WO2004014574A2

WO2004014574A2 - Method for producing structured surfaces

Info

Publication number: WO2004014574A2
Application number: PCT/EP2003/006687
Authority: WO
Inventors: Markus Oles; Edwin Nun; Rolf Müller
Original assignee: Creavis Gesellschaft Für Technologie Und Innovation Mbh
Priority date: 2002-07-25
Filing date: 2003-06-25
Publication date: 2004-02-19
Also published as: WO2004014574A3; AU2003283009A1; AU2003283009A8; DE10233831A1

Abstract

The invention relates to a method for producing structured surfaces, said method consisting of the following steps: i.) a hardenable substance is applied to a surface as a carrier layer by means of a coating technique, ii.) particles are applied to said carrier layer by means of a coating technique, and iii.) the particles are then fixed to the carrier layer by hardening said carrier layer. The invention also relates to the structured surfaces produced by said method and to the use of the same, for example for producing films.

Description

Process for the production of structured surfaces

The invention relates to a method for producing structured surfaces by means of the coating method, and to the structured surfaces produced according to this method and their use.

The structuring of surfaces is generally known. In recent times, an increasing number of applications are known which generate completely new surface properties with the aid of nanostructured particles. In addition to scratch resistance of coatings, self-cleaning surfaces can also be produced. A particularly well-known example is the self-cleaning Lotus surface. A combination of micro and nanostructures and hydrophobicity can generate completely new properties.

To achieve a good self-cleaning of a surface, the surface must have a certain roughness in addition to a very hydrophobic surface. A suitable combination of structure and hydrophobicity makes it possible for even small amounts of moving water to take dirt particles adhering to the surface with them and to clean the surface (WO 96/04123, US 3,354,022).

State of the art according to EP 0 933 388 is that an aspect ratio of> 1 and a surface energy of less than 20 raN / m are required for such self-cleaning surfaces. The aspect ratio is defined here as the quotient of the height and the width of the structure. The aforementioned criteria are realized in nature, for example in the lotus leaf. The surface of the plant, formed from a hydrophobic, wax-like material, has elevations that are a few μm apart. Water drops essentially only come into contact with these tips. Such water-repellent surfaces are widely described in the literature.

CH 268 258 describes a process in which structured surfaces are produced by applying powders such as kaolin, talc, clay or silica gel. The powders are fixed on the surface by oils and resins based on organosilicon compounds (Examples 1 to 6). EP 0 909 747 describes a method for producing a self-cleaning surface. The surface has hydrophobic elevations with a height of 5 to 200 μm. Such a surface is produced by applying a dispersion of powder particles and an inert material in a siloxane solution and then curing. The structure-forming particles are fixed to the substrate by an auxiliary medium.

WO 00/58410 comes to the conclusion that it is technically possible to make the surfaces of objects artificially self-cleaning. The surface structures of elevations and depressions required for this have a distance between the elevations of the surface structures in the range from 0.1 to 200 μm and a height of the elevation in the range from 0.1 to 100 μm. The materials used for this must consist of hydrophobic polymers or permanently hydrophobized material. Detachment of the particles from the carrier matrix must be prevented.

The use of hydrophobic materials, such as perfluorinated polymers, for the production of hydrophobic surfaces is known. A further development of these surfaces is to structure the surfaces in the μm range to the nm range. No. 5,599,489 discloses a method in which a surface can be given a particularly repellent finish by bombarding it with particles of a corresponding size and subsequent perfluorination. Another method describes H. Saito et al. in "Service Coatings International 4 (1997), 168 ff". Here, particles of fluoropolymers are applied to metal surfaces, with a greatly reduced wettability of the surfaces thus produced against water with a significantly reduced tendency to freeze.

The principle is borrowed from nature. Small contact areas reduce the Van der Waals interaction, which is responsible for the adhesion to flat surfaces with low surface energy. For example, the leaves of the lotus plant are provided with raised areas made of wax, which reduce the contact area with the water.

Methods for producing these structured surfaces are also known. In addition to the detailed reproduction of these structures by a master structure in the injection molding or embossing process, processes are also known which use the application of particles to a surface (US Pat. No. 5,599,489). By using embossing stamps, the required structure is embossed in a UV-curing lacquer and then hardened. This technique can be used to produce films with different formats. Recently, more and more nanoparticles have been used to structure the surfaces. For this purpose, the nanoparticles must be bonded as firmly as possible to the surface.

