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Pharmaceutical Coating Technology (Part 12)

Mechanical properties of film coats Michael E.Aulton SUMMARY This chapter discusses the need for a film coat to possess the correct mechanical properties. One of the requirements of a film coat is that it should provide adequate protection to the dosage form. The capacity of the film coat to afford physical protection depends to a large extent on its mechanical characteristics. After considering those desirable properties, the chapter explains how to assess such properties. It also explains the need for a standardized approach to film preparation prior to testing. The main techniques that have been used successfully for the. | Page 288 12 Mechanical properties of film coats Michael E.Aulton SUMMARY This chapter discusses the need for a film coat to possess the correct mechanical properties. One of the requirements of a film coat is that it should provide adequate protection to the dosage form. The capacity of the film coat to afford physical protection depends to a large extent on its mechanical characteristics. After considering those desirable properties the chapter explains how to assess such properties. It also explains the need for a standardized approach to film preparation prior to testing. The main techniques that have been used successfully for the assessment of pharmaceutical film coat properties are indentation hardness and tensile testing. These techniques are described in detail and representative data for polymeric film coat formulations are presented. The source and consequences of internal stresses within a film coat are explained and the consequences with respect to film-coating defects are discussed. 12.1 INTRODUCTION 12.1.1 Desirable mechanical properties of polymeric film coats Tablets and pellets are film coated for many reasons. One of the requirements of a film coat is that it should provide adequate physical protection to the dosage form. The capacity of the film coat to afford this protection depends to a large extent on its mechanical characteristics. The coating must remain intact be durable and be resistant to chipping and cracking during handling. Both the film itself and the composite system i.e. film plus tablet or pellet substrate should therefore possess suitable mechanical properties. Page 289 The mechanical characteristics of polymer film coats are an important parameter in dictating their performance in pharmaceutical dosage forms. A commercial film coat does not consist of polymer alone but contains many other ingredients. Additives are often included for a specific reason either to assist processing or to improve performance. It should be appreciated