Electrostatic spray deposition (ESD) of polymeric powders on thermoplastic (PA66) substrate

This paper deals with a primerless electrostatic spray deposition process (ESD) for coating thermoplastic (PA66) substrates using epoxypolyester, metallic epoxy-polyester, and epoxy powder paint. A novel and never before used pretreatment system, based on a low speed cold spray of fine copper powders, applied a thin conductive film on the plastic substrate, which made the ESD possible. The focus of first part of the paper is on analyzing the influence of both electrical and aerodynamic process parameters on ESD process. Differences in behavior of the powders used were evident. Design of experiments (DOE) was used to plan experimental trials and related ANOVA tables were made and used as support instruments to interpret the experimental findings, process modeling, and to the understand physical phenomena involved in the deposition process. As a result, several process maps were produced in which consistent trends of coating thickness and average roughness vs. operative parameters are reported. Careful qualification of the polymeric films was also carried out using the most relevant performance indicators. The second part of the paper focuses on assessing the influence of exposure time on coating thickness and average roughness of the polymeric films, that is, once the electrical and aerodynamic parameters had been optimized. (c) 2005 Elsevier B.V. All rights reserved.