JP2023064697A - Carbon fiber precursor fiber, fiber for carbon fiber precursor fiber, method of producing carbon fiber precursor fiber, method of producing flame-resistant fiber, and method of producing carbon fiber - Google Patents

Abstract

To provide a carbon fiber precursor fiber capable of suppressing fusion between single fibers in flame-resistant treatment, while maintaining a high carbonization yield.SOLUTION: A carbon fiber precursor fiber of the disclosure includes an acrylamide-based polymer fiber, and a self-crosslinked product of a self-crosslinking silicone oil on a surface of the acrylamide-based polymer fiber.SELECTED DRAWING: None

Description

The present disclosure relates to carbon fiber precursor fibers, fibers for carbon fiber precursor fibers, methods for producing carbon fiber precursor fibers, methods for producing flame-resistant fibers, and methods for producing carbon fibers.

Carbon fiber has attracted attention as a material to replace metal materials because of its properties such as light weight, excellent mechanical strength, and resistance to corrosion.
As a method for producing carbon fibers, chemical fibers obtained by spinning polyacrylonitrile are applied with a silicone-based oil agent, heat-treated to obtain carbon fiber precursor fibers, and hundreds of carbon fiber precursor fibers that are single fibers are obtained. A method is known in which tens of thousands of fiber bundles are bundled together from a fiber bundle and then subjected to a flameproofing treatment and then a carbonization treatment (for example, Patent Documents 1 and 2). Patent Documents 1 and 2 specifically describe, as silicone-based oils, silicone oils prepared by diluting an oil containing amino-modified silicone, epoxy-modified silicone, ethylene oxide-modified silicone, and an emulsifier with water. ing.

On the other hand, an acrylamide-based polymer containing an acrylamide-based monomer is a water-soluble polymer, and when performing polymerization, spinning, etc., it is inexpensive and can use water, which has a low environmental impact, as a solvent. A reduction in fiber manufacturing costs is expected.

JP 2006-183159 A Japanese Patent Application Laid-Open No. 2008-202208 JP 2018-90791 A JP 2019-26827 A

However, when a fiber bundle of carbon fiber precursor fibers obtained by applying a conventional silicone oil agent to single fibers of acrylamide polymer is subjected to a flameproofing treatment, the surface of the carbon fiber precursor fibers is softened and the carbon fiber precursor fibers ( There is a risk that a flame-resistant fiber in which single fibers are fused together may be obtained. If such a flameproof fiber is subjected to a carbonization treatment, the parts where the carbon fiber precursor fibers are fused together may burn and cause defects, and the resulting carbon fiber may have reduced mechanical properties. Therefore, there is a demand for a carbon fiber precursor fiber that can suppress the fusion between single fibers in the flameproofing treatment.
Furthermore, from the viewpoint of reducing the manufacturing cost of carbon fibers, there is a demand for carbon fiber precursor fibers capable of achieving a high carbonization yield.
The carbonization yield indicates the percentage of the value obtained by dividing the mass of the carbon fiber by the mass of the flameproof fiber.

A problem to be solved by an embodiment of the present disclosure is a carbon fiber precursor fiber that can suppress fusion between single fibers in a flameproofing treatment while maintaining a high carbonization yield, and a carbon fiber precursor fiber. The object of the present invention is to provide a fiber for carbon fiber, a method for producing a carbon fiber precursor fiber, a method for producing a flameproof fiber, and a method for producing a carbon fiber.

In order to solve the above problems, the inventors of the present invention conducted intensive studies and found that a fiber bundle of carbon fiber precursor fibers composed of monofilaments of acrylamide-based polymer to which a conventional silicone-based oil was applied was subjected to a flame-resistant treatment. If applied, the surfaces of the carbon fiber precursor fibers may be softened, causing fusion between the carbon fiber precursor fibers. In order to suppress this, a self-crosslinking silicone oil is applied to the surface of the single fiber, and the silicone oil is crosslinked (hardened). The inventors have found that the fusion can be suppressed, and have completed the present disclosure.

Specific means for achieving the objectives are as follows.
<1> A carbon fiber precursor fiber comprising an acrylamide-based polymer fiber and a self-crosslinked product of a self-crosslinkable silicone oil present on the surface of the acrylamide-based polymer fiber.
<2> The carbon fiber precursor fiber according to <1>, wherein the content of the self-crosslinked product is 0.1 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the acrylamide polymer fiber.
<3> The acrylamide-based polymer fiber is made of an acrylamide-based polymer,
The carbon fiber precursor fiber of <1> or <2> above, wherein the acrylamide-based polymer contains 30 mol % or more of acrylamide-based monomer units with respect to all monomer units constituting the acrylamide-based polymer.
<4> The acrylamide-based polymer contains 40 mol% or more and 99.8 mol% or less of acrylamide-based monomer units and 0.1 mol% or more and 50 mol% or less of all monomer units constituting the acrylamide-based polymer. and 0.1 mol % or more and 30 mol % or less of unsaturated carboxylic acid monomer units.
<5> The carbon fiber precursor fiber according to any one of <1> to <4>, wherein the self-crosslinking silicone oil has an acrylic group or a methacrylic group.
<6> The carbon fiber precursor fiber according to any one of <1> to <5>, wherein the self-crosslinking silicone oil has a viscosity of 9 mm ² /s or more at 25°C.
<7> A fiber for carbon fiber precursor fiber, comprising an acrylamide-based polymer fiber and an uncrosslinked product of self-crosslinking silicone oil present on the surface of the acrylamide-based polymer fiber. <8> A method for producing a carbon fiber precursor fiber, comprising a step of subjecting the fiber for carbon fiber precursor fiber according to <7> to a cross-linking treatment.
<9> The method for producing a carbon fiber precursor fiber according to <8>, wherein the cross-linking treatment is an electron beam treatment.
<10> A method for producing a flame-resistant fiber, comprising a step of subjecting the carbon fiber precursor fiber according to any one of <1> to <6> to a flame-resistant treatment.
<11> A step of obtaining a flame-resistant fiber by the method for producing a flame-resistant fiber according to <10>;
a step of carbonizing the flame-resistant fiber;
A method of manufacturing carbon fiber, comprising:

According to the present disclosure, a carbon fiber precursor fiber, a fiber for a carbon fiber precursor fiber, and a carbon fiber precursor fiber capable of suppressing fusion between single fibers in a flameproofing treatment while maintaining a high carbonization yield , a method for producing a flame-resistant fiber, and a method for producing a carbon fiber.

In the present disclosure, the numerical range indicated using "-" includes the numerical values before and after "-" as the minimum and maximum values, respectively.
In the numerical ranges described step by step in the present disclosure, the upper limit or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described step by step. . In the numerical ranges described in this disclosure, the upper or lower limits of the numerical ranges may be replaced with the values given in the synthetic examples.

The term "step" in this specification includes not only independent steps, but also if the intended purpose of the step is achieved, even if it cannot be clearly distinguished from other steps. .

In the present disclosure, each component may contain multiple types of applicable substances. If there are multiple types of substances corresponding to each component in the carbon fiber precursor fiber, the content rate or content of each component is the amount of the multiple types of substances that exist in the carbon fiber precursor fiber, unless otherwise specified. It means the total content rate or content.

(1) Carbon Fiber Precursor Fiber The carbon fiber precursor fiber of the present disclosure includes an acrylamide-based polymer fiber and a self-crosslinked product of self-crosslinking silicone oil present on the surface of the acrylamide-based polymer fiber.

In the present disclosure, the term “carbon fiber precursor fiber” refers to fibers for carbon fiber production that have undergone cross-linking treatment and have not been subjected to either flameproofing treatment or carbonization treatment.

In the present disclosure, "acrylamide-based polymer fiber" refers to a single fiber made of an acrylamide-based polymer composition. The acrylamide-based polymer composition contains an acrylamide-based polymer and, if necessary, may contain additional components described later.

In the present disclosure, "acrylamide-based polymer" means a homopolymer of an acrylamide-based monomer or a copolymer of an acrylamide-based monomer and a monomer other than an acrylamide-based monomer (hereinafter referred to as another polymerizable monomer).

In the present disclosure, "self-crosslinking silicone oil" refers to silicone oil having self-crosslinking groups. Specifically, "self-crosslinking silicone oil" has a structure in which polysiloxane is the basic structure, and at least part of the side chains and terminal substituents of polysiloxane are substituted with self-crosslinking groups. A self-crosslinking group refers to a functional group capable of forming a crosslinked structure within a molecule by itself by an external stimulus such as an electron beam, ultraviolet rays, or heat, without the presence of other components. Polysiloxanes include polydimethylsiloxane, polymethylphenylsiloxane, polydiphenylsiloxane, polymethylhydrogensiloxane, and mixtures thereof. Substituents will be described later.
In the present disclosure, the term “self-crosslinked product of self-crosslinkable silicone oil” refers to a compound in which the self-crosslinkable groups of the self-crosslinkable silicone oil undergo an intramolecular crosslinking reaction to form a crosslinked structure. The presence of a crosslinked structure can be confirmed by the presence or absence of dissolution when the self-crosslinked product of the self-crosslinkable silicone oil after the self-crosslinking of the self-crosslinkable silicone oil coated with the acrylamide polymer is immersed in tetrahydrofuran. . That is, when dissolved, the compound is distinguished as not having a crosslinked structure.

