Analysis of stretch packaging technology

Stretch packaging is a new packaging technology adopted since the 1970s. It is developed from shrink packaging. Stretch packaging is a kind of packaging method that relies on a mechanical device to stretch and wrap the elastic film around the packaged object at room temperature, and then seals the ends. Since the stretch packaging does not require heating, the energy consumption is only 1/20 of the shrink packaging. Stretch packaging can be used to bundle individual items, and can also be used for collective packaging such as pallet packaging instead of small containers. Because it can reduce the cost of bulk cargo transportation and packaging by more than 30%, it is widely used in the packaging of various products such as hardware, minerals, chemicals, medicine, food, machinery, etc .; in the field of warehouse storage, it is also used abroad Stretch wrap film tray packaging for three-dimensional storage and transportation to save space and occupy space.

1 Stretched film

Stretched film (also called stretch film) does not need to be heat-shrinked during the packaging process. It is suitable for the packaging of certain products that cannot be heated, which is conducive to saving energy, facilitating container transportation, and reducing transportation costs.

1) Performance index of stretch packaging

The plastic film used for stretching must have certain self-adhesiveness, toughness, stretch rate, stress retention, required stretch range, optical properties and heat sealing properties.

â‘ Self-adhesive

The adhesion between the films after contact between the film and the package can be tightened without loosening during the stretching and wrapping process. Self-adhesiveness is affected by many external factors. Such as humidity, dust and contaminants. There are two main methods for obtaining a self-adhesive film. One is to process the film with a smooth and shiny surface; the second is to use additives to increase the adhesion, so that the surface of the film has a wetting effect, thereby improving the adhesion.

â‘¡ toughness

Toughness is the comprehensive property of the film against puncture and tear resistance. The tear resistance refers only to the degree of tear resistance of the film after being stretched and pierced. The dangerous value of the degree of tear resistance must be horizontal, that is, perpendicular to the machine operation direction, because tearing in this direction will make the package loose, even if the longitudinal tear occurs, the package can still remain strong.

â‘¢ Stretching

Stretching is the ability of a film to elastically stretch after being pulled. Increased longitudinal stretch will eventually make the film thinner and shorter in width. Although longitudinal stretching is beneficial, excessive stretching is often undesirable. Because this will make the film thinner and easier to tear, while increasing the tension applied to the package.

â‘£ Stress retention

Stress retention refers to the degree to which the tension applied to the film can be maintained during the stretch wrapping process.

â‘¤ Allowable stretching

Permissible stretching refers to the maximum stretching that can be applied to maintain various required characteristics under certain application conditions. The allowable stretch varies with different uses. The larger the permissible stretching, the less the film usage and the lower the packaging cost.

In addition to the above indicators, optical performance and heat sealing performance are important for some special packages.

What kind of stretch film is used and how thick the stretch film is depends on the type and shape of the product. Commodities are strong, high strength, and heavy weight. Plastic films with high strength, especially tensile strength and tear resistance, and thick films (such as 50 Î¼m thick) should be selected. The stretch rate can also be larger, such as 150 % ï½ž 170%. For fragile products, food, and light weight, the opposite is true. Ordinary stretch films with a thickness of 15 to 30 Î¼m and a stretch rate of 130% should be used.

2) Commonly used stretch film

Commonly used stretch film materials are PVC (polyvinyl chloride), LDPE (low density polyethylene), EVA (ethylene-vinyl acetate copolymer) and LLDPE (linear low density polyethylene).

Polyvinyl chloride film has the lowest cost, the earliest use, good self-adhesion, good stretchability and toughness, but poor stress retention. Low-density polyethylene has a low elongation and poor self-adhesion and puncture resistance. The ethylene-vinyl acetate copolymer film has good self-adhesiveness, stretchability and toughness, and stress retention. The linear low-density polyethylene film has the best comprehensive characteristics.

3) Stretching form of pallet mechanism packaging

The packaging of the stretched film must be stretched. The stretching forms of the mechanical packaging of the pallet include direct stretching and pre-stretching (as shown in Figure 1, where (a) represents direct stretching and (b) represents pre-stretching ).

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

There are two types of pre-stretching, one is roll pre-stretching, and the other is electric stretching.

Pre-stretching is done by two rolls next to the film roll. The two rollers pre-stretched by the roller are connected by a gear unit, and the stretching ratio can be different according to the gear ratio. The pulling force is generated by the turntable. Since the stretching is generated in a short distance, the friction between the roller and the film is large, so the film width does not shrink, and the original puncture performance of the film is also maintained. There is no stretching during actual winding, which reduces the breakage caused by sharp edges or corners. This pre-stretching can increase the stretching ratio 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. The stretching is completely independent of the rotation of the tray. Therefore, it is more adaptable, and light, heavy, and irregular goods are suitable. Due to the low tension during packaging, this method has a pre-stretch ratio of up to 300%, which greatly saves materials and reduces costs. Suitable for film thickness 15Î¼m ï½ž 24Î¼m. [next]

2 Main use forms of stretch packaging

sealed package. This kind of packaging is similar to shrink film packaging. The film wraps the tray completely around the tray, and then two hot claws heat seal the film at both ends. This is the earliest form of use of stretch film, and thus more packaging forms have been developed.

