Method for producing fiber, carbon fiber precursor fiber, and carbon fiber

Abstract

The present invention addresses the problem of improving carbon fiber productivity.　This method for producing fibers comprises a step for producing carbon fiber precursor fibers by solution spinning using a spinning dope that is a mixed solution comprising a low-molecular-weight carbon compound containing pitch, a high-molecular-weight carbon compound containing a polybenzimidazole derivative, and a solvent.

Description

Method for manufacturing fibers, carbon fiber residue fibers, and carbon fibers Cross-reference of related applications

[0001] This application is based on Japanese Patent Application No. 2024-160767, filed on 18 September 2024, and claims the benefit of priority thereunder, the entirety of which is incorporated herein by reference.

[0002] This disclosure relates to a method for producing fibers, carbon fiber precursor fibers, and carbon fibers.

[0003] Carbon fiber is lightweight, high-strength, and possesses excellent abrasion resistance, heat resistance, thermal expansion, acid resistance, and electrical conductivity, making it suitable for use in a wide range of fields. Carbon fiber is manufactured by carbonizing acrylic fibers or pitch (a by-product of petroleum, coal, coal tar, etc.) at high temperatures. The former is called PAN-based carbon fiber, and the latter is called pitch-based carbon fiber. The precursor fibers of carbon fiber are manufactured in bundles (tows), with 1000 fibers expressed as one unit (k). 12k and 24k are the main products and are called regular tow. Depending on the application, small tows such as 3k and large tows exceeding 50k are also available on the market.

[0004] International Publication No. 2015 / 170623

[0005] The challenges of carbon fiber include high manufacturing costs and low productivity. For PAN-based carbon fiber, one of the reasons is the high cost of polyacrylonitrile as a raw material. For pitch-based carbon fiber, although the pitch used as a raw material is relatively inexpensive, it cannot be spun into fibers by wet spinning and is manufactured by melt spinning. Therefore, it is not possible to spin regular toe-sized precursor fibers, and it is necessary to combine spun fibers beforehand in order to produce regular toe, which contributes to low productivity. In addition, pitch precursor fibers are composed of low molecular weight materials, making them brittle and difficult to handle, which is also a challenge.

[0006] This disclosure is made in view of these challenges, and its purpose is to improve the productivity of carbon fiber.

[0007] To solve the above problems, a method for producing fibers according to one aspect of the present disclosure comprises the step of producing carbon fiber precursor fibers by solution spinning using a mixed solution containing a low molecular weight carbon compound including pitch, a high molecular weight carbon compound including a polybenzimidazole derivative, and a solvent as a spinning stock (also called dope).

[0008] Another aspect of the present disclosure is a carbon fiber precursor fiber. This carbon fiber precursor fiber comprises a low molecular weight carbon compound containing pitch and a high molecular weight carbon compound containing a polybenzimidazole derivative.

[0009] Another aspect of the present disclosure is carbon fiber, which is obtained by carbonizing the above-mentioned carbon fiber precursor fibers.

[0010] A further aspect of the present disclosure is a method for producing fibers. This method comprises the step of producing carbon fiber precursor fibers by wet spinning, dry spinning, or wet-dry spinning, using a mixed solution containing a high molecular weight carbon compound comprising a polymer compound that does not contain oxygen atoms in its main chain, a low molecular weight carbon compound comprising at least one of by-products, residues, and waste generated when processing carbon-containing resources and having a molecular weight lower than that of the high molecular weight carbon compound, and a solvent as a spinning stock.

[0011] Another aspect of the present disclosure is a carbon fiber precursor fiber. This carbon fiber precursor fiber comprises a high molecular weight carbon compound which includes a polymer compound which does not contain oxygen atoms in its main chain, and a low molecular weight carbon compound which includes at least one of by-products, residues, and waste generated when processing carbon-containing resources and has a lower molecular weight than the high molecular weight carbon compound.

[0012] Another aspect of the present disclosure is carbon fiber, which is obtained by carbonizing the above-mentioned carbon fiber precursor fibers.

[0013] According to this disclosure, the productivity of carbon fiber can be improved.

[0014] This figure shows the carbon fiber precursor fibers of Example 1. This figure shows the carbon fiber precursor fibers of Example 2. This shows the molecular weight distribution of the pitch used in Example 3.

[0015] The method for producing fibers according to this disclosure comprises the step of producing carbon fiber precursor fibers by solution spinning using a solution containing a low molecular weight carbon compound, a high molecular weight carbon compound having a molecular weight greater than that of the low molecular weight carbon compound, and a solvent.

