EP3896193A1 - Timepiece component with an improved interferential optical system - Google Patents

Abstract

The invention relates to a horological component (1) formed of a body (10) based on a material to be decorated which is at least partially covered with at least one interference optical system (40), the latter comprising at least one at least one transmissive layer (30) formed on the basis of an oxide, carbide, sulfide or 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 (1). According to the invention, the interference optical system (40) further comprises an absorption layer (20) mounted under the transmission layer (30), the real part of which has the complex refractive index, for a wavelength of 550 nm, is at least equal to 1.25 making it possible to improve the precision of the colors obtained by the interference optical system (40).

Description

TECHNICAL FIELD OF THE INVENTION

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

The document EP 2 392 689 proposes to form a thin layer of red color on an article. Provision is made to deposit a metallic reflective layer on the article and, over it, an absorbent layer forming a color filter in order to emit red-colored radiation from incident white light. According to the variants, a transparent layer is present between the reflective layer and the absorbent layer and / or above the absorbent layer. It is therefore understood that only the red color is sought and that it is given by the transmission of the incident light in the absorbent layer (absorption of the blue spectral components of the incident light). It is specified that the refractive indices of the transparent and absorbent layers are sufficiently close to be free from interference effects seen as harmful. In fact, no interference effect is obtained by the transparent layer (s), that is to say a precise color cannot be selectively chosen from among several possible colors to obtain a predetermined decoration. , but only by the color filter formed by the absorbent layer. This is all the more true since only physical vapor deposition (PVD) methods are provided, the thickness irregularity of which does not make it possible to obtain a predictable and reproducible optical layer.

There are decorative treatments of watch components which use an atomic layer deposition step, generally abbreviated as “ALD method” coming from the English terms “Atomic Layer Deposition”. One of the advantages of the ALD method, over other thin film deposition methods such as, for example, physical vapor deposition is the uniformity of the deposition thickness. Such decorative treatments consist in depositing an outer protective layer of quasi-transparent ceramic material. We can cite the document CH 711 122 which describes a decorative treatment process 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 on top of the first lying down. A protective and / or decorative coating of white color is thus formed on the substrate.

Although these decorative treatments make it possible to obtain watch components having different colors, the variety of colors, which can be produced by varying the nature of the material deposited and / or the thickness of the layer obtained by the ALD method, is still insufficient. for decorative applications requiring very specific shades of color, in particular if the substrate is made of copper-based materials very frequently used for watch components.

SUMMARY OF THE INVENTION

The object of the invention is in particular to provide a watch component provided with an interference optical system capable of changing the visual appearance of at least part of the component allowing the latter to be selectively decorated in at least one shade of color. very precise among a wide variety of possible colors.

To this end, the invention relates to a watch component formed of 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 on the basis of an oxide, a carbide, a sulphide or a nitride which is obtained by an ALD method in order to at least partially transmit ambient light in order to modify the visual appearance of the watch component, characterized in that the interference optical system further comprises an absorption layer mounted under the transmission layer of which the real part of the complex refractive index, for a wavelength of 550 nm, is at least equal to 1, 25 making it possible to improve the precision of the colors obtained by the interference optical system.

Advantageously according to the invention, the interference optical system makes it possible to change the visual appearance of at least part of the component, that is to say depending on whether it covers the entire surface of the component or only a part, and according to at least one particular shade, that is to say according to whether the component comprises one (or more) optical interference system (s). The component, advantageously according to the invention, 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 small thickness in order to make the decoration of the component possible without any particular layout adaptation. .

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

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 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), 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 optimum value of 1, relatively constantly over the entire human visible spectrum.

This is made possible by the use of the absorption layer offering a complex refractive index with a real part n and an imaginary part k (also called the 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 based on an oxide, a carbide, a sulfide or nitride provided for the transmission layer (s).

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

The absorption layer comprises, for a wavelength of 550 nm, preferably an imaginary part of the complex refractive index at most equal to 3.5. Advantageously according to the invention, this limit of the imaginary part with that of the real part at least equal to 1.25, guarantee an interference contrast at least equal to 0.7.

