JP7632036B2 - Epoxy resin, curable resin composition, cured product, fiber-reinforced composite material, and fiber-reinforced resin molded product - Google Patents

Description

The present invention relates to an epoxy resin obtained from a phenolic resin having a specific structure, a curable resin composition containing the epoxy resin, a cured product obtained from the curable resin composition, a fiber-reinforced composite material, and a fiber-reinforced resin molded product.

Curable resin compositions, the essential components of which are epoxy resin and its curing agent, have excellent mechanical strength, heat resistance, water resistance, chemical resistance, and insulating properties in the cured product, and are therefore widely used in a wide range of applications, including as matrices for fiber-reinforced composite materials, heat dissipation components, paints, semiconductors, and printed wiring boards.

In particular, fiber-reinforced plastic molded products, which are reinforced with reinforcing fibers, have attracted attention for their lightweight yet excellent mechanical strength, and are being used in a wide range of structural applications, including housings and various components for automobiles, aircraft, ships, etc. In particular, the use of epoxy resins as matrix resins for carbon fiber composite materials (CFRP) is steadily increasing as their applications in the aircraft and automotive fields expand.

Currently, epoxy resins that are primarily used in carbon fiber composite materials include diglycidyl ether of bisphenol A and tetraglycidylamine of diaminodiphenylmethane (TGDDM) (see, for example, Patent Document 1). These epoxy resins meet a certain level of the required properties for carbon fiber composite materials, such as elastic modulus, strength, heat resistance, and moist heat resistance.

However, there is currently a market need for even higher heat resistance and higher elastic modulus, and the physical properties of the above epoxy resins do not yet fully meet market demands.

JP 2003-201388 A

The problem that the present invention aims to solve is to provide an epoxy resin capable of producing a cured product having high heat resistance and high bending properties (such as bending strength and bending modulus), a curable resin composition containing the epoxy resin, a cured product obtained from the curable resin composition, a fiber-reinforced composite material, and a fiber-reinforced resin molded product.

The inventors conducted extensive research to solve the above problems and discovered that a cured product obtained by using a curable resin composition containing an epoxy resin obtained from a phenolic resin having a specific structure exhibits high heat resistance and high bending properties (such as bending strength and bending modulus), which led to the completion of the present invention.

That is, the present invention relates to a reaction product of a catechol compound and an aliphatic ketone, the reaction product being a phenolic resin having at least two catechol skeletons derived from the catechol compound;
The present invention relates to an epoxy resin which is a reaction product having a glycidyl ether group obtained by reacting a phenolic hydroxyl group of the phenol resin with an epihalohydrin.

The present invention relates to a curable resin composition that contains the above-mentioned epoxy resin.

The present invention relates to a cured product obtained by subjecting the curable resin composition to a curing reaction.

The present invention relates to a fiber-reinforced composite material that contains the above-mentioned curable resin composition and reinforcing fibers.

The present invention relates to a fiber-reinforced resin molded product that contains the above-mentioned cured product and reinforcing fibers.

According to the present invention, the cured product obtained using the obtained epoxy resin is useful because it exhibits high heat resistance and high bending properties (such as bending strength and bending modulus).

[Phenol resin]
The present invention relates to an epoxy resin which is a reaction product of a catechol compound and an aliphatic ketone, the epoxy resin being characterized in that it is a reaction product having a phenolic resin having at least two catechol skeletons derived from the catechol compound, and a glycidyl ether group obtained by a reaction between a phenolic hydroxyl group of the phenolic resin and an epihalohydrin.
The phenolic resin is preferably polyfunctional because it contains at least two catechol skeletons (having two hydroxyl groups as substituents on an aromatic ring, and the two hydroxyl groups are in an ortho-position relationship with each other) derived from the catechol compound. The phenolic resin preferably contains at least two catechol skeletons, and may contain three or more catechol skeletons, but the phenolic resin is particularly preferably contains two catechol skeletons, because the phenolic resin has a low melt viscosity.

In the present invention, the "phenolic resin" refers to a resin containing a phenolic hydroxyl group, and the "epoxy resin" refers to a resin containing a glycidyl ether group. The "catechol skeleton" refers to a skeleton "having two hydroxyl groups as substituents on an aromatic ring, with the two hydroxyl groups in an ortho-position relationship with respect to each other," or a skeleton with the hydrogen atoms constituting the hydroxyl groups removed.

[Catechol compounds]
The phenolic resin is a reaction product of a catechol compound and an aliphatic ketone. The catechol compound is a dihydroxybenzene having hydroxyl groups at the 1st and 2nd positions, and may have a substituent on the aromatic ring of the catechol compound, but from the viewpoint of bending properties, it is particularly preferable that the catechol compound has no substituent (catechol). By using the catechol compound, the phenolic resin includes a catechol skeleton, and it is presumed that the intermolecular density is increased due to the π-π interaction between molecules based on the aromatic ring, and a cured product having excellent mechanical strength and heat resistance can be obtained, which is preferable.

The substituent may be a hydrocarbon group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a halogen atom, and the substituent may be an alkyl group such as a methyl group, and the position and number of the substituent are not particularly limited. If the number of carbon atoms in the hydrocarbon group or the like exceeds 4, the steric hindrance becomes too large, and the reactivity becomes too low during the synthesis of the phenolic resin or the synthesis of the epoxy resin described below, and the mechanical strength of the obtained cured product decreases, which is not preferable.

The catechol compound may be used alone or in combination with multiple compounds having different substituent positions.

[Aliphatic ketones]
The phenolic resin is characterized by being a reaction product of a catechol compound and an aliphatic ketone. By introducing a skeleton (e.g., -C(-R)(-R')-) based on the reaction between the catechol compound and the aliphatic ketone (e.g., represented by R-C(=O)-R', where R and R' are hydrocarbon groups) into the phenolic resin, the intermolecular interaction is appropriately weakened, resulting in a phenolic resin with low melt viscosity and excellent handleability, which is preferable. In addition, the resulting cured product is useful because it has an excellent balance between heat resistance and mechanical strength.

Examples of the aliphatic ketones include acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl amyl ketone (2-heptanone), cyclopentanone, cyclohexanone, isophorone, cycloheptanone, and cyclooctanone. Among these, acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone are preferred from the viewpoint of reactivity during synthesis of the phenolic resin and synthesis of the epoxy resin, and from the viewpoint of ease of availability.

The aliphatic ketones may be used alone or in combination with one another.

The phenol resin can be obtained by reacting a catechol compound represented by the following general formula (1) with an aliphatic ketone represented by the following general formula (2), to obtain a phenol resin represented by the following general formula (3).

