Lamination of Pharmaceutical Tablets: Classification and Influence of Process Parameters

Lamination is a common industrial problem during the production of pharmaceutical tablets. It corresponds to a failure of the tablet in one or several planes parallel to the surface and passing through the tablet band. But different kinds of lamination exist, and a classification of the different cases is proposed in this work. Type 1 corresponds to a multiple fracture caused by air entrapment. Type 2 occurs because of the shear stresses developing when the tablet goes out of the die. Type 3, which is limited to convex tablets, is due to a tensile stress developing at the center of the tablet at the end of the unloading that further propagates toward the band. One case of each type was studied experimentally in order to test three solutions classically used at the industrial level: slowing down the press, using a precompression and using a tapered die. Results shows that, in coherence with the proposed mechanisms, lamination type 1 can be mitigated by slowing down the press or using a precompression. For type 2, only the tapered die solution stopped lamination. None of the solutions completely solved lamination type 3. Nevertheless, the use of a tapered die decreased the severity of the problem avoiding the propagation of the crack until the surface.