Epoxy resin composition, prepreg and fiber-reinforced composite material

Abstract

The present invention addresses the problem of providing an epoxy resin composition excellent in terms of strength, elastic modulus, elastic modulus in wet-heat environments, and heat resistance after moisture absorption, the epoxy resin composition being suitable for use in applications such as prepregs and fiber-reinforced composite materials. The epoxy resin composition comprises the following constituent elements [A], [B], and [C] and satisfies the following requirements (1) and (2). [A]: An epoxy resin. [B]: An amine hardener. [C]: A phosphoric ester compound having a molecular weight of 250 or less. (1): To contain the constituent element [C] in an amount of 1-15 parts by mass per 100 parts by mass of the constituent element [A]. (2): The constituent element [A] has an average epoxy equivalent of 160 g / eq or less.

Description

[Technical Field]

[0001] The present invention relates to an epoxy resin composition suitable for use in fiber-reinforced composite materials for aerospace applications, general industrial applications, sports applications, and the like, as well as to a prepreg and a fiber-reinforced composite material each using the epoxy resin composition. [Background technology]

[0002] Fiber-reinforced composite materials using carbon fibers, aramid fibers, or the like as reinforcing fibers are widely used, taking advantage of their high specific strength and specific modulus, for structural materials for aircraft, automobiles, etc., sports applications such as tennis rackets, golf shafts, fishing rods, bicycles, and housings, and general industrial applications. As the resin composition used in these fiber-reinforced composite materials, thermosetting resins are mainly used from the viewpoints of heat resistance and productivity, and among these, epoxy resins are preferably used from the viewpoint of mechanical properties such as adhesion to reinforcing fibers.

[0003] In recent years, the application of fiber-reinforced composite materials to applications requiring further weight reduction has necessitated improvements in various physical properties, and improvements in the strength, elastic modulus, and heat resistance of the epoxy resin used as the matrix resin are required. Furthermore, when used in aerospace applications or as structural materials for vehicles, the resin must retain its physical properties sufficiently even under high temperature and / or high humidity conditions. Therefore, a technical challenge has been to simultaneously improve not only the strength and elastic modulus of the matrix resin, but also its elastic modulus in a humid and hot environment (wet and hot elastic modulus) and its heat resistance after moisture absorption (maintaining a sufficient glass transition temperature even after moisture absorption).

[0004] Various studies have been conducted to address this issue, including a method of improving the strength of a cured resin by combining an epoxy resin with a phosphite ester or a phosphate ester compound (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-199552 Summary of the Invention [Problem to be solved by the invention]

[0006] When the technology of Patent Document 1 is used, the strength of the obtained fiber-reinforced composite material is improved, but the mechanical properties under high temperature and / or high humidity conditions are not taken into consideration. That is, as described in the specification of Patent Document 1, the technology of Patent Document 1 aims to improve the flexural modulus or flexural strength of the obtained cured product by improving the adhesion between the carbon fiber and the matrix resin with the phosphate ester compound, but does not pay attention to the interaction between the crosslinked structure formed by curing the epoxy resin in the fiber-reinforced composite material and the phosphate ester-based compound, and therefore the above-mentioned properties are insufficient.

[0007] Therefore, an object of the present invention is to provide an epoxy resin composition that can be suitably used for prepregs and fiber-reinforced composite materials, and that has an excellent balance of strength, elastic modulus, elastic modulus under humid and hot environments, and heat resistance after moisture absorption. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention employs the following configuration: That is, a composition including the following components [A], [B], and [C] and satisfying the following condition (1): Or (4) The epoxy resin composition satisfies the above requirements. [A]: Contains two or more epoxy groups in one molecule Epoxy resin [B]: It is either an aliphatic polyamine or an aromatic polyamine, or both. Amine Curing Agent [C]: A phosphate ester compound having a molecular weight of 250 or less. (1): The component [C] is 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]. (2): Component [A] has an average epoxy equivalent of 160 g / eq or less. (3): In the cured product of the epoxy resin composition, component [A] and component [B] react to form a crosslinked structure, and component [C] is held within the network formed by the crosslinked structure. (4): When the total number of moles of epoxy groups in component [A] is E (mol) and the total number of moles of active hydrogen in component [B] is H (mol), the ratio (H / E) is 0.50 or more and 1.30 or less.

[0009] The present invention also provides a prepreg comprising the epoxy resin composition of the present invention and reinforcing fibers, and a fiber-reinforced composite material comprising a cured product of the epoxy resin composition of the present invention and reinforcing fibers. [Effects of the Invention]

[0010] According to the present invention, an epoxy resin composition can be obtained which is suitable for use in prepregs and fiber-reinforced composite materials and which has an excellent balance of strength, elastic modulus, elastic modulus under a humid and hot environment, and heat resistance after moisture absorption. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below. In the present invention, the term "not less than" means that the value is equal to or greater than the indicated value. The term "not more than" means that the value is equal to or smaller than the indicated value.

