Square bottom bag There are generally 5 faces, front and back, two sides, and bottom. The unique structure of the square bottom bag determines that it is more convenient to package three-dimensional goods or square products. This kind of bag not only takes into account the packaging meaning of the plastic bag, but also fully expands the new packaging ideas, so it is now widely used in people's life production.
With the wide application of square bottom bags, many products have been extended, such as elastic bottom square bags, string square bottom bags, anti-rust square bottom bags, plant flower box square bottom bags, blue square bottom bags, printed square bottom Bags and so on. Square bottom bags are generally transparent, and can also be made into various colors, such as red, blue, etc., with a thickness ranging from 2 to 15 filaments, the most widely used thickness is 8 filaments and 10 filaments, and Most of them are produced from brand new materials, with the characteristics of good transparency, high tensile strength, non-toxic, odorless, and strong toughness.
The square bottom bag has been very popular in recent years, but because of the difficulty of forming the bottom corner, the bottom heat seal has a maximum of eight layers, and the bag making requirements are relatively high. The heat sealing bag is the last process in the production process of plastic flexible packaging. If waste products are generated, a lot of waste will be generated. Therefore, in the production process, we must do a good job in all aspects.
1. Heat sealing temperature
The heat-seal temperature range of the heat-seal material is a key factor affecting and controlling the quality of the heat-seal. The temperature resistance of the printed substrate is good, such as BOPET, BOPA, etc., increasing the heat sealing temperature can improve the production rate; the temperature resistance of the printing substrate is poor, such as BOPP, try to use a lower heat sealing temperature; and by increasing the pressure, reduce Production speed or select low temperature heat sealable material to ensure heat seal strength. If the heat sealing temperature is too high, it is easy to melt and extrude the heat sealing material at the heat sealing position, which reduces the thickness of the heat sealing and increases the thickness and unevenness of the welded edge.
2. Heat sealing pressure
The heat sealing pressure is provided by the pressure spring on the bag making machine. The size of the heat sealing pressure is related to the performance, thickness and heat sealing width of the composite film. The heat sealing material has a higher activation energy, and the temperature increase has a greater influence on the decrease of its viscosity. Therefore, the required heat sealing pressure is smaller, and the molten material at the heat sealing part should be prevented from being squeezed out to reduce the heat sealing effect. However, PE and PP are non-polar materials with extremely small activation energy and high required pressure, which is beneficial to the heat sealing strength and interface sealing.
3. Heat sealing speed
The heat sealing speed reflects the production efficiency of the bag making machine and is also an important factor affecting the strength and appearance of the heat sealing. The faster the heat-seal speed, the heat-seal temperature should be increased accordingly to ensure that the heat-seal strength and heat-seal state reach the best value; under the same heat-seal temperature and pressure, the slower the heat-seal speed, the more fully the heat-sealing material will fuse , More firm, but can not cause root-breaking phenomenon.
4. Cooling situation
The cooling water of the bag making machine is generally tap water or circulating water around 20 ° C. Excessively high water temperature, insufficient cold seal knife pressure, poor cooling water circulation, and insufficient circulation volume will cause poor cooling and reduced heat seal strength.
5. Heat sealing times
Good heat sealing generally requires more than 2 times of heat sealing. The bottom of the flat-bottomed bag has a maximum of eight layers after molding. It is easy to produce insufficient heat seal strength at the molding position in the middle of the bottom material, and too many heat seals can easily cause root fracture. Generally, there are 5 groups of horizontal heat sealing devices for flat bottom bags.
6. Heat sealing knife clearance
The heat sealing knife gap refers to the pressure distance from which the predetermined heat sealing pressure is transmitted to the heat sealing surface when the upper heat sealing knife contacts the bottom plate. At the same film thickness and the same heat sealing speed, the heat sealing knife gap is small, the heat sealing time is relatively small, and the product's heat sealing strength will be reduced. Generally, the gap of the heat sealing knife is set at 1.0 ~ 1.5mm, which is related to the film thickness, transfer performance, bag making speed, etc.
7. Tension control
The tension control device is used to keep the film flat, easy to hem, intermittently feed evenly, and reduce shrinkage and warpage of the heat sealing part of the bag. The tension of the bag making machine is generally 0.1 ～ 0.15MPa. Due to the complicated bag-making process of the flat-bottomed bag, the distance of the film is long, and the tension control requirements of the main film and the organ material and the bottom material are high.
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