Prepreg and fiber-reinforced composite material

Abstract

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

Description

Prepreg and Fiber-Reinforced Composites

[0001] The present invention relates to prepregs and fiber-reinforced composite materials.

[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 are known to have a low concentration of hydrophilic groups in the cured product and 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 exhibits excellent heat resistance while maintaining the mechanical properties of the molded product after molding. Patent Document 2 also describes that adding a large amount of silica to 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 object of the present invention is to provide a prepreg having an improved water absorption rate (low water absorption), and 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

[20] .

[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): Component (A): cyanate ester resin; Component (B): curing agent; and Component (C): rubber particles. [2]: The prepreg according to [1], in which the content of component (C) is 1 to 25 mass% relative to the total mass of the matrix resin composition. [3]: The prepreg according to [1] or [2], in which the content of component (C) is 3 to 20 mass% relative to the total mass of the matrix resin composition. [4]: ​​The prepreg according to any one of [1] to [3], in which the mass ratio of component (A) to carbon fiber (component (A) / carbon fiber) in the prepreg is 0.2 to 0.6. [5]: The prepreg according to any one of [1] to [4], wherein the mass ratio of the content of the (C) component to the carbon fiber ((C) component / carbon fiber) in the prepreg is 0.005 to 0.2. [6]: The prepreg according to any one of [1] to [5], wherein the content of the (A) component is a thiophene-free cyanate ester resin. [7]: The prepreg according to any one of [1] to [6], wherein the (A) component contains a bisphenol A-type cyanate ester resin. [8]: The prepreg according to any one of [1] to [7], wherein the (B) component contains an imidazole compound, an aromatic amine, or a urea compound. [9]: The prepreg according to any one of [1] to [8], wherein the (B) component contains an imidazole compound.

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

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

[10] , wherein the component (C) comprises core-shell rubber particles.

[12] : The prepreg according to

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

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

[12] , wherein the matrix resin composition comprises an epoxy resin.

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

[13] , wherein the epoxy resin is contained in an amount of 0.1 to 30% by mass relative to the total mass of the matrix resin composition.

[15] : The prepreg according to

[13] or

[14] , wherein the epoxy resin contains a bisphenol A-type epoxy resin.

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

[15] , 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.

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

[16] , 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.

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

[17] , wherein the content of the (B) component is 0.1 to 3 parts by mass relative to 100 parts by mass of the (A) component.

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

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

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

[19] .

[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] One embodiment of the present invention relates to a prepreg. A prepreg is a reinforcing fiber substrate containing carbon fiber impregnated with a matrix resin composition. The matrix resin composition contains the following components (A), (B), and (C). The matrix resin composition may further contain optional components other than these components. Component (A): cyanate ester resin Component (B): curing agent Component (C): rubber particles In addition, in a prepreg according to one embodiment of the present invention, 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.

[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, during the cooling process from the end of curing back to room temperature, smooth shrinkage is prevented by 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, component (C) can effectively fill the 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 is preferably 1,000 to 100,000 Pa·s, more preferably 3,000 to 80,000 Pa·s, at 30°C.

[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), phenol novolac cyanate ester resin prepolymer (Arcsada Japan Co., Ltd., Primaset PT-30), bisphenol A cyanate ester resin prepolymer (Mitsubishi Gas Chemical Company, Inc., TA-500), phenol novolac cyanate ester resin prepolymer (Arcsada Japan Co., Ltd., Primaset PT-60), dicyclopentadiene structure-containing cyanate ester resin prepolymer (Arcsada Japan Co., Ltd., Primaset DT-4000), and bisphenol M cyanate ester resin prepolymer (Arcsada Japan Co., Ltd., Primaset LMP-500). Commercially available cyanate ester resins may be used alone or in combination of two or more.

[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 the matrix resin composition is greater than 50% by mass, preferably 55 parts by mass or more, more preferably 60 parts by mass or more, and even more preferably 80 parts by mass or more, relative to the total mass of the matrix resin composition. 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 parts by mass or less, more preferably 97 parts by mass or less, and even more preferably 97 parts by mass or less, relative to the total mass of the matrix resin composition. 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; for example, 55 to 99 parts by mass is preferred, 60 to 97 parts by mass is more preferred, and 80 to 97 parts by mass is even more preferred.

[0016] <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. Imidazole compounds enable primary curing of the matrix resin composition at a relatively low temperature of 150°C or less, thereby enabling the curing reaction to be carried out at low cost. Furthermore, they can also reduce the water absorption of prepregs and fiber-reinforced composite materials.

[0017] 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.

[0018] 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 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.

[0019] 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 under the trade names 2MZ-A, C11Z-A, 2E4MZ-A, and 2MA-OK (Shikoku Chemicals Corporation).

[0020] 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.

[0021] 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.

