Carbon fiber precursor fiber, fiber for carbon fiber precursor fiber, method for producing carbon fiber precursor fiber, method for producing flame-resistant fiber, and method for producing carbon fiber

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

[Technical field]

[0001] The present disclosure relates to a carbon fiber precursor fiber, a fiber for carbon fiber precursor fiber, a method for producing a carbon fiber precursor fiber, a method for producing an oxidation-resistant fiber, and a method for producing a carbon fiber. [Background technology]

[0002] Carbon fiber is attracting attention as a material to replace metal materials due to its characteristics such as light weight, excellent mechanical strength, and corrosion resistance. A known method for producing carbon fibers is to apply a silicone-based oil to chemical fibers obtained by spinning polyacrylonitrile, heat-treat the fibers to obtain carbon fiber precursor fibers, and then subject a fiber bundle obtained by bundling hundreds to tens of thousands of single carbon fiber precursor fibers to flame retardant treatment and then carbonization treatment (for example, Patent Documents 1 and 2). Patent Documents 1 and 2 specifically describe, as the silicone-based oil, a silicone oil prepared by diluting an oil consisting of amino-modified silicone, epoxy-modified silicone, ethylene oxide-modified silicone, and an emulsifier with water.

[0003] On the other hand, an acrylamide-based polymer containing an acrylamide-based monomer is a water-soluble polymer, and water, which is inexpensive and has a small environmental impact, can be used as a solvent when carrying out polymerization, spinning, etc., and therefore, a reduction in the production cost of carbon fibers is expected. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-183159 A [Patent Document 2] JP 2008-202208 A [Patent Document 3] JP 2018-90791 A [Patent Document 4] JP 2019-26827 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, when a flame-retardant treatment is applied to a fiber bundle of carbon fiber precursor fibers in which a conventional silicone-based oil is applied to a single fiber of an acrylamide-based polymer, the surface of the carbon fiber precursor fiber is softened, and a flame-retardant fiber in which the carbon fiber precursor fibers (single fibers) are fused together may be obtained. When such a flame-retardant fiber is carbonized, the fused carbon fiber precursor fibers burn at the site where they are fused together, causing defects, and the mechanical properties of the resulting carbon fiber may be reduced. Therefore, there is a demand for a carbon fiber precursor fiber that can suppress the fusion of single fibers during the flame-retardant treatment. Furthermore, from the viewpoint of reducing the production cost of carbon fibers, there is a demand for a carbon fiber precursor fiber that can achieve a high carbonization yield. The carbonization yield is expressed as a percentage of the mass of the carbon fiber divided by the mass of the flame-retardant fiber.

[0006] An object of the present invention is to provide a carbon fiber precursor fiber, a fiber for carbon fiber precursor fiber, a method for producing a carbon fiber precursor fiber, a method for producing a flame-retardant fiber, and a method for producing a carbon fiber, which are capable of suppressing fusion of single fibers to each other in a flame-retardant treatment while maintaining a high carbonization yield. [Means for solving the problem]

[0007] The present inventors have conducted intensive research to solve the above problems, and have found that when a fiber bundle of carbon fiber precursor fibers consisting of single fibers of an acrylamide polymer to which a conventional silicone-based oil agent has been added is subjected to flame retardant treatment, the surface of the carbon fiber precursor fibers is softened, and fusion of the carbon fiber precursor fibers may occur. In order to prevent this, a self-crosslinking silicone oil is added to the surface of the single fibers, and the silicone oil is crosslinked (cured), thereby making it possible to maintain a high carbonization yield while suppressing fusion of the single fibers in the flame retardant treatment, and thus the present disclosure has been completed.

[0008] The 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-crosslinking silicone oil on the surface of the acrylamide-based polymer fiber. <2> 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-based polymer fiber. <1> The carbon fiber precursor fiber according to claim 1. <3> the acrylamide-based polymer fiber is made of an acrylamide-based polymer, The acrylamide polymer contains 30 mol % or more of acrylamide monomer units based on the total monomer units constituting the acrylamide polymer. <1> or <2> Carbon fiber precursor fibers. <4> The acrylamide polymer contains 40 mol % or more and 99.8 mol % or less of acrylamide monomer units, 0.1 mol % or more and 50 mol % or less of vinyl cyanide monomer units, and 0.1 mol % or more and 30 mol % or less of unsaturated carboxylic acid monomer units, based on all monomer units constituting the acrylamide polymer. <3> The carbon fiber precursor fiber according to claim 1. <5> The self-crosslinking silicone oil has an acrylic group or a methacrylic group. <1> ~ <4> 13. A carbon fiber precursor fiber according to any one of claims 1 to 12. <6> The viscosity of the self-crosslinking silicone oil at 25°C is 9mm 2 / s or more <1> ~ <5> 13. A carbon fiber precursor fiber according to any one of claims 1 to 12. <7> A fiber for use as a precursor fiber for carbon fiber, comprising: an acrylamide-based polymer fiber; and an uncrosslinked product of a self-crosslinking silicone oil on the surface of the acrylamide-based polymer fiber. <8> The above <7> A method for producing a carbon fiber precursor fiber, comprising a step of subjecting the fiber for carbon fiber precursor fiber according to claim 1 to a crosslinking treatment. <9> The crosslinking treatment is an electron beam treatment. <8> A method for producing a carbon fiber precursor fiber according to claim 1. <10> The above <1> ~ <6> 2. A method for producing a flame-resistant fiber, comprising the step of subjecting the carbon fiber precursor fiber according to any one of claims 1 to 11 for flame-resistant treatment. <11> The above <10> A step of obtaining a flame-resistant fiber by the method for producing a flame-resistant fiber according to the present invention; A step of subjecting the flame-retardant fiber to a carbonization treatment; A method for producing carbon fibers, comprising: Effect of the Invention

[0009] According to the present disclosure, it is possible to provide a carbon fiber precursor fiber, a fiber for carbon fiber precursor fiber, a method for producing a carbon fiber precursor fiber, a method for producing a flame-retardant fiber, and a method for producing a carbon fiber, which are capable of suppressing fusion of single fibers to each other during flame-retardant treatment while maintaining a high carbonization yield. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In the present disclosure, a numerical range indicated using "~" includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively. In the numerical ranges described in the present disclosure in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In the numerical ranges described in the present disclosure, the upper or lower limit value of the numerical range may be replaced with the value shown in the synthesis examples.

[0011] In this specification, the term "process" refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0012] In the present disclosure, each component may contain multiple types of corresponding substances. When multiple types of substances corresponding to each component are present in the carbon fiber precursor fiber, the content or amount of each component means the total content or amount of the multiple types of substances present in the carbon fiber precursor fiber, unless otherwise specified.

[0013] (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 a self-crosslinking silicone oil on the surface of the acrylamide-based polymer fiber.

[0014] In the present disclosure, the term "carbon fiber precursor fiber" refers to a fiber for producing carbon fiber that has been subjected to a crosslinking treatment and has not been subjected to either a flame retardant treatment or a carbonization treatment.

[0015] In the present disclosure, the term "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 may contain additive components described below as necessary.

[0016] In the present disclosure, the term "acrylamide-based polymer" refers to 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 other polymerizable monomer).

[0017] In this disclosure, the term "self-crosslinking silicone oil" refers to a silicone oil having a self-crosslinking group. In detail, the "self-crosslinking silicone oil" has a structure in which a polysiloxane is used as a basic structure, and at least some of the substituents on the side chains and ends of the polysiloxane are replaced with self-crosslinking groups. The self-crosslinking group refers to a functional group that can form a crosslinked structure in the molecule by itself by external stimuli such as electron beams, ultraviolet rays, and heat, even without the presence of other components. Examples of polysiloxane include polydimethylsiloxane, polymethylphenylsiloxane, polydiphenylsiloxane, polymethylhydrogensiloxane, and mixtures thereof. The substituents will be described later. In this disclosure, "self-crosslinked silicone oil" refers to a compound in a state in which the self-crosslinking group of self-crosslinking silicone oil undergoes intramolecular crosslinking reaction to have a crosslinked structure.The confirmation of having a crosslinked structure can be performed by whether or not the self-crosslinked silicone oil that is applied with acrylamide polymer is dissolved when the self-crosslinked silicone oil is immersed in tetrahydrofuran after the self-crosslinking silicone oil is self-crosslinked.That is, when it is dissolved, it is classified as the compound not having a crosslinked structure.

