Epoxy resin composition, prepreg, and fiber-reinforced composite material

Abstract

The present invention addresses the problem of providing an epoxy resin composition having excellent recoverability and sufficient heat resistance. The epoxy resin composition contains the following components [A], [B] and [C], and contains 10-30 parts by mass of the component [B] per 100 parts by mass of the total epoxy resin. [A]: a bifunctional epoxy resin that is liquid at 23 DEG C; [B]: an epoxy resin having an average epoxy equivalent weight of 400-1200 and having a structure represented by formula (I), or an epoxy resin having an average epoxy equivalent weight of 150-500 and having a structure represented by formula (II) (in formula (I), R1 and R2 each represent a hydrogen atom or an alkyl group having 1-10 carbon atoms, and R1 and R2 may be the same as or different from each other; in addition, n1 represents an integer of 1 to 30. ) (In formula (II), R3 represents a bisphenol structure, and n2 represents an integer of 1-30. ); [C]: an aromatic diamine having a structure represented by formula (III) (in formula (III), R4 and R5 each represents a group selected from a hydrogen atom, a halogen atom, and an alkyl group having 1-8 carbon atoms, and R4 and R5 may be the same as or different from each other. ). # imgabs0 #

Description

Technical Field

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

[0002] Epoxy resins, due to their high strength, rigidity, heat resistance, and adhesive properties, are suitable as matrix resins for fiber-reinforced composite materials that are combined with reinforcing fibers such as carbon fibers, glass fibers, and aramid fibers.

[0003] In the manufacture of fiber-reinforced composite materials, prepregs, a sheet-like intermediate substrate formed by impregnating reinforcing fibers with epoxy resin, are widely used. Molded products are obtained by laminating the prepregs and then heating them to cure the epoxy resin. Prepregs can exhibit a wide variety of properties through their layering design, leading to their application in a variety of fields, including aircraft, automobiles, sports, and medicine.

[0004] In recent years, the use of fiber-reinforced composite materials has rapidly expanded. In addition to heat resistance and rigidity, epoxy resin compositions and fiber-reinforced composite materials are also required to exhibit excellent recyclability, including carbon neutrality. Epoxy resin compositions using 4,4'-diaminodiphenyl disulfide as a curing agent are known as matrix resins for such thermomechanically reshapeable fiber-reinforced composite materials (Patent Document 1).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2015 / 181054 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] The epoxy resin composition described in Patent Document 1 cannot be depolymerized using an organic solvent after curing the fiber-reinforced composite material. Therefore, the reinforcing fibers cannot be recovered from the fiber-reinforced composite material, resulting in poor recyclability.

[0010] To improve heat resistance, it is necessary to increase the crosslink density. On the other hand, a high crosslink density complicates the network, making it difficult to decompose and impossible to depolymerize through chemical treatment. Therefore, the present invention aims to overcome the trade-off between depolymerization and heat resistance in the above-mentioned prior art and provide an epoxy resin composition with excellent recyclability and sufficient heat resistance. Furthermore, it is also an object to provide a prepreg and fiber-reinforced composite material with excellent recyclability by using this epoxy resin composition as a matrix resin.

[0011] Means of solving the problem

[0012] The epoxy resin composition of the present invention has the following constitution.

[0013] 1. An epoxy resin composition comprising the following components [A], [B], and [C], wherein the epoxy resin of component [B] is contained in an amount of 10 to 30 parts by mass per 100 parts by mass of the total epoxy resin;

[0014] [A]: Bifunctional epoxy resin that is liquid at 23°C

[0015] [B]: an epoxy resin having an average epoxy equivalent of 400 to 1200 and a structure of formula (I) described below, or an epoxy resin having an average epoxy equivalent of 150 to 500 and a structure of formula (II)

[0016] [C]: an aromatic diamine having a structure of formula (III) described later.

[0017] 2. The epoxy resin composition according to 1 above, wherein component [A] is a bisphenol-type epoxy resin having an average epoxy equivalent of 160 to 200.

[0018] 3. The epoxy resin composition according to 1 or 2 above, wherein component [B] has the structure of formula (I), and is a bisphenol F-type epoxy resin having an average epoxy equivalent of 800 to 1200.

[0019] 4. The epoxy resin composition according to any one of 1 to 3 above, wherein component [C] is an aromatic diamine having a structure of formula (IV) described below, or an aromatic diamine having a structure of formula (IV) and a structural isomer thereof.

[0020] 5. The epoxy resin composition according to any one of 1 to 4 above, wherein the glass transition temperature of a cured product after curing at 150° C. to 220° C. for 120 minutes is 110° C. or higher.

[0021] 6. The epoxy resin composition according to any one of 1 to 5 above, further comprising, as component [D], 5 to 30 parts by mass of a trifunctional or tetrafunctional epoxy resin based on 100 parts by mass of the total epoxy resin.

[0022] 7. The epoxy resin composition according to any one of 1 to 6 above, further comprising a bifunctional naphthalene-type epoxy resin as component [E].

[0023] The present invention also relates to a prepreg comprising the epoxy resin composition and reinforcing fibers. Furthermore, the present invention relates to a fiber-reinforced composite material formed by curing the prepreg.

[0024] Effects of the Invention

[0025] According to the present invention, an epoxy resin composition having excellent recyclability and sufficient heat resistance can be obtained. DETAILED DESCRIPTION

[0026] The epoxy resin composition of the present invention contains the following components [A], [B], and [C] in a specific ratio described below.

[0027] [A]: Bifunctional epoxy resin that is liquid at 23°C

[0028] [B]: an epoxy resin having an average epoxy equivalent of 400 to 1200 and a structure of formula (I) described below, or an epoxy resin having an average epoxy equivalent of 150 to 500 and a structure of formula (II)

[0029] [C]: an aromatic diamine having a structure of formula (III) described later.

[0030] Each component is described below.