In the present disclosure, "having it on a surface" may mean being attached to a surface. "Adhesion" means that the self-crosslinking product of the self-crosslinking silicone oil is present on the surface of the acrylamide polymer fiber, in a bonding state such as a covalent bond or an ionic bond, or a state in which they are attracted to each other by van der Waals forces. Either In addition, the self-crosslinked product of the self-crosslinkable silicone oil may be present inside the acrylamide-based polymer fiber.

Since the carbon fiber precursor fiber of the present disclosure has the above configuration, it is possible to suppress fusion between single fibers in the flameproofing treatment while maintaining a high carbonization yield.

The reason why the above effect is exhibited is presumed as follows, but is not limited thereto.
When the self-crosslinking silicone oil self-crosslinks, a highly heat-resistant self-crosslinking product (film) is formed on the surface of the acrylamide polymer fiber. It is presumed that this makes it difficult for the single fibers to fuse with each other in the flameproofing treatment.
In addition, the self-crosslinking product includes a chemical structure to which the self-crosslinking group is bonded, and the chemical structure to which the self-crosslinking group is bonded is similar to the chemical structure of the carbon fiber precursor fiber. Therefore, the self-crosslinking product does not suppress the permeation of oxidizing gas during the flameproofing treatment, and hardly inhibits the progress of the flameproofing reaction (cyclization, partial oxidation). Furthermore, since fusion bonding between carbon fiber precursor fibers is suppressed, heat and oxidizing gas (oxidation) are easily transmitted to the inside of each carbon fiber precursor fiber during the flameproofing treatment. As a result, flameproofing reactions (cyclization, partial oxidation) tend to proceed. As a result, the carbonization yield is presumed to be high.
As described above, the carbon fiber precursor fiber of the present disclosure can suppress fusion between single fibers in the flameproofing treatment while maintaining a high carbonization yield. Therefore, the carbon fiber precursor fibers of the present disclosure can reduce the manufacturing cost of carbon fibers, and high-quality carbon fibers can be obtained from the carbon fiber precursor fibers of the present disclosure.

On the other hand, when a combination of a conventional silicone oil agent having an amino group and a silicone oil agent having an epoxy group is crosslinked, the resulting crosslinked product contains at least one of a hydroxyl group and an amino group. Therefore, conventional crosslinked products are highly likely to inhibit the permeation of oxygen. As a result, the progress of the flameproofing reaction becomes insufficient, and the carbonization yield is often low.
Conventional silicone-based oils are used to suppress fusion between single fibers of polyacrylonitrile fibers or flame-resistant fibers derived from polyacrylonitrile fibers, and are heat-treated at high temperatures to promote cross-linking reactions. Therefore, as conventional silicone oils, amino group-modified silicone oils or mixtures of two or more types of silicone oils such as amino group-modified silicone oils are used. However, even if a conventional silicone-based oil agent is directly applied to polyacrylamide fibers or polyacrylamide-based flame-resistant fibers, the effect of suppressing the fusion of single fibers is low. On the other hand, since the carbon fiber precursor resistant fiber of the present disclosure includes a self-crosslinking product of self-crosslinking silicone oil, fusion between single fibers can be suppressed in the flameproofing treatment.
In addition, since conventional polyacrylonitrile fibers are lipophilic, conventional silicone oils must be dispersed in an aqueous solution and applied to the polyacrylonitrile fibers. For that purpose, it was essential to adjust the viscosity of the silicone fluid using a surfactant. On the other hand, since the acrylamide-based polymer fiber in the present disclosure is water-soluble, it is not essential to adjust the viscosity of the self-crosslinking silicone oil using a surfactant. It is preferable not to adjust the viscosity of the self-crosslinking silicone oil because the surfactant tends to become a foreign matter and remain in the carbon fiber precursor-resistant fiber, leading to deterioration of the mechanical properties.

(1.1) Fineness of carbon fiber precursor fiber, etc. (1.1.1) Fineness The fineness of carbon fiber precursor fiber is not particularly limited, but is 1×10 ⁻⁸ tex/fiber to 100 tex/fiber. It is preferably a book, more preferably 1×10 ⁻⁶ tex/book to 60 tex/book, further preferably 1×10 ⁻³ tex/book to 40 tex/book, and 1×10 ⁻² tex/book to 10 tex/book is particularly preferred, 2×10 ⁻² tex/book to 5 tex/book is even more preferred, and 3×10 ⁻² tex/book to 1 tex/book is preferred. Most preferred.
By setting the fineness of the carbon fiber precursor fiber to 1×10 ⁻⁸ tex/fiber or more, the occurrence of yarn breakage is suppressed, thereby facilitating winding of the carbon fiber precursor fiber and stabilizing the flameproof treatment. tend to be able to improve
By setting the fineness of the carbon fiber precursor fiber to 100 tex/fiber or less, it is possible to reduce the difference in structure between the structure near the surface of the carbon fiber obtained by the flameproofing treatment and the structure near the center. Tensile strength and tensile modulus tend to be improved.

In the present disclosure, the fineness of a single fiber (tex/fiber) is measured by bundling 100 carbon fiber precursor fibers to prepare a fiber bundle, measuring the mass of this fiber bundle, and measuring the single fiber by the following formula. Find fineness.
Single fiber fineness (tex) = fiber bundle mass (g)/fiber length (m) x 1000/100 (fibers)

(1.1.2) Average Fiber Diameter The average fiber diameter of the carbon fiber precursor fiber is not particularly limited, but is preferably 3 nm to 300 μm, more preferably 30 nm to 250 μm, and 1 μm. It is more preferably ˜200 μm, particularly preferably 3 μm to 100 μm, even more preferably 4 μm to 50 μm, and most preferably 5 μm to 30 μm.
By setting the average fiber diameter of the carbon fiber precursor fiber to 3 nm or more, there is a tendency that the stability of the flameproofing treatment can be improved. By setting the average fiber diameter of the carbon fiber precursor fiber to 3 nm or more, it is possible to suppress the occurrence of thread breakage, thereby improving the ease of winding the carbon fiber precursor fiber and the stability of the flameproofing treatment. tend to be able to
By setting the average fiber diameter of the carbon fiber precursor fiber to 300 μm or less, the difference between the structure near the surface layer of the carbon fiber obtained by the flameproofing treatment and the structure near the center can be reduced, and the tensile strength of the carbon fiber can be reduced. It tends to be able to improve strength and tensile modulus.

In the present disclosure, the average fiber diameter is obtained by bundling 100 carbon fiber precursor fibers to prepare a fiber bundle, measuring the density of the fiber bundle using a dry automatic densitometer, and calculating the average fiber diameter by the following formula. Find the average fiber diameter of As the dry automatic density meter, Accupic II 1340 manufactured by Micromeritics Co. or a similar device can be used.
D={(Dt×4×1000)/(ρ×π×n)} ^1/2
[In the formula,
D represents the average fiber diameter (μm) of the single fibers that make up the fiber bundle,
Dt represents the fineness (tex) of the fiber bundle,
ρ represents the density of the fiber bundle (g/cm ³ ),
n represents the number (number) of single fibers constituting the fiber bundle.
Note that π is 3.14. ]

The carbon fiber precursor fibers may be in the form of fiber bundles (hereinafter referred to as "carbon fiber precursor fiber bundles"), and the carbon fiber precursor fiber bundles are preferably subjected to a flameproofing treatment. . A carbon fiber precursor fiber bundle is obtained by bundling a plurality of carbon fiber precursor fibers into one.
In the carbon fiber precursor fiber bundle, the number of filaments per bundle is not particularly limited, but is preferably 50 to 96,000 from the viewpoint of the productivity and mechanical properties of the flame-resistant fiber and carbon fiber. It is preferably 100 to 48,000, even more preferably 500 to 36,000, and particularly preferably 1,000 to 24,000.
By setting the number of filaments per bundle to 96,000 or less, it is possible to suppress the occurrence of uneven firing during the flameproofing treatment.

(1.2) Self-Crosslinked Material The carbon fiber precursor fiber of the present disclosure includes a self-crosslinked material of self-crosslinkable silicone oil. The self-crosslinked product is present on the surface of the acrylamide-based polymer fiber.
As a result, the bundling property and handling of the fibers can be improved, and fusion between the single fibers can be suppressed in the flameproofing treatment.

