Note: Descriptions are shown in the official language in which they were submitted.
1
FILM LINE AND METHOD FOR PRODUCING A FILM WEB
The invention relates to a method for producing a blown film web, a blown film
line and a film produced by same.
Blown film lines are extensively known in the prior art. They are used to
produce
large format films in the form of tubes made from melted thermoplastics.
Plastics
are supplied to the lines in granulated form which is then plasticized into a
viscous
mass under high pressure in extruders. This mass is formed into an annular
shape
in a die head and is discharged from the die head through an annular nozzle.
The
mass is already in the form of a film tube as it exits the annular nozzle. The
film
tube is drawn up or down along a tube forming zone in which compressed air is
introduced into the interior of the film tube. This leads to a transverse
stretching
of the film tube. The melt is cooled by an active cooling medium for the
ascending or descending film tube at a tolerable distance from the annular
nozzle. The path taken by the film tube passes through a calibration cage
followed by a flat lay which flattens the film. The flat lay unit pre-squeezes
the
double-layer film web. Squeezing then follows, with a virtually air-free
double-
layer film web ultimately being formed from the film tube. It is as of this
point at
the latest, or even as of the pre-squeezing stage itself, a double-layer film
web.
Blown film lines may have different orientations: In the past, production
usually
took place vertically from top to bottom; i.e. in the effective direction of
gravity,
nowadays, however, production is usually from the bottom upward, thus against
the effective direction of gravity. The first blown film lines in the top-to-
bottom
direction of production thereby took advantage of gravitational force.
However,
due to circumstances such as thinner melts being developed and efforts under-
taken to increase throughput, difficulties arose with the stability of the
film tube
.. immediately after exiting the nozzle. The film is still molten at that
point and,
depending on the film material and throughput, not able to support the weight
of
the film tube continuing to come down in the effective direction of gravity,
which
can lead to the film bubble ripping. If the film bubble rips, the line needs
to be
restarted, meaning a significant expenditure of time and money. With the
bottom-upward production direction; i.e. against the effective direction of
gravity,
the film tube is pulled off on the far side from the nozzle, i.e. at the top,
by a
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pair of rollers which takes up the weight of the film bubble at a point at
which
the film bubble has further cooled and can therefore bear this force.
Customary film materials for blown films are crystalline or semi-crystalline
materials, for example certain polyethylene or polypropylene compounds or even
certain polyamides and ethylene vinyl alcohols or ethylene vinyl acetates,
among
others. In multilayer films, the different layers consist of different
materials
having different properties such as printability, UV blocking properties or
diffusion barrier properties, for example. Blown films have a broad field of
.. application and are used for example as packaging film, including in
medical
technology or for food packaging, agrofoils, bags, laminating films, etc.
To support the cooling of the film bubble, thermoregulated external air is
usually
passed against the film bubble. The supporting air, i.e. the air introduced
into the
film bubble to inflate the film bubble, can also be thermoregulated and guided
in
a flow, whereby new cold air is continuously blown into the film bubble so as
to
also cool the film bubble from the inside.
Should the produced film be as transparent as possible, it needs to be cooled
down very quickly after the nozzle in order to severely inhibit or even
prevent the
crystallization of the melt as much as possible. Further positive effects of
rapid
cooling include, for example, high gloss, high puncture and tear resistance as
well as good thermoforming properties.
Heat transfer from plastic to air is much worse than that from plastic to
water.
Using water as a cooling medium to extract heat from the film tube is
therefore
obvious and also known. This is most easily achieved when the production
direction is in the direction of gravity; i.e. downward, since the water
itself can
then follow gravity and there is no risk of water flowing onto the nozzle,
which
needs to remain hot.
It can be problematic if the film tube has already been cooled down to such an
extent that the film web can only be minimally deformed or not even at all
after
the flat lay. Forces acting on the film web during further process steps can
then
lead to visual defects in the film or other losses in quality. It is therefore
critical
to find a suitable compromise between cooling the film down quickly enough to
Date Recue/Date Received 2023-10-16
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inhibit as much crystallization as possible and at the same time prevent
supercooling of the film.
