Prepreg, fiber-reinforced composite material, and method for manufacturing fiber-reinforced composite material

Abstract

One purpose of the present invention is to provide a prepreg and a fiber-reinforced composite material having excellent 90° flexural strength and an excellent elastic modulus while maintaining heat resistance.　A prepreg according to one example contains carbon fibers and a matrix resin containing epoxy resins. The prepreg contains, as an epoxy resin, an epoxy resin A that is one or both of a compound represented by a specific chemical formula (1) and a compound represented by a specific chemical formula (2), and the content of the epoxy resin A is 1-35 mass% of the total amount of the epoxy resins. The content of an epoxy resin B having at least one intramolecular sulfur atom is from 0 mass% to less than 3 mass% of the total amount of the epoxy resins, and the content of a novolac-type epoxy resin is from 0 mass% to less than 50 mass% of the total amount of the epoxy resins.

Description

Prepreg, fiber-reinforced composite material, and method for manufacturing fiber-reinforced composite material

[0001] The present invention relates primarily to a prepreg, a fiber-reinforced composite material, and a method for manufacturing a fiber-reinforced composite material. This application claims priority based on Japanese Patent Application No. 2024-48290, filed with the Japan Patent Office on March 25, 2024, the contents of which are incorporated herein by reference.

[0002] Fiber-reinforced composite materials, which combine a matrix resin with reinforcing fibers, are characterized by their light weight, high strength, and high rigidity. Therefore, they are widely used in a variety of applications, from sports and leisure to industrial applications such as automobiles and aircraft. In particular, molded articles obtained by molding fiber-reinforced composite materials into tubular shapes are widely used in sports and leisure applications, such as fishing rods, golf club shafts, ski poles, and bicycle frames.

[0003] One method for producing fiber-reinforced composite materials involves curing an intermediate material, i.e., a prepreg, in which a reinforcing material made of long fibers such as reinforcing fibers is impregnated with a matrix resin. This method has the advantage that the content of reinforcing fibers in the fiber-reinforced composite material can be easily controlled and can be designed to be high.

[0004] Epoxy resin compositions with excellent mechanical properties, heat resistance, and ease of handling are widely used as matrix resins in prepregs. Epoxy resin compositions used in sports and leisure applications, industrial applications, and the like often have compositions that provide high interfacial adhesion with carbon fibers because they may contain many highly reactive epoxy groups and highly polar hydroxyl groups, and because they use highly polar latent curing agents.

[0005] It is known that the mechanical properties of fiber-reinforced composite materials obtained by curing unidirectional prepregs vary greatly between the fiber axis direction of the carbon fibers and the direction approximately perpendicular to the fiber axis direction of the carbon fibers. Performance in the 0° direction is largely contributed to by the interfacial adhesion between the matrix resin and the carbon fibers, as well as the performance of the carbon fibers themselves. Meanwhile, performance in the 90° direction is largely contributed to by the strength, modulus of elasticity, and fracture strain of the matrix resin itself, as well as the interfacial adhesion between the matrix resin and the carbon fibers. In this specification, 0° refers to the fiber axis direction of the carbon fibers, and 90° refers to the direction approximately perpendicular to the fiber axis direction of the carbon fibers. The same applies hereinafter.

[0006] In sports, leisure, and industrial applications, fiber-reinforced composite materials are generally produced by laminating multiple prepregs according to a certain rule so that the 0° direction is offset. Therefore, it is essential to improve performance not only in the 0° direction but also in the 90° direction.

[0007] The use of flexible epoxy resins is known as a means of improving the performance of prepregs. Patent Document 1 discloses that a fiber-reinforced composite material with excellent fracture strain and heat resistance can be obtained by using a tetrafunctional epoxy resin containing sulfur atoms in the molecule as a matrix resin and an epoxy resin having a specific skeletal structure as a flexible epoxy resin. Patent Document 2 discloses that a fiber-reinforced composite material with excellent mechanical properties and impact resistance can be obtained by setting the tensile modulus and tensile elongation at break of the matrix resin within specific ranges. A flexible epoxy resin is used as the resin with the specific modulus and tensile elongation at break. Patent Document 3 discloses that an epoxy resin composition with excellent flexibility, sufficient heat resistance, and excellent demoldability can be obtained by using a flexible epoxy resin with a specific structure.

[0008] JP 2019-189750 A JP 2006-274110 A International Publication No. 2023 / 053834

[0009] One object of the present invention is to provide a prepreg and a fiber-reinforced composite material that are excellent in 90° flexural strength and elastic modulus while maintaining heat resistance.

[0010] According to one aspect of the present invention, there is provided a prepreg comprising a matrix resin containing an epoxy resin and carbon fibers, wherein the epoxy resin contains an epoxy resin A which is either or both of a compound represented by the following formula (1) and a compound represented by the following formula (2), the content of the epoxy resin A being from 1 to 35 mass% of the total amount of the epoxy resins, the content of the epoxy resin B having at least one sulfur atom in the molecule being from 0 to less than 3 mass% of the total amount of the epoxy resins, and the content of the novolac epoxy resin being from 0 to less than 50 mass% of the total amount of the epoxy resins:

[0011]

[0012]

[0013] In formula (1) and formula (2), X １ and X ２ are each independently a structural unit represented by the following formula (3), and Y １ and Y ２ are each independently an aliphatic hydrocarbon group having 20 or less carbon atoms, １ and n ２ are each independently 1 to 20.

[0014]

[0015] In formula (3), Z １ is a single bond or -CH ２ -, -C(CH ３ ) ２ -, -CH(CH ３ )-,-C(Ph)(CH ３ is a divalent group selected from the group consisting of groups represented by —C(═O)—, —O—, and —C(═O)—, １ R １ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m ２ R ２ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m １ and m ２are each independently an integer of 1 to 4.

[0016] According to another aspect of the present invention, there is provided a prepreg comprising a matrix resin containing an epoxy resin and carbon fibers, wherein the epoxy resin contains an epoxy resin A which is either or both of a compound represented by the following formula (4) and a compound represented by the following formula (5), the content of the epoxy resin A being from 1 to 35 mass% of the total amount of the epoxy resins, and the content of the epoxy resin B having at least one sulfur atom in the molecule being from 0 to 3 mass% of the total amount of the epoxy resins:

[0017]

[0018]

[0019] In formula (4) and formula (5), X ３ and X ４ are each independently a structural unit represented by the following formula (6), and Y ３ and Y ４ are each independently an aliphatic hydrocarbon group having 20 or less carbon atoms, ３ and n ４ are each independently 1 to 20.

[0020]

[0021] In formula (6), Z ２ is a single bond or -CH ２ -, -C(CH ３ ) ２ -, -CH(CH ３ )-,-C(Ph)(CH ３ is a divalent group selected from the group consisting of groups represented by —C(═O)—, —O—, and —C(═O)—, ３ R ３ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m ４ R ４ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m １ and m ２are each independently an integer of 1 to 4.

[0022] According to one aspect of the present invention, a prepreg and a fiber-reinforced composite material having excellent 90° bending strength and elastic modulus while maintaining heat resistance can be obtained.

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes in detail the preferred embodiments of the present invention. However, the following description is a representative example, and the present invention is not limited to the following description.

[0024] [Prepreg] One embodiment of the present invention relates to a prepreg. The prepreg according to the present embodiment contains a matrix resin containing an epoxy resin and carbon fibers. The prepreg according to one example contains an epoxy resin A, which is either or both of a compound represented by the following formula (1) and a compound represented by the following formula (2), wherein the content of the epoxy resin A is 1% by mass or more and 35% by mass or less of the total amount of the epoxy resins, the content of the epoxy resin B having at least one sulfur atom in the molecule is 0% by mass or more and less than 3% by mass of the total amount of the epoxy resins, and the content of the novolac epoxy resin is 0% by mass or more and less than 50% by mass of the total amount of the epoxy resins.

[0025]

[0026]

[0027] In formula (1) and formula (2), X １ and X ２ are each independently a structural unit represented by the following formula (3), and Y １ and Y ２ are each independently an aliphatic hydrocarbon group having 20 or less carbon atoms, １ and n ２ are each independently 1 to 20.

[0028]

[0029] In formula (3), Z １ is a single bond or -CH ２ -, -C(CH ３ ) ２ -, -CH(CH ３)-,-C(Ph)(CH ３ is a divalent group selected from the group consisting of groups represented by —C(═O)—, —O—, and —C(═O)—, １ R １ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m ２ R ２ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m １ and m ２ are each independently an integer of 1 to 4.

[0030] Another example of a prepreg contains an epoxy resin A which is either or both of a compound represented by the following formula (4) and a compound represented by the following formula (5), wherein the content of the epoxy resin A is 1% by mass or more and 35% by mass or less of the total amount of the epoxy resin, and the content of the epoxy resin B having at least one sulfur atom in the molecule is 0% by mass or more and less than 3% by mass of the total amount of the epoxy resin.

[0031]

[0032]

[0033] In formula (4) and formula (5), X ３ and X ４ are each independently a structural unit represented by the following formula (6), and Y ３ and Y ４ are each independently an aliphatic hydrocarbon group having 20 or less carbon atoms, ３ and n ４ are each independently 1 to 20.

[0034]

[0035] In formula (6), Z ２ is a single bond or -CH ２ -, -C(CH ３ ) ２ -, -CH(CH ３ )-,-C(Ph)(CH ３ is a divalent group selected from the group consisting of groups represented by —C(═O)—, —O—, and —C(═O)—,３ R ３ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m ４ R ４ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m １ and m ２ are each independently an integer of 1 to 4.

[0036] As will be shown in the results of the Examples below, a prepreg having the above-mentioned configurations improves the 90° flexural strength and elastic modulus while maintaining heat resistance. The reason for this effect is thought to be the improved interfacial adhesion between the carbon fiber and the matrix resin.

[0037] Each element will be described in detail below.

[0038] (Matrix Resin) The matrix resin contains an epoxy resin and a curing agent. The matrix resin may further contain other thermoplastic resins and additives. The matrix resin of the prepreg may be a thermosetting matrix resin. The thermosetting matrix resin forms a crosslinked structure when heated.

[0039] Epoxy resin A: Epoxy resin A is at least one epoxy resin selected from the group consisting of compounds represented by formula (1), compounds represented by formula (2), compounds represented by formula (4), and compounds represented by formula (5). Epoxy resin A having such a structure is a soft epoxy resin that is flexible and has good elasticity and impact resistance. When the matrix resin contains epoxy resin A, the interfacial adhesion between the carbon fiber and the matrix resin is improved, and excellent mechanical properties are exhibited.

[0040] In formula (1), formula (2), formula (4) and formula (5), X １ and X ２ , X ３ and X ４ are each independently a structural unit represented by formula (3) or formula (6).

[0041] Z １ and Z ２ As the group, -CH２ - or -C(CH ３ ) ２ - is preferred. １ and R ２ , R ３ and R ４ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group. Among these, a hydrogen atom, a phenyl group, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, or a tert-butyl group is preferred, a hydrogen atom, a phenyl group, a methyl group, an ethyl group, an isopropyl group, or a tert-butyl group is more preferred, and a hydrogen atom, a methyl group, an ethyl group, or an isopropyl group is even more preferred.

[0042] X １ and X ２ , X ３ and X ４ is a structural unit represented by formula (3) or formula (6), the bisphenol structural unit can be uniformly distributed throughout the epoxy resin, thereby improving the strength and elastic modulus of the matrix resin.

