosphonium with or without substituents. R is as defined above⁷Represents H or an organic group.

In the formula (7a), n1 is preferably an integer of 5 or less, more preferably an integer of 2 or less. The above Y is a group of compounds having a suitable water solubility and stability of the aqueous dispersion³preferably-COOM, and M is preferably H or NH from the viewpoint of being less likely to remain as an impurity and improving the heat resistance of the resulting molded article₄。

Examples of the perfluorovinyl alkyl compound represented by the formula (7a) include CF₂＝CFCF₂COOM (wherein M is as defined above).

In the above formula (7b), n2 is preferably an integer of 3 or less from the viewpoint of stability of the aqueous dispersion to be obtained, and Y is an integer of appropriate water solubility and stability of the aqueous dispersion to be obtained³preferably-COOM, and M is preferably H or NH from the viewpoint of being less likely to remain as an impurity and improving the heat resistance of the resulting molded article₄。

The modifying monomer preferably contains the modifying monomer (a), preferably contains at least one selected from the group consisting of compounds represented by general formula (5a), general formula (5b), general formula (6a), general formula (6b), general formula (6c), and general formula (6d), and more preferably contains a compound represented by general formula (5a) or general formula (5 b).

When the modified monomer contains the modified monomer (a), the content of the polymerized units based on the modified monomer (a) is preferably in the range of 0.00001 to 1.0 mass% with respect to PTFE. The lower limit is more preferably 0.0001% by mass, still more preferably 0.001% by mass, and yet more preferably 0.005% by mass. The upper limit is preferably 0.90 mass%, 0.50 mass%, 0.40 mass%, 0.30 mass%, 0.20 mass%, 0.15 mass%, 0.10 mass%, 0.08 mass%, 0.05 mass%, 0.01 mass% in this order.

The PTFE may have a core-shell structure. The core-shell structure is a conventionally known structure, and is a structure of primary particles in an aqueous dispersion liquid that can be produced by a method described in U.S. Pat. No. 6841594 or the like.

Examples of the polytetrafluoroethylene having a core-shell structure include a core-shell structure including a core portion of TFE homopolymer and a shell portion of modified PTFE, a core-shell structure including a core portion of modified PTFE and a shell portion of TFE homopolymer, and a core-shell structure including a core portion of modified PTFE and a shell portion of modified PTFE having a monomer composition different from that of the modified PTFE constituting the core portion.

The core-shell structured PTFE can be obtained, for example, as follows: first, a core portion (TFE homopolymer or modified PTFE) is produced by polymerizing TFE and, if necessary, a modified monomer, and then a shell portion (TFE homopolymer or modified PTFE) is produced by polymerizing TFE and, if necessary, a modified monomer.

The shell section is a portion having a predetermined thickness from the surface of the PTFE primary particle to the inside of the particle, and the core section is a portion constituting the inside of the shell section.

In the present specification, the core-shell structure includes all of the following cases: (1) the case where the core portion and the shell portion have different monomer compositions; (2) the case where the core portion and the shell portion have the same monomer composition, and the number average molecular weights of the two portions are different; (3) the core portion and the shell portion have different monomer compositions, and the number average molecular weights of the two portions are also different.

When the shell portion is modified PTFE, the content of the modified monomer in the shell portion is preferably 0.00001 to 1.0 mass%. More preferably 0.0001% by mass or more, further preferably 0.001% by mass or more, and further preferably 0.01% by mass or more. Further, it is more preferably 0.50% by mass or less, and still more preferably 0.30% by mass or less.

When the core portion is modified PTFE, the content of the modified monomer in the core portion is preferably 0.00001 to 1.0 mass%. More preferably 0.0001% by mass or more, and still more preferably 0.001% by mass or more. Further, it is more preferably 0.50% by mass or less, and still more preferably 0.30% by mass or less.

The average primary particle diameter of the PTFE is preferably 500nm or less, more preferably 400nm or less, and still more preferably 350nm or less. The production method of the present invention can produce PTFE having a small average primary particle size. The lower limit of the average primary particle diameter is not particularly limited, and may be, for example, 50nm or 100 nm. From the viewpoint of molecular weight, for example, in the case of high molecular weight PTFE, it is preferably 100nm or more, more preferably 150nm or more.

The average primary particle diameter can be measured by a dynamic light scattering method. The average primary particle size is determined by dynamic light scattering under conditions of 25 ℃, 1.3328 for the refractive index of the solvent (water), 0.8878mPa · s for the viscosity of the solvent (water), and 70 times of accumulation, to prepare an aqueous PTFE dispersion having a solid content concentration of about 1.0 mass%. As the dynamic light scattering method, for example, ELSZ-1000S (manufactured by Otsuka electronics Co., Ltd.) can be used.

The aspect ratio of the primary particles of PTFE is preferably 1.45 or less. The aspect ratio is more preferably 1.40 or less, further preferably 1.35 or less, further more preferably 1.30 or less, particularly preferably 1.25 or less, particularly preferably 1.20 or less, and particularly preferably 1.15 or less.

In the case of measurement in an aqueous dispersion, the aspect ratio is determined as follows: an aqueous dispersion of PTFE diluted to a solid content concentration of about 1 mass% was observed with a Scanning Electron Microscope (SEM), and 400 or more particles extracted at random were subjected to image processing and determined from the average of the ratio of the major axis to the minor axis. In the case of powder measurement, the aspect ratio is determined as follows: the modified PTFE powder is irradiated with an electron beam, added to an aqueous solution of a fluorine-based surfactant, and redispersed by ultrasonic waves, whereby an aqueous modified PTFE dispersion can be obtained. From the aqueous dispersion of modified PTFE, the aspect ratio was determined by the same method as the method for measurement of the aqueous dispersion.

In the PTFE, the Standard Specific Gravity (SSG) and the Melt Viscosity (MV) used as an index of the molecular weight are not particularly limited.

The average particle diameter (average secondary particle diameter) of the PTFE powder obtained by the production method of the present invention is preferably 100 to 2000. mu.m. The lower limit of the average secondary particle size is more preferably 200 μm or more, and still more preferably 300 μm or more. The upper limit of the average secondary particle size is preferably 1000 μm or less, more preferably 800 μm or less, and particularly preferably 700 μm or less. The average particle diameter is a value measured according to JIS K6891.

The PTFE has a Standard Specific Gravity (SSG) of preferably 2.280 or less, more preferably 2.200 or less, still more preferably 2.190 or less, and yet more preferably 2.180 or less. Further, it is preferably 2.130 or more. The SSG was measured by the water displacement method according to ASTM D792 using a sample molded according to ASTM D4895-89.

The peak temperature of the PTFE is preferably 348 ℃ or less, more preferably 346 ℃ or less, still more preferably 344 ℃ or less, yet more preferably 342 ℃ or less, and particularly preferably 340 ℃ or less. The peak temperature is a value measured by the following method. .

About 10mg of PTFE powder which had not been heated to a temperature of 300 ℃ or higher was precisely weighed, stored in a dedicated aluminum pan, and measured by TG/DTA (differential thermal weight and thermal weight simultaneous measurement apparatus). As for the peak temperature, the temperature of the aluminum plate was raised in the temperature range of 25 ℃ to 600 ℃ at 10 ℃/min under the atmospheric atmosphere, and the temperature corresponding to the maximum value of the Differential Thermal (DTA) curve was taken as the peak temperature.

The extrusion pressure of the PTFE is preferably 50.0MPa or less, more preferably 40.0MPa or less, preferably 5.0MPa or more, more preferably 10.0MPa or more, and even more preferably 15.0MPa or more. The extrusion pressure is a value determined by the following method.

21.7g of a lubricant (trade name: Isopar H (registered trademark), manufactured by Exxon corporation) was added to 100g of PTFE powder, and the mixture was mixed in a glass bottle at room temperature for 3 minutes. Next, the glass bottle was left at room temperature (25 ℃ C.) for at least 1 hour before extrusion to obtain a lubricating resin. Lubricating resin was passed through a hole (diameter 2.5mm, land length 11mm, lead-in angle 30 °) at room temperature at a rate of 100: a uniform bead (extrusion molded article) was obtained by paste extrusion at a reduction ratio of 1. The extrusion speed, i.e., the ram speed, was set to 20 inches/minute (51 cm/minute). The extrusion pressure is a value obtained as follows: the extrusion pressure was determined as the value obtained by measuring the load at which the extrusion load reached an equilibrium state in paste extrusion, and dividing the load by the cross-sectional area of the cylinder used for paste extrusion.

The PTFE described above generally has stretchability, fibrillating properties, and non-melt secondary processability.

The non-melt secondary processability is a property that the melt flow rate cannot be measured at a temperature higher than the crystallization melting point according to ASTM D1238 and D2116, that is, a property that the melt does not flow easily in the melting temperature region.

In the production of the PTFE, the carboxylic acid type hydrocarbon surfactant can be used in the range of use in the production method of the present invention. The concentration of the surfactant is not particularly limited as long as it is within the above range, and is usually added at the Critical Micelle Concentration (CMC) or less at the start of polymerization. When the amount is large, needle-like particles having a large aspect ratio are formed, and the aqueous dispersion is in the form of a gel and the stability is impaired.

The lower limit of the amount of the carboxylic acid type hydrocarbon surfactant to be used is preferably 0.0001% by mass, more preferably 0.001% by mass, still more preferably 0.01% by mass, and particularly preferably 0.1% by mass, based on the aqueous medium. The upper limit of the amount of the surfactant to be used is preferably 10 mass%, more preferably 5 mass%, still more preferably 3 mass%, and particularly preferably 2 mass% with respect to the aqueous medium.

The carboxylic acid type hydrocarbon surfactant may be added to the reaction vessel at a time before the start of polymerization, may be added at a time after the start of polymerization, may be added in several portions during polymerization, or may be continuously added during polymerization.

In the production of the above-mentioned PTFE, a persulfate, an organic peroxide, or a mixture thereof can be used as a radical polymerization initiator. Examples of the persulfate include ammonium persulfate and potassium persulfate. Examples of the organic peroxide include disuccinic acid peroxide and dipentanedioic acid peroxide.

As the redox-type polymerization initiator, a redox initiator in which an oxidizing agent and a reducing agent are combined is preferably used. Examples of the oxidizing agent include persulfates, organic peroxides, potassium permanganate, manganese triacetate, cerium ammonium nitrate, and the like. Examples of the reducing agent include bromate, diimine, and oxalic acid. Examples of the persulfate include ammonium persulfate and potassium persulfate. In order to increase the decomposition rate of the initiator, it is also preferable to add a copper salt or an iron salt to the combination of the redox initiators. Copper salt may be copper (II) sulfate, and iron salt may be iron (II) sulfate.

