Epoxy resin, epoxy resin composition, cured epoxy resin, and composite material

Abstract

The epoxy resin contains an epoxy compound with a mesogenic structure, and when cured, has a flexural modulus of 3.0 GPa or more at 23°C and a fracture toughness of 1.0 MPa m 1 / 2 or higher, and the glass transition temperature is 150°C or higher.

Description

Technical Field

[0001] The present disclosure relates to epoxy resins, epoxy resin compositions, cured epoxy resins, and composite materials.

Background Art

[0002] Epoxy resins are used in various applications taking advantage of their excellent heat resistance. In recent years, the application of fiber-reinforced composite materials using epoxy resins to structural materials has been progressing. Fiber-reinforced composite materials are also used in aircraft fuselages and the like, and excellent heat resistance and strength are required. Since epoxy resins can form a crosslinked structure and exhibit heat resistance and strength, various studies have been conducted on using them as resin materials for fiber-reinforced composite materials (see, for example, Patent Document 1 and Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, when applying an epoxy resin material to, for example, a fiber-reinforced composite material for aircraft, a method has been adopted in which a resin layer in which particles of a thermoplastic resin such as polyamide are dispersed is provided on the surface region of the prepreg of the epoxy resin and laminated. According to this method, while the fracture toughness in the compression direction can be enhanced, it is necessary to localize the particles of the thermoplastic resin in the surface region of the prepreg, and the manufacturing process is complicated.

[0005] In view of the above situation, an object of the present disclosure is to provide an epoxy resin capable of simplifying the manufacturing process of a fiber-reinforced composite material, as well as an epoxy resin composition, a cured epoxy resin, and a composite material using the epoxy resin.

Means for Solving the Problems

[0006] Means for solving the above problems include the following embodiments. <1> An epoxy resin containing an epoxy compound having a mesogenic structure, having a flexural modulus of 3.0 GPa or more and a fracture toughness of 1.0 MPa·m 1 / 2 or more at 23°C when cured, and having a glass transition temperature of 150°C or more. <2> The epoxy resin according to <1>, wherein the mesogenic structure includes a mesogenic structure represented by the following general formula (1).

[0007]

Chemical formula

[0008] In general formula (1), X represents a single bond or a linking group having at least one divalent group selected from the following group (A). Each Y independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. Each n independently represents an integer of 0 to 4. * represents a bonding site with an adjacent atom.

[0009]

Chemical formula

[0010] In group (A), each Y independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. Each n independently represents an integer of 0 to 4, k represents an integer of 0 to 7, m represents an integer of 0 to 8, and l represents an integer of 0 to 12. <3> The epoxy resin according to <2>, wherein the mesogenic structure represented by the general formula (1) includes a structure represented by the following general formula (2).

[0011]

Chemical formula

[0012] In the general formula (2), X represents a single bond or a linking group having at least one divalent group selected from the group (A). Each Y independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. Each n independently represents an integer of 0 to 4. * represents a bonding site with an adjacent atom. <4> The epoxy resin according to <2>, wherein the epoxy compound having the mesogenic structure has at least one structure selected from the group consisting of the following general formula (1-A), general formula (1-B), and general formula (1-C).

[0013]

Chemical formula

[0014] In the general formula (1-A), general formula (1-B), and general formula (1-C), X represents a single bond or a linking group having at least one divalent group selected from the group (A). Each Y independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. Each n independently represents an integer of 0 to 4. Each m independently represents an integer of 0 to 4. p represents an integer of 0 to 6. Each Z independently represents -O- or -NH-. R 1 and R 2 each independently represents an alkyl group having 1 to 8 carbon atoms. * represents a bonding site with an adjacent atom. <5> The epoxy compound having the mesogen structure has at least one structure selected from the group consisting of the following general formula (2-A), general formula (2-B), and general formula (2-C), and the epoxy resin according to any one of <2> to <4>.

[0015]

Chemical formula

[0016] In general formula (2-A), general formula (2-B), and general formula (2-C), X represents a single bond or a linking group having at least one divalent group selected from the group (A). Y each independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. n each independently represents an integer of 0 to 4. m each independently represents an integer of 0 to 4. p represents an integer of 0 to 6. Z each independently represents -O- or -NH-. R 1 and R 2 each independently represents an alkyl group having 1 to 8 carbon atoms. * represents a bonding site with an adjacent atom. <6> The structure represented by the general formula (2) includes at least one structure selected from the group consisting of the following general formula (3) and general formula (4), and the epoxy resin according to <3>.

[0017]

Chemical formula

[0018] In general formula (3) and general formula (4), R 3 ~R 6 each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. * represents a bonding site with an adjacent atom. <7> An epoxy resin composition containing the epoxy resin according to any one of <1> to <6> and a curing agent. <8> The epoxy resin composition according to <7>, wherein the curing agent contains a compound having two or more amino groups directly bonded to an aromatic ring. <9> The epoxy resin composition according to <7> or <8>, wherein the curing agent contains 3,3'-diaminodiphenyl sulfone. <10> An epoxy resin cured product which is a cured product of the epoxy resin composition according to any one of <7> to <9>. <11> A composite material comprising the epoxy resin cured product according to <10> and a reinforcing material. <12> The composite material according to <11>, wherein the reinforcing material contains a carbon material.

Effects of the Invention

[0019] According to the present disclosure, there are provided an epoxy resin capable of simplifying the manufacturing process of a fiber-reinforced composite material, an epoxy resin composition using the epoxy resin, an epoxy resin cured product, and a composite material.

Modes for Carrying Out the Invention

[0020] Hereinafter, modes for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values and their ranges, and they do not limit the present invention.

[0021] In the present disclosure, the term "step" includes not only a step independent from other steps, but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved. In the numerical range indicated by "~" in the present disclosure, the numerical values described before and after "~" are included as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, each component may contain a plurality of corresponding substances. When there are a plurality of substances corresponding to each component in the composition, the content rate or content of each component means the total content rate or content of the plurality of substances present in the composition, unless otherwise specified. In the present disclosure, the particles corresponding to each component may contain a plurality of types. When there are a plurality of types of particles corresponding to each component in the composition, the particle diameter of each component means a value for the mixture of the plurality of types of particles present in the composition, unless otherwise specified. In the present disclosure, the term "layer" includes not only the case where it is formed over the entire region where the layer exists when observing the region where the layer exists, but also the case where it is formed only in a part of the region. In the present disclosure, the term "lamination" indicates stacking layers, and two or more layers may be bonded, and two or more layers may be detachable. In the present disclosure, the "epoxy compound" means a compound having an epoxy group in the molecule. The "epoxy resin" is a concept that captures a plurality of epoxy compounds as an aggregate and means an uncured state.

[0022] ≪Epoxy Resin≫ The epoxy resin of the present disclosure contains an epoxy compound having a mesogenic structure, and when formed into a cured product, has a flexural modulus of 3.0 GPa or more at 23°C, a fracture toughness of 1.0 MPa·m 1 / 2 or more, and a glass transition temperature of 150°C or more. Hitherto, for example, in the case of fiber-reinforced composite materials for aircraft, a method has been adopted in which a resin layer in which particles of a thermoplastic resin are dispersed is provided on the surface region of a prepreg of an epoxy resin and this is laminated. According to this method, since the resin layer containing the flexible thermoplastic resin exists between the epoxy resin layers, it has been possible to improve the fracture toughness in the compression direction. On the other hand, when using the epoxy resin of the present disclosure that satisfies both a flexural modulus of 3.0 GPa or more and a fracture toughness of 1.0 MPa·m 1 / 2 or more, it has been found that a fiber-reinforced composite material that can be applied to the fuselage of an aircraft or the like can be produced by applying it to a reinforcing material such as carbon fiber without providing a resin layer containing a thermoplastic resin between the layers. When the epoxy resin has the above-mentioned elastic modulus and fracture toughness, for example, even without separately providing a resin layer in which a thermoplastic resin is dispersed, the occurrence of cracks in the cured product of the epoxy resin itself can be preferably suppressed, and it is considered that it becomes possible to produce a fiber-reinforced composite material for aircraft. Further, the epoxy resin of the present disclosure has a glass transition temperature of 150°C or higher and is also excellent in heat resistance as a fiber-reinforced composite material for aircraft. As described above, according to the epoxy resin of the present disclosure, in the production of a fiber-reinforced composite material, steps such as localizing particles of a thermoplastic resin in the surface region of the prepreg become unnecessary, and the process can be simplified.

