Liquid-cooled plasma processing

Abstract

The present invention relates to a method (200, 300, 400, 500, 600, 600', 600'', 700) for treating, in particular cleaning, reducing and / or coating, a workpiece (202, 302, 502, 602, 702), in which an atmospheric plasma jet (26, 230, 230', 330, 530, 630, 730, 730') is generated and the workpiece (202, 302, 502, 602, 702) to be treated, in particular the workpiece to be cleaned, reduced and / or coated, is heated. The present invention relates to a method (200, 300, 400, 500, 600, 600', 600", 700) in which a workpiece (202, 302, 502, 602, 702) is brought into contact with a liquid (210, 510, 610, 710) and an atmospheric plasma jet (26, 230, 230', 330, 530, 630, 730, 730') is impinged on a surface (204, 304, 504, 604, 704) of the workpiece (202, 302, 502, 602, 702) or on the liquid (210, 510, 610, 710). The present invention further relates to an apparatus (601) for treating, in particular cleaning, reducing and / or coating, a strip-shaped workpiece (602), in particular a metal strip, in particular for carrying out the aforementioned method.

Description

[Technical Field]

[0001] The present invention relates to a method for treating workpieces, in particular for cleaning, reducing and / or coating workpieces, as well as to an apparatus for treating, in particular for cleaning, reducing and / or coating strip-shaped workpieces.

[0002] Methods for reducing a workpiece are performed, for example, to achieve better thermal and / or electrical contact of the workpiece surface or better wetting, for example, with a solder. The reduction treatment of a workpiece is often intended to facilitate or even enable subsequent process steps on the workpiece, such as joining or soldering to other workpieces.

[0003] Various methods of reduction treatment are known in the prior art. Some of these methods use, for example, chemical reducing agents, such as fluxes. However, these chemical reducing agents are typically corrosive and release vapors that are harmful to health or are harmful to the body. Reduction methods using low-pressure plasma are also known, for example from Patent Document 1. However, these low-pressure methods have the disadvantage that, due to the necessary supply and discharge processes, they can only be integrated into continuous production operations, which requires a great deal of technical effort. Furthermore, these low-pressure methods make it difficult to perform selective reduction treatments, in which only certain parts of the workpiece surface are reduced.

[0004] The use of atmospheric plasma techniques for reduction has also been explored, but it has been found that this often results in rapid re-oxidation of the reduced workpiece surface, and therefore the workpiece surface in question may not be completely free of oxides.

[0005] Furthermore, various methods for coating workpieces using atmospheric plasma jets are known from the prior art, for example from US Pat. No. 5,629,999, and there is a need for further improvements in coating methods using atmospheric plasma jets.

[0006] Furthermore, various methods are known from the prior art for cleaning workpieces, especially for subsequent coatings, and there is also a need to carry out such cleaning methods efficiently. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2000 / 29642(A1) [Patent Document 2] European Patent No. 1 230 414(B1) Summary of the Invention [Problem to be solved by the invention]

[0008] Against this background, the present invention is based on the object of providing an improved method and an improved device for reliably treating, in particular cleaning, reducing and / or coating, workpieces, which are particularly suitable for in-line use and preferably allow selective treatment, in particular cleaning, reducing and / or coating, of the workpiece surface. [Means for solving the problem]

[0009] According to the present invention, the above-mentioned object is achieved by a method for treating a workpiece, in which an atmospheric plasma jet is generated, the workpiece to be treated is brought into contact with a liquid, and the atmospheric plasma jet is impinged on the workpiece surface to be treated, in particular on the workpiece surface to be cleaned, reduced and / or coated.

[0010] According to the present invention, the above-mentioned object is particularly achieved by a method for reducing a workpiece, in which an atmospheric plasma jet is generated, the workpiece to be reduced is brought into contact with a liquid, and the atmospheric plasma jet is caused to impinge on the workpiece surface and / or the liquid to be reduced. It has been found that in this way the workpiece surface can be reliably reduced.

[0011] The reduction treatment of the workpiece surface particularly means that the oxides on the workpiece surface are chemically converted so that, after the reduction treatment, the oxide components are completely absent or at least reduced on the now-reduced workpiece surface or on the section of the reduced workpiece surface. The oxides on the workpiece surface can be reduced, in particular, by removing oxygen from the oxides using, for example, species contained in the plasma jet and chemically bonding the oxygen in some other way. For example, in the reduction treatment of a copper workpiece surface, the removal of oxygen can convert, for example, copper oxides present on the surface into copper.

[0012] In the context of the present invention, previous tests of reducing the surface of a workpiece using an atmospheric plasma jet have shown that heating the workpiece primarily by the plasma jet leads to increased reoxidation of the workpiece surface. By contacting the workpiece with a liquid, the method described herein can achieve cooling of the workpiece in the area of ​​the surface to be reduced, making that area less susceptible to reoxidation after the reduction treatment. Furthermore, contact with the liquid at least partially covers the workpiece surface, thereby preventing or at least reducing direct contact between the workpiece surface and the oxygen-containing atmosphere in the environment, thereby also preventing or reducing reoxidation.

[0013] In the reduction process, an atmospheric plasma jet is generated and impinged on the workpiece surface and / or liquid to be reduced. Thus, the actual reduction of oxides on the workpiece surface can be achieved by impinging the atmospheric plasma jet on the workpiece surface, particularly on the section of the workpiece surface to be reduced. Additionally or alternatively, the reduction of oxides on the workpiece surface can be achieved by impinging the atmospheric plasma jet on a liquid, thereby plasma-activating the liquid, instead of directly impinging the atmospheric plasma jet on the workpiece. It has been found that the plasma-activated liquid can also exert a reducing effect on the workpiece surface. In this embodiment, particularly effective cooling and reduction by contact with an oxygen-containing atmosphere are achieved by the liquid.

[0014] It has also been found that impinging an atmospheric plasma jet on a liquid increases the effective range of the reduction treatment beyond the width of the plasma jet, because the liquid impinged by the plasma jet causes a reduction treatment on the workpiece surface even outside the direct area of ​​action of the plasma jet. Thus, unlike dry reduction treatments using a plasma jet in which only the area of ​​the workpiece surface that the plasma jet impinges on is subjected to a reduction treatment, this method allows a larger workpiece surface area to be subjected to a reduction treatment using the plasma jet, for example, allowing larger workpieces to be subjected to a plasma reduction treatment with fewer plasma nozzles or fewer transitions.

[0015] The reducing effect of the atmospheric plasma jet can be achieved by generating the atmospheric plasma jet using a reducing gas or reducing gas mixture, such as forming gas. Additionally or alternatively, a reducing agent can be added to the atmospheric plasma jet, or in some other way, the reducing agent can be brought into contact with a liquid, for example, with the surface of the workpiece to be reduced.

[0016] In particular, the method is used to reduce the at least partly metallic surface of a workpiece formed at least partly from a metal, for example a metal alloy. The metal may be, for example, copper.

[0017] In particular, the workpiece may be a strip-shaped workpiece, in particular a metal strip, which may be subjected to a reduction treatment, for example, in order to prepare the workpiece surface for a subsequent coating, in particular a coil coating.

[0018] According to the present invention, the above-mentioned object is further achieved by a method for coating a workpiece, in which an atmospheric plasma jet is generated, the workpiece to be coated is brought into contact with a liquid, and the atmospheric plasma jet is impinged on the workpiece surface and / or the liquid to be coated. It has been found that in this way the workpiece surface can be reliably and uniformly coated.

[0019] In particular, workpieces can be coated with a metal layer by the method.

[0020] For coating, a precursor, preferably a salt, is added to the liquid, and in particular the salt is dissolved in the liquid. In this way, it has been found that the precursor or the reaction product of the reaction of the precursor forms a coating, and the surface of the workpiece can be effectively coated. The atmospheric plasma jet or reactive species generated in the liquid by the atmospheric plasma jet, such as OH - However, the precursor or its components, particularly dissociated components of a salt dissolved in the liquid as a precursor, can be reduced by electron-accepting properties to cause a chemical redox reaction to form a coating on the surface of the workpiece. The dissociated components can be ionic residues of a salt, particularly cationic residues, particularly metal ionic residues of a salt.

[0021] For example, when a metal salt, such as a copper salt, is used as the precursor, the metal salt, such as Cu 2+The metal cations of the above can be reduced to elemental metal, e.g., Cu, by interaction with the atmospheric plasma jet or with a liquid on which the atmospheric plasma jet impinges, thereby depositing the elemental metal, e.g., Cu, on the workpiece surface to be coated, thus forming a metal coating, e.g., a copper coating.

