Epoxy resin composition, molding material for fiber-reinforced composite material, and fiber-reinforced composite material

Abstract

The purposes of the present invention are: to provide an epoxy resin composition having excellent impregnation into reinforcing fibers, excellent shapability under low-temperature conditions after thickening, and excellent heat resistance after curing; to provide a molding material for a fiber-reinforced composite material, said molding material having excellent shapability during handling and excellent fluidity during press molding; and to provide a fiber-reinforced composite material having excellent heat resistance and bending strength.　To achieve the abovementioned purposes, the present invention provides an epoxy resin composition containing all of the following components (A)-(D), wherein: the content of the component (A), in terms of 100 mass% of the total mass of the epoxy resin composition, is 30-95 mass%; and the ratio Wc / Wd of the content Wc of the component (C) to the content Wd of the component (D) is 0.01-10. Component (A) is an epoxy resin; component (B) is a curing agent; component (C) is a diisocyanate compound having consecutive double bonds, an alicyclic structure or a heterocyclic structure; and component (D) is a polyisocyanate compound excluding the component (C).

Description

[Technical field]

[0001] The present invention relates to an epoxy resin composition that is suitably used for fiber-reinforced composite materials such as aerospace parts and automotive parts, and to a molding material for fiber-reinforced composite materials and fiber-reinforced composite materials each using the same. [Background technology]

[0002] Fiber-reinforced composite materials, which are made of reinforcing fibers and matrix resins, have been used for structural materials for aircraft and automobiles, as well as for sports and general industrial applications such as tennis rackets, golf shafts, and fishing rods, taking advantage of their high specific strength and specific modulus. Glass fibers, aramid fibers, carbon fibers, and boron fibers are used as reinforcing fibers. Both thermosetting and thermoplastic resins are used as matrix resins, but thermosetting resins are often used from the viewpoints of heat resistance and productivity. Epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, bismaleimide resins, and cyanate resins are used as thermosetting resins. Among them, epoxy resins are preferably used from the viewpoints of adhesion and dimensional stability between the resin and reinforcing fibers, and mechanical properties such as the strength and rigidity of the resulting composite material.

[0003] Fiber-reinforced composite materials are manufactured by hand lay-up, filament winding, pultrusion, resin transfer molding (RTM), press molding of fiber-reinforced composite molding materials such as prepreg, towpreg, bulk molding compound (BMC), and sheet molding compound (SMC). These fiber-reinforced composite molding materials are manufactured by impregnating reinforcing fibers with a matrix resin. BMC and SMC are further manufactured by thickening the resin composition by leaving it at room temperature or by heat treatment. Such thickening techniques include a technique of dissolving or swelling thermoplastic particles or thermoplastic resin in epoxy resin, a technique of reacting epoxy groups with amines or acid anhydrides to form a crosslinked structure, and a technique of reacting isocyanate with hydroxyl groups to form polyurethane in the system.

[0004] In response to this situation, an epoxy resin composition has been disclosed that contains a hydroxyl group-containing vinyl ester as a hydroxyl group source and a urethane prepolymer obtained by reacting a previously prepared low molecular weight diol with 4,4'-diphenylmethane diisocyanate (Patent Document 1). Also, an epoxy resin composition has been disclosed that contains a liquid bisphenol A type epoxy and polymeric MDI as a hydroxyl group source (Patent Document 2). Furthermore, an epoxy resin composition has been disclosed that contains a urethane prepolymer obtained by reacting a previously prepared polyether polyol with TDI (Patent Document 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-78445 [Patent Document 2] Patent Application No. 2010-517848 [Patent Document 3] JP 2017-82128 A Summary of the Invention [Problem to be solved by the invention]

[0006] In epoxy resins using these thickening techniques, it is preferable that the resin viscosity at 30°C is low from the viewpoint of impregnation into reinforcing fibers. On the other hand, it is preferable that the viscosity of the resin after thickening is sufficient so that the resin does not leak from the fibers when left to stand. In addition, the viscosity of the resin changes depending on the seasonal temperature, and the viscosity of the resin increases especially at 0 to 10°C in winter, and the thickened resin may break when bent during molding. Therefore, in order to maintain good molding properties regardless of seasonal fluctuations, it is necessary that the thickened resin is sufficiently flexible even at low temperatures.

[0007] Furthermore, a molding material for a fiber-reinforced composite material obtained by using the above epoxy resin composition is required to have good fluidity during molding, and a fiber-reinforced composite material obtained by using the above molding material for a fiber-reinforced composite material is required to have sufficient heat resistance and bending strength so as not to deform when demolded.

[0008] According to the epoxy resin composition described in the above-mentioned Patent Document 1, the urethane prepolymer made of a low molecular weight aliphatic diol has a high viscosity at 30°C, and the incorporation of the urethane prepolymer reduces the heat resistance of the fiber-reinforced composite material. In order to suppress this reduction in heat resistance, it was necessary to incorporate a large amount of a highly viscous hydroxyl-containing vinyl ester. As a result, the viscosity of the resulting epoxy resin composition was high, and the impregnation of the reinforcing fiber was insufficient. In addition, the viscosity of the resin thickener at 10°C was high, and the shapeability under low temperature conditions was insufficient. The bending strength of the resulting fiber-reinforced composite material was also low.

[0009] According to the epoxy resin composition described in the aforementioned Patent Document 2, since the polymeric MDI has three or more isocyanate groups in one molecule, the heat resistance of the cured product of the epoxy resin composition is excellent, but the viscosity of the resin thickener at 10° C. is high and the moldability under low temperature conditions is insufficient. Therefore, the moldability of the obtained molding material for fiber-reinforced composite material is insufficient, and the flowability during molding is also insufficient.

[0010] According to the epoxy resin composition described in the aforementioned Patent Document 3, the urethane prepolymer obtained by reacting a polyether polyol prepared in advance with TDI has a flexible molecular skeleton consisting of aliphatic groups, and although the viscosity of the resin thickener of the obtained epoxy resin composition at 10°C is low, the heat resistance of the cured product is insufficient. Furthermore, since a high molecular weight urethane prepolymer is blended, the resin viscosity of the epoxy resin composition is high and the impregnation into the reinforcing fiber is insufficient. Furthermore, the bending strength of the obtained fiber-reinforced composite material is also low.

[0011] As described above, in the prior art, there was no technology that could maintain good impregnation into reinforcing fibers, while exhibiting excellent formability of a molding material for a fiber-reinforced composite material under low-temperature conditions, and further capable of exhibiting the heat resistance and bending strength of the resulting fiber-reinforced composite material.

[0012] Therefore, an object of the present invention is to overcome the drawbacks of the conventional techniques and to provide an epoxy resin composition which has excellent impregnation ability into reinforcing fibers, excellent shapeability under low temperature conditions after thickening, and excellent heat resistance after curing; further, by using such an epoxy resin composition, to provide a molding material for a fiber-reinforced composite material which has excellent shapeability during handling and flowability during press molding; and further, by using such a molding material for a fiber-reinforced composite material, to provide a fiber-reinforced composite material which has excellent heat resistance and bending strength. [Means for solving the problem]

[0013] In order to solve the above problems, the epoxy resin composition of the present invention has the following configuration: An epoxy resin composition comprising all of the following components (A) to (D), in which the content of component (A) is 30% by mass or more and 95% by mass or less based on the total mass of the epoxy resin composition (100% by mass), and the ratio Wc / Wd of the content Wc of component (C) to the content Wd of component (D) is 0.01 or more and 10 or less. Component (A): Epoxy resin Component (B): Hardener Component (C): A diisocyanate compound having consecutive double bonds, an alicyclic structure, or a heterocyclic structure. Component (D): Polyisocyanate compounds excluding component (C) Effect of the Invention

[0014] According to the present invention, there is provided an epoxy resin composition which has excellent impregnation ability into reinforcing fibers, excellent formability under low temperature conditions after thickening, and excellent heat resistance after curing. Furthermore, by using such an epoxy resin composition, it is possible to provide a molding material for a fiber-reinforced composite material which has excellent formability during handling and flowability during press molding. Furthermore, by using such a molding material for a fiber-reinforced composite material, it is possible to provide a fiber-reinforced composite material which has excellent heat resistance and mechanical properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Preferred embodiments of the present invention will be described below. First, the epoxy resin composition according to the present invention will be described.

