Carbon fiber precursor, 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 that can be produced into a carbon fiber precursor fiber that can be stretched at a high stretch ratio, and that can produce the carbon fiber precursor fiber while suppressing occurrence of yarn breakage even when melt-spinning is performed at a relatively low temperature using a multi-hole nozzle without using an organic solvent and wound up at a high speed.SOLUTION: A carbon material precursor of the present disclosure includes a diene-based polymer. The melt flow rate of the carbon fiber precursor measured according to ASTM D1238 at a temperature of 160°C and a load of 21.2 N is 10 g / 10 minutes or more.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a carbon fiber precursor, a 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 lightweight and has excellent mechanical properties, and as a result, carbon fiber composite materials are being developed for a variety of applications (e.g., aerospace applications, automotive applications, building materials, etc.).

[0003] As a method for producing carbon fibers, a method is known in which a fiber bundle obtained by spinning polyacrylonitrile or pitch is used as a precursor, which is subjected to a flame retardant treatment and then to a carbonization treatment (Patent Documents 1 to 3).

[0004] Polyacrylonitrile-based carbon fibers made from fibers obtained by spinning polyacrylonitrile have high mechanical properties and are therefore most widely used. Polyacrylonitrile-based carbon fibers are produced by wet spinning using an organic solvent (e.g., dimethyl sulfoxide, dimethylformamide, etc.) or dry-wet spinning. Therefore, energy is required to recycle the organic solvent, which may increase the production cost. There is a limit to increasing the spinning speed, for example, to 100 m / min or more. Here, the "spinning speed" refers to the winding speed when the fiber is wound. In addition, with polyacrylonitrile-based carbon fibers, toxic gases (e.g., hydrogen cyanide, etc.) are generated during the flame-retardant treatment.

[0005] On the other hand, when pitch is used as a raw material, it is possible to perform spinning by melt spinning without using an organic solvent. In addition, hydrogen cyanide is not generated during the flame-retardant treatment. However, melt spinning of pitch-based fibers generally requires high temperatures (specifically, 250°C or higher). This not only increases energy costs, but also makes the resulting fibers relatively brittle, and during the flame-retardant treatment, fusion between fibers and breakage of some fibers may occur easily. In other words, when pitch is used as a raw material, it may not be easy to handle (Patent Document 3).

[0006] Patent Documents 4 to 6 disclose fibers obtained by melt spinning 1,2-polybutadiene as a carbon fiber precursor that can be melt spun without using an organic solvent and does not generate hydrogen cyanide. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2006-183159 A [Patent Document 2] JP 2008-202208 A [Patent Document 3] Japanese Patent Application Publication No. 6-10215 [Patent Document 4] Japanese Patent Application Publication No. 48-82199 [Patent Document 5] Japanese Unexamined Patent Publication No. 48-92699 [Patent Document 6] Japanese Unexamined Patent Publication No. 49-106490 Summary of the Invention [Problem to be solved by the invention]

[0008] In Patent Documents 4 to 6, single fibers are obtained by melt spinning 1,2-polybutadiene. In Patent Documents 5 and 6, single fibers are obtained and then bundled to form a fiber bundle. In order to reduce costs by improving productivity in melt spinning, it is required to obtain a fiber bundle consisting of many fibers (multifilament) by winding it at high speed (e.g., spinning speed: 100 m / min or more) using a nozzle with multiple holes (e.g., number of holes: 36 or more) instead of single fibers.

[0009] However, when the 1,2-polybutadiene specifically disclosed in Patent Documents 4 to 6 is used, thread breakage tends to occur easily due to an increase in the number of holes in the nozzle and an increase in the spinning speed. When thread breakage occurs, the broken threads may wind around the conveying section (e.g., a roller, etc.), which may reduce the yield. In addition, if broken fibers accumulate in the conveying section, continuous melt spinning operation becomes difficult. Furthermore, during the melt spinning operation (e.g., when the fiber is paid out, when it is wound up, when it is conveyed, etc.), defects may occur on the fiber surface, which may reduce the strength of the fiber.

[0010] Furthermore, when the carbon fiber bundle obtained by melt spinning the 1,2-polybutadiene specifically disclosed in Patent Documents 4 to 6 is stretched at a high stretch ratio (for example, stretch ratio: more than 2 times), there is a risk of yarn breakage occurring. Patent Document 6 uses 1,2-polybutadiene with a high melting point (for example, melting point 192°C), and melt spinning at a high temperature of at least 192°C or higher is required. In order to reduce the energy required for spinning, it is desirable to reduce the spinning temperature of melt spinning (for example, preferably 150°C or lower).

[0011] Thus, there is a demand for a carbon fiber precursor that can be made into a carbon fiber precursor fiber that can be stretched at a high stretch ratio (e.g., stretch ratio: more than 2 times), and that can be used to produce a carbon fiber precursor fiber while suppressing the occurrence of yarn breakage, even when melt spinning is performed at a relatively low temperature (e.g., 160°C or lower) using a nozzle with multiple holes (e.g., number of holes: 36 or more) without using an organic solvent and the carbon fiber precursor fiber is wound up at a high speed (e.g., spinning speed: 100 m / min or more).

[0012] An object of the present invention is to provide a carbon fiber precursor that can be made into a carbon fiber precursor fiber that can be stretched at a high stretch ratio, and that can produce a carbon fiber precursor fiber while suppressing the occurrence of yarn breakage, even when melt-spinning is performed at a relatively low temperature using a multi-hole nozzle without using an organic solvent and wound up at a high speed. A problem to be solved by another embodiment of the present disclosure is to provide a carbon fiber precursor fiber that can be drawn at a high draw ratio. An object of another embodiment of the present disclosure is to provide 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 precursor fiber that can be stretched at a high draw ratio while suppressing the occurrence of yarn breakage, even when melt spinning is performed at a relatively low temperature using a multi-hole nozzle without using an organic solvent and the fiber is wound up at a high speed. [Means for solving the problem]

[0013] As a result of intensive research into the above-mentioned problems, the present inventors have found that, by melt spinning a multifilament using a carbon fiber precursor containing 1,2-polybutadiene and having a specific fluidity (mercury flow rate), it is possible to obtain a carbon fiber precursor fiber with reduced yarn breakage, and the obtained carbon fiber precursor fiber can be drawn at a high draw ratio. Furthermore, the present inventors have found that a crosslinked carbon fiber precursor fiber obtained by subjecting the carbon fiber precursor fiber to a crosslinking treatment such as electron beam irradiation is reduced in fusion during flame retardation, and that the obtained flame retardant fiber is reduced in yarn breakage due to tension application or thermal decomposition during carbonization.

[0014] Means for solving the above problems include the following embodiments. <1> Contains a diene polymer, A carbon fiber precursor having a melt flow rate of 10 g / 10 min or more, measured at a temperature of 160°C and a load of 21.2 N in accordance with ASTM D1238. <2> The said composition further comprises a plasticizing additive. <1> The carbon fiber precursor according to claim 1. <3> The diene polymer contains a diene monomer unit represented by the following formula (I): <1> or <2> The carbon fiber precursor according to claim 1.

[0015] [ka]

[0016] [In formula (I), R represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, and n represents an arbitrary number of repetitions.] <4> The above <1> ~ <3> 13. A carbon fiber precursor fiber comprising the carbon fiber precursor according to any one of claims 1 to 12. <5> The diene polymer is crosslinked to form a crosslinked diene polymer. <4> The carbon fiber precursor fiber according to claim 1. <6> The gel fraction is 30% or more. <4> or <5> The carbon fiber precursor fiber according to claim 1. <7> The method includes a step of spinning a carbon fiber precursor to obtain a carbon fiber precursor fiber, The carbon fiber precursor comprises a diene-based polymer, The method for producing a carbon fiber precursor fiber, wherein the carbon fiber precursor has a melt flow rate of 10 g / 10 min or more, measured in accordance with ASTM D1238 at a temperature of 160° C. and a load of 21.2 N. <8> The method further comprises a step of subjecting the carbon fiber precursor fiber to a crosslinking treatment, The gel fraction of the carbon fiber precursor fiber after the crosslinking treatment is 30% or more. <7> A method for producing a carbon fiber precursor fiber according to claim 1. <9> The above <7> or <8> A step of obtaining a carbon fiber precursor fiber by the method for producing a carbon fiber precursor fiber according to the present invention; A step of subjecting the carbon fiber precursor fiber to a heat treatment in an oxidizing atmosphere; A method for producing a flame-resistant fiber, comprising: <10> The above <9> 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

[0017] According to the present disclosure, a carbon fiber precursor can be provided that can be made into a carbon fiber precursor fiber that can be stretched at a high draw ratio, and that can produce a carbon fiber precursor fiber while suppressing the occurrence of yarn breakage even when melt-spinning is performed at a relatively low temperature using a multi-hole nozzle without using an organic solvent and wound up at high speed. According to the present disclosure, a carbon fiber precursor fiber that can be drawn at a high draw ratio can be provided. According to the present disclosure, there can be provided 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 precursor fiber that can be stretched at a high draw ratio while suppressing the occurrence of yarn breakage, even when melt spinning is performed at a relatively low temperature without using an organic solvent by using a multi-hole nozzle and winding up at high speed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] 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.

[0019] 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.

[0020] In the present disclosure, each component may contain multiple types of the corresponding substance. When multiple types of substances corresponding to each component are present in the carbon material precursor, the content or amount of each component means the total content or amount of the multiple types of substances present in the carbon material precursor, unless otherwise specified.

[0021] (1) Carbon fiber precursor The carbon fiber precursor of the present disclosure includes a diene-based polymer, and the carbon fiber precursor has a melt flow rate of 10 g / 10 min or more, measured according to ASTM D1238 at a temperature of 160° C. and a load of 21.2 N.

[0022] In the present disclosure, the term "carbon fiber precursor" refers to a raw material for a carbon fiber precursor fiber. The term "carbon fiber precursor fiber" refers to a fiber for producing a carbon fiber that has not been subjected to either a flame retardant treatment or a carbonization treatment. The term "diene polymer" refers to a polymer of a monomer containing a diene. The diene polymer may be a homopolymer or a copolymer.

[0023] Hereinafter, "melt flow rate measured in accordance with ASTM D1238 at a temperature of 160°C and a load of 21.2 N" will also be referred to as "MFR."

