The present invention relates to an epoxy resin composition, a cured epoxy resin, a prepreg, a fiber-reinforced composite material, a method for repairing a cured epoxy resin, a method for repairing a fiber-reinforced composite material, a method for remolding a cured epoxy resin, and a method for remolding a fiber-reinforced composite material. Epoxy resin cured product decomposition method and reinforced fiber recovery method for fiber-reinforced composite material

Abstract

The epoxy resin composition contains a polyphenol compound [A] containing at least a structural unit represented by general formula (1) and an epoxy resin [B], and the ratio (a) / (b) of the molar weight (a) of phenolic hydroxyl groups in the polyphenol compound [A] to the molar weight (b) of epoxy groups in the epoxy resin [B] is 0.25-1.5. When the stress generated when an external force is applied to a cured product obtained by curing to a curing degree of 90% or more at a temperature 60 DEG C higher than the glass transition temperature of the cured product is measured, the stress relaxation rate at the time point 1 hour from the start of the application of the external force is 90% or more.

Description

Technical Field

[0001] This disclosure relates to epoxy resin compositions, epoxy resin cured products, prepreg blanks, fiber-reinforced composite materials, methods for repairing epoxy resin cured products, methods for repairing fiber-reinforced composite materials, methods for remolding epoxy resin cured products, methods for remolding fiber-reinforced composite materials, methods for decomposing epoxy resin cured products, and methods for recycling reinforcing fibers from fiber-reinforced composite materials. Background Technology

[0002] Fiber-reinforced composite materials, obtained by combining reinforcing fiber materials such as carbon fiber, glass fiber, or aramid fiber with various matrix resins, are widely used in various fields and applications. In the past, in aerospace and industrial fields where high mechanical properties and heat resistance are required, thermosetting resins such as unsaturated polyester resin, epoxy resin, or polyimide resin were mainly used as matrix resins.

[0003] However, once these thermosetting resins have hardened, they lose their fluidity even when heated, making them impossible to reshape or deform. Consequently, scraps and defective products from the hardened material generated during the manufacturing process are discarded. Various improvements have been made to the manufacturing process to reduce waste, but it is difficult to reduce waste solely through process modifications.

[0004] Therefore, based on the above background, improvements to resin compositions have been studied. Among these, the following method has attracted attention: introducing chemically bonded sites (also known as dynamic covalently bonded sites) into the resin composition that can be exchanged through rebonding after pyrolysis or direct recombination of bonded components, thereby reusing scraps and defective molded products from the cured product. In this method, the exchangeable chemically bonded sites are pyrolyzed or continuously exchanged through heating, thereby releasing the constraints imposed by the network structure within the cured product, making the resin fluid and capable of being reformulated.

[0005] For example, Patent Document 1 discloses an epoxy resin composition that uses a compound containing disulfide bonds as chemical bonding sites that can be exchanged through direct recombination of the bonded components as a curing agent.

[0006] Patent Document 1: International Publication No. 2015 / 181054 Summary of the Invention

[0007] The problem that the invention aims to solve However, regarding the epoxy resin composition described in Patent Document 1, in order to achieve sufficient fluidity in the cured product, it is necessary to use excessive amounts of expensive compounds containing disulfide bonds. On the other hand, if a curing agent exceeding the theoretical equivalent is used relative to the epoxy resin, there is also the disadvantage that the heat resistance and mechanical properties of the cured product are greatly impaired.

[0008] This disclosure is made in view of the foregoing, and relates to epoxy resin compositions that exhibit excellent reformability or self-healing properties even when using compounds with dynamic covalent bonding sites that are close to the theoretical equivalent of epoxy resins, epoxy resin cured products obtained by curing the aforementioned epoxy resin compositions, prepreg blanks, fiber-reinforced composite materials, methods for repairing epoxy resin cured products, methods for repairing fiber-reinforced composite materials, methods for reforming epoxy resin cured products, methods for reforming fiber-reinforced composite materials, methods for decomposing epoxy resin cured products, and methods for recycling reinforcing fibers of fiber-reinforced composite materials.

[0009] Methods for solving problems The specific means to solve the above problems include the following methods.

[0010] <1> An epoxy resin composition comprising a polyphenolic compound [A] containing at least a structural unit represented by the following general formula (1) and an epoxy resin [B]. The ratio (a) / (b) of the molar amount of phenolic hydroxyl groups (a) in the aforementioned polyphenolic compound [A] to the molar amount of epoxy groups (b) in the aforementioned epoxy resin [B] is 0.25 or more and 1.5 or less. When an external force is applied to a cured product that has been cured to a degree of curing of 90% or more at a temperature 60°C higher than the glass transition temperature of the cured product, the stress relief rate at a time point of 1 hour from the start of the application of the external force is measured to be 90% or more.

[0011] [Chemical Formula 1] (In general formula (1), Y is an independent dynamic covalent bonding site, R 1a R 1b R 1c and R 1d At least one of them is a connecting bond with Y in other adjacent structural units, and the others independently represent any one of hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom, where n represents an integer from 2 to 500. <2> like <1> The epoxy resin composition wherein the aforementioned dynamic covalent bonding site is a group containing a disulfide bond.

[0012] <3> like <1> or <2> The epoxy resin composition, wherein the aforementioned polyphenolic compound [A] comprises a polyphenolic compound containing a structural unit represented by the following general formula (2).

[0013] [Chemical Formula 2] (In general formula (2), R) 2a R 2b and R 2c Each group independently represents any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom, where n represents an integer from 2 to 500. <4> like <1> ~ <3> The epoxy resin composition described in any one of the above-mentioned polyphenolic compounds [A] comprises a polyphenolic compound containing a structural unit represented by the following general formula (3).

[0014] [Chemical Formula 3] (In general formula (3), R3 independently represents any one of hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom, and n represents an integer from 2 to 500.) <5> like <1> ~ <4> The epoxy resin composition described in any one of the above statements is a curing agent.

[0015] <6> Epoxy resin cured products are those that make <1> ~ <5> The epoxy resin composition described in any one of the above is cured to form the epoxy resin composition.

[0016] <7> When epoxy resin cured products are brought into contact with a decomposing agent containing a reducing agent and heated at 100°C for 48 hours, more than 80% by mass of the cured product dissolves.

[0017] <8> An epoxy resin cured product, when brought into contact with a decomposing agent containing a reducing agent and heated, produces a compound having at least the structure shown in the following general formula (4).

[0018] [Chemical Formula 4] (in general formula (4), Indicates a connection key. R 4a R 4b and R 4c Each can independently represent any one of the following: a hydrogen atom, an aliphatic hydrocarbon group, an aromatic group, an alkoxy group, an amino group, or a halogen atom. <9> Prepreg blank, which is made of <1> ~ <5> The epoxy resin composition described in any one of the above is formed by impregnating a fiber-reinforced substrate having reinforcing fibers, wherein the content of the aforementioned reinforcing fibers is 25% to 75% by volume relative to the total volume of the prepreg blank.

[0019] <10> Fiber-reinforced composite materials, which contain <6> ~ <8> The epoxy resin cured product and the fiber-reinforced substrate having reinforcing fibers as described in any one of the above, wherein the content of the aforementioned reinforcing fibers is 25% to 75% by volume relative to the total volume of the fiber-reinforced composite material.

[0020] <11> A method for repairing epoxy resin cured materials includes the following steps: removing internal cracks or peeling. <6> ~ <8> The epoxy resin cured product described in any one of the above-mentioned epoxy resin cured products is heated at a temperature above the glass transition temperature of the aforementioned epoxy resin cured product, thereby repairing the aforementioned cracks or peeling.

[0021] <12> A method for repairing fiber-reinforced composite materials includes the following steps: repairing internally cracked or peeling composite materials. <10> The fiber-reinforced composite material is heated at a temperature above the glass transition temperature of the aforementioned fiber-reinforced composite material to repair the aforementioned cracks or peeling.

[0022] <13> A method for remolding epoxy resin cured products, comprising the following steps: ... <6> ~ <8> The epoxy resin cured product described in any one of the above-mentioned epoxy resin cured products is heated and pressurized at a temperature above the glass transition temperature of the epoxy resin cured product.

[0023] <14> A method for remolding fiber-reinforced composite materials includes the following steps: [The text abruptly ends here, so the translation stops.] <10> The fiber-reinforced composite material is heated and pressurized at a temperature above the glass transition temperature of the aforementioned fiber-reinforced composite material.

[0024] <15> A method for decomposing epoxy resin cured products includes the following steps: making... <6> ~ <8> The epoxy resin cured product described in any one of the above statements is in contact with a decomposing agent containing a reducing agent.

[0025] <16> A method for recycling reinforcing fibers in fiber-reinforced composite materials includes the following steps: making... <10> The fiber-reinforced composite material is in contact with a decomposing agent containing a reducing agent.

[0026] Invention Effects According to this disclosure, it is possible to provide epoxy resin compositions with excellent reformability or self-healing properties in cured products, even when using compounds with dynamic covalent bonding sites that are close to the theoretical equivalent of epoxy resins; epoxy resin cured products obtained by curing the aforementioned epoxy resin compositions; prepreg blanks; fiber-reinforced composite materials; repair methods for epoxy resin cured products; repair methods for fiber-reinforced composite materials; reforming methods for epoxy resin cured products; reforming methods for fiber-reinforced composite materials; decomposition methods for epoxy resin cured products; and methods for recycling reinforcing fibers of fiber-reinforced composite materials. Attached Figure Description

[0027] [ Figure 1 ] Figure 1 A graph showing the results of the stress relief measurement.

[0028] [ Figure 2 ] Figure 2 A graph showing the results of the stress relief mode separation analysis. Detailed Implementation

[0029] The following is a detailed description of one embodiment of this disclosure. However, this disclosure is not limited to the following embodiment. In the following disclosure, its constituent elements (including element steps, etc.) are not essential unless specifically stated otherwise. The same applies to numerical values ​​and their ranges; they are not intended to limit this disclosure.

[0030] In this disclosure, the values ​​before and after “~” in the numerical range indicated by “~” are included as the lower limit and upper limit, respectively.

[0031] In the numerical ranges described in this disclosure, the upper or lower limit of one numerical range can be replaced with the upper or lower limit of another numerical range described in other stages. Furthermore, the upper or lower limit of a numerical range described in this disclosure can be replaced with the values ​​shown in the embodiments.

[0032] In this disclosure, the percentage of each component in the composition refers to the total percentage of the various substances present in the composition, unless otherwise specified, when multiple substances belonging to each component are present in the composition.

[0033] In this public document, when multiple elements are listed using "or" or "or", unless otherwise explicitly stated, the possibility of combining multiple elements is not excluded as long as no technical contradiction arises.

[0034] In this disclosure, even when elements are expressed in a singular form, multiple instances are not excluded unless otherwise expressly stated, provided that no technical contradiction arises.

[0035] In this public document, multiple examples described separately can be combined to form new methods, provided they do not contradict each other.

[0036] ≪Epoxy Resin Compositions≫ The epoxy resin composition disclosed herein comprises a polyphenolic compound [A] containing at least a structural unit represented by the following general formula (1) and an epoxy resin [B]. The ratio (a) / (b) of the molar amount of phenolic hydroxyl groups (a) in the aforementioned polyphenolic compound [A] to the molar amount of epoxy groups (b) in the aforementioned epoxy resin [B] is 0.25 or more and 1.5 or less. When an external force is applied to a cured product that has been cured to a degree of curing of 90% or more at a temperature 60°C higher than the glass transition temperature of the cured product, the stress relief rate at a time point of 1 hour from the start of the application of the external force is measured to be 90% or more.

[0037] [Chemical Formula 5] In general formula (1), Y is an independent dynamic covalent bonding site, and R 1a R 1b R 1c and R 1d At least one of them is a connecting bond between it and Y in other adjacent structural units, and each of the others independently represents any one of hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom, and n represents an integer from 2 to 500.

[0038] The epoxy resin compositions disclosed herein provide excellent reformability or self-healing properties in the cured product, even when using compounds with dynamic covalent bonding sites in amounts close to the theoretical equivalent relative to the epoxy resin. It should be noted that, in this disclosure, reformability refers to the adhesion of multiple cured products to each other without visible grain boundaries on the surface. Self-healing refers to the disappearance or reduction of cracks in the cured product.

[0039] Although the function of the epoxy resin composition in this disclosure is not clear, it can be inferred as follows.

[0040] The epoxy resin composition disclosed herein comprises a polyphenolic compound [A] containing at least a structural unit represented by general formula (1) and an epoxy resin [B]. In general formula (1), Y is independently a dynamic covalent bonding site. In this disclosure, a dynamic covalent bonding site refers to a covalent bonding site that can be exchanged through rebonding after cleavage or through direct recombination of the bonded components.

[0041] More specifically, as shown in the reaction formulas below, dynamic covalent bonding sites are classified as follows: dissociative dynamic covalent bonding sites that undergo complete cleavage under specific conditions and then rebond under other conditions; cooperative dynamic covalent bonding sites that cooperate in bond dissociation and rebonding; and asociative dynamic covalent bonding sites that undergo dissociation after bond formation.

[0042] So-called dissociative-rebonding dynamic covalent bonding sites are bonding sites where the equilibrium constants of dissociation and rebonding reactions are highly temperature-dependent, and where dissociation and rebonding reactions occur in different temperature regions. In other words, they are bonding sites where two sets of covalent bonds temporarily dissociate completely in a high-temperature region, then exchange and rebond with each other in a low-temperature region, thereby reversibly forming a new combination of two sets of covalent bonds.