The present invention is based on the task of providing an improvement or an
alternative to the prior art
Summary of the invention
According to a first aspect, the task posed is solved by a method for
regulating a
degree of crystallization of a film tube during its production via a blown
film line,
wherein the blown film line has a processing station for the film tube,
wherein the blown film line exhibits a downward direction of production,
comprising the following steps:
a) defining a target temperature range of the film tube at least at one
specific
area of the processing station,
b) detecting an actual temperature of the film tube at the specific area of
the
processing station,
c) in the case of the actual temperature deviating from the target temperature
range, changing a production parameter ahead of the specific area of the
processing station in the production direction which exerts a direct or
indirect
influence on the actual temperature of the film tube at the specific area of
the processing station in order to drive the actual temperature into the
target
temperature range.
The target temperature range of the film tube depends on different parameters
such as the material and the system used. Advance testing, for example, can
determine the ideal film tube temperature range for the material and system
used
at the given parameters. Alternatively, the target temperature range could be
determined algorithmically. Utilizing a database which stores target
temperature
ranges for the material and the system used or for the system components used
is also conceivable.
Different devices are conceivable for detecting the film tube's actual
temperature.
A pyrometer such as an infrared measuring instrument or an infrared camera,
for
example, is generally used to detect temperatures of objects. It is possible
to
Date Recue/Date Received 2023-10-16
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detect the actual temperature of the film tube once, to detect it at discrete
intervals or to detect it continuously. Detecting at discrete intervals or
continuously can be advantageous in that doing so allows in-process control.
Furthermore, any potential fluctuations of the actual temperature can be
responded to as necessary.
Detecting the actual film tube temperature is generally possible at multiple
areas
of the processing station. In order to detect the influence of changed
production
parameters on the actual temperature, however, it should be detected at a
sufficient distance from the component exerting an influence on the film
tube's
actual temperature at the specific area of the processing station.
Driving the actual temperature into the target temperature range by changing a
production parameter ahead of the specific area of the processing station in
the
production direction which exerts a direct or indirect influence on the actual
temperature of the film tube at the specific area of the processing station
allows
an adapting of the actual temperature so that it approaches or enters into the
target temperature range.
A precision adjustment can thereby be made, whereby the film is cooled down
quickly enough so as to inhibit as much crystallization as possible on the one
hand and, on the other, prevent a supercooling of the film. Moreover, the
entire
film line can thereby be operated particularly efficiently in terms of energy
for the
simple reason of being able to avoid an energetically disadvantageous cooling
of
the film web and then subsequent heating of same.
The invention in detail
In one advantageous embodiment, the processing station exhibits water cooling
having a central passage for the film tube running through the water cooling
during operation of the blown film line.
Heat transfer from plastic to air is much worse than that from plastic to
water.
Using water as a cooling medium can therefore extract heat from the film tube
more quickly, thereby enabling a rapid decrease in the film tube's
temperature,
whereby the crystallization of the melt is again inhibited or even prevented
to the
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greatest extent possible. Further positive effects of rapid cooling are, for
example, high gloss, high puncture and tear resistance as well as good thermo-
forming properties of the film. The central passage enables even cooling over
the
surface of the film tube.
In an additional or alternative embodiment, the specific area on the
processing
station is situated directly after a film tube cooling section, wherein the
production parameter to be changed is the water temperature of the water
cooling. The specific area is advantageously directly after the water cooling.
Detecting the actual temperature directly after the film tube cooling section,
preferably directly after the water cooling, allows for detecting the full
extent of
the production parameter change on the actual temperature.
Changing the water temperature is simple for one skilled in the art to
implement.
The water can be selectively cooled or heated. This can either ensue
electrically
using heat exchangers or with fossil fuels. The water temperature is advan-
tageously varied by at most 50 K, preferentially at most 25 K, in particular
preferentially by at most 10 K, and particularly preferentially by at most 5
K.
