JP2007204875A - Method for producing carbon-fiber precursor fiber and carbon fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a carbon fiber excellent in tensile strength without impairing productivity and process passing property. <P>SOLUTION: A method for producing the carbon-fiber precursor fiber comprises spinning a spinning dope obtained by dissolving a polyacrylonitrile-based polymer having ≤0.5 mol% copolymer ratio of a monomer other than acrylonitrile and a polyalkylene glycol obtained by polymerizing substantially one alkylene glycol into a solvent and substantially not containing a silicone by a wet spinning method or a dry wet spinning method. The method for producing the carbon fiber comprises using the precursor fiber obtained by the above method. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a carbon fiber excellent in tensile strength, and further relates to a method for producing a carbon fiber precursor fiber suitable for producing the above-described high-performance carbon fiber.

  Carbon fibers are used in various applications because of their excellent mechanical and electrical properties. In recent years, in addition to conventional golf clubs and fishing rods such as sports applications and aircraft applications, the development of so-called general industrial applications such as automobile members, CNG tanks, seismic reinforcement of buildings, ship members, etc. has progressed. The level of characteristics is also increasing. For example, in aircraft applications, many structural members are being replaced with carbon fiber reinforced plastics for weight reduction, and carbon fibers that are compatible with high levels of tensile strength and tensile elastic modulus are required.

  Carbon fiber is industrially a flameproofing process in which precursor fibers such as polyacrylonitrile fiber and pitch fiber are heat-treated in air at 100 to 300 ° C., and a carbonizing process in which heat treatment is performed in an inert atmosphere at 300 to 3,000 ° C. It is manufactured through. Carbon fibers produced from polyacrylonitrile fibers are characterized by a higher tensile strength than carbon fibers produced from pitch fibers.

  In general, an ideal precursor fiber for obtaining carbon fiber having high tensile strength is a fiber using polyacrylonitrile (hereinafter referred to as homo-PAN) composed of 100 mol% of acrylonitrile, which does not contain a copolymer component. It is considered (Patent Document 1). However, if a fiber consisting only of homo-PAN is used as a carbon fiber precursor fiber, it is impractical industrially because it requires an extremely long heat treatment in the flameproofing process. When the is high, the decomposition reaction during the heat treatment becomes remarkable, and carbon fibers having high tensile strength cannot be obtained. In contrast, for example, by adding a monomer that accelerates the reaction in the flameproofing process, such as a vinyl carboxylate monomer, as a copolymerization component, a technique for shortening the time required for the flameproofing process and producing carbon fiber Has been proposed (for example, Patent Document 2). In addition, for the purpose of enhancing stretchability in the yarn production process, several mol% of a copolymer component may be copolymerized in addition to acrylonitrile. However, when the amount of copolymer components other than acrylonitrile is increased, the tendency of coalescence or fusion between single fibers during heat treatment after the flameproofing step becomes remarkable, and when such fibers are used as precursors, the resulting carbon fiber tension There is a problem that the strength decreases. This is because, due to the presence of a copolymer component other than acrylonitrile, oxidative decomposition other than the original flameproofing reaction occurs abruptly, and a tar-like product is generated, or the copolymer component is decomposed to generate acrylonitrile molecules. It is believed that the tensile strength of the resulting carbon fiber is reduced due to chain breakage and the like.

  As a technique for reducing the fiber bonding and fusing phenomenon in such a flameproofing process, a technique for adding a silicone substance to the spinning dope has been proposed (Patent Document 3). According to the technique disclosed in Patent Document 3, although troubles such as fluffing, spreading and yarn breakage of the original yarn are eliminated and improvement in operational stability is recognized, silicone is left as an impurity in the fiber, and thus obtained. There exists a problem that the intensity | strength of carbon fiber will fall.

As a technique for shortening the time required for the flameproofing process other than a technique using a copolymerization component, a technique for containing a peroxide in the carbon fiber precursor fiber has been proposed (Patent Document 4). However, in the technique disclosed in Patent Document 4, since a highly reactive peroxide is used, the reaction proceeds rapidly in the flameproofing process, and fusion is easily generated between single fibers. In fact, it cannot be said that the technology can be industrially realized because the run-off reaction is likely to occur because the exothermic rate is increased and the heat generation rate associated with the flameproofing reaction is increased.
JP 52-34027 A, p155 JP-A-48-63029 JP-A-55-103313 JP-A-48-87120

  An object of this invention is to obtain the carbon fiber excellent in tensile strength, without impairing productivity and process passability.

