JP2000248053A - Liquid epoxy resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition excellent in preservation stability and rapidly hardenable properties, and capable of providing a hardened product having improved heat resistance and water resistance by including an epoxy resin, a hardening agent and a specified hardening accelerator. SOLUTION: This composition comprises (A) an epoxy resin, (B) a hardening agent, (C) 0.1-20 pts.wt. hardening accelerator comprising a compound selected from (i) an organic acid salt of a hydroxyalkylated imidazole compound of formula I (R1 is H, a 1-17C alkyl or the like; R2 and R3 are each a 1-5C alkyl, a hydroxymethyl or the like with the proviso that at least one thereof is hydroxymethyl), (ii) an organic acid salt of a bisimidazole compound of formula II (R4 and R5 are each H, a 1-17C alkyl or the like; R6 and R7 are each a 1-5C alkyl, phenyl or the like), and (iii) an organic acid salt of a polyimidazole compound of formula III (R8 is H, a 1-17C alkyl or the like; n is 3-10; the groups are lineaply bonded and/or cyclically bonded at the terminals), and (D) optionally other auxiliaries.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to electric and electronic components,
The present invention relates to a liquid epoxy resin composition having improved long-term storage stability in insulation sealing, casting, and impregnation of a semiconductor chip or the like, and having excellent heat resistance and moisture resistance.

[0002]

2. Description of the Related Art Conventionally, transfer molding using a solid epoxy resin powder has been used as a sealing material for semiconductor devices. With the development of electronics in recent years, the demand for higher performance of electronic equipment is high, and the integration, miniaturization, and thinning of semiconductor packages are progressing, and plastic pin grid arrays, tape carrier packages,
The mounting form by spot sealing such as a plastic ball brid array, a flip chip, and a chip scale package has been shifted. In these mounting modes, a liquid epoxy resin composition having a low resin viscosity and a high fluidity is generally used. In this case, operations such as weighing, mixing / dispersing, and deaeration of the epoxy resin and the curing agent are required before use, but once the two liquids are mixed, the reaction proceeds gradually even at room temperature, so that the liquid viscosity increases. However, there has been a problem that the storage stability in one solution is remarkably deteriorated. For this reason, an epoxy resin using a latent curing accelerator which has excellent storage stability at room temperature and can be cured in a short time at an actual curing temperature has been developed. For example, JP-A-60-156719 discloses a hydroxymethylated imidazole compound as a curing accelerator, and JP-A-59-190972 discloses 2-ethyl-imidazole compound.
Bis compounds of 4-methylimidazoles, JP-A-5-2
No. 79456 discloses a polyimidazole compound. However, even when the above-described composition is used, it has been difficult to simultaneously satisfy particularly the storage stability, the rapid curing property, and the electrical properties after the water resistance test of the resin. In particular, since the anhydride-based curing agent is liquid, it has a problem in storage stability. For the purpose of improving such storage stability,
Although organic acid salts of imidazole compounds have been proposed, the hydroxymethylated imidazole, bisimidazole compounds, and polyimidazole compounds are insoluble or hardly soluble in organic solvents and water, and these organic acid salts are generally known. Did not.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to improve the heat resistance and water resistance of a cured product while having excellent storage stability and rapid curability. It is an object of the present invention to provide a liquid epoxy resin composition.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to solve various problems of the conventional curing accelerator, and as a result, have found that an organic acid salt of a specific imidazole compound can accelerate the curing of a liquid epoxy resin. It has been found that not only the storage stability at room temperature is significantly improved, but also the rapid curing property and the heat resistance and water resistance of a cured product are improved by using the agent, thereby completing the present invention.