[0031] (ingredient [A])

[0032] Component [A] used in this invention is a bifunctional epoxy resin that is liquid at 23°C. Here, n-functional epoxy refers to a substance having n epoxy groups in the molecule of the main component (structural isomers such as optical isomers, 2,2' isomers, and 2,4' isomers that differ only in the position of epoxy group substitution on the benzene or naphthalene rings are considered the same), and bifunctional epoxy resin refers to an epoxy resin having two epoxy groups in the molecule. Liquid means a viscosity of 25,000 mPa·s or less at 23°C. By melt-mixing the liquid with component [B] and kneading it with component [C], a resin composition with so-called latent curing properties can be obtained, which does not undergo a curing reaction at 23°C to 80°C but undergoes a curing reaction above 80°C. The viscosity of component [A] at 23°C is preferably 15,000 mPa·s or less, more preferably 7,000 mPa·s or less. By setting it to 15000mPa·s or less, the resin composition can be impregnated into the reinforcing fibers to produce a prepreg on the sheet. By setting it to 7000mPa·s or less, the fiber-reinforced composite material can be formed using a filament winding method or a resin transfer molding method. In 100 parts by mass of the total epoxy resin, component [A] is preferably included in 5 to 80 parts by mass, more preferably 50 to 70 parts by mass. By making component [A] 50 to 70 parts by mass in 100 parts by mass of the total epoxy resin, an epoxy resin composition having an excellent balance between the depolymerization property and the heat resistance of the cured product can be obtained (hereinafter, the depolymerization property of the cured product is sometimes referred to as depolymerization property). Examples of the epoxy resin of component [A] include bisphenol-type epoxy resins such as bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, or bisphenol S-type epoxy resin, biphenyl-type epoxy resin, naphthalene-type epoxy resin, epoxy resin having a fluorene skeleton, polypropylene glycol-type epoxy resin, polyethylene glycol-type epoxy resin, and long-chain aliphatic epoxy resin, which meet the above-mentioned definition of liquid.

[0033] Component [A] of the present invention is preferably a bisphenol-type epoxy resin, particularly preferably one with an average epoxy equivalent of 160 to 200. An average epoxy equivalent of 160 to 200 provides an epoxy resin composition having a glass transition temperature of 110°C or higher in the cured product and excellent heat resistance. Furthermore, this is preferred due to its excellent compatibility with component [B].

[0034] In the present invention, the average epoxy equivalent can be evaluated by performing potentiometric titration according to JIS-K7236 (2001). For example, approximately 300 mg of epoxy resin is weighed and placed in a glass beaker, followed by addition of 10 mL of chloroform. A magnetic stirrer is used to stir the mixture until the weighed components are dissolved in the chloroform. 20 mL of acetic acid is added to the solution, followed by addition of 10 mL of tetraethylammonium bromide acetic acid solution (0.4 g / mL acetic acid) and stirring. The electrode is immersed in the solution, and potentiometric titration is performed using a perchloric acid-acetic acid standard solution (0.1 mol / L) to calculate the average epoxy equivalent.

[0035] (ingredient [B])

[0036] Component [B] used in the present invention has a structure of formula (I) or formula (II). The average epoxy equivalent weight of the epoxy resin having the structure of formula (I) is 400 to 1200, and the average epoxy equivalent weight of the epoxy resin having the structure of formula (II) is 150 to 500.

[0037]

[0038] In formula (I), R 1 、R 2 is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, R 1 and R 2 They may be the same or different. In addition, n1 represents an integer of 1 to 30.

[0039]

[0040] In formula (II), R 3 represents a bisphenol structure, and n2 represents an integer of 1 to 30.

[0041] Hereinafter, in this specification, for example, “an epoxy resin having a structure of formula (I)” will be simply described as “an epoxy resin of formula (I)” or the like.

[0042] The average epoxy equivalent of the epoxy resin of formula (I) is 400 to 1200. When the average epoxy equivalent of the epoxy resin of formula (I) is 400 to 1200, an epoxy resin composition having an excellent balance between depolymerization properties and heat resistance can be obtained.

[0043] In the epoxy resin of formula (I), by making R 1 、R 2The epoxy resin of formula (I) is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, resulting in an epoxy resin composition with excellent heat resistance. The epoxy resin of formula (I) is bifunctional and has a long-chain structure. Therefore, when the disulfide bond in formula (III) described below is cleaved, it decomposes into large domain units, thereby improving depolymerization properties. Furthermore, since n1 in formula (I) is an integer of 1 to 30, an epoxy resin composition with an excellent balance between depolymerization properties and heat resistance can be obtained.

[0044] When component [B] of the present invention has the structure of formula (I), it is preferably a bisphenol F-type epoxy resin having an average epoxy equivalent weight of 800 to 1200. Using a bisphenol F-type epoxy resin with an average epoxy equivalent weight of 800 to 1200 can produce an epoxy resin composition with improved depolymerization properties and heat resistance. Furthermore, the plasticized resin composition formed after depolymerization of the cured product has a reduced viscosity, resulting in improved recyclability, which is preferred.

[0045] The average epoxy equivalent of the epoxy resin of formula (II) is 150 to 500. By setting the average epoxy equivalent of the epoxy resin of formula (II) to 150 to 500, an epoxy resin composition having an excellent balance between depolymerization and heat resistance can be obtained. The average epoxy equivalent of the epoxy resin of formula (II) is preferably 200 to 350. By setting the average epoxy equivalent of the epoxy resin of formula (II) to 200 to 350, an epoxy resin composition having an even better balance between depolymerization and heat resistance can be obtained. It should be noted that the molecular weight of the epoxy resin of formula (II) is preferably 450 or more.

[0046] In the epoxy resin of formula (II), R 3 The bisphenol structure provides an epoxy resin composition with excellent heat resistance. The bisphenol structure refers to a compound having two hydroxyphenyl groups, and examples thereof include bisphenol A, bisphenol E, bisphenol F, and bisphenol S. Of these, bisphenol A and bisphenol F are preferred to provide a low-viscosity epoxy resin of formula (II).

[0047] Furthermore, by setting n2 of the epoxy resin of formula (II) to an integer of 1 to 30, an epoxy resin composition having an excellent balance between depolymerization properties and heat resistance can be obtained.

[0048] By providing the epoxy resin of formula (II) with a disulfide bond, the epoxy resin composition can be depolymerized by cleaving the disulfide bond using a dissolving solution or hydrolysis treatment even after curing. Furthermore, the epoxy resin of formula (II), like the epoxy resin of formula (I), is bifunctional and has a long-chain structure, and also has its own disulfide bond. Therefore, upon cleavage of the disulfide bond in formula (III) and within itself, the epoxy resin decomposes into large domain units, further enhancing its depolymerization properties.

[0049] The epoxy resin of component [B] used in the present invention is contained in an amount of 10 to 30 parts by mass per 100 parts by mass of the total epoxy resin. That is, when an epoxy resin of formula (I) is selected as component [B], 10 to 30 parts by mass of the epoxy resin of formula (I) is contained per 100 parts by mass of the total epoxy resin, and when an epoxy resin of formula (II) is selected as component [B], 10 to 30 parts by mass of the epoxy resin of formula (II) is contained per 100 parts by mass of the total epoxy resin. When an epoxy resin of formula (I) and an epoxy resin of formula (II) are used in combination, the total amount of the two epoxy resins can be 10 to 30 parts by mass per 100 parts by mass of the total epoxy resin. By containing the epoxy resin of component [B] in the above-specified amount, an epoxy resin composition having an excellent balance between depolymerization properties and heat resistance can be obtained.

