Blown Film Extrusion
Blown Film Extrusion is the common name for the process in which plastic pellets are melted down to allow for the forming of plastic sheets or products, dependent on the customers need.
Before the process begins a computer is used to mix resin with any other additives to give the end product the properties it needs to perform the task it is being produced for. At the mixing phase it may also go through a process called regrind to reduce the customer’s costs.
Once the mixing is complete the mixture is heated to a high temperature and is then fed through an extruder. Following this the mixture is pumped through what is known as a rotating die ring which creates an upward tube of the thin polymer.
This tube is filled with air which is known as a ‘bubble’. The bubble acts in place for three functions:
- The pressure of the air in the tube causes the polymer to stretch and has an overall effect on the thickness of the finished polythene sheet.
- The speed at which the polymer is pulled upwards toward the nippers will have an overall effect on the thickness of the finished sheet.
- The bubble starts to cool the polymer as it moves upwards.
This tube is then fed through a series of rollers, known as ‘nippers’. The first set of nippers take the tube and flatten it before it is fed through a number of other nippers before it arrives at the slitting station.
The purpose of the slitting station is to split the flat tube into two separate roles of polythene which can then be wound onto its own core. Alternatively the tube may only be slit on one side to allow it to be wound onto a double width roller and create a double width polythene sheet.
Once on the core the sheets are then packaged up and are ready for shipping.
The extrusion process has taken many years to master and is constantly being refined to reduce costs and become more efficient. There are many other ways of producing polythene but this is one of the most common ways in which it is done.
Marpak Extrusions are flexible packaging specialists. For more information, please visit their website: Marpak Polythene Packaging