WO2019220426A1

WO2019220426A1 - Micro-nano patterned high-adhesion polymer coatings and method of production thereof

Info

Publication number: WO2019220426A1
Application number: PCT/IL2019/050499
Authority: WO
Inventors: Boaz Pokroy; Iryna POLISHCHUK; Larisa MARGULIS; Pablo Fabian Rios
Original assignee: Polygal Plastics Industries Ltd.; Plazit 2001 A.C.S. Ltd.
Priority date: 2018-05-15
Filing date: 2019-05-05
Publication date: 2019-11-21

Abstract

Composition of a polymer substrate with a coating deposited on at least one surface thereof, the coating having a nanosized or microsized texture pattern. The material composition of the coating is based on the material composition of the polymer substrate, such that the coating is adhered to and fully integrated with the polymer substrate. A method of preparation of the coating includes: producing a micro/nano patterned master, producing a replica of the master, producing a solvent-resistant micro/nano patterned template of the replica, producing a high-adhesion liquid coating, coating at least one surface of the polymer substrate with the coating, applying the template onto the coating, solidifying the coating by solvent evaporation, and removing the template to leave a negative imprinting of the template on the polymer substrate surface

Description

MICRO-NANO PATTERNED HIGH-ADHESION POLYMER COATINGS

AND METHODS OF PRODUCTION THEREOF

FIELD OF THE INVENTION

The present invention relates to coatings for polymer materials and methods of their production.

BACKGROUND OF THE INVENTION

Patterned surfaces are known to enhance the surface properties, such as (but not limited to) hydrophobicity (water repulsion) and hydrophilicity (water attraction). It has been shown that for a surface which is hydrophobic due to its chemistry, roughness may increase hydrophobicity (i.e., in accordance with the“Wenzel equation”). The finer the roughness the greater the hydrophobic effect, to a point that micro-nano textured hydrophobic surfaces may become super-hydrophobic, i.e. repel water totally. This phenomenon is popularly known as the“Lotus Effect”.

On the other hand, already hydrophilic surfaces may become more hydrophilic when roughened, and super-hydrophilic when micro-nano textured. Both super-hydrophobic and super-hydrophilic surfaces can be used (but not limited to) for self-cleaning or easy-cleaning, anti-icing, anti fouling, anti-graffiti, anti-fogging and anti-dripping applications. The advantages of these surfaces for various applications are obvious, for example: reducing maintenance costs, prevention of snow and ice build-up on aircrafts, protection from environmental pollution, improving and protecting greenhouse crops, and in transparent materials, maintaining the transparency in any conditions and for long time. Transparent polymer surfaces of the kind can be used as skylights, greenhouses, windows, walls, light openings, car glazing, car wrapping, solar collectors, optical lenses, electronic screens, cellular devices screens, etc. Opaque products can be used for building, interior design, medical rooms, aviation external parts, etc. Medical devices require hydrophobic or hydrophilic surface properties as well. The range of practical applications is endless. However, commercial methods for preparing transparent or non-transparent superhydrophobic plastic surfaces are scarce.

Scaling down the surface roughness is necessary not only to enhance the specific property, but also to maintain the surface transparency if needed. Amorphous polymers, such as (but not limited to) polycarbonate (PC), poly methyl methacrylate (PMMA), styrene acrylonitrile (SAN), polyethylene terephthalate (PET) and polystyrene (PS), are intrinsically highly transparent. Transparency and surface roughness are usually contradictory properties. A macro-pattern on the surface of these polymers disturbs and scatters the passage of light increasing the haze, reducing light transmission and distorting the see-through property. If the size of the surface pattern is reduced, the light scattering is reduced. The smaller the pattern scale, the better. When the size of the surface texture approaches the light wavelength scale, the haze is reduced, the surface becomes increasingly transparent and see-through properties can be maintained. In such a way, a micro-nano textured surface will render the unique properties of the surface while maintaining the light transmission and the see-through properties of the original polymer.

When a coating is applied onto a polymer, an adhesion interface is formed between the coating and the polymer substrate. Many coated products fail at this interface due to the lack of sufficient adhesion between the coating and the polymer surface. The coating will gradually peel-off and as a result its functionality will be reduced. This kind of adhesive failure is one of the most common reasons of the relatively short lifespan of the coated polymer products. Patterned super-hydrophobic, super-hydrophilic, anti-icing, antifouling, anti-fogging and anti-dripping surfaces have been attempted and achieved in various ways, also for polymer materials. However, all the technologies for producing this type of polymer surfaces face a common problem, namely lack of durability.

This drawback is the main barrier for industrial and commercial implementation of these technologies.

For example, super-hydrophobic technologies developed until today are based on the“Lotus Effect”. The lotus is a symbol of purity in Asian cultures. It grows in muddy waters, however it keeps clean and fresh without being harmed by dirt, pollution and living organisms. The leaf of the lotus is hydrophobic and micro-nano-rough, i.e. super-hydrophobic. The super-hydrophobicity creates a high contact angle of water with the solid surface, reaching above 150°C, and the micro-nano roughness reduces the area of contact leading to lower adhesion of water and dirt particles. Water drops roll easily on the leaf surface picking up dirt particles with them. This mechanism is known as self-cleaning lotus effect. However, at the same time fine roughness causes a durability problem common to all super hydrophobic, or generally speaking, all micro-nanoscopic textured surfaces. The smaller the scale of the texture, the better the property. On the other hand, the finer the texture, the lower the mechanical stability of the surface texture. The lotus leaf can cope with this problem because as a living organism it can grow and self-heal. This problem is even more critical for polymers since they have relatively soft surface as compared to metals and ceramics.

