Conductively modified thermoplastic olefins (TPOs) have been developed using low levels of conductive carbon fillers, <6 wt.%, without sacrificing the favorable mechanical and rheological properties exhibited by these materials for the automotive market. The bulk electrical properties of these materials exhibit traditional percolation behavior when the samples are compression molded. However, conductively modified injection molded materials exhibit a high surface resistivity, typically greater than 1016 ohm cm, which is compensated by a relatively low resistance interior, defined as a core resistance, of less than 109 ohm/cm. The threshold for electrostatic paintability has been identified based on core resistance measurements, electrostatic dissipation results, and electrostatic painting transfer efficiency data. The core resistance must be less that 109 ohm/cm for charge dissipation to occur and for any significant increase in paint film builds to be observed. Electrostatic painting of representative production rear bumper fascias at Visteon - Utica Plant have shown transfer efficiency increases relative to non-conductive parts for adhesion promoter, primer, basecoat, and clearcoat when conductive TPO resins are employed. This is true even with the use of conductive adhesion promoter and primers. Recent advancements in chemistries and processes which eliminate adhesion promoters, such as olefinic topcoats, plasma or flame surface treatments, or directly paintable TPO formulations, are targeted towards cost savings associated with process and/or coating elimination. However, by elimination of conductive surface coatings prior to electrostatic application of basecoat and clearcoat over non-conductive TPO parts, these potential cost savings are more than offset by a loss in painting efficiency. The use of conductive TPO parts enables these promoterless system approaches by maintaining the highest possible transfer efficiency levels in electrostatic painting processes.
