About Plastic Bag Manufacturing
It is interesting and fun to know how objects we use daily and often take for granted are made. Plastic bags are useful and come in different shapes and sizes, according to their purpose. The manufacturing procedure is simple and requires few elements. A simple, unprinted bag can be done in three steps that take only a few minutes.
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Granules
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The raw material used for making plastic bags is a chemical called polyethylene. Polyethylene granules are made out of polymers converted from petroleum and natural gas. A polymer is made of large molecules consisting in a linked series of repeated simple monomers. These repeated monomers can be used in many ways to make ethylene. The molecular chain resulting from processing ethylene is called polyethylene.
Granules can be also produced from recycled plastic, depending on its quality.
Film
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To make a bag, first manufacturers purchase or produce the film. The film used for plastic bags is usually made of polyethylene of high (HDPE) or low (LDPE) density. The raw material is melted and blown in the form of a tube by an extruder. As the film tube rises and travels though cooling areas, it gradually cools down and can be cut to a required width and put on a roll. When the film roll is finished, the machine automatically cuts the film and continues to roll it on another carton core.
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Printing
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After the roll of film is ready, it is transported to another department and is put into a printing machine. The machine prints one color at a time through impressions made by inking rollers. After the printing is complete, the film is rolled again on a carton core and sent to the next machine that will cut it into the desired size and shape.
Cut and Seal
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The printed (or non-printed) film is cut into the required size and shape. Usually, the same machine that cuts the film also seals it. Depending on the complexity of the bag, a few more steps are required. For example, a bag with handles will require more steps than a simple storage bag. While the film is rolled continuously, the machine cuts the handles, adds gussets to the bag and--in a simple step--cuts and heat-seals it.
Other Steps
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As there are a multitude of bags for different purposes, sometimes additional steps are required before the bag is cut and sealed. For a zip-lock bag, the machine attaches a plastic pad to the film by heat. Some products require bags with small holes, which are punched in before the bag is sealed as the film travels on conveyors. For bubble bags, the film is blown into a bubble wrap roll before it is cut and sealed. For bags with different properties, such as anti-static or anti-corrosive, the granules are mixed with chemicals before they are melted.
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References
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- Photo Credit Image by Flickr.com, courtesy of Mike Rolph
