JP2023084198A - Epoxy resin composition, prepreg, fiber-reinforced composite material and production method - Google Patents

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

The present invention relates to epoxy resin compositions, prepregs, fiber-reinforced composite materials, and manufacturing methods.

Fiber-reinforced composite materials are lightweight, high-strength, and high-rigidity, so they are used in a wide range of fields, such as sports and leisure applications such as fishing rods and golf shafts, and industrial applications such as automobiles and aircraft.

As a method of molding a composite material using a thermosetting resin as a matrix resin, there is a method of molding a prepreg (intermediate base material) formed into a sheet by impregnating a fiber-reinforced base material with an uncured thermosetting resin in advance. , a resin transfer molding method (RTM molding method) is known, in which a fiber-reinforced base material placed in a mold is impregnated with a liquid uncured thermosetting resin and cured to obtain a fiber-reinforced composite material.

In recent years, attention has been paid to the RTM molding method, which is low-cost and excellent in productivity, because there are few processes for manufacturing fiber-reinforced composite materials and does not require expensive equipment such as an autoclave. A tetrafunctional aromatic epoxy resin is generally used as the uncured thermosetting resin used in the RTM molding method.

In the epoxy resin composition used in the RTM molding method, in addition to the tetrafunctional aromatic epoxy resin, a low-viscosity bifunctional aromatic epoxy resin is added in order to improve the impregnation of the resin composition into the fiber-reinforced base material. Often used as a viscosity reducer.

However, when a bifunctional aromatic epoxy resin is used as a viscosity reducer, the crosslink density of the cured resin obtained by heat-curing the epoxy resin composition is lowered, and the heat resistance and heat resistance of the cured resin and fiber-reinforced composite material are reduced. There is a problem that the mechanical properties are degraded.

In the first place, a fiber-reinforced composite material using an epoxy resin composition as a matrix resin generally has low impact resistance, and improvement in the toughness of the epoxy resin cured product is required. Patent Literature 1 describes a method of imparting toughness to a cured epoxy resin by using a composition in which a thermoplastic resin is dissolved in an epoxy resin. According to this method, a certain degree of toughness can be imparted to the epoxy resin cured product.

However, in order to impart high toughness, a large amount of thermoplastic resin must be dissolved in the epoxy resin. As a result, an epoxy resin composition in which a large amount of thermoplastic resin is dissolved has a significantly high viscosity, making it difficult to impregnate the interior of the fiber-reinforced base material with a sufficient amount of resin. Therefore, defects such as voids are inherent in the fiber-reinforced composite material produced using such an epoxy resin composition, and there is a problem that the compression performance and damage tolerance of the fiber-reinforced composite material are lowered. .

JP-A-60-243113

The object of the present invention is to be able to produce a fiber-reinforced composite material having excellent heat resistance, compression properties and impact resistance. An object of the present invention is to provide an epoxy resin composition having good

That is, the present invention provides the following chemical formula (1) (where R ₁ to R ₄ each independently represent a hydrogen atom, an aliphatic hydrocarbon group, an alicyclic hydrocarbon group or a halogen atom, and X ₁ is —CH ₂ — , -O-, -S-, -CO-, -C(=O)O-, -OC(=O)-, -NHCO-, -CONH- or -SO ₂ -). and an epoxy compound [B] having a polycyclic aromatic ring structure or a heterocyclic structure.

According to the present invention, it is possible to produce a fiber-reinforced composite material having excellent heat resistance, compression properties and impact resistance. can provide an epoxy resin composition with good

The present invention will be described in detail below. A fiber reinforced composite material is sometimes abbreviated as "FRP", and a carbon fiber reinforced composite material as "CFRP".

[Epoxy compound [A]]
The epoxy resin composition of the present invention has the following chemical formula (1) (where R ₁ to R ₄ each independently represent a hydrogen atom, an aliphatic hydrocarbon group, an alicyclic hydrocarbon group or a halogen atom, and X ₁ is represents -CH ₂ -, -O-, -S-, -CO-, -C(=O)O-, -O-C(=O)-, -NHCO-, -CONH- or -SO ₂ - .) contains an epoxy compound [A] represented by

R ₁ to R ₄ are preferably hydrogen atoms in order to prevent inhibition of chemical reactions during curing of the epoxy resin composition. X ₁ is also preferably -O- for ease of compound synthesis.
When R ₁ to R ₄ are aliphatic hydrocarbon groups or alicyclic hydrocarbon groups, they preferably have 1 to 4 carbon atoms.

As the epoxy compound [A], an epoxy compound having an amine-type glycidyl group is preferably used, and more preferably tetraglycidyl-4,4'-diaminodiphenyl ether, tetraglycidyl-4,4'-diaminodiphenylmethane, tetraglycidyl-3, 4'-diaminodiphenyl ether and tetraglycidyl-3,3'-diaminodiphenylmethane, particularly preferably tetraglycidyl-3,4'-diaminodiphenyl ether are used.

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

As aromatic diamines, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 3,4 '-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl methane can be exemplified.

Among these, aromatic diamines in which two aromatic rings having amino groups are linked by an ether bond are preferable from the viewpoint of heat resistance. Particularly preferred are ortho-positioned aromatic diamines. Examples of this aromatic diamine include 3,4'-diaminodiphenyl ether and 3,4'-diaminodiphenyl sulfone.

Examples of epihalohydrin include epichlorohydrin, epibromohydrin, and epifluorohydrin. Among these, epichlorohydrin and epibromohydrin are particularly preferred from the viewpoint of reactivity and handleability.

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. Solvents used in the reaction include alcohol solvents such as ethanol and n-butanol, ketone solvents such as methyl isobutyl ketone and methyl ethyl ketone, aprotic polar solvents such as acetonitrile and N,N-dimethylformamide, and aromatic solvents such as toluene and xylene. group hydrocarbon solvents can be exemplified. Alcohol solvents such as ethanol and n-butanol, and aromatic hydrocarbon solvents such as toluene and xylene are particularly preferred.

The amount of the solvent to be used is preferably 1 to 10 times the weight of the aromatic diamine. Both Bronsted acids and Lewis acids can be suitably used as acid catalysts. Preferred Bronsted acids are ethanol, water and acetic acid, and preferred Lewis acids are titanium tetrachloride, lanthanum nitrate hexahydrate and boron trifluoride diethyl ether complex.

The reaction time is preferably 0.1 to 180 hours, more preferably 0.5 to 24 hours. The reaction temperature is preferably 20-100°C, more preferably 40-80°C.
Examples of alkaline compounds 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.

A phase transfer catalyst may be used during the cyclization reaction. Phase transfer catalysts such as quaternary ammonium salts such as tetramethylammonium chloride, tetraethylammonium bromide, benzyltriethylammonium chloride, and tetrabutylammonium hydrogen sulfate; phosphonium compounds such as tributylhexadecylphosphonium bromide and tributyldodecylphosphonium bromide; Crown ethers such as 18-crown-6-ether can be exemplified.

In the epoxy resin composition of the present invention, the ratio of the epoxy compound [A] to the total amount of the epoxy resin (epoxy resin base liquid) is preferably 40 to 90% by mass, particularly preferably 50 to 80% by mass. . When the proportion of the epoxy compound [A] is 40% by mass or more, it is possible to further improve the heat resistance and elastic modulus of the obtained cured resin. As a result, various mechanical properties of the resulting fiber-reinforced composite material are also improved. When the proportion of the epoxy compound [A] is 90% by mass or less, the viscosity of the resin composition can be lowered, and the impregnation of the fiber base material can be enhanced.

[Epoxy compound [B]]
The epoxy resin composition of the present invention contains an epoxy compound [B] having a polycyclic aromatic ring structure or heterocyclic ring structure. By including this epoxy compound [B], it is possible to reduce the viscosity of the epoxy resin composition and improve the impregnating property of the fiber-reinforced base material with the resin, thereby increasing the degree of freedom in designing the mold used in the RTM molding method. can be enhanced.

Moreover, by using this epoxy compound [B], unlike the epoxy compound [C] described later, the viscosity of the epoxy resin composition is reduced, while the heat resistance of the cured resin obtained can be improved.