[0012] The resin composition of the present invention contains, as essential components, component [A], component [B], and component [C]. In the present invention, the term "component" refers to each individual component contained in the resin composition.

[0013] The component [A] in the present invention is an epoxy resin. The epoxy resin of component [A] is preferably one containing two or more epoxy groups per molecule, since this increases the glass transition temperature of the cured product obtained by heat-curing the resin composition and improves heat resistance. Furthermore, an epoxy resin containing one epoxy group per molecule may also be blended. These epoxy resins may be used alone or in combination.

[0014] Examples of epoxy resins for component [A] include glycidyl amine types such as diaminodiphenylmethane type, diaminodiphenyl sulfone type, aminophenol type, metaxylenediamine type, and 1,3-bisaminomethylcyclohexane type, bisphenol type, phenol novolac type, orthocresol novolac type, glycidyl ether types such as trishydroxyphenylmethane type and tetraphenylolethane type, isocyanurate type, hydantoin type, etc. Among these, glycidyl amine type and glycidyl ether type epoxy resins are preferred because of their good balance of physical properties, and among these, diaminodiphenylmethane type, aminophenol type, and bisphenol type epoxy resins are particularly preferred.

[0015] From the viewpoint of mechanical properties under humid and hot environments and heat resistance after moisture absorption, the glycidyl ether epoxy resin is preferably contained in an amount of 20 to 80 parts by mass, more preferably 20 to 60 parts by mass, per 100 parts by mass of component [A]. By containing 20 to 80 parts by mass of the glycidyl ether epoxy resin per 100 parts by mass of component [A], it is possible to obtain a cured product in which the decrease in resin elongation under humid and hot conditions is small and which has a sufficient glass transition temperature even after moisture absorption.

[0016] Commercially available diaminodiphenylmethane epoxy resins include Sumiepoxy (registered trademark) ELM434 (manufactured by Sumitomo Chemical Co., Ltd.), Araldite (registered trademark) MY720 (manufactured by Huntsman Advanced Materials Co., Ltd.), Araldite (registered trademark) MY721 (manufactured by Huntsman Advanced Materials Co., Ltd.), Araldite (registered trademark) MY9512 (manufactured by Huntsman Advanced Materials Co., Ltd.), Araldite (registered trademark) MY9663 (manufactured by Huntsman Advanced Materials Co., Ltd.), Epotohto (registered trademark) YH-434 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), and jER (registered trademark) 630 (manufactured by Mitsubishi Chemical Corporation).

[0017] Commercially available diaminodiphenyl sulfone type epoxy resins include TG3DAS (manufactured by Mitsui Fine Chemicals, Inc.).

[0018] Commercially available aminophenol-type epoxy resins include ELM120 (manufactured by Sumitomo Chemical Co., Ltd.), ELM100 (manufactured by Sumitomo Chemical Co., Ltd.), jER (registered trademark) 630 (manufactured by Mitsubishi Chemical Corporation), Araldite (registered trademark) MY0500 (manufactured by Huntsman Advanced Materials Co., Ltd.), Araldite (registered trademark) MY0510 (manufactured by Huntsman Advanced Materials Co., Ltd.), Araldite (registered trademark) MY0600 (manufactured by Huntsman Advanced Materials Co., Ltd.), and Araldite (registered trademark) MY0610 (manufactured by Huntsman Advanced Materials Co., Ltd.).

[0019] Commercially available bisphenol A epoxy resins include "EPON (registered trademark)" 825 (manufactured by Mitsubishi Chemical Corporation), "Epiclon (registered trademark)" 850 (manufactured by DIC Corporation), "Epotohto (registered trademark)" YD-128 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), and DER-331 and DER-332 (all manufactured by The Dow Chemical Company).

[0020] Commercially available bisphenol F epoxy resins include Araldite (registered trademark) GY282 (manufactured by Huntsman Advanced Materials), jER (registered trademark) 806, jER (registered trademark) 807, and jER (registered trademark) 1750 (all manufactured by Mitsubishi Chemical Corporation), Epicron (registered trademark) 830 (manufactured by DIC Corporation), and Epotohto (registered trademark) YD-170 (manufactured by Nippon Steel Chemical & Material Co., Ltd.).

[0021] Commercially available isocyanurate epoxy resins include "TEPIC (registered trademark)"-S (manufactured by Nissan Chemical Industries, Ltd.), "TEPIC (registered trademark)"-G (manufactured by Nissan Chemical Industries, Ltd.), and "TEPIC (registered trademark)"-L (manufactured by Nissan Chemical Industries, Ltd.).

[0022] Furthermore, the epoxy resins that can be used in the epoxy resin composition of the present invention are not limited to the above-mentioned epoxy resins, and it goes without saying that epoxy resins other than those mentioned above can also be used.

