Anisotropic icephobic coating

Abstract

Articles including durable and icephobic polymeric coatings are disclosed. The polymeric coatings include a bonding layer which may contain a substantially fully cured polymeric resin providing excellent adhesion to metallic or polymer substrates. The polymeric coating further includes an outer surface layer which is smooth, hydrophobic and icephobic and, in addition to a substantially fully cured resin, contains silicone comprising additives near the exposed outer surface. The anisotropic polymeric coatings are particularly suited for strong and lightweight parts required in aerospace, automotive and sporting goods applications. A process for making the articles is disclosed as well.

Claims

1. A cured polymeric coating which is compositionally graded or layered to be anisotropic in the deposition direction, the cured polymeric coating comprising: a cured first chemical composition extending at least 2.5 microns in height from an outer surface of an underlying substrate; (ii) a cured second chemical composition having a different chemical composition than the cured first chemical composition, the cured second chemical composition comprising a polymeric resin and an icephobic material addition forming an exposed outer surface extending at least 2.5 microns in depth from the exposed outer surface, wherein the cured second chemical composition: a) contains the icephobic material addition representing up to 25% by weight of the cured second chemical composition; b) has a sand erosion value according to standard ASTM G76 at an impingement angle of 90 degrees of less than 10 mm.sup.3/kg; and c) has an ice adhesion value of less than 300 kPa as prepared when measured according to ERDC/CRREL Technical Note 03-4; and said cured polymeric coating has a total thickness of at least 10 microns, and the pull-off strength between the underlying substrate and the exposed outer surface of the cured polymeric coating, according to standard ASTM 4541D, is at least 250 psi.

2. The cured polymeric coating according to claim 1, wherein the cured polymeric coating exhibits no failure after being exposed to at least one temperature cycle according to ASTM B553-71 service condition 1.

3. The cured polymeric coating according to claim 1, wherein the cured polymeric coating at room temperature is free of liquids.

4. The cured polymeric coating according to claim 1, wherein the pull-off strength between the underlying substrate and the exposed outer surface of the cured polymeric coating, according to standard ASTM 4541D, is at least 300 psi.

5. The cured polymeric coating according to claim 1, wherein both the cured first chemical composition and the cured second chemical composition, prior to curing, comprise one or more curable epoxy resins with an EEW number of between 100 and 750.

6. The cured polymeric coating according to claim 1, wherein the cured first chemical composition forms the inner surface contacting the underlying substrate, and said inner surface is rough with a surface roughness of R.sub.a>1 micron; and the cured second chemical composition forms the exposed outer surface exposed to atmosphere; and said exposed outer surface is smooth with a surface roughness R.sub.a<1 micron.

7. The cured polymeric coating according to claim 1, wherein the cured second chemical composition has an ice adhesion value of less than 500 kPa after 5 icing/deicing cycles when measured according to ERDC/CRREL Technical Note 03-4.

8. The cured polymeric coating according to claim 1, wherein the cured second chemical composition has a contact angle for water at room temperature greater than 90°.

9. The cured polymeric coating according to claim 1, wherein the icephobic material addition of the cured second chemical composition is composed entirely of solids.

10. The cured polymeric coating according to claim 1, wherein the icephobic material addition of the cured second chemical composition comprises a polysiloxane.

11. The cured polymeric coating according to claim 10, wherein the polysiloxane of the cured second chemical composition comprises an epoxy modified silicone.

12. The cured polymeric coating according to claim 1, wherein the cured second chemical composition has a Shore D-Scale Hardness of at least 20.

13. A non-isotropic article comprising: a substrate at least partly covered by a layered and/or graded polymeric coating having a total thickness of at least 2.5 microns applied to at least a part of an outer surface of the substrate and forming an exposed outer surface of the article, wherein the polymeric coating, after curing: (i) contains an icephobic material addition representing up to 25% by weight of the cured polymeric coating; (ii) has a contact angle for water at room temperature greater than 90 degrees; and (iii) has an ice adhesion of less than 500 kPa as prepared and after 5 icing/deicing cycles when measured according to ERDC/CRREL Technical Note 03-4; wherein said non-isotropic article has a pull-off strength between the substrate and an exposed outer surface of the cured polymeric coating, according to standard ASTM 4541D, of at least 250 psi.

14. The non-isotropic article according to claim 13, wherein the substrate is formed of a metallic material or a polymeric material.

15. The non-isotropic article according to claim 13, wherein the cured polymeric coating has a Shore D-Scale Hardness of at least 20.

