JP7585671B2 - Epoxy resin composition for fiber-reinforced composite materials, prepreg and fiber-reinforced composite material - Google Patents

Description

The present invention relates to an epoxy resin composition that is preferably used as a matrix resin for fiber-reinforced composite materials suitable for aerospace applications, sports applications, and general industrial applications, as well as to a prepreg and a fiber-reinforced composite material that use the same as the matrix resin.

Fiber-reinforced composite materials using carbon fibers, aramid fibers, etc. as reinforcing fibers have excellent specific strength and specific elastic modulus, and are therefore widely used in structural materials for aircraft and automobiles, and in materials for sports such as tennis racket frames, golf shafts, fishing rods, and bicycle frames. Methods for producing fiber-reinforced composite materials include a method in which multiple prepregs, which are sheet-shaped molding materials in which reinforcing fibers are impregnated with an uncured resin composition, are laminated and then heated and cured, and a resin transfer molding method in which liquid resin is poured into reinforcing fibers placed in a mold and then heated and cured. Among these manufacturing methods, the method using prepregs has the advantage that it is easy to obtain high-performance fiber-reinforced composite materials, since the orientation of the reinforcing fibers can be strictly controlled and there is a high degree of freedom in designing the laminate structure. As the resin composition used in this prepreg, an epoxy resin composition with excellent mechanical properties, heat resistance, and handling properties is widely used.

Epoxy resin compositions used in fiber-reinforced composite materials are required to achieve both elastic modulus and deflection after curing. In particular, improved deflection is required to increase the 90° strength, impact resistance, and fatigue properties of fiber-reinforced composite materials. Reducing the crosslink density of the cured epoxy resin is an effective way to improve deflection, but lowering the crosslink density often results in a decrease in the elastic modulus, and there is a trade-off between the deflection and elastic modulus of the cured product. For this reason, achieving both the elastic modulus and deflection of the cured resin has been an extremely difficult task.

As a method for solving this problem, Patent Document 1 describes a method for improving the deflection and elastic modulus of the cured resin by using a phenolic compound in combination with a resin composition consisting of an epoxy resin, an amine-based curing agent, and a curing accelerator.

JP 2002-284852 A

However, even when the technology described in Patent Document 1 is used, the mechanical properties of the resulting cured resin and fiber-reinforced composite material are not sufficient, and further improvement in the mechanical properties is required.

Therefore, the objective of the present invention is to provide an epoxy resin composition that has excellent elastic modulus and deflection, as well as a prepreg and a fiber-reinforced composite material that use the epoxy resin composition.

The present invention employs the following means to solve the above problems. That is, the epoxy resin composition of the present invention is an epoxy resin composition for fiber-reinforced composite materials, which comprises the following components [A], [B], [C], and [D], and satisfies all of the following conditions (i) to (iii):
Component [A]: epoxy resin Component [B]: amine-based curing agent Component [C]: phenol compound Component [D]: curing accelerator Condition (i): When the ratio of the number of active hydrogens in component [B] to the number of epoxy groups in component [A] is XB, XB is in the range of 0.1 to 0.4.
Condition (ii): When the phenol compound represented by formula (1) among the components [C] is defined as [C1] and the ratio of the number of active hydrogens in the component [C1] to the number of epoxy groups in the component [A] is defined as XC1, XC1 is in the range of 0.3 to 0.9.

(In formula (1), R ₁ to R ₅ represent a hydrogen atom, a hydrocarbon group having 1 to 8 carbon atoms, a methoxy group, a hydroxyl group or a halogen, and may be the same or different, but at least two are hydroxyl groups. _{R 6} to R ₁₀ represent a hydrogen atom, a hydrocarbon group having 1 to 8 carbon atoms, a methoxy group or a halogen, and may be the same or different, and X represents any one of no element, SO ₂ , CH ₂ , CH(CH ₃ ), C(CH ₃ ) ₂ , S, O or C═O.)
Condition (iii): XB+XC1 is in the range of 0.4 to 1.0.

