WO2012082667A2

WO2012082667A2 - Article including airfoil or hydrofoil and method of making the same

Info

Publication number: WO2012082667A2
Application number: PCT/US2011/064515
Authority: WO
Inventors: Guglielmo M. Izzi; Daniel R. Fronek; Thomas Herdtle; Nelson D. Sewall; Mieczyslaw H. Mazurek; Danny L. Fleming; Vivian W. Jones
Original assignee: 3M Innovative Properties Company
Priority date: 2010-12-13
Filing date: 2011-12-13
Publication date: 2012-06-21
Also published as: WO2012082668A2; WO2012082667A3

Abstract

An article including an airfoil or hydrofoil is disclosed. On at least a portion of a surface of the airfoil or hydrofoil there is a seamless film having a series of substantially parallel peaks separated from each other by a series of substantially parallel valleys on a patterned first surface of the film, wherein the seamless film has a long dimension that is at least two meters long substantially aligned with the span of the airfoil or hydrofoil, and wherein an angle between the parallel peaks and valleys to the long dimension of the seamless film is at least five degrees. Methods of making the article are also disclosed.

Description

ARTICLE INCLUDING AIRFOIL OR HYDROFOIL AND

METHOD OF MAKING THE SAME

Cross Reference to Related Applications

This application claims priority to U. S. Provisional Application Nos. 61/422,395 and

61/422,406, both filed December 13, 2010, the disclosures of which are incorporated by reference herein in their entirety.

Background

It is desirable to reduce the turbulent flow when bodies pass through fluid media (e.g., when an airplane moves through air or a boat moves through water). Reducing turbulent flow can reduce drag, for example, and relatively small reductions in drag can significantly reduce the fuel needed to propel the body. Reduction in turbulent flow can also result in a reduction in noise, which is desirable for some applications.

Various films that can reduce turbulent flow are known and comprise a thermoplastic or thermoset polymeric film having a patterned surface that reduces drag, for example. Examples of these films can be found in U. S. Pat. Nos. 4,930,729 (Savill); 4,986,496 (Marentic et al.); 5,848,769 (Fronek et al.); 5,971,326 (Bechert); and 6,345,791 (McClure). These films, often referred to as riblet films, are typically prepared in continuous film processes with parallel grooves (also called riblets) extending in the machine direction. To apply such films, a tiling process is typically carried out in which the films are cut into strips and placed onto an airfoil or hydrofoil piece-by-piece to have the riblets correctly oriented in the main direction of fluid flow.

Summary

The tiling process for applying riblet films to airfoils or hydrofoils can be time-consuming and labor-intensive. Very precise placement of the film pieces is necessary so that there are no gaps between pieces that can increase turbulence, resulting in increased noise or drag. The present disclosure provides an article that includes an airfoil or hydrofoil with a seamless film on its surface. The seamless film has a series of substantially parallel peaks separated from one another by a series of substantially parallel valleys, which are useful, for example, for reducing the turbulent flow at the surface of the article. The seamless film is configured so that a portion of the airfoil or hydrofoil that is desired to be provided with a patterned surface (e.g., for drag reduction or noise reduction) may be covered with a single piece of film in which the substantially parallel peaks and substantially parallel valleys are oriented in the streamwise direction, where turbulence intensity is typically typically minimized.

The article according to the present disclosure can be made, for example, by film processes in which the series of substantially parallel peaks separated from each other by a series of substantially parallel valleys are at an angle to the machine direction of the film. A piece large enough to cover the desired area of the airfoil or hydrofoil can then be cut and placed on the surface. This process eliminates the need for the time-consuming and labor-intensive tiling operation of applying riblet films.

In one aspect, the present disclosure provides an article comprising:

an airfoil or hydrofoil having a spanwise direction; and

a seamless film on at least a portion of a surface of the airfoil or hydrofoil, the seamless film having a series of substantially parallel peaks separated from each other by a series of substantially parallel valleys on a patterned first surface of the film, wherein the seamless film has a long dimension that is at least two meters long substantially aligned with the spanwise direction of the airfoil or hydrofoil, and wherein an angle between the substantially parallel peaks and valleys to the long dimension of the seamless film is at least five degrees.

In another aspect, the present disclosure provides a method of making an article, the method comprising:

providing a film having a patterned first surface with a series of substantially parallel peaks separated from each other by a series of substantially parallel valleys, wherein the parallel peaks and parallel valleys are at an angle of at least five degrees to a machine direction of the film; and

applying the film to a surface of an airfoil or hydrofoil having a spanwise direction, wherein the film is applied such that the machine direction of the film is aligned with the spanwise direction of the airfoil or hydrofoil.

providing a film having a patterned first surface with a series of substantially parallel peaks separated from each other by a series of substantially parallel valleys, wherein the substantially parallel peaks and substantially parallel valleys are at an angle of at least five degrees to a machine direction of the film;

applying the film to a surface of a mold with the patterned first surface of the film exposed; forming a cavity between the patterned first surface of the film and a surface of an airfoil or hydrofoil having a spanwise direction, wherein the machine direction of the film is aligned with the spanwise direction of the airfoil or hydrofoil;

providing a curable resin in the cavity; and

curing the curable resin.

In this application, terms such as "a", "an" and "the" are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terms "a", "an", and "the" are used interchangeably with the term "at least one". The phrase "at least one of followed by a list refers to any one of the items in the list and any combination of two or more items in the list. All numerical ranges are inclusive of their endpoints and non-integral values between the endpoints unless otherwise stated.

The term "substantially parallel" when referring to peaks and valleys means that the peaks and valleys can deviate from parallel by up to 5 (in some embodiments, up to 2.5 or 1) degrees. The substantially parallel peaks and valleys may be linear or may have a slight curvature or slight oscillation. The oscillation or curvature may be to an extent such that it does not affect the turbulence reduction properties of the seamless film.

The term "peaks" refers to surface features of the seamless film in the form of projecting edges, which typically are generally pointed at least at a portion of their apexes. The term "valleys" refers to the hollow spaces formed in between the peaks.

The term "machine direction" (MD) as used herein denotes the direction of a running, continuous film. When a seamless portion of a continuous film is placed on the airfoil or hydrofoil, the machine direction corresponds to the long dimension "1" of the seamless film. As used herein, the terms machine direction and long dimension are typically used interchangeably. The term "cross-direction" (CD) as used above and below denotes the direction which is essentially perpendicular to the machine direction.

