Packaging materials and packaging forms used in shrink packaging machines
The packaging materials used in shrink packaging machines are mainly shrink films, and the heat shrinkage properties of shrink films play a major role in shrink packaging. At present, the most widely used shrink film materials are: polyvinyl chloride, polyethylene and polypropylene, followed by vinylidene chloride, polyester, polystyrene, chlorinated rubber film, nylon, resin and so on. Polyvinyl chloride is a good packaging material with wide sources and low cost. It is transparent and beautiful, with low shrinkage temperature and neat sealing. At the same time, it has low oxygen permeability and high temperature permeability, so it is more suitable for the packaging of water-containing vegetables and fruits. The disadvantages are poor impact resistance, poor cold resistance, easy to become brittle at low temperature, not as good as polyethylene in heavy packaging, and poor sealing strength. Polyethylene is characterized by high impact strength, low price, firm sealing and good moisture resistance, so it is widely used, especially in industrial packaging. The disadvantage is that the gloss and transparency are worse than that of polyvinyl chloride, and the oxygen barrier performance is poor. This material can be used for food packaging and shrink packaging that do not require strict appearance, but its shrinkage temperature is 20~50 °C higher than that of polyvinyl chloride. Therefore, after heat shrinking, air cooling is required. Polypropylene is characterized by the best transparency and gloss, good adhesion, water resistance, oil resistance and moisture resistance, and strong shrinkage. However, it has poor impact resistance and heat sealing performance, high shrinkage temperature and narrow range, and is mostly used for packaging and shrink packaging of thin and lightweight items. Other materials, such as polystyrene film, are mainly used for packaging letters; vinylidene chloride is mainly used for packaging meat food; the newly developed EVA (polymer of ethylene and vinyl acetate) has high impact strength, high transparency, and high heat resistance. It has good sealing performance and low shrinkage force, and is suitable for the packaging of protruding special-shaped objects; Ionomer, which has recently appeared, is a thermoplastic resin with covalent and ionic bonds, with large strength and elongation, and good adaptability to packaging items. It is suitable for shrink packaging of frozen food with protrusions for long-distance transportation. The packaging forms of shrink packaging machines are often divided into three types according to the shape and packaging requirements of the items: lap shrink packaging, which has a wide range of applications and adaptability; sleeve shrink packaging is suitable for items close to cubes, and does not require This type of packaging is often used when it is completely sealed, especially when a tray is placed under the product; cover-type shrink packaging uses shrink film to cover the item, and then heats the packaging. This type of packaging is mostly used for wrapping containers or trays. Items, heat shrink devices can be sprayed with hot air or heat shrink chambers.
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