阅读说明：本技术 聚乙烯醇系树脂、分散剂和悬浮聚合用分散剂 (Polyvinyl alcohol resin, dispersant, and dispersant for suspension polymerization ) 是由 村松雄介 山内芳仁 于 2018-05-15 设计创作，主要内容包括：本发明的课题在于,提供热处理程度不依赖于粒径那样的、热处理程度的分布小的PVA系树脂。本发明的聚乙烯醇系树脂的0.1重量％水溶液在280nm处的吸光度为0.3以上,且满足式(1)：0.9≤X<Sub>1</Sub>/Y<Sub>1</Sub>≤1.2。(式(1)中,X<Sub>1</Sub>表示粒径大于1000μm且为1680μm以下的聚乙烯醇系树脂的0.1重量％水溶液在320nm处的吸光度,Y<Sub>1</Sub>表示粒径大于212μm且为500μm以下的聚乙烯醇系树脂的0.1重量％水溶液在320nm处的吸光度)。(The present invention addresses the problem of providing a PVA-based resin having a small distribution of heat treatment levels, such that the degree of heat treatment does not depend on the particle size. The polyvinyl alcohol resin of the invention has an absorbance at 280nm of 0.1 wt% aqueous solution of 0.3 or more, and satisfies formula (1): x is more than or equal to 0.9 1 /Y 1 Less than or equal to 1.2. (in the formula (1), X 1 Denotes the absorbance at 320nm of a 0.1 wt% aqueous solution of a polyvinyl alcohol resin having a particle diameter of more than 1000 μm and not more than 1680 μm, Y 1 Indicating the absorbance at 320nm of a 0.1 wt% aqueous solution of a polyvinyl alcohol resin having a particle diameter of more than 212 μm and not more than 500 μm).)

1. A polyvinyl alcohol resin comprising at least a polyvinyl alcohol resin having a particle diameter of more than 1000 μm and not more than 1680 μm and a polyvinyl alcohol resin having a particle diameter of more than 212 μm and not more than 500. mu.m,

an absorbance at 280nm of a 0.1 wt% aqueous solution of the polyvinyl alcohol resin is 0.3 or more, and the following formula (1) is satisfied:

0.9≤X₁/Y₁≤1.2 (1)

in the formula (1), X₁Denotes the absorbance at 320nm of a 0.1 wt% aqueous solution of a polyvinyl alcohol resin having a particle diameter of more than 1000 μm and not more than 1680 μm, Y₁It represents the absorbance at 320nm of a 0.1 wt% aqueous solution of a polyvinyl alcohol resin having a particle diameter of more than 212 μm and not more than 500. mu.m.

2. The polyvinyl alcohol-based resin according to claim 1, which further satisfies the following formula (2):

0.8≤X₂/Y₂≤1.1 (2)

in the formula (2), X₂Denotes the absorbance at 280nm of a 0.1 wt% aqueous solution of a polyvinyl alcohol resin having a particle diameter of more than 1000 μm and not more than 1680 μm, Y₂It represents the absorbance at 280nm of a 0.1 wt% aqueous solution of a polyvinyl alcohol resin having a particle diameter of more than 212 μm and not more than 500. mu.m.

3. The polyvinyl alcohol resin according to claim 1 or 2, wherein the polyvinyl alcohol resin has a saponification degree of 60 to 99 mol%.

4. A dispersant comprising the polyvinyl alcohol resin according to any one of claims 1 to 3.

5. A dispersant for suspension polymerization, which comprises the polyvinyl alcohol resin according to any one of claims 1 to 3.

6. A method for producing the polyvinyl alcohol resin according to any one of claims 1 to 3,

the method comprises subjecting a polyvinyl alcohol resin having a carbonyl group in the molecule to a heat treatment to cause dehydration or a deacetylation reaction, and drying the resin before the heat treatment.

7. A polyvinyl alcohol resin obtained by the method for producing a polyvinyl alcohol resin according to claim 6.

Technical Field

The present invention relates to a polyvinyl alcohol resin (hereinafter, polyvinyl alcohol may be abbreviated as PVA), and more particularly, to a PVA resin suitable as a dispersant used when vinyl chloride is suspension-polymerized in the production of polyvinyl chloride, and a dispersant for suspension polymerization each containing the PVA resin.

Background

PVA-based resins have been conventionally used as various dispersants, and also as dispersants in polymerization of monomers (for example, dispersants for emulsion polymerization, dispersants for suspension polymerization, and the like).

