Composite material with a superhydrophobic surface and coating composition for superhydrophobic post-treatment of microstructured surfaces

Abstract

A composite material with a superhydrophobic surface comprising a first-level surface structure with elevations and / or depressions having at least one spatial dimension Δdmicro in the range of from 1 × 10−3 m to 1 × 10−6 m and a second-level surface layer covering the first-level surface structure and comprising aggregates of hydrophobic nanoparticles and at least partially crosslinked hydrophobic polymers, wherein the mass ratio of the total amount of hydrophobic nanoparticles to the total amount of at least partially crosslinked hydrophobic polymers is in the range of from 1:5 to 5:1, the average thickness of the second-level surface layer dnano is in the range of from 25 nm to 5000 nm, the second-level surface layer has elevations having at least one spatial dimension Δdnano in the range of from 5 nm to 1000 nm, the fluorine content is less than 1% by weight, and wherein the ratio of at least one of the at least one spatial dimension Δdmicro to the average thickness of the second-level surface layer dnano is at least 5:1.

Description

[0001] BASF Coatings GmbH

[0002] GlasuritstraBe 1 , 48165 Munster

[0003] Germany

[0004] Composite material with a superhydrophobic surface and coating composition for superhydrophobic post-treatment of microstructured surfaces

[0005] FIELD OF THE INVENTION

[0006] The present invention relates to a composite material with a superhydrophobic surface comprising a first-level surface structure (microstructure) and a (nanostructured) second- level surface layer covering the first-level surface structure and comprising aggregates of hydrophobic nanoparticles and at least partially crosslinked hydrophobic polymers. The present invention also relates to a coating composition for the production of superhydrophobic surfaces, the coating composition comprising a liquid phase comprising an organic solvent, and dissolved and / or emulsified in the liquid phase, one or more crosslinkable and hydrophobic polymers, and dispersed in the liquid phase one or more hydrophobic nano- particles. Furthermore, the present invention relates to a process of producing a composite material with a superhydrophobic surface.

[0007] BACKGROUND OF THE INVENTION

[0008] The superhydrophobicity of surfaces is known from nature and leads to highly water repellent materials with beneficial features such as drag reduction, easy-to-clean, self-cleaning, BASF 231086 dirt-repellent, anti-stain, anti-stick, anti-fogging, anti-icing, air-retaining, anti-adhesive, bioinert and / or non-fouling (non-biocidal anti-fouling) properties. These properties are highly relevant for applications in industrial products such as aircrafts, trains, ships or other means of (public) transportation, optical materials or sports equipment, (architectural) facades, disposable systems for handling aqueous media such as bioreactors, etc.

[0009] This is why composite materials with a superhydrophobic surface as well as manufacturing processes thereof have caught considerable attention since at least 20 years. Most research efforts have been directed to design materials by mimicry of nature wherein plants such as the famous lotus leaf (Nelumbo nucifera) or certain water ferns (e. g., Salvinia molesta) serve as examples for highly interesting materials with above mentioned properties.

[0010] However, it remains challenging to design and manufacture synthetic surface structures with comparable properties on industrial scale. Most of the synthetic materials and respective manufacturing processes thereof still suffer from performance issues, as they are not scalable, quite often require highly specialised, highly expensive equipment, lead to irre- producible results, and / or give inhomogeneous quality. Synthetic superhydrophobic composite materials up to today are in most cases not durable in environmental conditions, are not free of Substances of Very High Concern (SVHC) such as such as fluorinated compounds, especially per- and / or polyfluorinated alkyl substances (PFAS) and do not allow for practical handling, thus not fulfilling the requirements for commercialisation.

[0011] Many functional surfaces rely on certain structures which give rise to their primary functionality. As a first example, for the Salvinia effect (entrapping air), microstructures serving as capillaries are needed as first-level surface structures. Likewise, as a second example, to achieve the drag reduction effect which shark skin is known for, so-called riblet microstructures are best-suited. In this, the more hydrophobic these structures are made, the stronger the related effects become. In the first example, to boost the capillary forces contributing to the Salvinia effect, the surfaces of the microstructures serving as capillaries need to be as hydrophobic as possible to keep water out. Ideally, they should be superhydrophobic. In the second example, making the surface of existing riblet microstructures hydrophobic, ideally superhydrophobic, may give rise to secondary functionalities such as anti-icing and / or easy-to-clean and / or anti / non-fouling behaviour. These secondary functionalities are commercially beneficial by, e. g., reducing the de-icing effort, reducing the cleaning workload, and increasing a surface’s service lifetime, respectively. BASF 231086

[0012] To add superhydrophobic properties to predetermined functional microstructures (first-level (micro)structures), on top of these predetermined functional microstructures, second-level (nano)structures comprising strongly hydrophobic material need to be added while essentially maintaining the original first-level structures at the outer surface, so that these first- level structures can contribute to overall surface roughness and thus contribute to overall hydrophobicity, as well as retain their primary functionality. As materials with several interesting first-level structures are already being fabricated economically at industrial scale, it may be highly beneficial to take these materials from industrial-scale production as they are and to literally add on the second-level (nano)structures in a process that can be used as is for a broad range of such materials and / or that can be easily adapted to achieve this. This is in contrast to attempting to fabricate both the first-level and the second-level structures in an integrated process that would have to fulfill the requirements to create both structures simultaneously.

[0013] The resulting surfaces of target materials ideally are thus hierarchically structured and feature a (micro)structured surface topology as well as a thin layer featuring nanoroughness and covering the microstructure underneath. It is generally and theoretically known that such hierarchical structuring is beneficial for reliable superhydrophobicity, and nature succeeds in creating this. However, an important task here is not only to achieve reliable superhydrophobicity, but to essentially maintain arbitrary, original first-level structures at the same time. There are no technical real-world examples for this with good performance so far.

[0014] „Wang, D. et al. Design of robust superhydrophobic surfaces. Nature 582, 55-59 (2020). https: / / doi.org / 10.1038 / s41586-020-2331-8” (Wang 2020) discloses the design of robust superhydrophobic surfaces. These superhydrophobic surfaces are composed of a microstructured surface frame wherein the spaces between the parts of the microstructured surface frame are completely filled with mechanically fragile nanostructures. In Wang 2020 fluorinated fractal nanoclusters of silica were used as a model superhydrophobic nanomaterial. Accordingly, Wang 2020 effectively clogs the original, first-level microstructure instead of maintaining it, and additionally relies on fluorinated materials.

[0015] “He, W. et al. Transparent and superhydrophobic coating via one-step spraying for cultural relic protection against water and moisture. Colloids and Surfaces A: Physicochemical and Engineering Aspects 662 (2023) 130949. https: / / doi.Org / 10.1016 / j.colsurfe.2023.130949” (He 2023) discloses a transparent and superhydrophobic coating for specific substrates. Hydrophilic materials are used in the coating according to He 2023, and Fig 1 shows aggregates having diameters of more than at least 5 to 10 pm, which indicates that many BASF 231086 original, first-level microstructures would be severely altered and / or clogged if coated according to He 2023.

[0016] “Zhang, W. et al. Fabrication of a fluorine-free photocatalytic superhydrophobic coating and its long-lasting anticorrosion and excellent antibacterial abilities, Progress in Organic Coatings, Volume 184, 2023, 107806, ISSN 0300-9440, https: / / doi.Org / 10.1016 / j.porgcoat.2023.107806.” (Zhang 2023) discloses a superhydrophobic coating based on a hydrophilic epoxy resin. Because the thickness of the second- level surface layer in Zhang 2023 is very high, most original, first-level structures would be completely buried if coated according to Zhang 2023. Hence, this coating is compatible with substrates without first-level structures only.

[0017] “Turkoglu, S. et al. Structure-Property Relationships for Fluorinated and Fluorine-Free Superhydrophobic Crack-Free Coatings. Polymers 2024, 16, 885. https: / / doi.org / 10.3390 / polym16070885” (Turkoglu 2024) discloses a superhydrophobic coating based on a hydrophilic epoxy resin which is compatible with flat first-level glass substrates only. Because the thickness of the second-level surface layer in Turkoglu 2024 is very high, most original, first-level structures would be completely buried if coated according to Turkoglu 2024.

[0018] CN 104403453 A discloses a semiconductor superhydrophobic paint and preparation method thereof.

[0019] CN 108099185 A discloses a method for quickly preparing super-hydrophobic surface on matrix based on 3D printing.

[0020] CN 109943163 A discloses a method for rapidly preparing super-hydrophobic self-cleaning surface material by using PTFE micro-nano particle method.

[0021] US 10,577,511 B2 discloses STRETCHABLE HYDROPHOBIC MATERIALS AND METHODS FOR MAKING THE SAME.

[0022] WO 2013 / 042052 A1 discloses SUPERHYDROPHOBIC COATINGS AND METHODS OF PREPARATION.

[0023] WO 2018 / 193094 A1 discloses a REGENERATIVE SUPERHYDROPHOBIC COATING. BASF 231086

[0024] WO 2020 / 043796 A1 discloses a MULTILAYER SELF-ADHESIVE FOULING RELEASE FILM WITH TEXTURED SURFACE.

[0025] EP 2 822 704 B1 and WO 2013 / 131618 A2 disclose a GAS-CONTAINING SURFACE COVER, ARRANGEMENT, AND USE. Requirements for, i. a., air retention are discussed and microstructures (candidates for first-level surface structures) suitable for air retention are disclosed.

[0026] WO 2020 / 047052 A1 discloses a METHOD FOR PRODUCING AN AIR-RETAINING FILM WITH TEXTURED SURFACE AND AN AIR-RETAINING FILM WITH TEXTURED SURFACE. Specific, selected microstructures (candidates for first-level surface structures) are described as preferable for air retention.

[0027] DE 10 2018 003 141 A1 discloses structured surfaces and devices comprising the same and their application. Other, specific microstructures (candidates for first-level surface structures) are described as preferable for air retention.

[0028] EP 3 238 839 A1 discloses an object with friction reducing surface and, in particular, reduces the degassing of liquids.

[0029] CN 116285666 A discloses a superhydrophobic coating of micro-nano structure and its preparation method and application.

[0030] WO 2008 / 106494 A1 discloses nanotextured super or ultra hydrophobic coatings.

[0031] WO 2012 / 058090 A1 discloses superhydrophobic films and methods of making such films.

[0032] WO 2023 / 233137 A1 discloses a method of preparing a hierarchical surface.

[0033] As set forth above and below, production of those hierarchically structured superhydrophobic surfaces is complicated, and state-of-the-art processes and materials suffer from several problems and do in many cases not fulfil (all of) the requirements as set forth above or below. Foremost, the second-level (nano)structure must be in the form of a very thin film or layer. If not, the underlying first-level (micro)structure of the surface would be completely buried by the nanorough film or layer and would thus neither contribute to the hydrophobicity anymore nor, if applicable, retain its original, primary functionality. It is known that many BASF Coatings GmbH 231086 coating compositions which are used in the superhydrophobic post-treatment for microstructured surfaces result in a so called “clogging effect”, i. e., the second-level layer fills up the free space in between the first-level (micro)structures.

[0034] Furthermore, the durability of the resulting composite material, in particularthe durability of the very thin second-level nanorough surface, is an issue as in most use cases, the material is exposed to chemicals, heat, irradiation, mechanical stress, etc. To this end, compatibility of the first-level (micro)structured surface to the second-level (nano)structured surface layer is also important. Likewise, the materials used should be easily accessible and substantially free of Substances of Very High Concern (SVHC) such as PFAS. It is also desirable and beneficial that the materials itself (independent of their structural arrangement) are hydrophobic as this strongly contributes to reaching superhydrophobicity with the entire resulting composite material. The production method should also be feasible, scalable and reproducible.

[0035] There is a demand in industry for a composite material with a superhydrophobic surface comprising a microstructured first-level surface structure and a nanostructured second- level surface layer covering the first-level surface structure which is improved regarding the above-mentioned challenges and problems.

[0036] SUMMARY OF THE INVENTION

[0037] It was a primary object of the present invention to provide such an improved composite material with a superhydrophobic surface. The improved composite material with a superhydrophobic surface should preferably include a very thin second-level surface layer under preservation of the hierarchical structure, i. e., show no clogging effect. Furthermore, the improved composite material with a superhydrophobic surface should preferably be substantially free of Substances of Very High Concern (SVHC) such as fluorinated compounds, especially per- and / or polyfluorinated alkyl substances (PFAS), durable and be composed of easily accessible materials.

[0038] The invention is defined in the claims as attached.

[0039] The present invention concerns in its categories a composite material with a superhydrophobic surface, a coating composition for the production of superhydrophobic surfaces, BASF 231086 and a process of producing a composite material with a superhydrophobic surface. Embodiments, aspects or features disclosed for or in connection with one of these categories in each case analogously apply for the other categories of the invention.

[0040] If not stated otherwise, preferred embodiments, aspects or features of the present invention can be combined with other embodiments, aspects or features, especially with other preferred embodiments, aspects or features, irrespectively of the categories to which the embodiments, aspects or features relate. The combination of preferred embodiments, aspects or features with other preferred embodiments, aspects or features in each case again results in preferred embodiments, aspects or features.

