Shrink-wrap polymer films

Thermal shrinkage, accompanying release of moulded-in orientation, can be the cause of severe warping of pofymer mouldings when heated, but desirable effects can also be achieved. Shrink-wrap polymer films have caused a minor revolution in methods of packaging. Heat-shrinkable polymer tubes and cable insulation are currently finding wide application. 

Shape-memory polymers, 207 Shear, 124, 261 Shear-thickening fluids, 125 Shear-thinning fluids, 124-125 Shirakawa, Hideki, 74 Shivers, Joseph, 149 Shrink-wrap film, 207 Siemans, 72... 

Yoshimura et al. [1989] give a lengthy description of their invention, which was primarily aimed at producing film (Table 11.9) particularly suited for shrink wrapping, with many examples and extensive sets of results. The film is made from the following three groups of polymers (i) LDPE and a copolymer of ethylene, either with vinyl ester monomer, or with an unsaturated aliphatic monocarboxylic acid or its aliphatic ester (EVAc being the most desirable copolymer) (ii) one of the... 

See also Polyethylene polymer entries Polyethylene shrink film wrapping, 18 37 Poly(ethylene-stal-a-olefin), glass... 

Skin packaging is a combination of a pol3mier film sleeve with a bottom liner (cardboard or sheet polymer). The article is placed on the card liner and is wrapped into the inhibited shrinkage sleeve (Fig. 2.55a). The film ends are fixed on the card, which can also be made of an inhibited material. During heating the film shrinks skin tight around the article. Skin packaging is used for small-size machine parts, spares, tools etc. 

Freezing in of orientations is made use of with what are called heat-shrink films Heat-shrink films are stretched or drawn biaxially, and these films are used to solidly encapsulate mold components. The wrapped goods are then warmed, whereby the film expands slightly below the glass transition temperature (for amorphous polymers) or the melting temperature (for crystalline polymers). At the transition temperature, however, the molecular segments become mobile the molecules tend to assume their unperturbed dimensions and the film shrinks in upon itself. 

---