Prepreg, laminate, and fiber-reinforced composite material

Abstract

The present invention addresses the problem of improving the bondability between a fiber-reinforced composite material and an expanded metal, and to improve impact resistance of a bonded body of the fiber-reinforced composite material and the expanded metal. In order to address this problem, provided is a prepreg including a resin-impregnated sheet substrate in which both sides of a sheet-like fiber substrate are impregnated with an epoxy resin composition containing thermoplastic resin particles having an average particle size of 5 to 50 μm, and an expanded metal is laminated on at least one surface of the resin-impregnated sheet substrate.

Description

Prepregs, laminates, and fiber-reinforced composite materials

[0001] The present invention relates to prepregs, laminates of prepregs, and fiber-reinforced composite materials containing epoxy resin compositions.

[0002] Fiber-reinforced composite materials are often used in products requiring high specific modulus of elasticity and specific strength, such as aircraft components, wind turbine blades, automobile body panels, and laptop casings. However, depending on the fibers and resins used, fiber-reinforced composite materials can sometimes have conductivity issues. Therefore, they are sometimes used in combination with metals to compensate for this lack of conductivity.

[0003] On the other hand, it is generally known that resin materials used in fiber-reinforced composite materials have low affinity with metal materials. Therefore, the bonding strength at the interface between the resin and metal materials is low, which reduces the impact resistance of fiber-reinforced composite materials incorporating metal materials. Against this backdrop, various methods are being attempted to improve the bonding properties between fiber-reinforced composite materials and dissimilar materials such as metal materials.

[0004] Patent Document 1 describes how pre-treatment of a metal material with a silane coupling agent improves its adhesion to a resin material. Patent Document 2 describes how processing and roughening the surface of aluminum and aluminum alloy improves its adhesion to dissimilar materials.

[0005] Furthermore, Patent Document 3 describes the use of a fiber-reinforced composite material, which combines expanded metal (excellent in achieving both lightning resistance and weight reduction) with a surface film containing a fiber base material and a resin composition, for the purpose of providing lightning resistance to aircraft materials.

[0006] Japanese Patent Publication No. Hei 6-15773, Japanese Patent Publication No. 2012-41579, Japanese Patent Publication No. 2022-527496

[0007] Even with the technologies described in Patent Documents 1 and 2, the improvement in bonding strength between resin materials and metal materials was not always sufficient, and concerns remained regarding the impact resistance of fiber-reinforced composite materials incorporating metal materials.

[0008] In the technology described in Patent Document 3, the metal grid constituting the expanded metal may have sharp edges in the in-plane direction, that is, in the direction in which the repeating grid of the expanded metal extends, due to its manufacturing method. Stress concentration occurs at these points, which can easily cause delamination at the metal-resin interface, raising concerns about reduced impact resistance.

[0009] The problem that this invention aims to solve is to improve the bonding between fiber-reinforced composite material and expanded metal, and to improve the impact resistance of the bonded structure between the fiber-reinforced composite material and expanded metal.

[0010] [1] A prepreg comprising a resin-impregnated sheet substrate in which an epoxy resin composition containing thermoplastic resin particles with an average particle size of 5 to 50 μm is impregnated on both sides of a sheet-like fibrous substrate, wherein expanded metal is laminated on at least one surface of the resin-impregnated sheet substrate. [2] The prepreg according to [1], wherein a nonwoven fabric is used as the sheet-like fibrous substrate. [3] A damage area of ​​100 mm² determined by an impact resistance test conducted in accordance with ASTM D7136 / D7136M:2012. ２ The prepreg according to [1] or [2] above, which is as follows: [4] The prepreg according to any one of [1] to [3] above, wherein the resin constituting the thermoplastic resin particles is at least one resin selected from polyamide, polyimide, polyetherimide, polyamideimide, polysulfone, and polyethersulfone. [5] The prepreg according to any one of [1] to [4] above, wherein the average fiber diameter of the single fibers of the sheet-like fibrous substrate is 3 to 20 μm. [6] The prepreg according to any one of [1] to [5] above, wherein the sheet-like fibrous substrate satisfies the following formula (1).

[0011] 1.0 ≤ 4 × AW / (DEN × FD) ≤ 7.0 Equation (1) (where AW is the basis weight of the fiber material (unit: g / m) ２ DEN is the true density of the fiber base material (unit: g / m³). ３), FD represents the average fiber diameter (unit: m) of the fibers constituting the fibrous base material.) [7] A prepreg according to any one of [1] to [6], comprising 10 to 120 parts by mass of thermoplastic resin particles per 100 parts by mass of epoxy resin. [8] A laminate comprising at least one layer (this layer is referred to as "layer A") of the prepreg according to any one of [1] to [7], wherein the layer adjacent to layer A (this layer is referred to as "layer B") is composed of a prepreg without expanded metal, and the temperature difference between the peak top temperatures of the exothermic peaks of layer A and layer B, determined by the method described in the specification, is 1 to 100°C. [9] A fiber-reinforced composite material obtained by curing a laminate comprising at least one layer of the prepreg according to any one of [1] to [7].

[10] A fiber-reinforced composite material obtained by curing a laminate containing at least two layers of the prepreg described in any of [1] to [7], wherein the two layers of the at least two layers are adjacent to each other.

[0012] According to the present invention, it is possible to provide a prepreg with expanded metal that exhibits excellent impact resistance after molding, a laminate containing such prepreg, and a fiber-reinforced composite material obtained by curing and / or molding the laminate.

[0013] This is a schematic cross-sectional view of an example of the expanded metal-containing prepreg of the present invention. This is a schematic cross-sectional view of another example of the expanded metal-containing prepreg of the present invention. This is a schematic cross-sectional view of an example of the fiber-reinforced composite material of the present invention.

[0014] <Overview> The present invention provides a prepreg with expanded metal laminated on it (hereinafter sometimes referred to as "EM-equipped prepreg") which has layers of a member (referred to as "resin-impregnated sheet substrate") on both sides of a sheet-like fibrous substrate, in which an epoxy resin composition containing thermoplastic resin particles with an average particle size of 5 to 50 μm is impregnated, and expanded metal is laminated on at least one surface of the resin-impregnated sheet substrate.

[0015] Since the metal lattice of expanded metal has sharp edges in the in-plane direction due to its manufacturing method, in a fiber-reinforced composite material containing expanded metal, for example, when an impact is applied to the fiber-reinforced composite material, stress concentration occurs at the interface between the sharp metal edge and the resin. Therefore, in the fiber-reinforced composite material, cracks easily progress in the resin in contact with the sharp edge of the expanded metal, which has been the cause of the reduction in impact resistance.

[0016] Therefore, the present inventors adopted a member (resin-impregnated sheet-like base material) in which an epoxy resin composition containing thermoplastic resin particles having a specific particle size was impregnated on both sides of a sheet-like fiber base material, and made it a prepreg having a configuration in which expanded metal was laminated on at least one surface thereof, and found that a fiber-reinforced composite material exhibiting high impact resistance can be achieved.

[0017] <Epoxy Resin Composition> As the epoxy resin used in the epoxy resin composition of the prepreg with EM of the present invention, a commercially available epoxy resin can be used, and its details and specific examples are as described later. In addition to the epoxy resin, it can contain other components such as a curing agent, a curing accelerator, and a thermoplastic resin soluble in the epoxy resin described later. As described later, the epoxy resin composition impregnated into the sheet-like fiber base material contains thermoplastic resin particles having an average particle size of 5 to 50 μm.

