Charge-transfer complexes

Abstract

The purpose of the present invention is to provide a charge transfer complex which enables the achievement of a curable resin composition that has an excellent balance between curability and storage stability if used as an epoxy resin curing agent.　The present invention provides a charge transfer complex which has an imidazole moiety as an electron donor moiety. This charge transfer complex may be a compound (b) having an electron acceptor moiety, the compound (b) having accepted an electron contained in a compound (a) having an imidazole moiety, or a compound which has an imidazole moiety and an electron acceptor moiety in each molecule, wherein an electron contained in the imidazole moiety has been accepted by the electron acceptor moiety.

Description

[Technical Field]

[0001] The present invention relates to a charge-transfer complex, and more particularly to a charge-transfer complex having an imidazole moiety, an epoxy resin curing agent comprising the charge-transfer complex, and a curable resin composition containing the charge-transfer complex. [Background technology]

[0002] Epoxy resins are widely used industrially as components of paints, adhesives, various molding materials, and the like. When epoxy resins are used for the above purposes, they are usually used in combination with a curing agent, and various curing agents are known as such curing agents, such as acid anhydride-based curing agents, amine-based curing agents, and phenol-based curing agents.

[0003] The curing agents are used according to the application. For example, imidazole-based curing agents are anionic polymerization curing agents, unlike addition polymerization curing agents, and therefore can be cured with a small amount added. They are also useful in that they have low volatility and toxicity, making them suitable for use in electrical and electronic components.

[0004] However, when an epoxy resin curing agent is used alone, it is difficult to balance curability and storage stability. To improve storage stability, for example, Patent Document 1 proposes using a reaction product of an imidazole compound and an epoxy resin in an epoxy curing system, and Patent Document 2 proposes a curing agent composition for epoxy resins comprising a modified imidazole, a modified amine, and a phenol compound.

[0005] However, when these various modifications are carried out, the viscosity of the modified product increases, which impairs handling and workability, and so on, and thus no satisfactory product has been obtained. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent No. 4,066,625 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-297493 [Non-patent literature]

[0007] [Non-Patent Document 1] JORNAL OF POLYMER SCIENCE,PART A POLYMER CHEMISTRY 2016,54,2680-2688 [Non-patent document 2] JORNAL OF POLYMER SCIENCE,PART A POLYMER CHEMISTRY 2018,56,471-474 [Non-patent document 3] Composites Part B 17(2019)107380 [Non-patent document 4] Materials Letters 234(2019)379-383 Summary of the Invention

[0008] Therefore, an object of the present invention is to provide a charge-transfer complex which, when used as an epoxy resin curing agent, gives a curable resin composition having an excellent balance between curability and storage stability.

[0009] As a result of extensive investigations, the present inventors have found that a charge-transfer complex having an imidazole moiety as an electron donor is effective as an epoxy resin curing agent, and further that a resin composition obtained by combining this with an epoxy resin is a curable resin composition having an excellent balance between curability and storage stability, thereby arriving at the present invention.

[0010] That is, the present invention is a charge transfer complex having an imidazole moiety as an electron donating moiety.

[0011] The present invention also provides a curing agent for epoxy resins comprising the charge-transfer complex.

[0012] The present invention also relates to a curable resin composition containing an epoxy resin and the charge-transfer complex.

[0013] The charge-transfer complex of the present invention is useful as an epoxy resin curing agent because it can provide a curable resin composition excellent in curability and storage stability when combined with an epoxy resin. The use of the charge-transfer complex of the present invention can provide a resin composition suitable for applications such as one-component curing coatings and adhesives. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 shows the results of UV spectrum measurement of the charge-transfer complex of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] The charge transfer complex of the present invention will be described below. Charge-transfer complexes, also known as electron-donor-acceptor complexes, are associations of two or more different molecules through which charge can be transferred between them, or of a single molecule that has electron-accepting and electron-donating sites within it, allowing electrons to be transferred.

[0016] The charge transfer complex of the present invention is characterized in that the electron donating moiety is an imidazole moiety.

[0017] The charge-transfer complex may be, for example, a charge-transfer complex obtained by accepting an electron contained in a compound (a) having an imidazole moiety with a compound (b) having an electron-accepting moiety. The charge-transfer complex may also be a compound having an imidazole moiety and an electron-accepting moiety in its molecule, in which the electron-accepting moiety accepts an electron contained in the imidazole moiety.

