Watch component with an improved optical interference system comprising a nickel-based layer

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a component provided with an interference optical system for decorating it and in particular such an interference optical system allowing at least partial modification of the visual appearance of the component using at least one thin layer. TECHNICAL BACKGROUND OF THE INVENTION

[0002] There are decorative treatments of watch components that use an atomic layer deposition step, generally abbreviated to "ALD method" from the English term "Atomic Layer Deposition". One of the advantages of the ALD method, compared to other thin-layer deposition methods such as, for example, physical vapor deposition (PVD) notably described in document US 2013 / 029097, lies in the uniformity of the deposit thickness. Such decorative treatments consist of depositing an external protective layer of quasi-transparent ceramic material. We can cite document CH 711 122 which describes a decorative treatment method according to which a first rough and reflective layer is deposited on a substrate and a second at least partially transparent layer is deposited by an ALD method above the first layer. A white protective and / or decorative coating is thus formed on the substrate.Other known documents, such as CH709669A1, allow for a wider range of colors.

[0003] Although these decorative treatments make it possible to obtain watch components with different colors, the variety of colors, which can be achieved by varying the nature of the material deposited and / or the thickness of the layer obtained by the ALD method, is always insufficient for decorative applications requiring very specific color nuances, particularly if the substrate is made of copper-based materials very frequently used for watch components. SUMMARY OF THE INVENTION

[0004] The invention aims in particular to propose a watch component equipped with an interference optical system capable of changing the visual appearance of at least one part of the component allowing the latter to be selectively decorated according to at least one very precise shade of color from a wide variety of possible colors.

[0005] To this end, the invention relates to a watch component formed from a body based on a material to be decorated which is at least partially covered with at least one interference optical system, the latter comprising at least one transmission layer formed from an oxide, a carbide, a sulfide or a nitride which is obtained by an ALD method in order to at least partially transmit ambient light to modify the visual appearance of the watch component, characterized in that the interference optical system further comprises a nickel-based absorption layer mounted under the transmission layer to improve the accuracy of the colors obtained by the interference optical system.

[0006] Advantageously according to the invention, the interference optical system makes it possible to change the visual appearance of at least one part of the component, i.e. depending on whether it covers the entire surface of the component or only a part, and according to at least one particular shade, i.e. depending on whether the component comprises one (or more) interference optical system(s). The component, advantageously according to the invention, can therefore be selectively decorated according to at least one very precise color shade from a wide variety of possible colors and according to a very small thickness in order to make component decoration possible without adaptation of a particular implantation.

[0007] In addition, the absorption layer absorbs light across the entire visible spectrum (for the part of the light transmitted at the transmission layer - absorption layer interface) and also acts as a semi-reflective layer. It is through interference through the transmission layers that the color is modulated from the partially reflected light.

[0008] Indeed, the combination of the absorption layer under the transmission layer (or layers) allows the interference optical system to offer a very precise color shade among a wide variety of possible colors. More precisely, the interference optical system according to the invention makes it possible to selectively modulate the intensity of reflected light to offer high interference visibility, or high contrast C (unitless), i.e. at least equal to 0.7, preferably at least equal to 0.75 and ideally as close as possible to the optimal value of 1, in a relatively constant manner across the entire human visible spectrum.

[0009] This is made possible by the use of the nickel-based absorption layer offering a complex refractive index with a real part n and an imaginary part k (also called extinction coefficient) capable of forming a reflection coefficient at the interface between the absorption layer and the transmission layer close to that at the interface between the transmission layer and the air surrounding the watch component for materials formed from an oxide, a carbide, a sulfide or a nitride provided for the transmission layer(s).

[0010] Finally, advantageously according to the invention, it has been found that such a nickel-based absorption layer can offer these qualities relatively constantly across the entire human visible spectrum, which makes it possible to maintain color precision over a wide range of wavelengths for the incident light.

[0011] The invention may also include one or more of the following optional features, taken alone or in combination.

[0012] The absorption layer is preferably an alloy comprising at least 50% nickel by total weight of the alloy in order to optimize the reflection coefficient of light in the human visible spectrum. The absorption layer can thus be a binary alloy comprising, in addition to nickel, gold or zinc. It is understood that alloys of the Ni-Au or Ni-Zn type are only examples and are not the only ones allowing the advantages of the invention to be obtained.

[0013] According to a first example, the absorption layer may comprise from 50 to 70% nickel by total weight of the alloy and from 30 to 50% remaining gold. Preferably, the absorption layer comprises substantially 62.5% nickel by total weight of the alloy and 37.5% remaining gold.

[0014] According to a second example, the absorption layer may comprise from 50 to 97% nickel by total weight of the alloy and from 3 to 50% remaining zinc. Preferably, the absorption layer comprises between 80% and 90% nickel by total weight of the alloy and between 10% and 20% remaining zinc.

[0015] The absorption layer preferably has a thickness of at least 50 nm, and more preferably a thickness of at least 100 nm, so that the electromagnetic wave associated with the incident light cannot or can only barely reach the component below the absorption layer. Generally, the incident light is prevented from reaching the component or is absorbed when it is reflected at the interface between the component and the absorption layer. It has been found that an absorption layer with a thickness of 200 nm is satisfactory.

