CH715364A2 - A method of improving the adhesion of a silver tarnish protection layer to a substrate comprising a silver surface. - Google Patents

Abstract

The invention relates to a method for improving the adhesion of a silver tarnish protection layer to a substrate comprising a final silver surface, said method comprising the following steps: a) providing a substrate (1) with or without an initial silver surface b) depositing on said substrate (1) of step a) a layer (2) of an alloy of silver and copper comprising between 0.1% and 10% in weight of copper relative to the total weight of the alloy to obtain said final silver surface c) depositing on at least part of said final silver surface obtained in step b) at least one layer (4) of protection against tarnishing silver having a thickness between 1 nm and 200 nm.

Description

Field of the invention

The invention relates to a method for improving the adhesion of a protective layer against tarnishing of silver on a substrate comprising a silver surface. Such a substrate comprising a silver surface is in particular a timepiece covered with a thin layer of silver.

Background of the invention

In the field of watchmaking, it is customary to produce a timepiece by covering a substrate with a thin layer of silver, preferably deposited by galvanic means, in order to give the timepiece the very white and unique appearance of silver. Such a timepiece is for example a dial, made of brass or gold, covered with a thin layer of silver.

[0003] However, silver has the drawback of tarnishing over time. To solve this problem, it is known to protect the sensitive silver surface of the timepiece by the zaponnage method. Zapon is a cellulose varnish dilutable in a solvent. Zaponnage is a process which consists in applying several layers to the surfaces to be protected, for example by spraying, with Zapon varnish, then passing them in the oven to accelerate their hardening. The final coating has a total thickness of approximately 8 to 15 µm.

However, this Zapon varnish only imperfectly protects sensitive metals. In addition, the necessary thickness of Zapon varnish deposited erases fine structuring details, such as the guilloché pattern frequently used to decorate a dial. As a result, the details of the guilloche are not highlighted, and may even disappear under the layers of varnish. Finally, the layers of Zapon varnish modify the color and appearance of the protected silver surface by varying the L * parameter (from the CIE L * a * b * color space).

In order to replace the zaponnage method, it has been proposed to deposit a protective layer on the sensitive silver surface by an ALD method, as described in patent EP 1 994 202. This method makes it possible to deposit a extremely thin coating (50 nm to 100 nm) and very protective, the protection obtained being greater than the protection obtained with a coating of 10 μm of Zapon.

However, this ALD method has the main drawback of forming, on the silver surface of the substrate, a protective layer having poor adhesion to said silver surface, so that said protective layer deposited by ALD delaminates at the slightest solicitation, for example during final decoration operations by pad printing or other.

In addition, the use of an inadequate protective layer deposited on the silver surface of the substrate can have the disadvantage of attenuating the shine and the color of the silver and of modifying the aesthetic rendering of the surface. silver.

Summary of the invention

The present invention aims to remedy these drawbacks by proposing a method for improving the adhesion of a protective layer against tarnishing of silver on a substrate comprising a silver surface.

The present invention also aims to provide a method for obtaining a substrate having a silver surface effectively protected against tarnishing of silver while preserving the final appearance of said silver surface.

To this end, the invention relates to a method for improving the adhesion of a protective layer against tarnishing of silver on a substrate comprising a final silver surface, characterized in that it comprises the following steps: <tb> a) <SEP> have a substrate with or without an initial silver surface <tb> b) <SEP> deposit on said substrate of step a) a layer of a silver and copper alloy comprising between 0.1% and 10% by weight of copper relative to the total weight of l alloy to obtain said final silver surface <tb> c) <SEP> depositing on at least part of said final silver surface obtained in step b) at least one silver tarnish protection layer having a thickness of between 1 nm and 200 nm, preferably between 40 nm and 100 nm.

The present invention also relates to the use of a layer of a silver and copper alloy comprising between 0.1% and 10% by weight of copper relative to the total weight of the alloy deposited on a substrate with or without an initial silver surface in order to obtain a substrate having a final silver surface, for improving the adhesion of a protective layer against tarnishing of the silver deposited on said final silver surface, said protective layer against tarnishing of the silver having a thickness of between 1 nm and 200 nm, preferably between 40 nm and 100 nm.

