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

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

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

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

[0002] Epoxy resins, when cured with various curing agents, become cured products with excellent 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), which are made by impregnating and curing reinforcing fibers with epoxy resin and a curing agent as a matrix resin, can be imparted with properties such as light weight and high strength. In recent years, these materials have been widely used in aircraft structural components, wind turbine blades, automobile exterior panels, and computer applications such as IC trays and laptop computer housings, and demand for them is increasing. In particular, they are used as matrix resins for aircraft applications, taking advantage of the light weight and high strength properties of the molded products.

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

[0004] JP 2010-275492 A JP 2022-173168 A JP 2007-211254 A

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

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

[0007] That is, the present invention is as shown in the following [1] to [8]. In the present invention, "(Numerical value 1) to (Numerical value 2)" indicates that the upper and lower limits 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]

[0009] (In formula (1), n ​​is the average number of repeating units and is a real number in the range of 1 < n < 15.) [2] An epoxy resin represented by the following formula (1), in which a / b is 3.0 or more and 3.4 or less, where a is the epoxy equivalent and b is the softening point.

[0010]

[0011] (In formula (1), n ​​is the average number of repeating units and is a real number satisfying the condition 1<n<15.) [3] The epoxy resin according to the above item [1] or [2], which has a biomass degree of 50% or more. [4] A curable resin composition containing the epoxy resin according to any one of the above items [1] to [3] and a curing agent. [5] The curable resin composition according to the above item [4], wherein the curing agent is an amine-based curing agent. [6] A curable resin composition containing the epoxy resin according to any one of the above items [1] to [3], and at least one selected from the group consisting of 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, polybutadiene and modified products thereof, polystyrene and modified products thereof, polyethylene and modified products thereof, and a benzoxazine compound. [7] A cured product obtained by curing the curable resin composition according to the above item [4] or [5]. [8] A carbon fiber reinforced composite material obtained by curing the curable resin composition according to the above item [4] or [5].

[0012] According to the present invention, it is possible to provide an epoxy resin, a curable resin composition, and 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.

[0013] The evaluation results of Example 1 and Comparative Examples 1 and 2 are shown below.

[0014] Hereinafter, an embodiment of the present invention (hereinafter also referred to as "the present embodiment") will be described in further detail.

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

[0016]

[0017] (In formula (1), n ​​is the average number of repetitions and is a real number in the range of 1<n<15.)

[0018] In the formula (1), the value of n can be calculated from the number average molecular weight of the epoxy resin determined by gel permeation chromatography (GPC, detector: RI) or the area ratio of each separated peak. n is preferably a real number in the range 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, high heat resistance is obtained, and when it is 237 g / eq. or less, a high flexural modulus of elasticity is obtained. In other words, when the epoxy equivalent is 228 g / eq. or more and 237 g / eq. or less, the properties of high heat resistance and high flexural modulus of elasticity can both be achieved.

[0020] The softening point of the epoxy resin represented by formula (1) is preferably 67° C. or higher and 100° C. or lower, and more preferably 70° C. or higher and 80° C. or lower. A softening point of 67° C. or higher is preferable for storage and handling because resins do not block with each other even without refrigeration and can be stored at room temperature, whereas a softening point higher than 100° C. makes it difficult to mix uniformly with the curing agent, polymerization initiator, filler, etc., and is prone to poor curing.

[0021] In the epoxy resin of this embodiment, where a is the epoxy equivalent and b is the softening point, a / b is preferably 3.0 or more and 3.4 or less, and more preferably 3.1 or more and 3.3 or less. When a / b is 3.4 or less, the epoxy equivalent is low compared to a certain softening point, resulting in 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 becomes too high compared to the epoxy equivalent, restricting molecular motion during the curing reaction and resulting in partial insufficient curing, resulting in reduced heat resistance and thermal decomposition resistance. In other words, when the ratio is 3.0 to 3.4, a balance between curing density and curing reaction is achieved, allowing for the development of excellent properties.

