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It is then withdrawn with rollers.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.
