Molding materials for carbon fiber reinforced composite materials and carbon fiber reinforced composite materials

Abstract

This invention provides a molding material for carbon fiber reinforced composite materials that can be molded without problems regarding impregnation or curing even at relatively low temperatures, and a carbon fiber reinforced composite material that exhibits the interlaminar shear strength and compressive strength necessary for weight reduction. [Solution] A molding material for carbon fiber reinforced composite materials comprising an epoxy resin composition containing the following components (A) to (C) and carbon fibers satisfying the following conditions [a] to [c]. (A): Epoxy resin (B): Acid anhydride (C): At least one compound selected from the group consisting of tertiary amines, tertiary phosphines, and their Brønsted salts. [a]: The strand tensile strength is between 4 GPa and 8 GPa. [b]: The tensile modulus of the strand is between 230 GPa and 350 GPa. [c]: Surface specific oxygen concentration O / C is 0.05 or higher and 0.20 or lower.

Description

[Technical Field]

[0001] The present disclosure relates to a molding material for carbon fiber reinforced composite materials, and a carbon fiber reinforced composite material formed using the same. [Background Art]

[0002] Carbon fiber reinforced composite materials have come to be used in various fields including the aerospace field by taking advantage of their excellent light weight, mechanical properties, environmental resistance and the like. Along with this, higher productivity has been required, and it has also become required to respond to the molding of larger or complex-shaped members. As a molding method for carbon fiber reinforced composite materials that meets these demands, applications such as resin injection molding and pultrusion molding using liquid thermosetting resins have been progressing.

[0003] As a thermosetting resin, epoxy resin is preferably used because it generates no outgas during curing, has small curing shrinkage, and exhibits excellent adhesiveness, rigidity, toughness and the like after curing. Epoxy resins are roughly classified into amine curing systems, phenol curing systems, acid anhydride curing systems and the like depending on the curing agent combined therewith. In particular, acid anhydride-cured epoxy resins have low viscosity and tend to exhibit an excellent balance between fast curability and viscosity stability, and are considered to be suitable for molding larger or complex-shaped members in a shorter time even in the above molding methods.

[0004] The carbon fiber combined therewith also has a great influence on the development of moldability and molded article properties. The following studies have been conducted so far as molding materials for carbon fiber reinforced composite materials obtained by combining carbon fibers with an acid anhydride-cured epoxy resin. In Patent Document 1, a phosphonium salt or the like is used as a curing accelerator for an acid anhydride-cured epoxy, and Torayca T300-3K is used as the carbon fiber. Further, in Patent Document 2, a tertiary amine or the like is used as a curing accelerator for an acid anhydride-cured epoxy, and Torayca T700SC-12K is used as the carbon fiber. In Patent Document 3, DBU·2-ethylhexanoate or the like is used as a curing accelerator for an acid anhydride-cured epoxy, and Torayca T700SC-12K is used as the carbon fiber. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2016 / 158757 [Patent Document 2] Japanese Patent Publication No. 2017-119812 [Patent Document 3] International Publication No. 2013 / 115152 [Overview of the project] [Problems that the invention aims to solve]

[0006] The molding material for carbon fiber reinforced composite materials described in Patent Document 1 has a relatively high viscosity when molded at a low temperature of around 100°C, resulting in poor impregnation and insufficient curing reaction, leading to a low Tg of the molded product.

[0007] The molding material for carbon fiber reinforced composite materials described in Patent Document 2 could be molded without problems in terms of impregnation and curing even at relatively low temperatures, but the interlaminar shear strength was relatively low, and it still did not lead to weight reduction.

[0008] The molding material for carbon fiber reinforced composite materials described in Patent Document 3, when molded at relatively low temperatures, resulted in a low Tg of the molded product, and failed to achieve both interlaminar shear strength and compressive strength, thus still not leading to weight reduction.

