What are the factors that affect the heat seal strength of heat shrinkable film?

The drying process of the heat-shrinkable film adhesive refers to the process of volatilizing the solvent or water in the adhesive layer coated on the substrate to solidify the adhesive. Since it always takes a certain amount of time for the solvent or water to evaporate, drying is a relatively slow step in the production process of the protective film. The drying speed not only determines the production speed but also greatly affects the quality of the product. In actual production, each manufacturer regards the heat seal strength as an important quality index to control whether it is bag-making products or coil products used in automatic packaging production lines. The following is a simple analysis of the factors affecting the heat sealing strength of the heat shrinkable film based on the actual production experience: 1. Heat sealing time: The heat sealing time of the automatic packaging machine or the old bag making machine is determined by the machine speed. When the heat-sealing temperature and heat-sealing pressure remain unchanged, the longer the heat-sealing time, the stronger the bond between the heat-sealing layers. However, if the heat-sealing time is too long, the heat-sealed part of the composite film will appear wrinkles and unevenness, which will seriously affect the appearance quality of the product. 2. Heat sealing pressure: In order to ensure the heat sealing strength of plastic composite flexible packaging, a certain heat sealing pressure is essential. Therefore, the heat sealing pressure is required to be moderate and uniform during the heat sealing process. If the heat sealing pressure is insufficient or uneven, air bubbles will be generated in the heat sealing part and false welding will result in poor heat sealing. 3. Heat sealing temperature: Heat sealing temperature directly affects the heat sealing strength of plastic composite packaging products. Once the adhesive of the heat shrinkable film is applied, the solvent will evaporate quickly before it enters the dryer oven. However, due to the heat absorption of volatilization, the surface temperature of the adhesive layer decreases, so the volatilization rate also decreases. When the protective film enters the oven, the heat absorbed by the solvent volatilization is supplemented by the heat conducted from the outside. When the heat reaches equilibrium, the adhesive layer The surface temperature and the volatilization rate of the solvent can also be kept constant. The viscosity and other rheological properties of the heat shrinkable film adhesive are also factors that affect the coating process of the protective film. The greater the deviation of the rheological properties of the adhesive from the Newtonian fluid, the more likely to have various quality problems in the coating operation, especially when the adhesive is present. In terms of the nature of the swelling body, since its viscosity will increase rapidly with the increase of the coating speed during the coating process, a greater mechanical force must be used to spread the adhesive. Therefore, the faster the coating speed, the more difficult it is to obtain a uniform coating. Floor.