[0022] In the methods for coating workpieces described herein, reduction specifically refers to the receptivity of one or more electrodes. Oxygen may also participate in the chemical redox reaction, but this is not required.

[0023] In the method for coating the workpiece by bringing the workpiece into contact with a liquid, a uniform coating can be achieved, in particular with the precursor or the reaction product of the reaction of said precursor. In this way, the workpiece can also be cooled in the area of ​​the surface to be coated and / or protected from direct contact with oxygen-containing atmospheres in the environment, thereby counteracting the reversal of the redox reaction caused by the plasma jet or the oxidation of the reduced components or the oxidation of the workpiece surface.

[0024] In coating, an atmospheric plasma jet is generated and impinged on the workpiece surface and / or liquid to be coated. The actual coating of the workpiece surface can therefore be carried out, in particular, by impinging the atmospheric plasma jet on the workpiece surface, in particular on the section of the workpiece surface to be coated, whereby the coating material is formed from a liquid, in particular by a precursor or a reaction product of the reaction of said precursor. Additionally or alternatively, instead of impinging the atmospheric plasma jet directly on the workpiece, the coating of the workpiece surface can also be carried out by impinging the atmospheric plasma jet on a liquid, which is thereby plasma activated. The liquid thus plasma activated can then react with reactive species contained therein, such as OH. -It has been found that, due to the above, a redox reaction occurs with the precursor or its components dissolved in the liquid, particularly with dissociated components of the salt dissolved in the liquid as a precursor, thereby producing a coating on the surface of the workpiece. In this embodiment, the liquid also achieves particularly effective cooling and reduction by contact with an oxygen-containing atmosphere.

[0025] It has also been recognized that impinging an atmospheric plasma jet on a liquid increases the effective area of ​​the coating beyond the width of the plasma jet, because the liquid impinged by the plasma jet produces a coating on the workpiece surface outside the direct area of ​​action of the plasma jet. Thus, unlike dry coating with a plasma jet, in which only the area of ​​the workpiece surface impinged by the plasma jet is coated, the present method can be used to coat a larger workpiece surface area with the plasma jet, thereby, for example, allowing larger workpieces to be coated with fewer plasma nozzles or fewer transitions.

[0026] The atmospheric plasma jet can be generated using, for example, nitrogen (N2), argon, air, forming gas (nitrogen-hydrogen mixture) or argon-hydrogen mixture.

[0027] The plasma jet itself already has a certain reducing effect, even when generated with a generally non-reducing gas, such as nitrogen, so that it can cause redox reactions, for example, on salts or dissociated components of such salts dissolved in a liquid as precursors.

[0028] The atmospheric plasma jet is preferably generated with a reducing gas or gas mixture, such as forming gas or an argon-hydrogen mixture, to induce or enhance the redox reaction of the precursor in the liquid, particularly the salt or dissociated components of the salt dissolved in the liquid as the precursor. Additionally or alternatively, a reducing agent can be added to the atmospheric plasma jet, or the reducing agent can be brought into contact with the workpiece surface and / or liquid to be coated in some other way. For example, when the plasma jet is generated using air, nitrogen, or argon, a hydrogen-containing agent can be added to the plasma jet, or a liquid or a hydrogen-containing liquid can be used to provide hydrogen for the redox reaction. In this way, a stronger coating effect can be achieved.

[0029] The workpiece to be coated can be, for example, a workpiece made of polymer, glass, metal, wood, ceramic, leather or textile material, such as textile. The workpiece to be coated can consist of various materials, whereby the workpiece in the area of ​​the surface to be coated preferably consists of one or more of the following materials: polymer, glass, metal, wood, ceramic, leather or textile material.

[0030] The workpiece to be coated may be a strip-shaped workpiece, in particular a metal strip.

[0031] The present invention further solves the above-mentioned problem by a method for cleaning a workpiece, in particular by generating an atmospheric plasma jet, bringing the workpiece to be cleaned into contact with a liquid, and impinging the atmospheric plasma jet on the workpiece surface and / or the liquid to be cleaned. It has been found that in this way, the workpiece surface can be reliably and uniformly cleaned. The workpiece to be cleaned can be a strip-shaped workpiece, in particular a metal strip.

[0032] The above-mentioned object is further achieved by an apparatus for treating, in particular cleaning, reducing, and / or coating, strip-shaped workpieces, in particular metal strips, and in particular for carrying out the above-described methods for treating workpieces, in particular the above-described methods for reducing, coating, or cleaning, or each of these embodiments, comprising an immersion bath apparatus configured to guide the strip-shaped workpiece through the immersion bath and a plasma source for generating an atmospheric plasma jet, wherein the plasma source is arranged and configured to impinge the atmospheric plasma jet on the immersion bath of the immersion bath apparatus or on the strip-shaped workpiece guided through the immersion bath during operation. Such an apparatus allows strip-shaped workpieces, in particular metal strips, to be effectively and reliably treated, in particular subjected to reduction and / or coating and / or cleaning. Furthermore, the apparatus can be easily integrated inline into continuous production operations.

[0033] In particular, the plasma nozzle can be positioned and configured to impinge an atmospheric plasma jet onto a strip-shaped workpiece guided through an immersion bath device during operation. In this way, treatment, particularly cleaning and / or reduction treatment and / or coating, can be achieved by directly impinging the plasma jet onto the workpiece. Furthermore, the plasma nozzle can also be positioned and configured to impinge an atmospheric plasma jet onto the immersion bath during operation. As described above with respect to the method, it has been found that treatment effects, particularly cleaning and / or reduction effects and / or coatings, can also be achieved by impinging an atmospheric plasma jet onto a liquid in contact with the strip-shaped workpiece, thereby making direct impingement of the plasma jet onto the workpiece unnecessary.

[0034] Furthermore, impinging the plasma jet on the liquid of the immersion bath increases the treatment effect, in particular the reduction effect and / or coating and / or cleaning effect, beyond the width of the plasma jet, thereby allowing a wider strip surface on the workpiece surface to be treated with one plasma nozzle, and further has the advantage that treatment, in particular reduction treatment and / or coating and / or cleaning, is possible with a reduced number of plasma nozzles per given width required for treatment, in particular reduction treatment and / or coating and / or cleaning, of strip-shaped workpieces compared to, for example, dry plasma treatment methods, in particular dry plasma reduction methods or dry plasma coating methods or dry plasma treatment methods.

[0035] In particular, the immersion bath apparatus may comprise a container for holding a volume of liquid forming the immersion bath, and guide means positioned and configured to guide the strip-shaped workpiece through the immersion bath. Suitable guide means include, for example, guide rollers that can be easily incorporated into continuous production operations.

[0036] The apparatus may have dispensing means and receiving means configured to dispense the strip material before treatment, in particular before reduction and / or coating and / or cleaning, and to receive the strip material after treatment, in particular after reduction and / or coating and / or cleaning. The dispensing means and / or receiving means may, for example, be designed as rolls so that the strip material can be unwound from the dispensing means for dispensing or fed into the receiving means for receiving the strip material. This embodiment allows for compact storage of the material and advantageously reduces contact of its surface with an oxygen-containing atmosphere, thereby reducing the oxidizing effect of ambient air on the strip workpiece surface.

[0037] Furthermore, the apparatus may have conveying means for conveying the strip-shaped workpieces through the immersion bath apparatus. These conveying means may be formed by guide means, e.g., rotating rollers, and / or by dispensing means and receiving means, e.g., driven dispensing means and / or driven receiving means. Alternatively or additionally, separate conveying means may be provided.

[0038] Furthermore, the device may have sensors for measuring the temperature of the liquid and / or the workpiece, thereby allowing operation to be monitored and / or controlled. In particular, the temperature of the workpiece may be controlled, for example, upon exiting the immersion bath, so that heating of the strip-shaped workpiece above a predetermined temperature value is prevented in the immersion bath, for example by cooling, preferably with the aid of a provided coolant, so that a re-oxidation process or an oxidation process as a whole after exiting the immersion bath is prevented. If the temperature of the workpiece and / or the immersion bath rises excessively, for example, the cooling capacity of the provided coolant may be increased, the transport speed of the workpiece through the immersion bath and / or the intensity of the plasma jet may be adjusted.

