Epoxy resin composition, resin cured product, and fiber reinforced composite material

Abstract

To provide an epoxy resin composition having low viscosity, a long serviceable time, and rapid curability, a resin cured material and a fiber-reinforced composite material.SOLUTION: An epoxy resin composition containing a curing agent A, a curing agent B, a curing agent C, an epoxy resin D, an epoxy resin E and resin particles F. The curing agent A is an aromatic polyamine having a substituent at two ortho positions to the amino group, respectively, wherein the substituent is selected from alkyl groups, aromatic groups and halogen groups. The curing agent B is an aromatic polyamine that is liquid at 25°C. The curing agent C is an aromatic polyamine, wherein the aromatic polyamine is an aromatic polyamine that has only one electron-donating group at the ortho-position to the amino group or has no substituent at the ortho-position to the amino group. The epoxy resin D is constituted of an epoxy resin constituted of 4 or more glycidyl groups. The epoxy resin E is constituted of an epoxy resin constituted of a monomer containing two or three glycidyl groups.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a curing agent composition for epoxy resins, and more particularly to an epoxy resin composition, a resin cured product, and a fiber-reinforced composite material having a long pot life and rapid curability.

Background Art

[0002] Fiber-reinforced composite materials are lightweight, high-strength, and high-rigidity, and are therefore used in a wide range of fields such as sports and leisure applications such as fishing rods and golf shafts, and industrial applications such as automobiles and aircraft. As a method for molding a composite material using a thermosetting resin as a matrix resin, there are a resin transfer molding (RTM) method in which a liquid resin composition is impregnated into a fiber-reinforced base material placed in a mold and cured to obtain a fiber-reinforced composite material, and a method of molding a prepreg (intermediate base material) in which a resin is impregnated into a fiber-reinforced base material in advance and formed into a sheet shape, etc. are known.

[0003] In recent years, among them, in particular, the RTM molding method, which is a low-cost and highly productive manufacturing method that requires few steps for manufacturing a fiber-reinforced composite material and does not require expensive equipment such as an autoclave, has attracted attention. The composition of the matrix resin used in the RTM molding method mainly includes an epoxy resin and a curing agent, and may optionally include other additives. In order to obtain a cured product and a fiber-reinforced composite material having high mechanical properties, it is common to use an aromatic polyamine as the curing agent.

[0004] In the case of an epoxy resin composition used in the RTM molding method, in order to prevent the hardener from being filtered out when the epoxy resin composition is impregnated into the reinforcing fiber base material, the hardener and additives are often stored and used in a state dissolved in the epoxy resin serving as the main component. In this way, an epoxy resin composition in which a hardener and additives are dissolved and mixed in the main epoxy resin is referred to as a one-component epoxy resin composition. At this time, since the hardener exists in a state dissolved in the epoxy resin, the reaction between the epoxy resin and the hardener is relatively likely to occur, and there is a problem that the shelf life of the epoxy resin composition is shortened. Therefore, the one-component epoxy resin composition had to be stored frozen.

[0005] To solve this problem, a two-component epoxy resin composition that is mixed immediately before using the epoxy resin and the hardener has been studied. The two-component epoxy resin composition is composed of a main agent liquid containing an epoxy resin as a main component and a hardener liquid (hardener composition) containing a hardener as a main component, and is an epoxy resin composition obtained by mixing these two liquids immediately before use.

[0006] In the two-component epoxy resin composition, since the main agent liquid and the hardener liquid are mixed immediately before use, the ease of mixing is important. It is possible to use the hardener used in the one-component epoxy resin composition as the hardener of the two-component epoxy resin composition. However, as described in Patent Document 1, the aromatic polyamine hardener used in the one-component epoxy resin composition is usually solid, and poor mixing with the main agent liquid is likely to occur. Therefore, it is desirable that the hardener composition be liquid.

[0007] Examples of the epoxy resin composition using a liquid aromatic polyamine as a hardener include those described in Patent Documents 2 and 3. However, the resin cured product obtained from the epoxy resin composition described in Patent Documents 2 and 3 does not have the mechanical properties such as elastic modulus and fracture toughness required for industrial applications such as automobiles and airplanes, and improvement thereof is required.

[0008] In addition, in the RTM method, in order to produce fiber-reinforced composite materials with high efficiency, rapid curing is required to shorten the resin curing time. Patent Document 4 proposes a two-component epoxy resin composition with rapid curing using a compound having two or more aromatic rings having phenolic hydroxyl groups. However, when a compound having a phenolic hydroxyl group is added to an epoxy resin composition, the viscosity of the resin composition increases rapidly due to its high reactivity, and the pot life in RTM molding becomes extremely short, making it difficult to impregnate a sufficient amount of resin into the reinforcing fiber base material. Therefore, fiber-reinforced composite materials produced using such epoxy resin compositions have many defects such as voids. As a result, there has been a problem that the compressive performance and damage tolerance of the fiber-reinforced composite material structure decrease.

[0009] Thus, there has never been a two-component epoxy resin composition that has sufficient rapid curing to achieve high productivity of fiber-reinforced composite materials and also has high levels of heat resistance and mechanical properties required for industrial applications such as automobiles and aircraft.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0011] An object of the present invention is to solve the problems of the above-mentioned prior art and provide an epoxy resin composition having a low viscosity, a long pot life, and rapid curability. A further object of the present invention is to provide an epoxy resin composition, a resin cured product, and a fiber-reinforced composite material that are produced using this epoxy resin composition and have the heat resistance and mechanical properties required for industrial applications.

Means for Solving the Problems

[0012] As a result of investigations to solve the above problems, the present inventors have found that the above problems can be solved by using an epoxy resin composition comprising a combination of a predetermined epoxy resin, a curing agent, and a resin particle component, and have completed the present invention.

[0013] That is, the present invention is an epoxy resin composition containing a curing agent A, a curing agent B, a curing agent C, an epoxy resin D, an epoxy resin E, and a resin particle F, wherein the curing agent A is an aromatic polyamine having substituents at two ortho positions with respect to an amino group, the substituents being selected from an alkyl group, an aromatic group, and a halogen group, the curing agent B is an aromatic polyamine that is liquid at 25°C, the curing agent C is an aromatic polyamine that has only one electron-donating group at the ortho position with respect to the amino group or has no substituent at the ortho position, the epoxy resin D is composed of an epoxy resin composed of monomers containing four or more glycidyl groups, and the epoxy resin E is composed of an epoxy resin composed of monomers containing two or three glycidyl groups.

Effects of the Invention

[0014] According to the present invention, it is possible to provide an epoxy resin composition having a low viscosity, a long pot life, and rapid curability. It is also possible to provide an epoxy resin composition, a resin cured product, and a fiber-reinforced composite material having the heat resistance and mechanical properties required for industrial applications.

[0015] According to the present invention, it is further possible to provide an epoxy resin composition, a resin cured product, and a fiber-reinforced composite material that are produced using this epoxy resin composition and have heat resistance and mechanical properties required for industrial applications.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, the present invention will be described in detail. Note that the fiber-reinforced composite material may be abbreviated as "FRP", and the carbon fiber-reinforced composite material may be abbreviated as "CFRP".

[0017] 〔Hardener〕 The total amount of hardener A, hardener B, and hardener C contained in the epoxy resin composition of the present invention is an amount suitable for curing all the epoxy resins blended in the epoxy resin composition, and is appropriately adjusted according to the types of epoxy resins and hardeners used.

[0018] Specifically, the ratio of the number of epoxy groups contained in the epoxy resin in the epoxy resin composition of the present invention to the number of active hydrogens contained in hardener A, hardener B, and hardener C is preferably 0.7 to 1.3, more preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. If this ratio is less than 0.7 or exceeds 1.3, the molar balance between the epoxy groups and the active hydrogens is disrupted, the crosslink density of the resulting resin cured product becomes insufficient, and the heat resistance and mechanical properties such as elastic modulus and fracture toughness decrease.

[0019] In the present invention, when hardener A, hardener B, and hardener C are mixed and used as a hardener solution, the hardener solution becomes a uniform liquid when heated to a temperature of 200°C or lower, and the period during which it can maintain a uniform liquid state at room temperature is preferably 1 week or more, more preferably 3 weeks or more, and particularly preferably 1 month or more. If the period during which it can maintain a uniform liquid state at room temperature is less than 1 week, it becomes difficult to handle it as a substantially liquid hardener composition for thermosetting resins, and poor mixing with the epoxy main agent solution is likely to occur, which is not preferable.

[0020] 〔Hardener A〕 Hardener A is an aromatic polyamine having substituents at two ortho positions with respect to the amino group, and the substituents are selected from an alkyl group, an aromatic group, and a halogen group. Further, Hardener A is a solid at 25°C. By containing this Hardener A, when cured as a composition with an epoxy resin, an epoxy resin cured product having excellent mechanical properties such as heat resistance, elastic modulus, and fracture toughness can be obtained.

[0021] As the aromatic polyamine having substituents at two ortho positions with respect to the amino group and used as Hardener A, a compound represented by the following chemical formula (1) can be used.

[0022]

Chemical formula

[0023] However, in the above chemical formula (1), R1 to R4 are each independently any one of an aliphatic substituent, an aromatic substituent, an alkoxy group, and a halogen atom, and at least one substituent is any one of an aliphatic substituent having 1 to 6 carbon atoms, an aromatic substituent, and a halogen atom. X is any one of -CH2-, -CH(CH3)-, -C(CH3)2-, -S-, -O-, -SO2-, -CO-, -CONH-, -NHCO-, -C(=O)-, and -O-C(=O)-.

