Principle of blown film extrusion

Multilayer films, generally with three layers but more rarely up to nine layers, are obtainable with a sufficient number of extruders. 

This technique is commonly used to produce sheets and films of PVC and more rarely ABS and EVA. llie minimum thickness is commonly of the order of 25 pm. 

The number of rolls, their sizes and their configuration characterize the calender. Some possibilities are indicated below, without claiming to be exhaustive  

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