Prepreg, fiber-reinforced composite material, and method for producing molded body

Abstract

The purpose of the present invention is to provide a prepreg which uses a resin composition that can be cured in a short period of time and is capable of suppressing resin flow during molding, and which has high workability. A prepreg characterized in that the prepreg contains an epoxy resin composition and reinforcing fibers, the epoxy resin composition containing component (A): a urea compound; component (B): a thermoplastic resin; component (C): an epoxy resin having an oxazolidinone structure; and component (D): a bisphenol epoxy resin that is solid at 25 DEG C, and satisfies the following conditions (1) and (2). Condition (1): The minimum viscosity of the epoxy resin composition measured by a rheometer under the condition of 2 DEG C / min is in the range of 3.0-6.0 Pa.s. Condition (2): the gelation time value of the epoxy resin composition, as measured under the condition of 145 DEG C by CURELASTOMETER (Registered Trademark), is in the range of 2.0-5.0 min.

Description

Methods for manufacturing prepregs, fiber-reinforced composites and molded articles Technical Field

[0001] This invention relates to methods for manufacturing prepregs, fiber-reinforced composites, and molded articles. Background Technology

[0002] Fiber-reinforced polymer (FRP) composites, which combine resin and reinforcing fibers, are widely used in sports and leisure applications, automotive, and industrial applications due to their excellent lightweight, rigidity, and impact resistance. Tubular FRP structures are particularly common in sports and leisure applications such as fishing rods, golf club shafts, skis, and bicycle frames.

[0003] Fiber-reinforced composite materials can be obtained by curing and molding a prepreg, wherein the prepreg is obtained by impregnating a matrix resin into a reinforcement formed of continuous fibers such as reinforcing fibers. From the viewpoint of strength and elastic modulus performance, carbon fiber is widely used as the reinforcing fiber. From the viewpoint of adhesion to carbon fiber, epoxy resin is widely used as the matrix resin. Specific methods for obtaining fiber-reinforced composite materials from prepregs include, for example, molding using an autoclave, pressure molding, internal pressure molding, and oven molding.

[0004] For tubular molded bodies of fiber-reinforced composite materials, important characteristics include flexural strength in the longitudinal direction and crushing strength in the diametrical direction. Patent Document 1 discloses a resin composition for fiber-reinforced composite materials that balances both flexural strength in the longitudinal direction and crushing strength in the diametrical direction. Furthermore, for prepregs required for sports and leisure applications, industrial applications, and other applications, there is a pursuit for materials that can be repeatedly molded, contribute to increased productivity, and reduce costs. Patent Document 2 discloses a resin composition for fiber-reinforced composite materials that can cure quickly even at low temperatures and exhibits excellent mechanical properties and heat resistance.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 1998 / 044017

[0008] Patent Document 2: International Publication No. 2020 / 080474 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] High-cycle molding is performed under high temperature and high pressure, resulting in an increase in temperature and a significant decrease in viscosity of the resin composition constituting the prepreg during molding. According to the inventors' research, in conventional high-cycle molding, resin flows out of the prepreg due to heating and pressurization during the molding process, leading to unimpregnated portions of the resin composition, fiber twisting, and other appearance defects.

[0011] The present invention was made in view of the above-mentioned technical problems. That is, one of the objects of the present invention is to provide a prepreg that can cure in a short time and suppress resin flow during molding.

[0012] Solution for solving the problem

[0013] The present invention includes the following embodiments.

[0014] [1]: A prepreg, characterized in that the prepreg comprises an epoxy resin composition and reinforcing fibers, wherein the epoxy resin composition comprises the following components (A), (B), (C) and (D) and satisfies the following conditions (1) and (2).

[0015] (A) Component: Urea compound.

[0016] (B) Composition: thermoplastic resin.

[0017] (C) Component: Epoxy resin with an oxazolidinone structure.

[0018] (D) Component: Bisphenol type epoxy resin that is solid at 25°C (excluding component (C)).

[0019] Condition (1): The lowest viscosity of the epoxy resin composition, as determined by a rheometer at 2°C / min, is in the range of 3.0 Pa·s or more, 3.1 Pa·s or more, 3.2 Pa·s or more, 6.0 Pa·s or less, 5.9 Pa·s or less, 5.5 Pa·s or less, 5.0 Pa·s or less, or 4.5 Pa·s or less.

[0020] Condition (2): The gel time of the epoxy resin composition, as determined by CURELASTOMETER (registered trademark) at 145°C, is within the range of 2.0 min or more, 2.1 min or more, 2.3 min or more, or 2.5 min or more, 5.0 min or less, 4.9 min or less, 4.5 min or less, or 4.0 min or less.

[0021] [2]: According to the prepreg described in [1], wherein the median particle size (D50) of the (A) component, as determined by laser diffraction, is less than 8.0 μm or less than 7.0 μm.

[0022] [3]: The prepreg according to [1] or [2], wherein the (A) component comprises 2,4-bis(3,3-dimethylurea)toluene.

[0023] [4]: The prepreg according to any one of [1] to [3], wherein the (B) component is a thermoplastic resin that can be dissolved in the mixture of epoxy resins contained in the epoxy resin composition.

[0024] [5]: The prepreg according to any one of [1] to [4], wherein the weight average molecular weight of component (B) is 60,000 or more or 65,000 or more.

[0025] [6]: The prepreg according to any one of [1] to [5], wherein the weight average molecular weight of component (B) is less than 150,000 or less than 145,000.

[0026] [7]: The prepreg according to any one of [1] to [6], wherein the (B) component comprises polyvinyl formal resin.

[0027] [8]: The prepreg according to any one of [1] to [7], wherein the (C) component is solid at 25°C.

[0028] [9]: The prepreg according to any one of [1] to [8], wherein the epoxy equivalent of the (D) component is 300 g / eq or more or 350 g / eq or more.

[0029]

[10] : The prepreg according to any one of [1] to [9], wherein the epoxy equivalent of the (D) component is less than 1000 g / eq or less than 950 g / eq.

[0030]

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

[10] , wherein the (D) component is a bisphenol A type epoxy resin.

[0031]

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

[11] , wherein it contains more than 2% by mass, more than 2.5% by mass, or more than 3% by mass of the (A) component relative to the total mass of the epoxy resin composition.

[0032]

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

[12] , wherein the prepreg contains 10% or less, 9.5% or less, 8% or less or 5% or less of the (A) component relative to the total mass of the epoxy resin composition.

[0033]

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

[13] , wherein it contains more than 1% by mass, more than 1.5% by mass, or more than 2% by mass of the (B) component relative to the total mass of the epoxy resin composition.

[0034]

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

[14] , wherein the (B) component comprises 10% or less by mass, 9.5% or less by mass, 8% or less by mass or 5% or less by mass relative to the total mass of the epoxy resin composition.

[0035]

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

[15] , wherein, relative to the total mass of the epoxy resin composition, it comprises more than 30% by mass, more than 32% by mass, more than 35% by mass, or more than 40% by mass of the (C) component and the (D) component.

[0036]

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

[16] , wherein the prepreg comprises, relative to the total mass of the epoxy resin composition, a total of less than 60% by mass, less than 58% by mass, or less than 55% by mass of the (C) component and the (D) component.

[0037]

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

[17] , wherein the prepreg also satisfies the following condition (3).

[0038] Condition (3): The viscosity of the epoxy resin composition at 65°C is in the range of 10 Pa·s or more, 20 Pa·s or more, 50 Pa·s or more, 70 Pa·s or more, or 100 Pa·s or more.

[0039]

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

[18] , wherein the prepreg also satisfies the following condition (3).

[0040] Condition (3): The viscosity of the epoxy resin composition at 65°C is in the range of less than 1000 Pa·s, less than 900 Pa·s, less than 500 Pa·s, less than 300 Pa·s, or less than 200 Pa·s.

[0041]

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

[19] , wherein the prepreg further comprises the following (E) component.

[0042] (E) Ingredients: Selected from at least one of dicyandiamide and dicyandiamide derivatives.

[0043]

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

[20] , wherein the reinforcing fiber comprises carbon fiber.

[0044]

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

[21] .

[0045]

[23] : A prepreg comprising an epoxy resin composition and reinforcing fibers, the epoxy resin composition comprising the following components (A1), (B1), (C) and (D).

[0046] (A1) Ingredients: Urea compounds containing 2,4-bis(3,3-dimethylureo)toluene.

[0047] (B1) Composition: Polyvinyl alcohol formaldehyde resin with a weight average molecular weight of 60,000 or 65,000 or more.

[0048] (C) Component: Epoxy resin with an oxazolidinone structure.

[0049] (D) Component: Bisphenol type epoxy resin that is solid at 25°C (excluding component (C)).

[0050]

[24] : The prepreg according to

[23] , wherein the prepreg satisfies the following condition (1).

[0051] Condition (1): The lowest viscosity of the epoxy resin composition, as determined by a rheometer at 2°C / min, is in the range of 3.0 Pa·s or higher, 3.1 Pa·s or higher, or 3.2 Pa·s or higher.

[0052]

[25] : The prepreg according to

[23] or

[24] , wherein the prepreg satisfies the following condition (1).

[0053] Condition (1): The lowest viscosity of the epoxy resin composition, as determined by a rheometer at 2°C / min, is in the range of less than 6.0 Pa·s, less than 5.9 Pa·s, less than 5.5 Pa·s, less than 5.0 Pa·s, or less than 4.5 Pa·s.

[0054]

[26] : The prepreg according to any one of

[23] to

[25] , wherein the prepreg satisfies the following condition (2).

[0055] Condition (2): The gel time of the epoxy resin composition, as determined by CURELASTOMETER (registered trademark) at 145°C, is in the range of 2.0 min or more, 2.1 min or more, 2.3 min or more, or 2.5 min or more.

