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

Abstract

Provided are an epoxy resin having excellent heat resistance and bending strength, a curable resin composition, a cured product thereof, and a carbon fiber-reinforced composite material. The epoxy resin is represented by the following formula (1), and the epoxy equivalent of the epoxy resin is 210 g / eq. Or more and 218 g / eq. Or less. (In formula (1), n represents an average value of the number of repetitions and represents 1 lt; nlt; 15).

Description

Technical Field

[0001] This invention relates to epoxy resins, curable resin compositions, and cured products thereof, as well as carbon fiber reinforced composite materials. Background Technology

[0002] Epoxy resins, through the use of various hardeners, become cured materials with excellent mechanical properties, water resistance, chemical resistance, heat resistance, and electrical properties, and are widely used in adhesives, coatings, laminates, molding materials, and casting materials. Carbon fiber reinforced polymer (CFRP), made by impregnating reinforcing fibers with epoxy resin and hardener as the matrix resin and then curing it, offers lightweight and high-strength properties. Therefore, its applications in recent years have expanded significantly, including aircraft structural components, windmill blades, automotive exterior panels, and computer applications such as IC trays and laptop frames (casings), with demand steadily increasing. In particular, CFRP is used as a matrix resin in aircraft applications due to its lightweight and high-strength properties in molded products.

[0003] Thermosetting resins such as epoxy resins used as "resins used in matrix resins such as CFRP" are generally brittle, and high mechanical strength is required when they are used in structural materials for aerospace applications and vehicles. To compensate for the low flexural strength, toughness, and adhesion of these thermosetting resins, methods for adding high-strength and high-toughness thermoplastic resins to the thermosetting resin matrix are well known (Patent Documents 1 to 3). Specifically, the flexural strength and toughness of the prepreg are improved by incorporating particles of thermoplastic resins such as polyethersulfone, polyetherimide, and polyamide into the thermosetting resin matrix resin.

[0004] In recent years, the requirements for CFRP have become more stringent. When used as a structural material for aerospace and vehicles, it requires heat resistance of over 180°C and flexural strength of over 100MPa (Patent Documents 4 and 5).

[0005] [Existing Technical Documents]

[0006] [Patent Literature]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 60-243113

[0008] [Patent Document 2] Japanese Patent Application Publication No. 09-100358

[0009] [Patent Document 3] Japanese Patent Application Publication No. 2013-155330

[0010] [Patent Document 4] Japanese Patent Application Publication No. 2010-275492

[0011] [Patent Document 5] International Publication No. 2019-021879

[0012] [Patent Document 6] Japanese Patent Application Laid-Open No. 2007-211254. Summary of the Invention

[0013] [Problems to be Solved by the Invention]

[0014] An epoxy resin with low water absorption is described in Patent Document 6. However, the epoxy resin described in Patent Document 6 has low flexural strength and is brittle (low elongation), so it is difficult to be used as a CFRP material.

[0015] The present invention has been completed in view of the above circumstances, and an object thereof is to provide an epoxy resin, a curable resin composition, a cured product thereof, and a carbon fiber reinforced composite material having excellent heat resistance and flexural strength.

[0016] [Means for Solving the Problems]

[0017] That is, the present invention is the invention shown in the following [1] to [5]. Incidentally, in the present invention, "(numerical value 1) to (numerical value 2)" means that the upper and lower limits are included.

[0018] [1] An epoxy resin represented by the following formula (1), having an epoxy equivalent of 210 g / eq. or more and 218 g / eq. or less,

[0019]

[0020] (In formula (1), n is the average value of multiplicity and represents a real number of 1 < n < 15).

[0021] [2] A curable resin composition containing: the epoxy resin described in the preceding [1], and a curing agent.

[0022] [3] The curable resin composition according to the preceding [2], wherein the curing agent is an amine-based curing agent.

[0023] [4] A cured product obtained by curing the curable resin composition described in the preceding [2] or [3].

[0024] [5] A carbon fiber reinforced composite material comprising: a cured product obtained by curing the curable resin composition described in the preceding [2] or [3], and carbon fibers.

[0025] [Effects of the Invention]

[0026] According to the present invention, it is possible to provide an epoxy resin, a curable resin composition, a cured product thereof, and a carbon fiber reinforced composite material having excellent heat resistance and flexural strength of the cured product. Detailed Embodiments

[0027] Hereinafter, the embodiments of the present invention (hereinafter also referred to as "the present embodiment") will be further described in detail.

