Tablet coating defects or problems observed during tablet coating is a very important topic & in this article, we will discuss tablet sticking and picking,which are one of the most common defects observed during tablet coating operation.We will also discuss why sticking & picking defects occur and what is the possible solution to solve these defects or problems.
One important note is that this article is written, based on practical observations, so you will find an actual concept in this article.
Before going into details of picking or sticking defects, one main important thing to remember is that the smooth coating process is based on synchronization of different coating parameters like,
- Spray Rate
- Drying Temperate
- Pan Rotation Speed
- Automization Air Pressure
- Tablet Bed Temperature
- Spray Guns To Tablet Distance
- Spray Gun To Spray Gun Distance
You can read details of the above parameters in the following article.
Reasons And Remedies Of Tablet Sticking & Picking During Coating
Do not confuse the term tablet sticking & picking in coating operation with the same defects observed during tablet compression.
You can read tablet sticking & picking during compression operation in following,
Tablet Sticking and Picking During Compression
But here we are going to discuss the sticking and picking problems that are observed during the tablet coating process.
What Is Tablet Sticking & Picking In Coating?
Tablet sticking & Picking are two resembling defects during the tablet coating processes in which some portion of tablets film is removed or picked either due to attachment of tablets with a pan or with each other.
Reasons
Following may be the possible reasons which result in above-mentioned defects,
High Spray Rate
When tablets are coated at a high spray rate there is a chance of tablet over wetting and due to this sticking and picking defects may occur.
Logic
- During rotation, if tablets are over wet & not properly dried they stick with each other or with pan & when de-attachment occurs the part or portion of the film is removed.
Solution / Remedies
- If sticking or picking is observed due to a high spray rate, reduce the spray rate or increase the inlet air temperature or tablet bed temperature.
Lower Inlet Air Temperature
Low inlet air temperature may also result in tablet sticking and picking.
Logic
- When Inlet air temperature is low, tablets are not properly dried after passing below the spray guns, so sticking or picking may occur.
Solution
- As we discussed, due to low inlet air temperature the tablets are over-wet or are not properly dried so increase the inlet air temperature or tablet bed temperature to overcome this problem
- If tablet sticking/picking is observed due to low inlet air temperature the spray rate should also be reduced as a first response then maintain accordingly.
Low Tablet Bed Temperature
Tablet bed temperature is the temperature of the tablet surface. When the tablet surface is not properly warm it may result in sticking or picking.
Logic
- Same as in the case of low inlet air temperature.
Solution
- Increase the tablet bed temperature by increasing the inlet air temperature.
- The spray rate should be reduced and adjusted later on accordingly.
Low Pan Speed
If spray rate is high & pan speed is low it may also result in tablet sticking or picking.
Logic
When tablets are wet and are rotated at the low pan speed their chance to stick with each other & with the pan is increased.
In other words, contact time is increased.
Solution
- To reduce contact time and to counter the effect of a high spray rate the pan rotation speed should be increased.
Low Automization Pressure
If air pressure used to automize the spray droplets is low, it results in tablet sticking and picking.
Logic
- Low automization air pressure results in the production or generation of large droplets and it may over wet the tablet surface.
Solution
- If tablet Sticking or picking during the tablet coating process is observed due to large droplet size then reduce the droplet size by increasing the automization air pressure
Spray Guns To Tablet Bed Distance
If the distance between spray guns and tablet bed is decreased it results in sticking and picking.
Logic
- Due to reduced distance, the spray guns come closer to the tablet surface, so over wetting of tablets occurs which in return results in tablet sticking or picking during the coating operation.
Solution
- Increasing the spray guns to tablet bed distance results in proper drying of tablets during rotation.
Spray Gun To Spray Gun Distance
A proper distance between spray guns is maintained to ensure proper spray rate and to prevent spray overlapping. If the spray gun to spray gun distance is reduced it may result in tablet sticking or picking during the tablet coating operation.
Logic
Due to reduced spray gun to spray gun distance, tablets become over wet, due to spray overlapping.
Solution
- Increasing the spray gun to spray gun distance removes the problem of spray overlapping and overwetting.
Return Air Exhaust
If the return air exhaust is not properly working or it is opened at a low ratio, it may result in tablet sticking or tablet picking.
Logic
- Due to blockage or lower opening of return air exhaust, the inlet air may not be properly supplied or humidity inside the coating pan may increase, which results in a reduction of tablet bed temperature.
Solution
- Optimize the exhaust opening to ensure a proper airflow pattern.
Conclusion
Tablet sticking and picking during coating operation may occur due to a number of reasons and the main factor to overcome these problems is the synchronization of all the coating parameters.
If we want to increase the spray rate we will have to increase the inlet air temperature,pan speed and tablet bed temperature accordingly to avoid sticking or picking.
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