[0043] Cooperative dynamic covalent bonding sites are bonding sites where the equilibrium constants of dissociation and rebonding reactions have low temperature dependence and where the cleavage and rebonding of two sets of covalent bonds occur cooperatively within a specific temperature range. In other words, they are bonding sites where the dissociation of two sets of covalent bonds, the exchange of bonding partners, and rebonding occur simultaneously within a specific temperature range, thereby reversibly forming new combinations of two sets of covalent bonds.

[0044] Asociative dynamic covalent bonding sites are bonding sites that undergo dissociation reactions after bonding reactions. That is, they are covalent bonding sites that are in a free state after cleavage, and through heating, they form bonds with a certain set of covalent bonds and recombine, thereby reversibly forming a new set of covalent bonds.

[0045] That is, with regard to the cured epoxy resin composition of this disclosure, i.e., the epoxy resin cured product, the dynamic covalent bonding sites are reversibly exchanged by heating, thereby enabling the molecular network inside the cured product to change continuously, thus resulting in excellent flowability, remolding or self-healing properties.

[0046] [Chemical Formula 6] Furthermore, with respect to the epoxy resin composition of this disclosure, the ratio (a) / (b) of the molar amount (a) of the phenolic hydroxyl group in the polyphenol compound [A] to the molar amount (b) of the epoxy group in the epoxy resin [B] is 0.25 or more and 1.5 or less.

[0047] If the ratio (a) / (b) is less than 0.25, the properties brought by the dynamic covalent bonding sites in the polyphenol compound [A] cannot be fully utilized, and the remolding or self-healing properties are impaired. If the ratio (a) / (b) is greater than 1.5, the molar equilibrium between the epoxy groups in the epoxy resin [B] and the phenolic hydroxyl groups in the polyphenol compound [A] collapses, the crosslinking density of the resulting epoxy resin cured product becomes insufficient, and mechanical properties such as heat resistance, elastic modulus, or fracture toughness become lower.

[0048] Furthermore, regarding the epoxy resin composition of this disclosure, when an external force is applied to a cured product that has been cured to a degree of curing of 90% or more at a temperature 60°C higher than the glass transition temperature of the cured product, the stress relief rate at a time point of 1 hour from the start of the application of the external force is 90% or more.

[0049] In this disclosure, the stress relief rate at a time point one hour after the application of the external force is determined by the following formula.

[0050] [1 - (Stress 1 hour after the application of external force) / (Stress at the start of the application of external force)] × 100 In other words, a stress mitigation rate of over 90% at one hour from the start of the application of external force means that the stress, which was 100% at the start of the application of external force, gradually decreases to less than 10% after one hour, and the cured material becomes fluid. Because of this fluidity, the cured material can exhibit reshaping or self-healing properties.

[0051] As explained above, the epoxy resin compositions of this disclosure, due to the aforementioned mechanism, provide epoxy resin compositions with excellent reformability or self-healing properties in the cured product, even when using compounds with dynamic covalent bonding sites that are close to the theoretical equivalent relative to the epoxy resin. It should be noted that this disclosure is not limited to the aforementioned inference mechanism.

[0052] <Polyphenolic compound [A]> [General Formula (1)] The epoxy resin composition of this disclosure comprises a polyphenolic compound [A] containing at least a structural unit represented by the following general formula (1). Preferably, the epoxy resin composition of this disclosure comprises a polyphenolic compound [A] consisting of a structural unit represented by the following general formula (1).

[0053] [Chemical Formula 7] In general formula (1), Y is an independent dynamic covalent bonding site, and R 1a R 1b R 1c and R 1d At least one of them is a connecting bond between it and Y in other adjacent structural units, and each of the others independently represents any one of hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom, and n represents an integer from 2 to 500.

[0054] (Y) In general formula (1), Y is an independent dynamic covalent bonding site.

[0055] As the aforementioned dynamic covalent bonding site, it is preferably a group comprising at least one of the following groups: Diels-Alder type bond, imine bond, disulfide bond, ester bond, urethane bond, carbonate bond, vinylogous urethane bond, borate bond, and silyl ether bond.

[0056] It should be noted that Diels-Alder type bonds are temperature-dependent, dissociative-rebonding dynamic covalent bonding sites where the equilibrium constants of dissociation and rebonding reactions are highly dependent. These are covalent bonds where two sets of covalent bonds temporarily dissociate completely in a high-temperature region and then rebond in a low-temperature region. In other words, the exchange of bonding elements between two sets of covalent bonds that break down through heating, forming a new combination, can be reversibly achieved through two stages of heating.

[0057] Imine and disulfide bonds are cooperative dynamic covalent bonding sites with low temperature dependence on the equilibrium constants of dissociation and rebonding reactions. They are bonding sites where the cleavage and rebonding of two sets of covalent bonds occur cooperatively within a specific temperature range. In other words, they are bonding sites where the dissociation of two sets of covalent bonds, the exchange of bonding partners, and rebonding occur simultaneously within a specific temperature range, thereby reversibly forming new combinations of two sets of covalent bonds.

[0058] Ester bonds, urethane bonds, carbonate bonds, intercalated urethane bonds, borate bonds, and silyl ether bonds are bonding sites that undergo dissociation reactions after bonding formation. That is, they are covalent bonding sites that are in a free state after cleavage, which, upon heating, form bonds with a certain set of covalent bonds and recombine, thereby reversibly forming a new set of covalent bonds.

[0059] From the viewpoint that recrystallization can be achieved through a single stage of heating without requiring strict temperature control such as cooling, the aforementioned dynamic covalent bonding site is preferably a cooperative or asociative dynamic covalent bonding site. From the viewpoint that no catalyst is needed to promote bond exchange, the aforementioned dynamic covalent bonding site is more preferably a group comprising at least one selected from the group consisting of imine bonds, intercalated carbamate bonds, silyl ether bonds, and disulfide bonds. From the viewpoint that the bond exchange rate is very fast, the aforementioned dynamic covalent bonding site is preferably a group comprising a disulfide bond, and more preferably a disulfide bond.

[0060] Diels-Alder type bonds are represented by formula (Y-1-a) or formula (Y-1-b) below, disulfide bonds are represented by formula (Y-2) below, imine bonds are represented by formula (Y-3) below, ester bonds are represented by formula (Y-4) below, urethane bonds are represented by formula (Y-5) below, carbonate bonds are represented by formula (Y-6) below, intercalated urethane bonds are represented by formula (Y-7) below, borate ester bonds are represented by formula (Y-8) or formula (Y-9) below, and silyl ether bonds are represented by formula (Y-10) below.

[0061] [Chemical Formula 8] In the above equations (Y-1-a) to (Y-10), This indicates a connecting bond. In formula (Y-1-a), X is preferably oxygen or amino, and R in formulas (Y-7) and (Y-10) is... Y1 R Y2 and R Y3 Each is preferably an aliphatic hydrocarbon group, an aromatic group, or an alkoxy group, more preferably an aliphatic hydrocarbon group or an aromatic group having 4 or fewer carbon atoms, and even more preferably methyl, ethyl, or phenyl. In formula (Y-9), k and l are each preferably integers from 0 to 10, more preferably integers from 0 to 5, and even more preferably integers from 0 to 2.

[0062] (R) 1a R 1b R 1c and R 1d ) In general formula (1), R 1a R 1b R 1c and R 1dAt least one of the bonds is a linking bond with Y in other adjacent structural units, and the others independently represent any one of hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom. From the viewpoint of the heat resistance and mechanical properties of the cured product, hydrogen atom is preferred among the others. From the viewpoint of the toughness of the cured product, aliphatic hydrocarbon group is preferred among the others.

[0063] In general formula (1), it is more preferable that R 1a R 1b R 1c and R 1d Any one of them is a connecting bond between the Y in the adjacent structural unit and the other three connecting bonds independently represent any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom.

[0064] In general formula (1), it is further preferred that R 1d R serves as the connection bond between Y and other adjacent structural units. 1a R 1b and R 1c Each can independently represent any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom.

[0065] In general formula (1), it is particularly preferred that R 1d R serves as the connection bond between Y and other adjacent structural units. 1a and R 1c For hydrogen atoms, R 1b It represents any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom.

[0066] It should be noted that in general formula (1), R 1a R 1b R 1c and R 1d In this context, there can be one connection key between Y and other adjacent structural units, or two, three, or four connection keys between Y and other adjacent structural units.

[0067] R in general formula (1) 1a R 1b R 1c 、or R 1dIn this formulation, the aliphatic hydrocarbon group can be any group selected from straight-chain aliphatic hydrocarbon groups, branched aliphatic hydrocarbon groups, or alicyclic hydrocarbon groups, preferably an aliphatic hydrocarbon group with 1 to 18 carbon atoms, more preferably an aliphatic hydrocarbon group with 1 to 15 carbon atoms, and even more preferably an aliphatic hydrocarbon group with 1 to 10 carbon atoms. Furthermore, the aliphatic hydrocarbon group can be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group, more preferably a saturated aliphatic hydrocarbon group.

[0068] (n) In general formula (1), n ​​represents an integer from 2 to 500. When n is greater than 500, the viscosity of the polyphenol compound [A] increases, making mixing or handling with epoxy resin more difficult, and reducing its impregnation into the fiber-reinforced substrate. When n is less than 2, the heat resistance, flowability, reformability, and self-healing properties of the cured product are significantly reduced. n preferably represents an integer from 3 to 100, and more preferably an integer from 5 to 50.

[0069] [General formula (1-a) ~ (1-d)] The aforementioned polyphenolic compound [A] preferably comprises a polyphenolic compound containing a structural unit represented by any of the following general formulas (1-a) to (1-d). More preferably, the aforementioned polyphenolic compound [A] comprises a polyphenolic compound composed of a structural unit represented by any of the following general formulas (1-a) to (1-d). The aforementioned polyphenolic compound [A] is even more preferably a polyphenolic compound composed of a structural unit represented by any of the following general formulas (1-a) to (1-d). From the viewpoint of the solubility and thermal meltability of the polyphenolic compound in epoxy resin, the aforementioned polyphenolic compound [A] is extremely preferably a polyphenolic compound composed of a structural unit represented by the following general formula (1-a).

[0070] [Chemical Formula 9] In general formulas (1-a) to (1-d), Y is an independent dynamic covalent bonding site, and R 1e R 1f and R 1g Each group independently represents any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom, where n represents an integer from 2 to 500.

[0071] (Y) In general formulas (1-a) to (1-d), Y is an independent dynamic covalent bonding site.

[0072] The descriptions of Y in general formulas (1-a) to (1-d), including definitions, examples, and preferred methods, are the same as those in general formula (1).

[0073] (R) 1e R1f and R 1g ) In the general formulas (1-a) to (1-d), R 1e R 1f and R 1g Each can independently represent any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom. From the viewpoint of the heat resistance and mechanical properties of the cured product, R... 1e R 1f and R 1g Preferably, it contains hydrogen atoms. From the viewpoint of the toughness of the cured product, R... 1e R 1f and R 1g Preferably, it contains aliphatic hydrocarbon groups.

[0074] R in general formulas (1-a)~(1-d) 1e R 1f and R 1g In this formulation, the aliphatic hydrocarbon group can be any group selected from straight-chain aliphatic hydrocarbon groups, branched aliphatic hydrocarbon groups, or alicyclic hydrocarbon groups, preferably an aliphatic hydrocarbon group with 1 to 18 carbon atoms, more preferably an aliphatic hydrocarbon group with 1 to 15 carbon atoms, and even more preferably an aliphatic hydrocarbon group with 1 to 10 carbon atoms. Furthermore, the aliphatic hydrocarbon group can be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group, more preferably a saturated aliphatic hydrocarbon group.

[0075] (n) The descriptions of n in general formulas (1-a) to (1-d), including definitions, examples, and preferred methods, are the same as those in general formula (1).

[0076] [General Formula (2)] With regard to the epoxy resin composition of this disclosure, it is preferred that the aforementioned polyphenolic compound [A] comprises a polyphenolic compound containing a structural unit represented by the following general formula (2). More preferably, the aforementioned polyphenolic compound [A] comprises a polyphenolic compound composed of a structural unit represented by the following general formula (2). The aforementioned polyphenolic compound [A] is further preferably a polyphenolic compound composed of a structural unit represented by the following general formula (2).

[0077] [Chemical Formula 10] In general formula (2), R 2a R 2b and R 2c Each group independently represents any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom, where n represents an integer from 2 to 500.

[0078] That is, the polyphenolic compound [A] of this disclosure preferably has a phenolic structure and a disulfide bond in the structural unit, and has a phenolic hydroxyl group (OH group) and a disulfide bond in the ortho position of each phenolic structure.

[0079] (R) 2a R 2b and R 2c ) In general formula (2), R 2a R 2b and R 2c Each can independently represent any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom. From the viewpoint of the heat resistance and mechanical properties of the cured product, R... 2a R 2b and R 2c Preferably, it contains hydrogen atoms. From the viewpoint of the toughness of the cured product, R... 2a R 2b and R 2c Preferably, it contains aliphatic hydrocarbon groups.

[0080] R in general formula (2) 2a R 2b and R 2c In this formulation, the aliphatic hydrocarbon group can be any group selected from straight-chain aliphatic hydrocarbon groups, branched aliphatic hydrocarbon groups, or alicyclic hydrocarbon groups, preferably an aliphatic hydrocarbon group with 1 to 18 carbon atoms, more preferably an aliphatic hydrocarbon group with 1 to 15 carbon atoms, and even more preferably an aliphatic hydrocarbon group with 1 to 10 carbon atoms. Furthermore, the aliphatic hydrocarbon group can be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group, more preferably a saturated aliphatic hydrocarbon group.