The term "spanwise direction" as used herein refers to the predominant direction of the span of the airfoil or hydrofoil. The airfoil or hydrofoil need not follow a straight line along its span. The "spanwise direction" can be determined, for example, with a vector passing through a point on each end of the airfoil or hydrofoil.

The term "film" as used herein refers to a self-supporting construction that is formed

independently from the airfoil or hydrofoil and can be handled on its own. Generally, the film disclosed herein is not an in-situ formed coating or layer on a surface.

The term "wall unit" refers to the non-dimension distances used to describe the height of peaks or the distance between peaks. Wall units are determined by multiplying the actual distance by the scalar quantity (square root of τ/ρ) divided by υ, where τ is the wall shear stress, p is the fluid density, and υ is the fluid kinematic viscosity.

As used herein, the term "polymer" encompasses both homopolymers, which are made from a single monomer, and copolymers, which are made from more than one monomer. Brief Description of the Drawings

The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying drawings, in which:

FIG. 1 is an exploded perspective view of an embodiment of an article according to the present disclosure;

FIG. 2 is an embodiment of a cross-sectional view taken along line 2-2 in FIG. 1 ; FIG. 3 is a cross-sectional view similar to FIG. 2 but showing a different patterned surface useful in articles according to the present disclosure;

FIG. 4 is a cross-sectional view similar to FIG. 2 but showing another patterned surface useful in articles according to the present disclosure;

FIG. 5 is a cross-sectional view similar to FIG. 2 but showing yet another patterned surface useful in articles according to the present disclosure;

FIG. 6 is a cross-sectional view similar to FIG. 2 but showing yet another patterned surface useful in articles according to the present disclosure;

FIG. 7 is a fragmentary perspective of another embodiment of an article according to the present disclosure where the peaks do not have a uniform height along their entire lengths;

FIG. 8 is a fragmentary perspective of another embodiment of an article according to the present disclosure where the peaks progressively change in height along their lengths;

FIG. 9 is a fragmentary perspective of another embodiment of an article according to the present disclosure where the peaks are not continuous across the film; and

FIG. 10 is a schematic representation of a microrep Heating tool roll useful for the method according to the present disclosure having features formed in the outer surface.

Detailed Description

Reference will now be made in detail to embodiments of the disclosure, one or more examples of which are illustrated in the drawings. Features illustrated or described as part of one embodiment can be used with other embodiments to yield still a third embodiment. It is intended that the present disclosure include these and other modifications and variations.

An exemplary article according to present disclosure is illustrated in FIG. 1. Article 1 includes an airfoil 10 with a seamless film 5 on at least a portion of its surface. The airfoil may be, for example, an airplane wing, helicopter blade, wind turbine, propeller, or other rotor blade. In other embodiments, the article may include a hydrofoil (e.g., a boat hull, propeller). Airfoil 10 has a leading edge 7 and a trailing edge 9. Seamless film 5 has a series of substantially parallel peaks 22 separated from each other by a series of substantially parallel valleys 20 on a patterned first surface 1 1 of the film.

Seamless film 5 has a long dimension "1" that is at least two meters long and substantially aligned with the spanwise direction '"s" of airfoil 10. In some embodiments, the long dimension "1" of the seamless film is at least 4, 6, 10, 15, or 20 meters long and may be up to 40, 60, 80, or 100 meters long or longer. For example, seamless film 5 may be long enough to cover the entire span of the airfoil 10 or any desirable portion of the airfoil in the spanwise direction. The seamless film has a short dimension "w" that may have any width suitable for covering a desired portion surface of the airfoil or hydrofoil in the streamwise direction. For example, the short dimension "w" of the seamless film may be up to about 1 or 1.5 meter wide, which are common widths for continuous film, but may be as small as 25, 10, or 5 centimeters. It should be understood by a person having ordinary skill in the art that the long dimension "1" is longer than the short dimension "w" of the seamless film.

The substantially parallel peaks 20 and valleys 22 of seamless film 5 are oriented at an angle of at least five degrees to the long dimension "1" of the seamless film 5. In some embodiments, including the illustrated embodiment, the angle between the substantially parallel peaks 20 and valleys 22 and the long dimension "1" of the seamless film 5 is at least 10, 20, 30, or 45 degrees and may be up to 90 degrees. In some embodiments, the angle between the substantially parallel peaks 20 and valleys 22 and the long dimension "1" of the seamless film 5 is in a range from 20 to 90 degrees, 30 to 90 degrees, 60 to 90 degrees, or 75 to 90 degrees. In some embodiments, the substantially parallel peaks 20 and valleys 22 are perpendicular to the long dimension "1" of the seamless film 5. Advantageously, the angle between the parallel peaks 20 and valleys 22 and the long dimension "1" of the seamless film 5 can be tailored based on the aerodynamic requirements of the airfoil or hydrofoil, the shape of the airfoil or hydrofoil, and its configuration in use. Accordingly, in some embodiments of the methods according to the present disclosure, the method comprises obtaining aerodynamic requirements for the airfoil (or hydrodynamic requirements of the hydrofoil); and selecting an angle between the machine direction and the parallel peaks and valleys based at least partially on the aerodynamic requirements of the airfoil (or hydrodynamic requirements of the hydrofoil). In some of these embodiments, obtaining aerodynamic requirements includes determining the shape of the airfoil, the angle of attack, and expected wind speeds in use. In some embodiments, there is more than one series of substantially parallel peaks separated from each other by a series of substantially parallel valleys with each series oriented in a different direction. This may be useful, for example, depending on the aerodynamic requirements of the airfoil or the hydrodynamic requirements of the hydrofoil.

In some embodiments, including the embodiment illustrated in FIG. 2, the seamless film 5 is a multilayer film. An exemplary cross-sectional view of article 1 taken along line 2-2 in FIG. 1 is shown in FIG. 2. The patterned first surface 1 1 is shown as a top layer in FIG. 2. The multilayer seamless film 5 further comprises optional tie layer 12 which is useful in some embodiments for promoting adhesion to base layer 13. The article 1 further comprises an adhesive layer 14 disposed between base layer 13 and the surface of the airfoil 10. Exemplary materials useful for each layer are described in detail, below.

