Effect of the temperature on the adhesion and the morphology of thin metal films evaporated on polyethylene terephthalate

Abstract

The adhesion strength of different metallic thin films thermally evaporated (vacuum around 10 −6 mbar) onto polymer is correlated with the temperature of the polymer during the evaporation. The adhesion of the magnesium, aluminium, silver and copper thin films on polymer has been measured by a peel test. In parallel, transmission electron microscopy has been used to characterize the morphology of these films. The results show that the strength of the adhesion of all the metallic films used increases sharply for polymer temperatures above 100 °C. This increase in the dry adhesion may be related to the polymer annealing temperature before deposition. For a temperature above the glass transition, rearrangement of the polymer chains can occur, leading to an improvement in the adhesion. In contrast, the main factor for the wet adhesion seems to be the polyethylene terephthalate temperature during metal deposition. Atomic metallic diffusion may occur, leading to an increase, by cross-linking, in the cohesion of the polymer skin. A schematic representation of this metal-polymer cross-linking is proposed.