Dale Natoli is President of NatoliEngineering Company, Inc.,Saint Charles, MO, USA.Email: sales@natoli.com

IINNDDUUSSTTRRIIAALL PHARMACY • December 2011 • Issue 324

For most companies, sticking can bedifficult, if not impossible to avoid. At theproduction level, this can affect operatingefficiency and productivity, anddramatically increases manufacturingcosts – not to mention the effects ontablet quality, that can affect consumerconfidence and the perceivedeffectiveness of a product.

All too often, tablet manufacturers willrevert to a punch coating that promisesto eliminate sticking by promotingenhanced product release. In general,these coatings are costly and, in ourexperience, are less than 50 per centeffective. Also, adding a punch coating tothe equation introduces a variable that isdifficult to monitor and virtuallyimpossible to troubleshoot. Thus, beforedeciding on a coating, it is better toexplore the many different steel gradesthat can offer improved product release.These steels will typically be higher inchromium than standard tool steels andmuch easier to troubleshoot than apunch with a coating – when and ifsticking continues.

Consistency

The most important factors for consistenttablet production are tablet presscleanliness and proper maintenance.Improperly set or maintained lower

punch retainers is a common cause ofvariable tablet weight and hardness,whereas improper or inconsistent toolworking length would typically beresponsible for any deviation in tablethardness and thickness.

Improper fill cams can also beresponsible for inconsistencies in tabletproduction; if the fill cams are too deep,excessive granulation is taken into thedie, then discharged at the weight camand re-circulated. If the feeder cannotreclaim this granulation, it will bypass thefeeder and accumulate at the neck of theturret; hence, the centrifugal force of thespinning turret will propel thegranulation outward and refill the diesafter passing over the weight cam –resulting in weight variation.

Proper product flow is also crucial touniform tablet compression; granulationthat flows evenly is conducive to higher-quality tablets.

Speed

The most important contributor totableting speed – or indeed to tabletproduction – has been the acceptance ofmulti-tip tooling. This has been used fordecades in the industrial, food andconfection industries, but only in the last10 years has multi-tip tooling beenaccepted and used in the pharmaceuticalindustry on rotary tablet presses. Tabletmanufacturers producing micro-tabs areexperiencing speeds of over 5,000 tabletsper second. The main concern with usingmulti-tip tooling is the ability to compressconsistent-quality tablets and – if not –then the ability to validate the tabletreject system to ensure that out-of-spectablets are discharged.

We expect to see faster press speeds in thefuture, as this is the long-term scope forvirtually all premium tablet pressmanufacturers. Frank Stokes is believed tobe the engineer responsible for designingthe rotary tablet press during hisemployment with Parke Davis in the late1800s. The same basic design – using camsto vertically move the tooling through thevarious cycles of tablet compression in aturret, with upper and lower punches anddies – is still used today. The first rotarytablet presses produced 400 to 600 tabletsa minute, whereas the modern tablet

PROGRESSION INTABLET COMPRESSIONby Dale Natoli

The most common problem encountered in tabletmanufacture would have to be granulation adhering to

the tool face, commonly known as 'sticking'. Tabletmanufacturers often have to struggle through compressinga batch of sticky product, and sometimes – due to theseverity of the sticking – are unable to compress anytablets at all. Typically, sticking is unnoticed orunrecognised during product development and so willoften commence and/or worsen once the product reachesproduction when the dynamics of weight, friction, heat,powder flow, segregation and dwell time – to name but afew, come into play.