EP3731689A1

EP3731689A1 - Structure with improved adhesion

Info

Publication number: EP3731689A1
Application number: EP18826297.6A
Authority: EP
Inventors: Eduard Arzt; René HENSEL; Karsten Moh; Verena Nicola KÜMPER
Original assignee: Innocise GmbH
Current assignee: Innocise GmbH
Priority date: 2017-12-27
Filing date: 2018-12-18
Publication date: 2020-11-04
Also published as: US11787982B2; WO2019129540A1; CN111757686A; JP7291962B2; DE102017131347A1; US20210071046A1; JP2021507836A

Abstract

The invention relates to a structure with improved adhesion, in particular with improved force distribution. This is achieved by a structure with projections and a backing layer, the rigidity of the backing layer being variable, and the end faces defining a common surface.

Description

Structure with improved adhesion

description

Field of the invention

The invention relates to a structure with improved adhesion to surfaces, in particular with improved force distribution.

State of the art

The molecular adhesion between two objects can be enhanced or controlled by fiber-like surface structures. This principle is known as gecko effect. If a structured elastomer surface is pressed with a certain pressure force against a comparatively flat surface, van der Waals interactions can form. The reverible liability, ie the possibility of switching attachment and detachment, is also known from nature. When Verwen tion of columnar adhesive structures, ie structures which consist of a plurality of columnar projections, de ren faces form the contact surface for adhesion to a top surface, a detachment is usually triggers that by external influences the contact surface for Surface is reduced. The strength of the adhesion and also the type of detachment can be controlled by the structure of the dry-adhesive structure on the upper surface. This allows in contrast to normal adhesive joints a much higher control of the adhesion forces.

Especially for applications in which objects on certain surfaces must be reversibly fixed, such

Structures bring benefits.

One problem with such structures is that when pulling off an object, the tensile forces in the structure laterally disperse over the individual protrusions. This is due to deviations from a uniform load distribution (elastic load distribution) due to elastic interactions in the backing layer (backing layer) to which all projections are attached, or due to non-parallel orientation of the structure relative to the contacted surface (substrate). As a result, the liability is significantly reduced compared to the theoretically expected value.

This uneven force distribution occurs especially when the structures are connected by an elastic or viscoelastic back layer and is also reinforced when the upper surface of the object is convexly curved ge in the direction of the adhesive structures. The reason is the mechanical coupling of the structures via the deformable backing layer. This coupling is more pronounced for structures at the edge and for structures within the array: Due to a smaller number of adjacent structures, the adhesive structures are loaded more at the outer edge than the structures within the array. rays. Due to the unequal load, detachment / failure of the adhesive structures takes place from the edge. How strongly this inhomogeneous distribution affects the efficiency or viability of the entire adhesion structure depends on the number of structures that are claimed in an array. In general, the efficiency of an adhesive structure array decreases with an increasing number of structures involved in adhesion. That is, large arrays are more inefficient than small arrays. The actual efficiency can be determined by numerical methods.

A scientific analysis of the problem has been published by Bacca, Booth, Turner and McMeeking (Bacca et al., Journal of the Mechanics and Physics of Solids 2016, 96, 428-444, Load sharing in bioinspired fibrillar adhesives with backing layer interactions and interfacial misalignment) , The authors emphasize that a uniform force distribution can be achieved by adjusting the elasticity of the individual fibers, either via the modulation of the modulus of elasticity or the height of the projections. However, a clumping of the projections must be avoided.

task

The object of the invention is to provide a structure which has improved adhesion and in particular a verbes serte force distribution.

solution

This object is achieved by the inventions having the features of the independent claims. Advantageous developments of Inventions are characterized in the subclaims. The wording of all claims is hereby incorporated by reference into the content of this specification. The inventions also include all reasonable and in particular all mentioned combinations of independent and / or dependent claims.

The invention is characterized by a structure comprising a back layer, a plurality of protrusions on this backing layer, each protrusion having an end face, wherein all end faces span a common surface and the stiffness of the back layer varies towards at least one edge of the structure decreases.

Preference is given to a decrease in the stiffness to the edge by up to 50%, based on the highest rigidity, preferably by up to 30%, in particular a change in the rigidity by at least

? so ·

By varying the stiffness of the backing layer, it is sufficient that the coupling between the projections changes over the backing layer towards the edge. This significantly improves the adhesion of the structure.