[0023] The epoxy resin of the present disclosure may contain an epoxy resin having a mesogenic structure, and may or may not contain an epoxy resin having no mesogenic structure as long as it can satisfy the above-mentioned properties when formed into a cured product.

[0024] <Epoxy compound having a mesogenic structure> The mesogenic structure means a structure in which an epoxy resin, which is a reactant of an epoxy compound having this structure, may exhibit liquid crystallinity. Specifically, the mesogenic structure includes a biphenyl structure, a phenyl benzoate structure, a cyclohexyl benzoate structure, an azobenzene structure, a stilbene structure, a terphenyl structure, an anthracene structure, derivatives thereof, a structure in which two or more of these mesogenic structures are bonded via a linking group, and the like.

[0025] The number of mesogenic structures in one molecule of the epoxy compound may be one or two or more. The two or more mesogenic structures in the epoxy compound having two or more mesogenic structures may be different or the same.

[0026] An epoxy resin containing an epoxy compound having a mesogenic structure can form a higher-order structure in a cured product of an epoxy resin composition containing this epoxy resin. Here, the higher-order structure means a structure including a higher-order structure in which its components are arranged to form a microscopic ordered structure, and for example, a crystal phase and a liquid crystal phase correspond thereto. The presence or absence of such a higher-order structure can be determined by a polarizing microscope. That is, the presence or absence of a higher-order structure can be discriminated by the appearance of interference fringes due to polarization extinction in observation in a cross Nicol state. This higher-order structure usually exists in an island shape in the cured product of the epoxy resin composition to form a domain structure, and one of the islands corresponds to one higher-order structure. The components of this higher-order structure itself are generally formed by covalent bonds.

[0027] Examples of the higher-order structure formed in the cured state include a nematic structure and a smectic structure. The nematic structure and the smectic structure are each a kind of liquid crystal structure. The nematic structure is a liquid crystal structure in which the long axes of molecules are oriented in a uniform direction and have only orientational order. In contrast, the smectic structure has one-dimensional positional order in addition to orientational order and has a layer structure. The degree of order is higher in the smectic structure than in the nematic structure. Therefore, from the viewpoints of the thermal conductivity and fracture toughness of the cured product, it is more preferable to form a higher-order structure of the smectic structure.

[0028] Whether a smectic structure is formed in the cured product can be determined by X-ray diffraction measurement of the cured product. The X-ray diffraction measurement can be carried out using, for example, an X-ray diffractometer of Rigaku Corporation. In the present disclosure, when X-ray diffraction measurement is performed using CuKα1 line, with a tube voltage of 40 kV, a tube current of 20 mA, and in the range of 2θ = 1° to 30°, if diffraction peaks appear in the range of 2θ = 2° to 10°, it is determined that a smectic structure is formed in the cured product.

[0029] An epoxy resin containing an epoxy compound having a mesogenic structure is likely to form a higher-order structure when cured. Therefore, an epoxy resin containing an epoxy compound having a mesogenic structure tends to be superior in the fracture toughness of the cured product compared to an epoxy resin not containing an epoxy compound having a mesogenic structure.

[0030] The mesogenic structure may be a structure represented by the following general formula (1).

[0031]

Chemical formula

[0032] In general formula (1), X represents a single bond or a linking group having at least one divalent group selected from the following group (A). Each Y independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. Each n independently represents an integer of 0 to 4. * represents a bonding site with an adjacent atom.

[0033]

Chemical formula

[0034] In group (A), each Y independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. Each n independently represents an integer of 0 to 4, k represents an integer of 0 to 7, m represents an integer of 0 to 8, and l represents an integer of 0 to 12.

[0035] In the mesogenic structure represented by the general formula (1), when X is a linking group having at least one divalent group selected from the above group (A), the linking group is preferably a linking group having at least one divalent group selected from the following group (Aa), and more preferably a linking group having at least one divalent group selected from group (Aa) and having at least one cyclic structure.

[0036]

Chemical formula

[0037] In group (Aa), each Y independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. Each n independently represents an integer of 0 to 4, k represents an integer of 0 to 7, m represents an integer of 0 to 8, and l represents an integer of 0 to 12.

[0038] From the viewpoint of easily forming a higher-order structure in the cured product, the mesogenic structure represented by the general formula (1) preferably contains a mesogenic structure represented by the following general formula (2).

[0039]

Chemical formula

[0040] In general formula (2), X represents a single bond or a linking group having at least one divalent group selected from the group (A). Each Y independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. Each n independently represents an integer from 0 to 4. * represents a bonding site with an adjacent atom.

[0041] Preferred examples of the mesogenic structure represented by general formula (2) include mesogenic structures represented by the following general formula (3) or general formula (4).

[0042] [Chemical formula]

[0043] In general formula (3) or general formula (4), R 3 ~R 6 each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. * represents a bonding site with an adjacent atom.

[0044] R 3 ~R 6 are each independently preferably a hydrogen atom or an alkyl group having 1 to 2 carbon atoms, more preferably a hydrogen atom or a methyl group, and even more preferably a hydrogen atom. Also, it is preferable that 2 to 4 of R 3 ~R 6 are hydrogen atoms, more preferably 3 or 4 are hydrogen atoms, and even more preferably all 4 are hydrogen atoms. When any of R 3 ~R 6 is an alkyl group having 1 to 3 carbon atoms, it is preferable that at least one of R 3 and R 6 is an alkyl group having 1 to 3 carbon atoms.

[0045] The epoxy compound having a mesogenic structure may be an epoxy compound having a structure represented by the following general formula (1-m).

[0046] [Chemical formula]

[0047] In the general formula (1-m), the definitions and preferred examples of X, Y, and n are the same as those of X, Y, and n in the general formula (1) described above.

[0048] From the viewpoint of forming a higher-order structure in the cured product, the epoxy compound represented by the general formula (1-m) is preferably an epoxy compound having a structure represented by the following general formula (2-m).

[0049] [Chemical formula]

[0050] In the general formula (2-m), the definitions and preferred examples of X, Y, and n are the same as those of X, Y, and n in the general formula (1-m).

[0051] The epoxy compound represented by the general formula (1-m) is more preferably an epoxy compound having a structure represented by the following general formula (3-m) or general formula (4-m).

[0052] [Chemical formula]

[0053] In the general formulas (3-m) and (4-m), R 3 ~R 6 The definitions and preferred examples are the same as those of R 3 ~R 6 in the general formulas (3) and (4).

[0054] [Epoxy compounds other than epoxy compounds having a mesogenic structure] The epoxy resin may contain an epoxy compound other than the epoxy compound having a mesogenic structure. Examples of the epoxy compound other than the epoxy compound having a mesogenic structure include an epoxy compound having an aromatic ring. The epoxy compound having an aromatic ring is preferably a compound in which one or more glycidyl ether groups are bonded to the aromatic ring, and more preferably a compound in which two glycidyl ether groups are bonded to the aromatic ring. Examples of the aromatic ring include a benzene ring and a naphthalene ring. The epoxy compound other than the epoxy compound having a mesogenic structure may be used alone or in combination of two or more.

[0055] The epoxy compound other than the epoxy compound having a mesogenic structure preferably has two epoxy groups. When the number of epoxy groups is two, it tends to be possible to preferably form a cured product while suppressing the gelation of the epoxy resin.

[0056] Examples of the epoxy compound other than the epoxy compound having a mesogenic structure include an epoxy compound represented by the following general formula (1-a) and an epoxy compound represented by the following general formula (1-b).

[0057]

Chemical formula

[0058] In the general formula (1-a) and the general formula (1-b), Z each independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. p represents an integer of 0 to 4. q represents an integer of 0 to 6. p is preferably 0 to 2, and more preferably 0. q is preferably 0 to 4, more preferably 0 to 2, and even more preferably 0.

