METHOD FOR REMOVING COATINGS FROM SURFACES

Description

[0001] The invention relates to a method for removing coatings from surfaces, in particular coatings from surfaces that have become brittle due to environmental influences.

[0002] The application of coatings, for example, in the form of self-adhesive films, to surfaces such as the outer skin of aircraft is known in the art for various applications. In addition to the application of logos, lettering, or other graphic elements using appropriately designed films, aerodynamically functional films are also increasingly being used.

[0003] Aerodynamically functional films are known in various forms and applications from the state of the art and are regularly used to reduce wall shear stress on the surfaces of bodies subject to flow. These aerodynamically functional films typically have a microstructured surface. A common microstructure is the so-called riblet structure, with very small ribs running essentially along the main flow direction. Applying such riblet structures to the outer skin of an aircraft can reduce the aircraft's flow resistance and thus fuel consumption.

[0004] Films intended for application to the outer skin of an aircraft are usually thin for weight reasons. At the same time, they are exposed to considerable environmental influences. In addition to the airflow, which carries particles such as sand or ice and can mechanically damage the film or its aerodynamically functional surface, the film is regularly exposed to intense sunlight, especially on commercial aircraft at cruising altitude.

[0005] Due to the damage that occurs in practice, aerodynamically functional films, in particular, must be replaced regularly. However, it has been shown that removing films applied to the outer skin of an aircraft is often difficult due to their thinness and the brittleness caused by intense exposure to sunlight during operation. Complete and residue-free removal without damaging the outer skin is currently only possible using manual chemical or mechanical processes, which are very time-consuming. These processes can also generate dust and / or chemical residues that are hazardous to health or the environment.

[0006] A similar situation applies to coatings where paint is applied to the surface and, for example, into which a desired microstructure is embossed. These can also become brittle and must be laboriously removed for possible renewal.

[0007] In addition to the described application on the outer skin of aircraft, corresponding coatings are also used on other surfaces, for example on the rotor blades of wind turbines or on high-speed trains, where, however, they are exposed to similar environmental influences and must also be removed after damage before they can be replaced.

[0008] Document WO 2012 / 058729 describes a method for removing unwanted graffiti, in which a substrate to be protected is provided with a transparent sacrificial layer onto which any graffiti is applied. By applying an adhesive layer whose adhesion to the sacrificial layer is greater than that of the sacrificial layer to the substrate, and subsequently peeling off the adhesive layer, the sacrificial layer can be removed together with the graffiti located thereon. Document DE 10 2015 204 254 A1 describes a method for removing ink, paint, and / or varnish from surfaces, in which the adhesion of the ink is reduced with a cleaning agent before an adhesive strip is subsequently pressed onto the surface and immediately peeled off again. The ink is then said to adhere to the adhesive strip due to the already reduced adhesion to the surface and thus be removable.

[0009] Document US 2014 / 0272237 A1 discloses a riblet film which is said to be permeable to organic cleaning agents in such a way that the adhesive bond with the underlying surface can be broken by the superficial application of the corresponding cleaning agent.

[0010] The object of the present invention is therefore to provide a method for removing coatings from surfaces, in particular coatings embrittled by environmental influences, which is improved compared to the prior art.

[0011] This object is achieved by a method according to the main claim 1 or 3. Further developments are the subject of the dependent claims.

[0012] Accordingly, the invention according to claim 1 relates to a method for removing coatings from surfaces, comprising the steps: applying a suitably selected release agent over a large area to the coating to be removed to produce a material-to-material bond, such that the bond between the release agent and the coating to be removed is stronger than the bond between the coating to be removed and the surface, wherein the release agent is a flat release compound that is self-adhesive on at least one side, the release compound is deformable in the pressing direction and is pressed onto the coating to be removed with a self-adhesive side for application, and wherein the coating to be removed has a microstructured surface; and peeling off the release agent together with the coating to be removed adhering thereto.

[0013] Furthermore, the invention according to claim 3 relates to a method for removing coatings from surfaces, comprising the steps: Applying a suitably selected release agent over a large area to the coating to be removed to create a material-to-material bond such that the bond between the release agent and the coating to be removed is stronger than the bond between the coating to be removed and the surface, wherein the release agent is a curable substance which, upon curing, combines with the coating to be removed and which is liquid in its initial state, the coating to be removed having a microstructured surface; and removing the release agent together with the coating to be removed adhering to it.

[0014] First, some terms used in the context of the invention will be explained.

[0015] A first joint is "stronger" than a second joint if the first joint can withstand a load at which the second joint fails. For example, in the case of adhesive bonds, the bond strength of the first joint F H1 that must be overcome to release the first joint is greater than the bond strength of the second joint F H2 (F H1 > F H2).

[0016] Conversely, a first joint is considered "weaker" than a second joint if the first joint yields under identical load, while the second joint remains intact. In the case of adhesive bonds, the adhesive force of the first joint F H1 is smaller than the adhesive force of the second joint F H2 (F H1 < F H2 ).

