Epoxy resin composition, prepreg, and fiber-reinforced plastic

Abstract

This epoxy resin composition contains an epoxy resin (A) having an isocyanuric acid skeleton, and an epoxy resin (B) having an oxazolidone skeleton. The epoxy resin (A) and the epoxy resin (B) are blended as separate compounds different from one another.

Description

Epoxy resin compositions, prepregs, and fiber-reinforced plastics

[0001] This invention relates to epoxy resin compositions, prepregs, and fiber-reinforced plastics. This application claims priority under Japanese Patent Application No. 2025-051326, filed with the Japan Patent Office on March 26, 2025, the contents of which are incorporated herein by reference.

[0002] Fiber-reinforced plastics are lightweight and possess high strength and rigidity, making them widely used in applications ranging from leisure activities such as sports to industrial applications such as automobiles and aircraft. Prepregs are sometimes used in the manufacture of fiber-reinforced plastics. A prepreg is an intermediate material made by impregnating a reinforcing material, consisting of long or continuous fibers such as reinforcing fibers, with a matrix resin. Various epoxy resin compositions have been proposed as matrix resins for prepregs (for example, Patent Documents 1 and 2).

[0003] International Publication No. 2021 / 177089, International Publication No. 2006 / 109744

[0004] In the development of strength in fiber-reinforced plastics, the matrix resin plays a crucial role in stress transfer. To improve the efficiency of stress transfer, the matrix resin requires two properties: high adhesion and high modulus of elasticity. If the matrix resin has high adhesion, it can firmly integrate the fibers together. If the matrix resin fills and adheres to the spaces between filaments, stress is transferred through the matrix resin to adjacent filaments. As a result, more fiber filaments can effectively bear the load, contributing to the development of material strength. When good stress transfer is achieved by the matrix resin firmly adhering the fibers, the fiber-reinforced plastic can exhibit the excellent mechanical properties such as the inherent modulus of elasticity and strength of the reinforcing fibers. In addition, the higher the modulus of elasticity of the matrix resin, the better the efficiency of stress transfer.

[0005] The epoxy resin composition disclosed in Patent Document 1 contains an epoxy resin having an isocyanuric acid skeleton, primarily for the purpose of improving the elastic modulus of the cured product. However, according to the inventors' research, there is room for improvement in strength, toughness, and heat resistance of fiber-reinforced plastics obtained from prepregs containing the epoxy resin composition of Patent Document 1.

[0006] The epoxy resin composition disclosed in Patent Document 2 contains an epoxy resin having both an oxazolidone skeleton and an isocyanuric ring skeleton in a single molecule. The presence of both an oxazolidone skeleton and an isocyanuric ring skeleton in a single molecule increases the sterically bulkiness of the epoxy resin, thus restricting the relative positions of the oxazolidone skeleton and the isocyanuric ring skeleton. Considering this, the inventors' research indicates that fiber-reinforced plastics obtained from prepregs containing the epoxy resin composition of Patent Document 2 have room for improvement in both heat resistance and elastic modulus.

[0007] The present invention provides an epoxy resin composition suitable as a matrix resin for prepregs that yield fiber-reinforced plastics with improved elastic modulus, strength, toughness, and heat resistance.

[0008] Preferred embodiments include, but are not limited to, the following: [1] An epoxy resin composition containing an epoxy resin (A) having an isocyanuric acid skeleton and an epoxy resin (B) having an oxazolidone skeleton, wherein the epoxy resin (A) and the epoxy resin (B) are blended as different and separate compounds. [2] The epoxy resin composition according to [1], wherein the proportion of the epoxy resin (A) is 10% by mass or more of the total epoxy resin. [3] The epoxy resin composition according to [1] or [2], wherein the epoxy resin (A) has a structure derived from glycidyl isocyanurate. [4] The epoxy resin composition according to any one of [1] to [3], wherein the epoxy resin (A) has a structure derived from triglycidyl isocyanurate. [5] The epoxy resin composition according to any one of [1] to [4], further containing a general-purpose epoxy resin. [6] The epoxy resin composition according to any one of [1] to [5], further containing a curing agent. [7] The epoxy resin composition according to [6], comprising at least one selected from the group consisting of dicyandiamide, aromatic amine, and urea as the curing agent. [8] A prepreg comprising a matrix resin and carbon fibers, wherein at least a portion of the matrix resin is the epoxy resin composition according to any one of [1] to [7]. [9] A fiber-reinforced plastic comprising a cured product of the prepreg according to [8].

[10] A tubular body comprising a cured product of the prepreg according to [8].

[11] The tubular body according to

[10] , which is a golf club shaft or a fishing rod.

[0009] The present invention provides an epoxy resin composition suitable as a matrix resin for a prepreg that yields a fiber-reinforced plastic with improved elastic modulus, strength, toughness, and heat resistance.

[0010] [Epoxy resin composition] The epoxy resin composition of the present invention contains an epoxy resin (A) having an isocyanuric acid skeleton and an epoxy resin (B) having an oxazolidone skeleton. In the epoxy resin composition of the present invention, the epoxy resin (A) having an isocyanuric acid skeleton and the epoxy resin (B) having an oxazolidone skeleton are formulated as separate compounds different from each other. Therefore, as shown in the results of the examples described later, it is considered that strength, toughness and heat resistance are improved. Hereinafter, each component of the epoxy resin composition will be described in detail.

[0011] (Epoxy resin (A) having an isocyanuric acid skeleton) The epoxy resin (A) is not particularly limited as long as it is a compound having an isocyanuric acid skeleton and an epoxy group. Examples include, but are not limited to, epoxy resin (A) having a structure derived from glycidyl isocyanurate and epoxy resin (A) having a structure derived from triglycidyl isocyanurate.

[0012] Examples of the epoxy resin (A) having an isocyanuric acid skeleton include an isocyanuric acid derivative represented by the following formula (1).