[0050] Examples of commercially available epoxy resins of formula (I) as component [B] include bisphenol A-type epoxy resins such as "jER (registered trademark)" 1001, "jER (registered trademark)" 1004, and "jER (registered trademark)" 1007 (all manufactured by Mitsubishi Chemical Corporation), "EPICLON (registered trademark)" 1050, "EPICLON (registered trademark)" 3050, and "EPICLON (registered trademark)" 4050 (all manufactured by DIC Corporation). Examples of bisphenol F-type epoxy resins include "jER (registered trademark)" 4004P and "jER (registered trademark)" 4005P (all manufactured by Mitsubishi Chemical Corporation), and YDF-2001 and YDF-2004 (all manufactured by KOKDO Corporation).

[0051] Examples of commercially available epoxy resins of formula (II) as component [B] include "Frepp (registered trademark)" 50 and "Frepp (registered trademark)" 60 (both manufactured by Toray Fine Chemicals Co., Ltd.).

[0052] The epoxy resin composition of the present invention may further contain a trifunctional or tetrafunctional epoxy resin as component [D], preferably 5 to 30 parts by mass, more preferably 5 to 20 parts by mass, based on 100 parts by mass of the total epoxy resin.

[0053] Generally, when a trifunctional or tetrafunctional epoxy resin is added, the crosslink density increases, thereby improving heat resistance, but depolymerization properties decrease. However, by setting the content of component [D] to 5 to 30 parts by mass based on 100 parts by mass of the total epoxy resin, an epoxy resin composition with an excellent balance between depolymerization properties and heat resistance can be obtained. Furthermore, by setting the content of component [D] to 5 to 20 parts by mass based on 100 parts by mass of the total epoxy resin, an epoxy resin composition with an even better balance between depolymerization properties and heat resistance can be obtained.

[0054] Examples of the trifunctional or tetrafunctional epoxy resin of component [D] include naphthalene-type epoxy resins, epoxy resins having a fluorene skeleton, and glycidylamine-type epoxy resins such as tetraglycidyldiaminodiphenylmethane, tetraglycidylxylenediamine, triglycidylaminophenol, and triglycidylaminocresol. These can be used alone or in combination. In particular, N,N,N′,N′-tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol, and triglycidylaminocresol are preferred because they provide an epoxy resin composition that is liquid at 23°C and exhibits excellent heat resistance.

[0055] The epoxy resin composition of the present invention may further contain a bifunctional naphthalene-type epoxy resin as component [E]. The average epoxy equivalent of the bifunctional naphthalene-type epoxy resin is preferably 110 to 280, and more preferably 150 to 280. An average epoxy equivalent of 110 to 280 provides an epoxy resin composition having a glass transition temperature of 110°C or higher in the cured product and excellent heat resistance. An average epoxy equivalent of 150 to 280 provides an epoxy resin composition having a glass transition temperature of 130°C or higher in the cured product and excellent heat resistance. Furthermore, this is preferred because it exhibits excellent compatibility with component [A].

[0056] Component [E] is preferably contained in an amount of 5 to 80 parts by mass, more preferably 50 to 70 parts by mass, per 100 parts by mass of the total epoxy resin. By providing 50 to 70 parts by mass of component [E] per 100 parts by mass of the total epoxy resin, depolymerization properties are maintained while heat resistance is improved. Furthermore, even after mixing with component [A], the component remains liquid, providing excellent processability when processed into a prepreg.

[0057] By including the component [E], the naphthalene structure becomes rigid and the crosslinking density is reduced due to the bifunctional epoxy resin, and an epoxy resin composition having excellent heat resistance while maintaining depolymerization properties can be obtained.

[0058] Examples of commercially available bifunctional naphthalene-type epoxy resins as component [E] include "EPICLON (registered trademark)" HP-4032SS, "EPICLON (registered trademark)" HP-4032D, and "EPICLON (registered trademark)" HP-4770 (all manufactured by DIC Corporation), and diglycidyl compounds of 1,4'-dihydroxynaphthalene (manufactured by Air Water Performance Chemical Co., Ltd.).

[0059] Among these, "EPICLON (registered trademark)" HP-4770 is preferred in order to obtain an epoxy resin composition having excellent heat resistance and a glass transition temperature of a cured product of 130°C or higher.

[0060] (ingredient [C])

[0061] Component [C] in the present invention is an aromatic diamine having a structure represented by formula (III).

[0062]

[0063] In formula (III), R 4 、R 5 is a group selected from hydrogen atoms, halogen atoms and alkyl groups having 1 to 8 carbon atoms, R 4 and R 5 Can be the same or different.

[0064] In the aromatic diamine of formula (III), R 4 、R 5 Each of the substituents is a hydrogen atom, a halogen atom, and an alkyl group having 1 to 8 carbon atoms. This allows for an epoxy resin composition having an excellent balance between depolymerization and heat resistance. By providing the aromatic diamine of formula (III) with a disulfide bond within its structure, the cured epoxy resin composition can be depolymerized by utilizing the phenomenon that the disulfide bonds are cleaved by dissolution or hydrolysis after curing.

[0065] Examples of commercially available products of the aromatic diamine of formula (III) include 4,4′-diaminodiphenyl disulfide and 2,2′-diaminodiphenyl disulfide (all manufactured by Tokyo Chemical Industry Co., Ltd.).

[0066] Component [C] of the present invention is preferably an aromatic diamine having a structure of formula (IV) among the aromatic diamines represented by formula (III), or an aromatic diamine having a structure of formula (IV) and a structural isomer thereof.

[0067]

[0068] In formula (IV), R 4 、R 5 is a substituent selected from a hydrogen atom, a halogen atom and an alkyl group having 1 to 8 carbon atoms, R 4 and R 5 Can be the same or different.

[0069] In the structure of formula (IV), the amino group is located at the 2,2'-position, creating steric hindrance and resulting in a low crosslink density. This allows for an epoxy resin composition with a better balance between depolymerization and heat resistance. Furthermore, the use of a mixture of an aromatic diamine having the structure of formula (IV) and its structural isomers is preferred because the viscosity of the epoxy resin composition can be reduced by lowering the melting point due to the formation of a eutectic.

[0070] The glass transition temperature of the cured product of the epoxy resin composition of the present invention after curing at 150°C to 220°C for 120 minutes is preferably 110°C or higher, more preferably 130°C or higher, and even more preferably 150°C or higher. The glass transition temperature can be measured using a differential scanning calorimeter in accordance with JIS-K7121 (1999). Here, the cured product after curing at 150°C to 220°C for 120 minutes refers to a cured product cured by maintaining it at any temperature within the range of 150°C to 220°C for 120 minutes or longer.

