Influence of the punch shape on the core and shell structure of press-coated tablets

Press-coated tablets are a key technology to achieve delayed releases in chronotherapeutics. The drug release properties of this kind of tablets are linked to its unique core-shell structure. It is thus important to understand the influence of the process parameters on this structure. As different shapes can be used in the industry, we focused, in this study, on understanding the influence of punch shape on the final structure of a press-coated tablet. Experiments were performed using flat, bevel-edged and concave punches for the coating-compression to study the effect of the punch shape on the final properties of the core but also on the density distribution in the shell. The experiments were supported by numerical simulation to understand the mechanical effects in the powder compression process. It was found that the radial and axial stress state in the shell and in the core during compression is very dependent on the punch shape. The use of concave punches results in a more hydrostatic stress state compared to flat punches. The consequences on the structure are a more homogenous shell and less deformation of the core, which confirms that the tooling shape is a critical parameter to consider for the production of press-coated tablets.