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Bags or pouches are a type of packaging for containing frozen food, fresh produce, snack foods, hardware, gardening products, etc. They are often made from a single roll of film on a horizontal or vertical form fill sealing machine.
Most Plastic bags are made from polyethylene, more commonly known as polythene, which is made from crude oil and natural gas, non-renewable resources.
The most common way to produce polythene bags is by blown film extrusion, also called the tubular film process. In Blown film production process polythene melt is extruded through an annular slit die, usually vertically, to form a thin walled tube. Air is introduced via a hole in the centre of the die to blow up the into the tube causing it to expand and form a bubble. Mounted on top of the die, a high-speed air ring blows onto the hot film to cool it. The tube of film then continues upwards, continually cooling, until it passes through nip rolls where the tube is flattened to create what is known as a lay-flat tube of film.
This lay-flat or collapsed tube is then taken back down the extrusion tower via more rollers. The lay-flat film is then either kept as such or the edges of the lay-flat are slit off to produce two flat film sheets and wound up onto reels. If kept as lay-flat, the tube of film is made into bags by sealing across the width of film and cutting or perforating to make each bag. This is done either in line with the blown film process or at a later stage.
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