Influence of the punch head design on the physical quality of tablets produced in a rotary press

This study aims to investigate the influence of tablet punch head design on compaction and the resultant tablet mechanical properties. Tablets were prepared using flat-face punches with different head flat and head radius configurations, on a rotary tablet press with compression rolls of different diameters. The results showed that tablets produced using punches with head flats consistently displayed higher tensile strengths and lower capping tendencies. Exclusion of the head flat in the punch head geometry caused the compacts to undergo a state of continual deformation during the compaction cycle, possibly with increasing elasticity without the opportunity for more prolonged stress relaxation. Extension of head flat diameter produced small increments in dwell time and this could bring about significant improvements to the tablet mechanical quality. Changes to the punch head radius were found only to affect the compression profiles marginally, but this only produced insignificant differences in the tablet mechanical properties. A smaller compression roll allowed greater plastic flow during the dwell phase, but this was insufficient to effectively counteract the adverse effects due to increased strain rate during the consolidation phase, leading to deterioration of tablet mechanical quality.