Epoxy resin composition, prepreg, and fiber-reinforced composite material

Abstract

To provide an epoxy resin composition and a prepreg which achieve both storage stability and quick curability at a high level, and to provide a fiber-reinforced composite material having high water absorption resistance and mechanical characteristics.SOLUTION: The epoxy resin composition is used which contains an epoxy resin, a curing agent composition, and a curing accelerator. The epoxy resin contains 80 pts.mass or more of N,N,N',N'-tetraglycidyldiaminodiphenylmethane in 100 pts.mass of the epoxy resin. The curing agent composition comprises a combination of dicyandiamide, an aliphatic hydrazide compound, and an aromatic polyamine compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an epoxy resin composition, a cured resin, a fiber-reinforced composite material, and a method for producing the fiber-reinforced composite material. More specifically, the present invention relates to a fast-curing epoxy resin composition, a cured resin, a fiber-reinforced composite material, and a method for producing the fiber-reinforced composite material. [Background technology]

[0002] The present invention relates to an epoxy resin composition, a prepreg, and a fiber-reinforced composite material, and more particularly to an epoxy resin composition, a prepreg, and a fiber-reinforced composite material that can be molded in a short time and that produce molded articles having high water absorption resistance and mechanical properties.

[0003] Fiber-reinforced composite materials (hereinafter referred to as "FRP") are lightweight, strong, and rigid, and are therefore used in a wide range of fields, including sports and leisure applications such as fishing rods and golf shafts, and industrial applications such as automobiles and aircraft. A suitable method for producing FRP is to use an intermediate material (prepreg) in which a fiber reinforcement layer made of long fibers such as reinforcing fibers is impregnated with resin. Molded FRP products can be obtained by cutting the prepreg into the desired shape, shaping it, and curing it under heat and pressure.

[0004] In the aircraft industry, high mechanical properties such as heat resistance and impact resistance are required. Generally, prepregs using epoxy resins require a long molding time. Furthermore, molded articles obtained by curing prepregs using epoxy resins have insufficient water absorption resistance and absorb water at high temperatures, which can lead to a decrease in mechanical properties such as impact resistance.

[0005] Patent Document 1 discloses a prepreg comprising a fiber-reinforced substrate made of carbon fiber and an epoxy resin composition partially or completely impregnated into the fiber-reinforced substrate, characterized in that the epoxy resin composition contains an epoxy resin, dicyandiamide, and a specific aromatic amine. Carbon fiber-reinforced composite materials produced using this prepreg have high water absorption. Furthermore, this prepreg, which contains a urea-based accelerator, has a short gel time, allowing for molding in a short period of time. Furthermore, this prepreg, which contains thickening particles, has high press moldability and can stabilize the quality of CFRP. However, fiber-reinforced composite materials with even better mechanical properties are desired.

[0006] Patent Document 2 discloses a prepreg comprising a fiber-reinforced substrate made of carbon fiber and an epoxy resin composition partially or completely impregnated into the fiber-reinforced substrate, characterized in that the epoxy resin composition contains an epoxy resin, dicyandiamide, and an aromatic hindered amine. Carbon fiber-reinforced composite materials produced using this prepreg are imparted with water absorption resistance due to the effect of the hindered amine. Furthermore, this prepreg, which is composed of a urea-based accelerator, has a short gel time, allowing for molding in a short period of time. Furthermore, this prepreg, which is composed of thickening particles, has high press moldability and can stabilize the quality of CFRP. However, there is a demand for fiber-reinforced composite materials with improved mechanical properties. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2019-156982 [Patent Document 2] Patent Publication No. 2023-56441 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an epoxy resin composition and prepreg which achieve both high levels of storage stability and fast curing properties. Another object of the present invention is to provide a fiber-reinforced composite material which has excellent water absorption resistance and mechanical properties. [Means for solving the problem]

[0009] As a result of investigations aimed at solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using a combination of a predetermined epoxy resin, a curing agent composition, and a curing accelerator, and by using a combination of dicyandiamide, an aliphatic hydrazide compound, and an aromatic polyamine compound as the curing agent composition, and have thus completed the present invention.

[0010] The present invention that achieves the above object is described below.

[0011] [1] An epoxy resin composition comprising an epoxy resin, a curing agent composition, and a curing accelerator, the epoxy resin contains 80 parts by mass or more of N,N,N',N'-tetraglycidyldiaminodiphenylmethane per 100 parts by mass of the epoxy resin, Epoxy resin composition, characterized in that the curing agent composition comprises a combination of dicyandiamide, an aliphatic hydrazide compound, and an aromatic polyamine compound.

[0012] [2] The epoxy resin composition according to claim 1, wherein the content of the aliphatic hydrazide compound in the curing agent composition is in the range of 20% by mass or more and 70% by mass or less.

[0013] [3] The epoxy resin composition according to claim 1 or 2, further comprising a thermoplastic resin.

[0014] [4] The epoxy resin composition according to claim 1 or 2, further comprising thickening particles made of a polymer having one or more polymerization units selected from the group consisting of methacrylic acid ester compounds, acrylic acid ester compounds, and vinyl ester compounds.

[0015] [5] A reinforcing fiber substrate; the epoxy resin composition according to claim 1 impregnated in the reinforcing fiber substrate; A prepreg consisting of A prepreg characterized in that a part or all of the aliphatic hydrazide compound is present in the form of particles in the epoxy resin composition.

[0016] [6] A reinforcing fiber substrate; A cured resin product of the epoxy resin composition according to claim 1; A fiber-reinforced composite material characterized by being formed by combining the above. [Effects of the Invention]

[0017] According to the present invention, there are provided an epoxy resin composition and a prepreg which have both high storage stability and fast curing properties; and a fiber-reinforced composite material which has high water absorption resistance and excellent mechanical properties. DETAILED DESCRIPTION OF THE INVENTION

[0018] The epoxy resin composition, prepreg, and fiber-reinforced composite material of the present invention will be described below. Fiber-reinforced composite material may be abbreviated as "FRP," and carbon fiber-reinforced composite material may be abbreviated as "CFRP." Furthermore, unless otherwise specified, the various physical properties are measured at 25°C and atmospheric pressure. In this specification, the term "epoxy resin composition" refers to a substance in an uncured or semi-cured state, and after the epoxy resin composition has cured, it is called a cured product or a cured resin product.

[0019] 1. Epoxy resin composition The epoxy resin composition of the present invention comprises: Epoxy resin, a curing agent composition; A curing accelerator; An epoxy resin composition comprising: the epoxy resin contains 80 parts by mass or more of N,N,N',N'-tetraglycidyldiaminodiphenylmethane per 100 parts by mass of the epoxy resin, The curing agent composition is characterized by comprising a combination of dicyandiamide, an aliphatic hydrazide compound, and an aromatic polyamine compound. In the epoxy resin composition of the present invention, the content of the aliphatic hydrazide compound in the curing agent composition is preferably in the range of 20% by mass or more and 70% by mass or less. The epoxy resin composition of the present invention may contain a thermoplastic resin. The epoxy resin composition of the present invention may contain thickening particles made of a polymer having one or more polymerization units selected from the group consisting of methacrylate compounds, acrylate compounds, and vinyl ester compounds.