[0043] Examples of the structural unit represented by formula (3) or formula (6) include structural units derived from 2,2-bis(4-hydroxyphenyl)propane (i.e., bisphenol A), bis(4-hydroxyphenyl)methane (i.e., bisphenol F), 1,1-bis(4-hydroxyphenyl)ethane (bisphenol E), bis(4-hydroxyphenyl)diphenylmethane (i.e., bisphenol AP), 4,4′-dihydroxybiphenyl, and substituent-containing versions of these.

[0044] Examples of substituent-containing compounds include bis(4-hydroxyphenyl)-2,2-dichloroethylene (i.e., bisphenol C), 2,2-bis(4-hydroxy-3-isopropylphenyl)propane (i.e., bisphenol G), 4,4'-dihydroxy-3,3',5,5'-tetramethylbiphenyl, and 3,3',5,5'-tetramethylbisphenol F.

[0045] Among these, from the viewpoint of balancing economic efficiency and performance, the structural unit represented by formula (3) or formula (6) is preferably a structural unit derived from bisphenol F or bisphenol A. That is, in formula (3) or formula (6), Z １ and Z ２ Ga-CH ２ - or -C(CH ３ ) ２ It is preferable that −.

[0046] Y １ and Y ２ , Y ３ and Y ４ are each independently an aliphatic hydrocarbon group having 20 or less carbon atoms. An aliphatic hydrocarbon group having 20 or less carbon atoms refers to, for example, a structural unit between hydroxyl groups of the following raw materials. Examples of raw materials include (poly)oxyalkylene glycol, alkylene glycol, and cycloalkane glycol. The aliphatic hydrocarbon group may contain a heteroatom in addition to carbon and hydrogen. Examples of heteroatoms include nitrogen, oxygen, and phosphorus, with oxygen being preferred.

[0047] Examples of the (poly)oxyalkylene glycol include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0048] Examples of alkylene glycols include glycerol, triglycerol, 1,3-butylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,9-nonanediol, 1,10-decanediol, and 2,2-dimethyl-1,3-propanediol.

[0049] Examples of cycloalkane glycols include 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, tricyclodecanediol, tricyclodecanedimethanol, pentacyclopentadecanedimethanol, and pentacyclopentadecanediol.

[0050] For example, when referring to a structural unit derived from ethylene glycol, it refers to a structural unit between the hydroxyl groups of ethylene glycol.

[0051] Here, raw materials having hydroxyl groups are described, but this does not limit the method for producing epoxy resin A. Epoxy resin A can also be produced from a divinyl ether compound in which the hydroxyl group is replaced with a vinyl ether. If a polyvinyl ether compound is considered as the raw material, then Y １ and Y ２ , Y ３ and Y ４ indicates the structural unit between the divinyl ether groups.

[0052] From the viewpoint of improving affinity with the curing agent and the interface with the carbon fiber, the aliphatic hydrocarbon group having 20 or less carbon atoms is preferably an unbranched linear structural unit. Furthermore, from the viewpoint of economy, it is more preferable that the aliphatic hydrocarbon group contains a structural unit derived from oxyalkylene glycol or alkylene glycol.

[0053] Y １ and Y ２ , Y ３ and Y ４ When the structural unit is derived from oxyalkylene glycol, the interfacial adhesion with the carbon fiber is improved. In particular, a structural unit derived from polyethylene glycol is preferred.

[0054] Y １ and Y ２ , Y ３ and Y ４ When the structural unit is derived from alkylene glycol, the heat resistance and strength are further improved. In particular, a structural unit derived from butanediol or hexanediol is preferred.

[0055] n １ and n ２ , n ３and n ４ are each independently 1 to 20. １ and n ２ , n ３ and n ４ may each independently be 1 to 15, 1 to 10, or 1 to 8. １ , n ２ , n ３ and n ４ When n is equal to or greater than the lower limit of the above-mentioned range, the effect of improving the toughness of the matrix resin and the interfacial adhesion with the reinforcing fibers can be effectively obtained. １ , n ２ , n ３ , n ４ When is equal to or less than the upper limit of the above range, the effect of improving the toughness of the matrix resin and the interfacial adhesion with the reinforcing fibers can be effectively obtained without decreasing the heat resistance or significantly decreasing the curability.

[0056] The lower limit of the epoxy equivalent of the epoxy resin A is preferably 150 g / eq, more preferably 200 g / eq, and particularly preferably 250 g / eq. The upper limit is preferably 3000 g / eq, more preferably 2500 g / eq, and particularly preferably 2000 g / eq. When the epoxy equivalent is equal to or greater than the lower limit, the aliphatic hydrocarbon group in the epoxy resin A has a molecular weight sufficient to exhibit its performance, effectively improving the toughness of the matrix resin and the interfacial adhesion with the reinforcing fibers. When the epoxy equivalent is equal to or less than the upper limit, the molecular weight of the epoxy resin A or the aliphatic hydrocarbon group does not become excessively large, thereby suppressing an increase in the viscosity of the matrix resin. Furthermore, the toughness of the matrix resin and the interfacial adhesion with the reinforcing fibers can be effectively improved without decreasing heat resistance or significantly decreasing curability.

[0057] The epoxy equivalent is a value measured in accordance with JIS K7236. The epoxy equivalent can be adjusted by changing the conditions for synthesizing the epoxy resin A. For example, the epoxy equivalent of the epoxy resin A can be appropriately adjusted by changing the raw material charging ratio during production or by changing the polymerization time.

[0058] Commercially available epoxy resins A include, for example, Epiclon EXA-4816, Epiclon EXA-4850-150, Epiclon EXA-4850-1000, and Epiclon EXA-4822 manufactured by DIC Corporation.

[0059] The lower limit of the content of epoxy resin A is 1% by mass of the total amount of epoxy resin, preferably 5% by mass, more preferably 10% by mass, and even more preferably 15% by mass. When the content of epoxy resin A is equal to or greater than the lower limit, the interfacial adhesion between the matrix resin and the carbon fiber increases, and the performance of the carbon fiber composite material in the 90° direction is improved. The upper limit of the content of epoxy resin A is 35% by mass of the total amount of epoxy resin, preferably 30% by mass, more preferably 25% by mass, particularly preferably 20% by mass, and most preferably 15% by mass. When the content of epoxy resin A is equal to or less than the upper limit, deterioration in the performance of the carbon fiber composite material in the 0° direction and deterioration in heat resistance are suppressed.

[0060] The epoxy resin A may be used alone or in combination of two or more kinds.

[0061] Epoxy Resin B: Epoxy resin B is an epoxy resin having at least one sulfur atom in the molecule.

[0062] Examples of the epoxy resin B include an epoxy resin obtained by adding epichlorohydrin, a phenolic compound containing a sulfur atom in the molecule, an epoxy resin obtained by adding epichlorohydrin to an amine compound containing a sulfur atom in the molecule, and an epoxy resin obtained by adding epichlorohydrin to a sulfonamide compound containing a sulfur atom in the molecule.

[0063] Further examples of the epoxy resin B include a reaction product of another epoxy resin with an amine compound containing a sulfur atom in the molecule, a reaction product of another epoxy resin with a phenol compound containing a sulfur atom in the molecule, and a reaction product of another epoxy resin with a sulfonamide compound containing a sulfur atom in the molecule. One of the other epoxy resins may be used alone, or two or more of them may be used in combination.

[0064] When reacting another epoxy resin with a sulfur-containing compound, the sulfur-containing compound may be one of a sulfur-containing phenol compound, a sulfur-containing amine compound, a sulfur-containing sulfonamide compound, or the like, or two or more of them may be used in combination.

[0065] Examples of phenol compounds containing sulfur atoms include bis(4-hydroxyphenyl)sulfone (i.e., bisphenol S) and bis(4-hydroxyphenyl)sulfide. For example, bisphenol S is preferably used to obtain a rigid cured product.

[0066] The amine compound containing a sulfur atom in the molecule is not particularly limited, but examples thereof include those represented by the formula (3) or (6) below: １ or Z ２ Ga-S- and -SO ２ Examples of suitable amine compounds include those having a structural unit represented by the formula: -. More specifically, for example, 4,4'-diaminodiphenyl sulfone is preferably used.

[0067] Examples of sulfonamide compounds containing a sulfur atom in the molecule include benzenesulfonamide, aminobenzenesulfonamide, and hydroxybenzenesulfonamide. For example, when using hydroxybenzenesulfonamide, an epoxy resin can be produced by adding epichlorohydrin to the amino group and hydroxyl group. Among these, benzenesulfonamide and hydroxybenzenesulfonamide often contribute to improving the toughness of the matrix resin and the interfacial adhesion with the reinforcing fibers.

[0068] The reaction product of the other epoxy resin with the compound containing a sulfur atom in the molecule is, for example, a compound represented by the formula (3) or (6): Z １ or Z ２ Ga-S- and -SO ２ -, and a reaction product of an amine compound having a structural unit with a bisphenol A type epoxy resin. More specifically, a reaction product of 4,4'-diaminodiphenyl sulfone with a bisphenol A type epoxy resin is exemplified.

[0069] From the viewpoint of easy availability, a reaction product of 4,4'-diaminodiphenyl sulfone and bisphenol A type epoxy resin is preferred as the epoxy resin B. Because the reaction product of 4,4'-diaminodiphenyl sulfone and bisphenol A type epoxy resin has four or more functional groups in one molecule, it is possible to obtain a rigid, highly crosslinked cured product.

[0070] As the epoxy resin B, from the viewpoint of obtaining a rigid and highly crosslinked cured product, an epoxy resin having four or more functional groups, i.e., a tetrafunctional or higher epoxy resin, is preferred, and a tetrafunctional epoxy resin is more preferred.

[0071] The functionality of epoxy resin B refers to the number of epoxy groups contained in one molecule of epoxy resin B. The number of epoxy groups can be estimated from the amine compound and epoxy resin used. In general, the reaction between an amine compound and an epoxy resin is a reaction in which the epoxy resin adds to the active hydrogen of the amine compound. Therefore, if the amine compound used has at least four active hydrogens, it can be said that the resulting epoxy resin has at least four epoxy groups per molecule.

[0072] When detailed analysis is required, it can be performed by GPC analysis, a commonly known analytical method. For example, when a resin contains a component with a higher molecular weight than the theoretical molecular weight of the epoxy resin produced by the addition of the epoxy resin to all the active hydrogens of the amine compound, it is presumed to be an epoxy resin with at least tetrafunctionality. The number of functional groups in an epoxy resin is determined by considering the main components contained in the epoxy resin, excluding unreacted raw materials and reaction products of unreacted raw materials contained in the epoxy resin.

[0073] The content of epoxy resin B is 0% by mass or more and less than 3% by mass of the total amount of epoxy resin. In one example, the content of epoxy resin B may be 2% by mass or less, 1% by mass or less, or 0% by mass of the total amount of epoxy resin. When the content of epoxy resin B in the epoxy resin is less than 3% by mass, a decrease in storage stability is suppressed.

[0074] In one example, the content of the novolac epoxy resin may be 0% by mass or more but less than 50% by mass of the total amount of epoxy resin. The content of the novolac epoxy resin may be 0 to 45% by mass, 0 to 40% by mass, or 0 to 35% by mass of the total amount of epoxy resin. When the content of the novolac epoxy resin is equal to or greater than the lower limit of the above-mentioned numerical range, heat resistance and reactivity are improved. In addition, the effect of improving the toughness of the matrix resin and the interfacial adhesion with the reinforcing fibers is easily obtained. When the content of the novolac epoxy resin is equal to or less than the upper limit of the above-mentioned numerical range, heat resistance and reactivity are improved. In addition, the effect of improving the toughness of the matrix resin and the interfacial adhesion with the reinforcing fibers is easily obtained.