[0039] Furthermore, the apparatus can have several plasma sources. For treating, in particular reducing and / or coating and / or cleaning, large surfaces, such as wide strip-shaped workpieces or several strip-shaped workpieces arranged adjacent to one another, the plasma sources can be arranged in a direction transverse to the transport direction of the strip-shaped workpieces. Additionally or alternatively, several plasma sources can be provided along the transport direction of the strip-shaped workpieces to enable particularly rapid guiding of the strip-shaped workpieces with sufficient treatment effect, in particular sufficient reducing effect and / or sufficient coating and / or sufficient cleaning.

[0040] Various embodiments of the methods and devices are described below, where the individual embodiments in each case apply independently to methods for treatment, in particular methods for reduction treatment, coating and cleaning, and also to treatment devices, in particular reduction treatment devices and / or coating devices and / or cleaning devices. Furthermore, the individual embodiments can be combined with one another as required.

[0041] In one embodiment of the method for treatment, particularly for reduction and / or coating and / or cleaning, the workpiece is placed in the liquid volume, particularly by submerging the workpiece, before impinging the plasma jet on the surface or liquid. This increases the contact between the liquid and the workpiece, thereby achieving better cooling of the workpiece by the liquid, particularly in the area of ​​the workpiece surface to be treated, particularly to be reduced, coated, and / or cleaned. Furthermore, this reduces contact between the workpiece surface and an atmosphere that may contain oxygen. This prevents or at least reduces oxidation or reoxidation of the treated, particularly reduced, coated, and / or cleaned, workpiece surface. Preferably, the workpiece to be treated, particularly the workpiece to be reduced, coated, and / or cleaned, is placed in the liquid volume so that the liquid volume covers a height of at least 1 mm, preferably at least 3 mm, particularly preferably at least 5 mm, above the workpiece surface oriented toward the surface of the liquid volume.

[0042] In another embodiment of the method for treatment, in particular for reduction and / or coating and / or cleaning, the impingement of the atmospheric plasma jet is carried out in such a way that the part of the liquid volume located above the workpiece is locally displaced by the atmospheric plasma jet. In this way, the atmospheric plasma jet can be effectively impinged on the workpiece surface to be treated, in particular on the workpiece surface to be reduced and / or coated and / or cleaned, even when the workpiece is located in the liquid, in particular when it is submerged in the liquid. By locally displacing the liquid with the plasma jet, a stronger reduction effect and / or more targeted coating and / or cleaning can be achieved.

[0043] The atmospheric plasma jet can particularly effectively completely displace the liquid volume above the workpiece locally, so that locally at the plasma impact point no liquid remains or only a thin liquid film with a height above the workpiece surface of less than 1 mm, in particular less than 10 μm, for example in the size range of a few molecular layers, thereby achieving a substantially direct collision of the plasma jet with the workpiece, which results in a particularly intense and targeted treatment, in particular a reduction effect and / or coating and / or cleaning.

[0044] Due to the local displacement of the liquid, the workpiece remains well covered by liquid outside the plasma jet and can therefore be effectively cooled and / or shielded from the oxygen-containing atmosphere.

[0045] Alternatively, the atmospheric plasma jet can also displace a liquid volume above the workpiece, for example, so that a macroscopic liquid volume having a height of at least 1 mm, preferably at least 2 mm, and more preferably at least 3 mm, remains above the workpiece surface at the plasma impact point. In this way, a good and targeted treatment effect, in particular a reduction effect and / or coating and / or cleaning, can also be achieved. At the same time, the liquid is continuously covered by the liquid during plasma application, which achieves more efficient cooling of the workpiece surface and prevents direct contact with oxygen in the ambient atmosphere.

[0046] The displacement of the liquid volume, in particular the degree of displacement, is adjustable, for example, via the distance between the plasma nozzle and the workpiece surface and / or via the working gas flow or working gas pressure of the plasma nozzle.

[0047] Furthermore, the displacement of the liquid volume, and in particular the degree of displacement, can be adjusted by adjusting the liquid height above the workpiece. For example, a lower liquid height for local displacement of liquid allows sufficient local displacement of water to be achieved at a larger plasma nozzle-to-workpiece distance or at a lower working gas flow or working gas pressure.

[0048] In another embodiment of the method, in particular for cleaning and / or reducing treatment, the workpiece is brought into contact with a liquid by being impinged with the liquid during and / or after the impact of the plasma jet, in particular by being sprayed.

[0049] The impingement of the liquid may be carried out over the entire workpiece surface or may be carried out locally in the area of ​​the plasma jet impingement. By impinging the liquid on the workpiece surface during the plasma jet impingement, for example, the workpiece can be cooled if its temperature increases due to the plasma jet impingement and / or contact with an oxygen-containing atmosphere can be reduced. Furthermore, the reducing effect of the atmospheric plasma jet can be enhanced or generated primarily by impingement with the liquid, for example by using a liquid with a reducing effect, possibly under the action of the plasma jet.

[0050] Impingement on the workpiece, particularly spraying, can be performed in a tailored manner. In particular, embodiments of the method can avoid prolonged contact of the workpiece with the liquid over a large area, if necessary, which can be advantageous for certain applications or certain workpiece materials. By impinging during or after the plasma jet impingement, the properties of the liquid can be particularly adjusted, for example by controlling the temperature of the liquid. In addition, localized impingement has the advantage that less liquid is required.

[0051] In another embodiment of the method for treating, in particular the method for reducing and / or coating and / or cleaning, the atmospheric plasma jet is generated using a reducing working gas, in particular a hydrogen-containing working gas. The working gas can contain, for example, hydrogen (H2) and one or more inert gases, such as nitrogen (N2) or noble gases (e.g., Ar). One possible working gas is forming gas, which is, for example, a mixture of hydrogen and nitrogen. The forming gas can have, for example, a hydrogen content (H2) in the range of 1% to 15% by volume and a nitrogen content (N2) in the range of 99% to 85% by volume.

[0052] When a hydrogen-containing working gas is used, the hydrogen contained in the gas has a strong reducing effect on the workpiece together with the atmospheric plasma jet, or in the liquid if the liquid is the object of the plasma jet impingement. In particular, the plasma jet generated using the hydrogen-containing working gas has a reducing effect by itself without the need for other means, such as induction by a liquid. In this way, the liquid can be, for example, a hydrogen-free liquid or a liquid containing only hydrogen in a strongly bound form, such as an organic liquid.

[0053] In coating methods, the reducing effect of the plasma jet can be used in particular to reduce metal ions to elemental metals so that the workpiece is coated with the metal. The reduction of metal ions can be achieved in particular by reducing reactive species, such as OH, generated by impinging the plasma jet on the liquid. - This can be achieved by:

[0054] In another embodiment of the method for treatment, particularly the method for reduction treatment and / or coating and / or cleaning, a hydrogen-containing liquid, preferably a water-containing liquid, in particular water, is used as the liquid. In this way, the liquid can supply hydrogen, which in combination with the atmospheric plasma jet produces a strong reduction effect. In this case, for example, since the reduction effect is caused by hydrogen from the liquid, it is conceivable to generate the plasma jet using a non-reducing, e.g., inert, working gas. For example, air can be used to generate the atmospheric plasma jet, which reduces the operating costs of the method and the apparatus.

[0055] In particular, reactive species with a reducing effect, such as OH - can be generated by impinging a plasma jet on a liquid. In the coating process, for example, metal ions can be reduced to elemental metal by reactive species.

[0056] In one embodiment of the method for treatment, particularly the method for reducing and / or coating and / or cleaning, an organic liquid is used as the liquid. This is particularly advantageous when treating a workpiece made of a water-sensitive material, such as a material that is prone to corrosion, or when the presence of liquid water on the workpiece is detrimental to subsequent process steps. In particular, the use of an organic liquid can achieve rapid or simple drying of the material surface, especially when a highly volatile organic liquid is used.

[0057] The organic liquid may be, for example, a bromine-containing solution, which in addition to the reduction treatment and / or coating and / or cleaning, may also achieve a bactericidal effect on the workpiece surface. This embodiment is therefore particularly important for example for methods of producing workpieces intended for medical use or for contact with food.

