JP2016216657A - Epoxy resin composition, and fiber-reinforced composite material precursor and fiber-reinforced composite material using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber-reinforced composite material excellent in fatigue resistance characteristics under a condition high in repeated load stress.SOLUTION: There is provided an epoxy resin composition containing following component (A) and component (B), in which a cured article does not rupture when flexural strain of the cured article of the composition is 1.5 times or less of strain at a flexure maximum load. Component (A): an epoxy resin having an oxazolidone ring structure. Component (B): a curing agent.SELECTED DRAWING: None

Description

  The present invention relates to an epoxy resin composition, a fiber reinforced composite material precursor, and a fiber reinforced composite material that are suitably used for applications that require resistance to repeated loading (fatigue) of a load.

Since fiber reinforced composite materials are lightweight, have high strength and high rigidity, they are widely used from sports / leisure applications to industrial applications such as automobiles and aircraft. In particular, it is widely used for sports and leisure applications such as fishing rods, golf club shafts, and bicycle frames.
As a representative fiber reinforced composite material, fiber reinforced plastic is known. This fiber reinforced plastic is obtained, for example, by using an intermediate material obtained by impregnating a matrix resin into a reinforcing material composed of long fibers (continuous fibers) such as reinforcing fibers, that is, a prepreg, and laminating, heating, and molding them. Can do.

  For fiber reinforced composite materials such as those mentioned above, especially when applied to moving body applications such as bicycles, it is possible to reduce the weight of the member as well as static strength, so fatigue resistance characteristics and dynamic strength Improvement is demanded.

  For the purpose of application to the above-described sports and leisure uses, Patent Document 1 proposes a fiber-reinforced composite material using a thermosetting resin containing an epoxy resin having an oxazolidone ring as a matrix resin.

International Publication No. 98/44017 Pamphlet

  However, the fiber-reinforced composite material using the matrix resin described in Patent Document 1 is excellent in static strength such as bending strength and crushing strength in the diameter direction in a tubular molded body obtained using the matrix resin. However, the anti-fatigue property is not always sufficient, and the high level requirements as required for the above-mentioned moving body applications have not been answered.

As a result of intensive studies, the present inventors can obtain a fiber-reinforced composite material having excellent fatigue resistance under a high repeated load stress condition from an epoxy resin composition or a fiber-reinforced composite material precursor that satisfies the following configuration. I found out.
That is, the gist of the present invention is an epoxy resin composition containing the following component (A) and component (B), wherein the bending strain of the cured product of the composition is not more than 1.5 times the strain at the maximum bending load. In some cases, the cured product is an epoxy resin composition that does not break, is a fiber-reinforced composite material precursor composed of this and a reinforcing fiber, and is a fiber-reinforced composite material formed by curing this.
Component (A): Epoxy resin having an oxazolidone ring structure Component (B): Curing agent

Moreover, it is preferable that the bending elastic modulus of the hardened | cured material of the epoxy resin composition of this invention is 3 GPa or more.
Furthermore, in the epoxy resin composition of the present invention, the content of the component (A) is preferably in the range of 35 to 60% by mass of the total epoxy resin in the epoxy resin composition.
In the epoxy resin composition of the present invention, the component (B) is preferably dicyandiamide.
Furthermore, the epoxy resin composition of the present invention preferably contains a thermoplastic resin as the component (C).
Moreover, it is preferable that the epoxy resin composition of this invention contains polyvinyl formal as said component (C).
Furthermore, in the epoxy resin composition of the present invention, the content of the component (C) is in the range of 0.5 to 4 parts by mass with respect to 100 parts by mass of the total epoxy resin in the epoxy resin composition. preferable.
The fiber-reinforced composite material precursor of the present invention is preferably a prepreg in which the reinforcing fiber is impregnated with the epoxy resin composition.

  ADVANTAGE OF THE INVENTION According to this invention, the fiber reinforced composite material excellent also in the fatigue-proof characteristic on the conditions with a high repeated load stress can be provided.

