阅读说明：本技术 耐火化纤维、其制造方法、和碳纤维的制造方法 (Flame-resistant fiber, method for producing same, and method for producing carbon fiber ) 是由 森下卓也 成田麻美子 毛利诚 菊泽良弘 河合秀保 重光望 于 2020-09-14 设计创作，主要内容包括：一种耐火化纤维的制造方法,其特征在于,包含：一边对丙烯酰胺系聚合物纤维赋予0.07～15mN/tex的张力,一边将其在氧化性气氛中、200～500℃的范围内的耐火化处理温度下实施加热处理。(A method for producing a flame-resistant fiber, comprising: the acrylamide polymer fiber is subjected to a heat treatment in an oxidizing atmosphere at a flame-resistant treatment temperature in the range of 200 to 500 ℃ while imparting a tension of 0.07 to 15mN/tex to the fiber.)

1. A method for producing a flame-resistant fiber, comprising:

the acrylamide polymer fiber is subjected to a heat treatment in an oxidizing atmosphere at a flame-resistant treatment temperature in the range of 200 to 500 ℃ while imparting a tension of 0.07 to 15mN/tex to the fiber.

2. The method of producing a flameproofed fiber according to claim 1, wherein the heat treatment is performed until the side surface of the acrylamide polymer fiber has a Raman spectrum of 1590cm^-1The near G peak is relative to 1360cm^-1The intensity ratio of the nearby D peak becomes 0.5 or more.

3. The method for producing a flameproofed fiber according to claim 1, wherein the heat treatment is performed until the density of the acrylamide polymer fiber becomes 1.35 to 1.75g/cm³。

4. A method for producing a carbon fiber, comprising:

a fire resistant fiber produced by the method of any one of claims 1 to 3, and

and carbonizing the refractory fibers.

5. A flame-resistant fiber characterized by being derived from an acrylamide polymer and having a Raman spectrum of 1590cm on the side of the fiber^-1The near G peak is relative to 1360cm^-1The intensity ratio of the nearby D peak is 0.5 or more.

6. A fire-resistant fiber is characterized by being derived from an acrylamide polymer and having a density of 1.35 to 1.75g/cm³。

7. A method for producing a carbon fiber, comprising:

carbonizing the refractory fiber according to claim 5 or 6.

Technical Field

The present invention relates to a flameproofed fiber, a method for producing the same, and a method for producing a carbon fiber.

Background

As a method for producing carbon fibers, the following methods have been mainly used: a carbon fiber precursor obtained by spinning polyacrylonitrile is subjected to a flame-proofing treatment and then subjected to a carbonization treatment (for example, Japanese patent publication Nos. 37-4405, 2015-74844, 2016-40419 and 2016-113726). Polyacrylonitrile used in this method is not easily dissolved in an inexpensive general-purpose solvent, and therefore, an expensive solvent such as dimethylsulfoxide or N, N-dimethylacetamide is required for polymerization or spinning, which causes a problem of high production cost of carbon fibers.

Japanese patent application laid-open No. 2013-103992 discloses a carbon fiber precursor fiber comprising an acrylonitrile copolymer containing 96 to 97.5 parts by mass of an acrylonitrile unit, 2.5 to 4 parts by mass of an acrylamide unit, and 0.01 to 0.5 part by mass of a carboxylic acid-containing vinyl monomer. This acrylonitrile copolymer contains acrylamide units and carboxylic acid-containing vinyl monomer units contributing to the water solubility of the polymer, but these are contained in a small amount and therefore insoluble in water, and an expensive solvent such as N, N-dimethylacetamide is required for polymerization and molding (spinning), which causes a problem of high production cost of carbon fibers.

Further, when polyacrylonitrile or a copolymer thereof is subjected to a heat treatment, rapid heat generation occurs, and thermal decomposition of polyacrylonitrile or a copolymer thereof is accelerated, so that there is a problem that the yield of the carbon material (carbon fiber) is low. Therefore, in the production of a carbon material (carbon fiber) using polyacrylonitrile or a copolymer thereof, it is necessary to gradually increase the temperature over a long period of time to avoid rapid heat generation during the temperature increase in the refractorization treatment.

On the other hand, since an acrylamide polymer containing a large amount of acrylamide units is a water-soluble polymer, water which is inexpensive and has a small environmental load can be used as a solvent in polymerization and molding (film formation, sheet formation, spinning, and the like), and therefore, reduction in production cost of a carbon material can be expected. For example, jp 2018 a-90791 a describes a carbon material precursor composition containing an acrylamide polymer and at least one additive component selected from acids and salts thereof, and a method for producing a carbon material using the composition. Japanese patent application laid-open No. 2019-26827 discloses a carbon material precursor comprising an acrylamide/vinyl cyanide copolymer having 50 to 99.9 mol% of acrylamide monomer units and 0.1 to 50 mol% of vinyl cyanide monomer units, a carbon material precursor composition comprising the carbon material precursor and at least one additive component selected from acids and salts thereof, and a method for producing a carbon material using the composition. However, the production methods of these carbon materials do not always provide sufficient carbonization yield, and there is room for improvement.

Jp 2009-138313 a describes a method for producing a carbon fiber bundle by subjecting an acrylonitrile precursor fiber bundle to a flame-resistant treatment so that the densities of the fiber bundle before being charged into a flame-resistant furnace and the fiber bundle after passing through the respective zones satisfy predetermined conditions, using a flame-resistant furnace having n zones in which the temperatures can be controlled, and carbonizing the fiber bundle after the flame-resistant treatment in an inert atmosphere. In the method, the density of the precursor fiber bundle introduced into the 1 st zone is set to 1.15 to 1.19g/cm³The density of the fiber bundle passing through the nth zone, i.e., the density of the fiber bundle after the flame treatment, is controlled to be 1.33 to 1.37g/cm³。

Further, Japanese patent application laid-open No. 2018-178344 describes that a heat treatment is performed on an acrylonitrile precursor fiber bundle in an oxidizing atmosphere until the density becomes 1.22 to 1.24g/cm³Then, heat treatment is performed until the density becomes 1.32 to 1.35g/cm³Further, heat treatment is performed at 275 to 295 ℃ in an oxidizing atmosphere while applying a tension of 1.6 to 4.0mN/dtex until the density becomes 1.46 to 1.50g/cm³And then heat-treating the fire-resistant fiber bundle at 1200 to 3000 ℃ in an inert atmosphere to produce a carbon fiber bundle.

Disclosure of Invention

However, the density of the acrylamide polymer fiber in an oven-dried state is usually 1.22 to 1.31g/cm³A density (1.15 to 1.19 g/cm) of polyacrylonitrile-based polymer fiber in an oven-dry state different from that of polyacrylonitrile-based polymer fiber in chemical composition³) On the other hand, the conditions described in Japanese patent laid-open Nos. 2009-138313-2018-178344 cannot be adopted. That is, the method described in Japanese patent laid-open No. 2009-138313 requires that the polyacrylonitrile-based precursor fiber bundle be subjected to a temperature of less than 300 ℃ for a long time (for example, 70 ℃) in order to prevent thermal decomposition due to rapid heat generation of the polyacrylonitrile-based precursor fiber bundle at about 300 ℃Minute) to be used, and therefore, there is a problem in that productivity is low, and further, if the acrylamide-based polymer fiber bundle is subjected to the flameproofing treatment under the above-mentioned conditions, the density and the G/D value of the resultant flameproofed fiber bundle are lowered, and carbonization yield is lowered. Further, if the acrylamide polymer fiber bundle is subjected to the flame-resistant treatment under the conditions described in jp 2018-178344, there is a problem that fluff is generated in the flame-resistant fiber bundle and a part of single fibers constituting the fiber bundle is cut in the flame-resistant treatment because of high tension.

The invention provides a flame-resistant chemical fiber from an acrylamide polymer and having a high carbonization yield, a method for producing the same, and a method for producing carbon fiber capable of producing carbon fiber at a high yield.