[0059] Among them, the epoxy compound other than the epoxy compound having a mesogenic structure is preferably at least one of the epoxy compounds represented by the following general formula (1-c) to general formula (1-e).

[0060] [Chemical formula]

[0061] In general formula (1-c) to general formula (1-e), the definitions and preferred examples of Z, p, and q are the same as the definitions and preferred examples of Z, p, and q in general formula (1-a) and general formula (1-b).

[0062] [Epoxy compound having two or more mesogenic structures (specific epoxy compound)] The epoxy compound having a mesogenic structure may be an epoxy compound having two or more mesogenic structures (hereinafter, also referred to as "specific epoxy compound"). The epoxy compound having two or more mesogenic structures has a lower viscosity before curing and tends to have excellent handleability compared to the epoxy compound having one mesogenic structure (hereinafter, also referred to as "mesogenic epoxy monomer").

[0063] The structure of the specific epoxy compound is not particularly limited as long as it is an epoxy compound having two or more mesogenic structures. For example, the specific epoxy compound may be a dimer of a mesogenic epoxy monomer or a multimer of trimer or more. The two or more mesogenic structures in the specific epoxy compound may be the same as or different from each other.

[0064] The specific epoxy compound preferably has a structure in which at least two mesogenic structures are linked via a divalent aromatic group. In this case, the at least two mesogenic structures and the divalent aromatic group may be directly linked or linked via a linking group.

[0065] In the present disclosure, when the mesogenic structure of a specific epoxy compound contains a divalent aromatic group, the divalent aromatic group disposed between two mesogenic structures shall be different from the divalent aromatic group contained in the mesogenic structure.

[0066] Examples of the divalent aromatic group disposed between two mesogenic structures include a phenylene group, a divalent biphenyl group, and a naphthylene group. Examples of the phenylene group include a structure represented by the following general formula (5A), examples of the divalent biphenyl group include a structure represented by the following general formula (5B), and examples of the naphthylene group include a structure represented by the following general formula (5C).

[0067]

Chemical formula

[0068] In general formula (5A), general formula (5B), and general formula (5C), * represents the bonding position with an adjacent atom. Examples of the adjacent atom include an oxygen atom, a nitrogen atom, etc. R 1 and R 2 each independently represents an alkyl group having 1 to 8 carbon atoms. m each independently represents an integer of 0 to 4. p represents an integer of 0 to 6.

[0069] R 1 and R 2 are each independently preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group.

[0070] m is each independently preferably an integer of 0 to 2, more preferably an integer of 0 to 1, and even more preferably 0. p is preferably an integer of 0 to 2, and more preferably an integer of 0 to 1.

[0071] Among the structures represented by the general formula (5A), the structure represented by the following general formula (5a) is preferred. Among the structures represented by the general formula (5B), the structure represented by the following general formula (5b) is preferred. Among the structures represented by the general formula (5C), the structures represented by the following general formula (5c-1) and general formula (5c-2) are preferred. Specific epoxy compounds having such structures are considered to have high molecular stacking properties and to be more likely to form higher-order structures.

[0072]

Chemical formula

[0073] In general formula (5a), general formula (5b), general formula (5c-1), and general formula (5c-2), the definitions and preferred examples of R 1 , R 2 , m, and p are the same as the definitions and preferred examples of R 1 , R 2 and m, and p in general formula (5A), general formula (5B), and general formula (5C). * represents the bonding position with an adjacent atom.

[0074] The specific epoxy compound may be an epoxy compound having a structure represented by the following general formula (1-A), general formula (1-B), or general formula (1-C).

[0075]

Chemical formula

[0076] In general formula (1-A), general formula (1-B), and general formula (1-C), the definitions and preferred examples of X, Y, and n are the same as the definitions and preferred examples of X, Y, and n in general formula (1). Also, R 1 , R 2, the definitions and preferred examples of m and p are the same as those of R in General Formula (5A), General Formula (5B), and General Formula (5C). 1 R 2 , the definitions and preferred examples of m and p are the same. Z independently represents -O- or -NH- each. * represents the bonding site with an adjacent atom.

[0077] From the viewpoint of forming a higher-order structure in the cured product, the epoxy compound having the structure represented by General Formula (1-A) is preferably an epoxy compound having the structure represented by the following General Formula (2-A), the epoxy compound having the structure represented by General Formula (1-B) is preferably an epoxy compound having the structure represented by the following General Formula (2-B), and the epoxy compound having the structure represented by General Formula (1-C) is preferably an epoxy compound having the structure represented by the following General Formula (2-C).

[0078]

Chemical formula

[0079] In General Formula (2-A), General Formula (2-B), and General Formula (2-C), the definitions and preferred examples of X, Y, n, m, p, R 1 R 2 , and Z are the same as the definitions and preferred examples of X, Y, n, m, p, R 1 R 2 and Z in General Formula (1-A), General Formula (1-B), and General Formula (1-C). * represents the bonding site with an adjacent atom.

[0080] Examples of the epoxy compound having the structure represented by General Formula (1-A) include an epoxy compound having at least one structure selected from the group consisting of the following General Formula (3-A-1) to General Formula (3-A-4). Examples of the epoxy compound having a structure represented by the general formula (1-B) include an epoxy compound having at least one structure selected from the group consisting of the following general formulas (3-B-1) to (3-B-4). Examples of the epoxy compound having a structure represented by the general formula (1-C) include an epoxy compound having at least one structure selected from the group consisting of the following general formulas (3-C-1) to (3-C-4).

[0081]

Chemical formula

Chemical formula

[0082]

Chemical formula

[0083] In general formulas (3-A-1) to (3-A-4), general formulas (3-B-1) to (3-B-4), and general formulas (3-C-1) to (3-C-4), the definitions and preferred examples of R 1 , R 2 , m, p, and Z are the same as the definitions and preferred examples of R 1 , R 2 , m, p, and Z in general formulas (1-A), (1-B), and (1-C). The definitions and preferred examples of R 3 to R 6 are the same as the definitions and preferred examples of R 3 to R 6 in general formula (3) or general formula (4). * represents the bonding site with an adjacent atom.

[0084] In addition, the specific epoxy compound may have at least one structure selected from the group consisting of the following general formulas (1-a') and (1-b'). When the specific epoxy compound has at least one structure selected from the group consisting of (1-a') and (1-b'), the elastic modulus tends to increase.

[0085]

Chem.

[0086] In general formulas (1-a') and (1-b'), the definitions and preferred examples of Z, p, and q are the same as those of Z, p, and q in general formulas (1-a) and (1-b). * represents a bonding site with an adjacent atom.

[0087] Among the structures represented by general formula (1-a'), the structures represented by general formulas (1-c') and (1-d') are preferred. Among the structures represented by general formula (1-b'), the structure represented by general formula (1-e') is preferred.

[0088]

Chem.

[0089] In general formulas (1-c') to (1-e'), the definitions and preferred examples of Z, p, and q are the same as those of Z, p, and q in general formulas (1-c) to (1-e). * represents a bonding site with an adjacent atom.

[0090] The specific epoxy compound may be a reaction product of an epoxy compound having a mesogenic structure and a compound having a functional group capable of reacting with an epoxy group. Further, the specific epoxy compound may be a reaction product of an epoxy compound having a mesogenic structure, an epoxy compound other than the epoxy compound having a mesogenic structure, and a compound having a functional group capable of reacting with an epoxy group.

[0091] 〔Synthesis method of specific epoxy compound〕 The method for synthesizing a specific epoxy compound is not particularly limited. For example, the method for synthesizing a specific epoxy compound may involve reacting a compound having one mesogenic structure and an epoxy group (hereinafter also referred to as a mesogenic epoxy monomer), a compound having a functional group capable of reacting with an epoxy group, and, if necessary, an epoxy compound other than the epoxy compound having a mesogenic structure to obtain the specific epoxy compound.

