Epoxy resins, curable resin compositions, and cured products thereof, as well as carbon fiber reinforced composite materials

Abstract

The present invention provides an epoxy resin exhibiting excellent heat resistance and flexural modulus, a curable resin composition, cured products thereof, and a carbon fiber-reinforced composite material.　The epoxy resin is represented by general formula (1) and has an epoxy equivalent of 228-237 g / eq. (In formula (1), n is the average number of repetitions, and denotes a real number within the range 1<n<15.)

Description

Technical Field

[0001] The present invention relates to an epoxy resin, a curable resin composition, a cured product thereof, and a carbon fiber reinforced composite material.

Background Art

[0002] Epoxy resins can be cured with various curing agents to form cured products that are excellent in mechanical properties, water resistance, chemical resistance, heat resistance, electrical properties, etc., and are used in a wide range of fields such as adhesives, paints, laminates, molding materials, and casting materials. Carbon fiber reinforced composite materials (CFRP) obtained by impregnating and curing reinforcing fibers with an epoxy resin and a curing agent as a matrix resin can impart characteristics such as weight reduction and high strength, and in recent years, they have been widely used in aircraft structural members, wind turbine blades, automotive exterior panels, and computer applications such as IC trays and laptop computer housings (housings), and the demand for them is increasing. In particular, taking advantage of the lightweight and high-strength characteristics of the molded body, it is used as a matrix resin for aircraft applications.

[0003] In recent years, the required properties for CFRP have become stricter, and in particular, when applied to structural materials such as aerospace applications and vehicles, resins with better heat resistance and elastic modulus are required (Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 3 describes an epoxy resin with low water absorption. However, the epoxy resin described in Patent Document 3 has low heat resistance and a low elastic modulus, making it difficult to apply as a CFRP material.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide an epoxy resin, a curable resin composition, cured products thereof, and a carbon fiber reinforced composite material having high heat resistance and a high flexural elastic modulus.

Means for Solving the Problems

[0007] That is, the present invention is as set forth in the following [1] to [8]. In the present invention, “(numerical value 1) to (numerical value 2)” indicates that the upper and lower limit values are included. [1] An epoxy resin represented by the following formula (1) and having an epoxy equivalent of 228 g / eq. or more and 237 g / eq. or less.

[0008]

Chemical formula

[0009] (In formula (1), n is the average value of the number of repetitions and represents a real number of 1 < n < 15.) [2] An epoxy resin represented by the following formula (l), wherein when the epoxy equivalent is a and the softening point is b, a / b is 3.0 or more and 3.4 or less. <…>

[0010] <…>

Chemical formula

[0011] (In formula (1), n is the average value of the number of repetitions and represents a real number of 1 < n < 15.) [3] The epoxy resin according to the above [1] or [2], having a biomass content of 50% or more. [4] A curable resin composition containing an epoxy resin according to any one of [1] to [3] above and a curing agent. [5] The curable resin composition according to the previous item [4], wherein the curing agent is an amine-based curing agent. [6] A curable resin composition containing an epoxy resin according to any one of [1] to [3] above and at least one selected from a curing accelerator, a polymerization initiator, an epoxy resin other than the epoxy resin represented by the above formula (1), an active ester compound, a phenolic resin, a polyphenylene ether compound, a compound having an ethylenically unsaturated bond, an isocyanate resin, a polyamide resin, a maleimide compound, a cyanate ester resin, a polyimide resin, polybutadiene and its modified products, polystyrene and its modified products, polyethylene and its modified products, and a benzoxazine compound. [7] A cured product obtained by curing the curable resin composition according to the previous item [4] or [5]. [8] A carbon fiber reinforced composite material obtained by curing the curable resin composition according to the previous item [4] or [5]. [Effect of the Invention]

[0012] 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, the cured product of which has high heat resistance and a high flexural modulus of elasticity. [Brief Description of the Drawings]

[0013] [Figure 1] The evaluation results of Example 1 and Comparative Examples 1 to 2 are shown. [Modes for Carrying Out the Invention]

[0014] Hereinafter, embodiments according to the present invention (hereinafter also referred to as "the present embodiment") will be described in more detail.

[0015] The epoxy resin of the present embodiment is represented by the following formula (1).

[0016] [Chemical formula]

[0017] (In formula (1), n is the average value of the repetition number and represents a real number of 1 < n < 15.)

[0018] In the above formula (1), the value of n can be determined by the number average molecular weight measured by gel permeation chromatography (GPC, detector: RI) of the epoxy resin, or calculated from the area ratio of each separated peak. n is preferably a real number of 1 < n < 15, more preferably 1 < n < 10, and particularly preferably 1 < n < 5.

[0019] The epoxy equivalent of the epoxy resin of this embodiment is preferably 228 g / eq or more and 237 g / eq or less, more preferably 230 g / eq or more and 236 g / eq or less, and even more preferably 231 g / eq or more and 235 g / eq or less. When the epoxy equivalent is 228 g / eq or more, it has high heat resistance, and when it is 237 g / eq or less, it has a high flexural modulus. That is, by having an epoxy equivalent of 228 g / eq or more and 237 g / eq or less, the characteristics of high heat resistance and high flexural modulus can be achieved simultaneously.