The present inventors have found that the carbonization yield of a flame-resistant fiber can be improved by performing a heating treatment (flame-resistant treatment) in an oxidizing atmosphere at a predetermined flame-resistant treatment temperature while applying a predetermined tension to an acrylamide polymer fiber, and that carbon fibers can be obtained at a high yield by performing a carbonization treatment on a flame-resistant fiber, thereby completing the present invention.

That is, the method for producing a flame-resistant fiber of the present invention includes: the acrylamide polymer fiber is subjected to a heat treatment in an oxidizing atmosphere at a flame-resistant treatment temperature in the range of 200 to 500 ℃ while imparting a tension of 0.07 to 15mN/tex to the fiber.

In the method for producing a flameproofed fiber of the present invention, the heat treatment is performed until the side surface of the acrylamide polymer fiber reaches 1590cm in the Raman spectrum^-1The near G peak is relative to 1360cm^-1The intensity ratio of the nearby D peak is 0.5 or more, or until the density of the acrylamide polymer fiber is 1.35 to 1.75g/cm³. The heat treatment may be carried out until 1590cm in a Raman spectrum of the side surface of the acrylamide-based polymer fiber^-1The near G peak is relative to 1360cm^-1The intensity ratio of the nearby D peak is 0.5 or more, and the density is 1.35 to 1.75g/cm³。

The invention relates to a capsuleThe fiber is obtained from acrylamide polymer and has a Raman spectrum of 1590cm^-1The near G peak is relative to 1360cm^-1The intensity ratio of the nearby D peak is 0.5 or more, or the density is 1.35 to 1.75g/cm³。

The flame-retardant fiber of the present invention has a side surface of 1590cm in Raman spectrum^-1The near G peak is relative to 1360cm^-1The intensity ratio of the nearby D peak is 0.5 or more, and the density is 1.35 to 1.75g/cm³。

The method for producing a carbon fiber of the present invention is a method for carbonizing the refractory fiber of the present invention, and includes, for example: the method for producing a flame-resistant fiber of the present invention produces a flame-resistant fiber, and the flame-resistant fiber is subjected to carbonization treatment.

The reason why the refractory fiber having a high carbonization yield can be obtained by the method for producing a refractory fiber of the present invention is not yet determined, but the present inventors presume as follows. That is, since the acrylamide polymer fiber is subjected to a flame-resistant treatment while applying a predetermined tension thereto, and the polymer molecules are oriented and aligned along the fiber axis direction, the intramolecular cyclization reaction, the oxidation reaction, and the dehydration reaction proceed efficiently, and a structure in which carbon-membered rings are continuous is formed, and a flame-resistant fiber derived from an acrylamide polymer having a density in a specific range and an intensity ratio (G/D) of a G peak and a D peak in a raman spectrum on the side of the fiber of a specific value or more is obtained. The flameproofed fiber having such a raman peak intensity ratio (G/D) and/or density has a planar structure of carbon atoms at a certain ratio or more on the fiber side surface, and is high in density, and therefore, is excellent in heat resistance. It is further presumed that the refractory fibers having excellent heat resistance exhibit a high carbonization yield because the carbonization reaction proceeds efficiently because thermal decomposition during carbonization is suppressed.

On the other hand, when the flame-resistant treatment is performed without applying tension to the acrylamide polymer fiber, or when the flame-resistant treatment is performed on the powder or film of the acrylamide polymer, the orientation and alignment of the polymer molecules do not occur, so that the intramolecular cyclization reaction, the oxidation reaction, and the dehydration reaction do not easily proceed, and it is difficult to form a structure in which carbon six-membered rings are continuous. As a result, the strength ratio (G/D) and density of the G peak and D peak in the raman spectrum of the fiber side surface of the obtained flameproofed fiber become small, and the heat resistance becomes low, so that thermal decomposition occurs during carbonization treatment, and the carbonization yield is lowered.

According to the present invention, a flame-resistant fiber derived from an acrylamide polymer and having a high carbonization yield can be obtained. Further, by subjecting such refractory fibers to carbonization treatment, carbon fibers can be produced with high yield.

Detailed Description

The present invention will be specifically described below with reference to embodiments.

[ method for producing flame-resistant fiber ]

First, a method for producing the flame-resistant fiber of the present invention will be described. The method for producing a flameproofed fiber of the present invention is a method in which an acrylamide polymer fiber is subjected to a heat treatment in an oxidizing atmosphere at a flameproofing temperature in the range of 200 to 500 ℃ while applying a tension of 0.07 to 15 mN/tex.

(acrylamide Polymer)

The acrylamide polymer used in the present invention may be a homopolymer of an acrylamide monomer or a copolymer of an acrylamide monomer and another polymerizable monomer, but is preferably a copolymer of an acrylamide monomer and another polymerizable monomer from the viewpoint of improving the yield of flameproofing, the carbonization yield of flameproofed fibers, and the total yield of flameproofing and carbonization.

The acrylamide polymer used in the present invention is preferably soluble in at least one of an aqueous solvent (water, an alcohol, and a mixed solvent thereof) and an aqueous mixed solvent (a mixed solvent of the aqueous solvent and an organic solvent (tetrahydrofuran, and the like)). Thus, when the acrylamide polymer is spun, dry spinning, dry-wet spinning, or electrostatic spinning can be performed using the aqueous solvent or the aqueous mixed solvent, and thus, the flame-resistant chemical fiber and the carbon fiber can be produced safely at low cost. In addition, when the additive component described later is added to the acrylamide polymer, the aqueous solvent or the aqueous mixed solvent may be used for wet mixing, and the acrylamide polymer and the additive component described later may be mixed homogeneously and safely at low cost. The content of the organic solvent in the aqueous mixed solvent is not particularly limited as long as the acrylamide polymer that is insoluble or poorly soluble in the aqueous solvent can be dissolved by mixing with the organic solvent. Among these acrylamide polymers, from the viewpoint of enabling the production of flame-resistant chemical fibers and carbon fibers at a lower cost and with safety, an acrylamide polymer soluble in the aqueous solvent is preferable, and a (water-soluble) acrylamide polymer soluble in water is more preferable.

Further, the upper limit of the weight average molecular weight of the acrylamide polymer used in the present invention is not particularly limited, but is usually 500 ten thousand or less, and from the viewpoint of spinnability of the acrylamide polymer, it is preferably 200 ten thousand or less, more preferably 100 ten thousand or less, still more preferably 40 ten thousand or less, and particularly preferably 30 ten thousand or less. The lower limit of the weight average molecular weight of the acrylamide polymer is not particularly limited, but is usually 1 ten thousand or more, and from the viewpoint of the strength of the acrylamide polymer fiber, 2 ten thousand or more is preferable, 3 ten thousand or more is more preferable, and 4 ten thousand or more is particularly preferable. The weight average molecular weight of the acrylamide polymer can be measured by using gel permeation chromatography.

The lower limit of the content of the acrylamide monomer unit in the copolymer of the acrylamide monomer and another polymerizable monomer is preferably 50 mol% or more, more preferably 60 mol% or more, and particularly preferably 70 mol% or more, from the viewpoint of solubility in an aqueous solvent or an aqueous mixed solvent of the copolymer. The upper limit of the content of the acrylamide monomer unit is preferably 99.9 mol% or less, more preferably 99 mol% or less, even more preferably 95 mol% or less, particularly preferably 90 mol% or less, and most preferably 85 mol% or less, from the viewpoint of increasing the yield of flameproofing, the yield of carbonizing, and the total yield of flameproofing and carbonizing of the acrylamide polymer fiber.

The lower limit of the content of the other polymerizable monomer unit in the copolymer of the acrylamide monomer and the other polymerizable monomer is preferably 0.1 mol% or more, more preferably 1 mol% or more, even more preferably 5 mol% or more, particularly preferably 10 mol% or more, and most preferably 15 mol% or more, from the viewpoint of improving the yield of flameproofing and carbonization of the acrylamide polymer fiber, the carbonization yield of the flameproofed fiber, and the total yield of flameproofing and carbonization. The upper limit of the content of the other polymerizable monomer unit is preferably 50 mol% or less, more preferably 40 mol% or less, and particularly preferably 30 mol% or less, from the viewpoint of solubility in the aqueous solvent or aqueous mixed solvent of the copolymer.