[0092] The structure of the mesogenic epoxy monomer is not particularly limited, and it may be, for example, an epoxy compound having a structure represented by the general formula (1-m) described above. The epoxy compound other than the epoxy compound having a mesogenic structure is as described above.

[0093] The compound having a functional group capable of reacting with an epoxy group is not particularly limited, and it is preferably an aromatic compound having a functional group capable of reacting with an epoxy group.

[0094] Examples of the functional group capable of reacting with an epoxy group include a hydroxyl group, an amino group, an isocyanate group, etc. The number of the functional groups capable of reacting with the epoxy group in the aromatic compound having a functional group capable of reacting with an epoxy group may be one or two or more, and two is preferable. Further, the functional group may or may not be directly bonded to the aromatic ring, and may be linked to the aromatic ring via an alkylene oxide chain such as an ethylene oxide chain or a propylene oxide chain, an alkyl chain, or the like.

[0095] From the perspective of forming a smectic structure in the cured product, aromatic compounds having a functional group capable of reacting with an epoxy group include dihydroxybenzene compounds having a structure in which two hydroxyl groups are bonded to one benzene ring, diamino benzene compounds having a structure in which two amino groups are bonded to one benzene ring, dihydroxybiphenyl compounds having a structure in which one hydroxyl group is bonded to each of two benzene rings forming a biphenyl structure, diaminobiphenyl compounds having a structure in which one amino group is bonded to each of two benzene rings forming a biphenyl structure, dihydroxynaphthalene compounds having a structure in which two hydroxyl groups are bonded to one naphthalene ring, and diaminonaphthalene compounds having a structure in which two amino groups are bonded to one naphthalene ring. It is preferably at least one selected from the group consisting of (hereinafter also referred to as specific aromatic compounds).

[0096] Examples of the dihydroxybenzene compound include catechol, resorcinol, hydroquinone, and derivatives thereof. Examples of the diaminobenzene compound include 1,2-diaminobenzene, 1,3-diaminobenzene, 1,4-diaminobenzene, and derivatives thereof.

[0097] Examples of the dihydroxybiphenyl compound include 2,2'-dihydroxybiphenyl, 2,3'-dihydroxybiphenyl, 2,4'-dihydroxybiphenyl, 3,3'-dihydroxybiphenyl, 3,4'-dihydroxybiphenyl, 4,4'-dihydroxybiphenyl, and derivatives thereof. Examples of the diaminobiphenyl compound include 2,2'-diaminobiphenyl, 2,3'-diaminobiphenyl, 2,4'-diaminobiphenyl, 3,3'-diaminobiphenyl, 3,4'-diaminobiphenyl, 4,4'-diaminobiphenyl, and derivatives thereof.

[0098] Examples of the dihydroxynaphthalene compound include 1,2-dihydroxynaphthalene, 1,3-dihydroxynaphthalene, 1,4-dihydroxynaphthalene, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 1,8-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, and derivatives thereof. Examples of the diamino naphthalene compound include 1,2-diamino naphthalene, 1,3-diamino naphthalene, 1,4-diamino naphthalene, 1,5-diamino naphthalene, 1,6-diamino naphthalene, 1,7-diamino naphthalene, 1,8-diamino naphthalene, 2,3-diamino naphthalene, 2,6-diamino naphthalene, 2,7-diamino naphthalene, and derivatives thereof.

[0099] Examples of the derivative of the specific aromatic compound include a compound in which a substituent such as an alkyl group having 1 to 8 carbon atoms is bonded to the benzene ring or naphthalene ring of the specific aromatic compound. The specific aromatic compound may be used alone or in combination of two or more.

[0100] The functional group equivalent of the compound having a functional group capable of reacting with an epoxy group is not particularly limited. From the viewpoint of the reaction efficiency, the functional group equivalent of the compound having a functional group capable of reacting with an epoxy group (when the functional group is an amino group, the equivalent of active hydrogen) is preferably 65 g / eq to 200 g / eq, more preferably 70 g / eq to 150 g / eq, and even more preferably 75 g / eq to 100 g / eq.

[0101] The method for synthesizing a specific epoxy compound by reacting a mesogenic epoxy monomer, a compound having a functional group capable of reacting with an epoxy group, and, if necessary, an epoxy compound other than the epoxy compound having a mesogenic structure is not particularly limited. Specifically, for example, a mesogenic epoxy monomer, a compound having a functional group capable of reacting with an epoxy group, an epoxy compound other than the epoxy compound having a mesogenic structure used as necessary, and a reaction catalyst used as necessary are dissolved in a solvent and stirred while heating to synthesize a specific epoxy compound.

[0102] Alternatively, for example, a mesogenic epoxy monomer, a compound having a functional group capable of reacting with an epoxy group, an epoxy compound other than the epoxy compound having a mesogenic structure used as necessary, and a reaction catalyst used as necessary are mixed without using a solvent and stirred while heating to synthesize a specific epoxy compound.

[0103] The solvent is not particularly limited as long as it can dissolve a mesogenic epoxy monomer, a compound having a functional group capable of reacting with an epoxy group, and, if necessary, an epoxy compound other than the epoxy compound having a mesogenic structure, and can be heated to a temperature necessary for these compounds to react. Specifically, cyclohexanone, cyclopentanone, ethyl lactate, propylene glycol monomethyl ether, N-methylpyrrolidone, methyl cellosolve, ethyl cellosolve, propylene glycol monopropyl ether, etc. can be mentioned.

[0104] The amount of the solvent is not particularly limited as long as it can dissolve a mesogenic epoxy monomer, a compound having a functional group capable of reacting with an epoxy group, an epoxy compound other than the epoxy compound having a mesogenic structure used as necessary, and a reaction catalyst used as necessary at the reaction temperature. Although the solubility varies depending on the types of raw materials before the reaction, the type of the solvent, etc., for example, if the charged solid content concentration is in the range of 20% by mass to 60% by mass, the viscosity of the solution after the reaction tends to be in a preferable range.

[0105] The type of the reaction catalyst is not particularly limited, and an appropriate one can be selected from the viewpoints of reaction rate, reaction temperature, storage stability, etc. Specifically, imidazole compounds, organic phosphorus compounds, tertiary amines, quaternary ammonium salts, etc. can be mentioned. The reaction catalyst may be used alone or in combination of two or more.

[0106] From the viewpoint of the heat resistance of the cured product, an organic phosphorus compound is preferable as the reaction catalyst. Preferable examples of the organic phosphorus compound include organic phosphine compounds, compounds having intramolecular polarization formed by adding a compound having a π bond such as maleic anhydride, quinone compound, diazophenylmethane, and phenol resin to the organic phosphine compound, and complexes of organic phosphine compounds and organic boron compounds. Among them, a compound formed by adding an organic phosphine compound and a quinone compound is preferable.

[0107] Specific examples of the organic phosphine compound include triphenylphosphine, diphenyl(p-tolyl)phosphine, tris(alkylphenyl)phosphine, tris(alkoxyphenyl)phosphine, tris(alkylalkoxyphenyl)phosphine, tris(dialkylphenyl)phosphine, tris(trialkylphenyl)phosphine, tris(tetraalkylphenyl)phosphine, tris(dialkoxyphenyl)phosphine, tris(trialkoxyphenyl)phosphine, tris(tetraalkoxyphenyl)phosphine, trialkylphosphine, dialkylarylphosphine, alkyldiarylphosphine, etc.

[0108] Specific examples of the quinone compound include 1,4-benzoquinone, 2,5-toluquinone, 1,4-naphthoquinone, 2,3-dimethylbenzoquinone, 2,6-dimethylbenzoquinone, 2,3-dimethoxy-5-methyl-1,4-benzoquinone, 2,3-dimethoxy-1,4-benzoquinone, phenyl-1,4-benzoquinone, etc.

[0109] Specific examples of the organic boron compound include tetraphenyl borate, tetra-p-tolyl borate, tetra-n-butyl borate, and the like.

[0110] The amount of the reaction catalyst is not particularly limited. From the viewpoints of reaction rate and storage stability, it is preferably 0.1 to 1.5 parts by mass, more preferably 0.2 to 1 part by mass, based on 100 parts by mass of the total mass of the mesogenic epoxy monomer, an epoxy compound other than the epoxy compound having a mesogenic structure used as necessary, and a compound having a functional group capable of reacting with an epoxy group.

