Epoxy-based thermosetting powder coatings: Surface appearance, scratch adhesion and wear resistance

The deposition of protective coatings from thermosetting polymer powders is undergoing rapid growth as an ecological, economic and energy-efficient technology. Nevertheless, a combination of conflicting needs is characterizing new formulations: (i) minimization of premature crosslinking during material production and storage; (ii) film levelling and cross-linking at the lowest possible temperature in the least possible time. We address the problem by developing an experimental study in which the evolution of film morphology and its thermal, rheological, mechanical and tribological properties are analyzed in the light of film baking time and temperature. Experimental results show that smooth films can be achieved at relatively low baking time and temperature, while film mechanical performances are not yet fully developed. In contrast, good film strength, adhesion and wear endurance can be attained, only if longer baking time or higher temperature is set. However, a generalized scratch map, which correlates the adhesion strength of the polymeric films with the thermorheological behaviour of the base material, has been also built. Our results open up the possibility of predicting best baking programs and how full film performances are progressively established with time and temperature by better understanding of the mechanisms involved in polymeric films formation from loose powders. (C) 2007 Elsevier B.V. All rights reserved.