EP3732260A1

EP3732260A1 - Double-sided reversible adhesive structure

Info

Publication number: EP3732260A1
Application number: EP18830192.3A
Authority: EP
Inventors: Eduard Arzt; René HENSEL; Karsten Moh
Original assignee: Leibniz Institut fuer Neue Materialien Gemeinnuetzige GmbH
Current assignee: Leibniz Institut fuer Neue Materialien Gemeinnuetzige GmbH
Priority date: 2017-12-27
Filing date: 2018-12-14
Publication date: 2020-11-04
Also published as: WO2019129508A1; US20210071045A1; JP7372918B2; KR20200103725A; US11655396B2; JP2021508611A; DE102017131345A1; CN111511862B; CN111511862A

Abstract

The invention relates to an article having at least two faces that are suitable for dry adhesion and have different adhesion parameters. By suitably structuring the article it is possible, optionally in combination with a suitable contact pressure, to selectively control the release of surfaces contacted on said faces.

Description

Double-sided reversible adhesive structure

description

Field of the invention

The invention relates to an object having at least two Oberflä surfaces, each having at least one surface capable of dry adhesion, and methods for switchable Adhäsi on with such objects.

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. However, while the gecko realizes the detachment by "peeling" its adhesive fibers, this is often not possible for technical structures and usually only makes sense if shear adhesion, ie adhesion, should be used in the direction of the substrate / Obj ektoberflache. In the case of so-called normal adhesion, ie an adhesion force perpendicular to the object surface, the detachment must be initiated differently.

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 targeted control of adhesion forces.

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

Structures bring benefits.

When using columnar adhesive structures, i.

Structures, which consist of a variety of columnar jumps before, whose faces form the contact surface for adhesion to a surface, a replacement is usually triggered by the con tact surface is reduced to the surface by external influences.

It is known that the reduction of the contact surface caused by buckling of projections under pressure who can. With sufficient pressure load leads an elastic cal instability to kinking of the projections. This is also called Euler buckling. The critical force is:

F = C r / L) ² Eq

Here, E is the modulus of elasticity, I is the area inertia model, L is the length (height) of the projection and n is a factor in front of the mechanical clamping of the Projection. The area moment of inertia for a cylindrical structure is / nd = ^4/6. This results in the following cohesion: projections with high height, small diameter or low modulus bend at lower forces than projections with a short length, large diameter or high modulus of elasticity.

Especially in the handling of small objects, conven Liche holding devices come to their limits.

task

The object of the invention is to provide a structure which allows the selective handling of objects, in particular the targeted detachment.

solution

This object is achieved by the inventions having the features of the independent claims. Advantageous developments of the 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 object is achieved by an object which, at least on two surfaces each one capable of dry adhesion Has surface, wherein the two surfaces differ in at least one adhesive parameter.

Preference is given to surfaces whose adhesion to normal adhesion is based. These are in particular surfaces with structures which are based on vertical projections.

Preferably, at least one of the surfaces has a structure encompassing vertical projections. Particularly preferably, both surfaces have structures comprising vertical projections.

The dry adhesion surfaces are preferably arranged on different sides of the object. Preferred is a Anord voltage, so that according to the use of each of the surfaces can be contacted individually. In particular, at least two of the surfaces are arranged on different side surfaces of the object. The two surfaces can be parallel ge opposite or have an angle. In the case of a win angle, it is preferably an acute angle of less than 60 °, in particular less than 30 °. Preferably, mutually parallel side surfaces. The surfaces may also be concave or convex ge arched. This can be varied according to the application who the.

Adhesion parameters are understood to mean not only the adhesion force brought about by the structure, but also the force required to detach the structure. For example, structures may be removable under different conditions, for example by Euler buckling. Due to the buckling of the structure at high contact pressure, the Euler buckling reduces the adhesion force and dissolves the structure with less tensile force from the surface. Such a structure has therefore depending on the contact pressure two different adhesive forces.

If the contact pressure for the Euler kinking does not exceed ten, the adhesive force is usually high, i. the surface adheres firmly to the structure. If the contact pressure exceeds the value for the Euler buckling, the adhesion of the structure is reduced significantly and it can be replaced with much lower tensile force.

