Resin composition, composite material, and cured product of composite material

Abstract

This resin composition comprises: a vinyl ester resin (A) having an epoxy group and having an acid value of less than 1 KOHmg / g; at least one monomer (B) selected from radically polymerizable monomers and epoxy monomers; at least one component (C) selected from benzoic acid and benzoic acid derivatives; and a thickening component (D). In the resin composition, the content ratio of the component (C) to the component (D) ([at least one component selected from benzoic acid and benzoic acid derivatives] / [thickening component]) is more than 0.5 and 6.0 or less in terms of mass ratio.

Description

Resin Composition, Composite Material, and Cured Product of Composite Material

[0001] The present invention relates to a resin composition, a composite material, and a cured product of the composite material.

[0002] Fiber reinforced composite materials containing thermosetting resin compositions, reinforcing fibers, fillers, etc. can add mechanical strength to plastics having easy processability, non-corrosiveness, and light weight, and thus are widely used in members for electric and electronic equipment, building materials, members for vehicles, etc.

[0003] Fiber reinforced composite materials are manufactured by various methods. For example, as an intermediate material, a method using a prepreg in which a reinforcing material made of long fibers such as reinforcing fibers is impregnated with a matrix resin is widely used. As the matrix resin used in the prepreg, an epoxy resin composition containing an epoxy resin excellent in mechanical properties, heat resistance, and handleability is widely used (for example, Patent Document 1).

[0004] When the fiber reinforced composite material is a molded product having a shape that is difficult to produce by molding using a prepreg, for example, a molded product having a complicated shape with fine irregularities, a sheet molding compound (hereinafter referred to as "SMC") is widely used as an intermediate material. SMC is a compound in which a resin composition containing a thermosetting resin is impregnated into a sheet-like reinforcing fiber group in which short-cut reinforcing fibers are deposited. As the matrix resin used in SMC, those containing a vinyl ester resin or an unsaturated polyester resin are widely used (for example, Patent Documents 2 and 3).

[0005] While resin compositions containing epoxy resin require low-temperature storage, resin compositions containing vinyl ester resin or unsaturated polyester resin have the advantage of high storage stability and do not require low-temperature storage. Furthermore, while resin compositions containing epoxy resin require high temperatures and long curing times, resin compositions containing vinyl ester resin or unsaturated polyester resin do not require high temperatures and long curing times, resulting in higher productivity. On the other hand, glass fibers were widely used as reinforcing fibers for SMC, but in recent years, carbon fibers have sometimes been used for weight reduction. However, resin compositions containing vinyl ester resin or unsaturated polyester resin have inferior adhesion to carbon fibers compared to epoxy resins, resulting in lower CFRP strength.

[0006] Japanese Patent Publication No. 2021-116349, Japanese Patent Publication No. 2012-111909, Japanese Patent Publication No. 2020-94218

[0007] The present invention aims to provide a novel resin composition suitable for use as a resin composition for prepregs and SMCs, which exhibits excellent viscosity increasing properties. Furthermore, the present invention aims to provide a resin composition that exhibits good adhesion to carbon fibers, which, when used as a matrix resin for carbon fibers, yields carbon fiber reinforced plastic (hereinafter referred to as CFRP) with excellent curability and CFRP strength.

[0008] To achieve the above objective, the present invention provides the following means.

[0009] <Resin Compositions> [1] A resin composition comprising: a vinyl ester resin (A) having epoxy groups and having an acid value of less than 1 KOH mg / g; at least one monomer (B) selected from radical polymerizable monomers and epoxy monomers; at least one (C) selected from benzoic acid and benzoic acid derivatives; and a thickening component (D), wherein the content ratio of component (C) to component (D) in the resin composition ([at least one selected from benzoic acid and benzoic acid derivatives] / [thickening component]) is greater than 0.5 and 6.0 or less by mass ratio. [2] The resin composition of [1] wherein (A) is a reaction product of an epoxy compound (a-1) having two or more epoxy groups in one molecule and an unsaturated monobasic acid (a-2), and the total amount of carboxyl groups of (a-2) is 0.8 equivalents or less per 1 equivalent of the total amount of epoxy groups of (a-1). [3] The resin composition of [1] or [2], wherein the thickening component (D) is at least one selected from the group consisting of oxides and hydroxides of Group 2 elements. [4] The resin composition of any one of [1] to [3], further comprising an epoxy curing agent (E). [5] The resin composition of [4], wherein the epoxy curing agent (E) is at least one selected from the group consisting of phenolic curing agents, esteric curing agents, benzoxazine curing agents, acid anhydride curing agents, primary to tertiary amine curing agents, mercaptan curing agents, amide curing agents, blocked isocyanate curing agents, imidazole curing agents, active ester compounds, and latent curing agents. [6] The resin composition of any one of [1] to [5], further comprising a radical curing agent (F). [7] The resin composition of [6] wherein the radical curing agent (F) is at least one selected from the group consisting of peroxyester-based organic peroxides, hydroperoxide-based organic peroxides, dialkylperoxide-based organic peroxides, and peroxyketal-based organic peroxides.

[0010] <Composite materials> [8] A composite material comprising any resin composition from [1] to [7] and a fibrous base material (G). [9] The composite material of [8] wherein the fibrous base material (G) is at least one selected from carbon fiber and glass fiber.

[0011] <Cured product> A cured product of the composite material of

[10] [8] or [9].

[0012] According to the present invention, it is possible to provide a new resin composition suitable for use as a resin composition for prepregs and SMCs, which exhibits excellent viscosity-enhancing properties. Furthermore, according to the present invention, it is possible to provide a resin composition that exhibits good adhesion to carbon fibers, which can be used as a matrix resin for carbon fibers to obtain carbon fiber reinforced plastic (hereinafter referred to as CFRP) with excellent curability and CFRP strength.

[0013] [Resin Composition] The resin composition of this disclosure will be described in detail below. In the following description, the notation "a to b" indicating a numerical range indicates a numerical range that includes the endpoints a and b. That is, it means "a or more and b or less" (when a < b) or "a or less and b or more" (when a > b).

[0014] The resin composition of this disclosure comprises the following components (A) to (D): a vinyl ester resin (A) having an epoxy group and having an acid value of less than 1 KOH mg / g; at least one monomer (B) selected from radical polymerizable monomers and epoxy monomers; at least one substance (C) selected from benzoic acid and benzoic acid derivatives; and a thickening component (D), wherein the content ratio of component (C) to component (D) in the resin composition ([at least one substance selected from benzoic acid and benzoic acid derivatives] / [thickening component]) is greater than 0.5 and less than or equal to 6.0 by mass.

[0015] In addition to components (A) to (D), the resin composition of this disclosure may also contain an epoxy curing agent (E) and a radical curing agent (F).

[0016] <Component (A)> Component (A) is a vinyl ester resin having epoxy groups, and may also be a vinyl ester resin having at least one epoxy group at its terminal end.

[0017] Component (A) may be a reaction product of an epoxy compound (a-1) having two or more epoxy groups in one molecule and an unsaturated monobasic acid (a-2). Component (A) may have a polymerizable unsaturated bond obtained by a ring-opening reaction between the epoxy group in (a-1) and the carboxyl group in (a-2).

[0018] Component (A) may be obtained by making the amount of carboxyl group of (a-2) that reacts with the epoxy group in (a-1) less than an equivalent, thereby leaving the epoxy group intact. When the reaction is carried out in such a ratio, the unsaturated monobasic acid (a-2) reacts stoichiometrically to an equivalent extent, resulting in components that do not have epoxy groups, or conversely, components in which the unsaturated monobasic acid (a-2) has not reacted. However, in this disclosure, these are also included in component (A).

[0019] The amount of carboxyl groups of (a-2) to react with the epoxy groups in (a-1) may be such that the total amount of carboxyl groups of (a-2) is 0.2 to 0.8 equivalents (e.g., 20 to 80 moles) per 1 equivalent (e.g., 100 moles) of epoxy groups of (a-1), or it may be 0.3 to 0.75 equivalents (e.g., 30 to 75 moles), or 0.4 to 0.65 equivalents (e.g., 40 to 65 moles). If the total amount of carboxyl groups of the unsaturated monobasic acid (a-2) is 0.2 equivalents or more per 1 equivalent of epoxy groups of epoxy compound (a-1), a sufficient amount of ethylenically unsaturated groups is introduced into component (A), so the resin composition tends to exhibit good curability. If the total amount of carboxyl groups of the unsaturated monobasic acid (a-2) is 0.8 equivalents or less, a sufficient amount of unreacted epoxy groups remains in the vinyl ester resin (A), so adhesion to the fibrous substrate (G) is good.