[0024] In chemical formula (1), examples of the aliphatic substituent having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a neopentyl group, an n-hexyl group, and a cyclohexyl group. Examples of the aromatic substituent include a phenyl group and a naphthyl group. The aromatic polyamine of Hardener A is preferably an aromatic diamine, and among them, a 4,4'-diaminodiphenylmethane derivative is particularly preferred.

[0025] Specific examples of such aromatic polyamines include compounds represented by the following chemical formulas (2) to (5). These may be used alone or in combination.

[0026]

Chem.

[0027] 〔Hardener B〕 Hardener B is an aromatic polyamine that is liquid at 25°C. By containing this aromatic polyamine, a curing agent composition for a thermosetting resin that can maintain a liquid state at room temperature can be obtained.

[0028] As the aromatic polyamine of Hardener B, a phenylenediamine derivative or a 4,4'-diaminodiphenylmethane derivative is preferably used. Examples of such aromatic polyamines include compounds represented by the following chemical formula (6) or (7).

[0029]

Chem.

[0030] However, in Chemical Formula (6), R5 to R8 are each independently any one of a hydrogen atom, an aliphatic substituent, an alkoxy group, and a thioalkoxy group, and at least one substituent is either an aliphatic substituent having 1 to 6 carbon atoms or a thioalkoxy group.

[0031]

Chem.

[0032] However, in Chemical Formula (7), R9 to R 10 are each independently any one of an aliphatic substituent, a methoxy group, an alkoxy group, and a thioalkoxy group.

[0033] As the aromatic polyamine used as hardener B, specifically, compounds represented by the following chemical formulas (8) to (12) can be exemplified. These may be used alone or in combination.

[0034]

Chemical formula

[0035] 〔Hardener C〕 Hardener C is an aromatic polyamine, and the aromatic polyamine is an aromatic polyamine having only one electron-donating group at the ortho position to the amino group or having no substituent at the ortho position. The electron-donating group of the aromatic polyamine of hardener C is preferably a methyl group, an ethyl group, a propyl group, an isopropyl group, a methoxy group or an ethoxy group. By containing this hardener C, the curing reaction of the obtained epoxy resin composition is promoted, and rapid curability can be imparted to the epoxy resin composition.

[0036] As hardener C, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 4,4'-thiodianiline, 4,4'-diamino-3,3'-dimethyldiphenyl Examples thereof include lumethane, 1,1-bis(4-aminophenyl)cyclohexane, 3,3'-diaminobenzophenone, m-phenylenediamine, 2,4-diaminotoluene, 2,6-diaminotoluene, 2,4,6-trimethyl-1,3-phenylenediamine, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, o-dianisidine, 3,3',5,5'-tetramethylbenzidine. Among them, it is preferable to use 3,4'-diaminodiphenyl ether, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,3-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 2,6-diaminotoluene, m-phenylenediamine, and 3,4'-diaminodiphenyl ether, 1,3-bis(4-aminophenoxy)benzene, 2,6-diaminotoluene, m-phenylenediamine are preferred.

[0037] The melting point of curing agent C is preferably 200°C or lower, more preferably 150°C or lower, and particularly preferably 120°C or lower. When the melting point exceeds 200°C, it becomes difficult to obtain a liquid composition when curing agent C is mixed with curing agent A and curing agent B, and it is likely to be difficult to keep the obtained curing agent composition for thermosetting resin in a liquid state at room temperature, which is not preferable. Also, the curing agent C is solid at 25°C.

[0038] [Epoxy resin D] The epoxy resin composition of the present invention contains an epoxy resin D composed of a monomer containing four or more glycidyl groups. Epoxy resin D may be a homopolymer composed of one type of monomer, a copolymer composed of two or more types of monomers, or a mixture of a homopolymer and / or a copolymer.

[0039] The constituent monomer of epoxy resin D composed of a monomer containing four or more glycidyl groups is preferably represented by the following chemical formula (13).

[0040] [Chemistry]

[0041] (However, in Chemical Formula (13), each of R1 to R4 independently represents one selected from the group consisting of a hydrogen atom, an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and a halogen atom, and X represents one selected from -CH2-, -O-, -S-, -CO-, -C(=O)O-, -O-C(=O)-, -NHCO-, -CONH-, -SO2-. When R1 to R4 are an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, the number of carbon atoms is preferably 1 to 4.

[0042] As the constituent monomer of epoxy resin D, it is particularly preferable to be one or a combination of two or more selected from the group consisting of tetraglycidyl-4,4'-diaminodiphenyl ether, tetraglycidyl-4,4'-diaminodiphenylmethane, tetraglycidyl-3,4'-diaminodiphenyl ether, and tetraglycidyl-3,3'-diaminodiphenylmethane.

[0043] Epoxy resin D is preferably a homopolymer, copolymer, or a mixture thereof composed of these monomers. When R1 to R4 are hydrogen atoms, it is preferable because it is difficult to inhibit the formation of a special three-dimensional structure of the resin cured product. Also, since the synthesis of the compound becomes easy, X is preferably -O-.

[0044] The constituent monomer of epoxy resin D may be synthesized by any method. For example, an aromatic diamine as a raw material and an epihalohydrin such as epichlorohydrin are reacted, preferably in the presence of an acid catalyst, to obtain a tetrahalohydrin form, and then a cyclization reaction is carried out using an alkaline compound to obtain it. Specifically, it can be synthesized by the method of the examples described later.

[0045] Examples of aromatic diamines include 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, and 4,4'-diaminodiphenyl methane. Among these, aromatic diamines in which two aromatic rings having amino groups are linked by an ether bond are preferred from the viewpoint of heat resistance, and aromatic diamines in which one amino group is in the para position and the other amino group is in the ortho position with respect to the ether bond are more preferred. Examples of such aromatic diamines include 3,4'-diaminodiphenyl ether and 3,4'-diaminodiphenyl sulfone.

[0046] Examples of epihalohydrins include epichlorohydrin, epibromohydrin, and epifluorohydrin. Among these, epichlorohydrin and epibromohydrin are particularly preferred from the viewpoints of reactivity and handleability.

[0047] The mass ratio of the aromatic diamine as the raw material to the epihalohydrin is preferably 1:1 to 1:20, more preferably 1:3 to 1:10. Examples of the solvent used in the reaction include alcohol solvents such as ethanol and n-butanol, ketone solvents such as methyl isobutyl ketone and methyl ethyl ketone, aprotic polar solvents such as acetonitrile and N,N-dimethylformamide, and aromatic hydrocarbon solvents such as toluene and xylene. In particular, alcohol solvents such as ethanol and n-butanol, and aromatic hydrocarbon solvents such as toluene and xylene are preferred.

[0048] The amount of the solvent used is preferably 1 to 10 times the mass of the aromatic diamine. As the acid catalyst, both Bronsted acid and Lewis acid can be suitably used. As the Bronsted acid, ethanol, water, and acetic acid are preferred, and as the Lewis acid, titanium tetrachloride, lanthanum nitrate hexahydrate, and boron trifluoride diethyl ether complex are preferred.

[0049] The reaction time is preferably 0.1 to 180 hours, more preferably 0.5 to 24 hours. The reaction temperature is preferably 20 to 100 °C, more preferably 40 to 80 °C. Examples of the alkaline compound used in the cyclization reaction include sodium hydroxide and potassium hydroxide. The alkaline compound may be added as a solid or as an aqueous solution.

[0050] A phase transfer catalyst may be used during the cyclization reaction. Examples of the phase transfer catalyst include quaternary ammonium salts such as tetramethylammonium chloride, tetraethylammonium bromide, benzyltriethylammonium chloride, and tetrabutylammonium hydrogen sulfate; phosphonium compounds such as tributylhexadecylphosphonium bromide and tributyldodecylphosphonium bromide; and crown ethers such as 18-crown-6-ether.

[0051] In the epoxy resin composition of the present invention, the proportion of epoxy resin D in the total amount of epoxy resin (epoxy resin main agent solution) is preferably 50 to 90% by mass, particularly preferably 60 to 80% by mass. When the proportion of epoxy resin D is 50% by mass or more, the heat resistance and elastic modulus of the obtained resin cured product can be further improved. As a result, various mechanical properties of the obtained fiber-reinforced composite material are also improved.

[0052] [Epoxy Resin E] The epoxy resin composition of the present invention contains an epoxy resin E composed of a monomer containing two or three glycidyl groups. By containing this epoxy resin E, the viscosity of the epoxy resin composition can be reduced, the resin impregnation property into the reinforcing fiber base material can be improved, the pot life can be prolonged, and the design freedom of the mold used in the RTM molding method can be increased.

[0053] By using epoxy resin E and epoxy resin D in combination, the resin impregnation property into the reinforcing fiber base material can be improved, and a resin cured product and a fiber-reinforced composite material having heat resistance and a high elastic modulus can be obtained. As a constituent monomer of epoxy resin E, a monomer having two or three glycidyl groups is used. This is preferably an aromatic compound.

[0054] Examples of the monomer having two glycidyl groups include diglycidylaniline and its derivatives such as diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine, diglycidyl-xylidine, diglycidyl-mesitylene, diglycidyl-anisidine, diglycidyl-phenoxyaniline, diglycidyl-naphthylamine and its derivatives. It is preferable to use these.