[0018] There is no particular limitation on the method of handling the epoxy resin composition. For example, the epoxy resin composition can be handled in a normal state at normal temperature and pressure, or it can be dissolved in a solvent to reduce its viscosity and handled, or a partial reaction can be advanced by heat, light, etc. to make the epoxy resin composition more viscous and handled.

[0019] Generally, the reactivity of the epoxy resin composition when using a curing agent depends on the types of the epoxy resin and the curing agent used. The reactivity of the epoxy resin composition can be evaluated by the temperature of the exothermic peak when measured under heating conditions with a differential scanning calorimeter (DSC).

[0020] In other words, in the present invention, the exothermic peak of the prepreg is understood to be the exothermic peak of the epoxy resin composition constituting the prepreg (including cases where the composition consists only of epoxy resin). When measuring the exothermic peak of the epoxy resin composition and determining the temperature of the exothermic peak (exothermic peak temperature), it is determined by the following method. Measuring device: Differential scanning calorimeter (DSC Q2500: manufactured by TA Instruments). Measurement conditions: Measurement in a nitrogen atmosphere at a heating rate of 5°C / min in the range of 20 to 300°C. Identification of exothermic peak and exothermic peak temperature: In the obtained exothermic curve, the peak with a heat generation of 30 J / g or more is defined as the exothermic peak, and the peak top temperature of that exothermic peak is defined as the exothermic peak temperature. If two or more exothermic peaks with a heat generation of 30 J / g or more are observed, the lower temperature peak is used as the exothermic peak for determining the exothermic peak temperature.

[0021] The measuring device can be replaced with an equivalent device (a device that provides or is expected to provide the same measurement results as the above device).

[0022] <Epoxy Resin> The epoxy resin used in this invention refers to a compound having one or more epoxy groups in one molecule. Examples of such epoxy resins include epoxy resins that use compounds having amino groups or phenolic hydroxyl groups as precursors.

[0023] Specifically, examples of epoxy resins having a compound with an amino group as a precursor include tetraglycidyl diaminodiphenylmethane, triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, various isomers of triglycidyl aminocresol, N,N-diglycidyl-4-phenoxyaniline, N,N-diglycidyl-4-(4-methylphenoxy)aniline, N,N-diglycidyl-4-4-tert-butylphenoxy)aniline, and N,N-diglycidyl-4-(4-phenoxyphenoxy)aniline. Examples of epoxy resins having a compound with a phenolic hydroxyl group as a precursor include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolak type epoxy resin, and cresol novolak type epoxy resin. Brominated epoxy resins obtained by brominating these epoxy resins can also be used. Among them, epoxy resins having an aromatic amine represented by tetraglycidyl diaminodiphenylmethane as a precursor are most suitable for the present invention because they have good heat resistance and excellent adhesiveness to the fiber base material.

[0024] <Thermoplastic resin soluble in epoxy resin> The epoxy resin composition used in the EM-coated prepreg of the present invention may contain a thermoplastic resin soluble in epoxy resin. Preferably, such a thermoplastic resin is one having a main chain of bonds selected from the group consisting of carbon-carbon bonds, amide bonds, imide bonds, ester bonds, ether bonds, carbonate bonds, urethane bonds, thioether bonds, sulfone bonds, and carbonyl bonds. Furthermore, this thermoplastic resin may have a partially crosslinked structure, and may be crystalline or amorphous. Particularly preferred are resins selected from the group consisting of polyamide, polycarbonate, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyarylate, polyester, polyamide-imide, polyimide, polyetherimide, polyimide having a phenyltrimethylindan structure, polysulfone, polyethersulfone, polyetherketone, polyetheretherketone, polyaramid, polyethernitrile, and polybenzimidazole. Note that thermoplastic resins soluble in two or more epoxy resins may also be used.

[0025] The glass transition temperature (Tg) of the thermoplastic resin soluble in the epoxy resin is preferably 130 to 300°C, with a lower limit of 150°C or higher, more preferably 170°C or higher, and an upper limit of 270°C or lower, more preferably 240°C. If the glass transition temperature is 130°C or higher, the heat resistance of the EM-coated prepreg will be good, and it may be less prone to thermal deformation when used as a molded article. On the other hand, if the glass transition temperature is 300°C or lower, the thermoplastic resin will dissolve easily in the epoxy resin composition. The glass transition temperature of the thermoplastic resin can be measured using a differential scanning calorimeter (DSC) in accordance with JIS K7121:2012.

[0026] Furthermore, thermoplastic resins soluble in epoxy resins that have hydroxyl groups, carboxyl groups, thiol groups, or acid anhydrides as terminal functional groups are preferably used because they can react with the epoxy resin during the curing process of the epoxy resin composition. Specific examples include commercially available polyethersulfones such as "Sumika Excel®" PES3600P, PES5003P, PES5200P, PES7600P (all manufactured by Sumitomo Chemical Co., Ltd.), "Ultrason®" E2020PSR, E2021SR (both manufactured by BASF Corporation), and "GAFONE®" 3600RP, 3000RP (both manufactured by SolvayAdva). Examples of suitable materials include polyethersulfone copolymer oligomers (manufactured by ncedPolymers, Inc.), polyethersulfone and polyethersulfone copolymer oligomers as described in Japanese Patent Publication No. 2004-506789, and commercially available polyetherimides such as "Ultem®" 1000, "Ultem®" 1010, and "Ultem®" 1040 (all manufactured by SABIC). An oligomer refers to a polymer with a relatively low molecular weight, in which a finite number of monomers, ranging from 10 to 100, are bonded together.

[0027] A mixture of epoxy resin and a thermoplastic resin soluble in epoxy resin often yields better results than using epoxy resin alone. The brittleness of the epoxy resin is compensated for by the toughness of the thermoplastic resin, and the molding difficulty of the thermoplastic resin is compensated for by the epoxy resin, resulting in a well-balanced base resin.

[0028] In terms of balance, the ratio of epoxy resin to thermoplastic resin soluble in epoxy resin is preferably such that the amount of thermoplastic resin is 2 to 50 parts by mass, more preferably 2 to 40 parts by mass, and even more preferably 5 to 30 parts by mass, per 100 parts by mass of the total amount of epoxy resin blended.

[0029] In preparing the epoxy resin composition for fiber-reinforced composite materials of the present invention, it is preferable to first uniformly heat and knead the epoxy resin, a thermoplastic resin soluble in epoxy resin, and other additives if necessary at a temperature of about 150 to 170°C, then cool to a temperature of about 70°C, and then add and knead the curing agent. However, the method of blending each component is not particularly limited to this method.

[0030] <Thermoplastic Resin Particles> The epoxy resin composition used in the EM-equipped prepreg of the present invention contains thermoplastic resin particles with an average particle size of 5 to 50 μm. Alternatively, the average particle size of the thermoplastic resin particles contained in the epoxy resin composition is 5 to 50 μm. The lower limit of the average particle size of the thermoplastic resin particles is preferably 7 μm or more, more preferably 10 μm or more, and the upper limit is preferably 40 μm or less, more preferably 30 μm or less. By having thermoplastic resin particles with a large average particle size of 5 μm or more around the lattice constituting the highly rigid expanded metal, the damage area after impact in the fiber-reinforced composite material can be reduced. By setting the average particle size of the thermoplastic resin particles to 50 μm or less, the number of thermoplastic resin particles per unit weight of thermoplastic resin particles blended into the epoxy resin composition can be increased, and the amount of thermoplastic resin particles present around the sharp edges of the expanded metal in the fiber-reinforced composite material increases. As a result, the thermoplastic resin particles can mitigate the stress concentration at the interface between the sharp edges of the expanded metal and the epoxy resin composition during impact. The method for measuring the average particle size is described later.