In the present invention, by using the epoxy compound [A] described above and the epoxy compound [B] described above in combination, the resin impregnation property of the fiber-reinforced substrate is improved, and heat resistance and high elastic modulus are maintained. A cured resin and a fiber-reinforced composite material can be obtained.

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

Examples of the polycyclic aromatic ring structure include a naphthalene skeleton and an anthracene skeleton, and a naphthalene skeleton is preferred from the viewpoint of the physical properties of the cured resin. That is, as the epoxy compound [B] having a polycyclic aromatic ring structure or heterocyclic 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.

As the naphthalene derivative epoxy compound, bis(glycidyloxy)naphthalene is preferably used from the viewpoint of fluidity. Specifically, 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 , 2,7-bis(glycidyloxy)-1-[2-(glycidyloxy)-1-naphthylmethyl]naphthalene.

Among them, it is preferably selected from bis(glycidyloxy)-1,1′-binaphthalene and bis(glycidyloxy)-1-[(glycidyloxy)-1-naphthylmethyl]naphthalene, and these epoxy compounds [B] By using, the viscosity of the epoxy resin composition can be reduced and the heat resistance of the resin cured product can be improved.

By using an epoxy compound having a polycyclic aromatic ring structure as the epoxy compound [B], the cross-linking density of the cured product is excessively increased, unlike the tetrafunctional epoxy resin that is usually used to improve the heat resistance of the cured product. never Therefore, it is possible to prevent a decrease in toughness of the cured resin and the fiber-reinforced composite material.

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. be.

Triglycidyl isocyanurate derivative epoxy compounds are preferably from 1,3,5-triglycidyl isocyanurate, 1,3,5-tri(ethylglycidyl)isocyanurate and 1,3,5-tri(pentylglycidyl)isocyanurate selected. By using these compounds as the epoxy compound [B], the heat resistance and elastic modulus of the cured epoxy resin 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].

In the epoxy resin composition of the present invention, the mass ratio of the above epoxy compound [A] and the above epoxy compound [B] is preferably 50:50 to 99:1, more preferably 50:50 to 95:5. , particularly preferably 60:40 to 90:10. When the proportion of the epoxy compound [B] is 1% by mass or more, the viscosity of the resulting resin composition can be further reduced, and the handleability of the resin composition and compatibility with the RTM molding method can be further improved. Furthermore, the heat resistance and elastic modulus of the resin cured product to be obtained can be further improved. As a result, various mechanical properties of the resulting fiber-reinforced composite material are also improved. In addition, it is preferable that the proportion of the epoxy compound [B] is 50% by mass or less, since the deterioration of the heat resistance and elastic modulus of the obtained cured resin can be minimized.

[Epoxy compound [C]]
The epoxy resin composition of the present invention preferably further contains an aromatic epoxy compound [C] having a glycidyl ether group, in addition to the above epoxy compound [A] and epoxy compound [B].

In this case, the number of glycidyl ether groups/the number of aromatic rings of the aromatic epoxy compound [C] having a glycidyl ether group is two. By including this epoxy compound [C], the viscosity of the epoxy resin composition can be reduced, and the resin impregnation property of the fiber-reinforced base material can be improved.
The aromatic epoxy compound [C] having a glycidyl ether group is preferably diglycidylaniline and/or diglycidyltoluidine.

An aromatic compound having a glycidyl ether group is used as the epoxy compound [C]. The epoxy compound [C] is preferably diglycidylaniline or its derivatives such as diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine, diglycidyl-xylidine, diglycidyl-mesidine, diglycidyl-anisidine and diglycidyl. -phenoxyaniline, or diglycidyl-naphthylamine and derivatives thereof, more preferably diglycidyl-aniline, diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine and diglycidyl-phenoxyaniline.

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 life 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].

In the epoxy resin composition of the present invention, when the epoxy compound [C] is contained, it is preferable that the epoxy compound [ C] is included. If it is less than 1% by mass, the viscosity of the resin composition increases, and if it exceeds 80 parts by mass, the heat resistance of the cured resin is lowered, which is not preferable.

Assuming that the total weight of the epoxy compounds contained in the epoxy resin composition of the present invention is 100% by weight, the total weight of epoxy compound [A], epoxy compound [B] and epoxy compound [C] is preferably It occupies 70 to 100% by mass. If it is less than 70% by mass, the mechanical properties of the cured resin are lowered, which is not preferable.

In the epoxy resin composition of the present invention, the content of the epoxy compound [C] per total mass of the epoxy compounds (epoxy resin main component liquid) is preferably 5 to 50% by mass, more preferably 10 to 40% by mass. is. When the content of the epoxy compound [C] is 5% by mass or more, the viscosity of the resulting resin composition can be further reduced, and the handleability of the resin composition and compatibility with the RTM molding method can be further improved. can.

[Curing agent]
A known curing agent can be used in the epoxy resin composition of the present invention. In particular, it is preferable to use an amine-based curing agent from the viewpoint of 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.

Examples of amine-based curing agents 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 preferable because it is excellent in storage stability of the prepreg.
Aliphatic polyamines are preferred because they have high reactivity and enable a curing reaction at low temperatures. Examples of aliphatic polyamines include 4,4'-diaminodicyclohexylmethane, isophoronediamine, and m-xylylenediamine.

Aromatic polyamines are preferable because they are excellent in heat resistance and various mechanical properties. Examples of aromatic polyamines include diaminodiphenylsulfone, diaminodiphenylmethane, and toluenediamine derivatives. Aromatic diamine compounds such as 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl methane, and their derivatives having non-reactive substituents have excellent heat resistance. It is particularly preferable from the viewpoint of giving things. Here, the non-reactive substituent is the same as the non-reactive substituent described in the explanation of the epoxy resin.

In addition, 4,4'-methylenebis(2,6-diethylaniline) and 4,4' are added to improve the storage stability of the uncured epoxy resin composition and to improve the water absorption properties of the cured resin composition. Hindered amine compounds such as -methylenebis(2-ethyl-6-methylaniline) and 4,4'-methylenebis(2-isopropyl-6-methylaniline) are also preferably used.

Preferred aminobenzoic acid esters include trimethylene glycol di-p-aminobenzoate and neopentyl glycol di-p-aminobenzoate. Composite materials cured using these are inferior in heat resistance to various isomers of diaminodiphenylsulfone, but are excellent in tensile elongation.

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 having relatively well-balanced electrical, chemical and mechanical properties can be obtained. Therefore, the type of curing agent to be used is appropriately selected according to the application of the composite material.

When the epoxy resin composition of the present invention is used in the RTM molding method, a curing agent composed of an aromatic polyamine and having at least one aliphatic substituent, aromatic substituent, or halogen atom at the ortho position to the amino group. It preferably contains a curing agent consisting of an aromatic polyamine having such substituents. That is, it is preferable to include compounds represented by the following chemical formulas (2) and (3) as curing agents.

However, in chemical formula (2), 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 substituent The group is either an aliphatic substituent having 1 to 6 carbon atoms, an aromatic substituent, or a halogen atom. X ₂ is -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -S-, -O-, -SO ₂ -, -CO-, -CONH-, -NHCO-, It is either -C(=O)- or -OC(=O)-.

provided that in chemical formula (3), R ₉ to R ₁₂ are each independently a hydrogen atom, an aliphatic substituent, an aromatic substituent, a halogen atom, a methoxy group, an alkoxy group or a thioalkoxy group, and At least one substituent is an aliphatic substituent having 1 to 6 carbon atoms, an aromatic substituent, a halogen atom, a methoxy group, an alkoxy group or a thioalkoxy group. The one substituent is preferably an aliphatic substituent having 1 to 6 carbon atoms.

In chemical formulas (2) and (3), the aliphatic substituent preferably has 1 to 6 carbon atoms. Examples of aliphatic substituents include methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, neopentyl group, n-hexyl group and cyclohexyl group. exemplified. A phenyl group and a naphthyl group are illustrated as an aromatic substituent.

As a curing agent suitable for the RTM molding method, any polyamine having the above structure may be used. Specifically, 4,4'-diaminodiphenylmethane and its derivatives represented by the following chemical formulas (4) to (8); Phenylenediamines represented by the following chemical formulas (9) to (12) and derivatives thereof are exemplified.

The total amount of the curing agent contained in the epoxy resin composition of the present invention is an amount suitable for curing all the epoxy compounds contained in the epoxy resin composition, and the type of epoxy compound and curing agent used. adjusted accordingly.