In a further or alternative embodiment, the specific area on the processing
station is situated directly after a film tube cooling section, wherein the
production parameter to be changed is the volume of water of the water
cooling.
The specific area is advantageously directly after the water cooling.
Detecting the actual temperature directly after the film tube cooling section,
preferably directly after the water cooling, allows for detecting the full
extent of
the production parameter change on the actual temperature.
Changing the volume of water is simple for one skilled in the art to
implement.
Increasing the volume of water results in there being more cooling medium,
whereby increased heat exchange can occur between the film tube and the
cooling medium. More rapid cooling of the film tube can thus take place.
Conversely, reducing the volume of water results in a decreased heat exchange
and thus a slower cooling. The water volume is advantageously varied by at
most
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50 L/min, preferentially by at most 25 L/min, in particular preferentially by
at
most 10 L/min, and particularly preferentially by at most 5 L/min.
In an additional or alternative embodiment, the specific area on the
processing
station is situated directly after a film tube cooling section, wherein the
production parameter to be changed is the speed of the film tube. The specific
area is advantageously directly after the water cooling.
Detecting the actual temperature directly after the film tube cooling section,
preferably directly after the water cooling, allows for detecting the full
extent of
the production parameter change on the actual temperature.
Changing the film tube speed is simple for one skilled in the art to
implement. It
is conceivable to adjust the film tube speed by changing the rotational speed
of
the take-off rollers. It must hereby be noted that the rotational speed cannot
be
increased arbitrarily since the quality of the film may otherwise be impaired
up to
and including the film even ripping. A further possibility for adjusting the
film
tube speed is changing the extrusion speed, for example by adapting the amount
of extrudate. The film tube speed is advantageously varied by at most 50 m/s,
preferentially by at most 25 m/s, in particular preferentially by at most 10
m/s,
and particularly preferentially by at most 5 m/s.
In a further or alternative embodiment, the specific area on the processing
station is situated directly after a film tube cooling section, wherein the
production parameter to be changed is an interior temperature of the film
tube.
The specific area is advantageously directly after the water cooling.
Detecting the actual temperature directly after the film tube cooling section,
preferably directly after the water cooling, allows for detecting the full
extent of
the production parameter change on the actual temperature.
Changing the film tube's interior temperature is simple for one skilled in the
art
to implement. It is thus conceivable to thermoregulate the supporting air;
i.e. the
air introduced into the film bubble to inflate the film bubble, and guide it
in a
flow, whereby new cold air is continuously blown into the film bubble in order
to
also cool and/or heat the film bubble from the inside. The inside of the film
can
Date Recue/Date Received 2023-10-16
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furthermore be thermoregulated by a cooling and/or heating element such as a
cooling and/or heating cylinder, for example, with the interior temperature of
the
film tube thereby being adapted. The film tube's interior temperature is advan-
tageously varied by at most 50 K, preferentially by at most 25 K, in
particular
preferentially by at most 10 K, and particularly preferentially by at most 5
K.
In an additional or alternative embodiment, the specific area on the
processing
station is situated directly after a film tube cooling section, wherein the
production parameter to be changed is the distance to be covered within the
.. water cooling based on the film tube's direction of travel. The specific
area is
advantageously directly after the water cooling.
Detecting the actual temperature directly after the film tube cooling section,
preferably directly after the water cooling, allows for detecting the full
extent of
the production parameter change on the actual temperature.
Changing the distance to be covered within the water cooling based on the film
tube's direction of travel can for example be achieved by varying the height
of
the area in which the cooling water is discharged based on the direction of
flow
of the film. The distance to be covered within the water cooling based on the
film
tube's direction of travel is advantageously varied by at most 100 cm,
preferentially by at most 50 cm, in particular preferentially by at most 20
cm, and
particularly preferentially by at most 10 cm.
