JP6900728B2 - Method for manufacturing carbon fiber precursor acrylic fiber and carbon fiber bundle - Google Patents

Description

The present invention relates to a method for producing a carbon fiber precursor acrylic fiber and a carbon fiber bundle.

Since carbon fiber has excellent mechanical strength, it is extremely useful as an automobile member, an aerospace material, a sports / leisure material, an industrial material such as a pressure vessel, and the demand is expanding. In addition, it is expected to be used in a wider range of fields in the future.

Conventionally, the carbon fiber is obtained through the following steps using a precursor fiber bundle in which carbon fiber precursor acrylic fibers made of an acrylonitrile-based polymer or the like are bundled. First, tens to hundreds of weights of precursor fiber bundles are subjected to flame-resistant heat treatment in an oxidizing atmosphere at 200 to 300 ° C. in a flame-resistant step, and the obtained flame-resistant fiber bundles are subjected to flame-resistant heat treatment at 300 ° C. or higher in a carbonization step. It is fired in an inert atmosphere to obtain a carbon fiber bundle (for example, Patent Document 1).

International Publication No. 2013/015210

However, due to the chemical reaction that occurs in the flame resistance step and the carbonization step (hereinafter, these steps are also collectively referred to as "firing step"), the decomposition product containing a carbon atom is released as a gas and the carbonization yield is increased. There were problems such as low productivity and poor productivity.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a carbon fiber precursor acrylic fiber having a high carbonization yield after a firing step. Another object of the present invention is to provide a method for producing a high-quality carbon fiber bundle with a high carbonization yield and high productivity.

The present invention has the following aspects.
[1] The structural unit (A) represented by the following general formula (1) is 0.5 to 30% by mass, and the structural unit (B) represented by the following general formula (2) is 70 to 99.5% by mass. %, Carbon fiber precursor acrylic fiber.

In formula (1), R ¹ , R ² and R ³ are independently hydrogen atom, hydroxy group, amino group, sulfhydryl group, nitrile group, nitro group, phosphono group, sulfone group, halogen atom and carbon number 1 respectively. Alkyl groups of ~ 12; aryl groups of 6-12 carbon atoms, alkyloxy groups of 1-12 carbon atoms, aryloxy groups of 6-12 carbon atoms, alkylthio groups of 1-12 carbon atoms, 6-12 carbon atoms an arylthio group or an acyl group having a carbon number of 1 to 13, ^{R 4} is an alkylene group or an arylene group having 6 to 12 carbon atoms having 1 to 12 carbon atoms.

In formula (2), R ⁵ and R ⁶ independently have a hydrogen atom, a hydroxy group, an amino group, a sulfhydryl group, a nitrile group, a nitro group, a phosphono group, a sulfone group, a halogen atom, and 1 to 12 carbon atoms. Alkyl group, aryl group having 6 to 12 carbon atoms, alkyloxy group having 1 to 12 carbon atoms, aryloxy group having 6 to 12 carbon atoms, alkylthio group having 1 to 12 carbon atoms, arylthio group having 6 to 12 carbon atoms or It is an acyl group having 1 to 13 carbon atoms.

[2] The fiber bundle composed of the carbon fiber precursor acrylic fiber according to [1] is heated at 220 to 300 ° C. in an oxidizing atmosphere for 90 minutes or less, and then 800 to 800 in an inert gas atmosphere. A method for producing a carbon fiber bundle, which is heated at 2000 ° C.

According to the present invention, it is possible to provide a carbon fiber precursor acrylic fiber having a high carbonization yield after a firing step.
Further, according to the present invention, it is possible to provide a method for producing a high-quality carbon fiber bundle with a high carbonization yield and high productivity.

Hereinafter, an embodiment of the carbon fiber precursor acrylic fiber of the present invention will be described.
In the present specification, "(meth) acrylic" is a general term for acrylic and methacrylic acid, "(meth) acrylate" is a general term for acrylate and methacrylate, and "(meth) allyl" is a general term for allyl. It is a general term for metallic.

"Carbon fiber precursor acrylic fiber"
The carbon fiber precursor acrylic fiber of the present embodiment comprises the acrylonitrile-based copolymer composition shown below (hereinafter, also referred to as “copolymer composition (X)”).

<Copolymer composition (X)>
The copolymer composition (X) contains the structural unit (A) and the structural unit (B) shown below. The copolymer composition (X) may further contain the structural unit (C) shown below.

(Structural unit (A))
The structural unit (A) is a structural unit represented by the following general formula (1).

In formula (1), R ¹ , R ² and R ³ are independently hydrogen atom, hydroxy group, amino group, sulfhydryl group, nitrile group, nitro group, phosphono group, sulfone group, halogen atom and carbon number 1 respectively. Alkyl groups of ~ 12; aryl groups of 6-12 carbon atoms, alkyloxy groups of 1-12 carbon atoms, aryloxy groups of 6-12 carbon atoms, alkylthio groups of 1-12 carbon atoms, 6-12 carbon atoms an arylthio group or an acyl group having a carbon number of 1 to 13, ^{R 4} is an alkylene group or an arylene group having 6 to 12 carbon atoms having 1 to 12 carbon atoms.

