DE102020127401A1 - Apparatus and method for applying a textured coating and metal article having a textured coating - Google Patents

Abstract

An apparatus (1) and a method for applying a structured coating to a surface (2) of a metal object (3) and a metal object with such a structured coating are described. The apparatus (19) has an electrolyte reservoir (4) in which an electrolyte (7) containing metal ions is arranged and which is set up in such a way that during a coating process the electrolyte (7) can contact at least one area of the surface ( 2) of the metal object (3) can be brought into contact, via an electrode (5), which is in contact with the electrolyte (7) at least during the coating process and has a metal at least on a surface area contacted by the electrolyte (7), and via an interface for connecting a voltage source (6), which during the coating process is connected to the metal object (3) and the electrode (5) in an electrical circuit in such a way that the electrode (5) in contact with the electrolyte (7) has a anode and the metal object (3) to be coated which is in contact with the electrolyte forms a cathode characterized in that the electrode (5) has an electrode structure (8) on a surface facing the metal object (3) during the coating process, which, depending on the surface texture, shape and/or geometry of the surface (2) of the metal object (3 ) applied coating is executed.

Description

The invention relates to an apparatus and a method for applying a structured coating to a surface of a metal object and a metal object with such a coating. The apparatus for applying a structured coating has an electrolyte reservoir in which an electrolyte containing metal ions is arranged and which is set up in such a way that during a coating process the electrolyte can be brought into contact with at least one area of the surface of the metal object to be coated. Furthermore, the apparatus has an electrode which is in contact with the electrolyte at least during the coating process and has a metal at least on a surface area contacted by the electrolyte, and an interface for connecting a voltage source which is connected to the metal object and electrode during the coating process in such a way is connected in an electrical circuit such that the electrode in contact with the electrolyte forms an anode and the metal object to be coated in contact with the electrolyte forms a cathode.

The invention is in the field of electroplating, with which objects can be provided with a metallic coating by electrochemical deposition. In most cases, coating processes are used in which metallic coatings are applied to an object in an electrolytic bath. A current flows between the anode, which forms the positive pole, and the object to be coated, which forms the negative pole and thus the cathode. Two technical variants are known for producing the metallic coating. Either the anode contains a metal and continues to dissolve during the coating process, or the metal ions are separated from the electrolyte.

So far, galvanic processes have primarily been used to provide an object with a metal-containing layer as uniformly as possible. In addition, it is possible with specially designed electroplating processes to coat specific areas of an object and thus provide the object with an inscription or marking. In this context, the so-called pad galvanizing process is known as a special process in electroplating. This process is mainly used for cleaning or repairing metal coatings, but also for marking or writing on metal surfaces. The component to be coated is attached to the negative pole of an electroplating system, while the anode is attached to a plate or a rod of insoluble material wrapped in a cotton swab. The required electrolyte solution is fed to this specially designed tool via a hose line, or the plate or rod is dipped into an electrolyte bath together with the cotton swab.

A device for electrolytic coating of relatively small surface areas is from EP 0 370 239 A1 famous. The device described has a ridged anode and an electrolyte supply, the anode being surrounded by an absorbent material which is impregnated with the electrolyte from the electrolyte supply. Metal is deposited on the object to be coated by continuous or discontinuous movement of the objects to be coated along at least one anode edge. With the device described, contact pins, contact springs or contact strips in particular are partially galvanically coated with noble metals in order to improve the electrical properties, hardness or abrasion resistance at points that are important for later contacting.

Incidentally, from the WO 2016/098087 A1 Another special electroplating process is known. The method described is used to label a metallic object such as a piston rod. It is essential here that the object that is to be provided with a marking is covered with a template that is designed according to the desired inscription. By immersing the object covered with the stencil in an electrolyte bath or by contacting it with an electrolyte-soaked cotton pad and the current flow initiated between the anode and the object to be coated, it is now possible to either selectively remove metal from the area not covered by the stencil or to remove another one apply metal layer. After removing the stencil, the desired lettering is visible on the item.

In addition to the known methods for coating entire objects with a metal layer, electroplating methods are also known in order to coat comparatively small areas or even to apply a metallic marking to an object. For such a targeted inscription, however, it is necessary to first produce a suitable template and the object to be coated during to cover a large area during the coating process. What is particularly disadvantageous about this procedure for an industrial manufacturing process is that in addition to the actual coating process, the further steps of applying and removing a stencil in the exact position have to be carried out. Furthermore, the known devices and stencils for the realization of galvanic markings sometimes have a comparatively complex structure, in particular when not only simple markings are to be produced.

Proceeding from the solutions known from the prior art and the problems described, the invention is based on the object of specifying an apparatus and a method with which a metal object can be provided with a structured coating in a comparatively simple manner. Above all, it should be possible to produce a structured coating that enables a metallic object to be identified. A correspondingly structured coating should be able to be produced with an electroplating system that has the generally known structural design and still allows individualized marking of different metallic components or metallic surfaces. Furthermore, it should be possible with the technical solution to be specified to apply structured coatings to metal objects with different patterns that can be configured as needed without great effort. The respective coating should have a structure that represents an individual, specific identification of a metal object that, if possible, cannot be reproduced or can only be reproduced with relatively great effort.

The object described above is achieved with an apparatus according to claim 1 and a method according to claim 7. A metal article having a specially prepared textured coating is defined in claim 15. Advantageous embodiments of the invention are the subject matter of the dependent claims and are explained in more detail in the following description with partial reference to the figures.