[0020] The epoxy resin composition of the present invention is heat-cured at 180°C for 30 minutes, and the resulting cured product is then treated in a pressure cooker (HASTEST PC-422R8, manufactured by Espec Corporation) at 121°C for 24 hours to obtain a resin test piece. The glass transition temperature (Wet-Tg) of the test piece is preferably 130°C or higher, more preferably 140°C or higher, and particularly preferably 150°C or higher. A glass transition temperature of 150°C or higher is preferred because the product is less likely to deform even when the FRP is used under heat-exposed conditions, such as during painting.

[0021] The epoxy resin composition of the present invention preferably has a flexural modulus of 3.0 GPa or more, more preferably 3.2 GPa or more, of the cured product obtained by heat curing at 180°C for 30 minutes. If the flexural modulus is 3.0 GPa or more, FRP produced using the epoxy resin of the present invention can have excellent mechanical properties.

[0022] The epoxy resin composition of the present invention has a deformation mode I critical stress intensity factor KIc of 0.96 MPa m for the cured resin, as measured according to ASTM D5045. 1 / 2 It is preferable that the pressure is 1.00 MPa m or more. 1 / 2 When the content exceeds the lower limit, the fiber reinforced composite material obtained by using the epoxy resin composition of the present invention has better impact properties.

[0023] The epoxy resin composition of the present invention preferably achieves a degree of cure of 93% or more, and more preferably 95% or more, of the cured resin product obtained when heated at 180°C for 30 minutes. The degree of cure of the cured resin product is evaluated by DSC measurement of the heat release amount when the cured resin product is reheated after heating at 180°C for 30 minutes (see the Examples below). If the degree of cure is less than 93%, the rapid curing property is poor, and the productivity of the cured resin product and fiber-reinforced composite material is likely to decrease.

[0024] 1-1.Epoxy resin The epoxy resin composition of the present invention contains N,N,N',N'-tetraglycidyldiaminodiphenylmethane as the epoxy resin in an amount of 80 parts by mass or more relative to 100 parts by mass of the total epoxy resin. The amount of this epoxy resin blended is preferably 90 parts by mass or more relative to 100 parts by mass of the total epoxy resin. If the amount is less than 80 parts by mass, the mechanical properties of the resulting cured product may not be sufficiently high.

[0025] The epoxy resin composition of the present invention may contain an epoxy resin other than N,N,N',N'-tetraglycidyldiaminodiphenylmethane. There are no particular limitations on the type of epoxy resin. Specific examples include bifunctional epoxy resins such as bisphenol-type epoxy resins, alcohol-type epoxy resins, biphenyl-type epoxy resins, hydrophthalic acid-type epoxy resins, dimer acid-type epoxy resins, and alicyclic epoxy resins; glycidyl ether-type epoxy resins such as tetrakis(glycidyloxyphenyl)ethane and tris(glycidyloxyphenyl)methane; glycidylamine-type epoxy resins such as tetraglycidyldiaminodiphenylmethane; naphthalene-type epoxy resins; and novolac-type epoxy resins such as phenol novolac-type epoxy resins and cresol novolac-type epoxy resins.

[0026] Further examples include polyfunctional epoxy resins such as phenolic epoxy resins, etc. Also usable are various modified epoxy resins such as urethane-modified epoxy resins and rubber-modified epoxy resins.

[0027] In particular, epoxy resins having an aromatic group in the molecule are preferred, and epoxy resins having either a glycidyl amine structure or a glycidyl ether structure are more preferred.

[0028] Examples of epoxy resins having a glycidylamine structure include N,N,O-triglycidyl-p-aminophenol, N,N,O-triglycidyl-m-aminophenol, N,N-diglycidyl-o-toluidine, and N,N-diglycidylaniline.

[0029] Examples of epoxy resins having a glycidyl ether structure include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, phenol novolac type epoxy resins, and cresol novolac type epoxy resins.

[0030] If necessary, these epoxy resins may have a non-reactive substituent in the aromatic ring structure, etc. Examples of the non-reactive substituent include alkyl groups such as methyl, ethyl, and isopropyl groups; aromatic groups such as phenyl groups; alkoxyl groups; aralkyl groups; and halogen groups such as chlorine and bromine.

[0031] Examples of bisphenol-type epoxy resins include bisphenol A-type resins, bisphenol F-type resins, bisphenol AD-type resins, bisphenol S-type resins, etc. Specific examples include jER815, jER828, jER834, jER1001, and jER807 (product names) manufactured by Mitsubishi Chemical Corporation, Epomic R-710 (product name) manufactured by Mitsui Petrochemicals, and EXA1514 (product name) manufactured by Dainippon Ink and Chemicals, Inc.

[0032] Examples of alicyclic epoxy resins include Araldite CY-179, CY-182, and CY-183 (trade names) manufactured by Huntsman.

[0033] Examples of phenol novolac epoxy resins include jER152 and jER154 (trade names) manufactured by Mitsubishi Chemical Corporation, DEN431, DEN485, and DEN438 (trade names) manufactured by The Dow Chemical Company, and Epiclon N740 (trade name) manufactured by DIC Corp. Examples of cresol novolac epoxy resins include Araldite ECN1235, ECN1273, and ECN1280 (trade names) manufactured by Huntsman Chemical Company, EOCN102, EOCN103, and EOCN104 (trade names) manufactured by Nippon Kayaku Co., Ltd., Epotohto YDCN-700-10 and Epotohto YDCN-704 (trade names) manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., and Epiclon N680 and Epiclon N695 (trade names) manufactured by DIC Corp.

[0034] Examples of epoxy resins having a glycidyl amine structure include Sumiepoxy ELM434, Sumiepoxy ELM120, and Sumiepoxy ELM100 (trade names) manufactured by Sumitomo Chemical Co., Ltd.; Araldite MY0500, Araldite MY0510, Araldite MY0600, Araldite MY720, Araldite MY721, Araldite MY9512, Araldite MY9612, and Araldite MY9634 (trade names) manufactured by Huntsman Advanced Materials; jER604 and jER630 (trade names) manufactured by Mitsubishi Chemical Corporation; and Bakelite EPR494, Bakelite EPR495, Bakelite EPR496, and Bakelite EPR497 (trade names) manufactured by Bakelite AG.

[0035] Examples of various modified epoxy resins include urethane-modified bisphenol A type epoxy, such as Adeka Resin EPU-6 and EPU-4 (trade names) manufactured by Asahi Denka.

[0036] These epoxies can be appropriately selected and used alone or in combination of two or more.

[0037] 1-2. Curing agent composition and curing accelerator The epoxy resin composition of the present invention contains a curing agent composition comprising a combination of dicyandiamide, an aliphatic hydrazide compound, and an aromatic polyamine compound, and a curing accelerator.

