FR2766212A1 - Protective coating of decorative or functional metal article - Google Patents

Abstract

A surface treatment process for a decorative or functional metal article (10), especially of brass, bronze, aluminium (alloy), carbon steel, stainless steel, cast zinc or similar corrosion sensitive metal, involves depositing an intermediate layer (11) of corrosion resistant and biocompatible material prior to depositing a thin finish coating (12) for imparting predetermined aesthetic and/or functional properties. Preferably, the intermediate layer (11) consists of or includes a plated or vacuum deposited silver (alloy) layer. Also claimed is a decorative or functional metal article obtained by the above process.

Description

PROCESS FOR TREATING THE SURFACE OF A DECORATIVE OBJECT
OR FUNCTIONAL AND DECORATIVE OR FUNCTIONAL OBJECT REALIZED
ACCORDING TO THIS PROCESS
The present invention relates to a method of treating the surface of a decorative or functional object comprising a substrate made of a metallic material, in particular brass, bronze, aluminum or aluminum-based alloys, carbon steel, made of stainless steel, cast iron or the like, susceptible to corrosion, in which is deposited on said substrate at least one thin layer of a finishing coating conferring on said decorative or functional object predetermined aesthetic and / or functional characteristics.

It also relates to a decorative or functional object produced by this process and comprising a substrate made of a metallic material, in particular brass, bronze, aluminum or aluminum-based alloys, carbon steel, stainless steel, cast iron or the like, sensitive to corrosion, and at least one thin layer of a finishing coating deposited on said substrate and giving the decorative or functional object predetermined aesthetic and / or functional characteristics.

Many decorative or functional objects are made using materials such as brass, bronzes, aluminum or its alloys, zinc cast irons, carbon steels or stainless steels.

These substrates are sensitive to corrosion, and in order to meet the requirements required in their field of application, requirements which may be mechanical, electrical, optical or chemical, they are covered with metallic, or ceramic-type, hard coatings deposited by sputtering. . However, these thin thin coatings offer insufficient corrosion protection due to the conditions of growth of the layers. Indeed, for hard coatings deposited at low temperature (below 300oC), the germination and growth conditions of the layers result in a columnar structure perpendicular to the surface, which is generally not very dense and which presents important separations between the columns.

To overcome this drawback, the application of an galvanic intermediate layer of nickel or its alloys is often resorted to in order to constitute an effective barrier against corrosion. This metal, which is frequently used for decorative applications in watchmaking, jewelry or eyewear, for example, can cause allergic reactions in some individuals when these objects are in contact with the body.

The present invention proposes to overcome the drawbacks of known methods and to offer a method eliminating the risks of causing allergies in certain people sensitive to contact with objects having an undercoat made of nickel or its alloys to provide protection. of these objects against corrosion.

For this purpose, the process according to the invention is characterized in that at least one intermediate layer of a corrosion-resistant material having the following properties is deposited on the substrate, prior to the deposition of said thin layer of the finishing coating. bio-compatibility properties.

According to a preferred embodiment, said material of said intermediate layer is silver or one of its alloys.

According to a first embodiment, the deposition of said intermediate layer is carried out chemically or electrochemically from an electrolytic solution for galvanic application composed of the following substances. silver nitrate, silver fluoride, silver fluoborate, silver iodide, silver thiosulfate, silver pyrophosphate, silver succinimide, thiourea, or double silver and potassium cyanide.

According to a second embodiment, the deposition of said intermediate layer is carried out by vacuum deposition.

Preferably, said material of said intermediate layer is a silver alloy with at least one of the following elements: copper, tin, antimony, zinc, lead, bismuth, arsenic, germanium, indium, gold, palladium, platinum.

In an alternative embodiment, the intermediate layer is formed of several layers, at least one layer of which is made of silver or a silver alloy.

In this variant, it is possible to deposit on said substrate and under the silver layer a matt, semi-matt or shiny sublayer of copper or its alloys or zinc alloys and on said silver layer a layer of a precious metal chosen from the following metals: palladium, gold, platinum, rhodium Said layers can be deposited chemically or electrochemically.

