Epoxy resin composition, prepreg and fiber-reinforced composite material

Abstract

The present invention aims to provide an epoxy resin composition which is suitable for use in prepregs and fiber-reinforced composite materials and has excellent elastic modulus, strength and pot life. The present invention is an epoxy resin composition, which comprises the following components [A] to [C] and satisfies the following conditions (1) to (4): [A]: epoxy resin, [B]: aromatic diamine, [C]: a compound having a boiling point of 130°C or higher and a molecular weight m of 50 or higher and 250 or lower, which has no epoxy group in the molecule and has substantially no epoxy resin curing ability, (1): the ratio H / E of the number of moles H of active hydrogen of component [B] to the number of moles E of epoxy groups of component [A] is 0.50 or higher and 1.30 or lower. (2): at least a portion of component [C] satisfies the ratio m / M of its molecular weight m to the molecular weight M between theoretical crosslinking points of a cured product of the epoxy resin composition of 0.10 or higher and 0.60 or lower. (3) The ratio C / E of the number of moles C of component [C] satisfying the above condition (2) to the number of moles E of epoxy groups of component [A] is 0.01 or more and 0.20 or less. (4) The viscosity after being kept at 70°C for 2 hours is 5.0 times or less of the initial viscosity at 70°C.

Description

Technical Field

[0001] The present invention relates to an epoxy resin composition which is suitable for use in fiber-reinforced composite materials for aerospace applications, general industrial applications, sports applications, etc., and a prepreg and a fiber-reinforced composite material using the epoxy resin composition. Background Art

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

[0003] In recent years, in order to further apply fiber-reinforced composite materials to applications that require further lightweighting, various physical properties need to be improved. Therefore, in order to improve the various mechanical properties of fiber-reinforced composite materials, it is required to improve the elastic modulus, elongation, and strength of epoxy resin used as a matrix resin. However, epoxy resin cured products with high elastic modulus are generally brittle and tend to have low elongation and strength. Therefore, it is a technical issue to simultaneously improve the high elastic modulus, elongation, and strength.

[0004] In order to seek the improvement of this topic, various researches have been carried out. For example, the method (patent documentation 1) of seeking the improvement of elastic modulus and intensity by combining epoxy resin with nanofiller with specific structure has been studied. In addition, the method (patent documentation 2) of seeking the improvement of resin strength by mixing additives in order to reduce the dissolution of dicyandiamide used as curing agent. In addition, for the resin combination towards RTM molding method, the method (patent documentation 3) of using the liquid curing agent that is not easy to become defect has been studied.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-95675

[0008] Patent Document 2: International Publication No. 2019 / 181402

[0009] Patent Document 3: Japanese Patent Application Publication No. 2014-227473 Summary of the invention

[0010] Problems to be solved by the invention

[0011] When the technology of Patent Document 1 is used, it cannot be said that the mechanical properties of the obtained cured resin and fiber-reinforced composite material are sufficient, and further improvement of mechanical properties is required. In addition, when the technology of Patent Document 2 is used, although the effect of improving the strength of the resin is obtained, there is no consideration about the improvement of the elastic modulus, and a technology that can improve both the elastic modulus and the strength is required. In addition, when the technology of Patent Document 3 is used, the reactivity of the resin composition is high and does not have a sufficient pot life for use in prepregs.

[0012] Therefore, an object of the present invention is to provide an epoxy resin composition which can be suitably used for prepregs and fiber-reinforced composite materials and which has excellent elastic modulus, strength, and pot life.

[0013] Means for solving problems

[0014] The present invention adopts the following means to solve such problems: That is, an epoxy resin composition comprising the following components [A] to [C] and satisfying the following conditions (1) to (4).

[0015] [A]: Epoxy resin,

[0016] [B]: Aromatic diamine,

[0017] [C]: A compound having a boiling point of 130° C. or higher and a molecular weight m of 50 or higher and 250 or lower, having no epoxy group in the molecule and having substantially no epoxy resin curing ability.

[0018] (1): The ratio H / E of the number of moles H of active hydrogen in component [B] to the number of moles E of epoxy groups in component [A] is 0.50 or more and 1.30 or less.

[0019] (2) At least a part of the component [C] satisfies that the ratio m / M of the molecular weight m to the molecular weight M between theoretical crosslinking points of the cured product of the epoxy resin composition is 0.10 or more and 0.60 or less.

[0020] (3) The ratio C / E of the number of moles C of the component [C] satisfying the above condition (2) to the number of moles E of the epoxy groups of the component [A] is 0.01 or more and 0.20 or less.

[0021] (4): The viscosity after being kept at 70°C for 2 hours is 5.0 times or less of the initial viscosity at 70°C.

[0022] The present invention is also a prepreg formed of the epoxy resin composition of the present invention and reinforcing fibers.

[0023] The present invention also provides a fiber-reinforced composite material comprising a cured product of the epoxy resin composition of the present invention and reinforcing fibers.

[0024] Effects of the Invention

[0025] According to the present invention, an epoxy resin composition which can be suitably used for prepreg and fiber-reinforced composite materials and which is excellent in elastic modulus, strength and pot life can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a graph showing the relationship between the ratio C / E of the number of moles C of constituent [C] to the number of moles E of epoxy groups in constituent [A] and the elastic modulus in Example 2 (C / E=0.10), Example 5 (C / E=0.02), Example 6 (C / E=0.05), Example 7 (C / E=0.16), Comparative Example 1 (C / E=0.00) and Comparative Example 8 (C / E=0.23).