[0028] The epoxy resin of the present embodiment is an epoxy resin represented by the following formula (1), and its epoxy equivalent is preferably 210 g / eq. or more and 218 g / eq. or less, more preferably 211 g / eq. or more and 21 Eight g / eq. or less, even more preferably 213 g / eq. or more and 218 g / eq. or less. If the epoxy equivalent is 210 g / eq. or more, the heat resistance becomes good, and if it is 218 g / eq. or less, the flexural strength becomes good. That is, by making the epoxy equivalent 210 g / eq. or more and 218 g / eq. or less, the characteristics of heat resistance and flexural strength can be兼备.

[0029]

[0030] (In formula (1), n is the average value of the repetition number and represents a real number of 1 < n < 15).

[0031] . When the epoxy equivalent is 210 g / eq. or more, the heat resistance becomes good, and when it is 218 g / eq. or less, the flexural strength becomes good. That is, by making the epoxy equivalent 210 g / eq. or more and 218 g / eq. or less, the characteristics of heat resistance and flexural strength can be兼备. In the aforementioned formula (1), the value of n is the number average molecular weight obtained by the measurement of gel permeation chromatography (GPC, detector: RI) of the epoxy resin, or can be calculated from the respective area ratios of the separated peaks. n is preferably a real number of 1 < n < 15, more preferably 1 < n < 10, and particularly preferably 1 < n < 5.

[0032] The epoxy resin of the present embodiment can obtain a cured product with excellent heat resistance and flexural strength by controlling the epoxy equivalent. The flexural strength is preferably 100 to 130 MPa, more preferably 105 to 125 MPa, and even more preferably 110 to 120 MPa. If the flexural strength is less than 100 MPa, the flexural strength when making a carbon fiber reinforced composite material is insufficient, resulting in a decrease in reliability, so it is not preferred. In addition, the flexural strength of the present embodiment is measured according to the method described in the following examples.

[0033] In addition, the maximum flexural elongation of the cured product obtained from the epoxy resin of the present embodiment is particularly preferably 5% or more. Regarding the maximum value, there is no particular limitation, but the preferred maximum value is 7% or less. By making the maximum flexural elongation 5% or more, the brittleness of the cured product can be alleviated, and it will become a tough cured product.

[0034] The glass transition point (Tg) of the epoxy resin of the present embodiment is preferably 180 to 300 °C, more preferably 185 to 250 °C, still more preferably 190 to 200 °C, and particularly preferably 220 to 250 °C. If the glass transition point is less than 180 °C, it is difficult to apply it to components requiring heat resistance such as those related to aircraft engines. When in use, the resin will soften, and the mechanical strength will be significantly reduced, resulting in material damage, so it is not preferred. In addition, the glass transition point of the epoxy resin is generally related to the crosslinking density. If the crosslinking density increases, the glass transition point also increases. That is, if the glass transition point exceeds 300 °C, the crosslinking density increases and the cured product becomes brittle, so it is not preferred. In addition, the glass transition point (Tg) of the present embodiment is measured according to the method described in the following examples.

[0035] The epoxy resin represented by the foregoing formula (1) can be obtained by the reaction of a phenol resin represented by the following formula (2) with epihalohydrin.

[0036]

[0037] (In formula (2), n is the average value of the repetition number and represents a real number of 1 < n < 15).

[0038] The more preferred range of n in the foregoing formula (2) is the same as that of the above formula (1).

[0039] The foregoing epihalohydrin can be easily obtained on the market. The usage amount of epihalohydrin is preferably 2.0 to 10 moles, more preferably 3.0 to 8.0 moles, still more preferably 3.5 to 6.0 moles, relative to 1 mole of the hydroxyl group of the raw material phenol mixture. The epihalohydrin that can be used in the present embodiment preferably includes epichlorohydrin, α-methyl epichlorohydrin, β-methyl epichlorohydrin, epibromohydrin, etc., and particularly preferably epichlorohydrin that is easily obtained industrially.

[0040] In the above reaction, an alkali metal hydroxide can be used as a catalyst to promote the epoxidation step. The alkali metal hydroxides that can be used include sodium hydroxide, potassium hydroxide, etc. The solid of the alkali metal hydroxide can be used, or an aqueous solution of the alkali metal hydroxide can also be used. In the present embodiment, particularly from the aspects of solubility and operability, it is more preferred to use the solid of the alkali metal hydroxide formed into flakes. The usage amount of the alkali metal hydroxide is preferably 0.90 to 1.5 moles, more preferably 0.95 to 1.25 moles, still more preferably 0.99 to 1.15 moles, relative to 1 mole of the hydroxyl group of the raw material phenol mixture.

[0041] In addition, to promote the reaction, quaternary ammonium salts such as tetramethylammonium chloride, tetramethylammonium bromide, and trimethylbenzylammonium chloride can be added as catalysts. The amount of quaternary ammonium salt used is preferably 0.1 to 15 g, more preferably 0.2 to 10 g, relative to 1 mole of hydroxyl groups in the phenolic mixture.