[0056]

[27] : The prepreg according to any one of

[23] to

[26] , wherein the prepreg satisfies the following condition (2).

[0057] Condition (2): The gel time of the epoxy resin composition, as determined by CURELASTOMETER (registered trademark) at 145°C, is within the range of 5.0 min or less, 4.9 min or less, 4.5 min or less, or 4.0 min or less.

[0058]

[28] : The prepreg according to any one of

[23] to

[27] , wherein the median particle size (D50) of the (A1) component, as determined by laser diffraction, is 8.0 μm or less or 7.0 μm or less.

[0059]

[29] : The prepreg according to any one of

[23] to

[28] , wherein the (C) component is solid at 25°C.

[0060]

[30] : The prepreg according to any one of

[23] to

[29] , wherein the epoxy equivalent of the (D) component is 300 g / eq or more or 350 g / eq or more.

[0061]

[31] : The prepreg according to any one of

[23] to

[30] , wherein the epoxy equivalent of the (D) component is less than 1000 g / eq or less than 950 g / eq.

[0062]

[32] : The prepreg according to any one of

[23] to

[31] , wherein the (D) component is a bisphenol A type epoxy resin.

[0063]

[33] : The prepreg according to any one of

[23] to

[32] , wherein it contains more than 2% by mass, more than 2.5% by mass, or more than 3% by mass of the (A1) component relative to the total mass of the epoxy resin composition.

[0064]

[34] : The prepreg according to any one of

[23] to

[33] , wherein the prepreg contains 10% or less, 9.5% or less, 8% or less or 5% or less of the (A) component relative to the total mass of the epoxy resin composition.

[0065]

[35] : The prepreg according to any one of

[23] to

[34] , wherein it contains more than 1% by mass, more than 1.5% by mass, or more than 2% by mass of the (B1) component relative to the total mass of the epoxy resin composition.

[0066]

[36] : The prepreg according to any one of

[23] to

[35] , wherein the (B1) component comprises 10% or less by mass, 9.5% or less by mass, 8% or less by mass or 5% or less by mass relative to the total mass of the epoxy resin composition.

[0067]

[37] : The prepreg according to any one of

[23] to

[36] , wherein, relative to the total mass of the epoxy resin composition, it comprises more than 30% by mass, more than 32% by mass, more than 35% by mass, or more than 40% by mass of the (C) component and the (D) component.

[0068]

[38] : The prepreg according to any one of

[23] to

[37] , wherein the prepreg comprises, relative to the total mass of the epoxy resin composition, a total of less than 60% by mass, less than 58% by mass, or less than 55% by mass of the (C) component and the (D) component.

[0069]

[39] : The prepreg according to any one of

[23] to

[38] , wherein the prepreg also satisfies the following condition (3).

[0070] Condition (3): The viscosity of the epoxy resin composition at 65°C is in the range of 10 Pa·s or more, 20 Pa·s or more, 50 Pa·s or more, 70 Pa·s or more, or 100 Pa·s or more.

[0071]

[40] : The prepreg according to any one of

[23] to

[39] , wherein the prepreg also satisfies the following condition (3).

[0072] Condition (3): The viscosity of the epoxy resin composition at 65°C is in the range of less than 1000 Pa·s, less than 900 Pa·s, less than 500 Pa·s, less than 300 Pa·s, or less than 200 Pa·s.

[0073]

[41] : The prepreg according to any one of

[23] to

[40] , wherein the prepreg further comprises the following (E) component.

[0074] (E) Ingredients: Selected from at least one of dicyandiamide and dicyandiamide derivatives.

[0075]

[42] : The prepreg according to any one of

[23] to

[41] , wherein the reinforcing fiber comprises carbon fiber.

[0076]

[43] : A method for manufacturing a molded article, the method comprising: heating a prepreg containing an epoxy resin composition and reinforcing fibers disposed in a mold to a temperature of 130°C or higher or 140°C or higher, wherein the epoxy resin composition contains the following components (A1) and (B1).

[0077] (A1) Ingredient: 2,4-bis(3,3-dimethylurea)toluene.

[0078] (B1) Composition: Polyvinyl alcohol formaldehyde resin with a weight average molecular weight of 60,000 or 65,000 or more.

[0079]

[44] : The method for manufacturing a molded body according to

[43] , wherein the prepreg is configured into a tubular shape and heated, thereby manufacturing a tubular molded body.

[0080]

[45] : The method for manufacturing a molded body according to

[44] further includes a step of molding the tubular precursor by pressing it against a mold through an expansion of a medium from the interior of the tubular precursor in which the prepreg is configured as a tubular shape.

[0081]

[46] : The method for manufacturing a molded article according to any one of

[43] to

[45] , wherein the epoxy resin composition further comprises the following component (C).

[0082] (C) Component: Epoxy resin with an oxazolidinone structure.

[0083]

[47] : The method for manufacturing a molded article according to any one of

[43] to

[46] , wherein the epoxy resin composition further comprises the following (D) component.

[0084] (D) Component: Bisphenol type epoxy resin that is solid at 25°C (excluding (C) component: epoxy resin having an oxazolidinone structure).

[0085]

[48] : A method for manufacturing a molded article according to any one of

[43] to

[47] , wherein the epoxy resin composition comprises, with a total mass of 60% or less by mass, 58% or less by mass, or 55% or less by mass, the following (C) component and the following (D) component.

[0086] (C) Component: Epoxy resin with an oxazolidinone structure.

[0087] (D) Component: Bisphenol type epoxy resin that is solid at 25°C (excluding component (C)).

[0088]

[49] : The method for manufacturing a molded article according to any one of

[43] to

[48] , wherein the epoxy resin composition comprises, relative to the total mass of the epoxy resin composition, the following (C) component and the following (D) component together are 30% or more by mass, 32% or more by mass, 35% or more by mass, or 40% or more by mass.

[0089] (C) Component: Epoxy resin with an oxazolidinone structure.

[0090] (D) Component: Bisphenol type epoxy resin that is solid at 25°C (excluding component (C)).

[0091]

[50] : A method for manufacturing a molded body according to any one of

[43] to

[49] , wherein the tubular molded body has an annular curved portion, the manufacturing method comprising: a step of bending the tubular precursor into an annular shape.

[0092] Invention Effects

[0093] According to the present invention, a prepreg can be provided that can cure in a short time and suppress resin flow during molding. Detailed Implementation

[0094] The present invention will now be described in detail.

[0095] [Prepreg]

[0096] One embodiment of the present invention relates to a prepreg. The prepreg of the present invention comprises an epoxy resin composition and reinforcing fibers.

[0097] <Composition of the epoxy resin composition>

[0098] The epoxy resin composition contained in the prepreg of one embodiment preferably includes components (A), (B), (C), and (D) below, and also includes component (E) below.

[0099] (A) Component: Urea compound.

[0100] (B) Composition: thermoplastic resin.

[0101] (C) Component: Epoxy resin with an oxazolidinone structure.

[0102] (D) Component: Bisphenol type epoxy resin that is solid at 25°C (excluding component (C)).

[0103] (E) Ingredients: Selected from at least one of dicyandiamide and dicyandiamide derivatives.

[0104] Furthermore, the epoxy resin composition used in this embodiment preferably satisfies the following conditions (1) and (2), and also satisfies the following condition (3).

[0105] Condition (1): The lowest viscosity of the epoxy resin composition, as determined by a rheometer at 2 °C / min, is in the range of 3.0 to 6.0 Pa·s.

[0106] Condition (2): The gel time of the epoxy resin composition, as determined by CURELASTOMETER (registered trademark) at 145°C, is in the range of 2.0 to 5.0 min.

[0107] Condition (3): The viscosity of the epoxy resin composition at 65°C is in the range of 10 to 1000 Pa·s.

[0108] ((A) ingredient)

[0109] (A) is a urea compound. The urea compound generates isocyanate groups and dimethylamine by heating at high temperatures. The heat generated from their reaction with epoxy groups further promotes the reaction of the generated -NH groups with the epoxy groups. Therefore, by including (A) in the epoxy resin composition, resin flow during molding of the resulting prepreg can be suppressed.

[0110] There are no particular limitations on the urea compounds used; examples include aromatic dimethylureas obtained by bonding a dimethylurea group to an aromatic ring, and aliphatic dimethylureas obtained by bonding a dimethylurea group to an aliphatic compound. They can be used alone or in combination of two or more. From the viewpoint of reducing resin flow, aromatic dimethylureas are preferred.

[0111] Examples of aromatic dimethylureas include phenyl dimethylurea, methylene bis(phenyl dimethylurea), and tolyl bis(dimethylurea). More specifically, examples include 4,4'-methylene bis(phenyl dimethylurea) (MBPDMU), 3-phenyl-1,1-dimethylurea (PDMU), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 3-(3-chloro-4-methylphenyl)-1,1-dimethylurea, and 2,4-bis(3,3-dimethylurea)toluene (TBDMU). Among these, 2,4-bis(3,3-dimethylurea)toluene (TBDMU) is preferred from the viewpoint of reducing resin flow.

[0112] Examples of aliphatic dimethylureas include: dimethylurea obtained from isophorone diisocyanate and dimethylamine, dimethylurea obtained from m-phenylenediethylene diisocyanate and dimethylamine, and dimethylurea obtained from hexamethylene diisocyanate and dimethylamine.