[0027] Figure 2 This is a graph showing the relationship between the ratio C / E of the number of moles C of component [C] to the number of moles E of epoxy groups in component [A] and the strength in Example 2 (C / E=0.10), Example 5 (C / E=0.02), Example 6 (C / E=0.05), Example 7 (C / E=0.16), Comparative Example 1 (C / E=0.00) and Comparative Example 8 (C / E=0.23).

[0028] Figure 3 This is a graph showing the relationship between the ratio m / M of the molecular weight m of the component [C] to the theoretical cross-linking point molecular weight M of the cured product of the epoxy resin composition and the elastic modulus in Example 1 (m / M=0.29), Example 2 (m / M=0.35), Example 3 (m / M=0.55), Example 4 (m / M=0.40), Comparative Example 1, Comparative Example 4 (m / M=1.40), and Comparative Example 9 (m / M=0.68). It should be noted that Comparative Example 1 not including the component [C] is plotted at the position of m / M=0.00.

[0029] Figure 4 This is a graph showing the relationship between the ratio m / M of the molecular weight m of the component [C] to the theoretical molecular weight M between crosslinking points of the cured product of the epoxy resin composition and the strength in Example 1 (m / M=0.29), Example 2 (m / M=0.35), Example 3 (m / M=0.55), Example 4 (m / M=0.40), Comparative Example 1, Comparative Example 4 (m / M=1.40), and Comparative Example 9 (m / M=0.68). It should be noted that Comparative Example 1 not including the component [C] is plotted at the position of m / M=0.00. DETAILED DESCRIPTION

[0030] Hereinafter, the present invention will be described in detail. It should be noted that, in the present invention, the term "above" means the same as or greater than the numerical value shown there. In addition, the term "below" means the same as or less than the numerical value shown there.

[0031] The resin composition of the present invention contains components [A] to [C] as essential components. In the present invention, the "component" refers to a compound contained in the composition.

[0032] The component [A] in the present invention is an epoxy resin. The epoxy resin as the component [A] is preferably one containing two or more epoxy groups in one molecule because it can increase the glass transition temperature of the cured product obtained by heat-curing the resin composition and improve the heat resistance. In addition, an epoxy resin containing one epoxy group in one molecule can also be mixed. These epoxy resins can be used alone or mixed appropriately.

[0033] Examples of the epoxy resin of component [A] include diaminodiphenylmethane type, diaminodiphenylsulfone type, aminophenol type, bisphenol type, m-xylylenediamine type, 1,3-bisaminomethylcyclohexane type, isocyanurate type, hydantoin type, phenol novolac type, o-cresol novolac type, trihydroxyphenylmethane type, and tetraphenylethane type epoxy resins. Among them, diaminodiphenylmethane type, aminophenol type, and bisphenol type epoxy resins are particularly preferably used because of their good balance of physical properties.

[0034] Examples of commercially available diaminodiphenylmethane-type epoxy resins include ELM434 (manufactured by Sumitomo Chemical Co., Ltd.) and "Alarapton (registered trademark)" MY720 Made by スト・マテリアルズ Co., Ltd.), "アラルダイト (registered trademark)" MY721 ( Manufactured by ハンツマン·アドバンスト·マテリアルズ Co., Ltd.), "アラルダイト (registered Trademark)" MY9512 (manufactured by Hakuman Matsushita Co., Ltd.) , "アラルダイト (registered trademark)" MY9663 (ハンツマン·アドバンスト· Mitsubishi Chemical Co., Ltd.), "Etoto Chemical Co., Ltd." YH-434 (registered trademark), "jER (registered trademark)" 630 (Mitsubishi Chemical Co., Ltd.), etc.

[0035] Examples of commercially available products of diaminodiphenyl sulfone epoxy resins include TG3DAS (manufactured by Mitsui Chemicals, Inc.).

[0036] Examples of commercially available aminophenol type epoxy resins include ELM120 (manufactured by Sumitomo Chemical Co., Ltd.), ELM100 (manufactured by Sumitomo Chemical Co., Ltd.), and "jER (registered trademark)" 63 0 (Manufactured by Mitsubishi Microelectronics Co., Ltd.), "Alarac (registered trademark)" MY050 0(manufactured by Harman Chemical Co., Ltd.), "アラルイ" "ト(Registered Trademark)" MY0510 Made by ズ (Co., Ltd.), "Alarado (registered trademark)" MY0600 (ハンツマン・アドバンスト・マテリアルズ Co., Ltd.), "アラルダイト (registered trademark) ” MY0610 (manufactured by Harman Chemical Co., Ltd.), etc.

[0037] Commercially available products of bisphenol A type epoxy resins include "EPON (registered trademark)" 825 (manufactured by Mitsubishi Chemical Co., Ltd.), "Epicon (registered trademark)" 850 (manufactured by DIC Corporation), "Epot (registered trademark)" YD-128 (manufactured by Tohto Chemical Co., Ltd.), DER-331, and DER-332 (all manufactured by Daw Chemical Co., Ltd.).

[0038] Examples of commercially available bisphenol F-type epoxy resins include “Aldite (registered trademark)” GY282 (manufactured by Handman Artban Materials Co., Ltd.), “jER (registered trademark)” 806, “jER (registered trademark)” 807, and “jER (registered trademark)” 1750 (all manufactured by Mitsubishi Chemical Corporation), “Epicon (registered trademark)” 830 (manufactured by DIC Corporation), and “Epote (registered trademark)” YD-170 (manufactured by Tohto Chemical Industry Co., Ltd.).

