METHOD FOR OBTAINING A WATCH COMPONENT WHOSE SURFACE IS AT LEAST PARTIALLY COATED WITH A COLOR LAYER

Description

[0001] The present invention relates to a method for microfabricating a watch component, and more specifically to a method for obtaining surfaces coated with a colored layer, at least in certain areas, of such a component, said surfaces being surfaces made of silicon, oxidized silicon, or glass (optionally metallic glass). The invention particularly relates to such a method in which said surfaces are different sections of the surface of a wafer in which a batch of watch components is subsequently microfabricated. Alternatively, said surfaces could also each consist of the surface of one of the components in the batch of watch components, or even of the surface of one of the blanks in a batch of watch component blanks. The watch component obtained by the method according to the invention has its surface coated, at least in certain areas, with a paint, lacquer, or varnish having its own color.In the remainder of this document, the term "colored coating" will be used to refer generally to all colored varnishes, paints, lacquers, and similar products. Furthermore, "colored" will be defined as something "that has one or more colors." EARLIER ART

[0002] Reflecting both fashion and technology, the world of watchmaking places great importance on aesthetics. This is probably why the use of colors, particularly for hands and dials, has been widespread for so long.

[0003] Today, more and more watch components are made of glass, silicon, and / or oxidized silicon. However, these types of materials do not allow for good adhesion of the lacquers or paints currently available on the market. To address this problem, pretreating the surface to be painted with an oxygen plasma has been proposed. This solution achieves its goal. However, a drawback is that the plasma treatment only temporarily alters the surface condition of the substrate to be painted. The application of the lacquer or paint must therefore be carried out without delay.

[0004] It is also known to use a chemical adhesion promoter that encourages the formation of chemical bonds between the substrate and the lacquer. However, it turns out that, even though the adhesion of chemical promoters is longer than the effects of the plasma, it is also limited in time. Another drawback of known techniques is that they act in a roughly isotropic manner, and therefore do not allow for the treatment of only a portion of a component's surface.

[0005] Document DE 2425783 describes a watch dial comprising, successively from bottom to top, a base plate of synthetic resin, a reflective layer of Au, Ag, Al, Rh, Cr, Ni or Cu, a transparent layer made of one or two types of materials chosen from ZrO 2 , SiO 2 , MgO, MgF 2 , CaO, CeO 2 , CdS and ZnS, a semi-transparent layer of Au, Ag, Cu, Al, Cr or Ni and a colour layer.

[0006] Document EP 0819995 A1 describes a solar-powered watch dial comprising, successively from bottom to top, a ceramic substrate, an intermediate layer of glass or oxide, and a layer of paint. BRIEF SUMMARY OF THE INVENTION

[0007] One object of the present invention is to overcome the drawbacks of the prior art just described. The present invention achieves this object and others by providing a method for obtaining a silicon, silicon oxide, or glass surface coated with a colored layer at least in some areas, according to the attached claim 1.

[0008] It should be understood that the step of applying paint, lacquer, or varnish of a specific color (step b) can be carried out using any technique deemed appropriate by a person skilled in the art. For example, spraying, dipping, brushing, etc.

[0009] According to an advantageous embodiment of the invention, the metal layer deposited during step (a) is a titanium layer. As soon as the titanium comes into contact with an oxygen source such as air or water, a passive oxide layer a few nanometers thick forms instantly. Thereafter, the oxide layer grows only very slowly. This layer is highly adherent and resistant. It will protect the titanium from corrosion. Moreover, the layer is thin enough not to impair the adhesion of the colored layer. BRIEF DESCRIPTION OF THE FIGURES

[0010] Other features and advantages of the present invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which: there figure 1 is a schematic longitudinal cross-sectional view of a minute hand made of mono- or polycrystalline silicon, which constitutes a particular embodiment of a watch component according to the invention; figure 2 is a cross-sectional view along 2-2 of the figure 1 ; THE figures 3, 4 et 5 are three schematic diagrams illustrating respectively three steps of a particular method of implementing the process of the invention. DETAILED DESCRIPTION OF IMPLEMENTATION METHODS

[0011] There figure 1 Attached is a schematic vertical cross-sectional view of a minute hand made from mono- or polycrystalline silicon. It will be understood that the hand shown in the figure 1 This constitutes an exemplary embodiment of the watch component of the invention. As can be seen in this figure, in accordance with a widespread practice, the silicon body 3 of the hand 1 is coated on all sides with a layer of silicon oxide 5 approximately 1 micron thick. It will be understood, however, that according to variations of the embodiment shown in this example, the silicon might, for instance, not be coated with oxide, or the body of the hand 1 might be made of a material other than silicon. According to the invention, in fact, the choice of material from which the body of the watch component is made is not critical, provided that the surface covered by the adhesion layer and the colored layer is made of silicon, oxidized silicon, or glass, advantageously, oxidized silicon.