In all the variants, when said intermediate layer is obtained by chemical or electrochemical route it preferably has a thickness of between 1 and 50 micrometers and, when it is obtained by vacuum deposition, it preferably has a thickness of between 0 , 5 and 10 micrometers.

Advantageously, at least one layer of a material chosen from the following group of materials, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, aluminum, is deposited on said intermediate layer.

It is also possible to deposit on said intermediate layer at least one layer of a material chosen from the following group of materials: titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, aluminum, to which is added to the at least one of the elements chosen from the group of the following elements: carbon, nitrogen, oxygen, boron, silicon, fluorine, chlorine, sulfur, phosphorus.

Said layer deposited on said intermediate layer preferably has a thickness of between 0.1 and 10 micrometers.

The decorative or functional object according to the invention is characterized in that it further comprises, at least one intermediate layer of a material resistant to corrosion and having bio-compatibility properties disposed under the deposition of said thin layer of the finish coating.

According to a preferred embodiment, said material of said intermediate layer is silver or one of its alloys.

Said material of said intermediate layer is advantageously an alloy of silver with at least one of the following elements: copper, tin, antimony, zinc, lead, bismuth, arsenic, germanium, indium, gold, palladium, platinum with a title of money between 500 and 1000/00.

In an alternative embodiment, the intermediate layer comprises several layers, at least one layer of which is made of silver or a silver alloy.

Said intermediate layer preferably has a thickness between 1 and 50 micrometers, when it is deposited chemically or electrochemically, and between 0.5 and 10 micrometers when it is deposited under vacuum.

When the intermediate layer is formed of several layers, the object according to the invention advantageously comprises, between said substrate and the silver layer, a mat, semi-mat or shiny sublayer of copper or its alloys or tin alloys and on said silver layer a layer of a precious metal chosen from the following metals: palladium, gold, platinum, rhodium.

In all embodiments, the object according to the invention comprises on said intermediate layer at least one layer of a material chosen from the following group of materials: titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum , tungsten, aluminum.

 It can also include on said intermediate layer at least one layer of a material chosen from the following group of materials: titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten to which at least one of the elements has been added. chosen from the group of the following elements: carbon, nitrogen, oxygen, boron, silicon, fluorine, chlorine, sulfur, phosphorus.

Said layer deposited on said intermediate layer preferably has a thickness of between 0.1 and 10 micrometers.

The present invention will be better understood with reference to the description of nonlimiting examples of decorative or functional objects obtained with the method of the invention, and to the accompanying drawings in which FIG. 1 represents a cross-sectional view of a first embodiment of an object according to the invention, FIG. 2 represents a cross-sectional view of a second embodiment of an object according to the invention, and FIG. 3 represents a cross-sectional view of a third embodiment of an object according to the invention.

The first step of the process, which consists in depositing the intermediate layer on the metal substrate to protect it from corrosion, can be carried out by two known routes which are the chemical or electrochemical route or the physical deposition under vacuum in the gas phase. (commonly called PVD) or chemical in the gas phase (commonly called
CVD). This intermediate layer may, depending on the substrate used, consist of one to three metals which are silver or one of its alloys, which must be present in all combinations, associated with copper or palladium, the copper possibly being replaced by one of its alloys and palladium by another precious metal. The variants used are chosen according to the nature of the substrate on which they are to be deposited and the final surface condition desired for the object formed by said substrate.

When the deposition is carried out chemically or electrochemically, it is necessary to properly prepare the parts to be treated in order to obtain good adhesion of the deposited layer and a uniform appearance of the deposit. For example, to obtain a "glossy mirror" finish, you must first polish the part. On the other hand, on matt surfaces, the deposit will have a satin or semi-gloss appearance.

The preparation, which aims to rid the surface to be treated of all soils, greases, oxides or the like, generally comprises the following phases - chemical degreasing with or without ultrasound, - one or more pickling in an acid medium to remove the oxides, - cathode electrolytic degreasing.

After these various operations, if the intermediate layer comprises only one layer, the silver layer or one of its alloys is deposited by electroplating from an electrolytic solution composed of silver nitrate, or silver fluoride, silver fluoborate, silver iodide, silver thiosulfate, silver pyrophosphate, silver succinimide, thiourea, or double silver cyanide and potassium .

