WO2022137063A1

WO2022137063A1 - Superhydrophobic films

Info

Publication number: WO2022137063A1
Application number: PCT/IB2021/061962
Authority: WO
Inventors: John P. Baetzold; Mark J. Pellerite; Tri D. Pham; John J. Stradinger; Timothy J. Hebrink; Brian W. Lueck
Original assignee: 3M Innovative Properties Company
Priority date: 2020-12-21
Filing date: 2021-12-17
Publication date: 2022-06-30

Abstract

Superhydrophobic film articles have a microstructured surface. The microstructured surface is free of nanostructures and contains a random arrangement of protrusions that form cavities. The superhydrophobicity is achieved by the selection of the materials of which the microstructures are formed or by a surface coating on the microstructured surface.

Description

SUPERHYDROPHOBIC FILMS

Summary

Disclosed herein are superhydrophobic film articles. The superhydrophobic film articles have a microstructured surface. In some embodiments the superhydrophobicity is achieved by the selection of the materials of which the microstructures are formed, in other embodiments the superhydrophobicity is achieved by a surface coating on the microstructured surface. In both embodiments, the microstructured surface is free of a hierarchical structure, meaning that the microstructured surface does not have or require nanostructures to achieve superhydrophobicity.

In some embodiments, the superhydrophobic film articles comprise a film substrate comprising a fluorinated polymeric material with a first major surface and a second major surface, where the second major surface comprises a microstructured surface. The microstructured surface is substantially free of structures with a size of 1 micrometer or less. The microstructured surface comprises a plurality of substantially randomly arranged protrusions, each protrusion comprises a plurality of facets meeting at a peak, and the protrusions define cavities. The microstructured surface has an average static water contact angle of 130° or greater.

In other embodiments, the superhydrophobic film articles comprise a film layer of a thermoplastic polymeric material with a first major surface and a second major surface, where the second major surface comprises a micro structured surface. The microstructured surface is substantially free of structures with a size of 1 micrometer or less. The microstructured surface comprises a plurality of substantially randomly arranged protrusions, each protrusion comprising a plurality of facets meeting at a peak, and the protrusions define cavities. At least a portion of the microstructured surface has a coating covering it, where the coating comprises a low surface energy material. The coated microstructured surface has an average static water contact angle of 130° or greater. Brief Description of the Drawings

The present application may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying drawings.

Figure l is a cross-sectional view of an article of this disclosure.

Figure 2 is a cross-sectional view of another article of this disclosure.

Figure 3 is a cross-sectional view of another article of this disclosure.

Figure 4 is an SEM (scanning electron micrograph) of an embodiment of this disclosure.

Figure 5 is an SEM (scanning electron micrograph) of another embodiment of this disclosure.

Figure 6 is an SEM (scanning electron micrograph) of another embodiment of this disclosure.

In the following description of the illustrated embodiments, reference is made to the accompanying drawings, in which is shown by way of illustration, various embodiments in which the disclosure may be practiced. It is to be understood that the embodiments may be utilized and structural changes may be made without departing from the scope of the present disclosure. The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

Detailed Description

Hydrophobic films and coatings, and more particularly, superhydrophobic films and coatings have garnered considerable attention in recent years due to a number of attractive qualities. Generally, a film may be considered hydrophobic when it repels water. Often hydrophobicity and superhydrophobicity are described by the water contact angle. The water contact angle may be measured with a static contact angle measurement device, such as the Video Contact Angle System: DSA100 Drop Shape Analysis System from Kruess GmbH (Hamburg, Germany). In this particular system, a machine is equipped with a digital camera, automatic liquid dispensers, and sample stages allowing a hands-free contact angle measurement via automated placement of a drop of water (where the water drop has a size of approximately 5 pl). The drop shape is captured automatically and then analyzed via Drop Shape Analysis software. Static water contact angle may be generally understood as the general “water contact angle” described and claimed herein. In this disclosure, superhydrophobic layers and articles are those where the static water contact angle is at least 130°, often greater than 135° or even greater than 140°. Superhydrophobic films may further be understood as generally nonwettable, as water beads up and rolls off the surface of the film upon contact, leaving no liquid residue. The phenomenon is well known in nature through the Lotus effect shown by leaves of the genus Nelumbo and other flowering plants. Other measurements of water contact angle that can be useful in characterizing superhydrophobic surfaces include advancing and receding contact angles, tilt angle, and contact angle hysteresis (difference between advancing and receding contact angles). While high static water contact angles are critical in superhydrophobic behavior of surfaces, receding angle and tilt angle measurements can correlate with the surface’s ability to cause easy roll-off of accumulated droplets. For maximum superhydrophobic film performance, receding water contact angles should be as high as possible, preferably greater than 100 degrees, and consequently hysteresis and tilt angle should be as low as possible.

