Method for manufacturing flame-resistant fiber bundles, method for manufacturing carbon fiber bundles, and flame-resistant fiber bundles

Abstract

To provide a method for producing a flameproofed fiber bundle in which embrittlement after flameproofing is suppressed and the cutting of fibers is suppressed upon carbonization treatment which is executed while applying tension, and a flameproofed fiber bundle.SOLUTION: Provided is a method for producing a flameproofed fiber bundle in which an acrylamide polymer fiber bundle is subjected to heating treatment by a continuous type heat treatment device in which heating zones are divided into two or more zones and which can set temperatures per zone. Each heating zone has: a low temperature zone having a set temperature of less than 300°C; and a high temperature zone having a set temperature of 300°C or more. The heating zone 211 through which the acrylamide polymer fiber bundle 4 passes first is the low temperature zone, and a temperature difference between the low temperature zone and the high temperature zone at a place in which the low temperature zone and the high temperature are adjacent first is within 120°C. Also provided is a flameproofed fiber bundle which is derived from an acrylamide polymer and has an orientation of 44 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a method for producing flame-resistant fiber bundles, a method for producing carbon fiber bundles, and flame-resistant fiber bundles. [Background technology]

[0002] Because carbon fibers are lightweight and have excellent mechanical properties, carbon fiber composite materials are attracting attention as materials that can replace metal materials. One known method for manufacturing carbon fibers involves spinning polyacrylonitrile to obtain fiber bundles, then applying a flame-retardant treatment, followed by a carbonization treatment.

[0003] For example, Patent Document 1 discloses a method for producing carbon fibers by flame-retarding carbon fiber precursor fibers in air, and then carbonizing the flame-retarded fibers in an inert atmosphere. Furthermore, Patent Document 2 discloses a method for producing carbon fiber precursor fibers, which involves applying a silicone-based oil to a fiber having a polyacrylonitrile skeleton as a constituent component, such that the amount of oil component attached per dry weight of the fiber is 0.1 to 5% by weight, and a method for producing carbon fiber precursor fibers, which involves carbonizing these carbon fiber precursor fibers in an inert atmosphere at a temperature of 300°C to 3000°C.

[0004] On the other hand, acrylamide polymers containing acrylamide monomers as carbon fiber precursors are water-soluble polymers, and because they can use inexpensive and environmentally friendly water as a solvent during polymerization, spinning, etc., they are expected to reduce the manufacturing cost of carbon fibers.

[0005] For example, Patent Document 3 discloses a method for producing a carbon material, which involves subjecting a carbon material precursor made of an acrylamide / vinyl cyanide copolymer containing 50 to 99.9 mol% acrylamide monomer units and 0.1 to 50 mol% vinyl cyanide monomer units to flame-retardant treatment and then to carbonization treatment. Furthermore, Patent Document 4 discloses a method for producing a carbon material, which involves subjecting a carbon material precursor made of an acrylamide polymer having a weight-average molecular weight of 10,000 to 2,000,000 and a polydispersity of molecular weight (weight-average molecular weight / number-average molecular weight) of 5.0 or less to a flame-retardant treatment, and then subjecting it to a carbonization treatment.

[0006] Furthermore, as a method for producing flame-resistant fibers using acrylamide polymers, for example, Patent Document 5 discloses a method for producing flame-resistant fibers in which acrylamide polymer fibers are subjected to heat treatment in an oxidizing atmosphere at a flame-retardant treatment temperature in the range of 200 to 500°C while being subjected to a tension of 0.07 to 15 mN / tex. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2006-183159 [Patent Document 2] Japanese Patent Publication No. 2008-202208 [Patent Document 3] Japanese Patent Publication No. 2019-26827 [Patent Document 4] Japanese Patent Publication No. 2019-167516 [Patent Document 5] Japanese Patent Publication No. 2021-46629 [Overview of the project] [Problems that the invention aims to solve]

[0008] To produce long flame-resistant fiber bundles quickly, at low cost, and in large quantities, continuous heat treatment equipment is more suitable than batch-type heat treatment equipment. When producing flame-resistant fiber bundles and carbon fiber bundles from acrylamide polymers using continuous heat treatment equipment, there is a need for technology that can suppress the embrittlement of the flame-resistant fiber bundles after flame treatment and stably and continuously produce flame-resistant fiber bundles that can be carbonized without fiber breakage during carbonization. However, Patent Documents 4 and 5 do not disclose a technology for stably and continuously producing flame-resistant fiber bundles that suppress embrittlement and prevent fracture during carbonization using a continuous heat treatment apparatus.

[0009] This disclosure has been made in view of the problems of the above-mentioned prior art, and aims to provide a method for producing flame-resistant fiber bundles in which embrittlement after flame-retardant treatment is suppressed and fiber breakage is suppressed during carbonization treatment while tension is applied, as well as a flame-resistant fiber bundle and a method for producing carbon fiber bundles using flame-resistant fiber bundles obtained by the method for producing flame-resistant fiber bundles. [Means for solving the problem]

[0010] As a result of diligent research to achieve the above objective, the inventors of this invention have obtained the following findings. When acrylamide polymer fiber bundles are suddenly transported to a high-temperature atmosphere of over 300°C in a continuous heat treatment apparatus, the acrylamide polymer fiber bundles are rapidly heated, which may cause disruption of the crystal structure and the generation of voids, resulting in the embrittlement of the resulting flame-resistant fiber bundles. Since the carbonization process is carried out while applying tension, if the flame-resistant fiber bundles are brittle, there is a risk of them breaking during the carbonization process. In contrast, we found that by using a continuous heat treatment apparatus capable of providing two or more heating zones with different temperatures, with at least one low-temperature zone (below 300°C) and one high-temperature zone (above 300°C), where the first heating zone (the first zone) is the low-temperature zone, and where the temperature difference between the first adjacent low-temperature and high-temperature zones (in other words, the first high-temperature zone and the low-temperature zone immediately preceding it) is within 120°C, we can suppress the embrittlement of the flame-resistant fiber bundles and obtain flame-resistant fiber bundles that can withstand carbonization treatment in a short time. This is thought to be because reducing the temperature difference between the low-temperature and high-temperature zones suppresses the disruption of the crystal structure and the generation of voids caused by the rapid flame-retardant reaction, thereby suppressing the embrittlement of the flame-retardant fiber bundle.

[0011] It has also been found that rapid heating of an acrylamide-based polymer fiber bundle causes disorder of the crystal structure and decreases the orientation degree of the obtained flame-resistant fiber bundle, thereby resulting in embrittlement of the flame-resistant fiber bundle. As a result, it has been found that by controlling the orientation degree of the flame-resistant fiber bundle to 44 or more, embrittlement of the flame-resistant fiber bundle is suppressed, and a flame-resistant fiber bundle that can withstand carbonization treatment can be obtained.

[0012] Furthermore, it has been found that by setting the flame-resistance degree calculated from the infrared absorption spectrum of the flame-resistant fiber bundle to 1.10 or more, that is, by sufficiently performing flame-resistance treatment on the flame-resistant fiber bundle, the fiber bundle can withstand the heat of carbonization treatment when obtaining a carbon fiber bundle, and breakage of fibers during carbonization treatment can be suppressed.

[0013] That is, the method for producing a flame-resistant fiber bundle, the method for producing a carbon fiber bundle, and the flame-resistant fiber bundle of the present disclosure are as follows.

[0014] <1> This is a method for producing a flame-resistant fiber bundle, in which an acrylamide-based polymer fiber bundle is subjected to heat treatment in a continuous heat treatment apparatus having heating zones divided into two or more zones and allowing temperature setting for each zone, wherein the heating zones comprise a low-temperature zone having a set temperature of less than 300°C and a high-temperature zone having a set temperature of 300°C or higher, the heating zone through which the acrylamide-based polymer fiber bundle passes first is the low-temperature zone, and a temperature difference between the low-temperature zone and the high-temperature zone at an adjacent position between the first low-temperature zone and the high-temperature zone is 120°C or less. <2> The method for producing a flame-resistant fiber bundle according to <1>, wherein the set temperature of the low-temperature zone ranges from 200°C to 295°C. <3> The method for producing a flame-resistant fiber bundle according to <1>, wherein the set temperature of the high-temperature zone ranges from 300°C to 400°C. <4> The method for producing a flame-resistant fiber bundle according to <1>, which produces a flame-resistant fiber bundle having an orientation degree of 44 or more. <5> calculated from an infrared absorption spectrum, 1350 to 1380 cm-1 The peak intensity of the absorption peak originating from the naphthyridine ring, observed in the range of 1640-1660 cm⁻¹, is -1 The flame-retardant fiber bundle is produced in which the flame-retardant degree is 1.10 or higher, which is the ratio of the peak intensity of the absorption peak derived from the acrylamide group confirmed in the range to the flame-retardant degree. <1> A method for producing flame-resistant fiber bundles as described above. <6> <1> A method for producing a carbon fiber bundle, comprising the steps of: obtaining a flame-resistant fiber bundle by the method for producing a flame-resistant fiber bundle described in [reference]; and subjecting the flame-resistant fiber bundle to a carbonization treatment. <7> Flame-resistant fiber bundles derived from acrylamide polymers with an orientation degree of 44 or higher. <8> The infrared absorption spectrum of the aforementioned flame-resistant fiber bundle was calculated to be 1350-1380 cm⁻¹. -1 The peak intensity of the absorption peak originating from the naphthyridine ring, observed in the range of 1640-1660 cm⁻¹, is -1 The flame resistance degree is 1.10 or higher, which is the ratio of the peak intensity of the absorption peak derived from the acrylamide group observed in the range to the peak intensity of the absorption peak. <7> Flame-resistant fiber bundles as described above. [Effects of the Invention]

