JP2007113154A - Polyacrylonitrile-based polymer for carbon fiber precursor fiber, and method for producing carbon fiber precursor fiber and carbon fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing carbon fiber with high tensile strength and high tensile modulus without impairing its productivity and process smoothness. <P>SOLUTION: A polyacrylonitrile-based polymer for carbon fiber precursor fiber has an intrinsic viscosity [η] of 1.5-2.2, an oxidation depth D of 3.6-6.0μm when subjected to flameproofing treatment and a melting point Tm under moist heat of 191-200°C measured by DSC (differential scanning calorimetry). The methods for producing carbon fiber precursor fiber using the above polymer and the resultant carbon fiber are also provided, respectively. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a carbon fiber excellent in tensile strength and tensile elastic modulus. Furthermore, the present invention relates to a polymer for carbon fiber precursor fibers and a method for producing carbon fiber precursor fibers, which are suitable for producing the above-described high-performance carbon fibers.

Carbon fibers are used in various applications because of their excellent mechanical and electrical properties. In recent years, in addition to conventional golf clubs, fishing rods and other sports and aircraft applications, the development of automotive components, CNG tanks, seismic reinforcement of buildings, so-called general industrial applications such as ship members, and so on, A technique for stably obtaining high carbon fibers is desired.
Such a carbon fiber is obtained by flame-proofing and carbonizing a precursor fiber made of an acrylonitrile-based polymer. By specifying the copolymer composition of the acrylonitrile-based polymer, there is a method for obtaining a carbon fiber having the above properties. It has been reported.

For example, by using an acrylic acid or methacrylic acid ester derivative as a copolymerization component in an acrylonitrile-based polymer, the oxygen permeability is improved during the flame resistance treatment of the precursor fiber, and the oxygen concentration distribution in the flame resistant fiber is uniform. A technique has been proposed in which the inside of a single fiber is made flame-resistant uniformly by controlling it to improve the tensile strength and tensile elastic modulus of the resulting carbon fiber (see Patent Document 1). This technology introduces a functional group with large steric hindrance into the side chain of the carbon fiber precursor fiber, thereby weakening the intermolecular interaction of the carbon fiber precursor fiber and improving the oxygen permeability in the flameproofing process. However, in this method, since the interaction between the polymer molecules is weakened by the monomer to be copolymerized, the melting point of the carbon fiber precursor fiber is lowered under wet heat, and the single fiber breakage is likely to occur in the steam drawing process. There has been a problem that the amount of fluff generated in carbon fibers increases and the quality deteriorates.
Further, for example, in an acrylonitrile-based polymer, the amount of thermally crosslinkable vinyl alone is used to crosslink between the polymer chains constituting the polymer to improve the melting point under wet heat, so that the yarn making process and the flameproofing process A technique for stably obtaining carbon fibers by suppressing yarn breakage and fusion is proposed (see Patent Document 2). However, this technique has a problem in that carbon fibers having sufficient strength and elasticity cannot be obtained because molecular movement is suppressed by crosslinking, and oxygen permeability into the single fiber of the precursor fiber becomes low. there were.
JP-A-2-84505 No. 48-43579

  An object of the present invention is to provide a method for producing carbon fibers having excellent tensile strength and tensile elastic modulus without impairing productivity and processability.

In order to achieve this object, the polyacrylonitrile-based polymer for carbon fiber precursor fibers of the present invention has the following constitution. That is, the intrinsic viscosity [η] is 1.5 to 2.2, the oxidation depth D during the flameproofing treatment is 3.6 to 6.0 μm, and the melting point Tm under wet heat measured by a differential scanning calorimeter. Is a polyacrylonitrile-based polymer for carbon fiber precursor fibers having a temperature of 191 to 200 ° C.
In the polyacrylonitrile-based polymer for carbon fiber precursor fibers of the present invention, a vinyl compound represented by the following general formula (1) and having a molar volume of 50 to 400 cm ³ / mol is added to 100 mol parts of acrylonitrile. It is preferable that 0.1 to 1.5 mole parts of the copolymer be copolymerized.

