JP6631675B2 - Manufacturing method of carbon fiber - Google Patents

Description

The present invention relates to a method for producing a carbon fiber .

  Flame-resistant fibers are excellent in heat resistance and twist resistance, so they are widely used as spatter sheets to protect human bodies from high-heat iron powder or welding sparks scattered during welding work, etc. Demand in those areas is increasing. Further, the flame resistant fiber is also important as an intermediate raw material for obtaining a carbon fiber. Since the carbon fiber is excellent in mechanical properties, chemical properties and lightness, it is widely used in various applications such as aviation such as aircraft and rockets, aviation materials for space, and sporting goods such as golf shafts and fishing rods. .

  Furthermore, due to its light weight and excellent mechanical and chemical properties, carbon fiber is used in general industrial applications such as space applications, sports applications, civil engineering / architecture, pressure vessels, wind turbine blades, and recently in aircraft applications and automobiles. It has been adopted for applications.

  In particular, polyacrylonitrile (hereinafter abbreviated as PAN) -based carbon fiber is excellent in productivity and physical properties and quality of carbon fiber, and thus, industrialization has been actively promoted to this day. Generally, PAN-based carbon fiber is obtained by heating a PAN-based precursor fiber in air at 200 to 300 ° C. to make it flame-resistant and producing a flame-resistant fiber, and then heating and carbonizing under an inert atmosphere such as nitrogen. can get.

  However, since the oxidation treatment is an exothermic reaction in the solid state of fibers, heat easily accumulates inside the fibers, and once the conditions under which the oxidation reaction stably progresses are deviated, the oxidation reaction runs away and carbon Fibers can be damaged.

  Therefore, in the process of oxidizing the PAN-based carbon fiber, it is common to spend a long time and slowly advance the oxidization reaction in order to strictly control the progress rate of the oxidization reaction. It was hard to say that the method was highly productive.

  As one of the methods for solving the above technical problem, a method of obtaining a flame-resistant fiber by spinning after PAN-based polymer is flame-resistant, or a method of spinning PAN-based polymer into fiber, and then flame-resistant. Methods for obtaining flame resistant fibers have been studied.

As a method for obtaining a flame-resistant fiber by spinning a PAN-based polymer after flame-resistance, for example, Patent Document 1 discloses a method in which acrylonitrile (hereinafter abbreviated as AN) -based polymer powder is densified in an inert atmosphere. A method is disclosed in which a heat treatment is performed until the heat treatment reaches 1.20 g / cm ³ or more, and then the fibrous material that has been dissolved and fibrillated in a solvent is heat-treated. However, in this method, since the AN-based polymer powder that has not sufficiently progressed in flame resistance is used, the viscosity of the solution changes with time over time, and yarn breakage easily occurs. In addition, since a strong acid solvent such as sulfuric acid or nitric acid which easily decomposes an organic polymer is used as a solvent, it is necessary to use a device formed of a special material having corrosion resistance, which poses a cost problem. .

  Patent Literature 2 discloses a method in which a heat-treated AN-based polymer powder and an unheated AN-based polymer powder are mixed and dissolved in an acidic solvent. However, this method does not solve the problem of imparting corrosion resistance to the apparatus or instability of the solution as in the method described in Patent Document 1.

  On the other hand, as a method of heat-treating PAN in a solution, Non-Patent Document 1 discloses that PAN is converted into a polymer having a cyclized structure by heat-treating a solution of PAN in dimethylformamide (hereinafter abbreviated as DMF). Is disclosed. However, since it is a dilute solution having a polymer concentration of 0.5% and the viscosity is too low, it is substantially difficult to shape and form into fibers or the like. Can not be used as

  Non-Patent Document 2 discloses a method of denaturing PAN by reacting a primary amine with a PAN solution of dimethyl sulfoxide (hereinafter abbreviated as DMSO). However, the solution is intended to impart hydrophilicity to the PAN which has not undergone flame resistance.

  Further, Patent Literature 3 discloses a method for producing a flame-resistant polymer by modifying a DMSO solution of PAN with a nucleophilic agent such as an amine, and further performing an oxidation treatment with an oxidizing agent. However, in producing a flame-retarded polymer by applying this method, a decrease in the viscosity of the solution and a change in the viscosity of the solution with the lapse of time are observed with the progress of the flame-retardation. This affects stability, deterioration of physical properties of the obtained flame-resistant fiber and carbon fiber, and variation in physical properties between single fibers in a fiber aggregate. In addition, since a nitro- or quinone-based compound is used as an oxidizing agent, by-products such as amines and alcohols generated in the reaction cause an undesired reaction with the flame-resistant polymer, causing coloring of the coagulation bath in the spinning process.

  On the other hand, as a method of obtaining flame-resistant fiber by spinning a PAN-based polymer into fiber and then making it flame-resistant, Patent Document 4 discloses a technique of producing a flame-resistant fiber by subjecting a PAN-based precursor fiber to chemical treatment. An organic nucleophile represented by an amine compound as a cyclizing agent accelerator and an organic nitrogen compound represented by a nitro compound as an oxidizing agent have been disclosed. However, the technology described in Patent Document 4 has a problem that the chemical does not penetrate into the interior of the precursor fiber and the progress of the oxidization reaction is slow, so that it takes time for the oxidization treatment. Not reached.

  Patent Literature 5 discloses a technology in which PAN-based precursor fibers are subjected to heat treatment by adding elemental sulfur in order to eliminate structural inhomogeneity in the cross-sectional direction of carbon fibers due to insufficient oxygen diffusion. However, the technology described in Patent Literature 5 has not reached industrial production due to problems such as spinning stability and generation of reducing substances during firing.

JP-B-63-14093 JP-B-62-57723 WO 2007/018136 JP 2004-300600 A JP-A-58-109625

"Polymer Science (USSR)" (Polym. Sci. USSR), 1968, Vol. 10, p. 1537 "Journal of Polymer Science, Part A: Polymer Chemistry" (J. Polym. Sci. Part A: Polym. Chem.), 1990, Vol. 28, p. 1623

  In the above-described conventional method of producing a fiber by spinning after producing a flame-resistant polymer in a solution, since the molecular weight of the polymer decreases with the progress of the flame-resistance reaction, the viscosity decreases, and the drawability in the spinning process increases. It is thought to decrease.

  On the other hand, in the method of making the fiber after spun flame-retardant, it is difficult to uniformly treat the fiber with the known amine compound or elemental sulfur, etc. Therefore, it was unsuitable for industrial production because of reduced properties.

  The present invention has been made in view of the above circumstances, and by providing a method for producing high-quality flame-resistant fiber with high productivity, high-quality carbon fiber, high productivity, stable It is intended to be manufactured.

  The present invention has the following aspects.

The method of producing the carbon fiber of the present invention involves a polyacrylonitrile flame textiles a thiolate compound and denatured specific gravity 1.24 or 1.55 or less with an oxidizing agent polyacrylonitrile flame resistant fibers.

The present invention is a method for producing carbon fibers, in which a polyacrylonitrile-based flame resistant fiber is heat-treated at 300 ° C. or more and 3000 ° C. or less.

Further, the denaturation can be performed in a solution .

  Preferably, the solution is an ethylene glycol-based solvent.

  The thiolate-based compound is preferably a compound selected from the following general formula (1) or formula (2).

In the formula (1), M ₁ represents an alkali metal, and R ₁ is at least one functional group selected from a hydrocarbon group, a hydroxyl group, an amino group, a nitro group, a thiol group, an imino group, a nitrile group, and an azo group. It is selected from hydrocarbon groups containing groups.

In the formula (2), M ₂ represents an alkaline earth metal, and R ₂ and R ₃ are selected from a hydrocarbon group, a hydroxyl group, an amino group, a nitro group, a nitro group, a thiol group, an imino group, a nitrile group, and an azo group. Selected from hydrocarbon groups containing at least one functional group.

The oxidizing agent is preferably a compound containing at least one nitrogen atom, and has at least one functional group or structure selected from the group consisting of a nitro group, a nitroso group, an N-hydroxy structure, an N-oxide structure, and an N-oxyl structure. Are more preferred.

The modification is preferably performed in a solution containing 100 parts by mass of a solvent and 1 part by mass or more and 150 parts by mass or less of a thiolate-based compound at 120 ° C. or more and 250 ° C. or less, and 30 seconds or more and 120 minutes or less, and the polyacrylonitrile-based It is preferable that the sulfur content of the flame resistant fiber is 0.1% by mass or more and 30% by mass or less .

The present invention, the polyacrylonitrile-based flame-resistant fiber obtained by modifying polyacrylonitrile precursor fiber and its respective
It is preferable that Abs _{2240 ± 60} calculated from the infrared absorption spectrum (A) within the range of 2240 ± 60 cm ⁻¹ measured by infrared spectrometry using the following formula (3) is 70% or less .

Each of the polyacrylonitrile-based flame resistant fiber and the polyacrylonitrile-based precursor fiber was 2940 ± 160 cm by infrared spectroscopy. ^-1 Abs calculated by the following equation (4) using the area of the infrared absorption spectrum (B) in the range of _{2940 ± 160} Is preferably 70% or less.

2240 ± 60 cm by infrared spectroscopy of the polyacrylonitrile-based flame resistant fiber ^-1 Absorption spectrum (A) in the range of 2940 ± 160 cm ^-1 Abs calculated by the following general formula (5) using each area of the infrared absorption spectrum (B) within the range of _2240/2940 Is preferably 0.05 or more and 0.60 or less.

The modification can be performed in an aqueous solvent.

When the denaturation is carried out in an aqueous solvent, it is preferable that the temperature be 120 ° C. or more and 250 ° C. or less, the pressure be 0.18 MPa or more and 3.98 MPa or less, and the time be 30 seconds or more and 120 minutes or less.

When the modification is carried out in an aqueous solvent, the modification is preferably carried out so that the specific gravity of the polyacrylonitrile-based flame-resistant fiber is from 1.24 to 1.55.

Further, it is preferable to carry out the reaction so that the sulfur content of the polyacrylonitrile-based flame-resistant fiber is from 0.1% by mass to 30% by mass .

ADVANTAGE OF THE INVENTION According to this invention, a high-performance carbon fiber can be manufactured stably.

9 shows an infrared absorption spectrum of a PAN-based precursor fiber before and after modification with a thiolate (Example 6 ).

The flame-resistant fiber used in the method for producing a carbon fiber of the present invention can be obtained by the following two methods: [1] a PAN-based polymer is modified in a solution, and then the polymer is spun to obtain a flame-resistant fiber. It is characterized by being produced by a method of producing, or [2] a method of producing a flame-resistant fiber by modifying a PAN-based precursor fiber in a liquid phase containing a thiolate-based compound. Hereinafter, description will be made in order.
[1] A method for producing a flame-resistant fiber by spinning the PAN polymer after denaturing the PAN polymer in a solution [PAN-based partially cyclized polymer]
The PAN-based partially cyclized polymer of the present invention (hereinafter also referred to as a partially cyclized polymer) can be obtained by modifying a polyacrylonitrile-based polymer, and the PAN-based polymer and the partially-cyclized polymer after the modification treatment are obtained. Abs _{2240 ± 60} calculated from the area of the infrared absorption spectrum (A) within the range of 2240 ± 60 cm ⁻¹ measured by infrared spectrometry using the following formula (1) is 70% or less, and contains sulfur. Rate is from 0.3% by mass to 20.0% by mass.

  The partially cyclized polymer of the present invention is a polymer in which all or a part of a nitrile group which is a side chain of PAN is cyclized by modifying a PAN-based polymer as a precursor.