In the production of the TFE polymer, a known chain transfer agent can be used as the chain transfer agent, and examples thereof include saturated hydrocarbons such as methane, ethane, propane, and butane, halogenated hydrocarbons such as methyl chloride, methylene chloride, and difluoroethane, alcohols such as methanol and ethanol, and hydrogen, and preferably a gas state at normal temperature and pressure.

The amount of the chain transfer agent is usually 1ppm to 10000ppm, preferably 1ppm to 5000ppm, based on the total amount of TFE supplied. The amount may be 1ppm to 1000ppm or 1ppm to 500 ppm.

In the production of the PTFE, a saturated hydrocarbon having 12 or more carbon atoms, which is substantially inert in the reaction and is liquid under the reaction conditions, may be further used as a dispersion stabilizer for the reaction system in an amount of 2 to 10 parts by mass based on 100 parts by mass of the aqueous medium. As a buffer for adjusting the pH during the reaction, ammonium carbonate, ammonium phosphate, or the like may be added.

At the time of completion of the polymerization of the PTFE, an aqueous dispersion having a solid content concentration of 1.0 to 70% by mass and an average primary particle diameter of 50 to 500nm can be obtained. The aqueous dispersion liquid contains the surfactant and a fluoropolymer. By using the above surfactant, an aqueous dispersion of particles of TFE polymer having a fine particle diameter of 0.5 μm or less can be obtained.

The polymerization step in the production of PTFE is preferably a step including: a step (I) for obtaining a pellet comprising polymerized units based on TFE; and a step (II) for obtaining PTFE by polymerizing TFE in an aqueous medium containing the particles obtained in the step (I).

The particles obtained in step (I) are polymerized in an aqueous medium containing the particles obtained in step (I) as described above, whereby the number of particles of PTFE is increased and the yield can be increased.

When the polymerization step includes the step (II), the step (II) may be performed by directly using an aqueous dispersion containing the particles obtained in the step (I).

The step (II) may be performed by diluting or concentrating the aqueous dispersion containing the particles obtained in the step (I). The dilution or concentration may be carried out directly in the reactor, or may be carried out after recovering the aqueous dispersion containing the particles obtained in step (I) from the reactor. Therefore, the polymerization step may further include a step of recovering an aqueous dispersion liquid containing the particles obtained in step (I) after step (I) and before step (II).

The aqueous dispersion containing the particles obtained in step (I) may be subjected to a step of reducing the temperature to less than 50 ℃, less than 30 ℃ or less than 10 ℃ after step (I) and before step (II).

When the step (I) and the step (II) are continuously performed, the stirring may be temporarily stopped after the step (I), and then the stirring may be restarted to continue the step (II).

In the case where the step (I) and the step (II) are continuously performed, the stirring may be stopped after the step (I), the pressure in the reactor may be changed, the stirring may be restarted, and the step (II) may be continued.

In order to change the monomer composition ratio in the reactor, the pressure in the reactor may be reduced to atmospheric pressure after the step (I), and after charging each monomer into the reactor, the step (II) may be continued. After the step (I), the polymerization temperature may be changed to continue the step (II).

When the polymerization step includes the step (II), a redox initiator is particularly preferably used in the step (I). By using a redox initiator, the particle number of the above particles can be increased.

When the steps (I) and (II) are continuously performed, the redox initiator is stopped from being charged in the step (I), and then the polymerization initiator of the step (II) is charged, thereby continuously producing the polymer. Examples of the redox initiator include the redox initiators mentioned above.

When the polymerization step includes the step (II), a radical polymerization initiator may be used in the step (I). By using a radical polymerization initiator, the particle number of the above particles can be increased.

When the step (I) and the step (II) are continuously performed, the radical polymerization initiator is stopped from being charged in the step (I), and then the polymerization initiator in the step (II) is charged, whereby the continuous production is enabled. The radical polymerization initiator may be a radical polymerization initiator described later, and ammonium persulfate is preferable in the step (I). In the step (II), disuccinic acid peroxide is preferred. In the step (II), the radical polymerization initiator is preferably continuously or intermittently charged.

When the polymerization step includes the step (II), the step (I) is preferably a step of obtaining an aqueous dispersion having a particle concentration of 20.0 mass% or less. The solid content concentration is more preferably 15.0% by mass or less, further preferably 10.0% by mass or less, further preferably 8.0% by mass or less, and particularly preferably 5.0% by mass or less. The solid content concentration is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, further preferably 0.5% by mass or more, further preferably 0.8% by mass or more, particularly preferably 1.0% by mass or more, and particularly preferably 1.5% by mass or more.

The particles may be a TFE homopolymer composed only of polymerized units based on TFE, or may be modified PTFE having polymerized units based on TFE of 99.0 mass% or more and polymerized units based on a modified monomer of 1.0 mass% or less.

In the modified PTFE, the polymerized units based on the modified monomer (hereinafter also referred to as "modified monomer units") are preferably in the range of 0.00001 to 1.0 mass%. The lower limit of the modifying monomer unit is more preferably 0.0001% by mass, still more preferably 0.001% by mass, yet more preferably 0.005% by mass, and particularly preferably 0.009% by mass. The upper limit of the modifying monomer unit is preferably 0.90% by mass, more preferably 0.50% by mass, even more preferably 0.40% by mass, even more preferably 0.30% by mass, particularly preferably 0.10% by mass, and particularly preferably 0.05% by mass.

The average primary particle diameter of the particles obtained in the step (I) is preferably 300nm or less, more preferably 200nm or less, and still more preferably 150nm or less. The average primary particle diameter is preferably 0.1nm or more, more preferably 1.0nm or more, and still more preferably 3.0nm or more.

The aqueous medium in the step (II) preferably contains an aqueous medium contained in the aqueous dispersion containing the particles obtained in the step (I). In addition to the aqueous medium contained in the aqueous dispersion containing the above particles, other aqueous media may also be added.

The polymerization temperature and polymerization pressure in the step (II) are appropriately determined depending on the kind of the monomer to be used, the molecular weight of the target PTFE, and the reaction rate.

The polymerization pressure is preferably 0.05MPaG to 10 MPaG. The polymerization pressure is more preferably 0.3MPaG or more, further preferably 0.5MPaG or more, and further preferably 5.0MPaG or less, further preferably 3.0MPaG or less.

In particular, from the viewpoint of increasing the yield, it is preferably 1.0MPaG or more, and more preferably 2.0MPaG or more.

The step (II) may be performed in the presence of a carboxylic acid type hydrocarbon surfactant or may be performed in the absence of a carboxylic acid type hydrocarbon surfactant.

The step (II) is preferably a step of polymerizing TFE in an aqueous medium containing the particles in the presence of a carboxylic acid type hydrocarbon surfactant.

In the step (II), the amount of the carboxylic acid type hydrocarbon surfactant is preferably 0.0001 to 15% by mass relative to the aqueous medium. The lower limit is more preferably 0.001 mass%, and the upper limit is more preferably 1 mass%. If the amount is less than 0.0001% by mass, the dispersing power may be insufficient, and if it exceeds 15% by mass, the effect commensurate with the amount added may not be obtained. The amount of the carboxylic acid type hydrocarbon surfactant added is appropriately determined depending on the kind of the monomer used, the molecular weight of the target PTFE, and the like.

The step (II) preferably includes a step of continuously adding a carboxylic acid type hydrocarbon surfactant. The continuous addition of the carboxylic acid type hydrocarbon surfactant means, for example, that the carboxylic acid type hydrocarbon surfactant is not added all at once but is added over time or in portions. By including the above-mentioned continuous addition step, an aqueous dispersion having a smaller average primary particle size and more excellent stability can be obtained.

In the step (II), the amount of the carboxylic acid type hydrocarbon surfactant at the start of polymerization is preferably 1ppb or more with respect to the aqueous medium. The amount of the carboxylic acid type hydrocarbon surfactant at the start of polymerization is preferably 10ppb or more, more preferably 50ppb or more, further preferably 100ppb or more, and further more preferably 200ppb or more. The upper limit is not particularly limited, but is preferably 100000ppm, more preferably 50000ppm, for example. When the amount of the carboxylic acid type hydrocarbon surfactant at the start of polymerization is in the above range, an aqueous dispersion having a smaller average primary particle diameter and more excellent stability can be obtained. In addition, the aspect ratio of the primary particles can be further reduced.

In the step (II), the step of continuously adding the carboxylic acid type hydrocarbon surfactant is preferably performed such that the addition of the carboxylic acid type hydrocarbon surfactant to the aqueous medium is started when the concentration of PTFE formed in the aqueous medium is 10 mass% or less. The addition of the carboxylic acid type hydrocarbon surfactant is started more preferably at the concentration of 8.0% by mass or less, further preferably at the concentration of 5.0% by mass or less, further more preferably at the concentration of 4.0% by mass or less, particularly preferably at the concentration of 3.0% by mass or less, particularly preferably at the concentration of 2.0% by mass or less, particularly preferably at the concentration of 1.5% by mass or less, and particularly preferably at the concentration of 1.0% by mass or less. The addition is preferably started when the concentration is less than 0.60% by mass, more preferably 0.50% by mass or less, still more preferably 0.36% by mass or less, yet more preferably 0.30% by mass or less, particularly preferably 0.20% by mass or less, and particularly preferably 0.10% by mass or less. Further, it is preferable to start the addition simultaneously with the start of the polymerization in the step (II). The concentration is a concentration based on the total of the aqueous medium and PTFE.

By including the above steps, an aqueous dispersion having a smaller average primary particle size and more excellent stability can be obtained.

The carboxylic acid type hydrocarbon surfactant is preferably at least one selected from the group consisting of a surfactant (1-0) represented by the general formula (1-0), a surfactant (a) represented by the formula (a), a surfactant (b) represented by the formula (b), a surfactant represented by the formula (α), and a surfactant obtained by subjecting any one of them to radical treatment or oxidation treatment.

When the carboxylic acid type hydrocarbon surfactant is an aliphatic carboxylic acid type hydrocarbon surfactant, the aliphatic carboxylic acid type hydrocarbon surfactant is preferably at least one selected from the group consisting of a surfactant represented by the formula (α), a surfactant represented by the general formula (1-0A), and a surfactant obtained by subjecting the above surfactants to radical treatment or oxidation treatment.

When the polymerization step includes the step (II), the polymerization step preferably includes a step of subjecting the carboxylic acid type hydrocarbon surfactant to the radical treatment or the oxidation treatment.