It is also possible to detach a structure comprising projections by other deformation of the structures. This can be achieved for example by a shearing load parallel to the adhesive surface. The projections are deformed depending on their bending stiffness (E * I). This also reduces the adhesion force and removes the structure. It does not depend on the shear strength of the adhesive bond, but by the deformation of the structures leads to the reduction of the adhesive force. Structures which are easily bent can be easily removed by this mechanism. The shear stress can be caused by any movement parallel to the upper surface. This can be a linear movement or a turning. The advantage of the separation by shear stress is that no pressure perpendicular to the adhesive surface must be practiced, such as to trigger the Euler buckling. However, such adhesive compounds are susceptible to shear forces. The two surfaces can therefore also in their Ablösung required forces, i. Contact pressure for Euler buckling or shear load for detachment, different.

In the object according to the invention, the adhesive force of the two surfaces is preferably controlled so that the adhesive force at normal adhesion of a surface is higher than that of the other surfaces. This will result in contacting the two surfaces of the object with two surfaces preferred the surface with the lower adhesion again peeled off. The existing at replacement adhesive force can be reduced, for example, by triggering the Euler buckling or shear stress.

Preferably, the structure of at least one surface is chosen so that it can be triggered by a higher contact pressure, by Euler buckling. Preferably, the remaining after the Euler buckling adhesive force is lower than the adhesive force of the other structure. This can be preferentially replaced by triggering the Euler buckling this surface.

In a preferred embodiment, the structure with the higher adhesive force, the structure which has the lower contact pressure for triggering the Euler buckling.

The same applies to the separation via shear stress. After the shearing load, the adhesive force of this surface is preferably lower than the other surface. As a result, this area is preferably replaced before. The replacement via Euler buckling is preferred.

The adhesive force can also be influenced by the surface of the two surfaces available for adhesion, preferably by the projections present on the surface. The force for the collective buckling (Euler buckling) scaled with the same load distribution linearly with the number of jumps according to the following formula:

F = N (nn / L) ² EI where N is the number of protrusions. The structure can only comprise one projection. Preferably, a structure according to the invention comprises at least 10 protrusions, particularly preferably at least 20, in particular at least 50 protrusions.

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 surface.

In a preferred embodiment of the invention, the stem of the projection has an aspect ratio of height to diameter of 0.2 to 100, preferably from 0.5 to 20, particularly preferably between 2 and 5, based on its mean diameter. The aspect ratio for at least one of the structures is preferably selected as a function of the structure and of the material such that the detachment by the Euler buckling is possible for a specific contact pressure. An aspect ratio of from 3 to 20, in particular from 3 to 10, very particularly preferably from 5 to 10, is also preferred.

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 projections may have widened end faces, so-called "mushroom" structures.

In a preferred embodiment, the projections kei ne broadened faces.

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 10 ym to 2 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, in widened end faces, the surface of the end face of a projection 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.

The broadening of the end face of a projection means that such a projection is verbrei tert in the region of the end face. This broadening, which is also associated with a Verbreite tion of the diameter in the affected area, preferably affects only the portion immediately in front of the front surface and the face itself. It could be so ben ben, as if on a projection with a certain diam ser At the end a flat body with a small thickness WUR de laid, such as a disc on a cylinder. The widening can also have a conical shell shape aufwei sen, so that the broadening increases towards the end face. The broadening relates to a maximum of 20% of the vertical height, preferably a maximum of 10% of the vertical height, in particular a maximum of 2% of the vertical height, in relation to the total vertical height of a projection. As diameter relevant for the Euler buckling, the diameter without the broadening is then used.

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. Whether a particularly high or low modulus of elasticity is advantageous may also depend on whether the corresponding structure is to be suitable for Euler buckling.

The structures preferably differ on the opposite surfaces at least in the contact pressure necessary to trigger the Euler buckling.

Preferably, the structures on the opposing surfaces differ in at least one of the following properties selected from structure, in particular number of Vorsprün ge, diameter and / or height, and modulus of elasticity. This also leads to the change of the pressure required for Euler buckling pressure. The difference can be adjusted according to the application.