In addition, as a method for industrially producing a vinyl chloride resin, a method of suspension polymerization of a vinyl chloride monomer or a mixture of a vinyl chloride monomer and a monomer copolymerizable with the vinyl chloride monomer is known. In the polymerization, a dispersion agent (also referred to as a dispersion stabilizer) such as a PVA-based resin, methylcellulose, a vinyl acetate-maleic anhydride copolymer, or gelatin is used. Among them, various PVA-based dispersion stabilizers have been studied in view of improvement in physical properties such as bulk density, particle size distribution, porosity, plasticizer absorptivity, residual monomer, and the like of the obtained vinyl chloride-based polymer (resin) particles. Among the PVA-based dispersion stabilizers, from the viewpoint of improving the surface activity of the PVA-based dispersion stabilizer, a dispersion stabilizer of a PVA-based resin has been proposed which focuses on a carbonyl group in the PVA molecule and an ethylene group adjacent thereto.

PVA resins undergo dehydration or deacetylation reaction by heat treatment to produce vinylidene groups in the main chain, and are used as dispersion stabilizers for suspension, water-retaining materials, and the like in the production of polyvinyl chloride. It is also known that strength is improved by heat-treating a film-like or fibrous PVA-based resin.

The vinylidene group in the PVA based resin can be measured by, in particular, ultraviolet absorption spectrum of a 0.1 wt% aqueous solution. Note that the peak around 215nm is ascribed to [ -CO-CH ═ CH-]The peak near 280nm is [ -CO- (CH ═ CH)₂-]The peak near 320nm is [ -CO- (CH ═ CH)₃-]The structure of (1).

Various heat-treated PVA resins have been studied as stabilizers for suspension polymerization.

For example, a dispersion stabilizer for suspension polymerization, which further contains a metal having a valence of 2 to 3 in a PVA-based resin having a carbonyl group, is disclosed (for example, see patent document 1). In addition, a PVA having a specific block character (for example, see patent document 2) has been proposed. In recent years, a PVA that satisfies all the conditions of carbonyl group, end-capping property, and absorbance has been proposed (see, for example, patent document 3).

Disclosure of Invention

Problems to be solved by the invention

However, in patent document 1, after a metal salt or hydroxide is added to a saponified PVA-based resin, a solution containing a metal compound is removed, and the removed PVA-based resin (usually containing 40 wt% or more of the solvent at the time of saponification after removal) is heat-treated at a high temperature of 110 ℃. Further, since heat is used for the volatilization of the solvent at the initial stage of the heat treatment and heat is applied to the PVA-based resin from the volatilized portion, heat is applied from the vicinity of the surface while the solvent in the resin is not completely volatilized, and there is a possibility that the degree of heat treatment is distributed among particles and in the particles due to the uneven application of heat.

In addition, in patent document 2, the PVA-based resin obtained by drying is heat-treated at 60 ℃, but in the drying of a general PVA-based resin, since about 3 to 10 wt% of a solvent is contained, the drying is insufficient, and the distribution is generated by applying heat between particles or in the particles as in patent document 1, but the degree of heat treatment between particles or in the particles is similarly low as compared with patent document 1.

In patent document 3, in the melt heat treatment by an extruder, there is no problem with the distribution of the degree of heat treatment among particles or in the particles of the heat treatment, and the molten resin is usually cooled by a water bath, but the PVA-based resin is water-soluble, and the molten resin treated at a high temperature is difficult to cool, and there is a problem of poor productivity.

Means for solving the problems

However, the present inventors have conducted intensive studies in view of the above circumstances, and as a result, have found that: the present inventors have completed the present invention by finding that a PVA-based resin having a large particle size and a PVA-based resin having a small particle size have a small distribution of the degree of heat treatment, such that the degree of heat treatment does not depend on the particle size, by making the ratio of the absorbance at a specific wavelength close to 1.

That is, the gist of the present invention is <1> to <7> below.

[ claim 1] A polyvinyl alcohol resin comprising at least a polyvinyl alcohol resin having a particle diameter of more than 1000 [ mu ] m and not more than 1680 [ mu ] m and a polyvinyl alcohol resin having a particle diameter of more than 212 [ mu ] m and not more than 500 [ mu ] m, wherein a 0.1 wt% aqueous solution of the polyvinyl alcohol resin has an absorbance at 280nm of not less than 0.3 and satisfies the following formula (1).

0.9≤X₁/Y₁≤1.2 (1)

(in the formula (1), X₁Denotes the absorbance at 320nm of a 0.1 wt% aqueous solution of a polyvinyl alcohol resin having a particle diameter of more than 1000 μm and not more than 1680 μm, Y₁It represents the absorbance at 320nm of a 0.1 wt% aqueous solution of a polyvinyl alcohol resin having a particle diameter of more than 212 μm and not more than 500. mu.m. )

<2> the polyvinyl alcohol resin according to <1>, which further satisfies the following formula (2).

