carbon fiber composite materials

Abstract

To provide a carbon fiber composite material that can improve impact resistance.SOLUTION: A carbon fiber composite material includes: a carbon fiber having the strand strength of 7.5 to 8.5 GPa, the elongation of 2.65 to 3.20%, and the single fiber diameter of 4.0 to 6.0 μm; and an epoxy resin composition having amine type epoxy resin [A], thermoplastic resin [B] which dissolves into epoxy resin, and epoxy resin curing agent [C], where the degree of cure of the epoxy resin composition is 90% or more, and the storage elastic modulus of a cured product of the epoxy resin at 275°C when the cured product is heated at the speed of 5°C / min. by using a dynamic viscoelasticity measuring apparatus according to SACMA SRM 18R-94, and measured at the torsional mode of 1.0 Hz is 1 to 10 MPa. The carbon fiber composite material can improve impact resistance.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a high-elongation carbon fiber composite material obtained by combining high-elongation carbon fibers with excellent energy absorption properties with an epoxy resin composition that maximizes the performance of the fibers. [Background technology]

[0002] Polyacrylonitrile carbon fiber is a lightweight material with high strength and high elastic modulus, making it an essential material for reducing the weight of components. Another feature of carbon fiber is that it does not undergo plastic deformation, but rather elastic deformation. Therefore, carbon fiber has the advantage of being able to be used in a wider elongation range than metals, which undergo large plastic deformation.

[0003] In recent years, carbon fiber composite materials have been required to be both lightweight and impact resistant. To meet this requirement, research is being conducted into the design of resin compositions used in the matrix and sizing agents that change the interfacial properties between the carbon fiber and the matrix resin.

[0004] Attempts to improve the strand strength or elongation of carbon fibers have been made in the past. In Patent Document 1, precursor fibers were refined to reduce defects, resulting in carbon fibers with a maximum strand strength of 9.0 GPa (Example 8). In Patent Document 2, similarly, precursor fibers were refined and then stretched to obtain carbon fibers with a maximum strand strength of 8.0 GPa (Example 14) and an elongation of 2.60% (Comparative Examples 4 and 5). In Patent Document 3, carbon fibers with a maximum strand strength of 8.4 GPa (Example 3) were obtained by increasing the fracture toughness of the carbon fibers. In Patent Document 4, a carbon fiber with a maximum elongation of 2.68% (Example 15) was obtained using a technology that minimizes the decrease in strand strength even when the single fiber diameter of the carbon fiber is increased. In Patent Document 5, high elongation was achieved by adjusting production conditions such as polymer, spinning, and flame retardation, resulting in carbon fibers with a maximum elongation of 2.36% (Example 1). In Patent Document 6, carbon fibers with a maximum elongation of 2.60% (Example 4) are obtained by lowering the maximum temperature in the carbonization process in order to maximize the elongation of the carbon fibers. Patent Document 7 describes obtaining high-strength, high-elongation carbon fibers by adjusting the surface properties of the carbon fibers, but the elongation of the carbon fibers is only about 2.1%, which is at the general technical level for high-strength carbon fibers. Patent Document 8 obtains carbon fibers with a maximum elongation of 2.71% (Example 4) by adding boron to the polymer.

[0005] Furthermore, in Patent Document 9, a study is conducted to improve the impact resistance of carbon fiber composite materials by adding a modifier to the thermoplastic resin matrix.

[0006] In Patent Document 10, the impact resistance, tensile strength, and compressive strength of a carbon fiber composite material are improved by adjusting the rigidity modulus of the rubbery flat region above the glass transition point. In Patent Document 11, the interlaminar toughness and compressive strength in high-temperature environments of a carbon fiber composite material are improved by adjusting the rigidity modulus of the rubbery flat region above the glass transition point. In Patent Document 12, the compressive strength of a carbon fiber composite material is improved by adjusting the compressive yield stress of the cured resin. In Patent Document 13, the perforated plate tensile strength of a carbon fiber composite material is improved by combining carbon fiber having a specific single fiber strength with an epoxy resin composition of a specific composition. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-241230 [Patent Document 2] International Publication No. 2008 / 40963 [Patent Document 3] Japanese Patent Application Publication No. 2017-137614 [Patent Document 4] International Publication No. 97 / 45576 [Patent Document 5] Japanese Patent Application Laid-Open No. 2008-163537 [Patent Document 6] Japanese Patent Application Laid-Open No. 2005-256211 [Patent Document 7] Japanese Patent Application Laid-Open No. 2002-69754 [Patent Document 8] Japanese Patent Application Publication No. 11-152626 [Patent Document 9] Japanese Patent Application Publication No. 2018-59087 [Patent Document 10] Japanese Patent Application Laid-Open No. 2001-323046 [Patent Document 11] International Publication No. 2016 / 67736 [Patent Document 12] Japanese Patent Application Laid-Open No. 2003-277471 [Patent Document 13] International Publication No. 2014 / 115762 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the conventional techniques have the following problems.

[0009] In the technology of Patent Document 1, the carbon fiber single fiber diameter is small, and the strain energy per single fiber is small. In addition, the strand elastic modulus is high and the elongation is low, so sufficient impact resistance cannot be ensured in a bending stress field.

[0010] The technology of Patent Document 2 has the problem that the single fiber diameter of the carbon fiber is small, the strain energy per single fiber is small, and in addition, satisfactory elongation is not obtained.

[0011] The technology of Patent Document 3 has the problem that satisfactory elongation is not obtained, and the strand elastic modulus is high, so sufficient impact resistance cannot be ensured in a bending stress field.

[0012] The technology of Patent Document 4 does not provide sufficient levels of strand strength and elongation, and is therefore unable to ensure sufficient impact resistance. Furthermore, it was not anticipated that strand strength and elongation could be achieved at the same time.

[0013] The technology of Patent Document 5 does not ensure sufficient impact resistance.

[0014] In the technology of Patent Document 6, the strand modulus level was too low, and sufficient impact resistance could not be ensured.

[0015] In the technology of Patent Document 7, the elongation level was too low and sufficient impact resistance could not be ensured.

[0016] The technology of Patent Document 8 increases the elongation of carbon fibers, but the strand strength is low for those with high elongation, and since there is no concept of strain energy density, it was not anticipated that strand strength and elongation could be achieved at the same time.

[0017] Thus, there has not been a carbon fiber that satisfies all of the requirements for single fiber diameter, strand strength, and elongation.

[0018] Furthermore, although Patent Document 9 describes the composition of the thermoplastic resin being designed to improve the impact resistance of the carbon fiber composite material, it does not mention the mechanical properties of the carbon fiber itself.

[0019] In Patent Documents 10 to 12, the mechanical properties of the cured epoxy resin material are designed to maximize the mechanical properties of existing carbon fibers, but they do not focus on the elongation of the carbon fiber composite material, and the elongation level is not at a satisfactory level.

[0020] In Patent Document 13, the perforated plate tensile strength of a carbon fiber composite material was improved not only by improving the single fiber strength of the carbon fiber but also by combining it with a specific epoxy resin composition, but the elongation of the carbon fiber composite material was not at a satisfactory level.

[0021] The present invention aims to provide a carbon fiber composite material that has improved impact resistance. [Means for solving the problem]

[0022] In order to achieve the above object, the carbon fiber composite material of the present invention comprises carbon fibers having a strand strength of 7.5 to 8.5 GPa, an elongation of 2.65 to 3.20%, and a single fiber diameter of 4.0 to 6.0 μm, and an epoxy resin composition having an amine-type epoxy resin [A], a thermoplastic resin [B] that dissolves in the epoxy resin, and an epoxy resin curing agent [C], wherein the degree of cure of the epoxy resin composition is 90% or more, and the cured product of the epoxy resin has a storage modulus of 1 to 10 MPa at 275°C, measured in torsional mode at 1.0 Hz using a dynamic viscoelasticity measuring apparatus in accordance with SACMA SRM 18R-94, by heating at a rate of 5°C / min. [Effects of the Invention]

[0023] By using the carbon fiber composite material of the present invention, the impact resistance, which is expressed as the strain energy density of the carbon fiber composite material, can be improved. DETAILED DESCRIPTION OF THE INVENTION

[0024] The inventors focused on the strain energy density of carbon fibers in order to improve the impact resistance of carbon fiber composite materials. The strain energy density is the area of ​​the stress-strain curve obtained by a tensile property test of a resin-impregnated strand (hereinafter sometimes abbreviated as "strand"). However, since it is difficult to accurately calculate nonlinearity, in the present invention, the above-mentioned strand strength (MPa = J / mm 3 The approximate value calculated by dividing the product of strain energy density (-) and elongation (-) by 2 is the strain energy density. In other words, the strand strength and elongation of the carbon fiber are important. A high strain energy density of carbon fiber is expected to improve the impact resistance of the resulting carbon fiber composite material.