[0042] The reaction temperature is preferably 30 to 90°C, more preferably 35 to 80°C. Especially in this embodiment, for higher purity epoxidation, 50°C or higher is preferred, and particularly preferably 60°C or higher is even more preferred. 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 too short, the reaction will be incomplete; if the reaction time is too long, byproducts will form, which is undesirable.

[0043] After washing the reactants from these epoxidation reactions with water, or without washing, the surface halogen alcohols and solvents are removed under heating and reduced pressure. Furthermore, to further prepare epoxy resins with low hydrolytic halogen content, the recovered epoxy resin can be dissolved using a ketone compound with 4 to 7 carbon atoms (e.g., methyl isobutyl ketone, methyl ethyl ketone, cyclopentanone, cyclohexanone, etc.) as a solvent, and an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide is added to reliably achieve ring closure. In this case, the amount of alkali metal hydroxide used is preferably 0.01 to 0.3 moles, more preferably 0.05 to 0.2 moles, relative to 1 mole of hydroxyl groups in the phenol mixture used in the epoxidation process. The reaction temperature is preferably 50 to 120°C, and the reaction time is more preferably 0.5 to 2 hours.

[0044] After the reaction is complete, the generated salt is filtered and removed by washing with water, and the solvent is further removed by distillation under heating and reduced pressure, thereby obtaining the epoxy resin of this embodiment.

[0045] Regarding the synthesis method of phenolic resin represented by the aforementioned formula (2), when the reaction (condensation) of furfural and phenol is carried out, the amount of phenol is preferably 1.5 to 20 moles, and more preferably 3 to 10 moles, relative to 1 mole of furfural.

[0046] In terms of phenols, examples of disubstituted phenols include catechol, resorcinol, and hydroquinone, while examples of monosubstituted phenols include phenol, cresol, and xylenol. They can be used alone or in combination with two or more.

[0047] Solvents include, but are not limited to, methanol, ethanol, propanol, isopropanol, toluene, xylene, etc., and can be used alone or in combination with two or more. When using a solvent, the amount of solvent used is preferably 5 to 500 parts by weight relative to 100 parts by weight of phenol, and more preferably in the range of 10 to 300 parts by weight.

[0048] In the condensation reaction of furfural and phenols, an alkaline catalyst is preferred. Although condensation polymerization can also be carried out using acidic catalysts, reactions between furfural molecules can occur, leading to increased byproducts. Alternatively, organometallic compounds can be used as catalysts, but this is less costly. Specific examples of alkaline catalysts include 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 methoxy, sodium ethoxy, potassium methoxy, potassium ethoxy, and potassium tert-butoxy; and alkaline earth metal alkoxides such as magnesium methoxy and magnesium ethoxy, but these are not limited to these. Two or more catalysts can be used alone or in combination. The amount of catalyst used relative to 1 mole of phenol is preferably 0.005 to 2.0 moles, more preferably 0.01 to 1.1 moles.

[0049] The condensation reaction in the presence of these alkaline catalysts is preferably carried out in the range of 40 to 180°C, and more preferably in the range of 80 to 165°C. The condensation reaction time is preferably selected in the range of 0.5 to 10 hours. The resulting reactants are then neutralized in the system to become neutral, or repeatedly washed with water in the presence of a solvent, the water is separated and drained, and then the solvent and unreacted substances are removed under heating and reduced pressure, thereby obtaining the phenolic resin represented by formula (2) above.

[0050] The curable resin composition of this embodiment contains a curing agent. Examples of usable curing agents include amine-based curing agents, acid anhydride-based curing agents, amide-based curing agents, and phenol-based curing agents.

[0051] In the curing resin composition of this embodiment, an amine-based curing agent is preferred, especially in order to achieve a good balance between the resin viscosity of the curing resin composition and the heat resistance of the cured resin. Amine-based curing agents can include 3,3'-diaminodiphenyl sulfone (3,3'-DDS), 4,4'-diaminodiphenyl sulfone (4,4'-DDS), diaminodiphenylmethane (DDM), 3,3'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3'-di-tert-butyl-4,4'-diaminodiphenylmethane, 3,3'-diethyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-diisopropyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-di-tert-butyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane (TEDDM), 3,3 Diisopropyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3'-di-tert-butyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetraisopropyl-4,4'-diaminodiphenylmethane, 3,3'-di-tert-butyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetra-tert-butyl-4,4'-diaminodiphenylmethane, diaminodiphenyl ether (DADPE), bisaniline, benzyl dimethylaniline, 2-(dimethylaminomethyl)phenol (DMP-10), 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), 2-ethylhexanoate of 2,4,6-tris(dimethylaminomethyl)phenol, etc. Other examples include: aniline novolak, o-ethyl aniline novolak, aniline resin obtained by reacting aniline with xylene chloride, and aniline resin obtained by polycondensation of aniline with substituted biphenyls (such as 4,4'-bis(chloromethyl)-1,1'-biphenyl and 4,4'-bis(methoxymethyl)-1,1'-biphenyl) or substituted phenyls (such as 1,4-bis(chloromethyl)benzene, 1,4-bis(methoxymethyl)benzene and 1,4-bis(hydroxymethyl)benzene).

