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Film coat quality Michael E.Aulton and Andrew M.Twitchell SUMMARY This chapter discusses the desirable properties of polymer film coats with respect to their end usage. The mechanical properties of films were discussed fully in Chapter 12 and so this chapter concentrates on other aspects of film quality such as gloss and roughness, uniformity of film thickness and defects such as cracking, edge splitting, picking, bridging and foam filling of intagliations, etc. The methods of assessing film coat quality by visual observation, light section microscopy, surface profilimetry and scanning electron microscopy are discussed. Other techniques such as dissolution, adhesion measurements. | Page 363 13 Film coat quality Michael E.Aulton and Andrew M.Twitchell SUMMARY This chapter discusses the desirable properties of polymer film coats with respect to their end usage. The mechanical properties of films were discussed fully in Chapter 12 and so this chapter concentrates on other aspects of film quality such as gloss and roughness uniformity of film thickness and defects such as cracking edge splitting picking bridging and foam filling of intagliations etc. The methods of assessing film coat quality by visual observation light section microscopy surface profilimetry and scanning electron microscopy are discussed. Other techniques such as dissolution adhesion measurements and permeability measurements are mentioned briefly. The influence of formulation and process variables on the quality of the resulting film coat is then discussed and advice for the production of a smooth coat is provided. Coating defects are discussed with respect to their cause and suggestions are given for possible methods to reduce their incidence. 13.1 DESIRABLE AND ADVERSE PROPERTIES OF FILM COATS The required properties of a film coat are numerous. The coating may be added to a dosage form for cosmetic processing or functional drug delivery reasons. A discussion of the reasons for film coating has been given in Chapter 1 and a further discussion relating to desirable mechanical properties was given in Chapter 12. In the context of this chapter it is necessary to clarify the definitions of gloss and roughness and also to be aware of the correct terminology for the many possible coating defects that might occur. Page 364 Gloss Gloss can be defined as the attribute of the polymer surface which causes it to have a shiny or lustrous appearance. Rowe 1985 determined gloss values of film coats by measuring light reflected at 60 by flat-faced film-coated tablets. He reported that with organic solutions of HPMC increased polymer concentration and thus viscosity caused a reduction in the