  The method for producing a carbon fiber precursor fiber of the present invention has the following configuration in order to achieve the object of the present invention described above.

  That is, a polyacrylonitrile polymer in which the copolymerization ratio of monomers other than acrylonitrile is 0.5 mol% or less and a polyalkylene glycol obtained by substantially polymerizing one kind of alkylene glycol are dissolved in a solvent. And a carbon fiber precursor fiber is produced by spinning a spinning dope substantially free of silicone by a wet spinning method or a dry-wet spinning method.

  Moreover, in order to achieve the object of the present invention described above, the carbon fiber manufacturing method of the present invention has the following configuration. That is, the carbon fiber precursor fiber obtained by the manufacturing method described above is subjected to flame resistance treatment in air at a temperature of 200 to 300 ° C., and then pre-carbonized in an inert atmosphere at a temperature of 300 to 800 ° C. It is a method for producing carbon fiber that is carbonized in an inert atmosphere at a temperature of 1,000 to 2,000 ° C.

  According to the present invention, carbon fibers can be obtained from carbon fiber precursor fibers having a small amount of copolymerization components. As a result, not only can fusion between single fibers be prevented, but also the molecular chain can be broken at the copolymerization portion. It is possible to produce a carbon fiber having a high tensile strength that can be suppressed and has a fiber structure with few defects serving as a starting point of fracture. That is, high stretch in the firing process can be realized without impairing productivity and process passability, and thereby carbon fibers having excellent tensile strength can be produced.

  First, the manufacturing method of the carbon fiber precursor fiber of this invention is demonstrated.

  In the present invention, a polyacrylonitrile-based polymer having a copolymerization ratio of a monomer other than acrylonitrile (hereinafter referred to as copolymerization component) of 0.5 mol% or less and substantially one kind of alkylene glycol are polymerized. A spinning stock solution in which a polyalkylene glycol is dissolved in a solvent is used. The spinning dope should be substantially free of silicone compounds.

  In the present invention, as the polyacrylonitrile-based polymer, acrylonitrile is 99.5 mol% or more and the copolymer component is 0.5 mol% or less, preferably 99.8 mol% or more and the copolymer component is 0.00%. Those having 2 mol% or less are used, but most preferably, acrylonitrile is 100 mol%, that is, a copolymer component having a copolymerization ratio of substantially 0 mol%, that is, so-called homo PAN is used. The copolymerization component is not particularly limited as long as it is a monomer copolymerizable with acrylonitrile. For example, acrylic acid, methacrylic acid, itaconic acid and alkali metal salts thereof, ammonium salts and lower alkyl esters, acrylamide and derivatives thereof , Allyl sulfonic acid, methallyl sulfonic acid and their salts or alkyl esters, acrylate, methacrylate, etc. can be used, but the larger the copolymerization amount of the copolymerization component, the more the molecular fragmentation due to thermal decomposition at the copolymerization part. Since the tensile strength of the resulting carbon fiber decreases and the effects of the present invention cannot be obtained, the smaller the copolymerization amount of the copolymer component, the better.

  In the present invention, it is preferable to use a polyacrylonitrile polymer having an intrinsic viscosity in the range of 1.0 to 5.0. When the intrinsic viscosity is less than 1.0, the formability of the yarn is lowered, and therefore the speed at which the yarn taken out from the die is pulled, that is, the spinnability is lowered. Further, when the intrinsic viscosity is higher than 5.0, gelation tends to occur and stable spinning becomes difficult. The intrinsic viscosity of the polyacrylonitrile polymer can be controlled by the monomer concentration at the time of polymerization, the amount of the polymerization initiator or the chain transfer agent, and the like.