Examples of the acrylamide monomer include acrylamide; n-alkylacrylamides such as N-methylacrylamide, N-ethylacrylamide, N-N-propylacrylamide, N-isopropylacrylamide, N-N-butylacrylamide, and N-t-butylacrylamide; n-cycloalkylacrylamides such as N-cyclohexylacrylamide; dialkyl acrylamides such as N, N-dimethylacrylamide; dialkylaminoalkylacrylamides such as dimethylaminoethylacrylamide and dimethylaminopropylacrylamide; hydroxyalkyl acrylamides such as N- (hydroxymethyl) acrylamide and N- (hydroxyethyl) acrylamide; n-aryl acrylamides such as N-phenyl acrylamide; diacetone acrylamide; n, N '-alkylenebisacrylamides such as N, N' -methylenebisacrylamide; (ii) methacrylamide; n-alkylmethacrylamides such as N-methylmethacrylamide, N-ethylmethacrylamide, N-N-propylmethacrylamide, N-isopropylmethacrylamide, N-N-butylmethacrylamide and N-tert-butylmethacrylamide; n-cycloalkyl methacrylamides such as N-cyclohexyl methacrylamide; dialkyl methacrylamides such as N, N-dimethyl methacrylamide; dialkylaminoalkyl methacrylamides such as dimethylaminoethyl methacrylamide and dimethylaminopropyl methacrylamide; hydroxyalkyl methacrylamides such as N- (hydroxymethyl) methacrylamide and N- (hydroxyethyl) methacrylamide; n-arylmethacrylamides such as N-phenylmethylacrylamide; diacetone methacrylamide; n, N '-alkylene bismethacrylamide such as N, N' -methylenebismethacrylamide. These acrylamide monomers may be used alone in 1 kind, or in combination in 2 or more kinds. Among these acrylamide monomers, acrylamide, N-alkylacrylamide, dialkylacrylamide, methacrylamide, N-alkylmethacrylamide, and dialkylmethacrylamide are preferable from the viewpoint of improving solubility in an aqueous solvent or an aqueous mixed solvent, and acrylamide is particularly preferable.

Examples of the other polymerizable monomer include a vinyl cyanide monomer, an unsaturated carboxylic acid and a salt thereof, an unsaturated carboxylic acid anhydride, an unsaturated carboxylic acid ester, a vinyl monomer, and an olefin monomer. Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, 2-hydroxyethylacrylonitrile, chloroacrylonitrile, chloromethacrylonitrile, methoxyacrylonitrile, and methoxymethylacrylonitrile. Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, itaconic acid, and the like, examples of the salt of the unsaturated carboxylic acid include a metal salt (for example, sodium salt, potassium salt, and the like), an ammonium salt, an amine salt, and the like of the unsaturated carboxylic acid, examples of the unsaturated carboxylic acid anhydride include maleic anhydride, itaconic anhydride, and the like, examples of the unsaturated carboxylic acid ester include methyl acrylate, methyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, and the like, examples of the vinyl monomer include an aromatic vinyl monomer such as styrene, α -methylstyrene, and the like, vinyl chloride, vinyl alcohol, and the like, and examples of the olefin monomer include ethylene, propylene, and the like. These other polymerizable monomers may be used alone in 1 kind, or may be used in combination in 2 or more kinds. Among these other polymerizable monomers, a vinyl cyanide monomer is preferred, and acrylonitrile is particularly preferred, from the viewpoint of improving the spinnability of the acrylamide polymer, the carbonization yield of flameproofed fibers, and the total yield of flameproofing and carbonization, and an unsaturated carboxylic acid and a salt thereof are preferred from the viewpoint of solubility of the copolymer in an aqueous solvent or an aqueous mixed solvent.

As a method for synthesizing such an acrylamide polymer, a known polymerization reaction method such as radical polymerization, cationic polymerization, anionic polymerization, and living radical polymerization by a polymerization method such as solution polymerization, suspension polymerization, precipitation polymerization, dispersion polymerization, and emulsion polymerization (for example, inverse emulsion polymerization) can be used. Among the polymerization reactions, radical polymerization is preferred from the viewpoint of being able to synthesize an acrylamide polymer at low cost. In addition, in the case of using solution polymerization, it is preferable to use a solvent capable of dissolving the raw material monomer and the obtained acrylamide polymer as a solvent, and from the viewpoint of enabling safe synthesis at low cost, it is further preferable to use the aqueous solvent (water, alcohol, and the like, and a mixed solvent thereof) or the aqueous mixed solvent (a mixed solvent of the aqueous solvent and an organic solvent (tetrahydrofuran and the like)), and it is particularly preferable to use the aqueous solvent, and it is most preferable to use water.

In the radical polymerization, a conventionally known radical polymerization initiator such as azobisisobutyronitrile, benzoyl peroxide, 4 '-azobis (4-cyanovaleric acid), ammonium persulfate, potassium persulfate, or the like can be used as the polymerization initiator, and when the aqueous solvent or the aqueous mixed solvent is used as the solvent, a radical polymerization initiator soluble in the aqueous solvent or the aqueous mixed solvent (preferably the aqueous solvent, and more preferably water), such as 4, 4' -azobis (4-cyanovaleric acid), ammonium persulfate, potassium persulfate, or the like, is preferable. In addition, from the viewpoint of reducing the molecular weight of the acrylamide polymer and improving the spinning property of the acrylamide polymer, it is preferable to use a conventionally known polymerization accelerator such as tetramethylethylenediamine or a molecular weight modifier such as an alkylmercaptan such as n-dodecylmercaptan in place of the polymerization initiator, or to use the polymerization initiator in combination, it is preferable to use the polymerization initiator and the polymerization accelerator in combination, and it is particularly preferable to use ammonium persulfate and tetramethylethylenediamine in combination.

The temperature of the polymerization reaction is not particularly limited, but is preferably 35 ℃ or more, more preferably 40 ℃ or more, further preferably 50 ℃ or more, particularly preferably 70 ℃ or more, and most preferably 75 ℃ or more, from the viewpoint of reducing the weight average molecular weight Mw of the acrylamide polymer to be obtained and improving the spinnability of the acrylamide polymer.

(acrylamide Polymer fiber)

The acrylamide polymer fiber used in the present invention is formed of the above acrylamide polymer, and the fineness thereof is not particularly limited, but is preferably 1 × 10^-8About 100tex per root, more preferably about 1X 10^-660tex per root, more preferably 0.001 to 40tex per root, more preferably 0.01 to 10tex per root, particularly preferably 0.02 to 2tex per root, most preferably 0.03 to 0.4tex per root. When the fineness of the acrylamide polymer fiber is less than the lower limit, yarn breakage is likely to occur, and stable winding and flameproofing treatment tend to be difficult. On the other hand, when the content exceeds the upper limit, the difference in structure between the vicinity of the surface layer and the vicinity of the center of the flame-resistant fiber is large, and the tensile strength and the tensile elastic modulus of the obtained carbon fiber tend to decrease.

The average fiber diameter of the acrylamide polymer fiber is not particularly limited, but is preferably 3nm to 300. mu.m, more preferably 30nm to 250. mu.m, still more preferably 1 to 200. mu.m, yet more preferably 3 to 100. mu.m, particularly preferably 4 to 40 μm, and most preferably 5 to 20 μm. If the average fiber diameter of the acrylamide polymer fiber is less than the lower limit, yarn breakage tends to occur, and stable winding and flame-proofing treatment tend to be difficult. On the other hand, if the amount exceeds the upper limit, the difference in structure between the vicinity of the surface layer and the vicinity of the center of the flameproofed fiber is large, and the tensile strength and the tensile elastic modulus of the obtained carbon fiber tend to decrease.