[0058] In one embodiment of the method for treatment, in particular for reduction treatment and / or coating and / or cleaning, the atmospheric plasma jet is generated using a plasma nozzle having a nozzle opening from which the plasma jet is emitted during operation. In this way, the plasma jet can be directed specifically onto the workpiece surface to be treated. In particular, the use of such a plasma nozzle allows for targeted treatment, in particular reduction treatment and / or coating and / or cleaning, of specific sections of the workpiece surface. Furthermore, this allows for adjusting the distance from the plasma nozzle opening to the workpiece surface, thereby adjusting the treatment effect, in particular the reduction effect, coating and / or cleaning, or the displacement of liquid between the workpiece surface and the atmospheric plasma jet.

[0059] In one embodiment, the plasma nozzle and the workpiece are moved relative to each other during the impact of the plasma jet. In this way, a larger surface area of ​​the workpiece can be treated, in particular reduction and / or coating and / or cleaning. Furthermore, the desired treatment, in particular reduction and / or coating and / or cleaning, can be carried out in a predetermined section of the workpiece surface in this way.

[0060] In one embodiment, the atmospheric plasma jet is generated by an electrical discharge in a working gas. The plasma jet thus generated is easily alignable and has been found to be highly effective for reducing oxides on workpiece surfaces, particularly metal surfaces, and / or generating reactive species with a reducing effect. Furthermore, it has been shown that good coating and / or cleaning results can be achieved with such a plasma jet in the described coating or cleaning methods. Furthermore, the supply of a working gas containing various gases is possible. Additionally, the flow of the working gas can be adapted to provide sufficient reducing gas for the reduction or redox reaction and / or to achieve the desired liquid displacement between the workpiece surface and the atmospheric plasma jet.

[0061] In one embodiment of the method for treating, particularly the method for reducing and / or coating and / or cleaning, an atmospheric plasma jet is generated by an arc-like discharge in a working gas, which is generated by applying a high-frequency high voltage between electrodes. In this way, a reactive plasma jet is generated with a relatively low ion temperature, which reduces the tendency of the plasma jet to heat the workpiece or the liquid when it impinges, to re-oxidize the workpiece surface, or to oxidize metal ions that have been reduced to elemental metal.

[0062] In particular, to generate an arc-shaped discharge, at least two electrodes and a voltage source for applying a high-frequency high voltage to each electrode can be provided. The high-frequency high voltage for generating the high-frequency arc-shaped discharge has a voltage intensity in the range of 1 kV to 100 kV, preferably 1 kV to 50 kV, and more preferably 10 kV to 50 kV, and a frequency of 1 kHz to 300 kHz, particularly 1 kHz to 100 kHz, preferably 10 kHz to 100 kHz, and more preferably 10 kHz to 50 kHz.

[0063] In one embodiment, a precursor, particularly a metal-containing precursor, is or has been added to the liquid. The precursor is preferably a salt. Preferably, the salt is or has been dissolved in the liquid. A mixture of different precursors, particularly different salts, can also be or has been added to the liquid.

[0064] The salt may be a metal salt, which can coat the surface of the workpiece with a metal layer. In particular, the metal-containing salt can contain one or more of the following metals: Ag, Cu, Zn, Ni, Sn, and Au.

[0065] For example, an Ag-containing precursor can be added to the liquid or may be contained in the liquid, the Ag-containing precursor preferably being selected from the following list: silver acetate (CH3CO2Ag), silver carbonate (Ag2CO3), silver chloride (AgCl), silver iodide (AgI), silver nitrate (AgNO3), silver perchlorate hydrate (AgClO4.H2O), silver sulfate (Ag2SO4), silver bromide (AgBr), silver trifluoroacetate (CF3COOAg), silver chromate (Ag2CrO4), silver sulfide (Ag2S), silver citrate (C6H5Ag3O7), a mixture of two or more of the above compounds, or a mixture containing at least one of the above compounds.

[0066] For example, a Cu-containing precursor can be added to the liquid or can be contained in the liquid, and the Cu-containing precursor is preferably selected from the following list: bis(2,4-pentanedionato)copper(II) (C 10 H14 CuO4), copper(II)-2-ethylhexanoate (C 16 H 30 CuO2), copper glycine, tetraamine copper sulfate monohydrate, copper(II) acetate hydrate, copper(II) acetate anhydrous, copper(II) bromide, copper(II) carbonate, copper(II) chloride, copper(II) chloride dihydrate, copper(II) chloride anhydrous, copper(II) chloride solution, copper(II) citrate hemitrihydrate, copper(II) formate tetrahydrate, copper(II) gluconate, copper(II) nitrate trihydrate, copper(II) nitrate solution, copper(II) oxalate hemihydrate, copper(II) phosphate, copper(II) sulfate monohydrate, copper(II) sulfate pentahydrate, copper(II) sulfate anhydrous, copper(I) bromide, copper(I) chloride, copper(I iodide), copper(I) oxide, a mixture of two or more of the above compounds, or a mixture containing at least one of the above compounds.

[0067] For example, a Zn-containing precursor can be added to the liquid or can be contained in the liquid, the Zn-containing precursor preferably being selected from the following list: zinc acetate dihydrate, zinc acetate anhydrous, zinc ascorbate, zinc aspartate, zinc bromide anhydrous, zinc bromide solution, zinc carbonate, zinc chloride anhydrous, zinc citrate dihydrate, zinc citrate trihydrate, zinc formate anhydrous, zinc gluconate, zinc glycinate, zinc lactate dihydrate, zinc nitrate hexahydrate, zinc picolinate, zinc sulfate monohydrate, zinc sulfate heptahydrate, a mixture of two or more of the above compounds, or a mixture containing at least one of the above compounds.

[0068] For example, a Ni-containing precursor can be added to the liquid or can be contained in the liquid, the Ni-containing precursor preferably being selected from the following list: ammonium nickel(II) sulfate hexahydrate, nickel(II) acetate tetrahydrate, nickel(II) bromide anhydrous, nickel(II) bromide hydrate, nickel(II) bromide solution, nickel(II) carbonate, nickel(II) chloride hexahydrate, nickel(II) chloride anhydrous, nickel(II) chloride solution, nickel(II) citrate hydrate, nickel(II) formate dihydrate, nickel(II) gluconate, nickel(II) glycinate, nickel(II) lactate tetrahydrate, nickel(II) nitrate hexahydrate, nickel(II) nitrate solution, nickel sulfamate solution, nickel sulfate hexahydrate, nickel sulfate solution, a mixture of two or more of the above compounds, or a mixture containing at least one of the above compounds.

[0069] For example, a Sn-containing precursor can be added to the liquid or contained in the liquid, and the Sn-containing precursor is preferably selected from the following list: tin(IV) chloride, tin(II) bromide, tin(II) chloride, tin(II) fluoride, tin(II) iodide, tin(II) oxalate, tin(II) pyrophosphate, tin(II) selenide, tin(II) sulfate, tin(II) sulfide, tin(II) telluride, tin(IV) bromide, tin(IV) fluoride, tin(IV) iodide, tin(IV) sulfate, tin(IV) sulfate dihydrate, tin(IV) sulfide, a mixture of two or more of the above compounds, or a mixture containing at least one of the above compounds.

[0070] For example, an Au-containing precursor can be added to the liquid or contained in the liquid, and the Au-containing precursor is preferably selected from the following list: gold(III) chloride, gold(I) chloride, gold(III) chloride trihydrate, gold(V) fluoride, gold(I) acetylate, gold(I) azide, gold(I) bromide, gold(I) cyanide, gold(I) iodide, gold(I) oxide, gold(I) sulfide, gold(I) thiocyanate, gold(III) bromide, gold(III) chloride, gold(III) fluoride, gold(III) iodide, gold(III) selenite, gold(III) sulfide, a mixture of two or more of the above compounds, or a mixture containing at least one of the above compounds.

[0071] In particular, the liquid is a solvent for the salt. In particular, the liquid can be selected from the following list of liquids: water, alcohols such as ethanol, methanol or isopropanol, ketones such as acetone, acids such as organic or inorganic acids, dimethyl sulfoxide, amino solvents such as pyridine, propionitrile or ammonia, mixtures of two or more of the above solvents, and mixtures containing at least one of the above solvents. Preferably, a liquid in which the selected precursor has good solubility can be selected as the solvent.

[0072] The liquid can be heated, for example to a temperature above 30° C., preferably above 50° C., to increase the solubility of the precursors in the liquid.

[0073] Further additives can be added to the liquid, for example, to create a buffer solution that stabilizes the pH value. When a salt is used as a precursor, for example, a weak acid corresponding to the salt can be added to the liquid to create a buffer solution such as carbonic acid when a metal carbonate, for example, tin carbonate, is used as a precursor, or citric acid when a metal citrate, for example, copper(II) citrate, is used as a precursor.

