Based on the newly discovered powder primer failure mechanism, a joint project was undertaken by GM R&D, Meridian, AOC, and Ashland with the goal of developing powder primer capable class A SMC materials. To that end, more than 40 SMC formulations were prepared and molded into panels for powder primer application readiness. The panels were evaluated for shrinkage, surface profile, moisture absorption, and powder application. Based on these results, four of the SMC formulations were selected for plant trials. The panels molded with the selected SMC materials were sent through the ELPO and powder process of a GM vehicle production plant. Based on the observed results, it was concluded that the selected final four SMC formulations do not show powder primer popping due to air outgassing, and their moisture absorption is low enough to allow powder priming when there is no line stoppage. It was also noted that, in case of an extended line stoppage and subsequent moisture uptake by SMC panels, the conventional conductive coatings cannot slow down moisture outgassing. Therefore, there is a need to develop a new generation of conductive coatings, which can further slow down moisture penetration into the powder primer. Such experimental conductive coating was developed and modified through a series of iterations till a final formulation was arrived at. The modified version shows excellent adhesion to all substrates and passes all adhesion tests.
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