Curing accelerator, curable composition, and resin product

Abstract

A curing accelerator for an epoxy compound, said curing accelerator containing hexamethylenetetramine and an amine compound A other than hexamethylenetetramine.

Description

Hardening accelerator, curable composition, and resin product

[0001] The present disclosure relates to a hardening accelerator, a curable composition, and a resin product.

[0002] Compounds containing glycidyl groups are generally called epoxy compounds. Epoxy resins obtained by polymerizing (hardening) epoxy compounds have both heat resistance and moldability, and are thus widely used throughout today's society. Although epoxy compounds can be polymerized alone, from the perspective of the efficiency of the polymerization reaction, it is desirable to polymerize the epoxy compound in the presence of components such as a curing agent and a hardening accelerator to promote the polymerization reaction of the epoxy compound. In recent years, from the perspectives of energy consumption savings, carbon emission reduction, etc., the development of technologies that cause a polymerization reaction of epoxy compounds in a low temperature range (for example, 150°C or lower) has been desired. For example, it is known that when an amine compound is used as a curing agent for an epoxy compound, a rapid polymerization reaction of the epoxy compound occurs at a relatively low temperature (see, for example, Non-Patent Document 1).

[0003] Non-Patent Document 1: "Introduction to Epoxy Resins", Polymer Publications Co., Ltd. (1988)

[0004] The method of causing a polymerization reaction of an epoxy compound using an amine compound has room for improvement in terms of ease of reaction control and the like. For this reason, the development of new technologies that can improve the polymerization reactivity of epoxy compounds in a low temperature range has been desired. In view of the above circumstances, an object of the present disclosure is to provide a hardening accelerator that improves the polymerization reactivity of epoxy compounds in a low temperature range, a curable composition containing the hardening accelerator, and a resin product containing a cured product of the curable composition.

[0005] The specific means for achieving the above objectives are as follows: <1> A curing accelerator for epoxy compounds, comprising hexamethylenetetramine and an amine compound A other than hexamethylenetetramine. <2> The curing accelerator according to <1>, wherein the amine compound A comprises an imidazole compound. <3> The curing accelerator according to <2>, wherein the imidazole compound comprises at least one selected from the group consisting of imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, and 1-(2-cyanoethyl)-2-phenylimidazole. <4> The curing accelerator according to any one of <1> to <3>, wherein the amount of hexamethylenetetramine is 0.5 times or more and 40 times or less the amount of the amine compound A. <5> A curing accelerator according to any one of <1> to <4> for use under conditions in which the epoxy compound does not react with the phenol compound. <6> A curable composition comprising the curing accelerator according to any one of <1> to <5> and an epoxy compound. <7> The curable composition according to <6>, wherein the epoxy compound comprises an epoxy compound having two or more epoxy groups in its molecule. <8> The curable composition according to <6> or <7>, wherein the amount of amine compound A per Xg of epoxy compound having an epoxy equivalent of Xg / eq is 2mg to 100mg. <9> The curable composition according to any one of <6> to <8>, wherein the amount of hexamethylenetetramine per Xg of epoxy compound having an epoxy equivalent of Xg / eq is 50mg to 200mg. <10> The curable composition according to any one of <6> to <9>, further comprising water. <11> A curable composition according to any one of <6> to <10>, further comprising a solvent selected from methyl isobutyl ketone, ethanol, 1-propanol, and 1-methoxy-2-propanol. <12> A curable composition according to any one of <6> to <11>, which does not contain a phenol compound. <13> A resin product comprising a cured product of a curable composition according to any one of <6> to <12>.

[0006] The present disclosure provides a curing accelerator that improves the polymerization reactivity of epoxy compounds in a low-temperature range, a curable composition containing the curing accelerator, and a resin product containing a cured product of the curable composition.

[0007] The following describes in detail the forms for implementing this disclosure. However, this disclosure is not limited to the following embodiments. In the following embodiments, the components (including elemental steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit this disclosure.

