The express bags are classified into express plastic bags, express document seals, express bubble bags, express bone bags, express woven bags, etc.
1. Material of express plastic bag: PE commonly referred to as low density polyethylene (LDPE), PO commonly referred to as high density polyethylene (HDPE). The express plastic bag has the advantages of low cost and light weight.

According to the production process, it can be generally divided into: PE flat bag, self sealing bag, chain clip bag, envelope bag, punching bag, hand bag, zipper bag and PE film.
1. PE flat bags are the simplest production process. After film blowing by the machine, they are cut into bags on the bag making machine, and the bottom is sealed.

How to distinguish the quality of plastic bags? It is believed that many people still have no idea about this. They think that the vest bag is nothing but a trifle. It is good to choose it any way, and the product itself is not expensive. A few cents will not make them feel trapped even if they buy it badly. This idea is a big mistake.
Because for some big sellers, they will purchase in large quantities every time. If they pick out bad products, they will not be bad for one or two, but will lose a lot in batches. Therefore, Xiao Bian believes that it is necessary to introduce some skills to distinguish between good and bad vest bags here.
Some good plastic vest bags on the market generally include three aspects: alkali resistance, tensile strength and crack resistance. Of course, alkali resistance is the core.

PE bag is a thermoplastic resin made of ethylene through polymerization. In industry, it also includes ethylene and a small amount of α- Copolymers of olefins. Polyethylene is odorless, non-toxic, feels like wax, has excellent low temperature resistance (use temperature can reach - 70~- 100 ℃), good chemical stability, can withstand the corrosion of most acids and alkalis (not resistant to acids with oxidation properties), insoluble in general solvents at room temperature, low water absorption, and excellent electrical insulation performance; However, polyethylene is very sensitive to environmental stress (chemical and mechanical effects) and has poor heat aging resistance. PE bag is a thermoplastic resin made of ethylene through polymerization. In industry, it also includes ethylene and a small amount of α- Copolymers of olefins.