[0016] The interference optical system may comprise several transmission layers stacked on top of each other over the absorption layer in order to be able to select a precise color. Indeed, it is advantageously possible by selecting the nature and thickness of these stacks, to modulate the intensity of reflected light in order to create a very precise shade of color on the component.

[0017] At least one first transmission layer is stacked on at least one second transmission layer with different refractive indices respectively, making it possible to vary the color of the component according to the variations in nature, refractive index and thickness of each transmission layer. It is thus preferred to alternate a transmission layer with a low refractive index, i.e. for example between 1.45 and 1.95 at a wavelength of 620 nm, with another transmission layer with a high refractive index, i.e. for example between 2.1 and 3.0 at a wavelength of 620 nm, to more precisely modulate the reflected light and more easily adjust the desired color shade. Preferably, the interference optical system comprises a stack of transmission layers, i.e. without the thickness of the absorption layer, the total thickness of which is less than 2 µm.

[0018] The watch component may form all or part of a watch casing or movement. Without limitation, the material of the body to be decorated may be made of metal, glass, silicon, polymer or a combination of these materials.

[0019] The invention also relates to a method of manufacturing a watch component as presented above, characterized in that The process involves the following steps: forming a body; depositing, on at least a portion of the body, a nickel-based absorption layer; depositing, by an ALD method, at least one transmission layer on the absorption layer, each transmission layer being formed from an oxide, a carbide, a sulfide or a nitride in order to form an interference optical system on the body.

[0020] Advantageously according to the invention, the method makes it possible to obtain an interference optical system making it possible to change the visual appearance of at least one part of the component. The component can therefore be selectively decorated according to at least one very precise shade of color from a wide variety of possible colors and according to a very low thickness in order to make component decoration possible without any particular layout adaptation.

[0021] Indeed, the combination of the absorption layer under the transmission layer (or layers) allows the interference optical system to offer a very precise shade of color from a wide variety of possible colors in a relatively constant manner across the entire human visible spectrum. This is made possible by the use of the nickel-based absorption layer offering a complex refractive index with a real part n and an imaginary part k (also called extinction coefficient) capable of forming a reflection coefficient at the interface between the absorption layer and the transmission layer close to that at the interface between the transmission layer and the air surrounding the watch component for materials formed from an oxide, a carbide, a sulfide or a nitride provided for the transmission layer(s).

[0022] Finally, advantageously according to the invention, the ALD method allows a very thin and uniform layer deposition. Thus, the uniformity of the thickness of the transmission layer(s) provides a determining quality for the interference optical system, in particular through the sharpness of the colors obtained.

[0023] The invention may also include one or more of the following optional features, taken alone or in combination.

[0024] The body can be formed from metal, glass, silicon, polymer or a combination of these materials. It is understood that, thanks to the invention, the type of material of the body is no longer an obstacle to the desired color for the decoration of the watch component.

[0025] The method may comprise, between the step of forming the body and the step of depositing the absorption layer, a step of depositing at least one adhesion layer to facilitate the mounting of the interference optical system on the body. Indeed, depending on the materials used for the body, it may be difficult to deposit the nickel-based absorption layer.

[0026] The step of depositing the absorption layer can be carried out by electrodeposition, by an autocatalytic deposition process, by a physical vapor deposition process or by a chemical vapor deposition process.

[0027] The deposition step, by the ALD method, can form at least a first transmission layer stacked on at least a second transmission layer with respectively different refractive indices making it possible to vary the color of the watch component. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Other features and advantages of the invention will become clear from the description given below, for information purposes only and in no way limiting, with reference to the appended drawings, in which: there Figure 1 is a graphical representation of the variations of a color shade as a function of the variations in thickness of two transmission layers according to the invention; Figure 2 is a diagram of the evolution of the minimum and maximum reflection coefficients and of the contrast C as a function of the wavelength of a brass component covered with a single layer of alumina (Al 2 O 3 ); the Figure 3 is a diagram of the evolution of the minimum and maximum reflection coefficients and of the contrast C as a function of the wavelength of a brass component covered with an interference optical system according to the invention; Figure 4is a schematic representation of a covered component of an example of an interference optical system according to the invention; Figure 5 is a diagram illustrating a high contrast area (C greater than 0.75) desired by the invention whose interference optical system comprises a single transmission layer of silicon oxide (SiOz) with respect to the real and imaginary parts of the refractive index of different absorption layer materials; Figure 6 is a diagram illustrating a high contrast area (C greater than 0.75) desired by the invention whose interference optical system comprises a single transmission layer of zinc oxide (ZnO) with respect to the real and imaginary parts of the refractive index of different absorption layer materials; Figure 7is a diagram illustrating a high contrast area (C greater than 0.75) desired by the invention whose interference optical system comprises a single transmission layer of alumina (Al 2 O 3 ) with respect to the real and imaginary parts of the refractive index of different absorption layer materials; figure 8 is a diagram illustrating a high contrast area (C greater than 0.75) desired by the invention whose interference optical system comprises a single transmission layer of tantalum oxide (Ta 2 O 5 ) with respect to the real and imaginary parts of the refractive index of different absorption layer materials; Figure 9is a diagram illustrating a high contrast area (C greater than 0.75) desired by the invention whose interference optical system comprises a single transmission layer of zirconia (ZrO 2 ) with respect to the real and imaginary parts of the refractive index of different absorption layer materials; Figure 10 is a diagram illustrating a high contrast area (C greater than 0.75) desired by the invention whose interference optical system comprises a single transmission layer of hafnium oxide (HfO 2 ) with respect to the real and imaginary parts of the refractive index of different absorption layer materials; Figure 11is a diagram illustrating a high contrast region (C greater than 0.75) desired by the invention whose interference optical system comprises a single transmission layer of titanium oxide (TiO 2 ) with respect to the real and imaginary parts of the refractive index of different absorption layer materials. DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

[0029] In the various figures, identical or similar elements bear the same references, possibly with the addition of an index. The description of their structure and function is therefore not systematically repeated.