Abs _{2240 ± 60} of the partially cyclized polymer of the present invention is 70% or less. When the Abs _{2240 ± 60} is 70% or less, modification to a flame-resistant polymer described later easily occurs. Abs _{2240 ± 60} is preferably at most 50%, more preferably at most 30%. The lower limit is not particularly limited, and may be 0%. The infrared spectroscopy is performed by a method described later.

  The sulfur content of the partially cyclized polymer of the present invention is from 0.3% by mass to 20.0% by mass. When the sulfur content is 0.3% by mass or more, the effect of the present invention is likely to appear. Further, when the sulfur content is 20.0% by mass or less, it is possible to prevent the carbonization yield from being extremely reduced. The sulfur content is preferably from 1.0% by mass to 18.0% by mass, more preferably from 5.0% by mass to 15.0% by mass. The measurement of the sulfur content in the present invention is performed by a method described later.

  The partially cyclized polymer of the present invention preferably has a number average molecular weight of 100,000 or more and 1,000,000 or less. If it is 100,000 or more, the yarn can be stably formed in the spinning step, and if it is 1,000,000 or less, the solubility is good. It is more preferably from 100,000 to 500,000, and further preferably from 150,000 to 300,000.

In the present invention, the number average molecular weight is a value measured by gel permeation chromatography (GPC). The number average molecular weight is the following formula when there are Ni polymers having a molecular weight of Mi. Number average molecular weight (Mn) = Σ (NiMi) / Σ (Ni)
Is the value represented by As the number average molecular weight, a relative value in terms of polystyrene is used.

  In the present invention, a PAN-based polymer having a structure derived from acrylonitrile (hereinafter, also referred to as AN) is used as the precursor polymer from the viewpoint of the progress of the oxidization resistance and the solubility. When the PAN-based polymer is a copolymer, it preferably contains 85 mol% or more, more preferably 90 mol% or more, and more preferably 92 mol% of AN-derived structural units from the viewpoint of solubility and reactivity. % Is more preferable. The method for synthesizing the PAN-based polymer is not particularly limited, and for example, a solution polymerization method, a suspension polymerization method, a slurry polymerization method, an emulsion polymerization method, or the like can be used.

  Examples of the copolymerization component of the PAN-based polymer include metal salts of allylsulfonic acid, metal salts of methallylsulfonic acid, acrylates, methacrylates, and acrylamide. In addition to the above-mentioned copolymerization component, a compound containing a vinyl group can be copolymerized as a component for promoting flame resistance. Examples of the compound include acrylic acid, methacrylic acid, and itaconic acid, and a part or all of these may be neutralized with an alkali component such as ammonia. The number average molecular weight of the PAN-based polymer is not particularly limited, but may be, for example, 1,000 to 1,000,000.

[PAN-based flame-resistant polymer]
The PAN-based flame-resistant polymer of the present invention (hereinafter also referred to as a flame-resistant polymer) is a PAN-based flame-resistant polymer obtained by further modifying the PAN-based partially cyclized polymer with an oxidizing agent. Abs _{2940 ± 160} calculated by the following formula (2) from the area of the infrared absorption spectrum (B) within the range of 2940 ± 160 cm ⁻¹ measured by infrared spectroscopy is 70% or less. And the sulfur content is 0.3% by mass or more and 20.0% by mass or less, and the specific gravity is 1.26 or more.

  The flame resistant polymer of the present invention is a polymer obtained by modifying the partially cyclized polymer of the present invention with an oxidizing agent.

Abs _{2940 ± 160} of the flame resistant polymer of the present invention is 70% or less. When Abs _{2940 ± 160} is 70% or less, improvement in flame resistance can be confirmed. Abs _{2940 ± 160} is preferably at most 50%, more preferably at most 30%. The lower limit is not particularly limited, and may be 0%. The infrared spectroscopy is performed by a method described later.

  The sulfur content of the flame-resistant polymer of the present invention is from 0.3% by mass to 20.0% by mass. When the sulfur content is 0.3% by mass or more, the effect of the present invention is likely to appear. Further, when the sulfur content is 20.0% by mass or less, it is possible to prevent the carbonization yield from being extremely reduced. The sulfur content is preferably from 1.0% by mass to 18.0% by mass, more preferably from 5.0% by mass to 15.0% by mass.

  The specific gravity of the flame-resistant polymer of the present invention is 1.26 or more. When the specific gravity is 1.26 or more, a clear improvement in flame resistance can be confirmed. The specific gravity is preferably 1.28 or more, more preferably 1.30 or more. The upper limit of the specific gravity is not particularly limited, but may be, for example, 1.50 or less. The measurement of the specific gravity in the present invention is performed by a method described later.

  The number average molecular weight of the flame resistant polymer of the present invention is preferably 100,000 or more and 1,000,000 or less. The number average molecular weight is more preferably from 150,000 to 900,000 from the viewpoint of spinnability in the subsequent spinning step, and even more preferably from 200,000 to 500,000.

  In addition, the structure of the flame-resistant polymer using the PAN-based polymer as a precursor has not been completely elucidated. However, a document analyzing the PAN-based flame resistant fiber ("Journal of Polymer Science, Part A: Polymer Chemistry Edition" (J. Polym. Sci. Part A: Polym. Chem. Ed.), 1986, Vol. 24, p. 3101), it is considered that a flame-resistant polymer has a structure such as a naphthyridine ring, an acridone ring, or a hydrogenated naphthyridine ring generated by a cyclization reaction or an oxidation reaction of a nitrile group. It is generally called a ladder polymer. Unreacted nitrile groups may remain in the flame-resistant polymer as long as the flame resistance is not impaired, and trace cross-linking may occur between molecules of the flame-resistant polymer unless the solubility is impaired.

[PAN-based partially cyclized polymer-containing solution]
The PAN-based partially cyclized polymer-containing solution of the present invention (hereinafter also referred to as a partially cyclized polymer-containing solution) has a concentration of the PAN-based partially cyclized polymer of from 1.0% by mass to 50.0% by mass. Is dissolved in the solvent. When the concentration is 1.0% by mass or more, productivity during molding is improved. Further, when the concentration is 50.0% by mass or less, a decrease in fluidity due to the progress of gelation is prevented, and molding is facilitated. The concentration is preferably from 10.0% by mass to 20.0% by mass, more preferably from 12.0% by mass to 18.0% by mass. Here, the concentration of the partially cyclized polymer in the partially cyclized polymer-containing solution is determined by the following equation.

Concentration of the partially cyclized polymer (% by mass) = 100 × mass of the partially cyclized polymer / mass of the partially cyclized polymer-containing solution The mass of the partially cyclized polymer was calculated from the partially cyclized polymer-containing solution using an evaporator. After distilling off the solvent, it is obtained as a mass of a solid component remaining when the temperature is raised to 200 ° C. in a nitrogen gas at 40 ° C./min and the solvent is completely removed using a thermo mass spectrometer (TG). When a solid polymer can be separated using an appropriate coagulating liquid (precipitant), the solid polymer can be obtained directly from the mass of the coagulated polymer.

  The viscosity of the partially cyclized polymer-containing solution can be appropriately selected in a preferable range depending on the shaping method, the molding method, the molding temperature, the type of the die, the mold, and the like of the partially cyclized polymer. However, from the viewpoint of spinning during spinning, the solution viscosity at 25 ° C. is preferably 10 to 100,000 poise, more preferably 10 to 10,000 poise, and still more preferably 10 to 1,500 poise. The viscosity is a value measured by a method described below. Even when the solution viscosity is out of the above range, the solution can be adjusted to an appropriate viscosity by heating or cooling during spinning and used.

  As the solvent for dissolving the partially cyclized polymer, a polar organic solvent is preferable from the viewpoint of the solubility of the partially cyclized polymer. Examples of the polar organic solvent include organic solvents having a hydroxyl group, an amino group, an amide group, a sulfonyl group, a sulfone group, a mercapto group, and the like. Examples of the polar organic solvent include an organic solvent having good compatibility with water.

  Examples of these organic solvents include (a) glycol solvents such as ethylene glycol, diethylene glycol, triethylene glycol, and polyethylene glycol having a molecular weight of about 200 to 1,000, (b) dimethyl sulfoxide (DMSO), dimethylformamide (DMF), Aprotic polar solvents such as dimethylacetamide (DMAc) and N-methylpyrrolidone; (c) monoethanolamine, diethanolamine, triethanolamine, N-aminoethylethanolamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, Amine solvents such as pentaethylenehexamine, N-aminoethylpiperazine, orthophenylenediamine, metaphenylenediamine, and paraphenylenediamine; It can be used.

  Examples of thiol solvents having good compatibility with water include mercaptoethanol having a hydroxyl group, mercaptopropanol, mercaptobutanol, thioglycerol, thiodiethanol, and dithiothreitol.

  Examples of the thiol having a carboxyl group having good compatibility with water include thioglycolic acid, ammonium thioglycolic acid, sodium thioglycolic acid, potassium thioglycolic acid, and thiolactic acid.

  Further, as a thiol having an amino group having good compatibility with water, for example, aminoethanethiol, aminopropanethiol, aminobutanethiol, aminopentanethiol, monoamino-substituted alkanethiol such as aminohexanethiol, di, tri, tetra, And pentaamino-substituted alkanethiols.

  These solvents may be used singly or as a mixture of two or more.

  Among these solvents, the PAN-based polymer which is a precursor polymer is easily dissolved, and the partially cyclized polymer is easily solidified in water to form a dense and hard polymer, so that it is suitable for wet spinning. From the viewpoint of, at least one solvent selected from DMSO, DMF and DMAc is preferable.

  When the partially cyclized polymer is water-soluble, other solvents such as water and a water-soluble solvent may be used in combination with the polar organic solvent, as long as the object of the present invention is not hindered. In particular, the use of water is preferable from the viewpoints of cost and productivity because it is relatively easy to remove the solvent during the molding described below.

[PAN-based flame-resistant polymer-containing solution]
The PAN-based flame-resistant polymer-containing solution of the present invention (hereinafter also referred to as a flame-resistant polymer-containing solution) is prepared by dissolving the PAN-based flame-resistant polymer in a solvent at a concentration of 1.0% by mass or more and 50.0% by mass or less. I have. When the concentration is 1.0% by mass or more, productivity during molding is improved. Further, when the concentration is 50.0% by mass or less, a decrease in fluidity due to the progress of gelation is prevented, and molding is facilitated. The concentration is preferably from 10.0% by mass to 20.0% by mass, more preferably from 12.0% by mass to 18.0% by mass. The concentration of the flame-resistant polymer in the solution containing the flame-resistant polymer can be determined in the same manner as the concentration of the partially-cyclized polymer in the solution containing the partially-cyclized polymer.

  The viscosity of the flame-resistant polymer-containing solution can be appropriately selected depending on the shaping method of the flame-resistant polymer, the molding method, the molding temperature, the type of a die, a mold, and the like. However, from the viewpoint of spinning during spinning, the solution viscosity at 25 ° C. is preferably 10 to 100,000 poise, more preferably 10 to 10,000 poise, and still more preferably 10 to 1,500 poise. The viscosity is a value measured by a method described below. Even when the viscosity is out of the above range, it can be adjusted to an appropriate viscosity by heating or cooling during spinning and used.

