One among the recent development in the field of film manufacture is this Blown Film Extrusion which is also referred as Tubular film. This process covers the extrusion of plastic through circular die and later on followed by a bubble-like expansion. There are various advantages in manufacturing film following this new technology. This technique can be employed to manufacture multi-layered co-extruded films that carry high barrier advantages like food packaging. They are capable to allow uniformity in mechanical properties, to get rid of end effects like presence of irregular temperature and edge that may result from the flat die form of film extrusion.
With this blown film extrusion one can control the width of the film and also its thickness by controlling the air volume inside the bubble along with the output of extruder and the speed of haul-off. This technology also helps to produce both gusseted and flat tubing in single process. In this process, they extrude plastic melt through annular shaped slit die in order to form thin size wall tube. They introduce air in its centre resulting in a balloon shaped structure. An air ring blows at high speed into this hot film in order to make it cool. The tube is then continued in the upward direction while cooling till it pass the nip rolls where it gets flattened resulting in ‘lay-flat’ film tube. It is then withdrawn with rollers. The film is then kept in its original form or it can be slit to make two flat shaped film sheets. Materials that are more commonly used include polyethylenes, pp, evoh and pa.
The ratio of expansion between blown tube and die should be 4 to 1.5 times of the diameter of die. One can also control the drawdown that is present between the cooled films and melt wall thickness in both the longitudinal and radial directions by changing the air volume that is present in bubble and also be adjusting the speed of haul-off. The major advantage of this technique is that one can make use of recycling plastic and hence the process becomes more environment friendly.
Blown film produced from recycling plastic can be employed in both sheet and tube form. The technology can be deployed in industry packaging, consumer packaging, laminating film, barrier film, medical products packaging, agricultural films and many more.