[0025] The carbon fiber of the present invention has a strand strength of 7.5 to 8.5 GPa, preferably 7.8 to 8.5 GPa, and more preferably 8.0 to 8.5 GPa. Strand strength is an index showing the resistance to breakage when a load is applied to a carbon fiber. The strand strength of a carbon fiber can be evaluated according to the tensile test of a resin-impregnated strand described in JIS R7608:2004. A strand strength of 7.5 GPa or more makes it easy to increase the strain energy density. There is no upper limit to the strand strength, but a strand strength of 8.5 GPa or more tends to achieve a satisfactory level of strain energy density. The strand strength can be controlled by suppressing defects, improving fracture toughness, and the like, by producing the carbon fiber according to the production method described below.

[0026] The carbon fiber of the present invention has an elongation of 2.65% or more, preferably 2.75% or more, more preferably 2.85% or more, and even more preferably 2.95% or more. The elongation of carbon fiber can be evaluated according to the tensile test of a resin-impregnated strand described in JIS R7608:2004. Measuring the elongation of carbon fiber is difficult because the stress-strain curve is nonlinear. However, in this tensile test, the elongation is calculated by dividing the above-mentioned strand strength by the strand modulus. An elongation of 2.65% or more facilitates an increase in strain energy density. While there is no upper limit to the elongation, an elongation of 3.20% is often sufficient to increase the strain energy density. The elongation of carbon fiber can be adjusted by controlling the production conditions of the carbon fiber so as to achieve a balance between strand strength and strand modulus.

[0027] The carbon fiber of the present invention has a single fiber diameter of 4.0 to 6.0 μm, preferably 4.5 μm or more, more preferably 5.0 μm or more, and even more preferably 5.3 μm or more. Because the breaking load per single fiber is determined by the strand strength and the cross-sectional area of ​​the single fiber, the single fiber diameter affects the breaking load per single fiber. Furthermore, the larger the single fiber diameter, the higher the single fiber compressive strength of the carbon fiber tends to be, and the greater the energy absorption tends to be. Therefore, a single fiber diameter of 4.0 μm or more tends to increase energy absorption. An upper limit of 6.0 μm for the single fiber diameter is often sufficient to ensure sufficient impact resistance. The single fiber diameter of carbon fiber can be calculated from the total fineness, density, and number of filaments of the carbon fiber. Furthermore, when the number of filaments is unknown, the single fiber diameter can be evaluated by embedding the carbon fiber in resin, observing the cross section with an optical microscope, determining the cross-sectional area of ​​the single fiber through image processing, and calculating it as the circle-equivalent diameter. If the two measurement methods do not agree, the former value is used. The monofilament diameter can be controlled by the diameter of the precursor fiber and the draw ratio in subsequent steps.

[0028] The carbon fiber of the present invention preferably has a strain energy density of 95 J / mm 3 or more, more preferably 100 J / mm 3More preferably, it is 105 J / mm 3 The strain energy density is 95J / mm 3 Above this level, energy absorption is often sufficient, and there is no upper limit, but 140 J / mm 3 In some cases, the value of energy absorption may be saturated depending on the balance with other properties. Strain energy density can be adjusted by controlling the manufacturing conditions of carbon fiber so as to achieve both strand strength and elongation.

[0029] The carbon fiber of the present invention preferably has a strand modulus of 240 to 300 GPa, more preferably 250 to 290 GPa, and even more preferably 250 to 280 GPa. The strand modulus is an index showing the resistance to deformation when a load is applied to the carbon fiber. The strand modulus of a carbon fiber can be evaluated according to the tensile test of a resin-impregnated strand described in JIS R7608:2004. The stress-strain curve of a carbon fiber exhibits a downwardly convex nonlinearity, but in the present invention, the strand modulus is measured in a strain range of 0.1 to 0.6%. A strand modulus of 240 GPa or more facilitates an increase in strain energy density. A strand modulus of 300 GPa or less provides high compressive strength and high energy absorption of the carbon fiber. The strand modulus can be controlled by the maximum temperature in the carbonization step, the heat treatment time at the maximum temperature, the heating rate, the draw ratio, and the like.

[0030] The carbon fiber of the present invention preferably has a total fineness of 0.8 g / m or more, more preferably 0.9 g / m or more. The total fineness refers to the mass per meter of the carbon fiber bundle and is related to the single fiber diameter and number of filaments of the carbon fiber. The higher the total fineness, the easier it is to increase the productivity of carbon fiber composite materials. Therefore, if the total fineness is 0.8 g / m or more, carbon fiber composite materials with excellent impact resistance can be obtained with good productivity. A total fineness of 2.0 g / m or less is preferable because it allows carbon fiber composite materials of appropriate thickness to be obtained, resulting in improved impact resistance. The total fineness can be controlled by adjusting the single fiber diameter or the number of filaments, but if the number of filaments is too high, uniform production becomes difficult and strand strength tends to decrease.

[0031] The carbon fiber of the present invention preferably has a density of 1.75 to 1.85 g / cm 3 The higher the density of carbon fiber, the denser the microstructure, and the greater the strand strength. Therefore, the density is 1.75 g / cm 3 If it is above this level, the energy absorption is likely to be at a satisfactory level, 1.85g / cm 3 If the density is less than 1.78 g / cm, the elongation is high and the energy absorption is high and easy to maintain. 3 The upper limit of the density is more preferably 1.83 g / cm 3 The density of the carbon fiber can be controlled by the draw ratio and the temperature rise rate in the carbonization process.

[0032] Next, a method for producing carbon fibers suitable for obtaining the carbon fibers of the present invention will be described.

[0033] Known industrial methods for producing carbon fiber include a flame-resistant process in which polyacrylonitrile-based carbon fiber precursor fiber (hereinafter sometimes abbreviated as precursor fiber) is converted into flame-resistant fiber in an oxidizing atmosphere at 200 to 310°C, a pre-carbonization process in which pre-carbonization is performed in an inert atmosphere at 500 to 1,200°C, and a carbonization process in which carbonization is performed in an inert atmosphere at 1,000 to 1,500°C.

[0034] A polyacrylonitrile polymer is preferably used as a raw material for producing the precursor fiber. In the present invention, a polyacrylonitrile polymer is a polymer in which acrylonitrile accounts for at least 90 to 100 mol % of the polymer. In producing the precursor fiber, the polyacrylonitrile polymer preferably contains a copolymerization component from the viewpoint of improving strand strength. As a monomer that can be used as the copolymerization component, a monomer containing one or more carboxylic acid groups or amide groups is preferably used from the viewpoint of promoting flame resistance.

[0035] When producing the precursor fiber, either a dry-wet spinning method or a wet-wet spinning method may be used as the spinning method, but it is preferable to use the dry-wet spinning method, which is advantageous for the strand strength of the resulting carbon fiber. The spinning process comprises a spinning step in which a spinning solution is discharged from a spinneret into a coagulation bath using the dry-wet spinning method and spun into fibers, a water-washing step in which the fibers obtained in the spinning step are washed in a water bath while being stretched, and a dry-heat treatment step in which the fibers obtained in the water-washing step are dry-heat treated. It is preferable that the process also includes a steam-stretching step in which the fibers obtained in the dry-heat treatment step are steam-stretched, as necessary. The order of the steps can be appropriately reversed. The spinning solution is prepared by dissolving the polyacrylonitrile-based polymer described above in a solvent in which polyacrylonitrile is soluble, such as dimethyl sulfoxide, dimethylformamide, or dimethylacetamide.

[0036] The coagulation bath preferably contains the solvent used in the spinning solution, such as dimethyl sulfoxide, dimethyl formamide, or dimethyl acetamide, and a so-called coagulation promoter. The coagulation promoter may be one that does not dissolve the polyacrylonitrile polymer and is compatible with the solvent used in the spinning solution. Specifically, water is preferably used as the coagulation promoter.

