JP2016125173A - Carbon fiber bundle and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon fiber bundle having excellent tensile strength, tensile elasticity and shear elasticity even with large average single fiber fineness and high hydrophilicity and a manufacturing method therefor.SOLUTION: There is provided a carbon fiber bundle satisfying σ/GPa≥10.6-0.75d/μm (1) and E/GPa≥420-25d/μm (2), where d (μm) is average single fiber diameter of single fibers and E (GPa) is resin impregnated strand tensile elasticity of the carbon fiber and σ (GPa) is resin impregnated strand tensile strength in the carbon fiber consisting of a plurality of single fibers and having nitrogen content of 8 to 18 mass% at d=7.5 to 9.0 μm.SELECTED DRAWING: None

Description

  The present invention relates to a high-quality, high-performance carbon fiber bundle that satisfies excellent tensile strength, tensile modulus, and shear modulus, has excellent affinity with water, and has less fluff, and a method for producing the same. .

  Carbon fiber is used as a reinforcing fiber for composite materials due to increasing environmental problems.For example, tire fibers that use water in the manufacturing process are used for applications where the reinforcing fiber itself requires hydrophilicity. There is a strong demand for higher performance and quality. Increasing the mechanical properties of carbon fiber contributes to reducing the weight of components such as pressure vessels. Therefore, the mechanical properties such as tensile strength, tensile modulus, and shear modulus are improved in a balanced manner, and at the same time, the cost of the final component is reduced. From the point of view, the high quality of the carbon fiber that does not reduce the productivity due to fuzz and the like is an important issue.

  In a brittle material such as carbon fiber, for example, the tensile strength can be increased by reducing the defect size according to the Griffith equation or increasing the fracture toughness value. In particular, the improvement of the fracture toughness value is effective in that a high tensile strength can be achieved without depending on the state of the defect size (Patent Document 1).

  In order to enhance the mechanical properties such as tensile strength and tensile modulus in a well-balanced manner, it is important to eliminate the difference between the inner and outer structures existing in the cross section of the single fiber. As a method to improve the mechanical properties while suppressing the difference between the inner and outer structures of the single fiber cross-section so far, for example, by making flame resistance in the liquid phase in flame resistance, the flame resistance time is shortened and the performance of the carbon fiber is improved. The method of doing is proposed (patent document 2). Moreover, in the proposal of patent document 3, the temperature control area | region of a flameproofing process is made into 2-3, and the internal / external structure difference control of a flameproofing fiber is performed by controlling the specific gravity increase rate with respect to flameproofing time. In the proposal of Patent Document 4, the oxygen atmosphere in the flameproofing furnace and the flameproofing temperature are controlled in accordance with the specific gravity of the flameproofing fiber, and the difference between the internal and external structures due to insufficient oxygen supply is suppressed.

  Moreover, in order to improve compressive strength, the method of raising torsional elastic modulus is known (patent documents 5-7).

  Also, because it has a high saturated moisture content and a high affinity for water, it manufactures tire cords, papers, and cement reinforcements that have been obtained through a manufacturing process using water, such as resorcin formalin latex. As for carbon fibers that are preferably used in this case, techniques for reducing the tensile elastic modulus of carbon fibers by lowering the carbonization temperature are known (Patent Documents 8 and 9).

WO97 / 45576 pamphlet JP 2004-300600 A JP 2006-283225 A JP-A-10-251923 JP 09-170170 A JP 05-214614 A JP 2013-202803 A Japanese Patent Laid-Open No. 61-119717 JP-A 62-265329

  In general, when trying to achieve higher performance of carbon fiber, attempts are often made by reducing the average single fiber fineness, but if the average single fiber fineness is reduced, the quality deteriorates due to problems such as fluff. It becomes easy to do. On the other hand, it is known that when the average single fiber fineness is increased, an internal / external structure difference is generated in the flameproofing process, and the performance is significantly reduced. In order to achieve high performance while increasing the average single fiber fineness, there was a technology that tried to reduce the difference between the inner and outer structures in the prior art, but by adding other copolymer components to reduce the difference between the inner and outer structures A lot of fluff was generated, and not only the quality but also the performance was lowered. In the proposal of Patent Document 1 for the purpose of improving the tensile strength, the silicone oil agent, the single fiber fineness, and the inner / outer structure difference are controlled, but in the examples, a large amount of the copolymer component is added as 3.5 to 5.7 mol%. Therefore, the tensile elastic modulus remained at a low level of 235 to 270 GPa, and when the carbonization temperature was raised to increase this, the tensile strength was greatly reduced, and the shear elastic modulus was also at a low level.

  In the proposal of Patent Document 2 which studied the suppression of the difference between the inner and outer structures, the liquid phase flameproofing technology has achieved a significant reduction in flameproofing time and high tensile strength and tensile modulus. The difference has not improved, and the shear modulus has not improved. In addition, the proposal of Patent Document 3 does not reach the quantitative control of the internal / external structural difference, and the expression of the elastic modulus potential is limited. In the proposal of Patent Document 4, the effect of suppressing the inner and outer structures by supplying oxygen is small, and neither the tensile strength nor the tensile elastic modulus has been greatly improved. As described above, the proposals in Patent Documents 2 to 4 attempt to control the difference between the inner and outer structures, but have not reached the quantitative control, and although there are examples in which the tensile elastic modulus can be improved, the tensile strength, the shear elasticity The rate was not high at the same time.