[0071] Specifically, the cured resin obtained under the above conditions was heated from 25°C to 300°C at a heating rate of 10°C / min, held at 300°C for 3 minutes, and then rapidly cooled to 25°C at a cooling rate of 30°C / min. In a differential scanning calorimetry chart (with thermal energy on the vertical axis and temperature on the horizontal axis) of the heating process from 25°C to 300°C, in the step-like change portion of the glass transition, the point where a straight line equidistant from the extension lines of each baseline in the vertical direction intersects the curve of the step-like change portion of the glass transition is the glass transition temperature.

[0072] Generally, there is a correlation between the glass transition temperature and the depolymerization property. The higher the glass transition temperature, the higher the durability and the longer the material life. By making the glass transition temperature of the cured product obtained under the above conditions to be 110°C or more, it can be used for secondary structural materials such as interior materials in aerospace applications, and can be used for high heat-resistant applications such as bicycles, windmills, ships, railway vehicles, and laptop computer shells in general industrial applications. In addition, by making the glass transition temperature of the cured product to be 130°C or more, it can be used for automotive structural components for general industrial applications. Furthermore, by making the glass transition temperature of the cured product to be 150°C or more, it can be used for primary structural materials for aircraft such as main wings, tail planes, and landing beams in aerospace applications. In addition, the glass transition temperature of the cured product obtained under the above conditions is preferably 250°C or less. By making the glass transition temperature to be 250°C or less, the crosslinking density of the cured product can be within a range that allows depolymerization.

[0073] As described above, by combining components [A] to [C], the trade-off between heat resistance and ease of depolymerization is overcome, and excellent heat resistance is achieved. This allows for durability in actual use environments while maintaining sensitivity to depolymerization treatment, thereby enabling recyclability and being preferred.

[0074] The epoxy resin composition of the present invention may contain, within the scope of not losing the effectiveness of the present invention, thermoplastic resins, rubber particles, inorganic particles such as silica, nanoparticles such as CNTs and graphene, etc., in order to adjust viscoelasticity, improve the viscosity and draping properties of the prepreg, and enhance the mechanical properties and toughness of the resin composition. Examples of thermoplastic resins soluble in epoxy resins include polyvinyl formal, polyvinyl butyral, and other polyvinyl acetal resins, polyvinyl alcohol, phenoxy resins, polyamides, polyimides, polyvinyl pyrrolidone, polysulfones, and polyethersulfones. Examples of rubber particles include crosslinked rubber particles and core-shell rubber particles in which a heteropolymer is grafted onto the surface of the crosslinked rubber particles.

[0075] In the preparation of the epoxy resin composition of the present invention, kneading can be performed by machines such as a kneader, planetary mixer, three-roll mill, and twin-screw extruder. If uniform kneading can be performed, manual mixing can also be performed using a beaker or a scraper.

[0076] The prepreg of the present invention comprises at least one selected from carbon fiber, glass fiber and aramid fiber as reinforcing fiber in the above-mentioned epoxy resin composition. The reinforcing fiber can be a reinforcing fiber that has been surface treated. As surface treatment, in addition to the coating treatment of the metal as an electrical conductor, there is also treatment using a coupling agent, treatment using a sizing agent, treatment using a bunching agent, adhesion treatment of an additive, etc. In addition, these reinforcing fibers can be used alone or in combination of two or more. Wherein, from the perspective of lightweight effect, it is preferred to use carbon fibers such as polyacrylonitrile (PAN), asphalt, and rayon that are excellent in specific strength and specific rigidity. In addition, from the perspective of the economic efficiency of the fiber-reinforced composite material obtained, it is preferred to use glass fiber, especially from the perspective of the balance between mechanical properties and economic efficiency, it is preferred to use carbon fiber and glass fiber. And then, from the perspective of the impact resistance and shapeability of the fiber-reinforced composite material obtained, it is preferred to use aramid fiber, especially from the perspective of the balance between mechanical properties and impact resistance, it is preferred to use carbon fiber and aramid fiber. In addition, from the perspective of improving the conductivity of the resulting fiber-reinforced composite material, reinforcing fibers coated with metals such as nickel, copper, and ytterbium may also be used. Among them, PAN-based carbon fibers are more preferably used due to their excellent mechanical properties such as strength and elastic modulus.

[0077] Prepreg production methods include impregnating a reinforcing fiber substrate with the epoxy resin composition of the present invention. Examples of impregnation methods include hot melt methods (dry methods). In this case, the fiber weight content of the prepreg can be adjusted by varying the amount of resin applied to the release paper.

[0078] As a method for molding the prepreg, for example, a press molding method, an autoclave molding method, a bag molding method, a tape wrapping method, an internal pressure molding method, etc. can be appropriately used.

[0079] The reinforcing fibers contained in the prepreg of the present invention may be in the form of a fabric. When the fabric is a fabric, the fabric weave is preferably a plain weave, a twill weave, a satin weave, or the like. By making a plain weave, a twill weave, a satin weave, or the like, the prepreg has excellent handling properties as a sheet and excellent shape-following properties during lamination, making it easy to form components of complex shapes. Here, excellent shape-following properties mean that in the process of laminating the reinforcing fiber fabric or the like to a forming mold having a three-dimensional shape, the reinforcing fiber fabric or the like can be distributed along the shape without destroying the fiber orientation, thereby obtaining a molded body that is satisfactory in terms of quality and performance. In addition, in the process of laminating the reinforcing fiber fabric or the like to a forming mold having a three-dimensional shape, a preform is made using the reinforcing fiber fabric or the like, but at this time, a finishing process is required to cut the parts of the substrate that are not distributed along the shape of the forming mold with scissors or a cutter, or to fix the parts that do not become the final product with tape. The finishing process consumes a lot of time and labor, resulting in material loss.

[0080] The reinforcing fibers contained in the prepreg of the present invention may be in the form of discontinuous fibers. By making the reinforcing fibers in the form of discontinuous fibers, when the sheet-like prepreg is molded by applying external force, it becomes easier to shape it into a complex shape.

[0081] Furthermore, when the reinforcing fibers are discontinuous fibers, they are preferably randomly dispersed in bundles in the prepreg. This facilitates shaping into a complex shape when external force is applied to the prepreg for molding.

[0082] In addition, regarding the form of the reinforcing fibers, in the case of discontinuous fibers, it is also preferred that they are randomly dispersed in a roughly monofilament shape in the prepreg. In the case of discontinuous fibers, by making the discontinuous reinforcing fibers randomly dispersed in a roughly monofilament shape, the number of reinforcing fibers present as fiber bundles in the prepreg decreases. Therefore, the weak parts at the ends of the fiber bundles of the reinforcing fibers can be minimized, which can provide excellent reinforcement efficiency and isotropy. Here, the so-called roughly monofilament shape refers to the reinforcing fiber monofilaments being present in the form of a fine fineness bundle of less than 500. The reinforcing fibers are more preferably dispersed in a monofilament shape, that is, in a manner existing in the form of monofilaments, and more preferably monofilament-shaped single fibers are randomly dispersed. In the case of discontinuous fibers, the reinforcing fibers can be in a non-woven fabric-like form.