The present invention is an epoxy resin composition containing the following component (A) and component (B), wherein the bending strain of a cured product of the composition is 1.5 times or less of the strain at the maximum bending load. Is characterized in that the cured product does not break, and further exists in its use.
Component (A): Epoxy resin having an oxazolidone ring structure Component (B): Curing agent

[Bending strain of cured epoxy resin composition]
In the epoxy resin composition of the present invention, when the bending strain of the cured product is 1.5 times or less of the strain at the maximum bending load, this is characterized in that it does not break, and the fiber reinforcement obtained It is possible to achieve excellent fatigue resistance characteristics for the composite material. This is because the cured product of the epoxy resin composition of the present invention can suppress the occurrence of microcracks even when a load is applied during repeated fatigue and the deformed product is deformed. The strain at the time of rupture of the cured product is more preferably 1.7 times or more of the strain at the maximum bending load.
Further, the breaking strain of the cured resin of the epoxy resin composition of the present invention is preferably 10% or more, and more preferably 12% or more.

[Bending elastic modulus of cured product of epoxy resin composition]
In the epoxy resin composition of this invention, it is preferable that the bending elastic modulus of the hardened | cured material is 3 GPa or more. This is because when the bending elastic modulus is 3 GPa or more, the amount of deformation of the fiber reinforced composite material obtained by using this cured product or this epoxy resin composition when repeated load (fatigue) is applied, This is because the occurrence of microcracks can be suppressed and more excellent fatigue resistance characteristics tend to be realized. More preferably, it is 3.1 GPa or more.

[Epoxy resin composition]
“Component (A): Epoxy resin having an oxazolidone ring structure”
In the present invention, an epoxy resin having an oxazolidone ring structure is used as the component (A). As an epoxy resin having an oxazolidone ring structure, AER4152, XAC4151 (manufactured by Asahi Kasei E-Materials Co., Ltd.), ACR1348 (manufactured by ADEKA Co., Ltd.), DER852, DER858 (manufactured by Dow Chemical Company) are commercially available. Two or more of these may be used in combination. By using an epoxy resin having an oxazolidone ring structure, the adhesion between the cured resin (matrix resin) and the reinforcing fiber in the case where a fiber-reinforced composite material is obtained by using the epoxy resin composition of the present invention and the reinforcing fiber together is obtained. In addition, there is a tendency to improve, and furthermore, the occurrence of microcracks at the interface between the matrix resin and the reinforcing fibers during repeated loading (fatigue) tends to be suppressed.

  The content of component (A) is preferably in the range of 35 to 60% by mass of the total epoxy resin contained in the epoxy resin composition of the present invention. This is because the adhesiveness with the above-mentioned reinforcing fiber tends to be at a sufficient level by setting the component (A) to 35% by mass or more. More preferably, it is 40 mass% or more. Moreover, it is because there exists a tendency for compatibility with the other component used for the epoxy resin composition of this invention, especially a thermoplastic resin to become favorable by making a component (A) into 60 mass% or less. More preferably, it is 50 mass% or less.

“Component (B): Curing Agent”
Component (B) that is a curing agent for epoxy resin includes amine type, acid anhydride type (carboxylic acid anhydride, etc.), phenol type (phenol novolac resin, etc.), mercaptan type, Lewis acid amine complex type, onium salt type. And imidazole type. These may have any structure as long as the epoxy resin can be cured. Above all, there is no performance change due to moisture in the epoxy resin composition before curing, and it has a long-term stability at a relatively low temperature. Amine type curing agents are preferred in that they tend to complete the curing. These curing agents may be used alone or in combination of two or more.

  Examples of amine-type curing agents include aromatic amines such as diaminodiphenylmethane and diaminodiphenylsulfone, aliphatic amines, imidazole derivatives, dicyandiamide, tetramethylguanidine, thiourea-added amines, and isomers and modified forms thereof. . Among these, dicyandiamide is particularly preferable in terms of excellent prepreg storage.

