Prepreg and fiber-reinforced composite material

Abstract

Provided is a prepreg having an improved water absorption rate (low water absorption). Also provided is a fiber-reinforced composite material having an improved water absorption rate while maintaining heat resistance. This prepreg has a reinforcing fiber base material, which contains carbon fibers, impregnated with a matrix resin composition. The reinforcing fiber base material contains carbon fibers. The matrix resin composition contains component (A): a cyanate ester resin, component (B): a curing agent, and component (C): rubber particles. The content of component (A) is more than 50 mass% and the content of component (C) is 0.1-30 mass% with respect to the total mass of the matrix resin composition.

Description

Prepreg and Fiber-Reinforced Composites

[0001] This application claims priority from PCT / JP2024 / 019016, filed in Japan on May 23, 2024, the contents of which are incorporated herein by reference.

[0002] Fiber-reinforced composite materials are lightweight, strong, and rigid, and are therefore widely used in a variety of applications, from sports and leisure to industrial applications such as automobiles and aircraft. One method for producing fiber-reinforced composite materials is to use an intermediate material, i.e., a prepreg, in which a reinforcing fiber substrate is impregnated with a matrix resin. Epoxy resins are widely used as matrix resins due to their mechanical properties. In particular, epoxy resins are most commonly used as matrix resins for fiber-reinforced composite materials using reinforcing fibers such as carbon fiber and glass fiber. However, the use of epoxy resins can sometimes result in insufficient heat resistance, and it is known that cyanate ester resins can be used to improve heat resistance.

[0003] Cyanate ester resins form triazine rings upon heating, resulting in compositions with high heat resistance. Furthermore, cyanate ester resins have a low concentration of hydrophilic groups in the cured product, and are known to exhibit lower water absorption compared to cured products of epoxy resins, bismaleimide resins, and other resins. Therefore, fiber-reinforced composite materials using cyanate ester resins as the matrix resin are particularly advantageously used in aerospace applications. Patent Document 1, for example, describes a prepreg using a cyanate ester resin as the matrix resin, in which silica particles having a specific particle size are included to obtain a prepreg that maintains mechanical properties and exhibits excellent heat resistance after molding. Patent Document 2 also describes that incorporating a large amount of silica into a prepreg using a cyanate ester compound improves heat resistance and coating properties.

[0004] International Publication No. 2021 / 18745 International Publication No. 2017 / 170375

[0005] One of the objects of the present invention is to provide a prepreg having an improved water absorption rate (low water absorption), or to provide a fiber-reinforced composite material having an improved water absorption rate while maintaining heat resistance.

[0006] The present invention includes the following embodiments [1] to

[21] .

[0007] [1]: A prepreg in which a reinforcing fiber substrate containing carbon fiber is impregnated with a matrix resin composition, the matrix resin composition comprising the following components (A), (B), and (C), wherein the content of component (A) is greater than 50 mass% and the content of component (C) is 0.1 to 30 mass% relative to the total mass of the matrix resin composition: Component (A): cyanate ester resin Component (B): curing agent Component (C): rubber particles [2]: A prepreg in which a reinforcing fiber substrate containing carbon fiber is impregnated with a matrix resin composition, the matrix resin composition comprising the following components (A) and (C), wherein the content of component (A) is greater than 50 mass% and the content of component (C) is 4 to 30 mass% relative to the total mass of the matrix resin composition. Component (A): cyanate ester resin Component (C): rubber particles [3]: The prepreg according to [1], wherein the content of component (C) is 1 to 25 mass% relative to the total mass of the matrix resin composition. [4]: ​​The prepreg according to [1] or [3], wherein the content of component (C) is 3 to 20 mass% relative to the total mass of the matrix resin composition. [5]: The prepreg according to any one of [1] to [4], wherein the mass ratio of the content of component (A) to the content of carbon fiber (component (A) / carbon fiber) in the prepreg is 0.2 to 0.6, preferably 0.3 to 0.5. [6]: The prepreg according to any one of [1] to [5], wherein the mass ratio of the content of component (C) to the content of carbon fiber (component (C) / carbon fiber) in the prepreg is 0.005 to 0.2, preferably 0.01 to 0.1. [7]: The prepreg according to any one of [1] to [6], wherein the component (A) contains a thiophene-free cyanate ester resin. [8]: The prepreg according to any one of [1] to [7], wherein the component (A) contains a bisphenol A-type cyanate ester resin. [9]: The prepreg according to any one of [1] to [8], wherein the component (B) contains an imidazole compound, an aromatic amine, or a urea compound.

[10] : The prepreg according to any one of [1] to [9], wherein the component (B) contains an imidazole compound.

[11] : The prepreg according to any one of [1] to

[10] , wherein the component (B) contains an imidazole compound having a triazine ring skeleton.

[12] : The prepreg according to any one of [1] to

[11] , wherein the component (C) contains core-shell rubber particles.

[13] : The prepreg according to

[12] , wherein the core component of the core-shell rubber particles contains polybutadiene or styrene-butadiene.

[14] : The prepreg according to any one of [1] to

[13] , wherein the matrix resin composition contains an epoxy resin.

[15] : The prepreg according to any one of [1] to

[14] , wherein the matrix resin composition contains an epoxy resin in an amount of 0.1 to 30% by mass, preferably 1 to 20% by mass, and more preferably 3 to 15% by mass, relative to the total mass of the matrix resin composition.

[16] : The prepreg according to

[14] or

[15] , wherein the epoxy resin is a compound containing a bisphenol A-type epoxy resin.

[17] : The prepreg according to any one of [1] to

[16] , wherein the mass ratio of the content of the (A) component to the content of the (C) component ((A) component / (C) component) is 30 or less, preferably 25 or less.

[18] : The prepreg according to any one of [1] to

[17] , wherein the mass ratio of the content of the (B) component to the content of the (C) component ((B) component / (C) component) is 0.5 or less, preferably 0.4 or less.

[19] : The prepreg according to any one of [1] to

[18] , wherein the content of the (B) component is 0.05 to 5 parts by mass, preferably 0.1 to 3 parts by mass, per 100 parts by mass of the (A) component.

[20] : The prepreg according to any one of [1] to

[19] , wherein the reinforcing fiber substrate is a sheet of aligned carbon fiber bundles.

[21] : A fiber-reinforced composite material obtained by curing the prepreg according to any one of [1] to

[20] .

[0008] According to a preferred embodiment of the present invention, a prepreg having an improved water absorption rate can be obtained, and a fiber-reinforced composite material having an improved water absorption rate while maintaining heat resistance can be obtained.

[0009] The present invention will be described in detail below. [Prepreg] (First Embodiment) One embodiment of the present invention relates to a prepreg. The prepreg is obtained by impregnating a reinforcing fiber substrate containing carbon fiber with a matrix resin composition. The matrix resin composition of the prepreg according to the first embodiment (hereinafter also referred to as "matrix resin composition (I)") contains the following components (A) and (C). The matrix resin composition (I) may further contain optional components other than these components. Component (A): cyanate ester resin Component (C): rubber particles Furthermore, in the prepreg according to the first embodiment, the content of component (A) is greater than 50% by mass and the content of component (C) is 4 to 30% by mass, relative to the total mass of the matrix resin composition (I).

[0010] As mentioned above, cyanate ester resins form triazine rings upon heating, resulting in cured products with high heat resistance. However, because the cured product has a high crosslink density, smooth shrinkage is prevented during the cooling process back to room temperature after curing due to the strong constraints of the crosslinking points, resulting in the formation of relatively large voids within the three-dimensional network structure. Furthermore, voids are also formed at the interface between the cyanate ester resin and the reinforcing fiber substrate. By including the specified amounts of components (A) and (C) in the matrix resin composition (I), component (C) can effectively fill voids within the three-dimensional network structure and at the interface between the cyanate ester resin and the reinforcing fiber substrate in a cyanate ester resin exhibiting high heat resistance. This is believed to enable the production of prepregs with improved water absorption and fiber-reinforced composite materials with improved water absorption while maintaining heat resistance.