0.8≤X₂/Y₂≤1.1 (2)

(in the formula (2), X₂Represents the absorbance at 280nm of a 0.1 wt% aqueous solution of a polyvinyl alcohol resin having a particle size of more than 1000 μm and not more than 1680. mu.m,Y₂it represents the absorbance at 280nm of a 0.1 wt% aqueous solution of a polyvinyl alcohol resin having a particle diameter of more than 212 μm and not more than 500. mu.m. )

<3> the polyvinyl alcohol resin according to <1> or <2>, wherein the polyvinyl alcohol resin has a saponification degree of 60 to 99 mol%.

<4> a dispersant containing the polyvinyl alcohol resin according to any one of <1> to <3 >.

<5> a dispersant for suspension polymerization, which comprises the polyvinyl alcohol resin according to any one of the above <1> to <3 >.

<6> A method for producing the polyvinyl alcohol resin according to any one of <1> to <3>, the method comprising subjecting a polyvinyl alcohol resin having a carbonyl group in the molecule to a heat treatment to cause dehydration or a deacetylation reaction, and drying the polyvinyl alcohol resin before the heat treatment.

<7> a polyvinyl alcohol resin obtained by the method for producing a polyvinyl alcohol resin <6 >.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a PVA-based resin having a small distribution of the degree of heat treatment can be obtained. Therefore, by using the PVA-based resin, effects such as an increase in the amount of the PVA-based resin that effectively functions in suspension polymerization of vinyl chloride, an increase in the number of adsorption sites with respect to vinyl chloride particles, and a uniform reaction can be obtained.

Detailed Description

The following description of the constituent elements is an example (representative example) of the embodiment of the present invention, but is not limited to these contents.

In the present invention, the (meth) allyl group means an allyl group or a methallyl group, the (meth) acrylic group means an acrylic group or a methacrylic group, and the (meth) acrylate group means an acrylate group or a methacrylate group.

The present invention will be described in detail below.

The PVA-based resin of the present invention comprises at least a PVA-based resin having a particle size of more than 1000 μm and not more than 1680 μm and a PVA-based resin having a particle size of more than 212 μm and not more than 500 μm, and the absorbance of a 0.1 wt% aqueous solution at 280nm is not less than 0.3 and satisfies the following formula (1).

0.9≤X₁/Y₁≤1.2 (1)

(in the formula (1), X₁Denotes the absorbance at 320nm of a 0.1 wt% aqueous solution of a PVA-based resin having a particle diameter of more than 1000 μm and not more than 1680 μm, Y₁It represents the absorbance at 320nm of a 0.1 wt% aqueous solution of a PVA-based resin having a particle diameter of more than 212 μm and not more than 500. mu.m. )

The PVA-based resin has a particle size that varies depending on the stirring conditions in the saponification step, the pulverization conditions in the drying step, and the like. In the present invention, the PVA-based resin has a particle size of about 10 to 3000 μm, and includes at least a PVA-based resin having a particle size of more than 1000 μm and not more than 1680 μm and a PVA-based resin having a particle size of more than 212 μm and not more than 500 μm.

The PVA-based resin of the present invention has an absorbance at 280nm of 0.3 or more in an ultraviolet absorption spectrum when prepared into a 0.1 wt% aqueous solution. When the absorbance of the 0.1 wt% aqueous solution at 280nm is 0.3 or more, the adsorption property to vinyl chloride particles is improved. The absorbance of the 0.1 wt% aqueous solution at 280nm is preferably 0.35 or more, more preferably 0.4 or more, and the upper limit is not particularly limited, preferably 0.8 or less, more preferably 0.7 or less.

In order to set the absorbance at 280nm to 0.3 or more, for example, a method of subjecting a PVA-based resin having a carbonyl group in the molecule to a heat treatment to cause dehydration or a reaction of removing acetic acid may be mentioned. The above method introduces conjugated double bonds into the PVA based resin, and therefore, the absorbance at 280nm can be set to 0.3 or more.

The vinylidene group in the PVA-based resin can be measured by measuring the ultraviolet absorption spectrum of a 0.1 wt% aqueous solution of the PVA-based resin. Note that the peak around 215nm is ascribed to [ -CO-CH ═ CH-]The peak near 280nm is [ -CO- (CH ═ CH)₂-]The peak near 320nm is [ -CO- (CH ═ CH)₃-]The structure of (1).