[0041] In accordance with the primary object of the invention as stated above, the present invention relates to a composite material with a superhydrophobic surface comprising a) a first-level surface structure with elevations and / or depressions having at least one spatial dimension Admicro in the range of from 1 x 10“3m to 1 x w6m, b) a second-level surface layer covering the first-level surface structure and comprising aggregates of hydrophobic nanoparticles and at least partially crosslinked hydrophobic polymers, wherein i) the mass ratio of the total amount of hydrophobic nanoparticles to the total amount of at least partially crosslinked hydrophobic polymers is in the range of from 1 :5 to 5:1 , ii) the average thickness of the second-level surface layer dnano is in the range of from 25 nm to 5000 nm, iii) the second-level surface layer has elevations having at least one spatial dimension Adnano in the range of from 5 nm to 1000 nm, iv) the fluorine content determined by combustion ion chromatography is less than 1 % by weight, wherein the ratio of at least one of the at least one spatial dimension Admicro to the average thickness of the second-level surface layer dnano is at least 5:1. BASF 231086

[0042] Herein and throughout the present text, the term “superhydrophobic surface” designates a surface exhibiting static water contact angles of at least 140° and droplet roll-off angles of no more than 20° as measured by an optical goniometer using droplets with a volume of 10 pL which is in accordance with definitions found in prior art.

[0043] The superhydrophobic surface preferably exhibits static water contact angles of at least 150° and droplet roll-off angles of no more than 15°, more preferably no more than 10°, as measured by an optical goniometer using droplets with a volume of 10 pL.

[0044] Herein and throughout the present text, the term “hydrophobic” in relation to any defined compound or component such as polymers or nanoparticles designates a compound or component that, when dissolved / dispersed in a suitable solvent, cast onto a flat substrate non-soluble in said solvent, and dried, gives rise to a film that exhibits static water contact angles of at least 80°.

[0045] Preferably, the hydrophobic compound or component when dissolved / dispersed in a suitable solvent, cast onto a flat substrate non-soluble in said solvent, and dried, gives rise to a film that exhibits static water contact angles of at least 90°.

[0046] Herein and throughout the whole text the term “composite material with a superhydrophobic surface” includes composite materials with two or more different surfaces wherein at least one of those surfaces - but not necessarily all surfaces - features a part that is superhydrophobic. E.g., a composite material in the three-dimensional form of a cube has six different sides (surfaces). According to the present invention at least one of those six sides comprises a superhydrophobic surface, but not necessarily the whole side must be superhydrophobic.

[0047] Herein and throughout the present text, the term “polymers” designates, in accordance with common understanding of the term, a material comprising polymer molecules, i. e., molecules “of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass” (IUPAC Goldbook, “macromolecule (polymer molecule)”: https: / / goldbook.iupac.org / terms / view / M03667, retrieved 2027-06-27). Commonly as well as herein and throughout the present text, these units of repetition are called repeating units or (co)monomers. Also in accordance with the general understanding in the field, (co)monomers used as starting material to form polymers are chemically changed upon BASF 231086 polymerisation. E.g., an acrylate monomer as starting material originally comprises a double bond which reacts in propagation in order to form the polymer molecule. The skilled person will understand and account for the different chemical structures of (co)monomers as starting material or within the polymer molecule respectively. Herein and throughout the present text, the number of repetitions of said units is not particularly limited, i. e., the term polymers as used herein also includes oligomers, i. e., molecules consisting of a few repeating units (monomers).

[0048] Herein and throughout the present text, the term “crosslinked [...] polymers” designates polymers wherein a bond, several bonds, or a short sequence of bonds links one polymer molecule to another. These links may take the form of covalent bonds or ionic bonds, preferably the links are covalent bonds. Links are generally formed by reactions involving sites or groups on existing polymer molecules, e. g., via C,H-insertion crosslinking (CHic), or by interactions between existing polymer molecules. Preferably many of these links are formed, and collectively, they connect most individual polymer molecules, thus forming an (insoluble) network of crosslinked polymer molecules.

[0049] The polymers as comprised in the second-level surface layer are defined as “at least partially” crosslinked which means that not every single polymer molecule must be linked to another polymer molecule. It is preferred, that at least 50%, more preferably at least 80%, of the polymer molecules are crosslinked.

[0050] Furthermore and preferably, polymer molecules are also crosslinked to the first-level surface structure and / or to the hydrophobic nanoparticles as present in the composite material.

[0051] The inventors of the present invention have found that the crosslinks between polymer molecules, and preferably also the crosslinks between polymer molecules and the first- level surface structure and / or the crosslinks between polymer molecules and the hydro- phobic nanoparticles, as present in the composite material, lead to a highly hydrophobic polymer network and strengthen the second-level surface layer. The crosslink network of polymers provides for a good mechanical, chemical and thermal resistance of the second- level surface layer and thus beneficially leads to a composite material with a high durability even though said second-level surface layer is very thin. BASF 231086

[0052] The mixture of aggregates of hydrophobic nanoparticles and at least partially crosslinked hydrophobic polymers within the second-level surface layer according to the present invention, in particular the mixture as defined by the mass ratio of the total amount of hydrophobic nanoparticles to the total amount of at least partially crosslinked hydrophobic polymers in the range of from 1 :5 to 5:1 , advantageously provides for a good mechanical, chemical and thermal resistance of the second-level surface layer and / or gives rise to favourable nanoroughness.

[0053] In that regard preferred is a composite material according to the invention, wherein the mass ratio of the total amount of hydrophobic nanoparticles to the total amount of at least partially crosslinked hydrophobic polymers is in the range of from 1 :3 to 3:1 , preferably of from 1 :2 to 2:1 , more preferably of from 1 :1 .4 to 1 .4:1 . It has been found that a balanced mass ratio of the main components of the second-level surface, i. e. hydrophobic nanoparticles and at least partially crosslinked hydrophobic polymers, is beneficial in terms of manufacturing process, durability, creation of nanoroughness and compatibility with different substrates I first-level surface structures.

[0054] The hydrophobic nature of the main components of the surface layer, i. e., the aggregates of hydrophobic nanoparticles and the at least partially crosslinked hydrophobic polymers, lead to an increase in hydrophobicity of the composite material.

[0055] According to the present invention, the fluorine content determined by combustion ion chromatography of the composite material is less than 1 % by weight, preferably is less than 0.1 % by weight, more preferably is less than 0.01 % by weight. In contrast to many state- of-the-art materials with superhydrophobic surfaces, the composite material according to the present invention thus does not rely on the presence of fluorinated compounds which is beneficial since fluorinated compounds are considered as Substances of Very High Concern (SVHC).

[0056] Herein and throughout the whole text the term “fluorine content” designates all kind of free or bound fluorine within the composite material or coating composition, is thus not limited to elemental fluorine but also includes fluorine atoms or ions as present in fluorinated compounds in the form of molecules or salts. The fluorine content can be determined according to state of the art procedures known to the skilled person, in particular can be determined by combustion of the sample with subsequent detection by ion chromatography to detect fluorine, in short: combustion ion chromatography. BASF Coatings GmbH 231086

[0057] Furthermore, the composite material according to the invention is characterized by an average thickness of the second-level surface layer dnano in the range of from 25 nm to 5000 nm. Preferred is a composite material according to the invention, wherein the second-level surface layer has an average thickness dnano in the range of from 50 nm to 2000 nm, preferably from 50 nm to 1000 nm. Herein and throughout the present text, the term “average thickness” designates the thickness of a layer on average and does not mean that the thickness of every individual cross-section of the layer lies within the defined range, i. e., a surface layer with an average thickness in the range of from 25 nm to 5000 may comprise certain parts of the layer wherein the thickness is below 25 nm or above 5000 nm.

[0058] Accordingly, the present invention advantageously provides for a very thin second-level surface layer with an overall average thickness below 5000 nm, preferably below 2000 nm, even more preferably below 1000 nm, which reduces material costs and which preserves the microstructure of the underlying first-level surface structure with elevations and / or depressions having at least one spatial dimension Admicro in the range of from 1 x 10-3m to 1 x 10~6m, i. e., no clogging effect is present in the composite materials according to the present invention. The microstructure can thus still contribute to the overall superhydrophobicity of the surface of the composite material and / or retain its own, primary functionality.

[0059] Preferably, the first-level surface structure has elevations and / or depressions having two or three spatial dimensions Admicro in the range of from 1 x 10-3m to 1 x 10-6m.

[0060] Herein and throughout the whole text the term “elevations” designates three-dimensional structures which are protruding from the underlying surface, wherein those three-dimensional structures may be of any kind of shape.

[0061] Herein and throughout the whole text the term “depressions” designates three-dimensional structures that are set off from the surrounding surface as deepening like valleys, grooves and the like, wherein those three-dimensional structures may be of any kind of shape.

[0062] Even more preferably, the first-level surface structure has elevations with an average vertical distance of elevation peaks to elevation bases Admicro-verticai in the range of from 1 x 10-3m to 1 x i o-6m and / or (preferably “and”) an average next-neighbour lateral distance of adjacent elevations Ad micro-iaterai in the range of from 1 x 1 o-3m to 1 x 1 o-6m.

[0063] Even more preferably, the first-level surface structure has depressions with an average vertical distance of depression peaks to depression bases Admicro-verticai in the range of from BASF 231086

[0064] 1 x 10-3m to 1 x i o-6m and / or (preferably “and”) an average next-neighbour lateral distance of adjacent depressions Ad micro-iaterai in the range of from 1 x 1 O~3m to 1 x 1 O~6m.

[0065] Preferred is a composite material according to the invention, wherein the elevations of the first-level surface structure are homogeneous in height with a standard deviation of corresponding vertical distances of elevation peaks to elevation bases of at most 15%.

[0066] Also preferred is a composite material according to the invention, wherein the depressions of the first-level surface structure are homogeneous in depth with a standard deviation of corresponding vertical distances of depression peaks to depression bases of at most 15%.

[0067] Also preferred is a composite material according to the invention, wherein the elevations and / or depressions of the first-level surface structure are periodically distributed over the surface of the first-level surface structure with a standard deviation of corresponding lateral distances of elevations and / or depressions of at most 15%.

[0068] Said preferred embodiments of the present invention lead to a highly homogenous geometrical structure of the first-level microstructured surface which beneficially contributes to the superhydrophobicity of the composite material and makes production processes more reliable and economically viable. The regular geometry of the first-level microstructure also allows for a good compatibility with the second-level surface layer.

[0069] In that regard, a composite material according to the invention is also preferred wherein the elevations and / or depressions of the first-level surface structure are repeating units of defined three-dimensional arrays of structures, wherein repeating units are in direct contact with neighbouring repeating units or are not in contact with neighbouring repeating units.

[0070] In some cases in the literature three-dimensional structures are designated as “two-dimensional” since repeating units are constantly repeated in one spatial direction so that the impression of two-dimensionality is created. This is inter alia the case for riblet or louver structures. These supposedly two-dimensional structures are explicitly included in the present invention.

[0071] Particularly preferred are repeating units selected from one or more of the following three- dimensional structures: pillars, ridges, grooves, louvers, prisms such as ribs and riblets, pyramids, cones, serpentine-shaped structures, serrated-shaped structures, hexagonal- BASF 231086 shaped structures, diamond-shaped structures, parallelogram-shaped structures, honey- comb-shaped structures, circular-shaped structures, dot-shaped structures, star-shaped structures, line-shaped structures, net-shaped structures, polygonal structures, preferably triangular structures, quadrangular structures, particularly preferably rectangular structures and square structures, pentagonal structures, hexagonal structures, heptagonal structures and octagonal structures, wire-shaped structures, elliptical structures, oval structures and grid-shaped structures, and mixtures or inverted versions or combinations thereof. More preferably the repeating units are pillars or pyramids or prisms such as ribs and riblets.

[0072] It is preferred that the elevations and / or depressions of the first-level surface are repeating units as defined above and which are arranged in arrays of structures along the surface of the first-level surface structure, wherein the geometrical formations are preferably selected from one or more of the following formations: serpentine-shaped formations, serratedshaped formations, hexagonal-shaped formations, diamond-shaped formations, parallelogram-shaped formations, honeycomb-shaped formations, circular-shaped formations, dotshaped formations, star-shaped formations, line-shaped formations, net-shaped formations, polygonal formations, preferably triangular formations, quadrangular formations, particularly preferably rectangular formations and square formations, pentagonal formations, hexagonal formations, heptagonal formations and octagonal formations, wireshaped formations, elliptical formations, oval formations and grid-shaped formations, and mixtures or inverted versions or combinations thereof.

[0073] The second-level surface layer according to the invention has elevations having at least one spatial dimension Adnano in the range of from 5 nm to 1000 nm. Preferred is a composite material according to the invention, wherein the second-level surface layer has elevations having at least one spatial dimension Adnano in the range of from 10 to 500 nm, preferably in the range of from 10 nm to 250 nm, more preferably elevations having an average vertical distance of elevation peaks to elevation bases Adnano-verticai in the range of from 10 nm to 250 nm. In other words: the second-level surface layer is “nanorough” and not flat. By combining this nanoroughness with the hydrophobic nature of the main components of the surface layer, the surface of the composite material becomes particularly superhydrophobic.

[0074] The vertical distance of elevation peaks to elevation bases of the second-level surface layer is determined based on the local geometry of the first-level surface structure underneath the respective elevations.

