Silicone elastomer seals for molded plastic parts

Abstract

A process is described for bonding a silicone elastomer seal to a molded plastic part such as a plastic electric connector. Prior to molding aromatic polyamide pellets are pretreated with an aminofunctional silicone fluid. The pretreated polymer pellets are then molded in the presence of moisture to form a molded plastic part. Molding is performed at a temperature sufficient to chemically graft the amino function of the silicone fluid to the aromatic carbonyl function of the aromatic polyamide and to form silanol groups within the aminofunctional silicone fluid. The molded plastic part is coated with an organofunctional alkoxysilane having at least one vinyl group. The coated molded plastic part is heated in the presence of moisture, converting the alkoxysilane into a siloxane polymer with vinyl and silanol groups. These silanol groups then react with the silanol groups of the aminofunctional silicone fluid. Thereafter, a liquid silicone elastomer is applied to the coated molded plastic part. The elastomer contains sufficient Si--H groups to react with vinyl groups contained in the siloxane polymer formed from the alkoxysilane. The molded plastic part is heated to form a covalent bond between vinyl groups of the siloxane polymer and Si--H groups of the elastomer, whereby the liquid silicone elastomer forms a seal which is bonded to the molded plastic part.