Tablet Coating Machine
Tablet Coating Pan
The sugar coating process factually or anciently has involved the application of various coating fluids on a bed of tablets in a conventional coating pan, which is fitted by supplying dry air to the tablet and also exhaust to remove moisture and dusted air from the coating pan.
Generally, after the required volume of liquid has been applied, there is some time required to allow the tablets to mix and the liquid got fully dispersed throughout the batch.
To make easy the uniform transport of liquid, the tablet is stirred by the hand or in the larger pans to overcome the mixing problem that is associated with dead
spots.
Lastly,
the tablets are dried by blowing the air on the surface of the tablet
bed.
In the early stages of the film coating process, the equipment that are used was already used in the sugar coating techniques.
Although, the dipping or ladling of coating liquids during the film coating techniques has already been used. Generally, by using the spray technique liquid is applied. There are two types of spray equipment that are essentially used include:
1) Hydraulic (Airless) Spray
In this spray technique, the coating liquid is pumped under pressure to a spray nozzle with a small orifice and the atomization of liquid occurs as it expands quickly on coming out from the nozzle.Generally, airless-spray techniques are used in large-scale film-coating operations employing organic solvents
2) Air Spray
In this spray technique, the liquid is pumped under minimum pressure or no pressure to the nozzle and is finally atomized by means of a blast of compressed air that makes a contact with the liquid as it passes from the nozzle aperture.The air-spray techniques are used in both either in small-scale laboratories or in all aqueous film-coating operations.
The application of spray makes able to finely atomized droplets of the coating solution that is to be delivered across the surface of the moving tablet mass in a way that achieves uniform coverage during the time that prevents the adjacent tablets from sticking together as the coating solution is dried rapidly. The spray application is a continuous process.
In the early stages of the film coating process, the insufficient drying conditions inside the coating apparatus, preferably using airless coating techniques with organic solvent-based formulations.
During the non-spray part of the cycle, this spray technique allowed the excess solvent to be removed and due to this, the risk of sticking and picking is reduced.
Although, during recent advancements, the improvement in drying capabilities shows the preferred use of spray techniques because this allows the uniform coatings to be applied in a shorter process.
The film coating formulations are based on volatile organic solvents that make capable of acceptable processing time to achieve. Though, in the sugar-coating process, conventional pans have acceptable properties with regard to the mixing mass of the tablet.
During the twentieth century when aqueous film coating was introduced, it shows a serious challenge to the continued use of conventional processing equipment (Tablet coating machine).
Due to the limitations in both drying as well as mixing capabilities, this resulted in increased processing time which result in compromised product quality and longer stability.
These problems have been eliminated as the coating-pan design has developed or evolved and coating process techniques have improved.
The conventional, solid-wall coating pans usually known as Pellegrini has limitations. These are generally angular pan that rotates on the horizontal axis, show significant improvement in the sugar coating process, and are also approved for film coating as well because due to the presence of an integral baffle system the uniform mixing of coating is achieved.
The capacity of Pellegrini pans ranges from the 10-kg laboratory scale-up to 1000 kg for high-output production.
In solid-wall coating pan designs, the drying air is blown only on the surface of the tablet bed, so the drying capacity is limited. To minimize its limitations many attempts have been made to improve the air exchange on the tablet bed.
The introduction of the side-vented pan concept is a major advance in pan coating technology, which originated by Eli Lilly. Originally this is called the Accela-cota.
The main features of side-vented coating pans are as follows:
1) The angular pan that rotates on a horizontal axis, fitted with an integral baffle system.
2) A completely enclosed coating system.
3) A perforated pan that allows drying air to be pulled through a falling bed of tablets while the coating liquid is applied to the surface of tablets using a spray-atomization technique.
The side-vented coating pans exhibited:
1) The design allows multidirectional airflow.
2) The coating pans are designed to allow continuous processing.
3) Depending on the density of the products the interchangeable coating pan represents the batch capacities which are in the range of 3 to 40 kg.
4) Effective cleaning system that enhances good manufacturing processes compliance.
5) The coating process is fully automated and computerized.
Fluidized-Bed Coating Equipment
The fluidized-Bed coating technique was initially used in the pharmaceutical industry for drying as well as for the granulation process.
Although many attempts have been made for using this technique in the Film-coating process. Through, the introduction of the Wurster concept, significant advances came in coating techniques.
When the coating that is based on organic solvents was used mainly, the Wurster process was very frequently used for the coating of solid dosage forms or tablets.
