Forming materials and fiber-reinforced composite materials

Abstract

The purpose of the present invention is to provide: a molding material from which a carbon fiber reinforced composite material having excellent impact resistance and tensile strength is obtained; and a molding material from which a glass fiber reinforced composite material, that has high bending strength and impact resistance, has excellent weather resistance, and can suppress a decrease in bending strength after water absorption, is obtained.　In order to achieve the purpose, the molding material according to the present invention is a molding material formed of an epoxy resin composition and a carbon fiber and / or a glass fiber, wherein the epoxy resin composition includes all of [A] to [C], the carbon fiber satisfies conditions [a] and [b], and the glass fiber has a surface functional group capable of forming a covalent bond with an isocyanate group. [A] Epoxy resin having at least two oxylan groups in molecule [B] Epoxy resin curing agent having at least two isocyanate groups in molecule [C] Catalyst [a] Having substantially perfect circular cross section [b] Average fiber diameter of 4.0-8.0 μm

Description

Technical Field

[0001] The present invention relates to a molding material and a fiber-reinforced composite material.

Background Art

[0002] A fiber-reinforced composite material (FRP) composed of reinforcing fibers and a matrix resin can be designed with materials that take advantage of the reinforcing fibers and the matrix resin. Therefore, its applications are expanding in fields such as the aerospace field, the sports field, and the general industrial field.

[0003] As the reinforcing fibers, glass fibers, aramid fibers, carbon fibers, boron fibers, etc. are used. Also, as the matrix resin, either a thermosetting resin or a thermoplastic resin can be used, but from the viewpoints of heat resistance and productivity, a thermosetting resin is often used. As the thermosetting resin, epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, bismaleimide resins, cyanate resins, etc. are used. Among them, epoxy resins are preferably used from the viewpoints of the adhesiveness between the resin and the reinforcing fibers, dimensional stability, and mechanical properties such as the strength and rigidity of the obtained composite material.

[0004] When a fiber-reinforced composite material is used for large members such as automobiles, aircraft, and wind turbine blades, the fiber-reinforced composite material is required to be lightweight and high-strength. Also, since these are often used outdoors, it is required that the strength does not decrease even when exposed to moisture such as rain and humidity. Therefore, good impregnability is required for the matrix resin and the reinforcing fiber base material used in these fiber-reinforced composite materials.

[0005] For the molding of fiber-reinforced composite materials, methods such as the prepreg method, hand lay-up method, filament winding method, pultrusion method, RTM (Resin Transfer Molding) method, film bag molding method, and press molding method are applicable. In particular, when productivity is required, the RTM method, film bag molding method, and press molding method, which are excellent in productivity, are preferably used.

[0006] The matrix resin used in the molding method of the fiber-reinforced composite material as described above is a low-molecular thermosetting resin in a liquid or semi-solid state at room temperature in order to sufficiently impregnate the reinforcing fiber base material. Since the cured product of the thermosetting resin generally has lower toughness than the thermoplastic resin, the problem was that the fiber-reinforced composite material using such a thermosetting resin had relatively low impact resistance.

[0007] Among the above-described reinforcing fibers, carbon fibers are preferably used because a fiber-reinforced composite material that is lightweight and has excellent mechanical properties such as strength and elastic modulus can be obtained. In order to improve the adhesiveness between the carbon fiber and the matrix resin, the carbon fiber is often treated electrochemically or chemically to introduce functional groups such as hydroxyl groups and carboxyl groups on the surface. However, when the matrix resin cures, it does not react efficiently with the functional groups on the surface of the carbon fiber, resulting in the problem that the adhesiveness between the carbon fiber and the matrix resin is not improved and the impact resistance is low.

[0008] For example, in Reference 1, an amine-cured epoxy resin is used as the matrix resin, and core-shell rubber particles are added to improve toughness. In addition, in Reference 2, an acid anhydride-cured epoxy resin is used as the matrix resin, which is characterized by having low viscosity and fast curing properties.

[0009] In addition, for the large members described above, since cost reduction and weight reduction are possible, glass fiber is also preferably used as the reinforcing fiber. The obtained fiber-reinforced composite material is required to have high strength and weather resistance so that the resin can be impregnated into the reinforcing fiber base material during molding and can withstand a harsh use environment for a long time.

[0010] For example, Cited Document 3 uses a predetermined epoxy resin component and an amine compound as the matrix resin of the fiber-reinforced composite material, and is characterized by having low viscosity and low water absorption. Further, Cited Document 4 uses an acid anhydride-cured epoxy resin as the matrix resin, and is characterized by having low viscosity and fast curability.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0012] The epoxy resin of Cited Document 1 still has poor toughness, and the addition of core-shell rubber particles results in high viscosity at the injection temperature and poor impregnability. Further, the epoxy resin of Cited Document 1 also has poor adhesion to the reinforcing fiber, and the impact resistance of the fiber-reinforced composite material obtained using it is also poor. The epoxy resin of Cited Document 2 cannot be said to have sufficient toughness and adhesion to the reinforcing fiber, and there are problems in improving the impact resistance of the fiber-reinforced composite material obtained using it.

[0013] In addition, although the epoxy resin of Reference Document 3 has low viscosity and low water absorption, its adhesiveness when combined with reinforcing fibers is still insufficient, and there are problems with the strength of the fiber-reinforced composite material obtained using it. Furthermore, although the epoxy resin of Reference Document 4 is excellent in the impregnability of the resin into the reinforcing fiber base material, its water absorption and adhesiveness with the reinforcing fibers are not sufficient, and there are problems with the strength and weather resistance of the fiber-reinforced composite material obtained using it.

[0014] An object of the present invention is to provide a molding material for obtaining a carbon fiber-reinforced composite material having excellent impact resistance and tensile strength using an epoxy resin composition having good impregnability. Further, by using an epoxy resin composition having good impregnability and glass fibers excellent in adhesiveness with such an epoxy resin composition, a glass fiber-reinforced composite material having high bending strength and impact resistance and excellent weather resistance, that is, capable of suppressing a decrease in bending strength after water absorption, is provided.

Means for Solving the Problems

[0015] The molding material of the present invention for solving the above problems is a molding material comprising an epoxy resin composition, carbon fibers and / or glass fibers, wherein the epoxy resin composition contains all of the following [A] to [C], the carbon fibers satisfy the following conditions [a] and [b], and the glass fibers have a surface functional group capable of forming a covalent bond with an isocyanate group. [A] An epoxy resin having at least two oxirane groups in the molecule [B] An epoxy resin curing agent having at least two isocyanate groups in the molecule [C] A catalyst [a] Having a substantially circular cross-section [b] The average fiber diameter is in the range of 4.0 to 8.0 μm

Effects of the Invention

[0016] According to the present invention, by using a combination of carbon fibers satisfying specific conditions and an epoxy resin composition having a specific configuration, while using an epoxy resin composition having good impregnability and a reinforcing fiber base material, a fiber-reinforced composite material excellent in impact resistance and tensile strength can be obtained. Further, by using a combination of glass fibers satisfying specific conditions and an epoxy resin composition having a specific configuration, while using an epoxy resin composition having good impregnability and a reinforcing fiber base material, a fiber-reinforced composite material having high flexural strength and impact resistance and capable of suppressing a decrease in flexural strength after water absorption can be obtained.

Mode for Carrying Out the Invention

[0017] The molding material of the present invention is a molding material comprising an epoxy resin composition and carbon fibers and / or glass fibers, wherein the epoxy resin composition contains all of the following [A] to [C], the carbon fibers satisfy the following conditions [a] and [b], and the glass fibers have a surface functional group capable of forming a covalent bond with an isocyanate group. [A] An epoxy resin having at least two oxirane groups in the molecule [B] An epoxy resin curing agent having at least two isocyanate groups in the molecule [C] A catalyst [a] Having a substantially circular cross-section [b] The average fiber diameter is in the range of 4.0 to 8.0 μm.

[0018] A first preferred embodiment of the molding material of the present invention is composed of an epoxy resin composition and carbon fibers.

[0019] In the molding material of the present invention, it is essential that the carbon fibers have a substantially circular cross-section. Here, having a substantially circular cross-section means that the ratio (r / R) of the major axis R to the minor axis r of the cross-section of a single fiber measured using an optical microscope is 0.9 or more. Here, the major axis R refers to the diameter of the circumscribed circle of the cross-sectional shape of a single fiber, and the minor axis r refers to the diameter of the inscribed circle of the cross-sectional shape of a single fiber. If it is not circular, the injection time into the reinforcing fiber base material using such carbon fibers of the matrix resin becomes long, which may cause the occurrence of an unimpregnated region.

[0020] In addition, in the molding material of the present invention, it is essential that the carbon fiber has an average fiber diameter measured using an optical microscope in the range of 4.0 to 8.0 μm, preferably in the range of 5.0 to 7.0 μm, and more preferably in the range of 5.3 to 7.0 μm. If the average fiber diameter is less than 4.0 μm, the impact resistance of the fiber-reinforced composite material using such carbon fiber will decrease. On the other hand, if the average fiber diameter exceeds 8.0 μm, the tensile strength of the fiber-reinforced composite material using such carbon fiber will decrease.

[0021] In the molding material of the present invention, it is preferable that the carbon fiber further satisfies the following condition [c]. [c] The surface specific oxygen concentration O / C is in the range of 0.03 to 0.20.

[0022] Here, the surface specific oxygen concentration is the O 1s peak area [O 1s and the C 1s peak area [C 1s , and the surface specific oxygen concentration O / C = ([O 1s / [C 1s ) / (sensitivity correction value) is specified by calculation. The surface specific oxygen concentration O / C is more preferably in the range of 0.05 to 0.20, and even more preferably in the range of 0.05 to 0.15. When O / C is 0.20 or less, the fiber-reinforced composite material using such carbon fiber is likely to have sufficient tensile strength. When O / C is 0.05 or more, the fiber-reinforced composite material using such carbon fiber is likely to have sufficient impact resistance. As means for setting the surface specific oxygen concentration O / C within the above range, for example, methods such as changing the type and concentration of the electrolytic solution during electrolytic oxidation treatment and changing the amount of electricity can be mentioned.

[0023] In the molding material of the first preferred embodiment of the present invention, in addition to carbon fibers, inorganic fibers such as glass fibers, metal fibers, and ceramic fibers, polyamide fibers, polyester-based fibers, polyolefin-based fibers, novoloid fibers, etc., and metal wires, metal meshes, metal non-woven fabrics, etc. made of gold, silver, copper, bronze, brass, phosphor bronze, aluminum, nickel, steel, stainless steel, etc. can be used in combination to the extent that the effects of the present invention are not impaired.

[0024] In the molding material of the first preferred embodiment of the present invention, it is preferable that the content of carbon fibers in all fibers is 30% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more. If the content of carbon fibers is within the above range, it is preferable because a fiber-reinforced composite material that is lightweight and excellent in mechanical properties such as impact resistance, strength, and elastic modulus can be obtained.

[0025] In the molding material of the present invention, the carbon fibers may be either short fibers or continuous fibers, or both may be used in combination. Continuous fibers are preferable in order to obtain a fiber-reinforced composite material with a high Vf.

[0026] In the molding material of the present invention, carbon fibers may be used in the form of strands, but a base material made of carbon fibers processed into forms such as mats, woven fabrics, knits, blades, and unidirectional sheets is preferably used. Among them, a woven fabric that easily obtains a fiber-reinforced composite material with a high Vf and has excellent handleability is preferably used.

