|
The
shrink-wrap process has two stages: enveloping the pack in shrink wrap
either totally or partially and applying heat to the shrink wrap film to
activate the material's memory of its non-stretched molecular chains.
Shrink wrap is used for two applications: transit and display.
1. Transit
Polyethylene offers the right strength at the lowest cost, thus serving
the purpose of transit packaging. A typical application is collating
individual packs with or without trays. The most frequent use of
collating involves the packaging of cans, bottles, or cartons for
distribution.
A sleeve or bundle sealer is used in conjunction with a shrink tunnel.
Two rolls of material are used to produce a sleeve of film around the
pack, which is then processed through the heat tunnel. These open
sleeves do not generally decrease pack integrity, although the tunnel
can be modified to have the hole closed through excess, annealed film.
Various equipment is available for this process. You can may find a full
range of manual, semi-automatic, and fully automatic sealers. At maximum
throughput, you can find lines with speeds of up to 200 packs per
minute.
In polyethylene processing, the shrink-wrap film must reach a near-melt
state which, after which cooling, will provide maximum shrinkage.
Consequently, tunnels require cooling devices if high output speeds are
needed.
Any of this equipment may be used to wrap individual packs when
collation is not required, but some protection is needed. Applications
vary from radiators to office doors and bolts of cloth.
2.
Display
The same processes above are used in display shrink-film applications
when products naturally require a sleeve. Gift wrap and wallpaper rolls
are examples. The principles remain the same, although the sealer and
tunnel are modified to accommodate individual rolls with small
diameters.
A total wrap is used for mainstream display applications. This means
that the sealer must create a two-dimensional bag around the product.
The product and this bag are then sent through a heat tunnel to achieve
shrinkage. This is done by using an L-sealer and folded film. The
product is placed between the two layers of film and put into the sealer
manually. The seal is made and the pack is then placed on the tunnel
conveyor. This continuous process produces an element of scrap film.
Semi-automation can be applied to the seal head and pack support. The
sealing process and removal of the pack to the tunnel are then
automated. The clamping of the sealer head is done using either a
solenoid or a pneumatic ram.
Full automation of an L-sealer allows packs to be fed automatically into
the film and through to the sealer.
Manual vs. Automatic Sealers
Over the last few years, manual and fully automatic sealers are most
often used, with semi-automatic sealers relatively little used. Little
speed advantage is gained from using a semi-automatic sealer. Also, cost
is a significant influence, as automatic equipment can be purchased at
prices not much higher than those for semi-automatic equipment. A manual
machine produces about 10 packs per minute, while a fully automatic
machine produces about 20 packs per minute, with a maximum output of
about 25 to 35 packs per minute.
The use of a manual sealer and tunnel has decreased significantly and
been replaced by the use of a combined seal and shrink machine, commonly
referred to as a chamber. These machines have a small footprint and
usually operate from a single phase. The sealer head has a plastic
enclosure and heat is stored within the unit to enable a combined seal
and shrink operation.
Side-seal and flow-wrap machines offer speeds approaching 100 packs per
minute. The purpose remains the same, which is to wrap the pack in a
two-dimensional bag of shrink-wrap film.
Flat film is frequently used, although many machines apply folded film.
The sealer can process individual packs at a much higher rate when it
can seal at a higher rate.
Cross seals require the sealing device to travel with the pack, while
side-seal or overlap-seal mechanisms allow film to be sealed
continuously. These same machines may be applied to other bagging
applications such as the mailing of magazines.
Machinery may be customized to take advantage of a particular
shrink-wrap film's attributes to produce an appropriate pack. One
example is the customization of this process to allow for
modified-atmosphere packaging of food with barrier shrink film.
About our site and Terms of use |
Warehouse |
Supplies |
Equipment
|
