Shrink wrap
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Please help improve this article or section by expanding it. Further information might be found on the talk page or at requests for expansion. (January 2007) |
Shrink wrap, also shrinkwrap or shrink film, is a material made up of polymer plastic film. When heat is applied to this material it shrinks tightly over whatever it was covering.
Shrink wrap is commonly used as an overwrap on many types of packaging: CDs, DVDs, cartons, books, beverage cans, large appliances, pallet loads, etc. It can be the primary covering for some foods such as cheese and meats. It is also used to cover boats after manufacture and for winter storage.
Heat-shrink tubing is used to seal electric wiring.
Shrink bands are applied over parts of packages for tamper resistance or labels. It can also combine two packages or parts.
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[edit] Composition
The most commonly used shrink wrap is polyolefin. It is available in a variety of thicknesses, clarities, strengths and shrink ratios. The two primary films are either crosslinked, or non crosslinked. Other shrink films include PVC and several other compositions.
Coextrusions and laminations are available for specific mechanical and barrier properties for shrink wrapping food.
Current trends are to improve film properties which may lead to reduced caliper (source reduction) and to improve process efficiency (cost and energy savings).
[edit] Manufacture
A shrink film can be made to shrink in one direction (unidirectional or mono-directional) or in both directions (bidirectional).
Films are stretched when they are warm to orient the molecules from their initial random pattern. Cooling the film sets the film's characteristics until it is reheated: this causes it to shrink back toward its initial dimensions.
[edit] Use
Shrink wrap is applied over or around the intended item, often by automated equipment. It is then sent through a heat tunnel or oven for shrinking. Heat guns are also used for large items.
Shrink wrap can be supplied in several forms. Flat rollstock can be wrapped around a product but Centerfolded film is by far the most popular, supplied on a roll the plastic is folded in half: product is placed in the center portion, the remaining three edges are sealed to form a bag, and the package then heated which causes the bag to shrink and conform to the product placed in the bag.Less popular are the pre-formed Shrink bags[plastic bags]] with one end open: the product is placed in the bag, sealed, and sent for heat shrinking.
[edit] See also
[edit] References
- Brody, A. L., and Marsh, K, S., "Encyclopedia of Packaging Technology", John Wiley & Sons, 1997, ISBN: 0-471-06397-5