The intrinsic viscosity of a polyacrylonitrile polymer should be calculated based on the specific viscosity measured at 25 ° C. using an Ostwald viscometer by dissolving the polyacrylonitrile polymer in dimethylformamide. Can do. Specifically, the measurement is performed according to the following procedure. 150 mg of a polyacrylonitrile-based polymer that has been heat-treated at 120 ° C. for 2 hours and dried completely is dissolved at 50 ° C. in 50 ml of 0.1 mol / liter of sodium thiocyanate added dimethylformamide. The temperature of the obtained solution was adjusted to 25 ° C., and the Ostwald viscometer previously adjusted to 25 ° C. was used to measure the drop time between the marked lines with an accuracy of 1/100 second. ). Similarly, dimethylformamide added with 0.1 mol / liter of sodium thiocyanate in which the polyacrylonitrile-based polymer is not dissolved is also measured, and the dropping time is defined as t ₀ (seconds). Then, the intrinsic viscosity [η] is calculated using the following formula.
[Η] = {(1 + 1.32 × η _sp ) ^1/2 −1} /0.198
η _sp = t / t ₀ −1
In the present invention, the polymerization method for producing the polyacrylonitrile-based polymer can be selected from a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, etc., and acrylonitrile and a copolymerization component are uniformly polymerized. For the purpose, it is preferable to use a solution polymerization method. When the polymerization is performed using a solution polymerization method, a solvent in which polyacrylonitrile is soluble, such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, or the like is used as a solvent. Among them, it is preferable to use dimethyl sulfoxide from the viewpoint of solubility of polyacrylonitrile.

  In the present invention, a spinning stock solution in which the polyacrylonitrile-based polymer described above is dissolved in a solvent is used. The spinning stock solution may further contain a polyalkylene glycol obtained by substantially polymerizing one kind of alkylene glycol. is necessary. Such polyalkylene glycol decomposes itself in the flameproofing process to generate radicals. The generated radicals trigger the cyclization reaction of polyacrylonitrile, and the reaction proceeds in a chain manner, so that the flame resistance reaction is promoted. Polyalkylene glycol obtained by copolymerizing two or more types of alkylene glycol may be contained in a certain amount, but when such polyethylene glycol is contained, the decomposition start temperature in the flameproofing process is constant. Therefore, since the flameproofing reaction does not proceed uniformly and the tensile strength of the resulting carbon fiber may decrease, a polyalkylene glycol other than a polyalkylene glycol obtained by substantially polymerizing one kind of alkylene glycol is The amount should be less, preferably 0.2 parts by weight, preferably 0.1 parts by weight, more preferably 0.05 parts by weight or less based on 100 parts by weight of the polyacrylonitrile polymer. Specific examples of the polyalkylene glycol used in the present invention include polymethylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol and the like. In consideration of dropping off by washing in the yarn forming process, polypropylene glycol, It is more preferable to use butylene glycol. It is preferable that the weight average molecular weight (henceforth molecular weight) of polyalkylene glycol is 200-30,000. If the molecular weight is too large, the viscosity becomes too high and it is difficult to uniformly disperse in the spinning dope, which may cause defects in the resulting carbon fiber. If the molecular weight is too small, the viscosity decreases, and it becomes difficult to uniformly mix with the spinning dope. Here, the polyalkylene glycol obtained by substantially polymerizing one kind of alkylene glycol means that the main component alkylene glycol is 99% by weight or more, and if it is 1% by weight or less, the second alkylene glycol. May be polymerized. Moreover, as long as it is a polyalkylene glycol obtained by substantially polymerizing one kind of alkylene glycol, two or more kinds of such polyalkylene glycols may be used in combination.

  The mixed composition in the spinning dope is 0.1 to 25 parts by weight, preferably 5 to 15 parts by weight of polyalkylene glycol obtained by substantially polymerizing one kind of alkylene glycol with respect to 100 parts by weight of the polyacrylonitrile polymer. The solvent in which polyacrylonitrile is soluble in 100 parts by weight is preferably 100 to 1,000 parts by weight, and preferably 200 to 900 parts by weight. If the mixing ratio of the polyalkylene glycol is too small, the effect of promoting the flame resistance reaction is not sufficiently obtained, and if it is too large, the residue derived from the polyalkylene glycol remains in the fiber even after the flame resistance process. The carbon fiber defect may increase, and the tensile strength of the carbon fiber may decrease. In addition, if the solvent is too small, the viscosity of the spinning dope becomes too high, and if the solvent is too much, the viscosity of the spinning dope becomes too low to perform spinning in many cases.