Current“lotus effecf-inspired developments and technologies for polymer surfaces are typically sensitive and weak to abrasion stresses, with low durability and short life-span, which makes them unsuitable for most practical applications. Furthermore, polymer materials are relatively sensitive materials. Under outdoor conditions of UV radiation, rain, snow and wind, they will be degraded, scratched and abraded.

PCT Patent Application Publication No. WO 2019/008589, entitled: “Micro-nano patterned anti-abrasive polymeric coatings and a method of production thereof”, discloses a composition made of a polymeric substrate having deposited on at least one surface thereof a cross-linked polymeric coating layer. The coating layer is characterized by: a nanosized or microsized surface pattern; a pencil hardness of 2H to 9H; and a water contact angle in the range of 130° to 170° or 10° to 50°.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there is thus provided a coating for a polymer substrate. The coating includes a nanosized or microsized texture pattern. The material composition of the coating is based on the material composition of a polymer substrate to be coated, such that the coating is adhered to and fully integrated with the polymer substrate when applied to at least one surface thereof.

In accordance with another aspect of the present invention, there is thus provided a composition including a polymer substrate with a coating deposited on at least one surface thereof. The coating includes a nanosized or microsized texture pattern. The material composition of the coating is based on the material composition of the polymer substrate, such that the coating is adhered to and fully integrated with the polymer substrate. The coating may be further characterized by a visible light transparency in the range of 70% to 90%. The coating may comprise at least one UV absorbent additive. The coating may comprise at least one anti-abrasion additive. The coating may be characterized by a water contact angle of at least 150°. The coating may be characterized by a water contact angle of less than 50°. The coating may be covalently adhered to the polymer substrate. The coating may comprise a texture pattern comprising an array of at least one of: pillars; and holes. The median height or depth of the pillars or the holes may be in the range of: 2pm to 20pm. At least one dimension of length, width, and/or diameter of the pillars or holes may be in the range of 10Onm to 5pm. The median spacing of the pillars or the holes may be in the range of: 1 pm to 20pm. The pillars or holes may comprise a shape of: round; band shaped; sleeve-shaped; elliptical; square; rectangular; triangular; hexagonal; conical; star-shaped; and/or truncated cone shaped. The array may cover from 0.5% to 95% of the total area of the surface of the polymer substrate. The composition may be further characterized by a delta-E color shift of no greater than 10, after 2000 hours of accelerated weather exposure according to ASTM G155. The composition may be further characterized by a yellowness index of less than 10 according to ASTM E313, after 2000 hours of accelerated weather exposure according to ASTM G155. The coating may further comprise at least one hydrophobic additive or at least one hydrophilic additive.

In accordance with another aspect of the present invention, there is thus provided a method for preparing a coating for a polymer substrate. The method includes the procedures of: producing a micro/nano patterned master, producing a replica of the master, and producing a solvent-resistant micro/nano patterned template of the replica. The method further includes the procedures of: producing a high-adhesion liquid coating, wherein the material composition of the coating is based on the material composition of the polymer substrate to be coated, such that the coating will be adhered to and fully integrated with the polymer substrate, and coating at least one surface of the polymer substrate with the coating. The method further includes the procedures of: applying the solvent-resistant template onto the coating, solidifying the coating by solvent evaporation, and removing the template to leave a negative imprinting of the template on the polymer substrate surface. The method may further include the procedure of adding at least one hydrophilic chemical additive to the coating, to render a hydrophilic coating. The method may further include the procedure of adding at least one hydrophobic chemical additive to the coating, to render a hydrophobic coating. The method may further include the procedure of adding at least one anti-abrasion additive to the coating, to render an abrasion resistant coating. The method may further include the procedure of adding at least one UV absorbent additive to the coating, to render a UV protective coating. The method may further include the procedure of treating at least one surface of the coating with at least one hydrophilic chemical entity, to render an ultra-hydrophilic surface. The method may further include the procedure of treating at least one surface of the coating with at least one hydrophobic chemical entity, to render an ultra-hydrophobic surface. The method may further include the procedure of cleaning the surface of the polymer substrate before applying the coating. The coating may be applied from multiple sides or surfaces of the polymer substrate. The method may be implemented in: a batch process; a semi-continuous process; a continuous process; and/or an on-line process. The polymer substrate may be in the form of a sheet or a film. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

Figure 1 is a block diagram of a method for preparing a coating for a polymer substrate, operative in accordance with an embodiment of the present invention;

Figure 2 is a collection of images relating to a micro-patterned silicon master, constructed and operative in accordance with an embodiment of the present invention;

Figure 3 is a sequence of images depicting stages in the production of a solvent-resistant template of a micro/nano patterned silicon replica, to be used to impress the micro/nano pattern onto a coated polymer surface, operative in accordance with an embodiment of the present invention;