[0081] (n) In general formula (2), n represents an integer from 2 to 500. When n is greater than 500, the viscosity of the polyphenol compound [A] increases, making mixing or handling with epoxy resin more difficult, and reducing its impregnation into the fiber-reinforced substrate. When n is less than 2, the heat resistance, flowability, reformability, and self-healing properties of the cured product are significantly reduced. n preferably represents an integer from 3 to 100, and more preferably an integer from 5 to 50.

[0082] [General Formula (3)] With regard to the epoxy resin composition of this disclosure, it is preferred that the aforementioned polyphenolic compound [A] comprises a polyphenolic compound containing a structural unit represented by the following general formula (3). More preferably, the aforementioned polyphenolic compound [A] comprises a polyphenolic compound composed of a structural unit represented by the following general formula (3). The aforementioned polyphenolic compound [A] is further preferably a polyphenolic compound composed of a structural unit represented by the following general formula (3).

[0083] [Chemical Formula 11] In general formula (3), R3 independently represents any one of hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom, and n represents an integer from 2 to 500.

[0084] (R3) In general formula (3), R3 independently represents any one of hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom. From the viewpoint of heat resistance and mechanical properties of the cured product, R3 is preferably hydrogen atom. From the viewpoint of toughness of the cured product, R3 is preferably aliphatic hydrocarbon group. From the viewpoint of workability of epoxy resin composition (uncured product), R3 is preferably quaternary carbon.

[0085] In formula (3), R3 can be any group of straight-chain aliphatic hydrocarbon group, branched aliphatic hydrocarbon group, or alicyclic hydrocarbon group, preferably an aliphatic hydrocarbon group with 1 to 18 carbon atoms, more preferably an aliphatic hydrocarbon group with 1 to 15 carbon atoms, and even more preferably an aliphatic hydrocarbon group with 1 to 10 carbon atoms. In addition, the aliphatic hydrocarbon group can be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group, more preferably a saturated aliphatic hydrocarbon group.

[0086] (n) In general formula (3), n represents an integer from 2 to 500. When n is greater than 500, the viscosity of the polyphenol compound [A] increases, making mixing or handling with epoxy resin more difficult, and reducing its impregnation into the fiber-reinforced substrate. When n is less than 2, the heat resistance, flowability, reformability, and self-healing properties of the cured product are significantly reduced. n preferably represents an integer from 3 to 100, and more preferably an integer from 5 to 50.

[0087] (Examples of compounds represented by general formula (3)) When each of R3 in general formula (3) is an aliphatic hydrocarbon group with one carbon atom, the mechanical properties of the cured product are improved, and therefore it is preferred. As an example of a compound represented by general formula (3), a compound with the following chemical formula (3-1) can be cited.

[0088] [Chemical Formula 12] In chemical formula (3-1), n ​​represents an integer from 2 to 500, preferably an integer from 3 to 100, and more preferably an integer from 5 to 50.

[0089] When R3 in general formula (3) is a methoxy group, the mechanical properties of the cured product, especially the elastic modulus, are improved, and therefore it is preferred. As an example of a compound represented by general formula (3), a compound with the following chemical formula (3-2) can be cited.

[0090] [Chemical Formula 13] In chemical formula (3-2), n represents an integer from 2 to 500, preferably an integer from 3 to 100, and more preferably an integer from 5 to 50.

[0091] As the polyphenolic compound [A] of this disclosure, examples of compounds with the following chemical formulas (3-3) and (3-4) can also be cited. When each of the R3 groups in the general formula (3) is an aliphatic hydrocarbon group containing 4 to 5 carbon atoms, the crystallinity of the polyphenolic compound is reduced, thereby improving the workability of the epoxy resin composition (i.e., the uncured product), which is therefore preferred.

[0092] [Chemical Formula 14] [Chemical Formula 15] In chemical formulas (3-3) and (3-4), n represents an integer from 2 to 500, preferably an integer from 3 to 100, and more preferably an integer from 5 to 50.

[0093] Properties of polyphenolic compound [A] The weight-average molecular weight of the polyphenolic compound [A] in this disclosure is preferably 5,000 to 100,000, more preferably 5,000 to 10,000, and even more preferably 500 to 5,000. It should be noted that in this disclosure, the weight-average molecular weight is determined by gel permeation chromatography (GPC) of a sample that has been pre-silylated using silylating agents such as N,O-bis(trimethylsilyl)trifluoroacetamide.

[0094] The softening point of the polyphenolic compound [A] in this disclosure, as determined according to JIS K5601-2-2:1999 (ISO 4625:1980), is preferably 30°C to 150°C, more preferably 50°C to 120°C, and even more preferably 70°C to 110°C. It should be noted that in this disclosure, the softening point is determined according to JIS K5601-2-2:1999 (ISO 4625:1980).

[0095] The hydroxyl equivalent of the polyphenolic compound [A] disclosed herein is preferably 160 g / Eq to 1000 g / Eq, more preferably 160 g / Eq to 500 g / Eq, and even more preferably 160 g / Eq to 300 g / Eq. It should be noted that, in this disclosure, the hydroxyl equivalent of the polyphenolic compound is determined by the hydroxyl value obtained using the acetylation method shown in JIS K0070:1992 (ASTM D2896-15), and calculated using the following formula.

[0096] [Hydroxy equivalent] = 56.1 × 1000 ÷ [Hydroxy value] [Synthetic method of polyphenolic compound [A]] The polyphenolic compound [A] disclosed herein can be synthesized using any method, for example, by reacting a phenolic analog compound as a starting material with sulfur chloride. More specifically, it can be synthesized using the methods described in the examples below.

[0097] Regarding phenol analog compounds used as raw materials, examples include: R in general formula (1). 1a R 1b R 1c and R 1d Phenol with 3 hydrogen atoms; R in general formula (1) 1a R 1b R 1c and R 1d The phenols are cresols with two hydrogen atoms and one methyl atom, ethylphenols with an ethyl atom, cyclohexylphenols with a cyclohexyl group, methoxyphenols with a methoxy group, aminophenols with an amino group, hydroxybenzaldehyde with an aldehyde group, hydroxybenzoic acid with a carboxyl group, or halogenated phenols with halogen groups such as chlorine, bromine, or iodine.

[0098] Furthermore, R in general formula (1) 1a R 1b R 1c and R 1d The group in the middle that is not a connecting bond between the Y in the adjacent structural unit. Individual examples include aliphatic hydrocarbon groups with 1 to 18 carbon atoms, unsaturated aliphatic hydrocarbon groups with 2 to 18 carbon atoms, aromatic groups with 6 to 12 carbon atoms, or alicyclic hydrocarbon groups with 3 to 10 carbon atoms. Alternatively, each can be an alkoxy group having an aliphatic hydrocarbon group with 1 to 18 carbon atoms, an unsaturated aliphatic hydrocarbon group with 2 to 18 carbon atoms, an aromatic group with 6 to 12 carbon atoms, or an alicyclic hydrocarbon group with 3 to 10 carbon atoms.

[0099] [Types of structural units in polyphenolic compound [A]] The polyphenolic compound [A] in this disclosure may be a polyphenolic compound containing a structural unit represented by one general formula (1), or may contain a polyphenolic compound containing two or more structural units represented by general formula (1).

[0100] The structural unit represented by general formula (1) in all structural units of the polyphenol compound [A] is preferably 10 mol% to 100 mol%, more preferably 50 mol% to 100 mol%, and even more preferably 90 mol% to 100 mol%.

[0101] The polyphenolic compound [A] disclosed herein may contain structural units other than those represented by the general formula (1).

[0102] The structural units that may be included in the polyphenolic compound [A] of this disclosure, other than the structural unit represented by general formula (1), include, for example, hydrocarbon groups, heterocyclic groups, -NH-, -SO-, -SO2-, -CO-, -O-, -COO-, -OCO-, -S-, -SS-, and groups formed by combining two or more of these. Examples of hydrocarbon groups include alkyl groups and aryl groups. The heterocyclic group may be a non-aromatic heterocyclic group or an aromatic heterocyclic group. The heterocyclic group is preferably a 5-membered ring or a 6-membered ring. Examples of heteroatoms constituting the heterocyclic group include nitrogen atoms, oxygen atoms, or sulfur atoms. The heterocyclic group may be a monocyclic or a fused ring.

[0103] [Polyphenol compound curing agent] The polyphenolic compound [A] disclosed herein is preferably a curing agent. In this disclosure, the polyphenolic compound used as a curing agent is also referred to as a "polyphenolic compound curing agent". The polyphenolic compound [A] preferably has a dynamic covalent bonding site and two or more phenolic hydroxyl groups, and does not have an epoxy group in its chemical structure. As shown in the above general formula (1), the polyphenolic compound [A] of this disclosure has an aromatic ring, which has phenolic hydroxyl groups (OH groups) and substituents at the dynamic covalent bonding site (Y). The aromatic ring may also have substituents in addition to these.

[0104] It is inferred that the cured epoxy resin composition of this disclosure, i.e., the epoxy resin cured product, has reformability and self-healing properties due to the dynamic covalent bonding sites (Y) included in the above general formula (1). It is inferred that the high heat resistance, elastic modulus, and strength of the cured epoxy resin composition of this disclosure, i.e., the epoxy resin cured product, are due to the rigid aromatic rings included in the above general formula (1).

[0105] Curing agents other than polyphenolic compound [A] The epoxy resin composition disclosed herein may include, in addition to the polyphenolic compound [A] represented by general formula (1), a known curing agent for curing epoxy resin. As a curing agent other than the polyphenolic compound [A], any curing agent capable of curing epoxy resin may be used, without particular limitation, and may be suitably selected according to the intended use, etc.

[0106] Specifically, as curing agents other than polyphenolic compounds [A], examples include dicyandiamide, polyphenolic compound curing agents other than those represented by the above general formula (1), various isomers of aromatic amine curing agents, and aminobenzoic acid esters. Dicyandiamide is preferred due to its excellent storage stability of the prepreg blanks described later. Furthermore, aromatic diamine compounds such as 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, and 4,4'-diaminodiphenylmethane, and their derivatives having non-reactive substituents, are particularly preferred because they can produce cured products with high heat resistance. In addition, 3,3'-diaminodiphenyl sulfone is most preferred because it can produce cured products with high heat resistance and high elastic modulus. Examples of non-reactive substituents include alkyl groups such as methyl, ethyl, and isopropyl, aromatic groups such as phenyl, and halogen groups such as alkoxy, aralkyl, chlorine, and bromine.

[0107] <Epoxy Resin [B]> The epoxy resin [B] contained in the epoxy resin composition of this disclosure may be any known epoxy resin. The epoxy resin [B] may be monofunctional, difunctional, polyfunctional, or a glycidyl ether or glycidyl amine. The epoxy resin [B] may be any epoxy resin that reacts with the aforementioned polyphenolic compound [A], and may be suitably selected according to the intended use, etc.

[0108] As for epoxy resin [B], specifically, examples can be given as follows: Tetraglycidyl-4,4'-diaminodiphenylmethane, tetraglycidyl-4,4'-diaminodiphenyl sulfone, tetraglycidyl-3,3'-diaminodiphenyl sulfone, tetraglycidyl-4,4'-diaminodiphenyl ether, tetraglycidyl-3,4'-diaminodiphenyl ether, tetraglycidyl-4,4'-bis(dithiodiphenylamine), and tetraglycidyl-4,4'-bis(dithiodiphenylamine), and their derivatives, etc., are all tetrafunctional glycidylamine type epoxy resins. Triglycidyl-m-aminophenol, triglycidyl-p-aminophenol, triglycidyl isocyanurate, and their derivatives are all trifunctional epoxy resins. Diglycidyl aniline and its derivatives, including diglycidyl-o-toluidine, diglycidyl-m-toluidine, diglycidyl-p-toluidine, diglycidyl-ditoluidine, diglycidyl-trimethyltoluidine, diglycidyl-anisidine, diglycidyl-phenoxyaniline, and diglycidyl-naphthylamine and its derivatives, are 2-functional glycidyl amine type epoxy resins. Bisphenol A-diglycidyl ether, bisphenol F-diglycidyl ether, bisphenol S-diglycidyl ether, resorcinol diglycidyl ether, 1,6-naphthol diglycidyl ether, and 4,4'-dithiodiphenol diglycidyl ether, and their derivatives, etc., are 2-functional glycidyl ether type epoxy resins. Phenol Novolac type epoxy resin, cresol Novolac type epoxy resin, and their derivatives, etc., are multifunctional glycidyl ether type epoxy resins. In addition, glycidyl ester type epoxy resins such as diglycidyl phthalate, hexahydrodiglycidyl phthalate, dimer diglycidyl phthalate, and their derivatives; etc.

[0109] These epoxy resins can be used alone or in combination.

[0110] Among these epoxy resins, bisphenol A-diglycidyl ether, bisphenol F-diglycidyl ether, bisphenol S-diglycidyl ether, resorcinol diglycidyl ether, and 1,6-naphthol diglycidyl ether, etc., which are difunctional glycidyl ether type epoxy resins, are particularly preferred due to the high workability of the epoxy resin composition and the high reformability of the cured epoxy resin.

[0111] [Weight-average molecular weight of epoxy resin [B]] The epoxy resin [B] of this disclosure preferably has a weight-average molecular weight of 100 to 5000, more preferably 150 to 2000, and even more preferably 200 to 1500.

