A New Fluidized Bed Coating Process Via Photo-Initiated Cationic Polymerization

An ultraviolet (UV) photo-polymerization particle coating process was developed by coupling the photo-initiated cationic polymerization with the fluidized bed coating techniques. Unlike the conventional air-suspension coating in the fluidized bed, the new process employs a UV curable composition instead of a solvent/water-borne system as a coating material, which has a rapid curing rate and virtually no inhibition to oxygen and moisture. A modified fluidized bed coater equipped with a quartz window allows UV light to penetrate and to initiate the curing of photo-sensitive polymerizable chemicals coated on the particles. A UV-curable liquid composed of cycloaliphatic epoxide, oxetane, and triarylsulfonium cationic photo-initiator was specifically formulated for the fluidized bed particle coating process. A systematic experimental approach including photo-Differential Scanning Calorimetry, Fourier Transform Infrared Spectroscopy, and tackiness measurements has been developed to characterize the curing mechanism of the cationic UV curable formulations and to optimize the chemical compositions. The effects of the UV curable chemicals, viscosity of coating liquid, and the fluidization operating conditions on the physical properties of coated particles have been thoroughly investigated. Under optimized conditions, this novel process is very efficient as follows: particles can be coated very rapidly with ultra-thin films of the cured chemicals, with little, if any, formation of particulate agglomeration. POLYM. ENG. SCI., 49:1107-1116, 2009. (C) 2009 Society of Plastics Engineers