Capsule Filling Equipment and Procedures

There are different styles and trends for everything in life, even those that apply to the dietary supplement industry. One trend in capsule filling enjoying a reemergence is the liquid-filled hard-gelatin capsule. The ability to fill a two-piece hard capsule with a liquid substance has been around for more than 150 years, although the advantages of it have only recently been rediscovered, becoming particularly popular in the nutritional market.

The first gelatin capsule was manufactured in 1834 in Paris, becoming an overnight success due to its ability to disguise the unpleasant taste and obnoxious odors of medicines that were popular at that time. The original patent included using both liquid and powder fills, and was widely used in Europe for both oils and ethereal extracts, and in the United States for pill masses and powders. In 1846, a Parisian pharmacist developed a two-piece capsule to compete against the one-piece hard gelatin. Commercial production of the capsule started in the United States during the 1870s and in Europe during the 1950s.

Capsule production and usage did not undergo any significant changes until the 1930s, when soft gelatin capsules were invented. Soon it became a trend for liquid substances to be filled into soft gelatin capsules, and hard gelatin capsules were allocated for dry fill only. The hard gelatin capsule came into its own in Europe during the late 1960s with the development of automatic filling machines designed to fill powders and granules. This remained until the late 1970s when filling hard gelatin capsules with semi-solid materials reemerged, and subsequently, machine manufacturers developed the necessary filling equipment to allow commercial production.

This rediscovered ability to fill hard gelatin capsules with liquid opened up a range of possibilities for capsule manufacturers and spawned a viable alternative to soft-gelatin capsule technology. For starters, ingredients that have low melting points are unstable when exposed to oxygen or moisture, and ingredients that require bioavailability enhancement could now be placed into liquid-filled hard-gelatin capsules. Recent research indicates liquid-filled hard-gelatin capsules provide improved bioavailability over tablet formulation, as well as improved sustained release.

Another advantage liquid-filled hard-gelatin capsules have over soft-gelatins is the manufacturing process of the hard-gelatin capsules. Since two-piece capsule manufacturing does not require some of the solvents commonly used in the manufacturing of soft-gelatin capsules, the result is a healthier and more environmentally friendly capsule.

Vitamins, in particular, have benefited from the reemergence of the liquid-filled hard gelatin capsules. Oily products, such as vitamins E and A, can be filled and sealed in this manner without adding thickening agents. This allows maximum concentration of the substance with minimum capsule size, while also reducing the risk of capsule instability.

As more non-water-soluble ingredients enter the nutritional pipeline, liquid-filled hard-gelatin capsules become more widely used, creating a greater need for the proper filling and sealing machinery to produce such capsules. A hard gelatin capsule is usually sealed by applying a gelatin band to the link between the body and cap of the capsule. In the mid-to-late '80s, a leading pharmaceutical company introduced a capsule-sealing machine designed specifically to meet these needs. The machine works by applying a low viscosity gelatin band that is drawn between the cap and body by capillary action. If any bubbles appear, they are quickly rolled away by a second application of sealing solution. The second application is thinner than the first, resulting in a smooth, liquid-tight seal. The seal is then air-dried, avoiding any heat that might cause bubbles. This sealing process is used for another reason as well--heat or solvents can cause brittleness in gelatin capsules. Brittleness can result in losses during transportation and packaging, not to mention the customer's dissatisfaction when attempting to remove the capsules from a blister package, only to have them break or crack open.

There are several benefits to gelatin band sealing, including:

A critical step in the capsule handling process is rectification. Leading capsule manufacturers use a capsule-filling machine with a specifically designed and patented three-drum rectification system. This continuous motion roller rectification system determines the orientation of a capsule by permitting the capsule to rest at different levels in a cavity. If a capsule enters the cavity body first, it is transferred as is. If it enters the cavity cap first, stationary fingers lay it over before the transfer. The system utilizes three continuously rotating drums to accomplish the rectification. It is simple, fast and extremely gentle.

The filling of two-piece capsules with liquid formulations is not without its own set of problems. The use of volumetric pumps certainly provides one of the most accurate means of dosing available; however, the handling of a capsule body filled with a low viscosity liquid requires special care that is not a concern with dry formulations. Intermittent motion can result in spillage when higher speeds are reached. In addition, the hydraulic pumping action created when a cap is applied to a liquid filled capsule can result in improper joined lengths.

Manufacturers concerned with quality have addressed this problem by using a capsule filling machine specifically designed to meet these needs. This machine has been designed to separate, dose, and join 28 capsules per stroke--more than twice as many as other capsule fillers--while handling the liquid filled capsule body slowly and deliberately, yet maintaining an output of 80,000 capsules per hour. As a result, the mechanical speed of this filling machine is less than half that of other machines but the output remains comparable.

Although the technology for filling hard gelatin capsules with liquid has been around since the mid 1800s, like every other trend, it has enjoyed recent popularity again, as more and more capsule manufacturers are finding the benefits of liquid-filled hard-gelatin capsules far outweigh other capsule options. Not only can a stable product with excellent bioavailability be produced, it can also be produced in-house with rapid and efficient filling machine equipment, thus offering a legitimate alternative to the soft gelatin capsule.

Tamara Smith is the department head of marketing at Shionogi Qualicaps, a manufacturer of empty two-piece capsules and related filling and sealing equipment. She may be reached at [email protected].