Film formation on precious metal surfaces in the presence of epoxy resins

The purpose of this study was to determine the effect of exposure conditions, resin composition, and resin treatment on film formation on metal surfaces exposed to epoxy resin.

Epoxy rods were prepared from novolac hardened by 4-4' methylenedianiline (MDA). The curing and post curing temperatures were 60, 125 °C and 125, 160 °C. The composition of the epoxies used were 27.0 and 31. 5 parts (MDA) per 100 parts epoxy.

The metals investigated were pure gold, silver, and copper; gold-copper alloys; gold-silver alloys; and electroformed gold-copper alloys. The alloys ranged in composition from 75 to 92 per cent gold. These samples were cleaned, weighed, placed in individual, covered, glass containers with the epoxy rods, and then were exposed at 30, 60, and 90 °C.

The change in weight of the metal samples was determined at intervals of about. 30 days for five months. Weight increases of 0.1 to 0.4 milligram were observed for the samples exposed to the epoxy rods, and were negligible for samples stored without epoxy rods.

The contaminating materials, apparently, are organic compounds consisting of unreacted monomer and degradation products. The film forms from a heavy, stagnant, low-lying, vapor-phase from the epoxy, with the vapors adsorbed or reacted on the surface of the metal samples. Film formation is not affected to any appreciable extent by the combined effect of increased curing temperatures and increased hardener content. The effect of increasing the temperature from 30 °C to 60 or 90 °C, on the rate of film formation was inconclusive. Epoxy film formation was observed on all metal samples tested, pure gold, copper, and silver; gold-copper and gold-silver alloys. The metal composition affects the rate of film formation with the rate increasing with decreased golJ composition for both copper and silver alloys.