CH719817A2 - Iridescent article and its manufacturing process - Google Patents

Abstract

The invention relates to an article with an iridescent color obtained by interference effect, said article comprising a substrate (2) covered with a single layer or a stack (3) of layers with at least two layers, said single layer or said stack (3) having a variable thickness giving this iridescent color. The present invention also relates to the method of manufacturing said article.

Description

Technical field of the invention

[0001] The present invention relates to an article and in particular to a watch component covering or the movement, presenting an iridescent effect. It also relates to the manufacturing process of said article.

Technology background

The creation of colors by interference of light reflected on multilayer structures is known. In the prior art, several documents are known using the interference effect to produce an article in a given color. We can for example cite document EP 3 608 728 which discloses a thermocompensated and colored spiral spring for a timepiece comprising a silicon core with on at least one face intended to be visible after assembly within the timepiece a interference layer made of silicon oxide, the interference layer having a thickness less than or equal to 1 µm giving said face a color by interference effect.

[0003] None of these known documents proposes a multicolor article.

Summary of the invention

[0004] The present invention therefore aims to provide a multi-colored article. More precisely, it relates to an article presenting an iridescent color due to interference effect. By the adjective iridescent or by the noun iridescence we mean that the article has a reflection reminiscent of the colors of the rainbow.

[0005] More specifically, the present invention relates to an article with an iridescent color obtained by interference effect, said article comprising a substrate covered with a single layer or a stack of layers with at least two layers, said single layer or said stack having a variable thickness giving this iridescent color.

[0006] Indeed, in order to create an iridescence effect, the path traveled by the light in the material must be different. This is the case, for example, when using a prism to break up light into different colors. The difference in path due to the refractive index allows light to be broken down into blue to red. By depositing thin transparent layers on the substrate with a stack of layers of non-constant thickness, it is possible to obtain a different interference color depending on the position opposite the stack. To obtain this effect, the process must be mastered in order to reproduce these variations in thickness from one item to another or, on the contrary, to create unique pieces.

[0007] The present invention thus also relates to the method of manufacturing said article. According to a variant, the variable thickness of the single layer or the stack is obtained during deposition by using a cache or a mask to hide one or more locations during the deposition of each layer or certain layers of the stack or by placing the substrate on a non-planar support. According to another variant, the single layer or the stack of layers obtained at the end of the deposition step has a substantially constant thickness, and the variation in thickness is achieved by subsequently structuring the single layer or the stack of layers. layers.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, with reference to the appended drawings.

Brief description of the figures

[0009] Figure 1 schematically represents the stack of layers with a variable thickness to obtain the iridescent effect according to the invention.

[0010] Figure 2 shows a schematic view of the step of depositing the layers to form a stack.

[0011] Figure 3 schematically represents a layer deposition step with a cover or a mask to vary the thickness of the deposited layer.

Figure 4 is another variant with the positioning of the substrate on an inclined support to vary the thickness of the layer.

[0013] Figure 5 represents an iridescent glasses produced with the method according to the invention.

Detailed description of the invention

The present invention relates to an article with an iridescent color obtained by interference effect. Regarding the item, it may be a constituent element of watches, jewelry, bracelets, etc. or more generally of an external part of a portable element such as a shell of a mobile telephone. In the watchmaking field, this article can be a trim component such as a caseband, a back, a bezel, a pusher, a bracelet link, a dial, a hand, a dial index, etc. Preferably, it is a transparent bezel that has this iridescent effect. As an illustration, a bezel 1 with an iridescent color according to the invention is shown schematically in Figure 5. It can also be a component of the movement such as a plate, an oscillating mass or a spiral spring.

[0015] According to the invention, the article is provided with a substrate 2 on which at least one layer 4 is deposited. All of the layers 4 form a stack 3. By extension, below, we will speak of stacking even if there is only one layer. According to the invention, this stack has a variable thickness as shown schematically in Figure 1. Here we will focus more on defining the invention as a function of the thickness of the stack rather than the thickness of each layer. Indeed, it could prove complex on the final product to determine the thickness, or even the average thickness, for each individual layer or even the composition of each layer. This requires techniques such as Tof-SIMS, SEM with Wavelength Dispersive Spectroscopy (WDS) to analyze each layer in cross-section.

[0016] Thus, the stack has a non-constant thickness which gives this iridescent effect to the article. By non-constant we mean a variation of at least 2% compared to the maximum thickness. Thus, if Y is the maximum thickness of the layer, the thickness of the layer is considered non-constant if this thickness is less than or equal to 0.98*Y in one or more places. For example, if the maximum thickness is 10 µm, we will consider that the layer has a non-constant thickness if it is less than or equal to 9.8 µm at one or more points of the stack. Typically, the stack has a maximum thickness Y of between 200 nm and 20 µm, between 200 nm and 10 µm, between 200 nm and 5 µm, between 200 nm and 1.5 µm. Preferably, it has a maximum thickness Y of between 500 nm and 1.5 µm. Over the entire surface of the substrate, the stack has a variable thickness between 0 and this maximum value of 20 µm, 10 µm, 5 µm and 1.5 µm. Indeed, it cannot be excluded that at certain points, the substrate is devoid of deposited layers. Preferably, the stack has a variable thickness of between 100 nm and 20 μm. More preferably, it has a variable thickness of between 500 nm and 10 µm, or even 5 µm. Even more preferably, it has a variable thickness of between 500 nm and 1.5 µm.

