Tablet Pro — Part 5

The Inspection Process — Tablet press tooling must be checked in-house. Tooling inspection should take place when the tools are first received from the vendor and then re-checked on a regular basis.

If the product is abrasive causing advanced wear, then inspection should occur with great frequency. Products with a history will allow for less frequent inspection. Two inspections must take place after each cleaning; visual and working length. The operator must inspect tools before they are installed in the press and when removing the from the press for cleaning.

Common Defects

Making tablets batch after batch without an occasional defect would be unusual. Some products start up with problems and end with them. Tablet to tablet weight variations create tablet defects. Consistent tablet weight is essential to making a good tablet. Without good and consistent weight control, solving other defects will be difficult (if not impossible) because of how a tablet press operates. Some of the most common tablet defects are:

1. Weight variation
2. Friability variation
3. Picking & Sticking
4. Capping
5. Laminating
6. Chipping
7. Mottled
8. Double pressing

Often problems with compression can be associated with many root causes. One very common issue is machine start up. The tablet press is cold. The steel is cleaned and bare metal can allow granules to stick to these metal surfaces. The reason a lubricant is in the product is to prevent granules from sticking. Many companies are very accustomed to a double start up. The first one distributes powders which begin to stick, especially to the punches and to the die table. The operator will often remove the stuck granules and then at second start up no sticking occurs because the working surfaces are now protected by the lubricant.

Picking and Sticking

Picking and Sticking occurs when granules stick to the punch faces during compression. Sometimes the punch face design and debossing can be modified to eliminate the problem. Other times granules are not dried properly. They become case hardened during the drying process, which means that the granules are wet on the inside.

During compression these granules break open and the wet product sticks to the punch faces. If this occurs, the drying process must be improved. To overcome sticking on the press, increase hardness by making the tablet thinner and increase dwell time to make the wet granules adhere to other granules rather than the punch face.

Also, if a blend is incomplete this could mean that the lubricant in the formula is not protecting the granule from sticking to the punch cup surface. If all else fails polish the punch cup surface.

Weight, Hardness, and Friability

Tablet weight is the key to controlling hardness and friability. Controlling tablet weights within a tight range will contribute to better tablet hardness and friability. Many variables can influence weight fluctuations. The key weight control factors are product uniformity in particle size and density, proper tablet press set-up, and control of flow rates into the die cavity.

However, the importance of weight control cannot be over emphasized. Weights must be uniform in order to trouble shoot most other tablet defects.

Friability testing is done by tumbling tablets to see how well they will withstand the tumbling action which replicates typical handling situations. This test is done to make certain that the tablet does not fracture or break apart. Too much friability means that the tablet chips or fractures break away from the rest of the tablet.

Michael D. Tousey