[0011] <Component (A)> The component (A) is a cyanate ester resin. The cyanate ester resin represents a cyanate ester monomer, a cyanate ester oligomer, or a mixture thereof, and may have a substituent within a range that does not impair the effects of the present invention. Specific examples of cyanate ester resins include bifunctional cyanate ester resins such as bisphenol A dicyanate, 4,4'-methylenebis(2,6-dimethylphenylcyanate), 4,4'-ethylidene diphenyl dicyanate, hexafluorobisphenol A dicyanate, bis(4-cyanate-3,5-dimethylphenyl)methane, 1,3-bis(4-cyanatephenyl-1-(methylethylidene))benzene, bis(4-cyanatephenyl)thioether, and bis(4-cyanatephenyl)ether; polyfunctional cyanate ester resins derived from phenol novolac, cresol novolac, and dicyclopentadiene structure-containing phenolic resins; and prepolymers in which these cyanate ester resins are partially triazine-modified. From the viewpoint of imparting heat resistance and toughness by improving crosslink density, it is preferable that the cyanate ester resin contain two or more cyanate groups per molecule. One type of cyanate ester resin may be used alone, or two or more types may be used in combination. Two or more cyanate ester resins having different degrees of polymerization may be mixed.

[0012] The viscosity of the cyanate ester resin is preferably 1,000 Pa·s or more, more preferably 3,000 Pa·s or more, at 30°C from the viewpoint of improving handleability when made into a prepreg. The viscosity of the cyanate ester resin is preferably 100,000 Pa·s or less, more preferably 80,000 Pa·s or less, at 30°C from the viewpoint of ensuring tackiness that facilitates lamination during molding. The upper and lower limits of the viscosity of the cyanate ester resin can be arbitrarily combined. For example, the viscosity of the cyanate ester resin is preferably 1,000 to 100,000 Pa·s, more preferably 3,000 to 80,000 Pa·s, at 30°C. The viscosity of the cyanate ester resin at 30°C is a value measured using a rheometer.

[0013] Examples of commercially available cyanate ester resins include, but are not limited to, bisphenol A cyanate ester resin (Mitsubishi Gas Chemical Company, Inc., TA), a prepolymer of a phenol novolac cyanate ester resin (Arcsada Japan Co., Ltd., Primaset PT-30), a prepolymer of a bisphenol A cyanate ester resin (Mitsubishi Gas Chemical Company, Inc., TA-100), a prepolymer of a phenol novolac cyanate ester resin (Arcsada Japan Co., Ltd., Primaset PT-60), a prepolymer of a bisphenol A cyanate ester resin (Mitsubishi Gas Chemical Company, Inc., TA-1500), a prepolymer of a dicyclopentadiene structure-containing cyanate ester resin (Arcsada Japan Co., Ltd., Primaset DT-4000), and a prepolymer of a bisphenol M cyanate ester resin (Arcsada Japan Co., Ltd., Primaset LMP-500). One of the commercially available cyanate ester resins may be used alone, or two or more of them may be used in combination.

[0014] From the viewpoint of obtaining a fiber-reinforced composite material having an excellent balance between mechanical properties and heat resistance, the component (A) is preferably a thiophene-free cyanate ester resin, i.e., a cyanate ester resin having no thiophene ring in the molecule, more preferably a bisphenol A-type cyanate ester resin or a phenol novolac-type cyanate ester resin, and even more preferably a bisphenol A-type cyanate ester resin.

[0015] The content of component (A) in matrix resin composition (I) is greater than 50% by mass, preferably 55% by mass or greater, more preferably 60% by mass or greater, and even more preferably 80% by mass or greater, relative to the total mass of matrix resin composition (I). By setting the content of component (A) at or above the lower limit, sufficient heat resistance can be imparted to the fiber-reinforced composite material. The content of component (A) is preferably 96% by mass or less, more preferably 95% by mass or less, even more preferably 93% by mass or less, and may even be 90% by mass or less, relative to the total mass of matrix resin composition (I). Setting the content of component (A) at or below the upper limit can ensure the toughness of the fiber-reinforced composite material. The upper and lower limits for the content of component (A) can be arbitrarily combined, and may be, for example, greater than 50% by mass but not greater than 96% by mass, 55 to 95% by mass, 60 to 93% by mass, 80 to 93% by mass, or 80 to 90% by mass.

[0016] <Component (C)> Component (C) is rubber particles. By including rubber particles in the matrix resin composition (I), voids within the three-dimensional network structure of component (A) are filled after curing, and the rubber particles themselves are less likely to absorb water than component (A), resulting in improved water absorption. Synthetic rubber or natural rubber can be used as the rubber particle component, and examples include those having a structure derived from (meth)acrylic acid alkyl ester, butadiene, isoprene, chloroprene, styrene, α-alkylstyrene, acrylonitrile, and methacrylonitrile. Examples of rubber particles include silicone rubber particles, silicone-acrylic composite rubber particles, fluororubber particles, ethylene vinyl acetate rubber particles, acrylonitrile-butadiene rubber particles, styrene-butadiene rubber particles, acrylic rubber particles, and core-shell rubber particles. Core-shell rubber particles are preferred from the viewpoint of improving the water absorption of prepregs and fiber-reinforced composite materials. An example of a core-shell structure is a structure in which a particulate core component, mainly composed of a crosslinked rubber-like polymer, is coated with a shell component polymer, which is different from the core component, by graft polymerization onto the surface of the particulate core component, thereby coating the surface of the particulate core component partially or entirely with the shell component.

[0017] Examples of the core component of the core-shell structure include butadiene rubber (BR), acrylic rubber (ACM), silicone rubber (Si), butyl rubber (IIR), nitrile rubber (NBR), styrene butadiene rubber (SBR), isoprene rubber (IR), and ethylene propylene rubber (EPR). As the core component, polybutadiene or a crosslinked rubber polymer composed of styrene and butadiene is preferred because it is highly effective in improving the mechanical properties and heat resistance of the fiber-reinforced composite material, and it is more preferred that the core component contains polybutadiene.

[0018] The shell component of the core-shell structure is preferably graft-polymerized onto the core component and covalently bonded to the polymer constituting the core component. As the component constituting the shell component, for example, a polymer obtained by polymerizing at least one selected from the group consisting of an acrylic acid ester monomer, a methacrylic acid ester monomer, and an aromatic vinyl monomer can be used.

[0019] When a crosslinked rubber polymer composed of styrene and butadiene is used as the core component, the shell component is preferably one obtained by graft polymerizing a mixture of methyl methacrylate, a (meth)acrylic acid ester, and styrene, an aromatic vinyl compound, onto the core component. Functional groups that react with component (A) or epoxy resins, such as hydroxyl groups, carboxyl groups, and epoxy groups, may be introduced.

[0020] Commercially available core-shell rubber particles using silicone-acrylic composite rubber include, for example, products under the product name "S-2030" (manufactured by Mitsubishi Chemical Corporation), "SRK-200A" (manufactured by Mitsubishi Chemical Corporation), and "S-2200" (manufactured by Mitsubishi Chemical Corporation). Commercially available core-shell rubber particles using butadiene rubber include, for example, products under the product name "C-223A" (manufactured by Mitsubishi Chemical Corporation) and "C-140A" (manufactured by Mitsubishi Chemical Corporation).

[0021] Component (C) may be dispersed in component (A) using a stirrer, a roll mill, or the like during preparation of matrix resin composition (I). However, by using a core-shell rubber particle-dispersed epoxy resin, which is a masterbatch in which component (C) has been dispersed in component (A) in advance, not only can the preparation time for matrix resin composition (I) be shortened, but also component (C) can be uniformly dispersed in matrix resin composition (I).

[0022] Examples of commercially available masterbatches include, but are not limited to, epoxy resins containing acrylic rubber under the product name "BPF307" (manufactured by Nippon Shokubai Co., Ltd.) and "BPA328" (manufactured by Nippon Shokubai Co., Ltd.), epoxy resins containing butadiene rubber under the product name "MX-154" (manufactured by Kaneka Corporation), and epoxy resins containing silicone rubber under the product name "MX-962" (manufactured by Kaneka Corporation).

[0023] The number average particle diameter of component (C) is preferably 0.01 μm or more, more preferably 0.1 μm or more. By setting the number average particle diameter of component (C) to the lower limit or more, the effect of improving water absorption is increased. The number average particle diameter of component (C) is preferably 1 μm or less, more preferably 0.6 μm or less. By setting the number average particle diameter of component (C) to the upper limit or less, the effect of improving mechanical properties is increased. The upper and lower limits of the number average particle diameter of component (C) can be arbitrarily combined; for example, 0.01 to 1 μm is preferred, and 0.1 to 0.6 μm is more preferred.

