Insights into powder coating excellence: Unveiling the effects of particle-size distribution

Particle-size distribution (PSD) significantly influences the performance of powder coatings. In this study, polyester-coating powders with similar median diameters (D₅₀) but varying PSDs were prepared. The PSD was characterized by span and two self-defined parameters, $E_5$ (vol% $<$5 μm) and $E_{80}$ (vol% $>$ 80 μm). The effects of PSD on the powder properties and film performances were investigated comprehensively, including static and dynamic powder flowability, deposition characteristics, deposition efficiency, inner film structure, appearances and film performances. When powder coatings had similar D₅₀ values, greater span values correlated with poor powder flowability, less compact deposition, and increased voids in the final films, resulting in inferior surface appearances and compromised performances. Moreover, $E_5$ primarily influenced powder flowability, deposition efficiency, and powder occupancy. In contrast, $E_{80}$ significantly impacts powder bridging in the deposition layer, thickness uniformity, appearance, and film performances. The above findings provide valuable insights for coating manufacturers to improve powder coating quality by optimizing PSD, paving the way for broader applications of powder coatings.