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74 TABLETING


Gerd Hüffmann reveals how a compaction simulator can deliver a realistic tableting scale up


From R&D into production W


hen turning pharmaceutical powder into a tablet


by means of a tablet press, there are many challenges. Te challenge becomes even greater when tablet parameters established during R&D should become the basis for a successful commercial scale production. Te master challenge is to establish (in R&D) the most important tablet qualities and to transfer them all successfully to a production scale machine. Tablet weight is the first quality to consider. Te contents of API are defined by the tablet weight, which is the most critical parameter for the pharmacist! Tablet hardness is next on the list. Te disintegration and dissolution time is the next critical parameter for the pharmacist. Te third quality is tablet thickness. Te total height can be a critical issue for the packaging of the final tablet. To provide this transfer or scale-up capability, the R&D tablet press in question must provide the following features and function:


l Able to handle all common tablet shapes and sizes


l Able to compress not only single layer tablets, but multi- layer, ring tablets and core in core (tab in tab) tablets as well


l Able to work with all common tool standards and sizes (EU,


TSM, B, D, D-441, etc)


l Last but not least, it has to replicate the working sequence of a modern rotary press with a driven (forced) feed system, a regulated powder dosing and the application of pre- and main compression forces as well as ejection force measurement


Rotary tablet press Commonly a (smaller) rotary press is being used successfully for the R&D portion of the task. Tis finds its limitations once serious scale-up becomes part of the equation, simply for one common reason: the pitch circle diameter of these presses typically ranges from approximately 150 to 280mm, while large-scale production presses typically have a PCD ranging from 550 to 800mm. Terefore the actual punch speed of an R&D rotary press is always considerably slower than that of the rotary press later used in production. As an example, the dwell


time of a rotary R&D press with a pitch circle diameter of 180mm running with EU-B type punches at 70rpm is around 12,8ms. A production press with a PCD of, for instance, 700mm, would only have a dwell of 3,689 ms available at the same rotation speed. Tis means that the very important tableting parameter of dwell time cannot be adequately simulated, leaving to chance if


it will be possible to obtain the required tablet hardness and to avoid capping of tablets at speed. Te answer to all scale-up challenges and the ultimate scale-up tool is a compaction simulator such as the Styl’One Evolution from Romaco Kilian. Tis is a flexible, single-stroke tablet press that can assist with the development of single to five layer tablets, as well as core tablets (tab in tab). To fulfil all tableting


requirements this simulator is fully instrumented to measure compaction forces (tamping force, pre- and main compaction force), as well as ejection forces and punch displacement. Compaction cycles can either be force- or displacement controlled to replicate all commercially available control systems. It can operate with gravity feed for pure R&D applications and with force-feed fill shoes when up-scaling to a rotary press is required. Most important is the ability


to replicate the compaction cycle of a rotary press at a given operational speed. For this purpose, unrestricted compaction profiles can be created, as the press is fully programmable. Te Styl’One Evolution compaction simulator has a compression system made up of two pistons on which the punches are fixed (Euro, TSM formats). Te lower and upper punches are linked to a


The operating cycle of the rotary tablet press. What happens inside the die occurs in five stages. First is filling of first layer via fill cam. Next is re-dosing of first layer. Third is final compaction for de-aeration (pre-pressure). Fourth is final compaction (main-pressure). Fifth is ejection of tablet


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