[0075] According to the present invention, the ratio of at least one of the at least one spatial dimension Admicro of the elevations and / or depressions in the first-level surface structure to BASF Coatings GmbH 231086 the average thickness of the second-level surface layer dnano is at least 5:1 . Preferred is a composite material according to the invention, wherein the ratio of the average vertical distance of elevation peaks to elevation bases Admicro-verticai of the elevations in the first-level surface structure to the average thickness of the second-level surface layer dnano is at least 5:1 and / or (preferably “and”) wherein the ratio of the average next-neighbour lateral distance of adjacent elevations Admicro-iaterai of the first-level surface structure to the average thickness of the second-level surface layer dnano is at least 5:1 . This applies to depressions in the first-level surface structure vice versa.

[0076] The composite material according to the present invention is thus characterized by a hierarchical surface structure, wherein the elevations of the first-level microstructured surface are covered by a thin second-level nanolayer without clogging the voids, gaps and / or spaces that are spanned by the elevations of the first-level. This leads to highly superhydrophobic properties of the overall composite material surface since i) the first-level microstructured surface and ii) the second-level nanolayer both contribute roughness to the effect. This applies to depressions in the first-level surface structure vice versa.

[0077] Preferred is a composite material according to the invention, wherein the ratio of at least one of the at least one spatial dimensions Adnano of the elevations in the second-level surface layer, preferably the average vertical distance of elevation peaks to elevation bases Ad nano-vertical to the average thickness ofthe second-level surface layerdnano, is at least 1 :10, preferably is at least 1 :5.

[0078] Accordingly, the geometric structure of the second-level surface layer is finely balanced in terms of its average thickness with regard to its elevation structures. The so called “nanoroughness” is incorporated by the elevations in the second-level surface layer without sacrificing any mechanical stability of the second surface layer.

[0079] Preferred is a composite material according to the invention, wherein at least 50%, preferably at least 70%, more preferably at least 80% of the surface of the first-level surface structure is covered with the second-level surface layer. Even more preferred is a composite material according to the invention, wherein at least 90%, preferably at least 95%, of the surface ofthe first-level surface structure is covered with the second-level surface layer.

[0080] Said high rate of surface coverage is beneficial in terms of reliability of superhydrophobicity of the overall surface of the composite material and specifically, the stability of the superhydrophobicity in case of prolonged contact with water, since large areas of a hierarchically BASF 231086 structured surface with microstructures and nanostructures on top of each other synergistically contribute to superhydrophobicity, and since the higher the rate of coverage, the less probable it becomes that, e. g., a particular water droplet will come into contact with a region not covered with the second-level surface layer, i. e., a region that may not be superhydrophobic.

[0081] The composite material according to the present invention preferably has anti-icing and / or easy-to-clean and / or self-cleaning and / or anti-fogging and / or anti / non-fouling and / or airretaining properties. Without wishing to be bound by theory, this is an effect of the superhydrophobicity as described above and below, optionally further boosted by specific first- level structures such as structures already known for these effects, including common airretaining structures as disclosed in, e. g., EP 2 822 704 B1. The latter have also been disclosed as exhibiting anti / non-fouling properties (see M. Mail et al., Beilstein J. Nanotech- nol. 2022, 13, 1370-1379; https: / / doi.org / 10.3762 / bjnano.13.113).

[0082] Accordingly, preferred is a composite material according to the invention, wherein the composite material is a drag-reducing material, in particular a riblet material. Even more preferred the composite material is a component of aircrafts, trains, ships or other means of transportation, turbines including wind turbines, gas turbines, turbines in pumps, turbines in hydroelectric and tidal power plants, propellers, aerofoils, pipes, hydrofoils and / or sports equipment such as surfboards, stand-up paddle boards, ski or sledges.

[0083] Also preferred is a composite material according to the invention, wherein the composite material is an anti-icing and / or easy-to-clean and / or self-cleaning and / or anti-fogging material, preferably an optical material or a riblet material. Even more preferred the composite material is a component of indoor lightings, outdoor lightings, optical devices, lidar sensors, radar sensors, laser-based systems, heads-up displays, augmented / virtual reality device, aircrafts, trains, ships or other means of transportation, turbines including wind turbines, gas turbines, turbines in pumps, turbines in hydroelectric and tidal power plants, propellers, aerofoils, pipes, hydrofoils, windows, solar cells, and / or sports equipment such as surfboards, stand-up paddle boards, ski or sledges.

[0084] Further preferred is a composite material according to the invention, wherein the composite material is an air-retaining material, preferably also an anti / non-fouling material. Even more preferred the composite material is a component of pipes, offshore structures, surfboards, ship hulls, ship propellers, hydrofoils, underwater turbines, pumps, hydroelectric power plants, tidal power plants, aquariums, swimming pools, water containers or water tanks including ships' ballast water tanks, bioreactors, fermenters. BASF Coatings GmbH 231086

[0085] Further preferred is a composite material according to the invention, wherein the composite material is a porous material. Even more preferred the composite material is a membrane, a woven or non-woven fabric and / or paper.

[0086] Accordingly, the composite material according to the present invention is very versatile and suitable fora wide variety of different applications. It can serve as (i) drag-reducing material, (ii) anti-icing and / or easy-to-clean and / or self-cleaning and / or anti-fogging material, (iii) airretaining material, anti / non-fouling material and (iv) porous material.

[0087] A composite material with a superhydrophobic surface according to any of the preceding claims, wherein

[0088] - the composite material is a component of aircrafts, trains, ships or other means of transportation, turbines including wind turbines, gas turbines, turbines in pumps, turbines in hydroelectric and tidal power plants, propellers, pipes or sports equipment such as surfboards, stand-up paddle boards, ski or sledges, or

[0089] - the composite material is a component of indoor lightings, outdoor lightings, optical devices, lidar sensors, radar sensors, laser-based systems, heads-up displays, aug- mented / virtual reality devices, or

[0090] - the composite material is a component of pipes, offshore structures, surfboards, ship hulls, ship propellers, hydrofoils, underwater turbines, pumps, hydroelectric power plants, tidal power plants, aquariums, swimming pools, water containers or water tanks including ships' ballast water tanks, or

[0091] - the composite material is a membrane, a woven or non-woven fabric, and / or paper.

[0092] In accordance with the primary objective of the invention as stated above, the present invention relates to a coating composition for the production of superhydrophobic surfaces, comprising BASF 231086 a) a liquid phase comprising i) an organic solvent, and ii) dissolved and / or emulsified in the liquid phase, one or more crosslinkable and hydrophobic polymers, wherein the one or at least one of the more than one crosslinkable and hydrophobic polymers comprises one or more active (co-)monomers as crosslinking moiety, capable of forming chemical bonds to neighbouring polymers and / or organic substrates and / or hydrophobic nanoparticles, b) dispersed in the liquid phase one or more hydrophobic nanoparticles, wherein

[0093] - the composition contains less than 1 % by weight of fluorine determined by combustion ion chromatography,

[0094] - the mass ratio of the total amount of hydrophobic nanoparticles to the total amount of crosslinkable hydrophobic polymers in the coating composition is in the range of from 1 :5 to 5:1.

[0095] It has been found by the inventors of the present invention that the above-defined coating composition is particularly suitable for superhydrophobic post-treatment of microstructured surfaces and reliably results in a composite material with a superhydrophobic surface, preferably in a composite material with a superhydrophobic surface as defined above or below.

[0096] The coating composition according to the present invention can be applied by a wide variety of different coating processes as described in more detail below. It is compatible with a wide variety of different microstructured substrates, and is in particular suitable for covering a first-level surface structure with elevations and / or depressions having at least one spatial dimension dmicro in the range of from 1 x 10-3m to 1 x w6m. It has been found that a wide variety of substrates, materials and / or surfaces can be reliably and reproducibly covered by the coating composition according to the present invention, each time resulting in a second-level surface layer covering the first-level surface structure and comprising aggregates of hydrophobic nanoparticles and at least partially crosslinked hydrophobic poly- BASF 231086 mers. The high share of highly hydrophobic material within the coating composition guarantees for capillary repulsion to block water from entering the voids between the first-level surface structure when the coating composition is applied thereon.

[0097] The inventors have thus identified a coating composition as defined above and with preferred embodiments as defined below, wherein said coating composition allows for a thin coating showing good adhesion to the microstructured substrate below and good cohesion within the coating itself to achieve mechanical durability. It was a particular challenge that the coating composition needs to be selected and / or tailored to exhibit strong interaction forces. Hydrophobic materials typically feature weak intermolecular interaction forces, e. g., alkanes essentially feature only Van-der-Waals forces. This is why most state-of-the-art systems up to today rely on the utilization of strongly hydrophilic materials such as epoxy resins to achieve mechanical durability. Accordingly, while hydrophobicity is desired, this is in conflict with the requirement forstrong interactions. To circumvent this, chemical bonds needed to be introduced. To achieve this, the polymers of the coating composition are crosslinkable, i. e., able to form crosslinks with themselves and should preferably also chemically attach to the substrate and the nanoparticles.

[0098] An important aspect of the present invention pertains to a coating composition, wherein the one or at least one of the more than one crosslinkable and hydrophobic polymers comprises one or more active (co-)monomers as crosslinking moiety, capable of forming chemical bonds to neighbouring polymers and / or organic substrates and / or hydrophobic nanoparticles. The term “active” designates that the crosslinking moiety in most cases acts as the active and / or activatable part in the crosslinking mechanism. Said activity can be dormant and only be triggered by outer stimuli such as irradiation, heat, catalysts and / or the presence of a (passive) reaction partner. E. g., in the case of C,H-insertion crosslinking (CHic reaction) the one or more active (co-)monomers as crosslinking moiety are preferably (co-)monomers with groups that are, upon photochemical and / or thermal activation, able to insert into C-H bonds of neighbouring entities to crosslink the polymer and / or to bind to surfaces, such as those of the first-level surface structures and / or the hydrophobic nanoparticles.

[0099] Correspondingly, the coating composition according to present invention contains bifunctional polymers since the polymers are i) hydrophobic and ii) crosslinkable. In contrast to state of the art coating compositions as inter alia described in CN 116 285 666 A or WO 2008 / 106494 A1 , crosslinking of a coating composition according to present invention does not require an additional low molecular weight crosslinking agent, also called curing agents or initiators. BASF 231086

[0100] It is preferred that the coating composition according to present invention is free of any low molecular weight crosslinking agents, also called curing agents or initiators.

[0101] Said low molecular weight crosslinking agents (also called curing agents or initiators) usually have a molecular weight below 1000 g / mol. Low molecular weight crosslinking agents are thus clearly distinguishable from the crosslinkable and hydrophobic polymers as present in the coating compositions according to the present invention which usually feature an average molecular weight Mw of more than 1800 g / mol.

[0102] It is particularly preferred that the coating composition according to present invention is free of any low molecular weight crosslinking agents which are based on tin such as dibutyltin dilaurate which are for example used in the coating compositions described in CN 116 285 666 A. Said compounds, in particular dibutyltin dilaurate, are disadvantageous as they feature severe hazards, toxicity and a hard to control reactivity.

[0103] It is also particularly preferred that the coating composition according to present invention is free of any low molecular weight crosslinking agents selected from the group of peroxide, peroxy compounds, benzoin derivatives, acetophenone derivatives, benzilketals, ahydrox- yalkylphenones, a -aminoalkylphenones, O-acyl a-oximinoketones, acylphosphine oxides, acylphosphonates, thiobenzoic S-esters, azo compounds, azide compounds, triazines, compounds with Si-Si bonds, biimidazoles, quinones, benzophenones, xanthones, thioxanthones, ketocoumarins, aromatic 1 ,2 diketones and phenylglyoxylates which are for example used in the coating compositions described in WO 2008 / 106494 A1. Said compounds are disadvantageous as they feature severe hazards, toxicity and a hard to control reactivity.

[0104] Preferred is a coating composition according to the invention, wherein the composition contains less than 0.1 % by weight of fluorine determined by combustion ion chromatography, preferably less than 0.01 % by weight of fluorine. According to this preferred embodiment of the present invention, the presence of Substances of Very High Concern (SVHC) such as fluorinated compounds, especially per- and / or polyfluorinated alkyl substances (PFAS), is avoided which is environmentally and economically beneficial.

[0105] Also preferred is a coating composition according to the invention, wherein the mass ratio of the total amount of hydrophobic nanoparticles to the total amount of crosslinkable hydrophobic polymers in the coating composition is in the range of from 1 :3 to 3:1 , preferably of from 1 :2 to 2:1 , more preferably of from 1 :1 .4 to 1 .4:1 . These preferred mass ratios allow BASF Coatings GmbH 231086 for a reliable and reproducible formation of a highly stable, nanorough coating or layer on microstructured surfaces which leads to second-level surface structures as defined above.

[0106] Further preferred is a coating composition according to the invention, wherein at least 50% by weight, preferably at least 70% by weight, more preferably at least 75% by weight, of at least one (co)monomer used for making the crosslinkable and hydrophobic polymers are obtained from renewable, plant-based raw materials, preferably are obtained from vegetable oils, more preferably are obtained from rapeseed oil. According to this preferred embodiment of the present invention, the carbon footprint of the coating composition can be considerably be reduced without sacrificing any of the beneficial properties of the coating composition.

[0107] Another preferred aspect of the present invention pertains to a coating composition, wherein the one or at least one of the more than one crosslinkable and hydrophobic polymers comprises one or more hydrophobic side chains. As already stated above and in contrast to many state of the art coating compositions, the inventors have identified that the presence of hydrophobic polymers which are best and feasibly created by incorporation of hydrophobic side chains contributes to the superhydrophobicity of the second-level surface structure obtained by application of the coating composition. Preferably, the one or more hydrophobic side chains may also serve as target functionalities for crosslinking and thus contribute to the stability and durability of resulting coatings or layers.