16. The non-isotropic article according to claim 13, wherein the icephobic material addition, in its cured form, is composed entirely of solids.

17. The non-isotropic article according to claim 13, wherein the non-isotropic article exhibits no failure after being exposed to at least one temperature cycle according to ASTM B553-71 service condition 1.

18. The non-isotropic article according to claim 13, wherein the cured polymeric coating has a cured first chemical composition and a cured second chemical composition having a different chemical composition than the cured first chemical composition, wherein the cured first chemical composition forms the inner surface contacting the substrate, said inner surface is rough with a surface roughness of R.sub.a>1 micron, and wherein the cured second chemical composition forms the exposed outer surface exposed to atmosphere, said exposed outer surface is smooth with a surface roughness R.sub.a<1 micron.

19. A non-isotropic article comprising: (i) a substrate; and (ii) a polymeric coating compositionally graded or layered to be anisotropic in a deposition direction, having a total thickness of at least 10 microns, applied to at least part of an outer surface of the substrate, and having an inner surface in intimate, direct contact with the substrate, and comprising: (a) a cured first chemical composition comprising a polymeric resin at an interface between said polymeric coating and the substrate extending at least 2.5 microns in height from the outer surface of the substrate; (b) a cured second chemical composition having a different chemical composition than the cured first chemical composition, comprising a polymeric resin and an icephobic material addition forming an exposed outer surface of said non-isotropic article extending at least 2.5 microns in depth from the exposed outer surface, wherein the cured second chemical composition: (i.b) contains the icephobic material addition composed entirely of solids; (ii.b) has a Shore D-Scale Hardness of at least 20; (iii.b) has a sand erosion value according to standard ASTM G76 at an impingement angle of 90 degrees of less than 10 mm.sup.3/kg; (iv.b) is hydrophobic; and (v.b) has an ice adhesion of less than 300 kPa as prepared and of less than 500 kPa after 5 icing/deicing cycles when measured according to ERDC/CRREL Technical Note 03-4.

20. The non-isotropic article according to claim 19, wherein the icephobic material addition represents up to 25% by weight of the cured second chemical composition.

21. The non-isotropic article according to claim 20, wherein said icephobic material addition comprises a polysiloxane.

22. The non-isotropic article according to claim 21, wherein said polysiloxane comprises an epoxy modified silicone.

23. The non-isotropic article according to claim 19, wherein said polymeric coating in both the cured first chemical composition and the cured second chemical composition, prior to curing, comprises one or more curable epoxy resins with an EEW number of between 100 and 750.

24. The non-isotropic article according to claim 19, wherein the pull-off strength between the substrate and the exposed outer surface of the polymeric coating, according to standard ASTM 4541 D, is at least 250 psi.

25. The non-isotropic article according to claim 19, wherein said exposed outer surface is smooth with a surface roughness R.sub.a≤1 micron, and wherein the cured first chemical composition forms the inner surface, said inner surface is rough with a surface roughness of R.sub.a>1 micron.

26. The non-isotropic article according to claim 19, wherein said substrate is a metallic material or a polymeric material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features and advantages of the invention will be appreciated upon reference to the following drawings, in which:

(2) FIGS. 1 and 3 are graphs showing the wetting angle, ice adhesion, Shore D hardness as well as the sand erosion properties for impingement angles of 90° and 30° for various polymeric coatings.

(3) FIGS. 2 and 4 are graphs showing the pull-off adhesion strength of selected polymeric coatings applied to various substrates.

DETAILED DESCRIPTION OF THE INVENTION

(4) It is well known that the formation, adhesion, and accumulation of ice, snow, frost, glaze, rime, or their mixtures can cause severe problems for solar panels, wind turbines, aircrafts, heat pumps, power lines, telecommunication equipment, as well as land vehicles and marine vessels. These problems generate safety hazards and can result in failure. To address these issues, the fundamentals of interfaces between gases, liquids and solids and solid surfaces at low temperatures need to be taken into account and various approaches to form “icephobic” (pagophobic) surfaces have been proposed. As the person skilled in the art knows different properties may be required to prevent the formation and adhesion of ice, snow, glaze, rime, and frost.

(5) Icephobicity is the ability of a solid surface to repel ice or prevent ice formation due to a certain topographical structure and/or chemical composition of the surface. Icephobic surfaces in this specification are defined by an ice adhesion strength of typically <350 kPa, preferably <300 kPa, and more preferably <200 kPa. Slippery, liquid infused porous surfaces (SLIPS) have been proposed for reducing ice adhesion to values as low as 10 kPa, however, after a few icing-deicing cycles, ice adhesion gradually increases to over 200 kPa. Furthermore, the mechanical durability of SLIPS surfaces is typically poor. Many other approaches have been proposed as well which are capable of reducing the icephobicity, however, achieving and maintaining both icephobicity and long-term durability remains a challenge.

