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The history of the production of bar-
rier films, is mainly associated tothree-layer co-extrusion
lines, witha barrier of nylon, bound to thestructural polymer by
means of theinterposition of a tying layer.
While being suitable for requiredpurposes, these early
structuresshowed a strong tendency to curl(curling effect), made
even worseby the substantial thickness of the
layer required to ensure that thebarrier was sufficient. This
intrinsicdefect was the main driving force toquickly move towards
the productionof geometrically balanced structures,bringing the
nylon in the core centralposition, thus developing a five
layersymmetric structures, produced bythree extruders, which
universallyand definitively opened and devel-oped the barrier film
industry.
The arrival of EVOH , together withthe development of more
performingtie resins in the application fields,gave way to the
design of the firstasymmetric structures, with a seal-ing layer
different from the mainstructural body. Systems with fourextruders
and one head with fivelayers were the almost standard linelayout,
which remained a benchmark
of setup.
At the same time there were devel-opments and improvements as
faras packaging was concerned, withthe consequent need to extend
theapplication range of available films.Above all, sterilising
treatment inautoclave identified the limits of asingle barrier
products, whether PA or EVOH , in terms of sensitivity to
moisture and relevant drop in theoxygen barrier values.Macchi
had to give an answer to anumber of requirements to be facedin the
same time:
- need to produce a barrier structuremade by the simultaneous
usageof both PA and EVOH
- process strongly asymmetricalstructures
- produce structures using two orthree different barriers to
optimisethe film performance and allow fur-ther thickness
reduction
Briefly, these are the reasons whichhave led us to the present
produc-tion of five, seven and nine layermachines, along with the
develop-ment of extrusion screws, innovativehead concepts and a
total re-design-
ing of the entire system, from take-off units to winding
systems.
Complete line for barrier film
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The main feature of this technology
is that the residence time of the meltinside the head was highly
reduced.
The density of the assembly, themoderate volume with the
additionaladvantage that this design allows forthe same flow-path
on all the layers,offer an excellent flexibility for thechoice of
polymers which can beused and also leading to an improve-ment of
the time requested for prod-
uct changeover, with a significantreduction in the purging
process. The word barrier film immediatelybrings to mind the food
packag-ing sector, whilst there are manynon-food applications, like
the phar-maceutical-medical, automotive orindustrial
specialities.
And it goes without saying that,
besides the extrusion process,these kinds of expensive films
mustbe wrapped and transformed in per-fectly wound reels with the
degreeof attention and technology that theydeserve. Macchi has a
full array oftechnology-oriented devices to fullycomplement such
very dedicatedproduction systems.
Double station BOPlus automatic winder
Thickness control system detail
9 layer die head scheme
Decurling tank