[0024] Since the carbon fiber precursor of the present disclosure has the above-mentioned configuration, it can be made into a carbon fiber precursor fiber that can be stretched at a high stretch ratio (e.g., stretch ratio: more than 2 times), and even if it is melt spun at a relatively low temperature (e.g., 160°C or less, preferably 150°C or less) using a nozzle with multiple holes (e.g., number of holes: 36 or more) without using an organic solvent and wound up at a high speed (e.g., spinning speed: 100 m / min or more), the occurrence of yarn breakage can be suppressed to produce a carbon fiber precursor fiber. This effect is believed to be due to, but not limited to, the following reasons. In order to suppress the occurrence of thread breakage even when melt spinning is performed using a multi-hole nozzle and wound at high speed, it is necessary to stably supply the molten carbon fiber precursor to each hole. An MFR of 10 g / 10 min or more indicates that the fluidity of the molten carbon fiber precursor is high. Therefore, the molten carbon fiber precursor of the present disclosure is more likely to spread to each hole in the nozzle than in the past. In other words, the molten carbon fiber precursor is more likely to be stably supplied to each hole. As a result, the carbon fiber precursor of the present disclosure can produce a carbon fiber precursor fiber while suppressing the occurrence of thread breakage even when melt spinning is performed at a relatively low temperature using a multi-hole nozzle without using an organic solvent and wound at high speed. Furthermore, the obtained carbon fiber precursor fiber can be drawn at a high draw ratio. The carbon fiber precursor of the present disclosure includes a diene-based polymer, and therefore the carbon fiber precursor of the present disclosure can be melt spun to produce a carbon fiber precursor fiber without using an organic solvent. As a result, it is presumed that the carbon fiber precursor of the present disclosure can be made into a carbon fiber precursor fiber that can be stretched at a high draw ratio, and that even if the carbon fiber precursor fiber is melt spun at a relatively low temperature using a multi-hole nozzle without using an organic solvent and wound up at high speed, the occurrence of yarn breakage can be suppressed and a carbon fiber precursor fiber can be produced.

[0025] In addition, in the carbon fiber precursor of the present disclosure, a cyanide compound is not an essential component. Therefore, the carbon fiber precursor of the present disclosure can be a carbon fiber precursor fiber in which generation of hydrogen cyanide is suppressed.

[0026] The form of the carbon material precursor is not particularly limited, and examples thereof include powder, pellets, lumps, solutions (e.g., aqueous or non-aqueous solutions), suspensions (i.e., slurry liquids), and the like. The term "pellets" refers to particles made of the carbon material precursor. Pellets can be obtained, for example, by melting the carbon material precursor in a melt kneading device or the like, discharging it from a nozzle to solidify, and then granulating it with a pelletizer or by pulverization.

[0027] The MFR of the carbon fiber precursor is 10 g / 10 min or more. From the viewpoint of improving the spinnability and stretchability of the carbon material precursor, the MFR is more preferably 11 g / 10 min or more, even more preferably 14 g / 10 min or more, particularly preferably 20 g / 10 min or more, and most preferably 30 g / 10 min or more. From the viewpoint of suppressing the occurrence of yarn breakage caused by the viscosity of the molten carbon fiber precursor being too low when stretched at a high stretch ratio, the MFR is preferably 2000 g / 10 min or less, more preferably 1500 g / 10 min or less, even more preferably 1000 g / 10 min or less, particularly preferably 900 g / 10 min or less, and most preferably 800 g / 10 min or less.

[0028] Examples of methods for adjusting the MFR of the carbon fiber precursor to 10 g / 10 min or more include the first method and the second method. The first method refers to a method of selecting a diene polymer component having an MFR of 10 g / 10 min or more. The second method refers to a method of adding a plasticizing additive described later to a diene polymer component having an MFR of less than 10 g / 10 min. In the first method, by including a diene polymer having a specific number average molecular weight at a specific content ratio, the MFR can be adjusted to 10 g / 10 min or more by the plasticizing effect. The specific number average molecular weight is, for example, usually 30,000 or less, preferably 20,000 or less, more preferably 10,000 or less, even more preferably 9000 or less, and particularly preferably 8000 or less. The specific content ratio of the diene polymer is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, even more preferably 1 mass% or more, particularly preferably 2 mass% or more, and most preferably 3 mass% or more with respect to 100 mass% of the total diene polymer in the carbon fiber precursor.

[0029] In the present disclosure, "improving the spinnability of a carbon material precursor" means that melt spinning can be performed using a multi-hole nozzle to produce carbon fiber precursor fibers with reduced occurrence of yarn breakage even when wound at high speed. In the present disclosure, "improving the stretchability of the carbon material precursor" means that the carbon fiber precursor fiber can be stretched at a higher stretch ratio.

[0030] (1.1) Diene polymers The carbon fiber precursor comprises a diene-based polymer.

[0031] The diene polymer is preferably a polymer containing a diene monomer unit represented by the following formula (I) (hereinafter also referred to as "diene monomer unit (I)"). By including the diene monomer unit (I), an intramolecular cyclization reaction and / or an intermolecular crosslinking reaction can be promoted by an external stimulus, and the fusion of single fibers during the flame retardant treatment can be reduced. The external stimulus is, for example, at least one selected from radiation treatment, ultraviolet treatment, heat treatment, acid treatment, addition of a crosslinking agent, and addition of a radical initiator.

[0032] [ka]

[0033] In formula (I), R represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, and n represents an arbitrary repeating number (that is, an integer of 1 or more).

[0034] The diene polymer may contain only one type of diene monomer unit (I), or may contain two or more types.

[0035] The "organic group" represented by R preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 to 3 carbon atoms, from the viewpoint of improving the yield of the obtained carbon fibers. Examples of the "organic group" represented by R include hydrocarbon groups. At least a part of the carbon atoms constituting the hydrocarbon group may be substituted with a group substituted with a halogen atom (e.g., a chlorine atom, a bromine atom, or a fluorine atom), an oxygen atom, a nitrogen atom, or a sulfur atom. The hydrocarbon group may be linear or branched, or may contain a ring structure.

[0036] The hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. Among them, the hydrocarbon group is preferably an aliphatic hydrocarbon group, more preferably an alkyl group, and even more preferably a linear alkyl group. Specifically, the hydrocarbon group is preferably a hydrocarbon group having 1 to 10 carbon atoms (preferably 1 to 6 carbon atoms), such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a sec-butyl group, a pentyl group, an isopentyl group, a neopentyl group, a hexyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 2,2-dimethylbutyl group, a 2,3-dimethylbutyl group, a heptyl group, a 2-methylhexyl group, a 3-methylhexyl group, a 2,2-dimethylpentyl group, a 2,3-dimethylpentyl group, a 2,4-dimethylpentyl group, a 3-ethylpentyl group, a 2,2,3-trimethylbutyl group, an o-methyl ...2,3-ethylpentyl group, a 2,2,3-trimethylbutyl group, a 2,3-ethylpentyl group, a 2,3-ethylpentyl group, a 2,3-ethylpentyl group, a 2,3-ethylpentyl group, a 2,3-ethylpentyl group, a 2,3-ethylpentyl group, a 2,3-ethylpentyl group, octyl group, methylheptyl group, dimethylhexyl group, 2-ethylhexyl group, 3-ethylhexyl group, trimethylpentyl group, 3-ethyl-2-methylpentyl group, 2-ethyl-3-methylpentyl group, 2,2,3,3-tetramethylbutyl group, nonyl group, methyloctyl group, 3,7-dimethyloctyl group, dimethylheptyl group, 3-ethylheptyl group, 4-ethylheptyl group, trimethylhexyl group, 3,3-diethylpentyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, and eicosyl group. From the viewpoint of further suppressing fusion between fibers during flame retardant treatment, R is preferably a hydrogen atom or a methyl group.

[0037] Examples of raw materials for producing a diene polymer containing a diene monomer unit (I) include 1,3-butadiene, isoprene, 2-ethyl-1,3-butadiene, 2-propyl-1,3-butadiene, 2-butyl-1,3-butadiene, 2-pentyl-1,3-butadiene, 2-hexyl-1,3-butadiene, 2-heptyl-1,3-butadiene, 2-octyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 2-methoxy-1,3-butadiene, 2-ethoxy-1,3-butadiene, 2-propoxy-1,3-butadiene, 2-isopropoxy-1,3-butadiene, 2-hexyloxy-1,3-butadiene, and myrcene. Only one type of raw material may be used for producing a diene polymer containing a diene monomer unit (I), or two or more types may be used in combination.

[0038] An example of a raw material for producing a diene polymer containing a diene monomer unit (I) in which "R" in formula (I) is a hydrogen atom is 1,3-butadiene. An example of a raw material for producing a diene polymer containing a diene monomer unit (I) in which "R" in formula (I) is a methyl group is isoprene. The raw material for producing a diene polymer containing a diene monomer unit (I) is preferably at least one selected from the group consisting of 1,3-butadiene and isoprene.

[0039] The content of the diene monomer unit (I) is not particularly limited. The content of the diene monomer unit (I) is preferably 1 mol% or more, more preferably 5 mol% or more, even more preferably 10 mol% or more, even more preferably 30 mol% or more, particularly preferably 40 mol% or more, even more particularly preferably 50 mol% or more, particularly preferably 60 mol% or more, and most preferably 70 mol% or more, based on the total amount of the diene polymer. The upper limit of the content of the diene monomer unit (I) is not particularly limited. The content of the diene monomer unit (I) may be 100 mol%.

[0040] The diene polymer may contain a structural unit derived from another conjugated diene monomer different from the diene monomer unit (I). Examples of the other conjugated diene monomer include 1,2-butadiene, 1-pentyl-1,3-butadiene, 1-hexyl-1,3-butadiene, 1-heptyl-1,3-butadiene, 1-octyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1-hexyloxy-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, and 3-butyl-1,3-octadiene.