(In the general formula (1), R1 to R6 are composed of atomic groups composed of hydrogen, carbon, nitrogen, oxygen, or sulfur atoms)
Further, in the polyacrylonitrile-based polymer for carbon fiber precursor fiber of the present invention, it is also preferable that the flame resistance promoting component is further copolymerized in an amount of 0.1 to 1.0 mol part per 100 mol parts of acrylonitrile. .
In order to achieve the above object, the method for producing a carbon fiber precursor fiber of the present invention has the following configuration. That is, a method for producing a carbon fiber precursor fiber in which the polyacrylonitrile-based polymer is spun by a wet or dry wet method, and is subjected to steam drawing after a dry heat treatment, wherein the Tm (° C.), the temperature Td of the dry heat treatment (° C.) and steam stretching temperature Ts (° C.) are carbon fiber precursor fibers that satisfy the following expressions (2) and (3).
(Tm-30) ≦ Td ≦ (Tm-10) (2)
(Tm-50) ≦ Ts ≦ (Tm-30) (3)
Moreover, in order to achieve the said objective, the manufacturing method of the carbon fiber of this invention has the following structure. That is, the carbon fiber precursor fiber produced by the above-described method is subjected to flameproofing treatment at a draw ratio of 0.90 to 1.20 in air at 200 to 300 ° C., and then in an inert atmosphere at 300 to 800 ° C. This is a carbon fiber manufacturing method in which preliminary carbonization is performed at a draw ratio of 1.00 to 1.30, and carbonization is performed at an draw ratio of 0.97 to 1.10 in an inert atmosphere at 1000 to 2000 ° C.

  According to the present invention, high stretching in the firing step can be realized without impairing productivity and processability, and thereby carbon fibers excellent in tensile strength, tensile elastic modulus and compressive strength can be produced.

In the present invention, by controlling the intrinsic viscosity, oxygen permeability, and heat resistance under wet heat of the polymer to be used in a specific range, not only can the polymer be highly spinnable, but a uniform flame resistant structure can be obtained. In addition to being able to obtain carbon fibers with high mechanical properties by improving the stretchability in the carbonization process, efficient and stable steam stretching and dry heat stretching with less thread breakage and single fiber adhesion in the yarn making process. This makes it possible to obtain a carbon fiber with high stability and high strength and high elastic modulus.
It is essential that the intrinsic viscosity of the acrylonitrile polymer of the present invention is 1.5 to 2.2, preferably 1.4 to 2.0, more preferably 1.5 to 1.9. If the intrinsic viscosity is too small, the spinnability at the time of coagulation decreases, and if it is too large, the polymer tends to gel and stable spinning becomes difficult. Here, the intrinsic viscosity of the polyacrylonitrile polymer can be determined as follows. That is, 150 mg of a polyacrylonitrile-based polymer that had been heat-treated at 120 ° C. for 2 hours and completely dried was dissolved in 50 ml of dimethylformamide added with 0.1 mol / liter of sodium thiocyanate at 25 ° C. The temperature of the resulting 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. Seconds). Similarly, 0.1 mol / liter added dimethylformamide sodium thiocyanate in which the polyacrylonitrile polymer was not dissolved was also measured, and the dropping time was defined as t0 (seconds). The intrinsic viscosity [η] was calculated using the following formula. In the examples described later, special grades manufactured by Wako Pure Chemical Industries, Ltd. were used for both sodium thiocyanate and dimethylformamide.
[Η] = {(1 + 1.32 × ηsp) ^ (1/2) −1} /0.198
ηsp = (t / t0) −1
The intrinsic viscosity of the polyacrylic tolyl polymer can be controlled by the monomer concentration during polymerization, the amount of initiator and chain transfer agent, and the like. As the initiator, azobisbutyronitrile, azobismethylvaleronitrile, azobis-4-methoxy-2,4-dimethylvaleronitrile, or the like is preferably used. Chain transfer agents include mercapto compounds such as dodecyl mercaptan and monothioglycol, secondary amines such as methylpentylamine, tertiary amines such as triethylamine and n-tripropylamine, and phosphoric acids such as hypophosphorous acid. A compound or the like is preferably used.

