Drying of alkyd emulsion paints

The drying and film formation of long oil alkyd emulsions was investigated with emphasis on loss of dry upon storage. The main reason for loss of dry was adsorption of the cobalt (drier) on pig ment surfaces as a precipitated hydroxide. Titanium dioxides with alumina surface treatment and organic pigments were most detrimental to drying. Acrylate- and phosphate-based dispersants also deactivated the cobalt, presumably due to complexation and precipitation of the cobalt. Emulsions prepared with an emulsifiable cobalt drier containing 2,2'-bipyridyl (complexing agent for cobalt) showed the best resistance to loss of dry. Atomic force microscopy of films formed from the emulsions showed that the emulsifier migrated to the film surface which, when washed with water, leaves holes or pits in the film. The pits were arranged in a hexagonal pattern characteristic of Benard cells, which form due to surface tension and/or temperature gradients generated in the film during evaporation of water.