[0008] In this disclosure, numerical ranges indicated using "~" include the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit of one numerical range may be replaced by the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in this disclosure, the upper or lower limit of that numerical range may be replaced by the values ​​shown in the examples. In this disclosure, each component may contain multiple types of the corresponding substance. If multiple types of the substance corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple types of substances present in the composition, unless otherwise specified. In this disclosure, each particle corresponding to each component may contain multiple types of particles. If multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for the mixture of the multiple types of particles present in the composition, unless otherwise specified. In this disclosure, the term "layer" includes cases where, when observing the region in which the layer exists, it is formed not only over the entire region but also over only a portion of the region.

[0009] <Curing Accelerator> One embodiment of the present disclosure is a curing accelerator for epoxy compounds, comprising hexamethylenetetramine and an amine compound A other than hexamethylenetetramine.

[0010] As shown in the examples described later, when a combination of hexamethylenetetramine and amine compound A other than hexamethylenetetramine is used as a curing accelerator for epoxy compounds, excellent polymerization reactivity of the epoxy compound is exhibited in the low-temperature range (e.g., below 150°C). Furthermore, curable compositions containing hexamethylenetetramine and amine compound A other than hexamethylenetetramine together with the epoxy compound exhibit excellent storage stability, as polymerization of the epoxy compound is less likely to occur in the temperature range below 50°C. Moreover, curable compositions containing hexamethylenetetramine and amine compound A other than hexamethylenetetramine together with the epoxy compound exhibit excellent polymerization reactivity in the low-temperature range (e.g., below 150°C) even when water is used as the solvent.

[0011] (Hexamethylenetetramine) The hexamethylenetetramine (also known as hexamine) contained in the curing accelerator of this disclosure is an amine compound represented by the following structural formula.

[0012]

[0013] Hexamethylenetetramine alone does not function as a curing accelerator for epoxy compounds. However, surprisingly, it was found that when hexamethylenetetramine is used in combination with amine compound A other than hexamethylenetetramine as a curing accelerator for epoxy compounds, the polymerization reactivity of the epoxy compound at low temperatures is improved compared to when amine compound A other than hexamethylenetetramine is used alone as a curing accelerator for epoxy compounds.

[0014] (Amine Compound A) The type of amine compound A other than hexamethylenetetramine included in the curing accelerator of this disclosure is not particularly limited as long as it is a compound that can function as a curing accelerator for epoxy compounds. Amine compound A may be a primary amine, a secondary amine, or a tertiary amine. Amine compound A may be selected from compounds having a structure represented as C=N-C (where one nitrogen atom is bonded to two carbon atoms by a double bond or a single bond).

[0015] Examples of amine compound A include imidazole compounds, 4-aminopyridine, 4-dimethylaminopyridine, tris(dimethylaminomethyl)phenol, diazabicycloundecene, diazabicyclononene, and diaminodiphenylmethane. The amine compound A contained in the curing accelerator of this disclosure may be one type or two or more types.

[0016] From the viewpoint of the polymerization reactivity of epoxy compounds in the low-temperature range, it is preferable that amine compound A contains an imidazole compound. The imidazole compound is an amine compound having a heterogeneous five-membered ring (also called an imidazole skeleton) with nitrogen atoms at positions 1 and 3. Specific examples of imidazole compounds include imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, and 1-(2-cyanoethyl)-2-phenylimidazole. When the curing accelerator of this disclosure contains an imidazole compound, the imidazole compound contained in the curing accelerator may be one type or two or more types.

[0017] The amine compound A contained in the curing accelerator may be water-soluble or not. Examples of water-soluble amine compound A include imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 4-aminopyridine, 4-dimethylaminopyridine, diazabicycloundecene, and diazabicyclononene. Hexamethylenetetramine is water-soluble.

