WO2012001132A1

WO2012001132A1 - Tribologically loadable mixed noble metal/metal layers

Info

Publication number: WO2012001132A1
Application number: PCT/EP2011/061070
Authority: WO
Inventors: Stefan Koppe
Original assignee: Schauenburg Ruhrkunststoff Gmbh
Priority date: 2010-06-30
Filing date: 2011-06-30
Publication date: 2012-01-05
Also published as: EP2588644A1; EP2588644B1

Abstract

The invention relates to a method for producing a mixed noble metal/metal layer that has particularly advantageous tribological properties, having the following steps: preparing a bath for the electroless deposition of a metal layer, said bath additionally containing at least one type of noble metal ions; introducing a substrate into the bath; and applying an electric voltage.

Description

Tribologically resilient precious metal / metal layers

description

Field of the invention

The invention relates to a method for producing tribologically resilient noble metal / metal layers. These are layers with a thickness of up to 50 ym. The invention also relates to substrates with such a coating and their use.

State of the art

Noble metal-containing metal layers are well known in the art. In this case, these layers are typically at least one noble metal in the mixture or Le ^¬ Government with at least one uned- compared to the noble metal lerem metal. Such layers make it possible to improve the properties of the less noble metal layer. This improvement may be in corrosion resistance, hardness, conductivity or biocidal properties. At the same time, a lower precious metal content makes the production of the layers more cost-effective. The layers also partly retain the advantageous properties of the less noble metal layers.

The layers can be deposited either by galvanic or electroless methods. In the electroless process noble metal ions are usually added to the known baths for the electroless deposition of a metal. That I is significantly easier to reduce the noble metal, it will ge ^¬ jointly deposited with the metal as a mixture. However, it is difficult to obtain layers with a high content of noble metal, in particular tribologically loadable layers, with such methods.

In galvanic processes corresponding solutions of metal salts and noble metal salts are deposited under tension from a bath. However, it is with galvanic process due to shielding effects not possible cavities or surrounded by Holräume networks, such as occur for example at Filterele ^¬ elements to coat evenly and in particular, fine structures such. B. structure elements in the range of less than 200 ym, contour resolution.

Pure noble metal layers which are deposited electrolessly, are often soft and do not show sufficient Abriebfes ^¬ ACTION. Contour resolution or fidelity and depth dispersion are not sufficient for complete and unadulterated coverage of tissue or slit structures. Although hard metals (eg cobalt) can be electrodeposited to form a higher abrasion resistance. The layers are not free from pores and are soon infiltrated or detached.

The document DE 10 2006 020 988 A1 describes, for example, the production of noble metal-containing nickel layers.

The document GB 1 222 969 describes the galvanic deposition of a metal from a bath, which is also suitable for electroless deposition of the same metal.

It is not possible with most methods to achieve high levels of the precious metal in the layer and to obtain equal ^¬ term good tribological properties of the coatings. This applies in particular to screens and nets in which the tribological properties play a special role. This is particularly important in filter elements for filtering fluids. task

The object of the invention is to overcome the disadvantages of the prior art and to provide a method by which precious metal-containing metal layers can be obtained, which in particular have advantageous tribological properties. The method should allow to coat nets or screens. In particular, the layers must be produced without pores in order to prevent infiltration, especially when used in fluids.

solution

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

The object is achieved by a method for depositing a precious metal / metal layer on a substrate, the fol ^¬ constricting the steps of: a) providing a bath for electroless deposition of a metal layer, which additionally contains at least one kind of noble metal ions;

b) introducing a substrate into the bath;

c) applying an electrical voltage.

In the following, individual process ^steps will be described in more detail. The steps need not necessarily be carried out in the order given, and at schil ^¬-promoting method may also further unspecified steps exhibit .

A noble metal / metal layer is a layer in which the proportion of noble metal in wt .-% is higher than the proportion of metal. The reverse applies to a metal / noble metal layer.

First, a bath for the electroless deposition of a metal layer, which additionally contains at least one kind of precio ^¬ tallionen is provided. Such electroless plating baths are known to those skilled in the art. It is a bath, which consists of z. B. an aqueous solution of a salt of a metal, which is to be deposited on the substrate by reduction of the salt. The reduction takes place without current through a reducing agent. In this case usually begins a deposition only when certain conditions, usually selected from pH and / or temperature of the bath. Such electroless process are often autocatalytic syste ^¬ me. This means that the deposited metal layer catalyzes the further deposition of metal. The thickness of the abge ^¬ different layer can be over the duration of the deposition con- trolled.

The skilled person is familiar with many metal / reducing agent systems for electroless deposition. Examples of electroless abge ^¬ separated metals are nickel, copper, palladium, silver or gold. As a reducing agent aldehydes, z. For example, formaldehyde, formic acid, borohydride compounds, for example

Alkylaminborane, dimethyl, diethylaminoborane or sodium borohydride, furthermore hydroxylamine, hydrazine, hydroxycarboxylic acids, their salts or thiourea or derivatives thereof, phosphorus compounds, for example hypophosphites such as

Sodium hypophosphite, are used. It can also be a redu ^¬ ornamental forming gas such as hydrogen, are passed through the bath.

Examples of metal / reducing agent systems are ^copper / formaldehyde, gold / formaldehyde, palladium / hypophosphite, silver / hypophosphite, nickel / borohydrides and nickel / hypophosphite. The proportions of metal and reducing agent in the bath depend on the metal and reducing agent used. Thus, the proportion of metal between 0.01 and 20 g / 1 and the content of reducing agent between 5 and 50 g / 1.