  As the solvent for dissolving the flame resistant polymer, the same solvent as the solvent for dissolving the partially cyclized polymer can be used. When water is used as the solvent in addition to the polar organic solvent, the amount of water is preferably 5 parts by mass or more and 300 parts by mass or less, and more preferably 10 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the flame-resistant polymer. It is more preferably at most 20 parts by mass, more preferably at most 20 parts by mass and at most 150 parts by mass.

[Method for producing PAN-based partially cyclized polymer]
The PAN-based partially cyclopolymer of the present invention can be produced by modification with a thiolate-based compound.

  The thiolate-based compound may be any as long as it exists as a thiolate in the reaction system, and may be in a thiol state or a thiolate salt state when handled. Examples of the thiol include alkyl mercaptans such as methyl mercaptan, ethyl mercaptan, propyl mercaptan, butyl mercaptan, pentyl mercaptan, hexyl mercaptan, heptyl mercaptan, octyl mercaptan, and alkylthiols such as structural isomers thereof; mercaptoethanol, mercapto Thiols having a hydroxyl group such as propanol, mercaptobutanol, thioglycerol, thiodiethanol and dithiothreitol; thiols having a carboxyl group such as thioglycolic acid, ammonium thioglycolic acid, sodium thioglycolic acid, potassium thioglycolic acid, and thiolactic acid; Aminoethanethiol, aminopropanethiol, aminobutanethiol, aminopentanethiol, aminohexa Thiols having amino groups such as alkanethiols substituted with a plurality of amino groups such as monoamino-substituted alkanethiols such as thiol, aminoheptanethiol and aminooctanethiol; di, tri, tetra, and pentaamino-substituted alkanethiols; benzenethiol and the like Thiols containing a benzene ring such as a derivative or a heterocyclic aromatic ring are exemplified.

  The thiolate-based compound can be easily produced by reacting a thiol with a metal hydroxide or the like. The production is preferably performed in a nitrogen atmosphere from the viewpoint of suppressing side reactions. As the thiol used at this time, the same thiol as the thiol can be used. The thiolate is considered to exist in the form of a lithium salt, a sodium salt, a potassium salt, and an ammonium salt, but is preferably present in the form of a sodium salt or a potassium salt from the viewpoint of ease of production and cost.

  The thiolate-based compound preferably has a functional group having an element such as oxygen, nitrogen, and sulfur in addition to the thiolate group. Examples of the functional group include a hydroxyl group. The thiolate-based compound is preferably a compound having two or more functional groups, including a thiolate group and a functional group other than the thiolate group, from the viewpoint of the solubility of the partially cyclized polymer and the flame-resistant polymer. One of these thiolate compounds may be used alone, or two or more of them may be used in combination. When the thiolate compound has, for example, a hydroxyl group as a functional group other than the thiolate group, modification may occur due to the hydroxyl group.

  The modification is effectively performed by using 10 to 250 parts by mass of the thiolate-based compound with respect to 100 parts by mass of the PAN-based polymer under the conditions of 80 to 300 ° C and 5 to 240 minutes. Can be flame resistant. It is more preferable to use 20 to 200 parts by mass of the thiolate-based compound and more preferably 40 to 150 parts by mass with respect to 100 parts by mass of the PAN-based polymer. Further, by setting the temperature at the time of denaturation (denaturation temperature) to 80 ° C. or more and 300 ° C. or less, the flame-resistant reaction proceeds. The denaturation temperature is more preferably from 100 ° C to 250 ° C, and even more preferably from 120 ° C to 200 ° C. Further, by setting the time of the denaturation treatment to 5 minutes or more and 240 minutes or less, appropriate treatment can be performed. 10 minutes or more and 200 minutes or less are more preferable, and 30 minutes or more and 180 minutes or less are still more preferable.

  The state in which the PAN-based polymer is “modified” by the thiolate-based compound as referred to herein means that the PAN-based polymer is acted on by the thiolate-based compound to cause a cyclization reaction or an oxidation reaction of the nitrile group. Is to form a flame-resistant structure in the structure. Examples of the flame-resistant structure include a naphthyridine ring, an acridone ring, and a hydrogenated naphthyridine ring structure.

  Whether or not the flame resistant structure is formed can be determined by increasing the specific gravity, sulfur content and mass of the polymer after modification (partially cyclized polymer), or the infrared absorption spectrum (IR method) of the polymer before and after modification. Can be confirmed by the value calculated from the area value of the specific peak measured by

  In the case of the IR method, a portion derived from the thiolate-based compound used is added as a new spectrum to the spectrum of the partially cyclized polymer modified with the thiolate-based compound as compared with the spectrum of the polymer before modification. You.

  In the case of the mass increasing method, the mass is increased with respect to the PAN-based polymer by being modified with a thiolate-based compound. The increase in the mass is preferably 1.1 to 3.0 times the mass of the PAN-based polymer. When the increase in mass is 1.1 times or more, the partially cyclized polymer is sufficiently dissolved to prevent the polymer component from being included as an impurity when producing a flame resistant fiber or a carbon molded product. it can. Further, when the increase in the mass is 3.0 times or less, the flame resistance of the obtained flame resistant fiber is improved. The increase in the mass is preferably 1.3 times or more and 2.6 times or less, more preferably 1.3 times or more and 2.2 times or less with respect to the mass of the PAN-based polymer.

[Method for producing PAN-based flame-resistant polymer]
The PAN-based flame-resistant polymer of the present invention can be oxidized (modified) using an oxidizing agent in addition to a nucleophilic agent, from the viewpoint of sufficiently promoting the flame resistance of the PAN-based partially cyclized polymer. The oxidizer may be added after the nucleophile has been added, or the nucleophile and the oxidizer may be added simultaneously. When the nucleophilic agent and the oxidizing agent are added at the same time, the nucleophilic agent and the oxidizing agent may be mixed in advance before adding the PAN-based polymer, or the PAN-based polymer, the nucleophilic agent and the oxidizing agent may be simultaneously added. You may mix.

  As the oxidizing agent, an organic or inorganic oxidizing agent can be used. Examples of the oxidizing agent include quinone-based substances such as benzoquinone and chloranil, nitro-based substances such as nitrobenzene, inorganic peroxides such as hydrogen peroxide and potassium peroxide, and permanganates such as potassium permanganate. . In the reaction, it is preferable to supply air to the reaction system in addition to the oxidizing agent from the viewpoint of increasing the efficiency of the modification reaction by the thiolate-based compound.

  In the present invention, the oxidizing agent is preferably a metal-based material from the viewpoint of reactivity. Examples of the metal-based compound include metal-based compounds such as palladium, platinum, rhodium, ruthenium, iridium, rhenium, gold, silver, copper, iron, tungsten, nickel, cobalt, chromium, calcium, vanadium, aluminum, titanium, zinc, and the like. Their alloys etc. are mentioned. Further, oxides of these metals and the like may be used. Among these, palladium-based substances such as palladium and palladium-containing substances are preferable from the viewpoint of reactivity. The palladium-based substance is preferably a palladium-based substance that is insoluble in a solution from the viewpoint of the ease of work to remove later, but may be a palladium-based substance that is soluble in a solvent. The form of the palladium-based substance may be a powder or a fixed bed. Further, it may be palladium alone, may be supported on a carrier, or may form a complex.

In the present invention, a palladium-based substance is mainly used as an oxidizing agent, but a palladium-based substance is known as a useful oxidizing agent. Also, a technique of catalytically oxidizing with a small amount of palladium has been disclosed (for example, "Chemical Reviews", 1978, Vol. 78, p. 317). However, such an oxidation reaction using palladium is intended to cause a low-molecular compound to react catalytically with high efficiency, and has a completely different technical idea from the present invention used for producing a flame-resistant polymer. The oxidation in the present invention means so-called dehydrogenation, but may mean the introduction of oxygen in producing a flame-resistant polymer. Whether or not the polymer has been oxidized can be examined by any method, for example, a method of comparing the peak intensity of 13C in 100 to 200 ppm in NMR and the peak intensity near 1580 cm ⁻¹ in IR spectrum with the raw material polymer. Can be

  The oxidation treatment can be performed at normal pressure, under pressure, or under reduced pressure. It is preferable to perform the reaction under normal pressure or reduced pressure from the viewpoint of reactivity. As a device used for the oxidation treatment, a known reaction vessel equipped with a stirrer, for example, a mixer such as an extruder or a kneader can be used alone or in combination.

  When palladium or a palladium-containing substance is used as the oxidizing agent, the content of palladium in the oxidizing agent is preferably 1.0% by mass or more, more preferably 5.0% by mass or more, and more preferably 10% by mass from the viewpoint of reactivity. The above is more preferred. The upper limit of the content is not particularly limited, but may be, for example, 50% by mass or less.

  From the viewpoint of reaction efficiency, the temperature of the oxidation treatment is preferably from 80 ° C to 300 ° C, more preferably from 120 ° C to 280 ° C, and still more preferably from 160 ° C to 250 ° C. From the viewpoint of productivity, the oxidation treatment time is preferably 5 minutes or more and 240 minutes or less, more preferably 10 minutes or more and 220 minutes or less, and even more preferably 20 minutes or more and 180 minutes or less.

  When a thiolate-based compound and an oxidizing agent are used at the same time, a mixture of a PAN-based polymer, a thiolate-based compound, an oxidizing agent, and a polar organic solvent is heated at an appropriate temperature to efficiently perform a dissolution treatment and a flame-proofing reaction. Can be done. The heating temperature is appropriately selected depending on the solvent, the thiolate-based compound, and the oxidizing agent to be used, but is preferably from 100 to 350 ° C, more preferably from 110 to 300 ° C, and still more preferably from 120 to 250 ° C.

  The method for producing a flame-resistant polymer in a solution of the present invention can suppress a decrease in the molecular weight of the polymer due to modification as compared with a method for producing a flame-resistant polymer in a conventional solution. This makes it possible to efficiently produce a flame-resistant polymer-containing solution having a viscosity suitable for spinning in the spinning step. Further, the draw ratio at the time of spinning can be increased, and a high-performance flame resistant fiber can be stably manufactured.

  Furthermore, when a metal-based substance is used as an oxidizing agent in the production of a flame-resistant polymer, the amount used can be reduced as compared with nitro-based compounds and quinone-based compounds conventionally used as oxidizing agents. Further, after completion of the reaction, it can be easily recovered from the flame-resistant polymer-containing solution and reused.

  In addition, the method for producing flame resistant fibers and carbon fibers of the present invention has the following advantages as compared with the conventional production method using an oven (the so-called Shindo method).

  In other words, in the method for producing flame-resistant fiber and carbon fiber by the Shindo method, when the precursor fiber having a large diameter is subjected to flame-resistance treatment, the degree of flame-resistance becomes uneven on the fiber surface and inside the fiber. There is a problem that physical properties are deteriorated. However, according to the production method of the present invention, the polymer which is the carbon fiber precursor is made flame-resistant in a solution, and then the fiber is formed. Therefore, it is easy to produce flame-resistant fibers and carbon fibers having a uniform structure.

[Manufacture of flame resistant fiber]
The flame resistant fiber of the present invention is obtained by spinning the solution containing a partially cyclized polymer or the solution containing a flame resistant polymer (hereinafter, also referred to as a polymer containing solution).

  The specific gravity of the flame resistant fiber of the present invention is preferably 1.24 to 1.60, more preferably 1.25 to 1.55, and still more preferably 1.26 to 1.50. When the specific gravity is 1.24 or more, the number of pores inside the single fiber is small, and the fiber strength is improved. Further, when the specific gravity is 1.60 or less, the denseness is moderate and the elongation is improved. The specific gravity is a value measured by a method described later.