[0013]

[0014] In formula (1), X １ , X ２ and X ３ are each independently an epoxy group, a substituent having an epoxy group, a glycidyl group, an allyl group, an alkyl group or a hydrogen atom, and X １ , X ２ and X ３ at least one of which is a substituent having an epoxy group.

[0015] Among these, X １ , X ２ and X ３ it is preferable that at least one of them has a structure having an epoxy group at the terminal of an alkyl chain having 1 to 6 carbon atoms excluding the epoxy group, and more preferably has a structure having an epoxy group at the terminal of an alkyl chain having 1 to 3 carbon atoms excluding the epoxy group.

[0016] (Epoxy resin (B) having an oxazolidone skeleton) The epoxy resin (B) may be any compound having an oxazolidone skeleton and epoxy groups, and is not particularly limited. The epoxy resin (B) may be synthesized or a commercially available product may be used. Examples of commercially available epoxy resins (B) include AER4152, AER4151, LSA3301, LSA2102 (all trade names, products of Asahi Kasei E-Materials Corporation), ACR1348 (trade name, product of ADEKA Corporation), DER852, DER858 (trade names, products of THE DOW CHEMICAL COMPANY), TSR-400 (trade name, product of DIC Corporation), and YD-952 (trade name, product of Nippon Steel Chemical & Material Corporation), but is not limited to these examples.

[0017] Examples of epoxy resins (B) having an oxazolidone skeleton include those having the structure represented by the following formula (2).

[0018]

[0019] In formula (2), R ２ , R ３ , R ４ Each of these is independently an epoxy group, a substituent having an epoxy group, a composite substituent having an epoxy group, an allyl group, an alkyl group, or a hydrogen atom, and R ２ , R ３ and R ４ At least one of these substituents is an epoxy group-containing substituent or a composite substituent.

[0020] The epoxy resins (A) and (B) described above are blended into the epoxy resin composition as distinct compounds. Blending them as distinct compounds allows for efficient intermolecular interactions, resulting in a stable packing structure. In addition, epoxy resins (A) and (B) can each independently participate in network formation during curing with their own molecular freedom. Therefore, the orientation of epoxy resins (A) and (B) towards the carbon fiber interface is improved. As a result, it is believed that the fiber-reinforced plastic can exhibit excellent heat resistance and mechanical properties. Blending them as distinct compounds means that epoxy resins (A) and (B) may be separate compounds from the time of blending, or they may become separate compounds after decomposition following blending.

[0021] (General-purpose epoxy resin) The epoxy resin composition may further contain a general-purpose epoxy resin. The general-purpose epoxy resin is not particularly limited as long as it is an epoxy resin other than epoxy resin (A) and epoxy resin (B). The general-purpose epoxy resin is not particularly limited as long as it contains one or more epoxy resin groups per molecule, but it is preferable to include one that contains two or more epoxy groups per molecule. It is preferable to use a general-purpose epoxy resin having two or more epoxy groups per molecule because it is possible to raise the glass transition temperature of the cured product obtained by heat curing the epoxy resin composition and improve its heat resistance. These general-purpose epoxy resins may be used alone or in appropriate combinations.

[0022] Examples of general-purpose epoxy resins include, for instance, bisphenol A type epoxy resins, bisphenol F type epoxy resins, novolac type epoxy resins, hydrophthalic acid type epoxy resins, bisphenol S type epoxy resins, resorcinol type epoxy resins, hydroquinone type epoxy resins, bisphenoxyethanol fluorene type epoxy resins, bisphenol fluorene type epoxy resins, biscresol fluorene type epoxy resins, and epoxy resins of diaminodiphenylmethane type, xylenediamine type, diaminodiphenyl sulfone type, aminophenol type, aniline type, bisphenol type, meta-xylenediamine type, 1,3-bisaminomethylcyclohexane type, isocyanurate type, hydantoin type, phenol novolac type, ortho-cresol novolac type, trishydroxyphenylmethane type, tetraphenylolethane type, and the like. Among these, diaminodiphenylmethane-type, aminophenol-type, and bisphenol-type epoxy resins are particularly preferably used due to their good balance of physical properties. One type of general-purpose epoxy resin may be used alone, or two or more types may be used in combination.

[0023] Commercially available products of diaminodiphenylmethane-type epoxy resins include ELM434 (manufactured by Sumitomo Chemical Co., Ltd.), ELM434VL (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.), "Epototo (registered trademark)" YH-434 (manufactured by Nittetsu Chemical & Materials Co., Ltd.), and "jER (registered trademark)" 604 (manufactured by Mitsubishi Chemical Corporation).

[0024] As a commercially available product of xylenediamine-type epoxy resin, "TETRAD (registered trademark)"-X (manufactured by Mitsubishi Gas Chemical Company, Inc.) may be mentioned. As a commercially available product of diaminodiphenyl sulfone-type epoxy resin, TG3DAS (manufactured by Mitsui Chemicals Fine Co., Ltd.) may be mentioned.

[0025] Examples of 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.). Examples of commercially available aniline-type epoxy resins include GAN and GOT (both manufactured by Nippon Kayaku Co., Ltd.).

[0026] Examples of bisphenol-type epoxy resins include bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, and bisphenol S-type epoxy resins.

[0027] Examples of commercially available bisphenol A-type epoxy resins include "jER (registered trademark)" 825, 827, 828, 834, 1003F, 1004F, 1005F, 1009F, 1004FS, 1006FS, 1007FS (manufactured by Mitsubishi Chemical Corporation), "Epiclon (registered trademark)" 850 (manufactured by DIC Corporation), "Epototo (registered trademark)" YD-128 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), and DER-331 and DER-332 (manufactured by Dow Chemical Company).