[0009] The purpose of this disclosure is to provide a carbon fiber reinforced composite material that improves upon the shortcomings of the conventional technology, allows for molding without problems in impregnation or curing even at relatively low temperatures, and exhibits the interlaminar shear strength and compressive strength necessary for weight reduction. [Means for solving the problem]

[0010] This disclosure, which aims to solve the above problems, has the following configuration. [1] A molding material for carbon fiber reinforced composite materials comprising an epoxy resin composition containing the following components (A) to (C) and carbon fibers satisfying the following conditions [a] to [c]. (A): Epoxy resin (B): Acid anhydride (C): At least one compound selected from the group consisting of tertiary amines, tertiary phosphines, and their Brønsted salts. [a]: The strand tensile strength is between 4 GPa and 8 GPa. [b]: The tensile modulus of the strand is between 230 GPa and 350 GPa. [c]: Surface specific oxygen concentration O / C is 0.05 or higher and 0.20 or lower. [2] The epoxy resin composition comprising component (D): core-shell rubber particles, as described in [1], a molding material for carbon fiber reinforced composite materials. [3] A molding material for carbon fiber reinforced composite materials according to [1] or [2], wherein component (A) comprises a glycidylamine type epoxy. [4] A molding material for carbon fiber reinforced composite materials according to any of [1] to [3], wherein the carbon fiber further satisfies the following conditions. [d]: The cross-sectional shape is substantially circular. A carbon fiber reinforced composite material obtained by curing a molding material for carbon fiber reinforced composite materials described in any of [5][1] to [4]. [Effects of the Invention]

[0011] By using the molding material for carbon fiber reinforced composite materials disclosed herein, molding can be performed without problems regarding impregnation and curing even at relatively low temperatures, and a carbon fiber reinforced composite material can be obtained that exhibits the interlaminar shear strength and compressive strength necessary for weight reduction. [Modes for carrying out the invention]

[0012] The molding material for carbon fiber reinforced composite materials disclosed herein comprises an epoxy resin composition containing the following components (A) to (C) and carbon fibers satisfying the following conditions [a] to [c]. (A): Epoxy resin (B): Acid anhydride (C): at least one compound selected from the group consisting of tertiary amines, tertiary phosphines, and Bronsted acid salts thereof [a]: strand tensile strength of 4 GPa or more and 8 GPa or less [b]: strand tensile modulus of 230 GPa or more and 350 GPa or less [c]: surface specific oxygen concentration O / C of 0.05 or more and 0.20 or less.

[0013] Component (A) is an epoxy resin. Such an epoxy resin is not particularly limited as long as it is a compound having an epoxy group in the molecule. Examples thereof include bisphenol A type epoxy resins, bisphenol F type epoxy resins, amine type epoxy resins, aliphatic epoxy resins, and the like. Epoxy resins may be used alone, or two or more types may be used in combination.

[0014] As commercially available products of bisphenol A type epoxy resins, for example, "jER (registered trademark)" 825, "jER (registered trademark)" 828 (all manufactured by Mitsubishi Chemical Corporation), "Epototo (registered trademark)" YD-128, "Epototo (registered trademark)" YD-8125 (all manufactured by Nippon Steel Chemical & Material Co., Ltd.), "DER (registered trademark)" 331, "DER (registered trademark)" 332 (all manufactured by Dow Chemical Company) and the like can be used.

[0015] As commercially available products of bisphenol F type epoxy resins, for example, "jER (registered trademark)" 806, "jER (registered trademark)" 807, "jER (registered trademark)" 4004P (all manufactured by Mitsubishi Chemical Corporation), "EPICLON (registered trademark)" 830 (manufactured by DIC Corporation), "Epototo (registered trademark)" YD-170, "Epototo (registered trademark)" YDF-8170C (all manufactured by Nippon Steel Chemical & Material Co., Ltd.) and the like can be used.

[0016] Examples of the amine type epoxy resin include tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol, diglycidylaniline, and the like.

[0017] Examples of the aliphatic epoxy resin include ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether.

[0018] Commercially available products of such aliphatic epoxy resins that can be used include, for example, "Denacol (registered trademark)" EX-810, "Denacol (registered trademark)" EX-841, "Denacol (registered trademark)" EX-211, "Denacol (registered trademark)" EX-212, "Denacol (registered trademark)" EX-214, "Denacol (registered trademark)" EX-252, "Denacol (registered trademark)" EX-931 (all manufactured by Nagase ChemteX Corporation), "Adeka Glycilol (registered trademark)" ED-503, "Adeka Glycilol (registered trademark)" ED-523, and "Adeka Glycilol (registered trademark)" ED-506 (all manufactured by ADEKA Corporation).

