APPAREIL ET METHODE DE FABRICATION DE PELLICULES POLYMERES A EPAISSEUR CONTROLEE, ET PELLICULES POLYMERES AINSI PRODUITS

DEVICE AND METHOD FOR THE MAKING OF POLYMERIC FILMS WITH CONTROLLED THICKNESS, AND POLYMERIC FILMS THEREOF

Abrégé anglais

Described herein are polyethylene geomembrane liners having a peripheral
longitudinal
welding edge. The thickness of the any longitudinal strip at desired position
is controlled
with a method and a device in contact with the molten polymer that provides
rapid
cooling. This thickened strip can be in the peripheral longitudinal edges. The
apparatus is
positioned above the die of a blown film extrusion line and before the
solidification point
of molten polymer. The device and method of using it described herein can be
used to
control the thickness of any type of plastic films in blown film process to
improve
physical mechanical properties at some parts of the films or simply in the
full width of
the film.

Revendications

CLAIMS
1. A plastic film having:
a. a main part formed of a film having an average thickness preferably of at
least 0.254 mm thick across the width; and
b. at least one area, preferably a longitudinal strip, having a thickness that
is
preferably at least about 5% higher than the average thickness of the main
part.
2. A plastic film according to claim 1, wherein: the at least one longitudinal
strip is
located at a peripheral edge of the plastic film.
3. A plastic film according to claim 1 or 2, wherein both longitudinal
peripheral
edges of the film are oversized and have a thickness that is at least 5%
higher than
the average thickness of the rest of the film.
4. A plastic film according to any one of claims 1 to 3, wherein the width of
an
oversized longitudinal peripheral edge ranges from about 1% to about 10% of
the
film width, preferably ranges from about 2% to about 6%.
5. A plastic film according to any one of claims 1 to 4, having two
longitudinal
peripheral oversized edges.
6. A plastic film according to any one of claims 1 to 5, wherein the shape of
the
peripheral edge, is such that the thickness reaches its maximum at the outer
edge(s) of the smooth edges.
7. A plastic film according to any one of claims 1 to 6, wherein the at least
longitudinal peripheral oversized edge is made of the same material of the
sheet.
8. A plastic film according to any one of claims 1 to 7, wherein at least the
thickness
of one of the longitudinal strips is different from the other thickened
strips.
9. A plastic film according to any one of claims 1 to 7, wherein the film is
made
from a natural or synthetic polymer, and is preferably made of at least one of
the
followings: High density Polyethylene (HDPE), Medium Density Polyethylene
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(MDPE), linear low density Polyethylene (LLDPE), Low density polyethylene
(LDPE) and Polyethylene for Raised Temperature (PERT) as well as
thermoplastic elastomers (TPEs) or thermoplastic olefins (TPOs), or any
combination thereof.
10. A plastic film of any one of claims 1-8 wherein the plastic film is filled
with any
kind of fillers, micro-fillers or nano-fillers such as, but not limited to,
short or
long glass fibers, talk, fire retardants, Carbon black or conductive
additives.
11. A plastic film of any one of claims 1-9, where the thickened areas are
only in
specific parts of the film, preferably on peripheral edges, more preferably in
a
discontinued way.
12. A plastic film of any one of claims 1 to 11, wherein the film is smooth at
either or
both sides of the film.
13. A plastic film of any one of claims 1 to 11, wherein the film is textured
on one
side or both sides of the film.
14. A plastic film of any one of claims 1 to 11, wherein the film is at least
partly
textured on at least one side of the film.
15. A plastic film of any one of claims 1 to 14, wherein the film is at least
partially
colored on at least one side of the film.
16. A plastic film of any one of claims 1 to 15, wherein the film is at least
partially
conductive on at least one side including or not the peripheral edges.
17. A plastic film, according to claims anyone of claims 1-16, wherein: the
longitudinal strip is located anywhere in the width of the plastic film and/or
in
continuous or discontinuous manner.
