Direct Adhesion between Electroless Nickel-P Plated Metals and NBR Compounds during Curing

Abstract

Abstract In this study, an examination was made of the various causative factors for the direct adhesion between nickel-P alloy (nickel alloy) and acrylonitrile-butadiene rubber (NBR) compounds during curing. In a high sulfur curing system (SV), direct adhesion was found to depend on time of exposure to air and not to occur after more than 48 h of exposure. In the peroxide curing system (PV), there was no adhesion at all regardless of the exposure time. The addition of triazine thiols to NBR compounds resulted in adhesion between NBR compounds and nickel alloy for exposures exceeding 48 h. Typical curing systems such as SV, low sulfur curing (LSV), sulfurless curing (SLV), and PV gave good NBR-nickel adherends when the NBR compounds contained the monosodium salt of triazine trithiol (TTN). In these system, peel strength in the adherends increased with triazine thiols, to a maximum, and then decreased. This parameter was influenced by the chemical structures of triazine thiols, such as those containing thiol(-SH) and the sodium salt of thiol (-SNa) groups, and by the exposure of nickel alloy to air. Peel strength decreased with the formation of nickel oxides on the surface. When the nickel oxides were removed from the nickel alloy surface, peel strength was recovered. High peel-strength adhesion between NBR compounds with TTN and nickel alloy is due to the formation of interfacial bonds and reinforcement layers at the adhesive interface during curing. Adherends consisting of NBR compounds with TTN and nickel alloy generally showed high heat resistance, oil resistance, and water resistance. The values for these parameters differed accordingly to the curing system and were optimal in the following order: SV < SV with TTN < PV with TTN.