Epoxy resin composition, prepreg, fiber-reinforced composite material, and method for recycling fiber-reinforced composite material

Abstract

The present invention addresses the problem of providing an epoxy resin composition that overcomes the trade-off in the prior art between depolymerizability and heat resistance, and that yields a cured product provided with sufficient heat resistance while having excellent recyclability. Furthermore, the purpose of the present invention is to provide a prepreg and a fiber-reinforced composite material having excellent recyclability, by using the epoxy resin composition as a matrix resin.　The epoxy resin composition includes components [A], [B], and [C], and the component [B] is contained in an amount of 30-70 parts by mass per 100 parts by mass of the total epoxy resin. Component [A]: a bifunctional naphthalene-type epoxy resin or a biomass-derived bisphenol-type epoxy resin. Component [B]: a urethane-modified epoxy resin. Component [C]: a curing agent.

Description

Epoxy resin composition, prepreg, fiber-reinforced composite material, and method for recycling fiber-reinforced composite material

[0001] The present invention relates to an epoxy resin composition having excellent recyclability, a prepreg and a fiber-reinforced composite material using the epoxy resin composition as a matrix resin, and a method for recycling the fiber-reinforced composite material.

[0002] Epoxy resin compositions are suitable for use as matrix resins in fiber-reinforced composite materials that are combined with reinforcing fibers such as carbon fibers, glass fibers, and aramid fibers, taking advantage of their high strength, rigidity, heat resistance, and adhesiveness.

[0003] Fiber-reinforced composite materials are generally manufactured using sheet-like intermediate substrates (prepregs) made of reinforcing fibers impregnated with epoxy resin. After laminating the prepregs, molded products are obtained by heating the laminate to harden the epoxy resin. Because a wide range of properties can be achieved by varying the laminate design of the prepregs, they are used in a variety of fields, including aircraft, automobiles, sports, and medicine.

[0004] In recent years, the applications of fiber-reinforced composite materials have been rapidly expanding, and there is a demand for epoxy resin compositions and fiber-reinforced composite materials that are carbon-neutral and have excellent recyclability in addition to heat resistance and rigidity. Epoxy resin compositions using urethane-modified epoxy resins are known as matrix resins for fiber-reinforced composite materials (Patent Document 1).

[0005] Japanese Patent Application Laid-Open No. 2024-7372

[0006] In the invention described in Patent Document 1, the epoxy resin composition cannot be depolymerized with an organic solvent after curing to form a fiber-reinforced composite material, and therefore the reinforcing fibers cannot be recovered again from the fiber-reinforced composite material, resulting in poor recyclability.

[0007] Increasing the crosslink density is an effective way to improve the heat resistance of fiber-reinforced composite materials. However, high crosslink density also leads to a complex network, making the materials more resistant to decomposition and making chemical depolymerization more difficult.

[0008] Therefore, an object of the present invention is to provide an epoxy resin composition that overcomes the trade-off between depolymerization ability and heat resistance that exists in the prior art, and that provides a cured product that has both excellent recyclability and sufficient heat resistance.A further object of the present invention is to provide a prepreg and a fiber-reinforced composite material that are excellent in recyclability by using the epoxy resin composition as a matrix resin.

[0009] The epoxy resin composition of the present invention has the following configuration: 1. An epoxy resin composition comprising components [A], [B], and [C], wherein component [B] is contained in an amount of 30 to 70 parts by mass per 100 parts by mass of the total epoxy resin. Component [A]: difunctional naphthalene-type epoxy resin or biomass-derived bisphenol-type epoxy resin. Component [B]: urethane-modified epoxy resin. Component [C]: curing agent. 2. The epoxy resin composition according to 1 above, further comprising a polyrotaxane as component [E]. 3. The epoxy resin composition according to 1 or 2 above, wherein component [B] is an epoxy resin in which a bisphenol-type epoxy resin is modified with polyurethane. 4. Epoxy resin composition according to the above item 3, wherein the polyurethane uses at least one polyhydroxy compound selected from the group consisting of polyether polyol, polycarbonate polyol, and polyester polyol, and at least one polyisocyanate compound selected from the group consisting of 1,6-hexamethylene diisocyanate, tolylene diisocyanate, isophorone diisocyanate, and an isocyanuric form of 1,6-hexamethylene diisocyanate. 5. An epoxy resin composition according to any one of the above items 1 to 4, wherein the content of component [B] is 30 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the total epoxy resin, and further contains the following components [F] and [H]: Component [F]: glycidylamine-type epoxy resin, and component [H]: thermoplastic resin. 6. An epoxy resin composition according to any one of the above items 1 to 5, wherein the glass transition temperature of the cured product after curing for 60 minutes at a temperature selected from 150°C to 200°C is 130°C or more. 7. A prepreg comprising the epoxy resin composition according to any one of items 1 to 6 above and at least one reinforcing fiber selected from the group consisting of carbon fiber, glass fiber, and aramid fiber. 8. The prepreg according to item 7 above, wherein the reinforcing fiber is in the form of a woven fabric or a discontinuous fiber. 9. The prepreg according to item 8 above, wherein the reinforcing fiber is in the form of a discontinuous fiber, and the discontinuous fiber is randomly dispersed in the form of a bundle or a substantially monofilament. 10. A fiber-reinforced composite material comprising a cured product of the epoxy resin composition according to any one of items 1 to 6 above and reinforcing fiber.11. A method for recycling a fiber-reinforced composite material, comprising steps (i) to (iii) using the fiber-reinforced composite material of item 10 above. (i) Processing the fiber-reinforced composite material into pellets having lengths of 2 to 100 mm. (ii) Depolymerizing the cured epoxy resin composition contained in the pellet-shaped fiber-reinforced composite material obtained in item (i) by treatment with a dissolving solution or hydrolysis treatment. (iii) Hot-pressing the pellet-shaped fiber-reinforced composite material in which the cured epoxy resin composition has been depolymerized in item (ii). 12. A fiber-reinforced composite material, the cured product of the epoxy resin composition of any one of items 1 to 6 above, comprising a depolymerized plasticized material and reinforcing fibers, wherein the plasticized material further comprises a benzoxazolone structure. 13. An automotive component using the fiber-reinforced composite material of item 10 above. 14. A sports component using the fiber-reinforced composite material of item 10 above. 15. An aircraft component using the fiber-reinforced composite material of item 10 above.

[0010] According to the present invention, it is possible to obtain an epoxy resin composition which provides a cured product having both excellent recyclability and sufficient heat resistance. Furthermore, by using the epoxy resin composition as a matrix resin, it is possible to provide a prepreg and a fiber-reinforced composite material which have excellent recyclability.

[0011] The epoxy resin composition of the present invention contains the following components [A], [B], and [C], with component [B] contained in a specific ratio described below: [A]: difunctional naphthalene-type epoxy resin or biomass-derived bisphenol-type epoxy resin [B]: urethane-modified epoxy resin [C]: curing agent Each of the components is described below.

[0012] In the present invention, an n-functional epoxy resin refers to one having n epoxy groups in the molecule of the main component (optical isomers and structural isomers that differ only in the substitution position of the epoxy group on the benzene ring or naphthalene ring, such as 2,2'-isomer and 2,4'-isomer, are treated as the same species), and a bifunctional epoxy resin refers to an epoxy resin having two epoxy groups in the molecule.

[0013] (Component [A]) Component [A] used in the present invention is a difunctional naphthalene-type epoxy resin or a biomass-derived bisphenol-type epoxy resin. When component [A] is a difunctional naphthalene-type epoxy resin, an average epoxy equivalent of 100 to 230 tends to provide an epoxy resin composition having a cured product with a glass transition temperature of 120°C or higher, and an average epoxy equivalent of 150 to 230 tends to provide an epoxy resin composition having a glass transition temperature of 130°C or higher.

