Motion Of Pigments In Thin Paint Films

Abstract

When thin paint layers are exposed to heat, evaporation of the solvent begins, and significant movement within the paint film occur, causing temperature and concentration gradients. A clear coat paint was used, which had a density of 988 kg/m3, viscosity of 240 cP and a surface tension of 26 mN/m and was mixed with spherical solid blue particles with a mean diameter 26 μm were added to the paint at 2% concentration of the total mass. A knife edge was used to coat stainless steel substrates at different thicknesses and placed in a convection oven at 121oC for 30 minutes. Images of the samples during the curing process were taken, showing how the pigments moved from low to high surface tension areas. Colour measurements were taken to show that increasing the thickness of the same paint significantly decreases the lightness value. Keywords-component; Mass transfer and drying, colour, boiling and evaporation, two-phase flow, surface-tension-driven, concentration gradient, self-organizing patterns, automotive paint