[0083] Next, the fiber-reinforced composite material of the present invention will be described.

[0084] The fiber-reinforced composite material, one aspect of the present invention, comprises a cured product of the epoxy resin composition of the present invention (hereinafter referred to as the "cured epoxy resin product of the present invention") as a matrix resin, typically formed by curing the prepreg of the present invention described above. More specifically, a fiber-reinforced composite material comprising the cured epoxy resin composition of the present invention as a matrix resin can be obtained by laminating prepregs comprising the epoxy resin composition of the present invention as a matrix resin, as needed, and then heating and curing them.

[0085] The depolymerization of the present invention refers to the entire process in which a polymerized substance decomposes under the action of external stimuli and eventually becomes a monomer. In the initial stage of depolymerization of epoxy resin cured material, it becomes a state in which only the surface swells or only the surface dissolves slightly. If it becomes such a state, when the epoxy resin cured material is joined to different components such as metal, separation and disintegration become easy, giving it recyclability. If the depolymerization proceeds further, the entire thickness direction is plasticized and becomes a rubbery state. When it becomes such a state, the epoxy resin cured material can sometimes be treated as a plastic resin and can be recycled by regeneration molding. As the final stage of depolymerization, the epoxy resin cured material dissolves significantly and becomes a state in which it no longer maintains its original shape. It should be noted that when depolymerization is carried out in a static state, even if it maintains its original shape on the surface, it is considered to be a state in which it does not maintain its original shape when it is moved and it cannot maintain its shape and collapses. When it becomes such a state, if it is a fiber-reinforced composite material, the reinforcing fibers contained inside can be recycled as recycled fibers (resources).

[0086] The method of depolymerizing and plasticizing the cured epoxy resin composition of the fiber reinforced composite material of the present invention by a dissolving liquid or hydrolysis treatment can be exemplified by thermal decomposition, supercritical water method, subcritical water method, superheated water vapor method, liquid phase decomposition method, dissolution method, and diol method. Considering the ease of depolymerization based on disulfide cleavage, a dissolution method using a dissolving liquid is preferred. Considering the fact that a neutralization treatment of the dissolving liquid and a cleaning treatment of the recovered fiber are not required, a superheated water vapor method is preferred. As the dissolving liquid of the present invention, there is no particular limitation as long as it can dissolve the epoxy resin cured material of the present invention, and for example, it contains at least one liquid selected from an acidic solution, an organic solvent, hydrogen peroxide, and an ionic liquid. These liquids can dissolve or plasticize the epoxy resin cured material of the present invention and can effectively depolymerize. The dissolving liquid can be used alone or in combination of two or more.

[0087] Examples of the acidic solution used as a dissolving solution for the epoxy resin composition include phosphoric acid, sulfuric acid, hydrochloric acid, and nitric acid. The acidic component may be used alone or in combination of two or more.

[0088] Examples of the organic solvent used as the above-mentioned dissolving liquid include aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, alcohol solvents, ketone solvents, ether solvents, amide solvents, or ester solvents, and N-methyl-2-pyrrolidone having a lactam structure. Among them, N-methyl-2-pyrrolidone is preferred because it has high water solubility and can be used to wash the recovered fiber with water. One organic solvent may be used alone or in combination of two or more. Examples of aliphatic hydrocarbon solvents include pentane, hexane, heptane, octane, and glycols. 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 them, acetone and methyl ethyl ketone are preferred because they are highly volatile and the recovered fiber is easy to dry. The organic solvent may contain a decomposition catalyst. Examples of the decomposition catalyst include iron oxide and alkali metal compounds.

[0089] Examples of the ionic liquid used as the dissolving solution include ionic liquids containing at least one cation selected from imidazolium, pyridinium, pyrrolidinium, quaternary ammonium, and quaternary phosphonium groups. The ionic liquids may be used alone or in combination of two or more.

[0090] The fiber-reinforced composite material of the present invention is preferred because it can provide a downcycled composite material by going through the steps (i) to (iii).

[0091] (i) The fiber length of the reinforcing fibers in the fiber-reinforced composite material is set to 2 to 100 mm.

[0092] (ii) The cured epoxy resin composition is depolymerized and plasticized by a dissolving agent or hydrolysis treatment.

[0093] (iii) The plasticized fiber-reinforced composite material is randomly dispersed and hot-pressed under conditions of 100 to 200° C. and 0.7 to 15 MPa.

[0094] Producing a downcycled composite material through steps (i) to (iii) allows the cured epoxy resin composition, which serves as the matrix resin in the fiber-reinforced composite material, to be recovered without depolymerizing and separating from the reinforcing fibers. This is advantageous because greenhouse gas emissions during recycling of the fiber-reinforced composite material are significantly reduced. Specifically, the downcycled composite material of the present invention is preferred due to its low environmental impact during production.

[0095] The processing (i) for reducing the fiber length of the reinforcing fibers in the fiber-reinforced composite material of the present invention to 2 to 100 mm can be performed using a hammer mill, a sand mill-type wet pulverizer, a granulator, a high-speed rotor pulverizer, a rotary shearing pulverizer, a ball mill, or the like. It should be noted that if all the fibers originally have a length of 2 to 100 mm, they can be used as they are.

[0096] The reinforcing fibers in downcycled composite materials preferably have a fiber length of 3 to 20 mm. This range improves fiber dispersion and yields a highly rigid composite material. Furthermore, a fiber length of 60 to 100 mm is also preferred. This range simplifies processing and reduces greenhouse gas emissions, making it particularly advantageous. Further processing and recycling of the composite material after use to a fiber length of 50 mm or less can significantly reduce greenhouse gas emissions.

[0097] The fiber-reinforced composite material as one aspect of the present invention is preferably used for sports applications, general industrial applications, and aerospace applications. More specifically, as sports components, it is preferably used for golf clubs, fishing rods, tennis or badminton rackets, hockey sticks, and ski poles. In addition, among general industrial components, it is preferably used for structural materials such as automobiles, bicycles, windmills, ships, and railway vehicles, and electronic equipment components such as housings (casings) of information equipment such as IC trays and laptop computers. Furthermore, among aerospace components, it is preferably used for primary structural materials of aircraft such as main wings, tail planes, and floor beams, and secondary structural materials such as interior materials.

[0098] Example

[0099] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the description of these examples.

[0100] 1. Materials used

[0101] <Epoxy resin>

[0102] The epoxy resins used in the comparative examples of this embodiment are listed below. Note that in Tables 1 to 4, epoxy equivalent weight is abbreviated as "EEW".

