Poly Shrink Film Manufacturing Process

Shrink packaging has been well established for over three decades. Due to it's practical and cost related advantages, it has found its use in many industries at various stages of packaging process.

Shrink Packaging can be divided into following groups:

a)Primary- where the product is totally enclosed for protection from abrasion, dust, moisture and for improved appeal.

b)Secondary- where a group of items is wrapped together to form a Sales unit, (Six-packs of Beer, Juice etc)

c)Distribution packaging-Where product is wrapped into a distribution unit which may stacked directly on the pallet ready for transportation. When walking through supermarket one only has to look on top of the shelves to see the extent of use of this packaging method.Most grocery and high volume beverage products will use cardboard trays for added rigidity of the pack. While the use tray is not always necessary, it does provide improved handling in automated warehouses.

Shrink Packaging Process

Shrink wrapping, bundle wrapping, etc, is a process during which a product item or a group of items in wrapped in a loose sleeve or envelope of plastic film, which upon application of heat shrinks and tightly conforms to the shape of enclosed contents. The key element of this process is Shrink Film.Shrink Film can be made from a variety of materials each having different strength, shrink characteristics transparency and lustre.

Polyvinylchloride (PVC), Polypropylene (PP) and Polyethylene (PE) are the three most commonly available materials.PVC, being one of the first materials used, is now being phased out due to its toxic properties, although still used abundantly in underdeveloped countries. Low Density Polyethylene (LDPE) is best suited for general packaging applications due to its relatively high strength and low cost.

Polyethylene Shrink film is manufactured in a vertical extrusion process where ethylene granules are heated under pressure to produce Polyethylene polymer.The polymer is forced upwards through a circular extrusion die to produce a very thin walled continuous tube of material, still in a semi-molten state as it emerges from the die. A controlled supply of air is fed up through the centre of the die to stretch the tube in the radial direction, thus forming a bubble. At the same time the tube is stretched in length by winding the film at a faster than it is extruded. As the film cools, the induced stretch is "memorized" in the film. Upon reheating the film, if unrestrained, will shrink a certain percentage in the width, referred to as % Shrink in TD (transverse direction), and in the length, % shrink in MD (machine direction).At the top end of the bubble the film tube is cool enough to be flattened and wound off as Lay-flat tubing, alternatively, it can be slit at one edge to produce Centre-folded material or slit at both edges to produce Flat sheet.