[0108] The one or more hydrophobic side chains are preferably selected from the group consisting of hydrocarbon groups and siloxanes, more preferably are selected from the group consisting of

[0109] - aromatic groups,

[0110] - linear, cyclic and / or branched alkyl groups,

[0111] - linear, cyclic and / or branched alkenyl groups,

[0112] - linear, cyclic and / or branched alkynyl groups, and

[0113] - linear, cyclic and / or branched alkyl-, alkenyl or alkynyl groups containing heteroatoms such as O, N, S, in particular alkoxy and poly(alkoxy) groups such as polypropylene oxide) or poly(butylene oxide) (polyTHF). BASF 231086

[0114] - hydrocarbon-functionalised siloxanes, preferably alkyl siloxanes, more preferably alkyl siloxanes comprising at least one RR’SiO unit, wherein R and R’ are independently selected from the group of linear and branched alkyls.

[0115] Preferably the one or more active (co-)monomers as crosslinking moiety, capable of forming chemical bonds to neighbouring polymers and / or organic substrates and / or hydrophobic nanoparticles are capable of forming chemical bonds by activation with radiation, in particular UV irradiation, sunlight or electron beams, and / or activation with heat in a state where the coating composition has a viscosity of at least 106mPa-s, preferably of at least 108mPa-s, more preferably of at least 101° mPa-s, i. e. the crosslinking ability is retained even at relatively high viscosities.

[0116] In a particular preferred embodiment of the present invention the one or more active (co-)monomers as crosslinking moiety are capable of forming chemical bonds by insertion into C-H bonds via C,H-insertion crosslinking (CHic). Said reaction is known to form stable covalent bonds upon simple activation procedures and thus reliably leads to a stable network of interconnected polymers which in consequence leads to highly robust and durable surface layers.

[0117] In yet another preferred embodiment of the present invention the one or more active (co-)monomers as crosslinking moiety, capable of forming chemical bonds to neighbouring polymers and / or organic substrates and / or hydrophobic nanoparticles comprise at least one functional group selected from the group consisting of

[0118] - C,H-insertion crosslinking (CHic) active groups, preferably substituted benzophenones, anthraquinones, thioxanthones, sulfonyl azides, aromatic azides, diazomethylenes with ester, sulfonyl and / or aromatic substituents, or other moieties capable of forming carbene, nitrene, or biradicaloid intermediates upon thermal or photochemical activation,

[0119] - azides,

[0120] - vinylic unsaturated groups,

[0121] - epoxy groups,

[0122] - isocyanate groups, BASF 231086

[0123] - carboxylic acid anhydride groups, and

[0124] - organic carbonates.

[0125] It is preferred that the one or more active (co-)monomers as crosslinking moiety constitutes 0.1 % to 20% by weight, preferably 1 % to 15% by weight, more preferably 2% to 10% by weight of the one or of at least one of the more than one crosslinkable and hydrophobic polymers.

[0126] It is also and particularly preferred that the coating composition according to the present invention comprises crosslinkable and hydrophobic polymers comprising

[0127] - one or more hydrophobic side chains, preferably hydrophobic side chains as defined above or below, and

[0128] - one or more active (co-)monomers as crosslinking moiety, preferably one or more active (co-)monomers as crosslinking moiety as defined above or below.

[0129] We note here, that the crosslinking process according to the present invention is not limited to the formation of crosslinks between polymers, but also and preferably pertains to crosslink formation between i) polymers and nanoparticles, ii) polymers and substrate (such as the first-level surface structures as defined above and below) and iii) nanoparticles and nanoparticles. Preferably, multiple crosslinks connect individual polymer molecules and / or nanoparticles to multiple targets such as other polymer molecules, nanoparticles, and / or substrate. Preferably, this leads to, i. a., individual polymer molecules being linked to the substrate and nanoparticles.

[0130] Another preferred aspect of the present invention pertains to a coating composition, wherein the one or at least one of the more than one crosslinkable and hydrophobic polymers has an average molecular weight Mw of more than 1800 g / mol.

[0131] Accordingly, the one or at least one of the more than one crosslinkable and hydrophobic polymers is not just an oligomer with very few repeating units having an average molecular weight Mw of less than 1800 g / mol such as, e. g., present in a two- or three-component epoxy resin primarily based on a monomer mixture. Preferably one or at least one of the more than one crosslinkable and hydrophobic polymers comprises at least 4, more preferably at least 6, even more preferably at least 8 repeating units. Said above-defined average BASF 231086 molecular weight Mwof more than 1800 g / mol is beneficial in terms of processability, crosslinking ability, viscosity and compatibility of the coating composition. Crosslinking can thus take place without low-molecular-weight reactive compounds, and therefore, handling of volatile, reactive compounds such as low-molecular-weight acrylates or isocyanates, many of which are CM R substances and / or allergens, is only necessary during polymer synthesis, which can take place in a well-controlled environment. Users of the coating composition on the other hand are not exposed to these critical substances and are therefore not at risk from them.

[0132] Preferred is a coating composition according to the present invention, wherein the one or at least one of the more than one crosslinkable and hydrophobic polymers is obtained from polymerisation of one or more (co-)monomers, preferably from radical polymerisation, more preferably from free-radical polymerisation.

[0133] Also preferred is a coating composition according to the present invention, wherein the one or at least one of the more than one crosslinkable and hydrophobic polymers comprises at least one (meth)acrylate (co-)monomer or at least one (meth)acryl amide (co-)monomer.

[0134] More preferably the one or at least one of the more than one crosslinkable and hydrophobic polymers comprises i) at least one (meth)acrylate (co-)monomer with a hydrophobic group, preferably a hydrocarbon group or a siloxane or at least one (meth)acryl amide (co-)monomer with a hydro- phobic group, preferably a hydrocarbon group or a siloxane, and ii) at least one (meth)acrylate (co-)monomer with a crosslinking functional group capable of forming chemical bonds to neighbouring polymers and / or organic substrates and / or hydrophobic nanoparticles or at least one (meth)acryl amide (co-)monomer with a crosslinking functional group capable of forming chemical bonds to neighbouring polymers and / or organic substrates and / or hydrophobic nanoparticles.

[0135] In another preferred embodiment of the coating composition according to the present invention the one or at least one of the more than one crosslinkable and hydrophobic polymers is a long-chain alkyl acrylate polymer comprising 0.1 to 20% by weight, preferably 1 to 15% by weight, more preferably 2 to 10% by weight, of one or more active (co-)mono- mers as crosslinking moieties capable of forming chemical bonds by insertion into C-H bonds via C,H-insertion cross-linking (CHic). BASF Coatings GmbH 231086

[0136] A coating composition according to the present invention is particularly preferred, wherein the one or at least one of the more than one crosslinkable and hydrophobic polymers comprises at least one, preferably at least two, of the following (meth)acrylate (co-)monomers:

[0137] - CH2=CR1-C(O)-O-CnH2n+1, with

[0138] R1= H, CH3, alkyl radical, preferably H or CHs, and n > 12, preferably n > 18, more preferably n = 22,

[0139] - substituted benzophenones, preferably 4-methacryloyloxy benzophenone,

[0140] - substituted diazomethylenes with one ester and one aromatic substituents, preferably 2- (2-diazo-(4-nitrophenyl) acetoxy) ethyl methacrylate (4-Nitro-PEDAz).

[0141] A coating composition according to the present invention is more particularly preferred, wherein the one or at least one of the more than one crosslinkable and hydrophobic polymers comprises as (meth)acrylate (co-)monomers: i) CH2=CR1-C(O)-O-CnH2n+i , with

[0142] R1= H, CH3, alkyl radical, preferably H or CHs, and n > 12, preferably n > 18, more preferably n = 22, and ii-1) substituted benzophenones, preferably 4-methacryloyloxy benzophenone, or ii-2) substituted diazomethylenes with one ester and one aromatic substituents, preferably 2-(2-diazo-(4-nitrophenyl) acetoxy) ethyl methacrylate (4-Nitro-PEDAz). BASF 231086

[0143] It has been found that substituted diazomethylenes with one ester and one aromatic substituents are particularly suitable crosslinking functionalities for forming crosslinks between polymers under activation with sun light.

[0144] A coating composition according to the present invention is even more particularly preferred, wherein the one or at least one of the more than one crosslinkable and hydrophobic polymers comprises the following two (meth)acrylate (co-)monomers:

[0145] - CH2=CR1-C(O)-O-CnH2n+i, with

[0146] R1= H, CH3, alkyl radical, preferably H or CHs, and n > 12, preferably n > 18, more preferably n = 22, and

[0147] - 4-methacryloyloxy benzophenone, wherein preferably the molar fraction of 4-methacryloyloxy benzophenone within the one or more crosslinkable and hydrophobic polymers is in a range of from 1 % to 15%, more preferably is in a range of from 3% to 10%.

[0148] Said above mentioned embodiments of crosslinkable and hydrophobic polymers pertaining to preferred (co-)monomers have been found to beneficially contribute to the hydrophobic properties of the polymers and to exhibit favourable performance in forming crosslinks with each other and also with the substrate and / or nanoparticles.

[0149] Preferred is a coating composition according to the present invention, wherein the one or at least one of the more than one hydrophobic nanoparticles is thermally stable until a temperature of at least 100 °C, preferably of at least 300 °C. Herein and throughout the whole text the term “thermally stable” designates that no phase transition, deformation, decomposition etc. takes place in the hydrophobic nanoparticles up to a defined temperature. BASF 231086

[0150] It is also preferred that the one or at least one of the more than one hydrophobic nanoparticles according to the invention is a surface-functionalized nanoparticle comprising a particle core and a particle surface.

[0151] The particle core of the surface-functionalized nanoparticle comprising a particle core and a particle surface preferably comprises at least 70% by weight of at least one inorganic compound, preferably at least 90% by weight, more preferably at least 95% by weight, even more preferably at least 97% by weight, wherein more preferably the inorganic compound is selected from the group consisting of metals, metal oxides, ceramics, silica, carbon and mixtures thereof; even more preferably the inorganic compound is selected from the group consisting of BeO, TiC>2, ZrC>2, MoSi2, WC, ZnO, BN, B4C, AI2O3, AIN, SiC, SisN4, SiC>2 and mixtures thereof; most preferably the inorganic compound is selected from the group consisting of TiC>2, ZrC>2, AI2O3, SiC>2 and mixtures thereof.

[0152] The particle surface of the surface-functionalized nanoparticle comprising a particle core and a particle surface preferably comprises one or more hydrophobic surface functionalities. Preferably the one or more hydrophobic surface functionalities are selected from the group consisting of hydrocarbon groups and siloxanes, more preferably selected from the group consisting of

[0153] - aromatic groups,

[0154] - linear, cyclic and / or branched alkyl groups,

[0155] - linear, cyclic and / or branched alkenyl groups,

[0156] - linear, cyclic and / or branched alkynyl groups,

[0157] - linear, cyclic and / or branched alkyl-, alkenyl or alkynyl groups containing heteroatoms such as O, N, S, in particular alkoxy and poly(alkoxy) groups such as polypropylene oxide) or poly(butylene oxide) (polyTHF), and

[0158] - hydrocarbon-functionalised siloxanes, preferably alkyl siloxanes, more preferably alkyl siloxanes comprising at least one RR’SiO unit, wherein R and R’ are independently selected from the group of linear and branched alkyls. BASF 231086

[0159] The particle surface of the surface-functionalized nanoparticle comprising a particle core and a particle surface preferably comprises one or more surface crosslinking target functionalities, preferably the one or more surface crosslinking target functionalities are capable of forming chemical bonds to neighbouring polymers, more preferably the one or more surface crosslinking target functionalities are at least partially identical to the one or more hydrophobic surface functionalities, even more preferably the one or more surface crosslinking target functionalities are the same as the one or more hydrophobic surface functionalities.

[0160] Even more preferably the particle surface of the surface-functionalized nanoparticle comprising a particle core and a particle surface comprises one or more hydrophobic surface functionalities, preferably those hydrophobic surface functionalities as defined above, and one or more surface crosslinking target functionalities, preferably those surface crosslinking target functionalities as defined above. As stated above the one or more surface crosslinking target functionalities are preferably the same as the one or more hydrophobic surface functionalities.

[0161] Particularly preferred hydrophobic nanoparticles according to the invention are orga- nosilane (HMDS)-treated fumed silica nanoparticles with a high specific surface area and pronounced hydrophobicity which preferably are also very easy to disperse and / or colorless. Examples of such a particularly preferred hydrophobic nanoparticles are AEROSIL® E 812 and AEROSIL® E 972 available from Evonik.

[0162] Accordingly, the hydrophobic nanoparticles according to the invention are hydrophobic, wherein said hydrophobicity is preferably obtained upon surface-functionalization with hydrophobic surface functionalities as described above. Furthermore, the hydrophobic nanoparticles are preferably also capable of forming crosslinks, such as those formed by virtue of crosslinking reactions binding to the crosslinking target functionalities as described above, in particular crosslinks to polymers, wherein crosslinking preferably takes place via C,H-insertion cross-linking (CHic). Said features of hydrophobic nanoparticles allow for i) highly hydrophobic and ii) highly stable properties of the resulting second-level surface layer upon application of the coating composition, which makes the coating composition suitable for a wide variety of applications including the manufacturing of composite materials with a superhydrophobic surface with good drag reduction, easy-to-clean, self-cleaning, anti-fogging air-retaining and / or anti / non-fouling properties.