Further, the acrylamide polymer fiber is not particularly limited, but preferably has a density of 1.22 to 1.31g/cm in an oven-dried state³More preferably 1.23 to 1.30g/cm³Particularly preferably 1.24 to 1.29g/cm³. By using an acrylamide polymer fiber having such a density, the cyclization reaction tends to be accelerated in the flameproofing treatment, and the density of the flameproofed fiber after the flameproofing treatment tends to be easily controlled within a predetermined range.

The acrylamide polymer fiber exhibits a high yield of flame resistance, a high carbonization yield, and a high total yield of flame resistance and carbonization, and thus can be used as it is for the production of flame resistant fibers and carbon fibers without adding an additive component such as an acid. By subjecting the acrylamide polymer fiber containing the additive component to a flame-resistant treatment while applying tension thereto, the formation of a cyclic structure by dehydration or deamination can be accelerated, and a flame-resistant fiber having a high carbonization yield can be obtained. In the flame-resistant fiber of the present invention, at least a part of the additive components and the residue thereof may remain. Further, the addition component may be added to the refractory fiber and then carbonized.

The content of these additives is preferably 0.1 to 100 parts by mass, more preferably 0.2 to 50 parts by mass, even more preferably 0.5 to 30 parts by mass, and particularly preferably 1 to 20 parts by mass, based on 100 parts by mass of the acrylamide polymer, from the viewpoint of further improving the carbonization yield and the total yield of flame-resistant and carbonization-resistant fibers produced from the acrylamide polymer fibers.

Examples of the acid include inorganic acids such as phosphoric acid, polyphosphoric acid, boric acid, polyboric acid, sulfuric acid, nitric acid, carbonic acid, and hydrochloric acid, and organic acids such as oxalic acid, citric acid, sulfonic acid, and acetic acid. The salts of these acids include metal salts (e.g., sodium salts, potassium salts, etc.), ammonium salts, amine salts, and the like, and ammonium salts and amine salts are preferred, and ammonium salts are more preferred. Among these additives, phosphoric acid, polyphosphoric acid, boric acid, polyboric acid, sulfuric acid, and ammonium salts thereof are preferable from the viewpoint of further improving the carbonization yield and the total yield of flameproofed and carbonized fibers made from acrylamide polymer fibers, and phosphoric acid, polyphosphoric acid, and ammonium salts thereof are particularly preferable.

The additive component is preferably soluble in at least one of the aqueous solvent and the aqueous mixed solvent (more preferably the aqueous solvent, particularly preferably water). In this way, when an acrylamide polymer fiber containing an additive component is produced, wet mixing can be performed using the aqueous solvent or the aqueous mixed solvent, and the acrylamide polymer and the additive component can be mixed uniformly and safely at low cost. Further, dry spinning, dry-wet spinning, or electrostatic spinning can be performed using the aqueous solvent or the aqueous mixed solvent, and the flame-resistant chemical fiber and the carbon fiber can be produced safely at low cost.

Such an acrylamide polymer fiber can be produced (manufactured) in the following manner. The acrylamide polymer or the acrylamide polymer composition containing the acrylamide polymer and the additive component is spun. In this case, melt spinning, spun bonding, melt blowing, or centrifugal spinning may be performed using the acrylamide polymer or the acrylamide polymer composition in a molten state, but when the acrylamide polymer or the acrylamide polymer composition is soluble in the aqueous solvent or the aqueous mixed solvent, from the viewpoint of improving spinning performance, it is preferable to dissolve the acrylamide polymer or the acrylamide polymer composition in the aqueous solvent or the aqueous mixed solvent and perform spinning using the obtained aqueous solution or aqueous mixed solution, or to perform spinning directly or after adjusting the concentration of the solution of the polymerized acrylamide polymer or the solution of the acrylamide polymer composition obtained by wet mixing described later to a desired concentration. Such spinning methods are preferably dry spinning, wet spinning, dry-wet spinning, gel spinning, flash spinning, or electrostatic spinning. Thus, an acrylamide polymer fiber having a desired fineness and average fiber diameter can be produced (manufactured) safely at low cost. In addition, from the viewpoint of enabling the acrylamide polymer fiber to be produced safely at a lower cost, it is preferable to use the aqueous solvent as the solvent, and it is particularly preferable to use water.

The concentration of the acrylamide polymer in the aqueous solution or the aqueous mixed solution is not particularly limited, and is preferably a high concentration of 20 mass% or more in terms of improvement in productivity and cost reduction. Further, if the concentration of the acrylamide polymer is not too high, the viscosity of the aqueous solution or the aqueous mixed solution increases, and the spinnability decreases, so it is preferable to adjust the concentration of the aqueous solution or the aqueous mixed solution to a concentration at which spinning is possible using the viscosity as an index.

As a method for producing the acrylamide polymer composition, there can be adopted: a method of directly mixing the additive component with the acrylamide polymer in a molten state (melt mixing), a method of dry-mixing the acrylamide polymer and the additive component (dry mixing), a method of dipping the acrylamide polymer molded into a fibrous form in an aqueous solution or an aqueous mixed solution containing the additive component or a solution in which the acrylamide polymer is not completely dissolved but the additive component is dissolved, or a method of passing the acrylamide polymer molded into a fibrous form through the solution, etc., but when the acrylamide polymer and the additive component to be used are soluble in the aqueous solvent or the aqueous mixed solvent, from the viewpoint of enabling uniform mixing of the acrylamide polymer and the additive component, a method of mixing the acrylamide polymer and the additive component in the aqueous solvent or the aqueous mixed solvent is preferable Method (wet mixing). In addition, as the wet mixing, in the case where the polymerization is performed in the aqueous solvent or the aqueous mixed solvent at the time of synthesizing the acrylamide polymer, a method of mixing the additive components after the polymerization or the like may be employed. The solvent may be removed from the obtained solution to recover the acrylamide polymer composition and use the composition for the production of carbon fibers described later, or the solution may be used as it is for the production of carbon fibers described later without removing the solvent. In the wet mixing, the aqueous solvent is preferably used as the solvent, and more preferably water is used, from the viewpoint that the acrylamide polymer composition can be produced safely at a lower cost. Further, the method for removing the solvent is not particularly limited, and at least one of known methods such as distillation under reduced pressure, reprecipitation, hot air drying, vacuum drying, and freeze drying can be used.

The acrylamide polymer fiber may be used in the form of a single fiber or a fiber bundle. When the acrylamide polymer fiber is used in the form of a fiber bundle, the number of filaments per yarn is not particularly limited, but is preferably 50 to 96000, more preferably 100 to 48000, further preferably 500 to 36000, and particularly preferably 1000 to 24000, from the viewpoints of high productivity and improvement in mechanical properties of the flame-resistant chemical fiber and the carbon fiber. When the average number of filaments per strand exceeds the upper limit, firing unevenness sometimes occurs at the time of the flameproofing treatment.

In addition, in such an acrylamide polymer fiber, a conventionally known oil agent such as a silicone oil agent may be applied from the viewpoint of improvement in bundling property and handling property of the fiber and prevention of adhesion between fibers.

(method for producing flame-retardant fiber)

The method for producing a flameproof fiber of the present invention is a method in which the acrylamide polymer fiber is subjected to a heat treatment (flameproofing treatment) in an oxidizing atmosphere (for example, in air) at a flameproofing temperature in the range of 200 to 500 ℃ while applying a tension of 0.07 to 15mN/tex to the fiber. The acrylamide polymer fiber used in the present invention is not easily decomposed by heat by a flame-resistant treatment, and exhibits a high flame-resistant yield because the structure of the acrylamide polymer is converted into a structure having high heat resistance by the flame-resistant treatment. Furthermore, the obtained flameproofed fiber has a structure having high heat resistance, and therefore exhibits a high carbonization yield. In particular, in the acrylamide polymer fiber containing the additive component, the deamination reaction or dehydration reaction of the acrylamide polymer is promoted by the catalytic action of the acid or salt thereof as the additive component, so that a cyclic structure (imide ring structure) or a structure in which 2 or more rings of multiple rings are continuous is easily formed in the molecule, and the structure of the acrylamide polymer is easily changed to a structure having high heat resistance, and therefore the yield of flame resistance, the yield of carbonization of the flame resistant fiber, and the total yield of flame resistance and carbonization are further increased.

