I. PE Film (Polyethylene): Low Melting Point, High Ductility, Requiring Precise Temperature Control and Low-Pressure Adaptation

• Heating System: It needs to support a wide temperature adjustment range of 50-200°C, and the temperature fluctuation must be controlled within ±2°C. If the temperature is too high (exceeding 150°C), PE film is prone to thermal shrinkage and edge sealing coking; if the temperature is too low (below 100°C), effective welding cannot be achieved, leading to leakage. Therefore, the bag making machine must be equipped with a high-precision thermocouple (error ≤±1°C) and a PID constant temperature control system to ensure real-time stability of the heat-sealing knife temperature.
• Edge Sealing Pressure: The recommended pressure range is 3-5kgf/cm². Due to the high ductility of PE film, excessive pressure will cause stretching and deformation of the film, resulting in edge sealing wrinkles; insufficient pressure cannot ensure tight bonding of the two layers of film, affecting sealing performance. Some high-end models are designed with a "segmented pressure adjustment" function, i.e., pre-pressing at 3kgf/cm² in the early stage of edge sealing, welding at 4kgf/cm² in the middle stage, and shaping at 3kgf/cm² in the later stage, to further improve flatness.
• Auxiliary Structure: Since PE film is easy to adhere to the heat-sealing knife, a Teflon coating (thickness 0.03-0.05mm) must be added to the surface of the heat-sealing knife, and a cold air cooling system (wind speed ≥5m/s) must be equipped to reduce the temperature to below 60°C within 1 second after edge sealing is completed to avoid adhesion.

II. PET Film (Polyethylene Terephthalate): High Melting Point, High Strength, Requiring Enhanced Heating and Rigid Support

• Heating System: It needs to be equipped with a high-power heating module (single knife power ≥5kW), support a temperature adjustment range of 100-300°C, and adopt high-frequency heating technology (frequency 20-40kHz). The traditional resistance heating method has a slow heating rate (it takes 5-8 minutes to reach 250°C from room temperature), while high-frequency heating can reach the set temperature within 2 minutes, with stronger heat penetration, ensuring that the inner layer of PET film (usually compounded with PE or CPP heat-sealing layer) is fully melted. In addition, the heat-sealing knife must be made of copper alloy (thermal conductivity ≥380W/(m·K)) to ensure uniform heat conduction.
• Pressure Control: The edge sealing pressure needs to be increased to 6-8kgf/cm². Due to the high rigidity of PET film, low pressure cannot make the two layers of film closely contact, so high pressure is required to ensure full bonding of the heat-sealing layer. At the same time, the bag making machine must be equipped with a servo pressure control system, with a pressure adjustment accuracy of ±0.2kgf/cm², to avoid uneven edge sealing strength caused by pressure fluctuations.
• Mechanical Structure: Since PET film has poor stretch resistance, the feeding system must adopt a combination of "servo motor + high-precision ball screw" to control the feeding accuracy within ±0.1mm, preventing the film from wrinkling due to stretching. In addition, the hardness of the rubber coating on the traction roller needs to be increased (Shore hardness 85-90 degrees) to improve friction and avoid slipping.

III. Aluminum-Plastic Composite Film: Multi-Layer Structure, High Barrier Property, Requiring Enhanced Sealing Performance and Consistency

• Heating System: It needs to adopt the "synchronous heating of upper and lower knives" design, with a temperature difference between the upper and lower heat-sealing knives ≤±5°C. The existence of the aluminum foil layer will hinder heat conduction; if the temperatures of the upper and lower knives are inconsistent, it is easy to cause incomplete fusion of the edge sealing on one side. At the same time, the heating power must reach 8-10kW to ensure that the heat penetrates the aluminum foil layer and fully melts the inner heat-sealing material (melting point 120-160°C).
• Pressure Control: The edge sealing pressure needs to be ≥6kgf/cm², and the pressure distribution must be uniform (deviation ≤±0.5kgf/cm²). The aluminum foil layer of the aluminum-plastic composite film is prone to "virtual sealing" due to insufficient local pressure, leading to oxygen or water vapor penetration. Therefore, some models will adopt "zonal pressure adjustment" technology, dividing the edge sealing area into 3-5 independent pressure zones to adapt to the sealing needs of different positions.
• Auxiliary Functions: It must be equipped with a "sealing detection module" to real-time detect the integrity of edge sealing through the negative pressure method (pressure -30kPa to -50kPa). If a leak is found (leakage rate ＞0.5kPa/s), the equipment will automatically mark and reject unqualified products, ensuring the product qualification rate ≥99.5%. In addition, due to the high stiffness of the aluminum-plastic composite film, the material receiving system must be equipped with a tension controller (tension range 5-15N) to prevent the roll from loosening or stretching deformation.

Summary