[0020] Component (A) has vinyl groups derived from (a-2). The ratio of vinyl groups (epoxy groups:vinyl groups) in (A) may be 2:8 to 8:2 in molar ratio. This ratio can be adjusted by the amount of (a-1) and (a-2) added.

[0021] Theoretically, the acid value of component (A) is 0 KOH mg / g. However, considering the acid that inevitably gets mixed in during manufacturing, it may not always be practical to set the acid value of component (A) to 0 KOH mg / g. Even if there is acid that inevitably gets mixed in during manufacturing, if the acid value of component (A) is less than 1 KOH mg / g, the viscosity of the resin composition becomes easier to control. The acid value of component (A) is preferably less than 0.5 KOH mg / g, and more preferably less than 0.1 KOH mg / g.

[0022] (A) The epoxy equivalent of component (A) may be 140 to 9000, 180 to 6000, or 240 to 3500, from the viewpoint of adhesion and rapid curing. When the epoxy equivalent is 140 or more, it exhibits excellent adhesion to carbon fibers for epoxy resins, which are commonly used as reinforcing fibers. When the epoxy equivalent is 9000 or less, it exhibits excellent adhesion to carbon fibers for vinyl ester resins and can be cured at low temperatures and in a short time.

[0023] (Epoxy compound (a-1)) Epoxy compound (a-1) is a compound having two or more epoxy groups in one molecule, and monomers, oligomers, and polymers in general can be used, and its molecular weight and molecular structure are not particularly limited. Epoxy compound (a-1) may be used alone or in combination of two or more types.

[0024] Examples of epoxy compounds (a-1) include biphenyl-type epoxy resins; bisphenol-type epoxy resins such as bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, bisphenol S-type epoxy resin, bisphenol AF-type epoxy resin, tetrabromobisphenol A-type epoxy resin, and tetramethylbisphenol F-type epoxy resin; stilbene-type epoxy resins; novolac-type epoxy resins such as phenol novolac-type epoxy resin and cresol novolac-type epoxy resin; polyfunctional epoxy resins such as triphenolmethane-type epoxy resin and alkyl-modified triphenolmethane-type epoxy resin; phenol aralkyl-type epoxy resins such as phenol aralkyl-type epoxy resin having a phenylene skeleton and phenol aralkyl-type epoxy resin having a biphenylene skeleton; dihydrox Examples include naphthol-type epoxy resins such as synaphthalene-type epoxy resins and epoxy resins obtained by glycidyl etherification of dimers of dihydroxynaphthalene; triazine-nucleus-containing epoxy resins such as triglycidyl isocyanurate and monoallyl diglycidyl isocyanurate; alicyclic polyepoxy compounds such as alicyclic diepoxyacetal, alicyclic diepoxyadipate, alicyclic diepoxycarboxylate, and vinylcyclohexene dioxide; bridged cyclic hydrocarbon compound-modified phenol-type epoxy resins such as dicyclopentadiene-modified phenol-type epoxy resins; glycidyl ester-type epoxy resins obtained by the reaction of a polybasic acid such as dimer acid with epichlorohydrin; and oxazolidone ring-containing epoxy resins obtained by the reaction of the epoxy resin with diisocyanate. In particular, bisphenol-type epoxy resins are preferred from the viewpoint of toughness, versatility, and cost, and one or more selected from bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, bisphenol S-type epoxy resin, and bisphenol AF-type epoxy resin are more preferred, and bisphenol A-type epoxy resin is even more preferred from the viewpoint of a good balance of toughness and strength as a fiber-reinforced plastic. The bisphenol structure makes it possible to increase the molecular weight of the epoxy compound. Component (A) may be obtained by a two-step reaction in which the epoxy resin and the bisphenol structure are reacted to increase the molecular weight, and then (a-2) is added.

[0025] The epoxy equivalent of epoxy compound (a-1) may be 170 to 1000, 170 to 500, 170 to 400, or 170 to 300, from the viewpoint of workability, so that the vinyl ester resin (A) does not gel. From the viewpoint of workability, epoxy compound (a-1) may be liquid at 25°C, and may have an epoxy equivalent of 300 or less.

[0026] (Unsaturated monobasic acid (a-2)) The unsaturated monobasic acid (a-2) may be a monocarboxylic acid having an ethylenically unsaturated group, and may be used alone or in combination of two or more. Examples of unsaturated monobasic acid (a-2) include (meth)acrylic acid, crotonic acid, and cinnamic acid. From the viewpoint of obtaining a resin composition with versatility, reactivity during the synthesis of vinyl ester resin (A), and good curability, it may be at least one selected from (meth)acrylic acid and crotonic acid, and from the viewpoint of workability, it may be liquid (meth)acrylic acid or methacrylic acid.

[0027] Furthermore, as the unsaturated monobasic acid (a-2), a half-ester of a compound having one hydroxyl group and one or more (meth)acryloyl groups with a dibasic acid or dibasic anhydride may be used.

[0028] Examples of acrylic monomers having one hydroxyl group and one or more (meth)acryloyl groups include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, hydroxyhexyl (meth)acrylate, polyethylene glycol monomethyl ether (meth)acrylate, polypropylene glycol monomethyl ether (meth)acrylate, polytetramethylene glycol monomethyl ether (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, nonylphenoxypolyethylene glycol (meth)acrylate, and phenoxypolypropylene glycol (meth)acrylate. From the viewpoint of mechanical properties (elongation at breaking point), compounds having both a hydroxyl group and an acryloyl group may also be used.

[0029] Known dibasic acids and their dibasic anhydrides can be used. For example, succinic acid, glutaric acid, adipic acid, sebacic acid, phthalic acid, fumaric acid, maleic acid, itaconic acid, tetrahydrophthalic acid, hexahydrophthalic acid, dimer acid, ethylene glycol 2mol maleic anhydride adduct, polyethylene glycol 2mol maleic anhydride adduct, propylene glycol 2mol maleic anhydride adduct, polypropylene glycol 2mol maleic anhydride adduct, dodecanediic acid, tridecanediic acid, octadecanediic acid, 1,16-(6-ethylhexadecane)dicarboxylic acid, 1,12-(6-ethyldodecane)dicarboxylic acid, and carboxyl-terminal butadiene / acrylonitrile copolymer (trade name Hycar CTBN) can be used.

[0030] The weight-average molecular weight Mw of component (A) may be 400 or more, 500 or more, or 600 or more, from the viewpoint of ease of reaction and workability. The weight-average molecular weight Mw of component (A) may be 6,500 or less, 3,500 or less, or 1,500 or less, from the viewpoint of impregnation into the fiber substrate (G).

[0031] The number-average molecular weight Mn of component (A) may be 200 or more, 300 or more, or 400 or more, from the viewpoint of ease of reaction and workability. The number-average molecular weight Mn of component (A) may be 3,000 or less, 2,000 or less, or 1,000 or less, from the viewpoint of impregnation into the fiber substrate (G).

[0032] (A) The Mw / Mn ratio of component (A) may be 1.0 or higher, 1.1 or higher, or 1.2 or higher, from the viewpoint of ease of controlling synthesis conditions. (A) The Mw / Mn ratio of component (A) may be 3.0 or lower, 2.5 or lower, or 2.0 or lower, from the viewpoint of suppressing variations in the physical properties of the resin composition. Here, Mw / Mn is an indicator of molecular weight distribution; a ratio of 1 indicates a monodisperse polymer, and a larger ratio means a wider molecular weight distribution.

[0033] Component (A) is preferably used after adjusting its viscosity using a solvent or reactive diluent, etc., from the viewpoint of workability, moldability, and curability. The adjusted viscosity may be 0.1 to 150 dPa·s, 0.3 to 100 dPa·s, 0.5 to 50 dPa·s, or 1 to 20 dPa·s in a 25°C environment.

[0034] (A) The component may be a single component or two or more components may be used in combination.

[0035] (A) The component may be a commercially available product, or it may be manufactured by the following method.

[0036] <Method for producing component (A)> In one embodiment, component (A) can be produced by mixing an epoxy compound (a-1) and an unsaturated monobasic acid (a-2) in a heat-stirred reaction vessel with at least one of a solvent and a reactive diluent as needed, and heating while stirring for 1 to 8 hours at 70 to 150°C, 80 to 140°C, or 90 to 130°C in the presence of a catalyst.