[0028] Examples of commercially available bisphenol F-type epoxy resins include "Araldite (registered trademark)" GY282 (manufactured by Huntsman Advanced Materials), "jER (registered trademark)" 806, 807, 4005P, 4007P, 4010P, 1750 (manufactured by Mitsubishi Chemical Corporation), "Epototo (registered trademark)" YD-170, YD-175, YDF2001, YDF2004 (manufactured by Nippon Steel Chemical & Material Co., Ltd.), and "Epiclon (registered trademark)" 830 (manufactured by DIC Corporation). In addition, as a commercially available alkyl-substituted tetramethylbisphenol F-type epoxy resin, YSLV-80XY (manufactured by Nippon Steel Chemical & Material Co., Ltd.) may be mentioned.

[0029] An example of a bisphenol S type epoxy resin is "Epiclon®" EXA-1515 (manufactured by DIC Corporation).

[0030] Commercially available epoxy resins containing a biphenyl skeleton include "jER®" YX4000H, YX4000, YX4000HS, YL6121HA, YL6677 (all manufactured by Mitsubishi Chemical Corporation) and NC-3000 (manufactured by Nippon Kayaku Co., Ltd.). Commercially available phenol novolac type epoxy resins include "jER®" 152, 154 (both manufactured by Mitsubishi Chemical Corporation) and "Epiclon®" N-740, N-770, N-775 (manufactured by DIC Corporation).

[0031] Commercially available cresol novolac type epoxy resins include "Epiclon®" N-660, N-665, N-670, N-673, N-680, N-695 (manufactured by DIC Corporation), and EOCN-1020, EOCN-102S, EOCN-104S (all manufactured by Nippon Kayaku Co., Ltd.).

[0032] A commercially available resorcinol-type epoxy resin is "Denacol®" EX-201 (manufactured by Nagase ChemteX Corporation). Commercially available epoxy resins having a naphthalene skeleton include "Epiclon®" HP4032 (manufactured by DIC Corporation), NC-7000, and NC-7300 (manufactured by Nippon Kayaku Co., Ltd.).

[0033] Commercially available trisphenylmethane-type epoxy resins include TMH-574 (manufactured by Sumitomo Chemical Co., Ltd.) and Tactix 742 (manufactured by Huntsman Advanced Materials Co., Ltd.).

[0034] Commercially available dicyclopentadiene-type epoxy resins include "Epiclon®" HP7200, HP7200L, HP7200H (manufactured by DIC Corporation), Tactix 558 (manufactured by Huntsman Advanced Materials), XD-1000-1L, and XD-1000-2L (all manufactured by Nippon Kayaku Co., Ltd.).

[0035] Furthermore, other epoxy compounds may be appropriately blended into the epoxy resin composition of the present invention.

[0036] (Blending ratio of each epoxy resin) The proportion of epoxy resin (A) is preferably 10% by mass or more of the total amount of epoxy resins in the epoxy resin composition. When the proportion of epoxy resin (A) is above the lower limit, the elastic modulus and strength of the matrix resin cured product are improved, and the strength of the resulting fiber-reinforced plastic is improved due to the synergistic effect with the fibers. Furthermore, the improved toughness of the matrix resin cured product delays crack propagation in the fiber-reinforced plastic, increasing the stress that can be withstood before fracture and improving the overall strength. The proportion of epoxy resin (A) is preferably 10 to 50% by mass of the total amount of epoxy resins in the epoxy resin composition, more preferably 10 to 40% by mass, and even more preferably 10 to 30% by mass. When the proportion of epoxy resin (A) is within the above numerical range, the resulting cured product and fiber-reinforced plastic tend to have good elastic modulus, strength, toughness, and heat resistance.

[0037] The proportion of epoxy resin (B) is preferably 10 to 60% by mass of the total epoxy resin in the epoxy resin composition, more preferably 10 to 50% by mass, and even more preferably 10 to 40% by mass. When the proportion of epoxy resin (B) is above the lower limit, the heat resistance, elastic modulus, and strength of the cured resin tend to be good. When the proportion of epoxy resin (B) is below the upper limit, the toughness of the cured resin tend to be good.

[0038] The total ratio of epoxy resin (A) and epoxy resin (B) is preferably 30 parts by mass or more, and more preferably 40 parts by mass or more, of the total amount of epoxy resin in the epoxy resin composition. On the other hand, it is usually 100 parts by mass or less, preferably 95 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 70 parts by mass or less. When the total ratio of epoxy resin (A) and epoxy resin (B) is above the lower limit, the heat resistance, elastic modulus, and strength of the cured resin tend to be good. When the total ratio of epoxy resin (A) and epoxy resin (B) is below the upper limit, the toughness of the cured resin tend to be good.

[0039] The mixing ratio of epoxy resin (A) and epoxy resin (B) in the epoxy resin composition is preferably 0.5 or more, more preferably 1.0 or more, even more preferably 1.5 or more, preferably less than 8.0, more preferably 7.0 or less, even more preferably 6.0 or less, and particularly preferably 5.0 or less, in terms of parts by mass of epoxy resin (B) / parts by mass of epoxy resin (A). In another embodiment, it is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more. When the mixing ratio of epoxy resin (A) and epoxy resin (B) in the epoxy resin composition is above the lower limit, the toughness of the cured resin product is good, and the crystallization of isocyanurate is suppressed, which tends to result in good appearance and handling properties. On the other hand, when it is below the upper limit, the elastic modulus and strength of the cured resin product tend to be good.

[0040] In the case of an epoxy resin composition containing a general-purpose epoxy resin, the proportion of the general-purpose epoxy resin is preferably 20 to 80% by mass of the total amount of epoxy resin in the epoxy resin composition, more preferably 30 to 80% by mass, even more preferably 40 to 80% by mass, and particularly preferably 40 to 70% by mass. When the proportion of the general-purpose epoxy resin is above the lower limit, the toughness of the cured resin tends to be good. When the proportion of the general-purpose epoxy resin is below the upper limit, the heat resistance, elastic modulus, and strength of the cured resin tend to be good.