(6) In order to enhance icephobicity, the exposed surface needs to generally exhibit poor adhesion characteristics, however, in most of the commercial applications the icephobic material layer is applied as a homogeneous coating onto a suitable substrate. As a consequence, the “inner surface” of such icephobic coatings, e.g., the surface contacting the underlying substrate, exhibits poor adhesion particularly when containing liquid icephobic additives. Delamination and flaking of the polymeric coating at the interface with the underlying substrate frequently limit its durability even if the coating is formulated to be hard and strong.

(7) In this specification therefore the inventors of the present disclosure propose to form anisotropic, icephobic coatings by minimizing adhesion on the exposed outer surface while maximizing adhesion on the inner surface to achieve a good bond at the interface with the underlying substrate. This is achieved by modifying the composition of the icephobic material coating in the deposition direction through layering and/or gradually modulating the chemical composition. In its simplest form the coating contains two layers of different composition.

(8) Epoxies are known for achieving excellent adhesion to a number of substrates including metals due to their polar nature and their ability to create chemical bonds to the surface upon cure. Hard and strong due to high crosslinking, cured epoxies can bear loads and resist wear caused by abrasion over the long term. This good mechanical strength, however, at high crosslink density flexibility decreases and epoxies are known for cracking due to their brittleness and inability to dissipate stresses. Cured epoxies layers require the addition of icephobic material additives to notably reduce ice-adhesion strength.

(9) Similarly, polyurethanes are commonly employed as coatings for preventing corrosion of metal articles and to make a variety of materials more durable. Polyurethanes are extremely resilient substances and their mechanical properties can be easily manipulated by optimizing their compositions.

(10) Silicones exhibit high elongation and flexibility that enable the dissipation of stresses and applied energy. Their strong Si—O bond and high surface energy make silicones resistant to atmospheric or chemical attack and less susceptible to degradation from sunlight, water uptake and ultraviolet (UV) light, thereby providing hydrophobic and icephobic properties for extended periods of time.

(11) The inventors of the present disclosure have discovered that combining the adhesion, abrasion resistance and mechanical strength of epoxies with the thermal stability, flexibility and icephobicity of silicones in hybrid systems yields strong and flexible materials with higher resistance to cracking in harsh environments while providing hydrophobic and icephobic properties. Starting out at the metallic or polymeric substrate surface representing the inner coating surface by applying a polymeric coating with a high epoxy content, preferably being substantially free of silicones or having a low silicone content assures a good bond between the polymeric coating and the underlying substrate. Then, as the thickness of the polymeric coating increases, the silicone contents in the deposition direction towards the outer exposed surface can be gradually or stepwise increased. Consequently, a polymeric coating is formed ending up with the highest silicone content at the outer, exposed surface, thus providing for an anisotropic polymeric coating which maintains excellent adhesion to the substrate surface while being icephobic on the exposed, outer surface. In one preferred embodiment the same epoxy resin is used throughout the coating, i.e., in both the bonding and the icephobic layer.

(12) Similarly, substituting polyurethanes based coatings for epoxies using otherwise the same approach can yield durable coatings with excellent icephobic properties and high adhesion to the underlying substrates.

(13) This invention relates to articles comprising durable, icephobic coatings. In its broadest aspect the present invention relates to article of manufacture comprising: (i) a substrate comprising a metallic or polymeric material having an outer surface in direct contact with (ii) an anisotropic polymeric coating which (a) on the interface between said polymeric coating and said substrate contains a substantially fully cured organic resin and is substantially free of icephobic additives; and (b) on its exposed outer surface contains the same substantially fully cured organic resin and furthermore contains one or more solid icephobic additives.

(14) In one preferred embodiment the substrate comprises a metallic material. Examples of suitable metallic materials include metals and alloys of aluminum, cobalt, magnesium, steel, nickel and titanium. The substrate can be an isotropic, layered or graded metallic construct comprising one or more continuous metal layers wherein at least one of the continuous metal layers is a microcrystalline and/or amorphous metal layer or a grain-refined layer having a grain size below 5,000 nm.