The interference optical system preferably comprises a reflection coefficient at the interface between the absorption layer and the transmission layer sufficiently close to that at the interface between the transmission layer and the air surrounding the watch component in order to present an interference contrast at least equal to 0.7, especially the visible human spectrum. Indeed, the interference contrast at least equal to 0.7, preferably at least equal to 0.75 and ideally as close as possible to the optimum value of 1 makes it possible to offer a very precise shade of color among a wide variety of colors. possible colors.

The absorption layer 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 only slightly reach the component below. of the absorption layer. Generally, incident light is prevented from reaching the component or is absorbed when 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.

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

At least a first transmission layer is stacked on at least a second transmission layer 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. It is thus preferred to alternate a transmission layer with a low refractive index, that is to say for example between 1.45 and 1.95 at a wavelength of 620 nm, with another layer transmission of high refractive index, that is to say 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 shade desired color. Preferably, the interference optical system comprises a stack of transmission layers, that is to say without the thickness of the absorption layer, the total thickness of which is less than 2 μm.

Preferably, each transmission layer is based on aluminum oxide (Al ₂ O ₃ ) and / or titanium oxide (TiO ₂ ) and / or zinc oxide (ZnO) and / or oxide silicon (SiO ₂ ) and / or zirconium oxide (ZrO ₂ ) and / or tantalum oxide (Ta ₂ O ₅ ) and / or hafnium oxide (HfO ₂ ).

The watch component can form all or part of a casing or a watch movement. In no way limiting, the material of the body to be decorated can thus be based on metal, glass, silicon, polymer or a combination of these materials.

• former un corps ;
• déposer, sur au moins une partie du corps, une couche d'absorption à base d'un matériau dont la partie réelle de l'indice de réfraction complexe, pour une longueur d'onde de 550 nm, est au moins égale à 1,25 ;
• déposer, par une méthode ALD, au moins une couche de transmission sur la couche d'absorption, chaque couche de transmission étant formée à base d'un oxyde, d'un carbure, d'un sulfure ou d'un nitrure afin de former un système optique interférentiel sur le corps.

The invention also relates to a method of manufacturing a watch component as presented above, characterized in that the method comprises the following steps:

• to form a body;
• deposit, on at least one part of the body, an absorption layer based on a material whose real part of the complex refractive index, for a wavelength of 550 nm, is at least equal to 1, 25;
• 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 interferential optical system on the body.

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 part of the component. The component can therefore be selectively decorated according to at least one very precise shade of color from among a wide variety of possible colors and according to a very small thickness in order to make possible the decoration of the component without any particular layout adaptation.

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 among a wide variety of possible colors relatively consistently over the entire spectrum. visible human. This is made possible by the use of the absorption layer offering a complex refractive index with a real part n and an imaginary part k (also called the extinction coefficient) including the real part, for a wavelength of 550 nm, is at least equal to 1.25 and 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 based on an oxide, a carbide, a sulfide or a nitride provided for the transmission layer (s).

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

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

During the deposition step, the absorption layer may also have an imaginary part of the complex refractive index, for a wavelength of 550 nm, at most equal to 3.5.

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

The method may include, 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 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 absorption layer.

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

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 timepiece component.

BRIEF DESCRIPTION OF THE DRAWINGS

• la figure 1 est une représentation graphique des variations d'une nuance de couleur en fonction des variations d'épaisseur de deux couches de transmission selon l'invention ;
• la figure 2 est un diagramme de l'évolution des coefficients de réflexion minimal et maximal et du contraste C en fonction de la longueur d'onde d'un composant en laiton recouvert d'une unique couche d'alumine (Al₂O₃) ;
• la figure 3 est un diagramme de l'évolution des coefficients de réflexion minimal et maximal et du contraste C en fonction de la longueur d'onde d'un composant en laiton recouvert d'un système optique interférentiel selon l'invention ;
• la figure 4 est une représentation schématique d'un composant recouvert d'un exemple de système optique interférentiel selon l'invention ;
• la figure 5 est un diagramme illustrant une zone de haut contraste (C supérieur à 0,75) souhaitée par l'invention dont le système optique interférentiel comporte une couche de transmission unique d'oxyde de silicium (SiO₂) par rapport aux parties réelles et imaginaires de l'indice de réfraction de différents matériaux de couche d'absorption ;
• la figure 6 est un diagramme illustrant une zone de haut contraste (C supérieur à 0,75) souhaitée par l'invention dont le système optique interférentiel comporte une couche de transmission unique d'oxyde de zinc (ZnO) par rapport aux parties réelles et imaginaires de l'indice de réfraction de différents matériaux de couche d'absorption ;
• la figure 7 est un diagramme illustrant une zone de haut contraste (C supérieur à 0,75) souhaitée par l'invention dont le système optique interférentiel comporte une couche de transmission unique d'alumine (Al₂O₃) par rapport aux parties réelles et imaginaires de l'indice de réfraction de différents matériaux de couche d'absorption ;
• la figure 8 est un diagramme illustrant une zone de haut contraste (C supérieur à 0,75) souhaitée par l'invention dont le système optique interférentiel comporte une couche de transmission unique d'oxyde de tantale (Ta₂O₅) par rapport aux parties réelles et imaginaires de l'indice de réfraction de différents matériaux de couche d'absorption ;