In the above general formula (1), the substituent R ¹ may be a hydrogen atom, a hydrocarbon group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or a halogen atom, and from the viewpoint of reactivity when used as a raw material and bending properties of a cured product, preferably, the hydrocarbon group having 1 to 4 carbon atoms includes a methyl group, an ethyl group, a propyl group, a butyl group, a t-butyl group, etc., the alkoxy group having 1 to 4 carbon atoms includes a methoxy group, an ethoxy group, a propyloxy group, a butoxy group, etc., and the halogen atom includes a fluorine atom, a chlorine atom, a bromine atom, etc. Among them, when the R ¹ is a hydrogen atom, the melt viscosity is low, the handling property is excellent, and the balance between bending properties and heat resistance is excellent, which is a preferred embodiment.

In the above general formula (1), m is preferably an integer of 0 to 3, and from the viewpoint of reactivity when used as a raw material and bending properties of the cured product, it is more preferably an integer of 0 or 1.

In the above general formula (2), R ² and R ³ are preferably each independently a hydrocarbon group having 1 to 4 carbon atoms, and from the viewpoint of the heat resistance and bending properties of the cured product, more preferably, R ² and R ³ are each independently a methyl group, an ethyl group, a propyl group, or a butyl group, and even more preferably, R ² and R ³ are both methyl groups. When R ² and R ³ are methyl groups or the like, the heat resistance and bending properties of the cured product are well balanced, and among them, when R ² and R ³ are both methyl groups, the melt viscosity is low, the handling is excellent, and the balance between bending properties and heat resistance is excellent, which is a preferred embodiment. In addition, R ² and R ³ may be bonded to form a cyclic structure (the aliphatic ketone includes an alicyclic ketone).

In the above general formula (3), n is preferably an integer of 0 to 3. Since the resulting phenolic resin or epoxy resin can be easily adjusted to a low viscosity and has excellent flowability and handling properties, n is more preferably an integer of 0 or 1, and even more preferably n is 0 (biscatechol A).

In addition, R ¹ , R ² , R ³ and m in the above general formula (3) are the same as those in the above general formulas (1) and (2).

The reaction ratio of the catechol compound and the aliphatic ketone is preferably in the range of 0.01 to 0.9 moles of the aliphatic ketone per mole of the catechol compound, and more preferably 0.1 to 0.7 moles, since this produces an epoxy resin with an excellent balance between melt viscosity and heat resistance in the cured product.

The reaction between the catechol compound and the aliphatic ketone is preferably carried out in the presence of an acid catalyst, since the reaction proceeds efficiently. Examples of the acid catalyst include inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; organic acids such as methanesulfonic acid, paratoluenesulfonic acid, and oxalic acid; and Lewis acids such as boron trifluoride, anhydrous aluminum chloride, and zinc chloride. In addition, co-catalysts such as mercaptocarboxylic acids such as thioglycolic acid, thiolactic acid, 2-mercaptopropionic acid, and 3-mercaptopropionic acid, and alkyl mercaptans such as propyl mercaptan, butyl mercaptan, pentyl mercaptan, hexyl mercaptan, heptyl mercaptan, octyl mercaptan, nonyl mercaptan, decyl mercaptan, undecyl mercaptan, and dodecyl mercaptan can also be used together with the acid catalyst. The amount of the acid catalyst used is preferably in the range of 0.01 to 5.0% by mass based on the total mass of the reaction raw materials (including the solvent).

The reaction between the catechol compound and the aliphatic ketone can usually be carried out at a temperature of 30 to 80°C for 1 to 20 hours. The reaction may be carried out in an organic solvent as necessary. The organic solvent used here is not particularly limited as long as it is an organic solvent that can be used under the above temperature conditions, and specific examples include methyl cellosolve, ethyl cellosolve, toluene, xylene, and methyl isobutyl ketone. When using these organic solvents, it is preferable to use them in the range of 10 to 500 mass% based on the total mass of the reaction raw materials.

After the reaction between the catechol compound and the aliphatic ketone is completed, unreacted reactant materials and by-products are distilled off to obtain a purified phenolic resin.
In addition, if a part of the catechol compound remains unreacted after the reaction between the catechol compound and the aliphatic ketone is completed, it may volatilize during the production of a cured product, which may cause voids or cause stoichiometric errors and adversely affect the bending properties of the resulting epoxy resin, so it is preferable that the amount of the catechol compound remaining is not large. Therefore, the content of the remaining (unreacted) catechol compound is preferably 20 area% or less in GPC area%, more preferably 10 area% or less. In addition, the GPC area% here refers to the value obtained by dividing the GPC peak area value of the remaining (unreacted) catechol compound by the sum of the GPC peak area values of all components.

The hydroxyl equivalent of the phenolic resin is preferably 50 to 110 g/equivalent, more preferably 60 to 100 g/equivalent, and even more preferably 65 to 90 g/equivalent. If the hydroxyl equivalent is within the above range, the functional group density in the cured product will be increased, and the heat resistance and mechanical strength of the resulting cured product will be excellent, which is preferable. The hydroxyl equivalent of the phenolic resin here is based on the measurement method for "hydroxyl equivalent of phenolic resin" in the examples below.

The melt viscosity (150°C) of the phenolic resin is preferably 5.0 dPa·s or less, more preferably 0.1 to 4.0 dPa·s, and even more preferably 0.5 to 3.0 dPa·s. If the melt viscosity of the phenolic resin is within the above range, it has low viscosity and excellent fluidity and handleability, and is therefore preferable because it also has excellent handleability during epoxy resin synthesis and during preparation of a cured product. The melt viscosity (150°C) here is measured using an ICI viscometer in accordance with ASTM D4287.

<Epoxy resin>
The present invention relates to an epoxy resin which is a reaction product of a catechol compound and an aliphatic ketone, the epoxy resin being characterized in that it is a reaction product having a phenolic resin having at least two catechol skeletons derived from the catechol compound, and a glycidyl ether group obtained by a reaction between a phenolic hydroxyl group of the phenolic resin and an epihalohydrin.
The epoxy resin is an epoxy resin into which a glycidyl ether group has been introduced by reacting a phenolic hydroxyl group of the phenol resin with epihalohydrin, and a cured product using the epoxy resin is preferable because it has excellent heat resistance and high bending properties (such as bending strength and bending modulus).

As the epoxy resin, for example, an epoxy resin having a glycidyl ether group (the “OX group” in formula (4)) represented by the following general formula (4) can be obtained by reacting a phenolic hydroxyl group of a phenol resin represented by the above general formula (3) with epihalohydrin.

In the above general formula (4), X is represented by the above general formula (5), and R ⁴ in the above general formula (5) is preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom. When R ⁴ is a hydrogen atom or the like, the bending properties and heat resistance are excellent, which is preferable. Among them, when R 4 is a hydrogen atom, the melt viscosity is low, which is a particularly preferable embodiment. In addition, all of X may be substituted with a glycidyl group represented by the above formula (5), or a part of X may be substituted.

In the above general formula (4), R ¹ , R ² , R ³ , m, and n are the same as those in the above general formulas (1) to (3).