18. A plastic film, according to anyone of the claims 1-17, wherein: the
plastic film is
a geomembrane liner, wherein the liner is used for waste containment,
contaminated soil containment, fluid containment, mining containment, capping,
secondary containment, dam, canal, fluid control.
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19. A plastic film, according to anyone of the claims 1-18, wherein: the
plastic film is
composed of n layers where n.gtoreq.2.
20. A plastic film, according to claim 19, wherein at least one layer is not
conductive
or partially conductive.
21. A plastic film, according to claim 19, wherein at least 2 layers are
coextruded.
22. A plastic film, according to claim 19, wherein at least 2 layers are
laminated on
each other.
23. A plastic film, according to claim 19, wherein at least one layer is of a
different
thickness profile than the other layer(s).
24. A plastic film, according to claim 19, wherein at least one layer is made
of a
synthetic or natural polymer.
25. A plastic film, according to claim 24, wherein at least one layer is made
of
flexible non-polymeric material such as metallic films e.g. Aluminium or
copper.
26. A plastic film, according to claim 25, wherein the film is a multilayer
sandwich
panel of one or more plastic layers and one or more metal layers like
Aluminium
to be used in construction applications, or laminated packaging film of
similar
structure in food packaging applications.
27. A roller made of a plastic film, according to any one of claims 1 to 26,
rolled on a
spool.
28. A device for cooling a molten plastic film and form a thickened part of
the plastic
film, the device comprising: at least one solid element with controlled
temperature adapted to be installed at a die exit of a polymer processing
extruder
and having a surface configured to be in contact with a surface of said molten
plastic film, the device allowing controlled cooling of at least one surface
of the
molten plastic, wherein said cooling is performed through conduction heat
exchange between the surface of said solid element and the surface of said
molten
polymer film.
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29. A device, according to claim 28, wherein the temperature of at least one
part of
the surface of the element in contact with the film is controlled in a way
that the
said heat exchange between said molten polymer surface and said surface of the
solid element generates a thickening effect on at least one longitudinal
strip.
30. A device, according to claims 28 and 29, wherein the surface of the solid
element
has a dimension of about a dimension of the thickened part of the molten
plastic
film to be obtained.
31. The device of any one of claims 28 to 30, wherein the solid element is a
straight
plate, preferably of the same size of longitudinal strip of a desired size or
the
whole perimeter of the film.
32. The device of any one of claim 28 to 30, wherein the solid element is a
curved
plate of a desired size.
33. The device of any one of claim 28 to 32, where there solid element is made
of n
sections, wherein each of the n sections are similar or different and
connected or
separated, the difference may be in surface temperature, in the size or in the
form
of the solid object to cover a strip or the whole perimeter of the film.
34. The device of any one of claim 29-33, wherein the device is static i.e.
not
moving, or is moving or vibrating in any direction such as, but not limited
to,
rotating as in a calendar, moving up and down the machine direction
(vertically)
or moving in transverse direction (horizontally), in a continued or a
discontinued
manner.
35. The device of any one of claims 29 to 34, wherein the temperature of the
solid
object is controlled by a fluid or a gas flowing in the other side or inside
the solid
object to cool down the interface with the film.
36. The device of any one of claims 29 to 35, wherein the film has a thickness
of .ltoreq.
0.254 mm for different applications such as, but not limited to, food
packaging,
shopping bags, silage films, mulch film or shrink films.
37. The device of any one of claims 29 to 35, wherein the film has a thickness
.gtoreqØ254
mm and preferably ranging from about 0.254 mm to 3 mm, and especially
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ranging from 0.5 mm to 2.5 mm used for various applications such as, but not
limited to, geomembranes, caps and covers.
38. A method of adjusting the thickness of plastic film using the device of
any one of
claims 29 to 35, wherein the molten polymer, being pushed out of the die of a
blown film process, comes in contact with the cooling surface of the said
solid
element, wherein the solid element is installed after the die exit and before
the
solidification of the molten plastic film and the temperature is adjusted in a
way
that it results in the desired thickness which is preferably at least 5%
higher in
thickness than the average thickness of the film.