  The polyacrylonitrile-based polymer of the present invention has an oxidation depth D during the flameproofing treatment of 3.6 to 6.0 μm, preferably 3.8 to 5.8 μm, from the viewpoint of improving stretchability in the carbonization step. More preferably, it is 4.0-5.5 micrometers. If the oxidation depth D is too small, the stretchability improving effect in the firing step is not clearly exhibited, and the tensile strength and tensile elastic modulus of the obtained carbon fiber may not be improved. There is a risk that the oxidation reaction in the flameproofing process will proceed excessively, the stretchability in the subsequent carbonization process will be reduced, and the yield of the resulting carbon fiber will be reduced. The oxidation depth D of the polyacrylonitrile polymer during the flameproofing treatment is measured as follows. First, the polymer is dissolved in a polyacrylonitrile-soluble solvent such as dimethyl sulfoxide or dimethylformamide so that the weight concentration is 25%, and then the solution is cast on a glass plate and fixed with a baker type applicator. Apply to a thickness of Next, the glass plate coated with the polymer is dried at 120 ° C. for 6 hours using a hot air dryer, and the solvent is removed to form a film having a thickness of 20 to 40 μm. The obtained film is heat-treated at 240 ° C. for 60 minutes and further at 250 ° C. for 60 minutes using a hot air dryer to perform flameproofing treatment. The obtained flame-resistant film is embedded in a resin and then polished, and the vertical section thereof is observed with an optical microscope at a magnification of 800 times. Since the oxidized portion and the non-oxidized portion can be distinguished by the difference in brightness, the thickness of the portion having a certain brightness from the film surface is measured at least 5 points, and the arithmetic average is the oxidation depth D (μm). To do.

  Further, the polyacrylonitrile polymer of the present invention has a melting point Tm under wet heat measured by a differential scanning calorimeter (hereinafter referred to as DSC), the heat resistance of the resulting carbon fiber precursor fiber, and consequently steam in the spinning process. From the viewpoint of improving stretchability, it is necessary to be 191 to 200 ° C. If the Tm is too high, steam at a higher temperature, that is, a higher pressure is required during the steam drawing, and the fiber breakage due to the high pressure becomes remarkable, resulting in a decrease in productivity and the quality of the obtained carbon fiber. , Mechanical properties are degraded. On the other hand, if Tm is too small, the adhesion between single fibers becomes remarkable, the temperature during drying and steam drawing in the yarn forming process must be lowered, and a longer treatment is required, resulting in productivity. And the quality and mechanical properties of the resulting carbon fiber are reduced. The melting point Tm under wet heat of the polyacrylonitrile polymer can be measured as follows. First, the polymer is freeze-pulverized to obtain a powder having a particle size of 100 mesh. 5 mg of the powder is precisely weighed and sealed with 5 mg of pure water in a DSC sample pan capable of sealing with a pressure resistance of 2 MPa or more. The differential calorific value is measured from room temperature to 220 ° C. at a rate of temperature increase of 10 ° C./min, and the peak of the endothermic peak appearing in the vicinity of 150 to 200 ° C. is defined as the melting point Tm under wet heat.

In the polyacrylonitrile-based polymer, in order to bring the oxidation depth at the time of flameproofing treatment and the melting point Tm under wet heat into the above-described ranges, the compound is represented by the following general formula (1), and the molar volume of the molecule is This can be achieved by copolymerizing a vinyl compound of 50 to 400 cm ³ / mol, preferably 80 to 350 cm ³ / mol, more preferably 100 to 300 cm ³ / mol.