[0111] The synthesis of the specific epoxy compound can be carried out using a reaction vessel such as a flask for a small-scale synthesis or a synthesis kettle for a large-scale synthesis. The specific synthesis method is as follows, for example. First, the mesogenic epoxy monomer and, if necessary, an epoxy compound other than the epoxy compound having a mesogenic structure are charged into a reaction vessel, a solvent is added if necessary, and the mixture is heated to the reaction temperature by an oil bath or a heat medium to dissolve the mesogenic epoxy monomer and, if necessary, the epoxy compound other than the epoxy compound having a mesogenic structure. A compound having a functional group capable of reacting with an epoxy group is added thereto, and then a reaction catalyst is added if necessary to initiate the reaction. Then, the specific epoxy compound can be obtained by distilling off the solvent under reduced pressure if necessary.

[0112] The reaction temperature is not particularly limited as long as the reaction between the epoxy group of the mesogenic epoxy monomer and, if necessary, the epoxy compound other than the epoxy compound having a mesogenic structure, and the functional group capable of reacting with the epoxy group proceeds. The reaction temperature is preferably in the range of, for example, 100°C to 180°C, more preferably in the range of 100°C to 150°C. By setting the reaction temperature to 100°C or higher, the time until the reaction is completed tends to be shorter. On the other hand, by setting the reaction temperature to 180°C or lower, the possibility of gelation tends to be reduced.

[0113] When synthesizing a specific epoxy compound, the mixing ratio of the epoxy compound used as a raw material (i.e., the mesogenic epoxy monomer and, if necessary, an epoxy compound other than the epoxy compound having a mesogenic structure) and the compound having a functional group capable of reacting with an epoxy group is not particularly limited. For example, the ratio (A:B) of the equivalent number (A) of epoxy groups to the equivalent number (B) of functional groups capable of reacting with epoxy groups may be a mixing ratio in the range of 10:10 to 10:0.01. From the viewpoints of the fracture toughness and heat resistance of the cured product, a mixing ratio in which A:B is in the range of 10:5 to 10:0.1 is preferable. From the viewpoint of the handleability of the specific epoxy compound, the ratio (A:B) of the equivalent number (A) of epoxy groups to the equivalent number (B) of functional groups capable of reacting with epoxy groups is preferably a mixing ratio in the range of 10:1.6 to 10:3.0, more preferably a mixing ratio in the range of 10:1.8 to 10:2.9, and even more preferably a mixing ratio in the range of 10:2.0 to 10:2.8. From the viewpoint of effectively achieving both flexural modulus and fracture toughness, the ratio (A:B) of the equivalent number (A) of epoxy groups to the equivalent number (B) of functional groups capable of reacting with epoxy groups is preferably a mixing ratio in the range of 10:1.0 to 10:3.0, more preferably a mixing ratio in the range of 10:1.4 to 10:2.6, and even more preferably a mixing ratio in the range of 10:1.6 to 10:2.4.

[0114] The structure of the specific epoxy compound obtained by synthesis can be determined by comparing the molecular weight of the specific epoxy compound presumed to be obtained from the reaction of, for example, the mesogenic epoxy monomer used in the synthesis, an epoxy compound other than the epoxy compound having a mesogenic structure used as necessary, and a compound having a functional group capable of reacting with an epoxy group, with the molecular weight of the target compound determined by liquid chromatography performed using a liquid chromatograph equipped with a UV and mass spectrometer detector.

[0115] Liquid chromatography uses, for example, "LaChrom II C18" manufactured by Hitachi, Ltd. as an analytical column, and using the gradient method, the mixing ratio (volume basis) of the eluent is changed continuously from acetonitrile / tetrahydrofuran / 10 mmol / l ammonium acetate aqueous solution = 20 / 5 / 75 to acetonitrile / tetrahydrofuran = 80 / 20 (from the start for 20 minutes) and then to acetonitrile / tetrahydrofuran = 50 / 50 (from the start for 35 minutes) for measurement. The flow rate is set at 1.0 ml / min. In the UV spectrum detector, the absorbance at a wavelength of 280 nm is detected, and in the mass spectrum detector, the ionization voltage is detected at 2700 V.

[0116] The epoxy resin preferably contains both a specific epoxy compound and a mesogenic epoxy monomer. When the specific epoxy compound and the mesogenic epoxy monomer are present in an appropriate ratio in the epoxy resin, the handleability before curing tends to be excellent. In addition, the crosslinking density during curing can be made higher, and an epoxy resin cured product with more excellent heat resistance tends to be obtained. The ratio of the specific epoxy compound and the mesogenic epoxy monomer present in the epoxy resin can be adjusted by the mixing ratio of the mesogenic epoxy monomer and the compound having a functional group capable of reacting with an epoxy group and other reaction conditions.

[0117] The content ratio of the mesogenic epoxy monomer contained in the epoxy resin is preferably 50% or less of the whole epoxy resin. An epoxy resin having a content ratio of the mesogenic epoxy monomer of 50% or less tends to have a lower viscosity when the temperature is raised and excellent handleability compared to an epoxy resin having a content ratio of the mesogenic epoxy monomer exceeding 50%. The reason is not clear, but it is presumed that when the ratio of the mesogenic epoxy monomer is 50% or less of the whole epoxy resin, the precipitation of crystals at a temperature below the melting temperature of the epoxy resin is more suppressed than when the content ratio of the mesogenic epoxy monomer exceeds 50%.

[0118] In the present disclosure, the content ratio of the mesogenic epoxy monomer in the epoxy resin can be calculated from a chart obtained by, for example, liquid chromatography. More specifically, it is determined as the ratio (%) of the area of the peak derived from the mesogenic epoxy monomer to the total area of the peaks derived from all the components constituting the epoxy resin in the chart obtained by liquid chromatography. Specifically, the absorbance of the epoxy resin to be measured at a wavelength of 280 nm is detected, and it is calculated by the following formula from the total area of all the detected peaks and the area of the peak corresponding to the mesogenic epoxy monomer.

[0119] Ratio (%) of the area of the peak derived from the mesogenic epoxy monomer = (Area of the peak derived from the mesogenic epoxy monomer / Total area of the peaks derived from all the components constituting the epoxy resin) × 100

[0120] Liquid chromatography is performed with the sample concentration set at 0.5% by mass, using tetrahydrofuran as the mobile phase and a flow rate of 1.0 ml / min. The measurement can be carried out, for example, using a high-performance liquid chromatograph "L6000" manufactured by Hitachi, Ltd. and a data analysis device "C-R4A" manufactured by Shimadzu Corporation. As the column, for example, "G2000HXL" and "G3000HXL", which are GPC columns manufactured by Tosoh Corporation, can be used.

[0121] From the viewpoint of improving handleability, the ratio of the mesogenic epoxy monomer is preferably 50% or less, more preferably 49% or less, and even more preferably 48% or less of the entire epoxy resin.

[0122] From the viewpoint of reducing the intrinsic viscosity (viscosity during melting), the ratio of the mesogenic epoxy monomer is preferably 35% or more, more preferably 37% or more, and even more preferably 40% or more of the entire epoxy resin.

[0123] <Bending elastic modulus, fracture properties, and glass transition temperature (Tg) when cured into a solid> The epoxy resin of the present disclosure has a flexural modulus of 3.0 GPa or more, a fracture toughness of 1.0 MPa·m 1 / 2 or more, and a glass transition temperature of 150 °C or more when cured. Hereinafter, each property when cured will be described in detail. Note that the above elastic modulus, fracture properties, and glass transition temperature are values when an epoxy resin composition containing 3,3'-diaminodiphenyl sulfone as a curing agent and having an equivalent ratio of the curing agent to the epoxy resin of 1:1 is cured under the conditions of 180 °C for 4 hours. Here, the equivalent ratio represents the ratio (equivalent number of functional groups: equivalent number of epoxy groups) of the equivalent number of functional groups of the curing agent contained in the epoxy resin composition (in the case of an amine curing agent, the equivalent number of active hydrogens) to the equivalent number of epoxy groups of the epoxy resin.