The invention relates to an apparatus for applying a structured coating to a surface of a metal object. For the purposes of the invention and the following description, a metal object is to be understood as meaning both an object consisting entirely of metal and a metallic layer on an object. The apparatus has an electrolyte reservoir in which an electrolyte containing metal ions is arranged and which is set up in such a way that during a coating process the electrolyte can be brought into contact with at least one area of the surface of the metal object to be coated, via an electrode which is in contact with the electrolyte at least during the coating process and has a metal at least on a surface area contacted by the electrolyte, and via an interface for connecting a voltage source, which is connected in an electrical circuit to the metal object and the electrode during the coating process in such a way that the electrode in contact with the electrolyte forms an anode and the metal object to be coated in contact with the electrolyte forms a cathode. The apparatus designed according to the invention is characterized in that the electrode has an electrode structure on a surface facing the metal object during the coating process, which is designed depending on the surface texture, roughness, shape and/or the geometry of the coating to be applied to the surface of the metal object. It is therefore essential for the apparatus designed according to the invention that the electrode used as anode has a suitable electrode structure on its surface, which enables a structured coating to be applied in a targeted manner to the metal object. It is generally conceivable that the electrode structure has a regular pattern, for example consisting of trenches and elevations and/or special geometric shapes or structures on the surface of the electrode. In this case, the pattern of the electrode structure can be distributed uniformly or non-uniformly over an entire side of the electrode or over a surface area. In addition, it is conceivable in an advantageous manner to integrate the voltage source, for example in the form of batteries or accumulators, into the apparatus, so that a particularly compact and at the same time mobile coating unit is created. It is also conceivable that the electrode has an electrode structure with at least two different patterns, which differ in terms of specific surface roughness, surface textures, shapes, structural elements and/or the use of specific geometric elements. Due to the technical solution according to the invention with a defined electrode structure on the anode, it is possible to apply a surface structure that is specifically designed, at least with regard to its rough structure, to a metallic object or a metallic surface, with the metal object to be coated representing the cathode in relation to the galvanic coating process.

Furthermore, it is possible in a preferred manner to apply a structured coating to a metallic object or the metallic surface of an object to be coated produce, whose structure amplitude is in the submillimeter range. In a particularly preferred manner, with an apparatus designed according to the invention, it is even possible to apply variable coatings in the micrometer or nanometer range to a metallic surface, for example a noble metal surface.

In general, the structuring of the electrode according to the invention and the coating of a metal object or at least a metal surface are carried out taking into account the so-called dog bone effect. This effect is based on the fact that the current density in the coating gap is not constant in the case of a galvanic coating. Rather, the current density is higher at exposed points, so that the applied layer is larger than in other areas, especially at edges, corners, protruding surfaces and points.

In contrast, the current density, and thus the layer thickness, is lower in the area of depressions or areas that are only comparatively slightly raised, in the so-called current shadow areas. Overall, the current density is thus regularly increased when coating a structured component on its raised component surfaces and/or when using an electrode structured according to the invention in a gap region adjoining the raised electrode regions and leads to greater layer thicknesses on the object to be coated. In order to at least partially counteract this effect, corners, edges, points and other raised structures of the electrode used according to the invention and/or of a structured object to be coated are therefore preferably rounded.

In a specific embodiment of the invention, the electrode structure has at least two different patterns, shapes, structural elements and/or geometries, at least during the coating process. In this way, it is possible to provide metal objects with an individual marking in a very variable manner, which enables the respective object to be identified easily.

A further special embodiment of the apparatus according to the invention provides that the electrode has at least one fastening element in order to connect at least one structural element of the electrode structure to the electrode in an exchangeable manner. With this technical configuration of the invention, it is possible to provide an electrode structure on the surface of the electrode by fastening one or a plurality of different structural elements as required, with the at least one structural element being fastened to or on the electrode forming the anode during the coating process using the fastening element. Such a fastening element can advantageously have clamping, plug-in and/or snap-on elements which preferably allow corresponding structural elements to be fastened and detached from an electrode without the use of tools. It is also conceivable to provide at least one screw as the fastening element, with which a suitable structural element of the electrode structure is fastened to the electrode.

The distance between the electrode structure of the electrode and the metallic surface is of particular importance for the coating of a metallic surface of an object. This distance, ie the gap width of the gap formed between the electrode structure and the metal surface to be coated, has a considerable influence on the formation of a structured coating on the metal surface of the object to be coated. According to a preferred embodiment of the invention, an average distance between the structured electrode, which forms the anode, and the object to be coated, which forms the cathode, is selected in a range from 1 to 2000 μm. Furthermore, it is of particular advantage if the structure heights, based on an area of 0.8 to 1.2 cm ² , preferably 1 cm ² , assume a value of up to 2000 μm. Furthermore, it is conceivable in an advantageous manner to provide a setting unit with which a width of the gap between the electrode structure of the electrode and the metal object can be adjusted in a targeted manner, in particular during the coating process. At least one distance sensor is preferably provided, which measures the gap distance, so that it is generally conceivable to set the gap width at least partially automatically and preferably in a controlled manner depending on the structured coating to be produced or already produced on the metal object.

In principle, any number of coating processes can be implemented with an electrode that has an electrode structure designed according to the invention. Since, according to the invention, metal ions are separated from the electrolyte, the electrode used as anode, in particular its electrode structure, wears out only very slightly or not at all, so that it can be used for a comparatively long time. With the aid of the apparatus according to the invention, a structured coating with a special coarse structure is applied in a targeted manner, depending on the electrode structure, on the metallic surface of the object to be coated. Depending on the specific design of the electrode structure, this rough structure can be comparatively small. In addition, it is conceivable that an electrode structure is formed from different electrode patterns arranged next to one another or one on top of the other, so that correspondingly individual or customizable surface structures can be produced on the metallic surface. In this case, the various electrode patterns can be part of separate structural elements which alone or together form the electrode structure, are integrated or can be integrated into it. Furthermore, it is conceivable to attach different electrode patterns interchangeably to the electrode forming the anode.