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 hydrogens contained in the curing agent is preferably 0.7 to 1.3, more preferably is 0.8 to 1.2, particularly preferably 0.9 to 1.1. If this ratio is less than 0.7 or more than 1.3, the molar balance between the epoxy groups and the active hydrogen will be disturbed, and the crosslink density of the resulting cured resin may be insufficient, resulting in poor heat resistance and elasticity. Mechanical properties such as modulus and fracture toughness may be reduced.

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

The epoxy resin-soluble thermoplastic resin adjusts the viscosity of the epoxy resin composition and improves the impact resistance of the obtained FRP. This epoxy resin-soluble thermoplastic resin is a thermoplastic resin that can partially or wholly dissolve in an epoxy resin at a temperature at which FRP is molded or at a temperature lower than that.

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

On the other hand, the term “epoxy resin-insoluble thermoplastic resin” refers to a thermoplastic resin that does not substantially dissolve in epoxy resin at temperatures at or below the FRP molding temperature. That is, when 10 parts by mass of a thermoplastic resin having an average particle size of 20 to 50 μm is mixed with 100 parts by mass of an epoxy resin and stirred at 190° C. for 1 hour, the particle size does not change by 10% or more. Refers to plastic resin.

The temperature for molding FRP is generally 100 to 190°C. Moreover, the particle size is visually measured with a microscope, and the average particle size means the average value of the particle sizes of 100 randomly selected particles.

When the epoxy resin-soluble thermoplastic resin is not completely dissolved, it is dissolved in the epoxy resin by heating during the curing process of the epoxy resin, and the viscosity of the epoxy resin composition can be increased. This makes it possible to prevent the epoxy resin composition from flowing (phenomenon in which the resin composition flows 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 an epoxy resin in an amount of 80% by mass or more at 190°C.

Specific examples of epoxy resin-soluble thermoplastic resins include polyethersulfone, polysulfone, polyetherimide, polycarbonate and the like. 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 resulting FRP will have insufficient impact resistance, and if it is more than 100,000, the viscosity will be extremely high and the handleability will be significantly deteriorated.

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

The epoxy resin-soluble thermoplastic resin preferably has a reactive group reactive with the epoxy resin or a functional group forming a hydrogen bond. Such an epoxy resin-soluble thermoplastic resin can improve the dissolution stability during the curing process of the epoxy resin. In addition, toughness, chemical resistance, heat resistance and resistance to moist heat can be imparted to the FRP obtained after curing.

A hydroxyl group, a carboxylic acid group, an imino group, and an amino group are preferable as the reactive group having reactivity with the epoxy resin. The use of hydroxyl-terminated polyethersulfone is more preferable because the resulting FRP has particularly excellent impact resistance, fracture toughness and solvent resistance.

The content of the epoxy resin-soluble thermoplastic resin contained in the epoxy resin composition is appropriately adjusted according to the viscosity. From the viewpoint of workability of the prepreg, it 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, based on 100 parts by mass of the epoxy resin contained in the epoxy resin composition. is. If it is less than 5 parts by mass, the resulting FRP may have insufficient impact resistance, which is not preferred. On the other hand, when the content of the epoxy resin-soluble thermoplastic resin exceeds 90% by mass, the viscosity becomes significantly high, and the handleability of the prepreg may be significantly deteriorated, which is not preferable.
The epoxy resin-soluble thermoplastic resin preferably contains a reactive aromatic oligomer (hereinafter also simply referred to as "aromatic oligomer") having amine end groups.

The epoxy resin composition has a high molecular weight due to a curing reaction between the epoxy resin and the curing agent during heat curing. The expansion of the two-phase region due to the increase in the molecular weight causes the aromatic oligomer dissolved in the epoxy resin composition to undergo reaction-induced phase separation. Due to this phase separation, a two-phase resin structure in which the cured epoxy resin and the aromatic oligomer are co-continuous is formed in the matrix resin. Also, since aromatic oligomers have amine end groups, they also react with epoxy resins. Since each phase in this co-continuous two-phase structure is strongly bonded to each other, solvent resistance is also improved.

This co-continuous structure absorbs external impact on the FRP and suppresses crack propagation. As a result, FRPs made using prepregs containing reactive aromatic oligomers with amine end groups have high impact resistance and fracture toughness.
As the aromatic oligomer, known polysulfones having amine end groups and polyether sulfones having amine end groups can be used. Preferably, the amine end groups are primary amine (--NH ₂ ) end groups.

The aromatic oligomer blended in the epoxy resin composition preferably has a weight average molecular weight of 8,000 to 40,000 as measured by gel permeation chromatography. If the weight average molecular weight is less than 8000, the effect of improving the toughness of the matrix resin is low, which is not preferable. On the other hand, if the weight-average molecular weight exceeds 40,000, the viscosity of the resin composition becomes too high, and processing problems such as difficulty in impregnating the reinforcing fiber layer with the resin composition tend to occur, which is not preferable. .

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

The form of the epoxy resin-soluble thermoplastic resin is preferably particulate. The particulate epoxy resin-soluble thermoplastic resin can be uniformly blended in the resin composition. In addition, the prepreg to be obtained has high moldability.

The average particle size of the epoxy resin-soluble thermoplastic resin is preferably 1-50 μm, more preferably 3-30 μm. If it is less than 1 μm, the viscosity of the epoxy resin composition will be significantly increased, and it may be difficult to add a sufficient amount of the epoxy resin-soluble thermoplastic resin to the epoxy resin composition, which is not preferable. On the other hand, if the thickness exceeds 50 μm, it may be difficult to obtain a sheet with a uniform thickness when processing the epoxy resin composition into a sheet, and the rate of dissolution in the epoxy resin is slowed, resulting in an unsatisfactory FRP. It is not preferable because it becomes uniform.

The epoxy resin composition may contain an epoxy resin-insoluble thermoplastic resin in addition to the epoxy resin-soluble thermoplastic resin. Part of the epoxy resin-insoluble thermoplastic resin and epoxy resin-soluble thermoplastic resin (the epoxy resin-soluble thermoplastic resin that remains undissolved in the matrix resin after curing) is in a state where the particles are dispersed in the FRP matrix resin. (The dispersed particles are hereinafter also referred to as “interlayer particles”). This interlayer particle suppresses the propagation of the impact received by the FRP. As a result, the impact resistance of the obtained FRP is improved.

Examples of epoxy resin-insoluble thermoplastic resins include polyamide, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyester, polyamideimide, polyimide, polyetherketone, polyetheretherketone, polyethylene naphthalate, polyethernitrile, and polybenzimidazole. Among these, polyamide, polyamideimide, and polyimide are preferred because of their high toughness and heat resistance.

Polyamide and polyimide are particularly excellent in improving the toughness of FRP. These may be used alone or in combination of two or more. Copolymers of these can also be used.

In particular, amorphous polyimide, nylon 6 (registered trademark) (polyamide obtained by ring-opening polycondensation reaction of caprolactam), nylon 11 (polyamide obtained by ring-opening polycondensation reaction of undecane lactam), nylon 12 (lauryl lactam) Polyamide obtained by the ring-opening polycondensation reaction), Nylon 1010 (polyamide obtained by the copolymerization reaction of sebacic acid and 1,10-decanediamine), amorphous nylon (also called transparent nylon, polymer crystals The heat resistance of the resulting FRP can be particularly improved by using a polyamide such as nylon, which does not undergo quenching or has a very slow crystallization rate of the polymer.

The content of the epoxy resin-insoluble thermoplastic resin in the epoxy resin composition is appropriately adjusted according to the viscosity of the epoxy resin composition. From the viewpoint of workability of the prepreg, it 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, based on 100 parts by mass of the epoxy resin contained in the epoxy resin composition. is. If it is less than 5 parts by mass, the resulting FRP may have insufficient impact resistance, which is not preferred. On the other hand, if it exceeds 50 parts by mass, the impregnability of the epoxy resin composition and the drapeability of the obtained prepreg may be deteriorated, which is not preferable.
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.

