Prepregs and fiber-reinforced composite materials

Abstract

The present invention provides a prepreg and fiber-reinforced composite material that exhibit excellent flame retardancy even when applied to molded products made of fiber-reinforced composite materials with a thick-walled design. [Solution] A prepreg comprising an epoxy resin composition containing the following components (A), (B), and (C), and a reinforcing fiber substrate. (A) Component: Epoxy resin (B) Component: Imidazole compound and / or imidazole compound derivative (C) Component: Organic salt represented by the following formula (1) [C1] TIFF2026074177000007.tif41170(R 1 ~R 6 Each of these independently represents a hydrogen atom, an amino group, an epoxy group, an alkyl group with 1 to 5 carbon atoms, or an aryl group with 6 to 10 carbon atoms.

Description

[Technical Field]

[0001] This invention relates to prepregs and fiber-reinforced composite materials. [Background technology]

[0002] Fiber-reinforced plastics (FRPs), which combine resin and reinforcing fibers, are used in a variety of applications due to their excellent lightness, rigidity, and impact resistance. Carbon fiber reinforced composites, in particular, are lightweight, high-strength, and highly rigid, making them widely used in sports and leisure applications such as fishing rods and golf shafts, as well as in automotive and aerospace applications. In recent years, in addition to the mechanical properties of carbon fiber reinforced composites, the electromagnetic shielding properties of carbon fibers have also been utilized, leading to their use as casings for electronic and electrical equipment such as laptop computers.

[0003] Fiber-reinforced composite materials are sometimes required to have flame retardant properties in various applications. For example, when fiber-reinforced composite materials are used in structures for electronic and electrical equipment or aircraft, the ignition of the fiber-reinforced composite material due to heat generation could cause a fire. Methods for imparting flame retardant properties to fiber-reinforced composite materials include adding brominated epoxy resin or phosphorus-based flame retardants to the matrix resin composition (Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-218573 [Patent Document 2] Japanese Patent Publication No. 2017-2202 [Overview of the project] [Problems that the invention aims to solve]

[0005] One of the objectives of the present invention is to provide a prepreg and fiber-reinforced composite material that exhibit excellent flame retardancy even when applied to molded products made of fiber-reinforced composite materials with a thick wall design. [Means for solving the problem]

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

[16] .

[0007] [1] A prepreg comprising an epoxy resin composition containing the following components (A), (B), and (C) and a reinforcing fiber substrate. (A) Component: Epoxy resin (B) Component: Imidazole compound and / or imidazole compound derivative (C) Component: Organic salt represented by the following formula (1)

[0008] [ka] ...Formula (1) (R 1 ~R 6 Each of these independently represents a hydrogen atom, an amino group, an epoxy group, an alkyl group with 1 to 5 carbon atoms, or an aryl group with 6 to 10 carbon atoms.

[0009] [2] The prepreg according to [1], wherein the 10% weight loss temperature of component (C) measured under a nitrogen atmosphere by thermogravimetric analysis is 300 to 400°C.

[0010] [3] The prepreg according to [1] or [2], comprising 40% by mass or more of nitrogen atoms in component (C).

[0011] [4] In formula (1) above, R 1 ~R 3 NH2, R 4 ~R 6 A prepreg as described in any of [1] to [3], wherein the atom is a hydrogen atom.

[0012] [5] A prepreg according to any one of [1] to [4], comprising 10 to 30 parts by mass of component (C) per 100 parts by mass of the epoxy resin composition.

[0013] [6] The prepreg according to any one of [1] to [5], further comprising the following component (D). (D) component: dicyandiamide and / or dicyandiamide derivative

[0014] [7] The prepreg according to any one of [1] to [6], further comprising the following component (E). (E) component: urea compound

[0015] [8] The prepreg according to any one of [1] to [7], wherein the 10% weight loss temperature measured in a nitrogen atmosphere by thermogravimetric analysis of the cured product obtained by curing the epoxy resin composition excluding the component (C) from the epoxy resin composition under the conditions of 140 °C for 1 hour is 300 to 400 °C.

[0016] [9] The epoxy resin composition according to any one of [1] to [8], wherein the viscosity of the epoxy resin composition at 60 °C is 10 to 1000 Pa·s.

[0017]

[10] The prepreg according to any one of [1] to [9], wherein the component (A) contains an epoxy resin having an oxazolidone structure.

[0018]

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

[10] , containing 1 to 10 parts by mass of the component (B) with respect to 100 parts by mass of the epoxy resin composition.

[0019]

[12] The prepreg according to [6], wherein the mass ratio of the component (B) to the component (D) ((B) component / (D) component) is 0.5 to 1.5.

[0020]

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

[12] , wherein the mass ratio of the component (B) to the component (C) ((B) component / (C) component) is 0.1 to 0.5.

[0021]

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

[13] , wherein the reinforcing fiber base material contains carbon fiber.

[0022] A fiber-reinforced composite material obtained by curing the prepregs described in

[15]

[14] .

