The gas permeability of PE film is large, and with the increase of density, its gas permeability is decreased. PE film has the characteristics of moisture resistance and little moisture permeability. According to the different manufacturing methods and control means, low density, medium density, high density polyethylene and crosslinked polyethylene can be manufactured.
The density of low density polyethylene is about 0 92g/cm2.. The product has good transparency and heat sealing, can be waterproof and moisture-proof, but the tensile strength is low, the tensile elongation is large, and it is easy to wrinkle. According to the different film forming process, it can be divided into blow molded film, salivation film, low foaming film and so on. The tensile strength and opening property of the blow molded film are better than that of the cast film, and it can be used for food bags and clothing bags. The casting film has uniform thickness, good surface gloss, transparency and heat sealing, and can be printed front and back, but the production cost is high.
Medium density polyethylene has a density of about 0.93~ 0.94g /cm2, and its performance is between high density and low density polyethylene.
The density of high-density polyethylene is 0.94--0.965g/cm2. The heat resistance and mechanical strength of the film are better than that of low-density polyethylene film, the tensile elongation is small, the film thickness is generally above 0.03mm, but the transparency is poor, and it is mainly used for positive printing, such as vest bags, garbage bags and lined bags.