[0015] According to this disclosure, it is possible to provide a method for producing flame-resistant fiber bundles in which embrittlement after flame-retardant treatment is suppressed and fiber breakage is suppressed during carbonization treatment while tension is applied, as well as flame-resistant fiber bundles and a method for producing carbon fiber bundles using flame-resistant fiber bundles obtained by the method for producing flame-resistant fiber bundles. [Brief explanation of the drawing]

[0016] [Figure 1] This is a cross-sectional view showing an example of a continuous heat treatment apparatus. [Figure 2] This is a cross-sectional view showing an example of a continuous heat treatment apparatus. [Figure 3] This is a cross-sectional view showing an example of a continuous heat treatment apparatus. [Modes for carrying out the invention]

[0017] The following describes an embodiment that is an example of this disclosure. These descriptions and examples are illustrative of embodiments and do not limit the scope of the embodiments.

[0018] In the numerical ranges described in stages within this embodiment, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described within this embodiment, the upper or lower limit of that range may be replaced with the values ​​shown in the examples. In this embodiment, the term "process" includes not only independent processes but also any process that cannot be clearly distinguished from other processes, as long as its intended purpose is achieved. In this embodiment, when describing embodiments with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of the members in each figure are conceptual, and the relative relationships between the sizes of the members are not limited thereto. In this embodiment, each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition.

[0019] First, the acrylamide polymer and acrylamide polymer fiber bundle used in this disclosure will be described.

[0020] (Acrylamide polymer) The acrylamide polymer used in this disclosure may be a homopolymer of acrylamide monomers or a copolymer of an acrylamide monomer and another polymerizable monomer. However, a copolymer of an acrylamide monomer and another polymerizable monomer is preferred from the viewpoint of improving the tensile modulus of the carbon fiber bundle and further improving the carbonization yield.

[0021] The lower limit of the content of acrylamide monomer units in the copolymer of the acrylamide monomer and other polymerizable monomers is preferably 50 mol% or more, more preferably 55 mol% or more, and particularly preferably 60 mol% or more, from the viewpoint of improving the solubility of the copolymer in aqueous solvents or aqueous mixed solvents. The upper limit of the content of acrylamide monomer units is preferably 99.9 mol% or less, more preferably 99 mol% or less, even more preferably 95 mol% or less, particularly preferably 90 mol% or less, and most preferably 85 mol% or less, from the viewpoint of improving the tensile modulus of the carbon fiber bundle and further improving the carbonization yield.

[0022] As a lower limit for the content of other polymerizable monomer units in the copolymer of the acrylamide monomer and other polymerizable monomers, from the viewpoint of improving the tensile modulus of the carbon fiber bundle and further improving the carbonization yield, it is preferably 0.1 mol% or more, more preferably 1 mol% or more, even more preferably 5 mol% or more, particularly preferably 10 mol% or more, and most preferably 15 mol% or more. Furthermore, as a upper limit for the content of other polymerizable monomer units, from the viewpoint of improving the solubility of the copolymer in aqueous solvents or aqueous mixed solvents, it is preferably 50 mol% or less, more preferably 45 mol% or less, and particularly preferably 40 mol% or less.

[0023] Examples of the acrylamide monomers include acrylamide; N-alkylacrylamides such as N-methylacrylamide, N-ethylacrylamide, Nn-propylacrylamide, N-isopropylacrylamide, Nn-butylacrylamide, and N-tert-butylacrylamide; N-cycloalkylacrylamides such as N-cyclohexylacrylamide; dialkylacrylamides such as N,N-dimethylacrylamide; dialkylaminoalkylacrylamides such as dimethylaminoethylacrylamide and dimethylaminopropylacrylamide; hydroxyalkylacrylamides such as N-(hydroxymethyl)acrylamide and N-(hydroxyethyl)acrylamide; N-arylacrylamides such as N-phenylacrylamide; diacetoneacrylamide; and N,N'-methylenebisacrylamide. N,N'-alkylene bisacrylamide; methacrylamide; N-alkyl methacrylamide such as N-methyl methacrylamide, N-ethyl methacrylamide, Nn-propyl methacrylamide, N-isopropyl methacrylamide, Nn-butyl methacrylamide, N-tert-butyl methacrylamide; N-cycloalkyl methacrylamide such as N-cyclohexyl methacrylamide; dialkyl methacrylamide such as N,N-dimethyl methacrylamide; dialkylaminoalkyl methacrylamide such as dimethylaminoethyl methacrylamide, dimethylaminopropyl methacrylamide; hydroxyalkyl methacrylamide such as N-(hydroxymethyl)methacrylamide, N-(hydroxyethyl)methacrylamide; N-aryl methacrylamide such as N-phenyl methacrylamide; diacetone methacrylamide; N Examples include N,N'-alkylene bismethacrylamides such as N'-methylenebismethacrylamide. These acrylamide monomers may be used individually or in combination of two or more. Among these acrylamide monomers, acrylamide, N-alkylacrylamide, dialkylacrylamide, methacrylamide, N-alkylmethacrylamide, and dialkylmethacrylamide are preferred from the viewpoint of high solubility in aqueous solvents or aqueous mixed solvents, and acrylamide is particularly preferred.

[0024] Examples of the aforementioned other polymerizable monomers include vinyl cyanide monomers, unsaturated carboxylic acids and their salts, unsaturated carboxylic acid anhydrides, unsaturated carboxylic acid esters, vinyl monomers, and olefin monomers. Examples of the aforementioned vinyl cyanide monomers include acrylonitrile, methacrylonitrile, 2-hydroxyethyl acrylonitrile, chloroacrylonitrile, chloromethacrylonitrile, methoxyacrylonitrile, and methoxymethacrylonitrile. Examples of the unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, crotonic acid, isocrotonic acid, etc. Examples of salts of the unsaturated carboxylic acids include metal salts (e.g., sodium salt, potassium salt, etc.), ammonium salts, amine salts, etc. Examples of the unsaturated carboxylic acid anhydrides include maleic anhydride, itaconic anhydride, etc. Examples of the unsaturated carboxylic acid esters include methyl acrylate, methyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, etc. Examples of the vinyl monomers include aromatic vinyl monomers such as styrene and α-methylstyrene, vinyl carboxylates such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl chloride, vinyl alcohol, etc. Examples of the olefin monomers include ethylene and propylene. These other polymerizable monomers may be used individually or in combination of two or more. Furthermore, among these other polymerizable monomers, vinyl cyanide monomers are preferred from the viewpoint of improving the spinnability and carbonization yield of the acrylamide polymer, acrylonitrile is particularly preferred, unsaturated carboxylic acids and their salts are preferred from the viewpoint of improving the solubility of the copolymer in aqueous solvents or aqueous mixed solvents, and unsaturated carboxylic acids and unsaturated carboxylic acid anhydrides are preferred from the viewpoint of improving the resistance to fusion of acrylamide polymer fiber bundles during flame-retardant treatment, acrylic acid, maleic acid, fumaric acid, itaconic acid, and maleic acid anhydride are more preferred.

[0025] There are no particular upper limits on the weight-average molecular weight of the acrylamide polymer used in this disclosure, but it is usually 5 million or less. From the viewpoint of improving the spinnability of the acrylamide polymer, it is preferably 2 million or less, more preferably 1 million or less, even more preferably 500,000 or less, even more preferably 300,000 or less, particularly preferably 200,000 or less, even more preferably 130,000 or less, and most preferably 100,000 or less. There are no particular lower limits on the weight-average molecular weight of the acrylamide polymer, but it is usually 10,000 or more. From the viewpoint of improving the strength of the flame-resistant fiber bundles and carbon fiber bundles, it is preferably 20,000 or more, more preferably 30,000 or more, and particularly preferably 40,000 or more. The weight-average molecular weight of the acrylamide polymer is measured using gel permeation chromatography.