[0055] More preferably, diglycidylaniline, diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine, diglycidyl-phenoxyaniline are used, and even more preferably, diglycidylaniline or diglycidyl-o-toluidine is used.

[0056] As the epoxy resin composed of monomers containing two or three glycidyl groups, an epoxy resin having a polycyclic aromatic hydrocarbon skeleton is preferable. Examples of the polycyclic aromatic hydrocarbon skeleton include a naphthalene skeleton and an anthracene skeleton. From the viewpoint of the physical properties of the resin cured product, the naphthalene skeleton is preferable.

[0057] The polycyclic aromatic hydrocarbon group may have a substituent in addition to the glycidyl group. Examples of the monomer having a naphthalene skeleton include 1,6-bis(glycidyloxy)naphthalene, 1,5-bis(glycidyloxy)naphthalene, 2,6-bis(glycidyloxy)naphthalene, 2,7-bis(glycidyloxy)naphthalene, 2,2'-bis(glycidyloxy)-1,1'-binaphthalene, 2,7-bis(glycidyloxy)-1-[2-(glycidyloxy)-1-naphthylmethyl]naphthalene. By using an epoxy resin having these compounds as constituent monomers, the viscosity of the epoxy resin composition can be reduced and the heat resistance of the resin cured product can be improved.

[0058] When an epoxy resin having a polycyclic aromatic hydrocarbon skeleton is used as an epoxy resin composed of monomers containing two or three glycidyl groups, the crosslinking density of the cured product does not increase excessively, so that a decrease in the toughness of the resin cured product can be prevented, which is preferable.

[0059] Among epoxy resins composed of monomers containing two or three glycidyl groups, as a constituent monomer of epoxy resin E, an aromatic compound having three glycidyl groups is preferable. As this epoxy resin, a triglycidylaminophenol derivative epoxy resin is preferable. Examples of the triglycidylaminophenol derivative epoxy resin include triglycidyl-m-aminophenol and triglycidyl-p-aminophenol. By containing this epoxy resin E, the viscosity of the epoxy resin composition can be decreased, and further the heat resistance of the resin cured product can be improved.

[0060] Among epoxy resins composed of monomers containing two or three glycidyl groups, as a constituent monomer of epoxy resin E, a heteroaromatic compound having three glycidyl groups is also preferable. That is, it is also preferable that epoxy resin E contains a triglycidyl isocyanurate derivative epoxy resin. Examples of the triglycidyl isocyanurate derivative epoxy resin include 1,3,5-triglycidyl isocyanurate, 1,3,5-tri(ethylglycidyl) isocyanurate, and 1,3,5-tri(pentylglycidyl) isocyanurate. By containing these, the heat resistance and elastic modulus of the epoxy resin cured product can be improved. Therefore, by using in combination with epoxy resin D, a resin cured product and a fiber-reinforced composite material maintaining heat resistance and a high elastic modulus can be obtained.

[0061] As the constituent monomers of epoxy resin E, one or a combination of two or more selected from diglycidylaniline, diglycidyl-o-toluidine, triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, 1,6-bis(2,3-epoxypropan-1-yloxy)naphthalene and 1,3,5-triglycidyl isocyanurate is particularly preferred. Epoxy resin E is particularly preferably a homopolymer, copolymer or a mixture thereof composed of these monomers.

[0062] Other examples of epoxy resin E include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, and cresol novolac type epoxy resin.

[0063] In the epoxy resin composition of the present invention, the content of epoxy resin E per total mass of the epoxy resin (epoxy resin main agent liquid) is preferably 10 to 50% by mass, more preferably 20 to 40% by mass. By setting the content of epoxy resin E relative to the total mass of the epoxy resin within this range, an epoxy resin composition having a viscosity and pot life suitable for the RTM molding method and high heat resistance can be produced.

[0064] [Resin particles F] The epoxy resin composition of the present invention contains resin particles F. The resin particles F are dispersed without dissolving in the epoxy resin composition and are also present in a dispersed state in the resin cured product after the epoxy resin composition is cured. When the resin cured product is used as the sea component, the resin particles F are present in the resin cured product as the island component.

[0065] By containing the resin particles F, high fracture toughness and impact resistance can be obtained in the resin cured product and the fiber reinforced composite material. As the resin particles F, for example, thermoplastic resin particles, thermosetting resin particles, or rubber particles can be used, and rubber particles are preferably used. Examples of the rubber particles include silicone rubber, butadiene rubber, styrene-butadiene rubber, and methyl methacrylate-butadiene-styrene rubber.

[0066] Commercially available products of the rubber particles used as the resin particles F include MX-153 (a product in which 33% by mass of butadiene rubber is singly dispersed in a bisphenol A type epoxy resin, manufactured by Kaneka Corporation), MX-257 (a product in which 37% by mass of butadiene rubber is singly dispersed in a bisphenol A type epoxy resin, manufactured by Kaneka Corporation), MX-154 (a product in which 40% by mass of butadiene rubber is singly dispersed in a bisphenol A type epoxy resin, manufactured by Kaneka Corporation), MX-960 (a product in which 25% by mass of silicone rubber is singly dispersed in a bisphenol A type epoxy resin, manufactured by Kaneka Corporation), MX-136 (a product in which 25% by mass of butadiene rubber is singly dispersed in a bisphenol F type epoxy resin, manufactured by Kaneka Corporation), MX-965 (a product in which 25% by mass of silicone rubber is singly dispersed in a bisphenol F type epoxy resin, manufactured by Kaneka Corporation), MX-217 (a product in which 25% by mass of butadiene rubber is singly dispersed in a phenol novolac type epoxy resin, manufactured by Kaneka Corporation), MX-227M75 (a product in which 25% by mass of styrene-butadiene rubber is singly dispersed in a bisphenol A novolac type epoxy resin, manufactured by Kaneka Corporation), MX-334M75 (a product in which 25% by mass of styrene-butadiene rubber is singly dispersed in a brominated epoxy resin, manufactured by Kaneka Corporation), MX-416 (a product in which 25% by mass of butadiene rubber is singly dispersed in a tetrafunctional glycidylamine type epoxy resin, manufactured by Kaneka Corporation), MX-451 (a product in which 25% by mass of styrene-butadiene rubber is singly dispersed in a trifunctional glycidylamine type epoxy resin, manufactured by Kaneka Corporation).

[0067] The average particle diameter of the resin particles F is preferably 1.0 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.3 μm or less. And the average particle diameter is preferably 0.03 μm or more, more preferably 0.05 μm or more, and particularly preferably 0.08 μm or more.

[0068] When the average particle diameter is 1 μm or less, in the step of impregnating the epoxy resin composition into the reinforcing fiber base material, the resin particles F are not filtered on the surface of the reinforcing fiber base material, and the impregnation into the inside of the reinforcing fiber bundle becomes easy. Thereby, poor impregnation of the resin can be prevented, and a fiber-reinforced composite material having excellent physical properties can be obtained.

[0069] The content of the resin particles F in the epoxy resin composition of the present invention is preferably 0.1 to 50% by mass, more preferably 0.5 to 20% by mass, and particularly preferably 1 to 15% by mass based on the total amount of the epoxy resin composition. By setting the content to 0.1% by mass or more, the fracture toughness and impact resistance of the resin cured product and the fiber composite material can be sufficiently improved.

[0070] The resin particles F can also be used as a masterbatch dispersed at a high concentration in the epoxy resin. In this case, it becomes easy to highly disperse the resin particles F in the epoxy resin composition.

[0071] 〔Composition ratio of epoxy resin composition〕 Based on the total mass of the curing agents contained in the epoxy resin composition of the present invention, the total of the curing agent A, the curing agent B, and the curing agent C accounts for 70 to 100% by mass, preferably 80 to 100% by mass. If it is less than 70% by mass, the heat resistance of the cured product may be insufficient.

[0072] In the epoxy resin composition of the present invention, the mass ratio of curing agent A to curing agent B is preferably 1:99 to 99:1, more preferably 20:80 to 80:20, and particularly preferably 40:60 to 70:30. When the proportion of curing agent A is less than 1, the mechanical properties such as heat resistance, elastic modulus, and fracture toughness of the resulting resin cured product tend to be insufficient, which is not preferable. On the other hand, when the proportion of curing agent A exceeds 99, it becomes difficult for the resulting curing agent composition for thermosetting resin to maintain a liquid state at room temperature, which is not preferable.

[0073] In the epoxy resin composition of the present invention, with respect to a total of 100 parts by mass of curing agent A and curing agent B, curing agent C is preferably contained in an amount of 1 to 43 parts by mass, more preferably 3 to 30 parts by mass, and even more preferably 5 to 20 parts by mass. When the amount of curing agent C is less than 1 part by mass, it becomes difficult to impart rapid curability to the resulting epoxy resin composition, which is not preferable. On the other hand, when it exceeds 43 parts by mass, the reactivity of the resulting epoxy resin composition becomes excessively high, and the pot life in RTM molding becomes extremely short, which is not preferable. In this case, it becomes difficult to impregnate a sufficient amount of resin into the reinforcing fiber base material, and the fiber-reinforced composite material produced using such an epoxy resin composition will contain many defects such as voids, and the compression performance and damage tolerance of the fiber-reinforced composite material structure will deteriorate.

[0074] 〔Other optional components〕 The epoxy resin composition of the present invention may contain a curing agent other than curing agent A, curing agent B, and curing agent C, an epoxy resin other than epoxy resin D and epoxy resin E, a thermosetting resin other than epoxy resin, a thermoplastic resin other than resin particle F, or other additives.