A number of modern-day applications employ superhydrophobic surfaces such as sun-facing surfaces of solar (photovoltaic) cells, in anti-icing applications, corrosion prevention, anti-condensation applications, wind blades, traffic signals, edge seals, antifouling applications, and drag reduction and/or noise reduction for automobiles, aircraft, boats and microfluidic devices, just to name a few. Such films may also have valuable anti-reflection properties. There have therefore been attempts to create superhydrophobic films either by structuring a film’s surface in a manner resembling that of the lotus leaf, coating the film with a hydrophobic chemical coating, or a combination thereof. Unfortunately, a number of these attempts have resulted in films that are not sufficiently durable in outdoor or other harsh environments. This is especially unfortunate due to the difficult conditions to which such films are exposed in the exemplary applications noted. Those attempts at producing films that are durable in harsh application environments may not display the highly superhydrophobic properties that are necessary for optimal performance. A number of superhydrophobic films may derive their superhydrophobic properties from the fact that they have microstructures or microparticles that are overlaid with nanostructures or nanoparticles. A great deal of difficulty arises, however, in preserving the nanoparticles or nanostructures on or near the peaks of the microstructures of the film as they degrade over time. PCT Publication No. WO 2012/058090 provides a solution to these issues, by preempting the wearing away of microstructures, and consequently, nanofeatures in or on those microstructures, or nanoparticles on those microstructures. The microstructures are truncated to provide a flat surface. This allows for a distribution of external forces (e.g. abrasion) over a larger area of the surface of the microstructures, resulting in a smaller force per area, such that the height of microstructures may be maintained, and the nanoparticles and nanofeatures may be preserved at greater length, providing for greater performance.

While many superhydrophobic materials have been developed for optical applications, such as WO 2012/058090 described above, new applications are being developed that do not require optical transparency (high transmission of visible light) but do require transmission of electromagnetic radiation of other wavelengths. In particular, fifth generation Gigahertz band (5G) infrastructure is a growing market area. Applications in the areas of self-driving cars, the internet of things (loT), telemedicine, and virtual reality (VR) can all benefit from the adoption of this technology. 5G applications require materials which have no/minimal interference with millimeter wavelengths. For example, 5G antennas must be free of materials that will interfere with the transmission and reception of signals. Accumulation of water in the form of liquid droplets or ice can cause signal loss or slower data transfer due to absorption of signals in the 5G frequency range (28-95 GHz). Development of solutions such as superhydrophobic films which can prevent water accumulation onto components such as antenna enclosures can greatly impact and improve their performance. However, these materials also need to retain the hydrophobic or superhydrophobic properties despite being exposed to the environment. As mentioned above, frequently superhydrophobicity is achieved through the use of a hierarchical structure of a microstructured surface with nanoparticles or nanofeatures.

In this disclosure, superhydrophobic films are presented that have superhydrophobicity that is not based upon a hierarchical structure of a microstructured surface with nanoparticles or nanofeatures, and therefore does not have nanostructures that are vulnerable to environmental aging. Rather the current superhydrophobic films have microstructured surfaces where the microstructural features form cavities. Therefore, if the microstructural features are partially degraded by environmental causes, the cavities remain and the superhydrophobicity is maintained. The superhydrophobicity in the films can be achieved either by embossing a microstructured pattern into a low surface energy material or by coating a low surface energy layer onto a film that has a microstructured pattern.

The term “superhydrophobic” as used herein refers to a layer or article that repels water and is very difficult to wet because it has a high static water contact angle. The static water contact angle is 130° or greater, more typically greater than 135°, or greater than 140°.

The term “(meth)acrylate” refers to monomeric acrylic or methacrylic esters of alcohols. Acrylate and methacrylate monomers or oligomers are referred to collectively herein as "(meth)acrylates”. Materials referred to as “(meth)acrylate -based” are materials that contain primary (meth)acrylate groups.

The terms “siloxane-based” as used herein refer to polymers or units of polymers that contain siloxane units. The terms silicone or siloxane are used interchangeably and refer to compounds with dialkyl or diaryl siloxane (-SiR2O-) units and may also contain other units.

The terms "room temperature" and "ambient temperature" are used interchangeably to mean temperatures in the range of 20°C to 25°C.

The term “adjacent” as used herein when referring to two layers means that the two layers are in proximity with one another with no intervening open space between them. They may be in direct contact with one another (e.g. laminated together) or there may be intervening layers.

The terms “polymer” and “macromolecule” are used herein consistent with their common usage in chemistry. Polymers and macromolecules are composed of many repeated subunits. As used herein, the term “macromolecule” is used to describe a group attached to a monomer that has multiple repeating units. The term “polymer” is used to describe the resultant material formed from a polymerization reaction. As used herein, the term "microstructure" means the configuration of features wherein at least 2 dimensions of the features are microscopic. The topical and/or cross- sectional view of the features must be microscopic.

As used herein, the term "microscopic" refers to features of small enough dimension so as to require an optic aid to the naked eye when viewed from any plane of view to determine its shape. One criterion is found in Modem Optic Engineering by W. J. Smith, McGraw-Hill, 1966, pages 104-105 whereby visual acuity, " . . . is defined and measured in terms of the angular size of the smallest character that can be recognized." Normal visual acuity is considered to be when the smallest recognizable letter subtends an angular height of 5 minutes of arc on the retina. At a typical working distance of 250 mm (10 inches), this yields a lateral dimension of 0.36 mm (0.0145 inch) for this object.

The term “fluorinated” as used herein refers to hydrocarbon materials, both monomers and polymers, where at least some of the hydrogen atoms have been replaced by fluorine atoms. Perfluorinated refers to materials in which essentially all hydrogen atoms have been replaced by fluorine atoms. The term “fluoro-based” refers to a material that contains fluorinated materials.