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 has its limitations when used, and the suitable film thickness is 17Î¼m ~ 35Î¼m;

Packed by hand. This kind of packaging is the simplest kind of wrapping film packaging. The film is mounted on a rack or is held by hand, and is rotated by the tray or the film around the tray. It is mainly used for repacking the damaged pallets and ordinary pallet packaging. This packaging speed is extremely slow, the suitable film thickness is 15Î¼m ~ 20Î¼m;

Pallet mechanical packaging. This is the most common and widest form of mechanical packaging. The tray is rotated or the film is rotated around the tray. The film is fixed on the bracket and can be moved up and down. This kind of packaging capacity is very large, about 15 to 18 trays per hour. Suitable film thickness is about 15Î¼m ï½ž 25Î¼m;

Horizontal mechanical packaging. Unlike other packaging, the film is turned around the item, suitable for long goods packaging, such as carpet, board, fiberboard, heterogeneous materials, etc .;

Paper tube packaging. This is one of the latest uses of stretch film. It is better to use stretch film packaging than old-fashioned paper tube packaging. Suitable film thickness is 30Î¼m ï½ž 120Î¼m;

The packaging of small items. This is the latest packaging form of stretch film, which not only reduces the consumption of materials, but also reduces the storage space of pallets. In foreign countries, this kind of packaging was originally introduced in 1984. Just one year later, many such packages appeared on the market. The packaging form has great potential. Suitable for film thickness 15 ï½ž 30Î¼m; tube and cable packaging. This is an example of the application of stretch film in special fields. The packaging equipment is installed at the end of the production line. The fully automatic stretch film can replace the tape to bind the material and also play a protective role. The applicable thickness is 15 ï½ž 30Î¼m.

3 Stretch packaging process

Stretch packaging methods can be divided into sales packaging methods and transportation packaging methods according to their uses. Different types of products use different packaging machinery, so there are many different packaging methods.

1) Sales and packaging

According to the degree of automation, it can be divided into three methods: manual stretch packaging, semi-automatic stretch packaging and fully automated stretch packaging.

â‘ Manual operation method

Generally, the packaged goods are manually placed in a shallow tray, especially crisp and soft products and multi-packed scattered products, which are easily damaged if the shallow tray is not used. However, some products (such as gadgets, etc.) themselves have a certain degree of rigidity and firmness, so you don't need a shallow dish.

â‘¡ Semi-automatic operation

Mechanizing or automating part of the processes in the packaging work can save manpower and improve production efficiency. The packaging form is mainly packaging with shallow trays.

An important part of packaging is wrapping and stretching. To mechanize these processes, the complexity of the machine structure must increase, the price must also increase, but the versatility is weakened. Although it can save a part of manpower and increase the output (the productivity is generally 15-20 pieces / min), but the overall calculation may not be cost-effective. If only the supply, output and heat sealing parts are automated, the packaging speed will not increase much. Therefore, semi-automatic operation is used less in practical applications.

â‘¢ Fully automatic operation

Although manual operation has many advantages, the labor intensity of workers is large, the movement is single and frequent, and the productivity is low and the cost is high. Therefore, manual operation has promoted the rapid development of fully automatic packaging.

At present, the packaging technology used in the automatic stretch packaging machine can be roughly divided into two types: the push-up operation method, which is mainly used for sales packaging; the continuous linear operation method, because the packaging volume is large and the product is not stable enough, Therefore, the use is subject to certain restrictions.

2) Transportation and packaging

Stretch packaging is used for transportation. It is lighter in weight and lower in cost than traditional wooden boxes and corrugated boxes, so it is widely used. This kind of packaging is mostly used for pallet assembly packaging, and sometimes for pallet-less assembly packaging.

According to the different film formats, there are two methods of stretch packaging:

â‘ Whole film packaging method

It is used to package the whole film with the same height or wider as the goods. This method is suitable for packing goods with a square shape, and has the advantages of high efficiency and economy. For example, the use of ordinary ships to load the packaging of exported goods, heavy and unstable goods, and occasions requiring high packaging efficiency per unit time. The disadvantage is the use of multiple width films.

â‘¡ Narrow film wrapping method

The width of the film is generally 50cm to 70cm. During packaging, the film is wrapped in a spiral form from top to bottom until the wrapping is completed, and about one third of the overlap between the two circles. This method is suitable for goods with high or inconsistent packing, and irregular or light-weight goods. For products of different sizes, only one type of stretch film is needed, so the cost is lower.

According to different stretch packaging equipment, there are two kinds of stretch packaging technology methods:

Rotary stretch packaging technology. Place the goods on a rotatable platform, stick the film ends to the goods, then rotate the platform, stretch the film while rotating to wrap it, cut the film after a few weeks, and stick the ends to the goods. The equipment used in this method is semi-automatic, that is, the film is glued at the beginning and cut off at the end.

Mobile stretch packaging process. Put the goods on the conveyor belt, pushed forward by the feeder or roller table, there is a gantry-style shelf in the packaging position, two film reels stand upright on both sides of the conveyor belt, and are equipped with friction stretching rollers. When starting packaging, first heat seal the ends of the two rolls of film on the goods. When the goods move forward, wrap the film on it and stretch the film at the same time. After reaching a certain position, use the sealer to gather the film Cut off and stick the end to the back of the goods.

Rotary and mobile stretch packaging equipment are available in automatic and semi-automatic types. In semi-automatic equipment, the film is bonded at the beginning and cut off at the end, all by manual operation.

Anti-Slip Paper

Anti Slip Paper,Anti Skid Paper,Anti Slip Pallet Paper,Anti Slip Kraft Paper

JINAN XINSHUNYUAN PACKING CO., LTD , https://www.xsy-packaging.com