In addition to the design of the electrode structure, the choice of a suitable electrolyte containing metal ions, the current density within the gap between the electrode and the surface to be coated and the duration of the current flow have an influence on the thickness and structure of the metal surface coating. By varying the parameters mentioned above, it is possible to produce a different structure of the coating on a metal surface. According to a particular embodiment of the invention, in this connection it is provided that the electrolyte is moved in particular within the gap. At least one pump element, one nozzle and/or one flow baffle is preferably provided for this purpose. It is conceivable, for example, to provide at least one pump with which the electrolyte is at least temporarily circulated and/or to arrange a perforated plate in such a way that the electrolyte experiences a flow deflection and/or a change in flow speed at least in certain areas. Alternatively or additionally, a further configuration provides that the structured electrode itself has holes and/or the special electrode structure has suitable holes. It is also conceivable to provide a sensor unit with which at least one property of the electrolyte, in particular the metal ion concentration, is recorded and, if necessary, unused electrolyte and/or at least one component is metered into the electrolyte reservoir. According to a preferred embodiment, a change in at least one electrolyte property, for example the conductivity and/or the metal ion concentration, is optically detected, with a color change preferably being recognized by an operator and/or at least one optical sensor.

When producing a structured coating on a metallic surface, it is essential that not only is the coarse structure of the coating produced as a function of the selected electrode structure, but that a fine structure is also produced. This fine structure created on the metal object to be coated has structures in the micro and nanometer range and is so individual that even if technically identical process parameters are set at different times, it is not possible to combine the same coarse structure, which depends on the selected electrode structure, with the same one produce fine structure. A coating of a metallic surface produced with the apparatus designed according to the invention cannot be produced a second time, even when using the same apparatus and the same process parameters, so that a structured coating of a metallic surface or a metal object produced in this way once represents an individual, non-reproducible marking. It is thus possible to create a unique identification of an object, since an identical identification of an object is not possible due to the fluctuations in the process parameters that cannot be actively influenced during an electroplating process, although they always occur, even if they are minimal.

It is therefore not even possible with the same apparatus designed according to the invention to produce a structured coating once it has been produced a second time. With the aid of an apparatus designed according to the invention, particularly unique markings can thus be produced, since not even experienced operating personnel would be able to use the same apparatus to produce a marking once produced a second time. Once the specifically structured coating has been completed, the objects marked in this way can be identified using suitable measurement or analysis methods. A marking produced with an apparatus designed according to the invention is applied in an advantageous manner to valuable objects, components manufactured using special know-how and/or safety-relevant components of machines, for example turbine blades, in order to avoid imitation or the production of inferior quality products or at least make it verifiable. Furthermore, it is conceivable in an advantageous manner to label components, in particular particularly valuable and/or safety-relevant components, and thus to monitor or track their use and further distribution over the component life cycle.

In order to provide evidence of the originality of a structured coating applied to a metallic object or a metallic surface of an object, it is conceivable, after the structured coating has been completed, to use X-ray diffractometry, UV/VIS spectroscopy, Michelson interferometry, reflectometry and/or or to measure the speckle interferometry and the measurement results secured and stored in a suitable manner. To prove whether an object is the object identified by the apparatus designed according to the invention, the object to be examined, in particular its structured coating, must be measured with the same, preferably under the same conditions and/or using the same measuring instruments, and the so obtained measurement results are compared with the original measurement results.

• - bei dem in einem Elektrolytspeicher ein Elektrolyt, der Metallionen aufweist, bevorratet und der Elektrolyt während eines Beschichtungsvorgangs zumindest mit einem zu beschichtenden Bereich der Oberfläche des Metallgegenstandes in Kontakt gebracht wird,
• - eine Elektrode aus einem Metall oder zumindest ein mit einem Metall beschichteter Oberflächenbereich der Elektrode während des Beschichtungsvorgangs mit dem Elektrolyten in Kontakt gebracht wird, und
• - bei dem eine Spannungsquelle, der Metallgegenstand und die Elektrode während des Beschichtungsvorgangs derart in einem elektrischen Stromkreis verschaltet werden, dass die mit dem Elektrolyten in Kontakt stehende Elektrode eine Anode und der zu beschichtende, mit dem Elektrolyten in Kontakt stehende Metallgegenstand eine Kathode bildet.

Furthermore, the invention also relates to a method for applying a structured coating to a surface of a metal object or the metallic surface of an object,

• - in which an electrolyte containing metal ions is stored in an electrolyte reservoir and the electrolyte is brought into contact during a coating process with at least one area of the surface of the metal object to be coated,
• - an electrode made of a metal or at least a metal-coated surface area of the electrode is brought into contact with the electrolyte during the coating process, and
• - in which a voltage source, the metal object and the electrode are connected in an electrical circuit during the coating process in such a way that the electrode in contact with the electrolyte forms an anode and the metal object to be coated, in contact with the electrolyte, forms a cathode.

The method according to the invention is characterized in that an electrode is provided which has an electrode structure in at least one area of its surface, which is designed as a function of a surface texture, a roughness and/or geometry of the structured coating to be applied to the metal object, the electrode is at least temporarily arranged in the electrolyte during the coating process in such a way that the electrode structure faces the metal object. With the aid of the method according to the invention, a specifically structured coating can be produced on a metallic surface in an advantageous manner by using a specifically structured electrode. Depending on the desired structure that is to be produced on the metallic surface, the electrode has a special electrode structure, with the surface texture, roughness, structure and/or geometry being adapted as required in a suitable manner. With the help of an electrode that has such an electrode structure, metal is applied from the electrolyte to the surface of the object to be coated during a galvanic coating process. In this case, a coating is produced on the object to be coated, the rough structure of which is specifically designed as a function of the selected electrode structure. In addition, a fine structure is superimposed on this coarse structure during the coating process, which has structures in the micrometer and nanometer range. This fine structure is not reproducible. With the aid of the method implemented according to the invention, a non-reproducible and therefore unique marking can thus in turn be produced on a metallic object.