Pursuant to the above-specified embodiments, "directly" is to be understood
here
as the distance of the specific area from the cooling section being less than
50 cm,
preferentially less than 20 cm, in particular preferentially less than 10 cm,
and
particularly preferentially less than 5 cm.
In a further or alternative embodiment, the specific area on the processing
station is situated ahead of a film tube cooling section, wherein the
production
parameter to be changed is a film tube entry temperature into the cooling
section. The specific area is advantageously directly ahead of the water
cooling.
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Detecting the actual temperature ahead of the film tube cooling section,
preferably ahead of the water cooling, allows for detecting the full extent of
the
production parameter change on the actual temperature before the film tube
enters into the cooling section. This thereby enables detecting the
contribution
the adapted film tube entry temperature makes to the actual temperature of the
film tube absent other components of the system such as the cooling section,
for
example, or other production parameter changes making a further contribution
to
the film tube's actual temperature.
Changing the film tube entry temperature into the cooling section can for
example be regulated by adapting the temperature control of the plastic
material
or the plasticized plastic in the extruder screw. It must hereby be noted that
the
plasticized plastic thereby needs to be at a sufficiently high enough
temperature
to produce a blown film. The film tube entry temperature into the cooling
section
is advantageously varied by at most 50 K, preferentially by at most 25 K, in
parti-
cular preferentially by at most 10 K, and particularly preferentially by at
most 5 K.
In an additional or alternative embodiment, the specific area on the
processing
station is situated on a cooling section of the film tube, wherein the
production
parameter to be changed is the water contact distance above the water cooling.
The specific area is advantageously situated on the water cooling.
Detecting the actual temperature directly on a film tube cooling section,
preferably on the water cooling, allows for detecting the full extent of the
production parameter change on the actual temperature. This thereby enables
detecting the contribution the adapted water contact distance makes to the
actual temperature of the film tube, wherein the contribution to the actual
temperature of the film tube made by other system components or other
production parameter changes is reduced.
Changing the water contact distance above the water cooling is simple for one
skilled in the art to implement. Conceivable would be adjusting the supply or
discharge of water above the water cooling. A change in the water contact
distance can be achieved by water being removed again from the film web at an
earlier or later point in relation to the film web's direction of travel.
Removing the
water from the film tube earlier can reduce the cooling efficiency. In
contrast,
Date Recue/Date Received 2023-10-16
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cooling efficiency is increased when the water is removed from the film tube
at a
later point. This modification can be realized by means of a height-adjustable
base plate of the water contact section, for example.
The heat transfer from plastic to water is significantly better than from
plastic to
air. Thus, even small changes to the water contact distance can achieve major
effects in terms of controlling the temperature of the film tube. The water
contact
distance above the water cooling is advantageously varied by at most 10 cm,
preferentially by at most 5 cm, in particular preferentially by at most 2 cm,
and
particularly preferentially by at most 1 cm.
In a further or alternative embodiment, the specific area on the processing
station is situated ahead of a flat lay unit of the film tube, wherein the
production parameter to be changed is a film tube entry temperature into the
flat lay unit.
Various production parameters are conceivable for adjusting the film tube
entry
temperature. The production parameters of the previous embodiments are to be
noted here.
Detecting the actual temperature ahead of a flat lay unit of the film tube
thereby
enables detecting the cumulative effect of modified production parameters on
the
film tube before it is laid flat for further processing and ultimately wound
onto
the winder. The film tube entry temperature in the flat lay unit is
advantageously
varied by at most 50 K, preferentially by at most 25 K, in particular
preferentially
by at most 10 K, and particularly preferentially by at most 5 K.
In an additional or alternative embodiment, the specific area on the
processing
station is situated ahead of the film tube take-off, wherein the production
parameter to be changed is a film tube entry temperature into the take-off.
Various production parameters are conceivable for adjusting the film tube
entry
temperature. The production parameters of the previous embodiments are to be
noted here.