[0019] Among these, glycidyl amine-type epoxy resins, particularly diglycidyl aniline, are preferably used as component (A) because they provide an excellent balance between the viscosity of the epoxy resin composition and mechanical properties such as flexural modulus and strength of the resulting cured product. In view of the large effect of improving the mechanical properties of the obtained cured product, it is preferable that glycidyl amine-type epoxy is contained in an amount of 15 to 100% by mass, more preferably 25 to 100% by mass, and even more preferably 35 to 100% by mass, based on 100% by mass of component (A).

[0020] Component (B) is an acid anhydride, specifically a carboxylic acid anhydride. More specifically, it refers to a compound having one or more acid anhydride groups capable of reacting with the epoxy groups of component (A) per molecule, and acts as a curing agent for epoxy resins. The number of acid anhydride groups contained in component (B) is preferably 4 or less per molecule.

[0021] Component (B) may be an acid anhydride that does not have an alicyclic structure, such as phthalic anhydride or succinic anhydride. However, from the viewpoint of being easy to handle as a low-viscosity liquid and the mechanical properties of the cured product, an acid anhydride having an alicyclic structure is preferred, and among these, a compound having a cycloalkane ring or a cycloalkene ring is more preferred.

[0022] Specific examples of acid anhydrides having such alicyclic structures include, for example, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyldihydronadic anhydride, 1,2,4,5-cyclopentanetetracarboxylic dianhydride, 1,2,3,6-tetrahydrophthalic anhydride, methyl-1,2,3,6-tetrahydrophthalic anhydride, nadic anhydride, methylnadic anhydride, bicyclo[2,2,2]octo-7-en-2,3,5,6-tetracarboxylic dianhydride, and 4-(2,5-dioxotetrahydrofuran-3-yl)-3-methyl-1,2,5,6-tetrahydrophthalic anhydride. Among these, acid anhydrides selected from hexahydrophthalic anhydride, tetrahydrophthalic anhydride, nadic anhydride, and their alkyl-substituted types are preferred as component (B) because they offer an excellent balance between the viscosity of the epoxy resin composition and the mechanical properties such as the flexural modulus and strength of the resulting cured product.

[0023] The proportions of component (A) and component (B) are preferably such that the ratio of the number of acid anhydride groups (H) in component (B) to the total number of epoxy groups (E) in component (A), the H / E ratio, is in the range of 0.8 to 1.2, more preferably in the range of 0.85 to 1.15, and even more preferably in the range of 0.9 to 1.1. If the H / E ratio is less than 0.8, polymerization of excess epoxy resins may proceed, leading to a decrease in the physical properties of the cured product. Similarly, if the H / E ratio is greater than 1.2, the presence of excess curing agent components may also lead to a decrease in the physical properties of the cured product.

[0024] Component (C) is at least one compound selected from the group consisting of tertiary amines, tertiary phosphines, and their Brønsted salts, preferably a tertiary amine or its Brønsted salt, and more preferably a tertiary amine. These act as curing accelerators for the development of rapid curing.

[0025] Tertiary amines are not particularly limited to compounds having a tertiary amino group, and include not only common tertiary amines with aliphatic, aromatic, or alicyclic structures, but also imidazoles and pyridines.

[0026] Examples of tertiary amines include common tertiary amines such as tributylamine, N,N-dimethylbenzylamine, diisopropylethylamine, triisopropylamine, dibutylethanolamine, diethylethanolamine, triisopropanolamine, triethanolamine, N,N-diisopropylethylamine, 1,8-diazabicyclo[5,4,0]-7-undecene (DBU), and 1,5-diazabicyclo[4,3,0]-5-nonene (DBN); imidazoles such as 2-methylimidazole, 2-phenylimidazole, 1,2-dimethylimidazole, 1-benzylimidazole, and 2-ethyl-4-methylimidazole; and pyridines such as pyridine, chloropyridine, lutidine, picoline, bipyridine, and pyrrole. Among these, DBU, 1,2-dimethylimidazole, and 2-ethyl-4-methylimidazole are preferred.

[0027] Tertiary phosphines are not particularly limited to compounds having a tertiary phosphino group, and include general tertiary phosphines having aliphatic, aromatic, or alicyclic structures.

[0028] Examples of tertiary phosphines include triphenylphosphine, tributylphosphine, trimethylphosphine, triisopropylphosphine, and tricyclohexylphosphine.

