(472f) Understanding the Role of Contact Spreading of Liquid in Particle Coating Applications: A Tumbling Drum Coating Study

Spray coating of powder and particulate products is an important process used in the Fast Moving Consumer Goods, Pharmaceutical and Foods Industries. Design and scale-up of spray coating is still largely an empirical process based on trial and error.  In the detergent industry, rotating spray drums are used to coat spray dried powders and additive ingredients with active liquid ingredients. The physical stability of final detergent products is strongly influenced by both the level and distribution of coating achieved; coating coverage should be high enough to ensure the consumer has correct dosage but low enough to avoid liquid bridging and physical caking of powders.

The aim of this project is to investigate the roles of liquid spray and subsequent contact spreading on particle coating distribution in tumbling drum coaters. A small scale tumbling drum spray coater has been developed to assist in design and scale up of continuous spray coating.  The focus of this work is to develop better understanding of the spray coating process, and to apply this understanding to batch and continuous spray coaters. 

In this study, a series of contact spreading experiments are performed with a range of model materials (glass microspheres and polyethylene glycol solutions at various viscosities).  Liquid coating distribution is measured though image analysis techniques using dyed liquid coatings.  The effect of rotation speed, residence time, particle size and binder viscosity on coating distribution are investigated, and the influence of these parameters on coating distribution are compared with anticipated theoretical effects.