DE 101 18 352 (not yet published at the time of this application) describes self-cleaning surfaces which are produced by first applying a hardenable carrier to the surface of the object by means of spraying, knife coating, brushing on or spraying on, and then the particles are sprayed on or powdered applied to the carrier and the carrier layer hardened.

EP 1 153 987 describes a coating composition consisting of a binder and a powder which has a hydrophobic surface and a BET surface area of at least 1 m ² / g. This coating agent is applied in a known manner to the substrates to be coated. The disadvantage here is that a high proportion of the particles which are necessary for the desired surface effect are completely enclosed by the binder and thus cannot contribute to the desired surface effect.

Two methods are currently available for the production of nanostructured surfaces in films:

1. In DE 102 05 782 (not yet published at the time of this application), nanoparticles are applied to the surface by a one-component mixture in the coating process. Due to the excess of nanoparticles in the suspension, individual nanoparticles emerge from the suspension and thus produce the desired effect.

2. In DE 102 05 783 and DE 101 38 037 (not yet published at the time of this application), the nanoparticles are bound in such a way that the polymer surfaces are dissolved or swelled by suitable solvents or swelling agents and the nanoparticles are in this layer store. After the solvent or swelling agent has evaporated, the particles sit firmly in the polymer matrix.

Technically, however, these methods reach their limits. While in the first method most of the particles are immersed in the solution and thus for the desired one If the surface effect is not available, the particles are only insufficiently bonded to the polymer matrix in the second method. The desired surface effect is therefore not permanent or not very pronounced in both methods. Another weak point of these two technologies is that these concepts cannot be transferred to existing coating systems.

It was therefore the object of the present invention to develop a method for producing structured surfaces for conventional coating plants.

Surprisingly, it was found that with the help of conventional coating systems, a carrier layer can be applied to the films, on which the particles can also be applied in a subsequent coating process step. The subsequent curing of the carrier layer, which can be initiated thermally or by means of UV radiation, is not hindered by this additional coating with particles. Through the series connection of the two coating processes, both the production of the carrier layer and the application of the particles can be optimized individually. Although the coating systems used for the method according to the invention have been known for a long time, it was not recognized that structured surfaces also result from connecting two coating processes in series, the carrier layer being applied in the first process and the particles being applied to the carrier layer in the second process advantageous properties. The solution to the problem was all the more surprising, especially since it was shown that the hardening of the carrier layer was not hindered by the particles applied.

The present invention relates to a method according to claim 1 for the production of structured surfaces by means of the coating method, the method following

Steps comprises: i.) Applying a curable substance as a carrier layer on a surface by means of a coating technology, ii.) Applying particles to the carrier layer by means of a coating technology and subsequent iii.) Fixing the particles to the carrier layer by hardening this carrier layer.

The present invention also relates to the resulting surfaces, which were produced according to the method according to the invention, and the use of the method according to the invention, for example for the production of films.

This method has the advantage that the generation of structured surfaces can be carried out using conventional coating systems. Another advantage is the good adhesion of the particles to the carrier layer, since the carrier layer hardens after the particles have been applied, in contrast to some methods according to the prior art. Furthermore, this method has the advantage that the particles only adhere to the surface of the object, e.g. a film, or on and / or in the carrier layer of the object and are not statistically distributed over the entire object. Another advantage of the method according to the invention is that scratch-sensitive surfaces are not damaged by particles present in the carrier layer when the particles are applied, since when a carrier layer is used and the particles are subsequently applied to this carrier layer, the scratch-sensitive surface of an object is already damaged by the carrier layer is protected.

The method according to the invention for producing structured surfaces is characterized in that the method has the following steps: i.) Applying a curable substance as a carrier layer on a surface by means of a coating technique, ii.) Applying particles to the carrier layer by means of a coating technique and subsequent iii.) Fixing the particles to the carrier layer by hardening the carrier layer.