[0018] The proportions of amine compound A and hexamethylenetetramine contained in the curing accelerator of this disclosure are not particularly limited. For example, the amount of hexamethylenetetramine contained in the curing accelerator of this disclosure is preferably 0.5 times or more the amount of amine compound A, more preferably 0.7 times or more, and even more preferably 1 time or more. When the amount of hexamethylenetetramine is 0.5 times or more the amount of amine compound A, the effect of promoting the polymerization reaction of epoxy compounds by the curing accelerator of this disclosure tends to be fully expressed. For example, the amount of hexamethylenetetramine contained in the curing accelerator of this disclosure is preferably 40 times or less the amount of amine compound A, more preferably 30 times or less, and even more preferably 15 times or less. When the amount of hexamethylenetetramine is 40 times or less the amount of amine compound A, the effect of promoting the polymerization reaction of epoxy compounds by the curing accelerator of this disclosure tends to be fully expressed.

[0019] The curing accelerator of this disclosure may be used under conditions in which the epoxy compound reacts with the cured product of the epoxy compound (e.g., a phenolic compound), or under conditions in which the epoxy compound does not react with the cured product of the epoxy compound (e.g., a phenolic compound). Examples of epoxy compound curing agents include epoxy compound curing agents that may be included in the curable composition described later.

[0020] <Curable Composition> One embodiment of the present disclosure is a curable composition comprising the curing accelerator of the present disclosure described above and an epoxy compound.

[0021] In this disclosure, an epoxy compound means a compound containing one or more epoxy groups in its molecule. From the viewpoint of polymerization reactivity, it is preferable that the epoxy compound included in the curable composition contains two or more epoxy groups in its molecule. The curable composition of this disclosure hardens by a polymerization reaction of the epoxy compound to form a cured product. The method for hardening the curable composition of this disclosure is not particularly limited, but from the viewpoint of economy, etc., it is preferable to harden it by heating. That is, the curable composition of this disclosure may be a thermosetting composition.

[0022] The type of epoxy compound included in the curable composition is not particularly limited and can be selected according to the intended use of the resin product obtained by curing the curable composition. Specifically, epoxy compounds include: novolac-type epoxy compounds (phenol novolac-type epoxy compounds, orthocresol novolac-type epoxy compounds, etc.) which are obtained by condensing or co-condensing a compound having a phenolic hydroxyl group (hereinafter also called a phenol compound) with an aliphatic aldehyde compound such as formaldehyde, acetaldehyde, or propionaldehyde under an acidic catalyst and then epoxidizing the novolac compound; triphenylmethane-type epoxy compounds which are obtained by condensing or co-condensing a phenolic compound with an aromatic aldehyde compound such as benzaldehyde or salicylaldehyde and then epoxidizing the triphenylmethane-type phenol compound; bisphenol-type epoxy compounds which are diglycidyl ethers of bisphenol compounds such as bisphenol A and bisphenol F; biphenyl-type epoxy compounds which are diglycidyl ethers of alkyl-substituted or unsubstituted biphenols; and stilbene-type epoxy compounds which are diglycidyl ethers of stilbene-based phenol compounds. Compounds; sulfur atom-containing epoxy compounds, such as diglycidyl ethers of bisphenol S; epoxy compounds, such as glycidyl ethers of alcohols, such as butanediol, polyethylene glycol, and polypropylene glycol; glycidyl ester type epoxy compounds, such as glycidyl esters of polycarboxylic acid compounds, such as phthalic acid, isophthalic acid, and tetrahydrophthalic acid; glycidylamine type epoxy compounds, such as aniline, diaminodiphenylmethane, and isocyanuric acid, in which the active hydrogen bonded to the nitrogen atom is replaced with a glycidyl group; dicyclopentadiene type epoxy compounds, which are epoxidized co-condensed compounds of dicyclopentadiene and phenol compounds; alicyclic epoxy compounds, such as vinylcyclohexene diepoxide, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, and 2-(3,4-epoxy)cyclohexyl-5,5-spiro(3,4-epoxy)cyclohexane-m-dioxane, in which the intramolecular olefin bond is epoxidized;Examples include paraxylylene-modified epoxy compounds, which are glycidyl ethers of paraxylylene-modified phenol compounds; metaxylylene-modified epoxy compounds, which are glycidyl ethers of metaxylylene-modified phenol compounds; terpene-modified epoxy compounds, which are glycidyl ethers of terpene-modified phenol compounds; dicyclopentadiene-modified epoxy compounds, which are glycidyl ethers of dicyclopentadiene-modified phenol compounds; cyclopentadiene-modified epoxy compounds, which are glycidyl ethers of cyclopentadiene-modified phenol compounds; polycyclic aromatic ring-modified epoxy compounds, which are glycidyl ethers of polycyclic aromatic ring-modified phenol compounds; naphthalene-type epoxy compounds, which are glycidyl ethers of naphthalene ring-containing phenol compounds; halogenated phenol novolac-type epoxy compounds; hydroquinone-type epoxy compounds; trimethylolpropane-type epoxy compounds; linear aliphatic epoxy compounds obtained by oxidizing olefin bonds with peracids such as peracetic acid; and aralkyl-type epoxy compounds, which are epoxidized aralkyl-type phenol compounds such as phenol aralkyl compounds and naphthol aralkyl compounds. Furthermore, epoxidized silicone compounds, epoxidized acrylic resins, and the like can also be cited as epoxy compounds. The epoxy compound included in the curable composition may be one type or two or more types.