[0026] Furthermore, it is preferable that the acrylamide polymer used in this disclosure is soluble in at least one of the following: aqueous solvents (water, alcohol, etc., and mixed solvents thereof) and aqueous mixed solvents (a mixed solvent of the aqueous solvent and an organic solvent (tetrahydrofuran, etc.)). This makes it possible to spin the acrylamide polymer using dry spinning, wet dry spinning, wet spinning, or electrospinning with the aqueous solvent or the aqueous mixed solvent, enabling the safe and low-cost production of flame-resistant fiber bundles and carbon fiber bundles. In addition, when compounding the acrylamide polymer with additive components described later, wet mixing using the aqueous solvent or the aqueous mixed solvent becomes possible, enabling the acrylamide polymer and the additive components described later to be mixed uniformly, safely, and at low cost. The amount of organic solvent in the compound solvent is not particularly limited, as long as it is sufficient to dissolve the acrylamide polymer, which is insoluble or sparingly soluble in the aqueous solvent, by mixing it with the organic solvent. Furthermore, among such acrylamide polymers, acrylamide polymers soluble in the aqueous solvent are preferred, and water-soluble (water-soluble) acrylamide polymers are more preferred, from the viewpoint of enabling the production of flame-resistant fiber bundles and carbon fiber bundles at a lower cost and with greater safety.

[0027] As a method for synthesizing such acrylamide polymers, known polymerization reactions such as radical polymerization, cationic polymerization, anionic polymerization, and living radical polymerization can be employed, carried out by polymerization methods such as solution polymerization, suspension polymerization, precipitation polymerization, dispersion polymerization, and emulsion polymerization (e.g., reversed-phase emulsion polymerization). Among the aforementioned polymerization reactions, radical polymerization is preferred from the viewpoint of producing the acrylamide polymer at low cost. Furthermore, when employing solution polymerization, it is preferable to use a solvent that dissolves the raw material monomers and the resulting acrylamide polymer. From the viewpoint of low-cost and safe production, it is more preferable to use an aqueous solvent (water, alcohol, etc., and mixed solvents thereof) or an aqueous mixed solvent (a mixed solvent of the aqueous solvent and an organic solvent (tetrahydrofuran, etc.)), particularly preferable to use an aqueous solvent, and most preferable to use water.

[0028] In the radical polymerization described above, conventionally known radical polymerization initiators such as azobisisobutyronitrile, benzoyl peroxide, 4,4'-azobis(4-cyanovaleric acid), ammonium persulfate, and potassium persulfate can be used as polymerization initiators. However, when using the aqueous solvent or the aqueous mixed solvent as the solvent, radical polymerization initiators soluble in the aqueous solvent or the aqueous mixed solvent (preferably the aqueous solvent, more preferably water), such as 4,4'-azobis(4-cyanovaleric acid), ammonium persulfate, and potassium persulfate, are preferred. Furthermore, from the viewpoint of improving the spinnability of the acrylamide polymer and improving the solubility of the acrylamide polymer in the aqueous solvent or the aqueous mixed solvent, it is preferable to use conventionally known polymerization accelerators such as tetramethylethylenediamine or molecular weight modifiers such as alkyl mercaptans such as n-dodecyl mercaptan in place of or in addition to the polymerization initiator. It is preferable to use the polymerization initiator and the polymerization accelerator in combination, and it is particularly preferable to use ammonium persulfate and tetramethylethylenediamine in combination.

[0029] There are no particular restrictions on the temperature at which the polymerization initiator is added, but from the viewpoint of improving the processability (spinability) of the acrylamide polymer, a temperature of 25°C or higher is preferred, 30°C or higher is more preferred, 35°C or higher is even more preferred, 40°C or higher is particularly preferred, and 45°C or higher is most preferred. Similarly, there are no particular restrictions on the temperature of the polymerization reaction, but from the viewpoint of improving the solubility of the acrylamide polymer in the aqueous solvent or the aqueous mixed solvent, a temperature of 40°C or higher is preferred, 60°C or higher is more preferred, and 70°C or higher is most preferred.

[0030] (Acrylamide polymer fiber bundle) The acrylamide polymer fiber bundle used in this disclosure consists of the acrylamide polymer and can be used as is in the production of flame-resistant fiber bundles and carbon fiber bundles without the addition of additives such as acids. However, from the viewpoint of improving the tensile modulus of the flame-resistant fiber bundles and carbon fiber bundles, it is preferable that the acrylamide polymer fiber bundle contains, in addition to the acrylamide polymer, at least one additive selected from the group consisting of acids and their salts. In the flame-resistant fiber bundles and carbon fiber bundles according to this disclosure, at least a portion of the additive and its residue may remain. Alternatively, the additive may be added to the flame-resistant fiber bundle and subjected to carbonization treatment.

[0031] The content of such additives suppresses the fusion of acrylamide polymer fiber bundles during flame-retardant treatment, and also improves the load-bearing capacity, strength, elastic modulus, and carbon yield of the flame-retardant fiber bundles at high temperatures. From the viewpoint of improving and further improving the tensile modulus of the carbon fiber bundle, the amount is preferably 0.05 to 100 parts by mass, more preferably 0.1 to 50 parts by mass, even more preferably 0.3 to 30 parts by mass, particularly preferably 0.5 to 20 parts by mass, and most preferably 1.0 to 10 parts by mass per 100 parts by mass of the acrylamide polymer.

[0032] Examples of the aforementioned acids include inorganic acids such as phosphoric acid, polyphosphoric acid, boric acid, polyboric acid, sulfuric acid, nitric acid, carbonic acid, and hydrochloric acid, and organic acids such as oxalic acid, citric acid, sulfonic acid, and acetic acid. Examples of salts of such acids include metal salts (e.g., sodium salts, potassium salts), ammonium salts, and amine salts, with ammonium salts and amine salts being preferred, and ammonium salts being more preferred. In particular, among these additive components, phosphoric acid, polyphosphoric acid, boric acid, polyboric acid, sulfuric acid, and their ammonium salts are preferred from the viewpoint of improving the load-bearing capacity, strength, elastic modulus, and carbonization yield of the flame-resistant fiber bundle at high temperatures, and further improving the tensile modulus of the carbon fiber bundle, with phosphoric acid, polyphosphoric acid, and their ammonium salts being particularly preferred.

[0033] Furthermore, in addition to the additive components, the acrylamide polymer fiber bundle may also contain various fillers such as chlorides like sodium chloride and zinc chloride, hydroxides like sodium hydroxide, carbon nanotubes, and nanocarbons like graphene, to the extent that they do not impair the effects of this disclosure.

[0034] The additive component is preferably soluble in at least one of the aqueous solvent and the aqueous mixed solvent (more preferably the aqueous solvent, and particularly preferably water). This allows for wet mixing using the aqueous solvent or the aqueous mixed solvent when producing acrylamide polymer fiber bundles, enabling uniform, low-cost, and safe mixing of the acrylamide polymer and the additive component. Furthermore, it enables dry spinning, wet dry spinning, wet spinning, or electrospinning using the aqueous solvent or the aqueous mixed solvent, making it possible to produce carbon materials safely and at low cost.

[0035] Such acrylamide polymer fiber bundles can be produced (manufactured) as follows. First, the acrylamide polymer or an acrylamide polymer composition containing the acrylamide polymer and the additive component is spun. At this time, melt spinning, spunbonding, melt blowing, or centrifugal spinning may be performed using the molten acrylamide polymer or acrylamide polymer composition. However, if the acrylamide polymer or acrylamide polymer composition is soluble in the aqueous solvent or the aqueous mixed solvent, from the viewpoint of improving spinability, it is preferable to dissolve the acrylamide polymer or acrylamide polymer composition in the aqueous solvent or the aqueous mixed solvent and spin using the resulting aqueous solution or aqueous mixed solution, or to spin using the solution of the polymerized acrylamide polymer or the solution of the acrylamide polymer composition obtained by the wet mixing described later, either as is or after adjusting to a desired concentration. Preferred spinning methods include dry spinning, wet spinning, wet-dry spinning, gel spinning, flash spinning, or electrospinning. This makes it possible to safely and inexpensively produce acrylamide polymer fibers or acrylamide polymer fiber bundles having the desired fineness and average fiber diameter. Furthermore, from the viewpoint of producing acrylamide polymer fiber bundles at an even lower cost and with greater safety, it is more preferable to use the aqueous solvent as the solvent, and it is particularly preferable to use water.

[0036] Furthermore, there are no particular restrictions on the concentration of the acrylamide polymer in the aqueous solution or the aqueous mixed solution, but a high concentration of 20% by mass or more is preferred from the viewpoint of improving productivity and reducing costs. By controlling the concentration of the acrylamide polymer so that it does not become too high, the viscosity of the aqueous solution or the aqueous mixed solution is reduced, and spinnability is improved. Therefore, the concentration of the aqueous solution or the aqueous mixed solution can be controlled using viscosity as an indicator to determine the spinnability. It is preferable to adjust the concentration.

