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Tips: Defining Stretch Film

Release Date:2011-08-30Hits:
Stretch film, also known shrink film, PVC is the earliest to the substrate, packaged with a DOA plasticizer and from self-adhesive role for the production of PVC stretch film. Because of environmental problems, high cost (relative PE ratio of major unit less packaging area), stretching and poor reasons, from 1994 to 1995, when the country began producing PE stretch film when phased out. PE stretch film with EVA as the first self-adhesive materials, but its high cost, but also taste, after development with PIB, VLDPE as the self-adhesive materials, the substrate now LLDPE based, including C4, C6, C8 and metallocene PE (MPE). LLDPE stretch film in the early blown as much, from the development to single-story, three; now the production of cast LLDPE stretch film based, the process shown below, this is because the production has a cast line thickness uniformity, transparency advantages, suitable for high power pre-stretch of the requirements. As the single-sided sticky tape can not do, applications are limited. Single, double cast in the choice of materials is not cast three wide, the high cost of formula, so it is still the ideal structure of three-layer co-extruded. High-quality stretch film should be transparent, vertical elongation, high yield point, high transverse tear strength, puncture and good performance characteristics.

Viscosity control

Good adhesion to the packaging of goods outside layer of the film and stick together to make a solid goods, packaging adhesive, there are two access methods: one is to add in the PIB polymer or parent material; the other is doped mixed VLDPE. PIB is translucent viscous liquid, add the need for special equipment directly or modify the equipment, generally used PIB masterbatch. PIB is to move out of a process, generally three days, also affected by temperature, high temperature adhesive strength; low temperature is not sticky, sticky after stretching significantly reduced. Therefore finished film preferably stored in a certain temperature range (recommended storage temperature 15 ℃ ~ 25 ℃). Mixing VLDPE, sticky bit weak, but there are no special requirements for equipment, viscosity is relatively stable, without time control, but also affected by temperature, the temperature is higher than 30 ℃ when the relatively sticky, somewhat less than 15 ℃, the viscosity can be By adjusting the amount of LLDPE adhesive layer, to achieve the desired viscosity. Three-layer co-extruded multi-use this method.

Stretch film production process conditions

Casting method of production as long, narrow flow channel, flow speed, melt temperature range is typically controlled at 250 ℃ ~ 280 ℃, casting cooling roll temperature was controlled at 20 ℃ ~ 30 ℃, the winding tension is lower, generally 10kg or less, to facilitate the viscous agent to move out, while reducing the finished membrane stress.

Physical and mechanical properties of the control

High degree of transparency is conducive to the identification of goods; high longitudinal elongation is conducive to pre-stretch and save material consumption; good puncture resistance and tear strength allows the membrane lateral tension in the high magnification encounter sharp corners or goods edge is not broken; high yield point to packaged goods more tightening. Cast production of the film transparency, does not focus on here. With the material comonomer increased the number of C atoms, branched-chain length increased, lower crystallinity, the resulting copolymer "wound or kink" effect increased, elongation rate, puncture strength and tear strength are also improved. The MPE is Gao polymer stereoregularity, molecular weight distribution is very narrow, can accurately control the polymer's physical properties, so there are further performance improvement; and because the MPE narrow molecular weight distribution, processing range is narrow, difficult to control processing conditions, usually Add 5% LDPE, to reduce the melt viscosity, increased film roughness. MPE prices are high, in order to reduce costs, usually MPE and C4-LLDPE with use, but not all C4-LLDPE can be associated with, should have a choice. Machine stretch film use more C6, C8 material, easy to process, to meet a variety of packaging requirements. Hand-packing stretch ratio as low, the use of C4 material. Material density also affect the film performance. As the density increases, the degree of orientation increased, roughness, vertical elongation rate, yield strength, but the lateral tear strength, puncture strength and light transmission rate of decline, the overall performance of all aspects, often in non-stick Add the appropriate amount of medium density layer linear polyethylene (LMDPE). Add LMDPE non-stick layer can also reduce the coefficient of friction, avoid packaged tray with tray adhesive. Chill roll temperature. Chill roll temperature, yield strength, but the rest of performance, it is generally the cooling I roll temperature was controlled at 20 ℃ ~ 30 ℃ appropriate. Cast the line tension effects and film flatness winding tightness, the use of PIB or parent material as adhesive layer, also affect the PIB's move to reduce the viscosity of the final film. Tension is generally not more than 10kg, is too great stress remaining in the roll, so that elongation performance, easily lead to broken membrane phenomenon. The application form stretch film stretch film applications is very broad, mainly used in conjunction with the tray, the whole set of fragmented commodity packaging, place a small container. Because it can reduce the volume of goods transport packaging costs more than 30%, which is widely used in metal, mining, chemical, pharmaceutical, food, machinery and other products on the packaging of the entire set; in the warehouse storage area, greater use abroad stretch film pallet packaging three-dimensional storage to save space and area.