[0022] The cured product of the epoxy resin of this embodiment has high heat resistance and a high flexural modulus. The flexural modulus is preferably 3.0 to 4.0 GPa. If the flexural modulus is less than 3.0 GPa, the strength of the resulting carbon fiber reinforced composite material will be insufficient, leading to reduced reliability, which is undesirable. 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 glass transition temperature (Tg). The 5% weight loss temperature is preferably 295°C or higher. The glass transition temperature (Tg) is preferably 210 to 300°C, more preferably 215 to 250°C, and even more preferably 216 to 230°C. Heat resistance below 210°C makes it difficult to apply to components requiring heat resistance, such as those around aircraft engines, and the resin softens during use, significantly reducing mechanical strength and leading to material damage, which is undesirable. In addition, the heat resistance of epoxy resins is generally correlated with crosslink density, and the higher the crosslink density, the higher the heat resistance. In other words, heat resistance above 300°C is undesirable because the crosslink density increases and the cured product becomes brittle. Note that 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 viewpoint of environmental issues, the biomass degree of the epoxy resin of this embodiment is preferably 50% or more. The upper limit of the biomass degree is not particularly limited and can be 100%, but in consideration of the balance with the cured physical properties, it is preferably 80%. A high biomass degree can also reduce the amount of fossil resource-based materials used, such as petroleum, and is therefore meaningful in terms of sustainable resource use. Therefore, it is preferable that the biomass degree of the curable resin composition after mixing with other materials is also high; specifically, it is preferably 20% or more, and more preferably 30% or more. The biomass degree of this embodiment is measured by the method described in the Examples below.

[0025] The epoxy resin represented by the formula (1) can be obtained by reacting a phenol resin represented by the following formula (2) with epihalohydrin.

[0026]

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

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

[0029] The epihalohydrin is readily available on the market. The amount of epihalohydrin used is preferably 2.0 to 10 mol, more preferably 3.0 to 8.0 mol, and even more preferably 3.5 to 6.0 mol, per mol of hydroxyl groups in the raw material phenol mixture. Preferred epihalohydrins that can be used in this embodiment include epichlorohydrin, α-methylepichlorohydrin, β-methylepichlorohydrin, and epibromohydrin, with epichlorohydrin being particularly preferred because it is easily available industrially.

[0030] In the above reaction, an alkali metal hydroxide can be used as a catalyst to promote the epoxidation step. Usable alkali metal hydroxides include sodium hydroxide, potassium hydroxide, etc. A solid or an aqueous solution thereof may be used, but in this embodiment, the use of a solid formed into flakes is particularly preferred from the standpoints of solubility and handling. The amount of alkali metal hydroxide used is preferably 0.90 to 1.5 mol, more preferably 0.95 to 1.25 mol, and even more preferably 0.99 to 1.15 mol, per mol of hydroxyl groups in the raw material phenol mixture.

[0031] To promote the reaction, a quaternary ammonium salt such as tetramethylammonium chloride, tetramethylammonium bromide, or trimethylbenzylammonium chloride may be added as a catalyst. The amount of the quaternary ammonium salt used is preferably 0.1 to 15 g, 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 particular, in this embodiment, for higher purity epoxidation, a temperature of 50°C or higher is preferred, and 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 short reaction time is not preferred because the reaction does not proceed to completion, while a long reaction time is not preferred because by-products are produced.

[0033] The reaction products of these epoxidation reactions are washed with water, or without washing, and then heated under reduced pressure to remove epihalohydrin and solvent. Furthermore, to obtain epoxy resins with a reduced hydrolyzable halogen content, the recovered epoxy resins can be dissolved in a ketone compound having 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 the solution 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 mol, more preferably 0.05 to 0.2 mol, per mol of hydroxyl groups in the raw phenol mixture used in the 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 salt formed is removed by filtration, washing with water, or the like, and the solvent is then distilled off under heating and reduced pressure to obtain the epoxy resin of the present embodiment.

[0035] In the synthesis method of the phenolic resin represented by the formula (2), when furfural is reacted (condensed) with a phenol, the amount of the phenol is preferably 1.5 to 20 moles, particularly preferably 3 to 10 moles, per mole of furfural.