[0039] Furthermore, the epoxy resin composition of the present invention may also contain epoxy compounds other than those mentioned above as appropriate.

[0040] The component [B] in the present invention is an aromatic diamine. The polyamine included in the aromatic diamine group has a plurality of amino groups that can react with epoxy groups and functions as a curing agent. Among them, aromatic polyamines, especially aromatic diamines, are excellent as curing agents in that they can provide high mechanical properties and heat resistance to epoxy resin cured products.

[0041] Examples of the substances classified as aromatic diamines include 2,2'-diethyldiaminodiphenylmethane, 2,4-diethyl-6-methyl-m-phenylenediamine, 4,6-diethyl-2-methyl-m-phenylenediamine, diethyltoluenediamines such as 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'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 3,3'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3'-di-tert-butyl-4 ,4'-diaminodiphenylmethane, 3,3'-diethyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-di-tert-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-tert-butyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3'-di-tert-butyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetra-tert-butyl-4,4'-diaminodiphenylmethane, etc. Among them, 3,3'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl sulfone are preferred because the obtained cured product has excellent mechanical properties. In addition, since the increase in viscosity of the epoxy resin composition of the present invention when kept at 70°C can be suppressed and the pot life can be effectively improved, it is preferred to use a solid aromatic diamine, and it is particularly preferred to contain at least one of 3,3'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl sulfone.

[0042] Examples of commercially available aromatic diamines include Seikacua S (manufactured by Wakayama Seika Industries, Ltd.), MDA-220 (manufactured by Mitsui Chemicals, Inc.), “jERcua (registered trademark)” WA (manufactured by Mitsubishi Chemical Co., Ltd.), 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).

[0043] As for the mixing amount of the aromatic diamine in the present invention, it is important that the ratio H / E of the number of moles H of active hydrogen of the aromatic diamine to the number of moles E of epoxy groups of the constituent [A] is 0.50 or more and 1.30 or less (condition (1)), preferably 0.70 or more and 1.20 or less, more preferably 0.80 or more and 1.10 or less. By making H / E within such a range, a cross-linked structure can be appropriately formed by the reaction of the epoxy resin and the aromatic diamine, and a resin cured product with excellent strength and elongation can be obtained. In addition, by making H / E 0.80 or more and 1.10 or less, the constituent [C] described later is easily maintained in the cross-linked structure, and the elastic modulus, strength, and elongation are improved.

[0044] In the epoxy resin composition of the present invention, the ratio of the total number of moles of at least one of 3,3'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl sulfone to the number of moles E of the epoxy group of the component [A] ((the total number of moles of at least one of 3,3'-diaminodiphenyl sulfone and 4,4'-diaminodiphenyl sulfone) / E) is preferably 0.50 or more and 1.30 or less. By making it 0.50 or more and 1.30 or less, more preferably 0.70 or more and 1.20 or less, and further preferably 0.80 or more and 1.10 or less, the viscosity increase of the epoxy resin composition of the present invention when it is kept at 70°C can be suppressed, and the pot life can be effectively improved.

[0045] Component [C] is a compound having a boiling point of 130° C. or higher and a molecular weight m of 50 or higher and 250 or lower, having no epoxy group in the molecule and having substantially no epoxy resin curing ability. Here, compounds such as amines or phenols capable of addition reaction with epoxy resins, acid anhydrides capable of copolymerizing with epoxy resins, imidazoles capable of serving as self-polymerization initiators for epoxy resins, aromatic urea compounds, and tertiary amine compounds are compounds having epoxy resin curing ability and do not correspond to compounds having no epoxy resin curing ability.

[0046] In the cross-linked structure formed by the reaction of epoxy resin and aromatic diamine, constituent element [C] is not introduced into the cross-linked structure, but exists in the voids thereof, and this state is maintained after curing. As a result, the elastic modulus of the resulting epoxy resin cured product becomes higher. In addition, surprisingly, the inventors found that by mixing constituent element [C], an epoxy resin cured product having not only a high elastic modulus, but also a high elongation and high strength is obtained. The reason for this is not certain, but the inventors consider it as follows. Constituent element [C] does not react with epoxy resins and aromatic diamines that form a cross-linked structure because it does not have an epoxy group in the molecule and does not substantially have the curing ability of epoxy resin. Therefore, the inventors believe that constituent element [C] will not be bound by the cross-linked structure and covalent bonds formed by the reaction of epoxy resin and aromatic diamine, and will be appropriately maintained in the voids of the cross-linked structure, so that the voids in the cured product can be effectively filled, and the elastic modulus of the cured product becomes higher. The inventors also believe that when strain is applied to the cured product, the component [C] freely moves in the crosslinked structure, thereby alleviating the strain energy until the product is broken, thereby increasing the elongation and strength of the cured product.

[0047] In addition, by having a boiling point of component [C] of 130°C or more, more preferably 180°C or more, the volatilization of component [C] during the curing of the epoxy resin composition can be suppressed, and a cured resin and a fiber-reinforced composite material having excellent mechanical properties can be obtained. Further, the generation of voids in the obtained fiber-reinforced composite material and the reduction of mechanical properties can be suppressed. In the present invention, the boiling point is a value under normal pressure (101 kPa). In addition, when the boiling point under normal pressure cannot be determined, a converted boiling point converted to 101 kPa in a boiling point conversion chart can be used.