[0018] In the present disclosure, "having on the surface" may mean a state of being attached to the surface. "Attached" means that the self-crosslinked product of the self-crosslinking silicone oil is present on the surface of the acrylamide-based polymer fiber, and may be in any state of being bonded with a covalent bond or an ionic bond, or in a state of being attracted to each other by van der Waals forces. The self-crosslinked product of the self-crosslinking silicone oil may also be present inside the acrylamide-based polymer fiber.

[0019] Since the carbon fiber precursor fiber of the present disclosure has the above-mentioned configuration, it is possible to suppress fusion between single fibers during the flame retardant treatment while maintaining a high carbonization yield.

[0020] The reason why the above effect is achieved is presumed to be as follows, but is not limited to this. When the self-crosslinking silicone oil undergoes self-crosslinking, a highly heat-resistant self-crosslinked film is formed on the surface of the acrylamide polymer fiber. This is thought to make it difficult for the individual fibers to fuse together during the flame-retardant treatment. In addition, the self-crosslinked material contains a chemical structure in which a self-crosslinking group is bonded, and the chemical structure in which the self-crosslinking group is bonded is similar to the chemical structure of the carbon fiber precursor fiber. Therefore, during the flame retardant treatment, the self-crosslinked material does not suppress the permeation of oxidizing gas, and is less likely to inhibit the progress of the flame retardant reaction (cyclization, partial oxidation). Furthermore, since the occurrence of fusion between the 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 flame retardant treatment. This makes it easier for the flame retardant reaction (cyclization, partial oxidation) to proceed. As a result, it is presumed that the carbonization yield is high. As described above, the carbon fiber precursor fiber of the present disclosure can suppress fusion between single fibers during flame retardation treatment while maintaining a high carbonization yield. Therefore, the carbon fiber precursor fiber of the present disclosure can reduce the production cost of carbon fibers, and high-quality carbon fibers can be obtained from the carbon fiber precursor fiber of the present disclosure.

[0021] In contrast, when a combination of a conventional silicone-based oil having an amino group and a silicone-based oil having an epoxy group is crosslinked, the resulting crosslinked product contains at least one of a hydroxyl group and an amino group. Therefore, the conventional crosslinked product is highly likely to inhibit oxygen permeation. As a result, the flame retardant reaction proceeds insufficiently, and the carbonization yield is often low. Conventional silicone-based oils are used to suppress the fusion of single fibers of polyacrylonitrile fibers or flame-resistant fibers derived from polyacrylonitrile fibers, and are heat-treated at high temperatures to promote crosslinking reactions. Therefore, as conventional silicone-based oils, amino-modified silicone oils or mixtures of two or more types of silicone-based oils such as amino-modified silicone oils are used. However, even if conventional silicone-based oils are directly applied to polyacrylamide fibers or polyacrylamide flame-resistant fibers, the effect of suppressing the fusion of single fibers is low. On the other hand, the carbon fiber precursor resistant fiber of the present disclosure includes a self-crosslinked product of a self-crosslinking silicone oil, so that the fusion of single fibers can be suppressed during flame-resistant 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. To achieve this, it is necessary to adjust the viscosity of the silicone oil using a surfactant. On the other hand, since the acrylamide polymer fibers in the present disclosure are water-soluble, it is not necessary to adjust the viscosity of the self-crosslinking silicone oil using a surfactant. Since the surfactant remains in the carbon fiber precursor fiber as a foreign matter and tends to lead to a decrease in mechanical properties, it is preferable not to adjust the viscosity of the self-crosslinking silicone oil.

[0022] (1.1) Fineness of carbon fiber precursor fiber, etc. (1.1.1) Fineness The fineness of the carbon fiber precursor fiber is not particularly limited, but is preferably 1×10 -8 Preferably, the density is 1×10 -6 tex / line to 60tex / line is more preferable, and 1×10 -3 It is more preferable that the thickness is 1×10 -2 It is particularly preferable that the thickness is 2×10 -2 tex / line to 5tex / line is more preferable, and 3×10 -2 It is most preferable that the thickness is between tex / thread and 1 tex / thread. The fineness of the carbon fiber precursor fiber is 1×10 -8 By making the fiber count at least tex / fiber, the occurrence of yarn breakage is suppressed, which tends to improve the ease of winding the carbon fiber precursor fiber and the stability of the flame retardant treatment. By setting the fineness of the carbon fiber precursor fiber to 100 tex / fiber or less, the difference in structure between the surface layer of the carbon fiber obtained by the flame retardant treatment and the center layer can be reduced, and the tensile strength and tensile modulus of the carbon fiber can be improved.

[0023] In the present disclosure, the measurement of the single fiber fineness (tex / fiber) is performed by bundling 100 carbon fiber precursor fibers to prepare a fiber bundle, measuring the mass of this fiber bundle, and calculating the single fiber fineness according to the following formula. Single fiber fineness (tex) = fiber bundle mass (g) / fiber length (m) x 1000 / 100 (pieces)

[0024] (1.1.2) Average fiber diameter The average fiber diameter of the carbon fiber precursor fibers is not particularly limited, but is preferably 3 nm to 300 μm, more preferably 30 nm to 250 μm, even more preferably 1 μm to 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 making the average fiber diameter of the carbon fiber precursor fiber 3 nm or more, the stability of the flame retardant treatment tends to be improved. By making the average fiber diameter of the carbon fiber precursor fiber 3 nm or more, the occurrence of yarn breakage can be suppressed, and thus the ease of winding the carbon fiber precursor fiber and the stability of the flame retardant treatment tend to be improved. 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 flame retardant treatment and the structure near the center can be reduced, and the tensile strength and tensile modulus of the carbon fiber tend to be improved.

[0025] In the present disclosure, the average fiber diameter is determined by bundling 100 carbon fiber precursor fibers to prepare a fiber bundle, measuring the density of the fiber bundle using a dry automatic density meter, and calculating the average fiber diameter of the single fibers constituting the fiber bundle using the following formula. Note that, as the dry automatic density meter, an Accupyk II 1340 manufactured by Micromeritics or an apparatus equivalent thereto can be used. D = {(Dt × 4 × 1000) / (ρ × π × n)} 1 / 2 [During the ceremony, D represents the average fiber diameter (μm) of the single fibers constituting the fiber bundle, Dt represents the fiber bundle fineness (tex), ρ is the density of the fiber bundle (g / cm 3 ), n represents the number of single fibers that make up the fiber bundle. In addition, π is 3.14.

[0026] The carbon fiber precursor fiber may be in the form of a fiber bundle (hereinafter referred to as "carbon fiber precursor fiber bundle"), and is preferably subjected to the flame retardant treatment in the form of a carbon fiber precursor fiber bundle. The 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 from the viewpoint of the productivity and mechanical properties of the flame-resistant fiber and carbon fiber, it is preferably 50 to 96,000, more 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 flame-resistant treatment.

[0027] (1.2) Self-crosslinked products The carbon fiber precursor fiber of the present disclosure includes a self-crosslinked product of a self-crosslinking silicone oil. The self-crosslinked product is present on the surface of an acrylamide-based polymer fiber. This makes it possible to improve the bundling property and handling of the fibers, and also makes it possible to suppress fusion between the single fibers during the flame-retardant treatment.

[0028] The self-crosslinked product of the self-crosslinking silicone oil needs to be present on at least a portion of the surface of the acrylamide-based polymer fiber, and from the viewpoint of obtaining a carbon fiber precursor fiber that maintains a higher carbonization yield while further suppressing fusion of single fibers during flame retardation treatment, it is preferable that the self-crosslinked product adheres to the entire surface of the acrylamide-based polymer fiber as a coating.

