Medical Device Link.

Originally Published PMPN April 2002

OUR VIEW

Induction seals extend a product's shelf life and provide an effective means of tamper evidence.

Bill Zito, panel member, Packaging Line Security workshop, PMMI.

When it comes to package security, tamper evidence is a key requirement. While there are many methods for achieving tamper evidence, induction sealing continues to be one of the most popular. It forms a hermetic seal, which creates a protective barrier between the sealed product and the environment, and cannot be removed without leaving evidence of tampering. The seal also prevents leaks and, in most cases, can contribute to extending a product's shelf life. Unlike pressure-sensitive liners, which do not provide tamper-evidence, induction seals work equally well with liquid and dry products.

The noncontact induction heating process accomplishes the hermetic sealing of a container with a closure that includes a heat-sealable foil laminate. A two-piece inner seal may consist of a layer of pulpboard or foam, a layer of wax, aluminum foil, and a layer of heat-activated polymer. This type of inner seal leaves a pulpboard or foam liner inside of the cap and is used when a packager requires a secondary seal in the cap to prevent leakage after the induction seal has been removed. Another option is the single-piece inner seal, which functions the same as the two-piece inner seal but leaves nothing in the cap.

Manufacturers of induction sealing equipment have made tremendous technological advances over the last ten years. Highly efficient sealing heads have allowed for a significant reduction in the power required to seal a container. Power supplies have also become smaller with advances in electronic components.

Traditionally, high-speed cap sealers required water for cooling the sealing head. Today's waterless models keep pace with their water-cooled predecessors without the need for a water recirculator. Sealing-head design has also evolved to solve the needs of consumer-oriented packages such as dispenser-style caps. Other significant system advancements include microprocessor control, improved operator interfaces, remote-control capabilities, and integrated inspection and rejection capabilities.

With the correct type of container and inner-seal material, virtually all products can be sealed. Plastic containers with plastic caps are easiest to seal. Glass may need to be treated before the lip of the container will accept a seal, especially for liquid products.

While it is possible to induction seal containers with metal caps, it is not recommended. The metal cap is heated by the induction field, and the inner seal is heated by conduction from the heat in the metal cap. The hot metal cap presents a safety problem to workers who may inadvertently touch it. In addition, the cap may become so hot it melts the plastic threads on the container, or discolors the closure.

Suppliers of closures, bottles, or induction inner-seal materials can be a good source of information when looking for the right system. Buyers should examine the warranties offered by various suppliers, as service can be expensive. They can also benefit from reading the proposals carefully, investigating the vendor's reputation for product quality and service, and asking a lot of questions.

Bill Zito has spent more than 25 years assisting packagers with induction sealing solutions. He is an active member of many packaging organizations and was a recent panel member of the Packaging Machinery Manufacturers Institute's Packaging Line Security workshop. For a copy of Zito's technical paper, "The Myths and Mysteries of Induction Sealing Revisited," call 262/255-6070 or e-mail bzito@enerconmail.com.

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