Blistering is a common coating defect in pharmaceutical tablet coating processes. It typically appears as small bubbles or blisters between the coating film and the tablet core, or between different coating layers. The main causes are usually related to improper film curing, excessively rapid drying, or insufficient adhesion between the coating film and the underlying surface.
Why Does Blistering Occur in Tablet Coating?
When the coating solution dries too quickly, moisture or solvent can become trapped beneath the coating film. As the trapped material expands or evaporates, it may create localized bubbles and cause the coating to lift from the tablet surface.
Poor adhesion between the coating film and the tablet core can produce a similar result. Factors such as coating formulation, surface condition, spray rate, inlet-air temperature, airflow, and drying speed can all influence film formation and adhesion.
How to Reduce Coating Blistering
The drying conditions should be adjusted according to the specific formulation and tablet characteristics. In many cases, reducing the drying temperature and drying rate can provide the coating film with more time to form and adhere properly to the tablet surface.
At the same time, the film-forming conditions should be optimized to improve coating adhesion. This may involve adjusting the coating formulation, spray rate, airflow, or other process parameters rather than simply increasing the drying temperature.
A stable coating process requires good coordination between spraying, tablet movement, airflow, temperature, and drying time. Monitoring these parameters during production can help identify the cause of blistering and reduce recurring coating defects.
What Is a Pharmaceutical Coating Machine?
A pharmaceutical coating machine is a mechatronic processing system used for organic film coating, water-soluble film coating, and sustained- or controlled-release coating of tablets, pellets, confectionery products, and other solid materials.
By coordinating spraying, mixing, heated-air circulation, and exhaust, the machine provides controlled coating and drying conditions. Stable mechanical operation is also important for maintaining consistent tablet movement and spray coverage.
Hansheng Automation can manufacture custom precision components for coating machines according to customer drawings and technical specifications. We provide made-to-drawing machining for shafts, bushings, brackets, supports, spray-system components, and other non-standard parts used in pharmaceutical equipment. Prototype and small-batch production are supported, with machining processes selected according to the required material, dimensional tolerances, surface finish, and application requirements.