[0027] The ratio of the net volume of carbon fibers to the apparent volume of the woven fabric is defined as the filling rate of the woven fabric. The filling rate of the woven fabric is based on the areal density W (unit: g / m 2 ), thickness t (unit: mm), and density ρf of carbon fibers (unit: g / cm 3) is obtained by the formula of W / (1000t·ρf). The areal density and thickness of the fabric are determined in accordance with JIS R 7602:1995. Since it is easier to obtain a fiber-reinforced composite material with a higher Vf when the filling rate of the fabric is higher, the filling rate of the fabric is preferably in the range of 0.10 to 0.85, more preferably 0.40 to 0.85, and still more preferably 0.50 to 0.85.

[0028] A second preferred embodiment of the molding material of the present invention comprises an epoxy resin composition and glass fibers.

[0029] In the molding material of the present invention, it is essential that the glass fibers have surface functional groups capable of forming a covalent bond with an isocyanate group. It is known that silicon (Si-OH) bonded with a hydroxyl group called a silanol group exists on the surface of the glass fibers, and it is known that the chemical properties of the glass fiber surface can be improved by bonding a coupling agent or the like having various functional groups to the silanol group as needed. Here, having surface functional groups capable of forming a covalent bond with an isocyanate group means that at least one or more functional groups capable of forming a covalent bond with an isocyanate group by a chemical reaction exist on the surface of the glass fibers. When the glass fibers have surface functional groups capable of forming a covalent bond with an isocyanate group, an epoxy resin curing agent having at least two isocyanate groups in the [B] molecule contained in the epoxy resin composition can chemically bond with the glass fibers, and the adhesiveness between the glass fibers and the epoxy resin composition in the obtained fiber-reinforced composite material is improved, and it becomes easier to exhibit high strength. However, if the adhesiveness between the glass fibers and the epoxy resin composition is improved too much, the impact resistance may decrease as described later, and it is preferable that the surface of the glass fibers is appropriately treated with a coupling agent or the like.

[0030] In the molding material of the present invention, it is preferable that the surface functional group of the glass fiber is at least one functional group selected from the group consisting of a hydroxyl group, an oxirane group, an amino group, a thiol group, and a carboxyl group. When the glass fiber has a surface functional group as described above, it is easy to exhibit excellent adhesiveness at the interface between the glass fiber and the epoxy resin composition. Among them, from the viewpoint of moderately improving the adhesive strength, it is easy to form a covalent bond moderately with an epoxy resin curing agent having at least two isocyanate groups in the molecule, which is easy to mix with the epoxy resin composition. Therefore, it is preferable that the surface functional group of the glass fiber is an amino group.

[0031] In the molding material of the present invention, it is preferable that the glass fiber has a functional group having active hydrogen on its surface. Here, active hydrogen refers to a highly reactive hydrogen atom that is bonded to nitrogen, oxygen, or sulfur in an organic compound. For example, one amino group has two active hydrogens. Examples of the functional group having active hydrogen include a hydroxyl group, an amino group, a thiol group, and a carboxyl group.

[0032] In the molding material of the present invention, it is preferable that the surface functional group of the glass fiber is formed by being treated with at least one selected from the group consisting of a silane coupling agent, a titanium coupling agent, an aluminum coupling agent, and a zirconium coupling agent. The coupling agent may be used alone or in combination of two or more. If there are too many silanol groups on the surface of the glass fiber, the glass fiber and the epoxy resin curing agent having at least two isocyanate groups in the molecule contained in the epoxy resin composition are chemically strongly bonded and the adhesiveness is improved, but when an impact is applied and it breaks, the strength of the fiber cannot be utilized and the epoxy resin may be destroyed, so the impact resistance may decrease. Therefore, it is preferable that the surface of the glass fiber is appropriately treated with a coupling agent or the like.

[0033] In the molding material of the present invention, examples of the silane coupling agent used for glass fibers include amino group-containing silanes such as γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltriisopropoxysilane, γ-aminopropylmethyldimethoxysilane, γ-aminopropylmethyldiethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-(2-aminoethyl)aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropylmethyldiethoxysilane, γ-(2-aminoethyl)aminopropyltriisopropoxysilane, γ-ureidopropyltrimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, N-benzyl-γ-aminopropyltrimethoxysilane, N-vinylbenzyl-γ-aminopropyltriethoxysilane; thiol group-containing silanes such as γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropylmethyldiethoxysilane; oxirane group-containing silanes such as γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxysilane; carboxy group-containing silanes such as β-carboxyethyltriethoxysilane, β-carboxyethylphenylbis(2-methoxyethoxy)silane, N-β-(carboxymethyl)aminoethyl-γ-aminopropyltrimethoxysilane; and the like.

[0034] Examples of the titanium coupling agent include isopropyltri(N-aminoethyl-aminoethyl) titanate, tetraoctylbis(ditridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl) phosphite titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, bis(dioctyl pyrophosphate)ethylene titanate, isopropyltrioctanoyl titanate, isopropyldimethacrylisostearoyl titanate, isopropyltridodecylbenzenesulfonyl titanate, isopropylisostearyldiacryl titanate, isopropyltri(dioctyl phosphate) titanate, isopropyltricumylphenyl titanate, tetraisopropylbis(dioctyl phosphite) titanate, and the like.

[0035] Among them, silane coupling agents of amino group-containing silanes are preferable because they are easily compatible with the epoxy resin composition, can moderately improve the adhesive strength, and can improve the impact resistance.

[0036] When the molding material of the present invention contains a coupling agent, it is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 4 parts by mass, and even more preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the glass fiber. If the content rate of the coupling agent is within the above range, the wettability of the epoxy resin composition with respect to the glass fiber is improved, the adhesiveness and impregnation property are moderately improved, and the impact resistance can be improved, which is preferable.

[0037] As a method for forming the coupling agent layer, for example, there is a method of applying a solution containing a coupling agent to the surface of a glass fiber base material and then performing heat treatment. The solvent used for solubilizing the coupling agent is not particularly limited as long as it does not react with the coupling agent. Examples include aliphatic hydrocarbon solvents such as hexane, aromatic solvents such as benzene, toluene, and xylene, ether solvents such as tetrahydrofuran, alcohol solvents such as methanol and propanol, ketone solvents such as acetone, water, etc. One kind or a mixture of two or more kinds of these solvents is used.

[0038] In the molding material of the present invention, any kind of glass fiber can be used according to the application. Examples of glass fibers include E glass, A glass, C glass, D glass, R glass, S glass, ECR glass, NE glass, quartz, and fibers prepared from fiberizable glass compositions generally known as fluorine-free and / or boron-free E glass derivatives. In addition to glass fibers, inorganic fibers such as carbon fibers, metal fibers, and ceramic fibers, and organic synthetic fibers such as polyamide fibers, polyester fibers, polyolefin fibers, and novoloid fibers, and metal wires, metal meshes, metal non-woven fabrics, etc. made of gold, silver, copper, bronze, brass, phosphor bronze, aluminum, nickel, steel, stainless steel, etc. can be combined and used to the extent that the effects of the second preferred embodiment of the molding material of the present invention are not impaired.

[0039] In the second preferred embodiment of the molding material of the present invention, it is preferable that the content of glass fiber in all fibers is 30% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more. If the content of glass fiber is within the above range, it is preferable because a fiber-reinforced composite material excellent in mechanical properties such as impact resistance and strength and weather resistance can be obtained.

[0040] In the molding material of the present invention, the glass fiber may be either continuous fiber or short fiber, or both may be used in combination. Also, the continuous fiber may be cut into chopped strands (short fibers).

[0041] As the form of the glass fiber, it can be suitably used as a base material processed into a strand, mat, non-woven fabric, woven fabric, knit, blade, unidirectional sheet, etc. Among them, a woven fabric is preferably used because a fiber-reinforced composite material with a high fiber volume content (Vf) can be easily obtained and it has excellent handleability.

[0042] When using glass fiber in a woven fabric, a conventionally known two-dimensional woven fabric can be used. Such a structure is preferably any one selected from the group consisting of plain weave, twill weave, leno weave, mock leno weave, twill weave, double weave, and satin weave, and these weaving structures may be used alone or in combination.

[0043] The ratio of the net volume of the glass fiber to the apparent volume of the woven fabric is defined as the filling rate of the woven fabric. The filling rate of the woven fabric is calculated by the formula W / (1000t·ρf) from the areal density W (unit: g / m 2 ), thickness t (unit: mm), and density ρf of the glass fiber (unit: g / cm 3 ). The areal density and thickness of the woven fabric are determined in accordance with JIS R 7602:1995. In the woven fabric, since it is easier to obtain a fiber-reinforced composite material with a high fiber volume content (Vf) when the filling rate is high, the filling rate of the woven fabric is preferably in the range of 0.10 to 0.85, more preferably 0.40 to 0.85, and even more preferably 0.50 to 0.85.

[0044] When using chopped strand of glass fiber, its average fiber length is not limited, but it is 1 to 20 mm, preferably 3 to 10 mm. When the average fiber length of the chopped strand is within this range, the average fiber length in the glass fiber-reinforced composite material becomes appropriate, and the physical properties such as flexural strength tend to be improved, and the handling during mixing with the epoxy resin composition also tends to be improved.

[0045] The molding material of the present invention includes an epoxy resin composition. Such an epoxy resin composition essentially contains an epoxy resin having at least two oxirane groups in the molecule (hereinafter sometimes referred to as component [A]). By having such a structure, the mechanical properties and moldability of the fiber-reinforced composite material can be obtained. Among them, since it has a low viscosity, excellent impregnation property to reinforcing fibers, and excellent mechanical properties such as heat resistance and elastic modulus when made into a fiber-reinforced composite material, component [A] is preferably an epoxy resin having a number average molecular weight in the range of 200 to 800 and containing an aromatic group in the skeleton. The number average molecular weight of the epoxy resin is determined by GPC (Gel Permeation Chromatography) using, for example, a polystyrene standard sample. For an epoxy resin with a known epoxy equivalent, a numerical value calculated from the product of the epoxy equivalent and the number of epoxy functional groups can also be used.

[0046] Examples of the epoxy resin include bisphenol type epoxy resins and amine type epoxy resins.

[0047] Examples of the bisphenol type epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, or their halogenated, alkyl-substituted, or hydrogenated products. Specific examples of such epoxy resins are as follows.

[0048] Commercially available products of bisphenol A type epoxy resin include "jER (registered trademark)" 825, "jER (registered trademark)" 827, "jER (registered trademark)" 828 (all manufactured by Mitsubishi Chemical Corporation), "EPICLON (registered trademark)" 840, "EPICLON (registered trademark)" 850 (all manufactured by DIC Corporation), "Epoto (registered trademark)" YD-128, "Epoto (registered trademark)" YD-8125, "Epoto (registered trademark)" YD-825GS (manufactured by Nippon Steel Chemical & Material Co., Ltd.), "DER (registered trademark)" 331, "DER (registered trademark)" 332 (all manufactured by Dow Chemical Company), etc.

[0049] Examples of commercially available bisphenol F type epoxy resins include, for example, "jER (registered trademark)" 806, "jER (registered trademark)" 807, "jER (registered trademark)" 4004P (manufactured by Mitsubishi Chemical Corporation), "EPICLON (registered trademark)" 830 (manufactured by DIC Corporation), "Epotoate (registered trademark)" YD-170, "Epotoate (registered trademark)" YDF-8170C, "Epotoate (registered trademark)" YDF-870GS (manufactured by Nippon Steel Chemical & Material Co., Ltd.), and the like.

[0050] Examples of commercially available bisphenol AD type epoxy resins include, for example, EPOX-MK R710, EPOX-MK R1710 (manufactured by Printteck Co., Ltd.), and the like.