[0023] The component [A] has an average epoxy equivalent of 160 g / eq or less, the reason for which will be described later, and preferably contains 40 mass% or more of an epoxy resin having an epoxy equivalent of 130 g / eq or less, based on 100 mass% of component [A]. By containing 40 mass% or more, more preferably 50 mass% or more, and even more preferably 60 mass% or more of an epoxy resin having an epoxy equivalent of 130 g / eq or less, an excellent cured product having a sufficient glass transition temperature even after absorbing moisture can be obtained.

[0024] In the present invention, the epoxy equivalent is understood to be the mass (g / eq is used as the unit) of an epoxy resin containing 1 mole of epoxy groups.

[0025] Commercially available epoxy resins having an epoxy equivalent of 130 g / eq or less include, for example, "Sumiepoxy (registered trademark)" ELM434 (epoxy equivalent: 119 g / eq), "Araldite (registered trademark)" MY720 (epoxy equivalent: 119 g / eq), "Araldite (registered trademark)" MY721 (epoxy equivalent: 114 g / eq), "Araldite (registered trademark)" MY9512 (epoxy equivalent: 126 g / eq), "Araldite (registered trademark)" MY9663 (epoxy equivalent: 126 g / eq), and "Epotohto (registered trademark)" YH-434 (epoxy equivalent: 120 g / eq), "jER (registered trademark)" 604 (epoxy equivalent: 120 g / eq), TG3DAS (epoxy equivalent: 136 g / eq), ELM120 (epoxy equivalent weight: 118g / eq), ELM100 (epoxy equivalent weight: 118g / eq), jER (registered trademark) 630 (epoxy equivalent weight: 98g / eq), Araldite (registered trademark) MY0500 (epoxy equivalent weight: 110g / eq), Araldite (registered trademark) MY0510 (epoxy equivalent weight: 101g / eq), Araldite (registered trademark) MY0600 (epoxy equivalent weight: 106g / eq), Araldite (registered trademark) MY0610 (epoxy equivalent weight: 99g / eq), TEPIC (registered trademark) -S (epoxy equivalent weight: 100g / eq), TEPIC (registered trademark) -G (epoxy equivalent weight: 100g / eq), TEPIC (registered trademark) -L (epoxy equivalent weight: 100g / eq), and the like.

[0026] These may be used alone or in combination of two or more.

[0027] The component [B] is an amine curing agent. The amine curing agent has an amino group that can react with an epoxy group, and functions as a curing agent by reacting with the epoxy group.

[0028] Examples of amine curing agents include aliphatic polyamines and aromatic polyamines, among which aromatic polyamines are preferred because they can impart high mechanical properties and heat resistance to the cured epoxy resin. These amine curing agents may be used alone or in combination.

[0029] Aromatic polyamines include diethyltoluenediamines such as 2,2'-diethyldiaminodiphenylmethane, 2,4-diethyl-6-methyl-m-phenylenediamine, 4,6-diethyl-2-methyl-m-phenylenediamine, and 4,6-diethyl-m-phenylenediamine, 4,4'-methylenebis(N-methylaniline), 4,4'-methylenebis(N-ethylaniline), 4,4'-methylenebis(N-sec-butylaniline), N,N'-di-sec-butyl-p-phenylenediamine, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, and 3,3'-diisopropyl-4,4'-diaminodiphenylmethane. , 3,3'-di-t-butyl-4,4'-diaminodiphenylmethane, 3,3'-diethyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane, 3,3'-diisopropyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetra-t-butyl-4,4'-diaminodiphenylmethane, and the like. Of these, 3,3'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl sulfone are preferably used because they provide cured products with particularly excellent mechanical properties.

[0030] Commercially available aromatic polyamines include Seikacure S (manufactured by Wakayama Seika Kogyo Co., Ltd.), MDA-220 (manufactured by Mitsui Chemicals, Inc.), jER Cure (registered trademark) W (manufactured by Mitsubishi Chemical Corporation), and 3,3'-DAS (manufactured by Mitsui Chemicals, Inc.), Lonzacure (registered trademark) M-DEA (manufactured by Lonza Corporation), Lonzacure (registered trademark) M-DIPA (manufactured by Lonza Corporation), Lonzacure (registered trademark) M-MIPA (manufactured by Lonza Corporation), and Lonzacure (registered trademark) DETDA 80 (manufactured by Lonza Corporation).

[0031] The amount of amine curing agent used in the present invention is preferably such that the ratio (H / E) is 0.50 or more and 1.30 or less, more preferably 0.70 or more and 1.20 or less, and even more preferably 0.80 or more and 1.10 or less, where E (mol) is the total number of moles of epoxy groups in the epoxy resin (component [A]) and H (mol) is the total number of moles of active hydrogen in the amine curing agent (component [B]). By setting the H / E ratio within this range, a crosslinked structure can be appropriately formed by the reaction between the epoxy resin and the amine curing agent, resulting in a cured resin with excellent strength and elongation. In addition, by setting the H / E ratio to 0.50 or more and 1.30 or less, the component [C] (described later) is more easily retained in the crosslinked structure, resulting in improved modulus and strength.

