Particle coating in fluidized bed coater enhanced with electrostaticity

Abstract

Experimental results of coating of glass beads with aqueous solution containing HPMC as a coating liquid within a 16 liters top-spray fluidized bed enhanced by electrostaticity was significantly dependant on operating variables which were fluidizing air velocity (2.2 to 4.3 m/s), flow rate of coating agent (10 to 20 ml/min), size of core particles (590 and 1,033 [mu]m) and electricity potential applied to a spraying nozzle (0 to (-4) kV). Coating efficiency, coating film thickness and packed bulk of coated particles were affected by those operating variables. Increasing of fluidizing air velocity, coating efficiency and coating film thickness became hindered due to the higher evaporating rate of sprayed droplets became promoted with the increasing air velocity then they transformed to fine particulate dispersing away before coming into contact with core particles. While larger core particles led to more difficulty to be fluidized, resulting in a lesscontact among the core particles and sprayed droplets. On the other hand, an increase in flow rate of coating liquid could increase the coating film thickness and the coating efficiency. This could be implied that the higher the flow rate the larger the droplets sprayed out from the nozzle which increased the possibility of contact among the core particles and droplets. Meanwhile, an increase in electrical potential applied to the nozzle would lead to an increase in the attractive force among the charged droplets and the core particles therefore the coating efficiency could become more enhanced.