Tablet Coating Machines

Sponsored Links

Tablet Coating Machines

Table Coating Machine is the mechanical device that coats the outer surface of tablet with a thin layer of coating material

  • To mask the taste, odor and color of the drug.
  • To provide physical and chemical protection for the drug.
  • To control the release of the drug from the tablet.
  • To protect the drug from gastric environment.
  • To improve the pharmaceutical elegance by special color and contrasting printing.
  • To incorporate another drug or formula adjuvant in the coating to avoid chemical incompatibilities.

Read about Classification , Mechanism , Advantages

What is the definition of tablet coating machine?

What are the types and sub types of tablet coating machine?

How the tablet coating machines works?

What are the important parameters to be considered in coating machines?

What are the main coatings done in coating machine?

What are the advantages of tablet coating machines?

What is the definition of tablet coating machine?

The principles of tablet coating are relatively simple. Tablet coating is the application of a coating composition to a moving bed of tablets with the concurrent use of heated air to facilitate evaporation of the solvents.

The distribution of the coating is done by the movement of the tablets either perpendicular or vertical to the application of the coating composition.

What are the types and sub types of tablet coating machine?

Tablet coating is done by using different varieties of coating machines. So the coating equipments are divided into following three types.

The standard coating pan

  1. Pellegrini pan
  2. Immersion sword system
  3. Immersion tube system

The perforated coating pan

  1. Accela-cota
  2. Hi-coater systems
  3. Driacoater
  4. Glatt coater

The fluidized bed or air suspension coater

  1. High pressure airless systems
  2. Low pressure air atomized systems

How the tablet coating machines works?

Several companies have developed their own coating machines to accommodate their coating processes. Most of the systems are based on these three basic designs.

The standard coating pan systems:

It consists of a circular metal pan mounted somewhat angularly on the stand.

The pan is 8 to 60 inches in diameter and is rotated on its horizontal axis by a motor.

Heat air is directed into the pan and onto the tablet bed surface and is exhausted by means of the ducts positioned through the front of the pan.

Coating solution is applied on to the tablets by spraying the material on to the rotating tablet bed by using atomized systems which produce a faster and even distribution of solutions.

A significancy drying efficiency of the standard coating pan can be achieved but pellegrini, immersion sword and immersion tube systems.

a, b, c) Standard coating pans with different shapes

Simplified diagram of standard coating pans

Pellegrini pan:

This system has a baffled pan and a diffuser that distributes the drying air uniformly over the tablet bed surface.

Pellegrini pan

Immersion sword system:

In this system drying air is introduced through a perforated metal sword device that is immersed in the tablet bed.

Simplified diagram of immersion sword system

Immersion tube system:

In this the tube is immersed into the tablet bed. The tube delivers the heated air and the spray nozzle is built in the tip of the tube.

Simplified diagram of immersion tube system

The perforated pan systems:

In this all the equipment types consists of perforated or partially perforated drum that is rotated on its horizontal axis in an enclosed housing.

Accela-cota & Hi-coater systems:

In these equipments the drying air is directed into the drum, is passed through the tablet bed and is exhausted through perforations in the drum.

  1. Accela-cota b) Hi-coater systems

Simplified diagrams of a) accela-cota b) Hi-coater systems

Driacoater:

In this the drying air is introduced through the hollow ribs located on the inside periphery of the drum. As the coating pan rotates the rib dip into the tablet bed and drying air passes up through and fluidized the tablet bed exhaust is from the back of the pan.

  1. Driacoater systems b) simplified diagram of diracoater system

Glatt coater:

It is the latest perforated pan coater. The drying air can be directed from the inside the drum through the tablet bed and out an exhaust duct.

Alternatively with an optional split chamber plenum, drying air can be directed in the reverse manner up through the drum perforations for partial fluidization of the tablet bed.

In all these four perforated pan systems the coating solution is applied to the surface of the rotating bed of the tablets through spraying nozzles that are positioned inside the drum.

Glatt coater system

Fluidized bed or air suspension systems:

Fluidization of the tablet mass is achieved in a columnar so that more air enters the center of the column, causing the tablet to raise in the center. The movement of the tablets is upwards through the center of the chamber. There by then fall toward the chamber wall and move downward to re-enter the air stream at the bottom column is used to direct the tablet movement within the main column.

Coating solutions are continuously applied from the spray nozzles located at the bottom of the chamber and sprayed on to the top of the cascading tablet bed by nozzles located in the upper region of the chamber.