[0075] Examples of novolac epoxy resins include those derived from cresol novolac, phenol novolac, bisphenol A novolac, and cardanol novolac. Among these, cresol novolac epoxy resins are preferred because they can improve heat resistance without significantly reducing the toughness of the matrix resin. Cardanol novolac epoxy resins can be used from the perspective of reducing carbon footprint.

[0076] Other epoxy resins: The matrix resin further contains, as an epoxy resin, an epoxy resin other than the epoxy resin A and the epoxy resin B. The other epoxy resins other than the epoxy resin A and the epoxy resin B are not particularly limited as long as they are compounds having an epoxy group. One type of other epoxy resin may be used alone, or two or more types may be used in combination.

[0077] Other epoxy resins include, for example, bisphenol A type epoxy resins; bisphenol F type epoxy resins; heterocyclic epoxy resins containing a ring structure derived from isosorbide, a triisocyanurate ring, an oxazolidone ring, or the like in the molecule; glycidylamine type epoxy resins such as triglycidylaminophenol, tetraglycidyldiaminodiphenylmethane, diglycidylaniline, diglycidyltoluidine, and tetraglycidylxylenediamine; polycarboxylic acids such as dimer acid, trimer acid, isophthalic acid, terephthalic acid, phthalic acid, and hydrophthalic acid. Examples of such epoxy resins include glycidyl ester epoxy resins derived from carboxylic acids, benzenediol epoxy resins derived from resorcinol, catechol, hydroquinone, dihydroanthracene, etc., aromatic epoxy resins derived from dihydroanthrahydroquinone, dihydroxydiphenyl ether, dihydroxynaphthalene, trishydroxyphenylmethane, tetraphenylolethane, etc., bisphenoxyethanol fluorene epoxy resins, bisphenol fluorene epoxy resins, and biscresol fluorene epoxy resins. Additionally, epoxy resins having an oxirane ring produced by oxidation of an allyl group can also be used.

[0078] The other epoxy resin preferably includes at least one epoxy resin selected from the group consisting of bisphenol A type epoxy resins, bisphenol F type epoxy resins, heterocyclic type epoxy resins, condensed ring type epoxy resins, novolac type epoxy resins, glycidyl amine type epoxy resins, and glycidyl ester type epoxy resins.

[0079] Curing agent: The curing agent is not particularly limited as long as it is a compound that contributes to the curing of the epoxy resin. The curing agent preferably contains at least one selected from the group consisting of dicyandiamides, urea compounds, imidazoles, acid hydrazide compounds, and amines. From the viewpoint of the balance between the moldability of the resulting prepreg and the toughness of the fiber-reinforced composite material, it is preferable to use dicyandiamides. From the viewpoint of the appearance quality of the prepreg, it is preferable to use urea compounds. Furthermore, from the viewpoint of the heat resistance of the resulting fiber-reinforced composite material, it is preferable to use aromatic polyamines or imidazoles. One type of curing agent may be used alone, or two or more types may be used in combination. Amines may be included as other curing agents.

[0080] The dicyandiamides may be, for example, dicyandiamide or an adduct thereof with another epoxy resin listed in the epoxy resin section. The dicyandiamides may be used alone or in combination of two or more.

[0081] Examples of the urea compound include aromatic urea in which a ureido group is bonded to an aromatic ring, and aliphatic urea in which a ureido group is bonded to an aliphatic chain. One type of urea compound may be used alone, or two or more types may be used in combination.

[0082] Examples of the aliphatic urea include dimethylurea obtained from isophorone diisocyanate and dimethylamine, dimethylurea obtained from m-xylylene diisocyanate and dimethylamine, and dimethylurea obtained from hexamethylene diisocyanate and dimethylamine.

[0083] Examples of aromatic ureas include aromatic dimethylureas such as phenyldimethylurea, methylenebis(phenyldimethylurea), tolylenebis(dimethylurea), etc. Examples of aromatic dimethylureas include 4,4'-methylenebis(phenyldimethylurea) (MBPDMU), 3-phenyl-1,1-dimethylurea (PDMU), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 3-(3-chloro-4-methylphenyl)-1,1-dimethylurea, and 2,4-bis(3,3-dimethylureido)toluene (TBDMU).

[0084] From the viewpoint of curing acceleration and imparting heat resistance to the cured resin, phenyldimethylurea, methylenebis(phenyldimethylurea), and tolylenebis(dimethylurea) are more preferred, and DCMU, PDMU, and TBDMU are particularly preferred from the viewpoints of ease of procurement, improved curability, and the ability of the cured resin to exhibit high heat resistance.

[0085] Examples of imidazoles that can be used include imidazole derivatives, imidazole adducts, clathrate imidazoles, microencapsulated imidazoles, and imidazole compounds coordinated with stabilizers. The nitrogen atoms having unshared electron pairs in the structure of imidazoles activate epoxy groups, thereby accelerating curing. One type of imidazole may be used alone, or two or more types may be used in combination.

[0086] Examples of imidazole derivatives include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-phenylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazolium trimellitate, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazolium trimellitate, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazolium trimethylimidazole, Mellitate, 2,4-diamino-6-(2'-methylimidazolyl-(1'))-ethyl-s-triazine, 2,4-diamino-6-(2'-undecylimidazolyl-(1'))-ethyl-s-triazine, 2,4-diamino-6-(2'-ethyl-4-methylimidazolyl-(1'))-ethyl-s-triazine, 2,4-diamino-6-(2'-methylimidazolyl-(1'))-ethyl-s-triazine isocyanuric acid adduct, 2-phenylimidazole isocyanuric acid adduct, 2-methylimidazole isocyanuric acid adduct, 1-cyanoethyl-2-phenyl-4,5-di(2-cyanoethoxy)methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole.

[0087] Imidazole adducts, clathrated imidazoles, microencapsulated imidazoles, and stabilizer-coordinated imidazole compounds are imidazole derivatives modified by these methods. These compounds have their activity suppressed by adduct treatment, clathrated treatment with foreign molecules, microencapsulation treatment, or by coordinating stabilizers to the imidazole derivatives, and exhibit excellent pot life at low temperatures while also exhibiting high curing and curing acceleration capabilities.

[0088] The acid hydrazide compound may be an aromatic hydrazide compound or an aliphatic hydrazide compound. One type of acid hydrazide compound may be used alone, or two or more types may be used in combination.

[0089] Examples of aromatic hydrazide compounds include salicylic acid hydrazide, benzoic acid hydrazide, 1-naphthoic acid hydrazide, terephthalic acid dihydrazide, isophthalic acid dihydrazide, 2,6-naphthoic acid dihydrazide, 2,6-pyridine dihydrazide, 1,2,4-benzenetrihydrazide, 1,4,5,8-naphthoic acid tetrahydrazide, and pyromellitic acid tetrahydrazide. One type of aromatic hydrazide compound may be used alone, or two or more types may be used in combination.

[0090] Examples of the aliphatic hydrazide compounds include formhydrazide, acetohydrazide, propionic acid hydrazide, oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, pimelic acid dihydrazide, sebacic acid dihydrazide, 1,4-cyclohexane dihydrazide, tartaric acid dihydrazide, malic acid dihydrazide, iminodiacetic acid dihydrazide, N,N'-hexamethylenebissemicarbazide, citric acid trihydrazide, nitriloacetic acid trihydrazide, cyclohexane trihydrazide, Examples of the aliphatic hydrazide compound include carboxylic acid trihydrazide, a dihydrazide compound having a hydantoin skeleton such as 1,3-bis(hydrazinocarbonoethyl)-5-isopropylhydantoin, preferably a valine hydantoin skeleton (a skeleton in which the carbon atoms of the hydantoin ring are substituted with isopropyl groups), tris(1-hydrazinocarbonylmethyl)isocyanurate, tris(2-hydrazinocarbonylethyl)isocyanurate, tris(3-hydrazinocarbonylpropyl)isocyanurate, and bis(2-hydrazinocarbonylethyl)isocyanurate. One type of aliphatic hydrazide compound may be used alone, or two or more types may be used in combination.

[0091] Examples of amines include chain aliphatic polyamines (e.g., diethylenetriamine, tetraethylenepentamine, hexamethylenediamine, 1,3-pentanediamine, 2-methylpentamethylenediamine), alicyclic polyamines (e.g., isophoronediamine, 4,4'-methylenebiscyclohexylamine, 4,4'-methylenebis(2-methylcyclohexylamine), bis(aminomethyl)norbornane, 1,2-cyclohexanediamine, 1,3-bisaminomethylcyclohexane), aromatic polyamines (e.g., m -xylylenediamine, 4,4'-methylenedianiline, 4,4'-methylenebis(2-methylaniline), 4,4'-methylenebis(2-ethylaniline), 4,4'-methylenebis(2-isopropylaniline), 4,4'-methylenebis(2-chloroaniline), 4,4'-methylenebis(2,6-dimethylaniline), 4,4'-methylenebis(2,6-diethylaniline), 4,4'-methylenebis(2-isopropyl-6-methylaniline), 4,4'-methylenebis(2-ethyl-6-methylaniline), 4,4' -methylenebis(2-bromo-6-ethylaniline), 4,4'-methylenebis(N-methylaniline), 4,4'-methylenebis(N-ethylaniline), 4,4'-methylenebis(N-sec-butylaniline), 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-cyclohexylidenedianiline, 4,4'-(9-fluorenylidene)dianiline, 4,4'-(9-fluorenylidene)bis(N-methylaniline), 4,4'-diaminobenzanilide, 4,4'-oxydiamin Examples of suitable amines include aniline, 2,4-bis(4-aminophenylmethyl)aniline, 4-methyl-m-phenylenediamine, 2-methyl-m-phenylenediamine, N,N'-di-sec-butyl-p-phenylenediamine, 2-chloro-p-phenylenediamine, 2,4,6-trimethyl-m-phenylenediamine, 2,4-diethyl-6-methyl-m-phenylenediamine, 4,6-diethyl-2-methyl-m-phenylenediamine, 4,6-dimethyl-m-phenylenediamine, and trimethylenebis(4-aminobenzoate).

[0092] The amines may be used alone or in combination of two or more. The amines may be adducted or blocked with other epoxy resins.

[0093] When dicyandiamides are used as the curing agent, the content of the curing agent is preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, per 100 parts by mass of the total epoxy resin components, from the viewpoint of sufficiently curing the epoxy resin. Furthermore, the content is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, even more preferably 20 parts by mass or less, and particularly preferably 15 parts by mass or less, per 100 parts by mass of the total epoxy resin components. The above upper and lower limits can be arbitrarily combined. For example, the content may be 0.5 parts by mass or more and 40 parts by mass or less, 0.5 parts by mass or more and 30 parts by mass or less, or 1.0 parts by mass or more and 15 parts by mass or less, per 100 parts by mass of the total epoxy resin components.

[0094] The ratio of the number of moles of active hydrogen in dicyandiamide to the total number of moles of epoxy groups contained in the matrix resin is preferably 0.3 or more, more preferably 0.4 or more, and is preferably 1.1 or less, more preferably 1.0 or less. The lower and upper limits of the ratio of the number of moles of active hydrogen in dicyandiamide can be arbitrarily combined, and may be, for example, preferably 0.3 to 1.1, or may be 0.4 to 1.0.