[0041] The average epoxy equivalent of the total epoxy resin contained in the epoxy resin composition can be, for example, 100 to 400 g / eq. From the viewpoint of toughness of the cured product and fiber-reinforced plastic, the average epoxy equivalent of the total epoxy resin contained in the epoxy resin composition is preferably 150 g / eq or more, more preferably 160 g / eq or more, and even more preferably 170 g / eq or more. From the viewpoint of heat resistance of the cured product and fiber-reinforced plastic, the average epoxy equivalent of the total epoxy resin contained in the epoxy resin composition is preferably 300 g / eq or less, more preferably 290 g / eq or less, and even more preferably 280 g / eq or less. The epoxy equivalent of epoxy resin (A) can be, for example, 90 to 200 g / eq, and from the viewpoint of elastic modulus of the cured product and fiber-reinforced plastic, 95 to 120 g / eq is preferred. The epoxy equivalent of epoxy resin (B) can be, for example, 200 to 600 g / eq, and from the viewpoint of elastic modulus and heat resistance of the cured product and fiber-reinforced plastic, 200 to 500 g / eq is preferred. The epoxy equivalent of the general-purpose epoxy resin can be, for example, 100 to 3000 g / eq, and 150 to 2500 g / eq is preferred from the viewpoint of toughness of the cured product and fiber-reinforced plastic.

[0042] The average epoxy equivalent can be calculated as follows when multiple epoxy resins are used in combination. For example, the calculation method will be explained using the case where three types of epoxy resins are used in combination. １ (g / eq) epoxy resin 1 is W １ Parts by mass, epoxy equivalent is E ２ (g / eq) epoxy resin 2 is W ２ Parts by mass, epoxy equivalent is E ３ (g / eq) epoxy resin 3 is W ３ When compounded in parts by mass, the average epoxy equivalent can be calculated using the following formula: Average epoxy equivalent = (W １ +W ２ +W ３ ) / (W １ / E １ +W ２ / E ２ +W ３ / E ３ )

[0043] (Curing agent) The epoxy resin composition may further contain a curing agent. The curing agent is not particularly limited as long as it is a compound that contributes to the curing of epoxy groups. As curing agents, amine-based curing agents such as dicyandiamide, aliphatic amine curing agents, alicyclic amine curing agents, aromatic amine curing agents, and amine complex curing agents can be used, as well as urea-based curing agents, imidazole-based curing agents, acid anhydride-based curing agents, phenol-based curing agents, etc. Among these, at least one selected from the group consisting of aliphatic amine curing agents, aromatic amine curing agents, and urea-based curing agents is preferred in terms of storage stability of the epoxy resin composition and mechanical properties of the cured product.

[0044] Since dicyandiamide has a melting point of approximately 210°C, it is not easily compatible with epoxy resins in the low-temperature range. Therefore, using dicyandiamide as a curing agent improves the storage stability of the epoxy resin composition. Examples of commercially available dicyandiamides include DICY7, DICY15 (both products of Mitsubishi Chemical Corporation), and DICYANEX1400F (product of Evonik Japan Co., Ltd.). The dicyandiamide content is preferably 1 to 15 parts by mass, and more preferably 2 to 10 parts by mass, per 100 parts by mass of the total epoxy resin in the epoxy resin composition. Since the heat resistance and mechanical properties of the cured resin tend to be better, the number of moles of active hydrogen in the dicyandiamide is preferably 0.3 to 0.9 times, and more preferably 0.4 to 0.8 times, relative to the total number of moles of epoxy groups in the epoxy resin of the epoxy resin composition. Dicyandiamide may be used alone, two or more types may be used in combination, or it may be used in combination with a different type of curing agent.

[0045] Examples of aromatic amines include 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'-diisopropyl-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, and 3,3'-di-t-butyl-5,5'-di Examples include, but are not limited to, ethyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetraisopropyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetra-t-butyl-4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 4,4'-methylene-bis[2-isopropyl-6-methylaniline], m-phenylenediamine, m-xylylenediamine, and diethyltoluenediamine. Among these, 4,4'-diaminodiphenylsulfone and 3,3'-diaminodiphenylsulfone are preferred because they offer even better heat resistance and mechanical properties. 4,4'-diaminodiphenylsulfone is preferred because it can maintain the tack life of the prepreg for a long period of time. 3,3'-diaminodiphenylsulfone is preferred because it can increase the elastic modulus and strength of the cured product. Furthermore, 4,4'-diaminodiphenylsulfone and 3,3'-diaminodiphenylsulfone may be combined simultaneously. Aromatic amines may be used alone, in combination of two or more, or in combination with other curing agents.

[0046] Urea-based curing agents have a dimethylureide group in their molecule and, upon heating at high temperatures, generate isocyanate groups and dimethylamine, thereby activating epoxy groups. Examples of urea-based curing agents include aromatic dimethylurea, in which the dimethylureide group is bonded to an aromatic ring, and aliphatic dimethylurea, in which the dimethylureide group is bonded to an aliphatic compound. Aromatic dimethylurea is preferred because it offers high heat resistance and flexural strength.

[0047] The content of the urea-based curing agent is preferably 1 to 15 parts by mass, and more preferably 1 to 10 parts by mass, based on 100 parts by mass of the total epoxy resin contained in the epoxy resin composition. If the content of the urea-based curing agent is 1 part by mass or more, it tends to accelerate the curing of the epoxy resin contained in the epoxy resin composition, thereby improving the mechanical properties and heat resistance of the cured product. On the other hand, if the content of the urea-based curing agent is 15 parts by mass or less, it tends to maintain high heat resistance and toughness of the resin cured product.