[0124] 〔Flexural modulus〕 The flexural modulus at 23 °C when the epoxy resin of the present disclosure is cured is 3.0 GPa or more, preferably 3.1 GPa or more, and more preferably 3.2 GPa or more. The upper limit of the above flexural modulus is not particularly limited, and may be, for example, 5.0 GPa. The flexural modulus of the cured product can be measured by three-point bending measurement based on JIS K7171 (2016). Specifically, it is measured by the method described in the examples below.

[0125] 〔Fracture toughness〕 The fracture toughness value when the epoxy resin of the present disclosure is cured is 1.0 MPa·m 1 / 2 or more, preferably 1.3 MPa·m 1 / 2 or more, more preferably 1.5 MPa·m 1 / 2 or more, particularly preferably 1.8 MPa·m 1 / 2 or more, and particularly preferably 2.0 MPa·m 1 / 2 or more. The upper limit of the above fracture toughness is not particularly limited, and may be, for example, 3.0 MPa·m 1 / 2 for example. The fracture toughness value of the cured product can be measured by performing three-point bending measurement based on ASTM D5045. Specifically, it can be measured by the method described in the examples below.

[0126] 〔Glass transition temperature〕 When the epoxy resin of the present disclosure is a cured product, the glass transition temperature is 150 °C or higher, more preferably 155 °C or higher, and even more preferably 160 °C or higher. The upper limit of the glass transition temperature is not particularly limited, and may be, for example, 180 °C. The glass transition temperature of the cured product can be measured, for example, as follows. Cut the cured product into strip shapes to prepare test pieces, and perform dynamic viscoelastic measurement in the tensile mode. The measurement conditions are a frequency of 10 Hz, a heating rate of 5 °C / min, and a strain of 0.1%. In the obtained temperature-tanδ relationship diagram, the temperature at which tanδ is maximum may be regarded as the glass transition temperature. As the evaluation apparatus, for example, RSA-G2 (TA Instruments) can be used.

[0127] The flexural modulus at 23 °C when it is a cured product is 3.0 GPa or more, the fracture toughness is 1.0 MPa·m 1 / 2 The method for preparing an epoxy resin such that the flexural modulus is 3.0 GPa or more, the fracture toughness is 1.0 MPa·m or more, and the glass transition temperature is 150 °C or higher is not particularly limited. For example, the flexural modulus, fracture toughness, and glass transition temperature can be adjusted by adjusting the types, formulations, etc. of various components contained in the epoxy resin. For example, an epoxy resin composition containing an epoxy compound having a mesogenic structure can form a higher-order structure when it is a cured product. Therefore, the fracture toughness can be adjusted by adjusting the formulation of the epoxy compound having a mesogenic structure. Further, the flexural modulus can be adjusted by adjusting the epoxy equivalent of the epoxy compound to increase the crosslinking density in the cured product, or by using an epoxy compound having a bulky substituent to reduce the free volume. Furthermore, the glass transition temperature can be adjusted by adjusting the formulation of the mesogen-containing epoxy resin and the epoxy equivalent of the epoxy compound.

[0128] <Physical Properties of Epoxy Resin> 〔Weight-Average Molecular Weight〕 The weight-average molecular weight (Mw) of the epoxy resin is not particularly limited. From the viewpoint of reducing viscosity, the weight-average molecular weight (Mw) of the epoxy resin is preferably 500 to 3000, more preferably 700 to 2500, and even more preferably 800 to 2000.

[0129] In the present disclosure, the number-average molecular weight (Mn) and the weight-average molecular weight (Mw) are values obtained by liquid chromatography. Liquid chromatography is performed with a sample concentration of 0.5 mass%, using tetrahydrofuran as the mobile phase and a flow rate of 1.0 ml / min. The calibration curve is prepared using a polystyrene standard sample, and Mn and Mw are measured in terms of polystyrene conversion values using the calibration curve. The measurement can be performed, for example, using a high-performance liquid chromatograph "L6000" manufactured by Hitachi, Ltd. and a data analysis device "C-R4A" manufactured by Shimadzu Corporation. As the column, for example, "G2000HXL" and "G3000HXL" which are GPC columns manufactured by Tosoh Corporation can be used.

[0130] 〔Epoxy Equivalent〕 The epoxy equivalent of the epoxy resin is not particularly limited. From the viewpoints of fluidity of the epoxy resin, thermal conductivity of the cured product, and compatibility between fracture toughness and flexural modulus, etc., it is preferably 245 g / eq to 500 g / eq, more preferably 250 g / eq to 450 g / eq, and even more preferably 260 g / eq to 400 g / eq. In the present disclosure, the epoxy equivalent is measured by the perchloric acid titration method.

[0131] 〔Viscosity〕 The viscosity of the epoxy resin is not particularly limited and can be selected according to the use of the epoxy resin. From the viewpoint of handleability, the viscosity of the epoxy resin at 100 °C is preferably 200 Pa·s or less, more preferably 100 Pa·s or less, and even more preferably 20 Pa·s or less. The viscosity of the epoxy resin at 100 °C can be measured in a vibration mode using a rheometer (MCR-301, manufactured by Anton Paar). For example, it can be measured using a parallel plate part with a diameter of 12 mm, at a frequency of 1 kHz, a gap of 0.2 mm, and a strain of 2%.

[0132] ≪Epoxy Resin Composition and Epoxy Resin Cured Product≫ The epoxy resin composition of the present disclosure contains the epoxy resin of the present disclosure and a curing agent. The epoxy resin cured product of the present disclosure is a cured product of the epoxy resin composition of the present disclosure. From the viewpoint of fracture toughness, it is preferable that the epoxy resin composition can form a smectic structure or a nematic structure when cured.

[0133] <Curing Agent> The curing agent is not particularly limited as long as it is a compound capable of undergoing a curing reaction with the epoxy resin. Specific examples of the curing agent include amine curing agents, phenol curing agents, acid anhydride curing agents, polymercaptan curing agents, polyaminoamide curing agents, isocyanate curing agents, blocked isocyanate curing agents, and the like. The curing agent may be used alone or in combination of two or more.

[0134] From the viewpoint of forming a higher-order structure in the cured product of the epoxy resin composition, as the curing agent, an amine curing agent or a phenol curing agent is preferable, and an amine curing agent is more preferable. As the amine curing agent, an amine curing agent having an aromatic ring and an amino group is preferable, an amine curing agent in which the amino group is directly bonded to the aromatic ring is more preferable, and an amine curing agent having two or more amino groups directly bonded to the aromatic ring is even more preferable. Examples of the aromatic ring include a benzene ring and a naphthalene ring.

[0135] Specific examples of the amine curing agent include 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl ether, 4,4'-diamino-3,3'-dimethoxybiphenyl, 4,4'-diaminophenyl benzoate, 1,5-diaminonaphthalene, 1,3-diaminonaphthalene, 1,4-diaminonaphthalene, 1,8-diaminonaphthalene, 1,3-diaminobenzene, 1,4-diaminobenzene, 4,4'-diaminobenzanilide, trimethylene-bis-4-aminobenzoate, and the like.

[0136] From the viewpoint of forming a smectic structure in the cured product of the epoxy resin composition, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 1,3-diaminobenzene, 1,4-diaminobenzene, 4,4'-diaminobenzanilide, 1,5-diaminonaphthalene, 4,4'-diaminodiphenyl methane, and trimethylene-bis-4-aminobenzoate are preferred. From the viewpoint of obtaining a cured product with low water absorption and high fracture toughness, 3,3'-diaminodiphenyl sulfone is more preferred.

[0137] Examples of the phenol curing agent include low molecular weight phenol compounds and phenol novolak resins obtained by linking low molecular weight phenol compounds with a methylene chain or the like to form a novolak. Examples of the low molecular weight phenol compounds include monofunctional phenol compounds such as phenol, o-cresol, m-cresol, and p-cresol, bifunctional phenol compounds such as catechol, resorcinol, and hydroquinone, and trifunctional phenol compounds such as 1,2,3-trihydroxybenzene, 1,2,4-trihydroxybenzene, and 1,3,5-trihydroxybenzene.

