The present invention generally relates to geomembrane liners, and more particularly to multilayer polyethylene geomembrane liners with textured surfaces showing high friction angles that enables them to be used at critical designs.
Polyethylene geomembranes are used extensively as a part of liquid containment systems in different applications such as in modern landfills or heap leach in mining industry. In all those applications the geomembrane is part of a system including geotextile and/or geosynthetic 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 described in U.S. Pat. Nos. 4,885,201, 5,403,126 and 5,258,217.
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.
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 a 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 (Chapter 3, HDPE Geomembranes; in A Guide to Polymeric Geomembranes, John Schiers, 2009, John 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 (U.S. Pat. No. 5,763,047) 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. There are some other methods of texturizing the surface of films in general and geomembranes specifically. Among them is embossing method that is used in cast film processes where a desired pattern can be embossed on the film (U.S. Pat. No. 4,290,248). Another method is called spray-on method (U.S. Pat. No. 5,728,424) where a compatible resin is sprayed on the film right out of the die at high enough temperature to create a molecular level interaction with the surface molecules (welding).
Many of these methods are created for the cast film process technic. The only industrial method now for the blown film process is via foaming skin layer as described above. Since the texturizing technic is almost the same, the final frictional properties of the films are more dependant on the initial formulation of the skin layer rather than on the technic itself. This difference is very obviously observed in the industry between a conductive geomembrane (e.g. Solmax Conductive PE geomembrane) and a regular PE geomembrane. The former shows a special structure at the surface which results in increased friction angles way higher than the regular materials.
But there is a very important technical problem with that type of material and that is welding over the edges between the adjacent liners. Due to the special skin formulations of conductive products, there is a high content of carbon black in the skin layer. This un-melt-able ingredient interferes with the welding process on the site in a way that the speed of welding reduces dramatically and the installers need to get special training on that. In some other conditions, the installers even need to get a specially designed welding machine for that specific type of geomembrane (U.S. Pat. No. 9,033,620B2).
On the other hand, designers are increasing the safety factors every day and this translates to designing higher friction factor geomembranes. This is easier to reach for the cast film process, but a great portion of the geomembrane industry is using the blown film process.
Hence, the suppliers of geomembranes using the blown film process are in certain need for a new material and/or method to develop high friction factor geomembranes without the troubles indicated above.
The invention is directed to 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 (TPOs), as long as every two adjacent layers are compatible.
It is disclosed a new formulation to be used in the skin layers, 2, of the multilayer PE film of textured plastic films to improve frictional properties.
In an embodiment of this invention, the skin layer is formulated in a way that it resists cell coalescence in cell growth step of foaming. This ability avoids coalescence and therefore very small cells are created and maintained until reaching the surface and rupture.
Additionally, the solubility of the gas, injected directly to the melt or created during processing, and dispersion of the gas within the molten polymer is considerably improved. This results in more homogeneous cell dispersion over the surface and better friction factors.
In another embodiment of this invention, the final formulation of the skin layer is expressed as:
In another embodiment of this invention, the final formulation of the skin layer is expressed as:
In accordance with a preferred embodiment, the composition of the skin layer as disclosed herein, the said Carbon black is replaced by about the same amount of Titanium dioxide (TiO2) additive.
In accordance with a preferred embodiment, one of the layers of the multilayer PE liners disclosed herein may be free of carbon black.
In accordance with a preferred embodiment, one of the layers of the multilayer PE liners disclosed herein is free of carbon black and comprises Titanium oxide (TiO2).
In accordance with a preferred embodiment, the other layers of the multilayer plastic film can be of any composition of polymers and/or additives and/or fillers.
In another embodiment of the invention the textured layer, is a part of a composite multilayer structure of polymeric and metallic layers in a form of sandwich panel that is laminated on each other.
In accordance with a preferred embodiment, the adaptable structure of the multilayer liner disclosed herein will allow the manufacturer to design targeted formulations at each layer. For instance, in a 3-layer structure,
Other and further aspects and advantages of the present invention 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
The features of the present invention which are believed to be novel are set forth with particularity in the appended claims.
The above and other objects, features and advantages of the invention will become more readily apparent from the following description, reference being made to the accompanying drawings in which:
A novel textured geomembrane 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.
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 applications 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.
As used herein % or wt. % means weight % unless otherwise indicated. When used herein % refers to weight % as compared to the total weight percent of the phase or composition that is being discussed.
By “about”, it is meant that the value of weight %, time, pH or temperature can vary within a certain range depending on the margin of error of the method or device used to evaluate such weight %, time, pH or temperature. A margin of error of 10% is generally accepted.