[0024] The content of component (C) in matrix resin composition (I) is 4 to 30 mass% relative to the total mass of matrix resin composition (I). The lower limit of the content of component (C) is preferably 4.5 mass%, more preferably 5 mass%, and even more preferably 6 mass%. The upper limit of the content of component (C) is preferably 25 mass%, more preferably 20 mass%. By setting the content of component (C) at or above the lower limit, a fiber-reinforced composite material with improved water absorption is more likely to be obtained, while by setting the content at or below the upper limit, a decrease in rigidity of the fiber-reinforced composite material is more likely to be suppressed. The lower and upper limits of the content of component (C) can be arbitrarily combined; for example, 4 to 25 mass% is preferred, 5 to 25 mass% is more preferred, and 6 to 20 mass% is even more preferred.

[0025] From the viewpoint of obtaining a fiber-reinforced composite material having excellent mechanical properties and heat resistance, the mass ratio of the content of the component (A) to the component (C) in the matrix resin composition (I) (component (A) / component (C)) is preferably 30 or less, and more preferably 25 or less. From the viewpoint of rapid curing of the prepreg, the content ratio of the component (A) / component (C) is preferably 1 or more, and more preferably 3 or more. The lower limit and upper limit of the component (A) / component (C) can be arbitrarily combined; for example, 1 to 30 is more preferable, and 3 to 25 is more preferable.

[0026] <Optional Components> The matrix resin composition (I) may further contain optional components other than the components described above. Examples of the optional components include an epoxy resin, a thermoplastic resin, a curing reaction catalyst, and an additive, and it is preferable that the matrix resin composition (I) contains an epoxy resin.

[0027] The inclusion of an epoxy resin inhibits the formation of a rigid triazine skeleton within the fiber-reinforced composite material, allowing for smooth shrinkage during the cooling process from curing to room temperature. This results in a fiber-reinforced composite material with excellent toughness. The epoxy resin is not particularly limited, but examples include bisphenol-type epoxy resins, biphenyl-type epoxy resins, naphthalene-type epoxy resins, phenol novolac-type epoxy resins, cresol novolac-type epoxy resins, glycidylamine-type epoxy resins, and epoxy resins having an oxazolidone structure. These epoxy resins may be used alone or in combination. Examples of bisphenol-type epoxy resins include bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol E-type epoxy resins, bisphenol S-type epoxy resins, bisphenol AF-type epoxy resins, and bisphenol BP-type epoxy resins. Bisphenol A-type epoxy resins, in particular, facilitate the dispersion of component (C). Furthermore, when component (A) is a bisphenol A-type cyanate ester resin, they facilitate the dispersion of both component (A) and component (C).

[0028] The content of the epoxy resin in the matrix resin composition (I) is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, based on the total mass of the matrix resin composition (I), from the viewpoint of improving the water absorption of the fiber-reinforced composite material and enhancing the dispersibility of each component. Furthermore, from the viewpoint of the heat resistance of the fiber-reinforced composite material, the content of the epoxy resin is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and particularly preferably 10% by mass or less. The lower and upper limits of the epoxy resin content can be arbitrarily combined; for example, 0.1 to 30% by mass is preferred, 1 to 20% by mass is more preferred, and 3 to 15% by mass is even more preferred.

[0029] Examples of thermoplastic resins include polyamide, polyester, polycarbonate, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyetheretherketone, polyetherketone, polyetherimide, polyimide, polytetrafluoroethylene, polyether, polyolefin, polyarylate, polysulfone, polyacrylonitrilestyrene, polystyrene, polyacrylonitrile, polymethyl methacrylate, acrylonitrile-butadiene-styrene copolymer (ABS resin), acrylonitrile-ethylene-propylene-diene-styrene copolymer (AES resin), acrylonitrile-styrene-alkyl (meth)acrylate copolymer (ASA resin), polyvinyl chloride, polyvinyl formal, and phenoxy resin, but are not limited thereto. These thermoplastic resins may be used alone or in combination of two or more. From the viewpoint of excellent resin flow controllability, phenoxy resin, polyethersulfone, polyetherimide, and polyvinyl formal are preferred as thermoplastic resins.

[0030] The structure of the curing catalyst is not limited as long as it accelerates the curing of the cyanate ester resin. Examples of the curing catalyst include, but are not limited to, acid anhydrides, phenols, and boron chloride amine complexes. One type of curing catalyst may be used alone, or two or more types may be used in combination.

[0031] More specific examples of additives include flame retardants such as metal phosphinates, aluminum hydroxide, and magnesium hydroxide; inorganic oxides such as antimony compounds, zinc borate, zinc stannate, Mo compounds, ZrO, zinc sulfide, zeolites, and titanium oxide; silicone oils, wetting and dispersing agents, antifoaming agents, defoamers, natural waxes, synthetic waxes, metal salts of straight-chain fatty acids, acid amides, esters, and paraffins; inorganic fillers such as powders and glass fibers, and carbon fibers having a fiber length of approximately 0.01 mm to 10 mm, such as crystalline silica, fused silica, calcium silicate, alumina, calcium carbonate, talc, and barium sulfate; colorants such as carbon black and red iron oxide; and silane coupling agents. These may be used alone or in combination of two or more. When inorganic compounds such as inorganic oxides are included as additives, the content thereof is preferably 30 parts by mass or less, and more preferably 20 parts by mass or less, relative to the total mass of the matrix resin composition, from the viewpoint of improving the toughness of the fiber-reinforced composite material.

[0032] <Preferred Composition> As a combination of the component (A) and the component (C) contained in the matrix resin composition (I), a combination of any of the following components (A1) to (A4) with any of the following components (C1) to (C5) is preferred, a combination of any of the components (A1) to (A4) with any of the components (C2) to (C5) is more preferred, a combination of any of the components (A2) to (A4) with any of the components (C3) to (C5) is more preferred, a combination of any of the components (A3) to (A4) with any of the components (C4) to (C5) is even more preferred, and a combination of the component (A4) with the component (C5) is particularly preferred. Component (A1): cyanate ester resin containing two or more cyanate groups per molecule Component (A2): thiophene-free cyanate ester resin Component (A3): at least one of bisphenol A-type cyanate ester resin and phenol novolac-type cyanate ester resin Component (A4): bisphenol A-type cyanate ester resin Component (C1): one or more selected from silicone rubber particles, silicone-acrylic composite rubber particles, and core-shell rubber particles Component (C2): core-shell rubber particles Component (C3): core-shell rubber particles whose core component contains polybutadiene or styrene-butadiene copolymer Component (C4): core-shell rubber particles whose core component contains polybutadiene or styrene-butadiene, and whose shell component is graft-polymerized with one or more selected from acrylic acid ester monomers, methacrylic acid ester monomers, and aromatic vinyl monomers Component (C5): Core-shell rubber particles in which the core component contains polybutadiene or styrene butadiene, and the shell component is graft-polymerized with a mixture of methyl methacrylate and styrene.

[0033] The matrix resin composition (I) preferably contains any of the following optional components (D1) to (D2) in addition to a combination of any of the components (A1) to (A4) and any of the components (C1) to (C5). A more preferred combination is a combination of any of the components (A1) to (A4), any of the components (C2) to (C5), and any of the components (D1) to (D2). A more preferred combination is a combination of any of the components (A2) to (A4), any of the components (C3) to (C5), and any of the components (D1) to (D2). A further preferred combination is a combination of any of the components (A3) to (A4), any of the components (C4) to (C5), and any of the components (D1) to (D2). A particularly preferred combination is a combination of the components (A4), the components (C5), and the components (D2). Component (D1): Epoxy resin. Component (D2): Bisphenol A epoxy resin.

[0034] The matrix resin composition (I) may contain, relative to the total mass of the matrix resin composition (I), more than 50 mass% and not more than 96 mass% of the component (A) and 4 to 30 mass% of the component (C), 55 to 96 mass% of the component (A) and 4 to 30 mass% of the component (C), 60 to 96 mass% of the component (A) and 4 to 25 mass% of the component (C), or 80 to 90 mass% of the component (A) and 4 to 20 mass% of the component (C), provided that the sum of the components (A) and (C) does not exceed 100 mass%.

[0035] Furthermore, the matrix resin composition (I) may contain, relative to the total mass of the matrix resin composition (I), more than 50 mass% but not more than 95 mass% of the (A) component, 4 to 30 mass% of the (C) component, and 0.1 to 30 mass% of an epoxy resin, 55 to 95 mass% of the (A) component, 4 to 30 mass% of the (C) component, and 0.1 to 30 mass% of an epoxy resin, 60 to 95 mass% of the (A) component, 4 to 25 mass% of the (C) component, and 1 to 20 mass% of an epoxy resin, or 80 to 90 mass% of the (A) component, 4 to 20 mass% of the (C) component, and 3 to 15 mass% of an epoxy resin, provided that the sum of the (A), (C), and epoxy resin does not exceed 100 mass%.