[0032] Component [C] is a phosphate ester compound with a molecular weight of 250 or less. In the crosslinked structure formed by the reaction of the epoxy resin and the amine curing agent, component [C] is not chemically incorporated into the crosslinked structure itself, but rather exists within the network formed by the crosslinked structure (including between the molecular chains of molecules formed by component [A] and component [B]; the same applies hereinafter), and this state is maintained even after curing. This results in a high elastic modulus of the resulting cured epoxy resin. Furthermore, surprisingly, the resulting cured epoxy resin exhibits an excellent balance of not only the elastic modulus but also the strength, the elastic modulus under wet heat, and the heat resistance after moisture absorption. While the reason for this is unclear, the inventors believe it to be as follows: Specifically, it is important that the molecular weight of component [C] is 250 or less, so that component [C] is properly retained within the network formed by the crosslinked structure formed by the reaction of the epoxy resin and the amine curing agent, resulting in a dense cured product without the generation of voids, and a high elastic modulus of the cured product. Furthermore, when strain is applied to the cured product, component [C] moves freely within the crosslinked structure, easing the strain energy leading to fracture, thereby increasing the strength of the cured product. Furthermore, at this time, component [C] has a strongly polarized phosphoryl structure (P=O) within the molecule, which causes intermolecular interactions between component [C] and the polar functional groups in the crosslinked structure formed by the reaction of the epoxy resin and amine curing agent, and this allows the component to remain appropriately held within the network formed by the crosslinked structure even when absorbing moisture or in a high-temperature environment, which is thought to result in higher elastic modulus under wet and hot conditions and higher heat resistance after absorbing moisture.

[0033] When the molecular weight of the component [C] is 250 or less, preferably 220 or less, more preferably 210 or less, and even more preferably 190 or less, the component [C] is appropriately retained within the network formed by the crosslinked structure formed by the reaction of the epoxy resin with the amine curing agent, and a cured product excellent in strength, elastic modulus, and elastic modulus under humid heat can be obtained.Furthermore, when the molecular weight of the component [C] is 100 or more, the component [C] is appropriately retained within the network formed by the crosslinked structure formed by the reaction of the epoxy resin with the amine curing agent, and a cured product excellent in strength, elastic modulus, and elastic modulus under humid heat can be obtained, which is preferable.

[0034] Furthermore, the boiling point of component [C] is preferably 180°C or higher, more preferably 200°C or higher, and even more preferably 230°C or higher, because this can suppress volatilization of component [C] during curing of the epoxy resin composition, thereby enabling the production of a cured resin or fiber-reinforced composite material with excellent mechanical properties, and further suppressing the generation of voids and deterioration of mechanical properties in the resulting fiber-reinforced composite material. In the present invention, the boiling point is a value at normal pressure (101 kPa). Furthermore, if the boiling point at normal pressure cannot be measured, the converted boiling point converted to 101 kPa using a boiling point conversion chart can be used.

[0035] Examples of such component [C] include trimethyl phosphate, triethyl phosphate, dimethyl phenylphosphonate, diethyl phenylphosphonate, and dimethyl methylphosphonate. Among these, phenylphosphonic acid alkyl ester compounds, such as dimethyl phenylphosphonate and diethyl phenylphosphonate, which have an aromatic ring in the molecule, are preferred because they provide particularly excellent mechanical properties for the resulting cured resin. Furthermore, among the components [C], phenylphosphonic acid alkyl ester compounds are preferred because they have a high boiling point and can suppress the generation of voids in fiber-reinforced composite materials. These compounds may be used alone or in combination.

[0036] It is important that the content of component [C] in the epoxy resin composition of the present invention is 1 part by mass or more and 15 parts by mass or less per 100 parts by mass of component [A]. By incorporating component [C] in an amount of 1 part by mass or more, more preferably 5 parts by mass or more, a cured product with excellent strength and elastic modulus can be obtained. Furthermore, by incorporating component [C] in an amount of 15 parts by mass or less, more preferably 12 parts by mass or less, a cured product with excellent elastic modulus under wet heat and heat resistance after moisture absorption can be obtained.

[0037] Component [D] is a thermoplastic resin. The epoxy resin composition of the present invention preferably further contains component [D]. By blending component [D], the tackiness of the resulting prepreg and the fluidity of the matrix resin when the prepreg is heat-cured can be controlled within appropriate ranges.

[0038] Such thermoplastic resins are preferably thermoplastic resins having a polyaryl ether skeleton. Examples include polysulfone, polyphenylsulfone, polyethersulfone, polyetherimide, polyphenylene ether, polyetheretherketone, and polyetherethersulfone. These thermoplastic resins having a polyaryl ether skeleton may be used alone or in combination. Among these, polyethersulfone is preferred because it can impart toughness to the resulting fiber-reinforced composite material without reducing its heat resistance or mechanical properties.

