Effect of Powder Particle Size and Charging Efficiency on Film Build and Surface Finish

Abstract

Powder coating, a solvent-free technique, is influenced heavily by powder particle size and electrostatic charging efficiency. This study investigates how these two factors affect film build and surface finish using epoxy-polyester hybrid powders categorized into fine (<20 µm), medium (20–40 µm), and coarse (>40 µm) sizes. Coatings were applied to steel panels using a corona-type spray gun under consistent voltage and flow conditions. Post-application, panels were cured and evaluated for film thickness and surface roughness. Fine powders yielded the smoothest surface (Ra = 0.8 µm) but had the lowest film build (35 µm) due to reduced charging efficiency (55%). Coarse powders achieved higher film build (65 µm) but resulted in rougher finishes (Ra = 2.0 µm). Medium particles offered a balanced performance with adequate surface finish (Ra = 1.2 µm) and film build (50 µm). Charging efficiency increased with particle size, highlighting the trade-off between deposition and surface quality. This study suggests that optimizing powder distribution and charging parameters can significantly enhance coating outcomes.

Keywords: Powder coating, Particle size, Electrostatic charging, Film build, Surface roughness, Epoxy-polyester