[0031] Furthermore, the present invention does not preclude the epoxy resin composition used in the EM-equipped prepreg from containing two or more types of thermoplastic resin particles.

[0032] Thermoplastic resin particles have a lower elastic modulus and higher affinity with epoxy resins compared to materials such as thermosetting resin particles and inorganic particles. Therefore, when an impact is applied, cracks are less likely to form between the thermoplastic resin particles and the epoxy resin. The thermoplastic resin particles deform and absorb energy, preventing the formation of cracks, which is why they are preferably used.

[0033] Examples of materials for thermoplastic resin particles include one or more resins selected from cross-linked acrylonitrile butadiene rubber, cross-linked styrene butadiene rubber, acrylic rubber, core-shell rubber, polyvinyl acetate, polyamide, polycarbonate, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyarylate, polyester, polyamide-imide, polyimide, polyetherimide, polysulfone, polyethersulfone, polyetheretherketone, polyaramid, polybenzimidazole, polyethylene, polypropylene, cellulose acetate, and cellulose butyrate. Among these, polyamide particles are particularly preferred because their excellent toughness can greatly improve the impact resistance of fiber-reinforced composite materials. Among polyamides, nylon 12, nylon 11, and nylon 6 / 12 copolymers provide particularly good adhesive strength with thermosetting resins. In particular, it is preferable to use the aforementioned polyamide particles as thermoplastic resin particles. Examples of commercially available polyamide particles include SP-500 and "Trepearl®" TN (both manufactured by Toray Industries, Inc.), "Orgasol®" 1002D, 2002, and 3202 (all manufactured by ATOCHEM Inc.), and "Trogamide®" T5000 (manufactured by Polypla Evonik Inc.).

[0034] The epoxy resin composition used in the EM-equipped prepreg of the present invention preferably contains 10 to 120 parts by mass of thermoplastic resin particles per 100 parts by mass of epoxy resin. The content of thermoplastic resin particles is preferably 30 parts by mass or more, more preferably 50 parts by mass or more, and preferably 100 parts by mass or less per 100 parts by mass of epoxy resin. If the content of thermoplastic resin particles is 10 parts by mass or more per 100 parts by mass of epoxy resin, the number of thermoplastic resin particles in the EM-equipped prepreg increases, resulting in a fiber-reinforced composite material that exhibits high impact resistance. If the content is 120 parts by mass or less, the viscosity of the epoxy resin composition can be kept low in the film-forming process (the film-forming process described later), making it easier to form a thin film, and thus the EM-equipped prepreg has excellent passage through the manufacturing process.

[0035] Examples of thermoplastic resin particle shapes include spherical, non-spherical, porous, needle-shaped, whisker-shaped, or flake-shaped. The particle form may also be porous or hollow. Of these, spherical particles are preferred because they do not reduce the flow properties of the epoxy resin composition, resulting in excellent impregnation into the fiber substrate and adhesion of the expanded metal to the epoxy resin composition. Furthermore, they reduce delamination between the expanded metal and the cured epoxy resin caused by impact to the fiber-reinforced composite material, thus providing a fiber-reinforced composite material with high impact resistance. Spherical particles are also preferred from the viewpoint of viscoelasticity of the epoxy resin composition used in EM-coated prepregs because they do not reduce the flow properties of the epoxy resin composition. The sphericity of the thermoplastic resin particles is preferably 90 to 100, more preferably 95 or higher, and even more preferably 97 or higher. A sphericity of 90 or higher for the thermoplastic resin particles eliminates stress concentration points, providing high impact resistance to the fiber-reinforced composite material. The sphericity of thermoplastic resin particles is determined by taking photographs of the particles magnified 200 times or more using a scanning electron microscope, randomly selecting 30 particles, measuring their short and long axes, calculating the sphericity of each particle using the following formula, and using the numerical average value.

[0036] Sphericity = (Particle's minor axis / Particle's major axis) × 100.

[0037] Here, regarding the average particle size, including the average particle size of thermoplastic resin particles, 50 particles are randomly selected from the prepreg or epoxy resin composition to be measured, and the particles are photographed using a scanning electron microscope at a magnification (e.g., 200x or more) sufficient to accurately measure their particle size. The diameter of the circle circumscribing each primary particle in the photograph is taken as the particle size of that particle, and the number average of the particle sizes of the 50 particles measured is taken as the average particle size.

[0038] In this invention, thermoplastic resin particles exist in a dispersed state within the epoxy resin composition. When the thermoplastic resin particles are dispersed in the epoxy resin composition, they alleviate the stress concentration at the interface between the sharp edges of the expanded metal and the epoxy resin composition when the fiber-reinforced composite material is subjected to impact, thereby resulting in a fiber-reinforced composite material that exhibits high impact resistance.

[0039] <Curing Agent> The epoxy resin composition used in the EM-equipped prepreg of the present invention can be used with a curing agent. The curing agent described herein is a compound having an active group that can react with the epoxy group or glycidyl group of the epoxy resin. Specific examples of curing agents include, for example, dicyandiamide, aromatic polyamines, aminobenzoic acid esters, various acid anhydrides, phenol novolac resins, cresol novolac resins, polyphenol compounds, imidazole derivatives, aliphatic amines, tetramethylguanidine, thiourea adduct amines, carboxylic acid anhydrides such as methylhexahydrophthalic anhydride, carboxylic acid hydrazides, carboxylic acid amides, polymer captans, and Lewis acid complexes such as boron trifluoride ethylamine complexes.

[0040] By using aromatic polyamines as curing agents, epoxy resin cured products with good heat resistance can be obtained. In particular, among aromatic polyamines, various isomers of diaminodiphenylsulfone are the most suitable curing agents for obtaining epoxy resin cured products with good heat resistance.

[0041] Furthermore, when using dicyandiamide as a curing agent, combining it with urea compounds, such as 3,4-dichlorophenyl-1,1-dimethylurea, or imidazoles as curing accelerators (described later), allows for curing at relatively low temperatures while achieving high heat and water resistance during curing. Additionally, curing epoxy resins with acid anhydrides yields cured products with lower water absorption compared to curing with amine compounds. Moreover, using latent versions of these curing agents, such as microencapsulated versions, provides excellent storage stability for EM-coated prepregs. The optimal amount of curing agent varies depending on the type of epoxy resin and curing agent. For example, with aromatic amine curing agents, it is preferable to add them in stoichiometric equivalent amounts. However, by setting the ratio of the amount of active hydrogen in the aromatic amine curing agent to the amount of epoxy groups in the epoxy resin to 0.7-0.9, a resin with a higher modulus of elasticity after curing may be obtained compared to using the same equivalent amounts of both, which is also a preferred embodiment. These curing agents may be used individually or in combination.