[0036] Examples of phenols include disubstituted phenols such as catechol, resorcinol, and hydroquinone, and monosubstituted phenols such as phenol, cresol, and xylenol, and these may be used alone or in combination of two or more.

[0037] Examples of the solvent include, but are not limited to, methanol, ethanol, propanol, isopropanol, toluene, xylene, etc., and these 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 condensation reaction, a base catalyst is preferably used. Polycondensation is possible with an acidic catalyst, but reactions between furfurals occur, resulting in increased by-products. Alternatively, an organometallic compound can be used, but this is cost-inefficient. 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 may be used alone or in combination of two or more. The amount of catalyst used is preferably 0.005 to 2.0 times, more preferably 0.01 to 1.1 times, the moles per mole of phenol.

[0039] The condensation reaction in the presence of these base catalysts is 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 selected preferably in the range of 0.5 to 10 hours. The reaction product thus obtained is neutralized so that the system becomes neutral, or is repeatedly washed with water in the presence of a solvent, and then the water is separated and drained, and the solvent and unreacted materials are removed under heating and reduced pressure, thereby obtaining the phenolic resin represented by formula (2).

[0040] The curable resin composition of the present 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 the present embodiment, an amine curing agent is preferred, since it can achieve a good balance between the resin viscosity of the curable resin composition and the heat resistance of the cured resin. Examples of amine-based curing agents 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-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), 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, and the like can be used. Other examples include aniline novolak, orthoethylaniline novolak, aniline resins obtained by reacting aniline with xylylene chloride, and aniline resins obtained by polycondensation of aniline with substituted biphenyls (4,4'-bis(chloromethyl)-1,1'-biphenyl, 4,4'-bis(methoxymethyl)-1,1'-biphenyl, etc.) or substituted phenyls (1,4-bis(chloromethyl)benzene, 1,4-bis(methoxymethyl)benzene, 1,4-bis(hydroxymethyl)benzene, etc.).

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

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

[0044] Examples of phenolic curing agents include polyhydric phenols (bisphenol A, bisphenol F, bisphenol S, fluorene bisphenol, 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 (for example, phenol, alkyl-substituted phenol, naphthol, alkyl-substituted naphthol, dihydroxybenzene, and dihydroxynaphthalene, etc.); and aldehydes (formaldehyde, acetaldehyde, benzaldehyde, p-hydroxybenzaldehyde, o-hydroxybenzoates, benzophenone ... phenolic resins obtained by condensation of the phenols with 4,4'-bis(chloromethyl)-1,1'-biphenyl and 4,4'-bis(methoxymethyl)-1,1'-biphenyl, or substituted phenyls (1,4-bis(chloromethyl)benzene, 1,4-bis(methoxymethyl)benzene, 1,4-bis(hydroxymethyl)benzene, or the like); 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 the formula (2) as the entire amount of the curing agent or as a part thereof.

[0046] In the curable resin composition of this embodiment, the amount of curing agent used is preferably 0.7 to 1.2 equivalents relative to 1 equivalent of the epoxy group of the epoxy resin. If the amount is less than 0.7 equivalents relative to 1 equivalent of the epoxy group or if it exceeds 1.2 equivalents, curing may be incomplete and good cured physical properties may not be obtained.

[0047] Furthermore, a curing accelerator may be blended into the curable resin composition of this embodiment as needed. The gelation time can also 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. The curing accelerator is used in an amount of 0.01 to 5.0 parts by weight per 100 parts by weight of the epoxy resin, as needed.

