Continuous Improvement in Tablet Coating and Dry Granulation - Pharmaceutical Technology

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Continuous Improvement in Tablet Coating and Dry Granulation
Recent advances in equipment design and operation in spraying, drying, and mixing can improve the tablet-coating process.

Pharmaceutical Technology
pp. s12-s16

Dry granulation and roller compaction

Continuous dry granulation is an established process in the pharmaceutical industry. Today, it is not only applied for moisture- and temperature-sensitive materials but also for large-volume solid-dosage products. In comparison with classical wet-granulation techniques, a sophisticated drying system is not required for processing. This elimination of the drying system avoids large investments for production equipment and space and lowers manufacturing costs. An additional benefit to having an one-unit operation is its suitability for installation in a one-floor operation. The dry granulator can be fed with a single intermediate bulk container (IBC). To enable a continuous process, an enlarged power-feed hopper can be used with a level sensor and adequate holding capacity to enable the change-out of additional IBCs without interrupting the process.

On the discharge side, a simple plug-flow pneumatic conveying system can be used to transfer the resulting granulation into a receiving IBC for future blending and processing. This reduction in handling equipment can further reduce the capital costs with a dry-granulation system.

Furthermore, for large-volume throughputs, the fast roller-compaction process is paramount to efficient processing. This efficiency enables the production of different products and product batch sizes with one single machine (4). The market already offers various dry granulators, which can be described by the arrangement of the two compaction rollers. They can be mounted horizontally, vertically, or on an incline.

Depending on the supplier, the rollers differ in width, diameter, and surface properties. Furthermore, roller compactors are distinguished between fixed-gap and moveable gap compactors, whereas the moveable roller compactors are state of the art. Only moveable roller compactors, however, ensure homogeneous ribbon porosity at constant compaction pressure.

The granulation step, where the ribbons are transferred into final granules, is usually integrated in the roller-compaction equipment and is performed in one or two steps (5, 6). With this in mind, manufacturers introduced a dry granulator with an electromechanical roller drive and massive roller shafts mounted in a horizontal manner.

With this newly developed machine, minimal time is needed to achieve a steady state during process start-up, and parallel gap is ensured during the whole production time. The proportional-integral-derivative (PID) loop control minimizes the gap deviations during processing and enables constant granule porosities. The granulation step is achieved using a conical sieve, which gently transforms the ribbons into final granules even at high material throughputs. Due to different sieve setups, the desired particle-size distribution can be obtained.


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