The shrink wrap process involves two stages – the enveloping of the pack in shrink wrap either totally or partially and – the application of heat to the shrink wrap film which activates the material’s memory of its non-stretched molecular chains.

The application of shrink wrap can be divided into two principal types – transit and display.

Transit

The purpose of transit packaging is to offer the lowest cost option for packaging. The material used is almost exclusively polyethylene, which will provide the appropriate strength at the lowest available cost. A typical application is the collation of individual packs with or without tray support. The most frequent use of the forgoing involves the packaging of a quantity of cans or bottles or cartons for distribution.

The equipment used involves a sleeve or bundle sealer working in conjunction with a shrink tunnel. Two rolls of material produce a sleeve of film around the pack, which is then processed through the tunnel. Generally, these open sleeves do not cause any disadvantages to the pack integrity although a modification can be made to the tunnel whereby an attempt is made to have the hole closed through excess, annealed film.

A considerable amount of automation is offered for this process so that one may find a full range of manual, semi and fully automatic sealers and at maximum through-put, one can find lines with speeds of up to 200 packs per minute.

The processing of polyethylene is distinguished by the need for the shrink wrap film to reach an almost melt state, after which cooling will provide significant additional shrink. As a consequence, tunnels require specific cooling devices if elevated output speeds are needed.

All of this equipment may be used to wrap individual packs where collation is not required but a degree of protection is needed. Applications may vary from radiators through to office doors and bolts of cloth.

Display

The identical processes are also applied but with display shrink film where products have a natural requirement to use a sleeve. Gift wrap and wallpaper rolls fall into this category. The principles remain the same although both the sealer and tunnel will be modified to accommodate individual rolls with appropriately small diameters.

Turning to mainstream display applications, the main characteristic is the use of a total wrap.

In every single case, the sealer must now create a flat, two-dimensional bag around the product.

The product and this bag are then processed through a shrink tunnel to achieve the desired effect.

At the most basic level, this is achieved using an L-Sealer and folded film. The product is manually placed between the two layers of film and again manually placed into the sealer. The seal is completed and the pack placed on the tunnel conveyor. This is a continuous process that also produces an element of scrap film.

Automation is applied to the seal head and also to the pack support. Then, the seal process and the removal of the pack to the tunnel become automated. Generally, this is regarded as semi-automation. The clamping of the sealer head will be carried out using either a solenoid or a pneumatic ram.

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