Perforated drum coating machines are popular in the industry and the following need to be addressed when considering the purchase of a machine:
- Air capacity – the amount of air flowing through the bed will determine the amount of water or solvent that can be removed during the coating process.
- Coating composition – the coating composition includes the ingredients that are applied to the surface as well as to the solvent that acts as a carrier for the ingredients. The solvent is removed during the coating process by the flow of air through the coating machine. To speed up this process the incoming air can be heated, however, there is a fine balance between the rate at which solvent can be evaporated and the rate at which the coating liquid can be introduced.
- Tablet surface area – it is easy to weigh a batch of tablets that are to be coated, to give an idea of the amount of coating solution that needs to be applied. However, it is the surface area of the tablets that determines the total amount of coating solution required. The size of the tablets and nature of their surface can significantly affect the coating conditions and quantities of solution required. The total area/weight ratio decreases quite significantly from a smaller to a larger tablet.
- Efficiency of equipment – conventional sugar coating efficiency is not very efficient and 60% is deemed to be acceptable. The efficiency depends on the coating material that is collected on the pan walls.