Measurements of the Vertical Pressure Distribution on the Surfaces in Contact with Punches for Potassium Chloride Tablets

Abstract

During the compaction in a die with a single-punch, the particles of potassium chloride powders cause fracture and fragmentation, and these phenomena are recognised even by the naked eye. On the photomicrographs of the surfaces in contact with upper and lower punches, the particle contact-area was measured. A significant relationship (Eq. (5)) was obtained between punch pressure and the ratio of actual contact-area to total surface area. Using Eq. (5), the radial distribution of the vertical pressure on the two surfaces was determined. This contact-area method is suitable for pharmaceutical powder beds, which are soft and water-soluble. On the surfaces in contact with the upper punch, the pressure distribution curves had the maximum value at the periphery, and they crossed at the average punch pressure of 1000 [kg/cm²]. As the thickness of the tablets increased, the gradients of these curves were intensified. On the surfaces in contact with the lower punch, the curves had the maximum value at the center, and the shape of the curves did not change on increasing tablet thickness.