[0029] Brønsted salts are salts formed by the addition of proton-containing acid compounds. Proton-containing acid compounds are not particularly limited and include various carboxylic acids, sulfonic acids, organic acids such as phenols, and inorganic acids such as hydrochloric acid, hydrofluoric acid, sulfuric acid, and phosphoric acid.

[0030] Examples of Brønsted salts of tertiary amines include the phenolic salt of DBU (U-CAT SA1, manufactured by Sunapro Co., Ltd.), the octoylate of DBU (U-CAT SA102, manufactured by Sunapro Co., Ltd.), the p-toluenesulfonate of DBU (U-CAT SA506, manufactured by Sunapro Co., Ltd.), the formate of DBU (U-CAT SA603, manufactured by Sunapro Co., Ltd.), the orthophthalate of DBU (U-CAT SA810), and the phenol novolac resin salts of DBU (U-CAT SA810, SA831, SA841, SA851, 881, manufactured by Sunapro Co., Ltd.). Among these, the octoylate of DBU is preferred.

[0031] The content of component (C) is preferably 0.1 parts by mass or more and 25 parts by mass or less, when the mass of component (A) is 100 parts by mass. By having a component (C) content of 0.1 parts by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 6.0 parts by mass or more, the desired carbon fiber reinforced composite material can be obtained with a shorter curing time. Furthermore, by having a component (C) content of 25 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less, an epoxy resin composition with excellent viscosity stability after formulation can be obtained. Any combination of the above upper and lower limits may be used.

[0032] Component (D) is core-shell rubber particles. Due to the toughness-improving effect of component (D), the resulting cured product exhibits excellent toughness and impact resistance.

[0033] In order to balance the ease of handling of the resulting epoxy resin composition with the toughness improvement effect, when the mass of component (A) is 100 parts by mass, it is preferable that component (D) is included in 0.5 to 30 parts by mass, more preferably 1 to 25 parts by mass, even more preferably 2 to 20 parts by mass, and particularly preferably 3 to 15 parts by mass.

[0034] In the above-mentioned molding material for carbon fiber reinforced composite materials, the carbon fibers have a strand tensile strength of 4 GPa or more and 8 GPa or less, preferably 5 GPa or more and 8 GPa or less. If it is less than 4 GPa, the strength characteristics of the carbon fiber reinforced composite material will be insufficient, and it will not lead to weight reduction of the component.

[0035] In the above-mentioned molding material for carbon fiber reinforced composite materials, the carbon fibers have a strand tensile modulus of 230 GPa or more and 350 GPa or less. If it is less than 230 GPa, the rigidity of the carbon fiber reinforced composite material will be insufficient, and it will not lead to weight reduction of the component. On the other hand, if it exceeds 350 GPa, the strength characteristics of the carbon fiber reinforced composite material will be insufficient, and again it will not lead to weight reduction of the component.

[0036] In the above-mentioned molding material for carbon fiber reinforced composite materials, the carbon fibers have a surface specific oxygen concentration (O / C) of 0.05 to 0.20, preferably 0.08 to 0.20, more preferably 0.10 to 0.20, and most preferably 0.12 to 0.20. Here, the surface specific oxygen concentration is determined by calculating the surface specific oxygen concentration O / C = ([O1s] / [C1s]) / (sensitivity correction value) from the O1s peak area [O1s] and C1s peak area [C1s] using X-ray photoelectron spectroscopy. A means to set the surface specific oxygen concentration O / C within the above range is, for example, to change the amount of electricity during the electrolytic oxidation treatment. If it is less than 0.05, adhesion with the resin will be insufficient, the interlaminar shear strength of the carbon fiber reinforced composite material will be insufficient, and it will not lead to weight reduction of the component.

[0037] In the above-mentioned molding material for carbon fiber reinforced composite materials, it is preferable that the cross-sectional shape of the carbon fibers is substantially circular. This improves the impregnation of the resin, allowing for a higher fiber volume content Vf in the carbon fiber reinforced composite material, which leads to a reduction in the weight of the component. Here, the cross-sectional shape of the carbon fiber can be indicated by the ratio of the major axis R to the minor axis r (r / R) of the cross-section of a single filament, measured using an optical microscope. The major axis R refers to the diameter of the circumscribed circle of the cross-sectional shape of the single filament, and the minor axis r refers to the diameter of the inscribed circle of the cross-sectional shape of the single filament. A cross-sectional shape that is substantially circular means that r / R is 0.9 or greater, and a cross-sectional shape that is flat means that r / R is less than 0.9.

