Thermoset thin film primers: influence of substrate, layer thickness and wettability of additives in laboratory testing

Abstract

Steel sheets are often protected from corrosion using primers in combination with a top coat. However, the effectiveness of primers alone has not been extensively studied. Here, we use a selection of complementary corrosion tests for benchmarking the performance of thin-film primers across a set of varying engineering parameters such as thickness, wettability, and substrate. Five established tests were selected, covering all predominant mechanisms that may occur, namely tests for cathodic and anodic delamination and barrier protection. Electrochemical investigations, among others, were carried out to evaluate the corrosion behavior, while structural properties were analyzed using techniques such as SEM. A total of nine primer formulations were tested in a layer thickness range of 3–9 µm, on GI and ZM-coated steel. Both layer thickness and substrate strongly influence performance, and to a lesser degree the primer formulation. Further, hydrophobization has a beneficial effect on cathodic delamination, while white rust formation is enhanced due to pigment leaching limitations. This suggests that competing effects can be traced well using the combination of the suggested five tests.