[0163] Also preferred is a coating composition according to the present invention, wherein the organic solvent BASF 231086

[0164] - is liquid at a temperature in the range of from 15 °C and 55 °C, preferably in the range of from 15 °C to 39 °C, and / or (preferably “and”)

[0165] - comprises one or more solvents selected from the group consisting of substituted and non-substituted linear, branched, and cyclic alkanes, alkenes, alkynes, chlorinated alkanes, alcohols, substituted and non-substituted aromatic and heteroaromatic compounds, preferably selected from the group consisting of linear, branched, and cyclic alkanes and substituted or non-substituted aromatic compounds which are liquid at a temperature in the range of from 15 °C and 55 °C, more preferably selected from the group consisting of linear, branched, and cyclic alkanes containing 5 to 16 carbon atoms and aromatic compounds comprising one benzene ring such as benzene, toluene, xylene isomers and mesitylene.

[0166] Also preferred is a coating composition according to the present invention, wherein

[0167] (a) the concentration of the total amount of hydrophobic nanoparticles, preferably surface- functionalized hydrophobic nanoparticles with a particle core comprised of an inorganic compound selected from the group consisting of TiC>2, ZrC>2, AI2O3, SiC>2 and mixtures thereof, is in a range of from 0.1 g / L to 100 g / L, preferably 1 to 100 g / L, more preferably 5 g / L to 25 g / L, based on the total volume of the coating composition, and / or

[0168] (b) the concentration of the total amount of crosslinkable polymers in the coating composition is in a range of from 0.1 g / L to 100 g / L, preferably 1 to 100 g / L, 5 g / L to 25 g / L, based on the total volume of the coating composition.

[0169] In accordance with the primary objective of the invention as stated above, the present invention relates to a process of producing a composite material with a superhydrophobic surface, preferably a composite material with a superhydrophobic surface as defined above or below, at least comprising the following steps: BASF 231086 a) preparing or providing a coating composition according to the invention, b) wetting the surface or parts of the surface of a material having a first-level surface structure with elevations and / or depressions having at least one spatial dimension Admicro in the range of from 1 x 10“3m to 1 x 1 o-6m, with the prepared or provided coating composition, so that the first-level surface structure is covered by the coating composition, c) drying the wetted material, so that organic solvent of the coating composition evaporates, d) at least partially crosslinking the one or more crosslinkable and hydrophobic polymers so that a composite material with a superhydrophobic surface is obtained.

[0170] Preferably the step of at least partially crosslinking the one or more crosslinkable and hydrophobic polymers is initiated by radiation and / or heat.

[0171] Preferred is a process according to the present invention, wherein the step of wetting the surface of a material having a first-level surface structure with elevations and / or depressions having at least one spatial dimension Admicro in the range of from 1 x 10-3m to 1 x 10-6m with the prepared or provided coating composition is carried out by any object-coating method such as dip coating or spray coating, and / or roll-to-roll coating method such as Mayer rod coating, slot-die coating, curtain coating or gravure coating, preferably by dip coating and / or spray coating, more preferably by dip coating.

[0172] Also preferred is a process according to the present invention, wherein the step of drying the wetted material is carried out by drying in air, preferably for a time in the range of from 0.1 s to 1 h, preferably drying in air without any additional technical means. Accordingly, the process does not consume actively supplied energy which makes it environmentally and economically attractive.

[0173] Furthermore, the overall process and the individual process steps according to the present invention are very simple and do not require for complex machinery, thus allowing for practical handling in a wide variety of applications and with different kinds of material. The process according to the present invention also has a much lower energy consumption than processes known in the art which usually require hours of heating in order to obtain a second-level surface structure. BASF 231086

[0174] The process as described above allows for the production of very thin, nanorough, and strongly hydrophobic coating layers. As the coating layer is very thin, the first-level surface structure remains unchanged, i. e., is not levelled or filled, and many of its functionalities are retained. The coating layer synergistically adds the superhydrophobic function of the composite material surface. Moreover and favourably, the step of crosslinking the one or more crosslinkable and hydrophobic polymers facilitates and enhances durability of the second-level surface layer. These resulting (nano)layers can be used on various substrates for various applications, e. g., for Salvinia effect, anti-icing / easy-to-clean riblets or optics, and are generally useful for adding I enhancing superhydrophobicity on top of another functionality or surface structure obtained by first-level (micro)structures.

[0175] The resulting composite material with a superhydrophobic surface is hierarchically structured as it features suitable first-level structures, e.g., gas-retaining structures known from literature, which can be made according to any suitable process and any suitable material, preferably by continuous roll-to-roll processes.

[0176] Further preferred is a process according to the present invention, wherein the coating composition according to the present invention is prepared by completely or partially dissolving the one or more crosslinkable and hydrophobic polymers in the organic solvent, preferably under stirring, at a temperature in the range from 30 °C to 60 °C, followed by addition of the hydrophobic nanoparticles, preferably under stirring.

[0177] Also preferred is a process according to the present invention, further comprising one or more of the following additional steps:

[0178] - shaking, stirring, and / or otherwise mixing the prepared or provided and optionally stored coating composition before the step of wetting,

[0179] - removing dust and / or other contaminations from the surface of the material having a first- level surface structure with elevations and / or depressions having at least one spatial dimension Admicro in the range of from 1 x 10“3m to 1 x w6m, preferably by washing with water and / or at least one solvent before the step of wetting, more preferably by rinsing with and / or by immersion in water and / or at least one solvent, preferably a solvent selected from isopropanol, acetone and ethanol. BASF Coatings GmbH 231086

[0180] In some cases it can be beneficial to wash the composite material with a solvent, preferably by a solvent as present in the coating composition, after the step of at least partially crosslinking. Said step of at least partially crosslinking may also be identical to the step of drying.

[0181] Also preferred is a process according to the present invention, wherein the step of wetting the surface or parts of the surface of the material having a first-level surface structure with elevations and / or depressions having at least one spatial dimension dmicro in the range of from 1 x 10-3m to 1 x 1 O~6m with the prepared or provided coating composition is carried out by dip coating the material into the prepared or provided coating composition with a retraction speed of at least 0.05 m / min, preferably of at least 0.15 m / min, more preferably at least 0.5 m / min.

[0182] In accordance with the primary objective of the invention as stated above, the present invention further relates to the use of a coating composition according to the present invention for the production of a superhydrophobic surface.

[0183] EXAMPLES

[0184] The following examples according to the present invention are meant to further explain and illustrate the present invention without limiting its scope.

[0185] 1. Coating composition for the production of superhydrophobic surfaces:

[0186] 1.1 Materials:

[0187] The following materials have been used as preferred embodiments of components in the coating composition. We note that any other materials fulfilling the definitions as set forth in the claims are also suitable.

[0188] Hydrophobic nanoparticles: fumed silica, i. e., silica nanoparticles, post-treated with hexa- methyldisilazane (HMDS) to achieve hydrophobic surface functionalities, Aerosil E 812 ex Evonik. According to the manufacturer, the BET specific surface area is about 230- 290 m2 / g. Own measurements by transmission electron microscopy show that primary particles of Aerosil E 812 have an average diameter of 10 ± 4 nm.

[0189] Crosslinkable and hydrophobic polymers: Poly(behenyl acrylate co (4-methacryloyloxy benzophenone)) (P(BehAc-co-MABP) with a molar fraction of MABP = 5% based on the BASF Coatings GmbH | 231086 total amount of substance, prepared by free-radical polymerisation using azobisisobu- tyronitrile (AIBN), having an average molecular weight Mw in the range of 25 to 150 kDa depending on the reaction conditions of the free-radical polymerisation and with the following general formula (I):

[0190] In one example, P(BehAc-co-MABP) was prepared by free-radical polymersiation as follows: Behenyl acrylate (50 g, available from BASF labelled “Behenyl Acrylate 22 F (BEA 22 F)”, used as received) was dissolved in chloroform (50 mL) and flushed over neutral alumina to remove any inhibitor. Afterwards, chloroform was removed at reduced pressure, followed by drying in high vacuum over night. The solid was combined with 4-methacrylo- yloxy benzophenone (MABP; synthesised according to literature; 1.75 g) and redissolved in toluene (100 mL) at 60 °C in a three-neck flask. The solution was purged with nitrogen for 20 min before closing the flask to retain a nitrogen atmosphere. The solution was retained at about 58 °C. AIBN (0.43 g) was dissolved in toluene (5 mL) and the mixture was stirred for 48 h. According to reaction control by thin-layer chromatography (cyclohex- ane / ethyl acetate 20:1 ; staining with KMnC ), this corresponded to full monomer conversion. The reaction mixture was then slowly added to warm acetone (45 °C; 2 L). The precipitate was filtered off and dried in high vacuum over night. Characterisation by DSC and NMR confirmed that the opaque, crystalline solid obtained was P(BehAc-co-MABP) with a molar fraction of MABP of about 5%.

[0191] According to the manufacturer, parts of the behenyl acrylate used (BASF, “Behenyl Acrylate 22 F (BEA 22 F)”) are from biogenic material such as plant-based material, preferably from vegetable oil such as canola oil. This can be shown by C-14 analysis. Preferably, the part from biogenic material is the behenyl chain. Accordingly, both the behenyl acrylate itself and the P(BehAc-co-MABP) comprise a share of material from renewable sources. When all the behenyl chains in pure behenyl acrylate are from renewable sources, this BASF 231086 corresponds to a share of atoms of at least about 81 % by mass. The share in the P(BehAc- co-MABP) can be calculated on this basis.

[0192] 1 .2 Preparation of the coating composition according to the invention (CC-I):

[0193] A coating composition according to the present invention was prepared by dissolving crosslinkable and hydrophobic polymers in toluene at a temperature of about 40 to 60 °C followed by adding and dispersing hydrophobic nanoparticles under stirring, each in concentrations of 10 g / L or 15 g / L respectively. The mass ratio of the total amount of hydrophobic nanoparticles to the total amount of crosslinkable hydrophobic polymers in the liquid phase was 1 :1. The resulting coating composition contained less than 0.01 % by weight of fluorine determined by combustion ion chromatography.

[0194] The fluorine content was determined by combustion ion chromatography as follows: The sample is thermohydrolysed at about 1000 °C in an oxygen-water vapor stream. The evolved hydrogen fluoride is absorbed into an aqueous solution, and detected as fluoride ions by ion chromatography. Detection is achieved by monitoring conductivity, wherein conductivity of the eluent is reduced by suitable suppressor equipment.

[0195] It has been found that the coating compositions according to the present invention can be stored up to 4 weeks until used in a coating process (as described below) without sacrificing any of the beneficial properties. In some cases shaking and / or stirring of the coating composition, in particular of a coating composition which has been stored for a longer period of time, prior to the coating process may be beneficial as this recreates a (meta-)stable dispersion

[0196] 2. Process of producing a composite material with a superhydrophobic surface from materials having a first-level surface structure and coating compositions:

[0197] The following production methods P-1 and P-2 of producing a composite material with a superhydrophobic surface according to the invention have been tested and can be used with good results.

[0198] In each case a coating composition according to the invention (CC-I) is prepared or provided. BASF 231086

[0199] Also in each case a material having a first-level surface structure with elevations having at least one spatial dimension Admicro in the range of from 1 x 10-3m to 1 x 1 O~6m according to the invention or for comparative reasons a reference material with a flat surface not having a first-level surface structure with elevations having at least one spatial dimension Admicro in the range of from 1 x 10-3m to 1 x 10-6m not according to the invention is prepared or provided and wetted with the respective coating composition as described in detail for each process below.

[0200] The following materials having a first-level surface structure with elevations having at least one spatial dimension Admicro in the range of from 1 x 1 o-3m to 1 x 1 o-6m according to the invention have been used as preferred example materials (we note that any other material with a microstructured surface is also suitable):

[0201] M-11 : Material prepared via a method as described in WO 2021058658 A1 , claim 1 , by performing, in this order, the steps 1 , 2-i, 3-i, 4, 5-i. Said material M-11 comprises a substrate S2 as described in WO 2021058658 A1 and a coating C2 derived from a commercial, radiation-curable coating composition C2a which comprises at least one urethane acrylate, at least one photoinitiator, and also commercial additives, corresponding to a preferred coating composition C2a as described in WO 2021058658 A1. Said material M-11 has on at least one part of at least one surface a first-level surface structure comprising multiple elevations having two spatial dimensions Admicro of = 10 pm (height and base width), wherein the elevations are repeating units of defined three-dimensional structures in the form of pillars, i. e., truncated cones. The elevations in the form of pillars are i) homogeneous in height with a standard deviation of corresponding vertical distances of elevation peaks to elevation bases of at most 15%, ii) periodically distributed within the first level surface structure with a standard deviation of corresponding next-neighbour lateral distances of elevations of at most 15% and iii) arranged in a hexagonal formation within the first level surface structure.

