Coating Process Optimization


Tablets are coated to protect the active ingredients and help with swallowing. Monitoring the dew point of tablet coating dryers saves on energy and, together with measurement of water activity, temperature and humidity ensures product quality.

Using a chilled mirror hygrometer – such as Michell’s Optidew 501 – to monitor the output of the tablet dryer ensure the most efficient operation and reduces running costs. Rotronic’s HygroLab, together with spot measurements with handheld devices, provides accurate readings of water activity which are essential for product quality.

The Rotronic Monitoring System RMS is a continuous online real-time monitoring system. It measures all important parameters, stores the data safely in the database and makes the information available to all authorised users via the Internet.

Tablet coating usually takes place within a perforated rotating drum. There are angled baffles placed in the drum that, along with the air flow inside, help mix the tablet bed. This allows the tablets to be lifted and turned from the peripheries to the centres of the drum to ensure that all surfaces of the tablets are evenly and uniformly coated with the sprayed coating or deposited coating. The atmosphere within this rotating drum needs to be closely controlled for temperature and dew point or relative humidity to ensure that the coating is uniform and smooth in appearance.

Once the coating is applied the drying of the coating takes place by drawing heated air through the tablet bed from a fan. This air flow also requires temperature, humidity and volume control to ensure controlled drying and extraction. Monitoring the dew point of both the inflow and outflow of this air gives an indication of the progress of the drying process. This allows the drying time to be kept to a minimum, reducing overall costs of the drying process. Water activity measurement is another important parameter. Knowing and understanding aw values helps to control the colour and texture of the tablets.

Knowledge of the water activity of pharmaceutical solids (proteins, drugs, and excipients) is essential to obtain a solid dosage form with optimal chemical, physical, microbial, and shelf-life properties. Water activity (aw) influences the chemical stability, microbial stability, flow properties, compaction, hardness, and dissolution rate of dosage forms of pharmaceuticals, proteins, biopharmaceuticals, nutraceuticals, and phytochemicals.

Spot measurement with handheld measuring devices can give you specific insights on relative humidity, temperature and psychrometric parameters within your production or storage areas.