JPH042638B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to an epoxy resin adhesive containing a novel imidazole acid addition salt. <Prior Art> Epoxy resins are widely used in electronic and electrical parts because of their good electrical properties, adhesive properties, and moisture resistance. In the field of these adhesives, particularly high performance has recently been required. For example, in addition to improving the properties of cured products such as adhesion, there is a need for products that can be cured at low temperatures in a short time and that do not change the physical properties of uncured products during storage, which can improve productivity. There is. To address these needs, two-component adhesives that store the epoxy resin component and curing agent component separately are common, but the two must be mixed each time they are used, making formulation and mixing difficult. Problems such as defective products and material loss occur due to mistakes. Therefore, there is a strong demand for a so-called latent one-component adhesive that does not cure as it is even if an epoxy resin and a curing agent are mixed in advance. Moreover, the latent one-component adhesive must not cause unexpected gelation when stored at room temperature, that is, must have excellent storage stability. A one-component conductive adhesive for electronic components using 2-phenyl-4-methyl-5-hydroxymethylimidazole with a high melting point as a latent curing accelerator is known (Japanese Patent Application Laid-Open No. 142270/1983). ). <Problems to be Solved by the Invention> However, although this one-component adhesive has good storage stability, it has poor adhesive strength at a low temperature of about 100°C. Therefore, the present inventors developed 1-cyanoethyl-2-ethylimidazole trimellistate ("New Epoxy Resin", Shokodo, published May 10, 1985), which is known as a latent curing accelerator. When the latent one-component adhesive used was examined, it was found that although the storage stability was good and the adhesive strength was somewhat improved, it was still unsatisfactory. That is, there is a strong desire for an adhesive that has both excellent storage stability and adhesive strength. Therefore, as a result of intensive study, the present inventors found that
A new imidazole acid addition salt has been discovered, and when this compound is used as an epoxy resin curing agent or curing accelerator, it has excellent storage stability and adhesive strength, and also cures quickly when heated at relatively low temperatures. The present inventors have discovered that they act as a so-called latent curing agent or latent curing accelerator, and have completed the present invention. <Means for solving the problems> That is, the present invention is an epoxy resin adhesive containing an epoxy resin and a novel imidazole acid addition salt represented by the following general formula [] (hereinafter referred to as imidazole acid addition salt). . (In the formula, R ₁ represents a hydrogen atom, a C ₁ to C ₁₈ alkyl group, a benzyl group, or a β-cyanoethyl group, and R ₂ represents a hydrogen atom, a C ₁ to _{C 18} alkyl group, a phenyl group, or a halogen-substituted phenyl group. group or C ₁
~ Represents a _C4 alkyl group-substituted phenyl group. Further, R ₃ and R ₄ each represent a hydrogen atom, a C ₁ to C ₁₈ alkyl group, a phenyl group, a benzyl group, or a hydroxymethyl group. ) Hereinafter, the configuration of the present invention will be explained in detail. The adhesive of the present invention contains an epoxy resin and an imidazole acid addition salt. The imidazole acid addition salt used in the adhesive of the present invention is a new compound and is prepared, for example, by the following method. (A) Imidazole compound represented by the following general formula [] (hereinafter referred to as "imidazole []")
and hydroxybenzoic acid represented by the following general formula [] (hereinafter referred to as ``hydroxybenzoic acid []'') are each dissolved in an organic solvent and then mixed; or (B) imidazole [] in a solvent-free system. ] and hydroxybenzoic acid [ ] are heated and mixed in a molten state. (In the formula, R ₁ to _{R 4} have the same meanings as in the above general formula [].) Specific examples of such imidazole [] are 2
-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, 2-phenylimidazole, 1-(β-cyanoethyl)2-ethylimidazole, 2-phenyl-4-methyl-5-
Hydroxymethylimidazole, 2-phenyl-
4,5-dihydroxymethylimidazole, 2-
p-Tolyl-4-methylimidazole, 2-undecylimidazole, 2-phenyl-4,5-
Examples include dibenzylimidazole and 2-phenyl-5-benzylimidazole. Further, specific examples of hydroxybenzoic acid [] include 2,3-dihydroxybenzoic acid, 2,4-
Dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 2,6-dihydroxybenzoic acid, 3,5
-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, and the like. Of these, 2,3-
Dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid, 2,6
-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, and 3,4-dihydroxybenzoic acid are preferably used. In these preparations, the molar ratio of hydroxybenzoic acid [ ] to imidazole [ ] was 0.7.
A range of 1.3 to 1.3 times the mole is preferred. In the preparation method (A), the solvent used is
Examples include esters such as ethyl acetate and methyl acetate, ethers such as diethyl ether and dimethyl ether, ketones such as acetone and methyl ethyl ketone, and acetonitrile. The preparation temperature is preferably around room temperature, but is not particularly limited. The imidazole acid addition salt thus obtained is a stable solid compound at room temperature. Such imidazole acid addition salts are used as curing agents or curing accelerators for epoxy resins. When imidazole acid addition salt is used as a curing agent for epoxy resin, as a composition of imidazole acid addition salt and epoxy resin,
When used as a curing accelerator for epoxy resins, it is used in the form of a composition of imidazole acid addition salt, epoxy resin, and curing agent. When imidazole acid addition salt is used as a curing agent, it is usually 0.1 to 0.1 to 100 parts by weight of epoxy resin.
200 parts by weight, preferably 1 to 100 parts by weight, and when used as a curing accelerator, usually 0.1 to 100 parts by weight, preferably 0.1 to 10 parts by weight, per 100 parts by weight of the epoxy resin. Imidazole acid addition salts exhibit the effect of improving storage stability and adhesive strength by being included as the main curing agent or curing accelerator in epoxy resin compositions, but do not impair the properties of imidazole acid addition salts. It may contain other curing agents or curing accelerators within a certain range. The other curing agent used here is not particularly limited as long as it is a normal epoxy resin curing agent.
