Epoxy resin, curable resin composition, cured product thereof, and carbon fiber-reinforced composite material

Abstract

Provided are an epoxy resin having excellent heat resistance, a curable resin composition, a cured product thereof, and a carbon fiber-reinforced composite material. This epoxy resin is represented by formula (1), and in a chromatogram of high performance liquid chromatography, when a is the peak area of a compound represented by formula (2) and b is the peak area of a compound represented by formula (3), b / a is 0.012-0.050. (In formula (1), n is the average value of the number of repetitions, which represents 1 lt; nlt; 15 is a real number. Each X independently represents a monovalent group represented by formula (a) or formula (b), and at least one is a monovalent group represented by formula (a); and * represents a bond to an oxygen atom).

Description

TECHNICAL FIELD

[0001] The present application relates to an epoxy resin, a curable resin composition, and a cured product of these, and a carbon fiber-reinforced composite material. BACKGROUND

[0002] Epoxy resins are utilized in a wide range of fields such as adhesives, paints, laminated boards, molding materials, casting materials, and the like, by being cured with various curing agents to become cured products having excellent mechanical properties, water resistance, chemical resistance, heat resistance, electrical properties, and the like. Carbon fiber-reinforced composites (CFRPs) in which an epoxy resin and a curing agent are impregnated into a reinforcing fiber and cured as a matrix resin are increasingly in demand in recent years because they can impart characteristics such as lightweight and high strength, and are thus widely used in aircraft structural members, windmill blades, automobile outer panels, IC trays, laptop housings, and the like. In particular, the matrix resin is used in aircraft applications that take advantage of the lightweight and high strength of the molded body.

[0003] Cured products of thermosetting resins such as epoxy resins used as the matrix resin of CFRPs and the like are generally brittle, and when used as a structural material for aerospace applications, vehicles, and the like, require a high degree of mechanical strength. In order to compensate for the low flexural strength, toughness, adhesion, and the like of thermosetting resins, methods of adding a high-toughness thermoplastic resin to a thermosetting resin matrix are well known (Patent Documents 1 to 3). Specifically, the flexural strength and toughness of a prepreg are improved by combining particles of a thermoplastic resin such as a polyether sulfone, a polyether imide, a polyamide, or the like, with a thermosetting resin matrix resin.

[0004] In recent years, the required characteristics of CFRPs have become more stringent, and in particular, when used as a structural material for aerospace applications or vehicles and the like, a resin having even more excellent heat resistance is required (Patent Document 4).

[0005] [Patent Document]

[0006] [Patent Document]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 60-243113

[0008] [Patent Document 2] Japanese Patent Application Laid-Open (kokai) No. 09-100358

[0009] [Patent Document 3] Japanese Patent Application Laid-Open (kokai) No. 2013-155330

[0010] [Patent Document 4] Japanese Patent Application Laid-Open (kokai) No. 2010-275492

[0011] [Patent Document 5] Japanese Patent Application Laid-Open (kokai) No. 2007-211254. SUMMARY

[0012] [Problems to be Solved by the Invention]

[0013] An epoxy resin having low water absorption is described in Patent Literature 5. However, the epoxy resin described in Patent Literature 5 is difficult to use as a CFRP material because of low heat resistance.

[0014] The present application was completed in view of the above-described circumstances, and aims to provide an epoxy resin having excellent heat resistance, a curable resin composition, and a cured product of these, and a carbon fiber-reinforced composite material.

[0015] [Means for Solving the Problems]

[0016] That is, the present application is as shown in the following [1] to [6]. In addition, "(numerical value 1) to (numerical value 2)" in the present application indicates the inclusion of the upper and lower limits.

[0017] [1] An epoxy resin represented by the following formula (1), which, in a chromatogram of high performance liquid chromatography, when a peak area of a compound represented by the following formula (2) is set to a and a peak area of a compound represented by the following formula (3) is set to b, b / a is 0.012 or more and 0.050 or less.

[0018]

[0019] In formula (1), n is an average value of the number of repetitions, which represents a real number of 1 < n < 15; X is each independently a monovalent group represented by formula (a) or formula (b), at least one of which is a monovalent group represented by formula (a); and * is bonded to an oxygen atom.

[0020]

[0021]

[0022] [2] The epoxy resin according to the preceding [1], which has an epoxy equivalent of 200 g / eq. or more and 220 g / eq. or less.

[0023] [3] A curable resin composition containing the epoxy resin according to the preceding [1] or [2], and a curing agent.

[0024] [4] The curable resin composition according to the preceding [3], wherein the curing agent is an amine-based curing agent.

[0025] [5] A cured product obtained by curing the curable resin composition according to the preceding [3] or [4].

[0026] [6] A carbon fiber-reinforced composite material obtained by curing the curable resin composition according to the preceding [3] or [4].

[0027] [Effects of the Invention]

[0028] According to the present application, an epoxy resin, a curable resin composition, and a cured product thereof, and a carbon fiber-reinforced composite material, each of which has excellent heat resistance of a cured product, can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 HPLC chart for Synthesis Example 1.

[0030] Figure 2 HPLC chart for Synthesis Example 2.

[0031] Figure 3 HPLC chart for Synthesis Example 3.

[0032] Figure 4 HPLC chart for Synthesis Example 4.

[0033] Figure 5 HPLC chart for Synthesis Example 5.

[0034] Figure 6 HPLC chart for Synthesis Example 6.

[0035] Figure 7 HPLC chart for Synthesis Example 7. DETAILED DESCRIPTION

[0036] Hereinafter, an embodiment of the present application (hereinafter, also referred to as "the present embodiment") will be described in further detail.

[0037] The epoxy resin of the present application is represented by the following formula (1), and when the peak area of a compound represented by the following formula (2) is set as a, and the peak area of a compound represented by the following formula (3) is set as b in a chromatogram of high performance liquid chromatography, b / a is 0.012 or more and 0.050 or less.

[0038]

[0039] In formula (1), n is an average value of the number of repetitions, and represents a real number of 1 < n < 15; X is each independently a monovalent group represented by formula (a) or formula (b), at least one of which is a monovalent group represented by formula (a); and * is bonded to an oxygen atom.

[0040]

[0041]

[0042] In the aforementioned formula (1), the value of n is obtained from the number average molecular weight determined by gel permeation chromatography (GPC, detector: RI) of the epoxy resin, or is calculated from the area ratio of each peak after separation. n is more preferably a real number of 1 < n < 15, even more preferably 1 < n < 10, and particularly preferably 1 < n < 5.

[0043] In the epoxy resin of the present embodiment, by controlling the value of b / a, a hardened product having excellent heat resistance can be obtained. Specifically, b / a is preferably 0.012 or more and 0.050 or less, more preferably 0.014 or more and 0.040 or less, and even more preferably 0.015 or more and 0.030 or less. Although the reason why the heat resistance becomes good when b / a is 0.12 or more is not clear, it is considered that the molecules become less mobile due to the influence of hydrogen bonds because a certain amount of the compound represented by the aforementioned formula (3) is contained. When b / a is greater than 0.050, the compound represented by the aforementioned formula (3) becomes more, and the crosslinking points at the time of hardening become less, and thus the glass transition point (Tg) decreases. In the present embodiment, HPLC (high performance liquid chromatography) is determined by the method described in the Examples below.