The term “alkyl” refers to a monovalent group that is a radical of an alkane, which is a saturated hydrocarbon. The alkyl can be linear, branched, cyclic, or combinations thereof and typically has 1 to 20 carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl.

The term “aryl” refers to a monovalent group that is aromatic and carbocyclic. The aryl can have one to five rings that are connected to or fused to the aromatic ring. The other ring structures can be aromatic, non-aromatic, or combinations thereof. Examples of aryl groups include, but are not limited to, phenyl, biphenyl, terphenyl, anthryl, naphthyl, acenaphthyl, anthraquinonyl, phenanthryl, anthracenyl, pyrenyl, perylenyl, and fluorenyl.

Disclosed herein are film articles that have superhydrophobicity that is not based upon a hierarchical structure, but rather on a microstructured surface with microstructured features that define cavities. The microstructured surface is not hierarchical, meaning that the microstructured surface is substantially free of deliberately introduced nanostructural features, that is to say features such as nanostructures or nanoparticles with a size of 1 micrometer or less. In some embodiments, the superhydrophobic properties are retained even upon exposure to environmental conditions. The environmental conditions can be modeled in a variety of ways. Examples of environmental aging conditions that the current microstructured superhydrophobic films can be exposed while retaining the superhydrophobic properties include sand abrasion, UV exposure, or a combination thereof.

In some embodiments, the superhydrophobic film articles comprise a film substrate comprising a fluorinated polymeric material with a first major surface and a second major surface, where the second major surface comprises a microstructured surface. The microstructured surface is substantially free of structures with a size of 1 micrometer or less. The microstructured surface comprises a plurality of substantially randomly arranged protrusions, where the protrusions comprising a plurality of facets meeting at a peak, and where the protrusions define cavities. The microstructured surface has an average static water contact angle of 130° or greater. In some embodiments, the microstructured surface retains an average static water contact angle of 130° or greater after aging according to ASTM G-154-1. The aging test ASTM G-154-1 is a UV-aging test. In some embodiments, the microstructured surface retains an average static water contact angle of 120° or greater after a sand abrasion test as described by ASTM F 735. In some embodiments, the microstructured surface has an average static water contact angle of 140° or greater.

The film substrate may be a monolithic film substrate, meaning that the entire film substrate may be comprised of a single polymeric or copolymeric material. In other embodiments, the film substrate may be a multi-layer substrate with two or more layers of different material. In these embodiments, the layer that forms the second major surface of the film substrate is a fluorinated polymeric material. These multi-layer substrates are described in greater detail below.

A wide range of fluorinated polymeric materials are suitable for use in the superhydrophobic film articles of this disclosure. Typically, the fluorinated polymeric material comprises a fluorinated polymer or copolymer. In some embodiments, the fluorinated polymer or copolymer comprises at least one polymer or copolymer comprising at least one of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride. Examples of suitable fluorinated polymers or copolymers include PTFE (polytetrafluoroethylene), THV (terpolymers of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride), PVDF (polyvinylidene fluoride), HTE (terpolymers of hexafluoropropylene, tetrafluoroethylene, and ethylene), PFA (perfluoro alkoxy), PVF (polyvinyl fluoride), or FEP (copolymers of tetrafluoroethylene and hexafluoropropylene). Many of these fluoropolymer resins are commercially available from a range of suppliers including 3M, DuPont, Asahi Glass, and Solvay.

In some embodiments, the fluorinated polymeric material further comprises at least one additive selected from fluorochemical additives, glass beads, glass bubbles, microspheres, nanosilica particles, glass fibers, PTFE (polytetrafluoroethylene) micropowders, or combinations thereof. Particularly suitable additives include Fumed silica (e.g. CAB-O-SIL TS-610 fumed silica from CABOT) and Nanodiamonds from Carbodeon.

As mentioned above, in some embodiments the film substrate comprises a multilayer substrate. The use of multi-layer substrates can be advantageous for a wide range of reasons including cost reasons and performance reasons. In some embodiments, it may be desirable that the material layer that forms the first major surface of the film substrate has a higher surface energy to permit, for example, easier adhesive attachment of the film article to a substrate surface.

The multi-layer construction may comprise 2 layers. In this construction, the first layer forms the second major surface of the film substrate, and the first layer may comprise a fluorinated or a non-fluorinated material. This first layer is referred to in this embodiment and the following embodiments as a base layer. The second layer forms the first major surface of the film substrate and comprises a fluorinated material as described above. Typically, the film substrate comprises greater than two layers.

If the base layer is a fluorinated material, it typically is selected from the materials described above. More typically, the base layer is formed from a non-fluorinated material. A wide range of materials can be used to form the base layer when the base layer comprises a non-fluorinated material. The base layer may be thermoplastic polymer as described below. Examples of suitable polymeric materials include styrene-acrylonitrile, cellulose acetate butyrate, cellulose acetate propionate, cellulose triacetate, polyether sulfone, poly(meth)acrylate such as polymethylmethacrylate, polyolefins, polyurethane, polyester, polycarbonate, polyvinyl chloride, polystyrene, polyethylene naphthalate, or copolymers or blends thereof. In some embodiments, the base layer comprises a (meth)acrylate, a polyolefin, a polyurethane, or a combination thereof.

