The Role of Particle Filtration in Industrial Scale EPD Processes

Electrophoretic deposition or EPD is a well established method for creating decorative and protective coatings and other structures on various electroconductive substrates. The formation of these coatings and structures can be prejudiced by the presence of oversized or contaminant particles as well as excess or contaminant electrolytes resulting in appearance and performance problems in the final product. Nuisance particles come from diverse sources and are an inevitability in industrial environments. Efficient and effective particle capture strategies are therefore essential. In water-based EPD processes, control over the content electrolytes and other continuous phase materials can be accomplished using tangential or cross-flow filtration where the permeate contains the undesirable materials and can be treated or disposed of outside the system. But for particles and other disperse phase materials, dead-end filtration techniques are required. Here the undesirable materials are captured, concentrated and retained on the filter medium within the system. Disposal only occurs as a result of discarding or treating the filter medium itself. Many types of dead-end filtration media are commercially available. Retention size and materials of construction all have relevance for system compatibility and effectiveness of particle capture. Practical experience shows that selection of the correct type of particle filtration optimises process quality. Using inappropriate filter media can be not just ineffective, but actively detrimental. This paper describes commonly available particle filter systems and how they interact with industrial EPD process.