Enabling Electrostatic Painting of Automotive Polymers with Low Cost Carbon Nanofibers

Applied Sciences, Inc. (ASI) investigated the use of inexpensive carbon nanofiber (CNF) to impart electrical conductivity to polymer systems to allow the use of electrostatic painting (ESP) techniques to paint these polymers in the same manner as metals without the need for a solvent- based primer coat. The production of polymer composites that can be electrostatically painted with no additional processing steps will remove a major barrier to the replacement of metal parts with composites parts on automobiles. The full development of this technology will increase the use of composite components in the automotive industry, which is in consonance with the efforts of the automotive industry to reduce weight, increase fuel efficiency, and eliminate corrosion while maintaining appearance, performance, and low-cost. Incorporating carbon nanofiber into polymers at low loadings is known to create composites that can carry electrical currents while simultaneously increasing mechanical properties. Composites produced from a variety of commercially available composite fabrication techniques (e.g., injection molding, compression molding, long fiber thermoplastics processing, sprayable gelcoat); different polymers (PP, PEEK, PC, Nylon, PE); and carbon nanofiber types and grades were tested under this program. The composites tested all had electrical conductivities between 10-4 to 10-6 S/cm, with loadings as low as 2 weight percent of carbon nanofiber. The conductive composites were painted using ESP techniques, and then tested for surface finish quality, adhesion, and abrasion resistance. The conductive composites received the paint with no alterations in the painting process and behaved similarly to metal. The CNF neither affected the surface quality, nor did it impact the adhesion of the paint to the composite surface. The best nanofiber variant proved to be the XT version, and the best processing methods were the long fiber thermoplastics processing and the sprayable gelcoat. The sprayable gelcoat allows the ability to selectively place conductivity at the surface of the composite. Overall, the program was successful in demonstrating that composites made conductive with the addition of CNF can be electrostatically painted without the addition of a conductive primer coat. Elimination of the conductive primer will eliminate approximately 0.23 lbs of volatile organic compound (VOC) emission per automobile, or about 18 percent of the total VOC emissions related to painting and finishing. ESP of polymers will reduce manufacturing costs by about $100 per vehicle. The net present value of this is conservatively estimated at $500 M for the industry over the next 15 years. Ultimate savings could reach $2 B annually. Conductive composites have further potential of being used in numerous under-the-hood applications and other areas where electrical conductivity is needed, and more widely as electronic enclosures, composite electrostatic precipitators, anti/deicing heaters for aircraft, and anti-static flooring, countertops, and truck bed liners. ASI and its partners will pursue further cost-reduction strategies in Phase II to enhance the attractiveness of this technology. Technical advances and increased production capacity developed during the Phase II effort are expected to increase this cost savings.