[0052] Examples of acid anhydride-based hardeners include: phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, and methylhexahydrophthalic anhydride.

[0053] Examples of amide-based curing agents include dicyandiamide, or polyamide resins synthesized from dimers of linolenic acid and ethylenediamine.

[0054] Phenolic curing agents include: polyphenols (bisphenol A, bisphenol F, bisphenol S, fluorenebisphenol, terpene diphenols, 4,4'-dihydroxybiphenyl, 2,2'-dihydroxybiphenyl, 3,3',5,5'-tetramethyl-(1,1'-biphenyl)-4,4'-diol, hydroquinone, resorcinol, naphthalene glycol, tris(4-hydroxyphenyl)methane, and 1,1,2,2-tetra(4-hydroxyphenyl)ethane, etc.); and aldehydes (formaldehyde, acetaldehyde, benzaldehyde, p-hydroxybenzaldehyde, o-hydroxybenzaldehyde, etc.) composed of phenols (e.g., phenol, alkyl-substituted phenols, naphthol, alkyl-substituted naphthol, dihydroxybenzene, and dihydroxynaphthalene, etc.) and aldehydes (formaldehyde, acetaldehyde, benzaldehyde, p-hydroxybenzaldehyde, o-hydroxybenzaldehyde). Phenolic resins obtained by condensation of furfural, ketones (such as p-hydroxyacetophenone and o-hydroxyacetophenone), or dienes (such as dicyclopentadiene and tricyclopentadiene); phenolic resins obtained by polycondensation of the aforementioned phenols with substituted biphenyls (such as 4,4'-bis(chloromethyl)-1,1'-biphenyl and 4,4'-bis(methoxymethyl)-1,1'-biphenyl) or substituted phenyls (such as 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 phenolic resins; halogenated phenols such as tetrabromobisphenol A and brominated phenolic resins.

[0055] In the curing resin composition of this embodiment, it is also preferable to use the phenolic resin represented by the aforementioned formula (2) as part of the total amount or portion of the curing agent.

[0056] In the curable resin composition of this embodiment, the amount of curing agent used is preferably 0.7 to 1.2 equivalents relative to the epoxy group equivalents of the epoxy resin. If the amount is less than 0.7 equivalents or more than 1.2 equivalents relative to the epoxy group equivalents, there is a risk that the curing will be incomplete and good curing properties cannot be obtained.

[0057] Furthermore, a curing accelerator may be incorporated into the curing resin composition of this embodiment, depending on the requirements. The gelation time can be adjusted by using a curing accelerator. Examples of usable curing accelerators include: imidazoles such as 2-methylimidazole, 2-ethylimidazole, and 2-ethyl-4-methylimidazole; tertiary amines such as 2-(dimethylaminomethyl)phenol and 1,8-diaza-bicyclo[5,4,0]undecene-7; phosphines such as triphenylphosphine; and metal compounds such as tin octoate. 0.01 to 5.0 parts by weight of curing accelerator may be used relative to 100 parts by weight of epoxy resin, depending on the requirements.

[0058] Other epoxy resins may also be incorporated into the curable resin composition of this embodiment. Specific examples include: condensation polymers of phenols (phenol, alkyl-substituted phenols, aromatic-substituted phenols, naphthol, alkyl-substituted naphthol, dihydroxybenzene, alkyl-substituted dihydroxybenzene, dihydroxynaphthalene, etc.) with various aldehydes (formaldehyde, acetaldehyde, alkyl aldehydes, benzaldehyde, alkyl-substituted benzaldehyde, hydroxybenzene, naphthal, glutaraldehyde, o-phthalaldehyde, crotonaldehyde, cinnamaldehyde, etc.); polymers of phenols with various diene compounds (dicyclopentadiene, terpenes, vinylcyclohexene, norcamphene, vinylnorcamphene, tetrahydroindene, divinylbenzene, divinylbiphenyl, diisopropenylbiphenyl, butadiene, isoprene, etc.); condensation polymers of phenols with ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, acetophenone, benzophenone, etc.); and polymers formed by the reaction of phenols with substituted biphenyls (4,4...). Phenolic resins obtained by condensation polymerization of '-bis(chloromethyl)-1,1'-biphenyl and 4,4'-bis(methoxymethyl)-1,1'-biphenyl, etc., or substituted phenyl groups (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 propylene ether-based epoxy resins obtained by glycidylating alcohols, etc., alicyclic epoxy resins represented by 4-vinyl-1-cyclohexene diepoxide and 3,4-epoxycyclohexylmethyl-3,4'-epoxycyclohexane carboxylate, epoxy propylene amine-based epoxy resins represented by tetraglycyldiaminodiphenylmethane (TGDDM) and triglycyl-p-aminophenol, epoxy propylene ester-based epoxy resins, etc., but generally usable epoxy resins are not limited to these.