[0023] The epoxy equivalent of the epoxy compound is not particularly limited. For example, the epoxy equivalent of the epoxy compound may be in the range of 100 g / eq to 1500 g / eq. The epoxy equivalent of the epoxy compound shall be the value measured by the method in accordance with JIS K 7236:2009.

[0024] The epoxy compound contained in the curable composition may be a liquid at room temperature (25°C) or a solid at room temperature (25°C).

[0025] The epoxy compound contained in the curable composition may be soluble or dispersible in water. If the epoxy compound in the curable composition is soluble or dispersible in water, water can be used as the solvent for the curable composition, which is advantageous in terms of economy, safety, and other factors. Examples of water-soluble epoxy compounds include epoxy compounds having hydrophilic functional groups, such as glycerol polyglycidyl ether. Examples of water-dispersible epoxy compounds include bisphenol-type epoxy compounds.

[0026] In one embodiment, the curable composition of the present disclosure may include a phenol novolac type epoxy compound or a cresol novolac type epoxy compound as the epoxy compound. When a curable composition comprising a phenol novolac type epoxy compound or a cresol novolac type epoxy compound as the epoxy compound and the curing accelerator of the present disclosure is heated, a two-stage polymerization reaction can be produced, comprising a first-stage curing reaction in a temperature range of 130°C or lower, and a second-stage curing reaction in a temperature range of 130°C or higher. When the curing reaction of the curable composition includes a two-stage curing reaction, the molecular chains of the epoxy compound are gently crosslinked in the first-stage curing reaction, thereby suppressing volume increase due to temperature rise while maintaining moldability. Therefore, the occurrence of cracks, fissures, etc. in the molded article during the second-stage curing reaction can be suppressed. The degree of the first-stage curing reaction and the second-stage curing reaction can be adjusted by the mixing ratio of the imidazole compound and hexamethylenetetramine in the curing accelerator of the present disclosure, respectively. The degree of curing in the first and second stages can also be adjusted by including an epoxy compound that does not contain a phenol skeleton, or a phenol novolac compound or cresol novolac compound that does not contain an epoxy group, in the curable composition.

[0027] The amount of the curing accelerator of the present disclosure contained in the curable composition of the present disclosure is not particularly limited. For example, the amount of the curing accelerator of the present disclosure contained in the curable composition of the present disclosure is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the epoxy compound. When the amount of the curing accelerator of the present disclosure is 1 part by mass or more per 100 parts by mass of the epoxy compound, the effect of promoting the polymerization reaction of the epoxy compound by the curing accelerator of the present disclosure tends to be sufficiently exhibited. For example, the amount of the curing accelerator of the present disclosure contained in the curable composition of the present disclosure is preferably 30 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the epoxy compound. When the amount of the curing accelerator of the present disclosure is 30 parts by mass or less per 100 parts by mass of the epoxy compound, the polymerization reaction of the epoxy compound does not tend to be excessive, and a good cured product tends to be obtained.

