Shrink packaging technology

Shrink packaging A method of wrapping a product or package with a shrink film and then heating to shrink the film to wrap the product or package. Shrink wrap is a very promising packaging technology that is widely used in sales packaging and transportation packaging.
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First, the main features

1. Good protection performance, transparent gloss, low processing cost, light weight. 
2. The shrink wrap can closely adhere to the package and can evenly bind and fix the items, eliminating the cumbersome operation of tying materials such as packing tapes. 
3. Shrink packaging allows tightly packed items to shrink and take up less space. Because the plastic film has good toughness and cushioning properties, the contents are fully fixed, so it can effectively prevent the impact of shock and vibration on the contents, and the package is compact and not easily damaged. 
4. Shrink packaging can be used for the collection and packaging of pallets. It can tightly pack articles and trays, save packaging costs, and effectively protect the product. 
5. Shrink packaging can realize mechanized packaging, which is convenient for supporting the production line. The packaging efficiency is greatly improved, the packaging equipment is simple, the work is stable, and the versatility is good.
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Second, the material selection

Shrink film is the main type of shrink wrap. According to the characteristics that the thermoplastic plastic is restored under the heating conditions, during the process of forming the film from the plastic raw material, it is heated and stretched in advance and cooled to make a shrink film. The manufacturing method includes a secondary film stretching method in which a sheet-shaped film is formed, and then stretched along the longitudinal axis and the transverse axis, and a primary stretching method simultaneously performing stretching in two directions. Stretch or one-stretch method.

Currently used more shrink film material is: polyvinyl chloride, polyethylene and polypropylene, followed by vinylidene chloride, polyester, polystyrene, chlorinated rubber film and nylon resin. The main considerations in selection are shrinkage, shrinkage ratio, shrinkage tension, shrinkage temperature, and heat sealability. PVC shrink temperature is relatively low and wide range, shrinkage temperature is 40 ~ 160 °C, thermal shrinkage, good workability, but low impact strength, is not conducive to sealed packaging; polyethylene impact strength, low price, sealing Strong, good for packaging equipment. In addition, the recent ethylene vinyl acetate copolymer shrink film has high impact strength, high transparency, low softening point, good heat sealing performance, small shrink tension, and unbreakable packaging. It is suitable for the packaging of protruding parts of equipment and special-shaped equipment. The main technical indicators of shrink film are: shrinkage ratio and shrinkage ratio, shrink tension, shrinkage temperature and heat sealability. Shrinkage includes longitudinal and transverse aspects: The test method is to first measure the original length of the film L1, then immersed in 120 °C glycerin 1 ~ 2s, and then cooled with water; measured length L2, then: Shrinkage (% ) = (L1-L2)/L1 x 100% where: L1 - the length of the film before shrinking: L2 - the length of the film after shrinking. 

At present, the shrinkage film used for packaging mostly requires a shrinkage of about 50% in both longitudinal and transverse directions; a special film for sealing at the bottle cap also requires a one-way shrinkage rate of 25% to 50%, both horizontally and vertically. The shrinkage rate is not equal, and the ratio is called shrinkage ratio. The lower the shrinkage temperature, the better, and the adverse effects on articles (especially fresh foods, fiber products, etc.) are less. Because the packaged articles need to be sealed on both sides or sides before entering the heat-shrink tunnel for shrinkage, the heat-sealability of the film should also be good, and sufficient heat-seal strength is required. After repeated trials and comparisons, we chose polyethylene (PE) and polyvinyl chloride (PVT) transparent shrink plastic films as shrink packaging materials.
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Third, method selection