In addition, in the method for producing a flameproofed fiber of the present invention, from the viewpoint of improving the carbonization yield and the total yield of flameproofing and carbonization of the obtained flameproofed fiber, it is preferable to perform the heat treatment (flameproofing treatment) until the side surface of the acrylamide polymer fiber reaches a raman spectrum of 1360cm^-1Nearby peak (D peak) 1590cm^-1The intensity ratio (G/D) of the nearby peak (G peak) is 0.5 or more, or the density of the acrylamide polymer fiber is 1.35 to 1.75G/cm³Further, it is preferable that the heat treatment (flame-proofing treatment) is performed until the G/D is 0.5 or more and the density of the acrylamide polymer fiber is 1.35 to 1.75G/cm³. Thus, a refractory fiber having a higher carbonization yield can be obtained.

Further, in the method for producing a flameproof fiber of the present invention, the tension applied to the acrylamide polymer fiber is 0.07 to 15mN/tex, preferably 0.10 to 12mN/tex, more preferably 0.15 to 10mN/tex, still more preferably 0.20 to 7.5mN/tex, particularly preferably 0.30 to 5.0mN/tex, and most preferably 0.35 to 1.5 mN/tex. When the tension applied to the acrylamide polymer fiber is less than the lower limit, the density of the G/D and the acrylamide polymer fiber is less than a predetermined range, and the carbonization yield of the flame-resistant fiber tends to decrease, while when the tension exceeds the upper limit, the acrylamide polymer fiber may be cut during the flame-resistant treatment. In the present invention, the tension (unit: mN/tex) applied to the acrylamide polymer fiber is a value obtained by dividing the tension (unit: mN) applied to the acrylamide polymer fiber during the flameproofing treatment by the fineness (unit: tex) of the acrylamide polymer fiber in an absolutely dry state, that is, the tension applied to the acrylamide polymer fiber per unit average fineness. The tension applied to the acrylamide polymer fiber can be adjusted by adjusting a load sensor, a spring, a weight, or the like on the outlet side of a heating device such as a flameproofing furnace.

In the method for producing a flame-resistant fiber of the present invention, the flame-resistant treatment is performed at a temperature in the range of 150 to 500 ℃, preferably at a temperature in the range of 200 to 450 ℃, and more preferably at a temperature in the range of 250 to 420 ℃, but is not particularly limited. The treatment for making refractory at such a temperature includes not only the treatment for making refractory at the highest temperature (treatment temperature for making refractory) at the time of the treatment for making refractory described later, but also the treatment for making refractory in a temperature raising process or the like before the treatment temperature for making refractory.

The maximum temperature (the temperature for the flame-resistant treatment) during the flame-resistant treatment is a temperature in the range of 200 to 500 ℃, preferably a temperature in the range of 250 to 500 ℃, further preferably a temperature in the range of 280 to 450 ℃, further preferably a temperature in the range of 290 to 420 ℃, further preferably a temperature in the range of 300 to 400 ℃, particularly preferably a temperature in the range of 305 to 390 ℃, and most preferably a temperature in the range of 310 to 380 ℃. If the temperature of the flame-resistant treatment is lower than the lower limit, the deamination reaction and dehydration reaction of the acrylamide polymer are not promoted, and it is difficult to form a cyclic structure (imide ring structure) in the molecule, so that the heat resistance of the flame-resistant fiber produced tends to be low, and the flame-resistant yield of the acrylamide polymer fiber, the carbonization yield of the flame-resistant fiber, and the total yield of flame-resistant and carbonization tend to be reduced, while the flame-resistant fiber produced tends to be thermally decomposed when the temperature exceeds the upper limit.

Further, in the method for producing a flameproofed fiber of the present invention, if a predetermined tension is applied to the acrylamide polymer fiber at the flameproofing temperature (highest temperature at the time of flameproofing), the predetermined tension may or may not be applied in a temperature raising process or the like before the flameproofing temperature, but from the viewpoint of obtaining a sufficient tension applying effect, the predetermined tension is preferably applied also in the temperature raising process or the like. Further, the tension may be applied from the beginning of the temperature rise process or the like, or may be applied at a half-track stage.

In the method for producing a flame-resistant fiber of the present invention, after the heat treatment is performed while applying a predetermined tension at the flame-resistant treatment temperature (highest temperature at the time of flame-resistant treatment), the heat treatment may be performed while applying a tension other than the predetermined tension or without applying any tension at a temperature higher than the flame-resistant treatment temperature.

The duration of the flame-resistant treatment (the heating time at the maximum temperature) is not particularly limited, and the treatment can be carried out for a long time (for example, longer than 2 hours), but is preferably 1 to 120 minutes, more preferably 2 to 60 minutes, still more preferably 3 to 50 minutes, and particularly preferably 4 to 40 minutes. When the heating time in the refractorization treatment is not less than the lower limit, the carbonization yield can be improved, and when the heating time is within 2 hours, the cost can be reduced.

[ flameproofed fiber ]

The flame-retardant fiber of the present invention is derived from an acrylamide polymer and has a side Raman spectrum of 1590cm^-1The peak in the vicinity (G peak) was found to be 1360cm^-1The intensity ratio (G/D value) of the nearby peak (D peak) is 0.5 or more, or the density is 1.35 to 1.75G/cm³The fibers of (1). In addition, in the flame-resistant fiber of the present invention, the G/D value is preferably 0.5 or more, and the density is preferably 1.35 to 1.75G/cm³。

When the G/D value is less than the lower limit, a structure formed of a carbon six-membered ring is not sufficiently formed on the fiber side surface, which means that a sufficient ring structure is not formed in the fiber center, and therefore, the carbonization yield of the flame-resistant fiber and the total yield of the flame-resistant and carbonization are reduced. The G/D value is preferably 0.5 to 2.0, more preferably 0.6 to 1.5, particularly preferably 0.7 to 1.3, and most preferably 0.8 to 1.0. In order to obtain a flameproofed fiber having a G/D value higher than the upper limit, it is necessary to increase the energy by extending the flameproofing treatment time, and in addition, in the flameproofed fiber having a G/D value higher than the upper limit, the effect of improving the carbonization yield tends to be saturated by increasing the G/D value, so from the viewpoint of productivity, it is preferable that the G/D value is not more than the upper limit. In the method for producing a flameproofed fiber of the present invention, the acrylamide polymer fiber is preferably subjected to the heat treatment (flameproofing treatment) until the G/D value is reached.

When the density of the flame-resistant fiber is less than the lower limit, the heat resistance and structural denseness of the flame-resistant fiber are insufficient, and therefore the carbonization yield, the total yield of flame-resistant and carbonization, and the strength of the carbon fiber are reduced. On the other hand, in order to obtain a flameproofed fiber having a density higher than the upper limit, it is necessary to increase the energy by extending the flameproofing treatment time, and the effect of improving the carbonization yield by increasing the density of the flameproofed fiber tends to be saturated in a flameproofed fiber having a density higher than the upper limit. In addition, the density of the flame-resistant fiber is preferably 1.36 to 1.70g/cm from the viewpoints of the carbonization yield of the flame-resistant fiber, the total yield of flame-resistant and carbonization, the improvement in the strength of the carbon fiber, and the reduction in energy accompanying heating at the time of flame-resistant treatment³Further preferably 1.37 to 1.65g/cm³More preferably 1.39 to 1.60g/cm³Particularly preferably 1.40 to 1.58g/cm³Most preferably 1.44 to 1.55g/cm³. In the method for producing a flameproofed fiber of the present invention, the acrylamide polymer fiber is preferably subjected to the heat treatment (flameproofing treatment) until the density is reached.

