Heat shrink film classification and characteristics

Heat shrink film is a common packaging film. In packaging applications, it is often used to shrink by heat to achieve body-fitting effects or cluster wrapping; at the same time, it is used to protect the contents from contamination or damage. The principle of heat shrinkage is to orient the active molecular segments near the melting point or glass transition temperature when producing the film, and then cool down to the crystallization point or below the glass transition temperature to quickly solidify the molecular orientation; when reheated to the melting point At or above the glass transition temperature, the polymer chain segments will become mobile again, and the originally oriented molecular chain segments begin to curl up and align, and the film shrinks macroscopically.

Classification of heat shrink film

Heat shrinkable films can be roughly divided into two categories, barrier shrinkable films and non-barrier shrinkable films. There are several sub-categories under the two major categories. Below is a brief introduction to the characteristics of each shrink film.

Barrier shrink films are mostly 5-9 layer co-extrusion structures containing barrier materials (EVOH, PVDC), produced by three-bubble blown film process. It is generally used in meat or fresh food packaging that has certain requirements for oxygen barrier properties. This type of shrink film market is specific, but the production technology is difficult, so the added value is high.

Non-barrier shrink films come in many varieties. According to different raw materials and processes, it can be roughly divided into four categories (PVC shrink film, PE shrink film, POF shrink film, and other shrink films).

PVC heat shrink film Features

PVC shrink film is one of the shrink films with the longest history. It is produced by the double-bubble process using PVC through two inflations. PVC shrink film has the characteristics of high transparency, high stiffness and low shrinkage temperature. In recent years, POF shrink film has occupied a large number of PVC shrink film markets in the field of display packaging. However, in the shrink bottle label market, relying on the characteristics of low cost, high shrinkage ratio and easy printing, PVC shrink film still occupies most of the market share.

PE heat shrink film features

PE heat shrinkable film is another shrinkable film with a long history. As the name implies, PE heat shrinkable film is a heat shrinkable film produced with polyethylene as raw material. Unlike 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 (LDPE) containing a large number of long-chain branched structures is generally used as the raw material for production. Only in this way can a film with sufficient lateral shrinkage be obtained. In recent years, with the development of catalyst technology and polymerization process, some new metallocene polyethylene and linear low density polyethylene can provide good lateral shrinkage performance while providing excellent mechanical properties. Therefore, a large number of high-transparency, high-strength PE shrink films have appeared on the market.

POF heat shrink film features

POF shrink film has developed very rapidly in recent years. Ordinary POF shrink film is a three-layer co-extruded structure of ter-PP surface layer and linear low-density polyethylene (LLDPE) core layer. Similar to PVC shrink film, POF shrink film is also produced by double bubble method. Since the second bubble is not easily stabilized, the requirements for linear low density polyethylene in the formulation are very high. Dow's 2045 is considered a common raw material for POF membranes. Cross-linked film is a high-end product in POF shrink film. Unlike ordinary POF membranes, crosslinked membranes are pure PE structures. The production process is also slightly different from the ordinary double bubble method. When producing crosslinked membranes, PE bubbles need to be crosslinked by electron beam irradiation before the second bubble. Compared with ordinary POF film, cross-linked film has better shrinkage and heat sealing performance, and can adapt to different packaging machines and contents. In addition, the production process is complex and difficult, and the added value is much higher than that of ordinary POF membranes.

In addition to the several common shrink films introduced earlier, there are also some special shrink films. Such as shrink film for PETG and PS substrates. These films are all produced by a flat film stretching process. During the stretching process, the stretching ratio in the vertical and horizontal directions can be adjusted to obtain a uniaxially shrinkable film. With the strengthening of environmental awareness, PETG shrink film has begun to partially replace the position of PVC shrink film on bottle labels.