[0012] There figure 2 is a cross-section along 2-2 of the figure 1 Note that the schematic representation of the figure 2 The proportions between the thicknesses of the different layers are not respected; the aim being to facilitate the reading of the drawing. As shown in the figures, an adhesion layer 7 covers the SiO₂ surface of the upper face of the needle 1. According to the invention, the layer 7 can be made of titanium, chromium, tantalum, their oxides and nitrides, as well as alloys of these metals. The layer 7 can advantageously be made of titanium, chromium, tantalum and their oxides, and preferably of titanium or titanium oxide. An example of an alloy is titanium-tungsten. The thickness of the adhesion layer is advantageously at least 5 nanometers, most advantageously between 10 and 50 nanometers, and preferably between 10 and 25 nanometers.Choosing a bonding layer no thicker than 50 nanometers prevents its presence from disrupting the thermal or mechanical behavior of the part. It can also be seen that the bonding layer 7 is covered by a colored layer, referenced as 9. Thanks to the features of the invention, the coating, based on paint, lacquer, or varnish with its own color, adheres perfectly to the surface of the watch component, and no alteration is normally observed over the long term, provided that the watch component is an internal component, for example, a hand, a screw, a dial, a bridge, a mainplate, an oscillating weight, etc.

[0013] As everyone knows, watch hands, such as the minute hand 1, are very small. In fact, their width rarely exceeds a few hundred microns. In this regard, the plaintiff observed that the colored layer formed on the upper surface of the minute hand 1 sometimes exhibits a circumferential ridge (not shown). This ridge is an edge effect caused by the surface tension present in the liquid colored layer at the time of its application. The circumferential ridge is due to an accumulation of liquid in the areas where the layer 9 straddles two surfaces that form an angle with each other. In the case of the minute hand 1, the two surfaces in question can be the horizontal upper surface and the vertical edge of the hand 1. The plaintiff succeeded in preventing such edge effects from occurring by roughening the surface intended to be coated with the colored layer.

[0014] THE figures 3, 4 et 5 Attached are three schematic diagrams similar to that of the figure 2 , and each illustrating the result of a distinct step in a process for obtaining a surface coated with a colored layer at least in some places and which conforms to an exemplary embodiment of the invention. figures 3, 4 et 5 These are schematic cross-sectional views showing the evolution of the draft of an hour hand 51 during its production. As was already the case in the first example, the hand 51 has a body made of crystalline silicon (referenced 53) coated on all sides by a layer of silicon oxide 55 with a thickness of approximately 1 micron.

[0015] By referring first to the figure 3 As can be seen in the present example, the process for obtaining a surface coated with a colored layer, at least in some areas, begins with a step of roughening the oxidized silicon surface that forms the upper face of the needle blank 51. Those skilled in the art already have several micromachining methods available for making a surface matte, or in other words, rough. The applicant's patent application EP 3764169 A1 describes a particularly advantageous method for making a surface matte. This method comprises the following steps: Deposit a sacrificial layer of resin over the area to be matted. This sacrificial layer is created without exposing the resin or annealing it. Then, etch the sacrificial resin layer using deep reactive ion etching (DRIE). Continue etching long enough to transfer inhomogeneities from the sacrificial layer to the area of ​​the silicon surface to be matted, thus rendering it rough.

[0016] It should be noted that in the illustrated example, the rough surface is formed by the silicon oxide layer 55 which covers the upper face of the body of the needle 51. It will be understood, however, that according to other embodiments of the process of the invention, the silicon surface of the body of the needle 51 could have been roughened prior to the formation of the silicon oxide coating 55.

[0017] Now, referring to the figure 4 As can be seen, an adhesion layer 57 covers the rough SiO₂ surface of the needle blank 51. According to the invention, the layer 57 is made of titanium, chromium, tantalum, their oxides and nitrides, as well as alloys of these metals. The adhesion layer 57 is formed by physical vapor deposition (PVD) or chemical vapor deposition (CVD). Physical vapor deposition is the preferred method. Indeed, one advantage of PVD is its compatibility with techniques such as photolithography (lift-off type), masking, or mechanical masking, which allow certain selected areas of the surface to be protected from the deposition. In this example, the adhesion layer 57 is made of titanium. A titanium adhesion layer has the advantage of withstanding prolonged exposure to ambient air without losing its effectiveness.This capability allows, in particular, the application of paints, lacquers, or varnishes with their own colors to the primer layer to be delayed by several days, if necessary. It is clear that this can be especially useful when applying several different colors. PVD and CVD deposition techniques have the advantage of allowing for very thin primer layers. In this example, the thickness of layer 57 is between 5 and 50 nanometers. This thickness is sufficiently small for the primer layer 57 to reproduce the surface texture without significantly diminishing it.

