Early LLDPE stretch film to blown film as much, from single-layer development to two-layer, three-layer; now with the cast method of production of LLDPE stretch film is mainly, the process is shown in the figure below, this is because of the production of the cast line has a uniform thickness, transparency and high quality, can be applied to the requirements of the pre-stretching of the high rate. Due to the single-layer casting can not do one-sided adhesion, the application areas are limited. Single and double-layer cast in the material selection is not as wide as three-layer cast, the formula cost is also high, so it is still three layers **** extrusion structure is more ideal. High-quality stretch film should be characterized by high transparency, high longitudinal elongation, high yield point, high transverse tear strength and good puncture performance.
Production process conditions cast method of production due to the long and narrow flow channel, flow speed, melt temperature range is generally controlled at 250 ℃ ~ 280 ℃, the temperature control of the cast cooling rollers at 20 ℃ ~ 30 ℃, the winding tension should be low, generally within 10kg, in order to facilitate the viscosity agent to migrate out of the finished film at the same time to reduce the internal stresses. Adhesive control of good adhesion to make the goods outside the packaging film layer and layer stick together to make the goods solid, adhesion to get two main methods: one is in the polymer to add PIB or its mother material; the other is blended VLDPE. PIB is a semi-transparent viscous liquid, directly add the need for special equipment or equipment to carry out reforms, generally used PIB mother material. To three days, but also by the temperature, high temperature viscosity; low temperature is not too sticky, after stretching viscosity greatly reduced. Therefore, the finished film is best stored in a certain temperature range (recommended storage temperature of 15 ℃ ~ 25 ℃). Doped VLDPE, viscosity is slightly worse, but there are no special requirements for equipment, viscosity is relatively stable, not controlled by the time, but also by the temperature, the temperature is higher than 30 ℃ is relatively sticky, lower than 15 ℃ viscosity is slightly worse, can be adjusted by adjusting the amount of viscous layer of LLDPE, in order to achieve the desired viscosity. Three-layer **** extrusion is mostly used in this way. Physical and mechanical properties of the control of high transparency is conducive to the identification of goods; high longitudinal elongation is conducive to pre-stretching, and saves material consumption; good puncture performance and transverse tear strength allows the film to meet the sharp corners or edges of the goods in high tensile multiplier does not break; a high yield point so that the packaging of the goods after the tighter. The high transparency of films produced by the cast method is not emphasized here. With the increase in the number of material *** polymer monomer C atoms, the length of the branch chain increases, the crystallinity decreases, the generation of *** polymer "winding or kinking" effect increases, so the elongation increases, the puncture strength and tear strength are also increased. MPE is a high structural regular polymer, molecular weight distribution is very narrow, you can accurately control the physical properties of the polymer, so there is a further improvement in performance; and because of the narrow molecular weight distribution of MPE, the processing range is also narrow, the processing conditions are difficult to control, usually add 5% of LDPE to reduce the viscosity of the melt, increase the flatness of the film. MPE is also expensive, in order to reduce the cost of MPE, it is usually used in the production of LDPE. MPE is used with C4-LLDPE, but not all C4-LLDPE can be used with it and should be selected. Machine stretch film is mostly made of C6 and C8 materials, which are easy to process and can meet various packaging requirements. Handmade packaging due to the low stretch multiplier, mostly using C4 materials. Material density also affects the performance of the film. With the increase in density, the degree of orientation increases, good flatness, longitudinal elongation increases, yield strength increases, but the transverse tear strength, puncture strength and light transmittance are reduced, so the performance of the integrated aspects, often in the non-adhesive layer to add the appropriate amount of medium density linear polyethylene (LMDPE). Adding LMDPE can also reduce the coefficient of friction of the non-sticky layer, to avoid the packaged tray and tray adhesion. Effect of cooling roll temperature. Cooling roll temperature increases, yield strength increases, but the rest of the performance decreases, so the general cooling I roll temperature control at 20 ℃ ~ 30 ℃ is appropriate. The tension of the casting line affects the flatness of the film and the tightness of the winding, and if PIB or its masterbatch is used as the adhesive layer, it also affects the migration of PIB and reduces the final viscosity of the film. Tension is generally not greater than 10kg, too large a stress residual in the film roll, so that the elongation and other properties decline, easily resulting in film breakage phenomenon. The application form of stretch film stretch film has a wide range of applications, mainly used in conjunction with the pallet, the whole set of scattered goods packaging, instead of small containers. As it can reduce the cost of bulk goods transportation and packaging by more than 30%, it is widely used in the whole set of packaging of hardware, minerals, chemicals, medicine, food, machinery