In a preferred embodiment, the stiffness of the backing layer decreases toward all edges of the structure. An edge of a structure is understood to mean the end of the arrangement of protrusions on the backing layer. The backing layer preferably has a gradient of stiffness in the direction of the edges parallel to the adhesive surface.

The change in stiffness can be achieved in different ways. In one embodiment of the invention This change is achieved in that the thickness of the back layer decreases towards at least one edge of the structure.

Since the end faces of the projections span a common surface, it is achieved by varying the thickness of the backing layer that the projections in the center of the structure are shorter, while the length of the projections increases towards the edge, the end faces of the projections still being suitable are to contact flat surfaces, since the end faces span a common surface.

The thickness of the backing layer decreases in the direction of at least one edge of the structure, preferably in the direction of at least two edges, in particular towards all edges. This can be achieved for example by a curved shape of the backing layer. Alternatively, it is also possible that the structure in the middle has a constant thickness of the backing layer, and they only towards the edge, z. B. in the last quarter, measured on the diameter of the structure, the thickness of the backing layer decreases.

By this modification of the backing layer is also achieved that larger objects are not gripped by large, difficult to produce Haftstrukturarrays, but alternatively by a variety of smaller adhesive structure arrays and replaced NEN and the edge effects on the smaller arrays hardly reduce the adhesive force.

When the thickness decreases toward the edge, it is understood that the thickness decreases at least in the area at the edge. This means that in any case at the edge of the structure, the thickness of the backing layer decreases steadily. The resulting structure indicates the edges compared to the middle of the backing layer longer before cracks.

By this structure it is achieved that the structure is also suitable for adhesion to flat surfaces, and yet has an improved distribution of force.

In addition, in the intentional detachment for the purpose of placing objects, the detachment first begins at the edge and then proceeds inward. As a result, a controlled detachment with improved local precision he goes.

In another embodiment of the invention, the change in rigidity is achieved by modifying the modulus of elasticity of the backing layer accordingly. This can be done by a gradient within the material. This is preferably achieved in that the backing layer has at least two regions with different modulus of elasticity. The backing layer is constructed in particular on the expansion from the individual areas so that a difference in the adhesive force of the structure is achieved.

In a preferred embodiment, these areas are formed as layers, in particular as layers whose perpendicular right thickness varies. As a result, the rigidity of the backing layer at a certain point depends on the ratio of the different layers. The thickness of the respective layers, the stiffness of the backing layer controlled who the. In a preferred embodiment, towards the edge, the vertical portion of regions with a high modulus of elasticity decreases, so that the stiffness decreases. This means that the thickness of the layers changes accordingly.

The use of multiple layers has the advantage that the length of the projections can remain constant, which facilitates the manufacture and stability of the structures. At the same time, the backing layer can be made more easily multilayered, which facilitates the adjustment of rigidity for different applications.

In one embodiment of the invention, the backing layer comprises 2, 3 or 4 layers with different modulus of elasticity, preferably 2 layers with different modulus of elasticity.

The layers do not have to extend over the entire surface of the backing layer. Preferably, the layers extend over the entire surface of the structure

The outermost layer can also be fixedly connected to a carrier or be part of a carrier of the structure according to the invention. Importantly, it has an impact on the adhesion of the structure.

In a preferred embodiment, the backing layer has a first layer on which the projections are arranged. Un ter of this layer, a second layer is arranged. Both layers have a common interface. If the modulus of elasticity of the first layer is greater than that of the second layer, the thickness of the second layer preferably decreases in the direction of at least one edge, while the thickness of the first layer th layer increases. This can be achieved, for example, by virtue of the fact that the boundary surface of the two layers is curved in the direction of the projections, ie is convex. If the modulus of elasticity of the first layer is higher, it is the other way around, ie the interface is correspondingly concave-shaped and the thickness of the second layer increases accordingly.

Preferred is a convex interface. Preferably, the

Parabolic, hemispherical shaped to cup-shaped or wan nenförmig. Particularly preferably, the curvature of the interface is described by a straight polynomial (polynomial function with even exponents).

In a preferred embodiment of the invention, the thickness of the backing layer is constant with respect to all layers.

In a preferred embodiment, the modulus of elasticity of the first layer corresponds to the elastic modulus of the jumps before.

The elastic modulus of the back layer is preferably 50 kPa to 3 GPa. The modulus of elasticity is preferably 50 kPa to 5 GPa, in particular 100 kPa to 1 GPa, particularly preferably 500 kPa to 100 MPa.