The use of such a layer of silver and copper alloy deposited on a substrate makes it possible to create Cu radicals on the surface which will ensure the adhesion of the protective layer against tarnishing of silver. while preserving the silvery shine of the substrate.

Brief description of the drawings

Other features and advantages will emerge clearly from the description given below, by way of indication and in no way limitative, with reference to the appended drawings, in which: <tb> fig. 1 <SEP> is a schematic view of a first variant of substrate treated according to the present invention; and <tb> fig. 2 <SEP> is a schematic view of a second variant of substrate treated according to the present invention.

Detailed description of preferred embodiments

The present invention relates to a method for improving the adhesion of a protective layer against tarnishing of silver on a substrate comprising a final silver surface.

The first step a) of the method according to the invention consists in providing a substrate 1 with or without an initial silver surface.

Such a substrate is for example a timepiece or jewelry item, and in particular a timepiece cladding element. In particular, the substrate may be a dial of a timepiece, which may have on its surface a structure, such as a guilloche, that is to say a set of lines with fine details, which intersect in order to obtain a decorative effect. To this end, step a) of the method comprises a sub-step according to which said structuring is carried out on the surface of the substrate.

The substrate 1 is preferably metallic. It can be made of brass, based on gold, yellow or white, or silver, or any other metal or metallic alloy, precious or not, suitable.

Referring to FIG. 1, there is shown a substrate 1 treated according to a first variant of the invention according to which the substrate 1 can be without an initial silver surface or comprise an intrinsic silver surface. In the first case, the substrate may for example be made of brass, based on gold, yellow or white, or any other metal or metallic alloy, precious or not, suitable with the exception of silver. In the second case, the substrate 1 is based on silver, in solid silver for example, and intrinsically has an initial silver surface.

Referring to FIG. 2, there is shown a substrate 10 treated according to a second variant of the invention according to which the substrate 10 is not silver-based and comprises an initial silver surface obtained by a deposit, according to a substep of the step a), an intermediate layer 20 of substantially pure silver on said substrate 10. Such a layer 20 is preferably deposited galvanically. The substrate 10 can itself be made of brass and covered with a layer of precious metal, for example deposited galvanically, for example a layer of gold. The substrate 10 can also be made of solid precious metal, for example solid gold.

Said layer 20 of substantially pure silver may have a thickness of between 200 nm and 3000 nm.

According to one embodiment, the layer 20 of substantially pure silver has a thickness between 200 nm and 600 nm, preferably between 300 nm and 500 nm in order to form a coating of fine silver.

According to another embodiment, the layer 20 of substantially pure silver has a thickness of between 1000 nm and 3000 nm, preferably between 1500 nm and 2500 nm in order to constitute a coating of thick silver.

Such a thick silver coating has the advantage of obtaining an intermediate layer of substantially pure silver free of porosities, in order to then obtain, as will be seen below, a layer of silver and copper according to step b) without porosity and thus ensuring increased adhesion of the silver tarnish protection layer on said layer of silver and copper.

According to the invention, the substrate 1, 10 of step a) is then treated according to step b) which consists in depositing on said substrate 1.10 of step a) a layer 2 of a silver and copper alloy comprising between 0.1% and 10% by weight of copper relative to the total weight of the alloy to obtain a substrate 1, 10 having a final silver surface.

Preferably, the layer 2 of silver and copper alloy has a thickness between 200 nm and 600 nm, more preferably between 300 nm and 400 nm.

Preferably, the silver and copper alloy comprises between 0.2% and 8% by weight, preferably between 0.5% and 7% by weight, of copper relative to the total weight of the alloy. The proportion of copper relative to silver is chosen so as to create enough Cu radicals on the surface which will then ensure the adhesion of the protective layer against tarnishing of silver, without altering the color of the silver. since the layer of silver and copper alloy forms the final silver surface of the substrate.