As a method for introducing a vinylidene group into a PVA-based resin, for example, a PVA-based resin having a carbonyl group in the molecule is subjected to a heat treatment to cause dehydration or a deacetylation reaction, thereby introducing a vinylidene group into the main chain of the PVA-based resin.

The ultraviolet absorption spectrum of the PVA based resin can be obtained by measuring the absorbance of a 0.1 wt% aqueous solution of the PVA based resin at wavelengths of 215nm, 280nm and 320nm using an ultraviolet-visible near-infrared spectrophotometer (for example, "V-560" manufactured by Nippon Kabushiki Kaisha). The measurement was performed using a sample container (cell) having a thickness of 1 cm.

The PVA-based resin of the present invention satisfies the following formula (1).

0.9≤X₁/Y₁≤1.2 (1)

In the formula (1), X₁Denotes the absorbance at 320nm of a 0.1 wt% aqueous solution of a PVA-based resin having a particle diameter of more than 1000 μm and not more than 1680 μm, Y₁It represents the absorbance at 320nm of a 0.1 wt% aqueous solution of a PVA-based resin having a particle diameter of more than 212 μm and not more than 500. mu.m. X is above₁/Y₁When the amount is too small or too large, the distribution of the heat treatment degree becomes large.

The above formula (1) is preferably 0.92. ltoreq. X₁/Y₁X is not more than 1.1, particularly preferably 0.95 not more than X₁/Y₁Less than or equal to 1.05. Said X₁/Y₁The closer to 1.0, the smaller the distribution of the degree of heat treatment, and the most preferable value is 1.0.

Absorbance (X) at 320nm of a 0.1 wt% aqueous solution of a PVA-based resin having a particle diameter of more than 1000 μm and not more than 1680 μm₁) And an absorbance (Y) at 320nm of a 0.1 wt% aqueous solution of a PVA-based resin having a particle diameter of more than 212 μm and not more than 500 μm₁) The PVA-based resin was sieved with JIS Z8801-1:2000 "Standard Sieve" and the absorbance was measured by the method described above.

The PVA resin of the present invention preferably satisfies the following formula (2).

0.8≤X₂/Y₂≤1.1 (2)

(in the formula (2), X₂Denotes the absorbance at 280nm of a 0.1 wt% aqueous solution of a polyvinyl alcohol resin having a particle diameter of more than 1000 μm and not more than 1680 μm, Y₂It represents the absorbance at 280nm of a 0.1 wt% aqueous solution of a polyvinyl alcohol resin having a particle diameter of more than 212 μm and not more than 500. mu.m. )

The absorbance can be determined by the method described above.

X is above₂/Y₂When the amount is too small or too large, the distribution of the heat treatment degree becomes large. The above formula (2) is preferably 0.92. ltoreq. X₂/Y₂X is not more than 1.1, particularly preferably 0.95 not more than X₂/Y₂Less than or equal to 1.05. Said X₂/Y₂The closer to 1.0, the smaller the distribution of the degree of heat treatment, and the most preferable value is 1.0.

The ratio of absorbance at 320nm to absorbance at 280nm (320nm/280nm) when the PVA-based resin of the present invention is prepared as a 0.1 wt% aqueous solution is preferably 0.3 or more, more preferably 0.4 or more, and still more preferably 0.5 or more. When the absorbance ratio is too small, the surface-active ability tends to be low and the suspension polymerization stability tends to be low when the copolymer is used as a dispersant for suspension polymerization. The upper limit is not particularly limited, and is usually about 3 from the viewpoint of productivity.

In the present invention, as a method for producing a PVA-based resin, for example, a method in which a PVA-based resin having a carbonyl group in the molecule is subjected to a heat treatment to cause dehydration or a deacetylation reaction as described above can be cited.

First, a method for introducing a carbonyl group will be described. The following methods can be mentioned as the above-mentioned methods.

(i) A method in which a vinyl ester monomer is polymerized, the resulting polymer is saponified, and the resulting PVA-based resin is oxidized with an oxidizing agent such as hydrogen peroxide;

(ii) a method in which polymerization is carried out in the presence of a chain transfer agent such as an aldehyde or a ketone in the polymerization of a vinyl ester monomer, and the resulting polymer is saponified;

(iii) a method in which vinyl ester monomers are polymerized in the coexistence of 1-methoxy-vinyl acetate or the like, and the resulting polymer is saponified;

(iv) a method in which a gas is blown into the polymerization mixture to polymerize the vinyl ester monomer and the resulting polymer is saponified.

