Comparison of polyamide insulation coatings on metallic substrates using different coating methods

In order to find better coating methods for HTS wire, thin layer polyamide coatings were coated on substrate of aluminum foil using different coating methods, including pressured spray, brush, and dip coating techniques. The coating solution was made by polyamide powder dissolved in formic acid. The breakdown strength, dielectric constant, loss, mass density of the coating, and adhesion to the substrate were studied. The effects of substrate, surface properties, temperature and vacuum pressure during the solvent evaporation on the dielectric properties were also studied. It was found that pressured spray coating method was the best among coating techniques; however, the dielectric breakdown strength of the coating was less than that of commercial polyamide film. Dielectric constant and dissipation factor are higher than commercial polyamide film. The optical microscope was used to analyze surface morphology.