Coating uniformity: Influence of atomizing air pressure

The objective of this study was to investigate the influence of atomizing air pressure on the coating uniformity and the quality of the film coat. As parameters describing the coating uniformity, the mass variance of the film coated tablets and the variance of the film thickness within a tablet were used. For the examination of the properties of the film coat, the cumulative frequency of the tablet mass, the spray loss, the relative frequency of the film thickness, the minimum amount of polymer required for an enteric coating, and the swelling number were taken into consideration. For this study a Walther Pilot spray gun WA 50 with a liquid orifice diameter of 0.5 mm and a flat jet air cap was used. The experiments were carried out in a Bohle BLC 5 drum coater using four different atomizing air pressures between 0.5 and 2.0 bar. All other parameters were kept constant during the coating process. It could be shown that atomizing air pressure is an important factor influencing the quality and uniformity of a film coat. An increase in the atomizing air pressure will produce smooth tablets with a small mass variance. Due to a greater spray loss, the required minimum amount of polymer for an enteric coating is higher at an atomizing air pressure of 2.0 bar.