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Detecting the actual temperature ahead of the film tube's take-off thereby
enables detecting the cumulative effect of modified production parameters on
the
film tube before it goes through further process steps such as reversing. The
film
tube entry temperature in the take-off is advantageously varied by at most 50
K,
preferentially by at most 25 K, in particular preferentially by at most 10 K,
and
particularly preferentially by at most 5 K.
In an additional or alternative embodiment, the specific area on the
processing
station is situated after the film tube take-off, whereby the production
parameter
.. to be changed is a film tube exit temperature from the take-off.
Various production parameters are conceivable for adjusting the film tube exit
temperature. The production parameters of the previous embodiments are to be
noted here.
Detecting the actual temperature after the film tube's take-off thereby
enables
detecting the cumulative effect of modified production parameters on the film
tube
before it goes through further process steps such as reversing. The film tube
exit
temperature from the take-off is advantageously varied by at most 50 K,
.. preferentially by at most 25 K, in particular preferentially by at most 10
K, and
particularly preferentially by at most 5 K.
A plastic molding system constitutes a further aspect of the invention,
particularly
a blown film line or flat-film line or other system designed to produce a film
web
.. using a processing station, wherein the plastic molding system comprises a
means for detecting an actual temperature of the film tube at a specific area
of
the processing station for regulating a degree of crystallization of a film
tube
during its production and a control unit for changing a production parameter
which exerts a direct or indirect influence on the actual temperature of the
film
tube at the specific area of the processing station ahead of the specific area
of
the processing station in the production direction.
Detecting the actual temperature of the film tube at a specific area of the
processing station together with a control unit for changing a production
parameter which exerts a direct or indirect influence on the actual
temperature of
the film tube at the specific area of the processing station ahead of the
specific
Date Recue/Date Received 2023-10-16
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area of the processing station in the production direction allows changing
individual or multiple production parameters and thereby selectively
influencing
the degree of crystallization of a film tube. For example, the lowest possible
degree of film tube crystallization can be achieved while simultaneously
maintaining the film's deformability.
In an additional or alternative embodiment, the plastic molding system is a
blown
film line.
In an additional or alternative embodiment, the blown film line extrudes a
film
tube from top to bottom.
A top-to-bottom extruding of the film tube is particularly suitable in
combination
with water cooling since the water is conveyed along the machine direction
solely
by the force of gravity.
In an additional or alternative embodiment, the plastic molding system is
suited
to implementing the inventive method.
The following clarifications are made with respect to terminology:
It is expressly pointed out that in the context of the present patent
application,
indefinite articles and indefinite numerical details such as "one...,"
"two...," etc.
should generally be understood as a minimum indication; i.e. as "at least
one...,"
"at least two...," etc., unless the context or the specific text of a certain
passage
indicates that only "exactly one...," "exactly two...," is intended at that
point.
Furthermore, all numerical details as well as details on method parameters
and/or
device parameters are to be understood in the technical sense; i.e. are to be
understood as having the usual tolerances. Neither does explicitly specifying
the
"at least" or similar limitation allow drawing the inference that simply
stating
"one;" i.e. without specifying "at least" or similar, means "exactly one."
The previously described embodiments can be employed individually or also in
any combination with one another in configuring the inventive apparatus and
utilizing the inventive method.
Date Recue/Date Received 2023-10-16
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The following clarifications are made with respect to terminology:
"Crystallization" is to be understood as the molecular chains in the plastic
polymer becoming partially ordered when the melt solidifies. Starting from
crystallization nuclei, the molecular chains fold together and form so-called
lamellae separated by amorphous areas. The lamellas form superstructures such
as spherulites, for example. Crystallite formation is subject to the cooling
conditions, the additives and fillers in the polymer as well as the flow
conditions
during solidification. Subsequent stretching also changes the arrangement of
the
molecules and thus the properties of the material.
Understood by "processing station for the film tube" is the region of the line
up
to the winder.
Understood by "production parameter" is any parameter in the system which is
able to be adjusted and which exerts an influence on the temperature of the
film
tube.