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

The inclusion of resin particles is preferable because high fracture toughness and impact resistance can be obtained in the cured resin and fiber-reinforced composite material.
As resin particles, for example, thermoplastic resin particles, thermosetting resin particles, and rubber particles can be used, and rubber particles are preferably used. Examples of rubber particles include silicone rubber, butadiene rubber, styrene-butadiene rubber, and methyl methacrylate-butadiene-styrene rubber.

Commercially available rubber particles used as resin particles include MX-153 (33% by mass of butadiene rubber monodispersed in bisphenol A type epoxy resin, manufactured by Kaneka Corporation), MX-257 (bisphenol A type epoxy 37% by mass of butadiene rubber is dispersed in resin, manufactured by Kaneka Corporation), MX-154 (Bisphenol A type epoxy resin, 40% by mass of butadiene rubber is dispersed in a single dispersion, Co., Ltd. Kaneka), MX-960 (Bisphenol A type epoxy resin, 25% by mass of silicone rubber is monodispersed, Kaneka Corporation), MX-136 (Bisphenol F type epoxy resin, 25% by mass Single dispersion of butadiene rubber, manufactured by Kaneka Corporation), MX-965 (bisphenol F type epoxy resin with 25% by mass of silicone rubber uniformly dispersed, manufactured by Kaneka Corporation), MX-217 (25% by mass of butadiene rubber dispersed in phenol novolac type epoxy resin, manufactured by Kaneka Corporation), MX-227M75 (25% by mass of styrene butadiene rubber in bisphenol A novolac type epoxy resin Dispersed, manufactured by Kaneka Corporation), MX-334M75 (brominated epoxy resin, 25% by mass of styrene-butadiene rubber monodispersed, manufactured by Kaneka Corporation), MX-416 (tetrafunctional glycidylamine 25% by mass of butadiene rubber is monodispersed in a type epoxy resin, manufactured by Kaneka Corporation), MX-451 (25% by mass of styrene-butadiene rubber is monodispersed in a trifunctional glycidylamine type epoxy resin. Tamono, manufactured by Kaneka Corporation) can be exemplified.

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 diameter is 1.0 μm or less, in the step of impregnating the fiber-reinforced base material with the epoxy resin composition, the resin particles are not filtered on the surface of the fiber-reinforced base material, and the resin particles are impregnated inside the reinforcing fiber bundle. is facilitated, thereby preventing poor impregnation of the resin and obtaining a fiber-reinforced composite material having excellent physical properties, which is preferable.

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, based on 100% by mass of the total amount of epoxy resin in the total amount of the epoxy resin composition. , particularly preferably 1 to 15% by mass. A content of 0.1% by mass or more is preferable because the fracture toughness and impact resistance of the cured resin and fiber composite material can be sufficiently improved. On the other hand, a content of 50% by mass or less is preferable because the viscosity of the epoxy resin composition can be lowered and the impregnation of the fiber base material can be enhanced.

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

[Composition ratio of epoxy resin composition]
Based on the total weight of the epoxy compounds contained in the epoxy resin composition, the proportion of the epoxy compound [A] is preferably 40 to 90% by weight, more preferably 50 to 80% by weight. When the proportion of the epoxy compound [A] is 40% by mass or more, the heat resistance and elastic modulus of the obtained resin cured product can be further improved, and various mechanical properties of the obtained fiber-reinforced composite material are also improved. preferable. On the other hand, when it is 90% by mass or less, the viscosity of the epoxy resin composition can be lowered, and the impregnation of the fiber base material can be enhanced, which is preferable.

The content of the epoxy compound [B] is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, based on the total mass of the epoxy compounds contained in the epoxy resin composition. When the proportion of the epoxy compound [B] is 5% by mass or more, the viscosity of the resulting resin composition can be further reduced, and the handleability of the resin composition and compatibility with the RTM molding method can be further improved. Therefore, it is preferable. On the other hand, when the content is 50% by mass or less, it is possible to minimize the decrease in the heat resistance and elastic modulus of the resulting resin cured product, which is preferable.

The content of the epoxy compound [C] is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, based on the total mass of the epoxy compounds contained in the epoxy resin composition. When the proportion of the epoxy compound [C] is 5% by mass or more, the viscosity of the resulting resin composition can be further reduced, and the handleability of the resin composition and compatibility with the RTM molding method can be further improved. Therefore, it is preferable. On the other hand, when it is 50% by mass or less, it is possible to minimize the decrease in the heat resistance and elastic modulus of the cured resin obtained, which is preferable.

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. Within this range, a preferable molar balance between epoxy groups and active hydrogen is obtained, the crosslink density of the cured resin is high, and the cured resin is excellent in mechanical properties such as heat resistance, elastic modulus and fracture toughness. It is preferable because it can be obtained.

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

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; Particles in which a core material composed of is coated with a conductive substance can be exemplified.

As a flame retardant, a phosphorus-based flame retardant can be exemplified. The phosphorus-based flame retardant may be one containing a phosphorus atom in the molecule, and examples thereof include organic phosphorus compounds such as phosphoric acid esters, condensed phosphoric acid esters, phosphazene compounds and polyphosphates, and red phosphorus.

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. be able to. In particular, it is preferable to use silicate minerals. Commercially available silicate minerals include THIXOTROPIC AGENT DT 5039 (manufactured by Huntsman Japan KK).

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

Commercially available internal release agents include "MOLD WIZ (registered trademark)" INT1846 (manufactured by AXEL PLASTICS RESEARCH LABORATORIES INC.), Licowax S, Licowax P, Licowax OP, Licowax PE190, Licowax PED (manufactured by Clariant Japan), and stearyl. Stearate (SL-900A; manufactured by Riken Vitamin Co., Ltd.) can be exemplified.

[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 the prepreg method, the viscosity at 100° C. is preferably 0.1 to 500 Pa·s, more preferably 1 to 100 Pa·s. If it is less than 0.1 Pa·s, the resin tends to flow out from the prepreg, which is not preferable. On the other hand, if it exceeds 500 Pa·s, the prepreg tends to have unimpregnated portions, and as a result, voids and the like are likely to be formed in the obtained fiber-reinforced composite material, which is not preferable.

When the epoxy resin composition of the present invention is applied to the 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. is s. When the viscosity at 100° C. is 300 mPa·s or less, the epoxy resin composition can be easily impregnated into the fiber-reinforced base material, and the resulting fiber-reinforced composite material can be prevented from forming voids that cause deterioration in physical properties. It is preferable because it can be done. Note that the relationship between viscosity and impregnability also depends on the configuration of the fiber-reinforced base material.

The pot life when the epoxy resin composition of the present invention is applied to the RTM molding method varies depending on the molding conditions of the composite material. When the substrate is impregnated, the pot life is preferably 120 minutes or more, more preferably 180 minutes or more, until the viscosity exceeds 100 mPa·s when held at 100°C.

[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 main component liquid, and the mixture of the curing agent component is referred to as the curing agent liquid.

The epoxy resin composition of the present invention can be produced by mixing the epoxy compound [A], the epoxy compound [B], and optionally other epoxy compounds and a curing agent. The thermoplastic resin component, resin particles, and other optional components may be mixed with the epoxy resin base liquid and then mixed with the curing agent liquid, and the thermoplastic resin component, resin particles, and other optional components may be mixed with the curing agent liquid. After that, it may be mixed with the epoxy resin main agent liquid. The order of these mixtures does not matter.

The epoxy resin composition may be in a one-liquid state in which each component is uniformly mixed, or may be in a slurry state in which some components are dispersed as solids.
Any conventionally known method may be used as the method for producing the epoxy resin composition. The mixing temperature is, for example, 40 to 180°C, preferably 50 to 160°C, more preferably 50 to 120°C. If the temperature exceeds 180° C., the curing reaction proceeds immediately, and the impregnation of the fiber-reinforced base material may deteriorate, or the physical properties of the cured product may deteriorate, which is not preferable. On the other hand, when the temperature is less than 40°C, the viscosity of the epoxy resin base agent is high, and mixing may become substantially difficult, which is not preferable.

A conventionally known machine can be used as the mixing machine. Specific examples include roll mills, planetary mixers, kneaders, extruders, Banbury mixers, mixing vessels equipped with stirring blades, and horizontal mixing tanks. Mixing of each component can be performed in air or under an inert gas atmosphere. When mixing in air, an atmosphere with controlled temperature and humidity is preferred. For example, it is preferable to mix at a temperature controlled at a constant temperature of 30° C. or less or in a low humidity atmosphere with a relative humidity of 50% RH or less.