[0036] <Method for Producing Matrix Resin Composition (I)> The matrix resin composition (I) can be obtained, for example, by mixing the above-described components. Examples of methods for mixing the components include using a mixer such as a three-roll mill, planetary mixer, kneader, homogenizer, or homodisper. From the perspective of uniformly dispersing component (C), it is preferable to add a masterbatch in which component (C) is dispersed in an epoxy resin to component (A) or a mixture containing component (A) and any optional components. Alternatively, a film of the matrix resin composition (I) can be obtained by applying the matrix resin composition (I) to a release paper or the like and curing it. When used as a film, a viscosity of the matrix resin composition (I) at 30°C of 100 to 1,000,000 Pa·s provides excellent control of the tackiness of the prepreg surface and excellent workability. The viscosity of the matrix resin composition (I) at 30°C is measured using a rheometer.

[0037] <Reinforcing Fibers> The reinforcing fibers are present in the prepreg as a reinforcing fiber substrate (a single fiber assembly of reinforcing fibers), and are preferably in the form of a sheet. The reinforcing fibers may be long fibers (continuous fibers) or short fibers having a length of, for example, 0.01 to 30 cm. The orientation of the fibers in the reinforcing fiber substrate may be such that the reinforcing fibers are aligned in one direction or in a random direction. Examples of the form of the reinforcing fiber substrate include woven reinforcing fibers, nonwoven reinforcing fibers, and sheets in which long reinforcing fibers are aligned in one direction. From the viewpoint of being able to mold a fiber-reinforced composite material with high specific strength and specific modulus, it is preferable to use a sheet (UD substrate) made of a bundle of reinforcing fibers in which the long fibers are aligned in one direction for the prepreg. From the viewpoint of ease of handling, it is preferable to use a woven reinforcing fiber for the prepreg.

[0038] The weight of the reinforcing fiber substrate is 10 g / m ２ More than 4000g / m ２ In the case of a UD substrate, the basis weight is 10 g / m ２ More than 300g / m ２ The following may also be used.

[0039] The reinforcing fiber substrate contains carbon fibers. This allows the resulting fiber-reinforced composite material to be lightweight and have excellent mechanical properties. The reinforcing fiber substrate may further contain glass fibers, nylon fibers, aramid fibers, boron fibers, etc. The number of carbon fibers in the carbon fiber bundles used in the reinforcing fiber substrate is preferably 1,000 to 70,000. A sheet-like reinforcing fiber substrate can be formed by using multiple carbon fiber bundles and aligning the fibers in one direction.

[0040] From the viewpoint of the rigidity of the obtained fiber-reinforced composite material, the strand tensile strength of the carbon fiber is preferably 1.5 to 9 GPa, and the strand tensile modulus of the carbon fiber is preferably 150 to 260 GPa. The strand tensile strength and strand tensile modulus of the carbon fiber can be measured in accordance with JIS R7601:1986. The fiber diameter of the carbon fiber can be 3 to 15 μm.

[0041] <Method for Producing Prepreg> The prepreg of the first embodiment can be produced, for example, by the following procedure. First, the matrix resin composition (I) is applied to one side of the surface of a carrier film (first carrier film). Similarly, another carrier film (second carrier film) is prepared, one side of which is coated with the matrix resin composition (I). Next, the surfaces of the first carrier film and the second carrier film coated with the matrix resin composition (I) are oriented toward the reinforcing fiber substrate, forming a laminate in which the reinforcing fiber substrate and the matrix resin composition (I) are sandwiched between the first carrier film and the second carrier film. The obtained laminate is pressed to impregnate the reinforcing fiber substrate with the matrix resin composition (I), thereby obtaining a prepreg.

[0042] The content of the matrix resin composition (I) in the prepreg of the first embodiment (hereinafter referred to as the "resin content") is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, relative to the total mass of the prepreg. When the resin content is equal to or greater than the lower limit, adhesion between the reinforcing fibers and the matrix resin is easily obtained. The resin content of the prepreg is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. When the resin content is equal to or less than the upper limit, the mechanical properties of the resulting fiber-reinforced composite material are further improved. The upper and lower limits of the resin content can be arbitrarily combined; for example, 15 to 50% by mass is preferred, 20 to 45% by mass is more preferred, and 25 to 40% by mass is even more preferred.

[0043] In the prepreg of the first embodiment, the mass ratio of the component (A) to the carbon fiber (component (A) / carbon fiber) is preferably 0.2 or more, more preferably 0.3 or more, and preferably 0.6 or less, more preferably 0.5 or less. When the component (A) / carbon fiber ratio is within the above range, the heat resistance of the fiber-reinforced composite material is improved. The upper and lower limits of the component (A) / carbon fiber ratio can be arbitrarily combined, and for example, 0.2 to 0.6 is preferred, and 0.3 to 0.5 is more preferred.

[0044] In the prepreg of the first embodiment, the mass ratio of the component (C) to the carbon fiber (component (C) / carbon fiber) is preferably 0.005 or more, more preferably 0.01 or more, and preferably 0.2 or less, more preferably 0.1 or less. When the component (C) / carbon fiber ratio is within the above range, the water absorption of the fiber-reinforced composite material is improved. The upper and lower limits of the component (C) / carbon fiber ratio can be arbitrarily combined, and for example, 0.005 to 0.2 is preferred, and 0.01 to 0.1 is more preferred.

[0045] Second Embodiment A prepreg according to a second embodiment is a prepreg in which a reinforcing fiber substrate containing carbon fibers is impregnated with a matrix resin composition (hereinafter also referred to as "matrix resin composition (II)"). The matrix resin composition (II) contains components (A), (B), and (C). The matrix resin composition (II) may further contain optional components other than these components. Component (A): cyanate ester resin Component (B): curing agent Component (C): rubber particles Furthermore, in the prepreg according to the second embodiment, the content of component (A) is greater than 50% by mass and the content of component (C) is 0.1 to 30% by mass, relative to the total mass of the matrix resin composition (II).

[0046] In the prepreg according to the second embodiment, the matrix resin composition (II) contains the specified amounts of components (A) and (C), which allows component (C) to effectively fill voids within the three-dimensional network structure and at the interface between the cyanate ester resin and the reinforcing fiber substrate in the highly heat-resistant cyanate ester resin. This is believed to enable the production of a prepreg with improved water absorption and a fiber-reinforced composite material with improved water absorption while maintaining heat resistance.

[0047] <Component (A)> The description of the component (A) in the first embodiment also applies to the component (A) in the second embodiment.

[0048] The content of component (A) in matrix resin composition (II) is greater than 50% by mass, preferably 55% by mass or greater, more preferably 60% by mass or greater, and even more preferably 80% by mass or greater, relative to the total mass of matrix resin composition (II). By setting the content of component (A) at or above the lower limit, sufficient heat resistance can be imparted to the fiber-reinforced composite material. The content of component (A) is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less, relative to the total mass of matrix resin composition (II). It may also be 96 parts by mass or less, 95 parts by mass or less, 93.9 parts by mass or less, or 93 parts by mass or less. Setting the content of component (A) at or below the upper limit ensures the toughness of the fiber-reinforced composite material. The upper and lower limits for the content of component (A) can be arbitrarily combined, and may be, for example, greater than 50% by mass but not greater than 99% by mass, 55 to 98% by mass, 60 to 97% by mass, 80 to 97% by mass, or 80 to 93.9% by mass.

[0049] <Component (B)> Component (B) is a curing agent and is not limited as long as it can cure component (A). Examples of component (B) include imidazole compounds; dicyandiamide and / or dicyandiamide derivatives; amine-based curing agents such as aliphatic amines, alicyclic amines, and aromatic amines; and urea compounds. From the viewpoint of obtaining a prepreg with excellent thermal stability and low-temperature curing properties, component (B) preferably contains an imidazole compound, an aromatic amine, or a urea compound, and more preferably contains an imidazole compound. The imidazole compound enables primary curing of matrix resin composition (II) at a relatively low temperature of 150°C or less, thereby enabling the curing reaction to occur at low cost. It also reduces the water absorption of prepregs and fiber-reinforced composite materials. Component (A) and epoxy resin react to form oxazolidone rings, which then cure into a resin having both triazine and oxazolidone ring crosslinks. The inclusion of component (B) improves the reactivity, enabling the production of a prepreg that can be cured at low temperatures.

