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Pharmaceutical Coating Technology (Part 2)

The chapter commences by reviewing the properties of the broad classes of materials used in film coating, polymers, plasticizers, pigments and solvents (or vehicles). An initial consideration of the polymers shows that while processing is most commonly performed using these materials in solution, there are systems which utilize polymers in suspension in water. The mechanism of coalescence and film formation for these types of materials are discussed. The individual polymers are dealt with in some detail and an attempt is made to divide them into functional and non-functional coating polymers. Functional polymers being defined as those which modify the. | Page 6 2 Film-coating materials and their properties John E.Hogan SUMMARY The chapter commences by reviewing the properties of the broad classes of materials used in film coating polymers plasticizers pigments and solvents or vehicles . An initial consideration of the polymers shows that while processing is most commonly performed using these materials in solution there are systems which utilize polymers in suspension in water. The mechanism of coalescence and film formation for these types of materials are discussed. The individual polymers are dealt with in some detail and an attempt is made to divide them into functional and non-functional coating polymers. Functional polymers being defined as those which modify the pharmaceutical function of the compressed tablet for instance an enteric or modified releae film. However this distinction is sometimes blurred as one coating polymer can fall into both groups. The essential polymer characteristics of solubility solution viscosity film permeability and mechanical properties are described in terms of ultimate film requirements. In the treatment and description of plasticizers some prominence is given to their effect on the mechanical properties of the film and its permeability characteristics especially to water vapour. A section is provided on the assessment of plasticizer activity on film-coating polymers. The section on pigments describes how they function as opacifiers and also their ability to modify the permeability of a film to gases. In considering the solvents and vehicles used in film-coating techniques a discussion is provided of the respective merits of aqueous and non-aqueous processing. The chapter is concluded by some examples of formulae of film-coating systems which illustrate several of the principles described previously. Page 7 2.1 INTRODUCTION A film coating is a thin polymer-based coat applied to a solid dosage form such as a tablet granule or other particle. The thickness of such a coating is .