That is, the present invention provides an epoxy resin, a curing agent,
In the liquid epoxy resin composition comprising a curing accelerator, and further, if necessary, other auxiliaries, as a curing accelerator,
The following general formula (1)

[0006]

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(Wherein, R1 is a hydrogen atom, having 1 to 1 carbon atoms)
7 represents an alkyl group or a phenyl group, R2 and R3 represent an alkyl group having 1 to 5 carbon atoms, a hydroxymethyl group or a benzyl group, and at least one of R2 and R3 is a hydroxymethyl group. Organic acid salt of imidazole compound of general formula (2)

[0008]

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(Wherein R4 and R5 are hydrogen atoms and carbon atoms 1
Represents an alkyl group or a phenyl group, and R6, R7
Represents an alkyl group having 1 to 5 carbon atoms, a phenyl group or a benzyl group), and an organic acid salt of a bisimidazole compound represented by the following general formula (3):

[0010]

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(Wherein R8 is a hydrogen atom, having 1 to 17 carbon atoms)
Wherein n is an integer of 3 to 10, and is a linear and / or terminal-bound cyclic body) selected from the group consisting of organic acid salts of polyimidazole compounds A liquid epoxy resin composition comprising one or more compounds.

Hereinafter, the present invention will be described in detail.

The organic acid salt of a hydroxyalkylated imidazole compound, the organic acid salt of a bisimidazole compound and the organic acid salt of a polyimidazole compound used as a curing accelerator in the present invention are represented by the above-mentioned general formula (1) and general formula (1). One or more compounds selected from the group of compounds represented by (2) and the general formula (3). In the general formula (1), R
1 represents a hydrogen atom, an alkyl group having 1 to 17 carbon atoms or a phenyl group, R2 and R3 represent an alkyl group having 1 to 5 carbon atoms,
Represents a hydroxymethyl group or a benzyl group, R2, R3
Is at least one hydroxymethyl group. If the number of carbon atoms of R1 exceeds 17, and the number of carbon atoms of R2 and R3 exceeds 5, there is a problem in rapid curability. In the general formula (2), R4 and R5 represent a hydrogen atom, an alkyl group having 1 to 17 carbon atoms or a phenyl group, and R6 and R7 represent an alkyl group having 1 to 5 carbon atoms, a phenyl group or a benzyl group. R4 and R5 have 1 carbon atom
When the number of carbon atoms of R7 and R6 and R7 exceeds 5, there is a problem in rapid curability. In the general formula (3), R8 represents a hydrogen atom, an alkyl group having 1 to 17 carbon atoms or a phenyl group, and n represents 3 to
It is an integer of 10 and is a cyclic body having a linear and / or terminal bond. If the number of carbon atoms in R8 exceeds 17, there is a problem in the rapid curability. When n is less than 3 and more than 10, not only industrial production is difficult, but also there is a problem in terms of rapid curing.

In the present invention, the organic acid salts of the imidazole compounds represented by the above-mentioned general formulas (1), (2) and (3) are used as starting materials for hydroxyalkylimidazole compounds, bisimidazole compounds and polyimidazole compounds. In a curing agent such as methanol, water, another organic solvent or an acid anhydride containing an organic acid, while dispersing the fine particles by mechanical pulverization and reacting them. The method of dispersing the fine particles in an organic solvent is not particularly limited as long as it is a generally known fine particle production method, but other than a ball mill, a compression crusher, an impact crusher, a roller mill, a high-speed rotation mill, a medium stirring mill, a jet mill, High-speed stirring with a stirring blade can be applied. The amount of the organic acid used in the production of the organic acid salt is not particularly limited, but considering the storage stability, the imidazole group 1
0.2 mol or more, more preferably 0.1 mol, per mol.
It is preferably at least 5 moles. The solvent used in the reaction is not particularly limited, but water, alcohols such as methanol, ethanol, propanol, and isopropanol, dioxane, acetonitrile, dimethyl sulfoxide, dimethylformamide, formamide,
Organic solvents such as N-methylpyrrolidone and methyl cellosolve can be used. More preferably, a solvent such as water, methanol, ethanol, propanol, isopropanol, ethylene glycol, dioxane, acetonitrile, and methyl cellosolve, in which the generated salt is insoluble or hardly soluble, is suitably used. Solvents such as dimethylsulfoxide, dimethylformamide, formamide, and N-methylpyrrolidone are not suitable because the formed salt is easily dissolved and a post-treatment is required to remove the crystalline salt. The reaction temperature is not particularly limited, but may be in the range of 10 to 120 ° C, more preferably 10 to 70 ° C.