[0075] Examples of curing agents other than curing agent A, curing agent B, and curing agent C include aliphatic polyamines, various isomers of aromatic amine-based curing agents, amino benzoate esters, and acid anhydrides.

[0076] Examples of aliphatic polyamines include 4,4'-diaminodicyclohexylmethane, isophoronediamine, and m-xylylenediamine. Examples of amino benzoate esters include trimethylene glycol di-p-aminobenzoate and neopentyl glycol di-p-aminobenzoate. Cured products and fiber-reinforced composite materials cured using these curing agents have high tensile elongation.

[0077] Examples of acid anhydrides include 1,2,3,6-tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and 4-methylhexahydrophthalic anhydride. When these curing agents are used, the pot life of the uncured resin composition is long, and a cured product with relatively well-balanced electrical, chemical, and mechanical properties can be obtained.

[0078] As epoxy resins other than epoxy resin D and epoxy resin E, for example, monofunctional epoxy resins can be used. Among them, epoxy resins containing an aromatic group are preferably used, and more preferably, epoxy resins containing either a glycidylamine structure or a glycidyl ether structure are used. Alicyclic epoxy resins can also be suitably used.

[0079] These epoxy resins may have non-reactive substituents on an aromatic ring structure or the like, if necessary. Examples of non-reactive substituents include alkyl groups such as methyl group, ethyl group, and isopropyl group, aromatic groups such as phenyl group, alkoxyl groups, aralkyl groups, and halogen groups such as chlorine and bromine. Examples of thermosetting resins other than epoxy resins include vinyl ester resins, benzoxazine resins, bismaleimide resins, and bismaleimide-triazine resins.

[0080] In addition to the resin particles F, the epoxy resin composition of the present invention may contain a thermoplastic resin as a component to be dissolved in the epoxy resin composition. The thermoplastic resin improves the fracture toughness and impact resistance of the resulting fiber-reinforced composite material. Such a thermoplastic resin may be dissolved in the epoxy resin composition during the curing process of the epoxy resin composition.

[0081] Specific examples of the thermoplastic resin include polyethersulfone, polysulfone, polyetherimide, and polycarbonate. These may be used alone or in combination of two or more.

[0082] As this thermoplastic resin, polyethersulfone or polysulfone having a weight average molecular weight (Mw) in the range of 8000 to 100000 measured by gel permeation chromatography is particularly preferable. When the weight average molecular weight (Mw) is 8000 or more, the impact resistance of the resulting FRP becomes sufficient, and when it is 100000 or less, an epoxy resin composition having good handleability can be obtained without a significant increase in viscosity.

[0083] The molecular weight distribution of this thermoplastic resin is preferably uniform, and the polydispersity (Mw / Mn), which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn), is preferably 1 to 10, more preferably 1.1 to 5.

[0084] This thermoplastic resin preferably has a reactive group having reactivity with the epoxy resin or a functional group forming a hydrogen bond. Such a thermoplastic resin can improve the dissolution stability during the curing process of the epoxy resin. In addition, fracture toughness, chemical resistance, heat resistance, and wet heat resistance can be imparted to the resulting fiber-reinforced composite material after curing.

[0085] As the reactive group having reactivity with the epoxy resin, a hydroxyl group, a carboxylic acid group, an imino group, an amino group, etc. are preferable. Using a hydroxyl group-terminated polyethersulfone is more preferable because the resulting fiber-reinforced composite material has particularly excellent impact resistance, fracture toughness, and solvent resistance.

[0086] The content of the thermoplastic resin contained in the epoxy resin composition is appropriately adjusted according to the viscosity. When the thermoplastic resin is contained, from the viewpoint of impregnation into the fiber-reinforced base material, it is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the epoxy resin contained in the epoxy resin composition. By containing 0.1 part by mass or more, the resulting fiber-reinforced composite material exhibits sufficient fracture toughness and impact resistance. By the content being 10 parts by mass or less, the viscosity of the epoxy resin composition does not increase significantly, impregnation into the fiber-reinforced base material becomes easy, and the properties of the resulting fiber-reinforced composite material are improved.

[0087] The thermoplastic resin preferably contains a reactive aromatic oligomer having an amine terminal group (hereinafter, also simply referred to as "aromatic oligomer"). The epoxy resin composition is polymerized by the curing reaction of the epoxy resin and the curing agent during heat curing. By the expansion of the two-phase region due to the polymerization, the aromatic oligomer dissolved in the epoxy resin composition causes reaction-induced phase separation. By this phase separation, a two-phase structure of the cured epoxy resin and the aromatic oligomer becoming co-continuous is formed in the matrix resin. Further, since the aromatic oligomer has an amine terminal group, a reaction with the epoxy resin also occurs. Since each phase in this co-continuous two-phase structure is firmly bonded to each other, the solvent resistance is also improved.

[0088] This co-continuous structure absorbs an external impact on the fiber-reinforced composite material and suppresses crack propagation. As a result, the fiber-reinforced composite material produced using the epoxy resin composition containing the reactive aromatic oligomer having an amine terminal group has high impact resistance and fracture toughness.

[0089] As this aromatic oligomer, known polysulfone having an amine terminal group and polyethersulfone having an amine terminal group can be used. The amine terminal group is preferably a primary amine (-NH2) terminal group.

[0090] When an aromatic oligomer is blended into an epoxy resin composition, it is preferable that the weight average molecular weight measured by gel permeation chromatography of the aromatic oligomer is 8,000 to 40,000. When the weight average molecular weight is 8,000 or more, the effect of improving the toughness of the matrix resin is high. Also, when the weight average molecular weight is 40,000 or less, processing advantages such as the viscosity of the resin composition not becoming too high and the resin composition being easily impregnated into the reinforcing fiber base material can be obtained.

[0091] As the aromatic oligomer, commercially available products such as "Virantage DAMS VW-30500 R P (registered trademark)" (manufactured by Solvay Specialty Polymers) can be preferably used.

[0092] The form of the thermoplastic resin before being blended into the epoxy resin composition is preferably particulate. The particulate thermoplastic resin can be uniformly blended and dissolved in the resin composition. In the epoxy resin composition of the present invention, as other additives, for example, conductive particles, flame retardants, inorganic fillers, and internal mold release agents may be blended.

[0093] Examples of the conductive particles include conductive polymer particles such as polyacetylene particles, polyaniline particles, polypyrrole particles, polythiophene particles, polyisothianaphthene particles, and polyethylene dioxythiophene particles; carbon particles; carbon fiber particles; metal particles; and particles in which a core material made of an inorganic material or an organic material is coated with a conductive substance.

[0094] Examples of the flame retardant include phosphorus-based flame retardants. The phosphorus-based flame retardant may be any one containing a phosphorus atom in the molecule, and examples thereof include organic phosphorus compounds such as phosphate esters, condensed phosphate esters, phosphazene compounds, and polyphosphates, and red phosphorus.

[0095] Examples of the inorganic filler include aluminum borate, calcium carbonate, silicon carbonate, silicon nitride, potassium titanate, basic magnesium sulfate, zinc oxide, graphite, calcium sulfate, magnesium borate, magnesium oxide, and silicate minerals. In particular, it is preferable to use silicate minerals. As a commercially available product of silicate minerals, THIXOTROPIC AGENT DT 5039 (manufactured by Huntsman Japan Co., Ltd.) can be mentioned.

[0096] Examples of the internal release agent include metal soaps, vegetable waxes such as polyethylene wax and carnauba wax, fatty acid ester-based release agents, silicone oil, animal waxes, and fluorine-based nonionic surfactants. When these internal release agents are blended, the blending amount is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 2 parts by mass, based on 100 parts by mass of the epoxy resin. Within this range, the release effect from the mold is preferably exhibited.

[0097] Examples of commercially available products of the internal release agent include "MOLD WIZ (registered trademark)" INT1846 (manufactured by AXEL PLASTICS RESEARCH LABORATORIES INC.), Licowax S, Licowax P, Licowax OP, Licowax PE190, Licowax PED (manufactured by Clariant Japan Ltd.), and stearyl stearate (SL-900A; manufactured by Riken Vitamin Co., Ltd.).

[0098] 〔Properties of the epoxy resin composition〕 The epoxy resin composition of the present invention containing the above-mentioned curing agent A, curing agent B, curing agent C, epoxy resin D, epoxy resin E, and resin particles F can have the following properties.

[0099] The viscosity of the epoxy resin composition of the present invention at 100 °C is preferably 300 mPa·s or less, more preferably 0.1 to 100 mPa·s, and particularly preferably 0.5 to 50 mPa·s. When the viscosity at 100 °C is 300 mPa·s or less, the epoxy resin composition can be easily impregnated into the reinforcing fiber base material, and the formation of voids that cause a decrease in physical properties in the obtained fiber-reinforced composite material can be prevented. Note that the relationship between viscosity and impregnability also depends on the composition of the reinforcing fiber base material.

[0100] The pot life of the epoxy resin composition of the present invention varies depending on the molding conditions of the composite material. For example, when a large composite material is impregnated into a fiber base material at a relatively low impregnation pressure using the resin transfer molding method (RTM method), as the pot life, the time until the viscosity when held at 100 °C exceeds 5 0 mPa·s is preferably 40 minutes or more, more preferably 60 minutes or more, and particularly preferably 90 minutes or more.