  Moreover, as a component (B) of the epoxy resin composition of this invention, in order to improve the hardening activity of a hardening | curing agent, it is preferable to use a hardening adjuvant together. For example, when the epoxy resin curing agent is dicyandiamide, the curing aid is 3-phenyl-1,1-dimethylurea, 3- (3,4-dichlorophenyl) -1,1-dimethylurea (DCMU), 3- ( Urea derivatives such as 3-chloro-4-methylphenyl) -1,1-dimethylurea and 2,4-bis (3,3-dimethylureido) toluene are preferred, and the epoxy resin curing agent is carboxylic anhydride or novolak. When it is a resin, the curing aid is preferably a tertiary amine, and when the epoxy resin curing agent is diaminodiphenyl sulfone, the curing aid is an imidazole compound, a urea compound such as phenyldimethylurea (PDMU), or boron trifluoride. Amine complexes such as monoethylamine and boron trichloride amine complexes are preferred.

  As the component (B), a combination of dicyandiamide and DCMU is particularly preferable because it has excellent storage stability of the epoxy resin composition and tends to increase the toughness and bending strain (breaking strain) of the cured resin.

When the curing agent is dicyandiamide, the preferred amount of component (B) is the number of moles of active hydrogen of dicyandiamide relative to the number of moles of epoxy groups derived from all epoxy resins blended in the epoxy resin composition. When the blending amount is in the range of 0.5 to 1 time, the balance between the curing time and the storage stability of the epoxy resin composition tends to be excellent, and the mechanical properties of the cured product tend to be excellent. Therefore, it is preferable. Furthermore, by setting the number of moles in the range of 0.6 to 0.8 times, the mechanical properties of the cured product (resin bending strength, resin bending elastic modulus, resin breaking strain, etc.) tend to be further improved. preferable.
Moreover, the compounding quantity of a hardening adjuvant is set as the range of 0.5-20 mass parts with respect to 100 mass parts of total amounts of the epoxy resin contained in an epoxy resin composition, and the hardening time of an epoxy resin composition. This is preferable because it tends to be excellent in balance with storage stability and also has excellent mechanical properties of the cured product. More preferably, it is the range of 1-5 mass parts.

"Other epoxy resins"
In the present invention, an epoxy resin other than the component (A) can be appropriately used. Although it does not specifically limit as an epoxy resin, For example, the glycidyl ether type, the glycidyl amine type, the glycidyl ester type, and the alicyclic epoxy type, or two or more types selected from these types Mention may be made of compounds in which an epoxy group is present in the molecule. Moreover, these halides can also be mentioned.

  Specific examples of the glycidyl ether type epoxy resins include bisphenol A type epoxy resins (for example, “jER826”, “jER1001”, jER1002 ”, jER1004”, “EPON825”, “jER826”, “jER826” manufactured by Mitsubishi Chemical Corporation). , "JER828", "jER1001", "Epiclon 850" manufactured by DIC Corporation, "Epototo YD-128" manufactured by Nippon Steel Chemical Co., Ltd., "DER-331", "DER-332" manufactured by Dow Chemical Bisphenol F type epoxy resin (for example, “jER806”, “jER807”, “jER1750” manufactured by Mitsubishi Chemical Corporation, “Epicron 830” manufactured by DIC Corporation, manufactured by Nippon Steel Chemical Co., Ltd.) “Epototo YD-170”, “Epototo YD 175 "), bisphenol S type epoxy resin, bisphenol E type epoxy resin, resorcinol type epoxy resin (for example," Denacol EX-201 "manufactured by Nagase ChemteX Corporation), phenol novolac type. Epoxy resins (for example, “jER152” and “jER154” manufactured by Mitsubishi Chemical Corporation, “N775” and “Epiclon 740” manufactured by DIC Corporation, “EPN179” and “EPN180” manufactured by Huntsman Advanced Materials Co., Ltd.) Ethylene glycol or polyethylene glycol type epoxy resins (for example, “Denacol EX810”, “Denacol EX-861” manufactured by Nagase ChemteX Corporation, “Epolite 200E” manufactured by Kyoeisha Chemical Co., Ltd., etc.) Propylene glycol or polypropylene glycol type epoxy resin (for example, “Denacol EX-911”, “Denacol EX-941”, “Denacol EX-920”, “Denacol EX-921”, “manufactured by Nagase ChemteX Corporation” Denacol EX-931 ”,“ Epolite 70P ”,“ Epolite 200P ”,“ Epolite 400P ”manufactured by Kyoeisha Chemical Co., Ltd.,“ Epolide NT228 ”manufactured by Daicel Co., Ltd.), naphthalenediol type epoxy resin (eg, "Epototo ZX-1355" manufactured by Nippon Steel Chemical Co., Ltd.), dicyclopentadiene skeleton type epoxy resin (for example, "Epiclon HP-7200L" manufactured by DIC Corporation), and their positional isomers, Alkyl group, halogen And the like having a substituent such as