The step (II) can be performed, for example, as follows: polymerization can be carried out by charging an aqueous dispersion containing the above particles, TFE, if necessary, an aqueous medium, a modifying monomer, a hydrocarbon surfactant, and other additives into a polymerization reactor, stirring the contents of the reactor, maintaining the reactor at a predetermined polymerization temperature, and then adding a predetermined amount of a polymerization initiator to initiate polymerization. After the polymerization reaction is started, a monomer, a polymerization initiator, a chain transfer agent, the above-mentioned hydrocarbon surfactant, and the like may be added additionally according to the purpose. The hydrocarbon surfactant may be added after the polymerization reaction is started.

As the polymerization initiator, an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator is preferably used. The step (II) is preferably a step carried out in the presence of an oil-soluble radical polymerization initiator or a water-soluble radical polymerization initiator. In particular, an oil-soluble peroxide or a water-soluble peroxide, which will be described later, is preferably used as the polymerization initiator.

In the step (II), TFE and, if necessary, a modifying monomer are preferably polymerized in the substantial absence of a fluorosurfactant. The phrase "under the condition that the fluorinated surfactant is not substantially present" means that the fluorinated surfactant is 1ppm or less, preferably 100ppb or less, more preferably 10ppb or less, and further preferably 1ppb or less with respect to the PTFE obtained in the polymerization.

The PTFE powder (e.g., PTFE fine powder) obtained in the production method of the present invention may be used as a powder, or may be added to water and used in the form of an aqueous dispersion.

The obtained PTFE fine powder is preferably used for molding, and suitable applications include pipes for hydraulic systems and fuel systems of aircrafts, automobiles, and the like, and applications for flexible hoses and electric wire coating of reagents, vapors, and the like.

The obtained PTFE aqueous dispersion is preferably stabilized by adding a nonionic surfactant, concentrated, and added with an organic or inorganic filler according to the purpose to prepare a composition for various uses. The composition can be coated on a substrate made of metal or ceramic to form a coating film surface having non-tackiness, a low coefficient of friction, gloss, smoothness, abrasion resistance, weather resistance and heat resistance, and is suitable for coating of a roll, a cooking device or the like, impregnation processing of a glass cloth, or the like.

An organosol of PTFE can also be prepared from the aqueous PTFE dispersion described above. The organosol may contain the PTFE and an organic solvent, and examples of the organic solvent include ether solvents, ketone solvents, alcohol solvents, amide solvents, ester solvents, aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, halogenated hydrocarbon solvents, and N-methyl-2-pyrrolidone, dimethylacetamide, and the like can be used as appropriate. The preparation of the organosol can be carried out, for example, by the method described in International publication No. 2012/002038.

The aqueous dispersion of PTFE or the PTFE fine powder is preferably used as a processing aid. When the aqueous dispersion or the fine powder is used as a processing aid, the melt strength of the host polymer during melt processing can be improved by mixing the aqueous dispersion or the fine powder with the host polymer, and the mechanical strength, electrical characteristics, flame retardancy, dripping resistance during burning, and sliding properties of the obtained polymer can be improved.

The aqueous dispersion of PTFE or the PTFE fine powder is also preferably used as a battery adhesive and dust-proofing applications.

The aqueous dispersion of PTFE or the PTFE fine powder is preferably compounded with a resin other than PTFE and then used as a processing aid. The aqueous dispersion or the fine powder is suitable as a raw material for PTFE described in, for example, Japanese patent application laid-open Nos. 11-49912, 5804654, 11-29679 and 2003-2980. The processing aid using the aqueous dispersion or the fine powder is not inferior to the processing aids described in the above publications.

The aqueous dispersion of PTFE is preferably mixed with an aqueous dispersion of a melt-processable fluororesin and coagulated to form a coagulated powder. The above-described cocoagulated powder is suitable as a processing aid.

Examples of the melt-processable fluororesin include FEP, PFA, TFE/perfluoroallyl ether copolymer, ETFE, ethylene/TFE/HFP copolymer [ EFEP ], and the like, and FEP is preferable.

The aqueous dispersion preferably further contains the melt-processable fluororesin. Examples of the melt-processable fluororesin include FEP, PFA, TFE/perfluoroallyl ether copolymer, ETFE, EFEP, and the like. The aqueous dispersion containing the melt-processable fluororesin may be used as a coating material. The melt-processable fluororesin can sufficiently fuse the particles of the TFE polymer, and thus can improve the film-forming property and give a gloss to the obtained film.

The non-fluorine-containing resin to which the above-mentioned co-coagulated powder is added may be in the form of powder, granule or emulsion. From the viewpoint of sufficiently mixing the respective resins, it is preferable to perform the addition while applying a shearing force by a known method such as extrusion kneading or roll kneading.

The use of the aqueous dispersion is not particularly limited, and examples of the direct application in the form of an aqueous dispersion include: a coating layer formed by coating on a substrate, drying, and then baking as needed; impregnation which is obtained by impregnating a porous support such as a nonwoven fabric or a resin molded article with the resin, drying the impregnated support, and then preferably firing the dried support; examples of the cast film formed by coating a substrate such as glass on the substrate, drying the substrate, immersing the substrate in water as needed, and peeling the substrate to obtain a thin film include an aqueous dispersion type paint, a tent film, a conveyor belt, a printed circuit board (CCL), an adhesive for an electrode, a water repellent for an electrode, and the like.

The aqueous dispersion can be used as a coating aqueous coating material by blending a known blending agent such as a pigment, a thickener, a dispersant, a defoaming agent, an antifreezing agent, and a film-forming aid, or further compounding with another polymer compound.

In addition, the additive can be used for adhesives, binders, anti-dripping agents and other compounds for inhibiting the fall-off of the active material of the electrode, dust-inhibiting treatment for preventing the flying of sand, dust and the like, and the like.

In order to adjust the viscosity of the aqueous dispersion or to improve the miscibility with a pigment, a filler, or the like, an anionic surfactant may be preferably contained. The anionic surfactant may be appropriately added within a range that causes no problem in terms of economy and environment.

Examples of the anionic surfactant include a non-fluorinated anionic surfactant and a fluorine-containing anionic surfactant, and a non-fluorinated anionic surfactant containing no fluorine, that is, a hydrocarbon anionic surfactant is preferable.

For the purpose of adjusting the viscosity, the type of the anionic surfactant is not particularly limited as long as it is known, and for example, the anionic surfactants described in international publication No. 2013/146950 and international publication No. 2013/146947 can be used. Examples thereof include anionic surfactants having a saturated or unsaturated aliphatic chain having 6 to 40 carbon atoms, preferably 8 to 20 carbon atoms, and more preferably 9 to 13 carbon atoms. The saturated or unsaturated aliphatic chain may be either a straight chain or a branched chain, or may have a cyclic structure. The hydrocarbon may be aromatic or may have an aromatic group. The hydrocarbon may have a hetero atom such as oxygen, nitrogen, or sulfur.

Examples of the anionic surfactant include alkylsulfonates, alkylsulfates, alkylarylsulfates, and salts thereof; aliphatic (carboxylic) acids and salts thereof; alkyl phosphates, alkyl aryl phosphates, or salts thereof; and the like, among which alkyl sulfonates, alkyl sulfates, aliphatic carboxylic acids or salts thereof are preferred.

The alkyl sulfate or a salt thereof is preferably ammonium lauryl sulfate, sodium lauryl sulfate or the like.

As the aliphatic carboxylic acid or a salt thereof, succinic acid, capric acid, undecanoic acid, undecylenic acid, lauric acid, hydrogenated dodecanoic acid, or a salt thereof is preferable.

The amount of the anionic surfactant to be added depends on the kind of the anionic surfactant or other compounding agent, and is preferably 10ppm to 5000ppm based on the solid content of the fluoropolymer.

The lower limit of the amount of the anionic surfactant to be added is more preferably 50ppm or more, and still more preferably 100ppm or more. If the amount is too small, the viscosity-adjusting effect is poor.

The upper limit of the amount of the anionic surfactant to be added is more preferably 3000ppm or less, and still more preferably 2000ppm or less. If the amount is too large, the mechanical stability and storage stability of the aqueous dispersion may be impaired.

For the purpose of adjusting the viscosity of the aqueous dispersion, for example, methylcellulose, alumina sol, polyvinyl alcohol, carboxylated vinyl polymer, and the like may be blended in addition to the anionic surfactant.

For the purpose of adjusting the pH of the aqueous dispersion, a pH adjuster such as ammonia water may be added.

The aqueous dispersion may contain other water-soluble polymer compounds in a range not impairing the characteristics of the aqueous dispersion, if necessary.

The other water-soluble polymer compound is not particularly limited, and examples thereof include polyethylene oxide (dispersion stabilizer), polyethylene glycol (dispersion stabilizer), polyvinylpyrrolidone (dispersion stabilizer), phenol resin, urea resin, epoxy resin, melamine resin, polyester resin, polyether resin, acrylic silicone resin, silicone polyester resin, and polyurethane resin. In addition, preservatives such as isothiazolone, azole, bronopol, chlorothalonil, methylsulfonyltetrachloropyridine, carbendazim, 2- [ (dichlorofluoromethyl) -thio ] -1H-isoindole-1, 3- (2H) -dione (Fluor Folpet), sodium diacetate, diiodomethyl-p-tolylsulfone and the like may be contained.

The aqueous dispersion of PTFE is also preferably used as a dust-suppressing treatment agent. The dust-suppressing treatment agent can be used in the following method: a method in which a TFE polymer is fibrillated by mixing the TFE polymer with a dusting substance and applying a compression-shearing action to the mixture at a temperature of 20 to 200 ℃ to thereby suppress the dusting of the dusting substance; for example, Japanese patent No. 2827152, Japanese patent No. 2538783 and the like.

The aqueous dispersion of PTFE can be suitably used in, for example, a dust-suppressing treatment agent composition described in international publication No. 2007/004250, and can also be suitably used in a dust-suppressing treatment method described in international publication No. 2007/000812.

The dust-inhibiting agent is suitably used for dust-inhibiting treatment in the fields of building materials, soil stabilizers, solidification materials, fertilizers, incineration ash and hazardous substance leveling, explosion-proof, cosmetics, pet litter such as cat litter, and the like.

The aqueous Dispersion of PTFE is also preferably used as a raw material for obtaining TFE polymer fibers by a Dispersion Spinning method (Dispersion Spinning method). The dispersion spinning method is a method comprising: the TFE polymer fiber is obtained by mixing the aqueous dispersion of the TFE polymer with the aqueous dispersion of the matrix polymer, extruding the mixture to form an intermediate fiber structure, and firing the intermediate fiber structure to decompose the matrix polymer and sinter the TFE polymer particles.