[0048] The molecular weight m of component [C] is 50 to 250, more preferably 70 to 120. By setting the molecular weight of component [C] to be within such a range, component [C] is appropriately held in the voids of the crosslinked structure formed by the reaction of the epoxy resin and the aromatic diamine, and a cured product having excellent elastic modulus, strength, and elongation is obtained.

[0049] The component [C] is preferably a compound having at least one functional group selected from an amide group, a ketone group and a hydroxyl group in the molecule. When the component [C] has a highly polar functional group as described above in the molecule, a strong intermolecular interaction occurs between the hydroxyl group in the cross-linked structure formed by the components [A] and [B] and the component [C], and the component [C] is easily appropriately held in the voids of the cross-linked structure, thereby obtaining a particularly excellent effect of improving the elongation and strength.

[0050] As such constituent element [C], there can be mentioned amides such as N-methylformamide, N-methylacetamide, 2-pyrrolidone, N-methylpropionamide, N-ethylacetamide, N-methylacetanilide, N,N'-diphenylacetamide, and diols such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, and heptanediol. These compounds may be used alone or in combination as appropriate.

[0051] The theoretical molecular weight M between crosslinking points of the epoxy resin composition of the present invention is preferably 500 or less, more preferably 400 or less, and even more preferably 250 or less. When the theoretical molecular weight M between crosslinking points is within such a range, component [C] is easily retained in the gaps of the crosslinking structure formed by the reaction of the epoxy resin and the aromatic diamine, and a cured product having particularly excellent elastic modulus, strength, and elongation is obtained, which is preferred.

[0052] Here, the so-called theoretical molecular weight between crosslinking points M is a value derived by calculation from each component constituting the epoxy resin composition, and is a value obtained by dividing the mass W of the entire resin cured product obtained by curing the epoxy resin composition by the number N of crosslinking points possessed by the entire resin cured product. That is, it can be considered that the larger M is, the larger the void size in the crosslinking structure is. Here, the mass W of the entire resin cured product refers to the total mass of all epoxy resin components and polyamine components contained in the epoxy resin composition, and the components other than these are not used for calculation.

[0053] The theoretical molecular weight M between crosslinking points is obtained by the following calculation. First, when the epoxy resin composition contains k types (k is an integer) of epoxy resin components, the compounding amount of the i-th (i is an integer from 1 to k) epoxy resin component is set to a. i (Unit: g) When the epoxy resin composition contains l (l is an integer) polyamine components, the blending amount of the jth (j is an integer from 1 to 1) polyamine is defined as b j (unit: g), the mass W (unit: g) of the entire resin cured product can be calculated by formula (1).

[0054]

[0055] The epoxy equivalent of the i-th epoxy resin component is set to E i , let the number of epoxy groups in one molecule of the i-th epoxy resin component be x i In addition, the active hydrogen equivalent of the jth polyamine component is denoted by H j , let the number of active hydrogen atoms in one molecule of the jth polyamine component be y jThe number N of crosslinking points contained in the entire cured resin is obtained in different ways when the mixing ratio of epoxy resin to polyamine is a stoichiometric amount, when polyamine is in excess, and when epoxy resin is in excess. Which method is used is determined by the mixing ratio index β indicating the mixing ratio of epoxy resin to polyamine obtained by formula (2).

[0056]

[0057] Here, when β=1, the mixing ratio of epoxy resin to polyamine is a stoichiometric amount, and the number of crosslinking points N is obtained by formula (3). The number of crosslinking points N represents the number of crosslinking points generated by the reaction of all reactive epoxy groups with all active hydrogens of polyamine.

[0058]

[0059] When β>1, the polyamine is in excess of the stoichiometric amount, and the number N of crosslinking points is calculated by formula (4).

[0060]

[0061] When β<1, the epoxy resin is in excess of the stoichiometric amount, and the number N of crosslinking points is calculated by equation (5).

[0062]

[0063] Here, E i × i , and H j ×y j represent the average molecular weight of the i-th epoxy resin component and the average molecular weight of the j-th polyamine component, respectively. i -2) represents the number of crosslinking points generated by the reaction of all epoxy groups in the ith epoxy resin component 1 molecule with the active hydrogen of the polyamine and introduced into the crosslinking structure. j -2) represents the number of crosslinking points generated by the reaction of all active hydrogens in one molecule of the jth polyamine with epoxy groups and introduced into the crosslinking structure. For example, in the case where the i-th epoxy resin component is a tetrafunctional epoxy resin, one molecule has four epoxy groups, and the number of crosslinking points generated becomes 4-2, which is 2. In the case of a monofunctional epoxy resin, the number of crosslinking points generated is calculated as 0. In addition, in the case where each molecule of the j-th polyamine component has two active hydrogens, the number of crosslinking points generated becomes 2-2, which is 0. Using W and N obtained by the above formula, the theoretical molecular weight M between crosslinking points is calculated by formula (6).