[0101] 〔Method for producing epoxy resin composition〕 The epoxy resin composition of the present invention can be produced by mixing an epoxy resin main agent liquid, a curing agent liquid, and resin particles F. The resin particles F may be mixed with the epoxy resin main agent liquid first and then with the curing agent liquid, or the resin particles F may be mixed with the curing agent liquid first and then with the epoxy resin main agent liquid. The order of these mixings does not matter. As the state of the epoxy resin composition, it may be in a one-liquid state in which each component is uniformly mixed, or in a slurry state in which some components are dispersed as solids.

[0102] Any conventionally known method may be used for the method for producing the epoxy resin composition. The mixing temperature is, for example, 40 to 180 °C, preferably 50 to 160 °C, and more preferably 50 to 120 °C. If it exceeds 180 °C, the curing reaction may proceed immediately, resulting in a decrease in the impregnability to the reinforcing fiber base material or a decrease in the physical properties of the cured product. If it is less than 40 °C, the viscosity of the epoxy resin main agent may be high, and mixing may be substantially difficult.

[0103] As the mixing mechanical device, a conventionally known one can be used. As specific examples, a roll mill, a planetary mixer, a kneader, an extruder, a Banbury mixer, a mixing container equipped with stirring blades, and a horizontal mixing tank can be exemplified. The mixing of each component can be carried out in the atmosphere or in an inert gas atmosphere. When mixing in the atmosphere, an atmosphere with controlled temperature and humidity is preferable. For example, it is preferable to mix in a temperature controlled at a constant temperature of 30°C or lower, or in a low humidity atmosphere with a relative humidity of 50%RH or lower.

[0104] 〔Method for producing curing agent liquid〕 The curing agent liquid contains curing agent A, curing agent B, and curing agent C. Curing agent A, curing agent B, and curing agent C are mixed, including other components as necessary, and used as the curing agent liquid. As the state of this curing agent liquid, it may be in a one-liquid state in which each component is uniformly miscible, or in a slurry state in which some components are dispersed as solids.

[0105] Any conventionally known method may be used as the method for producing the curing agent liquid. The mixing temperature is, for example, 50 to 200°C, preferably 50 to 150°C, and more preferably 80 to 120°C. If it exceeds 200°C, the components to be added may be thermally decomposed. On the other hand, if it is less than 50°C, the solid curing agent A and curing agent C will not melt, and it will be difficult to melt into curing agent B, so it becomes difficult to obtain the curing agent liquid which is a liquid thermosetting resin curing agent composition.

[0106] As the mixing mechanical device, a conventionally known one can be used. As specific examples, a roll mill, a planetary mixer, a kneader, an extruder, a Banbury mixer, a mixing container equipped with stirring blades, and a horizontal mixing tank can be exemplified. The mixing of each component can be carried out in the atmosphere or in an inert gas atmosphere. When mixing in the atmosphere, an atmosphere with controlled temperature and humidity is preferable. For example, it is preferable to mix in a temperature controlled at a constant temperature of 30°C or lower, or in a low humidity atmosphere with a relative humidity of 50%RH or lower.

[0107] 〔Method for Producing Epoxy Resin Main Agent Liquid〕 The epoxy resin main agent liquid used for producing an epoxy resin composition can be produced by mixing epoxy resin D, epoxy resin E, resin particles F if necessary, and other optional components. The order of these mixtures does not matter. As the state of the epoxy resin main agent liquid, it may be in a one-liquid state in which each component is uniformly miscible, or in a slurry state in which some components are dispersed as solids.

[0108] Any conventionally known method may be used for the method for producing the epoxy resin main agent liquid. The mixing temperature is, for example, 40 to 200 ° C, preferably 50 to 100 ° C, more preferably 50 to 90 ° C. When it exceeds 200 ° C, the self-polymerization reaction of the epoxy resin may partially proceed, resulting in a decrease in the impregnability to the reinforcing fiber base material, or a decrease in the physical properties of the cured product produced using the obtained epoxy resin main agent liquid. When it is less than 40 ° C, the viscosity of the epoxy resin main agent is high, and mixing may be substantially difficult.

[0109] As the mixing mechanical device, a conventionally known one can be used. Specific examples include a roll mill, a planetary mixer, a kneader, an extruder, a Banbury mixer, a mixing container equipped with stirring blades, and a horizontal mixing tank. The mixing of each component can be performed in the air or in an inert gas atmosphere. When mixing is performed in the air, an atmosphere in which the temperature and humidity are controlled is preferable. For example, it is preferable to mix in a constant temperature of 30 ° C or lower or a low humidity atmosphere of 50% RH or lower in relative humidity.

[0110] 〔Resin Cured Product〕 The epoxy resin composition of the present invention can be cured to obtain a resin cured product. The obtained resin cured product can have the following properties. The degree of cure of the cured product after heating the epoxy resin composition at 180 ° C for 40 minutes, evaluated by measuring the degree of dielectric cure, is preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more from the viewpoint of the productivity of the fiber-reinforced composite material.

[0111] The glass transition temperature in the dry state (dry-Tg) is preferably 140 °C or higher, more preferably 170 °C or higher, and particularly preferably 180 °C or higher. The glass transition temperature at saturation water absorption (wet-Tg) is preferably 120 °C or higher, more preferably 150 to 200 °C.

[0112] The room temperature dry bending modulus (RTD-FM) measured by the JIS K7171 method is preferably 3.0 GPa or higher, more preferably 3.3 to 10.0 GPa, and even more preferably 3.5 to 9.0 GPa. By exceeding 3.0 GPa, the fiber-reinforced composite material obtained using the epoxy resin composition of the present invention has excellent mechanical properties.

[0113] The bending modulus after water absorption during heating (HTW-FM) measured by the JIS K7171 method is preferably 2.4 GPa or higher, more preferably 2.5 to 9.0 GPa, and particularly preferably 2.8 to 8.0 GPa. The critical stress intensity factor KIc for mode I deformation measured by ASTM D5045 is preferably 0.7 MPa·m 1 / 2 or higher, more preferably 0.8 to 3.0 MPa·m 1 / 2 or more.

[0114] 〔Fiber-reinforced composite material〕 A fiber-reinforced composite material can be obtained by compounding and curing a fiber-reinforced substrate and the epoxy resin composition of the present invention. Examples of the fibers of the reinforcing fiber substrate include carbon fiber, glass fiber, aramid fiber, silicon carbide fiber, polyester fiber, ceramic fiber, alumina fiber, boron fiber, metal fiber, mineral fiber, rock fiber, and slag fiber.

[0115] Among these reinforcing fibers, carbon fiber, glass fiber, and aramid fiber are preferred. Carbon fiber is more preferred because a fiber-reinforced composite material with good specific strength and specific modulus, being lightweight and high-strength, can be obtained. Among carbon fibers, polyacrylonitrile (PAN)-based carbon fibers are particularly preferred because of their excellent tensile strength.

[0116] When using PAN-based carbon fibers as the reinforcing fibers, their tensile modulus is preferably 100 to 600 GPa, more preferably 200 to 500 GPa, and even more preferably 230 to 450 GPa. The tensile strength is preferably 2000 to 10000 MPa, and more preferably 3000 to 8000 MPa.

[0117] When using carbon fibers as the reinforcing fibers, the diameter of the carbon fibers is preferably 4 to 20 μm, and more preferably 5 to 10 μm. By using such carbon fibers, the mechanical properties of the obtained fiber-reinforced composite material can be improved.

[0118] In the present invention, the reinforcing fibers are preferably treated with a sizing agent. In this case, with respect to the mass of the reinforcing fibers to which the sizing agent is attached, the attachment amount of the sizing agent is preferably 0.01 to 10% by mass, more preferably 0.05 to 3.0% by mass, and even more preferably 0.1 to 2.0% by mass. A larger attachment amount of the sizing agent tends to strengthen the adhesiveness between the reinforcing fibers and the matrix resin. On the other hand, a smaller attachment amount tends to result in excellent interlaminar toughness of the obtained composite material.

[0119] For the fiber-reinforced base material, it is preferable to use a reinforcing fiber sheet formed by forming the reinforcing fibers into a sheet shape. Examples of the reinforcing fiber sheet include a sheet in which a number of reinforcing fibers are aligned in one direction, a two-way fabric such as a plain weave or twill weave, a multi-axial fabric, a non-woven fabric, a mat, a knit, a braid, and a paper made by papermaking the reinforcing fibers. Among them, it is preferable to use a one-way alignment sheet, a two-way fabric, or a multi-axial fabric base material formed by forming the reinforcing fibers into a sheet shape as continuous fibers, because a fiber-reinforced composite material having more excellent mechanical properties can be obtained.

[0120] The two-direction fabric or multi-axis fabric substrate may be formed by laminating and stitching a plurality of unidirectional alignment sheets. In this case, in order to improve the interlaminar toughness of the obtained fiber-reinforced composite material, a nonwoven fabric layer of a thermoplastic resin may be disposed on one side of the unidirectional alignment sheet and then laminated to form a fabric. Examples of the nonwoven fabric layer of the thermoplastic resin include fibers made of polyester resin fibers, polyamide resin fibers, polyether sulfone resin fibers, polysulfone resin fibers, polyether imide resin fibers, polycarbonate resin fibers, and resin mixtures thereof.

[0121] The basis weight and number of laminations of the unidirectional alignment sheet can be appropriately set according to the use of the fiber-reinforced composite material. For example, the basis weight of the unidirectional alignment sheet is, for example, 100 to 300 g / m 2 , preferably 150 to 250 g / m 2 . The thickness of each layer of the unidirectional alignment sheet of the reinforcing fiber substrate is preferably 0.01 to 3 mm, more preferably 0.05 to 1.5 mm.