[0041] The diene polymer may contain structural units derived from other polymerizable monomers. Examples of other polymerizable monomers include aromatic vinyl monomers such as styrene, α-methylstyrene, α-methyl-p-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, p-bromostyrene, 2-methyl-1,4-dichlorostyrene, 2,4-dibromostyrene, vinylnaphthalene, and indene; linear olefin monomers such as ethylene, propylene, and 1-butene; cyclic olefin monomers such as cyclopentene and 2-norbornene; non-conjugated diene monomers such as 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, dicyclopentadiene, and 5-ethylidene-2-norbornene; methyl Examples of the α,β-unsaturated carboxylic acid esters include (meth)acrylate, ethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, monomethyl maleate, monomethyl itaconate, dimethyl itaconate, ethyl itaconate, and diethyl itaconate; vinyl cyanide monomers such as (meth)acrylonitrile; nitrogen-containing vinyl monomers such as (meth)acrylamide and dimethylaminoethyl (meth)acrylamide; α,β-unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, fumaric acid, and itaconic acid; α,β-unsaturated carboxylic anhydrides such as maleic anhydride and itaconic anhydride; sulfo group-containing vinyl monomers such as vinyl sulfonic acid; halogenated vinyl monomers such as vinyl chloride; vinyl carboxylates such as vinyl acetate, vinyl butyrate, and vinyl pivalate; and vinyl alcohol. The other polymerizable monomers may be used alone or in combination of two or more.

[0042] In the diene polymer, when "R" in formula (I) is a hydrogen atom, the 1,2-bond content is not particularly limited, and may contain cis-1,4-bonds and trans-1,4-bonds. In the diene polymer, when "R" in formula (I) is a hydrogen atom, the 1,2-bond content is preferably 1% or more, more preferably 5% or more, even more preferably 10% or more, even more preferably 30% or more, particularly preferably 50% or more, particularly preferably 80% or more, and most preferably 90% or more, from the viewpoint of reducing the fusion rate during flame retardant treatment and improving the carbonization yield due to the progress of intramolecular cyclization reaction by external stimuli. The 1,2-bond content of the diene polymer may be 100%, but from the viewpoint of reducing the production (polymerization) cost for increasing the 1,2-bond content of the diene polymer, it is preferably 99.5% or less, more preferably 99% or less. The "1,2-bond content" refers to the percentage of 1,2-bonds when the total of the cis 1,4-bonds, trans 1,4-bonds, and 1,2-bonds constituting the diene polymer is taken as 100%. The percentage of 1,2-bonds is 1 H-Nuclear Magnetic Resonance (NMR) 13 This can be confirmed by C-NMR. In the diene polymer, when "R" in formula (I) is a methyl group, the content ratio of the 3,4-bond corresponding to the diene monomer unit (I) is not particularly limited, and may contain cis-1,4-bond, trans-1,4-bond, or 1,2-bond. In the diene polymer, when "R" in formula (I) is a methyl group, the content ratio of the 3,4-bond is preferably 1% or more, more preferably 5% or more, even more preferably 10% or more, even more preferably 30% or more, particularly preferably 50% or more, particularly preferably 80% or more, and most preferably 90% or more, from the viewpoint of reducing the adhesion rate during flame retardant treatment due to the progress of intramolecular cyclization reaction by external stimuli and improving the carbonization yield. When "R" in formula (I) is a methyl group, the 3,4-bond content of the diene polymer may be 100%, but from the viewpoint of reducing the production (polymerization) cost for increasing the 3,4-bond content of the diene polymer, it is preferably 99.5% or less, and more preferably 99% or less. The "3,4-bond content" refers to the proportion of 1,2-bonds when the total of the 3,4-bonds, cis 1,4-bonds, trans 1,4-bonds, and 1,2-bonds constituting the diene polymer when "R" in formula (I) is a methyl group is taken as 100%. The 3,4-bond content is 1 H-Nuclear Magnetic Resonance (NMR) 13 This can be confirmed by C-NMR. In the present disclosure, the stereoregularity of the diene polymer is not particularly limited, and may be any of isotactic, syndiotactic, and atactic. The ratio of these is not particularly limited.

[0043] The diene polymer contained in the carbon fiber precursor may be a mixture of a plurality of diene polymers having different number average molecular weights (hereinafter also referred to as "diene polymer components"). The number average molecular weight of the diene polymer contained in the carbon fiber precursor is not particularly limited. From the viewpoint of improving the spinnability of the carbon fiber precursor, the number average molecular weight of the diene polymer component is preferably 5 million or less, preferably 1 million or less, more preferably 500,000 or less, even more preferably 200,000 or less, particularly preferably 100,000 or less, even more preferably 50,000 or less, and most preferably 30,000 or less. The number average molecular weight of the diene polymer component is preferably 500 or more from the viewpoint of improving the anti-fusion properties during flame retardation of the carbon fiber precursor, and is preferably 800 or more, more preferably 1000 or more, and particularly preferably 2000 or more from the viewpoint of the strength of the carbon fiber precursor and the carbon fiber. When the diene polymer component is a mixture of a plurality of diene polymers having different number average molecular weights, from the viewpoint of improving the spinnability of the carbon fiber precursor, the diene polymer component preferably contains a diene polymer having a number average molecular weight of 30,000 or less, more preferably a diene polymer having a number average molecular weight of 20,000 or less, even more preferably a diene polymer having a number average molecular weight of 10,000 or less, particularly preferably a diene polymer having a number average molecular weight of 9000 or less, and most preferably a diene polymer having a number average molecular weight of 8000 or less. When the diene polymer component contains a diene polymer having a number average molecular weight of 30,000 or less, it acts as a plasticizer, increasing the MFR and improving the spinnability. As such a diene polymer, a commercially available product may be used. Examples of commercially available diene polymers include those with the trade names "RB-810", "RB-820", "RB-830" and "RB-840" (all manufactured by ENEOS Materials), and those with the trade names "B-1000", "B-2000", "B-3000", "BI-2000" and "BI-3000" (all manufactured by Nippon Soda Co., Ltd.). Examples of commercially available hydroxyl-containing diene polymers having hydroxyl groups at the ends of diene polymers include those with the trade names "G-1000", "G-2000", "G-3000", "GI-1000", "GI-2000" and "GI-3000" (all manufactured by Nippon Soda Co., Ltd.). Examples of commercially available epoxy-containing diene polymers having epoxy groups introduced by oxidation of the vinyl groups of diene polymers include those with the trade names "JP-100" and "JP-200" (all manufactured by Nippon Soda Co., Ltd.). Commercially available (meth)acrylic group-containing diene polymers having (meth)acrylic groups introduced at the ends via urethane bonds or the like include, for example, "TE-2000" and "TEAI-1000" (both manufactured by Nippon Soda Co., Ltd.). Commercially available isocyanate group-containing diene polymers having isocyanate groups introduced at the ends include, for example, "TP-1001" (both manufactured by Nippon Soda Co., Ltd.). Commercially available carboxyl group-containing diene polymers having carboxyl groups introduced include, for example, "GQ-1000" (both manufactured by Nippon Soda Co., Ltd.).

[0044] In the present disclosure, the number average molecular weight and weight average molecular weight of the diene polymer are measured by gel permeation chromatography under the following conditions. As a measuring device, HLC-8220GPC manufactured by Tosoh Corporation or a device equivalent thereto can be used. In the present disclosure, the diene polymer is dissolved in the following eluent, and then filtered using a membrane filter with a pore size of 0.45 μm to obtain a solution, which is used as a measuring solution. (Measurement conditions) Column: TSKgel GMH HR -H x 2 Eluent: Chloroform ·Eluent flow rate: 1.0ml / min Column temperature: 40℃ Molecular weight standard: Standard polystyrene Detector: Refractive index detector

[0045] The MFR of the diene polymer is not particularly limited. From the viewpoint of improving spinnability in multi-holes, the MFR of the diene polymer is preferably 3 g / 10 min or more, more preferably 6 g / 10 min or more, even more preferably 8 g / 10 min or more, even more preferably 10 g / 10 min or more, particularly preferably 15 g / 10 min or more, and most preferably 20 g / 10 min or more. From the viewpoint of preventing a decrease in the tensile strength of the obtained diene polymer fiber, the MFR is preferably 1000 g / 10 min or less, more preferably 800 g / 10 min or less, and even more preferably 500 g / 10 min or less.

[0046] The melting point of the diene polymer is not particularly limited. When the diene polymer component contains one or more diene polymers, the melting point of at least one diene polymer is preferably 30°C or higher, more preferably 40°C or higher, even more preferably 50°C or higher, and particularly preferably 60°C or higher, from the viewpoint of preventing bleed-out to the surface of the flame-retardant treatment. The melting point of the diene polymer is preferably 160°C or lower, more preferably 150°C or lower, even more preferably 145°C or lower, and particularly preferably 140°C or lower, from the viewpoint of improving spinnability in a large number of fibers and reducing energy costs by realizing melt spinning at a relatively low temperature. The method for measuring the melting point of the diene polymer is a method using differential scanning calorimetry (DSC). In detail, the melting point of the diene polymer indicates the peak temperature (°C) of the main peak of melting.

[0047] The presence of diene-based polymers in carbon fiber precursors is 1 H-Nuclear Magnetic Resonance Spectrum (NMR) and 13 This can be confirmed by C-NMR analysis, infrared spectroscopy analysis, etc.

[0048] (1.2) Plasticizing Additives The carbon fiber precursor preferably further contains a plasticizing additive in addition to the diene polymer, so that even if the diene polymer has an MFR of less than 10 g / 10 min, the MFR of the carbon fiber precursor can be adjusted to 10 g / 10 min or more.

[0049] The plasticizing additive preferably contains an olefin-based polymer and / or an aromatic vinyl-based polymer from the viewpoint of improving the spinnability and stretchability of the carbon fiber precursor. When a diene-based polymer is mixed with an olefin-based polymer and / or an aromatic vinyl-based polymer as a plasticizing additive, the MFR of the carbon fiber precursor increases, and the spinnability and stretchability of the carbon fiber precursor fiber are improved. By irradiating the carbon fiber precursor fiber with an electron beam, not only the crosslinking reaction between diene polymers, the crosslinking reaction between olefin polymers, or the crosslinking reaction between aromatic vinyl polymers, but also the crosslinking reaction between diene polymers and olefin polymers and the crosslinking reaction between diene polymers and aromatic vinyl polymers proceeds. These crosslinking reactions lead to the suppression of fusion during flame retardation and the improvement of carbonization resistance during preliminary carbonization and carbonization. The olefin-based polymer and aromatic vinyl-based polymer may be either linear or branched. The olefin-based polymer and aromatic vinyl-based polymer may be a hydrogenated olefin-based polymer or a hydrogenated aromatic vinyl-based polymer. The hydrogenated olefin-based polymer may be a hydrogenated diene-based polymer that has been subjected to hydrogenation.