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

This epoxy resin main liquid contains the epoxy compound [A] and the epoxy compound [B], which are the constituent components of the epoxy resin composition of the present invention, and optionally any other epoxy compound, thermoplastic resin component, and resin particles. and other optional components. The order of these mixtures does not matter.
The state of the epoxy resin base liquid may be a one-liquid state in which each component is uniformly mixed, or a slurry state in which a part of the components are dispersed as solids.

You may use any conventionally well-known method for the manufacturing method of an epoxy-resin main ingredient liquid. The mixing temperature is, for example, 40 to 200°C, preferably 50 to 100°C, more preferably 50 to 90°C. If the temperature exceeds 200°C, the self-polymerization reaction of the epoxy resin partially progresses, resulting in a decrease in the impregnation property of the fiber-reinforced base material, and the physical properties of the cured product produced using the resulting epoxy resin base liquid are decreased. It is not preferable because there are cases where If the temperature is less than 40°C, the viscosity of the epoxy resin base agent is high, and mixing may become substantially difficult, which is not preferred.

As a mechanical device used for mixing, a conventionally known device can be used. Specific examples include roll mills, planetary mixers, kneaders, extruders, Banbury mixers, mixing vessels equipped with stirring blades, and horizontal mixing tanks. Mixing of each component can be performed in air or under an inert gas atmosphere. When mixing in air, it is preferable that the temperature and humidity are controlled. For example, it is preferable to mix at a temperature controlled at a constant temperature of 30° C. or less or in a low humidity atmosphere with a relative humidity of 50% RH or less.

[Method for producing curing agent liquid]
The curing agent liquid used for the two-liquid type epoxy resin composition contains a curing agent and other optional components. The curing agent liquid may be in a one-liquid state in which each component is uniformly mixed, or may be in a slurry state in which a part of the components are dispersed as solids.

Any conventionally known method may be used as the method for producing the curing agent liquid. The mixing temperature is, for example, 50 to 200°C, preferably 50 to 150°C, more preferably 80 to 120°C. If the temperature exceeds 200°C, the added components may be thermally decomposed, which is not preferable. On the other hand, when the temperature is lower than 50° C., if there are solid curing agent components, they do not melt and become difficult to mix, making it difficult to obtain a uniform curing agent liquid, which is not preferable.

As a mechanical device used for mixing, a conventionally known one can be used. Specific examples include roll mills, planetary mixers, kneaders, extruders, Banbury mixers, mixing vessels equipped with stirring blades, and horizontal mixing tanks. Mixing of each component can be performed in air or under an inert gas atmosphere. When mixing in the atmosphere, it is preferable to carry out in an atmosphere in which the temperature and humidity are controlled. For example, it is preferable to mix at a temperature controlled at a constant temperature of 30° C. or less or in a low humidity atmosphere with a relative humidity of 50% RH or less.

[Properties of cured resin]
A resin cured product can be obtained by curing the epoxy resin composition of the present invention. The obtained resin cured product can have the following properties.

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

Room temperature dry flexural modulus (RTD-FM) measured by JIS K7171 method is preferably 3.0 GPa or more, more preferably 3.3 to 10.0 GPa, further preferably 3.5 to 9.0 GPa. When the viscosity exceeds 3.0 GPa, the fiber-reinforced composite material obtained by using the epoxy resin composition of the present invention has excellent mechanical properties, which is preferable.

The flexural modulus after water absorption at elevated temperature (HTW-FM) measured by the JIS K7171 method 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 by ASTM D5045 is preferably 0.7 MPa·m ^1/2 or more, more preferably 0.8 to 3.0 MPa·m ^1/2 .

[Fiber-reinforced composite material]
A fiber-reinforced composite material (FRP) can be obtained by compounding and curing a fiber-reinforced base material and the epoxy resin composition of the present invention. That is, according to the present invention, there is provided a fiber-reinforced composite material comprising the epoxy resin cured product described above and a fiber-reinforced base material.

[Fiber-reinforced base material]
Examples of reinforcing fibers used in the fiber-reinforced base material 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 slag fibers. be able to.

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

When PAN-based carbon fibers are used as the reinforcing fibers of the fiber-reinforced base material, the tensile modulus is preferably 100 to 600 GPa, more preferably 200 to 500 GPa, still more preferably 230 to 450 GPa. The tensile strength is preferably 2000-10000 MPa, more preferably 3000-8000 MPa.

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

In the present invention, the reinforcing fibers of the fiber-reinforced base material are preferably treated with a sizing agent. In this case, the amount of the sizing agent attached is preferably 0.01 to 10% by mass, more preferably 0.05 to 3.0% by mass, and particularly preferably 0% by mass, based on the mass of the reinforcing fibers to which the sizing agent is attached. .1 to 2.0% by mass. An adhesion amount within this range is preferable because excellent adhesiveness between the reinforcing fibers and the matrix resin and excellent interlaminar toughness in the obtained composite material can be obtained.

As the fiber-reinforced base material, it is preferable to use a reinforcing fiber sheet in which reinforcing fibers are formed into a sheet. As the reinforcing fiber sheet, for example, a sheet in which a large number of reinforcing fibers are arranged in one direction, a bidirectional woven fabric such as a plain weave or a twill weave, a multiaxial woven fabric, a nonwoven fabric, a mat, a knit, a braid, and a paper made of reinforced fibers. can be mentioned. Among them, it is preferable to use a unidirectional aligned sheet, a bidirectional woven fabric, or a multiaxial woven fabric base material in which reinforcing fibers are formed into a sheet as continuous fibers, since a fiber-reinforced composite material having more excellent mechanical properties can be obtained.

The bidirectional woven fabric or multiaxial woven fabric substrate may be obtained by laminating and stitching a plurality of unidirectional aligning sheets. In this case, in order to improve the interlaminar tenacity of the obtained fiber-reinforced composite material, a layer of thermoplastic resin nonwoven fabric may be arranged on one side of the unidirectionally arranged sheet and then laminated to form a woven fabric. Examples of thermoplastic resin nonwoven fabric fibers include polyester resin fibers, polyamide resin fibers, polyethersulfone resin fibers, polysulfone resin fibers, polyetherimide resin fibers, polycarbonate resin fibers, and fibers made of mixtures of these resins. be able to.

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

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

As a method for compounding with the fiber-reinforced base material, the fiber-reinforced base material and the resin composition may be compounded in advance like a prepreg described later. For example, resin transfer molding method (RTM molding method), hand layup method, Compositing may be performed during molding such as by a filament winding method, a pultrusion method, or the like.
A fiber-reinforced composite material (FRP) can be obtained by combining a fiber-reinforced base material and the epoxy resin composition of the present invention, followed by curing under specific conditions by heating and pressing.

[Prepreg]
The prepreg of the present invention is a prepreg comprising the epoxy resin composition of the present invention described above and a fiber-reinforced base material, which is a fiber-reinforced base material and the epoxy resin of the present invention impregnated therein. composition.

The prepreg of the present invention is a prepreg in which a fiber-reinforced base material is partially or wholly impregnated with the epoxy resin composition described above. The content of the above epoxy resin composition in the entire prepreg is preferably 15 to 60% by mass, more preferably 20 to 55% by mass, particularly preferably 25 to 50% by mass, based on the total mass of the prepreg. If the content is less than 15% by mass, voids and the like may occur in the resulting fiber-reinforced composite material, which may deteriorate the mechanical properties, which is not preferable. If the content exceeds 60% by mass, the reinforcing effect of the reinforcing fibers becomes insufficient, and the mechanical properties relative to the mass may become substantially low, which is not preferable.

[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 base material with the above epoxy resin composition of the present invention to obtain a prepreg. A hot melt method or a solvent method is preferably used for this impregnation.

In the hot-melt method, an uncured resin composition is applied in the form of a thin film on release paper to form a resin composition film, and the resin composition film is laminated on a fiber-reinforced base material and pressed under pressure. In this method, the resin composition is impregnated into the fiber-reinforced substrate layer by heating.

As a method for forming a resin composition film from a resin composition, any conventionally known method can be used. Specifically, using a die extrusion, an applicator, a reverse roll coater, a comma coater, etc., a resin composition film is obtained by casting the resin composition onto a support such as a release paper or a film. can be done.

