The coating process Graham SUMMARY 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. | Page 170 7 The coating process Graham SUMMARY 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. PROCESS DEVELOPMENT OF AQUEOUS FILM COATING Coating of tablets and pills is one of the oldest techniques available to the pharmacist and references can be traced as far back as 1838. The sugar-coating process was regarded as more of an art than a science and its application and technology remained secretive and in the hands of very few. Although a very elegant product was obtained its main disadvantage was the processing time which could last up to Page 171 five days. Many modifications were advocated to improve the basic process such as air suspension techniques in a fluidized bed the use of atomizing systems to spray on the sugar-coating the use of aluminium lakes of dyes to improve the evenness of colour and more .
