The Art Of Tablet Compression

These days, tablet compression can be regarded as more of an art than a science. IPT Editor Pam Barnacal interviews Dale Natoli, Vice President of Natoli Engineering Company, Inc, about the many factors that must be kept in mind to ensure the fast, consistent production of high-quality tablets.

Question: What are the most common problems encountered in day-to-day tablet production and how can these be avoided?

Answer: From the perspective of a tablet-tooling supplier, the most common problem encountered would have to be granulation adhering to the tool face, commonly phrased as ‘sticking'. It is not uncommon for tablet manufacturers to struggle through compressing a batch of sticky product, and sometimes – due to the severity of the sticking – to be unable to compress any tablets at all. Typically, sticking is not noticed or recognised during product development and so it will often commence and/or worsen once the product reaches production when the dynamics of weight, friction, heat, powder flow, segregation and dwell time – to name but a few – come into play.

For most companies, sticking can be difficult – if not impossible – to avoid and requires painstaking troubleshooting, together with a well-organised design of experiments. At the production level, this can be detrimental as it affects operating efficiency and productivity, and dramatically increases manufacturing costs – not to mention the effects on tablet quality, that can affect consumer confidence and the perceived effectiveness of a product.

For most companies, sticking can be difficult – if not impossible – to avoid and requires painstaking troubleshooting, together with a well-organised design of experiments. At the production level, this can be detrimental as it affects operating efficiency and productivity, and dramatically increases manufacturing costs – not to mention the effects on tablet quality, that can affect consumer confidence and the perceived effectiveness of a product.

Question: What are the most important factors for consistent tablet production?

Answer: Tablet press cleanliness and proper maintenance is crucial for consistent tablet production. Improperly set or maintained lower punch retainers is a common cause of variable tablet weight and hardness, whereas improper or inconsistent tool working length would typically be responsible for any deviation in tablet hardness and thickness. Improper fill cams can also be responsible for inconsistencies in tablet production; if the fill cams are too deep, excessive granulation is taken into the die, then discharged at the weight cam and recirculated. If the feeder cannot reclaim this granulation, it will bypass the feeder and accumulate at the neck of the turret; hence, the centrifugal force of the spinning turret will propel the granulation outward and refill the dies after passing over the weight cam – resulting in weight variation. Proper product flow is also crucial to uniform tablet compression; granulation that flows evenly is conducive to higher-quality tablets.

Question: What have been the most important contributors to increased tabletting speeds, and is there much scope for further increases in the future?

Answer: The most important contributor to tabletting speed – or indeed to tablet production – has been the acceptance of multi-tip tooling. This has been used for decades in the industrial, food and confection industries, but it has only been in the last ten years that multi-tip tooling has been accepted and used in the pharmaceutical industry on rotary tablet presses. Tablet manufacturers producing micro-tabs are experiencing speeds of over 5,000 tablets per second. The main concern with using multi-tip tooling is the ability to compress consistent-quality tablets and – if not – then the ability to validate the tablet reject system to ensure that out-of-spec tablets are discharged.

Yes, I do expect to see faster press speeds in the future, as this is the long-term scope for virtually all premium tablet press manufacturers. Frank Stokes is believed to be the engineer responsible for designing the rotary tablet press during his employment with Parke Davis in the late 1800s. The same basic design – using cams to vertically move the tooling through the various cycles of tablet compression in a turret, with upper and lower punches and dies – is still used today. The first rotary tablet presses produced 400 to 600 tablets a minute, whereas the modern tablet presses of today can produce more than 100,000 tablets per minute. Innovation is simply matter of time.