Induction sealing
Induction sealing, otherwise known as cap sealing,
is a non-contact method of heating an inner seal to
hermetically seal the top of plastic and glass containers.
This sealing process takes place after the container has
been filled and capped.
An induction sealed bottle
1 How it works
Automatic Waterless Induction Sealer
The closure is supplied to the bottler with an aluminum
foil layer liner already inserted. Although there are var
ious liners to choose from, a typical induction liner is
multi-layered. The top layer is a paper pulp that is gen
erally spot-glued to the cap. The next layer is wax that
An induction sealer with a conveyor
is used to bond a layer of aluminum foil to the pulp. The
bottom layer is a polymer film laminated to the foil. After
the cap or closure is applied, the container passes under an
induction coil, which emits an oscillating electromagnetic
field. 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,
which is absorbed into the pulp backing and releases the
foil from the cap. The polymer film also heats and flows
onto the lip of the container. When cooled, the polymer
creates a bond with the container resulting in a hermet
ically sealed product. Neither the container nor its con
tents are negatively affected; The heat generated does not
harm the contents.[1]
It is possible to overheat the foil causing damage to the
seal layer and to any protective barriers. This could re
sult in faulty seals, even weeks after the initial sealing pro
cess, so proper sizing of the induction sealing is vital to
determine the exact system necessary to run a particular
product.
Sealing can be done with either a hand held unit or on a
conveyor system.
A more recent development (which suits a small number
of applications better) allows for induction sealing to be
used to apply a foil seal to a container without the need
for a closure. In this case, foil is supplied pre-cut or in
a reel. Where supplied in a reel, it is die cut and trans
ferred onto the container neck. When the foil is in place,
it is pressed down by the seal head, the induction cycle
is activated and the seal is bonded to the container. This
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