Issue link: https://www.e-digitaleditions.com/i/1163217
Tablets & Capsules September 2019 39 The pressure applied to the die during tableting is not uni- form, which sometimes causes uneven and heterogeneous pressure on finished tablets. Over lubrication of particles insulates them and prevents the bonding required to form hard tablets. Following these principles, the proper ratio of diffusion and axial blending combined with the correct component blending time and blender speed, will produce a high degree of homogeneity in the blend. Equipment supplier differences In the past, twin-shell and double-cone blenders were under patent. With those patents expiring, any company can make a blender, and those blenders may be SUPAC plished by having lubricant particles in direct contact with or close to the die wall. These particles are smeared on the die-wall surface as the punch tip moves into the die bore, effectively forming a film of lubricant, which is not necessarily uniform or continuous. Some of the lubricant remains on the punch tips and in the die after tablet compression. Thus, the nature of lubrication between the formulation and the die wall is mixed, where both adequate and inade- quate contact between the unprotected metal surfaces of the punch and die results in smooth tablet ejection or par- tial adhesion/release and sometimes even partial seizure, which produces lamination at the bottom of the tablet. Problem/change Effect on final blend Effect on lubrication (same blending time) Effect on compressed tablets Increase in bulk density of a major component/Change in target fill level • Greater bulk density • Decreased blender occupancy • More particle coverage each rotation • Softer tablets • Longer disintegration time • Lamination Shift in the morphology of the lubricant, especially magnesium stearate • Flatter particles • Increased particle coverage each rotation • Softer tablets • Longer disintegration time • Lamination Upward shift in the bulk density of the lubricant, magnesium stearate • Finer particles • Greater surface area • Increased particle coverage each rotation • Softer tablets • Longer disintegration time • Lamination Underfilling blender by more than 10% • Decreased blender occupancy • Increased particle coverage each rotation • Softer tablets • Longer disintegration time • Lamination Overfilling blender by more than 10% • Uneven blend lubrication • Over lubricated in some areas and under lubricated in some areas • Picking/sticking • Softer tablets Change in lubricant screening • Greater or smaller particle size • Particle coverage • Picking/sticking • Softer tablets Change in batch size • Blender occupancy changes • Varies Change in blender supplier • New blender may or may not be equivalent • May alter lubrication • Varies Table 2 Causes of soft tablets in tablet compression Figure 3 Various baffle configurations for octagonal blenders