Aquarex

PAC K A G I N G
Thanks to watercooling, films can be
produced with especially good optical
and mechanical
properties (figures:
Windmöller & Hölscher)
New Packaging Solutions
Thanks to Rapid Cooling
Extrusion. Water-cooling can achieve very high cooling rates for blown film extrusion. The result is soft, elastic films with near-amorphous molecular structures.
The resulting low tendency to curl is a clear advantage when asymmetric multilayer film structures are processed further.
LENNART EDERLEH
TILL BERGMANN
INGO PUTSCH
trong pressure from competition in
the packaging sector continues to
push demands on the manufacturers
of raw materials and machines to develop more sustainable packaging solutions.
S
Translated from Kunststoffe 5/2014, pp. 26–31
Article as PDF-File at www.kunststoffeinternational.com; Document Number: PE111673
14
In the flexible packaging sector, pouches
are showing the strongest growth. Their
advantages of reduced packaging weight
together with the resulting lower production and logistic costs are behind its expansion into new applications [1].
Water-Cooled
Blown Film Extrusion
Blown film extrusion and cast film extrusion are currently the conventional
processes for manufacturing films for
flexible packaging solutions. Whereas
classic blown film extrusion with plastics
melt by convective cooling exhibits
schows relatively slow cooling rates of 20
to 80 K/m, cast film extrusion can achieve
approx. ten times higher values thanks to
contact cooling on the chill roll. However, with water-cooled blown film extrusion, even higher cooling rates can be
achieved on the order to 1,000 to
3,000 K/m [2]. That means that films
© Carl Hanser Verlag, Munich
Kunststoffe international 5/2014
Internet-PDF-Datei. Diese PDF Datei enthält das Recht zur unbeschränkten Intranet- und Internetnutzung, sowie zur
Verbreitung über elektronische Verteiler. Eine Verbreitung in gedruckter Form ist mit dieser PDF-Datei nicht gestattet.
PAC K A G I N G
Fig. 1. In water-cooled blown film extrusion, the film tube is extruded downward
manufactured by this technology exhibit
a range of properties that makes them especially interesting for flexible packaging.
Due to such rapid cooling, crystallization
processes can be inhibited, thereby enabling films to be produced with nearamorphous molecular structure while
lending very good surface gloss and high
transparency to such films. At the same
time, the amorphous structure of the
films makes them very soft and puncture
resistant. Moreover, they can be processed
very well by thermoforming.
In Aquarex brand, water-cooled blown
film extrusion from Windmöller &
Hölscher KG of Lengerich, Germany, the
film tube is extruded vertically downward
(Fig. 1). As in conventional blown film
lines, different materials are plasticized in
several extruders and combined into a
multi-layer annular gap flow. The melt
tube exiting the die is drawn off down-
ward and simultaneously blown via internal pressure. A controlled water calibrator then directs water onto the film
bubble so that the molten plastic cools off
rapidly. The film tube is then laid flat and
pulled off and either subjected to thermofixing or transferred to a single or dual
winder. All the time, the proven components of Windmöller & Hölscher’s entire
conventional modular blown-film line
Varex II, e.g., extruders, dies, automation
and winders, are in operation. Thus, films
composed of as many as 11 layers can be
produced with up to 1,600 mm working
width and ranging in thickness from 30
to 300 µm. This innovative cooling concept achieves high production outputs in
conjunction with low overall height of
the entire line.
Infusion Bags
Fig. 2. The strong demands placed on infusion bags can be met when the films are manufactured by
water-cooled blown film extrusion
Kunststoffe international 5/2014
A typical application for water-cooled
blown film are pouches to fill medicinal
infusion solutions with, often referred to
as infusion bags (Fig. 2). This type of packaging fulfills very high optical and mechanical requirements. The preferred raw
materials used here are modified PP types
manufactured especially for medical applications. Since the films come in contact with the infusion solution, rigid requirements have to be met in terms of
materials asepsis and ambient hygiene in
the production facilities, so that no harmful particles reach the film. By using
cleaned air in the film bubble, a hermetically sealed space can be relatively sim- >
www.kunststoffe-international.com
Internet-PDF-Datei. Diese PDF Datei enthält das Recht zur unbeschränkten Intranet- und Internetnutzung, sowie zur
Verbreitung über elektronische Verteiler. Eine Verbreitung in gedruckter Form ist mit dieser PDF-Datei nicht gestattet.
15
PAC K A G I N G
and dried fruit. Where perishable food
stuffs are involved, or longer shelf life is
demanded, multi-layer barrier films are
used. They are characterized by special
functional layers that reduce permeability to water and/or moisture, gases and
aromas. Typically speaking, these films
have a symmetric structure with 5, 7, 9,
or 11 layers, whereby the functional layers of PA and EVOH are arranged symmetrically in the middle of the structure
(Fig. 4). Since these materials are incompatible with PE, bonding layers have to be
included in order to ensure sufficient inter-layer adhesion. Each of the outer PE
layers has to exhibit good printability or
high surface gloss. On the other hand,
good sealability must be ensured in order
to produce pillow packaging.