The prepreg of the present invention is a prepreg made of reinforcing fibers and the above-mentioned epoxy resin composition.

Furthermore, the fiber-reinforced composite material of the present invention is a fiber-reinforced composite material consisting of reinforcing fibers and a cured product of the above-mentioned epoxy resin composition.

According to the present invention, an epoxy resin composition having excellent elastic modulus and deflection, as well as a prepreg and a fiber-reinforced composite material using the epoxy resin composition, can be obtained.

The epoxy resin composition of the present invention contains the following essential components: [A] epoxy resin, [B] amine-based curing agent, [C] phenolic compound, and [D] curing accelerator. First, we will explain these components.

(Component [A])
The component [A] in the present invention is an epoxy resin. An epoxy resin is a compound having an epoxy group in the molecule. When [A] is an epoxy resin having two or more epoxy groups in one molecule, it is preferable because the glass transition temperature of the resin cured product obtained by curing the epoxy resin composition is high. A monofunctional epoxy resin having one epoxy group in one molecule may be contained within a range that does not significantly adversely affect the heat resistance and mechanical properties of the prepreg or fiber-reinforced composite material of the present invention.

Examples of such epoxy resins include bisphenol A type, bisphenol F type, diaminodiphenylmethane type, diaminodiphenylsulfone type, aminophenol type, metaxylenediamine type, 1,3-bisaminomethylcyclohexane type, isocyanurate type, hydantoin type, phenol novolac type, orthocresol novolac type, trishydroxyphenylmethane type, and tetraphenylolethane type epoxy resins. These epoxy resins may be used alone or in combination.

Commercially available bisphenol A epoxy resins include jER (registered trademark) 828 (manufactured by Mitsubishi Chemical Corporation), Epiclon (registered trademark) 850 (manufactured by DIC Corporation), Epototo (registered trademark) YD-128 (manufactured by Tohto Kasei Co., Ltd.), and DER-331 and DER-332 (all manufactured by The Dow Chemical Company).

Commercially available bisphenol F type epoxy resins include "Araldite (registered trademark)" GY282 (manufactured by Huntsman Advanced Materials), "jER (registered trademark)" 806, "jER (registered trademark)" 807, "jER (registered trademark)" 1750 (all manufactured by Mitsubishi Chemical Corporation), "Epicron (registered trademark)" 830 (manufactured by DIC Corporation), and "Epotohto (registered trademark)" YD-170 (manufactured by Tohto Kasei Co., Ltd.).

Commercially available diaminodiphenylmethane type epoxy resins include ELM434 (manufactured by Sumitomo Chemical Co., Ltd.), "Araldite (registered trademark)" MY720 (manufactured by Huntsman Advanced Materials Co., Ltd.), "Araldite (registered trademark)" MY721 (manufactured by Huntsman Advanced Materials Co., Ltd.), "Araldite (registered trademark)" MY9512 (manufactured by Huntsman Advanced Materials Co., Ltd.), "Araldite (registered trademark)" MY9663 (manufactured by Huntsman Advanced Materials Co., Ltd.), "Epotohto (registered trademark)" YH-434 (manufactured by Tohto Kasei Co., Ltd.), and "jER (registered trademark)" 630 (manufactured by Mitsubishi Chemical Corporation).

Commercially available diaminodiphenylsulfone type epoxy resins include TG3DAS (manufactured by Mitsui Fine Chemicals, Inc.).

Commercially available aminophenol type epoxy resins include ELM120 (Sumitomo Chemical Co., Ltd.), ELM100 (Sumitomo Chemical Co., Ltd.), jER (registered trademark) 630 (Mitsubishi Chemical Co., Ltd.), Araldite (registered trademark) MY0500 (Huntsman Advanced Materials Co., Ltd.), Araldite (registered trademark) MY0510 (Huntsman Advanced Materials Co., Ltd.), Araldite (registered trademark) MY0600 (Huntsman Advanced Materials Co., Ltd.), and Araldite (registered trademark) MY0610 (Huntsman Advanced Materials Co., Ltd.).