[0020] The softening point of the epoxy resin represented by the above formula (1) is preferably 67 °C or more and 100 °C or less, and more preferably 70 °C or more and 80 °C or less. When the softening point is 67 °C or more, the resins do not block even without refrigerated storage, enabling storage at room temperature, which is preferable in terms of storage handling. When it is higher than 100 °C, it becomes difficult to uniformly mix with a curing agent, polymerization initiator, filler, etc., and curing defects are likely to occur.

[0021] In this embodiment, when the epoxy resin has an epoxy equivalent of a and a softening point of b, the a / b ratio is preferably 3.0 to 3.4, and more preferably 3.1 to 3.3. When a / b is 3.4 or less, the epoxy equivalent is low relative to a certain softening point, resulting in a high curing density and good heat resistance, thermal decomposition resistance, and elastic modulus. On the other hand, when a / b is less than 3.0, the softening point is too high relative to the epoxy equivalent, restricting molecular movement during the curing reaction and resulting in partial insufficient curing, thus reducing heat resistance and thermal decomposition resistance. In other words, when a / b is between 3.0 and 3.4, a balance is achieved between curing density and curing reaction, allowing for the expression of excellent properties.

[0022] The cured epoxy resin of this embodiment has high heat resistance and a high flexural modulus. A flexural modulus of 3.0 to 4.0 GPa is preferable. A flexural modulus of less than 3.0 GPa is undesirable because it results in insufficient strength and reduced reliability when used as a carbon fiber reinforced composite material. The flexural modulus of this embodiment is measured by the method described in the examples below.

[0023] Heat resistance can be evaluated by the 5% weight loss temperature and the glass transition temperature (Tg). The 5% weight loss temperature is preferably 295°C or higher. The glass transition temperature (Tg) is preferably 210°C to 300°C, more preferably 215°C to 250°C, and even more preferably 216°C to 230°C. A heat resistance of less than 210°C makes it difficult to apply to components requiring heat resistance, such as around aircraft engines. This is undesirable because the resin softens during use, significantly reducing mechanical strength and leading to material breakage. Furthermore, the heat resistance of epoxy resins generally correlates with crosslinking density; higher crosslinking density results in higher heat resistance. Therefore, a heat resistance exceeding 300°C is undesirable because the crosslinking density increases, making the cured product brittle. The 5% weight loss temperature and glass transition temperature (Tg) in this embodiment are measured using the method described in the examples below.

[0024] From the perspective of environmental issues, the biomass content of the epoxy resin of the present embodiment is preferably 50% or more. The upper limit of the biomass content is not particularly limited and may be 100%, but from the balance with the cured physical properties, it is preferably 80%. A high biomass content can also mean reducing the usage amount of fossil resource-based materials represented by petroleum, etc., so it is also significant from the point of sustainable use of resources. Therefore, in the curable resin composition after being mixed with other materials, it is also preferable that the biomass content is high. Specifically, it is preferably 20% or more, and more preferably 30% or more. The biomass content of the present embodiment is measured by the method described in the examples below.

[0025] The epoxy resin represented by the above formula (1) can be obtained by the reaction of a phenol resin represented by the following formula (2) and epihalohydrin.

[0026]

Chemical formula

[0027] (In formula (2), n is the average value of the number of repetitions and represents a real number of 1 < n < 15.)

[0028] The preferable range of n in the above formula (2) is the same as that of the above formula (1).

[0029] The epihalohydrin can be easily obtained from the market. The usage amount of epihalohydrin is preferably 2.0 to 10 moles, more preferably 3.0 to 8.0 moles, and even more preferably 3.5 to 6.0 moles with respect to 1 mole of the hydroxyl group of the raw material phenol mixture. Examples of the epihalohydrin that can be used in the present embodiment preferably include epichlorohydrin, α-methylepichlorohydrin, β-methylepichlorohydrin, epibromohydrin, etc. In particular, epichlorohydrin, which is easily available industrially, is preferable.

[0030] In the above reaction, an alkali metal hydroxide can be used as a catalyst to accelerate the epoxidation step. Examples of alkali metal hydroxides that can be used include sodium hydroxide and potassium hydroxide. Solid materials or aqueous solutions thereof may be used, but in this embodiment, the use of solid materials molded into flakes is particularly preferred in terms of solubility and handling. The amount of alkali metal hydroxide used is preferably 0.90 to 1.5 moles, more preferably 0.95 to 1.25 moles, and even more preferably 0.99 to 1.15 moles per mole of hydroxyl groups in the raw material phenol mixture.

[0031] Furthermore, quaternary ammonium salts such as tetramethylammonium chloride, tetramethylammonium bromide, and trimethylbenzylammonium chloride may be added as catalysts to accelerate the reaction. The amount of quaternary ammonium salt used is preferably 0.1 to 15 g, and more preferably 0.2 to 10 g, per mole of hydroxyl groups in the raw material phenol mixture.

[0032] The reaction temperature is preferably 30 to 90°C, more preferably 35 to 80°C. In this embodiment in particular, a temperature of 50°C or higher is preferred for higher purity epoxidation, and a temperature of 60°C or higher is particularly preferred. The reaction time is preferably 0.5 to 10 hours, more preferably 1 to 8 hours, and particularly preferably 1 to 3 hours. A reaction time that is too short is undesirable because the reaction will not proceed completely, and a reaction time that is too long is undesirable because byproducts will form.

