RS20240060A1 - Composite material consisting of substrate with adhesion-promoting copper layer and chromium-containing top layer, and method for producing same - Google Patents

Abstract

The invention relates to a composite material having a chromium-containing top layer, comprising an adhesion-promoting layer located on a substrate and a chromium-containing top layer located on the adhesion-promoting layer, wherein: - the substrate consists of a material selected from the group comprising copper, nickel-free copper alloys, plastics material coated with copper, steel coated with copper and diecast zinc products coated with copper; - the adhesion-promoting layer contains at least 99.9 wt.% copper; and - the adhesion-promoting layer is located directly on the substrate and the top layer is located directly on the side of the adhesion-promoting layer that is remote from the substrate.

Description

COMPOSITE MATERIAL CONSISTING OF SUBSTRATE

WITH A COPPER LAYER THAT PROMOTES ADHESION AND A TOP LAYER THAT

CONTAINS CHROME AND THE PROCEDURE FOR OBTAINING IT

The subject invention relates to a composite material with an upper layer containing chromium, a process for obtaining it as well as for its application, especially in the field of sanitary ware and/or as a component that conducts water.

Fittings and other components are often installed in the sanitary area, which are chrome-plated to achieve good resistance to corrosion and wear. For better adhesion as well as for the attractive shine of chrome, it is applied in the state of the art to the bottom layer with nickel or nickel, which improves adhesion.

Nickel has been known for decades to cause unwanted reactions on the skin, and in Europe it is one of the most common contact allergens. The sale of items that have a nickel-containing coating is therefore only allowed if strict requirements are followed.

In the usual galvanic coating of brass fittings with nickel and subsequent deposition of chromium from the electrolyte, which contains chromium(VI) compounds, nickel is also deposited in the area of the opening in the interior of the fittings due to the good ability of applying the electrolyte. These nickel layers are not completely covered by subsequent chromium plating with hexavalent chromium. In contact with drinking water, due to the potential difference between the chromium oxide layer and the nickel layer, the nickel dissolves, which can therefore get into the drinking water. When drinking water stagnates, nickel contents are measured, which are significantly above the limit values contained in the Rulebook on drinking water from June 19, 2020. In fact, the nickel limit value of 10 µg nickel per rebar was exceeded by most rebars in the dynamic drilling test according to DIN 16058.

In addition to being released from water-conducting components, nickel can also be released from the lower layers of other chrome-plated items that contain nickel and act as a contact allergen, especially from consumable items that come into contact with the human body or foodstuffs, such as parts of a ballpoint pen, grill grates or bread baskets. Especially in contact with sweat, an increased release of nickel is observed here.

In the prior art, in order to prevent the release of nickel into the drinking water from the fittings that conduct water, the openings in the fittings are closed or supplied with plastic hoses. Mechanical removal of the applied nickel layer as well as removal of the nickel layer by pickling and application of a non-conductive top layer are known solutions in the state of the art to prevent release in the area of drinking water conduction.

A common alternative to the nickel underlayer in the jewelry and clothing industry is a white bronze alloy layer, which contains copper and tin alloy components. The disadvantage of this coating, however, is that it has so far been deposited from cyanide electrolytes and that leveling and degree of gloss are limited. Chrome plating in a chrome bath, which contains chromium(VI) compounds, often has disadvantages.

WO 2013/164165 A1 describes composite materials with a chromium top layer, which do not have a nickel bottom layer. The upper chromium layer is deposited from the electrolyte, which contains hexavalent chromium. Three additional layers are placed between the top layer of chromium and the substrate, namely a first layer on the substrate containing copper, a layer of copper, tin and/or zinc alloy located above this layer and above this layer a third layer containing chromium, copper, gold, palladium or iron.

DE 102005041375 A1 describes a process for obtaining decorative surface structures on objects, especially sanitary objects such as fittings and showers, preferably using an intermediate layer containing nickel. In the process, decorative surfaces on objects are obtained, for example, by partially removing the metal coating. The disadvantage of this procedure is that the deposition is carried out in extremely toxic, cyanide electrolytes.

