Influence of coating formulation variables and processing on the adhesion of melamine-crosslinked polyester primer to urethane-crosslinked epoxy electrocoat

The role of spray-primer formulation chemistry towards robustness of adhesi on to an epoxy-based electrocoat was examined for a range of coatings repre sentative of those used in automotive OEM applications. For coatings exhibi ting degraded adhesion performance, high-resolution X-ray photoelectron spe ctroscopy (XPS) identified the presence of a surface-active polyether-based anti-cratering agent (ACA) formulated into the epoxy-based electrocoat at the primer/electrocoat interface. The adhesion performance of the better-pe rforming systems was found to be related to the spray-primer's ability to a ccommodate the ACA by either absorbing or displacing it from the electrocoa t surface, thus diluting it to concentrations no longer adversely affecting adhesion.