Pallet with corrugated fiberboard boxes being stretch wrapped
Pallet with corrugated fiberboard boxes being stretch wrapped

Stretch wrap or stretch film is a highly stretchable plastic film that is wrapped around items. The elastic recovery keeps the items tightly bound. In contrast, shrink wrap is applied loosely around an item and shrinks tightly with heat. While it is visually similar to plastic food wrap it is not usually made of material rated as safe for food contact.

It is frequently used to secure pallet loads to one another but also may be used for bundling smaller items. Types of stretch film include bundling stretch film, hand stretch film, extended core stretch film, machine stretch film and static dissipative film.

Materials

The most common stretch wrap material is linear low-density polyethylene or LLDPE, which is produced by copolymerization of ethylene with alpha-olefins, the most common of which are butene, hexene and octene. The use of higher alpha-olefins (hexene or octene) gives rise to enhanced stretch film characteristics, particularly in respect of elongation at break and puncture resistance. Other types of polyethylene and PVC can also be used. Many films have about 500% stretch at break but are only stretched to about 100 – 300% in use. Once stretched, the elastic recovery is used to keep the load tight.

There are two methods of producing stretch wrap. 1) Blown: the resin is melted and extruded through an annular die, it is air-cooled. This is a slower process but provides for higher cling quality. Blown film is not a consistent extrusion process, leading to inconsistencies across the film web. The cost of production is also higher due to the quantity that can be produced per hour. 2) Cast: the film is extruded through a slot die, then passed over cooling rollers. This makes the cooling process quick. Cast films are more consistent and have better performance characteristics. The cling quality is not as good as blown but more can be produced in an hour with lower costs.

Other properties such as break strength, cling, clarity, tear resistance, static discharge, etc. are also important.

Functions

In pallet unitizing, stretch wrap can have several functions:

Making sure boxes stay on the pallet and properly aligned is an important consideration in warehouse distribution, especially as the demands for increased throughput continues to rise.

Application

Typical fully automatic rotary arm stretch wrapper
Typical fully automatic rotary arm stretch wrapper

Categories and sub-categories of stretch wrappers:

Manual (or Hand) Wrappers:

Semi-Automatic Wrappers:

Typical fully automatic turntable stretch wrapper
Typical fully automatic turntable stretch wrapper

Automatic Wrappers:

Typical fully automatic rotary ring stretch wrappers
Typical fully automatic rotary ring stretch wrappers

Automatic wrappers are generally a variant of a semi-automatic system. Automatic wrappers include a conveyor system to automatically load the wrapping machine and automatic systems to apply, seal, and cut the film.

See also

References

  1. ^ Dahll, R K; Sharma (August 2012). "Effect of shrink wrap packaging for maintaining quality of cucumber during storage". Journal of Food Science and Technology. 49 (4): 495–499. doi:10.1007/s13197-011-0284-5. PMC 3550898. PMID 23904659.
  2. ^ US 4102513, Guard, Twyman, "Film wrapping dispenser", published 1978-07-25 
  3. ^ US 4248392, Parry, John C., "Apparatus for application of plastics stretch films", published 1981-02-03 

Further reading