[0014] In the present invention, when component [A] is a difunctional naphthalene-type epoxy resin, the use of a difunctional naphthalene-type epoxy resin results in a rigid naphthalene structure, thereby providing a cured product with excellent heat resistance, and the use of a difunctional epoxy resin results in a low crosslink density, thereby providing an epoxy resin composition in which the cured product maintains depolymerization properties while still providing excellent heat resistance.

[0015] In the present invention, commercially available bifunctional naphthalene-type epoxy resins that can be used as component [A] include EPICLON (registered trademark) HP-4032SS, EPICLON (registered trademark) HP-4032D, and EPICLON (registered trademark) HP-4770 (all manufactured by DIC Corporation), and diglycidyl 1,4'-dihydroxynaphthalene (manufactured by Air Water Performance Chemicals Inc.). Of these, EPICLON (registered trademark) HP-4770 is preferred because it is likely to give an epoxy resin composition that has a glass transition temperature of 130°C or higher when cured even at a curing temperature of 150°C.

[0016] In the present invention, component [A] is preferably a biomass-derived bisphenol epoxy resin because its biomass origin reduces greenhouse gas emissions. Biomass-derived bisphenol epoxy resins are biomass-derived bisphenol epoxy resins made from epichlorohydrin produced from vegetable oil-derived glycols. When component [A] is a bifunctional biomass-derived bisphenol epoxy resin, the crosslink density is reduced, resulting in an epoxy resin composition with excellent heat resistance while maintaining depolymerization properties in the cured product. When component [A] is a biomass-derived bisphenol epoxy resin, its average epoxy equivalent is preferably 150 to 220. Such an average epoxy equivalent makes it easier to obtain an epoxy resin composition with a cured product having a glass transition temperature of 120°C or higher.

[0017] In the present invention, commercially available examples of biomass-derived bisphenol epoxy resins that can be used as component [A] include bisphenol A epoxy resins such as "Briozen (registered trademark)" YD-128G (biomass ratio: 28%) and "Briozen (registered trademark)" YD-127G (biomass ratio: 28%) (both manufactured by Aditya Birla Chemicals), and bisphenol F epoxy resins such as "Briozen (registered trademark)" YDF-170LCG (biomass ratio: 30%, manufactured by Aditya Birla Chemicals).

[0018] The biomass origin can be confirmed by measuring the presence or absence of carbon isotope (C14) that is only contained in materials of biological origin in accordance with ASTM D6866-20.

[0019] In the present invention, the average epoxy equivalent can be evaluated by potentiometric titration in accordance with JIS K 7236:2001. For example, approximately 300 mg of epoxy resin is weighed and placed in a glass beaker, and 10 mL of chloroform is added. The solution is stirred using a magnetic stirrer until the weighed components are dissolved in the chloroform. 20 mL of acetic acid is added to the above solution, followed by 10 mL of tetraethylammonium bromide acetate solution (0.4 g / mL acetic acid) and stirring. An electrode is immersed in the above solution, and potentiometric titration is performed using a perchloric acid-acetic acid standard solution (0.1 mol / L), allowing the average epoxy equivalent to be calculated.

[0020] (Component [B]) In the present invention, component [B] is a urethane-modified epoxy resin having a urethane bond. Component [B] is preferably an epoxy resin obtained by modifying a bisphenol-type epoxy resin with polyurethane, and an epoxy resin composition having an excellent balance between depolymerization property and heat resistance can be obtained. Examples of bisphenol-type epoxy resins that serve as the base for such urethane-modified epoxy resins include bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, and bisphenol S-type epoxy resins. Among these, urethane-modified epoxy resins based on bisphenol A-type epoxy resins are preferred because of their easy availability.

[0021] The polyurethane preferably uses at least one polyhydroxy compound selected from the group consisting of polyether polyols, polycarbonate polyols, and polyester polyols, and at least one polyisocyanate compound selected from the group consisting of 1,6-hexamethylene diisocyanate, tolylene diisocyanate, isophorone diisocyanate, and an isocyanurate of 1,6-hexamethylene diisocyanate. By using an epoxy resin modified with such a polyurethane, an epoxy resin composition can be obtained that exhibits an excellent balance between depolymerization ability and heat resistance in the cured product.

[0022] The average epoxy equivalent of component [B] is preferably 200 to 320, which allows for the production of an epoxy resin composition that has an excellent balance between depolymerization property and heat resistance.

[0023] The urethane-modified epoxy resin, component [B] of the present invention, can be depolymerized even after the epoxy resin composition of the present invention has cured, because the urethane bonds are cleaved by treatment with a solvent or hydrolysis. In the present invention, a bifunctional epoxy resin is used as component [A], and therefore the cured product obtained by curing the epoxy resin composition of the present invention has a low crosslink density, and therefore decomposition occurs in large domain units upon cleavage of the urethane bonds, further improving depolymerization properties.

[0024] Component [B] is contained in an amount of 30 to 70 parts by mass relative to 100 parts by mass of the total epoxy resins contained in the epoxy resin composition of the present invention. By including the epoxy resin of component [B] in this range, an epoxy resin composition having an excellent balance between depolymerization ability and heat resistance can be obtained. From this perspective, it is preferable that component [B] be contained in an amount of 35 to 60 parts by mass relative to 100 parts by mass of the total epoxy resins. Here, "total epoxy resins" refers to the above-mentioned components [A] and [B], as well as components [F] and [G], which will be described later, and other epoxy resins, and "100 parts by mass of total epoxy resins" refers to the total amount of components [A], [B], [F], [G], and other epoxy resins, converted into 100 parts by mass.

[0025] Commercially available products of component [B] include ADEKA RESIN (registered trademark) EPU-73B, ADEKA RESIN (registered trademark) EPU-73S, and ADEKA RESIN (registered trademark) EPU-1395 (all manufactured by ADEKA Corporation). Alternatively, the urethane-modified epoxy resins described in WO 2006 / 132093 can also be used.

[0026] It is preferred that the content of component [B] is 30 parts by mass or more and 60 parts by mass or less per 100 parts by mass of the total epoxy resin, and that the composition further contains the following components [F] and [H]: Component [F]: glycidylamine-type epoxy resin; and Component [H]: thermoplastic resin.

[0027] Examples of the glycidylamine type epoxy of component [F] include N,N,N',N'-tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol, triglycidylaminocresol, diglycidylaniline, and N,N-diglycidyl-4-phenoxyaniline.

[0028] Examples of the thermoplastic resin of component [H] include polysulfone, polyethersulfone, and polyetherimide. Normally, component [B] and the thermoplastic resin of component [H] have poor compatibility, and component [B] cannot dissolve the thermoplastic resin of component [H]. However, the glycidyl amine-type epoxy resin of component [F] acts as a compatibilizer between component [B] and component [H], making it possible to dissolve component [H] in component [B].

[0029] The glycidylamine-type epoxy resin of component [F] is preferably contained in an amount of 5 to 30 parts by mass, and more preferably 5 to 15 parts by mass, based on 100 parts by mass of the total epoxy resins contained in the epoxy resin composition. By controlling the content of the glycidylamine-type epoxy resin of component [F] to 5 to 30 parts by mass based on 100 parts by mass of the total epoxy resins contained in the epoxy resin composition, an epoxy resin composition can be obtained that has an excellent balance between the depolymerization properties of the cured product obtained by curing the epoxy resin composition and its effect as a compatibilizer between component [B] and the thermoplastic resin when preparing the epoxy resin composition.

