The hottest shrink packaging is widely used in sal

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Shrinkpacking is widely used in sales and transportation packaging. Shrinkpacking is a packaging method that wraps products or packages with shrinkable film, and then heats the film to shrink and wrap the products or packages tightly. Shrink packaging is a promising packaging technology, which is widely used in sales packaging and transportation packaging

I. main features

1. Good protective performance, transparent and shiny, low processing cost and light weight.

2. Shrink packaging can cling to the package, and can bind and fix the items evenly, eliminating the cumbersome operation of binding materials such as packing belts

3 ﹐ shrink packaging can make loose items tightly bound together and reduce the occupied space. Because the plastic film has good toughness and cushioning performance, and the contents are fully fixed, it can effectively prevent the impact of impact and vibration on the contents, and the packaging is compact and not easy to be damaged.

4. Shrink packaging can be used for the collective packaging of pallets, which can tightly wrap items with pallets, save packaging costs that can provide plastic modification, mass production of functional materials and other technical support for plastic enterprises in Dongguan, and effectively protect products.

5 shrink packaging can realize mechanized packaging, which is convenient for matching with the production line. The packaging efficiency is greatly improved, and the packaging equipment is simple, stable and versatile.

II. Material selection

shrink film is the most important kind of shrink packaging materials. According to the characteristics that thermoplastic will recover under heating conditions, in the process of making film from plastic raw materials, it is heated and stretched in advance, and then cooled to make shrinkage film. The manufacturing methods include the secondary stretching method of making flake films and then stretching along the longitudinal and transverse axes respectively, the primary stretching method of stretching in two directions at the same time, and the method of making cylindrical films first for secondary stretching or primary stretching.

at present, the most commonly used shrink film materials are PVC, polyethylene and polypropylene, followed by vinylidene chloride, polyester, polystyrene, chlorinated rubber film and nylon resin. The shrinkage rate, shrinkage ratio, shrinkage tension, shrinkage temperature and heat sealing property of the material are mainly considered when selecting. PVC has a relatively low shrinkage temperature and a wide range, with a shrinkage temperature of 40 ~ 160 ℃. It has fast thermal shrinkage and good working performance, but its impact strength is low, which is not conducive to sealed packaging; Polyethylene has high impact strength, low price, firm sealing, and good packaging effect for equipment. In addition, the recently appeared ethylene vinyl acetate copolymer shrink film has high impact strength, high transparency, low softening point, good heat sealing performance, small shrinkage tension, and is not easy to be damaged. It is suitable for the packaging of equipment with protrusions and special-shaped equipment. The main technical indicators of shrink film are: shrinkage rate and shrinkage ratio, shrinkage tension, shrinkage temperature and heat sealing. The shrinkage rate includes longitudinal and transverse aspects: the test method is to measure the original length L1 of the film, then immerse it in glycerin at 120 ℃ for 1 ~ 2S, and then cool it with water; Measured length L2, then: shrinkage (%) = (L1-L2)/l1 × 100% where: L1 - length of film before shrinkage: L2 - length of film after shrinkage

at present, most shrink films used for packaging require a shrinkage rate of 5 in both vertical and horizontal directions. Food contact materials using these materials or additives will become about 0% of back-to-back products; The film used for sealing at the special bottle cap also requires that the one-way shrinkage rate is 25% - 50%. If the shrinkage rates in the vertical and horizontal directions are different, the ratio is called the shrinkage ratio The lower the shrinkage temperature, the better, and the less adverse effects on items (especially fresh food, fiber products, etc.).

because the wrapped articles need to be sealed on both sides or three sides before entering the heat shrinking tunnel for shrinkage, the heat sealing performance of the film should also be good, and there should be sufficient heat sealing strength.

after repeated tests and comparison and identification, we selected polyethylene (PE) and polyvinyl chloride (PVC) transparent shrink plastic films as shrink packaging materials.

III. method selection

the shrink packaging process is generally carried out in two steps. The first is pre packaging, which uses shrink film to pack the products and heat seal the necessary openings and seams; Then there is heat shrinking, and the pre packaged products are heated in the heat shrinking equipment.

