JP2015010290A - Carbon fiber bundle and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon fiber bundle excellent in excellent tensile elastic modulus and compression strength and its production method.SOLUTION: A carbon fiber bundle has a single fiber compression strength of 4.8 GPa or higher, measured by the compression fragmentation method of a single-fiber composite, a number of fiber fractures under the single fiber apparent stress of 15.3 GPa of 2.0 fractures/mm or greater, measured by the tensile fragmentation method of a single fiber composite, and preferably a crystallite size of 2.2-4.0 nm.

Description

  The present invention is a carbon having excellent compressive strength and tensile elastic modulus which is suitably used for aircraft members, spacecraft members, automobile members and ship members, as well as sports applications such as golf shafts and fishing rods and other general industrial applications. The present invention relates to a fiber bundle and a manufacturing method thereof.

  Carbon fiber has contributed to weight reduction of aircraft by being used for aircraft applications as a reinforcing fiber of fiber reinforced composite material due to its high specific strength and specific modulus. The flow of is being accelerated. For reducing the weight of aircraft, it is most effective to improve the tensile modulus of carbon fiber that governs the rigidity of the carbon fiber reinforced composite material. Therefore, it is required to have a wide balance of physical properties such as further improvement of mechanical properties of carbon fiber, and further improvement of tensile / compressive strength and perforated plate tensile / compressive strength as a carbon fiber reinforced composite material. In particular, it was extremely difficult to increase the compressive strength and perforated plate compressive strength of the unidirectional carbon fiber reinforced composite material. The compressive strength of the carbon fiber reinforced composite material is mainly governed by the single fiber compressive strength of the carbon fiber and the shear modulus of the resin. Although techniques for controlling the carbon fiber surface characteristics (Patent Documents 1 and 2) and surface morphology (Patent Document 3) have been proposed in order to increase the composite compressive strength, the single fiber compressive strength of carbon fibers cannot be improved. There wasn't.

  Methods for measuring the single fiber compressive strength of carbon fibers are the loop method (Non-patent document 1), the recoil method (Non-patent document 2), the direct compression method (Non-patent document 3), and the single fiber composite compression fragmentation method (Non-patent document 1). References 4 and 5) have been developed in various ways, and it is necessary to consider differences between measurement methods. Here, when the apparent compressive strength by the loop method is compared with other methods, the single fiber compressive strength by the loop method of T800H, T300, M40, and M46 used in Non-Patent Document 1 is 7.7, 4,. Although it is 5, 3.0, and 1.8 GPa, the non-patent document 3 has T800H and T300 single fiber compressive strengths of 2.3 and 1.8 GPa, respectively, and non-patent document 2 has M40 and M46 single fibers. The compressive strength is 1.2 and 1.2 GPa, respectively, and the apparent compressive strength by the loop method needs to be compared as a relative value. Non-Patent Document 5 describes the single fiber compressive strength of many carbon fibers, but the value was about 3.5 GPa at maximum even when the crystallite size was reduced. Many efforts have been made to increase the single fiber compressive strength of the carbon fiber itself by evaluating the single fiber compressive strength of the carbon fiber using these methods. It is generally known that the single fiber compressive strength of the carbon fiber itself can be increased by lowering the carbonization temperature and controlling the crystallite size to be small. Therefore, a technique for improving the tensile elastic modulus by increasing the stretch ratio of the flameproofing process, the preliminary carbonization process, and the carbonization process (these are collectively referred to as a firing process) has been proposed (for example, Patent Document 4). ). In Patent Document 4, by increasing the crystal orientation degree of the carbon fiber by stretching, even if the carbonization treatment is performed at a low temperature, a tensile elastic modulus equivalent to that of the carbon fiber treated at a high temperature is obtained, and the carbonization treatment temperature is lowered. The single fiber compressive strength improvement effect by this is enjoyed. In patent document 4, the technique which improves the drawability in a baking process is applied by controlling the molecular weight distribution of polyacrylonitrile precisely. Although the carbonization treatment temperature reduction can obtain the effect of increasing the compressive strength, it did not exceed the conventionally obtained single fiber compressive strength level. Patent Document 5 proposes a technique of increasing the stretch ratio in the firing step and controlling the single fiber compressive strength (MPa) / tensile elastic modulus (GPa) ≧ 5.5, but the carbon fiber compressive strength is less than 2 GPa. And did not reach a satisfactory level. In Patent Document 6, efforts are made to improve the perforated plate compressive strength under high-temperature moisture absorption and the post-impact compressive strength of the carbon fiber reinforced composite material by using carbon fibers having a non-circular cross-sectional shape. No good carbon fiber reinforced composite material properties were obtained.

  In addition, in order to increase the single fiber compressive strength of carbon fibers, there has been a study of flame resistance conditions for polyacrylonitrile-based carbon fiber precursor fibers (hereinafter referred to as precursor fibers). Patent Document 7 discloses a method of carbonization treatment after washing the flame resistant fiber with a solvent. The obtained carbon fiber has an apparent compression strength of 8.6 GPa by the loop method, and is a single fiber compression of carbon fiber. The level was not satisfactory. Patent Document 8 proposes a technique for controlling the torsional elastic modulus to 17 GPa or more for the purpose of increasing the single fiber compressive strength of the carbon fiber by setting the total time required for the flameproofing process to 70 minutes or more and less than 120 minutes. ing. In Patent Document 9, the surface of the single fiber has a different element other than C, H, N, and O such as boron, and is controlled to have low crystallinity so that the torsional elastic modulus and the apparent compressive strength by the loop method are disclosed. Techniques for improving the quality have been proposed. Among these, the apparent compressive strength by the loop method achieved a value of 10.8 GPa at the maximum, but the single fiber compressive strength of the carbon fiber was still not at a satisfactory level.

JP 2010-229572 A JP 2009-242971 A JP 2009-046770 A JP 2011-213774 A JP 2010-111972 A International Publication No. 96/21695 JP 2007-186802 A JP 2002-194626 A JP 09-170170 A

Proceedings of the Fourth Japan-U. S. Conference on Composite Materials. 1988. p. 548-557. “Journal of Materials Science” (Switzerland), 1993, 28, p. 1611. “Carbon”, 2011, 39, p. 635-645. “Journal of Materials Science” (Switzerland), 1994, 29, p. 786-799. “Journal of Materials Science” (Switzerland), 2013, 48, p. 2104-2110.

  An object of the present invention is to provide a carbon fiber bundle suitable for obtaining a carbon fiber reinforced composite material excellent in both compressive strength and perforated plate compressive strength, and a method for producing the same.

  In order to achieve the above object, the present invention has any one of the following configurations.

  [1] The number of fiber breaks when the single fiber compressive strength is 4.8 GPa or more according to the compression fragmentation method of the single fiber composite and the single fiber apparent stress is 15.3 GPa according to the tensile fragmentation method of the single fiber composite. Carbon fiber bundles of 2.0 pieces / mm or more.

  [2] The single fiber compressive stress (GPa) in which the number of single fiber breakage at the time of compressive stress loading exceeds 0.1 / 10 mm by the compression fragmentation method of the single fiber composite is 90% or more of the single fiber compressive strength [1 ] The carbon fiber bundle as described in.

  [3] The carbon fiber bundle according to [1] or [2], wherein the average tearable distance is 550 to 850 mm.

  [4] The carbon fiber according to any one of [1] to [3], wherein the single fiber composite has a single fiber apparent stress of 6.8 GPa when the single fiber apparent stress is 6.8 GPa. bundle.

  [5] The carbon fiber bundle according to any one of [1] to [4], wherein the crystallite size is 2.2 to 4.0 nm.

[6] The shear modulus g is 19 GPa or more, the initial tensile modulus E ₀ is 305 GPa or more, and the relationship between the shear modulus and the initial tensile modulus is in the range of the following equation: [1] to [5] A carbon fiber bundle according to any one of the above.

[7] The polyacrylonitrile-based precursor fiber bundle has an intensity ratio of 1453 cm ⁻¹ peak to 1370 cm ⁻¹ peak intensity in the infrared spectrum of 0.72 to 0.85, and an intensity of 1254 cm ⁻¹ peak to 1370 cm ⁻¹ peak intensity. Flame proofing is performed so that the ratio is 0.50 to 0.65, and the pre-carbonized fiber bundle obtained by pre-carbonizing the flame-resistant fiber bundle is carbonized, and the aliphatic epoxy compound (A) and the aromatic epoxy compound ( The manufacturing method of the carbon fiber bundle which apply | coats the sizing agent containing B).

[8] The pre-carbonized fiber bundle is carbon in a temperature range of 1200 to 2000 ° C. in an inert atmosphere, the average tearable distance of the pre-carbonized fiber bundle is 450 to 700 mm, and the carbonization tension satisfies the formula (2). The method for producing a carbon fiber bundle according to [7].
4.9 ≦ carbonization tension (mN / dtex) ≦ −0.0225 × (average tearable distance (mm)) + 23.5 (2)

  ADVANTAGE OF THE INVENTION According to this invention, the carbon fiber bundle used in order to produce the unidirectional carbon fiber reinforced composite material which expresses the outstanding compressive strength and perforated board compressive strength is obtained. The carbon fiber reinforced composite material obtained by using the carbon fiber bundle of the present invention greatly contributes to weight reduction of the aircraft and can improve the fuel consumption rate of the aircraft.

