SURFACE MODIFICATION OF PET FILMS WITH RF PLASMA AND ADHESION OF IN-SITU EVAPORATED AL ON PET

PET (Polyethylene terephthalate) films were modified with two different plasmas, nitrogen and oxygen, as a function of treatment times and RF powers. Firstly, the chemical composition of the plasma-modified PET films was investigated by XPS. In the case of nitrogen plasma, the formation of amine, imine and amide groups is detected. A slight diffusion of nitrogen-containing species into the PET bulk is also observed by angle-resolved XPS measurements. The appearance of alcohol, carbonyl and carboxyl functions is observed in the case of oxygen plasma treatment. After thermal deposition of an aluminium film, peel tests reveal that the Al/PET adhesion increases as follows: untreated < nitrogen plasma < oxygen plasma treatment. Secondly, after several successive depositions of thermally evaporated Al on oxygen plasma treated PET film, XPS was used to study the chemistry at the interface. The XPS results reveal that the additional reactive sites created on the PET surface by the treatment explain the significant improvement in Al/PET adhesion observed for plasma-modified samples.