JPS6268874A - Adhesive composition - Google Patents

Abstract

PURPOSE:The titled composition having improved solvent resistance, undrooping properties and spot welding properties, containing a specific rubber modified epoxy resin, electrically conductive powder such as zinc, etc., dicyandiamide and silica fine powder in a specific ratio. CONSTITUTION:The aimed composition containing (A) 100pts.wt. rubber modified epoxy resin obtained by reacting (i) 70-95wt% liquid phenolic novolak type epoxy resin with (ii) 5-30wt% carboxyl-group containing liquid rubber-like polymer, (B) 5-50pts.wt. one or more electrically-conductive powder (preferably scaly graphite) selected from powder of zinc, aluminum, nickel, stainless steel and graphite, (C) 2-20pts.wt. dicyandiamide and (D) 0.5-10pts.wt. silica fine powder (having hydrophobic surface).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an adhesive composition, and more particularly to an adhesive composition containing an epoxy resin as one of its components.

[Conventional technology]

As is well known, epoxy resins have various excellent properties, such as heat resistance, anticorrosion, and adhesive properties, and they also have the advantage of being able to impart properties to the cured product depending on the purpose of use by changing the formulation. .

Furthermore, it can be used in various forms such as liquid, paste, sheet, and powder, making it extremely convenient to use. For this reason, epoxy resins are widely used in various fields.

Because epoxy resin has such excellent properties, it is used for structural and semi-structural purposes such as adhesion of steel plates for coils in electrical parts, adhesion of motor ferrite and magnets in electrical parts, and adhesion of hemming parts in automobile parts. It is used as an adhesive.

However, such adhesives are weak against solvents such as alcohol-based adhesives such as methanol and ethanol, gasohol-based mixtures of alcohol and gasoline, glycol-based adhesives, and water/glycol mixed systems, and cannot be used under these conditions. When an immersion test was conducted, the adhesive strength was significantly reduced and could not be put to practical use.

[Objective and Summary of the Invention] The present inventor has focused on the above-mentioned conventional difficulties, and as a result of continuing intensive research in order to solve these difficulties, a liquid phenol novolac type epoxy resin containing 70 to 95% by weight and carboxyl groups has been developed. A rubber-modified epoxy resin obtained by substantially reacting with 5 to 30% by weight of a rubbery polymer is used as a resin component,
In addition, by blending a specific amount of a specific curing agent component called dicyandiamide, conductive powder, and fine powder silica, the desired purpose was achieved, and the product had excellent solvent resistance, non-sagging properties, and spot weldability. It was discovered that an adhesive composition could be obtained, and the present invention was thus completed. That is, the present invention provides (a) liquid phenol novolac type epoxy resin 70-
95% by weight and carboxyl group-containing liquid rubbery polymer 5
100 parts by weight of a rubber-modified epoxy resin obtained by substantially reacting with ~30% by weight, (b) zinc, aluminum,
5 to 50 parts by weight of one or more conductive powders selected from the group consisting of nickel, stainless steel, and graphite powders, (c) 2 to 20 parts by weight of dicyandiamide, and (d)
The present invention relates to an adhesive composition characterized in that it contains 0.5 to 10 parts by weight of finely powdered silica.

[Effect]

In the adhesive composition of the present invention, by using a rubber-modified epoxy resin, a so-called sea-island structure is formed during heat curing, and this rubber phase relieves residual stress during curing, and the epoxy resin cured product Demonstrates the effect of preventing a decrease in adhesion. The rubber-modified epoxy resin used has a reaction between the carboxyl group of the liquid rubbery polymer and the epoxy resin, so there is a bond at the interface between the rubber phase and the epoxy resin phase, resulting in a two-phase system with a sea-island structure. Despite this, the strength of the cured resin is effectively maintained, and the physical properties do not deteriorate due to poor compatibility, which occurs when an epoxy resin and a rubbery polymer are simply mixed.

On the other hand, when a rubber-modified epoxy resin is not used, since there is no stress-relaxing component, residual stress is retained during curing, resulting in a resin coating that is strained and its adhesion reduced.

In the present invention, a liquid phenol novolac type epoxy resin is used as the raw material epoxy resin used to produce the rubber-modified epoxy resin from the viewpoint of solvent resistance. In particular, those having 2 to 4 epoxy groups in one molecule are preferred in order to increase the crosslinking density and maintain solvent resistance. At this time, if an epoxy resin other than the above-mentioned liquid phenol novolac type is used, such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, diluted aliphatic epoxy resin, glycidyl ester type epoxy resin, etc., the desired solvent resistance will not be achieved. This is not desirable as it tends to decrease. The reason for this is that with these other epoxy resins, the crosslinking density becomes coarse and the solvent resistance decreases. However, this does not preclude the use of other epoxy resins in combination, as long as the crosslinking density is not particularly significantly reduced, and they may be used together in an amount of about 30% by weight or less of the epoxy resin.

