Friction related leveling study of antifouling coatings using a 3D measurement system.

Improving leveling of antifouling (AF) coatings will diminish the outermost surface unevenness, which therefore reduces skin friction and sites of weakness, i.e. starting points for coating breakdown and biofouling. Consequently, it is important to improve leveling to enhance the overall performance of AF coatings, though the benefits will be meaningful only before biofouling develops. Leveling of coatings has not been widely studied, which is attributed to not only the complexity of the phenomenon but also the lack of appropriate approaches. In this work, an approach combining a 3D measurement system and a refitted automatic coating film application system was originally developed for leveling study. Although spray application produces a distribution of waviness on ship hulls, we strive to obtain representative waviness and it was found that a special made spiral applicator provided surface patterns similar to that. Using this approach, effects of coating ingredients (additives and solvents) on leveling of traditional AF coatings were studied. One wetting agent and one less volatile solvent were found to be very effective. Silicone oil showed more effects on waviness than roughness. Importantly, three leveling stages were found for low viscosity AF coatings whereas only the last stage was available for high viscosity ones, which was also well-supported by evaporation tests. (Funding provided by Blue INNOship, CoaST and Hempel Foundation)