[0016] When using a coagulation bath for solvent removal in the solution spinning of low molecular weight carbon compounds, the compounds typically do not form fibers even when dissolved in a solvent and extruded from the spindle into the coagulation bath, or if they do, they are extremely brittle and difficult to handle. Furthermore, even when a coagulation bath is not used, as in dry spinning, the compounds are extremely brittle and difficult to handle during solvent removal, making them unsuitable for solution spinning alone. However, our experiments have revealed that even such low molecular weight carbon compounds can be fibrousized by solution spinning, such as wet spinning, by using a mixed solution with a higher molecular weight carbon compound as the spinning stock. This allows for the production of carbon fiber precursors using relatively inexpensive low molecular weight carbon compounds as raw materials, significantly reducing the cost of carbon fiber production. Additionally, since low molecular weight carbon compounds, which previously could only be fibrousized by melt spinning, can now be fibrousized by solution spinning, it becomes possible to spin precursor fibers from regular toe to large toe, dramatically improving productivity. Examples of solution spinning include wet spinning, dry spinning, wet-dry spinning, gel spinning, and liquid crystal spinning.

[0017] Low molecular weight carbon compounds may have an average molecular weight of less than 3000. The molecular weight of low molecular weight carbon compounds may be, for example, less than 5000, less than 4000, less than 3000, less than 2500, less than 2000, less than 1500, less than 1000, less than 900, less than 800, less than 700, less than 600, less than 500, less than 400, less than 300, less than 200, or less than 100.

[0018] Low molecular weight carbon compounds may include at least one of the by-products, residues, and waste generated when processing carbon-containing resources. Resources may include at least one of petroleum, coal, biomass, and plastics. Since by-products, residues, and waste generated when processing these resources can be obtained inexpensively, mixing them with high molecular weight carbon compounds as raw materials for carbon fibers can significantly reduce the cost of manufacturing carbon fibers. Resource processing may include refining, processing, recycling, disposal, and manufacturing products using resources as raw materials. Low molecular weight carbon compounds may include pitch, shale oil, ethylene bottom oil, residual oil, coal tar, hypercoal, bio-oil, waste plastics, and any combination of two or more of these, which are generated when processing petroleum, coal, biomass, and plastics. Low molecular weight carbon compounds may also include those obtained by heat treatment, hydrogenation, vacuum distillation, extraction of solvent-soluble components, etc., from these by-products, residues, and wastes.

[0019] Low molecular weight carbon compounds may be carbon compounds that are not suitable for solution spinning on their own. Low molecular weight carbon compounds may be carbon compounds that do not form fibers when spun as a solution dissolved in a solvent on their own, or even if they do form fibers, they may only have a strength that is not practical (for example, a tensile strength of less than 100 MPa). According to the technology of this disclosure, even such low molecular weight carbon compounds can be used to produce fibers with practical strength by solution spinning, such as wet spinning, by using a mixed solution with a high molecular weight carbon compound as the spinning stock.

[0020] The high molecular weight carbon compound may have an average molecular weight of 3000 or more. The molecular weight of the high molecular weight carbon compound may be, for example, 1000 or more, 2000 or more, 3000 or more, 4000 or more, 5000 or more, 6000 or more, 7000 or more, 8000 or more, 9000 or more, or 10000 or more.

[0021] High molecular weight carbon compounds may include polymer compounds containing carbon. Polymer compounds are molecules with a large molecular weight and have a structure composed of many repetitions of units substantially or conceptually obtained from molecules with a small molecular weight. High molecular weight carbon compounds may include polymers in which any carbon compound containing carbon is used as a monomer. High molecular weight carbon compounds may also include polymer compounds that do not contain oxygen atoms in their main chain. Polymer compounds included in high molecular weight carbon compounds preferably do not contain at least oxygen atoms in their main chain, and more preferably do not contain sulfur atoms. This makes it possible to produce fibers with higher strength than when polymer compounds containing oxygen atoms in their main chain are included. Examples of polymer compounds containing oxygen atoms in their main chain are polyethylene oxide, polyethylene glycol, and polybenzoxazole (PBO). High molecular weight carbon compounds may include, for example, thermoplastic resins such as polyacrylonitrile (PAN), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyvinyl acetate (PVAc), polyurethane (PUR), polytetrafluoroethylene (PTFE), polylactic acid, acrylonitrile butadiene styrene (ABS) resin, acrylic resin (PMMA), polyamide (PA), polycarbonate (PC), polyethylene terephthalate (PET), polyester (PEs), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), and polyimide (PI); thermosetting resins such as epoxy resin (EP), phenolic resin (PF), melamine resin (MF), and urea resin (UF); functional polymers such as polyacrylamide; natural polymer compounds such as cellulose, amylose, starch, and chitin; and copolymers of any two or more combinations thereof. High molecular weight carbon compounds may also be copolymers of acrylonitrile with methacrylic acid or itaconic acid.