In the case of multiple layers, the modulus of elasticity of at least one layer is 50 kPa to 3 GPa. The modulus of elasticity is preferably 50 kPa to 5 GPa, in particular 100 kPa to 1 GPa, particularly preferably 500 kPa to 100 MPa. The modulus of elasticity of at least one layer is preferably 50 kPa to 20 MPa, preferably 100 kPa to 10 MPa. The modulus of elasticity of the at least one high elastic modulus layer is independently thereof at least 1 MPa, more preferably 1 MPa to 3 GPa, preferably 2 MPa to 1 GPa.

The ratio of the moduli of elasticity of the layer with the lowest modulus of elasticity and the layer with the highest modulus of elasticity is preferably greater than 1: 2, preferably greater than 1: 100, in particular greater than 1: 500, most preferably greater than 1: 1000, in particular over 1: 1500. Such high differences have a particularly advantageous effect.

The thickness of the backing layer can be selected according to the application. Depending on the height of the projections, the maximum thickness may be up to 5 cm, preferably up to 3 cm. It can also be less than 1 cm, for example less than 5 mm.

The thickness is chosen so that ei ne corresponding improvement in the adhesive force is achieved even with variation of the thickness. Be preferred is a variation of the thickness by up to 50%, starting from the maximum thickness, preferably by up to 30%, in particular by at least 5%.

In the case of multiple layers, the thickness is selected so that an improvement in the adhesive force is achieved. In the case of several layers, the thickness of at least two layers for changing the stiffness preferably varies by at least 2% based on the maximum thickness of the backing layer, preferably by at least 5%, preferably by at least 30%.

The thickness of a layer can be at 0, if it is not present in this area. In the layer with the lowest modulus of elasticity is given to before that their minimum thickness (d) relative to the senkrech th height of the projections (L) is less than 1, preferably if it is the layer on which the projections are arranged.

Preference is given to structures which comprise a large number of projections (pillars) which each have at least one respective stem and comprise an end face pointing away from the surface. With this face, the projections come into contact with the surface to which they are to adhere.

Under the vertical height of the end face of the distance of the end face is understood to the surface on which the Vorsprün ge are arranged.

In a preferred embodiment of the invention, the projections of each structure of the invention are columnar ausgebil det. This means that it is preferably formed perpendicular to the surface projections having a stem and an end face, wherein the stem and the end face may have any cross-section (for example, circular, oval, rectangular, square, rhombic, hexagonal , pentagonal, etc.).

Preferably, the projections are formed so that the perpendicular right projection of the end face on the base of the jump ahead with the base surface forms an overlap surface, where at the overlap surface and the projection of the overlap surface on the end face a body span, which lies completely within the projection , In a preferred embodiment of the invention, the overlap area comprises at least 50% of the base area, preferably at least 70% of the base area, particularly preferably the overlapping area comprises the entire base area. The projections are therefore preferably not inclined be.

In a preferred embodiment, the end face is paral lel aligned with the base surface and the surface. If the faces are not aligned parallel to the surface and therefore have different vertical heights, the vertical height of the face is considered to be the vertical height of the face.

In one embodiment, the end face of the projections is larger than the base, so-called "mushroom" structures.

In a preferred embodiment of the invention, the stem of the projection has an aspect ratio of height to diameter of 0.5 to 100, preferably 1 to 10, particularly preferably 1 to 5, based on its mean diameter.

In this case, the average diameter is understood to be the diameter of the circle which has the same area as the corresponding cross section of the projection, averaged over the entire height of the projection.

The end faces span a common surface. By this is meant that the end faces can be part of a continuous area, for example a plane. It can also be a curved surface. The end faces of the projections may themselves be structured to increase their surface area. In this case, the average vertical height of the end face is considered as the vertical height of the projections.

In a preferred embodiment, the vertical height of all projections in a range of 1 ym to 10 mm, preferably 1 ym to 5 mm, in particular 1 ym to 2 mm, preferably in a range of 1 ym to 1 mm.

In a preferred embodiment, the base area of the surface corresponds to a circle with a diameter between 0.1 ym to 5 mm, preferably 0.1 ym and 2 mm, in particular before given to 1 ym and 500 ym, more preferably between 1 ym and 100 ym. In one embodiment, the base is a circle having a diameter between 0.3 ym and 2 mm, preferably 1 ym and 100 ym.

