Heat shrinkable film is a common packaging film. In packaging applications, it is often used to heat the shrinkage characteristics to achieve a skin packaging or bundle wrapping. It can also be used to protect content from contamination or damage.
The heat shrink packaging machine utilizes the principle of heat shrinkage of the shrink film. After the raw material is melted, the film is stretched under an external force at a predetermined temperature, and the macromolecules cannot slip each other. When it cools below the crystallization point or glass transition temperature, the molecular orientation is rapidly solidified. When it is reheated to above the melting point or glass transition temperature, the polymer segment will be reactivated, so the originally oriented molecular segment begins to distort and macroscopically appears as film shrinkage.
Heat shrinkable films can be broadly classified into two types, barrier shrink films and non-barrier shrink films.
The barrier shrink film is mostly a 5~9-layer co-extruded structure containing a barrier material (EVOH, PVDC), which is produced by a three-bubble coextrusion film process. It is generally applied to meat or fresh food packaging that has certain requirements for oxygen barrier properties.
Non-barrier shrink films have many classifications. According to different raw materials and processes, they are roughly classified into four types (PVC shrink film, PE shrink film, POF shrink film, and other shrink film).
- PVC shrink film
- PVC shrink film is one of the oldest shrink films in history. It is produced by a double bubble process using two inflations of PVC. PVC shrink film has the characteristics of high transparency, high stiffness and low shrinkage temperature. The uppermost layer of this surface film is lacquer, the main component in the middle is polyvinyl chloride, and the lowermost layer is a back-coated adhesive. It is a popular and widely used synthetic material in the world today.
- PE shrink film
- The PE heat shrinkable film is a heat shrinkable film produced by using polyethylene as a raw material. Unlike PVC shrink film, PE shrink film is produced by a common blown film process. Since the processing temperature is high (far exceeding the melting point of polyethylene), low density polyethylene (LDPE) containing a large amount of long-chain branched structure is generally used as a raw material for production. With the development of catalyst technology and polymerization processes, this film provides excellent mechanical properties while providing better lateral shrinkage.
- PE film is widely used in the whole collection packaging of wine, cans, mineral water, various beverages, cloth and other products. The product has good flexibility, strong impact resistance, tear resistance.