[0029] The content of the self-crosslinked material is not particularly limited, and is preferably 0.1 to 20 parts by mass, more preferably 0.2 to 15 parts by mass, and even more preferably 0.3 to 10 parts by mass, relative to 100 parts by mass of the acrylamide polymer fiber. By making the content of the self-crosslinked product 0.1 parts by mass or more, the self-crosslinked product of the silicone oil can more effectively suppress fusion of the single fibers with each other. By setting the content of the self-crosslinking material to 20 parts by mass or less, crosslinking of the silicone oil between the carbon fiber precursor fibers can be suppressed, and fusion of the single fibers to each other can be suppressed. The content of the self-crosslinked material can be measured by thermogravimetric analysis, elemental analysis, etc. In the thermogravimetric analysis, the content of the self-crosslinked material can be measured from the amount of weight loss.

[0030] (1.2.1) Self-crosslinking silicone oil The self-crosslinking silicone oil contains a self-crosslinking group. The self-crosslinking group refers to a group that generates radicals by an external stimulus. In the present invention, the external stimulus is preferably an electron beam, an ultraviolet ray, heat, etc., and more preferably an electron beam. Specifically, the self-crosslinking group preferably contains at least one of a mono-substituted ethylene group, a 1,1-disubstituted ethylene group, and a 1,2-disubstituted ethylene group. Examples of the mono-substituted ethylene group include a vinyl group, a vinylcarbonyl group, a vinyl ester group, an acryl group, an acrylamide group, an allyl group, an allyl ether group, a 4-vinylbenzene group, and a 4-allylbenzene group. Examples of the 1,1-disubstituted ethylene group include an isopropenyl group, a methacryl group, a methacrylamide group, and a 4-isopropenylbenzene group. Examples of the 1,2-disubstituted ethylene group include a maleimide group, a fumaric acid ester group, and a fumaramide group. Among these self-crosslinking groups, the self-crosslinking group is preferably an acrylic group, a methacrylic group, an acrylamide group, or a methacrylamide group from the viewpoint of affinity with an acrylamide polymer, and is more preferably an acrylic group or a methacryl group from the viewpoint of polymerizability.

[0031] Self-crosslinking silicone oil can be structured such that at least a part of the substituents on the side chain and end of polysiloxane are replaced with self-crosslinking groups.As the substituents, methyl group, ethyl group, propyl group and other alkyl groups, phenyl group, methylphenyl group and other aryl groups can be mentioned.Among these, the substituent is more preferably methyl group or phenyl group, and more preferably methyl group.

[0032] The self-crosslinking silicone oil may be a commercially available product.

[0033] 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 9 mm from the viewpoint of preventing volatilization during the crosslinking process and allowing the crosslinking reaction to proceed efficiently. 2 / s or more is preferable, and 20 mm 2 / s or more is more preferable. The upper limit of the viscosity of the self-crosslinking silicone oil at 25°C is 100,000 mm2 from the viewpoint of adhering the self-crosslinking silicone oil to the surface of the acrylamide polymer fiber with a more uniform film thickness. 2 / s or less is preferable, and 10000 mm 2 It is more preferable that the ratio is equal to or less than 1 / s. The viscosity of the self-crosslinking silicone oil at 25°C indicates the value measured at 25°C using an Ubbelohde viscometer. If the self-crosslinking silicone oil is a commercially available product and the value is given in the catalog, the viscosity of the self-crosslinking silicone oil at 25°C shall be the value given in the manufacturer's catalog.

[0034] Examples of self-crosslinking silicone oils include products from Shin-Etsu Chemical Co., Ltd. and SILTECH Co., Ltd. Examples of Shin-Etsu Chemical Co., Ltd.'s products 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", and "X-22-2404". SILTECH's products 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" etc.

[0035] (1.3) Acrylamide polymer fiber The carbon fiber precursor fibers of the present disclosure include acrylamide-based polymer fibers, and may include two or more types of acrylamide-based polymer fibers.

[0036] The acrylamide-based polymer fibers are preferably formed using an acrylamide-based polymer composition, the resin component of which contains an acrylamide-based polymer.

[0037] (1.3.1) Acrylamide polymers The acrylamide polymer may be a homopolymer of an acrylamide monomer, or a copolymer of an acrylamide monomer and a monomer other than an acrylamide monomer (hereinafter referred to as other polymerizable monomer). From the viewpoints of fusion suppression, carbonization yield, shape stability, and tensile strength of the flame-resistant fiber, the acrylamide polymer is preferably a copolymer of an acrylamide monomer and another polymerizable monomer.

[0038] (1.3.1.1) Acrylamide monomer units The content of acrylamide-based monomer units in the acrylamide-based polymer is preferably 30 mol % or more, more preferably 40 mol % or more, even more preferably 50 mol % or more, particularly preferably 55 mol % or more, and most preferably 60 mol % or more, based on all monomer units constituting the copolymer. By ensuring that the content of the acrylamide-based monomer unit is 30 mol % or more, the solubility of the acrylamide-based polymer before crosslinking in an aqueous solvent or an aqueous mixed solvent tends to be improved. The upper limit of the content of the acrylamide monomer unit is not particularly limited, but from the viewpoints of suppression of fusion, carbonization yield, and shape stability, it is preferably 99.9 mol % or less, more preferably 99.8 mol % or less, even more preferably 95 mol % or less, particularly preferably 90 mol % or less, and most preferably 85 mol % or less.

[0039] Examples of acrylamide monomers include acrylamide, ethacrylamide, crotonamide, itaconic acid diamide, cinnamic acid amide, maleic acid diamide, N-alkylacrylamides such as N-methylacrylamide, N-ethylacrylamide, Nn-propylacrylamide, N-isopropylacrylamide, Nn-butylacrylamide, and N-tert-butylacrylamide, N-cycloalkylacrylamides such as N-cyclohexylacrylamide, dialkylacrylamides such as N,N'-dimethylacrylamide, dialkylaminoalkylacrylamides such as dimethylaminoethylacrylamide and dimethylaminopropylacrylamide, hydroxyalkylacrylamides such as N-(hydroxymethyl)acrylamide and N-(hydroxyethyl)acrylamide, N-arylacrylamides such as N-phenylacrylamide, diacetoneacrylamide, and N,N'-methylenebisacrylamide. alkylenebisacrylamides; methacrylamide; N-alkyl methacrylamides such as N-methylmethacrylamide, N-ethylmethacrylamide, Nn-propylmethacrylamide, N-isopropylmethacrylamide, Nn-butylmethacrylamide, and N-tert-butylmethacrylamide; N-cycloalkyl methacrylamides such as N-cyclohexylmethacrylamide; dialkyl methacrylamides such as N,N'-dimethylmethacrylamide; dialkylaminoalkyl methacrylamides such as dimethylaminoethylmethacrylamide and dimethylaminopropylmethacrylamide; hydroxyalkyl methacrylamides such as N-(hydroxymethyl)methacrylamide and N-(hydroxyethyl)methacrylamide; N-aryl methacrylamides such as N-phenylmethacrylamide, diacetone methacrynoleamide; and N,N'-alkylene bismethacrylamides such as N,N'-methylene bismethacrylamide. From the viewpoint of the solubility of the acrylamide-based polymer in an aqueous solvent or an aqueous mixed solvent, among the above-mentioned acrylamide-based monomers, acrylamide, N-alkylacrylamide, dialkylacrylamide, methacrylamide, N-alkylmethacrylamide or dialkylmethacrylamide is preferred, and acrylamide is more preferred. The acrylamide monomers may be used alone or in combination of two or more kinds.

[0040] (1.3.1.2) Other polymerizable monomer units When the acrylamide-based polymer is a copolymer of an acrylamide-based monomer and another polymerizable monomer, the content of the other polymerizable monomer units in the copolymer is, from the viewpoints of fusion suppression, carbonization yield, and shape stability, 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, based on the total monomer units constituting the copolymer. 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, even more preferably 50 mol % or less, particularly preferably 45 mol % or less, and most preferably 40 mol % or less.

[0041] Examples of other polymerizable monomers include vinyl cyanide monomers, unsaturated carboxylic acids and their salts, unsaturated carboxylic anhydrides, unsaturated carboxylic esters, vinyl alcohol monomers, vinyl carboxylate monomers, and olefin monomers.