[0044] The glass transition point (Tg) of the epoxy resin of the present embodiment is more preferably 170 to 300°C, even more preferably 172 to 250°C, and even more preferably 174 to 200°C. If the glass transition point does not reach 170°C, it is difficult to adapt to members required to have heat resistance such as an engine related member of an airplane, and the resin softens at the time of use, and the mechanical strength significantly decreases to cause breakage of the material, and thus is not preferable. In addition, the glass transition point of the epoxy resin is generally related to the crosslinking density, and if the crosslinking density becomes high, the glass transition point becomes high. That is, if the glass transition point exceeds 300°C, the crosslinking density becomes high, and the mechanical strength of the hardened product becomes brittle, and thus is not preferable. In addition, the glass transition point (Tg) of the present embodiment is determined by the method described in the Examples below.

[0045] The epoxy equivalent of the epoxy resin of the present embodiment is more preferably 200 g / eq. or more and 220 g / eq. or less, even more preferably 204 g / eq. or more and 218 g / eq. or less, and even more preferably 213 g / eq. or more and 218 g / eq. or less.

[0046] The epoxy resin represented by the aforementioned formula (1) can be obtained by the reaction of a phenol resin represented by the following formula (4) and an epihalohydrin.

[0047]

[0048] In formula (4), n is the average value of the number of repetitions, and represents a real number of 1 < n < 15.

[0049] The more preferable range of n in the aforementioned formula (4) is the same as that in the aforementioned formula (1).

[0050] The above-mentioned epichlorohydrin can be easily obtained on the market. The amount of the epichlorohydrin used is preferably 2.0 to 10 moles, more preferably 3.0 to 8.0 moles, and still more preferably 3.5 to 6.0 moles, relative to 1 mole of the hydroxyl group of the phenol resin represented by the formula (4). The epichlorohydrin that can be used in the present embodiment can be preferably exemplified by epichlorohydrin, α-methyl epichlorohydrin, β-methyl epichlorohydrin, epibromohydrin, and the like, and is particularly preferably epichlorohydrin, which is easily obtained industrially.

[0051] In the above reaction, an alkali metal hydroxide can be used as a catalyst for promoting the epoxidation step. The alkali metal hydroxide that can be used can be exemplified by sodium hydroxide, potassium hydroxide, and the like. A solid of the alkali metal hydroxide can also be used, and an aqueous solution of the alkali metal hydroxide can also be used. In the present embodiment, a solid of the alkali metal hydroxide shaped into a tablet is preferably used from the viewpoints of solubility and handleability. The amount of the alkali metal hydroxide used is preferably 0.90 to 1.5 moles, more preferably 0.95 to 1.25 moles, and still more preferably 0.99 to 1.15 moles, relative to 1 mole of the hydroxyl group of the phenol resin represented by the formula (4).

[0052] In addition, a quaternary ammonium salt such as tetramethylammonium chloride, tetramethylammonium bromide, trimethylbenzylammonium chloride, and the like can also be added as a catalyst for promoting the reaction. The amount of the quaternary ammonium salt used is preferably 0.1 to 15 g, and more preferably 0.2 to 10 g, relative to 1 mole of the hydroxyl group of the phenol resin represented by the formula (4).

[0053] The reaction temperature is preferably 30 to 90°C, and more preferably 35 to 80°C. In particular in the present embodiment, in order to perform epoxidation at a higher purity, the temperature is preferably 50°C or higher, and particularly preferably 60°C or higher. The reaction time is preferably 0.5 to 10 hours, more preferably 1 to 8 hours, and particularly preferably 1 to 3 hours. If the reaction time is short, the reaction is not completed, and if the reaction time is long, a by-product is formed, which is not preferred.

[0054] After washing the reaction product of the epoxidation reaction (mixture A containing the epoxy resin represented by the aforementioned formula (1)) with water, or without washing with water, the table halogen alcohol and solvent and the like are removed under heating and reduced pressure to obtain a mixture B containing the epoxy resin represented by the aforementioned formula (1). The mixture B contains the epoxy resin represented by the aforementioned formula (1) and a small amount of residual solvent and a by-product salt. In order to further form an epoxy resin having a small amount of hydrolyzable halogen, the mixture B can be dissolved in a ketone compound having a carbon number of 4 to 7 (e.g., methyl isobutyl ketone, methyl ethyl ketone, cyclopentanone, cyclohexanone, or the like) or an aromatic hydrocarbon compound having a carbon number of 6 to 10 (e.g., toluene, xylene, or the like) as a solvent, and an aqueous solution of an alkali metal hydroxide such as sodium hydroxide, potassium hydroxide, or the like is added to perform a reaction. In Patent Document 5, only the aqueous solution of the alkali metal hydroxide is added to perform a reaction, but in the present embodiment, water and / or alcohol is further added to the aqueous solution of the alkali metal hydroxide to perform a reaction. As a result, the compound represented by the aforementioned formula (3) is generated, and it is found that the heat resistance can be thus improved. The amount of the alkali metal hydroxide used is preferably 0.01 to 0.3 mol, and more preferably 0.05 to 0.2 mol, with respect to 1 mol of the hydroxyl group of the phenol resin represented by the aforementioned formula (4) used in the epoxidation. The amount of water used is 10 to 40% by weight, and preferably 15 to 25% by weight, with respect to the theoretical yield of the epoxy resin represented by the aforementioned formula (1). The alcohol can be exemplified by, for example, methanol, ethanol, propanol, isopropanol, or the like. The amount of alcohol used is 5 to 40% by weight, and preferably 15 to 25% by weight, with respect to the theoretical yield of the epoxy resin represented by the aforementioned formula (1). The total amount of water and alcohol used is 15 to 60% by weight, and preferably 20 to 50% by weight, with respect to the theoretical yield of the epoxy resin represented by the aforementioned formula (1). The reaction temperature is preferably 50 to 120°C, and the reaction time is more preferably 0.5 to 2 hours.

[0055] After the reaction is completed, the generated salt is removed by filtration, washing with water, or the like, and further, the solvent is distilled off under heating and reduced pressure, whereby the epoxy resin of the present embodiment can be obtained.

[0056] In the case of performing the reaction (condensation) of furfural and a phenol as a method for synthesizing the phenol resin represented by the aforementioned formula (4), the amount of the phenol is preferably 1.5 to 20 mol, and particularly preferably 3 to 10 mol, with respect to 1 mol of furfural.

[0057] As the phenol, in the case of a 2-substituted phenol, catechol, resorcinol, p-benzene diol can be exemplified, and in the case of a 1-substituted phenol, phenol, cresol, dimethyl phenol can be exemplified, and these can be used alone or in combination with two or more kinds.

[0058] The solvent used in the synthesis of the phenol resin can be exemplified by methanol, ethanol, propanol, isopropanol, toluene, xylene, etc., but is not limited thereto, and can be used alone or in combination of two or more. In the case of using the solvent, the amount used is preferably in the range of 5 to 500 parts by weight, and more preferably in the range of 10 to 300 parts by weight, with respect to 100 parts by weight of the phenol.

