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

Abstract

To provide an epoxy resin composition that enables the production of a fiber-reinforced composite material having excellent heat resistance, compression properties and impact resistance, and is also easy to impregnate due to low initial viscosity, and further has good handleability due to long pot life.SOLUTION: An epoxy resin composition comprises an epoxy compound [A] having a glycidyl group-substituted amino group and represented by a specific chemical structure, and an epoxy compound [B] having a polycyclic aromatic ring structure or a heterocyclic ring structure.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an epoxy resin composition, a prepreg, a fiber-reinforced composite material, and a manufacturing method thereof. [Background technology]

[0002] Fiber-reinforced composite materials 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.

[0003] Known methods for molding composite materials that use thermosetting resin as the matrix resin include molding a prepreg (intermediate substrate) formed into a sheet by impregnating a fiber-reinforced substrate with uncured thermosetting resin in advance, and resin transfer molding (RTM) in which a fiber-reinforced substrate placed in a mold is impregnated with liquid uncured thermosetting resin and cured to obtain a fiber-reinforced composite material.

[0004] In recent years, RTM molding has attracted attention because it offers low cost and excellent productivity due to the few steps required to manufacture fiber-reinforced composite materials and the lack of the need for expensive equipment such as autoclaves. Tetrafunctional aromatic epoxy resins are generally used as the uncured thermosetting resins used in RTM molding.

[0005] In epoxy resin compositions used in the RTM molding method, a low-viscosity difunctional aromatic epoxy resin is often used as a viscosity reducer in addition to a tetrafunctional aromatic epoxy resin to improve the impregnation of the resin composition into fiber-reinforced substrates.

[0006] However, when a difunctional aromatic epoxy resin is used as a viscosity reducer, the crosslink density of the cured resin obtained by heat-curing the epoxy resin composition decreases, resulting in a problem of reduced heat resistance and mechanical properties of the cured resin and fiber-reinforced composite material.

[0007] Fiber-reinforced composite materials using an epoxy resin composition as a matrix resin generally have low impact resistance, and there is a demand for improving the toughness of cured epoxy resin products. Patent Document 1 describes a method for imparting toughness to cured epoxy resin products by using a composition in which a thermoplastic resin is dissolved in an epoxy resin. This method makes it possible to impart a certain degree of toughness to cured epoxy resin products.

[0008] However, to impart high toughness, a large amount of thermoplastic resin must be dissolved in the epoxy resin. As a result, an epoxy resin composition containing a large amount of thermoplastic resin has a significantly high viscosity, making it difficult to impregnate a sufficient amount of resin into the fiber-reinforced substrate. Therefore, fiber-reinforced composite materials prepared using such epoxy resin compositions have inherent defects such as voids, resulting in problems such as reduced compressive performance and damage tolerance of the fiber-reinforced composite materials. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 60-243113 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide an epoxy resin composition which can be used to produce a fiber-reinforced composite material having excellent heat resistance, compression properties, and impact resistance, and which has a low initial viscosity that allows for easy impregnation, and a long pot life that makes it easy to handle. [Means for solving the problem]

[0011] That is, the present invention provides an epoxy resin composition comprising an epoxy compound [A] represented by the following chemical formula (1) (wherein R1 to R4 each independently represent a hydrogen atom, an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or a halogen atom, and X1 represents -CH2-, -O-, -S-, -CO-, -C(=O)O-, -OC(=O)-, -NHCO-, -CONH-, or -SO2-), and an epoxy compound [B] having a polycyclic aromatic ring structure or a heterocyclic ring structure.

[0012] [ka] [Effects of the Invention]

[0013] According to the present invention, it is possible to produce a fiber-reinforced composite material having excellent heat resistance, compression properties, and impact resistance, and it is also possible to provide an epoxy resin composition which has a low initial viscosity, which allows for easy impregnation, and a long pot life, which makes it easy to handle. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below. Note that fiber reinforced composite material may be abbreviated as "FRP" and carbon fiber reinforced composite material may be abbreviated as "CFRP."

[0015] [Epoxy compound [A]] The epoxy resin composition of the present invention contains an epoxy compound [A] represented by the following chemical formula (1) (wherein R1 to R4 each independently represent a hydrogen atom, an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or a halogen atom, and X1 represents -CH2-, -O-, -S-, -CO-, -C(=O)O-, -OC(=O)-, -NHCO-, -CONH-, or -SO2-).

[0016] [ka]

[0017] To prevent inhibition of the chemical reaction during curing of the epoxy resin composition, R1 to R4 are preferably hydrogen atoms, and X1 is preferably —O— to facilitate synthesis of the compound. When R1 to R4 are aliphatic hydrocarbon groups or alicyclic hydrocarbon groups, they preferably have 1 to 4 carbon atoms.

[0018] Epoxy compound [A] Teha An epoxy compound having an amine-type glycidyl group is used, more preferably tetraglycidyl-4,4'-diaminodiphenyl ether, tetraglycidyl-4,4'-diaminodiphenylmethane, tetraglycidyl-3,4'-diaminodiphenyl ether and tetraglycidyl-3,3'-diaminodiphenylmethane, and particularly preferably tetraglycidyl-3,4'-diaminodiphenyl ether.

[0019] The epoxy resin composition of the present invention may contain by-products and unreacted substances produced during the synthesis of the epoxy compound [A]. The epoxy compound [A] may be synthesized by any method. For example, it can be obtained by reacting the raw materials, aromatic diamine and epihalohydrin such as epichlorohydrin, preferably in the presence of an acid catalyst, to obtain a tetrahalohydrin compound, which is then subjected to a cyclization reaction using an alkaline compound. Specifically, it can be synthesized by the method described in the Examples below.

[0020] 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'-diaminodiphenylmethane.

[0021] Among these, from the viewpoint of heat resistance, aromatic diamines in which two aromatic rings each having an amino group are linked by an ether bond are preferred, and aromatic diamines in which one amino group is located at the para-position and the other amino group is located at the ortho-position relative to the ether bond are particularly preferred. Examples of such aromatic diamines include 3,4'-diaminodiphenyl ether and 3,4'-diaminodiphenyl sulfone.

[0022] Examples of epihalohydrin include epichlorohydrin, epibromohydrin, and epifluorohydrin. Among these, epichlorohydrin and epibromohydrin are particularly preferred from the viewpoints of reactivity and ease of handling.

[0023] The mass ratio of the raw materials, aromatic diamine and epihalohydrin, is preferably 1:1 to 1:20, more preferably 1:3 to 1:10. Examples of solvents used in the reaction include alcoholic 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, alcoholic solvents such as ethanol and n-butanol, and aromatic hydrocarbon solvents such as toluene and xylene are preferred.

[0024] The amount of the solvent used is preferably 1 to 10 times by mass relative to the aromatic diamine. Either a Brønsted acid or a Lewis acid can be suitably used as the acid catalyst. Preferred Brønsted acids include ethanol, water, and acetic acid, and preferred Lewis acids include titanium tetrachloride, lanthanum nitrate hexahydrate, and boron trifluoride diethyl ether complex.

[0025] The reaction time is preferably 0.1 to 180 hours, more preferably 0.5 to 24 hours, and 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.

[0026] A phase transfer catalyst may be used in 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.

[0027] In the epoxy resin composition of the present invention, the proportion of the epoxy compound [A] relative to the total amount of epoxy resin (epoxy resin base liquid) is preferably 40 to 90 mass%, particularly preferably 50 to 80 mass%. When the proportion of the epoxy compound [A] is 40 mass% or more, the heat resistance and elastic modulus of the resulting cured resin product can be further improved. As a result, various mechanical properties of the resulting fiber-reinforced composite material are also improved. Furthermore, when the proportion of the epoxy compound [A] is 90 mass% or less, the viscosity of the resin composition can be reduced, thereby improving the impregnation ability into the fiber substrate.

[0028] [Epoxy compound [B]] The epoxy resin composition of the present invention contains an epoxy compound [B] having a polycyclic aromatic ring structure or a heterocyclic ring structure. By containing this epoxy compound [B], the viscosity of the epoxy resin composition can be reduced, improving the resin impregnation into a fiber-reinforced substrate, and increasing the degree of freedom in designing a mold used in an RTM molding method.

[0029] Furthermore, unlike the epoxy compound [C] described below, the use of this epoxy compound [B] can improve the heat resistance of the resulting cured resin material while reducing the viscosity of the epoxy resin composition.

[0030] In the present invention, by using the above-mentioned epoxy compound [A] and the above-mentioned epoxy compound [B] in combination, it is possible to improve the resin impregnation property of a fiber-reinforced substrate and to obtain a cured resin and a fiber-reinforced composite material that maintain heat resistance and a high elastic modulus.

[0031] The epoxy compound [B] having a polycyclic aromatic ring structure or a heterocyclic ring structure may be a monomer of a compound having a polycyclic aromatic ring structure or a monomer of a compound having a heterocyclic ring structure, or may be an oligomer thereof, and preferably a monomer of a compound having a polycyclic aromatic ring structure or a monomer of a compound having a heterocyclic ring structure is used.

[0032] Examples of this polycyclic aromatic ring structure include a naphthalene skeleton and an anthracene skeleton, and from the viewpoint of the physical properties of the cured resin, a naphthalene skeleton is preferred. That is, as the epoxy compound [B] having a polycyclic aromatic ring structure or a heterocyclic ring structure, a naphthalene derivative epoxy compound or an anthracene derivative epoxy compound is preferably used, and a naphthalene derivative epoxy compound is particularly preferably used. The polycyclic aromatic ring structure may have a substituent other than the glycidyl group.