The average fiber diameter of the flame-resistant fiber of the present invention is not particularly limited, but is preferably 3nm to 300. mu.m, more preferably 30nm to 150. mu.m, still more preferably 1 to 60 μm, yet more preferably 3 to 20 μm, particularly preferably 4 to 15 μm, and most preferably 5 to 10 μm. If the average fiber diameter of the flame-resistant fibers is less than the lower limit, the transferability of the flame-resistant fiber bundle before and during carbonization is reduced, and the fibers are partially cut, while if it is more than the upper limit, the difference in structure between the vicinity of the surface layer and the vicinity of the center of the fibers during carbonization is large, and therefore the tensile strength and tensile elastic modulus of the obtained carbon fibers tend to be reduced.

In addition, the average fiber diameter of the flameproofed fiber of the present invention is preferably 5% or more smaller than the average fiber diameter of the acrylamide polymer fiber before flameproofing treatment, more preferably 10% or more smaller, even more preferably 15% or more smaller, particularly preferably 20% or more smaller, particularly preferably 25% or more smaller, and most preferably 30% or more smaller, from the viewpoint of improving the carbonization yield of the flameproofed fiber.

Further, the flame-resistant fiber of the present invention preferably has an infrared absorption spectrum of about 1644 to 1653cm^-1And/or about 1560-1595 cm^-1Can observe an infrared absorption peak. At about 1644 to 1653cm^-1The flame-resistant fiber having an infrared absorption peak in the range of (1) is excellent in transferability before and during carbonization treatment. In addition, the thickness is about 1560-1595 cm^-1The flame-resistant fiber having an infrared absorption peak in the range of (1) has high strength, and a carbon fiber obtained from the flame-resistant fiber also has high strength. Furthermore, about 1644 to 1653cm^-1The infrared absorption peak in the range of (1) is an absorption peak of stretching vibration of a carbonyl group derived from acrylamide, and is about 1560 to 1595cm^-1The infrared absorption peak in the range of (b) is an absorption peak derived from a ladder structure composed of 2 or more carbon six-membered rings formed by an intramolecular cyclization reaction at the time of the flame-resistant treatment.

[ method for producing carbon fiber ]

The method for producing a carbon fiber of the present invention is a method for carbonizing the refractory fiber of the present invention, and includes, for example, a step of producing a refractory fiber by the method for producing a refractory fiber of the present invention and a step of carbonizing the refractory fiber.

As a method for carbonizing the refractory fibers, the refractory fibers are subjected to a heat treatment (carbonization treatment) in an inert atmosphere (in an inert gas such as nitrogen, argon, or helium) at a temperature higher than the temperature at the time of the refractory treatment. Thus, the refractory fibers are carbonized to obtain desired carbon fibers. The heating temperature in such carbonization treatment is preferably 500 ℃ or higher, and more preferably 1000 ℃ or higher. The "carbonization treatment" in the present invention may include graphitization by heating at 2000 to 3000 ℃ in an inert gas atmosphere. The upper limit of the heating temperature is preferably 3000 ℃ or lower, more preferably 2500 ℃ or lower. Further, the heating time in the carbonization treatment is not particularly limited, but is preferably 30 seconds to 60 minutes, and more preferably 1 to 30 minutes. In the carbonization treatment, the heat treatment may be performed a plurality of times, for example, a heat treatment (pre-carbonization treatment) may be performed at a temperature lower than 1000 ℃, a heat treatment (carbonization treatment) may be performed at a temperature of 1000 ℃ or higher, and a heat treatment (graphitization treatment) may be performed at a temperature of 2000 ℃ or higher.

The average fiber diameter of the carbon fiber obtained in this way is not particularly limited, but is preferably 3nm to 300 μm, more preferably 30nm to 150 μm, still more preferably 1 to 60 μm, yet more preferably 3 to 20 μm, particularly preferably 4 to 15 μm, and most preferably 5 to 10 μm. If the average fiber diameter of the carbon fibers is less than the lower limit, when a composite material is produced using a resin or the like as a matrix, if the matrix viscosity is high, the resin or the like may not sufficiently impregnate the carbon fiber bundles, and the tensile strength of the composite material may decrease.

The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples. The respective acrylamide polymer powders and the respective acrylamide polymer fibers used in the examples and comparative examples were prepared by the following methods.

Preparation example 1

100 parts by mass of a monomer comprising 75 mol% of Acrylamide (AM) and 25 mol% of Acrylonitrile (AN) and 4.36 parts by mass of tetramethylethylenediamine were dissolved in 566.7 parts by mass of ion-exchanged water, and 3.43 parts by mass of ammonium persulfate was added to the resulting aqueous solution under stirring in a nitrogen atmosphere, followed by heating at 70 ℃ for 150 minutes, then heating to 90 ℃ over 30 minutes, and then heating at 90 ℃ for 1 hour to conduct polymerization (polymerization rate: 87%). The resulting aqueous solution was dropped into methanol to precipitate a copolymer, which was recovered and dried under vacuum at 80 ℃ for 12 hours to obtain a water-soluble powder of AN acrylamide/acrylonitrile copolymer (AM/AN copolymer, AM/AN 80 mol%/20 mol%) as powder (p-1).

Preparation example 2

100 parts by mass of Acrylamide (AM) and 8.78 parts by mass of tetramethylethylenediamine were dissolved in 2912 parts by mass of ion-exchanged water, and 1.95 parts by mass of ammonium persulfate was added to the resulting aqueous solution with stirring in a nitrogen atmosphere, followed by polymerization at 60 ℃ for 3 hours. The obtained aqueous solution was dropped into methanol to precipitate a homopolymer, which was recovered and vacuum-dried at 80 ℃ for 12 hours to obtain a water-soluble polyacrylamide (PAM, AM ═ 100 mol%) powder (p-2).

Production example 1

AN acrylamide polymer fiber (f-1) was produced by dissolving the AM/AN copolymer (AM/AN 80 mol%/20 mol%) powder (p-1) obtained in preparation example 1 in ion-exchanged water and dry-spinning the resulting aqueous solution.

Fineness of < acrylamide Polymer fiber >

100 of the obtained acrylamide polymer fibers (f-1) were collected into a bundle to prepare an acrylamide polymer fiber bundle, and the mass of the fiber bundle was measured to calculate the fineness of the fiber bundle by the following formula:

the fineness [ tex ] of the fiber bundle is the mass [ g ]/fiber length [ m ] x 1000[ m ] of the fiber bundle

The fineness of the single fibers constituting the fiber bundle (the fineness of the acrylamide polymer fiber (f-1)) was determined, and the result was 0.33tex per fiber.

Average fiber diameter of < acrylamide Polymer fiber >

The density of the acrylamide polymer fiber bundle was measured using a dry automatic densitometer ("アキュピック II 1340" manufactured by マイクロメリティックス), and the average fiber diameter of the single fibers constituting the fiber bundle (the average fiber diameter of the acrylamide polymer fiber (f-1)) was determined by the following formula and found to be 18 μm.