The epoxy resin composition of the present invention may contain epoxy resins other than those mentioned above as appropriate, provided that the object of the present invention is not impaired.

(Component [B])
The component [B] of the present invention is an amine-based curing agent, for example, an aromatic amine such as diaminodiphenylmethane or diaminodiphenylsulfone, or an aliphatic amine such as dicyandiamide, triethylenetetramine, or isophoronediamine.

The amine-based curing agent preferably contains aromatic amines and/or dicyandiamide, because the resulting resin composition has excellent storage stability and curing properties. Among these, dicyandiamide is more preferably used, because it has better storage stability and curing properties.

In the present invention, when the content of the component [B] is the equivalent ratio of the epoxy resin in the epoxy resin composition to the amine-based curing agent, that is, the ratio of the number of active hydrogens in the amine-based curing agent to the number of epoxy groups in the epoxy resin in the epoxy resin composition (number of active hydrogens in the amine-based curing agent/number of epoxy groups in the epoxy resin) is XB, XB must be in the range of 0.1 to 0.4, and XB is preferably in the range of 0.1 to 0.3. By setting XB in this range, a resin cured product with excellent elastic modulus and deflection can be obtained. Usually, in order to obtain an epoxy resin cured product with excellent deflection, the number of epoxy groups in the epoxy resin and the number of active hydrogens in the curing agent are made equal to each other in order to reduce unreacted functional groups as much as possible, that is, XB is often made close to 1.0, but in the present invention, since the component [C] described later also reacts with the epoxy resin, it is important to reduce the content of the component [B].

(Component [C])
The component [C] of the present invention is a phenol compound, such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, bisphenol Z, dihydroxynaphthalene, (phenylenediisopropylidene)bisphenol, and halogen- or alkyl-substituted derivatives thereof.

In the present invention, the epoxy resin composition must contain a phenol compound [C1] represented by formula (1).

(In formula (1), R ₁ to R ₅ represent a hydrogen atom, a hydrocarbon group having 1 to 8 carbon atoms, a methoxy group, a hydroxyl group or a halogen, and may be the same or different, but at least two are hydroxyl groups. _{R 6} to R ₁₀ represent a hydrogen atom, a hydrocarbon group having 1 to 8 carbon atoms, a methoxy group or a halogen, and may be the same or different, and X represents any one of no element, SO ₂ , CH ₂ , CH(CH ₃ ), C(CH ₃ ) ₂ , S, O or C═O.)
The inventors have found that by including [C1] as a phenolic compound, it is possible to achieve both an extremely high level of elastic modulus and deflection of the resin cured product. Conventionally, it has been known that the use of a compound such as bisphenol A in an epoxy resin composition increases the deflection of the epoxy resin cured product, but there was a problem of a decrease in elastic modulus. This is thought to be due to the fact that a rigid bisphenol compound is inserted between the crosslinking points, causing a small gap. [C1] is a compound having two aromatic rings in the molecule, and two or more hydroxyl groups are bonded to one of the aromatic rings. It is believed that when the hydroxyl group reacts with the epoxy group and is incorporated into the crosslinking structure, the aromatic ring without the hydroxyl group fills the gap, thereby improving the elastic modulus compared to compounds having hydroxyl groups on both aromatic rings, such as bisphenol A.

Examples of the phenol compound [C1] include 4-benzylresorcinol, 4-(α-methylbenzyl)resorcinol, 2-(phenylsulfonyl)-1,4-benzenediol, phenylhydroquinone, 2,3-dihydroxybiphenyl, 2,4-dihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, 3,4-dihydroxybenzophenone, and 2,4-dihydroxy-5-tert-butylbenzophenone. Among these, 2,4-dihydroxybenzophenone is preferably used because it has suitable solubility in epoxy resins and is easy to handle.