[0033] As the naphthalene derivative epoxy compound, from the viewpoint of fluidity, bis(glycidyloxy)naphthalene is preferably used.Specific examples include bis(glycidyloxy)-1,1'-binaphthalene, bis(glycidyloxy)-1-[(glycidyloxy)-1-naphthylmethyl]naphthalene, 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, and 2,7-bis(glycidyloxy)-1-[2-(glycidyloxy)-1-naphthylmethyl]naphthalene.

[0034] Among these, it is preferable to select from bis(glycidyloxy)-1,1'-binaphthalene and bis(glycidyloxy)-1-[(glycidyloxy)-1-naphthylmethyl]naphthalene, and by using these epoxy compounds [B], it is possible to reduce the viscosity of the epoxy resin composition and improve the heat resistance of the cured resin.

[0035] By using an epoxy compound having a polycyclic aromatic ring structure as the epoxy compound [B], unlike tetrafunctional epoxy resins that are usually used to improve the heat resistance of cured products, the crosslink density of the cured product does not increase excessively, thereby preventing a decrease in the toughness of the cured resin product and fiber-reinforced composite material.

[0036] When a compound having a heterocyclic structure is used as the epoxy compound [B] having a polycyclic aromatic ring structure or a heterocyclic structure, the epoxy compound [B] having a heterocyclic structure is preferably a triglycidyl isocyanurate derivative epoxy compound.

[0037] The triglycidyl isocyanurate derivative epoxy compound is preferably selected from 1,3,5-triglycidyl isocyanurate, 1,3,5-tri(ethylglycidyl)isocyanurate, and 1,3,5-tri(pentylglycidyl)isocyanurate. By using these compounds as the epoxy compound [B], the heat resistance and elastic modulus of the epoxy resin cured product can be improved. The epoxy resin composition of the present invention may contain by-products and unreacted substances produced during the synthesis of the epoxy compound [B].

[0038] In the epoxy resin composition of the present invention, the mass ratio of the epoxy compound [A] to the epoxy compound [B] is preferably 50:50 to 99:1, more preferably 50:50 to 95:5, and particularly preferably 60:40 to 90:10. By ensuring that the proportion of the epoxy compound [B] is 1% by mass or more, the viscosity of the resulting resin composition can be further reduced, improving the resin composition's handleability and suitability for RTM molding. Furthermore, the heat resistance and elastic modulus of the resulting cured resin can be further improved. As a result, various mechanical properties of the resulting fiber-reinforced composite material are also improved. Furthermore, it is preferable that the proportion of the epoxy compound [B] is 50% by mass or less, since this minimizes the decrease in the heat resistance and elastic modulus of the resulting cured resin.

[0039] [Epoxy compound [C]] The epoxy resin composition of the present invention preferably contains, in addition to the above-mentioned epoxy compound [A] and epoxy compound [B], a glycidyl aryl group The epoxy resin further contains an aromatic epoxy compound [C] having the following formula:

[0040] In this case, Grisiji aryl group Glycidide of aromatic epoxy compound [C] having ru The number of aromatic rings / the number of aromatic rings is 2. By including this epoxy compound [C], the viscosity of the epoxy resin composition can be reduced, and the resin impregnation into the fiber-reinforced substrate can be improved. Grisigi aryl group The aromatic epoxy compound [C] having the formula (I) is preferably diglycidyl aniline and / or diglycidyl toluidine.

[0041] As the epoxy compound [C], glycidyl aryl groupAs the epoxy compound [C], preferably, diglycidyl aniline or its derivatives such as diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine, diglycidyl-xylidine, diglycidyl-mesidine, diglycidyl-anisidine, diglycidyl-phenoxyaniline, or diglycidyl-naphthylamine or its derivatives are used, and more preferably, diglycidyl aniline, diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine, or diglycidyl-phenoxyaniline is used.

[0042] Among these, N,N-diglycidyl-aniline or N,N-diglycidyl-o-toluidine is particularly preferred. By using these compounds as the epoxy compound [C], the usable time of the epoxy resin composition can be extended, and the degree of freedom in designing the mold used in the RTM molding method can be increased. The epoxy resin composition of the present invention may contain by-products and unreacted substances produced during the synthesis of the epoxy compound [C].

[0043] When the epoxy resin composition of the present invention contains the epoxy compound [C], the epoxy compound [C] is preferably contained in an amount of 1 to 80 parts by mass per 100 parts by mass of the total of the epoxy compound [A] and the epoxy compound [B]. If the amount is less than 1% by mass, the viscosity of the resin composition increases, which is not preferable, while if the amount is more than 80 parts by mass, the heat resistance of the cured resin product decreases, which is not preferable.

[0044] When the total mass of the epoxy compounds contained in the epoxy resin composition of the present invention is taken as 100 mass%, the total of the epoxy compound [A], the epoxy compound [B] and the epoxy compound [C] preferably accounts for 70 to 100 mass% of the total mass of the epoxy compounds. If it is less than 70 mass%, the mechanical properties of the cured resin will be reduced, which is undesirable.

[0045] In the epoxy resin composition of the present invention, the content of the epoxy compound [C] relative to the total mass of the epoxy compounds (epoxy resin base liquid) is preferably 5 to 50 mass%, more preferably 10 to 40 mass%. When the content of the epoxy compound [C] is 5 mass% or more, the viscosity of the resulting resin composition can be further reduced, and the handleability of the resin composition and its suitability for RTM molding can be further improved.

[0046] [Curing agent] Known curing agents can be used in the epoxy resin composition of the present invention. In particular, the use of an amine-based curing agent is preferred from the viewpoint of the mechanical properties of the cured product. The epoxy resin composition of the present invention may or may not contain this curing agent in advance. An epoxy resin composition that does not contain a curing agent is in a state that can be mixed with a curing agent before or during curing.

[0047] Examples of the amine-based curing agent include latent curing agents such as dicyandiamide, aliphatic polyamines, various isomers of aromatic amine-based curing agents, aminobenzoic acid esters, and acid anhydrides. Dicyandiamide is preferred because it provides excellent storage stability to the prepreg. Aliphatic polyamines are preferred because they have high reactivity and allow for a curing reaction at low temperatures. Examples of aliphatic polyamines include 4,4'-diaminodicyclohexylmethane, isophoronediamine, and m-xylylenediamine.

[0048] Aromatic polyamines are preferred because they have excellent heat resistance and various mechanical properties. Examples of aromatic polyamines include diaminodiphenyl sulfone, diaminodiphenylmethane, and toluenediamine derivatives. Aromatic diamine compounds such as 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, and 4,4'-diaminodiphenylmethane, as well as their derivatives having non-reactive substituents, are particularly preferred from the viewpoint of providing cured products with good heat resistance. Here, the non-reactive substituents are the same as those described in the explanation of epoxy resins.

[0049] Furthermore, in order to improve the storage stability of the uncured epoxy resin composition and to provide excellent water absorption properties to the cured resin, hindered amine compounds such as 4,4'-methylenebis(2,6-diethylaniline), 4,4'-methylenebis(2-ethyl-6-methylaniline), and 4,4'-methylenebis(2-isopropyl-6-methylaniline) are also preferably used.

[0050] Trimethylene glycol di-p-aminobenzoate and neopentyl glycol di-p-aminobenzoate are preferred aminobenzoates. Composite materials cured using these esters have inferior heat resistance but superior tensile elongation compared to various isomers of diaminodiphenyl sulfone.

[0051] 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 is obtained. Therefore, the type of curing agent to be used is appropriately selected depending on the application of the composite material.

[0052] When the epoxy resin composition of the present invention is used in an RTM molding method, it is preferable to contain a curing agent comprising an aromatic polyamine having at least one aliphatic, aromatic, or halogen atom substituent at the ortho position relative to the amino group, i.e., a compound represented by the following chemical formula (2) or (3) as the curing agent.

[0053] [ka]

[0054] In chemical formula (2), R5 to R8 are each independently a hydrogen atom, an aliphatic substituent having 1 to 6 carbon atoms, an aromatic substituent, or a halogen atom, and at least one of the substituents is an aliphatic substituent having 1 to 6 carbon atoms, an aromatic substituent, or a halogen atom. X2 is -CH2-, -CH(CH3)-, -C(CH3)2-, -S-, -O-, -SO2-, -CO-, -CONH-, -NHCO-, -C(=O)-, or -OC(=O)-.

[0055] [ka]

[0056] However, in chemical formula (3), R9 to R 12 are each independently any one of a hydrogen atom, an aliphatic substituent, an aromatic substituent, a halogen atom, a methoxy group, an alkoxy group, and a thioalkoxy group, and at least one substituent is any one of an aliphatic substituent, aromatic substituent, halogen atom, methoxy group, alkoxy group, and thioalkoxy group having 1 to 6 carbon atoms. Preferably, the one substituent is an aliphatic substituent having 1 to 6 carbon atoms.

[0057] In chemical formulas (2) and (3), the carbon number of the aliphatic substituent is preferably 1 to 6. Examples of the aliphatic substituent 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.

[0058] The curing agent suitable for the RTM molding method may be any polyamine having the above structure, and specific examples include 4,4'-diaminodiphenylmethane and its derivatives represented by the following chemical formulas (4) to (8); and phenylenediamine and its derivatives represented by the following chemical formulas (9) to (12).