  The carbon fiber bundle of the present invention has a single fiber compressive strength of 4.8 GPa or more, preferably 5.0 GPa or more, more preferably 5.3 GPa or more, according to the compression fragmentation method of a single fiber composite. If the single fiber compressive strength is 4.8 GPa or more, the compressive strength and effective plate compressive strength of the carbon fiber reinforced composite material can be greatly improved. The higher the single fiber compressive strength, the better. The compression fragmentation method for single fiber composites is a method of counting the number of fiber breaks at each compression strain while applying compression strain stepwise to a composite in which single fibers of a carbon fiber bundle are embedded in a resin (single fiber composite). The single fiber compressive strength of the fiber can be examined. In order to convert single fiber composite compressive strain when fiber breaks into single fiber compressive strength, it is necessary to consider the difference between single fiber composite compressive strain and fiber compressive strain, and the elastic modulus nonlinearity at each fiber compressive strain. is there. Therefore, the single fiber compressive stress is obtained by fitting a stress-strain curve obtained by tensile testing the resin-impregnated strand with a quadratic function and extending the fitting line to the compressive strain side. The single fiber compressive strength is defined as a single fiber compressive stress when the number of breaks exceeds 1/10 mm.

  The carbon fiber bundle of the present invention has a single fiber compressive stress of 90% or more of the single fiber compressive strength by a single fiber composite compression fragmentation method in which the number of single fiber breaks when a compressive stress is applied exceeds 0.1 / 10 mm. It is preferable. In the perforated plate of the quasi-isotropic laminated material of the carbon fiber reinforced composite material, the compressive stress in which the carbon fiber is loaded in the region where the carbon fiber around the circular hole starts to be compressed and the single fiber breakage number is 0.1. Single fiber compressive stresses over 10/10 mm show good agreement. Since the compression failure of the carbon fiber largely governs the perforated plate compressive strength, the single fiber compression number of the single fiber breakage exceeds 0.1 / 10 mm from the viewpoint of increasing the perforated plate compressive strength of the carbon fiber reinforced composite material. The index of stress is effective.

  The carbon fiber bundle of the present invention has a fiber breakage number of 2.0 pieces / mm or more, preferably 3.0 pieces / mm or more when the single fiber apparent stress by the tensile fragmentation method of the single fiber composite is 15.3 GPa. It is. In the process of compressive fracture in a perforated plate of quasi-isotropic laminated material, a kink band is first formed at a stress concentration portion around the circular hole, and then the kink band gradually develops. When the number of fiber breaks is less than 2.0 pieces / mm, the kink band develops without the carbon fibers being able to bear the compressive stress when the number of fiber breaks increases due to a decrease in the interfacial adhesion between the carbon fibers and the matrix resin. It becomes easy to do and perforated board compressive strength falls. Stress is transferred to the carbon fiber between the break points from the break point where the stress burden is 0 by interfacial shear with the resin, but especially when the number of breaks increases in this way, the fiber stress is difficult to increase, so the fiber breaks Numbers are saturated. Therefore, it should be mentioned here that the actual fiber stress is lower than the single fiber apparent stress. The single fiber composite may be broken before the single fiber apparent stress is applied up to 15.3 GPa. If the number of fiber breaks is saturated, the number of breaks can be substituted. Here, saturation means when the number of fiber breaks is Δ0.2 / mm when the change in strain of the single fiber composite is Δ1%.

  The carbon fiber bundle of the present invention preferably has a fiber breakage number of 0.3 pieces / mm or less, more preferably 0.2 or less when the single fiber apparent stress by the tensile fragmentation method of the single fiber composite is 6.8 GPa. Pieces / mm or less, more preferably 0.1 pieces / mm or less. If the fiber stress at which the number of fiber breaks is around 0.3 pieces / mm is too low, the balance between the compressive strength and the tensile strength is deteriorated, and the perforated plate compressive strength is likely to be lowered.

  The carbon fiber bundle of the present invention preferably has a crystallite size of 2.2 to 4.0 nm, and more preferably 2.4 to 4.0 nm. In the carbon fiber bundle, the crystallite size increases as the carbonization temperature rises, and the tensile elastic modulus improves mainly due to the accompanying increase in crystal orientation. Therefore, the crystallite size easily develops the tensile elastic modulus. It is a good index to evaluate If the crystallite size is 2.2 nm or more, it is preferable because the tensile elastic modulus is easily developed. Controlling the crystallite size to 4.0 nm or less maintains the shear elastic modulus of the carbon fiber high, and the carbon fiber reinforced composite. This is preferable from the viewpoint of developing an excellent balance of physical properties of the material. Usually, the single fiber compressive strength of the carbon fiber often shows the maximum when the crystallite size is around 2.0 nm, but the present invention shows a very high single fiber compressive strength despite the large crystallite size. is there. The crystallite size of the carbon fiber bundle can be controlled mainly by the carbonization temperature.

The carbon fiber bundle of the present invention has a shear modulus of preferably 19 GPa or more, more preferably 20 GPa or more, and further preferably 21 GPa or more. The shear elastic modulus described in the present invention refers to the shear elastic modulus in 12 directions when the fiber axis direction is one direction and the direction perpendicular to the fiber axis is two or three directions, and the torsion elastic modulus is 23 directions. Therefore, it is not proportional to the shear modulus described in the present invention. There are various methods for evaluating the shear modulus of carbon fiber, but in the present invention, a method of calculating from a stress-strain curve obtained by tensile testing a resin-impregnated strand is used. That is, a coefficient is obtained so that the stress s (GPa) -strain e (-) curve is fitted to the equation (3) in the range of stress 0 to 3 GPa, and shear elasticity is obtained using the orientation function <cos ² j>. The modulus g and the initial tensile modulus E ₀ are calculated.

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 described in Non-Patent Document 5, the higher the shear elastic modulus of the carbon fiber, the higher the single fiber compressive strength of the carbon fiber, and it is preferable to increase the shear elastic modulus of the carbon fiber. In addition, since the evaluation method differs from the shear elastic modulus described in Non-Patent Document 5, absolute values cannot be compared. 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, the production conditions that contribute to the single fiber compressive strength of the carbon fiber bundle are clarified by examining the stress-strain curve on the tensile side in detail for the carbon fiber bundle obtained under various production conditions. A method for producing a carbon fiber bundle for controlling the shear elastic modulus and single fiber compressive strength of the carbon fiber will be described later.

  The carbon fiber bundle of the present invention preferably has an initial tensile elastic modulus of 305 GPa or more, more preferably 330 GPa or more, and further preferably 350 GPa or more. In general, it is known that the single fiber compressive strength decreases as the tensile elastic modulus increases. If the initial tensile elastic modulus is 305 GPa or more, it is preferable because the balance between the tensile elastic modulus and the single fiber compressive strength is excellent. The initial tensile elastic modulus is calculated from the stress-strain curve obtained by tensile testing the resin-impregnated strand as described above. The initial tensile elastic modulus of the carbon fiber bundle can be controlled mainly by the carbonization temperature and the carbonization tension during the carbonization.

In the carbon fiber bundle of the present invention, the relationship between the shear elastic modulus g and the initial tensile elastic modulus E ₀ is preferably in the range of the following formula (1).

In general, as the carbonization temperature is increased, the crystallinity of the carbon fiber tends to increase. However, as the crystallinity increases, the shear elastic modulus of the carbon fiber decreases and the initial tensile elastic modulus increases. This equation expresses the relationship, and it is preferable in terms of increasing the single fiber compressive strength to express a high shear modulus even when the carbonization temperature and the firing process tension such as carbonization tension are constant. The shear modulus control of the carbon fiber can be performed as described above. As a specific example, the carbon fiber bundle can be controlled within the range of the formula (1) by following the carbon fiber bundle manufacturing method of the present invention described later.

  The carbon fiber bundle of the present invention preferably has an average tearable distance of 550 to 850 mm. When the distance is less than 550 mm, the matrix resin is less likely to be impregnated between the single fibers, which may reduce the compressive strength of the carbon fiber reinforced composite material. When the distance exceeds 850 mm, the width is widened in the prepreg processing. May be unsuitable for producing a thin prepreg with a low basis weight.

  The carbon fiber bundle of the present invention is formed by bundling carbon fiber single fibers, and the number of single fibers is preferably 3000 to 60000. In the present invention, the carbon fiber bundle is preferably substantially untwisted. As used herein, “substantially untwisted” means that there is no twist or no more than 0.5 turns per 1 m of carbon fiber bundle, even if there is a twist. When the carbon fiber is untwisted, when used as a reinforcing fiber for a carbon fiber reinforced composite material, the carbon fiber bundle is excellent in spreading property and the carbon fiber reinforced composite material is often excellent in physical properties.