The carboxyl group-containing liquid rubbery polymer used in the present invention usually has a molecular weight of 1000 to 5000 and 1
The average number of carboxyl groups per molecule is 1
．． 5 to 2.5, preferably 1.8 to 2.4, and a linear one having carboxyl groups at both ends of the molecule is preferred. Further, from the viewpoint of compatibility with the epoxy resin, a liquid butadiene-acrylonitrile copolymer rubber containing 10 to 30% by weight, preferably 15 to 25% by weight of acrylonitrile is preferred.

Specific examples of these include, for example, Hycar CTBNs (BF Gutdrich Chemical (B, F), which are known as commercially available products).

(manufactured by Goodrich Chemical Co.), which contains about 10 to 30% by weight of acrylonitrile, is a liquid nitrile rubber with an acid equivalent of 0.07 per 100g, and has a number average molecular weight of about 3400. It is something. More specifically, r13 as CTBN
00X8J, r1300x9J, "130Qx13J,
Examples include r1300x15j.

The content of the liquid rubbery polymer in the rubber-modified epoxy resin used in the present invention is preferably 5 to 30% by weight.

If the rubbery polymer content is less than 5% by weight, it is difficult to fully exhibit the stress relaxation effect due to the addition of the rubbery polymer, and if it exceeds 30% by weight, the crosslinking density tends to become coarse and solvent resistance tends to decrease.

When producing the rubber-modified epoxy resin used in the present invention, the epoxy resin and the above-mentioned rubbery polymer are usually heated at a temperature of about 70 to 160°C to a temperature of 0.5 to 5.0 °C.
Melt and mix for about an hour. At this time, it is preferable that the rubber-modified epoxy resin obtained by melting contains substantially no carboxyl groups. However, it is not necessary to completely prevent carboxyl groups from being contained, and even if a small amount of carboxyl groups remains, it can be used sufficiently in the present invention, and usually about 10% or less of the initial number of carboxyl groups remains. Also good.

The epoxy equivalent of the rubber-modified epoxy resin used in the present invention is about 150 to 5,000, preferably about 170 to 3,000. This means that even after all the carboxyl groups of the rubbery polymer have reacted with the epoxy groups, they must still have the above epoxy equivalent weight.

The reason for this is that the rubber-modified epoxy resin needs to maintain reactivity as an epoxy resin. In order to obtain such a rubber-modified epoxy resin, for example, when producing the resin, 2 epoxy groups are added per equivalent of carboxyl group.
．． It is preferable to mix the carboxyl group-containing rubbery polymer and the epoxy resin so that the amount is 3 equivalents.

In the present invention, it is essential to use the above-mentioned rubber-modified epoxy resin, but the rubber-modified epoxy resin can be used not only alone but also in combination with other unmodified epoxy resins. cases are also included. When used together, the rubbery polymer content of the entire resin component should be 5 to 5.
Make it 30% by weight.

As a curing agent component in the present invention, it is essential to use a specific curing agent called dicyandiamide, which is usually used in an amount of 2 to 20 parts by weight per 100 parts by weight of rubber-modified epoxy resin.
It is used in parts by weight, preferably in the range of 4 to 10 parts by weight. By using this dicyandiamide as a curing agent component, the heat resistance and solvent resistance of the cured product and the storage stability of the adhesive composition are improved. In this case, if the amount of dicyandiamide is less than 2 parts by weight, curing will be delayed even if a curing accelerator is used in combination, and if it exceeds 20 parts by weight, dicyandiamide will be excessive and will tend to remain as an unreacted product.

In the present invention, a curing accelerator can be used in combination.

Examples of such curing accelerators include imidazoles, guanidines, substituted phenyldimethylureas, and tertiary amines.

In the present invention, conductive powder is used for the purpose of imparting spot weldability. At this time, as the conductive powder, one or more of zinc, aluminum, nickel, stainless steel, and graphite powder is used, and the amount used is 1/1 of the resin component.
5 to 50 parts by weight, preferably 10 to 4 parts by weight
It is 0 parts by weight. If the amount is less than 5 parts by weight, conductivity cannot be imparted and spot weldability is difficult to obtain. In addition, if the amount exceeds 50 parts by weight, the resin viscosity of the adhesive composition increases, making it difficult to apply during work, and the wettability of the adhesive surface may also be poor. A scale-like graphite powder is preferable because it is easily conductive. Note that conductivity here means having conductivity to the extent that spot welding is possible.

