ABSTRACT
In recent years tablet coating has undergone several fundamental changes. The original sugar-coating technique has been largely replaced by film-coating processes using organic solvents. The organic solvents are now being replaced by water because of the development of suitable polymers, improvements in the coating process, and legislation regulating the discharge of pollutants into the environment. This change has resulted in increased interest in equipment designed for film-coating based on cylindrical-shaped side-vented pans which allow the drying air to be drawn through the tablet bed. However, the process is complex and requires careful monitoring and control to ensure satisfactory results. The empirically derived conditions are not fundamentally understood and there are important differences in the operation of the commercially available equipment. This chapter discusses some of the theory behind the spraying process and describes the instrumentation and performance of these systems. It illustrates how considerable process improvements can be made by the application of heat and mass transfer theory and how changes in parts of the equipment can provide a reduction in the overall coating cycle.