Examples of the halogen atom in R ^{1 to} R ³ include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
The alkyl group, aryl group, alkyloxy group (alkoxy group), aryloxy group, alkylthio group, and arylthio group may be linear or branched, respectively, and substituents (for example, fluorine atom, chlorine atom, bromine) may be used. It may have a halogen atom such as an atom or an iodine atom, a hydroxy group, an amino group, a sulfhydryl group, a nitrile group, a nitro group, etc.).
Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group and the like.
Examples of the aryl group include a phenyl group, a benzyl group, a naphthyl group and the like.
Examples of the alkyloxy group include a methoxy group, an ethoxy group, a protoxy group, a butoxy group and the like.
Examples of the aryloxy group include a phenoxy group, a benzyloxy group, a naphthyloxy group and the like.
Examples of the alkylthio group include a methylthio group, an ethylthio group, a propylthio group and the like.
Examples of the arylthio group include a phenylthio group, a benzylthio group, a naphthylthio group and the like.

The acyl group is represented by ^{R 7-CO-.} R ⁷ is a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, a hydroxy group and a hydrocarbon group. Examples of the hydrocarbon group include an alkyl group having 1 to 12 carbon atoms and an aryl group having 6 to 12 carbon atoms. The hydrocarbon group may be linear or branched, and the substituent (for example, a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a hydroxy group, an amino group, a sulfhydryl group, a nitrile group, etc. It may have a nitro group, etc.).
Examples of the acyl group include an acetyl group, a propionyl group, a benzoyl group and the like.

R ¹ and R ² are preferably hydrogen atoms from the viewpoint of polymerization rate.
R ³ is preferably a substituent having less steric hindrance, such as a hydrogen atom or a methyl group, in terms of maintaining the crystallinity of the carbon fiber precursor acrylic fiber obtained by spinning the copolymer composition (X).

In R ^4, alkylene group having 1 to 12 carbon atoms, an arylene group having 6 to 12 carbon atoms may each be straight chain or branched chain, also a substituent (e.g., fluorine atom, chlorine atom, bromine atom, It may have a halogen atom such as an iodine atom, a hydroxy group, an amino group, a sulfhydryl group, a nitrile group, a nitro group, etc.).
Examples of the alkylene group include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group and a decylene group.
Examples of the arylene group include a phenylene group and a naphthylene group.
R ⁴ is preferably an ethylene group.

Examples of the monomer (hereinafter, also referred to as “monomer (a)”) that is the source of the structural unit (A) include N- (cyanomethyl) acrylamide, N- (cyanoethyl) acrylamide, and N- (cyano). Propyl) acrylamide, N- (cyanobutyl) acrylamide, N- (4-cyanophenyl) acrylamide, N, N- (dicyanomethyl) acrylamide, N, N- (dicyanoethyl) acrylamide, N- (cyanomethyl) methacrylamide, N -(Cyanoethyl) methacrylicamide, N- (cyanopropyl) methacrylicamide and the like can be mentioned. Among these, N-cyanoethylacrylamide is preferable from the viewpoint of polymerizable property.
These monomers (a) may be used alone or in combination of two or more.

When the total of all the units constituting the copolymer composition (X) is 100% by mass, the ratio of the structural unit (A) is 0.5 to 30% by mass, which is 2 to 25% by mass. It is preferably 3 to 20% by mass, and more preferably 3 to 20% by mass. In particular, when the copolymer composition (X) contains the following structural unit (C), the ratio of the structural unit (A) is preferably 1 to 25% by mass.
When the ratio of the structural unit (A) is 0.5% by mass or more, a carbon fiber precursor acrylic fiber having a high carbonization yield after the firing step can be obtained. On the other hand, if the ratio of the structural unit (A) is 30% by mass or less, the ratio of the structural unit (B) described later can be sufficiently secured, so that high quality carbon fiber can be obtained without impairing the mechanical properties of the carbon fiber. Obtainable.

(Structural unit (B))
The structural unit (B) is a structural unit represented by the following general formula (2).

In formula (2), R ⁵ and R ⁶ independently have a hydrogen atom, a hydroxy group, an amino group, a sulfhydryl group, a nitrile group, a nitro group, a phosphono group, a sulfone group, a halogen atom, and 1 to 12 carbon atoms. Alkyl group, aryl group having 6 to 12 carbon atoms, alkyloxy group having 1 to 12 carbon atoms, aryloxy group having 6 to 12 carbon atoms, alkylthio group having 1 to 12 carbon atoms, arylthio group having 6 to 12 carbon atoms or It is an acyl group having 1 to 13 carbon atoms.

In R ⁵ and R ⁶ , examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
The alkyl group, aryl group, alkyloxy group (alkoxy group), aryloxy group, alkylthio group, and arylthio group may be linear or branched, respectively.
Examples of the alkyl group, aryl group, alkyloxy group, aryloxy group, alkylthio group, arylthio group, and acyl group in R ^{5 to R 6} include those exemplified above in the description of ^{R 1 to} R ^{3, respectively.}
R ⁵ and R ⁶ are preferably hydrogen atoms from the viewpoint of obtaining high quality carbon fibers without impairing the mechanical properties of the carbon fibers.

Examples of the monomer (hereinafter, also referred to as “monomer (b)”) that is the source of the structural unit (B) include (meth) acrylonitrile, α-cyanoacrylate, dicyanovinylidene, and fumaronitrile ethyl. Can be mentioned. Among these, (meth) acrylonitrile is preferable from the viewpoint of polymerizability and mechanical properties when carbon fibers are used.
These monomers (b) may be used alone or in combination of two or more.

