The adhesion of film coatings to tablet surfaces--the effect of some direct compression excipients and lubricants.

The effect of some direct compression excipients and lubricants on the adhesion of hydroxypropyl methyl cellulose films has been examined using a specially designed tensile testing apparatus (Fisher & Rowe, 1976). The adhesion was found to be influenced by both the roughness, including microporosity, of the tablet surface and its polarity. Tablets prepared from microcrystalline cellulose showed very high adhesions despite having relatively smooth surfaces, owing to the surface being saturated with hydroxyl groups able to form hydrogen bonds with the corresponding groups on the polymer. The addition of magnesium or calcium stearate to the tablet was found to decrease the adhesion, but the addition of stearic acid caused a significant increase. The effect of lubricant concentration on the adhesion could be expressed by an equation similar to that proposed by Hofrichter & McLaren (1948) for the adhesion of vinyl chloride/vinyl acetate copolymers to regenerated cellulose.