Effect of Annealing Temperature on Adhesion of Polyester Film to Electrolytically Chromium Coated Steel

Abstract

Recently, Electrolytically Chromium Coated Steel (ECCS) laminated with biaxially oriented polyester films has been applied to container materials. These laminated materials for containers are usually subjected to heat treatments under dry and wet conditions in the can-making and filling processes. Sufficient adhesion of polyester film to ECCS is essential even under these severe conditions to fulfilling the required properties as a container material.
In this paper we studied effects of annealing temperature between 50°C and 240°C on the adhesion of a polyethylene terephthalate (PET) film and a copolymerized ethylene terephthalate/isophthalate (PET/I) film to ECCS in connection with structural changes of the polyester. The adhesivity was evaluated by T-peel tests, and the properties of polyester were evaluated by density measurements, molecular weight and dynamic viscoelastic spectroscopy. The adhesivity of both the films related with crystallization and thermal degradation of polyester by annealing. The PET/I film showed better adhesivity than the PET film after annealing at temperatures between 160°C and 180°C, because the PET/I film has the more relaxed amorphous phase than the PET film in this temperature range, which exhibits a higher degree of an amorphous state.