• la figure 9 est un diagramme illustrant une zone de haut contraste (C supérieur à 0,75) souhaitée par l'invention dont le système optique interférentiel comporte une couche de transmission unique de zircone (ZrO₂) par rapport aux parties réelles et imaginaires de l'indice de réfraction de différents matériaux de couche d'absorption ;
• la figure 10 est un diagramme illustrant une zone de haut contraste (C supérieur à 0,75) souhaitée par l'invention dont le système optique interférentiel comporte une couche de transmission unique d'oxyde d'hafnium (HfO₂) par rapport aux parties réelles et imaginaires de l'indice de réfraction de différents matériaux de couche d'absorption ;
• la figure 11 est un diagramme illustrant une zone de haut contraste (C supérieur à 0,75) souhaitée par l'invention dont le système optique interférentiel comporte une couche de transmission unique d'oxyde de titane (TiO₂) par rapport aux parties réelles et imaginaires de l'indice de réfraction de différents matériaux de couche d'absorption.

Other features and advantages of the invention will emerge clearly from the description which is given below, by way of indication and in no way limiting, with reference to the appended drawings, in which:

• the figure 1 is a graphic representation of the variations of a color shade as a function of the variations in thickness of two transmission layers according to the invention;
• the 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;
• the figure 4 is a schematic representation of a component covered with an example of an interference optical system according to the invention;
• the figure 5 is a diagram illustrating a high contrast zone (C greater than 0.75) desired by the invention, the interference optical system of which comprises a single transmission layer of silicon oxide (SiO ₂ ) with respect to the real and imaginary parts of the refractive index of different absorption layer materials;
• the figure 6 is a diagram illustrating a high contrast zone (C greater than 0.75) desired by the invention, the interference optical system of which 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;
• the figure 7 is a diagram illustrating a high contrast zone (C greater than 0.75) desired by the invention, the interference optical system of which 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;
• the figure 8 is a diagram illustrating a high contrast zone (C greater than 0.75) desired by the invention, the interference optical system of which comprises a single transmission layer of tantalum oxide (Ta ₂ O ₅ ) with respect to real and imaginary parts of the refractive index of different absorption layer materials;

• the figure 9 is a diagram illustrating a high contrast zone (C greater than 0.75) desired by the invention, the interference optical system of which comprises a single transmission layer of zirconia (ZrO ₂ ) with respect to the real and imaginary parts of the index refraction of different absorption layer materials;
• the figure 10 is a diagram illustrating a high contrast zone (C greater than 0.75) desired by the invention, the interference optical system of which comprises a single transmission layer of hafnium oxide (HfO ₂ ) with respect to the real and imaginary parts the refractive index of different absorption layer materials;
• the figure 11 is a diagram illustrating a high contrast zone (C greater than 0.75) desired by the invention, the interference optical system of which 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

In the various figures, identical or similar elements bear the same references, optionally added to an index. The description of their structure and function is therefore not systematically repeated.

In what follows, the orientations are the orientations of the figures. In particular, the terms “upper”, “lower”, “left”, “right”, “above”, “below”, “towards the front” and “towards the rear” are generally understood to mean with respect to the direction of representation of the figures.