The self-crosslinking product of the self-crosslinking silicone oil only needs to be present on at least a part of the surface of the acrylamide polymer fiber. From the viewpoint of making the carbon fiber precursor fiber more restrained, etc., it is preferable that the surface of the acrylamide-based polymer fiber is adhered as a coating to the entire surface.

The content of the self-crosslinked product is not particularly limited, and is preferably 0.1 to 20 parts by mass, more preferably 0.2 to 15 parts by mass, relative to 100 parts by mass of the acrylamide polymer fiber. It is more preferably 0.3 parts by mass to 10 parts by mass.
By setting the content of the self-crosslinking material to 0.1 parts by mass or more, the self-crosslinking material of the silicone oil can exhibit the effect of suppressing the fusion between single fibers.
By setting the content of the self-crosslinking material to 20 parts by mass or less, it is possible to suppress the cross-linking of the silicone oil between the carbon fiber precursor fibers and the fusion between the single fibers.
The content of the self-crosslinked product can be measured by thermogravimetric analysis, elemental analysis, or the like. In thermogravimetric analysis, the self-crosslinking product content can be measured from the amount of weight loss.

(1.2.1) Self-crosslinking silicone oil Self-crosslinking silicone oil contains a self-crosslinking group. A self-crosslinkable group refers to a group that generates radicals upon an external stimulus. In the present invention, the external stimulus is preferably an electron beam, ultraviolet rays, heat, or the like, more preferably an electron beam. Specifically, the self-crosslinkable group preferably contains at least one monosubstituted ethylene group, 1,1-disubstituted ethylene group, or 1,2-disubstituted ethylene group.
The monosubstituted ethylene group includes, for example, vinyl group, vinylcarbonyl group, vinyl ester group, acryl group, acrylamide group, allyl group, allyl ether group, 4-vinylbenzene group, 4-allylbenzene group and the like.
The 1,1-disubstituted ethylene group includes, for example, an isopropenyl group, a methacryl group, a methacrylamide group, a 4-isopropenylbenzene group and the like.
The 1,2-disubstituted ethylene group includes, for example, a maleimide group, a fumarate ester group, a fumaramido group, and the like.
Among these self-crosslinkable groups, the self-crosslinkable group is preferably an acryl group, a methacryl group, an acrylamide group, or a methacrylamide group from the viewpoint of affinity with the acrylamide polymer, and from the viewpoint of polymerizability. Therefore, it is more preferably an acrylic group or a methacrylic group.

The self-crosslinking silicone oil may have a structure in which at least part of the side chains and terminal substituents of polysiloxane are substituted with self-crosslinking groups. Examples of substituents include alkyl groups such as methyl group, ethyl group and propyl group, and aryl groups such as phenyl group and methylphenyl group. Among these, the substituent is more preferably a methyl group or a phenyl group, and more preferably a methyl group.

A commercial product may be sufficient as a self-crosslinking silicone oil.

The viscosity of the self-crosslinking silicone oil at 25°C is not particularly limited.
The lower limit of the viscosity of the self-crosslinking silicone oil at 25° C. is preferably 9 mm ² /s or more, more preferably 20 mm ² /s or more, from the viewpoint of efficient progress of the crosslinking reaction without volatilization during the crosslinking treatment. is more preferred.
The upper limit of the viscosity of the self-crosslinking silicone oil at 25° C. is preferably 100000 mm ² /s or less from the viewpoint of attaching the self-crosslinking silicone oil to the surface of the acrylamide polymer fiber with a more uniform film thickness, and is preferably 10000 mm. It is more preferably ² /s or less.
The viscosity of the self-crosslinking silicone oil at 25°C is the value at 25°C measured by an Ubbelohde viscometer. If the self-crosslinking silicone oil is a commercial product and the catalog value is used, the viscosity of the self-crosslinking silicone oil at 25°C is the manufacturer's catalog value.

Examples of self-crosslinking silicone oils include Shin-Etsu Chemical Co., Ltd. products and SILTECH products. The products of Shin-Etsu Chemical Co., Ltd. include "X-22-164C", "X-22-164", "X-22-164AS", "X-22-164A", "X-22-164B", " X-22-164E", "X-22-2445", "X-22-174ASX", "X-22-174BX", "KF-2012", "X-22-2426", "X-22- 2404” and the like. The products of SILTECH include "Silmer ACR D2", "Silmer ACR Di-10", "Silmer ACR Di-50", "Silmer ACR Di-400", "Silmer ACR Di-1508", "Silmer OH ACR Di -10", "Silmer OH ACR Di-50", "Silmer OH ACR Di-100", "Silmer OH ACR Di-400", "Silmer OH ACR C50", "Silmer OH ACR C7-F", "Silmer VIN C50", "Silmer VIN J10", "Silmer VIN 70", "Silmer VIN 100", "Silmer VIN 200", "Silmer VIN 1000" and the like.

(1.3) Acrylamide-Based Polymer Fiber The carbon fiber precursor fiber of the present disclosure includes acrylamide-based polymer fiber, and may include two or more types of acrylamide-based polymer fiber.

The acrylamide-based polymer fiber is preferably formed using an acrylamide-based polymer composition. The resin component of the acrylamide-based polymer composition contains an acrylamide-based polymer.

(1.3.1) Acrylamide-based polymer The acrylamide-based polymer may be a homopolymer of an acrylamide-based monomer. may be a copolymer of
The acrylamide-based polymer is preferably a copolymer of an acrylamide-based monomer and another polymerizable monomer from the viewpoints of fusion suppression, carbonization yield, shape stability, tensile strength of the flame-resistant fiber, and the like.

(1.3.1.1) Acrylamide-based Monomer Units The content of acrylamide-based monomer units in the acrylamide-based polymer is preferably 30 mol% or more with respect to the total monomer units constituting the copolymer. It is more preferably at least 50 mol %, even more preferably at least 50 mol %, particularly preferably at least 55 mol %, and most preferably at least 60 mol %.
When the acrylamide-based monomer unit content is 30 mol % or more, the solubility of the acrylamide-based polymer before cross-linking in an aqueous solvent or an aqueous mixed solvent tends to be improved.
The upper limit of the content of acrylamide-based monomer units is not particularly limited, but from the viewpoint of fusion suppression, carbonization yield and shape stability, it is preferably 99.9 mol% or less. It is more preferably 8 mol % or less, still more preferably 95 mol % or less, particularly preferably 90 mol % or less, and most preferably 85 mol % or less.

Acrylamide-based monomers include acrylamide; ethacrylamide; crotonamide; itaconic acid diamide; cinnamic acid amide; maleic acid diamide; N-alkylacrylamides such as n-butylacrylamide and N-tert-butylacrylamide; N-cycloalkylacrylamides such as N-cyclohexylacrylamide; dialkylacrylamides such as N,N'-dimethylacrylamide; dimethylaminoethylacrylamide and dimethylaminopropyl dialkylaminoalkylacrylamides such as acrylamide; hydroxyalkylacrylamides such as N-(hydroxymethyl)acrylamide and N-(hydroxyethyl)acrylamide; N-arylacrylamides such as N-phenylacrylamide; diacetone acrylamide; N,N'-methylene N,N'-alkylenebisacrylamide such as bisacrylamide; methacrylamide; N-methylmethacrylamide, N-ethylmethacrylamide, Nn-propylmethacrylamide, N-isopropylmethacrylamide, Nn-butylmethacrylamide, N-alkyl methacrylamides such as N-tert-butyl methacrylamide; N-cycloalkyl methacrylamides such as N-cyclohexyl methacrylamide; dialkyl methacrylamides such as N,N'-dimethyl methacrylamide; dimethylaminoethyl methacrylamide, dimethyl dialkylaminoalkyl methacrylamides such as aminopropyl methacrylamide; hydroxyalkyl methacrylamides such as N-(hydroxymethyl) methacrylamide and N-(hydroxyethyl) methacrylamide; N-aryl methacrylamides such as N-phenyl methacrylamide; acetone methacrylamide; and N,N'-alkylenebismethacrylamide such as N,N'-methylenebismethacrylamide.
Among the acrylamide-based monomers described above, acrylamide, N-alkylacrylamide, dialkylacrylamide, methacrylamide, N-alkylmethacrylamide or dialkylmethacrylamide is preferable from the viewpoint of the solubility of the acrylamide-based polymer in an aqueous solvent or an aqueous mixed solvent. Acrylamide is more preferred.
Acrylamide-based monomers may be used alone or in combination of two or more.

(1.3.1.2) Units of Other Polymerizable Monomers When the acrylamide-based polymer is a copolymer of an acrylamide-based monomer and another polymerizable monomer, the copolymer contains other polymerizable monomer units. The amount is preferably 0.1 mol % or more, preferably 1 mol % or more, based on the total monomer units constituting the copolymer, from the viewpoints of fusion inhibition, carbonization yield and shape stability. 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 solubility of the acrylamide-based polymer in an aqueous solvent or an aqueous mixed solvent, the upper limit of the content of other polymerizable monomer units is preferably 70 mol% or less, more preferably 60 mol% or less. It is more preferably 50 mol % or less, particularly preferably 45 mol % or less, and most preferably 40 mol % or less.