The "machine direction" is the designated path of the film starting from the
extrusion at the nozzle through to the winder. The machine direction therefore
varies inasmuch as it runs around multiple rollers and possibly also turning
bars.
The "film web" is a tubular film web, whereby the tube is separated on one or
both sides after having been laid flat or is left in tubular form.
The invention will be described in greater detail below on the basis of
exemplary
embodiments referencing the figures. Shown therein
Fig. 1 a schematic sketch of a detail of an inventive blown film line
from the
nozzle to behind the calibration zone
Fig. 2 a schematic sketch of the enlarged detail A from Fig. 1
Fig. 1 shows a detail of a blown film line according to the invention from the
nozzle 110 to behind the calibration zone 200 as a schematic sketch. The film
tube extruded from the nozzle 110 is inflated into the film bubble 600 and
passes
Date Recue/Date Received 2023-10-16
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through the calibration zone 200 by first entering the base chamber 210. The
base chamber 210 has a base chamber cooling fluid inlet 211 through which the
cooling fluid, e.g. water able to be provided with an additive, is applied
through
the base chamber 210 to the exterior of the film bubble 600. The film bubble
600
then runs into the calibration insert 220. The calibration insert 220 exhibits
a
vertical expansion IK. The cooling fluid introduced through the base chamber
cooling fluid inlet 211 and the calibration insert cooling fluid inlet 221
forms a
cooling fluid film 230 on the exterior of the film bubble 600 situated between
the
exterior of the film bubble 600 and the inner wall of the calibration unit and
cools
the film bubble 600 very efficiently, whereby the film bubble 600 is precisely
calibrated at the same time, wherein visible contact marks on the surface of
the
film are significantly minimized or even eliminated, both in terms of their
frequency as well as their magnitude.
Fig. 2 shows the enlarged detail A from Fig. 1 as a schematic sketch. The
annular surface 222 transitions with a second radius rR into the inside slope
R of
the edge forming an angle a with the annular surface. For its part, the inside
slope R transitions at a first angle a into the inlet slope E on the inner
surface of
the calibration insert 220. The first radius (rE) is thereby in the range of
0.5 mm
to 5mm, preferentially in the range of 1 mm to 3 mm, and particularly
preferentially in the range of 1 mm to 2 mm. The second radius (rR) is in the
range of 1 mm to 10 mm, preferentially in the range of 3mm to 7 mm, and
particularly preferentially in the range of 4mm to 6mm. The edge itself rises
by a
height (hR) above the annular surface, wherein the height (hR) is in a range
of 1
mm to 30 mm, preferentially 5 mm to mm 20 mm, and particularly preferentially
8 to 15 mm. The inlet slope E forms an angle (b) to the vertical which is
between
0.50 and 20 , preferentially between 1 and 10 , and particularly
preferentially
between 1.5 and 5 . The vertical expansion of the inlet slope E has a
vertical
extension IE of 5 mm to 20 mm, preferentially 10 mm to 15 mm, and particularly
preferentially 11.5 mm to 12.5 mm.
The embodiments shown here only represent examples of the present invention
and should therefore not be construed as limiting. Alternative embodiments
entertained by those skilled in the art are equally included within the
protective
scope of the present invention.
Date Recue/Date Received 2023-10-16
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List of reference numerals used
110 annular nozzle, nozzle
210 base chamber
211 base chamber cooling fluid inlet
220 calibration insert
221 calibration insert cooling fluid inlet
222 annular surface
230 cooling fluid film
241 cooling fluid outlet
600 film bubble
hR edge height
E inlet slope
IE inlet slope vertical extension
IK calibration insert vertical extension
R inside slope
rE first radius, radius at the transition from the inside slope to the
inlet slope
rR second radius, radius at the transition from the annular surface to
the
inside slope
A detail
X general production direction
a angle between the inside slope and annular surface
b angle between the inlet slope and the vertical or the central axis
of the
calibration insert
Date Recue/Date Received 2023-10-16
