There are two types of flexible packaging, namely stretch wrap packaging and various bags. Stretch wrap packaging is composed of a plastic film that has not yet formed a packaging shape. The film is simply wound on one or more products to be packaged and fixed in place in some form. The plastic bag is made into a certain shape before the product is put in or while the product is put in. The most common is to heat seal the plastic edge to form this shape.
1) Stretch wrap packaging
One of the biggest applications of plastic film in packaging is stretch-wrap packaging, which binds the goods on the pallet together to make them integrated and enter the circulation. The most commonly used plastic film is low-density polyethylene, which is stretched as it is wound on products and pallets, usually spirally wound. After wrapping, the film is cut, and the film head is glued to the goods, usually self-adhesive. After the stretching force is released, the film wants to return to its unstretched size to produce a binding force, which acts on the goods to bind the goods and keep them in place when they are moved during circulation.
In addition to the function of bundling, stretch-wrap packaging can also prevent the goods from damp, dust and abrasion. Stretch wrap packaging can also provide this kind of protection for a single variety of goods, and it can also bundle goods that are less than a pallet load.
Although stretch wrap packaging is conceptually simple, the structure is quite complex. For each layer of stretch wrap packaging, the ideal result is to stick to the underlying layer, but it is not desirable that adjacent shrink-wrapped goods stick to each other or to other objects in contact with it. Therefore, stretch wrap packaging may have a multi-layer structure, and adhesives are added to the inner layer to enhance bonding. In addition to LLDPE, low-density polyethylene, polyvinyl chloride, ethylene-vinyl acetate copolymer and other polymers are also used as stretch wrap films.
2) Shrink packaging
Shrink packaging is an alternative to bundled stretch wrap packaging. When the shrink wrap is exposed to a heat source, the originally aligned (orientated) molecules try to return to a lower energy, unstretched random coil structure. The product prevents the film from returning to its unstretched size, and the material acts on the product. Strive to bind the goods.
In order to bundle goods on pallets, stretch wrap packaging is more common than shrink packaging because it requires less energy and is more economical. Shrink packaging is more commonly used as a bundled packaging to bundle two or several products (same or different), rather than a full pallet of goods.
Shrink packaging is often used for product protection rather than binding, applications ranging from meat to toys. It can be designed to form a tight shell around the entire product, which is well protected from dirt, moisture and abrasion. Usually, the film is made into a loose bag before the film is tightly shrunk to the product in the shrink tunnel. LDPE and LLDPE are commonly used materials for shrink films. The amount of PVC and PP is less, as are some special films.