[0023]

[16] The fiber-reinforced composite material according to

[15] , wherein the flame retardancy test according to the UL-94V standard for the fiber-reinforced composite material is V-0 with a test piece 2.0 mm thick. [Effects of the Invention]

[0024] The prepreg of the present invention exhibits excellent flame retardancy even when applied to molded products made of fiber-reinforced composite materials with a thick-walled design. Specifically, it exhibits flame retardancy equivalent to V-0 in a 2.0 mm thick test specimen according to the UL-94V standard. Furthermore, the prepreg of the present invention enables molding in a short time. [Brief explanation of the drawing]

[0025] [Figure 1] This is a schematic diagram showing an example of a heat flow curve. [Modes for carrying out the invention]

[0026] The present invention will be described in detail below. [Prepreg] One embodiment of the present invention relates to a prepreg. The prepreg according to the embodiment comprises an epoxy resin composition containing components (A), (B), and (C) and a reinforcing fiber substrate. (A) Component: Epoxy resin (B) Component: Imidazole compound and / or imidazole compound derivative (C) Component: Organic salt represented by the following formula (1)

[0027] [ka] ...Formula (1) (R 1 ~R 6 Each of these independently represents a hydrogen atom, an amino group, an epoxy group, an alkyl group with 1 to 5 carbon atoms, or an aryl group with 6 to 10 carbon atoms.

[0028] A prepreg can be manufactured, for example, by the following procedure. First, an epoxy resin composition containing components (A) to (C) is applied to one side of a carrier film (first carrier film). Similarly, another carrier film (second carrier film) is prepared with the epoxy resin composition applied to one side. Next, the surfaces of the first and second carrier films coated with the epoxy resin composition are positioned to face the reinforcing fiber substrate, forming a laminate in which the reinforcing fiber substrate and the epoxy resin composition are sandwiched between the first and second carrier films. The resulting laminate is then pressurized to impregnate the reinforcing fiber substrate with the epoxy resin composition, thereby obtaining a prepreg. The content of the epoxy resin composition in the prepreg (hereinafter referred to as "resin content") is preferably 15 to 50% by mass, more preferably 20 to 45% by mass, and even more preferably 25 to 40% by mass, relative to the total mass of the prepreg. If the resin content is above the lower limit, the adhesion between the reinforcing fiber and the epoxy resin composition is excellent, and if it is below the upper limit, the mechanical properties of the resulting fiber-reinforced composite material are further enhanced.

[0029] [Epoxy resin composition] The epoxy resin composition comprises the aforementioned components (A), (B), and (C). The epoxy resin composition may further contain the following components (D) and (E). (D) Component: Dicyandiamide and / or dicyandiamide derivative (E) Component: Urea compound

[0030] <(A) component> Component (A) is an epoxy resin. The epoxy resin is not particularly limited, but examples include bisphenol-type epoxy resins, biphenyl-type epoxy resins, naphthalene-type epoxy resins, phenol novolac-type epoxy resins, cresol novolac-type epoxy resins, glycidylamine-type epoxy resins, and epoxy resins having an oxazolidone structure. These epoxy resins may be used individually or in combination of two or more. Since a fiber-reinforced composite material with an excellent balance of mechanical properties and flame retardancy can be obtained, the epoxy resin composition preferably contains at least a phenol novolac-type epoxy resin, a bisphenol-type epoxy resin, or an epoxy resin having an oxazolidone structure, and more preferably contains both a bisphenol-type epoxy resin and an epoxy resin having an oxazolidone structure. It is believed that the epoxy resin having an oxazolidone structure, by thermal decomposing simultaneously with combustion, allows the nitrogen atoms contained within the structure to dilute the flammable gas, thereby efficiently imparting flame retardancy to the epoxy resin composition. 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 AF type epoxy resin, and bisphenol BP type epoxy resin. Among these, bisphenol A type epoxy resin or bisphenol F type epoxy resin is preferred because it allows for the production of fiber-reinforced composite materials with an excellent balance of cost and mechanical properties. Examples of glycidylamine-type epoxy resins include tetraglycidyldiaminodiphenylmethane type epoxy resin, triglycidyl-p-aminophenol, and triglycidyl-m-aminophenol. From the viewpoint of flame retardancy and ease of handling of the prepreg, the content of component (A) is preferably 50 parts by mass or more, and more preferably 60 parts by mass or more, per 100 parts by mass of the epoxy resin composition. The content of component (A) can be 95 parts by mass or less per 100 parts by mass of the epoxy resin composition.

