The primary objective of the current work was to investigate process variables affecting weight gain coating variability (CV) in pan coating devices. The effects of pan speed, pan loading, baffle design, spray area and spray shape were investigated. A CCD camera was installed in a 24 in. pan coater to monitor the movement of particles inside the coater using machine vision. The tablets in the bed were coated with 4% black Opadry^TM. An identical white tracer tablet was coated with 4% clear Opadry^TM and introduced in the bed of black coated tablets. Information on particle circulation time (time between successive tablet sightings at bed surface), surface time (time spent by the particle in spray zone), and the velocities parallel and perpendicular to the cascading layer of particles was obtained.

This video-imaging technique enables in-situ study of particle motion as the tablets pass under the spray gun, unlike other studies conducted from outside the side-wall of the pan. Another major advantage of this technique is that full frames of image data need not be stored for post-processing, and a 30 min experiment typically generates a data file of size 40-60 kb.¹ This technique provides a scientific approach to evaluating CV versus a case study approach that is generally used. It is also an independent and unbiased method to quantify the effect of drum internals (baffles) based on mixing inside the pan.² The data generated is used as input to a mechanistic model to predict CV from measurements using Monte-Carlo (MC) simulation. The simulation allows parametric effects to be studied ex-situ and initial optimization can be performed.

The movement of tablets was compared with spherical particles to study the effect of tablet shape. The average velocity (parallel to the flow direction) of tablets (standard round placebos) in the cascading layer was found to be significantly higher than spheres. A linear model (R²>0.98) best described the variation of velocity as a function of pan speed for all operating conditions for both spheres and tablets.^3,4 Monte Carlo simulations results showed that CV decreases with increasing pan speed and coating time. The effect of spray shape and spray area on CV was studied. It was found that an increase in spray area caused a decrease in CV, although the spray shape did not affect the CV independently. A model to predict CV, as a function of tablet size, pan speed, and pan loading, was developed from the Monte Carlo simulation results. Coating runs were conducted in order to verify the predictions from the model. Good agreement was obtained between the predicted CV (from the model) and the experimentally obtained CV.

In the future, this technique can also be effectively used to develop scale-up models, test the effects of parameter changes in CV, and subsequently reduce the time required to get a product to market.

References

1. Sandadi S., Pandey P., Turton R., In-situ, near real-time acquisition of particle motion in a rotating pan coating equipment using imaging techniques, Chemical Engineering Science, 59(24), 5807-5817, 2004

2. Pandey P., Turton R., A study to quantify the effects of mixing aids during a coating operation in an industrial scale rotating pan coater, The AAPS Journal, 6(S1), 2004

3. Pandey P., Turton R., Movement of different shaped particles inside a pan coating device using novel video-imaging techniques, AAPS PharmSciTech, 6(2), article #34, E237-244, 2005

4. Pandey P., Song Y., Kahiyan F., Turton R., Simulation of particle movement in a pan coating device using discrete element modeling and its comparison with video-imaging experiments, Powder Technology, 161(2), 79-88, 2006