Experimental and Theoretical Study of Tablet Flow in a Lab Scale Pan Coater

The coating of tablets using a film coating operation has become a common process in the pharmaceutical industry to add color distinction, physical protection, or taste masking properties to the final product.  Given the delicate nature of some tablets, it is important to know how certain process parameters may affect the tablet motion and interactions within a coating pan.  In recent years, in silico computer simulations have become a common trend for trying to predict this behavior using techniques like Discrete Element Methods (DEM) to compare/calibrate to actual experimental/physical conditions.

The aim of this work is to develop DEM simulations for a laboratory film coating pan (Labcoat 24” O'Hara Technologies, USA) and calibrate the model using experimental measurements from the same instrument.  The model was developed around a 12-16 kg fill of the coating pan with 10/32” Round Standard Curve placebo tablets, with comparisons being performed on the distribution of spray zone residence time of selected tablets and the bed cycle time. 

Experimental data was generated using tracking tracers and a video imaging system that was placed inside the coater.  The images used a rectangular region of the tablet bed surface as the spray zone, and the frequency of the tracer in the spray zone was extracted using automated image processing, see Fig.1.

Fig. 1: Schematic of the experimental setup; the same size and location of the spray zone is also used in the DEM simulations.

Simulations were performed using the commercial software EDEM 2.4 (DEM Solutions, UK) where the tablet shape was approximately reproduced using 8 partially intersecting spheres (“glued sphere” approach).  A post-processing algorithm was developed featuring the same zone as was imaged as the spray zone in the experiments to track the spray and bed residence times of selected tablets.

The simulation results showed good agreement with the experimental data, helping to calibrate and validate the model and its parameters.  The validated DEM simulation can be used to show local tablet velocity and collision forces, and how they relate to the operating conditions of the coating pan.  With further development of this DEM approach and understanding the hardness of different tablet systems, it may become possible to design and optimize coating pans and process conditions for ideal coating operations with minimal tablet damage.