Figure 4 is a collection of images relating to a micro-patterned solvent-resistant template, constructed and operative in accordance with an embodiment of the present invention;

Figure 5 is a photographic image of a micro-patterned epoxy template applied onto a polycarbonate sheet coated with a high adhesion coating, constructed and operative in accordance with an embodiment of the present invention; Figure 6 is a photographic image of the polymer patterned surface after the applied coating of Figure 5 has solidified and the micro-patterned template has been peeled off, constructed and operative in accordance with an embodiment of the present invention;

Figure 7 is a high-resolution scanning electron microscopic (HR-

SEM) image of a top view of the resultant solidified high-adhesion coating of Figure 6, operative in accordance with an embodiment of the present invention;

Figure 8 is a magnified view of the FIR-SEM image of Figure 7; Figure 9 is a FIR-SEM image of a top view of another examplary high-adhesion coating, operative in accordance with an embodiment of the present invention;

Figure 10 is a magnified view of the HR-SEM image of Figure 9;

Figure 1 1 is a photographic image of a micro-patterned chemical resistant PDMS template before being applied onto a polycarbonate sheet coated with a high adhesion coating, constructed and operative in accordance with an embodiment of the present invention;

Figure 12 is a photographic image of the polymer patterned surface after the applied coating of Figure 1 1 has solidified and the micro- patterned PDMS template has been peeled off, constructed and operative in accordance with an embodiment of the present invention; Figure 13 is a HR-SEM image of a top view of the resultant solidified high-adhesion coating of Figure 12, operative in accordance with an embodiment of the present invention;

Figure 14 is a magnified view of the FIR-SEM image of Figure 13; Figure 15 is a further magnified view of the FIR-SEM image of

Figure 13;

Figure 16 is a photographic image showing contact angle measurements on a micro-patterned polymer high-adhesive coating after treatment with fluorosilanes, constructed and operative in accordance with an embodiment of the present invention; and

Figure 17 is a schematic illustration of a coating process when a solvent resistant template is introduced as a micro-nano textured roll which continuously patterns the coating base of the polymer solution.

DET AILED DESCRIPTION OF THE EMBODIMENTS

The present invention overcomes the disadvantages of the prior art by providing a micrometric and/or nanometric patterned high-adhesion coatings to be applied onto the surface of a polymer material, and methods for preparing such coatings. Micrometric/nanometric sized patterned coatings can be used to render highly durable surfaces on transparent or opaque (non-transparent) polymers. In addition, the coatings may be provided with special properties, such as ultra-hydrophobicity or ultra- hydrophilicity, enabling effective usage of the coated material in various applications, such as: self-cleaning, easy-cleaning, anti-fouling, anti-icing, anti-fogging, or anti-dripping applications. The present invention attempts to address the problem of low durability of existing micro-nano patterned polymer surfaces, by forming a micro-nano pattern through a high-adhesion coating which fully integrates with the polymer and will not peel off, thereby increasing the overall lifespan of the polymer substrate and the properties which it exhibits. The coatings of the present invention do not need to undergo a time-consuming hardening process, such as thermal curing, or an expensive hardening process, such as ultraviolet (UV) curing. Rather, the coating is solidified and hardened via a straightforward and quick process of solvent evaporation via natural drying. This hardening process significantly minimizes production time, while also allowing for an "on-line application", meaning that the coating can be applied at the same production line and at the same time as the product itself (e.g. an extruded polymer sheet or film).

In order to improve the UV resistance of polymers, UV additives may be added to the bulk of the polymer or to the coating. Commercial UV protective additives are available for most types of polymers. By adding UV additives to the high-adhesion coating, additional protection against UV degradation will be achieved, significantly improving the life expectancy of the micro-nano patterned coated polymer. Moreover, the high-adhesion coating can comprise special additives, such as abrasion resistant additives, which are commercially available for many polymers. These additives will also increase the lifespan of the coated product and preserve the unique property of its surface for long period.

According to an embodiment of the present invention, there is provided a composition including a polymeric substrate with a high- adhesion coating deposited on at least one surface thereof. For example, the coating may be deposited on two surfaces of the substrate, e.g., two opposite surfaces. The term "coating", and any grammatical derivative thereof, as used herein, refers to a coating that (i) is positioned above the substrate; (ii) is in contact with the substrate or an intermediate coating arranged between the substrate and the coating; and (iii) does not necessarily completely cover the substrate. For example, the coating may cover a portion of the substrate, such as a surface or a portion thereof, or a body or a portion thereof. Furthermore, the term "coating", and any grammatical derivative thereof, as used herein, refers to a separate and distinct layer of material from an underlying material. For example, the coating may form a substantially continuous layer on a substrate. The coating may have a thickness in the range of 10Onm to 30pm, including any value and range therebetween (e.g., 500nm, 600nm, 700nm, 800nm, 900nm, or 1 pm). The coating may be physically or covalently adhered to the substrate.

The coating of the present invention is characterized by a micrometric and/or nanometric sized pattern. The terms "micro/nano pattern" and "micro-nano pattern" are used interchangeably herein to refer to such a micrometric and/or nanometric sized pattern.