[0018] Now, referring to the figure 5As can be seen, a colored layer 59 covers the tack coat 57, which coats the upper face of the needle blank 51. In this example, the colored layer is a layer of paint. As already mentioned, the paint application step can be carried out using any technique deemed suitable by a person skilled in the art. For example, spraying, dipping, brushing, etc. It will be noted that the surface of the colored layer is flat. Indeed, the paint has filled the irregularities of the substrate due to its surface tension; for example, the paint used could be opaque red paint from the Berluran® brand.

[0019] It will be understood that various modifications and / or improvements, obvious to a person skilled in the art, can be made to the embodiments and implementations described herein without departing from the scope of the present invention as defined by the appended claims. In particular, the deposition of the titanium layer by PVD or CVD may be preceded by a step of protecting the surface, so that only certain areas of the surface, including the areas to be colored, are exposed to the metal in the vapor phase. According to this variant, preferably, an additional step of removing, or chemically dissolving, the protection applied at the beginning of the process is interposed between the deposition of the titanium layer and the application of the colored layer.

[0020] Furthermore, according to yet another implementation method, at least one additional layer of metal can be deposited between the primer and the color layer. The metal for this additional layer can be chosen from among the noble metals or platinum group metals, as well as their alloys. These include gold, ruthenium, rhodium, palladium, osmium, iridium, platinum, and ruthenium. Advantageously, the metal for this additional layer is gold. This intermediate layer between the primer and the color layer can have an interesting aesthetic effect on the color layer, particularly on paint, such as enhancing its brightness or hue. Thus, a gold layer deposited by PVD or CVD on a titanium primer will allow the color of the paint layer, or more generally, the color layer, to have greater brilliance.

[0021] It will also be understood that the extent of the paint, lacquer, or varnish layer with its own color will be included within the extent of the primer layer. According to yet another method of application, the colored layer only partially covers the primer layer. This particular method of application allows for playing with the overlapping surfaces of the primer layer, at least one additional metal layer, and / or at least one colored layer, in order to reveal different layers of color and thus create shapes and / or borders.

Claims

1. Method for obtaining a surface covered by a coloured layer at least in areas on a timepiece component, said surface being a surface made of silicon, silicon dioxide, glass or metallic glass, and the method comprising the following steps: a) depositing a bonding layer (7; 57) of metal over the exposed expanse of said surface by PVD or CVD, the metal being selected from among titanium, chromium, tantalum, the alloys of said metals as well as their oxides and nitrides; b) applying a paint, a lacquer or a varnish having a self colour on the bonding layer (7; 57); characterised in that it comprises, before step a), a micro-machining step consisting of roughening the surface intended to be covered by the bonding layer.

2. Method for obtaining a surface covered by a coloured layer as claimed in claim 1, characterised in that the bonding layer (7; 57) deposited during step a) has a thickness of at least 5 nanometres, advantageously a thickness between 10 and 50 nanometres, and preferably a thickness between 10 and 25 nanometres.

3. Method for obtaining a surface covered by a coloured layer as claimed in claim 1 or 2, characterised in that the bonding layer (7; 57) deposited during step a) is a titanium layer.

4. Method for obtaining a surface covered by a coloured layer as claimed in any one of claims 1, 2 and 3, characterised in that an intermediate step is introduced between step (a) and step (b), the intermediate step consisting of depositing at least one additional layer of metal before moving to step (b).

5. Method for obtaining a surface covered by a coloured layer as claimed in any one of claims 1, 2 and 3, characterised in that step (a) is preceded by a prior step consisting of protecting said surface so that only certain areas thereof, including the area to be covered by a coloured layer, are exposed; and in that an intermediate step is introduced between step (a) and step (b), the intermediate step consisting of removing, or chemically dissolving, the protection put into place during the prior step.

6. Method for obtaining a surface covered by a coloured layer as claimed in claim 5, characterised in that said surface is protected by using lift-off-type photolithography, resist masking or mechanical masking.

7. Method for obtaining a surface covered by a coloured layer as claimed in claim 5 or 6, characterised in that a sub-step is introduced between step (a) and the intermediate step, the sub-step consisting of depositing at least one additional layer of metal.

8. Method for obtaining a surface covered by a coloured layer as claimed in any one of the preceding claims, characterised in that the timepiece component is an internal timepiece component, for example a hand, a screw, a dial, a bar, a plate, an oscillating weight, etc.

9. Method for obtaining a surface covered by a coloured layer as claimed in any one of the preceding claims, characterised in that the timepiece component (1; 51) is a hand made of silicon.