  In the proposals of Patent Documents 5 to 7, the torsional elastic modulus is defined as one type of shearing elastic modulus, and attempts are made to improve the shearing elastic modulus by increasing this. In Patent Document 5 or 6, ion implantation or electron beam irradiation is used to increase the torsional elastic modulus, and the shear elastic modulus is satisfactory because it includes lattice defects because the covalent bonds are cut and rearranged. It is not something to do. In addition, in the examples, carbon fibers having a relatively small diameter are treated, and the ion implantation distance from the surface is short, so that the effect is limited for those having a large diameter. Patent Document 7 describes that even if the single fiber fineness is larger than usual, the carbon fiber physical properties equivalent to those of a normal product are expressed, and the shear elastic modulus is specified to be 4 GPa or more, but at a completely satisfactory level. There is no.

  As described above, although techniques for improving the tensile modulus and shear modulus independently can be seen, there are techniques for satisfying the tensile modulus and shear modulus at a high level and achieving low costs. Absent.

  Further, in the proposals of Patent Documents 8 and 9, the saturated moisture content of carbon fiber is high and the affinity for water is high, but the difference in internal and external structures is not eliminated, so that the tensile elastic modulus is as low as 180 to 200 GPa. Cannot be a substitute for commercially available carbon fiber.

  In view of such circumstances, the present invention provides a carbon fiber bundle having a high tensile strength, tensile elastic modulus and shear elastic modulus even when the average single fiber fineness is large, and a method for producing the same. For the purpose.

In order to achieve the above object, the carbon fiber bundle of the present invention has one of the following configurations.
[1] In a carbon fiber bundle composed of a plurality of single fibers, the average single fiber diameter of the single fibers is d (μm), the resin-impregnated strand tensile elastic modulus of the carbon fiber bundle is E (GPa), and the resin impregnation When the strand tensile strength is σ (GPa),
σ / GPa ≧ 10.6−0.75 d / μm (1)
E / GPa ≧ 420−25d / μm (2)
, A carbon fiber bundle having d of 7.5 to 9.0 μm and a nitrogen content of 8 to 18% by mass.
[2] The carbon fiber bundle according to [1], wherein the shear elastic modulus is 13 to 20 GPa.
[3] The carbon fiber bundle according to [1] or [2], wherein the blackened thickness of the outer peripheral portion of the cross section perpendicular to the fiber axis direction of the carbon fiber single fiber is 3.2 μm or more.

Moreover, the manufacturing method of the carbon fiber bundle of this invention has either of the following structures.
[4] A carbon fiber bundle in which a polyacrylonitrile-based precursor fiber bundle containing 99.1 to 99.99% by mass of polyacrylonitrile and 0.01% by mass or more of a copolymer component is flameproofed and then carbonized. In the production method, the copolymer component has a Tg of the homopolymer of 50 to 250 ° C., and the flame resistance treatment has a nitrile consumption rate of 10 to 20% when the flame resistance treatment time is 30 minutes, and flame resistance. A method for producing a carbon fiber bundle having a nitrile consumption rate of 50 to 95% and a carbonization temperature of 800 to 1150 ° C. at the end of the carbonization treatment.
[5] The method for producing a carbon fiber bundle according to [4], wherein the flameproofing treatment time during which the nitrile consumption rate is 20% to 60% is 6 to 25 minutes.

  According to the present invention, a carbon fiber bundle exhibiting excellent tensile elastic modulus by effectively suppressing a difference in inner and outer structures in a single fiber cross section and having high affinity with water due to low carbonization treatment temperature. Is obtained. For this reason, it is easy to increase the average single fiber fineness, provides high quality, high performance, and provides a method for producing high-performance carbon fiber bundles when water-based resin systems are used as matrix resins. can do.

  The configuration of the carbon fiber bundle of the present invention and the preferred form for carrying out the present invention will be described in detail below.

  The carbon fiber bundle of the present invention has a nitrogen content of 8 to 18% by mass, preferably 10 to 16% by mass, and more preferably 12 to 15% by mass. When it is less than 8% by mass, the affinity with water is insufficient, and when it exceeds 18% by mass, the tensile elastic modulus cannot be satisfied. The carbon fiber bundle of the present invention having a high affinity with water exhibits a high physical property in a resin system using water when making a composite material. The nitrogen content can be measured by an elemental analysis test and can be controlled by the carbonization temperature and the carbonization time. It is preferable to control the carbonization temperature to approximately 1000 ° C.

  The average single fiber diameter d (μm) of the single fibers constituting the carbon fiber bundle of the present invention is 7.5 to 9.0 μm, preferably 7.5 to 8.5 μm, and more preferably 8.0. -8.5 [mu] m. The smaller the average single fiber diameter, the more the resin-impregnated strand tensile elastic modulus (hereinafter sometimes simply referred to as “tensile elastic modulus”) / shear elastic modulus tends to improve, while the average single fiber diameter is 7.5 μm. In the above case, it becomes high quality without fluff, and when it is 9.0 μm or less, the flexibility of the carbon fiber bundle can be maintained, and the occurrence of fluff when making a composite material can be reduced. The average single fiber diameter can be calculated from the mass per unit length of the carbon fiber bundle, the specific gravity, and the number of single fibers. The average single fiber diameter can be controlled by adjusting the single fiber fineness of the polyacrylonitrile-based precursor fiber.

