Development of adhesive technology for PTFE on metal substances - surface modification of PTFE by plasma etching treatment

摘要

Polytetrafuluoroethylene (PTFE) is widely applied to many industrial products because of its excellent combination of thermal, electrical and mechanical properties as well as chemical resistance. The low surface energy which forms the backbone of the stable polymer chain exhibites difficult adhesion to other substances requiring surface pretreatment such as chemical etching before adhesion. Current pre-treatments of PTFE surface include chemical etching by naphthalene-sodium solution and other chemicals. However, a substitute treating procedure for chemical etching is required to protect the environment. On the other hand, epoxy based adhesives are widely used with PTFE, and possess relatively strong adhesive strength after chemical etching. However, the lower heat resistance of epoxy adhesives compared with that of PTFE limits the operating temperature of its products. An adhesive agent with higher thermal stability is required to solve this problem. Both the improvement on thermal stability of adhesives and the surface pre-treatment procedure instead of chemical etching were investigated in order to establish the appropriate technology for adhesion of PTFE on metallic substances. Consequently, the polyimide based adhesive modified with epoxy resin which had suitable affinity to PTFE were improved to resist up to 200℃. Furthermore, plasma treatments onto PTFE surface in argon gas was found to increase the adhesive strength more than the conventional treatment of naphthalene-sodium solution. The SEM (Scanning Electron Microscope) analysis clarified that the effect of plasma irradiation on PTFE adhesion depended upon an "anchor effect" by roughing the surface of PTFE. In addition, it was found that optimum conditions such as reactive gas pressure, temperature and others existed for plasma pre-treatment of PTFE to obtain satisfied adhesive strength.