The above-mentioned method (ii) is industrially preferable, and particularly, a method of obtaining a carbonyl group-containing PVA-based resin by polymerizing a vinyl acetate monomer in the presence of a chain transfer agent such as an aldehyde or a ketone and further saponifying the polymerization product is particularly advantageous. This method will be described in detail below.

Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl caprate, vinyl laurate, vinyl palmitate, vinyl stearate, and other linear or branched saturated fatty acid vinyl esters. From the practical viewpoint, vinyl acetate is preferred, and vinyl acetate is usually used alone or in combination with a fatty acid vinyl ester compound other than vinyl acetate.

Examples of the aldehydes as the chain transfer agent used in this method include acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, etc., and examples of the ketones include acetone, methyl ethyl ketone, hexanone, cyclohexanone, etc. Among them, aldehydes are preferable, and acetaldehyde is particularly preferable from the viewpoint of productivity such as solvent recovery. The amount of the chain transfer agent to be added varies somewhat depending on the chain transfer constant of the chain transfer agent to be added, the polymerization degree of the PVA-based resin to be targeted, and the like, and is usually 0.1 to 5% by weight, preferably 0.5 to 3% by weight, based on the vinyl ester monomer. The chain transfer agent may be initially charged at a time, or may be charged at the time of polymerization reaction, and the molecular weight distribution of the PVA-based resin may be controlled by charging by any method.

In the case of polymerizing a vinyl ester monomer, particularly vinyl acetate, there is no particular limitation, and a known polymerization method can be arbitrarily used, and usually solution polymerization using an alcohol such as methanol, ethanol, or isopropyl alcohol as a solvent is carried out. Needless to say, bulk polymerization, emulsion polymerization, and suspension polymerization may be carried out. In the solution polymerization, any means such as batch charging and one-time charging may be used as the method for charging the vinyl ester monomer. The polymerization reaction is carried out using a known radical polymerization catalyst such as azobisisobutyronitrile, acetyl peroxide, benzoyl peroxide, lauroyl peroxide, azobisdimethylvaleronitrile, azobismethoxyvaleronitrile, or the like. The reaction temperature is selected from the range of about 40 ℃ to the boiling point.

In this case, if necessary, a modified PVA-based resin obtained by copolymerizing a vinyl ester-based monomer and a polymerizable monomer may be used. Examples of the monomer include olefins such as ethylene, propylene, isobutylene, α -octene, α -dodecene, and α -octadecene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic anhydride, and itaconic acid, salts thereof, and monoalkyl esters or dialkyl esters thereof; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; olefin sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid, and salts thereof; polyoxyalkylene (meth) allyl ethers such as alkyl vinyl ethers, N-acrylamidomethyltrimethylammonium chloride, allyltrimethylammonium chloride, dimethylallylvinyl ketone, N-vinylpyrrolidone, vinyl chloride, vinylidene chloride, polyoxyethylene (meth) allyl ether, and polyoxypropylene (meth) allyl ether; polyoxyalkylene (meth) acrylates such as polyoxyethylene (meth) acrylate and polyoxypropylene (meth) acrylate; polyoxyalkylene (meth) acrylamides such as polyoxyethylene (meth) acrylamide and polyoxypropylene (meth) acrylamide; about 0.1 to 10 mol% of a hydroxyl group-containing α -olefin such as polyoxyethylene (1- (meth) acrylamide-1, 1-dimethylpropyl) ester, polyoxyethylene vinyl ether, polyoxypropylene vinyl ether, polyoxyethylene allylamine, polyoxypropylene allylamine, polyoxyethylene vinylamine, polyoxypropylene vinylamine, 3-buten-1-ol, 4-penten-1-ol and 5-hexen-1-ol, and a derivative such as an acyl compound thereof can be copolymerized.

Further, 3, 4-dihydroxy-1-butene, 3, 4-diacyloxy-1-butene, 3-acyloxy-4-hydroxy-1-butene, 4-acyloxy-3-hydroxy-1-butene, 3, 4-diacyloxy-2-methyl-1-butene, 4, 5-dihydroxy-1-pentene, 4, 5-diacyloxy-1-pentene, 4, 5-dihydroxy-3-methyl-1-pentene, 4, 5-diacyloxy-3-methyl-1-pentene, 5, 6-dihydroxy-1-hexene, 5, 6-diacyloxy-1-hexene, And compounds having a glycol such as glycerol monoallyl ether, 2, 3-diacetoxy-1-allyloxypropane, 2-acetoxy-1-allyloxy-3-hydroxypropane, 3-acetoxy-1-allyloxy-2-hydroxypropane, glycerol monovinyl ether, glycerol monoisopropenyl ether, vinyl ethylene carbonate, and 2, 2-dimethyl-4-vinyl-1, 3-dioxolane. The monomer may be copolymerized in an amount of 0.1 to 10 mol%.

