JPH0196278A - Adhesive - Google Patents

Abstract

PURPOSE:To obtain an adhesive having excellent storage stability as well as excellent adhesive strength, by blending an epoxy resin with a novel imidazole acid addition salt used a curing (accelerating) agent. CONSTITUTION:An epoxy resin is blended with a novel imidazole acid addition salt expressed by formula I (R1 is H, 1-18C alkyl, etc.; R2 is H, phenyl, etc.; R3 and R4 are H or benzyl; n is 1 or 2) used as a curing (accelerating) agent to provide the adhesive. Further more, as the compound expressed by formula I, e.g. 2,6-dihydroxybenzoic acid addition salt of 2-phenyl-4-methyl-imidazole. The compound expressed by formula I is e.g. obtained by melting and blending an imidazole expressed by formula II with a hydroxy-benzoic acid expressed by formula III at a molar ratio of 0.7-1.3 times mol. while heating.

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 are common, in which the epoxy resin component and the curing component are stored separately, 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-deep type adhesive that does not harden as it is even if an epoxy resin and a hardening agent are mixed in advance.

Moreover, the latent-deep type adhesive must not cause unexpected gelation when stored at room temperature, that is, it must have excellent storage stability.

High melting point 2-phenyl-4- as a latent curing accelerator
A liquid-type conductive adhesive for electronic components using methyl-5-hydroxymethylimidazole is known (Japanese Patent Application Laid-open No.
9-142270).

<Problems to be Solved by the Invention> However, although the deep type 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 trimellitate, which is known as a latent curing accelerator ("New Epoxy Resin J, Shokodo, 198
When we investigated a latent-deep type adhesive using the same paper (published on May 10, 2013), we found that although the storage stability was good and the adhesive strength was improved to some extent, it was still unsatisfactory.

That is, there is a strong desire for an adhesive that has both excellent storage stability and adhesive strength.

The inventors of the present invention conducted extensive research and discovered a new addition salt of imidazole acid. When this compound is used as an epoxy resin curing agent or curing accelerator, it has excellent storage stability and improved adhesive strength. The present invention has been completed based on the discovery that the present invention is excellent, and furthermore, it acts as a so-called latent curing agent or latent curing accelerator, which cures quickly when heated and cured at a relatively low temperature.

Means for Solving the Problems〉 That is, the present invention provides an epoxy resin and the following general formula [I
] This is an epoxy resin adhesive containing a novel imidazole acid addition salt (hereinafter referred to as imidazole acid addition salt).

(In the formula, R1 is a hydrogen atom, a C1 to CI8 alkyl group,
Represents a benzyl group or β-cyanoethyl group, R2
is a hydrogen atom, an alkyl group of 01 to CI8, a phenyl group,
Represents a halogen-substituted phenyl group or a 01-C4 alkyl group-substituted phenyl group. Further, R3 and R4 each represent a hydrogen atom, a C1 to C18 alkyl group, a phenyl group, a benzyl group or a hydroxymethyl group, and n is 1 or 2. ) 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) An imidazole compound represented by the following general formula (II) (hereinafter referred to as "imidazole [■]") and a hydroxybenzoic acid represented by the following general formula (I[[) (hereinafter referred to as "imidazole [■]")
(referred to as "Hydroxybenzoic acid [■]") is dissolved in an organic solvent and then mixed; or (B) in a solvent-free system, imidazole CI [) and hydroxybenzoic acid (I []) are heated and melted. How to mix in the state.

\OH) n (In the formula, R1-R4 and n represent the same meanings as in the above-mentioned -tubular type [Engine]) Specific examples of such imidazole CI[] include 2-ethyl-4-methylimidazole, 2-7enyl-4-methylimidazole, 2-phenylimidazole, 1-(β
-cyanoethyl)2-ethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole,
2-Phenyl-4,5-dihydroxymethylimidazole, 2-p-1 Louis-4-methylimidazole, 2-
Examples include undecylimidazole, 2-phenyl-4,5-dibenzylimidazole, and 2-phenyl-5-benzylimidazole.

Further, specific examples of hydroxybenzoic acid CI [[) include 2,3-dihydroxybenzoic acid, 2.4-dihydroxybenzoic acid, 2.5-dihydroxybenzoic acid, 2,6-
Examples include dihydroxybenzoic acid, 3.5-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 2-hydroxybenzoic acid, 3-hydroxybenzoic acid, and 4-hydroxybenzoic acid. Among 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 (I[) to imidazole [Ir] is between 0.7 and 1.3.
A double molar range is preferred.

In the preparation method (8), examples of the solvent used include esters such as ethyl #acid and methyl acetate, ethers such as diethyl ether and dimethyl ether, ketones such as acetone and methyl ethyl getone, 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, it is used as a composition of imidazole acid addition salt and epoxy resin, and when it is used as a curing accelerator for epoxy resin, it is used as a composition of imidazole acid addition salt, epoxy resin, and curing agent. It is used in the form of a composition with.