[0059] In the condensation reaction of the furfural and the phenol, an alkali catalyst is preferably used. An acid catalyst can also be used for the condensation, but the reaction of the furfural with each other also occurs, and the number of by-products increases. In addition, a method of using an organometallic compound as a catalyst is also available, but is disadvantageous in terms of cost. Specific examples of the alkali catalyst can be exemplified by alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide; alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide; alkali metal alkoxides such as sodium methoxide, sodium ethoxide, potassium methoxide, potassium ethoxide, and potassium tert-butoxide; alkaline earth metal alkoxides such as magnesium methoxide and magnesium ethoxide; and the like, but are not limited thereto, and can be used alone or in combination of two or more. The amount of the catalyst used is preferably in the range of 0.005 to 2.0 times the molar amount, and more preferably in the range of 0.01 to 1.1 times the molar amount, with respect to 1 mole of the hydroxyl group of the phenol.

[0060] The condensation reaction in the presence of these alkali catalysts is preferably performed in the range of 40 to 180°C, and particularly preferably in the range of 80 to 165°C. The time of the condensation reaction can be selected in the range of 0.5 to 10 hours. The reaction product thus obtained is neutralized in a manner to become neutral in the system, or is repeatedly washed with water in the presence of a solvent, and then water is separated and drained, after which the solvent and unreacted materials are removed under heating and reduced pressure, whereby the phenol resin represented by the aforementioned formula (4) is obtained.

[0061] The curable resin composition of the present embodiment contains a hardening agent. The hardening agent that can be used can be exemplified by, for example, amine-based hardening agents, acid anhydride-based hardening agents, amide-based hardening agents, and phenol-based hardening agents, etc.

[0062] In the curable resin composition of the present embodiment, in order to balance the resin viscosity of the curable resin composition and the heat resistance of the resin cured product, an amine-based hardener is preferable. Examples of the amine-based hardener include 3,3'-diamino diphenyl sulfone (3,3'-DDS), 4,4'-diamino diphenyl sulfone (4,4'-DDS), diamino diphenyl methane (DDM), 3,3'-diisopropyl-4,4'-diamino diphenyl methane, 3,3'-di-t-butyl-4,4'-diamino diphenyl methane, 3,3'-diethyl-5,5'-dimethyl-4,4'-diamino diphenyl methane, 3,3'-diisopropyl-5,5'-dimethyl-4,4'-diamino diphenyl methane, 3,3'-di-t-butyl-5,5'-dimethyl-4,4'-diamino diphenyl methane, 3,3',5,5'-tetraethyl-4,4'-diamino diphenyl methane (TEDDM), 3,3'-diisopropyl-5,5'-diethyl-4,4'-diamino diphenyl methane, 3,3'-di-t-butyl-5,5'-diethyl-4,4'-diamino diphenyl methane, 3,3',5,5'-tetraisopropyl-4,4'-diamino diphenyl methane, 3,3'-di-t-butyl-5,5'-diisopropyl-4,4'-diamino diphenyl methane, 3,3',5,5'-tetra-t-butyl-4,4'-diamino diphenyl methane, diamino diphenyl ether (DADPE), benzyl dimethyl aniline, 2-(dimethylaminomethyl)phenol (DMP-10), 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), 2-ethylhexanoate of 2,4,6-tris(dimethylaminomethyl)phenol, and the like. Further examples include aniline novolak, o-ethylaniline novolak, aniline resin obtained by the reaction of aniline and chlorinated xylene, aniline resin obtained by the polycondensation of aniline and a substituted biphenyl (4,4'-bis(chloromethyl)-1,1'-biphenyl and 4,4'-bis(methoxymethyl)-1,1'-biphenyl, etc.) or a substituted phenyl (1,4-bis(chloromethyl)benzene, 1,4-bis(methoxymethyl)benzene, and 1,4-bis(hydroxymethyl)benzene, etc.), and the like.

[0063] Examples of the acid anhydride-based hardener include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methyl nadic anhydride, hexahydrophthalic anhydride, and methylhexahydrophthalic anhydride, and the like.

[0064] Examples of the amide-based hardener include dicyandiamide, or a polyamide resin synthesized from the dimer of eleostearic acid and ethylenediamine, and the like.

[0065] The phenol-based hardening agent can include, for example, polyphenols (bisphenol A, bisphenol F, bisphenol S, fluorene bisphenol, terpene diol, 4,4'-dihydroxydiphenyl, 2,2'-dihydroxydiphenyl, 3,3',5,5'-tetramethyl-(1,1'-biphenyl)-4,4'-diol, p-benzene diol, m-benzene diol, naphthalene diol, para-(4-hydroxyphenyl)methane, and 1,1,2,2-tetra-(4-hydroxyphenyl)ethane); phenol resins obtained by condensation of phenols (e.g., phenol, alkyl-substituted phenol, naphthol, alkyl-substituted naphthol, dihydroxybenzene, and dihydroxynaphthalene) with aldehydes (formaldehyde, acetaldehyde, benzaldehyde, p-hydroxybenzaldehyde, o-hydroxybenzaldehyde, and furfural), ketones (p-hydroxyacetophenone and o-hydroxyacetophenone), or dienes (dicyclopentadiene and tricyclopentadiene); phenol resins obtained by condensation of the aforementioned phenols with substituted biphenyls (4,4'-bis(chloromethyl)-1,1'-biphenyl and 4,4'-bis(methoxymethyl)-1,1'-biphenyl), or substituted phenyls (1,4-bis(chloromethyl)benzene, 1,4-bis(methoxymethyl)benzene, and 1,4-bis(hydroxymethyl)benzene); modified products of the aforementioned phenols and / or the aforementioned phenol resins; halogenated phenols such as tetrabromobisphenol A and brominated phenol resins.

[0066] In the curable resin composition of the present embodiment, it is also preferable to use the phenol resin represented by the aforementioned formula (4) as the entirety or a portion of the hardening agent.

[0067] In the curable resin composition of the present embodiment, the amount of hardening agent used is preferably 0.7 to 1.2 equivalents per 1 equivalent of the epoxy groups of the epoxy resin. If the amount of hardening agent used is less than 0.7 equivalents per 1 equivalent of the epoxy groups, or more than 1.2 equivalents, the hardening will not be complete, and good hardening properties will not be obtained.

[0068] In the curable resin composition of the present embodiment, a hardening accelerator can also be added as needed. By using a hardening accelerator, the gelation time can be adjusted. Examples of hardening accelerators that can be used include imidazoles such as 2-methylimidazole, 2-ethylimidazole, and 2-ethyl-4-methylimidazole; tertiary amines such as 2-(dimethylaminomethyl)phenol and 1,8-diazabicyclo[5,4,0]undecene-7; phosphines such as triphenylphosphine; and metal compounds such as tin octoate. The hardening accelerator can be used in an amount of 0.01 to 5.0 parts by weight per 100 parts by weight of the epoxy resin, as needed.