[0051] Examples of amine type epoxy resins include, for example, tetraglycidyl diaminodiphenylmethane, tetraglycidyl diaminodiphenylsulfone, triglycidyl aminophenol, triglycidyl aminocresol, diglycidylaniline, diglycidyl toluidine, tetraglycidyl xylylenediamine, or halogen, alkyl-substituted products, hydrogenated products, etc. thereof. Specific examples of such epoxy resins include the following.

[0052] Examples of commercially available tetraglycidyl diaminodiphenylmethane include "Sumiepoxy (registered trademark)" ELM434 (manufactured by Sumitomo Chemical Co., Ltd.), YH434L (manufactured by Nippon Steel Chemical & Material Co., Ltd.), "jER (registered trademark)" 604 (manufactured by Mitsubishi Chemical Corporation), "Araldite (registered trademark)" MY720, "Araldite (registered trademark)" MY721 (manufactured by Huntsman Advanced Materials), and the like.

[0053] Examples of commercially available tetraglycidyl diaminodiphenylsulfone include TG3DAS (manufactured by Mitsui Chemicals Fine Co., Ltd.), and the like.

[0054] Examples of commercially available triglycidyl aminophenol or triglycidyl aminocresol include "Sumiepoxy (registered trademark)" ELM100, "Sumiepoxy (registered trademark)" ELM120 (both manufactured by Sumitomo Chemical Co., Ltd.), "Araldite (registered trademark)" MY0500, "Araldite (registered trademark)" MY0510, "Araldite (registered trademark)" MY0600 (all manufactured by Huntsman Advanced Materials), "jER (registered trademark)" 630 (manufactured by Mitsubishi Chemical Corporation), and the like.

[0055] Examples of commercially available diglycidylaniline include GAN (manufactured by Nippon Kayaku Co., Ltd.), PxGAN (manufactured by Toray Fine Chemical Co., Ltd.), and the like.

[0056] Examples of commercially available diglycidyl toluidine include GOT (manufactured by Nippon Kayaku Co., Ltd.), and the like.

[0057] Examples of commercially available tetraglycidyl xylylenediamine and its hydrogenated products include "TETRAD (registered trademark)"-X, "TETRAD (registered trademark)"-C (both manufactured by Mitsubishi Gas Chemical Company, Inc.), and the like.

[0058] Among them, tetraglycidyl diaminodiphenylmethane and triglycidyl diaminophenol are preferably used in terms of having both high elastic modulus and high heat resistance.

[0059] The epoxy resin composition used in the present invention essentially contains [B] an epoxy resin curing agent having at least two isocyanate groups in the molecule (hereinafter sometimes referred to as component [B]). Such isocyanate groups mainly react with the oxirane groups of component [A] to form bonding points of the oxazolidone ring, thereby exhibiting high heat resistance. Among them, in order to provide higher heat resistance, it is preferable that component [B] contains an aromatic structure.

[0060] Examples of the component [B] include aliphatic isocyanates such as ethylene diisocyanate, trimethylene diisocyanate, dodecamethylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, propylene-1,2-diisocyanate, 2,3-dimethyltetramethylene diisocyanate, butylene-1,2-diisocyanate, butylene-1,3-diisocyanate, 1,4-diisocyanate hexane, cyclopentene-1,3-diisocyanate, isophorone diisocyanate, 1,2,3,4-tetraisocyanate butane, butane-1,2,3-triisocyanate, α,α,α’,α’-tetramethylxylylene diisocyanate; aromatic isocyanates such as p-phenylene diisocyanate, 1-methylphenylene-2,4-diisocyanate, naphthalene-1,4-diisocyanate, tolylene diisocyanate, diphenyl-4,4-diisocyanate, benzene-1,2,4-triisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate (MDI), diphenylpropane diisocyanate, tetramethylene xylylene diisocyanate, polymethylene polyphenyl polyisocyanate; aliphatic isocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, hexamethylene diisocyanate; alicyclic isocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylene bis(4-cyclohexyl isocyanate), isopropylidene dicyclohexyl diisocyanate; and those having a structure in which these are linked with a methylene group or the like. These polyisocyanate compounds and the like may be used alone or in admixture of two or more kinds.

[0061] Examples of commercially available aliphatic isocyanates include HDI (manufactured by Tosoh Corporation), "Duránate (registered trademark)" D101, "Duránate (registered trademark)" D201 (manufactured by Asahi Kasei Corporation), and the like.

[0062] Examples of commercially available aromatic isocyanates include "Lupranate®" MS, "Lupranate®" MI, "Lupranate®" M20S, "Lupranate®" M11S, "Lupranate®" M5S, "Lupranate®" T-80, "Lupranate®" MM-103, "Lupranate®" MM-102, "Lupranate®" MM-301 (manufactured by BASF INOAC Polyurethane Co., Ltd.), "Millionate®" MT, "Millionate®" MT-F, "Millionate®" MT-NBP, "Millionate®" NM, "Millionate®" MR-100, "Millionate®" MR-200, "Millionate®" MR-400, "Coronate®" T-80, "Coronate®" T-65, "Coronate®" T-100 (manufactured by Tosoh Corporation), "Cosmonate®" PH, "Cosmonate®" M-50, "Cosmonate®" T-80 (manufactured by Mitsui Chemicals Fine Co., Ltd.), and the like.

[0063] Examples of commercially available alicyclic isocyanates include "Takenate®" 600, "Fortimo®" 1,4-H6XDI (manufactured by Mitsui Chemicals, Inc.), and the like.

[0064] It is also possible to incorporate these epoxy resins and epoxy resin curing agents, or substances obtained by pre-reacting a part of them, into the composition. This method may be effective for viscosity adjustment and improvement of storage stability.

[0065] The epoxy resin composition used in the present invention must contain a [C] catalyst. Such a catalyst is composed of a compound that can promote the curing reaction between the oxirane group of [A] and the isocyanate group of [B]. By including such a catalyst, excellent productivity can be achieved, and a highly active and highly selective oxazolidone cyclization reaction can proceed, enabling the expression of well-balanced mechanical properties.

[0066] The catalyst used in the present invention is not particularly limited, but preferably a basic catalyst, more preferably amines or their derivatives or ammonium salts, imidazoles or their derivatives or imidazolium salts are used. These catalysts may be used alone or in combination of two or more.

[0067] When the molding material of the present invention is cured while raising the temperature from 30 °C at a rate of 10 °C / min, it is preferable that a specific degree of cure X at which the absorbance ratio Da / (Da+Db) at the degree of cure X is in the range of 0.4 to 1 exists in the range of 85 to 95%. That is, when cured while raising the temperature from 30 °C at a rate of 10 °C / min, it is preferable that the absorbance ratio Da / (Da+Db) is in the range of 0.4 to 1 at any degree of cure X in the range of 85 to 95% (for example, the degree of cure of 90%).

[0068] The absorbance ratio described here means a value calculated by the absorbance ratio Da / (Da+Db) from the absorbance Da of the absorption caused by the C=O double bond of the carboxyl group of the oxazolidone ring and the absorbance Db of the absorption caused by the C=O double bond of the carboxyl group of the isocyanurate ring of the cured product of the epoxy resin composition, using FT-IR of Attenuated Total Reflection (total reflection measurement method, hereinafter sometimes simply referred to as "ATR method"). For example, when measured by FT-IR (ATR method) with a resolution of 4 cm -1 , and the number of integrations is 32 times, the absorbance of the absorption near 1760 cm -1 is taken as Da, and the absorbance of the absorption near 1710 cm -1 is taken as Db, and it can be calculated therefrom.

[0069] The absorbance ratio Da / (Da + Db) at the specific degree of cure X is preferably in the range of 0.4 to 1, more preferably in the range of 0.5 to 1, and even more preferably in the range of 0.7 to 1. By this, while maintaining heat resistance, a structure with few crosslinking points is formed, and it becomes easier to obtain a cured product with high strength and high toughness. Note that the closer the absorbance ratio Da / (Da + Db) is to 1, the more preferable it is as it tends to have a low degree of crosslinking and excellent heat resistance. As means for setting the absorbance ratio Da / (Da + Db) within the above range, for example, methods such as increasing the content of component [A] and raising the curing temperature can be mentioned.

[0070] When the epoxy resin composition used in the present invention is cured while increasing the temperature from 30°C at a rate of 10°C / min, it is preferable that a specific degree of cure Y exists in the range of 15 to 25% such that the absorbance ratio Da / (Da + Db) at the degree of cure Y is in the range of 0.01 to 1. As means for setting the degree of cure Y within the above range, for example, methods such as increasing the content of component [A] and raising the curing temperature can be mentioned. That is, when cured while increasing the temperature from 30°C at a rate of 10°C / min, it is preferable that the absorbance ratio Da / (Da + Db) is in the range of 0.01 to 1 at any degree of cure Y in the range of 15 to 25% (for example, a degree of cure of 20%).

[0071] When the absorbance ratio Da / (Da + Db) at the specific degree of cure Y is in the range of 0.01 to 1, preferably in the range of 0.05 to 1, and more preferably in the range of 0.1 to 1, it becomes possible to suppress reactions that tend to increase the number of crosslinking points occurring earlier, and the resulting fiber-reinforced composite material is less likely to become brittle. Also, since significant thickening at the initial stage of curing can be avoided, the surface quality is further improved.

[0072] The second preferred embodiment of the molding material of the present invention can exhibit high flexural strength in the resulting fiber-reinforced composite material by using a combination of specific glass fibers and an epoxy resin composition. Generally, the flexural strength is a value calculated from the relationship between strain and stress when a rectangular test piece is placed horizontally, both ends of the test piece are supported, and the central part is compressed with a indenter, and represents the stress at which cracks or fractures occur with respect to the flexural load. When a flexural load is applied to a fiber-reinforced composite material, the locations where fracture occurs include the interface between the fiber and the resin or inside the resin. If the interface adhesion between the fiber and the resin is strong or the resin is brittle, fracture occurs inside the resin (cohesive fracture). On the contrary, if the interface adhesion between the fiber and the resin is low or the resin is strong, fracture occurs at the interface between the fiber and the resin (interface fracture). That is, the flexural strength can be an index representing both the interface adhesion between the fiber and the resin and the strength of the resin itself.

[0073] The second preferred embodiment of the molding material of the present invention has excellent adhesiveness at the interface between the glass fiber and the epoxy resin composition, and the epoxy resin composition itself has high flexural strength. Therefore, in a flexural test using strip-shaped test pieces (length 60 mm, width 10 mm, thickness 2 mm) with a curing degree in the range of 85 to 95% (for example, a curing degree of 90%), the flexural strength is preferably 250 MPa or more, more preferably 260 MPa or more, and even more preferably 270 MPa or more. The upper limit value of the above flexural strength is not particularly limited, but is, for example, 1000 MPa. Therefore, the molding material of the present invention has the above flexural strength, for example, 250 to 1000 MPa, 260 to 1000 MPa, 270 to 1000 MPa, etc. As means for setting the flexural strength within the above range, for example, methods such as changing the type of silane coupling agent, the concentration of the silane coupling agent solution, and the immersion time in the silane coupling agent solution, and using those having an aromatic structure as component [A] and component [B] can be mentioned.