When the total of all the units constituting the copolymer composition (X) is 100% by mass, the ratio of the structural unit (B) is 70 to 99.5% by mass, and 70 to 98.9% by mass. It is preferably 80 to 97% by mass, and more preferably 80 to 97% by mass. In particular, when the copolymer composition (X) contains the following structural unit (C), the ratio of the structural unit (B) is preferably 80 to 98.9% by mass.
When the ratio of the structural unit (B) is 70% by mass or more, high quality carbon fiber can be obtained without impairing the mechanical properties of the carbon fiber. On the other hand, when the ratio of the structural unit (B) is 99% by mass or less, the ratio of the structural unit (A) can be sufficiently secured, so that a carbon fiber precursor acrylic fiber having a high carbonization yield after the firing step can be obtained. be able to.

(Structural unit (C))
The structural unit (C) is a structural unit derived from a monomer containing a carboxy group.
Examples of the monomer containing a carboxy group (hereinafter, also referred to as “monomer (c)”) include methacrylic acid, acrylic acid, fumaric acid, itaconic acid, maleic acid, crotonic acid, vinyl benzoic acid, and monobutyl maleate. Examples thereof include esters, monomethyl esters of itaconic acid, and butyl esters of itaconic acid. Among these, methacrylic acid is preferable from the viewpoint of shortening the firing time.
These monomers (c) may be used alone or in combination of two or more.

When the total of all the units constituting the copolymer composition (X) is 100% by mass, the ratio of the structural unit (C) is preferably 0.1 to 5% by mass, preferably 0.5 to 5% by mass. More preferably, it is 1.5% by mass.
When the ratio of the structural unit (C) is 0.1% by mass or more, the flame resistance reaction can be promoted and the productivity of firing can be improved. On the other hand, when the ratio of the structural unit (C) is 5% by mass or less, the deterioration of the mechanical properties of the carbon fiber can be suppressed.

(Arbitrary unit)
The copolymer composition (X) may contain units other than the structural unit (A), the structural unit (B) and the structural unit (C) (hereinafter, also referred to as “arbitrary unit”), if necessary. Good.
The monomer (hereinafter, also referred to as “arbitrary monomer”) that is the source of the arbitrary unit is not particularly limited as long as it can be copolymerized with at least the monomer (a) and the monomer (b). However, (meth) acrylates such as methyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate and hexyl (meth) acrylate; vinyl ketones such as methyl vinyl ketone and isopropyl methyl ketone; (meth) acrylamide. , N-methyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide and other acrylamides; vinyl chloride, vinyl bromide, vinylidene chloride and other halogenated vinyl monomers; styrene , Α-Methylstyrene and other aromatic vinyl monomers; Maleimide, phenylmaleimide and other maleimides; (meth) allylsulfonic acid, (meth) allyloxybenzenesulfonic acid, styrenesulfonic acid and other sulfonic acid group-containing vinyl monomers Dimers and salts thereof; vinyl monomers containing a phosphate group and salts thereof; vinyl acetate, N-vinylpyrrolidone and the like can be mentioned.
These arbitrary monomers may be used alone or in combination of two or more.

When the total of all the units constituting the copolymer composition (X) is 100% by mass, the ratio of arbitrary units is preferably 29.4% by mass or less, and preferably 10% by mass or less. More preferred.

(Molecular weight)
The mass average molecular weight of the copolymer composition (X) is preferably 200,000 to 800,000. When the mass average molecular weight of the copolymer composition (X) is 200,000 or more, the spinnability is improved. On the other hand, when the mass average molecular weight of the copolymer composition (X) is 800,000 or less, it is possible to suppress a decrease in solubility and gelation during the preparation of the spinning stock solution.
The mass average molecular weight of the copolymer composition (X) is a polystyrene-equivalent value of the molecular weight measured by gel permeation chromatography (GPC).

(Production method)
The copolymer composition (X) is known, for example, solution polymerization, suspension polymerization, emulsification polymerization or the like of monomer (a), monomer (b), monomer (c) and arbitrary monomer. It can be obtained as a copolymer (Z) polymerized by a polymerization method. It is desirable to remove impurities such as unreacted monomers from the copolymer (Z) obtained by polymerization.
The copolymer composition (X) can also be obtained by mixing the copolymer (Z) obtained by the above polymerization with the acrylonitrile-based copolymer (Y) described below.

<Acrylonitrile-based copolymer (Y)>
The acrylonitrile-based polymer (Y) is a polymer obtained by using acrylonitrile as a main monomer and polymerizing the monomer. The acrylonitrile-based polymer (Y) may be a homopolymer obtained only from acrylonitrile, or a vinyl-based monomer copolymerizable with acrylonitrile and acrylonitrile, which are the main components (however, the monomer (a)). It may be a copolymer of.).

When the total of all the units constituting the acrylonitrile polymer (Y) is 100% by mass, the ratio of the acrylonitrile unit is preferably 70% by mass or more, and the ratio of the vinyl monomer unit is 30% by mass or less. preferable. More preferably, the proportion of the acrylonitrile unit is 90 to 98% by mass, and the proportion of the vinyl-based monomer unit is 2 to 10% by mass.

The vinyl-based monomer is not particularly limited as long as it can be copolymerized with acrylonitrile, and is, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and hexyl (meth). (Meta) acrylates such as acrylates, cyclohexyl (meth) acrylates, uralyl (meth) acrylates, 2-ethylhexyl (meth) acrylates, 2-hydroxyethyl (meth) acrylates, hydroxypropyl (meth) acrylates, diethylaminoethyl (meth) acrylates, etc. Kind; (meth) acrylic acid, itaconic acid, (meth) acrylamide, N-methylol acrylamide, diacetone acrylamide, styrene, vinyl toluene, vinyl acetate, vinyl chloride, vinylidene chloride, vinyl bromide, vinylidene bromide, vinyl fluoride , Unsaturated monomers such as vinylidene fluoride; p-sulfophenylmetharyl ether, (meth) allylsulfonic acid, styrenesulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid, and alkali metal salts thereof. ..
These vinyl-based monomers may be used alone or in combination of two or more.