[0028] The amount of curing accelerator contained in the curable composition of this disclosure may be such that the amount of amine compound A is 2 mg / eq to 100 mg / eq relative to the epoxy equivalents of the epoxy compound. That is, if the epoxy equivalent of the epoxy compound contained in the curable composition is X g / eq, the amount of amine compound A relative to X g of epoxy compound may be 2 mg to 100 mg. When the amount of amine compound A relative to the epoxy equivalents of the epoxy compound is 2 mg / eq or more, the polymerization reaction of the epoxy compound tends to be sufficiently promoted. When the amount of amine compound A relative to the epoxy equivalents of the epoxy compound is 100 mg / eq or less, the polymerization reaction of the epoxy compound does not tend to be excessive, and a good cured product tends to be obtained.

[0029] The amount of curing accelerator contained in the curable composition of this disclosure may be such that the amount of hexamethylenetetramine is 50 mg / eq to 200 mg / eq relative to the epoxy equivalents of the epoxy compound. That is, if the epoxy equivalents of the epoxy compound contained in the curable composition are X g / eq, the amount of hexamethylenetetramine relative to X g of the epoxy compound may be 50 mg to 200 mg. When the amount of hexamethylenetetramine relative to the epoxy equivalents of the epoxy compound is 50 mg / eq or more, the polymerization reaction of the epoxy compound tends to be sufficiently promoted. When the amount of hexamethylenetetramine relative to the epoxy equivalents of the epoxy compound is 200 mg / eq or less, the polymerization reaction of the epoxy compound does not tend to be excessive, and a good cured product tends to be obtained.

[0030] The curable composition of this disclosure may or may not contain a curing agent for an epoxy compound. For example, the curable composition of this disclosure may not contain a phenol compound. As the curing agent for the epoxy compound, any known curing agent containing active hydrogen that can react with the epoxy compound can be used without particular limitation. Specific examples of curing agents for epoxy compounds include phenol compounds, acid anhydrides, and amine compounds. Examples of phenol compounds include phenol novolac compounds, cresol novolac compounds, and phenol aralkyl compounds. Examples of acid anhydrides include docecenyl succinic anhydride, polyazelaic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, trimellitic anhydride, pyromellitic anhydride, and benzophenonetetracarboxylic anhydride. Specific examples of amine compounds include aliphatic amine compounds, aromatic amine compounds, dicyandiamide, and melamine. The curable composition may contain only one or two or more curing agents.

[0031] The curable composition may contain a solvent. The solvent is used, for example, to adjust the viscosity of the curable composition. Curable compositions containing a solvent are suitably used, for example, when producing a film-like cured product or when applying a cured product to the surface of a substrate. It is preferable that the solvent be removed before or during the curing reaction of the curable composition.

[0032] The type of solvent included in the curable composition is not particularly limited. From the viewpoint of ease of removal from the curable composition, a solvent with a boiling point of 150°C or lower is preferred, and a solvent with a boiling point of 130°C or lower is more preferred. From the viewpoint of ease of handling at room temperature, a solvent with a boiling point of 50°C or higher is preferred.

[0033] Examples of suitable solvents to be included in the curable composition include acetone, methyl ethyl ketone, methyl isobutyl ketone, hexane, heptane, octane, toluene, xylene, methanol, ethanol, 1-propanol, butanol, 1-methoxy-2-propanol, 2-methoxyethanol, 2-ethoxyethanol, 2-methoxyethyl acetate, 2-methoxy-1-methylethyl acetate, 1-methoxy-2-propanol, tetrahydrofuran, 1,4-dioxane, ethyl acetate, butyl acetate, acetonitrile, dibutyl ether, and water. From the viewpoint of curability at low temperatures, the curable composition may contain a solvent selected from methyl isobutyl ketone, ethanol, 1-propanol, 1-methoxy-2-propanol, and water.

[0034] If the curable composition contains a solvent, the components contained in the curable composition may or may not be dissolved in the solvent. If the components contained in the curable composition are not dissolved in the solvent, the curable composition may contain components such as dispersants and emulsifiers to disperse the components contained in the curable composition in the solvent.