[0038] The molding material for the carbon fiber reinforced composite material described above is not particularly limited as long as it contains the carbon fibers and the epoxy resin composition, and may be in a state where the epoxy resin composition is completely impregnated throughout the carbon fibers, or in a state where it is impregnated only in part of the carbon fibers. Furthermore, the epoxy resin composition may be in an unreacted state, or in a state where it has partially reacted and reached the B stage.

[0039] In the above-mentioned molding material for carbon fiber reinforced composite materials, the carbon fiber content is preferably in the range of 40% by mass or more and 90% by mass or less. If the carbon fiber content is 40% by mass or more, the mass of the resulting carbon fiber reinforced composite material will not be excessive, and the advantages of carbon fiber reinforced composite materials, such as superior specific strength and specific modulus, will be more easily realized. Furthermore, if the carbon fiber content is 90% by mass or less, the impregnation of the epoxy resin composition into the carbon fibers will be excellent.

[0040] A carbon fiber reinforced composite material obtained by curing the above-mentioned molding material for carbon fiber reinforced composite materials is also one aspect of this disclosure.

[0041] The carbon fibers may be short fibers, continuous fibers, or a combination of both. Continuous fibers are preferred in order to obtain a carbon fiber reinforced composite material with excellent mechanical properties and a high fiber mass content.

[0042] When continuous fibers are used as carbon fibers, examples include fibrous structures such as long fibers aligned in one direction, single tows, woven fabrics, knits, nonwoven fabrics, mats, and braids, with an average fiber diameter of 3 μm to 12 μm being preferred.

[0043] In the carbon fiber reinforced composite materials described above, carbon fibers may be used in the form of strands, but a base material made of carbon fibers processed into forms such as mats, fabrics, knits, braids, or unidirectional sheets is preferably used. Among these, fabrics are preferably used because they make it easy to obtain carbon fiber reinforced composite materials with high Vf and have excellent handling properties.

[0044] The molding method for carbon fiber reinforced composite materials is not particularly limited, but methods such as RTM (Resin Transfer Molding), film bag molding, pultrusion, and press molding, which offer excellent productivity, are preferably used. [Examples]

[0045] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to the descriptions of these examples.

[0046] <Resin raw materials> The components used in the epoxy resin composition in this embodiment are as follows: 1. Component (A): Epoxy resin • "GAN (registered trademark)" (N,N'-Diglycidylaniline, manufactured by Nippon Kayaku Co., Ltd.) • “EPICLON®” 830 (Bisphenol F type epoxy resin, manufactured by DIC Corporation) 2. Component (B): Acid anhydride • "MHAC-P (registered trademark)" (methyl-3,6-endomethylene-1,2,3,6-tetrahydrophthalic anhydride, manufactured by Resonaq Corporation) 3. Component (C): At least one compound selected from the group consisting of tertiary amines, tertiary phosphines, and their Brønsted salts. • “DBU (registered trademark)” (1,8-diazabicyclo[5.4.0]undecene-7, manufactured by Sunapro Co., Ltd.) • "Curezol (registered trademark)" 1,2-DMZ (1,2-dimethylimidazole, manufactured by Shikoku Chemicals Co., Ltd.) • "Hokko TPP (registered trademark)" (triphenylphosphine, manufactured by Hokko Sangyo Co., Ltd.) • “U-CAT (registered trademark)” SA102 (DBU·2-ethylhexanoate, manufactured by Sunapro Co., Ltd.) 4. Components (D): Core-shell rubber particles • "KaneAce (registered trademark)" MX-267 (a masterbatch consisting of 63 parts by mass of liquid bisphenol F type epoxy resin ("EPON (registered trademark)" 863, manufactured by Momentive Specialty Chemicals) and 37 parts by mass of core-shell polymer particles, manufactured by Kaneka Corporation) 5. Other ingredients • "TPP-PB (registered trademark)" (tetraphenylphosphonium bromide, manufactured by Hokko Sangyo Co., Ltd.) • Benzyltriethylammonium chloride (manufactured by Tokyo Chemical Industry Co., Ltd.).