[0074] Further features and advantages of the method and apparatus will become apparent from the following description of exemplary embodiments, which proceeds with reference to the accompanying drawings, in which: FIG. [Brief explanation of the drawings]

[0075] [Figure 1] FIG. 1 is a diagram showing a plasma nozzle for generating an atmospheric plasma jet. [Figure 2] FIG. 1 illustrates a first exemplary embodiment of a method for reducing a workpiece. [Figure 3] FIG. 1 illustrates a second exemplary embodiment of a method for reducing a workpiece. [Figure 4] FIG. 10 illustrates a third exemplary embodiment of a method for reducing a workpiece. [Figure 5] FIG. 10 illustrates a fourth exemplary embodiment of a method for reducing a workpiece. [Figure 6] FIG. 1 shows an exemplary embodiment of an apparatus for reducing and / or coating and / or cleaning a strip-shaped workpiece, and another exemplary embodiment of a method for reducing and / or coating and / or cleaning using the apparatus. [Figure 7] 1 illustrates an exemplary embodiment of a method for coating and optionally cleaning a work piece. [Figure 8] FIG. 8 shows a photograph of a workpiece coated using the method according to FIG. 7. [Figure 9] FIG. 8 shows a photograph of another workpiece coated using the method according to FIG. 7.

[0076] Before describing exemplary embodiments of the method and apparatus, the structure and operation of a suitable plasma source, shown in FIG. 1, will be described.

[0077] FIG. 1 shows a plasma source in the form of a plasma nozzle 2 which generates an ambient plasma jet 26 .

[0078] The plasma nozzle 2 has a metal nozzle tube 4 that tapers conically to a nozzle orifice 6. At the end opposite the nozzle orifice 6, the nozzle tube 4 has a swirl device 8 with an inlet 10 for a gas flow, in particular a working gas, such as nitrogen, air or forming gas.

[0079] The intermediate wall 12 of the swirl device 8 has a ring hole 14 that is set at a predetermined angle in the circumferential direction of the swirling gas flow. Therefore, the gas flows in the downstream conically tapered section of the nozzle tube in the form of a vortex 16, the center of which extends along the longitudinal axis of the nozzle tube. An electrode 18 is centrally located below the intermediate wall 12 and protrudes coaxially into the nozzle tube in the direction of the tapered section. The electrode 18 is electrically connected to the intermediate wall 12 and other parts of the swirl device 8. The swirl device 8 is electrically insulated from the nozzle tube 4 by a ceramic tube 20. A high-frequency high voltage generated by a transformer 22 is applied to the electrode 18 via the swirl device 8. A working gas flow 23 is supplied to the inlet 10 via a conduit (not shown). The nozzle tube 4 is grounded. The applied voltage generates a high-frequency discharge in the form of an arc 24 between the electrode 18 and the nozzle tube 4. Therefore, the electrode 18 connected to the transformer and the grounded nozzle tube 4 serve as discharge means 25, which is configured to generate a high-frequency, high-voltage discharge in the form of an arc 24, i.e., an arc-like discharge, in the gas flow 23.

[0080] In this specification, the terms "arc," "arc discharge," or "arc-like discharge" are used as a phenomenological description of a discharge when the discharge occurs in the form of an arc. The term "arc" is also used elsewhere when the discharge is in the form of a DC discharge having a substantially constant voltage value. However, in this invention, we are dealing with a high frequency discharge in the form of an arc, i.e., a high frequency arc-like discharge.

[0081] Note that due to the swirling flow of the working gas, the arc here is channeled in a vortex core on the axis of the nozzle tube 4 and only branches towards the wall of the nozzle tube 4 in the region of the nozzle opening 6. The working gas, rotating at a high flow rate in the region of the vortex core and thus in the immediate vicinity of the arc 24, comes into close contact with the arc and is therefore partially converted into a plasma state, whereby an atmospheric plasma jet 26 is emitted from the plasma nozzle 2 through the nozzle opening 6.

[0082] FIG. 2 shows a schematic diagram of a first exemplary embodiment of a method for reducing a workpiece 202 .

[0083] In the method 200, a liquid volume 212 of liquid 210 is provided in a container 218 provided for this purpose, and the workpiece 202 to be treated is placed, in particular submerged, in the liquid 210 so that the liquid 210 acts on the surface 204 of the workpiece 202 to be reduced, in particular covered by the liquid 210 with a cover height of, for example, 5 mm. Preferably, the surface 204 of the workpiece 202 to be treated is oriented towards the liquid surface 213 of the liquid volume 212. The liquid 210 can be, for example, a hydrogen-containing liquid, preferably a water-containing liquid, in particular water, or an organic liquid.

[0084] 1, an atmospheric plasma jet 230 is generated by a plasma nozzle 228, which may be configured, for example, as the plasma nozzle 2 shown in Figure 1, by a high frequency, high voltage discharge in a working gas emerging from a nozzle opening 232 of the plasma nozzle 228. The working gas may be a reducing working gas, in particular a forming gas, or a non-reducing working gas, for example air.

[0085] The plasma jet 230 is directed toward the surface 204 of the workpiece 202 to be reduced, which in the exemplary embodiment is submerged. In the exemplary embodiment, the working gas flow of the plasma nozzle 228 is adjusted so that the atmospheric plasma jet 230 locally displaces the liquid 210 substantially completely between the plasma nozzle 228 and the surface 204, such that no liquid remains in the processing region 214 on the surface 204 of the workpiece 202, or only a thin liquid film is present in the processing region 214, thereby causing the plasma jet 230 to impinge substantially directly on the surface 204 in the processing region 214.

[0086] The impact of the atmospheric plasma jet 230 on the surface 204 of the workpiece 202 subjects the surface to a reduction process in which any oxides present there, possibly a continuous oxide layer (schematically shown in the figure by a thick black line on the workpiece surface), are effectively reduced, so that after the impact of the atmospheric plasma jet 230, the surface 204 of the treatment region 214 has a significantly lower oxide content or is completely oxide-free (schematically shown in the figure by a hatched area on the workpiece surface).

[0087] The plasma nozzle 228 and workpiece 202 are moved relative to one another so that the workpiece surface 204 is reduced in predetermined sections or completely, leaving a reduced workpiece surface. In Figure 2, for example, the plasma nozzle 228 is moved relative to the workpiece 202 using a traverse device 229.

[0088] The impact of the ambient plasma jet 230 introduces thermal energy locally into the workpiece 202, particularly onto the surface 204 of the workpiece 202 in the treatment region 214. This heat can be effectively dissipated by contact with the liquid 210, particularly when the liquid 210 flows back to the previous impact region and re-covers the previous treatment region upon shutting off or moving the plasma nozzle. In this way, the liquid 210 acts on the treatment region 214 immediately after the reduction treatment, thereby providing efficient cooling. Furthermore, the return flow of the liquid reduces, particularly prevents, contact with any oxygen-containing atmosphere, thereby directly suppressing reoxidation, particularly until the workpiece has sufficiently cooled.

[0089] In particular, the distance from the plasma nozzle 228 to the surface 204 of the workpiece 202 can be adjusted to sufficiently displace the liquid 210 and cause direct impingement of the plasma jet 230 on the workpiece surface 204. Additionally or alternatively, the flow or pressure of the working gas introduced into the plasma nozzle 228 can be adjusted. Furthermore, the volume 212 of liquid present between the surface 204 of the workpiece 202 and the plasma nozzle 228 can be adjusted via the filling amount of the container 218 with the liquid 210 and / or via the positioning of the workpiece 202.

[0090] Figure 3 shows a schematic diagram of another exemplary embodiment of a method for reduction-treating a workpiece 302. The method 300 shown in Figure 3 is similar to the method 200 shown in Figure 2. Corresponding components are labeled with the same reference numerals and are referenced in conjunction with the description of Figure 2.

[0091] Method 300 differs from method 200 in that multiple plasma nozzles 328 are provided to generate respective atmospheric plasma jets 330, thereby allowing a larger area of ​​workpiece surface 304 of workpiece 302 to be simultaneously subjected to reduction treatment in each treatment zone 314. Each of plasma nozzles 328 may have a structure and mode of operation similar to plasma nozzle 2 of FIG.

