EP0258283B1 - Method for depositing on a substrate a wear-resistant decorative coating layer, and object produced according to this method - Google Patents

Abstract

PCT No. PCT/CH87/00014 Sec. 371 Date Oct. 2, 1987 Sec. 102(e) Date Oct. 2, 1987 PCT Filed Feb. 3, 1987 PCT Pub. No. WO87/04812 PCT Pub. Date Aug. 13, 1987.A method for depositing a wear-resistant decorative coating on a substrate, comprising a first stage of vacuum deposition on the surface of the substrate of a layer of at least one metal of the group titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybedenum, tungsten and aluminium, to which is added at least one element of the group carbon, nitrogen, oxygen, boron, silicon, fluorine, chlorine, sulfur and phosphorus; a second stage including activation of the first layer by ionic bombardment under vacuum conditions and simultaneous deposition of a second fine layer of a metal or metal alloy; and a third stage involving galvanic deposition of a third layer of a decorative metal coating over the second layer.

Description

The present invention relates to a method for depositing on a substrate a wear-resistant decorative coating and having externally a predetermined desired color, this substrate constituting at least part of a decorative and / or utility object, in particular a piece of horology, in which, during a first step, at least one first wear-resistant layer having a color close to said desired color is deposited under vacuum on the surface of the substrate.

It also relates to decorative or utility objects, produced by this process, the aesthetic aspect of which is important.

It is very often asked that the surfaces of decorative objects have a golden color. When these objects are not solid gold, but made of a non-noble metal such as brass, stainless steel, zinc, etc., this golden appearance can be obtained by applying a surface coating of gold or gold alloy, most often by a galvanic process. If this coating is to be resistant to wear and corrosion, its thickness must at least reach 10 micrometers.

To this end, a base layer consisting of a 14 or 18 carat precious metal alloy is generally galvanically deposited. However, the corrosion resistance of these alloys is often insufficient, and their color does not correspond exactly to the colors of solid alloys, such as those defined for example by the standards of the Swiss watch industry NIHS 03-50 (alloy, 1N14, 2N18, 3N, 4N, 5N).

The corrosion resistance of gold plating, as well as their color, can be improved by galvanic application of a surface layer of gold alloy having a purity greater than or equal to 22 carats, and corresponding exactly to the desired color. .

Given the high price of gold and its low wear resistance, attempts have been made to replace gold plating with hard coatings deposited under vacuum or in the gas phase. By way of example, titanium nitride coatings, deposited by chemical reactions in the gas phase, by reactive evaporation, by ion spraying or by cathode sputtering, are commonly applied to decorative objects made of metal, carbides or sintered metal nitrides. , or ceramic. These coatings have the advantage of being very resistant to wear and having a golden appearance.

However, the color obtained by these methods is only approximately that of gold, and a trained eye easily detects the difference. This lack of equivalence will be highlighted below with reference to Figures 2 to 5.

On the other hand, obtaining very dense and corrosion-resistant titanium nitride coatings by ion spraying or sputtering involves very high states of compressive stress in the layer, and consequently shear stresses between the layer and the base material which promote the separation of the coating. In order to somewhat reduce these shearing effects, the German publication DE-2431448 describes a process making it possible to vary the concentration of nitrogen during deposition in an increasing manner towards the outside of the layer. Furthermore, the British publication GB-A-1555467 describes a process intended to avoid certain drawbacks of the very conventional treatments for gaseous nitriding of steels, in particular the surface formation of a layer sensitive to corrosion, and which consists in remove this layer by ion stripping under vacuum and cover the surface with a metallic deposit obtained by introducing vapor of the material to be deposited in the deposition chamber, and with an electrolytic coating. This coating is not intended for a decorative function.

For an anti-wear application, US Patent No. 3,857,682 proposes to deposit a thin layer of gold under vacuum over the titanium nitride. This idea was taken up in the American patent No. 4,252,862 and Swiss Patent No. 631,040, applied to the decorative field, with the aim of giving the surface of titanium nitride the exact color of gold, or of a gold alloy. During the use of a part thus coated, the wear of the gold coating only occurs on the sharp corners and reveals the coating of titanium nitride whose color can be distinguished from that of the rest of the coating. .