The hydroxyalkylimidazole compound, bisimidazole compound and polyimidazole compound in the present invention can be produced by a generally known production method, and are not particularly limited. For example, imidazoles as starting materials On the other hand, it can be obtained by reacting about 0.5 to 3 moles of formaldehyde or paraformaldehyde in a solvent containing a base at a reaction temperature of 40 to 150 ° C.

The starting materials for the hydroxyalkylimidazole compound of the present invention include, for example, 2-methylimidazole, 2-ethylimidazole, 2-propylimidazole, 2-isopropylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-
Ethyl-4-methylimidazole, 2-phenyl-4-
Methylimidazole, 2-phenylimidazole, 2-
Preferred examples include p-toluyl-imidazole and 2-o-toluyl-imidazole.

Preferred starting materials for the bisimidazole compound in the present invention include, for example, 2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, etc. Phenyl-4-methylimidazole is particularly preferred.

The starting materials for the polyimidazole compound of the present invention include, for example, 2-methylimidazole,
2-ethylimidazole, 2-propylimidazole,
2-isopropylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2-p-toluyl-imidazole, 2-
Suitable examples include o-toluyl-imidazole.

The anionic species of the organic acid salt of the imidazole compound in the present invention is not particularly limited. For example, aromatic carboxylic acids such as benzoic acid, phthalic acid, trimellitic acid and pyromellitic acid, formic acid, acetic acid and succinic acid , Tartaric acid,
Examples include aliphatic carboxylic acids such as octylic acid and adipic acid, and tetra-substituted phenylborates, and phthalic acid, trimellitic acid, and aromatic carboxylic acids such as pyromellitic acid are particularly preferable in terms of storage stability and resin properties. .

In the present invention, the amount of the curing accelerator used is not particularly limited, but is 0.1 to 20 parts by weight, more preferably 0.1 to 1 part by weight, per 100 parts by weight of the epoxy resin.
The range of 5 parts by weight is preferable in view of storage stability, production speed and economy.

In the present invention, as the curing accelerator, a compound represented by the above general formula may be used alone or as a mixture, and further used in combination with or mixed with a known curing accelerator within a range not to impair the effects of the present invention. can do.

Known curing accelerators include triethylamine, N, N, N ', N ", N"', N '"-hexamethyltriethylenetetramine, N, N, N'-trimethylaminoethyl. Piperazine, triethylenediamine, N,
Tertiary amines such as N-dimethylbenzylamine, tris (dimethylaminomethyl) phenol, N, N-dimethylcyclohexylamine, lauryldimethylamine, 1,8-diazabicyclo (5.4.0) -7-undecene; 2-methylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole,
Imidazole compounds such as 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-methylimidazole, 2-methylimidazoline, 2-phenylimidazoline, 2-ethyl-4-methylimidazoline, 2-undecylimidazoline And imidazolines such as 2-heptadecyl imidazoline, and organic phosphine compounds such as triphenylphosphine, tributylphosphine and tri (4-methylphenyl) phosphine. Also, Lewis acid salts, organic acid salts of these amine compounds, epoxy resin type, urea type, isocyanate type, acid anhydride type, modified products such as hydrazide type by adduct formation, benzylphosphonium salt, benzylsulfonium salt, benzyl Ammonium salts, benzylpyridinium salt-type cationic polymerization catalysts, microcapsule-type, photopolymerization-type latent curing accelerators, and the like are also appropriately used as long as the function of the curing accelerator of the present invention is not lost.

The epoxy resin in the present invention is not particularly limited, but for example, bisphenol A
Epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, glycidyl dimer acid epoxy resin, polyalkylene ether epoxy resin, phenol novolak epoxy resin, orthocresol novolak epoxy resin, biphenyl epoxy resin, diphenyl epoxy resin Cyclopentadiene type epoxy resin, naphthol type epoxy resin, naphthalene type epoxy resin, alicyclic epoxy resin, heterocyclic epoxy resin,
Diglycidyl epoxy resin, glycidylamine type epoxy resin, halogenated bisphenol A type epoxy resin and the like are preferably used, and one type or a mixture of two or more types is used.

