Effects of film coatings on tablet hardness

The effects of five conventional film-coating materials on tablet hardness were studied. Placebos showed apparently linear increases in hardness as coatings were applied. Completely coated samples exhibited hardness increases from 50 to 140%, with a corresponding 3% increase in tablet weight. Equations were derived relating hardness changes to the "breaking strength" of the film on the tablet. Findings indicate that the coatings exert their influence primarily along the diameter of the tablet in a direction perpendicular to an applied compressional force. Furthermore, the coating process itself did not alter core hardness since tablets from which the film could be stripped showed original values.