Surface graft copolymerization of poly(tetrafluoroethylene) film with simultaneous lamination to copper foil

Abstract

A simple, one-step process of surface thermal graft copolymerization of argon plasma-pretreated poly(tetrafluoroethylene) (PTFE) films with simultaneous lamination of copper foils, or with similarly plasma-pretreated PTFE films, was demonstrated. The simultaneous thermal grafting and lamination process was carried out at 120°C under atmospheric conditions. The monomers used for the graft copolymerization were 1-vinyl imidazole (VIDz), 4-vinyl pyridine (4VP), and 2-vinyl pyridine (2VP). The adhesion strengths are reported as lap shear adhesion strengths and T-peel adhesion strengths. The adhesion strength between the polymer and the metal was further enhanced by the presence of a crosslinking agent in the monomer. Adhesion strengths exceeding 7 N/cm were achieved for the Cu foil/PTFE laminates. X-ray photoelectron spectroscopic (XPS) studies of the delaminated Cu foil/PTFE assembly revealed that the joint failed by cohesive failure inside the PTFE film. The strong adhesion between PTFE and Cu arises from the charge-transfer interaction between the nitrogen moiety of the grafted polymer and the Cu atom, as well as from the fact that the graft chains are covalently tethered on the PTFE film surface as a result of the graft copolymerization process.