The phenolic resin can be reacted with epihalohydrin to obtain the desired epoxy resin. For example, the reaction can be carried out by using 2 to 10 moles of epihalohydrin per mole of phenolic hydroxyl groups in the phenolic resin, and reacting for 0.5 to 30 hours at a temperature of 20 to 120°C while adding 0.9 to 2.0 moles of basic catalyst per mole of phenolic hydroxyl groups all at once or in portions.

Specific examples of the basic catalyst include alkaline earth metal hydroxides, alkali metal carbonates, and alkali metal hydroxides. Among these, alkali metal hydroxides are preferred because of their excellent catalytic activity, and specifically, sodium hydroxide, potassium hydroxide, and the like are preferred.

After the reaction is complete, the reaction mixture is washed with water, and the unreacted epihalohydrin and organic solvent are removed by distillation under reduced pressure with heating. In order to obtain an epoxy resin with even fewer hydrolyzable halogens, the obtained epoxy resin can be dissolved in an organic solvent again, and an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide can be added to carry out the reaction. In this case, a phase transfer catalyst such as a quaternary ammonium salt or crown ether can be present in order to improve the reaction rate. When a phase transfer catalyst is used, the amount used is preferably 0.1 to 3.0 parts by mass per 100 parts by mass of the epoxy resin. After the reaction is complete, the salt formed is removed by filtration or washing with water, and the organic solvent is removed by distillation under reduced pressure with heating, to obtain the desired epoxy resin of the present invention.

The epoxy equivalent of the epoxy resin is preferably 120 to 400 g/equivalent, more preferably 130 to 300 g/equivalent, and even more preferably 120 to 200 g/equivalent. When the epoxy equivalent of the epoxy resin is within the above range, the crosslink density of the cured product is increased, and the heat resistance of the resulting cured product is excellent, which is preferable. The epoxy equivalent is measured in accordance with JIS K7236.

The melt viscosity (150°C) of the epoxy resin is preferably 2.0 dPa·s or less, more preferably 0.01 to 1.0 dPa·s, and even more preferably 0.1 to 0.6 dPa·s. If the melt viscosity of the epoxy resin is within the above range, it is preferable because it has low viscosity, excellent fluidity and handleability, and the moldability of the resulting cured product is also excellent. The melt viscosity (150°C) here is measured using an ICI viscometer in accordance with ASTM D4287.

<Curable resin composition>
The present invention relates to a curable resin composition containing the epoxy resin. The curable resin composition contains the epoxy resin, and thus the curable resin composition has excellent handleability and the obtained cured product has high heat resistance and high bending properties (such as bending strength and bending modulus), making it useful.

The curable resin composition of the present invention may further contain, in addition to the epoxy resin, other resins (including other epoxy resins), curing agents, additives, solvents, etc., as long as the effects of the present invention are not impaired.

[Other epoxy resins]
As the other epoxy resin, various epoxy resins can be used, and examples thereof include naphthalene skeleton-containing epoxy resins such as 2,7-diglycidyloxynaphthalene, α-naphthol novolac type epoxy resins, β-naphthol novolac type epoxy resins, polyglycidyl ether of α-naphthol/β-naphthol co-condensed type novolac, naphthol aralkyl type epoxy resins, and 1,1-bis(2,7-diglycidyloxy-1-naphthyl)alkane; bisphenol type epoxy resins such as bisphenol A type epoxy resins and bisphenol F type epoxy resins; biphenyl type epoxy resins such as biphenyl type epoxy resins and tetramethylbiphenyl type epoxy resins; novolac type epoxy resins such as phenol novolac type epoxy resins, cresol novolac type epoxy resins, bisphenol A novolac type epoxy resins, and biphenyl novolac type epoxy resins; tetraphenylethane type epoxy resins; dicyclopentadiene-phenol addition reaction type epoxy resins; phenol aralkyl type epoxy resins; and phosphorus atom-containing epoxy resins. Examples of the phosphorus atom-containing epoxy resin include an epoxidized product of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (hereinafter abbreviated as "HCA"), an epoxidized product of a phenolic resin obtained by reacting HCA with quinones, an epoxy resin obtained by modifying a phenol novolac epoxy resin with HCA, an epoxy resin obtained by modifying a cresol novolac epoxy resin with HCA, an epoxy resin obtained by modifying a bisphenol A epoxy resin with a phenolic resin obtained by reacting HCA with quinones, etc. These may be used alone or in combination of two or more kinds.

[Other resins]
The curable resin composition of the present invention may contain other resins in addition to the epoxy resin and other epoxy resins. In this specification, the term "other resins" refers to resins other than epoxy resins.

Specific examples of the other resins include, but are not limited to, active esters, maleimide resins, bismaleimide resins, polymaleimide resins, polyphenylene ether resins, polyimide resins, cyanate ester resins, benzoxazine resins, triazine-containing cresol novolac resins, cyanate ester resins, styrene-maleic anhydride resins, allyl group-containing resins such as diallyl bisphenol and triallyl isocyanurate, polyphosphate esters, and phosphate ester-carbonate copolymers. These other resins may be used alone or in combination of two or more.

[Curing agent]
The epoxy resin composition of the present invention may contain a curing agent together with the epoxy resin. By containing the curing agent, a cured product having excellent heat resistance can be obtained.

The curing agent used here includes amine compounds, amide compounds, acid anhydrides, phenolic resins, etc., which may be used alone or in combination of two or more. Note that the phenolic resin used as the curing agent is different from the phenolic resin having the specific structure in the present invention.

Examples of the amine compound include diaminodiphenylmethane, diethylenetriamine, triethylenetetramine, diaminodiphenylsulfone, isophoronediamine, imidazole, BF ₃ -amine complex, and guanidine derivatives.

Examples of the amide-based compounds include dicyandiamide, aliphatic dibasic acids, dimer acids, and polyamide resins synthesized from carboxylic acid compounds of fatty acids and amines such as ethylenediamine.

Examples of the acid anhydride include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, and methylhexahydrophthalic anhydride.

Examples of the phenolic resin include phenol novolac resin, cresol novolac resin, aromatic hydrocarbon formaldehyde resin modified phenolic resin, dicyclopentadiene phenol addition type resin, phenol aralkyl resin (Zylok resin), polyhydric phenol novolac resin synthesized from polyhydric hydroxy compounds such as resorcinol novolac resin and formaldehyde, naphthol aralkyl resin, trimethylol methane resin, tetraphenylol ethane resin, naphthol novolac resin, naphthol-phenol co-condensed novolac resin, naphthol Examples of polyphenol compounds include cresol co-condensed novolac resin, biphenyl modified phenol resin (a polyphenol compound in which the phenol nucleus is linked by a bismethylene group), biphenyl modified naphthol resin (a polyphenol compound in which the phenol nucleus is linked by a bismethylene group), aminotriazine modified phenol resin (a polyphenol compound in which the phenol nucleus is linked by a melamine, benzoguanamine, etc.), and alkoxy group-containing aromatic ring modified novolac resin (a polyphenol compound in which the phenol nucleus and the alkoxy group-containing aromatic ring are linked by formaldehyde).

