Application Note

Recommended Mixing Equipment For Tablet Coatings

Source: Charles Ross and Son Company

Designed for high-speed powder dispersion, the Ross Solids/Liquid Injection Manifold (SLIM) Mixer is well proven in the preparation of tablet coatings. This technology features a unique rotor/stator assembly that draws solids into a high shear zone for rapid mixing with the liquid vehicle.

Dry ingredients like hydroxypropyl methylcellulose (HPMC), sodium carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), alginates, gums, talc, titanium dioxide and fine powdered colorants are wetted out more efficiently in a SLIM Mixer compared to conventional batch systems where powders are added to the top of vigorously agitated liquid. The SLIM rotor not only turns at high speeds but also generates a powerful vacuum that combines solids and liquids sub-surface – at precisely the point where intense agitation takes place. A very uniform consistency is achieved in just a few turnovers so that viscosity loss due to over-mixing is easily avoided. In addition to the short cycle time, issues like floating powders, foaming and excessive dusting are also eliminated.

Particle size distribution is an important mixing parameter because large agglomerates can clog spray nozzles in the coating operation. Ross offers Ultra-High Shear Mixers for tablet coatings requiring aggressive size reduction. Turning at tip speeds over 11,000 ft/min, these new generation rotor/stator devices feature complex geometries and extremely close tolerances, subjecting the product to thousands of intense shearing events in each pass. The level of dispersion achieved is superior to most multi-stage rotor/stators and colloid mills. In certain applications, Ultra-High Shear Mixers are considered to be ideal alternatives to high pressure homogenizers because they deliver comparable size reduction at much higher flowrates and require simpler maintenance.