[0016] The epoxy resin composition of the present invention contains all of the following components (A) to (D), in which the content of component (A) is 30% by mass or more and 95% by mass or less based on the total mass of the epoxy resin composition (100% by mass), and the ratio Wc / Wd of the content Wc of component (C) to the content Wd of component (D) is 0.01 or more and 10 or less. Component (A): Epoxy resin Component (B): Hardener Component (C): A diisocyanate compound having consecutive double bonds, an alicyclic structure, or a heterocyclic structure. Component (D): A polyisocyanate compound other than component (C).

[0017] The epoxy resin of component (A) in the present invention is not particularly limited as long as it is a compound containing one or more epoxy groups in the molecule. Examples of component (A) include bisphenol A type epoxy resin, bisphenol F type epoxy resin, biphenyl type epoxy resin, dicyclopentadiene type epoxy resin, and epoxy resins modified with these. In addition, phenol novolac type epoxy resin, cresol type epoxy resin, glycidylamine type epoxy resin such as tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol, and tetraglycidylamine, glycidyl ether type epoxy resin such as tetrakis(glycidyloxyphenyl)ethane and tris(glycidyloxymethane), and epoxy resins modified with these, brominated epoxy resins obtained by brominating these epoxy resins, and polyglycidyl ethers of aliphatic alcohols, but are not limited thereto. Examples of the aliphatic alcohol include 1,4-butanediol, 3-methyl-1,5-pentanediol, diethylene glycol, neopentyl glycol, 1,6-hexanediol, 1,9-nonanediol, cyclohexanedimethanol, propylene glycol, glycerin, polyglycerin, trimethylolpropane, butyl alcohol, isobutyl alcohol, s-butyl alcohol, 2-ethylhexanol, stearyl alcohol, isostearyl alcohol, lauryl alcohol, etc. Two or more of these epoxy resins may be used in combination as component (A).

[0018] In the epoxy resin composition of the present invention, it is preferable that component (A) is a hydroxyl group-containing epoxy resin that is liquid at 30° C. By using such an epoxy resin, it becomes easier to obtain a molding material for a fiber-reinforced composite material that has better shapeability and excellent flow properties under low-temperature conditions.

[0019] Commercially available bisphenol A type epoxy resins include "jER (registered trademark)" 825, "jER (registered trademark)" 826, "jER (registered trademark)" 827, "jER (registered trademark)" 828, "jER (registered trademark)" 834, "jER (registered trademark)" 1001, "jER (registered trademark)" 1002, "jER (registered trademark)" 1003, "jER (registered trademark)" 1004, "jER (registered trademark)" 1005, "jER (registered trademark)" 1006, "jER (registered trademark)" 1007, "jER (registered trademark)" 1009, "jER (registered trademark)" 1010, "jER (registered trademark)" 1011, "jER (registered trademark)" 1012, "jER (registered trademark)" 1013, "jER (registered trademark)" 1014, "jER (registered trademark)" 1015, "jER (registered trademark)" 1016, "jER (registered trademark)" 1017, "jER (registered trademark)" 1018, "jER (registered trademark)" 1019, "jER (registered trademark)" 1020, "jER (registered trademark)" 1021, "jER (registered trademark)" 1022, "jER (registered trademark)" 1023, "jER (registered trademark)" 1024, "jER (registered trademark)" 1025, "jER (registered trademark)" 1026, "jER (registered trademark)" 1027, "jER (registered trademark)" 1028, "jER (registered trademark)" 1029, "jER (registered trademark Examples of such an epoxy resin include "jER (registered trademark)" 1004AF, "jER (registered trademark)" 1007, and "jER (registered trademark)" 1009 (all manufactured by Mitsubishi Chemical Corporation), "Epicron (registered trademark)" 850 (manufactured by DIC Corporation), "Epotohto (registered trademark)" YD-128 (manufactured by Nippon Steel & Sumitomo Metal Chemical Co., Ltd.), "DER (registered trademark)"-331, and "DER (registered trademark)"-332 (manufactured by The Dow Chemical Company).

[0020] Commercially available bisphenol F type epoxy resins include jER (registered trademark) 806, jER (registered trademark) 807, jER (registered trademark) 1750, jER (registered trademark) 4004P, jER (registered trademark) 4007P, and jER (registered trademark) 4009P (all manufactured by Mitsubishi Chemical Corporation), Epicron (registered trademark) 830 (manufactured by DIC Corporation), Epotohto (registered trademark) YDF-170, Epotohto (registered trademark) YDF2001, and Epotohto (registered trademark) YDF2004 (all manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.). Commercially available alkyl-substituted tetramethylbisphenol F type epoxy resins include Epotohto (registered trademark) YSLV-80XY (Nippon Steel & Sumikin Chemical Co., Ltd.).

[0021] An example of the bisphenol S type epoxy resin is "Epiclon (registered trademark)" EXA-1515 (manufactured by DIC Corporation).

[0022] Commercially available phenol novolac type epoxy resins include "jER (registered trademark)" 152, "jER (registered trademark)" 154 (both manufactured by Mitsubishi Chemical Corporation), "Epicron (registered trademark)" N-740, "Epicron (registered trademark)" N-770, and "Epicron (registered trademark)" N-775 (all manufactured by DIC Corporation).

[0023] Commercially available cresol novolac epoxy resins include "Epicron (registered trademark)" N-660, "Epicron (registered trademark)" N-665, "Epicron (registered trademark)" N-670, "Epicron (registered trademark)" N-673, "Epicron (registered trademark)" N-695 (all manufactured by DIC Corporation), EOCN-1020, EOCN-102S, EOCN-104S (all manufactured by Nippon Kayaku Co., Ltd.), and the like.

[0024] Commercially available polyglycidyl ethers of aliphatic alcohols include "Denacol (registered trademark)" EX-321, "Denacol (registered trademark)" EX-313, "Denacol (registered trademark)" EX-314, "Denacol (registered trademark)" EX-411, "Denacol (registered trademark)" EX-412, "Denacol (registered trademark)" EX-512, "Denacol (registered trademark)" EX-521, "Denacol (registered trademark)" EX-612, "Denacol (registered trademark)" EX-614, "Denacol (registered trademark)" EX-614B (all manufactured by Nagase ChemteX Corporation), "Epiol (registered trademark)" G-100 (manufactured by NOF Corporation), SR-GLG, SR-DGE, SR-TMP, SR-SEP, and SR-4GL (all manufactured by Sakamoto Pharmaceutical Industry Co., Ltd.).