Fig. 3. The vertical Form-Fill-Seal
process is illustrated here by this
heavy duty sack production
Asymmetric Multi-Layer Films
Wherever symmetric structures are involved, sealing presents a challenge. On
the one hand, a processing point has to
be found at which a stabile seal seam
forms. On the other hand, the side of the
film in contact with the sealing jaw must
not get too hot; otherwise it sticks to the
ply created, whose cleanliness can be ensured and that later constitutes the inside
of the infusion bag. During flattening in
the pull-off, air is completely removed
from between the films to prevent soiling. Rapid cooling and the resulting texture make the film soft, similar to a soft
PVC film, even though a PP is involved.
The combination of good film weldability and high puncture resistance is also a
strong motive behind this application,
since infusion bags have to be tight and
repeatedly survive a 1 m fall without leaking. The film must then be soft enough to
ensure pleasant haptics and very good
emptying. All the requirements mentioned can be fulfilled using water-cooled
blown film extrusion to manufacture the
films.
Form-Fill-Seal Packaging
Infusion bags represent a special shape of
packaging produced by the Form-FillSeal process (FFS). In addition to medical
technology, these products are also used
in industry and food packaging sector
(Fig. 3). Stand-up pouches, bags with a side
gusset and simple pillow pouches are in
widespread use. Depending on the design
of the filling equipment, a distinction is
made between horizontal and vertical systems. The film can be fed either as a tube
16
7-layer
Symmetric
y
Asymmetric
y
9-layer
Symmetric
y
Asymmetric
y
P
PA
H
HV
PPE
H
HV
PPA
EEVOH
PPA
H
HV
Fig. 4. Typical
barrier films with
symmetric and
asymmetric
structure. Asymmetric films with
PA in the border
layer accelerate
sealing at the
bottling plant
PPE
© Kunststoffe
or as flat rollstock that is welded to a tube
at first. The actual bags then take form via
transverse welds. Besides mechanical stability and the film’s optical properties,
sealability and strength in the vicinity of
the seal seams are of primary importance.
Since the described pouch version is
suitable in principle for all flowable and
free-flowing packaged goods, it finds wide
use in the food sector. For example, in
Asian countries, milk is packaged almost
exclusively in pillow pouches. In the Middle East, the main packaged goods are edible oils, ghee (clarified butter), rice, nuts
sealing jaw. Impurities can then arise, and
the filling equipment has to be shut down
in order for the impurities to be wiped
away, or to replace the sealing jaws. In order to avoid sticking, the film surface in
contact with the sealing jaw can be
equipped with a thermally stable material, e.g., PA. This can be achieved by laminating a second film, but every additional processing step admittedly generates
additional costs. As an alternative, an
asymmetric film structure can also be
manufactured by co-extrusion in which
the thermally more stable material is in-
© Carl Hanser Verlag, Munich
Kunststoffe international 5/2014
Internet-PDF-Datei. Diese PDF Datei enthält das Recht zur unbeschränkten Intranet- und Internetnutzung, sowie zur
Verbreitung über elektronische Verteiler. Eine Verbreitung in gedruckter Form ist mit dieser PDF-Datei nicht gestattet.
PAC K A G I N G
PA
PE Frost line:
120–80 °C
PE solidifies + shrinks
PA solid
PE
PA
PA Frost line:
180–140 °C
PA solidifies + shrinks
PE molten + elastic
PE
PA
Die orifice:
> 220 °C
Entirely molten
PE
© Kunststoffe
Fig. 5. With conventional blown film extrusion, curling often occurs on asymmetric structures
cluded in a border layer of a multi-layered film (Fig. 4). This approach eliminates
the laminating process, thereby reducing
the overall cost of manufacturing the film.
In both cases, higher temperatures can reduce sealing time in the FFS equipment
and with it the cycle time.
The marked difference in the melting
temperatures of PA and PE certainly has
its disadvantages when processing is done
by conventional blown film extrusion
(Fig. 5). In a 3-layer structure from PA and
PE where the PA layer is on the inside of
the tube, the PA very quickly devolves to
its solid state after exiting the die opening. It solidifies at the frost line of the PA,
while the PE is still present in its molten
state and thus can compensate for volume
shrinkage in the PA by elastic deformation. In the area of the PE frost line, the
PA has already solidified and can no
longer compensate for PE shrinkage by
elastic deformation. The film has a strong
tendency to roll up. This effect is termed
curling. Such curling is disadvantageous
for further processing in the FFS process,
since it complicates film handling in the
FFS machine, thereby slowing down the
process. Similar effects can be observed
to a lesser degree when the melt is cooled
on one side on the chill roll in a cast film
line. In the case of water-cooled blown
film extrusion, the curling phenomenon
almost never appears. Thanks to intensive and rapid melt cooling by contact
with cold water, the frost lines of PA and
PE lie to a certain degree on the same level, so that no curling occurs (Fig. 6). Consequently, the restrictions to further processing disappear.