For example, phenolic compounds such as phenol novolac, cresol novolac, 3,3'-diallyl-4,4 ^- dihydroxybisphenol A, 4,4 ^- diaminodiphenylsulfon,
3,3'-diaminodiphenylsulfone, 4,
4'-methylenebis(2-ethylaniline), 4,
4'-methylenebis(2,6-diethylaniline),
Amine compounds such as 4,4'-methylenebis(2-ethyl-6-methylaniline), acid anhydrides such as phthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, trimellitic anhydride, pyromellitic anhydride, Dicyandiamide, aromatic amine adducts of dicyandiamide (modified dicyandiamide), diaminomaleonitrile and its derivatives, melamine and its derivatives, amine imide compounds, polyamines, addition compounds consisting of epoxy and imidazoles, hydrazides such as adipic acid hydrazide and isophthalic acid hydrazide. Examples include compounds, imidazoles, and the like. The epoxy resin used in the adhesive of the present invention is not particularly limited as long as it is a compound having one or more epoxy groups per molecule; for example, bisphenol A diglycidyl ether, tetrabromobisphenol A diglycidyl ether, , phloroglucinol triglycidyl ether, tetraglycidyl diaminodiphenylmethane, triglycidylmethaminophenol, phenol novolak type epoxy, cresol novolak type epoxy, bisphenol C glycidyl ether, 1,
diglycidyl ether of 5-naphthalenediol, diglycidyl ether of 1,6-naphthalenediol, 1,4'-bis(2,3-epoxypropoxy)-3,3',5,5'-tetramethylbiphenyl, 4,4'-bis(2,3-epoxypropoxy)biphenyl, 4,4'-bis(2,3-epoxypropoxy)-3,3',5,5'-tetraethylbiphenyl, resorcin diglycidyl ether,
Neopentyl glycol diglycidyl ether,
Allyl glycidyl ether, phenyl glycidyl ether, p-tert-butylphenyl glycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, dibromophenyl glycidyl ether, glycidyl phthalimide, methylglycidyl ether-p-tert. Examples include butylphenol, vinylcyclohexene dioxide, triglycidyl ether of tris(4-hydroxyphenyl)methane, and the like. The adhesive of the present invention contains an epoxy resin and an imidazole acid addition salt in a total amount of 0.1 to 100%. A rubber component, a powdered filler, a diluent, a coloring agent, a pigment, a flame retardant, and the like are added to the adhesive of the present invention as necessary. Examples of the rubber component are not particularly limited, and include, for example, nitrile rubber modified with a carboxyl group-containing compound, modified polybutadiene rubber, styrene block copolymer, silicone rubber, and the like. Examples of powdered fillers include metal oxides such as aluminum oxide and magnesium oxide;
metal hydroxides such as aluminum hydroxide; metal carbonates such as calcium carbonate and magnesium carbonate;
Diatomaceous earth powder, basic magnesium silicate, calcined clay, finely powdered silica, fused silica, crystalline silica, carbon black, kaolin, finely powdered mica, quartz powder, graphite, asbestos, molybdenum disulfide, antimony trioxide, etc., as well as fibers. quality reinforcing agents and fillers, such as inorganic fibers such as glass fibres, rock wool, ceramic fibres, asbestos and carbon fibres, synthetic fibers such as paper, pulp, wood flour, linters and polyamide fibres, silver in granular or flake form Examples include metals such as powder, copper powder, and nickel powder. Diluents include, for example, liquid low-viscosity epoxy compounds such as the aforementioned phenyl glycidyl ether and vinyl cyclohexene dioxide, cellosolves such as butyl cellosolve acetate, ethyl cellosolve, and butyl cellosolve, γ-butyrolactone,
Examples include lactones such as ε-caprolactone and 4-valerolactone, aromatic compounds such as benzene, toluene, and xylene, esters such as ethyl acetate and methyl acetate, and ketones such as methyl ethyl ketone and methyl isobutyl ketone. Examples of colorants and pigments and flame retardants include titanium dioxide, yellow carbon black, iron black, molybdenum red, navy blue, cadmium yellow, cadmium red, inorganic phosphorus such as red phosphorus, and organic phosphorus such as triphenyl phosphate. , decabromodiphenyl ether, hexabromobenzene, and other bromine compounds. The means for mixing the components of the adhesive of the present invention is not particularly limited, and any method may be employed such as heating and melt mixing, kneading using a roll or kneader, mixing using an appropriate organic solvent, and dry mixing. can. <Function> Imidazole acid addition salt is an acid addition salt in which the basicity of imidazole is protected by hydroxybenzoic acid, and is therefore a stable compound at room temperature. Imidazole acid addition salts have extremely ideal effects as a latent curing agent when used as a curing agent for epoxy resins, and as a latent curing accelerator when used as an epoxy resin curing accelerator. That is,
At around room temperature, the basicity of imidazole in imidazole acid addition salts is protected by hydroxybenzoic acid and its function as a curing agent or curing accelerator is suppressed, but when heated to the curing temperature, the salt dissociates. Demonstrates sufficient power as a curing agent or curing accelerator. The imidazole acid addition salt used in the present invention has excellent storage stability and is useful as an epoxy resin curing agent or curing accelerator for short-time curing at low temperatures.
Adhesives for glass, ceramics, etc., conductive adhesives or insulating adhesives for capacitors, semiconductor die bonding, membrane switches, etc., and adhesives for electronic/electrical parts such as light receiving elements, light emitting elements, and liquid crystal parts. Useful in all epoxy adhesive fields. Examples Next, examples will be shown to specifically explain the present invention, but these examples do not limit the present invention. Reference Example 1 (Preparation example of imidazole acid addition salt) 2,6-dihydroxybenzoic acid 4.0g (2.60×
10 ^-2 mol) was dissolved in 90 ml of ethyl acetate. Separately,
3.28 g (2.07 x 10 ^-2 mol) of 2-phenyl-4-methylimidazole (manufactured by Shikoku Kasei Co., Ltd.) was dissolved in ethyl acetate.
The solution was dissolved in 240 ml while heating, and added dropwise to the dihydroxybenzoic acid solution prepared above while stirring. After the obtained slurry was filtered, the crystals were dried. yield
5.88g, mp210~216℃. Formation of an acid addition salt was confirmed by IR spectrum measurement, and elemental analysis confirmed that imidazole and acid formed an acid addition salt at a 1:1 (molar ratio). Various imidazole acid addition salts B, C, D, E, F, G and H shown in Table 1 were prepared by the same operation. Moreover, imidazole acid addition salt is 2
It was prepared by mixing equimolar amounts of -phenyl-4-methyl-5-hydroxymethylimidazole and 2,6-dihydroxybenzoic acid, and heating the mixture to 200°C to melt it. Table 1 shows the melting points of these imidazole acid addition salts.