[0113] The median particle size (D50) of component (A), as determined by laser diffraction, is preferably 8.0 μm or less, more preferably 7.0 μm or less. Setting the median particle size (D50) of component (A) to 8.0 μm or less improves the thixotropy of the epoxy resin composition and suppresses resin flow during molding. Furthermore, the surface area relative to the mass of component (A) increases, thus increasing the reaction rate and allowing the epoxy resin composition to cure in a shorter time. The median particle size (D50) of component (A) can be adjusted by pre-crushing component (A) using a bead mill or a three-roll mill. For laser diffraction, an AEROTRAC SPR (model: 7340) (manufactured by Nikkiso Co., Ltd.) can be used, for example. There is no particular limitation on the lower limit of the median particle size (D50) of component (A), which can be, for example, 0.1 μm or more.

[0114] Furthermore, the median particle size (D50) of component (A), as determined by laser diffraction, is preferably below the average fiber diameter of the carbon fibers contained in the reinforcing fiber matrix. If the median particle size (D50) is below the average fiber diameter of the carbon fibers, component (A) will not be localized on the surface of the prepreg, thus improving the surface appearance quality. In addition, by distributing component (A) throughout the fiber-reinforced composite material, poor curing is less likely to occur, and resin flow during molding can be suppressed.

[0115] The content of component (A) relative to the total mass of the epoxy resin composition is preferably 2% by mass or more, more preferably 2.5% by mass or more, and even more preferably 3% by mass or more. By setting the content of component (A) to the lower limit or above, resin flow during molding can be suppressed. Furthermore, the content of component (A) relative to the total mass of the epoxy resin composition is preferably 10% by mass or less, more preferably 9.5% by mass or less, even more preferably 8% by mass or less, and particularly preferably 5% by mass or less. By setting the content of component (A) to the upper limit or below, an epoxy resin composition with excellent storage stability and mechanical properties can be obtained. The preferred lower and upper limits of the content of component (A) can be combined arbitrarily, for example, it can be set to 2 to 10% by mass, 2 to 9.5% by mass, 2.5 to 8% by mass, or 3 to 5% by mass.

[0116] (Component B)

[0117] (B) is a thermoplastic resin. The thermoplastic resin is formulated to control viscoelasticity. By including (B) in the epoxy resin composition, the viscosity of the epoxy resin composition can be adjusted, and by making it exhibit high thixotropy, resin flow during molding can be suppressed. (B) is preferably a component that can dissolve in the mixture of epoxy resins contained in the epoxy resin composition. Here, dissolution refers to a state in the epoxy resin composition where the state of the particles cannot be confirmed by optical methods such as optical microscopy or visual inspection.

[0118] The weight-average molecular weight of component (B) is preferably 60,000 or more, more preferably 65,000 or more. By setting the weight-average molecular weight of component (B) to the lower limit or above, the minimum viscosity of the epoxy resin composition is increased, and resin flow during molding can be suppressed. Furthermore, the weight-average molecular weight of component (B) is preferably 150,000 or less, more preferably 145,000 or less. By setting the weight-average molecular weight of component (B) to the upper limit or below, resin flow during molding can be suppressed, and the workability of the prepreg at room temperature can be improved. The preferred lower and upper limits of the weight-average molecular weight of component (B) can be arbitrarily combined, for example, set to 60,000 to 150,000 or 65,000 to 145,000. The weight-average molecular weight of component (B) is determined using GPC (gel permeation chromatography) and by the method described later.

[0119] Component (B) may include, but is not limited to, polyamide, polyester, polycarbonate, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyetheretherketone, polyetherketone, polyetherimide, polyimide, polytetrafluoroethylene, polyether, polyolefin, polyarylate, polysulfone, polyacrylonitrile styrene, 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 alcohol formal, phenoxy resin, etc. These thermoplastic resins may be used alone or in combination of two or more. From the viewpoint of suppressing resin flow, polyvinyl alcohol formal resin is preferred. By using polyvinyl alcohol formal resin, resin flow during molding can be suppressed.

[0120] Commercially available products of polyvinyl alcohol formaldehyde resin include, for example: VINYLEC L (catalog weight average molecular weight: 66,000), VINYLEC H (catalog weight average molecular weight: 73,000), VINYLEC E (all trade names, manufactured by JNC Corporation), etc., but are not limited to these.

[0121] The content of component (B) relative to the total mass of the epoxy resin composition is preferably 1% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2% by mass or more. By setting the content of component (B) to the lower limit or above, the epoxy resin composition can exhibit high thixotropy, thereby suppressing resin flow during molding. Furthermore, the content of component (B) relative to the total mass of the epoxy resin composition is preferably 10% by mass or less, more preferably 9.5% by mass or less, even more preferably 8% by mass or less, and particularly preferably 5% by mass or less. By setting the content of component (B) to the upper limit or below, the workability of the prepreg at room temperature is improved. The preferred lower and upper limits of the content of component (B) can be combined arbitrarily, for example, it can be set to 1-10% by mass, 1-9.5% by mass, 1.5-8% by mass, or 2-5% by mass.

[0122] (C) component)

[0123] (C) is an epoxy resin with an oxazolidinone structure. By including (C) in the epoxy resin composition, the viscosity of the epoxy resin composition increases, which can suppress resin flow during molding.

[0124] The oxazolidinone structure is generated through an addition reaction between the isocyanate group and the epoxy group. There are no particular limitations on the method for manufacturing epoxy resins with the oxazolidinone structure; for example, by reacting an isocyanate compound with an epoxy resin in the presence of a catalyst used in the formation of the oxazolidinone ring, an epoxy resin with the oxazolidinone structure can be obtained in approximately theoretical quantities. The isocyanate compound and epoxy resin are preferably reacted in an equivalence ratio (isocyanate compound: epoxy resin) in the range of 1:2 to 1:10. If the equivalence ratio of the isocyanate compound to the epoxy resin is within the above range, there is a tendency for further improvement in the heat resistance and water resistance of the cured resin.

[0125] The isocyanate compound used as a raw material for component (C) is not particularly limited, but in order to introduce the oxazolidinone structure into the epoxy resin backbone, an isocyanate compound having multiple isocyanate groups is preferred. Furthermore, in order to give the cured resin high heat resistance, a diisocyanate with a rigid structure is preferred. Specific examples of isocyanate compounds include: methane diisocyanate, butane-1,1-diisocyanate, ethane-1,2-diisocyanate, butane-1,2-diisocyanate, trans-vinylene diisocyanate, propane-1,3-diisocyanate, butane-1,4-diisocyanate, 2-butene-1,4-diisocyanate, 2-methylbutene-1,4-diisocyanate, 2-methylbutane-1,4-diisocyanate, pentane-1,5-diisocyanate, 2,2-dimethylpentane-1,5-diisocyanate, hexane-1,6-diisocyanate, heptane-1,7-diisocyanate, and octane-1,8-diisocyanate. Ester, nonane-1,9-diisocyanate, decane-1,10-diisocyanate, dimethylsilane diisocyanate, diphenylsilane diisocyanate, ω,ω'-1,3-dimethylphenyl diisocyanate, ω,ω'-1,4-dimethylphenyl diisocyanate, ω,ω'-1,3-dimethylcyclohexane diisocyanate, ω,ω'-1,4-dimethylcyclohexane diisocyanate, ω,ω'-1,4-dimethylnaphthalene diisocyanate, ω,ω'-1,5-dimethylnaphthalene diisocyanate, cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate, 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate Ester, dicyclohexylmethane-4,4'-diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 1-methylbenzene-2,4-diisocyanate, 1-methylbenzene-2,5-diisocyanate, 1-methylbenzene-2,6-diisocyanate, 1-methylbenzene-3,5-diisocyanate, diphenyl ether-4,4'-diisocyanate, diphenyl ether-2,4'-diisocyanate, naphthalene-1,4-diisocyanate, naphthalene-1,5-diisocyanate, biphenyl-4,4'-diisocyanate, 3,3'-dimethylbiphenyl-4,4'-diisocyanate, 2,3'-dimethoxybisphenyl-4,4'-diisocyanate The compounds include difunctional isocyanates such as cyanates, diphenylmethane-4,4'-diisocyanate, 3,3'-dimethoxydiphenylmethane-4,4'-diisocyanate, 4,4'-dimethoxydiphenylmethane-3,3'-diisocyanate, norbornene diisocyanate, diphenylsulfite-4,4'-diisocyanate, and diphenyl sulfone-4,4'-diisocyanate; trifunctional or higher isocyanate compounds such as polymethylene polyphenyl isocyanate and triphenylmethane triisocyanate; polymers such as dimers or trimers of the isocyanate compounds; end-capped isocyanates masked by alcohols or phenols; and dicarboxylate compounds, but are not limited to these.These isocyanate compounds can be used alone or in combination of two or more.

[0126] Of the aforementioned isocyanate compounds, from the viewpoint of improving the heat resistance of the cured resin, difunctional or trifunctional isocyanate compounds are preferred, difunctional isocyanate compounds are more preferred, and difunctional isocyanate compounds having a backbone selected from isophorone, benzene, toluene, diphenylmethane, naphthalene, norbornene, polymethylene, polyphenylene-based polyphenyl, and hexamethylene are even more preferred. By having a moderately high number of functional groups in the isocyanate compound, the decrease in storage stability of the epoxy resin composition can be suppressed. Furthermore, by having a moderately low number of functional groups in the isocyanate compound, the decrease in heat resistance of the cured resin can be suppressed.