[0059] [ka]

[0060] [ka]

[0061] The total amount of curing agent contained in the epoxy resin composition of the present invention is an amount suitable for curing all of the epoxy compounds blended in the epoxy resin composition, and is adjusted appropriately depending on the types of epoxy compounds and curing agents used.

[0062] Specifically, the ratio of the number of epoxy groups contained in the epoxy compound in the epoxy resin composition of the present invention to the number of active hydrogen atoms contained in the curing agent 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 epoxy groups and active hydrogen atoms will be disrupted, and the crosslink density of the resulting cured resin may be insufficient, and mechanical properties such as heat resistance, elastic modulus, and fracture toughness may be reduced.

[0063] [Thermoplastic resin component] The epoxy resin composition of the present invention may further contain a thermoplastic resin. Examples of the thermoplastic resin include an epoxy resin-soluble thermoplastic resin and an epoxy resin-insoluble thermoplastic resin.

[0064] The epoxy resin-soluble thermoplastic resin adjusts the viscosity of the epoxy resin composition and improves the impact resistance of the resulting FRP. This epoxy resin-soluble thermoplastic resin is a thermoplastic resin that can be partially or completely dissolved in epoxy resin at or below the temperature at which the FRP is molded.

[0065] Here, "partially dissolved in epoxy resin" means that when 100 parts by mass of epoxy resin is mixed with 10 parts by mass of thermoplastic resin having an average particle size of 20 to 50 μm and stirred at 190°C for 1 hour, the particles disappear or the particle size (particle diameter) changes by 10% or more.

[0066] On the other hand, an epoxy resin-insoluble thermoplastic resin refers to a thermoplastic resin that is substantially insoluble in epoxy resin at or below the temperature at which FRP is molded. That is, when 100 parts by mass of epoxy resin is mixed with 10 parts by mass of a thermoplastic resin having an average particle size of 20 to 50 μm and the mixture is stirred at 190°C for 1 hour, the particle size does not change by 10% or more.

[0067] Generally, the temperature at which FRP is molded is 100 to 190° C. The particle size is measured visually using a microscope, and the average particle size refers to the average value of the particle sizes of 100 randomly selected particles.

[0068] If the epoxy resin-soluble thermoplastic resin is not completely dissolved, it dissolves in the epoxy resin when heated during the epoxy resin curing process, thereby increasing the viscosity of the epoxy resin composition, thereby preventing the epoxy resin composition from flowing out of the prepreg due to a decrease in viscosity during the curing process. The epoxy resin-soluble thermoplastic resin is preferably a resin that dissolves in the epoxy resin at 190°C in an amount of 80 mass % or more.

[0069] Specific examples of epoxy resin-soluble thermoplastic resins include polyethersulfone, polysulfone, polyetherimide, polycarbonate, etc. These may be used alone or in combination of two or more. The epoxy resin-soluble thermoplastic resin contained in the epoxy resin composition is particularly preferably polyethersulfone or polysulfone having a weight-average molecular weight (Mw) measured by gel permeation chromatography in the range of 8,000 to 100,000. If the weight-average molecular weight (Mw) is less than 8,000, the impact resistance of the resulting FRP may be insufficient, while if it is more than 100,000, the viscosity may be significantly increased, resulting in significantly worsened handleability.

[0070] The epoxy resin-soluble thermoplastic resin preferably has a uniform molecular weight distribution. In particular, the polydispersity index (Mw / Mn), which is the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn), is preferably in the range of 1 to 10, and more preferably in the range of 1.1 to 5.

[0071] The epoxy resin-soluble thermoplastic resin preferably has a reactive group or a functional group capable of forming a hydrogen bond with the epoxy resin. Such an epoxy resin-soluble thermoplastic resin can improve the solubility stability of the epoxy resin during the curing process. Furthermore, it can impart toughness, chemical resistance, heat resistance, and moist heat resistance to the cured FRP.

[0072] The reactive group reactive with epoxy resins is preferably a hydroxyl group, a carboxylic acid group, an imino group, or an amino group. Hydroxyl-terminated polyethersulfone is more preferred because the resulting FRP has particularly excellent impact resistance, fracture toughness, and solvent resistance.

[0073] The content of the epoxy resin-soluble thermoplastic resin in the epoxy resin composition is adjusted appropriately depending on the viscosity. From the viewpoint of prepreg processability, the content is preferably 5 to 90 parts by mass, more preferably 5 to 40 parts by mass, and particularly preferably 15 to 35 parts by mass, per 100 parts by mass of the epoxy resin contained in the epoxy resin composition. If the content is less than 5 parts by mass, the impact resistance of the resulting FRP may be insufficient, which is not preferred. On the other hand, if the content of the epoxy resin-soluble thermoplastic resin exceeds 90% by mass, the viscosity may increase significantly, which may significantly deteriorate the handleability of the prepreg, which is not preferred. The epoxy resin-soluble thermoplastic resin preferably contains a reactive aromatic oligomer having an amine terminal group (hereinafter also simply referred to as "aromatic oligomer").

[0074] During heat curing, epoxy resin compositions undergo a curing reaction between the epoxy resin and the curing agent, resulting in a high molecular weight. As the two-phase region expands with increasing molecular weight, the aromatic oligomer dissolved in the epoxy resin composition undergoes reaction-induced phase separation. This phase separation results in the formation of a two-phase structure within the matrix resin, in which the cured epoxy resin and aromatic oligomer are co-continuous. Furthermore, since the aromatic oligomer contains amine end groups, it also reacts with the epoxy resin. Because the phases in this co-continuous two-phase structure are firmly bonded to each other, solvent resistance is also improved.

[0075] This co-continuous structure absorbs external impacts and suppresses crack propagation in the FRP. As a result, FRP fabricated using prepregs containing reactive aromatic oligomers with amine end groups exhibits high impact resistance and fracture toughness. The aromatic oligomer may be a known polysulfone having an amine end group or a polyethersulfone having an amine end group, and the amine end group is preferably a primary amine (—NH2) end group.

[0076] The aromatic oligomer blended into the epoxy resin composition preferably has a weight-average molecular weight of 8,000 to 40,000 as measured by gel permeation chromatography. A weight-average molecular weight of less than 8,000 is undesirable because it reduces the effect of improving the toughness of the matrix resin. On the other hand, a weight-average molecular weight of more than 40,000 is undesirable because it increases the viscosity of the resin composition too much, making it difficult for the resin composition to penetrate into the reinforcing fiber layer and other processing problems.

[0077] As the aromatic oligomer, a commercially available product such as "Virantage DAMS VW-30500 RP (registered trademark)" (manufactured by Solvay Specialty Polymers) can be preferably used.

[0078] The epoxy resin-soluble thermoplastic resin is preferably in the form of particles. The particulate epoxy resin-soluble thermoplastic resin can be uniformly blended into the resin composition. In addition, the resulting prepreg has high moldability.

[0079] The average particle size of the epoxy resin-soluble thermoplastic resin is preferably 1 to 50 μm, more preferably 3 to 30 μm. If the particle size is less than 1 μm, the viscosity of the epoxy resin composition will increase significantly, making it difficult to add a sufficient amount of epoxy resin-soluble thermoplastic resin to the epoxy resin composition, which is undesirable. On the other hand, if the particle size exceeds 50 μm, it may be difficult to obtain a sheet of uniform thickness when processing the epoxy resin composition into a sheet, and the dissolution rate in the epoxy resin will be slow, resulting in non-uniformity in the obtained FRP, which is also undesirable.

[0080] In addition to the epoxy resin-soluble thermoplastic resin, the epoxy resin composition may also contain an epoxy resin-insoluble thermoplastic resin. Part of the epoxy resin-insoluble thermoplastic resin and the epoxy resin-soluble thermoplastic resin (the epoxy resin-soluble thermoplastic resin that remains undissolved in the matrix resin after curing) become dispersed as particles in the matrix resin of the FRP (hereinafter, these dispersed particles are also referred to as "interlayer particles"). These interlayer particles suppress the propagation of impacts received by the FRP. As a result, the impact resistance of the resulting FRP is improved.

[0081] Examples of epoxy resin-insoluble thermoplastic resins include polyamide, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyester, polyamideimide, polyimide, polyether ketone, polyether ether ketone, polyethylene naphthalate, polyether nitrile, and polybenzimidazole. Among these, polyamide, polyamideimide, and polyimide are preferred because of their high toughness and heat resistance.

[0082] Polyamides and polyimides are particularly effective in improving the toughness of FRP. They may be used alone or in combination of two or more. Copolymers of these may also be used.

[0083] In particular, the heat resistance of the resulting FRP can be improved by using polyamides such as amorphous polyimide, Nylon 6 (registered trademark) (a polyamide obtained by the ring-opening polycondensation reaction of caprolactam), Nylon 11 (a polyamide obtained by the ring-opening polycondensation reaction of undecane lactam), Nylon 12 (a polyamide obtained by the ring-opening polycondensation reaction of lauryllactam), Nylon 1010 (a polyamide obtained by the copolymerization reaction of sebacic acid and 1,10-decanediamine), and amorphous nylon (also called transparent nylon, which does not crystallize or whose polymer crystallization rate is extremely slow).

[0084] The content of the epoxy resin-insoluble thermoplastic resin in the epoxy resin composition is adjusted appropriately depending on the viscosity of the epoxy resin composition. From the viewpoint of prepreg processability, the content is preferably 5 to 50 parts by mass, more preferably 10 to 45 parts by mass, and particularly preferably 20 to 40 parts by mass, per 100 parts by mass of the epoxy resin contained in the epoxy resin composition. If the content is less than 5 parts by mass, the impact resistance of the resulting FRP may be insufficient, which is undesirable. On the other hand, if the content exceeds 50 parts by mass, the impregnation property of the epoxy resin composition and the drapeability of the resulting prepreg may be reduced, which is undesirable. The preferred average particle size and shape of the epoxy resin-insoluble thermoplastic resin are the same as those of the epoxy resin-soluble thermoplastic resin.