Shrink packaging operations are generally performed in two steps. The first is pre-packaging, packaging the product with a shrink film, heat-sealing the necessary mouth and seams, and then heat-shrinking to heat the pre-packaged product in a heat-shrinking device. 
1. Pre-packaged work. When pre-packaged, the film size should be 10% to 20% larger than the size of the device. If the size is too small, the filling is inconvenient, and the shrinkage tension is too large, and the film may be punctured; if the size is too large, the shrinkage tension is not enough and the package is not tight or smooth. The maximum shrink film used can be determined based on the size and weight of the device and the required contraction tension.
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There are three ways to shrink packaging:
1 Open at both ends: If you use a tubular film, you can use the slide slot to push the device into the tube; if you use a flat film, you need to roll up and down two flat films. After the previous package has been cut off and sealed, the two films are sealed and the product is then manually pushed into the upright film by machine or hand. After being in place, the closure mechanism falls, and the other side of the device is heat sealed and simultaneously sealed. shear. After heat shrinking, both ends of the package shrink to form an oval opening. 
2 Sealed on all sides: Wrap around the product (when flat film is used) or both ends (when using tube film). For equipment packaging that requires good sealing. The L-type sealing method can be used for the folded film. In this method, the film is folded on the roll, the film is pulled out to a certain length in a horizontal position, the open end is stretched by means of a mechanism or by hand, and the equipment is pushed to the crease. Before this, the last heat-sealed cut is left. The next transverse joint, plus a total of two seams, does not need to be sealed. Then use a "L" type heat-sealing shear to press down from the back of the equipment product and the film joint and heat-seal the shear seam to complete one longitudinal joint at a time. Easy to operate, consignment or semi-automatic can be; with a single roll flat film can be pillow-shaped bag. This method is to use a single roll of flat film, the first longitudinal seam to form a tube, the equipment wrapped in it, and then sealed transverse joints and cut into a pillow-type packaging. After the four-side sealing method is pre-sealed, the internal residual air expands during heat shrinkage, making the film shrink difficult and affecting the quality of packaging. Therefore, the puncture needle is often installed near the sealing device, and the puncture needle punctures the bleed hole on the film during heat sealing. After the heat shrinkage, the pores at the sealing seam can often be closed by themselves. 
3 Open at one end: use a film to make a big bag on the bottom, and then put the bag on the tray of the stacking equipment from top to bottom, and then bring the tray to heat shrink. Pallet shrink packaging is a fast growing method in transport packaging. The main features are: Products can be packed in a certain number of units firmly, not loose in the transport, can be stacked in the open air. 
2. Heat shrinking operation. The equipment used for heat shrinking is called a heat shrink tunnel (also called heat shrink tunnel) and consists of a conveyor belt and a heating chamber. The heat shrinking process is: placing the prepackage on the conveyor belt, the conveyor belt running at the specified speed, sending it to the heating chamber, blowing hot air to the package for heating; leaving the heating chamber after the heat shrinking, cooling naturally, from the conveyor belt Remove it. When the volume is large and the heat-shrinkage temperature is high, the cooling fan is often accelerated after leaving the heating chamber. After comparing the above methods, the process we chose was: using a 0.25mm thick PE film or PVC plate (sheet) plastic to make the container -> loading material -> heat shrinking machine heating - - shrinking - - sealing - cooling —→Examination—→Tag.
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Fourth, machine selection

There are many kinds of shrink packaging machines at home and abroad. Small shrink packaging machines are mainly used to pack small parts and components, and are mostly used for pillow-shaped bag packaging. L-type sealing packaging machines and plate heat sealing packaging machines are suitable for various sizes of packaging; Shrink packaging machines are mainly used for corrugated cartons and large bags of product packaging. After repeated investigation and research and repeated trials, we chose the RS600/400 dual-use heat shrink packaging machine. The machine is used for the sealed packaging of large parts and packages. It is suitable for shrink packaging of polyethylene (PE) 5 and polyvinyl chloride (PVC) materials. The machine is composed of furnace body, cold box, heat and power supply. With the characteristics of long tunnel, sufficient heat, large power and fast cooling, it is an ideal packaging equipment for shrinking various large and heavy equipment. The machine uses a quartz tube attack as a source of heat. Adjust the pressure from top to bottom, constant temperature from room temperature to 250°C, suitable for shrinkage of films with different thicknesses. Transmission using electromagnetic frequency variable speed motor, great power, smooth operation. The upper box adopts a flip type, and the lower box bottom plate can be pulled out to one side for maintenance and cleaning. A vortex fan is installed in the drying tunnel to ensure uniform heat in the drying tunnel. The outlet cooling box is designed with the characteristics of thin film that is hot and cold, ensuring the quality of the packaging. 
Now, the machine is mainly used for packing ordnance maintenance equipment of polyethylene (PE) material with a thickness of 0.12mm, 0.18mm and a width of 1000mm.