[0092] The plasma nozzle 328 and workpiece 302 are moved relative to one another so that the surface 304 of the workpiece 302 can be reduced in predetermined sections or completely, leaving a reduced workpiece surface. In Figure 3, for example, the vessel 318 containing the workpiece is moved relative to the plasma nozzle 328 using a traverse device 329.

[0093] Figure 4 shows a schematic diagram of another exemplary embodiment of a method for reduction-treating a workpiece 202. The method 400 shown in Figure 4 is similar to the method 200 shown in Figure 2. Corresponding components are labeled with the same reference numerals and are referenced in conjunction with the description of Figure 2.

[0094] Method 400 differs from method 200 in that the distance from plasma nozzle 228 to workpiece 202 and / or the flow or pressure of working gas supplied to plasma nozzle 228 are set so that liquid 210 between plasma nozzle 228 and surface 204 of workpiece 202 is displaced in processing region 214, leaving a macroscopic liquid film 416 only on workpiece surface 204 in processing region 214. Thus, plasma jet 230 impinges on liquid 210 specifically in liquid film 416.

[0095] In this manner, the liquid 210 in the liquid film 416 is excited or activated by the atmospheric plasma jet 230. It has been found that the reduction effect of the activated liquid 210 effectively reduces oxides on the surface 204 of the workpiece 202 in the processing region 214. Therefore, the indirect action on the surface 204 of the workpiece 202 by the liquid film 416 remaining between the surface 204 of the workpiece 202 and the atmospheric plasma jet 230 can also be used to perform reduction processing of the workpiece.

[0096] The fact that the surface 204 of the workpiece 202 is covered by the liquid film 416 during the reduction process means that the thermal energy introduced by the plasma jet 230 is absorbed and dissipated by the liquid 210, thereby preventing significant heating of the workpiece 202. Also, contact with an oxygen-containing atmosphere is prevented, which effectively suppresses reoxidation in particular overall.

[0097] Furthermore, tests have shown that the reducing effect of the plasma jet 230 impinging on the liquid 210 is not locally limited to the immediate treatment area 214 where the plasma jet 230 acts on the liquid 210. Rather, the reducing effect of the liquid 210 impinging on the plasma jet 230 was observed at distances from the plasma jet 230, likely due to the dispersion of reducing species in the liquid 210 generated by the plasma jet 230.

[0098] Therefore, instead of directly impinging the liquid 210 with the plasma jet 230 in the region of the surface 204 of the workpiece 202, the liquid 210 can also be impinged with the plasma jet 230 at a location away from the surface 204 of the workpiece 202, as shown schematically in FIG. 4 by the location of the plasma nozzle 228' indicated by the dashed line. In this embodiment, the liquid 210 is impinged with the plasma jet 230' emitted from the plasma nozzle 228' at a predetermined distance from the workpiece surface 204. Tests have shown that such impact on the liquid 210 produces a reducing effect, thereby reducing the workpiece surface 204. In this embodiment, it is also possible to simultaneously subject multiple workpieces 202 disposed in the liquid volume 212 to a reducing treatment, for example, to remove oxides from each workpiece surface 204.

[0099] FIG. 5 shows a schematic diagram of another embodiment of a method for reducing a workpiece 502 .

[0100] In the method 500, a workpiece 502 having a surface 504 to be reduced is positioned such that the surface 504 of the workpiece 502 is accessible.

[0101] An ambient plasma jet 530 is generated by a plasma nozzle 528, which may be configured, for example, as the plasma nozzle 2 shown in Figure 1, and directed toward the workpiece surface 504, causing the plasma jet 530 to impinge on the treatment region 514 of the workpiece surface 504. To generate the plasma jet 530, the plasma nozzle 528 is supplied with a hydrogen-containing working gas, for example, forming gas. The plasma jet 530 therefore has a reducing effect, thereby reducing oxides present on the workpiece surface 504.

[0102] During and / or after the impact of the atmospheric plasma jet 530, the workpiece surface 504 is impacted with the liquid 510, particularly in a state atomized by the spraying device 516. This effectively dissipates the thermal energy introduced by the atmospheric plasma jet 530 from the workpiece surface 504, thereby reducing the heating of the workpiece surface 504 and making it less susceptible to re-oxidation. Furthermore, the reduced workpiece surface 504 is covered by the liquid 510, which reduces contact with the oxygen-containing atmosphere and thus further inhibits re-oxidation.

[0103] The flow rate of the liquid 510 is preferably set at the spray device 516 so that the liquid 510 fully impinges on the treatment area 514, thereby achieving sufficient cooling of the workpiece 502 at the workpiece surface 504.

[0104] The liquid 510 may be, for example, water. It has been found that in this embodiment, the use of a hydrogen-containing working gas for the plasma nozzle 528 is not necessary, as the hydrogen contained in the water in combination with the plasma jet 530 already provides a reducing effect, and an inert gas or air can be used instead.

[0105] Alternatively, the liquid 510 may be an organic liquid, for example, if the workpiece surface 504 is sensitive to water or if rapid drying is required after the reduction treatment.

[0106] The plasma nozzle 528 and workpiece 502 can be moved relative to one another to reduce or completely reduce the workpiece surface 504 in predetermined sections. As the plasma nozzle 528 is moved, the spray device 516 is preferably also moved and / or adjusted in orientation to maintain impingement of the liquid 510 on the treatment region 514.

[0107] In another embodiment not shown, the method 500 can be performed using multiple plasma sources 528 and / or multiple atomizing devices 516, similar to the method 300 shown in FIG.

[0108] FIG. 6 shows an exemplary embodiment of an apparatus for reducing and / or coating and / or cleaning strip-shaped workpieces.

[0109] The apparatus 601 comprises an immersion bath device 617 with an immersion tank 618 for holding a liquid volume 612 of liquid 610, thereby forming an immersion bath 620. The immersion tank 618 is open at the top, so that the strip-shaped workpiece 602 can be introduced into and removed from the immersion bath 620, for example to allow in-line integration into a continuous production process.

[0110] The immersion bath apparatus 617 further comprises guide means 622 arranged and configured to guide the strip-shaped workpiece 602 through the immersion bath 620. Preferably, the guide means 622 are arranged and configured in such a way that the strip-shaped workpiece 602 can be guided during operation at least in sections, in particular at least in the treatment area 614, completely below the surface 613 of the liquid volume 612, so that the workpiece surface 604 of the strip-shaped workpiece 602 to be reduced and / or coated and / or cleaned is covered by the liquid 610 in the treatment area 614. In the present example, the guide means 622 are designed as guide rollers.

[0111] The apparatus 601 further comprises a plasma source 628 in the form of a plasma nozzle for generating an atmospheric plasma jet 630, which may be configured, for example, as the plasma nozzle 2 of Figure 1. The plasma nozzle 628 is positioned and configured to direct, during operation, an atmospheric plasma jet issuing from the plasma nozzle 628 towards a workpiece surface 604 in the treatment region 614 of a strip-shaped workpiece 602 that is guided through the immersion bath 620 by a guide means 622. The distance from the plasma nozzle 628 to the workpiece surface 604 of the strip-shaped workpiece 602 (traverse device 629) and / or the working gas flow or working gas pressure of the plasma nozzle 628 can be adapted so that the liquid 610 in the treatment area is substantially completely (as shown in Figure 6) or partially (similar to Figure 4 or Figure 7), and the workpiece surface 604 can be subjected to reduction treatment and / or coating and / or cleaning by direct impingement of the plasma jet 630 on the workpiece surface 604 and / or by impingement of the liquid 610 on an area of ​​the workpiece surface 604.

[0112] In an alternative embodiment, the plasma nozzle 628 may be positioned so that the plasma jet 630 is directed toward the liquid 610 at a location away from the strip-shaped workpiece 602 (similar to the plasma nozzle 228' shown in dashed lines in FIG. 4).

[0113] Furthermore, the apparatus 601 may have a distributing means 624 for distributing the strip-shaped workpiece 602 having a workpiece surface 604 to be reduced and / or coated and / or cleaned and / or a receiving means 626 for receiving the strip-shaped workpiece 602 after the reduction treatment. In this example, the distributing means 624 and the receiving means 626 are preferably designed as driven rollers so that the strip-shaped workpiece 602 is unwound from the distributing means 624 for distribution and fed into the receiving means 626 for reception.

[0114] In the case of driven dispensing means 624 and receiving means 626, these are also conveying means for conveying the strip-shaped workpiece 602 through the immersion bath 620. The conveying means can also be formed by guide means 622 if they are driven.