39. A method of claim 38, wherein both longitudinal peripheral edge being
oversized
and having a thickness that is at least 5% higher than the average thickness
of the
rest of the sheet.
40. A method of claim 38, wherein the width of an oversized longitudinal
peripheral
edge ranges from about 1% to about 10% of the film width, preferably ranges
from about 2% to about 6%.
41. A method of claim 38, wherein the film has two longitudinal peripheral
oversized
edges.
42. A method of claim 38, wherein the shape of the peripheral edge, after
cooling
with the method mentioned in this invention, is such that the thickness
reaches its
maximum at about the outer edge of the smooth edges.
43. A method of claim 38, wherein the thickened strip of the molten polymer
has
undergone a morphological transformation resulting in different molecular
structure such as different crystallinity and/or molecular orientation and/or
density.
44. A method of claim 38, wherein the device is installed all around the
perimeter of
the film to affect the whole width of the final film.
45. A method of anyone of claims 38 to 44, wherein the film is made from a
natural
or synthetic polymer, and is preferably made of at least one of the
followings:
High density Polyethylene (HDPE), Medium Density Polyethylene (MDPE),
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linear low density Polyethylene (LLDPE), Low density polyethylene (LDPE) and
Polyethylene for Raised Temperature (PERT) as well as thermoplastic elastomers
(TPEs) or thermoplastic olefins (TPOs), or any combination thereof.
46. A method of anyone of claims 38 to 44, wherein the thickened areas are
only in
certain spots of the film or peripheral edges in a discontinued way.
47. A method of anyone of claims 38 to 44, wherein the edges are characterized
by a
thickness of at least 5% higher than the average thickness of the rest of the
film
and with at least one edge which does not contain any conductive media.
48. A method of anyone of claims 38 to 44, wherein the film is smooth at
either or
both sides.
49. A method of anyone of claims 38 to 44, wherein the film is textured on one
side
or both sides.
50. A method of anyone of claims 38 to 44, wherein the film is colored on one
or both
sides.
51. A method of anyone of claims 38 to 44, wherein the liner is conductive on
one
side or both sides including or excluding the peripheral edges.
52. Any use of the polymeric film as defined in anyone of claims 1 to 26 or a
polymeric film obtained by the device of any one of claims 28 to 37 or through
the method defined in anyone of claims 38 to 44, in applications such as
geomembrane liners, capping and covers, packaging films, shopping bags, shrink
films, silage films and similar.
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Description

CA 02953375 2017-01-03
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DEVICE AND METHOD FOR THE MAKING OF POLYMERIC FILMS WITH
CONTROLLED THICKNESS, AND POLYMERIC FILMS THEREOF
Field of the Invention
[0001] The present invention belongs to the field of polymeric material, and
generally
relates to an apparatus and method for cooling a relatively thick polymer
after die exit in
blown film processing.
Background of the Invention
[0002] Polyethylene geomembranes are used extensively as a part of liquid
containment
systems in different applications such as in modem landfills or heap leach in
mining
industry. In all those applications the geomembrane is part of a system
including
geotextile and/or geosynthetie clay liner (GCL) as well as geomembranes. The
integrity
of this lining system is dependent on the cohesion between the different
layers. Since the
regular gluing mechanism cannot be used for this application with all the
chemicals used
and the big scale of the work, that integrity depends on the friction between
the layers.
The surface of the geomembranes can be texturized to increase friction via
different
methods such as US4885201, US5403126 and US5258217.
[0003] There are different methods for producing polymeric films namely Cast
film
process and blown film process. In the latter process, the molten polymer is
pushed into
a die with annular die-exit where it forms a tube being pulled upward by the
winders. The
die exit is equipped with high efficiency high pressure air cooling system
which blows
cool air on the surface of the film from both sides to cool down the polymer
and freeze
the molecular structure as early as possible. The efficiency of the cooling
system will
determine the final properties of the film. The tube diameter and film
thickness are
controlled by blow-up and take-up ratios.
[0004] Today most of the Polyethylene geomembranes are made in three layers by
co-
extrusion, similar to the trend in food packaging film industry. Multilayer
structure
provides the possibility to customise the product for different applications.