[0059] In the curable resin composition of this embodiment, well-known additives may be incorporated as needed. Specific examples of additives that can be used include: polybutadiene and its modified derivatives, modified acrylonitrile copolymers, polyphenylene ether, polystyrene, polyethylene, polyimide, fluororesin, maleimide compounds, cyanate ester compounds, polysiloxane gel, polysiloxane oil, and surface treatment agents for inorganic fillers such as silica, alumina, calcium carbonate, quartz powder, aluminum powder, graphite, talc, clay, iron oxide, titanium oxide, aluminum nitride, asbestos, mica, and glass powder, as well as fillers such as silane coupling agents, mold release agents, carbon black, phthalocyanine blue, and phthalocyanine green.

[0060] In the curable resin composition of this embodiment, well-known maleimide compounds may be incorporated as needed. Specific examples of usable maleimide compounds include: 4,4'-diphenylmethane bismaleimide, polyphenylmethane maleimide, m-phenyl bismaleimide, 2,2'-bis[4-(4-maleimidephenoxy)phenyl]propane, 3,3'-dimethyl-5,5'-diethyl-4,4'-diphenylmethane bismaleimide, 4-methyl-1,3-phenyl 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 maleimides, etc., but are not limited to these. These may be used alone or in combination of two or more. When incorporating maleimide compounds, curing accelerators may be added as needed. These may include the aforementioned curing accelerators, or free radical polymerization initiators such as organic oxides and azo compounds.

[0061] The curable resin composition of this embodiment can be made into a varnish-like composition (hereinafter simply referred to as varnish) by adding an organic solvent. Examples of solvents used include: amide solvents such as γ-butyrolactone, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and N,N-dimethylimidazolidine; sulfone solvents such as tetramethylene sulfone; ether solvents such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, propylene glycol, propylene glycol monomethyl ether, propylene glycol monomethyl ether monoacetate, and propylene glycol monobutyl ether; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, and cyclohexanone; and aromatic solvents such as toluene and xylene. The solvent is preferably used such that the concentration of solids after removing the solvent from the resulting varnish is in the range of 10 to 80% by weight, more preferably 20 to 70% by weight.

[0062] The curable resin composition of this embodiment can also be used as a resin sheet, prepreg, or carbon fiber reinforced composite material.

[0063] The curable resin composition of this embodiment can be coated onto one or both sides of a support substrate to be used as a resin sheet. Examples of coating methods include: casting, extruding the resin from a nozzle or die using a pump or extruder and adjusting the thickness with a scraper, calendering with rollers to adjust the thickness, and spraying using a sprayer. Furthermore, in the layer-forming step, heating can be performed within a temperature range that avoids thermal decomposition of the curable resin composition. Calendering or grinding processes can also be performed as needed. Examples of support substrates include porous substrates made of paper, cloth, or nonwoven fabric; plastic films or sheets such as polyethylene, polypropylene, polyethylene terephthalate, and polyester films; meshes; foams; metal foils; and laminates thereof, but are not limited to these. The thickness of the support substrate is not particularly limited and can be appropriately determined according to the application.

[0064] The prepreg of this embodiment can be obtained by heating and melting the curable resin composition and / or resin sheet of this embodiment to reduce its viscosity and impregnate it into a fiber substrate.

[0065] Alternatively, the prepreg of this embodiment can be obtained by impregnating a varnish-like curable resin composition into a fiber substrate and then heating and drying it. After cutting the prepreg into the desired shape and stacking them, the curable resin composition is heated and cured while applying pressure to the stack using a pressing method, autoclave forming method, sheet winding method, etc., thereby obtaining the carbon fiber reinforced composite material of this embodiment. In addition, copper foil or organic film may also be stacked during the stacking of the prepreg.

[0066] In addition to the above-described method, the carbon fiber reinforced composite material forming method of this embodiment can also be formed by well-known methods. For example, resin transfer molding (RTM method) can also be used, which involves cutting, stacking, and shaping a carbon fiber substrate (usually carbon fiber fabric) to create a preform (a preform before resin impregnation), placing the preform in a molding mold and closing the mold, injecting resin to impregnate the preform and allowing it to harden, opening the mold, and removing the molded product.