[0037] Examples of the catalyst include tertiary amines such as triethylamine, triethylenediamine, N,N-dimethylbenzylamine, N,N-dimethylaniline, 2,4,6-tris(dimethylaminomethyl)phenol, and diazabicyclooctane; phosphorus compounds such as triphenylphosphine and benzyltriphenylphosphonium chloride; diethylamine hydrochloride; and quaternary ammonium salts such as trimethylbenzylammonium chloride and tetradecyldimethylbenzylammonium chloride. These may be used individually or in combination of two or more. From the viewpoint of slowly promoting the reaction rate of vinyl ester resin synthesis, suppressing resin gelation, and easily controlling the molecular weight distribution, at least one of the phosphorus compounds and quaternary ammonium salts may be used, and from the viewpoint of reaction rate, a phosphorus compound may be used.

[0038] The amount of catalyst used may be 0.01 to 3 parts by mass, 0.03 to 2 parts by mass, or 0.05 to 1 part by mass per 100 parts by mass of the epoxy compound (a-1) and the unsaturated monobasic acid (a-2), from the viewpoint of promoting the reaction, suppressing the thickening of the vinyl ester resin (A), and ensuring the storage stability of the obtained reaction product.

[0039] The solvent and reactive diluent are used as needed from the viewpoint of facilitating the uniform mixing of the epoxy compound (a-1) and the unsaturated monobasic acid (a-2). The mixing method is not particularly limited and can be carried out by known methods.

[0040] The solvent is not particularly limited as long as it is inert to the epoxy compound (a-1) and the unsaturated monobasic acid (a-2). For example, known solvents with a boiling point of 70 to 150°C at 1 atmosphere, such as methyl isobutyl ketone (MIBK), can be used. The solvent may be used alone or in combination of two or more.

[0041] As the reactive diluent, those inert to the epoxy compound (a-1) are used. In this embodiment, however, it is also possible to use an ethylenically unsaturated group-containing monomer (B) described later as the reactive diluent. As the reactive diluent, it is possible to use an ethylenically unsaturated group-containing monomer (B) described later that is inert to the epoxy compound (a-1). The ethylenically unsaturated group-containing monomer (B) is reactive with the unsaturated monobasic acid (a-2), but it is possible to use it while suppressing the reaction by using a polymerization inhibitor or the like in combination.

[0042] From the viewpoint of suppressing the progress of the polymerization reaction, a polymerization inhibitor may be added. The polymerization inhibitor preferably used is the one described in the section of [Other Components] below. When adding a polymerization inhibitor, the addition amount may be, for example, 0.0001 to 3.0 parts by mass, 0.001 to 1.0 parts by mass, or 0.005 to 0.3 parts by mass with respect to a total of 100 parts by mass of the epoxy compound (a-1) and the unsaturated monobasic acid (a-2).

[0043] <Component (B)> Component (B) is at least one monomer selected from a radically polymerizable monomer and an epoxy monomer, and is a monomer excluding methacrylic acid. Component (B) copolymerizes with component (A). From the viewpoint of also copolymerizing with component (C), it is more preferable for component (B) to contain a radically polymerizable monomer. Component (B) contributes to reducing the viscosity of the resin composition and further contributes to the fiber impregnation property of the composite material.

[0044] The radically polymerizable monomer may be a monomer having a carbon-carbon unsaturated double bond, or may be a monomer having a vinyl group or a (meth)acryloyl group.

[0045] Examples of the monomer having a vinyl group include styrene, p-chlorostyrene, vinyl toluene, α-methylstyrene, dichlorostyrene, divinylbenzene, t-butylstyrene, vinyl acetate, diallyl phthalate, diallyl isophthalate, triallyl isocyanurate, and the like. Further, vinyl benzyl compounds such as vinyl benzyl butyl ether, vinyl benzyl hexyl ether, vinyl benzyl octyl ether, divinyl benzyl ether, and the like can be mentioned.

[0046] Examples of the monomer having a (meth)acryloyl group include (meth)acrylic acid, (meth)acrylate, and the like. The (meth)acrylate may be monofunctional or polyfunctional.

[0047] Examples of monofunctional (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl, lauryl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, stearyl (meth)acrylate, tridecyl (meth)acrylate, phenoxyethyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, ethylene glycol monomethyl ether (meth)acrylate, ethylene glycol monoethyl ether (meth)acrylate, ethylene glycol monobutyl ether (meth)acrylate, and ethylene glycol monohexyl ether (meth)acrylate. Examples include ethylene glycol mono-2-ethylhexyl ether (meth)acrylate, diethylene glycol monomethyl ether (meth)acrylate, diethylene glycol monoethyl ether (meth)acrylate, diethylene glycol monobutyl ether (meth)acrylate, diethylene glycol monohexyl ether (meth)acrylate, diethylene glycol mono-2-ethylhexyl ether (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, tricyclodecanyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, caprolactone-modified hydroxyalkyl (meth)acrylate, and allyl (meth)acrylate.

[0048] Examples of polyfunctional (meth)acrylates include alkane diol di(meth)acrylates such as ethylene glycol di(meth)acrylate, 1,2-propylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,4-butylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and 1,6-hexanediol di(meth)acrylate, as well as diethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and polytetramethylene glycol di(meth)acrylate. Examples include polyoxyalkylene glycol di(meth)acrylates, as well as trimethylolpropane di(meth)acrylate, glycerin di(meth)acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, pentaerythritol diacrylate monostearate, 1,3-bis((meth)acryloyloxy)-2-hydroxypropane, ethoxylated bisphenol A di(meth)acrylate, tris-(2-(meth)acryloxyethyl) isocyanurate, etc.

[0049] Examples of monomers having a (meth)acryloyl group other than (meth)acrylate include acryloylmorpholine, 2-hydroxyethyl (meth)acrylamide, 2-hydroxyethyl-N-methyl (meth)acrylamide, and 3-hydroxypropyl (meth)acrylamide.

[0050] (B) Component (B) may be one or more selected from the group consisting of styrene, diallyl phthalate, phenoxyethyl methacrylate, benzyl methacrylate, and diethylene glycol dimethacrylate, from the viewpoint of workability, curability, and fiber impregnation of the composite material including the resin composition.

[0051] The epoxy monomer may be monofunctional or polyfunctional. Preferably, the epoxy monomer has a viscosity of 1 dPa·s / 25°C or less.

[0052] Monofunctional epoxy monomers include, for example, alkylene oxides; epoxy-substituted alicyclic hydrocarbons, such as cyclohexene oxide, cyclooctene oxide, cyclododecene oxide, vinylcyclohexene monooxide, (+)-cis-limonene oxide, (+)-cis,trans-limonene oxide, (-)-cis,trans-limonene oxide, and α-pinene oxide; epoxy-substituted aromatic hydrocarbons; monoepoxy-substituted alkyl ethers of monohydric alcohols or phenols, such as glycidyl ethers of aliphatic, alicyclic, and aromatic alcohols; aliphatic, alicyclic, and aromatic mono Examples include monoepoxy-substituted alkyl esters of monocarboxylic acids, such as glycidyl esters of carboxylic acids; monoepoxy-substituted alkyl esters of polycarboxylic acids in which other carboxyl groups are esterified with alkanols; alkyl and alkenyl esters of epoxy-substituted monocarboxylic acids; epoxy alkyl ethers of polyhydric alcohols in which other OH groups are esterified or etherified with carboxylic acids or alcohols; and monoesters of polyhydric alcohols and epoxy monocarboxylic acids in which other OH groups are esterified or etherified with carboxylic acids or alcohols.

[0053] Examples of polyfunctional epoxy monomers include diglycidyl ethers of aliphatic glycols, such as 1,4-butanediol diglycidyl ether (BDDGE), 1,6-hexanediol diglycidyl ether (HDDGE), neopentyl glycol diglycidyl ether, and 1,4-cyclohexanedimethanol diglycidyl ether; polyalkylene glycol diglycidyl ethers, particularly polypropylene glycol diglycidyl ether; diglycidyl ethers of bisphenol-A epichlorohydrin epoxy resins; diglycidyl ethers of bisphenol-A polyether epoxy adducts; and polycarbonate diol glycidyl ethers. Additionally, diepoxy monomers include biunsaturated fatty acids C １ -C １８ Examples include alkyl ester diepoxy; diglycidyl dimer acid; vinylcyclohexene diepoxy; and limonene diepoxy.

[0054] (B) Component may be a single type or two or more types may be used in combination.

[0055] <Component (C)> Component (C) is a thickening agent, and at least one selected from benzoic acid and benzoic acid derivatives is used. The benzoic acid and benzoic acid derivatives may be benzoic acid, 2-methylbenzoic acid (ortho position), 3-methylbenzoic acid (meta position), 4-methylbenzoic acid (para position), p-vinylbenzoic acid, p-phenylbenzoic acid, m-chlorobenzoic acid, 2-propylbenzoic acid, or benzoic acid and 2-methylbenzoic acid (ortho position), and from the viewpoint of thickening properties, benzoic acid may be used. Component (C) may be used alone or in combination of two or more.

