EP4414092A1 - Modular microstructure element - Google Patents

Abstract

The invention is based on the object of creating a superhydrophobic structure that can be easily produced by mass production, that is easy to demold and that can be easily replicated and has a modular structure. For this purpose, a modular component is provided which is constructed from several repeatable individual elements (13) and comprises several microstructure elements (5) which rise perpendicular to a main extension plane (11) of a base body (3) or form depressions therein and which end at at least two different distances from the main extension plane, the distances following a periodically repeating function. In addition, a manufacturing method for the individual elements and a module to be manufactured therefrom is specified.

Description

In recent years, structures that exhibit the so-called Lotus effect have become increasingly important. For example, this effect is described in the article " Lotus effect in wetting and self-cleaning" Biotribology Volume 5, March 2016, pages 31-43 by Zhang et. al . discussed. The patent literature also shows an increasing number of publications in this area.

Many different manufacturing methods are established. EP 2 636 501 B1 (Owner: Mitsubishi Rayon Co Ltd., priority date: 26 May 2011 ) presents a roll-to-roll molding and curing process for microstructured objects. In the US 2007/0259156 A1 (inventor: Roger Kempers et. al., filing date: May 3, 2006 ) a 3-D printing process is proposed, especially for randomly distributed distances.

In the US 2017/0144202 A1 (Applicant: The board of trustees of the University of Illinois, priority date: February 17, 2009 ) superhydrophobic films are shown that demonstrate selective control of the hydrophobic properties by bending the film by varying the distance between neighboring macrostructures. The effects of different distances between cylindrical microstructures on the wetting angle are discussed. Curing of plastics in lithographically produced molds is explained as an example of a manufacturing process.

The literature hardly deals with the properties of raised or curved surfaces that are supposed to have superhydrophobic properties. Usually only flat objects are discussed. One exception is the US 2012/0177881 A1 (Inventor: Sen Yung Lee et. Al, priority date January 11, 2011 ) in which a superhydrophobic microstructure on a base body with multiple protrusions of different heights is disclosed and mass production options such as embossing and micro/nano imprint lithography are proposed to avoid venting problems.

In the US 2019/ 0 212 859 A1 (Inventors: Michael Milbocker and Lucas Bluecher ) describes an interlacing of touchscreen modules in one embodiment. A tiled structure of a large number of structured elements is provided in a first hierarchy level, which creates the touchscreen property through interlacing of shear forces. Only the second hierarchy level with a smaller structure serves as a hydrophobic surface. This hierarchical structure of the structural elements has the disadvantage that from the second hierarchy level, which is responsible for the hydrophobic properties, the structure becomes complex and no simple repetitions of the structures of the second hierarchy level are possible. In the US 2019/ 0 1333 222 A1 (Inventor: Michael Milbocker and Lucas Bluecher ) different dimensions of the elements of a similar hierarchical structure of structural elements are described. Here too, the structures of the second hierarchy level are complex and cannot be created by simply repeating modules.

In the EN 10 2014 119 470 A1 A structured surface is described that allows the adhesion forces to be switched step by step. The contact of liquids is used in the manufacturing process described there, but otherwise plays no role.

The disclosure content of these publications is incorporated into this application.

A distinction can be made between different effects based on the hydrophobic properties of a material with microstructures. On the one hand, a self-cleaning effect can be achieved by the beading of large liquid drops, and on the other hand, the formation of condensation and mist on surfaces with microstructures can be avoided in order to prevent fogging and the impairment of visibility through the treated surfaces or in reflection from them.

The invention is based on the object of creating a superhydrophobic structure which can be easily produced by mass production, which is easy to demold, which is easy to replicate and which has a modular structure.

This object is achieved by a component according to claim 1. The possible uses of such a component are shown in claim 11. Claim 12 describes a method for production. Further aspects of the invention are discussed in the dependent claims.

Hydrophobic structures form a wetting angle of greater than 90° with a water droplet. Structures on which a water droplet forms a wetting angle of greater than 105° are defined as superhydrophobic. The wetting angle is the angle that the surface of a liquid droplet forms with the surface of a solid. The volume of the droplet filled with liquid is included in the wetting angle.