[0018] Examples of the compound having an imidazole moiety, which is component (a) of the charge-transfer complex, include imidazoles having an alkyl group, such as 2-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-isopropylimidazole, 2-undecylimidazole, and 2-heptadecylimidazole; 1-benzyl-2-imidazole, 1-benzyl-2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, and 1-phenylmethyl-2-phenylimidazole. imidazoles having an aromatic group such as 2-aminopropylimidazole; imidazoles having an aminoalkyl group such as 2-aminopropylimidazole; imidazoles having a cyano group such as 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, and 1-cyanoethyl-2-phenylimidazole; imidazoles having a hydroxymethyl group such as 2-phenyl-4,5-dihydroxymethylimidazole and 2-phenyl-4-methyl-5-hydroxymethylimidazole;1-Butoxycarbonylethyl-2-methylimidazole, 1-Butoxycarbonylethyl-2-ethyl-4-methylimidazole, 1-Butoxycarbonylethyl-2-phenylimidazole, 1-(2-ethylhexyl)carbonylethyl-2-methylimidazole, 1-(2-ethylhexyl)carbonylethyl-2-ethyl-4-methylimidazole, 1-(2-ethylhexyl)carbonylethyl-2-phenylimidazole, 1-Octyloxycarbonylethyl-2-methyl Imidazole, 1-octyloxycarbonylethyl-2-ethyl-4-methylimidazole, 1-octyloxycarbonylethyl-2-phenylimidazole, Hexanediol bis(2-methylimidazolyl ethanoate) ester, Hexanediol bis(2-ethyl-4-methylimidazolyl ethanoate) ester, Hexanediol bis(2-phenylimidazolyl ethanoate) ester, Decanediol bis(2-methylimidazolyl ethanoate) ester, Decanediol bis(2-methylimidazolyl ethanoate) ester bis(2-ethyl-4-methylimidazolyl ethanoate) ester, decanediol bis(2-phenylimidazolyl ethanoate) ester, tricyclopentane dimethanol bis(2-methylimidazolyl ethanoate) ester, tricyclopentane dimethanol bis(2-ethyl-4-methylimidazolyl ethanoate) ester, tricyclopentane dimethanol bis(2-phenylimidazolyl ethanoate) ester, 1-(2-hydroxynaphthylmethyl)-2-methylimidazole, Examples of suitable imidazole compounds include imidazoles having an ester bond, such as 1-(2-hydroxynaphthylmethyl)-2-ethyl-4-methylimidazole and 1-(2-hydroxynaphthylmethyl)-2-phenylimidazole; and special imidazoles, such as 2,3-dihydro-1H-pyrrolo(1,2a)benzimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, imidazole silane, and 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine. Furthermore, the imidazole compounds listed above may be modified with an epoxy compound, polycarboxylic acid, isocyanuric acid, or the like.

[0019] Examples of the epoxy compounds include polyglycidyl ethers of mononuclear polyhydric phenol compounds such as hydroquinone, resorcinol, pyrocatechol, and phloroglucinol; dihydroxynaphthalene, biphenol, methylenebisphenol (bisphenol F), methylenebis(ortho-cresol), ethylidenebisphenol, isopropylidenebisphenol (bisphenol A), isopropylidenebis(ortho-cresol), tetrabromobisphenol A, 1,3-bis(4-hydroxycumylbenzene), 1,4-bis(4-hydroxycumylbenzene), 1,1,3-tris(4-hydroxyphenyl)butane, 1,1,2,2-tetra(4-hydroxyphenyl)ethane, thiobisphenol, sulfobisphenol, oxybisphenol, phenol novolac, orthocresol novolac, ethylphenol novolac, butylphenol novolac, octylphenol novolac, resorcinol novolac, and terpene phenols. Polyglycidyl ethers of polynuclear polyhydric phenol compounds; polyglycidyl ethers of polyhydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, hexanediol, polyethylene glycol, polypropylene glycol, thioglycol, dicyclopentadiene dimethanol, 2,2-bis(4-hydroxycyclohexyl)propane (hydrogenated bisphenol A), glycerin, trimethylolpropane, pentaerythritol, sorbitol, and bisphenol A-alkylene oxide adducts; glycidyl esters of aliphatic, aromatic, or alicyclic polybasic acids such as maleic acid, fumaric acid, itaconic acid, succinic acid, glutaric acid, suberic acid, adipic acid, azelaic acid, sebacic acid, dimer acid, trimer acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, trimesic acid, pyromellitic acid, tetrahydrophthalic acid, and endomethylenetetrahydrophthalic acid, and homopolymers or copolymers of glycidyl methacrylate;Epoxy compounds having a glycidylamino group such as N,N-diglycidylaniline, bis(4-(N-methyl-N-glycidylamino)phenyl)methane, diglycidyl orthotoluidine, N,N-bis(2,3-epoxypropyl)-4-(2,3-epoxypropoxy)-2-methylaniline, N,N-bis(2,3-epoxypropyl)-4-(2,3-epoxypropoxy)aniline, and N,N,N',N'-tetra(2,3-epoxypropyl)-4,4-diaminodiphenylmethane; vinylcyclohexene diepoxide Epoxidized compounds of cyclic olefin compounds such as cyclopentadiene diepoxide, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-6-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate; epoxidized conjugated diene polymers such as epoxidized polybutadiene and epoxidized styrene-butadiene copolymer; and heterocyclic compounds such as triglycidyl isocyanurate.

[0020] Examples of the polycarboxylic acid include maleic acid, fumaric acid, itaconic acid, succinic acid, glutaric acid, suberic acid, adipic acid, azelaic acid, sebacic acid, dimer acid, trimer acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, trimesic acid, pyromellitic acid, tetrahydrophthalic acid, and endomethylenetetrahydrophthalic acid.

[0021] Among the imidazole compounds, unmodified compounds such as 2-methylimidazole and 2-ethyl-4-methylimidazole are more preferred because they can be cured by adding a relatively small amount and can also function as a curing accelerator when combined with other curing agents.