Invention task

The task of the present invention is to provide an alternative composite material, which overcomes the aforementioned disadvantages known in the state of the art and is characterized by a simple structure with few layers. Preferably, the composite material according to the invention should be characterized by good corrosion properties and an attractive gloss of the chromium-containing top layer. Furthermore, an ecologically acceptable and health-safe procedure for the production of composite material should be provided.

General description of the invention

The invention solves this task with the features of the claim and in particular with a composite material with a top layer containing chromium, which includes an adhesion-promoting layer placed on the substrate and a top layer containing chromium, placed on the adhesion-promoting layer, wherein

- the substrate consists of a material selected from the group consisting of copper, nickel-free copper alloys, copper-plated plastic, copper-plated steel and copper-plated zinc die-cast products;

- the adhesion-enhancing layer contains at least 99.9 wt. % of copper; and

- the adhesion-promoting layer is placed directly on the substrate and the top layer is placed directly on the side of the adhesion-promoting layer that lies against the substrate.

According to the invention, the composite material is completely nickel-free, so nickel is not contained either in the adhesion-enhancing layer or in the top layer containing chromium. It is very surprising that it is possible to completely omit nickel in the lower layer below the upper chromium-containing layer, since nickel is known in the prior art to serve in the lower layer to provide scratch and wear resistance of the overlying chromium-containing layer, as well as to provide the shine typical of chrome coatings. From the state of the art known composite materials with a top layer of chrome, which are completely nickel-free, the lack of scratch and wear resistance as well as the shine associated with the absence of nickel must be compensated by a complex production process, which leads to a multi-layer composite material. The composite material according to the invention, in contrast, requires only two layers on the substrate and at the same time has good corrosion properties as well as a gloss that is indistinguishable from conventional chrome coatings with a nickel underlayer.

The excellent characteristics of the composite material according to the invention are achieved in particular by placing a layer directly below the upper layer, which contains chromium, which promotes adhesion, which is 99.9 wt. %, and preferably 100 wt. % of copper. Copper is a metal, which is anyway contained in the substrate according to the invention, which consists of copper, nickel-free copper alloy, copper-clad plastic, copper-clad steel or copper-clad zinc die-cast product. According to the invention, both the substrate and the layer that improves adhesion, as well as the top layer, which contains chromium, are nickel-free, so that there is no danger of increased, and therefore unacceptable, release of nickel from the composite material, and especially with components that conduct water, there is no fear of release of nickel into drinking water. The composite material according to the invention therefore meets the requirements in accordance with . § 17 paragraph 2 of the Rulebook on drinking water (TrinkwV 2001), or the composite material according to the invention is below the maximum permissible values specified in this regulation.

In addition, the composite material according to the invention has excellent corrosion stability, because in the dynamic drilling test according to DIN EN 16058 in water obtained after 4 hours of stagnation, it shows a release of copper below 0.4 mg/l, a release of chromium below 0.2 mg/l, a release of nickel below 0.1 mh/l, a release of zinc below 5 mg/l and a release of lead below 4.0 µg/l. More accurate measurement results will be listed below.

The adhesion-promoting layer preferably has a layer thickness of 5-30 µm, especially 10 to 15 µm.

The top layer containing chromium preferably has a layer thickness of 0.1-0.5 µm.

In a preferred embodiment, the composite material according to the invention consists of a substrate, a layer that promotes adhesion and an upper layer containing chromium, wherein the upper layer is optionally passivated.

The invention also relates to the process for obtaining a composite material with an upper layer of chrome, which includes subsequent processes or consists of them:

a) pre-treatment of the substrate to be coated, wherein the substrate consists of a material selected from the group consisting of copper, copper alloys, copper-clad plastic, copper-clad steel and die-cast zinc products;

b) electrolytic deposition of an adhesion-promoting layer on the previously treated substrate to be coated, wherein the adhesion-promoting layer contains at least 99.9 wt. % of copper;

c) electrolytic deposition of the top layer containing chromium directly on the side of the adhesion-promoting layer, which lies against the substrate.