A component according to the invention has a base body. The base body can be, for example, a film, a transparent and/or a reflective object. When viewed macroscopically, the base body is preferably approximately flat. This means that an extension of the base body in one spatial direction is at least a factor of 5 smaller than an extension in the other two spatial directions. The two Spatial directions in which the extension of the base body is greatest span a main extension plane. In the case of a rolled-up film or other rolled-up surface, the term main extension plane refers to the unrolled flat state. In this application, the z-direction is considered to be the direction perpendicular to the main extension plane. A zero point of the z-axis is the minimum of all intersection edges of the microstructure elements with the base body. To search for an origin in the Z-direction, you can proceed as follows: You look for a surface that is uneven in one direction, for example an x-direction, which is referred to here as curved; a surface that is uneven in two directions, i.e. in the x and y directions, is referred to as arched.

A large number of microstructure elements rise from the base body perpendicular to the main extension plane or alternatively form depressions in the base body. These microstructure elements increase the contact angle with a liquid drop, in particular with a water drop, and thus give the component according to the invention superhydrophobic properties.

To avoid sharp edges, the microstructure elements are spatially separated from one another. They therefore do not form a coherent unit. With roundings, the component according to the invention can be produced more easily and in a stable form in a two-photon polymerization process, which is described below.

According to the invention, the component is designed to be modular, i.e. several individual elements are put together as if according to the modular principle. The individual elements are therefore constructed in the same way and form the component according to the invention by being repeated multiple times in a row. It is advantageous for the modular construction of a component according to the invention if the repeating individual elements are constructed as simply as possible. For example, substructures of the microstructure elements can be dispensed with. In addition, the number of individual microstructure elements on an individual element can be limited. Preferably, an individual element has fewer than fifteen individual microstructure elements, particularly preferably fewer than ten. This modular construction is also promoted by the fact that a repeating periodic function is selected to represent differences in the ends of the microstructure elements that are remote from the base body in the z direction. The different distances between the ends of the microstructure elements in the z direction increase the contact angle of the liquid drops, increase the water-repellent effect and reduce the contact area between the drops and the microstructure elements.

The microstructure elements can take on one or more shapes, selected from the group of cylindrical or conical (truncated) structures or have the shape of a polygon extending perpendicular to the main plane of extension. The microstructure elements can have a constant diameter or a constant lateral dimension in their course perpendicular to the main plane of extension, or they can taper. Tapered structures have the advantage that they are easier to demold during embossing or injection-compression molding. Examples of these are cylindrical columns or pointed, pyramidal needles. With tapered structures, an even larger wetting angle is possible provided the surface tension of the drop is not destroyed. Structures in which the lateral dimension in the z direction is constant have greater stability. Cylindrical or conical structures are easier to produce due to the symmetry. Structures with a polygonal projection into the main plane of extension, especially with a rectangular checkerboard-like basic structure, have the advantage that negative impressions look the same as positive shapes. This means that, unlike with cylindrical microstructure elements, elevations in the negative also become holes, but the checkerboard pattern is retained. This is particularly advantageous if a base area in the main plane of extension is to be divided exactly in half between the elevations of the microstructure elements and the valleys, which is then also retained in the negative.

According to one embodiment of the invention, all microstructure elements have the same height, which is defined as the extension between the point of contact with the base body and the end remote from the base body, but due to a curvature or curvature of a surface of the base body, they end at a different height distance from the main extension plane, i.e. at a different point in the z-direction that runs perpendicular to the main extension plane. The curvature or curvature of the surface can be described as a periodic function. Examples of such functions are, in the simplest case, sinusoidal surfaces. Since, according to Fourier's theorem, all periodic functions can be represented as series of sine functions, and the limitations then lie in the production, harmonics are of course also included. The microstructure elements are located at different phase positions of the curved surface. Here, the change in the base body over the diameter of the microstructure element is neglected when measuring the height. In production, however, this is compensated for by the two-photon polymerization similar to 3D printing.

According to another embodiment of the invention, different end points on a flat surface of the base body are defined by different heights of the Microstructure elements are achieved. This can be achieved, for example, by individually producing each individual microstructure element on the base body, for example by means of two-photon polymerization. The microstructure elements can be attached with a sinusoidal height distribution above the base body. The height of the microstructure elements differs by the phase position on the base body. The height therefore follows a periodic function, in particular a sine function. This can also be a function f(x,y) that repeats periodically in two spatial directions. If the wavelengths in the x and y directions are different, a preferred direction can be specified in which the liquid drops should roll off.