In the first process step - process step i.) - using a coating technique, a curable substance is applied as a carrier layer to the surface of the object to be modified. The curable substance of the carrier layer is preferably a lacquer which can be cured by means of thermal energy and / or electromagnetic radiation and which advantageously at least mixtures of mono- and / or polyunsaturated acrylates and / or methacrylates and / or polyurethanes and / or silicone acrylates and / or Has urethane acrylates. This lacquer of the process according to the invention particularly preferably has polymers and / or copolymers of mono- and / or polyunsaturated acrylates and / or methacrylates. It is also possible that the curable paint Compounds with functional groups, such as hydroxyl groups, epoxy groups, amine groups, or fluorine-containing compounds, such as perfluorinated esters of acrylic acid. This is particularly advantageous when the compatibility of paint and hydrophobic particles, such as Aerosil R 8200, is matched to one another using N- [2- (acryloyloxy) ethyl] -N-ethylperfluorooctane-l-sulfonamide. As lacquers, not only lacquers based on acrylic resin can be used, but also lacquers based on polyurethane or lacquers that have polyurethane acrylates or silicone acrylates. In a particular embodiment of process step i.) Of the process according to the invention, an adhesive is used as the curable backing layer. In a further embodiment of the method according to the invention, a polymer melt is applied in method step i.).

The carrier layer is advantageously applied to the surface of the object, e.g. a film applied. In a preferred embodiment of method step i.) Of the method according to the invention, the carrier layer is applied by means of the roll coating. The process variants of roll coating are described in the “Coatings Technology Handbook” (ed .: D. Satas, Arthur A. Tracto; Marcel Dekker, Ine; ISBN 0-8247-0439-8; Chapter 18, page 165 ff.). In a further embodiment of the method according to the invention, the carrier layer is applied by means of knife coating, dip coating, slide coating or curtain coating. These techniques are known to the person skilled in the art and are also described in "Coatings Technology Handbook". The coating can be done on one side as well as on both sides. The carrier layer is preferably applied in a thickness of 1 to 100 μm, preferably in a thickness of 5 to 50 μm.

In the subsequent process step - process step ii.) - the particles are applied to the carrier layer using a coating technique. Depending on the viscosity of the curable substance, it may be advantageous to allow the curable substance of the carrier layer to harden or to dry before the particles are applied. Ideally, the viscosity of the curable substance is selected so that the particles applied can at least partially sink into the carrier layer, but the carrier layer or the particles applied to it no longer run when the surface is placed vertically. If the particles on the Carrier layer have been applied, they slowly sink into the carrier layer. The viscosity of the carrier layer can be varied by the hardening of the carrier layer which begins immediately after the particles have been applied. Depending on how quickly the carrier layer hardens, the penetration depth of the particles can be adjusted. The degree of connection of the particles to the carrier layer can be controlled via the penetration depth of the particles into the carrier layer. Technically, the penetration depth can be adjusted with the speed of the object to be coated in the coating system or the intensity of the electromagnetic radiation that initiates the hardening of the carrier layer. The irradiance of the lamps in the process according to the invention is preferably from 50 W / cm ² to 1000 W / cm ² . The coating speed of the coating system in the process according to the invention is preferably from 1 m / min to 300 m / min, preferably from 30 m / min to 300 m / min.

A wide variety of compounds from many areas of chemistry can be used as particles. The particles preferably have at least one material selected from silicates, doped silicates, minerals, aluminum oxide, metal oxides, mixed oxides, silicas, pigments, polymers and metal powders, preferably metal powders coated with silica. Most preferably, the particles comprise fumed silicas or precipitated silicas, particularly aerosils ^®, Al ₂ O _3, SiO _2, TiO _2, ZrO _2, sheathed with Aerosil ^® R974 zinc powder, preferably microns with a particle size of 1 or pulverulent polymers, such as cryogenically ground or spray-dried polytetrafluoroethylene (PTFE) or perfluorinated copolymers or copolymers with tetrafluoroethylene or mixtures of the aforementioned substances.

Particles are preferably used which have an average particle diameter of 0.01 to 100 μm, preferably 0.02 to 50 μm and particularly preferably 0.05 to 30 μm. However, particles are also suitable which, when dry, accumulate from primary particles to form agglomerates or aggregates with a size of 0.2 to 100 μm.

