[Influence of compression pressure and die-wall pressure on tablet sticking]

An eccentric-type tablet machine fitted with 8-mm-diameter flat-faced punches was used to measure the forces of upper and lower punches, die-wall pressure, tablet ejection force, and scraper pressure (SCR), a type of shear stress, to evaluate sticking behavior. The shear stress between the surfaces of the tablet and lower punch was determined using an SCR detection system. Mean surface roughness (R(a)) of tablets, measured by laser scanning microscopy, was used to estimate the magnitude of sticking. Tablet tensile strength tended to increase with compression pressure, which is consistent with previous reports. SCR decreased with increasing compression pressure for samples at all formulations (i.e., for different kinds and percentages of lubricant). R(a) associated with sticking increased with SCR, indicating that the adhesive force between the particles of the tablet surface and the lower punch surface plays an important role in sticking. Multiple linear regression analysis with SCR as the response variable was conducted. Upper and lower punch force, die-wall pressure, tablet ejection force, SCR, percentage of lubricant, and tensile strength of tablet were selected as explanatory variables. Results of this analysis indicate that the incidence of sticking decreased when either the lower punch force or die-wall pressure increased, where, of these two, increasing the lower punch force had a stronger effect on decreasing SCR.