[0035] The curable composition may further contain components other than those described above (other components). Specific examples of other components include curing catalysts, inorganic fillers, rust inhibitors, defoaming agents, viscosity modifiers, tack-imparting agents, foaming agents, leveling agents, friction modifiers, crosslinking agents, surfactants, metal deactivators, colorants, fragrances, and the like.

[0036] The state of the curable composition before curing is not particularly limited and can be selected according to the method of use of the curable composition. For example, the curable composition before curing may be in a fluid state such as a varnish or paste, or it may be in a non-fluid state such as a powder, tablet, or film. In this disclosure, "curable composition before curing" means a curable composition in which the epoxy compound (and optionally included curing agent) contained in the curable composition has not been completely cured. Therefore, a curable composition in which the epoxy compound (and optionally included curing agent) contained in the curable composition has been partially cured also falls under the category of "curable composition before curing".

[0037] In one embodiment, the curable composition of the present disclosure can be suitably used as a paint. In this disclosure, "paint" means a material for forming a coating film on the surface of a substrate. Because the curable composition of the present disclosure exhibits excellent polymerization reactivity of epoxy compounds in low temperature ranges, a coating film consisting of a cured product of the curable composition can be formed on the substrate even when the substrate has low heat resistance.

[0038] In one embodiment, the curable composition of the present disclosure can be suitably used as a material for forming an insulating layer on the surface of a substrate. Because the curable composition of the present disclosure exhibits excellent polymerization reactivity of epoxy compounds in the low-temperature range, an insulating layer consisting of a cured product of the curable composition can be formed on the substrate even when the substrate has low heat resistance.

[0039] <Resin Products> One embodiment of the present disclosure is a resin product comprising a cured product of the curable composition of the present disclosure described above. The shape of the resin product is not particularly limited and can be selected according to the application of the resin product. In one embodiment, the resin product of the present disclosure may be integrated with an article other than the resin product. For example, the resin product of the present disclosure may be placed on the surface of a substrate in the form of a coating, an insulating layer, etc. The type of substrate to be integrated with the resin product of the present disclosure is not particularly limited and may be an organic material such as resin, an inorganic material such as metal, glass, or ceramic, or a combination thereof. In one embodiment, the resin product of the present disclosure may be an injection molded article. The method for obtaining the injection molded article is not particularly limited and can be carried out using a known molding apparatus.

[0040] The resin products of this disclosure can be obtained, for example, by heating the curable composition of this disclosure described above. The temperature at which the curable composition is heated is not particularly limited as long as it is a temperature at which the polymerization reaction of the epoxy compound contained in the curable composition occurs. The heating temperature (maximum temperature) can be, for example, 200°C or less, 180°C or less, 160°C or less, 150°C or less, or 140°C or less. The method of heating the curable composition is not particularly limited and can be carried out using known apparatus.

[0041] The present disclosure will be described in further detail below with reference to examples, but the present disclosure is not limited in any way by these examples.

[0042] <Examples 1 to 9, Comparative Examples 1 to 6> (Preparation of curable composition)The materials (parts by mass) shown in Tables 1 and 2 were thoroughly mixed in a mortar to prepare a curable composition. The details of the materials are as follows. Epoxy compound 1: Phenol novolak type epoxy compound (manufactured by DIC Corporation, Epiclon N-775, epoxy equivalent: 184 to 194 g / eq) Epoxy compound 2: Cresol novolak type epoxy compound (manufactured by DIC Corporation, Epiclon N695, epoxy equivalent: 209 to 219 g / eq) Phenol compound: Straight phenol novolak resin (manufactured by Kashu Co., hexamine-free, hydroxyl equivalent: 104 g / eq) Imidazole compound: 2-Ethyl-4-methylimidazole (manufactured by Fujifilm Wako Pure Chemical Corporation) Hexamine: Hexamethylenetetramine (manufactured by Fujifilm Wako Pure Chemical Corporation)