[0042] Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, 2-hydroxyethyl acrylonitrile, chloroacrylonitrile, chloromethyl acrylonitrile, ethoxyacrylonitrile, and vinylidene cyanide. Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, crotonic acid, and isocrotonic acid. Examples of the salt of the unsaturated carboxylic acid include metal salts (for example, sodium salts, potassium salts, etc.), ammonium salts, and amine salts of the unsaturated carboxylic acid.

[0043] Examples of the unsaturated carboxylic acid anhydride include maleic anhydride and itaconic anhydride. Examples of the unsaturated carboxylate include methyl acrylate, methyl methacrylate, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate. Examples of the vinyl monomer include aromatic vinyl monomers such as styrene and α-methylstyrene, vinyl chloride, and vinyl alcohol. Examples of the olefin monomer include ethylene, propylene, isopropylene, and butadiene.

[0044] Among the above-mentioned other polymerizable monomers, from the viewpoints of spinnability, fusion inhibition, carbonization yield, and shape stability of the acrylamide-based polymer, the other polymerizable monomer is preferably a vinyl cyanide-based monomer, and more preferably acrylonitrile. Among the above-mentioned other polymerizable monomers, from the viewpoint of the solubility of the copolymer before crosslinking in an aqueous solvent or an aqueous mixed solvent, the other polymerizable monomer is preferably an unsaturated carboxylic acid or a salt thereof, and more preferably acrylic acid, maleic acid, fumaric acid or itaconic acid. Among the above-mentioned other polymerizable monomers, from the viewpoints of fusion suppression, carbonization yield, and shape stability, the other polymerizable monomer is preferably an unsaturated carboxylic acid or an unsaturated carboxylic acid anhydride, and more preferably acrylic acid, maleic acid, fumaric acid, itaconic acid, or maleic acid anhydride. The above-mentioned other polymerizable monomers may be used alone or in combination of two or more.

[0045] From the viewpoints of the solubility of the copolymer in an aqueous solvent or an aqueous mixed solvent, spinnability, fusion suppression, carbonization yield, and shape stability, the acrylamide-based polymer is particularly preferably a copolymer of an acrylamide-based monomer, a vinyl cyanide-based monomer, and an unsaturated carboxylic acid, and is most preferably a copolymer of acrylamide, acrylonitrile, and acrylic acid. From the viewpoints of spinnability, fusion inhibition, carbonization yield and shape stability, the content of vinyl cyanide monomer units in the copolymer is preferably 0.1 mol % to 50 mol %, more preferably 1 mol % to 45 mol %, and even more preferably 5 mol % to 40 mol %. From the viewpoints of the solubility of the copolymer in an aqueous solvent or an aqueous mixed solvent, the suppression of fusion, the carbonization yield, and the shape stability, the content of the unsaturated carboxylic acid monomer unit in the copolymer is preferably 0.1 mol % to 50 mol %, more preferably 0.1 mol % to 40 mol %, even more preferably 0.1 mol % to 30 mol %, particularly preferably 1 mol % to 30 mol %, and most preferably 2 mol % to 20 mol %.

[0046] Among them, acrylamide-based polymer fibers include copolymers, The copolymer preferably comprises 40 mol % or more and 99.8 mol % or less of acrylamide-based monomer units, 0.1 mol % or more and 50 mol % or less of vinyl cyanide-based monomer units, and 0.1 mol % or more and 30 mol % or less of unsaturated carboxylic acid monomer units, based on all monomer units constituting the copolymer.

[0047] From the viewpoints of fusion suppression, carbonization yield, and shape stability, the content of the acrylamide-based polymer relative to the mass of the carbon fiber precursor fiber of the present disclosure is preferably 80 mass% to 99.9 mass%, and more preferably 85 mass% to 99.7 mass%.

[0048] Acrylamide-based polymers have a peak at about 1644 cm in the infrared absorption spectrum. -1 ~1653cm -1It is preferable that an infrared absorption peak is observed in the range of The infrared absorption peak is an absorption peak derived from the stretching motion of the carbonyl group in the acrylamide monomer unit. The infrared absorption spectrum is measured by infrared spectroscopy. Specifically, the measurement range is 400 cm -1 ~4000cm -1 , resolution 193m -1 The infrared absorption spectrum is measured by the ATR (Attenuated Total Reflection) method with 32 accumulations. As a measuring device, for example, a Fourier transform infrared spectrometer "Nicolet iS20" manufactured by Thermo Scientific or a device equivalent thereto can be used.

[0049] (1.4)Additional ingredients The carbon fiber precursor fiber of the present disclosure may contain at least one additional component selected from the group consisting of acids and salts thereof. The carbon fiber precursor fiber is excellent in fusion inhibition, carbonization yield, and shape stability, and therefore may not contain an added component such as an acid, but the carbon fiber precursor fiber (i.e., an acrylamide-based polymer composition) may contain at least one added component selected from the group consisting of acids and their salts in addition to the acrylamide-based polymer. By subjecting the carbon fiber precursor fiber containing the above-mentioned added component to a flame retardant treatment, the formation of a cyclic structure due to a dehydration reaction, a deammonia reaction, etc. is accelerated, and the fusion inhibition, carbonization yield, and shape stability tend to be further improved. In the flame-retardant fiber, at least a part of the additive component and its residue may remain. Furthermore, the additive component may be added to the flame-retardant fiber and then carbonized.

[0050] Examples of the acid 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 salts of the above acids include metal salts (sodium salts, potassium salts, etc.), ammonium salts, amine salts, guanidine salts, urea salts, melamine salts, imidazole salts, etc., with ammonium salts and amine salts being preferred, and ammonium salts being more preferred. Among the above-mentioned additive components, from the viewpoints of fusion inhibition, carbonization yield, and shape stability, phosphoric acid, polyphosphoric acid, boric acid, sulfuric acid, or ammonium salts thereof are preferred, phosphoric acid, polyphosphoric acid, 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.

[0051] From the viewpoints of carbonization yield, fusion inhibition, and shape stability, the content of the additive component is preferably 0.1 parts by mass to 100 parts by mass, more preferably 0.2 parts by mass to 50 parts by mass, even more preferably 0.5 parts by mass to 30 parts by mass, and particularly preferably 1 part by mass to 20 parts by mass, relative to 100 parts by mass of the acrylamide-based polymer contained in the carbon fiber precursor fiber.

[0052] (2) Fibers for carbon fiber precursors The fiber for carbon fiber precursor fiber of the present disclosure includes an acrylamide-based polymer fiber and an uncrosslinked product of a self-crosslinking silicone oil on the surface of the acrylamide-based polymer fiber.

[0053] 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, and even more preferably 0.3 to 10 parts by mass, relative to 100 parts by mass of the acrylamide polymer fiber. By making the content of the uncrosslinked material 0.1 parts by mass or more, the silicone oil after self-crosslinking can more effectively suppress the fusion of the single fibers with each other. By keeping the content of uncrosslinked materials at 20 parts by mass or less, crosslinking of silicone oil between carbon fiber precursor fibers during self-crosslinking can be suppressed, and fusion of single fibers to each other can be suppressed. The method for measuring the content of uncrosslinked matter is the same as that described in the Examples.

[0054] In the present disclosure, the term "fiber for carbon fiber precursor fiber" refers to a precursor fiber for carbon fiber precursor fiber that has not been subjected to any of crosslinking, flame retardant treatment, and carbonization treatment. The fiber for carbon fiber precursor fiber becomes a carbon fiber precursor fiber when it is subjected to crosslinking treatment. The fiber for carbon fiber precursor fiber itself is not directly subjected to any of flame retardant treatment and carbonization treatment. In the present disclosure, the term "uncrosslinked self-crosslinking silicone oil" refers to a self-crosslinking silicone oil in a state where the self-crosslinking silicone oil is not crosslinked.

[0055] Since the fiber for carbon fiber precursor fiber of the present disclosure has the above-mentioned configuration, when the self-crosslinking silicone oil self-crosslinks, it is possible to suppress fusion of single fibers to each other during flame retardant treatment while maintaining a high carbonization yield.