  Specific examples of the glycidylamine type epoxy resin include tetraglycidyldiaminodiphenylmethane (for example, “Sumiepoxy ELM434” manufactured by Sumitomo Chemical Co., Ltd., “Araldite MY720”, “Araldite MY721”, “Araldite” manufactured by Huntsman Advanced Materials, Inc. MY9512 ”,“ Araldite MY9612 ”,“ Araldite MY9634 ”,“ Araldite MY9663 ”,“ jER604 ”manufactured by Mitsubishi Chemical Corporation, etc.), diglycidylaniline (for example,“ GAN, GOT manufactured by Nippon Kayaku Co., Ltd. ”) And tetraglycidylxylenediamine (for example, “TETRAD-X” manufactured by Mitsubishi Gas Chemical Co., Ltd.).

  Specific examples of the glycidyl ester type epoxy resin include phthalic acid diglycidyl ester (for example, “Epomic R508” manufactured by Mitsui Chemicals, “Denacol EX-721” manufactured by Nagase ChemteX Corporation), and the like. ) Tetrahydrophthalic acid diglycidyl ester, (methyl) hexahydrophthalic acid diglycidyl ester (for example, “Epomic R540” manufactured by Mitsui Chemicals, Inc., “AK-601” manufactured by Nippon Kayaku Co., Ltd., etc.) , Isophthalic acid diglycidyl ester, dimer acid diglycidyl ester (for example, “jER871” manufactured by Mitsubishi Chemical Corporation, “Epototo YD-171” manufactured by Nippon Steel Chemical Co., Ltd., etc.), and various isomers thereof. There is a body.

  Typical examples of the alicyclic epoxy type epoxy resins include compounds having a cyclohexene oxide group, a tricyclodecene oxide group, a cyclopentene oxide group, and the like. Specifically, a vinylcyclohexene diepoxide, a vinylcyclohexene monoepoxide, ( 3 ′, 4′-epoxycyclohexane) methyl 3,4-epoxycyclohexanecarboxylate (for example, “Celoxide 2021P” manufactured by Daicel Corporation, “CY179” manufactured by Huntsman Advanced Materials Corporation), and the like. (3 ′, 4′-epoxycyclohexane) octyl 3,4-epoxycyclohexanecarboxylate (for example, “Celoxide 2081” manufactured by Daicel Corporation), 1-methyl-4- (2-methyloxirani) ) -7-oxabicyclo [4.1.0] heptane (for example, “Celoxide 3000” manufactured by Daicel Corporation), 2- (3,4-epoxycyclohexyl-5,5-spiro-3,4) -Epoxy) cyclohexane-m-dioxane, bis (3,4-epoxycyclohexylmethylene) adipate, bis (3,4-epoxycyclohexylmethylene) adipate, bis (2-methyl-4,5-epoxycyclohexylmethylene) acipate, etc. .

