EP2588644B1 - Tribologically loadable mixed noble metal/metal layers - Google Patents

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 μm. 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. As a rule, these layers consist of at least one noble metal in a mixture or alloy with at least one less noble metal than the noble 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 noble 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 The precious metal is much easier to reduce, it is deposited together 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 not possible with electroplating methods due to shielding effects, evenly coat cavities or hollows surrounded by nets, as they occur for example in filter elements and in particular fine structures, eg. B. structure elements in the range of less than 200 microns, contour resolution.

Pure noble metal layers, which are deposited without current, are often soft and do not show sufficient abrasion resistance. Contour resolution or fidelity and depth dispersion are not sufficient for complete and unadulterated coverage of tissue or slit structures. Although hard metals (for example cobalt) can be galvanically co-deposited to form a higher abrasion resistance. The layers are not free from pores and are soon infiltrated or detached.

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

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

It is not possible with most methods to achieve high levels of the noble metal in the layer and at the same time to obtain 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.

1. a) Bereitstellung eines Bades zur stromlosen Abscheidung einer Metallschicht, welches zusätzlich mindestens eine Art von Edelmetallionen enthält;
2. b) Einbringen eines Substrats in das Bad;
3. c) Anlegen einer elektrischen Spannung.

The object is achieved by a method for depositing a noble metal / metal layer on a substrate, comprising the following steps:

1. a) providing a bath for the electroless deposition of a metal layer, which additionally contains at least one kind of noble metal ions;
2. b) introducing a substrate into the bath;
3. c) applying an electrical voltage.

In the following, individual process steps are described in more detail. The steps need not necessarily be performed in the order given, and the method to be described may include other steps not mentioned 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 / precious metal layer.

First, a bath for electroless deposition of a metal layer, which additionally contains at least one kind of noble metal ions, 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 methods are often autocatalytic systems. This means that the deposited metal layer catalyzes the further deposition of metal. The thickness of the deposited layer can be controlled over the duration of the deposition.

The skilled person is familiar with many metal / reducing agent systems for electroless deposition. Examples of electrolessly deposited metals are nickel, copper, palladium, silver or gold. As a reducing agent aldehydes, z. As formaldehyde, formic acid, borohydride compounds, for example alkylamine boranes, 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. Also, a reducing gas, such as hydrogen, can be passed through the bath.

Examples of metal / reductant 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 / l and the content of reducing agent between 5 and 50 g / l.

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 may also be added proportionally. 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. For example, 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 kind of noble metal ions. 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 may preferably have alkyl groups or aryl groups, which in turn may advantageously be partially fluorinated. Most preferably, the counterions are trifluoromethanesulfonate, methanesulfonate and / or toluenesulfonate. They may also be salts in which the noble metal ions are complexed with ligands or chelate ligands, such as ethylenediamine, polyethylene glycols or thioethanol derivatives, such as 2,2-ethylene-di-thiodiethanol.

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 / l, most preferably between 0.1 and 1 g / l.

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 complexing agents can also reduce the amount of precious metal needed.

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

Preferred complexing agents are those in the specification WO 01/92606 A1 on pages 7 to 9 and preferably in EP 1 285 104 B1 in the paragraphs [0025] to [0027] described organic sulfur compounds, which are hereby incorporated by reference.

These organic sulfur compounds preferably have the following general formula:

XR ¹ - [ZR ² ] _n -ZR ³ -y (I)

in which n = 0 to 20, preferably 0 to 10, particularly preferably 0 to 5, X and Y are each independently -OH, -SH or -H, Z is in each case a sulfur atom or an oxygen atom and the radicals Z in the case n> 1 in formula (I), in each case identical or different, R ¹ , R ² and R ³ independently of one another each represent an optionally substituted linear or branched alkylene group and the radicals R ² in the case n> 1 in formula (I) are the same 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. As 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. Example, represent an alkylene radical which is substituted with an SH group or with an SR ⁴ group.

• n: 1,
• R¹, R² und R³ unabhängig voneinander eine Alkylengruppe, die mindestens zwei Kohlenstoffatome aufweist,
• und für den Fall, dass nur ein Z ein Schwefelatom darstellt, ist X und/oder Y eine SH-Gruppe und für den Fall, dass Z ausschließlich ein Sauerstoffatom ist, stellen X und Y eine SH-Gruppe dar.