It can be advantageous if the particles used have a structured surface. Particles are preferably used which have an irregular fine structure in the nanometer range, that is to say in the range from 1 to 1000 nm, preferably from 2 to 750 nm and particularly preferably from 10 to 100 nm, on their surface. The used Silicas preferably have a dibutyl phthalate adsorbtion, based on DIN 53 601, from 100 to 350 ml / 100 g, preferably from 150 to 250 ml / 100 g.

The particles for generating self-cleaning surfaces preferably also have hydrophobic properties in addition to the jagged structures. The particles themselves can be hydrophobic, such as particles containing PTFE, or the particles used can have been made hydrophobic. The particles can be made hydrophobic in a manner known to the person skilled in the art (pigment series, number 18, from Degussa AG). This is preferably done by treatment with at least one compound selected from the group of alkylsilanes, alkyldisilazanes or perfluoroalkylsilanes. Typical hydrophobic particles are very fine powders, for example, such as Aerosil ^® R 8200 (Degussa AG).

In a preferred embodiment of the method according to the invention, the particles are applied by means of a coating technique, in which a suspension comprising particles is applied as a film to the carrier layer. The particles are preferably present in an alcohol selected from ethanol, 2-propanol and methanol, or suspended in a mixture of these compounds. When choosing the suspension medium, care must be taken to ensure that the suspension forms a film on the carrier layer. Furthermore, the suspension medium should preferably not dissolve or dissolve the paint.

The suspension of the particles is advantageously applied to the carrier layer by means of a coating process. In a preferred embodiment of process step ii.) Of the process according to the invention, the suspension of the particles is applied to the carrier layer by means of the roll coating. The process variants of roll coating are described in the "Coatings Technology Handbook" (Ed .: D. Satas, Arthur A. Tracto; Marcel Dekker, Ine; ISBN 0-8247-0439-8; Chapter 18, page 165 ff.). Furthermore, the suspension with the particles can be applied to the carrier layer using the slot coating coating technology In a further embodiment of the method according to the invention, the suspension is applied by means of knife coating, dip coating, slide coating or curtain coating Techniques are known to the person skilled in the art and are also described in the “Coatings Technology Handbook”.

Before process step iii.) It can be advantageous if the particles are fixed before the carrier layer, the liquid components of the suspension are removed. The suspension medium can be removed by evaporation or volatilization, wherein the evaporation or volatilization can be accelerated by using elevated temperatures or by using negative pressure or vacuum.

In a further embodiment of process step ii.) Of the process according to the invention, the particles are applied dry to the carrier layer. This can be done, for example, by means of an electrostatic coating, preferably by means of an electrostatic spraying process. The spraying of powders using an electrostatic spraying method is known. A powder spray gun with external high-voltage electrodes is usually used for this. In the electrostatic spraying process, the powder is charged through the external high-voltage electrodes, the so-called corona electrodes. The heights of the elevations achieved in this embodiment of the method according to the invention are preferably from 40 to 120 μm with a particle size range of the particles used from 0.05 to 100 μm. For the electrostatic charging of the particles, high-voltage values of preferably from 30 to 110 kV, preferably from 40 to 90 kV and very particularly preferably from 50 to 80 kV are used in the process according to the invention. The current strength is preferably from 20 to 75 mA, preferably from 25 to 60 mA. The amount of particles transported in the air stream is preferably from 0.1 to 100 g / min in the process according to the invention. The pressure at which the particles leave the nozzle in the process according to the invention is preferably from 0 to 4 bar, preferably from 0.5 to 1.5 bar.

In a process variant of process step ii.) Of the process according to the invention, the electrostatic coating can be carried out by means of powder spray guns which achieve the necessary electrostatic charging of the particles exclusively by means of triboelectric processes. The particles are charged positively.