[0037] The washing bath used in the washing step is preferably a multi-stage washing bath having a temperature of 30 to 98°C. The draw ratio in the washing step is preferably 2 to 6 times. Thereafter, an oil agent made of silicone or the like is preferably applied to the fibers to improve strand strength. Such a silicone oil agent preferably contains amino-modified silicone.

[0038] The drying heat treatment step can be carried out by a known method, for example, at a drying temperature of 100 to 200°C.

[0039] After the above-mentioned water washing step and dry heat treatment step, if necessary, steam drawing is carried out to obtain a precursor fiber suitable for obtaining the carbon fiber of the present invention. The steam drawing is carried out in pressurized steam at a draw ratio of preferably 2 to 6 times.

[0040] In order to increase the strand strength of carbon fiber, the flame-resistant fiber obtained in the flame-resistant process must have a wavelength of 1,370 cm in the infrared spectrum. -1 The peak intensity at 1,453 cm -1 The ratio of the peak intensities is in the range of 0.70 to 0.75, and the peak intensity at 1,370 cm -1 The peak intensity at 1,254 cm -1 It is preferable to control the ratio of the peak intensities of the 1,453 cm peak in the infrared spectrum to be in the range of 0.50 to 0.65. -1 The peak at 1,370 cm is derived from alkenes and decreases as the flame resistance increases. -1 Peak and 1,254cm -1 The peak at 1,370 cm is due to the flame-resistant structure, and increases as the flame resistance progresses. -1 The peak intensity at 1,453 cm -1 The ratio of the peak intensities of the peaks at 1,370 cm and 1,370 cm is about 0.63 to 0.69, which indicates that in the flame-resistant treatment step of the present invention, it is preferable that the obtained flame-resistant fiber retains more alkene-derived structures than usual. -1The peak intensity at 1,254 cm -1 The peak intensity ratio decreases as the flameproofing process progresses, and the decrease is particularly large in the early stages. However, depending on the flameproofing conditions, the peak intensity ratio may not become 0.65 or less even if the time is increased.

[0041] In order to achieve a ratio of these two peak intensities within the desired range, the conditions should basically be set by focusing mainly on the following: a small amount of copolymerization component contained in the polyacrylonitrile polymer constituting the precursor fiber, a high degree of crystalline orientation of the precursor fiber, a small single fiber fineness of the precursor fiber, and a higher flame-stabilizing temperature in the latter half. Specifically, the flame-stabilizing step is performed in such a way that the peak intensity ratio of 1,370 cm in the infrared spectrum is -1 The peak intensity at 1,453 cm -1 a first flame-stabilizing step in which the fiber is flame-stabilized for 8 to 25 minutes, preferably 8 to 15 minutes, until the ratio of the peak intensities of the fibers obtained by the first flame-stabilizing step is in the range of 0.98 to 1.10; -1 The peak intensity at 1,453 cm -1 The ratio of the peak intensities is in the range of 0.70 to 0.75, and the peak intensity at 1,370 cm in the infrared spectrum is -1 The peak intensity at 1,254 cm -1 It is preferable to carry out this in two stages: a first flame-stabilizing step in which flame-stabilization is carried out for 5 to 14 minutes, preferably 5 to 10 minutes, until the peak intensity ratio reaches a range of 0.50 to 0.65; and a second flame-stabilizing step in which flame-stabilization is carried out for 5 to 14 minutes, preferably 5 to 10 minutes.

[0042] The flame-stabilizing temperature in the first flame-stabilizing step is preferably set to 200 to 250°C, more preferably 230 to 250°C, in order to control the infrared spectrum within the above-mentioned range.

[0043] The second flame-stabilizing step is performed at a higher flame-stabilizing temperature than the first flame-stabilizing step. The flame-stabilizing time in the second flame-stabilizing step can be shortened by adjusting the flame-stabilizing temperature higher, but the appropriate flame-stabilizing temperature depends on the characteristics of the precursor fiber. The flame-stabilizing temperature is preferably set to 280 to 310°C, more preferably 280 to 300°C, and even more preferably 285 to 295°C, in order to control the infrared spectrum within the above-mentioned range. The flame-stabilizing temperature does not need to be constant, and may be set in multiple stages. To increase the strand strength of the resulting carbon fiber, it is preferable to set the flame-stabilizing temperature high and the flame-stabilizing time short.

[0044] In the present invention, flame-proofing refers to heat-treating the precursor fiber at 200 to 310°C in an oxygen-containing atmosphere.

[0045] The flame-stabilizing time referred to here means the time the fiber remains in the flame-stabilizing furnace. The flame-stabilized fiber refers to the fiber after the flame-stabilizing process and before the preliminary carbonization process. The peak intensity referred to here refers to the absorbance at each wavelength after baseline correction of the infrared spectrum obtained by sampling a small amount of the flame-stabilized fiber and measuring the spectrum; no peak division is performed. The sample concentration during infrared spectrum measurement is diluted with KBr to 0.67% by mass. Thus, the infrared spectrum should be measured each time the flame-stabilizing condition settings are changed, and the conditions should be examined according to the preferred manufacturing method described below. By appropriately controlling the infrared spectrum peak intensity ratio of the flame-stabilized fiber, the strand strength of the resulting carbon fiber can be controlled.

[0046] The total treatment time for the flame-resistant treatment step can be appropriately selected preferably within the range of 13 to 20 minutes. Furthermore, for the purpose of improving the strand strength of the resulting carbon fiber, the treatment time for the flame-resistant treatment is set so that the specific gravity of the resulting flame-resistant fiber is preferably within the range of 1.28 to 1.32, more preferably 1.30 to 1.32. A more preferable treatment time for the flame-resistant treatment step depends on the flame-resistant temperature. The specific gravity of the flame-resistant fiber must be 1.28 or higher, otherwise the strand strength of the carbon fiber may decrease. A specific gravity of the flame-resistant fiber of 1.32 or lower can increase the strand strength. The specific gravity of the flame-resistant fiber is controlled by the treatment time and the flame-resistant temperature in the flame-resistant treatment step. Furthermore, the timing for switching from the first flame-resistant treatment step to the second flame-resistant treatment step is preferably set so that the specific gravity of the fiber is within the range of 1.21 to 1.23. In this case, the conditions for the flame-resistant treatment step are controlled with priority given to satisfying the above-mentioned range of the infrared spectrum intensity ratio. The preferred ranges of the flameproofing treatment time and temperature vary depending on the properties of the precursor fiber and the copolymer composition of the polyacrylonitrile polymer.

[0047] In the pre-carbonization step, in which the fiber bundle obtained in the flame-resistant treatment step is pre-carbonized, the obtained flame-resistant fiber is heat-treated in an inert atmosphere at a maximum temperature of 500 to 1,200°C until the specific gravity reaches preferably 1.5 to 1.8. The draw ratio in the pre-carbonization step is preferably 1.16 to 1.25. If the draw ratio in the pre-carbonization step is 1.16 or more, the strand modulus is likely to be increased, and the strand strength is likely to be increased. If the draw ratio in the pre-carbonization step is 1.25 or less, the strand modulus is likely to be suppressed to 300 GPa or less.

[0048] The pre-carbonized fiber is carbonized in an inert atmosphere, preferably at a maximum temperature of 1,000 to 1,500° C., more preferably at a maximum temperature of 1,100 to 1,300° C., and even more preferably at a maximum temperature of 1,150 to 1,250° C. The maximum temperature in the carbonization step is preferably lower from the viewpoint of increasing the elongation of the resulting carbon fiber, but if it is too low, the strand strength may decrease, and therefore it is preferable to set the temperature taking both into consideration.

[0049] Furthermore, the treatment time X at the maximum temperature in the carbonization step is preferably 20 to 60 seconds, more preferably 20 to 38 seconds. The treatment time X at the maximum temperature in the carbonization step refers to the time required for the fibers to pass through the section in the carbonization furnace that has the highest temperature. Carbonization furnaces often have multiple sections that are controlled so that the temperature increases stepwise using heater blocks. Each section is considered to have a constant temperature in the calculation. The shorter the treatment time at the maximum temperature, the more easily the strand modulus can be controlled to be low, so the treatment time X is preferably 60 seconds or less. If the treatment time X is 20 seconds or more, a stable strand modulus is likely to be obtained.