  In addition to the polyalkylene glycol described above, other polymers may be mixed in the spinning dope, but may remain as impurities in the resulting carbon fiber and cause a decrease in tensile strength. In particular, silicone remains in the carbon fiber obtained even in a very small amount and the tensile strength is lowered, so that it is not substantially contained in the spinning dope. Specifically, the amount of silicone is preferably 0.2 parts by weight, preferably 0.1 parts by weight, more preferably 0.05 parts by weight or less based on 100 parts by weight of the polyacrylonitrile-based polymer. Examples of silicone include unmodified dimethyl silicone, amino-modified silicone, and polyether-modified silicone. Further, even if it does not remain in the obtained fiber, it is better not to contain as much as possible a substance with rapid decomposition such as peroxide. For example, with respect to 100 parts by weight of polyacrylonitrile-based polymer It should be stopped at 0.2 parts by weight, preferably 0.1 parts by weight, more preferably 0.05 parts by weight or less.

  The above-described polyacrylonitrile-based polymer and the above-described polyalkylene glycol are dissolved in a solvent to prepare a spinning dope. Examples of the solvent used here include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and the like, and dimethyl sulfoxide is more preferable from the viewpoint of solubility. When a solution polymerization method is used to obtain a polyacrylonitrile-based polymer, the above-described polyalkylene glycol may be dissolved in the solution after polymerization to obtain a spinning stock solution.

  It is preferable that the polyacrylonitrile polymer and the polyalkylene glycol are uniformly mixed in the spinning dope. If not mixed uniformly, the flameproofing reaction does not proceed uniformly, and as a result, the tensile strength of the carbon fiber may be reduced. The method for uniformly mixing is not limited, but may be stirred and mechanically mixed, or ultrasonic vibration may be used in combination. Specific examples of the mixing device include a kneader, a planetary mixer, a twin screw extruder, a three roll, a homomixer, a dissolver, a ball mill, and a bead mill.

  The spinning dope obtained above is spun without leaving for 4 hours or more, more preferably 3 hours or more, and even more preferably 2 hours or more after mixing. If the spinning solution is allowed to stand for a long time without being stirred or vibrated, polyalkylene glycol aggregates, and when pyrolyzed, voids are generated and the tensile strength of the carbon fiber may be reduced.

  It is preferable to mix evenly as much as possible by stirring or vibrating the spinning solution before spinning. Further, before spinning the spinning solution, it is preferable to pass the polymer raw material and impurities mixed in each step, for example, through a filter having an opening of 1 μm or less in order to obtain a high-strength carbon fiber.

  In the present invention, a carbon fiber precursor fiber is produced by spinning the above-described spinning solution by a wet spinning method or a dry-wet spinning method. In order to increase the density of the obtained carbon fiber precursor fiber and to increase the mechanical properties of the obtained carbon fiber, it is preferable to use a dry and wet spinning method. In the case of the wet spinning method, the spinning solution is directly discharged from the die into a coagulation bath and coagulated. In the case of the dry-wet spinning method, the spinning solution is once discharged into the air from the die, and then introduced into a coagulation bath and coagulated.

  In the present invention, the coagulation bath preferably contains a solvent such as dimethyl sulfoxide, dimethylformamide, or dimethylacetamide used as a solvent for the spinning dope and a so-called coagulation promoting component. As the coagulation accelerating component, a component that does not dissolve the acrylonitrile-based polymer and is compatible with the solvent used in the spinning dope can be used. Specifically, it is preferable to use water.

  After the spinning dope is introduced into a coagulation bath to form a coagulated yarn, usually a carbon fiber precursor fiber is obtained through a washing step, an in-bath drawing step, an oil agent applying step, a drying heat treatment step, and a steam drawing step. It is done. However, the solidified yarn may be directly stretched in the bath without the water washing step, or may be stretched in the bath after the solvent is removed by the water washing step. Such stretching in a bath is usually preferably performed in a single or a plurality of stretching baths adjusted to a temperature of 30 to 98 ° C. The draw ratio is preferably 1 to 5 times, and more preferably 2 to 4 times.

