Issue link: https://www.e-digitaleditions.com/i/1371139
10 May/June 2021 Tablets & Capsules followed by an Acryl-Eze (Colorcon) delayed- release coating (20 percent w/w solids). In this example, the total tablet throughput rate was 26 kg/h, using a seal coat target weight gain of 2 per- cent, and a delayed-release coating target weight gain of 10 percent. Effective delayed-release perfor- mance was achieved at a 6 percent weight gain for the delayed-release coating layer. • If desired, the spray rate can be varied in each seg- ment, within limits defined by thermodynamic constraints. The data shown in Table 1 summarize some typical processing conditions that have been successfully used for the application of an intermediate solids coating system using a Driaconti-T coater. While this article is primarily focused on continuous pan coating processes, attempts have been made to develop continuous fluid-bed coating processes as well. For example, Hampel, et al. [4] have described a continuous pellet-coating technology based on the Wurster process. This example more closely resembles a semi-continuous process. Uncoated pellets are introduced into the processing chamber, a cer- tain amount of coating is applied, and then subsequently more uncoated pellets are introduced into the chamber while some coated pellets (larger particles) empty through a particle sluice into a separation chamber. In the separation chamber, particle size is measured by means of gas flow; larger particles are allowed to exit, while smaller particles are returned to the coating chamber. The assumption is that the larger particles have acquired the appropriate amount of coating, while the smaller particles have not. A potential problem with this concept is that the starting uncoated pellets exhibit a certain particle size distribution, with a range of pellet sizes. Particles that were larger initially could be allowed to exit the process with less than the target amount of coating applied, while particles that were smaller initially may not be allowed to exit the process despite having the target amount of coating applied. The Driaconti-T semi-continuous coater offered by Driam, shown in Figure 3, is designed around a single extended processing chamber with several segments (typ- ically seven) equipped with gates (or flaps) that can be programmed to allow product to transfer from one segment to the next at preset intervals. (Note that, while the dwell time is flexible, for obvious reasons, it must be the same in each segment.) The Driaconti-T provides important coating flexibility, since: • The dwell time in each segment can be varied to suit the product being coated. This flexibility allows the operator to select shorter dwell times for low-weight-gain cosmetic coatings and longer dwell times for modified-release coatings that require higher target weight gains. • A different coating formulation can be applied in each segment. For example, Cunningham, et al. [3] have described the application of a two-part delayed-release coating based on an Opadry (Colorcon) clear seal coat (10 percent w/w solids) Figure 3 Schematics of the Driaconti-T semi-continuous coater Loading hopper with vibrating chute Drive Coating drum Spray arm Discharge funnel In Phase 1 Phase 2 Phase 3 Phase 4 Phase 5 Phase 6 Out Flap position during film coating Flap position during product transfer Photo 1: Recently introduced lower-throughput, fully continuous coaters, such as the O'Hara FCC 75, can handle the output from a typical high-speed tableting process.