The influence of additives on the spreading coefficient and adhesion of a film coating formulation to a model tablet surface

The surface energies of film coating formulations based on hydroxypropyl me thylcellulose and containing microcrystalline cellulose, lactose and Tween 20, respectively, have been assessed. The approach taken allowed the compon ents of the surface energy, in terms of the Lifshitz-van der Waals and the acid-base contributions, to be determined. Spreading coefficients of these coating formulations were determined on a model tablet surface whose surfac e energy had been similarly characterised. The determined spreading coeffic ients were high and positive indicating that spreading and wetting would no t be a controlling factor in the formation of an adequate film coat. The ad hesion of the coats to the core was measured and showed that the inclusion of additives influenced the adhesion of the film. Maximum adhesion was obta ined when microcrystalline cellulose was included in the coating formulatio n that presumably allowed a strong interaction with the same component in t he tablet core. Adhesion was enhanced when the tablet cores were made at a higher compaction force. Atomising air pressure had little influence on the adhesion. (C) 2001 Elsevier Science B.V. All rights reserved.