[0042] Examples of commercially available hardening agents include Seika Cure S (manufactured by Wakayama Seika Kogyo Co., Ltd.), MDA-220, 3,3'-DAS (both manufactured by Mitsui Chemicals, Inc.), "Lonza Cure®" M-DEA, M-DIPA, M-MIPA, DETDA80 (all manufactured by Lonzacure Inc.), and "jER Cure®" DICY7, DICY15, W (all manufactured by Mitsubishi Chemical Corporation).

[0043] The timing of adding the curing agent to the epoxy resin composition is not particularly limited; it is also possible to add a portion of the epoxy resin composition after the reaction. This method can be effective in adjusting viscosity and improving storage stability.

[0044] <Other Additives> The epoxy resin composition used in the EM-coated prepreg of the present invention may contain various additives as needed. The types of additives are not particularly limited, but examples include curing accelerators, curing inhibitors, flame retardants, light stabilizers, antioxidants, and defoaming agents.

[0045] Here, examples of commercially available products of the curing accelerator include "Curezol (registered trademark)" 1.2DMZ, C11Z, C17Z (manufactured by Shikoku Kasei Co., Ltd.), DCMU99 (manufactured by Hodogaya Chemical Co., Ltd.), "Omicure (registered trademark)" U-24M, U-52M (manufactured by CVC Thermoset Specialties). When these are used in combination with dicyandiamide in particular, a high curing acceleration effect can be obtained.

[0046] <Sheet-like fiber base material> The sheet-like fiber base material (hereinafter, sometimes simply referred to as "fiber base material" in this section) used in the prepreg with EM of the present invention will be described. Examples of the form of the fiber base material include woven fabrics, knitted fabrics, non-woven fabrics, meshes, and the like.

[0047] In the present invention, the basis weight of the fiber base material is preferably 10 to 100 g / m ２ . The basis weight of the sheet-like fiber base material is preferably 15 g / m ２ or more, preferably 21 g / m ２ or more as the lower limit, and preferably 60 g / m ２ or less, more preferably 25 g / m ２ or less as the upper limit. When the basis weight of the fiber base material is 10 g / m ２ or more, the number of reinforcing fibers per unit basis weight increases, so cracks in the fiber-reinforced composite material generated by impact are suppressed and the impact resistance is improved. When the basis weight of the fiber base material is 100 g / m ２ or less, the rigidity becomes small, so the prepreg with EM has excellent drapability.

[0048] Here, the basis weight (unit: g / m ２ ) of the prepreg with EM, the basis weight (unit: g / m <000001​​​​​​The basis weight of the EM-attached prepreg is calculated by dividing by ( ). Next, the sample is immersed and stirred in a solvent that dissolves epoxy resin such as acetone, but does not dissolve the fiber substrate and expanded metal. Then, the sample is filtered (for example, using a 0.2 μm polytetrafluoroethylene filter), the filtered material is thoroughly washed with the solvent, and the fiber substrate and expanded metal are separated and recovered. After that, the solvent is completely removed in an oven (for example, if acetone is used as the solvent, leave it in an oven set to 100°C for 15 minutes or more), the fiber substrate and expanded metal are recovered separately, the mass of the recovered fiber substrate and expanded metal is measured separately, and the area (100 cm²) is measured. ２ The basis weight of the fiber substrate and the expanded metal are calculated by dividing by ( ). Note that if materials other than the fiber substrate and expanded metal are considered to be resin compositions, the basis weight of the resin composition can be obtained by subtracting the basis weight of the fiber substrate and the expanded metal from the basis weight of the EM-coated prepreg.

[0049] For each of the above weights, the aforementioned 100 cm was taken from five randomly selected locations in the EM-treated prepreg. ２ A sample is taken, and the arithmetic mean of each sample (a total of 5 measurements) is used.

[0050] The fibers constituting the fibrous base material may be either continuous fibers or short fibers, but short fibers are preferable because the overlap between fibers in the EM-coated prepreg increases, increasing its bulk, which in turn increases the rigidity of the EM-coated prepreg and improves its handling properties. When the fibers constituting the fibrous base material are short fibers, the average fiber length is preferably 2 to 30 mm. The lower limit of the average fiber length is more preferably 4 mm or more, and the upper limit is preferably 15 mm, and even more preferably 13 mm. On the other hand, regardless of whether the fibers are short fibers or not, the average fiber diameter of the fibers constituting the fibrous base material is preferably 3 to 20 μm. The upper limit of the average fiber diameter is preferably 12 μm or less, and even more preferably 8 μm or less. When the average fiber length is 2 mm or more, it is not necessary to increase the number of fibers per unit basis weight, and the rigidity can be reduced, resulting in excellent drape properties of the EM-coated prepreg. The same applies when the average fiber diameter is 3 μm or more. When the average fiber length is 30 mm or less, the number of reinforcing fibers per unit basis weight can be increased, thereby suppressing cracks in the fiber-reinforced composite material caused by impact and improving impact resistance. From a similar viewpoint, it is more preferable when the fiber diameter of the reinforcing fibers is 20 μm or less.

[0051] Fiber diameter or length is measured by observing the fiber substrate with an optical microscope, randomly selecting 20 fibers from the observed image, measuring the fiber diameter or length of each fiber, and taking the arithmetic mean. As mentioned above, the fiber substrate used for observation may be the same fiber substrate sample taken when measuring the basis weight of the fiber substrate.

[0052] In the present invention, the fibrous base material preferably satisfies the following formula (1).

[0053] 1.0 ≤ 4 × AW / (DEN × FD) ≤ 7.0 Equation (1) Here, AW is the basis weight of the fiber material (unit: g / m ２ DEN is the true density of the fiber base material (unit: g / m³). ３ FD represents the average fiber diameter (unit: m) of the fibers that make up the fibrous base material.

[0054] Here, the lower limit of [4 × AW / (DEN × FD)] is preferably 2.5 or more, more preferably 4.0 or more, even more preferably 5.0 or more, and particularly preferably 5.8 or more. This [4 × AW / (DEN × FD)] is calculated over a certain area (for example, 1 m²). ２ ) has meaning as an index representing the surface area of ​​the fibers contained in the fibrous base material, and if all the fibers contained in the fibrous base material are of the same diameter and have a cylindrical shape, it can be seen as the sum of the lateral surfaces of the cylindrical fibers (for reference, when the diameter of the circle at the base of the cylinder is d and the height is h, the volume of the cylinder is 1 / 4 × π × d ２ The lateral surface area of ​​a cylinder is expressed as π × d × h. Also, [lateral surface area] / [volume] is [4 / d]. If [4 × AW / (DEN × FD)] is 1.0 or greater, cracks in the fiber-reinforced composite material caused by impact can be suppressed, and impact resistance can be improved. Also, if [4 × AW / (DEN × FD)] is 7.0 or less, the drape of the prepreg will be good.

[0055] Here, the true density of the fibrous material is the density determined according to the liquid weighing method using water as described in JIS Z 8807:2012. The density is [g / cm³]. ３ It is sometimes calculated using ] as the unit, but in the application of formula (1), [g / m ３ The conversion is applied by converting to [ ]. The conversion in terms of fiber diameter is the same. The fiber substrate used to measure the true density of the fiber substrate may be the same fiber substrate obtained when determining the basis weight of the fiber substrate as described above.

[0056] Examples of fibers that make up the fibrous base material include carbon fibers, boron fibers, high-strength polyethylene fibers, tungsten carbide fibers, PBO fibers, polyester fibers, vinylon fibers, aramid fibers, and glass fibers, which may be used individually or in combination of two or more types.