[0050] Examples of the imidazole compound include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazolium trimellitate, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4- Examples of the methylimidazole derivatives include, but are not limited to, diamino-6-(2'-methylimidazolyl-(1'))-ethyl-s-triazine, 2,4-diamino-6-(2'-undecylimidazolyl-(1'))-ethyl-s-triazine, 2,4-diamino-6-(2'-ethyl-4-methylimidazolyl-(1'))-ethyl-s-triazine, 2,4-diamino-6-(2'-methylimidazolyl-(1'))-ethyl-s-triazine·isocyanuric acid adduct, 2-phenylimidazole·isocyanuric acid adduct, 2-methylimidazole·isocyanuric acid adduct, 1-cyanoethyl-2-phenyl-4,5-di(2-cyanoethoxy)methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole. The imidazole compounds may be used alone or in combination of two or more.

[0051] Among imidazole compounds, imidazole compounds having a triazine ring skeleton are preferred because they can enhance the primary curing properties of the matrix resin composition (II) at 150°C or less. Imidazole compounds having a substituent with a triazine ring are more preferred, and imidazole compounds having a 1,3,5-triazine (also simply referred to as triazine or s-triazine) ring at the nitrogen atom at the 1-position of the imidazole ring are even more preferred. The triazine ring and imidazole ring may be directly bonded, but are preferably bonded via an alkylene group having 1 to 4 carbon atoms, and more preferably via an ethylene group. The substituent with a triazine ring preferably has amino groups at the 2- and 4-positions of the triazine ring. The imidazole compound having a substituent with a triazine ring may be an adduct of isocyanuric acid.

[0052] Preferable imidazole compounds containing a substituent having a triazine ring include 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, and isocyanuric acid addition salts of 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine. In view of the excellent balance between low-temperature curing properties and thermal stability, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine and the isocyanuric acid addition salt of 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine are more preferred. These are commercially available, for example, under the trade names 2MZ-A, C11Z-A, 2E4MZ-A, and 2MA-OK (Shikoku Chemical Industry Co., Ltd.). Particles of imidazole compounds containing a substituent having a triazine ring include, but are not limited to, 2MZA-PW (Shikoku Chemical Industry Co., Ltd.) and 2MAOK-PW (Shikoku Chemical Industry Co., Ltd.).

[0053] Examples of aromatic amines include 3,3'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-4,4'-diaminodiphenylmethane, 3,3'-diethyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-diisopropyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane, 3,3'-diisopropyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3'-diisopropyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, , 3'-di-t-butyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetraisopropyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetra-t-butyl-4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, m-phenylenediamine, m-xylylenediamine, and diethyltoluenediamine are examples of aromatic amines, but are not limited thereto. One aromatic amine may be used alone, or two or more aromatic amines may be used in combination.

[0054] Examples of the urea compound include, but are not limited to, aromatic dimethylurea in which a dimethylureido group is bonded to an aromatic ring, and aliphatic dimethylurea in which a dimethylureido group is bonded to an aliphatic compound. One type of urea compound may be used alone, or two or more types may be used in combination.

[0055] The component (B) is preferably contained in the matrix resin composition (II) of the prepreg as particles. By containing the component (B) in the matrix resin composition (II) as particles, the component (B) exists as a solid in the resin composition below a specific temperature and is therefore less likely to act as a catalyst for the curing reaction, but dissolves in the matrix resin composition (II) at temperatures above a specific temperature and is more likely to promote the curing reaction, making it easier to ensure both thermal stability and low-temperature curing properties.

[0056] The number average particle diameter of component (B) is preferably 1 μm or more, more preferably 3 μm or more. By setting the number average particle diameter of component (B) to the lower limit or more, thermal stability is more easily ensured. The number average particle diameter of component (B) is preferably 15 μm or less, more preferably 10 μm or less. By setting the number average particle diameter of component (B) to the upper limit or less, low temperature curing properties are more easily exhibited. The upper and lower limits of the number average particle diameter of component (B) can be arbitrarily combined; for example, 1 to 15 μm is preferred, and 3 to 10 μm is more preferred. The number average particle diameter can be measured using a laser diffraction / scattering method.

[0057] The content of component (B) in matrix resin composition (II) is preferably 0.05 parts by mass or more, and more preferably 0.1 parts by mass or more, per 100 parts by mass of component (A). By setting the content of component (B) to the lower limit or more, sufficient primary curing properties can be easily achieved even at temperatures of 150°C or lower. The content of component (B) is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less. By setting the content of component (B) to the upper limit or less, storage stability at room temperature can be easily maintained. The upper and lower limits of the content of component (B) can be arbitrarily combined; for example, 0.05 to 5 parts by mass is preferred, and 0.1 to 3 parts by mass is more preferred.

[0058] <Component (C)> The description of the component (C) in the first embodiment also applies to the component (C) in the second embodiment.

[0059] The content of component (C) in matrix resin composition (II) is 0.1 to 30 mass% relative to the total mass of matrix resin composition (II). The lower limit of the content of component (C) is preferably 1 mass%, more preferably 3 mass%, even more preferably 4 mass%, and particularly preferably 5 mass%. The upper limit of the content of component (C) is preferably 25 mass%, more preferably 20 mass%. By setting the content of component (C) at or above the lower limit, a fiber-reinforced composite material with improved water absorption is more likely to be obtained, while by setting the content at or below the upper limit, a decrease in rigidity of the fiber-reinforced composite material is more likely to be suppressed. The lower and upper limits of the content of component (C) can be arbitrarily combined, and may be, for example, 1 to 30 mass%, 2 to 30 mass%, 3 to 30 mass%, 4 to 30 mass%, 5 to 30 mass%, 1 to 25 mass%, 3 to 20 mass%, 4 to 20 mass%, or 5 to 20 mass%.

[0060] From the viewpoint of obtaining a fiber-reinforced composite material having excellent mechanical properties and heat resistance, the mass ratio of the content of the component (A) to the component (C) in the matrix resin composition (II) (component (A) / component (C)) is preferably 30 or less, and more preferably 25 or less. From the viewpoint of rapid curing of the prepreg, the content ratio of the component (A) / component (C) is preferably 1 or more, and more preferably 3 or more. The lower limit and upper limit of the component (A) / component (C) can be arbitrarily combined; for example, 1 to 30 is more preferable, and 3 to 25 is more preferable.

[0061] From the viewpoint of improving the water absorption rate of the fiber-reinforced composite material, the mass ratio of the content of the (B) component to the (C) component ((B) component / (C) component) in the matrix resin composition (II) is preferably 0.5 or less, and more preferably 0.4 or less. From the viewpoint of rapid curing of the prepreg, the content of the (B) component / (C) component is preferably 0.01 or more, and more preferably 0.02 or more. The lower and upper limits of the content of the (B) component / (C) component can be arbitrarily combined; for example, 0.01 to 0.5 is more preferable, and 0.02 to 0.4 is more preferable.

[0062] <Optional Components> The explanation of the optional components in the first embodiment also applies to the optional components in the second embodiment. As explained in the first embodiment, epoxy resins are preferred as optional components in the second embodiment as well, because they suppress the formation of a rigid triazine skeleton in the fiber-reinforced composite material and allow shrinkage to proceed smoothly during the cooling process from the end of curing to room temperature. In particular, bisphenol A epoxy resins and bisphenol F epoxy resins easily disperse components (B) and (C), and when component (A) is a bisphenol A cyanate ester resin, they easily disperse all of components (A) to (C).

[0063] From the viewpoint of improving the water absorption rate and enhancing the dispersibility of each component, the content of the epoxy resin in the matrix resin composition (II) is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, relative to the total mass of the matrix resin composition (II). The content of the epoxy resin is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. The lower and upper limits of the epoxy resin content can be arbitrarily combined; for example, 0.1 to 30% by mass is preferred, 1 to 20% by mass is more preferred, and 3 to 15% by mass is more preferred.

