Heat Distribution and Airflow Channelling in the Coater

With the aim of improving process and tablet quality in film coating Lödige Process Technology has introduced a new technical solution by which the air and thus heat energy is evenly distributed over the entire tablet bed.

In contrast to conventional coating systems, in the ‘airflow around the coating drum’ process the air is inserted via a distributor pipe and circulates around the coater drum. The air enters the drum over an enlarged area, ensuring a very even, almost turbulence-free airflow inside the coater, especially in the nozzle zone, guaranteeing optimum coating results. Thermal imaging cameras were systematically used in the development of the process – the first time in this area of application.

In tablet coating, the airflow has a decisive influence on the coating process. Turbulence in the nozzle zone will cause fouling of the inside walls of the coater, the nozzles and spray arm. This may reduce the operational life in campaign production, or – when the encrustation becomes detached – lead to a deterioration in product surface quality. Furthermore, an uneven airflow results in unbalanced temperature distribution in the drum. In the ‘cold zones’, the freshly sprinkled tablets dry poorly, with a risk of twin formation. On the other hand, in hot spots the tablets will be overheated, leading to rough surfaces.

Turbulence must be prevented at all costs, particularly when organic solvents such as acetone or ethanol are involved, as spray drying and consequential defects in the film-coated tablets may otherwise occur.

All these imperfections can be reliably prevented with the ‘airflow around the coating drum’.

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