Improving pigment dispersing in powder coatings with block copolymer dispersants

The effect of three block copolymer dispersants with a poly(2-vinylpyridine) anchor block and a poly(epsilon-caprolactone) buoy block on the dispersing of TiO2 pigments in a polyester powder coating has been studied with digital image analysis on scanning electron micrographs. The mixing in a lab-scale extruder resulted in a virtually complete break-up of the pigment agglomerates. The average TiO2 particle size was only slightly reduced after further treatment of the TiO2 pigments with an dispersant. However,a significant change in the colloidal stability of the dispersions was observed. Without dispersants, the pigments reagglomerated when heated to 200 degrees C and 235 degrees C. This reagglomeration was completely suppressed by the use of dispersants, as a result of a steric layer around the TiO2 particles.