Frictional Properties of Tablet Lubricants

Some frictional properties of tablet lubricants were determined. The friction coefficients and the adhesion forces of six lubricants were evaluated by the method proposed previously. The ejection force against the radial force for each lubricant yielded a straight line through the origin, so that the adhesion forces of these lubricants were estimated to be almost zero. All lubricants had low friction coefficients when they alone were compressed. The value for metal stearate was the smallest and that for talc was the largest. The affinity of the lubricants to the die wall, another important property of the lubricants, was also determined. After the die wall was conditioned by the tabletings of each lubricant alone, the serial tabletings of lactose granulates in the die were carried out. The increasing rate of ejection force in the conditioned die in a serial tableting was different for every pretreatment of each lubricant. The affinity of magnesium stearate to the die wall surface was superior to that of other lubricants.