[0074] Moreover, in the second preferred embodiment of the molding material of the present invention, since both the glass fiber and the epoxy resin composition have low water absorption, it is possible to suppress a decrease in flexural strength before and after water absorption. The retention rate of the flexural strength obtained from a flexural test performed after immersing a strip-shaped test piece (length: 60 mm, width: 10 mm, thickness: 2 mm) having a degree of cure in the range of 85 to 95% (for example, a degree of cure of 90%) in a constant temperature water bath at 98°C for 48 hours is preferably 75% or more, more preferably 80% or more, and even more preferably 85% or more. Since the retention rate of the flexural strength after water absorption is excellent, it can be suitably used for applications such as blades for wind power generation that are used outdoors for a long time.

[0075] In addition, the flexural test in the second preferred embodiment of the molding material of the present invention shall be performed in accordance with JIS K7171-1994 except that the length of the test piece is 60 mm and the thickness is 2 mm.

[0076] The excellent adhesiveness at the interface between the glass fiber and the epoxy resin composition in the second preferred embodiment of the molding material of the present invention can also be evaluated by the amount of resin adhered to the surface of the glass fiber exposed on the fracture surface of the test piece after the flexural test. When the adhesiveness at the interface between the glass fiber and the epoxy resin composition is excellent, the failure mode in the flexural test becomes cohesive failure instead of interfacial failure, and a large amount of resin adheres to the surface of the glass fiber exposed on the fracture surface of the test piece after the flexural test. On the other hand, when the adhesiveness at the interface between the glass fiber and the epoxy resin composition is insufficient, the failure mode in the flexural test becomes interfacial failure instead of cohesive failure, and the amount of resin adhering to the surface of the glass fiber exposed on the fracture surface of the test piece after the flexural test is small.

[0077] In the second preferred embodiment of the molding material of the present invention, the resin adhesion amount on the exposed glass fiber surface of the fracture surface of the test piece after the bending test (conforming to JIS K7171-1994) can be determined by calculating the area ratio of the portion displayed in white when silicon element is displayed in white and carbon element is displayed in black in the elemental mapping image obtained by observing the entire fracture surface of the test piece with a scanning electron microscope - energy dispersive X-ray spectrometer (SEM-EDX) using image analysis software (Media Cybernetics Image-Pro Plus Ver3.0). The larger the area ratio of the silicon element, the more the silicon element on the glass fiber surface is detected, which means that the glass fiber surface is exposed and no resin is attached. Note that the "entire fracture surface" of the observed test piece refers to observing both the fracture surfaces of test piece 1 and test piece 2 when the test piece breaks and is divided into test piece 1 and test piece 2 (corresponding to a width of 10 mm × thickness of 4 mm).

[0078] When determining the resin adhesion amount on the exposed glass fiber surface of the fracture surface of the test piece after the bending test (conforming to JIS K7171-1994) in the second preferred embodiment of the molding material of the present invention, the following (Formula 1) can be used. S1 = S / (Vf / 100) ··· (Formula 1) S1: Area ratio of silicon element on the glass fiber surface S: Area ratio of silicon element of the entire fracture surface Vf: Fiber volume content (%) of the glass fiber reinforced composite material.

[0079] For example, when the Vf of the glass fiber reinforced composite material is 18% and the area ratio of the silicon element on the entire fracture surface is 0.15, the area ratio of the silicon element on the glass fiber surface is S1 = 0.15 / (18 / 100) = 0.83. Since the second aspect of the molding material of the present invention is excellent in the adhesiveness between the glass fiber and the epoxy resin composition, when observing the fracture surface after the bending test (conforming to JIS K7171-1994) with a scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDX), the area ratio (S1) of the silicon element on the glass fiber surface in the obtained elemental mapping image is preferably in the range of 0 to 0.90, more preferably in the range of 0 to 0.85, and even more preferably in the range of 0 to 0.80. As means for making the area ratio (S1) of the silicon element fall within the above range, for example, methods such as changing the type of silane coupling agent, the concentration of the silane coupling agent solution, and the immersion time in the silane coupling agent solution can be mentioned.

[0080] The first aspect of the fiber-reinforced composite material of the present invention is obtained by curing the molding material of the present invention.

[0081] The second aspect of the fiber-reinforced composite material of the present invention is composed of a cured epoxy resin containing 1 mmol / g or more of an oxazolidone ring and carbon fibers satisfying the following conditions [a] and [b]. [a] Having a substantially circular cross-section [b] The average fiber diameter is in the range of 4.0 to 8.0 μm.

[0082] The third aspect of the fiber-reinforced composite material of the present invention includes a cured epoxy resin containing 1 mmol / g or more of an oxazolidone ring and glass fibers having surface functional groups covalently bonded to isocyanate groups in the cured epoxy resin, and the area ratio (S1) of the silicon element on the glass fiber surface in the elemental mapping image obtained when observing the fracture surface after the bending test (conforming to JIS K7171-1994) described in the specification with a scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDX) is in the range of 0 to 0.9.

[0083] The epoxy resin composition used in the present invention is characterized by a small initial increase in viscosity, a long injectable time, and the ability to cure in a short time. Therefore, it is most suitable for the RTM method that keeps the mold temperature constant from injection to demolding. However, it is applicable to the RTM method that raises the temperature and cures after resin injection, as well as all molding methods using liquid thermosetting resins, such as hand lay-up, pultrusion, and filament winding, other than the RTM method. It is effective in shortening the molding time and improving the impregnation property to the reinforcing fiber in any molding method. As other molding methods, there are a vacuum bag method in which a flexible mold for applying pressure is covered and airtight sealed after impregnating a reinforcing fiber base material with varnish and stacking and molding, and a press method in which a molding material (for example, sheet molding compound (SMC)) in which an epoxy resin composition containing a reinforcing fiber in advance is formed into a sheet shape is compression molded with a mold, etc.

[0084] As a method for manufacturing the molding material and the fiber-reinforced composite material of the present invention, the above-mentioned RTM method will be described in more detail as an example. A method of manufacturing a molding material by injecting and impregnating a heated epoxy resin composition into a base material made of reinforcing fibers disposed in a heated mold, and manufacturing a fiber-reinforced composite material by curing it in the mold can be mentioned.

[0085] The temperature for heating the epoxy resin composition is determined from the relationship between the initial viscosity and the viscosity increase of the epoxy resin composition in terms of the impregnation property to the base material made of reinforcing fibers. Specifically, the temperature for heating the epoxy resin composition is preferably 30 to 100°C, more preferably 40 to 80°C.

[0086] Incidentally, the molding temperature (heating and curing temperature) of the epoxy resin composition is preferably in the range of 100 to 200°C, more preferably in the range of 120 to 180°C. By being in the above range, while avoiding significant thickening in the initial stage of curing, the time required for curing can be shortened, and at the same time, by relaxing the thermal shrinkage after demolding, a fiber-reinforced composite material with good surface quality can be obtained. Further, since the absorbance ratio Da / (Da+Db) of the cured product of the epoxy resin composition becomes high, a fiber-reinforced composite material excellent in the balance between toughness and heat resistance can be obtained.

[0087] Also, in such a molding method, it is preferable to use a mold having a plurality of injection ports and select appropriate conditions according to the fiber-reinforced composite material to be obtained, such as injecting the epoxy resin composition simultaneously from the plurality of injection ports or sequentially with a time difference. This is because it has the freedom to cope with molded products of various shapes and sizes. There is no limitation on the number and shape of such injection ports, but in order to enable injection in a short time, the more injection ports, the better, and the arrangement is preferably at a position where the flow length of the resin can be shortened according to the shape of the molded product.

[0088] The injection pressure when injecting the epoxy resin composition is usually 0.1 to 1.0 MPa, and preferably 0.1 to 0.6 MPa from the viewpoints of injection time and economic efficiency of the equipment. Also, the VaRTM (Vacuum-Assisted Resin Transfer Molding) method of evacuating the inside of the mold and injecting the epoxy resin composition can also be used. Even when performing pressure injection, it is preferable to evacuate the inside of the mold before injecting the epoxy resin composition to suppress the generation of voids.

[0089] When determining the resin adhesion amount on the exposed glass fiber surface of the fracture surface of the test piece after the bending test (in accordance with JIS K7171-1994) in the third aspect of the fiber-reinforced composite material of the present invention, the above (Formula 1) can also be used. Since the third aspect of the fiber-reinforced composite material of the present invention is excellent in the adhesiveness between the glass fiber and the epoxy resin composition, the area ratio (S1) of the silicon element on the glass fiber surface is 0 to 0.90, preferably 0 to 0.85, and more preferably 0 to 0.80. The means for setting the area ratio (S1) of the silicon element within the above range is as described above.

[0090] The fiber-reinforced composite material of the present invention preferably has an absorbance ratio Da / (Da + Db) in the range of 0.4 to 1, more preferably in the range of 0.5 to 1, and even more preferably in the range of 0.7 to 1. When the absorbance ratio Da / (Da + Db) is lower than 0.4, the number of cross-linking points becomes too large, resulting in a decrease in strength and toughness. Note that the closer the absorbance ratio Da / (Da + Db) is to 1, the more preferably it has a tendency of low cross-linking and excellent heat resistance.

[0091] Here, the absorbance ratio is specified by calculating the absorbance ratio = Da / (Da + Db) from the absorbance Da of the absorption caused by the C=O double bond of the carboxyl group of the oxazolidone ring and the absorbance Db of the absorption caused by the C=O double bond of the carboxyl group of the isocyanurate ring in FT-IR (ATR method). Further, the absorbance ratio Da / (Da + Db) of the fiber-reinforced composite material obtained by curing a molding material containing an epoxy resin composition and reinforcing fibers to a specific degree of cure is substantially equal to the absorbance ratio Da / (Da + Db) of the cured product of the epoxy resin composition at the specific degree of cure. In the present invention, the absorbance ratio of the cured product of the epoxy resin composition at a specific degree of cure may be regarded as the absorbance ratio of the fiber-reinforced composite material at the specific degree of cure.

[0092] In the present invention, it is assumed that the degree of cure of the fiber-reinforced composite material obtained by curing a molding material containing an epoxy resin composition and reinforcing fibers is the same value as the degree of cure of the cured product of the epoxy resin composition contained in the fiber-reinforced composite material.

[0093] In order for the fiber reinforced composite material of the present invention to have a high specific strength or specific modulus, its fiber volume fraction Vf is preferably in the range of 40 to 85% when the reinforcing fiber is carbon fiber, and more preferably in the range of 45 to 85%. Also, when the reinforcing fiber is glass fiber, it is preferably in the range of 15 to 85%, and more preferably in the range of 20 to 80%. The fiber volume fraction Vf of the fiber reinforced composite material referred to here is a value defined and measured as follows in accordance with ASTM D3171:1999, and refers to a state after an epoxy resin composition is injected into a substrate made of reinforcing fiber and cured. That is, the fiber volume fraction Vf of the fiber reinforced composite material can be calculated from the thickness h of the fiber reinforced composite material using the following (Equation 2). Vf(%)=(Af×N) / (ρf×h) / 10 (Formula 2) Af: 1 sheet of reinforced fiber substrate 1m 2 Mass per unit (g / m 2 ) N: Number of layers of the base material made of reinforcing fiber (sheets) ρf: Density of reinforcing fiber (g / cm 3 ) h: Thickness of the fiber-reinforced composite material (test piece) (mm).

[0094] In addition, from the fiber-reinforced composite material, 1 base material made of reinforcing fibers × 1 m 2 In order to specify the mass Af per unit area, the number of layers N of the substrate made of reinforcing fibers, and the density ρf of the reinforcing fibers, the substrate made of reinforcing fibers may be separated and taken out from the fiber-reinforced composite material by the combustion method, nitric acid decomposition method, or sulfuric acid decomposition method based on JIS K 7075: 1991. The density of the reinforcing fibers used in this case is the value measured based on JIS R 7603: 1999.

