The tablet coating defects list is very extensive including various defects which we observe during the practical operation of the coating process.
Here we are going to discuss a very common tablet coating defect that is usually observed during the coating process of color tablets.
Why Do We Use Color In Coating Suspension?
A common thought which comes into the minds of the people dealing with tablet coating processes,especially when they observe color variation is that it should be a white coating suspension instead of color coating suspension to run our tablet coating operation more efficiently without color variation defects.
So the question is why we use different colors in tablet coating formulations.
The answer is,use of color in tablet coating formulations is recommended because of the main reasons given below,
- We use color in our coating suspensions to make tablets more appealing.
- Colors are added in tablet coating formulations to avoid the chances of a mix-up.
- Suppose we have a product with two different strengths i.e 5 mg and 10 mg having the same tablet weight and shape and is compressed using the same tooling i.e 9 mm.There may be the chances of mixing up so we can add color to the coating formulation of one strength to avoid mix up.
- Colors are added to the tablet coating suspension for brand identification.
- Colored tablets are easy to remember for elderly or less educated patients.
- Color may also be added in coating formulation to compete with market competitors.
- To mask the color of API and to give uniform color.
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What Is Color Variation
Color variation is a common tablet coating defect in which the color of tablets is not uniform.
Science Of Color Variation
- Color variation is a coating defect so let’s discuss what is the term used for defect-free color coating.
- Color uniformity is the term that is used for smooth and accurate color coating. Color uniformity means the color of all tablets in a batch is similar and there is no color difference between individual tablets and tablets of different batches of the same product.
- Color uniformity is achieved if color is properly deposited over the tablet’s surface & is related to the tablet weight gain after the coating process.
- If tablet weight gain is less than the recommended values the color of tablets may not be uniform due to less accumulation of color over the tablets.
Reasons & Remedies For Color Variation
Now we will discuss why color variation occurs during the tablet coating process and how it can be prevented or overcome.
Following are the main factors that may result in color variation
- Inlet Air Temperature
- Tablet Bed Temperature
- Gun To bed Distance
- Spray Rate
- Pan Speed
- Exhaust
Inlet Air Temperature
Control of inlet air temperature may be the major contributor to color variation defects during the tablet coating process.
How?
If the inlet air temperature is very high than the recommended set value it results in loss of color along with coating material due to the rapid evaporation of the solvent.
Due to the rapid evaporation of solvent less amount of color & coating material is deposited over the tablet surface as a result of over drying effect.
Solution
- Do not increase the inlet air temperature without increasing the spray rate.
- Try to reduce the suction of exhaust to minimize the coating material loss.
Tablet Bed Temperature
An unusual rise in Tablet bed temperature may also result in color variation of coated tablets due to the loss of coating material containing colors.
Solution
- Decrease the inlet air temperature.
- Increase the spray rate to reduce tablet bed temperature.
Gun To bed Distance
Increased distance between spray guns and tablets bed may also result in coated tablets’ color variation because less amount of coating material containing color is deposited over tablet surface due to early evaporation of the solvent.
Solution
- Maintain optimum distance between spray guns and tablet bed.
- Increase the Spray rate if you have to increase the distance.
Spray Rate
If our spray rate is low and inlet air temperature or tablet bed temperature is high it may also result in color variation due to the dusty environment which is an indication of early solvent evaporation.
Due to early solvent evaporation, the solvent evaporates before reaching the tablet surface and the coating material is not properly deposited over the surface of rotating tablets.
Solution
- Increase the spray rate.
- Decrease the inlet air temperature.
Coating Pan Speed
Speed of the coating pan may also affect the color uniformity of the coated tablets.
Slow pan speed may result in large uneven dark color patches over the surface of rotating tablets which may take more time to become uniform.
The reason is that if pan speed is low and spray rate is high the contact time of applied spray is increased which is not spread uniformly.
Solution
- Gradually increase the pan speed along with the spray rate.
- Increased pan speed results in increased tablet rotation so contact time is decreased but number of showers per minute are increased & color is being applied over a large surface area of the tablet in less time period.
Exhaust
If the coating pan exhaust opening is high it will result in loss of color along with coating material.
Solution
Exhaust openings should be optimized to minimize the loss of coating material.
Conclusion
Tablet Color variation is a common tablet coating defect that mainly occurs due to loss of color along with coating material due to mishandling of tablet coating process parameters.
Always adjust temperature and spray rate in a synchronized manner to prevent product loss & to get color uniformity in a batch.
Coating pan outlet air or exhaust, pan speed & spray guns to tablet bed distance should also be critically monitored to ensure a smooth coating process for color tablets.
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