[0127] Various epoxy resins can be used as raw materials for component (C), but in order to efficiently introduce the oxazolidinone structure into the epoxy resin backbone, epoxy resins with epoxy groups at both ends of the molecule are preferred. Specific examples of epoxy resins include: epoxy resins derived from diphenols such as bisphenol A, bisphenol F, bisphenol AD, bisphenol S, tetramethylbisphenol A, tetramethylbisphenol F, tetramethylbisphenol AD, tetramethylbisphenol S, tetrabromobisphenol A, and biphenyl; epoxy resins derived from tri(glycidoxyphenyl)alkanes such as 1,1,1-tris(4-hydroxyphenyl)methane, 1,1,1-(4-hydroxyphenyl)ethane, and 4,4-[1-[4-[1-(4-hydroxyphenyl)-1-methylethyl]phenyl]ethylidene]bisphenol; and epoxy resins derived from phenolic varnishes such as phenolic varnish, cresol varnish, and bisphenol A varnish, but are not limited to these. These epoxy resins can be used alone or in combination of two or more. From the viewpoint of suppressing excessive viscosity increase of component (C), bisphenol A type epoxy resin, bisphenol F type epoxy resin, and biphenyl type epoxy resin are preferred as epoxy resins.

[0128] An addition reaction product obtained by mixing and reacting one molecule of a toluene-based diisocyanate, such as toluene diisocyanate, as an isocyanate compound, with two molecules of bisphenol A diglycidyl ether, which is an epoxy resin, is particularly preferred because it provides good workability of the prepreg at room temperature and good heat resistance of the cured resin. Examples of such toluene-based diisocyanates include 1-methylbenzene-2,4-diisocyanate, 1-methylbenzene-2,5-diisocyanate, 1-methylbenzene-2,6-diisocyanate, and 1-methylbenzene-3,5-diisocyanate.

[0129] Commercially available epoxy resins having an oxazolidinone structure include, for example: AER4152, AER4151, LSA3301, LSA2102 (all trade names, manufactured by Asahi Kasei E-Materials Co., Ltd.); ACR1348 (trade name, manufactured by ADEKA Co., Ltd.); DER (registered trademark, hereinafter the same) 852 and 858 (both trade names, manufactured by Dow Chemical Japan Co., Ltd.); TSR-400 (trade name, manufactured by DIC Co., Ltd.); YD-952 (trade name, manufactured by NIPPON STEELC Chemical & Material Co., Ltd.), etc., but are not limited to these. All are preferred for use in this invention, and YD-952 is particularly preferred. (C) Components may be used alone or in combination of two or more.

[0130] Component (C) is preferably solid at 25°C. By making component (C) solid at 25°C, the viscosity of the epoxy resin composition increases, thus suppressing the resin flowability during molding and reducing the tendency of resin to flow out of the prepreg due to heating and pressurization.

[0131] ((D) component)

[0132] Component (D) is a bisphenol-type epoxy resin that is solid at 25°C, excluding component (C). By including component (D) in the epoxy resin composition, the viscosity of the epoxy resin composition increases, thus suppressing resin flow during molding and preventing resin leakage from the prepreg caused by heating and pressurization. In other words, resin flow in the resulting prepreg is suppressed.

[0133] The softening point of component (D) is preferably 30°C or higher, more preferably 40°C or higher, and even more preferably 50°C or higher. There is no particular limitation on the upper limit of the softening point of component (D), for example, it can be 150°C or lower.

[0134] The epoxy equivalent of component (D) is preferably 300 g / eq or more, more preferably 350 g / eq or more. By setting the epoxy equivalent of component (D) to the lower limit or above, both the reactivity of the epoxy resin composition and the inhibition of resin flow during molding can be taken into account. Furthermore, the epoxy equivalent of component (D) is preferably 1000 g / eq or less, more preferably 950 g / eq or less. By setting the epoxy equivalent of component (D) to the upper limit or below, the impregnation of the epoxy resin composition with the reinforcing fiber substrate is improved. The preferred lower and upper limits of the epoxy equivalent of component (D) can be combined arbitrarily, for example, it can be set to 300–1000 g / eq or 350–950 g / eq.

[0135] As for component (D), there are no particular limitations as long as it is a bisphenol-type epoxy resin that is solid at 25°C. These bisphenol-type epoxy resins can be used alone or in combination of two or more. Examples of bisphenol-type epoxy resins include: bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol E type epoxy resin, bisphenol S type epoxy resin, bisphenol C type epoxy resin, bisphenol M type epoxy resin, bisphenol AF type epoxy resin, bisphenol BP type epoxy resin, etc. Among these, bisphenol A type epoxy resin is preferred from the viewpoint of improving the mechanical properties of the epoxy resin composition.

[0136] Commercially available bisphenol A type epoxy resins that are solid at 25°C include, for example, YD-011, YD-012, YD-013, and YD-014 (all trade names, manufactured by NIPPON STEEL Chemical & Material Co., Ltd.); jER1001, jER1002, jER1003, and jER1004 (all trade names, manufactured by Mitsubishi Chemical Co., Ltd.), but are not limited to these. (D) Components may be used alone or in combination of two or more.

[0137] The total content of components (C) and (D) relative to the total mass of the epoxy resin composition is preferably 30% by mass or more, more preferably 32% by mass or more, further preferably 35% by mass or more, and particularly preferably 40% by mass or more. By setting the total content of components (C) and (D) to the lower limit value or above, the minimum viscosity of the epoxy resin composition is increased, and resin flow during molding can be suppressed. Furthermore, the total content of components (C) and (D) relative to the total mass of the epoxy resin composition is preferably 60% by mass or less, more preferably 58% by mass or less, and further preferably 55% by mass or less. By setting the total content of components (C) and (D) to the upper limit value or below, the impregnation of the epoxy resin composition into the reinforcing fiber substrate is improved, and the generation of voids in the molded fiber-reinforced composite material can be suppressed. The preferred lower and upper limits of the total content of components (C) and (D) can be arbitrarily combined, for example, they can be set to 30-60% by mass, 32-60% by mass, 35-58% by mass, or 40-55% by mass.

[0138] (E) component)

[0139] Component (E) is selected from at least one of dicyandiamide and dicyandiamide derivatives. Dicyandiamide and dicyandiamide derivatives have high melting points and low compatibility with epoxy resins in low-temperature regions. By including component (E) in the epoxy resin composition, an epoxy resin composition that suppresses resin flow during molding and has an excellent pot life is obtained, and a cured resin product with high mechanical properties is also obtained.

[0140] Examples of dicyandiamide derivatives include substances formed by bonding dicyandiamide with various compounds such as epoxy resins, vinyl compounds, acrylic compounds, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxides. From a reactivity point of view, dicyandiamide is preferred as component (E).

[0141] When the epoxy resin composition contains component (E), from the viewpoint of suppressing resin flow in the epoxy resin composition, the content of component (E) is preferably 4% by mass or more, more preferably 4.5% by mass or more, relative to the total mass of the epoxy resin composition. From the viewpoint of the storage stability of the epoxy resin composition, the content of component (E) is preferably 14% by mass or less, more preferably 13.5% by mass or less, relative to the total mass of the epoxy resin composition. The preferred lower and upper limits of the content of component (E) can be arbitrarily combined, for example, it can be set to 4 to 14% by mass or 4.5 to 13.5% by mass.

[0142] (Other ingredients)

[0143] The epoxy resin composition may also contain components other than those described above (hereinafter, sometimes referred to as "other components"). Examples of other components include curing agents other than component (A), epoxy resins other than components (C) and (D), rubber particles, additives, etc.

[0144] As for other curing agents, there are no structural limitations as long as they are used to cure epoxy resins. For example, in addition to amine-based curing agents such as dicyandiamide, aliphatic amines, alicyclic amines, aromatic amines, and imidazole compounds, acid anhydrides, phenols, and boron chloride-amine complexes can also be listed. These curing agents can be used alone or in combination of two or more.

[0145] Other epoxy resins that are liquid or semi-solid at 25°C can be used. Examples include, but are not limited to, bisphenol-type epoxy resins, biphenyl-type epoxy resins, naphthalene-type epoxy resins, phenol-formaldehyde varnish-type epoxy resins, cresol-formaldehyde varnish-type epoxy resins, and glycidylamine-type epoxy resins, which are liquid or semi-solid at 25°C. Epoxy resins that are solid at 25°C, such as bisphenol-type epoxy resins, biphenyl-type epoxy resins, naphthalene-type epoxy resins, phenol-formaldehyde varnish-type epoxy resins, cresol-formaldehyde varnish-type epoxy resins, and glycidylamine-type epoxy resins, can also be used. These epoxy resins can be used alone or in combination of two or more.

[0146] As rubber particles, synthetic rubber and natural rubber can be used, including rubber particles with structures derived from alkyl (meth)acrylates, butadiene, isoprene, chloroprene, styrene, α-alkylstyrene, acrylonitrile, and methacrylonitrile. Examples of rubber particles include, but are not limited to, 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. They can be used alone or in combination of two or more. By including rubber particles in the epoxy resin composition, the flowability of the epoxy resin composition can be suppressed, thus suppressing the resin flow of the resulting prepreg.

[0147] Within the scope of not impairing the effects of the present invention, various known additives may be used. Examples of additives include: inorganic fillers, internal release agents, organic pigments, inorganic pigments, etc. More specifically, examples include: flame retardants (phosphonic acid metal salts, aluminum hydroxide, magnesium hydroxide, etc.); inorganic oxides and other auxiliary agents (antimony compounds, zinc borate, zinc stannate, Mo compounds, ZrO, zinc sulfide, zeolite, titanium dioxide, etc.); silicone oils, wetting and dispersing agents, defoamers, defoaming agents, natural waxes, synthetic waxes, linear fatty acid metal salts, acid amides, esters, paraffin waxes, and other release agents; crystalline silica, fused silica, calcium silicate, alumina, calcium carbonate, talc, barium sulfate, and other powders; inorganic fillers such as glass fibers and carbon fibers with a fiber length of approximately 0.01 mm to 10 mm; colorants such as carbon black and iron oxide red; silane coupling agents, etc., but not limited to these. They may be used individually or in combination of two or more.