Other polymerizable monomers include vinyl cyanide-based monomers, unsaturated carboxylic acids and salts thereof, unsaturated carboxylic acid anhydrides, unsaturated carboxylic acid esters, vinyl alcohol-based monomers, vinyl carboxylate-based monomers, and olefin-based monomers. are mentioned.

Vinyl cyanide monomers include acrylonitrile, methacrylonitrile, 2-hydroxyethyl acrylonitrile, chloroacrylonitrile, chloromethyl acrylonitrile, ethoxyacrylonitrile, vinylidene cyanide and the like.
Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, crotonic acid, and isocrotonic acid.
Salts of unsaturated carboxylic acids include metal salts of unsaturated carboxylic acids (eg, sodium salts, potassium salts, etc.), ammonium salts, amine salts, and the like.

Examples of unsaturated carboxylic anhydrides include maleic anhydride and itaconic anhydride.
Examples of unsaturated carboxylic acid esters include methyl acrylate, methyl methacrylate, 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate.
Examples of vinyl-based monomers include aromatic vinyl-based monomers such as styrene and α-methylstyrene, vinyl chloride, and vinyl alcohol.
Examples of olefinic monomers include ethylene, propylene, isopropylene, and butadiene.

Among the other polymerizable monomers described above, vinyl cyanide monomers are preferable from the viewpoint of the spinnability, anti-fusing properties, carbonization yield and shape stability of the acrylamide-based polymer. It is preferably acrylonitrile, more preferably acrylonitrile.
Among the other polymerizable monomers described above, from the viewpoint of the solubility of the copolymer in an aqueous solvent or an aqueous mixed solvent before crosslinking, the other polymerizable monomers are unsaturated carboxylic acids and salts thereof. Preferred are acrylic acid, maleic acid, fumaric acid and itaconic acid.
Among the other polymerizable monomers described above, the other polymerizable monomer is preferably an unsaturated carboxylic acid or an unsaturated carboxylic acid anhydride, from the viewpoint of the fusion suppression property, carbonization yield and shape stability. , acrylic acid, maleic acid, fumaric acid, itaconic acid or maleic anhydride.
The above other polymerizable monomers may be used alone or in combination of two or more.

From the viewpoint of the solubility, spinnability, anti-fusing properties, carbonization yield and shape stability of the copolymer in an aqueous solvent or aqueous mixed solvent, the acrylamide-based polymer contains an acrylamide-based monomer and a vinyl cyanide-based monomer. , an unsaturated carboxylic acid, and most preferably a copolymer of acrylamide, acrylonitrile and acrylic acid.
From the standpoints of spinnability, anti-fusing properties, carbonization yield and shape stability, the vinyl cyanide-based monomer unit content in the copolymer is preferably 0.1 mol % to 50 mol %. It is more preferably 1 mol % to 45 mol %, even more preferably 5 mol % to 40 mol %.
From the viewpoint of the solubility of the copolymer in an aqueous solvent or aqueous mixed solvent, the anti-fusing property, the yield of carbonization, and the shape stability, the content of unsaturated carboxylic acid monomer units in the copolymer is 0.1. It is preferably mol% to 50 mol%, more preferably 0.1 mol% to 40 mol%, even more preferably 0.1 mol% to 30 mol%, and 1 mol% to 30 mol%. %, most preferably 2 mol % to 20 mol %.

Among them, the acrylamide-based polymer fiber contains a copolymer,
The copolymer contains 40 mol% or more and 99.8 mol% or less of acrylamide-based monomer units and 0.1 mol% or more and 50 mol% or less of vinyl cyanide-based monomer units with respect to all monomer units constituting the copolymer. It preferably consists of a monomer unit and 0.1 mol % or more and 30 mol % or less of unsaturated carboxylic acid monomer unit.

From the viewpoint of fusion suppression, carbonization yield, and shape stability, the content of the acrylamide polymer relative to the mass of the carbon fiber precursor fiber of the present disclosure is preferably 80% by mass to 99.9% by mass. It is more preferably 85% by mass to 99.7% by mass.

The acrylamide-based polymer preferably has an infrared absorption peak in the range of about 1644 cm ⁻¹ to 1653 cm ⁻¹ in the infrared absorption spectrum.
The above infrared absorption peak is an absorption peak derived from stretching motion of the carbonyl group in the acrylamide-based monomer unit.
The infrared absorption spectrum is measured using infrared spectroscopy.
Specifically, the infrared absorption spectrum is measured by an ATR (attenuated total reflection) method with a measurement range of 400 cm ⁻¹ to 4000 cm ⁻¹ , a resolution of 193 m ⁻¹ , and 32 integration times.
As a measuring device, for example, a Fourier transform infrared spectroscopic device "Nicolet iS20" manufactured by Thermo Scientific or a similar device can be used.

(1.4) Additional Component The carbon fiber precursor fiber of the present disclosure can contain at least one additional component selected from the group consisting of acids and salts thereof.
Since the carbon fiber precursor fiber is excellent in fusion suppression property, carbonization yield and shape stability, it does not need to contain an additive component such as an acid. may contain, in addition to the acrylamide-based polymer, at least one additive component selected from the group consisting of acids and salts thereof. By applying a flameproofing treatment to the carbon fiber precursor fiber containing the above additive components, the formation of a cyclic structure is accelerated due to dehydration reaction, deammonification reaction, etc., and the fusion suppression property, carbonization yield and shape stability are further improved. tend to be
At least a part of the additive component and its residue may remain in the flame-resistant fiber. Further, carbonization treatment may be performed by adding an additive component to the flameproof fiber.

Examples of acids include inorganic acids such as phosphoric acid, polyphosphoric acid, boric acid, sulfuric acid, nitric acid and carbonic acid, and organic acids such as oxalic acid, citric acid and sulfonic acid.
Examples of the acid salts include metal salts (sodium salts, potassium salts, etc.), ammonium salts, amine salts, guanidine salts, urea salts, melamine salts, imidazole salts, etc., and ammonium salts and amine salts are preferred. is more preferred.
Among the above-described additive components, phosphoric acid, polyphosphoric acid, boric acid, polyboric acid, sulfuric acid, or ammonium salts thereof are preferable from the viewpoint of adhesion suppression properties, carbonization yield, and shape stability. Boric acid or ammonium salts thereof are more preferred, and phosphoric acid, polyphosphoric acid, ammonium salts of phosphoric acid, or ammonium salts of polyphosphoric acid are even more preferred.

The content of the additive component is 0.1 parts by mass to 100 parts by mass with respect to 100 parts by mass of the acrylamide-based polymer contained in the carbon fiber precursor fiber, from the viewpoint of carbonization yield, fusion suppression property, and shape stability. is preferably 0.2 parts by mass to 50 parts by mass, more preferably 0.5 parts by mass to 30 parts by mass, particularly 1 part by mass to 20 parts by mass preferable.

(2) Fibers for Carbon Fiber Precursor Fibers The fibers for carbon fiber precursor fibers of the present disclosure include acrylamide-based polymer fibers and uncrosslinked self-crosslinking silicone oil present on the surfaces of the acrylamide-based polymer fibers.

The content of the uncrosslinked material is not particularly limited, and is preferably 0.1 to 20 parts by mass, more preferably 0.2 to 15 parts by mass, based on 100 parts by mass of the acrylamide polymer fiber. It is more preferably 0.3 parts by mass to 10 parts by mass.
By setting the content of the uncrosslinked material to 0.1 parts by mass or more, the effect of suppressing the fusion between single fibers by the silicone oil after self-crosslinking can be further exhibited.
By setting the content of the uncrosslinked material to 20 parts by mass or less, it is possible to suppress crosslinking of the silicone oil between the carbon fiber precursor fibers during self-crosslinking, and to suppress fusion between single fibers.
The method for measuring the content of the uncrosslinked material is the same as the method described in Examples.

In the present disclosure, “fibers for carbon fiber precursor fibers” refer to precursor fibers of carbon fiber precursor fibers that have not been subjected to any of cross-linking treatment, flameproofing treatment and carbonization treatment. The fibers for carbon fiber precursor fibers become carbon fiber precursor fibers when subjected to a cross-linking treatment. Neither the flameproofing treatment nor the carbonization treatment is directly applied to the carbon fiber precursor fiber itself.
In the present disclosure, "uncrosslinked product of self-crosslinking silicone oil" refers to self-crosslinking silicone oil in a state in which the self-crosslinking silicone oil is not crosslinked.