The coating of the present invention may be formed with a defined texture or pattern, such as pillars or holes. For example, the coating may be formed in an array or an alignment of pillars or holes. The cross-section of the pillar or hole may not be constant and may form a draft angle. The shape of the pillars or holes may be, for example: cylindrical, conical, squared, pentagonal, hexagonal, star-shaped; or a random shape. A conical pillar or hole may have a truncate shape. An array of pillars or holes may have a total solid area coverage from about 0.5% to about 95%, relative to the total area of the underlying surface. An array or alignment of pillars or holes may be arranged along a straight line. The median distance (or "spacing") between pillars or holes may be in the range of 100nm to 20pm, including any value and range therebetween. For example, the spacing may be in the range of 1 pm to 20pm. The height of the pillars may be in the range of 2pm to 20pm. The depth of the holes may be in the range of 2pm to 20pm. The length or width of the pillars or holes may be in the range of 10Onm to 5pm. The aforementioned dimensions may represent the median dimensions of a plurality of pillars or holes in an array or alignment.

The coating of the present invention is deposited on the surface of a polymeric material referred to herein as a "substrate". The surface of the substrate may be hard or soft, and may be a pure polymer, copolymer, polymer blend, filled polymer, reinforced polymer or any combination thereof. Polymer substrates may include (but not limited to), such as: polypropylene (PP), polycarbonate (PC), high-density polyethylene (HDPE), amorphous polymers such as (but not limited to) polymethyl methacrylate (PMMA), polycarbonate (PC), styrene acrylonitrile (SAN), polyethylene terephthalate (PET) and polystyrene (PS), unplasticized polyvinyl chloride (PVC), and fluoropolymers including but not limited to polytetrafluoroethylene (PTFE, Teflon, or any combination of the above. Further exemplary substrates may include: shape memory polymers, rubbers, elastomers and biopolymers. Fillers, extenders and reinforcements introduced to the polymer substrate may include, for example: dies and pigments, titanium dioxide, calcium carbonate, carbon fibers, carbon black, carbon nanotubes, metal powders, ceramic powders nanometals, nanoceramics, inorganic nanotubes, graphene, fullerenes, glass fibers, glass beads, mica, silicates, nanosilicates, wood fillers, and any other inorganic or organic extender, filler or reinforcement that can be added to the bulk of the polymer substrate. The substrate may be in the form of a sheet or a film. The surface of the substrate may be modified by various chemical and mechanical processes, including for example: self- assembled monolayers (SAMs), physical vapor deposition (PVD), lithography and plasma etching. The substrate surface may be crystalline or non-crystalline, and may be utilized without further modification of its crystalline nature. The thickness of a substrate film may be in the range of 100nm to 500pm, and the thickness of a substrate sheet may be in the range of 500pm to 60mm.

The coating of the present invention may be characterized with one or more properties, such as: ultra-hydrophobicity (also known as "super-hydrophobicity); ultra-hydrophilicity (also known as "super- hydrophilicity") ; and high transparency. The term ultra-hydrophobicity may refer to a water-repelling property of the coating surface, forming a static contact angle between the water and the surface of above at least 120° (e.g., above 130°, 140°, or 150°). The term "ultra-hydrophillic" may refer to a water-attracting property of the coating surface forming a static contact angle of less than 50° or below (e.g., less than 30°, 20°, 10° or 5°). The "static contact angle" describes the angle formed by a liquid substance with respect to the substrate surface at the location where the free surface of quiescent liquid contacts the horizontal surface of the substrate. The static contact angle may be measured using techniques known in the art, such as the sessile drop technique. A drop of liquid is formed on the tip of a hypodermic needle attached to a screw syringe. The syringe is fastened to a stand which reduces irregularities that are produced by manual drop deposition. The substrate is then raised until it touches the drop using the Y control of the stage. The drop is the then brought into the field of view and onto the focal point of the microscope by x-y translation of the stage and an image is captured, from which the static contact angle may be calculated.

The term "high transparency" may refer to a light transmission of at least 70%, or in the range of 70%-95%, of the light (e.g., visible light), as determined using known methods and standards for measuring transparency of plastics (e.g., ASTM D1746, ASTM D1003). The composition may exhibit transparency and structural integrity (i.e., without any visible cracks). Other properties which the coating may be characterized by may include: self-cleaning (i.e., generally keeps the surface clean without applying mechanical force or detergent to loosen and remove visual contaminations); easy-cleaning; anti-fouling (i.e., reducing or preventing water from condensing thereof in the form of water droplets); anti-icing (i.e., preventing ice from forming at the surface or selected portions thereof); anti-fogging (i.e., preventing water vapor from condensing onto the surface in the form of small water drops or redistributing them in the form of a continuous film of water in a very thin layer); anti-dripping; and the like. A characteristic property of the coating may be durable, in the sense that the property (e.g., ultra-hydrophobicity; ultra-hydrophilicity; transparency) remains stable when subject to different environmental conditions. In particular, the relevant property (e.g., measured contact angle) may change less than a selected amount (e.g., less than 10% or 5% or 1 %) over a selected period (e.g., a week, a month a year), when subject to environmental changes, such as natural or artificial temperature and humidity changes, natural solar or artificial light radiation exposure, effects of mechanical stresses, human handling, cleaning agents, climate variations (e.g., wind, rain, snow, acid rain); and the like. The characteristic property of the coating may not change significantly over time, when maintained at room temperature, at elevated temperatures (e.g., 70-90°C), or at lower temperatures (e.g., -50°C).