One of the
advantages of multilayer structure is using different materials in the core
and skin layers
to get the benefits of both materials such as HD/LL/HD combination (Cahpter 3,
HDPE
Geomembranes; in A Guide to Polymeric Geomembranes, John Schiers, 2009, John
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Wiley & Sons). Another very important benefit of multilayer structure is the
possibility
of texturizing the skin layers without affecting the physical-mechanical
properties of the
thick core layer. JD Green (US5763047) introduces a method of texturizing the
surface
layer of the geomembranes with nitrogen or any other blowing agent. This
dissolved
blowing agent bursts into projections on the surface of the film at the die
exit due to the
sudden pressure drop. This phenomenon results in randomly textured surface.
[0005] Though textured surface brings a great advantage but it imposes some
difficulty to
the installations. In-field installations by fusion welding technic can be
very problematic
with textured surfaces. In order to solve that problem, a technique is
provided to reduce
texturizing the surface at the overlap edges where most of the welding is
applied
(US5804112). In this technique the flow of outer layers is simply blocked at
the die to
provide a peripheral edge. So at the peripheral edge a pretty easy welding can
be
performed.
[0006] When blocking the skin layers at the die exit, due to the lower
thickness and
higher stress concentration on the peripheral edge region a necking phenomenon
(i.e.
reducing the thickness or Thinning) occurs at that part. Then the resulted
thin areas act as
weak points and cannot pass the norms of the industry (GRI GM 13) which
specifies that
minimum thickness should be 10% below the average thickness. This phenomenon
is
more pronounced in some specific surfaces such as the liners with electrically
conductive
layer (hereafter, "conductive liner") (US 5288168), where the necking problem
becomes
so pronounced that it can make the peripheral edges up to around 15% thinner
than the
nominal thickness of the geomembrane in both smooth and textured surfaces.
Consequently they have to trim the peripheral edge which brings the difficulty
of welding
afterwards. The conductive layer poses a lot of complexity to the welding
process to a
point that GSE Lining Inc. has introduced a very special welding machine for
this kind of
material (US9033620B2). And obviously it increases the cost of finished
geomembranes
lined systems considerably, plus the troubles of working with that machine for
the
welders.
[0007] To better control the thickness of the films, many attempts have been
observed so
far, especially in thin film industry. H.Upmeier (US4339404) proposed to
install a
thickness controlling sensors over the entire perimeter of the tube. These
sensors will
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measure the thickness at each spot and then adjust the cooling capacity at the
die exit
(temperature and pressure of air jets) based on the film thickness profile.
[0008] In some other cases, some researchers have tried to impose some
unbalanced
thickness profile to the film due to the requirements in some specific
applications such as
tie bags (US6139186). This is achieved by increasing the cooling capacity of
the air jets
at the proper positions to freeze in earlier and get thicker material. But
this is not always
feasible for every film thicknesses (higher thicknesses would not be easily
changed by air
cooling capacity). Additionally, it requires permanent changes in the die and
cooling
capacity (air rings).
[0009] Another recent patent (US9193107) is on using an apparatus for
differential
cooling of the plastic film where they are using throttling valves to spray a
fluid (water)
on specific areas of the thin films (less than 20 mil). Obviously it has some
advantages,
such as not needing to modify the whole die structure and effective cooling as
per their
claims. But on the other hand, it involves some other disadvantages e.g. it
would not be
as efficient in thicker films such as geomembranes (20 to 100 mils).
Additionally, the
amount of evaporated steam for an effective cooling is remarkable and may make
a mess
in the die exit to cool down that big diameter of a tube such as the
geomembranes.
[0010] Another attempt has also been done to use a mandrel to cool down the
film
surface at the die exit. But since it is installed in the inner part, it is
problematic to use
this system. Since there is no access and/or direct control over the cooling
piece or film
surface structure until the film is out of the winders and inversed to observe
the effect.