[0030] (Component [G]) In the present invention, the following component [G] may be contained as another epoxy resin.

[0031] Component [G]: A bifunctional epoxy resin component [G] other than components [A], [B], and [F] is preferably contained in an amount of 10 to 70 parts by mass, more preferably 20 to 70 parts by mass, and even more preferably 40 to 70 parts by mass, based on 100 parts by mass of the total epoxy resin contained in the epoxy resin composition of the present invention. By adjusting the content of component [G] to 10 to 70 parts by mass based on 100 parts by mass of the total epoxy resin contained in the epoxy resin composition of the present invention, an epoxy resin composition with an excellent balance between depolymerization property and heat resistance can be obtained.

[0032] Examples of component [G] include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, and bisphenol S-type epoxy resins, biphenyl-type epoxy resins, epoxy resins having a fluorene skeleton, polypropylene glycol-type epoxy resins, polyethylene glycol-type epoxy resins, and long-chain aliphatic epoxy resins, as long as they are bifunctional and do not fall under the category of components [A], [B], or [F].

[0033] (Component [C]) In the present invention, component [C] is a curing agent. Examples of curing agents include amines, acid anhydrides, and imidazoles, but any structure that can cure an epoxy resin is acceptable. Among these, amines are preferred because they provide excellent heat resistance to the matrix resin after curing and excellent pot life for the prepreg.

[0034] Examples of amines include aromatic amines such as diaminodiphenylmethane, diaminodiphenyl sulfone, and diethyltoluenediamine, aliphatic amines, dicyandiamide, and their isomers and modifications. Diaminodiphenyl sulfone and dicyandiamide are particularly preferred because they provide excellent heat resistance of the cured matrix resin and excellent pot life of the prepreg. When dicyandiamide is used as a particulate curing agent, the particle size of the particulate curing agent is preferably 3 to 15 μm. This range ensures both a good reaction rate during curing and a long pot life during storage. The particle size can be measured by laser scattering particle size distribution measurement.

[0035] (Component [D]) The epoxy resin composition of the present invention may contain a curing catalyst as component [D]. Examples of the curing catalyst of component [D] include urea-based curing catalysts, hydrazide-based curing catalysts, tertiary amines, imidazoles, and phenols. In particular, when component [C] is dicyandiamide, a urea-based curing catalyst is preferred from the viewpoints of curing acceleration during curing and pot life during storage. Commercially available curing catalysts include DCMU99 (manufactured by Hodogaya Chemical Co., Ltd.), "Omicure (registered trademark)" U-24M and U-52M (manufactured by CVC Thermoset Specialties), UDH-J (manufactured by Ajinomoto Fine-Techno Co., Ltd.), CDH, MDH, SUDH, ADH, and SDH (manufactured by Nippon Finechem Co., Ltd.), "DDH-S and IDH-S" (manufactured by Otsuka Chemical Co., Ltd.), and "Kao Raiser (registered trademark)" No. 20 (manufactured by Kao Corporation), "Curezol (registered trademark)" 1.2DMZ, C11Z, C17Z (manufactured by Shikoku Chemicals Co., Ltd.), and the like.

[0036] The curing catalyst of component [D] is preferably contained in an amount of 0.1 to 15 parts by mass, based on 100 parts by mass of the total amount of all epoxy resins. This range is preferable because it allows for both acceleration of curing during curing and an extended pot life during storage.

[0037] (Component [E]) The epoxy resin composition of the present invention preferably further contains a polyrotaxane as component [E]. Component [E] is preferably contained in an amount of 1 to 25 parts by mass, and more preferably 5 to 15 parts by mass, per 100 parts by mass of the total epoxy resin. By adjusting the content of component [E] to 1 to 25 parts by mass, per 100 parts by mass of the total epoxy resin, the depolymerization properties of the cured product can be improved. Furthermore, adjusting the content to 5 to 15 parts by mass is preferable, as this results in a cured product of the epoxy resin composition having an excellent balance between depolymerization properties and heat resistance.

[0038] Component [E] is a compound having a structure in which a linear polymer passes through the opening of a cyclic molecule and blocking groups are attached to both ends of the linear polymer to prevent the cyclic molecule from falling off, and is therefore preferred because it provides an excellent balance between the depolymerization property and heat resistance of the cured product of the epoxy resin composition.

[0039] Examples of the chain polymer constituting the polyrotaxane include molecules that can thread through the rings of multiple cyclic molecules. Examples of the chain polymer include polyethylene glycol, polyethylene oxide, polypropylene glycol, polylactic acid, polycaprolactone, polyethylene, polypropylene, polyvinyl acetal, polyvinyl methyl ether, polyvinylpyrrolidone, polyacrylamide, polymethyl acrylate, polymethyl methacrylate, and polystyrene. The chain polymer may have a branched chain as long as it is configured to be able to thread through the rings of the above-mentioned cyclic molecules.

[0040] Both ends of the chain polymer preferably have reactive groups capable of reacting with blocking groups to prevent cyclic molecules from falling off the chain polymer. Examples of reactive groups include amino groups, hydroxyl groups, carboxyl groups, thiol groups, disulfides, vinyl groups, acryloyl groups, methacryloyl groups, and sulfo groups. Among these, amino groups and carboxyl groups are preferred, as they facilitate bonding of the blocking groups described below to both ends of the chain polymer.

[0041] In the present invention, the blocking group bonded to the linear polymer in the polyrotaxane of component [E] is not particularly limited as long as it acts to prevent cyclic molecules from detaching from the linear polymer. Examples of the blocking group include a dinitrophenyl group, cyclodextrin, adamantane group, trityl group, fluorescein, silsesquioxane, pyrene, alkyl group-substituted benzene, and steroid. Among these, an adamantane group or cyclodextrin is preferred, as it allows for the production of a cured epoxy resin composition with excellent depolymerization properties.

[0042] In the present invention, examples of the cyclic molecules constituting the polyrotaxane of component [E] include α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and derivatives thereof, as well as crown ethers, benzocrowns, dibenzocrowns, dicyclohexanocrowns, and derivatives thereof. The cyclic molecules may further have a reactive group. Examples of such reactive groups include hydroxyl groups, carboxyl groups, amino groups, epoxy groups, isocyanate groups, thiol groups, and aldehyde groups.

[0043] In the present invention, the inclusion ratio of the polyrotaxane of component [E] is the mass ratio of the amount of cyclic molecules actually enclosing the linear polymer relative to the maximum amount of cyclic molecules enclosing the linear polymer. The inclusion ratio can be determined by nuclear magnetic resonance spectroscopy (NMR). The inclusion ratio of the polyrotaxane of component [E] is preferably 0.1 to 35% by mass, more preferably 5 to 35% by mass. By setting the inclusion ratio to 0.1 to 35% by mass, it is possible to impart recyclability to the epoxy resin composition. By setting the inclusion ratio to more preferably 5 to 35% by mass, and even more preferably 25 to 35% by mass, it is possible to improve the depolymerization properties of the cured product of the epoxy resin composition.

[0044] Commercially available polyrotaxanes of component [E] include "SeRM (registered trademark)" SH3400P (polycaprolactone-modified polyrotaxane, inclusion rate 28% by mass), "SeRM (registered trademark)" PR02 (inclusion rate 2% by mass), "SeRM (registered trademark)" SH2400P (inclusion rate 28% by mass), and "SeRM (registered trademark)" SH1300P (inclusion rate 28% by mass) (all manufactured by ASM Corporation).