[0050] The olefin-based polymer is not particularly limited, and examples thereof include homopolymers and copolymers of olefin-based monomers. Examples of the olefin-based monomer include ethylene, propylene, 1-butene, cis-2-butene, trans-2-butene, isobutene, 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, 3-methyl-1-butene, 2,3-dimethyl-2-butene, 1-butene, 1-hexene, 1-octene, 1-nonene, 1-decene, cyclopentene, and 2-norbornene. The olefin-based monomer may be used alone or in combination of two or more.

[0051] Examples of polymerizable monomers other than olefin monomers include diene monomers such as 1,2-propanediene, methylallene, 1,2-butadiene, 1,3-butadiene, isoprene, 2,3-dimethylbutadiene, 1,3-pentadiene, 1,4-pentadiene, dicyclopentadiene, chloroprene, 1,5-hexadiene, 1,4-hexadiene, 1,4-cyclohexadiene, 1,6-heptadiene, 1,7-octadiene, and 5-ethylidene-2-norbornene; styrene, α-methylstyrene, α-methyl-p-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, p-bromostyrene, 2-methyl-1,4-dichlorostyrene, 2,4-dibromo ... Examples of the other polymerizable monomers include aromatic vinyl monomers such as styrene, vinyl naphthalene, and indene; α,β-unsaturated carboxylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, monomethyl itaconate, dimethyl itaconate, ethyl itaconate, and diethyl itaconate; cyanide vinyl monomers such as (meth)acrylonitrile; nitrogen-containing vinyl monomers such as (meth)acrylamide and dimethylaminoethyl (meth)acrylamide; α,β-unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, fumaric acid, and itaconic acid; α,β-unsaturated carboxylic anhydrides such as maleic anhydride and itaconic anhydride; sulfo group-containing vinyl monomers such as vinyl sulfonic acid; halogenated vinyl monomers such as vinyl chloride; vinyl carboxylates such as vinyl acetate, vinyl butyrate, and vinyl pivalate; and vinyl alcohol. The other polymerizable monomers may be used alone or in combination of two or more.

[0052] Examples of olefin polymers (copolymers of olefin monomers) having structural units derived from olefin monomers include ethylene-propylene copolymers, ethylene-1-butene copolymers, ethylene-4-methyl-1-pentene copolymers, ethylene-1-hexene copolymers, ethylene-propylene-dicyclopentadiene copolymers, ethylene-propylene-5-vinyl-2-norbornene copolymers, ethylene-propylene-1,4-hexadiene copolymers, ethylene-propylene-1,4-cyclohexadiene copolymers, polystyrene-poly(ethylene / propylene) block copolymers (SEP), ... Preferred examples of the polystyrene-based copolymer include ethylene-poly(ethylene / propylene)-polystyrene block copolymer (SEPS), polystyrene-poly(ethylene / butylene)-polystyrene block copolymer (SEBS), polystyrene-poly(ethylene-ethylene / propylene)-polystyrene block copolymer (SEEPS), and ethylene-1-octene copolymer; propylene-based copolymers such as propylene-1-butene-4-methyl-1-pentene copolymer and propylene-1-butene copolymer; 1-hexene-4-methyl-1-pentene copolymer, and 4-methyl-1-pentene-1-octene copolymer. The aromatic vinyl polymer is not particularly limited, and examples thereof include homopolymers and copolymers of aromatic vinyl monomers. Examples of aromatic vinyl monomers include styrene, α-methylstyrene, α-methyl-p-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, p-tert-butylstyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, p-bromostyrene, 2-methyl-1,4-dichlorostyrene, 2,4-dibromostyrene, vinylnaphthalene, and indene. Only one type of aromatic vinyl monomer may be used, or two or more types may be used in combination. Preferred examples of aromatic vinyl polymers include styrene-butadiene-styrene block copolymers (SBS), styrene-isoprene-styrene block copolymers (SIS), acrylonitrile-butadiene-styrene (ABS) resins, and methyl (meth)acrylate-acrylonitrile-butadiene-styrene (MABS) resins.

[0053] The content of the plasticizing additive is not particularly limited, but is preferably 0.1 parts by mass to 100 parts by mass relative to 100 parts by mass of the diene polymer. From the viewpoint of improving the spinnability and drawability of the carbon fiber precursor and suppressing fusion during flame retardation treatment, the content of the plasticizing additive is preferably 0.5 parts by mass to 70 parts by mass relative to 100 parts by mass of the diene polymer, more preferably 1 part by mass to 60 parts by mass, even more preferably 2 parts by mass to 50 parts by mass, even more preferably 3 parts by mass to 40 parts by mass, particularly preferably 4 parts by mass to 30 parts by mass, and particularly preferably 4 parts by mass to 20 parts by mass.

[0054] (1.3) Other additives The carbon fiber precursor may or may not contain other additives within a range that does not impair the effects of the present disclosure. Examples of other additives include antioxidants, oxidizing agents, release agents, lubricants, plasticizers, colorants, crosslinking agents (e.g., ultraviolet crosslinking agents, etc.), crosslinking assistants (e.g., ultraviolet crosslinking assistants, etc.), crosslinking catalysts (e.g., acid catalysts, etc.), crosslinking retarders, reinforcing materials (fillers such as carbon nanotubes, graphene, cellulose nanofibers, carbon black, and glass fibers), antiaging agents, light stabilizers (ultraviolet absorbers, ultraviolet scattering agents, etc.), light shielding agents, softeners, antistatic agents, compatibilizers, compatibilizers, radical initiators, etc. As the release agent, conventionally known ones are preferably used as appropriate, and it is particularly preferable to use carnauba wax. The content of the release agent is not particularly limited, and is preferably 0.05 to 5 parts by mass, and more preferably 0.1 to 3 parts by mass, relative to 100 parts by mass of the diene polymer. From the viewpoint of improving spinnability, the content of the release agent is further preferably 0.3 parts by mass or more, and particularly preferably 0.5 parts by mass or more.

[0055] (2) Carbon fiber precursor fiber The carbon fiber precursor fibers of the present disclosure consist of the carbon fiber precursor of the present disclosure.

[0056] The carbon fiber precursor fiber of the present disclosure has the above configuration, and therefore can be stretched at a high stretch ratio (for example, a stretch ratio of more than 2 times).

[0057] (2.1) Crosslinked diene polymer It is preferable that the diene polymer contains a crosslinked diene polymer obtained by crosslinking, whereby fusion between the carbon fiber precursor fibers is suppressed during the flame retardant treatment.

[0058] The crosslinked diene polymer has a structure formed by intramolecular crosslinking (including intramolecular cyclization reaction between adjacent vinyl groups) and / or intermolecular crosslinking.

[0059] (2.1.1) Intramolecular crosslinking An example of a structure formed by an intramolecular cyclization reaction between adjacent vinyl groups (a polymerization reaction of vinyl groups when the diene monomer units (I) are continuously introduced (as a chain) as repeating units) is a chemical structure shown in the following formula (II).

[0060] [ka]

[0061] In formula (II), R 14 ~R 17 each independently represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, and a represents an integer of 0 or more.

[0062] When a repeating structural unit having a 1,4-trans bond unit or a 1,4-cis bond unit is contained, the structure formed by the intramolecular cyclization reaction can be a chemical structure represented by formula (III).

[0063] [ka]

[0064] In formula (III), R 12 and R 13 each independently represents a hydrogen atom or an organic group having 1 to 20 carbon atoms.

[0065] (2.1.2) Gel fraction When the carbon fiber precursor fiber contains a crosslinked diene polymer obtained by crosslinking a diene polymer, the gel fraction of the carbon fiber precursor fiber is preferably 30% or more, which can suppress fusion during the flame retardant treatment.

[0066] "Gel fraction" is an index of the degree of crosslinking. A higher gel fraction indicates a higher degree of crosslinking. The method for measuring the gel fraction is the same as that described in the Examples.

[0067] From the viewpoint of preventing fusion during flame retardation and improving carbonization resistance, the gel fraction is more preferably 40% or more, even more preferably 50% or more, particularly preferably 60% or more, even more preferably 80% or more, and most preferably 90% or more. The gel fraction is preferably 100% or less. In terms of reducing production costs, it is preferable to increase the gel fraction with a small dose of electron beams. From the viewpoint of reducing costs, the gel fraction is preferably 99.9% or less.

[0068] (2.1.3) Content The content of the crosslinked diene polymer is not particularly limited, but is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, particularly preferably 70% by mass or more, particularly preferably 80% by mass or more, and most preferably 90% by mass or more, based on the total mass of the carbon fiber precursor fiber. The content of the crosslinked diene polymer may be 100% by mass. The fact that the carbon fiber precursor fiber contains a crosslinked diene polymer means that: 1 H-Nuclear Magnetic Resonance Spectrum (NMR) and 13 This can be confirmed by C-NMR analysis, infrared spectroscopy analysis, etc.

[0069] (2.2) 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 It is more preferable that the fineness is 0.001 tex / fiber to 60 tex / fiber, even more preferable that the fineness is 0.001 tex / fiber to 40 tex / fiber, even more preferable that the fineness is 0.01 tex / fiber to 10 tex / fiber, particularly preferable that the fineness is 0.02 tex / fiber to 2 tex / fiber, and most preferable that the fineness is 0.03 tex / fiber to 0.4 tex / fiber. When the fineness of the carbon fiber precursor fiber is within the above range, thread breakage is unlikely to occur, and stable winding and flame-retardant treatment can be performed. In addition, the structural difference between the surface layer and center of the flame-retardant fiber is not too large, and the tensile strength and tensile modulus of the obtained carbon fiber tend not to decrease.

[0070] The single fiber fineness (tex / fiber) is measured 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)

[0071] (2.3) Average fiber diameter The average fiber diameter of the carbon fiber precursor fiber is not particularly limited, but is preferably 10 nm to 300 μm, more preferably 30 nm to 250 μm, even more preferably 500 nm to 200 μm, even more preferably 1 μm to 100 μm, particularly preferably 2 μm to 60 μm, and most preferably 3 μm to 40 μm. When the average fiber diameter of the carbon fiber precursor fiber is within the above range, thread breakage is unlikely to occur, and stable winding and flame-resistant treatment can be performed. In addition, the structural difference between the surface layer and the center of the flame-resistant fiber is not too large, and the tensile strength and tensile modulus of the obtained carbon fiber tend not to decrease. The method for measuring the average fiber diameter is the same as the method described in the examples.