[0056] The fiber for carbon fiber precursor fiber of the present disclosure has the same configuration as the carbon fiber precursor fiber of the present disclosure, except that the self-crosslinking silicone oil is in a non-self-crosslinking state.

[0057] (3) Method for producing carbon fiber precursor fiber The method for producing a carbon fiber precursor fiber according to the present disclosure includes a step of subjecting a fiber for carbon fiber precursor fiber to a crosslinking treatment (hereinafter referred to as a "crosslinking treatment step"), which will be described later. This results in the carbon fiber precursor fiber of the present disclosure.

[0058] The method for producing a carbon fiber precursor fiber may include, in addition to the crosslinking treatment step, a step of preparing a fiber for carbon fiber precursor fiber (hereinafter, "preparation step"). The preparation step is carried out before the crosslinking treatment step. Hereinafter, a method for producing a carbon fiber precursor fiber including a preparation step and a crosslinking treatment step will be described.

[0059] (3.1) Preparation process In the preparation step, a fiber for carbon fiber precursor fiber is prepared, thereby obtaining the fiber for carbon fiber precursor fiber of the present disclosure.

[0060] The method for preparing the fiber for carbon fiber precursor fiber is not particularly limited, and an example thereof includes a method in which an acrylamide-based polymer composition is spun, a self-crosslinking silicone oil is applied to the obtained acrylamide-based polymer fiber, and the self-crosslinking silicone oil is allowed to self-crosslink.

[0061] (3.1.1) Acrylamide-based polymer composition The acrylamide-based polymer composition is a raw material for acrylamide-based polymer fibers. The acrylamide polymer composition contains an acrylamide polymer and, if necessary, the above-mentioned additive components.

[0062] The acrylamide polymer to be used may be a commercially available product, or may be one synthesized by a conventionally known method. The synthesis of an acrylamide polymer can be carried out by utilizing a known polymerization reaction such as radical polymerization, cationic polymerization, anionic polymerization, living radical polymerization, etc. Among the above polymerization reactions, radical polymerization is preferred from the viewpoint of reducing synthesis costs. The synthesis of an acrylamide polymer can be carried out by utilizing a polymerization method such as solution polymerization, suspension polymerization, precipitation polymerization, dispersion polymerization, or emulsion polymerization (for example, inverse phase emulsion polymerization). When synthesizing an acrylamide-based polymer by solution polymerization, it is preferable to use a solvent in which the raw material monomers and the resulting acrylamide-based polymer are soluble. From the viewpoint of low-cost and safe synthesis, it is more preferable to use an aqueous solvent or an aqueous mixed solvent, and even more preferable to use an aqueous solvent. The aqueous solvent may be water, alcohol, a mixture of these, etc., with water being particularly preferred. The aqueous mixed solvent means a mixed solvent of the above aqueous solvent and an organic solvent, and the organic solvent may, for example, be tetrahydrofuran.

[0063] In the synthesis of an acrylamide polymer by radical polymerization, it is preferable to use a polymerization initiator. As the polymerization initiator, a conventionally known radical polymerization initiator such as azobisisobutyronitrile, benzoyl peroxide, 4,4'-azobis(4-cyanovaleric acid), ammonium persulfate, potassium persulfate, etc. can be used. When an aqueous solvent or an aqueous mixed solvent is used as the solvent, a radical polymerization initiator soluble in the aqueous solvent or the aqueous mixed solvent, such as 4,4'-azobis(4-cyanovaleric acid), ammonium persulfate, or potassium persulfate, is preferred. From the viewpoint of lowering 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 regulator in place of or together with the polymerization initiator, and it is more preferable to use a polymerization initiator and a polymerization accelerator in combination. The polymerization accelerator may, for example, be tetramethylethylenediamine. The molecular weight regulator may, for example, be an alkyl mercaptan compound such as n-dodecyl mercaptan. It is particularly preferable to use ammonium persulfate as a polymerization initiator in combination with tetramethylethylenediamine as a polymerization promoter.

[0064] The temperature of the polymerization reaction is not particularly limited, but from the viewpoint of improving the spinnability of the acrylamide polymer, it is preferably 35°C or higher, more preferably 40°C or higher, even more preferably 50°C or higher, and particularly preferably 70°C or higher.

[0065] The acrylamide polymer may be a homopolymer of an acrylamide monomer, or a copolymer of an acrylamide monomer and another polymerizable monomer. Preferred embodiments of the acrylamide monomer and the other polymerizable monomer have been described above, and therefore will not be described here.

[0066] The content of acrylamide-based monomer units in the acrylamide-based polymer is preferably 30 mol % or more, more preferably 40 mol % or more, even more preferably 50 mol % or more, particularly preferably 55 mol % or more, and most preferably 60 mol % or more. When the content of the acrylamide monomer unit 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 the acrylamide monomer unit is not particularly limited, but from the viewpoints of suppression of fusion, carbonization yield, and shape stability, it is preferably 99.9 mol % or less, more preferably 99.8 mol % or less, even more preferably 95 mol % or less, particularly preferably 90 mol % or less, and most preferably 85 mol % or less.

[0067] 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 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 viewpoints of fusion inhibition, carbonization yield, and shape stability. 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, even more preferably 50 mol %, particularly preferably 45 mol % or less, and most preferably 40 mol % or less.

[0068] Examples of methods for producing an acrylamide-based polymer composition include a method of directly mixing an additive component with a molten acrylamide-based polymer (melt mixing), a method of dry-blending an acrylamide-based polymer with an additive component (dry mixing), and a method of immersing or passing an acrylamide-based polymer formed into a fibrous shape in an aqueous solution or aqueous mixed solution containing the additive component, or a solution in which the acrylamide-based polymer is not completely dissolved but the additive component is dissolved, or a dispersion in which the additive component is dispersed. When the acrylamide-based polymer and the additive component are soluble in an aqueous solvent or an aqueous mixed solvent, a method of mixing the acrylamide-based polymer and the additive component in an aqueous solvent or an aqueous mixed solvent (wet mixing) is preferred, from the viewpoint of enabling the acrylamide-based polymer and the additive component to be mixed uniformly. Wet mixing may be performed by mixing the additive components in the aqueous solvent or aqueous mixed solvent in which the acrylamide polymer has been synthesized.

[0069] In the wet mixing, from the viewpoint of producing an acrylamide polymer composition safely and at lower cost, it is preferable to use an aqueous solvent as the solvent, and it is more preferable to use water.

[0070] When the acrylamide polymer composition is produced by wet mixing, the solvent may or may not be removed. The method for removing the solvent is not particularly limited, and at least one of known methods such as reduced pressure distillation, reprecipitation, hot air drying, vacuum drying, and freeze drying can be used.

[0071] (3.1.2) Spinning The method for spinning the acrylamide-based polymer composition is not particularly limited, and may be, for example, melt spinning, spunbonding, melt blowing, or centrifugal spinning of a melt of the acrylamide-based polymer composition. When the acrylamide-based polymer composition is soluble in an aqueous solvent or an aqueous mixed solvent, from the viewpoints of spinnability, reduction in environmental load, cost, and safety, it is preferred to produce an acrylamide-based polymer fiber by dissolving the acrylamide-based polymer composition in an aqueous solvent or an aqueous mixed solvent and spinning the obtained aqueous solution or aqueous mixed solution. When the synthesis of the acrylamide-based polymer is carried out by solution polymerization, it is preferable to adjust the acrylamide-based polymer solution to a desired concentration as necessary and then spin the solution to produce an acrylamide-based polymer fiber. When the acrylamide-based polymer composition is produced by wet mixing, it is preferable to adjust a solution of the acrylamide-based polymer composition to a desired concentration as necessary, and then spin the solution to produce an acrylamide-based polymer fiber.

[0072] The 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, which allows acrylamide-based polymer fibers having a desired fineness and average fiber diameter to be produced safely at low cost. From the viewpoint of producing acrylamide-based polymer fibers safely at lower cost, it is preferable to use an aqueous solvent as the solvent, and it is more preferable to use water.