The coating of the present invention may also be characterized by abrasion resistance. Abrasion resistance may be measured using methods and instruments known in the art, such as a Taber Abrasion Machine. For example, the coating may have an abrasion resistance of less than 15% or 10% haze change according to ASTM D1003.

The coating may also be characterized by a defined pencil hardness. The term“pencil hardness” as used herein is meant to include but not be limited to a surface hardness defined by the hardest pencil grade that just fails to mark the coated surface. Typically, the pencil hardness of the abrasion resistant sheet is in the range of H to 6H. The weather resistance of the coating may be characterized by delta E color shift of 0.2 to 10, after 2000 hours of accelerated weather exposure, as tested according to ASTM G155 (or similar known methods). The term“delta E” is indicative of the difference between the color value after exposure and at the start of the exposure. The weather resistance of the coating may be characterized by a Delta Yellowness Index (Delta Yl) of less than 10, less than 5, less than 3, or less than 1 or less than 0.5, ASTM E313 after 2000 hours of accelerated weather exposure, as tested according to ASTM G155 (or similar known methods). The term“delta Yl” is indicative of the difference between the yellowness value after exposure and at the start of the exposure.

Reference is now made to Figure 1 , which is a block diagram of a method for preparing a coating for a polymer substrate, operative in accordance with an embodiment of the present invention. In procedure 1 12, a micro/nano patterned master is produced. The master is fabricated with a microsized or nanosized texture pattern, such as using a soft-lithography fabrication technique. The master may be fabricated and shaped in the form of an array of pillars or holes, such as by using photolithography, etching, or laser-patterning techniques.

In procedure 1 14, a replica of the master is produced. The replica may be produced by copying the micro/nano patterned master into an elastomeric polymer replica. For example, the master may be covered by

PDMS and vacuum treated and cured to form a PDMS mold which can be re moved from the master. An example of the production of a replica is provided in Figure 3 discussed hereinbelow.

In procedure 1 16, a solvent-resistant micro/nano patterned template of the replica is produced. The template may be produced from a UV-curable epoxy, such as by pouring the epoxy over the PDMS mold. An example of the production of a replica template is provided in Figure 3 discussed hereinbelow.

In procedure 1 18, a high-adhesion liquid coating based on the same material as the polymer to be coated is produced. In particular, the coating is made from a polymer material chosen to be chemically identical to the substrate polymer, or at least chemically identical to the main component of the substrate polymer. For example, the coating may be a liquid mixture consisting of 5-20% solid polymer (e.g., polycarbonate) dissolved in a suitable solvent (e.g., dichloromethane). The coating mixture may have a desired viscosity that allows for penetration into the pattern of the solvent-resistant template. For example, the coating may have a proper viscosity in the range of 1 to 100 cP, depending on the scale of the pattern (i.e., where typically the finer the pattern the lower the viscosity). The viscosity may be regulated by changing the solvent-solid ratio of the coating. The term "high- adhesion" is used herein to mean that the coating becomes an integral part of the substrate. For example, the coating is fully (e.g., 100%) adhered to the underlying substrate, such that no physical interface is formed, and the coating cannot separate or peel off. ln an optional procedure 120, a hydrophilic chemical additive is added to the coating, to render a hydrophilic coating. For example, one or more hydrophilic additives, such as a hydrophilic silane, may be added and dispersed onto the coating.

In an optional procedure 122, a hydrophobic chemical additive is added to the coating, to render a hydrophobic coating. For example, one or more hydrophobic additives, such as a hydrophobic silane, may be added and dispersed onto the coating.

In an optional procedure 124, an anti-abrasion and/or an anti-UV additive is added to the coating, to render an abrasion and/or UV resistant coating. For example, one or more anti-abrasion additives, such as acrylic and glass microspheres, may be added and dispersed onto the coating, to render the coating abrasion resistant, and improving the life expectancy of the coated substrate. Alternatively or additionally, one or more UV absorbent additives may be added or dispersed onto the coating, to provide the coating with protection against UV degradation and further improving the life expectancy of the coated substrate. The coating may also be treated with other types of additives (i.e., in addition or instead of: hydrophilic, hydrophobic, abrasion protection, and UV protection additives). Alternatively, the coating may already contain functionalized additives or chemical side groups which may give the coating layer a desired functionality. In procedure 126, the coating is applied onto the surface of a polymer substrate. The polymeric substrate may be in the form of a sheet or a film. The coating may be applied from both sides or surfaces of the substrate. The coating may be applied using a suitable coating application technique, such as: roll coating, dip coating, spray coating, tambon coating, gravure coating, slot-die coating, comma-coating, or blade coating. The coating application may be an on-line process, such that the coating is applied at the same production line and time as the polymer product itself.