[0057] The fiber base material is preferably a nonwoven fabric. Nonwoven fabrics can grip epoxy resin compositions even with a low basis weight, making them effective in reducing the weight of EM-coated prepregs. Furthermore, using a nonwoven fabric as the fiber base material provides excellent drape, resulting in good handling of the EM-coated prepreg. Nonwoven fabrics can be composed of continuous fibers or short fibers, but for the same reason as above, it is preferable to use a nonwoven fabric made of short fibers for better handling.

[0058] In this invention, nonwoven fabric refers to the meaning defined in JIS L 0222 (2001). There are no particular limitations on the manufacturing method of the nonwoven fabric, but dry, wet, or spunbond methods can be used as web formation methods, and needle punching, chemical bonding, thermal bonding, spunlace, etc., can be used as bonding methods between fibers.

[0059] <Expanded Metal> The expanded metal used in the EM-equipped prepreg of the present invention differs from wire mesh, which is a woven fabric, in that it is a lattice-shaped metal body in which intersecting metal bodies at the grid points are integrated without boundaries. Furthermore, the grid of this expanded metal has a two-dimensional expansion, and the thickness at the grid points is generally approximately equal to the thickness at other parts. Note that metal bodies joined together by welding in the shape of wire or strips cannot be called expanded metal as defined in the present invention. Expanded metal is generally manufactured by making staggered cuts in a metal material and pressing it to create shapes with holes such as rhombic, tortoiseshell, circular, or elliptical, or by drilling holes in a sheet of metal material, and therefore has sharp edges.

[0060] Because expanded metal offers greater flexibility in deformation compared to non-perforated metal foil, prepregs with expanded metal have superior drape compared to prepregs with non-perforated metal foil.

[0061] The basis weight of expanded metal is 5 to 500 g / m². ２ This is preferable. The weight of this material should be 50 g / m². ２ Preferably, it should be 100 g / m² or more. ２It is more preferable that it be 450 g / m². ２ Preferably, it is 400 g / m ２ It is even more preferable that this is the case. Note that the basis weight of the expanded metal represents the mass relative to the area including the area of ​​the holes. The basis weight of such expanded metal is 5 g / m ２ With these specifications, the rigidity of the EM-treated prepreg becomes high and less prone to deformation, resulting in excellent handling. The expanded metal has a basis weight of 500 g / m². ２ The following conditions result in a prepreg with high drapeability due to the presence of EM (Effective Microcrystalline Substrate).

[0062] The metals that make up expanded metal can be selected from aluminum, iron, copper, silver, gold, bronze, titanium, copper phosphate, or combinations thereof such as bimetals and alloys.

[0063] Examples of commercially available expanded metals include "MicroGrid®" 2AL8-075F, 2CU4-100A, 2CU4-100FA, 18Cu1.1Cir29 (all manufactured by Dexmet), A1050 0.8t×W1.0×SW14.0 / LW25.0 L1000×S2000, and A1050 0.8t×W1.0×SW10.0 / LW20.0 L1000×S2000 (all manufactured by Okutani Wire Mesh Manufacturing Co., Ltd.).

[0064] <Expanded Metal Prepreg> The EM-equipped prepreg of the present invention includes a member (resin-impregnated sheet substrate) in which an epoxy resin composition containing thermoplastic resin particles with an average particle size of 5 to 50 μm (this epoxy resin composition may be simply referred to as "epoxy resin composition" in this section and the next section (i.e., the section <Method for Manufacturing Expanded Metal Prepreg>)) is impregnated on both sides of a sheet-like fiber substrate, and expanded metal is laminated on at least one surface of the resin-impregnated sheet substrate. Here, in the EM-equipped prepreg of the present invention, the expanded metal may be laminated on only one side of the epoxy resin composition layer, or it may be laminated on both sides. In the following description, in the EM-equipped prepreg in which expanded metal is laminated on only one side of the resin-impregnated sheet substrate, the side on which the expanded metal is provided will be referred to as the "expanded metal side," and the other side will be referred to as the "fiber substrate side."

[0065] The EM-equipped prepreg of the present invention is characterized in that a sheet-like fibrous base material is impregnated with an epoxy resin composition, so that both sides of the sheet-like fibrous base material are wet with the epoxy resin composition. Due to this characteristic, for example, in a configuration in which expanded metal is bonded to only one side, the expanded metal side of the EM-equipped prepreg can be attached to a prepreg without EM, and the other adhesive fibrous base material side can be attached to a support material such as a mold, and cured and / or molded to produce a fiber-reinforced composite material with a smooth surface.

[0066] The degree to which the sheet-like fibrous substrate in an EM-coated prepreg is wetted by the epoxy resin composition can be confirmed by observing the vicinity of both sides of the sheet-like fibrous substrate under a microscope. On both sides of the EM-coated prepreg, 10 locations on each side are observed under an optical microscope at 50x magnification (field of view: 4 mm x 4 mm or larger), and the number of fibers not wetted by the epoxy resin composition within a 10 cm x 10 cm area of ​​the EM-coated prepreg is counted. If the average number of fibers not wetted by the epoxy resin is 10 or less on both sides, the degree of wetting is good, and the adhesion between the EM-coated prepreg's fibrous substrate surface and the mold used for molding or the prepreg without EM is excellent. Whether or not a fiber is wetted by the epoxy resin can be determined by checking whether the fiber surface itself is exposed during the above observation; if the fiber surface itself is exposed, it is considered not wetted.

[0067] Furthermore, in the EM-equipped prepreg of the present invention, the impregnation of the epoxy resin composition may be carried out to the entire sheet-like fibrous substrate, or there may be an unimpregnated portion in the central part of the thickness direction of the sheet-like fibrous substrate. Figure 1 is a schematic cross-sectional view of the former example, in which the entire sheet-like fibrous substrate 1 is impregnated with epoxy resin 2 containing thermoplastic resin particles 4, and expanded metal 3 is laminated on one side of the resin-impregnated sheet substrate. Figure 2 is a schematic cross-sectional view of the latter example, in which the central part of the thickness direction of the sheet-like fibrous substrate 1 is not impregnated with epoxy resin 2 containing thermoplastic resin particles 4.

[0068] Furthermore, as can be seen from the illustrated example, in the EM-equipped prepreg of the present invention, it is sufficient that the sheet-like fibrous substrate is impregnated with the epoxy resin composition, and it is not necessary for the sheet-like fibrous substrate to be exposed on the surface. The surface of the resin-impregnated sheet substrate may be formed of an epoxy resin composition that does not contain the sheet-like fibrous substrate.

[0069] <Method for Manufacturing Expanded Metal-Coated Prepreg> There are no particular limitations on the method for manufacturing the EM-coated prepreg of the present invention, but for example, one method is to process an epoxy resin composition into a film, overlap the film of the epoxy resin composition on both sides of a sheet-like fibrous substrate, heat and / or press to impregnate the sheet-like fibrous substrate with the epoxy resin composition to produce a resin-impregnated sheet substrate, overlap expanded metal on at least one surface of the resin-impregnated sheet substrate, and bond and laminate the expanded metal to the resin-impregnated sheet substrate by heating and / or pressing. Here, the film formation of the epoxy resin composition can be achieved by coating the thermoplastic resin composition onto a support such as release paper or a thermoplastic film and drying it as needed. Alternatively, it can be cast onto a drum and peeled off the drum to form a film. Furthermore, the viscosity and handling properties can be adjusted by partially curing during the film formation process. In the above example, two films of the epoxy resin composition are required when impregnating both sides of the sheet-like fibrous substrate, and the composition and thickness of the two films of the epoxy resin composition may be the same or different.