[0122] According to the present invention, there is provided a fiber-reinforced composite material including a resin cured product obtained by curing the epoxy resin composition of the present invention and a fiber-reinforced substrate. The fiber-reinforced composite material provided by the present invention has a post-impact compression strength CAI (impact energy 30.5 J) measured by ASTM D7136, preferably 240 MPa or more, more preferably 250 to 400 MPa, and even more preferably 260 to 380 MPa.

[0123] The fiber-reinforced composite material provided by the present invention has a room temperature dry open-hole compression strength (RTD-OHC) measured by SACMA SRM3, preferably 260 MPa or more, more preferably 280 to 450 MPa, and even more preferably 300 to 400 MPa. The fiber-reinforced composite material provided by the present invention has a hot-wet open-hole compression strength (HTW-OHC) measured by SACMA SRM3, preferably 200 MPa or more, more preferably 220 to 400 MPa, and even more preferably 240 to 350 MPa.

[0124] [Method for manufacturing fiber-reinforced composite material] As a method of compounding a fiber-reinforced base material and an epoxy resin composition in order to obtain a fiber-reinforced composite material including a resin cured product formed by curing an epoxy resin composition and a fiber-reinforced base material, the fiber-reinforced base material and the resin composition may be compounded in advance. For example, they may be compounded during molding, such as by the resin transfer molding method (RTM method), the hand lay-up method, the filament winding method, or the pultrusion method.

[0125] After compounding a fiber-reinforced base material and the epoxy resin composition of the present invention, heating and curing can obtain a fiber-reinforced composite material. Therefore, according to the present invention, there is provided a method for manufacturing a fiber-reinforced composite material including a step of impregnating the above epoxy resin composition into a fiber-reinforced base material disposed in a mold and then heat-curing.

[0126] As a method for manufacturing a fiber-reinforced composite material using the epoxy resin composition of the present invention, known molding methods such as the RTM method, the autoclave molding method, and the press molding method can be exemplified. The resin composition of the present invention is particularly suitable for the RTM method.

[0127] From the viewpoint of efficiently obtaining a fiber-reinforced composite material with a complex shape, the RTM method is a preferable molding method. This RTM method is a method of impregnating and curing a liquid epoxy resin composition into a fiber-reinforced base material disposed in a mold to obtain a fiber-reinforced composite material.

[0128] In the present invention, as the mold used in the RTM method, a closed mold made of a rigid material may be used, or an open mold of a rigid material and a flexible film (bag) may be used. In the latter case, the fiber-reinforced base material can be installed between the open mold of the rigid material and the flexible film. As the rigid material, for example, metals such as steel and aluminum, fiber-reinforced plastics, wood, and gypsum can be used. As the material of the flexible film, for example, polyamide, polyimide, polyester, fluororesin, and silicone resin can be used.

[0129] When using a closed mold of a rigid material in the RTM method, it is usually carried out to apply pressure to clamp the mold and inject the epoxy resin composition under pressure. At this time, a suction port may be provided separately from the injection port and connected to a vacuum pump for suction. Suction may be performed, and the epoxy resin composition may be injected only by atmospheric pressure without using special pressurizing means. This method can be preferably used because a large member can be manufactured by providing a plurality of suction ports.

[0130] In the RTM method, when using an open mold of a rigid material and a flexible film, suction may be performed, and the epoxy resin may be injected only by atmospheric pressure without using special pressurizing means. In order to achieve good impregnation by injection only with atmospheric pressure, it is effective to use a resin diffusion medium. Further, prior to the installation of the fiber-reinforced base material, it is preferably performed to apply a gel coat to the surface of the rigid material.

[0131] In the RTM method, after the fiber-reinforced base material is impregnated with the epoxy resin composition, heat curing is performed. The mold temperature during heat curing is usually selected to be higher than the mold temperature at the time of injection of the epoxy resin composition. The mold temperature during heat curing is preferably 80 to 200 °C. The time for heat curing is preferably 1 minute to 20 hours. After the heat curing is completed, demolding is performed to take out the fiber-reinforced composite material. Thereafter, the obtained fiber-reinforced composite material may be heated at a higher temperature for post-curing. The temperature for this post-curing is preferably 150 to 200 °C, and the time is preferably 1 minute to 4 hours.

[0132] The impregnation pressure when impregnating the fiber-reinforced base material with the epoxy resin composition by the RTM method is appropriately determined in consideration of the viscosity of the resin composition, resin flow, etc. The specific impregnation pressure is, for example, 0.001 to 10 MPa, preferably 0.01 to 1 MPa. When obtaining a fiber-reinforced composite material using the RTM method, the viscosity of the epoxy resin composition preferably has a viscosity at 100 °C of 1 to 200 mPa·s.

Example

[0133] Hereinafter, the present invention will be described more specifically by way of examples. The components and test methods used in the examples and comparative examples are as follows. Note that the fiber-reinforced composite material may be abbreviated as "FRP", and in particular, the carbon fiber-reinforced composite material may be abbreviated as "CFRP".

[0134] 〔Components〕 (1) Curing agent A · 4,4'-Diamino-3,3'-diisopropyl-5,5'-dimethyldiphenylmethane (Lonzacure M-MIPA (product name) manufactured by Lonza, hereinafter abbreviated as "M-MIPA", melting point 70 °C, solid at 25 °C) · 4,4'-Diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane (MED-J (product name) manufactured by Kumiai Chemical Industry Co., Ltd., hereinafter abbreviated as "MED-J", melting point 76 °C, solid at 25 °C)

[0135] (2) Curing agent B · Diethyltoluenediamine (Heart Cure 10 (product name) manufactured by Kumiai Chemical Industry Co., Ltd., hereinafter abbreviated as "DETDA", liquid at 25 °C) · Dimethylthiotoluenediamine (Heart Cure 30 (product name) manufactured by Kumiai Chemical Industry Co., Ltd., hereinafter abbreviated as "DMTDA", liquid at 25 °C) · 4,4'-Diamino-3,3'-diethyldiphenylmethane (Kayhard A-A (product name) manufactured by Nippon Kayaku Co., Ltd., hereinafter abbreviated as "Kayhard AA", liquid at 25 °C)

[0136] (3) Curing agent C · 3,4'-Diaminodiphenyl ether (manufactured by Teijin Chemicals, hereinafter abbreviated as "3,4'-DAPE", melting point 80 °C, solid at 25 °C) · 1,3-Bis(4-aminophenoxy)benzene (manufactured by Tokyo Chemical Industry Co., Ltd., hereinafter abbreviated as "TPE-R", melting point 116 °C, solid at 25 °C) · m-Phenylenediamine (manufactured by Fujifilm Wako Pure Chemical Corporation, hereinafter abbreviated as "MPD", melting point 65 °C, solid at 25 °C)

[0137] (4) Epoxy resin D · Tetraglycidyl-4,4'-diaminodiphenylmethane (Araldite MY721 (product name) manufactured by Huntsman Corporation, hereinafter abbreviated as "4,4'-TGDDM") · Tetraglycidyl-3,4'-diaminodiphenyl ether (synthesized by the method of Synthesis Example 1, hereinafter abbreviated as "3,4'-TGDDE")

[0138] (5) Epoxy resin E · N,N-Diglycidyl-o-toluidine (GOT (product name) manufactured by Nippon Kayaku Co., Ltd., hereinafter abbreviated as "GOT") · N,N-Diglycidylaniline (GAN (product name) manufactured by Nippon Kayaku Co., Ltd., hereinafter abbreviated as "GAN") · Triglycidyl-p-aminophenol (Araldite MY0510 (product name) manufactured by Huntsman Corporation, hereinafter abbreviated as "TG-pAP") · 1,6-Bis(glycidyloxy)naphthalene (HP-4032SS (product name) manufactured by DIC Corporation, hereinafter abbreviated as "1,6-DON") · 1,3,5-Triglycidyl isocyanurate (TEPIC-S (product name) manufactured by Nissan Chemical Industries, Ltd., hereinafter abbreviated as "TEPIC") · Bisphenol A-diglycidyl ether (jER825 (product name) manufactured by Mitsubishi Chemical Corporation, hereinafter abbreviated as "DGEBA")

[0139] (6) Resin particles F · MX-416 (MX-416 (product name) manufactured by Kaneka Corporation, a masterbatch in which a particulate butadiene rubber component is dispersed in a glycidylamine type tetrafunctional epoxy resin at a concentration of 25% by mass) (the glycidylamine type tetrafunctional epoxy resin in the product corresponds to the epoxy resin D of the present invention)

[0140] (7) Carbon fiber strand · Carbon fiber 1: "Tenax (registered trademark)" IMS65 E23 830 tex (carbon fiber strand, tensile strength 5.8 GPa, tensile modulus 290 GPa, sizing agent adhesion amount 1.2% by mass, manufactured by Teijin Limited)

[0141] (8) Thermoplastic resin nonwoven fabric · Nonwoven fabric 1: A nonwoven fabric made of polyamide 12 resin by the spunbond method with a fiber basis weight of 5 g / m 2 of nonwoven fabric

