Keefer: These are major factors. Pharmaceutical R&D groups are involved in many different product development processes, trying to determine the best excipient choice for a particular product. Formulation characteristics, tablet specifications and granulation flow are all important factors in order to achieve consistent quality during tablet production.
Deakin: With regard to sticking, spatial heterogeneity of the ingredients within the tablet is critical. This is because of the possibility of one ingredient causing sticking; so if this ingredient is concentrated in one area of the compressed tablet, then the Van der Waal Forces in bulk behavior could initiate sticking.
To ensure improved tablet quality and consistency, and to avoid the possibility of sticking and picking, one should check the moisture content of the granule and increase lubrication in the granule if necessary. Also, check humidity within the compression room.
Granule characteristics will always play a major part in the behaviour of the product during compression. Quality product, formulation and process controls will always assist in the compression of a successful tablet.
Barzanti: To obtain a tablet, the powder to be compressed must possess very precise physical and mechanical properties. A good flowability is required for consistent filling of the product in the die, while at the same time the granulate must feature enough compressible and cohesivene properties to form a tablet. As a general note, a high content of fines should be avoided as it is one of the major causes of problems during tabletting and this is why a granulation process is normally required.
The choice of excipient and granulation specs are of major importance to obtain a tablet of good quality and consistency and of course these are different from product to product. Performing tests of the complete process — granulation, blending and tabletting — can be of great help in understanding how the processing parameters can be adjusted to achieve the best result. With this aim, IMA makes available to customers a team of process specialists and a process and development laboratory where all the appropriate instrumentation is available to carry out different technological tests.
Speed is critical in today’s tabletting production environment, what have been the most effective speed-increasing developments in recent years and what is the outlook for bettering the production rates currently being achieved?
Keefer: Production speed is definitely a key factor, however making consistent quality tablets to certain specifications with limited machine downtime seems to be even more important. High production speeds without maintaining quality is a recipe for disaster. The tablet presses and automation features continue to improve as far as mechanical capabilities, but sometimes the product granulation can be a major limiting factor due to poor flow characteristics that ultimately affect the machine production speeds.
Deakin: Whilst increased tablet output is a main driver for most tablet manufacturers, increased tablet press speed is not always the answer. Productivity can be increased by the use of multi-tip tooling without the need to increase tablet press speed.
Increased tablet press speeds can have a negative impact on tablet quality because of a reduction in dwell time, which reduces with increased speed. This may cause issues such as air entrapment, leading to capping and scrapped tablets, sticking and tablet weight variation caused by poor flow.
There are available solutions for reduced dwell time, an example being the EU441 extended dwell tooling, although these types of innovation mean considerable outlay as the turret and associated parts of the tablet press have to be changed to accommodate the tooling design.
There is an option to modify the head flat of a standard B or D type punch, which has to be done in a controlled way but can increase dwell time without the need for major modifications to the tablet press. This is a relatively small enlargement of the head flat and it can help reduce the negative effect of increased press speed.
Barzanti: Speed depends on two main factors — accurate feeding of powder into the die and dwell time, i.e. the time during which compression is applied, ejecting the air contained in the powder and locking the particles in place.
In 1994, IMA introduced the COMPRIMA tablet press, which we believe still represents the real innovation in tablet compression at high speed. The powder is fed from an upper loading hopper into the central rotor area and moves towards the dies through the specially shaped radial channels, pushed by the centrifugal force generated by turret rotation. This system ensures accurate and consistent feeding of the dies, even at high production speeds and with difficult-to-handle products, while at the same time minimising the quantity of air incorporated into the powder and to be ejected during the compression process.
It is a unique system owing to the fact that if offers an extended dwell time, made possible by the combination of compression wheels and bearings applied on punch heads, which results in a longer compression time, even at high speeds.