The mass average molecular weight of the acrylonitrile-based polymer (Y) is preferably 200,000 to 800,000, more preferably 300,000 to 500,000. When the mass average molecular weight of the acrylonitrile-based polymer (Y) is 200,000 or more, the spinnability is improved. On the other hand, when the mass average molecular weight of the acrylonitrile-based polymer (Y) is 800,000 or less, it is possible to suppress a decrease in solubility and gelation during the preparation of the spinning stock solution.
The mass average molecular weight of the acrylonitrile-based polymer (Y) is a value obtained by converting the molecular weight measured by GPC into polystyrene.

The acrylonitrile-based polymer (Y) can be obtained by a known polymerization method such as solution polymerization, suspension polymerization, or emulsion polymerization. It is desirable to remove impurities such as unreacted monomers from the acrylonitrile-based polymer (Y) obtained by the polymerization.

Carbon fiber precursor When the acrylic fiber contains an acrylonitrile-based polymer (Y), the mass ratio of the copolymer (Z) to the acrylonitrile-based polymer (Y) (copolymer (Z): acrylonitrile-based polymer (Y). )) Is preferably 0.5: 99.5 to 70:30. When the proportion of the copolymer (Z) is 0.5% or more, the effect of improving the carbonization yield can be obtained. On the other hand, when the proportion of the copolymer (Y) is 30% or more, spinning can be performed satisfactorily.

<Additives>
The carbon fiber precursor acrylic fiber may contain an additive.
Examples of the additive include carbon materials such as carbon black, carbon nanotubes, and fullerenes; and glass materials such as colloidal silica and glass fiber.
The ratio of the additive to the total mass of the carbon fiber precursor acrylic fiber is preferably 30% by mass or less.

<Manufacturing method>
The carbon fiber precursor acrylic fiber is obtained by spinning a spinning stock solution containing the above-mentioned copolymer composition (X) by a known method.
The spinning stock solution may contain the above-mentioned additives, if necessary.

The solvent used in the spinning stock solution is not particularly limited, and examples thereof include organic solvents such as dimethylacetamide, dimethyl sulfoxide, and dimethylformamide; and aqueous solutions of inorganic compounds such as zinc chloride and sodium thiocyanate. Dimethylacetamide is preferable because it is difficult for metals to be mixed into the fibers obtained by spinning and the process is simplified, and among them, the coagulated yarn and the moist heat drawn yarn are highly dense. Especially preferable.

The spinning stock solution preferably has a copolymer concentration of a certain level or higher in order to obtain a dense coagulated yarn and to develop an appropriate viscosity and fluidity. Specifically, the total concentration of the copolymer composition (X) in the spinning stock solution is preferably 15 to 30% by mass, more preferably 18 to 25% by mass.

The method for spinning the undiluted spinning solution is not particularly limited, but a wet spinning method, a dry wet spinning method, a dry spinning method, or the like can be applied.
Then, the coagulated yarn obtained by the wet spinning method, the dry wet spinning method, the dry spinning method, or the like is subjected to conventionally known water washing, bath stretching, oiling, drying densification, stretching, etc. as necessary. Acrylic fiber, which is a carbon fiber precursor having fineness, is used.

Examples of the oil agent include conventionally known silicone-based oil agents and oil agents composed of organic compounds containing no silicon, but in addition to these, it is possible to prevent adhesion between single fibers in the flame resistance step and carbonization step described later. If it is, it can be suitably used as an oil agent.
It is preferable that the fibers to which the oil agent is applied are dried and densified by heating. It is efficient to carry out the drying treatment in contact with a roll heated to 50 to 200 ° C.
Further, it is preferable that the dried fibers are continuously stretched. The method of stretching is not particularly limited, but a dry heat stretching method, a hot plate stretching method, a steam stretching method, or the like can be applied.

The carbon fiber precursor acrylic fiber is usually manufactured and handled as a fiber bundle (hereinafter, also referred to as “precursor fiber bundle”) which is an aggregate of aligned single fibers. The number of single fibers contained in one fiber bundle is preferably 200 to 300,000, more preferably 300 to 200,000, and even more preferably 400 to 100,000. When the number of single fibers is within the above range, it is easy to handle the precursor fiber bundle in the flame resistance step and the carbonization step, and it is also easy to handle when molding the obtained carbon fiber bundle into a composite material. ..

The fiber density of the precursor fiber bundle is preferably 1.17~1.21g / cm ^3, more preferably 1.18~1.20g / cm ^3. When the fiber density of the precursor fiber bundle is within the above range, the residual amount of the carbon fiber bundle obtained through the flame resistance step and the carbonization step described later increases, which is advantageous in terms of economy.
The fiber density of the precursor fiber bundle is a value measured by the density gradient tube method based on JIS K 7112.

<Effect>
Since the carbon fiber precursor acrylic fiber of the present embodiment described above is composed of the copolymer composition (X) containing the above-mentioned structural unit (A) in a specific amount, the carbonization yield after the firing step is high. Therefore, the carbon fiber precursor acrylic fiber of the present invention is suitable for producing a carbon fiber bundle having a high carbonization yield.