By “human visible spectrum” is meant the wavelength range between 380 and 780 nm within the meaning of standard ISO / CIE 11664-3: 2019 of the International Commission on Illumination “CIE”.

By "timepiece" is meant all types of time measuring or counting instruments such as clocks, clocks, watches, etc.

The term “watch movement” is understood to mean all types of mechanism capable of counting time, whether they are powered by mechanical energy (for example a barrel) or electrical energy (for example a battery).

By “dressing” is meant 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.

By “based on” is meant a material or alloy having substantially at least 50% by total mass or weight of a given element.

In what follows, unless otherwise indicated, all the percentages (%) indicated are percentages by total mass or weight (in English "weight").

The invention generally relates to a component 1 formed of a body 10 based on a material to be decorated. According to the invention, the body 10 of 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 whole of the external surface of the body 10 or only a part, such as a face or a part of a face.

In addition, advantageously according to the invention, 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 above- below, each interference optical system 40 allows component 1 to be able to be selectively decorated according to at least one very precise shade of color from among a large variety of possible colors and according to a very small thickness. It will be understood that it is therefore possible to make the decoration of component 1 without adapting the particular layout of the latter.

Component 1 was developed to apply to the watchmaking field. Thus, the component can form all or part of a watch covering such as all or part of a dial, of a display such as a hand or a disc, of a case, of a bracelet, of a crystal. or a control member 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, of a resonator such as a balance-spring mechanism, of a source energy such as a barrel, an automatic winding system or a battery, a cog such as a mobile or a toothed wheel, a spring, a screw, a bridge or a platinum. In no way limiting, the material of the body 10 to be decorated can thus be based on metal, glass, silicon, polymer, or a combination of these materials. By way of example, component 1 can be a dial whose body 10 is made of brass or soft iron. According to another example, component 1 may be a needle, the body 10 of which is made of a titanium-based alloy.

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

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

In fact, the ALD method is a method for depositing atomic layers therefore allowing deposition in a very thin and uniform layer, that is to say typically at ± 1 nm. In fact, 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 in 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 serving to remove the precursor and the superfluous reaction products before the introduction of the other precursor. Advantageously, the ALD technology makes it possible to deposit layers on a surface having a very high aspect ratio, since the reaction takes place on a monolayer of precursor gases adsorbed directly on the surface. The ALD method being very well known, it will not be further explained below.

According to the invention, each transmission layer 30 preferably comprises a ceramic material which the very small thickness makes quasi-transparent to the human visible spectrum. The ceramics, deposited in crystalline and / or amorphous form, can 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 can also be formed based on a carbide, for example metallic, on a sulfide, for example metallic, or on a nitride, for example metallic, without departing from the scope of the invention.

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 as to the possible diversity of color shades. this is in particular the case, for example, for brass and other copper-based alloys which are widely used in the manufacture of watch components.

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

où les coefficients de réflexion minimale R_min et de réflexion maximale R_max sont donnés par: $$R_{\mathit{min}}={\left(\frac{\sqrt{R_1}-\sqrt{R_2}}{1-\sqrt{R_1{R}_2}}\right)}^2$$

$$R_{\mathit{max}}={\left(\frac{\sqrt{R_1}+\sqrt{R_2}}{1+\sqrt{R_1{R}_2}}\right)}^2$$

The value of the contrast C is in particular a function of the reflection of the incident light, for a given wavelength, at the various 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: $$\mathrm{VS}=\frac{R_{\mathit{max}}-R_{\mathit{min}}}{R_{\mathit{max}}+R_{\mathit{min}}}$$

where the minimum reflection coefficients R _min and maximum reflection R _max are given by: $$R_{\mathit{min}}={\left(\frac{\sqrt{R_1}-\sqrt{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}}{1-\sqrt{R_1{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}}\right)}^2$$

$$R_{\mathit{max}}={\left(\frac{\sqrt{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">R</figure-callout>}}_1}+\sqrt{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}}{1+\sqrt{R_1{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}}\right)}^2$$

