Early LLDPE stretched films were mostly blown films, which developed from single layer to two or three layers. At present, LLDPE stretched film is mainly produced by tape casting, and its technological process is shown in the following figure. This is because the production of casting production line has the advantages of uniform thickness and high transparency, which can meet the requirements of high-speed pre-stretching. Because single-layer casting can't be bonded on one side, its application field is limited. Single-layer casting and double-layer casting are not as extensive in material selection as three-layer casting, and the formula cost is also high, so the structure of three-layer extrusion is ideal. High-quality stretched film should have high transparency, high longitudinal elongation, high yield point, high transverse tear strength and good puncture performance.
Production process conditions: the advantages of tape casting method are long and narrow flow channel, high flow rate, generally controlled melt temperature in the range of 250℃ ~ 280℃, temperature of casting cooling roller in the range of 20℃ ~ 30℃, and low winding tension, generally within 10kg, so as to facilitate the outward migration of adhesive and reduce the internal stress of finished film. The viscosity is well controlled. Stickiness makes the packaging film outside the goods stick together, making the goods firm. There are two main ways to obtain viscosity: one is to add PIB or its masterbatch to the polymer; The other is mixed VLDPE. PIB is a translucent viscous liquid, so direct addition requires special equipment or modification of equipment, and PIB masterbatch is generally used. There is a process for PIB to move out, which usually takes three days. In addition, it is also affected by temperature, which is sticky when the temperature is high. It will not be too sticky at low temperature, and the viscosity will be greatly reduced after stretching. Therefore, the finished membrane should be stored in a certain temperature range (the recommended storage temperature is 15℃ ~ 25℃). The viscosity of mixed VLDPE is slightly poor, but there is no special requirement for equipment. The viscosity is relatively stable, not controlled by time, but also affected by temperature. When the temperature is higher than 30℃, it is relatively viscous, and it is slightly worse when it is lower than 15℃. The required viscosity can be achieved by adjusting the amount of LLDPE in the adhesive layer. This method is often used for three-layer extrusion. The control of physical and mechanical properties and high transparency are conducive to the identification of goods; High longitudinal elongation is beneficial to pre-stretching and saves material consumption; Good puncture performance and transverse tear strength enable the film to touch the sharp corner or edge of the goods without breaking under high stretch ratio; High yield point makes the packaged goods safer. The film produced by tape casting method has high transparency and will not be discussed here. With the increase of the number of carbon atoms in the monomer of material * * *, the branch length increases, the crystallinity decreases, and the "winding or kinking" effect of the polymer increases, so the elongation increases, and the puncture strength and tear strength also increase. MPE is a highly stereoregular polymer with narrow molecular weight distribution, which can accurately control the physical properties of the polymer, so its properties have been further improved. Due to the narrow molecular weight distribution, narrow processing range and difficult control of processing conditions of MPE, 5% LDPE is usually added to reduce the melt viscosity and increase the flatness of the film. The price of MPE is also high. In order to reduce the cost, MPE and C4-LLDPE are usually used together, but not all C4-LLDPE can be used together, so we should choose. Stretched films for machines are mostly made of C6 and C8 materials, which are easy to process and can meet various packaging requirements. Due to the low stretch ratio, C4 materials are mostly used for manual packaging. The density of materials will also affect the properties of thin films. With the increase of density, the orientation degree is improved, the flatness is good, the longitudinal elongation and yield strength are improved, but the transverse tear strength, puncture strength and light transmittance are decreased. Therefore, considering all aspects of performance, an appropriate amount of medium density linear polyethylene (LMDPE) is usually added to the non-adhesive layer. The addition of LMDPE can also reduce the friction coefficient of non-adhesive layer and avoid the adhesion between packaging trays. Influence of cooling roller temperature. When the temperature of cooling roller increases, the yield strength increases, but other properties decrease, so it is appropriate to control the temperature of cooling roller I at 20℃ ~ 30℃. The tension of the casting production line affects the smoothness and winding tightness of the film. If PIB or its masterbatch is used as the adhesive layer, it will also affect the migration of PIB and reduce the final viscosity of the