Leveling measurements of antifouling coatings using an optical profilometer: Effects of additives and solvent concentration and type

Ship hulls require smooth antifouling coating surfaces to decrease frictional drag and avoid sites of weakness for biofouling. Consequently, the leveling properties of antifouling coatings should be understood and optimized. In the present work, a novel approach to quantitatively measure leveling properties of coating films was developed.

Using this approach, dynamic surface textures during leveling of selected model antifouling formulations were measured using a combination of a three-dimensional (3D) profilometer and a retrofitted automatic film application system. It was found that the leveling process is strongly coupled to the solvent evaporation rate and the associated development in coating viscosity.

For low viscous coatings, three leveling stages were observed. High viscous coatings, on the other hand, only went through one leveling stage. Experimental data showed that an underlying tie-coat (relative to a flat acrylic panel) had negative effects on the smoothness of the top coat. In addition, using an anti-sagging agent enabled control of sagging, but resulted in negative effects on leveling.

Nevertheless, it was still possible to obtain good leveling performance with anti-sagging agent in a formulation. The effects of minor amounts of three types of additives and two types of solvents on leveling of the model formulations during (and after) spraying application were found to be less significant than those seen from drawdown application.

It is therefore important to take into account the application method when studying leveling phenomena.