Issue link: https://www.e-digitaleditions.com/i/962670
12 April 2018 Tablets & Capsules For example, Freund-Vector's production-size units are designed to accommodate batches of 25 to 95 percent of the pan's total working volume. To determine whether and where your batch size fits into your coating pan's batch-size range, you'll need to use the bulk density of the tablet cores you're working with to calculate the total volume of your batch and divide that by your coating pan's total working volume. Since most coating pans can accommodate a wide batch size range, you may need to adjust your operating parameters depending on where your batch size falls in that range. For example, when working at the lower end of your pan's range, it's common to use a lower-profile baffle to ensure proper mixing of the tablet bed. This will decrease any chance of overspray that could occur as a result of the standard baffles protruding from the smaller tablet bed. When running outside of your coating pan's range, it's common to see tablet coating defects, the most common being low tablet weight gain caused by overspray and coating buildup on the baffles and pan wrap. Coating-pan speed Once your batch size is established, you can determine the proper rotational speed for your coating pan to provide even coating and consistent weight gain on the tablets. If you run your pan too slowly, the tablet bed may lag or pause intermittently. When this occurs, some tablets may spend too much time in the spray zone and become over-wet, which could lead to sticking or picking defects. If the pan speed is too fast, the tablets may begin to move erratically through the spray zone rather than traveling uniformly with the rest of the bed, which can produce undercoated tablets. The goal is to achieve a uniform, cascading motion as the tablets travel through the spray zone. Spray-gun setup Once you've determined the proper pan speed, you can set up your spray guns. The number of spray guns will be determined by the size and design of your coating pan. For example, Freund-Vector coating pans use between one and 12 spray guns spaced evenly 7 inches (177.8 millimeters) apart. If the spray guns are spaced inconsistently, you may see an overlapping spray pattern or dead spots in the spray zone. This can cause over- wetting or streaking, either of which will negatively affect coating uniformity. Once the spray guns are installed, you can turn on the pan and adjust the angle and distance of the guns relative to the tablet bed. These adjustments need to be done as the tablets are tumbling to ensure proper coverage of the tablet bed. To do this, divide your tablet bed into thirds and adjust the guns so that they are perpendicular to the tablet bed and are aimed to deliver the solution between the bed's first (highest) and second (middle) thirds. If the guns are aimed too high, the spray will coat the tablets near the top of the tablet bed, where the bed depth is shallower. This can cause coating to build up on the pan wrap, decreasing yield and adversely affecting product article isn't a comprehensive guide to coater setup and operation; it's just a beginning step toward continuous improvement and training for coating equipment operators. Film coater basics A typical perforated pan tablet coater, as shown in Figure 1, is comprised of the following basic components: 1. A coating pan (or drum) with internal mixing baffles; 2. A spray system consisting of one or more atomizing spray guns mounted inside the coating pan and connected via a hose and pump to a solution tank; 3. A process air handling system, including a fan or blower, an inlet filter, heating elements, and a dehumid- ification unit with cooling coils and/or desiccant; and 4. An exhaust air handling system, including a fan or blower and an exhaust filter (not shown). During coating, an operator loads a batch of tablets into the coating pan, which rotates on a horizontal axis. As the pan rotates, the mixing baffles lift and mix the tablets, creating a cascading motion in the tablet bed. The spray guns atomize and direct the coating solution at the cascading tablets, coating them evenly as they pass through the spray zone. At the same time, the process-air fan forces heated, conditioned air into the pan to dry the coated tablets, and the exhaust fan creates negative pressure inside the coater, drawing the process air through the tablet bed and carrying away the evaporated moisture or solvent. A batch coater's critical operating parameters include the batch size, the coating-pan speed, the spray-gun setup, the spray rate, the tablet bed temperature, and the process airflow rate and dew point. Batch size Batch size is perhaps the most fundamental coating parameter since it helps you determine all the other parameters. The size of your batch will directly affect pan speed, spray gun setup, spray rate, bed temperature, and process airflow. Your coating equipment supplier can provide you with a batch size range for your coating pan measured as a percentage of the pan's total working volume. Figure 1 Perforated pan tablet coater Tablet bed Exhaust blower Mixing baffle Spray gun Heating elements Inlet blower Cooling coils Coating pan Solution tank Solution pump