In a further process variant of process step ii.) Of the process according to the invention, the electrostatic coating can be carried out by means of the corona spray process. The spraying of powders using electrostatic spraying methods is known per se. A powder spray gun with external high-voltage electrodes is usually used. By external high-voltage electrodes, the so-called Corona electrodes, powder is charged on the electrostatic powder spray gun. Due to the high voltage of approximately 100 kV applied to the corona electrode, ions are generated in the air in the method according to the invention, which electrostatically charge the powder particles. The powder particles are negatively charged. In the method according to the invention, high voltage values in the range from 30 to 110 kV, preferably from 40 to 90 kV and very particularly preferably from 50 to 80 kV are preferably used for electrostatic charging. The current intensity is preferably from 20 to 75 mA and preferably from 25 to 60 mA. The amount of powder transported in the air stream can be from 0.1 to 100 g / min in the process according to the invention. The conveying air used here for conveying the particles preferably has a pressure of more than 0 to 4 bar and preferably 0.5 to 1.5 bar.

The carrier layer is preferably not yet or only partially hardened before method step ii.) Of the method according to the invention, so that the particles applied in method step ii.) Are able to partially penetrate into the carrier layer.

In the last method step - method step iii.) - of the method according to the invention, the carrier layer with the incompletely penetrated particles is hardened in order to ensure that the particles are fixed on or in the carrier layer. The carrier layer can be cured by polymerization or crosslinking of the components of the carrier system. The carrier layer is particularly preferably hardened by UV radiation or thermal energy, depending on the material of the carrier layer system used in each case. The irradiance of the lamps preferably varies from 50 to 1000 W / cm ² . When an adhesive is used as the backing layer, curing is preferably carried out by the water vapor in the air. With some materials of the carrier layer, chemically initiated curing is advantageous. If a polymer melt is used as the carrier layer, curing preferably takes place by cooling the carrier layer.

Depending on the thickness of the carrier layer and the diameter of the particles used, it may be necessary to limit the time which elapses between the application of the particles and the hardening of the carrier layer in order to avoid complete immersion of the particles in the carrier layer. The hardenable substance is preferably applied within 0.1 to 10 seconds, preferably within 1 to 5 seconds after the application of the particles hardened.

It can also be advantageous to provide the particles with hydrophobic properties after being fixed on or in the carrier layer. This can e.g. in that the particles of the treated surface are given hydrophobic properties by treatment with at least one compound from the group of the alkylsilanes or the perfluoroalkylsilanes. The treatment is preferably carried out by the particle-containing surface which is to be rendered hydrophobic in a solution which contains a hydrophobicizing reagent, e.g. Alkylsilanes, has, is immersed, excess hydrophobicizing agent dripped off and the surface is annealed at the highest possible temperature. The maximum applicable temperature is limited by the softening temperatures of the carrier layer and / or the object and is preferably from 100 to 350 ° C., preferably from 200 to 300 ° C.

The surfaces according to the invention are preferably produced by the method according to the invention. Structured surfaces, particularly preferably nanostructured surfaces, are preferably produced by means of the method according to the invention.

The surfaces according to the invention preferably have a layer with elevations which are formed by the particles themselves, with an average height of 0.02 to 25 μm and an average distance of 0.02 to 25 μm, preferably with an average height of 0.05 to 10 μm and / or an average distance of 0.05 to 10 μm and very particularly preferably with an average height of 0.05 to 4 μm and / or an average distance of

0.05 to 4 μm. The surfaces according to the invention very particularly preferably have elevations with an average height of 0.25 to 1 μm and an average distance of 0.25 to 1 μm. In the sense of the present, the mean distance between the surveys

Invention understood the distance of the highest elevation of one elevation to the next highest elevation. If an elevation has the shape of a cone, the tip of the cone represents the highest elevation of the elevation. If the elevation is a cuboid, the uppermost surface of the cuboid represents the highest elevation of the elevation.

The wetting of bodies and thus the self-cleaning property can be described by the contact angle that a drop of water forms with the surface. A wedge angle 0 ° means complete wetting of the surface. The static contact angle is generally measured using devices in which the contact angle is optically determined. Static contact angles of less than 125 ° are usually measured on smooth hydrophobic surfaces. The present surfaces with self-cleaning properties have static contact angles of preferably greater than 130 °, preferably greater than 140 ° and very particularly preferably greater than 145 °. It was also found that a surface only has good self-cleaning properties if it has a difference between the advancing and retreating angles of at most 10 °, which is why surfaces according to the invention preferably have a difference between the advancing and retracting angles of less than 10 °, preferably less than 5 ° and particularly preferably have less than 4 °. To determine the angle of progression, a drop of water is placed on the surface by means of a cannula and the drops on the surface are enlarged by adding water through the cannula. During the enlargement, the edge of the drop glides over the surface and the contact angle is determined. The retraction angle is measured on the same drop, only the water is withdrawn from the drop through the cannula and the contact angle is measured while the drop is being reduced. The difference between the two angles is called hysteresis. The smaller the difference, the less the interaction of the water drop with the surface of the surface and the better the lotus effect.