[0064]

[0065] Here, as an example, the theoretical molecular weight between crosslinking points M of the resin cured product of the epoxy resin composition formed by 90 g of epoxy resin 1 (epoxy groups: 3, epoxy equivalent: 98 g / eq), 10 g of epoxy resin 2 (epoxy groups: 2, epoxy equivalent: 135 g / eq), and 44.7 g of polyamine 1 (active hydrogen: 4, active hydrogen equivalent: 45 g / eq) is calculated. First, the mass W of the entire resin cured product is 144.7 g according to formula (1). In addition, β calculated by formula (2) is 1, so the number of crosslinking points N possessed by the entire resin cured product is calculated as 0.803 by formula (3). Therefore, the theoretical molecular weight between crosslinking points M of the resin cured product is calculated as 180 by formula (6).

[0066] In the epoxy resin composition of the present invention, it is also important that at least a portion of the constituent element [C] satisfies the ratio m / M of its molecular weight m to the molecular weight M between the theoretical crosslinking points of the cured product of the epoxy resin composition is greater than 0.10 and less than 0.60 (condition (2)). The present invention improves the elastic modulus, strength, and elongation of the resin cured product by mixing constituent elements [C] of an appropriate molecular weight relative to the void size of the crosslinked structure formed by the reaction of the epoxy resin and the aromatic diamine. However, the void size of the crosslinked structure formed by the reaction of the epoxy resin and the aromatic diamine varies one by one depending on the type of epoxy resin and aromatic diamine used. Therefore, by making m / M within the above range, constituent element [C] is appropriately maintained in the void of the crosslinked structure, and a cured product with excellent elastic modulus, strength, and elongation is obtained. By making m / M preferably greater than 0.30 and less than 0.50, a cured product with particularly excellent elastic modulus, strength, and elongation is obtained.

[0067] In the epoxy resin composition of the present invention, it is important that the ratio C / E of the number of moles C of the constituent element [C] satisfying the above condition (2) to the number of moles E of the epoxy group of the constituent element [A] is greater than 0.01 and less than 0.20 (condition (3)). By making C / E within such a range, the constituent element [C] is appropriately maintained in the void portion of the cross-linked structure formed by the reaction of the epoxy resin and the aromatic diamine, and a cured product having excellent elastic modulus, strength, and elongation is obtained. In addition, by making the above m / M greater than 0.30 and less than 0.50, and further making C / E preferably greater than 0.07 and less than 0.20, a cured product having a particularly high elastic modulus is obtained. In addition, by making the above m / M greater than 0.30 and less than 0.50, and further making C / E preferably greater than 0.01 and less than 0.13, a cured product having a particularly high strength is obtained. Furthermore, by setting the m / M to 0.30 or more and 0.50 or less, and further preferably setting C / E to 0.07 or more and 0.13 or less, a cured product having particularly excellent elastic modulus and strength can be obtained.

[0068] It is also important that the viscosity of the resin composition of the present invention when maintained at 70°C for 2 hours is 5.0 times or less of the initial viscosity at 70°C (condition (4)). By making such a ratio (also referred to as "viscosity increase ratio") 5.0 times or less, more preferably 3.0 times or less, and further preferably 2.5 times or less, the viscosity change of the resin composition in the process of kneading the resin composition and the process of impregnating the resin composition into the reinforcing fiber is reduced, and the storage period can be prolonged. In addition, the deviation of the flow amount of the resin composition during molding can be reduced, and the variation of the resin content contained in the fiber-reinforced composite material can be suppressed, so that a fiber-reinforced composite material with stable dimensions and mechanical properties can be obtained.

[0069] By using a solid substance, particularly at least one of 3,3′-diaminodiphenyl sulfone and 4,4′-diaminodiphenyl sulfone, as the aromatic diamine of component [B], the viscosity increase ratio can be effectively suppressed.

[0070] The epoxy resin composition of the present invention has excellent elastic modulus, strength and elongation, and is suitable for use as a matrix resin of a fiber-reinforced composite material. That is, the fiber-reinforced composite material of the present invention is formed of a cured product of the epoxy resin composition of the present invention and reinforcing fibers.

[0071] As a method for obtaining a fiber-reinforced composite material, there are hand lay-up method, RTM method, filament winding method, drawing molding method, etc., a method of impregnating a resin composition into reinforcing fibers in a molding process, and a method of molding a prepreg obtained by impregnating a resin composition into reinforcing fibers in advance by an autoclave method or a compression molding method. Among them, in order to precisely control the configuration of the fibers and the proportion of the resin and maximize the characteristics of the composite material, it is preferred to pre-preg formed of an epoxy resin composition and reinforcing fibers. That is, the prepreg of the present invention is formed of an epoxy resin composition and reinforcing fibers of the present invention.

[0072] As the reinforcing fibers used in the prepreg of the present invention and the fiber-reinforced composite material of the present invention, carbon fibers, graphite fibers, aramid fibers, glass fibers, etc. can be preferably cited, but carbon fibers are particularly preferred. The form and arrangement of the reinforcing fibers are not limited, and fiber structures such as long fibers, single tows, woven fabrics, knitted fabrics, and braids that are pulled in one direction can be used. As reinforcing fibers, two or more carbon fibers, glass fibers, aramid fibers, boron fibers, PBO fibers, high-strength polyethylene fibers, alumina fibers, and silicon carbide fibers can be used in combination.

[0073] Specific examples of the carbon fiber include acrylic, pitch, and rayon carbon fibers, and acrylic carbon fibers having particularly high tensile strength are preferably used.

[0074] As the form of carbon fiber, twisted yarn, untwisted yarn and untwisted yarn can be used. However, in the case of twisted yarn, the orientation of the filaments constituting the carbon fiber is not parallel, which becomes a cause of reduced mechanical properties of the obtained carbon fiber reinforced composite material. Therefore, it is preferred to use untwisted yarn or untwisted yarn that has a good balance between the formability and strength characteristics of the carbon fiber reinforced composite material.