As for the content of the component [C1] in the present invention, when the equivalent ratio of the epoxy resin to the phenol compound [C1] in the epoxy resin composition, i.e., the ratio of the number of active hydrogens in the phenol compound [C1] to the number of epoxy groups in the epoxy resin in the epoxy resin composition (number of active hydrogens in the phenol compound [C1]/number of epoxy groups in the epoxy resin) is XC1, XC1 must be in the range of 0.3 to 0.9, and is preferably in the range of 0.3 to 0.7.

When the sum of XB and XC1 is XB+XC1, XB+XC1 must be in the range of 0.4 to 1.0, and preferably in the range of 0.5 to 1.0. By setting XC1 and XB+XC1 in this range, a cured resin with excellent elastic modulus and deflection can be obtained.

(Component [D])
The component [D] of the present invention is a curing accelerator, specifically, a curing accelerator for an epoxy resin and a phenolic compound, and promotes the reaction between the component [A] and the component [C]. In order to enhance the reactivity of the epoxy resin and the phenolic compound, it is necessary that the epoxy resin composition contains a curing accelerator. As the curing accelerator, it is preferable to use at least one curing accelerator selected from the group consisting of aromatic urea compounds, imidazole derivatives, and phosphorus compounds, in order to achieve both storage stability and curability of the epoxy resin composition.

Examples of the aromatic urea compound include 3-phenyl-1,1-dimethylurea, 3-(3-chloro-4-methylphenyl)-1,1-dimethylurea, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, toluene bisdimethylurea, etc. Commercially available aromatic urea compounds include DCMU-99 (manufactured by Hodogaya Chemical Co., Ltd.) and "Omicure (registered trademark)" 24 (manufactured by PTI Japan Co., Ltd.).

Examples of the imidazole derivatives include 1-benzyl-2-methylimidazole, 1-benzyl-2-ethylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, and 1-cyanoethyl-2-phenylimidazole. Commercially available imidazole derivatives include "Cureduct (registered trademark)" P-0505, 1B2MZ, 1B2PZ, 2MZ-CN, 2E4MZ-CN, and 2PZ-CN (all manufactured by Shikoku Chemical Industry Co., Ltd.).

Examples of the phosphorus compounds include triphenylphosphine, tri-o-tolylphosphine, tris(p-methoxyphenyl)phosphine, triphenylphosphine triphenylborane, and tetraphenylphosphonium tetraphenylborate. Commercially available phosphorus compounds include "Hokuko TPP (registered trademark)", "TOTP (registered trademark)", and "TPP-K (registered trademark)" (all manufactured by Hokko Chemical Industry Co., Ltd.).

The content of the curing accelerator [D] is preferably 1 to 8 parts by mass, more preferably 1.5 to 6 parts by mass, and even more preferably 2 to 4 parts by mass, per 100 parts by mass of the epoxy resin [A]. By including the curing accelerator [D] in this range, an epoxy resin composition can be obtained that has an excellent balance between storage stability and curing speed and provides a cured resin with good physical properties.

(Component [E])
The epoxy resin composition of the present invention may contain a thermoplastic resin as component [E], as long as the effects of the present invention are not lost. Although the thermoplastic resin is not an essential component of the present invention, by including it in the epoxy resin composition, it is possible to control the viscoelasticity and impart toughness to the cured product.

Examples of such thermoplastic resins include polymethyl methacrylate, polyvinyl formal, polyvinyl butyral, polyvinyl acetal, polyvinyl pyrrolidone, polymers containing at least two kinds of constituents selected from aromatic vinyl monomers, vinyl cyanide monomers, and rubber polymers, polyamides, polyesters, polycarbonates, polyarylene oxides, polysulfones, polyethersulfones, polyimides, etc. Examples of polymers containing at least two kinds of constituents selected from aromatic vinyl monomers, vinyl cyanide monomers, and rubber polymers include acrylonitrile-butadiene-styrene copolymers (ABS resins), acrylonitrile-styrene copolymers (AS resins), etc. Polysulfones and polyimides may have an ether bond or an amide bond in the main chain.

