Tablet Pro — Part 6

Capping & Lamination — Capping is often referred to as air entrapment. During compression, air is evacuated from between the granules to allow the granules to lock to one another. If the “air” does not escape during the compression process the top of the tablet (the tablet cap) wants to come off. The tooling (punches and dies) are designed to allow air to escape during compression along the upper punch tip and die wall. This is why capping occurs on the top “cap” of the tablet. Capping is not just air entrapment. During compression air evacuation pushes the very fine dry granules out with the air. It is these dry and light particles that do not want to lock together, resulting in tablet “caps” wanting to come off the tablet.

Lamination is when the tablet splits apart anywhere except at the upper cap. Lamination is often blamed on over compressing. Too much compression force flattens out the granules and they no longer lock together.

Lamination can also occur when groups of fine and light particles do not lock together. These groups of fine and light particles simply will not compress well. Reducing thickness and increasing dwell time will give these particles more of a chance.

Dwell time can be increased by adding pre-compression or slowing the machine speed down. Machining a taper into the die will help eliminate capping and lamination.

Chipping — Many tablets are sensitive to chipping after compression. First make certain that the punch tip edges are not damaged. Some punch tip designs are more sensitive to damage from handling than others. Once confirmed that the chips are not being created by damaged punches then make certain that the “take off blade” is set correctly for proper ejection off the machine. If the blade is too high it will allow the tablet to wedge under the blade causing chipping. If the tablet is friable the tablet can become chipped as the tablet travels off the press, down the tablet chute, through the tablet metal detector, tablet Deduster and finally into the collection bin.

Transferring finished tablets must be done carefully. Many times investigations into chipped tablets discover poor handling and transfer of tablet bins from compression to storage and then onto the packaging floor. Packaging machinery can also cause chipping.

Double Impressions — Double Impressions will happen on a tablet press when the punches are allowed to twist or jump. Round punch tips want to twist naturally due to the rotation of the press. Double impressions usually occur on the bottom of the tablet from the lower punches. It usually means that the lower punch retainers are loose and the punches are jumping during compression.

Make certain the lower punch retainers are clean and not worn. They do need to be replaced often. When a machine starts up it is cold. As it warms up, lower punch retainers can become loose and may need to be tightened to prevent double impressions. Therefore, it is important to check them often at start-up.

Also, many newer machines now use punch seals. As seals become worn they will allow the punches to bounce or twist during compression.

Fines — Ask any operator what they would rather do; run a press or clean-it. The answer is usually that they would rather run it. A press can run as long as it stays clean and the tooling is lubricated. Another way to say this is that dust is what causes us to stop and clean the machine. If we had a formula with very little dust the machine would run cleaner and longer because the dust was not present and therefore unable to make the machine dirty.

Many companies must stop the press and perform partial or complete cleanups in the middle of a batch. This immediately tells us that they have contamination issues and the lubricant on the punches or lack of lubricant is the issue due to variations in fine dusty products…also commonly referred to as Fines.

Fines are the dust in the formula that can cause capping, dust can become airborne and land on the lubricant and dry it up, resulting in possible black specks on the tablet.

Tablet Press Operation

Lets run a press. It must be clean and set up correctly before we can begin.

Step 1: Rotate the machine by hand or in jog mode as the powder is first introduced.

Step 2: Adjust tablet weights into an acceptable range, keep in mind we are in jog and weights will drop as speeds increase, so set the weight on the high side of your target.

Step 3: Adjust final tablet thickness by raising the lower main pressure roll.

Step 4: Adjust speed to acceptable expected speed as defined by your SOP’s.

Step 5: Add Precompression as needed to achieve hardness range and achieve proper compression.

Step 6: Make final adjustments to weight, thickness and speed to attain final hardness.

Batch Variations and Changes

When a machine starts-up the operator must understand that the tablet press is cold. As the press runs it will warm-up. If a press becomes too warm the product may stick to the die table resulting in densified material which will migrate into the tablet creating a visual defect, a gray or dark spot.

As the product runs on the press some segregation usually takes place. Fines migrate one way and larger particles another. At some point these groups of fines or large particles will enter the die causing a big increase or decease in weight or compressibility. If a group of fine particles enter a die cavity the result maybe capping. The point is that segregation is not only possible, but it is very likely with products that have a wide variety of particles sizes with various densities. A poorly blended batch will result in many variation on the tablet press. Remember that the tablet press is the report card for how well the product was prepare for the press.

Michael D Tousey, Technical Director/CEO