[0069] The curable resin composition of the present embodiment can also incorporate other epoxy resins. Specific examples of epoxy resins that can be incorporated include: condensation polymers of phenols (phenol, alkyl-substituted phenol, aromatic-substituted phenol, naphthol, alkyl-substituted naphthol, dihydroxybenzene, alkyl-substituted dihydroxybenzene, dihydroxynaphthalene, etc.) and various aldehydes (formaldehyde, acetaldehyde, alkyl aldehyde, benzaldehyde, alkyl-substituted benzaldehyde, hydroxybenzaldehyde, naphthaldehyde, glutaraldehyde, phthaldehyde, crotonaldehyde, cinnamaldehyde, etc.), polymers of phenols and various diene compounds (dicyclopentadiene, terpene, vinylcyclohexene, norbornadiene, vinyl norbornene, tetrahydroindene, divinylbenzene, divinylbiphenyl, diisopropenylbiphenyl, butadiene, isoprene, etc.), condensation polymers of phenols and ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, phenylacetone, benzophenone, etc.), phenol resins obtained by condensation polymerization of phenols and substituted biphenyls (4,4'-bis(chloromethyl)-1,1'-biphenyl and 4,4'-bis(methoxymethyl)-1,1'-biphenyl, etc.) or substituted phenyls (1,4-bis(chloromethyl)benzene, 1,4-bis(methoxymethyl)benzene, and 1,4-bis(hydroxymethyl)benzene, etc.), condensation polymers of bisphenols and various aldehydes, epoxy propyl ether epoxy resins obtained by epoxy propylating alcohols, alicyclic epoxy resins represented by 4-vinyl-1-cyclohexene diepoxide and 3,4-epoxycyclohexylmethyl-3,4'-epoxycyclohexane carboxylate, epoxy propyl amine epoxy resins represented by tetra-epoxypropyl diamino diphenyl methane (TGDDM) and tri-epoxypropyl-p-aminophenol, epoxy propyl ester epoxy resins, and the like. The epoxy resins are not limited to these as long as they are generally used.

[0070] The curable resin composition of the present embodiment can incorporate known additives as needed. Specific examples of additives that can be used include: polybutadiene and modified products thereof, modified products of acrylonitrile copolymers, polyphenylene ether, polystyrene, polyethylene, polyimide, fluororesin, maleimide-based compounds, cyanate-based compounds, silicone gel, silicone oil, and inorganic fillers such as silica, alumina, calcium carbonate, quartz powder, aluminum powder, graphite, talc, clay, iron oxide, titanium oxide, aluminum nitride, asbestos, mica, glass powder, and surface treatment agents for fillers such as silane coupling agents, release agents, carbon black, phthalocyanine blue, phthalocyanine green, and colorants.

[0071] In the curable resin composition of the present embodiment, a known maleimide-based compound can be blended as needed. Specific examples of the maleimide-based compound that can be used include 4,4'-diphenylmethane bismaleimide, polyphenylmethane maleimide, m-phenylene bismaleimide, 2,2'-bis[4-(4-maleimidephenoxy)phenyl]propane, 3,3'-dimethyl-5,5'-diethyl-4,4'-diphenylmethane bismaleimide, 4-methyl-1,3-phenylene bismaleimide, 4,4'-diphenyl ether bismaleimide, 4,4'-diphenyl sulfone bismaleimide, 1,3-bis(3-maleimidephenoxy)benzene, 1,3-bis(4-maleimidephenoxy)benzene, biphenyl aralkyl type maleimide, and the like, but are not limited to these. These can be used alone or in combination of two or more. When a maleimide-based compound is blended, a hardening accelerator can be blended as needed, and the aforementioned hardening accelerator, or a radical polymerization initiator such as an organic peroxide, an azo compound, or the like can be used.

[0072] The curable resin composition of the present embodiment can be added with an organic solvent to form a varnish-like composition (hereinafter simply referred to as a varnish). The solvent used can include, for example, γ-butyrolactone, an amide-based solvent such as N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylimidazolidinone, a sulfone such as tetramethylene sulfone, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol, propylene glycol monomethyl ether, propylene glycol monomethyl ether monoacetate, propylene glycol monobutyl ether, a ketone-based solvent such as methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, an aromatic-based solvent such as toluene, xylene, and the like. The concentration of the solid content of the solvent in the obtained varnish after removal of the solvent is preferably in the range of 10 to 80% by weight, more preferably 20 to 70% by weight.

[0073] The curable resin composition of the present embodiment can also be used as a resin sheet, a prepreg, or a carbon fiber-reinforced composite material.

[0074] The curable resin composition of the present embodiment can also be applied to one or both sides of a support substrate and used as a resin sheet. Examples of the application method include casting, a method in which resin is extruded from a nozzle or a die by a pump or an extruder and the thickness is adjusted with a doctor blade, a method in which the thickness is adjusted by calendering with a roll, a method in which spraying is performed using a sprayer, and the like. In the step of forming the layer, the process can also be performed while heating within a temperature range in which thermal decomposition of the curable resin composition is avoided. In addition, calendering, grinding, and the like can also be performed as needed. Examples of the support substrate include a porous substrate composed of paper, cloth, nonwoven fabric, and the like, a plastic film or sheet such as polyethylene, polypropylene, polyethylene terephthalate, and polyester film, a mesh, a foam, a metal foil, a laminate of these, and the like, but are not limited to these. The thickness of the support substrate is not particularly limited and can be appropriately determined according to the intended use.

[0075] By heating and melting the curable resin composition and / or resin sheet of the present embodiment to reduce the viscosity and impregnate the fiber substrate, a prepreg of the present embodiment can be obtained.

[0076] In addition, a prepreg of the present embodiment can also be obtained by impregnating a curable resin composition in the form of a varnish into a fiber substrate and drying it by heating. After the prepreg is cut into a desired shape and stacked, the stack is subjected to pressure by press molding, autoclave molding, sheet winding molding, and the like, and the curable resin composition is heated and hardened, whereby a carbon fiber-reinforced composite material of the present embodiment can be obtained. In addition, a copper foil or an organic film can also be stacked during the stacking of the prepreg.

[0077] In addition, the carbon fiber-reinforced composite material of the present embodiment can also be formed by a known method other than the above-described methods. For example, a resin transfer molding technique (RTM method) can also be used, in which a carbon fiber substrate (generally, a carbon fiber fabric is used) is cut, stacked, and shaped to produce a preform (a preform before impregnation of resin), the preform is disposed in a molding die and the die is closed, resin is injected to impregnate the preform and hardened, the die is opened, and the formed product is removed.

[0078] In addition, a method such as a vacuum assisted resin transfer molding (VaRTM) method, a Seeman's Composite Resin Infusion Molding Process (SCRIMP) method, a Controlled Atmospheric Pressure Resin Infusion (CAPRI) method described in Japanese Patent Application Laid-Open No. 2005-527410, which is a method of exhausting a resin supply tank to a pressure lower than atmospheric pressure, using cyclic compression, and controlling net molding pressure, and the like, which is one of the RTM methods, can also be used. The resin infusion process is more appropriately controlled by the VaRTM method, in particular.

[0079] In addition, a film stacking method of sandwiching a fiber base material with a resin sheet (film), a method of adhering a powdered resin to a reinforcing fiber base material in order to improve impregnation, a forming method (Powder Impregnated Yarn) of using a flow layer or a fluid slurry method in a process of mixing a resin in a fiber base material, a method of mixing a resin fiber in a fiber base material can also be used.

[0080] The carbon fiber can include an acrylic, pitch, Rayon, and the like, and an acrylic carbon fiber having high tensile strength is preferable. The carbon fiber can be used as a twisted yarn, an untwisted yarn, and the like, but an untwisted yarn or a non-twisted yarn is preferable in order to balance the formability and strength characteristics of the fiber-reinforced composite material.

[0081] [Examples]

[0082] The present application is further specifically described by way of synthesis examples and examples. The materials, processing contents, processing procedures, and the like shown below can be appropriately changed without departing from the gist of the present application. Therefore, the scope of the present application should not be construed as being limited to the specific examples described below.