[0038] 1-2-1. Dicyandiamide In the present invention, dicyandiamide is used as a curing agent for the above epoxy resin because of its excellent curability and the physical properties of the resulting cured product. Specific examples of dicyandiamide (DICY) include jER Cure DICY7 and DICY15 (trade names) manufactured by Mitsubishi Chemical Corporation.

[0039] The amount of dicyandiamide blended is preferably in the range of 2 to 5 parts by mass, and more preferably in the range of 2 to 4 parts by mass, per 100 parts by mass of the total epoxy resin. When the amount of dicyandiamide blended is 2 parts by mass or more, sufficient crosslink density and a sufficient curing rate can be obtained. When the amount of dicyandiamide blended is 5 parts by mass or less, defects such as a decrease in the mechanical properties of the cured product and cloudiness of the cured product due to the presence of an excess curing agent can be suppressed.

[0040] 1-2-2. Curing accelerator Dicyandiamide is preferably used in combination with a urea-based curing accelerator. Because dicyandiamide is not very soluble in epoxy resins, it must be heated to a high temperature of 160°C or higher to fully dissolve. However, by using it in combination with a urea-based curing accelerator, the dissolution temperature can be lowered.

[0041] Examples of urea-based curing accelerators include phenyldimethylurea (PDMU) and toluenebisdimethylurea (DBDMU).

[0042] Curing accelerators other than urea compounds include imidazole compounds and imidazole-adduct compounds. The use of imidazole compounds and imidazole-adduct compounds induces internal heat generation during the reaction, making it possible to increase the solubility of dicyandiamide.

[0043] Examples of imidazole compounds include Curesol 2PHZ-PW, 2E4MZ-A, and C11Z-CN (trade names) manufactured by Shikoku Chemicals Corporation, etc. Examples of imidazole-adduct compounds include Amicure PN-31 and PN-50 (trade names) manufactured by Ajinomoto Fine-Techno Co., Ltd.

[0044] The amount of the curing accelerator to be added is preferably in the range of 1 part by mass or more and 8 parts by mass or less per 100 parts by mass of the total epoxy resin. However, the total amount of dicyandiamide and the curing accelerator is preferably in the range of 2 parts by mass or more and 12 parts by mass or less per 100 parts by mass of the total epoxy resin. When the total amount of dicyandiamide and curing accelerator is 2 parts by mass or more, sufficient crosslink density and a sufficient curing rate are obtained.When the total amount of dicyandiamide and curing accelerator is 12 parts by mass or less, problems such as deterioration of mechanical properties of the cured product and turbidity of the cured product due to the presence of an excess of curing agent can be suppressed.

[0045] 1-2-3. Aromatic polyamines In the present invention, an aromatic polyamine is further used as a curing agent. The aromatic polyamine used in the present invention is represented by the following formula (1):

[0046] [ka]

[0047] (In chemical formula (1), R1 to R8 each independently represent a hydrogen atom, an aliphatic substituent having 1 to 6 carbon atoms, an aromatic substituent, or a halogen atom; and X represents -CH2-, -CH(CH3)-, -C(CH3)2-, -S-, -SO2-, -O-, -CO-, -CONH-, or -C(=O)-.) It is a compound represented by the formula:

[0048] Specific examples include compounds represented by the following formulas (2) to (6).

[0049] [ka]

[0050] [ka]

[0051] [ka]

[0052] [ka]

[0053] [ka]

[0054] The amount of aromatic polyamine blended is in the range of 3 to 20 parts by mass, preferably 5 to 20 parts by mass, per 100 parts by mass of the total epoxy resin. If the amount of aromatic polyamine blended is less than 3 parts by mass, sufficient crosslinking cannot be formed in the cured product, and sufficient mechanical properties cannot be obtained. Furthermore, if the amount of aromatic polyamine blended is more than 20 parts by mass, the reaction between the epoxy resin and the aromatic polyamine will deteriorate the storage stability of the prepreg.

[0055] 1-2-4. Aliphatic dihydrazide compounds In the present invention, an aliphatic dihydrazide compound is further used as a latent curing agent. The aliphatic dihydrazide compound used in the present invention preferably has a melting point in the range of 160°C to 200°C. If the melting point is lower than 160°C, the reaction between the epoxy resin and the aliphatic dihydrazide compound will deteriorate the storage stability of the prepreg. If the melting point is higher than 200°C, the compound may not melt within the reaction time or the reaction with the epoxy resin may not proceed completely. As a result, problems such as a decrease in the mechanical properties of the cured product or cloudiness of the cured product may occur.

[0056] Examples of the aliphatic dihydrazide compounds include adipic acid dihydrazide, sebacic acid dihydrazide, and dodecanediohydrazide.

[0057] The amount of the aliphatic dihydrazide compound is in the range of 3 to 20 parts by mass, preferably 5 to 15 parts by mass, per 100 parts by mass of the total epoxy resin. If the amount of the aliphatic dihydrazide compound is less than 3 parts by mass, sufficient crosslinking cannot be formed in the cured product, and sufficient mechanical properties cannot be obtained. If the amount of the aliphatic dihydrazide compound is more than 20 parts by mass, the compound may not melt within the reaction time or the reaction with the epoxy resin may not proceed completely. This results in problems such as a decrease in the mechanical properties of the cured product and cloudiness of the cured product.

[0058] The content of the aliphatic hydrazide compound in the curing agent composition is preferably in the range of 20% by mass to 70% by mass, more preferably in the range of 30% by mass to 60% by mass. If it is less than 20% by mass, storage stability is likely to decrease. If it exceeds 70% by mass, the proportion of the latent curing agent is too high, and the curing reaction may be insufficient.

[0059] 1-3. Thermoplastic resin The epoxy resin composition of the present invention may contain a thermoplastic resin. As the thermoplastic resin, a group of thermoplastic resins belonging to engineering plastics, such as polysulfone, polyetherimide, polyphenylene ether, polyamide, polyacrylate, polyaramid, polyester, polycarbonate, polyphenylene sulfide, polybenzimidazole, polyimide, polyethersulfone, polyketone, polyetherketone, polyetheretherketone, and polyvinyl formal, is more preferably used. Polyimide, polyetherimide, polysulfone, polyethersulfone, and polyvinyl formal are particularly preferably used because of their excellent heat resistance, toughness, and ease of handling.

[0060] The thermoplastic resin may be blended in any form. For example, a powdered thermoplastic resin may be kneaded and dispersed in the epoxy resin using a kneader or the like, or the thermoplastic resin may be dissolved in the epoxy resin by heating in the epoxy resin. The epoxy resin composition preferably contains a thermoplastic resin to be dissolved in the epoxy resin and a thermoplastic resin to be dispersed in the epoxy resin in combination.

[0061] The particle size of the powdered thermoplastic resin is preferably 0.2 μm or more and 100 μm or less, and more preferably 0.5 μm or more and 80 μm or less.