[0022] The high molecular weight carbon compound may include a polybenzimidazole derivative. The polybenzimidazole derivative is a heterocyclic polymer compound containing benzimidazole represented by formula (1) as a repeating unit, for example, represented by formula (2). The polybenzimidazole derivative represented by formula (2) is soluble in strong acids and can be formed into fibers by solution spinning.

[0023] The present inventors have newly developed a polybenzimidazole derivative that is soluble in organic solvents. The polybenzimidazole derivative of this disclosure is a copolymer comprising a repeating unit A represented by formula (3) and a repeating unit B represented by formula (4). Here, R １ R is a divalent aromatic group such as a phenylene group. ２ These are divalent hydrocarbon groups such as alkylene groups and cycloalkylene groups. In particular, as the repeating unit A, R is represented by formula (5). １ It is preferable that the group is a 1,4-phenylene group, and the repeating unit B is R as represented by formula (6). ２ A group in which the group is a 1,4-cyclohexylene group is preferred.

[0024] As the repeating unit B, R is expressed in equation (7). ２ Those in which the group is a 1,3-adamantyl group are also preferred.

[0025] Since the polybenzimidazole derivatives of this disclosure are soluble in many organic solvents, they are easy to handle, and productivity can be greatly improved whether they are used to produce fibers by solution spinning alone or by solution spinning using a mixed solution with a low molecular weight carbon compound as described above.

[0026] R １This may include allylene (arenediyl) groups such as p-phenylene group, m-phenylene group, o-phenylene group, 2,2'-biphenylene group, 4,4'-biphenylene group, 1,4-naphthylene group, 2,3-naphthylene group, and 1,8-naphthylene group, or aromatic heterocyclic groups such as 3,4-pyrrolediyl group, 3,4-franziyl group, 2,5-thiophenediyl group, 3,5-isoxazolediyl group, 2,6-pyridinediyl group, 2,5-pyrazinediyl group, 4,6-pyrimidinediyl group, 4,7-indolediyl group, 2,4-quinolinediyl group, 2,3-quinoxalinediyl group, 3,3-oxetanediyl group, and 1,3-dioxolane-2,2-diyl group, or groups in which one or more hydrogen atoms of these are substituted with any substituent. The substituents may be alkyl groups, heteroalkyl groups, alkenyl groups, heteroalkenyl groups, alkynyl groups, heteroalkynyl groups, cycloalkyl groups, heterocycloalkyl groups, aryl groups, heteroaryl groups, alkoxy groups, hydroxyl groups, carboxyl groups, acyl groups, amino groups, nitro groups, cyano groups, diazo groups, thiol groups, sulfo groups, halogens, and the like.

[0027] R ２is an alkylene (alkanediyl) group such as a methylene group, 1,1-ethylene group, 1,2-ethylene group, 1,2-propylene group, 1,3-propylene group, 1,2-butylene group, 1,3-butylene group, 1,4-butylene group, 1,2-pentylene group, 1,3-pentylene group, 1,4-pentylene group, 1,5-pentylene group, 1,2-hexylene group, 1,3-hexylene group, 1,4-hexylene group, 1,5-hexylene group, 1,6-hexylene group, or a cycloalkylene (cycloalkanediyl) group such as a 1,2-cyclopropylene group, 1,2-cyclobutylene group, 1,3-cyclobutylene group, 1,2-cyclopentylene group, 1,3-cyclopentylene group, 1,2-cyclohexylene group, 1,3-cyclohexylene group, 1,4-cyclohexylene group, an alkenylene group, a cycloalkenylene group, a 1,3-adamantyl group, or a group in which one or more hydrogen atoms thereof are substituted with an arbitrary substituent. The substituent may be an alkyl group, a heteroalkyl group, an alkenyl group, a heteroalkenyl group, an alkynyl group, a heteroalkynyl group, a cycloalkyl group, a heterocycloalkyl group, an aryl group, a heteroaryl group, an alkoxy group, a hydroxy group, a carboxyl group, an acyl group, an amino group, a nitro group, a cyano group, a diazo group, a thiol group, a sulfo group, a halogen, or the like.

[0028] PAN-based carbon fiber precursor fibers and pitch-based carbon fiber precursor fibers melt during the process of carbonization by heat treatment at high temperature and cannot maintain the fiber shape. Therefore, an infusibilization (flame resistance) treatment is required prior to carbonization. However, the carbon fiber precursor fiber obtained by fibrillating the polybenzimidazole derivative of the present disclosure can be carbonized while maintaining the fiber shape without performing an infusibilization treatment, so that the manufacturing cost and energy consumption of carbon fibers can be significantly reduced and the productivity can be significantly improved.