[0031] The content of epoxy resin having an oxazolidone structure per 100 parts by mass of total epoxy resin components is preferably 10 parts by mass or more, and more preferably 20 parts by mass or more, since this yields a reinforced fiber-reinforced composite material with excellent adhesion to reinforcing fibers and flame retardancy. The content of epoxy resin having an oxazolidone structure is preferably 60 parts by mass or less, and more preferably 50 parts by mass or less, per 100 parts by mass of total epoxy resin components, since this yields a prepreg with excellent tack and drape, and a reinforced fiber-reinforced composite material with few voids. The content of bisphenol-type epoxy resin per 100 parts by mass of total epoxy resin components is preferably 30 parts by mass or more, and more preferably 40 parts by mass or more, from the viewpoint of cost and mechanical properties. The content of bisphenol-type epoxy resin can be 100 parts by mass or less per 100 parts by mass of total epoxy resin components, and from the viewpoint of the tack and flame retardancy of the prepreg, it is preferably 60 parts by mass or less, and more preferably 50 parts by mass or less. The content of phenol novolac type epoxy resin can be 5 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the total epoxy resin components.

[0032] <(B) component> Component (B) is an imidazole compound and / or an imidazole compound derivative. Even when component (C) is included, the curing of the epoxy resin composition can be accelerated. When imidazole compounds and / or imidazole compound derivatives are incorporated into the resin composition in combination with component (D), the epoxy resin composition can be cured in a shorter time. Examples of imidazole compounds include 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole.

[0033] The imidazole derivative may be at least one derivative selected from the group consisting of imidazole adducts, inclusion-type imidazoles, microcapsule-type imidazoles, and imidazole compounds coordinated with a stabilizer.

[0034] Specific examples of imidazoles before adducting, heteromolecular inclusion, microcapsulation, or coordination of stabilizers include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazolium trimellitate, 1-cyanoethyl-2-undecylimidazole trimellitate, 1-cyanoethyl Ethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-(2'-methylimidazolyl-(1'))-ethyl-s-triazine, 2,4-diamino-6-(2'-undecylimidazolyl-(1'))-ethyl-s-triazine, 2,4-diamino-6-(2'-ethyl-4-methylimidazolyl-(1'))-ethyl-s-triazine, 2,4-diamino-6-(2'-methylimidazo Examples include lyl-(1'))-ethyl-s-triazine isocyanurate adduct, 2-phenylimidazole isocyanurate adduct, 2-methylimidazole isocyanurate adduct, 1-cyanoethyl-2-phenyl-4,5-di(2-cyanoethoxy)methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, and 2-phenyl-4-methyl-5-hydroxymethylimidazole. Component (B) may be used alone or in combination of two or more.

[0035] The content of component (B) with respect to 100 parts by mass of the epoxy resin composition is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of accelerating curing. The content of component (B) with respect to 100 parts by mass of the epoxy resin composition is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, from the viewpoints of storage stability and mechanical properties.

[0036] <Component (C)> Component (C) is an organic salt represented by the following formula (1). Component (C) can contribute to suppressing combustion by the nitrogen gas generated in the thermal decomposition process diluting the oxygen concentration. No toxic gases such as hydrogen halide are generated even when incinerated after use.

[0037]

Chemical formula

[0038] In formula (1), the alkyl group having 1 to 5 carbon atoms for R 1 ~R 6 includes a methyl group, an ethyl group, a propyl group, a butyl group, an isopropyl group, a t-butyl group, etc. From the viewpoint of flame retardancy, a methyl group or an ethyl group is preferred. The aryl group having 6 to 10 carbon atoms includes a phenyl group, a xylyl group, a tolyl group, a naphthyl group, etc. From the viewpoint of flame retardancy, a phenyl group is preferred. From the viewpoint of dispersibility in the epoxy resin, it is preferred that R 1 ]>[[]]~R 3 is NH2 and R 4 ~R 6 is a hydrogen atom (melamine cyanurate). Melamine cyanurate is an organic salt formed by the neutralization reaction of melamine, which is a base, and cyanuric acid, which is an acid.

[0039] Component (C) preferably has a 10% weight loss temperature in thermogravimetric analysis (TGA) within the range of 300 to 400°C. By setting the 10% weight loss temperature within the range of 300 to 400°C, nitrogen gas contained in component (C) is generated simultaneously with the thermal decomposition of component (A), thus diluting the flammable gas generated during combustion and efficiently imparting flame retardancy to the epoxy resin cured product. Thermogravimetric analysis can be performed using a TGA (TA Instruments, TGA550) under a nitrogen atmosphere and conditions of 10°C / min.

[0040] From the viewpoint of flame retardancy, component (C) preferably contains 40% by mass or more nitrogen atoms of the total component (C), and more preferably 45% by mass or more nitrogen atoms. Component (C) may contain 60% by mass or less nitrogen atoms of the total component (C). The nitrogen content can be determined by (amount of nitrogen contained in the component) / (molecular weight of the total component) × 100. The amount of nitrogen can be measured by elemental analysis using the combustion method.

[0041] Component (C) is preferably granular in form due to its excellent elastic modulus of the cured product. The average particle size of the granular component (C) is preferably 10 μm or less, and more preferably 5 μm or less, from the viewpoint of improving the appearance of the fiber-reinforced composite material. The average particle size can be measured using a particle size analyzer that uses the light scattering method (AEROTRAC SPR Model 7340, manufactured by Nikkiso Co., Ltd.). Here, the average particle size is the particle size that corresponds to 50% of the cumulative value of the particle size distribution measured by the particle size analyzer.