The production method of the present invention can also produce high molecular weight PTFE. The production method of the present invention can produce PTFE having a molecular weight equivalent to that of a production method using a conventional fluorosurfactant without using a conventional fluorosurfactant.

In the case of producing high molecular weight PTFE, the polymerization temperature is preferably 30 ℃ or higher, more preferably 40 ℃ or higher, and still more preferably 50 ℃ or higher. Further, it is preferably 100 ℃ or lower, more preferably 95 ℃ or lower. The polymerization pressure is preferably 0.5MPaG or more, preferably 0.7MPaG or more, preferably 1.0MPaG or more, and further preferably 5.0MPaG or less, more preferably 4.0MPaG or less, and further preferably 3.0MPaG or less.

The high molecular weight PTFE powder obtained by polymerization has stretchability and non-melt processability, and is also useful as a raw material for a stretched body (porous body). When the stretched product is a film (stretched PTFE film or porous PTFE membrane), stretching can be performed by a known PTFE stretching method. By stretching, the high molecular weight PTFE is easily fibrillated to form a PTFE porous body (film) composed of nodules and fibers.

The paste extrudate in the form of a sheet or a rod is preferably roll-stretched in the extrusion direction, whereby a uniaxially stretched film can be obtained.

Further, a biaxially stretched film can be obtained by stretching in the width direction with a tenter or the like.

It is also preferable to perform a semi-firing treatment before stretching.

The stretched PTFE body is a porous body having a high porosity, and can be suitably used as a filter medium for various precision filtration filters such as air filters and reagent filters, a support material for polymer electrolyte membranes, and the like.

Further, the resin composition is also useful as a material for products used in the fields of fibers, medical treatment, electrochemistry, sealing materials, air filtration, ventilation/internal pressure control, liquid filtration, general consumables, and the like.

Specific applications are exemplified below.

Field of electrochemistry

Dielectric prepreg, EMI shielding material, heat transfer material, and the like. More specifically, a printed circuit board, an electromagnetic shielding material, an insulating heat transfer material, an insulating material, and the like.

Field of sealing materials

Gaskets, pump diaphragms, pump pipes, aircraft seals, and the like.

The field of air filtration

ULPA filters (for semiconductor manufacturing), HEPA filters (for hospital and semiconductor manufacturing), cylindrical cartridge filters (for industrial use), bag filters (for industrial use), heat-resistant bag filters (for exhaust gas treatment), heat-resistant pleated filters (for exhaust gas treatment), SINBRAN filters (for industrial use), catalytic filters (for exhaust gas treatment), filters with adsorbent (HDD assembly), breather filters (HDD assembly and the like), filters for vacuum cleaners (for vacuum cleaners), general-purpose multilayer felt materials, cartridge filters for GT (for GT compatible exchanges), cooling filters (for electronic equipment housings), and the like.

Ventilation/internal pressure regulation field

A material for freeze drying such as a freeze drying container, a ventilation material for automobiles suitable for an electronic circuit or a lamp, a container suitable for container use such as a container cover, a protective ventilation use suitable for electronic equipment including a small terminal such as a tablet terminal or a mobile phone terminal, a medical ventilation use, and the like.

Field of liquid filtration

A semiconductor liquid filtration filter (for semiconductor production), a hydrophilic PTFE filter (for semiconductor production), a filter suitable for chemicals (for reagent treatment), a filter for a pure water production line (for pure water production), a backwashing type liquid filtration filter (for industrial wastewater treatment), and the like.

General field of consumable materials

Clothing, cable guide tubes (suitable for movable wires for motorcycles), clothing for motorcycles, cast pads (medical protectors), dust collector filters, horns (musical instruments), cables (signal cables for guitars, etc.), strings (for string instruments), etc.

Field of fiber

PTFE fibers (fibrous materials), sewing threads (fabrics), knitting threads (fabrics), ropes, and the like.

Medical field

In vivo implants (stretchings), artificial blood vessels, catheters, general surgery (tissue augmentation materials), head and neck articles (dura mater substitutes), oral health (tissue regeneration medicine), plastic surgery (taping), and the like.

The production method of the present invention can also produce low molecular weight PTFE.

The low molecular weight PTFE can be produced by polymerization, or the high molecular weight PTFE obtained by polymerization can be reduced in molecular weight by a known method (thermal decomposition, radiation decomposition, or the like).

In the case of producing low molecular weight PTFE, the polymerization temperature is preferably 30 ℃ or higher, more preferably 40 ℃ or higher, and still more preferably 50 ℃ or higher. Further, it is preferably 100 ℃ or lower, more preferably 90 ℃ or lower, and still more preferably 80 ℃ or lower. The polymerization pressure is preferably 0.3MPaG or more, preferably 0.4MPaG or more, preferably 0.5MPaG or more, and further preferably 5.0MPaG or less, more preferably 4.0MPaG or less, and further preferably 3.0MPaG or less.

Low molecular weight PTFE (also referred to as PTFE fine powder) having a molecular weight of 60 ten thousand or less is excellent in chemical stability, extremely low in surface energy, and less prone to fibrillation, and is therefore suitable for the production of plastics, inks, cosmetics, paints, greases, office automation equipment parts, toners, and the like as an additive for the purpose of improving sliding properties, texture of the surface of a coating film, and the like (see, for example, japanese patent application laid-open No. 10-147617).

Further, low molecular weight PTFE can be obtained by dispersing a polymerization initiator and the above surfactant in an aqueous medium in the presence of a chain transfer agent to polymerize TFE or a monomer copolymerizable with TFE, and TFE.

In the present invention, high molecular weight PTFE means PTFE having non-melt processability and fibrillating properties. The low molecular weight PTFE means PTFE having melt processability and no fibrillation.

The non-melt processability means that the melt flow rate cannot be measured at a temperature higher than the crystallization melting point according to ASTM D1238.

The Standard Specific Gravity (SSG) of the high molecular weight PTFE is preferably 2.130 to 2.280. The standard specific gravity was measured by the water displacement method according to ASTM D792 using a sample molded according to ASTM D4895-89. In the present invention, "high molecular weight" means that the standard specific gravity is within the above range.

The low molecular weight PTFE has a melt viscosity of 1X 10 at 380 deg.C²Pa·s～7×10⁵Pa · s. In the present invention, "low molecular weight" means that the melt viscosity is in the above range.

The melt viscosity of the high molecular weight PTFE is significantly higher than that of the low molecular weight PTFE, and it is difficult to measure the exact melt viscosity. On the other hand, the melt viscosity of the low molecular weight PTFE can be measured, but it is difficult to obtain a molded article useful for measuring the standard specific gravity from the low molecular weight PTFE, and it is difficult to measure the accurate standard specific gravity. Therefore, in the present invention, the standard specific gravity is used as an index of the molecular weight of the high molecular weight PTFE, and the melt viscosity is used as an index of the molecular weight of the low molecular weight PTFE. In addition, no method is known for measuring the molecular weight of the high molecular weight PTFE and the low molecular weight PTFE, which can be directly specified.

The peak temperature of the high molecular weight PTFE is preferably from 333 ℃ to 347 ℃, more preferably from 335 ℃ to 345 ℃. The peak temperature of the low-molecular-weight PTFE is preferably 322 to 333 ℃ and more preferably 324 to 332 ℃. The peak temperature is a temperature corresponding to a maximum value in a heat of fusion curve when the temperature of PTFE which has not been heated to a temperature of 300 ℃ or higher is raised at a rate of 10 ℃/min using a differential scanning calorimeter [ DSC ].

In the heat of fusion curve when the temperature of PTFE that has not been heated to a temperature of 300 ℃ or higher is raised at a rate of 10 ℃/min by a differential scanning calorimeter [ DSC ], the high molecular weight PTFE preferably has at least 1 endothermic peak in the range of 333 to 347 ℃ and the heat of fusion at 290 to 350 ℃ calculated from the heat of fusion curve is 62mJ/mg or more.

An unfired tape (raw tape) can also be obtained from the PTFE fine powder obtained by using the surfactant.

The surfactant, the by-product and decomposed product of the surfactant by-produced by the surfactant, and the residual monomer can be reused by recovering the surfactant, the by-product and decomposed product of the surfactant by-produced by the surfactant, and the residual monomer from the waste water produced by the condensation or washing and/or the exhaust gas produced by the drying step and purifying the recovered materials. The method for recovering and purifying is not particularly limited, and the recovery and purification can be carried out by a known method. For example, the method can be carried out by the method described in Japanese patent publication No. 2011-520020.

(II) melt-processable fluororesin

(1) In the production method of the present invention, polymerization of FEP is preferably carried out at a polymerization temperature of 10 to 150 ℃ and a polymerization pressure of 0.2 to 8.0 MPaG. In the case of producing FEP, the polymerization temperature is more preferably 30 ℃ or higher, still more preferably 40 ℃ or higher, and still more preferably 50 ℃ or higher. Further, it is more preferably 130 ℃ or lower, still more preferably 120 ℃ or lower, particularly preferably 110 ℃ or lower, and still more preferably 100 ℃ or lower. The polymerization pressure is preferably 0.5MPaG or more, preferably 1.0MPaG or more, preferably 1.2MPaG or more, and more preferably 6.0MPaG or less, and further preferably 5.0MPaG or less.

The preferred monomer composition (mass%) of FEP is TFE: HFP (60-95): (5-40), more preferably (85-92): (8-15). The FEP may be further modified with perfluoro (alkyl vinyl ether) as the component 3 in a range of 0.1 to 2 mass% based on the total monomers.

In the polymerization of FEP, the surfactant may be used in the range used in the production method of the present invention, and is usually added in an amount of 0.0001 to 10% by mass based on 100% by mass of the aqueous medium.

In the polymerization of FEP, cyclohexane, methanol, ethanol, propanol, ethane, propane, butane, pentane, hexane, carbon tetrachloride, chloroform, dichloromethane, methyl chloride, etc. are preferably used as the chain transfer agent, and ammonium carbonate, disodium hydrogen phosphate, etc. are preferably used as the pH buffer.

Pellets can be prepared by melt-extruding the FEP powder obtained by the production method of the present invention. In addition, as long as the extrusion conditions are generally capable of forming pellets, melt extrusion can be performed by appropriately setting the extrusion conditions.

In the production method of the present invention, the FEP obtained may have-CF at a site of at least one of the polymer main chain and the polymer side chain₃、-CF₂H and the like terminal groups, preferably-COOH, -CH₂OH、-COF、-CF＝CF-、-CONH₂、-COOCH₃The content of isothermically labile groups (hereinafter referred to as "labile end groups") is low or absent.