For the same diameter and height, for example, it is given to before if the ratio of the moduli of elasticity is greater than 2, preferably greater than 5, so that the forces necessary for buckling forces sufficiently differ.

Preferably, the triggering of the Euler buckling required contact pressure differs by at least a factor of 2, before given by at least a factor of 5. The materials of the projections can be chosen freely according to the requirements by 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 acrylic nitrile / 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, Formalde hyd resins, vinyl ester resins, polyethylenes as homo- or Copoly mers, and mixtures and copolymers of the aforementioned Materia 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 thermoplastic elastomers (TPEs) which can be based on different polymers, for example thermoplastic copolyamides (TPA), thermoplastic polyesters terelastomers / thermoplastic copolyesters (TPEs), thermoplastic elastomers based on olefins (TPO), predominantly PP / EPDM (PP: polypropylene) , Styrene block copolymers (TPS) such as SBS, SEBS, SEPS, SEEPS and MBS) or thermoplastic elastomers Urethane base (TPU), z. Elastollan, Desmopan, Texin or Utechllan, and thermoplastic vulcanizates (TPV).

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

In a preferred embodiment, the structures also have a backing layer on which the projections are arranged. This is preferably made of the same material as the projections.

The object itself can be made of any materials. On its surface at least the two structures are arranged.

The two opposing structures are preferably net angeord on two mutually parallel side surfaces of the object. Preferably, the two structures each cover over 50%, preferably over 70% of the respective side surface of the object.

In a preferred embodiment, the distance of the two side surfaces is smaller than the smallest diameter of the two surfaces covered by the structures, in particular the ratio of smallest diameter and distance is at least

2: 1.

In a further embodiment of the invention, the object is an adhesive pad which has one of the aforementioned structures on both sides. Preferably, both structures are arranged in each case on the front and back of a flat body, preferably with egg ner thickness of at least 0.1 mm, preferably at least 0.2 mm, in particular at least 0.5 mm. Depending on the desired application, the maximum thickness may be up to 2 cm, preferably up to 1 cm, in particular up to 6 mm.

Preferably, the body decouples the two structures arranged on it, so that an Euler buckling of one structure does not affect the other structure. This can be achieved, for example, by the thickness of the body and / or by its modulus of elasticity. For example, both structures can be arranged on both sides of a plate made of a material having a modulus of elasticity higher by a factor> 100, for example a plate made of plastic or metal.

The invention also relates to a method for selective adhesion for an object according to the invention.

In the following, individual process steps are described in more detail. The steps do not necessarily have to be performed in the order given, and the method to be described may also have other steps not mentioned.

In a first step, the first surface is contacted with a first surface and the second surface with a second surface. It does not have to contact the entire area who the. It is contacted as large an area as is needed for Adhäsi on. Therefore, only parts of the surfaces can be contacted. Optionally, the contacting may include pressing to improve adhesion. However, without triggering the Euler buckling.

The two contacted surfaces do not have to be the same size. It is also possible to contact several surfaces simultaneously on one surface, for example if several objects are to adhere to the surface simultaneously by adhesion.

As a result of the contacting, an adhesive force is formed between the surfaces and the respectively contacting surfaces.

Preferably, the contacting takes place in a direction perpendicular to the surface and surface.

Preferably, the main component of the adhesive force between a surface and surface is perpendicular to the surface and surface (Nor malhaftung).

For detachment, at least one of the contacted surfaces is moved away from the object until one of the two surfaces is detached from the object. Preferably, the path is moved perpendicular to the contacted surfaces. The movement can also be caused by the movement Be only one of the surfaces.

In a preferred embodiment, before the moving away of the surfaces, the Euler buckling is additionally brought about by a contact pressure for this structure which is sufficient for one of the structures. As a result, the adhesive force of this fa ce is greatly reduced, which leads to the preferred detachment of contacted on this surface surface. By suitable selection of the two surfaces, or their structures, it is therefore possible to control, via the contact pressure exerted before the detachment, which of the two surfaces is to be removed.