[0115] The apparatus 601 can be used to carry out a method 600 for reducing a strip-shaped workpiece 602 by guiding the workpiece 602 through an immersion bath 620 by a conveying means and impinging a plasma jet 630 on the surface 604 to be reduced and / or on the liquid 610. In this way, an oxide layer can be reduced from the surface of the strip-shaped workpiece 602. In Figure 6, the workpiece with the oxide layer is shown schematically as a black strip and the reduced workpiece as a hatched strip.

[0116] Additionally or alternatively, the apparatus 601 can be used to carry out a method 600' for coating a strip-shaped workpiece 602 by guiding the workpiece 602 through an immersion bath 620 by a conveying means and impinging a plasma jet 630 on the surface 604 to be coated and / or on the liquid 610. A metal salt is dissolved in the coating liquid 610. Reactive species generated in the liquid 610 by the plasma jet 630 reduce metal ions of the metal salt dissociated in the liquid to elemental metal, which is then deposited as a metal layer on the surface of the strip-shaped workpiece 602. In this way, the surface of the strip-shaped workpiece 602 can be coated with a metal layer.

[0117] The apparatus 601 can additionally or alternatively be used to carry out a method 600'' for cleaning a strip-shaped workpiece 602 by guiding the workpiece 602 through an immersion bath 620 by a conveying means and impinging a plasma jet 630 on the surface 604 to be cleaned and / or on the liquid 610. Reactive species generated in the liquid 610 by the plasma jet 630 can interact with impurities on the surface of the strip-shaped workpiece 602 to be cleaned and chemically decompose them and / or separate them from the surface. In this way, the surface of the strip-shaped workpiece 602 can be cleaned.

[0118] FIG. 7 shows a schematic diagram of a first exemplary embodiment of a method for coating and optionally cleaning a workpiece 702 .

[0119] In the method 700, a liquid volume 712 of liquid 710 is provided in a container 718 provided for this purpose, and the workpiece 702 to be treated is placed, in particular submerged, in the liquid 710 so that the liquid 710 acts on the surface 704 of the workpiece 702 to be coated, in particular so that it is covered with the liquid 710 to a covering height of, for example, 5 mm. Preferably, the surface 704 of the workpiece 702 to be coated is oriented towards a liquid surface 713 of the liquid volume 712.

[0120] Liquid 710 contains a metal salt, such as an Ag, Cu, Zn, Ni, Sn, or Au salt, dissolved therein as a precursor. The liquid is a solvent for the metal salt. Depending on the metal salt used, liquid 710 can be, for example, water; an alcohol, such as ethanol, methanol, or isopropanol; a ketone, such as acetone; an acid, such as an organic or inorganic acid; dimethyl sulfoxide; an amino-based solvent, such as pyridine, propionitrile, or ammonia; or a mixture of two or more of the above solvents. To increase the solubility of the metal salt in liquid 710, liquid 710 can also be heated, for example, to a temperature above 30°C, preferably above 50°C. Furthermore, other substances, such as a weak acid corresponding to the metal salt, can be added to liquid 710 to form a buffer solution to stabilize the pH.

[0121] 1, an atmospheric plasma jet 730 is generated by a plasma nozzle 728, which may be configured similarly to the plasma nozzle 2 shown in Figure 1, by a radio frequency, high voltage discharge in a working gas that is emitted from a nozzle opening 732 of the plasma nozzle 728. The working gas may be a reducing working gas, in particular a forming gas, or a non-reducing working gas, for example, air.

[0122] The plasma jet 730 is directed toward the surface 704 of the workpiece 702 to be coated, which is submerged in this exemplary embodiment. In this exemplary embodiment, the flow or pressure of the working gas supplying the plasma nozzle 728 is set so that the liquid 710 between the plasma nozzle 728 and the surface 704 of the workpiece 702 in the processing region 714 is displaced only to the extent that a macroscopic liquid film 716 still remains on the workpiece surface 704 in the processing region 714. Thus, the plasma jet 730 impinges on the liquid 710 specifically in the liquid film 716. Alternatively, the flow or pressure of the working gas supplying the plasma nozzle 728 can be set so that only a microscopic liquid film remains on the workpiece surface 704 in the processing region 714.

[0123] By impinging the plasma jet on the liquid 710 or the liquid film 716, a redox reaction occurs on the metal cations of the salts dissociated in the liquid. 2+ ) is reduced to elemental metal (e.g., Cu) in the region of the workpiece surface 704, thereby forming a metal layer 740 on the workpiece surface 704. For example, the redox reaction may be Me x+ (aq)+xe - →Me 0 (s) where Me x+ (aq) represents x times the amount of ionized metal ions dissolved in water, and xe - indicates x electrons, and Me 0 (s) represents the reduced metal as a solid. Electrons are especially important in reactions such as O2+2H2O+4e - →4OH - According to the above, OH is generated by impinging a plasma jet 730 on a liquid 710. - can be supplied by

[0124] This means that the redox reaction, e.g. Me x+ (aq)+4OH - →Me 0 (s) + O2 + 2H2O This means that it can proceed as follows.

[0125] The plasma nozzle 728 and workpiece 702 are moved relative to one another so that the workpiece surface 704 can be coated in predetermined sections or completely, leaving a reduced workpiece surface. In Figure 7, for example, the plasma nozzle 728 is moved relative to the workpiece 702 using a traverse device 729.

[0126] Because the surface 704 of the workpiece 702 is covered by the liquid film 716 during coating, the thermal energy introduced by the plasma jet 730 can be absorbed and dissipated by the liquid 710, thereby preventing significant heating of the workpiece 702. The liquid film 716 also prevents contact with the oxygen-containing atmosphere, thereby inhibiting oxidation of the elemental metal formed during the redox reaction or the formation of oxides on the coated surface, especially until the workpiece has cooled sufficiently.

[0127] Furthermore, tests have shown that the coating produced by the redox reaction on the precursors as the plasma jet 730 impinges on the liquid 710 is not locally limited to the immediate treatment area 714 where the plasma jet 730 acts on the liquid 710. Rather, the redox reaction can also be achieved on precursors at a predetermined distance from the plasma jet 730, resulting in a detectable coating on the workpiece surface 704, likely due to reduced species, e.g., OH, generated in the liquid 710 by the plasma jet 730. - is dispersed in the liquid 710, which allows the metal ions to be reduced to elemental metal at a predetermined distance from the plasma jet 730.

[0128] Thus, instead of impinging the liquid 710 directly with the plasma jet 730 in the region of the surface 704 of the workpiece 702, the plasma jet 730 can also be impinged at a location away from the surface 704 of the workpiece 702, as shown schematically in FIG. 7 by the location of the plasma nozzle 728' shown in dashed lines. In this embodiment, the liquid 710 is impinged by the plasma jet 730' emitted from the plasma nozzle 728' at a predetermined distance from the workpiece surface 704. Experiments have shown that such impingement on the liquid 710 produces a reduction effect, whereby metal ions are reduced to elemental metal in the region of the workpiece surface 704, which then deposits on the workpiece surface 704. This embodiment also allows, for example, simultaneous coating of multiple workpieces 702 disposed in the liquid volume 712.

[0129] Species generated in the liquid 710 by the plasma jet 730, such as OH - can also interact with any impurities, e.g., organic impurities, on the workpiece surface 704 and, in particular, chemically transform them and / or dissolve them from the workpiece surface 704. In this way, cleaning of the workpiece surface 704 can also be achieved, in particular before coating.

[0130] Basically, the coating of the workpiece can also be carried out by adding, in particular introducing or dissolving a precursor, in particular a salt, for example a metal salt, into a liquid according to one of the embodiments of the method described with reference to Figures 2 to 5. Furthermore, the exemplary embodiments of the method shown in Figures 2 to 5 can also be used to clean the workpiece surface.

[0131] An experiment was conducted to test the coating method shown in FIG.

[0132] <Experiment 1> Plastic acrylonitrile butadiene styrene (ABS) cards were coated with silver. For this purpose, an uncoated card was placed in a liquid volume 712 (see Figure 7) so that the upper side of the card to be coated was covered with a macroscopic liquid film of a few millimeters. In experiment 1, the liquid 710 was water (H2O) in which the metal salt silver nitrate (AgNO3) was dissolved as precursor at a concentration of 5 g AgNO3 per 100 mL H2O.

