THE EFFECT OF THERMAL-STRESSES ON THE EMI (ELECTROMAGNETIC-INTERFERENCE) SHIELDING OF CONDUCTIVE PLASTICS

The electrical properties of a number of filled and coated plastics were examined after subjecting the materials to rigorous thermal cycling between minus 20 and 80 degree C. Filled compounds that obtained their conductivity through the addition of carbon based conductive fillers maintained their conductivity throughout the thermal cycling. Compositions which contained metal fillers were able to maintain their conductivity only when a high temperature thermally stable polymer was used as the polymer matrix. Plaques coated by a zinc arc spray or with acrylic paints containing graphite, silver, and nickel particles were unaffected by thermal cycling. Plaques coated with an acrylic paint containing copper particles lost most of their conductivity during the changes in sample temperature.