  The residual amount of the solvent contained in the flame resistant fiber is preferably 10% by mass or less, more preferably 5% by mass or less, and still more preferably 1% by mass or less. When the residual amount of the solvent is 10% by mass or less, flame resistance is improved.

  The flame resistant fiber of the present invention can be produced through a step of spinning the above-mentioned polymer-containing solution and a step of removing the solvent used in the spinning step.

  As a method of spinning the polymer-containing solution into a fibrous form, a wet spinning method or a dry-wet spinning method can be adopted. In these spinning methods, a spinning solution is discharged from a spinneret into a coagulation bath and coagulated to obtain a coagulated yarn. As the coagulation bath solution, a solution containing a solvent contained in the spinning solution and a coagulation promoting component can be used.

  When the polymer is insoluble in water, water can be used as the coagulation promoting component. The ratio between the solvent and the coagulation accelerating component in the coagulation bath liquid and the coagulation bath temperature can be appropriately selected in consideration of the denseness, surface smoothness, spinnability and the like of the obtained coagulated yarn. Fibers can be formed as long as the coagulation bath concentration allows coagulation. For example, when water is used as a coagulation promoting component, the ratio of solvent / water (volume ratio) is preferably 30/70 to 70/30, and 40/70. / 60 to 60/40 is more preferred. The coagulation bath temperature can be selected in the range of 0 to 100 ° C. according to the purpose. As the coagulation bath solution, alcohols having low affinity for water, such as propanol and butanol, can also be used.

  Next, the obtained coagulated yarn can be drawn in a drawing bath or washed with a washing bath.

  Thereafter, the coagulated fiber is further dried and stretched to obtain a flame resistant fiber.

  A known method can be adopted as a drying method. The drying temperature can be 50 to 450 ° C., and generally, it is performed for a long time at a low temperature and for a short time at a high temperature.

  When stretching after drying, the specific gravity of the dried fiber is preferably from 1.15 to 1.5, more preferably from 1.2 to 1.4, and even more preferably from 1.2 to 1.35. Further, the elongation of the single fiber in the dried fiber assembly is preferably 0.5 to 20%. Stretching is carried out in a state where the fiber contains water, such as bath stretching using hot water or hot water, stretching using steam (steam), heating stretching in which a fiber is preliminarily applied with water and then stretched by a dry heating device or a roll. It is preferable to carry out by a heating method. This is because when a thiolate-based compound is used as a nucleophile in the production of a partially cyclopolymerized polymer, the thiolate-modified flame-resistant polymer is largely plasticized by water, and the present inventors have found this fact. Was. It is difficult to draw and orient a fiber made of a molecule having a rigid chemical structure like the flame-resistant polymer of the present invention. In general, a polymer having a rigid molecular chain has a high melting point and a high glass transition point, and thermal decomposition often occurs without plasticization only by increasing the temperature. However, as a result of intensive studies, the present inventors have found that the thiolate-modified flame-resistant polymer of the present invention can be stretched in a specific temperature range and a specific range of moisture content.

  The flame-resistant fiber obtained by the Shindo method is difficult to be stretched because a crosslink is randomly formed between molecules by an oxidation reaction. On the other hand, the thiolate-modified flame-resistant polymer of the present invention has almost no cross-links between molecules, and the presence of water molecules cuts off the interaction between the molecules of the flame-resistant polymer. Has the characteristic of plasticizing. Therefore, using the polymer-containing solution of the present invention, flame-resistant fibers obtained by a wet spinning method or a dry-wet spinning method can be efficiently stretched in water, and have a high density and a high degree of orientation. can do.

  It is preferable to dry the flame resistant fiber thus drawn, if necessary. The moisture content of the flame resistant fiber is preferably 10% or less, more preferably 5% or less. A known method can be used as a drying method.

Abs _{2240 ± 60} of the flame resistant fiber after drying is preferably 10% or more and 50% or less. Abs _{2240 ± 60} calculates the ratio of the peak area of the nitrile group of the flame-resistant polymer constituting the flame-resistant fiber to the peak area of the nitrile group of the PAN-based polymer by the same method as in the measurement of Abs _{2240 ± 60.} It is a value obtained by When Abs _{2240 ± 60} is 10% or more, the flexibility of the polymer chain of the flame-resistant polymer is secured, and smooth stretching is possible. Abs _{2240 ± 60} is more preferably 20% or more, and still more preferably 25% or more. Further, when Abs _{2240 ± 60} is 50% or less, a heat treatment step to be performed later can be performed at a low temperature and in a short time, and the load on equipment can be reduced. Abs _{2240 ± 60} is more preferably 40% or less, and still more preferably 35% or less.

  It is preferable that the flame-resistant fiber after drying is further heat-treated as necessary. By performing heat treatment after stretching, a crosslinked structure is formed between molecular chains, and deterioration of the final product when exposed to high temperatures or chemicals can be suppressed. The heat treatment method is not particularly limited, and a known method can be used. The heat treatment temperature is preferably from 200 ° C to 400 ° C.

[Manufacture of carbon fiber]
The carbon fiber of the present invention is obtained by firing the above-mentioned flame resistant fiber. Specifically, it can be obtained by subjecting the flame-resistant fiber to a high-temperature heat treatment in an inert atmosphere, ie, a so-called carbonization treatment. For example, a carbon fiber can be obtained by subjecting the flame resistant fiber to a heat treatment at 300 ° C. or more and less than 2000 ° C. in an inert atmosphere. The obtained carbon fiber is further heated at 2000 to 3000 ° C. in an inert atmosphere to obtain a carbon fiber having a developed graphite structure.

  The specific gravity of the carbon fiber of the present invention is preferably from 1.6 to 2.4. If the specific gravity is 1.6 or more, the fiber is not easily broken, and if it is 2.4 or less, generation of defects in the carbon fiber can be suppressed.

The sulfur content of the carbon fiber of the present invention is preferably from 0.3% by mass to 20.0% by mass from the viewpoint of physical properties such as strength and elastic modulus. The content is more preferably from 0.5% by mass to 18.0% by mass, further preferably from 1.0% by mass to 16.0% by mass.
[2] A method for producing a flame-resistant fiber by modifying a PAN-based precursor fiber in a liquid phase containing a thiolate-based compound
[PAN-based precursor fiber]
In the present invention, as the PAN-based precursor fiber, a homopolymer of acrylonitrile (AN) (PAN homopolymer) or a copolymer of acrylonitrile and another monomer (PAN-based copolymer) can be used. . (Hereinafter, the PAN homopolymer and the PAN copolymer are collectively abbreviated as “PAN polymer”).
In order to enhance the spinning stability of the PAN-based precursor fiber and to improve the quality and performance of the carbon fiber, the PAN-based polymer should contain from 90.0 mol% to 99.98 mol% of structural units derived from AN. Is preferred. If the number of structural units derived from AN is too large, the spinning stability will be reduced, and if it is too small, the heat resistance of the PAN-based precursor fiber will be reduced. The structural unit derived from AN is more preferably 94.0 mol% or more and 99.9 mol%.

The monomer to be copolymerized is not particularly limited as long as it is a monomer copolymerizable with AN. For example, acrylates such as methyl acrylate and ethyl acrylate; methacrylates such as ethyl methacrylate; acrylic acid; Unsaturated monomers such as methacrylic acid, maleic acid, itaconic acid and acrylamide; methallyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid and alkali metals thereof. These other monomers can be used alone or in combination of two or more.
[Method for producing PAN polymer]
The method for polymerizing the PAN polymer is not particularly limited, and a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, or the like can be used.
[Manufacture of PAN-based precursor fiber]
Using a known method such as a wet spinning method or a dry-wet spinning method, a polymer solution in which a PAN-based polymer is dissolved in a solvent (hereinafter, referred to as “spinning solution”) is spun from a spinneret and introduced into a coagulation bath. Then, by coagulation, the PAN-based precursor fiber used in the present invention can be obtained.

  As a solvent for dissolving the PAN-based polymer, an organic solvent or an inorganic solvent can be used. Among the organic solvents, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methylpyrrolidone, and sulfolane are particularly excellent in solubility of the PAN-based polymer and excellent in spinning stability. This is preferred. These solvents can be used alone or in combination of two or more. Further, for the coagulation bath, a solution in which a coagulant (eg, water) is added to the above-described solvent can be used.

  After spinning the above spinning stock solution into a coagulation bath to coagulate into a filament, the obtained filament is subjected to a washing treatment, a drawing treatment, an oiling treatment and a drying treatment, and finally to a PAN-based precursor fiber. Is obtained. In the stretching treatment, the yarn immediately after coagulation may be stretched in a stretching bath without being washed with water, or may be stretched in a stretching bath after removing the solvent in the washing bath. Such a stretching treatment can be performed in a single or a plurality of stretching baths whose temperature is controlled at 30 to 98 ° C.

  After the above-described stretching treatment, a method of applying an oil agent containing a silicone compound to the yarn can be used for the oil agent applying process. As the silicone-based oil, those containing an amino-modified silicone having high heat resistance are preferable.

  In the drying treatment, a method in which the yarn is brought into contact with a roll heated to 50 to 200 ° C. is efficient. The PAN-based precursor fiber obtained by the drying treatment preferably has a water content of 1.0% by weight or less.

  The number of filaments per yarn of the PAN-based precursor fiber bundle used in the present invention is preferably 1,000 to 300,000, more preferably 3,000 to 100,000, and still more preferably 6,000 to 100,000. The number is preferably 50,000, particularly preferably 12,000 to 24,000.

The single fiber fineness of the PAN precursor fiber used in the present invention is preferably 0.6 dtex or more and 30 dtex or less, more preferably 1.0 dtex or more and 25 dtex or less, and further preferably 2.0 dtex or more and 20 dtex or less.
[Method for producing PAN-based flame-resistant fiber]
The present invention relates to a method for producing a carbon fiber, in which a PAN-based flame-resistant fiber is heat-treated at 300 ° C. or more and 3000 ° C. or less, wherein the flame-resistant fiber is obtained by modifying a PAN-based polymer with a thiolate-based compound, and has a specific gravity of 1%. It is a flame resistant fiber having a size of 24 or more and 1.55 or less.

  The term “modified with a thiolate-based compound” used herein means that a thiolate-based compound acts on a PAN-based polymer to cause a cyclization reaction or oxidation reaction of a nitrile group, resulting in a flame-resistant structure in the structure of the polymer. Is formed. Examples of the flame-resistant structure include a naphthyridine ring, an acridone ring, and a hydrogenated naphthyridine ring structure.

  Whether or not the flame-resistant structure is formed is calculated from the specific gravity of the polymer after modification, the sulfur content, or the area value of a specific peak of the polymer before and after modification measured by an infrared absorption spectrum (IR). It can be confirmed by the value given.

  In the present invention, it is preferable to modify the PAN-based precursor fiber under the condition that the specific gravity of the flame resistant fiber is in the range of 1.24 to 1.55. If the ratio is less than 1.24, the heat resistance will be insufficient and the thread will break in the subsequent carbonization step, which will deteriorate the operability and also lower the quality and quality of the obtained carbon fiber. If it is larger than 1.55, the densification in the subsequent pre-carbonization step is hindered, and the quality and quality of the obtained carbon fiber are reduced. The specific gravity of the flame resistant fiber is more preferably 1.30 or more and 1.50 or less, and still more preferably 1.33 or more and 1.38 or less.

  The details of the PAN polymer and the thiolate compound will be described later.

