Issue link: https://www.e-digitaleditions.com/i/1163217
42 September 2019 Tablets & Capsules Subsequently, the powder inside the die travels to the main compres- sion roll, which places a relatively large amount of pressure on the pow- der blend. This large-magnitude pressure results in significant com- pression—volume reduction—and significant compaction—bond for- mation—and forms a durable tablet within the die. Once formed, the tablet travels to the ejection cam, which elevates the lower punch along an angle and ejects the tablet from the die so it can be collected. Tablet lubricants A critical excipient during the ejec- tion process is the lubricant. In fact, for the majority of tableting blends, if no lubricant is included, the tablet press will eventually seize due to material building up on the die walls. Also, without a lubricant in the blend, the tablet would undergo extremely high ejection forces due to friction between the tablet and the die wall. High-pressure ejection can harm the press and damage the tablet by weak- ening or destroying the bonding that occurred during compaction. While lubricants are necessary, they can negatively impact tablet functionality and durability. Lubri- cants are hydrophobic and tend to prolong disintegration and dissolu- tion times and inhibit bonding between other ingredients during compaction. This is particularly true for magnesium stearate, which is the most widely used tablet lubricant due to its efficiency in reducing ejection force and maintaining clean punch surfaces. Compounding these issues, magnesium stearate is a surface-act- ing lubricant, which means that it lubricates by spreading over the par- ticle surfaces of other tablet ingredi- ents, which can inhibit bonding and repel the water required for tablet disintegration and dissolution. In contrast, a less widely used tab- let lubricant, hydrogenated vegetable oil Type I (HVO), functions in the free fraction, which means it doesn't spread over ingredient particle sur- faces during blending. This reduces its inhibition of bonding and disinte- gration and dissolution, yet its pres- The height of the weight-adjust- ment ramp determines the amount of powder the press will draw into the die, and therefore, the tablet weight. The aspirated powder contained in the die and resting on top of the lower punch proceeds along the tab- let press toward the precompression roll. If engaged, the precompression roll reduces the volume of the pow- der in the die by applying a relatively light compression that typically expels air from the powder blend. Tablet compaction The compaction portion of the direct-compression unit operation consists of a homogeneous powder blend being gravity-fed into a feed frame or fluidized feeder located on the tablet press' die table. This powder is aspirated into the die cavity when the die and lower punch pass below the feed frame and the punch is drawn downward along the fill cam.