In the present invention, when the tensile strength of the resin-impregnated strand of the carbon fiber bundle (hereinafter, also simply referred to as tensile strength) is σ (GPa), the following formula σ / GPa ≧ 10.6−0.75 d / μm.・ (1)
Satisfied. Generally, the larger the average single fiber diameter of the carbon fiber, the lower the physical properties of the entire carbon fiber due to the lower physical properties of the carbon fiber inner layer. Since the single fiber in the carbon fiber of the present invention has a suppressed difference in internal and external structures, the carbon fiber has a high level of tensile strength, tensile modulus, and shear modulus at the same average single fiber diameter. In the formula (1) of the present invention, “σ / GPa ≧ 11.0-0.75 d / μm” is preferable, and “σ / GPa ≧ 11.5-0.75 d / μm” is more preferable. If the tensile strength of the carbon fiber of the present invention is high, the composite material tensile strength can be satisfied, and although there is no particular upper limit, it is about 8 GPa empirically. The measurement is performed by a resin impregnated strand tensile test method specified by JIS described later. In order to satisfy the tensile strength of the present invention, it is important to increase the shear elastic modulus while suppressing the difference between the inner and outer structures. Details of the method for producing such a carbon fiber bundle will be described later.

The carbon fiber bundle of the present invention satisfies the following formula (2) when the resin-impregnated strand tensile elastic modulus is E (GPa).
E / GPa ≧ 420−25 d / μm (2).

  In the tensile elastic modulus of the carbon fiber bundle, since a simple compound rule is established, the tensile elastic modulus decreases linearly as the proportion of the inner layer having low physical properties increases. Therefore, as the average single fiber diameter is larger, the expression of the tensile elastic modulus tends to be limited. In the carbon fiber bundle of the present invention, since the difference between the inner and outer structures is largely suppressed, the tensile elastic modulus is hardly lowered and the tensile elastic modulus is expressed at a high level. In the formula (2) of the present invention, “E / GPa ≧ 420−20 d / μm” is preferable, and “E / GPa ≧ 420−15 d / μm” is more preferable. The tensile elastic modulus of the carbon fiber bundle of the present invention is easily expressed even in a region where the average single fiber fineness is large because the difference between the inner and outer structures is suppressed. The measurement is performed by a resin impregnated strand tensile test method defined by JIS described later. Details of the method for producing such a carbon fiber bundle will be described later.

The carbon fiber bundle of the present invention preferably has a shear elastic modulus of 13 to 20 GPa, more preferably 14 to 20 GPa, and further preferably 15 to 20 GPa. If the carbonization temperature is increased from around 1000 ° C, the shear modulus tends to increase, but the affinity with water decreases, so it is necessary to increase the shear modulus as much as possible in a state where the shear modulus is low. It is. In order to achieve such a high shear modulus while maintaining a high affinity with water, it is necessary that the difference between the inner and outer structures is suppressed, and the ratio of the blackening thickness described later is required to be large. . Although there are various methods for evaluating the shear modulus of the carbon fiber bundle, in the present invention, a method of calculating from a stress-strain curve obtained by performing a tensile test on the resin-impregnated strand is used. That is, a coefficient is obtained so that the stress σ (GPa) −strain ε (−) curve is fitted to the equation (2) in the range of stress 0 to 3 GPa, and shear elasticity is obtained using the orientation function <cos ² ψ>. to calculate the rate g and the initial tensile modulus of elasticity E _0.

  This equation is derived by the present inventors from Equation (5) of Carbon, 1991, 29, 1267-79 and Equation (9) of Carbon, 1994, 32, 615-619. As can be seen from this equation, the tensile strain changes more slowly as the tensile stress is applied (the tensile elastic modulus increases), and the compressive strain changes larger (the compressive elastic modulus decreases) as the compressive stress is applied. In terms of the relationship with the shear modulus, the greater the shear modulus, the weaker the increase in tensile modulus against tensile stress. In other words, it can be said that it is difficult to simultaneously increase the tensile elastic modulus while increasing the shear elastic modulus. In order to control the shear modulus, it is important to control the flameproof structure by eliminating the difference between the internal and external structures and setting the conditions for the polyacrylonitrile copolymer and the flameproofing process. A specific method for producing a carbon fiber bundle that controls the shear modulus and tensile modulus of carbon fiber will be described later.

  In the carbon fiber bundle of the present invention, the blackened thickness of the outer peripheral portion of the cross section perpendicular to the fiber axis direction of the carbon fiber single fiber is preferably 3.2 μm or more, more preferably 3.3 μm or more. The blackened thickness of the outer peripheral portion of the cross section perpendicular to the fiber axis direction of the single carbon fiber is a region where the degree of orientation of the crystal portion is high and the tensile modulus is high. The thicker the blackened thickness, the more easily the difference between the inner and outer structures is increased when the average single fiber fineness is increased, and both the tensile modulus and shear modulus are more likely to be exhibited.

  Regarding the tensile modulus, the tensile modulus is expressed in proportion to the outer layer ratio defined by the area ratio (%) of the blackened thickness portion of the outer peripheral portion of the cross section perpendicular to the fiber axis direction of the carbon fiber monofilament to the entire cross section. To do. By controlling the outer layer ratio, it is possible to control the tensile modulus even for carbon fiber bundles having different finenesses. In the carbon fiber bundle of the present invention, the outer layer ratio is 90 area% or more. Since the difference between the inner and outer structures can be largely suppressed, it is preferable because the tensile elastic modulus can be efficiently expressed and the reduction of the tensile strength can be prevented. Further, the outer layer ratio can be controlled by the thickness of the blackened thickness and the diameter of the single fiber. When the outer layer ratio is 100% by area, there is no difference between the inner and outer structures.