[0033] After washing the reactants from these epoxidation reactions with water, or without washing, the epihalohydrins and solvents are removed by heating under reduced pressure. Furthermore, to obtain an epoxy resin with fewer hydrolyzable halogens, the recovered epoxy resin can be dissolved in a ketone compound having 4 to 7 carbon atoms (for example, 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 carry out the reaction and ensure 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, per mole of hydroxyl groups in the raw material phenol mixture used for epoxidation. The reaction temperature is preferably 50 to 120°C, and the reaction time is preferably 0.5 to 2 hours.

[0034] After the reaction is complete, the generated salt is removed by filtration, washing with water, etc., and the solvent is further removed by distillation under reduced pressure and heating to obtain the epoxy resin of this embodiment.

[0035] In the synthesis method of the phenolic resin represented by formula (2) above, when a reaction (condensation) of furfural with phenols is carried out, the amount of phenols is preferably in the range of 1.5 to 20 moles, and particularly preferably 3 to 10 moles, per mole of furfural.

[0036] As for phenols 、1 Phenol as a substituted phenol raised Get ru.

[0037] Examples of solvents include methanol, ethanol, propanol, isopropanol, toluene, and xylene, but are not limited to these; they may be used alone or in combination of two or more. When a solvent is used, the amount used is preferably in the range of 5 to 500 parts by weight, more preferably 10 to 300 parts by weight, per 100 parts by weight of phenol.

[0038] In the above condensation reaction, it is preferable to use a base catalyst. Although polycondensation is possible with an acidic catalyst, reactions between furfural compounds also occur, resulting in a large number of by-products. There is also a method using organometallic compounds, but it is disadvantageous in terms of cost. Specific examples of base 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 methoxide, sodium ethoxide, potassium methoxide, potassium ethoxide, and potassium tert-butoxide; and alkaline earth metal alkoxides such as magnesium methoxide and magnesium ethoxide. However, the catalyst is not limited to these, and one or more catalysts may be used in combination. The amount of catalyst used is preferably 0.005 to 2.0 moles, more preferably 0.01 to 1.1 moles, per mole of phenol.

[0039] These condensation reactions in the presence of base catalysts are preferably carried out in the range of 40 to 180°C, particularly preferably in the range of 80 to 165°C, and the reaction time can be preferably selected in the range of 0.5 to 10 hours. The reactants thus obtained are neutralized to make the system neutral, or washed repeatedly with water in the presence of a solvent, then the water is separated and drained, and the solvent and unreacted substances are removed under heating and reduced pressure to obtain the phenol resin represented by formula (2).

[0040] The curable resin composition of this embodiment contains a curing agent. Examples of curing agents that can be used include amine-based curing agents, acid anhydride-based curing agents, amide-based curing agents, and phenol-based curing agents.

[0041] In the curable resin composition of this embodiment, an amine curing agent is preferred because it can achieve a good balance between the resin viscosity of the curable resin composition and the heat resistance of the cured resin product. Examples of amine-based curing agents include 3,3'-diaminodiphenylsulfone (3,3'-DDS), 4,4'-diaminodiphenylsulfone (4,4'-DDS), diaminodiphenylmethane (DDM), 3,3'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-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-t-butyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane (TEDDM), and 3,3'-diisopropyl-5,5'-diethyl-4 ,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetraisopropyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetra-t-butyl-4,4'-diaminodiphenylmethane, diaminodiphenyl ether (DADPE), bisaniline, benzyldimethylaniline, 2-(dimethylaminomethyl)phenol (DMP-10), 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), 2-ethylhexanoic acid ester of 2,4,6-tris(dimethylaminomethyl)phenol, etc. can be used. Other examples include aniline novolac, orthoethylaniline novolac, aniline resins obtained by the reaction of aniline with xylylene chloride, and aniline resins 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).

[0042] Examples of acid anhydride-based curing agents include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, and methylhexahydrophthalic anhydride.

[0043] Examples of amide-based curing agents include dicyandiamide, or polyamide resins synthesized from a linolenic acid dimer and ethylenediamine.

[0044] Phenolic curing agents include polyhydric phenols (bisphenol A, bisphenol F, bisphenol S, fluorenebisphenol, terpene diphenol, 4,4'-dihydroxybiphenyl, 2,2'-dihydroxybiphenyl, 3,3',5,5'-tetramethyl-(1,1'-biphenyl)-4,4'-diol, hydroquinone, resorcinol, naphthalenediol, tris-(4-hydroxyphenyl)methane and 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, etc.); phenols (e.g., phenol, alkyl-substituted phenol, naphthol, alkyl-substituted naphthol, dihydroxybenzene and dihydroxynaphthalene, etc.) and aldehydes (formaldehyde, acetaldehyde, benzaldehyde, p-hydroxybenzaldehyde, o-hydroxy Phenolic resins obtained by condensation of phenols (such as sibenzaldehyde and furfural), ketones (such as p-hydroxyacetophenone and o-hydroxyacetophenone), or dienes (such as dicyclopentadiene and tricyclopentadiene); phenolic resins obtained by polycondensation of the 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 phenols and / or the phenolic resins; and halogenated phenols such as tetrabromobisphenol A and brominated phenolic resins.

[0045] In the curable resin composition of this embodiment, it is also preferable to use the phenol resin represented by formula (2) as all or part of the curing agent.