Preference is given in formula (I)

• n: 1,
• R ¹ , R ² and R ³ are each independently an alkylene group having at least two carbon atoms,
• and in the case 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.

• Bis- (hydroxyethyl)-sulfid : HO-CH₂-CH₂-S-CH₂-CH₂-OH;
• 3,6-Dithiaoctandiol-1,8 : HO-CH₂-CH₂-S-CH₂-CH₂-S-CH₂-CH₂-OH;
• 3,6-Dioxaoctandithiol-1,8 : HS-CH₂-CH₂-O-CH₂-CH₂-O-CH₂-CH₂-SH;
• 3,6-Dithia-1,8-dimethyloctandiol-1,8 : HO-CH(CH₃)-CH₂-S-CH₂-CH₂-S-CH₂-CH (CH₃) -OH;
• 4,7-Dithiadecan : H₃C-CH₂-CH₂-S-CH₂-CH₂-S-CH₂-CH₂-CH₃;
• 3,6-Dithiaoctan : H₃C-CH₂-S-CH₂-CH₂-S-CH₂-CH₃;
• 3,6-Dithiaoctandithiol-1,8 : HS-CH₂-CH₂-S-CH₂-CH₂-S-CH₂-CH₂-SH.

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 each -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-CH ₂ -CH ₂ -S-CH ₂ -CH ₂ -S-CH ₂ -CH ₂ -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-1,8-dimethyloctanediol-1,8: HO-CH (CH ₃ ) -CH ₂ -S-CH ₂ -CH ₂ -S-CH ₂ -CH (CH ₃ ) -OH;
• 4,7-dithiadecane: H ₃ C-CH ₂ -CH ₂ -S-CH ₂ -CH ₂ -S-CH ₂ -CH ₂ -CH ₃ ;
• 3,6-dithiaoctane: H ₃ C-CH ₂ -S-CH ₂ -CH ₂ -S-CH ₂ -CH ₃ ;
• 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 the complexing agent (s) to the noble metal ions (molar amount of all complexing agents: molar amount of noble metal ions) is 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 metal or alkaline earth metal salts, for example hydroxides, chlorides, bromides, nitrates, fluoroborates, for example 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 0.1 g / l to 1 g / l, preferably 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 is introduced into the bath. 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, steel, in particular stainless steel.

Non-metallic substrates are for example plastics, such as polypropylene, polyethylene, polycarbonates, polyimides, polyamides 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 stopper or sticky nickel. A thin nickel film is deposited on the surface.

The substrate is preferably a mesh, sieve or grid, preferably with a mesh size of less than 1 mm, particularly preferably less than 500 μm. But there are also much finer networks with a mesh size of less than 100 microns, preferably less than 50 microns possible. The wire thickness is over 5 microns, preferably over 10 microns, for example between 50 microns and 1000 microns. 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 example, a graphite, nickel or silver electrode can be used. Preferred is a graphite electrode.

The ratio of the area of the anode in the bath and the projected 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. Preferably, the bath is brought to a temperature of 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. Preference is given to temperatures of below 70 ° C, preferably between 30 ° C and 70 ° C, more preferably between 50 ° C and 70 ° C.

The pH of the bath is preferably in the acidic range below of pH 6, preferably between 4.0 and 5.0, more preferably between 4.2 and 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 galvanic processes.

It has surprisingly been found that with the deposition of a noble metal / metal layer from 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 believed that the background electroless deposition of the metal induces deposition of the noble metal / metal layer even in the field-unfavorable regions. Without the tension support, no well-adherent layer is obtained.

At the same time, the process is very fast. Thus, a layer thickness of 1 to 5 microns can already be obtained within 1 to 5 minutes. However, layer thicknesses of 0.1 μm to 5 μm, preferably 0.1 μm to 1 μm, 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 treatments, 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 before carrying out the process in a chemical nickel bath and electrolessly deposited a chemical nickel layer. As a result, the adhesion of the deposited with current support coating on the substrate is significantly improved.

Such a bath contains the already described components of a chemical nickel bath. These are at least one nickel salt and a reducing agent in the stated quantitative ranges. The bath may also contain complexing agents for nickel ions in the ranges indicated.