This makes it possible, for example, to greatly simplify the handling of small objects. Thus, the inven tion proper object could be configured, for example, as a Haftpad. A stamp or gripper contacts the first surface and the object according to the invention thus adheres to the stamp or gripper, which can now contact the other surface of the object objects. If the adhesive force to the article is greater than the adhesive force to the punch or gripper, objects can be easily picked up and stored. To detach the object according to the invention from the punch or gripper, a higher contact pressure can then be exerted, so that the Euler kinking occurs on the contact surface with the punch or gripper.

In another embodiment, the Euler buckling can be used to hold objects. Thus, the inven tion proper object could adhere to one or more objects, which are received by different punches or grippers. The dry adhesive bond to the articles is then stronger than the bond to the stamp or gripper. Only with increased contact pressure and thus brought about Euler buckling the objects are detached from the object of the invention.

Further details and features will become apparent from the fol lowing description of preferred embodiments in conjunction with the subclaims. Here, the respective gen characteristics on their own or to several in combination with each other to be realized. 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 object with opposing structures, which differ in the height (length) of the projections (Example 1), the diameter (Example 2) or the modulus of elasticity (Example 3) the. Below is the side view of an object with two structures according to Example 2 with Di = 0.8 mm and Ü ₂ = 0.4 mm and L _I = L ₂ = 1.6 mm and E _I = E ₂ = 2 MPa Darge presents;

Fig. 2 Representation of the measured force under load and

Relief (path) of the structure shown in Figure 1;

Fig. 3 Schematic representation for the preparation of the double-sided reversible adhesive structures;

4 shows the measuring arrangement for determining the adhesion force as a function of the penetration depth;

Fig. 5 controlled detachment of the object according to the invention; Fig. 6 adhesive force as a function of a structure according to Example 1 of Figure 1; and

FIG. 7 adhesive force as a function of a structure according to example 2 of FIG. 1. Fig. 1 shows in the upper part of various examples of ob jects with two opposing structures, which have säulenar term projections, which in turn have slightly widened faces (mushrooms). In Example 1, the structures differ in the height of their projections (Li other than L ₂ ). In Example 2, the diameter of the projections is different (Di is not D ₂ ). In Example 3, the modulus of elasticity of the structures is different (Ei not equal to E ₂ ). These differences mean that, in addition to different adhesive force, in particular the Euler buckling in the structures takes place under different forces.

FIG. 2 shows the behavior of the object depicted in FIG. 1 (below) with different loads. For this purpose, both structures of the object are contacted with a surface. Now, if an external pressure on the object perpendicular to the contact surfaces is exerted (contact pressure), both structures are pressed together (path is negative). If the pressure is now reduced again, i. the contacted surfaces or one of the contacted surfaces move away from the object, an adhesive force can be measured ("pull" in Figure 2) until the object comes off. This behavior is shown in Figure 2 by the solid line.

Now exceeds the pressure during pressing the limit to Eu ler buckling, there is an elastic buckling and thus to reduce the contact surface of the buckling structure with the surface contacted to this structure. It comes to a drop in the measured force when removing the surfaces. Now, the force to be applied is significantly lower and the upper surface can be replaced with much less force. There- at the dissolves the structure for which the Euler buckling was solved.

FIG. 3 shows a possibility for producing double-sided adhesive structures. An uncrosslinked, liquid polymer (pre-polymer) is poured into a multi-part casting mold. The casting mold contains inserts that serve as a template (negative mold) for the adhesive structures. After crosslinking, the double-sided adhesive structure is removed from the mold.

FIG. 4 shows the measuring arrangement for determining the adhesion forces as a function of the penetration depth. The adhesion is measured on both sides against glass substrates. A glass substrate (un ten) is mounted on a tilting table for aligning the adhesive to the substrate surfaces. During the measurement, the upper substrate is brought into contact and pressed with a defined penetration depth. The contact force (compressive force) is recorded. After pressing, the substrates are pulled apart and the adhesive force (tensile force) is determined.

FIG. 5 shows how this principle can be exploited with the object on FIG. A structure according to Example 1 of Figure 1 is used, ie the projections on the two sides differ in their height. When contacting both structures can be controlled by the contact pressure (also referred to as penetration depth), for which of the two structures, the detachment takes place (at the same contacted Oberflä surfaces). At a contact pressure, which does not lead to an Euler buckling (Figure 5 left column), the structure is removed in the Auseinan, which has a lower adhesive force. The lower figure shows that the upper structure of the object has dissolved. This is also the side having the shorter protrusions. If, on the other hand, a contact pressure is selected which leads to Euler kinking in one of the structures, the adhesion to the structure is markedly reduced, which leads to the preferred detachment of this structure

Structure leads (Figure 5 right column).