[0085] [Resin particles] The epoxy resin composition of the present invention may further contain resin particles. The resin particles are present in a dispersed state in the epoxy resin composition without being dissolved, and are present in the cured resin product after the epoxy resin composition is cured in a dispersed state in the cured resin product. When the cured resin product is considered to be a sea component, the resin particles are present in the cured resin product as island components.

[0086] The inclusion of resin particles is preferred because it allows the cured resin and fiber-reinforced composite material to have high fracture toughness and impact resistance. Examples of resin particles that can be used include thermoplastic resin particles, thermosetting resin particles, and rubber particles, and preferably rubber particles, such as silicone rubber, butadiene rubber, styrene-butadiene rubber, and methyl methacrylate-butadiene-styrene rubber.

[0087] Commercially available rubber particles used as resin particles include MX-153 (bisphenol A epoxy resin with 33% by mass of butadiene rubber dispersed therein, manufactured by Kaneka Corporation), MX-257 (bisphenol A epoxy resin with 37% by mass of butadiene rubber dispersed therein, manufactured by Kaneka Corporation), MX-154 (bisphenol A epoxy resin with 40% by mass of butadiene rubber dispersed therein, manufactured by Kaneka Corporation), MX-960 (bisphenol A epoxy resin with 25% by mass of silicone rubber dispersed therein, manufactured by Kaneka Corporation), MX-136 (bisphenol F epoxy resin with 25% by mass of butadiene rubber dispersed therein, manufactured by Kaneka Corporation), and MX-965 (bisphenol F epoxy resin with 25% by mass of silicone rubber dispersed therein, manufactured by Kaneka Corporation). Examples of such epoxy resins include MX-217 (phenol novolac epoxy resin with 25% by mass of butadiene rubber dispersed therein, manufactured by Kaneka Corporation), MX-227M75 (bisphenol A novolac epoxy resin with 25% by mass of styrene butadiene rubber dispersed therein, manufactured by Kaneka Corporation), MX-334M75 (brominated epoxy resin with 25% by mass of styrene butadiene rubber dispersed therein, manufactured by Kaneka Corporation), MX-416 (tetrafunctional glycidylamine epoxy resin with 25% by mass of butadiene rubber dispersed therein, manufactured by Kaneka Corporation), and MX-451 (trifunctional glycidylamine epoxy resin with 25% by mass of styrene butadiene rubber dispersed therein, manufactured by Kaneka Corporation).

[0088] The average particle size of the resin particles is preferably 1.0 μm or less, more preferably 0.5 μm or less, and particularly preferably 0.3 μm or less. The average particle size is preferably 0.03 μm or more, more preferably 0.05 μm or more, and particularly preferably 0.08 μm or more. When the average particle size is 1.0 μm or less, the resin particles are not filtered off by the surface of the fiber-reinforced substrate during the step of impregnating the fiber-reinforced substrate with the epoxy resin composition, and impregnation into the interior of the reinforcing fiber bundles is facilitated. This makes it possible to prevent poor resin impregnation and to obtain a fiber-reinforced composite material with excellent physical properties, which is preferable.

[0089] The content of resin particles in the epoxy resin composition is preferably 0.1 to 50% by mass, more preferably 0.5 to 20% by mass, and particularly preferably 1 to 15% by mass, relative to 100% by mass of the total amount of epoxy resin in the entire epoxy resin composition. A content of 0.1% by mass or more is preferred because it can sufficiently improve the fracture toughness and impact resistance of cured resin products and fiber composite materials. On the other hand, a content of 50% by mass or less is preferred because it can reduce the viscosity of the epoxy resin composition and improve impregnation into fiber substrates.

[0090] The resin particles can also be used as a masterbatch in which they are dispersed at a high concentration in an epoxy resin, which makes it easier to highly disperse the resin particles in the epoxy resin composition.

[0091] [Composition ratio of epoxy resin composition] Based on the total mass of the epoxy compounds contained in the epoxy resin composition, the proportion of the epoxy compound [A] is preferably 40 to 90 mass%, more preferably 50 to 80 mass%. A proportion of the epoxy compound [A] of 40 mass% or more can further improve the heat resistance and elastic modulus of the resulting cured resin product, and various mechanical properties of the resulting fiber-reinforced composite material can also be improved, which is preferable. On the other hand, a proportion of 90 mass% or less can lower the viscosity of the epoxy resin composition, which can improve the impregnation ability into the fiber substrate, which is preferable.

[0092] Based on the total mass of the epoxy compounds contained in the epoxy resin composition, the content of the epoxy compound [B] is preferably 5 to 50 mass%, more preferably 10 to 40 mass%. A proportion of the epoxy compound [B] of 5 mass% or more is preferred because it further reduces the viscosity of the resulting resin composition, thereby further improving the handleability of the resin composition and its suitability for RTM molding. On the other hand, a proportion of 50 mass% or less is preferred because it minimizes the decrease in the heat resistance and elastic modulus of the resulting cured resin product.

[0093] Based on the total mass of the epoxy compounds contained in the epoxy resin composition, the content of the epoxy compound [C] is preferably 5 to 50 mass%, more preferably 10 to 40 mass%. A proportion of the epoxy compound [C] of 5 mass% or more is preferred because it further reduces the viscosity of the resulting resin composition, further improving the handleability of the resin composition and its suitability for RTM molding. On the other hand, a proportion of 50 mass% or less is preferred because it minimizes the decrease in the heat resistance and elastic modulus of the resulting cured resin.

[0094] The ratio of the total number of epoxy groups in the epoxy compound contained in the epoxy resin composition to the total number of active hydrogens contained in the curing agent is preferably 0.7 to 1.3. This range is preferable because it provides a favorable molar balance between epoxy groups and active hydrogens, and allows for the production of a cured resin product with a high crosslink density and excellent mechanical properties such as heat resistance, elastic modulus, and fracture toughness.

[0095] [Other optional ingredients] The epoxy resin composition of the present invention may contain other additives such as conductive particles, flame retardants, inorganic fillers, and internal mold release agents.

[0096] Examples of conductive particles include conductive polymer particles such as polyacetylene particles, polyaniline particles, polypyrrole particles, polythiophene particles, polyisothianaphthene particles, and polyethylenedioxythiophene particles; carbon particles; carbon fiber particles; metal particles; and particles in which a core material made of an inorganic or organic material is coated with a conductive substance.

[0097] An example of the flame retardant is a phosphorus-based flame retardant, which may be any flame retardant containing a phosphorus atom in the molecule, and examples of the flame retardant include organic phosphorus compounds such as phosphate esters, condensed phosphate esters, phosphazene compounds, and polyphosphates, as well as red phosphorus.

[0098] 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, and silicate minerals. In particular, silicate minerals are preferably used. Commercially available silicate minerals include THIXOTROPIC AGENT DT 5039 (manufactured by Huntsman Japan Co., Ltd.).

[0099] Examples of internal mold release agents include metal soaps, vegetable waxes such as polyethylene wax and carnauba wax, fatty acid ester-based mold release agents, silicone oil, animal wax, and fluorine-based nonionic surfactants. When these internal mold release agents are added, the amount added is preferably 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 mold release effect from the mold is optimally exhibited.

[0100] 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.).

[0101] [Properties of Epoxy Resin Composition] The epoxy resin composition of the present invention can have the following properties. When the epoxy resin composition of the present invention is applied to a prepreg method, the viscosity at 100°C is preferably 0.1 to 500 Pa·s, more preferably 1 to 100 Pa·s. If the viscosity is less than 0.1 Pa·s, the resin tends to flow out of the prepreg, which is undesirable. On the other hand, if the viscosity exceeds 500 Pa·s, unimpregnated portions tend to be formed in the prepreg, which is undesirable because voids and the like tend to form in the resulting fiber-reinforced composite material.

[0102] When the epoxy resin composition of the present invention is applied to an RTM molding method, the viscosity 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. A viscosity at 100°C of 300 mPa·s or less facilitates impregnation of the epoxy resin composition into a fiber-reinforced substrate and prevents the formation of voids that cause a decrease in the physical properties of the resulting fiber-reinforced composite material. The relationship between viscosity and impregnation ability also depends on the composition of the fiber-reinforced substrate.

[0103] The pot life of the epoxy resin composition of the present invention when applied to an RTM molding method varies depending on the molding conditions for the composite material. For example, when a large composite material is impregnated into a fiber substrate using an RTM molding method at a relatively low impregnation pressure, the pot life is preferably 120 minutes or more, more preferably 180 minutes or more, as the time until the viscosity exceeds 100 mPa s when maintained at 100°C.

[0104] [Method for producing epoxy resin composition] In the epoxy resin composition of the present invention, the mixture of epoxy compounds is referred to as the epoxy resin base liquid, and the mixture of curing agent components is referred to as the curing agent liquid.

[0105] The epoxy resin composition of the present invention can be produced by mixing epoxy compound [A], epoxy compound [B], and, if necessary, other epoxy compounds and a curing agent. The thermoplastic resin component, resin particles, and other optional components may be mixed into an epoxy resin base liquid and then mixed with a curing agent liquid, or the thermoplastic resin component, resin particles, and other optional components may be mixed into a curing agent liquid and then mixed with an epoxy resin base liquid. The order of mixing these steps is not important.