  Specific examples of epoxy resins having epoxy groups of both glycidyl ether type and glycidyl amine type include triglycidylaminophenol and triglycidylaminocresol (for example, “Sumiepoxy ELM-100” and “Sumiepoxy” manufactured by Sumitomo Chemical Co., Ltd.). "ELM-120", Mitsubishi Chemical Corporation "jER630", Huntsman Advanced Materials Corporation "Araldite MY0500", "Araldite MY0510", "Araldite MY0600", "Araldite MY0610", Nippon Steel Chemical Co., Ltd. "Epototo YDCN-701" manufactured by the company, etc.).

These epoxy resins may be used individually by 1 type, and may use 2 or more types together.
Among these epoxy resins, bisphenol type epoxy resins are preferred because they tend to have good compatibility with other components used in the epoxy resin composition of the present invention, particularly thermoplastic resins.
Moreover, it is preferable to make epoxy resins other than these components (A) into the range of 40-65 mass% of all the epoxy resins contained in the epoxy resin composition of this invention. This is because by setting the content of the epoxy resin to 40% by mass or more, the compatibility with other components used in the epoxy resin composition of the present invention, particularly the thermoplastic resin, tends to be good. is there. More preferably, it is 50 mass% or more. Moreover, it is because it exists in the tendency for adhesiveness with the above-mentioned reinforced fiber to become a sufficient level by setting it as 65 mass% or less. More preferably, it is 60 mass% or less.

  Furthermore, among the above-mentioned bisphenol type epoxy resins, those having a molecular weight of 600 or more are preferable because they tend to improve the breaking strain of the above-mentioned cured resin. However, this content is more preferably in the range of 3 to 20% by mass of the total epoxy resin contained in the epoxy resin composition of the present invention in order to maintain the flexural modulus of the cured resin of the epoxy resin composition. Is in the range of 5-10% by weight.

“Component (C): Thermoplastic resin”
The epoxy resin composition of the present invention can contain a thermoplastic resin as necessary. This thermoplastic resin may be an elastomer or may contain one or more thermoplastic resins. By using these thermoplastic resins, the toughness of the cured product of the epoxy resin composition of the present invention can be improved, and the viscoelasticity can be changed to optimize the viscosity, storage elastic modulus and thixotropy. . Component (C) is selected from the group consisting of carbon-carbon bond, amide bond, imide bond, ester bond, ether bond, carbonate bond, urethane bond, urea bond, thioether bond, sulfone bond, imidazole bond and carbonyl bond. A thermoplastic resin having a main bond in the main chain is preferred. Examples of such thermoplastic resins include phenoxy resin, polyvinyl formal, polyacrylate, polyamide, polyaramid, polyester, polycarbonate, polyphenylene sulfide, polybenzimidazole, polyimide, polyetherimide, polysulfone, and polyethersulfone. Can do.

  These thermoplastic resins can be appropriately selected and used as necessary, and among them, polyvinyl formal is particularly preferable. This can improve the elastic modulus of the cured product of the epoxy resin composition of the present invention by using polyvinyl formal as the component (C), and when the resin containing polyvinyl formal is used as a prepreg, This is because the tackiness is improved and the sticking property and peelability between prepregs tend to be good.

  Moreover, it is preferable to make content of a component (C) into the range of 0.5-4 mass parts with respect to 100 mass parts of all the epoxy resins in the epoxy resin composition of this invention. This is because when the content of the component (C) is 0.5 parts by mass or more, the tackiness of the prepreg is improved and the resin flexural modulus tends to be improved. More preferably, it is 1 mass part or more, More preferably, it is 2 mass part or more. Moreover, it is because there exists a tendency for the resin bending distortion (breaking strain) to become high by setting it as 4 mass parts or less. More preferably, it is 3 parts by mass or less.

"Other additives"
The epoxy resin composition of the present invention may contain a solid additive as another component. Examples of the additive include inorganic particles such as silica, alumina, titanium oxide, zirconia, clay mineral, talc, mica, and ferrite, and carbonaceous components such as carbon nanotubes and fullerenes. These additives have an effect of imparting thixotropy to an uncured resin composition, an effect of improving the elastic modulus and heat resistance of a cured product of the resin composition, and an effect of improving fatigue strength and wear resistance. . In addition, particles of metal, carbon black, copper oxide, tin oxide, and the like can be included to improve conductivity.