[0046] In the curable resin composition of this embodiment, the amount of curing agent used is preferably 0.7 to 1.2 equivalents per equivalent of epoxy groups in the epoxy resin. If the amount is less than 0.7 equivalents or more than 1.2 equivalents per equivalent of epoxy groups, curing may be incomplete, and good cured properties may not be obtained.

[0047] Furthermore, a curing accelerator may be added to the curable resin composition of this embodiment as needed. The gelation time can also be adjusted by using a curing accelerator. Examples of curing 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 octylate. The curing accelerator is used in amounts of 0.01 to 5.0 parts by weight per 100 parts by weight of epoxy resin, as needed.

[0048] In the curable resin composition of this embodiment, other epoxy resins may be blended, specifically including phenols (phenol, alkyl-substituted phenol, aromatic-substituted phenol, naphthol, alkyl-substituted naphthol, dihydroxybenzene, alkyl-substituted dihydroxybenzene, dihydroxynaphthalene, etc.) and various aldehydes (formaldehyde, acetaldehyde, alkylaldehyde, benzaldehyde, alkyl-substituted benzaldehyde, hydroxybenzaldehyde, naphthaldehyde). Polycondensates of phenols (glutaraldehyde, phthalaldehyde, crotonaldehyde, cinnamaldehyde, etc.), polymers of phenols and various diene compounds (dicyclopentadiene, terpenes, vinylcyclohexene, norbornadiene, vinylnorbornene, tetrahydroindene, divinylbenzene, divinylbiphenyl, diisopropenylbiphenyl, butadiene, isoprene, etc.), and phenols and ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, acetophenone, benzo Examples include polycondensates of phenols (such as phenones), phenol resins obtained by polycondensation of 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), polycondensates of bisphenols with various aldehydes, glycidyl ether epoxy resins obtained by glycidylating alcohols, alicyclic epoxy resins such as 4-vinyl-1-cyclohexene diepoxide and 3,4-epoxycyclohexylmethyl-3,4'-epoxycyclohexanecarboxylate, glycidylamine epoxy resins such as tetraglycidyldiaminodiphenylmethane (TGDDM) and triglycidyl-p-aminophenol, and glycidyl ester epoxy resins, but are not limited to these as long as they are commonly used epoxy resins.

[0049] The curable resin composition of this embodiment may contain known additives as needed. Specific examples of additives that can be used include active ester compounds, phenolic resins, compounds having ethylenically unsaturated bonds, isocyanate resins, polyamide resins, benzoxazine compounds, polybutadiene and its modified products, modified acrylonitrile copolymers, polyphenylene ether compounds, polystyrene and its modified products, polyethylene and its modified products, polyimide resins, fluororesins, maleimide compounds, cyanate ester resins, silicone gels, silicone oils, and 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; surface treatment agents for fillers such as silane coupling agents; release agents; and colorants such as carbon black, phthalocyanine blue, and phthalocyanine green.

[0050] Examples of active ester compounds include phenol esters, thiophenol esters, N-hydroxyamine esters, and esters of heterocyclic hydroxy compounds.

[0051] Examples of polyphenylene ether compounds include SA-9000 (manufactured by SABIC, a polyphenylene ether compound having a methacrylic group) and OPE-2St 1200 (manufactured by Mitsubishi Gas Chemical Company, a polyphenylene ether compound having a styrene structure).

[0052] Compounds containing ethylenically unsaturated bonds include reaction products of phenolic resins with halogenated compounds containing ethylenically unsaturated bonds (chloromethylstyrene, allyl chloride, methyl chloride, acrylate chloride, methacrylate chloride, etc.), reaction products of ethylenically unsaturated phenols (2-allylphenol, 2-propenylphenol, 4-allylphenol, 4-propenylphenol, eugenol, isoeugenol, etc.) with halogenated compounds (1,4-bis(chloromethyl)benzene, 4,4'-bis(chloromethyl)biphenyl, 4,4'-difluorobenzophenone, 4,4'-dichlorobenzophenone, 4,4'-dibromobenzophenone, cyanuryl chloride, etc.), reaction products of epoxy resins or alcohols with (meth)acrylic acids (acrylic acid, methacrylic acid, etc.), and acid-modified products thereof.

[0053] Examples of isocyanate resins include aromatic diisocyanates such as p-phenylenediisocyanate, m-phenylenediisocyanate, p-xylenediisocyanate, m-xylenediisocyanate, 2,4-tollylenediisocyanate, 2,6-tollylenediisocyanate, 4,4'-diphenylmethanediisocyanate, and naphthalenediisocyanate; aliphatic or alicyclic diisocyanates such as isophorone diisocyanate, hexamethylenediisocyanate, 4,4'-dicyclohexylmethanediisocyanate, hydrogenated xylenediisocyanate, norbornene diisocyanate, and lysine diisocyanate; polyisocyanates such as biuret compounds of one or more isocyanate monomers, or isocyanate compounds obtained by trimerizing the above diisocyanate compounds; and polyisocyanates obtained by urethane reaction between the above isocyanate compounds and polyol compounds.

