Shrink film is a common packaging film. In packaging applications, the phenomenon of thermal shrinkage is often used to achieve placement or wrapping effects. At the same time, it is also used to protect the contents from contamination or damage. Shrink film can be divided into four categories according to different raw materials and processes (PVC shrink film, PE shrink film, POF shrink film and other shrink films).

Shrink film

1. Characteristics of PVC shrink film

PVC shrink film is one of the longest shrink films in history. It is produced by double-bubble process of secondary expansion of PVC. PVC shrink film has the characteristics of high transparency, high stiffness and low shrinkage temperature. In recent years, in the field of display packaging, POF shrink film has occupied a large amount of PVC shrink film market. However, in the shrink bottle label market, PVC shrink film still occupies most of the market share due to its low cost, high shrinkage rate and easy printing. However, due to the generation of harmful insect gases during processing, its use is increasingly restricted by environmental protection requirements.

2. Characteristics of PE shrink film

PE shrink film is another shrink film with a long history. As the name implies, PE shrink film is a heat shrinkable film made of polyethylene. Different from PVC shrink film, PE shrink film is produced by ordinary blown film process. Due to the high processing temperature (far exceeding the melting point of polyethylene), low-density polyethylene with a large number of long-chain branched structures is generally used as the raw material for production. In this way, a film with sufficient shrinkage can be obtained. In recent years, with the development of catalyst technology and polymerization technology, some new metallocene polyethylene and linear low density polyethylene can provide excellent mechanical properties and good shrinkage. Therefore, a large number of highly transparent and high-strength PE shrink films have appeared on the market.

3. Characteristics of POF shrink film

POF shrink film has developed rapidly in recent years. Ordinary POF shrink film is a three-layer co-extrusion structure, the surface layer is ter-PP, and the core layer is LLDPE. Similar to PVC shrink film, POF shrink film is produced by double bubble method. Since the second layer of bubbles is not easy to stabilize, the requirements for linear low density polyethylene in the formulation are very high. Cross-linked film is a high-end product in POF shrink film. Different from ordinary POF film, cross-linked film is a pure PE structure. The production process is also slightly different from the common double bubble method, which needs to be supplemented by electron irradiation crosslinking process to change the structure of the polymer chain from a linear structure to a body structure. Compared with ordinary POF film, cross-linked film has better shrinkage and heat sealing performance, and can adapt to different packaging machinery and contents.