R. Wesdyk et al., FACTORS AFFECTING DIFFERENCES IN FILM THICKNESS OF BEADS COATED IN FLUIDIZED-BED UNITS, International journal of pharmaceutics, 93(1-3), 1993, pp. 101-109
Previous work (Wesdyk et al., Int. J. Pharm., 65 (1990) 69-76) demonst
rated that various size beads, dispersed in a single bed, display diff
erences in film thickness when coated in a fluidized bed apparatus equ
ipped with a Wurster column. The differences in film thickness were at
tributed to differences in fluidization patterns and velocities of the
various size beads. The present study examines the effect of spray mo
de and process parameters on the variation of film thickness for a fix
ed particle size range and distribution. Beads with a size distributio
n in the no. 14-no. 20 mesh range were coated with an aqueous polymeri
c dispersion using top, bottom, and tangential spray fluidized bed uni
ts. Film thickness of the coated beads was measured using a scanning e
lectron microscopic method. It was observed that unlike batches coated
in the bottom spray (Wurster) mode, the batches coated in the top and
tangential spray modes exhibited no trend in film thickness. These re
sults are consistent with the differences observed in the surface area
normalized release rates of the various size beads coated in the thre
e spray modes. The results also indicated that for the bottom spray mo
de, a reduction in the atomizing air pressure, while substantially red
ucing differences in fluidization patterns, had only a marginal effect
in reducing the differences in film thickness.