[0030] In all that follows, the orientations are the orientations of the figures. In particular, the terms "upper", "lower", "left", "right", "above", "below", "forward" and "backward" are generally understood to refer to the direction in which the figures are represented.

[0031] The term "human visible spectrum" means the wavelength range between 380 and 780 nm as defined in the ISO / CIE 11664-3:2019 standard of the International Commission on Illumination "CIE".

[0032] By "timepiece" we mean all types of instruments for measuring or counting time such as clocks, small clocks, watches, etc.

[0033] By "watch movement" we mean all types of mechanism capable of counting time, whether powered by mechanical energy (for example a barrel) or electrical energy (for example a battery).

[0034] By "dressing" we mean all types of devices capable of containing, displaying, decorating and / or controlling a watch movement such as, for example, all or part of a case, a bracelet or a display.

[0035] By "based on" is meant a material or alloy having substantially at least 50% by total mass or weight of a given element.

[0036] In the following, unless otherwise indicated, all percentages (%) indicated are percentages by total mass or weight.

[0037] The invention generally relates to a component 1 formed from a body 10 based on a material to be decorated. According to the invention, the body 10 of the component 1 is, advantageously, at least partially covered with at least one interference optical system 40 in order to change the visual appearance of the part of the body 10 on which the interference optical system 40 is mounted. Indeed, the interference optical system 40 can cover the entire external surface of the body 10 or only a part, such as a face or a part of a face.

[0038] Furthermore, advantageously according to the invention, the component 1 can be decorated according to at least one particular shade of color depending on whether it comprises one or more interference optical system(s) 40. Indeed, as better explained below, each interference optical system 40 allows the component 1 to be able to be selectively decorated according to at least one very precise shade of color from a large variety of possible colors and according to a very small thickness. It is understood that it is therefore possible to make the decoration of component 1 without adaptation of the particular implantation of the latter.

[0039] Component 1 was developed to apply to the watchmaking field. Thus, the component can form all or part of a watch exterior such as all or part of a dial, a display such as a hand or a disc, a case, a bracelet, a crystal or a control organ such as a crown or a push button. Component 1 can also form all or part of a movement such as all or part of an escapement device such as a Swiss lever mechanism, a resonator such as a balance-spring mechanism, a power source such as a barrel, an automatic winding system or a battery, a gear train such as a mobile or a toothed wheel, a spring, a screw, a bridge or a plate. Without limitation, the material of the body 10 to be decorated can thus be based on metal, glass, silicon, polymer, or a combination of these materials.For example, component 1 may be a dial whose body 10 is made of brass or soft iron. According to another example, component 1 may be a hand whose body 10 is made of a titanium-based alloy.

[0040] Of course, the invention cannot be limited to the field of watchmaking. Thus, the invention could also be applied in other fields such as, for example, jewelry, jewelry, leather goods, tableware, optical instruments or writing instruments.

[0041] The interference optical system 40 comprises at least one transmission layer 30 covering at least a portion of the component 1 in order to at least partially transmit ambient light to modify the visual appearance of the component 1. Each transmission layer 30 can be obtained from physical vapor deposition or chemical vapor deposition in order to preferably deposit a thickness of between 1 and 100 nm. However, chemical vapor deposition is preferred and, more precisely, an ALD method for its ability to precisely deposit thin layers of material.

[0042] Indeed, the ALD method is an atomic layer deposition process thus allowing a very thin and uniform layer deposition, that is to say typically at ± 1 nm. Indeed, more than the value of the thickness, it is the uniformity of the thickness of the transmission layer(s) 30 which is particularly decisive for the quality of the interference optical system 40 in particular by the sharpness of the colors obtained. The ALD method consists of exposing a surface successively to different chemical precursors in order to obtain ultra-thin layers of metallic compounds, oxides or other materials. It is based on self-saturated surface reactions which take place sequentially allowing controlled growth. In general, a cycle of an ALD method comprises at least two injections of precursors, these injections being separated by a purge step used to eliminate the precursor and the superfluous reaction products before the introduction of the other precursor.Advantageously, ALD technology allows the deposition of layers on a surface with a very high aspect ratio, because the reaction takes place on a monolayer of precursor gases adsorbed directly on the surface. Since the ALD method is well known, it will not be explained further below.

[0043] According to the invention, each transmission layer 30 preferably comprises a ceramic material whose very small thickness makes it almost transparent to the human visible spectrum. The ceramics, deposited in crystalline and / or amorphous form, may in particular comprise oxides, in particular metallic oxides, such as aluminum oxide (alumina, Al 2 O 3 ), zinc oxide (ZnO), titanium oxide (TiO 2 ), silicon oxide (SiO 2 ), zirconium oxide (zirconia, ZrO 2 ), tantalum oxide (Ta 2 O 5 ) and hafnium oxide (HfO 2 ). Each transmission layer 30 may also be formed from a carbide, for example metallic, a sulfide, for example metallic, or a nitride, for example metallic, without departing from the scope of the invention.