Optionally, the polymer substrate surface may be cleaned to remove dust or contamination before applying the coating. Such cleaning may provide a clean coating and enhance the desired surface properties. For example, the surface of the polymer substrate may be treated with an ionizing air gun in order to remove static charges in the polymer surface that attract dust particles. The polymer surface may also be cleaned with a polar solvent, such as 1 -propanol, using a soft cloth that does not leave any residues (e.g. deer skin cloth). Additionally, or alternatively, the polymer surface may be pre-treated by surface activating techniques, such as plasma, corona or flame.

Stabilizing the coating may also be performed. For example, once the coating is applied onto the polymer surface, the coating is left to set (or "flash-off") for a period of between 90 to 300 seconds (also referred to as "flash off period"). The flash-off may be performed at room temperature (e.g., at a temperature between 22°C to 28°C). The flash-off period may allow for obtaining the desired coating stabilization. The flash-off period may be shortened by external means, such as temperature, vacuum, and/or forced convection.

In procedure 128, the solvent-resistant template is applied onto the coating. The template may be pressed onto the coating in such a way that the coating penetrates, at least to some extent, into the micro-nano pattern of the polymeric template. The solvent-resistant template may be applied by any suitable pressure means, including but not limited to: manual, press, caterpillar, or roll-press (as in Figure 1 1 ). Optionally, venting channels are configured into the polymeric template in order to properly vent the air that may be trapped within the pattern (i.e., to avoid trapping of air into the pattern depletions such that the pattern cannot be fully replicated). If the replication is not satisfactory, the coating viscosity may be reduced with a solvent (as described hereinabove)

In procedure 130, the coating is solidified by solvent evaporation.

In particular, the solvent is above its evaporation temperature, such as in an oven or heating apparatus.

In procedure 132, the template is removed to leave a negative imprinting of the template on the polymer substrate surface. In particular, the template is peeled off from the solidified coating, leaving a positive micro-nano pattern on the coating surface.

In an optional procedure 134, the surface of the coating is treated with hydrophilic chemical entities, to render an ultra-hydrophilic surface. For example, the coating surface may be chemically treated with one or more hydrophilic precursors, such as a hydrophilic silane, using a chemical treatment process known in the art.

In an optional procedure 136, the surface of the coating is treated with hydrophobic chemical entities, to render an ultra-hydrophobic surface. For example, the coating surface may be chemically treated with one or more hydrophobic precursors, such as a hydrophobic silane, (e.g. fluorosilanes) using a chemical treatment process known in the art.

The method of Figure 1 may be implemented in an iterative manner, such that at least some of the procedures are performed repeatedly and/or continuously. In general, the method may be performed as a batch process, a semi-continuous (step and repeat) process, or a continuous process. The method may be implemented in an alternative order or sequence than described hereinabove, where the order of steps should not be construed as limiting.

Reference is now made to Figure 2, which is a collection of images, referenced 142, 144, 146, 148, relating to a micro-patterned silicon master, constructed and operative in accordance with an embodiment of the present invention. Image 142 is a photographic image showing a micro- patterned silicon wafer fabricated via photolithography and ion-etching techniques. In particular, a 2 inch (50.8 mm) diameter [100]-oriented silicon wafer with a silicon dioxide (S1O2) layer of 100nm is fabricated. The sample was patterned with 1818 photoresist by GCA Autostep 200 DSW i-line Wafer Stepper UV exposure followed by tetra-methyl ammonium hydroxide (TMAH) aqueous alkaline development. The pattern was transferred onto the silicon dioxide layer, used as a hard mask, by CF₄/0₂ reactive ion etching (RIE) in a 790 PlasmaTherm tool. The subsequent etching of silicon pillars to the depth of 10pm is carried out in a PlasmaTherm Versaline inductively coupled plasma (ICP) system by a deep reactive ion etching (DRIE) process. The etching process is terminated with C₄F8 plasma (which is known to deposit a thin Teflon-like layer) in order to induce hydrophobic properties to the etched silicon surface, followed by removal of residual photoresist in a commercial solvent solution. Image 144 is a high-resolution scanning electron microscopic (FIR-SEM) image showing a top view of the silicon micro-pattern. Image 146 is a HR-SEM image showing a top view of the pattern, tilt 7°. Image 148 is a FIR-SEM image showing the dimension of the pattern.

Reference is now made to Figure 3, which is a sequence of images depicting stages in the production of a solvent resistant template of a micro/nano patterned silicon replica, to be used to impress the micro/nano pattern onto a coated polymer surface, operative in accordance with an embodiment of the present invention. The template is a micro/nano patterned UV-cured solvent-resistant template produced from epoxy using a double-replication process. In a first stage (referenced 151 ), the initial silicon master is covered by polydimethyl siloxane (PDMS, Dow-Sylgard 184), and then vacuum treated for 1 hour and cured at 80°C for 3 hours. In the second and third stages (referenced 152, 153, respectively), a PDMS mold is formed, where the mold can be easily removed from the silicon master. In the fourth stage (referenced 154), a UV-curable epoxy OG-178 (Epoxy Technology) is poured over the PDMS mold and UV-cured until reaching full curing. Following full curing, the micro-nano patterned solvent- resistant epoxy replica is peeled off from the PDMS in the next stage (referenced 155). This solvent-resistant cured replica will be used as a template to impress the micro-nano pattern onto the coated polymer surface.