[0103] [ingredient [A]]

[0104] "jER (registered trademark)" 825 (bisphenol A-type epoxy resin, average epoxy equivalent: 175, viscosity at 23°C: 7000 mPa·s, manufactured by Mitsubishi Chemical Corporation)

[0105] "EPALLOY (registered trademark)" 5000 (hydrogenated bisphenol A-type epoxy resin, viscosity at 23°C: 2000 mPa·s, average epoxy equivalent: 220, manufactured by Hanzman Co., Ltd.).

[0106] [Ingredient [B]]

[0107] "jER (registered trademark)" 1001 (bisphenol A-type epoxy resin, a compound having the structure of formula (I), average epoxy equivalent: 475, solid at 23°C, manufactured by Mitsubishi Chemical Corporation)

[0108] "jER (registered trademark)" 1004 (bisphenol A-type epoxy resin, a compound having the structure of formula (I), average epoxy equivalent: 925, solid at 23°C, manufactured by Mitsubishi Chemical Corporation)

[0109] "jER (registered trademark)" 4004P (bisphenol F-type epoxy resin, a compound having the structure of formula (I), average epoxy equivalent: 908, solid at 23°C, manufactured by Mitsubishi Chemical Corporation)

[0110] "jER (registered trademark)" 4005P (bisphenol F-type epoxy resin, a compound having the structure of formula (I), average epoxy equivalent: 1075, solid at 23°C, manufactured by Mitsubishi Chemical Corporation)

[0111] "Frepp (registered trademark)" 60 (epoxy resin, compound having the structure of formula (II), average epoxy equivalent: 279, semi-solid at 23°C, manufactured by Toray Fine Chemicals Co., Ltd.)

[0112] "Frepp (registered trademark)" 50 (epoxy resin, a compound having the structure of formula (II), average epoxy equivalent: 327, semi-solid at 23°C, manufactured by Toray Fine Chemicals Co., Ltd.).

[0113] [Ingredient [D]]

[0114] "Sumi Epokishi (registered trademark)" ELM434 (N,N,N',N'-tetraglycidyldiaminodiphenylmethane, average epoxy equivalent: 120, manufactured by Sumitomo Chemical Co., Ltd.)

[0115] [Ingredient [E]]

[0116] "EPICLON (registered trademark)" HP-4032D (naphthalene-type epoxy resin, average epoxy equivalent: 142, viscosity at 23°C: 39,000 mPa·s, manufactured by DIC Corporation)

[0117] "EPICLON (registered trademark)" HP-4770 (a bifunctional naphthalene-type epoxy resin that is solid at 23°C, average epoxy equivalent: 204, manufactured by DIC Corporation).

[0118] [Epoxy resins other than components [A], [B], [D], and [E]]

[0119] "jER (registered trademark)" 1007 (bisphenol A-type epoxy resin having the structure of formula (I) but an average epoxy equivalent weight of 1975, manufactured by Mitsubishi Chemical Corporation)

[0120] "jER (registered trademark)" 4007P (bisphenol F-type epoxy resin, having the structure of formula (I), but with an average epoxy equivalent of 2250, manufactured by Mitsubishi Chemical Corporation)

[0121] "Frepp (registered trademark)" 125X (an epoxy resin having a disulfide bond, having the structure of formula (II), but with an average epoxy equivalent weight of 850, manufactured by Toray Fine Chemicals Co., Ltd.)

[0122] In addition, in Table 4, "epoxy resins other than components [A], [B], [D], and [E]" are simply referred to as "other epoxy resins."

[0123] <Curing Agent>

[0124] [Ingredient [C]]

[0125] 4,4'-Diaminodiphenyl disulfide (an aromatic diamine having the structure of formula (III) but not the structure of formula (IV), manufactured by Tokyo Chemical Industry Co., Ltd.)

[0126] 2,2'-Diaminodiphenyl disulfide (aromatic diamine, a compound having a structure of formula (IV), manufactured by Tokyo Chemical Industry Co., Ltd.).

[0127] [Aromatic diamines other than component [C]]

[0128] 4,4'-Diaminodiphenyl sulfone (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0129] In addition, in Tables 1, 2, and 4, "aromatic diamines other than component [C]" are simply referred to as "other aromatic diamines."

[0130] 2. Sample preparation method

[0131] [Method for preparing epoxy resin composition]

[0132] Specified amounts of component [A], component [B], component [D], and component [E] as epoxy resin components were added to a stainless steel beaker, heated to 40 to 150° C., and mixed appropriately until the components were dissolved.

[0133] The prepared mixture of epoxy resin components was cooled to 60° C. or lower, and component [C] and other aromatic diamines were added thereto, followed by kneading at 60° C. for 30 minutes to obtain an epoxy resin composition.

[0134] [Method for producing cured resin]

[0135] The epoxy resin composition obtained by the above-described [Epoxy Resin Composition Preparation Method] was degassed in a vacuum and then injected into a mold set to a thickness of 1 mm using a Teflon (registered trademark) spacer. The epoxy resin composition was then cured by heating it from 30°C to 180°C at a rate of 1.0°C per minute in a hot air oven and then maintaining it at 180°C for 120 minutes. The temperature was then lowered to 30°C and released from the mold, resulting in a 1 mm thick cured resin product.

[0136] [Method for producing fiber-reinforced composite materials]

[0137] The epoxy resin composition prepared according to the above-mentioned [Method for Preparing the Epoxy Resin Composition] was impregnated into unidirectionally arranged carbon fibers "Toreka (registered trademark)" T700S-12K-60E (manufactured by Toray Industries, Ltd., with a unit area weight of 150 g / m 2 ) to obtain a prepreg. The obtained prepreg was cut into pieces of 200 mm in length and 200 mm in width. Five sheets were stacked so that the fibers were perpendicular to each other. The prepreg was then clamped in a mold and pressurized at 3.5 MPa in a press heated to 150-200°C 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.

[0138] It should be noted that Vf (unit: %) refers to the volume ratio of reinforcing fibers in the fiber-reinforced composite material, and is specifically determined by the following formula.

[0139] Vf=(W×100) / (ρ×T)

[0140] W: per cm 2 The mass of reinforcing fibers in the reinforcing fiber matrix (g / cm 2 )

[0141] ρ: Density of reinforcing fiber (g / cm 3 )

[0142] T: thickness of fiber reinforced composite material (cm).

[0143] 3. Evaluation Method

[0144] [Measurement method of glass transition temperature]

[0145] 5 mg of a sample was weighed from the 1 mm thick cured resin obtained by the above-mentioned [Preparation Method of Cured Resin] into a sample pan and measured using a differential scanning calorimeter Q-2500 (manufactured by TA Instruments) in accordance with JIS-K7121 (1999).