  Regarding the shear modulus, up to a certain point, the shear modulus tends to increase in proportion to the blackening thickness, and if it is 3.2 μm, a sufficiently high shear modulus of 10 GPa or more is satisfied, and the diameter d (μm) Even if the carbon fiber has a fineness of 8 to 9 μm, a high shear modulus can be achieved without impairing the tensile modulus. The blackened thickness of such a carbon fiber monofilament can be achieved by controlling the progress of the flameproofing reaction with respect to the reaction time, and the blackened thickness is obtained by embedding a carbon fiber bundle in a resin and It can be measured by polishing a cross section perpendicular to the direction and observing the cross section with an optical microscope (details will be described later).

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

  In the method for producing a carbon fiber bundle of the present invention, the polyacrylonitrile-based precursor fiber bundle is flame-resistant, preferably pre-carbonized and carbonized to obtain a carbon fiber bundle. In the present invention, flame resistance refers to heat treatment at an oxygen atmosphere concentration of ± 5 mass% in air at 200 to 400 ° C., and preferred embodiments thereof are the nitrile consumption rate and flame resistance treatment time described below. Dependent.

  First, the polyacrylonitrile-based precursor fiber bundle during the flameproofing treatment is subjected to flameproofing treatment so that the nitrile consumption rate becomes 10 to 20% when the flameproofing treatment time is 30 minutes, and then the nitrile consumption rate Is flame-proofed to 50-95%. The nitrile consumption rate in the present invention is the ratio of the amount of nitrile groups in the polyacrylonitrile-based precursor fiber consumed by the reaction when flameproofing treatment is performed as described later, and the rate of progress of the flameproofing reaction and Can think. By suppressing the initial consumption of the nitrile group and increasing the oxygen diffusion rate, it is possible to cause the flameproofing reaction by passing oxygen to the center of the cross section of the single fiber. Since the flameproofing temperature region is sufficiently high, the amount of oxygen diffusion can be controlled by the flameproofing time, and if it is 30 minutes, a flameproofed fiber bundle having no difference in internal and external structures in the cross section can be obtained. If it is less than 30 minutes, oxygen permeation during the flameproofing treatment tends to be insufficient, and a difference in internal and external structure is easily observed in the cross section. It is necessary to advance the flameproofing reaction while suppressing nitrile consumption for such time. Therefore, if the nitrile consumption rate is 10 to 20% when the flameproofing treatment time is 30 minutes, a large amount of unreacted nitrile groups remain as 80 to 90%, so that the nitrile is maintained while maintaining sufficient oxygen permeation. It is possible to encourage consumption. When the nitrile consumption rate exceeds 20%, oxygen permeation is not in time for the consumption behavior of the nitrile group, and a difference in structure between the inside and outside of the flame-resistant fiber is easily observed. When the nitrile consumption rate is less than 10%, it cannot withstand the contraction in the longitudinal direction of the fiber accompanying the subsequent change in the flameproof structure, and fluff is likely to occur. Such a nitrile consumption rate can be evaluated by a relative value of peak intensity derived from a nitrile group by infrared spectrum measurement, and a detailed measurement method will be described later.

  And after performing a flameproofing process so that a nitrile consumption rate will be 10 to 20% at the time of 30 minutes, a nitrile consumption rate is 50 to 95%, preferably 60 to 95%, more preferably 75 to 95%. Flame-resistant treatment is performed so that By setting the nitrile consumption rate of the flameproof fiber bundle before carbonization within such a range, the carbonization yield can be increased. If the nitrile consumption rate is 50% or more under a low carbonization temperature, a carbonization yield of 55% or more can be obtained, but if the nitrile consumption rate exceeds 95%, flame resistance has progressed too much, The carbon fiber is brittle and has a low shear modulus.

  In the method for producing the carbon fiber bundle of the present invention, in the step of flameproofing the polyacrylonitrile-based precursor fiber bundle, the flameproofing treatment time is 6 to 25 minutes while the nitrile consumption rate reaches 20% to 60%. It is preferable to perform flameproofing treatment. By setting the flameproofing treatment time after the induction period of the flameproofing treatment to such a range, the amount of decomposition reaction during the flameproofing reaction can be suppressed, so that carbon fibers having a high shear modulus can be easily obtained. If the flameproofing treatment time is within 25 minutes, the shear elastic modulus is likely to increase with respect to the normal flameproofing conditions, and if it is less than 6 minutes, it is difficult to control the progress of flameproofing. Easy to lead to structural differences. The nitrile consumption rate is measured by measuring the infrared spectrum of the flame-resistant fiber bundle. The flameproofing treatment amount and the flameproofing treatment time can be controlled by adjusting the flameproofing treatment temperature in accordance with the type and amount of the copolymer component described later.

  In the present invention, a polyacrylonitrile-based polymer is used as a raw material for the production of a polyacrylonitrile-based precursor fiber bundle. In the present invention, as the polyacrylonitrile-based polymer, 99.1 to 99.99% by mass of the acrylonitrile copolymer excluding the polymerization initiator and chain transfer agent component at the end of the polymer is obtained by polymerizing acrylonitrile. Use what The ratio is more preferably 99.5 to 99.99% by mass, and still more preferably 99.9 to 99.99% by mass. The closer the proportion of the acrylonitrile monomer in the acrylonitrile copolymer is to 100% by mass, the more the internal and external structural differences disappear and the physical properties can be improved. However, if it exceeds 99.99% by mass, the effect of promoting flame resistance by the copolymer component can be obtained. However, the shear modulus decreases. Further, if it is less than 99.1% by mass, satisfactory internal / external structure difference and shear elastic modulus cannot be achieved.