  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, pre-carbonized, and carbonized to obtain a carbon fiber bundle. At that time, the polyacrylonitrile-based precursor fiber bundle has an intensity ratio of 1453 cm ⁻¹ peak to 1370 cm ⁻¹ peak intensity in the infrared spectrum of 0.72 to 0.85, and an intensity of 1254 cm ⁻¹ peak to 1370 cm ⁻¹ peak intensity. Flame resistance is achieved so that the ratio is 0.50 to 0.65. The 1453 cm ⁻¹ peak is derived from an alkene and decreases with the progress of flame resistance, and the 1370 cm ⁻¹ peak and the 1254 cm ⁻¹ peak are considered to be flame resistant structures (respectively considered to be naphthyridine ring and hydrogenated naphthyridine ring structure). It increases with the progress of flame resistance. That is, in 1453Cm ^-1 peak intensity ratio of the relative 1370 cm ^-1 peak intensity is about 0.63 to 0.69 in the case of oxidized fiber bundle having a specific gravity of 1.35, as possible to reduce the peak derived from polyacrylonitrile In general, the carbonization yield is increased, but in the present invention, conditions for leaving many alkenes are set. Such a structure is considered to be effective in increasing the shear elastic modulus of the carbon fiber by being decomposed in the preliminary carbonization step. Furthermore, what is important is to set the oxidization conditions 1254Cm ^-1 peak intensity ratio of the relative 1370 cm ^-1 peak intensity are compatible such that from 0.50 to 0.65. A peak of 1254 cm ⁻¹ is often observed in a portion where flame resistance is insufficient, and it is considered that when this structure becomes a carbon fiber, there is an effect of reducing the shear modulus. The peak intensity ratio decreases with the progress of flame resistance, and the initial decrease is particularly large. However, depending on the flame resistance conditions, the peak intensity ratio may not be 0.65 or less even if the time is increased. In order to satisfy these two peak intensity ratios within the intended range, basically, the amount of the copolymer component contained in the polyacrylonitrile polymer is small, and the crystal orientation of the polyacrylonitrile precursor fiber bundle. The conditions may be set mainly focusing on the fact that the degree is high, the fineness of the polyacrylonitrile-based precursor fiber bundle is reduced, and the flameproofing temperature is lowered. The peak intensity described here is the absorbance at each wavelength after baseline correction of the spectrum obtained by sampling a small amount of flame-resistant fiber and measuring the infrared spectrum. Not performed. Further, the sample concentration is measured by diluting with KBr so as to be 0.67% by mass. In this way, each time the flameproofing condition setting is changed, the infrared spectrum is measured, and the conditions may be examined by trial and error according to a suitable manufacturing method described later. By appropriately controlling the infrared spectrum peak intensity ratio of the flameproof fiber, the single fiber compressive strength of the carbon fiber can be increased.

  In the present invention, the flameproofing treatment time can be suitably selected within a range of preferably 10 to 100 minutes, but is obtained for the purpose of improving the shear modulus and single fiber compressive strength of the obtained carbon fiber bundle. The flameproofing treatment time is set so that the specific gravity of the flameproofing fiber is preferably in the range of 1.22 to 1.28, more preferably 1.22 to 1.24. More preferable flameproofing treatment time depends on the flameproofing temperature. If the specific gravity of the flameproof fiber is not 1.22 or more, the physical properties such as the tensile elastic modulus of the carbon fiber bundle may be lowered. If the specific gravity is 1.28 or less, the single fiber compressive strength can be increased. The specific gravity of the flameproof fiber is controlled by the flameproofing treatment time and the flameproofing temperature. In the present invention, the flame resistance of the polyacrylonitrile-based precursor fiber is preferably controlled such that the peak intensity ratio of the infrared spectrum falls within the above range, specifically air at 200 to 300 ° C. It is preferably carried out in the air, and more preferably in the air at 210 to 240 ° C. The preferable range of the flameproofing treatment time and flameproofing temperature varies depending on the characteristics of the polyacrylonitrile-based precursor fiber bundle and the copolymer composition of the polyacrylonitrile-based polymer.

  In the present invention, the polyacrylonitrile-based polymer used for the production of the polyacrylonitrile-based precursor fiber bundle includes a copolymer component from the viewpoint of efficiently performing the flameproofing treatment. In general, the greater the amount of copolymerization component, the easier the flameproofing reaction will proceed, and it becomes easier to induce a local flameproofing reaction within the single fiber, making it difficult to uniformly flameproof within the single fiber. The amount of is preferably smaller. A preferable amount of the copolymerization component is 0.05 to 1.0% by mass. Preferred examples of the copolymer component include those having one or more carboxyl groups or amide groups from the above viewpoint. Specifically, acrylic acid, methacrylic acid, itaconic acid, crotonic acid, citraconic acid, ethacrylic acid, maleic acid and mesaconic acid are preferred, itaconic acid, maleic acid and mesaconic acid are more preferred, and itaconic acid is most preferred. . In the present invention, the polyacrylonitrile-based polymer means that at least acrylonitrile is the main constituent of the polymer skeleton, and the main constituent usually occupies 94 to 100% by mass of the polymer skeleton. Say that.

  As a polymerization method for producing a polyacrylonitrile-based polymer preferably used in the present invention, a known polymerization method can be selected. The spinning solution preferably used in the production of the carbon fiber bundle of the present invention is obtained by dissolving the polyacrylonitrile polymer in a solvent in which a polyacrylonitrile polymer such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide is soluble. is there. The polyacrylonitrile polymer used in the present invention is preferably a spinning solution having a concentration of 15 to 23% by mass.

  The method for producing a polyacrylonitrile-based precursor fiber bundle preferably used in the production of the carbon fiber bundle of the present invention includes a spinning process in which spinning is performed by discharging from a spinneret by a dry and wet spinning method, and a fiber obtained in the spinning process is bathed in water. A water washing step for washing in, a water bath drawing step for drawing the fibers obtained in the water washing step in a water bath, and a drying heat treatment step for drying and heat treating the fibers obtained in the water bath drawing step. And a steam stretching step of steam stretching the fiber obtained in the drying heat treatment step.

  In the present invention, the coagulation bath preferably contains a solvent such as dimethyl sulfoxide, dimethylformamide and dimethylacetamide used as a solvent for the spinning solution 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. The cross-sectional shape of the single fiber of the polyacrylonitrile-based precursor fiber bundle can be controlled according to the conditions of the coagulation bath, and it is preferable to control the cross-sectional shape to be close to a circle from the viewpoint of making the flameproofing reaction proceed uniformly.

  The water bath temperature in the water washing step is preferably 20 ° C. to 100 ° C. using a water bath having a plurality of stages. Moreover, it is preferable that the draw ratio in a water bath extending process is 1-5 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 polyacrylonitrile-based precursor that is preferably used in the production of a carbon fiber bundle by performing steam stretching as necessary after the water washing step, water bath stretching step, oil agent application step, and drying heat treatment step performed by a known method. A body fiber bundle is obtained. In the present invention, the steam stretching is preferably performed at least three times or more in the pressurized steam.

  In the present invention, the degree of crystal orientation of the polyacrylonitrile-based precursor fiber is preferably 92 to 96%, more preferably 93 to 96%. The higher the degree of crystal orientation, the more difficult the flameproofing reaction proceeds. Therefore, the infrared spectrum peak intensity ratio of the flameproofed fiber bundle is preferably controlled within the range of the present invention, and the degree of crystal orientation is preferably 92% or more. This is sufficient from this point of view. The degree of crystal orientation can be controlled by setting the product of the draw ratio in the water bath drawing process and the draw ratio in the steam drawing process to 10 times or more.

  In the present invention, the polyacrylonitrile-based precursor fiber bundle is preferably adjusted so that the fineness is 0.80 dtex or less, more preferably 0.60 dtex or less, and still more preferably 0.45 dtex or less. When the fineness is 0.80 dtex or less, the non-uniformity of the flameproofing reaction in the single fiber is likely to be reduced, and the infrared spectrum peak intensity ratio of the flameproofed fiber bundle is easily controlled within the range of the present invention. Such fineness can be controlled by adjusting the discharge amount of the spinning solution and the spinning speed.

  Subsequent to the flame resistance, preliminary carbonization is performed. In the preliminary carbonization step, the obtained flame-resistant fiber bundle is preferably heat-treated in an inert atmosphere at a maximum temperature of 500 to 1200 ° C. until the specific gravity is 1.5 to 1.8.

Subsequent to the preliminary carbonization, carbonization is performed. In the present invention, in the carbonization step, the obtained pre-carbonized fiber bundle is carbonized in an inert atmosphere at a maximum temperature of 1200 to 2000 ° C. so that the carbonization tension satisfies the formula (2). It is a method, Comprising: It is preferable that it is a manufacturing method of the carbon fiber bundle whose average tearable distance of a pre-carbonized fiber bundle is 450-700 mm.
4.9 ≦ carbonization tension (mN / dtex) ≦ −0.0225 × (average tearable distance (mm)) + 23.5 (2).

  The temperature of the carbonization step is preferably higher from the viewpoint of increasing the strand elastic modulus of the carbon fiber to be obtained, but if it is too high, the single fiber compressive strength may decrease, and it is necessary to set the temperature in consideration of both. good. A more preferred temperature range is 1350-1900 ° C, and a more preferred temperature range is 1600-1900 ° C.

  The tension (carbonization tension) in the carbonization step is represented by a value obtained by dividing the tension (mN) measured on the outlet side of the carbonization furnace by the fineness (dtex) of the polyacrylonitrile-based precursor fiber when it is completely dried. When the tension is lower than 4.9 mN / dtex, the crystallite orientation of the carbon fiber cannot be increased, and a high strand elastic modulus is not exhibited. Further, the tension is preferably higher from the viewpoint of increasing the strand elastic modulus of the carbon fiber to be obtained, but if it is too high, the process passability and the quality may be lowered, and in a range satisfying the formula (2). It is preferable to set. The meaning of the first-order coefficient −0.0225 on the right-hand side of Equation (2) is a tension gradient that can be set with an increase in the average tearable distance, and the constant term 23.5 is used to reduce the average tearable distance to the limit. This tension can be set when the length is shortened.

  The tearable distance of the pre-carbonized fiber bundle in the carbonization step is an index that represents the entangled state of the fiber bundle, and is determined as follows. First, the fiber bundle is cut to a length of 1160 mm, and one end thereof is fixed on a horizontal base so as not to move with an adhesive tape (this point is referred to as a fixing point A). One end of the fiber bundle that is not fixed is divided into two with fingers, and one of the ends is tensioned and fixed on the table so as not to move with an adhesive tape (this point is referred to as a fixing point B). Move the other of the two halves along the table so that the fixed point A becomes a fulcrum and does not come loose, rest at a position where the linear distance from the fixed point B is 500 mm, and fix it on the table so that it does not move with adhesive tape. (This point is called a fixed point C). The area surrounded by the fixed points A, B, and C is visually observed, the entanglement point farthest from the fixed point A is found, and the distance projected on the straight line connecting the fixed point A and the fixed point B is 1 mm at the minimum scale. Read with the ruler of, and make the tearable distance. The arithmetic average value of 30 measurements of the above operation is defined as the average tearable distance. A method of measuring the tearable distance is shown in FIG. In this measurement method, the entanglement point farthest from the fixed point A is the point where the linear distance from the fixed point A is the longest and three or more single fibers having no slack are entangled.