According to one aspect of the invention, the lateral dimension of the microstructure elements is between 2 µm and 10 µm. The lateral dimension is defined as the largest extension of a microstructure element in a plane coplanar to the main extension plane. Unless otherwise stated, the lateral dimension is the mean height of the cutting edge of the microstructure element with the surface of the base body. In the case of cylindrical, columnar microstructure elements, the term "lateral dimension" means the diameter, in the case of rectangular microstructure elements, the largest edge length.

To achieve the water-repellent effect, heights of the microstructure elements between 8 µm and 20 µm have proven to be suitable. Heights of around 10 µm are particularly suitable, which may vary by the amplitude of the periodically repeating function.

The microstructure elements are spaced apart by between 1 and 30 µm, preferably between 8 and 15 µm, particularly preferably between 10 µm. The distance between two microstructure elements is defined as the shortest lateral distance along a vector that lies in the main plane of extension, for example along the x or y vector or along a linear combination thereof, between two edges that form the respective microstructure elements with the surface of the base body. According to one aspect, a self-cleaning effect can be achieved at distances between 5 and 30 µm in that liquid droplets that run off and are directed to the edge of the component carry dirt particles with them. At smaller distances between the microstructure elements between 1 µm and 5 µm, the formation of condensation by mist droplets can be prevented even more effectively in that mist droplets that form are torn apart by the narrower distances and are then quickly pushed off the component by the hydrophobic properties. This effect can be exploited even more if the microstructure elements are designed as negatives, i.e. as depressions. However, in this configuration the removal of larger dirt particles is severely limited.

The distances between the microstructure elements vary according to one embodiment. This can be achieved, for example, by a predetermined mean distance and a predetermined standard deviation of the distance. The distances are then normally distributed and statistical. The distances between the microstructure elements can also have a gradient structure, for example, have larger values at one edge of the component than at an end further away from it. This allows water drops to be deflected in a targeted direction. Other targeted and defined distributions of the microstructure elements are also conceivable.

Materials from which components according to the invention are manufactured include PMMA, ACRYLIC, PP, PE-HD or PEEK.

A concrete example of the parameters of a component according to the invention is a sinusoidally curved base body with a wavelength of 30 µm and a curvature amplitude of 3 µm with columnar cylindrical microstructure elements that are arranged at a distance of 10 µm and have a constant diameter of 5 µm over the height. In this example, the difference between the height of two adjacent microstructure elements is up to 3 µm.

Components according to the invention can be used, for example, as films, on optical elements, for example in road traffic or for shower cubicles or in humid environments.

To produce the modular component, the invention provides for providing several individual elements, arranging the individual elements in a pattern and then assembling them.

One possible method for producing the individual elements or a master for the individual elements that are to be replicated is two-photon lithography or two-photon polymerization. This takes advantage of the fact that very high intensities or a very high photon density are required to double the frequency of an excitation source, for example a laser in the visible or near-infrared spectral range. This photon density is only achieved in the focus of an ultra-short laser pulse in the femtosecond range. Instead of the resin hardening along the entire light path, it is possible for the hardening to be concentrated at a precise point. In the non-hardened areas, i.e. in the places where the necessary intensity to generate the resonance frequency of the photoinitiator, i.e. a chemical that is released by the If the required curing time is not achieved, the uncured monomer is removed by rinsing with ethanol, for example. This makes it possible to form the microstructure elements at different heights with the required accuracy. Systems and monomers as well as photoinitiators for carrying out two-photon polymerization are commercially available.

Both positive and negative forms can also be produced from individual elements produced by two-photon polymerization by means of metallic coating and single or multiple galvanic molding, from which individual elements can then be produced by means of embossing, injection molding or nanoimprinting processes. Roll-to-roll processes are also conceivable in which the individual elements are repeatedly applied to a roller and transferred in negative to a substrate, e.g. a film or its not yet cured monomers, but after initiation of polymerization. The transfer of the microstructures to a liquid substrate, i.e. to not yet cured polymers, can also be carried out using a fixed frame.