[0048] The curable resin composition of the present embodiment may contain other epoxy resins. Specific examples thereof include phenols (phenol, alkyl-substituted phenol, aromatic-substituted phenol, naphthol, alkyl-substituted naphthol, dihydroxybenzene, alkyl-substituted dihydroxybenzene, dihydroxynaphthalene, etc.) and various aldehydes (formaldehyde, acetaldehyde, alkyl aldehyde, benzaldehyde, alkyl-substituted benzaldehyde, hydroxybenzaldehyde, naphthaldehyde, etc.). , glutaraldehyde, phthalaldehyde, crotonaldehyde, cinnamaldehyde, etc.), polymers of phenols and various diene compounds (dicyclopentadiene, terpenes, vinylcyclohexene, norbornadiene, vinylnorbornene, tetrahydroindene, divinylbenzene, divinylbiphenyl, diisopropenylbiphenyl, butadiene, isoprene, etc.), polymers of phenols and ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, acetophenone, benzo[a]thiazolinone, benzo[b ... phenolic resins obtained by polycondensation of phenols and substituted biphenyls (4,4'-bis(chloromethyl)-1,1'-biphenyl and 4,4'-bis(methoxymethyl)-1,1'-biphenyl, etc.) or substituted phenyls (1,4-bis(chloromethyl)benzene, 1,4-bis(methoxymethyl)benzene, 1,4-bis(hydroxymethyl)benzene, etc.); polycondensates of bisphenols and various aldehydes; glycidyl ether epoxy resins obtained by glycidylating alcohols, etc.; alicyclic epoxy resins typified by 4-vinyl-1-cyclohexene diepoxide and 3,4-epoxycyclohexylmethyl-3,4'-epoxycyclohexanecarboxylate, etc.; glycidylamine epoxy resins typified by tetraglycidyldiaminodiphenylmethane (TGDDM) and triglycidyl-p-aminophenol, etc.; glycidyl ester epoxy resins, etc., but are not limited to these, so long as they are commonly used epoxy resins.

[0049] The curable resin composition of the present embodiment can be blended with known additives as needed.Specific examples of usable additives 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, mold release agents, and colorants such as carbon black, phthalocyanine blue, and phthalocyanine green.

[0050] Examples of the active ester compound include active ester compounds such as 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] Examples of the compound having an ethylenically unsaturated bond include reaction products of a phenol resin with an ethylenically unsaturated bond-containing halogen-based compound (chloromethylstyrene, allyl chloride, methallyl chloride, acrylic acid chloride, methacrylic acid chloride, etc.), reaction products of an ethylenically unsaturated bond-containing phenol (2-allylphenol, 2-propenylphenol, 4-allylphenol, 4-propenylphenol, eugenol, isoeugenol, etc.) with a halogen-based compound (1,4-bis(chloromethyl)benzene, 4,4'-bis(chloromethyl)biphenyl, 4,4'-difluorobenzophenone, 4,4'-dichlorobenzophenone, 4,4'-dibromobenzophenone, cyanuric chloride, etc.), reaction products of an epoxy resin or alcohols with (meth)acrylic acids (acrylic acid, methacrylic acid, etc.), and acid-modified products thereof.

[0053] Examples of the isocyanate resin include aromatic diisocyanates such as p-phenylene diisocyanate, m-phenylene diisocyanate, p-xylene diisocyanate, m-xylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and naphthalene diisocyanate; aliphatic or alicyclic diisocyanates such as isophorone diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hydrogenated xylene diisocyanate, norbornene diisocyanate, and lysine diisocyanate; polyisocyanates such as biuret compounds of one or more types of isocyanate monomers or isocyanate compounds obtained by trimerizing the above diisocyanate compounds; and polyisocyanates obtained by a urethanization reaction between the above isocyanate compounds and polyol compounds.