[0056] <Component (D)> Component (D) is a thickening component that has the effect of increasing the viscosity of the resin composition over time and is used as a thickening agent. Component (D) may be at least one selected from the group consisting of oxides and hydroxides of Group 2 elements. Component (D) may be used alone or in combination of two or more. By incorporating component (D) into the resin composition, the resin composition before thickening can be made low viscosity to improve impregnation into the reinforcing fiber group, and the viscosity can be increased after impregnation into the reinforcing fiber group, thereby improving the shape retention and handling properties of SMC and prepregs.

[0057] Examples of oxides of Group 2 elements include magnesium oxide, calcium oxide, and barium oxide. Examples of hydroxides of Group 2 elements include magnesium hydroxide, calcium hydroxide, and barium hydroxide. Among these, magnesium oxide may also be used from the viewpoint of thickening effect, versatility, and cost.

[0058] <Content ratio of component (C) and component (D)> The content ratio of component (C) and component (D) in the resin composition ([at least one selected from benzoic acid and benzoic acid derivatives] / [thickening component]) may be greater than 0.5 and 6.0 or less by mass ratio, may be between 1.0 and 5.5, or between 2.0 and 5.0. When component (D) is included in the thickener, the mass of component (D) refers to the mass of component (D) (hereinafter referred to as "pure content") included in the thickener. When the content ratio of component (C) and component (D) is within the above range, the resin composition has good thickening properties.

[0059] For example, if component (D) is magnesium oxide, it is presumed that component (C), which is the acid, and component (D), which is the magnesium oxide, thicken the resin composition through the following mechanism. First, magnesium oxide undergoes hydrolysis under acidic conditions to form Mg(OH) ２ It generates Mg(OH) ２The acid undergoes a neutralization reaction, forming an ionic bond. Subsequently, the hydroxyl groups of component (A) and some of the ester groups coordinate to the Mg ion, forming a coordinate bond and increasing the molecular weight in the longitudinal direction. Note that a higher amount of hydroxyl groups in component (A) results in a greater thickening effect. Component (A), which structurally readily forms hydrogen bonds with other hydroxyl groups, becomes more cohesive as its molecular weight increases, leading to increased viscosity (i.e., gelation).

[0060] Conventionally, common thickening methods for SMC include metal thickening using metal oxides such as magnesium oxide, and isocyanate thickening using polyfunctional isocyanates. Metal thickening is widely used as a thickening method that utilizes the carboxyl groups of unsaturated polyester resins, or by introducing carboxyl groups into vinyl ester resins and utilizing those carboxyl groups. Isocyanate thickening is widely used as a thickening method that utilizes the hydroxyl groups of vinyl ester resins. However, SMC obtained by isocyanate thickening has poor moldability. This is presumed to be because isocyanate thickening aims to increase viscosity by polymerization through the introduction of urethane bonds by the reaction of hydroxyl groups contained in vinyl ester resins with isocyanate, and the urethane bonds have strong cohesive energy, and localized aggregates called hard domains are formed by intermolecular forces (hydrogen bonds) between the urethane bonds, which are hard segments. Furthermore, a technique is known in which carboxyl groups are introduced into the hydroxyl groups of vinyl ester resins, followed by metal thickening using metal oxides such as magnesium oxide. However, when carboxyl groups are introduced into the hydroxyl groups of vinyl ester resins that have epoxy groups, the carboxyl groups react with the epoxy groups, preventing the introduction of carboxyl groups, and thus the metal thickening technique cannot be utilized. In addition, repeated reactions between carboxyl groups and epoxy groups increase the molecular weight, resulting in high viscosity. Moreover, the reaction between epoxy groups and carboxyl groups reduces the number of epoxy groups, making it impossible to obtain a resin composition with good adhesion to carbon fibers for epoxy resins, which are commonly used as reinforcing fibers. On the other hand, as described above, this disclosure involves hydrolyzing a thickener, which is at least one selected from the group consisting of oxides and hydroxides of Group 2 elements, under acidic conditions in a resin composition to coordinate the hydroxyl groups of component (A) and some ester groups to the ions of the Group 2 elements, thereby increasing the viscosity. Since this is not an isocyanate thickening method, it exhibits excellent moldability.Furthermore, since this disclosure is not a conventional metal thickening method that introduces carboxyl groups to hydroxyl groups of vinyl ester resins, as described above, it is possible to avoid the reaction in which carboxyl groups react with epoxy groups, and to obtain a resin composition that exhibits the effects of the epoxy groups in component (A) and has good adhesion to carbon fibers for epoxy resins, which are commonly used as reinforcing fibers.

[0061] <Component (E)> Component (E) is an epoxy curing agent. By combining component (E) with component (A), a composition that can be cured in a short time can be obtained. In addition, the curing of the epoxy groups contained in component (A) proceeds in parallel, further improving the physical properties.

[0062] Component (E) can be any epoxy resin curing agent that reacts with component (A) to produce a three-dimensional cured product, and is not particularly limited, but examples include phenolic curing agents, esteric curing agents, benzoxazine curing agents, acid anhydride curing agents, primary to tertiary amine curing agents, mercaptan curing agents, amide curing agents, blocked isocyanate curing agents, imidazole curing agents, active ester compounds, and latent curing agents.

[0063] In this disclosure, "latent curing agent" refers to an agent that does not react with functional groups such as epoxy groups under normal storage conditions (room temperature, under visible light, etc.) of a liquid resin composition, but exhibits reactive activity towards functional groups when exposed to heat or light, thereby curing the liquid resin composition.

[0064] These may be used individually or in combination of two or more. From the viewpoint of curing properties, they may be imidazole-based curing agents, blocked isocyanate-based curing agents, and latent curing agents; from the viewpoint of versatility, they may be imidazole-based curing agents and blocked isocyanate-based curing agents; and from the viewpoint of low temperature and rapid curing, they may be imidazole-based curing agents.

[0065] <Component (F)> Component (F) is a radical curing agent. Component (F) is not particularly limited as long as it is used as a radical curing agent for component (A). From the viewpoint of stability after mixing with component (A), the 10-hour half-life temperature of component (F) may be 60 to 180°C, 90 to 175°C, or 100 to 160°C.

[0066] (F) Examples of component F include diacyl peroxides such as benzoyl peroxide, peroxyesters such as t-butyl peroxybenzoate, hydroperoxides such as cumene hydroperoxide, dialkyl peroxides such as dicumyl peroxide, ketone peroxides such as methyl ethyl ketone peroxide and acetylacetone peroxide, peroxyketals such as 1,1-di(t-butylperoxy)cyclohexane, alkyl peresters, and parkerbonate organic peroxides. From the viewpoint of curability, peroxyester organic peroxides, hydroperoxide organic peroxides, dialkyl peroxide organic peroxides, and peroxyketal organic peroxides may be used, and from the viewpoint of storage stability of SMC, peroxyester organic peroxides and peroxyketal organic peroxides may be used. From the viewpoint of low synergistic effect with metal-containing compounds and better storage stability of SMC, peroxyketal organic peroxides may be used. It may be one or more selected from the group consisting of t-butyl peroxybenzoate, t-butyl peroxy-2-ethylhexanoate, 1,1-di(t-butyl peroxy)cyclohexane, 1,1-di(t-amyl peroxy)cyclohexane, t-amyl peroxy-2-ethylhexanoate, 1,1-di(t-hexyl peroxy)cyclohexane, and cumyl hydroperoxide. From the viewpoint of ease of storage, it may be t-butyl peroxybenzoate, 1,1-di(t-butyl peroxy)cyclohexane, 1,1-di(t-amyl peroxy)cyclohexane, or 1,1-di(t-hexyl peroxy)cyclohexane. From the viewpoint of storage stability of SMC, it may be 1,1-di(t-butyl peroxy)cyclohexane, 1,1-di(t-amyl peroxy)cyclohexane, or 1,1-di(t-hexyl peroxy)cyclohexane.

[0067] <Other Components> Other components may include, for example, catalysts, polymerization inhibitors, stabilizers, thixotropes, curing retarders, curing accelerators, photopolymerization initiators, surfactants, interface modifiers, wetting and dispersing agents, defoamers, leveling agents, coupling agents, light stabilizers, waxes, flame retardants, fillers, plasticizers, internal release agents, low-shrinkage agents, toners, viscosity reducers, separation inhibitors, compatibilizers, and other additives. The amount of these additives is not particularly limited as long as it does not hinder the effects of the present invention.

