In the process of bag making, a heat sealing temperature is needed to heat the adhesive film to an appropriate viscous flow state. In the selection of heat sealing temperature, it is necessary to consider comprehensively according to the characteristics of heat sealing material, the thickness of the film, the number of hot sealing pressing, the size of the heat sealing area, etc.
If the number of hot pressing in the same part increases, the temperature can be appropriately lowered; If the heat sealing area increases, the heat sealing temperature can be adjusted higher. The most common bag making material used by hot sealing and cold cutting bag making machine is PVC plastic, which is a kind of amorphous polymer, so there is no fixed melting point, only a melting temperature range, and also a temperature region between solid phase and liquid phase.
When PVC plastic is heated to this temperature range, the film will enter a molten state, allowing the bag to form. At this time, the upper limit and lower limit of the temperature range respectively represent the decomposition temperature and viscous flow temperature of PVC, and the difference between them is the key to determine the difficulty of heat sealing.
In the process of bag making, the heat sealing strength is affected by the heat sealing temperature. The higher the heat sealing temperature is, the heat sealing strength will increase, but when it reaches a certain temperature, the heat sealing strength will not change. If the heat sealing temperature is too high, the heat sealing material at the welding place will be damaged, and the heat sealing strength of the seal and the impact resistance of the bag will be affected. Therefore, the heat sealing temperature should be higher than the melting temperature of the heat sealing material, and the temperature should not be too high.
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