A special embodiment provides that an average distance between the structured electrode, which represents the anode, and the object to be coated, which forms the cathode, is set to a value in a range from 1 to 2000 μm. Furthermore, it is of particular advantage if an electrode structure with structure heights of up to 2000 μm relative to an area of 0.8 to 1.2 cm ² , preferably 1 cm ² , is produced. In this context, however, it is also pointed out that the solution according to the invention is not limited to specific size ranges from a technical point of view. Rather, economic boundary conditions, such as the costs for the material used to produce a structured electrode, generally form limits for a sensible application of the invention.

Furthermore, it can preferably be provided that the electrode structure is changed between two coating processes, ie in particular between the coating of two different objects. It is conceivable here for the electrode structure to contain a pattern or a combination of at least two patterns. Furthermore, it is conceivable for the electrode structure to be a fixed component of the electrode and to be completely replaced in order to change a rough structure of a structured coating that can be produced on a metal object. It is also conceivable that the electrode has an at least partially replaceable electrode structure.

In this context, it is particularly advantageous if different structural elements with different patterns, surface roughness, surface textures and/or geometric elements are provided, which can be attached to an electrode as required. In this way, it is possible to produce structured coatings with an individualized rough structure by first certain structural elements alone and / or at least two structural elements in Kom combination can be selected and attached to the electrode, thus forming the electrode structure of the electrode during coating.

In a further embodiment it is provided that after the structured coating has been produced, an image, another recording, a measured value and/or a data set is generated which represents at least one property specific to the structured coating. With the help of a suitable measurement, measurement data are thus generated and preferably stored in a data memory, which are specific to the structured coating applied in each case, in particular not only for the coarse structure but also for the fine structure. The image, the other recording, the measured value and/or the data set is preferably generated at least partially with an X-ray diffraction, UV/VIS spectroscopy, Michelson interferometry, reflectometry and/or with a speckle interferometry measurement. These measuring methods are particularly suitable for detecting the fine structure superimposed on the coarse structure and thus making it possible to compare two coatings. In this context, it is advantageously conceivable that the image, the other recording, the measured value and/or the data set can be combined with at least one image, other recording, measured value and/or data set generated at another point in time and/or made available in some other way is compared and on the basis of the comparison information is generated with regard to a degree of similarity of the compared images, other recordings, measured values and/or data sets and thus with regard to a possible identity of the objects marked with the examined coating. This technical solution thus enables an object to be checked to determine whether the examined object is the object provided with the initial coating at a different point in time. Since the fine structure of the structured coating produced on the metallic surface cannot be reproduced even when the same method is carried out using the same process parameters, the method according to the invention can be used to produce a non-reproducible and therefore unique identification of an object that has a metallic surface at least in some areas .

Furthermore, the invention also relates to a metal object, in particular a metal object that at least partially has a precious metal, with a unique marking that was produced with an apparatus or a device according to one of the embodiments described above. The invention thus also relates to objects which have a metallic surface at least in some areas and which are provided with a marking based on the invention. The use of the technical solution according to the invention is particularly suitable for marking valuable, security-relevant objects or objects otherwise at risk of imitation, so that imitation or counterfeiting of the objects is excluded or at least detectable due to the non-reproducible structured coating applied to them. It is particularly important for this that the structured coating produced with an apparatus designed according to the invention or a method executed according to the invention cannot even be produced by a user who uses the same apparatus and/or the same method parameters. Furthermore, it is important that the apparatus according to the invention and the corresponding method can be used flexibly. With the help of specially designed electrodes, not only can specific structures be produced on a metal surface, but larger surfaces can generally also be coated and, in particular, catalytic surfaces can be specifically enlarged. A very special field of application for the invention is the production of optical sensors with plasmonic nanostructures. The applied metallic nanostructures can be used here in an advantageous manner, for example as optical converters for biomolecular sensors.

• 1: Schematische Darstellung eines erfindungsgemäß ausgeführten Apparats;
• 2: Gegenüberstellung zweier unterschiedlich ausgebildeter Elektrodenstrukturen;
• 3: Darstellung der Feldlinien sowie der resultierenden Stromdichte in einem Spalt zwischen unterschiedlich ausgeführten Elektrodenstrukturen und der zu beschichtenden Oberfläche;
• 4: Darstellung der Feldlinien sowie der resultierenden Strom- und Feldliniendichte bei gleichbleibender Spaltbreite und Veränderung der Strukturbreite der Elektrodenstruktur;
• 5: Draufsicht auf eine Elektrodenstruktur, die aus mehreren Strukturelementen mit unterschiedlichen, austauschbaren Oberflächenmustern gebildet wird;
• 6: Schematische Darstellung des Grundaufbaus eines erfindungsgemäß ausgeführten Apparats;
• 7: Schnittansicht eines als Mikrozelle ausgeführten Apparats gemäß der Erfindung;
• 8: Schnittansicht eines als Stift ausgeführten Apparats gemäß der Erfindung;
• 9: Schnittansicht eines als Aufsatz ausgeführten Apparats gemäß der Erfindung;
• 10: Schnittansicht eines erfindungsgemäß ausgeführten Apparats;
• 11: Detailansicht eines Halters zur Aufnahme eines zu beschichtenden Gegenstandes sowie
• 12: Schematische Darstellung unterschiedlich ausgeführter Elektrodenstrukturen als Einzelstrukturen.