[0095] When dicyandiamides are used, they may be used in combination with urea compounds, acid hydrazides, and imidazoles from the viewpoint of ease of handling during molding.

[0096] When a dicyandiamide and a urea compound are used in combination, the mass ratio (dicyandiamide / urea compound) is not particularly limited, but can be, for example, 1.0 to 20. Using them in combination in this range can improve the reactivity.

[0097] When dicyandiamides and imidazoles are used in combination, the mass ratio (dicyandiamides / imidazoles) is not particularly limited, but can be, for example, 0.01 to 10. Using them in combination in this range can improve reactivity and exhibit excellent heat resistance. In this combination, the imidazoles may be blended as a curing accelerator for the dicyandiamides, or the dicyandiamide may be blended as a curing accelerator for the imidazoles.

[0098] When a dicyanamide, a urea compound, and an imidazole are used in combination, the mass ratio (imidazole / urea compound) is not particularly limited, but can be, for example, 0.01 to 20. By using them in combination within this range, it is possible to easily adjust the reactivity and heat resistance.

[0099] When a dicyandiamide is used in combination with an acid hydrazide compound or an amine, the mass ratio (dicyandiamide / acid hydrazide compound or dicyandiamide / amine) is not particularly limited, but can be, for example, 0.01 to 20. Using a combination in this range can improve reactivity.

[0100] When an acid hydrazide or an amine is used as the curing agent, the content of the curing agent is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, per 100 parts by mass of the total epoxy resin components, from the viewpoint of sufficiently curing the epoxy resin. Furthermore, the content is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, even more preferably 100 parts by mass or less, and particularly preferably 80 parts by mass or less, per 100 parts by mass of the total epoxy resin components. If the content is equal to or greater than the lower limit, sufficient heat resistance tends to be obtained and the elastic modulus tends to be excellent. If the content is equal to or less than the upper limit, the toughness of the matrix resin tends to be excellent.

[0101] The number of moles of active hydrogen of the acid hydrazides or amines is preferably 0.01 times or more, more preferably 0.05 times or more, and preferably 2.0 times or less, more preferably 1.5 times or less, and particularly preferably 1.2 times or less, the total number of moles of epoxy groups contained in the matrix resin. Within the above ranges, the heat resistance is improved, and the toughness of the matrix resin and the interfacial adhesion with the reinforcing fibers are likely to be improved.

[0102] The upper and lower limits for the number of moles of active hydrogen in the acid hydrazides or amines can be arbitrarily combined. The number of moles of active hydrogen in the acid hydrazides or amines may be, for example, 0.01 to 2.0 times or 0.1 to 1.5 times. These limits may be appropriately determined taking into account the epoxy resin contained in the matrix resin, the acid hydrazides or amines used, the production conditions, and the like.

[0103] The active hydrogen of acid hydrazides is the hydrogen on the terminal nitrogen, not including the hydrogen attached to the N adjacent to the carbonyl group. In the case of aliphatic polyamines, the hydrogen on the nitrogen is used as the active hydrogen for calculations. In the case of aromatic polyamines, the hydrogen of the amino group on the aromatic ring is used as the active hydrogen for calculations.

[0104] Amines can also be blended as auxiliary agents to improve heat resistance. In this case, for example, dicyandiamides and urea compounds are used as curing agents to sufficiently cure the epoxy resin. When amines are further added as additives, the blending amount is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, and preferably 20 parts by weight or less, and even more preferably 15 parts by weight or less, per 100 parts by mass of the matrix resin. Within the above-mentioned ranges, the reaction between the epoxy resin and the curing agent is not inhibited, and heat resistance can be improved without impairing the toughness of the matrix resin or the interfacial adhesion with the reinforcing fibers.

[0105] When an acid hydrazide compound or an amine is used, a urea compound or an imidazole may be used in combination. When an acid hydrazide compound or an amine is used in combination with a urea compound, the mass ratio (acid hydrazide compound or amine / urea compound) can be, for example, 1.0 to 200. When an acid hydrazide compound or an amine is used in combination with an imidazole, the mass ratio (acid hydrazide compound or amine / imidazole) can be, for example, 0.01 to 10.

[0106] Thermoplastic resin: The matrix resin may further contain a thermoplastic resin, which can control polarity, inhibit or induce phase separation, and improve moldability by controlling melt attraction.

[0107] Examples of thermoplastic resins include polyamide, polyester, polycarbonate, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyetheretherketone, polyetherketone, polyimide, polytetrafluoroethylene, polyether, polyolefin, polyarylate, polysulfone, polyacrylonitrilestyrene, polystyrene, polyacrylonitrile, polymethyl methacrylate, ABS (acrylonitrile-butadiene-styrene copolymer), AES (acrylonitrile-ethylene-propylene-rubber-styrene copolymer), ASA (acrylonitrile-acrylic-rubber-styrene copolymer), polyvinyl chloride, polyvinyl acetal resins such as polyvinyl butyral resin and polyvinyl formal resin, phenoxy resin, acrylic block copolymers, and resins obtained by block copolymerization of these thermoplastic resins.

[0108] From the viewpoint of suppressing resin extrusion during molding, polyether sulfone, polyvinyl acetal resins such as polyvinyl butyral resin and polyvinyl formal resin, and phenoxy resin are more preferred.

[0109] From the viewpoint of further improving the toughness of the matrix resin and the interfacial adhesion with the reinforcing fibers, acrylic block copolymers are preferred, and diblock copolymers and triblock copolymers described below are particularly preferred.

[0110] As the acrylic block copolymer, a diblock copolymer represented by block B-block M and a triblock copolymer represented by block M-block B-block M are more preferred.

[0111] The blocks in the acrylic block copolymer may be linked by a covalent bond, or may be linked by an intermediate molecule that is bonded to each of the other blocks via a covalent bond.

[0112] Block M is a block composed of a homopolymer of methyl (meth)acrylate, a homopolymer of (meth)acrylic acid, or a copolymer having 50 mass% or more of structural units derived from methyl (meth)acrylate and / or structural units derived from (meth)acrylic acid (hereinafter also referred to as "copolymer P1").

[0113] When the block M1 is a block M1 made of a copolymer P1, the content of structural units derived from methyl (meth)acrylate in the copolymer P1 is preferably 50% by mass or more, more preferably 75% by mass or more, based on the total structural units.

[0114] Block M1 may contain a structural unit derived from a (meth)acrylic monomer other than methyl (meth)acrylate and (meth)acrylic acid. The other (meth)acrylic monomer is not particularly limited, and examples thereof include glycidyl (meth)acrylate and tert-butyl (meth)acrylate.

[0115] Block B has a glass transition temperature (Tg) of 20° C. or lower and is a block made of a polymer that is incompatible with the polymer of block M. Since a fiber-reinforced composite material with excellent toughness can be obtained, the Tg of block B is preferably 0° C. or lower, more preferably −20° C. or lower. The lower the Tg of block B, the more preferable it is, but the lower limit can be, for example, −100° C.

[0116] Block B is preferably an elastomer block. Examples of monomers for the elastomer block include butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 2-phenyl-1,3-butadiene. These monomers may be used alone or in combination of two or more.

[0117] Block B may be hydrogenated. In terms of excellent toughness, block B is preferably a polydiene, and more preferably polybutadiene, polyisoprene, or a random copolymer thereof, or a polydienes obtained by partially or completely hydrogenating these.

[0118] Examples of polybutadiene include 1,2-polybutadiene (Tg: about 0° C.) and 1,4-polybutadiene (Tg: about −90° C.), with 1,2-polybutadiene being preferred in terms of its excellent impact resistance and toughness.

[0119] Block B of the elastomer may contain an alkyl (meth)acrylate. Examples of alkyl (meth)acrylates include ethyl acrylate (-24°C), butyl acrylate (-54°C), 2-ethylhexyl acrylate (-85°C), hydroxyethyl acrylate (-15°C), and 2-ethylhexyl methacrylate (-10°C). Note that the values ​​in parentheses indicate the Tg of block B when only the respective (meth)acrylic acid esters are used. Of these alkyl (meth)acrylates, butyl acrylate is preferred.

[0120] Since block B and block M are incompatible, the (meth)acrylic acid ester used in block B is different from the (meth)acrylic acid ester used in block M. Block B preferably consists mainly of 1,4-polybutadiene, poly(butyl acrylate), or poly(2-ethylhexyl acrylate).

[0121] The two blocks M in the triblock copolymer represented by block M-block B-block M may be the same or different from each other. The two blocks M may be made of the same monomer but have different molecular weights.

[0122] When a triblock copolymer represented by block M-block B-block M and a diblock copolymer represented by block B-block M are used in combination, the blocks M may be the same or different. When a triblock copolymer represented by block M-block B-block M and a diblock copolymer represented by block B-block M are used in combination, the blocks B may be the same or different.

[0123] The block copolymer can be produced, for example, by anionic polymerization, for example, by the methods described in European Patent Nos. 0524054 and 0749987. The thermoplastic resins may be used alone or in combination of two or more.

[0124] When the matrix resin contains a thermoplastic resin, the content thereof can be adjusted within the range of 0.5 to 30 parts by mass per 100 parts by mass of the total epoxy resin. From the viewpoint of suppressing resin extrusion during molding, the lower limit is preferably 1.0 part by mass and the upper limit is preferably 25 parts by mass.

[0125] Additives: The matrix resin may further contain additives as needed. Examples of additives include stabilizers, polymerization inhibitors, flame retardants, mold release agents, inorganic fillers, organic fillers, organic pigments, and inorganic pigments. One type of additive may be used alone, or two or more types may be used in combination.

[0126] Examples of stabilizers and polymerization inhibitors include linear carbodiimide compounds and cyclic carbodiimide compounds from the viewpoint of inhibiting hydrolysis, and stabilizers using clathrate compounds and stabilizers using boric acid compounds from the viewpoint of stabilizing the curing agent. In addition to inhibiting hydrolysis, carbodiimide compounds and cyclic carbodiimide compounds can react quantitatively with functional groups on carbon fibers, so they can also be used as assistants to improve the interfacial adhesion between the matrix resin and reinforcing fibers.

[0127] Examples of the flame retardant include phosphorus-based flame retardants (e.g., phosphorus-containing epoxy resins, red phosphorus, phosphazene compounds, phosphates, and phosphoric acid esters), and inorganic flame retardants such as hydrated metal compounds (e.g., aluminum hydroxide and magnesium hydroxide) and inorganic oxides (e.g., antimony compounds, zinc borate, zinc stannate, Mo compounds, ZrO, zinc sulfide, zeolite, and titanium oxide nanofillers).

[0128] Examples of the release agent include silicone oil, wetting and dispersing agents, antifoaming agents, defoaming agents, natural waxes, synthetic waxes, metal salts of straight-chain fatty acids, acid amides, esters, and paraffins.

[0129] Examples of inorganic fillers include powders of crystalline silica, amorphous silica, fused silica, calcium silicate, alumina, calcium carbonate, talc, barium sulfate, and the like; glass fibers; and short carbon fibers.

[0130] Examples of organic fillers include cellulose fiber, flax fiber, ramie fiber, hemp fiber, and wood flour. The fibers of the organic filler may be in the form of continuous fiber, nanofiber, or milled fiber, and may have been subjected to a surface hydrophilic or hydrophobic treatment.