[0106] The epoxy resin composition may be in a one-liquid state in which the components are uniformly mixed, or in a slurry state in which some of the components are dispersed as solids. The epoxy resin composition may be produced by any conventionally known method. The mixing temperature is, for example, 40 to 180°C, preferably 50 to 160°C, and more preferably 50 to 120°C. Temperatures above 180°C are not preferred because the curing reaction proceeds immediately, which may result in a decrease in the impregnation into the fiber-reinforced substrate or a decrease in the physical properties of the cured product. On the other hand, temperatures below 40°C are not preferred because the viscosity of the epoxy resin base material is high, making mixing substantially difficult.

[0107] Conventionally 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 in the air, an atmosphere in which the temperature and humidity are controlled is preferred. For example, mixing is preferably performed at a constant temperature of 30°C or less, or in a low-humidity atmosphere with a relative humidity of 50% RH or less.

[0108] [Method for producing epoxy resin base liquid] When the epoxy resin composition of the present invention is applied to an RTM molding method, it can be applied to the RTM molding method as a two-component epoxy resin composition in which an epoxy resin base liquid and a curing agent liquid are mixed immediately before use.

[0109] This epoxy resin base liquid can be produced by mixing the epoxy compound [A] and the epoxy compound [B], which are the components of the epoxy resin composition of the present invention, with any other epoxy compound, thermoplastic resin component, resin particles, and other optional components as required, in any order. The state of the epoxy resin base liquid may be a single liquid state in which the components are uniformly mixed, or may be a slurry state in which some components are dispersed as solids.

[0110] Any conventionally known method may be used to produce the epoxy resin base liquid. The mixing temperature is, for example, 40 to 200°C, preferably 50 to 100°C, and more preferably 50 to 90°C. Temperatures above 200°C are not preferred because they may partially promote the self-polymerization reaction of the epoxy resin, reducing the impregnation of the fiber-reinforced substrate and / or reducing the physical properties of the cured product produced using the resulting epoxy resin base liquid. Temperatures below 40°C are not preferred because the viscosity of the epoxy resin base liquid is high, making mixing substantially difficult.

[0111] Conventional known mechanical devices can be used for mixing. 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 in the air, it is preferable that the temperature and humidity are controlled. For example, it is preferable to mix at a constant temperature of 30°C or less, or in a low-humidity atmosphere with a relative humidity of 50% RH or less.

[0112] [Method for producing hardener liquid] The curing agent liquid used in the two-component epoxy resin composition contains a curing agent and other optional components. The curing agent liquid may be in the form of a single liquid in which the components are uniformly mixed, or in the form of a slurry in which some of the components are dispersed as solids.

[0113] Any conventionally known method may be used to produce 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. Temperatures above 200°C are undesirable because the added components may thermally decompose. On the other hand, temperatures below 50°C are undesirable because, if there are solid curing agent components, they do not melt and are difficult to mix, making it difficult to obtain a uniform curing agent liquid.

[0114] Conventional known mechanical devices can be used for mixing. 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 in the air, it is preferable to perform the mixing in an atmosphere where the temperature and humidity are controlled. For example, it is preferable to mix at a constant temperature of 30°C or less, or in a low-humidity atmosphere where the relative humidity is 50% RH or less.

[0115] [Properties of cured resin] The epoxy resin composition of the present invention can be cured to give a cured resin product, which can have the following properties:

[0116] The glass transition temperature in a dry state (dry-Tg) is preferably 170°C or higher, and more preferably 180°C to 250°C. The glass transition temperature (wet-Tg) at saturated water absorption is preferably 150°C or higher, and more preferably 160 to 200°C.

[0117] The room temperature dry flexural modulus (RTD-FM) measured by JIS K7171 is preferably 3.0 GPa or more, more preferably 3.3 to 10.0 GPa, and even more preferably 3.5 to 9.0 GPa. A modulus exceeding 3.0 GPa is preferred because the fiber-reinforced composite material obtained using the epoxy resin composition of the present invention has excellent mechanical properties.

[0118] The heating and post-water absorption flexural modulus (HTW-FM) measured according to JIS K7171 is preferably 2.4 GPa or more, more preferably 2.5 to 9.0 GPa, and particularly preferably 2.8 to 8.0 GPa. The deformation mode I critical stress intensity factor KIc measured according to ASTM D5045 is preferably 0.7 MPa m 1 / 2 or more, more preferably 0.8 to 3.0 MPa m 1 / 2 is.

[0119] [Fiber-reinforced composite materials] A fiber-reinforced composite material (FRP) can be obtained by combining a fiber-reinforced substrate with the epoxy resin composition of the present invention and curing the resulting composite. That is, the present invention provides a fiber-reinforced composite material comprising the above-mentioned cured epoxy resin and a fiber-reinforced substrate.

[0120] [Fiber reinforced substrate] Examples of reinforcing fibers used in the fiber-reinforced substrate include carbon fibers, glass fibers, aramid fibers, silicon carbide fibers, polyester fibers, ceramic fibers, alumina fibers, boron fibers, metal fibers, mineral fibers, rock fibers, and slug fibers.

[0121] Among these reinforcing fibers, carbon fiber, glass fiber, and aramid fiber are preferred. Carbon fiber is more preferred because it has good specific strength and specific modulus, and can produce a lightweight, high-strength fiber-reinforced composite material. Among carbon fibers, polyacrylonitrile (PAN)-based carbon fiber is particularly preferred because it has excellent tensile strength.

[0122] When PAN-based carbon fibers are used as the reinforcing fibers of the fiber-reinforced substrate, the tensile modulus is preferably 100 to 600 GPa, more preferably 200 to 500 GPa, and even more preferably 230 to 450 GPa, and the tensile strength is preferably 2000 to 10000 MPa, and even more preferably 3000 to 8000 MPa.

[0123] When carbon fibers are used as the reinforcing fibers of the fiber-reinforced substrate, the diameter of the carbon fibers is preferably 4 to 20 μm, more preferably 5 to 10 μm. By using such carbon fibers, the mechanical properties of the resulting fiber-reinforced composite material can be improved.

[0124] In the present invention, the reinforcing fibers of the fiber-reinforced substrate are preferably treated with a sizing agent. In this case, the amount of sizing agent attached is preferably 0.01 to 10 mass%, more preferably 0.05 to 3.0 mass%, and particularly preferably 0.1 to 2.0 mass%, relative to the mass of the reinforcing fibers to which the sizing agent is attached. An attachment amount within this range is preferable because it can achieve excellent adhesion between the reinforcing fibers and the matrix resin and excellent interlaminar toughness in the resulting composite material.

[0125] As the fiber-reinforced substrate, it is preferable to use a reinforcing fiber sheet formed from reinforcing fibers in a sheet form. Examples of this reinforcing fiber 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. Among these, the use of a unidirectionally aligned sheet, a bidirectional fabric, or a multiaxial fabric substrate formed from continuous reinforcing fibers in a sheet form is preferred because it allows for the production of a fiber-reinforced composite material with superior mechanical properties.

[0126] The bidirectional or multiaxial woven fabric substrate may be formed by stacking and stitching together multiple unidirectionally aligned sheets. In this case, to improve the interlaminar toughness of the resulting fiber-reinforced composite material, a layer of thermoplastic resin nonwoven fabric may be placed on one side of the unidirectionally aligned sheets and then laminated to form a woven fabric. Examples of fibers for the thermoplastic resin nonwoven fabric include polyester resin fibers, polyamide resin fibers, polyethersulfone resin fibers, polysulfone resin fibers, polyetherimide resin fibers, polycarbonate resin fibers, and fibers made from mixtures of these resins.

[0127] The basis weight and number of layers of the unidirectionally aligned sheets can be appropriately set depending on the application of the fiber-reinforced composite material. The basis weight of the unidirectionally aligned sheets is, for example, 100 to 300 g / m 2 , preferably 150 to 250 g / m 2 The thickness of each layer of the unidirectionally aligned sheet of fiber-reinforced substrate is preferably 0.01 to 3 mm, and more preferably 0.05 to 1.5 mm.

[0128] [Method for producing fiber-reinforced composite material] As a method for compounding a fiber-reinforced substrate with an epoxy resin composition to obtain the fiber-reinforced composite material of the present invention, it is preferable to employ a method in which the fiber-reinforced substrate and an uncured epoxy resin composition are compounded in advance, and then the uncured epoxy resin composition is cured.

[0129] As a method for compounding with a fiber-reinforced substrate, the fiber-reinforced substrate and the resin composition may be compounded in advance, as in the case of a prepreg described below, or compounding may be performed during molding, for example, by a resin transfer molding method (RTM molding method), a hand lay-up method, a filament winding method, a pultrusion method, or the like. A fiber-reinforced composite material (FRP) can be obtained by compounding a fiber-reinforced substrate with the epoxy resin composition of the present invention and then curing the composite by heating and pressurizing under specific conditions.

[0130] [Prepreg] The prepreg of the present invention is a prepreg comprising the above-mentioned epoxy resin composition of the present invention and a fiber-reinforced substrate, and this prepreg comprises a fiber-reinforced substrate and the above-mentioned epoxy resin composition of the present invention impregnated therein.