The rate of electroless deposition is essentially determined by the temperature and / or the pH of the bath. The conditions are determined by the metal / reducing agent system used. The temperature is preferably above 50 ° C, preferably above 70 ° C, more preferably between 80 and 90 ° C, most preferably between 86 ° C and 90 ° C, z. At 88 ° C. The pH is preferably between 4.0 and 6.0, preferably between 4.2 and 4.6, very particularly preferably 4.4.

In a further embodiment of the invention, the previously deposited chemical nickel layer has a noble metal content of up to 30% by weight. For this purpose, a bath already described for the process according to the invention is preferably used. 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 is between 0.01 to 0.1 g / l, preferably between 0.01 and 0.06 g / l, more preferably between 0.01 and 0.05 g / l or 0.01 and 0 , 04 g / l.

The bath additionally contains at least one complexing agent 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 added in an amount such that the molar ratio of the complexing agent (s) to the noble metal ions (molar amount of all complexing agents: molar amount of noble metal ions) is at least 1, preferably 10: 1 to 1: 1, particularly preferably 3: 1 amounts to.

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 noble metal in the deposited layer is achieved at a significantly reduced content of noble metal ions. During deposition, it may be necessary to restore the content of precious metal by further metering.

This may, in a preferred embodiment, be accomplished by having the electrochemical potential between electrolyte, i. Bad, 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 contains the same noble metal as the layer deposited in the method according to the invention. This significantly improves the adhesion of the layer deposited in steps a) to c) on the substrate. In addition, the noble metal content of this first layer gives better conductivity, which improves the deposition on this layer in steps a) to c).

Also, noble metal doping in the first layer allows the use of very low field strengths in voltage-enhanced deposition, likely due to the 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 precious metal is at least one bath, preferably in both baths, silver. As a result, layers can be obtained which show 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 nickel / phosphorus.

The invention also 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 ,

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. The content of phosphorus in the respective layer is 0.1% by weight to 30% by weight, preferably between 0.1% by weight and 10% by weight, particularly preferably 0.1% by weight. 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 on the surface has a thickness of 0.1 .mu.m to 5 .mu.m, preferably from 0.1 .mu.m to 1 .mu.m, while the underlying layer has a thickness of 0.5 to 50 .mu.m, preferably from 0.5 .mu.m to 15 has μm.

By means of this first layer, particularly low field strengths can be realized in the deposition of the noble metal / nickel layer. 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 / phosphorus / noble metal layer. The content of 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. Preferably, the substrate has at least one cavity completely or partially enclosed by a net, sieve, filter, fabric or sponge. Examples of such substrates are filter elements, filter cartridges or V-filters.

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 may be used in an application selected from the group of filters, valves, restrictors, radial and / or filter elements, filter screens, V-filters, architecture, decoration, machinery and equipment of the chemical industry, finishing in the electrical industry ,

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

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 / l 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 proved to be particularly efficient when a pH in the range of 4.2 to 4.6, preferably 4.4, is set. 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 boron compound, dimethylaminoborane, diethylaminoborane 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.

If appropriate, the bath also contains at least one complexing agent which is in particular selected from the group consisting of monocarboxylic acids, dicarboxylic acids, hydroxycarboxylic acids, ammonia and alkanolamines. The complexing agent is in a concentration in a range of 1 to 15 g / l in the bath. Complexing agents complex nickel ions and thus prevent excessively high concentrations of free nickel ions. This stabilizes the solution and suppresses the precipitation of, for example, nickel phosphite.

If appropriate, the bath also contains at least one accelerator which is in particular selected from the group comprising 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 / l 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 consisting 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.

The bath usually also contains at least one pH buffer, which is in particular a sodium salt of a complexing agent and / or the associated corresponding acid. The buffer is usually present in a concentration in the range of 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 of sulfuric acid, hydrochloric acid, sodium hydroxide, sodium carbonate and / or ammonia. The pH regulator is advantageously present in a concentration in a range of 1 to 30 g / l in the bath. pH regulators make it possible to readjust the pH of the bath.

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 electroless nickel bath additionally contains 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 / l of silver or silver ions. The silver is preferred to the bath as a solution a silver salt added. It may be necessary to add the solution very slowly.