In some embodiments, the film substrate comprises a three-layer construction. The base layer comprises a non-fluorinated material. The other layers comprise fluorinated copolymeric materials. The fluorinated copolymeric materials are different from each other, but they may comprise the same class of polymers. For example, the two fluorinated copolymeric layers may both be THV polymers, but with different monomer mixtures. Among the advantages of this approach is to provide a gradient of surface energies across the cross-section of the substrate such that good interlayer adhesion is maintained. For example, if a non-fluorinated base layer is used, it may be desirable that the second layer (directly adjacent to the base layer) have an intermediate surface energy so that the second layer adheres well to the base layer. The third layer (directly adjacent to the second layer) can have a lower surface energy to provide the desirable superhydrophobic properties and can adhere more strongly to the second layer than it would to base layer.

Additionally, the multi-layer construction may comprise greater than three layers. In some embodiments, the film substrate comprises four layers, a base layer comprising a non-fluorinated material as described above, and three fluorinated material layers. Again, as described above, the fluorinated material layers generally form a gradient of decreasing surface energy (i.e. the layer in contact with the base layer has the highest surface energy and the layer that forms the first major surface has the lowest surface energy). In some embodiments, the three fluorinated layers are present in a sequence so as to provide a three-layer construction atop the non-fluorinated base layer. In these constructions, the three-layer construction may have the sequence: a first layer comprising PVDF (polyvinylidene fluoride); a second layer comprising THV (terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride); and a third layer comprising a different THV. In this construction, the first layer is in contact with the non- fluorinated layer and the third layer comprises the second major surface of the film substrate.

In other embodiments, the film substrate comprises five layers, a base layer comprising a non-fluorinated material as described above, and four fluorinated material layers. Again, as described above, the fluorinated material layers generally form a gradient of decreasing surface energy (i.e. the layer in contact with the base layer has the highest surface energy and the layer that forms the first major surface has the lowest surface energy). In some embodiments, the four fluorinated layers are present in a sequence so as to provide a three-layer construction atop the non-fluorinated base layer. In these constructions, the four-layer construction may have the sequence: a first layer comprising PVDF (polyvinylidene fluoride); a second layer comprising THV (terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride); a third layer comprising a different THV; and a fourth layer comprising FEP (a copolymer of tetrafluoroethylene and hexafluoropropylene). In this construction, the first layer is in contact with the non-fluorinated layer and the fourth layer comprises the second major surface of the film substrate.

As described above, the second major surface of the film substrate comprises a microstructured surface. The microstructured surface can be prepared by embossing the film substrate with a microstructured fabricating tool, as is well understood in the art. Particularly suitable fabricating tools and methods are described in PCT Publication No. WO 2018/130926, US Patent Publication No. 2020/0064525, and US Patent Nos. 10,295,710 and 10,605,965 to prepare optical films. It should be noted that the current film articles are not designed to have the optical properties of the films of PCT Publication No. WO 2018/130926, US Patent Publication No. 2020/0064525, and US Patent Nos. 10,295,710 and 10,605,965, rather the current films have similar microstructured surfaces.

The film substrates of this disclosure can be made by fabricating a tool having a microstructured surface, and microreplicating this microstructured surface on the first major surface of the film substrate. Fabrication of the tool can involve electrodepositing a first layer of a metal under conditions that produce a first major surface with a relatively high average roughness, followed by covering up the first layer by electrodepositing a second layer of the same metal on the first layer, under conditions that produce a second major surface with a relatively lower average roughness, i.e., lower than that of the first major surface. Before microreplication, the fabricating tool surface may be further treated, e.g., coated with a thin layer of a different metal such as for purposes of passivation or protection. By forming the structured surface using electrodeposition techniques rather than techniques that require cutting of a substrate with a diamond tool or the like, large area tool surfaces can be prepared in substantially less time and at reduced cost. The microstructured surface of the film substrate may possess a degree of irregularity or randomness in surface profile characterized by an ultra-low periodicity. Typically, the structured surface comprises substantially randomly arranged protrusions. Typically, the protrusions have a height of 100 micrometers or less. In the optical references described above, the structures currently described as protrusions are referred to as prisms. In this disclosure, the protrusions are referred to as protrusions, as the term “prisms” implies optical effects that are not a part of the current disclosure. It should be noted that the same patterns described for use in optical films have surprisingly been found to be useful to form films that have superhydrophobicity. The protrusions comprise a plurality of facets meeting at a peak. As used herein, the term facet refers to the faces of the protrusions. Generally, the facets are planar. The protrusions define cavities. The protrusions and the cavities formed by the array of protrusions have a size that may be expressed in terms of an equivalent circular diameter (ECD), and the structures may have an average ECD of less than 15 micrometers, or less than 10 micrometers, or in a range from 4 to 10 micrometers.

The cavities formed by the structures can have a wide variety of shapes and sizes. In some cases, the cavities have an average diameter of at least 4 micrometers. Like the structures, the cavities generally have an average diameter of less than 15 micrometers or less than 10 micrometers.

As mentioned above, the microstructured surface is substantially free of deliberately introduced structures with a size of 1 micrometer or less. While it is understood that normal surface roughness can provide structures with a size of 1 micrometer or less, it is well understood by those of skill in the microstructure art that this refers to the fact that no structures with a size of 1 micrometer or less are specifically formed in the microstructured surface. Additionally, it should be noted that unlike superhydrophobic surfaces that have nanostructured surfaces and require nanostructured surfaces to have superhydrophobicity, the current superhydrophobic surfaces do not require nanostructured features to have superhydrophobicity. In this way, the current articles are not subject to the loss of superhydrophobicity if fragile nanostructures are damaged.

