Understanding induction sealing

Induction sealing is a non-contact heating process that accomplishes the hermetic sealing of a container with a closure that includes a heat-sealable foil laminate. The typical induction innerseal begins as a multi-laminate liner inside a closure made up of the following layers:
  1. layer of pulpboard
  2. a layer of wax
  3. aluminum foil
  4. a layer of polymer

Layer of polymer (d) is compatible with the container material and capable of heat sealing to the lip of the container as is illustrated in Figure 1.

When the closure is placed onto the container and is passed through an electromagnetic field produced by the sealing head, several things occur. An electromagnetic current, called an eddy current, is induced into the foil portion, resulting in a resistance-type heating effect. The heated foil melts the wax layer, which is absorbed into the pulpboard, releasing the foil from the pulpboard, and the polymer coating melts, hermetically sealing the foil to the lip of the container.

When the closure is opened (released) the inner seal is welded to the lip of the container, and the pulpboard remains on the inner side of the closure.

High speeds can be obtained using this process making it well suited for high capacity production lines.

Single Piece Foils

Unlike the previously mentioned foil with pulpboard backing, the liner is laminated with a foam or paper backing. When the liner (c) is heated causing the polymer (d) to adhere to the container, the entire liner with backing is attached to the mouth of the container. There is no separation of components when the cap is removed.

Lining Material & Tamper Evidence

Depending on the inner seal material used, this seal can meet the FDA requirements for "tamper evident" packaging or the seal can provide leakage protection and shelf life extension, often referred to as a "freshness seal". Many varieties of innerseal materials have been developed and are available from a number of suppliers. Assistance from the suppliers is available in selecting the proper liner required for the multitude of products and a variety of containers.

If you have questions or experience problems with your Enercon cap sealer please contact us at 262-255-6070 or via our web contact form.


Figure 1: The layers of an induction sealing liner.