(15) In another preferred embodiment the substrate comprises a polymer or polymer composite. Suitable polymers include any known thermoplastic or thermoset. Suitable polymer composites can contain a material selected from the group consisting of carbon, carbon fibers, graphite, graphite fibers, carbon nanotubes and graphene. Other additions such as glass, glass fibers, as well as inorganic and organic fibers are contemplated as well.

(16) The polymeric coating applied to the substrate is anisotropic in the deposition direction, e.g., layered or compositionally graded. The composition of the polymeric coating in contact with the substrate and near the interface with the substrate is chosen to maximize the adhesion strength between the polymeric coating and the substrate. In contrast, the composition of the exposed outer surface of the polymeric coating is chosen to maximize erosion performance and icephobic properties. The transition of the composition of the polymeric coating from the “bonding surface” to the “icephobic surface” can be gradual, e.g., by changing the chemical composition from an epoxy or polyurethane rich and silicone free to an epoxy or polyurethane and silicone containing outer surface providing a graded polymer layer. Alternatively, distinct layers of various compositions can be applied to transition from an epoxy or polyurethane rich, silicone-free to an epoxy or polyurethane and silicone containing outer surface. In the case of layering, at a minimum, two distinct polymer layers are applied; however, a multilayer laminate with a total of up to 100 sublayers can be applied. Combination of layered and graded sublayers is also included in the scope of this invention.

(17) In an alternative embodiment the anisotropic polymeric coating is not directly applied to the substrate but formed independently and provided with an adhesive film or an adhesive tape in contact with the bonding layer and the exposed adhesive film is protected by a release liner. Before use, the release liner is removed and the coating is applied to the substrate in a way that the adhesive film forms an intermediate layer between the substrate and the anisotropic polymeric coating. The adhesive film can be epoxy based providing high adhesive strength and preferably cures at or near room temperature. Other options include rubber-, silicone- or acrylic-based adhesive tapes which can also be pressure sensitive adhesives. In one preferred embodiment the adhesive layer replaces the bonding layer and is applied directly onto the icephobic layer. Such an approach can be used to apply the icephobic coating conveniently onto any part to render it icephobic, it is particularly suitable for use in repair and overhaul, e.g., where there is a requirement to patch eroded or deteriorated sections of the coating.

(18) The present invention is based on the discovery that, in the case of applying an icephobic organic coating to a metallic or polymeric substrate surface, an isotropic coating does not readily achieve the desired overall performance as either adhesion to the underlying substrate or icephobic properties or both are unduly compromised which can have a significant effect on performance and durability. Monolithic coatings optimized for icephobicity were found to have rather poor adhesion to the substrate materials of interest and perform poorly on extended durability tests such as sand or rain erosion frequently resulting in part or the entire coating flaking off the underlying substrate surface resulting in premature failure.

(19) Typically, the polymeric coating according to this invention uses the same ingredients throughout, e.g., the same curable epoxy or polyurethane resin, the same curing agent formulation etc. termed “basic coating formulation”. The main difference in the chemical formulations near the “bonding surface” when compared to near the “icephobic surface” is, that, in the case of the “near bonding layer surface” the coating comprises merely the “basic coating formulation” with the optional addition of adhesion promoters, and elastomers. In contrast, “near the outer icephobic surface” the coating comprises the “basic coating formulation” with the addition of between 1 and 20 wt % of an “icephobic additive” with the optional addition of other additives, including, but not limited to, abrasive materials to enhance the hardness and erosion resistance of outer and near-outer surface and pigments to achieve any desired color. Consequently, the chemical composition throughout the polymeric coating is similar assuring excellent adhesion of sublayers, if any, to each other and excellent overall cohesive strength of the entire coating. This approach is far superior to, e.g., applying a distinct polymer primer to the substrate followed by the deposition of a distinct and unrelated, icephobic polymeric coating, which can lead to delamination of the “unrelated” polymer layers during use.

(20) Accordingly, the polymeric coating applied to the metallic or polymeric material substrate is anisotropic and comprises, on the surface in contact with the substrate material, a “bonding layer” comprising a curable resin preferably free of silicones and, on the exposed outer surface an “icephobic layer” which, in addition to the same curable resin, contains at least 1 and up to 25 weight percent of a modified silicone.

(21) Both, the bonding layer and the outer icephobic layer have a thickness of at least 5 microns, preferably at least 25 microns and more preferably at least 50 microns.

(22) The bonding layer is deposited directly onto the substrate material and subsequently typically at least partially cured and another cure is performed after the icephobic top coat is applied. Depending on the number of sublayers the total number of curing steps involved is at least 2 but as many as 10+ curing cycles can be used, depending on the number of sublayers applied and the final properties desired.