Tablet cores that are friable and prone to chipping and edge abrasion may be difficult to coat even under the optimum conditions in the fluidized bed systems, owing to the relatively rough tablet to tablet impact and tablet chamber contact.

The two types of systems used to apply a finely divided spray coating solutions or suspensions onto the tablets.

  1. Fluidized bed coater b) Simplified diagram of fluidized bed coater

High pressure airless systems:

In this air less spray liquid is pumped at high pressure (250 to 3000 pounds per square inch gauge) through a small orifice (0.009 inch to 0.02 inch id) in the fluid nozzle which results in a finely divided spray.

The degree of the atomization and the spray rate are controlled by the fluid pressure, orifice size and viscosity of the liquid.

High pressure airless systems

Low pressure air atomized systems:

In this the liquid is pumped through somewhat larger orifice (0.02 to 0.06 inch id) at relatively low pressure (5 to 50 psig). Low pressure (10 to 100psig) air contacts the liquid stream at the tip of the atomizer and a finely divided spray is produced.

The degree of atomization is controlled by the fluid pressure, fluid cap orifice, viscosity of the fluid, air pressure and the air cap design.

Low pressure air atomized systems

What are the important parameters to be considered in coating machines?

Mostly the perforated coating machines are most widely used in the industry.

The important parameters to be considered during the coating process are

  1. Air capacity
  2. Coating composition
  3. Tablet surface area
  4. Equipment efficiency

Air capacity:

This represents the quantity of water or solvents that can be removed during the coating process, which depends on the quantity of air flowing through the tablet bed.

Coating composition:

The coating composition contains the ingredients that are to be applied on the tablet surface and the solvents which acts as a carriers for the ingredients. These solvents are essentially removed during the coating process. The inlet air provide the heat to evaporate the water. The exhaust air becomes cooler and contains more water owing to the evaporation of the solvent from the coating composition.

Tablet surface area:

The quantity of the tablets needed for coating has already been considered, but the size of the tablet and the presence of the dobossed feature also effect the coating conditions. The total surface area per unit weight decreases significantly from the smaller to larger tablets.

Equipment efficiency:

The coating efficiency for the conventional sugar coating is much less and 60% would be acceptable. The coating efficiency mainly depends on the amount of the coating material that collects on the pan walls.

What are the main coatings done in coating machine?

Coating is the last critical step in the tablet production cycle. The successful application of the coating solution formula provides the visual characteristics for the product thus the quality of the product can be judged on this final production step.

Based on the type of coating materials used the type of the coating machines can be selected. It includes sugar coating and film coating.

Sugar coating also called as conventional process involves the following steps

  • Sealing
  • Subcoating
  • Smoothing
  • Finishing
  • Polishing

Film coating also called as contemperory process involves the following methods

  • Pan pour method
  • Pan spray method

The film coating and the sugar coating processes mostly uses the same equipment for the coating process.

Coating system

What are the advantages of tablet coating machines?

Standard coating pan:

  • It is a continuous process.
  • It can reduce the drying time.
  • It is applicable for sugar and film coating.
  • The improvement in the drying efficiency can be improved by pellegrini pan, immersion sword and immersion tube systems.
  • It is a rapid process.
  • It takes less time to coat the materials.

Perforated pan systems:

  • Directly the drying air is passed into the drum.
  • Several air flow configurations are possible in Glatt coater.
  • It shows high coating capacity.
  • It is applicable to both sugar and film coating processes.
  • It shows more efficiency in drying of tablet bed.

Fluidized or air suspension systems:

  • In this coating solution is continuously applied from the spray nozzles.
  • High pressure airless systems and low pressure air atomized systems are results in finely divided spray.
  • These systems are used effectively.
  • Airless systems were most primarily used in air suspension coaters.

References

  1. Lieberman, Herbert A, Lachman, Leon (2009), Industrial pharmacy: Pharmaceutical dosage form-tablets. Banglore, Pune. ISBN:978-81-239-1679-8.
  2. http://wikipedia.org/wiki/Tableting
  3. Gilbert S. Banker(2002), Modern Pharmaceutics: Pharmaceutical dosage form-tablets. 4th edition. New York. ISBN: 0-8247-0674-9.
  4. Ansel howard C, Allen V, Popovich G, Ansel's Pharmaceutical dosage form-tablet. 8th edition. ISBN: 0-7817-4612-4.

About the Author

Saraswathi.B's picture
Author: Saraswathi.B

Assistant Professor in St. johns college of pharmacy

You May Also Like..