Kunststoffe international 5/2014
on the outside can remedy the situation
in two ways. For one thing, the barrier effect of PA against oil seepage is markedly higher; for another, sealing at the bottling plant could be accelerated by PA’s
thermal stability, and cycle time shortened at the same time. This film is currently being manufactured at considerable expense by laminating a biaxial oriented PA film onto a PE film.
If an asymmetric film were developed
with PA in the border layer for watercooled blown film extrusion, a packaging
solution could be presented that not only has the above-mentioned positive
properties for further processing, but advantages from an economic point of view,
as well. Moreover, such films have
brighter surface gloss and greater transparency than the standard films available
on the market. Thanks to the PA outer
layer, bottling plant cycle times could be
PE
PA
Die orifice:
> 220 °C
Entirely molten
PE
PA
Water-cooling:
PA + PE solidify + shrink
© Kunststoffe
Fig. 6. Curling during the manufacture of asymmetric films can be avoided by water-cooled blown
film extrusion
Product Development as
Illustrated by Oil Packaging
Since texture alters mechanical properties
of the film, a conventional blown film formula cannot be directly applied to the
version produced with water-cooling. To
demonstrate the potential of this technology, Windmöller & Hölscher performed
a complete product development from
formula to qualification of the finished
packaging solution. Pillow packaging for
edible oil was developed in a joint project with one of India’s largest producers
of such oils (Fig. 7). This edible oil is filled
in a bottling plant mainly in clean 3-layer PE film by the vertical FFS method.
Since edible oil diffuses through PE, these
packaging bags are soon moistened by
thin oil film in a supermarket display. The
use of an asymmetric composite with PA
increased from approx. 30 to 40 cycles per
minute. Thus corresponds to the mechanical capacity of the machines. At the
same time, sealing jaw life would increase
significantly, thereby additionally improving the economics of the overall
process.
Interesting in this connection is the
qualification according to the “Indian
Standard” of the oil packaging filled
thereby. It allows for the packaging of pillow pouches in normal boxes and trucking them more than 2,000 km on Indian
highways. Subsequently, a count is taken
of the packages damaged underway. According to the oil producer, no damaged
pouches could be found following transport – something that had never happened in the past. The thus developed
packaging solution eliminates the additional laminating process, thereby im- >
www.kunststoffe-international.com
Internet-PDF-Datei. Diese PDF Datei enthält das Recht zur unbeschränkten Intranet- und Internetnutzung, sowie zur
Verbreitung über elektronische Verteiler. Eine Verbreitung in gedruckter Form ist mit dieser PDF-Datei nicht gestattet.
17
PAC K A G I N G
a soft, elastic film characterized by very
good weldability. The resulting low tendency to curl is a clear advantage when
asymmetric multi-layer composites are
processed further. REFERENCES
1 N.N.: Converted Flexible Packaging - Industry
Market Research, Market Share, Market Size,
Sales, Demand Forecast, Market Leaders, Company Profiles, Industry Trends. Industry Study 3094,
The Freedonia Group Inc., Cleveland, OH, USA,
November 2013
2 Leopold, T.: Film Production: System Options for
Wafer-Thin Protection, Kunststoffe international
102 (2012) 7, pp. 45-48
Fig. 7. Pillow pouches for edible oil in an Indian supermarket
proving the economics of bottling and
providing improved protection for the
packaged goods.
Conclusion
The demands placed on today’s packaging solutions make it necessary to contin-
18
ue to develop existing raw materials and
production methods. Using water-cooled
blown film extrusion, films can be manufactured with properties spectra that
clearly differ from those obtained by
blown and cast film extrusion. Rapid melt
cooling with water leads to near-amorphous molecular structure. The result is
THE AUTHORS
DIPL.-ING. LENNART EDERLEH, born in 1975, is
Technical Sales Director for Windmöller & Hölscher’s
blown film lines.
DIPL.-ING. TILL BERGMANN, born in 1981, is
process specialist for water-cooled blown film extrusion at Windmöller & Hölscher.
DIPL.-ING. INGO PUTSCH, born in 1967, is Technical Sales Manager at Windmöller & Hölscher and additionally responsible for Aquarex water-cooled extrusion lines.
© Carl Hanser Verlag, Munich
Kunststoffe international 5/2014
Internet-PDF-Datei. Diese PDF Datei enthält das Recht zur unbeschränkten Intranet- und Internetnutzung, sowie zur
Verbreitung über elektronische Verteiler. Eine Verbreitung in gedruckter Form ist mit dieser PDF-Datei nicht gestattet.