Tablet Capping and Rectification

Tablet capping is an portion of tablets cup normally near the apex ,does not completely bond and separates from the rest of tablet there are many potential causes of tablet capping . Primary cause is air entrapment .

Root causes of capping

1. Too much depth of concavity in punches .
2. Excessive quantity of fines .
3. High compression force at Precompression .
4. J hooks are formed on tooling .
5. Too high speed of feeder is introducing air in blend and tablet caps later due to that air .
6. compressing deep in die .
7. Excessive fines are generated in milling and fines tend to form layer on tablet during compression and later cap .
8. Speed of tablet press is high whole tablet is not formed or insufficient Dwell time .
9. Powder is not compressing horizontally due to centrifugal force of machine and flow problems .

Upper punch penetration problem sometimes leads to capping penetration control for tablets is Ideally between 1.5-2.0 mm . A setting of 2.0 mm means the lower punches will meet upper punches 2.0 mm inside die .The major cause of capping is entrapped air If punch penetration is too deep in die the air will have Insufficient space to evacuate and air will be entrapped in Tablet which will cap later .So, to overcome the problem Either Punch penetration can be changed or use of Tapered die will sort out the problem

Feeder speed too fast is also an problem leads to capping because Faster moving feeder will entrap the air inside the blend and subsequently into the tablet which will later cap

Precompression is aimed to remove the entrapped air in blend not to make tablets too much precompression also leads to capping because too thin thickness tends to create a tablet and final compression will tend to make another layer or creates fractures in tablet .

Excessive quantity of fines is another major reason of capping as excessive quantity of fines will collect on topmost layer of tablet during compression and as the pressure of punches is removed the fines on the top of tablet with weaker bonds will cap .

Powder is deposited unevenly in die and does not compress horizontally is another major reason of capping as we know the running machine has centrifugal force which tends to through blend outside the die causing uneven distribution to rectify this problem Tail over die assembly is used .

Tooling condition is another major ranking problem of capping sometimes J hooks are formed on the tips of punches which pulls the tablet apart . To rectify this problem Polishing of Punch tips is better option .

Tooling design sometimes leads to capping like tablets formed in Flat faced beveled edge(FFBE)  punches tends to cap .

Excessive press speed gives less Dwell times to tablets . Decreasing the speed will control the capping in this case .