Tablet coating is the process of applying a thin layer (often less than 1 mm) of a material onto the surface of a tablet to mask unpleasant tastes or provide additional functionality. The coating layer usually consists of one or more polymers, such as cellulose derivatives, polyvinyl alcohol, or methacrylic acid copolymers, and may include other additives such as plasticizers, colorants, and anti-adherents.
The tablet coating process starts with the preparation of the coating solution, which typically involves dissolving the polymer(s) and other additives in a solvent system. The choice of solvent depends on the properties of the polymer and the coating equipment used. Common solvents include water, alcohols, and chlorinated solvents.
Once the coating solution is prepared, the tablets are loaded onto a coating machine. The coating machine consists of a rotating drum or pan, which tumbles the tablets while the coating solution is sprayed or atomized onto the surface of the tablets using an atomizer or spray nozzle. As the solvent evaporates from the coating solution, the polymer(s) form a solid layer on the tablet surface.
The coating process may be performed in one or multiple layers, depending on the desired thickness and functionality of the coating. In between each coat, the tablets may be dried using hot air, infrared radiation, or a vacuum to remove residual solvent and improve the adhesion of subsequent layers.
The final coated tablets may be polished using a glazing agent to improve their appearance and provide additional protection against environmental factors such as moisture, heat, and light. Coating can also be used for the controlled release of active ingredients, protection against gastric acid, and targeting specific absorption sites in the body.
Overall, tablet coating plays an important role in the pharmaceutical industry, helping to improve the safety, efficacy, and patient compliance of oral solid dosage forms.