Effect of ion current on transfer efficiency and appearance in the powder coating process

Often, the formulation chemistry of powder is optimized based on functional and aesthetic requirements, such as UV protection, chip resistance, weatherability, and the glossiness of the powder coated film. Once the formulation chemistry of a powder is finalized, it becomes necessary to adjust the physical parameters of the powder and the application engineering processes for best appearance and highest transfer efficiency (TE). In this paper, theoretical aspects and experimental data are provided on the effect of ion current density on the charging of particles, TE, and appearance of the cured film. The onset of back corona as a function of the product of charge-to-mass ratio (Q/M) and the thickness of the powder layer on the conducting substrate are discussed. To examine the TE and appearance in the absence of free ion current, comparisons are made between the performance of corona charging and tribo charging guns.