(In the general formula (1), R1 to R6 are composed of atomic groups composed of hydrogen, carbon, nitrogen, oxygen, or sulfur atoms)
Here, the molar volume is a value obtained by dividing the molecular weight by the specific gravity at 20 ° C., and is an index corresponding to the bulkiness of the monomer. In general, the larger the molar volume, the greater the effect of improving oxygen permeability, and if it is too small, the effect of oxygen permeability is reduced, whereas if it is too large, the molecule is too bulky, so When there is a significant decrease in yarn breakage during spinning, due to a significant decrease in melting point under wet heat, a decrease in yield due to excessive oxidation during flame resistance, and a further decrease in the density of the resulting carbon fiber There is.
Examples of the compound represented by the general formula (1) and having a molar volume of 100 to 300 cm ³ / mol include 2,3-dimethyl 1,3-butadiene, 1,4-diphenyl 1,3-butadiene, and pentadie. Nar, 1,3-hexadiene, 2,5-dimethyl 2,4-hexadiene, 2,4-dimethyl 1,3-pentadiene, 2,4-hexadienal, 1,6-diphenyl 1,3,5-hexa Triene, 1-isopropyl 4-methyl 1,3-cyclohexadiene, heptadienal, 1,3,5-cycloheptatriene, 7-methyl 3-methylene 1,6-octadiene, 2,4-decadiene 1-ol, 2, 4-Decadienal and divinylbenzene are exemplified, and the compound is represented by the general formula (1) and has a molar volume of 80 to 350 cm ³ / mol. In addition to the above compound group, isoprene, 3-methyl 1,2-butadiene, pentadiene, 1,3-cyclohexadiene are exemplified, and further represented by the general formula (1) and having a molar volume of 50 the compound is ~400cm ³ / mol, in addition to the above described compounds, furan, butadiene diepoxide, 1,1,4,4-tetraphenyl butadiene, 1,2,3,4-tetraphenyl Examples thereof include 1,3-cyclopentadiene and tetraphenylcyclopentadienone. In the polyacrylonitrile-based polymer of the present invention, in order to bring the oxidation depth at the time of flameproofing treatment and the melting point Tm under wet heat into the ranges described above, the amount of copolymerization of the vinyl compound described above is based on 100 mol parts of acrylonitrile. It is good to set it as 0.1-1.5 mol part, Preferably it is 0.2-1.2 mol part, More preferably, it is 0.3-1.0 mol part. If the copolymerization amount is too small, the effect of improving the oxygen permeability of the carbon fiber precursor fiber is reduced. Conversely, if the amount is too large, the amount of intermolecular crosslinking of the carbon fiber precursor fiber is increased. In some cases, carbon fibers having high strength and high elasticity cannot be obtained.
In the present invention, the polyacrylonitrile-based polymer contains 0.1 to 1.0 mole, preferably 0. 0, of a flame retardant component as a copolymerization component with respect to 100 mole of acrylonitrile in addition to the vinyl compound described above. It is desirable to include 12 to 0.4 mole part, more preferably 0.15 to 0.30 mole part. Copolymerization of the flame resistance-promoting component is desirable for the purpose of increasing productivity because the processing time of the flame resistance process can be shortened by rapid flame resistance. When the amount of copolymerization of the flame resistance promoting component is too small, the effect of promoting flame resistance, which is the effect thereof, becomes small. The more the amount of copolymerization of the flameproofing promoting component, the more the flameproofing reaction is promoted. However, if it is too much, the exothermic rate increases, and there is a risk that a runaway reaction may be caused by the accumulation of reaction heat. .
Specific examples of the flame resistance promoting component include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid, acrylamide, and methacrylamide. From the viewpoint of increasing the melting point under wet heat of the acrylic fiber for carbon fiber precursor, it is desirable to maintain the yarn forming property by adding a small amount of a compound having a high flame resistance promoting ability to suppress a decrease in the melting point under wet heat. From that viewpoint, as the flame retardant promoting component, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid, mesaconic acid are preferable, and itaconic acid, maleic acid, mesaconic acid are more preferably used. It is done.
As a polymerization method for producing the polyacrylonitrile-based polymer for carbon fiber precursor fiber in the present invention, a known polymerization method such as solution polymerization, suspension polymerization, emulsion polymerization or the like can be selected. From the viewpoint of polymerization, solution polymerization is preferably used. As the solution in the case of solution polymerization, an organic solvent in which polyacrylonitrile is soluble, such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide or the like is generally used.
Next, the manufacturing method of the carbon fiber precursor fiber of this invention is demonstrated.
As the carbon fiber precursor fiber of the present invention, the above-described polyacrylonitrile polymer for carbon fiber precursor fiber is used. Usually, such a polymer is dissolved in a polyacrylonitrile-soluble solvent such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide or the like to obtain a spinning dope. When using solution polymerization, it is preferable that the solvent used for the polymerization and the solvent used for the spinning dope are the same because the step of re-dissolution is unnecessary. The concentration of the polymer in the spinning dope is preferably 10 to 40% by weight from the viewpoint of stock solution stability.
It is preferable to obtain a high-strength carbon fiber by removing the spinning raw solution through a filter having an opening of 1 μm or less before spinning to remove the polymer raw material and impurities mixed in each step.

  The spinning solution is spun from the die by a wet spinning method or a dry-wet spinning method, and introduced into a coagulation bath to coagulate the fibers. From the viewpoint of improving the denseness of the obtained carbon fiber precursor fiber, the dry and wet spinning method is more preferable.

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

  After being introduced into a coagulation bath and solidifying the yarn, it is washed with water, subjected to stretching in the bath and application of oil as necessary, and then subjected to drying heat treatment and steam stretching to obtain a carbon fiber precursor fiber.

  Here, the solidified yarn may be stretched directly in a stretching bath without being washed with water, or may be stretched in a bath after removing the solvent by washing. Such stretching in the bath is usually performed in a single or a plurality of stretching baths whose temperature is adjusted to 30 to 98 ° C., and the stretching ratio is 1 to 5 times, preferably 2 to 4 times.

  After bath drawing, for the purpose of preventing adhesion between single fibers, it is preferable to apply an oil agent made of silicone or the like to the yarn. Such a silicone oil agent is preferably a modified silicone and an amino-modified silicone having high heat resistance.