  Conventionally, the hook drop method has been generally used as a method for evaluating the entangled state. As defined in JIS L1013 (2010), the degree of entanglement of the fiber bundle by the hook drop method is fixed to the upper part of the drooping device, the weight is suspended at the lower end of the fiber bundle, and the sample is placed vertically. After that, a hook with a weight of 10 g with a smooth surface of 0.6 mm in diameter is inserted so as to divide the fiber bundle into two parts 1 cm below the upper fixed end of the sample, and the descent distance is measured. .

  In the present invention, as the degree of entanglement of the pre-carbonized fiber bundle in the carbonization process, not by the conventional hook drop method, but by making the average tearable distance within a specific range, while avoiding the strength reduction of the carbon fiber high strength region High stretch tension in the carbonization process can be expressed. In order to apply a high drawing tension in the carbonization process, it is necessary to create a fiber bundle state in which the stress transmission ability between single fibers is high. For that purpose, it is important to form a fine entanglement network between single fibers. The conventional hook drop method is an evaluation at a “point” using a hook, whereas the tearable distance is an evaluation at a “surface” that looks at the entire bundle. Due to this difference, in the carbonization process, It is considered that a state for expressing a high stretching tension can be appropriately defined.

  In the present invention, the shorter the tearable distance of the pre-carbonized fiber bundle in the carbonization process, the higher the degree of entanglement, the higher the stress transmission ability between single fibers, and the higher the stretching tension in the carbonization process. If the distance is less than 450 mm, the single fiber compressive strength of the carbon fiber is likely to decrease. If the distance is 500 mm or more, the single fiber compressive strength varies (according to the compression fragmentation method of the carbon fiber single fiber composite described in the present invention). The difference between the single fiber compressive stress and the single fiber compressive strength in which the number of single fiber breaks when a compressive stress is applied exceeds 0.1 / 10 mm. If the entanglement treatment with a tearable distance exceeding 750 mm is not performed or weak, the other single fiber not ruptured bears the stress of the single fiber that breaks with a certain probability that is a carbonization process, It is easy to induce structural variations between single fibers. As the means for achieving the average tearable distance of the preliminary carbonized fiber, any method can be adopted as long as the numerical range described above can be achieved. In the present invention, as a method for controlling the average tearable distance, The entanglement process by the fluid to the fiber bundle is preferably used. Among them, it is preferable to perform the fluid entanglement process in any of the manufacturing process and the flameproofing process of the polyacrylonitrile-based precursor fiber, that is, in a place where a fiber bundle having a fiber elongation of 5% or more is processed. As the fluid used for the fluid entanglement treatment, both gas and liquid can be used, but air or nitrogen is preferable because it is inexpensive. In the fluid entanglement process, the fluid is preferably sprayed onto the fiber bundle using a nozzle, and the shape of the nozzle that sprays the fluid is not particularly limited, but it is preferable to use one having 2 to 8 ejection holes. The arrangement of the ejection ports is not particularly limited, but an even number of ejection holes are arranged so as to surround the fiber bundle so that the angle formed by the fiber bundle longitudinal direction and the fluid blowing direction is in the range of 88 ° to 90 °. It is preferable to arrange the jet holes at positions facing each other so as to form a pair of two holes. Other conditions such as fiber bundle tension and fluid discharge pressure during the fluid entanglement process may be examined so as to adjust the tearable distance appropriately. In the present invention, the pre-carbonized fiber is preferably substantially untwisted. As used herein, “substantially untwisted” means that there is no twist or no more than 0.5 turns per 1 m of carbon fiber bundle, even if there is a twist.

  The obtained carbon fiber bundle can be further heat-treated while being stretched at a temperature of 2000 ° C. or higher to control the crystallite size to be in the range of 4.0 nm.

  The obtained carbon fiber bundle has improved adhesiveness with the matrix resin, and the number of fiber breaks when the single fiber apparent stress is 15.3 GPa by the tensile fragmentation method of the single fiber composite is 2.0 pieces / mm or more. In general, an oxidation treatment is performed to introduce an oxygen-containing functional group and a sizing agent is applied. 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.

  In the present invention, examples of the electrolytic solution used in the liquid phase electrolytic oxidation include an acidic electrolytic solution and an alkaline electrolytic solution. From the viewpoint of adhesion, a liquid phase electrolytic oxidation is performed in an alkaline electrolytic solution, and then a sizing agent is applied. Is more preferable.

  Examples of the acidic electrolyte include inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, boric acid, and carbonic acid, organic acids such as acetic acid, butyric acid, oxalic acid, acrylic acid, and maleic acid, or ammonium sulfate and ammonium hydrogen sulfate. And the like. Of these, sulfuric acid and nitric acid exhibiting strong acidity are preferably used.

  Specific examples of the alkaline electrolyte include aqueous solutions of hydroxides such as sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide and barium hydroxide, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, Aqueous solutions of carbonates such as barium carbonate and ammonium carbonate, aqueous solutions of bicarbonates such as sodium bicarbonate, potassium bicarbonate, magnesium bicarbonate, calcium bicarbonate, barium bicarbonate and ammonium bicarbonate, ammonia, tetraalkylammonium hydroxide And an aqueous solution of hydrazine. Among these, from the viewpoint of not containing an alkali metal that causes curing inhibition of the matrix resin, an aqueous solution of ammonium carbonate and ammonium hydrogen carbonate or an aqueous solution of tetraalkylammonium hydroxide exhibiting strong alkalinity is preferably used.

  The concentration of the electrolytic solution used in the present invention is preferably in the range of 0.01 to 5 mol / liter, more preferably in the range of 0.1 to 1 mol / liter. When the concentration of the electrolytic solution is 0.01 mol / liter or more, the electrolytic treatment voltage is lowered, which is advantageous for the operating cost. On the other hand, when the concentration of the electrolytic solution is 5 mol / liter or less, it is advantageous from the viewpoint of safety.

  The temperature of the electrolytic solution used in the present invention is preferably in the range of 10 to 100 ° C, more preferably in the range of 10 to 40 ° C. When the temperature of the electrolytic solution is 10 ° C. or higher, the efficiency of the electrolytic treatment is improved, which is advantageous for the operating cost. On the other hand, when the temperature of the electrolytic solution is 100 ° C. or lower, it is advantageous from the viewpoint of safety.

  In the present invention, the amount of electricity in the liquid phase electrolytic oxidation is preferably optimized in accordance with the carbonization degree of the carbon fiber, and a larger amount of electricity is required when processing the carbon fiber having a high elastic modulus.

In the present invention, the current density in the liquid phase electrolytic oxidation is preferably in the range of 1.5 to 1000 amperes / m ² per 1 m ² of the surface area of the carbon fiber in the electrolytic treatment solution, more preferably 3 to 500 amperes. / M ^{2 in} the range. When the current density is 1.5 amperes / m ² or more, the efficiency of the electrolytic treatment is improved, which is advantageous for the operating cost. On the other hand, when the current density is 1000 amperes / m ² or less, it is advantageous from the viewpoint of safety.

  In the present invention, the total amount of electrolytic electricity employed in the electrolytic treatment is preferably 3 to 300 coulomb / g per gram of carbon fiber. If the total amount of electrolytic electricity is less than 3 coulombs / g, functional groups may not be sufficiently imparted to the carbon fiber surface, and the number of fiber breaks when the single fiber apparent stress by the fragmentation method of the single fiber composite is 15.3 GPa. May be less than 2.0 pieces / mm. On the other hand, if the total amount of electrolytic electricity exceeds 300 coulombs / g, defects on the surface of the carbon fiber single fiber may be enlarged, and the tensile strength of the carbon fiber may be reduced.

  In the present invention, it is preferable to wash and dry the carbon fiber after the electrolytic treatment. As a cleaning method, for example, a dip method and a spray method can be used. Especially, it is preferable to use a dip method from a viewpoint that washing | cleaning is easy, Furthermore, it is a preferable aspect to use a dip method, vibrating a carbon fiber with an ultrasonic wave. Also, if the drying temperature is too high, the functional groups present on the outermost surface of the carbon fiber are likely to disappear due to thermal decomposition, so it is desirable to dry at the lowest possible temperature. Specifically, the drying temperature is preferably 250 ° C. or lower. More preferably, drying is performed at 210 ° C. or lower.

  The present invention is a sizing agent-coated carbon fiber bundle which is a carbon fiber bundle coated with a sizing agent containing at least an aliphatic epoxy compound (A) and an aromatic epoxy compound (B). By using these in combination, the interfacial adhesion between the carbon fiber and the matrix resin is excellent. Therefore, by using such a sizing agent, the carbon fiber bundle of the present invention has a fiber breakage number of 2.0 pieces / mm or more when the single fiber apparent stress is 15.3 GPa according to the tensile fragmentation method of the single fiber composite. Can be controlled.