Although substantially parallel peaks 20 and substantially parallel valleys 22 appear visible in FIGS. 2 to 9, they are typically microscopic in size. The patterned first surface 1 1 may have any arrangement of the series of substantially parallel peaks 20 separated from each other by the series of substantially parallel valleys 22 useful for reducing turbulent flow as a fluid (e.g., air, gas, water, or other fluid) flows over the article according to the present disclosure or as the article according to the present disclosure moves through a fluid. In cross-section the patterned first surface 1 1 may have a variety of wave forms. In FIG. 2, the patterned first surface 1 1 has a symmetric saw tooth pattern, where each of the substantially parallel peaks 20 is identical as is each of the substantially parallel valleys 22. The base of the peak may be the same as the distance between peaks.

In the embodiment illustrated in FIG. 3, a series of substantially parallel, symmetric peaks 20 is separated by flat-bottomed valleys 26 on the patterned first surface 1 1 of seamless film 5. This configuration can be referred to as a skip tooth configuration. In a skip tooth configuration, the angle "a" between the side walls 25 and 27 of the peak cross-section may be the same or different for adjacent peaks. Useful angles "a" may be in the range from about 15 to 140 degrees, in some embodiments, in a range from 15 to 60 degrees. The distance between peaks may be smaller or larger than the height of the peaks. In some embodiments, the distance between peaks is from 0.5 to 4 times the height of the peaks.

FIGS. 4 and 5 illustrate different shaped peaks that can be useful in a skip tooth configuration. In the embodiment illustrated in FIG. 4, the peaks 40 have a pencil shape. That is, the side walls 45 and 47 of the peaks are substantially parallel to each other near the flat-bottomed valleys and then converge to form sharp ridges. The angle "b" between the side walls 45 and 47 depends, for example, on the distance between the side walls 45 and 47 when they are converging and may be in the range from about 15 to 140 degrees, in some embodiments, 15 to 60 degrees. In FIG. 4, angle "b" is about 30 degrees. In FIG. 5, the side walls 55 and 57 of peaks 50 also change direction. Near the flat-bottomed valleys, the angle "d" between side walls 55 and 57 is larger than the angle "c"' between side walls 55 and 57 at the apex. Again, useful angles "c" and "d" may be in the range from about 15 to 140 degrees, or 15 to 60 degrees. In FIG. 5, angle "c" is about 30 degrees, and angle "d" is about 53 degrees. The shape of peaks 50 shown in FIG. 5 can also be useful in a saw tooth configuration where there are not flat-bottomed valleys between peaks.

In some embodiments, some of the substantially parallel peaks when viewed in cross-section are larger in height than others of the parallel peaks. For example, FIG. 6 shows a series of parallel peaks 28 and 30 that are of different heights, separated by a series of parallel valleys 22.

Other variations in cross-sectional shape are envisioned. For example, each of the peaks and valleys may be asymmetric (e.g., have side walls with different lengths). The peaks and valleys may also be rounded (e.g., they may have concave side walls). Adjacent peaks may have the same height with different widths, or adjacent peaks may be different in both height and width.

In some embodiments, at least some of the parallel peaks vary in height along the length of the peaks. For example, in the fragmentary, perspective view of the article 71 illustrated in FIG. 7, peaks 70 are features that extend along the surface substantially in the x-direction. In the embodiment shown, the maximum height in the z-direction and spacing in the y-direction of peaks 70 are substantially uniform. Each peak 70 has a generally triangular cross-section in the y-z-plane. The height at the top edge 75 of the peaks 70 varies along the x-axis to form peaks 77 and valleys 79 in the x-z plane. The peaks 77 and valleys 79 are symmetrically spaced apart from one another along the top edge 75 of each peak 70. Peaks 77 and valleys 79 may have a variety of shapes. In the illustrated embodiment, each peak 77 has a generally arcuate shape in the x-z-plane, and each valley 79 has a substantially flat shape in the x-z-plane. In addition, the peaks 77 align with each other in the y-direction, and the valleys 79 align with each other in the y-direction. In other embodiments, peaks 77 may be offset from each other in the y-direction, and valleys 79 may be offset from each other in the y-direction. Positioning of peaks 77 and valleys 79 can be optimized to reduce turbulent flow across the surface of the article. In some embodiments, in terms of wall units, the spacing between peaks 77 in the x-direction is between 10 and 100.

While in FIG. 7, the height of the peaks is undulating along the length of the peaks, the embodiment of FIG. 8 illustrates peaks 80 that progressively change in height. In FIG. 8, the peaks 80 of seamless film 81 have a constant base width, but their height increases continuously along their length to give them an increasingly sharper triangular profile. In some embodiments, at the end where the peaks are shorter, the peaks can become progressively smaller and ultimately disappear. In some embodiments, the peaks are faired into the wall surface. The valleys may either narrow or widen as the peak or valley progresses from one end of the article to the other. In some embodiments, the height and/or width of a given peak or valley may change as the peak or valley progresses from one end of the article to the other. In some embodiments, the peaks 90 increase in size as they approach the trailing edge 9 of the airfoil or hydrofoil.

In some embodiments, at least some of the parallel peaks are discontinuous across the film. For example, the peaks and valleys may terminate for a portion of the article. In the embodiment illustrated in FIG. 9, the peaks 90 of seamless film 91 have short spanwise-extending gaps 99. The gaps may be less than the boundary layer thickness in the streamwise direction.