The average diameter of the strains is preferably between 0.1 .mu.m to 5 mm, preferably 0.1 .mu.m and 2 mm, in particular preferably between 1 .mu.m and 100 .mu.m. Preferably, the height and the median diameter are adjusted according to the preferred aspect ratio.

In a preferred embodiment, with widened end faces, the surface of the end face of a projection is at least 1.01 times, preferably at least 1.5 times as large as the area of the base of a projection. It may be greater by a factor of 1.01 to 20 or, for example, be 1.05 to 2 times larger in example. In a further embodiment, the end face is between 5% and 100% larger than the base area, particularly preferably between 10% and 50% of the base area.

In a preferred embodiment, the distance between two projections is less than 2 mm, in particular less than 1 mm.

The projections are preferably arranged periodically periodically.

The elastic modulus of the protrusions is preferably 50 kPa to 3 GPa. The modulus of elasticity is preferably 50 kPa to 5 GPa, in particular 100 kPa to 1 GPa, particularly preferably 500 kPa to 100 MPa.

The materials of the projections and the backing layer can be chosen according to the requirements of the skilled person. The protrusions may comprise, for example, the following materials: epoxy- and / or silicone-based elastomers, thermoplastic elastomers (TPE), polyurethanes, epoxy resins, acrylate systems, methacrylate systems, polyacrylates as homo- and copolymers, polymethacrylates as homo- and copolymers (PMMA, AMMA Acrylonitrile / methyl methacrylate), polyurethane (meth) acrylates, silicones, silicone resins, rubber such as R rubber (NR natural rubber, IR poly-isoprene rubber, BR butadiene rubber, SBR styrene-butadiene rubber, CR chloroprene rubber, NBR Nitrile rubber) M rubber (EPM ethene-propene rubber, EPDM ethylene-propylene rubber), unsaturated polyester resins, formaldehyde resins, vinyl ester resins, polyethylenes as homo- or copolymers, as well as mixtures and copolymers of the abovementioned materials. lien. Also preferred are elastomers approved for use in the packaging, pharmaceutical and food industries by the EU (in accordance with EU-VO No. 10/2011 of 14.01.2011, published on 15.01.2011) or FDA or silicone-free UV-curable resins the PVD and CVD process engineering. This is Po

polyurethane (meth) acrylates for polyurethane methacrylates, polyurethane acrylates, and mixtures and / or copolymers thereof.

Preference is given to epoxy- and / or silicone-based elastomers, polyurethane (meth) acrylates, polyuretanes, silicones, silicone resins (such as UV-curable PDMS), polyurethane (meth) acrylates or rubber (such as EPM, EPDM).

The backing layer is preferably also from one of the vorste existing materials, more preferably from the same mate rial as the projections.

In the case of several areas, at least one area is made of the aforementioned materials. The higher modulus layers may also be made of other materials such as plastics, metals, ceramics, preferably plastics such as thermosets or thermoplastics such as polystyrene, acrylonitrile-butadiene-styrene, polylactides, polyvinyl alcohol, polyamides such as polyamide PA 66). Preference is given to plastics which can be applied by injection molding or 3D printing.

The structures according to the invention are preferably prepared in Gussver.

The invention also relates to a process for producing a structure according to the invention. For this purpose, a mold is provided which has a negative structure of the structure comprising protrusions and a thickness-varying backing layer. The mold is filled in accordance with a curable precursor for the material of the backing layer and the projections. Thereafter, the precursor is cured depending on the material used, which can be done physically and / or chemically. For example, by heating or irradiation, for example with UV). The structure is removed from the mold and optionally subjected to further processing steps Be.

The invention also relates to a method for producing a structure according to the invention, in which the backing layer comprises at least two regions. For this purpose, a mold is provided which comprises a negative structure of the structure comprising protrusions and the backing layer. In addition, another body is be provided, which corresponds in its dimensions to a range of forth delivering back layer. This body may be arranged on a support or be part of it.

In the next step, a hardenable precursor is poured into the mold. In a next step, the further body is introduced into the mold so that it forms the later backing layer together with the precursor. It is possible that the body partially deformed and / or displaces the precursor, for example if it has a curved structure. The pre-stage and the body form the backing layer after hardening.

Since the body is pressed into the preliminary stage, it can also be called Inlet. Preferably, the body is of a material having a higher modulus of elasticity than the material in the mold after curing.

