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Film coating process Film coating plays a very important role and a number of problems in tablet coating are related to process setup. There are many variables that should be controlled in a process and we will understand how these variables are important to the film coating process. We will study the different types of equipment, which are available for film coating.
Basic requirements of film coating
1. Distribution
2. Mixing
3. Drying
4. Removal of solvent
The first requirement of the film coating process is that the coating suspension should be uniformly distributed throughout the tablet bed. Spray guns are commonly used for dispensing coating suspensions. Two different types of spray guns are used. Airless spray guns and air atomized spray guns. A problem with airless spray guns is that the spray rate cannot be controlled independently of air pressure. Thus an air atomized spray gun is used to coat the aqueous film.
There are three different types of guns, which are used such as 2 port guns, 3 port guns and 4 port guns. 2 port gun, port for fluid and other port for air pressure. In this gun actuation the gun firing pressure and atomization pressure are controlled by a pressure and thus both cannot be controlled independently of each other. In three-port guns, there are 2 ports for air pressure and 1 port for fluid. The active pressure and atom pressure of this gun can be controlled independently. In 3 port guns, the spray width is controlled by a screw on the gun which when opened allows air to flow in and increases the spray width. This may vary in spray width from batch to batch. Of the 4 port guns, 3 ports are air and 1 liquid port. Thus actuation pressure, atomization pressure and spray width can all be controlled independently by air pressure. This ensures uniformity of spray width from batch to batch.
