Six Factors of Heat Sealing Quality of Bag Making Machine (Part 1)

1. Heat sealing temperature

The selection of the heat sealing temperature of the composite film is closely related to the function and thickness of the composite substrate, the model, speed, and hot air pressure of the bag making machine, which directly affects 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 can not 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 wider the heat sealing temperature range, the better the heat sealing performance, 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 printing substrate. Otherwise, it will cause shrinkage and wrinkling of the heat-sealed part, which will reduce 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 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 after adding pressure, reduce Production speed or selection of low temperature heat sealable materials 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 function, 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 extremely small, and the required pressure is high, which is beneficial to the heat sealing strength and interface sealing.

The heat sealing pressure should be increased with the increase of the thickness of the composite film. If the heat sealing pressure is insufficient, it is difficult to heat the two layers of films, 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, 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 knife should be considered. The wider the width of the heat sealing knife, the greater the pressure required. The width of the heat sealing knife is too wide, which is easy to entrain air bubbles in the heat sealing part, and it is difficult to heat seal firmly. Generally, a hollow heat sealing knife can be used to strengthen the heat sealing fastness in the last seal. If the heat sealing knife of the same width is engraved on the surface, its actual contact 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 shows 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 increased accordingly to ensure that the heat-sealing strength and heat-sealing condition reach the optimum value; under the same heat-sealing temperature and pressure, the slower the heat-sealing speed, the better the fusion of the heat-sealing material. Sufficient and stronger, but not causing root-cutting phenomenon.

For domestic bag making machines, the length of heat sealing time is mainly determined by the speed of the bag making machine. To add heat sealing time, it is necessary to 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 knife, and the heat sealing time can be adjusted independently without changing the bag making speed, the operation and quality control of the bag making machine will be greatly facilitated.