[0131] To prevent resin from spilling out during molding, crystalline silica or amorphous silica can be used. The smaller the particle size of the crystalline or amorphous silica, the better the effect of preventing resin from spilling out. From the viewpoint of safety, amorphous silica is more preferable. Furthermore, to improve the biomass content, amorphous silica produced from natural raw materials can be used.

[0132] Method for Producing Matrix Resin: The matrix resin can be obtained, for example, by mixing the above-mentioned components. Examples of the method for mixing the components include methods using a mixer (e.g., a three-roll mill, a planetary mixer, a kneader, a homogenizer, or a homodisper).

[0133] The matrix resin can be used to produce a prepreg by impregnating carbon fibers with the matrix resin, as described below. The viscosity of the matrix resin composition at 30°C may be, for example, 100 to 1,000,000 Pa·s.

[0134] The viscosity of the matrix resin at 70°C is preferably 10 Pa s or more, more preferably 15 Pa s or more, even more preferably 20 Pa s or more, particularly preferably 30 Pa s or more, and preferably 1000 Pa s or less, more preferably 900 Pa s or less, even more preferably 850 Pa s or less, particularly preferably 800 Pa s or less, especially preferably 500 Pa s or less, and most preferably 300 Pa s or less. If the viscosity of the matrix resin is within the above range, the tackiness and drapeability of the prepreg tend to be excellent. When a prepreg is produced using a film made of an uncured matrix resin by the hot melt method described below, the excellent process passability makes it less likely for uneven thickness to occur in the film, and the quality of the resulting prepreg and carbon fiber composite material tends to be excellent.

[0135] The lower limit and upper limit of the viscosity of the matrix resin composition at 70° C. can be arbitrarily combined. The viscosity of the matrix resin composition at 70° C. may be, for example, 10 to 1000 Pa s, 15 to 900 Pa s, 20 to 850 Pa s, or 30 to 800 Pa s.

[0136] The viscosity of the matrix resin composition at 70°C is a value measured using a rheometer. Although the viscosity value of the matrix resin composition is a value at 70°C, it may be interpreted as a value at a temperature 10°C lower, that is, 60°C, or as a value 10°C higher, that is, 80°C, as long as the quality of the matrix resin and, in turn, the quality of the prepreg and carbon fiber composite material is not impaired.

[0137] The density of the matrix resin after curing is not particularly limited, but for example, the lower limit is 0.8 g / cm ３ More than 0.9 g / cm ３ More preferably, 1.0 g / cm ３The upper limit is particularly preferably 1.40 g / cm ３ Preferably, 1.35 g / cm or less ３ The following is more preferable: If the density of the matrix resin after curing is within the above-mentioned range, the carbon fiber composite material tends to have excellent specific strength (strength / density) and specific modulus (modulus / density), and tends to exhibit excellent performance while being lightweight.

[0138] (Carbon Fiber) The carbon fibers exist in the prepreg as a carbon fiber substrate (an aggregate of carbon fibers). The carbon fibers may be aligned in a single direction or randomly.

[0139] Examples of the form of the carbon fiber substrate include a carbon fiber woven fabric, a carbon fiber nonwoven fabric, and a sheet in which long carbon fibers are aligned in one direction (UD sheet). From the viewpoint of being able to form a fiber-reinforced composite material with high specific strength and specific modulus, the carbon fiber is preferably a UD sheet, and from the viewpoint of ease of handling, the carbon fiber is preferably a carbon fiber woven fabric.

[0140] The weight per unit area of ​​the carbon fiber substrate is not particularly limited, but is, for example, 10 g / m ２ More than 4000g / m ２ In the case of a UD sheet, the basis weight is 10 g / m ２ More than 300g / m ２ It can be as follows:

[0141] The fiber diameter of the carbon fiber is not particularly limited, but can be, for example, 3 to 15 μm. The number of carbon fibers in the carbon fiber bundle used for the carbon fiber substrate is not particularly limited, but, for example, 1,000 to 70,000 is preferable.

[0142] From the viewpoint of the rigidity of the fiber-reinforced composite material, the strand tensile strength of the carbon fiber is preferably 1.5 to 9 GPa, and the strand tensile modulus of the carbon fiber is preferably 150 to 450 GPa. The strand tensile strength and strand tensile modulus of the carbon fiber are values ​​measured in accordance with JIS R7601:1986.

[0143] The prepreg may contain reinforcing fibers other than carbon fiber. Examples of reinforcing fibers other than carbon fiber include glass fiber, aramid fiber, and boron fiber. When fibers other than carbon fiber are contained, the amount can be appropriately changed depending on the application and desired performance, but the amount can be, for example, 0.1 to 50 parts by weight per 100 parts by weight of reinforcing fiber. By keeping the amount within the above range, high physical properties derived from carbon fiber can be exhibited. Furthermore, using fibers other than carbon fiber improves impregnation with the matrix resin.

[0144] (Method for producing prepreg) The prepreg can be obtained, for example, by impregnating the above-mentioned matrix resin into a carbon fiber substrate. The method for impregnating the carbon fiber substrate with the matrix resin is not limited to the following, but examples thereof include the following methods.

[0145] - A wet method in which the matrix resin is dissolved in a solvent (e.g., methyl ethyl ketone, methanol) to reduce the viscosity, and then the carbon fiber substrate is impregnated with the matrix resin. - A hot melt method (dry method) in which the matrix resin is heated to reduce the viscosity, and then the carbon fiber substrate is impregnated with the matrix resin.

[0146] In the wet method, the carbon fiber substrate is impregnated with a matrix resin solution, and then the solvent is removed by heating or reducing the pressure inline or offline.

[0147] The hot melt method includes a method in which a matrix resin whose viscosity has been reduced by heating is directly impregnated into a carbon fiber substrate, and a method in which a matrix resin is first applied to the surface of a substrate such as release paper to prepare a film, and then the prepared film is superimposed on both sides or one side of the carbon fiber substrate, and the carbon fiber substrate is impregnated with the resin by heating and pressurizing.

[0148] The coating layer obtained by applying it to the surface of a substrate such as release paper may be used in the hot melt method as it is, or may be used in the hot melt method after curing the coating layer. The hot melt method is preferred because there is essentially no solvent remaining in the prepreg. The temperature when the matrix resin is impregnated into the carbon fiber substrate may be 50 to 120 ° C.

[0149] The content of the matrix resin in the prepreg is preferably 15 to 50 mass %, more preferably 20 to 45 mass %, and even more preferably 20 to 40 mass %, relative to the total mass of the prepreg, from the viewpoints of the mechanical properties of the fiber-reinforced composite material and the interfacial adhesion between the matrix resin and the carbon fiber.

[0150] [Fiber-reinforced composite material] A fiber-reinforced composite material is obtained by curing a prepreg. The fiber-reinforced composite material has a cured product of a prepreg or a cured product of a prepreg laminate having a plurality of prepregs. The fiber-reinforced composite material includes a cured product of a matrix resin contained in a prepreg and carbon fibers. The fiber-reinforced composite material can also be a cured product of a laminate in which two or more prepregs are laminated. The fiber-reinforced composite material can be obtained, for example, by laminating two or more of the above-mentioned prepregs and then molding the laminate by a method of applying pressure to the obtained laminate and heat-curing the matrix resin.

[0151] Examples of molding methods include, but are not limited to, press molding, autoclave molding, bagging molding, wrapping tape method, internal pressure molding, sheet wrap molding, RTM (Resin Transfer Molding) in which a reinforcing fiber filament or preform is impregnated with an epoxy resin composition and cured to obtain a molded product, VaRTM (Vacuum assisted Resin Transfer Molding), filament winding, and RFI (Resin Film Infusion).

[0152] The fiber-reinforced composite material may be tubular. That is, the fiber-reinforced composite material may be a tubular body. The tubular body may be formed, for example, by a sheet wrapping method in which a sheet-like prepreg, in which a plurality of unidirectionally aligned carbon fibers is impregnated with a matrix resin, is wrapped around a mandrel (core metal) and heated to harden.

[0153] When laminating multiple prepregs into a tubular shape, it is preferable that the orientation angle of the carbon fibers be within a range of ±20 to ±70° with respect to the longitudinal direction of the tube, and that the prepregs be arranged in a region extending from the inner wall of the tube to 50% of the thickness of the tube in the cross section of the tube, because this allows a tubular body with excellent torsional strength to be obtained.

[0154] In the cross section of the pipe, the prepreg is preferably arranged in a region from the inner wall of the pipe up to 40% of the pipe thickness, more preferably up to 30%, even more preferably up to 20%, and particularly preferably up to 10%. The region from the inner wall of the pipe up to s% of the pipe thickness in the cross section of the pipe refers to a region up to a position s% away from the inner wall of the pipe, where the innermost part of the pipe in the cross section is 0% and the outermost part is 100%.

[0155] When a tubular body is produced, an angle layer in which the carbon fibers are oriented at an angle of +20° to +70° or −20° to −70° relative to the longitudinal direction of the tubular body is included. In addition to the angle layer, at least one of a straight layer in which the carbon fibers are oriented at an angle of −5° to +5° and a hoop layer in which the carbon fibers are oriented at an angle of +85° to +95° or −85° to −+95° may be included.

[0156] When the prepreg of the present invention is used as a straight layer in a tubular body, it is also preferable that when a plurality of prepregs are laminated into a tubular shape, the orientation angle of the carbon fibers is within the range of −5° to +5° with respect to the longitudinal direction of the tube, and that the prepregs are arranged in a region from the outer wall of the tube up to 50% of the thickness of the tube in the cross section of the tube, because this allows a tubular body with excellent strength to be obtained.

[0157] It is more preferable to arrange the prepreg in the region of the pipe cross section from the outer wall to 60% of the pipe thickness, even more preferable to arrange the prepreg in the region of the pipe cross section from the outer wall to 70% of the pipe thickness, particularly preferable to arrange the prepreg in the region of the pipe cross section from the outer wall to 80% of the pipe thickness, and most preferable to arrange the prepreg in the region of the pipe cross section from the outer wall to 90% of the pipe thickness.

[0158] The region in the cross section of the pipe from the outer wall to s% of the thickness of the pipe is the region from the outer wall of the pipe to a position s% away, where the outermost part of the pipe in the cross section of the pipe is 0% and the innermost part is 100%.

[0159] The angle layers included in the tubular body may be only angle layers in which the carbon fibers have an orientation angle of +20° to +70°, or only angle layers in which the carbon fibers have an orientation angle of -20° to -70°, or may be both.

[0160] When both an angle layer containing carbon fibers with a positive orientation angle and an angle layer containing carbon fibers with a negative orientation angle are used, they may be paired to form a bias layer, which is preferable from the viewpoint of increasing torsional rigidity and torsional strength.

[0161] When the prepreg of the present invention is used for a tubular body, it is also preferable that when multiple prepregs are laminated into a tubular shape, at least two adjacent prepregs in the prepreg laminate are laminated so that the absolute value of the difference in fiber orientation angle between the prepreg on the outer wall side of the pipe and the prepreg on the inner wall side of the pipe is 25° or more. The absolute value of this difference is more preferably 30° or more, and even more preferably 35° or more. When the absolute value of this difference is equal to or greater than the above-mentioned lower limit, interlayer slippage between the prepregs is easily suppressed.