[0045] In the present invention, by combining the urethane-modified epoxy resin, which is component [B], with the polyrotaxane, which is component [E], a synergistic effect of the effect of the urethane bond, which is a dynamic covalent bond contained in the urethane-modified epoxy resin, and the effect of the molecular pulley in the polyrotaxane can be achieved, resulting in an epoxy resin composition having an excellent balance between depolymerization property and heat resistance in the cured product.

[0046] The structure of "SeRM (registered trademark)" SH2400P is shown below. The terminal hydroxyl groups of multiple cyclodextrins react with epoxy groups to become crosslinking points and are incorporated into the crosslinked structure. However, when the string-like polyethylene glycol that passes through the ring-shaped cyclodextrins is decomposed by the action of an external stimulus, the multiple rings that passed through the strings fall off all at once, which is thought to promote depolymerization.

[0047]

[0048] (Glass Transition Temperature of Cured Product) The epoxy resin composition of the present invention preferably has a glass transition temperature of 130°C or higher, more preferably 135°C or higher, and even more preferably 140°C or higher, after curing for 60 minutes at a temperature selected from 150°C to 200°C. The glass transition temperature can be measured using a differential scanning calorimeter in accordance with JIS K 7121:1999. Here, the cured product after curing for 60 minutes at a temperature selected from 150°C to 200°C refers to a cured product that has been cured by maintaining a constant temperature in the range of 150°C to 200°C for 60 minutes or longer. The temperature may be selected from 150°C to 180°C, and specific examples include 150°C or 180°C. In other words, it is preferable that the glass transition temperature of either the cured product after curing for 60 minutes at 150°C or 180°C is 130°C or higher.

[0049] Specifically, the cured product of the epoxy resin composition obtained under the above conditions is heated from 25° C. to 300° C. at a temperature increase rate of 10° C. / min, held at 300° C. for 3 minutes, and then rapidly cooled to 25° C. at a temperature decrease rate of 30° C. / min. As described in JIS K 7121:1999, in a differential scanning calorimetry chart (vertical axis represents thermal energy and horizontal axis represents temperature) during the above temperature increase process, when a point equidistant from a line extended from each baseline showing the state before and after the stepwise change accompanying the glass transition intersects with the curve of the stepwise change portion showing the glass transition state, that point is defined as the glass transition temperature.

[0050] Generally, the glass transition temperature and depolymerization property of a cured epoxy resin composition correlate with each other; the higher the glass transition temperature, the lower the depolymerization property. However, a high glass transition temperature has the advantage of providing a highly durable material with a long lifespan. By achieving a glass transition temperature of 110°C or higher, the cured product obtained under the above conditions can be used for secondary structural materials such as interior materials in aerospace applications, and for high-heat-resistant applications such as bicycles, wind turbines, ships, railway vehicles, and laptop computer housings in general industrial applications. Furthermore, by achieving a glass transition temperature of 130°C or higher, the cured product can be used for automotive structural components in general industrial applications. Furthermore, by achieving a glass transition temperature of 150°C or higher, the cured product can be used for primary structural materials for aircraft such as main wings, tails, and floor beams in aerospace applications. Furthermore, the glass transition temperature of the cured product obtained under the above conditions is preferably 250°C or lower, which allows the crosslink density of the cured product to fall within a depolymerizable range.

[0051] The epoxy resin composition of the present invention may contain thermoplastic resins, rubber particles, inorganic particles such as silica, nanoparticles such as carbon nanotubes (CNTs) and graphene, etc., for the purpose of adjusting viscoelasticity and improving the tack and drape properties of prepregs, or for the purpose of enhancing the mechanical properties and toughness of the epoxy resin composition, as long as the effects of the present invention are not lost. Examples of thermoplastic resins soluble in epoxy resins include polyvinyl acetal resins such as polyvinyl formal and polyvinyl butyral, polyvinyl alcohol, phenoxy resin, polyamide, polyimide, polyvinylpyrrolidone, polysulfone, and polyethersulfone. Examples of rubber particles include crosslinked rubber particles and core-shell rubber particles in which a different polymer is graft-polymerized onto the surface of crosslinked rubber particles. Furthermore, the epoxy resin composition may contain boric acid esters or the like for the purpose of enhancing the storage stability of the epoxy resin composition.

[0052] The epoxy resin composition of the present invention may be prepared by kneading using a machine such as a kneader, a planetary mixer, a three-roll mill, or a twin-screw extruder, or by mixing by hand using a beaker and a spatula, etc., provided that uniform kneading is possible.

[0053] (Reinforcing Fiber) The prepreg of the present invention contains the above-mentioned epoxy resin composition and at least one reinforcing fiber selected from the group consisting of carbon fiber, glass fiber, and aramid fiber. The reinforcing fiber may be surface-treated. Examples of surface treatments include metal coating as a conductor, treatment with a coupling agent, treatment with a sizing agent, treatment with a binder, and treatment with an additive. These reinforcing fibers may be used alone or in combination. Among these, polyacrylonitrile (PAN)-, pitch-, or rayon-based carbon fibers, which have excellent specific strength and specific rigidity, are preferred from the viewpoint of weight reduction. Glass fiber is preferred from the viewpoint of improving the economic viability of the resulting fiber-reinforced composite material, and a combination of carbon fiber and glass fiber is particularly preferred from the viewpoint of balancing mechanical properties and economic viability. Furthermore, aramid fiber is preferred from the viewpoint of improving the impact resistance and formability of the resulting fiber-reinforced composite material, and a combination of carbon fiber and aramid fiber is particularly preferred from the viewpoint of balancing mechanical properties and impact resistance. Furthermore, from the viewpoint of increasing the electrical conductivity of the resulting fiber-reinforced composite material, reinforcing fibers coated with metals such as nickel, copper, ytterbium, etc. Among these, PAN-based carbon fibers, which are excellent in mechanical properties such as strength and elastic modulus, can be more preferably used.

[0054] (Prepreg) The reinforcing fibers contained in the prepreg of the present invention may be in the form of a woven fabric. When the prepreg is a woven fabric, the weave is preferably a plain weave, a twill weave, a satin weave, or the like. Plain weave, twill weave, satin weave, or the like provides excellent handleability as a sheet-like prepreg and excellent shape conformability during lamination, facilitating the molding of complex-shaped components. Here, "excellent shape conformability during lamination" refers to the ability to conform to the shape of a reinforcing fiber woven fabric or the like without fiber orientation collapse during the process of laminating the fabric onto a three-dimensional mold, thereby producing a molded product with satisfactory quality and performance. In the process of laminating a preform onto a three-dimensional mold, a preform is created using a reinforcing fiber woven fabric or the like. If the fabric does not have excellent shape conformability during lamination, a trimming process is required in which portions of the substrate that do not conform to the mold shape are cut with scissors or a cutter, or portions that do not become part of the final product are fixed with tape. The trimming process requires a lot of time and effort, causes material loss, and increases industrial waste, but the application of the present invention aims to reduce this.

[0055] The reinforcing fibers contained in the prepreg of the present invention may be in the form of discontinuous fibers. By using discontinuous fibers as the reinforcing fibers, it becomes easier to form a complex shape when molding a sheet-like prepreg by applying an external force.

[0056] Furthermore, when the reinforcing fibers are discontinuous, they are preferably randomly dispersed in bundles in the prepreg, which makes it easier to mold the prepreg into a complex shape when an external force is applied to the prepreg to form it.