Thereafter, the precursor is cured. Thereby, the projections and the first area are formed. Thereafter, the structure is removed from the mold. The backing layer is formed by the cast structure and the additional body. The further body forms the second area of the backing layer.

The further body may already include several areas with un ferent modulus of elasticity.

The other body can be made in various ways who the. For example, it is possible to set it up via 3D printing. By the method according to the invention, the shape of the individual regions of the backing layer can be determined in a simple manner. In particular, the production of the projections and the final structure can be carried out in one step. By prior production of the further body, geometries can be obtained which are not possible by means of sequential casting methods.

The further body is preferably concave and has in its center the highest thickness.

Especially with very small and sensitive components, such as micro chips, integrated circuits, displays or touchscreens, the structure of the invention provides opportunities for precise handling without heavy load on the object. Thus, by improving the adhesion with adhesive structures with lower expansion can be worked. The area required for adhesion is significantly lower.

The invention therefore also relates to the use of the inventions to the invention structure for dry adhesion, in particular for Handling or attachment of objects via dry-adhesive adhesion.

Further details and features will become apparent from the fol lowing description of preferred embodiments in conjunction with the subclaims. Here, the respec conditions may be realized alone or in combination with each other in combination. The possibilities to solve the problem are not limited to the embodiments.

For example, area information always includes all - not mentioned - intermediate values and all imaginable subintervals.

The embodiments are shown in the figures schematically Darge. The same reference numerals in the individual figures denote NEN same or functionally identical or with respect to their functions corresponding elements. In detail shows:

Fig. 1 Schematic representation of an embodiment of the invention;

Fig. 2 Schematic representation of an embodiment of the invention;

Fig. 3 Schematic representation of an embodiment of the invention;

4 shows a schematic representation of an embodiment of the invention with a curved backing layer;

Fig. 5 shows a schematic representation of an embodiment of the invention with a multilayer backing layer;

Fig. 6 measurement of the adhesion force of different structures; Figure 7 shows a structure according to the invention in cross-section.

8 shows a schematic representation of the production of a structure according to the invention; 9 shows a schematic representation of the production of a structure according to the invention;

10 shows a schematic representation of an embodiment of the invention with a multilayer backing layer;

Fig. 11 Schematic representation of an embodiment of the invention He with multilayer backing layer.

Fig. 1 shows a schematic representation of a erfindungsge MAESSEN structure. On a backing layer 100, a plurality of projections 110 are arranged, which each have end faces 120. The surface of the back layer without the projections is convexly curved in this embodiment.

Fig. 2 shows a schematic representation of a erfindungsge MAESSEN structure. On a backing layer 100, a plurality of projections 110 are arranged, which each have end faces 120. The surface of the backing layer without the protrusions is roof-shaped or conically shaped in this embodiment. It is also possible that the thickness of the backing layer decreases only in one dimension. In this case, the surface of the backing layer is gabled without protrusions.

Fig. 3 shows a schematic representation of a erfindungsge MAESSEN structure. On a backing layer 100, a plurality of projections 110 are arranged, which each have end faces 120. In this embodiment, the thickness of the back layer in the middle of the structure is constant and only decreases towards the edges.

Fig. 4 shows a schematic representation of a erfindungsge MAESSEN structure with a curved backing layer 130 on the jumps before 110 are arranged. The faces of the projections 120 are at the same height and so span a plane. Therefore, over the width of the structure D, the height of the projections varies from the lowest height L _m in the middle to the highest height L _a at the edge of the structure.

Fig. 5 shows a schematic representation of a erfindungsge MAESSEN structure with a multilayer structure of the back layer. The backing layer has a first region 140 with a modulus of elasticity E2. In this area, the jumps before 110 are arranged. The backing layer still has a second region 150 with a modulus of elasticity Ei. E _! > E ₂ . Both regions 140, 150 are formed as layers and are arranged on each other. Its interface 160 is concave in the direction of the projections. As a result, the first region has a minimum thickness of d at the center of the structure. There is also the thickness of the second area is the largest.

Towards the two edges, the thickness of the first region increases while the thickness of the second region decreases. If the interface is concavely curved in all directions, for such a body, the stiffness increases towards all edges. The second region extends over the entire width D of the structure. The ratio of the minimum thickness d to the height of the projections is preferably less than 1.