D＝{(Dt×4×1000)/(ρ×π×n)}^1/2

[ in the above formula, D represents the average fiber diameter [ μm ] of the single fibers constituting the fiber bundle]And Dt represents the fineness of the fiber bundle [ tex ]]And ρ represents the density of the fiber bundle [ g/cm ]³]N represents a constitutionNumber of single fibers of fiber bundle]。〕

< Density of acrylamide Polymer fiber >

The resulting acrylamide polymer fiber (f-1) was dried under vacuum at 120 ℃ for 2 hours, completely dehydrated to be completely in an oven-dried state, and then left to cool to room temperature under vacuum, immediately thereafter, a dry automatic densitometer (マイクロメリティックス, アキュピック II1340, sample chamber capacity: 1 cm)³) The density of the acrylamide-based polymer fiber (f-1) was measured at room temperature in a helium atmosphere, and as a result, it was 1.26g/cm³。

Production example 2

The AM/AN copolymer (AM/AN 80 mol%/20 mol%) powder (p-1) obtained in preparation example 1 was dissolved in ion-exchanged water, and 3 parts by mass of phosphoric acid per 100 parts by mass of the AM/AN copolymer was added to the obtained aqueous solution to completely dissolve the same. The resulting aqueous solution was dry-spun to produce an acrylamide polymer fiber (f-2). The fineness, average fiber diameter and density of the acrylamide-based polymer fiber (f-2) were determined in the same manner as in production example 1, and as a result, the fineness was 0.38tex per fiber, the average fiber diameter was 19 μm, and the density was 1.26g/cm³。

(production example 3)

AN acrylamide polymer fiber (f-3) was produced in the same manner as in production example 2, except that 3 parts by mass of diammonium phosphate was added instead of phosphoric acid to 100 parts by mass of the AM/AN copolymer. The fineness, average fiber diameter and density of the acrylamide-based polymer fiber (f-3) were determined in the same manner as in production example 1, and as a result, the fineness was 0.46tex per fiber, the average fiber diameter was 21 μm, and the density was 1.26g/cm³。

Production example 4

AN acrylamide polymer fiber (f-4) was produced in the same manner as in production example 1, except that the AM/AN copolymer powder (p-1) obtained in production example 1 was not used, but a PAM (AM ═ 100 mol%) powder (p-2) obtained in production example 2 was dissolved in ion-exchanged water. The fineness, average fiber diameter and density of the acrylamide-based polymer fiber (f-4) were determined in the same manner as in production example 1, and the fineness was 0.40tex per fiber and the average fiber diameter20 μm, density 1.30g/cm³。

(example 1)

600 pieces of the acrylamide polymer fibers (f-1) obtained in production example 1 were bundled to prepare a precursor fiber bundle, which was placed in a heating furnace, heated from 50 ℃ at 10 ℃/min to 150 ℃ in an air atmosphere, and then heated from 150 ℃ at 10 ℃/min to 350 ℃ (the flameproofing temperature (the highest temperature at the time of flameproofing) while applying a tension of 0.2mN/tex to the precursor fiber bundle, and then further subjected to a heat treatment (flameproofing) at 350 ℃ (the flameproofing temperature (the highest temperature at the time of flameproofing) while applying a tension of 0.2 mN/tex) to the precursor fiber bundle, thereby obtaining a flameproofed fiber bundle.

The obtained 4 bundles of the fire-resistant fiber bundles were further bundled to prepare a fire-resistant fiber bundle composed of 2400 fire-resistant fibers, and the fire-resistant fiber bundle was conveyed into a heating furnace and subjected to a heat treatment (carbonization treatment) at 1000 ℃ for 3 minutes in a nitrogen atmosphere to obtain a carbon fiber bundle.

(example 2)

Instead of using the acrylamide polymer fibers (f-1), 350 acrylamide polymer fibers (f-2) obtained in production example 2 were bundled together to prepare a precursor fiber bundle, and a flame-resistant fiber bundle was prepared in the same manner as in example 1 except that a tension of 0.4mN/tex was applied to the precursor fiber bundle during the temperature raising process from 150 ℃ to 350 ℃ (the flame-resistant treatment temperature (highest temperature during flame-resistant treatment)) and the heating treatment at 350 ℃ (the flame-resistant treatment temperature (highest temperature during flame-resistant treatment)). A carbon fiber bundle was produced in the same manner as in example 1, except that the 8 fire-resistant fiber bundles were bundled to produce a fire-resistant fiber bundle consisting of 2800 fire-resistant fibers.

(example 3)

A flame-resistant fiber bundle and a carbon fiber bundle were produced in the same manner as in example 1 except that the acrylamide polymer fiber (f-1) was not used, and 600 pieces of the acrylamide polymer fiber (f-3) obtained in production example 3 were bundled together to produce a precursor fiber bundle, the flame-resistant treatment temperature (the highest temperature at the time of flame-resistant treatment) was set to 320 ℃ and the flame-resistant treatment time (the heating time at the highest temperature) was set to 30 minutes.

(example 4)

A flame-resistant fiber bundle and a carbon fiber bundle were produced in the same manner as in example 1, except that 600 pieces of the acrylamide polymer fibers (f-4) obtained in production example 4 were bundled to produce a precursor fiber bundle instead of using the acrylamide polymer fibers (f-1).

(example 5)

A flame-resistant fiber bundle and a carbon fiber bundle were produced in the same manner as in example 1, except that the flame-resistant treatment temperature (the highest temperature at the time of flame-resistant treatment) was changed to 300 ℃ and the flame-resistant treatment time (the heating time at the highest temperature) was changed to 30 minutes.

(example 6)

A flame-resistant fiber bundle and a carbon fiber bundle were produced in the same manner as in example 1 except that 600 pieces of the acrylamide polymer fibers (f-3) obtained in production example 3 were bundled together to produce a precursor fiber bundle, the flame-resistant treatment temperature (the highest temperature at the time of flame-resistant treatment) was changed to 300 ℃ and the flame-resistant treatment time (the heating time at the highest temperature) was changed to 30 minutes, instead of using the acrylamide polymer fibers (f-1).

(example 7)

A flameproof fiber bundle and a carbon fiber bundle were produced in the same manner as in example 1, except that the tension applied to the precursor fiber bundle was changed to 0.1mN/tex during the temperature raising process from 150 ℃ to 350 ℃ (the flameproofing temperature (the highest temperature during the flameproofing treatment)) and during the heat treatment at 350 ℃ (the flameproofing temperature (the highest temperature during the flameproofing treatment)).

Comparative example 1

A flameproof fiber bundle and a carbon fiber bundle were produced in the same manner as in example 1, except that the tension applied to the precursor fiber bundle was changed to 0.05mN/tex during the temperature raising process from 150 ℃ to 350 ℃ (the flameproofing temperature (the highest temperature during the flameproofing treatment)) and during the heat treatment at 350 ℃ (the flameproofing temperature (the highest temperature during the flameproofing treatment)).

Comparative example 2

A flameproofed fiber bundle and a carbon fiber bundle were produced in the same manner as in example 1, except that no tension was applied to the precursor fiber bundle.

Comparative example 3

The AM/AN copolymer (AM/AN 80 mol%/20 mol%) powder (p-1) obtained in preparation example 1 was placed in a heating furnace, heated from room temperature at 10 ℃/min to 350 ℃ (the temperature for refractoriness treatment (highest temperature at the time of refractoriness treatment)), and then subjected to heat treatment (refractoriness treatment) at 350 ℃ (refractoriness treatment temperature (highest temperature at the time of refractoriness treatment)) for 30 minutes to obtain a refractory powder.

The obtained refractory powder was placed in a heating furnace, heated from room temperature to 1000 ℃ at 20 ℃/min in a nitrogen atmosphere, and then subjected to a heating treatment (carbonization treatment) at 1000 ℃ for 3 minutes to obtain a carbon powder.

Comparative example 4

A refractory powder and a carbon powder were produced in the same manner as in comparative example 3, except that the refractory temperature (the highest temperature during the refractory treatment) was changed to 400 ℃.

Comparative example 5

The AM/AN copolymer (AM/AN 80 mol%/20 mol%) powder (p-1) obtained in preparation example 1 was dissolved in ion-exchanged water so that the AM/AN copolymer concentration was 20 mass%, and 3 parts by mass of diammonium phosphate was added to the obtained aqueous solution to completely dissolve the AM/AN copolymer 100 parts by mass. Water was distilled off from the obtained aqueous solution under reduced pressure, and the precipitated solid content was vacuum-dried and then pulverized to obtain a precursor mixed powder containing AN AM/AN copolymer and diammonium hydrogen phosphate.

A refractory powder and a carbon powder were produced in the same manner as in comparative example 3, except that the precursor mixed powder was used in place of the AM/AN copolymer powder (p-1) and the refractory treatment time (heating time at the maximum temperature) was changed to 10 minutes.

Comparative example 6

A refractory powder and a carbon powder were produced in the same manner as in comparative example 3, except that the refractory temperature (the highest temperature during the refractory treatment) was changed to 300 ℃ and the refractory time (the heating time at the highest temperature) was changed to 10 minutes.

