CH692151A5 - Electrodepositing gold plate after thermal relaxation of initial PVD layers and surface activation - Google Patents

Abstract

A gold plate is deposited on an object, after relaxation heat treatment of initial PVD layers and surface activation, by electroplating with a greater than 23 carat gold plate. A coating is deposited on an object by ion etching, PVD of a transition metal deposit, PVD of a hard material and PVD of a metallic anchoring layer, followed by the novel steps of relaxation heat treatment under a nitrogen/hydrogen atmosphere, activation of the anchoring layer by immersion in an acidic solution and electroplating with a greater than 23 carat gold plate. Preferred Features: The PVD operations are cathodic sputtering operations. The transition metal is pure titanium or zirconium and the anchoring layer is based on gold.

Description

The present invention relates to a method of depositing a coating on an object, in particular for covering a watch movement, such as a case or a bracelet element. More particularly, the present invention relates to objects comprising a "gold-plated" coating. The designation "gold plated" is determined by certain national laws, in particular as regards the thickness of the layer of gold coating. Depending on the country, the standards impose minimum thicknesses of 3 to 10 μm depending on the types of product. In most cases, a minimum thickness of between 3 and 6 mu m is sufficient to justify the designation "gold plated".

EP 0 258 283 B1 discloses a method of depositing a wear-resistant decorative coating on a substrate. The text of this patent is incorporated by reference into the present description.

Document EP 0 258 283 B1 describes a process consisting in applying a layer of titanium nitride to an object, then in depositing by a vacuum or gas phase process a thin layer of gold, then finally in carrying out a galvanic deposition of the same metal. The base layer is formed from a material chosen from a given group, in particular titanium or zirconium, associated with another element from a second group, in particular carbon and / or nitrogen. The primary purpose is to have a base layer of hard material and a secondary purpose of having a hard base layer having a color substantially similar to the color of gold. In a second phase of this process, an intense ion stripping is carried out and a thin metallic layer made of gold or a gold alloy is deposited simultaneously. This layer preferably has a thickness of between 0.01 and 1 μm. Then, on the thin metallic layer is deposited by a galvanic process a final layer in pure gold or in alloy of high carat gold.

Regarding the final layer deposited by a galvanic process, it is mentioned that its thickness is preferably between 0.1 and 30 μm. However, it is mentioned that the primary purpose of galvanic deposition is to give the surface of the object exactly the desired color, in particular the exact shade of gold desired. In the example given in column 6, page 4, of the document currently presented, the thickness of the final coating by galvanic deposition has a thickness of only 0.3 μm of 22-carat gold alloy having a corresponding color to standard 2N18.

In fact, several tests carried out within the framework of the present invention have shown that the process described in patent EP 0 258 283 B1 does not, as described, make it possible to obtain galvanic layers having a thickness of several micrometers. Indeed, the internal and surface tensions of the different layers deposited according to the process described in this document are too great to allow the deposition of a thick galvanic layer if a quality coating is desired, in particular a coating adhering correctly and not having not, after a certain period of use, cracks or problems of exfoliation of this coating or of the layers forming it. Tests have shown that the galvanic deposition of a layer of 22-carat gold alloy deposited directly after the formation of a thin metallic layer of gold by a vacuum or gas phase (PVD) deposition process, such as as proposed in the patent cited here, does not make it possible to obtain a quality coating with a thick galvanic layer, in particular a galvanic layer greater than 3 μm.

An object of the present invention is to provide such a coating deposition process also comprising a hard material layer and an outer layer formed of a precious metal, this coating having a higher quality, good wear resistance. and corrosion, and very good longevity.

Another object of the present invention is to provide such a method of depositing an outer layer formed of a precious metal, deposited on an inner layer formed of a hard material, which has a thickness of several micrometers, in particular a thickness at least 3 mu m in order to obtain decorative coatings with a thickness of gold or gold alloy sufficient to be able to receive the designation "gold plated" as defined in specific standards governing this designation.

To this end, the present invention relates to a method of depositing a coating on an object, in particular an object of watchmaking clothing, which comprises the following steps: A) ionic stripping of the surface of said object intended to receive said coating, B) intermediate deposition of a metal by a gas phase deposition technique (PVD); C) deposition of a layer of hard material by a gas phase deposition technique (PVD); said previously deposited metal forming an interface between this layer and said surface of said object; D) deposition of a metallic bonding layer by a gas phase deposition technique (PVD); this process being characterized in that it then comprises the following stages: E) thermal relaxation treatment under an atmosphere of hydrogenated nitrogen; F) activation of the metallic bonding layer by immersion of said object in an acid solution; G) deposit of a gold plating greater than 23 carats in a galvanic bath.