Read more - Solid oral dosage Forms (Tablet or Capsules)
In the film coating process, the fluidized-Bed equipment showed the most effective drying characteristics.
The selection of three fluidized-Bed coating processes is based on a particular type of insert that is determined by the nature and the functionality to be intended of the coating applied. Like;
1) Top-Spray Process (Granulator)
When a taste masking coating is applied, then this spray press is preferred. It is also suitable for hot-melt coatings.
2) Bottom-Spray Process (Wurster)
This process is preferred when the application of Modified-Release coating is required. This process is also suitable for drug layering when the dose of a drug is in the low-to-medium range.3) Tangential-Spray Process (Rotor)
This process is also preferred when the application of Modified-Release coating is required. This is ideal for drug layering when the dose is medium to high. It is also useful for producing spheroidal pellets from powders.Quality Control of Coated Tablets
The characteristics of appearance and drug availability are the most important aspects of coated tablets.The appearance of the coated tablet must be some color standard because if there are differences in the color that may occur then the quality control chemist will assume that there is a difference that occurred from previous lots.
It is very important to check the defects of tablets like picking and chipped edges. This can occur because of the physical abuse of the tablets either in their uncoated or coated forms.
It is also very important to ensure that this physical damage or abuse of the tablets does not exceed the limits.
For identification of the products, the coated tablets may be imprinted (mainly sugar-coated tablets), and the film-coated tablets bear a monogram.
From each batch, some tablets should be submitted to perform some tests like dissolution tests. It is totally depending upon the characteristics of the tablet core that is to be coated.
The coating of the tablets can modify the drug release profile. Even, when it is not intended to be administered either enteric or controlled-release products. This behavior can be very with each batch of tablets that is to be coated.
Problems Associated with Tablet Coatings
There are many problems that are associated with the coating of tablets including:1) Cracks formation in the coating.
2) Variations in the color of the coating.
3) Poor adhesion of the coating on the tablets.
4) Tablet abrasion or wearing off or rubbing off.
5) Fill in the tablet markings.
6) Rough surface of the tablets.
The poor adhesion of the coating occurs due to the high relative humidity inside the coating chamber. This happened when organic solvents were used with the high coating spray rate onto the coating tablets, the concentration of polymer in the coating solution as well as the temperature is too low that resulting in the slow rate of solvent evaporation.
Tablet Abrasion (or Wearing off)
Tablet abrasion may cause damage to the tablet surface. This occurs due to:1) The rotation speed of the pan.
2) Due to the inappropriate hardness of the tablet.
3) During the coating the tablet bed is too heavy.
4) Due to the irregular shape of the tablet.
Inappropriate Tablet Hardness
The hardness of the tablet may be improved by increasing the concentration of binder in the wet granulation process or by increasing the compaction pressure.The hardness that is produced by wet granulation is generally hard as compared to the other methods of granulation and hence, tablets produced by the wet granulation method are generally suitable for coating.
Irregular Tablet Shape
The abrasion or wearing off mainly occurs due to the irregular shape of tablets. This problem can be overcome by changing the shape of the tablets.The Tablet Bed is too Heavy During the Coating
This occurs due to the contact between tablets.To minimize this problem the loading of tablets within the coating chamber is reduced means the number of tablets to be loaded should be in a specified manner.
The rotation speed of the pan is high. So, by reducing the speed of the pan the contact between the tablets can be reduced.
Filling of Tablet Marking
Generally, manufacturers identified their products by either a name or marks that are embossed on the tablets.If the coating applied on the tablets is not proper manner then it will be deposited on the marks or name and the mark will get unnoticed.
This occurs due to applying a large volume of the coating solution, low air temperature, and too low rotation speed.
The Rough Surface of The Tablets
This is one of the major problems that occur during the coating of a tablet that exhibits a rough surface. To overcome this problem the spray rate can be increased and the inlet air temperature can be decreased.Coating Color Variations
Variations in the color of coated tablets occur due to:- Uneven coating process that results in the thickness of the coating.
- Improper mixing of color in the formulation.
- Migration of color components within the tablet's core.
It can be minimized by the use of a coating in which the components within the table core are insoluble.
Cracks Formation in the Coating
- The cracking formation in coating occurs due to the inappropriate coating formulation.
- The cracking in polymer coatings indicates that the concentration of plasticizers should be increased.
- Sometimes, the use of less stress resistance polymer can also cause this problem.
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