[0112] [Epoxy Equivalent of Epoxy Resin [B]] The epoxy equivalent of the epoxy resin [B] in this disclosure is preferably 80 g / Eq to 1000 g / Eq, more preferably 90 g / Eq to 500 g / Eq, and even more preferably 100 g / Eq to 300 g / Eq. It should be noted that the epoxy equivalent in this disclosure is calculated according to JIS K7236:2009 (ISO 3001:1999).

[0113] Synthesis method of epoxy resin [B] The epoxy resin [B] disclosed herein can be synthesized by any method, for example, by reacting an aromatic diamine, aminophenol, or diphenol as a starting material with a epichlorohydrin or other epihalohydrin to obtain a halohydrin, followed by a cyclization reaction using a basic compound.

[0114] <Compatibility in Epoxy Resin Compositions> The total amount of curing agent contained in the epoxy resin composition of this disclosure is sufficient to cure all the epoxy resin in the epoxy resin composition, and can be appropriately adjusted according to the type of epoxy resin or curing agent used.

[0115] The total amount of polyphenolic compound [A] and epoxy resin [B] contained in the epoxy resin composition of this disclosure is not particularly limited, but is preferably 50% by mass or more and 100% by mass or less with respect to the epoxy resin composition, more preferably 70% by mass or more and less than 100% by mass, and even more preferably 90% by mass or more and less than 100% by mass.

[0116] The preferred molar ratio of all epoxy groups to all active hydrogens in the epoxy resin composition of this disclosure is 1:0.5 to 1:1.5, more preferably 1:0.75 to 1:1.3, and even more preferably 1:0.9 to 1:1.2. If the molar ratio of all active hydrogens to all epoxy groups is small, the reformability of the resulting cured epoxy resin is easily reduced. If the molar ratio of all active hydrogens to all epoxy groups is large, the viscosity of the epoxy resin composition increases, and the impregnation into the fiber-reinforced substrate is easily reduced.

[0117] The total molar amount of all epoxy groups is determined by summing the molar amounts of epoxy groups obtained by dividing the mass of each epoxy resin contained in the epoxy resin composition by the equivalent amount of each epoxy resin.

[0118] The total molar amount of active hydrogen is calculated by summing the molar amount of phenolic hydroxyl groups from polyphenolic compound [A] contained in the epoxy resin composition, the molar amount of phenolic hydroxyl groups from polyphenolic compounds other than polyphenolic compound [A], and the molar amount of active hydrogen from curing agents (amines, etc.) other than polyphenolic compounds.

[0119] It should be noted that the molar amount of phenolic hydroxyl groups in a polyphenol compound is determined by dividing the mass of the polyphenol compound by the equivalent amount of each hydroxyl group.

[0120] The molar amount of active hydrogen in curing agents other than polyphenolic compounds (amines, etc.) is determined by dividing the molar amount of the curing agent other than polyphenolic compounds by the amount of active hydrogen contained in one molecule.

[0121] In the epoxy resin composition of this disclosure, the molar ratio (b) of the epoxy groups of epoxy resin [B] to the molar ratio (a) of the phenolic hydroxyl groups of polyphenolic compound [A] (=(a) / (b)) is 0.25 to 1.5, preferably 0.4 to 1.3, more preferably 0.7 to 1.2, and particularly preferably 1.0. According to the epoxy resin composition of this disclosure, even when the ratio (a) / (b) is 0.25 or more or less than 1.5, an epoxy resin composition with excellent reformability or self-healing properties in the cured product can be obtained.

[0122] That is, ratio (a) / (b) is the ratio of the molar amount (a) of phenolic hydroxyl groups (in unit mass) of the polyphenolic compound [A] to the molar amount (b) of epoxy groups (in unit mass of epoxy resin composition). In this disclosure, ratio (a) / (b) can be obtained by means of... 1 The integral area ratio of the peaks from phenolic hydroxyl groups to those from epoxy groups is determined by ¹H-NMR analysis of epoxy resin compositions.

[0123] In this disclosure, the use of a compound having a dynamic covalent bonding site in a theoretical amount relative to the epoxy resin means using the amount of compound with a dynamic covalent bonding site in which the molar amount of active hydrogen is 1 relative to the molar amount of epoxy group in the epoxy resin, i.e., in this case, the ratio (a) / (b) is 1.

[0124] In this published text, "close to the theoretical equivalent" means a ratio of (a) / (b) of more than 0.25 and less than 1.5.

[0125] <Curing Accelerator> In addition to the polyphenolic compound [A] and epoxy resin [B] described above, the epoxy resin composition disclosed herein may also contain a curing accelerator. The curing accelerator promotes the curing reaction of the epoxy resin composition and the prepreg impregnated therein, supplying a cured product with high elastic modulus and strength in a short production time. As a curing accelerator, any substance that promotes the curing reaction between the polyphenolic compound [A] and the epoxy resin [B] is acceptable, and there are no particular limitations. Examples include nitrogen-containing heterocyclic compounds such as imidazoles and tertiary amines, as well as their onium salts, phosphine salts, and phosphonium salts.

[0126] Specifically, examples of curing accelerators include imidazoles such as 2-ethyl-4-methylimidazole and 1-(2-cyanoethyl)-2-phenylimidazole, and their salts; tertiary amines such as diazabicycloundecene, diazabicyclononene, and tris(dimethylaminomethyl)phenol, and their salts; phosphines such as triphenylphosphine and tris(o-tolyl)phosphine; and phosphine salts, primarily tetraphenylphosphine tetraphenylborate.

[0127] The content of curing accelerator in the epoxy resin composition of this disclosure can be selected as needed and is therefore not particularly limited.

[0128] <Optional Ingredients> In the epoxy resin composition disclosed herein, thermoplastic resin, conductive particles, flame retardants, inorganic fillers, or internal mold release agents may be incorporated.

[0129] Thermoplastic resins improve the fracture toughness and impact resistance of the resulting fiber-reinforced composite materials. Examples of thermoplastic resins include epoxy-soluble thermoplastic resins and epoxy-insoluble thermoplastic resins.

[0130] The viscosity of the epoxy resin composition is adjusted by using epoxy resin-soluble thermoplastic resins, thereby improving the impact resistance of the resulting fiber-reinforced composite material.

[0131] Specific examples of epoxy resin-soluble thermoplastic resins include polyethersulfone, polysulfone, polyetherimide, and polycarbonate. These can be used alone or in combination of two or more. Polyethersulfone or polysulfone with a weight-average molecular weight (Mw) in the range of 8,000 to 100,000, as determined by gel permeation chromatography, is particularly preferred. If the weight-average molecular weight (Mw) is less than 8,000, the impact resistance of the resulting fiber-reinforced composite material becomes insufficient. Furthermore, if the weight-average molecular weight (Mw) is greater than 100,000, the viscosity of the epoxy resin composition sometimes increases significantly, and the workability deteriorates significantly. The molecular weight distribution of the epoxy resin-soluble thermoplastic resin is preferably uniform. In particular, the ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn), i.e., the polydispersity (Mw / Mn), is preferably in the range of 1 to 10, and more preferably in the range of 1.1 to 5.

[0132] The epoxy-soluble thermoplastic resin preferably has reactive groups that are reactive with epoxy resin or functional groups that can form hydrogen bonds. Such an epoxy-soluble thermoplastic resin can improve the solubility stability of the epoxy resin during the curing process. In addition, the epoxy-soluble thermoplastic resin can impart toughness, chemical resistance, heat resistance, and humid heat resistance to the fiber-reinforced composite material obtained after curing.

[0133] The reactive groups that are reactive with epoxy resin are preferably hydroxyl, carboxylic acid, imino, or amino groups. Polyethersulfone with a hydroxyl terminus is preferred, as it produces fiber-reinforced composites with particularly excellent impact resistance, fracture toughness, and solvent resistance.

[0134] A portion of the epoxy-insoluble thermoplastic resin or epoxy-soluble thermoplastic resin (e.g., epoxy-soluble thermoplastic resin that remains undissolved in the cured matrix resin) is dispersed as particles within the matrix resin of the fiber-reinforced composite material (hereinafter, these dispersed particles are also referred to as "interlaminar particles"). These interlaminar particles inhibit the propagation of impacts experienced by the fiber-reinforced composite material. As a result, the impact resistance of the resulting fiber-reinforced composite material is improved.

[0135] Examples of epoxy-insoluble thermoplastic resins include polyamides, polyacetals, polyphenylene ethers, polyphenylene sulfides, polyesters, polyamide-imides, polyimides, polyetherketones, polyetheretherketones, polyethylene naphthalate, polyether nitrile, and polybenzimidazole. Among these, polyamides, polyamide-imides, and polyimides are preferred due to their high toughness and heat resistance. Polyamides and polyimides are particularly effective in improving the toughness of fiber-reinforced composites. They can be used alone or in combination of two or more. Copolymers of these resins can also be used.

[0136] In particular, the heat resistance of the resulting fiber-reinforced composite material can be significantly improved by using polyamides such as amorphous polyimide, nylon 6 (registered trademark) (a polyamide obtained by ring-opening polycondensation of caprolactam), nylon 11 (a polyamide obtained by ring-opening polycondensation of undecanolactam), nylon 12 (a polyamide obtained by ring-opening polycondensation of laurolactam), nylon 1010 (a polyamide obtained by copolymerization of sebacic acid and 1,10-decanediamine), and amorphous nylon (also known as transparent nylon, a nylon that does not crystallize or crystallizes very slowly).

[0137] Examples of conductive particles include conductive polymer particles such as polyacetylene particles, polyaniline particles, polypyrrole particles, polythiophene particles, polyisothioindene particles, and polyethylenedioxythiophene particles; carbon particles; carbon fiber particles; metal particles; and particles obtained by coating a core material formed of inorganic or organic materials with a conductive substance.

[0138] Phosphorus-based flame retardants can be cited as examples. As a phosphorus-based flame retardant, any substance containing phosphorus atoms in its molecule is acceptable; there are no particular limitations. Examples include phosphate esters, condensed phosphate esters, phosphazene compounds, polyphosphates, and other organophosphorus compounds, as well as red phosphorus.

[0139] 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. Silicate minerals are particularly preferred. Specifically, THIXOTROPIC AGENT DT 5039 (manufactured by Huntsman Japan KK) is an example of a silicate mineral.

[0140] Examples of internal mold release agents include, for example, metal soaps, polyethylene wax, plant waxes such as carnauba wax, fatty acid ester-based mold release agents, silicone oil, animal wax, and fluorinated nonionic surfactants. The amount of these internal mold release agents is preferably 0.1 to 5 parts by weight, more preferably 0.2 to 2 parts by weight, relative to 100 parts by weight of the aforementioned epoxy resin. Within this range, a suitable demolding effect from the mold can be achieved.

[0141] As internal mold release agents, examples include "MOLD WIZ (registered trademark)" INT1846 (manufactured by AXELPLASTICS RESEARCH LABORATORIES INC.), Licowax S, Licowax P, Licowax OP, Licowax PE190, Licowax PED (manufactured by Clariant Japan KK), and stearyl stearate (SL-900A; manufactured by RIKEN VITAMIN CO., LTD.).

[0142] <Method for manufacturing epoxy resin composition> The epoxy resin compositions disclosed herein can be manufactured by mixing a polyphenol compound [A], an epoxy resin [B], and other components as desired. The order in which they are mixed is not limited.

[0143] The method for manufacturing the epoxy resin composition disclosed herein is not particularly limited, and any method known in the art may be used. An example of a mixing temperature is a range of 40°C to 120°C. At mixing temperatures above 120°C, partial curing may occur, reducing the impregnation within the fiber-reinforced substrate layer, or decreasing the storage stability of the resulting epoxy resin composition and the prepreg blanks manufactured using it. At mixing temperatures below 40°C, the viscosity of the epoxy resin composition is high, sometimes making mixing substantially difficult. A mixing temperature preferably ranges from 50°C to 100°C, and more preferably from 50°C to 90°C.

[0144] As a mixing apparatus, conventionally known devices can be used. Specific examples include roller mills, planetary mixers, kneaders, extruders, Banbury mixers, mixing vessels equipped with stirring blades, and horizontal mixing tanks. The mixing of the components can be carried out in the atmosphere or in an inert gas atmosphere. When mixing is carried out in the atmosphere, an atmosphere in which temperature and humidity are controlled is preferred. While not particularly limited, mixing is preferred, for example, at a constant temperature controlled to below 30°C and in a low humidity atmosphere with a relative humidity of below 50% RH.

[0145] <Application> The epoxy resin composition disclosed herein is preferably a curing agent, i.e., preferably an epoxy resin curing agent.

[0146] That is, in this disclosure, the epoxy resin curing agent comprises a polyphenolic compound [A] containing at least a structural unit represented by the following general formula (1) and an epoxy resin [B]. The ratio (a) / (b) of the molar amount of phenolic hydroxyl groups (a) in the aforementioned polyphenolic compound [A] to the molar amount of epoxy groups (b) in the aforementioned epoxy resin [B] is 0.25 or more and 1.5 or less. When an external force is applied to a cured product that has been cured to a degree of curing of 90% or more at a temperature 60°C higher than the glass transition temperature of the cured product, the stress relief rate at a time point of 1 hour from the start of the application of the external force is measured to be 90% or more.

[0147] [Chemical Formula 16] In general formula (1), Y is an independent dynamic covalent bonding site, and R 1a R 1b R 1c and R 1d At least one of them is a connecting bond between it and Y in other adjacent structural units, and each of the others independently represents any one of hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom, and n represents an integer from 2 to 500.

[0148] The preferred methods and specific examples of the polyphenolic compound [A], epoxy resin [B], ratio (a) / (b), and stress relief rate in the epoxy resin curing agent are the same as those of the preferred methods and specific examples of the polyphenolic compound [A], epoxy resin [B], ratio (a) / (b), and stress relief rate in the epoxy resin composition of this disclosure.