[0037] As a method for producing the acrylamide polymer composition, it is also possible to employ methods such as directly mixing the additive component with the molten acrylamide polymer (melt mixing), dry blending the acrylamide polymer and the additive component (dry mixing), or immersing or passing the acrylamide polymer, formed into fibers, through an aqueous solution or aqueous mixed solution containing the additive component, or a solution in which the acrylamide polymer is not completely dissolved but the additive component is dissolved. However, if the acrylamide polymer and the additive component used are soluble in the aqueous solvent or aqueous mixed solvent, a method of mixing the acrylamide polymer and the additive component in the aqueous solvent or aqueous mixed solvent (wet mixing) is preferred from the viewpoint of uniformly mixing the acrylamide polymer and the additive component. Furthermore, as a wet mixing method, when the polymerization of the acrylamide polymer is carried out in the aqueous solvent or aqueous mixed solvent, a method of mixing the additive component after polymerization can also be employed. Furthermore, the acrylamide-based polymer composition can be recovered by removing the solvent from the resulting solution and used in the production of the acrylamide-based polymer fiber bundle, or the resulting solution can be used directly in the production of the acrylamide-based polymer fiber bundle without removing the solvent. In addition, in the wet mixing process, it is preferable to use the aqueous solvent as the solvent, and more preferable to use water, from the viewpoint of producing the acrylamide-based polymer composition at a lower cost and more safely. Furthermore, there are no particular restrictions on the method of removing the solvent, and at least one of the known methods such as vacuum distillation, reprecipitation, hot air drying, vacuum drying, and freeze-drying can be employed.

[0038] Furthermore, as the acrylamide polymer fiber bundles of this disclosure, cross-linked acrylamide polymer fiber bundles that have been cross-linked by electron beam, ultraviolet light, heat, etc., from the viewpoint of improving strength and moisture resistance and suppressing fusion between fibers may also be preferably used. In addition, the acrylamide polymer fiber bundles of this disclosure may be those to which a conventionally known oil such as a silicone oil has been applied to the surface, from the viewpoint of improving bundling ability and suppressing fusion between fibers. In this disclosure, such acrylamide polymer fiber bundles (including cross-linked acrylamide polymer fiber bundles) are used as acrylamide polymer fiber bundles. There are no particular restrictions on the number of filaments per yarn in the acrylamide polymer fiber bundles, but from the viewpoint of improving the productivity and mechanical properties of flame-resistant fiber bundles and carbon fiber bundles, 50 to 96,000 is preferred, 100 to 48,000 is more preferred, 500 to 36,000 is even more preferred, and 1,000 to 24,000 is particularly preferred. By keeping the number of filaments per thread below the aforementioned upper limit, the occurrence of uneven firing during flame-retardant treatment can be suppressed.

[0039] [Method for manufacturing flame-resistant fiber bundles] Next, a method for producing flame-resistant fiber bundles according to this disclosure will be described. The method for producing flame-resistant fiber bundles according to this disclosure is a method for producing flame-resistant fiber bundles that heat-treats an acrylamide polymer fiber bundle in a continuous heat treatment apparatus in which the heating zone is divided into two or more zones and the temperature can be set for each zone. The heating zone has a low-temperature zone with a set temperature of less than 300°C and a high-temperature zone with a set temperature of 300°C or higher. The first heating zone that the acrylamide polymer fiber bundle passes through (i.e., the first zone) is the low-temperature zone, and the temperature difference between the set temperatures of the low-temperature zone and the high-temperature zone at the point where the low-temperature zone and the high-temperature zone first meet is set to within 120°C. From the viewpoint of increasing the degree of orientation of the flame-resistant fiber bundle, the temperature difference between the set temperatures of the low-temperature zone and the high-temperature zone at the point where the low-temperature zone and the high-temperature zone first meet is preferably 15 to 110°C, more preferably 20 to 100°C, even more preferably 25 to 95°C, and particularly preferably 30 to 90°C.

[0040] Furthermore, if there are multiple locations where a high-temperature zone is adjacent to a low-temperature zone, it is preferable to keep the temperature difference between the set temperatures of the low-temperature zone and the high-temperature zone within 120°C, more preferably 15-110°C, even more preferably 20-100°C, even more preferably 25-95°C, and even more preferably 30-90°C, not only at the location where the low-temperature zone and the high-temperature zone first meet, but also at two or more locations where the high-temperature zone follows the low-temperature zone. It is particularly preferable that, in all locations where a high-temperature zone is adjacent to a low-temperature zone, the temperature difference between the set temperatures of the low-temperature zone and the high-temperature zone be within 120°C, more preferably 15-110°C, even more preferably 20-100°C, even more preferably 25-95°C, and particularly preferably 30-90°C.

[0041] Here, "heating zone" refers to an area for heating the acrylamide polymer fiber bundles transported inside, and each zone has its own independently set temperature. Adjacent heating zones may or may not be separated by a partition wall with a window through which the acrylamide polymer fiber bundles are transported. Furthermore, the acrylamide polymer fiber bundles that have passed through one heating zone may have to exit the heating zone before entering the next heating zone. Furthermore, "set temperature" refers to the temperature set for each heating zone in a continuous heat treatment apparatus. In other words, it refers to the target temperature of the atmosphere within each heating zone as the acrylamide polymer fiber bundle passes through.

[0042] Here, the continuous heat treatment apparatus and heating zone will be explained using Figure 1.

[0043] Figure 1 is a cross-sectional view showing an example of a continuous heat treatment apparatus, which has five heating zones divided laterally. The continuous heat treatment apparatus 2A has a feed roll 6 and a winding roll 8. An acrylamide polymer fiber bundle 4 is stretched between the feed roll 6 and the winding roll 8 via a plurality of conveying rolls in between. The acrylamide polymer fiber bundle 4 is conveyed from the feed roll 6 side to the winding roll 8 side by the rotation of the feed roll 6 and the winding roll 8. The continuous heat treatment apparatus 2A has a heating device 20A between the feed roll 6 and the winding roll 8. The heating device 20A has five heating zones 211, 212, 213, 214, and 215 divided laterally. The heating zones 211, 212, 213, 214, and 215 can each be set to a different temperature. The acrylamide polymer fiber bundle 4 enters the heating device 20A from the entrance of heating zone 211, is sequentially transported through heating zones 211, 212, 213, 214, and 215, and is discharged from the exit of heating zone 215 towards the winding roll 8.

[0044] In the manufacturing of flame-resistant fiber bundles, heating zones 211, 212, 213, 214, and 215 are provided with a low-temperature zone with a set temperature of less than 300°C and a high-temperature zone with a set temperature of 300°C or higher. Heating zone 211 (i.e., the first zone) through which the acrylamide polymer fiber bundle 4 first passes is set as the low-temperature zone (less than 300°C). Furthermore, the temperature difference between the set temperatures of the low-temperature zone and the high-temperature zone at the point where the low-temperature zone and the high-temperature zone first meet is set to within 120°C.

[0045] For example, if heating zones 211 and 212 are set to low temperature zones (below 300°C) and heating zones 213, 214, and 215 are set to high temperature zones (above 300°C), then initially, the temperature difference between the set temperatures of adjacent areas where the low temperature zones and high temperature zones meet, that is, between heating zone 212 and heating zone 213, should be kept within 120°C. Furthermore, if heating zones 211 and 213 are set to low temperature zones (below 300°C) and heating zones 212, 214, and 215 are set to high temperature zones (300°C or higher), the temperature difference between the first adjacent low-temperature and high-temperature zones, i.e., between heating zone 211 and heating zone 212, should be within 120°C. It is also preferable that the temperature difference between the next adjacent high-temperature zone after another low-temperature zone, i.e., between heating zone 213 and heating zone 214, should also be within 120°C.

[0046] Next, a different embodiment of a continuous heat treatment apparatus and heating zone will be described with reference to Figure 2.

