Question: How to solve this problem of Capping in tablets, we are getting consistent problem of capping in our Paracetamol tablets where paracetamol is 500 mg and other excipients like starch, and talcum, and aerosil, magnesium stearate etcetera comprises about 60 mg. The Total weight of the tablet is 560 mg. It is round beveled and 13.5 mm round.

Answer: Following factors are responsible for tablet problems like Capping, lamination.

1.Granule Size.

2.Moisture content.

2.Binder proportion

3.Type of Binder.

4.Wet mixing kneading time.

5.Time for which chopper blades in the granulator are run.

6.Lubrication time.

7.Quality of punches.

Granule size:

Granules taken for paracetamol tablets of size 560 gm and 13.5 mm size diameter, should be of mesh size #16, during manufacturing there are following factors that affect the size of granules. For tablets of size more than 300 mg granules of mesh size predominantly required are #16 mesh. and below that #20 should be used.

Binding agent:

Binding agent preferred is starch paste, in combination with gelatin or pregelatinized starch. Pregelatinized starch gives good binding properties and also the disintegration time is also achieved within 5 to 10 minutes. Friability of the tablet too is kept within 0.3 to 0.5 %. Starch in combination with gelatin to make a paste is also a good binder, problem faced with this is the requirement of higher proportion of moisture content to be maintained for good compressibility of granules as compared with pregelatinized starch. Also alone starch when used as binder, fine proportion in granules also is more compared to other binding agents.

Moisture content of a tablet should be within 1.0 % for good compressibility, during compression this moisture in the granule gets reduced due to drying of granules during compression and transfer and compression due to crushing of granules.

The final moisture content in the final tablets comes down to 0.2 to .4 % depending on the type of product, on storage it further reduces almost to 0.1% and below. If the moisture content in paracetamol granules is less than 0.7% then the compressibility is lost and friability increases. Problems of capping and lamination occur.

Wet mixing is mixing of API and excipients in a granulator with binding agent, this is also called kneading. If wet mixing with binder paste is done for more time the granules become harder and harder, more the wet mixing higher will be the binding of the granules. An optimum time of wet mixing should be set during validation of batches.

After wet mixing in the Rapid mixer granulator during unloading the chopper blade is run, the speed of the blade run determines the size of the granules. If the speed is high the granules will be of finer size, and there will be friability and capping lamination of tablet, problems in tablet compression will arise for bigger size tablet, if the tablet is smaller than smaller size of granules is required (#20 mesh), then it will give good results on compression. The problem of weight variation will not arise for small tablets. Bigger granules are used for smaller tablets then problems of weight variation may arise. During passing the granules through a multi mill the face of blades is also detrimental. knives forward will give granules and knives backward will turn granules into fine powder.

Proportion of Magnesium stearate and Talcum, in the tablets also is critical for good compressibility of granules, if the proportion if more than tablets Disintegration time increases, and friability too increases, capping problem in tablets arises. More the lubrication time there will be these problems, the more the lubrication time will be the moisture available for compressibility of tablets. Therefore, minimum lubrication time just enough to impart lubrication and good flow to granules is required.

If the Dies and Punches being used are not having proper polish then also it will add to the problem of picking and sticking on the tablet faces and corners. Therefore timely polishing of punches is required.

Summary : If capping and lamination problems arise, check granules size, then if it’s less then, check moisture content , it should be around 0.5 to 0.7 % for good compressibility for paracetamol tablets. If the hardness is given on the compression machine is higher than the optimum then also tablets capping and lamination occur. Moreover the tablets property depends on the excipients added. If pregelatinized starch is added in dry mixing it will enhance the disintegrating property of the tablet.

Same when used as binder in wet mixing by making its paste, it gives very strong binding to granules.

How to solve the problem :

Polish dies and punches. Increase the moisture content of the granules to 0.7% Reduce the speed of the compression machine. Reduce the hardness given on pressure rollers of tablet compression machines. Lower the lubrication time. After these arrive at the optimum parameters and validate it on a bigger scale and do validation of the product with these changes.

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