The optimum dimensions of the peaks 20, 40, 50, 70, 80, or 90 are somewhat dependent upon the speed at which the airfoil or hydrofoil to be covered passes through the fluid (or the speed at which the fluid passes over the airfoil or hydrofoil). The size of the peaks may be selected for an airfoil, for example, to achieve maximum efficiency in the specific area of the blade and may depend on, for example, the local wind speed, the Reynolds number, the shape of the airfoil, and the angle of attack of the fluid over the airfoil. For more discussion on this topic with regard to drag reduction, see AIAA-88- 0138, "Drag Reduction for External Boundary Layers Using Riblets and Polymers," L. W. Reidy and G. W. Anderson, presented at the AIAA 26th Aerospace Sciences Meeting, Jan. 1 1- 14, 1988 at Reno, Nev. In some embodiments, the peaks may have a height of about 10 to 400 microns (about 0.4 to 16 mils) above the valleys. In some embodiments, when the seamless film is provided for drag reduction, the peaks may be about 20 to 150 microns (about 0.8 to 6 mils) high for high speed uses (e.g., aircraft). Higher peak heights (e.g., in the range from about 150 microns to 400 microns (about 6 to 16 mils) may be useful for noise reduction applications. As described above, in some embodiments, the peaks increase in size as they approach the trailing edge 9 of the airfoil or hydrofoil 10. In some of these embodiments, the peaks may have a height useful for noise reduction near the trailing edge 9 of the airfoil or hydrofoil 10, and they may have a height useful for drag reduction in the turbulent region closer to the laminar separation point.

The peak-to-peak spacing between adjacent peaks likewise may be adjusted depending on the application. A spacing of about 10 to 300 microns (about 0.4 to 12 mils) may be useful. In some embodiments (e.g., aircraft applications) a spacing of about 20 to 150 microns (about 0.8 to 6 mils) may be desirable for drag reduction.

In some embodiments, including embodiments where the seamless film is a multilayer film, the entire thickness of seamless film 5 is in a range from about 50 to 400 microns thick (about 2 to 16 mils), in some embodiments, about 75 to 150 microns (about 3 to 6 mils) thick. In general, the seamless film disclosed herein has a first patterned surface where the second surface, opposite the first patterned surface, is not provided with a pattern. That is the second surface is typically not provided with a series of substantially parallel peaks separated from one another by a series of substantially parallel valleys. It may be said that the second surface of the film is typically non-patterned or it may have some texturing but no perceptible pattern of organized features having a height of at least 0.1 wall unit or 1 micron. The pattern on the first surface of the film is also typically not carried through the entire film thickness. That is, the film typically does not bear a pattern that carries through its entire thickness. In some

embodiments, the second surface of the film, opposite the first patterned surface, is flat.

The seamless film 5 may be positioned on the airfoil or hydrofoil 10 such that the first patterned surface 1 1 will provide maximum reduction in turbulent flow. The seamless film 5 need not cover the entire surface of the airfoil or hydrofoil. Likewise the seamless film 5 need not have peaks and valleys over its entire area. For example, there may be a smooth transition between a non-patterned region to a patterned region on the first surface 1 1 of the film 5, where the peaks increase in height from the non- patterned region progressively into the patterned region. In some embodiments, the substantially parallel peaks and substantially parallel valleys extend over the length of the turbulent region on the upper surface of the airfoil or hydrofoil. In some embodiments, the substantially parallel peaks and substantially parallel valleys extend over the length of the turbulent region on both the upper surface and lower surface of the airfoil or hydrofoil.

In some embodiments, the first patterned surface 1 1 , which may be provided on a top layer of a multilayer film as shown in FIGS. 2 to 7, is typically sufficiently resistant to chemical and weather exposure to permit the use of seamless film 5 on a variety of airfoils and hydrofoils 10. For example, materials for first patterned surface 1 1 and at least the top layer of the seamless film 5 can be selected so that the film can withstand extended exposure to water, oil, fuel, solvents, and hydraulic fluids without a noticeable deterioration in its physical properties, performance, or appearance. Further, materials for the first patterned surface 1 1 or top layer can be selected so that the film 5 is not appreciably affected by rain, sand or particle erosion, or other harsh environmental agents to which the article 1 may be exposed during normal use. In some embodiments, it is desirable for the seamless film 5, particularly the top layer or first patterned surface 1 1, to be resistant to degradation by ultraviolet (UV) light and weatherable. Photo- oxidative degradation caused by UV light (e.g., in a range from 280 to 400 nm) may result in color change and deterioration of optical and mechanical properties of polymeric films. It is also typically desirable for seamless film 5 to show no substantial change in appearance or removability, even when subjected to accelerated weathering (e.g., ultraviolet radiation and moisture) for 500 hours according to the procedure described in ASTM G 53-95 "Standard Practice for Operating Light-and Water-Exposure Apparatus (Fluorescent UV Condensation Type) for Exposure of Non-Metallic Materials."

Several polymers are useful for making the seamless film 5. In some embodiments, the seamless film 5 including its first patterned surface 11 is made from a thermoplastic. In embodiments where the seamless film is a multilayer film, any of its layers may be independently thermoplastic. In some embodiments, the seamless film 5 including its first patterned surface is made from a thermoset. In embodiments where the seamless film is a multilayer film, any of its layers may be independently made from a thermoset. Useful materials for the seamless film 5 in any of its layers include polyurethanes, polyesters, polycarbonates, polyethers, polyimides, polyolefins, fluoropolymers, silicones, and combinations thereof.

A variety of stabilizers may be added to the seamless film 5 (e.g., in at least the top layer) to improve its resistance to UV light. Examples of such stabilizers include at least one of ultra violet absorbers (UVA) (e.g., red shifted UV absorbers (e.g., the TINUVTN family of stabilizers available from Ciba-Geigy Corp.)), hindered amine light stabilizers (HALS), or anti-oxidants. In some embodiments, a easy-to-clean coating may be applied to the top layer of the seamless film. The easy -to-clean coating may be a hydrophobic coating which includes a polymer matrix (e.g., a silicone or fluoropolymer) and nanoparticles dispersed therein. The nanoparticles may be, for example, polymer (e.g., fluoropolymer) particles, particles of a dielectric material (e.g., silica, alumina, zirconia, titania, or indium tin oxide particles), or metal (e.g., gold) particles. Further details regarding such hydrophobic coatings are described, for example, in copending applications with serial numbers 61/407820 and 61/407806, both filed October 28, 2010, the disclosures of which are incorporated by reference herein. In some embodiments, the easy-to-clean coating may comprise nanosilica and may be coated out of water.

Further details of such coatings are described in copending applications with serial numbers 61/390501 and 61/390498, both filed October 6, 2010, the disclosures of which are incorporated by reference herein. The seamless film in its various layers may also optionally include fillers such as glass, ceramic or polymeric bubbles; pigments; processing aids such as polyolefin polymers; and fire retardants.

