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 often blows through the paint leaving unacceptable craters in the final finish. The accepted solution to this problem in the SMC industry is to use a coating compound on the SMC part. The coating compound (called in‐mold coating (IMC)) is injected and cured on the SMC molding after its cure is complete, 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 adds 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‐rheological measurements to guide the optimization of the process and material parameters. Although with the powders currently available, the surface appearance is inferior to the one obtained with IMC, this process shows potential.