The invention is explained in more detail below, without restricting the general inventive concept, on the basis of specific embodiments with reference to the figures. show:

• 1 : Schematic representation of an apparatus designed according to the invention;
• 2 : Comparison of two differently designed electrode structures;
• 3 : Representation of the field lines and the resulting current density in a gap between differently designed electrode structures and the surface to be coated;
• 4 : Representation of the field lines and the resulting current and field line density with the same gap width and changing the structure width of the electrode structure;
• 5 : Top view of an electrode structure that is formed from a number of structural elements with different, interchangeable surface patterns;
• 6 : Schematic representation of the basic structure of an apparatus designed according to the invention;
• 7 Fig. 1: sectional view of an apparatus implemented as a microcell according to the invention;
• 8th Fig. 1: sectional view of a pen-embodied apparatus according to the invention;
• 9 Fig. 1: sectional view of an attachment designed apparatus according to the invention;
• 10 : sectional view of an apparatus designed according to the invention;
• 11 : Detailed view of a holder for holding an object to be coated and
• 12 : Schematic representation of differently designed electrode structures as individual structures.

1 shows a schematic representation of an apparatus 1 designed according to the invention for applying a structured coating to a metal object 3 arranged in an electroplating bath. An electrolytic tank 4 designed as a vessel contains an electroplating bath with the electrolyte 7 containing the metal ions of the object 3 to be coated has to be deposited metal. Suitable electrolytes 7 are in principle all known, in particular cyanide, acidic or sulfide electrolytes 7 in question. The electrode 5, which has a special electrode structure 8, and the metal object 3 to be coated are arranged in the electroplating bath with the electrolyte 7. During the coating process, the electrode 5 with its electrode structure 8 is the anode, which forms the positive pole, the metal object to be coated is the cathode, which forms the negative pole, with the anode and cathode being connected to a voltage source in a circuit in such a way that the anode a current flows through the electrolyte 7 to the cathode. As a result, a metal layer structured according to the electrode structure 8 is deposited on the metallic surface 2 to be coated from the metal ions dissolved in the electrolyte 7 due to a reduction reaction taking place at the cathode.

Essential to the in 1 The technical solution shown is that electrode 5 has a special electrode structure 8, here with uniform, parallel trenches, which is designed such that the respectively desired structured coating, which has a coarse structure and a fine structure superimposed on it, on the surface to be coated metallic object 3 is generated. A cover or mask shaped in a special way is therefore not necessary in order to produce a specifically structured coating, which is preferably used as a marking, on the object 3 to be coated. As will be explained in more detail below, a central control unit 14 and at least one setting unit 10 are also provided so that the current flow, in particular a current density gradient, in the gap 11 between the anode and the cathode can be set and changed in a targeted manner. In this context, the control unit 10 is designed in such a way that a gap width of the gap 11 between the electrode 5 with its electrode structure 8 and the surface 2 to be coated can be specifically changed and adjusted as required with high positioning and positional accuracy.

On the metal surface 2 to be coated, a structured coating is applied with the aid of the electrode 5 shown, which has a coarse structure dependent on the design of the electrode structure 8 and a specific fine structure. Depending on the electrode size, the selected electrode structure and the deposition time, structured coatings with structure heights of a few nanometers, optimally in the sub-millimetre range or from 1 to 100 mm can be produced. One of the prerequisites for generating a unique fine structure is that the distance between the electrode 5 with its electrode structure 8 and the object 3 to be coated can be set very precisely, since the inhomogeneity of the electric field distribution and thus the individualization of the fine structure would decrease for large distances. An aspect ratio, i.e. a ratio of the distance from electrode 5 to object 3 to be coated to the structure width, i.e. the average distance between adjacent elevations or depressions of electrode structure 8 on electrode 5, should be in the single-digit range and preferably be 1.

2 shows the comparison of two differently designed electrode structures 8 with which a structured coating with a desired coarse structure can be produced on a metal object 3 in a suitable manner. It is essential that due to the locally different distance between the electrode 5 with its special electrode structure 8 and the surface 2 to be coated, the metal deposition on the surface 2 to be coated can be influenced in a targeted manner. In 2 a) and 2 B) it can be clearly seen that significantly higher deposition rates can be achieved in the area of tips, edges or other raised areas of the electrode structure 8 than in adjacent, differently shaped areas due to the increased field strength in this area and thus higher current density. As the schematic representations in 2 1, the electrode structure 8 of the electrode 5 can, for example, have a plurality of trenches running parallel in the longitudinal direction according to FIG 2 a) or specially selected structural elements arranged in a grid, for example in the form of a cylin those that protrude from the base, as in 2 B) shown.

In the following shows 3 the field lines that occur during a coating process and represent the current density when using differently designed electrode structures 8. While the electrode structures 8 differ in the three illustrations a), b) and c), the metallic object 3 to be coated is plate-shaped in all three cases educated. The electrode structures 8 each have punctiform or linear elevations between which depressions or trenches are located. It can be clearly seen that depending on the configuration of the electrode structure 8 of an electrode 5 and the distance between the electrode structure 8 and the surface 2 to be coated, different structured coatings are produced on the surface 2 of the respective plate-shaped metal object 3 . For the formation of the respective field lines and thus the current density in the gap 11 between the electrode 5 and the surface 2 to be coated, the selected electrode structure 8 is decisive for the structure of the applied coating, in addition to the width of the gap 11 between the electrode 5 and the surface 2 to be coated. Depending on the desired rough structure, correspondingly suitable structural elements 12, for example with hemispheres, points, cylinders, tetrahedrons, cubes, cuboids and/or other geometric shapes, are selected in order to produce a suitable electrode structure 8.