In this case, R ₁ is the reflection coefficient at the air interface - transmission layer 30 and R ₂ is the reflection coefficient at the interface transmission layer 30 - body 10. The values of the coefficients R ₁ , R ₂ depend on the refractive indices of the transmission layer 30 and of the 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 which describes the behavior of light therein and depends on the measurement wavelength. In an absorbing medium, the complex refractive index ñ is a complex number, the imaginary part of which accounts for the attenuation of the wave according to the following relation:

ñ = 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 the extinction coefficient), that is to say the absorption capacity of the medium.

$$R_2=\frac{{\left(n_1+n_0\right)}^2+k_1^2}{{\left(n_1+n_0\right)}^2+k_1^2}$$

où n₀ est l'indice de réfraction de la couche 30 de transmission, n₁ est la partie réelle de l'indice de réfraction du corps 10, et k₁ est le coefficient d'extinction, parfois appelé coefficient d'absorption, du corps 10, pour la longueur d'onde de l'onde incidente.If it is assumed 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 at normal incidence, are calculated as follows: $${\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">R</figure-callout>}}_1={\left(\frac{{\mathrm{not}}_0-1}{{\mathrm{not}}_0+1}\right)}^2$$

$${\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">R</figure-callout>}}_2=\frac{{\left({\mathrm{not}}_1+{\mathrm{not}}_0\right)}^2+{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">k</figure-callout>}}_1^2}{{\left({\mathrm{not}}_1+{\mathrm{not}}_0\right)}^2+{\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">k</figure-callout>}}_1^2}$$

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.

The figure 2 presents an example of what the invention wishes to avoid. The figure 2 shows the change in contrast C for an alumina monolayer (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 approach each other, and, consequently, the contrast C remains much less than 1, and in particular in general less than 0.5, in the human visible spectrum. We can see that the contrast C even tends towards 0 for the more red colors. It emerges 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.

The inventors were able to discover, in view of the relationships cited above, that this chromatic limitation of the example of the figure 2 is due to the fact that the coefficients R ₁ and R ₂ of reflection at the two interfaces are very different, which results 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 to be obtained.

In general, 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 an air-TiO 2 interface. TiO ₂ - Al ₂ O ₃ interface.

More precisely, it emerges from the foregoing 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 layer (s) ( s) 30 and the body 10 of component 1 must likewise be relatively low, which may in particular be the case if the refraction indices n ₀ and n ₁ are close and the value of k ₁ is relatively low.

To reduce the luminance and thus to 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 layer (s) 30 of transmission , an absorption layer 20 whose coefficients of its complex refractive index allow the interference optical system 40 to obtain a high interference contrast C on the human visible spectrum. More precisely, it is wanted 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 horological component 1 on the human visible spectrum.

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 about ± 16% in the human visible spectrum, the contrast C typically exhibits a value preferred high contrast, that is to say at least equal to 0.7. For example, the coefficient R ₁ of reflection 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 coefficient R ₂ of reflection at a TiO ₂ - absorption layer 20 interface should preferably vary between approximately 43% - 11% and 33% - 1% on the human visible spectrum. Of course, the value R ₂ of reflection when it reaches 1.2% is at a limit below which it becomes difficult to find a material which can satisfy this characteristic. Thus, when we take the case of the coefficient R ₁ of reflection at an air - Al ₂ O ₃ interface evolving 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 coefficient R ₂ of reflection at the interface greater than that R ₁ of the air interface - Al ₂ O ₃ .

The purpose of the absorption layer 20 is therefore not 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, c 'that is to say selectively absorb and reflect the incident light in the interference optical system 40 to allow obtaining a great diversity of colors by the nature and thickness of each transmission layer 30 deposited against the layer 20 d 'absorption. 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.

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 shade of color among 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, relatively constantly over the entire human visible spectrum, high interference visibility, or high interference contrast C, c 'is to say at least equal to 0.7, preferably at least equal to 0.75 and ideally closest to the optimum value of 1.

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 only slightly 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 component 1 or is absorbed when reflected at the interface between body 10 of component 1 and absorption layer 20. It has been found that an absorption layer with a thickness of 200 nm is satisfactory. This absorption layer 20 can be deposited by various means, but preferably it is formed by electrodeposition such as electroplating. The absorption layer 20 can also be deposited by an electroless deposition process or a physical or chemical vapor deposition process.