[0047] Figure 2 is a cross-sectional view showing an example of a continuous heat treatment apparatus, which has three heating zones divided in the vertical direction. The continuous heat treatment apparatus 2B has a feed roll 6 and a winding roll 8. An acrylamide polymer fiber bundle 4 is stretched between the feed roll 6 and the winding roll 8 via a plurality of conveying rolls in between. The acrylamide polymer fiber bundle 4 is conveyed from the feed roll 6 side to the winding roll 8 side by the rotation of the feed roll 6 and the winding roll 8. The continuous heat treatment apparatus 2B has a heating device 20B between the feed roll 6 and the winding roll 8. The heating device 20B has three heating zones 221, 222, and 223 divided in the vertical direction. That is, heating zones 221, 222, and 223 have a configuration in which three heating zones are stacked in a stepped manner in the vertical direction. The heating zones 221, 222, and 223 can each be set to a different temperature. The acrylamide polymer fiber bundle 4 enters the heating device 20B from the entrance of heating zone 221, is transported within heating zone 221, and is then discharged outside from the exit of heating zone 221. Next, the acrylamide polymer fiber bundle 4 enters the heating device 20B again from the entrance of the second heating zone, i.e., heating zone 222, is transported within heating zone 222, and is then discharged outside from the exit of heating zone 222. Furthermore, the acrylamide polymer fiber bundle 4 enters the heating device 20B again from the entrance of the third heating zone, i.e., heating zone 223, is transported within heating zone 223, and is then discharged towards the winding roll 8 from the exit of heating zone 223.

[0048] In the manufacturing of flame-resistant fiber bundles, heating zones 221, 222, and 223 are provided with a low-temperature zone with a set temperature of less than 300°C and a high-temperature zone with a set temperature of 300°C or higher. Heating zone 221 (i.e., the first zone) through which the acrylamide polymer fiber bundle 4 first passes is set as the low-temperature zone (less than 300°C). Furthermore, the temperature difference between the set temperatures of the low-temperature zone and the high-temperature zone at the point where the low-temperature zone and the high-temperature zone first meet is kept within 120°C. For example, if heating zone 221 is set to a low temperature zone (below 300°C) and heating zones 222 and 223 are set to high temperature zones (300°C or higher), then initially, the temperature difference between the set temperatures of adjacent areas, i.e., heating zone 221 and heating zone 222, should be kept within 120°C.

[0049] Furthermore, another embodiment of a continuous heat treatment apparatus and heating zone will be explained with reference to Figure 3.

[0050] Figure 3 is a cross-sectional view showing an example of a continuous heat treatment apparatus, which has a total of 15 heating zones divided into 5 horizontally and 3 vertically. The continuous heat treatment apparatus 2C has a feed roll 6 and a winding roll 8. An acrylamide polymer fiber bundle 4 is stretched between the feed roll 6 and the winding roll 8 via multiple conveying rolls in between. The acrylamide polymer fiber bundle 4 is conveyed from the feed roll 6 side to the winding roll 8 side by the rotation of the feed roll 6 and the winding roll 8. The continuous heat treatment apparatus 2C has a heating device 20C between the feed roll 6 and the winding roll 8. The heating device 20C has a total of 15 heating zones 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, and 245, which are divided into 5 horizontally and 3 vertically. In other words, it has a configuration in which heating zones 231, 232, 233, 234, 235 divided horizontally into 5 sections, heating zones 236, 237, 238, 239, 240, and heating zones 241, 242, 243, 244, 245 are further stacked in 3 layers vertically. Zones 44 and 245 can each be set to a different temperature. The acrylamide polymer fiber bundle 4 enters the heating device 20C from the entrance of heating zone 231, is transported sequentially through heating zones 231, 232, 233, 234, and 235, and is temporarily discharged outside from the exit of heating zone 235. Next, the acrylamide polymer fiber bundle 4 is transported through the 6th to 10th heating zones. That is, it enters the heating device 20C again from the entrance of heating zone 236, is transported through heating zones 236, 237, 238, 239, and 240, and is temporarily discharged outside from the exit of heating zone 240. Furthermore, the acrylamide polymer fiber bundle 4 is transported through the 11th to 15th heating zones. In other words, the material enters the heating device 20C again from the entrance of heating zone 241, is transported through heating zones 241, 242, 243, 244, and 245, and is then discharged from the exit of heating zone 245 towards the winding roll 8.

[0051] In the manufacture of flame-resistant fiber bundles, heating zones 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, and 245 are provided with a low-temperature zone with a set temperature of less than 300°C and a high-temperature zone with a set temperature of 300°C or higher. Heating zone 231 (i.e., the first zone) through which the acrylamide polymer fiber bundle 4 first passes is set as the low-temperature zone (less than 300°C). Furthermore, the temperature difference between the set temperatures of the low-temperature zone and the high-temperature zone at the point where the low-temperature zone and the high-temperature zone first meet is set to within 120°C.

[0052] For example, if heating zones 231, 232, and 233 are set as low-temperature zones (below 300°C) and heating zones 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, and 245 are set as high-temperature zones (above 300°C), then initially, the temperature difference between the set temperatures of adjacent low-temperature and high-temperature zones, i.e., between heating zone 233 and heating zone 234, should be kept within 120°C. Furthermore, for example, if heating zones 231, 232, 233, and 236 are set as low-temperature zones (below 300°C), and heating zones 234, 235, 237, 238, 239, 240, and 241, 242, 243, 244, and 245 are set as high-temperature zones (above 300°C), then the temperature difference between the set temperatures of the first adjacent low-temperature and high-temperature zones, i.e., heating zone 233 and heating zone 234, should be kept within 120°C. It is also preferable that the temperature difference between the set temperatures of the next adjacent high-temperature zone after another low-temperature zone, i.e., heating zone 236 and heating zone 237, should also be kept within 120°C.

[0053] The temperature set for the low-temperature zone should be less than 300°C. In particular, by setting the temperature of the heating zone through which the acrylamide polymer fiber bundle first passes (i.e., the first zone) to less than 300°C, rapid heating can be avoided when flame-retarding the acrylamide polymer fiber bundle, thereby suppressing a decrease in the degree of orientation. Furthermore, it is preferable to set the temperature of the low-temperature zone to 200°C to 295°C.

[0054] The high-temperature zone should be set to a temperature of 300°C or higher. By setting the high-temperature zone to a temperature of 300°C or higher, the acrylamide polymer fiber bundle can be sufficiently made flame-resistant. Furthermore, it is preferable to set the temperature of the high-temperature zone to 300°C to 400°C.

[0055] There are no particular restrictions on the time of the flame-retardant treatment (i.e., the time during which the acrylamide polymer fiber bundle is transported within the heated zone), but it is preferably 1 to 120 minutes, more preferably 2 to 60 minutes, even more preferably 3 to 50 minutes, and particularly preferably 4 to 40 minutes.

[0056] In the method for manufacturing flame-resistant fiber bundles, it is preferable to transport the acrylamide polymer fiber bundle into the heating zone of a continuous heat treatment apparatus while applying tension, or after applying tension. This prevents the acrylamide polymer fiber bundle from fusing together during the flame-resistant treatment. The resulting flame-resistant fiber bundle exhibits improved properties, excellent load-bearing capacity at high temperatures, high strength, high modulus of elasticity, and high carbonization yield. There are no particular restrictions on the tension applied to the acrylamide polymer fiber bundle, but 0.002 to 30 mN / dtex is preferred, 0.004 to 20 mN / dtex is more preferred, and 0.007 to 5 mN / dtex is even more preferred. The tension applied to the acrylamide polymer fiber bundle (unit: mN / dtex) is the tension per unit fineness of the acrylamide polymer fiber bundle. The tension applied to the acrylamide polymer fiber bundle can be adjusted, for example, by load cells, springs, weights, etc., at the inlet and outlet sides of the heating device of a continuous heat treatment apparatus.

[0057] In the method for producing flame-resistant fiber bundles, the acrylamide polymer fiber bundle may be transported through the heating zone of a continuous heat treatment apparatus while being subjected to a stretching treatment. The stretching ratio in this case is preferably 1.3 to 100 times, more preferably 1.7 to 50 times, even more preferably 2.0 to 25 times, and particularly preferably 3.0 to 10 times. When the stretching ratio during the stretching treatment while transporting through the heating zone is above the lower limit, the fusion of the acrylamide polymer fiber bundle is sufficiently suppressed, and the load-bearing capacity, strength, elastic modulus, and carbonization yield of the flame-resistant fiber bundle at high temperatures are increased. On the other hand, when the stretching ratio is below the upper limit, the occurrence of yarn breakage during transport in the heating zone is suppressed.

[0058] The stretching ratio can be determined by the ratio of the feed rate (input rate) of the acrylamide polymer fiber bundle introduced into the continuous heat treatment apparatus to the feed rate (extraction rate) of the acrylamide polymer fiber bundle drawn out of the continuous heat treatment apparatus (extraction rate / input rate). It can also be determined by the ratio of the lengths of the acrylamide polymer fiber bundle to the flame-resistant fiber bundle (length of flame-resistant fiber bundle / length of acrylamide polymer fiber bundle). The stretching ratio can be controlled by adjusting the ratio of the feed rates (extraction rate / input rate) of the acrylamide polymer fiber bundle to the flame-resistant fiber bundle, the tension applied to the fiber bundle, the temperature during the stretching process, the moisture content of the acrylamide polymer fiber bundle, etc. For example, even if the temperature during the stretching process and the moisture content of the acrylamide polymer fiber bundle are the same, the stretching ratio changes depending on the composition of the acrylamide polymer, the presence or absence of additives in the acrylamide polymer fiber bundle, and the amount of additives. Therefore, the desired stretching ratio can be adjusted by adjusting the ratio of the feed speeds of the acrylamide polymer fiber bundle (drawing speed / introduction speed) and the tension applied to the fiber bundle (controlled by weights, springs, etc.).