In addition to 3 indicates 4 again in three illustrations the field lines which form during a coating process in the gap 11 between the electrode structure 8 and the surface 2 to be coated and which represent the current density in the gap 11. The object 3 to be coated is in turn designed in the form of a plate. In the three in 4 operating states shown was, like the 4 a), b ), and c), in each case one of the surface 2 to be coated facing electrode structure 8 with pointed structural elements is used. It is essential that the distance between adjacent elements of the electrode structure 8, ie the structure width, was changed in each case. It can be clearly seen that the spacing of the individual elements of the electrode structure 8 has a significant influence on the coarse structure of the coating deposited on the metal surface 2 to be coated, with the process parameters and settings otherwise being the same.

the 3 and 4 illustrate that it is possible by varying the structural elements 12 of an electrode structure 8 to produce coatings with a significantly different coarse structure on a metallic surface 2. The deposition rate that occurs during a coating process is changed in a targeted manner by varying the structural elements 12 of an electrode structure 8 . It is conceivable, for example, for an electrode structure 8 to have structural elements 12 that are angular, circular, oval, or have any other shape. In order to be able to produce the coatings shown above, which have a special coarse structure, the gap width, i.e. the distance between the electrode structure 8 and the surface 2 to be coated, must be selected to be very small, it being advantageous if this distance is controlled using a suitable control unit 10 can be set precisely and varied as required.

5 shows a plan view of an electrode structure 8 of an electrode 5, in which case at least one fastening element 9 is provided in order to fasten structural elements 12 provided with special patterns 13 to the electrode 5 individually or in combination in an exchangeable manner. It is conceivable, for example, for a groove to be provided in the area of the electrode 5, into which the corresponding structure elements 12, which have specific patterns 13 at least in certain areas on their surface, are inserted depending on the desired electrode structure 8 and thus combined with one another. The at least one structural element 12, each having a special pattern 13, can be fixed in the desired position using a screw, for example. In 5 four structural elements 12 with different patterns 13 are shown as an example, which have been attached to the electrode 5 next to one another, so that a structured coating with a coarse structure is produced during a galvanic coating process depending on the selected combination of structural elements 12 with different patterns 13 . By changing the arrangement of the structural elements 12 with their patterns 13, different coatings with different coarse structures can be deposited on a metallic surface 2 in a targeted manner.

6 shows a schematic connection of an apparatus 1 designed according to the invention for applying a structured coating to a metal-containing surface 2 of an object 3, in particular an object 3 consisting entirely of metal. It is essential for the invention that there is no or partially homogeneous coating, but rather a specifically structured coating of the surface 2 to be coated is to be realized. In particular, the coating should have an at least almost reproducible rough structure and a non-reproducible fine structure, so that the corresponding combinations tion of a coarse structure with a specific fine structure is not reproducible.

the inside 6 The apparatus 1 shown has, as the electrolyte reservoir 4, a container with an electrolyte 7, in which an electrode 5 with an electrode structure 8 shaped as required and a receptacle 15 for a metal object 3 to be coated are arranged. During the galvanic coating process, the structured electrode 5, which forms the anode, and the metal object 3 to be coated, which forms the cathode, are arranged in an electrical circuit with a voltage source 6, so that a current flows from the anode through the electrolyte 7 to the cathode , A metal being deposited on the metal object 3 by a reduction reaction from metal ions dissolved in the electrolyte 7 .
According to the 6 In the embodiment shown, a spacer 16 is provided, through which the required distance between the structured electrode 5 and the surface 2 to be coated can be reliably adjusted and maintained. Furthermore, a stirring element 17 is provided, by means of which the electrolyte 7 is caused to flow, at least in certain areas, if necessary, primarily in order to prevent or at least minimize concentration differences in relation to the metal ions dissolved in the electrolyte 7 in the electrolyte bath. In addition, at least one flow-conducting element 18 in the form of a perforated plate is arranged in the area of the gap 11 between the electrode 5 and the surface 2 to be coated. Alternatively or additionally, the structured electrode itself can have holes and/or the special electrode structure can have suitable holes.
The flow prevents a permanent disruptive formation of gas bubbles that may occur on the electrodes depending on the selected process parameters. In addition, the in 6 Apparatus 1 shown has a positioning unit 10, via which the electrode 5 is positioned relative to the surface 2 to be coated of the metal object 3 fixed in the receptacle 15.

7 shows a special embodiment of an apparatus 1 designed according to the invention as a so-called microcell. Such a microcell represents a highly integrative tool in which an electrode 5 is combined with an electrode structure 8 shaped as required, an electrolyte reservoir 4 and a receptacle 15 or a stop for a metal-containing surface 2 of an object 3 to be coated in a comparatively small space. In general, it is conceivable to also provide a voltage source 6, possibly with a compartment for at least one battery or one accumulator, in such a tool so that it can be used in a mobile, portable and self-sufficient manner. For coating a metal-containing surface 2, the in 7 tool shown is designed as an attachment that is placed at the desired location on an object 3 to be marked. After the attachment has been placed on the object 3 to be coated, the electrode 5 with its electrode structure 8 and the surface 2 to be coated are brought into contact with the electrolyte 7, which has metal ions. Due to a current flowing through the electrolyte 7, a metal can in turn be deposited in a targeted manner by reducing metal ions from the electrolyte 7 on the surface 2 to be coated. In this case, too, the suitably designed electrode structure 8 ensures that a coating with a specific coarse structure and a fine structure overlying it is produced on the surface 2 to be coated.

8th shows an alternative embodiment of such a microcell, which in this case has the same components as those related to FIG 7 have been explained, but is pin-shaped.
Regardless of whether it is designed as an attachment or pin, such a micro cell or tool has a spacer 16 or and a sealing element 19, which is in contact with the object 3 to be coated during the coating process, and can be placed anywhere on an object 3, e.g a metal object as in 9 is shown, are put on and thus, depending on the selected electrode structure 8, apply a coating consisting of a coarse structure and a fine structure superimposed on it.
Since the field strength at the electrode 5 and thus the current density decreases with the square of the distance between the electrode 5 and the object 3 to be coated, setting or being able to set the smallest possible distance is advantageous in order to be able to produce the desired structured coating. This is preferably achieved with the aid of suitable spacers 16 and/or an adjustment unit 10 . A control unit 10 is particularly preferably provided which has a piezo drive in order to carry out the adjustments required in each case with the required positioning accuracy. Furthermore, due to the small distance, it should be noted that a gradient in the electrolyte concentration forms during the galvanic deposition, since there is a greater decrease in the metal ions dissolved in the electrolyte 7 in the area of the surface 2 to be coated than in other areas. For this reason, in an apparatus 1 designed according to the invention, in particular if this is designed as a microcell is designed, flow-guiding elements 18 are provided in order to ensure that the electrolyte 7 is sufficiently mixed. This can include, for example, micro-perforated feeds in the structured electrode 5, micro-nozzles or micro-stirrers and/or comparatively small feed lines in the direction of the gap 11 between the electrode 5 and the surface 2 to be coated.

