If the composite packaging bag is not well sealed, it will affect the appearance and sealing performance. In this respect, it must not be sloppy. The quality of the heat sealing of the composite packaging bag is largely related to the following 6 points. 1. Heat sealing temperature The selection of the heat sealing temperature of the composite film is closely related to the performance, thickness of the composite substrate, the model, speed and hot air pressure of the bag making machine, which directly affects the strength of the heat sealing strength. The sealing temperature of the compound packaging bag is determined by the viscosity flow temperature or melting temperature of the heat sealing material. The high temperature of the heat sealing material cannot exceed the decomposition temperature of the heat sealing material. The temperature between the viscosity flow temperature and the decomposition temperature is the heat-seal temperature range of the heat-seal material, which is a key factor affecting and controlling the quality of the heat-seal. The wider the heat sealing temperature range, the better the heat sealing performance and the easier and more stable the quality control. At the same time, the heat sealing temperature of the composite film cannot be higher than the heat setting temperature of the printed substrate. Otherwise, it will cause shrinkage and wrinkling of the heat-sealed part, reducing the heat-sealing strength and the impact resistance of the bag. The temperature resistance of the printed substrate is good, such as BOPET, BOPA, etc., increasing the heat sealing temperature can increase the production rate; the temperature resistance of the printing substrate is poor, such as BOPP, try to use a lower heat sealing temperature, and increase the pressure and reduce Production speed or select low temperature heat sealable material to ensure heat seal strength. 2. Heat sealing pressure The hot air 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. Polar heat seal materials have higher activation performance, and the temperature increase has a greater influence on the decrease in viscosity, so the required heat seal pressure is smaller, which prevents the molten material at the heat seal location from being squeezed out, affecting the heat seal effect. However, PE and PP are non-polar materials with extremely low activation performance and high required pressure, which is beneficial to the heat seal strength and interface tightness. The heat sealing pressure should increase as the thickness of the composite film increases. If the heat sealing pressure is insufficient, the two films are difficult to heat seal, and it is difficult to exhaust the air bubbles sandwiched between the welds. If the heat sealing pressure is too high, the molten material will be squeezed away, the welding edge will be damaged, and the root will be broken. When calculating the heat sealing pressure, the width and actual surface area of ​​the required heat sealing rod should be considered. The wider the width of the heat seal rod, the greater the pressure required. If the width of the heat sealing bar is too wide, it is easy to entrap air bubbles in the heat sealing part, and it is difficult to heat seal firmly. Generally, a hollow heat sealing bar can be used to strengthen the heat sealing fastness at the last one. If the surface of the heat sealing rods with the same width is engraved, the actual contact area is greatly reduced, and the pressure per unit area is increased accordingly. This is beneficial for packaging bags with larger heat seal widths. 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 sealing speed, the heat sealing temperature should be increased accordingly to ensure that the heat sealing strength and heat sealing state reach the optimal value; under the same heat sealing temperature and pressure, the slower the heat sealing speed, the fusion of the heat sealing material will be more Fully and more solid, but can not cause root-breaking phenomenon. The length of heat-sealing time of the domestic bag-making machine is mainly determined by the speed of the bag-making machine. Increasing the heat sealing time must reduce the bag-making speed and reduce the production efficiency. If an independent frequency conversion motor is used to control the lifting and feeding of the heat sealing rod, and the heat sealing time is independently adjusted without changing the bag making speed, the operation and quality control of the bag making machine are greatly facilitated. 4. Cooling situation The cooling process is the process of setting the weld seam just melted under a certain pressure at a lower temperature, eliminating stress concentration, reducing the shrinkage of the weld seam, improving the flatness of the appearance of the bag, and improving the heat seal strength. The cooling water of the bag making machine is generally tap water or circulating water around 20 ° C. Excessively high water temperature, insufficient cooling rod pressure, poor cooling water circulation, and insufficient circulation volume will cause poor cooling and reduced heat seal strength. 5. Heat sealing times The longitudinal and transverse heat sealing of most bag-making machines adopt hot plate welding method. The number of longitudinal heat sealing depends on the ratio of the effective length of the heat sealing rod and the length of the bag. . Good heat sealing generally requires more than 2 times of heat sealing. Most of the horizontal heat sealing devices are 3 groups. In order to meet the requirements of wide-side heat sealing, lateral heat sealing devices are often added and the number of heat sealing times is increased to reduce the temperature of heat sealing and reduce the phenomenon of necking. For longer-sized packaging bags, multiple feeding techniques can be used to reduce the length of each feeding to one-half or one-third of the bag length, thereby increasing the number of heat seals and improving the heat sealing effect, but it will reduce production Efficiency, so some bag making machines increase the length of the longitudinal heat sealing rod to increase the number of heat sealing and ensure the quality of the heat sealing. 6. Heat sealing rod gap The heat-seal rod gap refers to the pressure distance that the predetermined hot-air pressure is transmitted to the heat-seal surface when the upper heat-seal rod contacts the bottom plate. At the same film thickness and the same heat sealing speed, the gap of the heat sealing rod is small, the heat sealing time is relatively small, and the heat sealing strength of the composite packaging bag will be reduced. Generally, the gap of the heat sealing rod is set at 1.0 ~ 1.5mm, which is related to the film thickness, transfer performance, bag making speed, etc.
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