[0146] The sample was heated from 25°C to 300°C at a heating rate of 10°C / minute, held at 300°C for 3 minutes, and then rapidly cooled to 25°C at a cooling rate of 30°C / minute. In the differential scanning calorimetry chart (with thermal energy on the vertical axis and temperature on the horizontal axis) of the heating process from 25°C to 300°C, the glass transition temperature was determined at the point where a line equidistant from the extension of each baseline on the vertical axis intersected the curve of the glass transition step-like change. This measurement was repeated three times, and the average of the obtained values ​​was taken as the glass transition temperature.

[0147] [Evaluation Method for Depolymerization Property of Epoxy Resin Composition]

[0148] The 1 mm thick cured resin obtained by the above-described [Preparation Method for Cured Resin] was processed into a 15 mm wide by 15 mm long square. Three test pieces were placed in a stainless steel beaker containing 65 g of a solution of either benzyl alcohol, methyl ethyl ketone (MEK), or N-methyl-2-pyrrolidone (NMP). The following criteria were used for evaluation. Each stainless steel beaker was covered and stored at 23°C.

[0149] There is no change in the epoxy resin cured product...

[0150] Only the surface swells or dissolves slightly...A

[0151] The entire thickness direction is plasticized and becomes rubbery...B

[0152] The epoxy resin cured material was significantly dissolved and did not retain its original shape...C.

[0153] (Example 1)

[0154] An epoxy resin composition was prepared according to the above-mentioned [Method for Preparing an Epoxy Resin Composition] using 70 parts by mass of "jER (registered trademark)" 825 corresponding to component [A] as the epoxy resin, 30 parts by mass of "jER (registered trademark)" 1001 corresponding to an epoxy resin having an average epoxy equivalent of 400 to 1200 and having the structure of formula (I) as component [B], and 26.5 parts by mass of 4,4'-diaminodiphenyl disulfide corresponding to component [C] as the curing agent.

[0155] Using this epoxy resin composition, an epoxy resin cured product was prepared according to the [Method for Preparing an Epoxy Resin Cured Product], and the glass transition temperature was measured according to the [Method for Measuring Glass Transition Temperature]. The glass transition temperature was 136°C, indicating good heat resistance.

[0156] The depolymerization property of MEK / 30 days evaluated according to the [Method for evaluating the depolymerization property of epoxy resin composition] was A, indicating that only a slight dissolution of the surface was observed, indicating good depolymerization property.

[0157] (Examples 2 to 21)

[0158] Epoxy resin compositions and epoxy resin cured products were prepared by the same method as in Example 1 except that the resin compositions were changed as shown in Table 1. The evaluation results are shown in Tables 1, 2, and 3.

[0159]

[0160]

[0161]

[0162] (Example 22)

[0163] The epoxy resin composition obtained in Example 1 was impregnated into unidirectionally arranged carbon fibers "Torayca (registered trademark)" T700S-12K-60E in the form of a sheet, and the carbon fibers had a unit area weight of 190 g / m 2 The obtained prepreg has good viscosity and excellent handling properties. The fiber-reinforced composite material obtained according to the [Method for producing a fiber-reinforced composite material] has a fiber volume content Vf of 65% and is of good quality.

[0164] (Example 23)

[0165] The epoxy resin composition obtained in Example 2 was impregnated into unidirectionally arranged carbon fibers "Torayca (registered trademark)" T700S-12K-60E in the form of a sheet, and the carbon fibers had a unit area weight of 190 g / m 2The obtained prepreg was difficult to handle due to the low viscosity and excessive tack of the resin composition. The fiber-reinforced composite material obtained according to the [Method for Producing Fiber-Reinforced Composite Material] had a fiber volume fraction Vf of 64%, indicating good quality.

[0166] (Example 24)

[0167] The prepreg obtained in Example 22 was shaped into a mold in the shape of an automobile roof, but the shape-following property was poor and complicated finishing was required.

[0168] (Example 25)

[0169] The epoxy resin composition obtained in Example 1 was impregnated into carbon fiber "Torayca (registered trademark)" T700S-12K-60E having a unit area weight of 192 g / m 2 The obtained fabric prepreg was shaped into a mold in the shape of the car roof and the result was excellent shape followability without the need for trimming.

[0170] (Example 26)

[0171] Carbon fiber "Toreka (registered trademark)" T700S-12K-60E was cut into 12 mm lengths and randomly dispersed in bundles or roughly monofilaments. The result was a unit area weight of 150 g / m 2 The epoxy resin composition obtained in Example 1 was impregnated into the nonwoven fabric to obtain a nonwoven prepreg. The obtained nonwoven prepreg was shaped in a mold in the shape of an automobile roof. The result showed that the shape-following performance was excellent and no trimming was required.

[0172] (Example 27)

[0173] The fiber-reinforced composite material obtained in Example 22 was pulverized using a biaxial mill to obtain chips containing reinforcing fibers with a fiber length of 5 to 100 mm. The resulting chips were treated with superheated steam at 300°C for 30 minutes, depolymerizing the cured epoxy resin in the fiber-reinforced composite material and causing plasticization. The plasticized chips were randomly dispersed and hot-pressed at 180°C and 10 MPa to produce a recycled molded plate.

[0174] (Comparative Example 1)

[0175] An epoxy resin composition and a cured epoxy resin product were prepared by the same methods as in Example 1, except that only 100 parts by mass of "jER (registered trademark)" 825, corresponding to component [A], was used as the epoxy resin. The resin composition and evaluation results are shown in Table 4. The resulting resin composition had good heat resistance, but insufficient depolymerization properties.

[0176] (Comparative Example 2)

[0177] An epoxy resin composition and a cured epoxy resin product were prepared using the same methods as in Example 1, except that 95 parts by mass of "jER (registered trademark)" 825, corresponding to component [A], and 5 parts by mass of "jER (registered trademark)" 1001, an epoxy resin having an average epoxy equivalent of 400 to 1200 and a structure of formula (I), corresponding to component [B], were used. The resin composition and evaluation results are shown in Table 4. The resulting resin composition had good heat resistance, but insufficient depolymerization properties.

[0178] (Comparative Example 3)

[0179] An epoxy resin composition and a cured epoxy resin product were prepared using the same methods as in Example 1, except that 60 parts by mass of "jER (registered trademark)" 825, corresponding to component [A], and 40 parts by mass of "jER (registered trademark)" 1001, an epoxy resin having an average epoxy equivalent of 400 to 1200 and a structure of formula (I), corresponding to component [B], were used. The resin composition and evaluation results are shown in Table 4. The resulting resin composition had good depolymerization properties but insufficient heat resistance.

