Mechanism of Cathodic Electrocoat Primer Cratering

Cathodic electrocoat primers (cathodic e-coat) have been widely adopted by the automobile industry. One drawback to these coatings is that they display a tendency for formation of crater-like features when applied to zinc-rich surfaces under typical automotive application conditions.

Our studies show that cratering susceptibility is an inherent property of zinc and that the craters result from localized dielectric breakdown of the e-coat film during deposition. Energy from the electric discharges displaces the e-coat at the discharge sites and locally cures the adjacent e-coat. During cure-baking, the locally cured e-coat does not re-flow to fill the voids created by the discharges, resulting in crater-like features in the cured e-coat film.