[0054] Examples of the maleimide compound include 4,4'-diphenylmethane bismaleimide, polyphenylmethane maleimide, m-phenylene bismaleimide, 2,2'-bis[4-(4-maleimidophenoxy)phenyl]propane, 3,3'-dimethyl-5,5'-diethyl-4,4'-diphenylmethane bismaleimide, 4-methyl-1,3-phenylene bismaleimide, 4,4'-diphenylether bismaleimide, 4,4'-diphenylsulfone bismaleimide, 1,3-bis(3-maleimidophenoxy)benzene, 1,3-bis(4-maleimidophenoxy)benzene, and Xylox-type maleimide compounds (anilix maleimide, manufactured by Mitsui Chemicals Fine Co., Ltd.), biphenylaralkyl-type maleimide compounds (solidified by distilling off the solvent under reduced pressure from a resin solution containing the maleimide compound (M2) described in Example 4 of JP 2009-001783 A), bisaminocumylbenzene-type maleimide (maleimide compounds described in WO 2020 / 054601 A), maleimide compounds having an indane structure described in Japanese Patent No. 6629692 or WO 2020 / 217679, MATERIAL STAGE Vol. 18, No. 12 2019 "Continued Epoxy Resin CAS Number Story - Curing Agent CAS Number Memorandum No. 31 Bismaleimide (1)" and MATERIAL STAGE Vol. 19, No. 12 2019 Examples of suitable maleimide compounds include those described in "Epoxy Resin CAS Number Story Continued - Curing Agent CAS Number Memorandum No. 32, Bismaleimide (2)" published in February 2019. These compounds may be used alone or in combination of two or more. When incorporating maleimide compounds, a curing accelerator may be incorporated as needed. These may include the aforementioned curing accelerators, as well as radical polymerization initiators such as organic peroxides and azo compounds.

[0055] Examples of cyanate ester resins include dicyanatobenzene, tricyanatobenzene, dicyanatonaphthalene, dicyanatobiphenyl, 2,2'-bis(4-cyanatophenyl)propane, bis(4-cyanatophenyl)methane, bis(3,5-dimethyl-4-cyanatophenyl)methane, 2,2'-bis(3,5-dimethyl-4-cyanatophenyl)propane, 2,2'-bis(4-cyanatophenyl)ethane, 2,2'-bis(4-cyanatophenyl)hexafluoropropane, bis(4-cyanatophenyl)sulfone, bis(4-cyanatophenyl)thioether, phenol novolac cyanate, and phenol-dicyclopentadiene co-condensates in which hydroxyl groups have been converted to cyanate groups.

[0056] The polyimide resin may be a mixture of the above diamines and tetracarboxylic dianhydrides (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 dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, methylene-4,4'-diphthalic dianhydride, 1,1-ethylidene-4,4'-diphthalic dianhydride, 2,2'-propylidene-4,4'-diphthalic dianhydride, 1,2-ethylene-4,4'-diphthalic dianhydride, 1,3-trimethylene-4,4'-diphthalic dianhydride, 1,4-tetramethylene-4,4'-diphthalic dianhydride, 1,5-pentamethylene-4,4'-diphthalic dianhydride, 4,4'-oxydiphthalic dianhydride, thio- 4,4'-diphthalic dianhydride, sulfonyl-4,4'-diphthalic 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 dianhydride, 1,4,5,8-naphthalenetetracarboxylic 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, Cyclohexane-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 -propylidene-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]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, rel-[1S,5R,6R]-3-oxabicyclo[3,2,1 ]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 acid anhydride), 9,9'-bis(3,4-dicarboxyphenyl)fluorene dianhydride, etc., reaction products thereof,

[0057] Examples of polybutadiene and modified products thereof, polystyrene and modified products thereof, and polyethylene and modified products thereof include polybutadiene, hydroxyl-terminated polybutadiene, (meth)acrylate-terminated polybutadiene, carboxylic acid-terminated polybutadiene, amine-terminated polybutadiene, styrene-butadiene rubber, RICON-100, RICON-181, RICON-184 (all manufactured by Cray Valley Chemical Industry Co., Ltd.), 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.), and SEP (styrene-ethylene-propylene copolymer: Septon 1020) Kuraray Co., Ltd.), 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 (styrene-ethylene / ethylene propylene-styrene block copolymer with a terminal hydroxyl group: 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 of such copolymers include ethylene-propylene copolymers, ethylene-styrene copolymers, ethylene-propylene-ethylidenenorbornene copolymers (EBT: K-8370EM, K-9330M, etc., manufactured by Mitsui Chemicals, Inc.), ethylene-propylene-vinylnorbornene copolymers (VNB-EPT: PX-006M, PX-008M, PX-009M, etc., manufactured by Mitsui Chemicals, Inc.), ethylene-vinyl alcohol copolymers, and ethylene-vinyl acetate copolymers;

[0058] Examples of the benzoxazine compound include benzoxazine P-d, Fa, and ALP-d (all manufactured by Shikoku Chemical Industry Co., Ltd.), JBZ-BA100N, JBZ-FA100N, JBZ-DP100N, JBZ-OP100N, JBZ-OP100D, and JBZ-OP100I (all manufactured by JFE Chemical Corporation), and BTBz (manufactured by Japan Material Technology Co., Ltd.).