The resin temperature when producing the film is appropriately determined according to the composition and viscosity of the resin composition. Specifically, the same temperature conditions as the mixing temperature in the method for producing the epoxy resin composition described above are preferably used. The impregnation of the resin composition into the fiber-reinforced base material layer may be performed in one step or in multiple steps.
The solvent method is a method in which the epoxy resin composition is made into a varnish using a suitable solvent, and the fiber-reinforced base material layer is impregnated with this varnish.

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. The impregnation temperature when the epoxy resin composition film is impregnated into the fiber reinforced substrate layer by the hot melt method is preferably 50 to 120°C, more preferably 60 to 110°C, and particularly preferably 70 to 100°C. If the impregnation temperature is lower than 50°C, the viscosity of the epoxy resin composition is high, and the fiber-reinforced base material layer may not be impregnated sufficiently, which is not preferable. On the other hand, if the impregnation temperature exceeds 120° C., the curing reaction of the epoxy resin composition proceeds, and the storage stability of the obtained prepreg may deteriorate, and the drape property may deteriorate, which is not preferable.

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 in consideration of the viscosity and resin flow of the resin composition. is, for example, 0.01 to 250 (N/cm), preferably 0.1 to 200 (N/cm).

[Autoclave molding method]
An autoclave molding method is preferably used as the method for producing the FRP of the present invention. In the autoclave molding method, a prepreg and a film bag are sequentially laid in the lower mold of the mold, the prepreg is sealed between the lower mold and the film bag, and the space formed by the lower mold and the film bag is evacuated. In addition, it is a molding method in which heat and pressure are applied in an autoclave molding device. As for the molding conditions, it is preferable that the heating rate is 1 to 50° C./min, and heating and pressing are performed at 0.2 to 0.7 MPa and 130 to 180° C. for 10 to 30 minutes.

[Press molding method]
The fiber reinforced composite material (FRP) of the present invention can be preferably produced by press molding. Production by press molding is performed by heating and pressurizing the prepreg of the present invention or a preform formed by laminating the prepregs of the present invention using a mold.

The mold is preferably preheated to the curing temperature. 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 a sufficient curing reaction can occur and FRP can be obtained with high productivity. Further, when the molding temperature is 210° C. or lower, the viscosity of the resin does not become too low, and excessive flow of the resin in the mold can be suppressed. As a result, outflow of the resin from the mold and meandering of the fibers can be suppressed, so that high-quality FRP can be obtained, which is preferable.

The pressure during molding is, for example, 0.05 to 2 MPa, preferably 0.2 to 2 MPa. When the pressure is 0.05 MPa or more, a moderate flow of the resin can be obtained, and appearance defects and voids can be prevented. In addition, since the prepreg adheres sufficiently to the mold, it is possible to manufacture FRP with a good appearance, which is preferable. On the other hand, when the pressure is 2 MPa or less, the resin is not caused to flow more than necessary, so that the resulting FRP is less likely to have poor appearance. In addition, since no excessive load is applied to the mold, deformation of the mold is less likely to occur. Molding time is preferably 1 to 8 hours.

[Resin transfer molding method (RTM molding method)]
A resin transfer molding method (RTM molding method) is a preferable molding method from the viewpoint of efficiently obtaining a fiber-reinforced composite material having a complicated shape. This RTM molding method is a method for obtaining a fiber-reinforced composite material, which includes a step of impregnating a fiber-reinforced base material placed in a mold with the liquid epoxy resin composition of the present invention and heat-curing it.
That is, according to the present invention, there is provided a method for obtaining a fiber-reinforced composite material, which includes a step of impregnating a fiber-reinforced base material placed in a mold with an epoxy resin composition and heat-curing it.

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 an open mold of rigid material and the flexible film.

Examples of rigid materials that can be used include metals such as steel and aluminum, fiber-reinforced plastics, wood, and gypsum. Polyamide, polyimide, polyester, fluororesin, and silicone resin, for example, can be used as the material of the flexible film.

When a closed mold made of a rigid material is used in the RTM molding method, it is common practice to clamp the mold under pressure and to inject the epoxy resin composition under pressure. At this time, a suction port may be provided separately from the injection port and connected to a vacuum pump for suction. The epoxy resin composition may be injected only at atmospheric pressure without using special pressurizing means by suction. This method can be preferably used because a large-sized member can be manufactured by providing a plurality of suction ports.

In the RTM molding method, when an open mold made of a rigid material and a flexible film are used, suction may be performed to inject the epoxy resin only at atmospheric pressure without using special pressurizing means. Use of a resin diffusion medium is effective in achieving good impregnation by injection only at atmospheric pressure. Furthermore, it is preferable to apply a gel coat to the surface of the rigid material prior to placing the fiber-reinforced substrate.

In the RTM molding method, the fiber-reinforced base material is impregnated with the epoxy resin composition and then heat-cured. 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 completed, the fiber-reinforced composite material is taken out by demolding. The resulting fiber-reinforced composite material may then be heated at a higher temperature for post-curing. The temperature for this post-curing is preferably 150 to 200° C., and the time is preferably 1 minute to 4 hours.

The impregnation pressure at which the epoxy resin composition is impregnated into the fiber-reinforced base material by the RTM molding method may be appropriately determined in consideration of the viscosity and resin flow of the resin composition. A specific impregnation pressure is, for example, 0.001 to 10 MPa, preferably 0.01 to 1 MPa.

[Properties of Fiber Reinforced Composite Material]
The present invention is also a fiber-reinforced composite material comprising the cured epoxy resin of the present invention and a fiber-reinforced base material.

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

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 preferably 260 MPa or more, more preferably 280 to 450 MPa, and particularly preferably 300 to 400 MPa.

The fiber-reinforced composite material provided by the present invention preferably has a perforated compressive strength after temperature rise water absorption (HTW-OHC) measured by SACMA SRM3 of preferably 200 MPa or more, more preferably 220 to 400 MPa, and particularly preferably 240 to 240 MPa. 350 MPa.

EXAMPLES The present invention will be described in more detail below with reference to examples. The components and test methods used in Examples and Comparative Examples are as follows. A fiber reinforced composite material is sometimes abbreviated as "FRP", and a carbon fiber reinforced composite material is sometimes abbreviated as "CFRP".

〔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 of Synthesis Example 1, hereinafter abbreviated as "3,4'-TGDDE")

Synthesis Example 1 Synthesis of 3,4'-TGDDE A four-necked flask equipped with a thermometer, dropping funnel, condenser and stirrer was charged with 1110.2 g (12.0 mol) of epichlorohydrin while purging with nitrogen. The temperature was raised to 70° C., and 200.2 g (1.0 mol) of 3,4′-diaminodiphenyl ether dissolved in 1000 g of ethanol was added dropwise over 4 hours. Further stirring for 6 hours completed the addition reaction to give N,N,N',N'-tetrakis(2-hydroxy-3-chloropropyl)-3,4'-diaminodiphenyl ether. Subsequently, after the temperature inside the flask was lowered to 25° C., 500.0 g (6.0 mol) of a 48% by weight NaOH aqueous solution was added dropwise over 2 hours, and the mixture was further stirred for 1 hour. After completion of the cyclization reaction, ethanol was distilled off, extraction was performed with 400 g of toluene, and washing was performed twice with 5% saline. When toluene and epichlorohydrin were removed from the organic layer under reduced pressure, 361.7 g (85.2% yield) of brown viscous liquid was obtained. The purity of 3,4'-TGDDE, which is the main product, was 84% (HPLC area %).