[0064] <Preferred Composition> As a combination of the components (A), (B), and (C) contained in the matrix resin composition (II), a combination of any of the following components (A1) to (A4), any of the following components (B1) to (B6), and any of the following components (C1) to (C5) is preferred, a combination of any of the components (A1) to (A4), any of the following components (B2) to (B6), and any of the following components (C1) to (C5) is more preferred, and a combination of any of the components (A1) to (A4) and any of the following components (B3) to (B6) is more preferred. ) and any of the following components (C2) to (C5) are more preferred; a combination of any of the (A2) to (A4) components, any of the following components (B4) to (B6), and any of the following components (C3) to (C5) are even more preferred; a combination of any of the (A3) to (A4) components, any of the following components (B5) to (B6), and any of the following components (C4) to (C5) are particularly preferred; and a combination of the (A4), the (B6), and the (C5) components is most preferred.Component (A1): a cyanate ester resin containing two or more cyanate groups per molecule; Component (A2): a thiophene-free cyanate ester resin; Component (A3): at least one of a bisphenol A-type cyanate ester resin and a phenol novolac-type cyanate ester resin; Component (A4): a bisphenol A-type cyanate ester resin; Component (B1): an imidazole compound, an aromatic amine, or a urea compound; Component (B2): an imidazole compound; Component (B3): an imidazole compound having a triazine ring skeleton; Component (B4): an imidazole compound having a substituent having a 1,3,5-triazine ring at the 1-position nitrogen of the imidazole ring. Component (B5): One or more selected from 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, and isocyanuric acid addition salts of 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine. Component (B6): At least one of 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine and isocyanuric acid addition salts of 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine. Component (C1): One or more selected from silicone rubber particles, silicone-acrylic composite rubber particles, and core-shell rubber particles. Component (C2): Core-shell rubber particles. Component (C3): Core-shell rubber particles whose core component contains polybutadiene or styrene-butadiene. Component (C4): Core-shell rubber particles whose core component contains polybutadiene or styrene-butadiene, and whose shell component is graft-polymerized to the core component with one or more selected from acrylic acid ester monomers, methacrylic acid ester monomers, and aromatic vinyl monomers. Component (C5): Core-shell rubber particles whose core component contains polybutadiene or styrene-butadiene, and whose shell component is graft-polymerized to the core component with a mixture of methyl methacrylate and styrene.

[0065] The matrix resin composition (II) preferably contains any one of the components (A1) to (A4), any one of the components (B1) to (B6), and any one of the components (C1) to (C5), and further contains any one of the following components (D1) to (D2) as an optional component. A combination of any one of the components (A1) to (A4), any one of the components (B2) to (B6), any one of the components (C1) to (C5), and any one of the components (D1) to (D2) is more preferred. A combination of any one of the components (A1) to (A4), any one of the components (B3) to (B6), and any one of the components (C2) to (C5) is more preferred. A combination of any of the components (A2) to (A4), any of the components (B4) to (B6), any of the components (C3) to (C5), and any of the components (D1) to (D2) is more preferred, a combination of any of the components (A3) to (A4), any of the components (B5) to (B6), any of the components (C4) to (C5), and any of the components (D1) to (D2) is particularly preferred, and a combination of the component (A4), the component (B6), the component (C5), and the component (D2) is the most preferred. Component (D1): Epoxy resin Component (D2): Bisphenol A type epoxy resin

[0066] The matrix resin composition (II) may contain, relative to the total mass of the matrix resin composition (II), more than 50 mass% and not more than 99 mass% of the (A) component and 0.1 to 30 mass% of the (C) component, and may contain 0.05 to 5 parts by mass of the (B) component per 100 parts by mass of the (A) component; it may contain 55 to 99 mass% of the (A) component and 0.1 to 30 mass% of the (C) component, and may contain 0.05 to 5 parts by mass of the (B) component per 100 parts by mass of the (A) component; it may contain 60 to 97 mass% of the (A) component and 1 to 25 mass% of the (C) component, and may contain 0.1 to 3 parts by mass of the (B) component per 100 parts by mass of the (A) component; or it may contain 80 to 97 mass% of the (A) component and 3 to 20 mass% of the (C) component, and may contain 0.1 to 3 parts by mass of the (B) component per 100 parts by mass of the (A) component. However, the total amount of components (A), (B) and (C) does not exceed 100% by mass.

[0067] The matrix resin composition (II) may contain, relative to the total mass of the matrix resin composition (II), more than 50 mass% and not more than 95 mass% of the (A) component, 4 to 30 mass% of the (C) component, and 0.1 to 3 parts by mass of the (B) component per 100 parts by mass of the (A) component; it may contain 55 to 95 mass% of the (A) component, 4 to 30 mass% of the (C) component, and 0.1 to 3 parts by mass of the (B) component per 100 parts by mass of the (A) component; it may contain 60 to 95 mass% of the (A) component, 4 to 25 mass% of the (C) component, and 0.1 to 3 parts by mass of the (B) component per 100 parts by mass of the (A) component; or it may contain 80 to 90 mass% of the (A) component, 4 to 20 mass% of the (C) component, and 0.1 to 3 parts by mass of the (B) component per 100 parts by mass of the (A) component. However, the total amount of components (A) and (C) does not exceed 100% by mass.

[0068] Furthermore, the matrix resin composition (II) may have a composition in which, relative to the total mass of the matrix resin composition (II), the component (A) is more than 50% by mass and not more than 99% by mass, the component (C) is 0.1 to 30% by mass, and the epoxy resin is 0.1 to 30% by mass, and the component (B) is 0.05 to 5 parts by mass per 100 parts by mass of the component (A); or the matrix resin composition (II) may have a composition in which, relative to the total mass of the matrix resin composition (II), the component (A) is 55 to 99% by mass, the component (C) is 0.1 to 30% by mass, and the epoxy resin is 0.1 to 30% by mass, and the component (B) is 0 parts by mass per 100 parts by mass of the component (A). The matrix resin composition (II) may contain 60 to 97 mass% of component (A), 1 to 25 mass% of component (C), and 1 to 20 mass% of epoxy resin, relative to the total mass of the matrix resin composition (II), and 0.1 to 3 mass% of component (B) per 100 mass parts of component (A); or the matrix resin composition (II) may contain 80 to 93.9 mass% of component (A), 3 to 20 mass% of component (C), and 3 to 15 mass% of epoxy resin, relative to the total mass of the matrix resin composition (II), and 0.1 to 3 mass% of component (B) per 100 mass parts of component (A), provided that the total of component (A), component (B), component (C), and epoxy resin does not exceed 100 mass%.

[0069] Furthermore, the matrix resin composition (II) may have a composition that contains, relative to the total mass of the matrix resin composition (II), more than 50% by mass and not more than 95% by mass of the component (A), 4 to 30% by mass of the component (C), and 0.1 to 30% by mass of the epoxy resin, and contains 0.1 to 3 parts by mass of the component (B) per 100 parts by mass of the component (A), and may have a composition that contains 55 to 95% by mass of the component (A), 4 to 30% by mass of the component (C), and 0.1 to 30% by mass of the epoxy resin, and contains 100 parts by mass of the component (A). It may be a composition containing 0.1 to 3 parts by mass of component (B) relative to 100 parts by mass of component (A), 60 to 93% by mass of component (A), 4 to 25% by mass of component (C), and 1 to 20% by mass of epoxy resin, and 0.1 to 3 parts by mass of component (B) relative to 100 parts by mass of component (A), or it may be a composition containing 80 to 90% by mass of component (A), 4 to 20% by mass of component (C), and 3 to 15% by mass of epoxy resin, and 0.1 to 3 parts by mass of component (B) relative to 100 parts by mass of component (A), provided that the total of component (A), component (C), and epoxy resin does not exceed 100% by mass.

[0070] <Method for Producing Matrix Resin Composition (II)> The matrix resin composition (II) can be obtained, for example, by mixing the above-described components. Examples of methods for mixing the components include using a mixer such as a three-roll mill, planetary mixer, kneader, homogenizer, or homodisper. From the perspective of uniformly dispersing component (C), it is preferable to add a masterbatch in which component (C) is dispersed in an epoxy resin to a mixture containing components (A) and (B), and, as necessary, optional components. Alternatively, a film of the matrix resin composition can be obtained by applying the matrix resin composition to release paper or the like and curing it. When used as a film, a viscosity of the matrix resin composition at 30°C of 100 to 1,000,000 Pa·s provides excellent control of the tackiness of the prepreg surface and excellent workability.

[0071] <Reinforcing Fiber> The description of the reinforcing fiber in the first embodiment also applies to the reinforcing fiber in the second embodiment.

[0072] <Method for Producing Prepreg> The prepreg of the second embodiment can be produced in the same manner as described in the first embodiment, except that the matrix resin composition (II) is used instead of the matrix resin composition (I).