[0162] Autoclave molding is preferred as a molding method that makes the most of the characteristics of the matrix resin, while press molding is preferred from the viewpoint of high productivity and ease of obtaining a high-quality fiber-reinforced composite material while making the most of the characteristics of the matrix resin.

[0163] When producing a fiber-reinforced composite material by press molding, it is preferable to clamp a prepreg or a preform produced by laminating prepregs in a mold previously prepared at a curing temperature and apply heat and pressure to cure the prepreg or preform. The temperature inside the mold during press molding is preferably 100 to 200°C. It is also preferable to cure the prepreg or preform under conditions of 1 to 15 MPa for 1 to 120 minutes.

[0164] The applications of the fiber-reinforced composite material are not particularly limited, and examples of suitable applications include, but are not limited to, bicycle parts, golf club shafts, tennis rackets, fishing rods, and hockey sticks.

[0165] The preferred embodiments described above include, but are not limited to, the following: [1] A prepreg containing a matrix resin containing an epoxy resin and carbon fibers, wherein the epoxy resin contains an epoxy resin A which is either or both of a compound represented by the following formula (1) and a compound represented by the following formula (2), the content of the epoxy resin A is 1% by mass or more and 35% by mass or less of the total amount of the epoxy resins, the content of the epoxy resin B having at least one sulfur atom in the molecule is 0% by mass or more and less than 3% by mass of the total amount of the epoxy resins, and the content of the novolac epoxy resin is 0% by mass or more and less than 50% by mass of the total amount of the epoxy resins.

[0166]

[0167]

[0168] In formula (1) and formula (2), X １ and X ２ are each independently a structural unit represented by the following formula (3), and Y １ and Y ２ are each independently an aliphatic hydrocarbon group having 20 or less carbon atoms, １ and n ２ are each independently 1 to 20.

[0169]

[0170] In formula (3), Z １ is a single bond or -CH ２ -, -C(CH ３ ) ２ -, -CH(CH ３ )-,-C(Ph)(CH ３ is a divalent group selected from the group consisting of groups represented by —C(═O)—, —O—, and —C(═O)—, １ R １are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m ２ R ２ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m １ and m ２ are each independently an integer of 1 to 4. [2] A prepreg containing a matrix resin containing an epoxy resin and carbon fibers, wherein the epoxy resin contains an epoxy resin A which is either or both of a compound represented by the following formula (4) and a compound represented by the following formula (5), the content of the epoxy resin A is 1% by mass or more and 35% by mass or less of the total amount of the epoxy resins, and the content of the epoxy resin B having at least one sulfur atom in the molecule is 0% by mass or more and less than 3% by mass of the total amount of the epoxy resins.

[0171]

[0172]

[0173] In formula (4) and formula (5), X ３ and X ４ are each independently a structural unit represented by the following formula (6), and Y ３ and Y ４ are each independently an aliphatic hydrocarbon group having 20 or less carbon atoms, ３ and n ４ are each independently 1 to 20.

[0174]

[0175] In formula (6), Z ２ is a single bond or -CH ２ -, -C(CH ３ ) ２ -, -CH(CH ３ )-,-C(Ph)(CH ３ is a divalent group selected from the group consisting of groups represented by —C(═O)—, —O—, and —C(═O)—, ３ R ３ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m ４R ４ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m １ and m ２ are each independently an integer of 1 to 4. [3] Z １ or Z ２ But -CH ２ - or -C(CH ３ ) ２The prepreg according to [1] or [2], wherein the aliphatic hydrocarbon group having 20 or less carbon atoms is linear. [4] The prepreg according to any one of [1] to [3], wherein the aliphatic hydrocarbon group having 20 or less carbon atoms is linear. [5] The prepreg according to any one of [1] to [4], wherein the aliphatic hydrocarbon group having 20 or less carbon atoms is a hexamethylene structural unit. [6] The prepreg according to any one of [1] to [5], wherein the epoxy resin B is a tetrafunctional or higher epoxy resin. [7] The prepreg according to any one of [1] to [6], wherein the content of the epoxy resin B is 1 mass% or less of the total amount of the epoxy resins. [8] The prepreg according to any one of [1] to [7], wherein the epoxy resin further contains at least one selected from the group consisting of bisphenol A type epoxy resin, bisphenol F type epoxy resin, heterocyclic type epoxy resin, condensed ring type epoxy resin, novolac type epoxy resin, glycidyl amine type epoxy resin, and glycidyl ester type epoxy resin. [9] The prepreg according to any one of [1] to [8], further containing a thermoplastic resin.

[10] The prepreg according to

[10] , wherein the thermoplastic resin is either or both of a diblock copolymer represented by block B-block M and a triblock copolymer represented by block M-block B-block M, wherein the block M is a homopolymer of methyl (meth)acrylate, a homopolymer of (meth)acrylic acid, or a copolymer having at least one of a structural unit derived from methyl (meth)acrylate and a structural unit derived from (meth)acrylic acid, and wherein the block B has a glass transition temperature of 20°C or lower and is a block of a polymer incompatible with the polymer of the block M.

[11] The prepreg according to any one of [1] to

[10] , further containing a curing agent.

[12] The prepreg according to

[11] , wherein the curing agent includes at least one selected from the group consisting of dicyandiamides, urea compounds, imidazoles, acid hydrazides, and amines.

[13] The prepreg according to any one of [1] to

[12] , wherein the matrix resin is impregnated into a unidirectionally aligned carbon fiber sheet.

[14] A fiber-reinforced composite material comprising a cured product of the prepreg according to any one of [1] to

[13] , or a cured product of a prepreg laminate comprising a plurality of the prepregs according to any one of [1] to

[13] .

[15] A bicycle part, a golf club shaft, a tennis racket, a fishing rod, or a hockey stick, comprising the fiber-reinforced composite material according to

[14] .

[16] The fiber-reinforced composite material according to

[14] or

[15] , which is tubular.

[17] The fiber-reinforced composite material according to

[16] , wherein, when a plurality of the prepregs are laminated into a tubular shape, the orientation angle of the carbon fibers is within a range of ±20 to ±70° with respect to the longitudinal direction of the tube, and the prepregs are arranged in a region from the inner wall of the tube to 50% of the thickness of the tube in the cross section of the tube.

[18] The fiber-reinforced composite material according to

[16] , wherein, when a plurality of the prepregs are laminated into a tubular shape, the orientation angle of the carbon fibers is within a range of -5° to +5° with respect to the longitudinal direction of the tube, and the prepregs are arranged in a region of the cross section of the tube from the outer wall to 50% of the thickness of the tube.

[19] The fiber-reinforced composite material according to any of

[16] to

[18] , wherein at least two adjacent prepregs in the prepreg laminate are laminated so that the absolute value of the difference in fiber orientation angle between the prepreg on the outer wall side of the tube and the prepreg on the inner wall side of the tube is 25° or more.

[20] A method for producing a fiber-reinforced composite material, comprising pressing the prepreg according to any of [1] to

[13] at 100 to 160°C.

[0176] The preferred embodiments described above further include, but are not limited to, the following: [A1] A prepreg containing a matrix resin containing an epoxy resin and a curing agent, and carbon fibers, wherein the content of epoxy resin A represented by at least one of formula (1) and formula (2) in the epoxy resin is 1 to 35 mass %, and the content of epoxy resin B containing at least one sulfur atom in the molecule is 2 mass % or less.

[0177]

[0178]

[0179] In formula (1) and formula (2), X is a bisphenol structural unit represented by the following formula (3), or a polyalkylene ether structural unit having 20 or less carbon atoms. When X is a bisphenol structural unit represented by the following formula (3), Y is a polyalkylene ether structural unit having 20 or less carbon atoms, and when X is a polyalkylene ether structural unit having 20 or less carbon atoms, Y is a bisphenol structural unit represented by the following formula (3). １ , n ２ is an integer from 1 to 20.

[0180]

[0181] In formula (3), Z is a single bond or —CH ２ -, -C(CH ３ ) ２ -, -CH(CH ３ )-,-C(pH)(CH ３ )-, -S-, -SO ２ R is a divalent group selected from the group consisting of groups represented by -, -O-, and -C(=O)-. １ and R ２ is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group. １ and R ２ may be the same or different. １ , m ２ are each independently an integer of 1 to 4.

[0182] [A2] In the formula (3), Z is —CH ２ - or -C(CH ３ ) ２-. [A3] The prepreg according to [A1] or [A2], wherein the polyalkylene ether structural unit in the formulas (1) and (2) is linear. [A4] The prepreg according to any one of [A1] to [A3], wherein the polyalkylene ether structural unit in the formulas (1) and (2) is a structural unit derived from hexanediol. [A5] The prepreg according to any one of [A1] to [A4], wherein X in the formulas (1) and (2) is a polyalkylene ether structural unit. [A6] The prepreg according to any one of [A1] to [A5], wherein the content of the epoxy resin A in the epoxy resin is 5 to 30 mass%. [A7] The prepreg according to any one of [A1] to [A6], wherein the content of the epoxy resin B in the epoxy resin is 1 mass% or less. [A8] The prepreg according to any one of [A1] to [A7], wherein the epoxy resin comprises at least one selected from the group consisting of bisphenol A epoxy resins, bisphenol F epoxy resins, heterocyclic epoxy resins, condensed ring epoxy resins, novolac epoxy resins, glycidyl amine epoxy resins, and glycidyl ester epoxy resins.

[0183] [A9] The prepreg according to any one of [A1] to [A8], wherein the curing agent comprises at least one selected from the group consisting of dicyandiamides, urea compounds, imidazoles, and acid hydrazides. [A10] The prepreg according to any one of [A1] to [A9], wherein a unidirectionally aligned carbon fiber sheet is impregnated with a matrix resin. [A11] A fiber-reinforced composite material obtained by curing the prepreg according to any one of [A1] to [A10]. [A12] The fiber-reinforced composite material according to [A11], which is tubular. [A13] A method for producing a fiber-reinforced composite material, comprising pressing the prepreg according to any one of [A1] to [A10] at 100 to 160°C.

[0184] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples in any way.

[0185] [Raw materials used] (Epoxy resin A) EXA4850: an epoxy resin in which, in formula (1), X is a bisphenol structural unit represented by formula (3) and Y is an aliphatic hydrocarbon group having 20 or less carbon atoms; manufactured by DIC Corporation, product name EPICLON EXA-4850-150 A-1: ​​an epoxy resin in which, in formula (2), X is a hexamethylene structural unit and Y is a structural unit derived from bisphenol F, obtained by Synthesis Example 1 described later A-2: an epoxy resin in which, in formula (2), X is a hexamethylene structural unit and Y is a structural unit derived from bisphenol F, obtained by Synthesis Example 2 described later

[0186] (Epoxy Resin B) B-1: A tetrafunctional epoxy resin having a sulfur atom in the molecule, obtained by Synthesis Example 3 described later. B-2: A difunctional epoxy resin having a sulfur atom in the molecule, obtained by Synthesis Example 4 described later. B-3: A trifunctional epoxy resin having a sulfur atom in the molecule, obtained by Synthesis Example 5 described later.