[0148] As a component of the epoxy resin composition, relative to the total mass of the epoxy resin composition, for example, a composition comprising 2 to 10% by mass of component (A), 1 to 10% by mass of component (B), and a total of 30 to 60% by mass of components (C) and (D) can be provided, and a composition further comprising 4 to 14% by mass of component (E) can also be provided. However, the total of all components shall not exceed 100% by mass. The lower and upper limits of the content of components (A) to (E) can be arbitrarily combined with the lower and upper limits described above for each component.

[0149] <Physical Properties of Epoxy Resin Compositions>

[0150] As described above, the epoxy resin composition satisfies conditions (1) and (2). At this point, the epoxy resin composition exhibits thixotropic properties, and the reaction initiation point becomes earlier. As a result, an epoxy resin composition for fiber-reinforced composite materials that can cure quickly and suppress resin flow during molding can be obtained.

[0151] (Condition (1))

[0152] The flowability of the resin during molding can be suppressed by setting the minimum viscosity of the epoxy resin composition within a specified range. Here, the minimum viscosity refers to the lowest viscosity measured by a rheometer at a rate of 2°C / min. For example, a HAAKE MARS 40 (manufactured by Thermo Fisher Scientific Co., Ltd.) can be used as the rheometer.

[0153] The epoxy resin composition has a minimum viscosity of 3.0 Pa·s or more, preferably 3.1 Pa·s or more, and more preferably 3.2 Pa·s or more. By setting the minimum viscosity to 3.0 Pa·s or more, the resin flowability during molding is reduced, significantly suppressing resin flow. Furthermore, the epoxy resin composition has a minimum viscosity of 6.0 Pa·s or less, preferably 5.9 Pa·s or less, more preferably 5.5 Pa·s or less, further preferably 5.0 Pa·s or less, and particularly preferably 4.5 Pa·s or less. By setting the minimum viscosity to 6.0 Pa·s or less, the impregnation of the epoxy resin composition with the reinforcing fiber substrate is improved. The preferred lower and upper limits of the minimum viscosity of the epoxy resin composition can be arbitrarily combined, for example, set to 3.0–6.0 Pa·s, 3.0–5.9 Pa·s, 3.1–5.5 Pa·s, 3.1–5.0 Pa·s, or 3.2–4.5 Pa·s.

[0154] The minimum viscosity of the epoxy resin composition can be adjusted to a specified range based on the content and median particle size of component (A) and the content and weight-average molecular weight of component (B).

[0155] (Condition (2))

[0156] The reaction start point of the epoxy resin composition can be adjusted by setting the gel time value, measured using CURELASTOMETER (registered trademark) at 145°C, within a specified range. For example, CURELASTOMETER 7TypeP (manufactured by JSR Trading Co., Ltd.) can be used as a CURELASTOMETER (registered trademark).

[0157] The gel time of the epoxy resin composition is 2.0 min or more, preferably 2.1 min or more, more preferably 2.3 min or more, and even more preferably 2.5 min or more. By setting the gel time to 2.0 min or more, the thermal stability of the epoxy resin composition is improved. Furthermore, the gel time of the epoxy resin composition is 5.0 min or less, preferably 4.9 min or less, more preferably 4.5 min or less, and even more preferably 4.0 min or less. By setting the gel time to 5.0 min or less, molding can be performed in a short time, thereby suppressing resin flow during molding. The preferred lower and upper limits of the gel time of the epoxy resin composition can be arbitrarily combined, for example, set to 2.0–5.0 min, 2.1–4.9 min, 2.3–4.5 min, or 2.5–4.0 min.

[0158] The gel time value of the epoxy resin composition can be adjusted to a specified range according to the content and median particle size of component (A), the content of component (E), and the mass ratio of component (A) to component (E).

[0159] (Condition (3))

[0160] The viscosity of the epoxy resin composition at 65°C can be determined using a rheometer at a rate of 2°C / min. For example, a HAAKE MARS 40 (manufactured by Thermo Fisher Scientific Co., Ltd.) can be used as the rheometer.

[0161] The viscosity of the epoxy resin composition at 65°C is preferably 10 Pa·s or more, more preferably 20 Pa·s or more, further preferably 50 Pa·s or more, particularly preferably 70 Pa·s or more, and most preferably 100 Pa·s or more. By achieving a viscosity of 10 Pa·s or more, sufficient adhesion is obtained on the surface of the prepreg. Furthermore, the viscosity of the epoxy resin composition at 65°C is preferably 1000 Pa·s or less, more preferably 900 Pa·s or less, further preferably 500 Pa·s or less, particularly preferably 300 Pa·s or less, and most preferably 200 Pa·s or less. By achieving a viscosity of 1000 Pa·s or less, the impregnation of the reinforcing fiber substrate and the molding processability of the prepreg are improved. The preferred lower and upper limits of the viscosity of the epoxy resin composition at 65°C can be arbitrarily combined, for example, they can be set to 10~1000Pa·s, 20~900Pa·s, 50~500Pa·s, 70~300Pa·s or 100~200Pa·s.

[0162] The viscosity of the epoxy resin composition at 65°C can be adjusted to a specified range based on the content and weight-average molecular weight of component (B), and the total content of components (C) and (D).

[0163] <Preferred example of epoxy resin composition>

[0164] The epoxy resin composition (hereinafter also referred to as "epoxy resin composition (I)") contained in the prepreg of the embodiment includes the following components (A1), (B1), (C) and (D), and also includes the following component (E).

[0165] (A1) Ingredients: Urea compounds containing 2,4-bis(3,3-dimethylureo)toluene.

[0166] (B1) Composition: Polyvinyl alcohol formaldehyde resin with a weight average molecular weight of 60,000 or more.

[0167] (C) Component: Epoxy resin with an oxazolidinone structure.

[0168] (D) Component: Epoxy resin that is solid at 25°C (excluding component (C)).

[0169] (E) Ingredients: Selected from at least one of dicyandiamide and dicyandiamide derivatives.

[0170] The median particle size (D50) of the (A1) component, as determined by laser diffraction, is preferably 8.0 μm or less, more preferably 7.0 μm or less. By setting the median particle size (D50) of the (A1) component to 8.0 μm or less, the thixotropic properties of the epoxy resin composition (I) can be improved, and resin flow during molding can be suppressed. Furthermore, the surface area relative to the mass of the (A1) component increases, thus increasing the reaction rate and allowing the epoxy resin composition (I) to cure in a shorter time. The median particle size (D50) of the (A1) component can be adjusted by pre-crushing the (A1) component using a bead mill or a three-roll mill. For the determination using laser diffraction, for example, an AEROTRAC SPR (model: 7340) (manufactured by Nikkiso Co., Ltd.) can be used. There is no particular limitation on the lower limit of the median particle size (D50) of the (A1) component; for example, it can be 0.1 μm or more.

[0171] Furthermore, the median particle size (D50) of the (A1) component, as determined by laser diffraction, is preferably below the average fiber diameter of the carbon fibers contained in the reinforcing fiber matrix. If the median particle size (D50) is below the average fiber diameter of the carbon fibers, the (A1) component will not be localized on the surface of the prepreg, thus improving the surface appearance quality. In addition, by distributing the (A1) component throughout the fiber-reinforced composite material, poor curing is less likely to occur, and resin flow during molding can be suppressed.

[0172] The content of component (A1) relative to the total mass of the epoxy resin composition (I) is preferably 2% by mass or more, more preferably 2.5% by mass or more, and even more preferably 3% by mass or more. By setting the content of component (A1) to the lower limit or above, resin flow during molding can be suppressed. Furthermore, the content of component (A1) relative to the total mass of the epoxy resin composition (I) is preferably 10% by mass or less, more preferably 9.5% by mass or less, even more preferably 8% by mass or less, and particularly preferably 5% by mass or less. By setting the content of component (A1) to the upper limit or below, an epoxy resin composition (I) with excellent storage stability and mechanical properties can be obtained. The preferred lower and upper limits of the content of component (A1) can be arbitrarily combined, for example, it can be set to 2 to 10% by mass, 2 to 9.5% by mass, 2.5 to 8% by mass, or 3 to 5% by mass.

[0173] The weight-average molecular weight of component (B1) is 60,000 or more, more preferably 65,000 or more. By setting the weight-average molecular weight of component (B1) to the lower limit or above, the minimum viscosity of the epoxy resin composition (I) is increased, and resin flow during molding can be suppressed. Furthermore, the weight-average molecular weight of component (B1) is preferably 150,000 or less, more preferably 145,000 or less. By setting the weight-average molecular weight of component (B1) to the upper limit or below, resin flow during molding can be suppressed, and the workability of the prepreg at room temperature can be improved. The preferred lower and upper limits of the weight-average molecular weight of component (B1) can be arbitrarily combined, for example, it can be set to 60,000 to 150,000, or 65,000 to 145,000.

[0174] The content of component (B1) relative to the total mass of the epoxy resin composition (I) is preferably 1% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2% by mass or more. By setting the content of component (B1) to the lower limit or above, the epoxy resin composition (I) can exhibit high thixotropy, thereby suppressing resin flow during molding. Furthermore, the content of component (B1) relative to the total mass of the epoxy resin composition (I) is preferably 10% by mass or less, more preferably 9.5% by mass or less, even more preferably 8% by mass or less, and particularly preferably 5% by mass or less. By setting the content of component (B1) to the upper limit or below, the workability of the prepreg at room temperature is improved. The preferred lower and upper limits of the content of component (B1) can be combined arbitrarily, for example, they can be set to 1 to 10% by mass, 1 to 9.5% by mass, 1.5 to 8% by mass, or 2 to 5% by mass.