The solvent of the bath is preferably water. However, it is also possible to add or add organic solvents if the solubility of the bath constituents in water is not sufficiently high. The organic solvents Kgs ^¬ NEN also be added proportionately. Suitable organic solvents are, in particular, lower alcohols. Preferably, only water is used as the solvent.

The metal salts used are usually the corresponding chlorides, sulfates, carbonates, acetates or nitrates. It is also possible to use mixtures of metal salts with different cations and / or anions.

The bath can also contain other additives. In ^¬ play oxocarboxylic acids or complexing agents, which prevent the decomposition of the bath.

The bath may also contain complexing agents for the ions of the metal salts to reduce the amount of free metal ions. Depending on the metal salt used, these may be carboxylic acids, amines, alkylamines, amino acids, phosphonates, cyanates, isocyanates, thiocyanates, ethers or thioethers. Examples of such compounds are citric acid,

Chelating ligands such as ethylenediaminetetraacetic acid, 1,3-diaminopropane, 1, 2-bis-β-aminopropylamino) ethane, 2-diethylaminoethylamine and diethylenetriamine or

Polyethylene glycols.

The bath additionally contains at least one type of noble metal ion. In this case, noble metal ions are ions of metals which, according to the series of voltages, have a greater reduction potential than the other metal salts for electroless deposition in the bath. The noble metal ions are preferably selected from the group comprising silver, gold, palladium, platinum, rhodium and copper. In the case of silver, in addition, the biocidal effect of silver-containing surfaces can be exploited.

The noble metals are preferably added as salts or solutions of their salts. Suitable salts are chlorides, sulfates, carbonates, acetates, nitrates, sulfonates, sulfites, alkyl sulfonates, thioalkane carboxylates, mercaptoalkanesulfonates, phosphates or phosphonates. The counterions can ^{vorzugswei ¬} se alkyl groups or aryl groups, which in turn may advantageously be partially fluorinated. The counterions are very particularly preferably trifluoromethanesulfonate, methanesulfonate and / or toluenesulfonate. They may be salts han ^¬ spindles and in which the noble metal ions with ligand or

Chelating ligands, such as ethylenediamine, polyethylene glycols or thioethanol derivatives, such as 2, 2-ethylene-di-thiodiethanol,

are complexed.

Examples of preferred salts of the noble metals are copper ^¬ sulfate, HAuCl _4, palladium sulfate, palladium nitrate, and

Palladium acetate, platinum chloride, rhodium chloride, silver nitrate and silver methanesulfonate.

The bath preferably contains a content of noble metal ions between 0.1 g / l and 3 g / l, preferably between 0.1 g / l and 2 g / l, particularly preferably between 0.1 g / l and 1.8 g / 1, very particularly ^¬ preferably between 0.1 and 1 g / 1.

The precious metal is preferably added as the salt solution of a noble metal salt.

In addition, at least one complexing agent for the noble metal ions can be added to the bath in order to reduce the amount of free noble metal ions. This suppresses the precipitation and nonspecific deposition of the noble metal on less noble metals. At the same time such Kom ^¬ formers and the amount of precious metal required can be reduced.

In a preferred embodiment of the invention, the at least one complexing agent is an acid-stable complexing agent. Such complexing agents are, for example, in the case of silver. wise under the name Slotoloy SNA 33 (company Schlötter) available.

Preferred complexing agents are those in the specification WO

01/92606 AI on pages 7 to 9 and preferably in EP 1 285 104 Bl in the paragraphs [0025] to [0027] described organic sulfur compounds, which is hereby incorporated by reference.

These organic sulfur compounds preferably have the following general formula:

XR - [Ζ-ΪΓ] NZR -Y (I) wherein n = 0 to 20, preferably 0 to 10, especially before ^¬ Trains t 0 to 5, is, X and Y are each independently -OH, - SH or - H, each Z is a sulfur atom or an oxygen atom and the radicals Z in the case n> 1 in formula (I) are identical or different, R ¹ , R ² and R ³ are each independently an optionally substituted linear or branched alkylene group and the radicals R ² in the case n> 1 in formula (I) are identical or different. Provided that Z is exclusively an oxygen atom, at least one of the radicals X, Y, R ¹ , R ² and R ^{3 contains} at least one sulfur atom.

Examples of alkylene groups are alkylene groups having 1 to 10, preferably 1 to 5, carbon atoms, e.g. Methylene,

Ethylene, n-propylene, iso-propylene, n-butylene, iso-butylene and tert-butylene groups. Examples of substituents of the alkylene groups are -OH, -SH, -SR ⁴ , wherein R ^{4 is} an alkyl group having 1 to 10 carbon atoms, e.g. A methyl, ethyl, n-propyl or iso-propyl group, is -OR ⁴ , -NH ₂ , NHR ⁴ and NR ⁴ 2 (where the two substituents R ^{4 may be the} same or different).

In the case that Z in formula (I) represents exclusively an oxygen atom, the sulfur-containing radicals X and / or Y may be an SH group and / or the sulfur-containing Radicals R ¹ , R ² and / or R ³ may, for. B. an alkylene depicting ^¬ len which is substitu ^¬ ated with an SH group or an SR ⁴ group.

Preference is given in formula (I)

- n: 1,

R ¹ , R ² and R ³ independently of one another have an alkylene group which has at least two carbon atoms,

and in the event that only one Z represents a sulfur atom, X and / or Y is an SH group and in the case where Z is exclusively an oxygen atom, X and Y represent an SH group.