[0095] The thickness h of the fiber-reinforced composite material is preferably measured using a micrometer specified in JIS B 7502:1994 or one with an accuracy equal to or higher than that, as described in JIS K 7072:1991. When the fiber-reinforced composite material has a complex shape and it is difficult to measure, a sample (a sample having a certain shape and size for measurement) may be cut out from the fiber-reinforced composite material and measured.

[0096] Also, as another method for calculating the fiber volume fraction (Vf), there is a method of heating the fiber-reinforced composite material in an electric furnace or the like to burn off organic substances such as the matrix resin. For example, a few grams of test pieces are cut out from the fiber-reinforced composite material, and after measuring their mass, the test pieces are heated in an electric furnace heated to 500°C for 1 hour to burn off organic substances such as the matrix resin, cooled to room temperature, and then the mass of the remaining reinforcing fibers is measured. The ratio of the mass of the reinforcing fibers to the mass of the sample before burning off organic substances such as the matrix resin is measured, the volumes of each are obtained from the density of the matrix resin and the density of the glass fibers, and the volume fraction of the reinforcing fibers can be measured.

[0097] As one of the preferred forms of the fiber-reinforced composite material of the present invention, a single ply can be mentioned. Also, as another preferred form, a sandwich structure in which single-ply fiber-reinforced composite materials are arranged on both sides of a core material, a hollow structure in which the periphery of a single-ply structure is covered, a so-called canape structure in which a single-ply fiber-reinforced composite material is arranged on one side of a core material, etc. can be mentioned.

[0098] As the core material of the sandwich structure and the canape structure, a honeycomb core made of aluminum or aramid, a foam core made of polyurethane, polystyrene, polyamide, polyimide, polyvinyl chloride, phenolic resin, acrylic resin, epoxy resin, etc. as materials, wood such as balsa, etc. can be mentioned. Among them, as the core material, a foam core is preferably used because a lightweight fiber-reinforced composite material can be obtained.

[0099] The second and third aspects of the fiber-reinforced composite material of the present invention include a cured epoxy resin containing 1 mmol / g or more of oxazolidone rings. The content of oxazolidone rings in the cured epoxy resin is preferably 1.5 mmol / g or more, more preferably 2 mmol / g or more. The upper limit of the content is not particularly limited, but is usually about 10 mmol / g. When the content is within the above range, an excellent balance of mechanical properties is exhibited. Such a content of oxazolidone rings can be calculated, for example, from the results of infrared spectroscopy (IR). As means for setting the content of oxazolidone rings within the above range, for example, methods such as increasing the content of component [A] and raising the curing temperature can be mentioned.

[0100] In the present invention, only by combining the above carbon fiber and the above epoxy resin composition, a fiber-reinforced composite material excellent in impact resistance and tensile strength can be obtained. The isocyanate groups contained in such an epoxy resin composition have high reactivity with functional groups such as hydroxyl groups, and efficiently react with functional groups such as hydroxyl groups on the surface of carbon fibers when the epoxy resin composition cures. That is, even when carbon fibers with usually low adhesiveness are used, good adhesiveness with the matrix resin is exhibited, and it becomes possible to obtain a fiber-reinforced composite material in which impact resistance and tensile strength are compatible at a high level. Further, only by combining the above glass fiber and the above epoxy resin composition, a fiber-reinforced composite material excellent in flexural strength, impact resistance, and weather resistance can be obtained. The isocyanate groups contained in such an epoxy resin composition have high reactivity with functional groups such as amino groups, and efficiently react with surface functional groups present on the surface of glass fibers when the epoxy resin composition cures. That is, appropriate adhesiveness between the glass fiber and the matrix resin is exhibited, and it becomes possible to obtain a fiber-reinforced composite material excellent in flexural strength, impact resistance, and weather resistance.

Examples

[0101] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples.

[0102] Examples 1 to 4. Reference Examples 5~7. For Comparative Examples 1 to 6, it is as described below (including Tables 1 and 2).

[0103] (1) Measurement of the surface specific oxygen concentration O / C of carbon fibers The surface specific oxygen concentration O / C was determined by X-ray photoelectron spectroscopy according to the following procedure.

[0104] First, from the carbon fiber bundle to be measured, after removing sizing agents and the like with a solvent, it was cut to about 5 mm, spread and arranged on a stainless-steel sample support table, and then measured under the following conditions. · Photoelectron escape angle: 90 degrees · X-ray source: MgKα1,2 · Vacuum degree inside the sample chamber: 1×10 -8 Torr Next, for the correction of the peak associated with charging during measurement, the binding energy value B.E. of the main peak of C 1S was adjusted to 284.6 eV.

[0105] Then, the C 1s peak area [O 1s was obtained by drawing a straight baseline in the range of 282 to 296 eV, and the O 1s peak area [C 1s was obtained by drawing a straight baseline in the range of 528 to 540 eV.

[0106] The surface specific oxygen concentration O / C was determined by the following formula from the ratio of the above O 1s peak area [O 1s , C 1s peak area [C 1s , and the sensitivity correction value specific to the apparatus. O / C = ([O 1s / [C 1s ) / (sensitivity correction value) Here, ESCA-750 manufactured by Shimadzu Corporation was used as the measuring apparatus, and the sensitivity correction value specific to the apparatus was set to 2.85. The number of test samples n = 3, and the average value was adopted.

[0107] (2) Measurement of the average fiber diameter of carbon fibers The carbon fiber bundles were embedded with an epoxy resin for embedding, polished in a direction perpendicular to the fibers using sandpaper, and then the cross-section was observed with an optical microscope at a magnification of 1000 times. Twenty single filaments were randomly selected from the field of view, their major axis R and minor axis r were measured, the average value of each was calculated, and {(average value of R) + (average value of r)} / 2 was taken as the average fiber diameter. Also, when (average value of r) / (average value of R) exceeded 0.9, it was judged to be substantially circular.

[0108] (3) Preparation of carbon fibers Carbon fibers [I] to [V] were prepared by the following production method.

[0109] <Carbon fiber [I]> Using a copolymer composed of 99.4 mol% acrylonitrile and 0.6 mol% methacrylic acid, an acrylic precursor fiber with a single fiber fineness of 0.08 tex and 12,000 filaments was obtained by the dry-wet spinning method.

[0110] This precursor fiber was heated in air at 240 - 280 °C with a draw ratio of 1.05 to convert it into a flame-resistant fiber. Then, the heating rate in the temperature range of 300 - 900 °C in a nitrogen atmosphere was set to 200 °C / min, heated with a draw ratio of 1.10, and then fired up to 1400 °C to promote carbonization. The areal density of the obtained carbon fiber was 0.50 g / m, and the density was 1.80 g / cm 3 It was.

[0111] Next, it was electrolytically oxidized at an electric charge of 3 C / g·cell using a 1.0 mol / L aqueous ammonium hydrogen carbonate solution as the electrolyte. Then, the carbon fiber after this electrolytic oxidation treatment was washed with water and dried in air at 150 °C to obtain carbon fiber [I].

[0112] The surface specific oxygen concentration O / C of carbon fiber [I] was 0.08, the average fiber diameter was 5.5 μm, and the cross-sectional shape had r / R of 0.95 and was substantially circular.

[0113] <Carbon fiber [II]> Carbon fiber [II] was obtained under the same conditions as carbon fiber [I], except that the electric charge during the electrolytic oxidation treatment was 30 C / g·cell.

[0114] The surface specific oxygen concentration O / C of carbon fiber [II] was 0.18, the average fiber diameter was 5.5 μm, the cross-sectional shape had r / R of 0.95 and was substantially circular.

[0115] <Carbon fiber [III]> Carbon fiber [III] was obtained under the same conditions as carbon fiber [I], except that the amount of electricity during the electrolytic oxidation treatment was 1 C / g·tank.

[0116] The surface specific oxygen concentration O / C of carbon fiber [III] was 0.03, the average fiber diameter was 5.5 μm, the cross-sectional shape had r / R of 0.95 and was substantially circular.

[0117] <Carbon fiber [IV]> Carbon fiber [IV] was obtained under the same conditions as carbon fiber [I], except that the amount of electricity during the electrolytic oxidation treatment was 100 C / g·tank.

[0118] The surface specific oxygen concentration O / C of carbon fiber [IV] was 0.22, the average fiber diameter was 5.5 μm, the cross-sectional shape had r / R of 0.95 and was substantially circular.

[0119] <Carbon fiber [V]> Carbon fiber [V] was obtained under the same conditions as carbon fiber [I], except that the spinning method of the acrylic-based precursor fiber was changed to the wet spinning method and the fineness of the single fiber of the obtained acrylic-based precursor fiber was 0.09 tex. The basis weight of the obtained carbon fiber was 0.50 g / m, and the density was 1.80 g / cm 3 It was.

[0120] The surface specific oxygen concentration O / C of carbon fiber [V] was 0.05, the average fiber diameter was 5.4 μm, and the cross-sectional shape was flat with r / R of 0.8.

[0121] (4) Fabrication of carbon fiber fabric The carbon fibers obtained above were aligned as warp threads to form a unidirectional sheet-like reinforcing fiber bundle group. Glass fiber ECE225 1 / 0 1Z (manufactured by Nitto Boseki Co., Ltd.) was used as the weft thread, and it was arranged at a density of 3 threads / cm in a direction orthogonal to the unidirectional sheet-like reinforcing fiber bundle group. Using a loom, the warp threads and the weft threads were woven so as to cross each other, and a carbon fiber fabric with a basis weight of 190 g / m 2 was obtained, in which the carbon fibers were substantially arranged in one direction.

[0122] (5) Production of non-woven fabric A non-woven fabric made of “UBESTA” (registered trademark) 3014U (polyamide 12, manufactured by Ube Industries, Ltd.) was produced by the meltblowing method. The basis weight of the obtained non-woven fabric was 7 g / m 2 and the average fiber diameter was 8 μm.

[0123] (6) Production of epoxy resin cured plate After degassing the epoxy resin composition in a vacuum, it was poured into a preheated plate, and an epoxy resin cured plate was produced by raising the temperature from 30°C to a predetermined temperature at a rate of 10°C / min using a dynamic viscoelasticity test apparatus (ATD: manufactured by Alpha Technologies LLC).

[0124] Here, the predetermined temperature is determined by the measurement described in (7) below.

[0125] (7) Measurement of the degree of cure of the epoxy resin cured plate 5 mg of the epoxy resin composition was sampled, and using a differential scanning calorimetry apparatus (DSC2910: manufactured by TA Instruments), the temperature was raised from 30°C to 350°C at a rate of 10°C / min for measurement to obtain an exothermic curve, and the total exothermic amount QT of the thermosetting resin was calculated by integrating the exothermic peak. When peaks of exotherm or endotherm due to decomposition reaction or the like were observed, the measurement was performed in the temperature range below those peaks.

[0126] 10 mg of the epoxy resin cured board prepared in (6) above was collected, and using a differential scanning calorimeter (DSC2910: manufactured by TA Instruments), the temperature was raised from 30 °C to 350 °C at a heating rate of 10 °C / min for measurement to obtain an exothermic curve, and the residual heat of exotherm QR of the epoxy resin cured product was calculated by integrating the exothermic peak. When peaks of exotherm or endotherm due to decomposition reaction or the like were observed, the measurement was performed in the temperature range below those peaks.

[0127] Here, the degree of cure (%) obtained by DSC was determined by degree of cure (%) = (QT - QR) / QT × 100.

[0128] Also, by this measurement, the temperatures at which the epoxy resin composition reached a specific degree of cure X (in this example, degree of cure 90%) and a specific degree of cure Y (in this example, degree of cure 20%) were calculated.