[0057] Alternatively, when the reinforcing fibers are discontinuous, they are preferably dispersed randomly in a substantially monofilament state in the prepreg. By dispersing discontinuous reinforcing fibers randomly in a substantially monofilament state, fewer reinforcing fibers exist as fiber bundles in the prepreg, minimizing weak portions at the fiber bundle ends of the reinforcing fibers, and providing excellent reinforcement efficiency and isotropy. Here, "substantially monofilament" refers to the presence of fine strands of less than 500 reinforcing fiber single yarns. It is more preferable that the reinforcing fibers are dispersed in a monofilament state, i.e., as single yarns, and it is even more preferable that the monofilament-like single fibers are dispersed randomly. When the reinforcing fibers are discontinuous, the reinforcing fibers may be in the form of a nonwoven fabric.

[0058] A method for producing a prepreg includes impregnating a reinforcing fiber substrate with the epoxy resin composition of the present invention. Examples of the impregnation method include the hot melt method (dry method). The fiber mass content of the prepreg can be adjusted by changing the amount of resin applied to the release paper.

[0059] As a method for molding the prepreg, for example, press molding, autoclave molding, bagging molding, wrapping tape method, internal pressure molding, etc. can be used appropriately.

[0060] Next, the fiber-reinforced composite material of the present invention will be described.

[0061] (Fiber-reinforced composite material) A fiber-reinforced composite material, which is one embodiment of the present invention, is a fiber-reinforced composite material containing reinforcing fibers and a cured product of the epoxy resin composition of the present invention as a matrix resin, and is typically obtained by curing the prepreg of the present invention described above. More specifically, a fiber-reinforced composite material containing a cured product of the epoxy resin composition of the present invention as a matrix resin can be obtained by laminating prepregs having the epoxy resin composition of the present invention as a matrix resin, as necessary, and then heating and curing the laminate.

[0062] (Method for Recycling Fiber-Reinforced Composite Material) The method for recycling a fiber-reinforced composite material of the present invention involves carrying out steps (i) to (iii) using the fiber-reinforced composite material of the present invention.

[0063] (i) The fiber-reinforced composite material is processed into pellets having a length of 2 to 100 mm. (ii) The cured epoxy resin composition contained in the pellet-shaped fiber-reinforced composite material obtained in (i) is depolymerized by treatment with a dissolving solution or hydrolysis treatment. (iii) The pellet-shaped fiber-reinforced composite material in which the cured epoxy resin composition has been depolymerized in (ii) is hot-pressed.

[0064] Here, the hot pressing in (iii) is preferably carried out under conditions of 100 to 290° C. and 0.7 to 15 MPa.

[0065] By carrying out the steps (i) to (iii), it becomes possible to recycle a fiber-reinforced composite material without depolymerizing the matrix resin to the extent that it is separated from the reinforcing fibers, which is preferable because it significantly reduces greenhouse gas emissions when recycling a fiber-reinforced composite material. In other words, the recycling method for a fiber-reinforced composite material of the present invention is preferable because it imposes a low environmental load during production.

[0066] (Step (i)) In this step, the fiber reinforced composite material is processed into pellets having a length of 2 to 100 mm.

[0067] This step can be carried out using a hammer mill pulverizer, a sand grind mill type wet pulverizer, a pelletizer, a high speed rotor type pulverizer, a rotary shear type pulverizer, a ball mill pulverizer, etc. The fiber length of the reinforcing fibers contained in the pellets processed from the fiber reinforced composite material is preferably 2 to 100 mm.

[0068] Conventional recycling methods for fiber-reinforced composite materials often involve processing long fibers into short fibers less than 2 mm in one go, but the fiber length of the reinforcing fibers in recycled composites is preferably 3 to 20 mm, which improves fiber dispersion and allows for the production of highly rigid composites, making the application of the present invention preferable. From another perspective, such fiber lengths are also preferably 60 to 100 mm, which simplifies the processing process and reduces greenhouse gas emissions. After using recycled products containing fibers of such fiber lengths as composite products, further processing them into a mid-range fiber length of 50 mm or less and repeatedly recycling them can significantly reduce greenhouse gas emissions.

[0069] (Step (ii)) In this step, the cured product of the epoxy resin composition contained in the pellet-shaped fiber-reinforced composite material obtained in (i) is depolymerized by treatment with a dissolving solution or hydrolysis treatment.

[0070] In the present invention, depolymerization refers to the overall process in which a polymerized substance is decomposed by the action of an external stimulus, etc., and includes the process in which the decomposition of the target substance progresses and ultimately results in a monomer. In the initial stage of depolymerization of a cured epoxy resin composition, only the surface of the cured product is swollen or slightly dissolved. In this state, even if the cured epoxy resin composition is bonded to a different material such as metal, separation and disassembly are facilitated, making it recyclable. As depolymerization progresses further, the target substance plasticizes throughout its thickness and becomes rubbery. In this state, the target substance can be treated as a plastic resin and recycled, for example, in a regenerated form. In the final stage of depolymerization, the target substance is significantly dissolved and loses its original shape. Note that even if the target substance appears to retain its original shape when depolymerized under static conditions, it is considered to be in a state in which it loses its original shape if it loses its shape and collapses when moved. In this state, if the material is a fiber-reinforced composite material, the reinforcing fibers contained therein can be recovered as recycled fibers (resources).

[0071] Methods for depolymerizing and plasticizing the cured product of the epoxy resin composition of the fiber-reinforced composite material of the present invention by treatment with a solvent or hydrolysis treatment include thermal decomposition, supercritical water, subcritical water, superheated steam, liquid-phase decomposition, dissolution, and glycol methods. Dissolution methods using a solvent are preferred from the viewpoint of facilitating depolymerization by cleavage of urethane bonds, while superheated steam methods are preferred from the viewpoint of eliminating the need for neutralization of the solvent or washing of the recovered fibers. The solvent used in the present invention is not particularly limited as long as it can dissolve the cured product of the epoxy resin composition of the present invention, but includes, for example, at least one liquid selected from acidic solutions, organic solvents, hydrogen peroxide solutions, and ionic liquids. These liquids are capable of dissolving or plasticizing the cured product of the epoxy resin composition of the present invention, thereby efficiently depolymerizing the target cured product.

[0072] Examples of acidic solutions used as solutions for dissolving the cured product of the epoxy resin composition include phosphoric acid, sulfuric acid, hydrochloric acid, and nitric acid.

[0073] Examples of organic solvents used as the dissolving solution include aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, alcohol solvents, ketone solvents, ether solvents, amide solvents, ester solvents, and N-methyl-2-pyrrolidone having a lactam structure. Among these, N-methyl-2-pyrrolidone is preferred because it is highly water-soluble and allows for the recovered fibers to be washed with water. Examples of aliphatic hydrocarbon solvents include pentane, hexane, heptane, octane, and glycol. Examples of aromatic hydrocarbon solvents include benzene, toluene, xylene, and tetralin. Examples of alcohol solvents include benzyl alcohol. Examples of ketone solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, and diacetone alcohol. Among these, acetone and methyl ethyl ketone are preferred because they are highly volatile and allow for easy drying of the recovered fibers. The organic solvent may contain a decomposition catalyst. Examples of decomposition catalysts include iron oxide and alkali metal compounds.

[0074] Examples of the ionic liquid used as the dissolving liquid include ionic liquids containing at least one cation selected from imidazolium-based, pyridinium-based, pyrrolidinium-based, quaternary ammonium-based, and quaternary phosphonium-based cations.

[0075] In any of the above cases, one type of solvent may be used alone, or two or more types of solvents may be used in combination.

[0076] (Step (iii)) In this step, the pellet-shaped fiber-reinforced composite material obtained by depolymerizing the cured product of the epoxy resin composition in (ii) is hot-pressed. The hot-pressing in step (iii) is preferably carried out under conditions of 100 to 290°C and 0.7 to 15 MPa, and more preferably under conditions of 100 to 200°C and 0.7 to 5 MPa. By carrying out the hot-pressing at 100 to 200°C and 0.7 to 5 MPa, the heating temperature is lowered and the plasticized fiber-reinforced composite material is cooled more quickly, thereby shortening the molding cycle. Note that a press capable of molding by the heat and cool method can also be used to shorten the molding cycle.

