Particle Coating in Fluidized Beds

Abstract

In this article, the coating of the particles is studied in different coating processes using various coating solutions. The solutions are mainly composed of solvent, polymer, plasticizer, colorant/opacifier and antitack agent. There are a number of polymeric solutions for the coating of the particles as explained in detail in this article. Different approaches have been used for the coating of the particles which can mainly be classified as melt coating, supercritical fluid coating, compression coating, and spray drying coating. Spray drying coating is considered as the most proper method for the coating of the multiparticulates (i.e., encapsulation) conducted in pan coaters and fluidized bed coaters. It is concluded that the fluidized bed coating method is the most promising and widely used technique for the coating of the particles in pharmaceutical, food, and agricultural industries. Accordingly, the coating of the particles in fluidized bed coating systems (i.e., top-spray fluidized bed, tangential-spray fluidized bed, and bottom-spray fluidized bed) is deeply described with the emphasis of the bottom-spray fluidized bed coating (Wurster) technique. This article concludes that the fluid bed coating technology has brilliant feature for the coating of the particles. It elucidates the advantages and limitations of each fluidized bed coating processes depending on the different application. The Wurster coating is the superior technique among the other coating methods in order to obtain uniform and high quality coating for the particulates. Finally, the coating mechanism in fluidized bed coaters is elaborated more deeply. The coating life cycle is divided into different stages including: (1) particle movement, (2) atomization, (3) wetting the particle surfaces, and (4) drying and film formation.