[0039] Examples of commercially available products of the component [D] include Sumikaexcel (registered trademark) PES5003P (manufactured by Sumitomo Chemical Co., Ltd.), Sumikaexcel (registered trademark) PES2603P (manufactured by Sumitomo Chemical Co., Ltd.), and Virantage (registered trademark) VW10700RFP (manufactured by Solvay Advanced Polymers, Inc.).

[0040] The content of component [D] is preferably 2 parts by mass or more per 100 parts by mass of component [A]. By including component [D] in an amount of 2 parts by mass or more, more preferably 5 parts by mass or more, it is possible to impart tackiness to the prepreg, resulting in a prepreg with excellent handleability. In addition, the fluidity of the resin during heat curing can be suppressed, resulting in a fiber-reinforced composite material with a uniform resin content. Furthermore, it is preferable to include component [D] in an amount of 20 parts by mass or less per 100 parts by mass of component [A]. By including component [D] in an amount of 20 parts by mass or less, more preferably 16 parts by mass or less, it is possible to suppress an excessive decrease in the fluidity of the resin during heat curing, resulting in a fiber-reinforced composite material with few voids.

[0041] As described above, the epoxy resin composition of the present invention preferably contains the components [A], [B], [C], and [D], and may be composed of the components [A], [B], [C], and [D] as shown in the examples. In this case, additives and the like may be contained within the range that does not affect the effects of the invention.

[0042] In the present invention, it is important that the average epoxy equivalent of all epoxy resins used as component [A] is 160 g / eq or less. When the average epoxy equivalent of the epoxy resins constituting component [A] is 160 g / eq or less, more preferably 140 g / eq or less, a cured product excellent in strength, elastic modulus, moist heat elastic modulus, and heat resistance after moisture absorption can be obtained. Furthermore, when the epoxy resins constituting component [A] have an average epoxy equivalent of 120 g / eq or more, the curing reaction is less likely to go out of control during curing of the epoxy resin, and a decrease in the mechanical strength of the obtained cured product can be suppressed, which is preferable.

[0043] Here, the average epoxy equivalent is defined as the value calculated by the following formula.

[0044]

number

[0045] (W i represents the mass (g) of the i-th epoxy resin, E i represents the epoxy equivalent (g / eq) of the i-th epoxy resin, and n is a positive integer indicating the number of types of epoxy resin used.) The component [C] used in the present invention is particularly suitable when combined with a component [A] having an average epoxy equivalent of 160 g / eq or less. When the average epoxy equivalent of component [A] is 160 g / eq or less, the number of epoxy groups contained in the resin composition increases, and therefore the number of hydroxyl groups generated by the ring-opening addition reaction between the epoxy groups and the amine curing agent also increases. As a result, intermolecular interactions are more likely to occur between the hydroxyl groups generated in the cured product and the polar functional groups contained in the phosphate ester compound, component [C], and the resulting cured resin product exhibits excellent strength, elastic modulus, moist heat elastic modulus, and heat resistance after moisture absorption.

[0046] Furthermore, when the average epoxy equivalent of component [A] is 160 g / eq or less, the crosslink density of the resulting cured epoxy resin product is high, resulting in a smaller network size of the crosslinked epoxy resin. As a result, component [C] is firmly held within the network formed by the crosslinked structure, and the resulting cured resin product has excellent strength, elastic modulus, elastic modulus under humid heat, and heat resistance after moisture absorption. Furthermore, when the average epoxy equivalent of component [A] is 110 g / eq or more, the amount of heat generated during curing of the epoxy resin composition is reduced, suppressing runaway reaction. This results in the resulting cured product having excellent strength, elastic modulus, elastic modulus under humid heat, and heat resistance after moisture absorption, which is preferable.

[0047] The epoxy resin composition of the present invention has excellent elastic modulus, strength, and elongation, and is suitable for use as a matrix resin in fiber-reinforced composite materials. That is, the fiber-reinforced composite materials of the present invention comprise a cured product of the epoxy resin composition of the present invention and continuous reinforcing fibers.

[0048] Methods for obtaining fiber-reinforced composite materials include methods in which reinforcing fibers are impregnated with a resin composition during the molding process, such as hand layup, RTM, filament winding, and pultrusion molding, and methods in which a prepreg in which reinforcing fibers have already been impregnated with a resin composition is molded using an autoclave or press molding process. Among these, prepregs composed of an epoxy resin composition and reinforcing fibers are preferred because they allow precise control of the fiber arrangement and resin ratio, thereby maximizing the properties of the composite material. In other words, the prepreg of the present invention is composed of the epoxy resin composition of the present invention and continuous reinforcing fibers. However, this does not exclude the inclusion of other components within a range that does not impair the objectives of the present invention.