Since the fiber for carbon fiber precursor fiber of the present disclosure has the above structure, when the self-crosslinking silicone oil is self-crosslinked, the fusion between the single fibers is suppressed in the flameproofing treatment while maintaining a high carbonization yield. can do.

The fibers for carbon fiber precursor fibers of the present disclosure have the same configuration as the carbon fiber precursor fibers of the present disclosure, except that the self-crosslinking silicone oil is not self-crosslinked.

(3) Method for producing carbon fiber precursor fiber The method for producing carbon fiber precursor fiber of the present disclosure includes a step of subjecting fibers for carbon fiber precursor fibers to a crosslinking treatment (hereinafter referred to as a “crosslinking treatment step”), which will be described later. including.
This yields the carbon fiber precursor fibers of the present disclosure.

The method for producing carbon fiber precursor fibers may include a step of preparing fibers for carbon fiber precursor fibers (hereinafter, “preparation step”) in addition to the cross-linking treatment step. The preparation step is performed before the cross-linking treatment step.
A case in which the method for producing carbon fiber precursor fibers includes a preparation step and a cross-linking treatment step will be described below.

(3.1) Preparation step In the preparation step, fibers for carbon fiber precursor fibers are prepared. Thereby, the fibers for carbon fiber precursor fibers of the present disclosure are obtained.

The method of preparing fibers for carbon fiber precursor fibers is not particularly limited. For example, an acrylamide-based polymer composition is spun, a self-crosslinking silicone oil is applied to the obtained acrylamide-based polymer fibers, and self-crosslinking is performed. and a method of self-crosslinking a reactive silicone oil.

(3.1.1) Acrylamide-based polymer composition The acrylamide-based polymer composition is a raw material for acrylamide-based polymer fibers.
The acrylamide-based polymer composition contains an acrylamide-based polymer and, if necessary, the above-described additive components and the like.

As the acrylamide-based polymer, a commercially available one may be used, or one synthesized by a conventionally known method may be used.
Synthesis of acrylamide-based polymers can be carried out by utilizing known polymerization reactions such as radical polymerization, cationic polymerization, anionic polymerization, and living radical polymerization. Among the above polymerization reactions, radical polymerization is preferred from the viewpoint of reducing synthesis costs.
Synthesis of acrylamide-based polymers can be carried out by utilizing polymerization methods such as solution polymerization, suspension polymerization, precipitation polymerization, dispersion polymerization, and emulsion polymerization (for example, inverse emulsion polymerization).
When synthesizing an acrylamide polymer by solution polymerization, it is preferable to use a solvent in which the raw material monomers and the obtained acrylamide polymer dissolve. It is more preferable to use an aqueous mixed solvent, and it is even more preferable to use an aqueous solvent.
Examples of the aqueous solvent include water, alcohol, mixed solvents thereof, and the like, and water is particularly preferable.
The aqueous mixed solvent means a mixed solvent of the above aqueous solvent and an organic solvent, and examples of the organic solvent include tetrahydrofuran and the like.

It is preferable to use a polymerization initiator in synthesizing an acrylamide-based polymer by radical polymerization.
As the polymerization initiator, conventionally known radical polymerization initiators such as azobisisobutyronitrile, benzoyl peroxide, 4,4'-azobis(4-cyanovaleric acid), ammonium persulfate, and potassium persulfate can be used. can be done.
When using an aqueous solvent or an aqueous mixed solvent as a solvent, 4,4'-azobis(4-cyanovaleric acid), ammonium persulfate, potassium persulfate, etc. soluble in aqueous solvents or aqueous mixed solvents Initiate radical polymerization agents are preferred.
From the viewpoint of reducing the molecular weight of the acrylamide-based polymer and improving the spinnability of the acrylamide-based polymer, it is preferable to use at least one of a polymerization accelerator and a molecular weight modifier instead of or together with the polymerization initiator. , a polymerization initiator and a polymerization accelerator are more preferably used in combination.
Tetramethylethylenediamine etc. are mentioned as a polymerization accelerator.
Examples of molecular weight modifiers include alkylmercaptan compounds such as n-dodecylmercaptan.
It is particularly preferable to use ammonium persulfate as a polymerization initiator and tetramethylethylenediamine as a polymerization accelerator in combination.

The temperature of the polymerization reaction is not particularly limited, and from the viewpoint of improving the spinnability of the acrylamide polymer, it is preferably 35°C or higher, more preferably 40°C or higher, and 50°C or higher. more preferably, and particularly preferably 70° C. or higher.

The acrylamide-based polymer may be a homopolymer of an acrylamide-based monomer or a copolymer of an acrylamide-based monomer and another polymerizable monomer. Preferred aspects of the acrylamide-based monomer and other polymerizable monomers have been described above, and therefore are omitted here.

The content of acrylamide-based monomer units in the acrylamide-based polymer is preferably 30 mol% or more, more preferably 40 mol% or more, further preferably 50 mol% or more, and 55 mol% or more. It is particularly preferable that the content is 60 mol % or more, and most preferably it is 60 mol % or more.
When the acrylamide-based monomer unit content is 30 mol % or more, the solubility in an aqueous solvent or an aqueous mixed solvent tends to be improved.
The upper limit of the content of acrylamide-based monomer units is not particularly limited, but from the viewpoint of fusion suppression, carbonization yield and shape stability, it is preferably 99.9 mol% or less. It is more preferably 8 mol % or less, still more preferably 95 mol % or less, particularly preferably 90 mol % or less, and most preferably 85 mol % or less.

When the acrylamide-based polymer is a copolymer of an acrylamide-based monomer and another polymerizable monomer, the content of the other polymerizable monomer unit in the copolymer is determined to improve the fusion suppression property, carbonization yield and shape stability. From the viewpoint of, it is preferably 0.1 mol% or more, more preferably 1 mol% or more, further preferably 5 mol% or more, particularly preferably 10 mol% or more, and 15 It is most preferably mol % or more.
From the viewpoint of improving the solubility of the acrylamide-based polymer in an aqueous solvent or an aqueous mixed solvent, the upper limit of the content of other polymerizable monomer units is preferably 70 mol% or less, more preferably 60 mol% or less. It is more preferably 50 mol %, particularly preferably 45 mol % or less, and most preferably 40 mol % or less.

Methods for producing an acrylamide-based polymer composition include a method of directly mixing additive components into a molten acrylamide-based polymer (melt mixing), a method of dry-blending the acrylamide-based polymer and additive components (dry mixing), and a method of containing additive components. An aqueous solution or aqueous mixed solution, or a solution in which the acrylamide-based polymer is not completely dissolved but the additive component is dissolved, or an acrylamide-based polymer formed into a fibrous form is immersed in a solution or a dispersion in which the additive component is dispersed. A method of passing through is mentioned.
When the acrylamide-based polymer and the additive component are soluble in an aqueous solvent or an aqueous mixed solvent, the acrylamide-based polymer and the additive component can be mixed in an aqueous solution from the viewpoint that the acrylamide-based polymer and the additive component can be uniformly mixed. A method of mixing in a solvent or an aqueous mixed solvent (wet mixing) is preferred.
Wet mixing may be performed by mixing additional components in the aqueous solvent or aqueous mixed solvent in which the acrylamide-based polymer was synthesized.

In wet mixing, an aqueous solvent is preferably used as the solvent, and water is more preferably used, from the viewpoint that the acrylamide-based polymer composition can be produced safely at a lower cost.

When the acrylamide-based polymer composition is produced by wet mixing, the solvent may or may not be removed. The solvent removal method 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.

(3.1.2) Spinning The method for spinning the acrylamide-based polymer composition is not particularly limited. can be done by
When the acrylamide-based polymer composition is soluble in an aqueous solvent or an aqueous mixed solvent, the acrylamide-based polymer composition is dissolved in the aqueous solvent or the aqueous mixed solvent from the viewpoints of spinnability, environmental load reduction, cost and safety. It is preferable to produce an acrylamide-based polymer fiber by spinning using the resulting aqueous solution or aqueous mixed solution.
When synthesizing the acrylamide polymer by solution polymerization, it is preferable to adjust the solution of the acrylamide polymer to a desired concentration as necessary, and then spin it to produce the acrylamide polymer fiber.
When the acrylamide-based polymer composition is produced by wet mixing, it is preferred that the solution of the acrylamide-based polymer composition is adjusted to a desired concentration as necessary, and then spun to produce acrylamide-based polymer fibers.

Spinning is preferably carried out by a dry spinning method, a wet spinning method, a dry-wet spinning method, a gel spinning method, a flash spinning method or an electrospinning method. According to the above spinning method, acrylamide-based polymer fibers having desired fineness and average fiber diameter can be produced safely at low cost.
From the viewpoint that acrylamide-based polymer fibers can be produced safely at a lower cost, it is preferable to use an aqueous solvent as the solvent, and more preferable to use water.

