In the normal working process of the heat shrinkable packaging machine, the selection of heat shrinkable film materials is very important. First of all, the film is required to have a certain shrinkage rate in both vertical and horizontal directions. The shrinkage rate=(L1-L2)/L1*100%, L1 is The original length, L2 is the shrinkage length after immersion in glycerin at 120°C for 1-2S and water cooling. According to the heat-recovery property of heat-shrinkable plastic film, when the film is made from raw materials. It is heated and stretched in advance, and it becomes a shrink film after cooling. When the film is reheated, it shrinks and recovers.
Therefore, it is required that the film should have a shrinkage rate of about 50% in the longitudinal and transverse directions, and have sufficient heat-sealing strength and tensile strength, impact strength, tear strength, appropriate moisture resistance and oil resistance. At present, the most widely used shrink films are polyvinyl chloride (PVC), polyethylene (PE) and polypropylene (PP), followed by polyvinylidene chloride (pvdc), polyester (PET), polystyrene (EPS) ), ethylene-vinyl acetate copolymer (EVA) and so on.
Different film made by different raw material has their specific characteristics. PVC film is very easy to shrink, it can finish the shrinking and get a good tight package under 110 degree celsius and only stays for few seconds. But it has the toxic smell, not good to the packaging of food. PE film is strong with good force to protect the products inside, but it needs high temperature and long duration time for shrinking. POF is an ideal film material for most products shrink packaging. It’s shrinking temperature is moderate and has good tension to protect the products, transparent and beautiful packaging exterior with no smell.