[0142] (9) Carbon fiber multilayer fabric · Carbon fiber multi-axial fabric 1: Carbon fibers 1 aligned in one direction are made into a sheet with 190 g / m per layer, nonwoven fabric 1 is placed on one side of this sheet-like carbon fiber, and four layers are laminated and stitched at an angle of (+45 / V / 90 / V / -45 / V / 0 / V) (the total basis weight of carbon fibers in the fabric substrate is 760 g / m 2 ). 2 ) · Carbon fiber multi-axial fabric 2: Carbon fibers 1 aligned in one direction are made into a sheet with 190 g / m per layer, nonwoven fabric 1 is placed on one side of the sheet-like carbon fiber, and four layers are laminated and stitched at an angle of (-45 / V / 90 / V / +45 / V / 0 / V) (the total basis weight of carbon fibers in the fabric substrate is 760 g / m 2 ) Here, V represents nonwoven fabric 1 2 )

[0143] (10) Synthesis example of epoxy resin Synthesized by the method of Synthesis example 1 below Synthesis example 1 Synthesis of 3,4’-TGDDE 1110.2 g (12.0 mol) of epichlorohydrin was charged into a four-necked flask equipped with a thermometer, a dropping funnel, a condenser tube, and a stirrer. While purging with nitrogen, the temperature was raised to 70 °C, and 200.2 g (1.0 mol) of 3,4'-diaminodiphenyl ether dissolved in 1000 g of ethanol was added dropwise thereto over 4 hours. Stirring was continued for another 6 hours to complete the addition reaction, and N,N,N',N'-tetrakis(2-hydroxy-3-chloropropyl)-3,4'-diaminodiphenyl ether was obtained. Subsequently, after lowering the temperature inside the flask to 25 °C, 500.0 g (6.0 mol) of a 48 wt% aqueous NaOH solution was added dropwise thereto over 2 hours and stirring was continued for another 1 hour. After the cyclization reaction was completed, ethanol was distilled off, extraction was performed with 400 g of toluene, and washing was performed twice with 5% saline. When toluene and epichlorohydrin were removed from the organic layer under reduced pressure, 361.7 g (yield 85.2%) of a brown viscous liquid was obtained. The purity of the main product 3,4'-TGDDE was 84% (HPLC area%).

[0144] 〔Evaluation method〕 (1) Characteristics of the resin composition (1-1) Preparation of the epoxy resin composition The epoxy resin and resin particles were weighed at the ratios shown in Table 1 and mixed at 80 °C for 30 minutes using a stirrer to prepare a main epoxy resin solution. The curing agent components were weighed at the ratios shown in Table 1 and mixed at 80 °C for 30 minutes using a stirrer to prepare a curing agent solution. The separately prepared main epoxy resin solution and curing agent solution were mixed at 80 °C for 30 minutes using a stirrer to prepare an epoxy resin composition. In the composition shown in Table 1, the glycidyl groups of the epoxy resin and the amino groups of the curing agent are equivalent.

[0145] (1-2) Liquid retention characteristics of the curing agent solution The curing agent solution prepared in (1-1) above was allowed to stand at 25 °C for 1 week, and precipitation of solid components was visually confirmed. Those without precipitation were marked as "○", and those with observed precipitation were marked as "×".

[0146] (1-3) Initial viscosity and pot life The viscosity measurement was performed using a B-type viscometer TVB-15M manufactured by Toki Sangyo Co., Ltd. under the condition of 100 °C. The minimum measured value immediately after the start of the measurement was defined as the initial viscosity, and the time when the viscosity reached 50 mPa·s was defined as the pot life.

[0147] (1-4) Curing characteristics (DEA degree of cure) after heating at 180 °C for 40 minutes The curing characteristics were evaluated by using a dielectric analysis apparatus DEA288 Ionic manufactured by NETZSCH to calculate the DEA degree of cure α of the resin cured product after heating the uncured resin at 180 °C for 40 minutes according to the following formula. When this degree of cure is 90% or more, it can be evaluated as a resin composition having curing characteristics for 40 minutes. α(t = 40) =(logε”0 - logε” t=40 ) / (logε”0 - logε” ∞ ) × 100 (However, ε”0 is the maximum value of the dielectric loss at the start of the measurement, ε” t=40 is the dielectric loss value at the measurement time of 40 minutes, and ε” ∞ is the dielectric loss value at the measurement time of 180 minutes.) Measurement conditions Measurement temperature: 180 ± 2 °C isothermal Measurement frequency: 1 Hz Measurement sensor: IDEX 115 / 35 manufactured by NETZSCH

[0148] (2) Characteristics of the resin cured product (2-1) Preparation of the resin cured product The epoxy resin composition prepared in (1-1) above was degassed in vacuo for 60 minutes, and then injected into a stainless mold set to a thickness of 4 mm with a 4 mm thick Teflon (registered trademark) resin spacer. It was heat-cured at a temperature of 180 °C for 40 minutes to obtain a resin cured product with a thickness of 4 mm.

[0149] (2-2) Glass transition temperature after water absorption (wet-Tg) The glass transition temperature was measured according to the SACMA 18R-94 method. The resin test pieces were prepared with dimensions of 50 mm × 6 mm × 2 mm. Using a pressure cooker (manufactured by Espec, HASTEST PC-422R8), the water absorption treatment of the resin test pieces prepared under the conditions of 121 °C for 24 hours was carried out. Using a dynamic viscoelasticity measuring device Rheogel-E400 manufactured by UBM, under the conditions of a measurement frequency of 1 Hz, a heating rate of 5 °C / min, and a strain of 0.0167%, with the distance between the chucks set at 30 mm, the storage elastic modulus E’ of the water absorption-treated resin test pieces was measured from 50 °C to the rubber elastic region. logE’ was plotted against the temperature, and the temperature obtained from the intersection of the approximate straight line in the flat region of logE’ and the approximate straight line in the region where E’ transitions was recorded as the glass transition temperature (wet-Tg).

[0150] (2-3) Room temperature dry resin flexural modulus (RTD-FM) The test was carried out in accordance with JIS K7171 method. Using the resin cured plate obtained in (2-1) above resin test pieces were prepared with dimensions of 80 mm × 10 mm × 4 mm (thickness h). At an environmental temperature of 25 °C, with the distance between the supports L being 16 × h (thickness), a flexural test was carried out at a test speed of 2 mm / min, and the flexural strength and flexural modulus were measured.

[0151] (2-4) Toughness of resin cured product (critical stress intensity factor KIc for mode I deformation) In accordance with ASTM D5045, the toughness (KIc) was measured using a universal testing machine (Autograph manufactured by Shimadzu Corporation). The test was carried out in accordance with ASTM D5045 method. Using the resin cured plate obtained in (2-1) above, resin test pieces were prepared with dimensions of 50 mm × 8 mm (width W) × 4 mm. The crack length a was adjusted so that 0.45 ≦ a / W ≦ 0.55. The crack length a was observed using an optical microscope on the fracture surface after the fracture test, and the length to the tip of the crack and the average value of the crack lengths on both surfaces of the test piece were adopted.

[0152] (3) Characteristics of CFRP (3-1) Fabrication of CFRP The carbon fiber multi-axial fabric 1 and the carbon fiber multi-axial fabric 2 were cut into 300×300 mm pieces, and 3 pieces of the carbon fiber multi-axial fabric 1 and 3 pieces of the carbon fiber multi-axial fabric 2 were stacked on a 500×500 mm release-treated aluminum plate to form a laminate, for a total of 6 layers. Furthermore, on the laminate, the Release of the peel cloth, which is a base material with a release function, Ply C (manufactured by AIRTECH) and Resin Flow 90HT (manufactured by AIRTECH), a resin diffusion base material, were laminated. Then, hoses for forming a resin injection port and a resin discharge port were arranged, and the whole was covered with a nylon bag film, sealed with a sealing tape, and the inside was evacuated. Subsequently, the aluminum plate was heated to 120°C, the pressure inside the bag was reduced to 5 torr or less, and then the epoxy resin composition prepared in (1-1) above was heated to 100°C and injected into the vacuum system through the resin injection port. The injected epoxy resin composition filled the bag and was heated to 180°C while impregnating the laminate, and held at 180°C for 40 minutes to obtain a carbon fiber reinforced composite material (CFRP).

[0153] (3-2) Compressive strength after impact (CAI) The CFRP obtained in (3-1) above was cut into dimensions of 101.6 mm in width × 152.4 mm in length to obtain test pieces for the compressive strength after impact (CAI) test. The test was carried out in accordance with ASTM D7136. After measuring the dimensions of each test piece, for the impact test, a drop weight impact tester (Dynatup manufactured by Instron) was used to apply an impact energy of 30.5 J. After the impact, the damaged area of the specimen was measured with an ultrasonic flaw detector (SDS3600, HIS3 / HF manufactured by Krautkramer). After the impact, for the strength test of the specimen, strain gauges were attached one each on the left and right at a position 25.4 mm from the top and 25.4 mm from the side of the specimen, and a total of 4 strain gauges per specimen were attached to the front and back in the same way. Then, the crosshead speed of the testing machine (Autograph manufactured by Shimadzu Corporation) was set to 1.27 mm / min, and a load was applied until the specimen broke.

[0154] (3-3) Room temperature dry open-hole compressive strength (RTD-OHC) The CFRP obtained in the above (3-1) was cut into dimensions of width 38.1 mm × length 304.8 mm, and a hole with a diameter of 6.35 mm was drilled at the center of the test piece to obtain a test piece for the room temperature dry perforated compression strength (RTD-OHC) test. The test was carried out in an environmental temperature of 25 °C in accordance with SACMA SRM3, and the perforated compression strength was calculated from the maximum point load.

