Fluid bed encapsulation of particles: Principles and practice

The fluid bed encapsulation process consists of spraying a coating solution into a fluidized bed of solid particles. After several cycles of wetting-drying, a continuous film is formed. This paper provides an overview of the physical and transport phenomena involved in this process, especially in the so-called Wurster mode. Both qualitative and quantitative results are presented for several industrial applications. The main parameters affecting the process are flow-rate and pressure of the spraying liquid, composition and rheology of the coating solution, flow-rate and temperature of the fluidizing air. The particle size can range from 0.1 to several millimeters in equivalent diameter. The characteristics of the particle surface are important in determining adhesion of the liquid coating as well as its encapsulation properties.