Polymethyl methacrylate, polyvinyl formal, polyvinyl butyral, and polyvinyl pyrrolidone are preferred because they have good compatibility with many types of epoxy resins such as bisphenol A type epoxy resins and novolac type epoxy resins, and are highly effective in controlling the fluidity of epoxy resin compositions, with polyvinyl formal being particularly preferred. Examples of commercially available products of these thermoplastic resins include "Denka Butyral (registered trademark)" and "Denka Formal (registered trademark)" (manufactured by Denki Kagaku Kogyo Co., Ltd.), and "Vinylec (registered trademark)" (manufactured by JNC Corporation).

In addition, polysulfone, polyethersulfone, and polyimide have excellent heat resistance as resins themselves, and there are polymers with a resin skeleton that has moderate compatibility with glycidylamine-type epoxy resins such as tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol, triglycidylaminocresol, and tetraglycidylxylenediamine, which are epoxy resins often used in applications requiring heat resistance, such as structural components of aircraft. The use of these polymers is preferable because they have a large effect of controlling the flowability of the epoxy resin composition and also have the effect of increasing the impact resistance of fiber-reinforced resin composite materials. Examples of such polymers include polysulfones such as "Radel (registered trademark)" A (manufactured by Solvay Advanced Polymers) and "Sumikaexcel (registered trademark)" PES (manufactured by Sumitomo Chemical Co., Ltd.), and polyimides such as "Ultem (registered trademark)" (manufactured by GE Plastics Co., Ltd.) and "Matrimid (registered trademark)" 5218 (manufactured by Huntsman).

When the epoxy resin composition of the present invention contains a thermoplastic resin, it is preferable that the thermoplastic resin is contained in an amount of 1 to 60 parts by mass per 100 parts by mass of the epoxy resin contained in the epoxy resin composition.

(Other additives)
The epoxy resin composition of the present invention may contain, within the scope of not impairing the effects of the present invention, a coupling agent, thermosetting resin particles, conductive particles such as carbon black, carbon particles, metal-plated organic particles, or inorganic fillers such as silica gel, clay, etc. The addition of these has a viscosity adjusting effect of increasing the viscosity of the epoxy resin composition and reducing resin flow, an effect of improving the elastic modulus and heat resistance of the cured resin, and an effect of improving the abrasion resistance.

(Method for preparing epoxy resin composition)
In preparing the epoxy resin composition of the present invention, the components may be kneaded using a machine such as a kneader, a planetary mixer, a three-roll mill, or a twin-screw extruder, or may be mixed by hand using a beaker and a spatula, etc., so long as uniform kneading is possible.

(Fiber-reinforced composite materials)
The epoxy resin composition of the present invention is excellent in elastic modulus and deflection after curing, and is suitable for use as a matrix resin for fiber-reinforced composite materials. Methods for obtaining fiber-reinforced composite materials include methods in which the resin composition is impregnated into reinforcing fibers in a molding process, such as the hand lay-up method, the RTM method, the filament winding method, and the pultrusion molding method, and methods in which a prepreg in which the resin composition has been impregnated into reinforcing fibers in advance is molded by the autoclave method or the press molding method. Among these, it is preferable to prepare a prepreg made of the epoxy resin composition and reinforcing fibers in advance, since the fiber arrangement and the resin ratio can be precisely controlled and the properties of the composite material can be maximized.

Preferably, the reinforcing fibers used in the prepreg and fiber-reinforced composite material of the present invention include carbon fiber, graphite fiber, aramid fiber, glass fiber, etc., with carbon fiber being particularly preferred. There are no limitations on the shape or arrangement of the reinforcing fibers, and fiber structures such as long fibers aligned in one direction, single tows, woven fabrics, knits, and braids can be used. Two or more types of carbon fiber, glass fiber, aramid fiber, boron fiber, PBO fiber, high-strength polyethylene fiber, alumina fiber, silicon carbide fiber, etc. may be used in combination as the reinforcing fibers.