[0042] (C) As component (C), commercially available products may be used, or products synthesized by known manufacturing methods may be used. Manufacturing methods are disclosed in Japanese Patent Publication No. 7-188193 and Japanese Patent Publication No. 7-149739, etc. Examples of commercially available products include MC-4000, MC-4500, and MC-6000 (all trade names, manufactured by Nissan Chemical Industries, Ltd.).

[0043] From the viewpoint of flame retardancy, the content of component (C) per 100 parts by mass of the epoxy resin composition is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more. From the viewpoint of mechanical properties and appearance when used as a fiber-reinforced composite material, the content of component (C) per 100 parts by mass of the epoxy resin composition is preferably 40 parts by mass or less, and more preferably 30 parts by mass or less. From the viewpoint of rapid curing, the mass ratio of component (C) to component (B) in the epoxy resin composition ((B) component / (C) component) is preferably 0.1 or more, and more preferably 0.2 or more. From the viewpoint of flame retardancy, the mass ratio ((B) component / (C) component) is preferably 0.5 or less, and more preferably 0.4 or less.

[0044] <(D) component> Component (D) is dicyandiamide and / or a dicyandiamide derivative. Examples of dicyandiamide derivatives include those obtained by combining dicyandiamide with various compounds such as epoxy resins, vinyl compounds, acrylic compounds, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, but dicyandiamide is preferred from the viewpoint of reactivity.

[0045] From the viewpoint of accelerating curing, the content of component (D) per 100 parts by mass of the epoxy resin composition is preferably 1 part by mass or more, and more preferably 2 parts by mass or more. From the viewpoint of the toughness of the cured product, it is preferably 11 parts by mass or less, and more preferably 10 parts by mass or less, per 100 parts by mass of the epoxy resin composition.

[0046] The mass ratio of component (B) to component (D) (component (B) / component (D)) is preferably 0.5 to 1.5. Having the ratio of component (B) to component (D) within this range can improve the curing speed of the epoxy resin composition.

[0047] <(E) component> Component (E) is a urea compound. When heated at high temperatures, the urea compound generates isocyanate groups and dimethylamine, and the heat generated by the reaction of these with epoxy groups further accelerates the reaction between the generated -NH groups and epoxy groups, thereby improving the curing rate.

[0048] The urea compound is not particularly limited, but examples include aromatic dimethylurea, in which a dimethylureide group is bonded to an aromatic ring, and aliphatic dimethylurea, in which a dimethylureide group is bonded to an aliphatic compound. These may be used individually or in combination of two or more. Among these, aromatic dimethylurea is preferred from the viewpoint of improving the curing speed.

[0049] Examples of aromatic dimethylureas include phenyldimethylurea, methylenebis(phenyldimethylurea), and tolylenebis(dimethylurea). More specifically, examples include 4,4'-methylenebis(phenyldimethylurea) (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-dimethylureido)toluene (TBDMU). Among these, from the viewpoint of curing acceleration, it is more preferable to use at least one compound selected from the group consisting of phenyldimethylurea, methylenebis(phenyldimethylurea), and tolylenebis(dimethylurea).

[0050] Examples of aliphatic dimethylureas include dimethylurea obtained from isophorone diisocyanate and dimethylamine, dimethylurea obtained from m-xylylene diisocyanate and dimethylamine, and dimethylurea obtained from hexamethylene diisocyanate and dimethylamine.

[0051] The content of component (E) per 100 parts by mass of the epoxy resin composition is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more. A content of 0.5 parts by mass of component (E) promotes the curing of the epoxy resin composition. The content of component (E) is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the epoxy resin composition. A content of 10 parts by mass or less of component (E) yields a cured product with superior storage stability and mechanical properties.

[0052] <Physical properties of epoxy resin compositions> The viscosity of the epoxy resin composition at 60°C is preferably 5 Pa·s or higher, and more preferably 10 Pa·s or higher. A viscosity of 5 Pa·s or higher provides sufficient tackiness to the prepreg surface, reduces resin fluidity during molding, and suppresses disruption of reinforcing fibers. The viscosity of the epoxy resin composition at 60°C is preferably 2000 Pa·s or lower, and more preferably 1000 Pa·s or lower. A viscosity of 2000 Pa·s or lower improves impregnation into the reinforcing fiber substrate and the moldability of the prepreg.

[0053] The viscosity of the epoxy resin composition at 60°C can be measured using a rheometer (HAAKE MARS 40, manufactured by Thermo Fisher Scientific Co., Ltd.) at a rate of 2°C / min.

[0054] In thermogravimetric analysis (TGA) of the epoxy resin composition excluding component (C), the 10% weight loss temperature is preferably in the range of 300 to 400°C. By making the thermal decomposition behavior of the epoxy resin cured product and component (C) similar, the decomposition gas of component (C) can continuously cover the polymer surface during combustion, thereby efficiently imparting flame retardancy to the epoxy resin cured product.