  Further, in the method for producing a carbon fiber bundle of the present invention, in the copolymer component contained in 0.01% by mass or more in the polyacrylonitrile copolymer used for producing the polyacrylonitrile-based precursor fiber bundle, the copolymer component is The glass transition temperature (polymer Tg) when the polymer is used alone is 50 to 250 ° C, preferably 100 to 200 ° C, more preferably 120 to 160 ° C. By setting the polymer Tg in such a range, it is possible to perform flameproofing treatment without impairing the spinning property and the oxygen diffusibility into the polyacrylonitrile-based precursor fiber bundle. For this reason, when it exceeds 250 degreeC, since the difference of melting | fusing point with a polyacrylonitrile becomes large, it becomes easy to generate | occur | produce a fluff at the time of steam extending | stretching, and tensile strength falls. On the other hand, when the polymer Tg is lower than 50 ° C., the crystallinity of the polyacrylonitrile-based precursor fiber is increased, and thus the shear elastic modulus is easily lowered when carbonized.

  Such a polymer Tg can be observed as an inflection point of the specific capacity-temperature curve of the polymer by DSC measurement, and since it is often described in a product catalog, the value may be used. In order to control the polymer Tg, the main chain and side chain skeleton of the molecule may be adjusted, but those containing an alkyl chain in (meth) acrylate tend to have a low Tg.

  Examples of monomers having a polymer Tg of less than 50 ° C. and not suitable as a copolymerization component include isobutyl methacrylate (polymer Tg: 48 ° C.), n-butyl acrylate (polymer Tg: −54 ° C.), diethyl acrylamide (polymer Tg: 45 ° C) ethyl acrylate (polymer Tg: -22 ° C), lauryl methacrylate (polymer Tg: -65 ° C), isodecyl methacrylate (polymer Tg: -41 ° C), isobutyl acrylate (polymer Tg: -24 ° C) 2-hydroxyethyl acrylate (polymer Tg: −15 ° C.), 2-hydroxypropyl acrylate (polymer Tg: −7 ° C.), polyethylene glycol monomethacrylate (polymer Tg: −62 ° C.), lauryl acrylate (polymer Tg) : -3 ° C), n-butyl methacrylate (polymer) g: 20 ℃) and the like.

  On the other hand, the polymer Tg is 50 to 250 ° C., and examples of monomers suitable as a copolymerization component include itaconic acid (polymer Tg: 130 ° C.), tetrahydrofurfuryl methacrylate (polymer Tg: 60 ° C.), and methacrylic acid t. -Butyl (polymer Tg: 107 ° C), 4-vinylpyridine (polymer Tg: 142 ° C), 2-vinylpyridine (polymer Tg: 112 ° C), acryloylmorpholine (polymer Tg: 145 ° C), isobornyl methacrylate (polymer Tg) : 180 ° C), methacrylic acid (polymer Tg: 228 ° C), acrylamide (polymer Tg: 165 ° C) and the like, but this does not limit the definition of the copolymerization component of the present invention. In particular, the copolymer component contained in the polyacrylonitrile-based polymer preferably includes an unsaturated carboxylic acid as the flame retardant component, and examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, and itaconic acid. .

  In the production of the polyacrylonitrile-based precursor fiber bundle, the production method of the polyacrylonitrile-based polymer can be selected from known polymerization methods. In the production of a polyacrylonitrile-based precursor fiber bundle suitable for obtaining the carbon fiber bundle of the present invention, the spinning dope can be prepared from the polyacrylonitrile-based polymer described above, and polyacrylonitrile such as dimethylsulfoxide, dimethylformamide, and dimethylacetamide. It is dissolved in a soluble solvent.

  A method for producing a polyacrylonitrile-based precursor fiber bundle suitable for obtaining the carbon fiber bundle of the present invention will be described.

  In producing the polyacrylonitrile-based precursor fiber bundle, either a dry-wet spinning method or a wet-spinning method may be used as the spinning method, but a dry-wet spinning method advantageous to the shear elastic modulus of the obtained carbon fiber bundle is used. Is preferred. The spinning process includes a spinning process in which a spinning solution is discharged from a spinneret by a dry-wet spinning method and spinning, a water washing process in which fibers obtained in the spinning process are washed in a water bath, and a fiber obtained in the water washing process. It consists of a water bath stretching step for stretching in a water bath and a drying heat treatment step for subjecting the fibers obtained in the water bath stretching step to a dry heat treatment, and if necessary, a steam stretching step for steam stretching of the fibers obtained in the dry heat treatment step. May be included.

  In the production of the polyacrylonitrile-based precursor fiber bundle, it is preferable that the coagulation bath contains a solvent such as dimethyl sulfoxide, dimethylformamide, and 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 polyacrylonitrile polymer and is compatible with the solvent used in the spinning solution can be used. Specifically, it is preferable to use water as a coagulation promoting component.

  In the production of the polyacrylonitrile-based precursor fiber bundle, the water bath temperature in the water washing step is preferably washed using a water bath having a plurality of stages of 30 to 98 ° C.

  Moreover, it is preferable that the draw ratio in a water bath extending process is 2-6 times, More preferably, it is 2-4 times.

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

  A known method can be used for the drying heat treatment step. For example, the drying temperature is exemplified by 100 to 200 ° C.

  After the water washing step, the water bath stretching step, the oil agent applying step, and the drying heat treatment step performed by a publicly known method, if necessary, by performing steam stretching, a polymer suitable for obtaining the carbon fiber bundle of the present invention is obtained. An acrylonitrile-based precursor fiber bundle is obtained. In the present invention, the steam stretching is preferably performed at least 3 times, more preferably 4 times or more, and still more preferably 5 times or more in the pressurized steam.