[0047] <Preparation of epoxy resin composition> In a poly container, component (A): epoxy resin and component (D): core-shell rubber particles were added and kneaded appropriately until each component was miscible to obtain an epoxy main solution. In another poly container, component (B): acid anhydride and component (C): at least one compound selected from the group consisting of tertiary amines, tertiary phosphines, and their Brønsted salts were added and heated as necessary to make them miscible to obtain a curing agent solution. A predetermined amount of epoxy main solution and curing agent solution were mixed and kneaded in a universal stirrer for 2 minutes to obtain an epoxy resin composition. The resin composition is as shown in Table 1.

[0048] <Fabrication of carbon fibers> Carbon fibers [I] to [V] were produced using the following manufacturing methods.

[0049] <Carbon fiber[I]> Using a copolymer consisting of 99.4 mol% acrylonitrile and 0.6 mol% methacrylic acid, acrylic precursor fibers with a single fiber fineness of 0.08 tex and 12,000 filaments were obtained by wet-dry spinning.

[0050] This acrylic precursor fiber was heated in air at 240-280°C with a stretch ratio of 1.05 to convert it into a flame-resistant fiber. Then, it was heated in a nitrogen atmosphere in the temperature range of 300-900°C at a heating rate of 200°C / min with a stretch ratio of 1.10, and then calcined to 1,400°C to promote carbonization.

[0051] Next, an aqueous solution of ammonium bicarbonate with a concentration of 1.0 mol / L was used as the electrolyte, and the carbon fibers were subjected to electrolytic oxidation treatment in a 30 C / g· tank. Subsequently, the carbon fibers after this electrolytic oxidation treatment were washed with water and dried in air at 150°C to obtain carbon fiber [I].

[0052] The strand tensile strength of the carbon fiber [I] was 6.1 GPa, the strand tensile modulus was 294 GPa, the surface specific oxygen concentration (O / C) was 0.18, and the cross-sectional shape was substantially circular with an r / R ratio of 0.95.

[0053] <Carbon fiber[II]> Except for using a 3C / g· tank for the electrolytic oxidation treatment, carbon fiber [II] was prepared under the same conditions as carbon fiber [I], and carbon fiber [II] was obtained.

[0054] The strand tensile strength of the carbon fiber[II] was 5.8 GPa, the strand tensile modulus was 294 GPa, the surface specific oxygen concentration (O / C) was 0.08, and the cross-sectional shape was substantially circular with an r / R ratio of 0.95.

[0055] <Carbon fiber[III]> Except for using a 1 C / g· tank for the electrolytic oxidation treatment, carbon fiber [III] was prepared under the same conditions as carbon fiber [I], and carbon fiber [III] was obtained.

[0056] The strand tensile strength of the carbon fiber [III] was 6.0 GPa, the strand tensile modulus was 294 GPa, the surface specific oxygen concentration (O / C) was 0.03, and the cross-sectional shape was substantially circular with an r / R ratio of 0.95.

[0057] <Carbon fiber [IV]> The obtained acrylic precursor fiber had a single fiber fineness of 0.07 tex. Carbon fiber [IV] was obtained by preparing it under the same conditions as carbon fiber [II], except that the draw ratio during carbonization was changed to 1.00 and the maximum temperature during carbonization was changed to 1,200°C.

[0058] The strand tensile modulus of carbon fiber [IV] was 230 GPa, the strand tensile strength was 5.2 GPa, the surface specific oxygen concentration (O / C) was 0.12, and the cross-sectional shape was substantially circular with an r / R ratio of 0.94.

[0059] <Carbon fiber [V]> Carbon fiber [V] was obtained by changing the spinning method of the acrylic precursor fiber to a wet spinning method, and by preparing the acrylic precursor fiber under the same conditions as carbon fiber [IV], except that the single fiber fineness of the obtained acrylic precursor fiber was 0.08 tex.

[0060] The strand tensile strength of carbon fiber [V] was 3.5 GPa, the strand tensile modulus was 230 GPa, the surface specific oxygen concentration (O / C) was 0.10, and the cross-sectional shape was flattened with an r / R ratio of 0.80.

[0061] <Preparation of reinforced fiber substrates> The carbon fibers obtained in the above <Preparation of Carbon Fibers> are arranged in one direction and sewn together with stitching thread, resulting in a weight of 190 g / m². 2 A reinforced fiber base material was obtained. For the stitching thread, a 56dtex polyester yarn consisting of 24 filaments with a melting point Tma of 260°C was used. The knitted structure was a 1×1 modified tricot knit with a stitch length of 2.3 mm and a gauge length of 5 mm.