[0049] Preferred examples of the continuous reinforcing fibers used in the prepreg and fiber-reinforced composite material of the present invention include carbon fiber, graphite fiber, aramid fiber, and glass fiber, with carbon fiber being particularly preferred. The form and arrangement of the continuous reinforcing fibers are not particularly limited as long as the fibers are continuous, and fiber structures such as unidirectionally aligned long fibers, single tows, woven fabrics, knitted fabrics, and braided cords can be used. Two or more types of carbon fiber, glass fiber, aramid fiber, boron fiber, PBO fiber, high-strength polyethylene fiber, alumina fiber, and silicon carbide fiber can also be used in combination as the reinforcing fibers.

[0050] Specific examples of carbon fibers include acrylic, pitch, and rayon carbon fibers, and acrylic carbon fibers having particularly high tensile strength are preferably used.

[0051] The carbon fiber may be in the form of twisted yarn, untwisted yarn, or non-twisted yarn, but in the case of twisted yarn, the filaments constituting the carbon fiber are not oriented parallel to one another, which can cause a decrease in the mechanical properties of the resulting carbon fiber reinforced composite material. Therefore, untwisted yarn or non-twisted yarn is preferably used, as it provides a good balance between the formability and strength properties of the carbon fiber reinforced composite material.

[0052] The carbon fiber preferably has a tensile modulus of 200 GPa or more and 440 GPa or less. The tensile modulus of carbon fiber is affected by the crystallinity of the graphite structure that constitutes the carbon fiber, and the higher the crystallinity, the higher the modulus. This range is preferable because it achieves a high level of balance between the rigidity and strength of the carbon fiber reinforced composite material. A more preferred modulus is 230 GPa or more and 400 GPa or less, and even more preferably 260 GPa or more and 370 GPa or less. Here, the tensile modulus of carbon fiber is a value measured in accordance with JIS R7608 (2008).

[0053] The prepreg of the present invention can be produced by various known methods. For example, the prepreg can be produced by a hot melt method in which a resin composition is heated to reduce its viscosity and then impregnated into reinforcing fibers without using an organic solvent.

[0054] In addition, in the hot melt method, a resin composition whose viscosity has been reduced by heating can be directly impregnated into the reinforcing fibers, or a release paper sheet with a resin film can be first prepared by coating the resin composition on release paper or the like, and then a resin film can be placed on both sides or one side of the reinforcing fibers, and the resin composition can be impregnated into the reinforcing fibers by heating and pressurizing.

[0055] The content of continuous reinforcing fibers in 100 parts by mass of prepreg is preferably 30 parts by mass or more and 90 parts by mass or less. By setting the content to 30 parts by mass or more, more preferably 35 parts by mass or more, and even more preferably 65 parts by mass or more, the advantages of a fiber-reinforced composite material, such as excellent specific strength and specific modulus, can be easily obtained. In addition, when molding a fiber-reinforced composite material, excessive heat generation during curing can be prevented. On the other hand, by setting the content to 90 parts by mass or less, more preferably 85 parts by mass or less, the generation of voids in the composite material due to insufficient resin impregnation can be prevented. In addition, the tackiness of the prepreg can be maintained.

[0056] The fiber-reinforced composite material of the present invention can be produced, for example, by laminating the prepregs of the present invention described above in a predetermined form and curing the resin by applying pressure and heat. Methods for applying heat and pressure include press molding, autoclave molding, bagging molding, wrapping tape molding, and internal pressure molding.

[0057] The fiber-reinforced composite material of the present invention can be widely used in aerospace applications, general industrial applications, and sports applications. More specifically, in general industrial applications, it is suitable for use in structures such as automobiles, ships, and railway vehicles. In sports applications, it is suitable for use in golf shafts, fishing rods, and tennis and badminton rackets. [Example]

[0058] The present invention will be described in detail below with reference to examples. However, the scope of the present invention should not be construed as being limited to these examples. The unit "parts" used in the compositional ratios refers to parts by mass unless otherwise noted. Furthermore, measurements of various characteristics (physical properties) were carried out in an environment of 23°C and 50% relative humidity unless otherwise noted.

[0059] <Materials used in Examples and Comparative Examples> (1) Component [A]: Epoxy resin "Sumiepoxy (registered trademark)" ELM434 (diaminodiphenylmethane type epoxy resin, glycidylamine type epoxy resin, epoxy equivalent: 119 g / eq, manufactured by Sumitomo Chemical Co., Ltd.) "Epiclon (registered trademark)" 830 (bisphenol F type epoxy resin, glycidyl ether type epoxy resin, epoxy equivalent: 172 g / eq, manufactured by DIC Corporation).

[0060] (2) Component [B]: Amine curing agent Seikacure S (4,4'-diaminodiphenyl sulfone, active hydrogen equivalent: 62g / eq, manufactured by Wakayama Seika Kogyo Co., Ltd.).