Optionally, the step of pretreating the substrate to be coated comprises one or more steps selected from the group consisting of degreasing, rinsing or removing surface deposits, and activating the surface of the substrate.

The degreasing of the substrate can especially be done with the support of ultrasound and/or at an elevated temperature, preferably for 1-10 minutes. For example, a temperature of 50 to 95 °C, especially 80 to 90 °C, is suitable. A suitable commercial ultrasound-assisted degreaser is the product KASIT US-90 by KIESOW. Instead of with the support of ultrasound or additionally with degreasing with the support of ultrasound, degreasing can be done electrolytically, especially with the movement of the substrate and especially at an elevated temperature, for example at 35 to 70 °C, especially at 40 to 55 °C. A suitable commercial agent for electrolytic degreasing of substrates is the product SURFACLEAN V-149, from the company KIESOW.

An additional preferred step of pretreatment of the substrate to be coated is the removal of the film, which is preferably performed with movement of the substrate and/or at an elevated temperature for 1-10 minutes. Preferably, the temperature during film removal is 50 to 95 °C, especially 70 to 90 °C. A commercial product, which is suitable for removing the film, is the product EKASIT BTU-20, from the company KIESOW.

Another additional step of pretreatment of the substrate to be coated is to activate the surface of the substrate. It is particularly preferably carried out with blowing air and at room temperature, for example for 1 to 5 minutes. A suitable commercial means for activating the surface of the substrate is the product Activator 5, from the company KIESOW.

After each of the aforementioned pretreatment steps, the order of which is variable, a rinsing step is preferably performed, especially with water.

After the pretreatment of the substrate, in the process according to the invention, a layer that promotes adhesion is electrolytically deposited on the pretreated substrate, which consists of at least 99.9 wt. % copper and preferably consists entirely of copper. The deposition of the layer that improves adhesion to the substrate is preferably done from a galvanic sulfuric acid copper electrolyte at a temperature of 25 to 35 °C. The copper electrolyte contains especially 45-50 g/l of copper, 65-75 g/l of sulfuric acid and 80-160 mg/l of chloride. Furthermore, the electrolyte optionally contains additives to improve the grain, to control the leveling, to control the level of gloss and/or to adjust the strength of the adhesion-enhancing layer that is deposited.

The electrolytic deposition of the layer that enhances adhesion to the substrate is preferably carried out with a current density of 0.5 to 5 A/dm<2> for 15 to 30 minutes, during which the substrate moves in the electrolyte. In that period, the substrate is also preferably removed from the electrolyte for a short time and then immersed again.

In this way, the adhesion-enhancing layer is obtained as a high-gloss, nickel-free, light to dark red color, which is characterized not only by a high degree of gloss, but also by a high degree of leveling as well as increased surface hardness. The resulting layer furthermore has a high ductility as well as an extremely uniform layer thickness distribution and thus forms an excellently suitable underlayer for the chromium-containing upper layer.

In the method according to the invention, after the electrolytic deposition of the adhesion-promoting layer on the substrate, the chromium-containing layer is also directly deposited on the side of the adhesion-promoting layer that lies opposite the substrate. The deposition is done from a cyanide-free electrolyte, which contains chromium exclusively in the form of chromium(III) compounds and thus avoids chromium(VI) compounds, which are harmful to health and the environment. The pH-value of the electrolyte is preferably pH 3 to 5. A commercially available product, which can be used as an electrolyte, is the product TRISTAR 330 AF, Coventya, which can optionally be modified, especially by adjusting the desired pH value. Preferably, the deposition of the upper layer containing chromium is carried out at a temperature of approx. 50 to 60 °C and for a duration of approximately 5-20 minutes, preferably for a duration of 7-15 minutes. During the deposition, the substrate, previously coated with a layer that promotes adhesion, is preferably moved and optionally removed from the electrolyte for a short time and subsequently immersed again. Furthermore, the deposition of the upper layer containing chromium is optionally carried out by blowing air.