[0073] (3.1.3) Adhesion The method for applying the self-crosslinking silicone oil to the acrylamide-based polymer fiber is not particularly limited, and examples thereof include a coating method, a dipping method, a spraying method, a touch roll method, a guide oiling method, and the like, using a self-crosslinking silicone-based oil agent (hereinafter sometimes referred to as "oil agent").

[0074] (3.1.3.1) Self-crosslinking silicone oil The oil agent contains 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 that dilutes 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, the oil agent may contain an oil agent that does not contain a self-crosslinking group or an oil agent that contains a functional group other than a self-crosslinking group, within a range that does not impair the effect of the present invention.

[0075] The viscosity of the oil 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 of the self-crosslinking silicone-based oil at 25° C. indicates the value measured at 25° C. using an Ubbelohde viscometer. When the self-crosslinking silicone-based oil is a commercially available self-crosslinking silicone oil, the viscosity of the self-crosslinking silicone oil at 25° C. may be the value in the manufacturer's catalog.

[0076] In addition to the organic solvent, the oil may contain a lubricant, a moisture absorbent, a surfactant, a viscosity modifier, a release agent, a spreading agent, an antibacterial agent, a preservative, and the like, as necessary.

[0077] (3.2) Crosslinking treatment process In the crosslinking treatment step, the fibers for carbon fiber precursor fiber are crosslinked to obtain the carbon fiber precursor fiber. The fibers for carbon fiber precursor fibers may be subjected to a crosslinking treatment in the form of a fiber bundle.

[0078] (3.2.1) Crosslinking The crosslinking treatment is not particularly limited as long as it can cause the self-crosslinking silicone oil in the acrylamide-based polymer fiber to self-crosslink, and examples of the crosslinking treatment include a method of irradiating an oil agent on the surface of the acrylamide-based polymer fiber with an electron beam (hereinafter referred to as "electron beam treatment"), a method of irradiating an oil agent on the surface of the acrylamide-based polymer fiber with ultraviolet light, a method of heating and drying an oil agent on the surface of the acrylamide-based polymer fiber, etc. Among these, the crosslinking treatment is preferably an electron beam treatment from the viewpoints of energy efficiency and processing speed.

[0079] (3.2.1.1) Electron beam processing From the viewpoints of suppression of fusion, carbonization yield, and shape stability, the dose of the electron beam irradiated to the acrylamide-based polymer fiber is preferably 50 kGy to 10,000 kGy, more preferably 100 kGy to 5,000 kGy, and even more preferably 150 kGy to 1,000 kGy. The above-mentioned preferable range of the dose is the preferable range of the dose when the acrylamide-based polymer fiber is irradiated with an electron beam from one direction. When irradiating from two or more directions, the range is not limited to the above and it is preferable to adjust it appropriately.

[0080] When an electron beam is used as the actinic radiation, the dose is measured using a film dosimeter, etc. As the film dosimeter, for example, FTR-125 manufactured by Fujifilm Corporation, FWT-60 manufactured by Toyo Medic Co., Ltd., or a device equivalent thereto can be used.

[0081] From the viewpoints of suppressing fusion, carbonization yield, and shape stability, the acceleration voltage of the electron beam irradiated to the acrylamide-based polymer fibers is preferably adjusted to an acceleration voltage at which preferably 20% or more, more preferably 60% or more, and even more preferably 80% or more of the irradiated active light passes through the acrylamide-based polymer fibers. 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 penetration) and the back surface (after penetration) of the sample. It may also be calculated from a commonly disclosed relationship diagram between penetration depth and relative dose. Specifically, the acceleration voltage is preferably from 10 kV to 10 MV, more preferably from 100 kV to 3 MV, and further preferably from 150 kV to 1 MV. The above-mentioned preferred numerical range of the acceleration voltage is a preferred numerical range of the acceleration voltage when the acrylamide-based polymer fiber is irradiated with active light rays from one direction. When irradiating from two or more directions, the above-mentioned range is not limited, and it is preferable to appropriately adjust the range.

[0082] The irradiation with electron beams may be carried out in a batch manner or a continuous manner. The device used for actinic ray irradiation is not particularly limited, but when performing actinic ray irradiation in a batch system, CB250 / 30 / 20mA manufactured by Iwasaki Electric Co., Ltd. or a device equivalent thereto can be used. When performing actinic ray irradiation in a continuous system, electron beam irradiation device EBC800-35 manufactured by NHV Corporation or a device equivalent thereto can be used.

[0083] (4) Manufacturing method of flame-retardant fiber The method for producing a flame-resistant fiber according to the present disclosure includes a step of subjecting a carbon fiber precursor fiber to a flame-resistant treatment (hereinafter referred to as a "flame-resistant treatment step"). This makes it possible to maintain a high carbonization yield and obtain a flame-resistant fiber in which fusion between single fibers is suppressed. Acrylamide polymer fibers are less susceptible to thermal decomposition due to flame retardant treatment. Furthermore, the structure of the acrylamide / vinyl cyanide / unsaturated carboxylic acid copolymer is converted into a highly heat-resistant structure by flame retardant treatment. Therefore, the carbonization yield is high. In particular, in acrylamide-based polymer fibers containing additives, the catalytic action of the additives, such as acids and their salts, accelerates the deammoniating and dehydrating reactions of the acrylamide / vinyl cyanide / unsaturated carboxylic acid copolymer. This makes it easy for a ring structure (imide ring structure) or a structure with two or more consecutive rings to form within the molecule of the acrylamide-based polymer fiber. This makes it easy for the structure of the acrylamide / vinyl cyanide / unsaturated carboxylic acid copolymer to be converted into a structure with high heat resistance. As a result, the carbonization yield is even higher.

[0084] In the present disclosure, the term "flame retardation treatment" refers to subjecting a carbon fiber precursor fiber to a heat treatment in an oxidizing gas atmosphere.

[0085] (4.1) Flameproofing treatment The temperature of the flame retardant treatment is not particularly limited, but is preferably 150°C to 500°C, more preferably 200°C to 450°C, and further preferably 250°C to 420°C. The above temperature includes not only the maximum temperature during the flame-resistant treatment (flame-resistant treatment temperature) described below, but also the temperature during the temperature rise process up to the flame-resistant treatment temperature.

[0086] The maximum temperature during the flame retardant treatment (flame retardant treatment temperature) is preferably 200°C to 500°C, more preferably 250°C to 450°C, even more preferably 305°C to 440°C, particularly preferably 310°C to 430°C, and most preferably 315°C to 420°C. By setting the flame retardant treatment temperature at 200°C or higher, the deammoniating reaction and dehydration reaction of the acrylamide / vinyl cyanide / unsaturated carboxylic acid copolymer are easily accelerated, and a ring structure (imide ring structure) is easily formed in the molecule, which tends to improve the heat resistance and carbonization yield of the flame retardant fiber. By setting the flame-retardant treatment temperature to 500° C. or less, the flame-retardant fiber is less susceptible to thermal decomposition, which tends to reduce production costs.

[0087] The flame retardant treatment time (heating time at the flame retardant treatment temperature) is not particularly limited, but from the viewpoints of carbonization yield and production costs, it is preferably 1 to 120 minutes, more preferably 2 to 60 minutes, even more preferably 3 to 50 minutes, and particularly preferably 4 to 40 minutes. By setting the flame-proofing treatment time to 1 minute or more, the carbonization yield can be improved. By limiting the flame-proofing treatment time to 120 minutes or less, the manufacturing cost can be reduced.

[0088] (4.2) Stretching In the flame-retardant treatment of the carbon fiber precursor fiber, it is preferable to subject the carbon fiber precursor fiber to a stretching treatment. By subjecting the carbon fiber precursor fiber to a stretching treatment, the acrylamide-based polymer contained in the carbon fiber precursor fiber is oriented, and the tensile strength of the flame-retardant fiber tends to be improved. The stretching treatment is preferably carried out at least during heating at the flame-proofing treatment temperature. From the viewpoint of improving the tensile strength of the flame-resistant fiber, it is preferable to carry out a drawing treatment also during the temperature rise up to the flame-resistant treatment temperature.

