Adhesion enhancement of thermally evaporated aluminum to surface graft copolymerized poly(tetrafluoroethylene) film

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PT FE) film via UV-induced graft copolymerization with glycidyl methacrylate ( GMA) and 1-vinylimidazole (VIDz) were carried out to improve the adhesion w ith evaporated aluminum metal. The surface compositions of the graft copoly merized PTFE films were studied by X-ray photoelectron spectroscopy (XPS). The adhesion strength of the evaporated aluminum to the surface graft copol ymerized PTFE film was affected by the type of monomer used for graft copol ymerization, the graft concentration, the plasma post-treatment of the graf t copolymerized PTFE surface prior to metallization, and the extent of ther mal treatment after metallization. The optimum T-peel adhesion strengths of the A1/PTFE laminates were in excess of 10 and 5 N/cm, respectively, for t he GMA and VIDz graft copolymerized PTFE films. These adhesion strengths ar e significantly higher than those obtained between the evaporated aluminum and the pristine or plasma-pretreated PTFE film. The mechanism of adhesion enhancement and the failure of the metal-polymer assembly were also investi gated. It was observed that the failure occurred within the PTFE film. The strong adhesion between Al and PTFE arises from the charge-transfer interac tion between the Al atom and the epoxide moiety of the grafted GMA polymer, as well as from the fact that the graft chains are covalently tethered on the PTFE film surface as a result of the grafting process.