  In the production of the carbon fiber bundle, it is preferable to perform preliminary carbonization following the flame resistance. In the preliminary carbonization step, it is preferable to heat-treat the obtained flame-resistant fiber in an inert atmosphere at a maximum temperature of 500 to 800 ° C. until the specific gravity becomes 1.5 to 1.8.

  In the present invention, in the production of a carbon fiber bundle, the obtained flame-resistant fiber bundle is carbonized at a maximum temperature of 800 to 1150 ° C. in an inert atmosphere. In the production of a carbon fiber bundle, the temperature of the carbonization step is preferably higher from the viewpoint of increasing the tensile modulus of the obtained carbon fiber, but if it is too high, the nitrogen content decreases and the affinity for water is low. Since it decreases, it is better to set it in consideration of both. A preferred temperature range is 900-1050 ° C.

  The carbon fiber bundle obtained as described above is subjected to an oxidation treatment to introduce an oxygen-containing functional group in order to improve adhesion with the matrix resin. As the oxidation treatment method, vapor phase oxidation, liquid phase oxidation, and liquid phase electrolytic oxidation are used. From the viewpoint of high productivity and uniform treatment, liquid phase electrolytic oxidation is preferably used. The method of liquid phase electrolytic oxidation is not particularly specified, and may be performed by a known method.

  After the electrolytic treatment, a sizing treatment can also be performed in order to impart a focusing property to the obtained carbon fiber bundle. As the sizing agent, a sizing agent having good compatibility with the matrix resin can be appropriately selected according to the type of the matrix resin used in the composite material.

  The measuring method of various physical property values used in the present invention is as follows.

<Tensile strength, tensile modulus and shear modulus of carbon fiber bundle>
The tensile strength and tensile modulus of the carbon fiber bundle are determined according to the following procedure in accordance with the resin impregnated strand test method of JIS-R-7608 (2004). As the resin formulation, “Celoxide (registered trademark)” 2021P (manufactured by Daicel Chemical Industries) / 3 boron trifluoride monoethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) / Acetone = 100/3/4 (part by mass) is used. As curing conditions, normal pressure, temperature of 125 ° C., and time of 30 minutes are used. Ten resin-impregnated strands of the carbon fiber bundle are measured, and the average value is taken as the tensile strength. Strain is evaluated using an extensometer. The obtained stress σ (GPa) −strain ε (−) curve is obtained by fitting a coefficient to the formula (1) in the range of stress 0 to 3 GPa, and shear elasticity is obtained using the orientation function <cos ² ψ>. to calculate the rate g and the initial tensile modulus of elasticity E _0. As the tensile modulus E, a value in the strain range of 0.5 to 0.8% is used.

<Orientation function of carbon fiber bundle>
By aligning the carbon fiber bundles used for measurement and solidifying them with a collodion / alcohol solution, a square column measurement sample having a length of 4 cm and a side length of 1 mm is prepared. The prepared measurement sample is measured under the following conditions using a wide-angle X-ray diffractometer.

-X-ray source: CuKα ray (tube voltage 40 kV, tube current 30 mA)
-Detector: Goniometer + Monochromator + Scintillation counter-Scanning range: 2θ = 10-40 °
Scan mode: Step scan, step unit 0.02 °, counting time 2 seconds.

The orientation function <cos ² ψ> was measured as follows. The diffraction intensity distribution obtained by scanning the peak appearing in the vicinity of 2θ = 25 to 26 ° in the obtained diffraction pattern in the circumferential direction is fitted with a Gaussian distribution, and the following expression is obtained from the diffraction intensity distribution σ (ψ) after the fitting. Use to calculate.

<Specific gravity measurement>
1.0 to 3.0 g of carbon fiber is collected and dried at 120 ° C. for 2 hours. Next, after measuring the absolute dry mass A (g), it was impregnated with ethanol and sufficiently defoamed, and then the fiber mass B (g) in the solvent bath was measured, and the fiber specific gravity = (A × ρ) / (A The fiber specific gravity is determined by -B).

<Measurement of nitrogen content>
The measurement sample is finely cut carbon fiber (2 mg). The amount of nitrogen is calculated by evaluating the CHN amount of the carbon fiber using a CHN analyzer (DKSH vario EL cube).

<Blackening thickness and outer layer ratio of outer peripheral portion of cross section perpendicular to fiber axis direction of carbon fiber single fiber>
A carbon fiber bundle to be measured is embedded in a resin, a cross section perpendicular to the fiber axis direction is polished, and the cross section is observed using an objective lens having a magnification of 100 times that of an optical microscope. The blackening thickness of the difference between the inner and outer structures is measured from the cross-sectional microscopic image of the polished surface. The analysis is performed using image analysis software Image J. First, in a single fiber cross-sectional image, black and white area division is performed by binarization. For the luminance distribution in the single fiber cross section, the average value of the distribution is set as a threshold value and binarization is performed. The obtained binarized image is measured as the shortest distance from one point on the surface layer to the lined region from black to white in the direction of the fiber diameter d. This is measured for five points within the circumference of the same single fiber, and the average value is calculated as the blackening thickness at that level. Further, the outer layer ratio is calculated from the area ratio (%) of the blackened thickness portion with respect to the entire cross section perpendicular to the fiber axis direction of the single carbon fiber.

<Average single fiber diameter of carbon fiber>
A mass A _f (g / m) and a density B _f (g / cm ³ ) per unit length are determined for a carbon fiber bundle composed of a large number of carbon filaments to be measured. The number of filaments of the carbon fiber bundle to be measured is C _f, and the average single fiber diameter (μm) of the carbon fiber is calculated by the following formula.