(3.1.3) Adhesion The method of adhering the self-crosslinking silicone oil to the acrylamide polymer fiber is not particularly limited, and the self-crosslinking silicone oil agent (hereinafter sometimes referred to as "oil agent"). , a coating method, a dipping method, a spraying method, a touch roll method, a guide oiling method, and the like.

(3.1.3.1) Self-crosslinking silicone oil agent The oil agent contains a self-crosslinking silicone oil. The oil agent may be a self-crosslinking silicone oil alone, or may contain a self-crosslinking silicone oil and an organic solvent for diluting the self-crosslinking silicone oil. The organic solvent is a good solvent for the self-crosslinking silicone oil and a poor solvent for the acrylamide polymer. In addition, an oil containing no self-crosslinking group or an oil containing a functional group other than the self-crosslinking group may be contained within a range that does not impair the effects of the present invention.

The viscosity of the oil agent at 25°C is not particularly limited, and is the same as the range exemplified as the viscosity of the self-crosslinking silicone oil at 25°C.
The viscosity at 25°C of the self-crosslinking silicone oil is the value at 25°C measured by an Ubbelohde viscometer. When the self-crosslinking silicone oil is a commercially available self-crosslinking silicone oil, the viscosity of the self-crosslinking silicone oil at 25°C may be the manufacturer's catalog value.

In addition to the organic solvent, the oil may optionally contain smoothing agents, hygroscopic agents, surfactants, viscosity modifiers, releasing agents, spreading agents, antibacterial agents, preservatives, and the like.

(3.2) Crosslinking Treatment Step In the crosslinking treatment step, the fiber for carbon fiber precursor fiber is crosslinked. Carbon fiber precursor fibers are thus obtained.
The fiber for carbon fiber precursor fiber may be crosslinked in the form of a fiber bundle.

(3.2.1) Cross-linking treatment The cross-linking treatment is not particularly limited as long as the self-crosslinking silicone oil contained in the acrylamide polymer fiber can be self-crosslinked. Examples include a method of irradiating rays (hereinafter referred to as "electron beam treatment"), a method of irradiating an oil agent on the surface of the acrylamide polymer fiber with ultraviolet rays, and a method of heating and drying the oil agent on the surface of the acrylamide polymer fiber. be done. Among them, the cross-linking treatment is preferably electron beam treatment from the viewpoint of energy efficiency and processing speed.

(3.2.1.1) Electron Beam Treatment From the viewpoint of fusion suppression, carbonization yield and shape stability, the dose of the electron beam irradiated to the acrylamide polymer fiber should be 50 kGy to 10000 kGy. It is preferably from 100 kGy to 5000 kGy, even more preferably from 150 kGy to 1000 kGy.
The preferable numerical range of the dose described above is the preferable numerical range of the dose when the acrylamide-based polymer fiber is irradiated with an electron beam from one direction. It is preferable to adjust it as appropriate.

When electron beams are used as actinic rays, the dose is measured by using a film dosimeter or the like. As the film dosimeter, for example, FTR-125 manufactured by Fuji Film Co., Ltd., FWT-60 type manufactured by Toyo Medic Co., Ltd., or similar devices can be used.

From the viewpoint of fusion suppression, carbonization yield and shape stability, the acceleration voltage of the electron beam irradiated to the acrylamide polymer fiber is preferably 20% or more, more preferably 60% or more, of the irradiated actinic ray, More preferably, the accelerating voltage is adjusted such that 80% or more of the acrylamide-based polymer fibers are permeable.
When an electron beam is used as the actinic ray, the transmittance of the electron beam can be calculated from the difference in dose between the front surface (before transmission) and the rear surface (after transmission) of the sample. Alternatively, it may be calculated from a commonly disclosed relational diagram of penetration depth and relative dose.
Specifically, the acceleration voltage is preferably 10 kV to 10 MV, more preferably 100 kV to 3 MV, even more preferably 150 kV to 1 MV.
The preferable numerical range of the acceleration voltage described above is the preferable numerical range of the acceleration voltage when the acrylamide polymer fiber is irradiated with actinic rays from one direction. However, it is preferable to adjust it as appropriate.

The electron beam irradiation may be performed in a batch system or in a continuous system.
The device used for actinic ray irradiation is not particularly limited, but when performing actinic ray irradiation in batch mode, use CB250/30/20mA manufactured by Iwasaki Electric Co., Ltd. or an equivalent device. can do. In the case of continuous actinic ray irradiation, an electron beam irradiator EBC800-35 manufactured by NHV Corporation or a similar device can be used.

(4) Method for Producing Flame-Resistant Fiber The method for producing a flame-resistant fiber of the present disclosure includes a step of subjecting the carbon fiber precursor fiber to a flame-resistant treatment (hereinafter referred to as a “flame-resistant treatment step”).
As a result, a high carbonization yield can be maintained, and a flame-resistant fiber in which fusion between single fibers is suppressed can be obtained.
Acrylamide-based polymer fibers are less likely to be thermally decomposed by flame-resistant treatment. Furthermore, the structure of the acrylamide/vinyl cyanide/unsaturated carboxylic acid copolymer is converted into a highly heat-resistant structure by the flameproof treatment. Therefore, the carbonization yield is high.
In particular, in acrylamide-based polymer fibers containing additive components, the deammonification reaction and dehydration reaction of the acrylamide/vinyl cyanide/unsaturated carboxylic acid copolymer are promoted by the catalytic action of the acid or its salt as the additive component. be. Therefore, a cyclic structure (imide ring structure) or a structure in which two or more polycyclic rings are continuous is likely to be formed in the molecule of the acrylamide-based polymer fiber. As a result, the structure of the acrylamide/vinyl cyanide/unsaturated carboxylic acid copolymer is likely to be converted into a highly heat-resistant structure. As a result, the carbonization yield is even higher.

In the present disclosure, the term “flameproofing treatment” refers to subjecting carbon fiber precursor fibers to heat treatment in an oxidizing gas atmosphere.

(4.1) Flameproof Treatment The temperature of the flameproof treatment is not particularly limited, but is preferably 150°C to 500°C, more preferably 200°C to 450°C, and more preferably 250°C to 250°C. It is more preferably 420°C.
The above temperature includes not only the maximum temperature (flameproofing temperature) during the flameproofing treatment, which will be described later, but also the temperature in the process of raising the temperature up to the flameproofing treatment temperature.

The maximum temperature during the flameproofing treatment (flameproofing treatment temperature) is preferably 200°C to 500°C, more preferably 250°C to 450°C, even more preferably 305°C to 440°C, 310°C to 430°C is particularly preferred, and 315°C to 420°C is most preferred.
By setting the flameproof treatment temperature to 200°C or higher, the deammonification reaction and dehydration reaction of the acrylamide/vinyl cyanide/unsaturated carboxylic acid copolymer are likely to be promoted, and a cyclic structure (imide ring structure) is formed in the molecule. easy to form. Therefore, it tends to be possible to improve the heat resistance and carbonization yield of the flame-resistant fiber.
By setting the flameproofing treatment temperature to 500° C. or less, the flameproofed fiber is less likely to be thermally decomposed, and the manufacturing cost tends to be reduced.

The flameproofing treatment time (heating time at the flameproofing treatment temperature) is not particularly limited, but from the viewpoint of carbonization yield and production cost, it is preferably 1 minute to 120 minutes, and 2 minutes to 60 minutes. Minutes is more preferred, 3 to 50 minutes is even more preferred, and 4 to 40 minutes is particularly preferred.
By setting the flameproofing treatment time to 1 minute or more, the carbonization yield can be improved.
Manufacturing costs can be reduced by limiting the flameproofing treatment time to 120 minutes or less.

(4.2) Drawing Treatment During the flameproofing treatment of the carbon fiber precursor fibers, it is preferable to apply a drawing treatment to the carbon fiber precursor fibers. By subjecting the carbon fiber precursor fiber to a drawing treatment, the acrylamide polymer contained in the carbon fiber precursor fiber tends to be oriented and the tensile strength of the flameproof fiber tends to be improved.
The stretching treatment is preferably carried out at least during heating at the flameproofing temperature.
From the viewpoint of improving the tensile strength of the flame-resistant fiber, it is preferable to carry out the drawing treatment even during the process of raising the temperature to the flame-resistant treatment temperature.