[0129] (8) Measurement of absorbance ratio at specific degrees of cure X and Y Epoxy resin cured products with specific degrees of cure X (in this example, degree of cure 90%) and specific degree of cure Y (in this example, degree of cure 20%) prepared in (6) above were collected, and FT-IR (ATR method) was performed using an FT-IR apparatus (7000FT-IR: manufactured by Varian). The measurement conditions were a resolution of 4 cm -1 and the number of accumulations was 32 times.

[0130] The absorbance ratio Da / (Da + Db) was calculated from the absorbance Da of the absorption around 1760 cm -1 due to the C=O double bond of the carboxyl group of the oxazolidone ring and the absorbance Db of the absorption around 1710 cm -1 due to the C=O double bond of the carboxyl group of the isocyanurate ring.

[0131] (9) Preparation of epoxy resin composition Resin compositions [i] to [iii] were prepared by the following production method. The raw materials used here are as shown below.

[0132] [A] An epoxy resin having at least two oxirane groups in the molecule · "jER (registered trademark)" 828 (bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation) [B] An epoxy resin curing agent having at least two isocyanate groups in the molecule · "Lupranate (registered trademark)" M20S (manufactured by BASF INOAC Polyurethane Co., Ltd.) [C] Catalyst · "DBU (registered trademark)" (1,8 - diazabicyclo[5.4.0]undec - 7 - ene, manufactured by San Apro Ltd.) · TMAB (tetramethylammonium bromide, manufactured by Tokyo Chemical Industry Co., Ltd.).

[0133] Epoxy resins other than [A] · 4 - tert - butylphenyl glycidyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.) Epoxy resin curing agents having isocyanate groups other than [B] · 2 - phenylethyl isocyanate (manufactured by Tokyo Chemical Industry Co., Ltd.) Epoxy resin curing agents other than [B] · 3,3’ - DAS (3,3’ - diaminodiphenyl sulfone, manufactured by Mitsui Chemicals Fine Co., Ltd.) · HN - 5500 (methylhexahydrophthalic anhydride, manufactured by Hitachi Chemical Co., Ltd.).

[0134] <Resin composition [i]> 100 parts by mass of "jER (registered trademark)" 828 and 4 parts by mass of "DBU (registered trademark)" were kneaded to obtain a transparent viscous liquid. Then, 72 parts by mass of "Lupranate (registered trademark)" M20S was added and further kneaded to obtain an epoxy resin composition.

[0135] When the resin composition [i] was cured while raising the temperature from 30 °C at a rate of 10 °C / min, the absorbance ratio Da / (Da + Db) at a curing degree of 20% was 0.13, and the absorbance ratio Da / (Da + Db) at a curing degree of 90% was 0.71.

[0136] <Resin composition [ii]> 100 parts by mass of 4-tert-butylphenyl glycidyl ether and 4 parts by mass of "DBU (registered trademark)" were kneaded to obtain a transparent viscous liquid. Then, 66 parts by mass of "Lupranate (registered trademark)" M20S was added and further kneaded to obtain an epoxy resin composition.

[0137] When the resin composition [ii] was cured while heating from 30 °C at a rate of 10 °C / min, the absorbance ratio Da / (Da + Db) at a curing degree of 20% was 0.06, and the absorbance ratio Da / (Da + Db) at a curing degree of 90% was 0.19.

[0138] <Resin composition [iii]> 100 parts by mass of "jER (registered trademark)" 828 and 4 parts by mass of "DBU (registered trademark)" were kneaded to obtain a transparent viscous liquid. Then, 78 parts by mass of 2-phenylethyl isocyanate was added and further kneaded to obtain an epoxy resin composition.

[0139] When the resin composition [iii] was cured while heating from 30 °C at a rate of 10 °C / min, the absorbance ratio Da / (Da + Db) at a curing degree of 20% was 0.06, and the absorbance ratio Da / (Da + Db) at a curing degree of 90% was 0.18.

[0140] <Resin composition [iv]> 100 parts by mass of "jER (registered trademark)" 828 and 72 parts by mass of "Lupranate (registered trademark)" M20S were kneaded to obtain an epoxy resin composition.

[0141] The resin composition [iv] was heated from 30 °C at a rate of 10 °C / min, but a cured product with a curing degree of 90% could not be obtained.

[0142] <Resin composition [v]> 100 parts by mass of "jER (registered trademark)" 828 and 33 parts by mass of 3,3'-DAS were kneaded to obtain an epoxy resin composition.

[0143] When the resin composition [v] was cured while heating from 30 °C at a rate of 10 °C / min, the absorbance ratio Da / (Da + Db) at curing degrees of 20% and 90% was 0.

[0144] <Resin composition [vi]> 89 parts by mass of HN-5500 and 6 parts by mass of TMAB were kneaded at 80 °C to obtain a transparent curing agent solution. This was added to 100 parts by mass of “jER (registered trademark)” 828 and further kneaded to obtain an epoxy resin composition.

[0145] When the resin composition [vi] was cured while raising the temperature from 30 °C at a rate of 10 °C / min, the absorbance ratio Da / (Da + Db) at a curing degree of 20% and 90% was 0.

[0146] (10) Production of fiber-reinforced composite material and measurement of compressive strength after impact The carbon fiber fabric obtained above, cut to 395 mm × 395 mm, was placed in a mold having a plate-shaped cavity of 400 mm × 400 mm × 4.8 mm with the carbon fiber direction at 0°. While sandwiching nonwoven fabrics every other sheet, (45° / 0° / -45° / 90°) was repeated 3 times and 12 sheets were laminated. Then, while sandwiching nonwoven fabrics every other sheet, (90° / -45° / 0° / 45°) was repeated 3 times and 12 sheets were laminated and set, and mold clamping was performed with a press device. Next, it was maintained at a predetermined injection temperature, and the pressure was reduced to atmospheric pressure - 0.1 MPa with a vacuum pump, and the epoxy resin composition preheated to a predetermined injection temperature was injected at a pressure of 0.2 MPa. The temperature was raised to a predetermined curing temperature at 5 °C / min, and after a predetermined curing time elapsed, the mold was opened and demolded to obtain a fiber-reinforced composite material.

[0147] Also, for the obtained fiber-reinforced composite material, the compressive strength after impact was measured in accordance with JIS K 7089:1996.

[0148] (11) Production of fiber-reinforced composite material and measurement of tensile fracture strength A mold with a plate-shaped cavity of 400 mm × 400 mm × 1.2 mm was set with a carbon fiber fabric obtained above, cut into 395 mm × 395 mm, with the carbon fiber directions aligned, and six layers were laminated while sandwiching one non-woven fabric at a time. Then, the mold was clamped with a pressing device. Next, it was maintained at a predetermined injection temperature, and the pressure was reduced to atmospheric pressure - 0.1 MPa with a vacuum pump. An epoxy resin composition pre-heated to a predetermined injection temperature was injected at a pressure of 0.2 MPa. The temperature was raised at 5 °C / min to a predetermined curing temperature. After a predetermined curing time elapsed, the mold was opened and demolded to obtain a fiber-reinforced composite material.

[0149] Also, for the obtained fiber-reinforced composite material, the tensile fracture strength was measured in accordance with ASTM D3039.

[0150] (12) Resin impregnation property of reinforcing fibers Regarding the impregnation property in the resin injection process during the production of the fiber-reinforced composite material in (10) above, it was comparatively evaluated in the following three stages based on the void amount in the fiber-reinforced composite material. Those with a void amount in the fiber-reinforced composite material of less than 1% and substantially no voids were rated as "Good", those where no resin non-impregnated part was observed on the appearance of the fiber-reinforced composite material but with a void amount in the fiber-reinforced composite material of 1% or more were rated as "Fair", and those where a resin non-impregnated part was observed on the appearance of the fiber-reinforced composite material were rated as "Bad".

[0151] The void amount in the fiber-reinforced composite material was calculated from the area ratio of voids in the fiber-reinforced composite material by observing a smoothly polished cross-section of the fiber-reinforced composite material with an inclined optical microscope.

[0152] (Examples 1 - 4) Using [I] as the carbon fiber and [i] as the epoxy resin composition, a fiber-reinforced composite material was produced under the curing conditions shown in Table 1. In each case, both the compressive strength after impact and the tensile fracture strength of the obtained fiber-reinforced composite material were excellent. Also, no resin non-impregnated part or voids were observed, and it had excellent impregnation property.

[0153] ( Reference Example 5) A fiber-reinforced composite material was produced in the same manner as in Example 4, except that [II] was used as the carbon fiber. The obtained fiber-reinforced composite material had excellent compressive strength after impact, and the tensile fracture strength was at a satisfactory level. Also, no resin-unimpregnated portions or voids were observed, and the impregnation property was excellent.

[0154] ( Reference Example 6) A fiber-reinforced composite material was produced in the same manner as in Example 4, except that [III] was used as the carbon fiber. The obtained fiber-reinforced composite material had a satisfactory level of compressive strength after impact, and the tensile fracture strength was excellent. Also, no resin-unimpregnated portions or voids were observed, and the impregnation property was excellent. No impregnated portions or voids were observed, and the impregnation property was excellent.

[0155] ( Reference Example 7) A fiber-reinforced composite material was produced in the same manner as in Example 4, except that [IV] was used as the carbon fiber. The obtained fiber-reinforced composite material had excellent compressive strength after impact, and the tensile fracture strength was at a satisfactory level. Also, no resin-unimpregnated portions or voids were observed, and the impregnation property was excellent.

[0156] (Comparative Example 1) A fiber-reinforced composite material was produced in the same manner as in Example 4, except that [V] was used as the carbon fiber. By using carbon fibers with a flat cross-sectional shape, the obtained fiber-reinforced composite material was slightly inferior in compressive strength after impact and was inferior in tensile fracture strength. Also, it took time to inject the resin composition, and voids were observed in the cross-section of the obtained fiber-reinforced composite material.

[0157] (Comparative Example 2) A fiber-reinforced composite material was produced in the same manner as in Example 4, except that [ii] was used as the epoxy resin composition. Since a monofunctional epoxy resin was used, it was significantly inferior in compressive strength after impact and tensile fracture strength. There was also a problem with the impregnation property.

[0158] (Comparative Example 3) A fiber-reinforced composite material was produced in the same manner as in Example 4, except that [iii] was used as the epoxy resin composition. Since a monofunctional isocyanate was used, it was significantly inferior in compressive strength after impact and tensile fracture strength. There were also problems with impregnation.

[0159] (Comparative Example 4) [iv] was used as the epoxy resin composition, but a cured product with a curing degree of 90% could not be obtained under the curing conditions described in Table 2.

[0160] (Comparative Example 5) Using [I] as the carbon fiber and [v] as the epoxy resin composition, a fiber-reinforced composite material was produced under the curing conditions described in Table 1. The resulting fiber-reinforced composite material did not form an oxazolidone ring and was inferior in compressive strength after impact. Also, it took time to inject the resin composition, and voids were observed in the cross-section of the resulting fiber-reinforced composite material.

[0161] (Comparative Example 6) Using [I] as the carbon fiber and [vi] as the epoxy resin composition, a fiber-reinforced composite material was produced under the curing conditions described in Table 1. The resulting fiber-reinforced composite material did not form an oxazolidone ring and was inferior in compressive strength after impact.

[0162]

Table 1

[0163]

Table 2

[0164] Reference Examples 8 to 15 and Comparative Examples 7 to 13 are as described below (including Tables 3 and 4).

