Tablet coating is a critical process carried out in pharmaceutical industries for tablets. Tablet coating is done for a number of reasons, including taste masking and environmental protection.
Tablet coating machines are used to coat the tablets, where a perforated coating pan is used to rotate the tablets, and then the tablet coating suspension is sprayed over the tablets by atomization.The coating guns are used to shower the tablet coating suspension over tablets.
Tablet Coating Spray Gun
As the name indicates it is a gun like structure which is used to spray the coating suspension.These are small in size but their role in tablet coating process is very critical.
The tablet coating spray gun has a needle which passes through a small orifice. The spray gun has one supply for the compressed air and another for the coating suspension.
The solution from the coating suspension tank is delivered to the tablet coating spray guns through a peristaltic pump.
Role Of Compressed Air
The compressed air is used to create atomization, meaning the air pressure converts the liquid suspension into tiny droplets.
If compressed air will not be used, the coating suspension will be dropped on tablets in the form of liquid and will damage the whole batch.
Role Of Spray Gun Needle
The needle of a spray gun is pushed out of the orifice by the pressure of compressed air and it results in the creation of very fine droplets by automization.
Suppose a condition where the needle is not inserted into the spray gun, then this coating suspension will not be converted into fine droplets.
Size Of Coating Gun Needle
The needle of the coating gun is designed in such a way that it is thick from the backend and has a very sharp, narrow tip at the front end, which passes through the orifice. The size of the needle diameter plays an important role during the tablet coating process.
If the diameter of the needle is thick, meaning it is large in size, it will result in the production of large-sized droplets, and if the diameter of the coating gun needle tip is small in size it will result in tiny-sized droplets.
Drawbacks of a small-diameter gun tip
If the diameter of coating gun needle is short as discussed earlier, it will result in the production of very fine droplets and when fine droplets are produced which are very small in size it will result in material loss due to the evaporation of solvent before reaching to the tablet surface, due to this loss of coating material variation in the tablet colour is observed in case of colour coating and in case of drug coating, film coating or enteric coating the required weight gain may not be obtained.
Drawbacks of a large-diameter gun tip
If the diameter of tip of tablet coating spray gun is large meaning it is thick it will result in production of large size droplets, the large size droplets may result in tablet sticking and one main defect of large size droplets is that the large size droplets do not spread uniformly and the surface of tablets appear to be like mate finished or it do not have a smooth finish.
Example
Suppose we have three needle sizes and the diameter of the first needle is 0.6 mm, the diameter of the second needle is 0.9 mm, and the diameter of the 3rd needle is 1.2mm. Here we have three different types of sizes of the needle tip. Now, what will happen if we use the coating needle of 0.6 mm?
It has a very short diameter & it will result in the production of very fine mist, and loss of coating material will be observed.
When we use a needle of 1.2 mm, the large droplets will be produced.
When we use a 0.9 mm-sized needle, it will result in the production of optimised-sized droplets.
Conclusion
The diameter of the tablet coating gun’s needle plays an important role during the coating process. If the diameter of the coating needle is short, it will result in the production of very fine mist & vice versa.
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