Epoxy resin composition, epoxy resin cured product, prepreg, fiber-reinforced composite material, method for repairing epoxy resin cured product, method for repairing fiber-reinforced composite material, method for reshaping epoxy resin cured product, method for reshaping fiber-reinforced composite material, method for decomposing epoxy resin cured product, and method for recovering reinforcing fibers from fiber-reinforced composite material

Abstract

The epoxy resin composition contains at least an epoxy resin [A] and a curing agent [B]. The epoxy resin [A] contains at least a diglycidyl amine epoxy resin [A1] represented by formula (1). The curing agent [B] contains at least a curing agent [B1] containing a dynamic covalent bond site Y. [In formula (1), R1a to R1e each independently represent a hydrogen atom, a C1-20 aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, an alkoxy group, an amino group, or a halogen atom.]

Description

Epoxy resin composition, cured epoxy resin product, prepreg, fiber-reinforced composite material, method for repairing cured epoxy resin product, method for repairing fiber-reinforced composite material, method for remolding cured epoxy resin product, method for remolding fiber-reinforced composite material, method for decomposing cured epoxy resin product, and method for recovering reinforcing fibers from fiber-reinforced composite material

[0001] The present disclosure relates to an epoxy resin composition, a cured epoxy resin product, a prepreg, a fiber-reinforced composite material, a method for repairing a cured epoxy resin product, a method for repairing a fiber-reinforced composite material, a method for remolding a cured epoxy resin product, a method for remolding a fiber-reinforced composite material, a method for decomposing a cured epoxy resin product, and a method for recovering reinforcing fibers from a fiber-reinforced composite material.

[0002] Fiber-reinforced composite materials obtained by combining reinforcing fiber materials such as carbon fiber, glass fiber, and aramid fiber with various matrix resins are widely used in various fields and applications. Conventionally, in the aerospace and industrial fields, which require high mechanical properties and heat resistance, thermosetting resins such as unsaturated polyester resins, epoxy resins, and polyimide resins have mainly been used as matrix resins.

[0003] However, these thermosetting resins, once cured, do not retain fluidity even when heated, and therefore cannot be molded or deformed again, resulting in the disposal of leftover cured products and defective molded products generated during the manufacturing process. Although various improvements have been made to the manufacturing process in order to reduce the amount of discarded cured products, it has been difficult to reduce the amount of discarded cured products by improving the manufacturing process alone.

[0004] Therefore, in light of the above background, improvements in resin compositions have been investigated. In particular, a method of recycling cured product scraps and defective moldings by introducing exchangeable and / or recombinable chemical bonding sites (also referred to as dynamic covalent bonding sites) into a resin composition has attracted attention. In this method, the exchangeable and / or recombinable chemical bonding sites are cleaved by heating, thereby dissolving the internal network structure of the cured product, and the resin becomes fluid and can be remolded. For example, WO 2015 / 181054 discloses an epoxy resin composition using, as a curing agent, a compound containing a disulfide bond as the exchangeable and / or recombinable chemical bonding site. As another example, J. Am. Chem. Soc. 2022, 144, 12280-12289 discloses an epoxy resin composition using, as a curing agent, a compound containing a silyl ether bond as the exchangeable and / or recombinable chemical bonding site.

[0005] However, in the epoxy resin compositions described in WO 2015 / 181054 and J. Am. Chem. Soc. 2022, 144, 12280-12289, in order to obtain sufficient fluidity in the cured product, excessive amounts of expensive compounds, such as compounds containing disulfide bonds or silyl ether bonds, were required. This is thought to be due to the fact that the activation energy of the bond exchange reaction at the molecular level is higher than the binding energy of the rigid molecular network formed, and that the low amount of dynamic covalent bonding moieties introduced results in low collision frequency, resulting in poor bond exchange activity. On the other hand, using a curing agent in excess of the theoretical equivalent of the epoxy resin significantly impairs the heat resistance and mechanical properties of the cured product. In particular, disulfide bonds increase the degree of freedom of intramolecular rotation, which can easily impair the resin fracture toughness of the cured product. Furthermore, many compounds containing silyl ether bonds contain flexible alkyl chains, which reduces the rigidity of the molecular chains in the cured product and easily impairs mechanical heat resistance.

[0006] The present disclosure has been made in view of the above, and an object of the present disclosure is to provide an epoxy resin composition which uses a compound containing dynamic covalent bonding moieties in an amount equal to or less than the theoretical equivalent relative to the epoxy resin, yet which has excellent remoldability and self-repairing properties in the cured product; an epoxy resin cured product obtained by curing the epoxy resin composition, a prepreg, a fiber-reinforced composite material; a method for repairing an epoxy resin cured product, a method for repairing a fiber-reinforced composite material, a method for remolding an epoxy resin cured product, a method for remolding a fiber-reinforced composite material, a method for decomposing an epoxy resin cured product, and a method for recovering reinforcing fibers from a fiber-reinforced composite material.

[0007] Specific means for solving the above problems include the following aspects: <1> An epoxy resin composition comprising at least an epoxy resin [A] and a curing agent [B], wherein the epoxy resin [A] comprises at least a diglycidylamine-type epoxy resin [A1] represented by the following formula (1), and the curing agent [B] comprises at least a curing agent [B1] containing a dynamic covalent bond moiety Y:

[0008]

[0009] In formula (1), R １ａ , R １ｂ , R １ｃ , R １ｄ , and R １ｅ each independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, an alkoxy group, an amino group, or a halogen atom.

[0010] <2> The epoxy resin composition according to <1>, wherein the ratio (a1) / (a) of the molar amount of epoxy groups in the diglycidylamine epoxy resin [A1] to the molar amount of epoxy groups in the epoxy resin [A] is 0.05 or more and 1.0 or less. <3> The epoxy resin composition according to <1> or <2>, wherein the curing agent [B1] contains active hydrogen, and the ratio (b1) / (b) of the molar amount of active hydrogen in the curing agent [B1] to the molar amount of active hydrogen in the curing agent [B] is 0.1 or more and 1.0 or less. <4> The epoxy resin composition according to any one of <1> to <3>, wherein the ratio (b1) / (a) of the molar amount of active hydrogen in the curing agent [B1] to the molar amount of epoxy groups in the epoxy resin [A] is 0.6 or more and 1.5 or less. <5> The epoxy resin composition according to any one of <1> to <4>, wherein, after curing to a degree of cure of 90% or more to form a cured product, an external force is applied to the cured product at a temperature 40°C higher than the glass transition temperature of the cured product, and the resulting stress is measured, and the stress relaxation rate one hour after the start of application of the external force is 95% or more. <6> The epoxy resin composition according to any one of <1> to <5>, wherein the curing agent [B1] includes an amine-based curing agent represented by the following formula (2):

[0011]

[0012] In formula (2), R １ and R ２ each independently represent an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, an ether group, or a divalent group formed by combining two or more selected from the group consisting of an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, and an ether group, and Y represents a dynamic covalent bond moiety.

[0013] <7> The epoxy resin composition according to any one of <1> to <6>, wherein the dynamic covalent bond site Y contains a disulfide bond. <8> The epoxy resin composition according to any one of <1> to <7>, wherein the curing agent [B1] contains an amine-based curing agent represented by the following formula (3):

[0014]

[0015] <9> A cured epoxy resin product obtained by curing the epoxy resin composition according to <1>. <10> The cured epoxy resin product according to <9>, in which 80 mass% or more of the cured epoxy resin product dissolves when contacted with a decomposing agent containing a reducing agent and heated at 100°C for 48 hours. <11> A cured epoxy resin product in which, when contacted with a decomposing agent containing a reducing agent and heated at 100°C for 48 hours, a compound having at least a structure represented by the following formula (7) is produced:

[0016]

[0017] In formula (7), R ７ａ , R ７ｂ , R ７ｃ , R ７ｄ , and R ７ｅ each independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, an alkoxy group, an amino group, or a halogen atom, and * represents a bond.

[0018] <12> A prepreg obtained by impregnating a fiber-reinforced substrate having reinforcing fibers with the epoxy resin composition according to any one of <1> to <8>, wherein the content of the reinforcing fibers is 25% by volume to 75% by volume relative to the total volume of the prepreg. <13> A fiber-reinforced composite material comprising the cured epoxy resin according to any one of <9> to <11> and a fiber-reinforced substrate having reinforcing fibers, wherein the content of the reinforcing fibers is 25% by volume to 75% by volume relative to the total volume of the fiber-reinforced composite material. <14> A method for repairing a cured epoxy resin product according to any one of <9> to <11>, which has voids therein, by heating the cured epoxy resin product according to any one of <9> to <11> at a temperature equal to or higher than the glass transition temperature of the cured epoxy resin product, thereby repairing the voids. <15> A method for repairing a fiber-reinforced composite material, which comprises heating the fiber-reinforced composite material according to <13>, which has voids therein, at a temperature equal to or higher than the glass transition temperature of the fiber-reinforced composite material, thereby repairing the voids. <16> A method for remolding a cured epoxy resin product, comprising heating and pressurizing the cured epoxy resin product according to any one of <9> to <11> at a temperature equal to or higher than the glass transition temperature of the cured epoxy resin product. <17> A method for remolding a fiber-reinforced composite material, comprising heating and pressurizing the fiber-reinforced composite material according to <13> at a temperature equal to or higher than the glass transition temperature of the fiber-reinforced composite material. <18> A method for decomposing a cured epoxy resin product, comprising contacting the cured epoxy resin product according to any one of <9> to <11> with a decomposition agent containing a reducing agent. <19> A method for recovering reinforcing fibers from a fiber-reinforced composite material, comprising contacting the fiber-reinforced composite material according to <13> with a decomposition agent containing a reducing agent.

[0019] According to the present disclosure, there are provided an epoxy resin composition which uses a compound containing dynamic covalent bonding moieties in an amount equal to or less than the theoretical equivalent relative to the epoxy resin, yet which exhibits excellent remoldability and self-repairability in the cured product; an epoxy resin cured product obtained by curing the epoxy resin composition; a prepreg; a fiber-reinforced composite material; a method for repairing an epoxy resin cured product; a method for repairing a fiber-reinforced composite material; a method for remolding an epoxy resin cured product; a method for remolding a fiber-reinforced composite material; a method for decomposing an epoxy resin cured product; and a method for recovering reinforcing fibers from a fiber-reinforced composite material.

[0020] Fig. 1 is a graph showing the results of stress relaxation measurement. Fig. 2 is a graph showing the results of stress relaxation mode separation analysis. Fig. 3 is a graph showing the results of FT-IR (Fourier transform infrared spectroscopy; the same applies hereinafter) measurement of decomposition products of cured epoxy resin materials.

[0021] An embodiment of the present disclosure will be described in detail below. However, the present disclosure is not limited to the following embodiment. In the following disclosure, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure.

[0022] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the lower and upper limits, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit described in one numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in numerical ranges described in the present disclosure, the upper or lower limit described in a certain numerical range may be replaced with a value shown in the examples. In the present disclosure, when multiple substances corresponding to each component are present in the composition, the content of each component refers to the total content of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, when multiple elements are listed using "or," this does not exclude the combination of multiple elements unless a technical contradiction occurs, unless otherwise specified. In the present disclosure, even when an element is described in the singular, this does not exclude the presence of multiple elements unless a technical contradiction occurs, unless otherwise specified. In the present disclosure, multiple exemplary embodiments described separately may be combined with each other to form a new embodiment, unless mutually contradictory.

[0023] <Epoxy Resin Composition> The epoxy resin composition of the present disclosure contains at least an epoxy resin [A] and a curing agent [B], wherein the epoxy resin [A] contains at least a diglycidyl amine-type epoxy resin [A1] represented by formula (1), and the curing agent [B] contains at least a curing agent [B1] containing a dynamic covalent bond moiety Y.

[0024] The epoxy resin composition of the present disclosure uses a compound having dynamic covalent bonding sites in an amount equal to or less than the theoretical equivalent of the epoxy resin, yet exhibits excellent remoldability and self-repairability in the cured product. In this disclosure, "remoldability" refers to the state in which multiple cured products adhere to each other and no grain boundaries are visible on the surface, and "self-repairability" refers to the disappearance or reduction of cracks in the cured product. The effect of the epoxy resin composition of the present disclosure is unclear, but is presumed to be as follows.

[0025] In the present disclosure, a dynamic covalent bond site refers to a covalent bond site that can be exchanged and / or recombined. More specifically, a dynamic covalent bond site is a bond site that can reversibly exchange the bond partners in two pairs of covalent bonds cleaved by heating to form a new combination of two pairs of covalent bonds. Alternatively, a dynamic covalent bond site is a bond site that can reversibly recombine one pair of covalent bonds with another cleaved covalent bond by heating, thereby causing recombination. In other words, a cured epoxy resin product obtained by curing the epoxy resin composition of the present disclosure has excellent fluidity, remoldability, and self-repairing properties because the dynamic covalent bond sites are reversibly cleaved and exchanged and / or recombined by heating, allowing the molecular network within the cured epoxy resin product to continuously change.

[0026] Generally, amino groups have nucleophilic properties, and therefore, when a specific bond is activated, a nucleophilic substitution reaction proceeds, thereby promoting the bond dissociation of the target. On the other hand, tertiary amino groups also have excellent elimination properties, and the quaternary ammonium species generated by the nucleophilic substitution reaction have extremely high electrophilicity, so they undergo a nucleophilic substitution reaction again with other relatively mild nucleophiles. As a result, the tertiary amino group acts catalytically through a second nucleophilic substitution reaction, which can sometimes promote bond exchange at a specific bond.

[0027] In the epoxy resin composition of the present disclosure, the amino groups contained in the glycidylamine-type epoxy resin having a specific structure exert the above-mentioned effect, lowering the activation energy of the bond exchange reaction at the dynamic covalent bond site, thereby accelerating the bond exchange reaction, which results in the cured product having fluidity and effectively exhibiting remoldability and self-repairability.

[0028] As explained above, the epoxy resin composition of the present disclosure uses a compound having dynamic covalent bonding sites in an amount equal to or less than the theoretical equivalent relative to the epoxy resin, and yet provides an epoxy resin composition that exhibits excellent remoldability and self-repairing properties in the cured product. However, the present disclosure is not limited to the above-mentioned assumed mechanism.