  After the stretching process in the bath, it is preferable to apply an oil agent made of silicone or the like to the yarn for the purpose of preventing adhesion between the single fibers. As such a silicone oil agent, it is preferable to use a modified silicone, and it is more preferable to use a material containing an amino-modified silicone having high heat resistance.

  In the steam drawing step, the draw ratio is preferably 3 times or more, more preferably 4 times or more, and further preferably 5 times or more from the viewpoint of productivity and mechanical properties of the obtained carbon fiber.

  The carbon fiber precursor fiber thus obtained has a single fiber fineness of preferably 0.5 to 1.5 dtex, more preferably 0.55 to 1.0 dtex, and still more preferably 0.6 to 0.8 dtex. It is good to be. If the single fiber fineness is too small, the process stability of the yarn making process and the firing process may be reduced due to a decrease in spinnability and the occurrence of yarn breakage due to contact with rollers and guides, while the single fiber fineness is too large. In addition, the difference between the inner and outer structures of each single fiber after flame resistance becomes large, and the processability in the subsequent carbonization process may decrease, and the tensile strength and tensile modulus of the resulting carbon fiber may decrease.

  The obtained carbon fiber precursor fiber is usually a continuous fiber, and the number of filaments per yarn is preferably 1,000 to 3,000,000, more preferably 12,000 to 3 34,000,000, more preferably 24,000 to 2,500,000, and most preferably 36,000 to 2,000,000. The number of filaments per yarn is preferably larger for the purpose of improving productivity. However, if the number of filaments is too large, it may not be possible to uniformly treat the inside of the bundle.

  Next, the manufacturing method of the carbon fiber of this invention is demonstrated.

  The carbon fiber precursor fiber produced by the above-described method is subjected to flame resistance treatment in air at a temperature of 200 to 300 ° C., preferably with a draw ratio of 0.8 to 1.2, and then 300 to 800. In an inert atmosphere at a temperature of ° C., preferably pre-carbonized while stretching at a stretch ratio of 0.9 to 1.2, preferably in an inert atmosphere at a maximum temperature of 1,000 to 2,000 ° C. Is produced by carbonizing while stretching at a stretch ratio of 0.95 to 0.98.

  In the present invention, the preliminary carbonization treatment and carbonization treatment are performed in an inert atmosphere. As the gas used in the inert atmosphere, nitrogen, argon, xenon and the like can be preferably exemplified, and nitrogen is preferably used from an economical viewpoint. Can do. In the preliminary carbonization treatment, it is preferable to set the heating rate in the temperature range to 500 ° C./min or less. Further, the maximum temperature in the carbonization treatment is preferably set as appropriate according to the desired mechanical properties of the carbon fiber, but generally the higher the maximum temperature of the carbonization treatment, the higher the tensile elastic modulus of the resulting carbon fiber, Since the tensile strength reaches a maximum near 1,500 ° C., the maximum temperature for carbonization is more preferably 1,200-1,700 ° C. for the purpose of increasing both the tensile strength and the tensile modulus. More preferably, it is -1600 degreeC.

  The obtained carbon fiber can be subjected to electrolytic treatment for its surface modification. As an electrolytic solution used for the electrolytic treatment, an acidic solution such as sulfuric acid, nitric acid, hydrochloric acid, an alkali such as sodium hydroxide, potassium hydroxide, tetraethylammonium hydroxide, ammonium carbonate, ammonium bicarbonate or a salt thereof is used as an aqueous solution. be able to. Here, the amount of electricity required for the electrolytic treatment can be appropriately selected according to the carbonization degree of the carbon fiber to be applied.

  Such electrolytic treatment can optimize the adhesion with the carbon fiber matrix in the resulting composite material, the brittle breakage of the composite material due to too strong adhesion, the problem of lowering the tensile strength in the fiber direction, Although the tensile strength is high, the problem of poor adhesion to the resin and the absence of strength properties in the non-fiber direction has been resolved, and the resulting composite material has balanced strength properties in both the fiber and non-fiber directions. Will be expressed.

