Scale-down Experiments in a New Type of Pan Coater
Ronny Müller and Peter Kleinebudde
Institute for Pharmaceutics and Biopharmaceutics, Heinrich Heine University, Düsseldorf (Germany)
Scale-down strategies were investigated for important process parameters in drum coating (drum speed, inlet air volume, spray rate) and applied to Bohle Film Coaters (BFCs) in the range from BFC 600 to BFC 5. Coating uniformity (CU) of an organic based film and coating process efficiency (CPE) were determined precisely from tracer tablets and both parameters (CU and CPE) were used as analytic tools in order to compare the trials.
The scale-down from BFC 600 to BFC 40 was accomplished with same values for CU of approx. 3 % and CPE of 80-95 %. A successful scale-down of the inlet air volume was achieved by keeping the ratio of spray rate to inlet air volume con-stant. The scale-down of the drum speed from BFC 600 to BFC 40 was adopted us-ing a constant peripheral speed and the scale-down of the spray rate by achieving the same or higher number of passes per tablet through the spray zone.
In the actual study the scale-down from BFC 40 to BFC 10 or BFC 5 was more problematic. Neither a constant peripheral speed nor a constant Froude number resulted in an acceptable drum speed for the BFC 5/10; the optimal drum speed was between the two tested approaches. In BFC 5 a CU of 5.4-6.4 % and a CPE of 70-85 % were achieved.
A new method to determine the CU after a virtually infinitely run time (CU ) was introduced based on several samples of tracer tablets taken during the coating process. The CU was found to be 4.5 % for a trial in BFC 5.
Key words Bohle Film-Coater • Coating uniformity • Film coating, drum speed, scale-down, scale-up