In the saponification, the vinyl ester polymer obtained above is dissolved in an alcohol, and the saponification is carried out in the presence of an alkaline catalyst or an acidic catalyst. The concentration of the polymer in the alcohol is selected from the range of 20 to 50 wt%. Examples of the basic catalyst include basic catalysts such as hydroxides and alkoxides of alkali metals such as sodium hydroxide, potassium hydroxide, sodium methoxide, sodium ethoxide, and potassium methoxide, and examples of the acidic catalyst include aqueous solutions of inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as p-toluenesulfonic acid.

The amount of the catalyst used is required to be 1 to 100 millimolar equivalents relative to the vinyl ester monomer. In this case, the saponification temperature is not particularly limited, and it is preferable that: usually, the temperature is selected from the range of 10 to 70 ℃ and preferably 20 to 50 ℃. The reaction is usually carried out for 2 to 3 hours.

The PVA resin thus obtained contains carbonyl groups in its molecule, and the content thereof is preferably 0.05 mol% or more, and more preferably 0.1 mol% or more, and if the content is too small, the amount of generated vinylidene groups tends to be insufficient. The upper limit is usually 3 mol%.

The saponification degree of the PVA-based resin (measured according to JIS K6726) is preferably 60 to 99 mol%, more preferably 65 to 99 mol%, still more preferably 67 to 90 mol%, and particularly preferably 69 to 88 mol%. If the saponification degree is too low, the solubility of the PVA-based resin in water decreases, or the melting point becomes low, and the resins tend to aggregate together and agglomerate during heat treatment, whereas if the saponification degree is too high, the surface activity tends to decrease, the dispersibility of the vinyl chloride monomer tends to decrease, and lumps tend to be easily formed during suspension polymerization.

The PVA-based resin preferably has an average polymerization degree (measured according to JIS K6726) of 100 to 4000, more preferably 150 to 3000, and particularly preferably 200 to 1000. When the average polymerization degree is too small, the protective colloid tends to be too low and aggregation tends to occur during suspension polymerization, whereas when the average polymerization degree is too large, the amount of vinylidene groups at the terminals of the PVA-based resin tends to decrease and the surface-active ability tends to decrease.

From the viewpoint of promoting the deacetylation reaction, it is preferable that the PVA resin contains a salt or hydroxide of a metal having a valence of 2 to 3. Examples of the 2-to 3-valent metal include magnesium, calcium, zinc, aluminum, and the like, and examples of salts or hydroxides of these metals include magnesium acetate tetrahydrate, calcium acetate, calcium propionate, magnesium butyrate, magnesium carbonate, magnesium hydroxide, zinc acetate, aluminum hydroxide, and the like. Among them, magnesium acetate tetrahydrate and calcium acetate are preferably used from the viewpoint of being dissolved in water and/or methanol and being industrially easy to handle. The addition method of these compounds is not particularly limited as long as they are contained in the PVA-based resin, and the compounds may be added directly to the paste before saponification, the slurry after saponification, or the like, and the following methods are preferred: it is preferable that the PVA based resin slurry is dissolved in an alcohol such as methanol, ethanol or propanol or water, added to the saponified PVA based resin slurry in a solution form having a concentration of about 3 to 15 wt%, and distributed in the PVA based resin. The content of the compound in the PVA based resin is preferably 30 to 300. mu. mol/g, more preferably 40 to 200. mu. mol/g, relative to the PVA based resin, and when the content is too small, the amount of generated vinylidene tends to decrease, whereas when the content is too large, the PVA based resin tends to be colored and decomposed sharply.

In the present invention, it is preferable to contain a salt or hydroxide of a metal having a valence of 2 to 3 as described above, and a 1-valent metal compound such as sodium acetate other than these compounds may be used in combination within a range (1% by weight or less based on the salt or hydroxide of a metal having a valence of 2 to 3) that does not impair the effects of the present invention.

In the present invention, from the viewpoint of efficiency of introduction of vinylidene groups, it is preferable that the salt or hydroxide of the metal having a valence of 2 to 3 be contained in the PVA-based resin containing carbonyl groups in advance as described above, or the salt or hydroxide of the metal having a valence of 2 to 3 may be contained in the PVA-based resin containing no carbonyl groups and then the PVA-based resin may be subjected to heat treatment or the like to contain carbonyl groups.