  After the electrolytic treatment, a sizing treatment can be performed in order to give the carbon fiber a focusing property. As the sizing agent, a sizing agent having good compatibility with the resin can be appropriately selected according to the type of resin used.

  The carbon fiber obtained by the present invention is an aircraft member, a pressure vessel member, an automobile member, a fishing rod, by various molding methods such as autoclave molding as a prepreg, molding by resin transfer molding as a preform such as woven fabric, molding by filament winding, etc. It can be suitably used as a sports member such as a golf shaft.

Hereinafter, the present invention will be described more specifically with reference to examples. A method for measuring various physical property values used in this example will be described below.
<Specific gravity of flame resistant fiber>
The method described in JIS R7601 (1986) is followed. That is, 1.0 to 1.5 g of fiber was sampled, dried in air at 120 ° C. for 2 hours using a hot air dryer, measured for absolute dry mass B (g), and then known for specific gravity (specific gravity ρ). The fiber mass B (g) in ethanol is measured. And fiber specific gravity is calculated | required by following Formula, Fiber specific gravity = (Ax (rho)) / (AB). In this example, Wako Pure Chemical Industries special grade was used as ethanol without purification.
<Strand tensile strength of carbon fiber>
Determined according to JIS R7601 (1986) “Resin-impregnated strand test method”. The resin impregnated strand of carbon fiber to be measured was 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexyl-carboxylate (100 parts by weight) / 3 boron trifluoride monoethylamine (3 parts by weight) / acetone (4 weights). Part) is impregnated with carbon fiber or graphitized fiber and cured at 130 ° C. for 30 minutes. Further, the number of strands to be measured is 6, and the average value of each measurement result is the tensile strength. In this example, “Bakelite (registered trademark)” ERL4221 manufactured by Union Carbide Co., Ltd. was used as 3,4-epoxycyclohexylmethyl-3,4-epoxy-cyclohexyl-carboxylate.
<Intrinsic viscosity measurement>
<Intrinsic viscosity of polyacrylonitrile-based polymer>
150 mg of a polyacrylonitrile polymer dried by heat treatment at 120 ° C. for 2 hours is maintained at 25 ° C. and dissolved in 50 ml of dimethylformamide added with 0.1 mol / liter of sodium thiocyanate. The obtained solution was temperature-controlled in a hot water bath at 25 ° C., and the drop time between the marked lines was measured with an accuracy of 1/100 second using an Ostwald viscometer that was temperature-controlled at 25 ° C. in advance. Let time be t (seconds). Similarly, dimethylformamide added with 0.1 mol / liter of sodium thiocyanate in which the polyacrylonitrile-based polymer is not dissolved is also measured, and the drop time is defined as t ₀ (seconds). The intrinsic viscosity [η] is calculated using the following formula. In this example, Wako Pure Chemical Industries special grades were used for both sodium thiocyanate and dimethylformamide.
[Η] = {(1 + 1.32 × η _sp ) ^1/2 −1} /0.198
However,
η _sp = (t / t ₀ ) −1
[Examples 1-7, Comparative Examples 3-7]
100 parts by weight of a polyacrylonitrile polymer having an intrinsic viscosity of 1.8 shown in Table 1 and additives are dissolved in 400 parts by weight of dimethyl sulfoxide as a solvent with the composition shown in Table 1, and the mixture is stirred for 1 hour with a homomixer. Mixing was performed to obtain a spinning dope. The weight average molecular weights of various polymers used as additives are as follows. Polypropylene glycol: 1,000, polyoxyethylene oleate: 460, polyalkylene glycol ^{* 1} : 2,000, polyalkylene glycol ^{* 2} : 5,000, polydimethylaminosiloxane: 24,000.