[0180] (Comparative Example 4)

[0181] An epoxy resin composition and a cured epoxy resin were prepared using the same methods as in Example 1, except that 90 parts by mass of "jER (registered trademark)" 825, corresponding to component [A], and 10 parts by mass of "jER (registered trademark)" 1007, which has the structure of formula (I) but has an average epoxy equivalent of 1975 and does not correspond to any of components [A], [B], [D], or [E]. The resin composition and evaluation results are shown in Table 4. The resulting resin composition had good depolymerization properties but insufficient heat resistance.

[0182] (Comparative Example 5)

[0183] An epoxy resin composition and a cured epoxy resin product were prepared using the same methods as in Example 1, except that 90 parts by mass of "jER (registered trademark)" 825, corresponding to component [A], and 10 parts by mass of "jER (registered trademark)" 4007P, which has a structure of formula (I) but an average epoxy equivalent of 2250 and does not correspond to any of components [A], [B], [D], or [E], were used as the epoxy resin. The resin composition and evaluation results are shown in Table 4. The resulting resin composition had good depolymerization properties but insufficient heat resistance.

[0184] (Comparative Example 6)

[0185] An epoxy resin composition and a cured epoxy resin product were prepared using the same methods as in Example 1, except that 95 parts by mass of "jER (registered trademark)" 825, corresponding to component [A], and 5 parts by mass of "Frepp (registered trademark)" 50, an epoxy resin having an average epoxy equivalent of 150 to 500 and a structure of formula (II), corresponding to component [B], were used. The resin composition and evaluation results are shown in Table 4. The resulting resin composition had good heat resistance, but insufficient depolymerization properties.

[0186] (Comparative Example 7)

[0187] An epoxy resin composition and a cured epoxy resin product were prepared by the same method as in Example 1, except that 60 parts by mass of "jER (registered trademark)" 825, corresponding to component [A], and 40 parts by mass of "Frepp (registered trademark)" 50, an epoxy resin having an average epoxy equivalent of 150 to 500 and a structure of formula (II), corresponding to component [B], were used. The resin composition and evaluation results are shown in Table 4. The resulting resin composition had good depolymerization properties but insufficient heat resistance.

[0188] (Comparative Example 8)

[0189] An epoxy resin composition and a cured epoxy resin product were prepared using the same methods as in Example 1, except that 90 parts by mass of "jER (registered trademark)" 825, corresponding to component [A], and 10 parts by mass of "Frepp (registered trademark)" 125X, which has a structure of formula (II) but an average epoxy equivalent of 850 and does not correspond to any of components [A], [B], [D], or [E], were used as the epoxy resin. The resin composition and evaluation results are shown in Table 4. The resulting resin composition had good depolymerization properties but insufficient heat resistance.

[0190] (Comparative Example 9)

[0191] The epoxy resin composition and the epoxy resin cured product were prepared by the same method as in Example 1, except that "jER (registered trademark)" 825, corresponding to component [A], was used at 70 parts by mass, and "jER (registered trademark)" 1001, a compound epoxy resin having a structure of formula (I) with an average epoxy equivalent of 400 to 1200, corresponding to component [B], was used at 30 parts by mass. As the curing agent, an aromatic diamine other than component [C] was used instead of component [C]. The resin composition and evaluation results are shown in Table 4. The resulting resin composition had good heat resistance, but insufficient depolymerization properties.

[0192]

[0193] In addition, the numerical value of each component in a table|surface is a mass part when all the epoxy resin components contained in an epoxy resin composition are regarded as 100 mass parts.

Claims

1. An epoxy resin composition comprising the following components [A], [B], and [C], wherein the epoxy resin of component [B] is contained in an amount of 10 to 30 parts by mass per 100 parts by mass of the total epoxy resin; [A]: Bifunctional epoxy resin that is liquid at 23°C [B]: an epoxy resin having an average epoxy equivalent of 400 to 1200 and a structure of formula (I), or an epoxy resin having an average epoxy equivalent of 150 to 500 and a structure of formula (II) In formula (I), R 1 、R 2 is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, R 1 and R 2 They may be the same or different; in addition, n1 represents an integer from 1 to 30; In formula (II), R 3 represents a bisphenol structure, n2 represents an integer from 1 to 30; [C]: Aromatic diamine having the structure of formula (III) described below In formula (III), R 4 、R 5 is a group selected from a hydrogen atom, a halogen atom and an alkyl group having 1 to 8 carbon atoms, R 4 and R 5 Can be the same or different.

2. The epoxy resin composition according to claim 1, wherein component [A] is a bisphenol-type epoxy resin having an average epoxy equivalent weight of 160 to 200. 3 . The epoxy resin composition according to claim 1 , wherein component [B] has the structure of formula (I), and is a bisphenol F-type epoxy resin having an average epoxy equivalent of 800 to 1200.

4. The epoxy resin composition according to claim 1, wherein component [C] is an aromatic diamine having a structure of formula (IV), or an aromatic diamine having a structure of formula (IV) and a structural isomer thereof; In formula (IV), R 4 、R 5 is a group selected from a hydrogen atom, a halogen atom and an alkyl group having 1 to 8 carbon atoms, R 4 and R 5 Can be the same or different. The epoxy resin composition according to claim 1 , wherein the glass transition temperature of a cured product thereof after curing at 150° C. to 220° C. for 120 minutes is 110° C. or higher. 6 . The epoxy resin composition according to claim 1 , further comprising, as component [D], 5 to 30 parts by mass of a trifunctional or tetrafunctional epoxy resin based on 100 parts by mass of the total epoxy resin. 7 . The epoxy resin composition according to claim 1 , further comprising a bifunctional naphthalene-type epoxy resin as component [E]. 8 . A prepreg comprising the epoxy resin composition according to claim 1 and at least one reinforcing fiber selected from the group consisting of carbon fiber, glass fiber and aramid fiber. 9 . The prepreg according to claim 8 , wherein the reinforcing fibers are in the form of a fabric. 10 . The prepreg according to claim 8 , wherein the reinforcing fibers are in the form of discontinuous fibers. 11 . The prepreg according to claim 8 , wherein the reinforcing fibers are randomly dispersed in a bundle or substantially monofilament form.

12. A fiber-reinforced composite material formed by curing the prepreg according to claim 8.

13. A downcycled recycled composite material obtained from the fiber-reinforced composite material according to claim 12 through steps (i) to (iii); (i) the fiber length of the reinforcing fibers in the fiber-reinforced composite material is 2 to 100 mm; (ii) depolymerizing the cured epoxy resin composition by dissolving it in a solvent or performing a hydrolysis treatment to plasticize it; (iii) The plasticized fiber-reinforced composite material is randomly dispersed and hot-pressed under conditions of 100 to 200° C. and 0.7 to 15 MPa.

14. An aerospace component formed using the fiber-reinforced composite material according to claim 12.

15. A component for automobile use, formed using the fiber-reinforced composite material according to claim 12.

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