[0075] The tensile modulus of carbon fiber is preferably 200 GPa or more and 440 GPa or less. The tensile modulus of carbon fiber is affected by the crystallinity of the graphite structure constituting the carbon fiber, and the higher the crystallinity, the higher the elastic modulus. If it is within this range, the rigidity and strength of the carbon fiber reinforced composite material are all balanced at a high level, so it is preferred. The more preferred elastic modulus is 230 GPa or more and 400 GPa or less, and 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).

[0076] The prepreg of the present invention can be produced by various known methods, for example, by a hot melt method in which a resin composition is heated to reduce viscosity without using an organic solvent and then impregnated into reinforcing fibers.

[0077] In addition, for the hot melt method, a method of directly impregnating the reinforcing fibers with a resin composition that has been reduced in viscosity by heating, or a method of first preparing a release paper sheet with a resin film by temporarily applying the resin composition on release paper or the like, then overlapping the resin film with the reinforcing fiber side from both sides or one side of the reinforcing fibers, and heating and pressurizing to impregnate the reinforcing fibers with the resin composition, etc. can be used.

[0078] The content of reinforcing fibers in the prepreg is preferably 30% by mass or more and 90% by mass or less. By being 30% by mass or more, more preferably 35% by mass or more, and further preferably 65% ​​by mass or more, it is easy to obtain the advantages of fiber-reinforced composite materials with excellent specific strength and specific elastic modulus. In addition, when the fiber-reinforced composite material is formed, the heat release during curing can be suppressed from becoming too high. On the other hand, by being 90% by mass or less, more preferably 85% by mass or less, the generation of voids in the composite material caused by poor impregnation of the resin can be suppressed. In addition, the viscosity of the prepreg can be maintained.

[0079] The fiber-reinforced composite material of the present invention can be produced by laminating the prepreg of the present invention in a predetermined form and applying pressure / heat to cure the resin as an example. Among the methods of applying heat and pressure, press molding, autoclave molding, bag molding, wrapping tape, internal pressure molding, etc. are used.

[0080] The fiber-reinforced composite material of the present invention can be widely used for aerospace applications, general industrial applications, and sports applications. More specifically, for general industrial applications, it is suitable for use in structures such as automobiles, ships, and railway vehicles. For sports applications, it is suitable for use in golf clubs, fishing rods, tennis rackets, and badminton rackets.

[0081] Example

[0082] The present invention is described in detail below by way of examples. However, the scope of the present invention is not limited to these examples. It should be noted that the unit "part" of the composition ratio refers to parts by mass unless otherwise noted. In addition, the measurement of various characteristics (physical properties) is carried out under an environment of a temperature of 23° C. and a relative humidity of 50% unless otherwise noted.

[0083] <Materials used in Examples and Comparative Examples>

[0084] (1) Component [A]: Epoxy resin

[0085] ·"Aralado (registered trademark)" MY0600 (aminophenol type epoxy resin, epoxy equivalent: 1 18g / eq, the number of epoxy groups: 3, manufactured by Hinoman Chemical Co., Ltd.

[0086] "jER (registered trademark)" 825 (bisphenol A type epoxy resin, epoxy equivalent: 170 g / eq, number of epoxy groups: 2, manufactured by Mitsubishi Chemical Co., Ltd.)

[0087] Glycidol (molecular weight: 74, epoxy equivalent: 74 g / eq, number of epoxy groups: 1, boiling point: 167° C., manufactured by Tokyo Chemical Industry Co., Ltd.).

[0088] (2) Component [B]: Aromatic diamine

[0089] 3,3'-DAS (3,3'-diaminodiphenyl sulfone, active hydrogen equivalent: 62 g / eq, number of active hydrogen atoms: 4, manufactured by Mitsui Chemicals Fiine Co., Ltd.)

[0090] ・Seikacua S (4,4'-diaminodiphenyl sulfone, active hydrogen equivalent: 62 g / eq, number of active hydrogen atoms: 4, manufactured by Wakayama Seika Industries, Ltd.)

[0091] "jER Cycle (registered trademark)" WA (diethyltoluenediamine, active hydrogen equivalent: 45 g / eq, number of active hydrogens: 4, manufactured by Mitsubishi Chemical Corporation).

[0092] (3) Component [C]: a compound having a boiling point of 130° C. or higher and a molecular weight m of 50 to 250, having no epoxy group in the molecule and having substantially no epoxy resin curing ability.

[0093] 1,2-Ethylene glycol (boiling point: 197°C, molecular weight m: 62, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0094] 1,2-Propanediol (boiling point: 188°C, molecular weight m: 76, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0095] 1,2-Hexanediol (boiling point: 245°C, molecular weight m: 118, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0096] N-methylpropionamide (boiling point: 223°C, molecular weight m: 87, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0097] ·N,N'-diphenylacetamide (boiling point (converted value): 410°C, molecular weight m: 211, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0098] 1,2-Octanediol (boiling point: 267°C, molecular weight m: 146, manufactured by Tokyo Chemical Industry Co., Ltd.).

[0099] (4) Other compounds

[0100] ·Ethanol (boiling point: 78°C, molecular weight m: 46, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0101] N,N'-diphenyl-4-methoxybenzamide (boiling point: 468°C, molecular weight m: 303, manufactured by Tokyo Chemical Industry Co., Ltd.).