The upper layer containing chromium obtained in this way, which preferably has a layer thickness of 0.1 to 0.5 µm, is characterized by a very good application on profiled parts, as well as the fact that at higher current densities no burnt deposits occur and the obtained upper layer containing chromium does not contain any "wrinkles" or the like. easily the surface of the upper layer containing chromium does not contain chromium(VI) compounds, optically it corresponds to the surface deposited from the electrolyte with hexavalent chromium compounds.

Optionally, the process according to the invention comprises an additional step of passivating the top layer containing chromium. This is especially done for 1-10 minutes at room temperature or at a slightly elevated temperature, for example at 20-30 °C.

By applying an adhesion-promoting layer to a previously treated substrate and applying a chromium-containing top layer to the adhesion-promoting layer, with subsequent optional passivation of the surface of the chromium-containing top layer, a composite material according to the invention is obtained. It is optionally further cleaned, especially by rinsing and/or ultrasonic treatment in fully deionized water, followed by drying at an elevated temperature (40-90 °C) in oil-free air.

The composite material produced by the process according to the invention is tarnish-resistant and corrosion-resistant in accordance with DIN EN 248 and, due to the lack of nickel content, cannot cause allergies or unwanted skin reactions, which are known for nickel-containing composite materials. In addition, the composite material according to the invention cannot be distinguished in terms of gloss, color and haptic from a classical composite material with a chromium-containing top layer, which contains nickel in a layer located below the chromium-containing top layer and in which the chromium contained in the top layer is precipitated from an electrolyte containing chromium (VI) compounds.

Detailed description of the invention

The invention will now be described in more detail on the basis of exemplary embodiments and with reference to the figures of which

- Figure 1 shows a diagram of copper concentration in standing water from fittings coated according to the process according to the invention

- Figure 2 shows a diagram of chromium concentration in standing water from fittings coated according to the process according to the invention

- Figure 3 shows a diagram of nickel concentration in stagnant water from armatures coated according to the method according to the invention

- Figure 4 shows a diagram of zinc concentration in standing water from armatures coated according to the method according to the invention, i

- Figure 5 shows a diagram of lead concentration in standing water from fittings coated according to the method according to the invention

Example 1: Coating angle valves according to the method according to the invention and testing the coated angle valves in the dynamic drilling test according to DIN EN 16058

To compare the optical characteristics of conventional chromium-plated objects with a lower layer containing nickel and an upper layer of chromium, which is deposited from an electrolyte containing chromium (VI) compounds, and the characteristics of objects chromed according to the invention without a lower layer containing nickel and with an upper layer of chromium, which is deposited from an electrolyte containing chromium(III) compounds, 3 brass angle valves were chrome-plated using the usual method, and three brass angle valves were chrome-plated. by the method according to the invention.

Corner valves are valves that are installed under the sink and are used to shut off the water supply.

According to both procedures, the finished coated angle and valves are placed next to each other and subjected to an optical examination, during which no differences were found. All samples had a flawless, smooth surface with an identical gloss.

Three angle valves chromed according to the invention were then subjected to a dynamic drilling test according to DIN EN 16058 in order to test their corrosion resistance. For this purpose, for 14 weeks, at weekly intervals, water was released into the corner valves for a duration of four hours. This so-called the stagnant water was then tested for its copper, chromium, nickel, zinc and lead content. The results are given in figures 1 to 5, wherein the angle valves chromed according to the process of the invention are listed as samples 1 to 3. Each diagram also contains the results for a blank test, in which the water without previous stagnation was tested for its metal content in order to avoid contamination of the test water with said metals.

