The term floating is used for defects that cause color differences on the surface of the paint film in the form of shadows, stains or streaks (Fig.1). Flow occurs in the paint with the driving forces arising from the difference of gravity and surface tension. During this flow, floating occurs due to the inhomogeneous distribution of different pigments. This defect is the result of mobility in the coating, as in Bénard cells, and appears as color differences. The floating problem occurs in the horizontal plane in paints colored with two or more pigments, color differences may occur in different parts of the panel. The precautions to be taken are the same as for Bénard cells, which are the elimination of surface tension differences, the increase of viscosity to reduce mobility, the prevention or reduction of aggregation and reduction of the applied film thickness.

Fig 1.

(Fig.1: Floating defect in an industrial paint film)

The use of surfactants containing very low levels of silicon is also effective in reducing/preventing floating problems. The silicon compound layer formed on the surface causes a diffusion-controlled evaporation regime to dominate, even in the first stages when the solvent evaporation is more dynamic, resulting in a decrease in the velocities of the convection flows in the wet film.

As a result, pigment movements that cause macro-scale floating defects are reduced. In the case of using silicone containing surface additives, if another layer is applied on the surface, the quality of intercoat adhesion should be checked.