[0055] The curing time for the epoxy resin composition is preferably within 10 minutes at 140°C, and more preferably within 5 minutes. If curing is completed within the aforementioned time, it can be said that the resin composition has sufficient rapid curing properties for use in high-cycle press molding. The curing time can be achieved by using a flame retardant with high compatibility with the epoxy resin and no curing delay, and an imidazole-based curing agent in combination, but the rapid curing properties can be further improved depending on the amount and type of these agents.

[0056] The curing time of an epoxy resin composition can be estimated by reading the curing behavior of the epoxy resin composition during an isothermal process using a differential scanning calorimeter (DSC). Figure 1 schematically shows an example of a heat flow curve of an epoxy resin composition during an isothermal process at a constant temperature. The time t(e) when the heat flow curve reaches the baseline is defined as 100% curing, the time t(p) when it reaches H(p) is defined as the time to reach the maximum heat generation peak, and the time t(s) when the heat flow curve intersects with a horizontal line drawn from the baseline is defined as the curing start time. The heat generation amount H(p) at which the heat flow curve is maximum is defined as the maximum heat generation amount, and the heat generation amount H(e) at the point when the heat flow curve reaches the baseline is defined as the heat generation amount at 100% curing. Here, the time when the heat generation amount reaches H(e) + (H(p) - H(e)) × 0.9 is defined as 90% curing, and the time to reach 90% curing is defined as the recommended curing time.

[0057] The cured epoxy resin composition exhibits flame retardancy equivalent to V-0 in flame retardancy tests measured at a thickness of approximately 2 mm, based on evaluations according to the UL-94V standard. Here, flame retardancy equivalent to V-0 means that, based on the UL-94 standard, the conditions for V-0 are met when evaluated in a vertical burning test, including the burning rate, burning time, and whether or not ignition occurs due to dripping material.

[0058] <Optional ingredients> The epoxy resin composition may further contain components other than those described above (A) to (E) (hereinafter sometimes referred to as "optional components"). Examples of optional components include thermoplastic resins and additives.

[0059] Thermoplastic resins are blended to control viscoelasticity and impart toughness. Examples of thermoplastic resins include, but are not limited to, polyamides, polyesters, polycarbonates, polyethersulfones, polyphenylene ethers, polyphenylene sulfides, polyetherether ketones, polyetherimides, polyimides, polytetrafluoroethylenes, polyethers, polyolefins, liquid crystal polymers, polyarylates, polysulfones, 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 formal, phenoxy resins, and block polymers. These thermoplastic resins may be used individually or in combination of two or more types. In particular, phenoxy resin, polyethersulfone, polyetherimide, polyvinyl formal, and block polymer are preferred from the viewpoint of excellent resin flow control properties.

[0060] The epoxy resin composition may optionally contain various known additives, provided that they do not impair the effects of the present invention. Examples of additives include epoxy resin curing accelerators, inorganic fillers, internal mold release agents, organic pigments, and inorganic pigments.

[0061] More specifically, additives include hydrated metal compounds (aluminum hydroxide, magnesium hydroxide, etc.) as inorganic flame retardants, inorganic oxides and other auxiliary agents (antimony compounds, zinc borate, zinc stinate, Mo compounds, ZrO, zinc sulfide, zeolites, titanium dioxide nanofillers, etc.), silicone oil, wetting and dispersing agents, defoaming agents, natural waxes, synthetic waxes, metal salts of linear fatty acids, acid amides, esters, paraffins and other release agents, inorganic fillers such as powders of crystalline silica, fused silica, calcium silicate, alumina, calcium carbonate, talc, barium sulfate, glass fibers, and carbon fibers with a fiber length of approximately 0.01 mm to 10 mm, colorants such as carbon black and red iron oxide, and silane coupling agents. These may be used individually or in combination of two or more types.

[0062] <Method for producing epoxy resin composition> Epoxy resin compositions can be obtained, for example, by mixing the components described above. Methods for mixing the components include using mixers such as three-roll mills, planetary mixers, kneaders, homogenizers, and homodispersers. The epoxy resin composition can be used in the production of prepregs by impregnating it into a reinforcing fiber aggregate, as described later. Alternatively, an epoxy resin film can be obtained by applying the epoxy resin composition to release paper or the like and allowing it to harden. When used as a film, a viscosity of 100 to 1,000,000 Pa·s of the epoxy resin composition at 30°C provides excellent control over the tack of the prepreg surface and superior workability.