The unstable terminal group is chemically unstable, and thus not only lowers the heat resistance of the resin, but also causes an increase in the attenuation of the obtained electric wire.

In the production method of the present invention, it is preferable that the polymerization is terminated at every 1X 10⁶Unstable terminal group in number of carbon atoms and-CF₂The total number of H terminal groups is 50 or less. At each 1X 10 ⁶The total number of the above groups in the carbon atoms is more preferably less than 20, and still more preferably 5 or less. The above-mentioned unstable terminal group and-CF₂The H end groups may also be absent and all are-CF₃A terminal group.

Unstable terminal group and-CF₂The H end groups can be converted to-CF by fluorination₃End groups to stabilize it. The fluorination treatment method is not particularly limited, and a method of exposing the polymer to a fluorine radical source that generates fluorine radicals under fluorination treatment conditions may be mentioned. As the fluorine radical source, there may be mentionedFluorine gas and CoF₃、AgF₂、UF₆、OF₂、N₂F₂、CF₃OF and halogen fluoride (e.g. IF)₅、ClF₃) And the like. Among these, a method of directly contacting FEP obtained by the production method of the present invention with fluorine gas is preferable, and from the viewpoint of reaction control, the contact is preferably performed using diluted fluorine gas having a fluorine gas concentration of 10 mass% to 50 mass%. The diluted fluorine gas can be obtained by diluting the fluorine gas with an inert gas such as nitrogen gas or argon gas. The fluorine gas treatment is carried out at a temperature of, for example, 100 to 250 ℃. The treatment temperature is not limited to the above range, and may be set as appropriate depending on the situation. The fluorine gas treatment is preferably carried out by supplying diluted fluorine gas into the reactor continuously or intermittently. The fluorination treatment may be performed on dried powder after polymerization or on pellets after melt extrusion.

The FEP produced by the production method of the present invention has good moldability, is less likely to cause molding defects, and has good heat resistance, chemical resistance, solvent resistance, insulation properties, electrical properties, and the like.

The FEP powder obtained by the production method of the present invention may be fluorinated. The method for producing a fluorinated powder is a method for obtaining a fluorinated powder by supplying fluorine gas to the powder obtained by the method for producing a powder and fluorinating the powder.

The method for producing the FEP pellet is a method for obtaining a pellet by pelletizing the FEP obtained by the production method of the present invention.

The above pellets may be fluorinated. The method for producing fluorinated pellets is a method for obtaining fluorinated pellets by supplying fluorine gas to the pellets obtained by the method for producing pellets and fluorinating the fluorine gas.

Therefore, this FEP can be used for the production of various molded articles such as a covering material for electric wires, foamed electric wires, cables, wires, and the like, pipes, films, sheets, filaments, and the like.

(2) In the production method of the present invention, it is generally preferable that polymerization of a TFE/perfluoro (alkyl vinyl ether) copolymer such as PFA or MFA and a TFE/perfluoroallyl ether copolymer is carried out at a polymerization temperature of 10 to 130 ℃ and a polymerization pressure of 0.3 to 6.0 MPaG. In the case of producing a TFE/perfluoro (alkyl vinyl ether) copolymer, the polymerization temperature is more preferably 30 ℃ or higher, still more preferably 40 ℃ or higher, and still more preferably 50 ℃ or higher. Further, it is more preferably 120 ℃ or lower, still more preferably 110 ℃ or lower, and still more preferably 100 ℃ or lower. The polymerization pressure is preferably 0.5MPaG or more, preferably 1.0MPaG or more, more preferably 5.0MPaG or less, further preferably 4.0MPaG or less, and particularly preferably 3.0MPaG or less.

The preferred monomer composition (mol%) of the TFE/perfluoro (alkyl vinyl ether) copolymer is TFE: perfluoro (alkyl vinyl ether) ═ 90 to 99.7: (0.3-10), more preferably (97-99): (1-3). As the above perfluoro (alkyl vinyl ether), the formula: CF (compact flash)₂＝CFORf⁴(wherein Rf⁴A perfluoroalkyl group having 1 to 6 carbon atoms).

The preferred monomer composition (mol%) of the TFE/perfluoroallyl ether copolymer is TFE: perfluoro allyl ether ═ (90-99.7): (0.3-10), more preferably (97-99): (1-3). As the above-mentioned perfluoroallyl ether, the compound of the formula: CF (compact flash)₂＝CFCF₂ORf⁴(wherein Rf⁴A perfluoroalkyl group having 1 to 6 carbon atoms).

In the polymerization of the TFE/perfluoro (alkyl vinyl ether) copolymer and the TFE/perfluoroallyl ether copolymer, the surfactant may be used in the range used in the production method of the present invention, and is usually added in an amount of 0.0001 to 10% by mass based on 100% by mass of the aqueous medium.

In the polymerization of the TFE/perfluoro (alkyl vinyl ether) copolymer and the TFE/perfluoroallyl ether copolymer, cyclohexane, methanol, ethanol, propanol, propane, butane, pentane, hexane, carbon tetrachloride, chloroform, dichloromethane, methyl chloride, methane, ethane, etc. are preferably used as the chain transfer agent, and ammonium carbonate, disodium hydrogen phosphate, etc. are preferably used as the pH buffer.

Pellets can be prepared by melt-extruding powders of TFE/perfluoro (alkyl vinyl ether) copolymer such as PFA and MFA and TFE/perfluoroallyl ether copolymer obtained by the production method of the present invention. In addition, as long as the extrusion conditions are generally capable of forming pellets, melt extrusion can be performed by appropriately setting the extrusion conditions.

Among the above copolymers, fluorine gas treatment is preferably carried out for the purpose of improving the heat resistance thereof and further enhancing the effect of suppressing the transmission of a reagent in a molded article.

The fluorine gas treatment is performed by contacting the fluorine gas with a reagent permeation inhibitor. However, since the reaction with fluorine is very exothermic, it is appropriate to dilute fluorine with an inert gas such as nitrogen. The amount of fluorine in the fluorine gas/inert gas mixture is 1 to 100% by mass, preferably 10 to 25% by mass. The treatment temperature is 150 to 250 ℃, preferably 200 to 250 ℃, and the fluorine gas treatment time is 3 to 16 hours, preferably 4 to 12 hours. The gas pressure for the fluorine gas treatment is in the range of 1 to 10 atmospheres, and atmospheric pressure is preferably used. In the case of using the reactor under atmospheric pressure, the fluorine gas/inert gas mixture may be continuously passed into the reactor. As a result, the unstable terminal of the above copolymer is converted into-CF ₃Terminal, is thermostable.

As a method for molding the copolymer and the composition thereof, molding methods such as compression molding, transfer molding, extrusion molding, injection molding, blow molding, and the like can be applied in the same manner as conventional PFA.

The desired molded article can be obtained by such a molding method, and examples of the molded article include a sheet, a film, a gasket, a round bar, a square bar, a tube blank, a tube, a round groove, a square groove, a can, a wafer carrier, a wafer case, a beaker, a filter case, a flowmeter, a pump, a valve, a cock, a socket, a nut, a wire, a heat-resistant wire, and the like.

Among these, the present invention can be suitably used for various chemical reaction apparatuses, semiconductor manufacturing apparatuses, and pipes, tube blanks, tanks, connectors, and the like used in acid-based or alkali-based reagent supply apparatuses, and the like, which require impermeability to reagents.

Further, a nonionic surfactant may be appropriately added to an aqueous dispersion of a TFE/perfluoro (alkyl vinyl ether) copolymer and a TFE/perfluoroallyl ether copolymer such as PFA or MFA, and polyether sulfone, polyamideimide and/or polyimide, and metal powder may be dissolved or dispersed in an organic solvent as necessary to obtain a primer composition. A coating method which can be used for coating a metal surface with a fluororesin, comprising: the primer composition is applied to the surface of the metal, the melt-processable fluororesin composition is applied to the primer layer thus formed, and the melt-processable fluororesin composition layer is fired together with the primer layer.

(3) In the production method of the present invention, it is preferable that the polymerization of ETFE is carried out at a polymerization temperature of 0 to 100 ℃ and a polymerization pressure of 0.1 to 20 MPaG. In the case of producing ETFE, the polymerization temperature is preferably 20 ℃ or higher, more preferably 30 ℃ or higher, and still more preferably 40 ℃ or higher. Further, it is preferably 95 ℃ or lower, more preferably 90 ℃ or lower, and still more preferably 80 ℃ or lower. The polymerization pressure is preferably 0.5MPaG or more, more preferably 0.8MPaG or more, further preferably 1.0MPaG or more, and further preferably 20MPaG or less, more preferably 10MPaG or less, further preferably 5 or less.

The preferred monomer composition (mol%) of ETFE is TFE: ethylene (50-99): (50-1). The ETFE may be further modified with a 3 rd monomer in an amount of 0 to 20 mass% based on the total amount of the monomers. Preferably, TFE: ethylene: a 3 rd monomer ═ (63-94): (27-2): (1-10). The 3 rd monomer is preferably perfluorobutylethylene, 3,3,4,4,5,5,6,6,7,7,8,8, 8-tridecafluoro-1-octene, 2,3,3,4,4,5, 5-heptafluoro-1-pentene (CH)₂＝CFCF₂CF₂CF₂H) 2-trifluoromethyl-3, 3, 3-trifluoropropene ((CF)₃)₂C＝CH₂)。

In the polymerization of ETFE, the surfactant may be used in the range used in the production method of the present invention, and is usually added in an amount of 0.0001 to 10% by mass based on 100% by mass of the aqueous medium.

In the polymerization of ETFE, cyclohexane, methanol, ethanol, propanol, ethane, propane, butane, pentane, hexane, carbon tetrachloride, chloroform, methylene chloride, methyl chloride, or the like is preferably used as a chain transfer agent.

The powder of ETFE obtained by the production method of the present invention is melt-extruded to prepare pellets. In addition, as long as the extrusion conditions are generally capable of forming pellets, melt extrusion can be performed by appropriately setting the extrusion conditions.

The ETFE sheet may be formed into a sheet by extrusion molding. That is, ETFE powder or pellets may be melted, continuously extruded through a die, and cooled to obtain a sheet-like molded article. Additives may be added to ETFE.

As the additive, a known one can be suitably used. Specific examples thereof include ultraviolet absorbers, light stabilizers, antioxidants, infrared absorbers, flame retardants, flame-retardant fillers, organic pigments, inorganic pigments, and dyes. From the viewpoint of excellent weather resistance, inorganic additives are preferred.

The content of the additive in the ETFE sheet is preferably 20 mass% or less, and particularly preferably 10 mass% or less, based on the total mass of the ETFE sheet.