  In the method for producing a carbon fiber precursor fiber of the present invention, the drying heat treatment and the steam drawing are carried out by assuming that the melting point under wet heat measured by DSC of the polyacrylonitrile polymer is Tm (° C.) and the heat treatment temperature Td (° C.) and It is essential to set the steam stretching temperature Ts (° C.) within the range of the following formula.

(Tm-30) ≦ Td ≦ (Tm-10)
(Tm-50) ≦ Ts ≦ (Tm-30)
More preferably,
(Tm−20) ≦ Td ≦ (Tm−10)
(Tm-40) ≦ Ts ≦ (Tm-30)
It is. In general, polyacrylonitrile does not show a melting point under dry heat, but it is known that the melting point of the polyacrylonitrile drops when water coexists. Since the drying heat treatment and the steam drawing are performed in the presence of water, if the treatment temperature exceeds the melting point Tm under wet heat of the polyacrylonitrile-based polymer used, melting occurs, and the processability and the resulting carbon fiber precursor fiber, The mechanical properties of carbon fibers are reduced. As described above, since the melting point Tm under wet heat changes depending on the copolymerization component of the polyacrylonitrile-based polymer to be used and the amount of the copolymerization, setting the heat treatment temperature according to the Tm has high tensile strength and high This is important for obtaining a carbon fiber having a tensile modulus with high productivity.

  On the other hand, the higher the drying heat treatment temperature Ts, the more advantageous from the viewpoint of drying efficiency and the density of the resulting carbon fiber precursor fiber, and the higher the steam stretchability temperature Ts, the easier the plasticization proceeds. Since it is advantageous for improving the properties, the potential of the polyacrylonitrile-based polymer of the present invention can be maximized by controlling Td and Ts within the above range.

  In the present invention, the draw ratio in the steam drawing 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.

  In the present invention, the single fiber fineness of the carbon fiber precursor fiber is 0.5 to 1.5 dtex, preferably 0.55 to 1.0 dtex, more preferably 0.6 to 0.8 dtex. If the single fiber fineness is too small, the spinnability and process stability may decrease.If it is too large, the internal and external structural differences in flame resistance will increase, and the subsequent processability in the carbonization process will decrease. The tensile strength and tensile elastic modulus of the carbon fiber produced may decrease.

  In the present invention, the number of filaments per yarn of the carbon fiber precursor fiber is 1,000 to 3,000,000, preferably 12,000 to 3,000,000, more preferably 24,000 to 2. , 500,000, most preferably from 36,000 to 2,000,000. From the viewpoint of productivity, it is preferable that the number of filaments is large. 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.
In the method for producing carbon fiber of the present invention, the carbon fiber precursor fiber obtained as described above is subjected to flameproofing treatment at a draw ratio of 0.90 to 1.20 in air at 200 to 300 ° C. Pre-carbonization treatment is performed at a stretch ratio of 1.00 to 1.30 in an inert atmosphere at 800 ° C., and carbonization treatment is performed at a stretch ratio of 0.97 to 1.10 in an inert atmosphere at 1000 to 2000 ° C. Subsequently, the carbon fiber thus obtained can be graphitized at 2,000 to 3,000 ° C. in an inert atmosphere to obtain a graphitized fiber having a higher elastic modulus.

  In the present invention, the stretch ratio in the flameproofing treatment needs to be 0.90 to 1.20, preferably 0.95 to 1.15, more preferably 0.97 to 1.10. If the draw ratio is too small, the degree of orientation of the resulting flame-resistant fiber will be insufficient, and the mechanical properties of the resulting carbon fiber will decrease. Conversely, if it is too large, the processability will decrease due to the occurrence of fluff and yarn breakage. To do.

  In the present invention, the treatment time of the flameproofing treatment can be appropriately selected within a range of 10 to 100 minutes, but is set so that the specific gravity of the obtained flameproofing fiber is within a range of 1.3 to 1.35. Is preferable from the viewpoint of the process passability of the subsequent pre-carbonization process and the mechanical properties of the resulting carbon fiber.

  In the present invention, preliminary carbonization treatment, carbonization treatment, and graphitization treatment are performed in an inert atmosphere. Examples of the gas to be used include nitrogen, argon, and xenon, and nitrogen is preferably used from an economical viewpoint. .

  In the present invention, the temperature in the preliminary carbonization step needs to be 300 to 800 ° C., and the temperature rising rate in the range is preferably 500 ° C./min or less.