(23) In another aspect the invention provides a process for coating an article, said process comprising the steps of: providing an article of manufacture having an outer surface, or a predetermined portion thereof, comprised of a metallic or polymeric substrate material; coating the outer surface of the substrate material, or a predetermined portion thereof, with a curable polymeric resin of a first composition; substantially partially or fully curing the curable polymeric resin of the first composition to form a bonding layer; coating the outer surface of the bonding layer with a polymeric resin of a second composition comprising an icephobic additive; substantially fully curing the curable polymeric resin of the second composition to form a durable icephobic exposed outer surface;

(24) In another aspect the invention provides a process for applying a prepreg coating to an article, said process comprising the steps of: providing an article of manufacture having an outer surface, or a predetermined portion thereof, comprised of a metallic or polymeric substrate material; independently forming and substantially partially or fully curing a curable polymeric resin of the second composition comprising an icephobic additive to form a durable icephobic exposed outer surface; optionally applying onto the second composition layer a curable polymeric resin of a first composition and optionally partially or fully curing the curable polymeric resin of the first composition; applying onto the first composition layer, if present, an adhesive layer and optionally partially or fully curing the multilayer construct; optionally applying onto the adhesive layer a release liner; upon use removing the optional release liner from the multilayer construct and applying it to the metallic or polymeric substrate material so that the icephobic layer of the second composition becomes the exposed outer surface.

(25) Such processes result in achieving a very strong bond between the outer exposed coating surface and the underlying core substrate and the processes can be used to manufacture articles in which strong adhesion between the exposed polymeric coating and the underlying substrate is desired or necessary. In addition, the organic coating sublayers are formulated and/or processed to maximize cohesive strength within the polymeric coating sublayers themselves while achieving excellent adhesion between the sublayers as well. The processes are particularly suited for the manufacture of durable articles that require high water repellency, icephobicity, as well as abrasion resistance and flexural, tensile, torsional, impact and/or fatigue strength, such as required for sporting goods, automotive parts, aircraft components, building materials, industrials components exposed to the elements; and the like.

(26) It is desirable to pretreat the substrate surface before it receives the polymer coating. The pretreatment can comprise mechanical abrasion and/or etching. Etching can be, e.g., accomplished with permanganate or sulfochromic chemical etch, or with a plasma etch.

(27) The compositions comprising the curable resin can, for example, be applied by spraying. For this purpose, the composition desirably uses a solvent in a sufficient amount to obtain the viscosity suitable for spraying. It has been found that preferred solvents have a boiling point of less than 150° C., preferably less than 100° C. The importance of the boiling point of the solvent is related to the need to have the film substantially fully cured. It is important that, after curing, the polymeric coating has substantially no dissolved solvents and does not contain any liquids.

(28) When applied by spraying, both the bonding layer and the icephobic layer are generally applied at about 3 to 20 mg/cm.sup.2, preferably from 5 to 15 mg/cm.sup.2. Depending on the thickness desired, it may be advantageous to apply each composition in two or more sprayed layers, with a partial curing (for example 30 minutes at 140° C. or 90° C.) between applications.

(29) After applying the bonding layer and prior to depositing the icephobic outer layer, the bonding layer can be partially or fully cured as well as suitably pretreated. This pretreatment can comprise mechanically roughening and/or etching. Suitable etching processes include chemical etching processes and/or plasma etching.

(30) When applying the icephobic layer, the spraying process described for applying the bonding layer is essentially replicated. Alternative processes can be used as well including, but not limited to, painting, doctor blading and screen printing.

(31) While building up the entire polymeric coating, various curing steps can be performed and repeated, alternatively partial curing steps can be employed or the curing step can be deferred until the entire coating has been deposited.

(32) As the person skilled in the art of organic coatings would appreciate, the organic coating can be applied to the core substrate in an automated production line where, e.g., the substrate to be coated passes from one spray booth to the next with optional partial or total curing and/or surface treatments in between. A multilayer laminate coating can be produced, e.g., changing the composition of the “paint” in each spray station to achieve a “stepwise” transition from the bonding layer composition to the icephobic surface composition. While the organic coating of this invention relies on at least two distinct layers, a multitude of layers, such as 5, or 10 or even more transitional layers can be incorporated between the inner surface (in contact with the substrate) and the outer (exposed) surface of the organic coating. Similarly, rather than having a multilayer laminate with distinct chemical compositions, a gradual change in the composition can be affected in the coating deposition direction and combinations of layered and graded layers are within the scope of this invention as well.