When imidazole acid addition salt is used as a curing agent, it is usually used in an amount of 0.1 to 200 parts by weight, preferably 1 to 100 parts by weight, per 100 parts by weight of epoxy resin, and when used as a curing accelerator, it is usually used 0.1 to 100 parts by weight, preferably 0.1 parts by weight per 100 parts by weight of epoxy resin
~10 parts by weight are used. Imidazole acid addition salts exhibit the effect of improving storage stability and adhesive strength by being contained in epoxy resin compositions as a main curing agent or curing accelerator, but within the range of not impairing the properties of imidazole acid addition salts. It may contain other curing agents or curing accelerators.

Other curing agents used here are not particularly limited as long as they are normal epoxy resin curing agents, such as phenol novolak, cresol novolak, 3.3--
Phenolic compounds such as diallyl-4,4''-dihydroxybisphenol A, 4,4''-diaminodiphenylsulfone, 3,3-1diaminodiphenylsulfone, 4,4-methylenebis(2-ethylaniline)
, amine compounds such as 4.4-methylenebis(2,6-dinitylaniline), 4.4-methylenebis(2-ethyl-6-methylaniline), phthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydro Acid anhydrides such as phthalic anhydride, trimellitic anhydride, and anophylomellitic acid, dicyandiamide and aromatic amine adducts of dicyandiamide (modified dicyandiamide), diaminomaleonitrile and its derivatives, melamine and its derivatives,
Examples include amine imide compounds, polyamines, addition compounds of epoxy and imidazoles, hydrazide compounds such as adipic acid hydrazide and isophthalic acid hydrazide, and imidazoles.

The epoxy resin used in the adhesive of the present invention is not particularly limited as long as it has one or more epoxy groups per molecule; for example, bisphenol A diglycidyl ether, tetrabromo bisphenol A diglycidyl ether, loglucinol triglycidyl ether, tetraglycidyl diaminodiphenyl, methane,
triglycidyl meta-aminophenol, phenol novolac type epoxy, cresol novolac type epoxy,
Bisphenol C glycidyl ether, diglycidyl ether of 1,5-naphthalenediol, diglycidyl ether of 1,6-naphthalenediol, 4,4°-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-Tetraethyl biphenyl, resorcin diglycidyl ether, neopentyl glycol diglycidyl ether, allyl glycidyl ether, phenyl glycidyl ether, P-tert-butylphenyl glycidyl ether,
Adipic acid diglycidyl ester, 0-phthalic acid diglycidyl ester, dibromophenyl glycidyl ether, glycidyl phthalimide, methyl glycidyl ether-p-tert-butylphenol, vinylcyclohexene dioxide, tris(4-hydroxyphenyl)
Examples include triglycidyl ether of methane.

The adhesive of the present invention contains the epoxy resin and the 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.

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, and basic magnesium silicate. , fired 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 fibrous reinforcing agents and fillers, For example, inorganic fibers such as glass fiber, rock wool, ceramic fiber, asbestos and carbon fiber, synthetic fibers such as paper, pulp, wood flour, linters and polyamide fibers, silver powder in the form of fine particles or flakes, copper powder, nickel powder. Examples include metals such as.

Examples of diluents include liquid low-viscosity epoxy compounds such as the aforementioned phenyl glycidyl ether and vinyl cyclohexene dioxide, as well as cellosolves such as butyl cellosolve acetate, ethyl cellosolve, butyl cellosolve, and γ.
-Lactones such as butyrolactone, 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,
Inorganic phosphorus such as cadmium yellow, cadmium red, red phosphorus,
Examples include organic phosphorus such as triphenyl phosphate, decabromodiphenyl ether, and bromine compounds such as hexabromobenzene.

The means for mixing the components of the adhesive of the present invention is not particularly limited, and any method such as heating and melt mixing, kneading using a roll, kneader, etc., mixing using an appropriate organic solvent, and dry mixing may be used. Can be adopted.

<Function> Imidazole acid addition salt is a basic acid addition salt of imidazole protected with droxybenzoic acid, so it is 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. In other words, the basicity of imidazole in imidazole addition salts is protected by hydroxybenzoic acid at around room temperature and its function as a curing agent or curing accelerator is suppressed, but when heated to the curing temperature, the salt dissociates. and exhibits 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, for example, for adhesion of metals, plastics, wood, concrete, glass, ceramics, etc. All kinds of epoxy adhesives, including electrical adhesives or insulating adhesives for capacitors, semiconductor bonding, membrane switches, etc., as well as adhesives for electronic/electrical parts such as light-receiving elements, light-emitting elements, and liquid crystal parts. useful in the field.