(2) Epoxy compound [B]
・1,6-bis(glycidyloxy)naphthalene (HP-4032SS (product name) manufactured by DIC, hereinafter abbreviated as “1,6-DON”)
・ 1,3,5-triglycidyl isocyanurate (TEPIC-S (product name) manufactured by Nissan Chemical Co., Ltd., hereinafter abbreviated as “TEPIC”)

(3) Epoxy compound [C]
・N,N-diglycidyl-o-toluidine (GOT (product name) manufactured by Nippon Kayaku Co., Ltd., hereinafter abbreviated as “GOT”)
・N,N-diglycidylaniline (GAN (product name) manufactured by Nippon Kayaku Co., Ltd., hereinafter abbreviated as “GAN”)

(4) Other epoxy resins and bisphenol A-diglycidyl ether (manufactured by Mitsubishi Chemical Corporation jER825 (product name), hereinafter abbreviated as "DGEBA")

(5) Curing agent 4,4'-diamino-3,3'-diisopropyl-5,5'-dimethyldiphenylmethane (Lonzacure M-MIPA (product name) manufactured by Lonza, hereinafter abbreviated as "M-MIPA")
- 3,3'-diaminodiphenyl sulfone (manufactured by Konishi Chemical Industry Co., Ltd., hereinafter abbreviated as "3,3'-DDS")

(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”)

(7) Epoxy resin-soluble thermoplastic resin Polyethersulfone (Sumitomo Chemical Co., Ltd. Sumika Excel PES-5003P (product name), average particle size 20 μm, hereinafter abbreviated as “PES”)

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

(9) Carbon fiber strand/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% by mass, manufactured by Teijin Limited )

(10) Thermoplastic resin nonwoven fabric/nonwoven fabric 1: A nonwoven fabric having a fiber basis weight of 6 g/m ² and a melting point of 178°C, which is produced by a spunbond method using polyamide 12 resin.

(11) Carbon fiber multilayer fabric/carbon fiber multiaxial fabric 1: Carbon fibers 1 aligned in one direction are formed into a sheet of 190 g/m ² per layer, and a nonwoven fabric 1 is arranged on one side of this sheet-shaped carbon fiber. Then, 4 sheets were laminated and stitched at an angle of (+45/V/90/V/-45/V/0/V) (760 g/m ² total weight of carbon fiber base material). V indicates the nonwoven fabric 1 here.
・ Carbon fiber multiaxial fabric 2: Carbon fibers 1 aligned in one direction are made into a sheet of 190 g / m ² per layer, and nonwoven fabric 1 is arranged on one side of the sheet-shaped carbon fibers, (0 / V / - 45/V/90/V/+45/V) and stitched together (total weight of carbon fiber base material: 760 g/m ² ). V indicates the nonwoven fabric 1 here.

〔Evaluation methods〕
(1) Properties of resin composition (initial viscosity and pot life of epoxy resin composition for RTM molding method)
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 when the viscosity reached 50 mPa·s was taken as the pot life.

(2) Heat resistance of cured resin (glass transition temperature after water absorption (wet-Tg))
In order to evaluate the heat resistance of the cured resin, the glass transition temperature was measured according to the SACMA 18R-94 method. A cured resin material to be evaluated was cut and polished to prepare a test piece having dimensions of 50 mm×6 mm×2 mm. Using a pressure cooker (HASTEST PC-422R8, manufactured by Espec Co., Ltd.), the prepared resin test piece was subjected to water absorption treatment under the conditions of 121° C. and 24 hours. Using a dynamic viscoelasticity measuring device Rheogel-E400 manufactured by UBM, under the conditions of a measurement frequency of 1 Hz, a temperature increase rate of 5 ° C./min, and a strain of 0.0167%, the distance between chucks is 30 mm, and the rubber elastic region is measured from 50 ° C. The storage elastic modulus E' of the resin test piece subjected to water absorption treatment was measured. Log E′ was plotted against temperature, and the temperature obtained from the intersection of the approximate straight line of the flat region of log E′ and the approximate straight line of the transition region of E′ was recorded as the glass transition temperature (wet-Tg).

(3) Cured resin properties (room temperature dry resin flexural modulus (RTD-FM))
The test was performed according to the JIS K7171 method. A resin test piece having dimensions of 80 mm×10 mm×4 mm (thickness h) was prepared using a cured resin plate to be evaluated. A bending test was performed at an ambient temperature of 25° C., a distance L between fulcrums of 16×h (thickness), and a test speed of 2 mm/min to measure bending strength and bending elastic modulus.

(4) Properties of cured resin (toughness of cured resin (deformation mode I critical stress intensity factor KIc))
According to ASTM D5045, the toughness (KIc) was measured using a universal testing machine (Shimadzu Autograph). The test was performed according to ASTM D5045 method. A resin test piece having dimensions of 50 mm×8 mm (width W)×4 mm was prepared using a cured resin plate to be evaluated. The crack length a was adjusted so that 0.45≦a/W≦0.55. For the crack length a, the fracture surface after the fracture test was observed with an optical microscope, and the length to the tip of the crack and the average value of the crack lengths on both surfaces of the test piece were adopted.

(5) CFRP properties (compressive strength after impact (CAI))
The CFRP to be evaluated was cut into a size of 101.6 mm width×152.4 mm length to obtain a test piece for compressive strength after impact (CAI) test. Testing was performed according to ASTM D7136. After measuring the dimensions of each test piece, the specimen (sample) was subjected to an impact test using a falling weight type impact tester (Dynatup manufactured by Instron) to give an impact energy of 30.5 J. After the impact, the damaged area of the specimen was measured with an ultrasonic flaw detector (SDS3600, HIS3/HF manufactured by Krautkramer). After the impact, the strength test of the specimen was performed by attaching strain gauges on each side of the specimen at a position of 25.4 mm from the top and 25.4 mm from the side. After attaching the gauge, the crosshead speed of the testing machine (Autograph manufactured by Shimadzu Corporation) was set to 1.27 mm/min, and a load was applied until the specimen fractured.

(6) CFRP properties (room temperature dry open-pore compressive strength (RTD-OHC))
The CFRP to be evaluated is cut to a size of 38.1 mm in width and 304.8 mm in length, and a hole with a diameter of 6.35 mm is drilled in the center of the test piece, and the room temperature dry hole compressive strength (RTD-OHC) test is performed. got a piece The test was carried out according to SACMA SRM3 at an ambient temperature of 25°C and the open hole compressive strength was calculated from the maximum point load.

(7) Average particle size The cross section of the cured resin to be evaluated is observed at 25,000 times with a scanning electron microscope or transmission electron microscope, and the diameters of at least 50 particles are measured and averaged. Particle size was determined. In the above observation, when the particles were not perfectly circular, that is, when the particles were elliptical, the maximum diameter of the particles was taken as the particle diameter of the particles.

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

[Preparation of cured resin]
The epoxy resin composition for the RTM molding method prepared above is defoamed in vacuum for 60 minutes, and then poured into a stainless steel mold set to a thickness of 4 mm by a 4 mm thick Teflon (registered trademark) resin spacer. bottom. Heat curing was performed at a temperature of 180° C. for 120 minutes to obtain a resin cured product having a thickness of 4 mm.
Table 1 shows the properties of the obtained cured resin. 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 or higher, indicating high mechanical properties.

[Creation of CFRP]
Carbon fiber multiaxial fabric 1 and carbon fiber multiaxial fabric 2 were cut into 300 x 300 mm, and three carbon fiber multiaxial fabrics 1 and 3 carbon fiber multiaxial fabric were placed on a 500 x 500 mm release-treated aluminum plate. Three sheets of No. 2, totaling six sheets, were stacked to form a laminate.

Further, on the laminate, a peel cloth Release Ply C (manufactured by AIRTECH), which is a base material having a releasability function, and Resin Flow 90HT (manufactured by AIRTECH), which is a resin diffusion base material, were laminated. After that, a hose for forming a resin inlet and a resin outlet was arranged, the whole was covered with a nylon bag film, sealed with a sealant tape, and the inside was evacuated. Subsequently, the aluminum plate was heated to 120° C., and the pressure inside the bag was reduced to 5 torr or less, and then the epoxy resin composition for RTM molding method prepared above was heated to 100° C. and injected into the vacuum system through the resin inlet. bottom.

The injected epoxy resin composition for RTM molding fills the bag and impregnates the laminate, and the temperature is raised to 180° C. and held at 180° C. for 120 minutes to obtain a carbon fiber reinforced composite material (CFRP). rice field.
Table 1 shows the properties of the obtained CFRP. It showed a high CAI of 280 MPa or more and an excellent RTD-OHC of 300 MPa or more.

[Examples 2 to 6]
It was carried out in the same manner as in Example 1, except that the composition was changed as shown in Table 1. Table 1 shows the evaluation results.

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

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

[Example 7]
A prepreg was prepared and evaluated by the following procedure.