[0025] In the epoxy resin composition of the present invention, the content of component (A) is 30% by mass or more and 95% by mass or less in the total mass (100% by mass) of the epoxy resin composition. When the content of component (A) is 30% by mass or more, sufficient heat resistance can be exhibited. When the content of component (A) is 95% by mass or less, a sufficient effect of improving bending strength can be obtained. The content of component (A) is more preferably 50% by mass or more and 90% by mass or less.

[0026] The curing agent of component (B) in the present invention is not particularly limited as long as it can cure the epoxy resin, but examples thereof include amine-based, phenol-based, acid anhydride-based, mercaptan-based, imidazoles, tertiary amines, organic phosphorus compounds, urea compounds, ammonium salts, and sulfonium salts. Examples of amine-based curing agents include dicyandiamide, aromatic polyamines, aliphatic amines, aminobenzoic acid esters, thiourea-added amines, and hydrazides. Examples of phenol-based curing agents include bisphenols, phenol novolac resins, cresol novolac resins, and polyphenol compounds. Examples of acid anhydride-based curing agents include phthalic anhydride, maleic anhydride, succinic anhydride, and carboxylic anhydrides. Examples of mercaptan-based curing agents include polymercaptan and polysulfide resins. Among the above examples, amine-based curing agents are preferred.

[0027] In the epoxy resin composition of the present invention, it is particularly preferable that component (B) is dicyandiamide or a derivative thereof. Dicyandiamide is likely to impart high bending strength and heat resistance to the resin cured product. In addition, it is likely to provide excellent storage stability to the epoxy resin composition. In addition, the derivative of dicyandiamide means a compound obtained by bonding dicyandiamide with various compounds, and is excellent in that it is likely to impart high bending strength and heat resistance to the resin cured product, similar to dicyandiamide, and is also excellent in storage stability of the epoxy resin composition. Examples of the derivative of dicyandiamide include those obtained by bonding dicyandiamide with various compounds such as epoxy resin, vinyl compound, acrylic compound, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. These may be used alone or in combination of two or more. They may also be used in combination with dicyandiamide. Commercially available products of dicyandiamide include "jER Cure (registered trademark)" DICY7 and DICY15 (both manufactured by Mitsubishi Chemical Corporation).

[0028] The content of component (B) in the present invention is preferably 1 part by mass or more and 50 parts by mass or less relative to 100 parts by mass of component (A). More preferably, it is 8 parts by mass or more and 50 parts by mass or less. When the content of component (B) is 1 part by mass or more, a sufficient effect of improving curability is easily obtained. In addition, when the content of component (B) is 50 parts by mass or less, the heat resistance of the cured product of the obtained epoxy resin composition is more easily improved.

[0029] The component (C) in the present invention is not particularly limited as long as it is a diisocyanate compound having a continuous double bond structure, an alicyclic structure, or a heterocyclic structure. Here, examples of the continuous double bond structure include an allene structure, a carbodiimide structure, and an azide structure. The alicyclic structure is a cyclic chemical structure consisting of an aliphatic chain, such as a cycloalkane structure or a cycloalkene structure. The heterocyclic structure is a cyclic chemical structure containing at least two different elements in the ring, such as a uretdione ring, an isocyanurate ring, and a uretonimine ring. When the component (C) has such a continuous double bond structure, an alicyclic structure, or a heterocyclic structure, the functional group has a high reactivity with active hydrogen or an epoxy group, or the structure has a high rigidity, so that the cured product of the obtained epoxy resin composition exhibits high heat resistance.

[0030] The diisocyanate compound of component (C) is, for example, a diisocyanate compound having a continuous double bond structure, and may be a compound obtained by modifying a diisocyanate compound with a carbodiimide. Examples of this diisocyanate compound include aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, aralkyl diisocyanates, and mixtures thereof, such as 4,4'-diphenylmethane diisocyanate (MDI), 2,6-tolylene diisocyanate (2,6-TDI), 2,4-tolylene diisocyanate (2,4-TDI), naphthalene diisocyanate (NDI), 1-methoxybenzene-2,4-diisocyanate (MBDI), metaxylene diisocyanate (MXDI), 1,6-hexamethylene diisocyanate (HDI), and the like. ), 2,2,4-trimethylhexamethylene diisocyanate (TMHDI), 1,12-diisocyanatododecane (DDI), hydrogenated xylylene diisocyanate (HXDI), norbornane diisocyanate (NBDI), isophorone diisocyanate (IPDI), 2,4-bis(8-isocyanatooctyl)-1,3-dioctylcyclobutane (OCDI), 4,4'-dicyclohexylmethane diisocyanate (HMDI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), diphenyl sulfide-4,4'-diisocyanate, diphenyl sulfone-4,4'-diisocyanate, diphenyl ether-4,4'-diisocyanate, diphenyl ketone-4,4'-diisocyanate, and the like.

[0031] Examples of diisocyanate compounds having an alicyclic structure include hydrogenated xylylene diisocyanate (HXDI), norbornane diisocyanate (NBDI), isophorone diisocyanate (IPDI), 2,4-bis(8-isocyanatooctyl)-1,3-dioctylcyclobutane (OCDI), and 4,4'-dicyclohexylmethane diisocyanate (HMDI).

[0032] Examples of the diisocyanate compound having a heterocyclic structure include dimers and trimers of diisocyanate compounds. Examples of the diisocyanate compound include aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, aralkyl diisocyanates, and mixtures thereof. For example, 4,4'-diphenylmethane diisocyanate (MDI), 2,6-tolylene diisocyanate (2,6-TDI), 2,4-tolylene diisocyanate (2,4-TDI), naphthalene diisocyanate (NDI), 1-methoxybenzene-2,4-diisocyanate (MBDI), metaxylene diisocyanate (MXDI), 1,6-hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexyl diisocyanate (TDI), methyl 1,6-hexamethylene diisocyanate (M ... Examples of such diisocyanates include samethylene diisocyanate (TMHDI), 1,12-diisocyanate dodecane (DDI), hydrogenated xylylene diisocyanate (HXDI), norbornane diisocyanate (NBDI), isophorone diisocyanate (IPDI), 2,4-bis(8-isocyanatooctyl)-1,3-dioctylcyclobutane (OCDI), 4,4'-dicyclohexylmethane diisocyanate (HMDI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), diphenyl sulfide-4,4'-diisocyanate, diphenyl sulfone-4,4'-diisocyanate, diphenyl ether-4,4'-diisocyanate, and diphenyl ketone-4,4'-diisocyanate. As component (C), two or more of these diisocyanate compounds may be used in combination.

[0033] Commercially available products of component (C) include diisocyanates having a continuous double bond structure such as "Millionate (registered trademark)" MTL, "Cosmonate (registered trademark)" LL, "Cosmonate (registered trademark)" LK, "Cosmonate (registered trademark)" LT, "Cosmonate (registered trademark)" LI (all manufactured by Mitsui Chemicals, Inc.), "Lupranate (registered trademark)" MM-103 (manufactured by BASF INOAC Polyurethanes Co., Ltd.), etc. Examples of diisocyanate compounds having an alicyclic structure include "Desmodur (registered trademark)" I, "Desmodur (registered trademark)" W (all manufactured by Sumika Covestro Urethane Co., Ltd.), "Takenate (registered trademark)" 600, "NBID (registered trademark)" norbornane diisocyanate (all manufactured by Mitsui Chemicals, Inc.), dicyclohexylmethane-4,4'-diisocyanate (mixture of isomers) (manufactured by Tokyo Chemical Industry Co., Ltd.), etc. An example of a diisocyanate compound having a heterocyclic structure is "Desmodur (registered trademark)" N3400 (manufactured by Sumika Covestro Urethane Co., Ltd.).