(33) It is also possible to provide the icephobic polymer layer in freestanding form or supported such as a “pre-preg” as described above. The bonding layer film or pre-preg used in this process can be fabricated from the liquid epoxy formulation using standard industry practices used for fabricating thin film polymeric adhesive films and pre-pregs from solvent bearing formulations. The release liner protecting the adhesive film/transfer tape is removed before use and the anisotropic polymeric coating comprising an icephobic layer, a bonding layer and an additional adhesive layer or, alternatively, the adhesive layer is replacing the bonding layer altogether, is then applied to the substrate. For instance, the icephobic layer can be applied, e.g., sprayed onto the exposed surface of an adhesive tape which may have a release liner on the opposite side.

(34) Articles or coatings made according to the process of this invention find use in a variety of applications requiring improved durability while retaining enhanced hydrophobic and icephobic properties.

EXAMPLES

(35) The following is a description of Working Examples illustrating the benefits of the present disclosure, specifically the formulation of various polymeric coatings and methods of applying and curing the coatings as well as selected properties including the icephobic properties (Working Example I and III) as well as adhesion properties using a variety of substrates (Working Example II and IV).

Example I: Epoxy (EP) Coating Formulations, Application and Selected Properties

(36) Various coating formulations were investigated as follows: Nusil™, a commercial product (two-part silicone elastomer dispersed in xylene) available from NuSil™ Technology LLC, Carpinteria, Calif. 93013, USA, which is widely recognized for its icephobic properties as indicated above, was applied to selected substrates by doctor blade whereas the various inventive epoxy-based coatings were applied to the substrates by spraying using a gravity feed type, HVLP (high volume-low pressure) epoxy spray gun operated at 60 psi. In-house paint formulations are provided in Table 2 below. The coated substrates were subsequently cured in a furnace at 140° C. for 2 hours, except for Nusil™, which was cured according to the manufacturer's specifications using four temperatures and durations as follows: RT/30 min, 75° C./45 min, and 150° C./135 min. Total target loading for each sample was 8-12 mg/cm.sup.2 (thickness: 75-100 microns). If multiple layers were applied, e.g., an icephobic layer on top of the bonding layer, the thickness and loading for each layer was reduced to maintain the overall coating thickness/loading target and a curing step was performed after each layer. After curing, the exposed surface of all samples was smooth and had a surface roughness R.sub.a<1 μm.

(37) Cured coating samples produced were characterized as indicated in Table 3. For ease of comparison, the data of the various tests depicted in Table 3 are also shown in FIG. 1, namely the wetting angle, the ice adhesion according to the test described by the U.S. Army Engineer Research and Development Center, Hanover, N.H., USA, in the ERDC/CRREL Technical Note 03-4 (October 2003), the sand erosion value at impingement angles of 90° and 30° according to ASTM G76, and the Shore D hardness.

(38) TABLE-US-00002 TABLE 2 In-house Epoxy (EP) Paint Formulations Investigated. Epoxy Resin Icephobic Epoxy Bonding Layer Resin Top Layer Formulation [g] Formulation [g] Epoxy Resin (EEW = 550) 100 100 Elastomer 60 0 Curing Agent 5 5 Adhesion Promoter 8 0 Additives 15 0 Icephobic Additive: Epoxide 0 7.5 Functional Silicone Pre-Polymer Silicone Oil 0 0 Solvent 240 120

(39) The results indicate that all coating surfaces are hydrophobic, that an icephobic additive such as a silicone is required to achieve a low icephobicity value on the first cycle (Nusil™ and silicone top layer containing coatings) and that, after repeated icing/deicing cycles seven times, the ice adhesion of the samples containing the solid silicone remain largely unchanged (modified silicone top layer containing coatings).

(40) The data also reveal that the sand erosion values at 90° impingement with icephobic additions increase compared to the additive free formulation of the bonding layer, however, the erosion values at an impingement angle of 30° experience similar mass losses for all samples. In addition, the Shore D hardness values of the coatings containing epoxy resins are significantly higher than the one for Nusil™.