"Carbon fiber bundle"
The carbon fiber bundle can be obtained by subjecting a fiber bundle (precursor fiber bundle) composed of the carbon fiber precursor acrylic fiber of the present invention to a flameproof treatment and then carbonizing the fiber bundle.
Hereinafter, an example of a method for producing a carbon fiber bundle will be described.

<Manufacturing method>
The method for producing a carbon fiber bundle of the present embodiment includes a flame resistance step and a carbonization step shown below. The flame resistance process and the carbonization process are also collectively referred to as a "firing process".

(Flame resistance process)
The flame-resistant step is a step of heating the precursor fiber bundle at 220 to 300 ° C. for 90 minutes or less in an oxidizing atmosphere (flame-resistant treatment) to obtain a flame-resistant fiber bundle.
Here, the "oxidizing atmosphere" is an air atmosphere or an atmosphere containing known oxidizing substances such as oxygen, nitrogen dioxide, and sulfur dioxide. Among these, an air atmosphere is preferable as the oxidizing atmosphere from the viewpoint of economy.
The "oxidizing substance" means a substance that causes combustion of a substance by giving oxygen or a substance that can promote the combustion of a substance.

The method of flameproofing treatment is not particularly limited, and for example, a method using a conventionally known flameproofing furnace (hot air circulation furnace) or a method of contacting with a heated solid surface can be adopted.
In the method using a flameproof furnace, usually, the precursor fiber bundle that has entered the flameproof furnace is once taken out of the flameproof furnace, and then folded back by a folding roll arranged outside the flameproof furnace to make the flameproof furnace. The method of repeatedly passing through is adopted.
As a method of contacting the surface of the heated solid, a method of intermittently contacting the precursor fiber bundle with the surface of the heated solid is adopted.

The flame-resistant treatment temperature (flame-resistant treatment temperature) is preferably 220 to 300 ° C. When the flameproofing treatment temperature is 220 ° C. or higher, the runaway of the flameproofing reaction can be suppressed, and the flameproofing treatment can be efficiently performed. On the other hand, when the flame-resistant treatment temperature is 300 ° C. or lower, the flame-resistant treatment can be easily performed without thermally decomposing the polyacrylonitrile skeleton of the carbon fiber precursor acrylic fiber.

The time for performing the flame resistance treatment (flame resistance treatment time) is preferably 90 minutes or less, and more preferably 70 minutes or less. When the flame-resistant treatment time is 90 minutes or less, it is possible to easily prevent the flame-resistant treatment step from causing a decrease in productivity, and it is possible to efficiently produce a carbon fiber bundle. The lower limit of the flame resistance treatment time is not particularly limited, but is preferably 10 minutes or more, and more preferably 20 minutes or more. If the flameproofing treatment time is 10 minutes or more, sufficient oxygen can be easily diffused into the single fibers constituting the precursor fiber bundle.

In the flame-resistant step, it is preferable to heat the obtained flame-resistant fiber bundle until the fiber density becomes 1.3 to 1.43 g / cm ³ to perform the flame-resistant treatment, and more preferably 1.33 to 1.38 g /. It is cm ^3. When the fiber density of the flame-resistant fiber bundle is 1.30 g / cm ³ or more, heat fusion during the carbonization step is unlikely to occur, and the carbon fiber bundle can be easily produced. On the other hand, when the fiber density of the flame-resistant fiber bundle is 1.43 g / cm ³ or less, the deterioration of the performance of the carbon fiber bundle can be suppressed.
The fiber density of the flame-resistant fiber bundle is a value measured by the density gradient tube method based on JIS K 7112.

(Carbonization process)
The carbonization step is a step of heating the flame-resistant fiber bundle obtained by the flame-resistant step at 800 to 2000 ° C. in an inert gas atmosphere (carbonization treatment) to obtain a carbon fiber bundle.
Here, the "inert gas atmosphere" is an atmosphere that does not substantially contain known oxidizing substances such as oxygen, nitrogen dioxide, and sulfur dioxide. "Substantially" means that the volume concentration of the oxidizing substance is 1.0% by volume or less with respect to the total volume of the gas forming the inert gas atmosphere.
The "inert gas" means a gas that does not easily react with other substances and is chemically stable, and examples thereof include nitrogen, argon, and helium.

As a method of carbonization treatment, for example, in a state where the inert gas is introduced into the carbonization furnace, the flame-resistant fiber bundle is introduced and held, and then taken out to heat the flame-resistant fiber bundle and carry out the carbonization treatment.

The carbonization treatment temperature (carbonization treatment temperature) is preferably 800 to 2000 ° C. If the carbonization treatment temperature is 800 ° C. or higher, the carbonization treatment can be performed in a short time. On the other hand, when the carbonization treatment temperature is 2000 ° C. or lower, the deterioration of the mechanical characteristics due to the carbonization treatment can be suppressed.
The carbonization treatment temperature may be constant, or may be raised during the carbonization treatment. When raising the temperature, for example, multiple heating zones are set in the carbonization furnace, and the temperature of each heating zone is set so that the temperature rises from the upstream heating zone to the downstream heating zone, and the temperature is upstream. This can be achieved by sequentially passing the heat from the heating zone on the side toward the heating zone on the downstream side for processing.

The time for performing the carbonization treatment (carbonization treatment time) is not particularly limited, but is preferably 1 to 60 minutes, more preferably 10 to 40 minutes. If the carbonization treatment time is 1 minute or more, the carbonization yield tends to be higher. On the other hand, if the carbonization treatment time is 60 minutes or less, the mechanical properties of the obtained carbon fiber bundle tend to be improved. In addition, productivity can be maintained well.