[0029] The repeating unit A is R １ is an aromatic group, and is considered to contribute to the heat resistance of the polybenzimidazole derivative of the present disclosure. The repeating unit B is R ２Since it is a hydrocarbon group, it is thought to contribute to the solubility of the polybenzimidazole derivative of this disclosure in organic solvents. As a result, the polybenzimidazole derivative of this disclosure can be formed into fibers by solution spinning using an organic solvent, and can be carbonized without infusibility treatment, thereby further reducing the manufacturing cost and energy consumption of carbon fibers and further improving productivity. ２ When it is a cycloalkylene group, R ２ This allows for greater suppression of C-C bond breakage in that region, thereby improving the carbonization yield.

[0030] The content ratio of repeating unit A to repeating unit B may be 1:99 to 99:1. The content of repeating unit A may be 0.1% or more, 0.5% or more, 1% or more, 2% or more, 3% or more, 4% or more, 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more, based on the total number of repeating units A and B. The content of repeating unit A may be 99% or less, 98% or less, 97% or less, 96% or less, 95% or less, 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, 65% or less, 60% or less, 55% or less, 50% or less, 45% or less, 40% or less, 35% or less, 30% or less, 25% or less, 20% or less, 15% or less, 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, or 1% or less, based on the total number of repeating units A and B.

[0031] The content ratio of the low molecular weight carbon compound and the high molecular weight carbon compound may be 1:99 to 99:1. The content rate of the low molecular weight carbon compound may be 0.1% by weight or more, 0.5% by weight or more, 1% by weight or more, 2% by weight or more, 3% by weight or more, 4% by weight or more, 5% by weight or more, 6% by weight or more, 7% by weight or more, 8% by weight or more, 9% by weight or more, 10% by weight or more, 15% by weight or more, 20% by weight or more, 25% by weight or more, 30% by weight or more, 35% by weight or more, 40% by weight or more, 45% by weight or more, 50% by weight or more, 55% by weight or more, 60% by weight or more, 65% by weight or more, 70% by weight or more, 75% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, 95% by weight or more, 96% by weight or more, 97% by weight or more, 98% by weight or more, 99% by weight or more, based on the total weight of the low molecular weight carbon compound and the high molecular weight carbon compound. The content rate of the low molecular weight carbon compound may be 99% by weight or less, 98% by weight or less, 97% by weight or less, 96% by weight or less, 95% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, 75% by weight or less, 70% by weight or less, 65% by weight or less, 60% by weight or less, 55% by weight or less, 50% by weight or less, 45% by weight or less, 40% by weight or less, 35% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, 15% by weight or less, 10% by weight or less, 9% by weight or less, 8% by weight or less, 7% by weight or less, 6% by weight or less, 5% by weight or less, 4% by weight or less, 3% by weight or less, 2% by weight or less, 1% by weight or less, based on the total weight of the low molecular weight carbon compound and the high molecular weight carbon compound.

[0032] The solvent may be composed of only one type of solvent, or may be a mixture of two or more types of solvents. The solvent may contain an organic solvent. The solvent may be dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), dimethylacetamide, aqueous sodium thiocyanate solution, aqueous zinc chloride solution, tetrahydrofuran (THF), N-methylpyrrolidone (NMP), benzene, hexane, diethyl ether, toluene, chloroform, ethyl acetate, methylene chloride, acetone, acetonitrile, dimethylacetamide, formic acid, acetic acid, methanol, ethanol, etc.

[0033] The solvent may include a first solvent in which low molecular weight carbon compounds are soluble and a second solvent in which high molecular weight carbon compounds are soluble. The first solvent and the second solvent may be of the same type of solvent. The first solvent and the second solvent may be of different types of solvents. In the latter case, the first solvent and the second solvent preferably have compatibility. Since many of the combinations of the above-described organic solvents have compatibility, they can be used as the first solvent and the second solvent.

[0034] The content of the solvent may be 80 to 97% by weight or more based on the total weight of the solution. The content of the solvent may be 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, 95% by weight or more, 99% by weight or more based on the total weight of the solution. The content of the solvent may be 99% by weight or less, 97% by weight or less, 95% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, 75% by weight or less, 70% by weight or less, 65% by weight or less, 60% by weight or less, 55% by weight or less, 50% by weight or less based on the total weight of the solution.

[0035] The temperature at which the low molecular weight carbon compound is dissolved in the first solvent may be any temperature from the melting point to the boiling point of the first solvent, for example, it may be 25 to 80°C. This temperature may also be lower than the temperature at which the low molecular weight carbon compound melts.