[0067] Alternatively, methods belonging to the RTM method, such as Vacuum Assisted Resin Transfer Molding (VaRTM), Seeman's Composite Resin Infusion Molding Process (SCRIMP), and the method described in Japanese Patent Application Publication No. 2005-527410, which involves venting the resin supply tank until the pressure is lower than atmospheric pressure, using cyclic compression, and controlling the net forming pressure to more appropriately control the resin injection process, especially the Controlled Atmospheric Pressure Resin Infusion (CAPRI) method of VaRTM, etc.

[0068] Alternatively, a film stacking method in which resin sheets (films) are sandwiched between fiber substrates can be used; a method in which powdered resin is attached to a reinforcing fiber substrate to improve impregnation; a forming method in which a flow layer or fluid slurry method is used during the mixing of resin into the fiber substrate (powder impregnated yarn); and a method in which resin fibers are mixed into the fiber substrate.

[0069] Carbon fibers can include acrylic, pitch, and rayon-based fibers, with acrylic carbon fibers, which have high tensile strength, being the most preferred. Regarding the form of the carbon fiber, twisted, untwisted, and untwisted yarns can be used, but to achieve a good balance between the formability and strength properties of the fiber-reinforced composite material, untwisted or untwisted yarns are preferred.

[0070] [Example]

[0071] The following examples and embodiments are provided to further illustrate the present invention. The materials, processing methods, and procedures described below can be appropriately modified without departing from the spirit of the invention. Therefore, the scope of the present invention should not be construed as limited to the specific examples described below.

[0072] The analytical method is based on the following conditions.

[0073] ·Epoxy equivalent

[0074] Determined according to the method described in JIS K7236. Units are g / eq.

[0075] GPC (Gel Permeation Chromatography) Analysis

[0076] Manufacturer: Waters

[0077] Guard Columns: SHODEX GPC KF-601, KF-602, KF-602.5, KF-603

[0078] Flow rate: 0.5 ml / min.

[0079] Column temperature: 40℃

[0080] Solvent used: THF (tetrahydrofuran)

[0081] Detector: RI (Differential Refraction Detector)

[0082] [Synthesis example 1]

[0083] 254 parts by weight of phenol, 63 parts by weight of water, and 27 parts by weight of sodium hydroxide were placed in a flask equipped with a stirrer, reflux cooling tube, and heating device. After stirring and dissolving, the mixture was heated to 110°C, and 63 parts by weight of furfural were added dropwise over 2 hours. After reacting at 110°C for 3 hours, the temperature was raised to 145°C. During the heating process, the distilled water was removed from the system. After reaching 145°C, the mixture was immediately cooled to 80°C, and 63 parts by weight of water, 4 parts by weight of phosphoric acid, and 63 parts by weight of 35% hydrochloric acid were added for neutralization. After repeated washing with water, unreacted phenol was distilled off under heating and reduced pressure to obtain 112 parts by weight of the phenol resin represented by the aforementioned formula (2). Relative to 78 parts by weight of the phenolic resin represented by the aforementioned formula (2), 254 parts by weight of epichlorohydrin (ECH, hereinafter the same), 64 parts by weight of dimethyl sulfoxide (DMSO, hereinafter the same), and 13 parts by weight of water were placed in a reaction vessel, heated, and stirred. After the phenolic resin and ECH dissolved, 23 parts by weight of flake sodium hydroxide were added in batches over 2 hours while maintaining the temperature of the solution at 45°C. Then, the reaction was carried out at 45°C for 2 hours, and further at 70°C for 60 minutes. Subsequently, after repeated washing with water to remove by-product salts and DMSO, excess epichlorohydrin was distilled off from the oil layer under heating and reduced pressure. For the residue, 218 parts by weight of methyl isobutyl ketone was added and dissolved. This methyl isobutyl ketone solution was heated to 70°C, and 7 parts by weight of a 30% sodium hydroxide aqueous solution was added. After reacting for 1 hour, the reaction solution was repeatedly washed with water until the washing solution became neutral. Then, methyl isobutyl ketone was distilled off from the oil layer under heating and reduced pressure to obtain 101 parts by weight of the epoxy resin represented by the aforementioned formula (1) (n in formula (1) is 2.2). The epoxy equivalent of the obtained epoxy resin is 218 g / eq.