Between the flame-resistant step and the carbonization step, the flame-resistant fiber bundle is heated at a temperature lower than the carbonization treatment temperature (for example, 550 ° C. or higher and lower than 800 ° C.) in the inert gas. Pre-carbonization treatment may be performed (pre-carbonization step).
When the pre-carbonization step is performed, the "firing" includes a flame resistance step, a pre-carbonization step, and a carbonization step.

<Other processes>
The carbon fiber bundle obtained by the carbonization step can be used as it is as a carbon fiber bundle, but if necessary, a graphitized product by a known method may be used as a carbon fiber bundle. For example, a graphitized carbon fiber bundle can be obtained by heating the carbon fiber bundle in an inert atmosphere at a maximum temperature of more than 2000 ° C. and 3000 ° C. or lower.

In addition, a sizing treatment can be performed in order to impart the focusing property to the carbon fiber bundle.
The sizing agent used in the sizing treatment is not particularly limited as long as desired properties can be obtained, and examples thereof include sizing agents containing an epoxy resin, a polyether resin, an epoxy-modified polyurethane resin, and a polyester resin as main components. As a method of sizing treatment, a known method can be used.

<Use>
The carbon fiber bundle thus obtained is formed as a composite material by combining with, for example, a matrix resin, and is used for various purposes.
The matrix resin is not particularly limited, but for example, a thermocurable resin such as an epoxy resin or a phenol resin, a radical polymerization resin such as an acrylic resin, a vinyl ester resin or an unsaturated polyester resin, a thermoplastic acrylic resin, a polyamide resin or a polyimide resin. , Polyplastic resin such as polycarbonate resin, polypropylene resin, polyethylene resin and the like. Further, modified products of these resins can also be used. Moreover, you may use a commercially available product as a matrix resin.
The use of the composite material using the carbon fiber bundle is not particularly limited, and it can be used in a wide range of applications such as automobile members, aerospace materials, sports / leisure materials, and industrial materials such as pressure vessels.

<Effect>
According to the method for producing a carbon fiber bundle of the present embodiment described above, after heating the fiber bundle composed of the carbon fiber precursor acrylic fiber of the present invention in an oxidizing atmosphere at a specific temperature and for a specific time. Since it is heated at a specific temperature in an inert gas atmosphere, high-quality carbon fiber bundles can be produced with high carbonization yield with high productivity, and thus the production cost of carbon fiber bundles can be reduced.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.
The various measurement methods performed in this embodiment are as follows.

"Measurement / evaluation"
<Measurement of composition of copolymer (composition) and precursor fiber bundle>
The composition of the copolymer (composition) and the precursor fiber bundle (ratio of each monomer unit (mass%)) was ^{measured by 1} H-NMR method as follows.
Using a dimethyl sulfoxide-d6 solvent as the solvent, dissolve the copolymer (composition) or precursor fiber bundle, and use an NMR measuring device (manufactured by Nippon Denshi Co., Ltd., product name: GSZ-400 type) to integrate 500 times. The measurement was carried out under the condition of a measurement temperature of 80 ° C., and the ratio of each monomer unit was obtained from the integrated ratio of chemical shift.

<Measurement of mass average molecular weight of copolymer (composition)>
The mass average molecular weight of the copolymer (composition) is gel permeation chromatography (apparatus: manufactured by Toso Co., Ltd., product name: HLC-8220GPC, column: manufactured by Toso Co., Ltd., product name: TSK-GEL Super HZM-H. (Φ6.0 mm × 15 cm), developing solvent: 0.01 mol / L-LiCl DMF solution was used, and the mass average molecular weight was determined using polystyrene as a standard substance.

<Measurement of single fiber fineness of precursor fiber bundle>
The single fiber fineness means the weight per 10000 m of one fiber. The precursor fiber bundle was taken at 1.00 m, its mass was divided by the number of filaments, and then multiplied by 10,000 to obtain a single fiber fineness.

<Measurement of fiber density of precursor fiber bundle and flame resistant fiber bundle>
The fiber densities of the precursor fiber bundle and the flame resistant fiber bundle were measured by the density gradient tube method based on JIS K 7112.

<Measurement of carbonization yield>
The carbonization yield was calculated from the following formula by measuring the mass of the flame-resistant fiber bundle and the mass of the carbon fiber bundle.
Carbonization yield (%) = (mass of carbon fiber bundle / mass of flame-resistant fiber bundle) × 100

"Example 1"
<Manufacturing of copolymer (Z1)>
The following reagents were used as raw materials.
Monomer (a): N-cyanoethylacrylamide Monomer ( c ): Methacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd., Wako Special Grade,> 99%)
-Monomer ( b ): Acrylonitrile (manufactured by Kanto Chemical Co., Inc., special deer grade,> 98%)
-Redox polymerization initiator:
Ammonium persulfate (manufactured by Wako Pure Chemical Industries, Ltd., Wako special grade,> 98%)
Ammonium hydrogen sulfite (manufactured by Wako Pure Chemical Industries, Ltd., chemical grade, 45% to 55%
)
Ferrous sulfate _{(Fe 2 SO 4 · 7H 2} O) ( Wako Pure Chemical Industries, Ltd., Wako special grade, 99% to 102%)
・ PH adjuster:
Sulfuric acid (manufactured by Wako Pure Chemical Industries, Ltd., high-purity special grade,> 95%)
It was adjusted to dilute sulfuric acid in a 6% by mass aqueous solution with pure water and used.
・ Reaction terminator:
Oxalic acid (manufactured by Wako Pure Chemical Industries, Ltd., Wako special grade,> 98%), ammonium hydrogen carbonate (manufactured by Wako Pure Chemical Industries, Ltd., Wako first grade,> 98%)
An aqueous solution containing 0.456% by mass oxalic acid and 1.76% by mass ammonium hydrogencarbonate was prepared with pure water and used as a reaction terminator.
-Polymerization medium: pure water (electrical conductivity> 5 μS / cm)