[0072] (2.4) Fiber bundle The carbon fiber precursor fiber may be used as a single fiber, but is preferably used as a fiber bundle. When the carbon fiber precursor fiber is used as a fiber bundle, the number of single fibers per bundle (hereinafter also referred to as "filament number") is not particularly limited. From the viewpoint of high productivity and improved mechanical properties of the flame-resistant fiber and carbon fiber, the number of filaments is preferably 10 to 240,000, more preferably 20 to 144,000, further preferably 30 to 72,000, and particularly preferably 50 to 36,000. If the number of filaments is within the above range, uneven firing is unlikely to occur during the flame-resistant treatment. In order to increase the number of filaments, it is preferable to bundle a plurality of bundles consisting of one or a plurality of carbon fiber precursor fibers. From the viewpoint of reducing production costs, it is preferable to simultaneously form a plurality of carbon fiber precursor fibers by spinning the carbon fiber precursor. At this time, a multi-hole nozzle is used for spinning. From the viewpoint of reducing costs by improving productivity, the number of holes in the nozzle is preferably 2 or more, more preferably 10 or more, even more preferably 20 or more, and particularly preferably 30 or more.

[0073] (2.5) Lubricants From the viewpoints of improving the bundling property and handling of the fibers and preventing adhesion between the fibers, the carbon fiber precursor fibers may be coated with a known oil agent. Examples of the oil agent include silicone-based oil agents.

[0074] (2.6) Other additives The carbon fiber precursor fiber may or may not contain other additives within a range that does not impair the effects of the present disclosure. Examples of other additives include those similar to those exemplified as other additives contained in the carbon fiber precursor. The other additives contained in the carbon fiber precursor fiber are usually the same as the other additives contained in the carbon fiber precursor.

[0075] (3) Method for producing carbon fiber precursor fiber The method for producing a carbon fiber precursor fiber of the present disclosure includes a step of spinning a carbon fiber precursor to obtain a carbon fiber precursor fiber (hereinafter also referred to as a "spinning step"). The carbon fiber precursor includes a diene-based polymer. The melt flow rate of the carbon fiber precursor measured in accordance with ASTM D1238 under conditions of a temperature of 160°C and a load of 21.2 N is 10 g / 10 min or more.

[0076] The method for producing a carbon fiber precursor fiber according to the present disclosure has the above-mentioned configuration, and therefore, even if the fiber is spun at a relatively low temperature using a multi-hole nozzle without using an organic solvent and wound up at a high speed, the occurrence of yarn breakage can be suppressed and a carbon fiber precursor fiber that can be stretched at a high draw ratio can be produced. Furthermore, the obtained carbon fiber precursor fiber is less likely to fuse during the flame-retardant treatment described below.

[0077] (3.1) Spinning process The method for producing carbon fiber precursor fibers of the present disclosure includes a spinning step.

[0078] In the spinning step, a carbon fiber precursor is spun to obtain a carbon fiber precursor fiber. The carbon fiber precursor contains a diene polymer. The MFR of the carbon fiber precursor is 10 g / 10 min or more.

[0079] The carbon fiber precursor is the same as the carbon fiber precursor exemplified in the present disclosure. The carbon fiber precursor includes a diene-based polymer. The carbon fiber precursor may contain at least one of a plasticizing additive and an additive, if necessary.

[0080] The method of spinning the carbon fiber precursor is not particularly limited, and examples thereof include a spinning method using a melt of the carbon fiber precursor, a spinning method using a solution in which the carbon fiber precursor is dissolved in a solvent, and the like. Examples of the spinning method using a melt of the carbon fiber precursor include melt spinning, spunbonding, meltblown, and centrifugal spinning. Examples of the spinning method using a solution include dry spinning, wet spinning, dry-wet spinning, gel spinning, flash spinning, and electrospinning. From the viewpoint of being able to produce carbon fiber precursor fibers at low cost and under low environmental load, the method of spinning the carbon fiber precursor is preferably melt spinning, spunbonding, meltblown, or centrifugal spinning, and more preferably melt spinning.

[0081] A nozzle is used for melt spinning. The temperature of the nozzle (hereinafter, in the present disclosure, also referred to as "spinning temperature") is appropriately selected depending on the melting point of the diene polymer. The spinning temperature is preferably (melting point of diene polymer + 0°C) to (melting point of diene polymer + 100°C), more preferably (melting point of diene polymer + 5°C) to (melting point of diene polymer + 70°C), and even more preferably (melting point of diene polymer + 10°C) to (melting point of diene polymer + 50°C). When the carbon fiber precursor contains multiple types of diene polymers, the "melting point of diene polymer" refers to the melting point of the diene polymer with the highest melting point among the multiple types of diene polymers.

[0082] In the spinning step, the carbon fiber precursor fiber is usually wound around a roll or a paper tube by a winding device or the like. The speed at which the carbon fiber precursor fiber is wound around a roll or a paper tube (hereinafter also referred to as the "spinning speed") is preferably 100 m / min or more, more preferably 120 m / min or more, even more preferably 150 m / min or more, and particularly preferably 200 m / min or more, from the viewpoint of improving the productivity of the carbon fiber precursor fiber. The spinning speed may be 100 m / min or less, or may be 50 m / min or less, from the viewpoint of preventing thread breakage.

[0083] (3.2) Stretching process The method for producing carbon fiber precursor fibers of the present disclosure may or may not include a stretching step described below. The stretching step may be performed in the spinning step before the fiber bundle discharged from the nozzle of the spinning device is wound around a roll or a paper tube, or may be performed after the spinning step. When the stretching step is performed after the spinning step, it is preferable to perform the stretching step before the crosslinking step from the viewpoint of increasing the tensile strength of the fiber bundle and preventing the fibers from being cut during the crosslinking step, but it may be performed during or after the crosslinking step.

[0084] In the stretching step, the carbon fiber precursor fiber is stretched at room temperature (23°C). This tends to orient the diene polymer contained in the carbon fiber precursor fiber, and improve the tensile strength of the carbon fiber described below. The temperature during stretching may be room temperature or a temperature higher or lower than room temperature, but from the viewpoint of preventing thread breakage during stretching, room temperature or a temperature higher than room temperature is preferred. When the temperature is higher than room temperature, it is preferred to perform the stretching at a temperature at which the carbon fiber precursor fiber does not melt, and for example, 120°C or lower is preferred, 110°C or lower is more preferred, and 100°C or lower is even more preferred.

[0085] The method for stretching the carbon fiber precursor fiber is not particularly limited, and may be any known method.

[0086] The draw ratio of the carbon fiber precursor fiber is not particularly limited. From the viewpoint of reducing the fiber diameter and improving the tensile strength, the draw ratio of the carbon fiber precursor fiber is preferably 1.2 times or more, more preferably 1.5 times or more, even more preferably 2.0 times or more, even more preferably 3.0 times or more, particularly preferably 3.5 times or more, and most preferably 3.7 times or more. The draw ratio of the carbon fiber precursor fiber may be 1.2 times or less, or may be 1.1 times or less.

[0087] The "draw ratio of the carbon fiber precursor fiber" is represented by the following formula (A). Formula (A): Stretching ratio of carbon fiber precursor fiber = [(length of carbon fiber precursor fiber after stretching / length of carbon fiber precursor fiber before stretching)] × 100

[0088] The draw ratio can be controlled by adjusting the ratio (draw-out speed / introduction speed) between the feed speed (introduction speed) when the carbon material precursor fiber is transported to an apparatus (e.g., a drawing apparatus, a spinning apparatus, a heating apparatus, etc.) and the feed speed (draw-out speed) of the flame-resistant fiber drawn from a heating furnace or the like. The draw ratio can also be controlled by adjusting the tension applied to the fiber, the temperature and humidity during the drawing process, etc. The introduction speed and draw-out speed can be adjusted to the desired draw ratio by the rotation speed of rollers (e.g., feed rollers, nip rollers, etc.), and the tension applied to the carbon material precursor fiber can be adjusted to the desired draw ratio by weights, springs, etc.

[0089] (3.3) Crosslinking treatment process The method for producing a carbon fiber precursor fiber of the present disclosure preferably includes a crosslinking treatment step described below. The crosslinking treatment step is performed after the spinning step. When the method for producing a carbon fiber precursor fiber of the present disclosure includes a drawing step, the crosslinking treatment step may be performed before or after the drawing step.

[0090] In the crosslinking process, the carbon fiber precursor fiber is subjected to a crosslinking process. The gel fraction of the carbon fiber precursor fiber after the crosslinking process is not particularly limited, but is preferably 30% or more. This allows the diene polymer to be formed into the above-mentioned crosslinked diene polymer. As a result, fusion between the carbon fiber precursor fibers during the flame retardant treatment can be suppressed.

[0091] The method of the crosslinking treatment is not particularly limited, and examples thereof include a method of irradiating a carbon material precursor fiber with radiation (hereinafter also referred to as "radiation treatment"), a method of irradiating a carbon material precursor fiber with ultraviolet light (hereinafter also referred to as "ultraviolet light treatment"), a method of heating a carbon material precursor fiber (hereinafter also referred to as "heat treatment"), an acid treatment, addition of a crosslinking agent, addition of a radical initiator, and the like. Each of the radiation treatment, ultraviolet light treatment, heat treatment, acid treatment, addition of a crosslinking agent, and addition of a radical initiator may be a known method. When the diene polymer contains a diene monomer unit (I), the method of the crosslinking treatment is preferably one or more of radiation irradiation, ultraviolet light irradiation, heat treatment, acid treatment, addition of a crosslinking agent, and addition of a radical initiator, and more preferably radiation irradiation.

[0092] Examples of the radiation include X-rays, γ-rays, α-rays, β-rays, electron beams, neutron beams, proton beams, and heavy particle beams. Among them, from the viewpoint of obtaining a flame-resistant fiber bundle in which fusion and thread breakage during flame-resistant treatment are suppressed and fiber breakage does not occur during carbonization treatment, the radiation is preferably an electron beam. The irradiation with the electron beam may be performed by a batch method or a continuous method.

[0093] The radiation dose is preferably 20 kGy or more, more preferably 30 kGy or more, even more preferably 60 kGy or more, particularly preferably 80 kGy or more, even more preferably 150 kGy or more, and most preferably 400 kGy or more, from the viewpoint of reducing energy costs and reducing damage to the fibers, preferably 50 MGy or less, more preferably 10 MGy or less, even more preferably 5 MGy or less, particularly preferably 2000 kGy or less, and most preferably 1000 kGy or less. The above-mentioned preferred numerical range of the radiation dose is the preferred numerical range of the dose when the carbon material precursor fiber is irradiated with an electron beam from one direction. When irradiating from two or more directions, the preferred numerical range of the radiation dose is not limited to the above, and it is preferable to adjust it appropriately.