[0187] (Other epoxy resins) jER828: Bisphenol A type epoxy resin; manufactured by Mitsubishi Chemical Corporation, product name jER 828 jER872: Dimer acid modified bisphenol type epoxy resin; manufactured by Mitsubishi Chemical Corporation, product name jER 872 TSR960: Solvent-free rubber modified epoxy resin; manufactured by DIC Corporation, product name EPICLON TSR-960 YX7400: Aliphatic type epoxy resin; manufactured by Mitsubishi Chemical Corporation, product name jER YX7400 MY0600: Triglycidyl-m-aminophenol type epoxy resin; manufactured by Huntsman Japan, product name Araldite MY0600 YD952: Epoxy resin having an oxazolidone ring structure; manufactured by Nippon Steel Chemical & Material Co., Ltd., product name Epotohto YD-952 YX4000: Biphenol-type epoxy resin; manufactured by Mitsubishi Chemical Corporation, product name jER YX4000 jER1002: Bisphenol A-type epoxy resin; manufactured by Mitsubishi Chemical Corporation, product name jER 1002 jER4005P: Bisphenol F-type epoxy resin; manufactured by Mitsubishi Chemical Corporation, product name jER 4005P

[0188] (Curing agent) DICY: dicyandiamide; manufactured by Evonik Japan, product name DICYANEX 1400F PDMU: phenyldimethylurea; manufactured by PTI Japan, product name Omicure 94 DCMU: 3-(3,4-dichlorophenyl)-1,1-dimethylurea; manufactured by Hodogaya Chemical Co., Ltd. DCMU-99

[0189] (Thermoplastic resins) VINYLEC K: polyvinyl formal resin; manufactured by JNC Corporation, product name: VINYLEC K VINYLEC E: polyvinyl formal resin; manufactured by JNC Corporation, product name: VINYLEC E M22N: acrylic triblock copolymer represented by block M-block B-block M; manufactured by Arkema, product name: Nanostrength M22N

[0190] (Additives) L-07N: composition containing a boric acid ester compound; manufactured by Shikoku Chemical Industry Co., Ltd., product name CureDuct L-07N

[0191] (Carbon fibers) HR40: PAN-based carbon fiber; manufactured by Mitsubishi Chemical Corporation, Pyrofil HR40 12M MR70: PAN-based carbon fiber; manufactured by Mitsubishi Chemical Corporation, Pyrofil MR70 12P

[0192] [Method for manufacturing resin plate] The matrix resin was sandwiched between glass plates and placed in a hot air oven, and then the temperature was raised from room temperature to 130°C at a rate of 2°C / min. After reaching 130°C, the temperature was maintained for 120 minutes to heat-cure the resin, thereby obtaining a resin plate with a thickness of 2 mm.

[0193] [Method of manufacturing prepreg and fiber reinforced composite material] Using a roll coater, a matrix resin was applied to a release paper with a resin basis weight of 26.9 g / cm ２A resin film coated with the resin film was produced. Next, the resulting resin film was placed on both sides of a carbon fiber sheet, and the matrix resin was impregnated into the carbon fibers using a heated roll to obtain a unidirectional prepreg. The resulting prepreg was cut into a 300 mm x 300 mm piece, and 18 to 20 sheets were stacked so that all the fibers were oriented in the same direction to obtain a laminate. This laminate was heated in an autoclave at a pressure of 0.04 MPa at a rate of 2°C / min, held at 80°C for 60 minutes, and then heated at a pressure of 0.6 MPa at a rate of 2°C / min, and held at 130°C for 120 minutes to heat-cure the laminate, yielding a fiber-reinforced composite material with a thickness of 2.0 to 2.2 mm.

[0194] [Bending test of resin plate] Six test pieces, each 8 mm wide and 60 mm long, were cut out from the resin plate. The bending strength and bending modulus of the obtained test pieces were measured under the following conditions, and the average values ​​of the six pieces were calculated. In some tests, the breaking elongation and yield elongation were also measured.

[0195] Apparatus: Instron 5965 universal testing machine (manufactured by Instron) equipped with a three-point bending jig (indenter R = 5 mm, support R = 3.2 mm) Temperature: 23°C Humidity: 50% RH Distance between supports (L): thickness of test plate (d) x 16 Crosshead speed: 2 mm / min

[0196] [0° Bending Test and 90° Bending Test of Fiber-Reinforced Composite Material] The fiber-reinforced composite material was cut into the following shapes to prepare test pieces: Test piece for 0° bending test: length 127 mm x width 12.7 mm Test piece for 90° bending test: length 60 mm x width 12.7 mm

[0197] The test pieces for the 0° bending test were processed so that the carbon fibers were approximately parallel to the longitudinal direction of the test piece. The test pieces for the 90° bending test were processed so that the carbon fibers were approximately perpendicular to the longitudinal direction of the test piece. The bending strength, modulus of elasticity, and elongation at break of the obtained test pieces were measured under the following conditions. The strength and modulus in the 0° bending test were converted so that the fiber volume content (Vf) was 60%.

[0198] Apparatus: Instron 5965 universal testing machine (manufactured by Instron) equipped with a three-point bending jig (indenter R = 5 mm, support R = 3.2 mm) Temperature: 23°C Humidity: 50% RH Distance between supports (L): thickness of test piece (d) × 40 (0° bending test), thickness of test piece (d) × 16 (90° bending test) Crosshead speed (per minute) = (L × L × 0.01) / (6 × d)

[0199] [Evaluation of Heat Resistance] The heat resistance of the resin plate and fiber-reinforced composite material was evaluated by measuring the glass transition temperature as follows. The resin plate and fiber-reinforced composite material were processed into test pieces measuring 55 mm in length and 12.5 mm in width. The glass transition temperature (G'-Tg) of the obtained test pieces was measured under the following conditions. Log G' was plotted against temperature, and the temperature at the intersection of the approximation line of the flat region of log G' and the approximation line of the region where G' transitions was determined as the glass transition temperature. A high glass transition temperature indicates excellent heat resistance.

[0200] Apparatus: Rheometer ARES-RDA TA (manufactured by Instruments Co.) Measurement frequency: 1 Hz Heating rate: 5°C / min

[0201] Synthesis Example 1: Epoxy Resin A-1 To a 1 L glass flask equipped with a stirrer, a dropping funnel, and a thermometer, 141.8 parts of 1,6-hexanediol preheated to 45°C and 0.51 parts of boron trifluoride ethyl ether were added, and the mixture was heated to 80°C. While maintaining the temperature at 80 to 85°C, 244.3 parts of epichlorohydrin were gradually added dropwise, and the mixture was aged for 1 hour and then cooled to 45°C. Next, 528.0 parts of a 22% aqueous sodium hydroxide solution was added, and the mixture was heated to 45°C and vigorously stirred for 4 hours. The mixture was cooled to room temperature, the aqueous phase was separated and removed, and the mixture was heated under reduced pressure to remove unreacted epichlorohydrin and water, yielding 283.6 parts of crude 1,6-hexanediol diglycidyl ether. The resulting crude 1,6-hexanediol diglycidyl ether was purified by distillation using an Oldershaw distillation column (15 plates), with the fraction at 170-190°C at a pressure of 1300 Pa being the main fraction, yielding 127.6 parts of 1,6-hexanediol diglycidyl ether. The epoxy equivalent of the 1,6-hexanediol diglycidyl ether was 116 g / eq. 100 parts of the resulting 1,6-hexanediol diglycidyl ether, 55.2 parts of bisphenol F, and 0.40 parts of a 50% aqueous solution of tetramethylammonium chloride were placed in a pressure-resistant reactor and subjected to a polymerization reaction at 180°C for 5 hours under a nitrogen gas atmosphere to yield Epoxy Resin A-1. The epoxy equivalent of the epoxy resin A-1 according to JIS K7236 was 480 g / eq.

[0202] Synthesis Example 2: Epoxy resin A-2 1,6-hexanediol diglycidyl ether was obtained in the same manner as in Synthesis Example 1. 100 parts of the obtained 1,6-hexanediol diglycidyl ether, 69.3 parts of bisphenol F, and 0.15 parts of triphenylphosphine were placed in a pressure-resistant reactor and subjected to a polymerization reaction at 180°C for 5 hours in a nitrogen gas atmosphere to obtain epoxy resin A-2. The epoxy equivalent of the epoxy resin A-2 based on JIS K7236 was 1100 g / eq.

[0203] Synthesis Example 3 Epoxy Resin B-1 100 parts by mass of jER828 and 9 parts by mass of 4,4'-diaminodiphenyl sulfone were mixed and heated to 170°C to carry out a polymerization reaction for 1 to 3 hours, thereby obtaining Epoxy Resin B-1. During the polymerization reaction, the viscosity was measured every 30 minutes, and heating was stopped when the viscosity reached a suitable range.

[0204] Synthesis Example 4: Epoxy Resin B-2 A 5 L four-neck flask equipped with a stirrer, reflux condenser, and thermometer was charged with 250 g of benzenesulfonamide (manufactured by Tokyo Chemical Industry Co., Ltd.), 1177 g of epichlorohydrin, and 2.5 L of water, and the system was purged with nitrogen under reduced pressure. The mixture was heated to 40°C with stirring, and then 265 g of a 48.5 wt% aqueous sodium hydroxide solution was slowly added dropwise over 4 hours. After the dropwise addition, the mixture was maintained at 40°C for 1 hour to complete the reaction. Excess epichlorohydrin was distilled off from the product as an azeotrope at 30°C under reduced pressure. Methyl isobutyl ketone was added to the mixture, and the mixture was separated and the aqueous layer was removed to obtain crude epoxy resin B-2. 35 g of a 48.5 wt% aqueous sodium hydroxide solution was added to the crude epoxy resin B-2, and the mixture was allowed to react at 40°C for 1 hour. Sodium hydrogen phosphate was added to the reaction solution to neutralize the excess sodium hydroxide, and the by-product salt was removed by washing with water. Next, methyl isobutyl ketone was completely removed under warming and reduced pressure to obtain an epoxy resin B-2 having an epoxy equivalent of 182 g / eq.

[0205] Synthesis Example 5: Epoxy Resin B-3 A 5 L four-neck flask equipped with a stirrer, reflux condenser, and thermometer was charged with 252 g of 4-hydroxybenzenesulfonamide (manufactured by Tokyo Chemical Industry Co., Ltd.) and 2,830 g of epichlorohydrin, and the system was purged with nitrogen under reduced pressure. 16 g of a 50.0 wt % aqueous tetramethylammonium chloride solution was added to this mixture, and the temperature was raised to 90°C with stirring and continued for 8 hours. The mixture was then heated to 40°C with stirring, and 437 g of a 48.5 wt % aqueous sodium hydroxide solution was slowly added dropwise over 30 minutes. After the dropwise addition, the mixture was maintained at 40°C for 1 hour to complete the reaction. This mixture was washed with water to remove by-product salts and excess sodium hydroxide, and excess epichlorohydrin was then distilled off from the product at 120°C under reduced pressure to obtain crude epoxy resin B-3. This crude epoxy resin B-3 was dissolved in 671 g of methyl isobutyl ketone and 75 g of dimethyl sulfoxide, and 14 g of a 48.5 mass% aqueous sodium hydroxide solution was added, followed by a reaction at 40°C for 1 hour. Sodium hydrogen phosphate was added to the reaction solution to neutralize excess sodium hydroxide, and the by-product salt and dimethyl sulfoxide were removed by washing with water. Next, methyl isobutyl ketone was completely removed under heating and reduced pressure, yielding an epoxy resin composition B-3 having an epoxy equivalent of 141 g / eq.