The layer 2 of silver and copper alloy can be deposited directly on the substrate 1 as shown in FIG. 1 and replace the traditionally used fine silver coating. The layer 2 of silver and copper alloy can also be deposited on the intermediate layer of substantially pure silver 20 as shown in FIG. 2. The layer 2 of silver and copper alloy can be deposited by any suitable process, such as PVD (flash deposit), or galvanically by means of a suitable silver and copper galvanic bath.

Step c) of the method of the invention then consists in depositing on at least part of the final silver surface obtained in step b) at least one layer 4 of protection against tarnishing of the silver having a thickness between 1 nm and 200 nm, preferably between 1 nm and 100 nm, and more preferably between 40 nm and 100 nm.

Step c) can be carried out by a method chosen from the group comprising an ALD deposit (Atomic Layer Deposition), PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition), and sol-gel. Preferably, step c) is carried out by ALD deposition which makes it possible to form compact layers and to obtain extremely fine and very protective coatings, with a particularly good aesthetic finish. The details and parameters of such an ALD repository are known to those skilled in the art. They are for example described in patent EP 1 994 202. The layer AI2O3 can be obtained from a TMA precursor (Tri-Methyl-Aluminum) whose oxidation can be carried out with H2O, O2; or O3. The TiO2 layer can be obtained from TTIP (Titanium Iso ProPoxide) or else from TiCl4 (Tri Titanium Chloride), the oxidation of which can be carried out with H2O, O2 or O3.

Advantageously, to use the protective layer 4 against the tarnishing of the silver deposited in step c), a metal oxide is used, ideally as transparent as possible according to the desired thicknesses, preferably chosen from AI2O3, Ta2O5, HfO2. , ZnO, SiO2, and TiO2. Nitrides are also possible, such as SixNy for example. Stacking of different layers is also possible.

Preferably, step c) comprises a step C1) of depositing on at least part of said final silver surface obtained in step b) of a first layer 4a of AI2O3 and a step c2) of deposition, on the first layer 4a of AI2O3 obtained in step c1), of a second layer 4b of TiO2.

Advantageously, the first layer 4a of AI2O3 has a thickness of between 0.5 nm and 100 nm, preferably between 0.5 nm and 50 nm, and the second layer 4b of TiO2 has a thickness of between 0.5 nm and 100 nm, preferably between 0.5 nm and 50 nm.

More preferably, the first layer 4a of AI2O3 has a thickness between 30 nm and 50 nm and the second layer 4b of TiO2 has a thickness between 10 nm and 50 nm.

In a particularly preferred manner, the layer 4 of protection against tarnishing of silver is obtained by an ALD deposition of a first layer of Al2O3 having a thickness of between 30 nm and 50 nm and of a second layer 4b of TiO2 having a thickness of between 10 nm and 50 nm.

Such a combination of a first layer 4a of AI2O3 and of a second layer 4b of TiO2 having the thicknesses indicated above makes it possible to enhance the white color of the silver.

Advantageously, the method of the invention can combine deposition of protective layers and plasma treatment, before and / or after step c2), typically an Ar plasma, in order to reduce the internal tensions of the deposited protective layers. This combination makes it possible to soften the protective layers to make them less brittle during environmental stresses, such as mechanical, thermal or others.

Advantageously, the method of the invention may comprise, between step b) and step c), at least one step d) of plasma pretreatment of the final silver surface of the substrate obtained in step b ).

This step d) of plasma pretreatment consists in pickling the final silver surface of the substrate in order to eliminate in particular the AgS / Ag2S sulphides which have formed naturally on the surface of the substrate exposed to the air and which prevent good adhesion of the protective layer 4.

Advantageously, this step d) consists of a pretreatment by Ar plasma or Ar / H2 plasma.

According to one mode of implementation of the method of the invention, step c) is implemented directly after step d), without further complementary pretreatment.

Advantageously, the silver substrate 1, 10 can be heat treated before step b) or before step c) in order to relax any internal stresses linked to the machining steps or the deposition of previous layers. The temperatures and durations of treatments depend on the nature of the substrate and the layers and must not impact the aesthetics of the part before the deposition of the protective layer of step c). The thermal treatment parameters are known to those skilled in the art and do not require further details here.