Preference is given to compounds in which Z in each case represents a sulfur atom or an oxygen atom and the radicals Z are identical or different, R ¹ , R ² and R ^3, independently of one another, each represent an alkylene group which has 2 to 10 carbon atoms, n is 1 to 20, X and Y are each independently -OH, -SH or -H and in the event that only one Z represents a sulfur atom, X and / or Y-SH, and in the event that Z is exclusively an oxygen atom, X and Y are -SH. Alkylene groups having 2 to 5 carbon atoms are preferred, for example, ethylene-n-propylene, iso-propylene, n-butylene, iso-butylene and tert-butylene groups. Furthermore, the following organic sulfur compounds are preferred:

Bis (hydroxyethyl) sulfide: HO-CH 2 -CH 2 -S-CH 2 -CH 2 -OH;

3,6-dithiaoctanediol-1, 8: HO-CH2-CH2-S-CH2-CH2-S-CH2-CH2-OH;

3,6-dioxaoctanedithiol-1, 8: HS-CH 2 -CH 2 -O-CH 2 -CH 2 -O-CH 2 -CH 2 -SH;

- 3, 6-dithia-l, 8-dimethyloctandiol-l, 8: HO-CH (CH ₃₎ -CH ₂ -S- CH2-CH2-S-CH2-CH (CH ₃₎ -OH;

- 4,7-dithiadecane: H3C-CH2-CH2-S-CH2-CH2-S-CH2-CH2-CH3;

3,6-dithiaoctane: H3C-CH2-S-CH2-CH2-S-CH2-CH3;

3,6-dithiaoctanedithiol-1, 8: HS-CH 2 -CH 2 -S-CH 2 -CH 2 -S-CH 2 -CH 2 -SH. The at least one complexing agent is preferably added in an amount such that the molar ratio of / of complexing ^¬ neris) to the noble metal ions (molar amount of all complexing ^¬ ner: molar amount of noble metal ions) at least 1, preferably 5: 1 to 1: 1, particularly preferably 1.5: 1.

To increase the conductivity of the bath, conductive salts known from galvanic deposition can be added. These are usually alkali or alkaline earth, at ^¬ play, hydroxides, chlorides, bromides, nitrates,

Fluoroborates, such as potassium hydroxide, potassium chloride, sodium chloride, lithium chloride, lithium bromide or

Lithium hexafluoroborate. These salts are preferably present in the bath in an amount of from 0.1 g / 1 to 1 g / l, preferably from 0.4 g / l to 0.8 g / l.

The bath for electroless deposition of a metal layer is preferably a bath for depositing a chemically nickel layer, preferably a nickel / phosphorus and / or nickel / boron layer. This means that the metal salt used is a nickel salt and the reducing agent hypophosphites and / or borates.

In the next step, a substrate in the bath is ^¬ introduced. The substrate is preferably a conductive substrate. In this case, the conductivity can also be achieved by applying a conductive layer to the substrate.

Preferred metallic substrates are copper, bronze, aluminum ^¬ minium, steel, in particular stainless steel.

Non-metallic substrates include plastics, such as polypropylene, polyethylene, polycarbonates, polyimides, poly amide ^¬ or nylon. The decisive factor is that they survive the conditions of the deposition. These non-metallic substrates are preferably coated with a metallic layer.

It may be necessary to clean, degrease and / or activate the surface of the substrate prior to performing the process. This can be done, for example, by applying a thin metal layer, for example, by a so ^¬ called "nickel strike" done. This is also known as An ^¬ impact or adhesion nickel. In this case, a thin nickel film is deposited on the Oberflä ^¬ che.

The substrate is preferably a mesh, sieve or grille, be ^¬ vorzugt with a mesh size of less than 1 mm, particularly before ^¬ Trains t of less than 500 ym. But there are also much finer networks with a mesh size of less than 100 ym, preferably less than 50 ym possible. The wire thickness is more than 5 μm, preferably more than 10 μm, for example between 50 μm and 1000 μm. In this case, the inventive method also allows the coating of such networks, screens or grids, which enclose a cavity, such as filter elements, V-filter. Due to shielding effects such structures can not be coated on the inside with galvanic processes.

After being introduced into the bath, a voltage is applied between the substrate and an electrode. As an electrode while a graphite, nickel or silver electric ^¬ de example, can be used. Preferred is a graphite electrode.

The ratio of the area of the anode in the bath and the proji ^¬ ed workpiece surface (shadow area) is between 1: 0.5 and 1: 2, preferably 1: 1 (with a deviation of +/- 10%).

It may be necessary to bring the bath before applying the voltage to a certain temperature and / or a certain pH. The bath is preferably heated to a temperature of Tempe ^¬ about 50 ° C. The process can also be carried out at temperatures between 15 ° C and 90 ° C. In this case, especially at a high content of noble metal ions, the temperature should not be too high, since the electrolyte decomposes otherwise. Preferred are temperatures of below 70 ° C, preferably between 30 ° C and 70 ° C, particularly preferably Zvi ^¬ rule 50 ° C and 70 ° C.

The pH of the bath is preferably in the acidic range. terhalb of pH 6, preferably between 4.0 and 5.0, especially be ^¬ vorzugt 4.2 to 4.6.

Thereafter, a voltage is applied between an electrode and the substrate. In this case, the electrode is connected anodically and the substrate is cathodically connected. It may be necessary to vary the voltage over time, for example increasingly, decreasing or periodically.