[0175] Regarding components (C) to (E), as mentioned above, other components may also be included.

[0176] As a component of the epoxy resin composition (I), relative to the total mass of the epoxy resin composition (I), for example, a composition containing 2 to 10% by mass of component (A1), 1 to 10% by mass of component (B1), and a total of 30 to 60% by mass of components (C) and (D) can be provided, and a composition also containing 4 to 14% by mass of component (E). However, the total of all components shall not exceed 100% by mass. The lower and upper limits of the content of components (A1), (B1), and (C) to (E) can be arbitrarily combined with the lower and upper limits described above for each component.

[0177] The epoxy resin composition (I) preferably satisfies the conditions (1) and (2) above, and more preferably also satisfies the condition (3) above. The preferred embodiments of the conditions (1) to (3) above may also be appropriately combined in the epoxy resin composition (I).

[0178] <Method for manufacturing epoxy resin composition>

[0179] An epoxy resin composition is obtained, for example, by mixing the above-mentioned components. Methods for mixing the components include using a three-roll mill, a planetary mixer, a kneader, a homogenizer, a homogenizing disperser, and other mixers.

[0180] Epoxy resin compositions can be used to manufacture prepregs by impregnating reinforcing fiber substrates, as described later. Alternatively, epoxy resin compositions can be coated onto release paper or similar materials and cured to obtain epoxy resin film. When used as a film, if the viscosity of the epoxy resin composition at 30°C is 100–1,000,000 Pa·s, the adjustment of the surface tack and workability of the prepreg are excellent.

[0181] <Reinforcing Fibers>

[0182] The reinforcing fibers exist in the prepreg as a reinforcing fiber matrix, preferably in sheet form. It should be noted that the reinforcing fiber matrix refers to an aggregate of individual reinforcing fibers.

[0183] The reinforcing fibers can be long fibers (continuous fibers) or short fibers, such as 0.01 to 30 cm. The orientation of the fibers in the reinforcing fiber matrix can be either a unidirectional orientation or a random orientation. Examples of forms of the reinforcing fiber matrix include: reinforcing fiber fabrics, reinforcing fiber nonwovens, and sheets obtained by unidirectional doubling of long reinforcing fibers. From the viewpoint of being able to form fiber-reinforced composite materials with high specific strength and specific modulus of elasticity, it is preferable to use sheets composed of reinforcing fiber bundles obtained by unidirectional doubling of long fibers (hereinafter, sometimes referred to as "UD matrix") for prepregs. From the viewpoint of ease of operation, it is preferable to use reinforcing fiber fabrics for prepregs. The area weight of the reinforcing fiber matrix can be set to 10 to 4000 g / m². 2 The weight per unit area for UD substrates can also be set to 10–300 g / m². 2 .

[0184] Examples of reinforcing fibers include glass fiber, carbon fiber, nylon fiber, aramid fiber, and boron fiber. Among these, carbon fiber is preferred from the viewpoint of the mechanical properties and lightweight nature of the resulting fiber-reinforced composite material. The number of carbon fibers in the carbon fiber bundle used as the reinforcing fiber matrix is ​​preferably between 1,000 and 70,000. Multiple carbon fiber bundles can be used to form a sheet-like reinforcing fiber matrix obtained by spinning the fibers in one direction.

[0185] From the viewpoint of the rigidity of the obtained fiber-reinforced composite material, the tensile strength of the carbon fiber precursor is preferably 1.5–9 GPa, and the tensile modulus of elasticity of the carbon fiber precursor is preferably 150–260 GPa. The tensile strength and tensile modulus of elasticity of the carbon fiber precursor can be determined according to JIS R7601:1986.

[0186] The fiber diameter of carbon fiber can be set to 3–15 μm. If the fiber diameter of carbon fiber is above the lower limit mentioned above, then in processes used to process carbon fiber, such as combs and rollers, when the carbon fiber moves laterally and rubs against each other, or when the carbon fiber rubs against the roller surface, the occurrence of carbon fiber cutting or pilling can be suppressed. In addition, it can make the curing agent particles uniformly dispersed into the interior of the substrate and suppress resin flow during molding.

[0187] <Prepreg Manufacturing Method>

[0188] Prepregs are obtained, for example, by impregnating the aforementioned epoxy resin composition onto a reinforcing fiber substrate. The resulting prepreg is formed by impregnating an epoxy resin composition onto a reinforcing fiber substrate. Examples of methods for impregnating the epoxy resin composition onto the reinforcing fiber substrate include: a wet method where the epoxy resin composition is dissolved in a solvent such as methyl ethyl ketone or methanol and its viscosity is reduced, followed by impregnation onto the reinforcing fiber substrate; and a hot-melt method (dry method) where the epoxy resin composition is reduced in viscosity by heating and then impregnated onto the reinforcing fiber substrate, etc., but are not limited to these methods.

[0189] The wet process involves immersing the reinforcing fiber substrate in a solution of epoxy resin composition, then lifting it out and using an oven or similar method to evaporate the solvent. The hot-melt process includes methods such as directly impregnating the reinforcing fiber substrate with an epoxy resin composition that has been reduced in viscosity by heating; and methods that pre-prepare a film by temporarily coating the epoxy resin composition onto the surface of a substrate such as release paper, then overlapping the film from both sides or one side of the reinforcing fiber substrate, and subjecting it to heating and pressure, thereby impregnating the reinforcing fiber substrate with resin. The coating layer obtained by coating the surface of a substrate such as release paper can be used in an uncured state for the hot-melt process, or it can be used after the coating layer has cured. According to the hot-melt process, there is substantially no residual solvent in the prepreg, which is therefore preferable.

[0190] The prepreg can be manufactured, for example, by the following steps: First, a matrix resin is coated onto one side of a carrier film (first carrier film). Similarly, another carrier film (second carrier film) with a matrix resin coated on one side is prepared. Next, a laminate consisting of the first and second carrier films sandwiching the reinforcing fiber substrate and the matrix resin is formed, with the matrix resin-coated sides of the first and second carrier films facing towards the reinforcing fiber substrate. The resulting laminate is pressurized to impregnate the reinforcing fiber substrate with the matrix resin, thereby obtaining the prepreg.

[0191] The content of the epoxy resin composition in the prepreg (hereinafter also referred to as "resin content") relative to the total mass (100% by mass) of the prepreg is preferably 15 to 50% by mass, more preferably 20 to 45% by mass, and even more preferably 25 to 40% by mass. If the resin content is above the lower limit mentioned above, the adhesion between the reinforcing fiber and the epoxy resin composition can be sufficiently ensured. If the resin content is below the upper limit mentioned above, the mechanical properties of the fiber-reinforced composite material are further improved.

[0192] [Fiber-reinforced composite materials]

[0193] Fiber-reinforced composites are obtained by curing prepregs. That is, fiber-reinforced composites contain cured resins contained in the prepregs and reinforcing fibers.

[0194] One embodiment of the fiber-reinforced composite material is formed from a cured product of a reinforcing fiber substrate and an epoxy resin composition comprising components (A), (B), (C), and (D) as described above. Furthermore, if the epoxy resin composition satisfies conditions (1) and (2) as described above, the effect can be achieved in a short time, and resin flow during molding can be suppressed.

[0195] One embodiment of the fiber-reinforced composite material is formed from a cured product of a reinforcing fiber substrate and an epoxy resin composition (I), wherein the epoxy resin composition (I) comprises the aforementioned components (A1), (B1), (C), and (D).

[0196] <Manufacturing Methods of Fiber Reinforced Composite Materials>

[0197] Fiber-reinforced composite materials are obtained, for example, by laminating two or more of the aforementioned prepregs, applying pressure to the resulting laminate, and then heating and curing an epoxy resin composition. Examples of molding methods include: compression molding, autoclave molding, bag molding, winding tape molding, internal pressure molding, sheet wrapping, RTM (Resin Transfer Molding), VaRTM (Vacuum Assisted Resin Transfer Molding), filament winding, and RFI (Resin Film Infusion), but are not limited to these methods.

[0198] Autoclave molding is a method that involves layering prepregs, covering them with a backing film, and simultaneously degassing the layers while applying pressure and heat for curing. Because it allows for precise control of fiber orientation and minimizes voids, it produces high-quality molded products with excellent mechanical properties.

[0199] The winding method is a method of forming a tubular fiber-reinforced composite resin body (fiber-reinforced composite resin tubular body) by winding prepreg around a core such as a mandrel. It is preferred for manufacturing rod-shaped objects such as golf clubs and fishing rods. More specifically, the method is as follows: the prepreg is wound around a mandrel, and to fix the prepreg and apply pressure, a winding tape formed of thermoplastic film is wound around the outside of the prepreg. After heating and curing the epoxy resin composition in the prepreg in an oven, the core is pulled out to obtain the fiber-reinforced composite resin tubular body.

[0200] Internal pressure molding involves placing a preform, formed by winding prepreg onto an internal pressure-generating body such as a thermoplastic resin tube, in a mold. High-pressure gas is then introduced into the internal pressure-generating body to apply pressure, while the mold is simultaneously heated to perform molding. There are no particular limitations on the heating temperature, but higher temperatures shorten the molding time and are therefore preferred. Specifically, 120°C or higher is preferred, and 140°C or higher is more preferable. However, if the temperature is too high, lowering the mold temperature will take a considerable amount of time. Furthermore, if the prepreg is placed without lowering the temperature, curing may sometimes begin, preventing the epoxy resin composition from spreading evenly throughout the final molded object. This method is preferred for molding complex shapes such as golf clubs, bats, tennis rackets, badminton rackets, etc. Due to the high molding pressure, internal pressure molding results in faster curing, and on the other hand, more resin flow occurs during molding.