  In the present invention, the flame resistant fiber is characterized in that a PAN-based polymer is modified with a thiolate-based compound.

  Specifically, a method of modifying a PAN-based polymer or a PAN-based precursor fiber obtained by spinning a PAN-based polymer by a known method using a thiolate-based compound or a thiolate-based compound and an oxidizing agent is used. Can be mentioned. In particular, the method of modifying the PAN-based precursor fiber is preferable from the viewpoint that the modification treatment can be performed efficiently in a short time.

  The method for modifying the PAN-based precursor fiber is not particularly limited. For example, a method of treating the precursor fiber by allowing it to stay in a liquid phase or a gas phase, or a method of applying the compound to the surface of the precursor fiber and treating the precursor fiber can be used.

Among them, a method of modifying a PAN-based precursor fiber in a solution containing a thiolate-based compound or a solution containing a thiolate-based compound and an oxidizing agent is preferable from the viewpoint of excellent operability and productivity.
[Thiolate compounds]
Thiolate-based compounds have a high nucleophilicity and a property of being highly polarized, which enables a fast flame-resistant reaction in the present invention. The thiolate-based compound may be any compound that exists as a thiolate in the reaction system.

  The thiolate-based compound is a compound selected from the following general formula (1) or formula (2).

  (In the formula (1), M represents an alkali metal, and R is selected from the group consisting of a hydrocarbon group and an aryl group. R is a hydroxyl group, an amino group, a nitro group, a thiol group, an imino group, a nitrile group, It can contain at least one functional group selected from azo groups.)

(In the formula (2), M represents an alkaline earth metal, and R is selected from the group consisting of a hydrocarbon group and an aryl group. R represents a hydroxyl group, an amino group, a nitro group, a thiol group, an imino group, a nitrile. And at least one functional group selected from azo and azo groups.)
The thiolate compound can be easily synthesized generally by mixing and reacting a thiol compound with a metal hydroxide or the like. By performing the synthesis in a nitrogen atmosphere, side reactions can be suppressed.

Examples of thiols that can be used in the synthesis of thiolate-based compounds include, for example, alkyl thiols such as methyl mercaptan, ethyl mercaptan, propyl mercaptan, butyl mercaptan, pentyl mercaptan, hexyl mercaptan, heptyl mercaptan, octyl mercaptan, and structural isomers thereof. Thiols having a hydroxyl group such as mercaptoethanol, mercaptopropanol, mercaptobutanol, thioglycerol, thiodiethanol, dithiothreitol, thioglycolic acid, ammonium thioglycolic acid, sodium thioglycolic acid, potassium thioglycolic acid, thiolactic acid, etc. Thiols having a carboxyl group, or aminoethanethiol, aminopropanethiol, aminobutanethiol, aminopentane Alkanes having a plurality of amino groups, such as monoamino-substituted alkanethiols such as all, aminohexanethiol, aminoheptanethiol, and aminooctanethiol; and diamino-substituted / triamino-substituted / tetraamino-substituted / pentaamino-substituted alkanethiols of the same type. Thiols can be mentioned.
Thiolate-based compounds are known to exist in the form of alkali metal salts or alkaline earth metal salts. In the present invention, the alkali metals include lithium, sodium and potassium, and the alkaline earth metals include beryllium, magnesium and calcium. Sodium and potassium are preferred because the raw materials are inexpensive and the production stability of the flame-resistant fiber of the present invention is excellent.
The thiolate-based compound in the present invention can have one or more types of functional groups or structures selected from the group consisting of hydrocarbon groups and aryl groups, in addition to metal ions and thiolate groups. In addition, the thiolate-based compound of the present invention has a functional group having an element such as oxygen, nitrogen, and sulfur, so that the reactivity and solubility with the PAN-based precursor fiber are excellent. Is preferred. More specifically, the thiolate compound of the present invention can contain at least one functional group selected from a hydroxyl group, an amino group, a nitro group, a thiol group, and an azo group.
[Oxidant]
As the oxidizing agent used in the production method of the present invention, a compound containing at least one nitrogen atom is suitable. For example, a compound having at least one functional group selected from the group consisting of a nitro group, a nitroso group, an N-hydroxy structure, an N-oxide structure, and an N-oxyl structure is preferable from the viewpoint of excellent reaction efficiency of a flame-resistant reaction. In particular, a compound containing a nitro group is preferred because it is easy to handle and has high oxidizability. More specifically, aromatic nitro compounds such as nitrotoluene, nitrobenzene, nitroxylene, nitronaphthalene, nitrocatechol, and aminophenol are preferable from the viewpoint of excellent boiling point, solubility, and reaction efficiency.

Alternatively, an oxidizing agent selected from the group consisting of quinone compounds and metal oxides such as potassium permanganate and sodium permanganate can also be used.
[Oxidation reaction using thiolate compound and oxidizing agent]
The method of modifying the PAN-based precursor fiber may be a batch type or a continuous type, and can be selected according to the purpose. For example, a method can be used in which PAN-based precursor fibers are drawn from a bobbin or a fiber container, immersed in a solution, and continuously treated. Alternatively, a method in which the PAN-based precursor fiber is immersed in a solution in a bobbin or wrapped state and then batch-processed can be used. The method of treating a PAN-based precursor fiber in a bobbin wound state is preferable from the viewpoint of simplifying equipment and reducing costs.

  In the present invention, when a PAN-based precursor fiber is modified in a solution containing a thiolate-based compound or in a solution containing a thiolate-based compound and an oxidizing agent, the solution contains 100 parts by mass of a thiolate-based compound with respect to 100 parts by mass of a solvent. A solution containing 1 part by mass or more and 150 parts by mass or less of the compound can be used. It is preferably from 5 parts by mass to 140 parts by mass, more preferably from 10 parts by mass to 130 parts by mass. By appropriately controlling the concentration of the thiolate-based compound in the solution, the precursor fiber can be uniformly subjected to a flame-proof treatment up to the inside of the fiber.

  When an oxidizing agent is further contained, 1 to 150 parts by mass of the oxidizing agent can be added to 100 parts by mass of the solvent. Preferably it is 10 to 140 parts by mass, more preferably 20 to 130 parts by mass. By appropriately controlling the concentration of the oxidizing agent, the precursor fibers can be uniformly subjected to a flame-proof treatment even inside the fibers.

  The thiolate-based compound and the oxidizing agent are preferably dissolved in a solvent and used in the form of a solution. If the oxidizing agent is not soluble in the solvent, it may be used in the form of a suspension or emulsion.

  The solvent used in the present invention is preferably a polar solvent from the viewpoint of the solubility of the thiolate compound.

  The higher the boiling point of the solvent, the more preferable it is, specifically, preferably 120 ° C. or higher, more preferably 150 ° C. or higher, and further preferably 180 ° C. or higher.

  The solvent is preferably a water-soluble solvent, and examples thereof include a solvent having a hydroxyl group, an amino group, an amide group, a sulfonyl group, a sulfone group, a mercapto group, or the like.

  Specifically, glycol solvents such as ethylene glycol, diethylene glycol and triethylene glycol, aprotic polar solvents such as DMSO, DMF, DMAc and N-methylpyrrolidone, monoethanolamine, diethanolamine, triethanolamine, N-amino It is possible to use an amine solvent such as ethylethanolamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, N-aminoethylpiperazine, orthophenylenediamine, metaphenylenediamine, paraphenylenediamine, or water. it can. The solvents mentioned above can be used alone or in combination of two or more.

  The temperature for modifying the PAN-based precursor fiber is preferably from 120 ° C to 250 ° C from the viewpoint of reactivity, and more preferably from 160 ° C to 250 ° C. If the temperature is lower than 120 ° C., the flame-resistant reaction may be incomplete. If the temperature is higher than 250 ° C., the thiolate compound may be dimerized to generate a disulfide compound.

  Further, the modification treatment of the PAN-based precursor fiber may be performed under a pressurized state. By performing the denaturation treatment under pressure, it is possible to obtain the same effect at a lower temperature as compared with the case where the treatment is performed under the atmospheric pressure, and it is possible to further denature the precursor fiber more quickly. It becomes possible. The pressurizing condition is preferably from 0.18 MPa to 3.98 MPa. When it is 0.11 MPa or more and less than 0.18 MPa, the effect of rapidly denaturing the inside of the precursor fiber is insufficient, and when it exceeds 3.98 MPa, fusion between fibers tends to occur.

  When the PAN-based precursor fiber is modified under a pressurized state, a commercially available autoclave device can be used.

  When the denaturation is performed under a pressurized state, the solvent is preferably an aqueous solvent, and specific examples thereof include water.

  When the denaturation is performed under a pressurized state, the denaturation can be performed at a temperature of 120 ° C. or more and 250 ° C. or less and a time of 30 seconds or more and 120 minutes or less. If the temperature is lower than 120 ° C., the flame-resistant reaction may be incomplete. If the temperature is higher than 250 ° C., the thiolate compound may be dimerized to generate a disulfide compound. By performing the modification for 30 seconds or more and 120 minutes or less, the flame resistance reaction can be sufficiently advanced, and the physical properties of the finally obtained carbon fiber become excellent.

  When denatured under the above-mentioned pressurized state, it is necessary to carry out the treatment so that the specific gravity of the polyacrylonitrile-based flame-resistant fiber is 1.24 to 1.55 and the sulfur content is 0.1 to 30% by mass. It is.

If the specific gravity is less than 1.24, not only the heat resistance is insufficient, but the thread breakage occurs in the subsequent carbonization step, the operability is deteriorated, and the quality and quality of the obtained carbon fiber may be reduced. If the temperature exceeds 55 ° C., the densification in the subsequent pre-carbonization step is hindered, and the quality and quality of the obtained carbon fiber may be reduced. The specific gravity of the flame resistant fiber is more preferably 1.30 or more and 1.50 or less, and still more preferably 1.33 or more and 1.38 or less.
If the sulfur content is less than 0.1% by mass, voids may appear to cause a decrease in strength, and if it exceeds 30% by mass, the elastic modulus may be significantly reduced.

  The modification of the PAN-based precursor fiber is preferably performed for 30 seconds or more and 120 minutes or less. By performing the modification for 30 seconds or more and 120 minutes or less, the flame resistance reaction can be sufficiently advanced, and the physical properties of the finally obtained carbon fiber become excellent. 30 seconds or more and 60 minutes or less are desirable from the viewpoint of productivity.

  The modification of the PAN-based precursor fiber is preferably performed under the condition that the sulfur content of the flame-resistant fiber is in the range of 0.30% by mass to 30% by mass. If the sulfur content is less than 0.30 mass%, the progress of flame resistance becomes insufficient, and fluff is likely to be generated in the carbonization step. If it is more than 30% by mass, the generation of gases such as sulfur trioxide and thiazole in the carbonization step becomes remarkable, and the reduction in carbonization yield becomes remarkable. The sulfur content is preferably from 1.0% by mass to 18% by mass, more preferably from 5.0% by mass to 15% by mass.

  The measurement of the sulfur content and the specific gravity in the present invention is performed by the method described later.

The modified flame resistant fiber may be washed with water or an acidic solution and then introduced into the carbonization step. By passing the flame-resistant fiber through water or an acidic solution, metal ions (alkali metal, alkaline earth metal) derived from the thiolate-based compound attached to or bonded to the flame-resistant fiber can be removed.
[PAN flame resistant fiber]
According to the above method, the PAN-based precursor fiber is modified with a thiolate-based compound or a thiolate-based compound and an oxidizing agent to obtain a flame-resistant fiber. area ratio of the infrared absorption spectrum in the range of the is 2240 ± 60cm ^-1 or 2940 ± 160cm ^-1 measured spectrophotometrically, as sulfur content and specific gravity of the flame resistant fiber, a constant value range, processing Is preferred.

