Local analysis of the tablet coating process: Impact of operation conditions on film quality

Spray coating is frequently used in the pharmaceutical industry to control the release of the active pharmaceutical ingredient of a tablet or to mask its taste. The uniformity of the coating is of significant importance, as the coating usually has critical functional properties. However, coating uniformity is difficult to predict without significant experimental work, and even advanced particle simulations need to be augmented by CFD models to fully describe the coating uniformity on a single tablet. In this study we analyze the coating process by using detailed computational fluid dynamics (CFD) multiphase spray simulations. The impact and the deposition of droplets on tablets with different shape, as well as the production and evolution of the liquid film on the surface of the tablets are numerically modeled. Spray droplets are simulated with a Discrete Droplets Method (DDM) Euler Lagrange approach. Models for multi-component evaporation and particle/wall interaction are taken into account. The wall film is treated with a two-dimensional model incorporating submodels for interfacial shear force, film evaporation and heat transfer between film, solid wall and gas phase. Our simulations show how different physical parameters of the coating spray affect the coating process on a single tablet. For example, we analyze for the first time the deposition behavior of the droplets on the tablet. The outcome of our work provides a deeper understanding of the local interaction between the spray and the tablet bed, allowing a step forward in the design, scale-up, optimization and operation of industrial coating devices. Furthermore, it may serve as a basis for the combination with state-of-the art DEM particle simulation tools. (C) 2010 Elsevier Ltd. All rights reserved.