[0138] The content of the curing agent in the epoxy resin composition is not particularly limited. From the perspective of the efficiency of the curing reaction, the ratio of the equivalent number of functional groups of the curing agent contained in the epoxy resin composition (the equivalent number of active hydrogens in the case of an amine curing agent) to the equivalent number of epoxy groups of the epoxy resin (equivalent number of functional groups / equivalent number of epoxy groups) is preferably in an amount such that it is 0.3 to 3.0, and more preferably in an amount such that it is 0.5 to 2.0.

[0139] <Other components> The epoxy resin composition may contain other components other than the epoxy resin and the curing agent, if necessary. For example, it may contain a curing catalyst, a filler, etc. Specific examples of the curing catalyst include the compounds exemplified as reaction catalysts that can be used for the synthesis of specific epoxy compounds.

[0140] 〔Physical properties of the cured epoxy resin〕 Since the cured epoxy resin of the present disclosure is a cured product of the epoxy resin of the present disclosure, it can satisfy the characteristics that the flexural modulus at 23°C is 3.0 GPa or more, the fracture toughness is 1.0 MPa·m 1 / 2 or more, and the glass transition temperature is 150°C or more. The details of the flexural modulus, fracture toughness, and glass transition temperature are as described above.

[0141] 〔Uses of the epoxy resin composition and the cured epoxy resin〕 The uses of the epoxy resin composition and the cured epoxy resin are not particularly limited, and for example, they can be suitably used for the production of fiber-reinforced composite materials (FRP) used in aircraft, spacecraft, etc. In addition, the epoxy resin composition of the present disclosure can also be suitably used for a production method in which steps such as localizing particles of a thermoplastic resin in the surface region of a prepreg are omitted in the production of fiber-reinforced composite materials.

[0142] ≪Composite material≫ The composite material of the present disclosure includes the cured epoxy resin of the present disclosure and a reinforcing material.

[0143] <Reinforcing material> The material of the reinforcing material contained in the composite material is not particularly limited and can be selected according to the use of the composite material and the like. Specifically, examples of the reinforcing material include carbon materials, glass, aromatic polyamide resins (for example, Kevlar (registered trademark)), ultra-high molecular weight polyethylene, alumina, boron nitride, aluminum nitride, mica, silicon, and the like. The shape of the reinforcing material is not particularly limited, and examples include fibrous and particulate (filler) forms. From the viewpoint of the strength of the composite material, the reinforcing material is preferably a carbon material, and more preferably carbon fiber. The reinforcing material contained in the composite material may be one type or two or more types.

[0144] The form of the composite material is not particularly limited. For example, it may have a structure in which at least one cured product-containing layer containing a cured epoxy resin and at least one reinforcing material-containing layer containing a reinforcing material are laminated.

Examples

[0145] Next, the embodiments of the present disclosure will be specifically described by way of examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" and "%" are based on mass.

[0146] 〔Example 1〕 (Synthesis of Epoxy Resin 1) Into a 500 ml three-necked flask, 50 parts by mass of (4-{4-(2,3-epoxypropoxy)phenyl}cyclohexyl 4-(2,3-epoxypropoxy)benzoate, the compound of the following structural formula (1)) was added, and 26 parts by mass of EX201 (resorcinol type diglycidyl ether, Nagase ChemteX Corporation, epoxy equivalent 117 g / eq, trade name; the compound with p = 0 in formula (1-c)) was added. Further, 80 parts by mass of a synthetic solvent (cyclohexanone) was added to the three-necked flask. A condenser tube and a nitrogen inlet tube were installed in the three-necked flask, and a stirring blade was attached so as to be immersed in the solvent. This three-necked flask was immersed in an oil bath at 120 °C, and stirring was started. After confirming that the epoxy compound had dissolved and became a transparent solution, 8 parts by mass of 1,5-dihydroxynaphthalene and 0.5 parts by mass of a reaction catalyst (tetrabutylphosphonium laurate (TBPLA)) were added, and heating was continued in an oil bath at 120 °C. After continuing heating for 3 hours, cyclohexanone was distilled off under reduced pressure from the reaction solution, and the residue was cooled to room temperature (25 °C) to obtain Epoxy Resin 1.

[0147] [Chemical formula]

[0148] Next, 21 parts by mass of 3,3'-diaminodiphenyl sulfone as a curing agent was weighed out for 84.5 parts by mass of the obtained epoxy resin, respectively, into a stainless steel petri dish. Once heated to 180 °C on a hot plate, after the epoxy resin composition in the stainless steel petri dish had melted, it was stirred with a spatula and cooled to room temperature. Next, the epoxy composition was heated from room temperature to 180 °C at a heating rate of 2 °C per minute, and then heated at 180 °C for 4 hours to complete curing, obtaining a cured epoxy resin. This cured epoxy resin was cut out into a rectangular parallelepiped of 3.75 mm × 7.5 mm × 33 mm to prepare a test piece for fracture toughness evaluation. Further, the cured epoxy resin was cut out into a strip shape of 2 mm × 5 mm × 50 mm to prepare a test piece for flexural modulus evaluation.

[0149] As a result of evaluating the flexural modulus, fracture toughness, and glass transition temperature by the method described below, the flexural modulus at 23°C was 3.2 GPa, and the fracture toughness was 1.4 MPa·m 1 / 2 , and the glass transition temperature was 161°C.

[0150] [Example 2] (Synthesis of epoxy resin 2) Epoxy resin 2 was obtained in the same manner as in Example 1, except that 31 parts by mass of HP4032D (manufactured by DIC Corporation, trade name; a compound in which q = 0 in formula (1-e)), which is an epoxy compound having a naphthalene structure, was used instead of 26 parts by mass of EX201, and 8 parts by mass of 4,4-biphenol was used instead of 8 parts by mass of 1,5-dihydroxynaphthalene.

[0151] Furthermore, an epoxy resin cured product was obtained in the same manner as in Example 1, except that 22 parts by mass of 3,3'-diaminodiphenyl sulfone was used with respect to 89 parts by mass of the obtained epoxy resin, and each test piece was produced.

[0152] As a result of evaluating the flexural modulus, fracture toughness, and glass transition temperature by the method described below, the flexural modulus at 23°C was 3.0 GPa, and the fracture toughness was 1.2 MPa·m 1 / 2 , and the glass transition temperature was 173°C.

[0153] [Example 3] (Synthesis of epoxy resin 3) Epoxy resin 3 was obtained in the same manner as in Example 1, except that 26 parts by mass of EX201 was not used, 4 parts by mass of 1,5-dihydroxynaphthalene was used, and 0.5 parts by mass of 1,4-benzoquinone derivative of tributylphosphine (TBP2) was used instead of 0.5 parts by mass of tetrabutylphosphonium laurate (TBPLA).

[0154] Furthermore, an epoxy resin cured product was obtained in the same manner as in Example 1, except that 7 parts by mass of 3,3'-diaminodiphenyl sulfone was used with respect to 54.5 parts by mass of the obtained epoxy resin, and each test piece was produced.

[0155] As a result of evaluating the flexural modulus, fracture toughness, and glass transition temperature by the method described below, the flexural modulus at 23°C was 3.0 GPa, and the fracture toughness was 1.9 MPa·m 1 / 2 , and the glass transition temperature was 160°C.

[0156] [Comparative Example 1] (Synthesis of Epoxy Resin 4) Epoxy resin 4 was obtained in the same manner as in Example 1, except that 26 parts by mass of EX201 was not used and 5 parts by mass of 4,4-biphenol was used instead of 8 parts by mass of 1,5-dihydroxynaphthalene.

[0157] Furthermore, an epoxy resin cured product was obtained in the same manner as in Example 1, except that 10 parts by mass of 3,3'-diaminodiphenyl sulfone was used with respect to 55.5 parts by mass of the obtained epoxy resin, and each test piece was produced.