[0022] Component (B) is preferably contained in the matrix resin composition of the prepreg as particles. By containing component (B) in the matrix resin composition as particles, the component 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 at temperatures above a specific temperature and is more likely to promote the curing reaction, making it easier to achieve both thermal stability and low-temperature curing properties.

[0023] 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) at or above the lower limit, 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) at or below the upper limit, low-temperature curing properties are more easily achieved. 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. Particles of an imidazole compound containing a substituent having a triazine ring are also available as 2MZA-PW (Shikoku Chemicals Corporation) and 2MAOK-PW (Shikoku Chemicals Corporation).

[0024] The content of component (B) in the matrix resin composition 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) at or above the lower limit, 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) at or below the upper limit, storage stability at room temperature can be easily maintained. The upper and lower limits for 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.

[0025] <Component (C)> Component (C) is rubber particles. By including rubber particles in the matrix resin composition, 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, 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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).

[0030] Component (C) may be dispersed in component (A) using a stirrer, a roll mill, or the like during preparation of the matrix resin composition. 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 the matrix resin composition be shortened but also component (C) can be uniformly dispersed in the matrix resin composition.

[0031] 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).

[0032] 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.

[0033] The content of component (C) in the matrix resin composition is 0.1 to 30 mass% relative to the total mass of the matrix resin composition. The lower limit of the content of component (C) is preferably 1 mass%, more preferably 3 mass%, and even more 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; for example, 1 to 25 mass% is preferred, and 3 to 20 mass% is more preferred.

[0034] 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) (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 ratio 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.

[0035] From the viewpoint of improving the water absorption rate of the fiber-reinforced composite material, the mass ratio of the (B) component to the (C) component ((B) component / (C) component) is preferably 0.5 or less, and more preferably 0.4 or less. From the viewpoint of rapid curing of the prepreg, the (B) component / (C) component ratio is preferably 0.01 or more, and more preferably 0.02 or more. The lower and upper limits of the (B) component / (C) component ratio can be arbitrarily combined; for example, 0.01 to 0.5 is more preferable, and 0.02 to 0.4 is more preferable.

[0036] <Optional Components> The matrix resin composition 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 to include an epoxy resin.

[0037] The inclusion of an epoxy resin inhibits the formation of rigid triazine skeletons within the fiber-reinforced composite material, allowing for smooth shrinkage during the cooling process from curing to room temperature. Examples of epoxy resins include, but are not limited to, 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 components (B) and (C). Furthermore, when component (A) is a bisphenol A-type cyanate ester resin, they facilitate the dispersion of all components (A) to (C).

[0038] 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 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. 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 even more preferred.

[0039] 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.

[0040] 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.

[0041] More specific examples of additives include flame retardants such as metal phosphinate, aluminum hydroxide, and magnesium hydroxide, inorganic oxides such as antimony compounds, zinc borate, zinc stannate, Mo compounds, ZrO, zinc sulfide, zeolite, and titanium oxide, silicone oil, wetting and dispersing agents, antifoaming agents, defoamers, natural waxes, synthetic waxes, metal salts of straight-chain fatty acids, acid amides, esters, and paraffins, mold release agents such as crystalline silica, fused silica, calcium silicate, alumina, calcium carbonate, talc, and barium sulfate, inorganic fillers such as glass fibers and carbon fibers with a fiber length of about 0.01 mm to 10 mm, 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.

[0042] <Method for Producing Matrix Resin Composition> The matrix resin composition 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 other components (A) and (B). 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.

[0043] <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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] <Prepreg Manufacturing Method> The prepreg can be manufactured, for example, by the following procedure. First, a matrix resin composition is applied to one side of a carrier film (first carrier film). Similarly, another carrier film (second carrier film) is prepared, with the matrix resin composition applied to one side. Next, the surfaces of the first carrier film and the second carrier film coated with the matrix resin composition are oriented toward the reinforcing fiber substrate, forming a laminate in which the reinforcing fiber substrate and the matrix resin composition are sandwiched between the first carrier film and the second carrier film. The obtained laminate is pressurized to impregnate the reinforcing fiber substrate with the matrix resin composition, thereby obtaining a prepreg.

[0048] The content of the matrix resin composition in the prepreg (hereinafter referred to as "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. If the resin content is equal to or greater than the aforementioned 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. If the resin content is equal to or less than the aforementioned 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.

[0049] The mass ratio of the content of component (A) to the carbon fiber (component (A) / carbon fiber) in the prepreg 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, a range of 0.2 to 0.6 is preferred, and a range of 0.3 to 0.5 is more preferred.

[0050] The mass ratio of the content of component (C) to carbon fiber (component (C) / carbon fiber) in the prepreg 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 component (C) / carbon fiber is within the above range, the water absorption of the fiber-reinforced composite material is improved. The upper and lower limits of component (C) / carbon fiber can be arbitrarily combined, and for example, 0.005 to 0.2 is preferred, and 0.01 to 0.1 is more preferred.

