When the heat sealing material is determined, the heat sealing quality of stand up bags is directly related to the heat sealing process. Usually, the main control is the temperature, pressure and time of heat sealing.
Heat sealing theory
When the stand up bags is heat sealed above the heat sealing temperature, the plastic film becomes a viscous flow state; The heat sealing pressure causes the external force of mutual penetration and diffusion between the interfacial molecules of the plastic film in the viscous flow state.
A certain heat sealing time will make the interface molecules of the plastic film penetrate and diffuse each other as soon as possible, so that the interface disappears and becomes a whole, so it has good sealing performance.
Heat sealing temperature
The minimum heat sealing temperature of the heat sealing material depends on the melting temperature of the material. The heat sealing temperature should be higher than the melting temperature of the heat sealing material.
However, the technical indexes such as whether the sealed material is a single film or a composite film, film thickness, heat sealing pressure and heat sealing speed should be considered. Generally, the heat sealing pressure is high; Slow heat sealing speed; If the film thickness is large, the heat sealing temperature can be lower, and vice versa.
Heat seal pressure
The size of the heat sealing pressure also has a great impact on the heat sealing effect. The heat sealing pressure should be appropriate. When the heat sealing pressure is too low, the two layers of heat sealed materials are difficult to achieve real fusion, or it is difficult to catch up the gas in the middle of the seal, resulting in local leakage.
The heat sealing pressure is too large, and when the heat sealing temperature is slightly higher, the heat sealing knife will squeeze away the molten material in the sealing seam during heat sealing, resulting in hot cutting. If stand up bags is light, it will reduce the heat sealing strength of the seal and reduce the impact strength of the seal. Generally, the heat sealing temperature is high; Slow heat sealing speed; If the film material is thinner, the heat sealing pressure can be smaller, and vice versa.
Heat sealing time
Under the same heat sealing temperature and pressure, the longer the heat sealing time is, the stronger the interface of the heat sealing layer is. However, the longer the heat sealing time is, it is easy to cause resin oxidation at the sealing joint, but reduce the heat sealing effect.
At the same time, too long heat sealing time is also easy to cause wrinkle and deformation of sealing seam, affect the appearance and cause stand up bags leakage.