film. Generally, the pulling force shall not exceed 10kg. If the tension is too large, there will be residual stress in the film roll, which will reduce the elongation and other properties and easily lead to film breakage. The application form of stretch film has a wide range of applications, mainly in cooperation with pallets to package scattered goods as a whole, rather than small containers. Because it can reduce the transportation and packaging cost of bulk goods by more than 30%, it is widely used in the overall packaging of hardware, minerals, chemicals, medicine, food, machinery and other products. In the storage field, foreign countries also use stretched film pallet packaging for three-dimensional storage and transportation, saving space and occupying land. The use form of plastic wrap sealed packaging is similar to shrink film packaging. The film completely wraps the tray around the tray, and then two thermal clips heat seal the films at both ends together. This is the earliest use form of wrapping film, and later more packaging forms have been developed. This kind of packaging requires that the film width is enough to cover the tray, the tray is regular in shape and suitable for manual packaging, and the film thickness is17 ~ 35μ m. This kind of packaging is the simplest wrapped film packaging, and the film is placed on the shelf or held by hand, and rotated by or around the tray. It is mainly used for repackaging packaged pallets after being damaged, as well as ordinary pallet packaging. This packaging speed is slow, and the suitable film thickness is15 ~ 20 μ m; Stretched film winding machine packaging This is the most common and extensive form of mechanical packaging. The film can be moved up and down by rotating the tray or rotating the film around the tray. This kind of packaging capacity is very large, about 15 ~ 18 sheets per hour. The suitable film thickness is about 15 ~ 25 microns; Different from other packaging, horizontal mechanical packaging is suitable for packaging long articles, such as carpets, plates, fiberboards and special-shaped materials. Paper tube packaging This is one of the latest uses of packaging film, which is better than the old packaging film for paper tube packaging. The suitable film thickness is 30 ~120μ m; Packaging of small items This is the latest packaging form of packaging film, which can not only reduce the consumption of materials, but also reduce the storage space of pallets. In foreign countries, this kind of packaging was first introduced by 1984. Only one year later, many kinds of packaging forms appeared in the market, which has great potential. The suitable film thickness is15 ~ 30μ m; Packaging of pipes and cables This is an example of the application of wound film in special fields. Packaging equipment is installed at the end of the production line. Fully automatic stretching film can not only replace the adhesive tape binding material, but also play a protective role. The suitable thickness is15 ~ 30μ m ... The stretching form of pallet packaging The packaging of stretching film must be stretched, and the stretching forms of pallet mechanical packaging include direct stretching and pre-stretching. There are two kinds of pre-stretching, one is roller pre-stretching and the other is electric stretching. Direct stretching is the stretching between the tray and the film. This method has low draw ratio (about 15% ~ 20%). If the stretching ratio exceeds 55% ~ 60%, which exceeds the original yield point of the film, the width of the film is reduced, the puncture performance is also lost, and the film is easy to break. Moreover, under the tensile rate of 60%, the tensile force is still very large, which is likely to deform the goods for light goods. Pre-stretching is completed by two rollers. The two rollers pre-stretched by the rollers are connected through a gear set, and the stretching ratio can be different according to different gear ratios. The pulling force is generated by the turntable. Because stretching occurs in a short distance, the friction between the roller and the film is large, so the width of the film will not shrink, and the original puncture performance of the film is maintained. There is no stretching in the actual winding process, which reduces the fracture caused by sharp edges or corners. This pre-stretching can increase the stretching ratio to 1 10%. The stretching mechanism of electric pre-stretching is the same as that of roller pre-stretching, except that the two rollers are driven by electricity, and stretching has nothing to do with tray rotation. Therefore, it is more adaptable and suitable for light, heavy and irregular goods. Due to the low tension during packaging, the pre-stretching rate of this method is as high as 300%, which greatly saves materials and reduces costs. The suitable film thickness is15 ~ 24 μ m. The characteristics of wound film are unitary: this is one of the biggest characteristics of wound film packaging. Using the super-strong winding force and flexibility of the film, the product is tightly fixed and bound into a unit, so that the scattered small pieces become a whole. Even in unfavorable environment, the product will not be loose and separated, and