The Science Of Tableting

Andy Dumelow on using science to produce quality tablets

The increasing demand for solid dose products calls for innovative production processes to ensure high-quality tablets are manufactured efficiently. However, this can be challenging, with many formulations proving difficult to compress.

When looking at the compression process, the physical properties of the formulation plays a substantial part, with factors such as moisture content and abrasiveness affecting its compressibility.

The overall formulation composition must be carefully examined to ensure the correct tooling specification is used and reflect the product being compressed. Punches and dies must be selected according to the characteristics of the formulation being produced. Thanks to advances in materials science and coating technology, solutions to problematic formulas can be applied.

The Issue Of Sticking

One of the dominant problems in tablet manufacture is sticking. This is when granule builds up on the punch tip face or die bore. Sticking can negatively affect the appearance of the tablet and become so significant that production is interrupted.

There are many reasons for sticking, with one of the most common being moisture within the formulation. This can be a root cause of a rise in adhesive forces. This happens with the increase in capillary action between the tooling surface and the granule. Capillary forces are generated when moisture condenses into the gap between a particle and surface, creating a liquid bridge. The strength of these forces can depend upon the relative humidity, gap geometry and surface chemical condition. These capillary bridges increase the cohesive forces and help bind the tablet together but can also have a negative effect by increasing the adhesion forces between the granule and the punch tip faces, leading to sticking.

The formulation may have a high moisture content, but the environment in which the tablet is being compressed can compound the issue. Excess humidity in the compression room or areas where the formulation is stored prior to compaction can significantly increase the moisture content, affecting the product’s adhesion to the punch tips.

A good solution to solve sticking as a result of high moisture content is the application of an anti-stick coating. This helps the tablet tooling to repel rather than attract moisture to the steel. Coating technology has advanced considerably over the years, and when used in conjunction with high-quality tooling steel, tool coatings are increasingly seen as an acceptable means of solving production problems such as sticking. They allow for better tableting efficiency and output by reducing the requirement for tools to be taken out of production for additional cleaning and maintenance work to remove problematic residue.

Aggressive Formulations

New tool materials and treatments created through years of extensive research are also helping to solve production problems due to aggressive formulations.

Some ingredients are particularly abrasive and comprise hard and sharp elements, causing damage to the punch tip faces when under compression. Through repeated cyclic compression, these abrasive ingredients can scrape away at the punch tip surface and the bore of the die resulting in low quality tablets.

Hard granules can also impregnate the surface of the punch tip under high compression forces. Adherence of the granules due to pitted and worn surfaces of the punches can cause many problems that will negatively affect production, including capping, de-lamination and sticking. This abrasive action can be countered by advanced tooling materials and coatings selected for their wear resistant properties.

The correct choice of tool steel can make a significant impact on production. The tool material must be balanced to give optimum tooling performance and durability. These properties should include anti-stick, abrasion and corrosion resistance, compressive strength, hardness and resistance to chipping and cracking.  As the main component to interface with the final product, punches and dies must be metallurgically robust to ensure tool longevity and a lack of production issues.

It is important to also consider the tool coating. With the correct coating or treatment in place, some of the biggest challenges that can delay production, such as wear and sticking, can be prevented.

Make Or Break

Understanding a tablet’s formulation can either make or break production. If the characteristics of the formulation being compressed are not understood, the result will be a production run filled with problems. It is important that the tooling reflects the compressed formulations to ensure a quality, fault-free tablet.

By choosing and testing tooling materials and coatings selected for their specific properties, overall equipment effectiveness will be improved, production will be enhanced, volume numbers will increase, and downtime due to production problems will be reduced.

It is important to contact an experienced tooling manufacturer who understands the science behind tablet production and can introduce innovative solutions to tableting problems to maximise production capability.

Andy Dumelow is with iHolland

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