[0062] The amount of the thermoplastic resin to be added is preferably in the range of 5 parts by mass to 45 parts by mass, more preferably in the range of 10 parts by mass to 40 parts by mass, per 100 parts by mass of the epoxy resin.

[0063] 1-4. Thickening particles The epoxy resin composition of the present invention may contain thickening particles. The thickening particles in the present invention are particles that, when mixed with an epoxy resin composition and heated, swell at a predetermined temperature, thereby thickening the epoxy resin composition. Specifically, the thickening particles refer to resin particles that, when mixed at 10% by mass with the epoxy resin composition, increase the viscosity of the epoxy resin composition (viscosity after being held at 150°C for 30 seconds) by 10 times or more, preferably 50 times or more.

[0064] Examples of thickening particles include particles obtained by copolymerizing one or more unsaturated compounds with a crosslinkable monomer. Although not particularly limited, it is preferable that the thickening particles contain a resin having at least one of an acrylic acid ester compound, a methacrylic acid ester compound, and a vinyl compound as a monomer unit.

[0065] The epoxy resin composition of the present invention containing thickening particles has a low viscosity before the thickening particles swell. This facilitates resin impregnation into the fiber-reinforced substrate during prepreg production. Furthermore, during heat molding, the viscosity of the epoxy resin composition is increased within a predetermined temperature range using the thickening particles. Therefore, the epoxy resin composition has a temperature range in which viscosity change is gradual, and molding within this temperature range allows for control of resin flow within the prepreg. As a result, FRP produced using the prepreg of the present invention is less susceptible to molding defects such as resin drying.

[0066] The acrylate compound used in the thickening particles refers to a compound having an acrylate structure and its derivatives, and examples thereof include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, t-butyl acrylate, n-hexyl acrylate, and cyclohexyl acrylate.

[0067] The methacrylic acid ester compound used in the thickening particles refers to a compound having a methacrylic acid ester structure and its derivatives, and examples thereof include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, n-hexyl methacrylate, and cyclohexyl methacrylate.

[0068] The vinyl compound used in the thickening particles refers to a compound having a polymerizable vinyl structure, and examples thereof include styrene, α-methylstyrene, divinylbenzene, and compounds in which the aromatic rings of these compounds are substituted with various functional groups such as alkyl groups and halogen atoms.

[0069] The thickening particles may be a polymer consisting of one or more polymerized units of a methacrylic acid ester compound, an acrylic acid ester compound, or a vinyl compound, or may be a resin consisting of a mixture of two or more resins with different structures.Furthermore, the thickening particles may be a composite resin ionically crosslinked by adding (iii) metal ions to (i) a polymer consisting of at least one of an acrylic acid ester compound, a methacrylic acid ester compound, and a diene compound, and (ii) a polymer consisting of an acrylic acid ester compound or a methacrylic acid ester compound and a radically polymerizable unsaturated carboxylic acid.

[0070] The thickening particles are preferably polymers comprising one or more polymer units selected from the group consisting of methacrylic acid ester compounds, acrylic acid ester compounds and vinyl compounds, and more preferably alkyl methacrylate polymers.

[0071] The thickening particles preferably have an average degree of polymerization of 4,000 or more and 40,000 or less.

[0072] As thickening particles, it is also preferable to use commercially available products made of alkyl methacrylate polymers without a core-shell structure, such as Zefiac F325 and Zefiac F320 (both manufactured by Aica Kogyo Co., Ltd.). However, alkyl methacrylate polymers with a core-shell structure are not preferred because they are less likely to swell in a thermosetting resin composition due to the shell structure, and have a low viscosity-increasing effect.

[0073] The particle size of the thickening particles is not particularly limited, but the average particle size is preferably 0.3 μm to 10 μm, more preferably 0.5 μm to 0.8 μm. When thickening particles are added, the content is preferably 1 part by mass to 15 parts by mass, more preferably 2 parts by mass to 12 parts by mass, and particularly preferably 3 parts by mass to 10 parts by mass, per 100 parts by mass of the epoxy resin.

[0074] The thickening particles dispersed in the epoxy resin swell within the epoxy resin upon heating. The swelling of the thickening particles progresses with temperature and time, and the viscosity of the epoxy resin increases rapidly as the thickening particles swell.

[0075] The epoxy resin has a low viscosity before the thickening particles swell, so it has excellent impregnation properties into the reinforcing fiber substrate layer. When the thickening particles swell and the viscosity of the epoxy resin increases in the reinforcing fiber substrate layer, resin flow during molding is suppressed. As a result, both resin impregnation properties and resin flow suppression can be achieved at a high level.

[0076] The thickening start temperature (T1) of the epoxy resin composition containing the thickening particles is preferably 80° C. or higher and 110° C. or lower, and more preferably 85° C. or higher and 110° C. or lower. The thickening end temperature (T2) is preferably 85° C. or higher and 130° C. or lower, and more preferably 90° C. or higher and 130° C. or lower.

[0077] Furthermore, T2-T1 is preferably 5°C or higher and 20°C or lower, and more preferably 7°C or higher and 20°C or lower. If T2-T1 is lower than 5°C, the viscosity of the resin composition impregnated in the prepreg increases rapidly during molding, becoming too high and likely to cause defects such as voids inside the resulting FRP, resulting in poor performance. If T2-T1 exceeds 20°C, the viscosity of the resin composition impregnated in the prepreg becomes unstable during molding, causing the resin composition to flow rapidly, resulting in poor appearance and performance in the resulting FRP, such as resin drying and fiber meandering.

[0078] 1-5. Other additives The epoxy resin composition of the present invention may contain an inorganic filler, a flame retardant, and an internal mold release agent.

[0079] Examples of inorganic fillers include aluminum borate, calcium carbonate, silicon carbonate, silicon nitride, potassium titanate, basic magnesium sulfate, zinc oxide, graphite, calcium sulfate, magnesium borate, magnesium oxide, talc, mica, kaolin clay, montmorillonite, and metal hydroxides. Among these, talc and kaolin clay are preferred from the viewpoint of improving the resin elastic modulus. Examples of commercially available talc products include Nano Ace D1000 (manufactured by Nippon Talc Co., Ltd.), Nano Ace D-800 (manufactured by Nippon Talc Co., Ltd.), D-600 (manufactured by Nippon Talc Co., Ltd.), and FG-15 (manufactured by Nippon Talc Co., Ltd.). Also, an example of commercially available kaolin clay is Ultrex 96 (manufactured by KaMin LLC).

[0080] The average particle size D50 of inorganic fillers such as talc and kaolin clay is preferably 5 μm or less, more preferably 2 μm or less. Inorganic fillers with particle sizes larger than 5 μm have poor dispersibility in epoxy resins, making it difficult to obtain the effect of improving the elastic modulus.

[0081] The amount of inorganic filler such as talc or kaolin clay to be added is preferably in the range of 1 to 15 parts by mass, more preferably 3 to 10 parts by mass, per 100 parts by mass of epoxy resin. Addition of more than 15 parts by mass is economically undesirable because the effect of improving physical properties according to the amount added is limited.