[0070] Another impregnation method involves, for example, discharging a thermoplastic resin composition from a die coater onto a sheet-like fibrous substrate for impregnation. In this case, impregnation can be performed on one side of the sheet-like fibrous substrate at a time, or both sides can be impregnated simultaneously. Impregnation involves relative movement between the coating nozzle and the sheet-like fibrous substrate, but coating can be performed with either or both of them movable.

[0071] When impregnating a sheet-like fibrous substrate with an epoxy resin composition, it is preferable to minimize the number of pinholes contained within the prepreg. Pinholes are usually relatively small holes that penetrate the material and occur when the prepreg is stored for a predetermined period of time.

[0072] One method for reducing the number of pinholes in the prepreg is to impregnate a sheet-like fibrous substrate with an epoxy resin composition from both sides.

[0073] In the EM-equipped prepreg of the present invention, it is desirable that no pinholes are present. However, if pinholes are present, their maximum diameter is preferably 400 μm or less, and more preferably 200 μm or less. By having a maximum pinhole diameter of 400 μm or less, the flow of the epoxy resin composition during curing and molding facilitates the elimination of pinholes, thereby eliminating defects and improving uniformity, resulting in a fiber-reinforced composite material with high impact resistance.

[0074] The diameter of pinholes in prepreg can be determined by observation with an optical microscope, for example, using a VHX-5000 (manufactured by Keyence Corporation). Specifically, a sample of EM-coated prepreg is cut to a size of 10 cm x 10 cm at a random location, and the pinhole-generating area and the prepreg area are made easily distinguishable (for example, by attaching the EM-coated prepreg to drawing paper of a different color). The sample is then observed using an optical microscope at a magnification of 20x, and the size of the pinhole area that penetrates both sides of the prepreg is evaluated. ２ The hole with the largest diameter on the surface is extracted, and this diameter is taken as the maximum diameter of the pinhole. If the shape of the pinhole is not perfectly circular, the diameter of the point where the distance between the two points is longest within the hole is taken as the maximum diameter of the pinhole for each sample. The maximum diameter of the pinhole is determined by finding the maximum diameter of the pinhole for each of the five EM-attached prepreg pieces cut to the aforementioned size, and taking the average value of these values ​​as the pinhole size.

[0075] <Use of Expanded Metal-Coated Prepreg> There are no particular restrictions on the use of the EM-coated prepreg of the present invention. The EM-coated prepreg may be used in sheet form, or it may be used after adjusting the viscosity by allowing the curing process to progress, for example.

[0076] The EM-equipped prepreg of the present invention can be used by laminating multiple EM prepregs of the present invention together, or by laminating it with other prepregs (prepregs without expanded metal lamination may be hereinafter referred to as "EM-free prepregs") or resin composition films (including those made of resin) that do not contain reinforcing fibers (EM-free prepregs and the aforementioned resin composition films (including those made of resin) that do not contain reinforcing fibers are collectively referred to as "EM-free prepregs, etc."). The viscosity of these can also be adjusted by allowing curing to progress.

[0077] When using a laminated non-EM prepreg or the like on the side of an expanded metal laminated with an EM-equipped prepreg, it is preferable that the resin composition forming the surface of the laminated non-EM prepreg or the like facing the EM-equipped prepreg contains thermoplastic resin particles with an average particle size of 5 to 50 μm. In the fiber-reinforced composite material obtained by curing and / or molding such a laminate, the periphery of the lattice constituting the expanded metal is covered with more thermoplastic resin particles, thus improving impact resistance.

[0078] If the EM-equipped prepreg of the present invention is an EM-equipped prepreg in which expanded metal is laminated on one side of a resin-impregnated sheet substrate, then an EM-free prepreg or the like can be laminated onto either surface.

[0079] Furthermore, when laminating EM-equipped prepregs of the present invention, the process can be understood in the same way as when laminating EM-less prepregs, except that the laminated surfaces of the expanded metal should not face each other.

[0080] When laminating an EM-equipped prepreg with an EM-free prepreg (for convenience, the EM-equipped prepreg layer is referred to as "layer A," and the EM-free prepreg layer adjacent to layer A is referred to as "layer B"), the temperature difference between the peak exothermic temperature of the epoxy resin composition used in layer A and the peak exothermic temperature of the epoxy resin composition used in layer B is preferably 1 to 100°C. The upper limit of this temperature difference is more preferably 50°C or less, even more preferably 30°C, and particularly preferably 20°C or less. Here, it is acceptable for either the peak exothermic temperature of the epoxy resin composition used in layer A or the peak exothermic temperature of the epoxy resin composition used in layer B to be higher. When the temperature difference at the peak exothermic temperature is 100°C or less, the thermal residual stress between the portion corresponding to layer A and the portion corresponding to layer B is reduced after curing and molding of the laminate, thereby obtaining a fiber-reinforced composite material with excellent impact resistance. On the other hand, if the temperature difference is 1°C or more, the epoxy resin composition in one of the prepregs (or resin films) hardens first during the molding process. Therefore, after the epoxy resin composition that hardened first hardens, mixing between the prepreg epoxy resin composition that hardened first and the epoxy resin composition that hardens later is suppressed, thus suppressing the migration of thermoplastic resin particles contained in the portion originating from layer A (and layer B). Furthermore, for prepregs without EM that are not adjacent to the EM-equipped prepreg in the laminate, those with a temperature difference of 1 to 100°C at the peak of exothermic reaction compared to the EM-equipped prepreg may be used. For example, by using multiple identical prepregs without EM and laminating them together with the EM-equipped prepreg, the number of types of prepregs to be prepared can be reduced.

[0081] <Fiber-reinforced composite material> The EM-equipped prepreg of the present invention can be formed into the desired shape, including when it is laminated with itself or with EM-less prepregs, and then cured with epoxy resin to become a fiber-reinforced composite material. Known methods can be used for shaping and curing.

[0082] The fiber-reinforced composite material produced using the EM-equipped prepreg of the present invention is a highly impact-resistant material that can be applied to wind turbine blades, automobile body panels, and laptop computer casings, and is particularly useful in achieving both lightning resistance and impact resistance in aircraft components.

[0083] Figure 3 is a schematic cross-sectional view of an example of a fiber-reinforced composite material of the present invention, showing a laminate of a layer 6 of EM-equipped prepreg and a layer 7 of EM-free prepreg after curing. In this example, the EM-free prepreg is laminated onto the expanded metal surface of the EM-equipped prepreg, integrated, cured, and molded. In the fiber-reinforced composite material, epoxy resin flow occurs during the curing and molding process, and thermoplastic resin particles 4 contained in the epoxy resin composition can exist around the metal lattice constituting the expanded metal 3. As a result, stress concentration on the sharp edges of the expanded metal can be mitigated by the thermoplastic resin particles, and the fiber-reinforced composite material exhibits high impact resistance.