Also disclosed are superhydrophobic film articles comprising a thermoplastic material with a microstructured surface and a coating covering the microstructured surface. In some embodiments, the superhydrophobic film article comprises a film layer of a thermoplastic polymeric material with a first major surface and a second major surface, where the second major surface comprises a microstructured surface, and a coating covering at least a portion of the microstructured surface, the coating comprising a low surface energy material. The microstructured surface is substantially free of structures with a size of 1 micrometer or less. The microstructured surface comprises a plurality of substantially randomly arranged protrusions, the protrusions comprising a plurality of facets meeting at a peak, where the protrusions define cavities. The coated microstructured surface has an average static water contact angle of 130° or greater. In some embodiments, the coated microstructured surface has an average static water contact angle of 140° or greater.

The microstructured surface on the thermoplastic material is formed as described above. As in the microstructured surfaces described above, the cavities in the microstructured surface can have a wide variety of shapes and sizes. In some cases, the cavities have an average diameter of at least 4 micrometers. Like the structures, the cavities generally have an average diameter of less than 15 micrometers or less than 10 micrometers.

A wide range of thermoplastic polymeric materials are suitable for forming the thermoplastic film substrate. Examples of suitable polymeric materials include styreneacrylonitrile, cellulose acetate butyrate, cellulose acetate propionate, cellulose triacetate, polyether sulfone, poly(meth)acrylate such as polymethylmethacrylate, polyolefins, polyurethane, polyester, polycarbonate, polyvinyl chloride, polystyrene, polyethylene naphthalate, or copolymers or blends thereof. Particularly suitable thermoplastic film substrates include polyester, polyolefin, polyurethane, or combinations thereof.

A variety of techniques can be used to dispose the coating on the microstructured surface of the articles of this disclosure. In some embodiments, the coating is disposed on the microstructured surface by solvent coating or plasma coating.

In some embodiments, the coating is disposed on the microstructured surface by plasma coating. Plasma coating methods are described, for example, in the methods described in PCT Publication No. WO 2009/032815. In some embodiments, the plasma coating involves plasma coating of a siloxane-based material. A particularly suitable siloxane-based material is HMDSO (hexamethyl disiloxane). In some embodiments, the plasma coating involves plasma coating a fluoro-based material. A particularly suitable fluoro-based material is perfluoropropane.

The coating may have a variety of thicknesses. In some embodiments, where the coating is disposed on the microstructured surface by plasma coating, the plasma coating has a thickness of less than 200 nanometers.

In other embodiments, the coating is disposed on the microstructured surface by solvent coating. In these embodiments, a solution that contains a coating material is coated onto the microstructured surface. The coating can then be dried, and if the coating material is a curable material the coating can additionally be cured. In this context, solvents include a wide range of fluids including organic liquids such as hydrocarbon liquids, and non-organic fluids such as water. The solution can be coated onto the microstructure surface using a wide variety of coating techniques as are well understood in the art. In some embodiments, the solvent coated layer comprises a (meth)acrylate-based layer that is cured after coating. In other embodiments, the coating comprises a fluoropolymer or fluoro-based coating, or a silicone material. Examples include 3M NOVEC 2202, AGC Chemicals Company LUMIFLON fluoroethylene/vinyl ether coatings, and OMNOVA solutions SUNCRYL HP 114 acrylic based coatings.

In some embodiments, the coated microstructured surface is prepared not by disposing a coating onto the microstructured surface, but by incorporating a material into the material composition of the microstructured substrate that blooms to the surface of the microstructured substrate to form a surface coating. Examples of such materials include the polymeric materials referred to as “slip additives”. In some embodiments, these materials are silicone-acrylate materials, fluorocarbon-acrylate materials, or polyolefinacrylate materials. An example of a silicone-acrylate slip additive is TEGORAD 2300 from Evonik Industries.

In some embodiments, the superhydrophobic films prepared by coating also have good environmental durability. In some embodiments, the films retain an average static water contact angle of 130° or greater after sand abrasion testing according to ASTM F 735 or retain an average static water contact angle of 120° or greater after aging according to ASTM G- 154-1.

The superhydrophobic film articles of this disclosure may be more fully understood by reference to the Figures. Figure 1 is a cross-sectional view of an embodiment of a superhydrophobic fdm article of this disclosure. Base film 120 has microstructured surface 110. The protrusions on the microstructured surface 110 form cavities 130. In this embodiment, the film article is monolithic, meaning that the entire article comprises one material.

Figure 2 shows a cross-sectional view of another embodiment of a superhydrophobic film article of this disclosure. Microstructured surface 210 is in direct contact with base layer 220 at interface 212. Base layer 220 may be a multi-layer article. The protrusions on the microstructured surface 210 form cavities 230.

Figure 3 shows a cross-sectional view of another embodiment of a superhydrophobic film article of this disclosure. Microstructured surface 310 is in direct contact with base layer 320 at interface 312. Base layer 320 may be a multi-layer article. The protrusions on the microstructured surface 310 form cavities 330. Microstructured surface 310 has coating 340.