[0082] Examples of the flame retardant include phosphorus-based flame retardants, which are not particularly limited as long as they contain a phosphorus atom in the molecule, and examples thereof include organic phosphorus compounds such as phosphate esters, condensed phosphate esters, phosphazene compounds, and phosphinates.

[0083] Examples of commercially available internal release agents include metal soaps, vegetable waxes such as polyethylene wax and carnauba wax, fatty acid ester-based release agents, silicone oil, animal wax, and fluorine-based nonionic surfactants. The amount of these internal release agents added is preferably in the range of 0.1 to 5 parts by mass, more preferably 0.2 to 2 parts by mass, per 100 parts by mass of the epoxy resin. Within this range, the release effect from the mold is particularly well exhibited.

[0084] Examples of commercially available internal mold release agents include MOLD WIZ (registered trademark) INT1846 (manufactured by AXEL PLASTICS RESEARCH LABORATORIES INC.), Licowax S, Licowax P, Licowax OP, Licowax PE190, and Licowax PED (manufactured by Clariant Japan), and stearyl stearate (SL-900A; manufactured by Riken Vitamin Co., Ltd.).

[0085] 1-6. Method for producing epoxy resin composition The epoxy resin composition of the present invention can be produced by mixing an epoxy resin, dicyandiamide, a curing accelerator, an aromatic polyamine compound, and an aliphatic dihydrazide compound, in any order.

[0086] When a thermoplastic resin is mixed to improve impact resistance, the composition can be produced by mixing an epoxy resin, dicyandiamide, a curing accelerator, an aromatic polyamine compound, an aliphatic dihydrazide compound, and a thermosetting resin, in any order.

[0087] Furthermore, when thickening particles are further mixed, the composition can be produced by mixing an epoxy resin, dicyandiamide, a curing accelerator, an aromatic polyamine compound, an aliphatic dihydrazide compound, a thermosetting resin, and thickening particles, and the order of these steps does not matter.

[0088] Furthermore, when an inorganic filler is mixed, the composition can be produced by mixing an epoxy resin, dicyandiamide, a curing accelerator, an aromatic polyamine compound, an aliphatic dihydrazide compound, a thermosetting resin, thickening particles, and an inorganic filler, and the order of these ingredients does not matter.

[0089] The method for producing the epoxy resin composition is not particularly limited, and any conventionally known method may be used. The mixing temperature can be, for example, in the range of 40°C or higher and 120°C or lower. If the temperature exceeds 120°C, the curing reaction may proceed partially, reducing the impregnation into the fiber-reinforced substrate layer, and the storage stability of the resulting resin composition and the prepreg produced using it may be reduced. If the temperature is lower than 40°C, the viscosity of the resin composition may be high, making mixing substantially difficult. The temperature is preferably in the range of 50°C or higher and 100°C or lower, and more preferably in the range of 50°C or higher and 90°C or lower.

[0090] From the viewpoint of ease of handling during resin kneading, the epoxy resin composition of the present invention preferably has a viscosity at 60°C of less than 500 Pa·s, more preferably less than 300 Pa·s, and particularly preferably less than 200 Pa·s. If the viscosity is 500 Pa·s or more, problems may arise such that the load on the kneading device becomes too great during kneading of the resin composition, making it difficult to carry out the kneading, or that the viscosity immediately after removal is too high to handle.

[0091] Conventional known mixing machines can be used. Specific examples include a roll mill, a planetary mixer, a kneader, an extruder, a Banbury mixer, a mixing vessel equipped with stirring blades, and a horizontal mixing tank. The components can be mixed in the air or in an inert gas atmosphere. When mixing is carried out in the air, an atmosphere in which the temperature and humidity are controlled is preferred. Although not particularly limited, mixing is preferably carried out at a constant temperature of 30°C or less, or in a low-humidity atmosphere with a relative humidity of 50% RH or less.

[0092] 2. Prepreg The prepreg of the present invention comprises the above-mentioned epoxy resin composition of the present invention and a fiber-reinforced substrate, and the epoxy resin composition is partly or entirely impregnated into the layer of the fiber-reinforced substrate and is integrated with the fiber-reinforced substrate.

[0093] The epoxy resin composition content (RC) in the prepreg of the present invention is preferably in the range of 15% by mass to 60% by mass, more preferably 20% by mass to 50% by mass, and particularly preferably 25% by mass to 45% by mass, based on the total mass of the prepreg. If the content is less than 15% by mass, voids may occur in the resulting FRP, which may reduce the mechanical properties. If the content exceeds 60% by mass, the reinforcing effect of the reinforcing fibers may be insufficient, which may reduce the mechanical properties of the resulting FRP.

[0094] The epoxy resin composition content (RC) can be determined by immersing the prepreg in sulfuric acid to elute the resin composition impregnated in the prepreg. Specifically, it can be determined by the following method.

[0095] First, a test piece measuring 100 mm x 100 mm is prepared by cutting the prepreg into a piece, and its mass is measured. The prepreg test piece is then immersed in sulfuric acid and boiled if necessary. This decomposes the resin composition impregnated in the prepreg and dissolves it in the sulfuric acid. The remaining fibers are then filtered and washed with sulfuric acid, and then dried, and the mass of the fibers is measured. The resin composition content is calculated from the change in mass before and after the decomposition operation with sulfuric acid.

[0096] The prepreg of the present invention may have a structure consisting of a fiber-reinforced substrate, a reinforcing layer made of an epoxy resin composition impregnated into the fiber-reinforced substrate layer, and a resin coating layer laminated on the surface of the reinforcing layer. The thickness of the resin coating layer is preferably in the range of 2 μm to 50 μm. If the thickness of the resin coating layer is less than 2 μm, the tackiness may be insufficient, and the molding processability of the prepreg may be significantly reduced. If the thickness of the resin coating layer exceeds 50 μm, it may be difficult to wind the prepreg into a roll with a uniform thickness, and molding accuracy may be significantly reduced. The thickness of the resin coating layer is more preferably in the range of 5 μm to 45 μm, and particularly preferably in the range of 10 μm to 40 μm.

[0097] 2-1. Fiber-reinforced substrate When PAN-based carbon fibers are used as the fiber-reinforced substrate, their tensile modulus is preferably 100 GPa or more and 600 GPa or less, more preferably 200 GPa or more and 500 GPa or less, and particularly preferably 230 GPa or more and 450 GPa or less. The tensile strength is 2,000 MPa or more and 10,000 MPa or less, preferably 3,000 MPa or more and 8,000 MPa or less. The diameter of the carbon fibers is preferably 4 μm or more and 20 μm or less, more preferably 5 μm or more and 10 μm or less. The use of such carbon fibers can improve the mechanical properties of the resulting FRP.

