Basic knowledge of stretch film

Stretch film, is the earliest in China to use PVC as the base material, DOA as the plasticizer and self-adhesive function to produce PVC stretch film. Due to environmental problems, high cost (large relative PE ratio, less unit packaging area), poor stretchability and other reasons, when the domestic production of PE stretch film began in 1994 to 1995, it was gradually eliminated. PE stretch film was first made of EVA as self-adhesive material, but its cost is high and tasteful. Later, PIB and VLDPE were used as self-adhesive materials. The base material is now LLDPE, including C4, C6, C8 and metallocene PE. (MPE).

In the early days, LLDPE stretched films were mostly blown films, and developed from single-layer to two-layer and three-layer; now, LLDPE stretched films are mainly produced by casting method. It has the advantages of uniformity and high transparency and can be applied to the requirements of high-magnification pre-stretching. Since single-layer casting cannot achieve single-sided adhesion, the application field is limited. The material selection of single-layer and double-layer casting is not as wide as that of three-layer casting, and the formula cost is also high, so the structure of three-layer co-extrusion is still ideal. A high-quality stretch film should have the characteristics of high transparency, high longitudinal elongation, high yield point, high transverse tear strength, and good puncture performance.

Production process conditions

Casting production is due to the long and narrow flow channel and fast flow speed. The temperature range of the melt is generally controlled at 250 ° C ~ 280 ° C, the temperature of the casting cooling roll is controlled at 20 ° C ~ 30 ° C, and the winding tension is low. Within 10kg, to facilitate the migration of the viscous agent and reduce the internal stress of the finished film.

Sticky control

Good viscosity makes the packaging film layers and layers outside the goods stick together to make the goods firm. There are two main ways to obtain the viscosity: one is to add PIB or its masterbatch to the polymer; the other is to blend VLDPE. PIB is a translucent viscous liquid. Direct addition requires special equipment or equipment modification. Generally, PIB masterbatch is used. There is a process for PIB to move out, which usually takes three days. In addition, it is also affected by temperature. When the temperature is high, the viscosity is strong; when the temperature is low, it is not too sticky, and the viscosity is greatly reduced after stretching. Therefore, it is best to store the finished film within a certain temperature range (recommended storage temperature is 15 ℃ ~ 25 ℃). Blending VLDPE, the viscosity is slightly poor, but there is no special requirement for the 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 when the temperature is lower than 15 ℃, the viscosity is slightly worse, and it can be The desired viscosity is achieved by adjusting the amount of LLDPE in the adhesive layer. This method is mostly used in three-layer co-extrusion.

Packaging form of stretch film

Sealed package

This type of packaging is similar to shrink wrap, where the film wraps the tray around the tray, and then two heat grippers heat seal the film at both ends together. This is the earliest form of wrapping film, and more packaging forms have been developed from this

Full-width packaging

This kind of packaging requires that the film width is enough to cover the tray, and the shape of the tray is regular, so it is suitable for use with a film thickness of 17-35μm

Hand-packed

This kind of packaging is the simplest kind of wrapping film packaging, the film is loaded on a rack or by hand, and the film is rotated by the tray or the film is rotated around the tray. Mainly used for repackaging after the packaged pallet is damaged, and ordinary pallet packaging. This kind of packaging speed is slow, and the suitable film thickness is 15-20 μm;

Stretch film wrapping machine packaging

This is one of the most common and widespread forms of mechanical packaging. The tray rotates or the film rotates around the tray. The film is fixed on the support and can move up and down. This packing capacity is very large, about 15 to 18 trays per hour. The suitable film thickness is about 15-25μm;

Horizontal mechanical packaging

Different from another packaging, the film revolves around the item, which is suitable for the packaging of long goods, such as carpets, boards, fiberboards, special-shaped materials, etc.;

Packaging of paper tubes

It’s one of the newest uses for stretch wrap, and it’s better than old-fashioned paper tube wraps. The suitable film thickness is 30～120μm;

Packaging of small items

This is the latest packaging form of wrapping film, which can not only reduce material consumption but also reduce the storage space of pallets. In foreign countries, this kind of packaging was first introduced in 1984. Just one year later, many such packaging appeared on the market. This packaging format has huge potential. Suitable for the film thickness of 15 ~ 30μm;

Packaging of tubes and cables

This is an example of the application of stretch film in a special field. The packaging equipment is installed at the end of the production line, and the fully automatic stretch film can not only replace the tape to bind the material, but also play a protective role. The applicable thickness is 15 to 30 μm.

Stretch form of pallet mechanism packaging

The packaging of the stretch film must be stretched, and the stretching forms of pallet mechanical packaging include direct stretching and pre-stretching. There are two types of pre-stretching, one is roller pre-stretching and the other is electric stretching.