[0034] In the epoxy resin composition of the present invention, it is preferable that component (C) has the following chemical structure in the molecule.

[0035] C=C=C or N=C=N.

[0036] In the above chemical structure, = represents a double bond, -- represents a covalent bond, C represents a carbon atom, and N represents a nitrogen atom. By having such a chemical structure, component (C) has excellent skeletal rigidity, and the heat resistance of the cured product of the obtained epoxy resin composition is further improved.

[0037] In the epoxy resin composition of the present invention, it is more preferable that component (C) has a straight-chain structure. Here, the straight-chain structure means a structure in which carbon atoms are connected without branching. By using the straight-chain structure of component (C), it is possible to obtain superior shaping properties under low temperature conditions.

[0038] In the epoxy resin composition of the present invention, it is also preferable that component (C) is an aromatic isocyanate compound. When component (C) is an aromatic isocyanate compound, it becomes easier to obtain a cured product having better heat resistance.

[0039] In the epoxy resin composition of the present invention, the viscosity of component (C) at 30°C is preferably 10 mPa·s or more and 1000 mPa·s or less, more preferably 10 mPa·s or more and 600 mPa·s or less, and even more preferably 10 mPa·s or more and 300 mPa·s or less. Here, the viscosity is measured with an E-type viscometer. When the viscosity at 30°C is 10 mPa·s or more, the viscosity during resin impregnation does not become too low, so that the resin does not flow out of the reinforcing fibers and is easily impregnated uniformly into the reinforcing fiber substrate, and when the viscosity at 30°C is 1000 mPa·s or less, the impregnation into the reinforcing fibers is excellent, so that a high-quality fiber-reinforced composite material can be obtained.

[0040] The epoxy resin composition of the present invention contains, as component (D), a polyisocyanate compound excluding component (C).

[0041] Examples of component (D) include 4,4'-diphenylmethane diisocyanate (MDI), 2,6-tolylene diisocyanate (2,6-TDI), 2,4-tolylene diisocyanate (2,4-TDI), naphthalene diisocyanate (NDI), 1-methoxybenzene-2,4-diisocyanate (MBDI), xylylene diisocyanate (XDI), metaxylene diisocyanate (MXDI), 1,6-hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexa Examples of such polyisocyanates include methylene diisocyanate (TMHDI), 1,12-diisocyanate dodecane (DDI), tetramethylxylylene diisocyanate (TMXDI), diphenyl sulfide-4,4'-diisocyanate, diphenyl sulfone-4,4'-diisocyanate, diphenyl ether-4,4'-diisocyanate, diphenyl ketone-4,4'-diisocyanate, polymethylene polyphenyl polyisocyanate, and those having a structure in which these are linked via methylene groups, etc. These polyisocyanate compounds may be used alone or in combination of two or more.

[0042] In the epoxy resin composition of the present invention, it is more preferable that component (D) is a polyisocyanate compound having 3 to 10 isocyanate groups in one molecule. Having 3 or more isocyanate groups in one molecule is preferable because the flowability of a molding material for a fiber-reinforced composite material using the obtained epoxy resin composition is improved. Also, having 10 or less isocyanate groups in one molecule is preferable because the cured product of the obtained epoxy resin composition exhibits high heat resistance.

[0043] In the epoxy resin composition of the present invention, it is preferable that component (D) is an aromatic isocyanate compound. By using component (D) as an aromatic isocyanate compound, the cured product of the obtained epoxy resin composition tends to exhibit higher heat resistance.

[0044] Commercially available products of component (D) include "Duranate (registered trademark)" D101, "Duranate (registered trademark)" D201 (both manufactured by Asahi Kasei Corporation), "Lupranate (registered trademark)" MS, "Lupranate (registered trademark)" MI, "Lupranate (registered trademark)" M20S, "Lupranate (registered trademark)" M11S, "Lupranate (registered trademark)" M5S, "Lupranate (registered trademark)" T-80, "Lupranate (registered trademark)" MP-102, and "Lupranate (registered trademark)" MB-301 (all manufactured by BASF INOAC Polyurethanes Co., Ltd.), Examples of such polyurethane foams include HDI, Millionate (registered trademark) MR-100, Millionate (registered trademark) MR-200, Millionate (registered trademark) MR-400, Coronate (registered trademark) T-80, Coronate (registered trademark) T-65, and Coronate (registered trademark) T-100 (all manufactured by Tosoh Corporation), Cosmonate (registered trademark) PH, Cosmonate (registered trademark) T-80, and Takenate (registered trademark) 500 (all manufactured by Mitsui Chemicals, Inc.), and Sumidur (registered trademark) N3300 (manufactured by Sumika Covestro Urethane Co., Ltd.).

[0045] In the epoxy resin composition of the present invention, the ratio Wc / Wd of the content Wc of component (C) to the content Wd of component (D) is 0.01 or more and 10 or less. When Wc / Wd is 0.01 or more, the molding material for fiber reinforced composite material using the obtained epoxy resin composition exhibits higher fluidity. When Wc / Wd is 10 or less, the cured product of the obtained epoxy resin composition tends to exhibit higher heat resistance. Wc / Wd is preferably 0.1 or more and 10 or less.

[0046] In the epoxy resin composition of the present invention, it is more preferable that both of the components (C) and (D) are aromatic isocyanate compounds. By using both of the components (C) and (D) as aromatic isocyanate compounds, it becomes easier to obtain higher heat resistance of the cured product.

[0047] The total amount of isocyanate groups in components (C) and (D) in the present invention is preferably 0.8 equivalents or more and 1.8 equivalents or less relative to the amount of hydroxyl groups in component (A). More preferably, it is 1.0 equivalents or more and 1.7 equivalents or less. When the total amount of isocyanate groups in components (C) and (D) is 0.8 equivalents or more relative to the amount of hydroxyl groups in component (A), the viscosity of the resin thickener is easily improved, which is preferable. Also, when it is 1.8 equivalents or less, the cured product of the obtained epoxy resin composition exhibits higher heat resistance, which is preferable.

[0048] The epoxy resin composition of the present invention preferably further contains the following component (E). Component (E): At least one compound selected from the group consisting of quaternary ammonium salts, phosphonium salts, imidazole compounds, and phosphine compounds.

[0049] Examples of component (E) include quaternary ammonium salts such as tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium iodide, and tetrabutylammonium bromide, phosphonium salts such as allyltriphenylphosphonium bromide, diallyldiphenylphosphonium bromide, ethyltriphenylphosphonium chloride, ethyltriphenylphosphonium iodide, tetrabutylphosphonium acetate, tetrabutylphosphonium chloride, tetrabutylphosphonium bromide, and tetrabutylphosphonium iodide, imidazole compounds such as 2-phenylimidazole and 2-methylimidazole, and phosphine compounds such as triphenylphosphine. These components (E) can be used alone or in combination of two or more. Among these, quaternary ammonium salts and / or phosphine compounds are preferred as component (E) because they can significantly shorten the curing time.

[0050] The component (E) in the present invention is preferably contained in an amount of 1 part by mass or more and 15 parts by mass or less per 100 parts by mass of the component (A). When the component (E) is 1 part by mass or more per 100 parts by mass of the component (A), a sufficient effect of improving the curability can be obtained, and when the component (E) is 15 parts by mass or less, a sufficient effect of improving the curability can be obtained without causing a decrease in heat resistance, which is preferable.

