What are the production methods of Heat Shrinkable packaging films?
What are the production methods of Heat Shrinkable packaging films? What raw materials are used in its production?
The first method is the one-bubble method. That is, the polyethylene resin is plasticized by the extruder, and the film tube is blown out by the die die, and it is cooled immediately after stretching. The blowing ratio of this method is larger than that of drafting.
The second method is the two-bubble method. That is, the extruded film tube is slightly inflated, cooled immediately after stretching, then heated to a high elastic state for the second blowing and stretching, and cooled and shaped after reaching the specification requirements.
The third method is radiation crosslinking. The function of crosslinking is to destroy crystallization and can improve the shrinkage stress and strength of the shrink film. The technological process is similar to the two-bubble method, except that the film tube before the second stretching and inflating goes through an ultraviolet irradiation chamber to cause crosslinking inside the film, the gel value of crosslinking should be 7% to 9%.
Different processes have different requirements for raw materials and formulas. The raw materials used in the first two processes are low density polyethylene single component, and the melt flow rate is 2 ~ 59/10 min. The formula of radiation crosslinking method is to add about 1% crosslinking agent and a small amount of photosensitizer into polyethylene resin.