10 shows a schematic sectional view of an apparatus 1 designed according to the invention for producing a structured coating on the metallic surface 2 of an object 3, in particular an object 3 made entirely of metal 20 movable elements are arranged. An electrolyte container, in which an electrolyte 7 with metal ions is stored, is arranged on the device carrier 20 as an electrolyte reservoir 4 . Inside the electrolyte container is an electrode 5 with a special electrode structure 8 designed as a function of the coating to be produced, which dips into the electrolyte 7 and is held by an anode holder 21 . Above the anode holder 21 and connected to it is the first adjustment unit 10a, which enables movement of the anode holder 21 with the anode attached thereto in the plane of the drawing from right to left. The structured electrode 5, which forms the anode during the coating process, is moved relative to the surface 2 to be coated with the aid of this positioning unit 10. FIG.

Also inside the electrolyte container, fixed in a receptacle 16 and contacted by a cathode contact wire 22 made of platinum, is the metal object 3 to be coated. If a voltage source 6 is connected to the metal object 3 and the electrode 5 and activated, a current flows from the electrode 5 with its electrode structure 8, which is the anode and thus the positive pole here, a current to the metal object to be coated 3, which forms the cathode, ie the negative pole. Here, metal ions dissolved in the electrolyte 7 are dissolved out of the latter and the corresponding metal layer is deposited on the object 3 to be coated due to a reduction reaction. A metal coating with a specific rough structure and a fine structure overlying it is applied to the metal object 3 by the suitably selected electrode structure 8 .
In this context, it is conceivable, for example, to use a metallic bar to be coated as the cathode, which is coated with the aid of an electrode 5 structured on the surface facing the metallic bar during the coating process. In this way, specific markings that cannot be reproduced can be applied to a metal surface or other valuable objects.
As explained before, using the in 10 Apparatus 1 shown deposit both a coarse and a fine structure by means of a galvanic coating on the object 3 to be coated. According to the invention, the rough structure of the coating applied to the metal object 3 is produced by providing a suitably designed electrode structure 8 of an electrode 5 and can also be changed by changing the electrode structure 8 . In contrast, the fine structure, which is superimposed on the coarse structure, cannot be specifically influenced and, above all, is not reproducible even when using the same apparatus 1 and the same process parameters that can be set by the operator.
with the inside 10 Apparatus 1 shown can therefore not be produced reproducible markings on a metal object 3, so that a corresponding marking is to be regarded as unique.

A container holder 23 is provided below the electrolyte container, in which the electrolyte container is fixed and which can be moved in two directions with the aid of a suitable second actuating unit 10b, which does not coincide with the direction of movement of the actuating unit 10a which is arranged above the electrolyte container and to which the anode holder 21 is attached. coincide. Rather, the two actuating units 10a, 10b are designed in such a way that they can be used to realize three directions of movement that are arranged orthogonally to one another.

Incidentally, the in 10 Apparatus 1 shown, which has a suitable control unit 14 for controlling the two setting units 10a, 10b. A special function of the control unit 14 with the adjustment units 10a, 10b connected thereto consists in setting or changing the distance between the electrode 5 and the surface 2 to be coated as precisely as possible to a predetermined value.

Supplementary shows 11 shows part of an apparatus 1 designed according to the invention for the structured coating of the metallic surface 2 of an object 3 11 a receptacle 15 in which the object 3 to be coated can be fixed for the coating process. In the embodiment shown, the object 3 to be coated is a plate-shaped metal element with a 1 cm ² large polished surface 2. Generally all objects 3 that are made of metal or have at least one metallic surface 2 are suitable for a coating according to the invention. A structured coating can be produced on the surface 2 of these objects 3 using an apparatus 1 designed according to the invention and the corresponding methods. According to 11 the object 3 to be coated, which forms the cathode, ie the negative pole, during the coating process is contacted via a cathode contact wire 22 made of platinum. The receptacle 15, in which the object 3 to be coated, here a plate element, is fixed is made of an electrically non-conductive material, so that a current flow during the coating process takes place exclusively between the electrode structure 8 of the electrode 5 and the object 3 to be coated.

Finally shows 12 a plurality of electrodes 5 with different electrode structures 8, which allow the coating of a metallic surface 2 of an object 3, in particular a metal object 3. Depending on the selected electrode structure 3 or the individual structural elements 12 of such an electrode structure 8 , structured layers can be produced in a targeted manner on a metallic surface 2 , which layers are suitable for marking the object 3 . It is essential that the structured coating deposited on the metallic surface 2 has a coarse structure and a fine structure superimposed on it. While the coarse structure can be generated at least essentially in a targeted manner on the basis of the respectively selected electrode structure 8, the fine structure of the structured coating cannot be influenced in a targeted manner. In particular, the fine structure of a structured coating cannot be produced in a reproducible manner. The fine structure cannot be recognized with the naked eye, but special measuring methods such as X-ray diffractometry, UV/VIS spectroscopy, Michelson interferometry, reflectometry and/or speckle interferometry are required in order to detect or identify a corresponding fine structure .to record their properties and to secure them in terms of data technology.
Depending on the duration of a coating process in particular, it is conceivable that the coarse structure produced can either be seen with the naked eye or that additional technical equipment such as a magnifying glass or a microscope is also required for this.
Since by selecting a suitably designed electrode structure 8 and by combining structural elements 12 with different patterns 13 to form a special electrode structure 8, any number of different coarse structures can generally be produced with relatively little effort and, moreover, the fine structures superimposed on them can also be produced using the same apparatus 1 and the same process parameters are not reproducible, the technical solution described represents a preferred option for uniquely marking, for example, particularly valuable or security-relevant objects 3 and thus reliably preventing or at least making verifiable an attempt at imitation and/or fraud.

