Figure 1: In the coating process, each tablet receives numerous partial coatings, which leads to a homogeneous coating layer. The scanning electron microscopy (SEM) picture shows a cross-section of the coating layer on the tablet core. (ALL FIGURES COURTESY OF THE AUTHORS)

CHRIS ROGERS/GETTY IMAGES

Although drum coating is commonly used in the pharmaceutical industry, there have been relatively few scientific investigations reported in the literature. Moreover, process design has been based mostly on trial-and-error and operator experience. Recently, in addition to experimental work, advances in computational simulations have become an important tool for such investigations (5–8).

Figure 2: A schematic representation shows different process regimes of the coating process with an appropriate simulation approach used for each. For (a) and (c), colors denote velocity from slow (blue) to fast (red). In (b), the red color represents coating thickness; the tablet on the right in the lower box has a thicker coating.

The work aims to provide a deeper understanding of:

• The tablet-mixing process in an industrial pan coater, which allows optimization of the tablet residence time in the spray zone
• The local behavior of the spray droplets impacting on a single tablet, which leads to a wider understanding of film formation mechanisms
• The interaction between the spray and coater drying air, thus allowing a detailed analysis of the deposition efficiency of coating material on the tablet bed and insight into operative problems like overspray, filter plugging, or incomplete tablet-coat curing.