It follows from the three stages characterizing the method according to the invention that the internal stresses of the PVD multilayer coating, in particular the tensions at the interfaces of the PVD layers due to the different physical and chemical parameters characterizing these various layers, are greatly reduced so that the deposition said gold plating may have a relatively large thickness, that is to say several micrometers while having very good adhesion to said object covered with PVD layers.

Indeed, in the absence in particular of step E) essential to the present invention, as soon as the galvanic layer becomes too thick, cracking or exfoliation problems arise. On the other hand, thanks to the method according to the invention, the layers deposited by PVD are relaxed or relaxed. Thus, the internal and surface tensions of the object coated with PVD layers are reduced relative to the prior art. Thus, it is possible to deposit in good conditions the galvanic layer of precious metal and in particular to deposit a relatively thick layer to meet the various national standards governing the designation "gold plated".

In the case of depositing a thick galvanic layer, it has been shown in the context of the present invention that it is preferable to deposit a layer of gold greater than 23 carats.

Various additional steps or particular features of the steps mentioned above are given in secondary claims 2 to 12 as filed. These claims 2 to 12 form as many variants of implementing the method according to the invention as described above and claimed in independent claim 1.

By way of example only, a mode of implementation of a method for depositing a coating of an object meeting the standards of the designation "gold plated" will be described below, in particular as regards the minimum thickness of the gold layer and the quantity of gold required in this layer.

I. Preparation of the substrate

In order to remove the organic residues present on the surface of the substrate or of the object intended to receive a gold coating, and in order to ensure good adhesion of this coating on said surface, the object is immersed in an alkaline solution. based on soda and phosphate, then a double rinse is carried out in hard water and in demineralized water. Finally, drying is provided in the presence of hot air.

II. Vacuum or gas deposition

Once the object has been brought into the vacuum deposition enclosure, at least the surface on which the gold coating is provided is heated by radiation to a temperature between approximately 200 and 240 DEG C. This heating step allows ensure good temperature uniformity of the surface of said object, which is advantageous for the subsequent deposition steps.

To guarantee excellent adhesion of the PVD layers, an ionic etching of the surface of the object is first carried out using an argon gas brought into a plasma state by application of a constant bias voltage d 'about 1100 volts, the object or a support of this object forming the cathode so that the argon ions bombard said surface. This ion pickling is preferably carried out for 5 to 8 minutes.

Then, it is planned to deposit a metal, in particular a pure metal of titanium or zirconium. The deposition of this metal takes place under a constant bias voltage of between approximately 100 and 130 volts with an argon flow rate of 240 cm <3> per minute (volume measured under standard conditions) for approximately 7 to 8 minutes. The deposition of this pure metal forms a film or a thin transition layer capable of at least partially absorbing the internal stresses generated by the difference in coefficient of expansion between the surface of the object and the layer of hard material deposited subsequently, namely the PVD deposition of a layer of titanium or zirconium carbonitride which has a color close to the standard NIHS 2N color.

The deposition of the layer of titanium or zirconium carbonitride is carried out in particular with a constant bias voltage applied to said object and between approximately 120 and 150 volts, with a nitrogen flow rate of 36 cm <3> per minute (volume measured under standard conditions) and for approximately 27 to 40 minutes. It will be noted that these particular conditions form a particular mode of implementation in no way limiting. In the case of deposition of titanium carbonitride, the pure metal previously deposited is preferably titanium, while in the case of the deposition of a layer of zirconium carbonitride, the deposition of the pure metal is zirconium.

Finally, a last PVD gold deposit is made. This PVD gold deposit forms a metallic bonding layer for the subsequent deposition of the galvanic gold layer. This last PVD layer is formed from a gold alloy and in particular has a thickness of between approximately 0.1 and 0.2 μm. The deposition is carried out in particular with a constant bias voltage applied to the object being treated, this bias voltage being between approximately 20 and 50 volts.

III. Heat treatment

According to the invention and to reduce the internal tensions in the PVD layers deposited above, in particular to reduce the gradients of certain physical parameters at the interfaces or in other words to relax or relax the PVD layers or films, provision is made for heat treatment thus considerably increasing the adhesion of a subsequent galvanic deposition. To do this, the object covered with the PVD layers described above is brought into an oven in which an atmosphere of hydrogenated nitrogen is provided. This heat treatment is preferably carried out for at least one hour, in particular 1.5 hours, at a temperature of between approximately 510 and 550 DEG C.