[0054] Maleimide compounds include 4,4'-diphenylmethanebismaleimide, polyphenylmethanebismaleimide, m-phenylenebismaleimide, 2,2'-bis[4-(4-maleimidophenoxy)phenyl]propane, 3,3'-dimethyl-5,5'-diethyl-4,4'-diphenylmethanebismaleimide, 4-methyl-1,3-phenylenebismaleimide, 4,4'-diphenyletherbismaleimide, 4,4'-diphenylsulfonebismaleimide, 1,3-bis(3-maleimidophenoxy)benzene, 1,3-bis(4-maleimidophenoxy)benzene, and Zyloc-type maleimide compounds (anilix). Examples include maleimide (manufactured by Mitsui Chemicals Fine Co., Ltd.), biphenylaralkyl type maleimide compounds (solidified by solvent distillation under reduced pressure of a resin solution containing the maleimide compound (M2) described in Example 4 of Japanese Patent Publication No. 2009-001783), bisaminocumylbenzene type maleimide (maleimide compound described in International Publication No. 2020 / 054601), maleimide compounds having an indan structure described in Japanese Patent No. 6629692 or International Publication No. 2020 / 217679, and maleimide compounds described in MATERIAL STAGE Vol. 18, No. 12 2019 "Continued Epoxy Resin CAS Number Story - Curing Agent CAS Number Memo No. 31 Bismaleimide (1)" and MATERIAL STAGE Vol. 19, No. 2 2019 "Continued Epoxy Resin CAS Number Story - Curing Agent CAS Number Memo No. 32 Bismaleimide (2)". These may be used individually or in combination of two or more. When maleimide compounds are incorporated, a curing accelerator may be added as needed, and the aforementioned curing accelerators, organic peroxides, azo compounds, and other radical polymerization initiators can be used.

[0055] Examples of cyanate ester resins include dicyanatebenzene, tricyanatebenzene, dicyanatenaphthalene, dicyanatebiphenyl, 2,2'-bis(4-cyanatephenyl)propane, bis(4-cyanatephenyl)methane, bis(3,5-dimethyl-4-cyanatephenyl)methane, 2,2'-bis(3,5-dimethyl-4-cyanatephenyl)propane, 2,2'-bis(4-cyanatephenyl)ethane, 2,2'-bis(4-cyanatephenyl)hexafluoropropane, bis(4-cyanatephenyl)sulfone, bis(4-cyanatephenyl)thioether, phenol novolac cyanate, and phenol-dicyclopentadiene cocondensates in which the hydroxyl groups have been converted to cyanate groups.

[0056] As for the polyimide resin, the above diamine and tetracarboxylic dianhydride (4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-cyclohexene-1,2-dicarboxylic anhydride, pyromellitic dianhydride, 1,2,3,4-benzenetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4 '-Diphenylsulfonetetracarboxylic acid dianhydride, 2,2',3,3'-biphenyltetracarboxylic acid dianhydride, methylene-4,4'-diphthalic acid dianhydride, 1,1-ethylidene-4,4'-diphthalic acid dianhydride, 2,2'-propyridene-4,4'-diphthalic acid dianhydride, 1,2-ethylene-4,4'-diphthalic acid dianhydride, 1,3-trimethylene-4,4'-diphthalic acid dianhydride, 1,4-tetramethylene-4,4'-diphthalic acid dianhydride, 1,5-pentamethylene-4,4'-diphthalic acid dianhydride, 4,4'-oxydiphthalic acid dianhydride, thio-4 ,4'-diphthalic acid dianhydride, sulfonyl-4,4'-diphthalic acid dianhydride, 1,3-bis(3,4-dicarboxyphenyl)benzene dianhydride, 1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,3-bis[2-(3,4-dicarboxyphenyl)-2-propyl]benzene dianhydride, 1,4-bis[2-(3,4-dicarboxyphenyl)-2-propyl]benzene dianhydride, bis[3-(3,4-dicarboxyphenoxy)phenyl]methane dianhydride, bis [4-(3,4-dicarboxyphenoxy)phenyl]methane dianhydride, 2,2-bis[3-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, bis(3,4-dicarboxyphenoxy)dimethylsilane dianhydride, 1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldisiloxane dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride, 1,2,5,6-Naphthalenetetracarboxylic dianhydride, 3,4,9,10-Perylenetetracarboxylic dianhydride, 2,3,6,7-Anthracenetetracarboxylic dianhydride, 1,2,7,8-Phenanthrenetetracarboxylic dianhydride, Ethylenetetracarboxylic dianhydride, 1,2,3,4-Butanetetracarboxylic dianhydride, 1,2,3,4-Cyclobutanetetracarboxylic dianhydride, Cyclopentanetetracarboxylic dianhydride, Cyclohexane-1,2,3,4-Tetracarboxylic dianhydride, Cyclo Rohexane-1,2,4,5-tetracarboxylic acid dianhydride, 3,3',4,4'-bicyclohexyltetracarboxylic acid dianhydride, carbonyl-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, methylene-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, 1,2-ethylene-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, 1,1-ethylidene-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, 2,2- Propyridene-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, oxy-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, thio-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, sulfonyl-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, bicyclo[2,2,2]octo-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, rel-[1S,5R,6R]-3-oxabicyclo[3,2,1] Examples of reaction products include octane-2,4-dione-6-spiro-3'-(tetrahydrofuran-2',5'-dione), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic acid anhydride, ethylene glycol-bis-(3,4-dicarboxylic acid anhydride phenyl) ether, 4,4'-biphenylbis(trimellitic acid monoester anhydride), 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride, etc.