The tension applied to the carbon fiber precursor fiber during the drawing process is preferably 0.03 mN/tex to 500 mN/tex, more preferably 0.05 mN/tex to 400 mN/tex, and 0.07 mN. /tex to 200 mN/tex, and particularly preferably 0.1 mN/tex to 100 mN/tex.
If the tension applied to the carbon fiber precursor fiber is less than 0.03 mN/tex, the fusion between single fibers is not sufficiently suppressed, and the high-temperature load bearing capacity, strength, and carbonization yield of the flame-resistant fiber decrease. tend to
If the tension applied to the carbon fiber precursor fibers exceeds 500 mN/tex, the carbon fiber precursor fibers may be cut during the flameproofing treatment.
In the present disclosure, the tension (unit: mN/tex) applied to the carbon fiber precursor fiber is defined as the tension (unit: mN) applied to the carbon fiber precursor fiber during the flameproofing treatment. It shows the value divided by the fineness (unit: tex) in the absolute dry state, that is, the tension per unit fineness of the carbon fiber precursor fiber.
The tension can be adjusted by adjusting the inlet and outlet speeds of a heating device such as a flameproofing furnace, or by using load cells, springs, weights, air cylinders, and the like.

If a predetermined tension is applied to the acrylamide-based polymer fiber at the flameproofing treatment temperature (maximum temperature during flameproofing treatment), even if the prescribed tension is applied during the process of heating up to the flameproofing treatment temperature, etc. Although it is not necessary to apply tension, it is preferable that a predetermined tension is applied even in the temperature rising process, etc., from the viewpoint that the effect of applying tension can be sufficiently obtained. Moreover, the tension may be applied from an initial stage such as a temperature rising process, or may be applied from an intermediate stage.
Further, in the method for producing a flameproof fiber of the present invention, after the heat treatment is performed at the flameproofing treatment temperature (maximum temperature during the flameproofing treatment) while applying a predetermined tension, the temperature is higher than the flameproofing treatment temperature. The heat treatment may be performed while applying a tension other than a predetermined tension at the temperature or without applying a tension.

(4.3) Flame-resistant fiber Although the density of the flame-resistant fiber is not particularly limited, it is preferably 1.30 g/cm ³ to 1.75 g/cm 3 , more preferably 1.35 g/cm ³ to 1.75 g/cm ³ . It is more preferably 1.70 g/cm ³ , still more preferably 1.37 g/cm ³ to 1.65 g/cm ³ , and 1.39 g/cm ³ to 1.60 g/cm ³ . It is particularly preferred and most preferably between 1.44 g/cm ³ and 1.55 g/cm ³ .
When the density of the flame-resistant fiber is 1.30 g/cm ³ or more, the heat resistance of the flame-resistant fiber and the denseness of the structure are sufficient. Therefore, the carbonization yield tends to improve. The productivity of the flame-resistant fiber is excellent because the density of the flame-resistant fiber is 1.75 g/cm ³ or less.

The average fiber diameter of the flame-resistant fiber is not particularly limited, but from the viewpoint of the tensile strength of the obtained carbon fiber, it is preferably 3 nm to 300 μm, more preferably 30 nm to 150 μm, and 1 μm. It is more preferably ˜60 μm, even more preferably 2 μm to 30 μm, most preferably 3 μm to 20 μm, most preferably 4 μm to 15 μm.

From the viewpoint of carbonization yield, the average fiber diameter of the flame-resistant fiber is preferably 5% or more smaller, more preferably 10% or more smaller, and 15% or more smaller than the average fiber diameter of the carbon fiber precursor fiber. more preferably 20% or more, even more preferably 25% or more, and most preferably 30% or more.

(5) Carbon fiber manufacturing method The carbon fiber manufacturing method of the present disclosure includes a step of obtaining a flame-resistant fiber by a method of manufacturing a flame-resistant fiber, and a step of carbonizing the flame-resistant fiber (hereinafter, “carbonization step”). ). Carbon fibers are thus obtained.

In the present disclosure, the term “carbonization treatment” refers to a treatment for carbonizing carbon fiber precursor fibers, and more specifically, heat treatment is performed on carbon fiber precursor fibers in a low-oxygen atmosphere (preferably in an oxygen-blocked environment). indicates that

(5.1) Step of Obtaining Flame-Resistant Fiber The step of obtaining the flame-resistant fiber is the same as the method exemplified as the method for producing the flame-resistant fiber.

(5.2) Carbonization treatment step (5.2.1) Carbonization treatment As carbonization treatment, in an inert gas (nitrogen, argon, helium, etc.) atmosphere, the temperature of the flameproof fiber is higher than that in the flameproof treatment. A method of heat-treating at temperature and the like can be mentioned. “Carbonization treatment” may generally include “graphitization” performed by heating at 2000 to 3000° C. under an inert gas atmosphere. By subjecting the flame-resistant fiber to a carbonization treatment, the flame-resistant fiber is carbonized to obtain a carbon fiber.
The lower limit of the heating temperature for carbonization is preferably 500°C or higher, more preferably 1000°C or higher, even more preferably 1100°C or higher, particularly preferably 1200°C or higher, and 1300°C. It is most preferable that it is above.
The upper limit of the heating temperature for carbonization is preferably 3000° C. or less, more preferably 2500° C. or less.
The heating time for the carbonization treatment is not particularly limited, but is preferably 30 seconds to 60 minutes, more preferably 1 minute to 30 minutes.
In the present disclosure, “carbonization treatment” may generally include “graphitization” performed by heating at a temperature of 2000° C. to 3000° C. in an inert gas atmosphere.
The carbonization treatment may include multiple heat treatments.
A plurality of heat treatments may be performed in the carbonization treatment. For example, heat treatment (preliminary carbonization treatment) is first performed at a temperature of less than 1000 ° C., then heat treatment (carbonization treatment) is performed at a temperature of 1000 ° C. or higher, and further heat treatment (graphitization treatment) is performed at a temperature of 2000 ° C. or higher. )It can be performed.

(5.3) Carbon Fiber The average fiber diameter of the carbon fiber is not particularly limited, but from the viewpoint of tensile strength, it is preferably 3 nm to 300 μm, more preferably 30 nm to 150 μm, and 1 μm. It is more preferably ˜60 μm, particularly preferably 3 μm to 20 μm, even more preferably 4 μm to 15 μm, and most preferably 5 μm to 10 μm.
Since the average fiber diameter of the carbon fibers is 3 nm or more, when a composite material is produced using a resin or the like as a matrix, if the matrix has a high viscosity, insufficient impregnation of the resin or the like into the carbon fiber bundles is unlikely to occur, and the composite material The tensile strength of is improved.
When the average fiber diameter of the carbon fibers is 300 μm or less, the tensile strength of the carbon fibers tends to be less likely to decrease.

EXAMPLES Hereinafter, the above-described embodiment will be specifically described with reference to Examples, but the above-described embodiment is not limited to these Examples.

<Fiber fineness of acrylamide-based polymer fiber>
In this example, the fineness of a single fiber of the acrylamide-based polymer fiber was determined by bundling 100 obtained acrylamide-based polymer fibers to prepare a fiber bundle, measuring the mass of the fiber bundle, and using the following formula. Fineness (tex) was calculated.
Single fiber fineness (tex) = fiber bundle mass (g)/fiber length (m) x 1000/100 (fibers)

<Average fiber diameter of acrylamide-based polymer fiber>
In this example, the average fiber diameter of the acrylamide-based polymer fibers was measured by bundling 100 obtained acrylamide-based polymer fibers to prepare a fiber bundle, and using a dry automatic density meter (“Accupic II 1340” manufactured by Micromeritics). was used to measure the density (g/cm ³ ) of the fiber bundle, and the average fiber diameter (μm) of the single fibers constituting the fiber bundle was obtained by the following formula.
D={(Dt×4×1000)/(ρ×π×n)} ^1/2
[In the formula,
D represents the average fiber diameter (μm) of the single fibers that make up the fiber bundle,
Dt represents the fineness (tex) of the fiber bundle,
ρ represents the density of the fiber bundle (g/cm ³ ),
n represents the number (number) of single fibers constituting the fiber bundle. ]

(Example 1)
A monomer composition was prepared consisting of 63 mol % acrylamide (AM), 35 mol % acrylonitrile (AN) and 2 mol % acrylic acid (AA). 100 parts by mass of the monomer composition and 4 parts by mass of tetramethylethylenediamine were dissolved in 567 parts by mass of distilled water to obtain an aqueous solution.
In a nitrogen atmosphere, while stirring the resulting aqueous solution, 3 parts by mass of ammonium persulfate was added to the aqueous solution, heated at 70°C for 150 minutes, then heated to 90°C over 30 minutes, and then heated at 90°C for 1 hour. The polymerization reaction was carried out while holding.
The resulting aqueous solution was dropped into methanol to precipitate an AM/AN/AA copolymer, which was recovered and vacuum-dried at 100° C. for 12 hours to obtain an AM/AN/AA copolymer ( AM/AN/AA=63 mol %/35 mol %/2 mol %).

After dissolving the obtained AM/AN/AA copolymer in ion-exchanged water to form an aqueous solution, dry spinning was performed so that 0.4 tex/fiber and an average fiber diameter of about 20 μm were obtained to obtain acrylamide polymer fibers. got Next, self-crosslinking silicone oil (“X-22-164C” manufactured by Shin-Etsu Chemical Co., Ltd., self-crosslinking group: methacrylic group) (temperature: 25° C.) is applied to the entire surface of the acrylamide polymer fiber, A single fiber was obtained. 800 single fibers obtained were bundled to obtain a fiber bundle (800 fibers/bundle).