[0068] Polymerization inhibitors that have the effect of suppressing the progress of the polymerization reaction of the resin composition can be known, such as hydroquinone, methylhydroquinone, phenothiazine, catechol, 4-t-butylcatechol, and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl. These may be used individually or in combination of two or more. From the viewpoint of suppressing the progress of the reaction, hydroquinone, methylhydroquinone, catechol, or 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl may be used. From the viewpoint of ease of controlling curability, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl may be used.

[0069] [Composition of Resin Composition] The resin composition of this disclosure comprises component (A), component (B), component (C), and component (D), and may also contain other components, including other components described later. However, from the viewpoint of obtaining the effects of the present invention well, the total content of component (A), component (B), component (C), and component (D) in the resin composition is preferably 50 to 100% by mass, more preferably 65 to 100% by mass, and even more preferably 80 to 100% by mass.

[0070] The content of component (A) in the resin composition of this disclosure may be 20 to 95 parts by mass, 35 to 90 parts by mass, or 45 to 85 parts by mass per 100 parts by mass of the total of components (A) and (B). If the content of component (A) is 20 parts by mass or more per 100 parts by mass of the total of components (A) and (B), component (A) can easily increase the viscosity of the resin composition to a moderate degree. If the content of component (A) is 95 parts by mass or less per 100 parts by mass of the total of components (A) and (B), it can be easily impregnated into the fiber substrate. In this disclosure, the term "solids" refers to components in the resin composition other than volatile substances such as water and solvents. That is, the solids include liquid, syrup-like, or wax-like substances at room temperature around 25°C, and do not necessarily mean solids.

[0071] The content of component (B) in the resin composition of this disclosure may be 5 to 85 parts by mass, 10 to 65 parts by mass, or 15 to 55 parts by mass, based on 100 parts by mass of the total of components (A) and (B). If the content of component (B) is 5 parts by mass or more based on 100 parts by mass of the total of components (A) and (B), the viscosity of the resin composition after 1 hour is easily reduced and it becomes easier to impregnate the fibrous substrate. If the content of component (B) is 85 parts by mass or less based on 100 parts by mass of the total of components (A) and (B), the resin composition will have better viscosity-enhancing properties.

[0072] The content of component (C) in the resin composition of this disclosure may be more than 0.5 parts by mass and 6.0 parts by mass or less, 1.0 to 5.0 parts by mass, or 1.5 to 4.0 parts by mass, based on 100 parts by mass of the total of components (A) and (B). The content of component (C) in the resin composition of this disclosure may be such that, in the manufacturing process of the resin composition of this disclosure, after adding component (C) to components (A) and (B) and before adding component (D), the acid value of the mixture (a mixture of components (A), (B), and (C)) is 2.5 to 26.0 KOH mg / g, 3.0 to 22.0 KOH mg / g, or 5.0 to 18.0 KOH mg / g. If the content of component (C) is greater than 0.5 parts by mass relative to 100 parts by mass of the total of components (A) and (B), the viscosity of the resin composition after 1 hour is easily reduced and it becomes easier to impregnate the fiber substrate. Furthermore, the viscosity after 24 hours is easily increased, resulting in a resin composition with better viscosity-enhancing properties. The same effect is obtained when the content of component (C) is such that the acid value is 2.5 KOH mg / g or more. If the content of component (C) is 6.0 parts by mass or less relative to 100 parts by mass of the total of components (A) and (B), the resin composition with better viscosity-enhancing properties is obtained. The same effect is obtained when the content of component (C) is such that the acid value is 26.0 KOH mg / g or less.

[0073] The content of component (D) in the resin composition of this disclosure may be more than 0.5 parts by mass and 6 parts by mass or less, 0.6 to 2.5 parts by mass, or 0.7 to 1.7 parts by mass, based on 100 parts by mass of the total of components (A) and (B). If the metal component content of component (D) is 0.5 parts by mass or more based on 100 parts by mass of the total of components (A) and (B), the viscosity of the resin composition will be better. If the metal component content of component (D) is 6 parts by mass or less based on 100 parts by mass of the total of components (A) and (B), excessive viscosity of the resin composition will be easier to suppress. Here, the content of component (D) in terms of metal component means the mass content of the metal element contained in component (D).

[0074] If the resin composition of this disclosure contains component (E), the content of compound (E) in the resin composition may be 0.5 to 20 parts by mass, 1 to 15 parts by mass, or 2 to 10 parts by mass, based on 100 parts by mass of the total of components (A) and (B). When the content of component (E) is within the above range, a composition that can be sufficiently cured in a short time can be obtained, and the strength of the cured product is also good. Component (E) may be an N-methylpyrrolidone solution or an ethanol solution, but it is sufficient that the content of solids is within the above range.

[0075] If the resin composition of this disclosure contains component (F), the content of compound (F) in the resin composition may be 0.3 to 5 parts by mass, 0.5 to 4 parts by mass, or 0.8 to 3 parts by mass, based on 100 parts by mass of the total of components (A) and (B). When the content of component (F) is within the above range, a composition that can be sufficiently cured in a short time can be obtained, and the strength of the cured product is also good.

[0076] [Method for producing the resin composition] The method for producing the resin composition of this disclosure is not particularly limited, and the resin composition can be produced by mixing components (A) to (D). In addition, any components other than components (A) to (D), such as component (E), component (F), and the aforementioned other components, may be mixed.

[0077] The mixing method is not particularly limited and can be carried out using, for example, a disper, planetary mixer, kneader, etc. The mixing temperature is preferably 10 to 50°C, more preferably 15 to 40°C, and even more preferably 20 to 30°C from the viewpoint of ease of mixing.

[0078] Furthermore, in order to facilitate the uniform mixing of each component and to adjust the viscosity, component (A) may be pre-diluted with at least one of the solvent and the reactive diluent.

[0079] [Method for curing the resin composition] Any method that can heat the resin composition to the temperature required for curing is acceptable, for example, a heating furnace or heater can be used. The resin composition of this embodiment can usually be molded at a relatively low temperature in a short time, from a few minutes to several tens of minutes. The curing temperature can be, for example, 20 to 120°C. The heating time can be appropriately selected depending on the curing temperature, for example, between 1 to 40 minutes or 1 to 30 minutes. As long as curing is possible, the curing conditions are not particularly limited as long as the resin composition does not denature or decompose, and there is no particular problem even if the temperature is lower than the above range or if the time is long.

[0080] [Composite Material] The composite material of this disclosure includes the resin composition described above and a fiber base material (G). Specifically, examples of composite materials include UD tape, prepregs such as woven fabrics, sheet molding compound (SMC), UD cut sheets, preforms, etc., which can be suitably used in the manufacture of various molded products and the construction of structures. In this embodiment, prepregs or SMC are particularly preferred as the composite material. SMC is a sheet-like material in which a fiber base material cut into pieces of several centimeters is dispersed in a resin composition.

[0081] <Component (G)> Component (G) is a fibrous base material, and from the viewpoint of mechanical strength, for example, synthetic fibers such as polyamide (nylon), aramid fiber, vinylon, polyethylene fiber, polyester, and phenolic resin, as well as so-called reinforcing fibers such as carbon fiber, glass fiber, metal fiber, and ceramic fiber, and composite fibers thereof. These may be used individually or in combination of two or more types. Aramid fiber, carbon fiber, and glass fiber may also be used, and from the viewpoint of strength, hardness, availability, price, etc., carbon fiber or glass fiber may be used.

[0082] Any carbon fiber manufactured using various methods can be used. For example, pitch-based, PAN (polyacrylonitrile)-based, and vapor-deposited carbon fibers can be used. Any glass fiber manufactured using various methods can be used. For example, glass fibers such as E-glass, T-glass, and NE-glass can be used. The glass fibers may be long or short fibers, and are appropriately selected depending on the fiber substrate.

[0083] Examples of the form of component (G) include sheets, chopped strands, chops, milled fibers, etc. Examples of sheets include those formed by aligning multiple reinforcing fibers in one direction, two-way woven fabrics such as plain weave and twill weave, multi-axial woven fabrics, non-crimped woven fabrics, nonwoven fabrics, mats, knits, braids, paper made from reinforcing fibers, etc. The fiber base material (G) may be used alone or in combination of two or more types.

[0084] (G) If component is a sheet, it may be a single layer or multiple layers laminated together. From the viewpoint of impregnation of the resin composition, the thickness of the sheet may be, for example, 0.01 to 5 mm in the case of a single layer, and in the case of multiple layers laminated together, the total thickness may be 1 to 20 mm or 1 to 15 mm.