[0036] The temperature at which the high molecular weight carbon compound is dissolved in the second solvent may be any temperature from the melting point to the boiling point of the second solvent, for example, it may be 25 to 80°C. This temperature may also be lower than the temperature at which the high molecular weight carbon compound melts.

[0037] The low molecular weight carbon compound may include molecules that are 1% or more soluble in the above solvents, particularly organic solvents, among aromatic compounds having one or more benzene rings. The low molecular weight carbon compound may have two or more benzene rings. The two or more benzene rings may be fused. This molecule may also have heteroatoms or substituents.

[0038] The carbon fiber precursor fibers of this disclosure include a low molecular weight carbon compound and a high molecular weight carbon compound having a higher molecular weight than the low molecular weight carbon compound. The carbon fiber precursor fibers of this disclosure include a high molecular weight carbon compound containing a polymer compound that does not contain oxygen atoms in its main chain, and a low molecular weight carbon compound that contains at least one of by-products, residues, and waste generated when processing carbon-containing resources, and has a lower molecular weight than the high molecular weight carbon compound. The carbon fiber precursor fibers of this disclosure may be produced by the fiber production method described above. The carbon fiber precursor fibers of this disclosure can be determined to contain both a low molecular weight carbon compound and a high molecular weight carbon compound by dissolving them in an organic solvent or the like.

[0039] The average diameter of the carbon fiber precursor fibers of this disclosure may be 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, 9 μm or more, or 10 μm or more. The carbon fiber precursor fibers of this disclosure may be multifilaments. The carbon fiber precursor fibers of this disclosure may be 1 m or more, 5 m or more, 10 m or more, 20 m or more, 30 m or more, 40 m or more, 50 m or more, or continuous multifilaments. The carbon fiber precursor fibers of this disclosure may be multifilaments containing 10 or more, 50 or more, 100 or more, 500 or more, 1000 or more, 5000 or more, 10000 or more, 50000 or more, or 100000 or more fibers. The carbon fiber precursor fibers of this disclosure may be multifilaments containing bundles of multiple aligned fibers.

[0040] The method for producing carbon fiber precursor fibers according to this disclosure comprises the steps of simultaneously extruding the above-mentioned spinning solution from a plurality of holes in a spinneret to form fibers, and continuously winding the plurality of formed fibers in a bundle. The diameter of the holes in the spinneret may be 1 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, 9 μm or more, or 10 μm or more. The formed fibers may be wound continuously for 1 m or more, 5 m or more, 10 m or more, 20 m or more, 30 m or more, 40 m or more, or 50 m or more. The formed fibers may be wound in a bundle of 10 or more, 50 or more, 100 or more, 500 or more, 1000 or more, 5000 or more, 10000 or more, 50000 or more, or 100000 or more.

[0041] The method for producing fibers according to this disclosure may include a step of carbonizing the above-mentioned carbon fiber precursor fibers after infusibility treatment (flame resistance treatment). The method for producing fibers according to this disclosure may also include a step of carbonizing the carbon fiber precursor fibers produced by the above method without performing infusibility treatment (flame resistance treatment) if it is not necessary.

[0042] The carbon fibers of this disclosure are obtained by carbonizing the above-mentioned carbon fiber precursor fibers. The obtained carbon fibers may be subjected to surface treatments such as oxidation treatment, plasma treatment, and coating. This can introduce functional groups to the surface of the carbon fibers or modify the surface of the carbon fibers to improve strength, wear resistance, adhesion to resins, etc.

[0043] (Examples 1 and 2) Carbon fiber precursor fibers were produced by wet spinning using a solution containing pitch and a polybenzimidazole derivative containing repeating unit A of formula (5) and repeating unit B of formula (6) in weight ratios of 50:50 (Example 1) and 70:30 (Example 2). The carbon fiber precursor fibers of Example 1 obtained were left to stand for 30 minutes in a hot air furnace at 150°C, 200°C, 250°C, and 300°C, respectively, and the results are shown in Figures 1(a), 1(b), 1(c), and 1(d), respectively. At all temperatures, the carbon fiber precursor fibers did not melt and maintained their fiber shape. The carbon fiber precursor fibers of Example 2 obtained are shown in Figure 2. Even when the content of low molecular weight carbon compounds (pitch) in the spinning solution was 70% and 80%, carbon fiber precursor fibers that could be wound onto a bobbin could be produced.

[0044] (Example 3) A polybenzimidazole derivative containing repeating unit A of formula (5) and repeating unit B of formula (6) was synthesized by dehydration polycondensation of a mixture of terephthalic acid and 1,4-cyclohexanedicarboxylic acid with 3,3'-diaminobenzidine at 150 to 300°C. It was confirmed that the intrinsic viscosity, which is an indicator of molecular weight, can be controlled to about 2 to 15 by controlling the mixing ratio of terephthalic acid and 1,4-cyclohexanedicarboxylic acid. It was also confirmed that polybenzimidazole derivatives with a content ratio of repeating unit A to repeating unit B of 1:99 to 99:1 are soluble in solvents such as DMSO.