[0073] The content of the matrix resin composition (II) in the prepreg of the second embodiment (hereinafter referred to as the "resin content") is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, relative to the total mass of the prepreg. When the resin content is equal to or greater than the lower limit, adhesion between the reinforcing fibers and the matrix resin is easily obtained. The resin content of the prepreg is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. When the resin content is equal to or less than the upper limit, the mechanical properties of the resulting fiber-reinforced composite material are further improved. The upper and lower limits of the resin content can be arbitrarily combined; for example, 15 to 50% by mass is preferred, 20 to 45% by mass is more preferred, and 25 to 40% by mass is even more preferred.

[0074] In the prepreg of the second embodiment, the mass ratio of the component (A) to the carbon fiber (component (A) / carbon fiber) is preferably 0.2 or more, more preferably 0.3 or more, and preferably 0.6 or less, more preferably 0.5 or less. When the component (A) / carbon fiber ratio is within the above range, the heat resistance of the fiber-reinforced composite material is improved. The upper and lower limits of the component (A) / carbon fiber ratio can be arbitrarily combined, and for example, 0.2 to 0.6 is preferred, and 0.3 to 0.5 is more preferred.

[0075] In the prepreg of the second embodiment, the mass ratio of the component (C) to the carbon fiber (component (C) / carbon fiber) is preferably 0.005 or more, more preferably 0.01 or more, and preferably 0.2 or less, more preferably 0.1 or less. When the component (C) / carbon fiber ratio is within the above range, the water absorption rate of the fiber-reinforced composite material is improved. The upper and lower limits of the component (C) / carbon fiber ratio can be arbitrarily combined, and for example, 0.005 to 0.2 is preferred, and 0.01 to 0.1 is more preferred.

[0076] [Fiber-reinforced composite material] A fiber-reinforced composite material is obtained by curing the prepreg of the first embodiment or the second embodiment. That is, the fiber-reinforced composite material contains a cured product of the matrix resin composition contained in the prepreg and reinforcing fibers. One embodiment of the fiber-reinforced composite material is composed of a reinforcing fiber substrate and a cured product of the matrix resin composition, and the matrix resin composition contains a cured product of a cyanate ester resin and rubber particles. In the fiber-reinforced composite material, only one of the prepreg of the first embodiment and the prepreg of the second embodiment may be used, or both the prepreg of the first embodiment and the prepreg of the second embodiment may be used. Note that prepregs other than the prepreg of the first embodiment and the prepreg of the second embodiment may also be used in combination.

[0077] Examples of molding methods include press molding, autoclave molding, bagging molding, wrapping tape molding, internal pressure molding, and sheet wrap molding, as well as RTM (Resin Transfer Molding), VaRTM (Vacuum Assisted Resin Transfer Molding), filament winding, and RFI (Resin Film Infusion), which involve impregnating a reinforcing fiber filament or preform with an epoxy resin composition and curing it to obtain a molded product. Among these, autoclave molding is preferred from the viewpoint of easily obtaining a high-quality fiber-reinforced composite material. Autoclave molding is a method in which prepregs are laminated and covered with a backing film, and the prepreg laminate is pressurized and heat-cured while degassing. This method allows for precise control of fiber orientation and minimizes the generation of voids, resulting in a high-quality molded product with excellent mechanical properties.

[0078] It is also preferable to place the prepreg laminate in a mold and perform a primary cure at a low temperature, and then remove it from the mold and perform a secondary cure at a high temperature. The primary cure temperature can be, for example, 100 to 200°C, and from the viewpoint of sufficiently progressing the cure while suppressing resin flow and improving the appearance quality, 130 to 150°C is preferred. The secondary cure temperature can be 200 to 270°C. If the secondary cure temperature is 200°C or higher, a fiber-reinforced composite material with excellent heat resistance is likely to be obtained. If the secondary cure temperature is 270°C or lower, thermal decomposition of the matrix resin composition can be suppressed, and a fiber-reinforced composite material with excellent mechanical properties is likely to be obtained.

[0079] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples in any way.

[0080] [Raw Materials] <Component (A)> TA: bisphenol A cyanate ester resin, "CYTESTER (registered trademark) TA" manufactured by Mitsubishi Gas Chemical Company, Inc. TA-100: bisphenol A cyanate ester resin prepolymer, "CYTESTER (registered trademark) TA-100" manufactured by Mitsubishi Gas Chemical Company, Inc. TA-1500: bisphenol A cyanate ester resin prepolymer, "CYTESTER (registered trademark) TA-1500" manufactured by Mitsubishi Gas Chemical Company, Inc.

[0081] <Component (B)> 2MZA-PW: 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, "2MZA-PW" manufactured by Shikoku Chemical Industry Co., Ltd. Seikacure-S: 4,4'-diaminodiphenyl sulfone, "Seikacure-S" manufactured by Wakayama Seika Kogyo Co., Ltd. Aradur 9719-1: 3,3'-diaminodiphenyl sulfone, "Araldite Aradur 9719-1" manufactured by Huntsman Advanced Materials Omicure 94: 3-phenyl-1,1-dimethylurea, "Omicure 94" manufactured by PTI Japan Co., Ltd.

[0082] <Component (C)> MX-154: Masterbatch containing 60% by mass of bisphenol A epoxy resin and 40% by mass of core-shell rubber particles whose core component is polybutadiene rubber, manufactured by Kaneka Corporation "MX-154" MX-125: Masterbatch containing 75% by mass of bisphenol A epoxy resin and 25% by mass of core-shell rubber particles whose core component is styrene butadiene rubber, manufactured by Kaneka Corporation "MX-125" S-2030: Silicone-acrylic composite rubber, manufactured by Mitsubishi Chemical Corporation "S-2030" MX-962: Masterbatch containing 75% by mass of bisphenol A epoxy resin and 25% by mass of core-shell rubber particles whose core component is silicone rubber, manufactured by Kaneka Corporation "MX-962"

[0083] <Optional ingredients> YD-128: bisphenol A type epoxy resin, epoxy equivalent 189 g / eq, "YD-128" manufactured by Nippon Steel Chemical & Material Co., Ltd. 5003MP: polyethersulfone fine powder, "Sumikaexcel 5003MP" manufactured by Sumitomo Chemical Co., Ltd.

[0084] <Carbon fiber> Carbon fiber: "Pyrofil TR50S15L" manufactured by Mitsubishi Chemical Corporation (average fiber diameter 7 μm, specific gravity 1.82, tensile modulus 235 GPa)

[0085] [Evaluation of Heat Resistance of Cured Resin Products and Fiber-Reinforced Composite Materials] The heat resistance of cured resin products and fiber-reinforced composite materials was evaluated by measuring the glass transition temperatures (G'-Tg and tan δ) according to ASTM D4065. Specifically, test pieces were prepared by cutting the cured resin products and fiber-reinforced composite materials into pieces measuring 55 mm in length and 12.7 mm in width. Subsequently, DMA (dynamic viscoelasticity measurement) was performed using a TA Instruments ARES-G2 dynamic viscoelasticity measuring device to measure the storage modulus (G'). Log G' was plotted against temperature, and the glass transition temperature (G'-Tg) was determined as the temperature obtained from the intersection of the approximation line of log G' in the flat region before the transition to the rubbery state and the tangent line at the inflection point of the slope in the region where log G' transitions. The temperature at which the ratio of loss modulus (G") to storage modulus (G') (loss modulus / storage modulus) peaks was defined as the glass transition temperature (tan δ). Higher G'-Tg and tan δ indicate higher heat resistance. Measurements of G'-Tg and tan δ were carried out under the following conditions: measurement frequency: 1 Hz, measurement temperature range: about 30°C to about 400°C, heating rate: 5°C / min, and strain: 0.05%.

