Heat-shrink packaging

The higher crystalline fraction of the radiation cross-linked polyethylene even after a melt-freeze cycle has great technological merit for the heat-shrink packaging and electrical connector products. ... 

Experiments were conducted using three heat-shrink packaging films provided by a major shrink film manufacturer and supplier. These films comprised blends of linear low-density... 

Polyethylene shrink film wrapping of cormgated ftberboard trays is in common use outside of the United States. Equipment erects the trays, fills the trays with primary packages such as cans or jars, wraps the grouping in shrink film, and heat shrinks the combination. Shrink film wrapping keeps primary and secondary packaging materials clean and dry. 

An oven in the form of a tunnel mounted over or containing a continuous conveyor belt is used to shrink oriented films in the shrink packaging process. Also use a hot air blower on the film to provide the heat required in specific areas. 

Hot blown plastic films usually do not possess sufficient orientation to be heat shrinkable at temperatures below 100°C. For certain shrink packaging applications low temperature shrinkage is essential and can be obtained by biaxial orientation below the melting point. Radiation crosslinking was found to facilitate orientation of these copolymers greatly because of the much greater bubble stability which results from crosslinking. 

The packaging materials (including heat-shrink sleeves, if pre-decorated, and the printing on cans) are all subjected to continual dowsing in water, warm then hot then cold, over a long period of time. Care thus needs to be taken, and materials tested, when selecting the appropriate packaging format. 

This section covers package decoration formats rather than the detail of their printing. Packaging that is delivered pre-printed, such as cans and drinks cartons, is covered in Sections 9.6-9.8. Decoration formats include labels that are stuck on to packages and heat-shrink plastic sleeves, which may be applied through a labelling technology or as a pre-made sleeve and heat-shrunk into place. 

Specific gravity it is heated. Shrink film gives good protection to the products packaged and has excellent clarity. The density (mass per unit volume) of any material divided by that of water at a standard temperature, usually 4 °C. Since water s density is nearly 1.00 g/cc, density in g/cc and specific gravity are numerically nearly equal. 

In the use of shrink packaging where a polymer is oriented, wrapped around a package, and then heated to cause melting, shrinkage, and reduced orientation (see New Operations section, p. 174). 

One of the widely used effects of irradiation of PE is the so-called memory effect [Charlesby, 1960, 1987 Silverman, 1992]. PE is irradiated at RT in an inert atmosphere, and heated above the melting point, then stressed and given a particular shape. During the subsequent cooling, the crystallization fixes the imposed shape. However, upon reheating, the crystals melt and the cross-linked PE returns to its original unstressed shape. This memory effect is the basis of the production of many heat-shrink products, e.g., food-packaging film and electrical connectors [Bradley, 1984 Silverman, 1992]. 

Shrink film n. (1) Films which shrink when heated and are useful for packaging articles. (2) The pre-stretched or oriented film used in shrink packaging. 

There are two major markets for irradiated film. The first is packaging film for food and small parts. The irradiated film has improved strength and reduced perme-abihty. When oriented the film shrinks to conform to the contours of the product and has crystal clarity. The second market is heat shrink tubing for electrical connectors. Here the polyethylene is used together with cross-linked polyethylene to form a protective sleeve. The interlayer is polyethylene, which, when heated, flows to fill voids and completely encapsulates the wire. The outer layer is cross-linked polyethylene, which shrinks to form a compact protective sheet over the connector. 

If the sheet has been subjected to biaxial orientation during extrusion (see Section 14.2), heating above the deformation temperature will cause the sheet to shrink. A tight package can be made by wrapping an article in a biaxially oriented sheet followed by a brief heat treatment. Such shrink packaging with polypropylene film is widely used for everything from lettuce and meats to books and video tapes. 

A small quantity of flexible packaging material, usually oriented polypropylene, shrink polypropylene, or polyethylene, is used to overwrap paperboard cartons. The film is wrapped around the carton and sealed by heating. Products such as boxed chocolates, candies, and cookies are overwrapped, sometimes by a printed film. 

Films and sheets with high clarity, puncture resistance, impact strength, low heat-seal temperature used for shrink-wrap, heavy-duty shipping sacks, produce bags, bag-in-box food and technical packaging films... 

Shrink wrap is a film that is applied loosely around products, then sealed and shrunk by heating to take the shape of the contained products. It can be used to bind multiple packages, or to secure an entire pallet of packages, to bundle magazines and papers, to protect and display albums, CDs and so on. It is usually made of LLDPE, LDPE or polypropylene. 

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