and other products; in the field of warehouse storage, foreign countries also make more use of stretch film tray packaging for three-dimensional storage and transportation, in order to save the space and occupy the land. Wrap-around film is used in the form of sealed packaging, which is similar to shrink film packaging, where the film is wrapped around the pallet to wrap up the pallet, and then two heat grippers heat-seal the two ends of the film together. This is the earliest form of use of wrap-around film, and from this developed more forms of packaging full-width packaging this packaging requirements of the film width is enough to cover the pallet, the shape of the pallet rules, so the use of it, suitable for the film thickness of 17 ~ 35μm handmade packaging this packaging is the simplest one of the wrap-around film packaging, the film is mounted on a shelf or by hand, by the pallet rotation or film around the pallet turn. It is mainly used for repacking after the wrapped pallet is broken, and ordinary pallet packaging. This kind of packaging is slow, and the thickness of suitable film is 15-20μm; stretch film winding machine packaging which is one of the most common and widely used forms of mechanical packaging, by the pallet rotation or film rotation around the pallet, and the film is fixed in the bracket can be moved up and down. This kind of packaging capacity is large, about 15 to 18 trays per hour. Suitable film thickness is about 15～25μm; Horizontal mechanical packaging is different from other packaging, by the film rotating around the items, suitable for long goods packaging, such as carpets, plates, fiber boards, shaped materials, etc.; Paper tube packaging which is one of the newest uses of the wrap-around film, which is better than the old-fashioned paper tube packaging with wrap-around film packaging. Suitable film thickness is 30～120μm; Packing of small items, which is the newest packaging form of wrap-around film, can not only reduce the consumption of materials, but also reduce the storage space of pallets. In foreign countries, this kind of packaging was firstly introduced in 1984, and only one year later, many such packages appeared in the market, which has a great potential in this form of packaging. Suitable for film thickness of 15 to 30μm; packaging of tubes and cables This is an example of the application of wrap-around film in a special field, where the packaging equipment is installed at the end of the production line, and the fully automatic stretch film both replaces the tape to bind the material and acts as a protector. The applicable thickness is 15-30μm.Stretching Forms of Pallet Mechanical PackagingThe packaging of stretch film are subject to stretching.The stretching forms of pallet mechanical packaging are direct stretching and pre-stretching. Pre-stretching is divided into two types, a roller pre-stretching, an electric stretching. Direct stretching is completed between the tray and film stretching. This method of stretching times low (about 15% to 20%), if the stretching rate of more than 55% to 60%, more than the film's original yield point, the film width is reduced, puncture performance is lost, the film is easy to break. And in 60% stretch rate, the tension is also very large, for light goods, it is likely to make the goods deformed. Pre-stretching is done by two rolls. The two rolls of the pre-stretching rolls are linked together by a gear unit, and the stretching multiplier can be different depending on the gear ratio. The tension is generated by the turntable, and since the stretching is generated within a short distance and the friction between the rolls and the film is large, the film width does not shrink, and the film's original puncture properties are maintained. No stretching occurs during actual winding, reducing breakage due to sharp edges or corners. This pre-stretching can increase the stretching multiplier up to 110%. The stretching mechanism of electric pre-stretching is the same as that of roll pre-stretching, the difference is that the two rolls are driven by electricity and the stretching is completely independent of the rotation of the pallet. So it is more adaptable and suitable for light, heavy and irregular goods. Due to the low tension during packing, the pre-stretching multiplier of this method is as high as 300%, which greatly saves material and reduces cost. Suitable for film thickness 15～24μm. characteristics of wrap-around film unitization: this is one of the biggest characteristics of wrap-around film packaging. With the help of the film's strong winding force and retractability, the products can be compactly and fixedly bundled into a unit, so that the scattered small pieces can become a whole, and even under unfavorable environment, the products do not have any loosening and separating, and there are no sharp edges and stickiness to avoid causing damage. Primary protection: Primary protection provides surface protection for the product, forming a very light and protective appearance around the product, so as to achieve the purpose of dust-proof, oil-proof, moisture-proof, water-proof and anti-theft. What is more important is that wrap-around film packaging can make the packaged goods uniformly subjected to force, avoiding the uneven force causing damage to the goods, which cannot be done by the traditional packaging methods (strapping, packing, taping, etc.). Compression and fixation: with the help of the retraction force after the stretching of the winding film, the products can be wrapped and packed to form a compact unit without occupying space, so that the pallets of the products can be wrapped closely together, which can effectively