[0044] The inventors have noticed that at least one transmission layer 30 applied directly to the surface of a component 1 results in an interference optical system 40 limited in terms of the possible diversity of color shades. This is particularly the case, for example, for brasses and other copper-based alloys which are widely used in the manufacture of watch components.

[0045] To overcome this drawback, the inventors discovered that it was necessary that the interference visibility, also called the interference contrast or simply contrast C, through the interference optical system 40 which is deposited on the body 10 of the component 1 must have a high value, that is to say as close as possible to its optimal value of 1.

[0046] The value of the contrast C is in particular a function of the reflection of the incident light, for a given wavelength, at the different interfaces of the interference optical system 40. Taking the case of a single transmission layer 30 applied to the body 10, the contrast C is given by: C = R max − R min R max + R min where the minimum reflection coefficients R min and maximum reflection coefficients R max are given by: R min = R 1 − R 2 1 − R 1 R 2 2 R max = R 1 + R 2 1 + R 1 R 2 2

[0047] In this case, R 1 is the reflection coefficient at the interface between air and transmission layer 30 and R 2 is the reflection coefficient at the interface between transmission layer 30 and body 10. The values ​​of the coefficients R 1 , R 2 depend on the refractive indices of transmission layer 30 and body 10. The refractive index of air is assumed to be spectrally uniform and equal to 1. The refractive index is a dimensionless quantity characteristic of a medium that describes the behavior of light in it and depends on the measurement wavelength. In an absorbing medium, the complex refractive index ñ is a complex number whose imaginary part accounts for the attenuation of the wave according to the following relationship: n ˜ = n + ik n being the real part of the refractive index of the medium and k the imaginary part of the refractive index of the medium (also called extinction coefficient), i.e. the absorption capacity of the medium.

[0048] If we assume that the transmission layer 30 is non-absorbent (k = 0), the reflection coefficients at the interfaces, R 1 and R 2 , for a monochromatic light wave under normal incidence, are calculated as follows: R 1 = n 0 − 1 n 0 + 1 2 R 2 = n 1 − n 0 2 + k 1 2 n 1 + n 0 2 + k 1 2 where n 0 is the refractive index of the transmission layer 30, n 1 is the real part of the refractive index of the body 10, and k 1 is the extinction coefficient, sometimes called the absorption coefficient, of the body 10, for the wavelength of the incident wave.

[0049] There Figure 2 presents an example of what the invention seeks to avoid. The Figure 2shows the evolution of the contrast C for a monolayer of alumina (Al 2 O 3 ) deposited by an ALD method directly on a brass body 10 for the different wavelengths of the human visible spectrum. The coefficients R max and R min are approaching each other, and, consequently, the contrast C remains well below 1, and in particular generally below 0.5, in the human visible spectrum. It can be seen that the contrast C even tends towards 0 for the redder colors. It is clear from this limitation that the colors achievable by such an alumina-based transmission layer 30 on a brass body 10 are mainly shades of yellow and this with a very high luminance.

[0050] The inventors were able to discover, in view of the relationships cited above, that this chromatic limitation of the example of the Figure 2is due to the fact that the reflection coefficients R 1 and R 2 at the two interfaces are very different, resulting in an interference optical system 40 in which the coefficients R max and R min are relatively close. The contrast C is, therefore, relatively low, which limits the possible colors that can be obtained.

[0051] Generally, in the human visible spectrum, the reflection coefficients R at the interfaces in such an interference optical system 40 comprising the transmission layers 30 mentioned above are relatively low, typically less than 20%. For example, for a wavelength of 550 nm, the reflection coefficient at an air - TiO 2 interface is about 18%, about 6% at an air - Al 2 O 3 interface and about 4% at a TiO 2 - Al 2 O 3 interface.

[0052] More specifically, it is clear from the above that in order to obtain an interference optical system 40 with a high interference contrast C capable of giving an attractive color depth, the reflection coefficient R 2 at the interface between the transmission layer(s) 30 and the body 10 of the component 1 must also be similarly relatively low, which may in particular be the case if the refractive indices n 0 and n 1 are close and the value of k 1 is relatively low.

[0053] To reduce the luminance and thus make more colors accessible to the interference optical system 40 without being dependent on the material of the body 10, the interference optical system 40 according to the invention comprises, under the transmission layer(s) 30, an absorption layer 20 whose complex refractive index coefficients allow the interference optical system 40 to obtain a high interference contrast C on the human visible spectrum. More precisely, it is sought that the absorption layer 20 forms a reflection coefficient R 2 at the interface between the absorption layer 20 and the transmission layer 30 as close as possible to that R 1 at the interface between the transmission layer 30 and the air surrounding the watch component 1 on the human visible spectrum.

