PE film, or polyethylene film, is a film made of polyethylene plastic. There are two production methods: blow molding and extrusion. The former is to extrude the molten polyethylene plastic from a ring die to form a tube film, and use air pressure to blow the tube film into shape, then cool and roll it up; the latter is to extrude the molten polyethylene plastic from a flat slit die, and then cool and roll it up. PE film can be divided into low-density polyethylene film and high-density polyethylene film, which is generally milky white, translucent, odorless, tasteless and non-toxic. PE film has good impact and tear resistance, grease resistance, good water resistance, acid resistance and alkali resistance; but its air tightness is poor, and it must be surface treated before printing. It is widely used in the packaging of various industrial and agricultural products; it can also be compounded with paper, aluminum foil, etc. to make composite films.

Polyethylene

PE film is moisture-proof and has low moisture permeability. Polyethylene film (PE) can produce products with different properties such as low-density, medium-density, high-density polyethylene and cross-linked polyethylene according to different manufacturing methods and control methods.

Low-density polyethylene

Its density is about 0.92g/cm3. Low-density polyethylene film has good transparency and heat-sealing properties, and is waterproof and moisture-proof; it has low tensile strength, large tensile elongation, and is easy to wrinkle. For films below 0.03mm, the tension should be controlled to be small, and the tension should be constant everywhere, especially when heated, it is more likely to deform, causing difficulty in color registration. Therefore, when drying, the surface temperature of the film should not be too high (within 55 degrees). According to the different film-forming processes, it can be divided into blown film (IPE), cast film (CPE), low-foaming film, etc. The tensile strength and opening of IPE film are better than those of CPE film. It is printed on the front and can be used as food bags, clothing bags, etc.; CPE film has uniform thickness, better surface gloss, transparency and heat-sealing properties than PE, and can be printed on both sides, but the production cost is high. CPE film is mainly used as the inner layer of composite bags and the packaging of cosmetics, pickles and cakes; low-foaming film has good decorative properties, thick texture, and is not easy to stretch and deform. It is printed on the front and used as New Year pictures, trademarks and handbags.

Medium-density polyethylene

Its density is about 0.93-0.94g/cm3, and its performance is between high-density and low-density polyethylene.

High-density polyethylene

The density is 0.94-0.965g/cm3. The heat resistance and mechanical strength of high-density polyethylene film are better than those of low-density polyethylene film, the tensile elongation is small, the film thickness is generally above 0.03mm, but the transparency is poor. It is printed on the front and is mainly used as vest bags, garbage bags and liner bags.

Cross-linked polyethylene

Because it has higher heat resistance, tensile strength, heat shrinkage and barrier properties than other polyethylene products, its use is further expanding. In 2014, it was mostly used as heat shrink packaging film.

Generally speaking, with the increase of density, mechanical properties and barrier properties will be improved accordingly, and heat resistance will also be good. Polyethylene of the same density also has different properties due to different film-forming processes. This is because the drooling method can cool quickly, with low crystallinity, high transparency, and low turbidity, but the molecular arrangement tends to be more irregular, so the barrier property is small, that is, the transmittance is large, the elongation is low, and the tear resistance is poor.

Production process

The film blowing machine is a mechanical device that heats and melts PE plastic particles and then blows them into film. First, add dry polyethylene particles into the lower hopper, and the weight of the particles themselves enters the screw from the hopper. When the particles come into contact with the bevel of the thread, the rotating bevel surface generates a thrust perpendicular to the bevel surface on the plastic, pushing the plastic particles forward. During the pushing process, due to the friction between the plastic and the screw, the plastic and the barrel, and the collision and friction between the particles, and also due to the external heating of the barrel, the plastic gradually melts. The molten plastic passes through the die filter to remove impurities and comes out from the die. After being inflated and cooled by the air ring, it is pressed by the herringbone plate and rolled into a tube by the traction roller.

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