In some embodiments, at least the first patterned surface 1 1 of the seamless film 5 comprises a fluoropolymer. Fluoropolymers typically are resistant to UV degradation even in the absence of stabilizers such as UVA, HALS, and anti-oxidants. Useful fluoropolymers include ethylene- tetrafluoroethylene copolymers (ETFE), tetrafluoroethylene-hexafluoropropylene copolymers (FEP), tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers (THV), polyvinylidene fluoride (PVDF), blends thereof, and blends of these and other fluoropolymers. Fluoropolymers, in particular those that contain polymerized units of vinylidene fluoride, have been found to have good chemical resistance and weatherability.

The first patterned surface 1 1 or seamless film 5 may, in some embodiments, be made from a blend of a fluoropolymer and a non-fluorinated polymer. Acrylic polymers, in particular those that contain polymerized units of short chain alkyl methacrylates, have been found to have good bonding properties and handling characteristics. Accordingly, in some embodiments, the first patterned surface 1 1 or seamless film 5 may be made from a blend of a fluoropolymer and an acrylic polymer. For example, a blend of polyvinylidene fluoride and polymethyl methacrylate can be used. First patterned surface 1 1 may comprise a blend of 70% to 100% by weight fluoropolymer and 0% to 30% by weight acrylic polymer, 70% to 90% by weight fluoropolymer and 10% to 30% by weight acrylic polymer, or about 90% by weight fluoropolymer and about 10% by weight acrylic polymer.

In some embodiments, including the embodiments illustrated in FIGS. 2, 3, and 6, the seamless film 5 is a multilayer film that includes optional tie layer 12. The composition of the tie layer can be selected, for example, depending on the composition of the first patterned surface layer 1 1 and the optional base layer 13 so that good adhesion and handling ability can be obtained. In some embodiments, tie layer 12 is made from a blend of a fluoropolymer and an acrylic polymer. In some of these embodiments, the same fluoropolymer and acrylic polymer that make up the first patterned surface 1 1 also make up the tie layer 12, but in different ratios. Tie layer 12 typically has a higher percentage of acrylic polymer, for example. Tie layer 12 may comprise, for example, a blend of 70% to 100% by weight acrylic polymer and 0% to 30% by weight fluoropolymer, 70% to 90% by weight acrylic polymer and 10% to 30% by weight fluoropolymer, or about 90% by weight acrylic polymer and 10% by weight fluoropolymer.

In embodiments described above for a seamless film comprising acrylic polymers, various acrylic polymers may be useful. For example, medium to low molecular weight acrylic resins having a weight average molecular weight below 750,000, including blends or copolymers comprising at least two materials selected from the group consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, and methacrylate copolymers may be useful.

In some embodiments wherein the seamless film is a multilayer film, the layer including first patterned surface 1 1 may be about 5 to 250 microns (about 0.2 to 10 mils) thick or about 10 to 40 microns (about 0.5 to 1.5 mils) thick. Tie layer 12 may be about 2.5 to 75 microns (about 0.1 to 3 mils) thick or about 3 to 12 microns (about 0.1 to 0.5 mils) thick. Overall, the combined thickness of layers 1 1 and 12 may be about 7.5 to 325 microns (about 0.3 to 13 mils) or about 15 to 50 microns (about 0.6 to 2.0 mils). If the combined thickness is greater than about 400 microns (16 mils), the conformability of the seamless film to the airfoil or hydrofoil may be decreased, and the weight and cost of the seamless film may be undesirably increased. In some embodiments, a seamless, multilayer film comprising a layer forming first patterned surface 1 1 and tie layer 12 may be attached to the surface of an airfoil or hydrofoil (e.g., using an adhesive layer as described below). In other embodiments, a seamless, multilayer film comprising a layer forming first patterned surface 1 1 and tie layer 12 may be attached to a base layer 13. Base layer 13 may be useful, for example, for providing strength and elongation to the seamless film, which can contribute to easy installation and removal of the seamless film. In some embodiments, base layer 13 is made from a material selected from thermoplastic urethanes, silicones, and poly(vinyl chloride). Examples of thermoplastic urethanes include polyester-urethane, polyether-urethane, and polycaprolactone-urethane. The base layer 13 can include UV stabilizers, antioxidants, fillers, pigments, and post-crosslinking additives.

In some embodiments, the material that forms the base layer 13 is more elastic than the materials that form the first patterned surface 1 1 and tie layer 12. The term "elastic" refers to any material that exhibits recovery from stretching or deformation. A material that is more elastic than another material has a higher tendency to recover from stretching or deformation. In some embodiments, the material that forms the reinforcing layer has an elongation of at least about 300%, without breaking. "Elongation" in terms of percent refers to [(the extended length-the initial length)/the initial length] multiplied by 100.

Base layer 13 may be about 35 to 300 microns (about 1.5 to 12 mils) or about 50 to 100 microns (about 2 to 4 mils) thick. When the thickness of the reinforcing layer is greater than about 300 microns, the resultant weight and cost of the seamless film may be undesirable.

Seamless film 5 may carry or bear a continuous or discontinuous graphic layer (e.g., graphic design, logo, or alpha-numeric characters) that can be aesthetic and/or functional. Graphic layers may be provided as an ink (e.g., a pigment dispersed in a compatible binder) and applied to first patterned surface 1 1, tie layer 12, or base layer 13 using any suitable printing technique.

Typically, article 1 further comprises an adhesive layer disposed between a second surface of the seamless film, opposite the patterned first surface of the seamless film, and the at least a portion of the surface of the airfoil or hydrofoil. In some embodiments, the adhesive layer comprises a pressure sensitive adhesive (PSA). PSAs are well known to those of ordinary skill in the art to possess properties including the following: (1) aggressive and permanent tack, (2) adherence with no more than finger pressure, (3) sufficient ability to hold onto an adherend, and (4) sufficient cohesive strength to be cleanly removable from the adherend. Materials that have been found to function well as PSAs are polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear holding power.