The thickness of the layer deposited by this electrochemical process varies between 1 and 50 micrometers depending on the nature and use of the object.

The silver alloys which can be used are preferably alloys with copper, tin, antimony, zinc, lead, bismuth, arsenic, germanium, indium, gold, palladium, platinum in which the titer of the silver is between 500 and 10 000/10.

With certain substrates, before depositing said silver layer, said substrate is coated with one or more sublayers of a metal such as copper, zinc, gold or the like also by galvanic deposition. Thus, for example, for a ferrous substrate, after degreasing and pickling, a copper sublayer is generally deposited from an alkaline or cyanide bath, for a stainless steel substrate the deposited sublayer is gold from a potassium auricyanide bath, and for an aluminum substrate, two sub-layers are deposited, the first being zinc from a sodium zincate bath and the second from copper from an alkaline cyanide bath.

Depending on the desired final appearance of the treated surface, the silver layer deposited on this sublayer can also be covered with a layer of a precious metal such as palladium, gold, platinum or rhodium.

The silver layer deposited on the sublayers is generally cathodic with respect to said sublayers and resists in particular oxygen, nitrogen, hydrogen, carbon monoxide, ammonia dry, halogens (the formation of insoluble halides protects the metal from further attack), acids such as hydrofluoric acid, organic acids, dilute acids, hot or cold and alkalis.

The deposition of the silver layer and of the layers which can constitute the intermediate layer can also be carried out by physical or chemical techniques of vacuum deposition in the gas phase, for example by sputtering, by vacuum evaporation or by ion spraying. These techniques make it possible to obtain thinner layers, the thickness of which can vary between 0.5 and 10 micrometers.

When the deposits are made by this route, in order to obtain good adhesion and a uniform appearance of the deposited layers, the substrates to be covered must, as for a galvanic deposit, be prepared correctly. This preparation of the surface to be treated generally comprises the following phases:
- chemical degreasing with or without ultrasound,
- pickling by ion bombardment under vacuum.

The second step of the process consists in depositing on said intermediate layer one or more so-called finishing layers of a metal or a ceramic intended to ensure good resistance of the coating to abrasion and tarnishing caused by sulfides of the atmosphere. The metal layer, which must be thin, is deposited by the vacuum deposition techniques already mentioned. The metals used depending on the desired surface condition are, for example, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten and aluminum.

This metallic layer, the thickness of which can vary between 0.1 and 10 micrometers, can also be covered with a coating of a ceramic material obtained from a metal such as, for example, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten and aluminum to which at least one element is added such as, for example, carbon, nitrogen, oxygen, boron, silicon, fluorine, chlorine, sulfur or phosphorus.

This process makes it possible to confer on the surface of objects intended mainly for the fields of jewelry, watchmaking and eyewear, and whose appearance is important, aesthetic and functional properties that the basic material does not have in which the object is made of, eliminating allergy problems linked to the use of nickel or its alloys.

FIG. 1 represents a view in partial section of an object whose surface is coated with a multilayer deposit according to the method described above. The object, consisting of a brass substrate 10, is first of all degreased and pickled, then it is immersed in a solution of potassium cyanide having a concentration of 20 g / l. It is then pre-silvered for thirty seconds in a bath at room temperature containing double cyanide of silver and potassium at the rate of 2.0 g / l, potassium cyanide at the rate of 80.0 g / l, potassium carbonate at a rate of 15.0 g / l and whose anodes are made of stainless steel, then coated with an intermediate layer II in silver with a thickness of 5 micrometers deposited by electroplating from a bath at a temperature of 20 " C containing respectively: - silver at a rate of 30.0 g / l, either silver cyanide at a rate of 37.5 g / l or double silver cyanide at a rate of 55.5 g / l, - "free" potassium cyanide at a rate of 60.0 g / l, - potassium carbonate at a rate of 10.0 g / l, - brighteners based on selenium salts at a rate of 1.0 g / l , - codeposition additives based on antimony salts at a rate of 3.0 g / l, and the anodes of which are made of pure silver.