  In the present invention, the epoxy equivalent of the sizing agent applied to the carbon fiber bundle is preferably 350 to 550 g / mol. Controlling within this range is preferable because the adhesion between the carbon fiber coated with the sizing agent and the matrix resin is improved. The epoxy equivalent of the carbon fiber bundle to which the sizing agent is applied in the present invention is the sizing agent from the carbon fiber bundle by immersing the carbon fiber bundle in a solvent typified by N, N-dimethylformamide and performing ultrasonic cleaning. After elution, the epoxy group is opened with hydrochloric acid, and it can be determined by acid-base titration. Epoxy equivalent is preferably 360 g / mol or more, and more preferably 380 g / mol or more. Moreover, 530 g / mol or less is preferable and 500 g / mol or less is more preferable. In addition, the epoxy equivalent of the sizing agent applied to the carbon fiber bundle can be controlled by the epoxy equivalent of the sizing agent used for application and the heat history in drying after application.

  In this invention, it is preferable that the aliphatic epoxy compound (A) eluted from a sizing agent application | coating fiber is 0.3 mass part or less with respect to 100 mass parts of carbon fiber bundles. It is preferable that the elution amount be 0.3 parts by mass or less because the physical properties of the obtained carbon fiber reinforced composite material are improved even when the carbon fiber bundle is stored for a long time. 0.1 mass part or less is more preferable, and 0.05 mass part or less is still more preferable. In this invention, the elution amount of the aliphatic epoxy compound (A) eluted from a carbon fiber bundle is calculated | required in the following procedures. After immersing 0.1 g of the carbon fiber bundle in 10 ml of a solution in which acetonitrile and chloroform are mixed at a volume ratio of 9: 1, the sizing agent is eluted from the carbon fiber bundle by performing ultrasonic cleaning for 20 minutes, and then 5 ml of the sample solution. The sample is collected, the solvent is distilled off in nitrogen, and the above-mentioned mixed solution of acetonitrile and chloroform is added to a constant volume until the volume becomes 0.2 ml to prepare a 25-fold concentrated solution. The solution is separated from the other peaks of the aliphatic epoxy compound (A) by liquid chromatography using a mixture of water and acetonitrile as a mobile phase and detected by an evaporative light scattering detector (ELSD). . Then, by creating a calibration curve using the peak area of the solution of the aliphatic epoxy compound (A) whose concentration is known in advance, and quantifying the concentration of the aliphatic epoxy compound (A) based on that, The elution amount of the aliphatic epoxy compound (A) with respect to 100 parts by mass of the carbon fiber bundle is determined.

  In this invention, it is preferable that 35-65 mass% of aliphatic epoxy compounds (A) are contained with respect to the apply | coated sizing agent whole quantity. Adhesiveness improves by being applied 35 mass% or more. Moreover, components other than aliphatic epoxy can be used as a sizing agent by being 65 mass% or less. It is preferable that 35-60 mass% of aromatic epoxy compounds (B) are contained with respect to the sizing agent whole quantity. By containing 35% by mass or more of the aromatic epoxy compound (B), the composition of the aromatic compound in the outer layer of the sizing agent can be kept high, so that it is often excellent in long-term storage stability. It is preferable because the adhesiveness can be increased by being 60% by mass or less.

  As an epoxy component in the sizing agent in the present invention, an aliphatic epoxy compound (A) and an aromatic epoxy compound (B) are included. The mass ratio (A) / (B) of the aliphatic epoxy compound (A) and the aromatic epoxy compound (B) is preferably 52/48 to 80/20. When (A) / (B) is 52/48 or more, the ratio of the aliphatic epoxy compound (A) present on the carbon fiber surface is increased, and the adhesion between the carbon fiber and the matrix resin is improved. As a result, the composite properties such as tensile strength of the obtained carbon fiber reinforced resin are preferably increased. Moreover, 80/20 or less is preferable because the amount of the highly reactive aliphatic epoxy compound present on the surface of the carbon fiber is reduced and the reactivity with the matrix resin can be suppressed. The mass ratio of (A) / (B) is more preferably 55/45 or more, and further preferably 60/40 or more. Moreover, 75/35 or less is more preferable, and 73/37 or less is further more preferable.

  In this invention, it is preferable that the adhesion amount of a sizing agent is the range of 0.1-3.0 mass parts with respect to 100 mass parts of carbon fiber bundles, More preferably, 0.2-3.0 mass parts Range. When the amount of the sizing agent is within such a range, high perforated plate compressive strength can be exhibited. The amount of sizing agent adhering is measured by collecting 2 ± 0.5 g of carbon fiber bundles coated with the sizing agent, and performing the heat treatment at 450 ° C. for 15 minutes in a nitrogen atmosphere before and after the heat treatment. It is the mass% of the value which remove | divided the variation | change_quantity by the mass before heat processing.

  The aliphatic epoxy compound (A) in the present invention is an epoxy compound containing no aromatic ring. Since it has a flexible skeleton with a high degree of freedom, it can have a strong interaction with carbon fibers. As a result, the adhesiveness of the sizing agent-coated carbon fiber is improved, which is preferable.

  In the present invention, the aliphatic epoxy compound (A) has one or more epoxy groups in the molecule. As a result, a strong bond between the carbon fiber and the epoxy group in the sizing agent can be formed. The number of epoxy groups in the molecule is preferably 2 or more, and more preferably 3 or more. In the case of an epoxy compound having two or more epoxy groups in the molecule, even if one epoxy group forms a covalent bond with the oxygen-containing functional group on the surface of the carbon fiber, the remaining epoxy group is covalently bonded to the matrix resin. Alternatively, it is preferable because a hydrogen bond can be formed and adhesion can be further improved. There is no particular upper limit on the number of epoxy groups, but 10 is sufficient from the viewpoint of adhesion.

  In the present invention, the aliphatic epoxy compound (A) is preferably an epoxy compound having 3 or more of 2 or more types of functional groups, and more preferably an epoxy compound having 4 or more of 2 or more types of functional groups. . The functional group possessed by the epoxy compound is preferably selected from a hydroxyl group, an amide group, an imide group, a urethane group, a urea group, a sulfonyl group, or a sulfo group in addition to the epoxy group. In the case of an epoxy compound having three or more epoxy groups or other functional groups in the molecule, even if one epoxy group forms a covalent bond with an oxygen-containing functional group on the carbon fiber surface, the remaining two or more The epoxy group or other functional group can form a covalent bond or a hydrogen bond with the matrix resin, and the adhesion is further improved. There is no particular upper limit on the number of functional groups containing an epoxy group, but 10 is sufficient from the viewpoint of adhesiveness.

  In this invention, it is preferable that the epoxy equivalent of an aliphatic epoxy compound (A) is less than 360 g / mol, More preferably, it is less than 270 g / mol, More preferably, it is less than 180 g / mol. When the epoxy equivalent is less than 360 g / mol, an interaction with the carbon fiber is formed at a high density, and the adhesion between the carbon fiber and the matrix resin is further improved. There is no particular lower limit of the epoxy equivalent, but 90 g / mol or more is sufficient from the viewpoint of adhesiveness.

  In the present invention, specific examples of the aliphatic epoxy compound (A) include, for example, a glycidyl ether type epoxy compound derived from a polyol, a glycidyl amine type epoxy compound derived from an amine having a plurality of active hydrogens, and a polycarboxylic acid. Examples thereof include an induced glycidyl ester type epoxy compound and an epoxy compound obtained by oxidizing a compound having a plurality of double bonds in the molecule.

  Examples of the glycidyl ether type epoxy compound include a glycidyl ether type epoxy compound obtained by a reaction with epichlorohydrin. Further, as glycidyl ether type epoxy compounds, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, trimethylene glycol, 1,2 -Butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, polybutylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,4 -Cyclohexanedimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, glycerol, diglycerol, polyglycerol, trimethylolpropane, pen Erythritol, sorbitol, and the arabitol, glycidyl ether type epoxy compound obtained by reaction of epichlorohydrin are also exemplified. Examples of the glycidyl ether type epoxy compound include a glycidyl ether type epoxy compound having a dicyclopentadiene skeleton.

  Examples of the glycidylamine type epoxy compound include 1,3-bis (aminomethyl) cyclohexane.

  Examples of the glycidyl ester type epoxy compound include a glycidyl ester type epoxy compound obtained by reacting dimer acid with epichlorohydrin.

  Examples of the epoxy compound obtained by oxidizing a compound having a plurality of double bonds in the molecule include an epoxy compound having an epoxycyclohexane ring in the molecule. Furthermore, the epoxy compound includes epoxidized soybean oil.

  Examples of the aliphatic epoxy compound (A) used in the present invention include epoxy compounds such as triglycidyl isocyanurate in addition to these epoxy compounds.

  In the present invention, the aliphatic epoxy compound (A) is at least one selected from one or more epoxy groups and a hydroxyl group, amide group, imide group, urethane group, urea group, sulfonyl group, carboxyl group, ester group and sulfo group. It is preferable to have one or more functional groups. Specific examples of the epoxy compound include, for example, a compound having an epoxy group and a hydroxyl group, a compound having an epoxy group and an amide group, a compound having an epoxy group and an imide group, a compound having an epoxy group and a urethane group, and an epoxy group and a urea group. Compounds having an epoxy group and a sulfonyl group, and compounds having an epoxy group and a sulfo group.

  Examples of the compound having a hydroxyl group in addition to an epoxy group include sorbitol-type polyglycidyl ether and glycerol-type polyglycidyl ether. Specifically, “Denacol (registered trademark)” EX-611, EX-612, EX -614, EX-614B, EX-622, EX-512, EX-521, EX-421, EX-313, EX-314, and EX-321 (manufactured by Nagase ChemteX Corporation).

  Examples of the compound having an amide group in addition to the epoxy group include an amide-modified epoxy compound. The amide-modified epoxy can be obtained by reacting an epoxy group of an epoxy compound having two or more epoxy groups with a carboxyl group of an aliphatic dicarboxylic acid amide.