Since the ETFE sheet is excellent in mechanical strength and appearance, it is suitable as a film material (such as a roofing material, a ceiling material, an outer wall material, an inner wall material, and a coating material) for a membrane structure building (such as a sports facility, a gardening facility, and an atrium).

In addition, the film is useful not only as a film material for a film structure building, but also in, for example, the following materials: outdoor use panels (sound-insulating wall, wind fence, wave barrier, garage top, shopping center, pedestrian side wall, roof material), glass scattering prevention film, heat-resistant and water-resistant sheet, building materials (tent material in tent warehouse, film material for sunshade, partial roof material for lighting, window material for glass replacement, film material for fire-proof partition, curtain, outer wall reinforcement, waterproof film, smoke-proof film, flame-retardant transparent partition, road reinforcement, interior decoration (lighting, wall surface, louver, etc.), exterior decoration (screen, signboard, etc.), living and leisure goods (fishing rod, racket, golf club, screen, etc.), automobile materials (hood, damping material, car body, etc.), aircraft materials, ship materials, home appliance, storage tank, container inner wall, filter, construction film materials, electronic materials (printed substrate, wiring substrate, etc.), and the like, An insulating film, a release film, or the like), a surface material of a solar cell module, a mirror protective material for solar power generation, a surface material of a solar water heater, or the like.

(4) The electrolyte polymer precursor can also be produced using the production method of the present invention. In the production method of the present invention, the polymerization of the electrolyte polymer precursor is preferably carried out at a polymerization temperature of 0 to 100 ℃ and a polymerization pressure of-0.05 MPaG to 5.0 MPaG. The electrolyte polymer precursor contains a vinyl ether monomer as shown below and is converted into an ion-exchange polymer by hydrolysis. In the case of producing the electrolyte polymer precursor, the polymerization temperature is more preferably 5 ℃ or higher, and still more preferably 10 ℃ or higher. Further, it is more preferably 80 ℃ or lower, and still more preferably 60 ℃ or lower. The polymerization pressure is preferably 0MPaG or more, preferably 0.02MPaG or more, more preferably 2.0MPaG or less, and further preferably 1.0MPaG or less.

Examples of the vinyl ether monomer used in the electrolyte polymer precursor include

General formula (150): CF (compact flash)₂＝CF-O-(CF₂CFY¹⁵¹-O)n-(CFY¹⁵²)_m-A¹⁵¹

(in the formula, Y¹⁵¹Represents a fluorine atom, a chlorine atom or-SO₂F groups or perfluoroalkyl groups. The perfluoroalkyl group may contain etheric oxygen and-SO₂And F group. n represents an integer of 0 to 3. n number of Y¹⁵¹May be the same or different. Y is¹⁵²Represents a fluorine atom, a chlorine atom or-SO₂And F group. m represents an integer of 1 to 5. m number of Y¹⁵²May be the same or different. A. the ¹⁵¹represents-SO₂X¹⁵¹、-COZ¹⁵¹or-POZ¹⁵²Z¹⁵³。X¹⁵¹Represents F, Cl, Br, I, -OR¹⁵¹or-NR¹⁵²R¹⁵³。Z¹⁵¹、Z¹⁵²And Z¹⁵³Same or different, represent-NR¹⁵⁴R¹⁵⁵OR-OR¹⁵⁶。R¹⁵¹、R¹⁵²、R¹⁵³、R¹⁵⁴、R¹⁵⁵And R¹⁵⁶The same or different, represents H, ammonium, an alkali metal, an alkyl group which may contain a fluorine atom, an aryl group, or a sulfonyl group-containing group). The preferred monomer composition (mol%) of the electrolyte polymer precursor is TFE: vinyl ether (50-99): (50-1), more preferably TFE: vinyl ether (50-93): (50-7).

The electrolyte polymer precursor may be modified with the 3 rd monomer in an amount of 0 to 20% by mass of the total monomers. Examples of the 3 rd monomer include polyfunctional monomers such as CTFE, vinylidene fluoride, perfluoroalkyl vinyl ether, and divinylbenzene.

The thus obtained electrolyte polymer precursor can be subjected to hydrolysis with an alkali solution and treatment with an inorganic acid after, for example, molding into a film shape, and used as a polymer electrolyte membrane for fuel cells, electrolysis devices, redox flow batteries, and the like.

In addition, the hydrolysis may be performed with an alkali solution while maintaining the dispersion state of the electrolyte polymer precursor, thereby obtaining an electrolyte polymer dispersion liquid.

Subsequently, the mixture is heated to 120 ℃ or higher in a pressurized container, and is dissolved in, for example, a water/alcohol mixed solvent to form a solution.

The solution thus obtained can be used as, for example, a binder for an electrode, or can be compounded with various additives and cast into a film for use in, for example, an antifouling coating film, an organic actuator, or the like.

The powder of the melt-processable fluororesin is suitable for use as a powder coating material. When the powder coating material comprising the melt-processable fluororesin powder is applied to a substrate, a coating having a smooth surface can be obtained. The melt-processable fluororesin powder having an average particle diameter of 1 to less than 100 μm is particularly suitable as a powder coating material for use in electrostatic coating, and the melt-processable fluororesin powder having an average particle diameter of 100 to 1000 μm is particularly suitable as a powder coating material for use in spin coating or spin molding.

The melt-processable fluororesin powder can be produced by a method in which the melt-processable fluororesin obtained by the production method of the present invention is dried and powdered to obtain a powder. The method for producing the melt-processable fluororesin powder is also one aspect of the present invention.

In the production method of the present invention, the surfactant, the by-product and decomposed product of the surfactant by-produced from the surfactant, and the residual monomer are recovered from the waste water produced by condensation or washing and/or the exhaust gas produced by the drying step and purified, whereby the surfactant, the by-product and decomposed product of the surfactant by-produced from the surfactant, and the residual monomer can be reused. The method for recovering and purifying is not particularly limited, and the recovery and purification can be carried out by a known method. For example, the method can be carried out by the method described in Japanese patent publication No. 2011-520020.

The method for recovering and purifying the surfactant, the decomposition product or by-product of the surfactant by-produced by the surfactant, and the residual monomer from the waste water produced by the condensation, the waste water produced by washing, and the exhaust gas produced by the drying step is not particularly limited, and conventionally known methods can be used, and examples thereof include the methods described in U.S. patent application publication No. 2007/15937, U.S. patent application publication No. 2007/25902, and U.S. patent application publication No. 2007/27251, and specifically, the following methods can be mentioned.

Examples of the method for recovering the surfactant, the decomposition product or by-product of the surfactant by-produced from the surfactant, and the residual monomer from the wastewater include the following methods: the wastewater is brought into contact with adsorbent particles such as ion exchange resin, activated carbon, silica gel, clay, zeolite, etc., to adsorb the surfactant, etc., and then the wastewater is separated from the adsorbent particles. If the adsorbent particles having the surfactant or the like adsorbed thereon are incinerated, the release of the surfactant or the like into the environment can be prevented.

The surfactant or the like may be desorbed and eluted from the ion exchange resin particles having the surfactant or the like adsorbed thereon by a known method and recovered. For example, when the ion exchange resin particles are anion exchange resin particles, the surfactant and the like can be eluted by bringing an inorganic acid into contact with the anion exchange resin. When a water-soluble organic solvent is subsequently added to the obtained dissolution liquid, the separation into two phases is usually carried out, and therefore, the surfactant and the like can be recovered by recovering and neutralizing the lower phase containing the surfactant and the like. Examples of the water-soluble organic solvent include polar solvents such as alcohols, ketones, and ethers.

Other methods for recovering the surfactant and the like from the ion exchange resin particles include a method using an ammonium salt and a water-soluble organic solvent, and a method using an alcohol and a desired acid. In the latter method, the ester derivative of the surfactant or the like is produced, and thus can be easily separated from the alcohol by distillation.

In the case where the above-mentioned waste water contains fluoropolymer particles or other solid components, it is preferred to remove them before the waste water is brought into contact with the adsorbent particles. Examples of the method for removing fluoropolymer particles and other solid components include a method of precipitating them by adding an aluminum salt or the like and then separating the wastewater from the precipitate, an electrocoagulation method, and the like. The removal can also be performed by a mechanical method, and examples thereof include a cross-flow filtration method, a depth filtration method, and a precoat filtration method.

From the viewpoint of productivity, the concentration of the unagglomerated fluoropolymer in the wastewater is preferably low, and the concentration is more preferably less than 0.4 mass%, particularly preferably less than 0.3 mass%.

As a method for recovering the surfactant and the like from the exhaust gas, there is a method of contacting the exhaust gas with deionized water, an alkaline aqueous solution, an organic solvent such as a glycol ether solvent and the like using a scrubber to obtain a scrubbing solution containing the surfactant and the like. When a high-concentration aqueous alkali solution is used as the aqueous alkali solution, the scrubbing solution can be recovered in a phase-separated state of the surfactant and the like, and thus the surfactant and the like can be easily recovered and reused. Examples of the alkali compound include alkali metal hydroxides and quaternary ammonium salts.

The scrubbing solution containing the surfactant and the like can be concentrated using a reverse osmosis membrane or the like. The concentrated scrubbing solution usually contains fluoride ions, but the above-mentioned surfactant and the like can be easily reused by further adding alumina after concentration to remove the fluoride ions. Alternatively, the adsorbent particles may be brought into contact with a scrubbing solution to adsorb the surfactant and the like, and the surfactant and the like may be recovered by the above-described method.

The surfactant and the like recovered by any of the above methods can be reused for the production of a fluoropolymer.

The present invention also relates to a method for producing an aqueous dispersion (hereinafter also referred to as "the 3 rd production method of the present invention"), comprising the steps of: the fluorine-containing compound represented by the general formula (1A) is removed or reduced by subjecting an aqueous fluoropolymer dispersion containing the fluorine-containing compound represented by the general formula (1A) to a heat treatment.

General formula (1A): h- (CF)₂)_m-COOH

(wherein m is 3 to 19.)

The fluorine-containing compound represented by the general formula (1) can be removed or reduced from the aqueous fluoropolymer dispersion by changing the fluorine-containing compound represented by the general formula (1) into a fluorine-containing compound represented by the general formula (1A) and then subjecting the aqueous dispersion to a heat treatment. Further, the gas containing the fluorine-containing compound represented by the general formula (1A) and water generated by heating is recovered, and the recovered gas is cooled as necessary, whereby an aqueous dispersion containing the fluorine-containing compound represented by the general formula (1A) and water can also be obtained.

The method for producing the aqueous dispersion preferably includes a step of recovering a gas containing the compound represented by the general formula (1A) and water, which is generated by the heat treatment.

