Aug 1, 2012
Coating for the Functionalization of Particles - An Application of Fluid Bed Technology or Spouted Bed Technology
Particles are coated in order to change their surface properties and by this means the behavior of the particles. Glatt offers different processes for the coating of different particles. This equipment choice allows the customer to choose specific levels of coating quality. The coating liquid can be a solution, suspension or melt. In all processes the coating liquid is sprayed onto the particles. Low viscosity and small droplets are required to ensure even spreading of the coating liquid on the surface of the particles.
When coating in the fluid bed the particles are fluidized and the coating liquid is sprayed into the bed while drying the particle. No over-wetting is allowed in order to prevent agglomeration of the particles. For many applications this technology is sufficient. A complete coverage of the particle surface requires a lot of coating material. Depending on the throughput, batch or continuous units can be used.
Compared to the fluid bed, the residence time in the ProCell is shorter, resulting in a more even coating in the continuous process. Also irregular particles (e.g. ceramic catalyst rings) can be coated since they are moved by the high air velocity in the slot.
The Wurster process allows a 100 coating with small amounts of coating material. The particles in the fluid bed are passing the bottom spray nozzle in an ordered flow pattern. While quickly moving upwards within the Wurster compartment they can be wetted without the danger of agglomeration. While moving downwards out-side the Wurster compartment they dry and another layer of coating can be supplied. The exactly controlled residence time in the coating zone ensures a very uniform coating.