[0048] Preferred aromatic dimethylureas include, for example, phenyldimethylurea, tolylenebis(dimethylurea), and methylenebis(phenyldimethylurea). Examples include 3-phenyl-1,1-dimethylurea (PDMU), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 3-(3-chloro-4-methylphenyl)-1,1-dimethylurea, 2,4-bis(3,3-dimethylureido)toluene (TBDMU), 4,4'-methylenebis(phenyldimethylurea) (MBPDMU), and dimethylurea obtained from m-xylylene diisocyanate and dimethylamine. PDMU, DCMU, TBDMU, and MBPDMU are more preferred in terms of curing acceleration ability and imparting heat resistance to the cured resin. Examples of aliphatic dimethylureas include dimethylurea obtained from isophorone diisocyanate and dimethylamine, and dimethylurea obtained from hexamethylene diisocyanate and dimethylamine. Urea-based curing agents may be used individually or in combination of two or more.

[0049] Commercially available urea-based curing agents may be used. Examples of commercially available products include, but are not limited to, the following: For example, PDMU: Omicure 94 (product of Huntsman Japan Co., Ltd.) For example, DCMU: DCMU-99 (product of Hodogaya Chemical Co., Ltd.) For example, TBDMU: Omicure 24 (product of Huntsman Japan Co., Ltd.), U-CAT 3512T (product of Sunapro Co., Ltd.) For example, MBPDMU: Technicure MDU-11 (product of A&C Catalists Co., Ltd.), Omicure 52 (product of Huntsman Japan Co., Ltd.) For example, aliphatic dimethylurea: U-CAT 3513N (product of Sunapro Co., Ltd.)

[0050] (Thermoplastic Resin) The epoxy resin composition may further contain a thermoplastic resin. Examples of thermoplastic resins include, but are not limited to, polyamide, polyester, polycarbonate, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyetheretherketone, polyetherketone, polyimide, polytetrafluoroethylene, polyether, polyolefin, liquid crystal polymer, polyarylate, polysulfone, polyacrylonitrile styrene, polystyrene, polyacrylonitrile, polymethyl methacrylate, ABS (acrylonitrile-butadiene-styrene copolymer), AES (acrylonitrile-ethylene propylene rubber-styrene copolymer), ASA (acrylonitrile-acrylic rubber-styrene copolymer), polyvinyl chloride, polyvinyl formal, polyvinyl butyral, phenoxy resin, block copolymer, and core-shell rubber. The thermoplastic resin may be used alone or in combination of two or more types.

[0051] The proportion of thermoplastic resin is preferably 1 to 30 parts by mass, more preferably 2 to 20 parts by mass, even more preferably 2 to 15 parts by mass, particularly preferably 3 to 10 parts by mass, and most preferably 3 to 8 parts by mass, based on 100 parts by mass of the total epoxy resin in the epoxy resin composition. It is preferable that the thermoplastic resin content is above the lower limit of the above numerical range because it tends to exhibit good resin flow controllability. It is also preferable that the thermoplastic resin content is below the upper limit of the above numerical range because it reduces the increase in viscosity of the epoxy resin composition.

[0052] (Additives) The epoxy resin composition may further contain various known additives as needed, to the extent that they do not impair the effects of the present invention. Examples of additives include epoxy resin curing accelerators, phosphorus-based flame retardants (e.g., phosphorus-containing epoxy resins, red phosphorus, phosphazene compounds, phosphates, phosphate esters), hydrated metal compound-based inorganic flame retardants (e.g., aluminum hydroxide, magnesium hydroxide), other flame retardant aids (e.g., antimony compounds, zinc borate, zinc stainate, Mo compounds, ZrO, zinc sulfide, zeolites, titanium dioxide nanofillers), silicone oil, wetting and dispersing agents, defoaming agents, defoaming agents, natural waxes, synthetic waxes, release agents such as metal salts of linear fatty acids, acid amides, esters, and paraffins, inorganic fillers such as powders such as crystalline silica, fused silica, calcium silicate, alumina, calcium carbonate, talc, and barium sulfate, and glass fibers and carbon fibers, colorants such as carbon black and red iron oxide, and silane coupling agents. Additives may be used individually or in combination of two or more types.

[0053] (Method for producing epoxy resin composition) The epoxy resin composition is obtained by heating and mixing the above-mentioned components. Methods for mixing the components include using a mixer such as a three-roll mill, planetary mixer, kneader, homogenizer, or homodisper.

[0054] [Prepreg] The prepreg contains a matrix resin and carbon fibers. In the prepreg of the embodiment, at least a portion of the matrix resin is the epoxy resin composition of the present invention.

[0055] (Carbon Fibers) Carbon fibers can be present in the prepreg as a carbon fiber substrate (an aggregate of carbon fibers), and it is preferable that it be in sheet form. The orientation of the fibers in the carbon fiber substrate may be such that the carbon fibers are arranged in a single direction or in a random direction. Examples of forms of the carbon fiber substrate include carbon fiber fabrics, carbon fiber nonwovens, and sheets in which long carbon fibers are aligned in one direction. From the viewpoint of being able to mold fiber-reinforced plastics with high specific strength and specific modulus, it is preferable to use a sheet consisting of a bundle of carbon fibers in which continuous fibers are aligned in a single direction as the prepreg. From the viewpoint of ease of handling, it is preferable to use carbon fiber fabrics as the prepreg. The basis weight of the carbon fiber substrate is, for example, 10 g / m². ２ More than 4000g / m ２ The following is possible:

[0056] The fiber diameter of the carbon fibers is preferably 3 to 12 μm. The number of carbon fibers in a carbon fiber bundle is preferably 1,000 to 70,000. A sheet-like carbon fiber substrate may be made by using multiple carbon fiber bundles and aligning the fibers in one direction, or a sheet-like carbon fiber substrate may be made by scattering chopped carbon fiber bundles. From the viewpoint of the rigidity of the resulting fiber-reinforced plastic, the strand tensile strength of the carbon fibers is preferably 1.5 to 9 GPa.

[0057] The tensile modulus of the carbon fiber strand is preferably 150 to 400 GPa. The tensile strength and tensile modulus of the carbon fiber strand are measured in accordance with JIS R7601:1986.