[0083] The analysis method was performed under the following conditions.

[0084] Hydroxyl equivalent

[0085] The amount of free acetic acid was measured in the following manner, and the unit is g / eq.

[0086] The phenol resin was reacted with excess acetic anhydride, and the amount of free acetic acid was measured by titration of a 0.5N KOH solution using a potentiometric titrator.

[0087] Reagents: acetic anhydride, triphenylphosphine, pyridine

[0088] Solvent: Tetrahydrofuran, Propylene glycol monomethyl ether

[0089] Automatic titrator: COM-1600 manufactured by HIRANUMA, INC.

[0090] Biuret: B-2000 manufactured by HIRANUMA, INC.

[0091] Epoxy equivalent

[0092] Measured according to the method described in JIS K-7236. Unit: g / eq.

[0093] HPLC (High Performance Liquid Chromatography)

[0094] LC-20AD manufactured by SHIMADZU CORPORATION

[0095] SPD-M20A manufactured by SHIMADZU CORPORATION

[0096] CTO-20A manufactured by SHIMADZU CORPORATION

[0097] Column: Intersil ODS-2.5 μm, 4.6 x 250 mm 40°C

[0098] Mobile Phase A: Acetonitrile (AN)

[0099] Mobile Phase B: Water (W)

[0100] The gradient elution with a slope was performed for the composition of the mobile phase in the following manner.

[0101] Time Program:

[0102] Between the start 0 minutes and 28 minutes, the ratio AN / W of the mobile phase A to the mobile phase B was changed from 50% / 50% to 100% / 0%.

[0103] Between the start 28 minutes and 40 minutes, the ratio AN / W of the mobile phase A to the mobile phase B was 100% / 0%.

[0104] The flow rate of the mobile phase was 1.0 mL / min.

[0105] The ultraviolet rays at the wavelength of 274 nm were detected by a photodiode array (PDA) which detects the ultraviolet rays at the wavelength of 200 nm to 274 nm.

[0106] GPC (Gel Permeation Chromatography)

[0107] Analysis device: ACQUITY APC System (manufactured by Waters Corporation)

[0108] Column: Guard column SHODEX GPC KF-601, KF-602 KF-602.5, KF-603

[0109] Flow rate: 0.5 ml / min.

[0110] Column temperature: 40°C

[0111] Solvent used: THF (tetrahydrofuran)

[0112] Detector: RI (differential refractive detector)

[0113] [Synthesis Example 1]

[0114] In a flask equipped with a stirrer, a reflux condenser, and a heating device, 254 parts by weight of phenol, 63 parts by weight of water, and 27 parts by weight of sodium hydroxide were placed, stirred, and dissolved, and then heated to 110°C, and 33 parts by weight of furfural was dropped over a period of 2 hours. After that, the mixture was allowed to react at 110°C for 3 hours, and then the temperature was raised to 145°C. While the temperature was being raised, the distilled water was removed from the system. After reaching 145°C, the mixture was immediately cooled to 80°C, 63 parts by weight of water was added, and 4 parts by weight of phosphoric acid and 63 parts by weight of 35% hydrochloric acid were added to perform neutralization. After repeating the water washing, the unreacted phenol was distilled off under heating and reduced pressure to obtain 90 parts by weight of the aforementioned phenol resin represented by formula (4). The hydroxyl equivalent weight of the obtained phenol resin was 141 g / eq. With respect to 78 parts by weight of the obtained phenol resin represented by formula (4), 254 parts by weight of epichlorohydrin (ECH, the same hereinafter), 64 parts by weight of dimethyl sulfoxide (DMSO, the same hereinafter), and 13 parts by weight of water were placed in a reaction vessel, heated, and stirred. After the phenol resin and ECH were dissolved, 23 parts by weight of flaky sodium hydroxide was placed in the reaction vessel in portions over a period of 2 hours while the temperature of the solution was maintained at 45°C. After that, the mixture was allowed to react at 45°C for 2 hours, and then at 70°C for 60 minutes. After that, the water washing was repeated, and the by-produced salt and dimethyl sulfoxide were removed, and then the excess epichlorohydrin was distilled off from the oil layer under heating and reduced pressure to obtain a mixture B containing an epoxy resin and a small amount of residual solvent and a small amount of by-produced salt. The theoretical yield of the epoxy resin in this reaction was 109 parts by weight.

[0115] To the resulting mixture B, 218 parts by weight of methyl isobutyl ketone was added and dissolved. This methyl isobutyl ketone solution was heated to 70°C, 22 parts by weight of water, 22 parts by weight of methanol, 7 parts by weight of 30% sodium hydroxide aqueous solution were added, and allowed to react for 1 hour, and then the water washing of the reaction liquid was repeated until the washing liquid became neutral. Then, under heating and reduced pressure, methyl isobutyl ketone was distilled off from the oil layer, and thereby 107 parts by weight of the aforementioned epoxy resin represented by the formula (1) (n = 1.7 in the formula (1)) was obtained. The epoxy equivalent of the resulting epoxy resin was 204 g / eq. The results of HPLC are shown in Table 1. Figure 1 The wave peaks of the compound represented by the aforementioned formula (2) were located at 13.5 minutes, 14.2 minutes, 15.3 minutes, and the wave peaks of the compound represented by the aforementioned formula (3) were located at 10.5 minutes, 11.3 minutes, 11.6 minutes. The ratio b / a of the sum b of the wave peak area at 10.5 minutes, the wave peak area at 11.3 minutes, and the wave peak area at 11.6 minutes to the sum a of the wave peak area at 13.5 minutes, the wave peak area at 14.2 minutes, and the wave peak area at 15.3 minutes was 0.015.

[0116] [Synthesis Example 2]

[0117] In a flask equipped with a stirrer, a reflux cooling tube, a heating device, 254 parts by weight of phenol, 63 parts by weight of water, and 27 parts by weight of sodium hydroxide were placed, and after stirring and dissolution, heated to 110°C, and 53 parts by weight of furfural was dropped for 2 hours. After that, it was allowed to react at 110°C for 3 hours, and then the temperature was raised to 145°C. While raising the temperature, the distilled water was removed to the outside of the system. After reaching 145°C, it was allowed to react for 4 hours. Then, it was cooled to 80°C, 63 parts by weight of water was placed, and 4 parts by weight of phosphoric acid and 63 parts by weight of 35% hydrochloric acid were added to neutralize. After repeating the water washing, the unreacted phenol was distilled off under heating and reduced pressure, and thereby 109 parts by weight of the aforementioned phenol resin represented by the formula (4) was obtained. The hydroxyl equivalent of the resulting phenol resin was 142 g / eq. With respect to 78 parts by weight of the resulting phenol resin represented by the aforementioned formula (4), 254 parts by weight of ECH, 64 parts by weight of DMSO, and 13 parts by weight of water were placed in a reaction vessel, and heated and stirred. After the phenol resin and ECH were dissolved, 23 parts by weight of flaky sodium hydroxide was placed in batches while maintaining the temperature of the solution at 45°C for 2 hours. After that, it was allowed to react at 45°C for 2 hours, and further at 70°C for 60 minutes. Then, after repeating the water washing, the by-produced salt and dimethyl sulfoxide were removed, and then the excess epichlorohydrin was distilled off from the oil layer under heating and reduced pressure, and thereby a mixture B containing an epoxy resin and a small amount of residual solvent and a small amount of by-produced salt was obtained. The theoretical yield of the epoxy resin in this reaction was 109 parts by weight.