[0054] Thus, it could be observed that by having a difference (R 2 - R 1 ) between the coefficients R 2 and R 1 in a range of approximately ± 16% in the human visible spectrum, the contrast C typically has a preferred value of high contrast, i.e. at least equal to 0.7. For example, the reflection coefficient R 1 at an air - TiO 2 interface evolving between approximately 27% and 17% on the human visible spectrum having a value of approximately 18% at the wavelength of 550 nm, the reflection coefficient R 2 at a TiO 2 - absorption layer 20 interface should preferentially evolve between approximately 43% - 11% and 33% - 1% on the human visible spectrum. Of course, the reflection value R 2 when it reaches 1.2% is at a limit below which it becomes difficult to find a material that can satisfy this characteristic.Thus, when we take the case of the reflection coefficient R 1 at an air - Al 2 O 3 interface varying between approximately 6.5% and 5.5% on the human visible spectrum, we understand that it will be more frequent to find materials making it possible to obtain a reflection coefficient R 2 at the interface higher than that R 1 of the air - Al 2 O 3 interface.

[0055] The absorption layer 20 is therefore not intended to reflect the maximum amount of light transmitted by the transmission layer(s) 30 but to adapt the reflection of this transmitted light in order to limit the luminance, that is to say to selectively absorb and reflect the incident light in the interference optical system 40 to enable a wide variety of colors to be obtained by the nature and thickness of each transmission layer 30 deposited against the absorption layer 20. It is therefore possible to obtain colors having color space parameters, such as for example CIELAB, with more precise values ​​so that the difference between the desired target and the color obtained is minimized and reproducible.

[0056] Advantageously according to the invention, the interference optical system 40 thus makes it possible to change the visual appearance of a component, that is to say in particular its color. Indeed, the combination of the absorption layer 20 under the transmission layer 30 allows the interference optical system 40 to offer a very precise color shade from a wide variety of possible colors. More precisely, the interference optical system 40 according to the invention makes it possible to selectively modulate the intensity of reflected light to offer, in a relatively constant manner over the entire human visible spectrum, high interference visibility, or high interference contrast C, that is to say at least equal to 0.7, preferably at least equal to 0.75 and ideally as close as possible to the optimal value of 1.

[0057] The absorption layer 20 preferably has a thickness at least equal to 50 nm, and more preferably a thickness at least equal to 100 nm, so that the electromagnetic wave associated with the incident light cannot or can only barely reach the body 10 of the component 1 below the absorption layer 20. The absorption layer 20 can thus have a thickness equal to 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 225 nm or 250 nm. Generally, incident light is prevented from reaching the body 10 of the component 1 or is absorbed when reflected at the interface between the body 10 of the component 1 and the absorption layer 20. An absorption layer 20 with a thickness of 200 nm has been found to be satisfactory. This absorption layer 20 may be deposited by various means, but preferably it is formed by electrodeposition such as electroplating.The absorption layer 20 may also be deposited by an autocatalytic deposition process or a physical or chemical vapor deposition process.

[0058] According to the particular example of a ceramic transmission layer 30 explained below such as, for example, based on a preferentially metallic oxide, a preferentially metallic carbide, a preferentially metallic sulfide or a preferentially metallic nitride, the inventors found that a nickel-based or zinc-based absorption layer 20 gave full satisfaction in particular because these layers had complex refractive indices making it possible to obtain a high contrast C.

[0059] To illustrate this, the figures 5 to 11 indicate, each for a single type of transmission layer 30 material, the location of different absorption layer 20 materials relative to a preferred high contrast area C. The Figure 5illustrates a high contrast region C for an interference optical system 40 with a single silicon oxide (SiO 2 ) transmission layer 30 with respect to the real and imaginary parts of the refractive index of different absorption layer 20 materials. Figure 6 illustrates a high contrast region C for an interference optical system 40 with a single zinc oxide (ZnO) transmission layer 30 relative to the real and imaginary parts of the refractive index of different absorption layer 20 materials. Figure 7 illustrates a high contrast region C for an interference optical system 40 with a single transmitting layer 30 of alumina (Al 2 O 3 ) with respect to the real and imaginary parts of the refractive index of different absorption layer 20 materials. figure 8illustrates a high contrast region C for an interference optical system 40 with a single transmission layer 30 of tantalum oxide (Ta 2 O 5 ) with respect to the real and imaginary parts of the refractive index of different absorption layer 20 materials. Figure 9 illustrates a high contrast region C for an interference optical system 40 with a single transmitting layer 30 of zirconia (ZrO 2 ) with respect to the real and imaginary parts of the refractive index of different absorption layer 20 materials. Figure 10 illustrates a high contrast region C for an interference optical system 40 with a single transmission layer 30 of hafnium oxide (HfO 2 ) with respect to the real and imaginary parts of the refractive index of different absorption layer 20 materials. Figure 11illustrates a high contrast region C for an interference optical system 40 with a single transmitting layer 30 of titanium oxide (TiO 2 ) relative to the real and imaginary parts of the refractive index of different absorption layer 20 materials.

[0060] In these examples, the high contrast area C represents an area in which the average contrast C over the human visible spectrum is at least approximately equal to 0.75, with the contrast being higher in the center of the area than at its borders. For simplicity, to calculate the average contrast C in these figures 5 to 11, it is assumed that the absorption layer 20 has a constant complex refractive index (n, k) over the spectral range between 340 and 780 nm, the contrast C is calculated for each wavelength included in the spectral range 340-780 nm, and the contrast C is averaged over the spectral range 340-780 nm. The values ​​of the refractive indices of the substrates indicated on the figures 5 to 11 are taken at 550 nm, which is in the middle of the 340-780 nm spectral range.

