Role Of Tablet Bed Temperature In Coating

Tablet bed is the term used for the total bulk weight added in the tablet coating pan or the load of tablets added in the tablet coating pan is known as tablet bed.In simple words the volume of coating pan occupied by rotating tablets is known as tablet bed.

In this article we will discuss 

  • What is the tablet bed temperature?
  • What is the role of tablet bed temperature in the tablet coating process?
  • How to achieve required tablet bed temperature?
  • Relation of tablet bed temperature with other tablet coating parameters.
  • How different types of tablet coating defects are related to the tablet bed temperature?
  • How can we overcome tablet coating defects?
Tablet bed temperature

What Is Tablet Bed Temperature?

The temperature of the tablets added in the tablet coating pan is known as tablet bed temperature means when we apply heat to the tablets,the surface of the tablets become hot and the temperature of the tablet surface in the tablet coating pan is known as tablet bed temperature.

Role Of Tablet Bed Temperature

The tablet bed temperature or temperature of tablets which are rotated in the coating pan play an important role in the coating operation.

Following are some main role

  • To dry the applied solvent.
  • To overcome tablet defects.
  • To protect the tablet surface under the influence of applied spray.

How to achieve required tablet bed temperature 

The tablet bed temperature is mainly dependent on the inlet air temperature.

We are familiar that hot air is applied to the tablets in the coating pan and this air is taken from the environment.

The environmental air is heated through the heaters installed in the processing unit of the tablet coater and then this hot air is supplied to the inside of the tablet coating pan.

This hot air comes in contact with the tablets added in the coating pan so the tablets inside the pan become hot & this temperature is known as tablet bed temperature.

The tablet bed temperature is directly related to the temperature of incoming hot air. 

Relation of tablet bed temperature with other tablet coating parameters 

The tablet bed temperature is dependent on other tablet coating parameters as well which are given as  

  • Inlet air Temperature
  • Spray Rate 
  • Spray Guns To Tablet Bed Distance 

Inlet Air Temperature 

Generally If inlet air temperature will be high our tablet bed temperature will also be high and if inlet air temperature is low our tablet bed temperature will also be low.

Spray Rate 

One of the most important contributory factors which affect the tablet bed temperature is the spray rate.

Now we will discuss what is the relationship between the tablet bed temperature and the spray rate and how inlet air temperature will affect the tablet bed temperature by increasing or decreasing the spray rate. 

The tablet bed temperature is greatly affected by the applied spray rate meaning if we keep our inlet air temperature constant the tablet spray rate will affect our tablet’s bed temperature.

Case Study 

Suppose we keep our inlet air temperature at 70°C and apply the solution over the tablet surface at the rate of 500 ml per minute & at these parameters our tablet bed temperature is 40°C.

Now If we increase the solution spray rate  from 500 ml per minute to 800 ml per minute and keep our inlet air temperature constant at 70 degree centigrade then our tablet bed temperature will be decreased and usually it may be around 35 or 36 degree centigrade.

Reason

Apart from having the same inlet air temperature our tablet bed temperature is reduced when we increase the spray rate due to reduced evaporation of solvent.

Spray Gun To Tablet Bed Distance

Spray guns to tablet bed distance is another contributory factor which affects the tablet bed temperature during the tablet coating process.

Example

Suppose we keep following parameters constant

Inlet air temperature= 70°C

Spray rate= 500ml/min

Tablet bed temperature= 40°

Gun to bed distance= 8 Inches 

What will happen to the tablet temperature if we increase or decrease the distance between the spray guns and the tablet bed?

Case Study 1

For case study 1 we increase the distance between the spray guns and tablet bed from 8 inches to 10 inches keeping all the above parameters constant.

Tablet bed temperature will be increased from 40°C to 43°C by increasing the distance between spray guns and tablet bed.

Case Study 2 

For case Study 2 we decrease the distance between the spray guns and tablet bed from 8 inches to 6 inches keeping all the above parameters constant.

Tablet bed temperature will be decreased from 40°C to 37°C by decreasing the distance between spray guns and tablet bed.

Reason 

How tablet bed temperature increases or decreases by changing the distance between the spray guns and tablet surface?

The reason is that when we  increase the distance, tablets become more dry due to rapid evaporation of solvent as solvent has to cover more distance.

When we decrease the distance our spray rate over the tablet surface is increased as solvent has to travel short distance & evaporation is also slow due to which tablets become wet and temperature of tablets is decreased.

Tablet Coating Defects Related To Tablet Bed Temperature

Following are most common defects which are directly related to the tablet bed temperature 

  • Less Weight Gain
  • Color Variation 
  • Sticking & Picking 
  • Twinning 

Less Weight Gain

If our tablet bed temperature is high the required weight gain will not be achieved.

Read following article for detailed learning 

Weight gain defect during tablet coating 

Color Variation 

If tablet bed temperature is very high the required color uniformity of the tablets will not be achieved.

Read following article for detailed learning

Color variation defect during tablet coating

Sticking & Picking

Sticking and picking are two most common tablet coating defects which occur due to the low tablet bed temperature.

Read following article for detailed learning

Sticking and picking during tablet coating 

Twining 

Twining defects are observed during the tablet coating process due to the low tablet bed temperature.

Read following article for detailed learning

Tablet twinning defect

Conclusion 

The tablet bed temperature must be synchronized with the other tablet coating parameters to make our tablet coating process smooth & defect free.

If our tablet bed temperature is low we should increase the inlet air temperature, reduce the applied spray rate or adjust the distance between the spray guns and the rotated tablets.

If tablet bed temperature is high we should increase the spray rate, reduce the inlet air temperature or gun to bed distance.

Image Credit

Image Source – Google | Image By – SPRINGER LINK

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