[0022] The compound having an electron-accepting moiety (component (b)) of the charge-transfer complex can be any compound that can accept electrons contained in the compound having an imidazole moiety (component (a)) in the presence of the compound having an imidazole moiety (component (a)). Examples of such compounds include imide compounds and aromatic compounds.

[0023] Among compounds having an electron-accepting moiety, imide compounds are preferred because they can be synthesized from a variety of raw materials, have a high degree of freedom in molecular design, and have excellent compatibility, making it easy to select compounds that are less likely to adversely affect the physical properties of the resulting curable resin composition. In particular, imide compounds having an aromatic skeleton in the molecule are preferred because they can produce curable resin compositions that are well-balanced between storage stability and curability.

[0024] Furthermore, the compound having an electron-accepting moiety as component (b) preferably has a lowest occupied molecular orbital (LUMO) of -1 eV or less, because when blended with an epoxy resin to form a curable resin composition, it provides a composition with excellent storage stability and curability. The lowest occupied molecular orbital (LUMO) is obtained, for example, by electronic structure calculation.

[0025] Specific examples of compounds having an electron-accepting site as component (b) are shown below.

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[0047] The amount of the compound having an electron-accepting moiety (component (b)) used is 0.01 to 20 moles, preferably 0.1 to 10 moles, and more preferably 0.2 to 8 moles, per mole of the compound having an imidazole moiety (component (a)). If the amount of the compound having an electron-accepting moiety used is less than 0.01 mole, when a charge-transfer complex obtained therefrom is used as an epoxy resin curing agent, the effect of imparting stability to the curable resin composition may not be obtained, whereas if the amount exceeds 20 moles, the curability of the curable resin composition may be adversely affected.

[0048] The method for producing the charge-transfer complex is not particularly limited, and it can be produced by mixing the components (a) and (b). If both components are liquid, the charge-transfer complex can be obtained by mixing them at room temperature. However, if at least one of the components is solid, they can be heated to melt them and mixed, or they can be mixed as a solution using a solvent.

[0049] When the charge-transfer complex of the present invention is a compound having an imidazole moiety and an electron-accepting moiety in the molecule, and the electron-accepting moiety accepts an electron contained in the imidazole moiety, the electron-accepting moiety may be any moiety that can accept an electron obtained at the imidazole moiety, and examples thereof include an imide moiety, an aromatic moiety, etc. In particular, an imide moiety is preferred because it allows for a variety of synthetic raw materials, a high degree of freedom in molecular design, and excellent compatibility, resulting in a compound that is less likely to adversely affect the physical properties of the resulting curable resin composition.

[0050] Examples of compounds having an imidazole moiety and an electron accepting moiety in the molecule include compounds represented by the following general formula (1).

[0051] [ka] In general formula (1), R 1 , R 2 and R 3 each independently represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, and R 4 represents a divalent hydrocarbon group of 1 to 10 carbon atoms which may have a substituent, and ring A represents a benzene ring which may have a substituent, a cyclohexane ring which may have a substituent, or a norbornene ring which may have a substituent.

[0052] In the formula (1), R 6 , R 7 and R 8Examples of the hydrocarbon group constituting the hydrocarbon group having 1 to 20 carbon atoms, which may have a substituent, include alkyl groups such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, amyl group, isoamyl group, sec-amyl group, tert-amyl group, hexyl group, heptyl group, octyl group, isooctyl group, tert-octyl group, 2-ethylhexyl group, nonyl group, isononyl group, decyl group, isodecyl group, undecyl group, dodecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, and eicosyl group; aryl groups such as phenyl group, naphthyl group, and anthracenyl group; and alicyclic groups such as cyclohexyl group. Also, R 9 Examples of hydrocarbon groups constituting the divalent hydrocarbon group having 1 to 10 carbon atoms, which may have a substituent, include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, and a decylene group. Also, R 6 ~R 9 Examples of the substituent in include an alkyl group, an alkoxy group, a haloalkyl group, a haloalkoxy group, a halogen atom, a nitro group, a nitrile group, an amino group, and a glycidyl ether group.