According to another mode of implementation, the method of the invention comprises an intermediate step e) complementary, between step d) and step c), of oxidative pretreatment, making it possible to create AgO / Ag2O forming covalent bonds between the AI2O3 present in the first layer 4a and the silver of the final silver surface of the substrate so as to promote the adhesion of the protective layer 4 on the substrate.

Alternatively, the oxidative pretreatment of step e) may consist of a pretreatment by oxidizing plasma with an oxidizing agent such as oxygen, or Ar / O2, making it possible to create the AgO / Ag2O sites.

The dosage of O2 in the plasma must be precise in order to create enough AgO / Ag2O sites, but which tend to yellow the silver, while guaranteeing the whiteness of the silver.

The plasma treatment parameters are known to those skilled in the art and do not require further details here.

According to another variant, the oxidizing pretreatment of step e) may consist in injecting water or hydrogen peroxide, liquid, into a vacuum pretreatment chamber causing the vaporization of the water or of the hydrogen peroxide, which in contact with the substrate, will form the AgO / Ag2O sites. The amount of water or hydrogen peroxide injected is of the order of a few tens of micromoles.

In a particularly advantageous manner, step e) is carried out without venting between step d) and said step e). To this end, the substrate pretreated according to step d) undergoes the additional pretreatment according to step e) without breaking the vacuum.

In addition, the substrate from step b) and pretreated according to step d) only or according to steps d) and e) is then advantageously transferred under vacuum to a deposition chamber, preferably by ALD deposition , for direct implementation of step c) on the pretreated substrate from step d) or steps d) and e), without venting the final silver surface of the substrate.

To this end, steps d) and e) of pretreatment and step c) of depositing the protective layer, preferably by ALD deposition, are advantageously implemented in the same overall processing machine in which the pretreatment device according to step d) or according to steps d) and e) is integrated into the device for depositing the protective layer 4, preferably by ALD deposition, allowing overall treatment without venting the final silver surface of the substrate, and preferably under vacuum, for the implementation of steps d), possibly e) if present, and c).

A substrate comprising a final silver surface, treated according to the method of the invention, has a layer of protection against tarnishing of silver without defect in adhesion. In addition, and in particular when the silver tarnish protective layer has been deposited by ALD, the very white effect of the silver is preserved despite the presence of the silver tarnish protective layer . If the substrate has been guilloche, the fine details of the guilloche are clearly visible despite the presence of said protective layer against tarnishing of silver.

Jewelery, writing instruments, eyewear and leather goods can also be advantageously treated by this process.

Claims (29)