[0029] <Epoxy resin [A]> The epoxy resin composition of the present disclosure contains an epoxy resin [A]. The epoxy resin [A] contained in the epoxy resin composition of the present disclosure contains at least a diglycidylamine-type epoxy resin [A1] represented by formula (1). In the present disclosure, the "diglycidylamine-type epoxy resin [A1] represented by formula (1)" is also simply referred to as the "diglycidylamine-type epoxy resin [A1]."

[0030] <Diglycidylamine-Type Epoxy Resin [A1]> The diglycidylamine-type epoxy resin [A1] is a diglycidylamine-type epoxy resin represented by the following formula (1).

[0031]

[0032] In formula (1), R １ａ , R １ｂ , R １ｃ , R １ｄ , and R １ｅ each independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, an alkoxy group, an amino group, or a halogen atom.

[0033] The aliphatic hydrocarbon group may have a substituent on the alkyl chain, or may be unsubstituted. The number of carbon atoms in the aliphatic hydrocarbon group, not including the number of carbon atoms in the substituent, is 1 to 20, preferably 1 to 10, and more preferably 1 to 5. Specific examples of the aliphatic hydrocarbon group include saturated aliphatic hydrocarbon groups such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an s-butyl group, a t-butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, a tetradecyl group, a hexadecyl group, and an octadecyl group, and unsaturated aliphatic hydrocarbon groups such as an allyl group and a vinyl group.

[0034] The alicyclic hydrocarbon group may have a substituent on the ring, or may be unsubstituted. The number of carbon atoms in the alicyclic hydrocarbon group, not including the number of carbon atoms in the substituent, is preferably 4 to 18, and more preferably 5 to 10. Specific examples of the alicyclic hydrocarbon group include a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, and a cyclohexenyl group.

[0035] The aromatic hydrocarbon group may have a substituent on the aromatic ring, or may be unsubstituted. The number of carbon atoms in the aromatic hydrocarbon group, not including the carbon atoms in the substituent, is preferably 6 to 18, and more preferably 6 to 15. Specific examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group and a naphthyl group.

[0036] The alkoxy group may have a substituent on the alkyl chain, or may be unsubstituted. The alkoxy group may be linear, branched, or cyclic. The number of carbon atoms in the alkoxy group, not including the number of carbon atoms in the substituent, is preferably 1 to 6, and more preferably 1 to 3. Specific examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propyloxy group, an isopropyloxy group, an n-butyloxy group, an isobutyloxy group, a t-butyloxy group, an n-pentyloxy group, an n-hexyloxy group, and a phenoxy group. The alkoxy group is preferably a methoxy group or a phenoxy group.

[0037] The amino group may have a substituent on the nitrogen atom, or may be unsubstituted. When the amino group has a substituent, examples of the substituent include an alkyl group and an aryl group. The number of carbon atoms in the substituted amino group is preferably 1 to 20, and more preferably 1 to 12. Specific examples of amino include a dimethylamino group, a diethylamino group, and a diphenylamino group.

[0038] Specific examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. The halogen atom is preferably a fluorine atom or a chlorine atom.

[0039] In formula (1), R １ａ , R １ｂ , R １ｃ , R １ｄ and R １ｅ are each independently preferably a hydrogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, an aromatic hydrocarbon group, an alkoxy group, or a halogen atom, more preferably a hydrogen atom, a methyl group, or a methoxy group, and even more preferably a hydrogen atom or a methyl group. １ａ is a hydrogen atom or a methyl group, and R １ｂ , R １ｃ , R １ｄ and R １ｅ is preferably a hydrogen atom.

[0040] Specific examples of the diglycidylamine type epoxy resin [A1] include diglycidyl aniline, diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine, diglycidyl-xylidine, diglycidyl-mesidine, diglycidyl-anisidine, diglycidyl-phenoxyaniline, and diglycidyl-naphthylamine. Among these, the diglycidylamine type epoxy resin [A1] is preferably at least one selected from the group consisting of diglycidyl aniline, diglycidyl-o-toluidine, diglycidyl-m-toluidine, and diglycidyl-p-toluidine, and more preferably at least one selected from diglycidyl aniline and diglycidyl-o-toluidine.

[0041] The diglycidylamine-type epoxy resin [A1] may be a synthetic product or a commercially available product. Examples of commercially available diglycidylamine-type epoxy resin [A1] include GAN manufactured by Nippon Kayaku Co., Ltd., GOT manufactured by Nippon Kayaku Co., Ltd., and EP-3980S manufactured by ADEKA Corporation.

[0042] The epoxy resin [A] may contain only one type of diglycidylamine-type epoxy resin [A1], or may contain two or more types thereof.

[0043] The average epoxy equivalent of the diglycidylamine epoxy resin [A1] is not particularly limited, but is preferably in the range of 80 g / eq or more and 300 g / eq or less, more preferably 85 g / eq or more and 200 g / eq or less, even more preferably 90 g / eq or more and 150 g / eq or less, and particularly preferably 100 g / eq or more and 120 g / eq or less.

[0044] In the present disclosure, the "average epoxy equivalent of the diglycidylamine-type epoxy resin [A1]" means the weighted average epoxy equivalent of all the diglycidylamine-type epoxy resins [A1] contained in the epoxy resin composition of the present disclosure. The epoxy equivalent of the diglycidylamine-type epoxy resin [A1] is a value measured by a method in accordance with JIS K 7236:2009 (ISO 3001:1999).

[0045] <Epoxy Resins Other Than Diglycidylamine-Type Epoxy Resin [A1]> The epoxy resin [A] may contain a known epoxy resin in addition to the diglycidylamine-type epoxy resin [A1]. The epoxy resin other than the diglycidylamine-type epoxy resin [A1] may be monofunctional, bifunctional, or polyfunctional. The epoxy resin other than the diglycidylamine-type epoxy resin [A1] may be, for example, a glycidyl ether compound or a glycidyl ester compound. The epoxy resin other than the diglycidylamine-type epoxy resin [A1] is not particularly limited as long as it reacts with the curing agent [B], and is appropriately selected depending on the intended use, etc.

[0046] Examples of epoxy resins other than the diglycidylamine-type epoxy resin [A1] include tetrafunctional glycidylamine-type epoxy resins, bifunctional glycidyl ether-type epoxy resins, polyfunctional glycidyl ether-type epoxy resins, glycidyl ester-type epoxy resins, and trifunctional epoxy resins. Specific examples of tetrafunctional glycidylamine-type epoxy resins include tetraglycidyl-4,4'-diaminodiphenylmethane, tetraglycidyl-4,4'-diaminodiphenylsulfone, tetraglycidyl-3,3'-diaminodiphenylsulfone, tetraglycidyl-4,4'-diaminodiphenylether, tetraglycidyl-3,4'-diaminodiphenylether, tetraglycidyl-4,4'-dithiodianiline, and derivatives thereof. Specific examples of difunctional glycidyl ether type epoxy resins include bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, bisphenol S diglycidyl ether, resorcinol diglycidyl ether, 1,6-naphthalenediol diglycidyl ether, and 4,4'-dithiodiphenol diglycidyl ether, as well as derivatives thereof. Specific examples of multifunctional glycidyl ether type epoxy resins include phenol novolac type epoxy resins and cresol novolac type epoxy resins, as well as derivatives thereof. Specific examples of glycidyl ester type epoxy resins include phthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, and dimer acid diglycidyl ester, as well as derivatives thereof. Specific examples of trifunctional epoxy resins include triglycidyl m-aminophenol, triglycidyl p-aminophenol, and triglycidyl isocyanurate, as well as derivatives thereof.

[0047] Among these epoxy resins, difunctional glycidyl ether type epoxy resins are particularly preferred because the epoxy resin composition is easy to handle and the cured epoxy resin is easily remoldable.

[0048] The epoxy resins other than the diglycidylamine-type epoxy resin [A1] may be synthetic products or commercially available products. Examples of commercially available epoxy resins other than the diglycidylamine-type epoxy resin [A1] include bisphenol A-diglycidyl ethers "jER825," "jER828," and "jER834" manufactured by Mitsubishi Chemical Corporation, and bisphenol F-diglycidyl ether "jER806" manufactured by Mitsubishi Chemical Corporation.

[0049] When the epoxy resin [A] contains an epoxy resin other than the diglycidylamine-type epoxy resin [A1], the epoxy resin [A] may contain only one type of epoxy resin other than the diglycidylamine-type epoxy resin [A1], or may contain two or more types of epoxy resins other than the diglycidylamine-type epoxy resin [A1].

[0050] The average epoxy equivalent of the epoxy resin [A] is not particularly limited, but is preferably in the range of 80 g / eq or more and 1000 g / eq or less, more preferably in the range of 90 g / eq or more and 500 g / eq or less, and even more preferably in the range of 100 g / eq or more and 300 g / eq or less.

[0051] In the present disclosure, the "average epoxy equivalent of the epoxy resin [A]" means the weighted average epoxy equivalent of all the epoxy resins [A] contained in the epoxy resin composition of the present disclosure. The epoxy equivalent of the epoxy resin [A] is a value measured by a method in accordance with JIS K 7236:2009 (ISO 3001:1999).

[0052] The proportion of the diglycidylamine-type epoxy resin [A1] contained in the epoxy resin [A] is not particularly limited, and is appropriately adjusted depending on the type of diglycidylamine-type epoxy resin [A1], the type of curing agent [B], the desired properties of the cured product, etc.

[0053] The ratio (a1) / (a) of the molar amount (a1) of epoxy groups in the diglycidylamine epoxy resin [A1] to the molar amount (a) of epoxy groups in the epoxy resin [A] is not particularly limited, but is preferably in the range of 0.05 to 1.0, more preferably 0.05 to 0.8, even more preferably 0.05 to 0.6, particularly preferably 0.2 to 0.5, and most preferably 0.3 to 0.5. When the ratio (a1) / (a) is 0.05 or more, the performance provided by the dynamic covalent bond moiety Y in the epoxy resin cured product is better exhibited, and the remoldability and self-repairability of the cured product tend to be further improved. Furthermore, when the ratio (a1) / (a) is 1.0 or less, the increase in free volume derived from glycidylamine is suppressed, and the mechanical properties, particularly strength, of the cured product tend to be further improved.

[0054] [Method for synthesizing epoxy resin [A]] When synthesizing the epoxy resin [A], there are no particular limitations on the method for synthesizing the epoxy resin [A]. The epoxy resin [A] may be synthesized by any method, and may be synthesized, for example, by reacting a raw material, such as an aromatic amine, aminophenol, or diphenol, with an epihalohydrin such as epichlorohydrin to obtain a halohydrin compound, and then subjecting the obtained halohydrin compound to a cyclization reaction using an alkaline compound.

[0055] <Curing Agent [B]> The epoxy resin composition of the present disclosure contains a curing agent [B]. The curing agent [B] contained in the epoxy resin composition of the present disclosure contains at least a curing agent [B1] containing a dynamic covalent bond moiety Y.

[0056] <Curing Agent [B1]> The curing agent [B1] is not particularly limited as long as it is a curing agent containing a dynamic covalent bond moiety Y. The curing agent [B1] may be an amine-based curing agent, an acid anhydride curing agent, a phenol-based curing agent, or a polyamide-based curing agent. Examples of amine-based curing agents include aliphatic amine-based curing agents and aromatic amine-based curing agents. Phenol-based curing agents are preferred because they tend to have low curing activity at room temperature, excellent latency, and produce cured products with high heat resistance. Aliphatic amine-based curing agents are more preferred because they can be synthesized and obtained inexpensively and tend to be economically advantageous. Acid anhydride curing agents are even more preferred because they tend to have long storage stability and produce cured products with a relatively good balance of electrical, chemical, and mechanical properties. Aromatic amine-based curing agents are particularly preferred because they tend to produce cured products with excellent heat resistance, mechanical properties, electrical properties, and chemical resistance.

[0057] The curing agent [B1] contains a dynamic covalent bonding moiety Y. The dynamic covalent bonding moiety Y is not particularly limited. The dynamic covalent bonding moiety Y is preferably a group containing at least one bond selected from the group consisting of an ester bond, an imine bond, a urethane bond, a carbonate bond, a vinylogous urethane bond, a boronic acid ester bond, a silyl ether bond, and a disulfide bond. From the viewpoint of not requiring a catalyst to promote the exchange and / or recombination, the dynamic covalent bonding moiety Y is more preferably a group containing at least one bond selected from the group consisting of an imine bond, a silyl ether bond, and a disulfide bond. Furthermore, from the viewpoint of extremely fast exchange and / or recombination, the dynamic covalent bonding moiety Y is preferably a group containing a disulfide bond, and more preferably a disulfide bond.

[0058] In addition, when heated, urethane bonds, carbonate bonds, vinylogous urethane bonds, boronic ester bonds, silyl ether bonds, and disulfide bonds are cleaved, and the binding partners of the two pairs of covalent bonds are exchanged to form a new combination of two pairs of covalent bonds, i.e., the two pairs of covalent bonds are reversibly dissociated and then recombined. On the other hand, when heated, ester bonds and imine bonds are reversibly recombined, with one pair of covalent bonds recombining with another cleaved covalent bond, causing recombination, i.e., the two pairs of covalent bonds are not dissociated simultaneously, and cleavage and recombination occur simultaneously.

[0059] The dynamic covalent bonding moiety Y preferably undergoes a concerted bond exchange without cleavage. Examples of the dynamic covalent bonding moiety Y that undergoes a concerted bond exchange without cleavage include a disulfide bond, an ester bond, a boronate ester bond, an imine bond, and a vinylogous urethane bond.

[0060] The ester bond is represented by the following formula (Y-1), the imine bond is represented by the following formula (Y-2), the urethane bond is represented by the following formula (Y-3), the carbonate bond is represented by the following formula (Y-4), the vinylogous urethane bond is represented by the following formula (Y-5), the boronic acid ester bond is represented by the following formula (Y-6) or (Y-7), the silyl ether bond is represented by the following formula (Y-8), and the disulfide bond is represented by the following formula (Y-9).

[0061]

[0062] In formulas (Y-1) to (Y-9), * represents a bond. Ｙ１ is preferably an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or an alkoxy group, more preferably an aliphatic hydrocarbon group or an aromatic hydrocarbon group having 1 to 4 carbon atoms, and even more preferably a methyl group, an ethyl group, or a phenyl group. In formula (Y-7), k and l are each independently preferably an integer of 0 to 10, more preferably an integer of 0 to 5, and even more preferably an integer of 0 to 2. R in formula (Y-8) Ｙ２ and RＹ３ are each independently preferably an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or an alkoxy group, more preferably an aliphatic hydrocarbon group or an aromatic hydrocarbon group having 1 to 4 carbon atoms, and further preferably a methyl group, an ethyl group, or a phenyl group.

