The shrinkage rate of Shenzhen POF shrink film includes longitudinal and transverse

The shrinkage rate of Shenzhen POF shrink film includes longitudinal and transverse. The test method is to measure the film length L1 first, then immerse the film in glycerin at 120°C for 1-2s, take it out and cool it with cold water, and then measure the length L2 where Ll— -Is the length of the film before shrinking; L2 is the length of the film after shrinking. At present, the shrink film used for packaging generally requires the same shrinkage in both longitudinal and transverse directions, about 50%; but in special cases, there are also unidirectional shrinkage, with a shrinkage rate of about 25% to 50%. There are also partially stretched films with unequal shrinkage rates in the longitudinal and transverse directions. The ratio of the shrinkage ratio in the vertical and horizontal directions is called the shrinkage ratio. Shrink tension Shrink tension refers to the tension applied to the package after the film shrinks. The shrinkage tension generated at the shrinkage temperature is closely related to the protection of the product. Rigid products such as packaging metal cans allow greater shrinkage tension, while some fragile or wrinkled products will be deformed or even damaged if they shrink too much. Therefore, the shrinkage tension of the shrink film must be selected appropriately. Shrinking temperature Shrinking film starts to shrink when heated to a certain temperature and stops shrinking when the temperature rises to a certain height. The temperature in this range is called the shrinkage temperature. For packaging operations, the package is heated in the heat shrinkage channel, and the temperature reached when the film shrinks to produce a predetermined tension is called the shrinkage temperature under the tension. The shrinkage temperature has a certain relationship with the shrinkage rate, and various films are different. In shrink packaging, the lower the shrinking temperature, the less adverse effects on the packaged products, especially fresh vegetables, fruits and textiles. Heat-sealability-In shrink packaging operations, two or three-sided heat sealing must be performed before heat shrinking, and the sealing seam is required to have high strength. The commonly used sealing methods for packaging include heat sealing, pulse fusion sealing, radiation sealing, and ultrasonic sealing. The heat sealing method is the most common method. During sealing, a flat plate (or disc) heated to a certain temperature is pressed on the superimposed film to seal. In order to prevent thermal shrinkage of the film during sealing, it should be sealed quickly, and it is best to take timely cooling measures immediately after sealing. Everyone knows that vegetables are easy to rot during transportation. Now that we see that vegetables are so intact and undamaged, it is our POF shrink film product packaging that plays a good protective role. Broccoli has a high respiratory intensity, and its physiological and metabolic activities are very vigorous after harvest. It will lose water and turn yellow in a short time, which will affect the commodity value of the vegetable itself. Therefore, vegetables must be pre-cooled in time after harvest to quickly remove field heat, reduce the center temperature and respiratory intensity of broccoli, so as to achieve the purpose of slowing down the metabolic activity of vegetables and extending the preservation period. At present, the pre-cooling link in domestic vegetable production areas is weak and lacks professional pre-cooling facilities; refrigerated transportation is rarely used during transportation. Retail links such as farmers' markets and supermarkets are mostly sold at room temperature without packaging. The facilities for selling fruits and vegetables are basically ordinary shelves and ordinary shelves. Humidification spray device (RH: 80%～90%) and refrigerated display cabinet (2～10℃). The corruption rate of vegetable circulation in China is 25% to 30%, which is the current status of vegetable circulation in China.