This intermediate layer 11 is then covered by a finishing layer 12 made of titanium intended to give the object its final aesthetic appearance and sufficient resistance to abrasion. This layer, the thickness of which can vary between 0.1 and 10 micrometers depending on the use of the object, is deposited by a physical gas vacuum deposition process known per se and which will not be described in more detail .

FIG. 2 represents a view in partial section of a second embodiment of an object whose surface is coated with a multilayer deposit of composition different from that of the coating of the object described above.

The object, consisting of a brass substrate 20, after degreasing and pickling, is immersed in a potassium cyanide solution having a concentration of 20 g / l. In this embodiment, it is then coated with an intermediate layer 21 formed on the one hand by a copper sublayer 211 and a silver layer 212. The sublayer 211 has a thickness of about 5 micrometers and is deposited by electroplating from an alkaline copper bath, at a temperature of 45 "C, containing respectively: - copper at a rate of 28.4 g / l, or a cuprous cyanide at a rate of 40.0 g / l, - free cyanide in sodium cyanide at a rate of 6 g / l, - sodium carbonate at a rate of 10 g / l, and whose anodes are made of pure copper.

Then deposited on this sublayer 211, after a pre-silvering of thirty seconds in a bath whose composition is identical to that of the bath described with reference to FIG. 1, the silver layer 212 of 10 micrometers intended to protect the subject to corrosion and obtained by electroplating from a bath, the composition of which is also identical to that of the bath described with reference to FIG. 1.

The finishing layer 22 consists, in this embodiment, of a layer 221 of titanium coated with a layer 222 of a ceramic material which, in this example, is titanium oxide. These two layers 221 and 222 are deposited by physical vacuum deposition in the gas phase.

The multilayer deposit with which the substrate 30 of the object partially covered by FIG. 3 is covered is composed of an intermediate layer 31 formed of a copper sublayer 311 on which is deposited a silver layer 312 covered with a layer of palladium 313 or any other precious metal such as platinum, gold or rhodium, depending on the function of the object and the desired surface condition. These three layers are deposited by electroplating, the precious metal baths used being known and marketed baths. As in the embodiment described with reference to FIG. 2, the finishing layer 32 consists of a first layer of titanium 321 covered by a layer of a ceramic material 322, here titanium oxide. These last two layers are obtained by vacuum deposition.

The present invention is not limited to the embodiments described but can undergo any modifications which are obvious to a person skilled in the art. In particular, it is understood that the deposition of the sublayers and of the silver layer can also be carried out by vacuum deposition techniques. When the silver layer is coated with a layer of precious metal it is possible to cover them directly with a ceramic material, all combinations being possible depending on the desired function and appearance. In addition, the composition of the baths as described can be modified without departing from the process according to the invention.

Claims (26)