[0085] The fiber base material (G) content in the composite material of this disclosure may be 10 to 70%, 20 to 70%, or 35 to 65% in terms of fiber volume content (Vf), from the viewpoint of moldability, ease of handling, and mechanical strength of the composite material. From the same viewpoint, it may be 20 to 80% by mass, 30 to 80% by mass, or 45 to 75% by mass, based on 100% by mass of the composite material. The resin composition content in the composite material of this disclosure may be 30 to 90%, 30 to 80%, or 35 to 65% in terms of fiber volume content (Vf), from the viewpoint of moldability, ease of handling, and mechanical strength of the composite material. From the same viewpoint, it may be 20 to 80% by mass, 20 to 70% by mass, or 25 to 55% by mass, based on 100% by mass of the composite material.

[0086] Furthermore, when impregnating a fiber substrate with a resin composition, the resin composition may be used as a mixture to which additives such as fillers (e.g., calcium carbonate, aluminum hydroxide), low-shrinkage agents (e.g., polystyrene), viscosity reducers, and colorants have been added. In this case, these additives may also be included in the composite material.

[0087] [Method for Manufacturing Composite Materials] The method for manufacturing the composite materials of this disclosure is not particularly limited and can be obtained by mixing the above-described resin composition and component (G) by a known method. In particular, the method for manufacturing the composite materials of this disclosure is one in which the resin composition is impregnated into component (G).

[0088] [Method for molding composite materials] Examples of methods for molding composite materials according to this disclosure include the hand lay-up method, the spray-up method, the autoclave molding method, the resin transfer molding method (RTM method), the vacuum-assisted resin transfer molding method (VaRTM method), the injection molding method, the infusion molding method, the press molding method, the press molding method using prepreg or sheet molding compound (SMC), the filament winding method, the tape or sheet winding method, and the pultrusion method. When the composite material is a prepreg or SMC, at least one method selected from the group consisting of the autoclave molding method, the injection molding method, the press molding method, the press molding method using prepreg or sheet molding compound (SMC), and the tape or sheet winding method is preferred.

[0089] The resin composition disclosed herein hardens quickly at low temperatures, and from the viewpoint of obtaining molded products with high hardness, it may be manufactured using hand lay-up, RTM, pultrusion, press molding, or press molding using prepreg or sheet molding compound (SMC). From the viewpoint of rapid hardening, it may be manufactured using pultrusion, press molding, or press molding using prepreg or sheet molding compound (SMC). From the viewpoint of ease of introduction of the molding method, it may also be manufactured using press molding.

[0090] In press molding using sheet molding compound (SMC), first, a resin composition is applied to a carrier film moving at a constant speed, and short fibers, which are chopped from continuous fibers by a rotary cutter, are randomly deposited on the coated lower carrier film. Then, the upper carrier film coated with the resin composition is placed over the chopped fibers with the resin side down and sent to a series of pressure rollers, where the air inside is pushed out of the sheet and the resin paste is impregnated into the fibers, forming a sheet molding compound.

[0091] [Cured product] The cured product of the present disclosure is obtained by radical polymerization of the composite material of the present disclosure by heating under appropriate pressure or atmospheric pressure after molding it into a desired shape.

[0092] The mechanical strength required for cured composite materials varies depending on the intended use. For example, in the case of fiber-reinforced plastics (CFRP) using carbon fiber substrates, the flexural strength of CFRP is generally around 200 to 3000 MPa. The flexural modulus of CFRP is also generally around 5 to 150 GPa. The above values ​​for flexural strength and flexural modulus are measured values ​​in accordance with JIS K7171:2016.

[0093] Next, specific embodiments of the present invention will be described, but the present invention is not particularly limited to those embodiments.

[0094] [Synthesis Example 1] Using the raw materials and mixing ratios shown in Table 1, component (A), specifically (A-1), was synthesized as follows. <Synthesis of Component (A)> 1679.6 g of epoxy compound (a-1) was placed in a 3 L four-neck separable flask equipped with a stirrer, reflux condenser, gas inlet tube, and thermometer, and heated to 110°C. Next, 0.59 g of methyl hydroquinone ("MH", manufactured by Seiko Chemical Co., Ltd.) as a polymerization inhibitor (0.03 parts by mass per 100 parts by mass of the total of (a-1) and (a-2)), 0.11 g of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl ("Polystop 7300P", manufactured by Hakuto Co., Ltd.) (0.005 parts by mass per 100 parts by mass of the total of (a-1) and (a-2)), and benzyltriphenylphosphonium chloride as an esterification catalyst ( 1.58 g of "TPP-ZC" (manufactured by Hokko Chemical Industry Co., Ltd.) (0.08 parts by mass per 100 parts by mass total of (a-1) and (a-2)) and 293 g of methacrylic acid (a-2) as an unsaturated monobasic acid (a-2) (0.5 equivalents of methacrylic acid groups per 1 equivalent of total epoxy groups of epoxy compound (a-1)) were added dropwise over approximately 30 minutes. The mixture was then heated to 125°C and reacted for approximately 2 hours. The reaction was terminated when the acid value fell below 1 KOH mg / g to obtain component (A), which is (A-1).

[0095] <Acid Value of Component (A)> The acid value was measured in accordance with JIS K6901:2008 "Partial Acid Value (Indicator Titration Method)". The mass of potassium hydroxide required to neutralize the acid component contained in component (A) was measured, and the acid value was determined. Specifically, a mixture was prepared by diluting component (A) obtained in the above synthesis example with styrene, which is an ethylenically unsaturated group-containing monomer (B), so that the content of component (A) was 65% by mass. The mass of potassium hydroxide required to neutralize the acid component contained in this mixture was measured. The acid value of component (A) was then calculated based on this measurement. An "Autoburette UCB-2000" (manufactured by Hiranuma Sangyo Co., Ltd.) was used as the titrator, and a mixed indicator of bromothymol blue and phenol red was used as the indicator. The acid value of (A-1) was 0.3 KOH mg / g. Although component (A) synthesized by the method described in the above synthesis example contains polymerization inhibitors and esterification catalysts, these are not acidic components and therefore do not affect the acid value of component (A).

[0096] <Molecular weight of component (A)> The weight-average molecular weight Mw and number-average molecular weight Mn were measured by GPC under the following measurement conditions. The weight-average molecular weight Mw of (A-1) was 1137 and the number-average molecular weight Mn was 741. (Measurement conditions) ・Apparatus: "Showdex® GPC-101" (manufactured by Resonac Co., Ltd.) ・Column: "Showdex® LF-804" (manufactured by Resonac Co., Ltd.) ・Detector: Differential refractometer "Showdex® RI-71S" (manufactured by Resonac Co., Ltd.) ・Column temperature: 40℃ ・Sample: 0.2 mass% tetrahydrofuran solution of vinyl ester resin ・Developing solvent: Tetrahydrofuran ・Flow rate: 1.0 mL / min ・Sample injection volume: 20 μL ・Standard sample: Polystyrene

[0097] <Epoxy equivalent of component (A)> The epoxy equivalent was measured in accordance with the hydrochloric acid method. Measurements were taken with N=2 and the average value was used. The epoxy equivalent of (A-1) was 687.

[0098] <Preparation of the mixture> 2267 g of (A-1) was cooled as component (A), and when the temperature reached 110°C or below, 1063 g of styrene (component (B)) was added to obtain (mixture-1), which is a mixture of 65% by mass of component (A) (based on the total mass of the blended components) and 35% by mass of component (B).

[0099] [Synthesis Examples 2-10] Component (A), consisting of (A-2) to (A-10), was synthesized in the same manner as in Synthesis Example 1, except that the amounts of (a-1) and (a-2) used were as shown in Table 1. The acid value of (A-2) to (A-10) was measured in the same manner as in Synthesis Example 1. The measurement results are shown in the "Acid Value" column of Tables 2-6 and the "Acid Value of Component (A)" column of Table 7. The molecular weight of (A-6) to (A-10) was measured in the same manner as in Synthesis Example 1. The measurement results are shown in the "Molecular Weight of Component (A)" column of Table 7.

[0100] (Mixture-2) to (Mixture-10), which are mixtures of component (A) and component (B), were obtained in the same manner as in Synthesis Example 1, except that the amounts of component (B) and additives used were as shown in Table 1.

