Tablet compaction to a constant load

Abstract

In studies of tablet compaction, it is usual to work at constant tabletting force (or pressure) or to correlate the tablet properties with the force. Owing to the friction between the tablet and the die wall, different forces are obtained on the upper and lower punch and it is not obvious which of the values is the most relevant one to use. In most studies on instrumented reciprocating tablet presses, the maximum upper punch force (UPF) is regarded as the tabletting force but the mean of the UPF and the maximum lower punch force, (LPF), has also been used (e.g. by Hersey et al., 1967). The lower punch force has been claimed to be independent of the die wall friction (Lammens et al., 1980, 198 1) and would be a useful measure of the tabletting force. There seem, however, to be few experimental data supporting the choice of the different force measures or their importance in compaction studies. In a recent study (Ragnarsson and Sjogren, 1983) we compressed a number of tablets of sodium chloride, anhydrous lactose and saccharose in a die which was lubricated at the beginning of each series. No lubricant was added during the series and the die wall friction consequently increased while all other factors were kept constant, As illustrated in Fig. 1, both the UPF and the LPF were affected by the