[0077] Furthermore, it is preferable that the pellet-shaped fiber reinforced composite material obtained by depolymerizing the cured product of the epoxy resin composition is randomly dispersed in a mold and on a platen surface and then hot-pressed.

[0078] In the fiber-reinforced composite material of the present invention, the cured product of the epoxy resin preferably contains a depolymerized plasticized product and reinforcing fibers, and the plasticized product preferably contains a benzoxazolone structure. When the plasticized product of the cured product of the epoxy resin composition contains a benzoxazolone structure, it has a melting point and can be repeatedly recycled as a thermoplastic resin. The benzoxazolone structure can be identified by analyzing the plasticized product with GC / MS. The benzoxazolone structure is an organic compound containing a benzo (aromatic) ring and a xazole (a five-membered nitrogen-containing compound).

[0079] It is also believed that the benzoxazolone structure is produced when a compound having a urethane bond connected to a benzene ring undergoes an intramolecular reaction during depolymerization of a cured epoxy resin due to the action of an external stimulus or the like.

[0080] The fiber-reinforced composite material according to one embodiment of the present invention is preferably used in sports applications, general industrial applications, and aerospace applications. More specifically, examples of sports application components include golf shafts, fishing rods, tennis and badminton rackets, hockey sticks, and ski poles. Examples of general industrial application components include structural materials for automobiles, bicycles, wind turbines, ships, and railway vehicles, as well as electronic device components such as IC trays and housings for information devices such as laptops. Among these, automotive application components are preferred because of the large amount of consumption and the significant effect of reducing environmental impact by applying the fiber-reinforced composite material of the present invention. Furthermore, in aerospace applications, the material is preferably used in aircraft application components, such as primary aircraft structural components such as main wings, tails, and floor beams, and secondary structural components such as interior materials.

[0081] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to the descriptions of these examples.

[0082] 1. Materials Used <Epoxy Resin> The epoxy resins used in the examples and comparative examples are listed below.

[0083] [Component [A]] (Biomass-derived bisphenol-type epoxy resins) "Briozen (registered trademark)" YD-128G (biomass-derived bisphenol A-type epoxy resin, average epoxy equivalent: 190, biomass ratio: 28%, manufactured by Aditya Birla Chemicals) "Briozen (registered trademark)" YDF-170LCG (biomass-derived bisphenol F-type epoxy resin, average epoxy equivalent: 170, biomass ratio: 30%, manufactured by Aditya Birla Chemicals) (difunctional naphthalene-type epoxy resins) "EPICLON (registered trademark)" HP-4032D (difunctional naphthalene-type epoxy resin, average epoxy equivalent: 142, manufactured by DIC Corporation) "EPICLON (registered trademark)" HP-4770 (difunctional naphthalene-type epoxy resin, average epoxy equivalent: 204, manufactured by DIC Corporation).

[0084] In the above, the biomass ratio of compounds for which no biomass ratio is listed is 0%.

[0085] [Component [B]] - "ADEKA RESIN (registered trademark)" EPU-73S (urethane-modified epoxy resin, average epoxy equivalent: 249, manufactured by ADEKA Corporation) - "ADEKA RESIN (registered trademark)" EPU-73B (urethane-modified epoxy resin, average epoxy equivalent: 247, manufactured by ADEKA Corporation) [Component [F]] - "SUMIEPOXY (registered trademark)" ELM434 (N,N,N',N'-tetraglycidyldiaminodiphenylmethane, tetrafunctional epoxy resin, average epoxy equivalent: 120, manufactured by Sumitomo Chemical Co., Ltd.) - "ARALDITE (registered trademark)" MY0500 (p-aminophenol-type epoxy resin, manufactured by Huntsman Advanced Materials Co., Ltd.) - Px-GAN (N,N-diglycidyl-4-phenoxyaniline, manufactured by Toray Fine Chemicals Co., Ltd.) [Component [G]] "jER (registered trademark)" 825 (bisphenol A type epoxy resin, average epoxy equivalent: 175, manufactured by Mitsubishi Chemical Corporation) "EPALLOY (registered trademark)" 5000 (hydrogenated bisphenol A type epoxy resin, average epoxy equivalent: 220, manufactured by Huntsman Chemical Co., Ltd.) [Other epoxy resins] "Epotohto (registered trademark)" YH-300 (polyglycidyl ether of trimethylolpropane, trifunctional epoxy resin, average epoxy equivalent: 143, manufactured by Nippon Steel Chemical & Material Co., Ltd.) <Components other than epoxy resins> [Component [C]] "4,4'-diaminodiphenyl sulfone" (manufactured by Tokyo Chemical Industry Co., Ltd.) "jER Cure (registered trademark)" DICY7T (dicyandiamide, manufactured by Mitsubishi Chemical Corporation).

[0086] [Component [D]] - "Omicure (registered trademark)" 24 (4,4'-methylenebis(phenyldimethylurea, manufactured by PTI Japan Co., Ltd.) [Component [E]] - "SeRM (registered trademark)" PR02 (polyrotaxane, inclusion rate 2%, cyclodextrin is hydroxyl-terminated, manufactured by ASM Corporation) - "SeRM (registered trademark)" SH2400P (polyrotaxane, inclusion rate 28%, cyclodextrin is hydroxyl-terminated, manufactured by ASM Corporation) [Component [H]] - "Sumikaexcel (registered trademark)" PES5003P (polyethersulfone, manufactured by Sumitomo Chemical Co., Ltd.) - "VIRANTAGE (registered trademark)" VW-10700RFP (polyethersulfone (Solvay Advanced Polymers). "ULTEM (registered trademark)" PEI1010P (polyetherimide, manufactured by SABIC).

[0087] [Boric acid ester] "Cureduct (registered trademark)" L-07E (a composition containing 5% by mass of a boric acid ester compound, manufactured by Shikoku Chemicals Corporation).

[0088] 2. Sample Preparation Method [Method for Preparing Epoxy Resin Composition] Component [A], component [B], component [F], component [G], component [E], and other epoxy resin components were placed in a stainless steel beaker in the amounts shown in the table, heated to 40 to 150°C, and appropriately kneaded until the components were compatible. When component [H] was added, the temperature was raised to 220°C, and kneaded until the thermoplastic resin was compatible.

[0089] The prepared mixture was cooled to 60°C or below, and the component [C], component [D], and boric acid ester were added in the amounts shown in the table, followed by kneading at 60°C for 30 minutes to obtain an epoxy resin composition.

[0090] [Method for producing a cured product of an epoxy resin composition] The epoxy resin composition obtained by the above [Method for preparing an epoxy resin composition] was degassed under reduced pressure and then poured into a mold set to a thickness of 1 mm using a Teflon (registered trademark) spacer. Next, the temperature was raised from 30°C to 150°C or 180°C at a rate of 1.0°C per minute in a hot air oven, and then maintained at that temperature for 120 minutes to cure the epoxy resin composition. The temperature was 180°C in examples using 4,4'-diaminodiphenyl sulfone as component [C], and 150°C in examples using jER Cure (registered trademark) DICY7T as component [C]. The temperature was then lowered to 30°C and the composition was demolded to produce a cured product of the epoxy resin composition with a thickness of 1 mm.