[0101]

[0102] [Example 1] <Preparation of Resin Composition> To the above (Mixture-1), 0.9 g of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (0.03 parts by mass per 100 parts by mass of the total of components (A) and (B)), 0.03 g of copper naphthenate, and 3 g of BYK-065 were added as additives. To the mixture with the additives added, 1.0 part by mass of benzoic acid (manufactured by Fushimi Pharmaceutical Co., Ltd.) was added as component (C), and the mixture was mixed for 1 minute at 2000 to 3000 rpm using a disperser (high-speed disperser "Homodisperser 2.5 type" manufactured by Primix Corporation). Then, 2.0 parts by mass of magnesium oxide (MgO content 1.0 part by mass) was added as component (D), and the mixture was mixed for 1 minute at 2500 to 3500 rpm using a disperser (high-speed disperser "Homodisperser 2.5 type" manufactured by Primix Corporation) to obtain resin composition (X-1).

[0103] <Acid Value After Adding Component (C)> During the preparation process of the resin composition, the acid value of the mixture after adding component (C) and before adding component (D) (a mixture of components (A), (B), and (C)) was determined using the same method as for the "Acid Value of Component (A)" described above. The measurement results are shown in the "Acid Value" column of Tables 2 to 7.

[0104] <Viscosity after Addition of Additives> During the preparation process of the resin composition described above, the viscosity of the mixture after the addition of the additive and before the addition of component (C) was measured. For the viscosity test, 300g of the mixture before the addition of component (C) was placed in a 300ml container immediately after preparation, and the mixture was stored in a sealed container during curing. The viscosity was measured at a temperature of 25°C using the following equipment. The measurement results are shown in the "Viscosity (25°C)" column of Table 2. "RB80 Viscometer" (manufactured by Toki Sangyo Co., Ltd.; rotor No. 2-4) Rotor No. 2: Rotation speed [rpm] 60, upper limit of measurement [dPa·s] 5 Rotor No. 3: Rotation speed [rpm] 60, upper limit of measurement [dPa·s] 20 Rotor No. 4: Rotation speed [rpm] 60, upper limit of measurement [dPa·s] 100 Rotor No. 4: Rotational speed [rpm] 30, upper measurement limit [dPa·s] 200

[0105] <Thickening Properties of Resin Composition> The thickening properties of the obtained resin composition (X-1) were measured. For the thickening properties test, 300g of the resin composition was placed in a 300ml container immediately after preparation, and the test was performed while storing it in a sealed container during curing. For the first 24 hours, the resin was cured in a 40°C environment, and the viscosity was measured at a resin temperature of 40°C. After 24 hours, the resin was cured in a 23°C environment, and measurements were continued. After 48 hours, the viscosity was measured at a resin temperature of 23°C. For viscosity measurement, the following two types of instruments were appropriately selected according to the viscosity range, and measurements were taken at a temperature of 23°C or 40°C. The measurement results and calculation results are shown in the "Thickening Properties" column of Table 2. (1) "RB80 type viscometer" (manufactured by Toki Sangyo Co., Ltd.; rotor No. 2-4) Rotor No. 2: rotation speed [rpm] 60, upper limit of measurement [dPa・s] 5 Rotor No. 3: Rotational speed [rpm] 60, upper limit of measurement [dPa·s] 20, Rotor No. 4: Rotation speed [rpm] 60, measurement limit [dPa·s] 100 (2) "HBDVE type viscometer" (manufactured by Eiko Seiki Co., Ltd.; T-bar spindle T-A to T-F, rotation speed: 1 rpm) T-bar spindle T-A: Measurement limit [dPa·s] 16,000 T-bar spindle T-B: Measurement limit [dPa·s] 32,000 T-bar spindle T-C: Measurement limit [dPa·s] 80,000 T-bar spindle T-D: Measurement limit [dPa·s] 160,000 T-bar spindle T-E: Measurement limit [dPa·s] 400,000 T-bar spindle T-F: Measurement limit [dPa·s] 800,000

[0106] [Example 2-16, Comparative Example 1-4] Resin compositions (X-2) to (X-16) and (X'-1) to (X'-4) were obtained in the same manner as in Example 1, except that the amounts of components (C) and (D) were as shown in Tables 2 to 5. The viscosity of each obtained resin composition was measured in the same manner as in Example 1. The measurement results are shown in the "Viscosity" column of Tables 2 to 7 below.

[0107] [Example 17] A resin composition (X-17) was obtained in the same manner as in Example 1, except that (Mixture-2) was used as a mixture of component (A) and component (B), and the amounts of component (C) and component (D) were as shown in Table 6. The viscosity of the obtained resin composition was measured in the same manner as in Example 1. The measurement results are shown in the "Viscosity" column of Table 6 below.

[0108] [Example 18] A resin composition (X-18) was obtained in the same manner as in Example 1, except that (Mixture-3) was used as a mixture of component (A) and component (B), and the amounts of component (C) and component (D) were as shown in Table 6. The viscosity of the obtained resin composition was measured in the same manner as in Example 1. The measurement results are shown in the "Viscosity" column of Table 6 below.

[0109] [Example 19] A resin composition (X-19) was obtained in the same manner as in Example 1, except that (Mixture-4) was used as a mixture of component (A) and component (B), and the amounts of component (C) and component (D) were as shown in Table 6. The viscosity of the obtained resin composition was measured in the same manner as in Example 1. The measurement results are shown in the "Viscosity" column of Table 6 below.

[0110] [Example 20] A resin composition (X-20) was obtained in the same manner as in Example 1, except that (Mixture-5) was used as a mixture of component (A) and component (B), and the amounts of component (C) and component (D) were as shown in Table 6. The viscosity of the obtained resin composition was measured in the same manner as in Example 1. The measurement results are shown in the "Viscosity" column of Table 6 below.

[0111] Table 2 (Examples 1 to 6, Comparative Examples 1 to 3) shows the results of changing the amount of benzoic acid, component (C), added. The mixture was cured at 40°C for the first 24 hours, and viscosity was measured at a resin temperature of 40°C. After 24 hours, it was cured at 23°C, and measurements were continued. After 48 hours, viscosity was measured at a resin temperature of 23°C. Table 3 (Examples 8 to 12, Comparative Example 4) shows the results of changing the amount of thickener, component (D), added. The mixture was cured at 40°C for the first 24 hours, and viscosity was measured at a resin temperature of 40°C. After 24 hours, it was cured at 23°C, and measurements were continued. After 48 hours, viscosity was measured at a resin temperature of 23°C. Table 4 (Examples 13 and 14) shows the results of curing at a constant temperature of 23°C and measuring viscosity, with Example 13 using the same formulation as Example 4 and Example 14 using the same formulation as Example 5. Table 5 (Examples 15 and 16) shows the results of viscosity measurements under the same conditions as Example 4 for Example 15 and Example 13 for Example 16, with component (C) being 2-methylbenzoic acid. Table 6 (Examples 17 to 20) shows the results of changing the monomer species of component (B).

[0112]

[0113]

[0114]

[0115]

[0116]

[0117] [Example 21] <Preparation of carbon fiber reinforced composite material> A resin composition (X-21) was obtained in the same manner as in Example 1, except that (mixture-6) was used as a mixture of component (A) and component (B), and the amounts of component (C) and (D) were as shown in Table 7. The viscosity of the obtained resin composition was measured in the same manner as in Example 1. The measurement results are shown in the "Viscousness" column of Table 7 below. Benzoic acid as component (C), 2-ethyl-4-methylimidazole (2E4MZ, 6.0 parts by mass per 100 parts by mass of the total resin composition) as an epoxy curing agent for component (E), 1,1-di(t-butylperoxy)cyclohexane (perhexa C, 1.0 part by mass per 100 parts by mass of the total resin composition) as an organic peroxide for component (F), and MD-504-2 (MgO) as a thickening agent containing component (D) were added to the obtained resin composition to obtain a mixture. A carbon fiber reinforced composite material was prepared using the above mixture and "TRK101M" (manufactured by Mitsubishi Chemical Corporation, TR50S 12L cross material plain weave = thickness 0.46 mm) as the carbon fiber of component (G) as follows.

[0118] <Preparation of Cured Products> Using the carbon fiber reinforced composite material described above, cured product samples were prepared by pressing before thickening and after thickening at 40°C for 48 hours. Specifically, seven layers of carbon fiber cloth sheets cut to 298 mm x 218 mm were laminated in the same direction, and a total of 80 g of resin composition was impregnated into each layer of the carbon fiber cloth sheets. These layers were then placed in a mold with an inner size of 300 mm x 220 mm. Spacer rings with a thickness of 3 mm were placed in the four corners of the mold, and the mold was pressed at a pressure of 7.4 MPa using a hydraulic molding machine (manufactured by Toho Press Manufacturing Co., Ltd.) and cured at 120°C for 5 minutes or 120°C for 10 minutes. The following physical properties were evaluated using the cured product sample before thickening and the cured product sample after thickening at 40°C for 48 hours. The measurement results are shown in the "CFRP Physical Properties" column of Table 7 below.