[0058] (Method for manufacturing prepregs) Prepregs are obtained by impregnating a carbon fiber substrate with an epoxy resin composition. Methods for impregnating a carbon fiber substrate with an epoxy resin composition include, but are not limited to, a wet method in which the epoxy resin composition is dissolved in a solvent such as methyl ethyl ketone or methanol to reduce its viscosity before being impregnated into the carbon fiber substrate, and a hot melt method (dry method) in which the epoxy resin composition is heated to reduce its viscosity before being impregnated into the carbon fiber substrate. The impregnation temperature is set according to the viscosity of the epoxy resin composition, but from the viewpoint of ensuring that the curing reaction of the epoxy resin composition does not start and that the epoxy resin composition is sufficiently impregnated into the carbon fibers, a temperature of 40 to 120°C is preferred, and 50 to 110°C is more preferred.

[0059] The wet method involves immersing a carbon fiber substrate in a solution of epoxy resin composition, then removing it and evaporating the solvent using an oven or the like. The hot melt method includes two approaches: one in which the epoxy resin composition, whose viscosity has been reduced by heating, is directly impregnated into the carbon fiber substrate; and another in which the epoxy resin composition is first applied to the surface of a substrate such as release paper to create a film, and then the film is placed on one or both sides of the carbon fiber substrate and heated and pressurized to impregnate the carbon fiber substrate with resin. The coating layer obtained by applying it to the surface of a substrate such as release paper may be used in the hot melt method while still uncured, or it may be used in the hot melt method after the coating layer has been cured. With the hot melt method, there is virtually no residual solvent in the prepreg.

[0060] The content of epoxy resin composition in the prepreg (hereinafter referred to as "resin content") is preferably 10 to 60% by mass, more preferably 15 to 55% by mass, and even more preferably 15 to 50% by mass, relative to the total mass of the prepreg. If the resin content is above the lower limit of the above numerical range, it is easier to ensure adhesion between the carbon fibers and the matrix resin. If the resin content is below the upper limit of the above numerical range, the mechanical properties of the fiber-reinforced plastic are further improved.

[0061] The carbon fiber content in the prepreg (hereinafter referred to as "fiber content") is preferably 30 to 85 volume%, more preferably 35 to 80 volume%, and even more preferably 40 to 80 volume% of the total volume of the prepreg. If the fiber content is above the lower limit within the above numerical range, the mechanical properties of the fiber-reinforced plastic are further improved. If the fiber content is below the upper limit within the above numerical range, it is easier to ensure adhesion between the carbon fibers and the matrix resin.

[0062] [Fiber-reinforced plastic] Fiber-reinforced plastic is obtained by curing a prepreg. That is, fiber-reinforced plastic contains a cured epoxy resin composition contained in the prepreg and carbon fibers. It can be manufactured as a cured product of a prepreg laminate in which one or more prepregs are laminated. For example, after laminating one or more of the above-mentioned prepregs, a molded product made of fiber-reinforced plastic can be obtained by molding the resulting laminate by applying pressure and heat curing, etc. The prepreg of the present invention may be laminated with other prepregs other than the prepreg of the present invention.

[0063] Examples of molding methods include press molding, autoclave molding, bagging molding, wrapping tape method, internal pressure molding, sheet wrap molding, and RTM (Resin Transfer Molding), VaRTM (Vacuum Assisted Resin Transfer Molding), filament winding, and RFI (Resin Film Infusion), which involve impregnating carbon fiber filaments or preforms with an epoxy resin composition and curing to obtain molded products. However, the method is not limited to these methods. Among these, autoclave molding is preferred from the viewpoint of easily obtaining high-quality fiber-reinforced plastics, and press molding is preferred from the viewpoint of obtaining high productivity.

[0064] When manufacturing fiber-reinforced plastics by press molding, it is preferable to heat and pressurize the prepreg or preform, which is made by laminating prepregs, between molds that have been pre-adjusted to a curing temperature. The temperature inside the mold during press molding is preferably 100 to 180°C. Furthermore, it is preferable to cure the prepreg or preform for 1 to 20 minutes under conditions of 1 to 15 MPa.

[0065] Fiber-reinforced plastics may have a tubular structure. That is, fiber-reinforced plastics may be tubular bodies. Tubular bodies may be manufactured, for example, by a sheet wrapping method which involves winding a sheet-like prepreg, in which multiple carbon fibers aligned in one direction are impregnated with a matrix resin, onto a mandrel (metal core material), and then heating and curing the mandrel together.

[0066] While the applications of fiber-reinforced plastics are not particularly limited, they are particularly suitable for use in sports and leisure products such as bicycle parts, golf club shafts, tennis rackets, fishing rods, and hockey sticks, as well as in industrial applications such as long carbon rolls, antennas, and electronic components.

[0067] The embodiments will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The various manufacturing conditions and evaluation result values ​​in the following examples can be considered as preferred upper or lower limits in the embodiments, and preferred numerical ranges can be arbitrarily generated by combining the aforementioned upper or lower limits with the values ​​of the following examples or values ​​from other examples.

[0068] [Raw Materials] The raw materials used in the examples are as follows:

[0069] (Epoxy resin (A)) TEPIC-S: Triglycidyl isocyanurate, epoxy equivalent 105 g / eq, product of Nissan Chemical Industries, Ltd.

[0070] (Epoxy resin (B)) TSR-400: Epoxy resin with an oxazolidone skeleton, epoxy equivalent 338 g / eq, product of DIC Corporation.