[0063] The concentration of the dynamic covalent bonding moiety Y relative to the total mass of the epoxy resin [A] and the curing agent [B] (so-called molar concentration) is not particularly limited, but is preferably in the range of 0.05 mmol / g to 2.0 mmol / g, more preferably 0.1 mmol / g to 1.5 mmol / g, and even more preferably 0.2 mmol / g to 1.2 mmol / g. When the concentration of the dynamic covalent bonding moiety Y relative to the total mass of the epoxy resin [A] and the curing agent [B] is 0.05 mmol / g or more, remoldability and self-repairability tend to be better exhibited. When the concentration of the dynamic covalent bonding moiety Y relative to the total mass of the epoxy resin [A] and the curing agent [B] is 2.0 mmol / g or less, mechanical properties tend to be less likely to be impaired.

[0064] The curing agent [B1] preferably contains a compound represented by the following formula (2) (a so-called amine-based curing agent), and more preferably is a compound represented by the following formula (2).

[0065]

[0066] In formula (2), R １ and R ２ each independently represent an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, an ether group, or a divalent group formed by combining two or more selected from the group consisting of an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, and an ether group, and Y represents a dynamic covalent bond moiety. The compound represented by formula (2) is a compound in which the dynamic covalent bond moiety Y and two amino groups are bonded to each other by R １ and R ２ It is an amine-based curing agent bonded via

[0067] The number of carbon atoms in the aliphatic hydrocarbon group is 1 to 20, preferably 1 to 18, more preferably 2 to 12, and even more preferably 2 to 6. Specific examples of the aliphatic hydrocarbon group include saturated aliphatic hydrocarbon groups such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an s-butyl group, a t-butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, a tetradecyl group, a hexadecyl group, and an octadecyl group, and unsaturated aliphatic hydrocarbon groups such as an allyl group and a vinyl group.

[0068] The number of carbon atoms in the alicyclic hydrocarbon group is preferably 4 to 18, and more preferably 5 to 10. Specific examples of the alicyclic hydrocarbon group include a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, and a cyclohexenyl group.

[0069] The number of carbon atoms in the aromatic hydrocarbon group is preferably 6 to 18, more preferably 6 to 15, and even more preferably 6 to 12. Specific examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group and a naphthyl group.

[0070] Specific examples of the divalent group formed by combining two or more groups selected from the group consisting of aliphatic hydrocarbon groups, alicyclic hydrocarbon groups, aromatic hydrocarbon groups, and ether groups having 1 to 20 carbon atoms include -(CH ２ -CH ２ -O) ３ -, -C ６ H ４ -O-C ６ H ４ - and -C ６ H ４ -O-C ２ H ４ - are some examples.

[0071] In formula (2), R １ and R ２are each independently preferably an aliphatic hydrocarbon group having 1 to 6 carbon atoms or an aromatic hydrocarbon group having 6 to 12 carbon atoms, and more preferably an ethyl group, an n-propyl group, or a phenyl group. In formula (2), Y is preferably an imine bond, a disulfide bond, or a silyl ether bond, more preferably a disulfide bond or a silyl ether bond, and even more preferably a disulfide bond.

[0072] The curing agent [B1] is preferably a compound containing an Ar-S-S-Ar structure, and specific examples include compounds represented by the following formula (3) (so-called amine-based curing agents) and compounds represented by the following formula (4) (so-called phenol-based curing agents), in which the dynamic covalent bonding site Y is a disulfide bond (Y-9). From the viewpoint of the heat resistance of the resulting cured product, the curing agent [B1] preferably contains a compound represented by the following formula (3), and more preferably is a compound represented by the following formula (3).

[0073]

[0074] Among the compounds represented by formula (3), the compound represented by formula (3-1) below is preferred as the curing agent [B1] from the viewpoint of the heat resistance of the resulting cured product. Among the compounds represented by formula (4), the compound represented by formula (4-1) below is preferred as the curing agent [B1] from the viewpoint of the heat resistance of the resulting cured product.

[0075]

[0076] Other examples of the curing agent [B1] include a compound represented by the following formula (5) in which the dynamic covalent bonding moiety Y is a silyl ether bond (Y-8) and a compound represented by the following formula (6).

[0077]

[0078] In formula (5), R １ , R ２ , R ３ and R ４each independently represent an aliphatic hydrocarbon group, alicyclic hydrocarbon group, aromatic hydrocarbon group, or alkoxy group having 1 to 20 carbon atoms, or a monovalent group formed by combining two or more selected from the group consisting of an aliphatic hydrocarbon group, alicyclic hydrocarbon group, aromatic hydrocarbon group, and alkoxy group having 1 to 20 carbon atoms, and n represents an integer of 1 to 20.

[0079] The number of carbon atoms in the aliphatic hydrocarbon group is 1 to 20, preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 3. Specific examples of the aliphatic hydrocarbon group include saturated aliphatic hydrocarbon groups such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an s-butyl group, a t-butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, a tetradecyl group, a hexadecyl group, and an octadecyl group, and unsaturated aliphatic hydrocarbon groups such as an allyl group and a vinyl group.

[0080] The number of carbon atoms in the alicyclic hydrocarbon group is preferably 4 to 18, and more preferably 5 to 10. Specific examples of the alicyclic hydrocarbon group include a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, and a cyclohexenyl group.

[0081] The number of carbon atoms in the aromatic hydrocarbon group is preferably 6 to 18, more preferably 6 to 15, even more preferably 6 to 12, and particularly preferably 6 to 10. Specific examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group and a naphthyl group.

[0082] The alkoxy group may be linear, branched, or cyclic. The number of carbon atoms in the alkoxy group is preferably 1 to 6, and more preferably 1 to 3. Specific examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propyloxy group, an isopropyloxy group, an n-butyloxy group, an isobutyloxy group, a t-butyloxy group, an n-pentyloxy group, and an n-hexyloxy group.

[0083] Specific examples of the monovalent group formed by combining two or more groups selected from the group consisting of aliphatic hydrocarbon groups, alicyclic hydrocarbon groups, aromatic hydrocarbon groups, and alkoxy groups having 1 to 20 carbon atoms include -CH ２ -Ph, -CH ２ -O-Ph, and -CH ２ -O-C ６ H １２ In this disclosure, "Ph" represents phenyl.

[0084] In formula (5), R １ , R ２ , R ３ and R ４ are each independently preferably an aliphatic hydrocarbon group having 1 to 6 carbon atoms or an aromatic hydrocarbon group having 6 to 12 carbon atoms, more preferably an aliphatic hydrocarbon group having 1 to 4 carbon atoms or an aromatic hydrocarbon group having 1 to 10 carbon atoms, and even more preferably a methyl group, an ethyl group, or a phenyl group. In formula (5), n preferably represents an integer of 1 to 12, more preferably an integer of 2 to 8, and even more preferably an integer of 2 to 6. In formula (5), the two n's may be the same or different.

[0085] In formula (6), R ５ and R ６ each independently represents a hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or an alkoxy group having 1 to 20 carbon atoms, and n represents an integer of 1 to 20. ５ and R ６ are each independently preferably an aliphatic hydrocarbon group having 1 to 6 carbon atoms or an aromatic hydrocarbon group having 6 to 12 carbon atoms, more preferably an aliphatic hydrocarbon group having 1 to 4 carbon atoms or an aromatic hydrocarbon group having 1 to 10 carbon atoms, and even more preferably a methyl group, an ethyl group, or a phenyl group. In formula (6), n preferably represents an integer of 1 to 12, more preferably an integer of 2 to 8, and even more preferably an integer of 2 to 6. In formula (6), the two n's may be the same or different.

[0086] Among the compounds represented by formula (5), the compound (5-1) is preferred as the curing agent [B1] from the viewpoint of the remoldability and self-repairing properties of the resulting cured product.

[0087]

[0088] The molecular weight of the curing agent [B1] is not particularly limited, but is preferably in the range of 100 to 1,000, more preferably in the range of 100 to 500, and even more preferably in the range of 100 to 300. In the present disclosure, the molecular weight of the curing agent [B1] is a value determined by mass spectrometry.

[0089] The curing agent [B1] preferably contains active hydrogen. When the curing agent [B1] contains active hydrogen, the active hydrogen equivalent of the curing agent [B1] is not particularly limited, but is preferably in the range of 25 g / eq or more and 250 g / eq or less, more preferably in the range of 25 g / eq or more and 150 g / eq or less, and even more preferably in the range of 25 g / eq or more and 100 g / eq or less. In the present disclosure, the active hydrogen equivalent of the curing agent [B1] is a value calculated from the amount of active hydrogen groups contained in the curing agent [B1] (the so-called active hydrogen value) using the following formula: [Active hydrogen equivalent] = 56.1 × 1000 ÷ [active hydrogen value] The active hydrogen value is the amine value determined by a method in accordance with JIS K 7237:1995 (ASTM E222-23) in the case of an amine-based curing agent, and is the hydroxyl value determined by a method in accordance with JIS K 0070:1992 (ASTM D2896-15) in the case of a phenol-based curing agent.

[0090] The remoldability and self-repairing properties of the cured epoxy resin product obtained by curing the epoxy resin composition of the present disclosure are presumed to be due to the dynamic covalent bonding moiety Y contained in the curing agent [B1], etc. The high heat resistance, elastic modulus, and strength of the cured epoxy resin product obtained by curing the epoxy resin composition of the present disclosure are presumed to be brought about by the rigid aromatic ring contained in the above formula (3) or formula (4).

[0091] The proportion of the curing agent [B1] contained in the curing agent [B] is not particularly limited and is adjusted appropriately depending on the type of curing agent [B1], the desired properties of the cured product, etc.

[0092] (Ratio (b1) / (b)) The ratio (b1) / (b) of the molar amount (b1) of active hydrogen in the curing agent [B1] to the molar amount (b) of active hydrogen in the curing agent [B] is not particularly limited, but is, for example, preferably in the range of 0.1 or more and 1.0 or less, more preferably in the range of 0.4 or more and 1.0 or less, even more preferably in the range of 0.7 or more and 1.0 or less, particularly preferably in the range of 0.9 or more and 1.0 or less, and most preferably 1.0. When the ratio (b1) / (b) is 0.1 or more, the performance brought about by the dynamic covalent bond moiety Y in the epoxy resin cured product is better exhibited, and therefore the remoldability and self-repairability of the cured product tend to be further improved.

[0093] In the present disclosure, the "molar amount (b) of active hydrogen in curing agent [B]" refers to the total molar amount of active hydrogen derived from curing agent [B] (hereinafter also referred to as "total molar amount of active hydrogen in curing agent [B]"). The total molar amount of active hydrogen in curing agent [B] is calculated from the sum of the molar amount of active hydrogen derived from curing agent [B1] and the molar amount of active hydrogen derived from curing agents other than curing agent [B1] contained in the epoxy resin composition. The "molar amount of active hydrogen derived from curing agent [B1]" is calculated by dividing the molar amount of curing agent [B1] contained in the epoxy resin composition by the number of active hydrogen contained in one molecule of the compound that is curing agent [B1]. The "molar amount of active hydrogen derived from curing agents other than curing agent [B1]" is calculated by dividing the molar amount of curing agents other than curing agent [B1] contained in the epoxy resin composition by the number of active hydrogen contained in one molecule of the compound that is a curing agent other than curing agent [B1].

[0094] <Curing Agents Other Than Curing Agent [B1]> In addition to the curing agent [B1], the curing agent [B] may contain a known curing agent that cures epoxy resins. The curing agent other than the curing agent [B1] is not particularly limited as long as it is a curing agent that can cure epoxy resins, and is appropriately selected depending on the intended use, etc. The curing agent other than the curing agent [B1] may contain active hydrogen.

[0095] Specifically, curing agents other than the curing agent [B1] include, for example, dicyandiamide, phenolic curing agents not containing the dynamic covalent bond moiety Y and various isomers thereof, aromatic amine curing agents not containing the dynamic covalent bond moiety Y and various isomers thereof, and aminobenzoic acid ester compounds. Dicyandiamide is preferred because it provides excellent storage stability to the prepreg, as described below. Among aromatic amine curing agents not containing the dynamic covalent bond moiety Y, aromatic diamine compounds such as 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, and 4,4'-diaminodiphenylmethane, and derivatives thereof having non-reactive substituents, are preferred because they can produce cured products with high heat resistance. Among aromatic diamine compounds, 3,3'-diaminodiphenyl sulfone is the most preferred because it can produce cured products with high heat resistance and elastic modulus. Examples of non-reactive substituents include alkyl groups such as methyl, ethyl, and isopropyl groups, aromatic groups such as phenyl groups, and halogen groups such as alkoxyl groups, aralkyl groups, chlorine, and bromine.

[0096] (Total Amount of Curing Agent [B]) The total amount of the curing agent [B] contained in the epoxy resin composition of the present disclosure is not particularly limited as long as it is an amount suitable for curing all of the epoxy resins [A] contained in the epoxy resin composition, and is adjusted appropriately depending on the types of the epoxy resins [A] or the curing agent [B].

[0097] (Total Amount of Epoxy Resin [A] and Curing Agent [B]) The total amount of the epoxy resin [A] and the curing agent [B] contained in the epoxy resin composition of the present disclosure is not particularly limited, but is, for example, preferably in the range of 50% by mass or more and less than 100% by mass, more preferably in the range of 70% by mass or more and less than 100% by mass, and even more preferably in the range of 90% by mass or more and less than 100% by mass, relative to the total mass of the epoxy resin composition.

[0098] (Ratio (b) / (a)) The ratio (b) / (a) of the molar amount (b) of active hydrogen in the curing agent [B] to the molar amount (a) of epoxy groups in the epoxy resin [A] is not particularly limited, but is, for example, preferably in the range of 0.5 to 2.0, more preferably in the range of 0.75 to 1.5, even more preferably in the range of 0.9 to 1.2, and particularly preferably 1.0. When the ratio (b) / (a) is within the above range, the balance between the molar amounts of epoxy groups in the epoxy resin [A] and the active hydrogen in the curing agent [B] is good, so that a cured epoxy resin product having sufficient crosslink density can be obtained, and the mechanical properties such as heat resistance, elastic modulus, and fracture toughness of the cured epoxy resin product tend to be further improved.