The surface texture of the films can be totally or partially 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, some of the layers are non-polymeric and/or a mix of polymeric and/or non-polymeric materials.
A novel product with improved Mohr-Coulomb peak friction angle of >30° and peak adhesion value of >15 kPa for a normal pressure of >100 kPa at stress curve undergone according to ASTM D-5321 against needle punched geotextile, and regular weldability properties is 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.
The average horizontal distance of the asperities' peaks from one peak to the nearest peak, 4 (
In accordance with a preferred embodiment, either or both skin layers, may have any combination of the followings:
The use of carbon black in exposed conditions will cause increasing the temperature of the liner under sun. The use of TiO2 in the outer layer will help the liner retain its Physical-thermal-mechanical properties for longer times due to its light reflection properties.
In accordance with a preferred embodiment, either or both skin layers, 2, may have any combination of the followings:
In a three-layer plastic film of 1.5 mm thick, with skin layers of 0.12 mm each, the following formulation has been used:
Blending the ingredients of each layer before feeding to the extrusion line, and processing, and injecting gas in the beginning of the metering zone of extruder of layer A to the molten plastic, will result in a structure shown in
In reference to the figures, it is also disclosed a plastic film comprising:
Preferably, the carbon black content of the skin layer is below 3%.
Preferably, at least one longitudinal strip of smooth surface is located at a peripheral edge of the plastic film.
Preferably, the plastic film is made of a natural or synthetic polymer, and is more preferably made of at least one of the followings: 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 (TPOs), or any combination thereof.
Preferably, 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.
Preferably, the plastic film is smooth at either sides of the film.
Preferably, the plastic film is textured on one side or both sides of the film.
Preferably, the plastic film is at least partially colored on at least one side of the film.
Preferably, the plastic film is at least partially conductive on at least one side.
Preferably, 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.
Preferably, the plastic film is composed of N layers, N being an integer, and N being superior or equal to 2.
Preferably, in the plastic film, at least one layer is not conductive, or only partially conductive.
Preferably, the plastic film has been obtained by coextrusion.
Preferably, the plastic film has been obtained partially or completely by lamination technique.
Preferably, the plastic film has been obtained by any combination of coextrusion and lamination techniques.
Preferably, in the plastic film, at least one layer is of a different thickness profile than the other layer(s).
Preferably, in the plastic film, at least one layer is made of a synthetic and/or of a natural polymer.
Preferably, in the plastic film, at least one layer is made of non-polymeric material such as metals, e.g. aluminum or copper.
Preferably, the plastic film is a multilayer sandwich panel of one or more plastic layers and of one or more metal layers, like aluminum, to be used in construction applications, or laminated packaging film of similar structure in food packaging applications.
It is also disclosed roller made of a plastic film as defined herein rolled on a spool.
It is also disclosed a method of producing a plastic film, comprising the steps of:
MDPE, HDPE and PERT resin of choice, preferably before extrusion feeding, more preferably before a hopper or in a hopper; and
Preferably, in the method, the die of the extruder is of the blown film die type.
Preferably, in the method, the die of the extruder is of the cast film die type.
Preferably, in the method, the blowing agent is N2 or CO2 or any mixture thereof and the blowing agent is injected into the molten polymer in metering zone of extruder screw.
Preferably, in the method, the blowing agent is a physical or chemical blowing agent premixed with the resin in the hopper or added separately in the initial zones of the extruder.
Preferably, in the method, 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), 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.
Preferably, in the method, the plastic film is smooth on either sides.
Preferably, in the method, the plastic film is textured on one side or both sides by using complementary extrusion equipment.
Preferably, in the method, the film is colored on one or both sides by adding a color masterbatch before extrusion takes place.
Preferably, in the method, the liner is conductive on one side or both sides including or excluding the peripheral edges.
It is also disclosed the use of the plastic film as defined herein or of a plastic film obtained by using the method defined herein, in applications such as geomembrane liners, capping and covers, packaging films, shopping bags, shrink films, silage films and similar.
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.
The present patent application claims the benefits of priority of commonly assigned U.S. Patent Application No. 62/526,796, entitled “Plastic Film Having High Friction Angle, Rollers, Method of Producing and Uses Thereof” and filed at the United States and Patent Trademark Office USPTO on Jun. 29, 2017.
Filing Document | Filing Date | Country | Kind |
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PCT/CA2018/050808 | 6/29/2018 | WO | 00 |
Number | Date | Country | |
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62526796 | Jun 2017 | US |