shrink wrap
 "Shrinkwrapped" redirects here. For the album, see Shrinkwrapped (album).
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 is 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.
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).
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.
Equipment
Shrink wrap equipment for packaging purposes, is primarily available in two formats.
The first type of shrink wrap machine, used for low to mid-volume packaging, is known as an I-bar sealer. This type of sealer uses one long bar to make single cuts along PVC or polyolefin film. Once the film is cut around a product using the I-bar, the film is typically shrunk using a heat gun, although a heat tunnel can be used.
The second type of shrink wrap machine is used for medium to high-volume packaging. It is known as an L-bar sealer. This is due to the L-shaped design of the cutting bar. The bar only requires one pass to cut film around a product. L-bar sealers can be used in conjunction with a heat gun or heat tunnel to finish shrinking the film around a product.
The wire element used in both types of machines, to cut the film, is often a heated wire or an impulse wire. Heated wires use heat to cut the shrink film. Impulse wires use pulses of electricity to cut the film and generally produce less odor and smoke.
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.
Shrink wrap can be used to wrap buildings. It is far superior to blue tarps for wrapping roofs after hurricanes, earthquakes, tornadoes and other disasters. Shrink wrap can be used for environmental containments to facilitate safe removal of asbestos, lead and other hazards.
External links
Flexible Packaging Association 
See also
Packaging
Stretch wrap
Shrink wrap contract, legal term
Shrink Rap (disambiguation)
References
Brody, A. L., and Marsh, K, S., "Encyclopedia of Packaging Technology", John Wiley & Sons, 1997, ISBN: 0-471-06397-5
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