1) Stretch Wrapping
One of the largest applications of plastic film in packaging is stretch-wrapping packaging, which means that the goods on the tray are bundled together to make it into one and enter circulation. The most commonly used plastic film is low density polyethylene, which stretches as it is wrapped around products and trays, typically spiral wound. After wrapping, the film is cut off and the film head is glued to the goods, usually self-adhesive. After the stretching force is released, the film is intended to return to its unstretched size and exert a binding force on the cargo, binding the cargo so that it remains immobile when it is moved during circulation.
In addition to bundling this function, stretch-wrapping packages also protect the cargo from moisture, dust, and abrasion. Stretch-wrapping packages can also provide this kind of protection for a single type of cargo, and can also bundle goods smaller than a pallet load.
Although stretch wrapping is conceptually simple, the structure is quite complicated. For each stretch wrapped package, the ideal result is to stick to the underlying layer, but it is not desirable that the adjacent shrink-wrapped items adhere to one another or stick to other objects that they are in contact with. Therefore, the stretch-wound package may have a multi-layered structure, adding a binder to the inner layer to enhance the adhesion. In addition to LLDPE, low-density polyethylene, polyvinyl chloride, ethylene-vinyl acetate copolymers, and other polymers are also used as stretch-wound films.
2) Shrink packaging
Shrink wrap is an alternative to bundle stretch wrapping. When the shrink wrap is exposed to a heat source, the originally aligned (orientated) molecules try to recover to a lower energy, unstretched random coil structure, the product prevents the film from returning to its unstretched dimensions, and the material acts on the product. Combine the goods.
Stretch-wound packaging is more common than shrink-wrapping for bundling goods on pallets because it requires less energy and is more economical. Shrink-wrapped packaging is more commonly used as a bale-wrapping package where two or more products (same or different) are bundled instead of a full pallet of goods.
Shrink packaging is often used for product protection rather than binding, from meat to toys. It can be designed to form a tight shell around the entire product, preventing dirt, moisture and wear. Usually, a loose bag is made before the film shrinks tightly in the product shrinking the tunnel. LDPE and LLDPE are commonly used materials for shrink films. PVC and PP are used in small amounts, as are some special films.
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