[0017] The invention recognizes that a coating applied to a surface that cannot be readily removed directly, particularly because it has become brittle or "embrittled" due to environmental influences, can be removed by first applying a release agent that bonds so strongly with the coating to be removed that, upon subsequent removal of the release agent, the coating adheres to the release agent and is thus removed together with the release agent. The tensile strength required for removal can be achieved solely by the release agent, so that the tensile strength of the coating to be removed and / or its degree of embrittlement are no longer important.

[0018] To ensure that the coating to be removed actually adheres to the release agent when the release agent is removed and is thus removed from the surface, the bond between the release agent and the coating to be removed must be stronger than the bond between the coating to be removed and the surface. Selecting a suitable release agent is straightforward if sufficient information is available about the bond between the coating to be removed and the surface, for example, the adhesive used. However, it can also be determined through simple tests directly on the coating to be removed.

[0019] According to one aspect of the invention, the release agent is a flat release compound that is self-adhesive on at least one side and is applied by pressing a self-adhesive side onto the coating to be removed. This pressing action creates the desired, integral bond between the release compound and the coating to be removed, which is necessary for the subsequent process.

[0020] In principle, the release liner can be a self-adhesive release film. However, to ensure a flat bond between the release liner and the coating to be removed, even in the event of damage and / or micro-structuring on the surface of the coating to be removed, the release liner must be deformable in the direction of contact. When the release liner is then pressed against the coating to be removed, it can conform to it and bond with it over its entire surface, regardless of whether there is damage and / or micro-structuring on the surface of the coating to be removed. The release liner can be plastically and / or elastically deformable.

[0021] Particularly in the case of deformable release liners, the tensile strength of the release liner may not be sufficient to allow the release liner, along with the coating adhering to it, to be easily removed from the surface. In these cases, it is particularly preferred for the release liner to have a tensile-strength release layer, preferably a release film, on the side remote from the coating to be removed. With a suitable release layer, the tensile strength of the release liner can be increased to enable the removal of the release agent, along with the coating to be removed, as provided for in the invention.

[0022] As an alternative to using a release compound as a stripping agent, according to a further aspect of the invention, a curable substance can be provided as a stripping agent, which, upon curing, bonds firmly to the coating to be removed. After curing, the substance forms a stripping agent suitable for removal, along with the coating to be removed adhering to it.

[0023] The curable substance is initially liquid. This makes it easy to apply the substance over a large area of ​​a coating that is to be removed. After curing, the substance is solid.

[0024] A mesh or textile can also be incorporated into the uncured substance over a large area, completely enclosing it in the uncured substance. After the substance has cured, the mesh or textile can increase the tensile strength of the release agent.

[0025] Regardless of how the release agent is formed, it is preferred if it is selected such that any bond between the release agent and the surface is weaker than the bond between the release agent and the coating to be removed. Furthermore, it is preferred if any bond between the release agent and the surface is also weaker than the bond between the coating to be removed and the surface. This ensures that even in the case of deliberate omissions in the coating to be removed or significant damage to the coating to be removed, in the area of ​​which the release agent comes into direct contact with the surface when pressed, the release agent can be removed easily and, in particular, without damaging the surface.

[0026] The methods according to the invention have proven particularly suitable for removing coatings with a microstructured surface. This applies in particular when the coating has a riblet structure - i.e., a riblet-shaped surface structure. Since the tensile strength of the coating is not important for the removal of the coating in the methods according to the invention,

[0027] As far as the coating itself is concerned, the coating to be removed can be made particularly thin and thus light and, in particular, can do without the additional tensile-resistant layers that are often otherwise provided for in the prior art.

[0028] The peelable coating can be a film bonded to the surface or a layer of paint applied to the surface, each possibly with a microstructured surface embossed into it. The surface can be, in particular, the outer skin of an aircraft, a high-speed train, or a wind turbine rotor blade.

[0029] The invention will now be described by way of example using preferred embodiments with reference to the accompanying drawings. In the drawings: Figures 1a-d: a schematic representation of a first embodiment of a method according to the invention; Figures 2a-d: a schematic representation of a second embodiment of a method according to the invention; and Figures 3a-c: a schematic representation of a third embodiment of a method according to the invention.

[0030] In Figure 1a To illustrate the first exemplary embodiment of a method according to the invention, a section of the outer skin of a commercial aircraft is shown as surface 1, on which, with the aid of a transfer film (not shown), individual riblets 3 are applied, which, although not directly connected to one another, together form a film-like coating 2 to be detached in the sense of the present invention.

