Surface appearance and mechanical strength of multi-layer polymeric films

This paper deals with the analysis of a multi-layer polymeric film made from a hybrid organic-inorganic bond-layer, a decorative epoxy-based basecoat and, finally, a protective polyurethane-based topcoat. The establishment of visual appearance and mechanical strength of the multi-layer polymeric films has been investigated by varying both baking time and temperature on a very wide range. Furthermore, two different two-step baking procedures (i.e., with and without full post-curing of the topcoat) were also proposed and comparatively evaluated. Improved trends of average roughness and mechanical strength of the multi-layer films were found at any time progressively higher baking time and/or temperature was set. Accordingly, the overall adhesion between multi-layer films and underlying metal surfaces was found to increase, as well. Nonetheless, experimental results show that even though satisfactory surface roughness and mechanical properties of the multi-layer films can be established over wide enough ranges of baking time and temperature with both baking procedures, an acceptable visual appearance is only achievable if the topcoat is superimposed at least on an almost fully cured basecoat. (C) 2007 Elsevier B.V. All rights reserved.