This heat treatment makes it possible to initiate the following galvanic deposition step on an object or a substrate covered with PVD layers having very limited internal and surface constraints.

IV. Galvanic deposit

Before the actual gold plating, a chemical degreasing is provided first by immersion of the object in an alkaline solution based on soda, phosphate and metasilicates for approximately 5 to 10 minutes, this solution having in particular a temperature of approximately 35 to 45 DEG C.

This chemical degreasing is followed by an electrolytic degreasing in an alkaline solution also based on soda, phosphate and metasilicates, with stirring. This electrolytic degreasing is carried out in particular for 1 to 3 minutes and the alkaline solution has a temperature of approximately 35 to 45 DEG C.

Following the aforementioned chemical and electrolytic degreasing, there is provision for activation of the object, namely of the last layer of PVD gold, by immersion of the object in an acid solution; this especially for about 1 minute and at room temperature.

Following these preliminary steps, a gold plating is planned in a galvanic bath. Preferably, a galvanic gold deposit with a thickness of 3 to 10 μm of gold greater than 23 carats is provided. The temperature of the galvanic bath is in particular approximately between 50 and 65 DEG C. The hardness of this thick galvanic layer is approximately 165 to 240 HV.

Following the thick galvanic deposition of gold of more than 23 carats, provision is made for the deposition of a surface coloring layer formed of a gold alloy, in particular a gold alloy of about 22 or 23 carats. The thickness of this surface layer is less than or substantially equal to 1 μm. Preferably, the hardness of this surface layer is between approximately 200 and 240 HV. The specific gravity in gold is approximately 17.3 g / cm <3>. The temperature of the galvanic bath for the deposition of this surface coloring layer is in particular between approximately 22 and 65 DEG C.

Those skilled in the art will understand that, without departing from the present invention, it is possible to deposit coatings of a precious metal other than gold.

Claims (12)

1. Method for depositing a coating on an object, in particular an object for covering a watch movement, which comprises the following steps:  A) ionic stripping of the surface of said object intended to receive said coating,  B) intermediate deposition of a metal by a gas deposition technique;  C) deposition of a layer of hard material by a gas deposition technique, said metal deposited beforehand forming an interface between this layer and said surface of said object;  D) deposition of a metallic bonding layer by a gas phase deposition technique; this process being characterized in that it then comprises the following stages:  E) thermal relaxation treatment under an atmosphere of hydrogenated nitrogen;  F) activation of the metallic bonding layer by immersion of said object in an acid solution;  G) deposit of a gold plating greater than 23 carats in a galvanic bath. 2. deposition method according to claim 1, characterized in that said object is degreased in an alkaline solution during an initial step. 3. Method according to claim 1 or 2, characterized in that said object is heated to a temperature between approximately 200 and 240 degrees celsius before said step B) or before said step A). 4. deposition method according to one of the preceding claims, characterized in that said ion etching is carried out for approximately 5 to 8 minutes with a bias voltage of an argon plasma of approximately 1100 volts. 5. deposition method according to one of the preceding claims, characterized in that said metal deposited during said step B) is formed by substantially pure titanium or zirconium, this layer being deposited by sputtering, a bias voltage included approximately between 100 and 130 volts being applied to said object. 6. deposition method according to one of the preceding claims, characterized in that said hard material is titanium or zirconium carbonitride, this hard material being deposited by sputtering with a bias voltage of said object of between approximately 120 and 150 volts. 7. deposition method according to one of the preceding claims, characterized in that said bonding layer is based on gold and has a thickness of between approximately 0.1 and 0.2 μm, a bias voltage of between approximately 20 and 50 volts being applied to said object. 8. deposition method according to one of the preceding claims, characterized in that said heat treatment is carried out over a period of at least one hour in a heat treatment chamber with a temperature between about 510 and 550 degrees celsius. 9. deposition method according to one of the preceding claims, characterized in that there is provided a chemical and / or electrolytic degreasing between steps E) and F). 10. deposition method according to one of the preceding claims, characterized in that said gold plating consists of substantially pure gold and has a thickness of at least 3 μm. 11. deposition method according to one of the preceding claims, characterized in that said step G) is followed by step:  H) deposition of a surface layer for coloring and formed of an alloy comprising for the most part gold. 12. The deposition method according to claim 11, characterized in that said surface layer is made of gold at approximately 22 or 23 carats, the thickness of this surface layer being less than or substantially equal to 1 mu m.