The voltage generates an auxiliary electric field. The voltage is applied so that a current density between 0.01 and 3 A / dm ² , preferably between 0.1 and 1 A / dm ² , more preferably between 0.1 and 0.7 A / dm ² , is set , This current density is significantly lower than the usual current density in gal ^¬ vanischen method.

It has surprisingly been found that with the deposition of a noble metal / metal layer of a bath for the electroless deposition of the metal layer layers can be obtained, which have particularly advantageous tribological properties ^¬. In addition, the layers obtained are very uniform, especially in substrates where this is not possible with purely galvanic methods. It is therefore assumed that the taking place in the background electroless From ^¬ decision of the metal brings about the deposition of the noble metal / metal layer also in the unfavorable from a field, areas. Without the tension support, no well-adherent layer is obtained.

At the same time, the process is very fast. So can be ^¬ already be obtained within 1 to 5 minutes, a layer thickness of 1 to 5 ym. However, layer thicknesses of 0.1 .mu.m to 5 .mu.m, preferably 0.1 .mu.m to 1 .mu.m, are preferred.

The resulting layers show a noble metal content of more than 60% by weight, preferably more than 80% by weight, particularly preferably more than 90% by weight.

After the deposition, further treatment steps may follow. This includes, for example, heat actions to harden the layers.

In a preferred embodiment, prior to carrying out the process, the substrate is coated with a chemically nickel layer. For this purpose, the substrate is introduced into a chemical nickel bath before the process is carried out and a chemically nickel layer is deposited without current. As a result, the adhesion of the deposited with current support coating on the substrate is significantly improved.

Such a bath contains the constituents of a chemical nickel bath already described. These are at least one Ni ^¬ ckelsalz and a reducing agent in the indicated Mengenbe ^¬ rich. The bath may also contain complexing agents for nickel ions in the ranges indicated.

The rate of electroless deposition is determined essentially by the temperature and / or by the pH of the bath. The conditions are determined by the used Me tall ^¬ / reducing agent system. The tempera ture ^¬ is preferably above 50 ° C, preferably above 70 ° C, especially be ^¬ vorzugt between 80 and 90 ° C, very particularly preferably be- see 86 ° C and 90 ° C, for example. At 88 ° C. The pH is between 4.0 and be ^¬ vorzugt 6.0, preferably 4.2 to 4.6, most preferably at 4.4.

In a further embodiment of the invention, the previously deposited chemically nickel layer has a noble metal content of up to 30% by weight. These previously written for the novel process bath is preferably introduced ^¬ sets. However, the content of noble metal ions is preferably lower by a factor of 10 to 20. As a result, this chemically nickel layer has a content of noble metal of up to 30 wt .-%, preferably between 1 and 10 wt .-%. The content of noble metal lies between 0.01 to 0.1 g / l, preferably between 0.01 and 0.06 g / l, particularly preferably between 0.01 and 0.05 g / l or 0.01 and 0 , 04 g / 1.

The bath additionally contains at least one complex Former for the noble metal ions, as already described for the other bath. In this case, acid-resistant complexing agents are preferred. Such are in the case of silver, for example, under the name Slotoloy SNA 33 (company Schlötter) available.

The at least one complexing agent is preferably in one

Amount added that the molar ratio of the complex or complex ^¬ neris) to the noble metal ions (molar amount of all complexing ^¬ ner: molar amount of noble metal ions) at least 1, preferably 10: 1 to 1: 1, particularly preferably 3: 1.

By using these complexing agents, the stability of the bath in the electroless deposition can be increased. At the same time, a deposition of a high content of precious metal is achieved in the deposited layer with significantly reduced levels of precio ^¬ tallionen. During deposition, it may be necessary to restore the content of precious metal by further metering.

This can be done in a preferred embodiment, characterized in that the electrochemical potential between Elektro ^¬ lyt, ie bath, and a reference electrode is measured. When changing the potential above a threshold, the metered addition of the precious metal can be triggered.

In a preferred embodiment, the previously deposited layer includes the same precious metal as that deposited in the OF INVENTION ^¬ to the invention process layer. As a result, the adhesion of the layer deposited in steps a) to c) on the substrate improves markedly. In addition, the noble metal content of said first layer imparts a better conductivity ^¬ ness, which improves the deposition onto this layer in the steps a) to c).

Also, noble metal doping in the first layer allows the use of very low field strengths in stress-assisted deposition, likely due to the increased conductivity of the noble metal. Despite in comparison to the galvanic deposition very low field strength can Contour-accurate, deep-scattering deposition with a noble metal ^¬ content of over 90 wt .-% can be achieved. This layer has at the same time a high abrasion resistance and in the case of silver a good depot effect.

The method for producing the first layer can also be used per se for the production of noble metal-containing metal layers.

Particularly preferably, the noble metal min ^¬ least a bath, preferably in both bathrooms to silver. As a result, it is possible to obtain layers which have a particularly good biocidal effect and at the same time have outstanding tribological properties.

In a preferred embodiment, the noble metal in both layers is silver, particularly preferred in both layers is the noble metal silver and the metal nickel, or Ni ^¬ ckel / phosphorus.

The invention furthermore relates to a coating on a substrate which has on the surface a noble metal / nickel layer which has a noble metal content of more than 60% by weight, preferably more than 80% by weight, particularly preferably more than 90% by weight. % on ^¬ points.

