Container goes to the sealing process already filled with product and with an aluminum foil liner already inserted into the cap. Typical induction liners are multi-layered. With small production volumes cover inserts are installed manually. Machine to insert the gaskets in lids may be installed on big manufactures. As the container passes under the induction coil (sealing head) the conductive aluminum foil liner begins to heat due to eddy currents. The heat melts the wax and releases the foil from the cap. The heat seal lacquer layer also heats and flows onto the lip of the container. When properly applied, induction lined caps provide a hermetic, leak proof, and tamper evident seal.
Tanks and caps must be made of glass or plastic. Presence of a metal in construction may make induction sealing impossible. Heat-sealing lacquer, which applied to the foil, exhibits adhesive properties to certain materials. It is important that lacquer matches material of the container. There are liners for polyethylene, polypropylene and glass containers. There are also universal liners for few types of the materials. Inserts differ in construction. There are separable(two-component) and inseparable(one-component) liners. First ones consist of hard base (remains on the cap after induction sealing) and foil with heat-sealing lacquer. They are connected with temporary adhesive(usually wax). One-component liners are inseparable combination of foil with lacquer and special layer that fills the gap between the cap and the neck of the tank.
Pre-carved inserts for induction sealing are usually supplied in plastic tubes in a directed way. This package allows quick and easy loading into the machine for placing inserts in the lid (Inserter) and eliminates operator error in foil orientation for proper sealing. Improperly oriented liner to the cover of the container and it will remain unsealed.
Construction of the liners
One-component (inseparable) inserts.
Inseparable gasket is installed into the cover and held there by means of grooves or protrusions. When sealing layer is heated by induction sealer it connects the foil and the neck of the container.After loosing the lid gasket remains entirely sealed to the neck of the container. To use product, you must remove the welded liner from neck. If the cap is screwed back, impermeability is no longer ensured.
Two-component (separable) inserts
Two-component inserts are pasted into the cover or held there by grooves or protrusions. When the foil is heated up, heat-sealing layer welds the foil to the neck of the container. Temporary adhesive(wax) that connects two parts of liner is absorbed by the base of the insert. Base layer closes gaps between the cap and the neck what gives us high quality of sealing with unideal tank. It also provides extra hermetization when cap is screwed. After cap is removed base layer stays inside of it.
Liners with barrier layers
Secondary barrier layer excludes contact between material of the base (cardboard) and the contents of the container once it was opened and closed with the cover. Barrier layer provides a "secondary seal". In this case, the wax is absorbed into the specially designed absorbent layer.
Barrier layer between the foil and the sealing layer is applied in the case of sealing the containers with aggressive content, which is able to penetrate through the sealing layer and the foil.
Characteristic of the opening
Depending on the composition of the heat-sealing lacquer, foil thickness and the presence of barrier layers in inserts for induction sealing they may have different characteristic of the opening or, in other words, different penetration method:
Easy penetration – foil is easily torn by finger. It is convenient for packing medicines and dietary supplements in the form of tablets and pills.
Durable sealing – foil may be torn only by hard object; it hardly may be torn by hands. This type of liner suits best for packing technical liquids.
Peeling – foil easily removes from the surface of the neck without any traces; special tear-off tabs are featured in this case. This type of liners used for packing of foodstuff.