EXAMPLES Next, examples will be shown to specifically explain the present invention, but these examples are not intended to limit the present invention.

Example 1 (Preparation example of imidazole acid addition salt) 2.6-dihydroxybenzoic acid 4. Og(2,60XI
2 mol) was dissolved in 90 ml of ethyl acetate.

Separately, 3.28 t (2,07X 10-2 mol) of 2-phenyl-4-methylimidazole (manufactured by Shikoku Kasei) was dissolved in 240 ml of ethyl acetate while heating.
This was added dropwise to the dihydroxybenzoic acid solution prepared above while stirring.

After filtering the obtained slurry liquid, the crystals were dried. Yield 5.88g, mp 210-216°C.

[Confirm the formation of acid addition salt by measuring L spectrum,
Moreover, it was confirmed by elemental analysis 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 operations. Imidazole acid addition salt I is prepared by mixing equimolar amounts of 2-phenyl-4-methyl-5-1 nitroxymethylimidazole and 2,6-dihydroxybenzoic acid, and
It was prepared by heating and melting.

Table 1 shows the melting points of these imidazole acid addition salts.

Table 1 Examples 2 to 5 (-Example of application as deep conductive adhesive) Bisphenol F type epoxy resin (epoxy equivalent 180.25°C viscosity 26 voids), phenyl glycidyl ether and addition prepared in Example 1 Salts A, E, F, and G are shown in Table 2.
(Here, the addition salt acts both as a curing agent and a curing accelerator). To these formulations, scaly silver powder having a thickness of 0.2 to 0.6 μm and a size of 2 to 10 μm was added in the proportions shown in Table 2, and the mixture was kneaded with a three-roll mill to prepare a conductive paste. - The pot life, adhesive strength, and specific resistance of the deep conductive adhesive were measured by the following methods, and the results are shown in Table 2.

The pot-life two-paste composition was stored at 25° C., and the mixing state was checked over time using a Subachella, and the number of days until stirring became impossible was measured.

Adhesive strength: 30#IX 25n++nX0.25IW
The tensile shear strength at 25° C. was measured using a test piece of 4270 mm (thickness).

Specific resistance = 10 pieces (width) x 50 sides (length) x O1
Measure the resistance value of one conductor width (thickness) and calculate the volume resistivity (Ω ・(to)).

As a substitute, 2-phenyl-4-methyl-5-hydroxymethylimidazole (
2P4MH2) (manufactured by Shikoku Kasei ■) and trimellitic acid salt of 1-cyanoethyl-2-ethylimidazole (2E
4MZ-CNS) (manufactured by Shikoku Kasei ■) in the proportions shown in Table 2, and otherwise prepared in the same manner as in Examples 2 to 5 above, and the physical properties were measured. The results obtained are shown in Table 2.

As is clear from Table 2, the adhesive of the present invention has good pot life and adhesive strength, but 2E4MZ-CN
When S and 2P4MH2 are used, the adhesive strength is weak. Furthermore, when 2E4MZ-CNS and 2P4MH2 are used, their specific resistance is too large to be used as a conductive adhesive for low-temperature curing.

Examples 6 to 9 (Application example of amine curing agent as curing accelerator) Bisphenol A type epoxy resin (manufactured by Yuka Shell ■, "Ebiko 828"), diaminodiphenylsulfone, and the addition prepared in Example 1 Salts A, B, C, and F were blended in the proportions shown in Table 3, and kneaded using a three-roll mill.

For these compositions, adhesive strength, glass transition temperature (
Tgl bot life and gelation time were measured by the following methods, and the results are shown in Table 3.

Adhesive strength: 10an x 2.50 x 0゜2 as adhesive
The tensile front strength at 25° C. was measured using an Aλ plate of (thickness) which was polished with a #120 sand vapor and then washed with trichlene.

Tg: Measured using DSC (manufactured by Daini Seikosha, Model 580) at a temperature increase rate of 40° C./in.

Pot life: Measure the number of days until a sample stored at a constant temperature of 35°C becomes unable to be stirred with a spatula.

Gelation time: Measured according to the hot plate method (JIS5909).

For comparison, a resin composition was prepared using salicylic acid instead of addition salts A, B, C, and P in the proportions shown in Table 3, and the other procedures were the same as above, and the physical properties of the resin composition were measured. Table 3
The results are shown below.

As is clear from Table 3, the adhesive of the present invention has a short gelation time, a long pot life, and high adhesive strength.

Examples 10 to 12 (Application example of acid anhydride curing agent as curing accelerator) Bisphenol A type epoxy resin (manufactured by Yuka Shell ■, "
Epicote 828”), 4-methylcyclohexane-1
, 2-dicarboxylic anhydride (Me-HHPA) (manufactured by Tokyo Kasei ■, reagent grade 1) and addition salt A prepared in Example 1
, F, and G were blended in the proportions shown in Table 4, and kneaded using a three-roll mill. For these compositions, the adhesive strength, Tg, 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 6-9.