[0099] In the present disclosure, the "molar amount (a) of epoxy groups in the epoxy resin [A]" means the total molar amount of epoxy groups in the epoxy resin [A] (hereinafter also referred to as the "molar amount of all epoxy groups in the epoxy resin [A]"). The molar amount of all epoxy groups in the epoxy resin [A] can be calculated from the sum of the molar amounts of epoxy groups obtained by dividing the mass of each epoxy resin [A] contained in the epoxy resin composition by its respective epoxy equivalent.

[0100] (Ratio (b1) / (a)) The ratio (b1) / (a) of the molar amount (b1) of active hydrogen in the curing agent [B1] to the molar amount (a) of epoxy groups in the epoxy resin [A] is preferably in the range of 0.6 to 1.5, more preferably in the range of 0.8 to 1.2, even more preferably in the range of 0.9 to 1.1, and particularly preferably 1.0. When the ratio (b1) / (a) is 0.6 or more, the performance provided by the dynamic covalent bonding moiety Y is well exhibited, and the remoldability and self-repairability of the cured product tend to be further improved. Furthermore, when the ratio (b1) / (a) is 1.5 or less, the balance between the molar amounts of epoxy groups in the epoxy resin [A] and active hydrogen in the curing agent [B1] is appropriate, and an epoxy resin cured product having a sufficiently high crosslink density can be obtained, and the mechanical properties of the epoxy resin cured product, such as heat resistance, elastic modulus, and fracture toughness, tend to be further improved.

[0101] The ratio (b1) / (a) is the epoxy resin composition １ The obtained １ This can be confirmed by the integrated area ratio of the peak derived from the epoxy group to the peak derived from active hydrogen in the H-NMR spectrum.

[0102] In the present disclosure, "using a theoretical equivalent amount of a compound containing dynamic covalent bonding moieties relative to an epoxy resin" means using a compound containing dynamic covalent bonding moieties in an amount such that the molar amount of active hydrogen in the compound containing dynamic covalent bonding moieties is 1 relative to the molar amount of epoxy groups in the epoxy resin of 1, in which case the ratio (b1) / (a) is 1.0. In the present disclosure, "using a theoretical equivalent or less amount of a compound containing dynamic covalent bonding moieties relative to an epoxy resin" means that the ratio (b1) / (a) is 1.0 or less.

[0103] <Curing Accelerator> The epoxy resin composition of the present disclosure may contain a curing accelerator in addition to the above-described epoxy resin [A] and curing agent [B]. The curing accelerator accelerates the curing reaction of the epoxy resin composition and the prepreg impregnated therewith, thereby forming a cured product having a high elastic modulus and strength in a short production time. The curing accelerator is not particularly limited as long as it accelerates the curing reaction between the epoxy resin [A] and the curing agent [B], and examples thereof include nitrogen-containing heterocyclic compounds such as imidazole compounds and tertiary amine compounds, as well as onium salts thereof, phosphine compounds, and phosphonium salts thereof.

[0104] Specific examples of the curing accelerator include imidazole compounds such as 2-ethyl-4-methylimidazole and 1-(2-cyanoethyl)-2-phenylimidazole, and salts containing these; tertiary amine compounds such as diazabicycloundecene, diazabicyclononene, and tris(dimethylaminomethyl)phenol, and salts containing these; phosphine compounds such as triphenylphosphine and tri(orthotolyl)phosphine; and phosphonium salts such as tetraphenylphosphonium tetraphenylborate.

[0105] When the epoxy resin composition of the present disclosure contains a curing accelerator, the content of the curing accelerator is not particularly limited and is set appropriately as needed.

[0106] <Other Components> The epoxy resin composition of the present disclosure may contain components other than the essential components, the epoxy resin [A] and the curing agent [B], and the optional curing accelerator (so-called other components). Examples of the other components include a thermoplastic resin, conductive particles, a flame retardant, an inorganic filler, and an internal mold release agent.

[0107] The thermoplastic resin improves the fracture toughness and impact resistance of the resulting fiber-reinforced composite material. Examples of the thermoplastic resin include epoxy resin-soluble thermoplastic resins and epoxy resin-insoluble thermoplastic resins.

[0108] The epoxy resin-soluble thermoplastic resin adjusts the viscosity of the epoxy resin composition and further improves the impact resistance of the resulting fiber-reinforced composite material. Examples of the epoxy resin-soluble thermoplastic resin include polyethersulfone, polysulfone, polyetherimide, and polycarbonate. The epoxy resin-soluble thermoplastic resin preferably contains at least one selected from polyethersulfone and polysulfone, and more preferably at least one selected from polyethersulfone and polysulfone. When the epoxy resin composition of the present disclosure contains an epoxy resin-soluble thermoplastic resin as the thermoplastic resin, it may contain only one type of the epoxy resin-soluble thermoplastic resin, or may contain two or more types of the epoxy resin-soluble thermoplastic resin.

[0109] The epoxy resin-soluble thermoplastic resin preferably has a weight-average molecular weight (Mw) of 8,000 or more and 100,000 or less as measured by gel permeation chromatography. When the weight-average molecular weight (Mw) of the epoxy resin-soluble thermoplastic resin is 8,000 or more, the impact resistance of the resulting fiber-reinforced composite material tends to be further improved. Furthermore, when the weight-average molecular weight (Mw) of the epoxy resin-soluble thermoplastic resin is 100,000 or less, the viscosity of the epoxy resin composition does not become too high, resulting in good handleability. The molecular weight distribution of the epoxy resin-soluble thermoplastic resin as measured by gel permeation chromatography is preferably narrow. The polydispersity (Mw / Mn), which is the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn), is preferably 1 to 10, more preferably 1.1 to 5.

[0110] The epoxy resin-soluble thermoplastic resin preferably has a reactive group reactive with the epoxy resin or a functional group capable of forming a hydrogen bond. Such an epoxy resin-soluble thermoplastic resin can improve the solubility stability of the epoxy resin during the curing process. Furthermore, such an epoxy resin-soluble thermoplastic resin can impart toughness, chemical resistance, heat resistance, and moist heat resistance to the fiber-reinforced composite material obtained after curing.

[0111] The reactive group reactive with the epoxy resin is not particularly limited, but is preferably, for example, a hydroxyl group, a carboxylic acid group, an imino group, or an amino group. The epoxy resin-soluble thermoplastic resin is preferably a hydroxyl-terminated polyethersulfone. When the epoxy resin composition of the present disclosure contains a hydroxyl-terminated polyethersulfone as the epoxy resin-soluble thermoplastic resin, the resulting fiber-reinforced composite material tends to have further improved impact resistance, fracture toughness, and solvent resistance.

[0112] A part of the epoxy resin-insoluble thermoplastic resin or the epoxy resin-soluble thermoplastic resin (i.e., the epoxy resin-soluble thermoplastic resin that remains undissolved in the matrix resin after curing) is in a state where its particles are dispersed in the matrix resin of the fiber-reinforced composite material. These dispersed particles suppress the propagation of impacts received by the fiber-reinforced composite material, thereby improving the impact resistance of the resulting fiber-reinforced composite material.

[0113] Examples of epoxy resin-insoluble thermoplastic resins include polyamide, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyester, polyamideimide, polyimide, polyetherketone, polyetheretherketone, polyethylene naphthalate, polyethernitrile, and polybenzimidazole. Among these, polyamide, polyamideimide, and polyimide are preferred due to their high toughness and heat resistance. Furthermore, polyamide and polyimide are particularly effective in improving the toughness of fiber-reinforced composite materials. When the epoxy resin composition of the present disclosure contains an epoxy resin-insoluble thermoplastic resin as a thermoplastic resin, it may contain only one type of the epoxy resin-insoluble thermoplastic resin, or two or more types, or it may contain a copolymer of two or more types of the epoxy resin-insoluble thermoplastic resin.

[0114] In particular, polyamides such as amorphous polyimide, Nylon 6 (registered trademark) (a polyamide obtained by a ring-opening polycondensation reaction of caprolactam), Nylon 11 (a polyamide obtained by a ring-opening polycondensation reaction of undecane lactam), Nylon 12 (a polyamide obtained by a ring-opening polycondensation reaction of lauryllactam), Nylon 1010 (a polyamide obtained by a copolymerization reaction of sebacic acid and 1,10-decanediamine), and amorphous nylon (also known as transparent nylon, which does not crystallize or has an extremely slow crystallization rate), can significantly improve the heat resistance of the resulting fiber-reinforced composite material.

[0115] Examples of conductive particles include conductive polymer particles such as polyacetylene particles, polyaniline particles, polypyrrole particles, polythiophene particles, polyisothianaphthene particles, and polyethylenedioxythiophene particles; carbon particles; carbon fiber particles; metal particles; and particles in which a core material made of an inorganic or organic material is coated with a conductive substance.

[0116] The flame retardant may be a phosphorus-based flame retardant. The phosphorus-based flame retardant is not particularly limited as long as it contains a phosphorus atom in the molecule. Examples of the phosphorus-based flame retardant include organic phosphorus compounds such as phosphate esters, condensed phosphate esters, phosphazene compounds, and polyphosphates, and red phosphorus.

[0117] Examples of inorganic fillers include aluminum borate, calcium carbonate, silicon carbonate, silicon nitride, potassium titanate, basic magnesium sulfate, zinc oxide, graphite, calcium sulfate, magnesium borate, magnesium oxide, and silicate minerals. Preferred inorganic fillers are silicate minerals. Specific examples of silicate minerals include THIXOTROPIC AGENT DT 5039 (manufactured by Huntsman Japan Co., Ltd.).

[0118] Examples of internal release agents include metal soaps, vegetable waxes such as polyethylene wax and carnauba wax, fatty acid ester-based release agents, silicone oils, animal waxes, and fluorine-based nonionic surfactants. When the epoxy resin composition of the present disclosure contains an internal release agent, the content of the internal release agent is not particularly limited, but is preferably 0.1 to 5 parts by mass, and more preferably 0.2 to 2 parts by mass, per 100 parts by mass of the epoxy resin [A]. When the content of the internal release agent in the epoxy resin composition of the present disclosure is within the above range per 100 parts by mass of the epoxy resin [A], the epoxy resin composition exhibits good mold release properties.

[0119] Examples of commercially available internal mold release agents include MOLD WIZ (registered trademark) INT1846 (manufactured by AXEL PLASTICS RESEARCH LABORATORIES INC.), Licowax S, Licowax P, Licowax OP, Licowax PE190, and Licowax PED (all manufactured by Clariant Japan K.K.), and Rikemal (registered trademark) SL-900A (manufactured by Riken Vitamin Co., Ltd.).

[0120] [Stress Relaxation Rate] When the epoxy resin composition of the present disclosure is cured to a degree of cure of 90% or more to form a cured product, and then an external force is applied to the cured product at a temperature 40°C higher than the glass transition temperature of the cured product, and the resulting stress is measured, the stress relaxation rate one hour after the start of application of the external force is preferably 95% or more, more preferably 97% or more, and even more preferably 99% or more. If the stress relaxation rate is 95% or more, the remoldability of the epoxy resin cured product and the fiber-reinforced composite material described below tends to be less impaired, and the strength and elastic modulus tend to be less likely to decrease.

[0121] The stress relaxation rate is a value calculated by the following formula for the change in modulus value G over time over 3,600 seconds (1 hour) that occurs in stress relaxation measurement. The modulus value is the value of stress that occurs when an external force is applied to cause distortion. [1-((G(min)) / (G(0))]×100 G(0) is the modulus value at the start of application of the external force (i.e., 0 seconds after the start of application of the external force). G(min) is the minimum modulus value at 3,600 seconds after the start of application of the external force, in other words, the minimum modulus value up to 3,600 seconds after the start of application of the external force. If the modulus value reaches the lower limit of measurement by the device within 3,600 seconds after the start of application of the external force, this value is used. If the modulus value does not reach the lower limit of measurement by the device within 3,600 seconds after the start of application of the external force, this value is used.

[0122] A stress relaxation rate of 95% or more one hour after the start of application of an external force means that the stress, which was 100% at the start of application of the external force, relaxes with the application of the external force and the passage of time, decreasing to less than 5% one hour after the start of application of the external force, and the cured product becomes fluid. By becoming fluid, the cured product can have remoldability and self-repairing properties.

[0123] [Stress Relaxation Mode Separation Analysis] Stress relaxation mode separation analysis will be described in detail. The stress relaxation behavior when stress is applied to the cured product of the epoxy resin composition of the present disclosure is approximated by a generalized Maxwell model. This generalized Maxwell model is a model in which multiple types of Maxwell elements, a two-element model in which a dashpot and a spring are arranged in series, are arranged in parallel. In this generalized Maxwell model, each constituent Maxwell element corresponds to one relaxation mode. In other words, the stress relaxation behavior when stress is applied to the generalized Maxwell model can be described as a linear sum of the behaviors of each constituent Maxwell element (each relaxation mode). Then, by separating the stress relaxation measurement results according to the linear sum equation of the generalized Maxwell model and evaluating the relaxation time for each relaxation mode, it becomes possible to quantitatively evaluate the bond exchange performance within the cured product of the epoxy resin composition of the present disclosure.

[0124] The modulus value G(t) over 3600 seconds resulting from stress relaxation measurements is approximated by the following formula until the correlation square coefficient R2 is greater than 0.999:

[0125]

[0126] In the above formula, t is time (unit: seconds), and G ０ is the modulus value G(0) at t = 0 seconds. ｉ is Σμ ｉ τ is an independent variable in the range satisfying τ = 1, and is a variable indicating the contribution (unit: %) of each term (so-called each relaxation mode) in this multi-dimensional linear equation. ｉ is the relaxation time (seconds) in each relaxation mode that is arbitrarily set, and is set to include a relaxation mode having a relaxation time that is sufficiently large relative to the measurement time. Furthermore, each relaxation mode is set so that its relaxation time is uniform across the same logarithmic range and uniform within the same logarithmic range. The number and range of relaxation modes to be set are not particularly limited, but it is preferable to have as many as possible in terms of, for example, calculation load.