1. Pre packaging operation. During pre packaging, the film size should be 10% - 20% larger than the equipment size. If the size is too small, the filling is inconvenient, and the shrinkage tension is too large, which may tear the film; The size is too large, and the shrinkage tension is not enough, and the package is not tight or flat

the shrinkage film used can be determined according to the size, weight and required shrinkage tension of the equipment. There are three shrink packaging methods:

① open at both ends: if a cylindrical film is used, the equipment can be pushed into the cylinder with the help of a chute; If flat film is used, two rolls of flat film are required. After the previous package is sealed and cut, the two films are sealed, and then the product is pushed to the upright film by machine or manually. After it is in place, the sealing and cutting mechanism falls, and the other side of the equipment is heat sealed and cut at the same time. After heat shrinkage, both ends of the package shrink to form an oval opening. ② four side sealed type: wrap the product around (when using flat film) or at both ends (when using cylindrical film). It is used for equipment packaging requiring good sealing.

L-shaped sealing method can be adopted for using half folded film. This method is to fold the film in half with a reel, pull the film out of a certain length and place it in a horizontal position, prop up the open end with a mechanism or manually, and push the equipment to the crease. Before that, a transverse seam is left after the last heat seal is cut, and there are two seams plus the crease, so there is no need to seal it again. Then use an "L" type heat seal cutter to press down and heat seal and cut from the connection between the rear of the equipment and the film, and complete one horizontal seam and one longitudinal seam at a time. Easy to operate, consignment or semi-automatic; Pillow bag type can be used for single roll flat film. This method is to use a single roll of flat film, first seal the longitudinal seam to form a barrel, wrap the equipment in it, then seal the transverse seam and cut it into pillow packaging.

after pre sealing with four side sealing method, the residual air inside will expand during thermal shrinkage, making it difficult for the film to shrink and affecting the packaging quality. Therefore, a bayonet is often installed next to the sealer. During heat sealing, the bayonet pierces the vent hole on the film. It is very important to seal it after heat shrinkage. The small holes at the seams can often be closed by themselves

③ open end: first make a large bag with square bottom with film, and then put this bag on the tray of stacking equipment from top to bottom, and then carry out heat shrinkage with the tray.

automatic zeroing: after computer-controlled experimental instructions, pallet shrink packaging is a method that has developed rapidly in transportation packaging. The main features are: the products can be firmly packed in a certain number of units, will not be loose during transportation, and can be stacked in the open air.

2. Heat shrink operation. The equipment used for heat shrinking is called heat shrinking channel (also known as heat shrinking tunnel), which is composed of conveyor belt and heating chamber. The heat shrinking process is: put the pre packaged parts on the conveyor belt, the conveyor belt runs at the specified speed, send it to the heating chamber, and use hot air to blow it to the package for heating; Leave the heating chamber after heat shrinking, and remove it from the conveyor belt after natural cooling

when the volume is large and the heat shrinkage temperature is high, the cooling fan is often used to accelerate the cooling after leaving the heating chamber.

after comparing the above methods, the process we selected is:

with a thickness of 0 25mm PE film or PVC plate (sheet) plastic container - → loading - → put it into the heat shrinking machine for heating - → shrinking - → sealing - → cooling - → inspection - → labeling.

IV. machine selection

there are many types of shrink packaging machines at home and abroad, of which small shrink packaging machines are mainly used to package small parts, and pillow bag packaging is mostly used; L-type sealing packaging machine and plate heat sealing packaging machine can be suitable for packaging of various sizes; The large shrink packaging machine is mainly used for the collective packaging of corrugated boxes and products packed in large bags. After repeated investigation and test, we chose rs600/400 dual-purpose heat shrinkable packaging machine.

this machine is used for sealing and packaging of large parts and complete sets of equipment. It is suitable for heat shrinkable packaging of polyethylene (PE) 5 and polyvinyl chloride (PVC). The machine is composed of furnace body, cold box, heating and power supply. With the characteristics of long furnace path, sufficient heat, large power and fast cooling, it is an ideal packaging equipment for shrinking various bulky and heavy equipment

the machine uses quartz tube as the heat source. Up and down pressure, constant temperature room temperature to 250 ℃, suitable for film shrinkage of various thicknesses. The transmission adopts electromagnetic frequency modulation variable-speed motor, which has great power and stable operation. The upper box adopts a flip type, and the bottom plate of the lower box can be pulled out to one side for maintenance and cleaning. A vortex fan is installed in the drying channel to ensure uniform heat in the drying channel. The export cooling box is designed with the characteristics that the film is hot and cold to ensure the quality of packaging. Now this machine is mainly used to set the thickness to 0 12mm、0. 18mm and 1000mm wide polyethylene (PE) material packaging ordnance maintenance equipment

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