Put 1.8 L of pure water in a separable flask with a capacity of 2 L, and while stirring with a double helical ribbon stirring blade (SUS316 W85 mm x H150 mm), add dilute sulfuric acid to adjust the pH to 3.0, 55 It was kept at ° C.
Next, 34.7 g of a 2.75 mass% aqueous solution of ammonium persulfate, 28.6 g of a 5.00 mass% aqueous solution of ammonium hydrogen sulfite, and ^{9.1 g of a 6.0 × 10 -4} mass% aqueous solution of ferrous sulfate were added. It was put into a separable flask and stirred to make it uniform. While continuing stirring, the monomer consisting of 89 parts by mass of acrylonitrile (AN), 10.0 parts by mass of cyanoethyl acrylamide, 1.00 parts by mass of methacrylic acid (MAA), and 30.7 parts by mass of pure water was uniformly dissolved. 238 g of the mixture was placed in a separable flask.
The separable flask was held at 55 ° C. and stirring was continued for 1 hour to obtain a polymer slurry.
While stirring the obtained polymer slurry, a reaction terminator was added until the pH reached 5.5 to stop the polymerization reaction.
Next, the polymerized slurry was washed and filtered with water at 70 ° C. three times with a suction filter, dried by heating in a steam dryer at 70 ° C. for two days, and then pulverized to obtain a powder of the copolymer (Z1). It was.
When the composition of the obtained copolymer (Z1) was measured by NMR, the cyanoethylacrylamide unit was 7.5% by mass, the acrylonitrile unit was 91.5% by mass, and the methacrylic acid unit was 1.0% by mass. That is, in the copolymer (Z1), the structural unit (A) 7.5 mass ^{in which R 1} , R ² and R ³ in the above general formula (1) are all hydrogen atoms and R ^{4 is an ethylene group. %, 91.5% by mass of the structural unit (B) in which R 5} and R ⁶ in the above formula (2) are both hydrogen atoms, and 1.0% by mass of the structural unit (C) derived from methacrylic acid. It is configured.
The measured weight average molecular weight of the copolymer (Z1), was 2.8 × 10 ^5.

<Manufacturing of copolymer (Y1)>
A copolymer in the same manner as the copolymer (Z1) except that a monomer mixture consisting of 94.0% by mass of acrylonitrile, 1.00% by mass of methacrylic acid and 5.0% by mass of acrylamide was used. (Y1) was obtained.
When the composition of the obtained copolymer (Y1) was measured by NMR, the acrylonitrile unit was 96.3% by mass, the methacrylic acid unit was 1.0% by mass, and the acrylamide unit was 2.7% by mass.
The measured weight average molecular weight of the copolymer (Y1), was 4.2 × 10 ^5.

<Manufacturing of precursor fiber bundle>
The obtained copolymer (Z1) and the copolymer (Y1) are mixed at a mass ratio (copolymer (Z1): copolymer (Y1)) = 1: 1 to form a copolymer composition (copolymer composition). It was set to X1). The obtained copolymer composition (X1) was dissolved in dimethylacetamide (DMAc) to prepare a spinning stock solution having a concentration of 21% by mass. This spinning stock solution was spun by a wet spinning method to obtain a precursor fiber bundle. As the coagulation bath, an aqueous solution of DMAc having a concentration of DMAc of 67% by mass and a temperature of 38 ° C. was used.
The single fiber fineness of the obtained precursor fiber bundle was 1.2 dtex, the number of filaments was 400, and the fiber density was 1.19 g / cm ³ . Moreover, when the composition of the precursor fiber bundle was measured by NMR, the cyanoethyl acrylamide unit was 3.8% by mass, the acrylonitrile unit was 93.8% by mass, the methacrylic acid unit was 1.0% by mass, and the acrylamide unit was 1.4. It was% by mass.

<Manufacturing of flame-resistant fiber bundles>
Using a hot air circulation type flame-resistant furnace, the precursor fiber bundle obtained in heated air at 260 ° C. was heated for 20 minutes (flame-resistant treatment) to obtain a flame-resistant fiber bundle.
When the flame-resistant treatment time was 20 minutes, the fiber density of the flame-resistant fiber bundle was 1.35 g / cm ³ .

<Manufacturing of carbon fiber bundles>
The obtained flame-resistant fiber bundle was heated in a nitrogen atmosphere as follows using a thermogravimetric analyzer (manufactured by Hitachi High-Technologies Corporation, "STA7300") to obtain a carbon fiber bundle.
First, the flame-resistant fiber bundle was held at 30 ° C. for 45 minutes with nitrogen introduced, and then the temperature was raised to a maximum temperature of 1400 ° C. at a heating rate of 20 ° C./min to obtain a carbon fiber bundle. The carbonization yield was calculated from the change in fiber mass due to the rise in atmospheric temperature. Specifically, the carbonization yield was calculated by dividing the mass of the carbon fiber bundle at 1400 ° C. by the mass of the flame-resistant fiber bundle before the temperature rise. The results are shown in Table 1.

