Although both sugar coating and film coating are utilized by a significant number of pharmaceutical companies worldwide, the film-coating process is the one most often preferred today. Film coating was formally introduced into the pharmaceutical industry in the middle of the last century. It should be noted that there has been a steady transition in the pharmaceutical industry, beginning with sugar coating, moving to film coating, and finally arriving at aqueous film coating.
Although film coatings are most often applied for their aesthetic qualities, they have an important role to play in improving product stability and robustness, as well as enhancing flavor attributes, facilitating ingestion, and modifying drug release characteristics.
Types of Film Coating
Film-coating formulations encompass those that are expected to allow a drug to be rapidly released from the dosage form, those that may possess special barrier properties (with respect to, for example, moisture or oxygen), and those designed to modify drug release characteristics and facilitate drug targeting. As such, these coating formulations are exemplified by:
- Organic solvent–based solutions of polymers
- Aqueous solutions or dispersions of polymers
- Hot-melt systems
- Powder coatings
Coating Machine
At the heart of any coating process is the coating vessel, which can take one of two forms:
- Coating pans
- Fluid-bed coating equipment
In the beginning, film-coating equipment was commonly derived from that used in the sugar-coating process, namely, conventional coating pans. The early days of film coating, however, coincided with the introduction of a fluid bed coating process developed by Dale Wurster, and this quickly became adopted for many film-coating operations.
Parts of Coating Machine
- Peristaltic pump
- Inlet Blower for the air handling unit
- Air exhaust section
- Coating solution tank
- Spraying guns
- PLC
Process Parameters of Tablet Coating
Fixed operating parameters
- Pan loading (kg)
- Drying air (cfm)
- Coating system (film coating/ sugar coating)
- Quantity of coating applied (% w/w)
- Pattern air pressure (bar)
Variable operating parameters
- Solids content of coating suspension (% w/w)
- Inlet-air temperature (°C)
- Spray rate (g per min)
- Atomizing air pressure (bar)
- Pan speed (rpm)
- Number of spray guns used
Major Steps of Coating Process
- Tablet loading
- Pre-heating
- Pre-jogging
- Spraying
- Drying
- Cooling
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