[0062] <Fabrication of carbon fiber reinforced composite materials> Eleven layers of the reinforced fiber substrate obtained in the above-mentioned <Preparation of Reinforced Fiber Substrate>, cut to 395mm x 395mm, were stacked with the carbon fiber direction aligned and placed in a mold having a plate-shaped cavity of 400mm x 400mm x 2mm. The mold was then clamped using a press device. Next, the temperature was maintained at 50°C, and the pressure was reduced to atmospheric pressure -0.1MPa using a vacuum pump. The epoxy resin composition obtained in the above-mentioned <Preparation of Epoxy Resin Composition>, which had been preheated to 50°C, was injected at a pressure of 0.2MPa. After heating treatment at 100°C for 1 hour, the mold was opened and demolded to obtain a carbon fiber reinforced composite material with the desired fiber volume content Vf of 58%.

[0063] <Evaluation of impregnation properties> In the above-mentioned <Fabrication of Carbon Fiber Reinforced Composite Materials>, the void ratio was evaluated by cross-sectional observation of the obtained carbon fiber reinforced composite material. Here, the void ratio is the percentage of the area occupied by voids relative to the area of ​​any given region when the polished cross-section of the carbon fiber reinforced composite material is observed with an optical microscope. Such voids refer to all types of voids in the carbon fiber reinforced composite material, including internal voids, surface pits, resin decay, and impregnation defects. Impregnation performance was evaluated on a three-point scale: good, medium, and poor. A void ratio of less than 0.3% was considered good, 0.3% to less than 1.0% was considered medium, and 1.0% or more was considered poor.

[0064] <Evaluation of Tg of carbon fiber reinforced composite materials> From the 2 mm thick carbon fiber reinforced composite material prepared in the above-mentioned "Fabrication of Carbon Fiber Reinforced Composite Material," a sample measuring 12.7 mm in width and 45 mm in length was cut using a diamond cutter. The DMA of this sample was measured in torsion mode using a dynamic viscoelasticity analyzer (ARES-G2: TA Instruments Inc.) under the following measurement conditions: torsional vibration frequency of 6.28 rad / s, strain of 0.08%, and heating rate of 5°C / min. The temperature at the inflection point of the storage modulus G' obtained from this measurement was defined as Tg.

[0065] <Evaluation of interlaminar shear strength of carbon fiber reinforced composite materials> From the 2 mm thick carbon fiber reinforced composite material prepared in the above-mentioned "Preparation of Carbon Fiber Reinforced Composite Material," a sample measuring 10 mm in width and 14 mm in length was cut using a diamond cutter. This sample was subjected to an interlaminar shear test of the carbon fiber reinforced composite material using an Instron universal testing machine (manufactured by Instron Corporation) in accordance with JIS K7078 (1991), and the interlaminar shear strength was measured.

[0066] <Evaluation of 0° compressive strength of carbon fiber reinforced composite materials> From the 2mm thick carbon fiber reinforced composite material prepared in the above-mentioned "Preparation of Carbon Fiber Reinforced Composite Material," a sample measuring 12.5mm in width and 78mm in length was cut using a diamond cutter. This sample was subjected to a 0° compression test for carbon fiber reinforced composite material using an Instron universal testing machine (manufactured by Instron Corporation) in accordance with JIS K7076 (1991), and its compressive strength was measured.

[0067] The following describes the sample preparation method and measurement results for each example.

[0068] (Example 1) An epoxy resin composition was obtained using 100 parts by mass of "EPICLON®" 830 as component (A), 104 parts by mass of "MHAC-P®" as component (B), and 3 parts by mass of "DBU®" as component (C), as described in <Preparation of Epoxy Resin Composition> above. A carbon fiber reinforced composite material was prepared by combining the obtained epoxy resin composition with a reinforced fiber substrate prepared using carbon fiber[II] according to <Preparation of Reinforced Fiber Substrate> above, and the properties were evaluated according to <Evaluation of Impregnation>, <Evaluation of Tg of Carbon Fiber Reinforced Composite Material>, <Evaluation of Interlaminar Shear Strength of Carbon Fiber Reinforced Composite Material>, and <Evaluation of 0° Compressive Strength of Carbon Fiber Reinforced Composite Material>. The results are shown in Table 1. It was confirmed that the impregnation was good, the Tg was excellent, and the interlaminar shear strength and 0° compressive strength were also good.