[0094] When the crosslinking treatment is one of radiation treatment and ultraviolet light, it is preferable to apply tension to the carbon material precursor fiber while crosslinking the carbon material precursor fiber. The tension applied to the carbon fiber precursor fiber is preferably 0.03 mN / dtex or more, more preferably 0.05 mN / dtex or more, even more preferably 0.1 mN / dtex or more, particularly preferably 0.3 mN / dtex or more, and most preferably 0.5 mN / dtex or more.

[0095] When the manufacturing method of the carbon fiber precursor fiber of the present disclosure includes a crosslinking treatment step, the carbon fiber precursor fiber may include a crosslinking agent (e.g., an ultraviolet crosslinking agent, etc.), a crosslinking auxiliary (e.g., an ultraviolet crosslinking auxiliary, etc.), a crosslinking catalyst (e.g., an acid catalyst, etc.), a radical initiator, etc.

[0096] (4) Manufacturing method of flame-retardant fiber The method for producing a flame-resistant fiber according to the present disclosure further includes a step of obtaining a carbon fiber precursor fiber by the method for producing a carbon fiber precursor fiber according to the present disclosure (hereinafter also referred to as a "first preparation step"), and a step of subjecting the carbon fiber precursor fiber to a heat treatment in an oxidizing atmosphere (hereinafter also referred to as a "flame-resistant treatment step"). The first preparation step and the flame-resistant treatment step are performed in this order.

[0097] The method for producing a flame-resistant fiber according to the present disclosure has the above-mentioned configuration, and therefore can provide a flame-resistant fiber that can suppress the occurrence of yarn breakage due to the application of tension or thermal decomposition during carbonization.

[0098] Hereinafter, the "heat treatment in an oxidizing atmosphere" will also be referred to as "flameproofing treatment".

[0099] (4.1) First preparation step In the first preparation step, carbon fiber precursor fibers are obtained by the method for producing carbon fiber precursor fibers of the present disclosure.

[0100] (4.2) Flameproofing treatment process In the flame-retardant treatment step, the carbon fiber precursor fiber is subjected to a heat treatment in an oxidizing atmosphere.

[0101] The flame retardant treatment is carried out by a known method.

[0102] (4.2.1) Flameproofing The temperature of the flame retardant treatment is not particularly limited, but is preferably 120°C to 500°C, more preferably 150°C to 480°C, even more preferably 170°C to 470°C, particularly preferably 180°C to 460°C, and most preferably 200°C to 450°C.

[0103] The maximum temperature of the flame retardant treatment is not particularly limited, but from the viewpoints of improving carbonization resistance and reducing production costs by shortening the treatment time, it is preferably 290°C or higher, more preferably 300°C or higher, and particularly preferably 330°C or higher.

[0104] Examples of the oxidizing atmosphere during the flame-resistant treatment include oxygen, ozone, air, nitrogen oxides, halogens, sulfurous acid gas, mixed gases of these, or mixed gases of these with inert gases, etc. Among these, the oxidizing atmosphere during the flame-resistant treatment is preferably air, a mixed gas of oxygen and air, a mixed gas of oxygen and an inert gas, or a mixed gas of air and an inert gas, and from the viewpoint of cost reduction, air is particularly preferable.

[0105] The flame-resistant treatment time (heating time at the maximum temperature) is not particularly limited and may be a long time (for example, more than 4 hours). The flame-resistant treatment time (heating time at the maximum temperature) is preferably 1 minute to 4 hours, more preferably 2 minutes to 2 hours, further preferably 3 minutes to 100 minutes, particularly preferably 4 minutes to 90 minutes, and most preferably 4 minutes to 60 minutes. By setting the flame-resistant treatment time (heating time at the maximum temperature) to 1 minute or more, the carbonization yield can be improved. By setting the flame-resistant treatment time (heating time at the maximum temperature) to 4 hours or less, the production cost of the flame-resistant fiber can be reduced.

[0106] (4.2.2) Stretching In the flame-resistant treatment step, tension may or may not be applied to the carbon fiber precursor fiber during the temperature rise process up to the flame-resistant treatment temperature described above. From the viewpoint of improving the tensile strength of the flame-resistant product, tension is preferably applied to the carbon fiber precursor fiber during the temperature rise process.

[0107] The timing at which the application of tension starts may be at an early stage of the temperature increase process or the like, or may be at an intermediate stage of the temperature increase process or the like.

[0108] (5) Carbon fiber manufacturing method The method for producing a carbon fiber according to the present disclosure includes a step of obtaining a flame-resistant fiber by the method for producing a flame-resistant fiber according to the present disclosure (hereinafter also referred to as a "second preparation step"), and a step of subjecting the flame-resistant fiber to a carbonization treatment (hereinafter also referred to as a "carbonization treatment step").

[0109] The term "carbonization treatment" refers to a treatment for carbonizing the flame-retardant fiber. More specifically, the term "carbonization treatment" refers to a heat treatment of the flame-retardant fiber in a low-oxygen atmosphere (preferably an environment in which oxygen is blocked). The term "carbonization treatment" generally includes "graphitization" which is performed by heating at 2000 to 3000°C in an inert gas atmosphere.

[0110] Since the carbon fiber manufacturing method of the present disclosure has the above configuration, carbon fibers having excellent tensile strength can be obtained.

[0111] (5.1) Second preparation process In the second preparation step, a flame-resistant fiber is obtained by the flame-resistant fiber production method of the present disclosure.

[0112] (5.2) Carbonization process In the carbonization process, the flame-retardant fiber is carbonized.

[0113] The method of carbonizing the flame-retardant fiber involves subjecting the flame-retardant fiber to a heat treatment in an inert atmosphere (in an inert gas such as nitrogen, argon, or helium) at a temperature higher than that in the flame-retardant treatment.

[0114] The heating temperature in 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 heating temperature in the carbonization treatment is preferably 3000° C. or lower, and more preferably 2500° C. or lower.

[0115] In the carbonization treatment, multiple heat treatments may be performed. For example, a heat treatment may be performed at a temperature less than 1000°C (hereinafter also referred to as "preliminary carbonization treatment"), followed by a heat treatment at a temperature of 1000°C or higher (hereinafter also referred to as "main carbonization treatment"). For example, a heat treatment (preliminary carbonization treatment) may be performed at a temperature less than 1000°C, followed by a heat treatment (carbonization treatment) at a temperature of 1000°C or higher, followed by a heat treatment (graphitization treatment) at a temperature of 2000°C or higher.

[0116] The heating time for the carbonization treatment is not particularly limited, but is preferably 30 seconds to 120 minutes, more preferably 30 seconds to 60 minutes, and even more preferably 1 second to 30 minutes. From the viewpoint of reducing production costs, the heating time is preferably within 20 minutes, and particularly preferably within 10 minutes.

[0117] (5.3) Carbon fiber The average fiber diameter of the carbon fibers thus obtained is not particularly limited. The average fiber diameter of the carbon fibers is preferably 10 nm to 300 μm, more preferably 30 nm to 150 μm, even more preferably 100 nm to 60 μm, even more preferably 1 μm to 40 μm, particularly preferably 2 μm to 30 μm, and most preferably 2.5 to 25 μm. If the average fiber diameter of the carbon fibers is within the above range, when a composite material is produced using a resin or the like as a matrix, if the viscosity of the matrix is ​​high, insufficient impregnation of the resin or the like into the carbon fiber bundle is unlikely to occur. Therefore, the tensile strength of the composite material is unlikely to decrease. EXAMPLES

[0118] The above embodiment will be specifically described below with reference to examples, but the above embodiment is not limited to these examples.

[0119] [1] Preparation The following diene polymers (a-1) to (a-9) and the following plasticizing additives (b-1) to (b-3) were prepared.

[0120] [1.1] Diene polymers Diene polymer (a-1): 1,2-polybutadiene ("RB840" manufactured by ENEOS Materials, 1,2-bond content: 94%, melting point: 126°C, density: 0.914g / cm 3 , Number average molecular weight: 47,000, Weight average molecular weight: 99,000, Melt flow rate (MFR, ASTM D1238 compliant, temperature 150°C, load 21.2N): 9g / 10min) Diene polymer (a-2): 1,2-polybutadiene (ENEOS Materials' "RB810", 1,2-bond content: 90%, melting point: 71°C, density: 0.901g / cm 3 , Number average molecular weight: 91,000, Weight average molecular weight: 210,000, Melt flow rate (MFR, ASTM D1238 compliant, temperature 150°C, load 21.2N): 3g / 10min) Diene polymer (a-3): 1,2-polybutadiene ("RB820" manufactured by ENEOS Materials, 1,2-bond content: 92%, melting point: 95°C, density: 0.906g / cm 3 , Number average molecular weight: 93,000, Weight average molecular weight: 210,000, Melt flow rate (MFR, ASTM d1238 compliant, temperature 150°C, load 21.2N): 3g / 10min) Diene polymer (a-4): 1,2-polybutadiene (ENEOS Materials' "RB830", 1,2-bond content: 93%, melting point: 105°C, density: 0.909g / cm 3 , Number average molecular weight: 69,000, Weight average molecular weight: 150,000, Melt flow rate (MFR, ASTM D1238 compliant, temperature 150°C, load 21.2N): 3g / 10min) Diene polymer (a-5): 1,2-polybutadiene ("B-1000" manufactured by Nippon Soda Co., Ltd., number average molecular weight: 1200, 1,2-bond content: 85% or more, 1,4-trans structure content: 15% or less, viscosity at 45°C: 10 poise, glass transition temperature: -44°C) Diene polymer (a-6): 1,2-polybutadiene ("B-2000" manufactured by Nippon Soda Co., Ltd., number average molecular weight: 2100, 1,2-bond content: 90% or more, 1,4-trans structure content: 10% or less, viscosity at 45°C: 62 poise, glass transition temperature: -29°C) Diene polymer (a-7): 1,2-polybutadiene ("B-3000" manufactured by Nippon Soda Co., Ltd., number average molecular weight: 3200, 1,2-bond content: 90% or more, 1,4-trans structure content: 10% or less, viscosity at 45°C: 210 poise, glass transition temperature: -21°C) Diene polymer (a-8): 1,2-polybutadiene ("BI-2000" manufactured by Nippon Soda Co., Ltd., number average molecular weight: 2200, 1,2-bond content: <7%, viscosity at 45°C: 60 poise, glass transition temperature: -51°C) Diene polymer (a-9): 1,2-polybutadiene ("BI-3000" manufactured by Nippon Soda Co., Ltd., number average molecular weight: 3300, 1,2-bond content: <7%, viscosity at 45°C: 180 poise, glass transition temperature: -44°C)