Average single fiber diameter of carbon fiber (μm)
= ((A _f / B _f / C _f ) / π) ^(1/2) × 2 × 10 ³ .

<Nitrile consumption rate>
Flame-resistant fiber used for measurement is measured by accurately weighing 2 mg after freezing and grinding, mixing it well with 300 mg of KBr, placing it in a molding jig, and pressurizing at 40 MPa for 2 minutes using a press. Make a tablet. The tablet is set in a Fourier transform infrared spectrophotometer, and the spectrum is measured in the range of 1500 to 2500 cm ⁻¹ . The background correction is performed by subtracting the minimum value from each intensity so that the minimum value in the range of 1700 to 2000 cm ⁻¹ becomes zero. As the Fourier transform infrared spectrophotometer, Parakin 1000 manufactured by PerkinElmer was used. A peak derived from a nitrile group is observed at 2240 cm ⁻¹ in the polyacrylonitrile-based precursor fiber. The rate of decrease in the integrated intensity of the peak can be applied as an index of the progress of flame resistance. For this reduction rate, the integrated intensity of the spectrum appearing at 2240 cm ⁻¹ is used. Using the state in which the polyacrylonitrile-based precursor fiber is not flameproofed as a reference value, the ratio of the spectrum obtained from the flameproofed fiber to the integrated intensity of the 2240 cm ⁻¹ peak is defined as the residual amount of nitrile and subtracted from 100%. Therefore, it is defined as the nitrile consumption rate in a certain flameproofing treatment time. A value obtained by dividing the difference in the nitrile consumption rate by the difference in the flameproofing time between the flameproofing fibers having different flameproofing treatment amounts was estimated as the average nitrile consumption rate. As flame resistance progresses, a shoulder is formed next to the peak, but it is not included.

<Abrasion fluff>
As an index indicating the ease of occurrence of fluff, the following rubbing fluff was measured. 5 stainless steel rods of 10 mm in diameter with a surface centerline average roughness (Ra) of Ra≈0.17 μm are passed in parallel at 50 mm intervals and carbon fiber yarns in contact with each other at an angle of 120 °. Arranged in a zigzag. The carbon fiber yarn with 24,000 filaments is passed at a speed of 3 m / min while adding 650 g of initial tension to the first, second, fourth and fifth stainless steel rods from the entry side when the carbon fiber yarn is running. The laser beam is irradiated from a direction perpendicular to the carbon fiber yarn. The number of times the laser beam is shielded is counted as the number of fluffs generated and displayed in number / m. When the number of fluff is less than 10 / m, ◎, when 10 / m or more and less than 20 / m, △ when 20 / m or more and less than 30 / m, or when 30 / m or more Was marked with x. ◎ and ○ are preferable ranges in the present invention.

<Water absorption rate>
Weigh 2.0 g of the carbon fiber bundle and dry it in an oven heated to 130 ° C. for 2 hours. The completely dried carbon fiber bundle is stored in a desiccator containing a saturated ammonium sulfate aqueous solution for 16 hours at 25 ° C. so that the carbon fiber bundle does not touch the saturated ammonium sulfate aqueous solution to absorb moisture. The water absorption is obtained from the mass change of the carbon fiber bundle before and after storage with respect to the mass of the carbon fiber bundle before storage.

(Examples 1-4, Comparative Examples 1-6)
A solution polymerization method using a polyacrylonitrile-based copolymer having a copolymer composition shown in Table 1 (99.5% by mass of acrylonitrile and 0.5% by mass of itaconic acid (polymer Tg: 130 ° C.)) using dimethyl sulfoxide as a solvent. To prepare a polyacrylonitrile copolymer. Furthermore, the polymer concentration was adjusted to 20% by mass to obtain a spinning solution. The obtained spinning solution was once discharged into the air from the spinneret, and was made into a coagulated yarn by a dry and wet spinning method introduced into a coagulation bath composed of an aqueous solution of 35% dimethyl sulfoxide controlled at 3 ° C. The coagulated yarn was washed with water by a conventional method, and then stretched 3.5 times in two warm water baths. Subsequently, an amino-modified silicone-based silicone oil agent is applied to the fiber bundle after stretching in the water bath, a drying densification treatment is performed using a heating roller at 160 ° C., and the number of single fibers is set to 12,000, and then pressurization is performed. By drawing 3.7 times in steam, the yarn drawing total draw ratio was 13 times, and a polyacrylonitrile-based precursor fiber bundle having a crystal orientation of 93% and a single fiber number of 12,000 was obtained. The discharge amount of the spinning solution from the die was adjusted so that the single fiber fineness of the polyacrylonitrile-based precursor fiber bundle was as shown in Table 1. Next, using the conditions of the flame resistance temperature and flame resistance time of the first flame resistance furnace (1 resistance) and the second flame resistance furnace (2 resistance) shown in Table 1, a polyacrylonitrile-based precursor in an air atmosphere oven The body fiber bundle was flameproofed while being stretched at a stretch ratio of 1, to obtain a flameproof fiber bundle.

  It should be noted that the flameproofing treatment time during which the nitrile consumption amount was 20% to 60% was calculated using the nitrile consumption rate at the 30 minute flameproofing treatment time point and the final time point. In other words, a linear approximation is performed with respect to the flameproofing time and the nitrile consumption for the 0 minute flameproofing time point (nitrile consumption 0%) to the 30 minute flameproofing time point and the 30 minute flameproofing time point to the final time point, respectively. The flameproofing treatment time during which the nitrile consumption was 20% to 60% was calculated.