The surfaces according to the invention with self-cleaning properties preferably have an aspect ratio of the elevations which are formed by the particles themselves of greater than 0.15. The elevations which are formed by the particles themselves preferably have an aspect ratio of 0.3 to 0.9, particularly preferably from 0.5 to 0.8. The aspect ratio is defined as the quotient of the maximum height and the maximum width of the structure of the surveys.

Particularly preferred surfaces according to the invention have particles with an irregular, airy, fissured fine structure, which preferably have elevations with an aspect ratio in the fine structures of greater than 1, particularly preferably greater than 1.5. The aspect ratio is in turn defined as the quotient from the maximum height to the maximum width of the survey. 1 shows the difference between the elevations formed by the particles and the elevations formed by the fine structure are illustrated schematically. The figure shows the surface of a surface-modified object X, which has a particle P (only one particle is shown to simplify the illustration). The elevation that is formed by the particle itself has an aspect ratio of approx. 0.71, calculated as the quotient from the maximum height of the particle mH, which is 5, since only the part of the particle that emerges from the surface of the surface modified Object X protrudes, contributes to the survey, and the maximum width mB, which is 7 in relation to it. A selected elevation E of the elevations, which is present on the particles due to the fine structure of the particles, has an aspect ratio of 2.5, calculated as the quotient of the maximum height of the elevation mH ′, which is 2.5 and the maximum width mB ', which is 1 in proportion.

It is advantageous if at least some of the particles, preferably more than 50% of the particles, are pressed into the carrier layer of the surface-modified article only up to 90% of their diameter. The surface therefore preferably has particles which are anchored in the surface with 10 to 90%, preferably 20 to 50% and particularly preferably 30 to 40% of their mean particle diameter, and thus with parts of their inherently fissured surface still from the carrier layer of the surface-modified Protrude objects. This ensures that the elevations which are formed by the particles themselves have a sufficiently large aspect ratio of preferably at least 0.15. In this way it is also achieved that the firmly connected particles are very durable connected to the surface of the carrier layer. The aspect ratio is defined here as the ratio of the maximum height to the maximum width of the elevations. According to this definition, a particle assumed to be ideally spherical, which projects 70% from the surface of the surface-modified object, has an aspect ratio of 0.7. It should be explicitly pointed out that the particles according to the invention need not have a spherical shape.

When using nanostructured particles which also have hydrophobic properties, the surface according to the invention can have self-cleaning properties.

Depending on the material used for the backing layer and the size and material of the particles can be achieved that the self-cleaning surfaces are semi-transparent. In particular, the surfaces according to the invention can be contact-transparent, that is to say that after creating a surface according to the invention on an inscribed object, this inscription can still be read, depending on the size of the font.

The method according to the invention can be used for the production of films. In this case, a carrier layer is applied to the film by means of the method according to the invention, onto or into which nanostructured particles are attached in a subsequent method step. With the aid of the method according to the invention, films with new properties, e.g. with self-cleaning surfaces.

The method and surfaces according to the invention are described with reference to FIGS. 2a to 3b, without the invention being restricted to them. In Fig. 2a and 2b are scanning electron microscopic (SEM) images of a ready to 8200 coated PET film in different magnification according to the method of the invention with Aerosil ^® R, wherein a knife coating process was used. The figures Fig. 3 a and 3b also show SEM images of a the inventive method with Aerosil ^® R 8200 as coated PET film of different in magnification, wherein an electrostatic coating system was used.

The following examples are intended to explain the surfaces according to the invention or the method for producing the surfaces in more detail, without the invention being restricted to these types of embodiments.