Reference is now made to Figure 4, which is a collection of images, referenced 162, 164, 166, 168, relating to a micro-patterned solvent-resistant template, constructed and operative in accordance with an embodiment of the present invention. Image 162 is a photographic image showing a micro-patterned elastomeric PDMS mold produced using the process of Figure 3. Image 164 is a photographic image showing a micro-patterned solvent-resistant template produced from epoxy OG-178 using the process of Figure 3. Image 166 is a high-resolution scanning electron microscopic (HR-SEM) image showing a top view of the epoxy pattern of image 164, with a tilt of 7°. Image 168 is a HR-SEM image showing the dimension of the epoxy pattern of image 164.

Reference is now made to Figure 5, which is a photographic image of a micro-patterned epoxy template applied onto a polycarbonate sheet coated with a high adhesion coating, constructed and operative in accordance with an embodiment of the present invention. Figure 5 shows a micro-patterned epoxy template produced using the process of Figure 3. The coating is composed of the same polycarbonate material of the polymer substrate on which the coating is applied, with the material dissolved in a solvent such as dichloromethane (e.g., at 20 weight percent). The coating may be applied by blade coating using a suitable film applicator instrument or tool (such as, for example, the Coatmaster 509 MC instrument). Reference is made to Figure 6, which is a photographic image of the polymer patterned surface after the applied coating of Figure 5 has solidified and the micro-patterned template has been peeled off, constructed and operative in accordance with an embodiment of the present invention.

Reference is now made to Figures 7 and 8. Figure 7 is a HR-SEM image of a top view of the resultant solidified high-adhesion coating of Figure 6, operative in accordance with an embodiment of the present invention. Figure 8 is a magnified view of the FIR-SEM image of Figure 7. The HR-SEM images of Figures 7 and 8 were captured using an In-Lens (Immersion Lens) SEM Detector. The coating includes a textured pattern with an array of pillars, where the pillars are 3x3pm length and width, with a height of 3.5-4.5pm and a pitch (i.e., the distance between the center of two adjacent pillars in an array) of 4pm.

Reference is now made to Figures 9 and 10. Figure 9 is a HR- SEM image of a top view of another exemplary high-adhesion coating, operative in accordance with an embodiment of the present invention. Figure 9 shows another example of a coating, where a different master was used, resulting in a textured pattern with holes rather than pillars. In particular, square holes (substantially square-shaped cross-section) are formed by using a master with pillars. The holes are 1x1 pm in length and width, with a depth of 3.5pm, and a pitch (i.e., distance between the centers of adjacent holes in the array) of 3pm. Figure 10 is a magnified view of the FIR-SEM image of Figure 9.

Reference is now made to Figures 1 1 , which is a photographic image of a micro-patterned chemical resistant PDMS template before being applied onto a polycarbonate sheet coated with a high adhesion coating, constructed and operative in accordance with an embodiment of the present invention. The coating is composed of the same polycarbonate material on which the coating is applied, and is prepared as a liquid mixture of solid polymer dissolved in a suitable solvent (e.g., dichloromethane). Figure 1 1 shows a scenario in which a master with pillars is used with only one replication, with the silicon based template (rather than an epoxy template), resulting in another textured pattern with pillars. Figure 12 is a photographic image of the polymer patterned surface after the applied coating of Figure 1 1 has solidified and the micro-patterned PDMS template has been peeled off, constructed and operative in accordance with an embodiment of the present invention.

Reference is now made to Figures 13, 14 and 15. Figure 13 is a HR-SEM image of a top view of the resultant solidified high-adhesion coating of Figure 12, operative in accordance with an embodiment of the present invention. The truncated conical pillars are 2pm in diameter, with a depth of 3pm, and a pitch (i.e., distance between the centers of adjacent pillars in the array) of 7pm. Figures 14 is a magnified view of the HR-SEM image of Figure 13. Figure 15 is a further magnified view of the HR-SEM image of Figure 13. The HR-SEM images of Figures 13, 14 and 15 were captured using an In-Lens (Immersion Lens) SEM Detector.

Reference is now made to Figure 16, which is a photographic image showing contact angle measurements on a micro-patterned polymer high-adhesive coating after treatment with hydrophobic fluorosilanes, constructed and operative in accordance with an embodiment of the present invention. A measurement was applied to a high-adhesive coating produced using a micro-patterned epoxy template (as in Figure 5 and 6), The measured contact angle formed by a sessile water drop (i.e., in accordance with the sessile drop technique for measuring contact angle) is approximately 154°. The measured surface contact angle exceeds 150°, thus revealing a super-hydrophobic surface. The image was captured using a microscope goniometer.

Reference is now made to Figure 17, which is a schematic illustration of a coating process when a solvent resistant template is introduced as a micro-nano textured roll which continuously patterns the coating base of the polymer solution. The process is applied on-line, i.e., at the same production line and the same time as the polymer sheet/film itself. The polymer substrate sheet or film coming from a continuous extrusion process is inserted between the support roll and the micro/nano textured roll. The specifically designed liquid coating is poured manually or mechanically into the bath. Auxiliary rolls pick up the coating and transfer it to the micro/nano textured roll (in accordance with roll coating techniques known in the art). The micro/nano texture roll presses on the polymer substrate sheet or film and transfers the coating onto it. Sprinklers apply the flourosilanes (F-treatment) onto the patterned coating surface. The oven produces the final evaporation of the solvent.