[Preparation of epoxy resin composition for prepreg method]
85 parts by mass of 3,4'-TGDDE as the epoxy compound [A], 15 parts by mass of 1,6-DON as the epoxy compound [B], and 30 parts by mass of PES as the soluble thermoplastic resin were weighed and stirred. Mixed at 120° C. for 30 minutes using a machine. After that, the temperature is lowered to 80° C., 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 are added and mixed for 30 minutes to obtain an epoxy resin for prepreg. A composition was prepared. In this ratio, the ratio of the total number of epoxy groups contained in the epoxy resin composition to the total number of active hydrogens contained in the curing agent is 1.0.

[Preparation of prepreg]
Using a reverse roll coater, the obtained epoxy resin composition for prepreg was applied onto release paper to prepare a resin film having a basis weight of 50 g/m ² . Next, carbon fibers were aligned in one direction so that the fiber mass per unit area was 190 g/m ² to prepare a sheet-like fiber-reinforced base material layer. The resin films were laminated on both sides of the fiber-reinforced base material layer, and heated and pressed under conditions of a temperature of 95° C. and a pressure of 0.2 MPa to produce a unidirectional prepreg having a carbon fiber content of 65% by mass.

[Evaluation of storage stability of prepreg]
After the obtained prepreg was stored at a temperature of 26.7° C. and a humidity of 65% for 10 days, the prepreg was cut and laminated on a mold for evaluation.
As a result of the evaluation, the prepreg after storage sufficiently followed even when laminated to a mold, and exhibited almost the same tack and drape properties as immediately after production. It was confirmed that the prepreg of the present invention has good handleability.

[Evaluation of molding voids]
After the obtained prepreg was stored at a temperature of 26.7 ° C. and a humidity of 65% for 10 days, the prepreg was cut into 150 mm × 150 mm, laminated in a lamination configuration [0] ₁₀ , and the laminate was compacted (laminated with vacuum pack body storage) and stored in an environment at a temperature of 23°C.
Thirty-two days after lamination, a CFRP laminate was molded by heating at 180° C. for 2 hours under a pressure of 0.59 MPa using a normal vacuum autoclave molding method. A test piece was cut out, the cross section was polished, and the presence or absence of voids was observed with a microscope.
As a result of the evaluation, it was confirmed that there were no voids in the cross section of the molded product, and that the prepreg of the present invention had good moldability.

[Evaluation of tackiness]
The tackiness of the prepreg was measured by the following method using a tack tester TAC-II (RHESCA CO., LTD.). As a test method, the obtained prepreg was set on a test stage held at 27°C, an initial load of 100 gf was applied with a φ5 tack probe held at 27°C, and it was pulled out at a test speed of 10 mm/sec. The maximum load at the time was obtained.
A tack probe test was performed on a prepreg immediately after production and a prepreg stored at a temperature of 26.7° C. and a humidity of 65% for 10 days.
As a result of 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. It was confirmed that the prepreg of the present invention has good handleability.

[Evaluation of drape property]
The drapeability of the prepreg was evaluated by the following test according to ASTM D1388. The obtained prepreg was cut in the direction of 90° with respect to the 0° fiber direction, and the drape property (flexural rigidity, mg×cm) against inclination with an inclination angle of 41.5° was evaluated. This evaluation was performed immediately after the prepreg was manufactured and after storage for a predetermined period at a temperature of 26.7° C. and a humidity of 65%.
As a result of the evaluation, the drape property after 20 days had not changed from that immediately after production. It was confirmed that the prepreg of the present invention has good handleability.

[Evaluation of impregnability]
The impregnability of the fiber base material with the resin was evaluated by the water absorption rate of the prepreg. The lower the water absorption of the obtained prepreg, the higher the impregnability of the resin.
The obtained prepreg was cut into a square with a side of 100 mm, and the mass (W ₁ ) was measured. After that, the prepreg was submerged in water in a desiccator. The pressure inside the desiccator was reduced to 10 kPa or less to replace the air and water inside the prepreg. The prepreg was taken out of water, the surface water was wiped off, and the mass (W ₂ ) of the prepreg was measured. From these measured values, the water absorption was calculated using the following formula.
Water absorption (%) = [( _W2 - _W1 )/ _W1 ] x 100
W ₁ : Mass of prepreg (g)
W ₂ : Mass (g) of prepreg after water absorption
As a result of evaluation, the water absorption rate was less than 10%. It was confirmed that the epoxy resin composition of the present invention has good impregnation properties.

By using the epoxy resin composition of the present invention, it is possible to produce a resin cured product having excellent mechanical properties. In addition, since the epoxy resin composition of the present invention has a low viscosity and a long pot life, it is easy to handle during molding and can produce a fiber-reinforced composite material having excellent quality and mechanical properties. Also, the prepreg of the present invention can be used to produce a fiber-reinforced composite material. The resulting fiber-reinforced composite material can be used as members of automobiles and aircraft.

Claims (17)

Chemical formula (1) below (where R ₁ to R ₄ each independently represent a hydrogen atom, an aliphatic hydrocarbon group, an alicyclic hydrocarbon group or a halogen atom, and X ₁ is —CH ₂ —, —O—, -S-, -CO-, -C(=O)O-, -O-C(=O)-, -NHCO-, -CONH- or -SO ₂ -) represents an epoxy compound [A ] and an epoxy compound [B] having a polycyclic aromatic ring structure or a heterocyclic structure.

2. The epoxy resin composition according to claim 1, wherein the epoxy compound [A] is an epoxy compound having an amine-type glycidyl group. 3. The epoxy resin composition according to claim 1, wherein the epoxy compound [A] is tetraglycidyl-3,4'-diaminodiphenyl ether. 4. The resin composition according to any one of claims 1 to 3, further comprising an aromatic epoxy compound [C] having a glycidyl ether group, wherein the glycidyl ether of the aromatic epoxy compound [C] having a glycidyl ether group 4. The epoxy resin composition according to any one of claims 1 to 3, wherein the number/number of aromatic rings is 2. 5. The epoxy resin composition according to any one of claims 1 to 4, wherein the aromatic epoxy compound [C] having a glycidyl ether group is diglycidylaniline and/or diglycidyltoluidine. 6. The epoxy resin composition according to any one of claims 1 to 5, wherein the epoxy compound [B] having a polycyclic aromatic ring structure or heterocyclic structure is a naphthalene derivative epoxy compound. 6. The epoxy resin composition according to any one of claims 1 to 5, wherein the epoxy compound [B] having a polycyclic aromatic ring structure or heterocyclic structure is a triglycidyl isocyanurate derivative epoxy compound. 7. The epoxy resin composition according to claim 6, wherein the naphthalene derivative epoxy compound is bis(glycidyloxy)naphthalene. 7. The naphthalene derivative epoxy compound according to claim 6, selected from bis(glycidyloxy)-1,1'-binaphthalene and bis(glycidyloxy)-1-[(glycidyloxy)-1-naphthylmethyl]naphthalene. Epoxy resin composition. 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. The epoxy resin composition according to claim 7, wherein 11. The epoxy resin composition according to any one of claims 1 to 10, wherein the mass ratio of epoxy compound [A] to epoxy compound [B] is 50:50 to 99:1. 12. The epoxy resin composition according to any one of claims 4 to 11, wherein the epoxy compound [C] is 1 to 80 parts by mass with respect to a total of 100 parts by mass of the epoxy compound [A] and the epoxy compound [B]. . Assuming that the total mass of the epoxy compounds contained in the epoxy resin composition is 100% by mass, the total mass of the epoxy compound [A], the epoxy compound [B] and the epoxy compound [C] accounts for 70 to 100% by mass of the total mass of the epoxy compounds. 13. The epoxy resin composition of any one of claims 4-12. A prepreg comprising the epoxy resin composition according to any one of claims 1 to 13 and a fiber-reinforced base material. A fiber-reinforced composite material comprising a cured product of the epoxy resin composition according to claim 14 and a fiber-reinforced base material. A method for producing a prepreg, comprising an impregnation step of impregnating a fiber-reinforced base material with the epoxy resin composition according to any one of claims 1 to 13 to obtain a prepreg. A method for producing a fiber-reinforced composite material, comprising the step of impregnating a fiber-reinforced base material placed in a mold with the epoxy resin composition according to any one of claims 1 to 13, followed by heat curing.