[0098] The fiber-reinforced substrate is preferably formed into a sheet for use. Examples of the fiber-reinforced substrate sheet include a sheet in which a large number of reinforcing fibers are aligned in one direction, a bidirectional fabric such as a plain weave or twill weave, a multiaxial fabric, a nonwoven fabric, a mat, a knit, a braid, and paper made from reinforcing fibers.

[0099] The thickness of the fiber-reinforced substrate sheet is preferably 0.01 mm or more and 3 mm or less, and more preferably 0.1 mm or more and 1.5 mm or less. These fiber-reinforced substrates may contain a known sizing agent in a known amount.

[0100] The prepreg of the present invention may be a strand prepreg in which carbon fibers are formed into strands. The strand prepreg is produced by splitting a sheet-like unidirectional prepreg. The width of the strand prepreg is preferably 3 mm or more and 20 mm or less, and more preferably 6 mm or more and 10 mm or less. The strand prepreg is preferably cut in the length direction to form a short fiber prepreg. The fiber length is preferably 5 mm or more and 100 mm or less, and more preferably 10 mm or more and 50 mm or less. The short fiber prepreg after cutting is preferably formed into a mat to form a prepreg mat.

[0101] 2-2. Prepreg manufacturing method The method for producing the prepreg of the present invention is not particularly limited, and any conventionally known method can be used. Specifically, the hot melt method and the solvent method can be preferably used.

[0102] The hot melt method is a method in which a resin composition is applied in the form of a thin film onto release paper to form a resin composition film, and the resin composition film is laminated onto a fiber-reinforced substrate and heated under pressure to impregnate the resin composition into the fiber-reinforced substrate layer.

[0103] The method for forming the resin composition into a resin composition film is not particularly limited, and any conventionally known method can be used. Specifically, a resin composition film can be obtained by casting the resin composition onto a support such as release paper or film using die extrusion, an applicator, a reverse roll coater, a comma coater, or the like. The resin temperature during film production is determined appropriately depending on the composition and viscosity of the resin composition. Specifically, the same temperature conditions as the mixing temperature in the above-mentioned method for producing an epoxy resin composition are preferably used. The epoxy resin composition can be impregnated into the fiber-reinforced substrate layer in one step or in multiple steps.

[0104] The solvent method is a method in which an epoxy resin composition is made into a varnish using an appropriate solvent, and the varnish is impregnated into the fiber-reinforced substrate layer.

[0105] Of these conventional methods, the prepreg of the present invention can be suitably produced by the hot melt method, which does not use a solvent.

[0106] When the epoxy resin composition film is impregnated into the fiber-reinforced substrate layer by the hot melt method, the impregnation temperature is preferably in the range of 50°C or higher and 120°C or lower. If the impregnation temperature is lower than 50°C, the viscosity of the epoxy resin composition is high and it may not be sufficiently impregnated into the fiber-reinforced substrate layer. If the impregnation temperature exceeds 120°C, the curing reaction of the epoxy resin may proceed, which may result in a decrease in the storage stability or drapeability of the obtained prepreg. The impregnation temperature is more preferably 60°C or higher and 110°C or lower, and particularly preferably 70°C or higher and 100°C or lower.

[0107] The impregnation pressure when the epoxy resin composition film is impregnated into the fiber reinforced substrate layer by the hot melt method is determined appropriately taking into consideration the viscosity and resin flow of the resin composition.

[0108] 3. Fiber-reinforced composite materials (FRP) The FRP of the present invention can be obtained by curing the prepreg of the present invention under heat and pressure. Examples of methods for producing FRP using the prepreg of the present invention include autoclave molding, press molding, internal pressure molding, and vacuum-assisted compressed air molding.

[0109] 3-1. Autoclave molding method The preferred method for producing the FRP of the present invention is the autoclave molding method. The autoclave molding method involves sequentially placing a prepreg and a film bag in the lower mold of a metal mold, sealing the prepreg between the lower mold and the film bag, evacuating the space formed by the lower mold and the film bag, and then applying heat and pressure in an autoclave molding machine. The molding conditions are preferably a temperature rise rate of 1°C / min to 50°C / min, and heating and pressure in the range of 0.2 MPa to 0.7 MPa, and in the range of 130°C to 180°C for 10 minutes to 30 minutes.

[0110] 3-2. Press molding method As a method for producing the FRP of the present invention, press molding is preferred from the viewpoint of high productivity and obtaining high-quality FRP by taking advantage of the characteristics of the epoxy resin composition that constitutes the prepreg. The FRP is produced by press molding by heating and pressurizing the prepreg of the present invention or a preform formed by laminating the prepreg of the present invention using a mold. It is preferable to preheat the mold to the curing temperature.

[0111] The temperature of the mold during press molding is preferably 130°C or higher and 180°C or lower. If the molding temperature is 130°C or higher, the curing reaction can be sufficiently initiated, allowing FRP to be obtained with high productivity. Furthermore, if the molding temperature is 180°C or lower, the resin viscosity will not become too low, preventing excessive flow of the resin within the mold. As a result, resin leakage from the mold and meandering of the fibers can be prevented, resulting in high-quality FRP.

[0112] The molding pressure is in the range of 0.2 MPa or more and 10 MPa or less. If the pressure is 0.2 MPa or more, the resin flows appropriately, preventing poor appearance and the occurrence of voids. In addition, the prepreg adheres well to the mold, allowing the production of FRP with a good appearance. If the pressure is 10 MPa or less, the resin does not flow more than necessary, making it less likely that the resulting FRP will have poor appearance. In addition, since no more load than necessary is applied to the mold, deformation of the mold is less likely to occur.

[0113] 3-3. Internal pressure molding method The internal pressure molding method is also preferably used as a method for producing the FRP of the present invention. The internal pressure molding method is a molding method in which prepreg is laid on the outside of a pouch-shaped internal pressure bag to obtain a prepreg laminate having the internal pressure bag inside, this prepreg laminate is placed in a mold and clamped, and the internal pressure bag is expanded within the mold to cause the prepreg to come into contact with the inner wall of the mold, and the prepreg is then heated and cured in this state.

[0114] A method for producing FRP using the internal pressure molding method will be described. First, the prepreg of the present invention is laid in the upper and lower halves of a mold. Next, an internal pressure bag is sandwiched between the upper and lower halves on which the prepreg has been laid, and the upper and lower halves are clamped together. This results in a prepreg laminate with the internal pressure bag inside. The internal pressure bag inside the mold is then expanded to inscribe the prepreg inside the mold against the inner wall of the mold, and the mold is heated in this state to heat-cure the prepreg. After a predetermined time has passed, the molded body is removed from the mold, and the internal pressure bag is removed to obtain the FRP.

[0115] From the viewpoint of productivity, it is preferable to preheat the mold to the curing temperature before laying the prepreg.

[0116] The material of the internal pressure bag is preferably a flexible and heat-resistant material such as nylon or silicone rubber.