[0045] A spinning stock solution, prepared by dissolving the polybenzimidazole derivative and pitch in a 50:50 weight ratio in DMSO, was discharged into a coagulation bath of room temperature water under conditions of tension on the fibers, and washed with water to produce carbon fiber precursor fibers. The obtained carbon fiber precursor fibers were calcined under conditions of tension on the fibers and wound onto bobbins. The tensile strength and elastic modulus of the produced carbon fibers were measured, and the tensile strength was 1.9 GPa and the elastic modulus was 180 GPa. These values ​​are higher than the intermediate target values ​​of 1.7 GPa and 170 GPa, which are set as required properties for carbon fibers for automobiles internationally, demonstrating that carbon fibers produced by the manufacturing method of this disclosure are practical for use in the manufacture of automobiles and the like. Note that the above measurements were taken without surface treatment on the produced carbon fibers, but it is expected that the tensile strength will be higher if the carbon fibers are surface treated.

[0046] The pitch used in Example 3 includes artificially synthesized pitch, as well as pitches produced during the refining process of petroleum and coal, such as slurry oil, coal tar, ethylene bottom oil, naphthalene, and carbon black oil, which have been subjected to heat treatment, hydrogenation, vacuum distillation, and extraction of solvent-soluble components. Figure 3 shows the molecular weight distribution of the pitch used in Example 3. (a) shows the molecular weight distribution of artificially synthesized pitch, (b) shows the molecular weight distribution of coal-based pitch, and (c) and (d) show the molecular weight distribution of petroleum-based pitch. Most of the pitches used in Example 3 had a molecular weight of 2000 or less, and the average molecular weight was in the range of 570 to 690.

[0047] (Example 4) Using a monopolymer of polyacrylonitrile (PAN) and pitch, and a copolymer of acrylonitrile (95%) and methacrylic acid (5%) and pitch as raw materials, carbon fiber precursor fibers were produced in the same manner as in Example 3. The carbon fiber precursor fibers were subjected to flame-retardant treatment at 300°C for 30 minutes, and then fired at 1300°C to obtain carbon fibers with sufficient strength.

[0048] (Example 5) Using two types of polyamic acids, formulas (8) and (9) below, and pitch as raw materials, carbon fiber precursor fibers were produced in the same manner as in Example 3. The carbon fiber precursor fibers were heat-treated at 300°C for 30 minutes, and then calcined at 1300°C to obtain carbon fibers with sufficient strength.

[0049] (Example 6) Using phenolic resin and pitch, a meta-type polybenzimidazole derivative and pitch, a polybenzimidazole derivative containing repeating unit A of formula (5) and repeating unit B of formula (7) and pitch, and polyacrylamide and pitch as raw materials, carbon fiber precursor fibers were produced in the same manner as in Example 3. The carbon fiber precursor fibers were calcined to obtain carbon fibers with sufficient strength.

[0050] (Comparative Examples 1-3) Carbon fibers were produced by firing regular yarn of polybenzoxazole (PBO), a polymer compound containing oxygen atoms in the main chain (Comparative Example 1), high modulus yarn of polybenzoxazole (PBO) (Comparative Example 2), and aramid fiber (Comparative Example 3), which are polymer compounds containing oxygen atoms in the main chain. When the strength and modulus of elasticity of each were measured, the strengths were 1.2 GPa (Comparative Example 1), 0.9 GPa (Comparative Example 2), and 0.3 GPa (Comparative Example 3), and the modulus of elasticity was 190 GPa (Comparative Example 1), 200 GPa (Comparative Example 2), and 120 GPa (Comparative Example 3). The tensile strength (1.9 GPa) of the carbon fiber of Example 3, which was made from a polymer compound that did not contain oxygen atoms in the main chain, was shown to be higher than the tensile strength (0.3-1.2 GPa) of the carbon fibers of Comparative Examples 1-3, which were made from polymer compounds containing oxygen atoms in the main chain.

[0051] The present disclosure has been explained above based on examples. These examples are illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of their components and processing processes, and that such modifications are also within the scope of the present disclosure.