Specifically, for the PAN-based flame-resistant fiber and the PAN-based precursor fiber obtained by the above method, the spectral area of the infrared absorption spectrum (A) in the range of 2240 ± 60 cm ⁻¹ measured by infrared spectroscopy is determined. It is preferable to perform the treatment under the condition that Abs _{2240 ± 60} calculated by the following general formula (3) is 70% or less.

By setting Abs _{2240 ± 60} to 70% or less, stable carbon fibers can be produced in the carbonization step following the flame-resistance step. Abs _{2240 ± 60} is preferably at most 50%, more preferably at most 30%. The lower limit is not particularly limited, and can be 0%. The infrared spectroscopy is performed by a method described later.

Further, the PAN-based flame-resistant fiber and the PAN-based precursor fiber obtained by the above-mentioned method are described below using the area of the infrared absorption spectrum (B) within the range of 2940 ± 160 cm ⁻¹ measured by infrared spectroscopy. Abs _{2940 ± 160} calculated by the equation (4) is preferably set to 70% or less. By performing the treatment under the condition that Abs _{2940 ± 160} is 70% or less, it is possible to suppress fiber breakage in the carbonization step after the flame resistance step, and to stably produce carbon fibers. Abs _{2940 ± 160} is preferably at most 50%, more preferably at most 30%. Note that the lower limit is not particularly limited and may be 0%.

Using the infrared absorption spectrum (A) in the range of 2240 ± 60 cm ⁻¹ and the infrared absorption spectrum (B) in the range of 2940 ± 160 cm ^{−1 in} the infrared spectroscopic measurement of the flame resistant fiber, Abs _2240/2940 calculated by the general formula (5) is preferably 0.05 or more and 0.60 or less. When Abs _2240/2940 is 0.05 or more, the fiber can have sufficient flame resistance. When the value of Abs _2240/2940 is 0.60 or less, the oxidation treatment has sufficiently proceeded, so that the carbonization treatment step performed after the oxidation treatment can be performed stably in a short time. Moreover, if it is 0.05 or more, the precursor fiber is subjected to excessive heat treatment, so that damage to the fiber can be suppressed.

The infrared spectroscopy is performed by a method described later.
[Method for producing carbon fiber, and carbon fiber]
The carbon fiber of the present invention is obtained by further carbonizing the flame resistant fiber obtained by the above method. Specifically, a carbon fiber can be obtained by subjecting the flame resistant fiber to a heat treatment (carbonization treatment) at a high temperature in an inert atmosphere. For example, a carbon fiber can be obtained by treating the flame-resistant fiber at 300 ° C. or higher and lower than 2000 ° C. in an inert atmosphere. The lower limit of the temperature is preferably 800 ° C or higher, more preferably 1000 ° C or higher, and still more preferably 1200 ° C or higher. The upper limit of the temperature is more preferably 1800 ° C or lower, and further preferably 1600 ° C or lower. Further, by heating the obtained carbon fiber under an inert atmosphere at a temperature of 2,000 ° C. or more and 3000 ° C. or less, a carbon fiber having a developed graphite structure can be obtained.

  The specific gravity of the carbon fiber of the present invention is preferably from 1.5 to 2.4, more preferably from 1.6 to 2.1, even more preferably from 1.6 to 1.9. When the specific gravity is 1.5 or more, it is easy to sufficiently develop strength. When the specific gravity is 2.4 or less, generation of defects can be suppressed.

  The sulfur content of the carbon fiber of the present invention is preferably from 0.1% by mass to 5.0% by mass from the viewpoint of physical properties such as strength and elastic modulus. The sulfur content is more preferably from 0.2% by mass to 3.0% by mass, even more preferably from 0.3% by mass to 1.0% by mass. If the sulfur content is less than 0.1% by mass, voids may appear to cause a decrease in strength, and if it is greater than 3.0% by mass, the elastic modulus may be significantly reduced.

[Surface treatment of carbon fiber]
The carbon fiber of the present invention may be electrolytically treated for surface modification. As the electrolytic solution used for the electrolytic treatment, for example, an acidic solution such as sulfuric acid, nitric acid, and hydrochloric acid, an alkali such as sodium hydroxide, potassium hydroxide, and tetraethylammonium hydroxide or a salt thereof can be used as an aqueous solution. The amount of electricity required for the electrolytic treatment can be appropriately selected depending on the applied carbon fiber.

  Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto. In the examples, each physical property value and characteristic were measured by the following methods.

<Swelling degree of coagulated yarn>
From the mass (W) after the adhering water on the surface of the coagulated yarn was sufficiently removed with a blotting paper and the mass (W0) after drying this at 150 ° C. for 1 hour using a hot air dryer, the following calculation was performed. The degree of swelling (B) (%) of the coagulated yarn was determined using the equation.

B (%) = {(W−W0) / W0} × 100
<Polymer concentration of partially cyclized polymer-containing solution and flame-resistant polymer-containing solution>
When the polymer was water-soluble, the polymer concentration was measured by the following method. About 15 mg of the polymer-containing solution was precisely weighed, and remained at a time when heated from 25 ° C. to 300 ° C. at a rate of 20 ° C./min from 25 ° C. using a thermal mass balance (product name: EXSTER6000, manufactured by SII Nanotechnology Inc.). The solid content was measured as the mass of the polymer. The mass of the polymer was divided by the mass of the polymer-containing solution to determine the polymer concentration (% by mass) in percentage.

  On the other hand, when the polymer completely solidified in water, the polymer concentration was measured by the following method. 5 g of the polymer-containing solution was treated with 1 L of water for 30 minutes. This treatment was repeated three times, and only the solid component was collected and dried at 120 ° C. for 1 hour to separate the polymer. The mass of the polymer was measured, and the mass of the polymer was divided by the mass of the polymer-containing solution to obtain the polymer concentration (% by mass) in percentage.

<Sulfur content>
The sulfur content was measured using an elemental analyzer (product name: vario EL cube, manufactured by Siebel-Hegner). The measurement conditions were as follows: combustion tube = 1150 ° C., reduction tube = 850 ° C., measurement mode = CHNS. The standard substance was sulfanilic acid (C: 41.61%, H: 4.07%, N: 8.09%, S: 18.50%).

<Viscosity of partially cyclized polymer-containing solution and flame-resistant polymer-containing solution>
The viscosity was measured using a cone-plate type rheometer (product name: AR550, manufactured by TA Instruments). The measurement was performed from 25 to 150 ° C, and the value at 25 ° C was used as a representative value.

<Single fiber tensile test for various fibers>
A tensile test was performed according to JIS L1015 (1981). A single fiber with a length of 25 mm is placed on a piece of paper with a smooth and glossy surface, and while the single fiber is loosely stretched, 2.5 mm at each end is fixed to the piece of paper with an adhesive to bond the single fiber. The length (sample length) of the portion not fixed with the agent was about 20 mm, and this was used as a sample of a single fiber tensile tester. This sample was attached to the grip of a single fiber tensile tester, and the monofilament was not cut near the upper grip, but only the piece of paper was cut with scissors, and the measurement was performed at a pulling speed of 20 mm / min. The measurement was performed 50 times, and the average value was taken as the tensile test result.

<Specific gravity measurement>
The specific gravity was measured in accordance with JIS R 7603.
<Measurement of carbonization yield>
A differential thermal / thermogravimetric simultaneous measurement device EXSTAR6000 manufactured by Seiko Instruments Inc. was used. The fibers were cut with scissors and a mortar, and the mass was measured at a heating rate of 40 ° C./min under a nitrogen atmosphere of 10 mg and 400 mL / min. The material of the sample pan was platinum, and α-alumina was used as a reference material.
The sample after the reaction treatment at a predetermined temperature (300 ° C. or lower) in the examples is referred to as a “pre-sample”, and the sample after heating to 970 ° C. is referred to as a “post-sample”. Using the mass (g) (the mass was measured to the last three digits), it was calculated by the following formula.
Carbonization yield (%) = mass (g) of rear sample / mass (g) of previous sample × 100
<Infrared spectroscopy>
The fiber bundle was cut every 1 m, and a portion of each of the three fiber bundles at the end of 10 mm was further cut and collected, and chopped in a glass bottle. Further, the sample was ground in a mortar to obtain a powdery sample. 1 mg of a sample was weighed, mixed with 200 mg of dried KBr in a mortar, and pulverized. This was pressed by a press machine to obtain a disc-shaped tablet having a diameter of 13 mm and a thickness of 0.5 mm, and transmission measurement was performed with an FT-IR apparatus (product name: Magna860, manufactured by Nicolet).
The spectrum was defined as a baseline using the image processing software Stream Essentials Version 1.8, and the area of the spectrum was quantitatively evaluated.
[Example 1 (reference) ]
A PAN-based polymer (number-average molecular weight = 190,000) obtained by polymerizing AN / acrylamide / methacrylic acid = 96/3/1 (mass ratio) was dissolved in DMSO to prepare a PAN-based polymer-containing solution. The solution containing the PAN-based polymer was heated to 160 ° C., and when the temperature became constant, a thiolate salt prepared from thioglycerol and sodium hydroxide was added. A containing solution was obtained. The viscosity of the partially cyclized polymer-containing solution was 55 poise. The polymer concentration was 18%. A part of the partially cyclized polymer-containing solution was put into warm water, the solidified polymer was separated by filtration, dried at 120 ° C., and analyzed for the partially cyclized polymer. Abs _{2240 ± 60} of the partially cyclized polymer was 17%, the sulfur content was 12%, and the number average molecular weight was 197,000.

10% by mass of palladium carbon powder was further added to the partially cyclized polymer-containing solution and reacted at 160 ° C. for 120 minutes to obtain a black flame-resistant polymer-containing solution. The amount of each raw material charged was PAN-based polymer / DMSO / thiolate salt / palladium carbon = 10/76/13/1 (mass ratio). The viscosity of the solution containing the flame resistant polymer was 60 poise at 25 ° C. Further, the polymer concentration was 15%. After removing the insoluble palladium carbon powder from the flame-resistant polymer-containing solution by pressure filtration, a part of the filtrate was poured into warm water, the solidified polymer was separated by filtration, and dried at 120 ° C. The polymer was recovered. Abs _{2240 ± 60} of the flame resistant polymer was 12%, Abs _{2940 ± 160} was 32%, the sulfur content was 10.2% by mass, the number average molecular weight was 196,000, and the specific gravity was 1.30.

  The flame-resistant polymer-containing solution subjected to pressure filtration was fiberized by a wet spinning device. Specifically, after passing the solution containing the flame-resistant polymer through the sintering filter, a mixed solution of DMSO and water at 20 ° C. (DMSO / water = 50/50 (DMSO / water = 50/50) through a die having 100 holes having a diameter of 0.05 mm. (Volume ratio)) to obtain a coagulated yarn. At this time, the degree of swelling of the coagulated yarn was 230%. Further, in a hot water bath at 100 ° C., the coagulated yarn was drawn three times while replacing most of the solvents with water. Then, after applying the amino silicone oil agent, it was dried in a hot air circulating furnace at 220 ° C. for 3 minutes to obtain a flame resistant fiber. The elongation of the flame resistant fiber was 5%, and the fineness was 1.0 dtex.

