Development of matte finishes in electrostatic (EFB) and conventional hot dipping (CHDFB) fluidized bed coating process

This study focuses on the correlation between the thermo-rheological properties of a thermosetting powder coating system with its surfacestructure build-up. Epoxy powder coating systems, which displayed surface matting and surface wrinkling, were examined. Firstly, the evolutionof the complex viscosity was correlated with the cure kinetic. Secondly, the structure build-up on the surface of the coatings was investigatedwith a combined SEM-CLA profilometry analysis at different stages of curing process for both EFB and CHDFB coating processes. Differentfinishes were found to characterize the films applied by using EFB and CHDFB coating processes as a result of the different way the film is heatedby. Finally, a strict relationship of film morphology to the degree of conversion and to the evolution of the complex viscosity was found out forboth EFB and CHDFB coating processes. The surface structure is built up after gelation point and continues to evolve after gelation with a fulldevelopment of the film fine structure. Differences were observed in the surface structure build-up when different curing temperature was used,thereby indicating an influence of minimum viscosity on achievable finishing.These experimental results lead to further advances in a better understanding of the formation of surface topography and morphology of polymericfilms. They also provide important indications for the settings of curing parameters in both EFB and CHDFB coating processes as well as for thedevelopment of new powder coating formulations.