[0043] (Measurement of heat generation amount and peak top) Using a differential scanning calorimeter (DSC), the heat generation amount (mJ / mg), peak top temperature (°C), and half-value width (°C) of the heat generation peak corresponding to the polymerization reaction of the epoxy compound contained in the curable composition were measured respectively. The measurement was carried out using DSC8500 (manufactured by Perkin Elmer), with the sample amount: 2.0 mg ± 0.5 mg, heating rate: 5 °C / min, and measurement range: 30 °C to 320 °C. When the heat generation peak of the epoxy compound and the heat generation peak of the phenol compound overlapped, peak separation was performed by approximation of the Kamal model (see the following Reference 1). Reference 1: J. of Industrial Chemistry, 16, 270 (1988)

[0044]

[0045] As shown in Tables 1 and 2, the curable compositions (Examples 1 to 9) containing the amine compound A (imidazole compound) and hexamethylenetetramine have a lower peak top temperature of the exothermic peak corresponding to the polymerization reaction of the epoxy compound and a tendency for the half-value width of the peak to become narrower compared to the curable compositions (Comparative Examples 1 and 4) containing neither the amine compound A (imidazole compound) nor hexamethylenetetramine and the curable compositions (Comparative Examples 2 and 5) containing the amine compound A (imidazole compound) but not hexamethylenetetramine. These tendencies suggest that the polymerization reaction of the epoxy compound in the curable compositions of Examples 1 to 9 proceeded at a low temperature and in a short time. No exothermic peak corresponding to the polymerization reaction of the epoxy compound was observed for the curable compositions (Comparative Examples 3 and 6) containing hexamethylenetetramine but not the amine compound A (imidazole compound). This is considered to be because the exothermic peak of the epoxy compound overlapped with the exothermic peak corresponding to the polymerization reaction of the phenol compound or the phenol moiety of the epoxy compound.

[0046] <Example 10> Using the cured composition obtained in Example 1, DSC including the following Steps 1 and 2 was carried out. Step 1: Heat from 30°C to 50°C at a heating rate of 5°C / min and hold at 50°C for 1 hour. Step 2: Heat to 320°C at a heating rate of 5°C / min. As a result of the DSC, only an exothermic peak with a peak top temperature of 131°C and a heat generation amount of 71 mJ / mg was observed as the exothermic peak corresponding to the polymerization reaction of the epoxy compound. The above results indicate that the polymerization reaction of the epoxy compound contained in the curable composition containing the amine compound A (imidazole compound) and hexamethylenetetramine is suppressed in the temperature range of 50°C or lower.

[0047] <Example 11> 600 mg of a water-dispersible epoxy compound, a bisphenol A type epoxy compound (ADEKA Corporation, Adeka Resin EM series), 30 mg of 2-ethyl-4-methylimidazole, 30 mg of hexamethylenetetramine, and 396 mg of titanium dioxide (rutile type) were mixed with 2900 mg of water to prepare a curable composition in which the epoxy compound and titanium dioxide were dispersed in water, and 2-ethyl-4-methylimidazole and hexamethylenetetramine were dissolved in water. This curable composition was applied to a glass plate and heated in a hot air oven at 130°C for 10 minutes. As a result, a layer consisting of the cured product of the curable composition was formed on the surface of the glass plate.

[0048] <Example 12> 1 g of bisphenol A type epoxy compound (Epomount main component, bisphenol A type epoxy compound content: 78% by mass, Refinetech Co., Ltd.), 39 mg of 2-ethyl-4-methylimidazole, and 39 mg of hexamethylenetetramine were mixed with 5 g of methyl isobutyl ketone to prepare a curable composition in which the epoxy compound, 2-ethyl-4-methylimidazole, and hexamethylenetetramine were dissolved in water. This curable composition was applied to a glass plate and heated in a hot air oven at 130°C for 10 minutes. As a result, a layer consisting of the cured product of the curable composition was formed on the surface of the glass plate.

[0049] <Example 13> A curable composition was prepared in the same manner as in Example 12, except that methyl isobutyl ketone was replaced with the same amount of ethanol. This curable composition was applied to a glass plate and heated in a hot air oven at 130°C for 10 minutes. As a result, a layer consisting of the cured product of the curable composition was formed on the surface of the glass plate.