[0131] The prepreg of the present invention is a prepreg in which a fiber-reinforced substrate is partially or entirely impregnated with the above-described epoxy resin composition. The content of the above-described epoxy resin composition in the entire prepreg is preferably 15 to 60 mass%, more preferably 20 to 55 mass%, and particularly preferably 25 to 50 mass%, based on the total mass of the prepreg. If this content is less than 15 mass%, voids may occur in the resulting fiber-reinforced composite material, which may reduce mechanical properties, which is undesirable. If this content exceeds 60 mass%, the reinforcing effect of the reinforcing fibers may be insufficient, resulting in substantially low mechanical properties relative to the mass, which is undesirable.

[0132] [Prepreg manufacturing method] The prepreg of the present invention can be produced by a production method including an impregnation step of impregnating a fiber-reinforced substrate with the epoxy resin composition of the present invention to obtain a prepreg. The impregnation is preferably carried out by a hot melt method or a solvent method.

[0133] The hot melt method is a method in which an uncured 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.

[0134] Any conventionally known method can be used to form the resin composition into a resin composition film. Specifically, the 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, etc.

[0135] 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 resin composition may be impregnated into the fiber-reinforced substrate layer in one step or in multiple steps. 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.

[0136] Among these conventional methods, the prepreg of the present invention can be suitably produced by a hot melt method that does not use a solvent. When an epoxy resin composition film is impregnated into a fiber-reinforced substrate layer by the hot melt method, the impregnation temperature is preferably 50 to 120°C, more preferably 60 to 110°C, and particularly preferably 70 to 100°C. If the impregnation temperature is less than 50°C, the viscosity of the epoxy resin composition will be high and the fiber-reinforced substrate layer may not be sufficiently impregnated, which is undesirable. On the other hand, if the impregnation temperature exceeds 120°C, the curing reaction of the epoxy resin composition will proceed, which may result in a decrease in the storage stability or drapeability of the resulting prepreg, which is undesirable.

[0137] The impregnation pressure when the epoxy resin composition film is impregnated into the fiber-reinforced base material layer by the hot melt method may be appropriately determined taking into consideration the viscosity and resin flow of the resin composition, and a specific impregnation pressure is, for example, 0.01 to 250 (N / cm), preferably 0.1 to 200 (N / cm).

[0138] [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 applying heat and pressure in an autoclave molding machine. The molding conditions are preferably a temperature rise rate of 1 to 50°C / min, and heating and pressurizing at 0.2 to 0.7 MPa and 130 to 180°C for 10 to 30 minutes.

[0139] [Press molding method] The fiber-reinforced composite material (FRP) of the present invention can be preferably produced by press molding, which is carried out 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.

[0140] It is preferable to heat the mold to the curing temperature in advance. The temperature of the mold during press molding is preferably 150 to 210°C. A molding temperature of 150°C or higher is preferable because it allows a sufficient curing reaction to occur and FRP can be obtained with high productivity. Furthermore, a molding temperature of 210°C or lower prevents the resin viscosity from becoming too low, and prevents excessive flow of the resin within the mold. As a result, it is possible to prevent resin from leaking out of the mold and meandering of the fibers, which is preferable because it allows high-quality FRP to be obtained.

[0141] The pressure during molding is, for example, 0.05 to 2 MPa, preferably 0.2 to 2 MPa. A pressure of 0.05 MPa or higher allows for appropriate resin flow, preventing poor appearance and the occurrence of voids. This is also preferred because the prepreg adheres sufficiently to the mold, allowing for the production of FRP with a good appearance. On the other hand, a pressure of 2 MPa or lower prevents the resin from flowing more than necessary, making it less likely for the resulting FRP to have poor appearance. Furthermore, since no more load than necessary is applied to the mold, deformation of the mold is less likely to occur. The molding time is preferably 1 to 8 hours.

[0142] [Resin Transfer Molding (RTM) Method] From the viewpoint of efficiently obtaining fiber-reinforced composite materials with complex shapes, resin transfer molding (RTM) is a preferred molding method. This RTM molding method is a method for obtaining fiber-reinforced composite materials, which comprises the steps of impregnating a fiber-reinforced substrate placed in a mold with the liquid epoxy resin composition of the present invention and curing the resulting material by heating. That is, the present invention provides a method for obtaining a fiber-reinforced composite material, which comprises the steps of impregnating an epoxy resin composition into a fiber-reinforced substrate placed in a mold and then curing the composition by heating.

[0143] In the present invention, the mold used in the RTM molding method may be a closed mold made of a rigid material, or an open mold made of a rigid material and a flexible film (bag). In the latter case, the fiber-reinforced substrate can be placed between the open mold made of a rigid material and the flexible film.

[0144] Examples of rigid materials include metals such as steel and aluminum, fiber-reinforced plastics, wood, and gypsum. Examples of flexible film materials include polyamide, polyimide, polyester, fluororesin, and silicone resin.

[0145] When a closed mold made of a rigid material is used in the RTM molding method, the mold is usually clamped under pressure and the epoxy resin composition is injected under pressure. A suction port may be provided in addition to the injection port and connected to a vacuum pump for suction. Suction may also be performed, and the epoxy resin composition may be injected under atmospheric pressure alone, without the use of special pressurizing means. This method is advantageous because it allows the production of large components by providing multiple suction ports.

[0146] When using an open mold made of a rigid material and a flexible film in the RTM molding process, suction can be applied and the epoxy resin can be injected at atmospheric pressure without using any special pressure means. To achieve good impregnation when injected at atmospheric pressure alone, it is effective to use a resin diffusion medium. Furthermore, it is preferable to apply a gel coat to the surface of the rigid material prior to installing the fiber-reinforced substrate.

[0147] In the RTM molding method, a fiber-reinforced substrate is impregnated with an epoxy resin composition, and then heat-curing is performed. The mold temperature during heat-curing is usually selected to be higher than the mold temperature during injection of the epoxy resin composition. The mold temperature during heat-curing is preferably 80 to 200°C. The heat-curing time is preferably 1 minute to 20 hours. After heat-curing is complete, the fiber-reinforced composite material is removed from the mold. Thereafter, the obtained fiber-reinforced composite material may be post-cured by heating at a higher temperature. The post-curing temperature is preferably 150 to 200°C, and the post-curing time is preferably 1 minute to 4 hours.

[0148] The impregnation pressure when the epoxy resin composition is impregnated into the fiber-reinforced substrate by the RTM molding method may be appropriately determined taking into consideration the viscosity of the resin composition, resin flow, etc. A specific impregnation pressure is, for example, 0.001 to 10 MPa, and preferably 0.01 to 1 MPa.

[0149] [Properties of fiber-reinforced composite materials] The present invention also relates to a fiber-reinforced composite material comprising the above-mentioned cured epoxy resin of the present invention and a fiber-reinforced substrate.

[0150] The fiber reinforced composite material of the present invention has a compressive strength after impact CAI (impact energy 30.5 J) measured according to ASTM D7136 of preferably 240 MPa or more, more preferably 250 to 400 MPa, and particularly preferably 260 to 380 MPa.

[0151] The fiber reinforced composite material of the present invention preferably has a room temperature dry open hole compressive strength (RTD-OHC) measured by SACMA SRM3 of 260 MPa or more, more preferably 280 to 450 MPa, and particularly preferably 300 to 400 MPa.

[0152] The fiber reinforced composite material provided by the present invention preferably has a hot-rolled open-hole compressive strength (HTW-OHC) measured by SACMA SRM3 of 200 MPa or more, more preferably 220 to 400 MPa, and particularly preferably 240 to 350 MPa. [Example]

[0153] The present invention will be described in more detail below with reference to examples. The components and test methods used in the examples and comparative examples are as follows. Fiber reinforced composite materials are sometimes abbreviated as "FRP," and carbon fiber reinforced composite materials are sometimes abbreviated as "CFRP."

[0154] 〔component〕 (1) Epoxy compound [A] Tetraglycidyl-4,4'-diaminodiphenylmethane (Araldite MY721 (product name) manufactured by Huntsman, hereinafter abbreviated as "4,4'-TGDDM") Tetraglycidyl-3,4'-diaminodiphenyl ether (synthesized by the method in Synthesis Example 1, hereinafter abbreviated as "3,4'-TGDDE")

[0155] Synthesis Example 1: Synthesis of 3,4'-TGDDE A four-neck flask equipped with a thermometer, dropping funnel, condenser, and stirrer was charged with 1110.2 g (12.0 mol) of epichlorohydrin. The temperature was raised to 70 °C while purging with nitrogen, and 200.2 g (1.0 mol) of 3,4'-diaminodiphenyl ether dissolved in 1000 g of ethanol was added dropwise over 4 hours. The mixture was stirred for an additional 6 hours to complete the addition reaction, yielding N,N,N',N'-tetrakis(2-hydroxy-3-chloropropyl)-3,4'-diaminodiphenyl ether. The temperature inside the flask was then lowered to 25 °C, and 500.0 g (6.0 mol) of 48 wt% aqueous NaOH solution was added dropwise over 2 hours and stirred for an additional hour. After the cyclization reaction was complete, the ethanol was distilled off, followed by extraction with 400 g of toluene and washing twice with 5% brine. Toluene and epichlorohydrin were removed from the organic layer under reduced pressure to obtain 361.7 g (yield 85.2%) of a brown viscous liquid. The purity of the main product, 3,4'-TGDDE, was 84% ​​(HPLC area %).

