What is aqueous coating?
The coating is one of the most important components of tablet manufacturing & there are many reasons why we apply a coat to tablets, if you are not familiar here with the reason why we apply coating, you must read the article given in the following link
In the current article, we will only discuss what is the aqueous coating?
As the name indicates, aqueous coating means water-based coating, if we want to learn about aqueous coating, first of all, we will have to look over types of tablet coating.
The coating is divided based on the type of solvent and there are three main types of tablet coating, one is aqueous coating, other one is organic coating and third one is the hydro alcoholic coating where both water & aqueous solvents are used
Aqueous Coating
The type of coating in which the water is used as a solvent is known as aqueous coating or water-based coating.
In aqueous coating we only use water, and no organic solvent is used so one question comes to mind why aqueous solvent is used?
When the technology was not very advanced, the organic coating was popular but with the passage of time the organic solvents were replaced with water because organic solvents are not environmentally friendly and are also harmful to humans whereas water is safe to use.
How is Aqueous Suspension prepared?
As per the formulation, the prescribed quantity of water is taken & then the excipients are added to the water to prepare the coating suspension.
After the addition of each excipient, the proper time is given for the mixing of solid materials in water to form a uniform suspension.
The mixing is performed usinga homogenizer where a vertex is created in the water and then each excipient is added to the vortex.
Percentage Dispersion
The main important factor during the formulation of tablet coating suspension is the percentage coating dispersion,o ur coating suspension must not be too thick to flow and not too thin to overflow.
An optimum aqueous coating concentration is usually 14 to 15% dispersion which is easy to spray over tablets after atomization.
Critical Monitoring
The aqueous coating requires more care and supervision as if the water is not properly evaporated it will penetrate into the core tablets so the tablet bed temperature is maintained at 38 to 42°C which ensures evaporation of water and deposition of solid contents over tablets.
If tablet bed temperature falls below 38°C the chances of water penetration in core tablets are increased which if not supervised carefully results in damage to the tablets.
Cost Effectiveness
High energy in the form of heat is required for aqueous coating to evaporate the water so the overall cost of the coating process using water-based suspension is high as compared to the organic solvent coating.
Less heat is required for evaporation of organic solvents and organic coating can also be performed easily in conventional tablet coating pans but for aqueous coating, the perforated tablet coating pans with efficient heat control systems are used.
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