Using an electron beam irradiation device "EBC800-35" manufactured by NHV Corporation, a continuous type under the conditions of a transport speed of 10 m/min, a feed tension of 75 g, a winding tension of 400 g, an acceleration voltage of 800 kV in the atmosphere, and an electron beam dose of 1100 kGy. was applied to the fiber bundle. Thus, a carbon fiber precursor fiber bundle was obtained.

(Example 2)
A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 1, except that the accelerating voltage was changed to 400 kV and the electron beam dose was changed to 300 kGy as the treatment conditions for the electron beam treatment.

(Comparative example 1)
A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 1, except that the fiber bundle was not subjected to electron beam treatment.

(Comparative example 2)
A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 1, except that the self-crosslinkable silicone oil was not applied to the acrylamide polymer fibers.

(Comparative Example 3)
The self-crosslinking silicone oil was changed to non-self-crosslinking silicone oil A (polydimethylsiloxane, self-crosslinking group: none, non-self-crosslinking group: none), and the fiber bundle was not subjected to electron beam treatment. Otherwise, the carbon fiber precursor fiber bundle was obtained in the same manner as in Example 1.

In the present disclosure, the non-self-crosslinking group refers to an organic group that is not a self-crosslinking group and is a group in which at least a portion of methyl groups at the side chains and terminals of polydimethylsiloxane is substituted.

(Comparative Example 4)
A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 1, except that the self-crosslinking silicone oil was changed to the non-self-crosslinking silicone oil A.

(Comparative Example 5)
Self-crosslinking silicone oil was changed to non-self-crosslinking silicone oil B (“X-22-164C” manufactured by Shin-Etsu Chemical Co., Ltd., self-crosslinking group: none, non-self-crosslinking group: amino group), A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 1, except that the fiber bundle was not subjected to electron beam treatment.

<<Measurement of oil adhesion amount>>
A certain amount of each of the carbon fiber precursor fiber bundles obtained in Examples 1 and 2 and Comparative Examples 1 to 5 was cut to obtain a test piece. The test piece was immersed in a solvent (eg, tetrahydrofuran) that does not dissolve silicone oil but dissolves silicone oil. The test piece was removed from the solvent and the solvent was completely removed under reduced pressure to obtain a residue. The amount of oil applied to each of the carbon fiber precursor fibers was calculated from the following formula.
Amount of oil applied (parts by mass) = [mass of residue (g)/mass of dried test piece after removal of oil (g)] x 100

(Flame resistant treatment)
In an air atmosphere, the carbon fiber precursor fiber bundles obtained in Examples 1 and 2 and Comparative Examples 1 to 5 were heated from room temperature to 350°C at a rate of 10°C/min while applying a tension of 0.4 mN/tex. After that, it was held at 350° C. for 30 minutes for flameproof treatment. As a result, a flameproof fiber bundle was obtained.

<<Measurement of fusion rate>>
The flameproof fiber bundle was cut with a cutter, and the cross section was observed with a digital microscope (manufactured by Keyence Corporation, "Digital Microscope VHX-7000").
A single fiber is a fiber with a fiber diameter expected from a carbon fiber precursor fiber bundle, and a fused fiber is a fiber thicker than the expected fiber diameter due to the fusion of two or more single fibers, and the number of observed fibers. (200 in terms of single fibers), the ratio of the number of single fibers contained in the fusion-bonded fibers to 100 was taken as the fusion rate. Table 1 shows the measurement results of the fusion rate. An acceptable range for the fusion rate is 20% or less.

<<Measurement of carbonization yield>>
The flameproof fiber bundle was heated from room temperature to 1000° C. at a rate of 20° C./min under a nitrogen atmosphere to obtain a carbon bundle. The carbonization yield was obtained by dividing the mass of the carbon fiber bundle by the mass of the flameproof fiber bundle before carbonization treatment and dividing the value by 100%. Table 1 shows the carbonization yield measurement results. An acceptable range for carbonization yield is 70% or higher.

The carbon fiber precursor fiber of Comparative Example 1 includes an acrylamide-based polymer fiber and an uncrosslinked product of self-crosslinking silicone oil.
The carbon fiber precursor fiber of Comparative Example 2 comprises an acrylamide-based polymer fiber subjected to electron beam treatment.
The carbon fiber precursor fiber of Comparative Example 3 includes an acrylamide polymer fiber and a coating film of non-self-crosslinking silicone oil A that has not been subjected to electron beam treatment.
The carbon fiber precursor fiber of Comparative Example 4 includes an acrylamide polymer fiber and a coating film of non-self-crosslinking silicone oil A that has been subjected to electron beam treatment.
The carbon fiber precursor fiber of Comparative Example 5 includes an acrylamide-based polymer fiber and a non-self-crosslinking silicone oil B coating film.
However, the carbon fiber precursor fibers of Comparative Examples 1 to 5 were not provided with the self-crosslinking product of the self-crosslinking silicone oil. Therefore, in Comparative Examples 1 to 5, the fusion rate was over 20% and the carbonization yield was less than 70%. From these results, it was found that the carbon fiber precursor fibers of Comparative Examples 1 to 5 could not suppress fusion between single fibers in the flameproofing treatment while maintaining a high carbonization yield.

From the measurement results of Comparative Examples 1 and 2, when the acrylamide-based polymer fiber coated with the self-crosslinking silicone oil is not subjected to the electron beam treatment, or when the acrylamide-based polymer fiber not coated with the self-crosslinking silicone oil is When the electron beam treatment was performed, the fusion rate was 30% or more, and the fusion rate could not be sufficiently reduced.
From the measurement results of Comparative Example 4, when the acrylamide polymer fibers coated with the non-self-crosslinking silicone oil were subjected to the electron beam treatment, the fusion rate was 26% or more, and sufficient single fibers could not be obtained. .
From the measurement results of Comparative Examples 3 and 5, when the acrylamide-based polymer fibers coated with the non-self-crosslinking silicone oil were not subjected to the electron beam treatment, the fusion rate was 78% or more, which is sufficient. No fiber was obtained.

The carbon fiber precursor fibers of Examples 1 and 2 comprise acrylamide-based polymer fibers and self-crosslinked products of self-crosslinkable silicone oil. Therefore, in Examples 1 and 2, the fusion rate was 20% or less and the carbonization yield was 70% or more. From these results, it was found that the carbon fiber precursor fibers of Examples 1 and 2 were capable of suppressing fusion between single fibers during the flameproofing treatment while maintaining a high carbonization yield.

Claims (11)

A carbon fiber precursor fiber comprising an acrylamide-based polymer fiber and a self-crosslinked product of a self-crosslinkable silicone oil present on the surface of the acrylamide-based polymer fiber. The carbon fiber precursor fiber according to claim 1, wherein the content of the self-crosslinked material is 0.1 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the acrylamide polymer fiber. The acrylamide-based polymer fiber is made of an acrylamide-based polymer,
The carbon fiber precursor fiber according to claim 1 or 2, wherein the acrylamide-based polymer contains 30 mol% or more of acrylamide-based monomer units with respect to all monomer units constituting the acrylamide-based polymer. The acrylamide-based polymer contains 40 mol% or more and 99.8 mol% or less of acrylamide-based monomer units and 0.1 mol% or more and 50 mol% or less of cyanide based on the total monomer units constituting the acrylamide-based polymer. 4. The carbon fiber precursor fiber according to claim 3, comprising a vinyl-based monomer unit and 0.1 mol % or more and 30 mol % or less of unsaturated carboxylic acid-based monomer unit. The carbon fiber precursor fiber according to claim 1 or 2, wherein the self-crosslinking silicone oil has an acrylic group or a methacrylic group. The carbon fiber precursor fiber according to claim 1 or 2, wherein the self-crosslinking silicone oil has a viscosity at 25°C of 9 mm ² /s or more. A carbon fiber precursor fiber comprising an acrylamide polymer fiber and an uncrosslinked self-crosslinkable silicone oil present on the surface of the acrylamide polymer fiber. A method for producing a carbon fiber precursor fiber, comprising the step of subjecting the fiber for carbon fiber precursor fiber according to claim 7 to a cross-linking treatment. The method for producing a carbon fiber precursor fiber according to claim 8, wherein the cross-linking treatment is electron beam treatment. A method for producing a flame-resistant fiber, comprising the step of subjecting the carbon fiber precursor fiber according to claim 1 or claim 2 to a flame-resistant treatment. A step of obtaining a flame-resistant fiber by the method for producing a flame-resistant fiber according to claim 10;
a step of carbonizing the flame-resistant fiber;
A method of manufacturing carbon fiber, comprising: