Epoxy resin composition, prepreg, and fiber-reinforced composite material

Abstract

The purpose of the present invention is to provide an epoxy resin composition which can be cured to obtain an epoxy resin cured product excelling in balance among flame retardancy, thermal conductivity and heat resistance, and a prepreg and a fiber-reinforced composite material using the same.　The epoxy resin composition including an epoxy resin which achieves this purpose includes [A] a bifunctional naphthalene epoxy resin, [B] a phosphorus-containing curing agent, and [C] thermally conductive particles.

Description

Epoxy resin composition, prepreg and fiber-reinforced composite material

[0001] The present invention relates to an epoxy resin composition, a prepreg, and a fiber-reinforced composite material having excellent fire resistance.

[0002] Composite materials, which use reinforcing fibers such as carbon fibers or glass fibers and a thermosetting resin such as epoxy resin or phenolic resin as a matrix resin, are used in a wide range of applications, including sports and leisure goods such as fishing rods and tennis and badminton rackets, as well as various industrial equipment, civil engineering and construction, and aerospace. Mechanical properties such as strength and elastic modulus have traditionally been important for these composite materials in terms of weight reduction, and they have been particularly well-suited for use as structural materials for aircraft and vehicles. However, as the use of composite materials has expanded, additional functionalities such as flame retardancy, heat conductivity, and electrical conductivity have also become increasingly desirable.

[0003] Regarding flame retardancy, methods for making composite materials flame retardant include a method of promoting the formation of char, which is a graphite-like carbonized layer formed on the surface of the matrix resin during combustion, thereby suppressing the diffusion of decomposition gases when the resin is thermally decomposed, a method of suppressing heat generation during combustion of the resin, and a method of suppressing decomposition of the resin in the early stages of combustion by the heat absorption effect of an inorganic filler containing a heat-absorbing agent.

[0004] To promote char formation in matrix resins, additives that make the material less flammable, known as flame retardants, are often added. Phosphorus compounds are commonly used as flame retardants, and several phosphorus compounds are used industrially. It is believed that phosphorus compounds convert to polyphosphoric acid, which has a dehydrating and carbonizing effect, during combustion, thereby promoting char formation. Flame retardant technologies using such phosphorus compounds include adding additive-type flame retardants such as red phosphorus or phosphate esters to epoxy resin compositions, and using reactive flame retardants that contain phosphorus atoms in their molecules and react with resins to introduce phosphorus atoms into the crosslinked structure of the resin.

[0005] Patent Document 1 reports a technology for obtaining a material that has excellent viscosity stability and char formation promoting effects as well as excellent mechanical properties, by using a flame retardant technology that uses an epoxy resin composition that contains a reactive diluent having a specific structure and an amine-based curing agent that contains a phosphorus atom and has a specific structure.

[0006] Furthermore, methods for promoting the thermal conductivity of composite materials include a method of forming a thermally conductive path inside the resin using a thermally conductive filler, and a method of using a resin with high thermal conductivity.

[0007] Patent Document 2 reports a technology for obtaining a thermally conductive resin sheet having excellent thermal conductivity, heat resistance, and adhesive strength by containing boron nitride particles as a thermally conductive filler and using a specific phenoxy resin and a phenolic curing agent in combination.

[0008] Patent Document 3 introduces a technology for obtaining an epoxy resin composition for an LED heat dissipation component, which has excellent thermal conductivity, fluidity, and moldability, and a cured product thereof, by using a resin containing a large amount of graphite particles as a thermally conductive filler and having a low melt viscosity.

[0009] International Publication No. 2019 / 082595 Japanese Patent Application Laid-Open No. 2016-155946 Japanese Patent Application Laid-Open No. 2020-164592

[0010] However, when the epoxy resin compositions described in these patent documents are used, the flame retardancy or heat resistance is insufficient, making it difficult to meet the flame retardancy and heat resistance requirements in the aerospace field. Furthermore, since it is necessary to blend a large amount of thermally conductive filler in order to obtain sufficient thermal conductivity, the resulting epoxy resin cured product has poor mechanical properties and poor fluidity, making it difficult to handle.

[0011] Therefore, an object of the present invention is to solve the above-mentioned problems, that is, to provide an epoxy resin composition that can give an epoxy resin cured product that has an excellent balance of flame retardancy, thermal conductivity, mechanical properties, and heat resistance, as well as a prepreg and a fiber-reinforced composite material that use the same.

[0012] The epoxy resin composition of the present invention is an epoxy resin composition containing an epoxy resin and has the following configuration: 1. It contains the following components [A] to [C]: [A] a difunctional naphthalene-type epoxy resin, [B] a phosphorus-containing curing agent, and [C] thermally conductive particles. 2. The epoxy resin composition according to above 1, wherein the mass content ratio of component [A] to component [B] is 0.3 to 1.5, and further contains, as component [A'], a tri- or tetrafunctional epoxy resin having two or less benzene ring structures, and the total amount of components [A] and [A'] is 90 parts by mass or more per 100 parts by mass of the total amount of epoxy resins. 3. The epoxy resin composition according to above 1 or 2, wherein component [A] has a structure represented by the following general formula (1) or (2):

[0013]

[0014] (In general formula (1), R １ represents a hydrocarbon group having 1 to 4 carbon atoms. 1 represents an integer of 0 to 3.

[0015]

[0016] (In general formula (2), R ２ and R ３ each independently represent a hydrocarbon group having 1 to 4 carbon atoms. m and n each independently represent an integer of 0 to 3.) 4. The epoxy resin composition according to any one of 1 to 3 above, wherein component [B] contains at least one amine-based curing agent selected from the group consisting of amine-based curing agents having a structure represented by the following general formula (3) and amine-based curing agents having a structure represented by the following general formula (4):

[0017]

[0018]

[0019] (In general formula (3), R ４ represents a hydrocarbon group having 1 to 4 carbon atoms. ５represents a hydrogen atom or an amino group.) 5. The epoxy resin composition according to any one of the above 1 to 4, wherein the epoxy resin composition contains 0.5 to 25 mass% of a filler made of graphite as component [C]. 6. The epoxy resin composition according to any one of the above 1 to 5, wherein the content of component [A] is 10 to 50 mass parts per 100 mass parts of the total epoxy resin. 7. The epoxy resin composition according to any one of the above 1 to 6, further containing component [D] a thermoplastic resin.

[0020] The prepreg of the present invention is a prepreg obtained by impregnating reinforcing fibers with the above-mentioned epoxy resin composition.

[0021] Furthermore, the fiber-reinforced composite material of the present invention is a fiber-reinforced composite material obtained by curing the above-mentioned prepreg, or a fiber-reinforced composite material containing reinforcing fibers and a cured epoxy resin obtained by curing the above-mentioned epoxy resin composition.

[0022] The present invention makes it possible to provide an epoxy resin composition that can be cured to give an epoxy resin cured product that has an excellent balance of flame retardancy, thermal conductivity, mechanical properties, and heat resistance, as well as a prepreg using the same.

[0023] The epoxy resin composition of the present invention comprises component [A] a difunctional naphthalene-type epoxy resin, component [B] a phosphorus-containing curing agent, and component [C] thermally conductive particles.

[0024] The bifunctional naphthalene-type epoxy resin of component [A] is a bifunctional epoxy resin having one or more naphthalene ring structures, and epoxy resins having one or two naphthalene ring structures are preferably used. Among these, if the structure of component [A] is represented by the following general formula (1) or (2), it is preferred because the epoxy resin cured product obtained by curing has excellent flame retardancy, thermal conductivity, heat resistance, or mechanical properties.

[0025]

[0026] (In general formula (1), R １represents a hydrocarbon group having 1 to 4 carbon atoms. 1 represents an integer of 0 to 3. In general formula (1), R １ is preferably a hydrocarbon group having 1 or 2 carbon atoms, and l is preferably 0 or 1.

[0027]

[0028] (In general formula (2), R ２ and R ３ each independently represents a hydrocarbon group having 1 to 4 carbon atoms; m and n each independently represent an integer of 0 to 3. In general formula (2), R ２ and R ３ are each independently preferably a hydrocarbon group having 1 or 2 carbon atoms, and m and n are each independently preferably 0 or 1.

[0029] Specific examples of component [A] include epoxy resins having a structure obtained by reacting a precursor such as 1,2-naphthalenediol, 1,3-naphthalenediol, 1,4-naphthalenediol, 1,5-naphthalenediol, 1,6-naphthalenediol, 1,7-naphthalenediol, 1,8-naphthalenediol, 2,3-naphthalenediol, 2,6-naphthalenediol, 2,7-naphthalenediol, 2-methyl-1,4-naphthalenediol, 3-methyl-1,8-naphthalenediol, 1-(2-hydroxy-naphthalen-1-ylmethyl)-naphthalen-2-ol, 1-(2-hydroxy-naphthalen-1-ylmethyl)-naphthalen-7-ol, or 1-(7-hydroxy-naphthalen-1-ylmethyl)-naphthalen-7-ol with epichlorohydrin in the presence of a basic catalyst, thereby converting the hydroxyl groups of the precursor to glycidyl ether groups. Among these, epoxy resins containing two naphthalene ring structures, as exemplified by general formula (2), are preferably used, and for example, epoxy resins having a structure obtained using 1-(2-hydroxy-naphthalen-1-ylmethyl)-naphthalen-2-ol as a precursor are particularly preferred because they have two rigid naphthalene skeletons and therefore tend to provide excellent heat resistance. The epoxy resins listed above as examples of component [A] may be used alone or in combination of two or more types.

[0030] In order to improve the crosslink density of the cured epoxy resin material and obtain a high thermal diffusivity, the epoxy resin composition of the present invention preferably further contains, as component [A'], a tri- or tetra-functional epoxy resin having two or less benzene ring structures. Here, the term "benzene ring structure" refers to a structure in which the benzene ring exists as an isolated aromatic ring, and does not include ring structures in which aromatic rings are condensed. Representative examples of such tri- or tetra-functional epoxy resins having two or less benzene ring structures include tri- or tetra-functional epoxy resins having one benzene ring structure and tetra-functional epoxy resins having two benzene ring structures. Examples of tri- or tetra-functional epoxy resins having one benzene ring structure include aminophenol-type epoxy resins such as N,N,O-triglycidyl-m-aminophenol, N,N,O-triglycidyl-p-aminophenol, and N,N,O-triglycidyl-4-amino-3-methylphenol. Examples of tetrafunctional epoxy resins having two benzene ring structures include diamine-type epoxy resins such as N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane, N,N,N',N'-tetraglycidyl-2,2'-diethyl-4,4'-diaminodiphenylmethane, and N,N,N',N'-tetraglycidyl-m-xylylenediamine. Among these, the use of tetrafunctional epoxy resins having two benzene ring structures is preferred because it improves crosslink density and makes it easier to obtain a cured epoxy resin product with high heat resistance and thermal diffusivity. The epoxy resins listed above as examples of component [A'] may be used alone or in combination of two or more.

[0031] The epoxy resin composition of the present invention may contain an epoxy resin other than components [A] and [A']. Examples of epoxy resins other than components [A] and [A'] include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol AD-type epoxy resins, and bisphenol S-type epoxy resins, epoxy resins having a biphenyl skeleton, monofunctional or tri- or higher functional epoxy resins having a naphthalene skeleton, and epoxy resins having a dicyclopentadiene skeleton.

[0032] The content of component [A] in the epoxy resin composition of the present invention is preferably 10 to 50 parts by mass relative to 100 parts by mass of the total epoxy resin, i.e., when the total mass of all epoxy resins contained in the epoxy resin composition, including component [A], is taken as 100 parts by mass, from the viewpoint of improving the mechanical properties of the resulting cured epoxy resin product and fiber-reinforced composite material. The content is more preferably 20 to 40 parts by mass.

[0033] Furthermore, the total content of component [A] and component [A'] in the epoxy resin composition of the present invention is preferably 90 parts by mass or more per 100 parts by mass of the total amount of epoxy resin, from the viewpoint of improving the heat resistance of the cured epoxy resin product obtained by curing.

[0034] Component [B] used in the epoxy resin composition of the present invention is a phosphorus-containing curing agent, i.e., a curing agent containing a phosphorus atom in its molecular structure. The curing agent referred to here is a curing agent for epoxy resins, and is a compound having an active group capable of reacting with an epoxy group. It is particularly preferred that component [B] contain at least one amine-based curing agent selected from the group consisting of amine-based curing agents having a structure represented by the following general formula (3) and amine-based curing agents having a structure represented by the following general formula (4), since this provides excellent flame retardancy and mechanical properties. A more preferred embodiment is one in which component [B] is used in combination with component [A] represented by general formula (1) or (2).

[0035]

[0036]

[0037] (In general formula (3), R ４ represents a hydrocarbon group having 1 to 4 carbon atoms. ５ represents a hydrogen atom or an amino group. ４ If the number of carbon atoms in R is small, the hydrophobicity of the phosphorus-containing curing agent having the structure represented by general formula (3) will be low, and the moisture absorption resistance of the obtained epoxy resin cured product may be low. ４ The carbon number of R is preferably 2 to 4. ４In general formula (4), R ５ When R is an amino group, the crosslinking density increases too much, and the toughness of the obtained epoxy resin cured product may be low. ５ is preferably a hydrogen atom.

[0038] Examples of phosphorus-containing curing agents represented by general formula (3) include bis(4-aminophenyl)methylphosphine oxide, bis(3-aminophenyl)methylphosphine oxide, bis(2-aminophenyl)methylphosphine oxide, bis(4-aminophenyl)ethylphosphine oxide, bis(3-aminophenyl)ethylphosphine oxide, bis(2-aminophenyl)ethylphosphine oxide, bis(4-aminophenyl)n-propylphosphine oxide, bis(3-aminophenyl)n-propylphosphine oxide, bis(4-aminophenyl)isopropylphosphine oxide, bis(3-aminophenyl)isopropylphosphine oxide, bis(4-aminophenyl)n-butylphosphine oxide, bis(3-aminophenyl)n-butylphosphine oxide, bis(4-aminophenyl)isobutylphosphine oxide, and bis(3-aminophenyl)isobutylphosphine oxide. Of these, bis(3-aminophenyl)n-butylphosphine oxide is preferred due to its excellent mechanical properties, flame retardancy, and moist heat resistance.

[0039] Examples of amine curing agents having a structure represented by general formula (4) include tris(4-aminophenyl)phosphine oxide, tris(3-aminophenyl)phosphine oxide, tris(2-aminophenyl)phosphine oxide, bis(4-aminophenyl)phenylphosphine oxide, bis(3-aminophenyl)phenylphosphine oxide, etc. Among these, tris(3-aminophenyl)phosphine oxide or bis(3-aminophenyl)phenylphosphine oxide is preferably used because of its excellent mechanical properties, and of these two compounds, the latter is more preferably used.

[0040] The content of component [B] in the epoxy resin composition of the present invention is preferably 10 to 100 parts by mass per 100 parts by mass of the total epoxy resin, from the viewpoint of improving the viscosity stability of the epoxy resin composition and the flame retardancy and mechanical properties of the resulting epoxy resin cured product and fiber-reinforced composite material, and the above content is more preferably 25 to 100 parts by mass.

[0041] In the epoxy resin composition of the present invention, the mass content ratio of component [A] to component [B] is preferably 0.3 to 1.5, from the viewpoint of achieving high flame retardancy and thermal conductivity in the resulting cured epoxy resin product, and this mass content ratio is more preferably 0.3 to 1.4. Here, the mass content ratio of component [A] to component [B] is the value obtained by dividing the mass proportion of component [A] contained in the entire epoxy resin composition by the mass proportion of component [B]. When a compound represented by general formula (1) or (2) is used as component [A], or when a compound having a structure represented by general formula (3) or (4) is used as component [B], the above mass content ratio is suitable.

[0042] In the epoxy resin composition of the present invention, when the content of phosphorus atoms in the epoxy resin composition is 0.1 to 5.0 mass%, the resulting epoxy resin cured product and fiber-reinforced composite material can achieve both flame retardancy and mechanical properties. The phosphorus atom content is preferably 0.3 to 4.0 mass%. The phosphorus atom content (mass%) here is calculated by dividing the mass (g) of phosphorus atoms in the total epoxy resin composition by the mass (g) of the total epoxy resin composition × 100. The mass of phosphorus atoms in the total epoxy resin composition is obtained by calculating the mass of phosphorus atoms per molecule of the compound of component [B] from the atomic weight of the phosphorus atoms, and multiplying this by the number of molecules of the compound of component [B] contained in the total epoxy resin composition, calculated from the number of moles.

[0043] The epoxy resin composition of the present invention may contain a curing agent other than component [B] in addition to component [B]. The curing agent referred to here is a curing agent for epoxy resins and is a compound having an active group capable of reacting with epoxy groups. Examples of curing agents other than component [B] include dicyandiamide, aromatic polyamines, aminobenzoic acid esters, various acid anhydrides, phenol novolac resins, cresol novolac resins, polyphenol compounds, imidazole derivatives, aliphatic amines, tetramethylguanidine, thiourea adduct amines, carboxylic acid anhydrides such as methylhexahydrophthalic anhydride, carboxylic acid hydrazides, carboxylic acid amides, polymercaptans, and Lewis acid complexes such as boron trifluoride ethylamine complexes. Among these, the use of aromatic polyamines as a curing agent facilitates the production of cured epoxy resins with good heat resistance. In particular, among aromatic polyamines, the use of various isomers of diaminodiphenyl sulfone, such as 4,4'-diaminodiphenyl sulfone and 3,3'-diaminodiphenyl sulfone, makes it easier to obtain a cured epoxy resin material with good heat resistance.

[0044] The content of the curing agent other than the component [B] is preferably 90 parts by mass or less relative to 100 parts by mass of the total amount of curing agents including component [B] and the curing agents other than component [B], i.e., when the total mass of all curing agents including component [B] contained in the epoxy resin composition is taken as 100 parts by mass, from the viewpoint of making it easier to improve the flame retardancy of the resulting epoxy resin cured product and fiber-reinforced composite material.

[0045] The epoxy resin composition of the present invention may contain a curing accelerator to enhance the curing activity of the curing agent. The curing accelerator referred to here is a compound that acts as a catalyst for the reaction between the epoxy resin and the curing agent and does not have an active group that can react with the epoxy group. Examples of the curing accelerator include urea derivatives such as 3-phenyl-1,1-dimethylurea, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 3-(3-chloro-4-methylphenyl)-1,1-dimethylurea, 4,4'-methylenebis(diphenyldimethylurea), and 2,4-toluenebis(3,3-dimethylurea), imidazole derivatives, triphenylphosphine, tetraphenylphosphonium tetraphenylborate, and tetraphenylphosphonium tetra(4-methylphenyl)borate.

[0046] The component [C] of the epoxy resin composition of the present invention is thermally conductive particles. The thermally conductive particles are preferably a filler made of boron nitride or graphite.

[0047] Of these two, graphite filler is more preferable, as its addition improves the thermal conductivity of the resin.

[0048] Specific examples of component [C] include flake boron nitride, spherical graphite, flake graphite, and flake graphite. Among these, flake graphite is particularly preferred because it is highly graphitized and has high thermal conductivity. These boron nitride and graphite of component [C] may be used alone as a filler, or both may be used in combination. It is also possible to use a mixture of two or more types of boron nitride, graphite, or a combination of both.

[0049] The average particle size of component [C] in the epoxy resin composition of the present invention, as determined by a particle size distribution analyzer using a laser diffraction method, is preferably 10 nm to 100 μm, from the viewpoint of obtaining high thermal conductivity and mechanical properties, more preferably 1 μm to 20 μm, and most preferably 1 μm to 5 μm.

[0050] The content of component [C] in the epoxy resin composition of the present invention is preferably 0.5% by mass to 25% by mass of the total epoxy resin composition, from the viewpoints of high thermal conductivity, mechanical properties, fluidity of the epoxy resin composition, and tackiness of the resulting prepreg. The above content is more preferably 1% by mass to 10% by mass. In particular, when a filler made of graphite is used as component [C], the above content is particularly preferred.

[0051] The epoxy resin composition of the present invention preferably further contains a thermoplastic resin component [D], preferably dissolved in the epoxy resin composition, in order to control the tackiness of the resulting prepreg, control the resin flowability when the epoxy resin composition is impregnated into reinforcing fibers during prepreg production, and enhance the toughness of the resulting fiber-reinforced composite material. The thermoplastic resin component [D] may be any compound that is soluble in the epoxy resin used at room temperature. Specific examples include polysulfone, polyphenylsulfone, polyethersulfone, polyetherimide, polyphenylene ether, polyetheretherketone, and polyetherethersulfone. Among these, thermoplastic resins having a polyarylether skeleton are preferred. These thermoplastic resins having a polyarylether skeleton may be used alone or in combination as appropriate. Polyethersulfone and polyetherimide are particularly preferred because they can impart toughness to the resulting fiber-reinforced composite material without reducing its heat resistance or mechanical properties. Furthermore, polyetherimide is preferred for its improved thermal diffusivity.

[0052] The amount of component [D] in the epoxy resin composition of the present invention is preferably 5 to 40 parts by mass, more preferably 10 to 35 parts by mass, and even more preferably 14 to 30 parts by mass, per 100 parts by mass of the total epoxy resin. By setting the amount of component [D] in this range, it is possible to ensure a balance between the viscosity of the epoxy resin, the tackiness of the resulting prepreg, and the mechanical properties of the resulting fiber-reinforced composite material.

[0053] In order to improve the impact resistance of the resulting fiber-reinforced composite material, the epoxy resin composition of the present invention preferably contains, as component [E], particles whose main component is a thermoplastic resin (thermoplastic resin particles). Unlike component [D], these thermoplastic resin particles are insoluble in the other constituents of the epoxy resin composition, do not have thermal conductivity, and exist as particles when the epoxy resin composition is made into a prepreg and further when the fiber-reinforced composite material is also made.

[0054] Polyamide is most preferred as the material for the thermoplastic resin particles, and among polyamides, polyamide 12, polyamide 6, polyamide 11, polyamide 66, polyamide 6 / 12 copolymer, and polyamides formed into a semi-IPN (interpenetrating polymer network) structure with an epoxy compound (semi-IPN polyamide) as described in Example 1 of JP-A-1-104624 provide particularly good adhesive strength with epoxy resins. These polyamide particles may be used alone or in combination of two or more types.

[0055] The epoxy resin composition of the present invention may contain a coupling agent, thermosetting resin particles, or an inorganic filler such as silica gel, carbon black, clay, carbon nanotubes, graphene, carbon particles, or metal powder, within the range that does not impair the effects of the present invention.

[0056] The prepreg of the present invention is obtained by impregnating reinforcing fibers with the epoxy resin composition of the present invention. That is, the above-described epoxy resin composition is used as a matrix resin, and this epoxy resin composition is composited with reinforcing fibers. Preferred examples of reinforcing fibers include carbon fibers, graphite fibers, aramid fibers, and glass fibers. Of these, carbon fibers are particularly preferred in terms of mechanical properties.

[0057] The prepreg of the present invention can be produced by various known methods, such as a wet method, a hot melt method, etc. Among these, the hot melt method is preferred because it is easy to achieve the effects of the present invention.

[0058] In the prepreg of the present invention, the weight of the reinforcing fiber is 100 to 1000 g / m ２It is preferable that the reinforcing fiber basis weight is 100 g / m ２ If the thickness is less than 1000 g / m, it is necessary to increase the number of layers to obtain a predetermined thickness when molding a fiber-reinforced composite material, which may make the layering work complicated. ２ If the fiber mass content exceeds this range, the drapeability of the prepreg tends to deteriorate. The fiber mass content in the prepreg is preferably 40 to 90% by mass, and more preferably 50 to 80% by mass. If the fiber mass content is less than 40% by mass, the resin ratio becomes relatively high, which may prevent the advantages of the excellent mechanical properties of the reinforcing fibers from being utilized, and may result in an excessively high heat generation during curing to produce a fiber-reinforced composite material. If the fiber mass content exceeds 90% by mass, impregnation with the resin may be insufficient, resulting in the resulting fiber-reinforced composite material having many voids.

[0059] The prepreg of the present invention may be in the form of a unidirectional (sometimes abbreviated as UD) prepreg, a woven fabric prepreg, or even a nonwoven fabric prepreg.

[0060] A first aspect of the fiber-reinforced composite material of the present invention is obtained by curing the prepreg of the present invention. Such a fiber-reinforced composite material can be obtained, for example, by laminating the prepreg of the present invention in a predetermined form and then applying heat and pressure to cure the resin. Here, known methods such as autoclave molding, press molding, bagging molding, wrapping tape molding, and internal pressure molding can be used to apply heat and pressure.

[0061] A second embodiment of the fiber-reinforced composite material of the present invention comprises a cured epoxy resin obtained by curing the epoxy resin composition of the present invention and reinforcing fibers. Such a fiber-reinforced composite material can be obtained by directly impregnating a reinforcing fiber substrate with a liquid epoxy resin composition and curing it, without using a prepreg. Specifically, such a fiber-reinforced composite material can be obtained by, for example, resin transfer molding, filament winding, pultrusion, or hand layup.

[0062] The upper and lower limits of the above-mentioned ranges can be combined in any way.

[0063] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Materials used in the examples and comparative examples of the present invention are listed below.

[0064] <Component [A]: Difunctional naphthalene-type epoxy resin> 1,6-naphthalenediol diglycidyl ether (EPICLON (registered trademark) HP-4032D, manufactured by DIC Corporation) 1-(2-hydroxy-naphthalen-1-ylmethyl)-naphthalen-2-ol diglycidyl ether (EPICLON (registered trademark) HP-4770, manufactured by DIC Corporation; bis(2-glycidyloxy-1-naphthyl)methane in the table) <Component [A']: Tri- or tetrafunctional epoxy resin having two or less benzene ring structures> N,N,N',N'-tetraglycidyl-4,4'-diaminodiphenylmethane (ARALDITE (registered trademark) MY721, manufactured by Huntsman Advanced Materials) N,N,O-triglycidyl-p-aminophenol (Araldite (registered trademark) MY510, manufactured by Huntsman Advanced Materials) <Epoxy resins other than components [A] and [A']> N,N-diglycidyl-p-phenoxyaniline (TOREP A-204E, manufactured by Toray Industries, Inc.) 2-phenylphenol glycidyl ether (OPP-G, manufactured by Sanko Co., Ltd.) Bisphenol A epoxy resin (jER (registered trademark) 825, manufactured by Mitsubishi Chemical Corporation) <Component [B]: Phosphorus-containing curing agent> Bis(3-aminophenyl)phenylphosphine oxide (BAPPO, manufactured by Katayama Chemical Industry Co., Ltd., a phosphorus-containing amine-based curing agent having a structure represented by general formula (4)).

[0065] <Curing agents other than component [B]> 4,4'-diaminodiphenyl sulfone (Seikacure S, manufactured by Wakayama Seika Kogyo Co., Ltd.) Biphenylaralkyl aromatic amine (BAN, manufactured by Nippon Kayaku Co., Ltd.) <Component [C]: Thermally conductive particles> Flake graphite (BF-3AK (average particle size 3 μm), manufactured by Chuetsu Graphite Industries Co., Ltd.) Flake boron nitride (Platelets 003, manufactured by 3M Japan Ltd.) <Component [D]: Thermoplastic resin> Polyethersulfone ("VIRANTAGE (registered trademark)" VW-10700RFP, manufactured by Solvay Advanced Polymers) Polyetherimide ("ULTEM (registered trademark)" EXUM9990, manufactured by SABIC).

[0066] The evaluation methods used in the examples and comparative examples of the present invention are as follows, where n=1 unless otherwise specified.

[0067] (1) Method for preparing an epoxy resin composition The components listed in Table 1 or Table 2, except for the curing agent, were charged into a kneading device, and the temperature was raised to 140°C or higher, followed by heat kneading. The temperature was then lowered to 80°C or lower, and the curing agent listed in Table 1 or Table 2 was added and stirred to obtain an epoxy resin composition.

[0068] (2) Evaluation of Flame Retardancy of Cured Epoxy Resin Products The flame retardancy of cured epoxy resin products was evaluated by measuring the char generation rate by thermogravimetry (TGA) as follows.

[0069] The epoxy resin composition prepared in (1) was degassed in a vacuum and then cured under the specified curing conditions described below in a mold containing 2 mm thick Teflon (registered trademark) spacers inserted therein to limit the thickness of the resulting cured epoxy resin to 2 mm, yielding a cured epoxy resin product with a thickness of 2 mm. Flame retardancy was evaluated using a thermogravimetric TG-DSC (PerkinElmer STA6000 System). Approximately 10 mg of test specimens were cut from the cured epoxy resin and heated simply in air at a rate of 10°C / min. The char generation rate (%) at 600°C was used as an index of flame retardancy. The char generation rate here is a value calculated by dividing the mass (g) of the thermal decomposition residue at 600°C by the mass (g) of the cured epoxy resin product before heating by 100.

[0070] Based on this measurement, the measured value was rounded off to the nearest tenth place.

[0071] Using this value, the flame retardancy evaluation criteria were set as follows:

[0072] Criteria for evaluation (flame retardancy): S: "Char generation rate at 600°C is 40% or more." A: "Char generation rate at 600°C is 30% or more and less than 40%." B: "Char generation rate at 600°C is 20% or more and less than 30%." C: "Char generation rate at 600°C is less than 20%." (3) Evaluation of thermal conductivity of cured epoxy resin material The thermal conductivity of cured epoxy resin materials was evaluated as follows.

[0073] The cured epoxy resin product prepared in (2) was cut into a 10 mm x 10 mm square, and the surface was blackened using Blackguard Spray (manufactured by Fine Chemical Japan Co., Ltd.). The thermal diffusivity of the sample was measured in accordance with ASTM E1461-01 (2001). The thermal diffusivity at 25°C was measured using a thermal diffusivity measuring device LFA467 HyperFlash (manufactured by NETZSCH). ２ The evaluation was performed in units of / s to two decimal places. The number of evaluations was set to n=3.

[0074] Based on this measurement, the criteria for thermal conductivity were set as follows:

[0075] Criteria (thermal conductivity): S: "Thermal diffusivity is 0.22 mm ２ / s or more." A: "Thermal diffusivity is 0.19 mm ２ / s or more 0.22mm ２ B: "Thermal diffusivity is less than 0.16 mm / s." ２ / s or more 0.19mm ２ C: Thermal diffusivity is 0.16 mm / s or less. ２ / s or less." (4) Evaluation of Mechanical Properties of Cured Epoxy Resin Products The mechanical properties of cured epoxy resin products were evaluated as follows.