To improve the gloss and color conformity of titan nitride coatings, Japanese publication No. 58.153.776 and European publication No. 38.294 describe a process for the combined deposition of titanium nitride and gold, intended to form over all or part of the thickness of the coating, a titanium nitride / gold compound. However, this procedure seems to pose corrosion problems, and the color obtained is also far from the standard colors of gold coatings.

Finally, the successive deposition of thin layers of titanium nitride and gold, by vacuum process, also improves the gloss of the coating.

• Le risque de décollement du revêtement provoqué par des contraintes de cisaillement aux surfaces de contact du nitrure de titane et de la matière de base.
• L'adhérence aléatoire, souvent mauvaise de l'or sur le nitrure de titane, sauf dans le cas d'un dépôt simultané de nitrure de titane et d'or.
• La difficulté d'obtenir une couleur standard par procédé de dépôt sous vide, et surtout de varier la couleur en fonction des demandes des utilisateurs, les procédés de dépôt d'or ou d'alliage d'or ne permettant pas de varier la couleur finale du revêtement d'un traitement à l'autre.

Unfortunately, all of these known methods have the main flaws:

• The risk of detachment of the coating caused by shear stresses on the contact surfaces of the titanium nitride and the base material.
• The random, often poor adhesion of gold to titanium nitride, except in the case of a simultaneous deposition of titanium nitride and gold.
• The difficulty of obtaining a standard color by vacuum deposition process, and above all to vary the color according to user requests, the gold deposition or gold alloy processes not allowing the final color to be varied coating from one treatment to another.

The present invention proposes to overcome these various drawbacks and in particular makes it possible to considerably improve the resistance to wear, adhesion and appearance of a deposit based on titanium nitride with final gold coating.

This object is achieved by the method according to the invention characterized in that said first layer comprises at least one metal chosen from the following: titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, aluminum, to which add at least one element chosen from the following: carbon, nitrogen, oxygen, boron, silicon, fluorine, chlorine, sulfur, phosphorus, so that the color of this first layer is close to said desired color, in that during from this first step, the proportion of the added element and the electrical polarization of the substrate are increased simultaneously from the inside to the outside of the layer, in that during a second step, this first layer by ion bombardment under vacuum, and a second thin layer of a metal and / or a metal alloy whose color is close to said desired color is deposited, in that during a first phase of the get In the second step, the first layer is ionically bombarded without depositing metal and / or decorative alloy, and in that during the second phase of the second step, the first layer is continued to be ionically bombarded by simultaneously depositing the second layer and progressively reducing ion bombardment, and in that during a third step, a third layer of decorative metallic coating having exactly said desired color is galvanically deposited on this second layer.

• La figure 1 représente une vue schématique illustrant les différentes phases du procédé selon l'invention,
• La figure 2 illustre le principe de la mesure de la couleur selon la norme de la Commission Internationale de l'Eclairage CIE 1976,
• La figure 3 est une représentation graphique illustrant la brillance de la surface colorée d'un revêtement de nitrure de titane en fonction de la quantité d'azote qu'il contient,
• La figure 4 illustre le taux de couleurs verte et rouge réfléchies par un revêtement de nitrure de titane en fonction de la quantité d'azote qu'il contient, et
• La figure 5 représente le taux de couleurs bleue et jaune réfléchies par un revêtement de nitrure de titane en fonction de la quantité d'azote qu'il contient.

The present invention will be better understood with reference to the description of exemplary embodiments and the attached drawing in which:

• FIG. 1 represents a schematic view illustrating the different phases of the method according to the invention,
• Figure 2 illustrates the principle of color measurement according to the standard of the International Commission on Lighting CIE 1976,
• FIG. 3 is a graphic representation illustrating the brightness of the colored surface of a coating of titanium nitride as a function of the quantity of nitrogen which it contains,
• FIG. 4 illustrates the rate of green and red colors reflected by a coating of titanium nitride as a function of the quantity of nitrogen which it contains, and
• FIG. 5 represents the rate of blue and yellow colors reflected by a coating of titanium nitride as a function of the quantity of nitrogen which it contains.