[0059] 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 the solvent that can be used include amide-based solvents such as γ-butyrolactones, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and N,N-dimethylimidazolidinone; sulfones such as tetramethylene sulfone; ether-based 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-based solvents such as methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, and cyclohexanone; and aromatic solvents such as toluene and xylene. The solvent is used so that the solids concentration excluding the solvent in the resulting varnish is preferably 10 to 80 wt %, more preferably 20 to 70 wt %.

[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 can be applied to one or both sides of a support substrate to form a resin sheet. Examples of application methods include casting, extruding the resin through a nozzle or die using a pump or extruder, adjusting the thickness with a blade, adjusting the thickness by calendaring with a roll, and spraying using a sprayer. The layer formation process may be performed while heating within a temperature range that avoids thermal decomposition of the curable resin composition. Furthermore, rolling, grinding, and other processes may be performed as necessary. 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 films; nets; foams; metal foils; and laminates thereof. The thickness of the support substrate is not particularly limited and can be determined appropriately depending on the application.

[0061] The curable resin composition and / or resin sheet of this embodiment can be heated and melted to reduce the viscosity, and then impregnated into a fiber substrate to obtain the prepreg of this embodiment.

[0062] Alternatively, the prepreg of this embodiment can be obtained by impregnating a fiber substrate with a varnish-like curable resin composition and drying it by heating. The prepreg is cut into a desired shape, laminated, and then the curable resin composition is heat-cured while applying pressure to the laminate by press molding, autoclave molding, sheet winding, or the like, to obtain the carbon fiber reinforced composite material of this embodiment. Copper foil or an organic film can also be laminated during lamination of the prepreg.

[0063] Furthermore, the carbon fiber reinforced composite material of this embodiment can be obtained by molding using known methods other than the above-mentioned methods. For example, a resin transfer molding technique (RTM method) can be used, in which a carbon fiber substrate (usually a carbon fiber fabric) is cut, laminated, and shaped to produce a preform (a preform before being impregnated with a resin), the preform is placed in a mold, the mold is closed, resin is injected to impregnate the preform, and the resin is cured, and the mold is then opened to remove the molded product. Also usable are types of RTM methods, such as the VaRTM method, the SCRIMP (Seeman's Composite Resin Infusion Molding Process), and the CAPRI (Controlled Atmospheric Pressure Resin Infusion) method, which is described in JP-A-2005-527410, in which a resin supply tank is evacuated to a pressure lower than atmospheric pressure, cyclic compression is used, and the net molding pressure is controlled to more appropriately control the resin injection process, particularly the VaRTM method.

[0064] Furthermore, a film stacking method in which a fiber substrate is sandwiched between resin sheets (films), a method in which powdered resin is attached to a reinforcing fiber substrate to improve impregnation, a molding method in which a fluidized bed or fluid slurry method is used in the process of mixing resin into a fiber substrate (Powder Impregnated Yarn), and a method in which resin fibers are mixed into a fiber substrate can also be used.

[0065] Examples of carbon fibers include acrylic, pitch, and rayon carbon fibers, and among these, acrylic carbon fibers, which have high tensile strength, are preferably used. The carbon fiber may be in the form of twisted yarn, untwisted yarn, or non-twisted yarn, but untwisted yarn or non-twisted yarn is preferred because it provides a good balance between the formability and strength properties of the fiber-reinforced composite material.