  There is no particular limitation on the production method of the epoxy resin composition of the present invention, and each component constituting this composition is sufficiently mixed by a general stirring and heating device such as a kneader or a planetary mixer, or a stirring and pressure heating device. Can be manufactured.

[Reinforcing fiber]
By using the epoxy resin composition of the present invention and reinforcing fibers in combination, a fiber-reinforced composite material precursor can be obtained. Various fibers can be used as the reinforcing fibers depending on the purpose of use of the fiber reinforced composite material. Specific examples include carbon fibers, graphite fibers, aramid fibers, silicon carbide fibers, alumina fibers, boron fibers, tungsten carbide fibers. And glass fiber. These may be used individually by 1 type and may be used in combination of 2 or more type. Among these, carbon fiber and graphite fiber are preferable because they are excellent in specific strength and specific elastic modulus.

  As the carbon fiber or graphite fiber that can be used in the present invention, any type of carbon fiber or graphite fiber can be used depending on the application, but a high strength carbon fiber having a tensile elongation of 1.5% or more is used. Suitable for strength development of fiber reinforced composite materials.

The form of the reinforcing fiber used in the present invention is a form in which the continuous fibers are aligned in one direction, a form in which the continuous fibers are used as a woven fabric, a form in which the tow is aligned in one direction and held by a weft auxiliary yarn, a plurality of sheets There are multi-axial warp knit forms that overlap unidirectional reinforcing fiber sheets in different directions and stitch together with auxiliary yarns, and non-woven forms of reinforcing fibers. And the form which arranged the continuous fiber in one direction is preferable. The basis weight of the reinforced fiber can be freely set according to the purpose of use of the fiber reinforced composite material, but 50 to 2000 g / m ² is a practically preferable range.

There are no particular restrictions on the method for producing the fiber-reinforced composite material precursor and the method for producing the fiber-reinforced composite material of the present invention. For example, general impregnation methods such as a hot melt prepreg method, a lacquer prepreg method, a filament winding method, a resin transfer molding (RTM) method, and a VaRTM method, and a curing method can be used.
These methods can be appropriately selected according to need, but the productivity of the fiber reinforced composite material is excellent, the straightness of the carbon fiber is excellent, and the strength development of the cured product is excellent. The fiber-reinforced composite material precursor is preferably a prepreg in which the reinforcing fiber is impregnated with the epoxy resin composition.

  In addition to the above, the method for producing the fiber-reinforced composite material of the present invention includes an autoclave molding method, a vacuum back molding method, an oven molding method, a press molding method, a continuous press molding method, a pultrusion molding method, an internal pressure molding method, a sheet wrap molding method, etc. The following general molding methods are mentioned.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited at all by these Examples.

<Raw materials>
Ingredient (A):
AER4152: bifunctional epoxy resin having an oxazolidone ring in the skeleton, DER858 manufactured by Asahi Kasei E-materials Co., Ltd .: bifunctional epoxy resin having an oxazolidone ring in the skeleton, DOW Co., Ltd., component (B):
DICY15: Dicyandiamide, manufactured by Mitsubishi Chemical Corporation DCMU99: 3- (3,4-dichlorophenyl) -1,1-dimethylurea, manufactured by PTI Japan Co., Ltd./Component (C):
Vinylec E: polyvinyl formal, manufactured by JNC Corporation YP70: phenoxy resin, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd., other epoxy resins:
jER1002: Bisphenol A type bifunctional epoxy resin, molecular weight 1200, manufactured by Mitsubishi Chemical Corporation jER828: Bisphenol A type bifunctional epoxy resin, molecular weight 370, manufactured by Mitsubishi Chemical Corporation jER807: Bisphenol F type bifunctional epoxy resin, molecular weight 335, Mitsubishi JER1004 manufactured by Chemical Co., Ltd .: Bisphenol A type bifunctional epoxy resin, molecular weight 1650, manufactured by Mitsubishi Chemical Corporation N775: phenol novolac type epoxy resin manufactured by DIC Corporation