Comparative example 7

A refractory powder and a carbon powder were produced in the same manner as in comparative example 3, except that the refractory temperature (the highest temperature during the refractory treatment) was changed to 300 ℃.

Comparative example 8

A precursor fiber bundle was produced by bundling 600 pieces of the acrylamide polymer fibers (f-4) obtained in production example 4 without using the acrylamide polymer fibers (f-1), and a flameproofed fiber bundle and a carbon fiber bundle were produced in the same manner as in example 1 except that a tension of 0.05mN/tex was applied to the precursor fiber bundle during the temperature raising process from 150 ℃ to 350 ℃ (the flameproofing temperature (highest temperature at the time of flameproofing)) and the heating process at 350 ℃ (the flameproofing temperature (highest temperature at the time of flameproofing)).

Comparative example 9

A flame-resistant fiber bundle and a carbon fiber bundle were produced in the same manner as in example 1 except that 600 acrylamide polymer fibers (f-4) obtained in production example 4 were bundled together without using the acrylamide polymer fiber (f-1), and a flame-resistant treatment temperature (highest temperature at the time of flame-resistant treatment) was set to 300 ℃.

Comparative example 10

A flame-resistant powder and a carbon powder were produced in the same manner as in comparative example 3, except that the PAM (AM ═ 100 mol%) powder (p-2) obtained in preparation example 2 was used instead of the AM/AN copolymer powder (p-1), and the flame-resistant treatment time (heating time at the highest temperature) was changed to 10 minutes.

< average fiber diameter of flame-resistant fiber >

The obtained flame-resistant fiber bundle was observed with a microscope (product "デジタルマイクロスコープ VHX-1000" manufactured by キーエンス K.K.), and fiber diameter measurement points of the individual fibers at 10 positions were arbitrarily selected, and the fiber diameters of the flame-resistant individual fibers constituting the flame-resistant fiber bundle were measured to determine the average value (average fiber diameter of the flame-resistant fibers). The results are shown in table 1.

[ Raman Spectroscopy of flameproofed fibers (or flameproofed powders) ]

The raman spectrum of the side surface (or the surface of the flameproofed powder) of the obtained flameproofed fiber bundle was measured at room temperature using a laser raman spectroscopy apparatus ("NSR-3300" manufactured by japan spectrographic corporation). The G peak (1590 cm) derived from the in-plane vibration of carbon atoms in the obtained Raman spectrum was obtained^-1Nearby peak) and D peak from defect (1360 cm)^-1Nearby peaks) intensity ratio (G/D) (height ratio from baseline to peak top). The results are shown in table 1.

< Density of flameproofed fiber (or flameproofed powder) >

The obtained flameproofed fiber bundle (or flameproofed powder) was dried under vacuum at 120 ℃ for 2 hours to completely remove water until it became an absolutely dry state, and then left to cool to room temperature under vacuum, immediately thereafter, a dry automatic densitometer (マイクロメリティックス, "アキュピック II 1340", available from K.K.: 1 cm) was used³) The density of the flameproofed fiber (or flameproofed powder) was measured at room temperature in a helium atmosphere. The results are shown in table 1.

< average fiber diameter of carbon fiber >

The obtained carbon fiber bundle was observed using マイクロスコープ ("デジタルマイクロスコープ VHX-1000" manufactured by キーエンス), and the fiber diameters of the single fibers at 10 positions were arbitrarily selected as measurement points, and the fiber diameters of the carbon fibers constituting the carbon fiber bundle were measured to determine the average value (average fiber diameter of the carbon fibers). The results are shown in table 1.

< yield of refractoriness >

The yield of the flame resistance was determined by the following formula

Yield of flame resistance [% ], mass of flame resistant fiber bundle (or flame resistant powder) [ mg ]/mass of precursor fiber bundle (or precursor powder) before flame resistance treatment [ mg ] × 100

The results are shown in table 1.

< carbonization yield >

The carbonization yield was determined by the following formula:

carbonization yield [% ], mass [ mg ] of carbon fiber bundle (or carbon powder)/mass [ mg ] of flame-resistant fiber bundle (or flame-resistant powder) before carbonization treatment × 100

The results are shown in table 1.

< Total yield of flame resistance and carbonization >

The total yield of the flame-resistant and carbonized products was determined by the following formula

Total yield [% ] is (yield of refractoriness/100) × (yield of carbonization/100) × 100

The results are shown in table 1.

As shown in table 1, in the cases (examples 1 to 7) in which the acrylamide polymer fibers were subjected to the flame-resistant treatment while being subjected to the predetermined tension, the peak intensity ratio (G/D) in the raman spectrum was large, and the density of the flame-resistant fibers was high, and the carbonization yield and the total yield of the flame-resistant and carbonization were improved, as compared with the cases (comparative examples 1 and 8) in which the flame-resistant treatment was performed under the applied tension less than the predetermined tension, the cases (comparative examples 2 and 9) in which the flame-resistant treatment was performed without applying tension, and the cases (comparative examples 3 to 7 and 10) in which the flame-resistant treatment was performed on the acrylamide polymer fibers.

Specifically, as is clear from the comparison between examples 1 and 7 and comparative examples 1 to 2 and the comparison between example 4 and comparative example 8, even when the flame-resistant treatment is performed at the same temperature and time, the peak intensity ratio (G/D) in the raman spectrum is higher in the case where a predetermined tension is applied (examples 1 and 7 and 4) and the carbonization yield and the total yield of flame-resistant and carbonization are improved, compared with the case where a tension is applied (comparative examples 1 and 8) and the case where no tension is applied (comparative example 2). It is clear from the comparison between example 1 and example 7 that the peak intensity ratio (G/D) in the raman spectrum is higher as the applied tension is higher, and that the higher the density of the flame-resistant fiber is, the higher the carbonization yield and the total yield of the flame-resistant and carbonization are.

Further, as is clear from a comparison between example 1 and example 2, even when the flame-resistant treatment is performed at the same temperature and for the same time, the acrylamide polymer fiber is produced by adding phosphoric acid to the acrylamide polymer, and the tension applied to the acrylamide polymer fiber is increased, so that the peak intensity ratio (G/D) in the raman spectrum is increased, and the density of the flame-resistant fiber is increased, whereby the carbonization yield and the total yield of flame-resistant and carbonization are improved.

Further, as is clear from a comparison between example 1 and example 5, even when the same tension is applied, the higher the temperature of the flame-resistant treatment (the highest temperature at the time of the flame-resistant treatment), the higher the peak intensity ratio (G/D) in the raman spectrum, and the higher the density of the flame-resistant fibers, the higher the carbonization yield and the total yield of flame-resistant and carbonization. Further, as is clear from a comparison between example 3 and example 6, even in the case of using an acrylamide polymer fiber produced by adding phosphate to an acrylamide polymer, when the same tension is applied, the higher the temperature of the flame-retardant treatment (the highest temperature at the time of the flame-retardant treatment), the higher the peak intensity ratio (G/D) in the raman spectrum, and the higher the density of the flame-retardant fiber, the higher the carbonization yield and the total yield of flame-retardant and carbonization.

As described above, the present invention can provide a flame-resistant fiber derived from an acrylamide polymer and having a high carbonization yield. Further, by subjecting the refractory fibers to carbonization treatment, carbon fibers can be produced with high yield. In addition, since the carbon fiber is excellent in various properties such as lightweight property, strength, elastic modulus, corrosion resistance, etc., it can be widely used for various applications such as materials for aviation, materials for space, materials for automobiles, pressure vessels, materials for civil engineering and construction, materials for robots, materials for communication equipment, materials for medical use, electronic materials, wearable materials, windmills, golf clubs, and sporting goods such as fishing rods.

The flameproof fiber of the present invention is excellent in heat resistance and flame retardancy, and therefore can be used as an intermediate material for carbon fibers, as well as a flameproof heat insulating material, a sputtering sheet, various filters, and the like.