In the present invention, when applying the adhesive composition to an adherend and curing it, it is necessary to prevent the resin from flowing or extruding, and for this purpose, the composition must be made non-sagging. There is a need. For this purpose, finely powdered silica is added as a thixotropic agent to 100 parts by weight of the resin component.
The content is 5 to 10 parts by weight, preferably 1 to 8 parts by weight.

As this fine powder silica, any of those conventionally used as thixotropic agents can be effectively used, but especially hydrophobic fine powder silica in which the silanol groups on the surface of the silica are converted to siloxane bonds by dialkylsilane etc. Powdered silica is preferred from the viewpoint of non-sagging and stability over time.

A silane coupling agent may be added to the adhesive composition of the present invention, and this addition greatly improves the water resistance of the cured product. Examples of the silane coupling agent include X5iY3 (non-hydrolyzable organic groups such as
Y is preferably a silane compound represented by a halogen, a hydrolyzable group such as an alkoxy group, and specifically a silane compound represented by γ-
Examples include aminopropyltriethoxysilane, vinyltriacetoxysilane, and γ-glycidoxypropyltrimethoxysilane.

The silane coupling agent usually has an epoxy resin component of 100%.
It is used in an amount of 5 parts by weight or less, preferably about 0.2 to 3 parts by weight.

In addition, in the adhesive composition of the present invention, calcium carbonate, quartz powder, gypsum, kaolin, clay, mica, talc, dolomite, alumina, water, etc. may be added within a range that does not inhibit the conductivity for spot weldability. Japanese alumina, zircon,
Various fillers such as titanium compounds, molybdenum compounds, and antimony compounds, pigments, anti-aging agents, and various other commonly used additive components can be appropriately blended depending on the use and desired properties.

Examples and comparative examples of the present invention will be shown below.

In addition, in the following, all parts mean parts by weight.

Example 1 90 parts of a liquid phenol novolac type epoxy resin with an epoxy equivalent of 170 to 180 and a carboxyl group-containing liquid rubbery polymer (butadiene acrylonitrile copolymer rubber with a molecular weight of 3400 and a functional group number of 1.9 containing 18% by weight of acrylonitrile) 10 A rubber-modified epoxy resin having an epoxy equivalent of 200 to 220 was obtained by reacting at 150°C for 2 hours.

To 100 parts of this rubber-modified epoxy resin, 8 parts of dicyandiamide, 3-(3,4-dichlorophenyl)-1,1
- 5 parts dimethyl urea, 20 parts scaly graphite, T
- 1 part of glycidoxypropyltrimethoxysilane and 3 parts of Aerosil rRY200J (hydrophobic fine powder silica manufactured by Nippon Aerosil Co., Ltd.) were mixed in a melt mixing pot at room temperature for 1 hour and passed through three rolls to form an adhesive composition. I got it.

Example 2 An adhesive composition was obtained in the same manner as in Example 1 except that 20 parts of stainless steel powder was used instead of the flaky graphite used in Example 1.

Comparative Example 1 An adhesive composition was obtained in the same manner as in Example 1 except that 3 parts of the flaky graphite used in Example 1 was used.

Comparative Example 2 An adhesive composition was obtained in the same manner as in Example 1, except that 60 parts of the flaky graphite used in Example 1 was used.

Comparative Example 3 An adhesive composition was obtained in the same manner as in Example 1, except that 0.3 parts of Aerosil rRY200J used in Example 1 was used.

Comparative Example 4 An adhesive composition was obtained in the same manner as in Example 1 except that 12 parts of Aerosil rRY200J used in Example 1 was used.

Comparative Example 5 An adhesive composition was obtained in the same manner as in Example 1 except that 1 part of dicyandiamide used in Example 1 was used.

Comparative Example 6 An adhesive composition was obtained in the same manner as in Example 1 except that 22 parts of dicyandiamide used in Example 1 was used.

Comparative Example 7 Using 100 parts of a rubber-modified epoxy resin obtained by reacting 97 parts of the liquid phenol novolac type epoxy resin used in Example 1 and 3 parts of the carboxyl group-containing liquid rubbery polymer at 150°C for 2 hours, all other An adhesive composition was obtained in the same manner as in Example 1.

