Adhesion of thermoplastic polyurethane elastomer onto galvanized steel

When a thermoplastic polyurethane elastomer (TPU) is applied onto galvanized steel by a hot melt process, the subsequent adhesion and its durability are very sensitive to the chemical bonds created at the interface. The effects of several surface treatments of galvanized steel were thus studied, including: degreasing, corona discharge, acidic etching, gas flame, and a cobalt catalyzed zinc conversion coating. Coupling primers were also investigated with organofunctional silane films formed on galvanized steel substrates from different solutions. The silane system was a traditional γ-APS with different deposition parameters, including the pH value of the applied solution and the solvent used. The adhesion was characterized before and after aging with a single wire pull-out test derived form the microbond test geometry and resulting in intrinsic interfacial shear strength values. A coupled experimental-finite element approach was used to consider residual stress profiles developed within the entire system. This led to an intrinsic parameter representing the intrinsic adhesion strength between the polymer and the metallic substrate. Effects of the different surface treatments, coupling primers, their chemical structure, and their surface topography on the adhesion and the hydrothermal aging behavior were discussed.