[0057] Polybutadiene and its modified products, polystyrene and its modified products, polyethylene and its modified products include polybutadiene, hydroxyl-terminated polybutadiene, terminally (meth)acrylated polybutadiene, carboxylic acid-terminated polybutadiene, amine-terminated polybutadiene, styrene-butadiene rubber, RICON-100, RICON-181, RICON-184 (all manufactured by Clay Valley), 1,2-SBS (manufactured by Nippon Soda Co., Ltd.), B-1000, B-2000, B-3000 (all manufactured by Nippon Soda Co., Ltd.); polystyrene, styrene-2-isopropenyl-2-oxazoline copolymer (Epocross RPS-1005, RP-61, both manufactured by Nippon Shokubai Co., Ltd.), SEP (styrene-ethylene-propylene copolymer: Septon 1020) SEPS (styrene-ethylene-propylene-styrene copolymer: Septon 2002, Septon 2004F, Septon 2005, Septon 2006, Septon 2063, Septon 2104, all manufactured by Kuraray Co., Ltd.), SEEPS (styrene-ethylene / ethylene-propylene-styrene block copolymer: Septon 4003, Septon 4044, Septon 4055, Septon 4077, Septon 4099, all manufactured by Kuraray Co., Ltd.), SEBS (styrene-ethylene-butylene-styrene block copolymer: Septon 8004, Septon 8006, Septon 8007L, all manufactured by Kuraray Co., Ltd.), SEEPS-OH (compound having hydroxyl groups at the ends of styrene-ethylene / ethylene-propylene-styrene block copolymer: Septon HG252) (Manufactured by Kuraray Co., Ltd.), SIS (styrene-isoprene-styrene block copolymer: Septon 5125, Septon 5127, both manufactured by Kuraray Co., Ltd.), Hydrogenated SIS (hydrogenated styrene-isoprene-styrene block copolymer: Hybrar 7125F, Hybrar 7311F, both manufactured by Kuraray Co., Ltd.), SIBS (styrene-isobutylene-styrene block copolymer: SIBSTAR073T, SIBSTAR102T, SIBSTAR103T (all manufactured by Kaneka Corporation), Septon V9827 (manufactured by Kuraray Co., Ltd.);Examples include ethylene-propylene copolymers, ethylene-styrene copolymers, ethylene-propylene-ethylidene norbornene copolymers (Mitsui Chemicals EBT: K-8370EM, K-9330M, etc.), ethylene-propylene-vinyl norbornene copolymers (Mitsui Chemicals VNB-EPT: PX-006M, PX-008M, PX-009M, etc.), ethylene-vinyl alcohol copolymers, and ethylene-vinyl acetate copolymers.

[0058] Examples of benzoxazine compounds include benzoxazine Pd, Fa, ALP-d (all manufactured by Shikoku Chemicals Co., Ltd.), JBZ-BA100N, JBZ-FA100N, JBZ-DP100N, JBZ-OP100N, JBZ-OP100D, JBZ-OP100I (all manufactured by JFE Chemical Corporation), and BTBz (manufactured by Nippon Materials Technology Co., Ltd.).

[0059] The curable resin composition of this embodiment can be converted into a varnish-like composition (hereinafter simply referred to as varnish) by adding an organic solvent. Examples of solvents that can be used include amide solvents such as γ-butyrolactones, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and N,N-dimethylimidazolidinone; sulfones 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 acetate, 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 used in a range such that the solid content concentration excluding the solvent in the resulting varnish is preferably 10 to 80% by weight, more preferably 20 to 70% by weight.

[0060] The curable resin composition of this embodiment can also be used as a resin sheet, prepreg, or carbon fiber reinforced composite material. The curable resin composition of this embodiment may be applied to one or both sides of a support substrate and used as a resin sheet. Application methods include, for example, casting, extruding the resin from a nozzle or die using a pump or extruder and adjusting the thickness with a blade, adjusting the thickness by calendering with a roll, and spraying using a sprayer. The layer formation process may be carried out while heating within a temperature range that avoids thermal decomposition of the curable resin composition. Furthermore, rolling, grinding, etc., may be performed as needed. Examples of support substrates include, but are not limited to, porous substrates made of paper, cloth, nonwoven fabric, etc., plastic films or sheets such as polyethylene, polypropylene, polyethylene terephthalate, and polyester film, nets, foams, metal foils, and laminates thereof. The thickness of the support substrate is not particularly limited and can be appropriately determined depending on the application.

[0061] 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 impregnating it into a fibrous substrate.

[0062] Alternatively, the prepreg of this embodiment can be obtained by impregnating a fibrous substrate with a varnish-like curable resin composition and then heating and drying it. After cutting the above prepreg into a desired shape and laminating it, the carbon fiber reinforced composite material of this embodiment can be obtained by applying pressure to the laminate using methods such as press molding, autoclave molding, or sheet winding molding while heating and curing the curable resin composition. Furthermore, copper foil or organic film can be laminated during the lamination of the prepreg.