[0149] ≪Epoxy Resin Cured Products≫ <Epoxy resin cured product of the first embodiment> The epoxy resin cured product of the first embodiment is formed by curing the epoxy resin composition of this disclosure.

[0150] There are no particular limitations on the method for curing the epoxy resin composition of this disclosure used to obtain the epoxy resin cured product of this disclosure, and known methods can be used for curing. As a method of curing, for example, after degassing in a vacuum, curing can be performed 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, more preferably at a temperature of 150°C to 180°C for 1 hour to 6 hours, thereby obtaining the epoxy resin cured product. Specifically, after degassing in a vacuum, curing can be performed 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, thereby obtaining the epoxy resin cured product.

[0151] Regarding the epoxy resin cured product of the first embodiment, it is preferable that when it is brought into contact with a decomposing agent containing a reducing agent and heated at 100°C for 48 hours, more than 80% by mass of the cured product dissolves.

[0152] It should be noted that the statement regarding the dissolution of more than 80% by mass of the cured product when it is brought into contact with a decomposing agent containing a reducing agent and heated at 100°C for 48 hours is the same as the statement in the <Epoxy Resin Cured Product of the Second Embodiment> described later.

[0153] Regarding the epoxy resin cured product of the first embodiment, it is preferable that, when it is brought into contact with a decomposing agent containing a reducing agent and heated, a compound comprising at least the structure shown in the following general formula (4) is generated. More preferably, regarding the epoxy resin cured product of the first embodiment, when it is brought into contact with a decomposing agent containing a reducing agent and heated, it decomposes into a compound comprising at least the structure shown in the following general formula (4).

[0154] [Chemical Formula 17] In general formula (4), This indicates a connecting bond. In general formula (4), "-C(OH)-" " Preferably, it is a linker bond between the structure and the epoxy resin, "-S- " Preferably, it is a linking bond between the structure and the reducing agent. R 4a R 4b and R 4c Each can independently represent any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom.

[0155] It should be noted that the description of generating a compound containing at least the structure shown in the above general formula (4) when it is brought into contact with a decomposing agent containing a reducing agent and heated, and the description of decomposing into a compound containing at least the structure shown in the above general formula (4), are the same as those in the description in the <Epoxy Resin Cured Product of the Third Embodiment> described later.

[0156] <Epoxy Resin Cured Product of Second Embodiment> Regarding the epoxy resin cured product of the second embodiment, when it is contacted with a decomposing agent containing a reducing agent and heated at 100°C for 48 hours, more than 80% by mass of the cured product dissolves. The epoxy resin cured product of the second embodiment exhibits excellent solubility; by contacting the epoxy resin cured product with a decomposing agent, it can be dissolved in low molecular weight compounds.

[0157] Regarding the aforementioned types of reducing agents, there are no particular restrictions as long as the epoxy resin cured product is dissolved. Any reducing agent can be used, depending on the type of bonds contained in the epoxy resin cured product.

[0158] Examples of reducing agents include dithiothreitol, 2-mercaptoethanol, 1-thioglycerol, glutathione, 2-mercaptoethylamine hydrochloride, cystine hydrochloride, and tris(2-carboxyethyl)phosphine hydrochloride, with those capable of reducing disulfide bonds being preferred. These reducing agents can be used alone or in combination.

[0159] Furthermore, these reducing agents can be used in a solvent-free manner, or they can be used by diluting them with a solvent to prepare a decomposing agent solution. The epoxy resin cured product of the second embodiment can also be dissolved by impregnation in a decomposing agent solution containing the reducing agent.

[0160] The amount of the decomposing agent solution used is not particularly limited and can be determined according to the shape of the epoxy resin cured product, dissolution conditions, etc. The amount of decomposing agent contained in the decomposing agent solution, on a mass basis, is preferably 0.5 to 1000 times the amount of the epoxy resin cured product, more preferably 0.5 to 100 times the amount, and particularly preferably 0.5 to 10 times the amount.

[0161] The concentration of the reducing agent in the decomposing agent solution is not particularly limited, but is preferably 0.1% to 99.9% by mass, more preferably 1% to 80% by mass, and particularly preferably 5% to 50% by mass.

[0162] Regarding the solvent used for dilution, there are no particular limitations as long as the reducing agent can be dissolved and the solidified material can be dissolved. It can be water or an organic solvent. Examples of organic solvents used for dilution include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, 1,4-dioxane, tetrahydrofuran, methanol, and ethanol. Polar organic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide are preferred because they can completely dissolve the solidified material.

[0163] In addition to the above, the dissolving agent may also contain some additives that promote dissolution. In particular, nitrogen-containing bases such as triethylamine, DBU (1,8-diazabicycloundecene), or ammonia are preferred due to their high dissolution-promoting effect when added.

[0164] In the above dissolution process, to promote dissolution, heating can be performed 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 stirring can be appropriately performed, and ultrasonic treatment can be performed if necessary. For example, the dissolution reaction can be carried out while stirring the decomposing agent at room temperature (25°C) or 80°C for 8 hours. In the above dissolution process, to promote dissolution, pressure can be applied at 0.1 MPa to 10 MPa (preferably 0.1 MPa to 1 MPa).

[0165] Regarding the epoxy resin cured product of the second embodiment, upon contact with and heating of a decomposing agent containing a reducing agent, it is preferable that at least 50% by mass of the cured product dissolves, more preferably at least 80% by mass of the cured product dissolves, even more preferably at least 95% by mass of the cured product dissolves, and extremely preferably at least 99% by mass of the cured product dissolves. Regarding the epoxy resin cured product of the second embodiment, upon contact with and heating of a decomposing agent containing a reducing agent, it is possible that at least 100% by mass of the epoxy resin cured product dissolves.

[0166] It should be noted that, in this disclosure, the percentage (mass%) of dissolved epoxy resin in the case where the epoxy resin cured product is dissolved is determined by dividing the mass of the residue obtained by filtering the solution obtained by dissolving the epoxy resin cured product by the mass of the epoxy resin cured product before dissolution.

[0167] <Epoxy Resin Cured Product of the Third Embodiment> Regarding the epoxy resin cured product of the third embodiment, when it is brought into contact with a decomposing agent containing a reducing agent and heated, a compound comprising at least the structure shown in the following general formula (4) is generated. More preferably, regarding the epoxy resin cured product of the third embodiment, when it is brought into contact with a decomposing agent containing a reducing agent and heated, it decomposes into a compound comprising at least the structure shown in the following general formula (4).

[0168] [Chemical Formula 18] In general formula (4), This indicates a connecting bond. In general formula (4), "-C(OH)-" " Preferably, it is a linker bond between the structure and the epoxy resin, "-S- " Preferably, it is a linking bond between the structure and the reducing agent. R 4a R 4b and R 4c Each can independently represent any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom.

[0169] From the viewpoint of the solubility of the decomposed resin, the molecular weight of the compound represented by general formula (4) is preferably 200 to 5000, more preferably 200 to 3000, and even more preferably 200 to 2000. It should be noted that in this disclosure, the molecular weight is determined by gel permeation chromatography (GPC) using chloroform and N,N-dimethylformamide as eluents.

[0170] The description of the decomposing agent containing a reducing agent in the epoxy resin cured product of the third embodiment, including definitions, examples, and preferred methods, is the same as that of the decomposing agent containing a reducing agent in the epoxy resin cured product of the second embodiment.

[0171] For example, when using a solution of N,N-dimethylformamide in 2-mercaptoethanol as a decomposition agent and heating, the epoxy resin cured product of the third embodiment generates a compound containing at least the structure shown in the following general formula (4-1).

[0172] [Chemical Formula 19] In general formula (4-1), This indicates a connecting bond. In general formula (4-1), "-C(OH)-" " Preferably, it is a bonding bond between the structure and the epoxy resin. 4a R 4b and R4c Each can independently represent any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom.

[0173] From the viewpoint of the solubility of the decomposed resin, the molecular weight of the compound represented by general formula (4-1) is preferably 200 to 5000, more preferably 200 to 3000, and even more preferably 200 to 2000.

[0174] The conditions for contacting the decomposing agent containing the reducing agent and heating are not particularly limited. Heating can be carried out at 25°C to 150°C (preferably 25°C to 60°C) for 1 hour to 48 hours (preferably 1 hour to 8 hours). Stirring can also be performed appropriately, and ultrasonic treatment can be performed if necessary. For example, the formation reaction can be carried out while stirring the decomposing agent at room temperature (25°C) or 80°C for 8 hours. In the above formation, in order to promote the formation, a pressure of 0.1 MPa to 10 MPa (preferably 0.1 MPa to 1 MPa) can be applied.

[0175] In this disclosure, it can be confirmed by LC-MS that the epoxy resin cured product of the third embodiment produces a compound comprising at least the structure shown in general formula (4). Alternatively, it can also be confirmed by... 1 We can confirm this using H-NMR.

[0176] <Epoxy resin cured products of the first to third embodiments> In this disclosure, the term "epoxy resin cured product" includes the epoxy resin cured products of the first to third embodiments.

[0177] The glass transition temperature (Tg) of the epoxy resin cured product disclosed herein is preferably 80°C to 300°C, more preferably 100°C to 200°C. When the glass transition temperature is below 80°C, the heat resistance is insufficient. As a result, voids and the like are easily formed in the obtained fiber-reinforced composite material.

[0178] It should be noted that the glass transition temperature in this disclosure can be determined using a differential scanning calorimeter. The cured material is heated from 30°C to 350°C at a rate of 10°C / min, and the inflection point in the resulting curve is taken as the glass transition temperature.

[0179] Regarding the epoxy resin cured product of this disclosure, the flexural modulus (hereinafter, sometimes referred to as FM) measured using the JIS K7171:2016 method (ISO 178:2019) is preferably 2.00 GPa or higher, more preferably 2.30 GPa to 30.00 GPa, even more preferably 2.50 GPa to 20.00 GPa, and may also be 2.50 GPa to 5.00 GPa. When the flexural modulus is less than 2.00 GPa, the properties of the resulting fiber-reinforced composite material tend to decrease.

[0180] It should be noted that the flexural modulus of elasticity in this disclosure can be determined in accordance with the JIS K7171:2016 method.

[0181] The flexural strength (FS) of the epoxy resin cured product in this disclosure is preferably 30 MPa or more, more preferably 60 MPa to 150 MPa, and even more preferably 80 MPa to 150 MPa. When the flexural strength is less than 30 MPa, the properties of the resulting fiber-reinforced composite material tend to decrease.

[0182] It should be noted that the bending strength in this disclosure is the maximum value of the bending stress determined in accordance with the JIS K7171:2016 method.

[0183] Regarding the epoxy resin cured product of this disclosure, the compressive strength (CS) measured using the JIS K7181:2011 method (ISO 604:2002) is preferably 200 MPa or more, more preferably 250 MPa to 400 MPa, and even more preferably 280 MPa to 350 MPa. When the compressive strength is less than 200 MPa, the properties of the resulting fiber-reinforced composite material tend to decrease.

[0184] It should be noted that the compressive strength in this disclosure can be determined in accordance with the JIS K7181:2011 method.

[0185] The degree of curing of the epoxy resin cured product disclosed herein is preferably 90% or more, more preferably 95% or more, and even more preferably 99% or more. Insufficient degree of curing can easily lead to poor toughness. The degree of curing can be determined using conventionally known evaluation methods, such as the method in JIS K7148-1:2015 (ISO 14322:2012), using an evaluation method based on differential scanning calorimetry (DSC).

[0186] <Stress Relief Rate> When an external force is applied to a cured product obtained by curing the epoxy resin composition of this disclosure to 90% or more of its degree of cure at a temperature 60°C higher than the glass transition temperature of the cured product, the stress relief rate at one hour from the start of the application of the external force is 90% or more. The stress relief rate at one hour from the start of the application of the external force is preferably 99.0% or more, more preferably 99.5% or more, and even more preferably 99.7% or more. This stress relief rate can be 100.0% or less.

[0187] When the stress relief rate is less than 90% at one hour from the start of the application of the external force, the reformability of the epoxy resin cured product and the fiber-reinforced composite material described later is impaired, and the strength and elastic modulus are easily reduced.

[0188] Here, the stress relief rate (%) is a value calculated using the following formula, taking into account the time change of the modulus value G over 3600 seconds during the stress relief measurement. The modulus value is the value of stress generated when an external force is applied to induce strain.

[0189] [1-((G(min)) / (G(0)))]×100 Here, G(0) is the modulus value at 0 seconds after the application of the external force. G(min) is the minimum modulus value up to 3600 seconds after the application of the external force. It is the value if the modulus value reaches the lower limit of the device within 3600 seconds, and the value at 3600 seconds if not.

[0190] [Stress Relief Mode Separation Analysis] The analysis of stress relief mode separation is described in detail.

[0191] The stress relief behavior of the epoxy resin cured product of this disclosure under stress is fitted using a generalized Maxwell model, which is a model obtained by connecting multiple two-element models, namely Maxwell elements, arranged in series and springs in parallel. In this generalized Maxwell model, each Maxwell element corresponds to one relief mode; that is, the stress relief behavior under stress applied to the generalized Maxwell model can be described as a linear summation of the behaviors of each Maxwell element (each relief mode). Furthermore, by separating the stress relief measurement results according to the linear summation formula of the generalized Maxwell model and evaluating the relief time obtained from each relief mode, the bond exchange performance within the epoxy resin cured product of this disclosure can be quantitatively evaluated.

