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HOT MELT GRANULATION ciency. The first commercial version of automated
electrostatic paint lines were developed with
During the conventional solvent-based coating significant contributions in the 1970s. Later many
process, a lot of energy is consumed for the models simulating electrostatic spray painting
evaporation of the large amount of solvent or based on Lagrange s approach were pro-
water used. Hot melt coating has been used as an posed.184,185 In the electrostatic fluidized bed
alternative method. The coating material is powder coating process, dry air is ionized by
melted by heating and sprayed on to the particles charging media. In electrostatic deposition pro-
which then is solidified by stream of cold air. cess charged materials are attracted to a
This is somewhat similar to the spray congealing grounded surface just like lightning seeks earth.
technology using spray dryer. By virtue of the Charging electrodes, fed by a high voltage supply
technique; the advantages are the processing (dc 0 100 kV) with a negative polarity on
time is short, there is no particle shrinkage, no electrodes is generally placed inside the bottom
drying step is required, low energy consumption, part of the bed so that the powder material would
no solvent needed, that is, low cost, flexible and be charged as the fluidizing air causes it to rise up
consistent. However main drawbacks are the size in an electrically grounded column. The charged
and density of the final product, the bed depth and particles repel each other and rise from the base of
air velocity. Further, it is suitable mainly for fats, the fluidizing bed chamber causing a cloud of
waxes and molten materials that are used in ionized powder. The charged particles are
liquid coating, taste masking or altering drug attracted to the substrate, temporarily adhering
release. This method is not suitable for thermo- to it before the curing process when a grounded
labile actives in which case the conventional rotor work-piece is dipped in the cloud. The core
technique is to be followed. Recent studies have technology platform of QtrolTM (Phoqus)186 is
shown, however, that a meltable binder can be an derived from electrostatic deposition, the well-
alternative to a polymer solution in fluidized bed proven technology behind photocopying. This
granulation.152 157 Previous studies with aqueous technology enables solid dosage forms to be coated
binder liquids in fluidized bed granulators in a controlled and precise manner to modify drug
reveal that larger binder droplet size158 162 and release characteristics. No solvent is employed
increased viscosity of binder liquid163 165 result and the process gives fine control over the
in larger agglomerates. During the agglomeration thickness and location of a coating on the surface
process using water as binder, small agglomerates of the tablet. The substrate (tablet) is electrically
(nuclei) are formed followed by growth by grounded so that when a high voltage is applied to
coalescence.166,167 There are series of papers the coater the coating particles gets attracted to
published on melt granulation.168 172 Recently the tablet and gets deposited onto its surface. The
comelt system was developed in fluidized bed thickness is controlled according to the potential
granulation.173 Several studies have described the difference between tablet and coater. The powder
effect of certain process variables on the melt is fixed to tablet core by applying radiant heat.
granulation of pharmaceutical type powders.174 178 The concept of electrostatic coating has been
It has been found that granules produced by fluid- studied by various research groups.187 192
bed granulation are more porous, less dense and Further research in this area of electrostatic
more compressible than granules from the high coating technique coupled with fluidized bed
shear granulation process.179 In practice dis- technology can be probed for further improve-
solved or molten coating polymer is sprayed into ments in this area. [ Pobierz całość w formacie PDF ]