"Example 2"
<Manufacturing of copolymer (Z2)>
The same weight as the copolymer (Z1) except that a monomer mixture consisting of 84.0% by mass of acrylonitrile, 1.00% by mass of methacrylic acid, and 15.0% by mass of cyanoethylacrylamide was used. A coalescence (Z2) was obtained.
When the composition of the obtained copolymer (Z2) was measured by NMR, the cyanoethylacrylamide unit was 10.0% by mass, the acrylonitrile unit was 89.0% by mass, and the methacrylic acid unit was 1.0% by mass. That is, in the copolymer (Z2), the structural unit (A) 10.0 mass ^{in which R 1} , R ² and R ³ in the above general formula (1) are all hydrogen atoms and R ^{4 is an ethylene group. %, The structural unit (B) 89.0% by mass in which R 5} and R ⁶ in the above formula (2) are both hydrogen atoms, and the structural unit (C) 1.0% by mass derived from methacrylic acid. It is configured.
The measured weight average molecular weight of the copolymer (Z2), was 8.0 × 10 ^5.

<Manufacturing of precursor fiber bundle>
Copolymer composition obtained by mixing the obtained copolymer (Z2) and the copolymer (Y1) at a mass ratio (copolymer (Z2): copolymer (Y1)) = 1: 9. The production of the precursor fiber bundle was produced in the same manner as in Example 1 except that the product (X2) was used.
The single fiber fineness of the obtained precursor fiber bundle was 1.2 dtex, the number of filaments was 400, and the fiber density was 1.19 g / cm ³ . Moreover, when the composition of the precursor fiber bundle was measured by NMR, the cyanoethyl acrylamide unit was 1.0% by mass, the acrylonitrile unit was 95.6% by mass, the methacrylic acid unit was 1.0% by mass, and the acrylamide unit was 2.4. It was% by mass.

<Manufacturing of flame-resistant fiber bundles and carbon fiber bundles>
Except for using the obtained precursor fiber bundle, the flame-resistant fiber bundle and the carbon fiber bundle were bundled in the same manner as in Example 1, and the carbonization yield was calculated. The results are shown in Table 1.
When the flame-resistant treatment time was 20 minutes, the fiber density of the flame-resistant fiber bundle was 1.34 g / cm ³ .

"Comparative Example 1"
<Manufacturing of precursor fiber bundle>
A precursor fiber bundle was produced in the same manner as in Example 1 except that the copolymer (Z1) was not used (that is, only the copolymer (Y1) was used).
The single fiber fineness of the obtained precursor fiber bundle was 1.2 dtex and the number of filaments was 400.

<Manufacturing of flame-resistant fiber bundles and carbon fiber bundles>
Except for using the obtained precursor fiber bundle, the flame-resistant fiber bundle and the carbon fiber bundle were bundled in the same manner as in Example 1, and the carbonization yield was calculated. The results are shown in Table 1.
When the flame-resistant treatment time was 20 minutes, the fiber density of the flame-resistant fiber bundle was 1.33 g / cm ³ .

As is clear from Table 1, the carbon fiber bundles of the respective examples in which the precursor fiber bundle composed of the copolymer composition (X1) or the copolymer composition (X2) was flame-resistant and carbonized have a structure. The carbonization yield was higher than that of the carbon fiber bundle of Comparative Example 1 in which only the copolymer (Y1) containing no unit (A) was used.
Further, the copolymer composition (X1) and the copolymer composition (X2) did not cause yarn breakage when spun in the state of being a spinning stock solution, and the spinnability was extremely good.

Claims (2)

It contains 0.5 to 30% by mass of the structural unit (A) represented by the following general formula (1) and 70 to 99.5% by mass of the structural unit (B) represented by the following general formula (2). , Carbon fiber precursor acrylic fiber.

(In formula (1), R ¹ , R ² and R ³ are independently hydrogen atom, hydroxy group, amino group, sulfhydryl group, nitrile group, nitro group, phosphono group, sulfone group, halogen atom and carbon number. Alkyl groups 1 to 12, aryl groups with 6 to 12 carbon atoms, alkyloxy groups with 1 to 12 carbon atoms, aryloxy groups with 6 to 12 carbon atoms, alkylthio groups with 1 to 12 carbon atoms, 6 to 12 carbon atoms an arylthio group or an acyl group having a carbon number of 1 to 13, ^{R 4} is an alkylene group or an arylene group having 6 to 12 carbon atoms having 1 to 12 carbon atoms.)

In formula (2), R ⁵ and R ⁶ are independently hydrogen atom, hydroxy group, amino group, sulfhydryl group, nitrile group, nitro group, phosphono group, sulfone group, halogen atom, and carbon number 1-12. Alkyl group, aryl group having 6 to 12 carbon atoms, alkyloxy group having 1 to 12 carbon atoms, aryloxy group having 6 to 12 carbon atoms, alkylthio group having 1 to 12 carbon atoms, arylthio group having 6 to 12 carbon atoms. Alternatively, it is an acyl group having 1 to 13 carbon atoms.) The fiber bundle composed of the carbon fiber precursor acrylic fiber according to claim 1 is heated at 220 to 300 ° C. in an oxidizing atmosphere for 90 minutes or less, and then at 800 to 2000 ° C. in an inert gas atmosphere. A method for producing a carbon fiber bundle to be heated.