[0063] <Reinforced Fiber> The reinforcing fibers exist in the prepreg as a reinforcing fiber base material (a collection of single reinforcing fibers), preferably in sheet form. The reinforcing fibers may be long fibers (continuous fibers), or short fibers, for example, 0.01 to 30 cm in length. The orientation of the fibers in the reinforcing fiber base material may be such that the reinforcing fibers are arranged in one direction or in random directions. Examples of forms of the reinforcing fiber base material include woven fabrics of reinforcing fibers, nonwoven fabrics of reinforcing fibers, and sheets in which long reinforcing fibers are aligned in one direction. From the viewpoint of being able to form fiber-reinforced composite materials with high specific strength and specific modulus, it is preferable to use a sheet (UD base material) consisting of bundles of reinforcing fibers in which long fibers are aligned in one direction as the prepreg, and from the viewpoint of ease of handling, it is preferable to use woven fabrics of reinforcing fibers as the prepreg. The basis weight of the reinforcing fiber base material is 10 g / m². 2 More than 4000g / m 2 The following is possible:

[0064] Examples of reinforcing fibers include glass fibers, carbon fibers, nylon fibers, aramid fibers, and boron fibers. Among these, carbon fibers are preferred from the viewpoint of mechanical properties and weight reduction of the resulting fiber-reinforced composite material. The number of carbon fibers in the carbon fiber bundle used in the reinforcing fiber base material is preferably 1,000 to 70,000. Multiple carbon fiber bundles can be used to create a sheet-like reinforcing fiber base material by aligning the fibers in one direction.

[0065] From the viewpoint of the rigidity of the resulting fiber-reinforced composite material, the tensile strength of the carbon fiber strands is preferably 1.5 to 9 GPa, and the tensile modulus of the carbon fiber strands is preferably 150 to 260 GPa. The tensile strength and tensile modulus of the carbon fiber strands can be measured in accordance with JIS R7601:1986.

[0066] The fiber diameter of the carbon fiber is preferably 3 to 12 μm. If the fiber diameter of the carbon fiber is greater than or equal to the lower limit above, in processes for processing carbon fibers, such as combs and rolls, when the carbon fibers move laterally and rub against each other or against the surface of the roll, the carbon fibers are less likely to break or accumulate lint.

[0067] <Fiber-reinforced composite materials> Fiber-reinforced composite materials are obtained by curing prepregs. That is, fiber-reinforced composite materials include a cured epoxy resin composition contained in the prepreg and reinforcing fibers. Fiber-reinforced composite materials are obtained, for example, by laminating two or more of the aforementioned prepregs, and then molding them by applying pressure to the resulting laminate while heating and curing the epoxy resin composition. In the flame retardancy test of fiber-reinforced composite materials according to the UL-94V standard, it is preferable that the test piece with a thickness of 2.0 mm is V-0.

[0068] Molding methods include press molding, autoclave molding, bagging molding, wrapping tape molding, internal pressure molding, sheet wrap molding, and RTM (Resin Transfer Molding), VaRTM (Vacuum assisted Resin Transfer Molding), filament winding, and RFI (Resin Film Infusion), which involve impregnating reinforcing fiber filaments or preforms with an epoxy resin composition and curing to obtain molded products. Among these, press molding is preferred from the viewpoint of high productivity and ease of obtaining high-quality fiber-reinforced composite materials.

[0069] When manufacturing fiber-reinforced composite materials by press molding, the prepreg or preform (made by laminating prepregs) can be cured by placing it in a mold pre-adjusted to the curing temperature and heating and pressurizing it. The temperature inside the mold during press molding is preferably 100 to 160°C. Furthermore, it is preferable to cure the prepreg or preform for 1 to 20 minutes under conditions of 1 to 15 MPa.

[0070] <Application> Fiber-reinforced composite materials are useful in applications requiring high flame retardancy, such as electrical and electronic casing materials and aircraft interior materials. They can be applied to casings for electrical and electronic equipment such as laptop computers, and interior components for aircraft and automobiles. They are also suitable for use in sports, general industrial, and aerospace applications. [Examples]

[0071] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention.

[0072] The raw materials used in the following examples and comparative examples are shown below.

[0073] [Raw materials] <(A) component> • jER828: Liquid bisphenol A type epoxy resin, epoxy equivalent 189 g / eq, manufactured by Mitsubishi Chemical Corporation. • YD-952: Oxazolidone type epoxy resin, manufactured by Nippon Steel Chemical & Material Co., Ltd. • YDPN-638: Phenolic novolac type epoxy resin, epoxy equivalent 180g / eq, manufactured by Nippon Steel Chemical & Material Co., Ltd.

[0074] <(B) component> • 2MZA-PW: 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, manufactured by Shikoku Chemicals Co., Ltd.

[0075] <(C) component> • MC-6000: Melamine cyanurate with the following structure, nitrogen content 49 wt%, average particle size 2 μm or less, manufactured by Nissan Chemical Corporation as "MC-6000".

[0076] [ka]

[0077] <(D) component> • Dicy15: Dicyandiamide, "jER Cure Dicy15" manufactured by Mitsubishi Chemical Corporation.

[0078] <(E) component> • Omicure94: 3-phenyl-1,1-dimethylurea, manufactured by PTI Japan Co., Ltd.