[0061] It is noted that for these types of transmission layers having quite different refractive indices, several nickel-based and zinc-based alloys make it possible to obtain an interference optical system 40 having a high contrast C, unlike, for example, a layer formed from a brass alloy (70% copper) or silver. Thus, for these ceramic transmission layer 30 materials, a nickel- or zinc-based absorption layer 20 offers a reflection coefficient R 2 at the interface between the absorption layer 20 and the transmission layer 30 close to that R 1 at the interface between the transmission layer 30 and the air surrounding the watch component 1 on the human visible spectrum.

[0062] Nickel (Ni) belongs to the group of elements known as transition metals in the periodic table of elements, also known as the Mendeleev table, which has good light absorption properties as it can form stable ions with "d" atomic orbitals that are only partially filled. In addition, in its pure form, i.e. containing at least 95% nickel, nickel has a silvery-white color that remains colorimetrically neutral.

[0063] Similarly, zinc (Zn), in its pure form, i.e. containing at least 95% zinc, has a light grey colour which remains neutral in terms of colourimetry.

[0064] Of course, depending on the type of material used for the transmission layer 30, an absorption layer 20 may be based on a material other than nickel or zinc in order, according to the invention, to offer a reflection coefficient R 2 at the interface between the absorption layer 20 and the transmission layer 30 close to that R 1 at the interface between the transmission layer 30 and the air surrounding the watch component 1 on the human visible spectrum.

[0065] As explained above, the interference optical system 40 may comprise several transmission layers 30 stacked on top of each other over the absorption layer 20 in order to be able to select a precise color. Indeed, it is advantageously possible, by selecting the nature and thickness of each layer 30 of this stack, to modulate the intensity of reflected light in order to create a very precise shade of color on the component 1.

[0066] According to a first variant, the interference optical system 40 comprises at least one transmission layer 30 made of aluminum oxide (Al 2 O 3 ). According to a second variant, the interference optical system 40 comprises at least one transmission layer 30 made of titanium dioxide (TiO 2 ). In a third preferred variant, the interference optical system 40 comprises at least one transmission layer 30 made of aluminum oxide (Al 2 O 3 ) and at least one transmission layer 30 made of titanium dioxide (TiO 2 ).

[0067] More generally, as seen in the example of the Figure 4, preferably according to the invention, at least one first transmission layer 30, 30a, 30c, 30e is stacked on at least one second transmission layer 30, 30b, 30d with respectively different refractive indices making it possible to vary the color of the component according to the variations in nature, refractive index and thickness of each transmission layer 30. It is thus preferred to alternate a transmission layer 30, 30a, 30c, 30e with a low refractive index, i.e. for example between 1.45 and 1.95 at a wavelength of 620 nm, with another transmission layer 30, 30b, 30d with a high refractive index, i.e. for example between 2.1 and 3.0 at a wavelength of 620 nm, to more precisely modulate the reflected light and more easily adjust the desired color shade.

[0068] Preferably, the interference optical system 40 comprises a stack of transmission layers 30, 30a, 30b, 30c, 30d, 30e, i.e. without the thickness of the absorption layer 20, the total thickness of which is less than 2 µm. During the studies carried out, it appeared that satisfactory colors were obtained for a stack of transmission layers 30, 30a, 30b, 30c, 30d, 30e with a total thickness of less than 300 nm.

[0069] In order to be able to obtain good interference power in an interference optical system 40 with several transmission layers 30, it is necessary to adapt the conditions described (see the mathematical relationships above) for the interference optical system 40 with a single transmission layer 30, which stipulate that the values ​​of the reflection coefficients at the various interfaces must be as close as possible to each other.

[0070] If we consider an interference optical system 40 with only two types of transmission layers 30 (high and low refractive indices, respectively n H and n B ), we must adapt the equations of the reflection coefficients at the interfaces, R 1 and R 2 , to the different cases (first transmission layer 30 deposited on the absorption layer 20 of index ne or n H , etc., last transmission layer 30 in contact with the air of index n B or n H ). In particular, we must take into account the reflection coefficient at the interfaces between layers of high and low refractive indices: R = n B − n H 2 + k B 2 n B + n H 2 + k B 2 where k B is the extinction coefficient of the low refractive index transmission layer 30 which can be considered negligible (just like the extinction coefficient of the high refractive index transmission layer 30).

[0071] The overall refractive index of the stack of transmission layers 30 is preferably between 1.45 and 2.7 over the human visible spectrum.

[0072] As an example, a graphical representation of the variations in a color shade as a function of the variations in thickness of two transmission layers 30 according to the invention is illustrated in Figure 1 . The interference optical system 40 comprises, for this example, a transmission layer 30 made of aluminum oxide (Al 2 O 3 ) with a low refractive index on the human visible spectrum, i.e. between 1.6 and 1.7, which is deposited above a transmission layer 30 of titanium oxide (TiO 2 ) with a high refractive index on the human visible spectrum, i.e. between 2.1 and 3.0. The large variation in shades obtained despite the small variations in thickness of each of the two transmission layers 30 is immediately noticeable.

[0073] As explained above, the absorption layer 20 aims to adapt the reflection coefficient at its interface with the first of the transmission layers 30 to the reflection coefficients of the other interfaces of the interference optical system 40, or even in this example the interfaces between a “high index” transmission layer 30 with a “low index” transmission layer 30 as well as the interface of the last transmission layer 30 with the air surrounding the component 1. For this purpose, the material of the transmission layer 20 can be modified to adapt the coefficients of its complex refractive index without losing any of its other qualities. In the example of nickel or zinc explained above, the absorption layer 20 can thus be an alloy comprising nickel or zinc in order to adapt its complex reflection index coefficients while maintaining high stability over the human visible spectrum.