[0061] (3) Component [C]: a phosphate ester compound having a molecular weight of 250 or less. Trimethyl phosphate (molecular weight: 140, boiling point: 197°C, manufactured by Tokyo Chemical Industry Co., Ltd.) Dimethyl phenylphosphonate (molecular weight: 186, boiling point: 247°C, manufactured by Tokyo Chemical Industry Co., Ltd.) Diethyl phenylphosphonate (molecular weight: 214, boiling point: 267°C, manufactured by Tokyo Chemical Industry Co., Ltd.).

[0062] (4) Component [D]: Thermoplastic resin "Sumikaexcel (registered trademark)" PES5003P (polyethersulfone, manufactured by Sumitomo Chemical Co., Ltd.).

[0063] (5) Other ingredients PX-200 (aromatic condensed phosphate ester, molecular weight: 687, manufactured by Daihachi Chemical Industry Co., Ltd.) 1,2-Hexanediol (molecular weight: 118, manufactured by Tokyo Chemical Industry Co., Ltd.).

[0064] <Various evaluation methods> The epoxy resin compositions of the examples and comparative examples were measured and evaluated using the following measurement methods.

[0065] (1) Three-point bending test of cured resin The uncured resin composition was degassed in a vacuum and then placed in a mold set to a thickness of 2 mm using a 2 mm Teflon (registered trademark) spacer. The temperature was raised from 30°C at a rate of 1.5°C / min and held at 180°C for 2 hours to cure the resin, yielding a 2 mm thick cured resin plate. Test pieces measuring 10 mm wide and 60 mm long were cut from the cured resin and tested in an Instron universal testing machine (manufactured by Instron Corporation) at a span of 32 mm, a crosshead speed of 2.5 mm / min, and six samples per test piece according to JIS K7171 (1994). The average values ​​of the modulus and strength were recorded as the modulus and strength of the cured resin, respectively. Furthermore, test pieces measuring 10 mm in width and 60 mm in length were cut out from the cured resin, and immersed in boiling water at 1 atmosphere for 20 hours to absorb moisture. Subsequently, a thermostatic chamber was used to bring the test pieces to 82°C, and three-point bending was carried out using an Instron universal testing machine (manufactured by Instron Corporation) with a span of 32 mm in accordance with JIS K7171 (1994) under the same conditions as above. The average value of the elastic modulus when the test pieces were subjected to three-point bending was recorded as the wet heat modulus.

[0066] (2) Measurement of the glass transition temperature (Tg) of the cured resin The uncured resin composition was degassed in a vacuum and then placed in a mold set to a thickness of 2 mm using a 2 mm Teflon® spacer. The temperature was raised from 30°C at a rate of 1.5°C / min and held at 180°C for 2 hours to cure the resin, yielding a 2 mm thick plate-shaped cured resin. Test pieces measuring 12.7 mm wide and 55 mm long were cut from the cured resin plate and immersed in boiling water at 1 atmosphere for 48 hours. The glass transition temperature (Tg after moisture absorption) was determined by DMA according to SACMA SRM18R-94. The glass transition temperature was determined as the temperature at the intersection of the tangent line in the glassy state and the tangent line in the transition state on the storage modulus G' curve. Measurements were performed at a heating rate of 5°C / min and a frequency of 1 Hz.

[0067] Example 1 (Preparation of Resin Composition) A resin composition was prepared by the following method.

[0068] In a kneading apparatus, 60 parts of Sumiepoxy (registered trademark) ELM434 and 40 parts of Epiclon (registered trademark) 830 were added as component [A] shown in Table 1, and 15 parts of Sumikaexcel (registered trademark) PES5003P were further added as component [D]. The mixture was heated to a target temperature of 150°C while kneading. After kneading for 1 hour at 150°C to dissolve component [D], the mixture was cooled to 70°C while kneading, and 45 parts of Seikacure S were added as component [B] and stirred for 30 minutes. Thereafter, 5 parts of trimethyl phosphate was added as component [C] and stirred for an additional 10 minutes to obtain a resin composition.

[0069] At this time, the average epoxy equivalent of the epoxy groups in the component [A] was 137 g / eq.

[0070] The obtained resin composition was subjected to three-point bending measurement of the cured resin, and the strength was 185 MPa, the elastic modulus was 3.7 GPa, the moist heat elastic modulus was 2.6 GPa, and the Tg after moisture absorption was 167° C. Compared with Comparative Example 1 (not containing component [C]) described later, excellent strength, elastic modulus, and moist heat elastic modulus were obtained without impairing the Tg after moisture absorption.

[0071] <Examples 2 to 5> According to the compounding ratios in Table 1, the components [A], [B], [C] and [D] were compounded in the same manner as in Example 1 to obtain resin compositions.

[0072] The results of various measurements in the examples are shown in Table 1. Even when the formulation of the resin composition was changed as in Examples 2 to 5, cured resin products were obtained that had an excellent balance of strength, elastic modulus, elastic modulus under wet heat, and Tg after moisture absorption.