Incidentally, a compound containing one epoxy group in the molecule used as the reactive diluent may be contained in a part thereof. The epoxy equivalent and viscosity of the epoxy resin are not particularly limited, but those having an epoxy equivalent in the range of 100 to 3000 are preferable in view of fluidity, heat resistance and chemical resistance of the resin.

The curing agent in the present invention is not particularly limited. For example, an organic acid anhydride, a phenol resin, an aliphatic amine, an aromatic amine or dicyandiamide can be used. Fluidity of the cured product,
Organic acid anhydrides are preferred in view of electrical characteristics and heat resistance. The organic acid anhydride is not particularly limited, for example, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, nadic anhydride, methylnadic anhydride, trialkyltetrahydroanhydride It is possible to use phthalic acid, phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, dodecenyl succinic anhydride, ethylene glycol anhydrotrimellit, glycerin trisanhydrotrimellit, etc. it can.

The amount of the organic acid anhydride to be added is appropriately determined depending on the purpose of use, the curing characteristics, and the type of the curing agent, and is not limited. However, the heat resistance, discoloration and other mechanical and electrical properties of the resin are not limited. Taking into account the mechanical properties, 0.5 to 1.5 equivalents, preferably 0.6 to 1.5 equivalents, per equivalent of epoxy group.
1.2 equivalents are added.

In the present invention, a compound that reacts with the epoxy resin may be used in addition to the acid anhydride-based curing agent. The compound that reacts with the epoxy resin is not particularly limited, for example, phenol novolak, o-cresol novolak, p-cresol novolak, t-butylphenol novolak, alkylphenols such as dicyclopentadiene cresol, ethylenediamine,
Diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, N
Aliphatic amines such as -hydroxyethylethylenediamine, tetra (hydroxyethyl) ethylenediamine,
Polyether polyamines such as triethylene glycol diamine, tetraethylene glycol diamine, diethylene glycol bis (propylamine), polyoxypropylene diamine, polyoxypropylene triamines, isophorone diamine, methadenediamine, N-aminoethyl piperazine, bis (4 -Amino-3-methyldicyclohexyl) methane, bis (aminomethyl) cyclohexane, 3,9-bis (3-aminopropyl) 2,
Alicyclic amines such as 4,8,10-tetraoxaspiro (5,5) undecane, norbornenediamine, m-
Xylenediamine, α- (m / p-aminophenyl) ethylamine, metaphenylenediamine, diaminodiphenylsulfone, diaminodiphenylmethane, diaminodiethyldimethyldiphenylmethane, α, α′-bis (4
Aromatic amines such as -aminophenyl) -p-diisopropylbenzene, amidoamines derived from the above amines and carboxylic acids, formic acid, acetic acid, propionic acid, acetic acid, valeric acid, caproic acid, 2-ethylhexanoic acid Monocarboxylic acids such as octylic acid, lauric acid, capric acid, stearic acid, oleic acid, linoleic acid, cyanoacetic acid, crotonic acid, pyruvic acid, salicylic acid, benzoic acid, hydroxystearic acid, acrylic acid, methacrylic acid, and adipine Dicarboxylic acids such as acid, azelaic acid, sebacic acid, succinic acid, maleic acid, isophthalic acid, phthalic acid, terephthalic acid, oxydiacetic acid, fumaric acid, oxalic acid, maleic acid, suberic acid, pimelic acid, glutaric acid, and malonic acid Polycarboxylic acids such as acids, trimellitic acid and pyromellitic acid; Phenols such as knol, cresol, catechol, pyrogallol, hydroquinone, nonylphenol, dodecylphenol, methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, dipropylene glycol, glycerin, trimethylolpropane, 2-ethylhexanol, octanol, Decyl alcohol,
Alcohols such as benzyl alcohol, sucrose, sorbitol, and isocyanates such as diphenylmethane diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, and xylylene diisocyanate.

The liquid epoxy resin composition of the present invention may contain, if necessary, other additives used in ordinary epoxy resin compositions, such as a filler, an organic compound and the like, as long as the object of the present invention is not impaired. Solvents, flame retardants, dyes, anti-tarnish agents, antioxidants, release agents, flexibility agents, liquid rubbers, leveling agents, tackifiers, coupling agents, defoamers, reactive or non-reactive dilutions Agents and the like can be appropriately compounded.