Specific examples of carbon fibers include acrylic, pitch and rayon carbon fibers, with acrylic carbon fibers being particularly preferred due to their high tensile strength.

The carbon fiber can be in the form of twisted yarn, untwisted yarn, or non-twisted yarn, but in the case of twisted yarn, the filaments that make up the carbon fiber are not oriented parallel, which can cause a decrease in the mechanical properties of the resulting carbon fiber reinforced composite material. Therefore, untwisted yarn or non-twisted yarn, which provide a good balance between the moldability and strength properties of the carbon fiber reinforced composite material, are preferably used.

The prepreg of the present invention can be manufactured by various known methods. For example, the prepreg can be manufactured by a hot melt method in which the resin composition is heated to reduce its viscosity without using an organic solvent, and then impregnated into the reinforcing fibers.

In addition, in the hot melt method, the resin composition, which has been made low viscosity by heating, can be directly impregnated into the reinforcing fibers, or the resin composition can be coated on a release paper or the like to produce a release paper sheet with a resin film, and then the resin film can be placed on either or both sides of the reinforcing fibers, and the resin composition can be impregnated into the reinforcing fibers by heating and pressurizing.

The content of reinforcing fibers in the prepreg is preferably 30 to 90% by mass, more preferably 35 to 85% by mass, and even more preferably 65 to 85% by mass. If the fiber mass content is low, the amount of resin is too high, and it may be difficult to obtain the advantages of a fiber-reinforced composite material, which has excellent specific strength and specific modulus. In addition, when molding a fiber-reinforced composite material, the amount of heat generated during curing may be too high. On the other hand, if the fiber mass content is too high, impregnation with the resin may be poor, and the resulting composite material may have many voids. In addition, the tackiness of the prepreg may be impaired.

The fiber-reinforced composite material of the present invention can be produced, for example, by laminating the above-mentioned prepregs of the present invention in a predetermined form and applying pressure and heat to harden the resin. Methods for applying heat and pressure include press molding, autoclave molding, bagging molding, wrapping tape method, and internal pressure molding.

The fiber-reinforced composite material of the present invention can be widely used in aerospace applications, general industrial applications, and sports applications. More specifically, in general industrial applications, it is suitable for use in structures such as automobiles, ships, and railway vehicles. In sports applications, it is suitable for use in golf shafts, fishing rods, and tennis and badminton rackets.

The present invention will be described in detail below with reference to examples. However, the scope of the present invention is not limited to these examples. The unit of "parts" in the composition ratio means parts by mass unless otherwise noted. Furthermore, measurements of various characteristics (physical properties) were performed in an environment with a temperature of 23°C and a relative humidity of 50% unless otherwise noted.

<Materials used in the Examples and Comparative Examples>.

(1) [A]: epoxy resin; [A]-1: "jER (registered trademark)" 828 (bisphenol A type epoxy resin, epoxy equivalent: 189 g/eq, manufactured by Mitsubishi Chemical Corporation).

(2) [B]: Amine-based curing agent [B]-1: “jER Cure (registered trademark)” DICY7 (dicyandiamide, active hydrogen equivalent: 21 g/eq, number of active hydrogens: 4, manufactured by Mitsubishi Chemical Corporation).

(3) [C]: a phenol compound corresponding to the phenol compound [C1]. [C1]-1: 2,4-dihydroxybenzophenone (active hydrogen equivalent: 107 g/eq, number of active hydrogens: 2, manufactured by Tokyo Chemical Industry Co., Ltd.).
[C1]-2: 4-benzylresorcinol (active hydrogen equivalent: 100 g/eq, number of active hydrogens: 2, manufactured by Tokyo Chemical Industry Co., Ltd.).
[C1]-3: 2,3-dihydroxybiphenyl (active hydrogen equivalent: 93 g/eq, number of active hydrogens: 2, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).
Phenol compounds not corresponding to [C1] [C]-4: Bisphenol A (active hydrogen equivalent: 114 g/eq, number of active hydrogens: 2, manufactured by Tokyo Chemical Industry Co., Ltd.).