[0086] [Evaluation of Water Absorption of Cured Resin] The water absorption of the cured resin was measured according to the following steps 1 to 5. 1. Two test pieces were prepared by processing a 2.0 mm thick cured resin into a length of 55 mm and a width of 12.7 mm. 2. The test pieces were thoroughly wiped with acetone, and the masses of the test pieces before water absorption were measured and designated W1. 3. Using a thermostatic water bath, one test piece was immersed in 70°C hot water for two weeks, and the other test piece was immersed in 70°C hot water for four weeks. When multiple test pieces were immersed, each test piece was wrapped in gauze to prevent direct contact between the test pieces. 4. The immersed test pieces were removed, and water droplets on the surface of the test pieces were thoroughly wiped off. The masses of the test pieces after water absorption were measured. The masses of the test pieces after two weeks of water absorption were designated W2a and W2b, respectively. 5. The water absorption rate after 2 weeks and after 4 weeks was calculated using the following formula: Water absorption rate after 2 weeks [%] = [(W2a - W1) / W1] x 100 Water absorption rate after 4 weeks [%] = [(W2b - W1) / W1] x 100

[0087] [Evaluation of Water Absorption of Fiber-Reinforced Composite Material] The water absorption of the fiber-reinforced composite material after 2 weeks and after 4 weeks was calculated according to the procedure described in [Evaluation of Water Absorption of Cured Resin Material]. Next, the fiber volume content (Vf) and resin content (Rc) of the actual molded product were determined by Archimedes' method, and the resin content was converted to 33% to calculate the water absorption after 2 weeks (converted to Rc 33%) and after 4 weeks (converted to Rc 33%).

[0088] [Evaluation of heat resistance of fiber-reinforced composite material after water absorption] The fiber-reinforced composite material after water absorption for 4 weeks, obtained in the above [Evaluation of water absorption of fiber-reinforced composite material], was used to evaluate the heat resistance of the fiber-reinforced composite material after water absorption. The heat resistance evaluation was carried out in the same manner as in the above [Evaluation of heat resistance of cured resin product and fiber-reinforced composite material], and was evaluated by DMA (dynamic viscoelasticity measurement) in accordance with ASTM D4065.

[0089] [Experimental Examples 1 to 23] <Production of Matrix Resin Composition> Matrix resin compositions were prepared as follows using the components shown in Tables 1 to 5. First, component (A), component (C), and optional components were weighed into a flask in the proportions shown in Tables 1 to 5, and then heated to 80 to 120°C using an oil bath to dissolve and mix. When component (B) was added, the mixture was then cooled to 70°C, and component (B) was added and mixed with stirring to obtain a matrix resin composition.

[0090] <Production of Cured Resin> The obtained matrix resin composition was poured into the gap between two 4 mm thick glass plates that had been treated with a release agent and sandwiched between them using a polytetrafluoroethylene (PTFE) spacer. The temperature was increased in an oven at a rate of 2°C / min and the oven ambient temperature was maintained at 135°C for 120 minutes to obtain a primary cured product. The primary cured product was then removed from the glass plates and, in a free-standing state, the temperature was increased in an oven at a rate of 0.3°C / min and the oven ambient temperature was maintained at 250°C for 120 minutes to obtain a secondary cured product. The secondary cured product was used as a cured resin, and the heat resistance and water absorption were evaluated, with the results shown in Tables 1 to 5.

[0091] <Production of prepreg> The obtained matrix resin composition was formed into a film using a hot melt coater (R-HC, manufactured by Hirano Tecseed Co., Ltd.), and the resin basis weight was 30.8 g / m ２ This resin film was coated with a carbon fiber having a fiber basis weight of 120 g / m2 obtained by aligning the carbon fibers. ２ and impregnated with a heated roll to a fiber basis weight of 125 g / m. ２ A prepreg having a resin content of 33% by mass was obtained. Tables 6 and 7 show the content of each component relative to the carbon fiber in the prepreg.

[0092] <Production of Fiber-Reinforced Composite Material> The resulting prepreg was cut into a 300 mm x 300 mm piece, and 18 sheets were stacked with the fiber orientation aligned to obtain a laminate. This laminate was heated in an autoclave at a rate of 2°C / min under a pressure of 0.6 MPa, held at 80°C for 120 minutes, and then heated at a rate of 2°C / min under a pressure of 0.6 MPa, held at 135°C for 60 minutes to be heat-cured and molded to obtain a primary cured product with a thickness of 2.0 mm. This primary cured product was heated in an oven in a free-standing state at a rate of 0.3°C / min, and held at an oven ambient temperature of 250°C for 120 minutes to obtain a secondary cured product. The secondary cured product was used as a fiber-reinforced composite material and evaluated for heat resistance and water absorption. The results are shown in Tables 6 and 7.

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[0100] As is clear from the results in Tables 1 to 5, the cured resin products obtained by curing the matrix resin compositions of Experimental Examples 1 to 14, and 23, which contained the specified amounts of component (A) and component (C), maintained their heat resistance while exhibiting improved water absorption compared to Comparative Examples 15 to 22, which did not contain component (C). Furthermore, as is clear from the results in Tables 6 and 7, the fiber-reinforced composite materials obtained using the matrix resin compositions of Experimental Examples 1, 2, 6, 9, 10, and 23 also exhibited improved water absorption and maintained their heat resistance before and after water absorption. In particular, Experimental Example 1, which incorporated component (C) relative to Experimental Example 16, exhibited a lower water absorption rate and also showed less deterioration in heat resistance after 4 weeks of water absorption. Furthermore, Experimental Example 2, which incorporated a higher proportion of component (C) relative to component (A), exhibited an even lower water absorption rate and less deterioration in heat resistance after 4 weeks of water absorption. Furthermore, Experimental Example 10, which incorporated a different component (C) from Experimental Example 16, exhibited a lower water absorption rate and showed better results than Experimental Example 16. Furthermore, compared to Experimental Example 22, Experimental Example 6, which contained component (C), had a lower water absorption rate and showed better results.

Claims

1. A prepreg in which a reinforcing fiber substrate containing carbon fiber is impregnated with a matrix resin composition, the matrix resin composition comprising the following components (A), (B), and (C), in which the content of component (A) is greater than 50% by mass and the content of component (C) is 0.1 to 30% by mass, based on the total mass of the matrix resin composition: Component (A): cyanate ester resin, Component (B): curing agent, and Component (C): rubber particles.

2. A prepreg in which a reinforcing fiber substrate containing carbon fiber is impregnated with a matrix resin composition, the matrix resin composition containing the following components (A) and (C), in which the content of component (A) is greater than 50 mass% and the content of component (C) is 4 to 30 mass% relative to the total mass of the matrix resin composition: Component (A): cyanate ester resin Component (C): rubber particles 3. The prepreg according to claim 1, wherein the content of component (C) is 1 to 25 mass % relative to the total mass of the matrix resin composition.

4. The prepreg according to claim 1, wherein the content of said component (C) is 3 to 20 mass % relative to the total mass of said matrix resin composition.

5. The prepreg according to claim 1 or 2, wherein the mass ratio of the component (A) to the carbon fiber (component (A) / carbon fiber) in the prepreg is 0.2 to 0.

6.

6. The prepreg according to claim 1 or 2, wherein the mass ratio of the component (C) to the carbon fiber (component (C) / carbon fiber) in the prepreg is 0.005 to 0.

2.

7. The prepreg according to claim 1 or 2, wherein component (A) comprises a thiophene-free cyanate ester resin.

8. The prepreg according to claim 1 or 2, wherein component (A) contains a bisphenol A cyanate ester resin.

9. The prepreg according to claim 1 or 2, wherein the component (B) comprises an imidazole compound, an aromatic amine, or a urea compound.

10. The prepreg according to claim 1 or 2, wherein component (B) includes an imidazole compound.

11. The prepreg according to claim 1 or 2, wherein the component (B) contains an imidazole compound having a triazine ring skeleton.

12. The prepreg according to claim 1 or 2, wherein component (C) contains core-shell rubber particles.

13. The prepreg of claim 12, wherein the core component of the core-shell rubber particles comprises polybutadiene or styrene butadiene.

14. The prepreg according to claim 1 or 2, wherein the matrix resin composition comprises an epoxy resin.

15. The prepreg according to claim 1 or 2, which contains 0.1 to 30 mass% of an epoxy resin relative to the total mass of the matrix resin composition.

16. The prepreg according to claim 14, wherein the epoxy resin is a compound containing bisphenol A type epoxy resin.

17. The prepreg according to claim 1 or 2, wherein the mass ratio of the content of the component (A) to the content of the component (C) (component (A) / component (C)) is 30 or less.

18. The prepreg according to claim 2, wherein the mass ratio of the content of the component (B) to the content of the component (C) (component (B) / component (C)) is 0.5 or less.

19. The prepreg according to claim 2, comprising 0.05 to 5 parts by mass of component (B) per 100 parts by mass of component (A).

20. The prepreg according to claim 1 or 2, wherein the reinforcing fiber substrate is a sheet of aligned carbon fiber bundles.

21. A fiber-reinforced composite material obtained by curing the prepreg according to claim 1 or 2.

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