Improvement on the first pass transfer efficiency of fine polymer coating powders for corona spraying process

Corona charge spraying has been widely used in the powder coating application, thanks to its outstanding charging performance leading to high coating efficiency. Yet, this spraying technology has not been working very well with fine powders that started to be used by powder industry in recent years. Fine powders are known as the powders that have median sizes smaller than 30 μm. Utilizing fine powders can improve coating quality and reduce film thickness. However, it has been experienced that the fine powders have much lower first pass transfer efficiency (FPTE). This study provided a solution for the problem by humidifying the powder coating particles. The gained moisture on the particle surfaces can reduce the powder resistivity. As a result, the electric field strength inside the deposited particle layer on the target is reduced, allowing more charged particles to be deposited. Therefore the FPTE of the fine powder is increased. Discovered by the experiments, a maximum of 17% increase in the FPTE was achieved with the humidified fine powder. The improved FPTE of the fine powder was comparable to the regular powder. The study also evaluated the influence of the increased humidity on the fine powder flowability. Based on the results obtained from the powder characterization tests, the suggested humidification process would not significantly deteriorate the fine powder flowability.