The coating surface and agglomeration of seed particles in a fluidized bed coater

Glass beads were coated in a fluidized bed by atomizing a suspension of nylon or silica fine powder. Polyvinyl alcohol (PVA) was used as a binder. The influences of the weight ratio of fine powder to binder in the suspension and index R, which quantitatively evaluates the drying condition in a fluidized bed on the coating efficiency, on the agglomeration among the core particles and on the coated layer surface were investigated. When the index R became high and the weight ratio of powder to binder decreased, the core particles easily agglomerated. Once agglomeration occurred, both the coating efficiency and the circularity, which evaluates the smoothness of the coated surface, became worse. Furthermore, the addition of the surfactant in the suspension made the circularity high and inhibited the agglomeration. In contrast, the hydrophobic surface of the core material made the coating efficiency at the early coating stage and circularity low, and it encouraged the agglomeration.