As the silver salt, silver nitrate, silver acetate or a silver salt of a sulfonic or thiocarboxylic acid such as silver methanesulfonate may be used.

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. The organic sulfur compounds preferred as complexing agents have already been described.

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

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 .-%, deposited.

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 metered addition is controlled by measuring 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 may be formed, for example, by treating the surface with a mixture of inorganic acids, nickel chloride, citric acid and acetic acid while applying a voltage. As a result, the surface is cleaned and at the same time a thin, 10 nm to 1 micron thick nickel layer deposited 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 / l, most preferably between 0.1 and 1 g / l.

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 generally alkali metal or alkaline earth metal salts, for example hydroxides, chlorides, bromides, nitrates, fluoroborates, for example potassium hydroxide, potassium chloride, sodium chloride, lithium chloride, lithium bromide or lithium hexafluoroborate.

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

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 transferred directly from one bath to the other bath.

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 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 galvanic processes.

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, i. 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 below pH 6, preferably between 4.0 and 5.0, more preferably between 4.2 and 4.6.

With the application of the voltage, a layer begins to deposit on the substrate, which majority consists of silver, preferably with a silver content of over 60 wt .-%, more preferably with a silver content of about 80 wt .-%, most preferably from about 90% by weight.

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

It is believed that the first deposited silver-containing nickel layer significantly improves the adhesion of this second layer. At the same time, the better conductivity favors the noble metal-containing nickel layer in combination with the simultaneously 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 cavities which are completely or partially enclosed by such sieve or net surfaces. Due to shielding effects, these substrates can not be evenly coated on the inside with purely galvanic processes. With the method according to the invention it is possible to apply a uniform layer both on the inside and on the outside of the substrate.

Fig. 1

eine schematische Darstellung eines Filterelements;

Fig. 2

eine schematische Darstellung einer bevorzugten Ausführungsform des Verfahrens der Erfindung;

Fig. 3

zeigt einen typischen Aufbau einer erfindungsgemäßen Schicht;

Fig. 4A,B

zeigen lichtmikroskopische Aufnahmen eines unbeschichteten Siebs;

Fig. 5A,B

zeigen lichtmikroskopische Aufnahmen des Siebs aus Fig. 4A, B nach der Beschichtung.

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. In detail shows:

Fig. 1

a schematic representation of a filter element;

Fig. 2

a schematic representation of a preferred embodiment of the method of the invention;

Fig. 3

shows a typical structure of a layer according to the invention;

Fig. 4A, B

show light micrographs of an uncoated screen;

Fig. 5A, B

show light micrographs of the screen Fig. 4A, B after the coating.

FIG. 1 shows a schematic representation of a filter element which can be coated by the method according to the invention, 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 is a cylinder 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 have fastening means for seals. Together with the caps 12, the filter body encloses a cavity. With the method according to the invention it is possible to provide the filter body on the inside and on the outside with a uniform, tribologically stable coating. 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 Material designation 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 metal / noble metal layer, wherein the layer has a noble metal content 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). This bath is - as already described - a bath for electroless deposition of a metal layer, which also contains precious 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 μm, preferably up to 1 μm, is obtained.

In a preferred embodiment, the metal layer is a nickel / phosphorus layer and the noble metal is silver. With the experience according to the invention, it is thus possible to obtain layers which consist of a nickel / phosphorus / silver layer and thereon a silver / nickel / phosphorus layer, in each case ordered 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 much 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 substrate coated in this way with at least two layers shows a particularly high tribological stability and is very well suited for filter elements in fluids, for example in cooling water circuits.

FIG. 3 shows a construction of a preferred embodiment of the invention. On a substrate (34) is a chemical nickel / phosphorus / silver layer (32) with a silver content of <10 wt .-% with a thickness between 0.5 and 15 microns arranged. On it is a silver / nickel / phosphor cover layer with a silver content of> 90 wt .-% and a thickness between 0.1 .mu.m and 1 .mu.m.

FIG. 4 shows shots of an uncoated screen / filter element as in FIG. 1 shown in different magnification. The scale is 200 μm in each case. The thickness of the horizontal wires is about 150 μm and 160 μm. The measured mesh sizes are between 85 μm and 143 μm.

