Issue link: https://www.e-digitaleditions.com/i/962670
14 April 2018 Tablets & Capsules Spray rate and bed temperature The coating solution spray rate and the tablet bed temperature for your application will be dictated by the coating solution formulation you're using. Spray rates for production pan coaters can range anywhere from 50 to 225 grams per minute per gun for aqueous coatings, and bed temperatures can range from 22° to 60°C. Consult your coating supplier to determine the proper spray rate setting and bed temperature for your coating solution. Operating outside of your solution's specific range can cause coating defects, so it's critical that you use the information provided by your supplier when setting up your coating process. Process airflow and dew point The final coating parameters we'll discuss are the process airflow and dew point. The process airflow is very important because it carries heat, which encourages evaporation and dries the coated tablets. The volume and moisture level of the process air determine the coating system's drying capacity. As with the other parameters, your optimal process airflow will vary depending on the coater's size, manufacturer, and other variables. For production-scale coating pans, Freund-Vector recommends starting with a process airflow of 550 cubic feet per minute per spray zone and adjusting the air volume up or down depending on the coating quality produced. However, you should consult with your coating equipment supplier for the recommended process airflow for your unit. The process air dew point is important for maintaining optimal spray rates in your coating system. Some customers I've worked with were using unconditioned process air and needed to decrease a coater's spray rate by as much as 50 percent to compensate for a change in local weather conditions. For this reason, we recommend conditioning the process airflow for any coating trial to remove moisture and achieve a dew point of 10°C. This is commonly done using a chiller; however, for some moisture-sensitive products, such as effervescent tablets, dew points as low as -5° to -10°C are necessary, which requires the use of a desiccant unit. Work with your supplier Coating equipment suppliers have a great deal of experience with and information about the coating systems they provide. The major producers of tablet coating materials also offer an array of tablet coating and solid dosage seminars. These seminars can be especially useful because they help coating equipment operators understand not only the coating process but also granulation and tableting, which affect coating performance. Thanks to advances in coating equipment and materials, the film coating process in fully perforated coating pans has become a less complex unit operation. However, it still requires skill, attention, and an understanding of the parameters and variables involved. By continuously educating yourself on techniques, learning from the experiences of others, and working closely with your coating equipment supplier, you can ensure the success of your coating process. T&C Nicholas S. Slater is a senior process scientist at Freund-Vector (319 377 8263, www.freund-vector.com). Figure 2 Spray-gun pattern air pressure a. Ideal spray pattern b. Pattern air pressure too low c. Pattern air pressure too high