[0050] The temperature rise rate Y in the carbonization step is preferably 0.40 to 1.1°C / sec, more preferably 0.40 to 1.0°C / sec, and even more preferably 0.40 to 0.60°C / sec. The temperature rise rate in the carbonization step affects the desorption rate of decomposition gases and therefore strand strength. In the present invention, the temperature rise rate is defined as the average temperature rise rate per second at which the fiber passes through the area where the temperature of a section exceeds 1,000°C when the fiber passes through multiple sections in a carbonization furnace controlled so that the temperature rises stepwise. Specifically, for example, if the fiber passes through the section with a temperature of 1,000°C in the carbonization furnace over 100 seconds before reaching the next section with a temperature of 1,100°C, the temperature rise rate is 1.0°C / sec. In another example, if the fiber passes through a 950°C section in the carbonization furnace and then through the next 1,150°C section over 200 seconds, the heating rate is 1.0°C / s. Furthermore, when the maximum temperature of the carbonization process is set to less than 1,100°C, the heating rate up to the maximum temperature is utilized. That is, if the maximum temperature is 1,050°C, and the fiber passes through a 1,000°C section in the carbonization furnace and then through the next 1,050°C section over 50 seconds, the heating rate is 1.0°C / s. The temperature of the first section in the carbonization furnace is preferably 1,000°C or lower. A heating rate of 0.40°C / s or higher facilitates stable strand modulus. A heating rate of 1.1°C / s or less facilitates suppression of strand strength degradation.

[0051] The treatment time X at the maximum temperature and the temperature rise rate Y in the carbonization step are preferably in the range of 0.015X≦Y≦0.015X+0.6. This formula was derived from the inventor's investigation into how to increase the elongation of carbon fiber. By adjusting the treatment time X and the temperature rise rate Y so that they satisfy this relationship, the elongation of carbon fiber can be easily increased.

[0052] The carbon fiber obtained as described above is preferably further subjected to an electrolytic surface treatment to introduce oxygen-containing functional groups. For the electrolytic surface treatment, any of gas phase oxidation, liquid phase oxidation, and liquid phase electrolytic oxidation can be used, but liquid phase electrolytic oxidation is preferably used from the viewpoint of high productivity and enabling uniform treatment. In the present invention, there are no particular restrictions on the method of liquid phase electrolytic oxidation, and it may be performed by a known method.

[0053] After the electrolytic surface treatment, the carbon fibers can be subjected to a sizing treatment to impart bundling properties to the resulting carbon fibers. As the sizing agent, a sizing agent having good compatibility with the matrix resin can be appropriately selected depending on the type of matrix resin used in the carbon fiber composite material.

[0054] Next, the carbon fiber composite material of the present invention will be described. The carbon fiber composite material of the present invention contains the above-mentioned carbon fiber of the present invention and, as a matrix resin, an amine-type epoxy resin [A], a thermoplastic resin [B] that dissolves in the epoxy resin, and an epoxy resin composition [C] containing an epoxy resin curing agent.

[0055] Examples of the amine-type epoxy resin [A] used in the present invention include tetraglycidyldiaminodiphenylmethane, tetraglycidyldiaminodiphenylsulfone, tetraglycidylxylylenediamine, triglycidylaminophenol, triglycidylaminocresol, diglycidylaniline, diglycidyltoluidine, or halogen-substituted, alkyl-substituted, or hydrogenated derivatives thereof. Among these, tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol, or halogen-substituted, alkyl-substituted, or hydrogenated derivatives thereof are preferred because they can impart elastic modulus and heat resistance.

[0056] Commercially available products of tetraglycidyldiaminodiphenylmethane include "Sumiepoxy" (registered trademark) ELM434 (manufactured by Sumitomo Chemical Co., Ltd.), YH434L (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.), "jER" (registered trademark) 604 (manufactured by Mitsubishi Chemical Corporation), "Araldite" (registered trademark) MY720, "Araldite" (registered trademark) MY721, "Araldite" (registered trademark) MY9512, and "Araldite" (registered trademark) MY9663 (all manufactured by Huntsman Advanced Materials).

[0057] Commercially available products of tetraglycidyldiaminodiphenyl sulfone include TG3DAS (manufactured by Mitsui Fine Chemicals, Inc.).

[0058] Commercially available tetraglycidylxylylenediamine and its hydrogenated products include "TETRAD" (registered trademark)-X and "TETRAD" (registered trademark)-C (both manufactured by Mitsubishi Gas Chemical Company, Inc.).

[0059] Commercially available triglycidyl aminophenol or triglycidyl aminocresol products include "Sumiepoxy" (registered trademark) ELM100 and "Sumiepoxy" (registered trademark) ELM120 (all manufactured by Sumitomo Chemical Co., Ltd.), "Araldite" (registered trademark) MY0500, "Araldite" (registered trademark) MY0510, and "Araldite" (registered trademark) MY0600 (all manufactured by Huntsman Advanced Materials), and "jER" (registered trademark) 630 (manufactured by Mitsubishi Chemical Corporation).

[0060] Commercially available diglycidylanilines include GAN (manufactured by Nippon Kayaku Co., Ltd.) and TOREP-E204 (manufactured by Toray Fine Chemicals Co., Ltd.).

[0061] Commercially available diglycidyl toluidine products include GOT (manufactured by Nippon Kayaku Co., Ltd.).

[0062] In the present invention, the amine-type epoxy resin [A] is preferably contained in an amount of 50 to 100 parts by mass, more preferably 70 to 100 parts by mass, per 100 parts by mass of the total epoxy resin. If the amount of the amine-type epoxy resin is less than 50 parts by mass per 100 parts by mass of the total epoxy resins, the resulting epoxy resin composition may have insufficient heat resistance and elastic modulus. Furthermore, when the epoxy resin is used as a carbon fiber composite material, the compressive strength may decrease.

[0063] In the epoxy resin composition of the present invention, the amine-type epoxy resin [A] preferably contains a difunctional amine-type epoxy resin and a trifunctional or higher functional amine-type epoxy resin. The inclusion of a difunctional amine-type epoxy resin extends the distance between crosslinking points, reduces the storage modulus at 275°C, and improves the elongation of the epoxy resin cured product. Furthermore, the incorporation of a trifunctional or higher functional amine-type epoxy resin improves heat resistance and elastic modulus, resulting in a well-balanced resin composition.

[0064] Furthermore, as long as the effects of the present invention are not impaired, the epoxy resin may contain other epoxy resin components in addition to the amine-type epoxy resin [A]. These may be added singly or in combination. Epoxy resins with a weight-average molecular weight of 400 or more are preferably used because they can extend the distance between crosslinking points and reduce the storage modulus at 275°C. Specifically, phenol novolac-type epoxy resins, cresol novolac-type epoxy resins, resorcinol-type epoxy resins, dicyclopentadiene-type epoxy resins, urethane- and isocyanate-modified epoxy resins, epoxy resins having a biphenyl skeleton, epoxy resins having a fluorene skeleton, and bisphenol-type epoxy resins such as bisphenol A, bisphenol F, bisphenol S, and bisphenol AD, as well as halogen-, alkyl-, and hydrogenated versions of these bisphenols, are used. Specific examples of such epoxy resins include the following:

[0065] Commercially available phenol novolac epoxy resins include "jER" (registered trademark) 152 and "jER" (registered trademark) 154 (all manufactured by Mitsubishi Chemical Corporation), "Epiclon" (registered trademark) N-740, "Epiclon" (registered trademark) N-770, and "Epiclon" (registered trademark) N-775 (all manufactured by DIC Corporation).

[0066] Commercially available cresol novolac epoxy resins include "Epiclon" (registered trademark) N-660, "Epiclon" (registered trademark) N-665, "Epiclon" (registered trademark) N-670, "Epiclon" (registered trademark) N-673, and "Epiclon" (registered trademark) N-695 (all manufactured by DIC Corporation), and EOCN-1020, EOCN-102S, and EOCN-104S (all manufactured by Nippon Kayaku Co., Ltd.).

[0067] Specific examples of resorcinol-type epoxy resins include "Denacol" (registered trademark) EX-201 (manufactured by Nagase ChemteX Corporation).