Further, the flame-resistant fiber bundle obtained from the flame-resistant fiber was preliminarily carbonized at 300 to 800 ° C in a nitrogen atmosphere, and then carbonized at 1500 ° C in a nitrogen atmosphere to obtain a carbon fiber bundle. The carbon fiber bundle had a sulfur content of 9%, a tensile modulus of 200 GPa, and a specific gravity of 1.81.
[Example 2 (reference) ]
A partially cyclized polymer-containing solution and a black flame-resistant polymer-containing solution were obtained in the same manner as in Example 1 except that DMF was used instead of DMSO as a solvent.

The viscosity of the partially cyclized polymer-containing solution was 70 poise. Further, the polymer concentration was 16%. Abs _{2240 ± 60} of the partially cyclized polymer was 20%, the sulfur content was 16%, and the number average molecular weight was 198,000.

The viscosity of the solution containing the flame resistant polymer was 75 poise at 25 ° C. Further, the polymer concentration was 16%. Abs _{2240 ± 60} of the flame resistant polymer was 13%, Abs _{2940 ± 160} was 36%, the sulfur content was 9.5% by mass, the number average molecular weight was 194,000, and the specific gravity was 1.31.

Thereafter, in the fiberization of the flame-resistant polymer-containing solution, the same procedure as in Example 1 was carried out except that a mixed solution of DMF and water (DMF / water = 50/50 (volume ratio)) was used instead of the mixed solution of DMSO and water. Similarly, a coagulated yarn, a flame-resistant fiber, a flame-resistant fiber bundle, and a carbon fiber bundle were obtained. The degree of swelling of the coagulated yarn was 250%. The elongation of the flame resistant fiber was 6%, and the fineness was 1.1 dtex. The carbon fiber bundle had a sulfur content of 8%, a tensile modulus of 210 GPa, and a specific gravity of 1.80.
[Example 3 (reference) ]
A partially cyclized polymer-containing solution and black were prepared in the same manner as in Example 2 except that the charged amount of each raw material was PAN-based polymer / DMF / thiolate salt / palladium carbon = 10/85/4/1 (mass ratio). Was obtained.

The viscosity of the partially cyclized polymer-containing solution was 82 poise. Further, the polymer concentration was 12%. Abs _{2240 ± 60} of the partially cyclized polymer was 40%, the sulfur content was 3.5%, and the number average molecular weight was 191,000.

The viscosity of the solution containing the flame resistant polymer was 90 poise at 25 ° C. Further, the polymer concentration was 12%. Abs _{2240 ± 60} of the flame resistant polymer was 22%, Abs _{2940 ± 160} was 45%, the sulfur content was 2.8% by mass, the number average molecular weight was 190,600, and the specific gravity was 1.27.

Thereafter, a coagulated yarn, a flame-resistant fiber, a flame-resistant fiber bundle, and a carbon fiber bundle were obtained in the same manner as in Example 2. The degree of swelling of the coagulated yarn was 190%. The elongation of the flame resistant fiber was 4%, and the fineness was 1.1 dtex. The carbon fiber bundle had a sulfur content of 2%, a tensile modulus of 190 GPa, and a specific gravity of 1.81.
[Example 4 (reference) ]
A partially cyclized polymer-containing solution and a black flame-resistant polymer-containing solution were obtained in the same manner as in Example 2 except that the reaction temperature was changed to 120 ° C.

The viscosity of the partially cyclized polymer-containing solution was 80 poise. Further, the polymer concentration was 14%. Abs _{2240 ± 60} of the partially cyclized polymer was 30%, the sulfur content was 6.1%, and the number average molecular weight was 193,000.

The viscosity of the solution containing the flame-resistant polymer was 92 poise at 25 ° C. Further, the polymer concentration was 14%. Abs _{2240 ± 60} of the flame resistant polymer was 23%, Abs _{2940 ± 160} was 49%, the sulfur content was 10.8% by mass, the number average molecular weight was 193,000, and the specific gravity was 1.30.

Thereafter, a coagulated yarn, a flame-resistant fiber, a flame-resistant fiber bundle, and a carbon fiber bundle were obtained in the same manner as in Example 2. The degree of swelling of the coagulated yarn was 240%. The elongation of the flame resistant fiber was 4%, and the fineness was 1.1 dtex. The carbon fiber bundle had a sulfur content of 9%, a tensile modulus of 200 GPa, and a specific gravity of 1.80.
[Example 5 (reference) ]
A partially cyclized polymer-containing solution and a black flame-resistant polymer-containing solution were obtained in the same manner as in Example 2 except that a PAN-based polymer (number average molecular weight = 191,000) containing 100% AN was used.

The viscosity of the partially cyclized polymer-containing solution was 68 poise. Further, the polymer concentration was 16%. Abs _{2240 ± 60} of the partially cyclized polymer was 22%, the sulfur content was 19%, and the number average molecular weight was 196,000.

The viscosity of the solution containing the flame-resistant polymer was 80 poise at 25 ° C. The polymer concentration was 18%. Abs _{2240 ± 60} of the flame resistant polymer was 11%, Abs _{2940 ± 160} was 33%, the sulfur content was 11.5% by mass, the number average molecular weight was 194,000, and the specific gravity was 1.33.

Thereafter, a coagulated yarn, a flame-resistant fiber, a flame-resistant fiber bundle, and a carbon fiber bundle were obtained in the same manner as in Example 2. The degree of swelling of the coagulated yarn was 200%. The elongation of the flame resistant fiber was 6%, and the fineness was 1.3 dtex. The carbon fiber bundle had a sulfur content of 3%, a tensile modulus of 210 GPa, and a specific gravity of 1.83.
[Comparative Example 1]
Monoethanolamine (MEA) was used in place of the thiolate salt, and orthonitrotoluene (ONT) was used in place of the palladium carbon powder. The charged amount of each raw material was PAN / DMSO / MEA / ONT = 10/78/6/6 ( Mass ratio), a partially cyclized polymer-containing solution and a black flame-resistant polymer-containing solution were obtained in the same manner as in Example 1.

The viscosity of the partially cyclized polymer-containing solution was 0.4 poise. Further, the polymer concentration was 11%. Abs _{2240 ± 60} of the partially cyclized polymer was 32%, the sulfur content was 0.02%, and the number average molecular weight was 5,600.

The viscosity of the flame-resistant polymer-containing solution was 1 poise at 25 ° C. Further, the polymer concentration was 15%. Abs _{2240 ± 60} of the flame resistant polymer was 20%, Abs _{2940 ± 160} was 40%, the sulfur content was 0.01%, the number average molecular weight was 5,500, and the specific gravity was 1.30.

Thereafter, a coagulated yarn was obtained in the same manner as in Example 1. The degree of swelling of the coagulated yarn was 240%. Further, in a hot water bath at 100 ° C., an attempt was made to draw the coagulated yarn three times while replacing most of the solvents with water, but the fiber could not be drawn and the fiber was cut, and a flame resistant fiber could not be obtained. Was.
[Comparative Example 2]
Monoethanolamine (MEA) was used in place of the thiolate salt, and orthonitrotoluene (ONT) was used in place of the palladium carbon powder. The charged amount of each raw material was PAN / DMF / MEA / ONT = 10/78/6/6 ( Mass ratio), a partially cyclized polymer-containing solution and a black flame-resistant polymer-containing solution were obtained in the same manner as in Example 2.

The viscosity of the partially cyclized polymer-containing solution was 4 poise. Further, the polymer concentration was 12%. Abs _{2240 ± 60} of the partially cyclized polymer was 35%, the sulfur content was 0.02%, and the number average molecular weight was 6,300.

The viscosity of the solution containing the flame-resistant polymer was 6 poise at 25 ° C. Further, the polymer concentration was 14.2%. Abs _{2240 ± 60} of the flame resistant polymer was 23%, Abs _{2940 ± 160} was 42%, the sulfur content was 0.01%, the number average molecular weight was 6,200, and the specific gravity was 1.32.

Thereafter, a coagulated yarn was obtained in the same manner as in Example 2. The degree of swelling of the coagulated yarn was 207%. Further, in a hot water bath at 100 ° C., an attempt was made to draw the coagulated yarn three times while replacing most of the solvents with water, but the fiber could not be drawn and the fiber was cut, and a flame resistant fiber could not be obtained. Was.
[Comparative Example 3]
Monoethanolamine (MEA) was used in place of the thiolate salt, and orthonitrotoluene (ONT) was used in place of the palladium carbon powder. The charged amount of each raw material was PAN / DMF / MEA / ONT = 13/78/3/6 ( Mass ratio), a partially cyclized polymer-containing solution and a black flame-resistant polymer-containing solution were obtained in the same manner as in Example 5.

The viscosity of the partially cyclized polymer-containing solution was 9 poise. Further, the polymer concentration was 15%. Abs _{2240 ± 60} of the partially cyclized polymer was 78%, the sulfur content was 0%, and the number average molecular weight was 23,000.

The viscosity of the solution containing the flame resistant polymer was 9 poise at 25 ° C. The polymer concentration was 15.0%. Abs _{2240 ± 60} of the flame resistant polymer was 56%, Abs _{2940 ± 160} was 55%, the sulfur content was 0%, the number average molecular weight was 8,400, and the specific gravity was 1.22.

Thereafter, a coagulated yarn was obtained in the same manner as in Example 5. The degree of swelling of the coagulated yarn was 170%. Further, in a hot water bath at 100 ° C., an attempt was made to draw the coagulated yarn three times while replacing most of the solvents with water, but the fiber could not be drawn and the fiber was cut, and a flame resistant fiber could not be obtained. Was.
[Comparative Example 4]
Monoethanolamine (MEA) was used in place of the thiolate salt, and orthonitrotoluene (ONT) was used in place of the palladium carbon powder. The charged amount of each raw material was PAN / DMF / MEA / ONT = 13/78/6/3 ( Mass ratio), a partially cyclized polymer-containing solution and a black flame-resistant polymer-containing solution were obtained in the same manner as in Example 5.

The viscosity of the partially cyclized polymer-containing solution was 2 poise. Further, the polymer concentration was 13%. Abs _{2240 ± 60} of the partially cyclized polymer was 32%, the sulfur content was 0%, and the number average molecular weight was 6,000.

The viscosity of the solution containing the flame-resistant polymer was 7 poise at 25 ° C. The polymer concentration was 15.0%. Abs _{2240 ± 60} of the flame resistant polymer was 20%, Abs _{2940 ± 160} was 84%, the sulfur content was 0%, the number average molecular weight was 5,800, and the specific gravity was 1.24.

Thereafter, a coagulated yarn was obtained in the same manner as in Example 5. The degree of swelling of the coagulated yarn was 210%. Further, in a hot water bath at 100 ° C., an attempt was made to draw the coagulated yarn three times while replacing most of the solvents with water, but the fiber could not be drawn and the fiber was cut, and a flame resistant fiber could not be obtained. Was.
[Comparative Example 5]
A partially cyclized polymer-containing solution and black were prepared in the same manner as in Example 2 except that the charged amount of each raw material was PAN-based polymer / DMF / thiolate salt / palladium carbon = 10/69/20/1 (mass ratio). Was obtained.

The viscosity of the partially cyclized polymer-containing solution was 50 poise. Further, the polymer concentration was 22%. Abs _{2240 ± 60} of the partially cyclized polymer was 8%, the sulfur content was 22%, and the number average molecular weight was 206,000.

The viscosity of the solution containing the flame resistant polymer was 64 poise at 25 ° C. The polymer concentration was 20%. Abs _{2240 ± 60} of the flame resistant polymer was 5%, Abs _{2940 ± 160} was 27%, the sulfur content was 26% by mass, the number average molecular weight was 194,000, and the specific gravity was 1.38.

