The cracking of film coatings on film-coated tablets—a theoretical approach with practical implications

Abstract

A theoretical approach of film cracking is presented using equations which allow for the calculation of both the internal stress in a film coating due to shrinkage of the film on evaporation of the solvent and the thermal stress due to differences in the thermal expansion of the film coating and tablet substrate during changes in temperature arising out of the coating processes. The practical implications of this approach in film formulation are discussed with particular reference to the choice of tablet core formulation, the grade of polymer used, the type and concentration of both plasticizers and pigments and the solvent system used in the coating process.

Effect of hydroxyl group content in ethyl cellulose on permeability in free films and coated membranes

“…One plausible explanation could be the decrease in solvent quality, as shown in Figure 1, as a result of the increase in the Huggins constant. The observed decrease in mechanical properties is similar to the findings of Rowe 16,17 that, the poorer the solvent, the lower the modulus of elasticity. This means that a solvent producing a low Huggins constant value is favorable when it comes to the mechanical properties.…”

Novel Film Modifiers to Alter the Physical Properties of Composite Ethylcellulose Films

“…Hence, /EM may be used to predict the incidence of edge splitting of a film coat (60). The larger its value the higher the stress crack resistance of a film.…”

“…An important parameter for evaluating the mechanical properties of film coatings applied to tablets is the incidence of cracking or edge splitting (60,68). The occurrence of film coating defects has been associated with the magnitude of internal stress in the film.…”

Thermal Characterization of Drug/Polymer and Excipient/Polymer Interactions in Some Film Coating Formulation

“…The results obtained indicate the consequences of this phenomenon in film coating practice would be dependent on the nature and extent of interaction between the excipient/drug and film coating polymer. It is generally accepted that plasticization, which manifests as a fall in Tg, Ts and/or crystallinity (Moelter & Schweizer 1949;Okhamafe & York 1985a, b), often lowers the incidence of film coating defects such as cracking, edge splitting and bridging of intagliation (Rowe 1981(Rowe , 1982. This is usually desirable.…”