On the diagram shown in figure one, it can be seen that the concentration of copper in the stagnant water in the first 8 weeks on average increased slightly, and in the last weeks of the observed time period it was approximately 0.15 mg/L. In accordance with the regulation on drinking water, the permissible limit value of copper in drinking water is 2 mg/l, which, however, was much lower in all three samples during the entire observation period. Even the concentration of 0.2 mg/l was exceeded in one sample in the meantime and only for about 4 weeks, so only a little copper from the samples got into the solution.

In the diagram shown in Figure 2, it can be seen that the concentration of chromium in the standing water was Omg/I almost during the entire time observed, so that no or almost no chromium reaches the solution from the valves coated according to the invention.

On the diagram shown in Fig.3, it can be seen that the concentration of nickel in stagnant water in the first 8 weeks on average increased slightly, and in the last weeks of the observed period it amounted to 7.0 µg/l. In accordance with the Rulebook on drinking water, the permissible limit value of nickel in drinking water is 0.1 mg/l, which was much lower in all three samples during the entire observation period. That nickel was present in the stagnant water at all was because the base body (substrate, which is coated according to the invention) used for the angle valves consisted of brass. Brass is a recyclable material, which therefore also contains traces of nickel. Over time, it dissolves in water, which can explain the nickel content found in stagnant water. With the coating according to the invention, there can be no additional loading of drinking water with nickel, because it is completely nickel-free.

In the diagram shown in the figure, it can be seen that the concentration of zinc in standing water in the first 8 weeks on average increased slightly, and in the last week of the observed period it decreased again, to stay at 2.5 mg/l. Since the coated substrate (angle valve) was a brass substrate, which is an alloy with copper and zinc as the main components, the zinc found in the stagnant water came from the brass substrate. Admittedly, zinc is completely harmless in the concentrations in which it is found, which is why the Rulebook on drinking water does not contain limit values for zinc in drinking water.

On the diagram shown in Figure 5, it can be seen that the concentration of lead in stagnant water in the first 6 weeks on average grew slightly and in the last weeks of the observed period amounted to approx. 3.0 µg/l. The lead found in standing water also comes from the brass substrate because brass contains lead for better machinability.

For the sake of completeness, it should be noted that the dynamic drilling test at the time of submission of the application had not yet been completed, as it was planned for a period of 26 weeks, and at the time of submission of the application, the results for weeks 1-14 were only available.

All in all, it can be said that the concentration of metals in drinking water is not increased by the coating process according to the invention, or does not increase significantly. The content of copper released from the adhesion-promoting layer and the brass substrate lies far below the prescribed limit value. No resp. is released from the upper layer containing chromium. almost no chromium, and the other released metals come exclusively from the brass substrate, whereby all the limit values of the Drinking Water Regulations regarding different metals are met here as well. they are far below them.

Thus, the coating process according to the invention can produce a composite material, which optically corresponds to the conventionally coated composite material (with a lower layer of nickel and an upper layer of chromium deposited from a hexavalent chromium electrolyte) but, unlike it, does not exceed the limit values prescribed by the Drinking Water Regulations, especially for the concentration of nickel in drinking water.

Example 2: Testing of coupling sleeves for water meters coated according to the invention

According to the method according to the invention for obtaining a composite material with an upper layer containing chromium, 20 base bodies of connecting bushings made of brass are subsequently coated without nickel and chromed. From the composite materials obtained in this way, ten samples were subjected to a test in a condensation atmosphere, and ten additional samples were subjected to a neutral salt water spray test.

The test in a condensation atmosphere according to DIN EN ISO 6270-2 is a reliable test procedure in coating technology and serves to clarify the behavior of coated samples in a humid environment. In this test, demineralized water was heated to 40°C and evaporated so that 100% condensed moisture was obtained in the test space, and water vapor was condensed on 10 samples. After 48 hours, the surface of the samples was examined in detail. At the same time, it turned out that no change on the surface could be determined. All samples were completely free of pores, swelling, cracks and deposits of corrosion products. Separation of the isthmus was not established either.