[0051] The epoxy resin composition of the present invention preferably has a viscosity of 0.01 Pa·s or more and 5 Pa·s or less, more preferably 0.01 Pa·s or more and 2 Pa·s or less, at 30°C, measured with an E-type viscometer immediately after preparation. When the viscosity at 30°C is 5 Pa·s or less, the impregnation into the reinforcing fibers is excellent. Also, when the viscosity at 30°C is 0.01 Pa·s or more, the viscosity during resin impregnation is not too low, the resin is less likely to flow out, and the reinforcing fibers are easily impregnated uniformly. Here, "immediately after preparation" refers to the point at which each component is mixed and stirred for 1 minute. Also, "viscosity immediately after preparation" refers to the viscosity of the epoxy resin composition measured after mixing each component and stirring for 1 minute.

[0052] The epoxy resin composition of the present invention preferably has a reaction initiation temperature of 5°C or higher and 80°C or lower, more preferably 10°C or higher and 60°C or lower, and more preferably 20°C or higher and 50°C or lower. If the reaction initiation temperature is 5°C or higher, it is easy to suppress a sudden increase in viscosity immediately after preparation. If the reaction initiation temperature is 80°C or lower, it is easy to suppress secondary reactions due to high temperatures, and more excellent formability is achieved. Here, the reaction initiation temperature is measured immediately after preparation using a differential calorimeter by the method described below.

[0053] The epoxy resin composition of the present invention has a viscosity at 30°C of preferably 100 Pa·s or more and 30,000 Pa·s or less, more preferably 100 Pa·s or more and 10,000 Pa·s or less, and even more preferably 100 Pa·s or more and 5,000 Pa·s or less, obtained by keeping the composition at 40°C for 24 hours. If the viscosity of the resin thickener at 30°C is 100 Pa·s or more, it is easy to suppress resin sagging when the epoxy resin composition is used as a molding material. Also, if it is 30,000 Pa·s or less, it is easy to shape the molding material using the epoxy resin composition without breaking even at low temperatures.

[0054] In the epoxy resin composition according to the present invention, the viscosity of the resin thickener at 130°C is preferably 1 Pa·s or more and 100 Pa·s or less, and more preferably 5 Pa·s or more and 100 Pa·s or less. If the viscosity of the resin thickener at 130°C is 1 Pa·s or more, a resin-rich portion is unlikely to be formed when a molding material using the epoxy resin composition is press-molded. Also, if the viscosity is 100 Pa·s or less, the substrate can be molded without underfilling up to the edge even when the molding material using the epoxy resin composition is press-molded, even if the substrate has a complex shape.

[0055] The heat resistance of the fiber-reinforced composite material obtained by using the epoxy resin composition of the present invention depends on the glass transition temperature of the resin cured product obtained by curing the epoxy resin composition. In order to obtain a fiber-reinforced composite material having high heat resistance, for example, the glass transition temperature of the resin cured product obtained by heating for 2 hours at a temperature of 140°C and completely curing is preferably in the range of 120°C to 250°C, and more preferably 130°C to 220°C. If the glass transition temperature is 120°C or higher, high heat resistance is imparted to the resin cured product obtained by curing the epoxy resin composition. If the glass transition temperature is 250°C or lower, the crosslink density of the three-dimensional crosslinked structure of the resin cured product obtained by curing the epoxy resin composition is not too high, and high mechanical properties are expressed. Here, the glass transition temperature of the epoxy resin cured product obtained by curing the epoxy resin composition is determined by measurement using a dynamic viscoelasticity measuring device (DMA). That is, a rectangular test piece cut out from the resin cured plate is used to perform DMA measurement at elevated temperature, and the temperature at the inflection point of the obtained storage modulus G' is taken as Tg. The measurement conditions were as described in the Examples.

[0056] The mechanical properties of a fiber-reinforced composite material using the epoxy resin composition of the present invention depend on the mechanical properties of the cured resin obtained by curing the epoxy resin composition. In order to obtain a fiber-reinforced composite material with high mechanical properties, it is preferable that the flexural strength of the cured resin obtained by heating for 2 hours at a temperature of 140°C and completely curing is 110 MPa or more, more preferably 120 MPa or more. If the flexural strength of the cured resin is 110 MPa or more, the fiber-reinforced composite material using the epoxy resin composition of the present invention can be used as an excellent member that does not break or deform even in an environment where it is subjected to strong external stress.

[0057] The molding material for fiber-reinforced composite materials of the present invention contains the epoxy resin composition of the present invention and reinforcing fibers. The molding material for fiber-reinforced composite materials of the present invention preferably consists of the epoxy resin of the present invention and reinforcing fibers.

[0058] The molding material for a fiber-reinforced composite material of the present invention is not particularly limited with respect to the type and length of the reinforcing fibers, the content ratio of the reinforcing fibers to the resin, and the like.

[0059] When the reinforcing fibers are used in a continuous form, examples of the reinforcing fibers include long fibers aligned in one direction, single tows, woven fabrics, knits, and braids. The reinforcing fibers preferably have an average fiber diameter of 3 μm to 12 μm and a reinforcing fiber mass fraction of 40% to 90%. If the reinforcing fiber mass fraction is 40% or more, the mass of the obtained fiber-reinforced composite material is not excessive, and the advantages of the fiber-reinforced composite material having excellent specific strength and specific elastic modulus are easily exhibited. If the reinforcing fiber mass fraction is 90% or less, the impregnation of the epoxy resin composition into the reinforcing fibers is easily excellent. Examples of fiber-reinforced composite materials obtained using such continuous fibers include prepregs and towpregs.

[0060] When discontinuous fibers are used as the form of reinforcing fibers, examples of the fibers include fiber structures such as nonwoven fabrics and mats, and the reinforcing fibers are preferably used with a fiber length of 5 mm to 100 mm, an average fiber diameter of 3 μm to 12 μm, and a reinforcing fiber mass fraction of 40% to 90%. If the reinforcing fiber mass fraction is 40% or more, the mass of the obtained fiber-reinforced composite material is not excessive, and the advantages of the fiber-reinforced composite material having excellent specific strength and specific elastic modulus are easily exhibited. In addition, if the reinforcing fiber mass fraction is 90% or less, the impregnation of the epoxy resin composition into the reinforcing fibers is easily excellent. Examples of molding materials for fiber-reinforced composite materials obtained using such discontinuous fibers include BMC and SMC. Among these, SMC is particularly preferably used from the viewpoints of productivity and freedom of shape of the molded body.

[0061] The form of the bundle of discontinuous fibers is not particularly limited, and various techniques can be applied. In the plane of the bundle of fibers where the width in the direction perpendicular to the arranging direction of the reinforcing fibers is maximum, the acute angles formed by the sides of the arrangement of the ends of the reinforcing fibers in the bundle of fibers with respect to the arranging direction of the reinforcing fibers are angle a and angle b, respectively. It is preferable that the angles a and b are 2° or more and 30° or less. The smaller the angles a and b of the sides formed by the arrangement of the ends of the reinforcing fibers in the bundle of fibers with respect to the arranging direction of the reinforcing fibers, the higher the homogeneity of the bundle of fibers and the resin becomes, so that the effect of improving the surface quality and strength of the fiber-reinforced composite material molded using the bundle of fibers is large. When the angles a and b are 30° or less, the effect is remarkable. However, on the other hand, the smaller the angles a and b are, the lower the handleability of the bundle of fibers themselves becomes. In addition, the smaller the angle between the arranging direction of the reinforcing fibers and the cutting blade, the lower the stability in the cutting process. Therefore, the angles a and b are preferably 2° or more. The angles a and b are more preferably 3° or more and 25° or less. In view of the balance between the surface quality and strength improvement effect of the fiber-reinforced composite material and the processability in the manufacturing process of the bundle-shaped assembly, the angles a and b are even more preferably 5° or more and 15° or less.

