TABLETING
should be 10% of main compression force, but this doesn’t always work. A low precompression force allows
the removal of air between the particles, decreasing capping potential. Te amount of precompression force is critical because too much force can increase capping. Te correct amount of precompression
force can be tested by rotating the turret manually while applying only precompression force. After the compact is ejected, it should appear to be an intact tablet, but when you squeeze it with your fingers it should fall apart back into the original particles. Tis shows that particles have not bonded together but instead are consolidated and closely packed. Te punch penetration determines
how high in the die bore the tablet is compressed. Since air travels upward during compression and escapes between the upper punch tip and the die, less punch penetration reduces the distance the air must travel to escape and minimises capping potential.
MAIN COMPRESSION FORCE A decrease in main compression force can also reduce capping. When a tablet reaches its maximum compactibility, it won’t increase in strength with additional compression force. Instead, the excess compression force can reduce interparticle bonding and cause capping. In that case, reducing the compression force may fix a capping issue.
Capping is when a break is
found across the horizontal plane of a tablet
TURRET SPEED Decreasing the tablet press’ turret speed may also reduce capping. An acceptable
that will survive the manufacturing process with minimal tablet defects, including capping.
TABLET PRESS CONFIGURATION Capping can be addressed without changing the formulation by adjusting tablet press parameters such as precompression force, punch penetration, main compression force, and turret speed. Precompression, or de-aeration, is
a compression stage before the main compression event that forms the final compacted tablet. Precompression force can consolidate the particles and remove entrapped air without creating a bond between particles. Precompression force
tablet strength might be achieved on a small R&D press, but when moved to production scale, the press may use a higher compression rate or a lower dwell time. If the formulation is strain-rate sensitive, compression speed will impact the tablet’s robustness. Such formulations require slower turret speeds.
TOOLING CONFIGURATION Features of the tooling can also be modified to reduce tablet capping, including using tapered dies or reconfiguring the punch heads.
TAPERED DIES A tapered die allows a higher rate of air removal from the die cavity. Te inner die cavity tapers outward toward the top of the die, which allows more room for the air to escape. To take advantage of this feature, adjust the punch penetration so the tablet is being compressed in the tapered area.
PUNCH HEAD CONFIGURATION A new punch head configuration may remediate capping issues. Extended punch head flats can increase dwell time which can increase the tablet strength in some cases. Recent studies have shown that reducing the head flat can resolve some capping issues at high speeds. In either case, head flats can play a major role in tablet robustness and capping potential.
Robert Sedlock is with with Natoli.
www.natoli.com
Changing the punch head configuration can help to solve some capping problems
www.scientistlive.com 43
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