[0202] M-I2: Material prepared via a method as described in WO 2021058658 A1 , claim 1 , by performing, in this order, the steps 1 , 2-ii, 3-ii, 4, 5-ii from another commercial, radiation- curable coating composition C2a which comprises at least one urethane acrylate, at least one photoinitiator, and also commercial additives, corresponding to a preferred coating composition C2a as described in WO 2021058658 A1. Said material M-I2 has on at least one part of at least one surface a first-level surface structure comprising multiple elevations having two spatial dimensions Admicro of = 10 pm to 200 pm (height and base width), wherein the elevations are repeating units of defined three-dimensional structures in the form of riblets. The elevations in the form of riblets are i) homogeneous in height with a BASF 231086 standard deviation of corresponding vertical distances of elevation peaks to elevation bases of at most 15%, ii) periodically distributed within the first level surface structure with a standard deviation of corresponding lateral distances of elevations of at most 15% and iii) arranged in parallel line-shaped formations within the first level surface structure.

[0203] M-I3: Material prepared via a method as described in WO 2021058658 A1 , claim 1 , by performing, in this order, the steps 1 , 2-i, 3-i, 4, 5-i. Said material M-I3 comprises a substrate S2 as described in WO 2021058658 A1 and a coating C2 derived from a commercial, radiation-curable coating composition C2a which comprises at least one urethane acrylate, at least one photoinitiator, and also commercial additives, corresponding to a preferred coating composition C2a as described in WO 2021058658 A1 . Said material M-I3 has at least on a part of one surface a first-level surface structure corresponding to a typical air retention structure comprising protruding elements and partition walls, as known from literature and as disclosed in EP 2822704 B1 .

[0204] M-I4: Material with essentially the same first-level structure as M-I3, but comprising nickel, made by conventional electrodeposition of nickel to replicate the first-level structures of a suitable original master such as a layer of photoresist on a silicon wafer, the layer of photoresist having been structured by any suitable (photo-)lithographic process such as one- photon lithography and / or two-photon lithography. Such photolithography and replication processes are well-known from the state of the art. Such replication processes may preferably be carried out multiple times consecutively to create multiple replicated copies in both positive and negative orientation, as needed.

[0205] The following reference material with a flat surface not having a first-level surface structure with elevations having at least one spatial dimension Admicro in the range of from 1 x 10-3m to 1 x i o-6m not according to the invention has been used:

[0206] M-R1 : Material fabricated as described for M-I3, except that said material M-R1 has a flat surface, i. e., it does not feature any elevations having at least one spatial dimension Admicro in the range of from 1 x 10-3m to 1 x 10-6m. While this is not required to achieve the same results, the material M-R1 in the present example was fabricated integrally with the material M-I3, i. e., as an integrated reference. In other words, M-I3 and M-R1 are separate surface regions of the same samples, the former featuring the first-level surface structure as described above, and the latter not featuring any such first-level surface structure.

[0207] 2.1 Dip coating process (P-1): BASF 231086

[0208] Materials M-11 , M-I2, M-I3, M-I4, and M-R1 respectively were cut in pieces of appropriate size, washed by immersion in isopropanol for at least 10 min, followed by rinsing with fresh isopropanol and acetone. For the dip coating process, the respective materials were then immersed into coating composition CC-I at a controlled speed, and promptly retrieved at the same speed. For a coating composition CC-I according to the invention with concentrations of crosslinkable and hydrophobic polymers and of hydrophobic nanoparticles of 10 g / L each a retrieval speed of 1 m / min was identified to be best, for a coating composition CC-I according to the invention with a concentration of crosslinkable and hydrophobic polymers and hydrophobic nanoparticles of 15 g / L each a retrieval speed of 0.2 m / min was identified to be best. Immersion speed and time spent between immersion and retrieval are less influential and were not varied. The resulting wetted materials were left hanging in constant fume hood air flow until their front side appeared dry.

[0209] In some cases curing of the coating layer via UV irradiation from a Stratagene Stratalinker 2400, A = 254 nm, with a dose of 1-2 J / cm2was performed after drying.

[0210] 2.2 Spray coating process (P-2):

[0211] Materials M-11 , M-I2, and M-I3 respectively were cut in pieces of appropriate size, washed by immersion in isopropanol for at least 10 min, followed by rinsing with fresh isopropanol and acetone after which the materials were again rinsed with either ethanol or isopropanol, and acetone, and passively dried in the fume hood immediately before spray coating. A coating composition CC-I according to the invention with a concentration of crosslinkable and hydrophobic polymers and hydrophobic nanoparticles of 10 g / L each was sprayed using a commercial pneumatic spray gun (commercial name SATA HVLP) with an air pressure of 2 bar through a nozzle with 1.3 mm diameter. Samples were left to dry at room temperature.

[0212] 3. Reference material with a hydrophobic surface but without a second-level surface layer

[0213] Furthermore, another reference material (M-R3; details below) having a first-level surface structure prepared from a silicone resin (SR-R; Zhermack ZA 50 LT, a commercially available two-component silicone resin) is prepared or provided, and used as is, without processing to create a second-level surface layer. The silicone resin SR-R is hydrophobic. Accordingly, the reference material prepared from SR-R without second-level surface layer serves to demonstrate the difference between a hydrophobic material (not according to the invention) and a superhydrophobic material (according to the invention); in other words, it BASF 231086 serves to demonstrate the differences of a material without the nanoroughness provided by the second-level surface layer according to the invention.

[0214] M-R3: Reference material having a first-level surface structure with elevations having at least one spatial dimension Admicro in the range of from 1 x 10“3m to 1 x 10-6m was prepared from SR-R. Following the manufacturer’s instructions, the two components were mixed at the recommended ratio and poured onto a composite material corresponding to S1 C1 as described in WO 2021058658 A1 , having on one surface, as first-level surface structure, the inverse of a typical air retention structure, as known from literature (e. g., as disclosed in EP 2822704 B1). After the entire sample was cured at room temperature for at least one day, the silicone film is peeled off the composite material S1 C1 . Microscopy revealed that on the surface area which was in contact with the structured region of the composite material S1 C1 , the silicone film had, as first-level surface structure, a typical air retention structure, as known from literature (e. g., as disclosed in EP 2822704 B1). Surfaces of Zhermack ZA 50 LT are highly hydrophobic, but not superhydrophobic (water contact angle about 114°, measured as described above or below). Hence, in combination with its first-level surface structure, M-R3 is expected to show an air retention effect, but it is expected to be less stable than that of M-I3 with added second-level surface layer from coating composition CC-I.

[0215] 4. Composite materials with a superhydrophobic surface:

[0216] Composite materials have been prepared from materials and coating compositions via processes as described above.

[0217] The resulting composite materials according to the invention contained less than 0.01 % by weight of fluorine determined by combustion ion chromatography as described in detail above.

[0218] The resulting composite materials have been analysed via scanning electron microscopy (SEM; JEOL JSM-IT800 HL) in order to investigate and characterize the geometrical structure of the surface. Corresponding results are depicted in Fig. 1 , Fig. 2 and Fig. 6.

[0219] As can be seen from the results of the scanning electron microscopy analysis composite materials according to the invention, i.e., composite materials obtained from a first-level surface structure with elevations and / or depressions having at least one spatial dimension Admicro in the range of from 1 x 1 O~3m to 1 x 1 O~6m which were coated with a coating BASF 231086 composition according to the invention in a process according to the invention and thus additionally featured a second-level (nano)surface layer covering the first-level surface structure and comprising aggregates of hydrophobic nanoparticles and at least partially crosslinked hydrophobic polymers feature a geometrical structure wherein the average thickness of the second-level surface layer dnano is in the range of from 25 nm to 5000 nm, and the second-level surface layer has elevations having at least one spatial dimension Adnano in the range of from 5 nm to 1000 nm.

[0220] Furthermore it can be seen from the scanning electron microscopy analysis that the ratio of at least one of the at least one spatial dimension dmicro to the average thickness of the second-level surface layer dnano is at least 5:1. The composite materials according to the present invention are thus characterized by a hierarchical surface structure, wherein the elevations of the first-level microstructured surface are covered by a thin second-level nanolayer without clogging the voids, gaps and / or spaces that are spanned by the elevations of the first-level.

[0221] The surfaces of composite materials according to the invention which have been prepared from materials and coating compositions via processes as described above all showed static water contact angles of at least 140° and droplet roll-off angles of no more than 20° as measured by an optical goniometer using droplets with a volume of 10 pL and thus fulfil the requirements to be labelled as superhydrophobic surface.

[0222] The wetting properties of the resulting composite materials have been analysed qualitatively via a simple droplet test.

[0223] For the droplet test, the respective composite materials were placed horizontally on a lab bench. Small droplets of = 3 mm - 5 mm in diameter were dispensed onto the surface of the respective composite material from a disposable plastic pipette and photographed. Then, the respective composite materials were moved horizontally on the lab bench, and it was assessed whether the droplets remained on the same location of the surface of the respective composite material (i. e., if they moved together with the respective composite material), or if they lagged behind due to inertia (i. e., in the extreme case, they would remain at the same position relative to the lab bench). The observed behaviour was rated as indicated by the following symbols: | BASF Coatings GmbH | 231086 | 231086WQ01 ~

[0224] • desired anti-wetting behaviour if droplets largely lagged behind the movement of the composite material, i. e., if droplets largely remained at the same position relative to the lab bench, x undesired wetting behaviour if droplets largely followed the movement of the com- posite material, i. e., if droplets largely remained on the same location of the surface of the respective composite material,

[0225] O in intermediate cases.

[0226] Results of the droplet test are summarised in Table 1 .

[0227] Table 1 Wetting properties according to droplet test

[0228] No Material Coating Process Wetting Note rating

[0229] 1-1 M-I2 CC-I P-1 cf. Fig. 5

[0230] 1-2 M-I2 no coating nonex

[0231] 1-7 M-R1 CC-I P-1 Q droplets nearly spherical, but partially stuck on their position on the sample

[0232] 1-8 M-R1 no coating nonex

[0233] 1-9 M-R3 no coating none Q

[0234] As can be seen from the results of the droplet tests performed, all composite materials with a superhydrophobic surface according to the invention, i. e., samples 1-1 , 1-3, 1-4 and 1-6 showed excellent properties in terms of their anti-wetting behaviour. All other samples not according to the invention showed distinctly worse results in terms of wetting behaviour. Accordingly surfaces with a hierarchical structure according to the invention are superiorto surfaces known from the art that are either completely flat, i. e. neither microstructured nor nanostructured, or that only show one kind of structural feature, i. e. featuring only microstructures or featuring only nanostructures. BASF Coatings GmbH 231086

[0235] The beneficial anti-wetting properties of composite materials according to the invention allow the conclusion to be drawn that these materials also have very good anti-icing and / or easy-to-clean and / or self-cleaning and / or anti-fogging properties. Accordingly, composite materials according to the invention are well suited for applications in indoor lightings, outdoor lightings, optical devices, lidar sensors, radar sensors, laser-based systems, headsup displays, augmented / virtual reality devices, aircrafts, trains, ships or other means of transportation, turbines including wind turbines, gas turbines, turbines in pumps, turbines in hydroelectric and tidal power plants, propellers, pipes or sports equipment such as surfboards, stand-up paddle boards, ski or sledges, etc.

[0236] Some of the resulting composite materials have also been subjected to an immersion test in order to determine the air retention effect. The test procedure of the immersion test was as follows: A composite material is immersed in water at ambient temperature and left there for 4 weeks. After every day the visual appearance of the surface of the composite material was investigated and characterized.

[0237] A visual appearance of the material which is characterized by a high brightness, somewhat matt gloss, and reflectivity which allows for rendition of colours and approximate shapes indicates the presence of a superhydrophobic surface having a good air retention effect, i.e. the presence of a composite material with a superhydrophobic surface comprising a first-level surface structure with elevations having at least one spatial dimension dmicro in the range of from 1 x l 0“3m to 1 x 10-6m and a nanorough second-level surface layer covering the first-level surface structure and comprising aggregates of hydrophobic nanoparticles and at least partially crosslinked hydrophobic polymers.

[0238] A visual appearance of the material which is characterized by other features such as i) a mix of gloss and whitish scattering with very limited reflectivity of colour and shape, or ii) a matt appearance and relatively dark colour, or iii) no scattering and normal reflectivity indicates the presence of a partially hydrophobic surface with a mediocre air retention effect or a very poor air retention effect.

[0239] The samples have been rated accordingly, wherein ++ stands for a very good air retention effect lasting at least 14 days, + stands for a good air retention effect lasting at least 5 days, | BASF Coatings GmbH | 231086

[0240] - stands for a relatively poor air retention effect lasting not more than 2 days and — for a no air retention effect.

[0241] The results of the immersion tests performed are summarized in table 2 below.

[0242] Table 2 air retention effect according to immersion test

[0243] No. material coating post-treat- rating comments ment process

[0244] 2-1 M-I3 CC-I P-1 ++ best sample; air re-

[0245] (microstructured) tention for at least

[0246] 15 days

[0247] 2-2 M-I3 CC-I P-1 but post- + air retention for

[0248] (microstructured) treated at about 10 days lower speed

[0249] 2-3 M-I3 CC-I P-2 + air retention for

[0250] (microstructured) about 7 days

[0251] 2-4 M-I3 no coating no post-treat- — no air retention at

[0252] (microstructured)ment a"

[0253] 2-5 M-R1 CC-I P-1 - continuous air film

[0254] (flat) in beginning, but not stable for more than 1-2 days

[0255] 2-6 M-R1 no coating no post-treat- — no air retention at

[0256] (flat)ment aH

[0257] 2-7 M-R3 no coating no post-treat- - air retention in the ment beginning, but quick decay: not stable for more than 1-2 days

[0258] As can be seen from the results of the immersion tests performed, all composite materials with a superhydrophobic surface according to the invention, i. e., samples 2-1 , 2-2 and 2-3, showed excellent properties in terms of air retention and lasted up to at least 7 days up to at least 15 days. All other samples not according to the invention showed distinctly worse results in terms of air retention. Accordingly surfaces with a hierarchical structure according to the invention are superior to surfaces known from the art that are either completely flat, i. e. neither microstructured nor nanostructured, or that only show one kind of structural feature, i. e. featuring only microstructures or featuring only nanostructures.

