Abstract
Adhesion aspects of laminated aluminium/polyester systems have been studied before and after mechanical deformation. The work has been carried out in collaboration with a producer of beverage cans, and the reasons for the adhesion reduction observed during the deep drawing and wall ironing process has provided the focal point for the work. Laminates were manufactured from commercial polyester film and commercially anodised (2 types) or chromium phosphated aluminium coil stock. The morphology of the pretreated aluminium surfaces has been investigated by using scanning electron microscopy. The chemical composition and the composition variation with depth of the pretreated aluminium surfaces have been studied by XPS sputter depth profiling. It is found that the CP and PAAI, PAAII pretreatments have reduced the amount of magnesium in the top layer of aluminium surfaces.An intimate contact between the polyester film and the aluminium substrate of the laminates and the thicknesses of the pretreated layers have been observed by cross- sectional TEM following sample preparation by chemical sample thinning and microtoming. Based on angle resolved XPS and SIMS investigation, the locus of failure of the can systems produced from the CP and PAAI treated aluminium has been defined as within the polyester film but very near the interface. The thickness of the residual polyester overlayers has been estimated. A peel test has been used to evaluate the adhesion level of the cans. The order of the adhesion level of the cans produced from different surface pretreated aluminium has been found to be; PAAII > CP > PAAI. Chemical exposure methods have been established to make the investigation of interfacial surfaces of the laminates possible by SEM. A shear lag analysis has been carried out to demonstrate the mechanical deformation behaviour of the laminates during the deep drawing and wall ironing process. A relationship between the thickness of the pretreated layer and the fragment size has been proposed. It is found that the pretreated layer fragment characteristics is very important. Fine and uniformly distributed fragments with small separation distance in the aluminium substrate of the cans contribute to the adhesion level through crack pinning effect. A comprehensive model for adhesion loss during deep drawing and wall ironing process has been proposed.