Exemplary useful PSAs include polyacrylates, such as those that comprise a polymer of an acrylate ester of acrylic acid with a non-tertiary alcohol. In some embodiments, the PSA comprises the polymerization product of 85 to 98% by weight of one or more (co)polymerizable acrylate ester monomers and 2 to 15% by weight of a copolymerizable acid or amide. Multifunctional acrylates, copolymerizable photoinitiators, or combinations of the two may also be present in a total amount of up to 0.5% by weight to provide some crosslinking, which can contribute to easy removability, better fluids resistance, and improved high temperature performance of the article. The adhesive layer may have any useful thickness and may be about 10 to 125 microns (about 0.4 to 5 mils), or about 12 to 50 microns (about 0.5 to 2 mils). Ultimately, removability is a balance among the peel adhesion, the degree of crosslinking, and the thickness of the bonding layer, and the toughness of the seamless film.

In some embodiments, the adhesive layer 14 comprises a curable adhesive (e.g., a thermally curable adhesive or moisture curable adhesive composition). Exemplary curable adhesives include silicones, epoxies, acrylates, cyano-acrylates, and urethanes. Several useful curable adhesives are commercially available. Exemplary useful epoxy adhesives include epoxy resin adhesives available from 3M Company, St. Paul, Minn. Under the trade designation "3M SCOTCH- WELD". Exemplary useful curable acrylates and cyanoacrylates include acrylate adhesives available under the trade designation "3M SCOTCH- WELD DP8005" and cyano-acrylate adhesives available under the trade designation

"PRONTO INSTANT ADHESIVES", both from 3M Company. Exemplary useful urethane adhesives include those that cure by exposure to moisture such as curable adhesives available from 3M Company under the trade designations "3M SCOTCH- WELD", grades "DP-605NS", "3592", "3535", and "3549".

Suitable adhesives for adhesive layer 14, including PSAs and curable adhesives, are described in further detail in U. S. Pat. Appl. Pub. No. 2004/0126541 (Dietz et al.).

Methods of making an article according to the present disclosure include providing a film having a patterned first surface with a series of substantially parallel peaks separated from each other by a series of substantially parallel valleys, wherein the parallel peaks and parallel valleys are at an angle of at least five degrees to a machine direction of the film. The substantially parallel peaks and valleys pattern may be imparted during the formation of a film, or alternatively, a pre-formed web comprising one or more layers may be provided and the substantially parallel peaks and valleys pattern formed in the surface layer to form the first patterned surface 11. Once manufactured, the film can be wound about a core into roll form for easy storage and shipping and later unwound for application.

In embodiments wherein the seamless film is a multilayer film, almost any combination of layers may be coextruded then joined to the remaining layers. The different layers may also be assembled by various sequential or tandem coating methods. Combinations of coating and extrusion may also be useful. It is useful for materials in adjacent, contacting layers to be compatible and either adhere together by themselves or be capable of being adhered together so as to provide sufficient interlayer adhesion that the seamless, multilayer film does not delaminate during normal use. In some embodiments, a large proportion of acrylic polymer in tie layer 12 promotes good adhesion between top layer comprising first patterned surface 1 1 and base layer 13. In some embodiments, the patterned first surface of the film is made by embossing (e.g., utilizing heat and/or pressure). In some embodiments, the patterned first surface of the film is made by microreplication.

One useful technique for making a microreplicating tool roll using for producing the patterned first surface on an article according to the present disclosure is by using a fly-cutting head adapted to move while cutting a groove down the length of a tool roll as described, for example, in U. S. Pat. Appl. Pub. No. 2009/0038450 (Campbell et al.). A schematic illustration of an exemplary tool roll 1 14 which can be made, for example, using this technique is shown in FIG. 10. In FIG. 10, tool roll 1 14 can be prepared by holding the roll stationary, and moving a fly-cutting head down the length of the tool roll to form a groove 150 that is the negative of peaks 20, 40, 50, 80, 90 described herein. At the completion of a single pass down the length of the tool roll, the tool roll may be indexed and the process repeated to form an adjacent groove 150. The position of the cutting elements can be controlled relatively precisely, and the position of a groove cut into the roll surface during a second or subsequent pass down the roll can be coordinated with the position of grooves or other features cut into the roll surface during a preceding pass, as shown in FIG. 10 at 155.

On a large or "macro-" scale, surface features cut into a tool roll may or may not extend uninterrupted across the length, width, or around the perimeter of the tool roll. For example, as schematically shown in FIG. 10, a tool roll may have a first pattern 150 on one portion of the roll and a second pattern 155 on a different portion of the roll with a transition zone (shown as the dots in FIG. 10) where the first pattern 150 may progressively change into the second pattern 155. The first pattern 150 and second pattern 155 may be any of those in FIGS. 2 to 9. Features can be cut into a tool roll at any desirable angle with respect to the axis of rotation (or an axis of symmetry) of the tool roll, such as at a 45 degree angle to that axis. Multiple features can be cut into a tool roll in successive passes of a fly-cutting head, or multiple features can be cut into a tool roll by successive passes of each cutting element during a single pass (such as a shallower groove cut by one cutting element and a deeper groove cut by the next succeeding cutting element). Multiple groove shapes and heights may also be incorporated by using a cutting tool with multiple tips such as those described in U.S. Pat. No. 7,140,812 (Bryan et al.).

A seamless film disclosed herein can be made from a microreplication tool (e.g., such as that schematically shown in FIG. 10) using several techniques (e.g., casting and curing a polymeric material on the tool, embossing, extrusion, compression molding, and injection molding). In other embodiments, the structure of the tool roll (a master tool) can be transferred on other media, such as to a belt or web of polymeric material, by a cast and cure process to form a tooling sheet. The tooling sheet can be laminated to a film (e.g., a multilayer film) using heat and/or pressure in order to impart the pattern of the tooling sheet to a surface of seamless film 5 to form the first patterned surface 1 1. This results in a seamless film having a first patterned surface 1 1 that corresponds to the surface of the master tool. The tooling sheet can also act as a carrier web to protect the first patterned surface 1 1 through any additional processing operations such as corona treating, substrate bonding layer attaching, slitting, or perforating. It can be removed at any time during the manufacture of article according to the present disclosure.

