QUANTITATIVE ESTIMATION OF INTERNAL-STRESS DEVELOPMENT IN AQUEOUS HPMC TABLET FILM COATS

Data have been produced on the parameters which influence the developm ent of internal stresses within aqueous HPMC film coats plasticized wi th glycerol in an attempt to calculate the magnitude of internal stres s generation. Films have been prepared under conditions which equate t o those experienced during film coating processes. The changes in mech anical and thermal properties of fresh films formed at different table t bed conditions have been studied during their ambient storage. The c ontribution of internal stresses from three sources are calculated ind ividually and a single equation is used to estimate the total internal stress within a film. This equation considers the contribution made b y the volumetric changes of the tablet core during ambient conditions in addition to those caused by other well-established mechanisms. The results of these calculations showed that the total internal stress is influenced, not only by these volumetric changes, but also by the con ditions in which the film coating process was performed. The possibili ty of the film coating undergoing failure is also discussed.