In the case of a roller or roll, the main extension plane is spanned by the vector of the roller or roll axis and a tangential vector on a support line of the roller. The main extension plane is thus virtually rolled up on the roller to form a main extension surface.

According to one embodiment, the roller can be moved in a z-direction perpendicular to the main extension plane. The movement can be carried out by means of a linear motor. The movement can be carried out in such a way that an existing curvature is compensated. The movement of the roller can thus amplify height differences.

The examples shown in the figures represent various embodiments without limiting the generality of the invention.

• Fig. 1 ein einzelnes Modul eines erfindungsgemäßen Elements.
• Fig. 2 zu einem erfindungsgemäßen Element zusammengesetzte Module
• Fig. 3 eine negative Abformung eines erfindungsgemäßen Elements mit einer sinusförmig gekrümmten Oberfläche des Grundkörpers
• Fig. 4 eine Ausführungsform eines erfindungsgemäßen Elements mit einem flachen Grundkörper und abgerundeten kegelförmigen Mikrostrukturelementen, deren Höhe einer Sinusfunktion folgt.
• Fig. 5 eine negative Abformung eines erfindungsgemäßen Elements nach Figur 4
• Fig. 6 eine Ausführungsform eines erfindungsgemäßen Elements zur Erzielung einer Anti-Fog-Wirkung.
• Fig. 7 eine negative Abformung eines erfindungsgemäßen Elements nach Figur 6
• Fig. 8 eine Ausführungsform eines erfindungsgemäßen Elements mit einer in zwei Richtungen gewölbten Oberfläche des Grundkörpers.
• Fig. 9 eine negative Abformung eines erfindungsgemäßen Elements nach Figur 8

They show in several views:

• Fig.1 a single module of an element according to the invention.
• Fig.2 Modules assembled to form an element according to the invention
• Fig.3 a negative impression of an element according to the invention with a sinusoidally curved surface of the base body
• Fig.4 an embodiment of an element according to the invention with a flat base body and rounded conical microstructure elements whose height follows a sine function.
• Fig.5 a negative impression of an element according to the invention Figure 4
• Fig.6 an embodiment of an element according to the invention for achieving an anti-fog effect.
• Fig.7 a negative impression of an element according to the invention Figure 6
• Fig.8 an embodiment of an element according to the invention with a surface of the base body curved in two directions.
• Fig.9 a negative impression of an element according to the invention Figure 8

In Figure 1 an individual element 13 of a component according to the invention is shown in two different views. The individual element 13 has a base body 3 with a surface 7 that is sinusoidally curved in one direction. Viewed from the macrostructure, the base body 3 is approximately flat. A main extension plane 11 can be defined, here for example the flat surface on a side of the base body 3 facing away from the curved surface 7. Several microstructure elements 5 are arranged on the base body at regular intervals 25 from one another. These intervals are, for example, 15 µm.

If the sine curve is averaged over a wavelength 15, this center line runs parallel to the main extension plane 11. The individual microstructure elements 5 run along a normal vector of this main extension plane 11. The microstructure elements 5 are arranged in a different phase position 17. The distances 21 of the end surfaces of the microstructure elements 5 from the main extension plane 11 differ by the difference 27.

For the sake of simplicity, only a sinusoidal curvature 9 is shown in one dimension. Of course, curvatures and bulges in two dimensions are also possible, especially if one wants to specify more than two different distances of the ends of the microstructure elements from the main extension plane.

In Figure 2 shows how several individual elements 13 form a component 1 according to the invention. An individual element 13 is delimited in the frame. The base body 3 forms a seamless unit. The main extension plane 11 runs continuously.

In Figure 3 a negative impression of an individual element 113 according to the invention with a sinusoidally curved surface of the base body is shown. A drop of water is drained away at the points where material is present. The surface tension of the water prevents the liquid drop from flowing into the microstructure elements designed as pores.

Fig.4 shows an embodiment of an individual element 213 according to the invention with a flat base body 203 and rounded conical microstructure elements 205, the height 219 of which follows a sine function. This embodiment shows a self-cleaning effect, since the water drop is repelled from the surface and guided away from the surface of the component according to the invention over an edge 229 and takes dirt particles with it as a drop. The different heights and the rounding of the microstructure elements additionally increase the contact angle.

