Investigation of Multi-Stage Deposition Techniques of Industrial EPD Paint for High Film Thickness and Multi-Layer Applications

Abstract

EPD paint systems are well established industrially for applying coatings to a wide variety of metal items. Being aqueous systems, deposition is principally driven by electrolysis rather than electrophoresis. Polarisation of the deposit by diffusing or retained electrolytic gas leads to a self-limiting rate of deposition. Self-limitation is beneficial for equalising thickness distribution, but prevents higher thicknesses that may be required for protection. If electrodeposition is interrupted and the polarising gas bubble blanket removed, electrodeposition can be resumed with electrophoresis becoming more significant, and higher thickness achieved. Multiple layers of different paint compositions are also possible. Substrate movement as opposed to whole bath agitation can be significant for refining the deposit. Studying the final composition of multiple layers of different paints provides insight into the deposition processes. Practical advantages include enhanced corrosion protection from higher thickness, and various functional attributes from multiple layering.