Shrink wrap is a generic term that defines the covering of a product with a transparent plastic film, or in some cases printed. This film is then sealed to form a loose bag around the product which is then tightly shrunk using a heat source, often a thermal shrink tunnel.
Since the bag that is formed around the product is loose, the shrink wrap is suitable for wrapping non-rectilinear objects. As long as the product is encased within the "bag", the shrinkage property of the film when heat is applied will ensure a skin-tight finish.
There are four types of shrink wrap systems: "Transit" wrap is when product passes through a curtain or film sleeve. The resulting shrink wrap film, after shrinkage has taken place, generally leaves ends open or "bull's eye". Using shrink tunnels with special conduits, full wrapping is possible, but the resulting seal is not attractive enough for display wrapping purposes. The film used is predominantly polyethylene or PE, which is generally the lowest cost film.
Shrink wrap "L-seal" style is used for display purposes. The product is introduced with centrefold film and an "L" shaped cutting and sealing arm seals and cuts the other two sides. Excess film is trimmed and removed. Polyolefin or PVC film is used with a shrinkage property of up to 40% when heat is applied. After traveling through the heat automatic shrink packing machine tunnel, the film contracts tightly around the product.
One of the characteristics of L seal shrink wrap is that the film must be perforated to allow air to escape as shrinkage occurs. This means that the resulting wrapper is not airtight and allows some transfer of aroma and bacteria. However, the perforations are so small that they cannot be easily sealed with the naked eye and with clever positioning the holes can be positioned so that they are in contact with the edges of the product being wrapped.
The third type of system is due more to flow wrap technology than an L seal. Like a flow wrap, the film is formed on a "shoe" when product, often a charger, is loaded at intervals. regularly spaced in the resulting film tube. A fin seal is made under the pack and an alternate blade seals the ends. This type of system is often used for magazine wrapping, either by shrink tunneling to achieve a skin-tight finish or simply by leaving a loose wrap.
The fourth type of shrink wrap is the shrink sleeve or shrink label. In this case, a ready-made "tube" of film is dropped onto a bottle before passing through a shrink tunnel. The tube shrinks, fits tightly to the bottle and provides a decorated label for the package or is used as a security device where the cap is attached to the bottle or jar. This technique is known as a shrink sleeve.
A wide range of machine speeds and sizes are available in the shrink wrap universe. Low cost manual shrink wrap systems are available for under £ 200 up to fully integrated high speed systems costing hundreds of thousands of pounds. The range of machine types is further complicated when integrated tray mounters and loaders are incorporated within the baler. The following paragraphs identify the main types of machines within each category.
Shrink packaging machines "Transit"
Transit shrink wrap is typically for products bundled in a cardboard tray of a can or jar bundle where the shrink wrap holds the bundle together.
The simplest type of manual machine consists of two rolls of film and a straight line sealing jaw. The product is manually pushed through the film strip and the sealing jaw is manually lowered, cutting and sealing the sleeve. The next package that is then pushed into the machine cleans the first one that then enters the shrink tunnel, sealing the polyethylene band tightly around the package. This type of system is very economical and a competent operator can reach speeds of up to 5 packages per minute.
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