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Knowledge points of PE film
- Jan 08, 2019 -

The permeability of PE film is large, and its permeability is decreased with the increase of density. PE film has moisture resistance and little moisture permeability. Polyethylene film (PE) can produce low density, medium density, high density polyethylene and crosslinked polyethylene products with different properties according to different manufacturing methods and control methods.

The density of low-density polyethylene (LDPE) is about 0.92g/cm3. Low density polyethylene film transparency and good sealing performance, waterproof, moisture-proof; low tensile strength, tensile elongation, easy wrinkled, thin film below 0.03mm, tension control should be small, and all the tension to a constant, especially easy to deform when heated, causing difficulties in color. Therefore, when drying, the film surface temperature should not be too high (within 550C). According to the film forming process, can be divided into blown film, cast film (IPE) (CPE), several low foaming film etc. IPE thin film tensile strength and opening than CPE film, with positive printing, can be used for food bags, clothing bags; CPE thin film thickness uniformity, surface gloss, transparency and thermal sealing ratio, PE, can be positive and negative printing, but the production cost is high; the CPE film is mainly used as the inner layer and the composite bag cosmetics, pickles and cake packaging; low foaming film decorative, thick texture, not easily tensile deformation, using positive printing, as New Year paintings trademarks and hand bag etc..

Medium density polyethylene (MDPE), whose density is about 0.93 ~ 0.94g/cm3, is between high density and low-density polyethylene.

The density of HDPE (HDPE) is 0.94 - 0.965g/cm3. The heat resistance and mechanical strength of HDPE film are better than LDPE film, the elongation at break is small, the film thickness is more than 0.03mm, but the transparency is poor. It is mainly used as vest bag, garbage bag and lining bag.

Because of its higher heat resistance, tensile strength, thermal shrinkage and barrier than other polyethylene products, crosslinked polyethylene (CLPE) has further expanded its use, and is mostly used as heat shrinkable packaging film at present.

Generally speaking, with the increase of density, mechanical properties and barrier properties will be increased accordingly, heat resistance, and life is good. Polyethylene with the same density has different properties because of the different film forming process. This is because the salivation method can fast cooling, low crystallinity, high transparency, turbidity is small, but more irregular arrangement of molecules, so the barrier is small, the transmittance of larger, lower elongation, tear resistance difference.

Production Process

Film blowing machine is a kind of mechanical equipment which melts and melts plastic particles and then blows them into film. First of all, the polyethylene particles drying to the hopper, by weight of the particles from the hopper into the screw thread, when the aggregate and the oblique edge contact, oblique edge rotating plastic face and oblique edges face vertical thrust, the plastic particles goes forward, pushing process, due to the collision and friction between the plastic screw plastic and cylinder and friction between particles, but also because the barrel external heating gradually melted. The melted plastic is filtered by the head, and the impurity is removed from the die head. After the air ring is cooled and inflated, it is pressed by the herringbone plate, and then the product film is rolled into the cylinder by the traction roller.