[0073] <Examples 6 to 9> Resin compositions were obtained by blending the components [A], [B], [C], and [D] in the same manner as in Example 1 above, according to the blending ratios in Table 1. The results of various measurements in the examples are shown in Table 1. Even when the blending ratio of the glycidylamine-type epoxy resin and the glycidyl ether-type epoxy resin in component [A] was changed as in Examples 6 to 9, cured resin products were obtained that exhibited an excellent balance between strength, elastic modulus, moist heat elastic modulus, and Tg after moisture absorption.

[0074] Example 10 A resin composition was obtained by blending the components [A], [B], and [C] in the same manner as in Example 1 above, according to the blending ratios in Table 1. The results of various measurements in this example are shown in Table 1. Compared to the case where component [D] was added, the strength and wet heat breaking strain of the cured product were slightly inferior, but a sufficiently excellent cured resin product was obtained.

[0075] <Comparative Examples 1 to 5> According to the compounding ratios in Table 1, the components [A], [B], and [D] (and the component [C] or a substitute thereof) were compounded in the same manner as in Example 1 to obtain resin compositions.

[0076] No equivalent to the component [C] was blended in Comparative Example 1. Comparing Comparative Example 1 with Example 1, it is clear that the incorporation of component [C] improves the strength, elastic modulus, and moist heat elastic modulus of the cured resin without impairing the Tg after moisture absorption.

[0077] In Comparative Example 2, PX-200 was blended in place of component [C]. PX-200 does not satisfy the requirement that the molecular weight of component [C] be 250 or less. Comparing Comparative Example 2 with Example 1, it is clear that when the molecular weight of component [C] is 250 or less, the strength, elastic modulus, moist heat elastic modulus, and Tg after moisture absorption of the resulting cured resin are excellent.

[0078] In Comparative Example 3, 1,2-hexanediol was blended in place of component [C]. Comparing Comparative Example 3 with Example 1, it is clear that blending the phosphate ester compound, which is component [C], results in superior wet heat modulus and Tg after moisture absorption.

[0079] In Comparative Example 4, 18 parts by mass of dimethyl phenylphosphonate was blended as the component [C]. Comparative Example 4 does not satisfy the requirement that the component [C] be 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]. Comparing Comparative Example 4 with Example 4, it is found that the inclusion of the component [C] 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] results in an excellent Tg after moisture absorption of the resulting cured resin product.

[0080] In Comparative Example 5, the average epoxy equivalent of the component [A] was 172 g / eq, which did not satisfy the requirement that the average epoxy equivalent of the component [A] be 160 g / eq. Comparing Comparative Example 5, in which 5 parts of dimethyl phenylphosphonate was blended, with Example 3, it was found that satisfying the requirement that the average epoxy equivalent of the component [A] be 160 g / eq or less resulted in excellent strength, elastic modulus, moist heat elastic modulus, and Tg after moisture absorption of the obtained cured resin product.

[0081] [Table 1]

Claims

1. An epoxy resin composition comprising the following components [A], [B], and [C] and satisfying the following conditions (1) to (4): [A]: Epoxy resin containing two or more epoxy groups in one molecule [B]: an amine curing agent which is either or both of an aliphatic polyamine and an aromatic polyamine [C]: A phosphate ester compound having a molecular weight of 250 or less. (1): The component [C] is 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]. (2): The component [A] has an average epoxy equivalent of 160 g / eq or less. (3): In the cured product of the epoxy resin composition, component [A] and component [B] react to form a crosslinked structure, and component [C] is held within the network formed by the crosslinked structure. (4): When the total number of moles of epoxy groups in the component [A] is E (mol) and the total number of moles of active hydrogens in the component [B] is H (mol), the ratio thereof (H / E) is 0.50 or more and 1.30 or less.

2. 2. The epoxy resin composition according to claim 1, wherein, based on 100% by mass of the component [A], 40% by mass or more of an epoxy resin having an epoxy equivalent of 130 g / eq or less is contained.

3. 3. The epoxy resin composition according to claim 1, wherein the component [A] accounts for 20 to 80% by mass of a glycidyl ether epoxy resin, based on 100% by mass of the component [A].

4. The epoxy resin composition according to any one of claims 1 to 3, comprising diaminodiphenyl sulfone as the component [B].

5. The epoxy resin composition according to any one of claims 1 to 4, further comprising the following component [D]: [D]: Thermoplastic resin

6. The epoxy resin composition according to any one of claims 1 to 5, comprising a phenylphosphonic acid alkyl ester as the component [C].

7. A prepreg comprising the epoxy resin composition according to any one of claims 1 to 6 and continuous reinforcing fibers.

8. A fiber-reinforced composite material comprising a cured product of the epoxy resin composition according to any one of claims 1 to 7 and continuous reinforcing fibers.

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