Process
• The extrusion of plastic melt is done via an annular slit die, generally vertically, for the formation of a thin walled tube.
• The introduction of air takes place through a hole present in the die's center for blowing up the tube just like a balloon.
• The cooling of the hot film is done by the high-speed air ring that blows onto it.
• The tube of the film continues its movement upwards (constantly cooling) till it is passed via nip rolls. Here, the tube is flattened for the creation of “lay-flat” tube of film.
• On the higher output lines, exchange of air (which is available in the bubble) takes place. This is called IBS (Internal Bubble Cooling).
• Then the lay-flat film is kept as it is or its edges are slit off for producing 2 flat film sheets & wound up onto the reels. If kept as it is, the film's tube is created into bags by the process of sealing all across the film's width along with cutting or perforating. This process is carried out at a later stage or in line with the process of blown film.
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