[0102] <Various evaluation methods>

[0103] The epoxy resin composition of each example was measured using the following measurement method.

[0104] (1) Three-point bending measurement of cured resin

[0105] After the uncured resin composition was degassed in a vacuum, the temperature was raised from 30°C at a rate of 1.7°C / min in a mold set to a thickness of 2 mm through a 2 mm thick "Teflon (registered trademark)" spacer, and the temperature was maintained at 125°C for 5 hours, and then the temperature was raised at a rate of 1.7°C / min and cured at 225°C for 2 hours to obtain a plate-shaped resin cured product with a thickness of 2 mm. A test piece with a width of 10 mm and a length of 60 mm was cut out from the cured resin, and a three-point bending measurement was performed according to JIS K7171 (1994) using an Instron universal testing machine (manufactured by Instron Co., Ltd.) with a span of 32 mm, a crosshead speed of 2.5 mm / min, and a number of samples of n=6. The elastic modulus, strength, and elongation at this time were set as the elastic modulus, strength, and elongation of the cured resin, respectively.

[0106] (2) Viscosity measurement of resin composition

[0107] Using a dynamic viscoelasticity device ARES-G2 (manufactured by Thei Instruments Co., Ltd.), the upper and lower measuring fixtures were parallel plates with a flat plate diameter of 40 mm, and the epoxy resin composition was set in a manner such that the distance between the upper and lower fixtures was 1 mm. The initial viscosity of the epoxy resin composition at 70°C and the viscosity when it was kept at 70°C for 2 hours in the state set in the device were measured in a torsion mode (measurement frequency: 0.5 Hz). In addition, the viscosity when kept at 70°C for 2 hours was divided by the initial viscosity at 70°C to obtain the viscosity increase ratio.

[0108] <Example 1>

[0109] (Preparation of resin composition)

[0110] A resin composition was prepared by the following method.

[0111] 100 parts of "Araldite (registered trademark)" MY0600 as component [A] listed in Table 1 were placed in a kneading device, and heated to a target temperature of 55 to 65° C. while kneading. 53 parts of 3,3'-DAS as component [B] were added and stirred for 30 minutes. Then, 5 parts of 1,2-ethylene glycol as component [C] were added and stirred for further 10 minutes to obtain a resin composition.

[0112] At this time, the ratio H / E of the number of moles H of active hydrogen in component [B] to the number of moles E of epoxy groups in component [A] was 1.00. In addition, the ratio C / E of the number of moles C of component [C] to the number of moles E of epoxy groups in component [A] was 0.10. In addition, the theoretical molecular weight M between crosslinking points of the epoxy resin composition containing components [A] and [B] was 216, the molecular weight m of component [C] was 62, and m / M was 0.29.

[0113] The obtained resin composition was subjected to a three-point bending test of the cured resin, and the results showed that the elastic modulus was 5.1 GPa, the strength was 225 MPa, and the elongation was 5.9%. Compared with Comparative Example 1 (not mixed with component [C]) described later, excellent elastic modulus, strength, and elongation were obtained. In addition, the viscosity when kept at 70°C for 2 hours was 2.2 times the initial viscosity at 70°C, and the storage life was sufficient.

[0114] <Examples 2 to 10, 12, Reference Example 1>

[0115] The components [A], [B] and [C] were blended in the same manner as in Example 1 according to the blending ratios shown in Tables 1 and 2 to obtain a resin composition.

[0116] The various measurement results of the examples are shown in Tables 1 and 2. When the resin composition was mixed as in Examples 2 to 10, 12 and Reference Example 1, excellent elastic modulus, strength and elongation of the cured resin were obtained. In addition, the viscosity increase ratio was also good.

[0117] <Comparative Examples 1 to 10>

[0118] The components [A] and [B] (and [C] or its substitute) were mixed in the same manner as in Example 1 according to the mixing ratios shown in Table 2 to obtain a resin composition.

[0119] A substance corresponding to component [C] was not mixed in Comparative Example 1. Comparison of Comparative Example 1 with Example 1 shows that the elastic modulus, strength, and elongation of the cured resin are improved by mixing component [C], and in particular, the strength and elongation are improved dramatically.

[0120] A substance corresponding to component [C] was not mixed in Comparative Example 2. Comparison between Comparative Example 2 and Example 6 shows that the elastic modulus and strength of the cured resin material were significantly improved by mixing component [C].

[0121] In Comparative Example 3, ethanol is blended instead of component [C]. Ethanol does not satisfy the conditions of component [C] that the boiling point is 130° C. or higher and the molecular weight m is 50 or higher and 250 or lower. Comparing Comparative Example 3 with Example 1, it is found that by blending component [C] that satisfies the requirements of a boiling point of 130° C. or higher and a molecular weight m of 50 or higher and 250 or lower, the elastic modulus, strength, and elongation of the obtained cured resin are improved.

[0122] In Comparative Example 4, N,N'-diphenyl-4-methoxybenzamide is blended instead of component [C]. N,N'-diphenyl-4-methoxybenzamide does not satisfy the condition that the molecular weight m in component [C] is 50 or more and 250 or less. In addition, the ratio m / M of the molecular weight m of component [C] to the molecular weight M between theoretical crosslinking points of the epoxy resin composition is 0.10 or more and 0.60 or less. If Comparative Example 4 is compared with Example 1, it can be seen that by satisfying the above conditions, the elastic modulus, strength, and elongation of the obtained resin cured product are improved.