According to the particular example of a ceramic transmission layer 30 explained below as, for example, based on a preferably metallic oxide, a preferably metallic carbide, a preferably metallic sulfide or a nitride Preferably metallic, the inventors have found that an absorption layer 20 based on nickel or based on zinc gives full satisfaction, in particular because these layers have complex refractive indices making it possible to obtain a high contrast C.

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 with respect to a preferred high contrast area C. The figure 5 illustrates a high contrast area C for an interference optical system 40 with a single transmitting layer 30 of silicon oxide (SiO ₂ ) with respect to the real and imaginary parts of the refractive index of different layer 20 materials. absorption. The figure 6 illustrates a high contrast region C for an interference optical system 40 with a single transmitting layer 30 of zinc oxide (ZnO) relative to the real and imaginary parts of the refractive index of different absorption layer 20 materials . The figure 7 illustrates a high contrast area C for an interference optical system 40 with a single transmissive layer 30 of alumina (Al ₂ O ₃ ) relative to the real and imaginary parts of the refractive index of different layer 20 materials of absorption. The figure 8 illustrates a high contrast region C for an interference optical system 40 with a single transmissive layer 30 of tantalum oxide (Ta ₂ O ₅ ) relative to the real and imaginary parts of the refractive index of different layer materials 20 absorption. The figure 9 illustrates a high area contrast C for an interference optical system 40 with a single transmission layer 30 of zirconia (ZrO ₂ ) versus the real and imaginary parts of the refractive index of different absorption layer 20 materials. The figure 10 illustrates a high contrast area C for an interference optical system 40 with a single transmission layer 30 of hafnium oxide (HfO ₂ ) relative to the real and imaginary parts of the refractive index of different layer materials 20 d 'absorption. The figure 11 illustrates 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 layer materials 20 of absorption.

In these examples, the high contrast area C represents an area in which the average contrast C on the human visible spectrum is at least approximately equal to 0.75, the contrast being higher at the center of the area than at its borders. For simplicity, to calculate the average C contrast 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 refractive index values 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.

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, at a layer formed from an alloy of brass (70% copper) or silver. Thus, for these ceramic materials with a transmission layer 30, an absorption layer 20 based on nickel or zinc offers a coefficient R ₂ of reflection at the interface between the absorption layer 20 and the near transmission layer 30. of that R ₁ at the interface between the transmission layer 30 and the air surrounding the clock component 1 on the human visible spectrum.

Nickel (Ni) belongs to the group of elements, called transition metals, of the periodic table of the elements, also called the Mendeleev table, which has good light absorption properties since it can form stable ions. with atomic "d" orbitals which are only partially filled. In addition, in pure form, that is to say comprising at least 95% nickel, the nickel has a silver-white color which remains neutral with regard to colorimetry.

Similarly, zinc (Zn), in pure form, that is to say comprising at least 95% zinc, zinc has a light gray color which remains neutral with regard to colorimetry.

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 coefficient R ₂ reflection 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 horological component 1 on the human visible spectrum.

As explained above, the interference optical system 40 may include 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 color. Indeed, it is advantageously possible, by selecting the nature and the 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 component 1.

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

More generally, as can be seen in the example of figure 4 , preferably according to the invention, at least a first transmission layer 30, 30a, 30c, 30e is stacked on at least a second transmission layer 30, 30b, 30d with respectively different refractive indices making it possible to vary the color of the component as a function of 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, that is to say for example between 1.45 and 1.95 at a wavelength of 620 nm, with another transmission layer 30, 30b, 30d of strong refractive index, that is to say for example between 2.1 and 3.0 at a wavelength of 620 nm, for more precisely modulate the reflected light and more easily adjust the desired shade of color.

Preferably, the interference optical system 40 comprises a stack of transmission layers 30, 30a, 30b, 30c, 30d, 30e, that is to say without the thickness of the absorption layer 20, of which the total thickness 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.

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 (cf. the mathematical relations above) for the interference optical system 40 to 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.