[0068] Commercially available dicyclopentadiene epoxy resins include "Epiclon" (registered trademark) HP7200, "Epiclon" (registered trademark) HP7200L, and "Epiclon" (registered trademark) HP7200H (all manufactured by DIC Corporation), Tactix 558 (manufactured by Huntsman Advanced Materials), XD-1000-1L, and XD-1000-2L (all manufactured by Nippon Kayaku Co., Ltd.).

[0069] Commercially available urethane and isocyanate-modified epoxy resins include AER4152 (manufactured by Asahi Kasei E-materials Corp.) and ACR1348 (manufactured by Asahi Denka Corp.), which have an oxazolidone ring.

[0070] Commercially available epoxy resins having a biphenyl skeleton include "jER" (registered trademark) YX4000H, "jER" (registered trademark) YX4000, and "jER" (registered trademark) YL6616 (all manufactured by Mitsubishi Chemical Corporation), and NC-3000 (manufactured by Nippon Kayaku Co., Ltd.).

[0071] Commercially available epoxy resins having a fluorene skeleton include ESF300 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.), "ONCOAT" (registered trademark) EX-1010, "ONCOAT" (registered trademark) EX-1011, "ONCOAT" (registered trademark) EX-1012, "ONCOAT" (registered trademark) EX-1020, "ONCOAT" (registered trademark) EX-1030, "ONCOAT" (registered trademark) EX-1040, "ONCOAT" (registered trademark) EX-1050, and "ONCOAT" (registered trademark) EX-1051 (all manufactured by Nagase ChemteX Corporation).

[0072] Commercially available bisphenol A epoxy resins include "Epotohto" (registered trademark) YD128 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.), "jER" (registered trademark) 825, "jER" (registered trademark) 828, "jER" (registered trademark) 834, "jER" (registered trademark) 1001, "jER" (registered trademark) 1004, "jER" (registered trademark) 1007, "jER" (registered trademark) 1009, and "jER" (registered trademark) 1010 (all manufactured by Mitsubishi Chemical Corporation).

[0073] Commercially available bisphenol F epoxy resins include "Epiclon" (registered trademark) 830 and "Epiclon" (registered trademark) 835 (both manufactured by DIC Corporation), "jER" (registered trademark) 806, "jER" (registered trademark) 807, "jER" (registered trademark) 4004P, "jER" (registered trademark) 4007P, "jER" (registered trademark) 4009P, and "jER" (registered trademark) 4010P (all manufactured by Mitsubishi Chemical Corporation), and "Epotohto" (registered trademark) YDF170 and "Epotohto" (registered trademark) YDF2001 (all manufactured by Nippon Steel & Sumitomo Metal Chemical Co., Ltd.).

[0074] Examples of bisphenol S type epoxy resins include "Epiclon" (registered trademark) EXA-1514 (manufactured by DIC Corporation).

[0075] Examples of bisphenol AD ​​type epoxy resins include "EPOMIK" (registered trademark) R710 and "EPOMIK" (registered trademark) R1710 (both manufactured by Printec Co., Ltd.).

[0076] The epoxy resin composition of the present invention is used by mixing or dissolving the thermoplastic resin [B].

[0077] In the present invention, by combining the above-mentioned amine-type epoxy resin [A] with the thermoplastic resin [B], high toughness can be obtained while avoiding a decrease in heat resistance, and when the material is made into a carbon fiber composite material, the elongation of the material is significantly improved.

[0078] The thermoplastic resin [B] in the present invention is in a crystalline state or a glassy state at room temperature and has thermoplastic properties.

[0079] The thermoplastic resin [B] is generally preferably a thermoplastic resin having a bond selected from the group consisting of carbon-carbon bonds, amide bonds, imide bonds, ester bonds, ether bonds, carbonate bonds, urethane bonds, thioether bonds, sulfone bonds, and carbonyl bonds in the main chain. Furthermore, this thermoplastic resin [B] may have a partially crosslinked structure and may be crystalline or amorphous. In particular, it is preferable that at least one resin selected from the group consisting of polyamide, polycarbonate, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyarylate, polyester, polyamideimide, polyimide, polyetherimide, polyimide having a phenyltrimethylindane structure, polysulfone, polyethersulfone, polyetherketone, polyetheretherketone, polyaramid, polyethernitrile, and polybenzimidazole is dissolved in any of the epoxy resins contained in the epoxy resin composition.

[0080] In the present invention, the thermoplastic resin [B] is contained in the epoxy resin composition in an amount of 8 to 40% by mass, preferably 8 to 35% by mass, more preferably 12 to 35% by mass, even more preferably 16 to 35% by mass, and most preferably 20 to 30% by mass. If the amount of thermoplastic resin [B] is less than 8% by mass, the toughness of the cured resin decreases, and the interlaminar toughness of the resulting fiber-reinforced composite material is insufficient. If the amount is more than 40% by mass, the viscosity of the thermosetting resin composition increases, resulting in insufficient processability and handling of the thermosetting resin composition and prepreg.

[0081] The weight-average molecular weight of the thermoplastic resin [B] is preferably in the range of 4,000 to 40,000 g / mol, more preferably 10,000 to 40,000 g / mol, and even more preferably 15,000 to 30,000 g / mol. If the weight-average molecular weight is lower than 4,000 g / mol, the elongation and toughness of the cured epoxy resin may be insufficient. If the weight-average molecular weight is higher than 40,000 g / mol, the viscosity of the epoxy resin may increase when the thermoplastic resin is dissolved in the epoxy resin composition, making kneading difficult and making it difficult to form a prepreg.

[0082] Furthermore, the glass transition temperature of the thermoplastic resin [B] in the present invention is preferably 150° C. or higher, more preferably 200° C. or higher, and even more preferably 220° C. or higher. If the glass transition temperature of the thermoplastic resin [B] is lower than 150° C., the carbon fiber composite material may be prone to thermal deformation.

[0083] Examples of such thermoplastic resin [B] include polycarbonate (glass transition temperature (also referred to as Tg): 150°C), polysulfone (Tg: 190°C), polyetherimide (Tg: 215°C), and polyethersulfone (Tg: 225°C). The glass transition temperature of such thermoplastic resin [B] is the glass transition temperature observed when, using DSC (differential scanning calorimetry), the temperature is raised from 30°C to a temperature at least 30°C higher than the predicted glass transition temperature at a heating rate of 20°C / min, held for 1 minute, then cooled to 0°C at a cooling rate of 20°C / min, held for 1 minute, and then measured again at a heating rate of 20°C / min.

[0084] Commercially available polycarbonate products include "Panlite" (registered trademark) K1300Y (manufactured by Teijin Limited). Commercially available polysulfone products include "Udel" (registered trademark) P-1700, "Udel" (registered trademark) P-3500LCD, and "Virantage" (registered trademark) DAMS VW-30500RP (all manufactured by Solvay Specialty Polymers). Commercially available polyetherimide products include "Ultem" (registered trademark) 1000 and "Ultem" (registered trademark) 1010 (all manufactured by SABIC). Commercially available polyethersulfone products include "Sumikaexcel" (registered trademark) PES3600P, "Sumikaexcel" (registered trademark) PES5003P, "Sumikaexcel" (registered trademark) PES5200P, and "Sumikaexcel" (registered trademark) PES7600P (all manufactured by Sumitomo Chemical Co., Ltd.), "Ultrason" (registered trademark) E2020P SR (manufactured by BASF), "Virantage" (registered trademark) VW-10200RP, and "Virantage" (registered trademark) VW-10700RP (all manufactured by Solvay Specialty Polymers).

[0085] Furthermore, as the terminal functional group of this thermoplastic resin [B], a hydroxyl group, a carboxyl group, an amino group, a thiol group, an acid anhydride, etc. are preferably used. Examples of thermoplastic resins having a hydroxyl group include polyvinyl acetal resins such as polyvinyl formal and polyvinyl butyral, polyvinyl alcohol, and phenoxy resin. Examples of thermoplastic resins having a sulfonyl group include polyether sulfone.

[0086] Specifically, commercially available phenoxy resins include "Fenototo" (registered trademark) YP-50 and "Fenototo" (registered trademark) YP-50S (both manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.).