  In the present invention, the draw ratio in the preliminary carbonization step needs to be 1.00 to 1.30, preferably 1.05 to 1.25, more preferably 1.08 to 1.20. If the draw ratio is too small, the degree of orientation of the resulting pre-carbonized fiber will be insufficient, and the mechanical properties of the resulting carbon fiber will be reduced. On the other hand, if the draw ratio is too large, the processability will be reduced due to the occurrence of fluff and yarn breakage. To do.

  In the present invention, it is necessary to set the maximum temperature in the carbonization treatment within a range of 1000 to 2000 ° C. according to the desired mechanical properties of the carbon fiber. In general, the higher the maximum temperature for carbonization, the higher the tensile modulus of the carbon fiber obtained, but the tensile strength becomes maximum at around 1500 ° C. From the viewpoint of increasing both the tensile strength and the tensile modulus, the maximum carbonization temperature is more preferably 1200 to 1700 ° C, and further preferably 1300 to 1600 ° C.

  In the present invention, the drawing ratio of the carbonization treatment needs to be 0.970 to 1.100, preferably 0.975 to 1.005, more preferably 0.980 to 1.000. If the draw ratio is too small, the degree of orientation and denseness of the resulting carbon fiber will be insufficient, and the mechanical properties will be reduced, while if too large, the processability will be reduced due to the occurrence of fluff and yarn breakage.

  In the present invention, when the graphitization treatment is performed, the stretching ratio is 1.000 to 1.200, preferably 1.005 to 1.150, and more preferably 1.010 to 0.1.100. If the draw ratio is too small, the degree of orientation and denseness of the graphitized fiber obtained will be insufficient and the mechanical properties will be reduced. If it is too large, the processability will be reduced due to the occurrence of fluff and yarn breakage.

  The obtained carbon fiber or graphitized fiber can be subjected to electrolytic treatment for 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 applied carbon fiber and graphitized fiber.

  Such electrolytic treatment can optimize the adhesion between the carbon fiber and graphite fiber and the matrix in the composite material obtained, the brittle breakage of the composite material due to too strong adhesion, and the problem that the tensile strength in the fiber direction decreases. Although the tensile strength in the fiber direction 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 a balance in both the fiber direction and the non-fiber direction. Excellent strength characteristics are developed.

  After the electrolytic treatment, a sizing treatment can also be performed in order to impart convergence to the obtained carbon fiber and graphitized fiber. 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 thus obtained according to the present invention preferably has a strand tensile strength of 6 GPa or more and a strand elastic modulus of 30 GPa or more, a strand tensile strength of 6.6 GPa or more, and a strand elastic modulus of 330 GPa or more. More preferably, the strand tensile strength is 7.0 GPa or more and the strand elastic modulus is 350 GPa or more.

  The graphitized fiber thus obtained according to the present invention preferably has a strand tensile strength of 5 GPa or more and a strand elastic modulus of 400 GPa or more, a strand tensile strength of 5.5 GPa or more, and a strand elastic modulus of 450 GPa or more. More preferably, the strand tensile strength is 6 GPa or more, and the strand elastic modulus is more preferably 500 GPa or more.

  The carbon fiber and graphitized fiber obtained by the present invention have high tensile strength and tensile modulus, that is, high elongation, and high modulus can be obtained at a relatively low firing temperature, so that the compressive strength is also high. Can be expressed. Therefore, autoclave molding as a prepreg, molding by resin transfer molding as a preform such as woven fabric, or molding by filament winding, sports members such as aircraft members, pressure vessel members, automobile members, fishing rods, golf shafts, etc. Can be suitably used.

