Higher barrier properties that are required
for food packaging have caused a shift in
multi layer plastic film to 5/7 layers in
the last few years. However, the increasing
demand of barrier properties from the more
demanding food industry has led to the development
of 9 layer co extruded film compositions in
the last 5 years. Experience with nine layers
opened the door to even more complex films.
10 layers offer even more opportunities to
use different structures and engineering polymers
like PET etc. High-barrier films are used
to extend shelf life of refrigerated products
like meat, poultry, cheese, and fish-and unrefrigerated
foods like powdered milk, nuts, pet food,
and wine. Besides high barrier, flexibility
is the most desired property- 9 layer film
with thin nylon layers is relatively flexible,
while 5 and 7 layer nylon barrier films are
stiff because the nylon layer is thicker.
The sparing use of expensive nylon is a major
attraction of 9 layer blown film as a 9 layer
film splits one thick nylon barrier layer
into several thin ones, enhancing barrier
performance out of less nylon, and improving
thermoformability. Stress cracking is avoided
as thinner layers of nylon allow the deep-formed
corners of a package to retain twice as much
barrier material as when forming rigid 5 layer
film. Thinner nylon layers also reduce film
curling, a common problem with 5 and 7 layer
films and allow thinner sealant layers. 9
layer film achieves more uniform gauge than
a 7 layer line.
Market growth for 9 and 10 layer blown film
has not been as rapid as when processors switched
from three layers to 5 and 7, because there
are many other ways to get the same barrier
effect, including multi-layer cast film, lamination,
metalizing, and coating.
The complex rheological properties of the
several polymers used make it extremely difficult
to process a 9 layer film. Machine builders
have not rushed into the nine-layer market
either. No European OEMs have ventured beyond
seven-layer dies, though Windmoeller &
Hoelscher in Germany and Macchi in Italy are
now working on them. The difficulties faced
to build and run 9 and 10 layer dies is evident
in the fact that even eight years later there
are still only 25 of them in the world, probably
at less than a dozen companies. Brampton is
the dominant supplier of lines for nine or
more layers. It has delivered three 10-layer
stack dies and 13 nine-layer ones, including
the world's largest-31.5 in. dia.
Although IBC is a common tool to increase
blown film output, usage with 9 layer films
is restricted as IBC could freeze the nylon
too quickly so that it doesn't adhere to the
next layer and delaminates.
Changeovers are expensive, making the processor
trying to line up production runs to avoid
change over more than two or three extruders
at a time.
The scrap generation and utilization is quite
difficult. Reducing scrap is a major problem.
The lines have very high output, so a production
run of a specialty nine-layer film might take
only two or three hours. The changeover to
run the next product could take as long or
longer. Sometimes less expensive all-polyolefin
films can be run to complete the purging of
a true nine-layer line.
Though these complexities affect the commercial
viability and take off of 9-layer film extrusion
system, it will give the niche product at
an optimum price and this segment is expected
to grow after 2010.