(41) TABLE-US-00003 TABLE 3 Selected Coating Properties Two-Layers Elastomer- Single/Homogenous Layer Free 6.7% Bonding Silicone Silicone Layer Containing Free plus Outer Epoxy Epoxy Exposed Layer Layer Surface (Icephobic (Bonding Icephobic Nusil ™ Layer) Layer) Layer Exposed Surface <1 <1 <1 <1 Roughness, R.sub.a [μm] Wetting Angle [°] 119 123 115 123 Cycle 1: 150 110 472 110 Ice Adhesion [kPa] Cycle 7: 305 110 691 110 Ice Adhesion [kPa] Sand Erosion Rate 4.1 4.9 1.9 4.9 @ 90° [mm.sup.3/kg] Sand Erosion Rate 2.1 1.8 1.9 1.8 @ 30° [mm.sup.3/kg] Shore Hardness 40 (scale A) 70-75 70-75 70-75  0 (scale D) (scale D) (scale D) (scale D)

Example II: Article Characterization

(42) A number of substrates were selected (4×4 inch panels) for this investigation, namely Al, Ti, stainless steel, carbon fiber reinforced composite and Nylon. The smooth substrates (R.sub.a<1 μm) were mechanically abraded with ultra-fine (500 grit) sand paper to a uniform finish, then cleaned and degreased by wiping with a suitable solvent and various coatings described in EXAMPLE I were applied as follows: (i) Nusil™, (ii) an epoxy based, silicone-free, bonding layer, (iii) an epoxy based icephobic layer and (iv) a two layer coating comprising the epoxy based bonding layer on the substrate followed by the epoxy based icephobic outer exposed layer.

(43) TABLE-US-00004 TABLE 4 Adhesion Property Evaluation Single/Homogenous Layer 2-Layers 6.7% Silicone Elastomer-Free Silicone Free Bonding Layer Containing Epoxy plus Outer Epoxy Layer Layer Exposed (Icephobic (Bonding Surface Nusil ™ Layer) Layer) Icephobic Layer Pull Off Adhesion 228 750 1322 1239 Strength from Titanium [psi] Pull Off Adhesion 213 691 1344 1337 Strength from Aluminum [psi] Pull Off Adhesion 201 471 1411 1420 Strength from Stainless Steel Grade 304 [psi] Pull Off Adhesion 210 872 1846 1887 Strength from Carbon Fiber Composite [psi] Pull Off Adhesion 247 428 942 945 Strength from Nylon [psi]

(44) The adhesion between the top/exposed surface of any coating and the base substrate was measured by the “pull-off strength” according to standard ASTM 4541D. For ease of comparison, the data of the various samples are depicted in Table 4 are also shown in FIG. 2. The data reveal that layers with the icephobic additive (Nusil™ and icephobic layer) applied directly to the varies substrates have the lowest bond strength, whereas the icephobic additive-free bonding layer and the two-layer structure comprising a bonding layer in direct contact with the substrate and an outer, exposed icephobic layer results in an overall pull-off strength, at times, that exceeded 800 psi as well as 1,000 psi. Articles containing the Nusil™ coating, in all instances, delaminated at the interface of the substrate and the coating. Articles containing a bonding layer in contact with the various substrates, in all instances, showed both signs of delamination as well as cohesive failure, revealing the impressive strength of these samples.

(45) These results indicate that an anisotropic coating (bonding layer+icephobic layer) provides a superior article with excellent durability, bond strength and long lasting icephobic properties.

Example III: Polyurethane (PU) Coating Formulations, Application and Selected Properties

(46) A thermoset polyurethane formulation which cures at room temperature with and without the addition of a modified silicone were applied to various substrates by spraying using a gravity feed type, HVLP (high volume-low pressure) spray gun operated at 60 psi and compared to the Nusil™ commercial product described above. In-house paint formulations are provided in Table 5 below. Total target loading for each sample was 8-12 mg/cm.sup.2 (thickness: 75-100 microns). After curing, the exposed surface of all samples was smooth and had a surface roughness R.sub.a<1 μm.

(47) Cured coating samples produced were characterized as indicated in Table 6. For ease of comparison, the data of the various tests depicted in Table 6 are also shown in FIG. 3, namely the wetting angle, the ice adhesion according to the test described by the U.S. Army Engineer Research and Development Center, Hanover, N.H., USA, in the ERDC/CRREL Technical Note 03-4 (October 2003), the sand erosion value at impingement angles of 90° and 30° according to ASTM G76, and the Shore D hardness.

