Dry coating in a rotary fluid bed.

A highly efficient dry coating process was developed to obtain an enteric film avoiding completely the use of organic solvents and water. Using hydroxypropyl methylcellulose acetate succinate (HPMCAS) an enteric coat should be obtained without adding talc as anti-tacking agent because of problems arising from microbiological contamination. Further on, a method was developed preparing isolated films in order to determine the glass transition temperature (T(g)) and the required process temperature. The process was conducted in the rotary fluid bed with a gravimetric powder feeder achieving an exact dosage in contrast to volumetric powder feeder. A three way nozzle was aligned tangential to the pellet bed movement feeding simultaneously powder and plasticizer into the rotary fluid bed. The determined coating efficiency of the talc-free formulation was high with 94% and storage stability regarding tacking could be achieved using colloidal silicium dioxide as top powder. The T(g) of the enteric coat could be determined analyzing the T(g) of isolated films obtained by coating celluloid spheres instead of pellets using the dry coating process in rotary fluid bed. The dry coating process has been demonstrated to be a serious alternative to conventional solvent or water based coating processes.