(Pre-drying)

The PVA resin obtained in the above manner is saponified and then dried to form a powdery PVA resin. In the present invention, it is preferable to first perform preliminary drying when drying the PVA-based resin. Examples of the drying method for the preliminary drying include reduced pressure drying, atmospheric drying, and hot air drying. The drying time is usually 10 minutes to 20 hours, preferably 1 hour to 15 hours, and the drying temperature is usually 40 to 120 ℃, more preferably 40 to 100 ℃, and particularly preferably 50 ℃ or higher and less than 80 ℃.

After the drying, the PVA-based resin often contains 1 to 10 wt% of a solvent (for example, methanol, ethanol, or the like) used in the saponification.

(drying before Heat treatment)

The PVA-based resin obtained by the above preliminary drying is subjected to a heat treatment to generate a double bond in the molecule, but in the present invention, it is preferable to further perform drying after the preliminary drying and before the heat treatment, that is, drying before the heat treatment.

The method of drying before the heat treatment may be the above-mentioned ordinary drying method, and from the viewpoint of drying efficiency, reduced pressure drying is particularly preferable.

In addition, after drying before the heat treatment, the PVA-based resin is preferably dried until the solvent is less than 1% by weight.

The pressure at the time of drying under reduced pressure is usually 20kPa or less, preferably 17.0kPa or less, and particularly preferably 13.0kPa or less. If the pressure is too high, it takes time to dry before the heat treatment, which is not preferable as a production process. The lower limit of the pressure is preferably as close to 0 kPa.

The drying conditions in the drying step are generally 40 to 120 ℃, preferably 50 to 120 ℃, more preferably 60 to 120 ℃, and particularly preferably 80 ℃ or higher and less than 120 ℃.

The time for drying before the heat treatment is appropriately selected in consideration of the temperature and pressure conditions, the weight of the object to be treated, and the like, and is preferably set within a range of 30 to 1200 minutes in general.

The PVA-based resin of the present invention is obtained by drying before the above heat treatment and then subjecting the resin to a heat treatment to cause dehydration or a dehydroacetic acid reaction to generate double bonds. The method of heat treatment is not particularly limited, and a method of subjecting the PVA-based resin to a specific heat treatment is generally exemplified. The temperature condition of the heat treatment is preferably 120 to 180 ℃, more preferably 140 to 155 ℃, and if the temperature condition is too low, the desired amount of vinylidene groups tends not to be obtained, whereas if the temperature condition is too high, the decomposition by the heat treatment becomes severe, the resin is melted, and the adhesion in the autoclave tends to become large.

The time for the heat treatment is preferably 0.5 to 6 hours, and more preferably 1.5 to 5 hours. If the treatment time is too short, the amount of vinylidene tends to decrease, whereas if the treatment time is too long, the amount tends to cause coloring of the PVA-based resin or the formation of water-insoluble components.

The heat treatment is preferably performed in an oxygen atmosphere having an oxygen concentration of 20 vol% or less, and more preferably in an atmosphere of 3 to 12 vol%. When the oxygen concentration is too high, the PVA-based resin tends to be intensely colored or to be insoluble. In the heat treatment, a PVA resin obtained by a known method containing the metal salt described above may be used, and the carbonyl group content of the PVA resin before the heat treatment is preferably 0.03 to 2.5 mol% in order to generate a sufficient amount of vinylidene group for obtaining a good surface activity.

The heat treatment may be carried out by any apparatus, and the following methods may be mentioned: (1) methods of treatment using heatable mixing devices, such as nauta mixers, conical dryers; (2) a method of treating the waste water with a general static dryer; (3) a method using a flask heated by a heat medium, for example, a method using a rotary evaporator, and the like. Among them, in the present invention, a heatable mixing device is preferable from the viewpoint of reducing the distribution of heat treatment.

The absorbance of a 0.1 wt% aqueous solution of the thus obtained PVA-based resin based on the ultraviolet absorption spectrum was 215nm [ a structure assigned to-CO-CH ═ CH]Is 0.1 or more, preferably 0.3 or more, 280nm [ belonging to-CO- (CH ═ CH)₂Structure of (a)]Is 0.3 or more, preferably 0.35 or more, 320nm [ belonging to-CO- (CH ═ CH)₃Structure of (a)]Is 0.1 or more, preferably 0.2 or more, and the absorbance ratio of 320nm/280nm is 0.3 or more, preferably 0.4 or more. If the amount is too low, the effect of suppressing foaming tends to be low in suspension polymerization of a vinyl compound such as vinyl chloride.