[0084] [Synthesis example 2]

[0085] In a flask equipped with a stirrer, reflux cooling tube, and 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. The mixture was then heated to 110°C, and 53 parts by weight of furfural were added dropwise over 2 hours. After reacting at 110°C for 3 hours, the temperature was raised to 145°C. During the heating process, the distilled water was removed from the system. After reaching 145°C, the mixture was allowed to react for 4 hours. Subsequently, the mixture was cooled to 80°C, and 63 parts by weight of water, 4 parts by weight of phosphoric acid, and 63 parts by weight of 35% hydrochloric acid were added for neutralization. After repeated washing with water, unreacted phenol was distilled off under heating and reduced pressure to obtain 109 parts by weight of the phenol resin represented by the aforementioned formula (2). Relative to 78 parts by weight of the obtained phenol resin represented by the aforementioned formula (2), 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, heated, and stirred. After dissolving the phenolic resin and ECH, 23 parts by weight of flake sodium hydroxide were added in batches over 2 hours while maintaining the temperature at 45°C. The reaction was then carried out at 45°C for 2 hours, followed by a further reaction at 70°C for 60 minutes. After repeated washing with water to remove byproduct salts and dimethyl sulfoxide, excess epichlorohydrin was distilled off from the oil layer under reduced pressure. 218 parts by weight of methyl isobutyl ketone were added to the residue and dissolved. This methyl isobutyl ketone solution was heated to 70°C, and 7 parts by weight of a 30% aqueous sodium hydroxide solution were added. After reacting for 1 hour, the reaction solution was repeatedly washed with water until the washing solution became neutral. Then, methyl isobutyl ketone was distilled off from the oil layer under reduced pressure, thereby obtaining 103 parts by weight of the epoxy resin represented by the aforementioned formula (1) (n in formula (1) is 2.1). The epoxy equivalent of the obtained epoxy resin was 213 g / eq.

[0086] [Synthesis example 3]

[0087] In a flask equipped with a stirrer, reflux cooling tube, and 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. The mixture was then heated to 110°C, and 44 parts by weight of furfural were added dropwise over 2 hours. After reacting at 110°C for 3 hours, the temperature was raised to 145°C. During the heating process, the distilled water was removed from the system. After reaching 145°C, the mixture was immediately cooled to 80°C, and 63 parts by weight of water, 4 parts by weight of phosphoric acid, and 63 parts by weight of 35% hydrochloric acid were added for neutralization. After repeated washing with water, unreacted phenol was distilled off under heating and reduced pressure to obtain 109 parts by weight of the phenolic resin represented by the aforementioned formula (2). Relative to 78 parts by weight of the obtained phenolic resin represented by the aforementioned formula (2), 254 parts by weight of ECH, 64 parts by weight of DMSO, and 13 parts by weight of water were fed into a reaction vessel, and the mixture was heated and stirred. After dissolving the phenolic resin and ECH, 23 parts by weight of flake sodium hydroxide were added in batches over 2 hours while maintaining the temperature at 45°C. The reaction was then carried out at 45°C for 2 hours, followed by a further reaction at 70°C for 60 minutes. After repeated washing with water to remove byproduct salts and dimethyl sulfoxide, excess epichlorohydrin was distilled off from the oil layer under reduced pressure. 218 parts by weight of methyl isobutyl ketone were added to the residue and dissolved. This methyl isobutyl ketone solution was heated to 70°C, and 7 parts by weight of a 30% aqueous sodium hydroxide solution were added. After reacting for 1 hour, the reaction solution was repeatedly washed with water until the washing solution became neutral. Then, methyl isobutyl ketone was distilled off from the oil layer under reduced pressure, thereby obtaining 103 parts by weight of the epoxy resin represented by the aforementioned formula (1) (n in formula (1) is 2.0). The epoxy equivalent of the obtained epoxy resin was 211 g / eq.

[0088] [Synthesis Example 4]

[0089] In a flask equipped with a stirrer, reflux cooling tube, and 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, dissolved, and heated to 110°C. 90 parts by weight of furfural were added dropwise over 2 hours. After reacting at 110°C for 3 hours, the temperature was raised to 145°C. During the heating process, the distilled water was removed from the system. After reaching 145°C, the reaction was allowed to proceed for 4 hours. Subsequently, the temperature was cooled to 80°C, and 63 parts by weight of water, 4 parts by weight of phosphoric acid, and 63 parts by weight of 35% hydrochloric acid were added for neutralization. After repeated washing with water, unreacted phenol was distilled off under heating and reduced pressure to obtain 120 parts by weight of the phenolic resin represented by the aforementioned formula (2). Relative to 78 parts by weight of the obtained phenolic resin represented by the aforementioned formula (2), 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, heated, and stirred. After dissolving the phenolic resin and ECH, 23 parts by weight of flake sodium hydroxide were fed in batches over 2 hours while maintaining the temperature at 45°C. The reaction was then carried out at 45°C for 2 hours, followed by a further reaction at 70°C for 60 minutes. After repeated washing with water to remove byproduct salts and dimethyl sulfoxide, excess epichlorohydrin was distilled off from the oil layer under reduced pressure. 218 parts by weight of methyl isobutyl ketone were added to the residue and dissolved. This methyl isobutyl ketone solution was heated to 70°C, and 7 parts by weight of a 30% aqueous sodium hydroxide solution were added. After reacting for 1 hour, the reaction solution was repeatedly washed with water until the washing solution became neutral. Then, methyl isobutyl ketone was distilled off from the oil layer under reduced pressure, thereby obtaining 90 parts by weight of the epoxy resin represented by the aforementioned formula (1) (n in formula (1) is 2.6). The epoxy equivalent of the obtained epoxy resin was 223 g / eq.