Thereafter, a coagulated yarn, a flame-resistant fiber, a flame-resistant fiber bundle, and a carbon fiber bundle were obtained in the same manner as in Example 2. However, during carbonization, sulfur trioxide or thiazole ring-based gas generation was observed. The degree of swelling of the coagulated yarn was 250%. The elongation of the flame resistant fiber was 6%, and the fineness was 1.4 dtex. The carbon fiber bundle had a sulfur content of 6%, a tensile modulus of 150 GPa, and a specific gravity of 1.80.
[Example 6]
A PAN copolymer (number average molecular weight 190,000) obtained by polymerizing AN / acrylamide (AAM) / methacrylic acid (MAA) = 96/3/1 (mass ratio) is dissolved in dimethylacetamide (DMAc). Then, a spinning dope having a concentration of 20% by mass was prepared.

  The spinning stock solution was kept in a coagulation bath (aqueous solution having a DMAc concentration of 50% by volume) controlled at 30 ° C. by using a spinneret having 3,000 holes and a hole diameter of 0.15 mm while maintaining the temperature at 40 ° C. Into a coagulated yarn by a wet spinning method for coagulation.

  After washing the coagulated yarn with water, the coagulated yarn was drawn 3.5 times in warm water, and an amino-modified silicone-based silicone oil was further applied to obtain a drawn yarn.

This drawn yarn is dried and densified using a heating roller at 160 ° C., and then drawn in a pressure steam of 0.3 MPa-G so that the total drawing ratio becomes 13 times. A PAN-based precursor fiber having a fineness of 1.5 dtex and 3,000 single fibers was obtained. The obtained PAN-based precursor fiber was immersed in a solution containing the components shown in Table 2 and denatured at 200 ° C. for 30 seconds to obtain a flame-resistant fiber. 1, posted infrared absorption spectrum after modification and before modifying the PAN-based precursor fiber (flame-resistant fiber).

  The flame resistant fiber was heated from 300 ° C. to 1000 ° C. at a rate of 500 ° C./min in an inert atmosphere and then carbonized at a maximum temperature of 1450 ° C. in an inert atmosphere to obtain a carbon fiber. The properties of the obtained flame-resistant fiber and carbon fiber were measured by the above-mentioned method. Table 2 shows the experimental conditions, and Tables 4 and 6 show the measurement results.

With respect to Example 6 and below and Comparative Example 6 and below, the production conditions of each Example are shown in Tables 3 and 4, and the characteristics of the obtained flame-resistant fiber and carbon fiber are shown in Tables 5 to 7. In Tables 2 to 6, the abbreviations of the reagents used are as shown in the table below. In the table below, AAM indicates acrylamide and MAA indicates methacrylic acid.

[Examples 7 to 11]
A flame-resistant fiber and a carbon fiber were obtained in the same manner as in Example 6 except that the reaction time was set as shown in Table 1 (1-120 minutes), and each physical property was evaluated. Table 2 shows the experimental conditions, and Tables 4 and 6 show the measurement results.
[Comparative Example 6]
Except that the thiolate-based compound and the oxidizing agent were not used, a flame-resistant fiber and a carbon fiber were obtained in the same manner as in Example 10, and each physical property was evaluated. Table 2 shows the experimental conditions, and Tables 4 and 6 show the measurement results.
[Comparative Example 7]
A flame-resistant fiber and a carbon fiber were obtained in the same manner as in Example 10 except that only the thiolate compound was omitted, and each physical property was evaluated. Table 2 shows the experimental conditions, and Tables 4 and 6 show the measurement results.
[Comparative Example 8]
A flame resistant fiber and a carbon fiber were obtained in the same manner as in Example 3 except that monoethanolamine was used instead of using the thiolate-based compound, and each physical property was evaluated. Table 2 shows the experimental conditions, and Tables 4 and 6 show the measurement results.
[Example 12]
A flame resistant fiber and a carbon fiber were obtained in the same manner as in Example 6 except that a PAN homopolymer was used as the PAN polymer, the reaction temperature was 120 ° C., the reaction time was 40 minutes, and the oxidizing agent was nitrobenzene. Each physical property was evaluated. Table 3 shows the experimental conditions, and Tables 5 and 6 show the measurement results.
Example 13
A flame-resistant fiber and a carbon fiber were obtained in the same manner as in Example 12 except that the reaction temperature was set to 150 ° C. and the reaction time was set to 20 minutes, and each physical property was evaluated. Table 3 shows the experimental conditions and Table 4 shows the measurement results.
[Example 14]
The flame-resistant fiber and the carbon fiber were prepared in the same manner as in Example 12 except that the thiolate compound was sodium-2-hydroxyethanethiolate, the oxidizing agent was orthonitrobenzene, the reaction temperature was 198 ° C., and the reaction time was 5 minutes. Then, each physical property was evaluated. Table 3 shows the experimental conditions, and Tables 4 and 6 show the measurement results.
[Example 15]
A flame-resistant fiber and a carbon fiber were obtained in the same manner as in Example 14 except that potassium-2-hydroxyethanethiolate was used as the thiolate-based compound, and each physical property was evaluated. Table 3 shows the experimental conditions and Table 5 shows the measurement results.
[Example 16]
A flame resistant fiber and a carbon fiber were obtained in the same manner as in Example 13 except that the thiolate-based compound was sodium-4-hydroxybenzenethiolate and the oxidizing agent was orthonitrotoluene, and each physical property was evaluated. Table 3 shows the experimental conditions, and Tables 5 and 6 show the measurement results.
[Example 17]
A flame-resistant fiber and a carbon fiber were obtained in the same manner as in Example 16 except that the thiolate-based compound was magnesium bis-2-hydroxyethanethiolate, and the compounding amount was as shown in Table 3, and each physical property was evaluated. did. Table 3 shows the experimental conditions, and Tables 5 and 6 show the measurement results.
[Example 18]
Example 12 was repeated except that the solvent was glycerin, the oxidizing agent was orthonitrotoluene, the blending amounts of the thiolate-based compound and the oxidizing agent were as shown in Table 3, the reaction temperature was 198 ° C., and the reaction time was 0.5 minute. Similarly, flame-resistant fibers and carbon fibers were obtained, and their physical properties were evaluated. Table 3 shows the experimental conditions, and Tables 5 and 6 show the measurement results.
[Example 19]
The flame-resistant fiber and the carbon fiber were prepared in the same manner as in Example 18, except that the solvent was ethylene glycol, the amounts of the thiolate-based compound and the oxidizing agent were as shown in Table 3, and the reaction time was 1.0 minute. Then, each physical property was evaluated. The experimental conditions are shown in Tables 3 and 6, and the measurement results are shown in Table 5.
[Example 20 (Reference Example) ]
Except that the oxidizing agent was not used and the reaction time was set to 120 minutes, flame-resistant fibers and carbon fibers were obtained and their physical properties were evaluated in the same manner as in Example 19. The experimental conditions are shown in Tables 3 and 6, and the measurement results are shown in Table 5.
[Comparative Example 9]
A flame-resistant fiber and a carbon fiber were obtained in the same manner as in Example 14 except that guanidine carbonate was used instead of the thiolate-based compound and N-hydroxyphthalimide was used as the oxidizing agent, and each physical property was evaluated. Table 3 shows the experimental conditions, and Tables 4 and 6 show the measurement results.
[Comparative Example 10]
The solvent was glycerin, the thiolate compound and the oxidizing agent were not used, the reaction temperature was 240 ° C., and the reaction time was 120 minutes, except that the flame-resistant fiber and the carbon fiber were obtained in the same manner as in Example 12. Physical properties were evaluated. The experimental conditions are shown in Tables 3 and 6, and the measurement results are shown in Table 5.
[Comparative Example 11]
The PAN-based precursor fiber used in Example 12 was heat-treated at a reaction temperature of 200 ° C. for 120 minutes in a condition where a solvent, a thiolate-based compound and an oxidizing agent were not used, that is, in air, to obtain a flame-resistant fiber and a carbon fiber. Then, each physical property was evaluated. Table 3 shows the experimental conditions, and Tables 5 and 6 show the measurement results.
[Example 21]
A flame resistant fiber and a carbon fiber were obtained in the same manner as in Example 8 except that the solvent was water, the oxidizing agent was nitrocatechol, the temperature was 200 ° C., and the pressure was 1.55 MPa. When processing at a pressure of 1.55 MPa, a commercially available autoclave device was used. The experimental conditions are shown in Table 7 and the measurement results are shown in Tables 8 and 9.
[Example 22]
A flame-resistant fiber and a carbon fiber were obtained in the same manner as in Example 21 except that the reaction time was 30 minutes, and each physical property was evaluated. The experimental conditions are shown in Table 7 and the measurement results are shown in Tables 8 and 9.
[Example 23]
Except that the reaction time was set to 60 minutes, a flame-resistant fiber and a carbon fiber were obtained in the same manner as in Example 21, and each physical property was evaluated. The experimental conditions are shown in Table 7 and the measurement results are shown in Tables 8 and 9.
[Comparative Example 12]
Example 22 was repeated except that the thiolate compound and the oxidizing agent were not used, but the fibers were fused during the reaction, and the fiber shape could not be maintained. The experimental conditions are shown in Table 7 and the measurement results are shown in Tables 8 and 9.

  In Table 1, TL indicates a thiolate salt, and Pd_C indicates palladium carbon.

According to the method for producing carbon fiber of the present invention , high-quality carbon fiber can be produced with high productivity. Further, the carbon fiber of the present invention has excellent mechanical properties and is suitable as a reinforcing fiber for a fiber-reinforced composite material, and also has excellent high-order workability.

Claims (3)

A polyacrylonitrile-based precursor fiber is modified with a thiolate-based compound and an oxidizing agent to obtain a polyacrylonitrile-based flame-resistant fiber having a specific gravity of 1.24 or more and 1.55 or less, and heat-treated at 300 ° C or more and 3000 ° C or less. So,
A method for producing a carbon fiber, wherein the modification is performed in a solution containing 100 parts by mass of a solvent and 1 part by mass to 150 parts by mass of a thiolate-based compound at 120 ° C. to 250 ° C. for 30 seconds to 120 minutes. A polyacrylonitrile-based precursor fiber is modified with a thiolate-based compound and an oxidizing agent to obtain a polyacrylonitrile-based flame-resistant fiber having a specific gravity of 1.24 or more and 1.55 or less, and heat-treated at 300 ° C or more and 3000 ° C or less. So,
A method for producing carbon fibers, wherein the polyacrylonitrile-based precursor fiber has a sulfur content of 0.1% by mass or more and 30% by mass or less. A polyacrylonitrile-based precursor fiber is modified with a thiolate-based compound and an oxidizing agent to obtain a polyacrylonitrile-based flame-resistant fiber having a specific gravity of 1.24 or more and 1.55 or less, and heat-treated at 300 ° C or more and 3000 ° C or less. So,
Performing the denaturation in an aqueous solvent,
The denaturation is performed at a temperature of 120 ° C. or more and 250 ° C. or less, a pressure of 0.18 MPa or more and 3.98 MPa or less, and a time of 30 seconds or more and 120 minutes or less,
Producing the carbon fiber, wherein the modification is performed so that the specific gravity of the polyacrylonitrile-based flame-resistant fiber is 1.24 to 1.55 and the sulfur content is 0.1 to 30% by mass. Method.