[0079] <Other additives> • OP935: Aluminum trisdiethylphosphinate, phosphorus atom content 23.0% by mass, average particle size 2-3 μm, maximum particle size less than 10 μm, decomposition temperature 300°C or higher, "Exolit OP935" manufactured by Clariant Japan Co., Ltd. • OP930: Aluminum trisdiethylphosphinate, phosphorus atom content 23.0% by mass, average particle size 3-5 μm, maximum particle size less than 20 μm, decomposition temperature 300°C or higher, "Exolit OP930" manufactured by Clariant Japan Co., Ltd. HCA-HQ-HS: 10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, phosphorus atom content 9.6%, average particle size 1-2 μm, manufactured by Sanko Co., Ltd.

[0080] <Carbon fiber> • Carbon fiber: "Pyrofil TR50S15L" manufactured by Mitsubishi Chemical Corporation

[0081] [Example 1] An epoxy resin composition was prepared as follows, using (A) jER828, YD-952, and YDPN-638 as components, (B) 2MZA-PW as component, (C) MC-6000 as component, (D) Dicy15 as component, and (E) Omicure94 as component. First, according to the composition listed in Table 1, jER828 (liquid) from component (A), and components (solid), (B), (D), and (E) were weighed into a container so that the mass ratio of solid to liquid components was 1:1, and then stirred and mixed. This was further finely mixed in a three-roll mill to obtain a curing agent masterbatch. Next, from the composition listed in Table 1, components other than component (C) and the curing agent masterbatch were weighed into a flask and heated to 120°C using an oil bath to dissolve and mix. Then, while cooling to about 100°C, component (C) was added and stirred and mixed, and when cooled to about 65°C, the curing agent masterbatch was added and stirred and mixed to obtain an epoxy resin composition. Using the obtained epoxy resin composition, a resin plate was made according to the epoxy resin plate manufacturing method described later. Various measurements and evaluations were performed according to the evaluation method described later. The results are shown in Table 1.

[0082] [Comparative Examples 1-3] An epoxy resin composition was prepared in the same manner as in Example 1, except that the compound composition was changed as shown in Table 1. A resin plate was then fabricated using this epoxy resin composition, and various measurements and evaluations were performed. The results are shown in Table 1.

[0083] [Method for manufacturing resin sheets] An uncured epoxy resin composition was preheated in an oven at an ambient temperature of 70°C for 10 minutes, and then cured at 140°C for 40 minutes (heating rate of 10°C / min) to obtain a resin sheet with a thickness of 2 mm.

[0084] <Prepreg fabrication method> An uncured epoxy resin composition was formed into a film using a hot melt coater (Hirano Texseed Co., Ltd., "R-HC"), with a resin basis weight of 41.7 g / m². 2 A resin film was prepared. This resin film was then used to create a resin film with carbon fibers aligned, resulting in a fiber weight of 125 g / m². 2 The carbon fiber sheet is laminated to both sides, impregnated with a heated roll, and has a fiber weight of 125 g / m². 2 A prepreg with a resin content of 40% by mass was obtained.

[0085] <Method for manufacturing fiber-reinforced composite boards 1> The prepreg using the epoxy resin composition of the example obtained in the <Prepreg Production Method> described above was cut to 298 mm x 298 mm, and 16 sheets were stacked so that the fiber direction was [0° / 90° / 0° / 90° / 0° / 90° / 0° / 90 / 90° / 0° / 90° / 0° / 90° / 0°] to obtain a laminate. This laminate was placed in a press molding die preheated to 140°C and press molded at 140°C for 5 minutes at a pressure of 4 MPa to obtain a 2.0 mm thick fiber-reinforced composite material board ([0° / 90° / 0° / 90° / 0° / 90° / 0° / 90 / 90° / 0° / 90° / 0° / 90° / 0°]).

[0086] <Method for fabricating fiber-reinforced composite boards 2> The prepreg using the epoxy resin composition of the comparative example obtained in the above-mentioned <Prepreg Production Method> was cut to 298 mm x 298 mm, and 16 sheets were stacked so that the fiber direction was [0° / 90° / 0° / 90° / 0° / 90° / 0° / 90 / 90° / 0° / 90° / 0° / 90° / 0° / 0°] to obtain a laminate. This laminate was placed in a press molding die preheated to 140°C and press-molded at 140°C for 10 minutes at a pressure of 4 MPa to obtain a 2.0 mm thick fiber-reinforced composite material board ([0° / 90° / 0° / 90° / 0° / 90° / 0° / 90 / 90° / 0° / 90° / 0° / 90° / 0°]).

[0087] [Evaluation Method] (1) UL-94V combustion test of resin boards and fiber-reinforced composite boards The obtained 2.0 mm thick resin plate and 2.0 mm thick fiber-reinforced composite material plate were processed into test specimens measuring 127 mm in length and 12.7 mm in width. A combustion test was conducted on these test specimens using a combustion testing machine (manufactured by Suga Test Machine Co., Ltd.) in accordance with the UL-94V standard. Specifically, the test specimens were mounted vertically in a clamp, and a 20 mm flame was applied for 10 seconds to measure the burning time. Five test specimens were subjected to the combustion test, and the number of samples that burned up to the clamp, the maximum burning time (max) for each sample, and the total burning time (total) for all five specimens were recorded. Based on these results, a rating [V-0, V-1, V-2, fail] was assigned. V-0 indicated the best flame retardancy, followed by V-1, V-2, and fail in increasing order of flame retardancy.