[0059] Furthermore, prior to the method for producing flame-resistant fiber bundles according to this disclosure, the acrylamide polymer fiber bundle may be subjected to pretreatment. For example, as pretreatment, the acrylamide polymer fiber bundle may be subjected to stretching under specific temperature conditions.

[0060] According to the method for manufacturing flame-resistant fiber bundles described herein, the degree of orientation in the flame-resistant fiber bundles can be easily controlled within the range described later. Furthermore, according to the method for manufacturing flame-resistant fiber bundles described herein, the degree of flame resistance in the flame-resistant fiber bundles can be easily controlled within the range described later.

[0061] [Flame-resistant fiber bundle] Next, we will describe the flame-resistant fiber bundle related to this disclosure. The flame-resistant fiber bundles of this disclosure are derived from an acrylamide-based polymer and have an orientation degree of 44 or higher. The carbonization process to obtain carbon fiber bundles is carried out while applying tension, so if the flame-resistant fiber bundles are brittle, there is a risk of them breaking during the carbonization process. In contrast, by controlling the degree of orientation of the flame-resistant fiber bundles to 44 or higher, the embrittlement of the flame-resistant fiber bundles can be suppressed, and flame-resistant fiber bundles that can withstand the carbonization process can be provided.

[0062] Furthermore, "derived from" acrylamide polymers means that the fiber bundle is a flame-resistant fiber bundle obtained by flame-retarding an acrylamide polymer fiber bundle.

[0063] The flame-resistant fiber bundle relating to this disclosure is a flame-resistant fiber bundle obtained by flame-retarding an acrylamide-based polymer fiber bundle.

[0064] ·Orientation degree The flame-resistant fiber bundles of this disclosure have an orientation degree of 44 or higher. By setting the orientation degree to 44 or higher, embrittlement of the flame-resistant fiber bundles is suppressed, and flame-resistant fiber bundles that can withstand carbonization treatment can be provided. From the viewpoint of suppressing embrittlement of flame-resistant fiber bundles and improving strength after carbonization, the lower limit of the degree of orientation is preferably 46 or higher, and more preferably 50 or higher. On the other hand, from the viewpoint of ensuring the flexibility of the flame-resistant fiber bundle, the upper limit of the degree of orientation is preferably 98 or less, and more preferably 95 or less.

[0065] With regard to controlling the degree of orientation of flame-resistant fiber bundles to 44 or higher, it is preferable to suppress the disorder of the crystal structure and thus suppress the decrease in the degree of orientation by avoiding rapid heating when flame-retarding acrylamide polymer fiber bundles. Furthermore, in order to control the orientation degree of the flame-resistant fiber bundle to 44 or higher, it is preferable to use a continuous heat treatment apparatus that can provide two or more heating zones with different temperatures, with at least one low-temperature zone (below 300°C) and one high-temperature zone (300°C or higher), where the first heating zone (the first zone) is the low-temperature zone, and the initial temperature difference between the low-temperature zone and the high-temperature zone is 120°C or less. By reducing the temperature difference between the low-temperature zone and the high-temperature zone, it is possible to suppress the disorder of the crystal structure and the generation of voids due to the rapid flame-retardant reaction, thereby suppressing the decrease in the orientation degree, and as a result, the embrittlement of the flame-resistant fiber bundle can be suppressed.

[0066] The degree of orientation of the flame-resistant fiber bundle in this disclosure is calculated from a two-dimensional intensity distribution map obtained by wide-angle X-ray scattering measurement. The circumferential intensity distribution for 2θ:20~30° is determined, and after Gaussian fitting of the obtained circumferential intensity distribution, the half-widths W1 and W2 (°) of the scattered rays are determined, and the degree of orientation is calculated using the following formula. Orientation degree=100×(360-(W1+W2)) / 360

[0067] • Flame resistance In this disclosure, the degree of flame resistance is defined as the infrared absorption spectrum of the flame-resistant fiber bundle, specifically the range of 1350–1380 cm⁻¹. -1 The peak intensity of the absorption peak originating from the naphthyridine ring, observed in the range of 1640-1660 cm⁻¹, is -1 This value represents the ratio of the peak intensity of the absorption peak derived from the acrylamide group observed within this range. The flame resistance of the flame-resistant fiber bundle is preferably 1.10 or higher. By achieving a flame resistance of 1.10 or higher, that is, by ensuring sufficient flame resistance, a flame-resistant structure with excellent heat resistance can be formed, enabling it to withstand the high tension and high temperatures during the carbonization process and suppressing fiber breakage during the carbonization process. From the viewpoint of suppressing fiber breakage during carbonization, the lower limit of the flame resistance is preferably 1.15 or higher, and more preferably 1.20 or higher. On the other hand, from the viewpoint of suppressing thermal decomposition due to excessive heat treatment, the upper limit of the flame resistance is preferably 2.00 or less, and more preferably 1.80 or less.

[0068] With respect to controlling the degree of flame resistance of the flame-resistant fiber bundle to 1.10 or higher, it is preferable to heat the acrylamide polymer fiber bundle at a set temperature of 300°C or higher when flame-retarding it, and more preferable to heat it at a set temperature of 315°C or higher.

[0069] The method for measuring the degree of flame resistance of flame-resistant fiber bundles will be described later.

[0070] In the flame-resistant fiber bundle, there are no particular restrictions on the average fiber diameter of the single fibers, but 1 to 50 μm is preferred, 2 to 40 μm is more preferred, 3 to 30 μm is even more preferred, 4 to 25 μm is particularly preferred, and 5 to 20 μm is most preferred. If the average fiber diameter of the single fibers of the flame-resistant fiber bundle is above the lower limit, the occurrence of yarn breakage is suppressed, and stable winding and carbonization treatment can be performed. On the other hand, if it is below the upper limit, the large difference in structure between the surface and the center of the single fibers of the resulting carbon fiber bundle is suppressed, and the tensile strength and tensile modulus can be increased.

[0071] [Method for manufacturing carbon fiber bundles] Next, a method for producing carbon fiber bundles according to this disclosure will be described. The method for producing a carbon fiber bundle according to the present disclosure includes the steps of obtaining a flame-resistant fiber bundle by the method for producing a flame-resistant fiber bundle according to the present disclosure, and subjecting the flame-resistant fiber bundle to a carbonization treatment.

[0072] The process for obtaining a flame-resistant fiber bundle by the method for producing a flame-resistant fiber bundle described herein has already been described, so its explanation will be omitted.

[0073] The process of applying a carbonization treatment to a flame-resistant fiber bundle will now be described. For example, the flame-resistant fiber bundle is subjected to a heat treatment (carbonization treatment) at a temperature higher than the temperature used in the flame-resistant fiber bundle manufacturing method of this disclosure, under an inert atmosphere (in an inert gas such as nitrogen, argon, helium, or xenon). As a result, the flame-resistant fiber bundle is carbonized, and the desired carbon fiber bundle is obtained. The heating temperature (maximum temperature) in the carbonization treatment is preferably 1000°C or higher, more preferably 1100°C or higher, even more preferably 1200°C or higher, and particularly preferably 1300°C or higher. The upper limit of the heating temperature is preferably 3000°C or lower, more preferably 2500°C or lower, and even more preferably 2000°C or lower. The "carbonization treatment" in this disclosure may generally include a "graphitization treatment" carried out by heating at 2000 to 3000°C under an inert gas atmosphere. There are no particular restrictions on the heating time in the carbonization treatment, but it is preferably 30 seconds to 60 minutes, and more preferably 1 to 30 minutes.

[0074] Furthermore, in the method for manufacturing carbon fiber bundles, it is preferable to perform a heat treatment (pre-carbonization treatment) at a temperature of less than 1000°C before the carbonization treatment. The pre-carbonization treatment may also be performed while stretching the flame-resistant fiber bundle.

[0075] Furthermore, in the method for manufacturing carbon fiber bundles, it is possible to perform multiple heat treatments on the flame-resistant fiber bundle, such as applying a pre-carbonization treatment, followed by carbonization treatment, and then graphitization treatment.

[0076] In the carbon fiber bundle thus obtained, there are no particular restrictions on the average fiber diameter of the single fibers, but 1 to 50 μm is preferred, 2 to 40 μm is more preferred, 3 to 30 μm is even more preferred, 4 to 25 μm is particularly preferred, and 5 to 20 μm is most preferred. When the average fiber diameter of the single fibers of the carbon fiber bundle is above the lower limit, when a composite material is made using a resin or the like as a matrix, sufficient impregnation of the resin or the like into the carbon fiber bundle occurs even when the viscosity of the matrix is ​​high, thereby increasing the tensile strength of the composite material. On the other hand, when it is below the upper limit, the tensile strength and tensile modulus of the carbon fiber bundle can be increased.

