Resealable plastic bags include all baggies designed with a closure mechanism that can open and be re-fastened for continued product containment. Many such bags are meant for reuse, making resealing essential. The possibility of multiple uses also requires manufacturers to produce bags of more durable materials than single use poly bags. Polypropylene, polyethylene and vinyl are popular options and are available in different grades or gauges with common thicknesses ranging between 2 and 6Mil.
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The sealing or closure mechanisms on resealable plastic bags are highly variable, since the feature is what makes the bag marketable. Zip lock bags are among the most popular as they produce a secure seal impermeable to air, water and other elements. Adhesive or tape strips also accomplish this, though the strength of the tape or adhesive may lessen over time, thus diminishing resealing capabilities. Drawstring and twist tie options are also available. Because they do not offer a complete seal, they are used more often as plastic shopping bags or for other applications in which environmental contamination is of little concern. Retail, electronics, food and chemical, medical and pharmaceutical, parts production and travel industries among others frequently use resealable bags for the storage, protection, transport and packaging of varied goods. Home and office applications abound as well as resealable bags offer accessible organization and containment.
As sealing mechanisms are most often fixed into place after the formation of the bag, resealable bags begin production much like any other plastic bag. The plastic resins are heated to form a viscous fluid. This fluid is then formed into film through casting, winding, sheet extrusion or blown film extrusion; the latter of which is most commonly used. Blown film extrusion uses a die with a central opening through which cool air is blown at a uniform rate. This produces a tube of plastic film that is of even thickness. After sufficient cooling the tube is collapsed and the material flattened. Edges and seams are formed through heat-sealing in order to produce the desired size and shape bag with one open edge. The closing mechanism is transfixed on this edge. For zipper locks, two separate molded plastic strips attached to adjacent surfaces. When pressed they form a tight seal. Adhesive or tape reclosable bags need apply the permanent or semi-permanent material to only one side. Drawstrings must be looped around the edge of the bag. It is important to consider the intended use and potential contents of a bag when selecting both film and seal material to avoid product contamination. Additional considerations include volume and dimensions as well as the color, opacity and surface quality of the bag.