FIG. 5 shows light micrographs of the same screen / filter element FIG. 4 after application of a coating according to the invention with a nickel / silver and a silver / nickel layer, as in FIG. 3 shown. The scale is 200 μm in each case. The thickness of the horizontal wires is now about 160 microns and 170 microns. The measured mesh sizes are between 40 μm and 120 μm. It can be seen clearly a uniform coating of the substrate. When used in cooling circuits over several weeks, such coated filters show a biocidal effect, without the coating detaching.

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

To a above-described electroless nickel bath is added silver in the form of silver methanesulfonate corresponding to a silver content of 0.025 g / l and an acid-resistant silver complexing agent (eg, Slotoloy SNA 33, manufactured by Schlötter) in an amount corresponding to 0.2 ml / l. 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 compensated by continuous addition of silver methanesulfonate. 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 increased further. 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 A1 of noble metal and noble metal content of the layer for silver are not possible in this way. The thus coated substrate was then provided with a silver / nickel layer according to the following specifications.

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, manufactured by Schlötter) in the amount corresponding to 4 ml / l to the bath and a commercial Galvanic silver approach salt, only the conductive salt, (eg Arguna CF, Umicore) according to an amount of conductive salt in the bath of 0.65 g / l 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 current density of the auxiliary field is between 0.1 and 1 A / dm ² . This is a significantly lower current density than conventional galvanic silver depositions. 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 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.

reference numeral

10

filter body

12

caps

200

Pretreatment of the substrate surface

210

Insert in a first bath

220

Electroless deposition in the first bath

230

Insert in a second bath

240

Stress-controlled deposition in the second bath

30

Ag-Ni-coating layer

32

NiP-Ag alloy

34

substratum

quoted literature

DE

10 2006 020 988 A1

GB

1 222 969

WHERE

01/92606 A1

EP

1 285 104 B1

Claims (14)

1. A method for depositing metal layers on a substrate, comprising the following steps:

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

   b) introducing the substrate into the first bath;

   c) currentless deposition of metal and noble metal ions from the first bath onto the substrate to form a first metal/noble metal layer having a noble metal content of up to 30 wt.-%;

   d) then introducing the substrate into a second bath for the currentless deposition of a metal layer, which additionally contains at least one type of noble metal ions, or leaving the substrate in the first bath;

   e) then applying a voltage between an anode, which is immersed in the bath, and the substrate, which is connected as a cathode; and

   f) galvanic deposition of a second noble metal/metal layer on the first layer on the substrate, wherein the second noble metal/metal layer has a noble metal content of greater than 60 wt.-%.
2. The method as claimed in the preceding claim, characterized in that
   at least one of the baths for the currentless deposition of a metal layer is a bath for the deposition of an electroless nickel layer.
3. The method as claimed in either of the preceding claims, characterized in that
   the noble metal ions are selected from the group containing silver, gold, palladium, platinum, rhodium, and copper.
4. The method as claimed in 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 as claimed in any one of the preceding claims, characterized in that
   at least one of the baths also contains at least one complexing agent for the noble metal ions.
6. The method as claimed in 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 as claimed in any one of the preceding claims, characterized in that
   a voltage is applied corresponding to a current density between 0.01 and 3 A/dm².
8. The method as claimed in any one of the preceding claims, characterized in that
   the first bath for the currentless deposition of a metal layer is a bath for the deposition of an electroless nickel layer.
9. The method as claimed in claim 8, characterized in that
   the noble metal in both layers is silver.
10. A coating on a substrate, characterized in that
    the coating has a noble metal/nickel/phosphorus layer or a noble metal/nickel/boron layer at the surface, which has a noble metal content of greater than 90 wt.-%.
11. The coating as claimed in claim 10, characterized in that
    the noble metal is silver.
12. A coated substrate obtained by a method as claimed in claims 1 to 9.
13. The coated substrate as claimed in any one of claims 10, 11 or 12, characterized in that
    the substrate is a net, sieve, filter, fabric, or sponge.
14. A use of a coated substrate as claimed in any one of claims 10 to 13

    - in the automotive field, in the sanitary field, in the jewelry field, in the drinking water field or drinking water treatment, for wastewater treatment, for filtering fluids, in cooling water circuits, in chemical plant construction, or in electrical engineering.

Images