[0259] The excellent properties in terms of air retention of composite materials according to the invention allow the conclusion to be drawn that these materials also have very good BASF Coatings GmbH 231086 anti / non-fouling properties and are well suited as drag-reducing materials. Accordingly, composite materials according to the invention are well suited for applications where drag reduction is needed, e.g. as a component of ships or other means of water transportation, turbines in pumps, turbines in hydroelectric and tidal power plants, propellers, pipes or sports equipment such as surfboards, stand-up paddle boards, ski or sledges, etc. Furthermore, composite materials according to the invention are well suited for applications where anti / non-fouling properties are desired, e.g. as a component of pipes, offshore structures, surfboards, ship hulls, ship propellers, hydrofoils, underwater turbines, pumps, hydroelectric power plants, tidal power plants, aquariums, swimming pools, water containers or water tanks including ships' ballast water tanks, etc.

[0260] BRIEF DESCRIPTION OF THE DRAWINGS

[0261] Further advantages, features and details of the invention result from the following description of the preferred embodiments as well as from the drawings. In the following, a summary of the figures is given.

[0262] Fig. 1 is a schematic drawing of the basic approach for creating hierarchically structured superhydrophobic surfaces according to the present invention.

[0263] Fig. 2 shows scanning electron microscopy (SEM) images of a composite material with a first-level surface structure and the resulting composite material with a superhydrophobic surface according to the present invention.

[0264] Fig. 3 shows a schematic representation of a composite material with a superhydrophobic surface according to the present invention.

[0265] Fig. 4 shows a schematic representation of a coating composition according to the present invention.

[0266] Fig. 5 shows the wetting behaviour of a composite material with a superhydrophobic surface according to the present invention.

[0267] Fig. 6 shows scanning electron microscopy (SEM) images of a composite material with a first-level surface structure and the resulting composite material with a superhydrophobic surface according to the present invention. BASF 231086

[0268] Fig. 7 shows the air retention effect of a composite material according to the present invention with internal references not according to the present invention, as observed in an immersion test.

[0269] DETAILED DESCRIPTION OF THE DRAWINGS

[0270] Fig. 1 shows in Fig. 1(a) a three-dimensional model of an example structure of a first-level surface structure with elevations having at least one spatial dimension Admicro in the range of from 1 x io-3m to 1 x w6m. Said model features a first-level surface structure comprising multiple elevations having two spatial dimensions Admicro of = 10 pm (height and base width), wherein the elevations are repeating units of defined three-dimensional structures in the form of pillars. The elevations in the form of pillars are i) homogeneous in height with a standard deviation of corresponding vertical distances of elevation peaks to elevation bases of at most 15%, ii) periodically distributed within the first level surface structure with a standard deviation of corresponding lateral distances of elevations of at most 15% and iii) arranged in a hexagonal formation within the first level surface structure. Fig. 1 (b) is an SEM image that shows a surface layer obtained from a coating composition according to the invention on a flat substrate. Fig. 1(c) is an SEM image showing a composite material according to the invention featuring a first-level surface structure with elevations having at least one spatial dimension Admicro in the range of from 1 x 1 o-3m to 1 x 1 o-6m, similar to the first-level surface structure shown in Fig. 1 (a), and a second-level nanorough surface layer covering the first-level surface structure and comprising aggregates of hydrophobic nanoparticles and at least partially crosslinked hydrophobic polymers, similarto the surface layer shown in Fig. 1 (b).

[0271] Fig. 2 shows in Fig.2(a) the SEM image of a sample of the material M-I2 with a first-level structure with elevations having at least one spatial dimension Admicro in the range of from 1 x i o-3m to 1 x i o-6m. Said material has on at least one part of at least one surface a first-level surface structure comprising multiple elevations having two spatial dimensions Admicro of = 10 pm to 200 pm (height and base width), wherein the elevations are repeating units of defined three-dimensional structures in the form of riblets. This sample corresponds to No 1-2 from Table 1 . The elevations in the form of riblets are i) homogeneous in height with a standard deviation of corresponding vertical distances of elevation peaks to elevation bases of at most 15%, ii) periodically distributed within the first level surface structure with a standard deviation of corresponding lateral distances of elevations of at most 15% and iii) arranged in parallel line-shaped formations within the first level surface structure. Fig. 2(b) displays two SEM images that show a composite material with a superhydropho- BASF 231086 bic surface according to the present invention, corresponding to sample No 1-1 from Table 1 , wherein the same underlying first-level structure as depicted in Fig. 2(a) is present. As can be seen in the SEM image, said microscale first-level structure is covered by an additional second-level surface layer prepared from a coating composition according to the present invention. In more detail: Fig. 2(b-1) shows the top-down view of the composite material in SEM at a low magnification; Fig. 2(b-2) shows the inclined view of the composite material in SEM at a higher magnification. The SEM images clearly show that the second- level surface layer is present and has elevations much smaller than the first-level structure. The first-level structure is not buried or clogged; in fact, on its size scale, it is not significantly changed. Accordingly, it is obvious that the ratio of at least one of the at least one spatial dimension Admicro to the average thickness of the second-level surface layer dnano is at least 5:1.

[0272] Fig. 3 shows a schematic representation of a composite material with a hierarchically structured superhydrophobic surface according to the present invention. As visualized in Fig. 3 said composite material comprises a first-level surface structure 201 with elevations in microscale dimensions having at least one spatial dimension Admicro in the range of from 1 x 10-3m to 1 x i o-6m 202. The elevations in microscale dimensions feature a vertical distance of elevation peaks to elevation bases Admicro-verticai 205 which is defined by the distance between the elevation peak of elevations in microscale dimensions 203 to the elevation base of elevations in microscale dimensions 204. The elevations in microscale dimensions also feature a next-neighbour lateral distance of adjacent elevations Ad micro-iaterai 206. The first-level surface structure 201 with elevations in microscale dimensions is covered by a second-level surface layer 211 which comprises elevations in nanoscale dimensions having at least one spatial dimension Adnano in the range of from 5 nm to 1000 nm 212. The elevations in nanoscale dimensions feature a vertical distance of elevation peaks to elevation bases Adnano-verticai 215 which are defined by the distance between the elevation peak of elevations in nanoscale dimensions 213 to the elevation base of elevations in nanoscale dimensions 214. The elevations in nanoscale dimensions also feature a next-neighbour lateral distance of adjacent elevations Ad nano-iaterai 216. The ratio of at least one of the at least one spatial dimension Admicro 205 and / or 206 to the average thickness of the second- level surface layer d nano is at least 5:1 .

[0273] Fig. 4 shows a schematic representation of a coating composition 101 according to the present invention. Said coating composition comprises a liquid phase, wherein the liquid phase comprises an organic solvent 104 and dissolved and / or emulsified in the liquid phase, one or more crosslinkable and hydrophobic polymers 102 and dispersed in the liquid phase one or more hydrophobic nanoparticles 103. The mass ratio of the total amount of BASF 231086 hydrophobic nanoparticles 103 to the total amount of crosslinkable hydrophobic polymers 102 in the coating composition 101 is in the range of from 1 :5 to 5:1 . The hydrophobic nanoparticles 103 don’t need to be identical, e. g., some nanoparticles may be primary particles while others may be aggregates of primary particles.

[0274] Fig. 5 shows the wetting behaviour of a composite material with a superhydrophobic surface according to the present invention. The wetting behaviour is investigated in a water droplet experiment. The composite material used in the water droplet experiment is similar to the one depicted in the SEM images of Fig. 2(b). Fig. 5(a) is a photo of water droplets on a composite material with a superhydrophobic surface according to the present invention. The superhydrophobicity, i. e., the fact that the surface exhibits a static water contact angle of at least 140°, can be visually seen in the pictures of the droplets on the surface. Fig. 5(b-1) is another photo of water droplets on a composite material with a superhydrophobic surface according to the present invention in a stationary state. As can be seen, the water droplets on the sample are almost spherical. They will very easily roll off when the sample is tilted or moved horizontally on the table. Fig. 5(b-2) is a photo sequence taken from snapshots of a video showing the water-repellent behaviour of the composite material shown in Fig. 5(b-1) when new water droplets are added from a pipette. Water droplets first bounce back upwards from the sample (cf. snapshots ®, ®, ®), and often roll off to the side subsequently (cf. snapshots © to ®).

[0275] Fig. 6 shows SEM images of a composite material according to the present invention. Fig. 6(a) shows the first-level surface structure of the material corresponding to M-l 1 , with elevations having at least one spatial dimension dmicro in the range of from 1 x 10“3m to 1 x i o-6m before coating, i. e., without the second-level surface layer. Said first-level surface structure has elevations in microscale dimensions, wherein the elevations are repeating units of defined three-dimensional structures in the form of pillars, i. e., truncated cones. The elevations in the form of pillars are i) homogeneous in height with a standard deviation of corresponding vertical distances of elevation peaks to elevation bases of at most 15%, ii) periodically distributed within the first level surface structure with a standard deviation of corresponding lateral distances of elevations of at most 15% and iii) arranged in a hexagonal formation within the first level surface structure. Fig 6(b) shows a composite material according to the present invention, wherein the same underlying first-level structure as depicted in Fig. 6(a) is present, with a second-level surface layer made from a preferred example of a coating composition according to the present invention (CC-I). As can be seen from the low-magnification SEM image Fig 6(b-1) and the high-magnification SEM image Fig 6(b-2) the first-level surface structure is homogeneously covered by the nanorough BASF 231086 second-level surface layer wherein the first-level surface structure is not buried or clogged; in fact, on its size scale, it is not significantly changed. Accordingly, it is obvious that the ratio of at least one of the at least one spatial dimension Admicro to the average thickness of the second-level surface layer dnano is at least 5:1 .

[0276] Fig. 7 shows a sample with typical air retention structures as first-level surface microstructures on one part of one surface, as known from literature (e. g., as disclosed in EP 2822704 B1), as described above for M-I3. The first-level surface microstructure is coated with the coating composition according to the invention by the process P-1 according to the invention in a first area (4) and not coated in a second area (1). On another part of the same surface, no such first-level structure has been created (“flat region”; corresponding to M- R1 as described above). Said “flat region” is coated with the coating composition according to the invention by the process according to the invention in a first area (3) and not coated in a second area (2). The sample was immersed in water at ambient temperature and left there for several days. The image shows the sample after being immersed in water in a plastic beaker for 15 d. Looking at light reflected from the surface of the sample with the superhydrophobic surface, a mirror effect reveals where air is trapped between the first- level structures. It can be seen from the image that:

[0277] (1) Area with first-level structure and without second-level coating layer (not according to the present invention): sample shows interference colours from the first-level structure; no mirror effect;

[0278] (2) Area without first-level structure and without second-level coating layer (not according to the present invention): sample is transparent here; no mirror effect;

[0279] (3) Area without first-level structure and with second-level coating layer (not according to the present invention): sample appears matte and slightly reflective.

[0280] (4) Area with first-level structure and with second-level coating layer according to the present invention: sample appears bright and highly reflective here, i. e., it shows a pronounced mirror effect here, note especially the red, shapely reflection of the red paper outside of the beaker, indicating best performance in terms of air retention effect.

[0281] List of reference signs:

[0282] 101 coating composition - M -

[0283] BASF Coatings GmbH | 231086

[0284] 102 crosshnkable and hydrophobic polymers

[0285] 103 hydrophobic nanoparticles

[0286] 104 organic solvent

[0287] 201 first-level surface structure 202 elevations in microscale dimensions having at least one spatial dimension Admicro in the range of from 1 x 10-3m to 1 x 1 o-6m

[0288] 203 elevation peak of elevations in microscale dimensions

[0289] 204 elevation base of elevations in microscale dimensions

[0290] 205 vertical distance of elevation peaks to elevation bases Admicro-verticai 206 next-neighbour lateral distance of adjacent elevations Admicro-iaterai

[0291] 211 second-level surface layer covering the first-level surface structure

[0292] 212 elevations in nanoscale dimensions having at least one spatial dimension dnano in the range of from 5 nm to 1000 nm

[0293] 213 elevation peak of elevations in nanoscale dimensions 214 elevation base of elevations in nanoscale dimensions

[0294] 215 vertical distance of elevation peaks to elevation bases Adnano-verticai

[0295] 216 next-neighbour lateral distance of adjacent elevations Adnano-iaterai

Claims

BASF Coatings GmbH231086CLAIMS1 . A composite material with a superhydrophobic surface comprising a) a first-level surface structure with elevations and / or depressions having at least one spatial dimension Admicro in the range of from 1 x 10“3m to 1 x w6m, b) a second-level surface layer covering the first-level surface structure and comprising aggregates of hydrophobic nanoparticles and at least partially crosslinked hydrophobic polymers, wherein i) the mass ratio of the total amount of hydrophobic nanoparticles to the total amount of at least partially crosslinked hydrophobic polymers is in the range of from 1 :5 to 5:1 , ii) the average thickness of the second-level surface layer dnano is in the range of from 25 nm to 5000 nm, iii) the second-level surface layer has elevations having at least one spatial dimension dnano in the range of from 5 nm to 1000 nm, iv) the fluorine content determined by combustion ion chromatography is less than 1 % by weight, wherein the ratio of at least one of the at least one spatial dimension Admicro to the average thickness of the second-level surface layer dnano is at least 5:1 .