(4) [D]: Curing accelerator [D]-1: DCMU-99 (3-(3,4-dichlorophenyl)-1,1-dimethylurea, manufactured by Hodogaya Chemical Industry Co., Ltd.).
[D]-2: Cureduct (registered trademark) P-0505 (epoxy-imidazole adduct, manufactured by Shikoku Chemical Industry Co., Ltd.).
[D]-3: TPP (triphenylphosphine, manufactured by Tokyo Chemical Industry Co., Ltd.).

<Method for preparing epoxy resin composition>
(1) Method for preparing a hardener master [B]-1 ("jER Cure (registered trademark)" DICY7) was added to 10 parts of [A]-1 ("jER (registered trademark)" 828) out of 100 parts, and the mixture was kneaded at room temperature using a kneading device. The mixture was passed between the rolls twice using a three-roll mill to prepare a hardener master.

(2) Method for Producing an Epoxy Resin Composition 90 parts of 100 parts of [A]-1 ("jER (registered trademark)" 828) (excluding the 10 parts of [A]-1 ("jER (registered trademark)" 828) used in (1) above) and the phenol compound [C] were charged into a kneading device, and the temperature was raised to 150°C while kneading, and a transparent viscous liquid was obtained by kneading for 30 minutes at 150°C. Next, the temperature was lowered to 60°C while continuing the kneading, and the curing agent master produced in (1) above and [D] the curing accelerator were charged, and the mixture was kneaded for 30 minutes at 60°C to obtain an epoxy resin composition.

The compositions of the epoxy resin compositions for each example and comparative example are shown in Tables 1 to 3.

<Method of Producing Cured Resin>
The epoxy resin composition prepared according to the above <Preparation method of epoxy resin composition> was degassed in a vacuum, and then heated from 30° C. to 130° C. at a rate of 2.5° C./min in a mold set to a thickness of 2 mm using a 2 mm thick Teflon (registered trademark) spacer, and cured at 130° C. for 90 minutes to obtain a plate-shaped cured resin product having a thickness of 2 mm.

<Measurement of Elastic Modulus and Bending Deflection of Cured Resin>
Test pieces measuring 10 mm in width and 60 mm in length were cut out from the cured resin products prepared according to the above <Method for Preparing Cured Resin Product> and subjected to three-point bending in accordance with JIS K7171 (1994) using an Instron universal testing machine (manufactured by Instron Corp.) with a span of 32 mm, a crosshead speed of 100 mm/min, and number of samples n=6. The average values of the elastic modulus and bending deflection were determined as the elastic modulus and bending deflection of the cured resin product, respectively.

Example 1
An epoxy resin composition was prepared according to the above <Method for preparing epoxy resin composition> using 100 parts of "jER (registered trademark)" 828 as [A] epoxy resin, 1.9 parts of "jER Cure (registered trademark)" DICY7 as [B] amine-based curing agent, 34.0 parts of 2,4-dihydroxybenzophenone as [C] phenol compound, and 3 parts of DCMU-99 as [D] curing accelerator.

In this epoxy resin composition, XB, which represents the ratio of the number of active hydrogens in the amine curing agent [B] to the number of epoxy groups contained in the epoxy resin [A], was 0.2. Furthermore, XC1, which represents the ratio of the number of active hydrogens in the phenol compound corresponding to [C1] to the number of epoxy groups contained in the epoxy resin [A], was 0.6. XB+XC1, which represents the sum of XB and XC1, was 0.8.

The obtained epoxy resin composition was cured by the method described above in <Method for producing cured resin> to produce a plate-shaped cured resin. Furthermore, a three-point bending test described in <Measurement of elastic modulus and bending deflection of cured resin> was carried out, and the elastic modulus was 3.6 GPa and the bending deflection was 17 mm, showing excellent elastic modulus and bending deflection.

<Examples 2 to 8>
Epoxy resin compositions and cured resins were prepared in the same manner as in Example 1, except that the resin compositions were changed as shown in Tables 1 and 2, respectively.