[0090] [Synthesis example 5]

[0091] In a flask equipped with a stirrer, reflux cooling tube, and 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. The mixture was then heated to 110°C, and 33 parts by weight of furfural were added dropwise over 2 hours. After reacting at 110°C for 3 hours, the temperature was raised to 145°C. During the heating process, the distilled water was removed from the system. After reaching 145°C, the mixture was immediately cooled to 80°C, and 63 parts by weight of water, 4 parts by weight of phosphoric acid, and 63 parts by weight of 35% hydrochloric acid were added for neutralization. After repeated washing with water, unreacted phenol was distilled off under heating and reduced pressure to obtain 90 parts by weight of the phenolic resin represented by the aforementioned formula (2). Relative to 78 parts by weight of the obtained phenolic resin represented by the aforementioned formula (2), 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, heated, and stirred. After dissolving the phenolic resin and ECH, 23 parts by weight of flake sodium hydroxide were added in batches over 2 hours while maintaining the temperature at 45°C. The reaction was then carried out at 45°C for 2 hours, followed by a further reaction at 70°C for 60 minutes. After repeated washing with water to remove byproduct salts and dimethyl sulfoxide, excess epichlorohydrin was distilled off from the oil layer under reduced pressure. 218 parts by weight of methyl isobutyl ketone were added to the residue and dissolved. This methyl isobutyl ketone solution was heated to 70°C, and 7 parts by weight of a 30% sodium hydroxide aqueous solution were added. After reacting for 1 hour, the reaction solution was repeatedly washed with water until the washing solution became neutral. Then, methyl isobutyl ketone was distilled off from the oil layer under reduced pressure, thereby obtaining 109 parts by weight of the epoxy resin represented by the aforementioned formula (1) (n in formula (1) is 1.7). The epoxy equivalent of the obtained epoxy resin was 204 g / eq.

[0092] [Examples 1 to 3, Comparative Examples 1 to 2]

[0093] Using the epoxy resins obtained in Synthetic Examples 1 to 5 as the main agent and 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane (TEDDM, manufactured by Tokyo Chemical Co., Ltd., with an active hydrogen equivalent of 78 g / eq.) as the curing agent, the mixtures were prepared according to the weight ratios shown in Table 1 and cured at 160°C for 6 hours to produce cured products.

[0094] The physical property values ​​are determined under the following conditions.

[0095] <Glass Transfer Point (Tg) Determination Conditions>

[0096] Dynamic viscoelasticity measuring instrument: TA-instruments, DMA-2980.

[0097] Temperature range: -30 to 280℃

[0098] Heating rate: 2℃ / minute

[0099] Tg: Set the peak temperature of the loss elastic modulus to Tg.

[0100] <Conditions for determining bending strength and maximum bending elongation>

[0101] • The measurements were performed in accordance with JIS K-7074.

[0102] [Table 1]

[0103]

[0104] The results in Table 1 confirm that the cured products of Examples 1 to 3 of this application have high glass transition temperatures, excellent heat resistance, and excellent flexural strength. On the other hand, it was confirmed that Comparative Example 1 had problems with flexural strength and maximum flexural elongation, and Comparative Example 2 had problems with heat resistance.

[0105] This application claims priority under Japanese Patent Application No. 2023-113998, filed on July 11, 2023.

Claims

1. An epoxy resin represented by the following formula (1), having an epoxy equivalent of 210 g / eq. or more and 218 g / eq. or less; In formula (1), n is the average value of the repetition number and represents a real number of 1 < n < 15.

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

3. The curable resin composition according to claim 2, wherein, The aforementioned curing agent is an amine-based curing agent.

4. A cured product obtained by curing the curable resin composition according to claim 2 or 3.

5. A carbon fiber reinforced composite material comprising: a cured product obtained by curing the curable resin composition according to claim 2 or 3, and carbon fibers.

Images