[0127] For example, when performing stress relaxation mode separation analysis in the range of 0 seconds to 3600 seconds for the cured epoxy resin material of the present disclosure, it is preferable to analyze using the following 25 types of relaxation modes (i.e., values ​​of τi): τi = 1, 2.5, 4, 5.5, 7, 8.5, 10, 25, 40, 55, 70, 85, 100, 250, 400, 550, 700, 850, 1000, 2500, 4000, 5500, 7000, 8500, 10000. In this case, τi is set to include the measurement time of 3600 seconds. ｉ The maximum value of τ ｉ = 10,000 (seconds). Furthermore, each relaxation mode is set so that its relaxation time is uniform within the same logarithmic range, such as 1, 4, 7, 10, 40, etc. The cured product of the epoxy resin composition of the present disclosure is then approximated by a linear sum of relaxation modes having 25 different relaxation times, and the stress relaxation behavior is measured.

[0128] Next, for each measured relaxation mode, the logarithm of the relaxation time is plotted on the horizontal axis and the logarithm of the stress is plotted on the vertical axis, and an approximate formula is obtained using the above formula. ｉ and μ ｉ On the horizontal axis, τ ｉ Plot the logarithm of μ on the vertical axis. ｉ τ, which has a peak in the distribution when plotted ｉ is the relaxation time of the separated relaxation modes. Furthermore, τ ｉ μ in the group ｉ τ that constitutes any peak for the sum of ｉ μ in ｉ The value of is the contribution (%) of the isolated relaxation mode.

[0129] Conventionally known devices and techniques can be used to measure stress relaxation. When measuring stress relaxation, it is sufficient to be able to track and record the change in stress over time after instantaneous application of an external force under isothermal conditions using a thermostatic device. Specific examples of stress relaxation measurements include measurements in shear mode using a rheometer device equipped with parallel plates, and measurements in bending or tension mode using dynamic mechanical analysis (DMA). Measurements are preferably performed in an inert gas atmosphere, with controlled humidity. Although not particularly limited, stress relaxation is preferably measured, for example, in a room with a low humidity atmosphere of 50% RH or less, with nitrogen flowing through the measurement device at a flow rate of 10 L / min or more.

[0130] The epoxy resin composition of the present disclosure is cured to a degree of cure of 90% or more to form a cured product, and then an external force is applied to the cured product at a temperature 40° C. higher than the glass transition temperature of the cured product. The stress relaxation behavior when the stress generated when the external force is applied to the cured product is measured is shown in Fig. 1. The results of the stress relaxation mode separation analysis show that the horizontal axis is τ ｉ Plot the logarithm of μ on the vertical axis. ｉIn the graph obtained by plotting the above, it is preferable that the graph has two or more relaxation mode groups having a distribution. In the graph, it is preferable that the contribution of the relaxation mode group having a relaxation time of more than 1000 seconds is 40% or less, more preferably the contribution of the relaxation mode group having a relaxation time of more than 1000 seconds is 25% or less, and even more preferably the contribution of the relaxation mode group having a relaxation time of more than 1000 seconds is 25% or less, the contribution of the relaxation mode group having a relaxation time of 200 to 1000 seconds is 50% or less, and the contribution of the relaxation mode group having a relaxation time of less than 200 seconds is 50% or more. An epoxy resin composition that, when made into the above cured product, gives a graph having two or more relaxation mode groups tends to be less likely to impair the creep properties of the epoxy resin cured product or fiber-reinforced composite material under high temperature conditions. Furthermore, when the cured product is obtained, if a graph having two or more relaxation mode groups is obtained and the contribution rate of the relaxation mode group having a relaxation time of more than 1000 seconds is 40% or less, the remoldability and self-repairability of the cured epoxy resin product or fiber-reinforced composite material tend to be less likely to be impaired.

[0131] <Method for Producing Epoxy Resin Composition> The method for producing the epoxy resin composition of the present disclosure is not particularly limited. The epoxy resin composition of the present disclosure may be produced by any conventionally known method. The epoxy resin composition of the present disclosure can be produced, for example, by mixing an epoxy resin [A], a curing agent [B], and, if necessary, a curing accelerator and other components. The order of mixing these components is not important. The mixing temperature is not particularly limited, and examples include 40°C to 120°C. A mixing temperature of 40°C or higher tends to prevent the viscosity of the epoxy resin composition from becoming too high, allowing for good mixing. A mixing temperature of 120°C or lower tends to prevent a partial curing reaction from proceeding, which can lead to a decrease in impregnation into the fiber-reinforced substrate layer, and a decrease in the storage stability of the resulting epoxy resin composition and prepregs produced using it. The mixing temperature is preferably 50°C to 100°C, and more preferably 50°C to 90°C.

[0132] The mixing means is not particularly limited. Examples of the mixing means include conventionally known mixing devices. Examples of the mixing device include a roll mill, a planetary mixer, a kneader, an extruder, a Banbury mixer, a mixing vessel equipped with stirring blades, and a horizontal mixing tank. The components can be mixed in the air or in an inert gas atmosphere. When mixing is performed in the air, an atmosphere in which the temperature and humidity are controlled is preferred. Although not particularly limited, the components are preferably mixed at a temperature controlled to a constant temperature of 30°C or less and in a low-humidity atmosphere with a relative humidity of 50% RH or less.

[0133] <Cured Epoxy Resin Product> The cured epoxy resin product of the present disclosure includes aspects of the cured epoxy resin product of the first embodiment and the second embodiment shown below. <Cured Epoxy Resin Product of the First Embodiment> The cured epoxy resin product of the first embodiment is obtained by curing the epoxy resin composition of the present disclosure. The method for curing the epoxy resin composition of the present disclosure to obtain the cured epoxy resin product of the first embodiment is not particularly limited, and the cured epoxy resin composition may be cured by a known method. The cured epoxy resin product of the first embodiment can be obtained, for example, by degassing the epoxy resin composition of the present disclosure in a vacuum, followed by curing at a temperature of 120°C to 200°C for 15 minutes to 24 hours, preferably at a temperature of 120°C to 180°C for 1 hour to 12 hours, and more preferably at a temperature of 150°C to 180°C for 1 hour to 6 hours. Specifically, the cured epoxy resin product of the first embodiment can be obtained, for example, by degassing the epoxy resin composition of the present disclosure in a vacuum, followed by curing at a temperature of 120°C for 2 hours, at a temperature of 150°C for 2 hours, and at a temperature of 180°C for 2 hours.

[0134] When the cured epoxy resin material of the first embodiment is brought into contact with a decomposer containing a reducing agent and heated at 100°C for 48 hours, preferably 80% by mass or more of the cured epoxy resin material dissolves, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 100% by mass, i.e., the entire cured epoxy resin material dissolves.

[0135] In the present disclosure, the dissolution rate (unit: mass %) of a cured epoxy resin material is measured by filtering a solution in which the cured epoxy resin material is dissolved and dividing the mass of the residue obtained by filtering the solution by the mass of the cured epoxy resin material before dissolution.

[0136] The reducing agent is not particularly limited as long as it dissolves the cured epoxy resin material, and can be appropriately selected depending on the type of bond contained in the cured epoxy resin material. Examples of reducing agents include dithiothreitol, 2-mercaptoethanol, 1-thioglycerol, glutathione, 2-mercaptoethylamine hydrochloride, cystine hydrochloride, and tris(2-carboxyethyl)phosphine hydrochloride. The reducing agent is preferably a reducing agent that reduces disulfide bonds. The reducing agents may be used alone or in combination.

[0137] The reducing agent may be used without a solvent, or may be used as a decomposer solution by diluting it with a solvent. The cured epoxy resin material of the second embodiment may be dissolved by immersing it in a decomposer solution containing a reducing agent. The amount of the decomposer solution used is not particularly limited and is determined depending on the shape of the cured epoxy resin material, dissolution conditions, etc. The amount of the decomposer contained in the decomposer solution is, for example, preferably 0.5 to 1000 times, more preferably 0.5 to 100 times, and even more preferably 0.5 to 10 times, the amount of the cured epoxy resin material by mass.

[0138] The concentration of the reducing agent in the decomposition agent solution is not particularly limited, but is, for example, preferably 0.1% by mass to 99.9% by mass, more preferably 1% by mass to 80% by mass, and even more preferably 5% by mass to 50% by mass.

[0139] The solvent used for dilution is not particularly limited as long as it can dissolve the reducing agent and the cured epoxy resin material, and may be water or an organic solvent. Examples of the organic solvent used for dilution include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, 1,4-dioxane, tetrahydrofuran, methanol, ethanol, etc., and polar organic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide are particularly preferred because they can completely dissolve the cured epoxy resin material.

[0140] The decomposer may contain, in addition to the reducing agent, an additive that promotes dissolution of the cured epoxy resin material. In particular, nitrogen-containing bases such as triethylamine, DBU (1,8-diazabicycloundecene), and ammonia are preferred because their addition has a high effect of promoting dissolution of the cured epoxy resin material.

[0141] When the cured epoxy resin product of the first embodiment is brought into contact with a decomposing agent containing a reducing agent and heated at 100°C for 48 hours, it is preferable that the product at least produces a compound having a structure represented by the following formula (7). When the cured epoxy resin product of the first embodiment is brought into contact with a decomposing agent containing a reducing agent and heated at 100°C for 48 hours, it is more preferable that the product decomposes into a compound having a structure represented by the following formula (7).

[0142]

[0143] In formula (7), R ７ａ , R ７ｂ , R ７ｃ , R ７ｄ and R ７ｅ each independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, an alkoxy group, an amino group, or a halogen atom, and * represents a bond.

[0144] The aliphatic hydrocarbon group may have a substituent on the alkyl chain, or may be unsubstituted. The number of carbon atoms in the aliphatic hydrocarbon group, not including the number of carbon atoms in the substituent, is 1 to 20, preferably 1 to 10, and more preferably 1 to 5. Specific examples of the aliphatic hydrocarbon group include saturated aliphatic hydrocarbon groups such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an s-butyl group, a t-butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, a tetradecyl group, a hexadecyl group, and an octadecyl group, and unsaturated aliphatic hydrocarbon groups such as an allyl group and a vinyl group.

[0145] The alicyclic hydrocarbon group may have a substituent on the ring, or may be unsubstituted. The number of carbon atoms in the alicyclic hydrocarbon group, not including the number of carbon atoms in the substituent, is preferably 4 to 18, and more preferably 5 to 10. Specific examples of the alicyclic hydrocarbon group include a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, and a cyclohexenyl group.

[0146] The aromatic hydrocarbon group may have a substituent on the aromatic ring, or may be unsubstituted. The number of carbon atoms in the aromatic hydrocarbon group, not including the carbon atoms in the substituent, is preferably 6 to 18, and more preferably 6 to 15. Specific examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group and a naphthyl group.

[0147] The alkoxy group may have a substituent on the alkyl chain, or may be unsubstituted. The alkoxy group may be linear, branched, or cyclic. The number of carbon atoms in the alkoxy group, not including the number of carbon atoms in the substituent, is preferably 1 to 6, and more preferably 1 to 3. Specific examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propyloxy group, an isopropyloxy group, an n-butyloxy group, an isobutyloxy group, a t-butyloxy group, an n-pentyloxy group, an n-hexyloxy group, and a phenoxy group. The alkoxy group is preferably a methoxy group or a phenoxy group.

[0148] The amino group may have a substituent on the nitrogen atom, or may be unsubstituted. When the amino group has a substituent, examples of the substituent include an alkyl group and an aryl group. The number of carbon atoms in the substituted amino group is preferably 1 to 20, and more preferably 1 to 12. Specific examples of amino include a dimethylamino group, a diethylamino group, and a diphenylamino group.

[0149] Specific examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. The halogen atom is preferably a fluorine atom or a chlorine atom.

[0150] In formula (7), R ７ａ , R ７ｂ , R ７ｃ , R ７ｄ and R ７ｅ are each independently preferably a hydrogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, an aromatic hydrocarbon group, an alkoxy group, or a halogen atom, more preferably a hydrogen atom, a methyl group, or a methoxy group, and even more preferably a hydrogen atom or a methyl group. ７ａ is a hydrogen atom or a methyl group, and R ７ｂ , R ７ｃ , R ７ｄ and R ７ｅ In formula (7), * in "-N-*" is preferably a bond to a structure derived from an epoxy resin, * in "-C(OH)-*" is preferably a bond to a structure derived from an epoxy resin, and * in "-S-*" is preferably a bond to a structure derived from a reducing agent.

[0151] The molecular weight of the compound having the structure represented by formula (7) is not particularly limited, but from the viewpoint of solubility, it is preferably 200 to 5000, more preferably 200 to 2000, and even more preferably 200 to 1000. In the present disclosure, the molecular weight of the compound having the structure represented by formula (7) is measured by gel permeation chromatography (GPC) using chloroform, N,N-dimethylformamide, or the like as an eluent.

[0152] The production of a compound containing the structure represented by formula (7) can be confirmed by FT-IR. １ This can also be confirmed by H-NMR.

[0153] <Cured Epoxy Resin Product of Second Embodiment> When the cured epoxy resin product of the second embodiment is brought into contact with a decomposing agent containing a reducing agent and heated at 100°C for 48 hours, a compound containing at least the structure shown in formula (7) below is produced. When the cured epoxy resin product of the second embodiment is brought into contact with a decomposing agent containing a reducing agent and heated at 100°C for 48 hours, it is preferred that the cured epoxy resin product is decomposed into at least the compound containing the structure shown in formula (7) below.

[0154]

[0155] In formula (7), R ７ａ , R ７ｂ , R ７ｃ , R ７ｄ and R ７ｅ each independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, an alkoxy group, an amino group, or a halogen atom, and * represents a bond.

[0156] The explanation and preferred aspects of formula (7) are the same as those of formula (7) in <Epoxy resin cured material of first embodiment>.

[0157] The molecular weight of the compound having the structure represented by formula (7) is not particularly limited, but from the viewpoint of solubility, it is preferably 200 to 5000, more preferably 200 to 2000, and even more preferably 200 to 1000. In the present disclosure, the molecular weight of the compound having the structure represented by formula (7) is measured by gel permeation chromatography (GPC) using chloroform and N,N-dimethylformamide as an eluent.

[0158] The description of the decomposer containing a reducing agent in the cured epoxy resin material of the second embodiment is the same as the description of the decomposer containing a reducing agent in the cured epoxy resin material of the first embodiment, including definitions, examples, preferred aspects, etc.

[0159] When the cured epoxy resin material of the second embodiment is heated using, for example, a solution of 2-mercaptoethanol in N,N-dimethylformamide as a decomposing agent solution, a compound including at least a structure represented by the following general formula (7-1) is produced.

