Polyester films have been used widely as laminate films of beverage and food cans due to their excellent properties of formability, corrosion resistance, and adhesion to steel sheets. Recently, excellent formability under a higher processing degree has been required in laminated steel sheets for drawn and ironing (DI) cans, which are used as beverage and food cans. Polyester films which are almost amorphous are used in this application since high formability is needed in the laminate film. In this study, we investigated the thermal crystallization behaviors of a near-amorphous oriented polyester film and a non-oriented film by thermal analysis and Raman spectroscopy. We found that the two types of films display different thermal crystallization behaviors.
Wax-added films are used as exterior films of laminated steel sheets for severe can-forming use. However, one difficulty in using wax-added film laminated steel sheets is the decreased coating adhesion which accompanies wax addition. Therefore, wax addition effects on coating adhesion were investigated using the surface free energy. Results demonstrated that wax on the polyethylene terephthalate (PET) film surface decreases the dipole force component (γ p ) of the surface free energy. The decrease in γ p of the laminated film decreases the work of adhesion between the film and the coating. X-Ray photoelectron spectroscopy analysis revealed that the decrease in γ p is attributable to a decrease in the ester bonds of PET that occurs along with increase of the wax ratio on the film surface. Furthermore, the laminated steel sheet coating adhesion was found to be related to the work of adhesion between the film and the coating, suggesting that the decreased coating adhesion caused by wax addition is explainable by the decrease in γ p of the laminated film caused by the increase of the wax ratio on the film surface.
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