Reference List

1

Apparatus for applying a textured coating

2

surface of a metal object

3

metal object

4

electrolyte storage

5

electrode

6

voltage source

7

electrolyte

8th

electrode structure

9

fastener

10

actuator

10 a

first actuator

10 b

second actuator

11

gap

12

structural element

13

Pattern

14

control unit

15

Recording for metal object

16

spacers

17

stirring element

18

flow-guiding element

19

sealing element

20

equipment carrier

21

anode holder

22

cathode contact wire

23

container holder

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 0370239 A1 [0004]
• WO 2016/098087 A1 [0005]

Claims (15)

Apparatus (1) for applying a structured coating to a surface (2) of a metal object (3), with an electrolyte reservoir (4), in which an electrolyte (7) having metal ions is arranged and which is set up in such a way that the Electrolyte (7) can be brought into contact during a coating process with at least one area of the surface (2) of the metal object (3) to be coated, with an electrode (5) which is in contact with the electrolyte (7) at least during the coating process and has a metal at least on a surface area contacted by the electrolyte (7), and with an interface for connecting a voltage source (6), which is connected to the metal object (3) and the electrode (5) in an electric circuit during the coating process in such a way, that the electrode (5) in contact with the electrolyte (7) is an anode and the electrode to be coated is in contact with the electrolyte Metal object (3) forms a cathode, characterized in that the electrode (5) has an electrode structure (8) on a surface facing the metal object (3) during the coating process, which, depending on the surface texture, shape and/or geometry of the Surface (2) of the metal object (3) to be applied coating is performed. apparatus after claim 1 , characterized in that the electrode structure (8) has at least two different patterns, shapes and/or geometries, at least during the coating process. apparatus after claim 1 or 2 , characterized in that the electrode (5) has at least one fastening element (9) in order to connect at least one electrode structure (8) to the electrode (5) in a completely or partially exchangeable manner. Apparatus according to claim one of the preceding claims, characterized in that at least one setting unit (10) is provided for setting a width of a gap (11) formed between the electrode (5) and the metal object (3) during the coating process. apparatus after claim 4 , characterized in that a ratio between the width of the gap (11) and an average distance between adjacent elevations and/or depressions of the electrode structure (8) assumes a value X and/or can be set to a value X by a setting unit (10), for which 9 ≥ X ≥ 1 holds. Apparatus according to one of the preceding claims, characterized in that the electrode (5) has platinum at least in sections in the area contacted by the electrolyte (7) during the coating process. Method for applying a structured coating to a surface (2) of a metal object (3), in which - an electrolyte (7) containing metal ions is stored in an electrolyte reservoir (4) and the electrolyte (7) during a coating process contains at least one area of the surface (2) of the metal object (3) to be coated is brought into contact, - an electrode (5) made of a metal or at least a metal-coated surface area of the electrode (5) during the coating process with the electrolyte (7) in is brought into contact, and in which - a voltage source (6), the metal object (3) and the electrode (5) are connected in an electrical circuit during the coating process in such a way that the electrode (5 ) forms an anode and the metal object (3) to be coated, which is in contact with the electrolyte (7), forms a cathode, characterized in that ss the electrode (7) is provided with at least one electrode structure (8) arranged in a region of its surface, which is carried out depending on a surface texture, shape and/or geometry of the structured coating to be applied to the metal object (3), and that the electrode ( 5) is arranged at least temporarily in the electrolyte (7) during the coating process in such a way that the electrode structure (8) faces the metal object (3). procedure after claim 7 , characterized in that a gap (11) with an average gap width is set between the electrode structure (8) and the surface (2) to be coated, so that a ratio between the gap width and an average distance between adjacent elevations and/or depressions of the electrode structure ( 8) takes a value X such that 9 ≥ X ≥ 1. procedure after claim 7 or 8th , characterized in that the electrode structure (8) is changed between two coating processes. Procedure according to one of Claims 7 until 9 , characterized in that the at least one electrode structure (8) is fastened to the electrode (5) in an exchangeable manner by means of a fastening element (9). Procedure according to one of Claims 7 until 10 , characterized in that the electrode structure (8) is formed from at least two structural elements (12) with different patterns (13). Procedure according to one of Claims 7 until 11 , characterized in that after the structured coating has been produced, an image, another recording, a measured value and/or a data set is generated which represents at least one property specific to the structured coating. procedure after claim 12 , characterized in that the image, the other recording, the measured value and/or data set is generated at least partially with an X-ray diffractometry, UV/VIS spectroscopy, Michelson interferometry, reflectometry and/or a speckle interferometry measurement . procedure after claim 12 or 13 , characterized in that the image, the other recording, the measured value and/or data set is compared with at least one image, other recording, measured value and/or data set generated at another point in time and/or made available in some other way and based on the Comparison information is generated in relation to a degree of similarity of the compared images, other recordings, measured values and / or data sets. Metal object (3), in particular metal object (3), which at least partially comprises a noble metal, with a unique structured coating produced with the apparatus (1) according to at least one of Claims 1 until 6 or with the method according to at least one of Claims 7 until 11 .

Images