These hardeners may be used alone or in combination of two or more.

In the curable resin composition of the present invention, the blending ratio of the epoxy resin component and the curing agent is preferably such that the active groups in the curing agent are 0.7 to 1.5 equivalents per total equivalent of epoxy groups in the epoxy resin component, since this gives a cured product with excellent curing properties and excellent heat resistance and toughness.

The additives include, for example, various additives such as curing accelerators, flame retardants, inorganic fillers, silane coupling agents, release agents, pigments, emulsifiers, and solvents, which can be contained in the curable resin composition as necessary.

[Curing accelerator]
Examples of the curing accelerator include phosphorus-based compounds, tertiary amines, imidazoles, organic acid metal salts, Lewis acids, amine complex salts, etc. Among them, from the viewpoint of excellent curability, heat resistance, electrical properties, moisture resistance reliability, etc., preferred are 2-ethyl-4-methylimidazole as an imidazole compound, triphenylphosphine as a phosphorus-based compound, and 1,8-diazabicyclo-[5.4.0]-undecene (DBU) as a tertiary amine.

[Flame retardant]
Examples of the flame retardant include inorganic phosphorus compounds such as red phosphorus, ammonium phosphates such as monoammonium phosphate, diammonium phosphate, triammonium phosphate, and ammonium polyphosphate, and phosphoric acid amides; phosphoric acid ester compounds, phosphonic acid compounds, phosphinic acid compounds, phosphine oxide compounds, phosphorane compounds, organic nitrogen-containing phosphorus compounds, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide. and organic phosphorus compounds such as cyclic organic phosphorus compounds such as 10-(2,7-dihydroxynaphthyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide and derivatives thereof reacted with compounds such as epoxy resins and phenolic resins; nitrogen-based flame retardants such as triazine compounds, cyanuric acid compounds, isocyanuric acid compounds, and phenothiazine; silicone-based flame retardants such as silicone oil, silicone rubber, and silicone resin; and inorganic flame retardants such as metal hydroxides, metal oxides, metal carbonate compounds, metal powders, boron compounds, and low-melting glass. When these flame retardants are used, the amount thereof is preferably in the range of 0.1 to 20 mass % in the curable resin composition.

[Inorganic filler]
The inorganic filler is blended, for example, when the curable resin composition of the present invention is used as a semiconductor encapsulation material. Examples of the inorganic filler include fused silica, crystalline silica, alumina, silicon nitride, and aluminum hydroxide. Among them, the fused silica is preferred because it allows a larger amount of the inorganic filler to be blended. The fused silica can be used in either crushed or spherical form, but it is preferred to mainly use spherical silica in order to increase the blending amount of the fused silica and suppress an increase in the melt viscosity of the curable resin composition. Furthermore, it is preferred to appropriately adjust the particle size distribution of the spherical silica in order to increase the blending amount of the spherical silica. The filler is preferably blended in a range of 0.5 to 95 parts by mass in 100 parts by mass of the curable resin composition.

The curable resin composition of the present invention may be prepared without a solvent or may contain a solvent. The solvent has a function of adjusting the viscosity of the curable resin composition. Specific examples of the solvent include, but are not limited to, ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ether-based solvents such as diethyl ether and tetrahydrofuran; ester-based solvents such as ethyl acetate, butyl acetate, cellosolve acetate, propylene glycol monomethyl ether acetate, and carbitol acetate; carbitols such as cellosolve and butyl carbitol; aromatic hydrocarbons such as toluene, xylene, ethylbenzene, mesitylene, 1,2,3-trimethylbenzene, and 1,2,4-trimethylbenzene; and amide-based solvents such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone. These solvents may be used alone or in combination of two or more.

In addition, when the curable resin composition of the present invention is used for applications such as conductive paste, a conductive filler such as silver powder or copper powder can be used.

<Cured Product>
The present invention relates to a cured product obtained by subjecting the curable resin composition to a curing reaction. Since the cured product is obtained from the curable resin composition containing the epoxy resin, the cured product can exhibit high heat resistance and high bending properties (such as bending strength and bending modulus), which is preferable.

The curable resin composition of the present invention can be obtained by uniformly mixing the above-mentioned components. The epoxy resin component, the curing agent, and optionally a curing accelerator are blended, and a cured product can be easily obtained by using this composition in the same manner as conventionally known methods. The obtained cured product can be a molded cured product such as a laminate, a cast product, an adhesive layer, a coating film, or a film.

As a method for obtaining a cured product by subjecting the curable resin composition to a curing reaction, for example, the heating temperature during heat curing is not particularly limited, but is preferably 100 to 300°C, and the heating time is preferably 1 to 24 hours.

<Uses of the curable resin composition>
Examples of applications in which the curable resin composition is used include printed wiring board materials, resin compositions for flexible wiring boards, interlayer insulating materials for build-up boards, insulating materials for circuit boards such as adhesive films for build-up, resin casting materials, adhesives, semiconductor encapsulation materials, semiconductor devices, prepregs, conductive pastes, build-up films, build-up boards, fiber-reinforced composite materials, and molded products obtained by curing the composite materials. Among these various applications, in the applications of printed wiring board materials, insulating materials for circuit boards, and adhesive films for build-up, the composition can be used as an insulating material for so-called electronic component-embedded boards in which passive components such as capacitors and active components such as IC chips are embedded in the board. Furthermore, among the above, taking advantage of the characteristics of the cured product having excellent high heat resistance and high elastic modulus, the curable resin composition of the present invention is preferably used for semiconductor encapsulation materials, semiconductor devices, prepregs, flexible wiring boards, circuit boards, build-up films, build-up boards, multilayer printed wiring boards, fiber-reinforced composite materials, and molded products obtained by curing the composite materials. A method for producing the fiber-reinforced composite material from the curable resin composition will be described below.

1. Semiconductor encapsulation material As a method for obtaining a semiconductor encapsulation material from the curable resin composition, the curable resin composition, the curing accelerator, and compounding agents such as inorganic fillers are melt-mixed sufficiently until homogeneous using an extruder, kneader, roll, etc. as necessary. In this case, fused silica is usually used as the inorganic filler, but when used as a high thermal conductivity semiconductor encapsulation material for power transistors and power ICs, it is preferable to use highly filled crystalline silica, alumina, silicon nitride, etc., which have a higher thermal conductivity than fused silica, or fused silica, crystalline silica, alumina, silicon nitride, etc. The filling rate is preferably in the range of 30 to 95 parts by mass of the inorganic filler per 100 parts by mass of the curable resin composition, and among them, in order to improve flame retardancy, moisture resistance, and solder crack resistance and to reduce the linear expansion coefficient, it is more preferable that the inorganic filler is 70 parts by mass or more, and even more preferable that the inorganic filler is 80 parts by mass or more.