In a further embodiment, the noble metal / nickel layer is a noble metal / nickel / phosphorus layer or noble metal / nickel / boron layer, preferably a noble metal / nickel / phosphorus layer. In this case, the content of Phos ^¬ phor is located in the respective layer at 0.1 wt .-% to 30 wt .-%, preferably between 0.1 wt .-% and 10 wt .-%, more preferably 0.1 wt. -% to 3 wt .-%, based on the proportion of nickel and phosphorus in the respective layer.

In a preferred development of the invention, a nickel / noble metal layer having a noble metal content of less than 30 wt.%, Preferably between 1 wt.% And 10 wt. This layer is preferably obtained by the above-described electroless method. In this case, the Layer at the surface has a thickness of 0.1 ym to 5 ym, preferably ^¬ from 0.1 ym to 1 ym, while the underlying layer has a thickness of 0.5 to 50 ym, preferably of 0.5 ym to 15 ym.

Through this first layer particularly low field can ^¬ strengthen in the deposition of the precious metal / nickel layer reali ^¬ Siert be. This will make the precious metal / nickel layer more uniform. Also, the formation of oxides is avoided by excessive current densities. The structure of the coating with different precious metal content gives the best results in terms of tribological stability.

In a further embodiment, the nickel / noble metal layer is a nickel / phosphorus / noble metal or nickel / boron / noble metal layer, preferably a nickel / phosphor / noble metal layer. This is the content

Phosphorus in the layer at 10 wt .-% to 30 wt .-% based on the proportion of nickel and phosphorus in the respective layer.

In another embodiment, the noble metal is silver. As a result, the coating has biocidal properties. Due to the multilayer structure with the layer with the highest silver content at the surface, these properties are particularly pronounced ^¬ . In addition, the multilayer structure of the coating gives a particularly good adhesion to the substrate, since the different layers are structurally well matched.

The coating may also contain additional layers. The two described layers preferably form the two uppermost layers of the coating. However, this may include, for example, further chemical nickel layers or also nickel layers, for example from a previous activation of the surface by a nickel strike.

In a further embodiment, the coating is produced by the method of steps a) to c), wherein before a noble metal-containing chemically nickel layer, preferably with the method also described, was deposited.

The invention also relates to a coated substrate, obtainable by the process according to the invention or with a coating according to the invention.

In a development of the invention, the coated substrate is a mesh, sieve, filter, fabric or sponge. The substrate preferably has at least one cavity which is completely or partially enclosed by a net, sieve, ^filter , fabric or sponge. Examples of such substrates are filter ^¬ elements, filter cartridges or V-filter.

The invention also relates to the use of the coated substrate in the automotive sector, sanitary area, jewelry area, drinking water area, in wastewater treatment, drinking water treatment, filtration of fluids, in cooling water circuits, in chemical plant engineering or in electrical engineering. For example, the coated substrate in an on ^¬ application selected from the group of filters, valves, Dros ^¬ seleinheiten, radial and / or filter elements, filter screens, V- filter design, decoration, machinery and installations in the chemical industry, finishing in the Electrical industry, to be used.

Further details and features will become apparent from the following description of preferred Ausführungsbeispie- len in connection with the dependent claims. In this case, the respective features can be implemented on their own or in combination with one another. The possibilities of solving the problem are not limited to the ^exemplary embodiments. For example, area information always includes all - not mentioned - intermediate values and all imaginable subintervals.

In a preferred embodiment of the invention, a first aqueous nickel electroless bath containing nickel in a range of 1 to 15 g / l and a first Content of reducing agent in a range of 20 to 50 g / 1 ready, this bath stirred well and then sets the pH to a value in the range of 4.0 to 6.0 or 4.5 to 5.0.

In addition, it has proven to be particularly efficient when a pH in the range of 4.2 to 4.6, preferably 4.4, is ^¬ sets. The pH can be adjusted, for example, by adding ammonia solution or hydrochloric acid or sulfuric acid.

The nickel ions of the bath are generally present as solutions of the salts nickel chloride, nickel sulfate, nickel carbonate and / or nickel acetate. The nickel content is usually in a range of 3 to 10 g / l.

As the reducing agent in the bath a phosphorus or boron compound ^¬ is preferably used. The reducing agent in the bath is preferably a hypophosphite. Most preferably, the reducing agent is sodium hypophosphite and / or

Potassium hypophosphite.

As the boron compound, dimethylaminoborane,

Diethylaminoboran or sodium borohydride can be used. The reducing agent is normally present in a concentration ranging from 32 to 42 g / l in the bath.

In the bathroom is optionally also at least one complexing ^¬ ner included, which is in particular selected from the group consisting of monocarboxylic acids, dicarboxylic acids, hydroxycarboxylic acids, ammonia, and alkanolamines. The complexing agent is present in an Konzentra ^¬ tion in a range of 1 to 15 g / 1 in the bathroom. Complexing agents complex nickel ions and thus prevent excessively high concentrations of free nickel ions. As a result, the solution is stabilized and the precipitation of, for example, nickel phosphite is suppressed.

In the bathroom is optionally also contain at least one promoter, which is in particular selected from the group ent ^¬ holding fluorides, borides and / or anions of mono- and

Dicarboxylic acids. The accelerator is usually in one Concentration in a range of 0.001 to 1 g / 1 in the bath before. Accelerators can, for example, activate hypophosphite ions and thus accelerate the deposition.

In customary nickel baths, it is also possible for at least one stabilizer to be present, which is in particular selected from the group of lead, tin, arsenic, molybdenum, cadmium, thallium ions and / or thiourea. The stabilizer is usually present in a concentration ranging from 0.01 to 250 mg / l in the bath. Stabilizers can prevent the decomposition of the solution by masking catalytically active reaction nuclei.