Figures 4-6 are SEM (scanning electron micrographs) of the surface of superhydrophobic film articles of this disclosure. Figure 4 is Example E4, Figure 5 is Example E10, and Figure 6 is Example E2.

Examples

Coated Superhydrophobic Films and Embossed Superhydrophobic Films were prepared by various methods. The resultant film-based articles provide high water contact angles as shown in the following examples. These examples are merely for illustrative purposes only and are not meant to be limiting on the scope of the appended claims. All parts, percentages, ratios, etc. in the examples and the rest of the specification are by weight, unless noted otherwise. The following abbreviations are used herein: nm = nanometer, in = inch, mil = one thousandth of an inch, cm = centimeter, ml = milliliter, deg = degree, RPM = revolutions per minute, FPM and ft/min = feet per minute, hrs = hours, Std dev = standard deviation, mJ/cm² =millijoules per centimeter squared, W/cm = Watts per centimeter, MHz = Mega Herts, SCCM = standard cubic centimeters per minute, mTorr = millitorr, °C = Centigrade, min = minute, s = seconds, % = percent .

Table 1. Materials

TEST METHODS

Water Contact Angle

A Kruss DSA100 system (Available from Kruss GmbH Hamburg Germany) was used to measure the contact angles of water on the surface of the films. Small strips of the films were carefully cut out (wearing gloves) and mounted to a glass slide. The system was programmed to dispense 5-10 microliters of deionized water at a rate of 195 microliters/minute. The sessile drop contact angle was determined by fitting the profile of the water droplet. Static water contact angles were measured by placing 5 microliter droplets on the film and using the instrument software to extract the contact angles on both sides of the drop profile. Advancing and receding angles were measured by adding or withdrawing, respectively, water from the droplet at a rate of 7 microliters/min. Water contact angle measurements (Degrees) were taken while the droplet edges were advancing or receding smoothly over the film surface. Average values and standard deviations obtained from measurements on at least three separate drops are shown in the data tables below.

Sand Abrasion Test

Film samples were subjected to an oscillating sand test (ASTM F 735 using a rotary oscillatory shaker made by VWR (Randor, PA)) where the test conditions were 50 grams of sand, 300 rpm for 15 minutes. In order to quantify the abrasion resistance, the water contact angle was measured before and after sand abrasion testing.

ASTM G154-1 Weathering Test

Film samples were subjected to accelerated weathering test protocol ASTM G154 cycle 1 for either 250 or 500 hours. Static water contact angles were measured before and after testing.

EXAMPLES

Coated Superhydrophobic Films

Preparatory - Replication Resin 1 (RR1)

A 125 ml amber glass jar was charged with 30 grams of Oligomer 1, 25 grams of Crosslinker 1, 0.3 grams of Initiator 1, 0.4 grams of Initiator 2, 0.28 grams of UV absorber, and 0.1 grams of HALS. The jar was sealed, a stir bar added, and placed on a magnetic stirrer. The mixture was stirred for 24 hours at room temperature. This was labelled as Replication Resin 1 (RR1).

Preparatory - Replication Resin with slip additive (RR2)

A 125 ml amber glass jar was charged with 30 grams of Oligomer 1, 25 grams of Crosslinker 1, 0.3 grams of Initiator 1, 0.4 grams of Initiator 2, 0.28 grams of UV absorber, 0.1 grams of HALS, and 0.3 grams of Slip additive. The jar was sealed, a stir bar added, and placed on a magnetic stirrer. The mixture was stirred for 24 hours at room temperature. This was labelled as Replication Resin with slip additive (RR2). Preparation of Replication Films:

30 grams of resin (RR1 or RR2) was poured over the replication tool (A flat microreplication tool with the inverse structure as shown in Fig. 15a/sample 6a of U.S. Pat. App. 2020/0064525 (Derks et al.). The replication tool was prepared according to the methods described in paragraphs 91 - 94. The replication fdm was prepared according to the methods described in paragraph 96). A sheet of 5 mil PET film was applied on top of the resin coated tool (primed side to the resin). The film was passed through a laminator in order to press the resin into the structure between the film and tool. The assembly was then passed through a UV curing system with a D bulb (Heraeus Nobelight Fusion UV Inc., Gaithersburg, MD). Curing took place at 100% power and 20 ft/min, 2 passes. The cured film was then removed from the tool. Microreplicated Resin Film 9 (F9) was prepared with the replication process described above using RR1 resin. Microreplicated Resin Film 10 (F10) was prepared with the replication process described above using RR2 resin.

Coated Superhydrophobic Film Examples

A series of Coated Superhydrophobic Films were prepared by overcoating Microreplicated Resin Films (F9 and F10). The overcoats were either plasma enhanced chemical vapor deposited (PECVD) surface coatings or solution coatings. Comparative Examples and Examples were prepared as described in Table 2 below.