The following chart (Table 1 ) shows a comparison between the original micro-pattern on the silicon (Sh) master and the final micro-pattern obtained on the surface of the coated polymer.

Table 1 :

While certain embodiments of the disclosed subject matter have been described, so as to enable one of skill in the art to practice the present invention, the preceding description is intended to be exemplary only. It should not be used to limit the scope of the disclosed subject matter, which should be determined by reference to the following claims.

Claims

1. A composition comprising a polymer substrate having deposited on at least one surface thereof a coating, the coating comprising a nanosized or microsized texture pattern,

wherein the material composition of the coating is based on the material composition of the polymer substrate, such that the coating is adhered to and fully integrated with the polymer substrate.

2. The composition of claim 1 , wherein the coating is further characterized by a visible light transparency in the range of 70% to

90%.

3. The composition of any of claims 1 to 2, wherein the coating comprises at least one ultraviolet (UV) absorbent additive.

4. The composition of any of claims 1 through 3, wherein the coating comprises at least one anti-abrasion additive.

5. The composition of any of claims 1 through 4, wherein the coating is characterized by a water contact angle of at least 150°.

6. The composition of any of claims 1 through 4, wherein the coating is characterized by a water contact angle of less than 50°.

7. The composition of any of claims 1 through 6, wherein the coating is covalently adhered to the polymer substrate.

8. The composition of any of claims 1 through 7, wherein the coating comprises a textured pattern comprising an array of at least one of: pillars; and holes.

9. The composition of claim 8, wherein the median height or depth of the pillars or the holes is in the range of: 2pm to 20pm.

10. The composition of any of claims 8 to 9, wherein at least one dimension of the pillars or holes is in the range of 100nm to 5pm, the dimension selected from the group consisting of: length; width; and diameter.

1 1. The composition of any of claims 8 through 10, wherein the median spacing of the pillars or the holes is in the range of: 1 pm to 20pm.

12. The composition of any of claims 8 through 1 1 , wherein the pillars or the holes comprises a shape selected from the group consisting of: round; band-shaped; sleeve-shaped; elliptical; square; rectangular; triangular; hexagonal; conical; star-shaped; and truncated cone shaped.

13. The composition of any of claims 8 through 12, wherein the array covers from 0.5% to 95% of the total area of the surface of the polymer substrate.

14. The composition of any of claims 1 through 13, further characterized by a delta-E color shift of no greater than 10, after 2000 hours of accelerated weather exposure according to ASTM G155.

15. The composition of any of claims 1 through 14, further characterized by a yellowness index of less than 10 according to ASTM E313, after 2000 hours of accelerated weather exposure according to ASTM

G155.

16. The composition of claim 1 , wherein the coating further comprises a substance selected from the group consisting of:

at least one hydrophobic additive; and

at least one hydrophilic additive.

17. A coating for a polymer substrate, the coating comprising a nanosized or microsized texture pattern,

wherein the material composition of the coating is based on the material composition of a polymer substrate to be coated, such that the coating is adhered to and fully integrated with the polymer substrate when applied to at least one surface thereof.

18. A method for preparing a coating for a polymer substrate, the method comprising the procedures of:

producing a micro/nano patterned master;

producing a replica of the master;

producing a solvent-resistant micro/nano patterned template of the replica;

producing a high-adhesion liquid coating, wherein the material composition of the coating is based on the material composition of the polymer substrate to be coated, such that the coating will be adhered to and fully integrated with the polymer substrate;

coating at least one surface of the polymer substrate with the coating;

applying the solvent-resistant template onto the coating; solidifying the coating by solvent evaporation; and

removing the template to leave a negative imprinting of the template on the polymer substrate surface.

19. The method of claim 18, further comprising the procedure of adding at least one hydrophilic chemical additive to the coating, to render a hydrophilic coating.

20. The method of claim 18, further comprising the procedure of adding at least one hydrophobic chemical additive to the coating, to render a hydrophobic coating.

21. The method of any of claims 18 to 20, further comprising the procedure of adding at least one anti-abrasion additive to the coating, to render an abrasion resistant coating.

22. The method of any of claims 18 to 21 , further comprising the procedure of adding at least one ultraviolet (UV) absorbent additive to the coating, to render a UV protective coating.

23. The method of claim 18, further comprising the procedure of treating at least one surface of the coating with at least one hydrophilic chemical entity, to render an ultra-hydrophilic surface.

24. The method of claim 18, further comprising the procedure of treating at least one surface of the coating with at least one hydrophobic chemical entity, to render an ultra-hydrophobic surface.

25. The method of any of claims 18 to 24, further comprising the procedure of cleaning the surface of the polymer substrate before applying the coating.

26. The method of any of claims 18 to 25, wherein the coating is applied from multiple sides or surfaces of the polymer substrate.

27. The method of any of claims 18 to 26, wherein the method is implemented in a manner selected from the group consisting of: a batch process;

a semi-continuous process;

a continuous process; and

an online process.

28. The method of any of claims 18 to 27, wherein the polymer substrate is in the form of a sheet or a film.