Examples of the filler include crystalline silica, fused silica, alumina, zirconium silicate, quartz powder, mineral silicate, calcium carbonate, barium sulfate, carbon black, coal tar, glass fiber, asbestos fiber, and boron fiber , Carbon fiber, cellulose powder, asbestos powder, slate powder, gypsum, aerosol, titanium dioxide,
Examples include graphite, iron oxide, and aluminum powder. Examples of the organic solvent include, but are not particularly limited to, toluene, xylene, methyl isobutyl ketone, ethyl acetate, and butyl acetate.

When the liquid epoxy resin composition of the present invention is produced, the epoxy resin, the curing agent, the curing accelerator and, if necessary, the filler and various additives may be kneaded with a known kneading machine. It is not limited. For example, it can be mixed with a three-roll, kneader, universal stirrer, ball mill, planetary mixer, homogenizer, homodisper, or the like, and degassed to obtain a one-part liquid epoxy composition. The resin composition thus obtained is used for insulation sealing, casting, impregnation and the like of electric and electronic parts by a known molding method such as a dispenser.

[0031]

The present invention is described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

<Production Example 1> Synthesis of pyromellitic acid salt of 2-phenyl-4,5-dihydroxymethylimidazole 7 gr (34 mmol) of 2-phenyl-4,5-dihydroxymethylimidazole and 8.6 gr of pyromellitic acid
(34 mmol) was placed in 300 ml of methanol, dispersed in fine particles by a ball mill, and reacted at room temperature. The precipitate was filtered and dried to obtain pyromellitic acid salt of 2-phenyl-4,5-dihydroxymethylimidazole (imidazole ring: pyromellitic acid = 2: 1 salt) in 10.1 gr (yield 90%).

In the same manner as in Preparation Example 1, trimellitate of 2-phenyl-4,5-dihydroxymethylimidazole (1: 1 salt in 94% yield), 2-methyl-
Pyromellitic acid salt of 4,5-dihydroxymethylimidazole (2: 1 salt in 85% yield) and pyromellitic acid salt of bis (2-phenyl-4-methylimidazole) compound (2: 1 salt in 90% yield) %), Pyromellitic acid salt of polyimidazole compound of 2-methylimidazole (2: 1)
Salt, yield 85%) and a pyromellitic acid salt of a polyimidazole compound of 2-phenylimidazole (90% yield of a 2: 1 salt).

<Production Example 2> A method similar to that of Production Example 1 was used, and dimethylformamide was used as a solvent.

Since the produced salt was dissolved in the solvent, the pyromellitic acid salt of 2-phenyl-4,5-dihydroxymethylimidazole could not be obtained.

<Production Example 3> Synthesis of tetraphenylborate salt of 2-phenyl-4,5-dihydroxymethylimidazole 5.2 gr (25 mmol) of 2-phenyl-4,5-dihydroxymethylimidazole was placed in 200 ml of water and dispersed. And add 25 ml of a 1N hydrochloric acid solution. 50 more
An aqueous solution of 8.6 gr (25 mmol) of tetraphenylborate sodium dissolved in ml of water is added dropwise. The reaction solution was filtered, washed with water, and dried to obtain 11.2 gr of tetraphenylborate salt of 2-phenyl-4,5-dihydroxymethylimidazole (86% yield of 1: 1 salt).

The thermosetting resin compositions obtained in the respective Examples and Comparative Examples were tested for the following items.

<Geling time>: JIS K5059 (1
997) at 150 ° C. by a hot plate method.

<Storage stability>: 25 ° C. using a B-type viscometer
Was measured, and the time (days) when the viscosity of the resin composition became twice the initial viscosity was measured and evaluated.

<Heat resistance>: The heat resistance of the cured resin is determined by DSC.
The evaluation was performed by measuring the glass transition temperature (Tg) using (SSC-5000 manufactured by SEIKO).

<Water resistance>: A pressure cooker test (PCT test) of a resin test piece of 100 × 100 × 2 mm at 125 ° C. and 0.25 MPa steam pressure × 20 hours.
After that, the volume resistance was measured and evaluated by comparing with the value before the PCT test. The volume resistance was 500 V at room temperature (20 ° C.) using R8340 manufactured by Advantest.
One minute after the voltage application, the volume resistance was measured.

