Analysis on stretch packaging technology

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 packaging method that relies on mechanical devices to stretch and tightly wrap the elastic film around the package at room temperature, and seal at its end. Since stretch packaging does not need to be heated, the energy consumption is only 1/20 of that of shrink packaging. Stretch packaging (b) aluminum alloy cable fault connection scheme, that is, at present, when connecting aluminum alloy cables in China, aluminum connectors such as copper aluminum transition terminals originally used for aluminum cables and aluminum alloy connectors that are not consistent with the cable performance are used as connection schemes, which can be used to pack single items, and can also be used for collective packaging such as pallet packaging to replace small containers. Because it can reduce the transportation and packaging cost of bulk goods by more than 30%, it is widely used in the whole package of hardware, minerals, chemical industry, medicine, food, machinery and other products; In the field of warehouse storage, foreign countries also use stretch wrapped film pallet packaging for three-dimensional storage and transportation to save space and land

1 stretched film

stretched film (also known as wrapping film) does not need heat shrinkage treatment in the packaging process. It is suitable for the packaging of some 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-adhesive, toughness, stretching rate, stress retention, required stretching range, optical properties and heat sealing properties

impact testing machine low temperature tank refrigeration system the console of the compressor has capacity regulating valve, ammonia pressure gauge, oil pressure gauge ① self-adhesive

the adhesion between films after contact can make the packaged products firm without loosening during the stretching and winding process and after wrapping. Self viscosity is affected by many external factors. Such as humidity, dust and pollutants. There are two main methods to obtain self-adhesive films. One is to process films with smooth and glossy surface; The second is to use additives that increase adhesion to produce a wetting effect on the surface of the film, so as to improve the 3.5.1. The bricks of Mu15, mu20 and mu25 can be used in foundations and other buildings; Mu10 bricks can only be used for building adhesion above the damp proof course

② toughness

toughness is the comprehensive property of film puncture resistance and tear resistance. Tear resistance only refers to the tear resistance of the film after tension and when it is punctured. The dangerous value of tear resistance must be horizontal, that is, vertical to the machine operation direction, because tearing in this direction will make the package loose. Even if tearing occurs longitudinally, the package can still remain firm

③ stretching

stretching is the ability of the film to produce elastic elongation after tension. The increase of longitudinal tension will eventually make the film thinner and shorter in width. Although longitudinal stretching is beneficial, over stretching is often undesirable. Because this will make the film thin and easy to tear, and increase the tension applied to the package

④ stress retention

stress retention refers to the extent to which the tension applied to the film can be maintained during the stretching and wrapping process

⑤ allowable tension

allowable tension refers to the maximum tension that can be applied to maintain various necessary characteristics under the condition of certain use. Allowable stretching varies with different applications. The larger the allowable stretch is, the less the film is used, and the lower the packaging cost is

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

what kind of wrapping film to choose and how thick the stretching film to use should be determined according to the type and shape of the commodity. The commodity is strong, high-strength and heavy. Plastic films with high strength, especially tensile strength and tear resistance, and films with large thickness (such as 50 m thick) should be selected. The tensile rate can also be a little higher, such as 150% - 170%. For fragile products, food and light weight, on the contrary, ordinary stretched film with a thickness of 15 ~ 30 m and a stretching rate of 130% should be selected

2) the commonly used stretch film must be operated in strict accordance with the experimental methods in the operating instructions and experimental standards distributed by the company.

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

PVC film has the lowest cost, the earliest use, good self-adhesive, good tensile and toughness, but poor stress retention. Low density polyethylene has low tensile ratio and poor self-adhesive and puncture resistance. Ethylene vinyl acetate copolymer film has good self adhesion, tensile property, toughness and stress retention. Linear low density polyethylene film has the best comprehensive characteristics

3) stretching form of pallet mechanism packaging

the packaging of stretching film must be stretched. The stretching form of pallet mechanical packaging includes direct stretching and pre stretching (as shown in Figure 1, in which (a) represents direct stretching, (b) represents pre stretching)

direct stretching is to complete stretching between the tray and the film. This stretching method has a low stretching ratio (about 15% - 20%), if the stretching ratio exceeds 55% - 60%, which exceeds the original yield point of the film, the film width is also reduced, the puncture performance is also lost, and the film is easy to break. And at 60% tensile rate, the tensile force is still large. For light goods, it is likely to deform the goods

there are two kinds of pre stretching, one is roller pre stretching, and the other is electric stretching

pre stretching is completed by two rolls second only to the film roll. The two pre stretched rollers are connected by gear units, and the stretching ratio can vary according to the gear ratio. The tension is generated by the turntable. As the stretching occurs in a short distance, the friction between the roll and the film is large, so the film width does not shrink, and the original puncture performance of the film is maintained. There is no stretching during actual winding, which reduces the fracture 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, except that the two rollers are driven by electricity, and the stretching is completely independent of the rotation of the pallet. Therefore, it has stronger adaptability. Light, heavy and irregular goods are applicable. 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 film thickness of 15 m ~ 24 M