PECVD Surface Coatings:

A silicon containing layer was applied to the microstructured surface of a film using a parallel plate capacitively coupled plasma reactor. The chamber has a cylindrical powered electrode with a surface area of 0.34 m². After attaching the film sample to the rotating drum electrode, the reactor chamber was pumped down to a base pressure of less than 1.3 Pa (1 mTorr). The machine was set up with R2 parameters listed in table below. Oxygen was introduced into the chamber at a flow rate of 600 SCCM. Treatment was carried out by coupling RF power into the reactor at a frequency of 13.56 MHz and an applied power of 600 watts for 30 s. A second step resulting in a deposited thin film on the microstructure was accomplished by stopping the flow of oxygen and evaporating and transporting HMDSO into the system. Treatment was carried out using a plasma enhanced CVD method by coupling RF power into the reactor at a frequency of 13.56 MHz and an applied power of 600 watts for Is. Following the completion of the second step, a second line of HMDSO was opened to the chamber in addition to the 120 SCCM of HMDSO. The combined flow rates resulted in a chamber pressure of 4.1 mTorr. Treatment was carried out by coupling RF power into the reactor at a frequency of 13.56 MHz and an applied power of 200 watts for 30 s. The process conditions yielded a surface coating thickness of <200 nm. For each step, RF power (watts) was applied to the electrode to generate the plasma after the stated gas flow had stabilized. Following completion of the plasma treatment, the RF power and gas supply were stopped, and the chamber was vented to the atmosphere.

Primary process variables the recipes that have been investigated and are summarized below.

R1

1. O2 etch at 600 watts, 600 seem flow, 30 seconds

2. HMDSO coating at 600 watts, 120 seem flow, 30 seconds

R2

1. O2 etch at 600 watts, 600 seem flow, 30 seconds

2. HMDSO coating at 200 watts, 120 seem flow, 30 seconds

R3

1. O2 etch @ 500 watts, 600sccm flow, 60 seconds

2. DLG (Diamond-Like Glass) coating @ 600 watts, 120 seem HMDSO, 80 seconds

3. Secondary DLG coating layer @ 200 watts, 120 seem HMDSO, 40 seconds

4. O2 etch-back @ 500 watts, 600 seem flow, 45 seconds

5. Film samples were removed from the chamber and immersed in 3M NOVEC 2202 for 30 seconds and removed to allow the solvent to evaporate, then thermally cured in an air oven @ 60C for overnight (approximately 20 hrs.)

Solution coatings: A solvent based acrylic coating (SBAC) was prepared according to the following procedure: The solvent based acrylic coating material was prepared by charging Monomer 1, Monomer 2, and Monomer 3, in monomer ratio of 50/50/0.4 in a blend of 50:50 ethyl acetate/heptanes having a solid contents of 60% by weight. Then 0.003 parts of Initiator 3, was charged followed by purging the contents in the container with nitrogen gas for 10 minutes. The container was sealed and placed in a rotary constant-temperature bath maintained at 50°C. The reaction was allowed to proceed for 24 hrs.

Solution coating procedure:

The solution of this copolymer was diluted to 1 wt% by a solvent mix of toluene/MEK (50wt%/50wt%) and coated on a desired film by a wire-wound rod (#3). The coated sample was irradiated under a high-pressure mercury vapor lamp (Fusion System Corporation; H bulb, 130w/cm) by passing twice at 40 fpm under nitrogen with UVA energy of 506mJ/cm².

Results for Coated Superhydrophobic Films:

Static Water Contact Angles were measured on these Examples and are reported in Table 2. A select number of Examples were put through Sand Abrasion and Weathering testing as described in Test Methods. The before and after Static Water Contact Angles are described in Table 3 and 4.

Table 2. Static Water Contact Angle results for Superhydrophobic Coated Films

E7

None | 132,6

| 1,7

Table 3. Sand Abrasion results for Superhydrophobic Coated Films

Table 4. Weathering results for Superhydrophobic Coated Films

Embossed Superhydrophobic Films

A flat microreplication tool with the inverse structure as shown in Fig. 15a/sample 6a of U.S. Pat. App. 2020/0064525 (Derks et al.). The replication tool was prepared according to the methods described in paragraphs 91 - 94. The replication film was prepared according to the methods described in paragraph 96. The tool was treated with a release coating to facilitate removal of the polymer copy from the tool. The tool release coating procedure is described below:

1. O2 etch @ 500 watts, 600sccm flow, 60 seconds

2. DLG (Diamond-Like Glass) coating @ 600 watts, 120 seem HMDSO, 80 seconds

3. Secondary DLG coating layer @ 200 watts, 120 seem HMDSO, 40 seconds 4. O2 etch-back @ 500 watts, 600 seem flow, 45 seconds

A sheet of polymer film F5 or F6 or F7 or F8 was placed on top of the tool. Then two sheets of 21 mil PTFE were placed around the tool and polymer film. The sandwich was placed between 2 aluminum plates of 0.0625 in thickness, and this assembly was placed between two steel plates of 0.25 in thickness. The entire assembly was placed into a Wabash hot press. Samples were heated to melt the polymer film (Platens were heated to 270°C for films F5, F6, and F8 and for film F7 300°C) under 1 ton for 5 minutes, then pressed under 5 tons for 5 minutes. Next, the assembly was removed from the press and placed between two tap water-chilled plates for 5 minutes. After cooling, the stack was disassembled, and the embossed film was peeled from the tool. Treated film samples were tested using Water Contact Angle, Weathering, and Sand Abrasion tests as described above. Water Contact Angles on samples of polymer films before and after embossing are shown in Table 5, Sand Abrasion in Table 6, and Weatherability in Table 7. Only static Water Contact Angles before and after sand abrasion and weatherability testing are reported.