there is no sharp edge and stickiness to avoid damage. Primary protection: Primary protection provides the surface protection of the product, forming a light and protective appearance around the product, thus achieving the purposes of dust-proof, oil-proof, moisture-proof, water-proof and theft-proof. It is particularly important to make the packaged goods uniformly stressed by wrapping film packaging, so as to avoid damage caused by uneven stress, which can not be done by traditional packaging methods (bundling, packaging, tape packaging, etc.). Compression fixity: the product is wrapped by the retraction force of the wrapping film after stretching, forming a compact unit whole that does not occupy space, so that the product trays are tightly wrapped together, which can effectively prevent the product from dislocation and movement during transportation, and at the same time, save costs: the use of plastic wrap for product packaging can effectively reduce the use cost. The packaging film is only about 65,438+05% of the original box packaging, about 35% of the heat shrinkable film and about 50% of the carton packaging. At the same time, it can reduce the labor intensity of workers and improve the packaging efficiency and packaging grade. To sum up, the application fields of stretched film are very extensive, but many domestic fields have not been involved, and many involved fields have not been widely used. With the expansion of application fields, the amount of stretched film will increase greatly, and its market potential is immeasurable. Therefore, it is necessary for us to vigorously promote the production and application of stretched films. Introduction of PE Stretched Film and Stretched Film PE Stretched film (also known as winding film) has high tensile strength, tear resistance and good self-adhesion, so it can wrap objects into a whole and prevent them from scattering during transportation. The film has excellent transparency. The wrapped object is beautiful and generous, which can make the object waterproof, dustproof and damage-proof. The film is widely used in pallet packaging of goods, such as electronics, building materials, chemicals, metal products, auto parts, wires and cables, daily necessities, food, paper making and other industries. Specification: 500mm machine film, 300 mm manual film, 350 mm, 450 mm, 500 mm thickness 15um-50um. Various specifications can be cut online. Viscosity is divided into single-sided adhesion and double-sided adhesion. Products are divided into two series: hand-wound film and machine-wound film. Features: the product has good cushioning strength, puncture resistance and tear resistance, thin thickness and good cost performance. It has high tensile strength, tear strength, transparency and good retraction force, the pre-stretching ratio is 400%, and it can be assembled, waterproof, dustproof, anti-scattering and anti-theft. Usage: used for pallet packaging and other winding packaging, widely used in foreign trade export, bottle and can making, paper making, hardware and electrical appliances, plastics, chemical industry, building materials, agricultural products, food and other industries. PE winding film is an industrial film packaging product with high tensile strength, high elongation, good self-adhesion and high transparency. It can be used for manual film winding and machine film winding, and can be widely used for centralized packaging of various goods. PE cling film is mainly made of several different brands of polyurethane resin, which has puncture resistance, super strength and high performance. It wraps the goods stacked on the pallet, making the packaging more stable and tidy and super waterproof. Widely used in foreign trade export, paper making, hardware, plastics and chemicals, building materials, food, medicine and other industries. PE stretched film: LLDPE stretched film is made of high-quality LLDPE as substrate, adding high-quality tackifier, heating, extruding, casting and cooling by cooling roller. It has the advantages of strong toughness, high elasticity, tear resistance, high viscosity, thin thickness, cold resistance, heat resistance, pressure resistance, dustproof, waterproof, single-sided bonding, double-sided bonding and so on, and can be used. PE slit laminating: It is made of high-quality LLDPE as the base material, adding high-quality tackifier, heating, extruding, casting and cooling by a cooling roller. It has the advantages of strong toughness, high elasticity, tear resistance, high viscosity, thin thickness, cold resistance, heat resistance, pressure resistance, dustproof, waterproof, single-sided bonding and double-sided bonding, and can save materials and labor when used. The principle of film rolling With the help of the super-strong winding force and flexibility of the film, the product is tightly and firmly bound into a unit, so that the scattered small pieces become a whole. Even in unfavorable environment, the product will not be loosely separated, without sharp edges and stickiness, and will not cause damage. Winding film can be divided into: PE winding film, PE winding film, PE stretch winding film, LLDPE stretch winding film, PE slit winding film and so on.