Pot life: The number of days until stirring of the sample stored at 20°C with a spatula became impossible was measured.

Transparency of cured product: 40nnnX 15mmX 1ra
The cured product having a thickness of m (thickness) was visually observed.

For comparison, instead of the above addition salts A, F, and G, triphenylphosphine (manufactured by K.I. Kasei ■) was blended in the proportions shown in Table 4, and a resin composition was prepared in the same manner as above.
Its physical properties were measured.

Table 4 shows the results.

As is clear from Table 4, the adhesive of the comparative example has an unsatisfactory pot life, but the adhesive of the present invention is excellent in both adhesive strength and pot life, and is also excellent in transparency.

Examples 13 to 14 (Application example as a curing accelerator when dicyandiamide is used as a curing agent) Bisphenol A type epoxy resin (manufactured by Yuka Shell (■,
'1 Epicote 828''), dicyandiamide, and addition salts A and F prepared in Example 1 were blended in the proportions shown in Table 5, and kneaded using a three-roll mill.

For these compositions, adhesive strength, gelation time, pot life, and heat loss during curing and at high temperatures were measured by the following methods, and the results are shown in Table 5.

Adhesion strength: Measured in the same manner as in Examples 2-5.

Pot life: Measured in the same manner as in Examples 10-12.

Gelation time: Measured in the same manner as in Examples 6-9.

Loss on heating A container made of aluminum was used, placed in the open, left for a specified period of time, and the loss on heating was measured.

Table 5 Note a) Curing conditions: 120°C, 1 hour.

b) A) was further left at 200°C for 5 hours.

C) Still stirrable at 30 days.

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 15 to 20 (Application example as powder adhesive) 11 Sumi Epoxy "ESCN-19" as epoxy resin
5XL (o-cresol novolac type epoxy resin, epoxy equivalent 195 g/eq, softening point 74°C, manufactured by Sumitomo Chemical Co., Ltd.) and novolac type materialized epoxy resin "BR"
EN'' (epoxy equivalent: 279, softening point: 80-90°C, manufactured by Nippon Kayaku ■) and phenol novolak resin H-1 (OH equivalent: 112 g/eq, softening point: 80-88°C) as a curing agent.
, manufactured by Meisho Kasei ■) and addition salt A prepared in Example 1,
B, C, D, H, and I were blended in the proportions shown in Table 6 to prepare a powder composition.

After mixing the obtained powder composition with a lab mixer,
The mixture was melted and mixed for 1 minute on a hot plate at 5 to 105°C. The resulting mass was pulverized again using a lab mixer, and then classified using a 60-mesh sieve to obtain a powder sample for evaluation.

Since 1,8-diazabicyclo(5,4,0)undecene-7 (DBU) of the comparative example is liquid, it was melt-mixed with a curing agent in advance and then prepared by the same operation as above.

In addition, 2-phenyl-4-methylimidazole (2P4
MZ) was prepared in the same manner as the above addition salts (A to ■).

The pot life, gelation time, Tg, and adhesive strength of these compositions were measured by the following methods, and the results are shown in Table 6.

Gelation time = gelation time at 177°C Example 6
Measurement was performed in the same manner as in steps 9 to 9.

Pot life: Storage stability at 35°C was measured.

i.e. preserved sample sampled at regular intervals and gelation at 177°C. Measure the time and gel immediately after preparation. Number of days when the time was less than 90% The pot life of the sample And so.

Tg: Measured in the same manner as in Examples 6-9.

Adhesive strength: Measured in the same manner as in Examples 2 to 4.6 <Effects of the invention> The adhesive of the present invention has excellent storage stability and adhesive strength,
Moreover, it 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 electrical conductivity in volumetric conductive adhesives, excellent fast curing in amine hardener systems, good transparency of the cured product in acid anhydride hardener systems, low heating loss in dicyandiamide hardener systems, etc. This is the effect of

Claims (2)

[Claims] (1) An adhesive containing an epoxy resin and a novel imidazole acid addition salt represented by the following general formula [I]. ▲There are mathematical formulas, chemical formulas, tables, etc.▼...[I] (In the formula, R_1 represents a hydrogen atom, an alkyl group of C_1 to C_1_8, a benzyl group, or a β-cyanoethyl group, and R_2 represents a hydrogen atom, and Alkyl group, phenyl group, halogen-substituted phenyl group or C_
1 to C_4 represents an alkyl group-substituted phenyl group, and R_3 and R_4 are each a hydrogen atom, C_1 to C_4
_1_8 represents an alkyl group, phenyl group, benzyl group or hydroxymethyl group, and n is 1 or 2. ) (2) The adhesive according to claim 1, wherein the novel imidazole acid addition salt is a compound where n is 2 in the general formula [I].