The Blown Film process
One way of producing plastic film is by a process called "blown film". (Another method is calendering)
The blown film process consists of injecting molten plastic into a blow film machine and blowing air through the molten plastic. This creates a bubble in the molten plastic, just like a person blowing a bubble in chewing gum.
The bubble is blown vertically, creating a long bubble like a party balloon.
Air is blown onto the outside of the balloon from a cooling ring at the base of the balloon. The air blown onto the outside, together with the air blown inside the balloon chills the balloon as the air rises. This cooling effect solidifies the plastic, creating the plastic film that we see used in carrier bags etc.
The top of the balloon is guided between rollers and then pinched to flattened the balloon.
The flattened balloon is guided on rollers to where it is wound onto a reel. The flattened balloon of plastic is called "lay-flat tube". Lay-flat tube can be heat sealed and perforated to make plastic bags, or it can be slit to form sheets of plastic.
Polyethylene (polythene) is the most common plastic used in blown film production.
Low density polyethylene and high density polyethylene are suitable for blown film production but other materials such as polypropylene (PP) and Polyamide/Nylon (PA) are sometimes blended with polyethylene or used to produce multi layered laminates.
Learn about Plastics
We use animations and supporting technology notes to describe plastics and plastics processes.
Animations illustrate plastics processes in probably the most clear way possible, making plastics processes easy to understand, easy to learn and easy to remember.
Our plastics technology notes and animations describe all the major processes including:
Our new Plastics Module developed from the work in the KS3 and KS4 D&T packages. It is a complete package that includes:
To make teaching easier, the technology theory notes and exercises are in digital format, making them suitable for computers and whiteboards; and in PDF format, which makes it simple to print and duplicate A4 theory notes and worksheets.
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