[0074] The inventors have for example found that an absorption layer 20 based on a binary alloy comprising gold or zinc in addition to nickel or nickel in addition to zinc was satisfactory. Of course, it is understood that alloys of the Ni-Au or Ni-Zn type, or of the Zn-Ni type are only examples and are not the only ones allowing the advantages of the invention to be obtained. It is of course possible to envisage other alloys than binary ones and, in particular, which could comprise more elements than two metals outside the usual so-called pollution compounds whose proportion by weight does not exceed 0.2% of the total mass of the alloy.

[0075] For example, the binary alloy Zn-Ni can be deposited by electroplating using an electrolyte bath whose base consists mainly of nickel sulfate hexahydrate 10 - 25%, nickel chloride hexahydrate 2.5 - 10%, zinc sulfate (mono-, hexa- and heptahydrate) 2.5 - 10%, sodium thiocyanate ≤ 2.5% and an electrometric pH (at 20 °C) of 5.8 to 6. The deposition temperature can be adjusted in a window between 22 °C and 17 °C. Preferably, it is regulated along the deposition at 18 °C and the current density of 0.12 to 0.15 A.dm -2< .

[0076] The resulting binary alloy comprises, for example, 60 to 80% zinc by total weight of the alloy and the remaining 20 to 40% nickel. In a specific example, the alloy comprises substantially 80% zinc and the remaining 20% ​​nickel and has a dark gray color. Figure 3shows the evolution of the contrast C for a monolayer of alumina (Al 2 O 3 ) deposited on an absorption layer 20 in such a zinc-nickel alloy. It emerges from the Figure 3 that the value of the contrast C remains advantageously greater than 0.8 over the entire human visible spectrum.

[0077] Like the figures 5 to 11 show, the alloy of substantially 80% zinc and 20% nickel exhibits a complex refractive index at a wavelength of 550 nm with n ≈ 1.8 and k ≈ 0.32. In another specific example, the alloy comprises substantially 70% zinc and the remaining 30% nickel and results in an interference optical system 40 having a contrast C similar to that of substantially 80% zinc and 20% nickel across the entire human visible spectrum. As the figures 5 to 11 show, the alloy of approximately 70% zinc and 30% nickel has a complex refractive index at a wavelength of 550 nm with n ≈ 2.1 and k ≈ 1.2.

[0078] For a binary Ni-Au alloy, the absorption layer 20 can be deposited by electroplating using an electrolyte bath composed of ammonium nickel sulfate at 10 - 25% and an electrometric pH (at 20 °C) of 5.7 to 5.9. The deposition temperature can be in the order of 65 - 75 °C. Preferably, it is regulated at 65 °C and the current density of 0.5 to 1.0 A.dm -2< .

[0079] The resulting binary alloy comprises, for example, 50 to 70% nickel by total weight of the alloy and the remaining 30 to 50% gold. Preferably, the alloy comprises 60 to 65% nickel and 35 to 40% gold. In a specific example, the alloy comprises substantially 62.5% nickel and 37.5% gold, and has a black-grey color. As the figures 5 to 11 show, the alloy of approximately 62.5% nickel and 37.5% gold has a complex refractive index at a wavelength of 550 nm with n ≈ 2.5 and k ≈ 1.4.

[0080] According to a second example, the absorption layer may comprise from 50 to 97% nickel by total weight of the alloy and from 3 to 50% remaining zinc. Preferably, the absorption layer comprises between 80% and 90% nickel by total weight of the alloy and between 10% and 20% remaining zinc. Alloys of this type and methods for depositing them by electroplating are described for example in document US 4,416,737.

[0081] It is noted that, according to different examples of the invention explained above, the high contrast C is obtained for a real part n of the refractive index of the absorption layer 20 based on nickel or based on zinc at a wavelength of 550 nm advantageously greater than or equal to 1.25, and preferably greater than or equal to 1.5 and even more preferably greater than or equal to 1.75, and / or an imaginary part k of the refractive index of the absorption layer 20 at a wavelength of 550 nm advantageously less than or equal to 3.5, and preferably less than or equal to 2.0, and even more preferably less than or equal to 1.5. These values ​​differ from the typical n and k values ​​of other metallic materials such as brass and silver which very often have a real part n value less than 1.0 and an imaginary part k value greater than 3.5 at a wavelength of 550 nm.

[0082] Furthermore, it has been observed that by having a difference (R 2 - R 1 ) between the reflection coefficient R 2 at the interface between the absorption layer 20 and the transmission layer 30 and that R 1 at the interface between the transmission layer 30 and the air surrounding the watch component 1 on the human visible spectrum comprised in a range of approximately ± 16%, the contrast C typically has a preferred value of high contrast, i.e. at least equal to 0.7. Preferably, the difference (R 2 - R 1 ) between the coefficients R 2 and R 1 is comprised between ± 13%, and even more preferably comprised between ± 10% in order to obtain an even higher contrast in the human visible spectrum.