Figure 5 is a negative impression of the individual element according to the invention from Figure 4 .

In Figure 6 an individual element 313 according to the invention is shown, in which the microstructure elements 305 are conical and are located on a sinusoidally curved surface 307 of the base body 303. The Figure 7 represented negative form to Figure 6 is particularly suitable for preventing the formation of fog, as any droplets that form are broken up.

The Figures 8 and 9 represent an embodiment of the invention in positive or negative impression, in which the surface of the base body is sinusoidally curved in two directions.

List of reference symbols

1 Component 3, 203, 303 Base body 5, 205, 305 Microstructure element 7, 307 surface 9 curvature 11 Main extension level 13, 113, 213, 313 Single element 15 wavelength 17 Phase position 19, 219 Height 21 Distance in z direction 23 diameter 25 Distance (Pitch) 27 difference 229 Edge

Claims (15)

Component (1) comprising a base body (3, 203, 303) which runs along a main extension plane (11), and several Microstructure elements (5, 205, 305) which rise at an angle between 89° and 91°, preferably perpendicular to the main extension plane (11) or form depressions at an angle between 89° and 91°, preferably perpendicular to the main extension plane, characterized in that the microstructure elements (5, 205, 305) are spatially separated from one another and the microstructure elements (5, 205, 305) end at at least two different distances from the main extension plane (11), which follow a periodically repeating function, in particular a sine function, and wherein the component is constructed modularly in several repeatable individual elements (13, 113, 213). Component (1) according to claim 1, characterized in that the base body (3, 303) has at least one surface (7, 307) which has a periodically repeating function, in particular a sinusoidally curved or arched surface, on which the microstructure elements (3, 305) are located in at least two different phase positions (17) and the microstructure elements (3, 305) have the same height (19) on their own. Component (1) according to claim 1, characterized in that all microstructure elements (205) are located on a flat surface parallel to the main extension plane, but differ in their height (219) by the phase position on the base body. Component (1) according to one of claims 1 to 3, characterized in that the periodically repeating function repeats itself periodically in two spatial directions and preferably has a different wavelength in each of the two spatial directions. Component (1) according to one of claims 1 to 4 , characterized in that the microstructure elements (5, 205, 305) have lateral dimensions, in particular diameters (23) between 2 µm and 10 µm and heights (19, 219) between 8 µm and 20 µm, wherein the lateral dimensions along the direction perpendicular to the main extension plane of the microstructure elements (5) can be constant or can taper with a greater distance from the main extension plane (11). Component according to one of claims 1 to 5, characterized in that the microstructure elements (5, 205, 305) in projection onto the main extension plane have a round, elliptical or polygonal cross-section or a combination thereof. Component according to one of claims 1 to 6, characterized in that the microstructure elements (5, 205, 305) are elevations and have a distance (25) between 5 and 30 µm, preferably a distance (23) between 8 and 15 µm, particularly preferably a distance of 10 µm. Component according to one of claims 1 to 6, characterized in that the microstructure elements (5, 205, 305) are depressions which have a distance between one another of between 1 µm and 5 µm. Component according to one of claims 1 to 8, characterized in that the component consists of one of the materials PMMA, ACRYLIC, PP, PE-HD or PEEK. Component according to one of claims 1 to 9 , characterized in that the individual element (13, 113, 213, 313) is produced by means of two-photon polymerization or by embossing or injection-compression molding using a mold produced by two-photon polymerization. Use of a component (1) according to one of claims 1 to 10 on films, optical elements, in particular retroreflectors and lenses, preferably in road traffic, shower cubicles and in humid environments. Method for producing a component according to claim 1 comprising the following steps i. Providing multiple individual elements ii. Arrangement of the individual elements in a pattern iii. Assembling the individual elements Method according to claim 12, characterized in that in step i the individual elements are produced by means of two-photon polymerization. Method according to claim 12, characterized in that before step i a master mold is produced by means of two-photon polymerization, the master mold is coated with metal and galvanically molded one or more times and before this molding the individual element is produced by means of embossing or injection molding or a roll-to-roll nanoimprint process, wherein the mold during embossing is preferably embedded in a liquid substrate, for example a resin, which is cured after embossing. Method according to claim 14, characterized in that the impression of the original form is fixed to a frame during embossing.

Images