In the bath, at least one pH buffer is typically included, in particular, is a sodium salt of a complexing ^¬ former and / or the associated corresponding acid. The buffer is usually present in a concentration ranging from 0.5 to 30 g / l in the bath.

If appropriate, the bath also contains at least one pH regulator, which is in particular selected from the group

Sulfuric acid, hydrochloric acid, sodium hydroxide, sodium carbonate and / or ammonia. The pH regulator is advantageously present in a concentration ranging from 1 to 30 g / l in the bath. pH regulators allow the pH of the bath

readjust.

The bath may also contain at least one wetting agent which is in particular selected from the group of ionic and / or nonionic surfactants. The wetting agent is preferably present in a concentration in a range of 0.001 to 1 g / l in the bath. Wetting agents increase the wetting of the surface to be nickeled and allow the production of very uniform layers.

This first chemical nickel bath additionally contains 0.01 to 0.1 g / 1, preferably between 0.01 and 0.06 g / 1, particularly before Trains t ^¬ between 0.01 and 0.05 g / 1 or 0.01 and 0.04 g / ^{l of} silver or silver ions. The silver is preferred to the bath as a solvent. solution of a silver salt. It may be necessary to add the solution very slowly.

Silver nitrate, silver acetate or a silver salt of a sulfonic or thiocarboxylic acid, for example silver methanesulfonate, can be used as the silver salt.

The bath preferably additionally contains at least one complexing agent for silver ions in order to stabilize the bath. In this case, acid-resistant complexing agents are preferred. Such are in the case of silver, for example, under the name Slotoloy SNA 33 (company Schlötter) available. As complex formers ^¬ preferred organic sulfur compounds have already been described.

The at least one complexing agent is preferably added in an amount such that the molar ratio of / of the complexing agent (s) to the noble metal ions (molar amount of all complexing ^¬ ner: molar amount of noble metal ions), preferably at least 1 10: 1 to 1: 1, more preferably 3: 1.

In this first bath, a substrate is introduced and at a temperature between 80 and 95 ° C, preferably 80 ° C and 90 ° C, preferably between 86 ° C and 90 ° C, particularly preferably at 88 ° C, a chemical nickel layer with a Silver content of up to 30 wt .-%, preferably between 1 to 10 wt .-%, abge ^¬ separated.

The thickness of this layer is between 0.5 .mu.m and 50 .mu.m, preferably between 0.5 .mu.m and 15 .mu.m.

During the deposition, it may be necessary to replenish the silver consumed by the deposition. The dosage can be done by single additions or continuously.

In a preferred embodiment, the

Addition metering controlled by the measurement of the electrochemical potential between the electrolyte and a reference electrode.

It may be advantageous that the surface of the substrate is pretreated, for example by a nickel strike. As a result, for example, oxide layers are removed on metallic substrates. Such a nickel-strike can ^¬ example as formed by treating the surface with a mixture of inorganic acids, nickel chloride, citric acid and acetic acid under application of a voltage. This cleans the surface and at the same time deposits a thin, 10 nm to 1 μm thick nickel layer on the substrate. Such a nickel strike is preferably carried out in the case of metallic substrates. The compositions are known to the person skilled in the art.

After depositing the first layer, the substrate is introduced into a second bath. This bath also corresponds to a bath for electroless deposition of nickel, which also contains additional silver.

The bath preferably contains, based on the silver ions, a content of silver between 0.1 g / l and 3 g / l, preferably between 0.1 g / l and 2 g / l, particularly preferably between 0.1 and 1.8 g / 1, most preferably between 0.1 and 1 g / 1.

The silver is preferably added as a salt solution of a silver salt.

The bath can still contain at least one conductive salt. These are usually inorganic salts. These are usually alkali or alkaline earth to, for example, hydro ^¬ hydroxides, chlorides, bromides, nitrates, fluoroborates such case ^¬ game potassium hydroxide, potassium chloride, sodium chloride,

Lithium chloride, lithium bromide or lithium hexafluoroborate.

In a preferred embodiment of the invention, the conductive salts in the amount for a content of 0.1 to 1 g / 1, be ^¬ preferably added between 0.4 to 0.8 g / 1.

Such conductive salts are also available as commercial solutions. An example of such a batch solution is Arguna CF (Umicore).

It may be necessary to briefly clean the substrate between the two baths, for example by immersion in a cleaning bath, for example water. Preference is given between the two baths carried out no cleaning steps. The substrates can be printed directly from a bath in the other bathroom on ^¬.

In this bath, a voltage is applied between the substrate and an electrode. In this case, the electrode is connected anodically and the substrate is cathodically connected.

The deposition is preferably carried out at a temperature between 21 ° C and 90 ° C. The temperature is usually below the critical temperature for the nickel bath, ie below 70 ° C, preferably between 30 ° C and 70 ° C, more preferably between 50 ° C and 70 ° C. As a result, a high ^content of silver ions in the electrolyte is possible without the electrolyte decomposing.

The pH of the bath is preferably in the acidic range un ^¬ terhalb of pH 6, preferably between 4.0 and 5.0, especially be ^¬ vorzugt 4.2 to 4.6.

With the application of the voltage starts to deposit a layer which is mainly loading of silver, preferably having a silver content of over 60 wt .-%, preferably be ^¬ Sonders having a silver content of over 80 wt .-%, quite on the substrate more preferably above 90% by weight.