  Examples of the compound having a urethane group in addition to the epoxy group include a urethane-modified epoxy compound. Specifically, “ADEKA RESIN (registered trademark)” EPU-78-13S, EPU-6, EPU-11, EPU- 15, EPU-16A, EPU-16N, EPU-17T-6, EPU-1348, EPU-1395 (manufactured by ADEKA Corporation) and the like. Alternatively, by reacting the terminal hydroxyl group of the polyethylene oxide monoalkyl ether with a polyvalent isocyanate equivalent to the amount of the hydroxyl group, and then reacting the isocyanate residue of the obtained reaction product with the hydroxyl group in the polyvalent epoxy compound. Can be obtained. Here, examples of the polyvalent isocyanate used include hexamethylene diisocyanate, isophorone diisocyanate, and norbornane diisocyanate.

  Examples of the compound having a urea group in addition to the epoxy group include a urea-modified epoxy compound. A urea-modified epoxy can be obtained by reacting an epoxy group of an epoxy compound having two or more epoxy groups with a carboxyl group of an aliphatic dicarboxylic acid urea.

  The aliphatic epoxy compound (A) used in the present invention is ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetra from the viewpoint of high adhesiveness. Propylene glycol, polypropylene glycol, trimethylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, polybutylene glycol, 1,5-pentanediol, neo Pentyl glycol, 1,6-hexanediol, glycerol, diglycerol, polyglycerol, trimethylolpropane, pentaerythritol, sorbitol, and arabitol , Glycidyl ether type epoxy compound obtained by reaction of epichlorohydrin is more preferable.

  Among the above, the aliphatic epoxy compound (A) in the present invention is preferably a polyether type polyepoxy compound and / or a polyol type polyepoxy compound having two or more epoxy groups in the molecule from the viewpoint of high adhesiveness.

  In addition, the aliphatic epoxy compound (A) is ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, trimethylene glycol, 1, 2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, polybutylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1, 4-cyclohexanedimethanol, glycerol, diglycerol, polyglycerol, trimethylolpropane, pentaerythritol, sorbitol, and arabitol, and epi More preferably glycidyl ether type epoxy compound obtained by reaction with Rorohidorin.

  In the present invention, the aliphatic epoxy compound is more preferably polyglycerol polyglycidyl ether.

  In the present invention, the aromatic epoxy compound (B) has one or more aromatic rings in the molecule. The aromatic ring may be an aromatic ring hydrocarbon composed only of carbon, or a heteroaromatic ring such as furan, thiophene, pyrrole or imidazole containing a heteroatom such as nitrogen or oxygen. The aromatic ring may be a polycyclic aromatic ring such as naphthalene or anthracene. In a fiber-reinforced composite material composed of sizing agent-coated carbon fibers and a matrix resin, a so-called interface layer in the vicinity of the carbon fibers may be affected by the carbon fibers or the sizing agent and have different characteristics from the matrix resin. When the epoxy compound has one or more aromatic rings, a rigid interface layer is formed, the stress transmission ability between the carbon fiber and the matrix resin is improved, and the mechanical properties such as the perforated plate compressive strength are improved. There is no particular upper limit on the number of aromatic rings, but 10 is sufficient from the viewpoint of suppressing the reaction with the mechanical properties and the matrix resin.

  In the present invention, the aromatic epoxy compound (B) has at least one kind in the molecule having one or more epoxy groups and one or more aromatic rings in the molecule. The functional group other than the epoxy group is preferably selected from a hydroxyl group, an amide group, an imide group, a urethane group, a urea group, a sulfonyl group, a carboxyl group, an ester group or a sulfo group, and two or more types are included in one molecule. Also good. In addition to the aromatic epoxy compound (B), an aromatic ester compound and an aromatic urethane compound are preferably used in order to improve the stability and high-order processability of the compound.

  In the present invention, the number of epoxy groups of the aromatic epoxy compound (B) is preferably 2 or more, and more preferably 3 or more. Moreover, it is preferable that it is 10 or less.

  In the present invention, the aromatic epoxy compound (B) is preferably an epoxy compound having 3 or more functional groups of 2 or more, more preferably an epoxy compound having 4 or more of 2 or more functional groups. . The functional group possessed by the epoxy compound is preferably selected from a hydroxyl group, an amide group, an imide group, a urethane group, a urea group, a sulfonyl group, or a sulfo group in addition to the epoxy group. In the case of an epoxy compound having three or more epoxy groups or other functional groups in the molecule, even if one epoxy group forms a covalent bond with an oxygen-containing functional group on the carbon fiber surface, the remaining two or more The epoxy group or other functional group can form a covalent bond or a hydrogen bond with the matrix resin, and the adhesion is further improved. There is no particular upper limit on the number of functional groups containing an epoxy group, but 10 is sufficient from the viewpoint of adhesiveness.

  In this invention, it is preferable that the epoxy equivalent of an aromatic epoxy compound (B) is less than 360 g / mol, More preferably, it is less than 270 g / mol, More preferably, it is less than 180 g / mol. When the epoxy equivalent is less than 360 g / mol, covalent bonds are formed at a high density, and the adhesion between the carbon fiber and the matrix resin is further improved. There is no particular lower limit of the epoxy equivalent, but 90 g / mol or more is sufficient from the viewpoint of adhesiveness.

  In the present invention, specific examples of the aromatic epoxy compound (B) include, for example, a glycidyl ether type epoxy compound derived from a polyol, a glycidyl amine type epoxy compound derived from an amine having multiple active hydrogens, and a polycarboxylic acid. Examples thereof include an induced glycidyl ester type epoxy compound and an epoxy compound obtained by oxidizing a compound having a plurality of double bonds in the molecule.

  Examples of the glycidyl ether type epoxy compound include bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetrabromobisphenol A, phenol novolac, cresol novolac, hydroquinone, resorcinol, 4,4′-dihydroxy-3,3 ′, 5. , 5′-tetramethylbiphenyl, 1,6-dihydroxynaphthalene, 9,9-bis (4-hydroxyphenyl) fluorene, tris (p-hydroxyphenyl) methane, and tetrakis (p-hydroxyphenyl) ethane. Examples of the glycidyl ether type epoxy include a compound and a glycidyl ether type epoxy compound having a biphenyl aralkyl skeleton.

  Examples of the glycidylamine type epoxy compound include N, N-diglycidylaniline, N, N-diglycidyl-o-toluidine, m-xylylenediamine, m-phenylenediamine, 4,4′-diaminodiphenylmethane and 9,9. -Bis (4-aminophenyl) fluorene.

  Further, for example, as a glycidylamine type epoxy compound, both the hydroxyl group and amino group of aminophenols of m-aminophenol, p-aminophenol, and 4-amino-3-methylphenol are reacted with epichlorohydrin. And an epoxy compound obtained.

  Examples of the glycidyl ester type epoxy compound include glycidyl ester type epoxy compounds obtained by reacting phthalic acid, terephthalic acid, and hexahydrophthalic acid with epichlorohydrin.

  As the aromatic epoxy compound (B) used in the present invention, besides these epoxy compounds, epoxy compounds synthesized from the above-mentioned epoxy compounds, for example, oxazolidone from bisphenol A diglycidyl ether and tolylene diisocyanate An epoxy compound synthesized by a ring formation reaction is exemplified.

  In the present invention, in addition to one or more epoxy groups, at least one functional group selected from a hydroxyl group, an amide group, an imide group, a urethane group, a urea group, a sulfonyl group, a carboxyl group, an ester group, and a sulfo group. Preferably used. For example, compounds having epoxy group and hydroxyl group, compounds having epoxy group and amide group, compounds having epoxy group and imide group, compounds having epoxy group and urethane group, compounds having epoxy group and urea group, epoxy group and sulfonyl Examples thereof include compounds having a group and compounds having an epoxy group and a sulfo group.

  Examples of the compound having an amide group in addition to the epoxy group include glycidyl benzamide and an amide-modified epoxy compound. The amide-modified epoxy can be obtained by reacting an epoxy group of an epoxy compound having two or more epoxy groups with a carboxyl group of a dicarboxylic acid amide containing an aromatic ring.

  Examples of the compound having an imide group in addition to the epoxy group include glycidyl phthalimide. Specific examples include “Denacol (registered trademark)” EX-731 (manufactured by Nagase ChemteX Corporation).

  As a compound having a urethane group in addition to an epoxy group, the terminal hydroxyl group of polyethylene oxide monoalkyl ether is reacted with a polyvalent isocyanate containing an aromatic ring having a reaction equivalent to the amount of the hydroxyl group, and then the reaction product obtained It can be obtained by reacting an isocyanate residue with a hydroxyl group in a polyvalent epoxy compound. Here, examples of the polyvalent isocyanate used include 2,4-tolylene diisocyanate, metaphenylene diisocyanate, paraphenylene diisocyanate, diphenylmethane diisocyanate, triphenylmethane triisocyanate, and biphenyl-2,4,4′-triisocyanate. It is done.

  Examples of the compound having a urea group in addition to the epoxy group include a urea-modified epoxy compound. The urea-modified epoxy can be obtained by reacting the epoxy group of an epoxy compound containing an aromatic ring having two or more epoxy groups with the carboxyl group of the dicarboxylic acid urea.

  Examples of the compound having a sulfonyl group in addition to the epoxy group include bisphenol S-type epoxy.

  Examples of the compound having a sulfo group in addition to the epoxy group include glycidyl p-toluenesulfonate and glycidyl 3-nitrobenzenesulfonate.

  In the present invention, the aromatic epoxy compound (B) is preferably either a phenol novolac epoxy compound, a cresol novolac epoxy compound, or tetraglycidyl diaminodiphenylmethane. These epoxy compounds have a large number of epoxy groups, a small epoxy equivalent, and have two or more aromatic rings. In addition to improving the adhesion between carbon fiber and matrix resin, fiber reinforced composite materials Improve mechanical properties such as 0 ° tensile strength. More preferred are phenol novolac epoxy compounds and cresol novolac epoxy compounds.