prevent the products from being misplaced and moving each other in the process of transportation, and at the same time, the adjustable stretching force can make the hard products tightly attached and make the soft products tightly closed, especially in the tobacco industry and the textile industry, where there are unique packaging effects. Cost-saving: The use of winding film can save the cost of packaging. Cost savings: the use of wrap-around film for product packaging, can effectively reduce the cost of using wrap-around film is only about 15% of the original box packaging, heat shrink film about 35%, about 50% of the carton packaging. At the same time, it can reduce the labor intensity of workers, improve the packaging efficiency and packaging grade. To sum up, the application of stretch film is very wide, and many domestic areas have not been involved, has been involved in many areas are not commonly used, with the expansion of the application, the amount of stretch film will grow greatly, and its market potential is immeasurable. Therefore, it is necessary for us to vigorously promote the production and application of stretch film.Introduction of PE stretch film and stretch filmPE stretch film (also known as winding film) has high tensile strength, tear strength, and good self-adhesive, so it can make the object wrapped into a whole, preventing from scattering and collapsing during transportation. The film has excellent transparency. The wrapped objects are beautiful and generous, and can make the objects waterproof, dustproof and damage-proof. The film is widely used for palletized packaging of goods, such as electronics, building materials, chemicals, metal products, auto parts, wires and cables, daily necessities, foodstuffs, paper making and other industries. Specification: machine film width 500mm, handmade film width 300mm, 350mm, 450mm, 500mm, thickness 15um-50um. online slitting various specifications. It can be slit into various specifications online. The adhesion is divided into single-side adhesion and double-side adhesion, and the products are divided into two series: manual winding film and machine winding film. Characteristics: The product has good cushioning strength, puncture and tear resistance, thin thickness and good performance-price ratio. It has high tensile strength, tear strength, transparency and good retraction force, pre-stretching multiplier 400%, can be assembled, waterproof, dustproof, anti-scattering and anti-theft. Use: It is used in pallet wrapping and other winding packaging, widely used in foreign trade and export, bottle and can making, papermaking, hardware and electrical appliances, plastics, chemical industry, building materials, agricultural products, food and other industries.PE winding film is an industrial film product with high tensile strength, high elongation, good self-adhesion, high transparency, etc. It is used for hand-wrapping, and can also be used for hand-wrapping, and can also be used for hand-wrapping with 400% pre-stretching multiplier. It can be used for hand wrapping film, also can be used for machine wrapping film, can be widely used in the centralized packaging of all kinds of goods. PE wrapping film is mainly made of several different grades of polyethylene resin mixed extrusion, with anti-puncture, super strength and high performance, the stacked in the pallet of the goods for wrapping packaging, so that the packaging is more solid and neat, more waterproof, is widely used in the foreign trade and export, papermaking, hardware, building materials, food and medicine industries. PE stretch film: LLDPE stretch film is made of high quality LLDPE as base material, with high quality tackifier, after heating, extruding, casting and then cooling by cold roller, it has the advantages of strong toughness, high elasticity, anti-tear, high adhesion, thin thickness, cold-resistant, heat-resistant, pressure-resistant, dust-proof, water-proof, and one-side and two-side adhesion, which can save material, labor and time. It can save materials, labor and time, and is widely used in papermaking, logistics, chemical industry, plastic materials, building materials, food, glass, etc. PE slit winding film: it is made of high-quality LLDPE as the base material, with high-quality viscosity increasing agent, and then cooled down by the cold roller after heating, extruding, and flow-delaying, and it has the advantages of strong toughness, high elasticity, tear-proof, high adhesiveness, thin thickness, cold-resistant, heat-resistant, pressure-resistant, dust-proof, water-proof, single-sided adhesion and double-sided adhesion, etc. It has the advantages of high flexibility, high adhesion, cold-resistant and pressure-proof, It has the advantages of strong toughness, high elasticity, anti-tear, high adhesion, thin thickness, cold resistance, heat resistance, pressure resistance, dust-proof, waterproof, single-side adhesion and double-side adhesion, etc. It can save materials, labor and time in use, and is widely used in papermaking, logistics, chemical industry, plastic raw materials, building materials, foodstuffs, glass and so on. The principle of winding film is that with the help of film's strong winding force and retractability, it can bundle the products into a unit compactly and fixedly, so that the scattered small pieces can become a whole, and even under unfavorable environment, the products will not have any loosening and separating, and there are no sharp edges and stickiness to avoid causing damage. Wrap film can be divided into: PE wrap film, PE wrap film, PE stretch wrap film, LLDPE stretch wrap film, PE slit wrap film and so on
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