Fig. 6 shows the measurement of the adhesion force of various

Structures on a glass surface. After contact with the surface, the samples were moved perpendicular to the surface until they reached a pre-load ("pressing") and then moved away from the surface until they were completely detached (distance in mm, "peel-off"). The forces acting on the structure and the surface were measured in the direction of movement. The necessary peel force is the force that needed for complete replacement. The measurement clearly shows that to detach a structure with two layers as shown in FIG. 7 (sample with inlet) a significantly higher force is required than for a sample prepared with the same dimensions without a multilayer back layer (sample on in let). ,

Fig. 7 shows a structure with projections on a back layer. The structure was cut in half, so that the cross section can be seen. The projections have egg NEN circular diameter and are periodically arranged regularly. They are arranged on a backing layer which comprises two regions, which in turn are formed as layers. It can be clearly seen that the thickness of the first area is the lowest with the protrusions in the middle. The second area forms a layer below the first area.

The concave curved surface is clearly visible. The height of the backing layer is known throughout the structure. Only the thickness of the two layers varies.

Fig. 8 shows schematically the preparation of an inventive Shen structure with varying thickness of the backing layer (backing layer). An appropriate mold is provided (left). In this, the pre-polymer for the material is filled and closed the mold with a lid (middle Dar position). The mold is completely filled. In the next step, the pre-polymer is cured, for example, crosslinked. After demolding from the mold (right) the fiction, contemporary structure is obtained.

Fig. 9 shows schematically the preparation of an inventive Shen structure with multilayer backing layer. There will be a Mold provided for the entire structure. In this form, the pre-polymer is filled (left). The pre-polymer is the precursor for the material of the protrusions and the first region of the backing layer. In addition, an inlet is provided on a carrier. This inlet can be produced, for example, via 3D printing. It is arranged on a support which can also form the cover of the casting mold. As much prepolymer is introduced into the mold that the mold is completely filled after insertion of the inlay (middle illustration) into the mold. Thereafter, the pre-polymer is cured and the structure demolded (right). In this way, a structure having a multilayer back layer is obtained.

10 shows an embodiment of the invention with a more layered backing layer comprising a first region 170 and a second region 180. On the first region, the projections 110 are arranged with end faces 120. The change in rigidity is achieved by having the thickness of the first region 170 lowest in the center and steadily increasing linearly toward the edge. Accordingly, the thickness of the second region 180 decreases. The interface is in this case depending on the three-dimensional structure of the structure roof-shaped or conical.

11 shows an embodiment of the invention with a more layered backing layer comprising a first region 190 and a second region 200. On the first region, the projections 110 are arranged with end faces 120. The change in rigidity is achieved by having the thickness of the first region 190 in the middle lowest, remaining constant, and then steadily increasing linearly towards the edge. Accordingly, the thickness of the second region 200 decreases. The border Area is in this case dependent on the three-dimensional structure of the structure roof-shaped with truncated gable or similar to a truncated cone.

Cover _Z oak backsheet

head Start

face

backing

first region of the backing layer

second area of the backsheet (Inlet) interface

first region of the backing layer

second region of the backing layer (inlet) first region of the backing layer

second area of the backing layer

Claims

claims

A structure comprising a backing layer, a plurality of protrusions on said backing layer, each protrusion having an end face, all faces defining a common surface, characterized in that the stiffness of the backing layer varies towards at least one edge of the structure.

2. Structure according to claim 1, characterized in that the rigidity of the backing layer decreases towards at least one edge of the structure.

3. Structure according to one of the preceding claims, characterized in that the thickness of the backing layer in each direction decreases towards Rich.

4. Structure according to one of the preceding claims, characterized in that the thickness of the backing layer in the region of the edge of the structure decreases steadily.

5. Structure according to one of the preceding claims, characterized in that the backing layer has at least two regions with different modulus of elasticity.

6. Structure according to claim 5, characterized in that the regions are formed as layers.

7. Structure according to one of the preceding claims, characterized in that the structures are formed like a column.

8. A process for producing a structure according to any one of claims 5 to 7, comprising the following steps:

a) providing a mold comprising the negative structure of the structure comprising protrusions and backing layer;

b) providing a further body, which in its dimensions corresponds to a region of the backing layer to be produced;

c) filling a hardenable precursor into the mold;

d) inserting the further body into the mold;

e) curing the precursor

f) demolding the structure from the mold.

9. Use of the structure according to any one of claims 1 to 7 for dry adhesion.