  In the present invention, when the prepreg is stored for a long time, the aromatic epoxy compound (B) is a phenol novolak type epoxy compound, a cresol novolak type epoxy compound, a tetraglycidyl diaminodiphenylmethane, a bisphenol A type epoxy compound or a bisphenol F type epoxy compound. From the viewpoint of stability and adhesiveness, it is preferably a bisphenol A type epoxy compound or a bisphenol F type epoxy compound.

  Furthermore, the sizing agent used in the present invention may contain one or more components other than the aliphatic epoxy compound (A) and the aromatic epoxy compound (B). Accelerator that enhances adhesion between carbon fiber and sizing agent. Convergence or flexibility is imparted to carbon fiber coated with sizing agent to improve handling, scratch resistance and fluff resistance, and improve matrix resin impregnation. In order to improve the long-term stability of the prepreg in the present invention, compounds other than (A) and (B) can be contained. For the purpose of stabilizing the sizing agent, auxiliary components such as a dispersant and a surfactant may be added.

  In the present invention, the carbon fiber has a surface oxygen concentration (O / C), which is a ratio of the number of atoms of oxygen (O) and carbon (C) on the fiber surface measured by X-ray photoelectron spectroscopy. The thing within the range of 05-0.50 is preferable, More preferably, it is a thing within the range of 0.06-0.30, More preferably, it is a thing within the range of 0.07-0.25. When the surface oxygen concentration (O / C) is 0.05 or more, an oxygen-containing functional group on the surface of the carbon fiber can be secured and strong adhesion with the matrix resin can be obtained. Moreover, when the surface oxygen concentration (O / C) is 0.50 or less, it is possible to suppress a decrease in the single fiber strength of the carbon fiber itself due to oxidation.

The surface oxygen concentration of the carbon fiber is determined by X-ray photoelectron spectroscopy according to the following procedure. First, carbon fibers from which dirt and the like adhering to the carbon fiber surface were removed with a solvent were cut into 20 mm, spread and arranged on a copper sample support base, and then AlKα ₁ and ₂ were used as X-ray sources. The inside of the chamber was measured at 1 × 10 ⁻⁸ Torr. As a correction value for the peak accompanying charging during measurement, the binding energy value of the C _1s main peak (peak top) is adjusted to 284.6 eV. The C _1s peak area is obtained by drawing a straight base line in the range of 282 to 296 eV, and the O _1s peak area is obtained by drawing a straight base line in the range of 528 to 540 eV. The surface oxygen concentration O / C is represented by an atomic ratio calculated by dividing the ratio of the O _1s peak area by the sensitivity correction value unique to the apparatus. When ESCA-1600 manufactured by ULVAC-PHI Co., Ltd. is used as the X-ray photoelectron spectroscopy apparatus, the sensitivity correction value unique to the apparatus is 2.33.

  The carbon fiber bundle of the present invention can be obtained by trial and error by paying attention to the points of the above preferred production method and according to the conventional means of those skilled in the art so that the fracture behavior of tensile fragmentation matches the scope of the present invention. As a result, the carbon fiber bundle that exhibits excellent single fiber compressive strength can exhibit high composite compressive strength.

  EXAMPLES Next, although an Example demonstrates this invention concretely, this invention is not restrict | limited by these Examples.

<Strand tensile strength, initial tensile elastic modulus and shear elastic modulus of carbon fiber bundle>
The strand tensile strength and strand elastic modulus of the carbon fiber bundle were 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 were used. Ten resin-impregnated strands of carbon fiber bundles were measured, and the average value was defined as the strand tensile strength. The strain was evaluated using an extensometer. The coefficient is obtained by fitting the obtained stress s-strain e curve to the equation (3) in the range of stress 0 to 3 GPa, and the shear modulus g and initial tensile elasticity are obtained using the orientation function <cos ² j>. The rate E ₀ is calculated.

The measurement of the orientation function is described below.

<Crystal size of carbon fiber bundle, orientation function>
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. About the prepared measurement sample, it measured on the following conditions using the wide angle X-ray-diffraction apparatus.

-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.

  In the obtained diffraction pattern, the full width at half maximum was obtained for the peak appearing in the vicinity of 2θ = 25 to 26 °, and the crystallite size was calculated from this value by the following Scherrer equation.

Crystallite size (nm) = Kλ / β ₀ cos θ _B
However,
K: 1.0, λ: 0.15418 nm (X-ray wavelength)
β ₀ : (β _E ² -β ₁ ² ) ^1/2
β _E : Apparent half width (measured value) rad, β ₁ : 1.046 × 10 ⁻² rad
θ _B : Bragg diffraction angle.

The orientation function <cos ² j> was measured as follows. The diffraction intensity distribution obtained by scanning the peak appearing in the vicinity of 2θ = 25 to 26 ° in the circumferential direction is fitted with a Gaussian distribution, and calculated from the diffraction intensity distribution r (j) after the fitting using the following equation. Asked.

In addition, Shimadzu Corporation XRD-6100 was used as said wide angle X-ray diffraction apparatus.

<Single fiber compressive strength of carbon fiber>
The measurement of the single fiber compressive strength by the compression fragmentation method of the single fiber composite was performed by the following procedures (a) to (e).

(A) Preparation of resin 190 parts by mass of bisphenol A type epoxy resin compound “Epototo (registered trademark)” YD-128 (manufactured by Nippon Steel Chemical Co., Ltd.) and diethylenetriamine (manufactured by Wako Pure Chemical Industries, Ltd.) 20.7 The mass part was put in a container, stirred with a spatula, and deaerated using an automatic vacuum deaerator.

(B) Sampling of carbon fiber single fiber and fixing to mold A carbon fiber bundle having a length of about 20 cm was divided into approximately four equal parts, and single fibers were sampled in order from the four bundles. At this time, the entire bundle was sampled as evenly as possible. Next, double-sided tape was applied to both ends of the perforated mount, and the single fibers were fixed to the perforated mount in a state where a constant tension was applied to the sampled single fibers. Next, a glass plate on which a polyester film “Lumirror (registered trademark)” (manufactured by Toray Industries, Inc.) was attached was prepared, and a 2 mm-thick spacer for adjusting the thickness of the test piece was fixed on the film. . A perforated mount with single fibers fixed thereon was placed on the spacer, and a glass plate on which a film was similarly attached was further set on the spacer with the surface on which the film was attached facing downward. At this time, in order to control the fiber embedding depth, a tape having a thickness of about 70 μm was attached to both ends of the film.

(C) From resin casting to curing The resin prepared in the procedure (a) was poured into the mold (the space surrounded by the spacer and the film) in the procedure (b). The mold into which the resin was poured was heated for 5 hours using an oven preliminarily heated to 50 ° C., and then cooled to a temperature of 30 ° C. at a temperature lowering rate of 2.5 ° C./min. Thereafter, the mold was removed and cut to obtain a test piece of 2 cm × 7.5 cm × 0.2 cm. At this time, the test piece was cut so that the single fiber was located within the center 0.5 cm width of the test piece width.

(D) Fiber Embedding Depth Measurement Fiber embedding depth for the test piece obtained in the procedure (c) above using a laser Raman spectrophotometer (JASCO NRS-3200) laser and a 532 nm notch filter. Measurements were made. First, a laser is applied to the surface of the single fiber, the stage height is adjusted so that the beam diameter of the laser becomes the smallest, and the height at that time is defined as A (μm). Next, a laser is applied to the surface of the test piece, the stage height is adjusted so that the beam diameter of the laser becomes the smallest, and the height at that time is defined as B (μm). The fiber embedding depth d (μm) was calculated by the following formula using the refractive index of the resin 1.732 measured using the above laser.

(E) Four-point bending test A compressive strain was applied to the test piece obtained in the above procedure (c) by four-point bending using a jig having an outer indenter interval of 50 mm and an inner indenter interval of 20 mm. The stepwise strain was applied every 0.1%, the specimen was observed with a polarizing microscope, and the number of breaks at the central part 5 mm in the longitudinal direction of the specimen was measured. The double value of the measured number of breaks was taken as the number of fiber breaks (pieces / 10 mm), and the compression stress calculated from the compressive strain with an average number of fiber breaks of 30 tests exceeding 1/10 mm was taken as the single fiber compressive strength. Further, the single fiber composite strain ε (%) was measured using a strain gauge attached at a position about 5 mm away from the center of the test piece in the width direction. The final compressive strain ε _c of the carbon fiber monofilament takes into account the gauge factor κ of the strain gauge, the fiber embedding depth d (μm) measured by the above procedure (d), and the residual strain 0.14 (%). The following formula was used.

<Crystal orientation of polyacrylonitrile-based precursor fiber bundle>
The crystal orientation degree of the polyacrylonitrile-based precursor fiber bundle was measured as follows. The fiber bundle is cut to a length of 40 mm, and 20 mg is precisely weighed and sampled so that the sample fiber axes are exactly parallel, and then a thickness of 1 mm is uniform using a sample adjusting jig. Sample fiber bundles were arranged. After impregnating with a thin collodion solution and fixing it so as not to lose its shape, it was fixed to a sample table for wide-angle X-ray diffraction measurement. From the half width (H °) of the spread of the profile in the meridian direction including the highest intensity of diffraction observed near 2θ = 17 °, using Cu Kα ray monochromated with a Ni filter as the X-ray source. The degree of crystal orientation (%) was determined using the following formula.
Crystal orientation degree (%) = [(180−H) / 180] × 100
In addition, Shimadzu Corporation XRD-6100 was used as said wide angle X-ray diffraction apparatus.

