EVALUATION OF SPRAY CHARACTERISTICS IN PHARMACEUTICAL TABLET COATING PROCESSES: THE INFLUENCES OF DRUM ROTATIONAL SPEED AND DRYING AIR FLOW RATE

摘要

In this study, drop size, velocity, and volume flux for sprays produced by a pharmaceutical nozzle (Spraying Systems 1/4-JAU-SUE15A-PA67288-45°-SS) were characterized using a Fiber-PDA system (Dantec). Spraying was performed in a 120 cm (24 in) diameter tablet pan-coater (Accela-Cota Model 10, Thomas Engineering, UK). The separate influences of drum rotational speed and drying air flow rate were studied by making measurements at four different pan-coater operating conditions: stationary drum with drying air turned on/off, and 8 rpm rotating drum with drying air turned on/off. For each case, four different spraying conditions (liquid supply rate and atomizing air pressure) were used. PDA scans were performed along the spray semi-major and semi-minor axes at two different axial distances (7.5 and 10 cm) from the atomizer tip.Results were as follows. When both the drying air and drum rotation were absent, increasing liquid supply rate while operating the atomizer at the lower of two atomizing air pressures decreased drop size. The opposite occurred when operating at the higher of the two atomizing air pressures. This suggests that the nozzle operated as a simplex pressure-swirl atomizer at lower levels of atomizing air pressure, but as an air-assist atomizer at higher levels of atomizing air pressure. Regardless, liquid supply rate had no significant effect on drop velocity. In contrast, a decrease in atomizing air pressure or an increase in axial distance always led to an increase in drop size and a decrease in drop velocity.Supplying drying air to the pan-coater resulted in up to a 6 m/s increase in drop velocity, but had mixed effects on drop size. When the spray gun was operated as an air assist atomizer, supplying drying air to the drum led to an increase in D32. The reverse was observed when the gun operated as a simplex pressure-swirl atomizer. These two observations are most evident when operating at the lower liquid supply rate (70g/min), suggesting that they may have arisen from drop evaporation. Increasing the drying air supply rate also reduced spray extent and volume flux magnitude.Adding drum rotation to the process generally led to (ⅰ) increased drop size and (ⅱ) increased drop velocity, (ⅰ) likely arose from the transport of small drops away from the spray zone, while (ⅱ) likely resulted from changes in droplet trajectories. Both are the result of the gas-phase swirling motion that is due to the drum rotation, (ⅰ) was most noticeable when the nozzle was operated as an air-assist atomizer. In addition, drum rotation decreased spray volume flux magnitude at the spray center, but increased it at other locations, essentially making the spray more dumbbell-shaped.Finally, the influence of drum rotation on drop velocity diminished when drying air flow was included. This was because the drying air momentum helped the drops oppose the effects of the swirling flow induced by the drum rotations.