If we consider an interference optical system 40 with two types of transmission layers 30 only (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 , in different cases (first transmission layer 30 deposited on absorption layer 20 of index n _B or n _H , etc., last transmission layer 30 in contact with air of index n _B or n _H ). In particular, the reflection coefficient must be taken into account at the interfaces between layers with high and low refractive indices: $$R=\frac{{\left({\mathrm{not}}_B-{\mathrm{not}}_{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">H</figure-callout>}}\right)}^2+{\mathrm{<figure-callout\; id="2"\; label="k\; B"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">k</figure-callout>}}_B^{}}{{\left({\mathrm{not}}_B+{\mathrm{not}}_{\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">H</figure-callout>}}\right)}^2+{\mathrm{<figure-callout\; id="2"\; label="k\; B"\; filenames="imgf0002.png,imgf0003.png"\; state="\{\{state\}\}">k</figure-callout>}}_B^{}}$$

where k _B is the extinction coefficient of the low refractive index transmission layer 30 which can be considered negligible (as is the extinction coefficient of the high refractive index transmission layer 30).

The global refractive index of the stack of transmission layers 30 is preferably between 1.45 and 2.7 on the human visible spectrum.

By way of example, a graphical representation of the variations of a shade of color as a function of the variations in thickness of two transmission layers 30 according to the invention is illustrated in FIG. 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, that is to say between 1.6 and 1.7, which is deposited on top of a transmission layer 30 of titanium oxide (TiO ₂ ) with a strong refractive index on the human visible spectrum, i.e. included between 2.1 and 3.0. One immediately notices the large variation in shades obtained despite the small variations in thickness of each of the two transmission layers 30.

As explained above, the purpose of the absorption layer 20 is 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 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 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 other of its 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 on the human visible spectrum.

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 is satisfactory. Of course, it is understood that the alloys of the Ni-Au or Ni-Zn type, or of the Zn-Ni type are only examples and are not the only ones making it possible to obtain the advantages of the invention. It is of course possible to envisage alloys other than binary ones and, in particular, which could comprise more elements than two metals apart from the usual so-called pollution compounds, the proportion by weight of which does not exceed 0.2% of the total mass of the alloy.

As an example, the binary Zn-Ni alloy 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 sulphate (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 set within a window between 22 ° C and 17 ° C. Preferably, it is regulated along the deposit at 18 ° C and the current density from 0.12 to 0.15 A.dm ^-2 .

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

Like the figures 5 to 11 As shown, 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 C contrast similar to that of substantially 80% zinc and 20% nickel on the entire human visible spectrum. Like the figures 5 to 11 As shown, the alloy of substantially 70% zinc and 30% nickel exhibits a complex refractive index at a wavelength of 550 nm with n ≈ 2.1 and k ≈ 1.2.

For a binary Ni-Au alloy, the absorption layer 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 of the order of 65 - 75 ° C. Preferably, it is regulated at 65 ° C and the current density from 0.5 to 1.0 A.dm ^-2 .

The binary alloy obtained comprises, for example, from 50 to 70% nickel by total weight of the alloy and from 30 to 50% remaining in 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 gray-black color. Like the figures 5 to 11 As shown, the alloy of substantially 62.5% nickel and 37.5% gold exhibits a complex refractive index at a wavelength of 550 nm with n ≈ 2.5 and k ≈ 1.4.

According to a second example, the absorption layer can 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% of nickel by total weight of the alloy and between 10% and 20% remaining in zinc. Alloys of this type and methods for depositing them by electroplating are described for example in the document US 4,416,737 .

It will be noted that, according to various 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 index refraction 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 n and k values typical of other metallic materials such as brass and silver which very often have a real part value n less than 1.0 and an imaginary part k value greater than 3.5 at a length wave of 550 nm.

In addition, it has been observed that by having a difference (R ₂ - R ₁ ) between the coefficient R ₂ of reflection at the interface between the absorption layer 20 and the transmission layer 30 and that R ₁ at l The interface between the transmission layer 30 and the air surrounding the clock component 1 on the human visible spectrum within a range of about ± 16%, the contrast C typically exhibits a preferred value of high contrast, that is, that is to say at least equal to 0.7. Preferably, the difference (R ₂ - R ₁ ) between the coefficients R ₂ and R ₁ is between ± 13%, and even more preferably between ± 10% in order to obtain an even higher contrast in the human visible spectrum. .