[0160]

[0161] In formula (7-1), R ７－１ａ , R ７－１ｂ , R ７－１ｃ , R ７－１ｄ and R ７－１ｅ each independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, an alkoxy group, an amino group, or a halogen atom, and * represents a bond.

[0162] The aliphatic hydrocarbon group may have a substituent on the alkyl chain, or may be unsubstituted. The number of carbon atoms in the aliphatic hydrocarbon group, not including the number of carbon atoms in the substituent, is 1 to 20, preferably 1 to 10, and more preferably 1 to 5. Specific examples of the aliphatic hydrocarbon group include saturated aliphatic hydrocarbon groups such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an s-butyl group, a t-butyl group, a pentyl group, a hexyl group, an octyl group, a decyl group, a dodecyl group, a tetradecyl group, a hexadecyl group, and an octadecyl group, and unsaturated aliphatic hydrocarbon groups such as an allyl group and a vinyl group.

[0163] The alicyclic hydrocarbon group may have a substituent on the ring, or may be unsubstituted. The number of carbon atoms in the alicyclic hydrocarbon group, not including the number of carbon atoms in the substituent, is preferably 4 to 18, and more preferably 5 to 10. Specific examples of the alicyclic hydrocarbon group include a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, and a cyclohexenyl group.

[0164] The aromatic hydrocarbon group may have a substituent on the aromatic ring, or may be unsubstituted. The number of carbon atoms in the aromatic hydrocarbon group, not including the carbon atoms in the substituent, is preferably 6 to 18, and more preferably 6 to 15. Specific examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group and a naphthyl group.

[0165] The alkoxy group may have a substituent on the alkyl chain, or may be unsubstituted. The alkoxy group may be linear, branched, or cyclic. The number of carbon atoms in the alkoxy group, not including the number of carbon atoms in the substituent, is preferably 1 to 6, and more preferably 1 to 3. Specific examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propyloxy group, an isopropyloxy group, an n-butyloxy group, an isobutyloxy group, a t-butyloxy group, an n-pentyloxy group, an n-hexyloxy group, and a phenoxy group. The alkoxy group is preferably a methoxy group or a phenoxy group.

[0166] The amino group may have a substituent on the nitrogen atom, or may be unsubstituted. When the amino group has a substituent, examples of the substituent include an alkyl group and an aryl group. The number of carbon atoms in the substituted amino group is preferably 1 to 20, and more preferably 1 to 12. Specific examples of amino include a dimethylamino group, a diethylamino group, and a diphenylamino group.

[0167] Specific examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. The halogen atom is preferably a fluorine atom or a chlorine atom.

[0168] In formula (7), R ７－１ａ , R ７－１ｂ , R ７－１ｃ , R ７－１ｄ and R ７－１ｅ are each independently preferably a hydrogen atom, an aliphatic hydrocarbon group having 1 to 5 carbon atoms, an aromatic hydrocarbon group, an alkoxy group, or a halogen atom, more preferably a hydrogen atom, a methyl group, or a methoxy group, and even more preferably a hydrogen atom or a methyl group. ７－１ａ is a hydrogen atom or a methyl group, and R ７－１ｂ , R ７－１ｃ , R ７－１ｄ and R ７－１ｅ is preferably a hydrogen atom. In formula (7-1), * in "-N-*" is preferably a bond to a structure derived from an epoxy resin, and * in "-C(OH)-*" is preferably a bond to a structure derived from an epoxy resin.

[0169] The molecular weight of the compound having the structure represented by formula (7-1) is not particularly limited, but from the viewpoint of solubility, it is preferably 200 to 5000, more preferably 200 to 2000, and even more preferably 200 to 1000.

[0170] The conditions for contacting and heating with a decomposer containing a reducing agent are not particularly limited, and may be, for example, heated at 25°C to 150°C (preferably 25°C to 60°C) for 1 hour to 48 hours (preferably 1 hour to 8 hours), with appropriate stirring or ultrasonic treatment if necessary. For example, the reaction to produce the compound having the structure represented by formula (7-1) may be allowed to proceed while stirring the cured epoxy resin material and the decomposer at room temperature (25°C) or 80°C for 8 hours. When the cured epoxy resin material is contacted and heated with a decomposer containing a reducing agent, a pressure of 0.1 MPa to 10 MPa (preferably 0.1 MPa to 1 MPa) may be applied in order to promote the production of the compound having the structure represented by formula (7-1).

[0171] The production of a compound having the structure represented by formula (7-1) can be confirmed by FT-IR. １This can also be confirmed by H-NMR.

[0172] <Physical Properties of Cured Epoxy Resin Product> The glass transition temperature (Tg) of the cured epoxy resin product of the present disclosure is not particularly limited, but is preferably 80°C to 300°C, and more preferably 100°C to 200°C. A glass transition temperature of 80°C or higher further improves the heat resistance of the cured epoxy resin product. As a result, voids and other defects tend to be less likely to form in the resulting fiber-reinforced composite material. A glass transition temperature of 300°C or lower is more moderate in the remolding and self-repair processes, which tends to prevent mechanical properties from being impaired by resin degradation. In the present disclosure, the glass transition temperature of the cured epoxy resin product is measured using a differential scanning calorimeter. Specifically, the temperature of the cured epoxy resin product is raised from 30°C to 350°C at a rate of 10°C / min, and the inflection point in the transition process of the obtained curve is taken as the glass transition temperature of the cured epoxy resin product.

[0173] The flexural modulus (FM) of the cured epoxy resin product of the present disclosure is not particularly limited, but is, for example, preferably 2.00 GPa or more, more preferably 2.30 GPa to 30.00 GPa, even more preferably 2.50 GPa to 20.00 GPa, and may be 2.50 GPa to 5.00 GPa. When the flexural modulus is 2.00 GPa or more, the properties of the resulting fiber-reinforced composite material tend not to deteriorate. In the present disclosure, the flexural modulus of the cured epoxy resin product is measured by a method in accordance with JIS K 7171:2016 (ISO 178:2010).

[0174] The flexural strength (FS) of the cured epoxy resin product of the present disclosure is not particularly limited, but is preferably 60 MPa or more, more preferably 80 MPa to 150 MPa, and even more preferably 100 MPa to 150 MPa. When the flexural strength is 60 MPa or more, the properties of the resulting fiber-reinforced composite material tend not to deteriorate. In the present disclosure, the flexural strength of the cured epoxy resin product is measured by a method in accordance with JIS K 7171:2016 (ISO 178:2010).

[0175] The degree of cure of the epoxy resin cured product of the present disclosure is not particularly limited, but is preferably 90% or more, more preferably 95% or more, and even more preferably 99% or more. If the degree of cure is insufficient, poor toughness is likely to occur. In the present disclosure, the degree of cure of the epoxy resin cured product is measured by a method in accordance with JIS K 7148-1:2015 (ISO 14322:2012).

[0176] Even if the cured epoxy resin material of the present disclosure has voids inside due to cracks, peeling, or the like, the voids can be repaired by subjecting the material to a process that includes heating.

[0177] <Prepreg> The prepreg of the present disclosure is a prepreg obtained by impregnating a fiber-reinforced substrate having reinforcing fibers with the epoxy resin composition of the present disclosure, and the content of the reinforcing fibers is 25% by volume to 75% by volume relative to the total volume of the prepreg.

[0178] The prepreg of the present disclosure is a prepreg in which a fiber-reinforced substrate is partially or entirely impregnated with the epoxy resin composition of the present disclosure. When the reinforcing fiber content in the prepreg of the present disclosure is 25% by volume or more, the reinforcing effect of the reinforcing fibers is sufficiently obtained, and the mechanical properties relative to mass tend to be substantially high. When the reinforcing fiber content in the prepreg of the present disclosure is 75% by volume or less, voids and the like are less likely to occur in the resulting fiber-reinforced composite material, and a decrease in mechanical properties tends to be less likely. The reinforcing fiber content in the prepreg of the present disclosure is preferably 45% by volume to 70% by volume, and more preferably 50% by volume to 65% by volume, relative to the total volume of the prepreg.

[0179] The prepreg of the present disclosure may be in the form of a tow prepreg in which the reinforcing fibers are formed into strands, an SMC (sheet molding compound) in which the reinforcing fibers are formed of short fibers with a fiber length of 5 mm to 100 mm, or a woven fabric prepreg in which the reinforcing fibers are formed of a woven fabric or a multi-layered woven fabric. A tow prepreg is a narrow intermediate substrate obtained by impregnating a reinforcing fiber bundle in which several thousand to several tens of thousands of reinforcing fiber filaments are aligned in one direction with a matrix resin composition and then winding the impregnated bundle around a bobbin such as a paper tube. In the present disclosure, the prepreg wound around a bobbin or the prepreg unwound after being wound is referred to as a "tow prepreg."

[0180] <Fiber-reinforced substrate> The type of fiber-reinforced substrate is not particularly limited. Examples of fiber-reinforced substrates include carbon fibers, glass fibers, aramid fibers, silicon carbide fibers, polyester fibers, ceramic fibers, alumina fibers, boron fibers, metal fibers, mineral fibers, rock fibers, and slag fibers. Among these, carbon fibers, glass fibers, or aramid fibers are preferred as the fiber-reinforced substrate, and carbon fibers are more preferred because they have good specific strength and specific modulus, and can produce lightweight, high-strength fiber-reinforced composite materials. Among carbon fibers, polyacrylonitrile (PAN)-based carbon fibers are particularly preferred as the fiber-reinforced substrate because of their excellent tensile strength.

[0181] When PAN-based carbon fibers are used as the fiber-reinforced substrate, the tensile modulus is preferably 100 GPa to 600 GPa, more preferably 200 GPa to 500 GPa, and even more preferably 230 GPa to 450 GPa. The tensile strength is preferably 2000 MPa to 10000 MPa, and more preferably 3000 MPa to 8000 MPa.

[0182] When carbon fibers are used as the fiber-reinforced substrate, the diameter thereof is preferably 4 μm to 20 μm, and more preferably 5 μm to 10 μm. By using such carbon fibers, the mechanical properties of the resulting fiber-reinforced composite material can be improved.

[0183] The fiber-reinforced substrate is preferably formed into a sheet for use. Examples of reinforcing fiber sheets include sheets in which a large number of reinforcing fibers are aligned in one direction, bidirectional fabrics such as plain weave or twill weave, multiaxial fabrics, nonwoven fabrics, mats, knits, braids, and paper made from fiber-reinforced substrates. Among these, the use of a unidirectionally aligned sheet, bidirectional fabric, or multiaxial fabric substrate in which the fiber-reinforced substrate is formed into a sheet as continuous fibers is preferred because it results in a fiber-reinforced composite material with superior mechanical properties. The thickness of the sheet-like fiber-reinforced substrate is preferably 0.01 mm to 3 mm, more preferably 0.1 mm to 1.5 mm.

[0184] <Method for producing prepreg> The method for producing the prepreg of the present disclosure is not particularly limited. The prepreg of the present disclosure may be produced by any conventionally known method. The hot melt method or solvent method can be suitably used as the method for producing the prepreg of the present disclosure.

[0185] The hot melt method is a method in which an epoxy resin composition is applied in the form of a thin film onto release paper to form an epoxy resin composition film, and the epoxy resin composition film is laminated onto a fiber-reinforced substrate and heated under pressure, thereby impregnating the fiber-reinforced substrate layer with the epoxy resin composition.

[0186] The method for forming an epoxy resin composition into an epoxy resin composition film is not particularly limited, and any conventionally known method can be used. Specifically, a resin composition film can be obtained by casting the epoxy resin composition onto a support such as release paper or film using die extrusion, an applicator, a reverse roll coater, a comma coater, or the like. The resin temperature during film production is determined appropriately depending on the composition or viscosity of the epoxy resin composition. Specifically, the same temperature conditions as the mixing temperature in the aforementioned method for producing the epoxy resin composition are preferably used. The epoxy resin composition can be impregnated into the fiber-reinforced substrate layer in one step or in multiple steps.

[0187] The solvent method is a method in which an epoxy resin composition is made into a varnish using an appropriate solvent, and the varnish is impregnated into the fiber-reinforced substrate layer.

[0188] Among conventional methods, the hot melt method, which does not use a solvent, is suitable as a method for producing the prepreg of the present disclosure.

[0189] When the epoxy resin composition film is impregnated into the fiber-reinforced substrate layer by the hot melt method, the impregnation temperature is preferably 50°C to 120°C. If the impregnation temperature is 50°C or higher, the viscosity of the epoxy resin composition does not become too high, and the fiber-reinforced substrate layer tends to be sufficiently impregnated. If the impregnation temperature is 120°C or lower, the curing reaction of the epoxy resin composition does not proceed easily, and the deterioration of the storage stability and drapeability of the obtained prepreg tends to be suppressed. The impregnation temperature is more preferably 60°C to 110°C, and even more preferably 70°C to 100°C.

[0190] The impregnation pressure when the epoxy resin composition film is impregnated into the fiber-reinforced substrate layer by the hot melt method is appropriately determined taking into consideration the viscosity of the epoxy resin composition, resin flow, etc. The impregnation pressure is preferably 0.01 N / cm to 250 N / cm, and more preferably 0.1 N / cm to 200 N / cm.

[0191] <Fiber-Reinforced Composite Material> The fiber-reinforced composite material of the present disclosure is a fiber-reinforced composite material comprising a cured epoxy resin product obtained by curing the epoxy resin composition of the present disclosure (i.e., the cured epoxy resin product of the present disclosure) and a fiber-reinforced substrate having reinforcing fibers, wherein the content of the reinforcing fibers is 25% by volume to 75% by volume relative to the total volume of the fiber-reinforced composite material. The fiber-reinforced composite material of the present disclosure preferably comprises a cured epoxy resin product obtained by curing the epoxy resin composition of the present disclosure (i.e., the cured epoxy resin product of the present disclosure) and a fiber-reinforced substrate having reinforcing fibers. The content of the reinforcing fibers in the fiber-reinforced composite material of the present disclosure is preferably 45% by volume to 70% by volume, and more preferably 50% by volume to 65% by volume, relative to the total volume of the fiber-reinforced composite material.

