CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2019/031071 filed on Aug. 7, 2019, claiming priority based on Japanese Patent Application No. 2018-148952 filed on Aug. 8, 2018.

TECHNICAL FIELD

The present invention relates to an epoxy compound, an epoxy resin, an epoxy resin composition, a prepreg, a fiber-reinforced composite material, and production methods for these. More specifically, the present invention relates to an epoxy compound having a novel structure; an epoxy, resin containing this epoxy compound; an epoxy resin composition containing this epoxy compound; a cured resin product obtained by curing this epoxy resin composition; a prepreg containing this epoxy resin composition; and a fiber-reinforced composite material containing this cured resin product.

BACKGROUND ART

Epoxy compounds are widely used as raw materials for pharmaceuticals, resins, paints and the like. In particular, an epoxy compound having a plurality of epoxy Groups is cured by reacting with an appropriate curing agent to form a cured resin product having excellent heat resistance, chemical resistance, mechanical properties and the like. Therefore, in particular, it is widely used as a matrix resin for a fiber-reinforced composite material (FRP).

The fiber-reinforced composite material is lightweight and has high strength and high rigidity, and thus is used in a wide range of fields such as sports/leisure applications such as fishing rods and golf shafts, and industrial applications such as automobiles and aircraft. As a method for molding a composite material containing an epoxy resin as a matrix resin, there is a method for molding a prepreg (intermediate base material) formed into a sheet by impregnating reinforcing material fibers with a resin in advance. Other molding methods include a resin transfer molding (RTM) method in which a liquid resin composition is impregnated into a reinforcing fiber base material placed in a mold, and cured to form a fiber-reinforced composite material.

In the production of FRP, a method of using an intermediate material (prepreg) in which a fiber reinforcing material layer made of long fibers such as reinforcing fibers is impregnated with a resin is suitably used. A molded product made of FRP can be obtained by cutting the prepreg into a desired shape, shaping it, and curing it under heat and pressure.

Materials used in the aircraft field are required to have high mechanical properties such as heat resistance and impact resistance. In general, a prepreg using an epoxy resin can provide a molded product having high mechanical properties. However, the prepreg using an epoxy resin requires a long molding time. Further, the molded product obtained by curing the prepreg using an epoxy resin has insufficient water absorption resistance, and the mechanical properties such as heat resistance and impact resistance may be deteriorated during water absorption.

In press molding which enables short-time molding, high-temperature and high-pressure conditions of 100 to 150° C. and 1 to 15 MPa are usually used (Patent Literature 1). The high-temperature and high-pressure conditions can shorten the curing time of the resin constituting the prepreg. In addition, the gas contained in the prepreg can be discharged by appropriately flowing the resin constituting the prepreg in the mold. However, when press molding is performed under the high-temperature and high-pressure conditions, the temperature of the resin constituting the prepreg rises and the resin viscosity decreases remarkably. As a result, depending on the structure of the mold, the resin flows out violently from the shear edge portion (hereinafter, the phenomenon that the resin flows out from the prepreg due to heating and pressurization in the molding process is referred to also as “resin flow”). Therefore, the obtained FRP has poor appearance such as unimpregnated portions of the resin composition (resin withering) and fiber meandering, and poor performance due to these.

Patent Literature 2 describes a method of using a high-viscosity epoxy resin or adding a thermoplastic: resin to an epoxy resin as a method for suppressing a resin flow. However, when a high-viscosity epoxy resin is used, the resin viscosity at room temperature (25° C.) also in Therefore, the handleability of the prepreg is extremely low, for example, the laminating operation becomes difficult.

Patent Literatures 3 to 5 each describe a prepreg for high-cycle press molding that is improved in handleability at room temperature and suppresses a resin flow without lowering of the glass transition temperature (Tg) or the curing rate. The resin used in each of the prepregs described in Patent Literatures 3 to 5 is a resin in which the resin viscosity is increased by dissolving a thermoplastic resin in a liquid epoxy resin. However, since the resin viscosity during the production of a prepreg is also high, the impregnation property of the resin into the reinforcing fiber base material layer is lowered, and voids may be generated in the FRP after molding.

In the field of aircraft, mechanical properties such as high heat resistance and impact resistance are required, and various methods have been proposed for the purpose of improving impact resistance and interlayer toughness. In particular, many methods have been proposed in which a material different from the matrix resin is placed between layers to absorb fracture energy (Patent Literature 6) However, the curing time of the resin generally takes 120 minutes or more, and it is difficult to perform short-time molding.

Further, Patent Literatures 1 to 6 nowhere mention the water absorption resistance of the obtained FRP.