[0156] (2) Epoxy compound [B] 1,6-bis(glycidyloxy)naphthalene (HP-4032SS (product name) manufactured by DIC Corporation, hereinafter abbreviated as "1,6-DON") 1,3,5-Triglycidyl isocyanurate (product name: TEPIC-S, manufactured by Nissan Chemical Industries, Ltd., hereinafter abbreviated as "TEPIC")

[0157] (3) Epoxy compound [C] N,N-diglycidyl-o-toluidine (product name: GOT, 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")

[0158] (4) Other epoxy resins Bisphenol A diglycidyl ether (product name jER825 manufactured by Mitsubishi Chemical Corporation, hereinafter abbreviated as "DGEBA")

[0159] (5) Hardener 4,4'-Diamino-3,3'-diisopropyl-5,5'-dimethyldiphenylmethane (Lonzacure M-MIPA (product name) manufactured by Lonza, hereafter abbreviated as "M-MIPA") 3,3'-Diaminodiphenyl sulfone (Konishi Chemical Industry Co., Ltd., hereafter abbreviated as "3,3'-DDS")

[0160] (6) Epoxy resin insoluble thermoplastic resin Polyamide 12 (TR-55 (product name), manufactured by M-Chemie Japan, average particle size 20 μm, hereinafter abbreviated as "PA12")

[0161] (7) Epoxy resin-soluble thermoplastic resin Polyethersulfone (Sumitomo Chemical Co., Ltd., Sumikaexcel PES-5003P (product name), average particle size 20 μm, hereafter abbreviated as "PES")

[0162] (8) Resin particles MX-416 (product name: MX-416, manufactured by Kaneka Corporation, average particle size: 0.11 μm, masterbatch prepared by dispersing a particulate butadiene rubber component in a glycidylamine-type tetrafunctional epoxy resin to a concentration of 25% by mass) (the glycidylamine-type tetrafunctional epoxy resin in the product contains 75% by mass of tetraglycidyl-4,4'-diaminodiphenylmethane, which corresponds to the epoxy compound [A] of the present invention.)

[0163] (9) Carbon fiber strands Carbon fiber 1: Tenax (registered trademark) IMS65 E23 830tex (carbon fiber strand, tensile strength 5.8 GPa, tensile modulus 290 GPa, sizing agent adhesion amount 1.2 mass%, manufactured by Teijin Limited)

[0164] (10) Thermoplastic resin nonwoven fabric Nonwoven fabric 1: Made of polyamide 12 resin, spunbonded to a fiber weight of 6 g / m 2 , nonwoven fabric with a melting point of 178°C

[0165] (11) Carbon fiber multilayer fabric Carbon fiber multiaxial fabric 1: 190g / m² of unidirectionally aligned carbon fiber 1 per layer 2 The nonwoven fabric 1 was placed on one side of the sheet-like carbon fiber, and four sheets were stacked at angles of (+45 / V / 90 / V / -45 / V / 0 / V) and stitched together (total weight of carbon fiber in the woven fabric substrate: 760 g / m 2 ) where V represents nonwoven fabric 1. Carbon fiber multiaxial fabric 2: 190g / m per layer of unidirectionally aligned carbon fiber 1 2 The nonwoven fabric 1 was placed on one side of the carbon fiber sheet, and four sheets were stacked at angles of (0 / V / -45 / V / 90 / V / +45 / V) and stitched together (the total weight of the carbon fiber in the woven fabric substrate was 760 g / m 2 ) where V represents nonwoven fabric 1.

[0166] [Evaluation method] (1) Resin composition characteristics (initial viscosity and pot life of epoxy resin composition for RTM molding) The viscosity of the epoxy resin composition was measured at 100°C using a B-type viscometer TVB-15M manufactured by Toki Sangyo Co., Ltd. The minimum measured value immediately after the start of measurement was taken as the initial viscosity, and the time until the viscosity reached 50 mPa s was taken as the pot life.

[0167] (2) Heat resistance of cured resin (glass transition temperature after water absorption (wet-Tg)) To evaluate the heat resistance of cured resins, the glass transition temperature was measured according to the SACMA 18R-94 method. The cured resins to be evaluated were cut and polished to prepare test specimens measuring 50 mm x 6 mm x 2 mm. The prepared resin 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 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).

[0168] (3) Resin cured product properties (room temperature dry resin flexural modulus (RTD-FM)) The test was conducted in accordance with JIS K7171. Resin test pieces were prepared using the cured resin plates to be evaluated, with dimensions of 80 mm x 10 mm x 4 mm (thickness h). A bending test was conducted at an ambient temperature of 25°C, with a support distance L of 16 x h (thickness) and a test speed of 2 mm / min, to measure the bending strength and bending modulus.

[0169] (4) Resin cured product properties (resin cured product toughness (deformation mode I critical stress intensity factor KIc)) Toughness (KIc) was measured using a universal testing machine (Shimadzu Autograph) in accordance with ASTM D5045. Tests were conducted in accordance with ASTM D5045. Resin test specimens measuring 50 mm x 8 mm (width W) x 4 mm were prepared using the cured resin plates to be evaluated. The crack length a was adjusted to 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 specimen were used.

[0170] (5) CFRP properties (compression after impact (CAI)) The CFRP samples were cut to 101.6 mm wide x 152.4 mm long to obtain specimens for compressive strength after impact (CAI) testing. Testing was performed in accordance with ASTM D7136. After measuring the dimensions of each specimen, impact testing was performed using a drop weight impact testing machine (Instron Dynatup) with an impact energy of 30.5 J. After impact, the damage area of ​​the specimen was measured using an ultrasonic flaw detector (Krautkrämer SDS3600, HIS3 / HF). After impact, strength testing was performed on the specimen by attaching one strain gauge on each side of the specimen at positions 25.4 mm from the top and 25.4 mm from the sides, with a total of four strain gauges attached to the front and back of the specimen. The crosshead speed of the testing machine (Shimadzu Autograph) was set to 1.27 mm / min, and the load was applied until the specimen broke.

[0171] (6) CFRP properties (room temperature dry perforated compressive strength (RTD-OHC)) The CFRP to be evaluated was cut to dimensions of 38.1 mm wide x 304.8 mm long, and a 6.35 mm diameter hole was drilled in the center of the specimen to obtain a test specimen for room temperature dry open-hole compressive strength (RTD-OHC) testing. The test was conducted at an ambient temperature of 25°C in accordance with SACMA SRM3, and the open-hole compressive strength was calculated from the maximum point load.

[0172] (7) Average particle size The cross section of the cured resin to be evaluated was observed at 25,000x magnification using a scanning electron microscope or a transmission electron microscope, and the diameters of at least 50 particles were measured and averaged to determine the average particle size. If the particles were not perfectly circular, i.e., elliptical, the maximum diameter of the particle was taken as the particle size of that particle.

[0173] Example 1 [Preparation of epoxy resin composition for RTM molding method] The epoxy resin, curing agent, and resin particles were weighed out in the proportions shown in Table 1 and mixed using a stirrer at 80°C for 30 minutes to prepare an epoxy resin composition for RTM molding. The properties of the obtained epoxy resin composition for RTM molding are shown in Table 1. The viscosity at 100°C was 50 mPa·s or less, and the pot life at 100°C was 120 minutes or more, demonstrating excellent handleability. In the epoxy resin composition shown in Table 1, the glycidyl groups contained in the epoxy resin and the amino groups in the curing agent are equivalent in weight.

[0174] [Preparation of cured resin] The epoxy resin composition for RTM prepared above was degassed in a vacuum for 60 minutes, then poured into a stainless steel mold set to a thickness of 4 mm using a 4 mm Teflon (registered trademark) resin spacer. It was then heated and cured at 180°C for 120 minutes to obtain a 4 mm thick cured resin product. The properties of the obtained cured resin are shown in Table 1. The wet-Tg was 160°C or higher, the flexural modulus was 3.3 GPa or higher, and the K1c was 0.8 MPa m 1 / 2 As a result, high mechanical properties were observed.

[0175] [Creating CFRP] Carbon fiber multiaxial fabric 1 and carbon fiber multiaxial fabric 2 were cut to 300 x 300 mm, and a total of six sheets, three sheets of carbon fiber multiaxial fabric 1 and three sheets of carbon fiber multiaxial fabric 2, were layered on a 500 x 500 mm release-treated aluminum plate to form a laminate.

[0176] Furthermore, a peel cloth substrate, Release Ply C (manufactured by AIRTECH), which is a substrate with a release function, and a resin diffusion substrate, Resin Flow 90HT (manufactured by AIRTECH), were laminated on the laminate. Then, hoses for forming a resin inlet and a resin outlet were installed, and the whole was covered with nylon bag film, sealed with sealant tape, and the inside was evacuated. The aluminum plate was then heated to 120°C, and the pressure inside the bag was reduced to 5 torr or less. The epoxy resin composition for RTM molding prepared above was then heated to 100°C and injected into the vacuum system through the resin inlet.

[0177] The injected epoxy resin composition for RTM filled the bag, and in this state impregnated the laminate, the temperature was raised to 180°C and held at 180°C for 120 minutes to obtain a carbon fiber reinforced composite material (CFRP). The properties of the obtained CFRP are shown in Table 1. It showed a high CAI of over 280 MPa and an excellent RTD-OHC of over 300 MPa.

[0178] [Table 1]

[0179] Examples 2 to 6 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.

[0180] Comparative Examples 1 to 4 The experiment was carried out in the same manner as in Example 1, except that the composition was changed as shown in Table 2. The evaluation results are shown in Table 2.