2. A composite material with a superhydrophobic surface according to claim 1 , wherein the first-level surface structure has i) elevations with- an average vertical distance of elevation peaks to elevation bases Admicro-verticai in the range of from 1 x 1 o-3m to 1 x 1 o-6m, wherein preferably the ratio of Ad micro-vertical to the average thickness of the second-level surface layer d nano is at least 5:1 ,BASF231086and / or- an average next-neighbour lateral distance of adjacent elevations Ad micro-iaterai in the range of from 1 x 10“3m to 1 x 1 o-6m, wherein preferably the ratio of Ad micro-lateral to the average thickness of the second-level surface layer d nano is at least 5:1 , and / or i) depressions with- an average vertical distance of depression peaks to depression bases Admicro-verticai in the range of from 1 x 1 o-3m to 1 x 1 o-6m, wherein preferably the ratio of Ad micro-vertical to the average thickness of the second-level surface layer d nano is at least 5:1 , and / or- an average next-neighbour lateral distance of adjacent depressions Ad micro-iaterai in the range of from 1 x 1 o-3m to 1 x 1 o-6m, wherein preferably the ratio of Ad micro-lateral to the average thickness of the second-level surface layer d nano is at least 5:1 .

3. A composite material with a superhydrophobic surface according to any of the preceding claims, wherein the elevations and / or depressions of the first-level surface structure- are homogeneous in height and / or depth with a standard deviation of corresponding vertical distances of elevation and / or depression peaks to elevation and / or depression bases of at most 15%, and / orBASF231086- are periodically distributed along the first-level surface with a standard deviation of corresponding lateral distances of elevations and / or depressions of at most 15%, and / or- are repeating units of defined three-dimensional structures, wherein repeating units are in direct contact with neighbouring repeating units or are not in contact with neighbouring repeating units, preferably the repeating units are selected from one or more of the following three-dimensional structures: pillars, ridges, grooves, louvers, prisms such as ribs and riblets, pyramids, cones, truncated versions of any of the former, serpen- tine-shaped structures, serrated-shaped structures, hexagonal-shaped structures, diamond-shaped structures, parallelogram-shaped structures, honey- comb-shaped structures, circular-shaped structures, dot-shaped structures, starshaped structures, line-shaped structures, net-shaped structures, polygonal structures, preferably triangular structures, quadrangular structures, particularly preferably rectangular structures and square structures, pentagonal structures, hexagonal structures, heptagonal structures and octagonal structures, wireshaped structures, elliptical structures, oval structures and grid-shaped structures, and mixtures or inverted versions or combinations thereof, more preferably the repeating units are pillars or pyramids or prisms such as ribs and riblets.

4. A composite material with a superhydrophobic surface according to any of the preceding claims, wherein- the mass ratio of the total amount of hydrophobic nanoparticles to the total amount of at least partially crosslinked hydrophobic polymers is in the range of from 1 :3 to 3:1 , preferably of from 1 :2 to 2:1 , more preferably of from 1 :1 .4 to 1 .4:1 , and / or- the fluorine content determined by combustion ion chromatography in the second- level surface layer is less than 0.1 % by weight, preferably is less than 0.01 % by weight.BASF Coatings GmbH2310865. A composite material with a superhydrophobic surface according to any of the preceding claims, wherein- the second-level surface layer has an average thickness dnano in the range of from 50 nm to 2000 nm, preferably from 50 nm to 1000 nm, and / or- the second-level surface layer has elevations having at least one spatial dimension Adnano in the range of from 10 to 500 nm, preferably in the range of from 10 nm to 250 nm, more preferably elevations having an average vertical distance of elevation peaks to elevation bases dnano-verticai in the range of from 10 nm to 250 nm.

6. A composite material with a superhydrophobic surface according to any of the preceding claims, wherein the ratio of at least one of the at least one spatial dimensions Adnano, preferably the average vertical distance of elevation peaks to elevation bases Adnano-verticai to the average thickness of the second-level surface layer dnano, is at least 1 :10, preferably is at least 1 :5.

7. A composite material with a superhydrophobic surface according to any of the preceding claims, wherein at least 50%, preferably at least 70%, more preferably at least 80% of the surface of the first-level surface structure is covered with the second-level surface layer.

8. A composite material with a superhydrophobic surface according to any of the preceding claims, wherein- the composite material is a component of aircrafts, trains, ships or other means of transportation, turbines including wind turbines, gas turbines, turbines in pumps, turbines in hydroelectric and tidal power plants, propellers, pipes or sports equipment such as surfboards, stand-up paddle boards, ski or sledges, or the composite material is a component of indoor lightings, outdoor lightings, optical devices, lidar sensors, radar sensors, laser-based systems, heads-up displays, augmented / virtual reality devices,BASF Coatings GmbH231086or- the composite material is a component of pipes, offshore structures, surfboards, ship hulls, ship propellers, hydrofoils, underwater turbines, pumps, hydroelectric power plants, tidal power plants, aquariums, swimming pools, water containers or water tanks including ships' ballast water tanks, or- the composite material is a membrane, a woven or non-woven fabric, and / or paper.

9. A coating composition for the production of superhydrophobic surfaces, comprising a) a liquid phase comprising i) an organic solvent, and ii) dissolved and / or emulsified in the liquid phase, one or more crosslinkable and hydrophobic polymers, wherein the one or at least one of the more than one crosslinkable and hydrophobic polymers comprises one or more active (co-)monomers as crosslinking moiety, capable of forming chemical bonds to neighbouring polymers and / or organic substrates and / or hydrophobic nanoparticles, b) dispersed in the liquid phase one or more hydrophobic nanoparticles, wherein- the composition contains less than 1 % by weight of fluorine determined by combustion ion chromatography,- the mass ratio of the total amount of hydrophobic nanoparticles to the total amount of crosslinkable hydrophobic polymers in the coating composition is in the range of from 1 :5 to 5:1 .

10. A coating composition according to claim 9, whereinBASF Coatings GmbH231086- the composition contains less than 0.1 % by weight of fluorine determined by combustion ion chromatography, preferably less than 0.01 % by weight of fluorine, and / or- the mass ratio of the total amount of hydrophobic nanoparticles to the total amount of crosslinkable hydrophobic polymers in the coating composition is in the range of from 1 :3 to 3:1 , preferably of from 1 :2 to 2:1 , more preferably of from 1 :1 .4 to 1 .4:1 , and / or- wherein at least 50% by weight, preferably at least 70% by weight, more preferably at least 75% by weight, of at least one (co)monomer used for making the crosslinkable and hydrophobic polymers are obtained from renewable, plant-based raw materials, preferably are obtained from vegetable oils, more preferably are obtained from rapeseed oil.

11. A coating composition according to claim 9 or 10, wherein the one or at least one of the more than one crosslinkable and hydrophobic polymers comprises- one or more hydrophobic side chains, preferably the one or more hydrophobic side chains are selected from the group consisting of hydrocarbon groups and siloxanes, more preferably are selected from the group consisting of- aromatic groups,- linear, cyclic and / or branched alkyl groups,- linear, cyclic and / or branched alkenyl groups,- linear, cyclic and / or branched alkynyl groups,- linear, cyclic and / or branched alkyl-, alkenyl or alkynyl groups containing heteroatoms such as O, N, S, in particular alkoxy and poly(alkoxy)BASF231086groups such as polypropylene oxide), poly(butylene oxide) or (poly- THF), and- hydrocarbon-functionalised siloxanes, preferably alkyl siloxanes, more preferably alkyl siloxanes comprising at least one RR’SiO unit, wherein R and R’ are independently selected from the group of linear and branched alkyls, and / or- one or more active (co-)monomers as crosslinking moiety capable of forming chemical bonds by activation with radiation, in particular UV irradiation, sunlight or electron beams, and / or activation with heat in a state where the coating composition has a viscosity of at least 106mPa-s, preferably of at least 108mPa-s, more preferably of at least 101° mPa-s more preferably the one or more active (co-)monomers as crosslinking moiety are capable of forming chemical bonds by insertion into C-H bonds via C,H-insertion crosslinking (CHic), wherein preferably the one or more active (co-)monomers as crosslinking moiety constitutes 0.1 % to 20% by weight, preferably 1 % to 15% by weight, more preferably 2% to 10% by weight of the one or of at least one of the more than one crosslinkable and hydrophobic polymers.

12. A coating composition according to any of claims 9 to 11 , wherein the one or at least one of the more than one crosslinkable and hydrophobic polymers- comprises one or more active (co-)monomers as crosslinking moiety, capable of forming chemical bonds to neighbouring polymers and / or organic substrates and / or hydrophobic nanoparticles with a functional group selected from the group consisting ofBASF231086- C,H-insertion crosslinking (CHic) active groups, preferably substituted benzophenones, anthraquinones, thioxanthones, sulfonyl azides, aromatic azides, diazomethylenes with ester, sulfonyl and / or aromatic substituents, or other moieties capable of forming carbene, nitrene, or biradicaloid intermediates upon thermal or photochemical activation- azides,- vinylic unsaturated groups,- epoxy groups,- isocyanate groups,- carboxylic acid anhydride groups, and- organic carbonates, and / or- has an average molecular weight Mwof more than 1800 g / mol, and / or- is obtained from polymerisation of one or more (co-)monomers, preferably from radical polymerisation, more preferably from free-radical polymerisation, and / or- comprises at least one (meth)acrylate (co-)monomer or at least one (meth)acryl amide (co-)monomer, preferably comprises i) at least one (meth)acrylate (co-)monomerwith a hydrophobic group, preferably a hydrocarbon group ora siloxane, or at least one (meth)acryl amideBASF231086(co-)monomer with a hydrophobic group, preferably a hydrocarbon group or a siloxane, and ii) at least one (meth)acrylate (co-)monomer with a crosslinking functional group capable of forming chemical bonds to neighbouring polymers and / or organic substrates and / or hydrophobic nanoparticles, or at least one (meth)acryl amide (co-)monomer with a crosslinking functional group capable of forming chemical bonds to neighbouring polymers and / or organic substrates and / or hydrophobic nanoparticles.

13. A coating composition according to any of claims 9 to 12, wherein the one or at least one of the more than one hydrophobic nanoparticles is- thermally stable until a temperature of at least 100 °C, preferably of at least 300 °C, and / or- a surface-functionalized nanoparticle comprising a particle core and a particle surface, wherein preferably- the particle core comprises at least 70% by weight of at least one inorganic compound, preferably at least 90% by weight, more preferably at least 95% by weight, even more preferably at least 97% by weight, wherein more preferably the inorganic compound is selected from the group consisting of metals, metal oxides, ceramics, silica, carbon and mixtures thereof, even more preferably the inorganic compound is selected from the group consisting of BeO, TiC>2, ZrC>2, MoSi2, WC, ZnO, BN, B4C, AI2O3, AIN, SiC, SisN4, SiC>2 and mixtures thereof, most preferably the inorganic compound is selected from the group consisting of TiC>2, ZrC>2, AI2O3, SiC>2 and mixtures thereof, and / or- the particle surface comprisesBASF231086i) one or more hydrophobic surface functionalities, preferably the one or more hydrophobic surface functionalities are selected from the group consisting of hydrocarbon groups and siloxanes, more preferably selected from the group consisting of- aromatic groups,- linear, cyclic and / or branched alkyl groups,- linear, cyclic and / or branched alkenyl groups,- linear, cyclic and / or branched alkynyl groups, and- hydrocarbon-functionalised siloxanes, preferably alkyl siloxanes, more preferably alkyl siloxanes comprising at least one RR’SiO unit, wherein R and R’ are independently selected from the group of linear and branched alkyls, and / or ii) one or more surface crosslinking target functionalities, preferably the one or more surface crosslinking target functionalities are capable of forming chemical bonds to neighbouring polymers, more preferably the one or more surface crosslinking target functionalities are at least partially identical to the one or more hydrophobic surface functionalities, even more preferably the one or more surface crosslinking target functionalities are the same as the one or more hydrophobic surface functionalities.BASF Coatings GmbH| 23108614. Process of producing a composite material with a superhydrophobic surface, preferably a composite material with a superhydrophobic surface according to any of claims 1 to 8, at least comprising the following steps: a) preparing or providing a coating composition according to any of claims 9 to 13, b) wetting the surface or parts of the surface of a material having a first-level surface structure with elevations and / or depressions having at least one spatial dimension Admicro in the range of from 1 x 10-3m to 1 x i o-6m, with the prepared or provided coating composition, so that the first-level surface structure is covered by the coating composition, c) drying the wetted material, so that organic solvent of the coating composition evaporates, d) at least partially crosslinking the one or more crosslinkable and hydrophobic polymers so that a composite material with a superhydrophobic surface is obtained.

15. Use of a coating composition according to any of claims 9 to 13 for the production of a superhydrophobic surface.

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