[0076] The cured epoxy resin product prepared in (2) was cut into a 10 mm × 60 mm square test piece, and a three-point bending test was performed on the test piece in accordance with JIS K7171 (2006) to evaluate its mechanical properties. The bending test was performed using an Instron 5565 universal testing machine (manufactured by Instron Corporation) under the conditions of a crosshead speed of 2.5 mm / min, a span length of 40 mm, an indenter diameter of 10 mm, and a fulcrum diameter of 4 mm, and the flexural modulus was measured.

[0077] Based on this measurement, the measured value was calculated in gigapascal units by rounding off to the first decimal place. The number of evaluations was set to n=5.

[0078] Using these values, the criteria for determining mechanical properties were set as follows:

[0079] Evaluation criteria (mechanical properties): S: "Flexural modulus of elasticity is 4.7 GPa or more". A: "Flexural modulus of elasticity is 4.1 GPa or more and less than 4.7 GPa". B: "Flexural modulus of elasticity is 3.5 GPa or more and less than 4.1 GPa". C: "Flexural modulus of elasticity is less than 3.5 GPa". (5) Evaluation of heat resistance of cured epoxy resin products The heat resistance of cured epoxy resin products was evaluated as follows.

[0080] The cured epoxy resin product prepared in (2) was cut into a test piece measuring 12.7 mm x 45 mm square, and the glass transition temperature of the test piece was measured by dynamic mechanical analysis (DMA) in accordance with ASTM 7028-07.

[0081] Based on this measurement, the measured value was calculated in degrees Celsius by rounding off to the nearest tenth place.

[0082] Using this value, the heat resistance evaluation criteria were set as follows:

[0083] Criteria for evaluation (heat resistance): S: "Glass transition temperature is 210°C or higher." A: "Glass transition temperature is 190°C or higher and lower than 210°C." B: "Glass transition temperature is 170°C or higher and lower than 190°C." C: "Glass transition temperature is lower than 170°C."

[0084] (Examples 1 to 8, Comparative Examples 1 to 6) Epoxy resin compositions were prepared by the above-mentioned (1) Method for preparing an epoxy resin composition, using the components in the ratios (parts by mass) shown in Tables 1 and 2. The epoxy resin cured products obtained by curing at a temperature of 180°C for 2 hours were evaluated for flame retardancy, thermal conductivity, mechanical properties, and heat resistance according to the above-mentioned (2) to (5). The evaluation results are shown in Tables 1 and 2.

[0085]

[0086]

Claims

1. An epoxy resin composition comprising the following components [A] to [C]: [A] a bifunctional naphthalene-type epoxy resin; [B] a phosphorus-containing curing agent; and [C] thermally conductive particles.

2. The epoxy resin composition according to claim 1, wherein the mass ratio of component [A] to component [B] is 0.3 to 1.5, and further comprises, as component [A'], a tri- or tetra-functional epoxy resin having two or less benzene ring structures, and the total amount of components [A] and [A'] is 90 parts by mass or more per 100 parts by mass of the total amount of epoxy resins.

3. The epoxy resin composition according to claim 1 or 2, wherein component [A] has a structure represented by the following general formula (1) or (2). (In general formula (1), R １ represents a hydrocarbon group having 1 to 4 carbon atoms; and l represents an integer of 0 to 3. (In general formula (2), R ２ and R ３ each independently represents a hydrocarbon group having 1 to 4 carbon atoms; m and n each independently represent an integer of 0 to 3.

4. The epoxy resin composition according to claim 1 or 2, wherein component [B] contains at least one amine-based curing agent selected from the group consisting of amine-based curing agents having a structure represented by the following general formula (3) and amine-based curing agents having a structure represented by the following general formula (4). (In general formula (3), R ４ represents a hydrocarbon group having 1 to 4 carbon atoms. ５ represents a hydrogen atom or an amino group.

5. The epoxy resin composition according to claim 1 or 2, which contains 0.5 to 25 mass% of a filler made of graphite as component [C].

6. The epoxy resin composition according to claim 1, wherein the content of component [A] is 10 to 50 parts by mass per 100 parts by mass of the total epoxy resin.

7. The epoxy resin composition according to claim 1, further comprising component [D] a thermoplastic resin.

8. A prepreg obtained by impregnating reinforcing fibers with the epoxy resin composition according to claim 1.

9. A fiber-reinforced composite material obtained by curing the prepreg according to claim 8.

10. A fiber-reinforced composite material comprising a cured epoxy resin obtained by curing the epoxy resin composition according to claim 1 and reinforcing fibers.

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