[0051] [Fiber-reinforced composite material] A fiber-reinforced composite material is obtained by curing a prepreg. That is, the fiber-reinforced composite material contains a cured product of a 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 a matrix resin composition, and the matrix resin composition contains a cured product of a cyanate ester resin and rubber particles.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] [Raw Materials] <Component (A)> TA: bisphenol A cyanate ester resin, "TA" manufactured by Mitsubishi Gas Chemical Company, Inc. TA-100: bisphenol A cyanate ester resin prepolymer, "TA-100" manufactured by Mitsubishi Gas Chemical Company, Inc. TA-1500: bisphenol A cyanate ester resin prepolymer, "TA-1500" manufactured by Mitsubishi Gas Chemical Company, Inc.

[0056] <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.

[0057] <Component (C)> MX-154: Masterbatch containing bisphenol A type epoxy resin and 40% by mass of core-shell rubber particles whose core component is polybutadiene rubber, "MX-154" manufactured by Kaneka Corporation MX-125: Masterbatch containing bisphenol A type epoxy resin and 25% by mass of core-shell rubber particles whose core component is styrene butadiene rubber, "MX-125" manufactured by Kaneka Corporation S-2030: Silicone-acrylic composite rubber, "S-2030" manufactured by Mitsubishi Chemical Corporation MX-962: Masterbatch containing bisphenol A type epoxy resin and 25% by mass of core-shell rubber particles whose core component is silicone rubber, "MX-962" manufactured by Kaneka Corporation

[0058] <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.

[0059] <Carbon fiber> Carbon fiber: "Pyrofil TR50S15L" manufactured by Mitsubishi Chemical Corporation (average fiber diameter 7 μm, specific gravity 1.82, tensile modulus 235 GPa)

[0060] [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%.

[0061] [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

[0062] [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%).

[0063] [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.

[0064] Examples 1 to 14, Comparative Examples 1 to 8 Production of Matrix Resin Compositions 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 dissolved and mixed by heating to 80 to 120°C using an oil bath. After that, the mixture was cooled to 70°C, and then component (B) was added and mixed by stirring to obtain a matrix resin composition.

[0065] <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.

[0066] <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 / m２ 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.

[0067] <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.

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075] As is clear from the results in Tables 1 to 3, the cured resin products obtained by curing the matrix resin compositions of Examples 1 to 14, which contained the specified amounts of component (A) and component (C), maintained their heat resistance while exhibiting improved water absorption compared to Comparative Examples 1 to 8, which did not contain component (C). Furthermore, as is clear from the results in Table 4, the fiber-reinforced composite materials obtained using the matrix resin compositions of the Examples also exhibited improved water absorption, maintaining their heat resistance before and after water absorption. In particular, Example 1, which incorporated component (C) relative to Comparative Example 2, exhibited a lower water absorption rate and also suppressed a decrease in heat resistance after 4 weeks of water absorption. Furthermore, Example 2, which incorporated a higher proportion of component (C) relative to component (A), exhibited an even lower water absorption rate and suppressed a decrease in heat resistance after 4 weeks of water absorption. Furthermore, Example 10, which incorporated a different component (C) from Example 1 relative to Comparative Example 2, exhibited a lower water absorption rate and better results than Comparative Example 2. Furthermore, Example 6, which incorporated component (C) relative to Comparative Example 9, exhibited a lower water absorption rate and 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. 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.

3. 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.

4. The prepreg according to claim 1, 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.

5. The prepreg according to claim 1, 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.

6. The prepreg according to claim 1, wherein component (A) is a thiophene-free cyanate ester resin.

7. The prepreg according to claim 1, wherein component (A) comprises a bisphenol A cyanate ester resin.

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

9. The prepreg according to claim 1, wherein component (B) comprises an imidazole compound.

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

11. The prepreg according to claim 1, wherein component (C) comprises core-shell rubber particles.

12. The prepreg of claim 11, wherein the core component of the core-shell rubber particles comprises polybutadiene or styrene butadiene.

13. The prepreg of claim 1, wherein the matrix resin composition comprises an epoxy resin.

14. The prepreg according to claim 1, comprising 0.1 to 30 mass % of an epoxy resin relative to the total mass of the matrix resin composition.

15. The prepreg of claim 13, wherein the epoxy resin comprises a bisphenol A type epoxy resin.

16. The prepreg according to claim 1, 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.

17. The prepreg according to claim 1, 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.

18. The prepreg according to claim 1, comprising 0.1 to 3 parts by mass of said component (B) per 100 parts by mass of said component (A).

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

20. A fiber-reinforced composite material obtained by curing the prepreg according to any one of claims 1 to 19.

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