[0117] The mold temperature during internal pressure molding is preferably in the range of 130°C or higher and 180°C or lower. If the molding temperature is 130°C or higher, the curing reaction can be sufficiently initiated, allowing FRP to be obtained with high productivity. Furthermore, if the molding temperature is 180°C or lower, the resin viscosity does not become too low, preventing excessive flow of the resin within the mold. As a result, resin leakage from the mold and meandering of the fibers are suppressed, resulting in high-quality FRP.

[0118] The molding pressure should be between 0.2 MPa and 2 MPa. If the pressure is 0.2 MPa or higher, the resin will flow properly, preventing poor appearance and voids. Furthermore, the prepreg will adhere well to the mold, resulting in FRP with a good appearance. If the pressure is 2 MPa or lower, flexible internal pressure bags such as nylon and silicone rubber are less likely to break.

[0119] 3-4. Vacuum-assisted compressed air method Vacuum-assisted pressure-pressure molding is also a preferred method for producing the FRP of the present invention. Vacuum-assisted pressure-pressure molding is a molding method in which a prepreg and a film bag are sequentially laid in the lower mold of a mold, the prepreg is sealed between the lower mold and the film bag, the space formed by the lower mold and the film bag is evacuated, and air pressure is applied inside the mold cavity formed by clamping the upper and lower molds together to heat and cure the prepreg.

[0120] A method for producing FRP using vacuum-assisted compressed air molding is described below. First, the prepreg of the present invention is laid in the lower mold of a mold. Next, a film bag is stacked on top of the prepreg, and the prepreg is sealed between the lower mold and the film bag. The space formed by the lower mold and the film bag is then evacuated, bringing the prepreg into contact with the lower mold. The mold is then clamped, and air pressure is applied to the mold cavity to further adhere the prepreg to the lower mold. The prepreg is then heated in this state to heat-cure it. After a predetermined time has passed, the molded body is removed from the mold, and the film bag is removed to obtain the FRP.

[0121] From the viewpoint of productivity, it is preferable that the lower mold has a heating mechanism that can heat it quickly.

[0122] The film bag is preferably made of a material that is flexible and has excellent heat resistance, such as nylon or silicone rubber.

[0123] The mold temperature is preferably in the range of 20°C to 50°C, with the prepreg and film bag stacked and evacuated, and then heated to a range of 130°C to 180°C at a temperature increase rate of 2 / min to 100°C / min. A molding temperature of 130°C or higher allows for a sufficient curing reaction, resulting in highly productive FRP production. Furthermore, a molding temperature of 180°C or lower prevents the resin viscosity from becoming too low, suppressing excessive flow of the resin within the mold and preventing resin leakage from the mold and meandering of the fibers, resulting in high-quality FRP production.

[0124] The molding pressure should be between 0.2 MPa and 2 MPa. If the pressure is 0.2 MPa or higher, the resin will flow properly, preventing poor appearance and voids. Furthermore, the prepreg will adhere well to the mold, resulting in FRP with a good appearance. If the pressure is 2 MPa or lower, flexible film bags such as nylon and silicone rubber are less likely to break.

[0125] The curing time in the manufacturing method of the present invention is 10 minutes or more and 30 minutes or less, which is shorter than conventional methods. In other words, it is possible to manufacture high-quality FRP with high productivity. [Example]

[0126] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The components and evaluation methods used in these examples and comparative examples are described below.

[0127] <Evaluation method> The evaluations carried out in the examples and comparative examples are as follows.

[0128] (1) Preparation of epoxy resin composition The epoxy resin, PES 2603MP, and PA1010 were added to a planetary mixer in the proportions shown in Table 1, and the mixture was heated to 120°C while stirring. After reaching 120°C, the mixture was stirred for one hour to dissolve the epoxy resin-soluble thermoplastic resin. The mixture was then cooled to 60°C while stirring, and the dissolved material was removed. The dissolved material, curing agent, accelerator, hydrazide compound, thickening particles, and inorganic filler were kneaded until homogeneous in a three-roll mill heated to 70°C to obtain an epoxy resin composition.

[0129] (2) Properties of cured resin (2-1) Preparation of cured resin The epoxy resin composition prepared in (1) above was degassed in a vacuum for 60 minutes, and then poured into a stainless steel mold set to a thickness of 4 mm using a 4 mm Teflon (registered trademark) resin spacer. The composition was then heated and cured at the curing temperature and for the curing time listed in Table 1, yielding a 4 mm thick cured resin.

[0130] (2-2) Glass transition temperature after water absorption (wet-Tg) Measurements were carried out according to the SACMA 18R-94 method. Resin test specimens measuring 50 mm x 6 mm x 2 mm were prepared using the cured resin plates obtained in (2-1) above. The prepared resin test specimens were subjected to water absorption treatment at 121°C for 24 hours using a pressure cooker (HASTEST PC-422R8, manufactured by Espec Corporation). The storage modulus (E') of the water-absorbed resin test specimens was measured using a Rheogel-E400 dynamic viscoelasticity analyzer manufactured by UBM under conditions of a measurement frequency of 1 Hz, a heating rate of 5°C / min, and a strain of 0.0167%, with a chuck distance of 30 mm, from 50°C to the rubber elastic region. Log E' was plotted against temperature, and the temperature calculated from the intersection of the approximation line for the plateau region of log E' with the approximation line for the transition region of E' was recorded as the glass transition temperature (wet-Tg).

[0131] (2-3) Room temperature dry resin flexural modulus (RTD-FM) The test was conducted in accordance with JIS K7171 method. Resin test pieces with dimensions of 80 mm × 10 mm × 4 mm (thickness h) were prepared using the resin-cured plates obtained in (2-1) above. A bending test was conducted at an ambient temperature of 25°C, with a support distance L of 16 × h mm, and a test speed of 2 mm / min, to measure the bending strength and bending modulus.

[0132] (2-4) Toughness of cured resin (deformation mode I critical stress intensity factor KIc) The toughness (KIc) was measured using a universal testing machine (Shimadzu Autograph) according to ASTM D5045. Resin test pieces measuring 50 mm x 8 mm (width W) x 4 mm were prepared using the resin-cured plates obtained in (2-1) above. The crack length a was adjusted to be 0.45≦a / W≦0.55. The crack length a was determined by observing the fracture surface after the fracture test using an optical microscope, and the length to the crack tip and the average crack length on both surfaces of the test piece were used.