[0031] To remove the coating 2, a stripping compound 5 is first applied as a stripping agent 6 to the coating 2 ( Figure 1b ) and then pressed onto the coating 2 or the surface 1. Since the release liner 5 is deformable and self-adhesive on the side facing the surface 1, a large-scale or full-surface material bond is achieved between the release liner 5 and the coating 2 ( Figure 1c ). The self-adhesive property of the release liner 5 is selected such that the material bond between the release liner 5 and the coating 2 is stronger than the bond between the coating 2 and the surface 1. At the same time, the material bond between the release liner 5 and the surface 1 in the areas of the coating 2 between the individual riblets 3 should be sufficiently weak so as not to subsequently damage the lacquer which regularly forms the outermost layer of the surface 1.

[0032] Once the release liner 5 has been completely applied and pressed down, the release liner 5 can be removed as a stripping agent 6 from the surface 1, whereby due to the above-described relationships of the individual connections between surface 1, coating 2 and release liner 5, the coating 2 adheres to the stripping agent 6 and is thus removed from the surface 1 ( Figure 1d ).

[0033] In Figure 2 A second embodiment of the method according to the invention is shown. On the surface 1 - for example, the outer skin of an aircraft - a basically continuous film with a microstructured surface comprising riblets 3 is arranged as a coating 2, which is to be removed ( Figure 2a ).

[0034] To remove the coating 2, comparable to the embodiment according to Figure 1 - first, a release compound 5 is applied as a release agent 6 with its self-adhesive side to the cover 2 ( Figure 2b) and then pressed onto the coating 2 or the surface 1, so that a material connection is created between the release agent 6 and the coating 2 ( Figure 2c ). The properties of the connection in relation to the connection between coating 2 and surface 1 correspond to the previous embodiment, which is why reference is made to the corresponding explanations.

[0035] On the side facing away from the surface 1, the release agent 6 has a release film 7 which is permanently connected to the release compound 5 or is integrally formed therewith, which increases the tensile strength of the release agent 6 in order to Figure 2d to facilitate the outlined removal of the release agent 6 together with the coating 2 adhering to it.

[0036] Figure 3 illustrates a third embodiment of a method according to the invention.

[0037] In this example, the coating 2 with riblets 3 is attached to the surface 1 - the outer skin of an aircraft - by means of a carrier film 4, whereby the connection between the coating 2 and the carrier film 4 is stronger than the connection between the carrier film 4 and the surface 1.

[0038] In this embodiment, a hardening gel-like substance 8 is applied to the coating 2 as the release agent 6, which, upon hardening, bonds firmly with the film 2 to be removed ( Figure 3b ). The resulting material bond between the release agent 6 and the coating 2 is stronger than the bond between the coating 2 and the surface 1, so that when the release agent 6 is removed after the substance 8 has completely hardened, the coating 2 adheres to the release agent and is thus removed from the surface 1 together with the carrier film 4 ( Figure 3c ).

Claims

1. Method for removing coatings (2) from surfaces (1), comprising the steps of: - applying, over a large area, a suitably selected stripping agent (6) to the coating (2) to be detached for the purpose of producing a cohesive bond, such that the bond between stripping agent (5) and coating (2) to be detached is stronger than the bond between coating (2) to be detached and the surface (1), wherein the stripping agent (6) is an at least one-sidedly self-adhesive areal stripping compound (5), the stripping compound (5) is deformable in the pressing-on direction and, for being applied, is pressed with a self-adhesive side onto the coating (2) to be detached, and wherein the coating (2) to be stripped off has a micro-structured surface; and - stripping off the stripping agent (6) together with the coating (2) to be detached adhering thereto.

2. Method according to Claim 1, characterized in that the stripping compound (5) has, on the side remote from the coating (2) to be detached, a tension-resistant stripping layer, preferably a stripping film (7).

3. Method for removing coatings (2) from surfaces (1), comprising the steps of: - applying, over a large area, a suitably selected stripping agent (6) to the coating (2) to be detached for the purpose of producing a cohesive bond, such that the bond between stripping agent (5) and coating (2) to be detached is stronger than the bond between coating (2) to be detached and the surface (1), wherein the stripping agent (6) is a curable substance (8) which is liquid in its initial state and which, when curing, bonds with the coating (2) to be detached, and wherein the coating (2) to be stripped off has a micro-structured surface; and - stripping off the stripping agent (6) together with the coating (2) to be detached adhering thereto.

4. Method according to one of the preceding claims, characterized in that the stripping agent (6) is selected in such a way that a possible bond between stripping agent (6) and the surface (1) is weaker than the bond between stripping agent (6) and coating (2) to be detached, preferably weaker than the bond between coating (2) to be detached and the surface (1).

5. Method according to one of the preceding claims, characterized in that the coating (2) to be stripped off comprises a riblet structure (3).

6. Method according to one of the preceding claims, characterized in that the coating (2) to be stripped off is a film adhesively bonded to the surface (1) or is a paint layer applied to the surface (1).

7. Method according to one of the preceding claims, characterized in that the surface (1) is the outer skin of an aircraft, of a high-speed train or of a wind-turbine rotor blade.