New Self-Lubricating Plastics

These plastics are blends of a thermoplastic resin and a small percentage of silicone. The silicone migrates to the surface of a molded or extruded part, thus generating a polymer film which serves as a boundary, or mixed-film lubricant. Hence, such materials are called migratory internally lubricated thermoplastics. They provide lower friction and wear than earlier internally lubricated thermoplastics and they eliminate the run-in period to bring the lubricant to the surface. A further enhancement of wear and friction properties has been achieved by adding both migratory-type polymer lubricants (silicone) and particle-type internal lubricants (such as polytetrafluorocarbon) . As these materials combine at the wear surface, they form a high-temperature grease. The PTFE acts both as a thickener and an extreme-pressure additive, and the silicone lubricant ensures continuous lubricity, both at startup and at high speeds. Tabulations of wear and friction properties and of physical and mechanical properties of acetal copolymer, nylon, polycarbonate and polystyrene with and without lubricant additives are presented.