[0052] This disclosure includes the following embodiments: [Embodiment 1] A method for producing carbon fiber precursor fibers by solution spinning using a mixed solution containing a low molecular weight carbon compound, a high molecular weight carbon compound having a higher molecular weight than the low molecular weight carbon compound, and a solvent as a spinning stock solution. [Embodiment 2] A method for producing carbon fiber precursor fibers by solution spinning using a mixed solution containing a low molecular weight carbon compound containing pitch, a high molecular weight carbon compound containing a polybenzimidazole derivative, and a solvent as a spinning stock solution. [Embodiment 3] The method according to Embodiment 2, wherein the carbon fiber precursor fibers are produced by wet spinning. [Embodiment 4] The method according to Embodiment 2, wherein the carbon fiber precursor fibers are produced by wet dry spinning. [Embodiment 5] The method according to any one of Embodiments 1 to 4, wherein the content ratio of the low molecular weight carbon compound to the high molecular weight carbon compound is 1:99 to 99:1. [Embodiment 6] The method according to any one of Embodiments 1 to 5, wherein the solvent is an organic solvent. [Aspect 7] The method according to any one of aspects 1 to 6, wherein the solvent comprises a first solvent in which the low molecular weight carbon compound is soluble and a second solvent in which the high molecular weight carbon compound is soluble. [Aspect 8] The method according to aspect 7, wherein the first solvent and the second solvent are of the same type. [Aspect 9] The method according to aspect 7, wherein the first solvent and the second solvent are different types of solvents that are compatible with each other. [Aspect 10] A carbon fiber precursor fiber comprising a low molecular weight carbon compound and a high molecular weight carbon compound having a higher molecular weight than the low molecular weight carbon compound. [Aspect 11] A carbon fiber precursor fiber comprising a low molecular weight carbon compound containing pitch and a high molecular weight carbon compound containing a polybenzimidazole derivative. [Aspect 12] The carbon fiber precursor fiber according to aspect 10 or 11, wherein the average molecular weight of the low molecular weight carbon compound is less than 3000. [Aspect 13] The carbon fiber precursor fiber according to any one of aspects 10 to 12, wherein the content ratio of the low molecular weight carbon compound to the high molecular weight carbon compound is 1:99 to 99:1. [Aspect 14] A carbon fiber obtained by carbonizing a carbon fiber precursor fiber described in any one of aspects 10 to 13.[Aspect 15] A method for producing carbon fiber precursor fibers, comprising the step of producing carbon fiber precursor fibers by wet spinning, dry spinning, or wet-dry spinning using a mixed solution containing a high molecular weight carbon compound having a polymer compound that does not contain oxygen atoms in its main chain, a low molecular weight carbon compound having a lower molecular weight than the high molecular weight carbon compound and at least one of by-products, residues, and waste generated when processing carbon-containing resources, and a solvent as the spinning stock solution. [Aspect 16] The method according to aspect 15, wherein the resource is at least one of petroleum, coal, biomass, and plastic. [Aspect 17] The method according to aspect 15 or 16, wherein the low molecular weight carbon compound is a carbon compound that is not suitable for solution spinning on its own. [Aspect 18] The method according to any one of aspects 15 to 17, wherein the average molecular weight of the low molecular weight carbon compound is less than 3000. [Aspect 19] The method according to any one of aspects 15 to 18, wherein the low molecular weight carbon compound is an aromatic compound having one or more benzene rings and is soluble in an organic solvent at a concentration of 1% or more. [Aspect 20] The method according to any one of aspects 15 to 19, wherein the high molecular weight carbon compound comprises a polybenzimidazole derivative. [Aspect 21] The method according to any one of aspects 15 to 20, wherein the high molecular weight carbon compound comprises polyacrylonitrile (PAN). [Aspect 22] The method according to any one of aspects 15 to 21, wherein the average diameter of the carbon fiber precursor fibers is 3 μm or more. [Aspect 23] The method according to any one of aspects 15 to 24, wherein the carbon fiber precursor fibers are multifilaments comprising bundles of multiple aligned fibers. [Aspect 24] The method according to any one of aspects 15 to 23, comprising the steps of simultaneously extruding the spinning solution from multiple holes of a spinneret to form fibers, and continuously winding the formed multiple fibers in a bundled state. [Aspect 25] A carbon fiber precursor fiber comprising a high molecular weight carbon compound containing a polymer compound that does not contain oxygen atoms in its main chain, and a low molecular weight carbon compound having a lower molecular weight than the high molecular weight carbon compound, comprising at least one of by-products, residues, and waste generated when processing carbon-containing resources. [Aspect 26] The carbon fiber precursor fiber according to aspect 25, which is a multifilament comprising a bundle of multiple aligned fibers.[Aspect 27] Carbon fiber obtained by carbonizing the carbon fiber precursor fiber described in Aspect 25 or 26. [Aspect 28] Copolymer (wherein R) comprising repeating unit A represented by formula (3) and repeating unit B represented by formula (4). １ is a divalent aromatic group, R ２ Polybenzimidazole derivatives containing a divalent hydrocarbon group. [Aspect 29] R １ This is a 1,4-phenylene group, and R ２ The polybenzimidazole derivative according to embodiment 28, wherein the group is a 1,4-cyclohexylene group. [Embodiment 30] R １ This is a 1,4-phenylene group, and R ２ The polybenzimidazole derivative according to embodiment 28, wherein the group is a 1,3-adamantyl group. [Embodiment 31] The polybenzimidazole derivative according to any one of embodiments 28 to 30, wherein the content ratio of repeating unit A to repeating unit B is 1:99 to 99:1.

