An experimental and theoretical study on effects of particle size distribution on flowability and film properties of organic powder coatings

Organic powder coatings have received increasing attention due to their environmental benefits. Given their pure solid form, particle size related parameters significantly influence fluidization, spraying, and the deposition state of particles on the substrate. Due to the broad particle size distribution (PSD) resulting from the top-down production process, the commonly employed medium particle size (D50) proves inadequate for accurately representing size related characteristics. This investigation concentrates on elucidating the effect of particle size distribution (PSD) and the synergistic effects of PSD and flow additives on the flowability and coating film properties of ultrafine powder coatings by theoretical analyses and experimental study. Narrowing the PSD proves advantageous in enhancing powder flowability, attributable to the reduced presence of fine particles. An optimal dosage of flow additives exists, markedly affected by the PSDs of powders, a narrower PSD reduces additive requirements while achieving the same levels of flowability. A moderate reduction in PSD can improve coating film performance, but an excessively low span compromises the apparent property of the film. Through tapped density and Micro-CT analysis, it is found that the powders with a medium PSD achieve denser deposition on the substrate, which can also be verified by the theoretical calculations that powders with a medium PSD are more likely to form a close packing on the substrate. This study provides theoretical guidance on enhancing the flowability and film properties of powder coatings.