Q: When I run a small production batch of a particular formulation with the same tablet press used to develop it, I get compressibility and disintegration issues. First I blend microcrystalline cellulose and disintegrant with the API for 10 min in a V blender. Then I add cabosil, talc, and more microcrystalline cellulose and blend the mixture for 5 min. Finally, I add magnesium stearate and blend for 3 min. In development, the turret speed was 30 rpm, and two punches were installed to generate the compaction profiles. The production run is also at 30 rpm, but with 10 punches. The paddle feeder speeds were set and the 19-mm full fill cam was used with a tablet weight of 100 mg.
A: Based on the information you provided, a production run should be successful, however the fill-cam-to-weight-cam setting could be problematic. The fill cam must provide a slightly higher volumetric fill than the weight-cam fill. Overfilling the die cavity and pushing out excess material to achieve the target weight can ensure tablet weight uniformity, but if the selected fill cam setting is much greater than the weight-cam setting, the excess material will recycle back into the paddle feeder, thus resulting in overblending, which will increase the lubricant efficiency, thus resulting in the problems you are experiencing.
Two approaches could help. You could select the appropriate fill cam based on the weight-cam setting. You can calculate the required weight-cam depth by dividing volume by the cross-sectional area of the punch tip. The volume that the formulation will occupy in the die is the tablet weight divided by the powder bulk density. Once the weight setting is determined, the proper fill cam should be slightly higher to provide a small overfill.
Also, using less lubricant would minimize the negative effects of overblending. The right amount of lubricant can be determined from a compaction profile using your instrumented tablet press. An external lubricant system can also help your process.
—Robert Sedlock, technical sales manager at Specialty Measurements
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