The PVA-based resin of the present invention preferably has a saponification degree (measured according to JIS K6726) of 60 to 99 mol%, more preferably 65 to 99 mol%, still more preferably 67 to 90 mol%, and particularly preferably 69 to 88 mol%. If the saponification degree is too small, the water dispersibility tends to decrease, whereas if the saponification degree is too large, the surface active ability tends to decrease, the dispersibility of vinyl chloride monomer tends to decrease, and a block tends to be easily formed during suspension polymerization.

The PVA-based resin of the present invention preferably has an average polymerization degree (measured according to JIS K6726) of 100 to 4000, more preferably 150 to 3000, and particularly preferably 200 to 1000. When the average polymerization degree is too small, the protective colloid tends to be too low and aggregation tends to occur during suspension polymerization, whereas when the average polymerization degree is too large, the amount of vinylidene groups at the terminals of the PVA-based resin tends to decrease and the surface-active ability tends to decrease.

The PVA-based resin of the present invention is useful as a dispersant for stably dispersing solid fine particles in a liquid, and is particularly useful as a dispersant for suspension polymerization.

Next, a method of suspension polymerization of a vinyl compound (vinyl chloride) using the PVA-based resin of the present invention as a dispersant will be described.

In the suspension polymerization, the PVA-based resin of the present invention is usually added to water or a heated aqueous medium as a dispersant, and vinyl chloride monomer is dispersed and polymerized in the presence of an oil-soluble catalyst. The PVA-based resin (dispersant) may be added in a powder state or in a solution state. The PVA resin has a low degree of saponification, and may be added in the form of an aqueous dispersion when forming an aqueous dispersion. In particular, the PVA-based resin in the solution state may be added in the form of an aqueous solution when the PVA-based resin is water-soluble, or may be dissolved in an organic solvent such as alcohol, ketone, or ester, or a mixed solvent of these organic solvents and water and added in the form of a solution even when the PVA-based resin is low in water solubility. Even if the degree of saponification is low, the PVA resin may be added directly to the aqueous dispersion when the PVA resin has self-dispersibility in water.

The dispersant may be fed at once in the initial stage of polymerization, or may be fed in portions during the polymerization. Alternatively, the catalyst to be used may be any catalyst as long as it is oil-soluble, and for example, benzoyl peroxide, lauroyl peroxide, diisopropyl peroxydicarbonate, α '-azobisisobutyronitrile, α' -azobis-2, 4-dimethylvaleronitrile, acetylcyclohexylsulfonyl peroxide, or a mixture thereof may be used. The polymerization temperature is arbitrarily selected from a range known to those skilled in the art.

In addition, a known stabilizer other than the PVA-based resin of the present invention, for example, a polymer substance may be used in combination. The polymer substance includes PVA having an average degree of polymerization of 100 to 4,000 and a degree of saponification of 30 to 95 mol% or a derivative thereof. Examples of the derivative of PVA include formalized compounds, acetalized compounds, butyralized compounds, urethane compounds, and esterified compounds with sulfonic acid, carboxylic acid, and the like of PVA. Further, the modified PVA-based resin can be exemplified. But is not necessarily limited thereto.

Examples of the polymer other than PVA include cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxybutyl methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, aminomethyl hydroxypropyl cellulose, and aminoethyl hydroxypropyl cellulose; starch, tragacanth, pectin (glue), alginic acid or a salt thereof, gelatin, polyvinylpyrrolidone, polyacrylic acid or a salt thereof, polymethacrylic acid or a salt thereof, polyacrylamide, polymethacrylamide, a copolymer of vinyl acetate and an unsaturated acid such as maleic acid, maleic anhydride, acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, a copolymer of styrene and the above unsaturated acid, a copolymer of vinyl ether and the above unsaturated acid, and a salt or an ester of the above copolymer. In the polymerization, various surfactants, inorganic dispersants, and the like may be used as an auxiliary in an appropriate combination, and the PVA-based resin of the present invention may be used as an auxiliary.

Further, not only homopolymerization of vinyl chloride but also copolymerization with a copolymerizable monomer may be performed. Examples of the copolymerizable monomer include vinylidene halide, vinyl ether, vinyl acetate, vinyl benzoate, acrylic acid, methacrylic acid and esters thereof, maleic acid or anhydride thereof, ethylene, propylene, styrene, and the like. In addition, in the polymerization of vinyl chloride, a polymerization regulator, a chain transfer agent, a gelation modifier, an antistatic agent, a pH adjuster, and the like, which can be used as appropriate, are optionally added. Although the above description has been made mainly of the polymerization of vinyl chloride, the dispersant of the present invention is not limited to the use for vinyl chloride, and may be used for the suspension polymerization of any vinyl compound such as styrene, methacrylate, and vinyl acetate.