The aqueous fluoropolymer dispersion containing the fluorine-containing compound represented by the general formula (1A) and the fluoropolymer can be obtained, for example, by adjusting the aqueous fluoropolymer dispersion obtained by polymerization of a fluorine-containing monomer using the carboxylic acid type hydrocarbon surfactant to be acidic. Examples of the method for adjusting acidity include: a method of adding an acid; a method of blowing an acid gas (e.g., carbon dioxide, sulfur trioxide, nitrogen dioxide, etc.); and the like. As the method of adding the acid, the kind of the acid, and the like, the same methods and kinds as those of the production methods 1 and 2 of the present invention can be adopted.

When the aqueous fluoropolymer dispersion obtained by polymerization after polymerization is acidic, the adjustment to acidity is not required.

The temperature of the above-mentioned heat treatment is preferably more than 150 ℃. Since the specific fluorine-containing compound can be reduced more efficiently, the temperature of the heat treatment (drying) is preferably 155 ℃ or more, more preferably 160 ℃ or more, further preferably 165 ℃ or more, further preferably 170 ℃ or more, particularly preferably 175 ℃ or more, and particularly preferably 180 ℃ or more.

The heat treatment is preferably carried out in the presence of water vapor. For example, the aqueous fluoropolymer dispersion can be heated in the presence of steam by charging the aqueous fluoropolymer dispersion into a reaction vessel and vaporizing water. The reaction vessel is preferably sealed.

The content of the fluorine-containing compound represented by the general formula (1A) contained in the aqueous fluoropolymer dispersion is not limited, and is, for example, about 1ppb to 10000ppm, preferably 100ppb or more, more preferably 1ppm or more, further preferably 10ppm or more, and particularly preferably 100ppm or more, relative to the fluoropolymer.

The aqueous dispersion subjected to the above-mentioned heat treatment may contain 1 kind of fluorine-containing compound represented by the general formula (1A), or may contain 2 or more kinds, and when 2 or more kinds are contained, the production method 3 of the present invention is particularly effective.

The aqueous dispersion to be subjected to the heat treatment may contain, as the fluorine-containing compound, a fluorine-containing compound having m of the general formula (1A) of 7 or less and a fluorine-containing compound having m of the general formula (1A) of 8 or more, or may contain, as the fluorine-containing compound, a fluorine-containing compound having m of the general formula (1A) of 8 or less and a fluorine-containing compound having m of the general formula (1A) of 9 or more.

The aqueous fluoropolymer dispersion may be one containing a fluorochemical compound having m of 3, 5, 7, 9, 11, 13, 15, 17 and 19 and not containing a fluorochemical compound having m of 4, 6, 8, 10, 12, 14, 16 and 18 among fluorochemical compounds contained in the general formula (1A), one containing a fluorochemical compound having m of 4, 6, 8, 10, 12, 14, 16, 18 and 20 and not containing a fluorochemical compound having m of 3, 5, 7, 9, 11, 13, 15, 17 and 19, or one containing all fluorochemical compounds having m of 3 to 19.

In the production method 3 of the present invention, the concentration of the fluorine-containing compound represented by the general formula (1A) in the aqueous fluoropolymer dispersion is not particularly limited, and any concentration of the aqueous fluoropolymer dispersion can be treated. In the aqueous fluoropolymer dispersion to be treated, the total amount of the fluorine-containing compound represented by the above general formula (1A) may be 0.01ppm or more, 0.1ppm or more, or 0.5ppm or more based on the fluoropolymer. The total amount may be 1ppm or more, 5ppm or more, 10ppm or more, or 100ppm or more with respect to the total amount of water. When the concentration of the fluorine-containing compound represented by the general formula (1A) in the aqueous fluoropolymer dispersion is not less than a certain value as described above, the production method 3 of the present invention exhibits higher removal efficiency.

In addition, in the aqueous fluoropolymer dispersion to be treated, the fluorine-containing compound represented by the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. By setting the total amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion to the above range, the removal efficiency can be further improved.

In the present specification, ppm and ppb refer to values obtained in terms of mass unless otherwise specified.

When the concentration of the fluorine-containing compound represented by the general formula (1A) in the aqueous fluoropolymer dispersion is not less than a certain value as described above, the production method 3 of the present invention exhibits higher removal efficiency.

Further, the amount of at least one kind of fluorine-containing compound having m of the above general formula (1A) of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 19 may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less, respectively, relative to the total amount of water. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 3 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 4 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 5 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 6 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 7 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 8 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m 9 of the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 10 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m 11 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 12 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m 13 of the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having 14 m in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having 15 m in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 16 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having 17 m in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m of 18 in the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The amount of the fluorine-containing compound having m 19 of the general formula (1A) may be 10000ppm or less, 5000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, or 200ppm or less based on the fluoropolymer. When the amount of the fluorine-containing compound in the aqueous fluoropolymer dispersion is in the above range, the removal efficiency can be further improved.

The aqueous fluoropolymer dispersion preferably contains substantially no salt of the fluorine-containing compound represented by the general formula (1A) (preferably, the fluorine-containing compound represented by the general formula (1) wherein M is represented by the general formula (1))¹Is a metal atom, NR⁵ ₄(R⁵H or an organic group having 1 to 10 carbon atoms), optionally substituted imidazolium, optionally substituted pyridinium, or optionally substituted phosphonium). The aqueous dispersion liquid substantially not containing the salt of the fluorine-containing compound represented by the general formula (1A) means that the salt of the fluorine-containing compound represented by the general formula (1A) is contained in an amount of 500ppb or less, respectively, with respect to all m.For example, the salt of the fluorine-containing compound having m of 3 in the general formula (1A) may be 400ppb or less, the salt of the fluorine-containing compound having m of 9 may be 400ppb or less, or the total amount of the salts of the fluorine-containing compounds having m of 3 to 19 may be 500ppb or less.

The aqueous fluoropolymer dispersion contains a fluorine-containing compound represented by the general formula (1A), water and a fluoropolymer.

As the fluoropolymer, all of the fluoropolymers described in the above-mentioned method for producing a fluoropolymer powder can be used.

For example, as the fluorine-containing polymer, a fluororesin having a fluorine substitution rate of 50% or more is preferable, and polytetrafluoroethylene is more preferable.

The heat treatment is preferably performed when the concentration of the fluorine-containing compound represented by the general formula (1A) in the aqueous dispersion is 1ppb to 1000000 ppm. When the concentration of the fluorine-containing compound is in the above range, the fluorine-containing compound represented by the general formula (1A) in the aqueous dispersion obtained can be removed or reduced.

The solid content concentration of the aqueous fluoropolymer dispersion is not limited, and may be, for example, 1.0 to 70% by mass. The solid content concentration is preferably 8.0% by mass or more, more preferably 10.0% by mass or more, and is preferably 60.0% by mass or less, more preferably 50.0% by mass or less. The solid content concentration is also preferably 10 to 25% by mass, preferably 10 to 22% by mass, and more preferably 10 to 20% by mass, from the viewpoint of reducing the non-condensable components.

The above production method may comprise a step of diluting the aqueous fluoropolymer dispersion with water. For example, the solid content can be diluted to a concentration of 10 to 25% by mass by the dilution.

While the embodiments have been described above, it should be understood that various changes in form and details may be made therein without departing from the spirit and scope of the claims.

Examples

The present invention will be described with reference to examples, but the present invention is not limited to the examples.

The respective numerical values of the examples were measured by the following methods.

Content of specific fluorine-containing compound

Hereinafter, a method for measuring the content of the compounds represented by the following general formulae (1) and (2) will be described.

General formula (1): (H- (CF)₂)_m-COO)_pM¹(wherein M is 3 to 19, M¹Is H, a metal atom, NR⁵ ₄An imidazolium with or without a substituent, a pyridinium with or without a substituent, or a phosphonium with or without a substituent. p is 1 or 2. )

General formula (2): (H- (CF)₂)_n-SO₃)_qM²(wherein n is 4 to 20. M)²Is H, a metal atom, NR⁵ ₄An imidazolium with or without a substituent, a pyridinium with or without a substituent, or a phosphonium with or without a substituent. q is 1 or 2. )

[ method for measuring the content of Compound represented by general formula (1) ]

Extraction from aqueous dispersions

The solid content of the aqueous dispersion was measured, and the amount of the aqueous dispersion corresponding to 0.5g of the solid content of PTFE was weighed in a 100mL screw tube. Then, together with water contained in the aqueous dispersion, water and methanol were added so that the extraction solvent was 40g (43.14mL) of water/methanol (50/50 vol%). After that, the mixture was sufficiently shaken until it was condensed. The solid content was removed, and the liquid phase was centrifuged at 4000rpm for 1 hour to extract a supernatant containing the compound represented by the general formula (1).

Extracting from the powder

10g (12.6mL) of methanol was added to 1g of the powder, and sonication was performed for 60 minutes to extract a supernatant containing the compound represented by the general formula (1).

Measurement of content of Compound represented by general formula (1) contained in extract

The content of the compound represented by the general formula (1) contained in the extract liquid is determined by converting the content into perfluorooctanoic acid.

Calibration curve of perfluorooctanoic acid

5 grades of 1ng/mL to 100ng/mL standard solutions of perfluorooctanoic acid in methanol of known concentration were prepared and measured using a liquid chromatography mass spectrometer (Waters, LC-MS acquisition UPLC/TQD). From the respective sample concentrations and the integrated values of the peaks, a and b were obtained by relational expression (1) using first order approximation.

A＝a×X+b (1)

A: peak area of perfluorooctanoic acid

X: concentration of Perfluorooctanoic acid (ng/mL)

Measurement apparatus constitution and LC-MS measurement conditions

[ Table 1]

MRM measurement parameters

[ Table 2]

The content of the compound represented by the general formula (1) having 4 to 20 carbon atoms contained in the extract liquid

A compound represented by the general formula (1) having 4 to 20 carbon atoms is measured using a liquid chromatography mass spectrometer. The peak area of the compound represented by the general formula (1) for each carbon number was determined for the extracted liquid phase by the MRM method.

MRM measurement parameters

[ Table 3]

TABLE 3

The content of the compound represented by the general formula (1) having (m +1) carbon atoms in the extract was calculated using the formula (3). A and b in the formula (3) are obtained from the formula (1).

XCm＝((ACm-b)/a)×((50×m+45)/413) (3)

XCm: the content (ng/mL) of the compound represented by the general formula (1) having carbon number (m +1) in the extract solution

ACm: the peak area of the compound represented by the general formula (1) having (m +1) carbon atoms in the extraction solution

The limit of quantitation in this assay was 1 ng/mL.