This deposition is preferably carried out for up to 5 minutes. As a result, layers having a thickness of up to 5 μm, preferably up to 1 μm, particularly preferably between 0.1 μm and 1 μm, are obtained.

It is assumed that the first-deposited silver ^¬ containing nickel layer improves the adhesion of this second layer interpreting ^¬ Lich. At the same time, the better conductivity Speed of the noble metal-containing nickel layer in combination with the simultaneous running electroless deposition uniform deposition even with substrates that are not to be coated with purely galvanic process.

Such substrates are in particular nets or screens, which are used in filter elements. These are voids which are completely or partially enclosed by such a screen or mesh ^¬ surfaces. Due to shielding effects, these substrates can not be evenly coated on the inside with purely galvanic processes. By OF INVENTION ^¬ to the invention method, it is possible to apply both the Innenais also on the outside of the substrate, a uniform layer.

The embodiments are shown schematically in the figures. The same reference numerals in the individual figures designate the same or functionally identical or with respect to their functions corresponding elements. 1 shows a schematic representation of a filter element;

Fig. 2 is a schematic representation of a preferred embodiment of the method of the invention;

Fig. 3 shows a typical structure of an inventive

Layer;

Fig. 4A, B show light micrographs of a

uncoated sieve;

Fig. 5A, B show light micrographs of the screen

Fig. 4 A, B after the coating.

Figure 1 shows a schematic representation of a filter ^¬ elements, which can be coated with the inventive method, in particular with a nickel / silver layer. The filter element consists of a cylindrical filter body 10. This consists of a net-like structure, which has a Zy linder forms. The two ends of the cylinder are closed with caps 12. On these caps also connection openings can be attached. The filter element may also include yet Fixed To ^¬ restriction means for seals. Together with the caps 12, the filter body encloses a cavity. With the method according to the invention, it is possible for the filter body on the inside and on the outside with a uniform,

tribologically stable coating to provide. In the case of silver-containing coatings, the filter element also has biocidal effects. The preferred material for the filter element is ^¬ stainless steel, eg 1.4404, 1.4301, 1.4571 Werkstoffbe ^¬ drawing according to AISI.

FIG. 2 shows the schematic sequence of a preferred embodiment of the invention. First, the substrate surface is cleaned and optionally pretreated with a nickel strike (200).

In the next step (210), the substrate is introduced into a first bath. This bath is a bath for the electroless deposition of a metal / noble metal layer, as already described.

In the first bath, a first layer is electrolessly deposited on the substrate (220). This layer is a tall Me ^¬ / noble metal layer, wherein the layer has a Edelmetallge ^¬ holding of up to 30 wt .-%. The deposition is carried out without current to obtain a uniform coating of the substrate.

After a layer of sufficient thickness is obtained, the substrate is placed in a second bath, optionally after purification steps (230). As already described, this bath is a bath for electroless deposition of a metal layer, which additionally contains noble metal ions.

In the next step, a voltage is applied between the substrate and an electrode (240). This leads to the deposition of a noble metal / metal layer. this is a Layer which has a content of noble metal of over 60 wt .-%.

The coating is carried out until a

Layer with a thickness of up to 5 ym, preferably up to 1 ym, is obtained.

In a preferred embodiment, the metal layer is a nickel / phosphorus layer and the noble metal is silver. The inventive read layers can thus be obtained which consists of a nickel / phosphorus / silver layer and thereon a silver / nickel / phosphorus layer best ^¬ hen, respectively according to the proportion in the layer. This combination of layers shows a particularly advantageous biocidal effect with at the same time very good tribological properties. Filter elements coated in this way are significantly longer lasting than just electrolessly coated filter elements or those with coatings of pure silver. The process is also much cheaper to perform than an electroless plating with the pure precious metal.

The in this way with at least two layers of coating preparing substrate exhibits a particularly high tribological Stabili ^¬ ty and is thereby very well for filter elements in the flui ^¬, for example in cooling water circuits.

Figure 3 shows a structure of a preferred embodiment of the invention. On a substrate (34), a chemical nickel / phosphorus / silver layer (32) with a silver content of <10 wt .-% with a thickness between 0.5 and 15 ym arranged. On top of this is a silver / nickel / phosphor cover layer with a silver content of> 90% by weight and a thickness between 0.1 μm and 1 μm.

4 shows recordings of an uncoated screen / filter element as shown in Figure 1 in different magnification ^¬ fication. The scale is 200 ym each. The thickness of the horizontal ^¬ right wires is about 150 ym and 160 ym. The gemes ^¬ Senen mesh widths are between 85 .mu.m and 143 .mu.m. FIG. 5 shows photomicrographs of the same sieve / filter element from FIG. 4 after application of a coating according to the invention with a nickel / silver and a silver / nickel layer, as shown in FIG. The scale is 200 ym each. The thickness of the horizontal wires is now about 160 ym and 170 ym. The measured mesh sizes are between 40 ym and 120 ym. It can be seen clearly a uniform coating of the substrate. When used in cooling circuits, such coated filters show a biocidal effect over several weeks without any detachment of the coating.

Example: 1. Electroless deposition of a silver-containing nickel layer

To an above-described chemical nickel bath is silver in form of silver methanesulfonate corresponding to a Sil ^¬ bordered part of 0.025 g / 1 and an acid resistant silver complexing agents (eg SLOTOLOY SNA 33, manufacturer Messrs. Schlötter) in an amount corresponding to 0.2 ml / 1 , The pH of the bath is adjusted to 4.4 with H ₂ SO ₄ . Thereafter, the bath is heated to 88 ° C and introduced a substrate made of stainless steel. The consumption of silver ions is by continuous

Addition of silver methanesulfonate balanced. This can be done by controlling the dosage by measuring the electrochemical potential between the electrolyte and a reference electrode.