In some embodiments of the methods disclosed herein, the film having a patterned first surface with a series of substantially parallel peaks separated from each other by a series of substantially parallel valleys, wherein the substantially parallel peaks and substantially parallel valleys are at an angle of at least five degrees to a machine direction of the film, is useful as a master, wherein the film is the negative of the pattern imparted to the surface of the airfoil or hydrofoil 10. In these embodiments, the method comprises applying the film to a surface of a mold with the patterned first surface of the film exposed, forming a cavity between the patterned first surface of the film and a surface of an airfoil or hydrofoil, wherein the machine direction of the film is aligned with the spanwise direction of the airfoil or hydrofoil, providing a curable resin in the cavity, and curing the curable resin. Additional information about such manufacturing techniques can be found in U.S. Pat. No. 4,576,850 (Martens), U.S. Pat. No. 5, 183,597 (Lu), and U.S. Pat. No. 5,468,540 (Lu).

In some embodiments, the seamless film disclosed herein further comprises an adhesive layer disposed on a second surface of the film, opposite the patterned first surface of the film. The adhesive layer can be useful, for example, for applying the film to the surface of the airfoil or hydrofoil 10.

Accordingly, in some embodiments, a method according to the present disclosure further comprises contacting the surface of the airfoil or hydrofoil with the adhesive layer. In some embodiments, adhesive layer 14 can be coated onto the second surface of the film. In some of these embodiments, the film is a multilayer film (e.g., comprising layers that have been previously joined together). A temporary, removable, protective liner may then be laminated to adhesive layer 14. In other embodiments, adhesive layer 14 can be coated onto a release liner and transfer laminated to the second surface of a film. In some of these embodiments, the film and the adhesive layer-coated release liner can be passed between rubber rolls, which may optionally be heated.

The temporary liner, useful in some embodiments, protects adhesive layer 14 from contamination by dirt and other materials can be applied and removed shortly before the film is applied to a surface of the airfoil or hydrofoil 10 or to the surface of a mold for forming a pattern on the airfoil or hydrofoil 10. The liner may be, for example, an untreated polyolefin sheet or a silicone- or fluorosilicone-treated paper or plastic sheet. In some embodiments, the release liner is a microstructured release liner or the adhesive layer is provided with a microstructure. See, e.g., U.S. Pat. App. Pub. Nos. US2007-021235 (Sherman et al.) and US2003- 129343 (Galkiewicz et al.) and PCT Int. Appl. Pub. No. WO09/058466 (Sherman et al.) and WO04/000569 (Graham et al.). Microstructured release liners and adhesives may be useful, for example, for preventing air bubbles from being trapped in the adhesive layer 14 when it is applied to the surface of the airfoil or hydrofoil 10.

In some embodiments, the film may also be stretched, if desired, to conform to the substrate surface and to remove unwanted wrinkles and air bubbles. Providing perforations or other discontinuities (e.g., slits) in the film can facilitate applying the film to the airfoil or hydrofoil and accommodates the passage of moisture and vapors through the film.

The methods described herein are in contrast to conventional methods of forming a series of substantially parallel peaks and valleys in a surface, which generally involve forming grooves running in the machine direction of the film. Since web-forming production lines typically have a width of up to about 1 or 1.5 meter wide, it is not possible to provide a seamless film with a width of great than 1 or 1.5 meter using conventional machine-direction-groove-forming processes. This has resulted in the aforementioned disadvantageous tiling process due to the size limit of a film that can be provided to an airfoil or hydrofoil with peaks and valleys extending in the streamwise direction. The articles and methods according to the present disclosure provide a solution to these problems.

Selected Embodiments of the Disclosure:

In a first embodiment, the present disclosure provides an article comprising:

an airfoil or hydrofoil having a spanwise direction; and

a seamless film on at least a portion of a surface of the airfoil or hydrofoil, the seamless film having a series of substantially parallel peaks separated from each other by a series of substantially parallel valleys on a patterned first surface of the film, wherein the seamless film has a long dimension that is at least two meters long substantially aligned with the spanwise direction of the airfoil or hydrofoil, and wherein an angle between the parallel peaks and valleys to the long dimension of the seamless film is at least five degrees.

In a second embodiment, the present disclosure provides an article according to the first embodiment, further comprising an adhesive layer disposed between a second surface of the seamless film, opposite the patterned first surface of the seamless film, and the at least a portion of the surface of the airfoil or hydrofoil.

In a third embodiment, the present disclosure provides an article according to the first or second embodiment, wherein the seamless film is a multilayer film.

In a fourth embodiment, the present disclosure provides an article according to any one of the first to third embodiments, wherein the angle between the substantially parallel peaks and valleys to the long dimension of the seamless film is in a range from seventy-five to ninety degrees.

In a fifth embodiment, the present disclosure provides an article according to any one of the first to fourth embodiments, wherein the parallel peaks and valleys are perpendicular to the long dimension of the seamless film.

In a sixth embodiment, the present disclosure provides an article according to any one of the first to fifth embodiments, wherein some of the parallel peaks when viewed in cross-section are larger in height than others of the parallel peaks. In a seventh embodiment, the present disclosure provides an article according to any one of the first to sixth embodiments, wherein at least some of the parallel peaks vary in height along their lengths.

In an eighth embodiment, the present disclosure provides an article according to any one of the first to seventh embodiments, wherein at least some of the parallel peaks progressively increase in size from a leading edge to a trailing edge of the airfoil or hydrofoil.

In a ninth embodiment, the present disclosure provides an article according to any one of the first to eighth embodiments, wherein at least some of the parallel peaks are interrupted by spanwise-extending gaps.

In a tenth embodiment, the present disclosure provides an article according to any one of the first to ninth embodiments, wherein at least some of the parallel valleys are flat-bottomed.

In an eleventh embodiment, the present disclosure provides an article according to any one of the first to tenth embodiments, wherein at least some of the parallel peaks have shapes with side-walls that change direction.

In a twelfth embodiment, the present disclosure provides an article according to any one of the first to eleventh embodiments, wherein there is more than one series of substantially parallel peaks separated from each other by a series of substantially parallel valleys with each series oriented in a different direction.

In a thirteenth embodiment, the present disclosure provides an article according to any one of the first to twelfth embodiments, wherein the long dimension of the seamless film is at least four meters long.

In a fourteenth embodiment, the present disclosure provides a method of making an article, the method comprising:

providing a film having a patterned first surface with a series of substantially parallel peaks separated from each other by a series of substantially parallel valleys, wherein the substantially parallel peaks and substantially parallel valleys are at an angle of at least five degrees to a machine direction of the film; and

In a fifteenth embodiment, the present disclosure provides a method according to the fourteenth embodiment, wherein the film further comprises an adhesive layer disposed on a second surface of the film, opposite the patterned first surface of the film, and wherein applying the film to the surface of the airfoil or hydrofoil comprises contacting the surface of the airfoil or hydrofoil with the adhesive layer.

