Overview Of The Film Coating Process And Difference Between Solvent And Aqueous Coating

Film Coating Process

Pharmaceutical tablets can be film coated in a single stage process that is rapid and results in minimal weight gain of at 2 – 3% compared with sugar coating which adds 60 to 80%. The film coat does not significantly affect the tablet’s disintegration process.

One benefit of film coating is that it is easy to automate, making it easier to comply with GMP requirements for Standard Operating Policy. It enables the tablet to maintain its shape and allows for embossing. A disadvantage with film coating is that it there is significant capital expenditure required for setting up the equipment and a large production area is necessary. Installation costs may also be high as well as ongoing energy cists,

Aqueous versus Solvent Film Coating

Aqueous Film Coats

  • Water is the most common solvent used
  • The process is non-toxic, no significant safety issues, and excess solvent can be released to the atmosphere
  • Aqueous coating requires more evaporation or drying by air than organic solvents.
  • The removal of water can take significantly longer than other solvents and may lead to mechanical problems as the tablets tumble inside the coating machine for longer periods.

Solvent Film Coats

  • Organic solvents are more volatile than water and therefore dry faster. Faster drying time due to the solvent’s volatility
  • It is necessary to follow safety protocols for the particular solvents
  • Modification of the equipment and production area may be required to ensure adequate ventilation of solvent
  • The company is responsible for environmental disposal of waste solvent.
  • Needs alteration to the equipment
  • Can be used for moisture sensitive products
  • Can impact on the smell and taste of the compounds to the tablets

The Process of Film Coating

  • Tablets are placed inside the coating drum which is then set to rotate, to mix the tablets.
  • Ambient air is heated and passes through perforations in base of the rotating drum to warm up the tablets. Air is circulated through the pellets as the drum rotates and exhausted through a vent system at the top or side of the drum.
  • A solution or suspension of the coating material is sprayed as fine droplets through the bet of tablets. To achieve uniform coating across the bed, the distance between the spray gun and tablet bed is measured and adjusted accordingly.
  • Once the droplets hit the surfaces of the tablets, it spreads into film on the surface before solvent is removed rapidly by the hot air.
  • The coating thickness on each tablet is increased as the tablets pass underneath the spray gun by the rotating drum.

Film Coating Components

  • The following are typical materials components used in the film coating process:
  1. Solvents – either water or organic solvents (e.g., chlorinated hydrocarbons, alcohols and esters.
  2. Film Formers or Polymers. These must:
    • be soluble to the solvent choice.
    • allow for the release of the drug in the body
    • be compatible to the core content of the tablet
    • form a clear, strong, non-tacky film.
  1. Plasticizers are added to help modify the properties of the polymer to aid the coating process. They must be miscible with the polymer.
  1. Colorants, such as water-soluble dyes or organic (water insoluble) pigments.
  2. Opacifiers. These are added to
  • help mask the primary colour
  • provide light protection
  • mask the tablet to prevent the core to be seen
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