The salt water spray test according to DIN EN ISO 9227 can essentially determine the corrosion resistance of the material or the protective layer on it.

During the test, ten samples were kept in a chamber for 48 hours, in which a 5% NaCI solution with a neutral pH value was continuously sprayed in the form of a mist at a temperature of 35 °C. This mist settled on the samples and covered them with a corrosive film of salt water.

After completing the salt water spray test, the samples were washed with deionized water, and the surface of the samples was inspected. It was found that individual samples had milk stains, which could be wiped off without leaving any residue. No sample showed any pores, swelling, or cracks in the coating. Separation of the isthmus was not established either.

The features of the invention mentioned in the previous description, in the pictures, as well as in the claims can be both individually and in arbitrary combinations, significant for the realization of the invention in its various forms of execution.

Claims (14)

PATENT REQUESTS 1. A composite material with a chromium-containing top layer, comprising an adhesion-promoting layer placed on the substrate and a chromium-containing top layer placed on the adhesion-promoting layer, wherein - the substrate consists of a material selected from the group consisting of copper, nickel-free copper alloys, copper-plated plastic, copper-plated steel, and copper-plated zinc die-casting products; - the adhesion-enhancing layer contains at least 99.9 wt. % of copper; and - the adhesion-promoting layer is placed directly on the substrate, and the upper layer is placed directly on the side of the adhesion-promoting layer, which lies against the substrate, 2. Composite material according to claim 1, characterized in that it consists of a substrate, an adhesion-enhancing layer and an upper layer, wherein the upper layer is optionally passivated. 3. Composite material according to one of claims 1 or 2, characterized in that the adhesion-promoting layer consists exclusively of copper. 4. Composite material according to one of the previous claims, characterized in that the layer that promotes adhesion has a layer thickness of 5 to 30 µm. 5. Composite material according to one of the preceding claims characterized in that the upper layer containing chromium has a layer thickness of 0.1 to 0.5 µm. 6. Composite material according to one of the previous requirements, characterized by the fact that during the dynamic drilling test according to DIN 16058 in standing water obtained after more than 4 hours, it shows a release of copper below 0.4 mg/l, a release of chromium below 0.2 mg/l, a release of nickel below 0.1 mg/l, a release of zinc below 5 mg/l and a release of lead below 4.0 µg/l. 7. Composite material according to one of the previous requirements, indicated by the fact that it corresponds to the requirements in accordance with § 17 paragraph 2 of the Ordinance on drinking water (TrinkwV 2001). 8. Composite material according to one of the previous requirements, characterized by being resistant to corrosion in accordance with DIN EN 248. 9. A process for obtaining a composite material with an upper layer containing chromium, which includes the following steps: a) pre-treatment of the substrate to be coated, wherein the substrate consists of a material selected from the group consisting of copper, copper alloys, copper-coated plastic, copper-coated steel and copper-coated zinc die-cast products; b) electrolytic deposition of the adhesion-promoting layer on the pretreated substrate to be coated, wherein the adhesion-promoting layer contains at least 99.9 wt. % of copper; s) electrolytic deposition of the upper layer containing chromium directly on the side of the adhesion-promoting layer, which lies against the substrate, whereby the deposition of the upper layer containing chromium is carried out from the electrolyte, which contains chromium exclusively in the form of chromium(III) compounds. 10. The method according to claim 9, characterized in that the electrolytic deposition of the adhesion-enhancing layer is performed with a current density of 0.5 to 5 A/dm<2> for a duration of 15 to 30 minutes. 11. The method according to one of claims 8 or 9, characterized in that the step of pretreatment of the substrate to be coated comprises one or more steps, selected from the group comprising degreasing, washing or removing surface deposits and activating the surface of the substrate. 12. The method according to one of the previous claims, characterized in that the deposition of the layer that promotes adhesion on the pretreated substrate at a temperature of 25-35 °C is carried out from a sulfuric acid electrolyte containing copper. 