[Table] Examples 1 to 3 (Application example as a one-component conductive adhesive) Bisphenol F type epoxy resin (epoxy equivalent: 180, viscosity at 25°C: 26 poise), phenyl glycidyl ether and Reference Example 1 The prepared addition salts A, E, and F were blended in the proportions shown in Table 2 (here, the addition salt acts both as a curing agent and as a curing accelerator). For these formulations, thicknesses of 0.2 to
Silver powder in the form of scales of 0.6 μm and 2 to 10 μm in size was added in the proportions shown in Table 2, and kneaded in a three-roll mill to prepare a conductive paste. The pot life, adhesive strength, and specific resistance of the one-component conductive adhesive were measured by the following methods, and the results are shown in Table 2. Pot life: paste composition at 25℃ or 40℃
The mixed state was checked over time using a spatiera, and the number of days until stirring became impossible was measured. Adhesive strength: Tensile shear strength at 25°C was measured using a 42 alloy test piece measuring 30 mm x 25 mm x 0.25 mm (thickness). Specific resistance: 10mm (width) x 50mm (length) x 0.1mm (thickness)
Measure the resistance value of the conductor width and calculate the volume resistivity (Ω・
cm) was calculated. For comparison, addition salt G, 2-phenyl-4-methyl-5-hydroxymethylimidazole (2P4MHz) (manufactured by Shikoku Kasei Co., Ltd.) was used instead of addition salts A, F, and G.
and 1-cyanoethyl-2-ethylimidazole trimellistate (2E4MZ-CHS) (manufactured by Shikoku Kasei Co., Ltd.) were blended in the proportions shown in Table 2,
All other preparations were made in the same manner as in Examples 1 to 3 above, and the physical properties were measured. The results obtained are shown in Table 2.