[0084] The impact resistance of fiber-reinforced composite materials can be evaluated by the following method. Specifically, a 6-inch x 4-inch sample is cut from the fiber-reinforced composite material, and the magnitude of the drop weight impact (in J) is determined by multiplying 6.7 J / mm by the thickness of the test piece (1.4 to 1.7 mm) according to ASTM D7136 / D7136M:2012. The test piece is then subjected to a drop weight impact of the determined magnitude. Subsequently, the damage area is measured using an ultrasonic flaw detector (such as an SDS-6500R manufactured by KJTD Co., Ltd.). The pulse repetition frequency is 1.25 kHz, the amplifier attenuator is adjusted to 30 to 40 dB to ensure clear waveform, and the ultrasonic flaw detection is performed at an operating speed of 300 mm / s. A smaller damage area indicates higher impact resistance of the sample.

[0085] The damage area after impact in the aforementioned test of the fiber-reinforced composite material was 100 mm². ２ The following is preferable: 60 mm ２ More preferably, the following: 40 mm ２ It is even more preferable that the damaged area is 100 mm². ２ The following indicates that fiber-reinforced composite materials have high impact resistance.

[0086] The present invention will be specifically described below with reference to examples. However, the present invention is not to be interpreted as being limited to these specific examples. Furthermore, various measurements and evaluations were performed in an environment with a temperature of 23°C and a humidity of 50% RH.

[0087] <Materials> (1) Epoxy resin - Epoxy resin A: Tetraglycidyl diaminodiphenylmethane (manufactured by Sumitomo Chemical Co., Ltd., ELM434) - Epoxy resin B: Bisphenol F type epoxy resin (manufactured by DIC Corporation, Epiclon 830) (2) Thermoplastic resin soluble in epoxy resin - Thermoplastic resin A: Polyethersulfone (manufactured by Sumitomo Chemical Co., Ltd., Sumika Excel 5003P) (3) Thermoplastic resin particles - Thermoplastic resin particles A: Nylon 12 particles (average particle size 7 μm, manufactured by Toray Industries, Inc., SP-500) - Thermoplastic resin particles B: Polyamide particles (average particle size 13 μm, manufactured by Toray Industries, Inc., Trepearl TN) (4) Curing agent - Curing agent A: 4,4'-diaminodiphenylsulfone (manufactured by Wakayama Seika Co., Ltd., Seika Cure-S) - Curing agent B: (5) Curing accelerator, curing accelerator A: 3-(3,4-dichlorophenyl)1,1-dimethylurea (Hodogaya Chemical Co., Ltd., DCMU99) (6) Core-shell rubber particles, rubber particles A: Core-shell rubber particles in which core-shell rubber particles with an average particle size of 0.1 μm are dispersed in 75% by mass of bisphenol F type epoxy resin. (Kaneka Corporation, Kaneace MX136) (7) Sheet-like fiber base material, fiber base material A: PET nonwoven fabric (fiber basis weight 12 g / m ２ Average fiber diameter 12 μm, average fiber length 12 mm, true density of fiber base material 1.4 g / cm³ ３ Technical Fiber Product (Optiveil 20202A) • Fiber base material B: PET nonwoven fabric (fiber basis weight 12 g / m²) ２ Average fiber diameter 6 μm, average fiber length 5 mm, true density of fiber base material 1.4 g / cm³ ３ (Manufactured by Technical Fiber Product, Optiveil 20254A) • Fiber base material C: Glass fiber nonwoven fabric (fiber basis weight 17 g / m²) ２Average fiber diameter 6 μm, average fiber length 6 mm, true density of fiber base material 2.6 g / cm³ ３ (Manufactured by Oribest Co., Ltd., Grabestos EVP-017) ・Fiber base material D: Glass fiber nonwoven fabric (fiber weight 20g / m²) ２ Average fiber diameter 6 μm, average fiber length 6 mm, true density of fiber base material 2.6 g / cm³ ３ (Manufactured by Oribest Co., Ltd., Grabestos EVP-020) ・Fiber base material E: Glass fiber nonwoven fabric (fiber weight 23g / m²) ２ Average fiber diameter 6 μm, average fiber length 6 mm, true density of fiber base material 2.6 g / cm³ ３ (Manufactured by Oribest Co., Ltd., Grabestos EVP-023) ・Fiber base material F: Glass filament fabric (Fiber base material basis weight 48g / m ２ Average fiber diameter 5 μm, true density of fiber base material 2.6 g / cm³ ３ (8) EM-free prepreg / EM-free prepreg A: Continuous carbon fiber prepreg (manufactured by Toray Industries, Inc., T800S / 3900-2B). (9) Expanded metal / EM-1: Expanded metal (basis weight 73.3 g / m²) ２ (Dexmet MicroGrid 2CU4-100FA).

[0088] <Evaluation Method> Impact resistance tests were conducted on fiber-reinforced composite materials prepared using the following method, and the temperature difference at the peak of heat generation was evaluated for prepregs with and without EM.

[0089] (1) Impact resistance test of fiber-reinforced composite material (drop weight impact test) A 1.6 mm thick sample was cut from the fiber-reinforced composite material, and the damaged area was measured according to the method described above.

[0090] (2) Evaluation of the temperature difference between the peak top temperatures of the exothermic peak of the EM-equipped prepreg and the exothermic peak of the non-EM-equipped prepreg (peak top temperature difference) 10 mg each of the EM-equipped prepreg and the non-EM-equipped prepreg were taken, placed in a Hermeric Pan (manufactured by TA Instruments), covered with Hermeric Lid (manufactured by TA Instruments), and pressurized to prepare test specimens. For each test specimen, measurements were taken in a nitrogen atmosphere at a heating rate of 5°C / min using a differential scanning calorimeter (DSC Q2500: manufactured by TA Instruments) in the range of 20 to 300°C. The peak top temperatures of the exothermic peaks of the EM-equipped and non-EM-equipped prepregs obtained from the measurements were determined, and the difference between them was calculated.

[0091] (3) Appearance evaluation of the resin film The quality of the prepared resin film was visually checked, and if there were areas on the release paper where the epoxy resin composition was not applied, or if the epoxy resin composition did not pass between the rolls of the knife coater, it was determined to be of poor quality.

[0092] <Example 1> In a kneader, epoxy resin and a thermoplastic resin soluble in epoxy resin in the materials and proportions listed in Table 1 were added, and the temperature was raised to 160°C while kneading. The mixture was then stirred for 1 hour to dissolve the thermoplastic resin in the epoxy resin and obtain a transparent, viscous liquid. After the temperature of this liquid was lowered to 70°C while kneading, thermoplastic resin particles and a curing agent were added and kneaded further to obtain an epoxy resin composition.

[0093] Next, the epoxy resin composition was applied onto release paper using a knife coater to produce two resin films (the sum of the basis weights of the two resin films is shown in the table as "Resin Basis Weight". The basis weights of the two resin films were assumed to be the same).

[0094] The resin film was placed on both sides of a sheet-like fibrous substrate shown in Table 1, and then sandwiched between release paper from the outside. Using a heat roll, the epoxy resin composition was impregnated into the sheet-like fibrous substrate through the release paper while heating and pressurizing at a temperature of 100°C and 1 atmosphere to obtain a resin-impregnated sheet substrate. After that, the release paper on one side was peeled off, EM-1 was placed on one side of the sheet material, and then another release paper was placed on top of it. Using a heat roll, the epoxy resin composition in the resin-impregnated sheet substrate and the expanded metal were bonded together while heating and pressurizing at a temperature of 100°C and 1 atmosphere to obtain an EM-coated prepreg.