[0053] Examples of the imidazole skeleton in the compound represented by the general formula (1) include imidazole skeletons having an alkyl group such as 2-methylimidazol-1-yl, 2-ethyl-4-methylimidazol-1-yl, 2-isopropylimidazol-1-yl, 2-undecylimidazol-1-yl, 2-heptadecylimidazol-1-yl, 2-phenylimidazol-1-yl, and 2-phenyl-4-methylimidazol-1-yl; 2-benzylimidazol-1-yl, 2-benzyl- imidazole skeletons having an aromatic group such as 4-methylimidazol-1-yl and 2-phenylmethyl-4-phenylimidazol-1-yl; imidazole skeletons having an aminoalkyl group such as 2-aminopropylimidazol-1-yl; imidazole skeletons having a cyano group such as 2-cyanoethyl-4-methylimidazol-1-yl, 2-cyanoethyl-4-undecylimidazol-1-yl, 2-cyanoethyl-methylimidazol-1-yl and 2-cyanoethyl-4-phenylimidazol-1-yl imidazole skeleton; imidazole skeleton having a hydroxymethyl group such as 2-phenyl-4,5-dihydroxymethylimidazol-1-yl and 2-phenyl-4-methyl-5-hydroxymethylimidazol-1-yl; 2-butoxycarbonylethyl-4-methylimidazol-1-yl, 2-butoxycarbonylethyl-4-methylimidazol-1-yl, 2-butoxycarbonylethyl-4-phenylimidazol-1-yl, 2-(2-ethylhexyl)carbonylethyl-4-methylimidazol-1-yl, Examples thereof include imidazole skeletons having an ester bond such as 2-(2-ethylhexyl)carbonylethyl-4-methylimidazol-1-yl, 2-(2-ethylhexyl)carbonylethyl-4-phenylimidazol-1-yl, 2-octyloxycarbonylethyl-4-methylimidazol-1-yl, 2-octyloxycarbonylethyl-4-methylimidazol-1-yl, and 2-octyloxycarbonylethyl-4-phenylimidazol-1-yl.

[0054] Furthermore, the compound represented by the general formula (1) preferably has a lowest occupied molecular orbital (LUMO) of -1 eV or less, because when this compound is blended with an epoxy resin to form a curable resin composition, it is possible to obtain a composition with excellent storage stability and curability. The lowest occupied molecular orbital (LUMO) is obtained, for example, by electronic structure calculation.

[0055] Specific examples of compounds having an imidazole moiety and an electron-accepting moiety in the molecule are shown below.

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[0058] A charge-transfer complex is a complex formed between an electron-donating moiety that donates electrons and an electron-accepting moiety that accepts electrons. Charge-transfer complexes undergo charge-transfer transitions in an excited state. This phenomenon can be confirmed by the presence of a new absorption band in the UV-vis absorption spectrum after complex formation that is longer in wavelength than the absorption bands in the UV-vis spectra of each raw material before complex formation.

[0059] The epoxy resin curing agent of the present invention comprises the charge-transfer complex. The charge-transfer complex of the present invention is stable in the presence of an epoxy resin and is an excellent curing agent for the epoxy resin.

[0060] Next, the curable resin composition of the present invention will be described. The curable resin composition of the present invention contains an epoxy resin and the charge-transfer complex.

[0061] The epoxy resin used in the present invention may be any resin having at least two epoxy groups in the molecule, and can be used without any particular limitation on the molecular structure, molecular weight, etc.

[0062] Examples of the epoxy resin include polyglycidyl ethers of mononuclear polyhydric phenol compounds such as hydroquinone, resorcinol, pyrocatechol, and phloroglucinol; and polynuclear phenols such as dihydroxynaphthalene, biphenol, methylene bisphenol (bisphenol F), methylene bis(ortho-cresol), ethylidene bisphenol, isopropylidene bisphenol (bisphenol A), isopropylidene bis(ortho-cresol), tetrabromobisphenol A, 1,3-bis(4-hydroxycumylbenzene), 1,4-bis(4-hydroxycumylbenzene), 1,1,3-tris(4-hydroxyphenyl)butane, 1,1,2,2-tetra(4-hydroxyphenyl)ethane, thiobisphenol, sulfobisphenol, oxybisphenol, phenol novolac, orthocresol novolac, ethylphenol novolac, butylphenol novolac, octylphenol novolac, resorcinol novolac, and terpene phenols. Polyglycidyl ethers of polyhydric phenol compounds; polyglycidyl ethers of polyhydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, hexanediol, polyethylene glycol, polypropylene glycol, thioglycol, dicyclopentadiene dimethanol, 2,2-bis(4-hydroxycyclohexyl)propane (hydrogenated bisphenol A), glycerin, trimethylolpropane, pentaerythritol, sorbitol, and bisphenol A-alkylene oxide adducts; glycidyl esters of aliphatic, aromatic, or alicyclic polybasic acids such as maleic acid, fumaric acid, itaconic acid, succinic acid, glutaric acid, suberic acid, adipic acid, azelaic acid, sebacic acid, dimer acid, trimer acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, trimesic acid, pyromellitic acid, tetrahydrophthalic acid, and endomethylenetetrahydrophthalic acid, and homopolymers or copolymers of glycidyl methacrylate;Epoxy compounds having a glycidylamino group such as N,N-diglycidylaniline, bis(4-(N-methyl-N-glycidylamino)phenyl)methane, diglycidyl orthotoluidine, N,N-bis(2,3-epoxypropyl)-4-(2,3-epoxypropoxy)-2-methylaniline, N,N-bis(2,3-epoxypropyl)-4-(2,3-epoxypropoxy)aniline, and N,N,N',N'-tetra(2,3-epoxypropyl)-4,4-diaminodiphenylmethane; vinylcyclohexene diepoxide Examples of epoxy resins include epoxidized cyclic olefin compounds such as cyclopentadiene diepoxide, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-6-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate; epoxidized conjugated diene polymers such as epoxidized polybutadiene and epoxidized styrene-butadiene copolymer; and heterocyclic compounds such as triglycidyl isocyanurate. These epoxy resins can also be used in a form internally crosslinked with a terminal isocyanate prepolymer or in a form polymerized with a polyvalent active hydrogen compound (such as a polyphenol, polyamine, carbonyl group-containing compound, or polyphosphate ester). The epoxy resins can be used alone or in combination of two or more.