[0201] Applications of fiber-reinforced composite materials

[0202] The fiber-reinforced composite resin of this invention is suitable for sports applications, general industrial applications, and aerospace applications. More specifically, in sports applications, it is suitable for use in golf clubs, fishing rods, tennis and badminton rackets, bicycle frames, hockey sticks, and skis. In general industrial applications, it is suitable for use in structural materials for moving bodies such as automobiles, ships, and railway vehicles, drive shafts, leaf springs, windmill blades, pressure vessels, flywheels, paper rolls, roofing materials, cables, and repair reinforcement materials.

[0203] [Manufacturing method of molded body]

[0204] The method for manufacturing the molded body of the present invention includes the following steps (1). Furthermore, the method for manufacturing the molded body of the present invention is preferably a method for manufacturing a tubular molded body, and more preferably includes the following steps (2).

[0205] Process (1): The process of heating the prepreg containing the epoxy resin composition and reinforcing fibers placed in the mold to above 130°C.

[0206] Step (2): A step of forming the tubular precursor by pressing it against a mold through an expansion of the medium from the inside of the tubular precursor in which the prepreg is configured as a tubular shape.

[0207] The following explanation will take the manufacture of a tubular molded body as an example, but the shape of the molded body is not limited to a tubular shape.

[0208] In the manufacture of tubular molded bodies, a prepreg is configured into a tubular shape to form a tubular precursor, which is then heated. The tubular precursor can be obtained, for example, by winding a prepreg containing a resin composition and reinforcing fibers onto a medium (internal pressure imparter) such as a thermoplastic resin hose. The resulting tubular precursor is placed in a mold and heated to 130°C or higher, preferably 140°C or higher, for molding. Molding can be performed by introducing high-pressure gas into the internal pressure imparter to expand the medium and press it from the inside of the tubular precursor into the mold.

[0209] Furthermore, the epoxy resin composition contained in the prepreg used in the manufacturing method of the molded article of the present invention contains the following components (A1) and (B1), and may also contain the following components (C) and (D).

[0210] (A1) Ingredient: 2,4-bis(3,3-dimethylurea)toluene.

[0211] (B1) Composition: Polyvinyl alcohol formaldehyde resin with a weight average molecular weight of 60,000 or more.

[0212] (C) Component: Epoxy resin with an oxazolidinone structure.

[0213] (D) Component: Epoxy resin that is solid at 25°C (excluding component (C)).

[0214] The content and preferred method of components (A1) and (B1) are the same as those of components (A) and (B) as described above. Furthermore, the specific components, content, and preferred methods of components (C) and (D) are as described above.

[0215] The total content of components (C) and (D) relative to the total mass of the epoxy resin composition is preferably 30-60% by mass, more preferably 35-60% by mass. If the total content of components (C) and (D) is above the lower limit mentioned above, resin flow during molding can be suppressed. Furthermore, if the total content of components (C) and (D) is below the upper limit mentioned above, sufficient adhesion is obtained on the surface of the prepreg.

[0216] As a prepreg used in the manufacturing method of the molded body of the present invention, a prepreg containing the above-described epoxy resin composition (I) can be used, for example.

[0217] In the manufacturing method of the molded body of the present invention, when the tubular molded body has an annular curved portion, a step of bending the tubular precursor into an annular shape may also be included. Examples of tubular molded bodies having an annular curved portion include those with a tubular frame forming an annular racket head, such as tennis or badminton rackets.

[0218] The present invention will now be described in more detail based on embodiments, but the present invention is not limited to any of the embodiments described below. The various manufacturing conditions and evaluation results in the embodiments described below have the meaning of preferred values ​​as upper or lower limits in the implementation of the present invention. The preferred range can be a range defined by a combination of the values ​​of the upper or lower limits and the values ​​of the embodiments described below, or the values ​​between the embodiments.

[0219] <Ingredients>

[0220] ((A) ingredient)

[0221] <(A1) Ingredient>

[0222] • Omicure24: 2,4-bis(3,3-dimethylureo)toluene, median particle size (D50) 6.0 μm, manufactured by PTI JAPAN Co., Ltd.

[0223] <(Other than (A1) ingredients>

[0224] • Omicure94: 3-Phenylon-1,1-Dimethylurea, median particle size (D50) 9.5 μm, manufactured by PTI JAPAN Co., Ltd. as "Omicure (Omicure) 94".

[0225] •DCMU-99: 3-(3,4-dichlorophenyl)-1,1-dimethylurea, median particle size (D50) 11.4 μm, manufactured by Hojiya Chemical Industry Co., Ltd.

[0226] (Component B)

[0227] <(B1) Ingredients>

[0228] •VINYLEC E: Micronized polyvinyl alcohol formaldehyde resin, manufactured by JNC Corporation as "VINYLEC E".

[0229] <(B1) component other than>

[0230] •VINYLEC K: Micronized polyvinyl alcohol formaldehyde resin, manufactured by JNC Corporation.

[0231] ·5003 MP: Fine powder of polyethersulfone, "Sumikaexcel 5003MP" manufactured by Sumitomo Chemical Co., Ltd.

[0232] (C) component)

[0233] • YD-952: An epoxy resin with an oxazolidinone structure, epoxy equivalent 340 g / eq, manufactured by NIPPON STEELC Chemical & Material Co., Ltd.

[0234] ((D) component)

[0235] • YD-012: Solid bisphenol A type epoxy resin, epoxy equivalent 655g / eq, manufactured by NIPPON STEEL Chemical & Material Co., Ltd.

[0236] • N-680: Cresol phenolic resin varnish type epoxy resin, epoxy equivalent 211g / eq, manufactured by DIC Corporation as "N-680".

[0237] (E) component)

[0238] ·Dicyanex1400F: Dicyandiamide, "Dicyanex1400F" manufactured by Evonik Japan Co., Ltd.

[0239] ·Dicy15: dicyandiamide, "jER cure Dicy15" manufactured by Mitsubishi Chemical Co., Ltd.

[0240] (Other ingredients)

[0241] YD-128: Liquid bisphenol A type epoxy resin, epoxy equivalent 189 g / eq, manufactured by NIPPON STEEL Chemical & Material Co., Ltd.

[0242] • AEROSIL RY-200, hydrophobic silica, manufactured by NIPPON AEROSIL Co., Ltd.

[0243] (Carbon fiber)

[0244] • Carbon fiber: “Pyrofil TR50S15L” manufactured by Mitsubishi Chemical Co., Ltd. (average fiber diameter 7μm, specific gravity 1.82, tensile modulus 235GPa).

[0245] <Rheometer Evaluation>

[0246] The epoxy resin composition was measured using a rheometer (HAAKE MARS 40, Thermo Fisher Scientific, Inc.) at 2°C / min, and the lowest viscosity was set as the minimum viscosity.

[0247] In addition, the viscosity of the epoxy resin composition at 65°C was also measured using the same rheometer.

[0248] <CURELASTOMETER Evaluation>

[0249] The epoxy resin composition was measured under the condition of 145°C by CURELASTOMETER (registered trademark, manufactured by JSR Trading Co., Ltd., 7 TypeP) to obtain the gel time value.

[0250] <Resin Flow Evaluation>

[0251] The resin flow rate during molding was measured according to the following steps 1 to 5.

[0252] 1. The prepreg was cut into 100 mm × 100 mm, and 8 sheets were laminated in such a way that the fiber direction was [0° / 90° / 0° / 90° / 90° / 0° / 90° / 0°] when viewed from above to produce a laminate.

[0253] 2. The weight W1 of the obtained laminate was measured.

[0254] 3. The laminate was heated and cured in an autoclave under the condition of a pressure of 0.6 MPa at a heating rate of 4°C / minute and held at 145°C for 30 minutes to be molded, and a fiber reinforced composite material with a thickness of 1.0 mm was produced.

[0255] 4. The resin flash part overflowing from the fiber reinforced composite material was removed, and the weight W2 of the remaining fiber reinforced composite material was measured.

[0256] 5. Based on the measured values of W1 and W2, the resin flow rate was calculated using the following formula.

[0257] Resin flow rate [%] = [(W1 - W2) / W1] × 100

[0258] <Measurement of Weight-Average Molecular Weight>

[0259] Regarding the weight-average molecular weights of VINYLEC E and VINYLEC K as the component (B), a 0.05 mass% tetrahydrofuran solution was prepared and determined as the weight-average molecular weight based on standard polystyrene conversion under the following analysis conditions.

[0260] (Analysis Conditions)

[0261] Apparatus: HLC-8320 GPC manufactured by TOSOH Corporation.

[0262] Chromatographic column: Connected in the order of the following (1) to (4).

[0263] (1) TSK guardcolumn Super HZ-L (guard column) 4.6mm I·D×2.0cmL.

[0264] (2) TSK gelSuper HZM-M 4.6mmI·D×15cmL.

[0265] (3) TSK gelSuper HZM-M 4.6mmI·D×15cmL.

[0266] (4) TSK gelSuper HZ2000 4.6mmI·D×15cmL.

[0267] Temperature of the constant temperature bath: 40℃.

[0268] Mobile phase: Tetrahydrofuran (stabilizer BHT).

[0269] Flow rate: 0.35 mL / min.

[0270] Injection volume: 10 μL.

[0271] Detector: RI.

[0272] Regarding the weight-average molecular weight of 5003 MP as component (B), a 0.4% by mass solution of dimethylformamide was prepared, and the weight-average molecular weight was determined based on the standard polystyrene conversion under the following analytical conditions.

[0273] Device: TOSOH HLC-8420 high-speed GPC.

[0274] Guard column: TSK guardcolumn α (6.0mm ID × 4.0cm L) manufactured by TOSOH.