  The obtained flame-resistant fiber bundle was carbonized in a nitrogen atmosphere having a maximum carbonization temperature of 1000 to 1200 ° C. shown in Table 1. The obtained carbon fiber bundle was subjected to surface treatment and sizing agent coating treatment to obtain a final carbon fiber bundle. In addition, the water absorption rate of the obtained carbon fiber bundle was 5.2 mass%. Table 2 shows the nitrogen content of the carbon fiber bundle, the single fiber diameter, the blackened thickness and the outer layer ratio of the outer periphery of the cross section perpendicular to the fiber axis direction of the carbon fiber single fiber, the tensile strength σ, the tensile elastic modulus E, The shear elastic modulus G, 10.6 to 0.75 d / μm which is the right side of the formula (1), 420 to 25 d / μm which is the right side of the formula (2), and fuzzing fluff are shown.

  Usually, carbon fiber tends to increase in tensile modulus and tensile strength in proportion to the decrease in single fiber diameter. That is, the formula defined in claim 1 shows the standard regarding the tensile strength and the tensile modulus corresponding to the single fiber diameter.

  In Comparative Example 1, since only the single fiber fineness was reduced to 0.7 d under the same flameproofing conditions as in Example 1, it became a high-performance carbon fiber, but the tensile strength and tensile modulus corresponding to the single fiber diameter were The standard was not met. Further, when used as a composite material, fluff was likely to occur and the appearance quality was impaired.

  In Comparative Example 2, since the temperature of the second flameproofing furnace was lowered to 250 ° C., the nitrile consumption was not sufficient, and the single fiber diameter was thinned to 7.1 μm, so fluff was generated when the composite material was made. In comparison with Examples 1 and 2, the appearance quality was greatly impaired.

  In Comparative Example 3, compared with Example 3, the temperature of the first flameproofing furnace was increased to 245 ° C., so the nitrile consumption at 30 minutes was 40%, so the difference between the inner and outer structures became larger, and the tensile elasticity The rate was greatly reduced. For this reason, the criteria of the tensile modulus and tensile strength corresponding to the single fiber diameter were not satisfied. The appearance quality of the carbon fiber was not preferable, and a lot of fuzz was observed.

  In Comparative Example 4, since the nitrile consumption was not sufficient in Comparative Example 2, the temperature of the second flameproofing furnace was lowered to 250 ° C. by adding a large amount of itaconic acid as 1.0% by mass, and at the final time point Although the nitrile consumption was 61%, the nitrile consumption at 30 minutes was also large, so the difference between the inner and outer structures became larger, and the tensile strength and shear modulus decreased. Further, the appearance quality of the carbon fiber was not preferable, and many fuzzed fluffs were observed.

  In Comparative Example 5, the amount of itaconic acid was increased to 1.0% by mass, and 1.0% by mass of isobutyl methacrylate was added. Therefore, the tensile strength and shear modulus were reduced although the internal and external structural differences were eliminated. In addition, the water absorption rate of the obtained carbon fiber bundle was 5.2% by mass, which was the same value as in Example 1. The appearance quality of the carbon fiber was not preferable, and a lot of fuzz was observed.

  In Example 4, the carbonization temperature was 1100 ° C. The water absorption of the obtained carbon fiber bundle was 1.2% by mass, and the hydrophilicity decreased.

  In Comparative Example 6, since carbonization was performed at a carbonization temperature of 1200 ° C., high tensile strength, tensile modulus, and shear modulus were obtained, but the nitrogen content was reduced. The water absorption of the obtained carbon fiber bundle was reduced to 0.4% by mass, and the hydrophilicity was greatly reduced.

The carbon fiber bundle in the present invention is suitably used for aircraft members, spacecraft members, automobile members, ship members, sports applications such as golf shafts and fishing rods, and other general industrial applications. In particular, since it has a high affinity for water, it is preferably used in the production of tire cords, paper, and cement reinforcing materials.

Claims (5)

In a carbon fiber bundle composed of a plurality of single fibers, the average single fiber diameter of the single fibers is d (μm), the resin-impregnated strand tensile elastic modulus of the carbon fiber bundle is E (GPa), and the resin-impregnated strand tensile strength Is σ (GPa),
σ / GPa ≧ 10.6−0.75 d / μm (1)
E / GPa ≧ 420−25d / μm (2)
, A carbon fiber bundle having d = 7.5 to 9.0 μm and a nitrogen content of 8 to 18% by mass. The carbon fiber bundle according to claim 1, wherein the shear elastic modulus is 13 to 20 GPa. The carbon fiber bundle according to claim 1 or 2, wherein a blackened thickness of an outer peripheral portion of a cross section perpendicular to the fiber axis direction of the single carbon fiber is 3.2 µm or more. In a method for producing a carbon fiber bundle, a polyacrylonitrile-based precursor fiber bundle containing 99.1 to 99.99% by mass of polyacrylonitrile and 0.01% by mass or more of a copolymer component is flameproofed, and then carbonized. The copolymer component has a Tg of the homopolymer of 50 to 250 ° C., and in the flameproofing treatment, the nitrile consumption rate is 10 to 20% when the flameproofing treatment time is 30 minutes, and the flameproofing treatment is completed. A method for producing a carbon fiber bundle, wherein carbonization treatment is performed at a maximum carbonization temperature of 800 to 1150 ° C. using a flameproof fiber bundle whose nitrile consumption at the time is advanced to 50 to 95%. The method for producing a carbon fiber bundle according to claim 4, wherein the flameproofing treatment time during which the nitrile consumption rate is 20% to 60% is 6 to 25 minutes.