Heat shrink film is a good film packaging material, which has the following advantages:

(1) Good transparency allows customers to directly see the packaged products, making it easy for customers to choose products;

(2) Tightly attached to the appearance of the product, it can be suitable for packaging various shapes of goods, with a wide range of packaging contents;

(3) Excellent anti-theft and dust resistance;

(4) Multiple products can be packaged in a heat shrink packaging bag to prevent the loss of individual small items and make it convenient for customers to carry;

(5) By selecting different resins and formulas, heat shrink films with different mechanical strengths and functions can be produced. They can be used for inner packaging with lower strength and smaller product weight, as well as transportation packaging (outer packaging) for mechanical products and building materials that require higher strength in containers.

Heat shrink film appeared in Germany during World War II, using PVDC and biaxially stretched to wrap weapons to prevent rusting. So, heat shrink film has been used in industrial packaging since its initial industrial production, and later it was used in food packaging, such as PVDC casing film for sausage packaging. The heat shrinkable film is stored in the film by using the energy that the film has been stretched longitudinally or transversely under the high elastic state. The purpose of packaging is achieved by using the memory effect that the thermoplastic plastic has on the shape before biaxial or unidirectional stretching and the function that it can recover the shape before stretching when encountering heat again. Heat shrinkable film is a specific application example of the memory effect of a wide range of polymers.

The production method of heat shrink film is to use extrusion blowing or extrusion salivation after resin particles enter the extruder to produce thick cylindrical or flat thick films. For crystalline polymers, in order to prevent and reduce crystallinity, cooling water quenching method should be used to cool the thick film, because the crystallized thick film cannot undergo bidirectional or unidirectional stretching, stretching will cause crystal damage and reduce the mechanical strength and performance of the film. A thick film was produced and reheated to a high elastic state between the glass transition temperature and the melting temperature of the resin, where mechanical longitudinal or transverse stretching was carried out, and then cooled to form a heat shrink film. For amorphous polymers, such as PVC, they can be directly cooled from a molten state to a high elastic state and then stretched. After cooling, they can be rolled into a heat shrink film without the need for sudden cooling and heating. The T g, T f, and tensile orientation temperature of various resins are listed in Table 1. The thermal shrinkage temperature, shrinkage rate, and shrinkage force of various plastics are shown in Table 2.

PVC is easy to meet the requirements of different strength and packaging performance due to its excellent transparency and easy modification. Excellent electrical insulation performance and excellent flame retardant self-extinguishing properties are widely used in the production of heat shrink films, used for printing labels, shrink sleeves for wire and cable joints, and shrink packaging.