[0275] Sample column: Connect three α-M (7.8 mm ID × 30 cm L) columns manufactured by TOSOH.

[0276] Temperature of the constant temperature bath: 40℃.

[0277] Mobile phase: dimethylformamide (containing 20 mM LiBr).

[0278] Flow rate: 1.0 mL / min.

[0279] Injection volume: 100μL.

[0280] Detector: RI.

[0281] [Examples 1-6, Comparative Examples 1-9]

[0282] <Preparation of the matrix resin composition>

[0283] According to the formulations shown in Table 1, epoxy resin compositions were prepared in the following manner.

[0284] First, component (B) and liquid bisphenol A epoxy resin were metered in a flask and heated to 150°C using an oil bath, and mixed until component (B) dissolved. Then, the mixture was cooled to 100°C, and components (C), (D), and silica were added and stirred. Next, the mixture was cooled to 65°C, and components (A) and (E) were added and stirred to obtain the epoxy resin composition. The rheological and curelastomester evaluation results of the epoxy resin composition are shown in Tables 1-3.

[0285] <Prepreg Manufacturing>

[0286] The obtained epoxy resin composition was formed into a film using a hot melt coating machine (manufactured by HIRANOTECSEED Co., Ltd., "R-HC"), and the resin film had a unit area weight of 32.3 g / m³. 2 A resin film was then laminated onto fibers obtained by spinning carbon fibers, with a unit area weight of 120 g / m². 2 Both sides of the carbon fiber sheet were impregnated with heated rollers to obtain a fiber unit area weight of 120g / m². 2 Prepreg with a resin content of 35% by mass.

[0287] <Manufacturing of Fiber Reinforced Composite Materials>

[0288] The obtained prepreg was cut into 100mm × 100mm pieces, and eight sheets were stacked in a top-view arrangement with the fiber orientation from bottom to top in the pattern of [0° / 90° / 0° / 90° / 90° / 0° / 90° / 0°] to obtain a laminate. The laminate was then heat-cured in an autoclave at a pressure of 0.6 MPa at a rate of 4°C / min, and held at 145°C for 30 minutes to obtain a fiber-reinforced composite material with a thickness of 1.0mm. Furthermore, the resin flow rate was evaluated during molding according to the evaluation method described above. The results are shown in Tables 1 to 3.

[0289]

[0290]

[0291]

[0292] As shown in Tables 1 to 3, Examples 1 to 6, which used epoxy resin compositions that meet the requirements of this invention, significantly suppressed resin flow rate during molding in the manufacture of fiber-reinforced composite materials compared to Comparative Examples 1 to 9, which do not meet the requirements of this invention. It is presumed that resin flow rate was similarly suppressed in other molding methods such as pressure molding, winding, internal pressure molding, sheet winding, RTM, and VaRTM.

[0293] This application claims priority based on Japanese Patent Application No. 2023-169784, filed in Japan on September 29, 2023, the contents of which are incorporated herein by reference.

Claims

1. A prepreg, characterized in that, The prepreg comprises an epoxy resin composition and reinforcing fibers, wherein the epoxy resin composition comprises the following components (A), (B), (C), and (D) and satisfies the following conditions (1) and (2): (A) Component: urea compound; (B) Component: thermoplastic resin; (C) Component: epoxy resin having an oxazolidinone structure; (D) Component: bisphenol type epoxy resin that is solid at 25°C, wherein component (C) is not included; Condition (1): The lowest viscosity of the epoxy resin composition, as determined by a rheometer at 2°C / min, is in the range of 3.0 to 6.0 Pa·s; Condition (2): The gel time of the epoxy resin composition, as determined by the registered trademark CURELASTOMETER at 145°C, is in the range of 2.0 to 5.0 min.

2. The prepreg according to claim 1, wherein, The median particle size D50 of component (A), as determined by laser diffraction, is less than 8.0 μm.

3. The prepreg according to claim 1 or 2, wherein, The ingredient (A) contains 2,4-bis(3,3-dimethylurea)toluene.

4. The prepreg according to claim 1 or 2, wherein, The (B) component is a thermoplastic resin that can dissolve in the mixture of epoxy resins contained in the epoxy resin composition.

5. The prepreg according to claim 1 or 2, wherein, The weight-average molecular weight of component (B) is above 60,000.

6. The prepreg according to claim 1 or 2, wherein, Component (B) comprises polyvinyl formal resin.

7. The prepreg according to claim 1 or 2, wherein, The component (C) is a solid at 25°C.

8. The prepreg according to claim 1 or 2, wherein, The epoxy equivalent of component (D) is 300–1000 g / eq.

9. The prepreg according to claim 1 or 2, wherein, The component (D) is a bisphenol A type epoxy resin.

10. The prepreg according to claim 1 or 2, wherein, The epoxy resin composition contains 2 to 10% by mass of component (A) relative to the total mass of the epoxy resin composition.

11. The prepreg according to claim 1 or 2, wherein, The epoxy resin composition contains 1 to 10% by mass of component (B) relative to the total mass of the epoxy resin composition.

12. The prepreg according to claim 1 or 2, wherein, The epoxy resin composition comprises, relative to its total mass, 30 to 60% by mass of the (C) component and the (D) component.

13. The prepreg according to claim 1 or 2, wherein, The prepreg also meets the following condition (3): the viscosity of the epoxy resin composition at 65°C is in the range of 10 to 1000 Pa·s.

14. The prepreg according to claim 1 or 2, wherein, The prepreg also contains the following component (E): selected from at least one of dicyandiamide and dicyandiamide derivatives.

15. The prepreg according to claim 1 or 2, wherein, The reinforcing fiber comprises carbon fiber.

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

17. A prepreg comprising an epoxy resin composition and reinforcing fibers, the epoxy resin composition comprising the following components (A1), (B1), (C), and (D): (A1) a urea compound comprising 2,4-bis(3,3-dimethylurea)toluene; (B1) a polyvinyl alcohol formaldehyde resin having a weight-average molecular weight of 60,000 or more; (C) an epoxy resin having an oxazolidinone structure; and (D) a bisphenol-type epoxy resin that is solid at 25°C. The ingredient (C) mentioned above is not included.

18. The prepreg according to claim 17, wherein, The prepreg satisfies the following conditions (1) and (2): Condition (1): The lowest viscosity of the epoxy resin composition, as measured by a rheometer at 2°C / min, is in the range of 3.0 to 6.0 Pa·s; Condition (2): The gel time of the epoxy resin composition, as measured by the registered trademark CURELASTOMETER at 145°C, is in the range of 2.0 to 5.0 min.

19. The prepreg according to claim 17 or 18, wherein, The median particle size D50 of the (A1) component, as determined by laser diffraction, is less than 8.0 μm.

20. The prepreg according to claim 17 or 18, wherein, The component (C) is a solid at 25°C.

21. The prepreg according to claim 17 or 18, wherein, The epoxy equivalent of component (D) is 300–1000 g / eq.

22. The prepreg according to claim 17 or 18, wherein, The component (D) is a bisphenol A type epoxy resin.

23. The prepreg according to claim 17 or 18, wherein, The epoxy resin composition contains 2 to 10% by mass of the (A1) component relative to the total mass of the epoxy resin composition.

24. The prepreg according to claim 17 or 18, wherein, The epoxy resin composition contains 1 to 10% by mass of the (B1) component relative to the total mass of the epoxy resin composition.

25. The prepreg according to claim 17 or 18, wherein, The epoxy resin composition comprises, relative to its total mass, 30 to 60% by mass of the (C) component and the (D) component.

26. The prepreg according to claim 17 or 18, wherein, The prepreg also meets the following condition (3): the viscosity of the epoxy resin composition at 65°C is in the range of 10 to 1000 Pa·s.

27. The prepreg according to claim 17 or 18, wherein, The prepreg also contains the following component (E): selected from at least one of dicyandiamide and dicyandiamide derivatives.

28. The prepreg according to claim 17 or 18, wherein, The reinforcing fiber comprises carbon fiber.

29. A method for manufacturing a molded article, the method comprising: The process of heating a prepreg containing an epoxy resin composition and reinforcing fibers placed in a mold to 130°C or higher, wherein the epoxy resin composition contains the following components (A1) and (B1): (A1) 2,4-bis(3,3-dimethylurea)toluene; (B1) polyvinyl alcohol formaldehyde resin with a weight average molecular weight of 60,000 or higher.

30. The method for manufacturing a molded article according to claim 29, wherein, The prepreg is configured into a tubular shape and heated to produce a tubular molded body.

31. The method for manufacturing a molded article according to claim 30, wherein, Also includes: The process of forming a tubular precursor by pressing it against a mold after the medium expands from the inside of the tubular precursor in which the prepreg is configured as a tubular shape.

32. The method for manufacturing a molded article according to claim 29 or 30, wherein, The epoxy resin composition further comprises the following component (C): an epoxy resin having an oxazolidinone structure.

33. The method for manufacturing a molded article according to claim 29 or 30, wherein, The epoxy resin composition further comprises the following component (D): bisphenol type epoxy resin which is solid at 25°C, wherein component (C): epoxy resin which is solid at 25°C is excluded.

34. The method for manufacturing a molded article according to claim 29 or 30, wherein, The epoxy resin composition comprises, relative to the total mass of the epoxy resin composition, 30 to 60% by mass of the following component (C) and component (D), wherein component (C) is an epoxy resin having an oxazolidinone structure; and component (D) is a bisphenol type epoxy resin that is solid at 25°C, wherein component (C) is not included.

35. The method for manufacturing a molded article according to claim 31, wherein, The tubular molded body has an annular curved portion, and the manufacturing method includes a step of bending the tubular precursor into an annular shape.

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