[0063] The curable resin composition of the present invention contains an epoxy resin and the charge-transfer complex. When a charge-transfer complex obtained from a compound having an imidazole moiety as component (a) and a compound having an electron-accepting moiety as component (b) is used, the composition can be produced by mixing the epoxy resin and the charge-transfer complex. Alternatively, the compound having an imidazole moiety as component (a) and the compound having an electron-accepting moiety as component (b) can be separately blended with an epoxy resin to form a charge-transfer complex in the curable resin composition, thereby producing the desired curable resin composition.

[0064] In the curable resin composition of the present invention, the amount of the charge-transfer complex used is not particularly limited, but is preferably 0.01 to 500 parts by mass, and more preferably 0.1 to 100 parts by mass, relative to 100 parts by mass of the epoxy resin. If the amount is less than 0.01 part by mass, the effect of improving curability and stability may not be obtained, and if the amount is more than 500 parts by mass, the physical properties of the cured product may be adversely affected.

[0065] In addition to the charge-transfer complex, the curable resin composition of the present invention can also contain a conventional epoxy resin curing agent, such as an acid anhydride curing agent, a phenolic curing agent, an amine curing agent, or a polythiol curing agent.

[0066] Examples of the acid anhydride curing agent include himic anhydride, phthalic anhydride, maleic anhydride, methyl himic anhydride, succinic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride-maleic anhydride adduct, benzophenonetetracarboxylic anhydride, trimellitic anhydride, pyromellitic anhydride, and hydrogenated methylnadic anhydride.

[0067] Examples of the phenol-based curing agent include polyhydric phenol compounds such as phenol novolac resin, cresol novolac resin, aromatic hydrocarbon formaldehyde resin-modified phenol resin, dicyclopentadiene phenol adduct resin, phenol aralkyl resin (Xyloc resin), naphthol aralkyl resin, trisphenylolmethane resin, tetraphenylolethane resin, naphthol novolac resin, naphthol-phenol co-condensed novolac resin, naphthol-cresol co-condensed novolac resin, biphenyl-modified phenol resin (a polyhydric phenol compound in which phenol nuclei are linked via bismethylene groups), biphenyl-modified naphthol resin (a polyhydric naphthol compound in which phenol nuclei are linked via bismethylene groups), aminotriazine-modified phenol resin (a compound having a phenol skeleton, a triazine ring, and a primary amino group in its molecular structure), and alkoxy group-containing aromatic ring-modified novolac resin (a polyhydric phenol compound in which phenol nuclei and alkoxy group-containing aromatic rings are linked via formaldehyde).

[0068] Examples of the amine curing agent include alkylenediamines such as ethylenediamine, 1,2-diaminopropane, 1,3-diaminopropane, 1,3-diaminobutane, 1,4-diaminobutane, hexamethylenediamine, and metaxylenediamine; polyalkylpolyamines such as diethylenetriamine, triethylenetriamine, and tetraethylenepentamine; 1,4-diaminocyclohexane, 1,3-diaminocyclohexane, 1,3-diaminomethylcyclohexane, 1,2-diaminocyclohexane, 1,4-diamino-3,6-diethylcyclohexane, 4,4'-diaminodicyclohexylmethane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, 4, Alicyclic polyamines such as 4'-diaminodicyclohexylpropane, bis(4-aminocyclohexyl) sulfone, 4,4'-diaminodicyclohexyl ether, 2,2'-dimethyl-4,4'-diaminodicyclohexylmethane, isophoronediamine, and norbornenediamine; aromatic polyamines such as diaminodiphenylmethane, diaminodiphenyl sulfone, diethyltoluenediamine, 1-methyl-3,5-diethyl-2,4-diaminobenzene, 1-methyl-3,5-diethyl-2,6-diaminobenzene, 1,3,5-triethyl-2,6-diaminobenzene, 3,3'-diethyl-4,4'-diaminodiphenylmethane, and 3,5,3',5'-tetramethyl-4,4'-diaminodiphenylmethane;N,N-dimethylaminoethylamine, N,N-diethylaminoethylamine, N,N-diisopropylaminoethylamine, N,N-diallylaminoethylamine, N,N-benzylmethylaminoethylamine, N,N-dibenzylaminoethylamine, N,N-cyclohexylmethylaminoethylamine, N,N-dicyclohexylaminoethylamine, N-(2-aminoethyl)pyrrolidine, N-(2-aminoethyl)piperidine, N-(2-aminoethyl)morpholine, N-(2-aminoethyl)piperazine, N-(2-aminoethyl)-N'-methylpiperazine, N,N-dimethylaminopropylamine, N,N-diethylaminopropylamine, N,N-diisopropylaminopropylamine, N,N-diallylaminopropylamine, N,N-benzylmethylaminopropylamine, N,N-dibenzylaminopropylamine N,N-Cyclohexylmethylaminopropylamine, N,N-Dicyclohexylaminopropylamine, N-(3-aminopropyl)pyrrolidine, N-(3-aminopropyl)piperidine, N-(3-aminopropyl)morpholine, N-(3-aminopropyl)piperazine, N-(3-aminopropyl)-N'-methylpiperidine, 4-(N,N-dimethylamino)benzylamine, 4-(N,N-diethylamino)benzylamine, 4-(N,N-diisopropylamino)benzylamine, N,N-dimethylisophoronediamine, N,N-dimethylbisaminocyclohexane, N,N,N'-Trimethylethylenediamine, N'-Ethyl-N,N-dimethylethylenediamine, N,N,N'-Triethylethylenediamine, N'-Ethyl-N,N-dimethylpropanediamine, N'-Ethyl-N,N-dibenzylaminopropylamine;N,N-(bisaminopropyl)-N-methylamine, N,N-bisaminopropylethylamine, N,N-bisaminopropylpropylamine, N,N-bisaminopropylbutylamine, N,N-bisaminopropylpentylamine, N,N-bisaminopropylhexylamine, N,N-bisaminopropyl-2-ethylhexylamine, N,N-bisaminopropylcyclohexylamine, N,N-bisaminopropylbenzylamine, N,N-bisaminopropylallylamine, bis[3-(N,N-dimethylaminopropyl)]amine, bis Examples of suitable dibasic acid dihydrazides include [3-(N,N-diethylaminopropyl)]amine, bis[3-(N,N-diisopropylaminopropyl)]amine, bis[3-(N,N-dibutylaminopropyl)]amine; dibasic acid dihydrazides such as oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, and phthalic acid dihydrazide; guanidine compounds such as dicyandiamide, benzoguanamine, and acetoguanamine; and melamine.