[0123] In Comparative Example 5, glycidol is blended instead of component [C]. Glycidol has an epoxy group in the molecule. By comparing Comparative Example 5 with Example 1, it can be seen that since component [C] does not have an epoxy group in the molecule, the elastic modulus, strength, and elongation of the obtained resin cured product are improved.

[0124] In Comparative Examples 6 and 7, the ratio H / E of the number of moles H of active hydrogen in component [B] to the number of moles E of epoxy groups in component [A] is not satisfied, that is, 0.50 or more and 1.30 or less. Comparative Examples 6 and 7 are compared with Example 1, and it is found that by satisfying the above conditions, the strength of the obtained cured resin is improved.

[0125] In Comparative Example 8, the ratio C / E of the number of moles C of component [C] to the number of moles E of epoxy groups of component [A] is not satisfied to be 0.01 or more and 0.20 or less. Comparing Comparative Example 8 with Example 1, it is found that by satisfying the above conditions, the elastic modulus, strength and elongation of the obtained cured resin are improved.

[0126] In Comparative Example 9, the ratio m / M of the molecular weight m of component [C] to the molecular weight M between theoretical crosslinking points of the epoxy resin composition containing components [A] and [B] is not satisfied, that is, 0.10 or more and 0.60 or less. Comparative Example 9 is compared with Example 1, and it is found that by satisfying the above conditions, the elastic modulus, strength, and elongation of the obtained cured resin are improved.

[0127] In Comparative Example 10, the condition that the viscosity of the epoxy resin composition when kept at 70° C. for 2 hours is 5.0 times or less of the initial viscosity at 70° C. is not satisfied. Therefore, the viscosity increase in the step of mixing the epoxy resin is large, and the pot life of the composition is short. Comparative Example 10 is compared with Example 1, and it is understood that by satisfying the above conditions, the obtained resin composition has a long pot life and excellent workability.

[0128] Here, when comparing Example 2, Example 5, Example 6, Example 7, Comparative Example 1, and Comparative Example 8, they are epoxy resin compositions containing the same component [A], component [B], and component [C], and only the compounding amount of component [C] is different. The relationship between the ratio C / E of the number of moles C of component [C] to the number of moles E of epoxy groups of component [A] and the elastic modulus is shown in the figure Figure 1 The relationship between the intensity and Figure 2 In. By Figure 1 , 2 It can be seen that in the epoxy resin composition of the present invention, a cured product having excellent elastic modulus, strength, and elongation can be obtained by 0.01≤C / E≤0.20. In addition, it can be seen that if 0.07≤C / E≤0.20, a cured product having particularly excellent elastic modulus can be obtained, and if 0.01≤C / E≤0.13, a cured product having particularly excellent strength can be obtained.

[0129] Furthermore, Example 1, Example 2, Example 3, Example 4, Comparative Example 1, and Comparative Example 9 are epoxy resin compositions containing the same component [A] and component [B] in the same mixing ratio, and the type of component [C] is different or not used. The relationship between m / M and elastic modulus is shown in FIG. Figure 3 The relationship between the intensity and Figure 4 In. By Figure 3 , 4 Comparison of Example 1, Example 2, Example 3, Example 4, Comparative Example 1, and Comparative Example 9 shows that in the resin composition of the present invention, by satisfying the relationship of 0.10≤m / M≤0.60, a cured product having excellent elastic modulus and strength of the cured resin is obtained. In addition, when the relationship of 0.30≤m / M≤0.50 is satisfied, a cured product having particularly excellent elastic modulus, strength, and elongation is obtained.

[0130] [Table 1]

[0131]

[0132] [Table 2]

[0133]

Claims

1. A prepreg, which is formed from an epoxy resin composition and reinforcing fibers, wherein the epoxy resin composition comprises the following components [A] to [C] and satisfies the following conditions (1) to (5), [A]: epoxy resin, [B]: Aromatic diamine, [C]: A compound having a boiling point of 130° C. or higher and a molecular weight m of 50 or higher and 250 or lower, having no epoxy group in the molecule and having substantially no epoxy resin curing ability, (1): The ratio H / E of the number of moles H of active hydrogen in component [B] to the number of moles E of epoxy groups in component [A] is 0.50 or more and 1.30 or less, (2): At least a portion of the component [C] satisfies the condition that the ratio m / M of the molecular weight m of the component and the molecular weight M between theoretical crosslinking points of the cured product of the epoxy resin composition is 0.10 or more and 0.60 or less, (3) The ratio C / E of the number of moles C of the component [C] satisfying the above condition (2) to the number of moles E of the epoxy groups of the component [A] is 0.01 or more and 0.20 or less, (4): The viscosity after being kept at 70°C for 2 hours is 5.0 times or less of the initial viscosity at 70°C, (5): The theoretical molecular weight M between crosslinking points of the cured product of the epoxy resin composition is 500 or less, The theoretical molecular weight between crosslinking points M is the value obtained by dividing the mass W of the entire cured resin obtained by curing the epoxy resin composition by the number N of crosslinking points possessed by the entire cured resin. Component [C] is a compound having at least one functional group selected from an amide group, a ketone group and a hydroxyl group in the molecule.

2. A fiber-reinforced composite material, which is formed from the prepreg according to claim 1.

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