[0118] To the resulting mixture B, 218 parts by weight of methyl isobutyl ketone was added and dissolved. This methyl isobutyl ketone solution was heated to 70°C, 22 parts by weight of water, 22 parts by weight of methanol, 7 parts by weight of 30% sodium hydroxide aqueous solution was added, allowed to react for 1 hour, and the water washing of the reaction liquid was repeated until the washing liquid became neutral. Then, under heating and reduced pressure, methyl isobutyl ketone was distilled off from the oil layer, whereby 103 parts by weight of the aforementioned epoxy resin represented by the formula (1) (n = 2.0 in the formula (1)) was obtained. The epoxy equivalent of the resulting epoxy resin was 214 g / eq. The results of HPLC are shown in Table 1. Figure 2 The wave peaks of the compound represented by the aforementioned formula (2) were located at 13.5 minutes, 14.2 minutes, 15.3 minutes, and the wave peaks of the compound represented by the aforementioned formula (3) were located at 10.5 minutes, 11.3 minutes, 11.6 minutes. The ratio b / a of the sum b of the wave peak area at 10.5 minutes, the wave peak area at 11.3 minutes, and the wave peak area at 11.6 minutes to the sum a of the wave peak area at 13.5 minutes, the wave peak area at 14.2 minutes, and the wave peak area at 15.3 minutes was 0.015.

[0119] [Synthesis Example 3]

[0120] In a flask equipped with a stirrer, a reflux cooling tube, a heating device, 254 parts by weight of phenol, 63 parts by weight of water, and 27 parts by weight of sodium hydroxide were placed, and after stirring and dissolution, heated to 110°C, and 63 parts by weight of furfural was dropped over a period of 2 hours. After that, it was allowed to react at 110°C for 3 hours, and then the temperature was raised to 145°C. While raising the temperature, the distilled water was removed to the outside of the system. After reaching 145°C, it was immediately cooled to 80°C, 63 parts by weight of water was placed, and 4 parts by weight of phosphoric acid and 63 parts by weight of 35% hydrochloric acid were added to neutralize. After repeating the water washing, the unreacted phenol was distilled off under heating and reduced pressure, and 112 parts by weight of the aforementioned phenol resin represented by the formula (4) was obtained. The hydroxyl equivalent of the resulting phenol resin was 147 g / eq. With respect to 78 parts by weight of the resulting phenol resin represented by the aforementioned formula (4), 254 parts by weight of epichlorohydrin (ECH, the same hereinafter), 64 parts by weight of dimethyl sulfoxide (DMSO, the same hereinafter), and 13 parts by weight of water were placed in a reaction vessel, and heated and stirred. After the phenol resin and ECH were dissolved, 23 parts by weight of flaky sodium hydroxide was placed in portions over a period of 2 hours while keeping the temperature of the solution at 45°C. After that, it was allowed to react at 45°C for 2 hours, and further at 70°C for 60 minutes. Then, after repeating the water washing, the by-produced salt and dimethyl sulfoxide were removed, and the excess epichlorohydrin was distilled off from the oil layer under heating and reduced pressure, and a mixture B containing an epoxy resin and a small amount of residual solvent and a small amount of by-produced salt was obtained. The theoretical yield of the epoxy resin in this reaction was 108 parts by weight.

[0121] To the resulting mixture B, 218 parts by weight of methyl isobutyl ketone was added and dissolved. This methyl isobutyl ketone solution was heated to 70°C, 22 parts by weight of water, 22 parts by weight of methanol, 7 parts by weight of 30% sodium hydroxide aqueous solution was added, and allowed to react for 1 hour, and the water washing of the reaction liquid was repeated until the washing liquid became neutral. Then, under heating and reduced pressure, methyl isobutyl ketone was distilled off from the oil layer, and thereby 103 parts by weight of the aforementioned epoxy resin represented by the formula (1) (n = 2.2 in the formula (1)) was obtained. The epoxy equivalent of the resulting epoxy resin was 218 g / eq. The results of HPLC are shown in Table 1. Figure 3 The wave peaks of the compound represented by the aforementioned formula (2) were located at 13.7 minutes, 14.4 minutes, 15.5 minutes, and the wave peaks of the compound represented by the aforementioned formula (3) were located at 10.7 minutes, 11.5 minutes, 11.8 minutes. The ratio b / a of the sum b of the wave peak area at 10.7 minutes, the wave peak area at 11.5 minutes, and the wave peak area at 11.8 minutes to the sum a of the wave peak area at 13.7 minutes, the wave peak area at 14.4 minutes, and the wave peak area at 15.5 minutes was 0.017.

[0122] [Synthesis Example 4]

[0123] In a flask equipped with a stirrer, a reflux cooling tube, a heating device, 254 parts by weight of phenol, 63 parts by weight of water, and 27 parts by weight of sodium hydroxide were placed, and after stirring and dissolution, heated to 110°C, and 53 parts by weight of furfural was dropped over 2 hours. After that, it was allowed to react at 110°C for 3 hours, and then the temperature was raised to 145°C. While raising the temperature, the distilled water was removed to the outside of the system. After reaching 145°C, it was allowed to react for 4 hours. Then, it was cooled to 80°C, 63 parts by weight of water was placed, and 4 parts by weight of phosphoric acid and 63 parts by weight of 35% hydrochloric acid were added to neutralize. After repeating the water washing, the unreacted phenol was distilled off under heating and reduced pressure, and thereby 109 parts by weight of the aforementioned phenol resin represented by the formula (4) was obtained. The hydroxyl equivalent of the resulting phenol resin was 142 g / eq. With respect to 78 parts by weight of the resulting phenol resin represented by the aforementioned formula (4), 254 parts by weight of ECH, 64 parts by weight of DMSO, and 13 parts by weight of water were placed in a reaction vessel, and heated and stirred. After the phenol resin and ECH were dissolved, 23 parts by weight of flaky sodium hydroxide was placed in portions over 2 hours while maintaining the temperature of the solution at 45°C. After that, it was allowed to react at 45°C for 2 hours, and further at 70°C for 60 minutes. Then, after repeating the water washing, the by-produced salt and dimethyl sulfoxide were removed, and the excess epichlorohydrin was distilled off from the oil layer under heating and reduced pressure, and thereby a mixture B containing an epoxy resin and a small amount of residual solvent and a small amount of by-produced salt was obtained. The theoretical yield of the epoxy resin in this reaction was 109 parts by weight.

[0124] To the resulting mixture B, 218 parts by weight of methyl isobutyl ketone was added and dissolved. This methyl isobutyl ketone solution was heated to 70°C, 22 parts by weight of water, 26 parts by weight of methanol, 7 parts by weight of 30% sodium hydroxide aqueous solution was added, allowed to react for 1 hour, and the water washing of the reaction liquid was repeated until the washing liquid became neutral. Then, under heating and reduced pressure, methyl isobutyl ketone was distilled off from the oil layer, whereby 101 parts by weight of the aforementioned epoxy resin represented by the formula (1) (n = 2.1 in the formula (1)) was obtained. The epoxy equivalent of the resulting epoxy resin was 213 g / eq. The results of HPLC are shown in Table 1. Figure 4 The wave peaks of the compound represented by the aforementioned formula (2) were located at 13.5 minutes, 14.2 minutes, 15.3 minutes, and the wave peaks of the compound represented by the aforementioned formula (3) were located at 10.5 minutes, 11.3 minutes, 11.6 minutes. The ratio b / a of the sum b of the wave peak area at 10.5 minutes, the wave peak area at 11.3 minutes, and the wave peak area at 11.6 minutes to the sum a of the wave peak area at 13.5 minutes, the wave peak area at 14.2 minutes, and the wave peak area at 15.3 minutes was 0.026.

