Effect of water content on sticking during compression

A rotary type tablet machine (Correct 12 HUK-AW, Kikusui, Co., Ltd.) fitted with flat-faced punches 8 mm in diameter was used to measure the scraper pressure (SCR), a kind of shear stress, as a direct means of evaluating sticking. The shear stress between the tablet and lower punch surface was determined using a system of SCR detection (strain gauge type, Okada Seiko Co., Ltd.).SCR increased with increasing compression pressure for samples at all water contents teste. The SCR had a tendency to increase up to a water content of 3%, then showed a decrease at a high water content. This suggests that the adhesive force between particles increases with increasing water content, but for high water content, shear stress decreased due to the effect of water as a lubricant. It is assumed that the sticking ratio increases proportionally with water content until about 3%.Mean surface roughness (Ra) of tablets due to sticking showed the same relationship between SCR and water content. The SCR increased with an increasing value of Ra. Thus, it was suggested that the adhesive force between particles and the punch surface plays an important role in sticking.