New spout-fluid bed apparatus for electrostatic coating of fine particles and encapsulation

The construction and performance of a new apparatus for coating and encapsulation of particle cores with diameters lower than 1 mm are discussed in detail. The process of electrostatic dry powder coating was carried out in a diluted, fast circulating spout-fluid bed. The spatial separation of the draft tube entrainment zone from the coating zone leads to the reduction of effects of particle-to-apparatus wall adhesion and pneumatic nozzles plugging. As a result, the fine product of high quality without aggregates, agglomerates and granules, in a short time (approx. 10 min) and at a low temperature (approx. 45 degrees C) was obtained. Coating powder was charged electrostatically and continuously fed to the apparatus column. In order to verify the performance of the device, a number of tests were carried out with the application of materials used for the production of enteric drugs in the pharmaceutical industry. The quality of obtained coats was investigated by microscopic methods and the kinetics of dissolution of color marker in aqueous solutions was determined. As a result of the research, we obtain microcapsules with a constant release rate of the marker substance in alkaline environment, over 25 times faster than in the acid medium, with only 0.31% release of marker in acid solution in 2 h, which is a sufficient level for gastric resistance. (C) 2012 Elsevier B.V. All rights reserved.