[0062] Means for cutting a continuous reinforcing fiber bundle for producing a bundle-like aggregate of discontinuous reinforcing fibers include, for example, rotary cutters such as a guillotine cutter, a roving cutter, etc. The continuous reinforcing fiber bundle is inserted into the cutting means and cut in a state in which the longitudinal direction of the continuous reinforcing fiber bundle and the direction of a cutting blade equipped on the cutting means are relatively oblique.

[0063] The method for producing the molding material for fiber-reinforced composite materials of the present invention is not particularly limited, but for example, the epoxy resin composition of the present invention is impregnated into reinforcing fibers by a method suitable for the shape of the reinforcing fibers, and then the resin composition is kept at a temperature of about room temperature to about 80°C for several hours to several days to reach a semi-cured state in which the viscosity increase of the resin composition is saturated, thereby obtaining the molding material for fiber-reinforced composite materials of the present invention. Here, the semi-cured state in which the viscosity increase of the resin composition is saturated is called a resin thickener. In the evaluation of the present invention, the thickening condition is adopted in which the epoxy resin composition is kept at 40°C for 24 hours to reach a semi-cured state in which the viscosity increase of the resin composition is saturated.

[0064] The reinforcing fiber is not particularly limited, and examples thereof include glass fiber, carbon fiber, graphite fiber, aramid fiber, boron fiber, alumina fiber, and silicon carbide fiber. Two or more of these reinforcing fibers may be mixed and used. The reinforcing fiber is preferably carbon fiber or graphite fiber, since it is easy to obtain a lighter and more durable molded product. In particular, the reinforcing fiber is preferably carbon fiber, since it is easy to obtain an excellent specific elastic modulus and specific strength, even in applications where there is a high demand for lighter materials and higher strength.

[0065] As the carbon fiber, any kind of carbon fiber can be used depending on the application, but from the viewpoint of impact resistance, it is preferable that the carbon fiber has a tensile modulus of at most 400 GPa. From the viewpoint of strength, it is preferable that the carbon fiber has a tensile strength of 4.4 GPa or more and 6.5 GPa or less, since it is easy to obtain a composite material having high rigidity and mechanical strength. It is also preferable that the carbon fiber has a tensile elongation of 1.7% or more and 2.3% or less. Therefore, a carbon fiber having the properties of a tensile modulus of at least 230 GPa, a tensile strength of at least 4.4 GPa, and a tensile elongation of at least 1.7% is most suitable.

[0066] Examples of commercially available carbon fibers include "TORAYCA (registered trademark)" T800G-24K, "TORAYCA (registered trademark)" T800S-24K, "TORAYCA (registered trademark)" T700G-24K, "TORAYCA (registered trademark)" T300-3K, and "TORAYCA (registered trademark)" T700S-12K (all manufactured by Toray Industries, Inc.). The method for producing a fiber-reinforced composite material using the epoxy resin composition according to the present invention is not particularly limited, but the hand lay-up method, the filament winding method, the pultrusion method, the resin transfer molding (RTM) method, the autoclave molding method of prepreg, and further, the press molding method of molding materials for fiber-reinforced composite materials such as prepreg, towpreg, bulk molding compound (BMC), sheet molding compound (SMC), etc. are preferably used.

[0067] The fiber-reinforced composite material of the present invention is obtained by curing the molding material for fiber-reinforced composite material of the present invention. In such fiber-reinforced composite materials, particularly in the case of fiber-reinforced composite materials used in the aircraft and automobile fields, high heat resistance and mechanical properties such as bending strength are required. The fiber-reinforced composite material of the present invention has excellent heat resistance and mechanical properties because the glass transition temperature of the epoxy resin cured product, which is the matrix resin, can be usually set to 120°C or more and 250°C or less, and the bending strength of the epoxy resin cured product can be set to 110 MPa or more. In addition, the molding material for fiber-reinforced composite material of the present invention does not flow only in advance during press molding, and exhibits excellent fluidity regardless of the molding temperature, and a fiber-reinforced composite material with very high homogeneity between the fiber and the resin can be obtained.

[0068] The method for producing the fiber-reinforced composite material of the present invention is not particularly limited, but the hand lay-up method, the filament winding method, the pultrusion method, the resin transfer molding (RTM) method, the autoclave molding method of prepreg, and further, the press molding method of molding materials for fiber-reinforced composite materials such as prepreg, towpreg, bulk molding compound (BMC), sheet molding compound (SMC), etc. are preferably used. EXAMPLES

[0069] The epoxy resin composition, molding material for a fiber-reinforced composite material, and fiber-reinforced composite material of the present invention will be described in more detail below with reference to examples.

[0070] <Resin raw materials> The following resin raw materials were used to obtain the epoxy resin compositions of the Examples and Comparative Examples. The numerical values ​​of each component in the column for the epoxy resin composition in the tables indicate the content, and the unit ("parts") is "parts by mass" unless otherwise specified.

[0071] 1. Component (A): Epoxy resin "Epotohto (registered trademark)" YD128 (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.): liquid bisphenol A type epoxy resin (hydroxyl equivalent: 1250 g / mol) "jER (registered trademark)" 154 (manufactured by Mitsubishi Chemical Corporation): Phenol novolac type epoxy resin (without hydroxyl groups) "jER (registered trademark)" 1001 (manufactured by Mitsubishi Chemical Corporation): solid bisphenol A type epoxy resin (hydroxyl equivalent: 313 g / mol) SR-DGE (manufactured by Sakamoto Pharmaceutical Co., Ltd.): diglycerol-type epoxy (hydroxyl equivalent: 435 g / mol) "Denacol (registered trademark)" EX-614 (manufactured by Nagase ChemteX Corporation): sorbitol-type epoxy resin (hydroxyl group equivalent: 229 g / mol).

[0072] 2. Component (B): Hardener "jER Cure (registered trademark)" DICY7 (manufactured by Mitsubishi Chemical Corporation): dicyandiamide.

[0073] 3. Component (C): Diisocyanate compound having consecutive double bonds, an alicyclic structure, or a heterocyclic structure "Desmodur (registered trademark)" N3400 (manufactured by Sumika Covestro Urethane Co., Ltd.): HDI uretdione "Desmodur (registered trademark)" I (manufactured by Sumika Covestro Urethane Co., Ltd.): isophorone diisocyanate "Desmodur (registered trademark)" W (manufactured by Sumika Covestro Urethane Co., Ltd.): dicyclohexylmethane-4,4'-diisocyanate · “Lupranate (registered trademark)” MM-103 (manufactured by BASF INOAC Polyurethanes Ltd.): Carbodiimide-modified MDI.

