Processability Study of In‐Mold Coating for Sheet Molding Compound Compression Molded Parts

In-mold coating (IMC) is applied to compression molded sheet molding compound (SMC) exterior automotive or truck body panels as an environmentally friendly primer to make the part conductive for subsequent electrostatic painting operations. The coating is a thermosetting liquid that when injected onto the surface of the part cures and bonds to provide a smooth conductive surface. In order to identify the processability of IMC for SMC, it is essential to predict the time available for flow, that is the time before the viscosity starts to increase as well as the time when the coating has enough structural integrity so that the mold can be opened without damaging the part surface (mold opening time). In the present work, we study cure behavior of IMC based on differential scanning calorimetry and rheological experiments and show its relevance to both flow and mold opening time for the IMC process during SMC compression molding. POLYM. ENG. SCI., 59:1688-1694 2019. (c) 2019 Society of Plastics Engineers