The present invention will be described more specifically. In the present invention, various physical property values can be determined by the methods described below.
<Intrinsic viscosity>
150 mg of a polyacrylonitrile-based polymer that has been heat-treated at 120 ° C. for 2 hours and completely dried is dissolved in 50 ml of dimethylformamide containing 0.1 mol / liter of sodium thiocyanate at 25 ° C. The temperature of the resulting 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. Seconds). Similarly, 0.1 mol / liter-added dimethylformamide with sodium thiocyanate in which the polyacrylonitrile-based polymer for carbon fiber precursor fibers was not dissolved was also measured, and the drop time was defined as t0 (seconds). The intrinsic viscosity [η] is calculated using the following formula.
[Η] = {(1 + 1.32 × ηsp) ^1/2 −1} /0.198
ηsp = (t / t0) −1
In this example, sodium thiocyanate and dimethylformamide were both special grades manufactured by Wako Pure Chemical Industries.
<Oxidation depth D during flameproofing treatment>
A polyacrylonitrile-based polymer to be measured is dissolved in dimethyl sulfoxide so as to have a weight concentration of 25% to form a solution, and then the solution is cast on a glass plate, and about 80 μm using a Baker type applicator. Apply to a thickness. Next, the glass plate coated with the polymer solution is dried in air at 120 ° C. for 6 hours using a hot air dryer to evaporate dimethyl sulfoxide to form a film having a thickness of about 20 μm. The obtained film is heat-treated at 240 ° C. in air for 60 minutes and further in air at 250 ° C. for 60 minutes using a hot air dryer to perform flameproofing treatment. The obtained flame-resistant film is polished after being embedded in a resin, and a cross section perpendicular to the film surface is observed with an optical microscope at a magnification of 800 times and photographed. In the cross section, the part where oxidation has progressed is observed as a dark layer, and the part which has not progressed is observed as a bright layer. Therefore, the distance from the film surface to the boundary between the dark layer and the bright layer is measured at five points on the photograph. The arithmetic average is defined as the oxidation depth D (μm).
<Melting point Tm under wet heat>
The polyacrylonitrile polymer to be used for measurement is freeze-ground in liquid nitrogen, and then passed through a sieve having an aperture of 0.5 mm to obtain a powder. 5 mg of this powder is precisely weighed and sealed in a DSC medium pressure pan (withstand pressure of 2 MPa) together with 5 mg of pure water. Using a DSC apparatus, DSC measurement was performed from room temperature to 220 ° C. at a rate of temperature increase of 10 ° C./min, and the temperature corresponding to the end of the endothermic peak appearing near 150 to 200 ° C. was read. And In the present example, a medium pressure pan ME29990 manufactured by Mettler was used as the medium pressure pan for DSC, and a DSC3100SA manufactured by Bruker was used as the DSC device.
<Flame resistant fiber specific gravity>
The method described in JIS R7601 (1986) is followed. That is, 1.0 to 1.5 g of fiber is collected and dried in air at 120 ° C. for 2 hours using a hot air dryer. After measuring the absolute dry mass A (g), it was impregnated in ethanol with a known specific gravity (specific gravity ρ), and the fiber mass B (g) in ethanol was measured. The following formula, fiber specific gravity = (A × ρ) / ( The fiber specific gravity D is obtained by AB). In this example, Wako Pure Chemicals special grade was used as ethanol without purification.
<Strand tensile strength and strand tensile modulus of carbon fiber>
Determined according to JIS R7601 (1986) “Resin-impregnated strand test method”.

In this example, the resin-impregnated strand of carbon fiber to be measured was “BAKELITE (registered trademark)” ERL 4221 (100 parts by weight) / 3 boron trifluoride monoethylamine (3 parts by weight) / acetone (produced by Union Carbide Corporation). 4 parts by weight) was impregnated into carbon fiber, and heat treated at 130 ° C. for 30 minutes and cured. Further, the number of strands measured was 6, and the arithmetic average value of each measurement result was taken as the tensile strength and tensile modulus of the carbon fiber.
<Steam stretchability in the yarn making process>
The yarn to be evaluated is measured for presence or absence of yarn breakage while changing the draw ratio by 0.1 times in pressurized steam at 145 ° C., and the maximum draw ratio at which no yarn breakage occurs is defined as steam drawability (times).
<Number of carbonized fuzz>
On the exit side of the carbonization step, the number of fluffs of the running yarn is visually measured over a length of 30 m, and the number of fluffs per 1 m is defined as the number of fluffs (pieces / m).
[Examples 1 to 4, Comparative Examples 1 to 6]
Azobisisobutyronitrile was started in 100 mol parts of acrylonitrile by a solution polymerization method using dimethyl sulfoxide as a solvent at the copolymerization ratio shown in Table 1 with the second component vinyl compound shown in Table 1 and the flame resistance promoting component shown in Table 1. Radical polymerization was performed as an agent to obtain a polyacrylonitrile-based polymer. About the obtained polymer, oxidation depth D (micrometer), melting | fusing point Tm (degreeC) under wet heat, and glass transition point Tg (degreeC) were measured.
The concentration of each polymer obtained was adjusted to 25% by weight in dimethyl sulfoxide, and then ammonia gas was blown until the pH reached 8.5 to neutralize itaconic acid, while the ammonium group was neutralized. Was introduced into a polyacrylonitrile copolymer to prepare a spinning dope. The obtained spinning dope is passed through a filter having a mesh opening of 0.5 μm, and at 40 ° C., once discharged into the air using a spinneret having a single hole diameter of 0.15 mm and a hole number of 6,000, 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 and then stretched 3.5 times in warm water, and an amino-modified silicone oil was further 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 subjected to a drying heat treatment using a roller heated to 165 ° C., and then drawn 3.7 times in a pressurized steam at 145 ° C. to give a total draw ratio of 13 times and a single fiber fineness of 0.1. A carbon fiber precursor fiber having 7 dtex and a filament number of 6,000 was obtained. In addition, steam stretchability was evaluated about the dry-heat-treated yarn.
Four carbon fiber precursor fibers obtained were combined to give a total filament number of 24,000, and subjected to a flame resistance treatment while being drawn in air at 240 to 260 ° C. at a draw ratio of 1.0. 1.35 flameproof fiber was obtained.
The obtained flame-resistant fiber was then subjected to preliminary carbonization while being stretched at a stretch ratio of 1.15 in a nitrogen atmosphere at 300 to 700 ° C., and further, the stretch ratio was 0 in a nitrogen atmosphere at a maximum temperature of 1500 ° C. To 99. Carbonization treatment was performed to obtain carbon fibers having a specific gravity of 1.80 to 1.83. At this time, the number of carbonized fluff was measured on the exit side of the carbonization step. Moreover, strand tensile strength and strand tensile elastic modulus were measured about the obtained carbon fiber.
Oxidation depth D (μm), melting point Tm (° C.) under wet heat, and glass transition point Tg (° C.), steam stretchability in the spinning process, number of carbon fiber fluff, strand tensile strength and strand tensile elasticity The results obtained for the rates are summarized in Table 2.