(48) TABLE-US-00005 TABLE 5 In-house Polyurethane (PU) Paint Formulations Investigated. PU Bonding Layer Icephobic PU Resin Formulation [g] Layer Formulation [g] Thermoset Polyurethane 100 100 Elastomer 0 0 Curing Agent 100 100 Adhesion Promoter 0 0 Additives 0 0 Icephobic Additive: 0 10 Epoxide Functional Silicone Pre-Polymer Silicone Oil 0 0 Solvent 200 200

(49) TABLE-US-00006 TABLE 6 Selected Coating Properties Single/Homogenous Layer Two-Layers 4.8% PU Bonding Silicone Silicone Layer plus Containing Free PU Outer Exposed PU Layer Layer Surface (Icephobic (Bonding Icephobic PU Nusil ™ Layer) Layer) Layer Exposed Surface <1 <1 <1 <1 Roughness, R.sub.a [μm] Wetting Angle [°] 119 120 120 120 Cycle 1: 150 137 363 137 Ice Adhesion [kPa] Cycle 5: 305 133 532 133 Ice Adhesion [kPa] Sand Erosion Rate 4.1 4.4 4.4 4.4 @ 90° [mm.sup.3/kg] Sand Erosion Rate 3.5 3.5 3.5 3.5 @ 45° [mm.sup.3/kg] Sand Erosion Rate 2.1 2.1 2.1 2.1 @ 30° [mm.sup.3/kg] Shore Hardness 40 (scale A) 20 20 20  0 (scale D) (scale D) (scale D) (scale D)

(50) The results indicate that all coating surfaces are hydrophobic, that an icephobic additive such as a silicone is required to achieve a low icephobicity value on the first cycle (Nusil™ and silicone top layer containing coatings) and that, after repeated icing/deicing cycles five times, the ice adhesion of the samples containing the solid silicone remain largely unchanged (modified silicone top layer containing coatings).

(51) The data also reveal that the sand erosion at all angles of impingement with are similar for all samples. In addition, the Shore D hardness values of the coatings containing PU resins are significantly higher than the one for Nusil™.

Example IV: Article Characterization

(52) A number of substrates were selected (4×4 inch panels) for this investigation, namely Al, Ti, stainless steel, carbon fiber reinforced composite and Nylon. The smooth substrates (R.sub.a<1 μm) were mechanically abraded with ultra-fine (500 grit) sand paper to a uniform finish, then cleaned and degreased by wiping with a suitable solvent and various coatings described in EXAMPLE III were applied as follows: (i) Nusil™, (ii) a thermoset polyurethane based, silicone-free, bonding layer, (iii) an thermoset polyurethane based icephobic layer and (iv) a two layer coating comprising the thermoset polyurethane based bonding layer on the substrate followed by the thermoset polyurethane based icephobic outer exposed layer.

(53) The adhesion between the top/exposed surface of any coating and the base substrate was measured by the “pull-off strength” according to standard ASTM 4541D. For ease of comparison, the data of the various samples are depicted in Table 7 are also shown in FIG. 4. The data reveal that layers with the icephobic additive (Nusil™ and icephobic layer) applied directly to the varies substrates have the lowest bond strength, whereas the icephobic additive-free bonding layer and the two-layer structure comprising a bonding layer in direct contact with the substrate and an outer, exposed icephobic layer results in an overall pull-off strength that exceeded 1,000 psi. Articles containing the Nusil™ coating, in all instances, delaminated at the interface of the substrate and the coating. Articles containing a bonding layer in contact with the various substrates, in all instances, showed both signs of delamination as well as cohesive failure, revealing the impressive strength of these samples.

(54) These results indicate that an anisotropic coating (bonding layer+icephobic layer) provides a superior article with excellent durability, bond strength and long lasting icephobic properties.

(55) TABLE-US-00007 TABLE 7 Adhesion Property Evaluation Single/Homogenous Layer 2-Layers 4.8% Silicone Silicone PU Bonding Containing PU Free PU Layer plus Outer Layer Layer Exposed Surface (Icephobic (Bonding Icephobic PU Nusil ™ Layer) Layer) Layer Pull Off Adhesion 228 1315 1423 1425 Strength from Titanium [psi] Pull Off Adhesion 213 1298 1455 1420 Strength from Aluminum [psi] Pull Off Adhesion 201 1024 1224 1210 Strength from Stainless Steel Grade 304 [psi] Pull Off Adhesion 210 1677 1685 1650 Strength from Carbon Fiber Composite [psi] Pull Off Adhesion 247 892 1192 1200 Strength from Nylon [psi]

VARIATIONS

(56) The foregoing description of the invention has been presented describing certain operable and preferred embodiments. It is not intended that the invention should be so limited since variations and modifications thereof will be obvious to those skilled in the art, all of which are within the spirit and scope of the invention.