[0087] In the present invention, the epoxy resin curing agent [C] is a curing agent for the epoxy resin contained in the epoxy resin composition of the present invention. It is a compound having active hydrogen capable of reacting with epoxy groups, and examples thereof include aromatic amines, aliphatic amines, acid anhydrides, and phenols. Specific examples of aromatic amines include diaminodiphenyl sulfone, diaminodiphenylmethane, diaminodiphenyl ether, diaminobenzanilide, toluenediamine, and diethyltoluenediamine. Among these, diaminodiphenyl sulfone or its isomers are preferably used. Diaminodiphenyl sulfone or its isomers are preferably used because they can produce cured epoxy resin products with good heat resistance. Examples of diaminodiphenyl sulfone isomers include 3,3'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl sulfone.

[0088] In resin transfer molding (RTM) and pultrusion molding, liquid diethyltoluenediamine is preferably used.

[0089] Examples of the aliphatic amine curing agent include isophorone diamine, m-xylene diamine, menthene diamine, diaminodicyclohexylmethane, etc. Examples of the acid anhydride include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, succinic anhydride, etc.

[0090] Examples of phenols include phenol novolac, cresol novolac, phenol aralkyls, bisphenols such as bisphenol A and bisphenol S, resorcinol, naphthalenediol, and hydroquinone.

[0091] The total amount of the epoxy resin curing agent [C] should be such that the number of moles of active hydrogen contained in [C] is 0.6 to 2.0 times the number of moles of epoxy groups contained in the entire epoxy resin composition. To improve compressive yield stress, this is preferably in the range of 0.6 to 1.0 times. To reduce the storage modulus at 275°C, this is preferably 1.1 to 1.8 times, and more preferably 1.2 to 1.5 times. When the number of moles of active hydrogen is 1.0 times or less the number of moles of epoxy groups contained in the entire epoxy resin composition, high crosslink density is achieved, making it easier to obtain high compressive yield stress. When the number of moles is 1.1 times or more, low crosslink density results in improved resin elongation. On the other hand, when the number of moles exceeds 2.0 times, heat resistance is significantly reduced and the viscosity of the epoxy resin composition increases, making prepreg preparation difficult.

[0092] Commercially available aromatic amines include Seikacure S (manufactured by Wakayama Seika Kogyo Co., Ltd.), MDA-220 (manufactured by Mitsui Chemicals, Inc.), "jER Cure" (registered trademark) W (manufactured by Mitsubishi Chemical Corporation), and 3,3'-DAS (manufactured by Mitsui Fine Chemicals, Inc.), "Lonzacure" (registered trademark) M-DEA, "Lonzacure" (registered trademark) M-DIPA, "Lonzacure" (registered trademark) M-MIPA, and "Lonzacure" (registered trademark) DETDA80 (all manufactured by Lonza).

[0093] These epoxy resin curing agents [C] may be used alone or in combination. The epoxy resin and the epoxy resin curing agent [C], or a pre-reaction product of a part of them, may also be blended into the composition. This method may be effective in adjusting viscosity and improving storage stability.

[0094] In the present invention, a cured epoxy resin product can be obtained by heat curing the epoxy resin composition of the present invention under temperature conditions that result in a degree of cure of 90% or more as determined by DSC. Such temperature conditions can be appropriately set depending on the type and amount of curing agent and accelerator. For example, when diaminodiphenyl sulfone is used as the curing agent, temperature conditions of 180°C for 2 hours can be suitably used. The degree of cure is calculated using the total calorific value QT of the epoxy resin composition and the residual calorific value QR of the cured product, as determined by DSC (differential scanning calorimetry), using the following formula: Curing degree (%)=(QT-QR) / QT×100.

[0095] In the present invention, the storage modulus of the cured epoxy resin material at 275°C, measured in a torsion mode at 1.0 Hz and heated at a rate of 5°C / min using a dynamic viscoelasticity measuring device in accordance with SACMA SRM 18R-94, is 1 to 10 MPa, preferably 5 to 9 MPa, and more preferably 6 to 8 MPa. This storage modulus is related to the ability to suppress stress concentration when tensile stress is applied to the carbon fiber composite material and breakage at the single fiber level begins. If the storage modulus is 1 MPa or more, the heat resistance of the cured epoxy resin material is sufficient, and if it is 10 MPa or less, the chain breakage of single fibers due to stress concentration can be suppressed, thereby increasing the elongation of the carbon fiber composite material.

[0096] In the present invention, the cured product of the epoxy resin composition preferably has a compressive yield strain of 10 to 15%, more preferably 11 to 15%. The compressive yield strain is a parameter related to the degree of crosslinking of the cured epoxy resin, and the lower the degree of crosslinking, the more the carbon fiber strand strength can contribute to the 0° tensile strength of the carbon fiber composite material. If this strain is 10% or more, the 0° tensile strength of the carbon fiber composite material is often satisfied, and if this strain is 15% or less, the relationship with the elastic modulus of the cured epoxy resin material is often satisfied. Details of such compression measurement will be described later. Since this strain can be controlled mainly by the degree of crosslinking and the distance between crosslink points, it can be adjusted by the type of epoxy curing agent, the ratio to the epoxy resin, the number of epoxy groups in the epoxy resin, etc.

[0097] In the present invention, the cured product of the epoxy resin composition has a compressive yield stress of preferably 90 to 140 MPa, more preferably 95 to 120 MPa, and even more preferably 100 to 110 MPa. The compressive yield stress is related to the interfacial adhesion between the carbon fiber and the cured epoxy resin, and if the compressive yield stress is 90 MPa or more, the interfacial adhesion strength is often satisfactory, while if it is 140 MPa or less, an excellent balance with the strain is often achieved.

[0098] In the present invention, the prepreg refers to the reinforcing fibers impregnated with the epoxy resin composition. The fiber mass fraction of the prepreg is preferably 40 to 90 mass%, more preferably 50 to 80 mass%. If the fiber mass fraction is too low, the mass of the resulting composite material will be too large, which may impair the advantage of the carbon fiber composite material, such as its excellent specific modulus. On the other hand, if the fiber mass fraction is too high, impregnation with the epoxy resin composition will be insufficient, and the resulting carbon fiber composite material will likely have many voids, which may significantly reduce its mechanical properties.

[0099] The form of the carbon fiber is not particularly limited, and for example, a continuous fiber sheet / tow aligned in one direction, a woven fabric, a mat, etc. may be used.

[0100] In the present invention, the epoxy resin composition can be produced by a method (wet method) in which the epoxy resin composition is dissolved in a solvent such as methyl ethyl ketone or methanol to reduce the viscosity and then impregnated into carbon fibers, or by a hot melt method (dry method) in which the epoxy resin composition is heated to reduce the viscosity and then impregnated into carbon fibers.

[0101] The carbon fiber composite material of the present invention is produced by laminating the obtained prepregs and then heat-curing the epoxy resin composition while applying pressure to the laminate, etc. Here, methods for applying heat and pressure include press molding, autoclave molding, bagging molding, wrapping tape method, and internal pressure molding.

[0102] The carbon fiber composite material of the present invention can be produced by a method of directly impregnating carbon fibers with an epoxy resin composition without using a prepreg, followed by heat curing, such as a molding method such as hand layup, filament winding, pultrusion, resin injection molding, or resin transfer molding. In these methods, it is preferable to prepare the epoxy resin composition by mixing two liquids, a base resin made of an epoxy resin and an epoxy resin curing agent, immediately before use.

[0103] The carbon fiber composite material of the present invention preferably has a 0° tensile strength of 4.0 GPa or more, more preferably 4.1 GPa or more, and even more preferably 4.2 to 4.5 GPa. The 0° tensile strength is a factor that influences the impact resistance of a carbon fiber composite material. The 0° tensile strength can be evaluated in accordance with JIS K7165 (2008). A 0° tensile strength of 4.0 GPa or more facilitates an increase in the strain energy density of the carbon fiber composite material. While there is no upper limit to the 0° tensile strength, a 0° tensile strength of 4.5 GPa or more tends to achieve a satisfactory level of strain energy density for the carbon fiber composite material. The 0° tensile strength can be controlled by the strand strength of the carbon fiber and the storage modulus of the cured epoxy resin.