Example 1:

A commercially available PET film (200 μm thick) was passed over a roller at a speed of 5 m / min. The lacquer (4 parts by weight of pentaerythretaetraacrylate; 12 parts by weight of hexanediol diacrylate; 4 parts by weight of methyl methacrylate, 0.4 parts by weight of Darocure 1173 and 2.8 parts by weight of Plex 4092F) was applied to the film by means of a coating process. This was done using a knife coating process as described in the "Coatings Technology Handbook". The coating was applied in a thickness of 50 μm. In the subsequent process step, the particles (50 g / m ² ) were lightly sprayed onto the paint using a spray gun at a pressure of 0.5 bar. Aerosil ^® R 8200 was used as the particle.

The carrier layer was cured with an irradiance of 250 W / cm ² .

The behavior of the sample was then characterized. The sample showed a very good lotus effect. Water droplets dripped off very well. The roll angle, i.e. the angle to the horizontal at which a drop rolls off independently, was 1.7 ° for a 60 μl drop of water. The advancing angle of a drop of water was 147.0 °, the retreat angle was 144.7 °. 2a and 2b show SEM images of the sample in different magnifications.

Example 2: The parameters of the coating system were set as in Example 1. However, the coating method was changed. An electrostatic coating was used in this example. This was done with an electrostatic coating system from the Nordson Surecoat company. The powder was applied to the not yet hardened paint. The following parameters were selected for the electrostatic coating: • Atomizing air 0.5 bar

• Gun supply 1 bar

• Vortex air 1 bar

• Current 25 mA at 40 kV

• Particles used: Aerosil ^® R 8200

The subsequent characterization of the surface showed a very good roll angle of 1.2 °. The advancing angle of a drop of water was 151.8 °, the retreat angle was 150.4 °. 3a and 3b show SEM images of the sample in different magnifications.

Claims

Claims;

1. A method for producing structured surfaces, characterized in that the method has the following steps: i.) Applying a curable substance as a carrier layer on a surface by means of a coating technique, ii.) Applying particles to the carrier layer by means of a coating technique and subsequent iii .) Fixing the particles to the carrier layer by hardening the carrier layer.

2. The method according to claim 1, characterized in that the coating technique of roll-coating is used in process step i.).

3. The method according to at least one of claims 1 or 2, characterized in that as a curable substance of the carrier layer, a lacquer, the at least mixtures of mono- and / or polyunsaturated acrylates and / or methacrylates and / or polyurethanes and / or silicone acrylates and / or Has urethane acrylates, or an adhesive is used.

4. The method according to at least one of claims 1 to 3, characterized in that the particles have an average particle diameter of 0.02 to 50 microns.

5. The method according to at least one of claims 1 to 4, characterized in that the particles have an irregular fine structure in the nanometer range on their surface.

6. The method according to at least one of claims 1 to 5, characterized in that that particles selected from minerals, aluminum oxide, silicates, silicas, metal oxides, mixed oxides, metal powders, pigments or polymers are used.

7. The method according to at least one of claims 1 to 6, characterized in that the particles have hydrophobic properties.

8. The method according to at least one of claims 1 to 7, characterized in that in process step ii.), A suspension comprising particles is applied as a film to the carrier layer.

9. The method according to claim 8, characterized in that the coating technique of roll coating is used in process step ii.).

10. The method according to claim 8 or 9, characterized in that the particles are present in an alcohol, selected from ethanol, 2-propanol and methanol, or in a mixture of these compounds in process step ii.).

11. The method according to at least one of claims 8 to 10, characterized in that the liquid components of the suspension are removed before the particles are fixed on the carrier layer.

12. The method according to at least one of claims 1 to 7, characterized in that in method step ii.) The particles are applied to the carrier layer by means of an electrostatic coating.

13. The method according to at least one of claims 1 to 12, characterized in that the hardening of the carrier layer is carried out thermally or by means of UV radiation.

14. Surface produced by a method according to at least one of claims 1 to 13.

15. Surface according to claim 14, characterized in that the surface has elevations with an average height of 0.02 to 25 microns and an average distance of 0.02 to 25 microns.

16. Surface according to claim 14 or 15, characterized in that the elevations which are formed by the particles themselves have an aspect ratio of 0.3 to 0.9.

17. Use of the method according to at least one of claims 1 to 13 for the production of structured surfaces or films.