[0119] <Fiber Volume Content (Vf) and Fiber Content (Mass %)> The cured sample was cut into a rectangular parallelepiped measuring 15 mm x 15 mm x approximately 2.5 mm to prepare test specimens. The mass of the test specimens was measured, and the specimens were heated in a muffle furnace (Yamato Scientific Co., Ltd., "Muffle Furnace FO510") in a crucible in an air atmosphere at 350°C for 3 hours, followed by heating at 625°C for 10 minutes. Under these conditions, carbon fibers do not burn. After natural cooling, the mass of the residual carbon fibers was measured to evaluate the carbon fiber content (mass %) and fiber volume content per unit volume in the cured material. The density of the cured resin was 1.15 g / cm³. ３ The density of the carbon fiber is 1.81 g / cm³. ３ The test was conducted with N=2, and the average value was taken.

[0120] <Bending Properties> A hardened sample was cut to 140 mm in length and 15 mm in width according to JIS K 7074-1988 to prepare a test specimen. The thickness of the obtained test specimen was approximately 2.5 mm. The bending strength and bending modulus were measured using a universal material testing machine ("Tensilon UCT-1T", manufactured by Orientec Co., Ltd., support distance 100 mm, test speed 7 mm / min) under conditions of 23°C and 50% RH. The test was performed with N=5 and the average value was taken.

[0121] <Judgment> The judgment criteria for the "Judgment" column in Table 7 below are as follows: Thickening control: "○: Thickens. Easy to control." "△: Thickens. Difficult to control." "×: Does not thicken." Curing properties: "○ 5 min." "△ 10 min." "× 10 min or more." CFRP strength: "○ 500 or more." "△ 300 or more." "× Less than 300."

[0122] [Example 22] A resin composition (X-22) was obtained in the same manner as in Example 1, except that (Mixture-7) was used as a mixture of component (A) and component (B), and the blending amounts of component (C) and component (D) were as shown in Table 7. The viscosity of the obtained resin composition was measured in the same manner as in Example 1. The measurement results are shown in the "Viscosity" column of Table 7 below. Using the obtained resin composition, a carbon fiber reinforced composite material and a cured product were prepared in the same manner as in Example 21, and their physical properties were evaluated. The measurement results are shown in the "CFRP Physical Properties" column of Table 7 below.

[0123] [Example 23] A resin composition (X-23) was obtained in the same manner as in Example 1, except that (Mixture-8) was used as a mixture of component (A) and component (B), and the blending amounts of component (C) and component (D) were as shown in Table 7. The viscosity of the obtained resin composition was measured in the same manner as in Example 1. The measurement results are shown in the "Viscosity" column of Table 7 below. Using the obtained resin composition, a carbon fiber reinforced composite material and a cured product were prepared in the same manner as in Example 21, and their physical properties were evaluated. The measurement results are shown in the "CFRP Physical Properties" column of Table 7 below.

[0124] [Example 24] A resin composition (X-24) was obtained in the same manner as in Example 1, except that (Mixture-9) was used as a mixture of component (A) and component (B), and the blending amounts of component (C) and component (D) were as shown in Table 7. The viscosity of the obtained resin composition was measured in the same manner as in Example 1. The measurement results are shown in the "Viscosity" column of Table 7 below. Using the obtained resin composition, a carbon fiber reinforced composite material and a cured product were prepared in the same manner as in Example 21, and their physical properties were evaluated. The measurement results are shown in the "CFRP Physical Properties" column of Table 7 below.

[0125] [Example 25] A resin composition (X-25) was obtained in the same manner as in Example 1, except that (Mixture-10) was used as a mixture of component (A) and component (B), and the blending amounts of component (C) and component (D) were as shown in Table 7. The viscosity of the obtained resin composition was measured in the same manner as in Example 1. The measurement results are shown in the "Viscosity" column of Table 7 below. Using the obtained resin composition, a carbon fiber reinforced composite material and a cured product were prepared in the same manner as in Example 21, and their physical properties were evaluated. The measurement results are shown in the "CFRP Physical Properties" column of Table 7 below.

[0126]

[0127] The following provides a detailed explanation of each component listed in Tables 1 through 7.

[0128] <Epoxy Compound (a-1)> 1) Bisphenol A type epoxy resin; "jER (registered trademark) 834", manufactured by Mitsubishi Chemical Corporation, epoxy equivalent 247

[0129] <Unsaturated monobasic acid (a-2)> 2) Methacrylic acid (MAA), manufactured by Mitsubishi Chemical Corporation

[0130] <(B) Components> 3) Styrene monomer, manufactured by Idemitsu Kosan Co., Ltd. 10) Phenoxyethyl methacrylate (PO-MA in the table); "Light Ester PO", manufactured by Kyoeisha Chemical Co., Ltd. 11) Diallyl phthalate; "Daiso Dap (registered trademark) monomer", manufactured by Osaka Soda Co., Ltd. 12) p-tert-butylphenyl glycidyl ether, "Adekaglycirol ED-509E", manufactured by ADEKA Corporation

[0131] <Additives> 4) 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4H-TEMPO in the table), "Polystop 7300P", manufactured by Hakuto Co., Ltd. 5) Copper naphthenate, manufactured by Toei Chemical Co., Ltd., copper content 5% by mass (5% Cu in the table) 6) "BYK-065", manufactured by BYK

[0132] <(C) Ingredients> 7) Benzoic acid, manufactured by Fushimi Pharmaceutical Co., Ltd. 8) 2-Methylbenzoic acid, manufactured by Tokyo Chemical Industry Co., Ltd.

[0133] <(D) Ingredients> 9) "Magmicron MD-504-2", manufactured by Mikuni Pigment Co., Ltd., magnesium oxide content 50% by mass

[0134] <(E) Ingredient> 2-ethyl-4-methylimidazole; "2E4MZ", manufactured by Shikoku Chemicals Holdings Co., Ltd.

[0135] <(F) Ingredient> 1,1-di(t-butylperoxy)cyclohexane; "Perhexa C", manufactured by NOF Corporation

[0136] As shown in Tables 2 to 7, the resin composition of the present invention exhibits excellent viscosity-enhancing properties. As shown in Table 7, the cured product of the present invention is easy to control in terms of viscosity. As shown in Table 7, the cured product of the present invention exhibits excellent curability. As shown in Table 7, the cured product of the present invention exhibits excellent CFRP strength.

[0137] The resin composition of the present invention is not particularly limited, but is suitable, for example, as a matrix resin for SMC and prepreg.

Claims

1. A resin composition comprising: a vinyl ester resin (A) having an epoxy group and having an acid value of less than 1 KOH mg / g; at least one monomer (B) selected from radical polymerizable monomers and epoxy monomers; at least one (C) selected from benzoic acid and benzoic acid derivatives; and a thickening component (D), wherein the content ratio of component (C) to component (D) in the resin composition ([at least one selected from benzoic acid and benzoic acid derivatives] / [thickening component]) is greater than 0.5 and less than or equal to 6.0 by mass ratio.

2. The resin composition according to claim 1, wherein (A) is a reaction product of an epoxy compound (a-1) having two or more epoxy groups in one molecule and an unsaturated monobasic acid (a-2), and the total amount of carboxyl groups of (a-2) is 0.8 equivalents or less per 1 equivalent of the total amount of epoxy groups of (a-1).

3. The resin composition according to claim 1, wherein the thickening component (D) is at least one selected from the group consisting of oxides and hydroxides of Group 2 elements.

4. The resin composition according to claim 1, further comprising an epoxy curing agent (E).

5. The resin composition according to claim 4, wherein the epoxy curing agent (E) is at least one selected from the group consisting of phenolic curing agents, esteric curing agents, benzoxazine curing agents, acid anhydride curing agents, primary to tertiary amine curing agents, mercaptan curing agents, amide curing agents, blocked isocyanate curing agents, imidazole curing agents, active ester compounds, and latent curing agents.

6. The resin composition according to claim 1, further comprising a radical curing agent (F).

7. The resin composition according to claim 6, wherein the radical curing agent (F) is at least one selected from the group consisting of peroxyester-based organic peroxides, hydroperoxide-based organic peroxides, dialkylperoxide-based organic peroxides, and peroxyketal-based organic peroxides.

8. A composite material comprising the resin composition according to claim 1 and a fibrous substrate (G).

9. The composite material according to claim 8, wherein the fibrous base material (G) is at least one selected from carbon fibers and glass fibers.

10. A cured product of the composite material according to claim 8.

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