  The obtained spinning solution was immediately passed through a filter with a mesh opening of 0.5 μm, and then discharged at 40 ° C. into a single hole having a diameter of 0.15 mm and a number of 6,000 holes in the air, and about 4 mm. After passing through the space, a coagulated yarn was obtained by a dry and wet spinning method introduced into a coagulation bath composed of an aqueous solution of 35% by weight dimethyl sulfoxide controlled at 3 ° C. The coagulated yarn was washed with water by a conventional method, and then stretched in warm water. Further, an amino-modified silicone-based silicone oil was added to obtain a stretched yarn in a bath having a single fiber fineness of 2.6 dtex. The drawn yarn in the bath is dried and heat-treated using a roller heated to 165 ° C., stretched 3.7 times in pressurized steam, and the total draw ratio is 13 times. The single fiber fineness is 0.7 dtex and the filament number is 6000. A carbon fiber precursor fiber was obtained. Four carbon fiber precursor fibers obtained were combined to obtain a total filament number of 24,000, and then stretched in air having a temperature distribution of 240 to 260 ° C. at a draw ratio of 1.0 for 100 minutes. Flame-resistant treatment was performed to obtain flame-resistant fibers. Subsequently, in a nitrogen atmosphere having a temperature distribution of 300 to 700 ° C., the obtained flame-resistant fiber is subjected to a preliminary carbonization treatment while being drawn at a draw ratio of 1.15, and further in a nitrogen atmosphere having a maximum temperature of 1500 ° C. Carbonization was performed with the draw ratio set to 0.99 to obtain continuous carbon fibers. Table 2 summarizes the specific gravity of the obtained flame-resistant fiber and the strand tensile strength and operability of the obtained carbon fiber.

In Comparative Example 3 in which polyoxyethylene oleate was mixed with the spinning solution, carbon fibers could not be obtained. In Comparative Example 4 in which polyalkylene glycol copolymerized with ethylene oxide and propylene oxide was mixed, flame resistance was not uniform. Therefore, yarn breakage occurred in the carbonization process. In Comparative Example 5 in which 0.3 part by weight of polydimethylaminosiloxane was mixed, the tensile strength was reduced because silicone remained in the carbon fiber although the process passability was good. In Comparative Example 6 in which benzoyl peroxide was mixed, the reaction rapidly progressed in the flameproofing process, yarn breakage occurred frequently in the carbonizing process, and the tensile strength of the obtained carbon fiber was low. Further, in Comparative Example 6 in which the polyacrylonitrile-based polymer contains a large amount of copolymer components, fusion occurs between the obtained carbon fibers, and not only the tensile strength is reduced, but also the winding of the roller in the carbonization process occurs frequently. The process passability was bad.
[Comparative Examples 1 and 2]
Flame-resistant fibers were obtained in the same manner as in Examples 1 to 4, except that polypropylene glycol was not mixed into the spinning dope. Carbon fibers were obtained from the obtained flame-resistant fibers in the same manner as in Examples 1 to 4, but carbon fiber could not be obtained because the flame resistance was not advanced in Comparative Example 1 which was homo-PAN. . In Comparative Example 2 containing a small amount of a copolymer component, yarn breakage occurred frequently in the carbonization process because the flame resistance was not sufficiently advanced. And the tensile strength of the carbon fiber obtained was low.

Claims (4)

  A polyacrylonitrile polymer having a copolymerization ratio of monomers other than acrylonitrile of 0.5 mol% or less and a polyalkylene glycol obtained by substantially polymerizing one kind of alkylene glycol are dissolved in a solvent. And the manufacturing method of the carbon fiber precursor fiber which spins the spinning stock solution which does not contain silicone substantially by the wet spinning method or the dry-wet spinning method.   The method for producing a carbon fiber precursor fiber according to claim 1, wherein the alkylene glycol is propylene glycol.   The method for producing a carbon fiber precursor fiber according to claim 1, wherein the polyacrylonitrile-based polymer has a copolymerization ratio of monomers other than acrylonitrile of substantially 0 mol%. The carbon fiber precursor fiber obtained by the production method according to any one of claims 1 to 3 is subjected to flame resistance treatment in air at a temperature of 200 to 300 ° C, and then inert at a temperature of 300 to 800 ° C. A method for producing carbon fiber which is pre-carbonized in an atmosphere and then carbonized in an inert atmosphere at a temperature of 1,000 to 2,000 ° C.