[0158] As a result of evaluating the flexural modulus, fracture toughness, and glass transition temperature by the method described below, the flexural modulus at 23°C was 2.7 GPa, and the fracture toughness was 2.0 MPa·m 1 / 2 , and the glass transition temperature was 155°C.

[0159] [Comparative Example 2] An epoxy resin cured product was obtained in the same manner as in Example 1, except that 40 parts by mass of 3,3'-diaminodiphenyl sulfone was used as a curing agent for 50 parts by mass of YH434 (tetraglycidyl diaminodiphenylmethane, Nippon Steel & Sumikin Chemical Co., Ltd.) and 50 parts by mass of jER825 (bisphenol A type epoxy resin, Mitsubishi Chemical Corporation), and each test piece was produced.

[0160] As a result of evaluating the flexural modulus, fracture toughness, and glass transition temperature by the method described below, the flexural modulus at 23°C was 3.9 GPa, and the fracture toughness was 0.7 MPa·m 1 / 2 , and the glass transition temperature was 175°C.

[0161] The evaluation methods for the flexural modulus, fracture toughness, and glass transition temperature are shown below.

[0162] [Measurement of Fracture Toughness Value] As an index of the fracture toughness of the cured epoxy resin, the fracture toughness value (MPa·m 1 / 2 ) was used. The fracture toughness value of the test piece was calculated by performing three-point bending measurement based on ASTM D5045. An Instron 5948 (Instron Corporation) was used as the evaluation apparatus.

[0163] [Measurement of Glass Transition Temperature] As an index of the heat resistance of the cured epoxy resin, the glass transition temperature (Tg) was used. The glass transition temperature of the test piece was calculated by performing dynamic viscoelastic measurement in the tensile mode. The measurement conditions were a frequency of 10 Hz, a heating rate of 5 °C / min, and a strain of 0.1%. In the obtained temperature - tanδ relationship diagram, the temperature at which tanδ was maximum was regarded as the glass transition temperature. An RSA-G2 (TA Instruments) was used as the evaluation apparatus.

[0164] [Measurement of Flexural Modulus] As an index of the elasticity of the cured epoxy resin, the flexural modulus (GPa) at 23 °C was determined. The flexural modulus of the test piece was calculated by performing three-point bending measurement based on JIS K7171 (2016). A tensilon (A&D Company, Limited) was used as the evaluation apparatus.

[0165] The cured products using Epoxy Resins 1 to 3 synthesized in Examples 1 to 3 had a flexural modulus of 3.0 GPa or more, a fracture toughness of 1.0 MPa·m 1 / 2 or more, and a glass transition temperature of 150 °C or more at 23 °C. Such epoxy resins are considered to be suitably applicable also to the production of fiber-reinforced composite materials in which processes such as localizing the particles of the thermoplastic resin in the surface region of the prepreg are omitted. On the other hand, when the above physical properties are not satisfied, it is difficult to simplify the manufacturing process of the fiber-reinforced composite material. For example, like the epoxy resin of Comparative Example 2, when made into a cured product, it has a flexural modulus of 3.0 GPa or more and a fracture toughness of 1.0 MPa·m 1 / 2When using an epoxy resin with a content less than a certain amount, it is necessary to improve the fracture toughness by means such as providing a layer in which a thermoplastic resin is dispersed when manufacturing a fiber-reinforced composite material for an aircraft. Therefore, the manufacturing process is not simplified. Also, like the epoxy resin of Comparative Example 1, an epoxy resin having a fracture toughness of 1.0 MPa·m 1 / 2 or more and a flexural modulus of less than 3.0 GPa is unlikely to be a substitute material for the resin for simplifying the manufacturing process from the viewpoint of the flexural modulus.

[0166] All documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually stated to be incorporated by reference.

Claims

1. Contains an epoxy compound having a mesogen structure, and when cured, has a flexural modulus of 3.0 GPa or more and a fracture toughness of 1.0 MPa·m １／２ or more, and a glass transition temperature of 150°C or more, and The epoxy compound having the mesogen structure includes a compound having one mesogen structure and an epoxy group, and an epoxy compound having a structure in which at least two mesogen structures are linked with a naphthylene group interposed therebetween, the content ratio of the compound having one mesogen structure and an epoxy group is 35% to 50% with respect to the total amount of the epoxy resin, and the epoxy compound having a structure in which at least two mesogen structures are linked with a naphthylene group interposed therebetween includes at least one of the following (i) to (iii). An epoxy resin. (i) A reaction product of a compound having one mesogen structure and an epoxy group; an epoxy compound other than the epoxy compound having a mesogen structure; and a dihydroxynaphthalene compound, (ii) A reaction product of a compound having one mesogen structure and an epoxy group; an epoxy compound having a naphthalene structure; and an aromatic compound having two hydroxyl groups, (iii) A reaction product of a compound having one mesogen structure and an epoxy group; and a dihydroxynaphthalene compound.

2. The epoxy resin according to claim 1, wherein the mesogen structure includes a mesogen structure represented by the following general formula (1). 【Chemical 1】 In the general formula (1), X represents a single bond or a linking group having at least one divalent group selected from the following group (A). Each Y independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. n independently represents an integer of 0 to 4. * represents a bonding site with an adjacent atom. [Chemical Formula 2] In group (A), each Y independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. n independently represents an integer of 0 to 4, k represents an integer of 0 to 7, m represents an integer of 0 to 8, and l represents an integer of 0 to 12.

3. The epoxy resin according to claim 2, wherein the mesogen structure represented by the general formula (1) includes a structure represented by the following general formula (2). 【Chemical Formula 3】 In general formula (2), X represents a single bond or a linking group having at least one divalent group selected from the group (A). Each Y independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. Each n independently represents an integer of 0 to 4. * represents a bonding site with an adjacent atom.

4. The epoxy resin according to claim 2, wherein the epoxy compound having the mesogenic structure has at least one structure selected from the group consisting of the following general formula (1-A), general formula (1-B), and general formula (1-C). [Chemical Formula 4] In general formula (1-A), general formula (1-B), and general formula (1-C), X represents a single bond or a linking group having at least one divalent group selected from the group (A). Each Y independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. Each n independently represents an integer of 0 to 4. Each m independently represents an integer of 0 to 4. p represents an integer of 0 to 6. Each Z independently represents -O- or -NH-. R １ and R ２ each independently represents an alkyl group having 1 to 8 carbon atoms. * represents a bonding site with an adjacent atom.

5. The epoxy resin according to any one of claims 2 to 4, wherein the epoxy compound having the mesogenic structure has at least one structure selected from the group consisting of the following general formula (2-A), general formula (2-B), and general formula (2-C). 【Chemical Formula 5】 In general formula (2-A), general formula (2-B), and general formula (2-C), X represents a single bond or a linking group having at least one divalent group selected from the group (A). Y each independently represents an aliphatic hydrocarbon group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a nitro group, or an acetyl group. n each independently represents an integer from 0 to 4. m each independently represents an integer from 0 to 4. p represents an integer from 0 to 6. Z each independently represents -O- or -NH-. R １ and R ２ each independently represents an alkyl group having 1 to 8 carbon atoms. * represents a bonding site with an adjacent atom.

6. The epoxy resin according to claim 3, wherein the structure represented by the general formula (2) includes at least one structure selected from the group consisting of the following general formula (3) and general formula (4). 【Chemical Formula 6】 In General Formula (3) and General Formula (4), R ３ ~R ６ each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. * represents a bonding site with an adjacent atom.

7. An epoxy resin composition containing the epoxy resin according to any one of claims 1 to 6 and a curing agent.

8. The epoxy resin composition according to claim 7, wherein the curing agent includes a compound having two or more amino groups directly bonded to an aromatic ring.

9. The epoxy resin composition according to claim 7 or claim 8, wherein the curing agent includes 3,3'-diaminodiphenyl sulfone.

10. An epoxy resin cured product which is a cured product of the epoxy resin composition according to any one of claims 7 to 9.

11. A composite material including the epoxy resin cured product according to claim 10 and a reinforcing material.

12. The composite material according to claim 11, wherein the reinforcing material includes a carbon material.

Images