[0091] [Method for producing a fiber-reinforced composite material] The epoxy resin composition prepared according to the above [Method for preparing an epoxy resin composition] was impregnated into a sheet of unidirectionally aligned carbon fiber "TORAYCA (registered trademark)" T700S-12K-60E (manufactured by Toray Industries, Inc.) to obtain a prepreg. The obtained prepreg was cut into a length of 200 mm (in the direction of carbon fiber orientation) and a width of 200 mm, and five sheets were stacked so that the fiber direction of adjacent prepregs was perpendicular to each other. The stack was then sandwiched between molds and pressed at 3.5 MPa in a press heated to 150 to 200°C, and heat-cured for 90 minutes. The mold was then removed from the press and cooled to 30°C using a metal plate to obtain a fiber-reinforced composite material.

[0092] 3. Evaluation Methods [Method for Measuring Glass Transition Temperature Tg] From the 1 mm thick cured product of epoxy resin composition obtained by the above [Method for Producing Cured Product of Epoxy Resin Composition], 5 mg of sample was weighed into a sample pan, and measurement was carried out using a differential scanning calorimeter Q-2500 (manufactured by TA Instruments) in accordance with JIS K 7121: 1999. The measurement method and the method for determining the glass transition temperature Tg from the measurement results are as described above.

[0093] [Method for Evaluating Depolymerization Properties of Cured Epoxy Resin Compositions] Three square test pieces, each 1 mm thick, were cut into 15 mm wide and 15 mm long squares from the cured epoxy resin composition obtained by the above-described [Method for Preparing Cured Epoxy Resin Compositions]. Each test piece was placed in a stainless steel beaker containing 65 g of either triethylene glycol or N-methyl-2-pyrrolidone (NMP) solution, and evaluated according to the following criteria. Each stainless steel beaker was capped and stored at 23°C. The cured epoxy resin composition was significantly dissolved and lost its original shape: A; plasticized throughout the entire thickness and in a rubbery state: B; only the surface was swollen or slightly dissolved: C; and the cured epoxy resin composition remained unchanged: N. [Method for Calculating Biomass Percentage (%) of Total Epoxy Resins] The biomass percentage of each epoxy resin was calculated by comparing the number of organic carbon atoms in the molecule in accordance with ASTM D6866 (2024). For example, bisphenol A epoxy has 43 organic carbon atoms, of which the vegetable oil-derived glycidyl group has 12 organic carbon atoms. Therefore, the biomass ratio is approximately 28% obtained by dividing 12 by 43. Next, the biomass ratio in all epoxy resins was calculated from "biomass-derived epoxy resin content (parts by mass) × biomass ratio (%) ÷ 100 (Equation (1))" when one type of biomass-derived epoxy resin was contained, assuming that all epoxy resins were 100 parts by mass. When multiple types of biomass-derived epoxy resins were contained, the biomass ratio was calculated as the sum of the values ​​calculated by Equation (1). [Method for measuring fiber volume content Vf (%) of fiber-reinforced composite material] The volume ratio of the reinforcing fibers contained in the fiber-reinforced composite material to the fiber-reinforced composite material was calculated using the following equation: Vf = (W × 100) / (ρ × T), where W is 1 cm of fiber-reinforced material. ２ The mass of the reinforcing fiber contained in ２ ) ρ: Density of reinforcing fiber (g / cm ３ ) T: thickness of the fiber reinforced composite material (cm).

[0094] Reference Example 1 An epoxy resin composition was prepared according to the above-mentioned [Method for preparing an epoxy resin composition] using 65 parts by mass of jER (registered trademark) 825, which corresponds to component [G], as the epoxy resin, 35 parts by mass of ADEKA RESIN (registered trademark) EPU-73S, which corresponds to the urethane-modified epoxy resin of component [B], and 31 parts by mass of 4,4′-diaminodiphenyl sulfone, which corresponds to component [C], as the curing agent.

[0095] A cured product of this epoxy resin composition was prepared according to the [Method for preparing a cured product of an epoxy resin composition] and measured according to the [Method for measuring glass transition temperature Tg]. The glass transition temperature was 167°C, demonstrating good heat resistance.

[0096] The depolymerization property of triethylene glycol / 14 days evaluated according to the [Method for evaluating depolymerization property of cured epoxy resin composition] was rated C, and only the surface of the cured material was slightly dissolved, indicating good depolymerization property.

[0097] Since no biomass-derived epoxy resin was used, the biomass ratio in the entire epoxy resin composition was 0%.

[0098] (Reference Examples 2 to 3, Examples 4 to 9, Examples 15 to 18) Epoxy resin compositions and cured products of the epoxy resin compositions were prepared in the same manner as in Example 1, except that the resin compositions were changed as shown in Table 1. The evaluation results are shown in Table 1.

[0099]

[0100] (Reference Example 10) The epoxy resin composition obtained in Reference Example 1 was impregnated into unidirectionally aligned carbon fiber sheets "TORAYCA (registered trademark)" T700S-12K-60E, to form a sheet having a basis weight of 190 g / m ２ The prepreg obtained had good tack and was easy to handle. The fiber-reinforced composite material obtained according to the [Method for Producing a Fiber-Reinforced Composite Material] had a fiber volume fraction Vf of 67% and was of good quality.

[0101] Reference Example 11 The prepreg obtained in Reference Example 10 was used to form a mold for the roof of an automobile, but the shape conformability was not necessarily good, and complicated trimming was required.

[0102] Reference Example 12 The epoxy resin composition obtained in Reference Example 1 was mixed with carbon fiber "TORAYCA (registered trademark)" T700S-12K-60E to a basis weight of 189 g / m ２ The resulting woven fabric prepreg was impregnated into a plain woven substrate so that the thickness of the woven fabric prepreg was 100 μm. When the resulting woven fabric prepreg was molded into a mold for the roof of an automobile, it exhibited excellent shape conformability and no trimming was required.

[0103] (Reference Example 13) Carbon fiber "TORAYCA (registered trademark)" T700S-12K-60E was cut into a length of 12 mm and randomly dispersed in bundles or approximately monofilaments, resulting in a basis weight of 150 g / m ２ A nonwoven fabric having the following characteristics was obtained. The obtained nonwoven fabric was impregnated with the epoxy resin composition obtained in Reference Example 1 to obtain a nonwoven fabric prepreg. When the obtained nonwoven fabric prepreg was used to mold a mold for the roof of an automobile, it exhibited excellent shape conformability and no trimming was required.

[0104] Reference Example 14: The fiber-reinforced composite material obtained in Reference Example 10 was pulverized using a biaxial pulverizer to obtain pellets containing reinforcing fibers with fiber lengths of 5 mm to 100 mm. The obtained pellets were treated with superheated steam at 300°C for 120 minutes, causing the cured epoxy resin composition of the fiber-reinforced composite material to depolymerize and plasticize. The plasticized pellets were randomly dispersed and hot-pressed at 180°C and 10 MPa, yielding a regenerated template.

[0105] (Example 19) The epoxy resin composition obtained in Example 7 was impregnated into a sheet of unidirectionally aligned carbon fiber "TORAYCA (registered trademark)" T700S-12K-60E, to form a carbon fiber sheet having a basis weight of 190 g / m ２The prepreg obtained had good tack and was easy to handle. The fiber volume fraction Vf of the fiber reinforced composite material obtained according to the [Method for producing a fiber reinforced composite material] was 68%, and the quality was good.

[0106] Example 20 The prepreg obtained in Example 19 was used to form a mold for the roof of an automobile, but the shape conformability was not necessarily good, and complicated trimming was required.