[0050] <Example 14> A curable composition was prepared in the same manner as in Example 12, except that methyl isobutyl ketone was replaced with the same amount of 1-propanol. This curable composition was applied to a glass plate and heated in a hot air oven at 130°C for 10 minutes. As a result, a layer consisting of the cured product of the curable composition was formed on the surface of the glass plate.

[0051] <Example 15> A curable composition was prepared in the same manner as in Example 12, except that methyl isobutyl ketone was replaced with the same amount of 1-methoxy-2-propanol. This curable composition was applied to a glass plate and heated in a hot air oven at 130°C for 10 minutes. As a result, a layer consisting of the cured product of the curable composition was formed on the surface of the glass plate.

[0052] <Example 16> A curable composition was prepared in the same manner as in Example 12, except that methyl isobutyl ketone was not used. This curable composition was applied to a glass plate and heated in a hot air oven at 130°C for 10 minutes. As a result, a layer consisting of the cured product of the curable composition was formed on the surface of the glass plate.

[0053] <Comparative Example 7> A curable composition was prepared in the same manner as in Example 15, except that hexamethylenetetramine was not used. This curable composition was applied to a glass plate and heated in a hot air oven at 130°C or 180°C for 10 minutes. As a result, at 180°C, a layer consisting of the cured product of the curable composition was formed on the surface of the glass plate, but at 130°C, no layer consisting of the cured product of the curable composition was formed on the surface of the glass plate.

[0054] <Comparative Example 8> A curable composition was prepared in the same manner as in Example 15, except that hexamethylenetetramine and 2-ethyl-4-methylimidazole were not used. This curable composition was applied to a glass plate and heated in a hot air oven at 130°C or 180°C for 10 minutes. As a result, no layer consisting of the cured product of the curable composition was formed on the surface of the glass plate at either 130°C or 180°C.

[0055] From these results, it was found that a curable composition containing an epoxy compound and amine compound A (imidazole compound) and hexamethylenetetramine as curing accelerators for the epoxy compound cures sufficiently even in an aqueous dispersion state at low temperatures.

[0056] The disclosures of Japanese Patent Application No. 2025-007062 and International Application PCT / JP2025 / 016127 are incorporated herein by reference in their entirety. All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard had been specifically and individually noted to be incorporated by reference.

Claims

1. A curing accelerator for epoxy compounds, comprising hexamethylenetetramine and an amine compound A other than hexamethylenetetramine.

2. The curing accelerator according to claim 1, wherein the amine compound A comprises an imidazole compound.

3. The curing accelerator according to claim 2, wherein the imidazole compound comprises at least one selected from the group consisting of imidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 1-(2-cyanoethyl)-2-ethyl-4-methylimidazole, and 1-(2-cyanoethyl)-2-phenylimidazole.

4. The curing accelerator according to claim 1, wherein the amount of hexamethylenetetramine is 0.5 times or more and 40 times or less the amount of amine compound A.

5. The curing accelerator according to claim 1, for use under conditions that prevent the epoxy compound from reacting with the phenol compound.

6. A curable composition comprising a curing accelerator according to any one of claims 1 to 5 and an epoxy compound.

7. The curable composition according to claim 6, wherein the epoxy compound comprises an epoxy compound having two or more epoxy groups in its molecule.

8. The curable composition according to claim 6, wherein the amount of amine compound A relative to Xg of epoxy compound having an epoxy equivalent of Xg / eq is 2mg to 100mg.

9. The curable composition according to claim 6, wherein the amount of hexamethylenetetramine per X g of epoxy compound having an epoxy equivalent of X g / eq is 50 mg to 200 mg.

10. The curable composition according to claim 6, further comprising water.

11. The curable composition according to claim 6, further comprising a solvent selected from methyl isobutyl ketone, ethanol, 1-propanol, and 1-methoxy-2-propanol.

12. The curable composition according to claim 6, which does not contain a phenol compound.

13. A resin product comprising a cured product of the curable composition described in claim 6.

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