Abstract
Static electrification in tablet formation and the behavior of crystals to compression were investigated on four inorganic and 10 organic crystalline medicines, from the records of upper- and lower-punch forces and static charge using a wire resistance strain gauge and specially designed vacuum tube voltmeter. Same amounts but of opposite signs of charges were found between the tablet and the insulated punches or die. The amount of static charge was not markedly different from the one obtained when punches and die were grounded and it remained on the tablet after compression. Therefore, it was evident that the static charge was formed by the friction between the crystal and die wall and not due to piezoelectricity. The following conclusions were drawn from the results obtained. 1) The increase of static charge was recognized with the increase of upper-punch force and the same tendency was found when finer crystalline particles were compressed. It may be explained from the increase of frictional surface area of different particle size or by the crushing of crystals. 2) Static electrification was reduced to 1/2 to 1/4 by the addition of lubricants. It may be caused by the reduction of friction and the presence of a third substance since frictional electrification is specially determined by the given combination of substances. 3) Increased ratio of transmittance of force from upper punch to lower punch by the addition of lubricant decreased with the increase of upper-punch force and the degree of decrease affected by the crushing of crystal, and the affinity between crystal and lubricant. 4) Static charge was reduced to 1/20 by the treatment of crystal with a nonionic surfactant. 5) The amount of static charge found on unit weight of crystals in tablet formation was nearly the same as that appearing on the crystal in the chute experiments reported previously.