Comparative Example 8 Performed except for using 100 parts of a rubber-modified epoxy resin obtained by reacting 65 parts of the liquid phenol novolac type epoxy resin used in Example 1 and 35 parts of the carboxyl group-containing liquid rubbery polymer at 150°C for 2 hours. An adhesive composition was obtained in the same manner as in Example 1.

Example 3 50 parts of the liquid phenol novolak type epoxy resin used in Example 1, and carboxyl group-containing liquid rubbery polymer (molecular weight 2000, butadiene rubber with functional group number 2) 5
20 parts of a rubber-modified epoxy resin obtained by reacting 0 part at 150°C for 1 hour, 80 parts of the liquid phenol novolac type epoxy resin described above, 20 parts of aluminum powder, 10 parts of flaky graphite powder, 5 parts of dicyandiamide, l- (3
,4-Dichlorophenyl)-1,1-dimethylurea and 2 parts of Aerosil R380J (trade name of hydrophilic fine powder silica manufactured by Nippon Aerosil Co., Ltd.) were dissolved and mixed in a mixing pot for 1 hour at room temperature, and 3 bottles were mixed. An adhesive composition was obtained by passing through a roll.

Comparative Example 9 20 parts of a rubber-modified epoxy resin obtained by reacting 50 parts of a liquid bisphenol A type epoxy resin with an epoxy equivalent of 185 to 200 and 50 parts of the carboxyl group-containing liquid rubbery polymer used in Example 3 at 150°C for 1 hour. An adhesive composition was obtained in the same manner as in Example 3 except that 80 parts of the liquid bisphenol A type epoxy resin described above was used.

Each of the adhesive compositions obtained in the above Examples and Comparative Examples was cured under predetermined heat curing conditions shown in Tables 1 and 2 below, and various properties were tested. The results are also listed in Tables 1 and 2 below. The test method for each characteristic is as follows.

<Viscosity> Using a Brookfield rotational viscometer rotor No. 7,
It was measured according to IS-6833 at 20° C. and 10 rp+m.

<Flowability> 0.10 g of the adhesive composition was placed on an aluminum plate (30X100X
The coating was applied on a surface of 15° C. mm, placed on an inclined plate with an inclination angle of 45°, and cured under predetermined curing conditions, and the distance flowed from the lower end was measured.

<Gel time> Measured at 150°C according to JIS-5909.

<Tensile shear adhesive strength> According to JIS-6850, a steel plate (JIS
-G3141.5PCG-3D, 100X25X1.6
Measurements were made at 23°C using a single overlap (mm, single overlap).

<Gasohol resistance> A tensile shear adhesion test piece coated with an adhesive composition and cured in gasoline containing 12% by weight of methanol at 60°C was immersed for 40 days, then a tensile test was conducted, and the adhesive strength retention rate was determined as shown below. Judgment was made based on the criteria.

Adhesive strength retention rate, 80% or more...080-60%
...△ Less than 60% ... × Ethylene glycol resistance> A tensile shear adhesion test piece was immersed in ethylene glycol at 100° C. and evaluated in the same manner as the gasohol resistance.

<Spot Welding Resistance> Spot welding was performed on the bonded portion of the uncured tensile shear adhesion test piece (described above) coated with the adhesive composition, and whether or not welding was possible was determined by ○×.

Table 2 [Effects of the Invention] As described above, the adhesive composition of the present invention exhibits excellent properties in solvent resistance, spot weldability, and non-sagging property.

(that's all)

Claims (6)

[Claims] (1) (A) 100 parts by weight of a rubber-modified epoxy resin obtained by substantially reacting 70 to 95% by weight of a liquid phenol novolac type epoxy resin and 5 to 30% by weight of a carboxyl group-containing liquid rubbery polymer; ) 5 to 50 parts by weight of one or more conductive powders selected from the group consisting of zinc, aluminum, nickel, stainless steel, and graphite powders, (c) 2 to 20 parts by weight of dicyandiamide, and (d) finely powdered silica. 0.5~10
An adhesive composition comprising: parts by weight. (2) The adhesive composition according to claim 1, wherein the liquid phenol novolac type epoxy resin has 2 to 4 epoxy groups in one molecule. (3) The adhesive composition according to claim 1 or 2, wherein the conductive powder is flaky graphite. (4) Claim 1, wherein the carboxyl group-containing liquid rubbery polymer is a liquid butadiene acrylonitrile copolymer rubber containing 10 to 30% by weight of acrylonitrile.
The adhesive composition according to any one of Items 1 to 3. (5) The adhesive composition according to any one of claims 1 to 4, wherein the surface of the finely powdered silica is hydrophobic. (6) The epoxy resin composition according to any one of claims 1 to 5, which contains a silane coupling agent.