<Infrared spectrum intensity ratio>
Flame-resistant fiber used for measurement is measured by precisely weighing 2 mg after freeze-grinding, mixing it well with KBr 300 mg, placing it in a molding jig, and pressurizing at 40 MPa for 2 minutes using a press. A tablet was prepared. This tablet was set in a Fourier transform infrared spectrophotometer, and the spectrum was measured in the range of 1000 to 2000 cm ⁻¹ . The background correction was performed by subtracting the minimum value from each intensity so that the minimum value in the range of 1700 to 2000 cm ⁻¹ would be zero. As the Fourier transform infrared spectrophotometer, Paragon 1000 manufactured by PerkinElmer was used.

<Perforated plate compressive strength>
This was performed according to ASTM D6484 (Open-hole Tensile Strength of Polymer Matrix Composite Laminates).

Test condition and room temperature (RTD): 69 ° F (20.6 ° C) ± 5 ° F
b. Laminated structure 16ply (45/90 / -45 / 0) _2s
c. After cutting the molding condition prepreg to a predetermined size and laminating it so as to have the configuration of b described above, a vacuum bag is formed, and the temperature is raised to 180 ° C. at a heating rate of 1.5 ° C./min using an autoclave. Then, it was cured at a pressure of 6 atm for 2 hours to obtain a pseudo isotropic laminated material (carbon fiber reinforced composite material).

d. Preparation of prepreg 35 parts by mass of tetraglycidyldiaminodiphenylmethane “Sumiepoxy (registered trademark)” ELM434 (manufactured by Sumitomo Chemical Co., Ltd.) and bisphenol A diglycidyl ether “jER (registered trademark)” 828 (Mitsubishi) 35 parts by mass of Chemical Co., Ltd.) and 30 parts by mass of N-diglycidylaniline “GAN (registered trademark)” (manufactured by Nippon Kayaku Co., Ltd.) and 14 parts by mass of “Sumika Excel (registered trademark)” After mixing and dissolving 5003P, 40 parts by mass of 4,4′-diaminodiphenylsulfone was kneaded to prepare an epoxy resin composition for a carbon fiber reinforced composite material.

The obtained epoxy resin composition was coated on a release paper with a resin basis weight of 52 g / m ² using a knife coater to prepare a resin film. This resin film is superposed on both sides of a sizing agent-coated carbon fiber (weight per unit area 190 g / m ² ) aligned in one direction, and a heat roll is used to heat and press at 100 ° C. and 1 atm. Was impregnated into a carbon fiber bundle to obtain a prepreg.

(Reference Examples 1-15)
A copolymer composed of 99.0% by mass of acrylonitrile and 1.0% by mass of itaconic acid was polymerized by a solution polymerization method using dimethyl sulfoxide as a solvent and 2,2′-azobisisobutyronitrile as an initiator, A polyacrylonitrile copolymer having a viscosity of 2.0 was produced. Ammonia gas was blown into the manufactured polyacrylonitrile-based polymer until the pH reached 8.5, and the polymer concentration was adjusted to 20% by mass to obtain a spinning solution. The obtained spinning solution was discharged into the air once at 40 ° C. using a spinneret having a diameter of 0.15 mm and a hole number of 6,000, passed through a space of about 4 mm, and then controlled at 3 ° C. 35 A coagulated yarn was obtained by a dry and wet spinning method introduced into a coagulation bath comprising an aqueous solution of% dimethyl sulfoxide. 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., two yarns are combined, and a single fiber After the number of yarns is 12,000, the yarn is stretched by 3.7 times in pressurized steam to increase the total draw ratio of yarn production to 13 times, and then entangled to obtain polyacrylonitrile having a crystal orientation of 93% and a single fiber number of 12,000. A system precursor fiber bundle was obtained. Here, the entanglement treatment means that the angle formed by the fiber bundle longitudinal direction and the fluid blowing direction is 90 °, and eight ejection holes are arranged so as to surround the fiber bundle, and each ejection hole is composed of two holes. Using fluid spray nozzles arranged at opposing positions so as to form a set, the tension of the fiber bundle was adjusted to 3 mN / dtex, and the fluid discharge pressure was set to 0.35 MPa. 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 0.4 to 1.3 dtex shown in Table 1. Next, using the conditions of flameproofing temperature and flameproofing time shown in Table 1, the polyacrylonitrile-based precursor fiber bundle was flameproofed while being stretched at a stretch ratio of 1 in an oven in an air atmosphere. A flameproof fiber bundle having the specific gravity shown was obtained.

(Reference Example 16)
A flame-resistant fiber bundle was obtained in the same manner as in Reference Example 7 except that the discharge pressure of the fluid used for the entanglement treatment was set to 0.05 MPa.

(Reference Example 17)
A flame-resistant fiber bundle was obtained in the same manner as in Reference Example 7 except that the entanglement treatment was not performed.

(Examples 1-5, Comparative Examples 1-9)
The pre-carbonized fiber bundle was obtained by subjecting the flame-resistant fiber bundle obtained in the Reference Example to a pre-carbonization treatment while stretching at a stretch ratio of 1.15 in a nitrogen atmosphere at a temperature of 300 to 800 ° C. The obtained pre-carbonized fiber bundle was carbonized at the maximum temperature and tension shown in Table 2 in a nitrogen atmosphere. As shown in Table 2, the obtained carbon fiber bundle was subjected to any one of the following surface treatments A or B and further sizing agent coating treatments A to C.

  Surface treatment A: An electrolytic surface treatment was performed using an aqueous ammonium hydrogen carbonate solution having a concentration of 0.1 mol / l as an electrolytic solution at an electric quantity of 80 coulomb per 1 g of carbon fiber bundle. The carbon fiber bundle subjected to the electrolytic surface treatment was subsequently washed with water and dried in heated air at a temperature of 150 ° C.

  Surface treatment B: When the obtained carbon fiber bundle is not surface-treated, it is called surface treatment B for convenience.

  Sizing agent coating treatment A: “jER (registered trademark)” 825 (manufactured by Japan Epoxy Resin Co., Ltd.), a diglycidyl ether of bisphenol A, and “Denacol (registered trademark)” EX-521 (polyglycerin polyglycidyl ether) Nagase ChemteX Co., Ltd.) mixed at a mass ratio of 20:50 was mixed with acetone to obtain an approximately 1% by mass acetone solution which was uniformly dissolved, and the surface was obtained by dipping using this acetone solution. After apply | coating to the processed carbon fiber bundle, it heat-processed for 180 second at the temperature of 210 degreeC, and obtained the carbon fiber bundle. The adhesion amount of the sizing agent was adjusted to 0.5 parts by mass with respect to 100 parts by mass of the surface-treated carbon fiber bundle.

  Sizing agent coating process B: A process in which no sizing agent is applied is referred to as a sizing agent coating process B for convenience.

  Sizing agent coating treatment C: The same as sizing agent coating treatment A except that “Denacol (registered trademark)” EX-521 (manufactured by Nagase ChemteX Corporation) was not used.

  The obtained carbon fiber bundle was subjected to various evaluations. The results are shown in Table 2.

  When a carbon fiber bundle having excellent single fiber compressive strength according to the present invention is used, the properties such as tensile elastic modulus, compressive strength, and perforated plate compressive strength of the carbon fiber reinforced composite material obtained by using the carbon fiber bundle are high in a balanced manner. Therefore, it can greatly contribute to the weight reduction of the aircraft and improve the fuel consumption rate of the aircraft.

Claims (8)

When the single fiber compressive strength is 4.8 GPa or more according to the compression fragmentation method of the single fiber composite and the single fiber apparent stress is 15.3 GPa according to the tensile fragmentation method of the single fiber composite, the number of fiber breaks is 2.0. Carbon fiber bundle that is at least pieces / mm. The single fiber compressive stress (GPa) in which the number of single fiber breaks when a compressive stress is applied exceeds 0.1 / 10 mm according to the compression fragmentation method of the single fiber composite is 90% or more of the single fiber compressive strength. Carbon fiber bundles. The carbon fiber bundle according to claim 1 or 2, wherein an average tearable distance is 550 to 850 mm. The carbon fiber bundle according to any one of claims 1 to 3, wherein the single fiber composite has a fiber breakage number of 0.3 pieces / mm or less when a single fiber apparent stress by a tensile fragmentation method is 6.8 GPa. The carbon fiber bundle according to any one of claims 1 to 4, wherein the crystallite size is 2.2 to 4.0 nm. The shear modulus g is 19 GPa or more, the initial tensile modulus E ₀ is 305 GPa or more, and the relationship between the shear modulus and the initial tensile modulus is in the range of the following formula. Carbon fiber bundles.

In the polyacrylonitrile-based precursor fiber bundle, the intensity ratio of 1453 cm ⁻¹ peak to 1370 cm ⁻¹ peak intensity in the infrared spectrum is 0.72 to 0.85, and the intensity ratio of 1254 cm ⁻¹ peak to 1370 cm ⁻¹ peak intensity is 0. The flame-resistant fiber bundle is pre-carbonized, and the pre-carbonized fiber bundle is carbonized, and the aliphatic epoxy compound (A) and the aromatic epoxy compound (B) are The manufacturing method of the carbon fiber bundle which apply | coats the sizing agent containing. The carbonization fiber bundle is carbonized in a temperature range of 1200 to 2000 ° C. in an inert atmosphere, an average tearable distance of the precarbonized fiber bundle is 450 to 700 mm, and a carbonization tension satisfies the formula (2). Item 8. A method for producing a carbon fiber bundle according to Item 7.
4.9 ≦ carbonization tension (mN / dtex) ≦ −0.0225 × (average tearable distance (mm)) + 23.5 (2)