[0011] So there is obviously a need to adjust the thickness of the
geomembranes in blown
film process to be able to provide a thick enough of peripheral edge to pass
the standards
of the industry and fulfill the mechanical properties requirements at the
welded edges.
[0012] It is also known in the industry that faster cooling of the films will
cause less
crystallinity and lower molecular orientation (more isotropic),and
consequently, more
isotropic mechanical properties and higher Environmental Stress Cracking
Resistance
(ESCR) in the geomembranes. Efficient cooling system will then be of various
benefits
to the industry of geomembranes.
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Summary of the Invention
[0013] This invention is directed to multilayer geomembrane liner of N layers,
N>2,
where there is an accurate control of the film thickness at all parts,
especially in the
textured geomembranes and more specifically at the edges of the textured
geomembranes.
[0014] The invention is directed to the multilayer polyethylene films having N
layers
where N>2; where each layer can be made of different kind of polyethylene such
as, but
not limited to: High density Polyethylene (HDPE), Medium Density Polyethylene
(MDPE), linear low density Polyethylene (LLDPE), Low density polyethylene
(LDPE)
and Polyethylene for Raised Temperature (PERT) as well as thermoplastic
elastomers
(TPEs) or thermoplastic olefins (TP0s).
[0015] It is disclosed a new method and apparatus of cooling down the
temperature of the
film between the die exit and the frost line in the blown film to address
various problems
in the thickness variation and mechanical properties of the geomembranes.
[0016] It is disclosed a device for cooling a molten plastic film and form a
thickened part
of the plastic film, the device comprising: at least one solid element with
controlled
temperature adapted to be installed at a die exit of a polymer processing
extruder and
having a surface configured to be in contact with a surface of said molten
plastic film, the
device allowing controlled cooling of at least one surface of the molten
plastic, wherein
said cooling is performed through conduction heat exchange between the surface
of said
solid element and the surface of said molten polymer film.
[0017] In one embodiment, the process involves a well-known process of blown
film
where the molten polymer is pushed upward through an annular die and includes
air rings
right at the die exit on one or both sides to cool down the liner. In a
customized distance
from the die exit and well before the frost line, a solid object is installed
in a way that its
surface is in contact with the liner surface. The temperature of the solid
object is
controlled by a cooling liquid from the other side of the solid surface in a
way that
cooling fluid is not in contact with the geomembrane.
[0018] In some embodiments, the solid object is in the form of solid curved
plate with a
curvature adjusted to the bubble of blown film.
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[0019] In some other embodiments, the solid object is a curved pipe of certain
diameter
having a flow of a working fluid inside to control the temperature.
[0020] In another embodiment of the invention, the plate is straight (not
curved) and in
contact with the film surface by pushing the film inward to achieve full
contact.
[0021] A subset of the embodiments may include a second set of solid objects
on top of
the first set to stabilize the film temperature or to avoid a temperature
shock and reduce
residual stresses in the film for some sensitive materials or some specific
thicknesses.
[0022] In some other embodiments, the cooling liquid is water to keep the
temperature of
the solid surface at a certain range. In some cases, this liquid can be an oil
to avoid
evaporation due to the heat exchange with the other side of solid surface
being in contact
with geomembrane hot surface.
[0023] Other and further aspects and advantages will be obvious upon an
understanding
of the illustrative embodiments about to be described or will be indicated in
the appended
claims, and various advantages not referred to herein will occur to one
skilled in the art
upon employment of the invention in practice.
Brief Description of the Drawings
[0024] The above and other aspects, features and advantages of the invention
will
become more readily apparent from the following description, reference being
made to
the accompanying drawings in which:
[0025] Figure 1 is showing the general simple concept of the blown film
process cooled
locally according to a preferred embodiment.
[0026] Figure 2 is a top view of the bubble and the plates according to a
preferred
embodiment..
[0027] Figure 3 is another setting for the solid object with two separate
plates in contact
with two parts of the film according to a preferred embodiment.
[0028] Figure 4 is another set up for the solid plate being a continuous plate
in contact
with the whole perimeter of the film acting equally on the whole surface of
the film
according to a preferred embodiment.