[0069] Modified amine-based curing agents obtained by modifying the above amines can also be used. Modification methods include dehydration condensation with carboxylic acid, addition reaction with epoxy resin, addition reaction with isocyanate, Michael addition reaction, Mannich reaction, condensation reaction with urea, and condensation reaction with ketone.

[0070] Examples of carboxylic acids that can be used to modify the amines include aliphatic, aromatic, or alicyclic polybasic acids such as maleic acid, fumaric acid, itaconic acid, succinic acid, glutaric acid, suberic acid, adipic acid, azelaic acid, sebacic acid, dimer acid, trimer acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, trimesic acid, pyromellitic acid, tetrahydrophthalic acid, hexahydrophthalic acid, and endomethylenetetrahydrophthalic acid.

[0071] Examples of epoxy compounds that can be used to modify the amines include the epoxy compounds exemplified above as epoxy compounds that can be used to modify the compound having an imidazole moiety, which is component (a) of the charge-transfer complex.

[0072] Examples of isocyanate compounds that can be used to modify the amines include aromatic diisocyanates such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, diphenylmethane-4,4'-diisocyanate, phenylene diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, 1,5-naphthylene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, 3,3'-dimethyldiphenyl-4,4'-diisocyanate, dianisidine diisocyanate, and tetramethylxylylene diisocyanate; isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate; Examples of suitable isocyanate compounds include alicyclic diisocyanates such as trans-1,4-cyclohexyl diisocyanate and norbornene diisocyanate; aliphatic diisocyanates such as tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4 and / or 2,4,4-trimethylhexamethylene diisocyanate and lysine diisocyanate; isocyanurate trimer, biuret trimer, and trimethylolpropane adduct of the above-listed diisocyanates; triphenylmethane triisocyanate, 1-methylbenzene-2,4,6-triisocyanate, and dimethyltriphenylmethane tetraisocyanate. Furthermore, these isocyanate compounds can be used in the form of modified compounds such as carbodiimide-modified, isocyanurate-modified, and biuret-modified compounds, or in the form of blocked isocyanates blocked with various blocking agents.

[0073] Examples of the polythiol curing agent include pentaerythritol tetrakis(3-mercaptopropionate), pentaerythritol tetrakis(thioglycolate), dipentaerythritol hexakis(3-mercaptopropionate), dipentaerythritol hexakis(3-mercaptobutyrate), 1,3,4,6-tetrakis(2-mercaptoethyl)-1,3,4,6-tetraazaoctahydropentalene- 2,5-dione, 1,3,5-tris(3-mercaptopropyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane, 4,8-, 4,7-, or 5,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, and 1,3,4,6-tetrakis(2-mercaptoethyl)glycoluril.

[0074] Examples of the imidazole curing agent include 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-isopropylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-aminopropylimidazole, and imidazole silane (for example, 2MUSIZ manufactured by Shikoku Chemicals Corporation). Furthermore, these imidazole compounds may be modified in the same manner as the amine-based curing agents, or imidazole salts obtained by salting the imidazoles with trimellitic acid, isocyanuric acid, boron, or the like.