[0074] 4. Component (D): Polyisocyanate compounds excluding component (C) "Sumidur (registered trademark)" N3300 (manufactured by Sumika Covestro Urethane Co., Ltd.): HDI isocyanate "Lupranate (registered trademark)" M20S (manufactured by BASF INOAC Polyurethanes Co., Ltd.): Polymeric MDI (polymethylene polyphenyl polyisocyanate) "Lupranate (registered trademark)" MI (manufactured by BASF INOAC Polyurethanes Co., Ltd.): Monomeric MDI (diphenylmethane diisocyanate) "Lupranate (registered trademark)" MP102 (manufactured by BASF INOAC Polyurethanes Co., Ltd.): urethane-modified MDI ·“Coronate (registered trademark)” T-100 (manufactured by Tosoh Corporation): TDI.

[0075] 5. Component (E): at least one compound selected from the group consisting of quaternary ammonium salts, phosphonium salts, imidazole compounds, and phosphine compounds. Tetrabutylammonium bromide (Tokyo Chemical Industry Co., Ltd.) Tetraphenylphosphonium bromide (Tokyo Chemical Industry Co., Ltd.).

[0076] <Preparation of Epoxy Resin Composition> Each component was mixed in the amount (parts by mass) shown in the table to prepare an epoxy resin composition.

[0077] <Measurement of Viscosity of Epoxy Resin Composition Immediately After Preparation> The specimen to be measured was measured at 30°C using an E-type viscometer equipped with a standard cone rotor (1°34' x R24) in accordance with "Viscosity measurement method using a cone-plate type rotational viscometer" in JIS Z8803 (1991). The E-type viscometer used was a TVE-30H manufactured by Tokimec Co., Ltd. The specimen was an epoxy resin composition immediately after preparation.

[0078] <Measurement of reaction initiation temperature of epoxy resin composition immediately after preparation> Using a sample to be measured, a differential calorimeter DSC25 manufactured by TA Corp. was used to measure the change in heat generation amount of the epoxy resin composition when the temperature was changed at 10°C intervals in the temperature range from 20°C to 130°C and kept constant at each temperature. In the obtained heat generation curve, the lowest temperature among the temperatures at which the heat generation amount reached a maximum within 5 minutes was determined as the reaction initiation temperature.

[0079] <Measurement of formability of epoxy resin composition after thickening at 10°C> The specimen to be measured was manually shaped into a hat-shaped mold and left for 5 minutes. Those that maintained their shape for more than 5 minutes without peeling from the mold were categorized as "A", those that maintained their shape for 1 to 5 minutes without peeling from the mold were categorized as "B", and those that maintained their shape for less than 1 minute without peeling from the mold, those that broke, or those that could not maintain their shape were categorized as "C". The hat-shaped aluminum mold used here was 300 mm long, 40 mm high, 40 mm wide at the top, 22 mm wide at the flange, and 15 mm radius at the curvature.

[0080] <Viscosity measurement of epoxy resin composition after thickening> Using a DMA (ARES manufactured by TA Instruments), the sample to be measured was placed on a stage heated to 30°C, the temperature was raised at 10°C / min, and the viscosity was measured. Note that the sample used was an epoxy resin composition containing the various components mixed and kept at 40°C for 24 hours. For example, the viscosity at 30°C is the viscosity when the sample reached 30°C, and the viscosity at each temperature was measured in the same manner.

[0081] <Production of Resin Curing Product> After degassing the epoxy resin composition prepared in the above <Preparation of Epoxy Resin Composition> in a vacuum, it was injected into a mold set to a thickness of 2 mm using a 2-mm-thick spacer made of "Teflon (registered trademark)". It was cured at a temperature of 140 °C for 2 hours to obtain a resin curing product with a thickness of 2 mm.

[0082] <Measurement of Glass Transition Temperature Tg of Resin Curing Product> A test piece with a width of 12.7 mm and a length of 40 mm was cut out from the resin curing product, and Tg was measured using DMA (ARES manufactured by TA Instruments). The measurement conditions were a heating rate of 5 °C / min. The temperature at the inflection point of the storage elastic modulus G' obtained from the measurement was defined as Tg.

[0083] <Measurement of Bending Strength of Resin Curing Product> The bending strength of the resin curing product obtained as described above was measured according to JIS K7074:1988. A test piece cut out to a width of 15 mm and a length of 100 mm was measured by a three-point bending test using an Instron universal testing machine (manufactured by Instron). The measurement was carried out at a crosshead speed of 5 mm / min, a span of 80 mm, a specimen diameter of 5 mm, and a fulcrum diameter of 2 mm, and the bending strength was measured. The bending strength was obtained by calculating the converted values measured for 5 samples and taking the average as the bending strength.

[0084] <Production of SMC> As the carbon fiber, "Torayca (registered trademark)" T700S-12K (manufactured by Toray Industries, Inc.) was used. By cutting the continuous carbon fiber strands at a desired angle and spraying them so as to uniformly disperse the bundle-like aggregate of carbon fibers, a discontinuous carbon fiber nonwoven fabric with an isotropic fiber orientation was obtained. A rotary cutter was used as the cutting device. The blade interval was set to 30 mm. Also, the basis weight of the discontinuous carbon fiber nonwoven fabric was 1 kg / m 2It was. The discontinuous carbon fiber nonwoven fabric was sandwiched between polyethylene films coated with the above epoxy resin composition so that the carbon fiber weight content of the resulting SMC was 50%, pressed with a roller, and impregnated with the above epoxy resin composition to obtain a sheet-like SMC precursor. This SMC precursor was held at 40 °C for 24 hours to thicken the resin, thereby obtaining SMC.

[0085] <Measurement of the formability of SMC at 10 °C> The specimen to be measured was manually shaped into a hat-shaped mold and then left for 5 minutes. At this time, those that maintained their form without peeling from the mold for more than 5 minutes were designated as "A", those that maintained their form without peeling from the mold for 1 minute or more and 5 minutes or less were designated as "B", those that maintained their form for less than 1 minute without peeling from the mold, or those in which the specimen broke, or those in which the shape of the specimen could not be maintained were designated as "C". Here, for the hat shape, an aluminum mold with a total length of 300 mm, a total height of 40 mm, a top surface width of 40 mm, a flange width of 22 mm, and a radius of curvature of 15 mm was used.

[0086] (Example 1 , 2, Reference Examples 3 and 4, Example 5 ~18) Resin compositions were prepared according to the preparation of the above resin composition with the types and contents (parts by mass) of each component described in Table 1, and the reaction start temperature and viscosity at 30 °C were measured. Also, after each epoxy resin composition was held at 40 °C for 24 hours to thicken, the viscosities at 30 °C and 130 °C were measured respectively, and the formability was measured under the condition of 10 °C. Furthermore, using the epoxy resin composition before thickening, a resin cured product and SMC of the epoxy resin composition were prepared. The reaction start temperature of the epoxy resin composition immediately after preparation was 80 °C or lower, and the viscosity at 30 °C was 5.0 Pa·s or lower. Also, the viscosity at 30 °C after thickening was 100 Pa·s or higher, the viscosity at 130 °C was 1 Pa·s or higher and 100 Pa·s or lower, the formability under the condition of 10 °C was B or higher, and it was excellent in formability under low temperature conditions. Furthermore, the Tg of the resin cured product obtained by curing such an epoxy resin composition was 120 °C or higher, and the flexural strength was 110 MPa or higher. Also, the formability of the SMC using such an epoxy resin composition under the condition of 10 °C was B or higher.