[0155] (4) Average particle diameter The cross-section of the resin cured product is observed at 25,000 times magnification with a scanning electron microscope or a transmission electron microscope, and the diameters of at least 50 or more particles are measured as the particle diameters of the resin particles, and the average particle diameter can be obtained by averaging them. In the above observation, when the particles are not circular i.e., when the particles are elliptical, the maximum diameter of the particle is taken as the particle diameter of the particle.

[0156] [Example 1] (Preparation of epoxy resin composition) The epoxy resin and resin particles F were weighed at the ratios shown in Table 1 and mixed at 80 °C for 30 minutes using a stirrer to prepare an epoxy resin main agent solution. The curing agent component was weighed at the ratios shown in Table 1 and mixed at 80 °C for 30 minutes using a stirrer to prepare a curing agent solution. These separately prepared epoxy resin main agent solution and curing agent solution were mixed at 80 °C for 30 minutes using a stirrer to prepare an epoxy resin composition. The properties of the obtained epoxy resin composition are shown in Table 1. In the composition described in Table 1, the glycidyl group of the epoxy resin and the amino group of the curing agent are equivalent.

[0157] (Preparation of resin cured product) After degassing the epoxy resin composition obtained above in a vacuum for 60 minutes, it was poured into a stainless mold set to a thickness of 4 mm by a 4 mm thick Teflon resin spacer. It was heat-cured at a temperature of 180 °C for 40 minutes to obtain a resin cured product with a thickness of 4 mm. The properties of the obtained resin cured product are shown in Table 1. The wet-Tg of the resin cured product is 150 °C or higher, the flexural modulus is 3.0 GPa or higher, and K1c is 0.7 MPa·m1 / 2 This was the case, and high mechanical properties were exhibited.

[0158] (Fabrication of Fiber Reinforced Composite Material) Next, the carbon fiber multi-axial fabric 1 and the carbon fiber multi-axial fabric 2 were cut into 300×300 mm pieces, and three pieces of the carbon fiber multi-axial fabric 1 and three pieces of the carbon fiber multi-axial fabric 2 were stacked on a 500×500 mm release-treated aluminum plate to form a laminate.

[0159] Furthermore, on the laminate, the Release Ply C (manufactured by AIRTECH) of the peel cloth, which is a base material with a release function, and the Resin Flow 90HT (manufactured by AIRTECH) of the resin diffusion base material were laminated. Then, hoses for forming a resin injection port and a resin discharge port were arranged, the whole was covered with a nylon bag film, sealed with a sealing tape, and the inside was evacuated. Subsequently, the aluminum plate was heated to 120°C, the pressure inside the bag was reduced to 5 torr or less, and then the epoxy resin composition prepared above was heated to 100°C and injected into the vacuum system through the resin injection port.

[0160] The injected epoxy resin composition filled the inside of the bag and was heated to 180°C while impregnating the laminate, and held at 180°C for 2 hours to obtain a carbon fiber reinforced composite material (CFRP). The properties of the obtained CFRP are shown in Table 1. All of them showed a high CAI of 250 MPa or more and an excellent RTD-OHC of 300 MPa or more.

[0161] 〔Examples 2 to 14〕 The same procedure as in Example 1 was carried out except that the composition was changed as shown in Table 1. The evaluation results are shown in Table 1.

[0162]

Table 1-1

[0163]

Table 1-2

[0164] [Comparative Examples 1 to 8] The procedure of Example 1 was repeated except that the composition was changed as shown in Table 2. The evaluation results are shown in Table 2.

[0165] [Table 2]

[0166] In Comparative Examples 1, 3, and 4, since Curing Agent B was not used, solids precipitated within one week in all cases. In Comparative Examples 1, 2, and 5, since Curing Agent C was not used, the DEA curing degree was significantly reduced and fast curability was not exhibited. In Comparative Example 6, since Epoxy Resin D was not used, the wet-Tg of the obtained resin cured product was as low as 116°C. In Comparative Example 7, since Epoxy Resin E was not used, the initial viscosity of the resin composition became as high as 131 mPa·s. In Comparative Example 8, since Resin Particles F were not used, the KIc of the obtained resin cured product was 0.57 MPa·m 1 / 2 and was low. [Industrial Applicability]

[0167] When the epoxy resin composition of the present invention is used, a resin cured product having excellent mechanical properties can be produced. Further, since the epoxy resin composition of the present invention has a low viscosity and a long pot life, it has high handleability during molding, and since the curing time is short, a fiber-reinforced composite material having excellent quality and mechanical properties can be produced with higher productivity than before. The obtained fiber-reinforced composite material can be used as a member of an automobile or an aircraft.

Claims

1. An epoxy resin composition comprising a curing agent A, a curing agent B, a curing agent C, an epoxy resin D, an epoxy resin E, and resin particles F, wherein the curing agent A is a solid at 25°C and is an aromatic polyamine having substituents at two ortho positions with respect to the amino group, the substituents being selected from an alkyl group, an aromatic group, and a halogen group and being a 4,4'-diaminodiphenylmethane derivative, the curing agent B is an aromatic polyamine that is liquid at 25°C, the curing agent C is a solid at 25°C and is an aromatic polyamine having a melting point of 150°C or lower, and the aromatic polyamine is an aromatic polyamine (excluding 4,4'-diaminodiphenylmethane derivatives) having only one electron-donating group at the ortho position with respect to the amino group or having no substituent at the ortho position, the epoxy resin D is composed of an epoxy resin composed of monomers containing four or more glycidyl groups, and the epoxy resin E is composed of an epoxy resin composed of monomers containing two or three glycidyl groups.

2. The epoxy resin composition according to claim 1, wherein the monomer containing four or more glycidyl groups of the epoxy resin D is represented by the following chemical formula. 【Chemical Formula 1】 (However, in Chemical Formula (1), R １ ~R ４ each independently represents one selected from the group consisting of a hydrogen atom, an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and a halogen atom, and X represents one selected from -CH ２ -, -O-, -S-, -CO-, -C(=O)O-, -O-C(=O)-, -NHCO-, -CONH-, -SO ２ -.)

3. The epoxy resin composition according to claim 2, wherein the monomer containing four or more glycidyl groups of epoxy resin D is one or a combination of two or more selected from the group consisting of tetraglycidyl-4,4'-diaminodiphenyl ether, tetraglycidyl-4,4'-diaminodiphenyl methane, tetraglycidyl-3,4'-diaminodiphenyl ether, and tetraglycidyl-3,3'-diaminodiphenyl methane.

4. The resin composition according to any one of claims 1 to 3, wherein epoxy resin D is contained in an amount of 50 to 90% by mass based on the total mass of the epoxy resins contained in the epoxy resin composition.

5. The epoxy resin composition according to any one of claims 1 to 4, wherein the monomer containing two or three glycidyl groups of epoxy resin E is one or a combination of two or more selected from the group consisting of diglycidylaniline, diglycidyl-o-toluidine, triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, 1,6-bis(2,3-epoxypropan-1-yloxy)naphthalene, and 1,3,5-triglycidyl isocyanurate.

6. The epoxy resin composition according to any one of claims 1 to 5, wherein the total of curing agent A, curing agent B, and curing agent C accounts for 70 to 100% by mass based on the total mass of the curing agents contained in the epoxy resin composition, the mass ratio of curing agent A to curing agent B is 1:99 to 99:1, and curing agent C is 1 to 43 parts by mass with respect to 100 parts by mass in total of curing agent A and curing agent B.

7. The epoxy resin composition according to any one of claims 1 to 6, wherein the electron donating group of the aromatic polyamine of curing agent C is a methyl group, an ethyl group, a propyl group, an isopropyl group, a methoxy group, or an ethoxy group.

8. The epoxy resin composition according to any one of claims 1 to 7, wherein the aromatic polyamine of curing agent B is a phenylenediamine derivative or a 4,4'-diaminodiphenyl methane derivative.

9. A mixture of hardener A, hardener B, and hardener C is a uniform liquid at a temperature of 80 to 200 °C, and after raising the liquid temperature to 200 °C and then lowering the liquid temperature to 25 °C and allowing it to stand at 25 °C for 1 week, it is a uniform liquid. The epoxy resin composition according to any one of claims 1 to 8.

10. The ratio of the number of total epoxy groups in the epoxy resin to the number of active hydrogens contained in the hardener is 0.7 to 1.

3. The epoxy resin composition according to any one of claims 1 to 9.

11. The average particle diameter of the resin particles is 1.0 μm or less. The epoxy resin composition according to any one of claims 1 to 10.

12. The degree of curing after heating at 180 °C for 40 minutes, evaluated by measuring the degree of dielectric curing, is 70% or more. The epoxy resin composition according to any one of claims 1 to 11.

13. A resin cured product obtained by curing the epoxy resin composition according to any one of claims 1 to 12.

14. A fiber-reinforced composite material comprising a resin cured product obtained by curing the epoxy resin composition according to any one of claims 1 to 12 and a fiber-reinforced base material.

15. The fiber-reinforced composite material according to claim 14, wherein the fiber-reinforced base material is a carbon fiber-reinforced base material.

16. A method for producing a fiber-reinforced composite material, comprising compositeizing and curing a fiber-reinforced base material and the epoxy resin composition according to any one of claims 1 to 12.

17. A method for producing a fiber-reinforced composite material, comprising impregnating the epoxy resin composition according to any one of claims 1 to 12 into a fiber-reinforced base material placed in a mold and then heat-curing.

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