According to a particularly advantageous embodiment, the method described consists in depositing under vacuum, for example by sputtering, by vacuum evaporation or by ion spraying, titanium in the presence of nitrogen on the surface of a metallic or non-metallic object. 10 schematically represented by FIG. 1. During this deposition, the quantity of nitrogen introduced into the treatment enclosure continuously varies from zero to a value defined by the desired result, so that the composition of the coating 11 starting from the gross surface of the The object gradually varies from pure titanium to a titanium nitride having an approximately stoichiometric composition. According to a particularly advantageous technique, the electrical polarization of the treated object is varied simultaneously, in order to gradually vary the mechanical compression stresses from a minimum value at the start of the coating to a maximum value at the end of the coating. Of this In this way, a coating is obtained which, starting from the gross surface of the object, presents a determined gradient of nitrogen concentration, resistance and mechanical stress. As a result, the coating obtained has minimal shear stresses on the contact surface of the object and the coating, as well as the desired optical, mechanical and anticorrosive surface properties.

After depositing the first layer of titanium nitride, the method consists in preparing the upper surface of this layer in order to make it suitable for receiving, thereafter a layer of gold or of gold alloy, deposited by galvanic process , having the desired final color, as close as possible to a standard color defined by the standards in use. For this, an activation of the titanium nitride surface is carried out during a first step of the second treatment phase by intense ion bombardment. After this first treatment step, gold atoms are deposited, forming an intermediate layer 12, during a second step of this second treatment phase. This deposition of gold atoms is carried out under vacuum by evaporation, by ion projection or by sputtering, while continuing to carry out an ion bombardment of the titanium nitride surface. During this second step, the power of this ion bombardment is gradually reduced.

When this operation is carried out, the activated titanium nitride surface is ready to receive a layer 13 of pure gold or of a gold alloy of high purity, deposited by a galvanic process, making it possible to give it the desired color. This color can be modified at will by changing the composition of the galvanic bath or by modifying the parameters defining the conditions of the galvanic deposition process. In this way, different objects of the same batch previously coated with a base layer of titanium nitride, then with a thin layer of gold, by a vacuum process, can be coated with a final layer having shades of different colors depending on whether they have been treated in a particular galvanic bath or according to whether the treatment conditions have been modified.

The embodiment described above, consisting in applying an object a base layer of titanium nitride, then depositing by a vacuum process a thin layer of gold, then performing a galvanic deposition of the same metal, can easily be generalized and applied to various other metals. The base layer which can have a thickness of between 0.1 and 20 micrometers, can be produced by vacuum deposition of at least one of the following metals: Titanium, Zirconium, Hafnium, Vanadium, Niobium, Tantalum , Chromium, Molybdenum, Tungsten and Aluminum. This deposit can be made in the presence of one of the following elements: Carbon, Nitrogen, Oxygen, Boron, Silicon, Fluorine, Chlorine, Sulfur and Phospore. As with titanium nitride, the level of these elements is gradually increased during the vacuum deposition phase of the metal or metals mentioned above.

At the same time, and as the coating increases in thickness, the objects to be treated are increasingly polarized. This makes it possible to obtain a coating having an increasing concentration of non-metallic elements and having states of increasing mechanical stresses.

During a second phase of the process, an intense ion stripping is carried out, and a thin metallic layer is deposited, partly simultaneously, which may be made of gold or of a gold alloy, but also of one or more precious metals such as for example Platinum, Palladium, Rhodium, Silver, Irridium, Osmium, Rhenium and Ruthenium. This second layer preferably has a thickness of between 0.01 and 1 μm (100 and 10′000 Å).

The final layer is then deposited by a galvanic process on the metal coating constituting the second layer. This galvanic deposit is generally gold or a high-carat gold alloy, for example a gold alloy at least 22 carats comprising, as an alloying element, Indium, Nickel, Cobalt , Cadmium, Copper, Silver, Palladium, Zinc or Antimony. However, this deposit can also consist of one or more precious metals such as Platinum, Palladium, Rhodium, Silver, Irridium, Osmium, Rhenium or Ruthenium, an alloy of one of these metals with one or more other metals, or possibly a non-precious metal or alloy.

The thickness of the surface layer, obtained by a galvanic process under clearly defined conditions allowing the desired shade and appearance to be obtained, is preferably between 0.1 and 30 micrometers.