Reinforcing fiber:
Carbon fiber (Mitsubishi Rayon Co., Ltd., TR50S)

<Preparation of epoxy resin composition>
Among the compositions shown in Table 1, a catalyst resin composition is prepared by uniformly dispersing DICY15 and DCMU99 shown in the same table in a part of jER828 with a three roll mill. Next, after the remaining components of each composition were heated and mixed, a catalyst resin composition prepared in advance was added, and further heated and mixed to prepare an epoxy resin composition.

<Preparation of cured resin plate of epoxy resin composition>
The obtained epoxy resin composition is sandwiched between glass plates with a spacer made of polytetrafluoroethylene having a thickness of 2 mm or 3 mm, heated at a heating rate of 2 ° C./min, and held at 130 ° C. for 90 minutes to be cured. Thus, a cured resin plate was obtained.

<Preparation of prepreg>
The resin film basis weight was set so that the resin content of the prepreg when using two films was 30% by mass, and the epoxy resin composition was applied to release paper with a film coater to obtain a resin film.
The resin film is pasted on both sides of carbon fiber having a fiber basis weight of 125 g / m ² (manufactured by Mitsubishi Rayon Co., Ltd., TR50S) and niped, and a prepreg having a fiber basis weight of 125 g / m ² and a resin content of 25% by mass is obtained. Obtained.

<Production of fiber reinforced composite material panel>
The obtained prepreg was laminated, the pressure was increased to 0.04 MPa with an autoclave, the temperature was raised to 80 ° C. at 2 ° C./min by evacuation, and held for 1 h. After holding, the pressure is increased to 0.6 MPa, the atmosphere is opened to the atmosphere (VENT) at 0.14 mpa, and the temperature is raised to 130 ° C. at 2 ° C./min. A fiber reinforced composite material panel was obtained by heating and curing at 130 ° C. for 90 minutes.

<Measurement method of resin plate bending test>
A 2 mm thick cured resin plate or fiber reinforced composite material panel is processed into a test piece (length 60 mm x width 8 mm), using an INSTRON 4465 measuring machine equipped with a 500 N load cell, in an environment of temperature 23 ° C. and humidity 50% RH. The bending strength, the bending elastic modulus, and the bending strain were measured under the conditions of an indenter R = 3.2 mm, a support R = 1.6 mm, and a ratio L / D = 16 of the distance between the supports and the thickness of the test piece. When the bending strain was 12% or more, the measurement was completed without breaking. When the bending strain broke at less than 12%, it was recorded as the breaking strain, and the average value of the measured values was taken as the bending breaking strain.

<Measurement of 0 ° bending strength of fiber reinforced composite material>
A test piece (length 130 mm × width 12.7 mm) was cut out from the fiber reinforced composite material panel so that the reinforcing fibers were oriented at 0 ° with respect to the longitudinal direction of the test piece. (Indenter 5 mmR, support 3.2 mmR, distance between supports: 40 times the thickness of the test piece) Instron's universal testing machine was used, and the crosshead speed was squared the distance between the supports × 0.01 / The bending strength was measured as 6 × thickness / min of the test piece.

<Measurement of 90 ° bending strength of fiber reinforced composite material>
A test piece (length 60 mm × width 12.7 mm) was cut out from the fiber reinforced composite material panel so that the reinforcing fibers were oriented at 90 ° with respect to the longitudinal direction of the test piece. (Indenter 5 mmR, support 3.2 mmR, distance between supports: 16 times the thickness of the test piece) A universal testing machine manufactured by Instron Corp. was used, and the crosshead speed was squared the distance between supports × 0.01 / The bending strength was measured as 6 × thickness / min of the test piece.