[0125] [Synthesis Example 5]

[0126] In a flask equipped with a stirrer, a reflux cooling tube, a heating device, 254 parts by weight of phenol, 63 parts by weight of water, and 27 parts by weight of sodium hydroxide were placed, and after stirring and dissolution, heated to 110°C, and 44 parts by weight of furfural was dropped for 2 hours. After that, it was allowed to react at 110°C for 3 hours, and then the temperature was raised to 145°C. While raising the temperature, the distilled water was removed to the outside of the system. After reaching 145°C, it was immediately cooled to 80°C, 63 parts by weight of water was placed, and 4 parts by weight of phosphoric acid and 63 parts by weight of 35% hydrochloric acid were added to neutralize. After repeating the water washing, the unreacted phenol was distilled off under heating and reduced pressure, and 109 parts by weight of the aforementioned phenol resin represented by the formula (4) was obtained. The hydroxyl equivalent of the resulting phenol resin was 142 g / eq. With respect to 78 parts by weight of the resulting phenol resin represented by the aforementioned formula (4), 254 parts by weight of ECH, 64 parts by weight of DMSO, and 13 parts by weight of water were placed in a reaction vessel, and heated and stirred. After the phenol resin and ECH were dissolved, 23 parts by weight of flaky sodium hydroxide was placed in batches while maintaining the temperature of the solution at 45°C for 2 hours. After that, it was allowed to react at 45°C for 2 hours, and further at 70°C for 60 minutes. Then, after repeating the water washing, the by-produced salt and dimethyl sulfoxide were removed, and the excess epichlorohydrin was distilled off from the oil layer under heating and reduced pressure, and a mixture B containing an epoxy resin and a small amount of residual solvent and a small amount of by-produced salt was obtained. The theoretical yield of the epoxy resin in this reaction was 109 parts by weight.

[0127] To the resulting mixture B, 218 parts by weight of methyl isobutyl ketone was added and dissolved. This methyl isobutyl ketone solution was heated to 70°C, 5 parts by weight of water, 7 parts by weight of 30% sodium hydroxide aqueous solution was added, allowed to react for 1 hour, and the water washing of the reaction liquid was repeated until the washing liquid became neutral. Then, under heating and reduced pressure, methyl isobutyl ketone was distilled off from the oil layer, whereby 103 parts by weight of the aforementioned epoxy resin represented by the formula (1) (n = 1.8 in the formula (1)) was obtained. The epoxy equivalent of the resulting epoxy resin was 207 g / eq.

[0128] The results of HPLC are shown in Table 1. Figure 5 The wave peaks of the compound represented by the aforementioned formula (2) were located at 13.5 minutes, 14.2 minutes, 15.3 minutes, and the wave peaks of the compound represented by the aforementioned formula (3) were located at 10.5 minutes, 11.3 minutes, 11.6 minutes. The ratio b / a of the sum b of the wave peak area at 10.5 minutes, the wave peak area at 11.3 minutes, and the wave peak area at 11.6 minutes to the sum a of the wave peak area at 13.5 minutes, the wave peak area at 14.2 minutes, and the wave peak area at 15.3 minutes was 0.009.

[0129] [Synthesis Example 6]

[0130] In a flask equipped with a stirrer, a reflux cooling tube, a heating device, 254 parts by weight of phenol, 63 parts by weight of water, and 27 parts by weight of sodium hydroxide were put, and after stirring and dissolution, heated to 110°C, and 40 parts by weight of furfural was added dropwise over 2 hours. After that, it was allowed to react at 110°C for 3 hours, and then the temperature was raised to 145°C. While raising the temperature, the distilled water was removed to the outside of the system. After reaching 145°C, it was allowed to react for 4 hours. Then, it was cooled to 80°C, 63 parts by weight of water was put, and 4 parts by weight of phosphoric acid, 63 parts by weight of 35% hydrochloric acid were added to neutralize. After repeating the water washing, under heating and reduced pressure, the unreacted phenol was distilled off, and 107 parts by weight of the aforementioned phenol resin represented by the formula (4) was obtained. The hydroxyl equivalent of the resulting phenol resin was 141 g / eq. With respect to 78 parts by weight of the resulting phenol resin represented by the aforementioned formula (4), 254 parts by weight of ECH, 64 parts by weight of DMSO, and 13 parts by weight of water were put in a reaction vessel, and heated and stirred. After the dissolution of the phenol resin and ECH, while keeping the temperature of the reaction liquid at 45°C, 23 parts by weight of flaky sodium hydroxide was added to the flask over 2 hours. After that, it was allowed to react at 45°C for 2 hours, and further at 70°C for 60 minutes. Then, after repeating the water washing, the by-produced salt and dimethyl sulfoxide were removed, and under heating and reduced pressure, the excess epichlorohydrin was distilled off from the oil layer, and a mixture B containing an epoxy resin and a small amount of residual solvent and a small amount of by-produced salt was obtained. The theoretical yield of the epoxy resin in this reaction was 109 parts by weight.

[0131] To the resulting mixture B, 218 parts by weight of methyl isobutyl ketone was added and dissolved. This methyl isobutyl ketone solution was heated to 70°C, 5 parts by weight of water, 7 parts by weight of 30% sodium hydroxide aqueous solution was added, allowed to react for 1 hour, and the water washing of the reaction liquid was repeated until the washing liquid became neutral. Then, under heating and reduced pressure, methyl isobutyl ketone was distilled off from the oil layer, whereby 90 parts by weight of the aforementioned epoxy resin represented by the formula (1) (n = 2.0 in the formula (1)) was obtained. The epoxy equivalent of the resulting epoxy resin was 211 g / eq.

[0132] The results of HPLC are shown in Table 1. Figure 6 The wave peaks of the compound represented by the aforementioned formula (2) were located at 13.5 minutes, 14.2 minutes, 15.3 minutes, and the wave peaks of the compound represented by the aforementioned formula (3) were located at 10.5 minutes, 11.3 minutes, 11.6 minutes. The ratio b / a of the sum b of the wave peak area at 10.5 minutes, the wave peak area at 11.3 minutes, and the wave peak area at 11.6 minutes to the sum a of the wave peak area at 13.5 minutes, the wave peak area at 14.2 minutes, and the wave peak area at 15.3 minutes was 0.009.