For the epoxy resin compositions of each example, XB, XC1, and XB+XC1 are as shown in Tables 1 and 2, respectively.

A three-point bending test was performed on the cured resin, and the elastic modulus and bending deflection were both good.

<Comparative Examples 1 to 6>
An epoxy resin composition was obtained in the same manner as in Example 1 using the resin composition in Table 3. The obtained epoxy resin composition was cured by the method described in the above-mentioned <Method of Producing Cured Resin Product> to produce a plate-shaped cured resin product.

For the epoxy resin compositions of each comparative example, XB, XC1, and XB+XC1 are as shown in Table 3.

Next, a three-point bending test was performed as described in <Measurement of elastic modulus and bending deflection of cured resin>. The evaluation results are shown in Table 3.

Comparative Example 1 did not contain the amine-based curing agent [B], so the cured resin was extremely brittle, and it was difficult to prepare test pieces for a three-point bending test of the cured resin, making it impossible to evaluate it.

In Comparative Example 2, XB was greater than 0.4, so the bending deflection of the cured resin in a three-point bending test was low at 13 mm.

In Comparative Example 3, XB + XC1 was greater than 1.0, so the cured resin was extremely brittle, and it was difficult to prepare a test piece for a three-point bending test of the cured resin, making it impossible to evaluate.

In Comparative Example 4, XC1 was less than 0.3, so the cured resin had a low deflection of 12 mm in a three-point bending test.

Comparative Example 5 did not contain the phenol compound [C], so the cured resin had a low deflection of 12 mm in a three-point bending test.

Comparative Example 6 contains bisphenol A as the [C] phenolic compound, but does not contain any phenolic compound corresponding to [C1], so the elastic modulus of the cured resin was a low 2.9 GPa in a three-point bending test.

Claims (8)

An epoxy resin composition for use in a fiber-reinforced composite material, comprising the following components [A], [B], [C] and [D], and satisfying all of the following conditions (i) to (iii):
Component [A]: epoxy resin Component [B]: amine-based curing agent Component [C]: phenol compound Component [D]: curing accelerator Condition (i): When the ratio of the number of active hydrogens in component [B] to the number of epoxy groups in component [A] is XB, XB is in the range of 0.1 to 0.4.
Condition (ii): The constituent element [C] contains 4-benzylresorcinol, 4-(α-methylbenzyl)resorcinol, phenylhydroquinone, 2,3-dihydroxybiphenyl, 2,4-dihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, 3,4-dihydroxybenzophenone or 2,4-dihydroxy-5-tert-butylbenzophenone as the constituent element [C1], and when the ratio of the number of active hydrogens in the constituent element [C1] to the number of epoxy groups in the constituent element [A] is defined as XC1, XC1 is in the range of 0.3 to 0.9.
Condition (iii): XB+XC1 is in the range of 0.4 to 1.0. 2. The epoxy resin composition for fiber-reinforced composite materials according to claim 1, wherein the component [C] contains 4-benzylresorcinol, 2,3-dihydroxybiphenyl or 2,4-dihydroxybenzophenone as the component [C1]. 3. The epoxy resin composition for fiber-reinforced composite materials according to claim 1 or 2, characterized in that it contains, as the component [D], at least one curing accelerator selected from the group consisting of aromatic urea compounds, imidazole derivatives and phosphorus compounds. 4. The epoxy resin composition for fiber-reinforced composite materials according to claim 1, wherein the component [B] is dicyandiamide. A prepreg comprising the epoxy resin composition for fiber-reinforced composite materials according to any one of claims 1 to 4 and reinforcing fibers. 6. The prepreg according to claim 5 , wherein the reinforcing fibers are carbon fibers. A fiber-reinforced composite material comprising a cured product of the epoxy resin composition for fiber-reinforced composite materials according to any one of claims 1 to 4 and reinforcing fibers. 8. The fiber-reinforced composite material according to claim 7, characterized in that the reinforcing fibers are carbon fibers.