1. Heat sealing temperature: the choice of heat sealing temperature of composite film is closely related to the performance and thickness of composite substrate, the model, speed and heat sealing pressure of bag making machine, which directly affects the level of heat sealing strength.
Second, heat sealing pressure: under the heat sealing temperature, heat sealing materials began to melt, pressure on the surface of the adhesive, make corresponding touch each other, penetration, diffusion, heat sealing materials has prompted film on the surface of the gas escape, make the distance between molecules on the surface of the heat sealing material, produce the bigger the molecular inter-atomic forces, and thereby the heat seal strength.
Heat sealing speed. Heat sealing speed reflects the production efficiency of bag making machine and is also an important factor affecting the strength and appearance of heat sealing. The faster the heat sealing speed is, the heat sealing temperature should rise accordingly to ensure that the heat sealing strength and heat sealing state meet the required values. Under the same heat sealing temperature and pressure, the slower the heat sealing speed is, the fusion of the heat sealing material will be about sufficient and stable.
Cooling condition. The cooling process is to finalize the weld seam just melted and sealed at a lower temperature under a specific pressure to eliminate stress concentration, reduce the shrinkage of the weld seam, increase the appearance flatness of the bag and increase the heat sealing strength. The cooling water of bag-making machine is generally tap water or circulating water at about 20¡æ. If the water temperature is too high, the pressure of the cooling rod is not enough, the cooling water circulation is not smooth, the circulation is not enough, etc., it will lead to bad cooling, and the heat seal strength will be affected.
Number of times of heat sealing: in continuous automatic filling equipment and some bag making machines, longitudinal heat sealing generally adopts the ring steel strip welding method of coated PTFE, while transverse heat sealing adopts hot plate welding method. But most bag making machines adopt hot plate welding method for longitudinal and transverse heat sealing. The longitudinal heat sealing times depend on the ratio of the length of the heat sealing rod to the length of the bag, while the transverse heat sealing times are determined by the number of groups of heat sealing devices of the machine. Good heat sealing generally requires heat sealing heat sealing times in more than two cooking. Most of the transverse heat sealing devices are in three groups. In order to meet the heat sealing requirements of wide edge, the transverse heat sealing device is often increased and the number of heat sealing is increased to reduce the heat sealing temperature and reduce the necking phenomenon. For long specifications of packaging bags, several times feeding technology can be used to reduce the length of each feeding to one half or one third of the bag length, thus increasing the number of heat sealing, change the heat sealing effect, but will reduce production efficiency, so some equipment to increase the length of longitudinal sealing rod, to increase the number of heat sealing, to protect the heat sealing quality.
6. Heat-sealing rod clearance refers to the applied distance between the predetermined heat sealing pressure and the heat sealing surface when the upper heat sealing rod contacts the bottom plate. When the film thickness is the same, the heat sealing speed is the same, the heat sealing rod gap is small, the heat sealing time is relatively small, the heat sealing strength of the product will be reduced. Generally, the gap between the heat sealing rod is set at 1 ~ 1.5mm, which is related to the thickness of the film, the transfer performance and the bag-making speed.