[0095] On the other hand, eight layers of EM-free prepreg A are stacked to form a pseudo-isotropic structure (stack configuration: [+45° / 0° / -45° / 90°]). ｓ The outermost surface was then superimposed with the expanded metal surface of the previously obtained EM-coated prepreg. In this state, curing was carried out in an autoclave at 6 atmospheres and 180°C for 2 hours, with a heating rate of 1.7°C / min to 180°C, to obtain a fiber-reinforced composite material. The results are shown in Table 1.

[0096] <Examples 2-6> EM-equipped prepregs were prepared in the same manner as in Example 1, except that the materials and composition used were changed as shown in Table 1, and fiber-reinforced composite materials were also obtained. The results are shown in Table 1.

[0097] A comparison in Examples 1 to 6 shows that using thermoplastic resins with a larger average particle size and smaller fiber diameters for the fibers constituting the fibrous base material reduces the damage area after dropping a weight and improves impact resistance.

[0098] Furthermore, by comparing Example 1 and Example 4, it can be seen that impact resistance can be improved by reducing the temperature difference between the peak top temperatures of the prepreg with EM and the prepreg without EM.

[0099] <Examples 7-14> EM-equipped prepregs were prepared in the same manner as in Example 1, except that the materials and composition used were changed as shown in Table 3, and fiber-reinforced composite materials were also obtained. The results are shown in Table 3.

[0100] By comparing Examples 7-9 with Example 4, it can be seen that the more thermoplastic resin particles are added, the better the impact resistance can be.

[0101] Furthermore, a comparison with Examples 10-12 and Example 4 shows that impact resistance can be improved by using a glass nonwoven fabric as the sheet-like fiber base material, increasing the fiber basis weight of the sheet-like fiber base material, or setting the factor obtained by formula (1) to a more appropriate range. A comparison between Example 13 and Examples 10-12 shows that impact resistance is reduced by using a woven fabric as the sheet-like fiber base material.

[0102] Furthermore, Example 14 incorporates a large amount of thermoplastic resin particles with a large average particle size, resulting in a small temperature difference between the peak top temperatures of the EM-equipped prepreg and the EM-free prepreg. Additionally, it uses a nonwoven fabric as the sheet-like fibrous base material in which the factor determined by formula (1) is within a favorable range. Therefore, it can be seen that Example 14 exhibits the greatest improvement in impact resistance compared to the other examples.

[0103] <Comparative Example 1> In a kneader, epoxy resin and a thermoplastic resin soluble in epoxy resin in the materials and proportions listed in Table 2 were added, and the temperature was raised to 160°C while kneading. The mixture was then stirred for 1 hour to dissolve the thermoplastic resin in the epoxy resin and obtain a transparent, viscous liquid. After the temperature of this liquid was lowered to 70°C while kneading, thermoplastic resin particles and a curing agent were added and kneaded further to obtain an epoxy resin composition. Next, the epoxy resin composition was coated with a knife coater to a resin basis of 100 g / m². ２ A resin film was prepared. EM-1 was placed on one surface of the resin film, and the outside was sandwiched with release paper. Using a heat roll, the expanded metal and the resin film were bonded together at a temperature of 100°C and 1 atmosphere while heating and pressurizing through the release paper, thereby producing a sheet-like material. Next, a fiber-reinforced composite material was obtained in the same manner as in Example 1, except that this sheet-like material was used instead of the resin-impregnated sheet substrate. The results are shown in Table 2. Comparative Example 1 was inferior in impact resistance because it did not use a sheet-like fiber substrate.

[0104] <Comparative Examples 2 and 3> EM-equipped prepregs were prepared in the same manner as in Example 1, except that the materials and composition used were changed as shown in Table 2, and fiber-reinforced composite materials were also obtained. In these examples, thermoplastic resin particles were not used. The results are shown in Table 2. Comparative Examples 2 and 3 had inferior impact resistance because thermoplastic resin particles were not used.

[0105] <Comparative Example 4> An EM-equipped prepreg was prepared in the same manner as in Example 1, except that the materials and composition used were changed as shown in Table 2, and a fiber-reinforced composite material was obtained. In this example, rubber particles A were used instead of thermoplastic resin particles. Here, rubber particles A is a material in which core-shell rubber is dispersed in bisphenol F type epoxy resin. In Table 2, for Kaneace MX-136, the amount of core-shell rubber particles included is listed, and the amount of the epoxy resin portion is included in the amount of epoxy resin B. The results are shown in Table 2. Comparative Example 4 contains core-shell rubber particles instead of thermoplastic resin particles, but the effect was limited and the impact resistance was inferior, partly because the average particle size was small at 0.1 μm.

[0106] <Comparative Example 5> An attempt was made to produce an EM-coated prepreg in the same manner as in Example 1, except that the materials and composition used were changed as shown in Table 2. However, during the resin film production stage, a large number of areas on the release paper were not coated with the epoxy resin composition in streaks, making it impossible to produce a resin film of good quality.

[0107]

[0108]

[0109]

[0110] 1...Sheet-like fiber base material 2...Epoxy resin 3...Expanded metal 4...Thermoplastic resin particles 5...Cured epoxy resin 6...Cured EM-coated prepreg layer 7...Cured EM-free prepreg layer

Claims

1. A prepreg comprising a resin-impregnated sheet substrate in which an epoxy resin composition containing thermoplastic resin particles with an average particle size of 5 to 50 μm is impregnated on both sides of a sheet-like fibrous substrate, wherein expanded metal is laminated on at least one surface of the resin-impregnated sheet substrate.

2. The prepreg according to claim 1, wherein a nonwoven fabric is used as the sheet-like fibrous base material.

3. Damage area of ​​100 mm² obtained by impact resistance testing conducted in accordance with ASTM D7136 / D7136M:2012 ２ The prepreg according to claim 1 or 2, which is as follows:

4. The prepreg according to claim 1 or 2, wherein the resin constituting the thermoplastic resin particles is at least one resin selected from polyamide, polyimide, polyetherimide, polyamideimide, polysulfone, and polyethersulfone.

5. The prepreg according to claim 1 or 2, wherein the average fiber diameter of the single fibers of the sheet-like fibrous base material is 3 to 20 μm.

6. The prepreg according to claim 1 or 2, wherein the sheet-like fibrous base material satisfies the following formula (1): 1.0 ≤ 4 × AW / (DEN × FD) ≤ 7.0 Formula (1) (where AW is the basis weight of the fibrous base material (unit: g / m) ２ DEN is the true density of the fiber base material (unit: g / m³). ３ FD represents the average fiber diameter (in meters) of the fibers constituting the fibrous base material.

7. The prepreg according to claim 1 or 2, comprising 10 to 120 parts by mass of thermoplastic resin particles with respect to a total of 100 parts by mass of epoxy resin.

8. A laminate comprising at least one layer (referred to as "layer A") of the prepreg described in claim 1 or 2, wherein a layer adjacent to layer A (referred to as "layer B") is composed of a prepreg without expanded metal, and the temperature difference between the peak top temperatures of the exothermic peaks of layer A and layer B, determined by the method described in the specification, is 1 to 100°C.

9. A fiber-reinforced composite material obtained by curing a laminate in which at least one layer of the laminate contains the prepreg described in claim 1 or 2.

10. A fiber-reinforced composite material obtained by curing a laminate containing the prepreg described in claim 1 or 2 in at least two layers of the laminate, wherein the two layers of the at least two layers are adjacent to each other.

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