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Transmission of light through automotive topcoat and primer layers can lead to degradation of the underlying electrocoat layer and to topcoat delamination. In order to protect against this, it is critical that transmission of both ultraviolet wavelengths and certain visible wavelengths be effectively blocked by the topcoat and primer layers. The clearcoat, basecoat and primer each have their own role and combine to protect against light transmission. The transmittance of these combined layers is typically measured by the Integrating Sphere UV-Visible Spectrophotometer. It would both simplify measurement of the topcoat systems and allow better system modeling if these layers could be measured separately and combined mathematically. We demonstrate here that absorbing and reflecting pigments can be effectively modeled using the Beer-Lambert law while results for scattering pigments are consistent with the Kubelka-Munk theory.

This study examined the effect of primers containing a conductive pigment on the resistance spot weldability of hot-dip galvanized steel. The pigment used was ferrophos, essentially Di-iron phosphide. Basically, two types of tests were used in this work. Current range tests were used to establish the effect these primers have on the effective ranges of weldability. Limited electrode life tests were used to infer the long term performance of the hot-dip galvanized steels with and without this paint. It was found that the addition of the Ferrophos bearing paints had pronounced effects on weldability. Typically, required current levels were reduced by several thousand amps, and effective current ranges were increased by 50 to 100 percent. During electrode life testing significant reductions were also noted both in the rates of electrode face diameter increase, and the degree of electrode pitting.