[0053] This disclosure is applicable to methods for manufacturing fibers, carbon fiber precursor fibers, and carbon fibers.

Claims

1. A method for producing carbon fiber precursor fibers, comprising the step of producing carbon fiber precursor fibers by solution spinning using a mixed solution containing a low molecular weight carbon compound containing pitch, a high molecular weight carbon compound containing a polybenzimidazole derivative, and a solvent as a spinning stock solution.

2. The method according to claim 1, for producing the carbon fiber precursor fibers by wet spinning.

3. The method according to claim 1, for producing the carbon fiber precursor fibers by wet and dry spinning.

4. The method according to any one of claims 1 to 3, wherein the content ratio of the low molecular weight carbon compound to the high molecular weight carbon compound is 1:99 to 99:

1.

5. The method according to any one of claims 1 to 3, wherein the solvent is an organic solvent.

6. The method according to any one of claims 1 to 3, wherein the solvent comprises a first solvent in which the low molecular weight carbon compound is soluble and a second solvent in which the high molecular weight carbon compound is soluble.

7. The method according to claim 6, wherein the first solvent and the second solvent are of the same type.

8. The method according to claim 6, wherein the first solvent and the second solvent are different types of solvents that are compatible with each other.

9. A carbon fiber precursor fiber containing a low molecular weight carbon compound containing pitch, a high molecular weight carbon compound containing a polybenzimidazole derivative, and 10. The carbon fiber precursor fiber according to claim 9, wherein the average molecular weight of the low molecular weight carbon compound is less than 3000.

11. The carbon fiber precursor fiber according to claim 9 or 10, wherein the content ratio of the low molecular weight carbon compound to the high molecular weight carbon compound is 1:99 to 99:

1.

12. Carbon fibers obtained by carbonizing the carbon fiber precursor fibers described in claim 9 or 10.

13. A method for producing carbon fiber precursor fibers, comprising the steps of producing carbon fiber precursor fibers by wet spinning, dry spinning, or wet-dry spinning, using a mixed solution containing a high molecular weight carbon compound having a polymer compound that does not contain oxygen atoms in its main chain, a low molecular weight carbon compound having a lower molecular weight than the high molecular weight carbon compound and at least one of by-products, residues, and waste generated when processing carbon-containing resources, and a solvent as the spinning stock solution.

14. The method according to claim 13, wherein the resource comprises at least one of petroleum, coal, biomass, and plastic.

15. The method according to claim 13 or 14, wherein the low molecular weight carbon compound is a carbon compound that is not suitable for solution spinning on its own.

16. The method according to claim 13 or 14, wherein the average molecular weight of the low molecular weight carbon compound is less than 3000.

17. The method according to claim 13 or 14, wherein the low molecular weight carbon compound comprises an aromatic compound having one or more benzene rings, and is soluble in an organic solvent at a concentration of 1% or more.

18. The method according to claim 13 or 14, wherein the high molecular weight carbon compound comprises a polybenzimidazole derivative.

19. The method according to claim 13 or 14, wherein the high molecular weight carbon compound comprises polyacrylonitrile (PAN).

20. The method according to claim 13 or 14, wherein the average diameter of the carbon fiber precursor fibers is 3 μm or more.

21. The method according to claim 13 or 14, wherein the carbon fiber precursor fiber is a multifilament comprising a bundle of multiple aligned fibers.

22. The method according to claim 21, comprising the steps of simultaneously extruding the spinning solution from a plurality of holes in a spinneret to form fibers, and continuously winding the plurality of formed fibers together in a bundle.

23. A carbon fiber precursor fiber comprising a high molecular weight carbon compound containing a polymer compound that does not contain oxygen atoms in its main chain, and a low molecular weight carbon compound having a lower molecular weight than the high molecular weight carbon compound, comprising at least one of by-products, residues, and waste generated when processing carbon-containing resources.

24. The carbon fiber precursor fiber according to claim 23, which is a multifilament comprising a bundle of multiple aligned fibers.

25. Carbon fibers obtained by carbonizing the carbon fiber precursor fibers described in claim 23 or 24.

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