【table】

[Table] As is clear from Table 2, the adhesive of the present invention has good pot life and adhesive strength, but when addition salt G is used, the pot life at 40° C. is poor and the specific resistance is large. Furthermore, when 2E4MZ-CNS and 2PMHz are used, the adhesive strength is weak. Furthermore, when 2E4MZ-CNS and 2P4MHz are used, their specific resistance is too large to be used as a conductive adhesive for low temperature curing. Examples 4 to 7 (Application example of amine curing agent as curing accelerator) Bisphenol A type epoxy resin (Yuka Shell
Co., Ltd., "Epicote 828"), diaminodiphenylsulfone, and addition salt A prepared in Reference Example 1,
B, C, and F were blended in the proportions shown in Table 3, and kneaded using a three-roll mill. The adhesive strength, glass transition temperature (Tg), pot life, and gelation time of these compositions were measured by the following methods, and the results are shown in Table 3. Adhesive strength: Using a 10 cm x 2.5 cm x 0.2 cm (thickness) Al plate as the adherend, it was sanded with #120 sandpaper and then cleaned with trichlene, and the tensile shear strength was measured at 25°C. did. Tg: using DSC (manufactured by Daini Seikosha Co., Ltd., model 580)
Measurement was performed at a heating rate of 40°C/min. Pot life: The number of days until a sample stored at a constant temperature of 35°C was no longer able to be stirred using a spatiera was measured. Gelation time: Measured according to the hot plate method (JIS5909). For comparison, instead of addition salts A, B, C, F,
Using salicylic acid, a resin composition was prepared by blending in the proportions shown in Table 3, and the other operations were the same as above.
The physical properties were measured and the results are shown in Table 3.

[Table] As is clear from Table 3, the adhesive of the present invention has a short gelation time and a long pot life. Moreover, the adhesive strength is high. Examples 8 to 9 (Application example of acid anhydride curing agent as curing accelerator) Bisphenol A type epoxy resin (Yuka Shell
Co., Ltd., “Epicote 828”), 4-methylcyclohexane-1,2-dicarboxylic anhydride (Me-
HHPA) (manufactured by Tokyo Kasei Co., Ltd., reagent grade 1) and addition salts A, F and G prepared in Reference Example 1 are shown in Table 4.
and kneaded using a three-roll mill. For these compositions, adhesive strength, Tg,
The pot life and transparency of the cured product were measured by the following methods, and the results are shown in Table 4. Adhesive strength, Tg: Measured in the same manner as in Examples 4-7. Pot life: The number of days until a sample stored at 20°C or 40°C could no longer be stirred using a spatiera was measured. Transparency of cured product: A cured product measuring 40 mm x 15 mm x 1 mm (thickness) was visually observed. For comparison, instead of the above addition salts A and F, addition salt G and triphenylphosphine (manufactured by K.I. Kasei Co., Ltd.) were blended in the proportions shown in Table 4, and the other procedures were the same as above to prepare the resin composition. A product was prepared and its physical properties were measured. Table 4 shows the results.