[0075] Commercially available products of the curing agent include, for example, ADEKA HARDNER EH-3636AS, ADEKA HARDNER EH-4351S (manufactured by ADEKA; dicyandiamide-type latent curing agent), ADEKA HARDNER EH-5011S, ADEKA HARDNER EH-5046S (manufactured by ADEKA; imidazole-type latent curing agent), ADEKA HARDNER EH-4357S, ADEKA HARDNER EH-5057P, ADEKA HARDNER EH-5057PK (manufactured by ADEKA; polyamine-type latent curing agent), AMICURE PN-23, AMICURE PN-40 (manufactured by Ajinomoto Fine-Techno Co., Ltd.; amine adduct-type latent curing agent), AMICURE VDH (manufactured by Ajinomoto Fine-Techno Co., Ltd.; hydrazide-type latent curing agent), and FUJICURE FXR-1020 (manufactured by T&K Co., Ltd.). Examples include TOKA (latent curing agent), Curazol (Shikoku Chemical Industry Co., Ltd.; imidazole-based curing agent), TS-G (Shikoku Chemical Industry Co., Ltd.; polythiol-based curing agent), DPMP, PEMP (SC Organic Chemical Co., Ltd.; polythiol-based curing agent), and PETG (Yodo Chemical Industry Co., Ltd.; polythiol-based curing agent). The curing agents may be used alone or in combination of two or more kinds.

[0076] The amount of the curing agent to be added is not particularly limited, but is preferably 0 to 500 parts by mass, and more preferably 0 to 100 parts by mass, per 100 parts by mass of the epoxy resin.

[0077] In the present invention, the curing agent can be used in combination with a known epoxy resin curing accelerator, if necessary. Examples of curing accelerators include phosphines such as triphenylphosphine; phosphonium salts such as tetraphenylphosphonium bromide; amines such as benzyldimethylamine and 2,4,6-tris(dimethylaminomethyl)phenol; quaternary ammonium salts such as trimethylammonium chloride; ureas such as 3-(p-chlorophenyl)-1,1-dimethylurea, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-phenyl-1,1-dimethylurea, isophorone diisocyanate-dimethylurea, and tolylene diisocyanate-dimethylurea; complexes of boron trifluoride and amines; and complexes of boron trifluoride and ether compounds. These curing accelerators may be used alone or in combination of two or more. The content of the epoxy resin curing accelerator is not particularly limited and can be appropriately determined depending on the application of the curable resin composition.

[0078] The curable resin composition of the present invention can contain a silane coupling agent. Examples of the silane coupling agent include γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-N'-β-(aminoethyl)-γ-aminopropyltriethoxysilane, γ-anilinopropyltriethoxysilane, γ-glycidoxypropyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxysilane, vinyltriethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, and γ-mercaptopropyltrimethoxysilane.

[0079] The curable resin composition of the present invention may contain a filler. Examples of the filler include silica such as fused silica and crystalline silica; powders such as magnesium hydroxide, aluminum hydroxide, zinc molybdate, calcium carbonate, silicon carbonate, calcium silicate, potassium titanate, beryllium, zirconia, zircon, fosterite, steatite, spinel, mullite, and titania, or beads obtained by spheronizing these; glass fiber, pulp fiber, synthetic fiber, and ceramic fiber.

[0080] The curable resin composition of the present invention can be used by dissolving it in various solvents, preferably organic solvents. Suitable organic solvents include ethers such as tetrahydrofuran, 1,2-dimethoxyethane, and 1,2-diethoxyethane; alcohols such as iso- or n-butanol, iso- or n-propanol, amyl alcohol, benzyl alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol; ketones such as methyl ethyl ketone, methyl isopropyl ketone, and methyl butyl ketone; aromatic hydrocarbons such as benzene, toluene, and xylene; triethylamine, pyridine, dioxane, and acetonitrile.

[0081] The curable resin composition of the present invention may further contain various other additives as needed. Examples of such additives include phosphorus-based antioxidants, phenolic antioxidants, and sulfur-based antioxidants; ultraviolet absorbers and hindered amine light stabilizers; phenolic compounds such as biphenol; reactive diluents such as monoalkyl glycidyl ethers; non-reactive diluents (plasticizers) such as dioctyl phthalate, dibutyl phthalate, benzyl alcohol, and coal tar; reinforcing materials such as glass cloth, aramid cloth, and carbon fiber; pigments; lubricants such as candelilla wax, carnauba wax, Japan wax, Ibota wax, beeswax, lanolin, spermaceti, montan wax, petroleum wax, aliphatic wax, aliphatic esters, aliphatic ethers, aromatic esters, and aromatic ethers; thickeners; thixotropic agents; antifoaming agents; rust inhibitors; and commonly used additives such as colloidal silica and colloidal alumina. In the present invention, adhesive resins such as cyanate ester resins, xylene resins, and petroleum resins can also be used in combination.

[0082] The resin composition of the present invention is not particularly limited in its application, but since it is possible to adjust the balance between curability and storage stability, it can be made into a one-component curing resin composition, and can be used as a coating material or adhesive for concrete, cement mortar, various metals, leather, glass, rubber, plastic, wood, cloth, paper, etc. [Example]

[0083] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to these examples in any way.

[0084] [Calculation of lowest occupied orbital (LUMO)] The lowest occupied molecular orbitals (LUMOs) of the compounds with electron-accepting moieties and the compounds with imidazole and electron-accepting moieties in the molecule used in the examples were calculated using Gaussian 09, EM64L-G09Rev.B.01, with geometry optimization performed without consideration of symmetry at the density half-function B3LYP / 6-31G(d,p) level. For each optimized structure, the stationary point was confirmed to be a local minimum by harmonic vibrational frequency calculations. The results are shown in Table 1.