<Measurement of interlaminar shear strength of fiber reinforced composite material>
A test piece (length 25 mm × width 6.3 mm) was cut out from the fiber reinforced composite material panel so that the warp direction of the reinforcing fiber was oriented at 0 ° with respect to the longitudinal direction of the test piece. Using a universal testing machine manufactured by Instron with a bending jig (indenter: 3.2 mmR, support: 1.6 mmR, distance between supports: 4 times the thickness of the test piece), the crosshead speed is adjusted to the distance between the supports. Interlaminar shear strength was measured as squared × 0.01 / 6 × thickness / minute of test piece.

<Measurement of bending fatigue strength of fiber reinforced composite material>
The fiber reinforced composite panel was processed into a test piece (length 130 mm × width 12.7 mm) so that the reinforcing fibers were oriented at 0 ° with respect to the longitudinal direction of the test piece. About this test piece, using a fatigue tester (manufactured by Shimadzu Corporation, product name: LD-05D), a three-point bending jig (indenter R = 5 mm, support R =) in an environment of a temperature of 23 ° C. and a humidity of 50% RH. 3.2 mm), and the ratio L / d = 40 between the distance between the supports (L) and the thickness (d) of the test piece was set. Record the number of times the test piece was broken by applying a load at a period of 1 Hz. The load was cycled between 10% and 100% of the set value. The load was changed and the same test was conducted. The load was measured 3 times for each load at 4 points or more. The obtained numerical values were plotted with the load stress against the number of ruptures, and approximated logarithmically to obtain an approximate line. Furthermore, a stress value of 1800 MPa was input to this approximate line, and the corresponding number of breaks was obtained.

<Example 1 and Comparative Example 1>
An epoxy resin composition, a cured resin plate, and a fiber reinforced composite material having the composition shown in Table 1 were produced by the above preparation procedure, production procedure, and measurement method, and various measurements were performed.

  As shown in Table 1, in both Example 1 and Comparative Example 1, the fiber reinforced material shows sufficient strength in static strength. However, Example 1 of the present invention was remarkably superior to Comparative Example 1 in repeated fatigue characteristics.

<Examples 2 to 12, Comparative Examples 2 to 3>
An epoxy resin composition and a cured resin plate having the compositions shown in Tables 2 and 3 were prepared by the above preparation procedure, preparation procedure, and measurement method, and various measurements were performed.

As shown in Tables 2 and 3, Examples 2 to 12 showed high bending strain and elastic modulus of the cured resin.
On the other hand, as shown in Table 3, in Comparative Examples 2-3, the bending strain of the cured resin was not sufficient.

  ADVANTAGE OF THE INVENTION According to this invention, the fiber reinforced composite material excellent also in the fatigue-proof characteristic in the conditions with high repeated load stress can be provided, and it is industrially useful.

Claims (10)

An epoxy resin composition comprising the following component (A) and component (B), wherein the cured product is cured when the bending strain of the composition is 1.5 times or less of the strain at the maximum bending load. An epoxy resin composition that does not break.
Component (A): Epoxy resin having an oxazolidone ring structure Component (B): Curing agent   The epoxy resin composition according to claim 1, wherein the cured product has a flexural modulus of 3 GPa or more.   The epoxy resin composition of Claim 1 or 2 whose content of the said component (A) is the range of 35-60 mass% of all the epoxy resins in the said epoxy resin composition.   The epoxy resin composition according to any one of claims 1 to 3, wherein the component (B) is dicyandiamide.   The epoxy resin composition as described in any one of Claims 1-4 containing a thermoplastic resin as a component (C).   The epoxy resin composition according to claim 5, wherein the component (C) is polyvinyl formal.   The content of the component (C) is in the range of 0.5 to 4 parts by mass with respect to 100 parts by mass of the total epoxy resin in the epoxy resin composition. Epoxy resin composition   A fiber-reinforced composite material precursor comprising the epoxy resin composition according to claim 1 and reinforcing fibers.   The fiber-reinforced composite material precursor according to claim 8, which is a prepreg in which the epoxy fiber composition is impregnated in the reinforcing fiber.   A fiber reinforced composite material obtained by curing the fiber reinforced composite material precursor according to claim 8.