Under these conditions, a non-porous, non-porous chemical nickel-silver alloy layer having a silver content of 1-10% by weight is deposited on the stainless steel.

A higher silver content is not available as the silver content in relation to the nickel content in the bath can not be further increased. Higher contents of silver lead to a Temperature from about 70 ° C to complete destabilization of the electrolyte (spontaneous self-precipitation). It is not possible to avoid this effect by increasing the levels of stabilizers or complexing agents without stopping the nickel-phosphorus reduction. In this respect the ranges given in DE 10 2006 020 988 AI of precious metal and precious metal content ^¬ the layer of silver are not possible. The thus coated substrate was then according to the follow ^¬ provide the information with a silver / nickel layer.

2. Stress-assisted deposition of a silver / nickel layer.

To a chemical nickel bath described above, silver in the form of silver methanesulfonate corresponding to a silver content in the bath of 0.6 g / l, an acid-resistant silver complexing agent (eg Slotoloy SNA 33, manufacturer Fa. Schlötter) in the amount corresponding to 4 ml / 1 based on the bath and a commercial Galvanisch silver approach salt, only the conductive salt, (eg Arguna CF, Umicore) according to an amount of

Conducting salt in the bath of 0.65 g / 1 was added. With this composition, the proportion of silver ions can be increased in comparison to the first bath so that no spontaneous reaction takes place.

In the bath graphite, nickel or silver electrodes, preferably graphite electrodes, introduced and applied an electrical voltage, wherein the introduced electrodes are connected anodically and the workpiece / substrate cathodically. The area of the anode corresponds approximately to the projected workpiece surface (ie a ratio of 1: 1). The power ^¬ density of the auxiliary field is between 0.1 and 1 A / dm ^2. This is a significantly lower current density than conventional gal ^¬ vanish silver deposits. This is usually 30 to 100 A / dm ² .

It can thus a contour-accurate, deep-scattering deposition of a silver-nickel alloy with a silver content of> 90 % By weight. The layer, or the combination of the nickel / silver and silver / nickel layer has a high abrasion resistance and from ^¬ depot effect with respect to the silver.

The coating obtained in the two-stage process still showed a biocidal effect and excellent stability even after continuous operation over several months in a cooling circuit ^¬ run.

Reference sign

10 filter body

12 caps

200 pretreatment of the substrate surface

210 introduction into a first bath

220 Electroless deposition in the first bath

230 insertion into a second bath

240 Voltage-controlled deposition in the second bath

30 Ag-Ni topcoat

32 NiP-Ag alloy

34 substrate

quoted literature

DE 10 2006 020 988 Al

GB 1 222 969

WO 01/92606 Al

EP 1 285 104 Bl

Claims

claims

A method of depositing a noble metal / metal layer on a substrate comprising the steps of:

a) providing a bath for the electroless deposition of a metal layer, which additionally contains at least one kind of noble metal ions;

b) introducing a substrate into the bath; and

c) applying an electrical voltage.

2. Method according to the preceding claim, characterized in that

the bath for the electroless deposition of a metal layer is a bath for depositing a chemically nickel layer.

3. The method according to any one of the preceding claims, characterized in that

the noble metal ions are selected from the group contained ^¬ tend silver, gold, palladium, platinum, rhodium and copper.

4. The method according to any one of the preceding claims, characterized in that

the voltage is applied at a bath temperature of less than 70 ° C.

5. The method according to any one of the preceding claims, characterized in that

the bath contains at least one complexing agent for the precio ^¬ tallionen.

6. The method according to any one of the preceding claims, characterized in that the content of noble metal ions in the bath is between 0.1 and 3 g / l.

7. The method according to any one of the preceding claims, characterized in that

the silver content of the layer obtained is more than 60% by weight.

8. The method according to any one of the preceding claims, characterized in that

a voltage corresponding to a current density between 0.01 and 3 A / dm ^{2 is} applied.

9. The method according to any one of the preceding claims, characterized in that

before carrying out the process, the substrate is electrolessly coated with a chemically nickel layer.

10. The method according to claim 9, characterized in that the previously deposited electroless nickel layer is a Ni ^¬ ckel / noble metal layer by weight and a precious metal content of up to 30 -.% Has.

11. The method according to claim 10, characterized in that the noble metal in both layers is silver.

12. coating on a substrate, characterized in that

the coating on the surface has a noble metal / nickel layer which has a noble metal content of more than 90% by weight.

13. A coating according to claim 12, characterized in that the noble metal / nickel layer is a tall precio ^¬ / nickel / phosphorus layer or noble metal / nickel / boron layer.

14. Coating according to one of claims 12 or 13, characterized in that

the precious metal is silver.

15. Coated substrate obtainable by a process of claims 1 to 11.

16. Coated substrate with a coating according to one of claims 12 to 14.

17. Coated substrate according to one of claims 15 or 16, characterized in that

the substrate is a net, sieve, filter, tissue or sponge.

18. Use of a coated substrate according to one of claims 15 to 17

- in the automotive sector, in the sanitary sector, in the jewelery sector, in drinking water or drinking water treatment, for wastewater treatment, for the filtration of fluids, in cooling water circuits, in chemical plant engineering or in electrical engineering.