[0063] Furthermore, the carbon fiber reinforced composite material of this embodiment can also be obtained by molding using known methods other than those described above. For example, a resin transfer molding (RTM) technique can be used, in which a carbon fiber substrate (usually carbon fiber fabric) is cut, laminated, and shaped to create a preform (a pre-molded body before resin impregnation), the preform is placed in a mold and the mold is closed, resin is injected to impregnate and harden the preform, and then the mold is opened to remove the molded product. Furthermore, various RTM methods can be used, such as the VaRTM method, the SCRIMP (Seeman's Composite Resin Infusion Molding Process) method, and the CAPRI (Controlled Atmospheric Pressure Resin Infusion) method, which more appropriately controls the resin injection process, particularly the VaRTM method, by evacuating the resin supply tank described in Japanese Patent Publication No. 2005-527410 to a pressure lower than atmospheric pressure, using circulating compression, and controlling the net molding pressure.

[0064] Furthermore, methods such as film stacking, which sandwiches the fiber substrate between resin sheets (films); attaching powdered resin to the reinforced fiber substrate to improve impregnation; molding methods (Powder Impregnated Yarn) that use a fluidized bed or fluid slurry method in the process of mixing resin with the fiber substrate; and methods that blend resin fibers into the fiber substrate can also be used.

[0065] Examples of carbon fibers include acrylic, pitch, and rayon-based carbon fibers, with acrylic-based carbon fibers being preferred due to their high tensile strength. While twisted, untwisted, and untwisted forms of carbon fibers can be used, untwisted or untwisted yarns are preferred because they offer a good balance between the moldability and strength characteristics of the fiber-reinforced composite material. [Examples]

[0066] The present invention will be described in more detail below with reference to synthesis examples and embodiments. The materials, processing content, processing procedures, etc., shown below can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

[0067] The analysis was performed under the following conditions. Epoxy equivalent The measurement was performed using the method described in JIS K-7236, and the unit is g / eq. ·Softening point The measurement was performed according to the method compliant with JIS K-7234, and the unit is °C. • Biomass content analysis (accelerator mass spectrometry) Measurements and calculations were performed in accordance with ASTM D6866-21. The unit is %, (%). • GPC (Gel Permeation Chromatography) Manufacturer: Waters Columns: Guard columns SHODEX GPC KF-601 (2 pieces), KF-602, KF-602.5, KF-603 Flow rate: 1.23ml / min. Column temperature: 25℃ Solvent used: THF (tetrahydrofuran) Detector: RI (Differential Refraction Detector)

[0068] [Synthesis Example 1] In a flask equipped with a stirrer, reflux condenser, and stirring device, 254 parts by weight of phenol, 63 parts by weight of water, and 27 parts by weight of sodium hydroxide were charged, stirred, dissolved, and heated to 110°C. 133 parts by weight of furfural were then added dropwise over 2 hours. The mixture was then reacted at 110°C for 3 hours, and then the temperature was raised to 145°C. During the heating process, the water distilled out was removed from the system. After reaching 145°C, the mixture was reacted for 4 hours. The mixture was then cooled to 80°C, 63 parts by weight of water was added, and neutralization was performed by adding 4 parts by weight of phosphoric acid and 63 parts by weight of 35% hydrochloric acid. After repeated washing with water, the unreacted phenol was removed by distillation under reduced pressure to obtain 205 parts by weight of the phenolic resin represented by formula (2). To 78 parts by weight of the phenol resin represented by the obtained formula (2), 254 parts by weight of epichlorohydrin (ECH, the same applies hereafter), 64 parts by weight of dimethyl sulfoxide (DMSO, the same applies hereafter), and 13 parts by weight of water were charged into a reaction vessel. After heating, stirring, and dissolution, 23 parts by weight of flake sodium hydroxide were added in installments over 2 hours while maintaining the temperature at 45°C. The reaction was then carried out further at 45°C for 2 hours and at 70°C for 60 minutes. After repeated washing with water to remove the by-product salts and dimethyl sulfoxide, excess epichlorohydrin was distilled off from the oil layer under reduced pressure, and 218 parts by weight of methyl isobutyl ketone was added to the residue and dissolved. This methyl isobutyl ketone solution was heated to 70°C, 7 parts by weight of a 30% sodium hydroxide aqueous solution was added, and the mixture was reacted for 1 hour. Then, the reaction solution was washed with water repeatedly until the washing solution became neutral. Next, methyl isobutyl ketone was distilled off from the oil layer under reduced heating pressure to obtain 94 parts by weight of the epoxy resin represented by formula (1) (where n in formula (1) is 3.9). The properties of the obtained epoxy resin are shown in Table 1.

[0069] [Synthesis Example 2] In a flask equipped with a stirrer, reflux condenser, and stirring device, 254 parts by weight of phenol, 63 parts by weight of water, and 27 parts by weight of sodium hydroxide were charged, stirred, dissolved, and heated to 110°C. 133 parts by weight of furfural were then added dropwise over 2 hours. The mixture was then reacted at 110°C for 3 hours, and then the temperature was raised to 145°C. During the heating process, the water distilled out was removed from the system. After reaching 145°C, the mixture was reacted for 4 hours. The mixture was then cooled to 80°C, 63 parts by weight of water was added, and neutralization was performed by adding 4 parts by weight of phosphoric acid and 63 parts by weight of 35% hydrochloric acid. After repeated washing with water, the unreacted phenol was removed by distillation under reduced pressure to obtain 205 parts by weight of the phenolic resin represented by formula (2). To 78 parts by weight of the phenol resin represented by formula (2) obtained, 181 parts by weight of ECH, 64 parts by weight of DMSO, and 13 parts by weight of water were charged into a reaction vessel. After heating, stirring, and dissolution, 23 parts by weight of flake sodium hydroxide were added in portions over 2 hours while maintaining the temperature at 45°C. The reaction was then carried out further at 45°C for 2 hours and at 70°C for 60 minutes. After repeated washing with water to remove by-product salts and dimethyl sulfoxide, excess epichlorohydrin was distilled off from the oil layer under reduced pressure and heating, and 218 parts by weight of methyl isobutyl ketone was added to the residue and dissolved. This methyl isobutyl ketone solution was heated to 70°C, 7 parts by weight of a 30% aqueous sodium hydroxide solution was added, and the mixture was reacted for 1 hour. After that, the reaction solution was washed with water repeatedly until the washing solution was neutral. Finally, 92 parts by weight of epoxy resin represented by formula (1) was obtained by distilling off the methyl isobutyl ketone from the oil layer under reduced pressure and heating (n in formula (1) is 4.3). The properties of the resulting epoxy resin are shown in Table 1.