【table】

[Table] As is clear from Table 4, the adhesive of the comparative example has an unsatisfactory pot life, but the adhesive of the present invention has excellent adhesive strength and pot life, and is also excellent in transparency. Examples 10 to 11 (Application example as a curing accelerator when dicyandiamide is used as a curing agent) Bisphenol A type epoxy resin (Yuka Shell
Co., Ltd., "Epicote 828"), dicyandiamide, and addition salts A and F prepared in Reference Example 1 were blended in the proportions shown in Table 5, and kneaded using a three-roll mill. The adhesive strength, gelation time, pot life, and heat loss during curing and at high temperatures of these compositions were measured by the following methods, and the results are shown in Table 5. Adhesive strength: Measured in the same manner as in Examples 1-3. Pot life: Measured in the same manner as in Examples 10-12. Gelation time: Measured in the same manner as in Examples 4-7. Loss on heating: An aluminum container was placed in an oven, left for a predetermined period of time, and the loss on heating was measured.

【table】

[Table] As is clear from Table 5, the adhesive of the present invention is excellent in both pot life and adhesive strength, and is also excellent in loss on heating. Examples 12 to 17 (Application example as a powder adhesive) “Sumi Epoxy” ESCN- as an epoxy resin
195XL (o-cresol novolak type epoxy resin, epoxy equivalent: 195 g/eq, softening point: 74°C, manufactured by Sumitomo Chemical Co., Ltd.) and novolak type brominated epoxy resin “BREN” (epoxy equivalent: 279, softening point: 80
~90°C, manufactured by Nippon Kayaku Co., Ltd.), phenol novolac resin H-1 (OH equivalent: 112 g/eq, softening point 80-88°C, manufactured by Meiwa Kasei Co., Ltd.) as a curing agent, and Reference Example 1. Addition salts A, B, C, D, H, and I were blended in the proportions shown in Table 6 to prepare a powder composition. The obtained powder composition was mixed in a lab mixer, and then melted and mixed on a hot plate at 95 to 105°C for 1 minute. The resulting mass was crushed again using a lab mixer and then classified using a 60-mesh sieve to obtain a powder sample for evaluation. Comparative example 1,8-diazabicyclo(5,4,
0) Since undecene-7 (DBU) is in a liquid state, it was melt-mixed with a curing agent in advance and then prepared in the same manner as above. Also, 2-phenyl-4-
Methylimidazole (2P4MZ) was prepared in the same manner as the addition salts (A to I) above. The pot life, gelling time,
Tg and adhesive strength were measured by the following methods, and the results are shown in Table 6. Gelation time: Gelation time at 177°C was measured in the same manner as in Examples 4-7. Pot life: Storage stability at 35°C was measured. That is, a stored sample was sampled at regular intervals, the gelation time at 177°C was measured, and the number of days in which the gelation time reached 90% or less of the gelation time immediately after preparation was defined as the pot life of the sample. Tg: Measured in the same manner as in Examples 4-7. Adhesive strength: Measured in the same manner as in Examples 1-3.

【table】

[Table] <Effects of the Invention> The adhesive of the present invention has excellent storage stability and adhesive strength, and can be rapidly cured at a practically advantageous low temperature. Furthermore, it can be applied to various uses, and can exhibit unique and excellent characteristics in each application. For example, good conductivity in one-component conductive adhesives, excellent fast curing properties in amine curing agent systems, good transparency of cured products in acid anhydride curing agent systems,
This is due to the effect of less heat loss in the dicyandiamide curing agent system.

Claims (1)

[Claims] 1. An adhesive containing an epoxy resin and a novel imidazole acid addition salt represented by the following general formula []. (In the formula, R ₁ represents a hydrogen atom, a C ₁ to C ₁₈ alkyl group, a benzyl group, or a β-cyanoethyl group, and R ₂ represents a hydrogen atom, a C ₁ to _{C 18} alkyl group, a phenyl group, or a halogen-substituted phenyl group. group or C ₁
~ Represents a _C4 alkyl group-substituted phenyl group. Further, R ₃ and R ₄ each represent a hydrogen atom, a C ₁ to C ₁₈ alkyl group, a phenyl group, a benzyl group, or a hydroxymethyl group.