2. Semiconductor Device As a method for obtaining a semiconductor device from the above-mentioned curable resin composition, a method can be mentioned in which the above-mentioned semiconductor encapsulating material is molded by casting, or using a transfer molding machine, an injection molding machine or the like, and then heated at 50 to 200° C. for 2 to 10 hours.

3. Prepreg As a method for obtaining a prepreg from the curable resin composition, a method can be mentioned in which the curable resin composition is made into a varnish by blending the following organic solvent, and then impregnating a reinforcing substrate (paper, glass cloth, glass nonwoven fabric, aramid paper, aramid cloth, glass mat, glass roving cloth, etc.) with the curable resin composition, and then heating at a heating temperature according to the type of solvent used, preferably at 50 to 170° C. The mass ratio of the resin composition and the reinforcing substrate used at this time is not particularly limited, but it is usually preferable to prepare the resin content in the prepreg to be 20 to 60 mass%.

The organic solvents used here include methyl ethyl ketone, acetone, dimethylformamide, methyl isobutyl ketone, methoxypropanol, cyclohexanone, methyl cellosolve, ethyl diglycol acetate, propylene glycol monomethyl ether acetate, etc., and the selection and appropriate amount of the solvent can be appropriately selected depending on the application. For example, when a printed circuit board is further produced from the prepreg as described below, it is preferable to use a polar solvent with a boiling point of 160°C or less, such as methyl ethyl ketone, acetone, or dimethylformamide, and it is also preferable to use it in a proportion such that the non-volatile content is 40 to 80% by mass.

4. Circuit Boards As a method for obtaining a printed circuit board from the above-mentioned curable resin composition, a method can be mentioned in which the above-mentioned prepregs are laminated by a conventional method, copper foil is appropriately laminated, and the laminate is heated and pressed at 170 to 300° C. under a pressure of 1 to 10 MPa for 10 minutes to 3 hours.

5. Flexible Wiring Board The method for producing a flexible wiring board from the curable resin composition includes a method comprising the following three steps. The first step is to apply a curable resin composition containing an active ester, an epoxy resin, and an organic solvent to an electrically insulating film using a coater such as a reverse roll coater or a comma coater. The second step is to heat the electrically insulating film to which the curable resin composition has been applied at 60 to 170° C. for 1 to 15 minutes using a heater to volatilize the solvent from the electrically insulating film and to bring the curable resin composition to a B-stage. The third step is to thermocompress a metal foil to the adhesive of the electrically insulating film to which the curable resin composition has been brought to a B-stage using a heating roll or the like (the compression pressure is preferably 2 to 200 N/cm and the compression temperature is preferably 40 to 200° C.). If sufficient adhesive performance is obtained by going through the above three steps, the process may be terminated here, but if complete adhesive performance is required, it is preferable to further post-cure under conditions of 100 to 200° C. for 1 to 24 hours. The thickness of the curable resin composition film after final curing is preferably in the range of 5 to 100 μm.

6. Build-up substrate The method for producing a build-up substrate from the curable resin composition includes a method consisting of the following three steps. The first step is a step of applying the curable resin composition, which is appropriately blended with rubber, filler, etc., to a circuit board on which a circuit is formed, using a spray coating method, a curtain coating method, etc., and then curing the composition. The second step is a step of forming a predetermined through-hole portion or the like as necessary, treating the surface with a roughening agent, washing the surface with hot water to form unevenness, and plating a metal such as copper. The third step is a step of repeating such operations in sequence as desired to alternately build up a resin insulating layer and a conductor layer of a predetermined circuit pattern. It is preferable to form a through-hole portion after forming the outermost resin insulating layer. The first step can be performed by laminating a build-up film that has been coated and dried to a desired thickness in advance, in addition to the above-mentioned solution coating. In addition, the build-up board of the present invention can be produced by forming a roughened surface by semi-curing the resin composition on the copper foil, and then heat-pressing the resulting resin-coated copper foil onto a wiring board having a circuit formed thereon at 170 to 250°C, thereby eliminating the need for a plating process.

7. Build-up Film [0043] Examples of a method for producing a build-up film from the curable resin composition include a method in which the curable resin composition is applied onto a support film to form a curable resin composition layer, thereby forming an adhesive film for a multilayer printed wiring board.

When producing a build-up film from a curable resin composition, it is essential that the film softens under the lamination temperature conditions in the vacuum lamination method (usually 70 to 140°C) and exhibits fluidity (resin flow) that allows resin to fill via holes or through holes in the circuit board at the same time as laminating the circuit board, and it is preferable to mix the above components to achieve this characteristic.

Here, the diameter of the through holes in a multilayer printed wiring board is usually 0.1 to 0.5 mm, and the depth is usually 0.1 to 1.2 mm, and it is usually preferable to make it possible to fill the resin within this range. When laminating both sides of the circuit board, it is desirable to fill about half of the through holes.

Specifically, the adhesive film can be produced by preparing the curable resin composition in a varnish form, applying the varnish-like composition to the surface of the support film (Y), and then drying the organic solvent by heating or blowing hot air onto the film to form a composition layer (X) made of the curable resin composition.

It is preferable that the thickness of the composition layer (X) formed is usually equal to or greater than the thickness of the conductor layer. Since the thickness of the conductor layer of a circuit board is usually in the range of 5 to 70 μm, it is preferable that the thickness of the resin composition layer is 10 to 100 μm.

In addition, the composition layer (X) in the present invention may be protected with a protective film described below. By protecting the resin composition layer with a protective film, it is possible to prevent the adhesion of dirt and the like to the surface of the resin composition layer and prevent scratches.

The above-mentioned support film and protective film may be made of polyolefins such as polyethylene, polypropylene, and polyvinyl chloride, polyesters such as polyethylene terephthalate (hereinafter sometimes abbreviated as "PET") and polyethylene naphthalate, polycarbonate, polyimide, and even release paper and metal foils such as copper foil and aluminum foil. The support film and protective film may be subjected to a mud treatment, a corona treatment, or a release treatment.

The thickness of the support film is not particularly limited, but is usually in the range of 10 to 150 μm, and preferably in the range of 25 to 50 μm. The thickness of the protective film is preferably 1 to 40 μm.

The support film (Y) is peeled off after laminating it onto the circuit board or after forming an insulating layer by heat curing. If the support film (Y) is peeled off after the adhesive film is heat cured, the adhesion of dust and the like during the curing process can be prevented. When peeling off after curing, the support film is usually subjected to a release treatment in advance.

8. Multilayer Printed Wiring Boards It is also possible to manufacture a multilayer printed wiring board using the film obtained as described above. In the manufacturing method of such a multilayer printed wiring board, for example, when the composition layer (X) is protected by a protective film, the protective film is peeled off, and then the composition layer (X) is directly laminated on one or both sides of the circuit board by, for example, a vacuum lamination method. The lamination method may be a batch method or a continuous method using a roll. In addition, the adhesive film and the circuit board may be heated (preheated) before lamination as necessary.

