Stretch Wrap

  (Also called Stretch film)

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.

It is frequently used to unitize pallet loads 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.

Contents

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.

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

Functions

Forklift truck loading stretch wrapped pallet load.

In pallet unitizing, stretch wrap can have several functions:

  • improved stability of products or packages, forming a unit load
  • more efficient handling and storage of unit loads
  • some degree of dust and moisture protection
  • some degree of tamper resistance and resistance to package pilferage

Making sure cartons stay on the pallet is an important consideration in warehouse distribution, especially as the demands for increased throughput continues to rise. Stretch wrapping is the most cost-effective way to keep loads secured, on a pallet.

Application

Typical fully automatic rotary arm stretch wrapper

Stretch wrap can be applied manually, semi-automatically or automatically.

Categories and sub-categories of stretch wrappers:

Manual (or Hand) Wrappers:

  • Extended Core: An extension of the film's core serves as a handle for wrapping; this type of wrapper offers little stretch control and is hard on hands.
  • Mechanical Brake: A simple structure supports a film roll and a mechanical brake system provides resistance creating stretch of the film.
  • Pole Wrappers: Similar to the Mechanical Brake system, but the roll and brake are at the end of an extended pole, creating an ergonomic design which eliminates the need to bend to wrap the bottoms of loads and strain to reach the tops of loads.

Semi-Automatic Wrappers:

  • Turntable Wrappers: The load to be wrapped sits on a turntable which spins the load relative to the film roll, which is housed in a carriage which can move up and down a fixed "mast". Stretch is achieved by rotating the load at a faster rate than the film is fed.
  • Orbital Wrappers: The film is housed in a carriage on a vertical ring, the load is fed horizontally through the eye of the rotating ring, applying film to the load.
  • Rotary Arm Wrappers: In this system, the load remains still while a rotating arm turns around it wrapping the load. This system is used for light loads or for speeds which would otherwise cause the load to topple due to high rotation speeds.

Automatic Wrappers:

Automatic wrappers are generally a variant of a semi-automatic system, which has had a conveyor system and automatic film cut and seal system applied to it.

See also

References

  1. http://www.stretchfilm.org/
  2. http://www.sdcexec.com/online/article.jsp?siteSection=15&id=11413&pageNum=4

Further reading

  • ASTM International D4649 Guide for Selection and Use of Stretch Wrap Films
  • Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6
  • M.Hildreth, "Maximizing your Stretch Film Operation", 2006, ISTA, Pre Shipment Testing

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