[0089] During the stretching treatment, the tension applied to the carbon fiber precursor fiber is preferably 0.03 mN / tex to 500 mN / tex, more preferably 0.05 mN / tex to 400 mN / tex, even more preferably 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, fusion between the single fibers is not sufficiently suppressed, and the load-bearing capacity, strength, and carbonization yield of the flame-retardant fiber at high temperatures tend to decrease. If the tension applied to the carbon fiber precursor fiber exceeds 500 mN / tex, the carbon fiber precursor fiber may be broken during the flame retardant treatment. In the present disclosure, the tension (unit: mN / tex) applied to the carbon fiber precursor fiber indicates the value obtained by dividing the tension (unit: mN) applied to the carbon fiber precursor fiber during the flame retardant treatment by the fineness (unit: tex) of the carbon fiber precursor fiber in an absolute dry state, that is, the tension per unit fineness of the carbon fiber precursor fiber. The tension can be adjusted by adjusting the speed at the inlet and outlet of a heating device such as a flame-proofing furnace, or by using a load cell, a spring, a weight, an air cylinder, or the like.

[0090] As long as a predetermined tension is applied to the acrylamide polymer fiber at the flame-retardant treatment temperature (the maximum temperature during the flame-retardant treatment), the predetermined tension may or may not be applied during the temperature rise process up to the flame-retardant treatment temperature, but from the viewpoint of obtaining a sufficient effect of the tension, it is preferable that the predetermined tension is also applied during the temperature rise process, etc. Moreover, the tension may be applied from the initial stage of the temperature rise process, etc., or from an intermediate stage. In addition, in the method for producing the flame-resistant fiber of the present invention, after a heat treatment is performed while applying a predetermined tension at the flame-resistant treatment temperature (the maximum temperature during the flame-resistant treatment), a heat treatment may be performed at a temperature higher than the flame-resistant treatment temperature while applying a tension other than the predetermined tension or without applying tension.

[0091] (4.3) Flame-retardant fibers The density of the flame-retardant fiber is not particularly limited, but is preferably 1.30 g / cm 3 ~1.75g / cm 3 and preferably 1.35 g / cm 3 ~1.70g / cm 3 More preferably, it is 1.37 g / cm 3 ~1.65g / cm 3 More preferably, it is 1.39 g / cm 3 ~1.60g / cm 3 It is particularly preferable that the density is 1.44 g / cm 3 ~1.55g / cm 3 It is most preferable that: Flame-resistant fiber density is 1.30g / cm 3 By satisfying the above, the heat resistance and the dense structure of the flame-retardant fiber are sufficient, and therefore the carbonization yield tends to be improved. Flame-resistant fiber density is 1.75g / cm 3 By satisfying the following, the productivity of the flame-resistant fiber is excellent.

[0092] 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, even more preferably 1 μm to 60 μm, even more preferably 2 μm to 30 μm, even more particularly preferably 3 μm to 20 μm, and most preferably 4 μm to 15 μm.

[0093] From the viewpoint of carbonization yield, the average fiber diameter of the flame-resistant fiber is preferably at least 5% smaller than the average fiber diameter of the carbon fiber precursor fiber, more preferably at least 10% smaller, even more preferably at least 15% smaller, even more preferably at least 20% smaller, particularly preferably at least 25% smaller, and most preferably at least 30% smaller.

[0094] (5) Manufacturing method of carbon fiber The method for producing carbon fibers according to the present disclosure includes a step of obtaining a flame-retardant fiber by a method for producing a flame-retardant fiber, and a step of subjecting the flame-retardant fiber to a carbonization treatment (hereinafter referred to as a "carbonization treatment step"). As a result, carbon fibers are obtained.

[0095] In the present disclosure, the term "carbonization treatment" refers to a treatment for carbonizing carbon fiber precursor fibers, and more specifically, refers to subjecting carbon fiber precursor fibers to a heat treatment in a low-oxygen atmosphere (preferably an environment in which oxygen is blocked).

[0096] (5.1) Process for obtaining flame-retardant fiber The process for obtaining the flame-resistant fiber is the same as the method exemplified above as the method for producing the flame-resistant fiber.

[0097] (5.2) Carbonization process (5.2.1) Carbonization The carbonization treatment may be a method of subjecting the flame-retardant fiber to a heat treatment in an inert gas (nitrogen, argon, helium, etc.) atmosphere at a temperature higher than that in the flame-retardant treatment. The "carbonization treatment" may include "graphitization" which is generally performed by heating at 2000 to 3000°C in an inert gas atmosphere. By subjecting the flame-retardant fiber to the carbonization treatment, the flame-retardant fiber is carbonized to obtain a carbon fiber. The lower limit of the heating temperature for the carbonization treatment 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 most preferably 1300°C or higher. The upper limit of the heating temperature in the carbonization treatment is preferably 3000° C. or lower, and more preferably 2500° C. or lower. The heating time for the carbonization treatment is not particularly limited, but is preferably from 30 seconds to 60 minutes, and more preferably from 1 minute to 30 minutes. In the present disclosure, the "carbonization treatment" may also include "graphitization" which is generally performed by heating at a temperature of 2000°C to 3000°C in an inert gas atmosphere. The carbonization process may include multiple heat treatments. In the carbonization treatment, multiple heat treatments may be performed. For example, a heat treatment (pre-carbonization treatment) may be performed first at a temperature less than 1000°C, then a heat treatment (carbonization treatment) may be performed at a temperature of 1000°C or higher, and then a heat treatment (graphitization treatment) may be performed at a temperature of 2000°C or higher.

[0098] (5.3) Carbon fiber The average fiber diameter of the carbon fibers 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, even more preferably 1 μm to 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. By setting the average fiber diameter of the carbon fibers to 3 nm or more, when a composite material is produced using a matrix such as resin, if the viscosity of the matrix is ​​high, insufficient impregnation of the resin into the carbon fiber bundles is less likely to occur, and the tensile strength of the composite material is improved. When the average fiber diameter of the carbon fibers is 300 μm or less, the tensile strength of the carbon fibers tends not to decrease. EXAMPLES

[0099] The above embodiment will be specifically described below with reference to examples, but the above embodiment is not limited to these examples.

[0100] <Single fiber fineness of acrylamide polymer fiber> In the present examples, the single fiber fineness of the acrylamide-based polymer fiber was determined by bundling 100 of the obtained acrylamide-based polymer fibers to prepare a fiber bundle, measuring the mass of this fiber bundle, and calculating the single fiber fineness (tex) according to the following formula. Single fiber fineness (tex) = fiber bundle mass (g) / fiber length (m) x 1000 / 100 (pieces)

[0101] <Average fiber diameter of acrylamide-based polymer fibers> In this example, the average fiber diameter of the acrylamide-based polymer fiber was measured by bundling 100 of the obtained acrylamide-based polymer fibers to prepare a fiber bundle, and measuring the density of the fiber bundle (g / cm) using a dry automatic density meter (Micromeritics' "AccuPic II 1340"). 3 ) was measured, and the average fiber diameter (μm) of the single fibers constituting the fiber bundle was calculated using the following formula. D = {(Dt × 4 × 1000) / (ρ × π × n)} 1 / 2 [During the ceremony, D represents the average fiber diameter (μm) of the single fibers constituting the fiber bundle, Dt represents the fiber bundle fineness (tex), ρ is the density of the fiber bundle (g / cm 3 ), n represents the number of single fibers that make up the fiber bundle.

[0102] Example 1 A monomer composition consisting of 63 mol% acrylamide (AM), 35 mol% acrylonitrile (AN), and 2 mol% acrylic acid (AA) was prepared. 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. Under a nitrogen atmosphere, 3 parts by mass of ammonium persulfate was added to the resulting aqueous solution while stirring it, and the solution was heated at 70°C for 150 minutes, then heated to 90°C over 30 minutes and held at 90°C for 1 hour to carry out a polymerization reaction. The obtained aqueous solution was dropped into methanol to precipitate the AM / AN / AA copolymer, which was then 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%).