<Curing conditions>: Test pieces for evaluation of heat resistance and water resistance were prepared by hot press pressure molding at 150 ° C. and 12 MPa × 2 hours.

Examples 1 to 6 A curing accelerator was added to 3-methyltetrahydrophthalic anhydride (Shin-Nippon Rika Chemicals Co., Ltd. MT-500) at the compounding ratio shown in Table 1 and mixed and dispersed using a ball mill for 24 hours. Let it.
Further, the organic acid anhydride and the curing accelerator dispersion liquid were mixed with a bisphenol A type epoxy resin (manufactured by Yuka Shell Co., Epicoat 828, epoxy equivalent 190) in accordance with the compounding ratio shown in Table 1, and the mixture was subjected to 6500 rpm and 1500 rpm using a laboratory mixer. After stirring for minutes, vacuum degassing was performed to prepare a liquid epoxy resin composition, and its curability, storage stability at 25 ° C., cured physical properties, and water resistance were measured. The results are shown in Table 1.

[0044]

[Table 1]

Comparative Examples 1 to 6 At the compounding ratio of Example 1, 2-phenyl-
4,5-dihydroxymethylimidazole, bis (2-
Ethyl-4-methylimidazole), 2-phenyl-
4,5-dihydroxymethylimidazole / tetraphenylborate salt, triphenylphosphine, tetraphenylphosphonium / tetraphenylborate salt, 1,8
-Diazabicyclo [5.4.0] undec-7-ene.
Perform a comparative test using tetraphenyl borate salt,
The results are shown in Table 2.

[0046]

[Table 2]

As shown in Examples 1 to 6 in Table 1, the epoxy resin composition of the present invention has a relatively high curing speed, a cured product having excellent storage stability and a high glass transition temperature. It is possible to manufacture. Further, since the decrease in the volume resistance after the PCT test is small, excellent water resistance and electrical characteristics can be achieved.

On the other hand, imidazoles, their organic acid salts, and borate salts shown in Comparative Examples 1 to 6 in Table 2 do not simultaneously satisfy all of the storage stability, rapid curability, and physical properties of the cured product. Did not.

[0049]

The liquid epoxy resin composition of the present invention not only has excellent storage stability at around room temperature, but also cures in a short time when heated, and significantly improves operability and productivity in resin production. Having. In addition, it significantly improves the heat resistance and water resistance of the obtained cured product, and is useful as an electrical insulating material for electronic components, a semiconductor sealing material, a casting material, and an impregnating material.

Claims (3)

[Claims] 1. A liquid epoxy resin composition containing an epoxy resin, a curing agent, a curing accelerator and, if necessary, other auxiliaries, wherein the curing accelerator is represented by the following general formula (1): ] (Wherein, R1 represents a hydrogen atom, an alkyl group having 1 to 17 carbon atoms or a phenyl group, R2 and R3 represent an alkyl group having 1 to 5 carbon atoms, a hydroxymethyl group or a benzyl group, and R2 and R3 represent An organic acid salt of a hydroxyalkylated imidazole compound represented by the following general formula (2): (In the formula, R4 and R5 represent a hydrogen atom, an alkyl group having 1 to 17 carbon atoms or a phenyl group, and R6 and R7 have 1 to carbon atoms.
5 represents an alkyl group, a phenyl group or a benzyl group), and an organic acid salt of a bisimidazole compound represented by the following general formula (3): (In the formula, R8 represents a hydrogen atom, an alkyl group having 1 to 17 carbon atoms or a phenyl group, n is an integer of 3 to 10, and is a linear and / or terminal-bonded cyclic body.) A liquid epoxy resin composition comprising at least one compound selected from the group consisting of organic acid salts of polyimidazole compounds. 2. The liquid epoxy resin composition according to claim 1, wherein the curing accelerator is used in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the epoxy resin. 3. The liquid epoxy resin composition according to claim 1, wherein the anion of the organic acid salt is an aromatic carboxylic acid.