[0071] (General-purpose epoxy resins) jER828: Bisphenol A type epoxy resin, epoxy equivalent 184-194 g / eq, product of Mitsubishi Chemical Corporation jER604: Tetraglycidyldiaminodiphenylmethane, epoxy equivalent 110-130 g / eq, product of Mitsubishi Chemical Corporation EPICLON N-660: Cresol novolac type epoxy resin, epoxy equivalent 200-215 g / eq, product of DIC Corporation jER807: Bisphenol F type liquid epoxy resin, epoxy equivalent 160-175 g / eq, product of Mitsubishi Chemical Corporation jER4005P: Bisphenol F type solid epoxy resin, epoxy equivalent 950-1200 g / eq, product of Mitsubishi Chemical Corporation GAN: N,N-diglycidylaniline, epoxy equivalent 125 g / eq, product of Nippon Kayaku Co., Ltd. ARALDITE MY0600: m-aminophenol type epoxy resin (triglycidyl-m-aminophenol), epoxy equivalent 106 g / eq, product of Huntsman Japan Co., Ltd. LCE-2615: Modified biphenol type epoxy resin (tough epoxy resin), epoxy equivalent 1300-1450 g / eq, product of Nippon Kayaku Co., Ltd. NC-3000-H: Biphenyl aralkyl type epoxy resin, epoxy equivalent 288 g / eq, product of Nippon Kayaku Co., Ltd. Kane Ace MX-136: Core-shell rubber-containing bisphenol F type epoxy resin masterbatch (rubber content 25% by mass, epoxy equivalent 210-235 g / eq), product of Kaneka Corporation

[0072] (Thermoplastic resins) Nanostrength M22N: Acrylic block copolymer (polymethyl methacrylate - polybutyl acrylate - polymethyl methacrylate, medium to high molecular weight type), Arkema Corporation product. VINYLEC K: Polyvinyl formal, weight-average molecular weight 40,000-54,000 (average degree of polymerization approximately 340), JNC Corporation product.

[0073] (Hardening agent) DICYANEX1400F: Dicyandiamide, active hydrogen equivalent 21 g / eq, product of Evonik Japan Co., Ltd. OMICURE94: PDMU, product of Huntsman Japan Co., Ltd.

[0074] [Example 1] (Preparation of epoxy resin composition) The epoxy resin and curing agent listed in Table 1 were weighed into a container so that the mass ratio of solid components to liquid components was 1:1, and mixed by stirring. The mixture obtained by stirring was further finely mixed in a three-roll mill to obtain a masterbatch containing the curing agent. Subsequently, the amount of epoxy resin not used in the preparation of the masterbatch containing the curing agent was weighed and mixed. A uniform viscosity liquid was obtained by stirring and mixing the epoxy resin mixture at 130 to 150°C. After cooling to 60 to 70°C, the masterbatch containing the curing agent was added so that the total amount of epoxy resin was 100 parts by mass. Further stirring and mixing was performed to obtain an uncured epoxy resin composition.

[0075] (Preparation of cured resin products) The uncured epoxy resin composition was degassed in a vacuum at approximately 65°C, and then injected between two glass plates or stainless steel plates to form a plate. The plate-shaped molded product was heated and cured by raising the temperature at 2°C / min and holding it in an oven at an ambient temperature of 130°C for 120 minutes to produce cured resin products with thicknesses of 2 mm and 3 mm, respectively.

[0076] (Measurement of flexural modulus and flexural strength) A test piece measuring 60 mm in length and 8 mm in width was cut from a 2 mm thick cured resin material. The flexural modulus and flexural strength of the cured epoxy resin composition were measured using a universal testing machine (INSTRON 5965, manufactured by INSTRON) equipped with a three-point bending jig (indenter R = 3.2 mm, support R = 3.2 mm, distance between supports L = 16 × test piece thickness 32 mm) under conditions of 23°C and 50% RH, with a crosshead speed of 2 mm / min. Specifically, the flexural modulus was calculated using the secant method in the bending strain range of 0.05 to 0.25% using the stress-strain curve obtained under the above measurement conditions. The maximum bending stress of the stress-strain curve obtained under the above measurement conditions was recorded as the flexural strength. The bending strength is preferably 150 MPa or higher, more preferably 160 MPa or higher, and even more preferably 170 MPa or higher. The bending modulus is preferably 3.50 GPa or higher, more preferably 3.60 GPa or higher, even more preferably 3.70 GPa or higher, particularly preferably 3.80 GPa or higher, and most preferably 4.00 GPa or higher.

[0077] (Glass Transition Temperature) The glass transition temperature is an indicator of heat resistance. The higher the glass transition temperature, the better the heat resistance. A test piece measuring 55 mm in length and 12.7 mm in width was cut from the 2 mm thick resin cured material prepared as described above. The glass transition temperature (G'onset) of this test piece was measured using a dynamic viscoelasticity measuring device, heated from 30 to 250°C at a heating rate of 5°C / min, at a frequency of 1 Hz and a strain of 0.05%. The glass transition temperature (G'onset) is the temperature obtained by plotting the logarithm of the storage modulus against temperature and finding the intersection point of the approximate straight line of logG' in the flat region before the transition to the rubber state and the tangent line at the inflection point of the slope in the region where logG' transitions. The G'onset was measured under the following conditions: measurement frequency: 1 Hz, measurement temperature range: approximately 30°C to approximately 250°C, heating rate: 5°C / min, strain: 0.05%. The glass transition temperature (G'onset) is preferably 80°C or higher, and more preferably 90°C or higher.

[0078] (Measurement of KIc) KIc is an index of plane strain fracture toughness. The higher the KIc, the better the toughness. A test specimen measuring 44 mm in length and 10 mm in width was cut from the 3 mm thick resin cured material prepared as described above. Using this test specimen, a universal testing machine (INSTRON 5965, manufactured by INSTRON) equipped with a three-point bending jig (indenter R = 5 mm, support R = 5 mm, distance L = 4 × 10 mm (test specimen width)) was used in an environment of 23°C and 50% RH. The test was performed with a crosshead speed of 10 mm / min and deformation mode I (open type), and the load at fracture was obtained. KIc was determined according to ASTM D5045 (2014). Initial pre-cracks were induced in the test specimen by sliding a razor blade across the specimen. KIc was 1.30 MPa·m １／２ The above is preferable.

[0079] [Examples 2-12, Comparative Examples 1-6] Except for changing the types and amounts of each component as shown in Tables 1 and 2, respectively, the epoxy resin composition was prepared, the resin cured product was made, and each physical property was measured under the same conditions as in Example 1.