[0133] The plasma nozzle 728 was operated using nitrogen (N) as the working gas, with the plasma jet directed at the liquid film 716 above the surface of the card to be coated and moving at a relative speed of 0.5 m / min relative to the surface of the card. To achieve greater coating thickness, the surface of the card was traversed by the plasma jet three times.

[0134] After the method was completed, the surface of the card had a silver coating. The coating was analyzed by LIBS (Laser-Induced Breakdown Spectroscopy) using a microscope EA300 type LIBS device commercially available from Keyence Deutschland GmbH. The LIBS device was used to examine the element-specific composition of the coating at several points (9 points in a 3x3 grid). It was determined that the coating was a silver layer. Furthermore, the ohmic resistance of the coating was measured using a multimeter, and it was determined that the coating was conductive, i.e., a conductive silver coating.

[0135] A photograph of a silver coated card is shown in Figure 8. The coating is visible in the form of lettering (arrow 802) and a surrounding frame (arrow 804). The uncoated area between the lettering and the frame (arrow 806) was created by a mask that was adhered to the card before the coating process and removed again after the coating process.

[0136] <Experiment 2> Another card made of plastic acrylonitrile butadiene styrene (ABS) was coated with copper. For this purpose, an uncoated card was placed in a liquid volume 712 (see Figure 7) so that the upper side of the card to be coated was covered with a macroscopic liquid film of several millimeters. In experiment 2, the liquid 710 was ethanol, in which silver salt was dissolved as precursor, with a concentration of 5 g AgNO3 per 100 mL of solution.

[0137] The plasma nozzle 728 was operated using nitrogen (N2) as the working gas, with the plasma jet directed towards the liquid film 716 above the surface of the card to be coated and moving at a relative speed of 0.5 m / min relative to the surface of the card.

[0138] At the end of the method, the surface of the card had a thin reddish-yellowish coating. The coating was examined by LIBS (Laser-Induced Breakdown Spectroscopy) using a microscope EA300 type LIBS device commercially available from Keyence Deutschland GmbH. The LIBS device was used to examine the element-specific composition of the coating at several points (9 points in a 3x3 grid). It was determined that the coating was a copper layer. Furthermore, the ohmic resistance of the coating was measured using a multimeter, and it was determined that the coating was conductive, i.e., a thin conductive copper layer.

[0139] A photograph of a copper coated card is shown in Figure 9. The coating (arrow 902) shows a barely visible stripe structure corresponding to the path of the plasma jet across the surface of the card, which disappears as the coating thickness increases, for example by passing the plasma jet over the surface several times. [Explanation of symbols]

[0140] 2, 228, 228', 328, 528, 628, 728, 728' Plasma nozzle 4 nozzle pipe 6, 232, 732 nozzle opening 8 Swirl Device 10 Entrance 12 Intermediate Wall 14 holes 16. Vortex 18 electrodes 20 Ceramic tube 22 Transformer 23 Gas flow 24 Electric Arc 25 Discharging means 26, 230, 230', 330, 530, 630, 730, 730' Plasma Jet 200, 300, 400, 500, 600, 600', 600'', 700 ways 202, 302, 502, 602, 702 Workpiece 204, 304, 504, 604, 704 Workpiece surface 210, 510, 610, 710 liquid 212, 612, 712 Liquid volume 213, 613, 713 liquid surface 214, 314, 514, 614, 714 processing areas 218, 718 container 229, 329, 629, 729 Traverse device 416, 716 liquid film 516 Spraying equipment 601 Equipment 617 Immersion bath equipment 618 Soaking tank 620 Immersion bath 622 Guide means 624 Distribution means 626 Receptor 740 Metal layer 802, 804, 902 coating area 806 Uncoated Area

Claims

1. A method (200, 300, 400, 500, 600, 600′, 600″, 700) for treating, in particular cleaning, reducing and / or coating, a workpiece (202, 302, 502, 602, 702), comprising: - atmospheric plasma jets (26, 230, 230', 330, 530, 630, 730, 730') are generated, the workpiece to be treated (202, 302, 502, 602, 702), in particular the workpiece to be cleaned, reduced and / or coated, is brought into contact with a liquid (210, 510, 610, 710), an atmospheric plasma jet (26, 230, 230′, 330, 530, 630, 730, 730′) is impinged on the surface (204, 304, 504, 604, 704) of the workpiece (202, 302, 502, 602, 702) to be treated, in particular on the workpiece surface (204, 304, 504, 604, 704) to be cleaned, reduced and / or coated, and / or on the liquid (210, 510, 610, 710); Method (200, 300, 400, 500, 600, 600', 600'', 700).

2. 2. The method of claim 1, wherein the workpiece (202, 302, 502, 602, 702) is brought into contact with the liquid (210, 510, 610, 710) by placing the workpiece (202, 302, 502, 602, 702) in a liquid volume (212, 612, 712), in particular by submerging the workpiece (202, 302, 502, 602, 702), before impinging the plasma jet (26, 230, 230', 330, 530, 630, 730, 730') on the surface (204, 304, 504, 604, 704) or the liquid (210, 510, 610, 710).

3. 3. The method of claim 2, wherein the impingement of the atmospheric plasma jet (26, 230, 230', 330, 530, 630, 730, 730') is performed such that a portion of the liquid volume (212, 612, 712) located above the workpiece (202, 302, 502, 602, 702) is locally displaced by the atmospheric plasma jet (26, 230, 230', 330, 530, 630, 730, 730').

4. 2. The method of claim 1, wherein the workpiece (202, 302, 502, 602, 702) is brought into contact with the liquid (210, 510, 610, 710) by impinging the liquid (210, 510, 610, 710) on the workpiece (202, 302, 502, 602, 702) during and / or after the impact of the plasma jet (26, 230, 230', 330, 530, 630, 730, 730') on the workpiece (202, 302, 502, 602, 702), in particular by being sprayed.

5. 5. The method according to any one of claims 1 to 4, wherein the atmospheric plasma jet (26, 230, 230', 330, 530, 630, 730, 730') is generated using a reducing working gas, in particular forming gas.

6. 6. The method according to claim 1, wherein a hydrogen-containing liquid, preferably a water-containing liquid, is used as the liquid (210, 510, 610, 710).

7. 6. The method according to claim 1, wherein an organic liquid (210, 510, 610, 710) is used as the liquid.

8. 8. The method according to claim 1, wherein the atmospheric plasma jet (26, 230, 230', 330, 530, 630, 730, 730') is generated using a plasma nozzle (2, 228, 228', 328, 528, 628, 728, 728'), the plasma nozzle (2, 228, 228', 328, 528, 628, 728, 728') having a nozzle opening (6, 232, 732) through which the plasma jet (26, 230, 230', 330, 530, 630, 730, 730') is emitted during operation.

9. 9. The method of claim 8, wherein the plasma nozzle (2, 228, 228', 328, 528, 628, 728, 728') and the workpiece (202, 302, 502, 602, 702) are moved relative to each other during impact of the plasma jet (26, 230, 230', 330, 530, 630, 730, 730').

10. 10. The method according to any one of claims 1 to 9, wherein the atmospheric plasma jet (26, 230, 230', 330, 530, 630, 730, 730') is generated by an electrical discharge in a working gas.

11. 11. The method according to any one of claims 1 to 10, wherein the atmospheric plasma jet (26, 230, 230', 330, 530, 630, 730, 730') is generated by an arc-like discharge in a working gas, which is generated by applying a high-frequency high voltage between electrodes.

12. 12. The method according to any one of claims 1 to 11, wherein a precursor, in particular a precursor containing a metal, is or has been added to the liquid (210, 510, 610, 710), said precursor preferably being a salt.

13. 13. The method according to any one of claims 1 to 12, wherein the workpiece is a strip-shaped workpiece (602), in particular a metal strip.

14. An apparatus (601) for treating, in particular cleaning, reducing and / or coating, a workpiece (602), in particular in the form of a strip, in particular a metal strip, for carrying out a method (600, 600', 600'') in particular according to claim 13, comprising: an immersion bath device (617) adapted to guide a strip-shaped workpiece through the immersion bath (620); a plasma source (2, 628) for generating an atmospheric plasma jet (26, 630); Equipped with the plasma source (2, 628) is arranged and configured to impinge, during operation, the atmospheric plasma jet (26, 630) on the immersion bath (620) of the immersion bath device (617) or on a strip-shaped workpiece (602) guided through the immersion bath (620); Device (601).

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