The method makes it possible to treat the surface of an object so as to dress it with a hard adherent and corrosion-resistant layer having approximately the desired color, then to carry out on this base layer a final coating having exactly the color desired and adhering perfectly to this base coat.

Various objects can be treated in this way. For example, a stainless steel watch case, previously degreased and dried, is placed in a cathode sputtering chamber under vacuum. During a first stage, it undergoes an ion bombardment with argon ions, so as to remove the last superficial traces of contaminant. The object is then negatively polarized at a few tens of volts, and we begin to deposit titanium by sputtering. As the thickness of the coating increases, the electric polarization of this object is gradually increased, and an increasing flow of nitrogen is introduced into the enclosure, so as to deposit an increasingly titanium nitride compound. richer in nitrogen. At the end of the titanium nitride deposition, when the coating thickness reaches one micrometer, the polarization of the object can rise to a value between 150 and 250 volts, and the proportion of nitrogen atoms in the titanium nitride will be approximately 50%. The surface color of the coating is then close to that of gold.

The next step is to bombard the titanium nitride layer with argon ions. As the power of this bombardment is reduced, a thin layer of gold is deposited by sputtering, with an increasing flow of gold atoms, until that this layer reaches a thickness of 0.1 micrometer. The watch case is then removed from the enclosure. It is given its final surface color by electrolytically applying a coating of 0.3 microns of 22-carat gold alloy, containing traces of indium and nickel, the color of which corresponds to the 2 N 18 standard.

According to another example, it is desired to deposit a thin layer of rhodium having good wear resistance on the exterior surface of a brass ball-point pen tube. After treatment of the surface by galvanic nickel plating, the object is introduced into the sputtering enclosure where it undergoes the same treatment as in the previous example. During the deposition of titanium, the nitrogen is replaced by a hydrocarbon, such as for example methane, so as to deposit a titanium carbide with an increasing proportion of carbon. Following the deposition of titanium carbide, and simultaneously with ion bombardment of the surface, a thin layer of silver is deposited by sputtering.

A final layer of rhodium is then galvanically deposited over the silver until this layer reaches a thickness of 0.3 micrometers.

Figure 2 illustrates the principle of measuring the color of the light reflected by the surface of an object according to the CIE 1976 standard of the International Commission on Lighting. Three quantities are measured and correspond to three axes defining a three-dimensional orthogonal coordinate system. The L axis defines the brightness, the - a, + a axis corresponds to the two complementary colors respectively green and red. The axis - b, + b corresponds to the two complementary colors respectively blue and yellow.

FIG. 3 represents a comparative graph between the brightness of titanium nitride and of various standard gold alloys. On the ordinate, the brightness is represented in arbitrary units and on the abscissa the rate of nitrogen entering into the composition of titanium nitride, according to an arbitrary unit. The shine of the surface of a coating of titanium nitride is represented by a curve 20. The brilliance of different gold alloys is represented by a succession of dots. It can be seen that the gloss of all the standard alloys represented is greater than all of the titanium nitride compounds.

FIG. 4 represents the quantity of green and red light reflected on the one hand by a coating of titanium nitride and on the other hand by various standard gold alloys. As before, the nitrogen content of the titanium nitride compound is plotted on the abscissa in an arbitrary unit. Curve 21 represents the quantity of green and red light reflected by the coating of titanium nitride.

FIG. 5 represents the quantity of blue and yellow light respectively reflected by a coating of titanium nitride and by various coatings of standard gold alloys. As previously, the nitrogen content in titanium nitride has been plotted on the abscissa in an arbitrary unit. Curve 22 represents the amount of blue and yellow light reflected by the titanium nitride coating as a function of its composition. The blue and yellow light reflected by the different alloys is represented by a succession of points.

It can be seen that, whatever the nitrogen content of the titanium nitride, it is impossible to exactly match a given standard alloy with a point on the curves representing titanium nitride. If we take for example the alloy 5N, the nearest point M on curve 21 corresponds to a titanium nitride whose nitrogen content is between four and five while the closest point on curve 22 corresponds to a titanium nitride whose nitrogen content is between three and four. The same observations can be made for the other standard gold alloys. As a result, it is impossible to obtain a titanium nitride surface coating which has exactly the appearance of a standard gold alloy, hence one of the major advantages of the process described.