Claims (6)

The intrinsic viscosity [η] is 1.5 to 2.2, the oxidation depth D during the flameproofing treatment is 3.6 to 6.0 μm, and the melting point Tm (° C.) under wet heat measured by a differential scanning calorimeter. ) Is a polyacrylonitrile-based polymer for carbon fiber precursor fibers having a temperature of 191 to 200 ° C. A vinyl compound represented by the following general formula (1) and having a molar volume of 50 to 400 cm ³ / mol is obtained by copolymerizing 0.1 to 1.5 parts by mole with respect to 100 parts by mole of acrylonitrile. 1. A polyacrylonitrile-based polymer for carbon fiber precursor fibers according to 1.

(In the general formula (1), R1 to R6 are composed of atomic groups composed of hydrogen, carbon, nitrogen, oxygen, or sulfur atoms) Furthermore, the acrylonitrile-type polymer for carbon fiber precursor fibers of Claim 2 formed by copolymerizing 0.1-1.0 mol part of flameproofing promotion components with respect to 100 mol part of acrylonitrile. A method for producing a carbon fiber precursor fiber, wherein the polyacrylonitrile-based polymer according to any one of claims 1 to 3 is spun by a wet or dry-wet method, and is subjected to steam drawing after a dry heat treatment, wherein the Tm (° C ), A carbon fiber precursor fiber manufacturing method in which the temperature Td (° C.) of the drying heat treatment and the temperature Ts (° C.) of the steam drawing satisfy the following formulas (2) and (3).
(Tm-30) ≦ Td ≦ (Tm-10) (2)
(Tm-50) ≦ Ts ≦ (Tm-30) (3) The carbon fiber precursor fiber produced by the method according to claim 4 is subjected to flameproofing treatment at a draw ratio of 0.90 to 1.20 in air at 200 to 300 ° C, and then an inert atmosphere at 300 to 800 ° C. A carbon fiber production method in which pre-carbonization is performed at a draw ratio of 1.00 to 1.30 and carbonization is performed at 1000 to 2000 ° C. in an inert atmosphere at a draw ratio of 0.97 to 1.10. The carbon fiber precursor fiber produced by the method according to claim 4 is subjected to flameproofing treatment at a draw ratio of 0.90 to 1.20 in air at 200 to 300 ° C, and then an inert atmosphere at 300 to 800 ° C. Pre-carbonized at a draw ratio of 1.00 to 1.30, carbonized at a draw ratio of 0.97 to 1.10 in an inert atmosphere of 1000 to 2000 ° C., and an inert atmosphere of 2000 to 3000 ° C. A method for producing graphitized fiber, wherein the graphitization is performed at a draw ratio of 1.00 to 1.20.