[0107] (Example 21) The epoxy resin composition obtained in Example 7 was mixed with carbon fiber "TORAYCA (registered trademark)" T700S-12K-60E having a basis weight of 189 g / m ２ The resulting woven fabric prepreg was impregnated into a plain woven substrate so that the thickness of the woven fabric prepreg was 100 μm. When the resulting woven fabric prepreg was molded into a mold for the roof of an automobile, it exhibited excellent shape conformability and no trimming was required.

[0108] (Example 22) Carbon fiber "TORAYCA (registered trademark)" T700S-12K-60E was cut into a length of 12 mm and randomly dispersed in bundles or approximately monofilaments, resulting in a basis weight of 150 g / m ２ The nonwoven fabric thus obtained was impregnated with the epoxy resin composition obtained in Example 7 to obtain a nonwoven fabric prepreg. When the nonwoven fabric prepreg thus obtained was used to mold a mold for the roof of an automobile, it exhibited excellent shape conformability and no trimming was required.

[0109] Example 23: The fiber-reinforced composite material obtained in Example 19 was pulverized using a biaxial pulverizer to obtain pellets containing reinforcing fibers with fiber lengths of 5 mm to 100 mm. The pellets were treated with superheated steam at 300°C for 120 minutes, causing the cured epoxy resin composition of the fiber-reinforced composite material to depolymerize and plasticize. The plasticized pellets were randomly dispersed and hot-pressed at 180°C and 10 MPa, yielding a regenerated template.

[0110] Comparative Example 1 An epoxy resin composition was prepared and a cured product of the epoxy resin composition was produced in the same manner as in Example 1, except that only 100 parts by mass of "jER (registered trademark)" 825, which corresponds to component [G], was used as the epoxy resin, resulting in a resin composition as shown in Table 2. The evaluation results are shown in Table 2. The heat resistance of the obtained cured product of the epoxy resin composition was good, but the depolymerization property was insufficient.

[0111] Comparative Example 2 An epoxy resin composition was prepared and a cured product of the epoxy resin composition was produced in the same manner as in Example 1, except that only 100 parts by mass of "jER (registered trademark)" 825, which corresponds to component [G], was used as the epoxy resin to produce the resin composition shown in Table 2. The resin composition and evaluation results are shown in Table 2. The heat resistance of the cured product of the obtained epoxy resin composition was good, but the depolymerization property was insufficient.

[0112] Comparative Example 3 An epoxy resin composition was prepared and a cured product of the epoxy resin composition was produced in the same manner as in Example 1, except that component [G] was not used as the epoxy resin and only 100 parts by mass of ADEKA RESIN (registered trademark) EPU-73B, which corresponds to component [B], was used, resulting in a resin composition as shown in Table 2. The resin composition and evaluation results are shown in Table 2. The cured product of the obtained epoxy resin composition had good depolymerization properties but insufficient heat resistance.

[0113] Comparative Example 4 An epoxy resin composition was prepared and a cured product of the epoxy resin composition was produced in the same manner as in Example 1, except that the resin composition was as shown in Table 2, using 50 parts by mass of ADEKA RESIN (registered trademark) EPU-73B, which corresponds to component [B], and 50 parts by mass of SUMIEPOXY (registered trademark) ELM434, another epoxy resin that is a tetrafunctional epoxy resin, without using component [G] as the epoxy resin. The resin composition and evaluation results are shown in Table 2. The heat resistance of the obtained cured product of the epoxy resin composition was good, but the depolymerization property was insufficient.

[0114] Comparative Example 5 An epoxy resin composition was prepared and a cured product of the epoxy resin composition was produced in the same manner as in Example 1, except that component [G] was not used as the epoxy resin, and 50 parts by mass of ADEKA RESIN (registered trademark) EPU-73B, which corresponds to component [B], and 50 parts by mass of Epotohto (registered trademark) YH-300, another epoxy resin corresponding to a trifunctional epoxy resin, were used to produce the resin composition shown in Table 2. The resin composition and evaluation results are shown in Table 2. The heat resistance and depolymerization property of the obtained cured product of the epoxy resin composition were insufficient.

[0115] Comparative Example 6 50 parts by mass of "Briozen (registered trademark)" YD-128G corresponding to component [A], 50 parts by mass of "ADEKA RESIN (registered trademark)" EPU-73B corresponding to component [B], and 5 parts by mass of "VIRANTAGE (registered trademark)" VW-10700RFP, a thermoplastic resin corresponding to component [H], were used as the epoxy resin, and stirred at 220°C for 3 hours, but the thermoplastic resin was not compatible with "ADEKA RESIN (registered trademark)" EPU-73B, and an epoxy resin composition could not be obtained.

[0116]

Claims

1. An epoxy resin composition comprising components [A], [B], and [C], where component [B] is contained in an amount of 30 to 70 parts by mass per 100 parts by mass of the total epoxy resin. Component [A]: a difunctional naphthalene-type epoxy resin or a biomass-derived bisphenol-type epoxy resin. Component [B]: a urethane-modified epoxy resin. Component [C]: a curing agent.

2. The epoxy resin composition according to claim 1, further comprising a polyrotaxane as component [E].

3. The epoxy resin composition according to claim 1, wherein component [B] is an epoxy resin in which a bisphenol-type epoxy resin is modified with polyurethane.

4. The epoxy resin composition according to claim 3, wherein the polyurethane uses as the polyhydroxy compound at least one selected from the group consisting of polyether polyol, polycarbonate polyol, and polyester polyol, and as the polyisocyanate compound at least one selected from the group consisting of 1,6-hexamethylene diisocyanate, tolylene diisocyanate, isophorone diisocyanate, and an isocyanurate of 1,6-hexamethylene diisocyanate.

5. The epoxy resin composition according to claim 1, wherein the content of component [B] is 30 to 60 parts by mass per 100 parts by mass of the total epoxy resin, and further comprises the following components [F] and [H]: Component [F]: glycidylamine-type epoxy resin; and Component [H]: thermoplastic resin.

6. The epoxy resin composition according to claim 1, wherein the glass transition temperature of the cured product after curing for 60 minutes at a temperature selected from the range of 150°C to 200°C is 130°C or higher.

7. A prepreg comprising the epoxy resin composition according to any one of claims 1 to 6 and at least one reinforcing fiber selected from the group consisting of carbon fiber, glass fiber, and aramid fiber.

8. The prepreg according to claim 7, wherein the reinforcing fibers are in the form of a woven fabric or discontinuous fibers.

9. The prepreg according to claim 8, wherein the reinforcing fibers are discontinuous fibers, and the discontinuous fibers are randomly dispersed in bundles or in a substantially monofilament shape.

10. A fiber-reinforced composite material comprising a cured product of the epoxy resin composition according to any one of claims 1 to 6 and reinforcing fibers.

11. A method for recycling a fiber-reinforced composite material, comprising steps (i) to (iii) using the fiber-reinforced composite material of claim 10. (i) The fiber-reinforced composite material is processed into pellets having lengths of 2 to 100 mm. (ii) The cured epoxy resin composition contained in the pellet-shaped fiber-reinforced composite material obtained in (i) is depolymerized by treatment with a dissolving solution or hydrolysis treatment. (iii) The pellet-shaped fiber-reinforced composite material from which the cured epoxy resin composition has been depolymerized in (ii) is hot-pressed.

12. A fiber-reinforced composite material comprising a cured product of the epoxy resin composition according to any one of claims 1 to 6, a depolymerized plasticizer, and reinforcing fibers, wherein the plasticizer further comprises a benzoxazolone structure.

13. An automobile component using the fiber-reinforced composite material according to claim 10.

14. A sports component made from the fiber-reinforced composite material according to claim 10.

15. An aircraft component using the fiber-reinforced composite material according to claim 10.

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