The content of the compound represented by the general formula (1) having (m +1) carbon atoms contained in the aqueous dispersion

The content of the compound represented by the general formula (1) having (m +1) carbon atoms contained in the aqueous dispersion is determined by the formula (5).

ZCm＝XCm×86.3 (5)

ZCm: the content (based on the fluoropolymer) of the compound represented by the general formula (1) having (m +1) carbon atoms contained in the aqueous dispersion

The content of the compound represented by the general formula (1) having (m +1) carbon atoms contained in the powder

The content of the compound represented by the general formula (1) having (m +1) carbon atoms contained in the powder is determined by the formula (4).

YCm＝XCm×12.6 (4)

YCm: the content (relative to the fluorine-containing polymer) of the compound represented by the general formula (1) having (m +1) carbon atoms contained in the powder

[ method for measuring the content of Compound represented by the general formula (2) ]

Extraction from aqueous dispersions

Extracting from the powder

10g (12.6mL) of methanol was added to 1g of the powder, and sonication was performed for 60 minutes to extract a supernatant containing the compound represented by the general formula (2).

Measurement of content of Compound represented by general formula (2) contained in extract

The content of the compound represented by the general formula (2) contained in the extract liquid is determined by conversion to perfluorooctanesulfonic acid.

Calibration curve for perfluorooctanesulfonic acid

5 grades of 1ng/mL to 100ng/mL standard solutions of perfluorooctanesulfonic acid in methanol of known concentration were prepared and measured using a liquid chromatography mass spectrometer (Waters, LC-MS acquisition UPLC/TQD). From the respective sample concentrations and the integrated values of the peaks, a and b were obtained by the following relational expression (1) using first order approximation.

A＝a×X+b (1)

A: peak area of perfluorooctanesulfonic acid

X: concentration of perfluorooctanesulfonic acid (ng/mL)

Measurement apparatus constitution and LC-MS measurement conditions

[ Table 4]

MRM measurement parameters

[ Table 5]

The content of the compound represented by the general formula (2) having 4 to 20 carbon atoms contained in the extract liquid

A compound represented by the general formula (2) having 4 to 20 carbon atoms is measured using a liquid chromatography mass spectrometer. The peak area of the compound represented by the general formula (2) for each carbon number was determined for the extracted liquid phase by the MRM method.

MRM measurement parameters

[ Table 6]

TABLE 6

The content of the compound represented by the general formula (2) having n carbon atoms in the extract was calculated using the formula (3). A and b in the formula (3) are obtained from the formula (1).

XSn＝((ASn-b)/a)×((50×n+81)/499) (3)

XSn: the content (ng/mL) of the compound represented by the general formula (2) having n carbon atoms in the extract solution

ASn: the peak area of the compound represented by the general formula (2) having n carbon atoms in the extraction solution

The limit of quantitation in this assay was 1 ng/mL.

The content of the compound represented by the general formula (2) having n carbon atoms contained in the aqueous dispersion

The content of the compound represented by the general formula (2) having n carbon atoms contained in the aqueous dispersion is determined by the formula (5).

ZSn＝XSn×86.3 (5)

ZSn: the content (based on the fluoropolymer) of the compound represented by the general formula (2) having n carbon atoms contained in the aqueous dispersion

The content of the compound represented by the general formula (2) having n carbon atoms contained in the powder

The content of the compound represented by the general formula (2) having n carbon atoms contained in the powder is determined by the formula (4).

YSn＝XSn×12.6 (4)

YSn: the content of the compound represented by the general formula (2) having n carbon atoms contained in the powder (based on the fluorine-containing polymer)

ZSn＝XSn×86.3 (5)

ZSn: the content (based on the fluoropolymer) of the compound represented by the general formula (2) having n carbon atoms contained in the aqueous dispersion

Average primary particle diameter

The measurement was performed by a dynamic light scattering method. An aqueous fluoropolymer dispersion having a fluoropolymer solid content of about 1.0% by mass was prepared and measured at 25 ℃ for 70 times using an ELSZ-1000S (available from Otsuka Denshi Co., Ltd.). The refractive index of the solvent (water) was 1.3328, and the viscosity of the solvent (water) was 0.8878 mPas.

Solid content concentration of aqueous PTFE dispersion

1g of the aqueous PTFE dispersion was dried in a forced air dryer at 150 ℃ for 60 minutes, and a value representing the ratio of the mass of the heating residue to the mass (1g) of the aqueous dispersion in percent was used.

Standard Specific Gravity (SSG)

The measurement was carried out by the water displacement method according to ASTM D792 using a sample molded according to ASTM D4895-89.

Synthesis example 1

658.0g of deionized water and 35.0g of sodium laurate were charged into a stirred reactor having an internal volume of 1L, and the reactor was closed, and oxygen was removed by replacing the inside of the system with nitrogen gas. The reactor was warmed to 90 ℃ and pressurized to 0.4MPaG with nitrogen. 6.90g of Ammonium Persulfate (APS) was charged and stirred for 3 hours. The stirring was stopped, the pressure was released until the reactor reached atmospheric pressure, and cooling was carried out. To the obtained surfactant aqueous solution, an aqueous ammonia solution was slowly added under stirring to obtain a surfactant aqueous solution a having a pH adjusted to 8.5. The sodium laurate concentration in this case was 4.75% by mass.

Synthesis example 2

Into an SUS autoclave having an internal volume of 3L, 1780g of deionized water, 90g of paraffin wax, and 0.270g of sodium laurate were charged, the reactor was sealed, and the system was purged with nitrogen gas to remove oxygen. The reactor was warmed to 85 ℃ and 7.0g of HFP was added, followed by increasing the pressure with TFE to 2.70 MPaG. An aqueous polymerization initiator solution prepared by dissolving 0.310g of Ammonium Persulfate (APS) in 20g of pure water was charged into the reactor. TFE was charged so that the reaction pressure was fixed at 2.70 MPaG. When 45g of TFE was charged, the stirring was stopped, and the pressure was released to atmospheric pressure. Immediately, the reactor was filled with TFE to a reaction pressure of 2.70 MPaG. The stirring was restarted and the reaction was continued. The aqueous surfactant solution a obtained in synthesis example 1 was immediately and continuously charged into a reactor. Further, an aqueous disuccinic peroxide solution having a concentration of 2.0 mass% was continuously charged into the reactor. When 685g of TFE had been charged, the stirring was stopped, and the pressure was released until the reactor reached atmospheric pressure. At the termination of the reaction, 47.0g of the surfactant aqueous solution A and 14.5g of the disuccinic acid peroxide aqueous solution were charged. The aqueous dispersion was taken out of the reactor, cooled, and paraffin was separated, and the average primary particle diameter contained in the obtained PTFE aqueous dispersion was 189 nm. The solid content concentration of the obtained PTFE aqueous dispersion was 26.8 mass%. The pH of the obtained PTFE aqueous dispersion was 6.0.

The content of the compound represented by the general formulae (1) and (2) was measured with respect to the aqueous PTFE dispersion. The results are shown in Table 7.

Example 1

Deionized water was added to the aqueous PTFE dispersion obtained in Synthesis example 2 to adjust the specific gravity (25 ℃ C.) to 1.080. 2.5L of the aqueous dispersion of PTFE having a specific gravity adjusted was charged into a 6L-capacity coagulation tank equipped with a stirring blade and a baffle.

Immediately 16g of nitric acid (10%) was added to adjust the pH to 1.8, while starting stirring at a stirring speed of 500 rpm. After the start of stirring, it was confirmed that the aqueous dispersion was in the form of a slurry to form wet PTFE powder, and stirring was continued for 1 minute.

Subsequently, wet PTFE powder was filtered, and 2.5L of the wet PTFE powder and deionized water were put into a coagulation tank, adjusted to 25 ℃, and the operation of washing the polymer powder at a stirring speed of 500rpm was repeated 2 times. After the washing, wet PTFE powder was filtered off, and dried by standing in a hot air circulation type drier at 210 ℃ for 18 hours to obtain PTFE powder.

The content of the salt of the compound represented by the general formula (1) contained in the wet PTFE powder obtained was measured by ion chromatography, and as a result, it was less than the quantitative limit (10 ppb).

The standard specific gravity of the obtained PTFE powder was 2.198.

The content of the compound represented by the general formulae (1) and (2) in the obtained PTFE powder was measured. The results are shown in Table 7.

Synthesis example 3

3560g of deionized and degassed water, 180g of paraffin wax, and 0.54g of sodium laurate were charged into a SUS autoclave having an internal volume of 6L, and the reactor was sealed, and the system was purged with nitrogen gas to remove oxygen. The reactor was warmed to 70 ℃ and TFE was charged to the reactor to make the reactor 2.76 MPaG. An aqueous solution prepared by dissolving 0.62g of Ammonium Persulfate (APS) in 20g of water and an aqueous solution prepared by dissolving 1.488g of disuccinic acid peroxide (DSP) in 20g of water were charged into a reactor as polymerization initiators. TFE was charged so that the reaction pressure was fixed at 2.76 MPaG. When 350g of TFE had been charged, the stirring was stopped, and the pressure was released until the reactor reached atmospheric pressure. The aqueous dispersion was taken out of the reactor, cooled and the paraffin was separated. The average primary particle diameter of the particles contained in the obtained PTFE aqueous dispersion was 157 nm. The solid content of the obtained PTFE aqueous dispersion was 8.9 mass%. The pH of the obtained PTFE aqueous dispersion was 5.3.

Comparative example 1

A PTFE powder was obtained in the same manner as in example 1 except that the aqueous PTFE dispersion obtained in synthesis example 3 was used, the specific gravity of the aqueous PTFE dispersion obtained in synthesis example 3 was adjusted to 1.050, and the aqueous PTFE dispersion was coagulated without using nitric acid to adjust the drying temperature to 150 ℃.

The standard specific gravity of the obtained PTFE was 2.184.

The content of the compound represented by the general formulae (1) and (2) in the obtained PTFE powder was measured. The results are shown in Table 7.

Comparative example 2

A PTFE powder was obtained in the same manner as in example 1, except that the specific gravity of the aqueous PTFE dispersion obtained in synthesis example 3 was adjusted to 1.050 using the aqueous PTFE dispersion obtained in synthesis example 3, and coagulation was performed without using nitric acid.

The content of the compound represented by the general formulae (1) and (2) in the obtained PTFE powder was measured. The results are shown in Table 7.

[ Table 7]

The limit of the amount of the aqueous dispersion was 86ppb/PTFE, and the limit of the amount of the powder was 13 ppb/PTFE.

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