The invention is not limited to the embodiments and variants presented and other embodiments and variants will be apparent to those skilled in the art. Thus, the embodiments and variants can be combined with one another without departing from the scope of the invention. In no way limiting, it can be envisaged to vary the nature and the number of transmission layer (s) 30 of the interference optical system 40 without departing from the scope of the invention.

By way of example, an interference optical system 40 according to the invention is illustrated on 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 can comprise aluminum oxide (Al ₂ O ₃ ) or an oxide stoichiometrically close to the latter, and can be deposited by successively using trimethylaluminum C ₆ H ₁₈ Al ₂ (TMA ) and low conductivity deionized water (eg 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 the precursors can be from 0.1 to 0.5 seconds, these injection steps being separated by purge steps with the nitrogen which last from 5 to 30 seconds.

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

For each transmission layer 30a, 30b, 30c, 30d, 30e, the number of cycles of the self-saturated growth is of course chosen as a function of the desired thickness.

Optionally, at least one adhesion layer 25 can be deposited between the absorption layer 20 and the body 10 of 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 gripping element to avoid in particular delamination between the absorption layer 20 on the body 10. Of course, with or without an adhesion layer 25, the surface of the body 10 of component 1 can be cleaned or prepared in another way before any deposition to facilitate its attachment.

Claims (13)

Watch component (1) formed by a body (10) based on a material to be decorated which is at least partially covered with at least one interference optical system (40), the latter comprising at least one layer (30) of transmission formed on the basis of 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 ( 1), characterized in that the interference optical system (40) further comprises an absorption layer (20) mounted under the transmission layer (30), the real part of which has the complex refractive index, for a length d wave of 550 nm is at least equal to 1.25, making it possible to improve the precision of the colors obtained by the interference optical system (40). Timepiece component (1) according to the preceding claim, in which the imaginary part (k) of the complex refractive index (ñ) of the absorption layer (20), for a wavelength of 550 nm, is at plus equal to 3.5. Timepiece component (1) according to claim 1 or 2, in which the interference optical system (40) comprises a reflection coefficient at the interface between the absorption layer (20) and the transmission layer (30) sufficiently close to that at the interface between the transmission layer (30) and the air surrounding the watch component (1) in order to present an interference contrast (C) at least equal to 0.7 over the entire visible human spectrum. Timepiece component (1) according to any one of the preceding claims, in which the absorption layer (20) has a thickness at least equal to 50 nm, preferably at least equal to 100 nm. Timepiece component (1) according to any one of the preceding claims, in which the interference 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 specific color. Watch component (1) according to the preceding claim, in which at least a first transmission layer (30) is stacked on at least a second transmission layer (30) with respectively different refractive indices making it possible to vary the color of the component watchmaker (1). Timepiece component (1) according to any one of the preceding claims, in which the material of the body (10) to be decorated is based on metal, glass, silicon, polymer or a combination of these materials. Method of manufacturing a watch component (1) according to any one of the preceding claims, characterized in that the method comprises the following steps: - forming a body (10); - depositing, on at least part of the body (10), an absorption layer (20) of which the real part of the complex refractive index, for a wavelength of 550 nm, is at least equal to 1 , 25; - depositing, by an ALD method, at least one transmission layer (30) on the absorption layer (20), each transmission layer (30) being formed based on an oxide, a carbide, a sulfide or a nitride to form an interference optical system (40) on the body (10). Method according to the preceding claim, in which, during the deposition step, the absorption layer (20) further exhibits an imaginary part (k) of the complex refractive index (ñ), for a wavelength of 550 nm, at most equal to 3.5. A method according to claim 8 or 9, wherein the body (10) is formed from metal, glass, silicon, polymer or a combination of these materials. A method according to any one of claims 8 to 10, 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 facilitate mounting of the interference optical system (40) on the body (10). A method according to any one of claims 8 to 11, wherein the step of depositing the absorption layer (20) is carried out by electrodeposition, by an electroless deposition process, by a physical vapor deposition process or by a chemical vapor deposition process. A method according to any one of claims 8 to 12, wherein the step of depositing, by the ALD method, forms at least a first transmission layer (30) stacked on at least a second transmission layer (30) with respectively different refractive indices making it possible to vary the color of the watch component (1).

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