Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1985-09-09
1987-04-28
Phynes, Lucille M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
528118, C08G 828, C08G 5940, C08G 6500
Patent
active
046615687
DESCRIPTION:
BRIEF SUMMARY
The present invention is concerned with an epoxy resin composition and a process for preparing electrical laminates using said composition. Heretofore, laminates used in the preparation of electrical circuit boards, have been conventionally produced by impregnating a supporting or reinforcing web with a resin composition, by passing the impregnated mat through a heated chamber where the resin composition is partially cured, and laminating one or more layers of the resin mat with a layer such as copper foil under the application of heat and pressure. The resin as employed for impregnating, in general, is referred to as "varnish", and the impregnated resin mat, conventionally, is referred to as "prepreg". The electrical laminate, in known manner, is processed into circuit boards.
In general, epoxy resins are employed for impregnating the reinforcing web. A typical epoxy resin composition for the application as presently described, comprises a brominated epoxy resin prepared from a diglycidyl ether of bisphenol A and a tetrabromobisphenol A, dicyandiamide as a hardener, an organic solvent such as acetone, and an accelerator or catalyst. Unfortunately, the glass transistion temperature of a cured epoxy resin prepared from this varnish composition is undesirably low, e.g. from 110.degree. to 135.degree. C. which often creates problems in the subsequent processing of the impregnated web. In addition, the dicyandiamide curing agent tends to crystallize in the varnish composition and also on the prepreg made therefrom.
An alternative varnish composition for application to a reinforcing web used in the production of electrical laminates, comprises a blend of a diglycidyl ether of bisphenol A and either bisphenol A or tetrabromobisphenol A and a dicyandiamide curing agent. The diglycidyl ether of bisphenol A is reacted in situ with bisphenol A and/or tetrabromobisphenol A and dicyandiamide during impregnation of the reinforcing web and the partial curing of the resin (see e.g. U.S. Pat. No. 3,738,862). Unfortunately, that varnish system does not exhibit higher glass transition temperatures than the varnish composition described previously. For these and other reasons, it is not widely employed commercially.
It is, therefore, highly desirable to provide an epoxy resin composition for the preparation of electrical laminates, which does not possess the afore-described deficiencies.
That problem is solved by the invention as defined in the claims.
Accordingly, in one form of embodiment the invention provides an epoxy resin composition comprising an epoxy resin, a hardener, an organic solvent and, optionally, an accelerator and other standard adjuncts and being characterized in that the hardener is the reaction product of one hexa-alkyl ether of a hexamethylol melamine having the general formula: ##STR1## wherein each R is individually an alkyl radical having from 1 to 4 carbon atoms with one polyhydric phenol and, optionally, one monohydric phenol, with the phenolic compound(s) and the hexa-alkyl ether of the hexamethylol melamine being reacted in an amount sufficient to provide at leat one reactive phenolic hydroxyl group for each alkoxy group.
When cured, the epoxy resin compositions of the present invention exhibit excellent properties. In particular, the cured resins exhibit substantially higher glass transistion temperatures, e.g. up to and exceeding 160.degree. C., than epoxy resins cured with dicyandiamide. In addition, the hardener component of the resin composition of the invention is soluble in most organic solvents generally used in preparing electrical laminates so that the problem of crystallization of the hardener as experienced with dicyandiamide, is effectively eliminated. Due to these and other properties, the resin compositions of the invention are particularly suitable as the varnish used in the preparation of electrical laminates.
In another form of embodiment, the invention is, therefore, directed to a process for preparing electrical laminates. The process comprises the following steps: an epoxy re
REFERENCES:
patent: 4393181 (1983-07-01), Allen
patent: 4467070 (1984-08-01), Kordomenos et al.
patent: 4537946 (1985-08-01), Lohse et al.
Klein Dieter H.
Koenig Raymond
Urscheler Robert
Karadzic Dragan J.
Phynes Lucille M.
The Dow Chemical Company
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