[0192] For the modulus value G(t) generated during the stress relief measurement over 3600 seconds, the following mathematical formula 1 is used to fit to the coefficient of determination R. 2 >0.999.

[0193] [Mathematical Expression 1] In mathematical formula 1, t is time (unit: seconds), and G0 is the modulus value G(0) at t=0 seconds. μ i Is it satisfied by Σμ i The independent variable within the range of 1 is a variable representing the contribution (in %) of each term (each mitigation mode) in the multivariate linear equation.

[0194] τ i The softening time (in seconds) for each softening mode is set in such a way that it includes softening modes with softening times that are sufficiently large relative to the measurement time. Furthermore, each softening mode is set such that its softening time is uniform across the same logarithmic range, becoming equal within the same logarithmic range. There are no particular limitations on the number and range of softening modes to be set, but from a computational load perspective, it is preferable to have as many as possible.

[0195] For example, when performing stress relief mode separation analysis on the epoxy resin cured product of this disclosure in the range of 0 seconds to 3600 seconds, the following 25 relief modes (τ) are preferably used. i The value of is analyzed.

[0196] τ i =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 It should be noted that, in this case, τ was set in a manner that included a measurement time of 3600 seconds. i The maximum value τ i =10000 (seconds). Furthermore, each mitigation mode, such as 1, 2.5, 4, 5.5, 7, ..., is set in such a way that its mitigation time becomes uniform within the same logarithmic range. Moreover, the stress mitigation behavior of the epoxy resin cured product of this disclosure is determined by fitting a linear summation of mitigation modes with 25 mitigation times.

[0197] Next, based on the curves obtained from plotting the logarithm of the mitigation time on the horizontal axis and the logarithm of the stress on the vertical axis for each mitigation mode, a fitting formula is obtained using Equation 1. Furthermore, regarding τ in the obtained fitting formula... i and μi , thus becoming the plotting of τ on the horizontal axis i The logarithm of μ is plotted on the vertical axis. i τ with a peak distribution at time i It is the mitigation time of the separated mitigation mode group.

[0198] Furthermore, relative to τ that constitutes each peak i μ in the group i The sum of τ, constituting an arbitrary peak i μ in i The value is the contribution (%) of the isolated mitigation pattern.

[0199] It should be noted that the stress relief measurement here can be performed using conventionally known apparatus and methods. Under isothermal conditions using a constant temperature apparatus, as long as the time change of stress after the instantaneous application of external force can be tracked and recorded, specific examples include measurements in shear mode based on a rheometer apparatus equipped with parallel plates, and measurements in bending or tensile mode based on dynamic viscoelasticity measurement (DMA). The measurement is performed in an inert gas atmosphere, preferably in an atmosphere with controlled humidity. Although there are no particular limitations, for example, it is preferable to perform the measurement by flowing nitrogen through the measuring apparatus at a flow rate of 10 L / min or more in a room with a low humidity atmosphere of less than 50% RH.

[0200] Regarding the stress relief behavior of the epoxy resin cured product obtained by curing the epoxy resin composition of this disclosure at [glass transition temperature of the cured product + 60] °C for 1 hour, the results of the stress relief mode separation analysis are plotted on the horizontal axis as follows: i The logarithm of μ is plotted on the vertical axis. i In the time-varying curve, it is preferable to have two or more distributed mitigation mode groups. More preferably, the curve preferably has at least one mitigation mode group with a mitigation time of less than 200 seconds and a mitigation mode group with a mitigation time of more than 1000 seconds, each contributing at least 10%. When only a single mitigation mode group is present, or even if multiple mitigation mode groups are present but only those with short mitigation times are present, the creep properties of epoxy resin cured materials or fiber-reinforced composite materials under high-temperature conditions are easily impaired.

[0201] ≪Prepreg blank≫ The prepreg blank of this disclosure is formed by impregnating the epoxy resin composition of this disclosure into a fiber-reinforced substrate having reinforcing fibers, wherein the content of the aforementioned reinforcing fibers is 25% to 75% by volume relative to the total volume of the prepreg blank of this disclosure.

[0202] The prepreg blank of this disclosure is a prepreg blank formed by impregnating a portion or the entirety of the epoxy resin composition of this disclosure into a fiber-reinforced substrate. When the content of reinforcing fibers relative to the total volume of the prepreg blank of this disclosure is greater than 75% by volume, voids or the like may sometimes occur in the resulting fiber-reinforced composite material, resulting in a decrease in mechanical properties. When the content of reinforcing fibers relative to the total volume of the prepreg blank of this disclosure is less than 25% by volume, the reinforcing effect provided by the reinforcing fibers may sometimes become insufficient, and substantially, the mechanical properties are lower relative to mass. The content of reinforcing fibers relative to the total volume of the prepreg blank of this disclosure is preferably 45% to 70% by volume, more preferably 50% to 65% by volume.

[0203] The shape of the prepreg blank in this disclosure can be a tow prepreg obtained by forming reinforcing fibers into strips, or an SMC (Sheet Molding Compound) obtained by forming reinforcing fibers using short fibers with a fiber length of 5 mm to 100 mm. The reinforcing fibers can be fabric prepreg blanks formed from woven fabrics or multi-layered woven fabrics.

[0204] A tow prepreg is a narrow-width intermediate substrate obtained by impregnating a matrix resin composition into a bundle of reinforcing fibers consisting of thousands to tens of thousands of reinforcing filaments arranged in a unidirectional direction, and then winding it onto a spool such as a paper tube. It should be noted that in this disclosure, the product obtained by winding it onto a spool, or the product obtained by unwinding it after winding, is referred to as "tow prepreg".

[0205] <Fiber-reinforced substrate> There are no particular limitations on the fiber-reinforced substrates used in this disclosure. Examples include carbon fiber, glass fiber, aramid fiber, silicon carbide fiber, polyester fiber, ceramic fiber, alumina fiber, boron fiber, metal fiber, mineral fiber, rock fiber, and slag fiber.

[0206] Among these fiber-reinforced substrates, carbon fiber, glass fiber, or aramid fiber are preferred. From the perspective of obtaining fiber-reinforced composite materials with good specific strength and specific modulus of elasticity, lightweight, and high strength, carbon fiber is more preferred. From the perspective of excellent tensile strength, polyacrylonitrile (PAN) based carbon fiber is particularly preferred.

[0207] When PAN-based carbon fibers are used in the fiber-reinforced matrix, the tensile modulus is preferably 100 GPa to 600 GPa, more preferably 200 GPa to 500 GPa, and particularly preferably 230 GPa to 450 GPa. Furthermore, the tensile strength is preferably 2000 MPa to 10000 MPa, more preferably 3000 MPa to 8000 MPa.

[0208] The diameter of the carbon fiber is preferably 4μm to 20μm, more preferably 5μm to 10μm. By using such carbon fibers, the mechanical properties of the resulting fiber-reinforced composite material can be improved.

[0209] The fiber-reinforced substrate is preferably formed into a sheet for use. Examples of reinforcing fiber sheets include sheets obtained by unidirectionally spinning multiple reinforcing fibers, biaxial fabrics such as plain weave or twill weave, multiaxial fabrics, nonwoven fabrics, felts, knitted fabrics, braided tapes, or paper obtained by papermaking the fiber-reinforced substrate. Among these, using unidirectionally spun sheets, biaxial fabrics, or multiaxial fabrics obtained by forming the fiber-reinforced substrate as continuous fibers into a sheet yields fiber-reinforced composite materials with superior mechanical properties, and is therefore preferred.

[0210] 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.

[0211] <Prepreg Manufacturing Method> The method for manufacturing the prepreg blank in this disclosure is not particularly limited, and any method known in the past can be used. Specifically, the hot-melt method or the solvent method is preferred.

[0212] The hot melt method is as follows: an epoxy resin composition is coated into a thin film on release paper to form a resin composition film, the resin composition film is laminated on a fiber-reinforced substrate, and heated under pressure, thereby impregnating the epoxy resin composition within the fiber-reinforced substrate layer.

[0213] There are no particular limitations on the method for preparing the epoxy resin composition into a resin composition film, and any method known in the art can be used. Specifically, the resin composition can be cast or molded on a support such as release paper or film using a die extruder, coater, reverse roller coater, or comma coater to obtain the resin composition film. The resin temperature during film production is appropriately determined based on the composition or viscosity of the epoxy resin composition. Specifically, it is preferable to use the same temperature conditions as the mixing temperature in the aforementioned epoxy resin composition manufacturing method. The impregnation of the epoxy resin composition into the fiber-reinforced substrate layer can be performed in one step or in multiple steps.

[0214] The solvent method is as follows: using a suitable solvent to prepare an epoxy resin composition into a varnish-like state, so that the varnish is impregnated in the fiber-reinforced substrate layer.

[0215] The prepreg blanks disclosed herein can preferably be manufactured using solvent-free hot-melt methods from these existing approaches.

[0216] When impregnating an epoxy resin composition film into a fiber-reinforced substrate layer using a hot-melt method, the impregnation temperature is preferably in the range of 50°C to 120°C. At impregnation temperatures below 50°C, the viscosity of the epoxy resin composition is high, and sometimes it cannot be sufficiently impregnated into the fiber-reinforced substrate layer. At impregnation temperatures above 120°C, the curing reaction of the epoxy resin composition occurs, sometimes resulting in reduced storage stability or drape of the obtained prepreg. An impregnation temperature is more preferably 60°C to 110°C, and particularly preferably 70°C to 100°C.

[0217] The impregnation pressure when impregnating an epoxy resin composition film into a fiber-reinforced substrate layer using a hot-melt method is appropriately determined taking into account factors such as the viscosity of the resin composition or resin flow.

[0218] The specific impregnation pressure is 0.01 N / cm to 250 N / cm, preferably 0.1 N / cm to 200 N / cm.

[0219] ≪Fiber Reinforced Composites≫ The fiber-reinforced composite material of this disclosure comprises a cured epoxy resin formed by curing the epoxy resin composition of this disclosure, and a fiber-reinforced substrate having reinforcing fibers, wherein the content of the aforementioned reinforcing fibers relative to the total volume of the fiber-reinforced composite material of this disclosure is 25% to 75% by volume. The fiber-reinforced composite material of this disclosure preferably consists of a cured epoxy resin formed by curing the epoxy resin composition of this disclosure, and a fiber-reinforced substrate having reinforcing fibers. The content of reinforcing fibers relative to the total volume of the fiber-reinforced composite material of this disclosure is preferably 45% to 70% by volume, more preferably 50% to 65% by volume.

[0220] The epoxy resin composition disclosed herein exhibits high impregnation and workability into fiber-reinforced substrates, enabling the production of fiber-reinforced composite materials with excellent properties. Furthermore, even if the epoxy resin cured product and fiber-reinforced composite material of this disclosure have internal cracks or delamination, these cracks and delaminations can be repaired by performing a process including heating.

[0221] <Manufacturing Methods of Fiber Reinforced Composite Materials> The fiber-reinforced composite material of this disclosure can be obtained by compounding a fiber-reinforced substrate having reinforcing fibers with an epoxy resin composition of this disclosure and then curing it. Alternatively, the fiber-reinforced composite material can be obtained by heating and pressurizing the prepreg blank of this disclosure under specific conditions and then curing it. As a method for manufacturing fiber-reinforced composite materials using the prepreg blank of this disclosure, known molding methods such as autoclave molding and pressure molding can be cited.

[0222] [Autoclave Molding Method] As the manufacturing method of the fiber-reinforced composite material disclosed herein, an autoclave molding method is preferably used. The autoclave molding method is as follows: a prepreg blank and a film bag are sequentially placed in the lower mold of a die; the prepreg blank is sealed between the lower mold and the film bag, creating a vacuum in the space formed by the lower mold and the film bag; and heating and pressurization are performed using an autoclave molding apparatus. The preferred molding conditions are: a heating rate of 1°C / min to 50°C / min, and heating and pressurization at 0.2MPa to 0.7MPa and 130°C to 180°C for 1 hour to 12 hours.

[0223] [Pressure molding method] As a method for manufacturing the fiber-reinforced composite material of this disclosure, a pressure molding method is preferred. The manufacturing of the fiber-reinforced composite material based on the pressure molding method is carried out by heating and pressurizing a preform formed by stacking prepreg blanks of this disclosure using a mold. The mold is preferably preheated to a curing temperature.

[0224] The mold temperature during pressure molding is preferably between 150°C and 210°C. If the molding temperature is above 150°C, the curing reaction can be sufficiently induced, resulting in fiber-reinforced composite materials with high productivity. Conversely, if the molding temperature is below 210°C, the viscosity of the resin composition will not become excessively low, suppressing excessive flow of the resin composition within the mold. As a result, the outflow of the resin composition from the mold and fiber kinking can be suppressed, thus yielding high-quality fiber-reinforced composite materials.

[0225] The molding pressure is preferably 0.05 MPa to 2 MPa, more preferably 0.2 MPa to 2 MPa. If the pressure is 0.05 MPa or higher, adequate flow of the epoxy resin can be obtained, preventing poor appearance and voids. Furthermore, the prepreg blank is sufficiently sealed to the mold, thus producing a fiber-reinforced composite material with a good appearance. If the pressure is 2 MPa or lower, the resin will not flow to the necessary extent, thus reducing the likelihood of poor appearance in the resulting fiber-reinforced composite material. Additionally, the mold will not be subjected to excessive load, thus reducing the likelihood of mold deformation.

[0226] The molding time is preferably 1 to 8 hours.

[0227] <Examples of fiber-reinforced composite materials> Examples of fiber-reinforced composite materials include, for example, fiber-reinforced plastics (FRP) or carbon fiber-reinforced plastics (CFRP).