In a sixteenth embodiment, the present disclosure provides a method of making an article, the method comprising:

providing a curable resin in the cavity; and

curing the curable resin.

In a seventeenth embodiment, the present disclosure provides a method according to any one of the fourteenth to sixteenth embodiments, wherein the film is a multilayer film.

In an eighteenth embodiment, the present disclosure provides a method according to any one of the fourteenth to seventeenth embodiments, wherein the patterned first surface of the film is made by microreplication.

In a nineteenth embodiment, the present disclosure provides a method according to any one of the fourteenth to seventeenth embodiments, wherein the patterned first surface of the film is made by embossing.

In a twentieth embodiment, the present disclosure provides a method according to any one of the fourteenth to nineteenth embodiments, wherein an angle between the parallel peaks and valleys to the machine direction of the film is in a range from seventy- five to ninety degrees.

In a twenty-first embodiment, the present disclosure provides a method according to any one of the fourteenth to twentieth embodiments, wherein the parallel peaks and valleys are perpendicular to the machine direction of the film.

In a twenty-second embodiment, the present disclosure provides a method according to any one of the fourteenth to twenty- first embodiments, wherein some of the parallel peaks when viewed in cross- section are larger in height than others of the parallel peaks.

In a twenty -third embodiment, the present disclosure provides a method according to any one of the fourteenth to twenty-second embodiments, wherein at least some of the parallel peaks vary in height along their lengths.

In a twenty-fourth embodiment, the present disclosure provides a method according to any one of the fourteenth to twenty -third embodiments, wherein at least some of the parallel peaks progressively increase in size from a leading edge to a trailing edge of the airfoil or hydrofoil.

In a twenty-fifth embodiment, the present disclosure provides a method according to any one of the fourteenth to twenty-fourth embodiments, wherein at least some of the parallel peaks are interrupted by spanwise-extending gaps. In a twenty-sixth embodiment, the present disclosure provides a method according to any one of the fourteenth to twenty-fifth embodiments, wherein at least some of the parallel valleys are flat- bottomed.

In a twenty-seventh embodiment, the present disclosure provides a method according to any one of the fourteenth to twenty-sixth embodiments, wherein at least some of the parallel peaks have shapes with side -walls that change direction.

In a twenty-eighth embodiment, the present disclosure provides a method according to any one of the fourteenth to twenty-seventh embodiments, wherein there is more than one series of substantially parallel peaks separated from each other by a series of substantially parallel valleys with each series oriented in a different direction.

In a twenty -ninth embodiment, the present disclosure provides a method according to any one of the fourteenth to twenty-eighth embodiments, wherein the film is seamless and at least two meters long in the machine direction.

In a thirtieth embodiment, the present disclosure provides a method according to any one of the fourteenth to twenty-ninth embodiments, further comprising:

obtaining aerodynamic requirements for the airfoil; and

selecting an angle between the machine direction and the parallel peaks and valleys based at least partially on the aerodynamic requirements of the airfoil. All patents and publications referred to herein are hereby incorporated by reference in their entirety. Various modifications and alterations of this disclosure may be made by those skilled in the art without departing from the scope and spirit of this disclosure, and it should be understood that this disclosure is not to be unduly limited to the illustrative embodiments set forth herein.

Claims

What is claimed is:

1. An article comprising:

an airfoil or hydrofoil having a span; and

a seamless film on at least a portion of a surface of the airfoil or hydrofoil, the seamless film having a series of substantially parallel peaks separated from each other by a series of substantially parallel valleys on a patterned first surface of the film, wherein the seamless film has a long dimension that is at least two meters long substantially aligned with the span of the airfoil or hydrofoil, and wherein an angle between the parallel peaks and valleys to the long dimension of the seamless film is at least five degrees.

2. An article according to claim 1, further comprising an adhesive layer disposed between a second surface of the seamless film, opposite the patterned first surface of the seamless film, and the at least a portion of the surface of the airfoil or hydrofoil.

3. An article according to claim 1 or 2, wherein the seamless film is a multilayer film.

4. An article according to any one of claims 1 to 3, wherein the angle between the parallel peaks and valleys to the long dimension of the seamless film is in a range from seventy-five to ninety degrees.

5. An article according to any one of claims 1 to 4, wherein some of the parallel peaks when viewed in cross-section are larger in height than others of the parallel peaks.

6. An article according to any one of claims 1 to 5, wherein at least some of the parallel peaks vary in height along the peaks.

7. An article according to any one of claims 1 to 6, wherein at least some of the parallel peaks are interrupted by spanwise-extending gaps.

8. An article according to any one of claims 1 to 7, wherein at least some of the parallel valleys are flat- bottomed.

9. A method of making an article, the method comprising:

providing a film having a patterned first surface with a series of parallel peaks separated from each other by a series of parallel valleys, wherein the parallel peaks and parallel valleys are at an angle of at least five degrees to a machine direction of the film; and applying the film to a surface of an airfoil or hydrofoil having a spanwise direction, wherein the film is applied such that the machine direction of the film is aligned with the spanwise direction of the airfoil or hydrofoil.

10. A method according to claim 9, wherein the film further comprises an adhesive layer disposed on a second surface of the film, opposite the patterned first surface of the film, and wherein applying the film to the surface of the airfoil or hydrofoil comprises contacting the surface of the airfoil or hydrofoil with the adhesive layer.

1 1. A method of making an article, the method comprising:

providing a curable resin in the cavity; and

curing the curable resin.

12. A method according to any one of claims 9 to 1 1, wherein the patterned first surface of the film is made by microreplication.

13. A method according to any one of claims 9 to 12, wherein the film is seamless and at least two meters long in the machine direction.

14. A method according to any one of claims 9 to 13, wherein the film is a multilayer film.

15. A method according to any one of claims 9 to 14, further comprising:

obtaining aerodynamic requirements for the airfoil; and

selecting an angle between the machine direction and the parallel peaks and valleys based at least partially on the aerodynamic requirements of the airfoil.