[0133] (2-5) Degree of hardening The epoxy resin composition prepared in (1) was subjected to DSC measurement (heating rate: 20°C / min) to obtain the amount of heat generated before curing. The cured resin product prepared in (2-1) was separately subjected to DSC measurement (heating rate: 20°C / min) to obtain the amount of heat generated after curing. The degree of cure was calculated from the values ​​of the calorific value before and after curing according to the following formula. Degree of cure [%] = (heat generation before cure [J / g] - heat generation after cure [J / g]) / heat generation before cure [J / g] x 100

[0134] (2-6) Storage stability The epoxy resin composition prepared in (1) above was subjected to DSC measurement (20°C / min) to measure its Sub-Tg after preparation. The epoxy resin composition prepared in (1) above was stored at 40°C for 14 days, and then subjected to DSC measurement (20°C / min) to measure its Sub-Tg after storage. 〇:Sub-Tg after storage - Sub-Tg after preparation ≦10℃ ×: Sub-Tg after storage - Sub-Tg after preparation >10℃

[0135] (3) Characteristics of fiber-reinforced composite materials (3-1) Preparation of unidirectional prepreg The unidirectional prepreg was prepared as follows: The epoxy resin composition obtained in (1) above was applied to a release paper using a reverse roll coater to form a film of 50 g / m 2 Next, a resin film with a fiber mass per unit area of ​​190 g / m was prepared. 2 A sheet-like fiber-reinforced substrate layer was produced by aligning the carbon fibers in one direction so that the carbon fibers were aligned in the following direction: The resin films were laminated on both sides of this fiber-reinforced substrate layer, and the layers were heated and pressed at a temperature of 100°C and a pressure of 0.2 MPa to produce a unidirectional prepreg with a carbon fiber content of 65% by mass.

[0136] (3-2) Open-hole compression test (room temperature test) (OHC (Dry)) A laminate of 24 sheets of the unidirectional prepreg prepared in (3-1) above in a [+45° / 90° / -45° / 0°] 3s configuration was placed in a bag, and the bag was heated in an autoclave at a rate of 2°C / min, and then heated to 180°C for 30 minutes to cure the laminate into a molded plate (carbon fiber reinforced composite material). During this time, the autoclave was pressurized to 0.5 MPa, and a vacuum was maintained inside the bag. The compressive strength of carbon fiber reinforced composite materials was measured at a test speed of 1.0 mm / min according to ASTM D6484. Five samples were used, and the average value was used.

[0137] (3-3) Open-hole compression test (moist heat treatment / high temperature test) (OHC (HTWE)) The compressive strength of carbon fiber reinforced composite materials was measured at a test speed of 1.0 mm / min according to ASTM D6484. Five samples were used, and the average value was used.

[0138] <Ingredients> The components used in the examples and comparative examples are as follows.

[0139] (epoxy resin) jER (registered trademark) 604: (tetraglycidyldiaminodiphenylmethane type epoxy resin, manufactured by Mitsubishi Chemical Corporation) jER (registered trademark) 828: (liquid bisphenol A epoxy resin, manufactured by Mitsubishi Chemical Corporation) GOT (trade name): (N'N-diglycidyl-o-toluidine, manufactured by Nippon Kayaku Co., Ltd.)

[0140] (dicyandiamide) DICY7: (Dicyandiamide, manufactured by Mitsubishi Chemical Corporation)

[0141] (curing accelerator) Omicure® 24: (2,4'-toluenebis(3,3-dimethylurea), manufactured by Huntsman) Amicure PN-31: (amine adduct type latent hardener, manufactured by Ajinomoto Fine-Techno Co., Ltd.) Curezol 2PHZ: (2-phenyl-4,5-dihydroxymethyl-imidazole, manufactured by Shikoku Chemicals Corporation)

[0142] (aromatic polyamines) Curehard MED-J: having the structure of the above chemical formula (2) (manufactured by Kumiai Chemical Industry Co., Ltd.) 3,3'-DAS: (3,3'-diaminodiphenyl sulfone, manufactured by Mitsui Chemicals Fine Co., Ltd.) 4,4'-DAS: (4,4'-diaminodiphenyl sulfone, manufactured by Mitsui Fine Chemicals, Inc.)

[0143] (Aliphatic dihydrazide compounds) Adipic acid dihydrazide: (Otsuka Chemical Co., Ltd., melting point: 177°C) Sebacic acid dihydrazide: (Otsuka Chemical Co., Ltd., melting point: 186°C) Dodecanedioic acid hydrazide: (Otsuka Chemical Co., Ltd., melting point: 188°C) (aromatic hydrazide compounds) Salicylic acid hydrazide: (Otsuka Chemical Co., Ltd., melting point: 145°C) Isophthalic dihydrazide: (Otsuka Chemical Co., Ltd., melting point: 215°C)

[0144] (thermoplastic resin) PES 2603MP: (Polyethersulfone, manufactured by Sumitomo Chemical Co., Ltd.) PA1010: (Polyamide 1010, manufactured by Daicel-Evonik)

[0145] (Thickening particles) Zefiac® F320: (Alkyl methacrylate polymer, manufactured by Aica Kogyo Co., Ltd.)

[0146] (Inorganic filler) Nano Ace D-1000: (Talc, manufactured by Nippon Talc Co., Ltd.) FG-15: (Talc, manufactured by Nippon Talc Co., Ltd.) Ultrex96: (Kaolin clay, manufactured by KaMin LLC)

[0147] [Table 1]

[0148] [Table 2]

[0149] In Comparative Example 1, a high-melting aromatic hydrazide compound was used, but not all of the aromatic hydrazide compound melted at the molding temperature, resulting in low reactivity. As a result, the glass transition temperature after water absorption and the toughness of the cured resin were low. The measured degree of cure was high, at 98%. This was because a large amount of undissolved aromatic hydrazide compound (unreacted material) was present in the sample used to measure the degree of cure. In Comparative Example 2, an aromatic hydrazide compound with a low melting point was used, but the latency of the curing agent was insufficient, resulting in poor storage stability. In Comparative Example 3, no aromatic hydrazide compound was used and the amount of aromatic polyamine compound was increased, but the storage stability was reduced due to the reaction of the amine. In Comparative Examples 4 and 5, the amount of the curing agent component was small, so the storage stability was high, but the degree of cure of the cured resin product was low.

Claims

1. An epoxy resin composition comprising an epoxy resin, a curing agent composition, and a curing accelerator, the epoxy resin contains 80 parts by mass or more of N,N,N',N'-tetraglycidyldiaminodiphenylmethane per 100 parts by mass of the epoxy resin, Epoxy resin composition, characterized in that the curing agent composition comprises a combination of dicyandiamide, an aliphatic hydrazide compound, and an aromatic polyamine compound.

2. 2. The epoxy resin composition according to claim 1, wherein the content of the aliphatic hydrazide compound in the curing agent composition is in the range of 20% by mass or more and 70% by mass or less.

3. The epoxy resin composition according to claim 1 or 2, further comprising a thermoplastic resin.

4. 3. The epoxy resin composition according to claim 1, further comprising thickening particles made of a polymer having one or more polymerization units selected from the group consisting of methacrylic acid ester compounds, acrylic acid ester compounds, and vinyl ester compounds.

5. A reinforcing fiber substrate; The epoxy resin composition according to claim 1 impregnated into the reinforcing fiber substrate; A prepreg consisting of A prepreg characterized in that a part or all of the aliphatic hydrazide compound is present in the form of particles in the epoxy resin composition.

6. A reinforcing fiber substrate; A cured resin product of the epoxy resin composition according to claim 1; A fiber-reinforced composite material characterized by being formed by combining the above.

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