[0165] (1) Glass fiber Glass fibers [I] to [VII] were prepared by the following production method.

[0166] (Glass fiber [I]) As the glass fiber substrate, an untreated cloth of KS7781 (manufactured by Nitto Boseki Co., Ltd., basis weight 303 g / m 2 , warp density 58 threads / 25 mm, weft density 53 threads / 25 mm) was prepared and cut into 3 mm lengths.

[0167] <Glass fiber [II]> As the glass fiber substrate, an untreated cloth of KS7781 (manufactured by Nitto Boseki Co., Ltd., basis weight 303 g / m 2 , warp density 58 threads / 25 mm, weft density 53 threads / 25 mm) was prepared and cut into 3 mm lengths. The cut glass fibers were immersed in a methanol solution (1% by mass) of 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KBM-403) as a coupling agent for 7 hours, and then dried in a hot air oven at 110 °C for 5 hours to remove the solvent.

[0168] <Glass fiber [III]> Glass fiber [III] was obtained under the same conditions as Glass fiber [II], except that the coupling agent was 3-aminopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-903).

[0169] <Glass fiber [IV]> Glass fiber [IV] was obtained under the same conditions as Glass fiber [II], except that the coupling agent was 3-mercaptopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-803).

[0170] <Glass fiber [V]> Glass fiber [V] was obtained under the same conditions as Glass fiber [II], except that the coupling agent was 3-trimethoxysilylpropyl succinic anhydride (manufactured by Shin-Etsu Chemical Co., Ltd., trade name X-12-967C).

[0171] <Glass fiber [VI]> Glass fiber [VI] was obtained under the same conditions as Glass fiber [II], except that the coupling agent was vinyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name KBM-1003).

[0172] <Glass fiber [VII]> Glass fiber [VII] was prepared under the same conditions as Glass fiber [II], except that the coupling agent was methyltrimethoxysilane (manufactured by Kanto Chemical Co., Inc.).

[0173] (2) Preparation of epoxy resin cured plate After degassing the epoxy resin composition in vacuo, it was cast onto a preheated plate, and an epoxy resin cured plate was prepared by heating it from 30 °C to a predetermined temperature at a rate of 10 °C / min using a dynamic viscoelasticity testing apparatus (ATD: manufactured by Alpha Technologies LLC).

[0174] Here, the predetermined temperature is determined by the measurement described in (3) below.

[0175] (3) Measurement of the degree of cure of the epoxy resin cured plate 5 mg of the epoxy resin composition was sampled, and using a differential scanning calorimetry apparatus (DSC2910: manufactured by TA Instruments), it was heated from 30 °C to 350 °C at a heating rate of 10 °C / min for heating measurement to obtain an exothermic curve, and the total exothermic amount QT of the thermosetting resin was calculated by integrating the exothermic peak. When peaks of exotherm or endotherm due to decomposition reaction or the like were observed, the measurement was carried out in the temperature range below those peaks.

[0176] 10 mg of the epoxy resin cured plate prepared in (2) above was sampled, and using a differential scanning calorimetry apparatus (DSC2910: manufactured by TA Instruments), it was heated from 30 °C to 350 °C at a heating rate of 10 °C / min for heating measurement to obtain an exothermic curve, and the residual exothermic amount QR of the epoxy resin cured product was calculated by integrating the exothermic peak. When peaks of exotherm or endotherm due to decomposition reaction or the like were observed, the measurement was carried out in the temperature range below those peaks.

[0177] Here, the degree of cure (%) obtained by DSC was determined by degree of cure (%) = (QT - QR) / QT × 100.

[0178] In this example, it was assumed that the degree of curing of the epoxy resin cured plate obtained in this manner was the same as the degree of curing of the fiber-reinforced composite material containing glass fibers in the epoxy resin cured plate.

[0179] Also, by this measurement, the temperatures at which the epoxy resin composition reaches a specific degree of curing X (in this example, a degree of curing of 90%) and a specific degree of curing Y (in this example, a degree of curing of 20%) were calculated.

[0180] (4) Measurement of absorbance ratio at specific degrees of curing X and Y Epoxy resin cured products with specific degrees of curing X (in this example, a degree of curing of 90%) and specific degree of curing Y (in this example, a degree of curing of 20%) prepared in the above (2) were collected, and FT-IR (ATR method) was performed using an FT-IR apparatus (7000FT-IR: manufactured by Varian). The measurement conditions were a resolution of 4 cm -1 and the number of accumulations was 32 times.

[0181] Note that the absorbance ratio Da / (Da + Db) is the absorbance Da of the absorption near 1760 cm -1 due to the C=O double bond of the carboxy group of the oxazolidone ring and the absorbance Db of the absorption near 1710 cm -1 due to the C=O double bond of the carboxy group of the isocyanurate ring.

[0182] In this example, it was assumed that the absorbance ratio at the specific degree of curing of the epoxy resin cured plate obtained in this manner was the same as the absorbance ratio at the specific degree of curing of the fiber-reinforced composite material containing glass fibers in the epoxy resin cured plate.

[0183] (5) Preparation of epoxy resin composition Resin compositions [i] to [vi] were prepared by the following production method. The raw materials used here are as shown below.

[0184] [A] Epoxy resin having at least two oxirane groups in the molecule · “jER (registered trademark)” 828 (bisphenol A type epoxy resin, manufactured by Mitsubishi Chemical Corporation) [B] Epoxy resin curing agent having at least two isocyanate groups in the molecule · "Lupranate (registered trademark)" M20S (manufactured by BASF INOAC Polyurethane Co., Ltd.) [C] Catalyst · "DBU (registered trademark)" (1,8-diazabicyclo[5.4.0]undec-7-ene, manufactured by San-Apro Ltd.) · TMAB (tetramethylammonium bromide, manufactured by Tokyo Chemical Industry Co., Ltd.).

[0185] Epoxy resins other than [A] · 4-tert-butylphenyl glycidyl ether (manufactured by Tokyo Chemical Industry Co., Ltd.) Epoxy resin curing agent having isocyanate groups other than [B] · 2-phenylethyl isocyanate (manufactured by Tokyo Chemical Industry Co., Ltd.) Epoxy resin curing agents other than [B] · 3,3’-DAS (3,3’-diaminodiphenyl sulfone, manufactured by Mitsui Chemicals Fine Co., Ltd.) · HN-5500 (methylhexahydrophthalic anhydride, manufactured by Hitachi Chemical Co., Ltd.).

[0186] <Resin composition [i]> 100 parts by mass of "jER (registered trademark)" 828 and 4 parts by mass of "DBU (registered trademark)" were kneaded to obtain a transparent viscous liquid. Then, 72 parts by mass of "Lupranate (registered trademark)" M20S was added and further kneaded to obtain an epoxy resin composition.

[0187] When the resin composition [i] was cured while raising the temperature from 30 °C at a rate of 10 °C / min, the absorbance ratio Da / (Da + Db) at a curing degree of 20% was 0.13, and the absorbance ratio Da / (Da + Db) at a curing degree of 90% was 0.71.

[0188] <Resin composition [ii]> 100 parts by mass of 4-tert-butylphenyl glycidyl ether and 4 parts by mass of "DBU (registered trademark)" were kneaded to obtain a transparent viscous liquid. Then, 66 parts by mass of "Lupranate (registered trademark)" M20S was added and further kneaded to obtain an epoxy resin composition.

[0189] When the resin composition [ii] was cured while raising the temperature from 30 °C at a rate of 10 °C / min, the absorbance ratio Da / (Da+Db) at a curing degree of 20% was 0.06, and the absorbance ratio Da / (Da+Db) at a curing degree of 90% was 0.19.

[0190] <Resin composition [iii]> 100 parts by mass of "jER (registered trademark)" 828 and 4 parts by mass of "DBU (registered trademark)" were kneaded to obtain a transparent viscous liquid. Then, 78 parts by mass of 2-phenylethyl isocyanate was added and further kneaded to obtain an epoxy resin composition.

[0191] When the resin composition [iii] was cured while raising the temperature from 30 °C at a rate of 10 °C / min, the absorbance ratio Da / (Da+Db) at a curing degree of 20% was 0.06, and the absorbance ratio Da / (Da+Db) at a curing degree of 90% was 0.18.

[0192] <Resin composition [iv]> 100 parts by mass of "jER (registered trademark)" 828 and 72 parts by mass of "Lupranate (registered trademark)" M20S were kneaded to obtain an epoxy resin composition.

[0193] The temperature of the resin composition [iv] was raised from 30 °C at a rate of 10 °C / min, but a cured product with a curing degree of 90% could not be obtained.

[0194] <Resin composition [v]> 100 parts by mass of "jER (registered trademark)" 828 and 33 parts by mass of 3,3'-DAS were kneaded to obtain an epoxy resin composition.

[0195] When the resin composition [v] was cured while raising the temperature from 30 °C at a rate of 10 °C / min, the absorbance ratio Da / (Da+Db) at curing degrees of 20% and 90% was 0.

[0196] <Resin composition [vi]> 89 parts by mass of HN-5500 and 6 parts by mass of TMAB were kneaded at 80°C to obtain a transparent curing agent solution. This was added to 100 parts by mass of "jER (registered trademark)" 828 and further kneaded to obtain an epoxy resin composition.

[0197] When the resin composition [vi] was cured while raising the temperature from 30°C at a rate of 10°C / min, the absorbance ratio Da / (Da + Db) at a curing degree of 20% and 90% was 0.

[0198] (6) Preparation of fiber-reinforced composite material The glass fiber produced in (1) above and the epoxy resin composition prepared in (5) above were mixed so that the fiber mass content (Wf) in the fiber-reinforced composite material was 30%, and set in a mold having a plate-shaped cavity of 400 mm × 400 mm × 2.4 mm, and clamped with a pressing device. This was heated to a predetermined curing temperature at a rate of 5°C / min, and after a predetermined curing time had elapsed, the mold was opened and demolded to obtain a fiber-reinforced composite material. At this time, Vf measured in accordance with ASTM D3171:1999 was 18%.

[0199] (7) Measurement of flexural strength A strip-shaped test piece with a length of 60 mm and a width of 10 mm was cut out from the fiber-reinforced composite material produced in (6) above, and using an Instron universal testing machine, with a span length of 32 mm and a crosshead speed of 2.0 mm / min, three-point bending was carried out in accordance with JIS K7171 (1999) to measure the flexural strength (σ1).

[0200] (8) Measurement of retention rate of flexural strength after water absorption A strip-shaped test piece with a length of 60 mm and a width of 10 mm was cut out from the fiber-reinforced composite material produced in (6) above and immersed in a constant temperature water bath at 98°C for 48 hours. This was then used with an Instron universal testing machine, with a span length of 32 mm and a crosshead speed of 2.0 mm / min, and three-point bending was carried out in accordance with JIS K7171 (1999) to measure the flexural strength after water absorption (σ2). Here, the retention rate (%) of the flexural strength after water absorption was determined by retention rate (%) = σ2 / σ1 × 100.

[0201] (9) Resin adhesion amount on the glass fiber surface after fracture The resin adhesion amount on the exposed glass fiber surface at the fracture surface of the test piece fractured in (7) above was comparatively evaluated in the following four levels from the elemental mapping image observed by scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDX). Those with the area ratio (S1) of silicon element on the glass fiber surface being 0 or more and 0.85 or less were rated as "Very Good", those exceeding 0.85 and being 0.90 or less were rated as "Good", those exceeding 0.90 and being 0.95 or less were rated as "Fair", and those exceeding 0.95 and being 1.0 or less were rated as "Bad".