Table 5. Water contact angles for flat and Embossed Superhydrophobic Films

Table 6. Sand abrasion results for embossed films

Table 7. Weathering results for embossed films

Claims

What is claimed is:

1. A superhydrophobic film article comprising: a film substrate comprising a fluorinated polymeric material with a first major surface and a second major surface, wherein the second major surface comprises a microstructured surface, wherein the microstructured surface is substantially free of structures with a size of 1 micrometer or less, where the microstructured surface comprising a plurality of substantially randomly arranged protrusions, each protrusion comprises a plurality of facets meeting at a peak, wherein the protrusions define cavities, and wherein the micro structured surface has an average static water contact angle of 130° or greater.

2. The superhydrophobic film article of claim 1, wherein the microstructured surface has an average static water contact angle of 140° or greater.

3. The superhydrophobic film article of claim 1, wherein the microstructured surface retains an average static water contact angle of 130° or greater after aging according to ASTM G-154-1, or retains an average static water contact angle of 120° or greater after sand abrasion testing according to ASTM F 735.

4. The superhydrophobic film article of claim 1, wherein the fluorinated polymeric material comprises a fluorinated polymer or copolymer.

5. The superhydrophobic film article of claim 4, wherein the fluorinated polymer or copolymer comprises at least one polymer of copolymer comprising at least one of tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride.

6. The superhydrophobic film article of claim 4, wherein the fluorinated polymer or copolymer comprises PTFE (polytetrafluoroethylene), THV (terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride), PVDF (polyvinylidene fluoride), HTE (a terpolymer of hexafluoropropylene, tetrafluoroethylene, and ethylene),

-24- PFA (perfluoro alkoxy), PVF (polyvinyl fluoride), or FEP (a copolymer of tetrafluoroethylene and hexafluoropropylene).

7. The superhydrophobic fdm article of claim 1, wherein the cavities have an average diameter of at least 4 micrometers.

8. The superhydrophobic film article of claim 1, wherein the film substrate comprising a fluorinated polymeric material further comprises at least one additive selected from fluorochemical additives; glass beads; glass bubbles; microspheres; nanosilica particles; glass fibers; PTFE (polytetrafluoroethylene) micropowders; or combinations thereof.

9. The superhydrophobic film article of claim 1, wherein the film substrate comprising a fluorinated polymeric material comprises a multi-layer substrate.

10. The superhydrophobic film article of claim 9, wherein the multi-layer substrate comprises a base layer comprising a non-fluorinated material, and at least two fluorinated copolymer layers, wherein the non-fluorinated material layer comprises the first major surface of the multi-layer substrate.

11. The superhydrophobic film article of claim 10, wherein the non-fluorinated material layer comprises a (meth)acrylate, a polyolefin, a polyurethane, or a combination thereof.

12. The superhydrophobic film article of claim 10, wherein the at least two fluorinated copolymer layers comprise three layers in sequential order comprising: a first layer comprising PVDF (polyvinylidene fluoride); a second layer comprising a THV (terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride; and a third layer comprising a different THV, wherein the third layer comprises the second major surface of the film substrate, and the first layer is in contact with the non- fluorinated layer.

13. The superhydrophobic film article of claim 10, wherein the at least two fluorinated copolymer layers comprise four layers in sequential order comprising: a first layer comprising PVDF (polyvinylidene fluoride); a second layer comprising a THV (terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride; a third layer comprising a different THV; and a fourth layer comprising FEP (a copolymer of tetrafluoroethylene and hexafluoropropylene), wherein the fourth layer comprises the second major surface of the film substrate, and the first layer is in contact with the non-fluorinated layer.

14. A superhydrophobic film article comprising: a film layer of a thermoplastic polymeric material with a first major surface and a second major surface, wherein the second major surface comprises a microstructured surface, wherein the microstructured surface is substantially free of structures with a size of 1 micrometer or less; and a coating covering at least a portion of the microstructured surface, the coating comprising a low surface energy material; wherein the microstructured surface comprises a plurality of substantially randomly arranged protrusions, each protrusion comprising a plurality of facets meeting at a peak, wherein the protrusions define cavities, wherein the coated microstructured surface has an average static water contact angle of 130° or greater.

15. The superhydrophobic film article of claim 14, wherein the coated microstructured surface has an average static water contact angle of 140° or greater.

16. The superhydrophobic film article of claim 14, wherein the coating is disposed on the microstructured surface by solvent coating or plasma coating.

17. The superhydrophobic film article of claim 16, wherein the coating is disposed on the microstructured surface by plasma coating of a siloxane material.

18. The superhydrophobic film article of claim 17 wherein the plasma coating has a thickness of less than 200 nanometers.

19. The superhydrophobic film article of claims 16, wherein the coating comprises a solvent coated (meth)acrylate-based coating, a fluoro-based coating, or a silicone-based coating.

20. The superhydrophobic film article of claim 14, wherein the thermoplastic film substrate comprises polyester, polyolefin, polyurethane, or combinations thereof.

21. The superhydrophobic film article of claim 14, wherein the cavities have an average diameter of at least 4 micrometers.

22. The superhydrophobic film article of claim 14, wherein the coated microstructured surface is abrasion resistant, retaining an average static water contact angle of 130° or greater after sand abrasion testing according to ASTM F 735 or retaining an average static water contact angle of 120° or greater after aging according to ASTM G-154-1.

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