JPH0457877A - Conductive adhesive - Google Patents

Abstract

PURPOSE:To improve one-liquid rapid curing property at low temperatures and long-term storage stability by dissolving an epoxy resin, a specific curing agent, a metallic filler and an isocyanate compound in an organic solvent composed primarily of butyl acetate. CONSTITUTION:An epoxy compound (e.g. glycidyl-etherified bisphenol A epoxy resin) is made to react with an imidazole compound to obtain a reaction product of a curing agent (a). Separately, butyl acetate and, if necessary, other organic solvent are mixed to obtain an organic solvent (b) composed mainly of the butyl acetate. The title adhesive is obtained by dissolving 100 pts.wt. (pts. hereunder) epoxy resin (c) (e.g. glycidyl-etherified bisphenol F epoxy resin), 5 - 40 pts. component (a), a conductive metallic filler (d) (e.g. silver powder), the ratio of the component (d) to the components (a) and (c) being 70 - 85 to 30 - 15, and isocyanate compound (e) (e.g. tolylene diisocyanate) in an amount of 0.1 - 10 pts. based on 100 pts. component (a), in the component (b).

Description

[Detailed description of the invention] (Industrial use portion W) The present invention relates to an adhesive composition having electrical conductivity.

(Prior Art) Conventionally, a conductive adhesive in which a conductive metal filler is dispersed in a curable resin has been used. Curing methods include those using energy such as heat, light, and electron beams, and curing of epoxy resins by heat is particularly frequently used. In addition, due to the speeding up of factory production lines and the heat resistance temperature of conductive adhesive adherends, conductive adhesives that harden at low temperatures and in a short time have been put into practical use.

(This is a problem that the invention aims to solve!) However, two-component adhesives are often used as low-temperature, short-curing adhesives, which pose a serious problem in terms of workability.

-Although liquid-based adhesives have been proposed, conventionally known epoxy resin-based one-component conductive adhesives have problems in terms of long-term storage at room temperature.

In view of the above circumstances, an object of the present invention is to provide a one-component, low-temperature, short-curing conductive adhesive that has excellent long-term storage stability at room temperature.

(Means for Solving the Problems) The conductive adhesive of the present invention comprises an epoxy resin, a curing agent made of a reaction product of an epoxy compound and an imidazole compound, a conductive metal filler, and an isocyanate compound with butyl acetate as an essential component. It has a structure in which it is dissolved or dispersed in an organic solvent to form a solution or paste.

As the epoxy compound in the curing agent made of the reaction product of an epoxy compound and an imidazole compound used in the present invention, either a monoepoxy compound or a polyepoxy compound can be used, but they are easy to obtain and chemically stable. From this point of view, polyepoxy compounds are preferred.

For example, glycidyl ether type epoxy resin of bisphenol A, glycidyl ether type epoxy resin of glycerin, glycidyl ether type epoxy resin of polyalkylene oxide, glycidyl ester type epoxy resin of dimer acid, glycidyl ether type epoxy resin of phenol novolak, brominated bisphenol A. Examples include glycidyl ether type epoxy resin of , glycidyl ether type epoxy resin of bisphenol F, alicyclic type epoxy resin, and the like. Particularly preferred is a bisphenol A glycidyl ether type epoxy resin.

Further, examples of the imidazole compound include imidazole or a derivative thereof, and an adduct of an imidazole compound and an epoxy compound. As a specific example, 2
-Methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, 2-heptadeciimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-
Examples include methylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, and the like.

An example of the reaction between an epoxy compound and an imidazole compound using specific compounds is as follows.

Epoxy-imidazole compounds as curing agents, generally used in powder form. Such curing agents are known per se, and are disclosed in, for example, JP-A-60-99179 and JP-A-1-1.
No. 13480.

Epoxy resins that can be cured with these curing agents include:
Polyepoxy compounds with epoxy-imidazole compounds as hardeners can be used. Particularly preferred are bisphenol A type glycidyl ether type epoxy resins or bisphenol F type glycidyl ether type epoxy resins.

The amount of the curing agent added is usually 5 to 40 parts by weight, preferably 10 to 30 parts by weight, per 100 parts by weight of the epoxy resin. If the amount of curing agent is less than the above range, the epoxy resin cannot be sufficiently cured, and if the amount of curing agent is more than the above range, curing at room temperature will proceed excessively, leading to an increase in viscosity during storage.

Next, as metal fillers for obtaining conductivity, silver,
Conventionally known conductive metal fillers, such as powders of copper, nickel, carbon, etc., and inorganic or polymeric cores coated with metal, can be used as appropriate. These may be used alone or in combination of two or more, and silver powder is particularly preferred.

The mixing ratio of the conductive metal filler and the curing agent to the epoxy resin is preferably 70:30 to 85:15 by weight.

The conductive adhesive of the present invention requires that an isocyanate compound is further added to the above composition, and that a solvent containing butyl acetate as a main component is used as a diluting solvent.

Isocyanate compounds to be used include, for example, monoisocyanate compounds such as phenyl isocyanate and tolyl isocyanate; polyesters such as tetramethylene diisocyanate, hexamethylene diisocyanate, tolylene diisocyanate, xylene diisocyanate, diphenylmethane diisocyanate, isopropylene cyclohexyl isocyanate, and lysine isocyanate. Examples include isocyanate compounds, and among these, tolylene diisocyanate is particularly desirable.