The lamination conditions are preferably a pressure bonding temperature (lamination temperature) of 70 to 140° C., a pressure bonding pressure of 1 to 11 kgf/cm ² (9.8×10 ⁴ to 107.9×10 ⁴ N/m ² ), and lamination under reduced pressure of an air pressure of 20 mmHg (26.7 hPa) or less.

9. Fiber-reinforced composite material The present invention relates to a fiber-reinforced composite material characterized by containing the curable resin composition and reinforcing fibers. The fiber-reinforced composite material can be produced from the curable resin composition by uniformly mixing each component constituting the curable resin composition to prepare a varnish, impregnating the varnish into a reinforcing base material consisting of reinforcing fibers, and then polymerizing the varnish. In particular, the epoxy resin of the present invention has a low melt viscosity and is therefore excellent in handleability, making it suitable for producing the fiber-reinforced composite material and preferable.

The curing temperature during this polymerization reaction is preferably in the range of 50 to 250°C, and it is particularly preferable to cure at 50 to 100°C to produce a tack-free cured product, and then further treat the product at a temperature of 120 to 200°C.

Here, the reinforcing fibers may be any of twisted, untwisted, and non-twisted yarns, but untwisted and non-twisted yarns are preferred because they provide both moldability and mechanical strength for the fiber-reinforced plastic member. Furthermore, the reinforcing fibers may be in the form of unidirectional fibers or woven fabrics. For woven fabrics, plain weave, satin weave, and other fabrics may be freely selected according to the part to be used and the application. Specifically, carbon fibers, glass fibers, aramid fibers, boron fibers, alumina fibers, silicon carbide fibers, and the like, which have excellent mechanical strength and durability, may be used, and two or more of these may be used in combination. Of these, carbon fibers are particularly preferred because they provide good strength for the molded product, and various types of carbon fibers such as polyacrylonitrile, pitch, and rayon can be used. Among these, polyacrylonitrile-based fibers are preferred because they can easily provide high-strength carbon fibers. Here, when impregnating a reinforcing base material made of reinforcing fibers with the varnish to produce a fiber-reinforced composite material, the amount of reinforcing fibers used is preferably an amount such that the volume content of the reinforcing fibers in the fiber-reinforced composite material is in the range of 40 to 85%.

10. Fiber-reinforced resin molded product The present invention relates to a fiber-reinforced resin molded product characterized by containing the cured product and reinforcing fibers. Examples of methods for producing a fiber-reinforced resin molded product from the curable resin composition include a hand lay-up method or a spray-up method in which fiber aggregate is laid in a mold and the varnish is multi-layered, a vacuum bag method in which a male or female mold is used to impregnate a base material made of reinforcing fibers with varnish, stack the varnish, and mold the molded product by stacking it, and then a flexible mold that can apply pressure to the molded product is placed over the molded product and the product is vacuum (reduced pressure) molded after being hermetically sealed, an SMC press method in which a sheet of varnish containing reinforcing fibers is compressed and molded in a mold, and an RTM method in which the varnish is injected into a mating mold in which fibers are laid out, to produce a prepreg in which the reinforcing fibers are impregnated with the varnish, and the prepreg is baked and hardened in a large autoclave. In particular, the epoxy resin of the present invention has a low melt viscosity and is therefore excellent in handleability, making it suitable for the production of the fiber-reinforced resin molded product, and is therefore preferable. The fiber-reinforced resin molded product obtained above is a molded product having reinforcing fibers and a cured product of the curable resin composition. Specifically, the amount of reinforcing fibers in the fiber-reinforced resin molded product is preferably in the range of 40 to 70% by mass, and from the viewpoint of strength, it is particularly preferable that the amount is in the range of 50 to 70% by mass.

11. Others Although the methods for producing semiconductor encapsulation materials, fiber-reinforced composite materials, etc. have been described above, other cured products can also be produced from the curable resin composition. The other cured products can be produced according to a general curing method for curable resin compositions. For example, the heating temperature conditions may be appropriately selected depending on the type of curing agent to be combined, the application, etc.

The present invention will be specifically explained below with reference to examples and comparative examples, but should not be construed as being limited to these. In the following, unless otherwise specified, all values are by weight. The phenolic resins and epoxy resins obtained below, and the cured products obtained using the epoxy resins, were measured and evaluated under the following conditions.

<Hydroxyl equivalent of phenolic resin>
The hydroxyl equivalent (g/equivalent) of the phenolic resin was measured according to the procedure and calculation formula shown below.
2.5 g of the phenolic resin obtained below was weighed out, triphenylphosphine 7.5 g, pyridine 7.5 g, and acetic anhydride 2.5 g were placed in a 500 mL Erlenmeyer flask and treated at 120° C. for 2.5 hours, after which 5 mL of distilled water was added to stop the reaction. The sample was then dissolved in 150 mL of tetrahydrofuran and 200 mL of propylene glycol monomethyl ether to prepare a sample solution.
Separately from the sample solution, 10 mL of distilled water and 2.5 g of acetic anhydride were precisely weighed, 10 g of pyridine was added, and the mixture was stirred for 10 minutes and allowed to stand for 20 minutes. Thereafter, the mixture was mixed with 150 mL of tetrahydrofuran and 200 mL of propylene glycol monomethyl ether to prepare a blank solution.
The obtained sample solution and blank solution were titrated with a 0.5 mol/L ethanolic potassium hydroxide solution (titration solution) using an automatic potentiometric titrator AT-510 (Kyoto Electronics Manufacturing Co., Ltd.), and the hydroxyl group equivalent was calculated using the following calculation formula.

[Blank formula]
BL = (titer of blank solution) x (theoretical titer of 2.5 g of acetic anhydride) / (theoretical titer of blank solution)
=Y×[(2.5/102.09)×2×(1000/5)]/[(W/102.09)×2×(1000/5)]
BL: blank value (mL)
Y: Titration volume of blank solution (mL)
W: Amount of acetic anhydride in blank measurement (g)

[Formula for calculating the hydroxyl equivalent of a sample]
Hydroxyl equivalent (g/equivalent)=S×1000/[{(BL×FA3/FA5)−EP1}×FA4]
S: sample amount (g)
FA3: Amount of acetic anhydride at the time of sample measurement (g)
FA4: Concentration of titrant (ethanolic KOH solution) (mol/L)
FA5: Amount of acetic anhydride at the time of sample measurement (g)
EP1: titer of sample (mL)

<Melt Viscosity Measurement (150°C)>
The melt viscosity (dPa·s) at 150° C. was measured using an ICI viscometer in accordance with ASTM D4287.

<Viscosity measurement (25°C)>
The viscosity (mPa·s) at 25° C. was measured using an E-type viscometer (TV-22, manufactured by Toki Sangyo Co., Ltd.).