[0133] [Synthesis Example 7]

[0134] In a flask equipped with a stirrer, a reflux cooling tube, a heating device, 254 parts by weight of phenol, 63 parts by weight of water, and 27 parts by weight of sodium hydroxide were placed, and after stirring and dissolution, heated to 110°C, and 53 parts by weight of furfural was dropped for 2 hours. After that, it was allowed to react at 110°C for 3 hours, and then the temperature was raised to 145°C. While raising the temperature, the distilled water was removed to the outside of the system. After reaching 145°C, it was allowed to react for 4 hours. Then, it was cooled to 80°C, 63 parts by weight of water was placed, and 4 parts by weight of phosphoric acid and 63 parts by weight of 35% hydrochloric acid were added to neutralize. After repeating the water washing, the unreacted phenol was distilled off under heating and reduced pressure, and 109 parts by weight of the aforementioned phenol resin represented by the formula (4) was obtained. The hydroxyl equivalent of the resulting phenol resin was 142 g / eq. With respect to 78 parts by weight of the resulting phenol resin represented by the aforementioned formula (4), 254 parts by weight of ECH, 64 parts by weight of DMSO, and 13 parts by weight of water were placed in a reaction vessel, and heated and stirred. After the phenol resin and ECH were dissolved, 23 parts by weight of flaky sodium hydroxide was placed in batches while maintaining the temperature at 45°C for 2 hours. After that, it was allowed to react at 45°C for 2 hours, and further at 70°C for 60 minutes. Then, after repeating the water washing, the by-produced salt and dimethyl sulfoxide were removed, and the excess epichlorohydrin was distilled off from the oil layer under heating and reduced pressure, and a mixture B containing an epoxy resin and a small amount of residual solvent and a small amount of by-produced salt was obtained. The theoretical yield of the epoxy resin in this reaction was 109 parts by weight.

[0135] To the resulting mixture B, 218 parts by weight of methyl isobutyl ketone was added and dissolved. This methyl isobutyl ketone solution was heated to 70°C, 7 parts by weight of water, 44 parts by weight of methanol, 7 parts by weight of 30% sodium hydroxide aqueous solution were added, allowed to react for 1 hour, and the water washing of the reaction liquid was repeated until the washing liquid became neutral. Then, under heating and reduced pressure, methyl isobutyl ketone was distilled off from the oil layer, whereby 103 parts by weight of the aforementioned epoxy resin represented by the formula (1) (n = 2.3 in the formula (1)) was obtained. The epoxy equivalent of the resulting epoxy resin was 266 g / eq.

[0136] The results of HPLC are shown in Table 1. Figure 7 The wave peaks of the compound represented by the aforementioned formula (2) were located at 13.5 minutes, 14.2 minutes, 15.3 minutes, and the wave peaks of the compound represented by the aforementioned formula (3) were located at 10.5 minutes, 11.3 minutes, 11.6 minutes. The ratio b / a of the sum b of the wave peak area at 10.5 minutes, the wave peak area at 11.3 minutes, and the wave peak area at 11.6 minutes to the sum a of the wave peak area at 13.5 minutes, the wave peak area at 14.2 minutes, and the wave peak area at 15.3 minutes was 0.267.

[0137] [Synthesis Example 8]

[0138] In a flask equipped with a stirrer, a reflux cooling tube, a heating device, 254 parts by weight of phenol, 63 parts by weight of water, and 27 parts by weight of sodium hydroxide were placed, stirred and dissolved, and then heated to 110°C. While maintaining the temperature at 110°C, 33 parts by weight of furfural was added dropwise over 2 hours. After the reaction was allowed to proceed at 110°C for 3 hours, the temperature was raised to 145°C. While raising the temperature, the distilled water was removed from the system. After the temperature was lowered to 80°C, 63 parts by weight of water was added, and 4 parts by weight of phosphoric acid and 63 parts by weight of 35% hydrochloric acid were added for neutralization. After the water washing was repeated, the unreacted phenol was distilled off under heating and reduced pressure, and 90 parts by weight of the aforementioned phenol resin represented by the formula (4) was obtained. The hydroxyl equivalent of the resulting phenol resin was 141 g / eq. In a reaction vessel, 254 parts by weight of ECH, 64 parts by weight of DMSO, and 13 parts by weight of water were placed with respect to 78 parts by weight of the resulting phenol resin represented by the aforementioned formula (4), and heated and stirred. After the phenol resin and ECH were dissolved, 23 parts by weight of flaky sodium hydroxide was added portionwise over 2 hours while maintaining the temperature of the solution at 45°C. Thereafter, the reaction was further carried out at 45°C for 2 hours and at 70°C for 60 minutes. Then, the excess epichlorohydrin and DMSO were distilled off under heating and reduced pressure, and a mixture B containing the epoxy resin represented by the formula (1), by-products, and a small amount of residual solvent was obtained. The theoretical yield of the epoxy resin in this reaction was 109 parts by weight.

[0139] To the resulting mixture B, 218 parts by weight of methyl isobutyl ketone was added for dissolution, and water washing was performed to remove the by-produced salt. This methyl isobutyl ketone solution was heated to 70°C, 22 parts by weight of water, 22 parts by weight of methanol, and 7 parts by weight of 30% sodium hydroxide aqueous solution were added, and allowed to react for 1 hour, and the water washing of the reaction liquid was repeated until the washing liquid became neutral. Then, under heating and reduced pressure, methyl isobutyl ketone was distilled off from the oil layer, and thereby 107 parts by weight of the aforementioned epoxy resin represented by the formula (1) (n in the formula (1) was 1.7) was obtained. The resulting epoxy resin had an epoxy equivalent weight of 204 g / eq.

[0140] [Examples 1 to 4, Comparative Examples 1 to 3]

[0141] Using the epoxy resins obtained in Synthesis Examples 1 to 7 as a main agent, and using 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane (abbreviation: TEDDM, manufactured by Tokyo Chemical Industry Co., Ltd., active hydrogen equivalent weight 78 g / eq.) as a hardening agent, they were mixed in the weight ratio shown in the blending composition of Table 1, and were hardened under the hardening conditions of 160°C for 6 hours to produce hardened products.

[0142] The measurement of the physical property values was performed under the following conditions.

[0143] [Measurement conditions of glass transition point (Tg)]

[0144] Thermomechanical measurement device (TMA): TMA Q400EM manufactured by TA-instruments

[0145] Temperature increasing rate: 2°C / minute

[0146] Measurement temperature range: 25°C to 300°C

[0147] Tg: The change point of the thermal expansion rate was set as Tg.

[0148] [Table 1]

[0149]

[0150] It was confirmed from the results of Table 1 that the hardened products of Examples 1 to 4 of the present application had a higher glass transition point than the hardened products of Comparative Examples 1 to 3, and had excellent heat resistance.

[0151] This application claims priority from Japanese Patent Application No. 2023-113999 filed on July 11, 2023.

Claims

1. An epoxy resin which is an epoxy resin represented by the following formula (1), and in the chromatogram of high performance liquid chromatography, when the peak area of the compound represented by the following formula (2) is set as a and the peak area of the compound represented by the following formula (3) is set as b, b / a is 0.012 or more and 0.050 or less; In formula (1), n is the average value of the repetition number, which represents a real number of 1 < n < 15; Xs are each independently a monovalent group represented by formula (a) or formula (b), and at least one is a monovalent group represented by formula (a); * is bonded to an oxygen atom; 。 2. The epoxy resin according to claim 1, having an epoxy equivalent of 200 g / eq. or more and 220 g / eq. or less.

3. A curable resin composition containing the epoxy resin according to claim 1 and a curing agent.

4. The curable resin composition according to claim 3, wherein, The curing agent is an amine-based curing agent.

5. A cured product obtained by curing the curable resin composition according to claim 3 or 4.

6. A carbon fiber reinforced composite material obtained by curing the curable resin composition according to claim 3 or 4.

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