FIG. 6 shows measured values obtained for an object according to example 1 of FIG. The adhesive force was measured as a function of the penetration depth. At low penetration depths, the double-sided structure is adhesive, with larger penetration depths low-adhesion. The detachment from the substrate changes from page 1 (filled dots) to page 2 (unfilled dots) with increasing depth of penetration. Points correspond to experimental data. The dashed line corresponds to the fitted sigmoid function for determining the asymptotic force values for the adhesive and low-adhesion area.

FIG. 7 shows measured values obtained for an object according to example 2 of FIG. The adhesive force was measured as a function of the penetration depth. At low penetration depths, the double-sided structure is adhesive, with larger penetration depths low-adhesion. The detachment from the substrate changes from page 1 (filled dots) to page 2 (unfilled dots) with increasing depth of penetration. Points correspond to experimental data. The dashed line corresponds to the fitted sigmoid function for determining the asymptotic force values for the adhesive and low-adhesion area.

The switching efficiency of all examined structural types is summarized in Table 1. The adhesive tensions, o _Pr ±, of both regimes (adhesive and low-adhesive) were derived from the asymptotic adhesive forces, F _{Pr ±} (see Figures 6 and 7) and the contact area, A, calculates: a _Pri = F _Pri / A.

The efficiency, S, results from S = 1-O _P , _K / O _P , _O , where o _p, o is the adhesion stress without kinking (at low penetration depths) and a _{p, K is} the adhesion stress after kinking of the structures (at high penetration depths). S can vary between 0 and 1, where 0 means no switching behavior and 1 the maximum switching efficiency. The results in Table 1 show that all double-sided adhesion structures have an efficiency greater than 0.5, where in some embodiments with S ~ 0.8 a very high

Have switching efficiency. The thickness of the layer between the two switching structures has only a small influence on the switching efficiency in the examples.

Preference is given to systems having a switching efficiency of more than 0.5, in particular more than 0.7.

Table 1

Adhesion voltage Adhesive voltage Switching efficiency, without after

" _Buckling ", s _r0 "buckling", s _rK

Example 1 28.0 kPa 7.5 kPa 07 3

(d = 1 mm)

Example 1 34.8 kPa 6, 0 kPa 0.83

(d = 2 mm)

Example 1 22.7 kPa 10.6 kPa 0.53

(d = 3 mm)

Example 1 28.1 kPa 13.6 kPa 0.52

(d = 5 mm)

Example 2 31.8 kPa 13.5 kPa 0.58

(d = 1 mm)

Example 2 33.3 kPa 7.6 kPa 0.77

(d = 5 mm)

Claims

claims

1. object, which has at least on two surfaces each one capable of dry adhesion surface, characterized in that the two surfaces differ in at least one adhesive parameter.

2. Object according to the preceding claim, characterized in that at least one of the surfaces comprises a structure comprising send vertical projections.

3. Object according to one of the preceding claims, that at de surfaces have a structure comprising vertical projections.

4. Object according to one of the preceding claims, characterized in that the adhesive force of the two surfaces is under different.

5. Object according to one of the preceding claims, characterized in that the two surfaces differ in structure and / or modulus of elasticity.

6. Object according to one of claims 1 to 5, characterized in that at least one surface has a structure whose adhesive force can be reduced by Euler buckling or shear load redu.

7. Object according to claim 6, characterized in that after the Euler buckling or shear stress resulting adhesion is less than the adhesive force of the other surface.

8. A method for selective adhesion for an object according to one of claims 1 to 7, comprising the following steps:

(a) contacting the first surface with a first surface and contacting the second surface with a second surface;

(B) moving away at least one of the surfaces from the object to the detachment of one of the two surfaces.

9. The method according to claim 8, characterized in that at least one of the surfaces has a structure and before the moving away of the surfaces by a sufficient contact pressure in one of the structures, the Euler buckling is brought about.