[0085] Example 1 2-Ethyl-4-methylimidazole (EMI) and N-(2-ethylhexyl)phthalimide (2EHPI) were mixed in a 1:1 ratio to obtain a homogeneous mixture. The UV spectrum (EMI + 2EHPI) of the resulting mixture is shown in Figure 1. For comparison, the UV spectrum of 2-ethyl-4-methylimidazole [EMI] and the UV spectrum of N-(2-ethylhexyl)phthalimide [2EHPI] were measured, and the sum of these UV spectra [sum(EMI+2EHPI)] is also shown in Figure 1. These results confirmed that the UV spectrum of a uniform mixture of 2-ethyl-4-methylimidazole (EMI) and N-(2-ethylhexyl)phthalimide (2EHPI) in a 1:1 ratio was shifted to the longer wavelength side from the combined UV spectrum of EMI and 2EHPI, confirming the formation of a charge-transfer complex.

[0086] [Examples 2 to 18 and Comparative Example 1] A curable resin composition containing a charge-transfer complex was produced by blending bisphenol A epoxy resin (BISAEP), 2-ethyl-4-methylimidazole (EMI), and the compounds exemplified as specific examples of the compound having an electron-accepting moiety in the blending ratio (molar) shown in Table 1. The obtained curable resin composition was used to carry out the following evaluations.

[0087] Examples 19 and 20 Curable resin compositions were produced by blending bisphenol A epoxy resin (BISAEP) and the compounds exemplified as specific examples of compounds having an imidazole moiety and an electron-accepting moiety in the molecule in the blending ratios (molar) shown in Table 1. The obtained curable resin compositions were used to carry out the following evaluations.

[0088] [Curability] The curable resin composition was placed in a glass bottle and heated to 150°C for 1 hour for curing. After confirming that the composition was completely solid and had no tack, those that had cured were marked with an ◯, and those that had not were marked with an X.

[0089] [Storage stability] The curable resin composition was placed in a glass bottle with a diameter of 13 mm and a height of 40 mm, filling it to one-fifth of the bottle from the bottom, and the bottle was then capped. The bottle was tilted 90° on a flat desk, and the state after one minute was observed to determine whether it had fluidity. If a change in the shape of the curable resin composition was observed, it was deemed to have fluidity; if no change was observed, it was deemed to have no fluidity. Evaluation was performed every day after leaving the bottle, and the evaluation was terminated when fluidity was lost. The number of days for which fluidity was maintained is shown in Table 1. If fluidity was maintained for three days or more, the storage stability was deemed to have passed (◯), and if it did not meet this requirement, it was deemed to have failed (×).

[0090] [Table 1]

[0091] As shown in the above examples, a novel charge-transfer complex was obtained. Furthermore, it is clear that the charge-transfer complex is useful as an epoxy resin curing agent, and that a curable resin composition containing an epoxy resin and the charge-transfer complex has excellent curability and storage stability. [Industrial Applicability]

[0092] According to the present invention, it is possible to provide a one-component curable resin composition that is particularly excellent in curability and storage stability, and the composition can be suitably used, for example, as an adhesive for electronic components, a sealant for electronic components, a casting material, a paint, a structural adhesive, and the like.

Claims

1. A charge transfer complex in which an electron contained in a compound (a) having an imidazole moiety as an electron donor moiety is accepted by a compound (b) having an electron acceptor moiety, A charge-transfer complex, wherein the compound (a) having an imidazole moiety is 2-methylimidazole or 2-ethyl-4-methylimidazole, and the compound (b) having an electron-accepting moiety is a compound selected from the following: 【Chemistry 1】 【Chemistry 2】 【Transformation 3】

2. 2. The charge-transfer complex according to claim 1, wherein the lowest unoccupied molecular orbital (LUMO) of the compound (b) having an electron-accepting site is −1 eV or less.

3. A charge transfer complex having an imidazole moiety as an electron donor moiety, A charge transfer complex, which is a compound represented by the following formula (1) having an imidazole moiety and an electron-accepting moiety in the molecule, in which the electron-accepting moiety accepts an electron contained in the imidazole moiety. 【Chemistry 4】 In general formula (1), R 1 , R 2 , and R 3 each independently represent a hydrogen atom or an optionally substituted hydrocarbon group having 1 to 20 carbon atoms, R 4 represents an optionally substituted divalent hydrocarbon group having 1 to 10 carbon atoms, and ring A represents a benzene ring, an optionally substituted cyclohexane ring, or an optionally substituted norbornene ring.

4. 4. The charge transfer complex according to claim 3, wherein the lowest unoccupied molecular orbital (LUMO) of the compound having an imidazole moiety and an electron-accepting moiety in the molecule is −1 eV or less.

5. A curing agent for epoxy resins, comprising the charge transfer complex according to any one of claims 1 to 4.

6. A curable resin composition comprising an epoxy resin and the charge-transfer complex according to any one of claims 1 to 4.

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