(11e) Estimation of Optimal Coating Performance Via Optimal Mixing Conditions in a Pancoater

Coating of particles (tablets) is done to mask the unpleasant taste or odor of the drug, to control the bioavailability of the API, and to increase shelf-life. The coating solution is sprayed in specific locations of the granular bed and uniformity of coating is achieved by interparticle collisions and overall mixing behavior in the coater. Thus, the knowledge of particle flow and mixing in a pan coater is critical to optimize the design and operation of coating equipment. Lactose made placebos of two colors are used to investigate axial and radial mixing in the pancoater. Video-imaging and discrete pocket sampler is used to quantify mixing and to finally estimate the optimal operating conditions for coating in a pan coater. DEM (Discrete element method) based numerical model is also developed and fine tuned with the experimental findings. The optimal mixing condition is estimated and used as the starting point of coating studies.

Optimal mixing conditions comprise of a particular orientation of the coater, a specific vessel speed and a fill volume. Keeping these conditions same, the coating fluid (aqueous solution of Opadry II) is sprayed intermittently at different flow rates and concentration. Vernier Caliper is used to measure the change in diameter of the particles. Moreover, DEM based modeling of spray coating is also achieved for same operational parameter set and spray characteristic (centers and the radii of the spray zones) used in the experiments. DEM Simulation provides the residence time distribution of all the particles passing through the spray zone. The coating variability in experiments is estimated at different spary fluid concentration and flow rate. The optimal values of spray fluid concentration and flow rate is estimated for higher and uniform coating. Coating mass distribution is quantified in the numerical model by the total number of particles passing through the spray zone and also the frequency distribution of the residence time of the coated particles. From, the simulations the coating variability decreases with increase in speed of the pancoater vessel. It was observed that the simulations over predicted the effect of speed when compared with the experiments but the trends are in good agreement for the effect of tilt of the vessel.