[0192] The epoxy resin composition of the present disclosure has high impregnation ability and handleability for a fiber-reinforced substrate, and can be used to produce a fiber-reinforced composite material with excellent properties. Furthermore, even if the fiber-reinforced composite material of the present disclosure has voids due to cracks, delamination, or the like, the voids can be repaired by subjecting the fiber-reinforced composite material to a process that includes heating.

[0193] <Method for producing fiber-reinforced composite material> The fiber-reinforced composite material of the present disclosure can be obtained by combining a fiber-reinforced substrate having reinforcing fibers with the epoxy resin composition of the present disclosure and curing the resulting composite. The fiber-reinforced composite material of the present disclosure can also be obtained by curing the prepreg of the present disclosure described above by heating and pressurizing it under specific conditions. Methods for producing a fiber-reinforced composite material using the prepreg of the present disclosure include known molding methods such as autoclave molding and press molding.

[0194] [Autoclave Molding Method] Autoclave molding is a preferred method for producing the fiber-reinforced composite material of the present disclosure. Autoclave molding involves sequentially placing a prepreg and a film bag in the lower mold of a metal mold, sealing the prepreg between the lower mold and the film bag, evacuating the space formed by the lower mold and the film bag, and then applying heat and pressure in an autoclave molding apparatus. The molding conditions are preferably a temperature rise rate of 1°C / min to 50°C / min, a pressure of 0.2 MPa to 0.7 MPa, and heating and pressurizing at 130°C to 180°C for 1 hour to 12 hours.

[0195] [Press molding method] Press molding is preferably used as a method for producing the fiber-reinforced composite material of the present disclosure. The fiber-reinforced composite material is produced by press molding by heating and pressurizing the prepreg of the present disclosure or a preform formed by laminating the prepregs of the present disclosure using a mold. The mold is preferably heated to a curing temperature in advance.

[0196] The temperature of the mold during press molding is preferably 150°C to 210°C. When the molding temperature is 150°C or higher, the curing reaction can be sufficiently induced, and fiber-reinforced composite materials tend to be obtained with high productivity. When the molding temperature is 210°C or lower, the viscosity of the epoxy resin composition does not become too low, and excessive flow of the epoxy resin composition in the mold can be suppressed. As a result, outflow of the epoxy resin composition from the mold and meandering of the fibers can be suppressed, and high-quality fiber-reinforced composite materials tend to be obtained.

[0197] The molding pressure is preferably 0.05 MPa to 2 MPa, and more preferably 0.2 MPa to 2 MPa. A pressure of 0.05 MPa or higher tends to provide adequate flow of the epoxy resin composition, preventing poor appearance and the occurrence of voids. Furthermore, the prepreg adheres well to the mold, tending to provide a fiber-reinforced composite material with good appearance. A pressure of 2 MPa or lower tends to prevent the epoxy resin composition from flowing more than necessary, making it less likely that the resulting fiber-reinforced composite material will have poor appearance. Furthermore, since no more load than necessary is applied to the mold, deformation of the mold and the like tends to be less likely. The molding time is preferably 1 hour to 8 hours.

[0198] <Examples of Fiber Reinforced Composite Materials> Examples of fiber reinforced composite materials include fiber reinforced plastics (FRP) and carbon fiber reinforced plastics (CFRP).

[0199] <<Method for Repairing Cured Epoxy Resin Materials>> The method for repairing cured epoxy resin materials disclosed herein includes heating a cured epoxy resin material having voids therein at a temperature equal to or higher than the glass transition temperature of the cured epoxy resin material, thereby repairing the voids. The cured epoxy resin materials disclosed herein have excellent self-repairing properties, and are capable of repairing voids that occur inside the material during molding or in the usage environment. Specific examples of voids include cracks and peeling.

[0200] The heating temperature is not particularly limited as long as it is equal to or higher than the glass transition temperature of the cured epoxy resin material. The heating temperature is preferably 160°C or higher, more preferably 180°C or higher, and even more preferably 200°C or higher. Conventional heating methods can be used, and the heating time can be set as desired. A specific example of the method for repairing a cured epoxy resin material disclosed herein is a method in which a cured epoxy resin material having internal voids is heated at 200°C for 1 hour using an autoclave or a blower dryer. Furthermore, the method for repairing a cured epoxy resin material disclosed herein may also include applying pressure in addition to the heating step. A mold or support frame may be used for applying pressure. The pressure applied during pressing is preferably 0.05 MPa to 2 MPa, more preferably 0.2 MPa to 2 MPa, and these pressures may be applied in stages.

[0201] <<Method for Repairing Fiber-Reinforced Composite Materials>> The method for repairing fiber-reinforced composite materials of the present disclosure includes heating a fiber-reinforced composite material having voids therein at a temperature equal to or higher than the glass transition temperature of the fiber-reinforced composite material, thereby repairing the voids. The fiber-reinforced composite material of the present disclosure has excellent self-repairing properties, and is capable of repairing voids that occur inside the material during molding or in the usage environment. Specific examples of voids include cracks and peeling.

[0202] The heating temperature is not particularly limited as long as it is equal to or higher than the glass transition temperature of the fiber-reinforced composite material. The heating temperature is preferably 160°C or higher, more preferably 180°C or higher, and even more preferably 200°C or higher. Conventional known techniques can be used for the heating method, and the heating time can be set as desired. A specific example of the method for repairing a fiber-reinforced composite material of the present disclosure is a method in which a fiber-reinforced composite material having voids therein is heated at 200°C for 1 hour using an autoclave or a blower dryer. Furthermore, the method for repairing a fiber-reinforced composite material of the present disclosure may also include applying pressure in addition to the heating. A mold or support frame may be used for applying pressure. The pressure during pressing is preferably 0.05 MPa to 2 MPa, more preferably 0.2 MPa to 2 MPa, and these pressures may be applied in stages.

[0203] <<Method for Remolding Cured Epoxy Resin Material>> The method for remolding a cured epoxy resin material of the present disclosure includes heating and pressurizing the cured epoxy resin material of the present disclosure at a temperature equal to or higher than the glass transition temperature of the cured epoxy resin material. The cured epoxy resin material of the present disclosure has excellent remoldability and can be remolded even after molding.

[0204] The heating temperature is not particularly limited as long as it is equal to or higher than the glass transition temperature of the cured epoxy resin material. The heating temperature is preferably 160°C or higher, more preferably 180°C or higher, and even more preferably 200°C or higher. Conventionally known techniques can be used for the heating method, and the heating time can be set as desired. Examples of heating means include an autoclave and a blower dryer. Examples of heating conditions include heating at 200°C for 1 hour. A mold or a support frame may be used for pressurization. The pressure during pressurization is preferably 0.05 MPa to 2 MPa, more preferably 0.2 MPa to 2 MPa, and these pressures may be applied stepwise.

[0205] <<Method for Remolding a Fiber-Reinforced Composite Material>> The method for remolding a fiber-reinforced composite material of the present disclosure includes heating and pressurizing the fiber-reinforced composite material of the present disclosure at a temperature equal to or higher than the glass transition temperature of the fiber-reinforced composite material. The fiber-reinforced composite material of the present disclosure has excellent remoldability and can be remolded even after molding.

[0206] The heating temperature is not particularly limited as long as it is equal to or higher than the glass transition temperature of the fiber-reinforced composite material. The heating temperature is preferably 160°C or higher, more preferably 180°C or higher, and even more preferably 200°C or higher. Conventionally known techniques can be used for the heating method, and the heating time can be set as desired. Examples of heating means include an autoclave and a blower dryer. Examples of heating conditions include heating at 200°C for 1 hour. A mold or a support frame may be used for pressurization. The pressure during pressurization is preferably 0.05 MPa to 2 MPa, more preferably 0.2 MPa to 2 MPa, and these pressures may be applied stepwise.

[0207] <<Method for Decomposing Cured Epoxy Resin Material>> The method for decomposing a cured epoxy resin material according to the present disclosure includes contacting the cured epoxy resin material according to the present disclosure with a decomposing agent containing a reducing agent. The cured epoxy resin material according to the present disclosure has excellent resin decomposition properties, and is capable of decomposing the cured epoxy resin material into low molecular weight compounds.

[0208] The reducing agent is not particularly limited as long as it decomposes the cured epoxy resin material, and can be appropriately selected depending on the type of bond contained in the cured epoxy resin material. Examples of reducing agents include dithiothreitol, 2-mercaptoethanol, 1-thioglycerol, glutathione, 2-mercaptoethylamine hydrochloride, cysterine hydrochloride, and tris(2-carboxyethyl)phosphine hydrochloride. The reducing agent is preferably a reducing agent that reduces disulfide bonds. The reducing agents may be used alone or in combination.

[0209] The reducing agent may be used without a solvent, or may be used as a decomposer solution by diluting it with a solvent. The cured epoxy resin material of the present disclosure may be decomposed by immersing it in a decomposer solution containing a reducing agent. The amount of the decomposer solution used is not particularly limited and is determined depending on the shape of the cured epoxy resin material, the decomposition conditions, etc. The amount of the decomposer contained in the decomposer solution is, for example, preferably 1 to 1,000 times, more preferably 1 to 100 times, and even more preferably 1 to 10 times, the amount of the cured epoxy resin material by mass.

[0210] The concentration of the reducing agent in the decomposition agent solution is not particularly limited, but is, for example, preferably 0.1% by mass to 99.9% by mass, more preferably 1% by mass to 80% by mass, and even more preferably 5% by mass to 50% by mass.

[0211] The solvent used for dilution is not particularly limited as long as it can dissolve the reducing agent and decompose the cured epoxy resin material, and may be water or an organic solvent. Examples of the organic solvent used for dilution include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, 1,4-dioxane, tetrahydrofuran, methanol, ethanol, etc., and polar organic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide are particularly preferred because they can completely dissolve the cured epoxy resin material.

[0212] The decomposer may contain, in addition to the reducing agent, an additive that accelerates the decomposition of the cured epoxy resin material. In particular, nitrogen-containing bases such as triethylamine, DBU, and ammonia are preferred because their addition has a high effect of accelerating the decomposition of the cured epoxy resin material.

[0213] In the method for decomposing a cured epoxy resin material according to the present disclosure, in order to accelerate the decomposition of the cured epoxy resin material, the material may be heated at 25°C to 150°C (preferably 25°C to 60°C) for 1 hour to 48 hours (preferably 1 hour to 8 hours), may be appropriately stirred, or may be subjected to ultrasonic treatment as necessary. For example, the decomposition reaction of the cured epoxy resin material may be allowed to proceed while stirring the cured epoxy resin material and the decomposing agent at room temperature (25°C) or 80°C for 8 hours. In the method for decomposing a cured epoxy resin material according to the present disclosure, in order to accelerate the decomposition of the cured epoxy resin material, a pressure of 0.1 MPa to 10 MPa (preferably 0.1 MPa to 1 MPa) may be applied.

[0214] By the method for decomposing an epoxy resin cured material according to the present disclosure, it is preferable that 80% by mass or more of the cured epoxy resin material is decomposed, more preferably 90% by mass or more, even more preferably 95% by mass or more, and it is particularly preferable that 100% by mass or more of the cured epoxy resin material is decomposed, i.e., the entire cured epoxy resin material is decomposed.

[0215] <<Method for recovering reinforcing fibers from a fiber-reinforced composite material>> The method for recovering reinforcing fibers from a fiber-reinforced composite material of the present disclosure includes contacting the fiber-reinforced composite material of the present disclosure with a decomposition agent containing a reducing agent. According to the method for recovering reinforcing fibers from a fiber-reinforced composite material of the present disclosure, by contacting the fiber-reinforced composite material of the present disclosure with the decomposition agent containing a reducing agent, the cured epoxy resin contained in the fiber-reinforced composite material is decomposed and / or dissolved, making it possible to recover the reinforcing fibers.

[0216] The description of the decomposition agent containing a reducing agent in the method for recovering reinforcing fibers from a fiber-reinforced composite material, including definitions, examples, preferred embodiments, etc., is the same as the description of the decomposition agent containing a reducing agent in the <<Method for Decomposing an Epoxy Resin Cured Material>>.

[0217] In the method for recovering reinforced fibers from a fiber-reinforced composite material according to the present disclosure, in order to promote decomposition and / or dissolution of the cured epoxy resin contained in the fiber-reinforced composite material, the fiber-reinforced composite material may be heated at 25°C to 150°C (preferably 25°C to 60°C) for 1 hour to 48 hours (preferably 1 hour to 8 hours), or may be appropriately stirred, or ultrasonicated as necessary. For example, the decomposition and / or dissolution reaction of the cured epoxy resin contained in the fiber-reinforced composite material may be allowed to proceed while stirring the fiber-reinforced composite material and the decomposing agent at room temperature (25°C) or 80°C for 8 hours. In the method for recovering reinforced fibers from a fiber-reinforced composite material according to the present disclosure, in order to promote decomposition and / or dissolution of the cured epoxy resin contained in the fiber-reinforced composite material, the fiber-reinforced composite material may be pressurized at 0.1 MPa to 10 MPa (preferably 0.1 MPa to 1 MPa).

[0218] The method for recovering reinforcing fibers from a fiber-reinforced composite material according to the present disclosure may include decomposing and / or dissolving a cured epoxy resin contained in the fiber-reinforced composite material, and then recovering the reinforcing fibers. The method for recovering the reinforcing fibers is not particularly limited, and the long fibers can be recovered by winding or by filtration. The recovered reinforcing fibers can be recycled into prepregs or fiber-reinforced composite materials. In this process, an oil agent such as a sizing agent may be applied again, if necessary.

[0219] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited thereto. The components and evaluation methods used in the examples and comparative examples are as follows.

[0220] The following epoxy resins and curing agents were prepared for use in the Examples and Comparative Examples. [Epoxy Resin [A]] <Diglycidylamine-Type Epoxy Resin [A1]> "GAN" (trade name) [diglycidyl aniline, epoxy equivalent: 103 g / eq, manufactured by Nippon Kayaku Co., Ltd.] <Epoxy Resins Other Than Diglycidylamine-Type Epoxy Resin [A1]> "jER828" (trade name) [bisphenol A-diglycidyl ether, epoxy equivalent: 189 g / eq, manufactured by Mitsubishi Chemical Corporation] The above "jER" is a registered trademark.

