Decreasing paint cost for sheet molding compound (SMC) compression molding

Finishing, in most cases, is the most expensive step for manufacturing plastic parts in automotive and truck industry; being electrostatic painting is the desired approach for improved quality. For plastic parts to be painted electrostatically, a conductive primer needs to be applied first. In the case of SMC compression molded parts, in-mold coating (IMC) is the primer material of choice, as it also serves to fill the surface porosity typical in SMC parts. To make the IMC conductive, the current approach is to add carbon black (CB), which results in a black colored primer. In this research, single wall carbon nanotube (SWCNT) was evaluated, as an alternative to CB, to develop a clearer version of conductive IMC. The effect of SWCNTs on both degree of lightness and electrical conductivity was experimentally evaluated. The results indicate that a clearer and slightly more conductive coating than standard IMC can be obtained by adding 0.15 wt% SWCNTs into the base IMC resin, which results in approximately 12.5% paint saving compared to standard IMC. The processability of the modified coating was shown to be only slightly less favorable than standard coating.