Tablets & Capsules

TC0417

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T Tablets & Capsules April 2017 13 coating Understanding the film coating process Gernot Warnke JRS Pharma The film coating process is characterized by a highly complex network of interdependent parameters. This article provides an analysis of the relevant parameters and their effects on the qual- ity of the coating. It also provides a parameter map to help you set up the coating process. he quality of film-coated tablets depends on three main factors: the properties of the substrate (e.g., the tablet cores), the film coating material, and the setup of the coating process. As long as the tablet cores have sufficient hardness, low friability, and an appropriate shape, they pose no particular issue in terms of achieving good coating results. Ready-to-use film coating materials, such as those my company supplies [1], are carefully designed to per- form well under a wide range of coating conditions and are very seldom cited as the root cause of coating defects. By contrast, how the coating process is set up ranks as the most common cause of problems in film coating. Analyzing the film coating process The film coating process is essentially a combination of three interwoven unit operations: •Application of the liquid coating material (typically a suspension) by atomization •Conversion of the liquid coating to a solid film coat- ing by drying, and •Uniformity of film application by simultaneously blending the cores. Each of these operations must be balanced to achieve the desired result: A substrate enrobed in a smooth film of uniform thickness. As Equation 1 shows, it is essential that the specific surface area of the substrate not vary from batch to batch: Film thickness = While tablets have well-defined dimensions, the parti- cle size distribution of sugar or cellulose spheres may be more variable, which affects the surface area to be coated. Likewise, if the dimensions of the tablets change, you (Applied coating weight x Density of dry film) (Substrate surface area) (1)

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