[0121] [1.2] Plasticizing additives Plasticizing additive (b-1): Polyethylene wax "PE520" manufactured by Clariant Chemicals, weight average molecular weight: 5500, viscosity at 140℃: approx. 0.65 Pa·s, melting point: 117℃~123℃ Plasticizing additive (b-2): Polyethylene oxide "PED191" manufactured by Clariant Chemicals, weight average molecular weight: 9100, viscosity at 140°C: approx. 1.8 Pa·s, melting point: 120°C to 125°C, acid value: 15 mg KOH / g to 19 mg KOH / g Plasticizing additive (b-3): Sanwax 151-P, a low molecular weight polyethylene manufactured by Sanyo Chemical Industries, density: 0.93 g / cm 3 , Number average molecular weight: 2000, Weight average molecular weight: 13000, Viscosity at 140℃: 0.29 Pa·s, Melting point: 102℃

[0122] [2] Examples and Comparative Examples [2.1] Examples 1 to 10 The diene polymers (a-1) to (a-9) were charged into the chamber of a Labo Plastomill ("10C100" manufactured by Toyo Seiki Seisakusho Co., Ltd., chamber: 100H, blade shape: roller type) in the mixing ratios shown in Table 1, and melt-kneaded. The screw rotation speed was 100 rpm, and the melt-kneading temperature was 150°C. The melt-kneading time was 5 minutes. In this way, a carbon fiber precursor containing a diene polymer component was obtained. The MFR measurement results of the obtained carbon fiber precursor, measured in accordance with ASTM D1238 under conditions of a temperature of 160°C and a load of 21.2 N, are shown in Table 1.

[0123] [2.2] Examples 11 to 15 The diene polymer (a-1) and the plasticizing additive were mixed in the ratio shown in Table 1 and fed into the chamber of a Labo Plastomill (Toyo Seiki Seisakusho Co., Ltd. "10C100", chamber: 100H, blade shape: roller type) and melt-kneaded. The screw rotation speed was 100 rpm, and the melt-kneading temperature was 150°C. The melt-kneading time was 5 minutes. In this way, a carbon fiber precursor containing a diene polymer and a plasticizing additive was obtained. The MFR measurement results of the obtained carbon fiber precursor were measured in accordance with ASTM D1238 under conditions of a temperature of 160°C and a load of 21.2 N. Table 1 shows the results.

[0124] [2.3] Example 16 The diene polymers (a-1) and (a-6) and the plasticizing additive (b-1) were mixed in the ratios shown in Table 1 and fed into the chamber of a Labo Plastomill (Toyo Seiki Seisakusho Co., Ltd., "10C100", chamber: 100H, blade shape: roller type) and melt-kneaded. The screw rotation speed was 100 rpm, and the melt-kneading temperature was 150°C. The melt-kneading time was 5 minutes. As a result, a carbon fiber precursor containing a diene polymer and a plasticizing additive was obtained. The MFR measurement results of the obtained carbon fiber precursor were measured in accordance with ASTM D1238 under conditions of a temperature of 160°C and a load of 21.2N. The results are shown in Table 1.

[0125] [2.4] Comparative Examples 1 to 4 As the carbon fiber precursor, a diene-based polymer shown in Table 1 was used. The MFR of the carbon fiber precursor is shown in Table 1.

[0000] [2.5] Spinning process A melt spinning apparatus equipped with a single screw extruder (screw diameter: 20 mm, screw shape: double flight) and a nozzle (nozzle hole diameter: 200 μm, number of holes: 36 holes) was prepared. The carbon fiber precursor was charged into the hopper of the single screw extruder of the melt spinning apparatus, and melt spinning was performed at the spinning temperature shown in Table 1. The carbon fiber precursor fiber bundle discharged from the nozzle hole of the melt spinning apparatus was wound up at a spinning speed of 100 m / min. The fiber diameter of the carbon fiber precursor fiber (single fiber) constituting the carbon fiber precursor fiber bundle is shown in Table 1.

[0126] [2.5.1] Evaluation of spinnability (anti-breakage properties) During the spinning process, the number of broken fibers at the nozzle (hereinafter also referred to as the "number of broken fibers") was measured one minute after the carbon fiber precursor fiber was discharged from the nozzle and winding was started. Using the measurement results of the number of broken fibers, the spinnability of the carbon fiber precursor fiber was evaluated according to the following evaluation criteria. The evaluation results of the spinnability are shown in Table 1. Acceptable evaluation results of spinnability are "A" or "B".

[0127] [2.5.2] Evaluation criteria for spinnability "A": 0 broken fibers out of 36 fibers "B": 1 broken fiber out of 36 fibers "C": 2 out of 36 fibers are broken "D": 3 out of 36 fibers are broken "E": 4 or more broken fibers out of 36 fibers

[0128] [2.6] Stretching process The carbon fiber precursor fiber bundles taken up in the spinning step were stretched at room temperature at stretch ratios of 1.5, 2.0, 3.0, 3.5, and 4.0, respectively, to obtain a carbon fiber precursor fiber bundle having a stretch ratio of 1.5, a carbon fiber precursor fiber bundle having a stretch ratio of 2.0, a carbon fiber precursor fiber bundle having a stretch ratio of 3.0, a carbon fiber precursor fiber bundle having a stretch ratio of 3.5, and a carbon fiber precursor fiber bundle having a stretch ratio of 4.0.

[0129] [2.6.1] Evaluation of extensibility The drawn carbon fiber precursor fiber bundle was visually observed to confirm whether it could be drawn without thread breakage while maintaining the number of carbon fiber precursor fiber bundles before drawing. The stretchability of the carbon fiber precursor fiber was evaluated according to the following evaluation criteria, based on the ratio at which it could be drawn without thread breakage while maintaining the number of carbon fiber precursor fiber bundles before drawing. The stretchability evaluation results are shown in Table 1. Acceptable stretchability evaluation results are "A", "B" or "C".

[0130] [2.6.2] Evaluation criteria for extensibility "A": Stretching ratio 4.0 times (no fiber breakage occurs at a stretching ratio of 4.0 times) "B": Stretching ratio 3.5 times (at least some of the fibers break at a stretching ratio of 4.0 times) "C": Stretching ratio 3.0 times (at least some of the fibers break at a stretching ratio of 3.5 times) "D": Stretching ratio 2.0 times (at least some of the fibers break at a stretching ratio of 3.0 times) "E": Stretching ratio 1.5 times (at least some of the fibers break at a stretching ratio of 2.0 times)

[0131] [2.7] Crosslinking process The carbon fiber precursor fiber bundles of Examples 1 to 16 obtained after the drawing treatment were subjected to a crosslinking treatment. Before the crosslinking treatment, six bundles of the carbon fiber precursor fiber bundles were aligned. As a result of the alignment, the number of carbon fiber precursor fibers constituting the carbon fiber precursor fiber bundles of Examples 8 and 13 was 210. The number of carbon fiber precursor fibers constituting the carbon fiber precursor fiber bundles of the other Examples excluding Examples 8 and 13 among Examples 1 to 16 was 216.

[0132] The carbon fiber precursor fiber bundle was irradiated with an electron beam to obtain a crosslinked carbon fiber precursor fiber bundle made of a crosslinked diene polymer. An electron beam irradiation device EBC800-35 manufactured by NHV Corporation was used for the electron beam irradiation. The electron beam irradiation was continuously performed while the carbon fiber precursor fiber bundle was transported at a speed of 20 m / min under an air atmosphere. The acceleration voltage was set to 800 kV. The dose of the electron beam was 550 kGy. The tension applied to the carbon fiber precursor fiber bundle during the crosslinking treatment was 3 mN / dtex. The carbon fiber precursor fibers of Comparative Examples 1 to 4 contained two or more broken fibers during spinning, and therefore, when the fibers were continuously irradiated with an electron beam while being transported, the broken fibers were wound around the transport roller.

[0133] In addition, in the carbon fiber precursor fibers of Comparative Examples 1 to 4 in which three or more fibers were broken during melt spinning, crosslinking treatment was not performed because when the fibers were continuously irradiated with an electron beam while being transported, the broken fibers would wrap around the transport rollers, resulting in a decrease in yield.

[0134] [2.7.1] Measurement of the average fiber diameter of carbon fiber precursor fibers The mass of the obtained fiber bundle was measured, and the mass per 1000 m was calculated as the fiber bundle fineness [tex], and the fineness of each single fiber constituting the fiber bundle (fineness of the carbon fiber precursor fiber) was obtained. Next, using a dry automatic density meter (Micromeritics' "AccuPic II 1340"), the density of the carbon fiber precursor fiber bundle after vacuum drying at 80°C for 12 hours was measured. The average fiber diameter of the single fibers constituting the fiber bundle (average fiber diameter of the carbon fiber precursor fiber) was calculated by the following formula (B). The calculation results of the average fiber diameter of the single fibers are shown in Table 1.

[0135] Formula (B): D={(Dt×4×1000) / (ρ×π×n)} 1 / 2 In the formula (B), D represents the average fiber diameter [μm] of the single fibers constituting the fiber bundle, Dt represents the fineness [tex] of the fiber bundle, and ρ represents the density [g / cm 3 n represents the number of single fibers that make up the fiber bundle.

[0136] [2.7.2] Evaluation of degree of crosslinking (gel fraction) after electron beam crosslinking A sample of 0.2 g was cut out from the crosslinked carbon fiber precursor fiber bundle. After drying at 80 ° C for 4 hours, the mass was precisely weighed using a precision electronic balance to obtain the initial mass (g). Next, the sample was immersed in 30 ml of toluene and left to stand in a hot air circulation oven at 60 ° C for 8 hours. The sample after standing was subjected to suction filtration using a membrane filter with a pore size of 1.0 μm (Omnipore TM membrane filter JAWP04700, manufactured by Merck) to separate the gel content. The separated gel content together with the membrane filter was air-dried in the atmosphere in a draft for 12 hours or more, and further left to stand in a hot air circulation oven at 90 ° C for 12 hours to remove the toluene. The masses of the gel content and the membrane filter after standing were precisely weighed using a precision electronic balance, and the gel fraction was calculated from the following formula (C).

