1. Heat-sealing temperature The choice of heat-sealing temperature of the composite film is closely related to the function, thickness, type, speed, and hot air pressure of the composite substrate, which directly affects the concavity and convexity of the heat-sealing strength. The sealing temperature of the composite film is determined by the viscous flow temperature or melting temperature of the heat-sealing material, and the high temperature of the heat-sealing material cannot exceed the decomposition temperature of the heat-sealing material. The temperature between the viscous flow temperature and the decomposition temperature is the heat sealing temperature range of the heat sealing material, which is a key factor affecting and controlling the quality of heat sealing. The larger the heat-sealing temperature range, the better the heat-sealing performance, and the simpler and more stable the quality control. Colleagues, the heat sealing temperature of the composite film should not 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 printing 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 after increasing the pressure, decreasing Production speed or choice of low temperature heat sealable material to ensure heat seal strength. 2. Heat sealing pressure The hot air pressure is supplied 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 polar heat sealing material has a high activation function, and the temperature rise has a great influence on the decrease of its viscosity, so the required heat sealing pressure is small, and the molten material at the heat sealing part is prevented from being extruded, which affects the heat sealing effect. While PE and PP are non-polar materials, the activation function is very small, and the required pressure is high, which is beneficial to the heat sealing strength and interface sealing. The heat sealing pressure should increase with the thickness of the composite film. If the heat sealing pressure is insufficient, the two layers of film will be difficult to heat seal, and it is difficult to exhaust the bubbles trapped in the center of the weld; if the heat seal pressure is too high, the molten material will be squeezed out, which will damage the welding edge and cause root breakage. When calculating the heat sealing pressure, the width and actual surface area of the required heat sealing rod should be considered. The wider the heat seal bar width, the greater the pressure required. If the width of the heat-sealing rod is too wide, it is easy to trap air bubbles in the heat-sealing part, and it is difficult to heat-seal vigorously. Generally, a hollow heat-sealing rod can be used to enhance the heat-sealing fastness in the final seal. If the surface of the heat-sealing rod of the same width is engraved, the actual touch area is greatly reduced, and the pressure per unit area increases accordingly, which is beneficial to the packaging bag with a larger heat-sealing width. 3. Heat-sealing speed The heat-sealing speed represents the production efficiency of the bag making machine, and is also an important factor affecting the heat-sealing strength and appearance. The faster the heat-sealing speed, the heat-sealing temperature should be moved accordingly to ensure that the heat-sealing strength and the heat-sealing condition reach the optimum value; under the same heat-sealing temperature and pressure, the slower the heat-sealing speed, the faster the fusion of the heat-sealing material will be. Full, more vigorous, but can not cause the phenomenon of root cutting. For domestic bag making machines, the length of heat sealing time is mainly selected by the speed of the bag making machine. To increase the heat sealing time, it is necessary to reduce the bag making speed and reduce the production efficiency. Assuming that 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 state The cooling process is to shape the welded seam just melted and sealed at a lower temperature under a certain pressure, eliminate stress concentration, reduce the shortening of the welded seam, improve the appearance of the bag, and promote heat sealing. strength process. The cooling water of the bag making machine is generally tap water or circulating water at about 20°C. If the water temperature is too high, the pressure of the cooling rod is not good, the circulation of cooling water is not smooth, and the circulation volume is not enough, etc., it will lead to poor cooling and decrease of heat sealing strength. 5. Number of heat sealing Most of the longitudinal and transverse heat sealing of bag making machines use hot plate welding method. The number of longitudinal heat sealing depends on the ratio of the useful length of the heat sealing rod to the length of the bag, and the number of transverse heat sealing is determined by the machine heat sealing. Device group number selection. Good heat sealing generally requires more than 2 times of heat sealing. Most of the transverse heat sealing equipment is 3 groups. In order to meet the heat sealing requirements of wide sides, transverse heat sealing equipment is often added, and the number of heat sealing is increased to reduce the heat sealing temperature and reduce the necking phenomenon. For long-standard 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, and then increase the number of heat-sealing times to improve the heat-sealing effect, but it will reduce production. Therefore, 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 heat sealing. 6. Heat-sealing rod vacancy The heat-sealing rod vacancy refers to the pressure interval during which the predetermined hot air pressure is transmitted to the heat-sealing surface when the upper heat-sealing rod touches the bottom plate. At the same film thickness and the same heat sealing speed, the vacancy of the heat sealing rod is small, the heat sealing time is relatively small, and the heat sealing strength of the product will decrease. Generally, the vacancy of the heat sealing rod is set at 1.0~1.5mm, which is related to the film thickness, transfer function, bag making speed, etc.
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