[0029] Figure 5 is a closer view of the cooling plate with the cooling liquid
inlet and
outlet according to a preferred embodiment.
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[0030] Figure 6 is a view of the inside of the plate showing cooling channels
and nuzzles
plus the cooling liquid or gas flow-in and flow-out, according to a preferred
embodiment.
[0031] Figure 7 is another set up the cooling plate where there are several
cooling unit
with different temperatures within one plate to control the temperature
differentially
according to a preferred embodiment.
[0032] Figure 8 is an illustrative representation of thick film product of
this invention an
its comparison with the existing products of the market.
[0033] Figure 9 is showing a few combinations of the thickened areas on the
films that is
possible via the method and device of this invention.
Detailed Description of the Preferred Embodiment
[0034] The films produced with this method may have an average thickness of
preferably
about 20 mils to about 120 mils. These films will be generally used in
application related
to, but not limited to, the geomembranes such as in primary and secondary
containments
of different liquids like water, leachate, slurry, sludge, tailings, pregnant
solution, brine
and similar or any other applications of geomembranes in the art.
[0035] The term "Peripheral Edge" means the parts of the film along the length
of the
film where is overlapped during installation to run fusion welding of two
adjacent panels
of films on or off the field. This can be from around 1 % to around 10% of the
whole film
width, and more specifically from 2% to 6% of the whole width of the film.
[0036] The surface texture of the films can be totally smooth or somehow
textured. The
film can be a monolayer or multilayer structure and each layer may or may not
have the
structure of the skin layer. In some cases, the skin layers are blocked in the
die and the
peripheral edges have the same structure and morphology as the core material.
In some
other cases, it has the same structure as the rest of the film.
[0037] A novel product with accurate control on the peripheral edge thickness,
a method
and apparatus to adjust the thickness of the geomembrane film after the die
exit and
before the frost line will be described hereinafter. Although the invention is
described in
terms of specific illustrative embodiments, it is to be understood that the
embodiments
described herein are by way of example only and that the scope of the
invention is not
intended to be limited thereby.
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[0038] A device for cooling a molten plastic film and form a thickened part of
the plastic
film is illustrated on Fig. 1.
[0039] The device 5 comprises at least one solid element with controlled
temperature
adapted to be installed at a die exit of a polymer processing extruder. The
solid element
has a surface configured to be in contact with a surface of said molten
plastic film. The
device allows controlled cooling of at least one surface of the molten
plastic, wherein said
cooling is performed through conduction heat exchange between the surface of
said solid
element and the surface of the molten polymer film.
[0040] Referring to Figure 1, the plastic is pushed out of the annular die 2
and blown to
form a bubble or a tube 1 at a desired diameter. The air-rings 3 blow very
high pressure
air on the surface of the geomembrane from both sides (inside and outside).
There are
various factors determining the thickness of the film including: the output of
the die, air
rings pressure inside and outside the bubble which forms the blow up ratio
(BUP), pulling
speed which produces take up ratio (TUR).
[0041] The cooling process is merely done by the high pressure air rings (air
jets)
blowing directly onto the film and cools down the film surface via convective
heat
transfer. Without introducing a permanent structural modification to the
existing die and
air ring structure, using any other convection method such as fluids or other
gasses will
not make a notable change in the efficacy of cooling due to the super high
output rate of
cooling air from the air-rings. So the main aspect of this invention is using
the conduction
heat exchange regime in order to quick drop of the film surface temperature to
a desired
temperature to avoid more necking at the specific spots or in the whole
perimeter of the
film tube.
[0042] In a first embodiment, a curved plate 5 or two curved plates 10, 11
(curved to the
curvature of the film as illustrated on Fig. 2 or 3), or simply straight plate
as illustrated on
Fig. 1, is pushed towards the outer surface of the film 1, via a holder rod 9
attached to
each plate, in a way that the two surfaces are completely in contact with each
other.