CITATION LIST

Patent Literature

Patent Literature 1: WO 2004/48435Patent Literature 2: JP 2005-213352 APatent Literature 3: JP 2009-292976 APatent Literature 4: JP 2009-292977 APatent Literature 5: JP 2010-248379 APatent Literature 6: JP 2011-190430 A.

SUMMARY OF INVENTION

Technical Problem

An object of the present invention is to solve the above-described problems of the prior art, and to provide an epoxy compound that enables production of a cured resin product having high water absorption resistance and a high elastic modulus, and has high impregnation property into a reinforcing fiber base material and excellent handleability. A further object of the present invention is to provide an epoxy resin composition, a prepreg, and a fiber-reinforced composite material, utilizing this epoxy compound (hereinafter, sometimes abbreviated as “FRP”; in particular, when the reinforcing fiber base material is carbon fiber, sometimes abbreviated as “CFRP”).

Solution to Problem

As a result of studies to solve the above problems, the present inventors have found that the above problems can be solved by using an epoxy compound having a predetermined structure, and have completed the present invention.

The present invention that achieves the above problems is as described below.

[1] An epoxy compound represented by the following chemical formula (1):



wherein X represents a C1-10 aliphatic hydrocarbon group, and R1and R2each independently represent one selected from the group consisting of a hydrogen atom, an aliphatic hydrocarbon group, an aromatic group, an alkoxy Group, and a halogen atom.

[2] The epoxy compound according to [1], which is represented by the following chemical formula (2)



wherein X represents a C1-10 aliphatic hydrocarbon Group, and R1and R2each independently represent one selected from the group consisting of a hydrogen atom, an aliphatic hydrocarbon group, an aromatic group, an alkoxy group, and a halogen atom.

[3] The epoxy compound according to [1] or [2], wherein X is a linear aliphatic chain group.

The inventions according to [1] to [3] are each directed to as epoxy compound having a predetermined structure. In the respective chemical formulas, X is preferably a linear aliphatic chain group.

[4] An epoxy resin containing the epoxy compound according to any one of [1] to [3] in an area ratio of 50% or more in HPLC measurement.

The invention according to [4] is directed to an epoxy resin containing the epoxy compound having a predetermined structure in a predetermined amount. This epoxy resin may only contain the epoxy compound according to [1] to [3] in a predetermined ratio, and the epoxy compound according to [1] to [3] does not necessarily have to be isolated.

[5] An epoxy resin composition containing at least:

the epoxy compound according to any one of [1] to [3]; and

a curing agent.

The invention according to [5] is directed to a composition in an uncured or semi-cured state, which contains at least the epoxy compound according to [1] to [3]; and a curing agent that reacts with the epoxy compound.

[6] A cured resin product obtained by curing the epoxy resin composition according to [5].

The invention according to [6] is directed to a cured resin product obtained after a curing reaction of the epoxy resin composition according to [5].

[7] A prepreg including:

a reinforcing fiber base material; and

the epoxy resin composition according to [5], which is impregnated into the reinforcing fiber base material.

[8] The prepreg according to [7], wherein the reinforcing fiber base material is a reinforcing fiber base material made of carbon fibers.

[9] A method for producing the prepreg according to [7], including impregnating the epoxy resin composition into the reinforcing fiber base material.

The inventions according to [7] to [9] are directed to a prepreg containing a reinforcing fiber base material and an epoxy resin composition impregnated into the reinforcing fiber base material, and a method for producing the same.

[10] A fiber-reinforced composite material containing:

the cured resin product according to [6]; and

a reinforcing fiber base material.

[11] A method for producing the fiber-reinforced composite material according to [10], including impregnating the epoxy resin composition according to [5] into the reinforcing fiber base material and curing the epoxy resin composition.

[12] A method for producing the fiber-reinforced composite material according to [10], including curing the prepreg according to [7] or [8].

The inventions according to [10] to [12] are directed to a fiber-reinforced composite material containing the cured resin product of the present invention and a reinforcing fiber base material, and a method for producing the same. The reinforcing fiber base material and the epoxy resin composition may be composited in advance, and then the resultant product (prepreg) is molded. Further, the reinforcing fiber base material and the cured resin may be molded and composited at the same time, not via formation of a prepreg.

Advantageous Effects of Invention

The epoxy resin composition containing the epoxy compound of the present invention enables production of a cured resin product having a high elastic modulus and high water absorption resistance. Further, the epoxy resin composition of the present invention has a low viscosity, and thus has high impregnation property into the reinforcing fiber base material and high handleability.

