Powder coating of Sheet Molding Compound (SMC) body panels

Sheet Molding Compound (SMC) compression molded parts are prone to porosity . During top coat baking, trapped air in the surface porosity expands and o ften blows through the paint leaving unacceptable craters in the final fini sh. The accepted solution to this problem in the SMC industry is to use a c oating compound on the SMC part. The coating compound (called in-mold coati ng (IMC)) is injected and cured on the SMC molding after its cure is comple te, but before removing it from the mold. Another potential solution is to powder coat the parts once they have been de-molded. While powder coating a dds time to the process, it is performed outside of the mold and frees the mold for the next molding cycle earlier than if the IMC process is used. In the present paper, we develop a simplified model for the powder coating of plastic parts. We show how the model can be combined with chemo-rheologica l measurements to guide the optimization of the process and material parame ters. Although with the powders currently available, the surface appearance is inferior to the one obtained with IMC, this process shows potential.