[0104] The carbon fiber composite material of the present invention preferably has an elongation of 2.5% or more, more preferably 2.6 to 2.8%. Such elongation can be evaluated using a strain gauge in accordance with JIS K7165 (2008). If the elongation of the carbon fiber composite material is 2.5% or more, it is easy to increase the strain energy density of the carbon fiber composite material. There is no upper limit to the elongation, but an elongation of 2.8% is often sufficient to increase the strain energy density of the carbon fiber composite material. The elongation of the carbon fiber composite material can be adjusted by the 0° tensile strength and strand modulus of the carbon fiber composite material. [Example]

[0105] The methods for measuring various physical properties used in the present invention are as follows.

[0106] <Total fineness> A 10 m length of carbon fiber is sampled and dried at 120°C for 2 hours, and the measured mass is divided by 10 to determine the total fineness, which is the mass per meter.

[0107] <density> The carbon fiber to be measured is dried at 120°C for 2 hours before measurement. A dry automatic density meter is used to measure the density, with nitrogen as the measurement medium and a 10cc sample container, and the sample volume is adjusted to 3-6cc. Measurements are performed three times, and the average value is used. For this measurement, an Accupyc 1330 dry automatic density meter manufactured by Shimadzu Corporation was used.

[0108] <Single fiber diameter> It is calculated from the obtained total fineness and density and the number of filaments of the carbon fiber used in the measurement.

[0109] <Strand strength, strand modulus, elongation> The strand strength, strand modulus, and elongation of carbon fiber are determined according to the following procedure, in accordance with the resin-impregnated strand test method of JIS R7608:2004. The resin formulation used is "Celloxide" (registered trademark) 2021P (manufactured by Daicel Chemical Industries, Ltd.) / boron trifluoride monoethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) / acetone = 100 / 3 / 4 (parts by mass), and the curing conditions are atmospheric pressure, 125°C, and 30 minutes. The strand strength, strand modulus, and elongation of 10 carbon fiber strands are measured, and the average value is used. The strain range when calculating the strand modulus is 0.1 to 0.6%.

[0110] <Strain energy density of carbon fiber> The strain energy density is calculated using the following formula: Strain energy density (J / mm 3 ) = strand strength (GPa) × 1,000 × elongation (%) / 100 / 2.

[0111] <Preparation of carbon fiber composite materials> (1) Preparation of epoxy resin composition A predetermined amount of the amine-type epoxy resin [A] or an epoxy resin other than [A] and the thermoplastic resin [B] are added to a kneader and kneaded at a temperature of 150°C or higher to dissolve the resin, yielding a transparent viscous liquid. After lowering the temperature to 60°C or lower while kneading, a predetermined amount of the epoxy resin curing agent [C] and other components are added, and the mixture is further kneaded to obtain an epoxy resin composition.

[0112] In the compositions 5 and 6 described below, a liquid obtained by mixing the amine-type epoxy resin [A] or an epoxy resin other than [A] at a temperature of 60°C or higher and a liquid obtained by mixing the component [C] at a temperature of 60°C or higher to dissolve the solid components are mixed together at a temperature of 60°C or lower, and the mixture is degassed under vacuum for 1 hour to obtain an epoxy resin composition.

[0113] (2) Prepreg fabrication For Compositions 1 to 4 described below, the epoxy resin composition is applied to release paper using a knife coater to prepare a resin film. Next, two resin films are placed on both sides of the carbon fibers, which are aligned in one direction in a sheet shape, and the resin is impregnated into the carbon fibers by heating and pressurizing, until the weight of the carbon fibers reaches 190 g / m. 2 A unidirectional prepreg having a mass fraction of the epoxy resin composition of 35.5% is obtained.

[0114] (3) Preparation of RTM laminate For compositions 5 and 6 described below, carbon fiber composite materials were produced by the RTM molding method described below.

[0115] Multiple fiber substrates, each with carbon fibers aligned in one direction in a sheet-like configuration to achieve a predetermined fiber basis weight, were stacked and placed on the surface of a planar aluminum mold. A release-treated polyester fabric was placed on top of the peel ply, followed by a polypropylene knit as a resin diffusion medium. The cavity was then sealed using a bag material and a sealant, except for the resin inlet and vacuum suction port, to form a cavity. The cavity was then evacuated through the vacuum suction port using a vacuum pump, and the vacuum level was adjusted to -90 kPa or less. The mold and preform were then heated to 70°C. A hot air dryer was used for temperature control. The resin composition was preheated at 70°C for 30 minutes, and the preheated liquid resin composition was placed in the resin inlet of the mold. The thermosetting resin composition was injected into the evacuated cavity by utilizing the pressure difference between the pressure inside the cavity and atmospheric pressure, thereby impregnating the aligned fiber substrate. When the resin composition reached the vacuum suction port, the resin injection port was closed, and the vacuum suction port was maintained for another hour while continuing to suction through the vacuum suction port, after which the vacuum suction port was closed.

[0116] The temperature was then raised from 70°C to 140°C at a rate of 1.5°C / min, pre-cured at 140°C for 2 hours, and then cooled to room temperature. The pre-cured product was removed from the mold, and the secondary materials such as the peel ply were removed. The temperature was then raised to 180°C at a rate of 1.5°C / min in a hot air dryer, and cured at 180°C for 2 hours to obtain a fiber-reinforced composite material (laminate).

[0117] <DSC cure degree measurement of cured resin> Five mg of the epoxy resin composition prepared in (1) above is sampled and measured using a DSC by increasing the temperature from 30°C to 350°C at a rate of 10°C / min to obtain an exothermic curve. The total calorific value QT of the epoxy resin composition is calculated by integrating the exothermic peak. The epoxy resin composition prepared in (1) above is degassed in a vacuum and cured at 180°C for 2 hours to obtain a cured epoxy resin. Five mg of the resulting cured resin is sampled and measured using a DSC by increasing the temperature from 30°C to 350°C at a rate of 10°C / min to obtain an exothermic curve. If a residual exothermic peak is present, the residual calorific value QR is calculated by integrating the exothermic peak. If no residual exothermic peak is present, QR is set to 0.

[0118] <Glass transition temperature of cured resin and storage modulus at 275°C measured in torsion mode at 1.0 Hz> A 10 mm wide, 40 mm long test piece was cut from a plate of cured epoxy resin obtained in the same manner as for the DSC cure measurement of the cured resin. Using a dynamic viscoelasticity measuring device (ARES, manufactured by TA Instruments), the test piece was mounted on a solid torsion jig and measured over a temperature range of 30 to 300°C at a heating rate of 5°C / min, a frequency of 1 Hz, and a strain of 0.1%. The glass transition temperature was determined as the temperature at the intersection of a tangent to the glass region and a tangent to the glass transition region in the resulting graph of storage modulus vs. temperature. The storage modulus at 275°C measured in torsional mode at 1.0 Hz was taken as the storage modulus at 275°C in the resulting graph of storage modulus vs. temperature. If multiple glass transition temperatures were observed, the lowest value was used as the glass transition temperature.

[0119] <Compressive yield stress and strain at compressive yield of cured epoxy resin> A 6mm thick plate of cured epoxy resin is prepared, and a cubic test piece with a side length of 6mm is cut out from the plate. The compressive yield stress and compressive yield strain are measured at a test speed of 1±0.2mm / min, with other conditions conforming to JIS K7181 (2011).

[0120] <0° tensile strength of carbon fiber composite materials> Using the unidirectional prepreg prepared by the above method, six plies were laminated together with the fiber direction aligned, and molded in an autoclave at 180°C for 2 hours under a pressure of 0.59 MPa at a heating rate of 1.5°C / min to produce a laminate. For RTM, the laminate was prepared by adjusting the fiber content to the same as that of the six prepreg plies using the above method. The 0° tensile strength (GPa) of this laminate was determined according to JIS K7165 (2008). The 0° tensile strength was calculated by converting the actual measured value to a carbon fiber volume fraction of 60%. Strain was measured using a strain gauge.

[0121] <Strain energy density of carbon fiber composite materials> The strain energy density is calculated using the following formula: Strain energy density (J / mm 3 ) = 0° tensile strength of carbon fiber composite material (GPa) × 1,000 × strain of carbon fiber composite material (%) / 100 / 2.

[0122] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0123] [Resin raw material] <Amine-type epoxy resin [A]> "Sumiepoxy" (registered trademark) ELM434 (tetraglycidyldiaminodiphenylmethane, manufactured by Sumitomo Chemical Co., Ltd.) GAN (N,N-diglycidylaniline, manufactured by Nippon Kayaku Co., Ltd.).