It is understood that the method is not limited to the treatment of the objects described by way of examples, but can be extended to various other purely decorative or utility objects for which the aspect is of great interest.

Claims (8)

1. Method of depositing on a substrate a decorative wear-resistant coating externally having a predetermined desired color, said substrate constituting at least a part of a decorative and /or utilitarian article, in particular a time piece, in which during a first stage vacuum deposition of at least a first wear-resistant layer having a color near the said desired color is effected on the substrate surface, characterized in that said first layer comprises at least one metal selected from the group consisting of: titanium, zirconium, hafnium, vanadium, niobium, tantalum, chronium, molybdenum, tungsten, aluminium, to which at least one element is added which is selected from the group consisting of carbon, nitrogen, oxygen, boron, silicon, fluorine, chlorine, sulphur, phosphorus, so that the color of this first layer be near the said desired color, in that during this first stage the proportion of the added element and the electric polarisation of the substrate are simultaneously varied in an increasing manner from the inside to the outside of the layer, in that during a second stage, this first layer is activated by ion bombardment under vacuum, and a second fine layer of a metal and/or a metallic alloy, whose color is near the said desired color, is deposited, in that during a first phase of the second stage, the first layer is subjected to ion bombardment without depositing decorative metal and/or alloy, and in that during the second phase of the second stage, ion bombardment of the first layer is continued while simultaneously depositing the second layer and in progressively reducing the ion bombardment, and in that during a third stage, a third decorative metallic coating layer having exactly the desired color is electro-plated on said second layer.

2. Method according to claim 1, characterized in that the second layer comprises at least one precious metal selected from the group consisting of: gold, platinum, palladium, rhodium, silver, iridium, osmium, rhenium, ruthenium and/or at least one alloy of gold with one of the elements from the group consisting of: indium, nickel, cobalt, cadmium, copper, silver, palladium, zinc, antimony.

3. Method according to claim 1, characterized in that the thickness of the second layer is comprised between 10 and 1′000 nm (100 and 10′000 Å).

4. Method according to claim 1, characterized in that the third electro-plated layer is composed of at least one metal selected from the group consisting of: gold, platinum, palladium, rhodium, silver, iridium, osmium, rhenium, ruthenium and/or an alloy of one of these metals with one or several other metals, and/or of an alloy of gold with one of the elements of the group: indium, nickel, cobalt, cadmium, copper, silver, palladium, zinc, antimony.

5. Method according to claim 1, characterized in that the thickness of the third layer is comprised between 0, 1 and 30 micrometers.

6. Decorative and/or utilitarian article obtained by the method according to claim 1 comprising on at least a part of its surface a wear-resistant coating externally having a predetermined color, this coating comprising a first layer of a wear-resistant metallic compound, a second layer of a wear-resistant deposition, and a third layer of an electro-plated metal and/or metallic alloy, characterized in that the first layer of the coating has a color near the said predetermined color and comprises at least a compound of at least one metal selected from the group consisting of: titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, aluminium and at least one element selected from the group consisting of: carbon, nitrogen, oxygen, boron, silicon, fluorine, chlorine, sulphur, phosphorus and in that the second layer has a color near the said predetermined color and comprises at least one precious metal selected from the group consisting of: gold, platinum, palladium, rhodium, silver, iridium, osmium, rhenium, ruthenium and/or at least one alloy of gold with one of the elements from the group consisting of: indium, nickel, cobalt, cadmium, copper, silver, palladium, zinc, antimony, and in that the third layer has exactly the predetermined color and comprises at least one precious metal selected from the group consisting of: gold, platinum, palladium, rhodium, silver, iridium, osmium, rhenium and/or an alloy of one of these metals with one or several other metals, and/or of an alloy of gold with one of the elements of the group: indium, nickel, cobalt, cadmium, copper, silver, palladium, zinc, antimony.

7. Article according to claim 6, characterized in that the thickness of the second layer is comprised between 10 and 1′000 nm (100 and 10′000 Å).

8. Article according to claim 6, characterized in that the thickness of the third layer is comprised between 0, 1 and 30 micrometers.

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