[0088] (2) Calculation of degree of curing and curing time of epoxy resin composition The curing time of the epoxy resin composition was estimated by reading the curing behavior of the epoxy resin composition during an isothermal process using a differential scanning calorimeter (DSC) (DA Instruments Japan Co., Ltd., "DSC250"). Approximately 10 mg of the resin composition was placed in an aluminum hermetic pan, and an empty aluminum hermetic pan was placed on the sample stage in the cell as a reference. The measurement was taken by holding the sample at 140°C for 40 minutes. Using the above method, the time to reach the maximum exothermic peak and the time to reach 90% curing were calculated.

[0089] [Table 1]

[0090] As is clear from the results in Table 1, the epoxy resin composition of Example 1 exhibited sufficient rapid curing properties, reaching a curing degree of 90% in less than 4 minutes. This is thought to be because component (C) was uniformly dispersed in the epoxy resin composition, preventing inhibition of reaction curing in the epoxy resin. Furthermore, the fiber-reinforced composite material board made using the epoxy resin composition of Example 1 was equivalent to V-0 in a 2.0 mm thick test specimen. On the other hand, the fiber-reinforced composite material boards made using the epoxy resin compositions of Comparative Examples 1 to 3 were equivalent to V-1 in a 2.0 mm thick test specimen, which differed from the trend of the resin boards. The difference in flame retardancy with thickness was due to the difference between the phosphorus-based flame retardant and component (C). When component (C) was used, the amount of nitrogen gas generated during the thermal decomposition process in the combustion area increased with increasing thickness, and it is thought that combustion was suppressed by further diluting the oxygen concentration. [Explanation of Symbols]

[0091] H(p): Maximum heat output H(e): Heat generated at 100% curing degree t(e): Time to reach 100% hardening t(p): Time to reach maximum heat output t(s): Curing start time

Claims

1. A prepreg comprising an epoxy resin composition containing the following components (A), (B), and (C), and a reinforcing fiber substrate. (A) Component: Epoxy resin (B) Component: Imidazole compound and / or imidazole compound derivative (C) Component: Organic salt represented by the following formula (1) 【Chemistry 1】 ...Formula (1) (R １ ~R ６ Each of these independently represents a hydrogen atom, an amino group, an epoxy group, an alkyl group with 1 to 5 carbon atoms, or an aryl group with 6 to 10 carbon atoms.

2. The prepreg according to claim 1, wherein the 10% weight loss temperature of component (C) measured under a nitrogen atmosphere by thermogravimetric analysis is 300 to 400°C.

3. The prepreg according to claim 1 or 2, wherein component (C) contains 40% by mass or more nitrogen atoms.

4. In the above formula (1), R １ ~R ３ NH ２ , R ４ ~R ６ The prepreg according to any one of claims 1 to 3, wherein is a hydrogen atom.

5. The prepreg according to any one of claims 1 to 4, comprising 10 to 30 parts by mass of component (C) per 100 parts by mass of the epoxy resin composition.

6. The prepreg according to any one of claims 1 to 5, further comprising the following component (D). (D) Component: Dicyandiamide and / or dicyandiamide derivative

7. The prepreg according to any one of claims 1 to 6, further comprising the following component (E). (E) Component: Urea compound

8. The prepreg according to any one of claims 1 to 7, wherein the epoxy resin composition obtained by removing component (C) from the epoxy resin composition is cured at 140°C for 1 hour, and the 10% weight loss temperature of the cured product, measured under a nitrogen atmosphere by thermogravimetric analysis, is 300 to 400°C.

9. The epoxy resin composition according to any one of claims 1 to 8, wherein the viscosity of the epoxy resin composition at 60°C is 10 to 1000 Pa·s.

10. The prepreg according to any one of claims 1 to 9, wherein component (A) comprises an epoxy resin having an oxazolidone structure.

11. The prepreg according to any one of claims 1 to 10, comprising 1 to 10 parts by mass of component (B) per 100 parts by mass of the epoxy resin composition.

12. The prepreg according to claim 6, wherein the mass ratio of component (B) to component (D) (component (B) / component (D)) is 0.5 to 1.

5.

13. The prepreg according to any one of claims 1 to 12, wherein the mass ratio of component (B) to component (C) (component (B) / component (C)) is 0.1 to 0.

5.

14. The prepreg according to any one of claims 1 to 13, wherein the reinforcing fiber base material includes carbon fibers.

15. A fiber-reinforced composite material obtained by curing the prepreg described in claim 14.

16. The fiber-reinforced composite material according to claim 15, wherein the flame retardancy test of the fiber-reinforced composite material according to the UL-94V standard is V-0 with a test piece 2.0 mm thick.

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