1. Method for improving the adhesion of a protective layer against tarnishing of silver on a substrate comprising a final silver surface, characterized in that it comprises the following steps: a) provide a substrate (1, 10) with or without an initial silver surface b) depositing on said substrate (1, 10) of step a) a layer (2) of an alloy of silver and copper comprising between 0.1% and 10% by weight of copper relative to the total weight of the alloy to obtain said final silver surface c) depositing on at least part of said final silver surface obtained in step b) at least one layer (4) of protection against tarnishing of silver having a thickness of between 1 nm and 200 nm, preferably between 40 nm and 100 nm. 2. Method according to claim 1, characterized in that, when the substrate (1) of step a) comprises an initial silver surface, said substrate is based on silver and intrinsically has said initial silver surface. 3. Method according to claim 1, characterized in that, when the substrate (10) of step a) comprises an initial silver surface, said substrate is not based on silver and said initial silver surface is obtained by depositing a layer (20) of substantially pure silver on said substrate. 4. Method according to claim 3, characterized in that the layer (20) of substantially pure silver has a thickness between 200 nm and 3000 nm. 5. Method according to claim 4, characterized in that the layer (20) of substantially pure silver has a thickness between 200 nm and 600 nm, preferably between 300 nm and 500 nm. 6. Method according to claim 4, characterized in that the layer (20) of substantially pure silver has a thickness between 1000 nm and 3000 nm, preferably between 1500 nm and 2500 nm. 7. Method according to one of the preceding claims, characterized in that the layer (2) of silver and copper alloy has a thickness between 200 nm and 600 nm, preferably between 300 nm and 400 nm. 8. Method according to one of the preceding claims, characterized in that the silver and copper alloy comprises between 0.2% and 8% by weight, preferably between 0.5% and 7% by weight, copper relative to the total weight of the alloy. 9. Method according to one of the preceding claims, characterized in that one uses to produce the layer (4) of protection against tarnishing of silver deposited in step c) a metal oxide chosen from AI2O3, Ta2O5 , HfO2, ZnO, SiO2 and TiO2, or a nitride. 10. Method according to one of the preceding claims, characterized in that step c) comprises a step c1) of depositing on at least part of said final silver surface obtained in step b) of a first layer ( 4a) of AI2O3 and a step c2) of deposition, on the first layer (4a) of AI2O3 obtained in step d), of a second layer (4b) of TiO2. 11. Method according to claim 10, characterized in that the first layer (4a) of AI2O3 has a thickness between 0.5 nm and 100 nm and in that the second layer (4b) of TiO2 has a thickness between 0.5 nm and 100 nm. 12. Method according to claim 11, characterized in that the first layer (4a) of AI2O3 has a thickness between 30 nm and 50 nm and in that the second layer (4b) of TiO2 has a thickness between 10 nm and 50 nm . 13. Method according to one of the preceding claims, characterized in that step c) is carried out by a method chosen from the group comprising an ALD, PVD, CVD, and sol-gel deposit. 14. Method according to claim 13, characterized in that step c) is carried out by ALD deposition. 15. Method according to one of claims 10 to 14, characterized in that it comprises, before and / or after step c2), a plasma treatment step. 16. Method according to one of the preceding claims, characterized in that it comprises, before step b) and / or before step c), a step of heat treatment of the substrate (1, 10) to relax d 'possible internal stresses in said substrate (1, 10). 17. Method according to one of the preceding claims, characterized in that it comprises, between step b) and step c), at least one step d) of plasma pretreatment of the final silver surface of the substrate obtained in step b). 18. The method of claim 17, characterized in that step d) of plasma pretreatment consists of a pretreatment by Ar plasma or Ar / H2 plasma. 19. Method according to one of claims 17 and 18, characterized in that step c) is carried out without venting the final silver surface of the substrate between step d) and said step c). 20. Method according to one of claims 17 and 18, characterized in that it comprises, between step d) and step c), a step e) of oxidative pretreatment. 21. The method of claim 20, characterized in that step e) of oxidative pretreatment consists of a plasma pretreatment with an oxidizing agent. 22. The method according to claim 20, characterized in that step e) of oxidative pretreatment consists in injecting liquid water or hydrogen peroxide into a vacuum pretreatment chamber. 23. Method according to claims 20 to 22, characterized in that step e) is carried out without venting the final silver surface of the substrate between step d) and said step e). 24. Method according to claims 20 to 23, characterized in that step c) is carried out without venting the final silver surface of the substrate between step e) and said step c). 25. The method of claim 24, characterized in that steps d), e) and c) are implemented in the same overall processing machine. 26. Method according to one of the preceding claims, characterized in that the substrate (1, 10) is a timepiece. 27. The method of claim 26, characterized in that a structuring is carried out on the surface of the substrate (1,10). 28. Method according to one of the preceding claims, characterized in that the substrate (1, 10) is metallic, and preferably based on gold or silver. 29. Use of a layer (2) of a silver and copper alloy comprising between 0.1% and 10% by weight of copper relative to the total weight of the alloy deposited on a substrate (1, 10 ) whether or not having an initial silver surface in order to obtain a substrate having a final silver surface, in order to improve the adhesion of a layer (4) of protection against tarnishing of the silver deposited on said final silver surface, said layer (4) protection against tarnishing of silver having a thickness between 1 nm and 200 nm, preferably between 40 nm and 100 nm.