[0221] [Curing Agent [B]] <Curing Agent [B1]> "4,4-DADS" [4,4'-dithiodianiline, active hydrogen equivalent: 62 g / eq, manufactured by Tokyo Chemical Industry Co., Ltd.] "2,2-DADS" [2,2'-dithiodianiline, active hydrogen equivalent: 62 g / eq, manufactured by Tokyo Chemical Industry Co., Ltd.] "APTMDS" [1,3-bis(3-aminopropyl)tetramethyldisiloxane, active hydrogen equivalent: 62 g / eq, manufactured by Tokyo Chemical Industry Co., Ltd.] <Curing Agents Other than Curing Agent [B1]> "MED-J" [trade name: CUREHARD MED-J, 4,4'-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane, active hydrogen equivalent: 71 g / eq, manufactured by Kumiai Chemical Industry Co., Ltd.] The above "CUREHARD" is a registered trademark.

[0222] [Curing accelerator] "TBD" [1,5,7-triazabicyclodecene, manufactured by Tokyo Chemical Industry Co., Ltd.]

[0223] Examples 1 to 5 and Comparative Examples 1 to 3 [1] Preparation of Epoxy Resin Compositions Epoxy resin [A] and other ingredients were weighed in the parts by mass shown in Table 1 below, and mixed using a stirrer at 80°C for 30 minutes to prepare epoxy resin compositions.

[0224] [2] Preparation of cured epoxy resin product and measurement of physical properties (2-1) Preparation of cured epoxy resin product The epoxy resin composition prepared in [1] above was degassed in a vacuum and then poured into a silicone resin mold set to a thickness of 4 mm using a 4 mm silicone resin spacer. The epoxy resin composition in the silicone resin mold was then cured at 120°C for 2 hours, at 150°C for 2 hours, and at 180°C for 2 hours to obtain a cured epoxy resin product with a thickness of 4 mm.

[0225] (2-2) Measurement of Glass Transition Temperature (Tg) The glass transition temperature of the cured epoxy resin material was measured in a nitrogen gas flow at a flow rate of 40 mL / min using a DSC Q2000 differential scanning calorimeter manufactured by TA Instruments. 5 mg±1 mg of the cured epoxy resin material prepared in (2-1) above was sampled and heated from 30°C to 350°C at a rate of 10°C / min, and the inflection point during the transition process on the obtained curve was recorded as the glass transition temperature of the cured epoxy resin material.

[0226] (2-3) Measurement of Stress Relaxation Rate The epoxy resin composition prepared in [1] above was set on 8 mmφ aluminum parallel plates with a gap distance of 2 mm, and cured at 120°C for 2 hours, 150°C for 2 hours, and 180°C for 2 hours to obtain an epoxy resin. Next, the obtained cured epoxy resin was held at a temperature 40°C higher than the glass transition temperature for 2 minutes, and then measured with 6.25 × 10 －３ The modulus value G generated when a displacement of 10 rad was applied was measured for 3600 seconds, and the resulting time plot was recorded. Stress relaxation was measured using a TA Instruments rheometer, Discovery DHR-2, in a nitrogen gas flow of 10 L / min. From the obtained time plot, the stress relaxation rate was calculated using the following formula: [1-((G(min)) / (G(0)))]×100, where G(0) is the modulus value at the start of application of the external force (i.e., 0 seconds after the start of application of the external force). G(min) is the minimum modulus value one hour after the start of application of external force, in other words, the minimum modulus value up to 3600 seconds after the start of application of external force. If the modulus value reaches the lower limit of measurement by the device within 3600 seconds, this value is used. If the modulus value does not reach the lower limit of measurement by the device within one hour after the start of application of external force, this value is used. In the present disclosure, the modulus value G(0) at 0 seconds after the start of application of external force was set to be the same as the modulus value G(0.1) at 0.1 seconds after the start of application of external force to determine the stress relaxation rate.

[0227] The results of the stress relaxation measurements are shown in Table 1 and Figure 1. In Example 1, stress relaxation occurred due to the application of an external force, and the stress relaxation rate 3600 seconds after the start of external force application was 99.7%. In Example 4, stress relaxation occurred due to the application of an external force, and the stress relaxation rate 3600 seconds after the start of external force application was 96.1%. On the other hand, in Comparative Example 1, the stress relaxation rate 3600 seconds after the start of external force application was 67.3%.

[0228] (2-4) Stress Relaxation Mode Separation Analysis The modulus value G(t) at 200°C recorded in (2-3) above was analyzed according to the above-mentioned [Stress Relaxation Mode Separation Analysis]. Stress relaxation mode separation analysis was performed in the range of 0 to 3600 seconds, and the analysis was performed in the following 25 modes: τi = 1, 2.5, 4, 5.5, 7, 8.5, 10, 25, 40, 55, 70, 85, 100, 250, 400, 550, 700, 850, 1000, 2500, 4000, 5500, 7000, 8500, 10000

[0229] The results of the stress relaxation mode separation analysis for Examples 1 and 4 and Comparative Example 1 are shown in Figure 2. In Example 1, the relaxation mode group with a relaxation time of less than 200 seconds had a contribution of 100%, and the relaxation mode group with a relaxation time of 100 seconds or more showed no contribution. In Example 4, the relaxation mode group with a relaxation time of less than 200 seconds had a contribution of 75%, and the relaxation mode group with a relaxation time of 1000 seconds or more had a contribution of 9%.

[0230] (2-5) Confirmation of Remoldability The cured epoxy resin product prepared in (2-1) above was crushed into chips with three sides of 1 mm or less, and the resulting chip-like cured epoxy resin product was used as a sample. Next, 0.7 g of the sample was placed in a mold equipped with an 8 mmφ cylindrical mold frame and preheated at 200°C for 5 minutes. A pressure of 25 MPa was applied in a press at 200°C for 30 minutes to prepare a remoldable sample. The obtained remoldable sample was visually observed. Remoldability was evaluated according to the following criteria, with A and B being considered to be within a practically acceptable range.

[0231] - Criteria - A: The surface of the remolded sample was smooth, and no grain boundaries of the chips were visible when light was passed through it. B: The surface of the remolded sample was smooth, but turbidity due to grain boundaries of the chips was visible when light was passed through it. C: The grain boundaries of the chips before molding were visible on the surface of the remolded sample.

[0232] (2-6) Confirmation of self-repairing ability The epoxy resin cured product prepared in (2-1) above was polished to a thickness of 2 mm, and a crack of about 2 mm was inserted using a razor. Furthermore, the sample was placed on the sample stage of a transmission electron microscope equipped with a heat stage, preheated to 120 ° C., heated to 200 ° C. at a rate of 20 ° C. / min, and finally held at 200 ° C. for 15 minutes to prepare a self-repairing sample. The obtained self-repairing sample was observed using a transmission electron microscope (n = 5). The self-repairing ability was evaluated according to the following criteria, with A and B being considered to be within a practically acceptable range.

[0233] - Criteria - A: The cracks in the self-repairing sample disappeared almost completely. B: The cracks in the self-repairing sample were partially reduced. C: The cracks in the self-repairing sample did not disappear or reduce in size.

[0234] (2-7) Confirmation of Resin Decomposition Property The cured epoxy resin product prepared in (2-1) above was cut into a piece of 1 cm x 1 cm x 0.4 mm, and one piece was immersed in 40 mL of an N,N-dimethylformamide solution containing 4 mL of 1-thioglycerol, and stirred at room temperature (25°C) and 80°C. The state of the solution after 8 hours was visually observed. Resin decomposition property was evaluated according to the following criteria, with A and B being considered to be within a range acceptable for practical use.

[0235] - Criteria - A: The cured epoxy resin material was completely decomposed at room temperature to become a homogeneous solution. B: The cured epoxy resin material was not completely decomposed at room temperature, but 80% by mass or more of the material was decomposed at 80°C. C: The cured epoxy resin material was decomposed by less than 80% by mass at both room temperature and 80°C.

[0236] (2-8) Flexural Modulus (FM) and Flexural Strength (FS) The flexural modulus and flexural strength of the cured epoxy resin product prepared in (2-1) above were measured according to a method in accordance with JIS K 7171:2016 (ISO 178:2010). The cured epoxy resin product was cut into a size of 80 mm x 20 mm x 4 mm (thickness h) to prepare a test piece. The test was conducted under the conditions of a support distance L (unit: mm) = 16 x 4 (thickness h) and a test speed of 2 mm / min, and the flexural modulus and flexural strength of the test piece were measured.

[0237] The various physical properties of the cured resin products obtained by curing the obtained epoxy resin compositions are shown in Table 1. The degree of cure of the cured epoxy resin products obtained by curing the epoxy resin compositions obtained in Examples 1 to 5 and Comparative Examples 1 to 3 was measured by a method (DSC method) in accordance with JIS K 7148-1:2015 (ISO 14322:2012), and was 99.9% or higher in all cases.

[0238]

[0239] From the above, it was found that the epoxy resin compositions of Examples 1 to 5 had excellent remoldability and self-repairing properties in the cured products, even though they used compounds containing dynamic covalent bonding moieties in amounts less than the theoretical equivalent relative to the epoxy resin.

[0240] (2-9) Confirmation of Decomposition Products The decomposition products of the cured epoxy resin material in Example 1 obtained in (2-7) Confirmation of Resin Decomposition Property were analyzed by FT-IR, and it was found that the decomposition products were compounds having the following structure. The analysis of the decomposition products of the cured epoxy resin material was carried out by the ATR method using a Nicolet iS20 FT-IR spectrophotometer manufactured by Thermo Fisher Scientific. The FT-IR measurement results of the decomposition products of the cured epoxy resin material in Example 1 are shown in Figure 3.

[0241]

[0242] From the above, it was confirmed that the cured epoxy resin products obtained by curing the epoxy resin compositions of Examples 1 to 5 have excellent resin decomposition properties and can be decomposed into the above-mentioned low molecular weight compounds.

[0243] The disclosure of Japanese Patent Application No. 2024-057145, filed on March 29, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. An epoxy resin composition comprising at least an epoxy resin [A] and a curing agent [B], wherein the epoxy resin [A] comprises at least a diglycidylamine-type epoxy resin [A1] represented by the following formula (1), and the curing agent [B] comprises at least a curing agent [B1] containing a dynamic covalent bonding moiety Y: In formula (1), R １ａ , R １ｂ , R １ｃ , R １ｄ , and R １ｅ each independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, an alkoxy group, an amino group, or a halogen atom.

2. The epoxy resin composition according to claim 1, wherein the ratio (a1) / (a) of the molar amount (a1) of epoxy groups in the diglycidylamine-type epoxy resin [A1] to the molar amount (a) of epoxy groups in the epoxy resin [A] is in the range of 0.05 or more and 1.0 or less.

3. The epoxy resin composition according to claim 1, wherein the curing agent [B1] contains active hydrogen, and the ratio (b1) / (b) of the molar amount (b1) of active hydrogen in the curing agent [B1] to the molar amount (b) of active hydrogen in the curing agent [B] is in the range of 0.1 or more and 1.0 or less.

4. The epoxy resin composition according to claim 1, wherein the ratio (b1) / (a) of the molar amount (b1) of active hydrogen in the curing agent [B1] to the molar amount (a) of epoxy groups in the epoxy resin [A] is in the range of 0.6 or more and 1.5 or less.

5. An epoxy resin composition according to claim 1, which has been cured to a degree of cure of 90% or more to form a cured product, and when an external force is applied to the cured product at a temperature 40°C higher than the glass transition temperature of the cured product, the stress generated is measured and the stress relaxation rate is 95% or more one hour after the start of application of the external force.

6. The epoxy resin composition according to claim 1, wherein the curing agent [B1] comprises an amine-based curing agent represented by the following formula (2): In formula (2), R １ and R ２ each independently represent an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, an ether group, or a divalent group formed by combining two or more selected from the group consisting of an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, and an ether group, and Y represents a dynamic covalent bond moiety.

7. The epoxy resin composition of claim 1, wherein the dynamic covalent bonding site Y comprises a disulfide bond.

8. The epoxy resin composition according to claim 1, wherein the curing agent [B1] comprises an amine-based curing agent represented by the following formula (3):

9. A cured epoxy resin product obtained by curing the epoxy resin composition according to claim 1.

10. The epoxy resin cured product according to claim 9, in which 80 mass % or more of the epoxy resin cured product dissolves when brought into contact with a decomposing agent containing a reducing agent and heated at 100°C for 48 hours.

11. A cured epoxy resin material that, when contacted with a decomposing agent containing a reducing agent and heated at 100°C for 48 hours, produces a compound containing at least a structure represented by the following formula (7): In formula (7), R ７ａ , R ７ｂ , R ７ｃ , R ７ｄ , and R ７ｅ each independently represents a hydrogen atom, an aliphatic hydrocarbon group having 1 to 20 carbon atoms, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, an alkoxy group, an amino group, or a halogen atom, and * represents a bond.

12. A prepreg obtained by impregnating a fiber-reinforced substrate having reinforcing fibers with the epoxy resin composition according to claim 1 or 2, wherein the content of the reinforcing fibers is 25 to 75 volume % relative to the total volume of the prepreg.

13. A fiber-reinforced composite material comprising the cured epoxy resin according to claim 9 or 10 and a fiber-reinforced substrate having reinforcing fibers, wherein the content of the reinforcing fibers is 25% to 75% by volume relative to the total volume of the fiber-reinforced composite material.

14. A method for repairing a cured epoxy resin material, comprising heating the cured epoxy resin material according to claim 9 or 10, which has voids therein, at a temperature equal to or higher than the glass transition temperature of the cured epoxy resin material, thereby repairing the voids.

15. A method for repairing a fiber-reinforced composite material, comprising heating the fiber-reinforced composite material according to claim 13, which has voids therein, at a temperature equal to or higher than the glass transition temperature of said fiber-reinforced composite material, thereby repairing said voids.

16. A method for remolding a cured epoxy resin product according to claim 9 or 10, comprising heating and pressurizing the cured epoxy resin product at a temperature equal to or higher than the glass transition temperature of the cured epoxy resin product.

17. A method for remolding a fiber-reinforced composite material, comprising heating and pressurizing the fiber-reinforced composite material according to claim 13 at a temperature equal to or higher than the glass transition temperature of said fiber-reinforced composite material.

18. A method for decomposing a cured epoxy resin material, comprising contacting the cured epoxy resin material according to claim 9 or 10 with a decomposing agent containing a reducing agent.

19. A method for recovering reinforcing fibers from a fiber-reinforced composite material, comprising contacting the fiber-reinforced composite material according to claim 13 with a decomposition agent containing a reducing agent.

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