<Epoxy equivalent of epoxy resin>
The epoxy equivalent (g/equivalent) of the resulting epoxy resin was measured according to JIS K7236.

<GPC Measurement>
The following measuring apparatus and conditions were used to confirm the synthesis of the phenolic resin obtained by the synthesis method described below, and the content (area %) of the remaining (unreacted) catechol compound in the phenolic resin was calculated based on the GPC measurement. The synthesis of the target product (epoxy resin) was also confirmed by the disappearance of the peak derived from the phenolic resin based on the GPC measurement.
Measurement equipment: "HLC-8320 GPC" manufactured by Tosoh Corporation,
Column: Guard column "HXL-L" manufactured by Tosoh Corporation
+ Tosoh Corporation "TSK-GEL G2000HXL"
+ Tosoh Corporation "TSK-GEL G2000HXL"
+ Tosoh Corporation "TSK-GEL G3000HXL"
+ Tosoh Corporation "TSK-GEL G4000HXL"
Detector: RI (differential refractometer)
Data processing: Tosoh Corporation's "GPC Workstation EcoSEC-WorkStation"
Measurement conditions: Column temperature 40°C
Developing solvent: Tetrahydrofuran
Flow rate: 1.0 ml/min. Standard: The following monodisperse polystyrene with known molecular weight was used in accordance with the measurement manual for the above-mentioned "GPC Workstation EcoSEC-WorkStation."
(Polystyrene used)
"A-500" manufactured by Tosoh Corporation
"A-1000" manufactured by Tosoh Corporation
"A-2500" manufactured by Tosoh Corporation
"A-5000" manufactured by Tosoh Corporation
"F-1" manufactured by Tosoh Corporation
"F-2" manufactured by Tosoh Corporation
"F-4" manufactured by Tosoh Corporation
"F-10" manufactured by Tosoh Corporation
"F-20" manufactured by Tosoh Corporation
"F-40" manufactured by Tosoh Corporation
"F-80" manufactured by Tosoh Corporation
"F-128" manufactured by Tosoh Corporation
Sample: 1.0% by mass in terms of epoxy resin solid content, obtained by filtering a tetrahydrofuran solution (50 μl) using a microfilter.
With regard to the content (area %) of the residual (unreacted) catechol compound in the phenolic resin, from the viewpoint of reducing the volatile content during curing and from the viewpoint of avoiding adverse effects on the bending properties of the obtained cured product, the content of the residual catechol compound is preferably 20 area % or less.

[Synthesis Example 1]
Synthesis of phenolic resin (P-1) 495.5g (4.50mol) of catechol, 4.9g (0.046mol) of 3-mercaptopropionic acid, 247.8g of 1,4-dioxane, and 52.5g (0.54mol) of 98% sulfuric acid were charged into a 2L flask equipped with a thermometer, a cooling tube, and a stirrer, and the temperature was raised to 40°C under nitrogen flow. While maintaining the temperature, 87.0g (1.55mol) of acetone was added dropwise over 1 hour, and the reaction was allowed to proceed for another 3 hours. After the reaction, 520.0g of methyl isobutyl ketone was charged and washed with water until neutral. Next, the system was dehydrated by azeotropy, and after passing through microfiltration, it was concentrated under reduced pressure at 150°C. Further, by distilling off unreacted catechol while blowing in water vapor, 236 g of phenolic resin (P-1) was obtained (residual catechol was 3.9% by GPC area %). The hydroxyl equivalent of the phenolic resin (P-1) was 72 g/equivalent, and the melt viscosity (150°C) was 0.7 dPa·s, and the synthesis was confirmed by GPC measurement. The measurement results are shown in FIG.

[Synthesis Example 2]
Synthesis of phenolic resin (P-2) 200.0g (1.82mol) of catechol, 220.0g of 1,4-dioxane, and 35.0g (0.36mol) of 98% sulfuric acid were charged into a 2L flask equipped with a thermometer, a cooling tube, and a stirrer, and the temperature was raised to 40°C under nitrogen flow. While maintaining the temperature, 60.0g (1.07mol) of acetone was dropped over 1 hour, and then the reaction was allowed to proceed for another 3 hours. After the reaction, 300.0g of methyl isobutyl ketone was charged and washed with water until it became neutral. Next, the system was dehydrated by azeotropy, and after passing through microfiltration, the mixture was concentrated under reduced pressure at 150°C to obtain 160g of phenolic resin (P-2) (residual catechol was 13.4% in GPC area%). The phenol resin (P-2) had a hydroxyl equivalent of 71 g/equivalent and a melt viscosity (150° C.) of 0.6 dPa·s, and its synthesis was confirmed by GPC measurement, the measurement results of which are shown in FIG.

[Example 1]
Synthesis of epoxy resin (E-1) 170.0 g (2.36 mol as hydroxyl group) of phenolic resin (P-1) and 873.6 g (9.44 mol) of epichlorohydrin were charged into a 2 L flask equipped with a thermometer, a cooling tube, and a stirrer, and the temperature was raised to 50 ° C. while stirring and dissolving. Next, 10.35 g of 50% tetramethylammonium aqueous solution was charged and reacted for 24 hours. Furthermore, 211.6 g of 49% sodium hydroxide aqueous solution (1.10 equivalents relative to hydroxyl group) was dropped over 3 hours, and further reacted at 50 ° C. for 1 hour. After completion of the reaction, 262.1 g of isopropyl alcohol was added, stirring was stopped, the water layer accumulated in the lower layer was removed, stirring was resumed, and unreacted epichlorohydrin was distilled off under reduced pressure at 150 ° C. 517.8 g of methyl isobutyl ketone was added to the obtained crude epoxy resin to dissolve it, and the mixture was repeatedly washed with 152.3 g of water until the pH of the washing solution became neutral. Next, the system was dehydrated by azeotropy, and after microfiltration, the solvent was distilled off under reduced pressure to obtain 270.0 g of the target epoxy resin (E-1). The obtained epoxy resin (E-1) was a viscous semi-solid at room temperature, had an epoxy equivalent of 152 g/equivalent, and a melt viscosity (150°C) of 0.2 dPa·s, and its synthesis was confirmed by GPC measurement. The measurement results are shown in FIG. 3.