At this time, the isocyanate compound added is 100% of the curing agent.
It is usually 01 to 10 parts by weight, preferably 1 to 5 parts by weight. If the amount added is less than 0.1 part by weight, the storage stability will be insufficient, and if it is more than 10 parts by weight, the curability will be significantly reduced and no electrical conductivity will be obtained.

As the method for adding the isocyanate compound, any of the following methods are effective: adding it when kneading the conductive filler into the resin, adding it to the curing agent in advance, adding it to the resin in advance, etc. It is also preferable to use a catalyst such as octyltin or dibutyltin dilaurate, which accelerates the reaction of the isocyanate compound.

As the diluting solvent, butyl acetate alone or a mixed organic solvent containing butyl acetate as a main component is used.

The amount of the diluting solvent added varies depending on the coating machine used when applying the adhesive, but it is usually such an amount that the viscosity of the solution or paste obtained is in the range of 5,000 to 400,000 cp1, preferably 20,000 to 70,000 ep.

By selectively using an isocyanate compound and butyl acetate in combination in this manner, remarkable storage stability at an appropriate viscosity can be imparted to a conductive adhesive having low-temperature, fast-curing characteristics. This is because the isocyanate compound blocks the surface of the curing agent, preventing the tertiary amine in the curing agent molecules from being exposed to the surface, and the effect of suppressing the reaction with the epoxy resin is noticeable when combined with butyl acetate. It is presumed that this is to do so.

In this way, a one-component low-temperature, short-time curing conductive adhesive with excellent long-term storage stability at room temperature is obtained.

Next, the present invention will be explained with reference to Examples and Comparative Examples.

Comparative Example and Example: 18 g of Epicoat 807 (bisphenol F type epoxy resin manufactured by Yuka Shell Epoxy ■) and Amicure MY-2
4 (Epoxy imidazole curing agent manufactured by Ajinomoto Co.) 4g
, and 78 g of scaly silver powder (particle size: 05 to 5 μm) were kneaded using three rolls.

Storage of this composition diluted with 8 g of toluene (composition A), diluted with 8 g of n-butyl acetate (composition B), and not diluted with solvent (composition C) The stability was compared. Show the results under your breath.

Tolylene diisocyanate was added to the composition B blended in the comparative example, Ig (composition), 2g (composition E),
4g (composition F) was added and the storage stability of each was compared. The results are shown below.

1 Viscosity change Initial viscosity 25°C x 7 days Composition A 38000 eP Gelled composition B 38000 cP 43
000 eP Composition C200000eP 20
5000 eP Composition D 38000 eP
40000 eP Composition E a800
0 cP 39000 eP Composition F
38000 eP 38000 eP2 Initial change in volume resistivity 25°C x 7 days 1 glaze A2-3 cutting 0-3Ω -m= Composition B 2-3X 10'-'Ωam 3-8X
10-'Ω・cm Composition C5-7X10-'Ω (1)
7-9X10-3Ω・Gloss composition D2-3X10-3Ω×Toe 4X10-'Ω・Nishiki composition E 3-4X10"
Ωan 3-4X 10-3Ω(2) Composition F 6
-7X10-3Ωam [y"7X10-'Ω帥--
- cannot be measured because the composition gelled 25°C x 30 days Gelled Gelled 48000 eP 43000 eP 39000 cP 25°C x 30 days 4-5 -3Ω 聽衷设计 To the composition blended in Example 1, 01g of octyltin was added as an isocyanate catalyst (referred to as composition G), and 0.1g of dibutyltin dilaurate was added (referred to as composition G).
The storage stability of composition H) was compared. The results are shown below.

1 Viscosity change Initial viscosity 25°C x 30 days Composition G 43000 eP 440
00 cP composition H43000cP 4800
0 cP2, early stage of depression 25℃ x 30 days 1-G 4-5xlO-30-am 4-5x
lOQam ball H4~5X10'-3Ωe+n 5-
6X10-3Ω (7) (Octyltin and dibutyltin dilaurate act as catalysts that promote blocking of tertiary amines exposed on the surface by isocyanate, and do not have much effect on viscosity or volume resistivity. (In order to quickly stabilize the viscosity and volume resistivity of the composition, the viscosity was measured using a BH type viscometer (No. 6 rotor, 20 rpm) in the comparative examples and examples above. The adhesive is at room temperature (25℃)
) as soon as the test was returned. To measure the volume resistivity value, conductive adhesive was applied to glass with a film thickness of 70 to 100μ, and the conductor was applied to a diameter of 1crn and 7clI+ and cured at 100°C for 30 minutes.The resistance value (R ) was measured using a digital multimeter, and the value was substituted into the following formula to calculate the volume resistivity value.

Volume specific resistance value = (RXt15)xl 0-' Ω(
2) R: Resistance value Ω t: Film thickness μ and adhesive strength of conductive adhesive on glass film thickness 70-10
Maintaining the 0 μ mark, apply the coating to a width of 5 cm and a length of 7 crn, and cure it with 5 ceramic chips (4.5 m) at 100°C for 30 minutes. When the adhesive strength of the conductive adhesives of the Examples was measured by pressing the chip against the chip at an angle of 100° and reading the strength when the chip fell off, the adhesive strength of the conductive adhesives of the Examples was all 100 kgf/ai1 or more.

Claims (1)

[Claims] A conductive adhesive prepared by dissolving or dispersing an epoxy resin, a curing agent made of a reaction product of an epoxy compound and an imidazole compound, a conductive metal filler, and an isocyanate compound in an organic solvent containing butyl acetate as an essential component.