When we use plastic packaging bags, the shapes and requirements of plastic packaging bags are different because of their different uses. Briefly talk about the heat sealing of plastic packaging bags. Common methods include manual heat sealing, high frequency, hot plate, pulse, ultrasonic, infrared radiation and hot air heat sealing. Let's talk about how the plastic packaging bag is heat sealed.

1. Simple heat sealing method Manual heat sealing method: often used for heat sealing of PE and PP single-layer films.
When heat-sealing, the blade of an ordinary soldering iron needs to be bent into an L shape with the help of a heat-resistant film, and then the wire is connected to the voltage stabilizer for thermostatic control. If the film leaves an edge at the seal, the heat seal strength will be greater. In actual operation, two layers of fine plain cloth should be laid first, and then a layer of non-deformable khaki cloth. The cloth pattern should be 45 or a straight line with the heat-sealing line, its function is to make the heat-sealed part produce a uniform pattern, thereby strengthening the structure of the pattern (playing the role of supporting bones and muscles), achieving the purpose of mutual penetration between molecules and improving the sealing interface The sealing performance.

2. High frequency method: The high frequency electric field generated by the tube self-excited oscillator is used to heat the plastic medium molecules and apply a certain pressure to achieve heat sealing.
Under the action of high-frequency electric field, the arrangement direction of the electrode and the polar molecule is opposite, the positive charge in the molecule turns to the negative electrode, and the negative charge turns to the positive electrode. If the direction of the electric field changes, the charge will also change its position. This charge displacement is called "polarization". "Polarization" means that the molecules are regularly oriented. Therefore, we have to overcome frictional resistance and consume a certain amount of energy, and when this energy consumption is converted into heat and released, then this is the cause of heat. Under the proper pressure of the bottom plate and the mold, the two films can be joined together.

3. Hot plate heat sealing method for heat sealing by external heating: first place two overlapping films between two heated metal plates (or heat one of them) until the surface layer melts, and then melts under pressure The surfaces quickly bond together and maintain pressure until it cools. The structure is simple, the cost is low, the service life is long, and it is not easily damaged.

4. Pulse method: first pressurize and melt the heat-sealed part, then cool and release the pressure. In general, a nickel-chromium belt is used as a heating element instead of a metal plate, and instantaneous current is introduced from the nickel-chromium belt for heating. When working, put the laminated plastic film on the workbench, press the heating element on the plastic film by manual or automatic control, and the current automatically flows into the nickel-chromium belt, so that the strong thermal energy pulse acts on the heat shield. After a short time, the current is cut off by the time relay, then cooled, decompressed, and heat sealed.

5. Ultrasonic method: The main component of the heat sealing machine is the transducer, the transducer is wound with a coil, and the coil is connected to the oscillator. Through the magnetic expansion effect, the high-frequency current is converted into mechanical vibration. The mechanical energy is emitted from the vibrating hair and then transmitted to the film in the form of waves. This generates effective force inside the film and forms between the two films on the vibration interface conflict. With the generation of heat and the increase in temperature, the film softens and melts, and the reaction force of the lower support table and the clamping force of the vibrating head make the polymer molecules on the hot cover diffuse mutually. Therefore, the molecules of the heat-sealing film have a strong binding force. In addition, there is also a hot air heat sealing method that uses hot air to blow hot air onto the surface of the plastic film for heat sealing. This method can be used for heat sealing of packaging.