[0087] Comparative Example 1 Resin compositions, cured resin products of epoxy resin compositions, and SMCs were prepared in the same manner as in Examples 1 to 18, except that the types and contents (parts by mass) of each component were as shown in Table 2, and various measurements were performed. The reaction initiation temperature of the epoxy resin composition immediately after preparation was poor at 100°C, and the viscosity at 30°C was 5.0 Pa·s or less. However, the viscosity at 30°C after thickening was good at 120 Pa·s, but poor at 130°C at 0.3 Pa·s, and the formability at 10°C was C, indicating poor formability at low temperatures. Furthermore, the Tg of the cured resin product obtained by curing the epoxy resin composition was poor at 115°C, and the bending strength was 108 MPa, indicating poor mechanical properties. Moreover, the formability of the SMC using the epoxy resin composition at 10°C was C.

[0088] Comparative Example 2 Resin compositions, cured resin products of epoxy resin compositions, and SMCs were prepared in the same manner as in Examples 1 to 18, except that the types and contents (parts by mass) of each component were as shown in Table 2, and various measurements were performed. The reaction initiation temperature of the epoxy resin composition immediately after preparation was poor at 90°C, and the viscosity at 30°C was 5.0 Pa·s or less. However, although the viscosity at 30°C after thickening was good at 1590 Pa·s, the viscosity at 130°C was poor at 0.7 Pa·s, and the formability at 10°C was C, indicating poor formability at low temperatures. Furthermore, the Tg of the cured resin product obtained by curing the epoxy resin composition was poor at 110°C, and the bending strength was 107 MPa, indicating poor mechanical properties. Moreover, the formability of the SMC using the epoxy resin composition at 10°C was C.

[0089] Comparative Example 3 Resin compositions, cured resin products of epoxy resin compositions, and SMCs were prepared in the same manner as in Examples 1 to 18, except that the types and contents (parts by mass) of each component were as shown in Table 2, and various measurements were performed. The reaction initiation temperature of the epoxy resin composition immediately after preparation was poor at 90°C, and the viscosity at 30°C was 5.0 Pa·s or less. However, after thickening, the viscosity at 30°C was poor at 0.4 Pa·s and the viscosity at 130°C was poor at 0.02 Pa·s, and the formability at 10°C was C, indicating poor formability at low temperatures. Furthermore, the Tg of the cured resin product obtained by curing the epoxy resin composition was poor at 106°C, and the bending strength was 80 MPa, indicating poor mechanical properties. Moreover, the formability of the SMC using the epoxy resin composition at 10°C was C.

[0090] Comparative Example 4 Resin compositions, cured resin products of epoxy resin compositions, and SMCs were prepared in the same manner as in Examples 1 to 18, except that the types and contents (parts by mass) of each component were as shown in Table 2, and various measurements were performed. The reaction initiation temperature of the epoxy resin composition immediately after preparation was poor at 130°C, and the viscosity at 30°C was poor at 5.0 Pa·s or more. In addition, the viscosity at 30°C after thickening was poor at 2 Pa·s and at 130°C was poor at 0.01 Pa·s, and the formability at 10°C was C, indicating poor formability at low temperatures. Furthermore, the Tg of the cured resin product obtained by curing the epoxy resin composition was poor at 80°C, and the bending strength was 87 MPa, indicating poor mechanical properties. In addition, the formability of the SMC using the epoxy resin composition at 10°C was C.

[0091] Comparative Example 5 Resin compositions, cured resins of epoxy resin compositions, and SMCs were prepared in the same manner as in Examples 1 to 18, except that the types and contents (parts by mass) of each component were as shown in Table 2, and various measurements were performed. The reaction initiation temperature of the epoxy resin composition immediately after preparation was 80°C, which was good, and the viscosity at 30°C was 5.0 Pa·s or less. In addition, the viscosity at 30°C after thickening was 140 Pa·s, which was good, but the viscosity at 130°C was 0.4 Pa·s, which was poor, and the formability at 10°C was C, which was poor under low temperature conditions. Furthermore, the Tg of the cured resin obtained by curing the epoxy resin composition was poor at 117°C, and the bending strength was 109 MPa, which was poor in mechanical properties. In addition, the formability of the SMC using the epoxy resin composition at 10°C was C.

[0092] Comparative Example 6 Resin compositions, cured resin products of epoxy resin compositions, and SMCs were prepared in the same manner as in Examples 1 to 18, except that the types and contents (parts by mass) of each component were as shown in Table 2, and various measurements were performed. The reaction initiation temperature of the epoxy resin composition immediately after preparation was poor at 100°C, and the viscosity at 30°C was 5.0 Pa·s or less. In addition, the viscosity at 30°C after thickening was poor at 80 Pa·s and at 130°C was poor at 0.1 Pa·s, and the formability at 10°C was C, indicating poor formability at low temperatures. Furthermore, the Tg of the cured resin product obtained by curing the epoxy resin composition was poor at 108°C, and the bending strength was 100 MPa, indicating poor mechanical properties. In addition, the formability of the SMC using the epoxy resin composition at 10°C was C.

[0093] [Table 1-1]

[0094] [Table 1-2]

[0095] [Table 1-3]

[0096]

Table 2

Claims

1. An epoxy resin composition comprising all of the following components (A) to (D), in which the content of component (A) is 50% by mass or more and 95% by mass or less based on a total mass of the epoxy resin composition (100% by mass), and the ratio Wc / Wd of the content Wc of component (C) to the content Wd of component (D) is 0.1 or more and 10 or less. Component (A): Epoxy resin Component (B): Hardener Component (C): Diisocyanate compound having an N=C=N chemical structure or a heterocyclic structure Component (D): Polyisocyanate compounds excluding diisocyanate compounds having consecutive double bonds, alicyclic structures, or heterocyclic structures

2. 2. The epoxy resin composition according to claim 1, wherein the viscosity of component (C) at 30° C. is 10 mPa·s or more and 1000 mPa·s or less.

3. 3. The epoxy resin composition according to claim 1, wherein component (C) has the following chemical structure in the molecule: N=C=N

4. 4. The epoxy resin composition according to claim 1, wherein the component (C) has a linear structure.

5. 5. The epoxy resin composition according to claim 1, wherein the component (D) is a polyisocyanate compound having 3 to 10 isocyanate groups in one molecule.

6. 6. The epoxy resin composition according to claim 1, wherein both of the component (C) and the component (D) are aromatic isocyanate compounds.

7. The epoxy resin composition according to any one of claims 1 to 6, further comprising the following component (E): Component (E): At least one compound selected from the group consisting of quaternary ammonium salts, phosphonium salts, imidazole compounds, and phosphine compounds.

8. The epoxy resin composition according to any one of claims 1 to 7, wherein the reaction initiation temperature is 5°C or higher and 80°C or lower.

9. 9. The epoxy resin composition according to claim 1, wherein a viscosity of a resin thickener obtained by keeping at 40° C. for 24 hours is 100 Pa s or more and 30,000 Pa s or less at 30° C., and a viscosity of the resin thickener at 130° C. is 1 Pa s or more and 100 Pa s or less.

10. 10. The epoxy resin composition according to claim 1, wherein the component (A) is a hydroxyl group-containing epoxy resin that is liquid at 30°C.

11. The epoxy resin composition according to any one of claims 1 to 10, wherein the component (B) is dicyandiamide or a derivative thereof.

12. A molding material for a fiber-reinforced composite material, comprising the epoxy resin composition according to any one of claims 1 to 11 and reinforcing fibers.

13. The molding material for a fiber-reinforced composite material according to claim 12, wherein the reinforcing fibers are carbon fibers.

14. A fiber-reinforced composite material obtained by curing the molding material for a fiber-reinforced composite material according to claim 12 or 13.

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