Pharma capsules with on-line viscosity control

Today's modern hardshell capsule manufacturing processes are high-speed operations requiring consistent and reliable viscosity measurement and control to assure proper capsule thickness and quality

High-volume manufacture of two-piece hardshell capsules for the pharmaceutical and medical markets is a major industry.

Hardshell gelatin capsules - made out of granulated gelatin from animal bones, skins, hooves, and connective tissue - are favoured because of their durability and digestibility.

They stand up to the rigours of packing, shipping, and handling.

Today's modern hardshell capsule manufacturing processes - still a major part of the industry - are high-speed operations requiring consistent and reliable viscosity measurement and control to assure proper capsule thickness and quality.

The process gradually adds a dry granular gelatin solution to hot water in a mixing tank.

Then, after a surfactant is introduced, high-speed stirring wets down the granules to allow for complete hydrolysis of the gelatin.

After it is aged, the gelatin solution is drawn into smaller tanks to properly prepare for and admit additives and dyes.

Too high a temperature will speed up the gelatin degradation process.

On the other hand, if the temperature is too low the gelatin dissolves too slowly, so the temperature is kept constant.

Most importantly, though, viscosity should not be changed in the operating machines when make-up solution is added.

So it is essential that an accurate viscosity adjustment be done prior to addition of the make-up solution.

In the capsule machines moulds, or 'pin-bars' are dropped into pans of coloured-gel which coats the mould 'pin-bars'.

Once extracted, air is blown onto them to set the gel.

In the drying process, the capsule moulds travel through dryers where large volumes of air are blown across the pins to dry the film.

Then the capsules are blown off the mould; a series of sorters and visual inspection filter out any defects.

These batches, sometimes 100,000 capsules at a time, are then put into an off-line dryer reducing the water content to about 15%.

Then they are ready for imprinting, packaging, testing and shipping.

On-line viscosity measurement has been used reliably in the gel-prep stage, when the granulated gel is wetted, mixed and dyes are added.

After the make-up gel is added to the machine, accurate viscosity measurement helps control deviations that affect capsule wall thicknesses (in all coating procedures, thickness is proportional to viscosity).

Tolerances are extremely tight in order to insure proper "fit" between each capsule half.

In the on-line dipping process, the mould pins emerge and the combination of lower temperature, drying and gravity-induced near-zero shear rate, increase the viscosity.

It is important to maintain the viscosity of the gel in the dip tray so that the capsule will be of the proper thickness.

Too thin of a capsule would dissolve too quickly when taken, or crack easily when handled.

Too thick a capsule would not dissolve easily when taken.

Maintaining proper viscosity causes the gel to 'set' into a film that gives each capsule the strength it needs to withstand the forces later exerted on it by the capsule-filling machine.

In the final stage, a small printing press is used to apply a manufacturer's logo, lot numbers, capsule dosage-size or other information on the ready-to-fill capsules.

An on-line viscometer can also be used to control ink-viscosity in this last phase.

The use of viscosity measurement and control is standard in the capsule industry.

Manufacturers often have dozens of hardshell capsule machines, usually with two on-line viscometers for each process line.

Low-cost Brookfield VTE-250 and TT220 have been the instruments of choice in countries like China, Canada, India, the United States and Europe.

Manufacturers value the Brookfield In-Line Viscometers because of their ability to provide linear electrical output signals directly to a read-out monitor or a process controller and because they know they can count on Brookfield Instrumentation for excellent viscosity measurements.

The benefits of online viscosity control include the following: 1) Insures uniform thickness of hardshell gelatin capsules halves, thus minimizing out of specification product and maximizing lot quality.

2) Assures higher production speeds through less downtime, thus producing more capsules per unit time.

3) Direct reading rotational design is reliable and durable, and requires little service or maintenance.

4) Linear output signal is directly proportional to viscosity.

One recent development is the advent of the Brookfield AST-100 On-Line Viscometer, with no moving parts, which permits continuous measurement of viscosity during gel prep as well as capsule manufacturing.

With many options now available to the capsule manufacturer for improved process control, there is a clear advantage to those who choose to make the investment.

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