[0124] <Epoxy resins other than [A]> "Epotohto" (registered trademark) jER825 (bisphenol A epoxy resin, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.) "Epiclon" (registered trademark) HP7200L (dicyclopentadiene-type epoxy resin, manufactured by DIC Corporation) "Araldite" AER4152 (epoxy resin with oxazolidone ring, manufactured by Asahi Kasei E-Materials Corporation).

[0125] <Thermoplastic resin [B]> "Sumikaexcel" (registered trademark) PES5003P (polyethersulfone, manufactured by Sumitomo Chemical Co., Ltd., weight average molecular weight: 47,000).

[0126] <Epoxy resin hardener [C]> -Seikacure S (manufactured by Wakayama Seika Kogyo Co., Ltd.). "jER Cure" (registered trademark) W (manufactured by Mitsubishi Chemical Corporation) 3,3'-DAS (Mitsui Chemicals Fine Co., Ltd.)

[0127] [Epoxy resin composition] The resin raw materials were kneaded according to the compositions shown in Table 1, and the characteristic values ​​are shown below (in Table 1, the numbers represent parts by mass). Furthermore, prepregs were prepared for compositions 1 to 4.

[0128] [Carbon fiber 1] A spinning solution containing a polyacrylonitrile copolymer and dimethyl sulfoxide as a solvent was first extruded into the air from a spinneret and then introduced into a coagulation bath consisting of an aqueous solution of dimethyl sulfoxide, to obtain coagulated yarns by a dry-wet spinning method.

[0129] This coagulated yarn was washed with water in a conventional manner and then stretched 3.5 times in a two-tank warm water bath. Subsequently, an amino-modified silicone-based silicone oil solution was applied to the fiber bundle after this water bath stretching, and a drying and densification treatment was performed using a heated roller at 160°C. After reducing the number of single fibers to 12,000, the fiber bundle was stretched 3.7 times in pressurized steam to a total spinning draw ratio of 13 times, and then entangled to obtain a carbon fiber precursor fiber bundle with a crystal orientation degree of 93% and a single fiber count of 12,000. The carbon fiber precursor fiber bundle had a single fiber fineness of 0.7 dtex.

[0130] Next, the carbon fiber precursor fiber bundle was subjected to a flame-stabilization treatment while being stretched at a draw ratio of 1 in an oven in an air atmosphere using conditions of a flame-stabilization temperature of 250°C and a flame-stabilization time of 11 minutes in the first flame-stabilization step, and a flame-stabilization temperature of 280°C and a flame-stabilization time of 6 minutes in the second flame-stabilization step, thereby obtaining a flame-stabilized fiber.

[0131] 1,370 cm in the infrared spectrum of the fiber after the first flame retardant treatment -1 The peak intensity at 1,453 cm -1 The ratio of the peak intensities at 1,370 cm in the infrared spectrum of the fiber after the second flame retardation treatment was 1.04. -1 The peak intensity at 1,453 cm -1 The peak intensity ratio is 0.70, 1,370 cm -1 The peak intensity at 1,254 cm -1 The peak intensity ratio was 0.61.

[0132] The obtained flame-resistant fiber was subjected to a pre-carbonization treatment in a nitrogen atmosphere at a maximum temperature of 800°C and a draw ratio of 1.22 to obtain a pre-carbonized fiber. The obtained pre-carbonized fiber was then subjected to a carbonization treatment in a nitrogen atmosphere at a maximum temperature of 1,200°C and a draw ratio of 0.950. The temperature rise rate during the carbonization process was 0.45°C / sec. The obtained carbon fiber was subjected to a surface treatment and a sizing agent coating treatment to obtain the final carbon fiber 1, whose physical properties are shown in Table 2.

[0133] [Carbon fiber 2-9] Carbon fibers were obtained in the same manner as in Example 1, except that the draw ratio in the pre-carbonization step, and the draw ratio, maximum temperature, treatment time at the maximum temperature, and temperature rise rate in the carbonization step were changed as shown in Table 2. The physical properties obtained are shown in Table 2.

[0134] [Carbon Fiber 10 and 11] Carbon fibers were obtained in the same manner as in Example 1, except that the single fiber fineness of the carbon fiber precursor fiber bundle was changed to 0.5 dtex or 0.8 dtex. The obtained physical properties are shown in Table 2.

[0135] [Reference examples 1~3] A flame-resistant fiber was obtained in the same manner as in Example 1, except that the first flame-resistant step was performed under conditions of a flame-resistant temperature of 240°C and a flame-resistant time of 82 minutes, and the second flame-resistant step was performed under conditions of a flame-resistant temperature of 250°C and a flame-resistant time of 85 minutes.

[0136] 1,370 cm in the infrared spectrum of the fiber after the first flame retardant treatment-1 The peak intensity at 1,453 cm -1 The ratio of the peak intensities at 1,370 cm in the infrared spectrum of the fiber after the second flame retardation treatment was 0.68. -1 The peak intensity at 1,453 cm -1 The peak intensity ratio is 0.50, 1,370 cm -1 The peak intensity at 1,254 cm -1 The ratio of the peak intensities was 0.56.

[0137] The obtained flame-resistant fiber was subjected to a pre-carbonization treatment in a nitrogen atmosphere at a maximum temperature of 800°C and a draw ratio of 1.17 to obtain a pre-carbonized fiber. The obtained pre-carbonized fiber was then carbonized in a nitrogen atmosphere at a maximum temperature and time shown in Table 2, with a draw ratio of 0.980. The temperature rise rate during the carbonization process was 0.35°C / sec. The obtained carbon fiber was subjected to a surface treatment and a sizing agent application treatment to obtain the final carbon fiber, and the physical properties of the resulting fiber are shown in Table 2. Simply changing the maximum temperature during the carbonization process, which is generally used to adjust the strand modulus, does not significantly change the strand strength, and it was found that when the strand strength level is high, it is necessary to finely adjust the conditions for the pre-carbonization process and the carbonization process shown in this example.

[0138] [Examples 1 to 7, Comparative Examples 1 to 15] Carbon fiber composite materials were prepared by combining the obtained carbon fibers 1 to 9 and resin compositions 1 to 6 as shown in Table 3, and mechanical properties were measured. The results are shown in Table 3. Although there is a tendency for the 0° tensile strength of the carbon fiber composite material to increase as the strand strength of the carbon fiber increases, it was found that this changes significantly depending on the combination with the epoxy resin composition. Furthermore, the elongation of the carbon fiber composite material exceeded 2.3%, and the product of the 0° tensile strength and elongation was higher than ever before.

[0139] [Table 1]

[0140] [Table 2]

[0141] [Table 3] [Industrial Applicability]

[0142] The carbon fiber composite material of the present invention has high impact resistance and large energy absorption, and can reduce the weight of components that require high impact resistance.

Claims

1. A carbon fiber composite material comprising: carbon fiber having a strand strength of 7.5 to 8.5 GPa, an elongation of 2.65 to 3.20%, and a single fiber diameter of 4.0 to 6.0 μm; and an epoxy resin composition having an amine-type epoxy resin [A], a thermoplastic resin [B] that dissolves in the epoxy resin, and an epoxy resin curing agent [C], wherein the degree of cure of the epoxy resin composition is 90% or more; and a cured product of the epoxy resin has a storage modulus of 1 to 10 MPa at 275°C, measured in a torsion mode of 1.0 Hz by heating at a rate of 5°C / min using a dynamic viscoelasticity measuring apparatus in accordance with SACMA SRM 18R-94.

2. The carbon fiber has a strand modulus of 240 to 300 GPa and a strain energy density of 95 J / mm ３ The carbon fiber composite material according to claim 1 .

3. 3. The carbon fiber composite material according to claim 1, wherein a cured product of the epoxy resin composition has a compressive yield stress of 90 to 140 MPa and a compressive yield strain of 10 to 15%.

4. 3. The carbon fiber composite material according to claim 1, which has a 0° tensile strength of 4.0 GPa or more and an elongation of 2.5% or more.

5. 3. The carbon fiber composite material according to claim 1, wherein the epoxy resin curing agent [C] is an aromatic amine.

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