1998-02-23

Conductive Thermoplastic Resin for Electrostatically Painted Applications 980983

The formulation of injection moldable thermoplastics with small loadings of graphite nanotubes provides sufficient conductivity in molded parts to allow for use in electrostatic painting applications. Normally, plastic parts need to be painted with a conductive primer prior to the electrostatic painting of base and clear coats. The use of conductive plastics eliminates the need for the priming step, and improves paint transfer efficiency and first pass yield. These elements provide obvious savings in materials and labor. What is less obvious, however, is the dramatic positive environmental impact that can occur through the reduction in emissions of volatile organic compounds (VOCs).
Graphite nanotube technology provides advantages over other technologies such as conductive carbon black. In order to reach the percolation threshold for conductivity in carbon-black-containing resins, the loading of carbon black required tends to embrittle the polymer. Fibrils are more effective at establishing percolation at lower loadings, so a significant loss in toughness is avoided.
This paper will focus on the development of a conductive polyphenylene ether/polyamide (PPE/PA) blend for electrostatic painting applications. Specifically, the application to be discussed is that of exterior mirror shells. The development of the resin has followed a rigorous design process based on extensive use of designed experiments and statistical analysis. This design process has resulted in a formulation and manufacturing process that will ensure acceptable electrostatic paintability.
Elements of this paper will include formulation design, assessment of electrostatic paintability, end-use performance in mirror shells, and paint performance, including discussion of the benefits realized in the paint shop.

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