[Example 2]
Synthesis of epoxy resin (E-2) 100.0 g of phenolic resin (P-2) (1.41 mol as hydroxyl group) and 513.9 g (5.56 mol) of epichlorohydrin were charged into a 2 L flask equipped with a thermometer, a cooling tube, and a stirrer, and the temperature was raised to 50 ° C. while stirring and dissolving. Next, 6.09 g of 50% tetramethylammonium aqueous solution was charged and reacted for 24 hours. Furthermore, 124.7 g of 49% sodium hydroxide aqueous solution (1.10 equivalents relative to hydroxyl group) was dropped over 3 hours, and further reacted at 50 ° C. for 1 hour. After completion of the reaction, 154.2 g of isopropyl alcohol was added, stirring was stopped, the water layer accumulated in the lower layer was removed, stirring was resumed, and unreacted epichlorohydrin was distilled off under reduced pressure at 150 ° C. 614.1 g of methyl isobutyl ketone was added to the obtained crude epoxy resin to dissolve it, and the mixture was repeatedly washed with 180.6 g of water until the pH of the washing liquid became neutral. The system was then dehydrated by azeotropy, and after microfiltration, the solvent was distilled off under reduced pressure to obtain 160.0 g of the target epoxy resin (E-2). The epoxy equivalent of the obtained epoxy resin (E-2) was 158 g/equivalent, and the melt viscosity (150°C) was 0.1 dPa·s, and its synthesis was confirmed by GPC measurement. The measurement results are shown in FIG. 4.

[Comparative Example 1]
Synthesis of epoxy resin (E-3) 165.0g (1.5mol) of catechol and 1110g (12mol) of epichlorohydrin were charged into a 2L flask equipped with a thermometer, a cooling tube, and a stirrer, and the temperature was raised to 50°C while stirring and dissolving. Next, 11.2g of benzyltrimethylammonium chloride was charged and reacted for 15 hours while maintaining the temperature at 50°C. Furthermore, 269.4g of 49% aqueous sodium hydroxide solution (1.10mol relative to hydroxyl groups) was dropped over 3 hours, and further reacted at 50°C for 1 hour. After the reaction was completed, 222.0g of n-butanol was added, stirring was stopped, the water layer accumulated in the lower layer was removed, stirring was resumed, and unreacted epichlorohydrin was distilled off under reduced pressure at 150°C. 566.1g of methyl isobutyl ketone and 94.5g of n-butanol were added to the crude epoxy resin obtained and dissolved. Further, 14.2 g of a 10% aqueous sodium hydroxide solution was added to this solution, and the mixture was reacted at 80° C. for 2 hours, after which washing with 185.0 g of water was repeated until the pH of the washing liquid became neutral. Next, the system was dehydrated by azeotropy, and after passing through microfiltration, the solvent was distilled off under reduced pressure to obtain 323.0 g of epoxy resin (E-3). The epoxy equivalent of the obtained epoxy resin (E-3) was 137 g/equivalent, and the viscosity (25° C.) was 1900 mPa·s, and the synthesis was confirmed by GPC measurement. The measurement results are shown in FIG. 5.

[Comparative Example 2]
Epoxy resin (E-4)
Bisphenol A type epoxy resin EPICLON 850S (epoxy equivalent: 188 g/equivalent) manufactured by DIC Corporation was used as epoxy resin (E-4). The viscosity (25° C.) was 13,500 mPa·s.

[Examples 3 to 4, Comparative Examples 3 to 4]
The obtained epoxy resin and 4,4'-diaminodiphenylsulfone as a curing agent were mixed so that [epoxy equivalent/active hydrogen equivalent] = 1/1, and melt mixed at 120 ° C to obtain an epoxy resin composition. Furthermore, the epoxy resin composition was poured between glass plates sandwiching 2 mm and 4 mm spacers, and a curing reaction was carried out at 150 ° C for 1 hour and then at 180 ° C for 3 hours to produce a cured product.

<Glass transition temperature (Tg)>
The resulting 2 mm thick cured product was cut into a size of 5 mm wide and 20 mm long to prepare a test piece. The test piece was measured using a viscoelasticity measuring device (DMA: Hitachi High-Tech Science Corporation's solid viscoelasticity measuring device "DMS6100", deformation mode: double-support bending, measurement mode: sine wave vibration, frequency 1 Hz, heating rate 3°C/min) to evaluate the temperature at which the elastic modulus change was maximum (the rate of change in tan δ was the largest) as the glass transition temperature.
The glass transition temperature (Tg) is preferably 220° C. or higher, and more preferably 230° C. or higher. If it is within the above range, high heat resistance can be exhibited, and the composition is useful.

<Measurement of bending strength, bending modulus, and bending strain>
The obtained cured product was cut into a size of 2 mm in thickness, 10 mm in width, and 80 mm in length, which was used as test piece 2. The bending strength, bending modulus, and bending strain of test piece 2 were measured according to JIS K6911 using a precision universal testing machine ("AUTOGRAPH AG-I" manufactured by Shimadzu Corporation).
The flexural modulus is preferably 3000 MPa or more, and more preferably 3500 MPa or more.
The bending strength is preferably 120 MPa or more, and more preferably 130 MPa or more.
The bending strain is preferably 3% or more, and more preferably 4% or more.
If it is within the above range, high bending properties can be exhibited, which is useful.

From the evaluation results in Table 1 above, it was confirmed that in Examples 3 and 4, by using epoxy resins obtained by using the phenolic resins having the desired specific structures obtained in Examples 1 and 2, it was possible to obtain cured products with high bending properties and high heat resistance.
On the other hand, in Comparative Example 3, the desired phenolic resin obtained by reacting a catechol compound with an aliphatic ketone was not used as in the Examples, but the catechol-type epoxy resin obtained in Comparative Example 1, which was synthesized using only the catechol compound, was used. As a result, the glass transition temperature was very low, and it was not possible to achieve both heat resistance and bending properties.
In Comparative Example 4, a commonly used bisphenol A type epoxy resin (Comparative Example 2) was used, but the glass transition temperature and flexural modulus were lower than those of the Examples, and it was not possible to achieve both heat resistance and flexural properties.

1 is a GPC spectrum chart of the phenol resin (P-1) obtained in Synthesis Example 1. 1 is a GPC chart of the phenol resin (P-2) obtained in Synthesis Example 2. 1 is a GPC chart of the epoxy resin (E-1) obtained in Example 1. 1 is a GPC chart of the epoxy resin (E-2) obtained in Example 2. 1 is a GPC chart of the epoxy resin (E-3) obtained in Comparative Example 1.

Claims (5)

a phenolic resin which is a reaction product of a catechol compound and an aliphatic ketone and has at least two catechol skeletons derived from the catechol compound;
The epoxy resin is a reaction product having a glycidyl ether group obtained by reacting a phenolic hydroxyl group of the phenol resin with an epihalohydrin, and is represented by the following general formula (4):
(In the above general formula (4), R ¹ is a hydrogen atom, R ² and R ³ are each independently a hydrocarbon group having 1 to 4 carbon atoms, m is an integer of 0 to 3, n is an integer of 0 to 3, X is represented by the above general formula (5), and R ⁴ in the above general formula (5) is a hydrogen atom or a methyl group.) A curable resin composition comprising the epoxy resin according to claim 1. A cured product obtained by subjecting the curable resin composition according to claim 2 to a curing reaction. A fiber-reinforced composite material comprising the curable resin composition according to claim 2 and reinforcing fibers. A fiber-reinforced resin molded product comprising the cured product according to claim 3 and reinforcing fibers.