13. The method according to one of the previous claims characterized in that after the deposition of the upper layer containing chromium on the layer that promotes adhesion, the passivation of the upper layer containing chromium is performed. 14. Use of a composite material with a chromium-containing top layer according to one of claims 1 to 8 in the field of sanitation and/or as a component that conducts drinking water. AMENDED PATENT CLAIMS FOR THE NATIONAL PHASE 1. A composite material with a chromium-containing top layer, comprising an adhesion-promoting layer placed on the substrate and a chromium-containing top layer placed on the adhesion-promoting layer, wherein - the substrate consists of a material selected from the group consisting of copper, nickel-free copper alloys, copper-plated plastic, copper-plated steel, and copper-plated zinc die-casting products; - the adhesion-enhancing layer contains at least 99.9 wt. % of copper; and - the adhesion-promoting layer is placed directly on the substrate, and the upper layer is placed directly on the side of the adhesion-promoting layer, which lies against the substrate, characterized in that the upper chromium-containing layer has a layer thickness of 0.1 to 0.5 µm. 2. Composite material according to claim 1, characterized in that it consists of a substrate, an adhesion-enhancing layer and an upper layer, wherein the upper layer is optionally passivated. 3. Composite material according to one of claims 1 or 2, characterized in that the adhesion-promoting layer consists exclusively of copper. 4. Composite material according to one of the previous claims, characterized in that the layer that promotes adhesion has a layer thickness of 5 to 30 µm. 5. Composite material according to one of the previous requirements, characterized by the fact that during the dynamic drilling test according to DIN 16058 in standing water obtained after more than 4 hours, it shows a release of copper below 0.4 mg/l, a release of chromium below 0.2 mg/l, a release of nickel below 0.1 mg/l, a release of zinc below 5 mg/l and a release of lead below 4.0 µg/l. 6. Composite material according to one of the previous requirements, indicated by the fact that it corresponds to the requirements in accordance with § 17 paragraph 2 of the Ordinance on drinking water (TrinkwV 2001). 7. Composite material according to one of the previous requirements, characterized by being resistant to corrosion in accordance with DIN EN 248. 8. Process for obtaining a composite material with an upper layer containing chromium, which includes the following steps: a) pre-treatment of the substrate to be coated, wherein the substrate consists of a material selected from the group consisting of copper, copper alloys, copper-coated plastic, copper-coated steel and copper-coated zinc die-cast products; b) electrolytic deposition of the adhesion-promoting layer on the pretreated substrate to be coated, wherein the adhesion-promoting layer contains at least 99.9 wt. % of copper; s) electrolytic deposition of the upper layer containing chromium directly on the side of the adhesion-promoting layer, which lies opposite the substrate, wherein the deposition of the upper layer containing chromium is carried out from the electrolyte, which contains chromium exclusively in the form of the chromium(III) compound, and wherein the upper layer containing chromium has a layer thickness of 0.1 to 0.5 pm. 9. The method according to claim 8, characterized in that the electrolytic deposition of the layer that promotes adhesion is performed with a current density of 0.5 to 5 A/dm<2> for a duration of 15 to 30 minutes. 10. The method according to one of claims 8 or 9, characterized in that the step of pretreatment of the substrate to be coated comprises one or more steps, selected from the group comprising degreasing, washing or removing surface deposits and activating the surface of the substrate. 11. The method according to one of the previous claims, characterized in that the deposition of the layer that promotes adhesion on the pretreated substrate at a temperature of 25-35 °C is carried out from a sulfuric acid electrolyte containing copper. 12. The method according to one of the previous claims characterized in that after the deposition of the upper layer containing chromium on the layer that promotes adhesion, the passivation of the upper layer containing chromium is performed. 13. Use of a composite material with a chromium-containing top layer according to one of claims 1 to 7 in the field of sanitation and/or as a component that conducts drinking water.