[0103] The obtained AM / AN / AA copolymer was dissolved in ion-exchanged water to obtain an aqueous solution, which was then dry-spun to obtain an acrylamide polymer fiber with an average fiber diameter of about 20 μm and a fiber density of 0.4 tex / fiber. Next, a self-crosslinking silicone oil (X-22-164C manufactured by Shin-Etsu Chemical Co., Ltd., self-crosslinking group: methacryl group) (temperature: 25°C) was applied to the entire surface of the acrylamide polymer fiber to obtain a single fiber. 800 of the obtained single fibers were bundled to obtain a fiber bundle (800 fibers / bundle).

[0104] Using an electron beam irradiation device "EBC800-35" manufactured by NHV Corporation, the fiber bundle was subjected to continuous electron beam treatment under the conditions of a conveying speed of 10 m / min, a feed tension of 75 g, a take-up tension of 400 g, an acceleration voltage of 800 kV in the atmosphere, and an electron beam dose of 1100 kGy. As a result, a carbon fiber precursor fiber bundle was obtained.

[0105] Example 2 A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 1, except that the treatment conditions for the electron beam treatment were changed to an acceleration voltage of 400 kV and an electron beam dose of 300 kGy.

[0106] 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 the electron beam treatment.

[0107] Comparative Example 2 A carbon fiber precursor fiber bundle was obtained in the same manner as in Example 1, except that the self-crosslinking silicone oil was not applied to the acrylamide-based polymer fiber.

[0108] Comparative Example 3 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 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.

[0109] In the present disclosure, the term "non-self-crosslinking group" refers to an organic group in which at least some of the methyl groups on the side chains and ends of polydimethylsiloxane have been substituted, and which is not a self-crosslinking group.

[0110] 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 non-self-crosslinking silicone oil A.

[0111] Comparative Example 5 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 a 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) and the fiber bundle was not subjected to electron beam treatment.

[0112] <<Measurement of oil adhesion amount>> A certain amount was cut out from each of the carbon fiber precursor fiber bundles obtained in Examples 1 and 2 and Comparative Examples 1 to 5 to obtain test pieces. The test pieces were immersed in a solvent (e.g., tetrahydrofuran) that does not dissolve the test pieces but dissolves silicone oil. The test pieces were removed from the solvent, and the solvent was completely removed under reduced pressure to obtain a residue. The amount of oil attached to each of the carbon fiber precursor fibers was calculated from the following formula. Amount of oil attached (parts by mass) = [mass of residue (g) / mass of dried test piece after oil removal (g)] x 100

[0113] (Flame-retardant treatment) The carbon fiber precursor fiber bundles obtained in Examples 1 and 2 and Comparative Examples 1 to 5 were subjected to a flame retardant treatment by increasing the temperature from room temperature to 350° C. at a rate of 10° C. / min under an air atmosphere while applying a tension of 0.4 mN / tex, and then maintaining the temperature at 350° C. for 30 minutes. As a result, a flame retardant fiber bundle was obtained.

[0114] <<Measuring the fusion rate>> The flame-retardant 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 fiber with a diameter predicted from the carbon fiber precursor fiber bundle was defined as a single fiber, and a fiber thicker than the predicted diameter resulting from the fusion of two or more single fibers was defined as a fused fiber. The fusion rate was calculated as the percentage of the number of single fibers contained in the fused fiber to the number of fibers observed (200 fibers in terms of single fibers). The measurement results of the fusion rate are shown in Table 1. The acceptable range of the fusion rate is 20% or less.

[0115] <<Measurement of carbonization yield>> The flame-retardant fiber bundle was heated from room temperature to 1000°C at a rate of 20°C / min in a nitrogen atmosphere to obtain a carbon bundle. The carbonization yield was determined as a percentage of the mass of the carbon fiber bundle divided by the mass of the flame-retardant fiber bundle before carbonization. The measurement results of the carbonization yield are shown in Table 1. The acceptable range of the carbonization yield is 70% or more.

[0116] [Table 1]

[0117] The carbon fiber precursor fiber of Comparative Example 1 includes an acrylamide polymer fiber and an uncrosslinked product of a self-crosslinking silicone oil. The carbon fiber precursor fiber of Comparative Example 2 includes an acrylamide-based polymer fiber that has been subjected to an 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 polymer fiber and a coating film of non-self-crosslinking silicone oil B. However, the carbon fiber precursor fibers of Comparative Example 1 to Comparative Example 5 did not have a self-crosslinked product of the self-crosslinking silicone oil. Therefore, in Comparative Example 1 to Comparative Example 5, the fusion rate was more than 20% and the carbonization yield was less than 70%. From these results, it was found that the carbon fiber precursor fibers of Comparative Example 1 to Comparative Example 5 could not suppress the fusion between single fibers in the flame retardant treatment while maintaining a high carbonization yield.

[0118] The measurement results of Comparative Example 1 and Comparative Example 2 show that when electron beam treatment was not performed on acrylamide-based polymer fibers coated with self-crosslinking silicone oil, or when electron beam treatment was performed on acrylamide-based polymer fibers not coated with self-crosslinking silicone oil, 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 fiber coated with non-self-crosslinking silicone oil was subjected to electron beam treatment, the fusion rate was 26% or more, and sufficient single fibers were not obtained. From the measurement results of Comparative Example 3 and Comparative Example 5, when the acrylamide-based polymer fiber coated with non-self-crosslinking silicone oil was not subjected to electron beam treatment, the fusion rate was 78% or more, and sufficient single fibers were not obtained.

[0119] The carbon fiber precursor fibers of Examples 1 and 2 include an acrylamide polymer fiber and a self-crosslinked product of a self-crosslinking 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 can suppress fusion between single fibers during flame retardant treatment while maintaining a high carbonization yield.

Claims

1. The present invention comprises an acrylamide polymer fiber and a self-crosslinked product of a self-crosslinking silicone oil on the surface of the acrylamide polymer fiber, The self-crosslinking silicone oil has a self-crosslinking group, The carbon fiber precursor fiber, wherein the self-crosslinking group comprises at least one of a mono-substituted ethylene group, a 1,1-disubstituted ethylene group, and a 1,2-disubstituted ethylene group.

2. The carbon fiber precursor fiber according to claim 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-based polymer fiber.

3. the acrylamide-based polymer fiber is made of an acrylamide-based polymer, 3. The carbon fiber precursor fiber according to claim 1, wherein the acrylamide-based polymer contains 30 mol % or more of acrylamide-based monomer units based on all monomer units constituting the acrylamide-based polymer.

4. 4. The carbon fiber precursor fiber according to claim 3, wherein the acrylamide-based polymer contains, relative to all monomer units constituting the acrylamide-based polymer, 40 mol % or more and 99.8 mol % or less of acrylamide-based monomer units, 0.1 mol % or more and 50 mol % or less of vinyl cyanide-based monomer units, and 0.1 mol % or more and 30 mol % or less of unsaturated carboxylic acid-based monomer units.

5. A carbon fiber precursor fiber as described in claim 1 or claim 2, wherein the self-crosslinking group has an acrylic group or a methacrylic group.

6. The viscosity of the self-crosslinking silicone oil at 25° C. is 9 mm ２ The carbon fiber precursor fiber according to claim 1 or claim 2, wherein the linear modulus is 1 / s or more.

7. The present invention comprises an acrylamide-based polymer fiber and an uncrosslinked self-crosslinking silicone oil on the surface of the acrylamide-based polymer fiber, The self-crosslinking silicone oil has a self-crosslinking group, The self-crosslinking group comprises at least one of a mono-substituted ethylene group, a 1,1-disubstituted ethylene group, and a 1,2-disubstituted ethylene group.

8. A method for producing a carbon fiber precursor fiber, comprising a step of subjecting the fiber for carbon fiber precursor fiber according to claim 7 to a crosslinking treatment.

9. The method for producing a carbon fiber precursor fiber according to claim 8 , wherein the crosslinking treatment is an electron beam treatment.

10. A method for producing a flame-retardant fiber, comprising the step of subjecting the carbon fiber precursor fiber according to claim 1 or 2 to a flame-retardant treatment.

11. A step of obtaining a flame-resistant fiber by the method for producing a flame-resistant fiber according to claim 10; A step of subjecting the flame-retardant fiber to a carbonization treatment; A method for producing carbon fibers, comprising:

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