What is Polythene Extrusion?

Blown film extrusion is one of the most significant polymer processing methods. Several million tonnes of polymer, mostly polyethylene are processed annually by this technique. While some applications for blown film are quite complex, such as scientific balloons, the majority of products manufactured on blown film equipment are used in commodity application with low profit margins, such as supermarket bags, refuse sacks, and other flexible packaging. Consequently sophisticated hardware, materials, and processing methods have been developed to yield film at very high output rates with both low dimensional variation and consistent solid-state properties.

Red Bull Stratos Polyethylene Balloon

The Balloon is constructed of strips of high-performance polyethylene (plastic) film that is only 0.0008 inches thick. In total, these strips would cover 40 acres if they were laid flat. Polyester-fibre reinforced load tapes are incorporated to do the weight bearing

Put simply blown polythene extrusion is the process through which polymer pellets are melted, formed and then cooled to make a continuous state. The basic process sounds very simple, however the actual manufacturing side can be very complicated.

In a typical process, blown film manufacturing involves feeding raw polymer pellets from a hopper to a heated extruder (1). Once inside the extruder, the polymer is pushed through a rotating screw and heated up until it enters a soft melted state or ‘melt’ as it is called (2). This soft ‘melt’ material is then pumped under continuous pressure through a ring shaped opening called a die (3). This material then leaves the die in the form of a tube, the tube is inflated with air to form a bubble.

When the desired thickness of the film is reached it is then air cooled into a solid state, then guided by collapsing boards into a ‘pinch’ or ‘nip’ roller at the very top of the bubble. From there the film travels back down the outside of the tower (4). At this point the film is known as Lay Flat Tube or LFT for short.

From here the film can then enter slitting stations which gives the option of converting it into different film variations. For example slitting both sides of the original flat tube can make two separate layers which can be separated and wound onto their own separate reels. The film can then be wound onto corrugated or plastic cores for shipment to the customer (5).

polythene extrusion diagram

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