Nonuniformity of particle coating on a size distribution of particles in a fluidized bed coater

The focus of the current work is to evaluate the effect that particle size has on the uniformity of coating received during a batch fluidized bed coating process. Batches of near-spherical Nu-Pareil(TM) sucrose particles comprising a wide range of sizes (548-1205 mu m) were formulated so as to have the same mass average particle size but with different size distributions. These batches were then coated under identical coating conditions using a coating medium of FD & C (Food, Drug, and Cosmetic) blue dye no. 1 dissolved in a suitable aqueous-based polymeric binder. At the end of each run the particles were sieved back to the different size fractions. From each size fraction 30 particles were chosen at random and analyzed for their blue dye content. The results showed that the amount of blue dye deposited on a given size of particle was proportional to the particle diameter to the power of 3.4 (d(p)(33.4)). The variance of blue dye content for different size cuts was also measured. It was found that the variance could also be correlated with particle diameter but that the dependence was lower than that for the mean (d(p)(3.0)). The experimental procedures and possible mechanistic explanations for these results are presented. (C) 2000 Elsevier Science S.A. All rights reserved.