[0206] [Examples 1 to 16, Reference Examples 1 and 2, Comparative Examples 1 to 3, and Comparative Examples 5 and 6] MY0600 and a curing agent were weighed into a container according to the composition shown in the table below, with the mass ratio of solid components to liquid components being 1:1, and the mixture was stirred to obtain a mixture. The resulting mixture was further mixed finely using a three-roll mill (Inoue Seisakusho Co., Ltd.) to obtain a curing agent masterbatch. Next, MY0600 and a thermoplastic resin, excluding the components used in the curing agent masterbatch, were weighed into a flask, heated to 140°C using an oil bath, and uniformly mixed. Subsequently, while slowly cooling to 100°C, an unblended epoxy resin shown in the table below was blended and uniformly mixed. Next, the mixture was slowly cooled to approximately 65°C, and L-07N and a curing agent masterbatch were added and mixed uniformly to obtain a matrix resin. A resin plate was obtained using the obtained matrix resin.

[0207] Using the obtained matrix resin and carbon fibers shown in the table below, prepregs and fiber-reinforced composite materials were obtained according to the manufacturing methods for prepregs and fiber-reinforced composite materials. The fiber weight per unit area of ​​the carbon fiber, resin weight per unit area, and matrix resin content of the prepreg, as well as the number of laminated layers of the fiber-reinforced composite material, used in the prepreg manufacturing are shown in the table below. The resin plate and fiber-reinforced composite material were subjected to bending tests and glass transition temperature measurements, and the evaluation results are shown in the table below. In Comparative Example 2, separation and a decrease in surface quality were observed during curing of the matrix resin, so the resin plate and fiber-reinforced composite material were not evaluated.

[0208] [Examples 17 and 18, Comparative Examples 4 and 7 to 16] According to the compositions listed in the tables below, jER828 and a curing agent were weighed into a container so that the mass ratio of solid components to liquid components was 1:1, and the mixture was stirred to obtain a mixture. The resulting mixture was further mixed finely using a three-roll mill (Inoue Seisakusho Co., Ltd.) to obtain a curing agent masterbatch. Next, jER828 and a thermoplastic resin, excluding the components used in the curing agent masterbatch, were weighed into a flask and heated to 150°C using an oil bath and uniformly mixed. Subsequently, while slowly cooling to 100°C, the unblended epoxy resin listed in the tables below was blended and uniformly mixed. Next, the mixture was slowly cooled to approximately 65°C, and the curing agent masterbatch was added and mixed uniformly to obtain a matrix resin. A resin plate was obtained using the resulting matrix resin.

[0209] Using the obtained matrix resin and the carbon fibers shown in the table below, prepregs and fiber-reinforced composite materials were obtained according to the manufacturing methods for prepregs and fiber-reinforced composite materials. The fiber weight per unit area of ​​the carbon fiber, resin weight per unit area, and matrix resin content of the prepreg in the prepreg manufacturing process, as well as the number of layers of the fiber-reinforced composite material, are shown in the table below. The resin plates and fiber-reinforced composite materials were subjected to bending tests and glass transition temperature measurements, and the evaluation results are shown in the table below.

[0210]

[0211]

[0212]

[0213]

[0214]

[0215]

[0216] As shown in Tables 1 to 6, in Examples 1 to 19, epoxy resin A, epoxy resin B, and novolac-type epoxy resin were used in amounts within the specified ranges. Specifically, in Examples 1 to 11 and 16, epoxy resin A was used within the specified range. In Examples 12, 13, 17, and 18, epoxy resin A was used within the specified range, and further, novolac-type epoxy resin was used within the specified range. In Example 19, epoxy resin A was used within the specified range, and epoxy resin B was used within the specified range. On the other hand, in Comparative Examples 1 to 4, 7, and 8, epoxy resin A was not used. In Comparative Example 6, the content of epoxy resin A was outside the specified range. In Comparative Example 5, epoxy resin A was used within the specified range, but the content of epoxy resin B was outside the specified range. In Comparative Examples 10 to 16, epoxy resin A was used within the specified range, but the content of novolac-type epoxy resin was outside the specified range. In Examples 1 to 11 and 16, the 90° bend properties were improved while maintaining the heat resistance and 0° bend properties compared to Comparative Examples 1 to 4, 7 and 8. In Comparative Example 6, the heat resistance could not be maintained. In Examples 12 and 13, by further using a novolac epoxy resin, the heat resistance was improved while maintaining the 90° bend properties.

[0217] A comparison of Examples 9 and 10 with Comparative Examples 7 and 8 reveals that the use of Epoxy Resin A similarly improved 90° flexural properties, even when different matrix resin contents or different carbon fibers were used in prepreg production. Example 19 exhibited improved 90° flexural properties compared to Comparative Example 5. Examples 17 and 18 exhibited improved fracture elongation, which is closely correlated with 90° flexural properties, compared to Comparative Examples 10 to 16. A comparison of Reference Examples 1 and 2 with Example 19 suggests that the use of a large amount of di- or trifunctional sulfur-containing epoxy resin improves 90° flexural strength due in part to the influence of sulfur atoms, but that a reduced use of large sulfur atoms adversely affects the density between crosslinks, further reducing the 90° flexural modulus. The epoxy equivalents of Epoxy Resin A-1 and Epoxy Resin A-2 used in this example were 480 g / eq and 1100 g / eq, respectively, but the epoxy equivalents could be easily increased or decreased by changing the synthesis conditions. For example, when an epoxy resin A having a larger epoxy equivalent is used, the viscosity can be adjusted to a value suitable for producing a prepreg by lowering the viscosity of the other epoxy resins.

[0218] While the present invention has been described above with reference to specific embodiments, these embodiments are presented as examples and do not limit the scope of the present invention. Each embodiment described in this specification can be modified in various ways within the scope of the effects of the invention, and can be combined with features described in other embodiments within the scope of feasibility.

[0219] According to one aspect of the present invention, a prepreg and a fiber-reinforced composite material having excellent 90° bending strength and elastic modulus while maintaining heat resistance can be obtained.

Claims

1. A prepreg containing a matrix resin containing an epoxy resin and carbon fiber, wherein the epoxy resin contains an epoxy resin A which is either or both of a compound represented by the following formula (1) and a compound represented by the following formula (2), the content of the epoxy resin A is 1% by mass or more and 35% by mass or less of the total amount of the epoxy resin, the content of the epoxy resin B having at least one sulfur atom in the molecule is 0% by mass or more and less than 3% by mass of the total amount of the epoxy resin, and the content of the novolac epoxy resin is 0% by mass or more and less than 50% by mass of the total amount of the epoxy resin. In formula (1) and formula (2), X １ and X ２ are each independently a structural unit represented by the following formula (3), and Y １ and Y ２ are each independently an aliphatic hydrocarbon group having 20 or less carbon atoms, １ and n ２ are each independently 1 to 20. In formula (3), Z １ is a single bond or -CH ２ -, -C(CH ３ ) ２ -, -CH(CH ３ )-,-C(Ph)(CH ３ is a divalent group selected from the group consisting of groups represented by —C(═O)—, —O—, and —C(═O)—, １ R １ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m ２ R ２ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m １ and m ２ are each independently an integer of 1 to 4.

2. A prepreg containing a matrix resin containing an epoxy resin and carbon fibers, wherein the epoxy resin contains an epoxy resin A which is either or both of a compound represented by the following formula (4) and a compound represented by the following formula (5), the content of the epoxy resin A being 1% by mass or more and 35% by mass or less of the total amount of the epoxy resin, and the content of the epoxy resin B having at least one sulfur atom in the molecule being 0% by mass or more and less than 3% by mass of the total amount of the epoxy resin. In formula (4) and formula (5), X ３ and X ４ are each independently a structural unit represented by the following formula (6), and Y ３ and Y ４ are each independently an aliphatic hydrocarbon group having 20 or less carbon atoms, ３ and n ４ are each independently 1 to 20. In formula (6), Z ２ is a single bond or -CH ２ -, -C(CH ３ ) ２ -, -CH(CH ３ )-,-C(Ph)(CH ３ is a divalent group selected from the group consisting of groups represented by —C(═O)—, —O—, and —C(═O)—, ３ R ３ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m ４ R ４ are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and m １ and m ２ are each independently an integer of 1 to 4.

3. Z １ or Z ２ But -CH ２ - or -C(CH ３ ) ２ The prepreg according to claim 1 or 2, wherein 4. The prepreg according to claim 1 or 2, wherein the aliphatic hydrocarbon group having 20 or less carbon atoms is linear.

5. The prepreg according to claim 1 or 2, wherein the aliphatic hydrocarbon group having 20 or less carbon atoms is a hexamethylene structural unit.

6. The prepreg according to claim 1 or 2, wherein the epoxy resin B is a tetrafunctional or higher epoxy resin.

7. The prepreg according to claim 1 or 2, wherein the content of epoxy resin B is 1 mass% or less of the total amount of epoxy resins.

8. The prepreg according to claim 1 or 2, further comprising at least one epoxy resin selected from the group consisting of bisphenol A epoxy resins, bisphenol F epoxy resins, heterocyclic epoxy resins, condensed ring epoxy resins, novolac epoxy resins, glycidyl amine epoxy resins, and glycidyl ester epoxy resins.

9. The prepreg according to claim 1 or 2, further comprising a thermoplastic resin.

10. The prepreg according to claim 9, wherein the thermoplastic resin is one or both of a diblock copolymer represented by block B-block M and a triblock copolymer represented by block M-block B-block M, wherein the block M is a homopolymer of methyl (meth)acrylate, a homopolymer of (meth)acrylic acid, or a copolymer having at least one of structural units derived from methyl (meth)acrylate and structural units derived from (meth)acrylic acid, and wherein the block B is a block of a polymer that has a glass transition temperature of 20°C or lower and is incompatible with the polymer of the block M.

11. The prepreg according to claim 1 or 2, further comprising a curing agent.

12. The prepreg according to claim 11, wherein the curing agent comprises at least one selected from the group consisting of dicyandiamides, urea compounds, imidazoles, acid hydrazide compounds, and amines.

13. The prepreg according to claim 1 or 2, wherein a carbon fiber sheet aligned in one direction is impregnated with the matrix resin.

14. A fiber-reinforced composite material comprising a cured product of the prepreg according to claim 1 or 2, or a cured product of a prepreg laminate comprising a plurality of prepregs according to claim 1 or 2.

15. A bicycle part, a golf club shaft, a tennis racket, a fishing rod or a hockey stick comprising the fiber-reinforced composite material of claim 14.

16. The fiber-reinforced composite material of claim 14, which is tubular.

17. The fiber-reinforced composite material according to claim 16, wherein, when a plurality of the prepregs are laminated into a tubular shape, the orientation angle of the carbon fibers is within the range of ±20 to ±70° with respect to the longitudinal direction of the tube, and the prepregs are arranged in a region extending from the inner wall of the tube to 50% of the thickness of the tube in the cross section of the tube.

18. The fiber-reinforced composite material according to claim 16, wherein, when a plurality of the prepregs are laminated into a tubular shape, the orientation angle of the carbon fibers is within the range of −5° to +5° with respect to the longitudinal direction of the tube, and the prepregs are arranged in a region extending from the outer wall of the tube to 50% of the thickness of the tube in the cross section of the tube.

19. The fiber-reinforced composite material according to claim 16, wherein at least two adjacent prepregs in the prepreg laminate are laminated so that the absolute value of the difference in fiber orientation angle between the prepreg on the outer wall side of the pipe and the prepreg on the inner wall side of the pipe is 25° or more.

20. A method for producing a fiber-reinforced composite material, comprising pressing the prepreg according to claim 1 or 2 at 100 to 160°C.

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