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

[0067] The analysis was carried out under the following conditions. Epoxy equivalent: Measured according to the method described in JIS K-7236, and expressed in g / eq. Softening point: Measured according to the method conforming to JIS K-7234, and expressed in °C. Biomass content analysis (accelerator mass spectrometry): Measured and calculated according to ASTM D6866-21, and expressed in %. GPC (gel permeation chromatography): Manufacturer: Waters Column: Guard column SHODEX GPC KF-601 (2 columns), KF-602, KF-602.5, KF-603 Flow rate: 1.23 ml / min Column temperature: 25 °C Solvent used: THF (tetrahydrofuran) Detector: RI (differential refractometer)

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

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

[0070] Synthesis Example 3: 254 parts by weight of phenol, 63 parts by weight of water, and 27 parts by weight of sodium hydroxide were charged into a flask equipped with a stirrer, a reflux condenser, and a stirring device. After stirring and dissolving, the mixture was heated to 110°C, and 90 parts by weight of furfural was added dropwise over 2 hours. The mixture was then reacted at 110°C for 3 hours, and then heated to 145°C. During the temperature increase, the distilled water was removed from the system. After reaching 145°C, the mixture was reacted for 4 hours. The mixture was then cooled to 80°C, and 63 parts by weight of water was charged. 4 parts by weight of phosphoric acid and 63 parts by weight of 35% hydrochloric acid were added for neutralization. After repeated water washing, unreacted phenol was distilled off under reduced pressure with heating to obtain 120 parts by weight of the phenolic resin represented by the formula (2). To 78 parts by weight of the resulting 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 flaky sodium hydroxide was added in portions over 2 hours while maintaining the temperature at 45°C. The reaction was then continued for 2 hours at 45°C and 60 minutes at 70°C. After repeated water washing to remove by-product salts and dimethyl sulfoxide, excess epichlorohydrin was removed from the oil layer under heating and 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, and 7 parts by weight of 30% aqueous sodium hydroxide was added. The reaction mixture was then allowed to react for 1 hour. The reaction solution was then repeatedly washed with water until the washings became neutral. The methyl isobutyl ketone was then removed from the oil layer under heating and reduced pressure by distillation, yielding 90 parts by weight of the epoxy resin represented by formula (1) (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 and 2] The epoxy resins obtained in Synthesis Examples 1 to 3 were used as the base resin, and 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane (abbreviation: TEDDM, manufactured by Tokyo Chemical Industry Co., Ltd., active hydrogen equivalent: 78 g / eq.) was used as the curing agent, and mixed in the weight ratios shown in Table 2. Curing was carried out at 160°C for 6 hours to produce cured products. The evaluation results are shown in Table 2 and FIG. 1.

[0072] Physical property values ​​were measured under the following conditions. <Conditions for measuring heat resistance (Tg)> Thermomechanical measuring apparatus (TMA): TMA Q400EM manufactured by TA-instruments Heating rate: 2°C / min Measurement temperature range: 25°C to 300°C Tg: The point at which the coefficient of thermal expansion changes was taken as Tg. <Thermal decomposition resistance test> Measuring apparatus: TG / DTA6200 manufactured by Hitachi High-Tech Science Corporation, oxygen blown in at 200 mL / min, heating rate: 10°C / min.

[0073] The biomass ratio of Synthesis Example 3 was not measured.

[0074]

[0075] From the results in Table 2 and FIG. 1, it was confirmed that the cured products of the examples had high heat resistance and high flexural modulus.

Claims

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. 【Chemistry 1】 (In formula (1), n ​​is the average number of repetitions and is a real number in the range of 1<n<15.)

2. An epoxy resin as described in claim 1, wherein a / b is 3.0 or more and 3.4 or less, where a is the epoxy equivalent and b is the softening point.

3. 3. The epoxy resin according to claim 1, having a biomass content of 50% or more.

4. A curable resin composition comprising the epoxy resin according to any one of claims 1 to 3 and a curing agent.

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

6. 4. A curable resin composition comprising the epoxy resin according to claim 1, a curing accelerator, a polymerization initiator, and at least one selected from the group consisting of 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, polybutadiene and modified products thereof, polystyrene and modified products thereof, polyethylene and modified products thereof, and a benzoxazine compound.

7. A cured product obtained by curing the curable resin composition according to claim 4.

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

Images