Film Blowing is the process of forming polythene sheets or a film using polythene pellets. The pellets are first crushed and melted into a viscous liquid. This molten liquid is then extruded vertically through a die. Air is injected through the centre of the die forming a balloon-like shape from the extruded polythene. The air entering replaces the air leaving thereby giving the extruded material a uniform thickness throughout.
As the extruded polythene is moving vertically upwards, and it passes through a cooling ring where the material gradually solidifies. Upon completion of the solidification process, the material is passed a set of nip rollers which flatten it and collapse the balloon-like shape resulting in the formation of two flat film layers. The films are then wound up on idler rolls to ensure uniform tension is applied through it. The film layers are also then corona treated to increase its surface adhesiveness, so that effective lamination occurs.
A recommended composition of 80% LLDPE (Linear Low Density Polyethylene) and 20% of (Low Density Polyethylene) is used in this production. There are machines with two inlets and machines with three inlets for pellets. Thereby by using different coloured pellets, a sheet of varying colours can be extruded. Even certain materials like nylon can be used in the mix for a variety of properties.
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| Film Blowing Process |
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