[0228] Repair methods for epoxy resin cured products The method for repairing epoxy resin cured materials disclosed herein includes the following steps: heating an epoxy resin cured material with internal cracks (cracks) or peeling at a temperature above the glass transition temperature of the epoxy resin cured material, thereby repairing the aforementioned cracks or peeling.

[0229] The epoxy resin cured products disclosed herein have excellent self-healing properties, and therefore can repair internal cracks and peeling that occur during molding or in the environment of use.

[0230] The heating temperature can be above the glass transition temperature of the epoxy resin cured material, and there are no particular limitations. Preferably, it is 160°C or higher, more preferably 180°C or higher, and particularly preferably 200°C or higher. The heating method can be any known method, and the heating time can be set arbitrarily. An autoclave or a blower-type dryer can be used, and treatment can be performed at 200°C for 1 hour. Furthermore, the epoxy resin cured material repair method of this disclosure may include a pressurization step, and if necessary, a mold or support frame can 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 can also be applied in stages.

[0231] Repair methods for fiber-reinforced composite materials The repair method for fiber-reinforced composite materials disclosed herein includes the following steps: heating a fiber-reinforced composite material with internal cracks (cracks) or peeling at a temperature above the glass transition temperature of the aforementioned fiber-reinforced composite material, thereby repairing the aforementioned cracks or peeling.

[0232] The fiber-reinforced composite material disclosed herein has excellent self-healing properties, and therefore can repair internal cracks and peeling that occur during molding or in the environment of use.

[0233] The heating temperature is not particularly limited as long as it is above the glass transition temperature of the fiber-reinforced composite material, but preferably 160°C or higher, more preferably 180°C or higher, and particularly preferably 200°C or higher. The heating method can be any known method, and the heating time can be set arbitrarily. It can be done using an autoclave or a forced-air dryer, or by treating at 200°C for 1 hour. Furthermore, the repair method for the fiber-reinforced composite material of this disclosure may include a pressurization step, and if necessary, a mold or 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 also be applied in stages.

[0234] <Remolding Methods for Cured Epoxy Resins> The remolding method for epoxy resin cured articles disclosed herein includes the following steps: heating and pressurizing the epoxy resin cured articles of this disclosure at a temperature above the glass transition temperature of the aforementioned epoxy resin cured articles.

[0235] The epoxy resin cured products disclosed herein exhibit excellent reformability and can be reformed after molding.

[0236] The heating temperature can be above the glass transition temperature of the epoxy resin cured product, and there are no particular limitations. Preferably, it is 160°C or higher, more preferably 180°C or higher, and particularly preferably 200°C or higher. The heating method can be any known method, and the heating time can be set arbitrarily. An autoclave or a blower-type dryer can be used, and the treatment can be carried out at 200°C for 1 hour. Furthermore, during pressurization, a mold or support frame can be used if necessary. The pressure during pressurization is preferably 0.05 MPa to 2 MPa, more preferably 0.2 MPa to 2 MPa, and these pressures can also be applied in stages.

[0237] <Reforming Methods for Fiber Reinforced Composite Materials> The remolding method for fiber-reinforced composite materials disclosed herein includes the following steps: heating and pressurizing the fiber-reinforced composite material of the present disclosure at a temperature above the glass transition temperature of the aforementioned fiber-reinforced composite material.

[0238] The fiber-reinforced composite material disclosed herein exhibits excellent reformability, and can be re-molded after molding.

[0239] The heating temperature is not particularly limited as long as it is above the glass transition temperature of the fiber-reinforced composite material, but preferably 160°C or higher, more preferably 180°C or higher, and particularly preferably 200°C or higher. The heating method can be any known method, and the heating time can be set arbitrarily. An autoclave or a blower-type dryer can be used, and the treatment can be carried out at 200°C for 1 hour. Furthermore, during pressurization, a mold or support frame can be used if necessary. The pressure during pressurization is preferably 0.05 MPa to 2 MPa, more preferably 0.2 MPa to 2 MPa, and these pressures can also be applied in stages.

[0240] <Decomposition Methods of Cured Epoxy Resins> The method for decomposing epoxy resin cured products disclosed herein includes the following steps: contacting the epoxy resin cured product of this disclosure with a decomposing agent containing a reducing agent. The epoxy resin cured product of this disclosure exhibits excellent resin decomposability, enabling the resin cured product to be decomposed into low-molecular-weight compounds.

[0241] Regarding the aforementioned types of reducing agents, there are no particular restrictions as long as the epoxy resin cured product is decomposed. Any reducing agent can be used, depending on the type of bonds contained in the epoxy resin cured product.

[0242] Examples of reducing agents include dithiothreitol, 2-mercaptoethanol, 1-thioglycerol, glutathione, 2-mercaptoethylamine hydrochloride, cystine hydrochloride, and tris(2-carboxyethyl)phosphine hydrochloride, with those capable of reducing disulfide bonds being preferred. These reducing agents can be used alone or in combination.

[0243] Furthermore, these reducing agents can be used in a solvent-free manner, or they can be used by diluting them with a solvent to prepare a decomposing agent solution. That is, the epoxy resin cured products of this disclosure can also be decomposed by impregnation in a decomposing agent solution containing a reducing agent.

[0244] There is no particular limitation on the amount of decomposing agent solution used, and it can be determined according to the shape of the epoxy resin cured product, decomposition conditions, etc. The amount of decomposing agent solution used, on a mass basis, is preferably 1 to 1000 times the amount of epoxy resin cured product, more preferably 1 to 100 times the amount of epoxy resin cured product, and particularly preferably 1 to 10 times the amount of epoxy resin cured product.

[0245] The concentration of the reducing agent in the decomposing agent solution is not particularly limited, but is preferably 0.1% to 99.9% by mass, more preferably 1% to 80% by mass, and particularly preferably 5% to 50% by mass.

[0246] Regarding the solvent used for dilution, there are no particular limitations as long as it can dissolve the reducing agent and decompose the solidified material; it can be water or an organic solvent. Examples of organic solvents for dilution include N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, 1,4-dioxane, tetrahydrofuran, methanol, and ethanol. Polar organic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and dimethyl sulfoxide are preferred because they can completely dissolve the decomposed solidified material.

[0247] In addition to the above, the decomposition agent may also contain additives that promote decomposition. Nitrogenous bases such as triethylamine, DBU, or ammonia are preferred due to their high decomposition-promoting effect when added.

[0248] In the above decomposition, to promote decomposition, heating can be performed 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 stirring can be performed appropriately, and ultrasonic treatment can be performed if necessary. For example, the decomposition reaction can be carried out while stirring the decomposing agent at room temperature (25°C) or 80°C for 8 hours. In the above decomposition, to promote decomposition, pressure can be applied at 0.1 MPa to 10 MPa (preferably 0.1 MPa to 1 MPa).

[0249] The decomposition method of the epoxy resin cured product according to this disclosure preferably results in decomposition of 50% or more by mass of the cured product, more preferably 80% or more by mass of the cured product, and even more preferably 95% or more by mass of the cured product. For the epoxy resin cured product of this disclosure, 100% by mass of the epoxy resin cured product is preferred.

[0250] Methods for recycling reinforcing fibers in fiber-reinforced composites The method for recycling reinforcing fibers in the fiber-reinforced composite material disclosed herein includes the following steps: contacting the fiber-reinforced composite material of this disclosure with a decomposing agent containing a reducing agent. For the fiber-reinforced composite material of this disclosure, the resin can be decomposed and / or dissolved by contacting it with a decomposing agent containing a reducing agent, thereby recovering the reinforcing fibers.

[0251] The description of the decomposing agent containing a reducing agent in the method for recycling reinforcing fibers of fiber-reinforced composites, including definitions, examples, and preferred methods, is the same as the description of the decomposing agent containing a reducing agent in the method for decomposing epoxy resin cured products.

[0252] In the above decomposition and / or dissolution, to promote decomposition and / or dissolution, heating can be performed 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 stirring can be performed appropriately, and ultrasonic treatment can be performed if necessary. For example, the decomposition and / or dissolution reaction can be carried out while stirring the decomposition agent at room temperature (25°C) or 80°C for 8 hours. In the above decomposition and / or dissolution, to promote decomposition and / or dissolution, pressure can be applied at 0.1 MPa to 10 MPa (preferably 0.1 MPa to 1 MPa).

[0253] The method for recycling reinforcing fibers in fiber-reinforced composite materials disclosed herein may also include the following steps: recovering the reinforcing fibers after decomposing and / or dissolving the resin. There are no particular limitations on the method for recycling the reinforcing fibers; long fibers can be wound up for recycling, or they can be recycled through filtration.

[0254] The recovered reinforcing fibers can be reused in prepregs or fiber-reinforced composites. During this process, sizing agents or other oils can be reapplied if necessary.

[0255] Other Implementation Methods of Epoxy Resin Curing Agents As another embodiment of epoxy resin curing agent, an epoxy resin curing agent comprising a polyphenolic compound [A2] containing a structural unit represented by the following general formula (2) can also be cited.

[0256] [Chemical Formula 20] In general formula (2), R 2a R 2b and R 2c Each group independently represents any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom, where n represents an integer from 2 to 500.

[0257] The preferred mode and specific examples of the polyphenolic compound [A2] containing the structural unit represented by general formula (2) are the same as the preferred mode and specific examples of the polyphenolic compound [A] containing the polyphenolic compound represented by general formula (2) in the epoxy resin composition of this disclosure.

[0258] In other embodiments of the epoxy resin curing agent, it is preferred that it further comprises epoxy resin [B]. The ratio (a2) / (b) of the molar amount of phenolic hydroxyl groups (a2) in the aforementioned polyphenolic compound [A2] to the molar amount of epoxy groups (b) in the aforementioned epoxy resin [B] is 0.25 or more and 1.5 or less. When an external force is applied to a cured product that has been cured to a degree of curing of 90% or more at a temperature 60°C higher than the glass transition temperature of the cured product, the stress relief rate at a time point of 1 hour from the start of the application of the external force is measured to be 90% or more.

[0259] The preferred methods and specific examples of epoxy resin [B], ratio (a2) / (b), and stress relief rate in other embodiments of epoxy resin curing agents are the same as those of the preferred methods and specific examples of epoxy resin [B], ratio (a) / (b), and stress relief rate in the epoxy resin composition of this disclosure.

[0260] Example The present disclosure will be described in more detail below with reference to embodiments, but the present disclosure is not limited thereto. It should be noted that the components and evaluation methods used in the embodiments and comparative examples are as follows.

[0261] <Preparation of Epoxy Resin Compositions> Synthesis of polyphenolic compound [A] [Synthetic Example 1] Synthesis of poly(tert-amylphenol disulfide) (hereinafter referred to as "APDS") [Chemical Formula 21] 600 mL of N,N-dimethylformamide (DMF) and 247 g (1.5 mol) of 4-(1,1-dimethylpropyl)phenol were added to a four-necked flask equipped with a thermometer, dropping funnel, condenser, and stirrer. After cooling to 0°C, 189 g (1.4 mol) of disulfide dichloride was added dropwise over 2 hours. After further heating to 25°C over 10 hours, the mixture was stirred at 45°C–50°C for 2 hours.

[0262] The resulting yellowish-brown solution was slowly heated to 170°C under reduced pressure, and DMF was removed by distillation.

[0263] The recovered product was then dissolved in 700 mL of diethyl ether, and 3500 mL of hexane was added dropwise to separate the gel-like product. Finally, it was dried at 150 °C to obtain a brown solid product.

[0264] The main product was poly(tert-amylphenol disulfide), with a yield of 279 g (yield 88% by mass) and a purity of 99% (HPLC area %). The hydroxyl value, determined according to JIS K0070:1992, was 241, and the hydroxyl equivalent was 233 g / Eq. The weight-average molecular weight, determined by gel permeation chromatography (GPC), was 3300, and the softening point was 92 °C.

[0265] [Synthetic Example 2] Synthesis of poly(tert-butylphenol disulfide) (hereinafter referred to as "BPDS") [Chemical Formula 22] The 4-(1,1-dimethylpropyl)phenol in Synthesis Example 1 was replaced with 4-(tert-butyl)phenol, and the same operation was performed otherwise, resulting in a brown viscous liquid.

[0266] The main product was poly(tert-butylphenol disulfide), with a yield of 252 g (yield 85% by mass) and a purity of 99% (HPLC area %). The hydroxyl value, determined according to JIS K0070:1992, was 244, and the hydroxyl equivalent was 230 g / Eq. The weight-average molecular weight, determined by GPC, was 1600, and the softening point was 98 °C.

[0267] [Synthetic Example 3] Synthesis of poly(methoxyphenol disulfide) (hereinafter referred to as "MOPDS") [Chemical Formula 23] The 4-(1,1-dimethylpropyl)phenol in Synthesis Example 1 was replaced with 4-(methoxy)phenol, and the same operation was performed to obtain a brown viscous liquid.

[0268] The main product was poly(methoxyphenol disulfide), with a yield of 223 g (yield 86% by mass) and a purity of 98% (HPLC area %). The hydroxyl value, determined according to JIS K0070:1992, was 295, and the hydroxyl equivalent was 190 g / Eq. The weight-average molecular weight, determined by GPC, was 1500, and the softening point was 115 °C.

[0269] As a comparative example, the following polyphenolic compounds were prepared.

[0270] • Novolac type phenolic resin (hereinafter referred to as "PN") (manufactured by DIC Corporation TD-2093Y, hydroxyl equivalent = 104 g / Eq) [Epoxy Resin [B]] As epoxy resin [B], the following epoxy resin is prepared.