[0070] [Synthesis Example 3] In a flask equipped with a stirrer, reflux condenser, and stirring device, 254 parts by weight of phenol, 63 parts by weight of water, and 27 parts by weight of sodium hydroxide were charged, stirred, dissolved, and heated to 110°C. 90 parts by weight of furfural were then added dropwise over 2 hours. The mixture was then reacted at 110°C for 3 hours, and then the temperature was raised to 145°C. During the heating process, the water distilled out was removed from the system. After reaching 145°C, the mixture was reacted for 4 hours. The mixture was then cooled to 80°C, 63 parts by weight of water was added, and neutralization was performed by adding 4 parts by weight of phosphoric acid and 63 parts by weight of 35% hydrochloric acid. After repeated washing with water, the unreacted phenol was removed by distillation under reduced pressure to obtain 120 parts by weight of the phenolic resin represented by formula (2). To 78 parts by weight of the obtained phenolic resin, 254 parts by weight of ECH, 64 parts by weight of DMSO, and 13 parts by weight of water were charged into a reaction vessel. After heating, stirring, and dissolution, 23 parts by weight of flake sodium hydroxide were added in portions over 2 hours while maintaining the temperature at 45°C. The reaction was then carried out further at 45°C for 2 hours and at 70°C for 60 minutes. After repeated washing with water to remove by-product salts and dimethyl sulfoxide, excess epichlorohydrin was distilled off from the oil layer under reduced pressure and heating, and 218 parts by weight of methyl isobutyl ketone was added to the residue and dissolved. This methyl isobutyl ketone solution was heated to 70°C, 7 parts by weight of a 30% aqueous sodium hydroxide solution was added, and the mixture was reacted for 1 hour. The reaction solution was then washed with water repeatedly until the washing solution was neutral. Finally, 90 parts by weight of epoxy resin represented by formula (1) was obtained by distilling off the methyl isobutyl ketone from the oil layer under reduced pressure and heating (where n in formula (1) is 2.6). The properties of the resulting epoxy resin are shown in Table 1.

[0071] [Example 1, Comparative Examples 1-2] The epoxy resins obtained in Synthesis Examples 1-3 were used as the main component, and 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane (abbreviated as TEDDM, manufactured by Tokyo Chemical Industry Co., Ltd., with an active hydrogen equivalent of 78 g / eq.) was used as the curing agent. The mixtures were mixed in the weight ratios shown in Table 2, and cured at 160°C for 6 hours to prepare the cured products. The evaluation results are shown in Table 2 and Figure 1.

[0072] The physical properties were measured under the following conditions. <Heat resistance (Tg) measurement conditions> Thermomechanical Measurement Device (TMA): TA-instruments TMA Q400EM Heating rate: 2°C / min Measurement temperature range: 25℃~300℃ Tg: The point at which the coefficient of thermal expansion changes is defined as Tg. <Heat Decomposition Resistance Test> Measurement device: TG / DTA6200, manufactured by Hitachi High-Tech Science Corporation, oxygen injection rate: 200 mL / min, heating rate: 10°C / min.

[0073] [Table 1] The biomass content of synthesis example 3 was not measured.

[0074] [Table 2]

[0075] The results in Table 2 and Figure 1 confirm that the cured products of the examples have high heat resistance and high flexural modulus.

Claims

1. An epoxy resin represented by the following formula (1), having an epoxy equivalent of 228 g / eq. to 237 g / eq., and where a / b is 3.0 to 3.4, with a epoxy equivalent of a and a softening point of b. 【Chemistry 1】 (In equation (1), n ​​is the average value of the number of repetitions and represents a real number between 1 and 15.)

2. The epoxy resin according to claim 1, wherein the biomass content is 50% or more.

3. A curable resin composition comprising the epoxy resin according to claim 1 or 2 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 curable resin composition comprising the epoxy resin according to claim 1 or 2, and at least one selected from a curing accelerator, a polymerization initiator, an epoxy resin other than the epoxy resin represented by formula (1), an active ester compound, a phenolic resin, a polyphenylene ether compound, a compound having an ethylenically unsaturated bond, an isocyanate resin, a polyamide resin, a maleimide compound, a cyanate ester resin, a polyimide resin, a polybutadiene and a modified thereof, polystyrene and a modified thereof, polyethylene and a modified thereof, and a benzoxazine compound.

6. A cured product obtained by curing the curable resin composition described in claim 3.

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

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