[0069] (Example 2) Except for replacing 50 parts by mass of “EPICLON®” 830 as component (A) with “GAN®”, the epoxy resin composition was prepared and various evaluations were carried out in the same manner as in Example 1. Although the Tg decreased slightly, the impregnation and interlaminar shear strength were good, and the 0° compressive strength was excellent.

[0070] (Example 3) Except for replacing component (C) with "Curesol®" 1,2-DMZ, the epoxy resin composition was prepared and various evaluations were carried out in the same manner as in Example 1. There were no problems with impregnation, and both Tg and interlaminar shear strength improved.

[0071] (Examples 4-5) Except for replacing component (C) as shown in Table 1, the epoxy resin composition was prepared and various evaluations were carried out in the same manner as in Example 1. Although the Tg decreased slightly, the interlaminar shear strength and 0° compressive strength were at acceptable levels.

[0072] (Example 6) Except for the use of carbon fiber[IV], the epoxy resin composition was prepared and various evaluations were carried out in the same manner as in Example 1. The interlaminar shear strength was greatly improved, and the 0° compressive strength was also excellent.

[0073] (Example 7) Except for incorporating 13.5 parts by mass of "Kaneace®" MX-267 as component (D) and using carbon fiber [IV], the epoxy resin composition was prepared and various evaluations were carried out in the same manner as in Example 2. The interlaminar shear strength was greatly improved, and the 0° compressive strength was also excellent.

[0074] (Comparative Examples 1-2) Except for changing the composition of the epoxy resin composition as shown in Table 1, the epoxy resin composition was prepared and various evaluations were carried out in the same manner as in Example 1. The impregnation deteriorated, and the Tg level was also insufficient.

[0075] (Comparative Example 3) Except for using carbon fiber [III], the epoxy resin composition was prepared and various evaluations were carried out in the same manner as in Example 1. Due to the reduced adhesion to the carbon fiber, the interlaminar shear strength was at an insufficient level, and the 0° compressive strength also deteriorated.

[0076] (Comparative Example 4) Except for using carbon fiber [V], the epoxy resin composition was prepared and various evaluations were carried out in the same manner as in Example 1. Due to the flattened cross-sectional shape of the carbon fiber, the impregnation deteriorated and the strand tensile strength decreased, resulting in an insufficient 0° compressive strength.

[0077] [Table 1]

[0078] Note that the units for each component in the table are parts by mass. [Industrial applicability]

[0079] The molding material for carbon fiber reinforced composite materials disclosed herein is excellent in that it can be molded without problems in impregnation or curing even at relatively low temperatures, and provides carbon fiber reinforced composite materials that exhibit the interlaminar shear strength and compressive strength necessary for weight reduction. As a result, the application of carbon fiber reinforced composite materials, which are required to have excellent productivity and to be able to handle large and complex-shaped components, will be expanded, leading to a reduction in energy consumption through weight reduction and is expected to contribute to the problem of global warming.

Claims

1. A molding material for carbon fiber reinforced composite materials comprising an epoxy resin composition containing the following components (A) to (C) and carbon fibers satisfying the following conditions [a] to [c]. (A): Epoxy resin (B): Acid anhydride (C): At least one compound selected from the group consisting of tertiary amines, tertiary phosphines, and their Brønsted salts. [a]: The strand tensile strength is 4 GPa or more and 8 GPa or less. [b]: The tensile modulus of the strand is between 230 GPa and 350 GPa. [c]: Surface specific oxygen concentration O / C is 0.05 or higher and 0.20 or lower.

2. The molding material for carbon fiber reinforced composite materials according to claim 1, wherein the epoxy resin composition comprises component (D): core-shell rubber particles.

3. The molding material for carbon fiber reinforced composite materials according to claim 1, wherein the component (A) comprises a glycidylamine type epoxy.

4. The molding material for carbon fiber reinforced composite materials according to claim 1, wherein the carbon fiber further satisfies the following conditions. [d]: The cross-sectional shape is substantially circular.

5. A carbon fiber reinforced composite material obtained by curing the molding material for carbon fiber reinforced composite materials according to claim 1.

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