[0271] Bisphenol A-diglycidyl ether (manufactured by Mitsubishi Chemical Corporation, JER825, epoxy equivalent = 176 g / Eq, hereinafter referred to as "DGEBA") Bisphenol F-diglycidyl ether (manufactured by Mitsubishi Chemical Corporation, jER806, epoxy equivalent = 168 g / Eq, hereinafter referred to as "DGEBF") Tetraglycidyl diaminodiphenylmethane (manufactured by NIPPON STEEL Chemical & Material Co., Ltd., YH-404, epoxy equivalent = 118 g / Eq, hereinafter referred to as "TGDDM") [Curing Accelerator] • Triphenylphosphine (manufactured by Tokyo Chemical Industry Co., Ltd., hereinafter referred to as "PPh3") ·2-Ethyl-4-methylimidazol (CUREZOL 2E4MZ manufactured by Shikoku Chemical Industry Co., Ltd., hereinafter referred to as "2E4MZ") ·1,8-Dazabicycloundecene (manufactured by Tokyo Chemical Industry Co., Ltd., hereinafter referred to as "DBU") <Examples 1-7 and Comparative Example 1> [1] Preparation of epoxy resin composition The polyphenol compound and epoxy resin are measured in the mass proportions listed in Table 1 below. They are mixed at 80°C using a roller mill until homogeneous. Then, a curing accelerator is added in the mass proportions listed in Table 1 below, and the mixture is kneaded again to prepare an epoxy resin composition.

[0272] [2] Preparation and property determination of epoxy resin cured products (2-1) Preparation of epoxy resin cured products The epoxy resin composition prepared in [1] was degassed in a vacuum and then injected into a silicone mold with a thickness of 4 mm, using a 4 mm thick silicone resin gasket. The mixture was 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.

[0273] (2-2) Determination of glass transition temperature (Tg) For the glass transition temperature, a differential scanning calorimeter (DSC) Q2000 manufactured by TA Instruments was used, and the measurement was performed in a nitrogen flow at a flow rate of 40 ml / min. 5 mg ± 1 mg of the epoxy resin cured product prepared in (2-1) was collected, and the temperature was increased from 30 °C to 350 °C at a rate of 10 °C / min. The inflection point in the resulting curve was recorded as the glass transition temperature.

[0274] (2-3) Determination of stress relief rate The epoxy resin composition prepared in [1] was placed in an 8mmΦ aluminum parallel plate with a gap distance of 2mm, and cured at 120°C for 2 hours, at 150°C for 2 hours, and at 180°C for 2 hours.

[0275] Next, after holding at [glass transition temperature of the cured product + 60] °C for 2 minutes, the product was subjected to an application of 6.25 × 10⁻⁶ °C. - 3 The modulus value G generated by the displacement in rad was measured for 3600 seconds, and its time coordinate graph was recorded. In the stress relief measurement, a Discovery DHR-2 rheometer manufactured by TA Instruments was used to measure the stress in a nitrogen flow of 10 L / min.

[0276] The stress mitigation rate is calculated using the following formula from the obtained time coordinate graph.

[0277] [1-((G(min)) / (G(0)))]×100 Here, G(0) is the modulus value at 0 seconds after the application of the external force. G(min) is the minimum modulus value up to 3600 seconds after the application of the external force. This value is used if the modulus value reaches the lower limit of the device's measurement within 3600 seconds, and otherwise, it is the modulus value at 3600 seconds. It should be noted that in this disclosure, the modulus value G(0) at 0 seconds after the application of the external force is considered to be the same as the modulus value G(0.1) at 0.1 seconds after the application of the external force to calculate the stress relief rate.

[0278] The results of the stress relief measurements are shown in Table 1 and... Figure 1 middle. Figure 1 In the diagram, the dotted line represents the results of Comparative Example 1, and the solid line represents the measurement results of Example 2. In Example 2, stress relief occurred by applying an external force, and the stress relief rate was 99.2% 3600 seconds after the application of the external force. On the other hand, in Comparative Example 1, even when an external force was applied, almost no stress relief occurred, and the stress relief rate was 0.3% 3600 seconds after the application of the external force.

[0279] (2-4) Stress relief mode separation analysis The modulus value G(t) recorded in (2-3) at 200℃ is analyzed according to the above [stress relief mode separation analysis].

[0280] It should be noted that the stress relief mode separation analysis was performed within the range of 0 seconds to 3600 seconds, using the following 25 modes.

[0281] τ i=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 The results of the stress relief mode separation analysis in Example 2 are shown below. Figure 2 middle. Figure 2 In the diagram, black circles represent the contribution of each mitigation pattern derived from the regression, and solid lines represent the smooth lines connecting them.

[0282] (2-5) Confirmation of Reshaping Properties The epoxy resin cured product prepared in (2-1) was crushed into flakes with three sides less than 1 mm. 0.7 g of the sample was placed in a mold with a cylindrical box having an 8 mm Φ and preheated at 200°C for 5 minutes. Further, a remolded sample was prepared by applying a pressure of 25 MPa to the sample at 200°C for 30 minutes.

[0283] The obtained reshaped samples were visually observed. Reshapeability was judged according to the following criteria, where A and B are considered practically acceptable ranges.

[0284] A: The surface of the reshaped sample is smooth, and even when light is transmitted through it, the grain boundaries of the fragments cannot be observed.

[0285] B: The surface of the reshaped sample is smooth, but when light is transmitted through it, turbidity caused by the grain boundaries of the debris is observed.

[0286] C: Grain boundaries of the pre-forming chips were observed on the surface of the reshaped sample.

[0287] (2-6) Confirmation of self-healing The epoxy resin cured material prepared in (2-1) was ground to a thickness of 2 mm, and a razor was inserted into a crack of about 2 mm. The sample was then placed on the sample stage of a transmission microscope with a heated stage, preheated to 120°C, and then heated to 200°C at a rate of 20°C / min. Finally, it was held at 200°C for 15 minutes to prepare a self-healing sample.

[0288] The obtained self-healing samples were observed using a transmission microscope with n=5 samples. The self-healing property was judged according to the following criteria, where A and B are considered to be practically acceptable ranges.

[0289] A: The cracks in the self-healing sample have almost completely disappeared.

[0290] B: The crack in the self-healing sample has shrunk.

[0291] C: No disappearance or reduction of cracks was observed in the self-healing sample.

[0292] (2-7) Confirmation of resin decomposability Cut the epoxy resin cured product prepared in (2-1) into 1cm×1cm×0.4mm pieces. Immerse a small piece in 40mL of N,N-dimethylformamide solution containing 4mL of 2-mercaptoethanol and stir at room temperature (25℃) and 80℃ respectively.

[0293] The state of the solution was observed visually after 8 hours. Resin decomposability was determined according to the following criteria, with A and B considered as practically acceptable ranges.

[0294] A: The epoxy resin cured product completely decomposes at room temperature, becoming a homogeneous solution.

[0295] B: The epoxy resin cured product did not completely decompose at room temperature, but decomposed by more than 80% by mass at 80°C.

[0296] C: The epoxy resin cured product decomposes at less than 80% by mass under any conditions at room temperature and 80°C.

[0297] (2-8) Flexural modulus of elasticity (FM) and flexural strength (FS) In the epoxy resin cured product prepared in (2-1), the test was carried out according to JIS K7171:2016. The resin test piece was prepared with dimensions of 80mm × 10mm × 4mm (thickness h). The distance between the support points L was 16 × 4 (thickness). The bending test was carried out at a test speed of 2mm / min, and the bending modulus of elasticity and bending strength were measured.

[0298] (2-9) Compressive strength (CS) The epoxy resin composition prepared in [1] was placed in a test tube with an 8 mm Φ, and then cured at 120°C for 2 hours, at 150°C for 2 hours, and at 180°C for 2 hours. The cured material was removed and cut in a way that the length was 15 mm, thereby obtaining a cylindrical cured material with a diameter of 15 mm × 8 mm Φ.

[0299] The compressive strength was determined by performing a compression test at a test speed of 0.2 mm / min in accordance with JIS K7181:2011.

[0300] The various physical properties of the cured resin products obtained by curing the epoxy resin compositions are shown in Table 1. It should be noted that the degree of curing of the epoxy resin compositions obtained in Examples 1 to 7 and Comparative Example 1, as evaluated by DSC, is 99.9% or higher.

[0301] [Table 1] (2-10) Identification of decomposition products The decomposition products of the epoxy resin cured products in Examples 1 to 3 obtained in the confirmation of resin decomposition in (2-7) were analyzed by LC-MS. The results showed that the decomposition products were compounds with a molecular weight of 1072 and the following structure.

[0302] [Chemical Formula 24] Based on the above, in Examples 1 to 7, epoxy resin compositions with excellent reformability or self-healing properties in the cured products can be provided. Furthermore, the reformability or self-healing properties in the cured products of prepregs formed by impregnating the epoxy resin composition of this disclosure with a fiber-reinforced substrate having reinforcing fibers, and fiber-reinforced composite materials comprising an epoxy resin cured product formed by curing the epoxy resin composition of this disclosure and a fiber-reinforced substrate having reinforcing fibers, are also excellent. In addition, the epoxy resin cured product of this disclosure is decomposed and dissolved by contact with a decomposing agent containing a reducing agent. Regarding the fiber-reinforced composite material of this disclosure, the reinforcing fibers of the fiber-reinforced composite material can be recovered by contacting it with a decomposing agent containing a reducing agent. Furthermore, the epoxy resin curing agent of this disclosure can be used as a curing agent.

[0303] It should be noted that the entire disclosure of Japanese Patent Application No. 2024-057150, filed on March 29, 2024, is incorporated herein by reference. Furthermore, all documents, patent applications, and technical standards described in this specification are incorporated herein by reference to the same extent as they are specifically and separately described.

Claims

1. An epoxy resin composition comprising a polyphenolic compound [A] containing at least a structural unit represented by the following general formula (1) and an epoxy resin [B]. The ratio (a) / (b) of the molar amount of phenolic hydroxyl groups (a) in the polyphenolic compound [A] to the molar amount of epoxy groups (b) in the epoxy resin [B] is 0.25 or more and 1.5 or less. When an external force is applied to a cured product that has been cured to a degree of cure of 90% or more at a temperature 60°C higher than the glass transition temperature of the cured product, the stress relief rate at one hour from the start of the application of the external force is measured to be 90% or more. [Chemical Formula 1] In general formula (1), Y is an independent dynamic covalent bonding site, and R 1a R 1b R 1c and R 1d At least one of them is a connecting bond between Y and other adjacent structural units, and the others each independently represent any one of hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom, and n represents an integer from 2 to 500.

2. The epoxy resin composition according to claim 1, wherein, The dynamic covalent bonding site is a group containing a disulfide bond.

3. The epoxy resin composition according to claim 1 or claim 2, wherein, As the polyphenolic compound [A], it comprises a polyphenolic compound containing a structural unit represented by the following general formula (2). [Chemical Formula 2] In general formula (2), R 2a R 2b and R 2c Each group independently represents any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom, where n represents an integer from 2 to 500.

4. The epoxy resin composition according to claim 1 or claim 2, wherein, As the polyphenolic compound [A], it comprises a polyphenolic compound containing a structural unit represented by the following general formula (3). [Chemical Formula 3] In general formula (3), R3 independently represents any one of hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom, and n represents an integer from 2 to 500.

5. The epoxy resin composition according to claim 1 or claim 2, wherein the epoxy resin is a curing agent.

6. An epoxy resin cured product, which is formed by curing the epoxy resin composition of claim 1.

7. An epoxy resin cured product, when brought into contact with a decomposing agent containing a reducing agent and heated at 100°C for 48 hours, has more than 80% by mass of the cured product dissolved.

8. An epoxy resin cured product, when brought into contact with a decomposing agent containing a reducing agent and heated, produces a compound having at least the structure shown in the following general formula (4). [Chemical Formula 4] In general formula (4), Indicates a connection key, R 4a R 4b and R 4c Each can independently represent any one of the following: hydrogen atom, aliphatic hydrocarbon group, aromatic group, alkoxy group, amino group, or halogen atom.

9. A prepreg blank formed by impregnating the epoxy resin composition of claim 1 or claim 2 into 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 prepreg blank.

10. A fiber-reinforced composite material comprising an epoxy resin cured product according to any one of claims 6 to 8, 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.

11. A method for repairing epoxy resin cured articles, comprising the following steps: heating the epoxy resin cured article of any one of claims 6 to 8, which has internal cracks or peeling, at a temperature above the glass transition temperature of the epoxy resin cured article, thereby repairing the cracks or peeling.

12. A method for repairing fiber-reinforced composite materials, comprising the steps of: heating the fiber-reinforced composite material of claim 10, which has internal cracks or peeling, at a temperature above the glass transition temperature of the fiber-reinforced composite material, thereby repairing the cracks or peeling.

13. A method for remolding an epoxy resin cured product, comprising the steps of heating and pressurizing the epoxy resin cured product according to any one of claims 6 to 8 at a temperature above the glass transition temperature of the epoxy resin cured product.

14. A method for remolding a fiber-reinforced composite material, comprising the steps of heating and pressurizing the fiber-reinforced composite material of claim 10 at a temperature above the glass transition temperature of the fiber-reinforced composite material.

15. A method for decomposing an epoxy resin cured product, comprising the step of contacting the epoxy resin cured product according to any one of claims 6 to 8 with a decomposing agent containing a reducing agent.

16. A method for recycling reinforcing fibers of a fiber-reinforced composite material, comprising the step of contacting the fiber-reinforced composite material of claim 10 with a decomposing agent containing a reducing agent.

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