Washcoating

Washcoating is a process used in manufacturing, particularly in the pharmaceutical and food industries, to apply a thin, protective or decorative layer to a solid dosage form, such as a tablet or a granule. This coating is typically a water-based solution or suspension containing polymers, plasticizers, colorants, and opacifiers. The primary purpose of a washcoat can be to improve the appearance of the product by masking imperfections, providing a uniform color, or adding a glossy finish. It can also serve to protect the core material from moisture, light, or oxidation, thereby extending its shelf life.

In pharmaceutical applications, washcoating can enhance swallowability and mask the unpleasant taste or odor of active ingredients. It's a crucial step in the production of many medications, ensuring both aesthetic appeal and functional integrity. The application process usually involves spraying the coating solution onto the tumbling dosage forms in a coating pan or fluid bed dryer. The controlled evaporation of the solvent leaves behind a thin, even film. Washcoats are generally applied before any subsequent functional coatings, such as enteric coatings or sustained-release coatings, as they provide a smooth surface for these more complex layers. The composition of the washcoat is carefully selected to ensure compatibility with the core material and to achieve the desired visual and protective properties without negatively impacting the drug's dissolution or bioavailability.