Extrusion - Film
Extrusion is one of the most common plastic processing method that is used to create rod, sheet, film, profile or pipes & tubes.
It is a continuous, high temperature and high pressure manufacturing method that results in lengths or rolls/coils of finished or semi-finished product.
Plastic film may be produced using a slit die but the most common method is the film blowing process. This process is basically the same as pipe or profile extrusion up to the die apart from the die orientation which is generally vertical and pointing upwards.
The molten plastic from the extruder passes through an annular die and emerges as a thin tube. An air supply to the inside of the tube ( as with pipe extrusion) prevents it from collapsing and indeed may be used to inflate it to a larger diameter. The bubble of molten plastic is then cooled using a jet of external air, called an air ring, as it is pulled upwards using a set of nip rollers that are positioned up to 20 metre above the die.
The nip rolls flatten the bubble into a double layer of film that can be spooled or printed on, cut into shapes and heat sealed into bags or other items.
Extrusion - Film Companies