[0043] As illustrated in detail on Figure 6, the temperature of each plate is
controlled by a
flowing liquid circulating within the plate(s): flow-in 6 and flow-out 7, via
some channels
and nuzzles inside the plate(s) or other side of the plate(s) 14. Upon
touching the surface
of the solid surface, the film surface temperature will rapidly drop to a
certain value due
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to the conduction heat transfer phenomenon. The temperature profile can be
constant at
all of its surface profile of the plate or be differentially controlled to
adjust the thickness
accordingly 15. Fig. 7 shows different temperatures of the plates identified
as Ti to T4.
The temperature of the plate is adjusted based on the thickness of the film,
temperature of
the melt, the desired thickness of that section and type of the resin. If
there is a type of
resin showing surface instability then either a second plate 16 can be
installed above the
first plate 5 and before the solidification of the polymer melt 4 and the
temperature of the
first said plate is increased to a value that does not produce instability and
the said second
plate will have lower temperature to conduct the heat transfer in longer
distance. The
whole purpose is to find the right temperature profile of the plate to result
in desired
thickness (see example).
[0044] In another embodiment of the invention, the plates are installed and
put in contact
with the peripheral edge of a smooth or textured multilayer geomembrane liner,
in order
to increase the thickness of the peripheral edges to values up to around 10%
above the
average thickness of the rest of the film. In a more specific case, smooth or
textured
surfaces are electrically conductive to be used in leak detection technic
(US5288168).
[0045] In another embodiment of the invention, the plate is cooled
differentially, i.e.
different temperatures are set on the plate in order to produce a differential
temperature
profile for the customized control of the film thickness. These temperature
profile zones
can be horizontal or vertical to the machine direction of the film.
[0046] In another embodiment of this invention illustrated on Figures 4 or 5,
instead of
using a plate to locally adjust the thickness, this plates is installed all
around the bubble,
in a continuous 12 or discontinues 13 manner, to help decreasing the height of
the frost
line to a desired height. This will, consequently, reduce the crystalline
content of the film
and increase the anisotropy in the film properties. The secondary effect would
be, but not
limited to, better environmental stress cracking resistance (ESCR) properties.
[0047] In another embodiment of the inventions some parts of the peripheral
edge are
optionally heated to reduce the thickening effect on those specific spots for
various
purposes such as ease of trimming down the line.
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CA 02953375 2017-01-03
File number: 12391-006
Date: 01-03-2017
[0048] The invention can also be directed to lined containment systems
comprising at
least one multilayer polyethylene (PE) geomembrane liner as defined in this
method or
made using the methods as defined herein.
[0049] In accordance with a preferred embodiment, this method can be used in
any type
of geomembranes in any type of processes to locally adjust the thickness of
the
geomembranes of different materials such as PVC, CSPE, fPP and similar.
100501 EXAMPLE
[0051] Two rectangular plates of 20mm thick and 0.1 m2 surface area were
prepared. A
cold water of 5 C was passed through the coils inside the plates. The plates
were put in
the configuration shown in Fig. 3 right after the air rings and well below the
solidification
of the molten polymer with a 5 cm distance from the middle of the peripheral
edges.
While the temperature of the polymer right after the air rings is around 155
C, the surface
temperature of the liner after the plates were down to around 120 C. But in
the middle of
the film where there are no plates, the temperature at the same position is
around 148 C.
This shows a 28 C difference which is a considerable reduction in temperature.
This
reduction increases the cooled areas thickness increase of about 20% above the
average
thickness of the rest of the film.
[0052] Figure 8 is a typical comparison of the existing products in the market
for
geomembranes, and the products of this invention. As it is observed, the
existing
products do not have the thick strips.
[0053] In Figure 9, some examples of the location of the thickened strips on
the plastic
film. It has to be mentioned that these locations are merely illustrative and
for the purpose
of the example, however, the mentioned thickened strips can be anywhere in the
widths
of the film in a continuous or separate way.
[0054] While illustrative and presently preferred embodiments of the invention
have been
described in detail hereinabove, it is to be understood that the inventive
concepts may be
otherwise variously embodied and employed and that the appended claims are
intended to
be construed to include such variations except insofar as limited by the prior
art.
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