[0202] The observation conditions of the SEM are as follows. Apparatus: "SU8220" manufactured by Hitachi High-Technologies Corporation, acceleration voltage: 5 kV, WD setting: 10 - 15 mm, current: 10 mA, magnification: 2000 times. Also, the measurement conditions by EDX are as follows. Apparatus: "Xflash5060" manufactured by BRUKER, acceleration voltage: 5 kV, WD setting: 10 - 15 mm, current: 5 - 15 mA, magnification: 2000 times.

[0203] (10) Resin impregnation property to the reinforcing fiber Regarding the impregnation property in the resin injection process during the production of the fiber-reinforced composite material in (6) above, it was comparatively evaluated in the following three levels based on the void amount in the fiber-reinforced composite material. Those with the void amount in the fiber-reinforced composite material being less than 1% and with substantially no voids were rated as "Good", those with no resin non-impregnated part observed in the appearance of the fiber-reinforced composite material but with the void amount in the fiber-reinforced composite material being 1% or more were rated as "Fair", and those with a resin non-impregnated part observed in the appearance of the fiber-reinforced composite material were rated as "Bad".

[0204] The void amount in the fiber-reinforced composite material was calculated from the area ratio of voids in the fiber-reinforced composite material by observing the smoothly polished cross-section of the fiber-reinforced composite material with an inclined optical microscope.

[0205] (11) Measurement of Charpy impact value A strip-shaped test piece with a length of 80 mm and a width of 10 mm was cut out from the fiber-reinforced composite material prepared in (6) above, and using an Instron pendulum-type testing machine, the back of the notch of the test piece was hammered in accordance with ISO179 / 1eA to measure the Charpy impact value.

[0206] ( Reference Examples 8 to 11) Using [I] as the glass fiber and [i] as the epoxy resin composition, a fiber-reinforced composite material was prepared under the curing conditions shown in Table 3. Both the flexural strength of the obtained fiber-reinforced composite material and the retention rate of the flexural strength after water absorption were excellent, and the Charpy impact value was at a satisfactory level. Also, the amount of resin adhered to the fracture surface was sufficient, and no resin-unimpregnated portions or voids were observed, indicating excellent impregnation properties.

[0207] ( Reference Example 12) Except for using [II] as the glass fiber, Reference a fiber-reinforced composite material was prepared in the same manner as in Example 11. The Charpy impact value of the obtained fiber-reinforced composite material was excellent, and the flexural strength and the retention rate of the flexural strength after water absorption were at a satisfactory level. Also, although the amount of resin adhered to the fracture surface was slightly inferior, no resin-unimpregnated portions or voids were observed, indicating excellent impregnation properties.

[0208] ( Reference Example 13) Except for using [III] as the glass fiber, Reference a fiber-reinforced composite material was prepared in the same manner as in Example 11. Both the flexural strength and the retention rate of the flexural strength after water absorption of the obtained fiber-reinforced composite material were extremely excellent, and the Charpy impact value was excellent. Also, the amount of resin adhered to the fracture surface was sufficient, and no resin-unimpregnated portions or voids were observed, indicating excellent impregnation properties.

[0209] ( Reference Example 14) Except for using [IV] as the glass fiber, ReferenceA fiber-reinforced composite material was produced in the same manner as in Example 11. Both the flexural strength, Charpy impact value of the obtained fiber-reinforced composite material and the retention rate of the flexural strength after water absorption were excellent. Also, the resin adhesion amount on the fracture surface was sufficient, and no resin-unimpregnated portions and voids were observed, indicating excellent impregnation properties.

[0210] ( Reference Example 15) A fiber-reinforced composite material was produced in the same manner as in Example 11, except that [V] was used as the glass fiber. The flexural strength and Charpy impact value of the obtained fiber-reinforced composite material were excellent, and the retention rate of the flexural strength after water absorption was at a satisfactory level. Also, the resin adhesion amount on the fracture surface was sufficient, and no resin-unimpregnated portions and voids were observed, indicating excellent impregnation properties. Reference A fiber-reinforced composite material was produced in the same manner as in Example 11, except that [V] was used as the glass fiber. The flexural strength and Charpy impact value of the obtained fiber-reinforced composite material were excellent, and the retention rate of the flexural strength after water absorption was at a satisfactory level. Also, the resin adhesion amount on the fracture surface was sufficient, and no resin-unimpregnated portions and voids were observed, indicating excellent impregnation properties.

[0211] (Comparative Example 7) A fiber-reinforced composite material was produced in the same manner as in Example 11, except that [VI] was used as the glass fiber. By using glass fiber having a surface functional group that does not form a covalent bond with an isocyanate group, the flexural strength and Charpy impact value of the obtained fiber-reinforced composite material were inferior. Also, the resin adhesion amount on the fracture surface was insufficient, and voids were observed in the cross-section of the obtained fiber-reinforced composite material. Reference A fiber-reinforced composite material was produced in the same manner as in Example 11, except that [VI] was used as the glass fiber. By using glass fiber having a surface functional group that does not form a covalent bond with an isocyanate group, the flexural strength and Charpy impact value of the obtained fiber-reinforced composite material were inferior. Also, the resin adhesion amount on the fracture surface was insufficient, and voids were observed in the cross-section of the obtained fiber-reinforced composite material.

[0212] (Comparative Example 8) A fiber-reinforced composite material was produced in the same manner as in Example 11, except that [VII] was used as the glass fiber. By using glass fiber having a surface functional group that does not form a covalent bond with an isocyanate group, the flexural strength and Charpy impact value of the obtained fiber-reinforced composite material were inferior. Also, the resin adhesion amount on the fracture surface was insufficient, and voids were observed in the cross-section of the obtained fiber-reinforced composite material. Reference A fiber-reinforced composite material was produced in the same manner as in Example 11, except that [VII] was used as the glass fiber. By using glass fiber having a surface functional group that does not form a covalent bond with an isocyanate group, the flexural strength and Charpy impact value of the obtained fiber-reinforced composite material were inferior. Also, the resin adhesion amount on the fracture surface was insufficient, and voids were observed in the cross-section of the obtained fiber-reinforced composite material.

[0213] (Comparative Example 9) A fiber-reinforced composite material was produced in the same manner as in Example 4, except that [ii] was used as the epoxy resin composition. Since a monofunctional epoxy resin having one oxirane group in the molecule was used, the flexural strength, Charpy impact value, and the retention rate of the flexural strength after water absorption were significantly inferior.

[0214] (Comparative Example 10) A fiber-reinforced composite material was produced in the same manner as in Example 11, except that [iii] was used as the epoxy resin composition. Since a monofunctional isocyanate curing agent having one isocyanate group in the molecule was used, the flexural strength, Charpy impact value, and retention rate of the flexural strength after water absorption were significantly inferior. Reference

[0215] (Comparative Example 11) Although [iv] was used as the epoxy resin composition, a cured product with a curing degree of 90% could not be obtained under the specified conditions.

[0216] (Comparative Example 12) Using [I] as the glass fiber and [v] as the epoxy resin composition, a fiber-reinforced composite material was produced under the curing conditions described in Table 4. The obtained fiber-reinforced composite material did not form an oxazolidone ring, and it took time to inject the resin composition. Voids were observed in the cross-section of the obtained fiber-reinforced composite material.

[0217] (Comparative Example 13) Using [I] as the glass fiber and [vi] as the epoxy resin composition, a fiber-reinforced composite material was produced under the curing conditions described in Table 4. The obtained fiber-reinforced composite material did not form an oxazolidone ring and was also inferior in adhesion to the glass fiber, so the flexural strength and Charpy impact value were inferior.

[0218]

Table 3

[0219]

Table 4

Industrial Applicability

[0220] ​Since the epoxy resin composition of the present invention has a low viscosity and the carbon fibers have a circular cross-sectional shape, it has excellent impregnation properties when the epoxy resin composition is injected into the reinforcing fibers. Furthermore, since the cured product of such an epoxy resin composition has excellent mechanical properties, it is possible to provide a fiber-reinforced composite material having both high impact resistance and high tensile strength. As a result, the application of fiber-reinforced composite materials to aircraft and automotive member applications in particular is progressing, and it is expected to contribute to improving fuel efficiency through further weight reduction and reducing greenhouse gas emissions.

[0221] In addition, since the epoxy resin composition has a low viscosity and the glass fibers have surface functional groups capable of forming covalent bonds with isocyanate groups, it has excellent impregnation properties when the epoxy resin composition is injected into the reinforcing fibers. Furthermore, since the adhesiveness between such reinforcing fibers and the epoxy resin composition is moderately improved, it is possible to provide a fiber-reinforced composite material having high flexural strength and impact resistance. Also, since the water absorption of the epoxy resin composition used in the present invention is low, it is possible to provide a fiber-reinforced composite material that suppresses a decrease in flexural strength after water absorption. As a result, it can be suitably used as a structural material for automobile outer panels, primary and secondary structural materials of aircraft, wind turbines, space equipment, railway vehicles, ships, etc. In addition, it can also be suitably used for electronic material applications such as semiconductors, IC trays, and notebook computers.

Claims

1. A molding material comprising an epoxy resin composition and carbon fibers, wherein the epoxy resin composition contains all of the following [A] to [C], and the carbon fibers satisfy the following conditions [a], [b], and [c]. [A] An epoxy resin having at least two oxirane groups in the molecule [B] An epoxy resin curing agent having at least two isocyanate groups in the molecule [C] A catalyst [a] Having a substantially circular cross-section [b] The average fiber diameter is in the range of 4.0 to 8.0 μm [c] The surface specific oxygen concentration O / C is in the range of 0.05 to 0.15 (Here, the surface specific oxygen concentration is determined by calculating O / C = ([O １ｓ peak area [O １ｓ ]) / ([C １ｓ peak area [C １ｓ ]) / (sensitivity correction value) in X-ray photoelectron spectroscopy. １ｓ ]) / ([C １ｓ ]) / (sensitivity correction value) in X-ray photoelectron spectroscopy.

2. The molding material according to claim 1, wherein when cured while increasing the temperature from 30 °C at a rate of 10 °C / min, there exists a specific degree of cure X in the range of 85 to 95% such that the absorbance ratio Da / (Da + Db) at the degree of cure X is in the range of 0.4 to 1. (Here, the absorbance ratio is determined by calculating absorbance ratio = Da / (Da + Db) from the absorbance Da of the absorption caused by the C=O double bond of the carboxyl group of the oxazolidone ring and the absorbance Db of the absorption caused by the C=O double bond of the carboxyl group of the isocyanurate ring in FT-IR (ATR method). Also, the degree of cure is determined by calculating degree of cure (%) = (QT - QR) / QT × 100 from the total heat of exotherm QT of the epoxy resin composition obtained by DSC at a heating rate of 10 °C / min and the residual heat of exotherm QR of the cured product.)

3. When cured while increasing the temperature from 30°C at a rate of 10°C per minute, there exists a specific degree of cure Y within the range of 15% to 25% such that the absorbance ratio Da / (Da + Db) at the degree of cure Y is in the range of 0.01 to 1. The molding material according to claim 1 or 2.

4. A fiber-reinforced composite material obtained by curing the molding material according to any one of claims 1 to 3.

5. The fiber-reinforced composite material according to claim 4, wherein the absorbance ratio Da / (Da + Db) is in the range of 0.4 to 1. (Here, the absorbance ratio is specified by calculating the absorbance ratio = Da / (Da + Db) from the absorbance Da of the absorption caused by the C=O double bond of the carboxyl group of the oxazolidone ring and the absorbance Db of the absorption caused by the C=O double bond of the carboxyl group of the isocyanurate ring in FT-IR (ATR method).)

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