[0080]

[0081]

[0082] [Discussion] Examples 1-12 all showed good elastic modulus, strength, toughness, and heat resistance. From the discussion of the results of each example and comparative example, the following became clear.

[0083] (Balancing Elastic Modulus and Toughness) Generally, in epoxy resin cured products, there is a trade-off relationship between elastic modulus and toughness (KIc). In fact, in Comparative Example 4, which used a modified biphenol-type epoxy resin (LCE-2615) known as a tough epoxy resin, KIc was 1.96 MPa·m １／２ Although it shows a high value, the flexural modulus remains at 3.70 GPa. In contrast, in Example 3, in which epoxy resin (A) and epoxy resin (B) were blended in 20 parts by mass each, a high KIc (1.93 MPa·m) was observed, which is at the same level as Comparative Example 4. １／２ While achieving the above, the flexural modulus has dramatically improved to 4.39 GPa. From these results, it can be said that by blending epoxy resin (A) and epoxy resin (B) as separate compounds, it is possible to achieve both a high modulus of elasticity exceeding 4.0 GPa and high toughness, which was difficult to achieve with conventional tough resins.

[0084] (Diversity of formulation design and effects of additives) According to the epoxy resin composition of this embodiment, properties can be controlled according to the application by adjusting the blending ratio and using additives in combination. For example, in Example 5, where the proportion of bisphenol F type solid epoxy resin was increased under the condition that 10 parts by mass of epoxy resin (A) was blended, Kic was 2.05 MPa·m １／２This demonstrated an extremely high toughness value. In addition, in Example 6, in which the liquid component was increased with the same formulation, the Tg improved to approximately 100°C, confirming that fine-tuning of the properties is possible. Furthermore, in Example 8, in which the amount of epoxy resin (B) was increased to 70 parts by mass, an extremely high heat resistance of 124°C was observed. The epoxy resin composition of this embodiment also exhibits good compatibility with various toughening agents. For example, in Example 10, which incorporated a block copolymer (Nanostrength M22N), the KIc was 2.80 MPa·m １／２ This recorded an extremely high toughness value. Furthermore, in Example 11, where the base resin composition was changed, a value of 2.36 MPa·m was also recorded. １／２ High toughness was obtained. As shown in the results of Examples 10 and 11, it was demonstrated that there is a high degree of freedom in compound design. In addition, in Example 9, in which a thermoplastic resin (polyvinyl formal) was added, and in Example 12, in which core-shell rubber was added, an excellent toughening effect was confirmed while maintaining a high modulus of elasticity. Thus, even in various examples in which the composition of the epoxy resin composition is changed, it is possible to exhibit excellent toughness while maintaining a high modulus of elasticity, etc.

[0085] (Contribution to heat resistance) In Examples 1-12, the glass transition temperature (G'onset) was maintained at 90°C or higher, and in many examples, at around 95°C, ensuring sufficient heat resistance required for sports applications and the like. In particular, in Comparative Example 5, which contained 10% by mass of epoxy resin (A) but did not contain epoxy resin (B), the glass transition temperature remained at 88°C. In contrast, in Example 5 and others, which combined the same amount of epoxy resin (A) with epoxy resin (B), a high heat resistance of 97°C or higher was maintained, suggesting that the combined use of epoxy resin (A) and epoxy resin (B) is important from the viewpoint of ensuring heat resistance.

[0086] (Summary) In contrast, in Comparative Example 3, which does not contain epoxy resin (B), and Comparative Example 6, which does not contain epoxy resin (B) but is a combination of multiple modified epoxy resins, the KIc was 1.7 MPa·m in all cases. １／２It remained in place and lacked sufficient toughness. As explained above, the results from each embodiment demonstrate that rigidity, toughness, and heat resistance can be controlled at a high level according to the purpose without sacrificing any of them.

[0087] This embodiment provides an epoxy resin composition suitable as a matrix resin for a prepreg, which yields a fiber-reinforced plastic with a highly balanced elastic modulus, strength, toughness, and heat resistance. In one preferred embodiment, the fiber-reinforced plastic of this embodiment has an extremely high elastic modulus exceeding 4.0 GPa in the matrix resin, resulting in excellent stress transmission efficiency and vibration damping. For this reason, it is particularly suitable for applications such as golf club shafts where fast flex recovery during swings and good feel are required, fishing rods where sensitivity to subtle impacts is required, and high-end sports equipment such as archery arrows, hockey rackets, and tennis rackets where high rigidity and responsiveness are required.

Claims

1. An epoxy resin composition comprising an epoxy resin (A) having an isocyanuric acid skeleton and an epoxy resin (B) having an oxazolidone skeleton, wherein the epoxy resin (A) and the epoxy resin (B) are blended as distinct compounds.

2. The epoxy resin composition according to claim 1, wherein the proportion of epoxy resin (A) is 10% by mass or more of the total epoxy resin.

3. The epoxy resin composition according to claim 1, wherein the epoxy resin (A) has a structure derived from glycidyl isocyanurate.

4. The epoxy resin composition according to claim 1, wherein the epoxy resin (A) has a structure derived from triglycidyl isocyanurate.

5. The epoxy resin composition according to claim 1, further comprising a general-purpose epoxy resin.

6. The epoxy resin composition according to claim 1, further comprising a curing agent.

7. The epoxy resin composition according to claim 6, wherein the curing agent contains at least one selected from the group consisting of dicyandiamide, aromatic amine, and urea.

8. A prepreg comprising a matrix resin and carbon fibers, wherein at least a portion of the matrix resin is the epoxy resin composition described in any one of claims 1 to 7.

9. A fiber-reinforced plastic comprising a cured prepreg according to claim 8.

10. A tubular body comprising a cured prepreg according to claim 8.

11. The tubular body according to claim 10, which is a shaft for a golf club or a fishing rod.

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