[0077] Furthermore, in the method for manufacturing carbon fiber bundles, it is preferable to subject the carbon fiber bundles to electrolytic treatment in order to modify the surface of the carbon fiber bundles and optimize their adhesion to the resin. This eliminates issues such as brittle fracture of the composite material due to strong adhesion when the carbon fiber bundles are formed with the resin, a decrease in tensile strength in the fiber axis direction, and the failure to exhibit strength characteristics in the direction perpendicular to the fiber axis direction, thereby ensuring that the strength characteristics are balanced in the fiber axis direction and the direction perpendicular to it. The resulting composite material is obtained.

[0078] Examples of electrolytes used in electrolytic treatment include aqueous solutions containing acids, alkalis, or salts thereof. Examples of acids include sulfuric acid, nitric acid, and hydrochloric acid, while examples of alkalis include sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, ammonium carbonate, and ammonium bicarbonate.

[0079] Furthermore, after electrolytic treatment of the carbon fiber bundle, the electrolyte may be removed by washing with water, followed by drying, and then a sizing agent may be added to improve adhesion with the resin. A compound having multiple reactive functional groups is preferred as such a sizing agent. There are no particular restrictions on the reactive functional groups, but functional groups that can react with carboxyl groups or hydroxyl groups are preferred, and epoxy groups are more preferred. In the sizing agent, the number of reactive functional groups present in one molecule of the compound is preferably 2 to 6, more preferably 2 to 4, and particularly preferably 2. By having a number of reactive functional groups within this range, the adhesion between the carbon fiber bundle and the resin is improved, and the intermolecular crosslinking density of the compounds constituting the sizing agent is reduced, suppressing the brittleness of the layer formed by the sizing agent, thereby increasing the tensile strength of the composite material of the carbon fiber bundle and the resin. [Examples]

[0080] The following describes embodiments of this disclosure, but this disclosure is not limited to these embodiments. In the following description, unless otherwise specified, "parts" and "%" all refer to mass.

[0081] (Preparation Example 1) • Acrylamide polymer fiber bundle (a-1) Acrylamide (AM) / Acrylonitrile (AN) / Acrylic Acid (AA) Terpolymer (AM / AN / AA = 60 mol% / 35 mol% / 5 mol%) 100 parts by mass of monomers consisting of 60 mol% AM, 35 mol% AN, and 5 mol% AA, and 5 parts by mass of tetramethylethylenediamine were dissolved in 400 parts by mass of deionized water. Ammonium persulfate was added to the resulting aqueous solution while stirring under a nitrogen atmosphere, and polymerization was carried out by heating at 80°C for 150 minutes. The resulting aqueous solution was added dropwise to methanol to precipitate the copolymer, which was collected and vacuum-dried at 80°C for 12 hours to obtain a water-soluble AM / AN / AA (60 mol% / 35 mol% / 5 mol%) copolymer. 100 parts by mass of the AM / AN / AA copolymer and 3 parts by mass of phosphoric acid were dissolved in deionized water, and dry spinning was performed using the resulting aqueous solution to produce acrylamide polymer fiber bundles (a-1) (800 fibers / bundle) with a fineness of approximately 0.4 tex / fiber and an average fiber diameter of approximately 20 μm. The fineness and average fiber diameter of the single fibers constituting the acrylamide polymer fiber bundle were determined by the following method, and the fineness was found to be 0.4 tex / fiber, and the average fiber diameter was 20 μm.

[0082] (Preparation Example 2) • Acrylamide polymer fiber bundle (a-2) Acrylamide (AM) / Acrylonitrile (AN) / Acrylic Acid (AA) Terpolymer (AM / AN / AA = 63 mol% / 35 mol% / 2 mol%) 100 parts by mass of monomers consisting of AM 63 mol%, AN 35 mol%, and AA 2 mol%, and 4 parts by mass of tetramethylethylenediamine were dissolved in 567 parts by mass of deionized water. Ammonium persulfate was added to the resulting aqueous solution while stirring under a nitrogen atmosphere, and polymerization was carried out by heating at 70°C for 150 minutes. The resulting aqueous solution was added dropwise to methanol to precipitate the copolymer, which was recovered and vacuum-dried at 80°C for 12 hours to obtain a water-soluble AM / AN / AA (63 mol% / 35 mol% / 2 mol%) copolymer. AM / AN / AA copolymer 100 parts by mass of the combined material and 3 parts by mass of phosphoric acid were dissolved in deionized water, and dry spinning was performed using the resulting aqueous solution to produce an acrylamide polymer fiber bundle (a-2) (800 fibers / bundle) such that the fineness of the single fibers constituting the acrylamide polymer fiber bundle was approximately 0.4 tex / fiber and the average fiber diameter was approximately 20 μm. The fineness and average fiber diameter of the single fibers constituting the acrylamide polymer fiber bundle were determined by the following method, and the fineness was found to be 0.4 tex / fiber and the average fiber diameter was 20 μm.

[0083] <Fineness of acrylamide polymer fibers> The mass of the obtained acrylamide polymer fiber bundles (800 fibers / bundle) was measured, and the mass per 1000 m was calculated as the fineness [tex] of the fiber bundle. The fineness of the individual fibers constituting the fiber bundle (the fineness of the acrylamide polymer fiber) was then determined.

[0084] <Average fiber diameter of acrylamide polymer fibers> The density of the acrylamide polymer fiber bundle after vacuum drying at 80°C for 12 hours was measured using a dry automatic densimeter (Micromeristics "AccuPic II 1340"). Formula: D={(Dt×4×1000) / (ρ×π×n)} 1 / 2 [In the above formula, D represents the average fiber diameter [μm] of the single fibers constituting the fiber bundle, Dt represents the fineness [tex] of the fiber bundle, and ρ represents the density [g / cm³] of the fiber bundle.] 3 ] represents the number of individual fibers that make up the fiber bundle, where n represents the number of individual fibers [fibers] that make up the fiber bundle. The average fiber diameter of the single fibers constituting the fiber bundle (the average fiber diameter of the acrylamide polymer fibers) was determined by this method.

[0085] <Electron beam irradiation> Acrylamide polymer fiber bundles (800 fibers / bundle) obtained in Preparation Examples 1 and 2 were coated with an oil (KP-420, manufactured by Shin-Etsu Chemical Co., Ltd.) to obtain acrylamide polymer fiber bundles. These acrylamide polymer fiber bundles were then subjected to continuous treatment at room temperature in an air atmosphere using an electron beam irradiation device EBC800-35 manufactured by NHV Corporation, with a transport speed of 10 m / min, an acceleration voltage of 800 kV, and a dose of 600 kGy, to obtain acrylamide polymer crosslinked fiber bundles.

[0086] <Stretching and flame-retardant treatment of acrylamide polymer cross-linked fiber bundles> After electron beam irradiation, acrylamide polymer crosslinked fiber bundles were subjected to simultaneous stretching and flame-retardant treatment using the continuous heat treatment apparatus shown in Figure 1 to continuously produce flame-retardant fiber bundles. The stretching ratio was adjusted by the ratio of the speed of the inlet roll (feed-out roll 6) to the speed of the outlet roll (wind-up roll 8). Samples for Examples 1-9 and Comparative Examples 1-2 were prepared according to Table 1. That is, zones 1-5 (i.e., heating zones 211, 212, 213, 214, and 215) were transported for the heat treatment times listed in Table 1. In Examples 7 and 8, a continuous heat treatment apparatus pre-set to 230°C was used to perform stretching at a stretching ratio of 2x, followed by flame-retardant treatment while stretching at a stretching ratio of 3x, resulting in a cumulative stretching ratio of 6x. In Example 9, the fiber bundles obtained in Example 8 were further subjected to flame-retardant treatment using the continuous heat treatment apparatus under the heat treatment conditions shown in Table 1 to obtain flame-retardant fiber bundles.