[0137] Gel fraction (%) = {(mass of gel fraction and membrane filter (g) - mass of membrane filter (g)) / initial mass of sample (g)} x 100

[0138] Using the calculated gel fraction, the crosslinking degree of the crosslinked carbon fiber precursor fiber was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1.

[0139] [2.7.3] Evaluation criteria for degree of crosslinking (gel fraction) of fiber after electron beam crosslinking "A": The gel fraction was 90% or more. "B": The gel fraction was 85% or more and less than 90%. "C": The gel fraction was less than 85%.

[0140] [2.8] Flameproofing process A crosslinked carbon fiber precursor fiber bundle (filament number of fiber bundles in Examples 8 and 13: 210, filament number of fiber bundles in other Examples: 216) was conveyed into a heat treatment device under an air stream while applying a tension of 20 cN. The crosslinked carbon fiber precursor fiber bundle was heat treated (flameproofed) while increasing the temperature from 200°C (inlet of the heat treatment device) to 350°C over 60 minutes. The crosslinked carbon fiber precursor fiber bundle was further flameproofed at 350°C for 30 minutes while applying a tension of 20 cN, and the flameproofed fiber bundle was continuously discharged from the outlet of the heat treatment device to obtain a flameproofed fiber bundle.

[0141] [2.8.1] Evaluation of fusion rate A fiber bundle for evaluation having a length of 3 cm was cut out from the flame-retardant fiber bundle. The cross section of this fiber bundle for evaluation was observed using a microscope (Keyence Corporation, "Digital Microscope VHX-7000"), and the number of fibers was counted. At this time, the number of fused fibers and the number of all fibers constituting the fiber bundle for evaluation were counted. For example, the number of fused fibers was counted as two when two fibers were fused to each other. The number of all fibers was counted by separating the fused fibers into the state before fusion. The fusion rate was calculated based on the following formula (D). The calculation results are shown in Table 1.

[0142] Formula (D): Fusion rate (%) = (number of fused fibers / total number of fibers) x 100

[0143] [2.9] Carbonization process Each flame-retardant fiber bundle (filament number of fiber bundles of Examples 8 and 13: 210, filament number of fiber bundles of other Examples: 216) was conveyed under a tension of 20 cN into a heat treatment device adjusted to 800°C under a nitrogen stream and subjected to a preliminary carbonization treatment (3 minutes) to produce a preliminary carbonized fiber. Next, the preliminary carbonized fiber was conveyed under a tension of 20 cN into a heat treatment device adjusted to 1400°C under a nitrogen stream and subjected to a carbonization treatment for 3 minutes to obtain a carbon fiber.

[0144] [2.9.1] Evaluation of carbonization resistance (whether or not fluff occurs due to fiber breakage) From the obtained carbon fibers, a fiber bundle (length 5 cm) for evaluation was cut out. The presence or absence of fuzz caused by cutting the fiber bundle for evaluation was observed visually and using a microscope (manufactured by Keyence Corporation, "Digital Microscope VHX-7000"). As a result, it was confirmed that in all fiber bundles of Examples 1 to 16, fiber bundles were obtained without fuzz caused by cutting of the fibers due to pyrolysis at high temperatures or application of tension.

[0145] [Table 1]

[0146] The MFR of the carbon fiber precursors of Comparative Examples 1 to 4 was not 10 g / 10 min or more. Therefore, in Comparative Examples 1 to 4, the spinnability was evaluated as "C" or "D", and the stretchability was evaluated as "D" or "E". As a result, it was found that the carbon fiber precursors of Comparative Examples 1 to 4 are not "carbon fiber precursors that can be made into carbon fiber precursor fibers that can be stretched at a high draw ratio, and that can produce carbon fiber precursor fibers while suppressing the occurrence of yarn breakage, even when melt-spun at a relatively low temperature using a multi-hole nozzle without using an organic solvent and wound up at high speed."

[0147] The MFR of the carbon fiber precursors of Examples 1 to 16 was 10 g / 10 min or more. Therefore, in Examples 1 to 16, the spinnability was evaluated as "A" or "B," and the stretchability was evaluated as "A," "B," or "C." As a result, it was found that the carbon fiber precursors of Examples 1 to 16 are "carbon fiber precursors that can be made into carbon fiber precursor fibers that can be stretched at a high stretch ratio, and that can produce carbon fiber precursor fibers while suppressing the occurrence of yarn breakage even when melt-spinning is performed at a relatively low temperature using a multi-hole nozzle without using an organic solvent and wound up at a high speed." From the comparison between Examples 3 and 4, and between Examples 9 and 10, they had high spinnability and stretchability even when melt-spinning was performed at a spinning temperature of 130°C, which is lower than 150°C. This is because the diene polymer (a-1) with a melting point of 126°C and the diene polymer with a small number average molecular weight were used in combination, and therefore high spinnability and stretchability were shown even at a spinning temperature of 130°C.

[0148] From Table 1, the carbon fiber precursors of Examples 1 to 16 having a MFR of a specific value (10 g / 10 min) or more were superior in spinnability and drawability compared to Comparative Examples 1 to 4, and fiber bundles having an average fiber diameter of 17 μm or less could be obtained by melt spinning at a relatively low temperature (130° C. or 150° C.). The evaluation result of the crosslinking degree after electron beam crosslinking was "A" or "B", and the carbon fiber precursors of Examples 1 to 16 had a high crosslinking degree. The fibers obtained by flame-retarding these had no fusion or a low fusion rate. Furthermore, the carbon fibers of Examples 1 to 16 obtained by performing preliminary carbonization and carbonization did not suffer from thread breakage due to thermal decomposition or the like during preliminary carbonization and carbonization, and had excellent carbonization resistance.

[0149] The following is further disclosed regarding the above embodiment.

[0150] The carbon fiber precursor of the first embodiment is a carbon fiber precursor that contains a diene polymer and has a melt flow rate of 10 g / 10 min or more, measured in accordance with ASTM D1238 under conditions of a temperature of 160° C. and a load of 21.2 N.

[0151] The carbon fiber precursor of the second embodiment is the carbon fiber precursor of the first embodiment, further comprising a plasticizing additive.

[0152] A carbon fiber precursor of a third embodiment is the carbon fiber precursor of the first embodiment or the second embodiment, in which the diene polymer contains a diene monomer unit represented by the following formula (I).

[0153] [ka]

[0154] [In formula (I), R represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, and n represents an arbitrary number of repetitions.]

[0155] The carbon fiber precursor fiber of the fourth embodiment is a carbon fiber precursor fiber made of the carbon fiber precursor of any one of the first to third embodiments.

[0156] A carbon fiber precursor fiber of a fifth embodiment is the carbon fiber precursor fiber of the fourth embodiment, which contains a crosslinked diene polymer obtained by crosslinking the diene polymer.

[0157] The carbon fiber precursor fiber of the sixth aspect is the carbon fiber precursor fiber of the fifth aspect, which has a gel fraction of 30% or more.

[0158] A seventh aspect of the method for producing a carbon fiber precursor fiber includes a step of spinning a carbon fiber precursor to obtain a carbon fiber precursor fiber, the carbon fiber precursor including a diene polymer, and the carbon fiber precursor has a melt flow rate of 10 g / 10 min or more, measured in accordance with ASTM D1238 under conditions of a temperature of 160° C. and a load of 21.2 N.

[0159] The method for producing a carbon fiber precursor fiber of an eighth aspect is the method for producing a carbon fiber precursor fiber of the seventh aspect, further comprising a step of subjecting the carbon fiber precursor fiber to a crosslinking treatment, and the carbon fiber precursor fiber after the crosslinking treatment has a gel fraction of 30% or more.

[0160] A ninth aspect of the method for producing a flame-resistant fiber includes the steps of obtaining a carbon fiber precursor fiber by the method for producing a carbon fiber precursor fiber of the seventh or eighth aspect, and subjecting the carbon fiber precursor fiber to a heat treatment in an oxidizing atmosphere.

[0161] A tenth aspect of the method for producing a carbon fiber includes the steps of obtaining a flame-resistant fiber by the method for producing a flame-resistant fiber of the ninth aspect of the present invention, and carbonizing the flame-resistant fiber.

Claims

1. Contains a diene polymer, A carbon fiber precursor having a melt flow rate of 10 g / 10 min or more, as measured in accordance with ASTM D1238 at a temperature of 160° C. and a load of 21.2 N.

2. 10. The carbon fiber precursor of claim 1, further comprising a plasticizing additive.

3. The carbon fiber precursor according to claim 1 , wherein the diene polymer contains a diene monomer unit represented by the following formula (I): 【Chemistry 1】 [In formula (I), R represents a hydrogen atom or an organic group having 1 to 20 carbon atoms, and n represents an arbitrary repeating number.]

4. A carbon fiber precursor fiber comprising the carbon fiber precursor according to any one of claims 1 to 3.

5. The carbon fiber precursor fiber according to claim 4 , further comprising a crosslinked diene polymer obtained by crosslinking the diene polymer.

6. The carbon fiber precursor fiber according to claim 5 , having a gel fraction of 30% or more.

7. The method includes a step of spinning a carbon fiber precursor to obtain a carbon fiber precursor fiber, The carbon fiber precursor comprises a diene-based polymer, The carbon fiber precursor has a melt flow rate of 10 g / 10 min or more, measured in accordance with ASTM D1238 at a temperature of 160° C. and a load of 21.2 N.

8. The method further comprises a step of subjecting the carbon fiber precursor fiber to a crosslinking treatment, The method for producing a carbon fiber precursor fiber according to claim 7 , wherein the carbon fiber precursor fiber has a gel fraction of 30% or more after the crosslinking treatment.

9. A step of obtaining a carbon fiber precursor fiber by the method for producing a carbon fiber precursor fiber according to claim 7 or 8; A step of subjecting the carbon fiber precursor fiber to a heat treatment in an oxidizing atmosphere; A method for producing a flame-resistant fiber, comprising:

10. A step of obtaining a flame-resistant fiber by the method for producing a flame-resistant fiber according to claim 9; A step of subjecting the flame-retardant fiber to a carbonization treatment; A method for producing carbon fibers, comprising:

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