Heat shrinkable film is mainly used for labels, heat shrinkable packaging or winding films. The polymer resins suitable for the preparation of heat shrinkable membranes are mainly PVC, PE, PS and PET. After the film is preheated, the heat shrinkable film is obtained through stretching and cooling stereotypes (as long as no heat treatment is applied). Under the Tf of the resin, the resin casting was stretched horizontally and longitudinally, and then cold, so that the resin molecular chain was frozen in the orientation state, forming a heat shrinkable film. It is an entropy reduction process from raw materials to generating heat shrinkable films. The thermodynamic state of the heat shrinkable film is unstable. When the shrinkage film is heat treated, the molecular chain that has been orientations will quickly revert to the random line (Quan Qutai), and the film will shrink. The label of special-shaped bottle can be prepared by using this characteristic of heat shrinkable film.
The parameters of heat shrinkable membrane include shrinkage rate, shrinkage tension and shrinkage temperature. Shenzhen Hua Le plastic products Co., Ltd. said that from the above three parameters, to get a higher shrinkage of the film, the need to use low crystallinity or low crystallinity of polymer resin suitable. Although the amorphous resin is orientated in the biaxial orientation, although the molecular chain is orientated, it does not crystallize. When the two preheating is received, all the orientated chains can shrink. Only the non crystallized orientation molecular chain can be constricted after the heat (lower treatment temperature, shorter treatment time); and the molecular chain of orientation crystallization is intended to be realized. It is necessary to destroy the lattice, which needs to increase the temperature to the melting point, and the relaxation time of the molecular chain is longer, which is not possible during the use of the shrinking film.
The higher the proportion of amorphous region, the greater the shrinkage force and the greater the shrinkage force of the heat shrinkable film made of the same material. The larger shrinkage film in the amorphous region has lower shrinkage temperature.