[0083] The invention is not limited to the embodiments and variants presented and other embodiments and variants will become clear to those skilled in the art. Thus, the embodiments and variants can be combined with each other without departing from the scope of the invention. By way of non-limiting example, it may be envisaged to vary the nature and number of transmission layer(s) 30 of the interference optical system 40 without departing from the scope of the invention.

[0084] As an example, an interference optical system 40 according to the invention is illustrated in Figure 4. The interference optical system 40 comprises a stack of five transmission layers 30a, 30b, 30c, 30d, 30e deposited by an ALD method. The transmission layers 30a, 30c, 30e may comprise aluminum oxide (Al 2 O 3 ) or an oxide stoichiometrically close to the latter, and may be deposited using successively trimethylaluminum C 6 H 18 Al 2 (TMA) and deionized water with low conductivity (for example below 1 µS.cm -1< ) ​​as precursors in an ALD reactor, preferably at temperatures below 200 °C. The transfer of precursors into the chamber is ensured by a continuous flow of nitrogen (N 2 ). The injection time for precursors can be 0.1 to 0.5 seconds, with these injection steps being separated by nitrogen purge steps lasting 5 to 30 seconds.

[0085] The transmission layers 30b, 30d may comprise titanium oxide (TiO 2 ) or an oxide stoichiometrically close thereto. They may be deposited using tetrakis(dimethylamino)titanium also known as TDMAT (Ti(NMe 2 ) 4 ) or titanium tetrachloride (TiCl4) and low conductivity deionized water as precursors in an ALD reactor at conditions similar to those for layers 30a, 30c, 30e.

[0086] For each transmission layer 30a, 30b, 30c, 30d, 30e, the number of cycles of self-saturated growth is of course chosen according to the desired thickness.

[0087] Optionally, at least one adhesion layer 25 can be deposited between the absorption layer 20 and the body 10 of the component 1 to facilitate the mounting of the interference optical system 40 on the body 10. Each layer 25, for example based on pure nickel or pure gold, can thus play the role of a bonding element to avoid in particular delamination between the absorption layer 20 on the body 10. Of course, with or without adhesion layer 25, the surface of the body 10 of the component 1 can be cleaned or prepared in another way before any deposition to facilitate its bonding.

Claims

1. Timepiece component (1) formed from a body (10) based on a material to be decorated which is at least partially covered with at least one interferential optical system (40), the latter comprising at least one oxide-, carbide-, sulphide- or nitride-based transmission layer (30) obtained by an ALD method to at least partially transmit ambient light to modify the visual appearance of the timepiece component (1), characterised in that the interferential optical system (40) further comprises a nickel-based absorption layer (20) installed under the transmission layer (30) in order to improve the precision of the colours obtained by the interferential optical system (40).

2. Timepiece component (1) according to the preceding claim, wherein the absorption layer (20) is an alloy comprising at least 50 % nickel by total weight of the alloy.

3. Timepiece component (1) according to the preceding claim, wherein the absorption layer (20) is a binary alloy comprising gold, in addition to nickel.

4. Timepiece component (1) according to the preceding claim, wherein the absorption layer (20) comprises 50 % to 70 % nickel by total weight of the alloy and the remaining 30 % to 50 % is gold.

5. Timepiece component (1) according to claim 2, wherein the absorption layer (20) is a binary alloy comprising zinc, in addition to nickel.

6. Timepiece component (1) according to the preceding claim, wherein the absorption layer (20) comprises 50 % to 97 % nickel by total weight of the alloy and the remaining 3 % to 50 % is zinc.

7. Timepiece component (1) according to any one of the preceding claims, wherein the thickness of the absorption layer (20) is at least equal to 50 nm, preferably at least equal to 100 nm.

8. Timepiece component (1) according to any one of the preceding claims, wherein the interferential optical system (40) comprises several transmission layers (30) stacked one on top of the other over the absorption layer (20) in order to be able to select a precise colour.

9. Timepiece component (1) according to the preceding claim, wherein at least one first transmission layer (30) is stacked on at least one second transmission layer (30) with respectively different refractive indices in order to vary the colour of the timepiece component (1).

10. Timepiece component (1) according to any one of the preceding claims, wherein the material of the body (10) to be decorated is based on metal, glass, silicon, polymer or a combination of these materials.

11. Method for manufacturing a timepiece component (1) according to any one of the preceding claims, characterised in that the method comprises the following steps: - forming a body (10); - depositing, on at least one part of the body (10), a nickel-based absorption layer (20); - depositing, using an ALD method, at least one transmission layer (30) on the absorption layer (20), each transmission layer (30) being oxide-, carbide-, sulphide- or nitride-based, to form an interferential optical system (40) on the body (10).

12. Method according to the preceding claim, wherein the body (10) is based on metal, glass, silicon, polymer or a combination of these materials.

13. Method according to claim 11 or 12, comprising, between the step of forming the body (10) and the step of depositing the absorption layer (20), a step of depositing at least one adhesion layer (25) to simplify the installation of the interferential optical system (40) on the body (10).

14. Method according to any one of claims 11 to 13, wherein the step of depositing the absorption layer (20) is carried out by electroplating, by an electroless plating method, by a physical or chemical vapour deposition process.

15. Method according to any one of claims 11 to 14, wherein the step of depositing, using the ALD method, forms at least one first transmission layer (30) stacked on at least one second transmission layer (30) with respectively different refractive indices in order to vary the colour of the timepiece component (1).