The amount of LLDPE used has accounted for 30% of the total amount of three major types of polyethylene, of which about 80% is used to produce various films. Although LLDPE is easy to form various films, it has a relatively narrow range of relative molecular mass (Mw/Wn=2.8 -5.0) compared with LDPE and HDPE, and has high shear viscosity under molding processing conditions. Performance is worse than LDPE and HDPE. The length of the side branch in the molecular structure of LLDPE affects the processing properties of LLDPE. The side branches have a large length and a relatively wide range of molecular mass distributions, and have a low viscosity at high shear rates, and also have better melt strength and bubble stability during extrusion blown film.
LLDPE has a low tensile viscosity over a wide range of deformation rates and can be used to produce high strength very thin films (especially C6, C8 LLDPE). The LLDPE film produced by the extrusion blown film method has small heat shrinkability, particularly lateral heat shrinkability. When LLDPE is subjected to high shear force, the viscosity is reduced to a small extent and is not sensitive to temperature. Therefore, when LLDPE is extruded, the melt temperature is easily increased and loses control; the extrusion power is increased, the die pressure is increased; the extruder load is increased, and the power consumption is increased (usually higher than the LDPE). 30%~50%). When the blown film is extruded, the melt fracture is easily caused at the extrusion film head, and the surface of the film tube is tarnished, and the bubble has a saw-like stripe. Moreover, since the melt strength of LLDPE is relatively low, the bubble stability is poor when the bubble is inflated, and in particular, when a thick film or a film having a large width is formed, the bubble is liable to sag.
In extrusion blown film forming, it is less common to use LLDPE. More often, LLDPE is often blended with other materials (LLDPE, HDPE, EVA) to produce a film.
(1) The blending amount of low-content LLDPE is below 20% to 30%, and blown film production can be carried out using existing equipment. For some extrusion blown film production equipment lines with good load carrying capacity, LLDPE can be added up to 40%.
(2) The blending amount of medium-content LLDPE is about 30% to 75%, and the production line needs to appropriately improve the equipment, such as widening the die gap and increasing the extruder extrusion power.
(3) The blending amount of high-content LLDPE is above 75%, and the production line needs to be modified.
The secondary processing properties of LLDPE blown film are similar to those of LDPE films. Before the film is printed and dry-composite, the surface of the film should be corona treated; the film can be crimped and sealed by hot melt method. Since the melting range of LLDPE is narrower and higher than that of LDPE, its heat sealability and thermal bond strength are higher than those of LDPE. After bonding the LLDPE film with an adhesive, it still has peelability. LLDPE can adopt extrusion blown film method, extrusion casting method, and produce single-layer or multi-layer co-extruded film; it can be combined with other materials by extrusion compounding method to produce composite film.
The use of LLDPE:
Extrusion blown film (single or multilayer) method. Shed film, mulch film, outdoor cover film, heavy packaging film, cleaning bag, shopping bag, functional film; extrusion blown film and extrusion casting (single layer or multi-layer) method. Film, packaging film, agricultural film, food bag, shopping bag extrusion blown film and extrusion casting (single layer or multilayer) are generally used. Stretch film, cling film, composite film base, packaging film, functional film.
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