Issue link: https://www.e-digitaleditions.com/i/1101841
12 April 2019 Tablets & Capsules sugar-coating processes, the mixing elements must not allow the highly sticky sugar-coated tablets any opportu- nity to get stuck in low- or no-flow recesses in the drum. Ramp-shaped mixing elements, as shown in Figure 2, are particularly suited to this process because they allow the sugar-coated tablets to glide over them, even if the tab- lets are very sticky. Spraying. To apply coating solution or suspension to an entire batch of tablets as quickly as possible, it's benefi- cial to maximize the number of spray nozzles and/or the tablet-bed surface area that's exposed to the spray guns during coating. For this reason, drum coaters with an extended drum, a longer spray arm, and more spray noz- zles, as shown in Figure 3, have become increasingly popu- lar for film coating processes in recent years. The extended drum flattens out the tablet bed, exposing a greater per- centage of tablets to the spray guns during operation. Depending on the coating solution and the required droplet size, film coaters use either airless or two-sub- stance spray nozzles. Airless nozzles, as shown in Figure 4, create an exceptionally homogeneous spray pattern at high pressure levels. As discussed earlier, it's critical to maintain the correct distance between the spray nozzles and the tablet bed to prevent either over-moistening the tablets or the coating droplets drying before reaching the tablet bed. Maintaining the correct angle between the nozzles and the tablet bed surface is also critical. Many modern film coaters use auxiliary motors to precisely reg- ulate the nozzle distance and angle automatically without requiring manual intervention by the operator. Monitoring the spraying process with two-substance nozzles is usually limited to the spray-air pressure, the pattern-air pressure, and the coating solution spray rate. Figure 4 Schlick PCA spray arm with airless nozzles and manifold supply Figure 3 Position and arrangement of film coater spray nozzles Spray arm Cleaning nozzle Tablet bed Spray pattern Spray nozzles Coating drum Figure 5 Typical production coating system Exhaust air system Control system Inlet air unit Cleaning unit Coating solution tank Dosing pump Coater HMI