[0181] [Table 2]

[0182] In Comparative Example 1, the epoxy compound [B] was not used, and therefore the initial viscosity of the epoxy resin composition was 100 mPa·s or more. In Comparative Example 2, the epoxy compound [C] was used instead of the epoxy compound [B], and therefore the wet-Tg of the obtained cured resin product was as low as 138°C. In Comparative Examples 3 and 4, the epoxy compound [A] was not used, and therefore the wet-Tg of the obtained cured resin was 150° C. or lower.

[0183] Example 7 Prepregs were prepared and evaluated according to the following procedure.

[0184] [Preparation of epoxy resin composition for prepreg method] 85 parts by mass of 3,4'-TGDDE as epoxy compound [A], 15 parts by mass of 1,6-DON as epoxy compound [B], and 30 parts by mass of PES as soluble thermoplastic resin were weighed out and mixed using a stirrer at 120°C for 30 minutes. The mixture was then cooled to 80°C, and 55 parts by mass of 3,3'-DDS as a curing agent and 35 parts by mass of PA12 as a non-soluble thermoplastic resin were added and mixed for 30 minutes to prepare an epoxy resin composition for prepreg. At these ratios, the ratio of the total number of epoxy groups in the epoxy resin composition to the total number of active hydrogens in the curing agent was 1.0.

[0185] [Preparation of prepreg] The obtained epoxy resin composition for prepreg was applied onto release paper using a reverse roll coater to give a coating thickness 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 95°C and a pressure of 0.2 MPa to produce a unidirectional prepreg with a carbon fiber content of 65% by mass.

[0186] [Evaluation of storage stability of prepreg] The obtained prepreg was stored at a temperature of 26.7°C and a humidity of 65% for 10 days, and then the prepreg was cut and laminated in a mold for evaluation. As a result of the evaluation, the prepreg after storage conformed well to the mold when laminated, and showed almost the same tack and drape as immediately after production. It was confirmed that the prepreg of the present invention has good handling properties.

[0187] [Evaluation of molding voids] The obtained prepreg was stored at a temperature of 26.7°C and a humidity of 65% for 10 days, and then cut into 150 mm x 150 mm pieces. 10 The laminate was subjected to a compaction treatment (storing the laminate in a vacuum pack) and stored in an environment at a temperature of 23°C. Thirty-two days after lamination, a CFRP laminate was formed using a conventional vacuum autoclave molding method, heated at 180°C for 2 hours under a pressure of 0.59 MPa. Test specimens were cut out, the cross sections polished, and the presence or absence of voids was observed under a microscope. As a result of the evaluation, it was confirmed that there were no voids in the cross section of the molded article, and that the prepreg of the present invention has good moldability.

[0188] [Evaluation of tackiness] The tackiness of the prepreg was measured using a tack testing device, TAC-II (RHESCA CO., LTD.), as follows: The prepreg was set on a test stage maintained at 27°C, and an initial load of 100 gf was applied using a φ5 tack probe also maintained at 27°C. The maximum load when the prepreg was pulled out at a test speed of 10 mm / sec was determined. Tack probe tests were performed on prepregs immediately after production and on prepregs stored at a temperature of 26.7°C and humidity of 65% for 10 days. As a result of the evaluation, the load immediately after production was 200 gf or more, and the tack retention rate after storage for 10 days was 50% or more, confirming that the prepreg of the present invention has good handleability.

[0189] [Evaluation of drapeability] The drapeability of the prepreg was evaluated by the following test in accordance with ASTM D1388. The obtained prepreg was cut in a direction at 90° to the 0° fiber direction, and the drapeability (flexural rigidity, mg × cm) at an inclination angle of 41.5° was evaluated. This evaluation was performed immediately after the prepreg was produced and after storage for a specified period at a temperature of 26.7°C and a humidity of 65%. As a result of the evaluation, the drapeability after 20 days was unchanged from that immediately after production, confirming that the prepreg of the present invention has good handleability.

[0190] [Evaluation of impregnation] The resin impregnation ability of the fiber substrate was evaluated based on the water absorption rate of the prepreg. The lower the water absorption rate of the obtained prepreg, the higher the resin impregnation ability. The obtained prepreg was cut into a square with sides of 100 mm, and its mass (W1) was measured. The prepreg was then submerged in water in a desiccator. The pressure inside the desiccator was reduced to 10 kPa or less, and the air inside the prepreg was replaced with water. The prepreg was removed from the water, the water on the surface was wiped off, and the mass (W2) of the prepreg was measured. The water absorption rate was calculated from these measured values ​​using the following formula: Water absorption rate (%)=[(W2-W1) / W1]×100 W1: Mass of prepreg (g) W2: Mass of prepreg after water absorption (g) As a result of the evaluation, the water absorption rate was found to be less than 10%, confirming that the epoxy resin composition of the present invention has good impregnation properties. [Industrial Applicability]

[0191] The epoxy resin composition of the present invention can be used to produce cured resin products with excellent mechanical properties. Furthermore, the epoxy resin composition of the present invention has low viscosity and a long pot life, making it easy to handle during molding, and fiber-reinforced composite materials with excellent quality and mechanical properties can be produced. Furthermore, the prepreg of the present invention can be used to produce fiber-reinforced composite materials. The resulting fiber-reinforced composite materials can be used as components for automobiles and aircraft.

Claims

1. The following chemical formula (1) (where R １ ~R ４ represents a hydrogen atom, and X １ Ha-CH ２ -, -O-, -S-, -CO-, -C(=O)O-, -OC(=O)-, -NHCO-, -CONH- or -SO ２ -, and an epoxy compound [A] represented by the formula (I) an epoxy compound [B] having a polycyclic aromatic ring structure or a heterocyclic ring structure; an aromatic epoxy compound [C] which is diglycidyl-aniline or a derivative thereof; comprising rubber particles and a curing agent; The rubber particles have a particle size of 0.03 to 1.0 μm and a content of 0.1 to 50 mass %, The curing agent is represented by the following chemical formula (2) (wherein R 5 to R 8 are each independently a hydrogen atom, an aliphatic substituent having 1 to 6 carbon atoms, an aromatic substituent, or a halogen atom, and at least one of the substituents is an aliphatic substituent having 1 to 6 carbon atoms, an aromatic substituent, or a halogen atom; and X 2 is —CH 2 —). or a compound represented by the following chemical formula (3) (wherein R 9 to R 12 are each independently any one of a hydrogen atom, an aliphatic substituent, an aromatic substituent, a halogen atom, a methoxy group, an alkoxy group, and a thioalkoxy group, and at least one substituent is any one of an aliphatic substituent having 1 to 6 carbon atoms, an aromatic substituent, a halogen atom, a methoxy group, an alkoxy group, and a thioalkoxy group), the mass ratio of the epoxy compound [A] to the epoxy compound [B] is 50:50 to 99:1, the epoxy compound [C] is 1 to 80 parts by mass relative to 100 parts by mass in total of the epoxy compound [A] and the epoxy compound [B], The total mass of the epoxy compounds contained in the epoxy resin composition is taken as 100 mass %, and the total of the epoxy compound [A], the epoxy compound [B] and the epoxy compound [C] accounts for 70 to 100 mass % of the total mass of the epoxy compounds. An epoxy resin composition characterized by: 【Chemistry 1】 【Chemistry 2】 【Transformation 3】

2. 2. The epoxy resin composition according to claim 1, wherein the epoxy compound [A] is tetraglycidyl-3,4'-diaminodiphenyl ether.

3. An epoxy resin composition according to claim 1 or 2, wherein the aromatic epoxy compound [C] is diglycidyl aniline and / or diglycidyl toluidine.

4. 4. The epoxy resin composition according to claim 1, wherein the epoxy compound [B] having a polycyclic aromatic ring structure or a heterocyclic ring structure is a naphthalene derivative epoxy compound.

5. 4. The epoxy resin composition according to claim 1, wherein the epoxy compound [B] having a polycyclic aromatic ring structure or a heterocyclic ring structure is a triglycidyl isocyanurate derivative epoxy compound.

6. 5. The epoxy resin composition of claim 4, wherein the naphthalene derivative epoxy compound is bis(glycidyloxy)naphthalene.

7. 5. The epoxy resin composition of claim 4, wherein the naphthalene derivative epoxy compound is selected from bis(glycidyloxy)-1,1'-binaphthalene and bis(glycidyloxy)-1-[(glycidyloxy)-1-naphthylmethyl]naphthalene.

8. 6. The epoxy resin composition according to claim 5, wherein the triglycidyl isocyanurate derivative epoxy compound is selected from 1,3,5-triglycidyl isocyanurate, 1,3,5-tri(ethylglycidyl)isocyanurate, and 1,3,5-tri(pentylglycidyl)isocyanurate.

9. An epoxy resin composition according to any one of claims 1 to 8, wherein the curing agent is 4,4'-diaminodiphenylmethane, a derivative thereof represented by the following chemical formulas (4) to (8), a phenylenediamine represented by the following chemical formulas (9) to (12), or a derivative thereof. 【Chemistry 4】 【Transformation 5】

10. A prepreg comprising the epoxy resin composition according to any one of claims 1 to 9 and a fiber-reinforced substrate.

11. A fiber-reinforced composite material comprising a cured product of the epoxy resin composition according to any one of claims 1 to 9 and a fiber-reinforced substrate.

12. A method for producing a prepreg, comprising an impregnation step of impregnating a fiber-reinforced substrate with the epoxy resin composition according to any one of claims 1 to 9 to obtain a prepreg.

13. A method for producing a fiber-reinforced composite material, comprising the steps of impregnating a fiber-reinforced substrate placed in a mold with the epoxy resin composition according to any one of claims 1 to 9, and then heat-curing the composition.

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