Direct stretching is done between the tray and the film. This method has a low stretch ratio (about 15% to 20%). If the stretch ratio exceeds 55% to 60%, it exceeds the original yield point of the film, the film width is reduced, and the puncture performance is also lost. easy to break. And at a 60% stretch rate, the pulling force is still very large, and for light cargo, it is likely to deform the cargo.

Pre-stretching is done by two rolls. The two rollers of the roller pre-stretching are connected by a gear unit. The stretching ratio can be different according to the gear ratio. The pulling force is generated by the turntable. Since the stretching is generated at a short distance, the friction force between the roller and the film It is also large, so the film width does not shrink, and the original puncture performance of the film is also maintained. No stretching occurs during actual winding, reducing breakage due to sharp edges or corners, and this pre-stretching can increase the stretch ratio up to 110%.

The stretching mechanism of electric pre-stretching is the same as that of roller pre-stretching. The difference is that the two rollers are driven by electricity, and the stretching is completely independent of the rotation of the tray. Therefore, it is more adaptable and suitable for light, heavy and irregular goods. Due to the low tension during packaging, the pre-stretching ratio of this method is as high as 300%, which greatly saves materials and reduces costs. Suitable for the film thickness of 15 to 24 μm.

Features of stretch film

Unitization: This is one of the biggest features of stretch film packaging. With the film’s superior winding force and retractability.

Primary protection: The primary protection provides surface protection of the product, forming a very light and protective appearance around the product, so as to achieve the purpose of dustproof, oil-proof, moisture-proof, waterproof and anti-theft. It is particularly important that the wrapping film packaging makes the packaged items evenly stressed to avoid damage to the items caused by uneven stress, which cannot be achieved by traditional packaging methods (bundling, packaging, tape and another packaging).

Compression fixation: The product is wrapped and packaged by the retraction force of the stretched film to form a compact unit that does not take up space as a whole so that the pallets of the product are tightly wrapped together, which can effectively prevent the product during transportation. The mutual dislocation and movement, and the adjustable tensile force can make the hard products close to each other and make the soft products tighten, especially in the tobacco industry and textile industry, which has a unique packaging effect.

Cost saving: The use of wrapping film for product packaging can effectively reduce the cost of use. The use of wrapping film is only about 15% 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 the stretch film are very wide, and many fields in China have not yet been covered, and many fields that have been involved are not widely used. With the expansion of application fields, the amount of stretch film will be greatly increased. , its market potential is immeasurable. Therefore, it is necessary for us to vigorously promote the production and application of the stretch film.

Introduction of PE stretch film and stretch film

PE stretch film (also known as stretch film) has high tensile strength, tear strength, and good self-adhesion, so it can wrap the object into a whole and prevent it from falling off during transportation. The film has excellent transparency. The wrapped object is beautiful and elegant and can make the object waterproof, dustproof and damage-proof. The film is widely used in the packaging of cargo pallets, such as the packaging and packaging of electronics, building materials, chemicals, metal products, auto parts, wires and cables, daily necessities, food, paper and other industries. Specifications: machine film width 500mm, manual film width 300mm, 350mm, 450mm, 500mm, thickness 15um-50um. Various specifications can be cut online. The stickiness is divided into single-side sticky and double-side sticky. The products are divided into two series: hand-wound film and machine-use film.

Features: The product has good buffer 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%. It can be assembled, waterproof, dustproof, anti-scattering and anti-theft. Uses: used for pallet wrapping and another wrapping packaging, widely used in foreign trade export, bottle and can making, paper making, hardware and electrical appliances, plastics, chemicals, building materials, agricultural products, food and other industries.

PE stretch film is an industrial film product with high tensile strength, high elongation, good self-adhesion and high transparency. It can be used for manual wrapping film, and can also be used for machine wrapping film, which can be widely used in the centralized packaging of various goods.

PE wrapping film is mainly mixed and extruded from several different grades of polyolefin resin, which has puncture resistance, super strength and high performance. The strong waterproof effect is widely used in foreign trade export, papermaking, hardware, plastic chemical, building materials, food and pharmaceutical industries.

PE stretch wrapping film: LLDPE stretch wrapping film is made of high-quality LLDPE as the base material, with the addition of a high-quality tackifier, after heating, extrusion, casting and then cooling by a chill 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 and double-sided adhesive, etc., which can save materials and labor when using it. , Save time, widely used in papermaking, logistics, chemical industry, plastic raw materials, building materials, food, glass and so on.

Stretch film principle

The wrapping film uses the super strong wrapping force and retractability of the film to bundle the product into a unit compactly and fixedly. Even in unfavorable environments, the product has no looseness and separation and no sharp edges and stickiness, so as not to cause damage.