1. Method for treating the surface of a decorative or functional object comprising a substrate made of a metallic material, in particular brass, bronze, aluminum or aluminum-based alloys, carbon steel, stainless steel , made of zinc cast iron or the like, sensitive to corrosion, in which is deposited on said substrate at least one thin layer of a finishing coating conferring on said decorative or functional object predetermined aesthetic and / or functional characteristics, characterized in that at least one intermediate layer of a material resistant to corrosion and having bio-compatibility properties is deposited on the substrate, prior to the deposition of said thin layer of the finishing coating. 2. Method according to claim 1, characterized in that said material of said intermediate layer is silver or one of its alloys. 3. Method according to claim 1, characterized in that one proceeds to the deposition of said intermediate layer by chemical or electrochemical means from an electrolytic solution for galvanic application composed of the following substances: silver nitrate, fluoride silver, silver fluoborate, silver iodide, silver thiosulfate, silver pyrophosphate, silver succinimide, thiourea, or double cyanide of silver and potassium. 4. Method according to claim 1, characterized in that one proceeds to the deposition of said intermediate layer by vacuum deposition. 5. Method according to claim 2, characterized in that said material of said intermediate layer is a silver alloy with at least one of the following elements: copper, tin, antimony, zinc, lead, bismuth, arsenic, germanium, indium, gold, palladium, platinum. 6. Method according to claim 1, characterized in that the intermediate layer is formed of several layers of which at least one layer is made of silver or a silver alloy. 7. Method according to claim 6, characterized in that is deposited on said substrate and under said silver layer a matte, semimate or shiny sublayer of copper or its alloys or tin alloys. 8. Method according to claim 6, characterized in that a layer of a precious metal chosen from the following metals is deposited on the silver layer: palladium, gold, platinum, rhodium. 9. Method according to claim 6, characterized in that said layers are deposited chemically or electrochemically. 10. Method according to claims 3 and 9, characterized in that said intermediate layer obtained chemically or electrochemically has a thickness between 1 and 50 micrometers. 11. Method according to claim 6, characterized in that said layers are deposited by vacuum deposition. 12. Method according to claims 4 and 11, characterized in that said intermediate layer obtained by vacuum deposition has a thickness of between 0.5 and 10 micrometers. 13. Method according to claim 1, characterized in that at least one layer of a material chosen from the following group of materials is deposited on said intermediate layer: titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, aluminum. 14. Method according to claim 1, characterized in that at least one layer of a material chosen from the following group of materials is deposited on said intermediate layer: titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, aluminum, to which at least one of the elements chosen from the group of the following elements is added carbon, nitrogen, oxygen, boron, silicon, fluorine, chlorine, sulfur, phosphorus. 15. Method according to any one of claims 13 or 14, characterized in that said layer deposited on said intermediate layer has a thickness between 0.1 and 10 micrometers. 16. Decorative or functional object obtained by the method according to any one of claims 1 to 15, comprising a substrate (10, 20, 30) made of a metallic material, in particular brass, bronze, aluminum or alloys with aluminum base, carbon steel, stainless steel cast zinc or the like, sensitive to corrosion, and at least one thin layer of a finishing coating deposited on said substrate and giving said decorative or functional object characteristics aesthetic and / or functional predetermined, characterized in that it further comprises at least one intermediate layer (11, 21, 31) of a material resistant to corrosion and having bio-compatibility properties disposed under the deposit of said thin layer of the finish coating (12, 22, 32). 17. Decorative or functional object according to claim 16, characterized in that said material of said intermediate layer (11) is silver or one of its alloys. 18. Decorative or functional object according to claim 16, characterized in that said material of said intermediate layer is a silver alloy with at least one of the following elements: copper, tin, antimony, zinc, lead, bismuth, arsenic , germanium, indium, gold, palladium, platinum with a silver titer of between 500 and 1000 O / oc. 19. Decorative or functional object according to claim 16, characterized in that said intermediate layer (21, 31) comprises several layers of which at least one layer (212, 312) is made of silver or a silver alloy. 20. Decorative or functional object according to claim 16, characterized in that said intermediate layer (11, 21, 31) has a thickness of between 1 and 50 micrometers when it is applied by a chemical or electrochemical deposition technique. 21. Decorative or functional object according to claim 16, characterized in that said intermediate layer (11, 21, 31) has a thickness of between 0.5 and 10 micrometers when it is applied by a vacuum deposition technique. 22. Decorative or functional object according to claim 19, characterized in that it comprises between said substrate (20, 30) and said silver layer (212, 312) a matt, semi-underlay (211, 311) matt or shiny copper or its alloys or tin alloys. 23. Decorative or functional object according to claim 19, characterized in that it comprises on said silver layer (312) a layer (313) of a precious metal chosen from the following metals: palladium, gold, platinum, rhodium . 24. Decorative or functional object according to claim 16, characterized in that it comprises on said intermediate layer (11, 21, 31) at least one layer (12, 221, 321) of a material chosen from the group of materials following: titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, aluminum. 25. Decorative or functional object according to claim 16, characterized in that it comprises on said intermediate layer (11, 21, 31) at least one layer (222, 322) of a material chosen from the following group of materials: titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, to which at least one of the elements chosen from the group of the following elements has been added: carbon, nitrogen, oxygen, boron, silicon, fluorine, chlorine, sulfur , phosphorus. 26. Decorative or functional object according to any one of claims 24 or 25, characterized in that said layer deposited on said intermediate layer (11, 21, 31) has a thickness between 0.1 and 10 micrometers.