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Development and new development of PVC thermal shrinkable film

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Heat shrinkable film is a good film packaging material, it has the following advantages: (1) good transparency, so that customers can directly see the goods were packed, which is convenient for the customers to choose goods; (2) close to the product shape, can be applied to various shapes of the packaging of goods, packing content widely; (3) excellent anti-theft, anti dust; (4) a variety of packaging in a heat shrinkable packaging bag, to prevent the loss of individual commodities, but also to facilitate customers to carry; (5) using resin and different formulations, can produce heat shrinkable film strength and the function of different machinery. Not only can be used for low strength and weight of goods within a small packaging, can also be used for mechanical products requirements and high strength container, building materials used in transport packaging (packaging).

The heat shrinkable film, which first appeared in Germany in the two World War, was used by PVDC, which was used to pack weapons after biaxial tension, to prevent rust. Therefore, the heat shrinkable film has been used in industrial packaging since the beginning of industrial production. Later, heat shrinkable films were used for food packaging, such as PVDC casing film for sausage packaging. Heat shrinkable film is the use of film in high elastic state under longitudinal or transverse stretching the energy stored in the film, the use of thermoplastic plastics with has the bidirectional or unidirectional stretching of the shape memory effect, recovery before stretching form can meet again in the heat to achieve the function of the package to. Heat shrinkable film is a specific application example of the memory effect of a wide range of polymers.

Production method of heat shrinkable film is to produce cylindrical film or plate thick film thickness method of resin particles into the extruder after blown film extrusion or extrusion casting, for crystalline polymers, in order to prevent and reduce the crystallinity, should use cooling water to quench cooling method of thick film, because of the thick film crystallization is not bidirectional or unidirectional tension, tension will make the crystal damage, reduce the mechanical strength and performance of film. The thick film is reheated to the T g to T f temperature of the resin, namely, the longitudinal or transverse stretching of the machine under the high elastic state between the glass transition temperature and the melting temperature, and then cooled into a heat shrinkable film. For amorphous polymers, such as PVC, it can be directly cooled from molten state to high elastic state, and then stretched. After cooling, it is rolled into heat shrinkable film without heating after quenching. The T g, T F and tensile orientation temperature of various resins are listed in Table 1. The thermal shrinkage temperature, shrinkage and contractile force of various kinds of plastics are shown in Table 2.

PVC is easy to meet the requirements of different strength and packaging performance because of its excellent transparency and easy modification. Because of its excellent electrical insulation and good flame retardant and self extinguishing properties, it is widely used in the production of heat shrinkable film, which is used for printing standard trunk, wire and cable joint shrink sleeve and shrink packaging.

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