[0087] <Evaluation of the degree of orientation of flame-resistant fiber bundles> Wide-angle X-ray scattering measurement of the flame-resistant fiber bundle was performed by the transmission method using "Nano-Viewer" manufactured by Rigaku Corporation. The flame-resistant fiber bundle was placed vertically, and the measurement was carried out under the conditions of a camera length of 64 mm, an exposure time of 15 minutes, and room temperature. The circumferential intensity distribution at 2θ: 20 to 30° was obtained from the resulting two-dimensional intensity. After Gaussian fitting of the obtained circumferential intensity distribution, the half-widths W1 and W2 (°) of the scattered radiation were determined, and the degree of orientation was calculated from the following formula. Degree of orientation = 100×(360-(W1+W2)) / 360

[0088] <Evaluation of Flame Resistance Degree of Flame-Resistant Fiber Bundle> The infrared absorption spectrum of the flame-resistant fiber bundle was measured by the total reflection measurement method (ATR crystal: Zn-Se, measurement wavenumber range: 650 to 4000 cm -1 , resolution: 0.482 cm -1 ) using a Fourier transform infrared spectrophotometer ("Nicolet 8700FT-IR" manufactured by Thermo Fisher Scientific K.K.). Further, based on the obtained infrared absorption spectrum, the flame resistance degree (peak intensity of the absorption peak derived from the naphthyridine ring confirmed in the range of 1350 to 1380 cm -1 / peak intensity of the absorption peak derived from the acrylamide group confirmed in the range of 1640 to 1660 cm -1 ) was obtained. When calculating the flame resistance degree, no baseline correction or the like was performed, and the peak intensity of the obtained infrared absorption spectrum was used as it was.

[0089] <Brittleness Evaluation of Flame-Resistant Fiber Bundle> To evaluate the brittleness of each flame-resistant fiber bundle, a load resistance test was performed. A fiber bundle with a length of 20 cm was cut out from the continuous fibers of the obtained flame-resistant fiber bundle (800 fibers / bundle), a 200 g weight was suspended from the end of the flame-resistant fiber bundle (800 fibers / bundle), and it was checked whether the flame-resistant fiber bundle broke. ○: The flame-resistant fiber bundle did not break. ×: The flame-resistant fiber bundle broke.

[0090] <Evaluation of Carbonization Resistance of Flame-Resistant Fiber Bundle> Each flame-resistant fiber bundle (4 bundles of 800 fibers / bundle, totaling 3200 fibers / bundle) was subjected to a tension of 50 gf and then transported to a heat treatment device heated to 800°C under a nitrogen atmosphere for carbonization treatment (3 minutes). The resulting carbon fiber bundles (5 mm wide, 3 m long) were then visually inspected for any breakage. ○: Visual inspection reveals no fractures. △: Visual inspection reveals one or more partial fractures less than 0.5 mm in width. ×: Visual inspection reveals one or more partial fractures with a width of 0.5 mm or more.

[0091] [Table 1]

[0092] In Examples 1-3 and 5-9, where the temperature difference between the low-temperature and high-temperature zones at adjacent locations was within 120°C, no embrittlement of the flame-resistant fiber bundles occurred, and the carbonization treatment was carried out without problems. I was able to do it. In Example 4, the temperature difference between the low-temperature zone and the high-temperature zone at the point where they were adjacent was within 120°C, and no embrittlement of the flame-resistant fiber bundle occurred. However, because the degree of flame resistance was 1.10 or less, partial fracture occurred during the carbonization treatment, although it was less than 0.5 mm. Examples 7 and 8 showed a higher degree of orientation due to the increased cumulative stretching ratio. Furthermore, Example 9 showed an even higher degree of orientation because the fiber bundles from Example 8 were subjected to additional flame-retardant treatment. On the other hand, in Comparative Examples 1 and 2, where the temperature difference between the low-temperature zone and the high-temperature zone at the point where they first meet was greater than 120°C, the degree of orientation was 43 or less, and embrittlement of the flame-resistant fiber bundle occurred. In addition, partial fractures of 0.5 mm or more occurred during the carbonization treatment. [Industrial applicability]

[0093] As described above, this disclosure provides a method for producing flame-resistant fiber bundles in which embrittlement after flame-retardant treatment is suppressed and fiber breakage is suppressed during carbonization treatment while tension is applied, as well as flame-resistant fiber bundles and a method for producing carbon fiber bundles using flame-resistant fiber bundles obtained by the method for producing flame-resistant fiber bundles.

[0094] Furthermore, because such carbon fiber bundles possess excellent properties such as lightness, rigidity, strength, elastic modulus, and corrosion resistance, they can be widely used as materials for various applications, such as aerospace materials, space materials, automotive materials, pressure vessels, civil engineering and construction materials, robotic materials, communication equipment materials, medical materials, electronic materials, wearable materials, wind turbines, golf shafts, fishing rods, and other sporting goods.

[0095] This disclosure includes the following aspects:

[0096] < <1> > A method for producing flame-resistant fiber bundles, comprising heat-treating an acrylamide polymer fiber bundle in a continuous heat treatment apparatus in which the heating zone is divided into two or more zones and the temperature can be set for each zone. A method for manufacturing flame-resistant fiber bundles, wherein the heating zone has a low-temperature zone with a set temperature of less than 300°C and a high-temperature zone with a set temperature of 300°C or higher, the heating zone through which the acrylamide polymer fiber bundle first passes is the low-temperature zone, and the temperature difference between the low-temperature zone and the high-temperature zone at the point where the low-temperature zone and the high-temperature zone first meet is 120°C or less. < <2> > The set temperature range for the low-temperature zone is set to 200°C to 295°C. <1> The method for producing flame-resistant fiber bundles as described above. < <3> > The temperature range for the aforementioned high-temperature zone is set to 300°C to 400°C. <1> > or < <2> The method for producing flame-resistant fiber bundles as described above. < <4> > To manufacture flame-resistant fiber bundles with an orientation degree of 44 or higher, <1> >~< <3> A method for producing flame-resistant fiber bundles as described in any one of the following items. < <5> > Calculated from infrared absorption spectra, 1350-1380 cm⁻¹ -1 The peak intensity of the absorption peak originating from the naphthyridine ring, observed in the range of 1640-1660 cm⁻¹, is -1 The flame-retardant fiber bundle is produced in which the flame-retardant degree is 1.10 or higher, which is the ratio of the peak intensity of the absorption peak derived from the acrylamide group confirmed in the range to the flame-retardant degree. <1> >~< <4> A method for producing flame-resistant fiber bundles as described in any one of the following items. < <6> > < <1> >~< <5> Flame-resistant by the method for producing flame-resistant fiber bundles described in any one of the items above. A method for producing a carbon fiber bundle, comprising the steps of obtaining a fiber bundle and subjecting the flame-resistant fiber bundle to a carbonization treatment. < <7> > Flame-resistant fiber bundles derived from acrylamide polymers with an orientation degree of 44 or higher. < <8> > The infrared absorption spectrum of the aforementioned flame-resistant fiber bundle was calculated to be 1350-1380 cm⁻¹. -1 The peak intensity of the absorption peak originating from the naphthyridine ring, observed in the range of 1640-1660 cm⁻¹, is -1 The flame resistance is characterized by a ratio of the peak intensity of the absorption peak derived from the acrylamide group observed in the specified range to the flame resistance of 1.10 or higher. <7> Flame-resistant fiber bundles as described above. [Explanation of Symbols]

[0097] 2A, 2B, 2C Continuous Heat Treatment Apparatus 4. Acrylamide polymer fiber bundle 6. Feed Roll 8 reel rolls 20A, 20B, 20C heating device 211, 212, 213, 214, 215, 221, 222, 223, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 245 Heating Zones

Claims

1. A continuous heat treatment apparatus in which the heating zone is divided into two or more zones and the temperature can be set for each zone, is used to manufacture flame-resistant fiber bundles by heat treatment while stretching acrylamide polymer fiber bundles to 1.7 to 50 times their original length. The heating zone has a low-temperature zone with a set temperature of less than 300°C and a high-temperature zone with a set temperature of 300°C or higher, the heating zone through which the acrylamide polymer fiber bundle first passes is the low-temperature zone, and the temperature difference between the low-temperature zone and the high-temperature zone at the point where the low-temperature zone and the high-temperature zone first meet is 120°C or less. The flame-resistant fiber bundle was determined from the infrared absorption spectrum of the flame-resistant fiber bundle to be 1350-1380 cm⁻¹. －１ The peak intensity of the absorption peak originating from the naphthyridine ring, observed in the range of 1640–1660 cm⁻¹, is －１ The flame resistance degree is 1.10 to 2.00, which is the ratio of the peak intensity of the absorption peak derived from the acrylamide group observed in the range. A method for producing flame-resistant fiber bundles, wherein the flame-resistant fiber bundle has an orientation degree of 44 or higher.

2. The method for producing a flame-resistant fiber bundle according to claim 1, wherein the set temperature range of the low-temperature zone is 200°C to 295°C.

3. The method for producing a flame-resistant fiber bundle according to claim 1, wherein the set temperature range of the high-temperature zone is 300°C to 400°C.

4. A method for producing a carbon fiber bundle, comprising the steps of: obtaining a flame-resistant fiber bundle by the method for producing a flame-resistant fiber bundle described in claim 1; and subjecting the flame-resistant fiber bundle to a carbonization treatment.

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