[0017] Preferably, the number of layers within the stack is between 1 and 1000, preferably between 2 and 100, and more preferably between 20 and 50. Typically, each layer has an average thickness of between 1 nm and 900 nm, preferably between 100 nm and 500 nm. Within the stack, each layer has a variable thickness. It is also possible for certain layers to have a constant thickness provided that the stack ultimately has a variable thickness.

[0018] The profile of the stack can be diverse. In Figure 1, it is shown for illustration purposes with a sinusoidal shape. Any shape is possible as long as the stack has a non-constant thickness. It can, for example, be a shape with a thickness varying linearly or even in a triangle.

[0019] Each layer can be a transparent, translucent, or semi-transparent layer. These may for example be oxides, nitrides, fluorides chosen from TiO2, Ta2O5, SiO2, Al2O3, MgF2, AlN, Ta2O5, Si3N4, ZnS, ZnO, ZrO2, Cr2O3, CeO2, Y2O3, HfN, HfC , HfO2, La2O3, MgO, Sb2O3, SiO, Se2O3, SnO2 and WO3. It could also be metallic layers with a metal chosen, for example, from Au, Cr, Ti, Al and Ta or even a semiconductor such as Si.

Preferably, the stack alternates a layer with a high refractive index, i.e. greater than 2 (for a wavelength of 550 nm), with a low index layer, i.e. less than 1.7 (for a wavelength of 550 nm). For example, it can be an alternation of layers of TiO2/SiO2 or Ta2O5/SiO2. It is also possible to alternate a layer with a high refractive index, i.e. greater than 2, with a medium index layer, i.e. between 1.7 and 2, with a low index layer, i.e. less than 1.7 (still for a wavelength of 550 nm). For example, it can be an alternation of layers of TiO2/Al2O3/SiO2.

[0021] The substrate can be of any type, for example. metallic, ceramic or polymeric. It could also be a substrate made of a precious or semi-precious stone such as sapphire. If it is transparent, the different layers can be directly deposited on the substrate. The iridescent effect can be visible on the side where the different layers are deposited or through the substrate. If the substrate is opaque, e.g. in the case of a ceramic or a metal, it is necessary to have a mirror interface in order to create a reflection of light on the surface and to have interference colors. Typically this is a metallic layer of Ti, Cr or Ag to create this mirror interface.

[0022] The deposition of the layers can be carried out by different methods including PVD (for Physical Vapor Deposition in English), CVD (for Chemical Vapor Deposition in English), sol-gel or ALD (for Atomic Layer Deposition in English). English). The variation in thickness can be carried out during deposition or subsequently by structuring the layer when there is a single layer or layers deposited when there are several layers. According to the first variant consisting of varying the thickness during deposition, there are several techniques. One technique consists of tilting the part so as to achieve a more or less linear variation in thickness. Thus, as shown schematically in Figure 4, the substrate 2 is deposited on an inclined support 6. Another technique consists of using a mask or cover 5 to obstruct certain areas during deposition (figure 3). The mask may be a lacquer, an adhesive, a photosensitive film, etc. For example, it can be deposited by photolithography, stereolithography, digital printing or manually for an adhesive or film which then resembles a cover. Another technique consists of creating shading of the substrate during deposition using a mask which modifies the dynamics of the material flows arriving on the surface and therefore the thickness. According to the second variant, several techniques can be used to structure the single layer or the layers deposited after deposition. We can, among others, cite laser engraving and photolithography.

[0023] Tests were carried out on glasses with a sapphire substrate. Alternating layers of silicon dioxide (SiO2) and tantalum pentoxide (Ta2O5) were deposited by PVD. The number of layers was between 20 and 50 with a maximum thickness Y of the stack between 800 nm and 1.5 µm. The glasses thus produced had a very beautiful iridescent effect.

Claims (19)

1. Article with an iridescent color obtained by interference effect, said article comprising a substrate (2) covered with a single layer (4) or with a stack (3) of layers (4) with at least two layers (4) , said single layer (4) or said stack (3) having a variable thickness giving this iridescent color. 2. Article according to the preceding claim, characterized in that said single layer (4) or said stack (3) has a maximum thickness Y and in that in one or more places the thickness is less than or equal to 0.98*Y . 3. Article according to the preceding claim, characterized in that the maximum thickness Y is between 200 nm and 20 µm, preferably between 200 nm and 1.5 µm, more preferably between 500 nm and 1.5 µm. 4. Article according to the preceding claim, characterized in that within said single layer (4) or said stack (3) the thickness is between 0 and said maximum thickness Y. 5. Article according to one of the preceding claims, characterized in that the number of layers (4) within the stack (3) is between 2 and 1000, preferably between 2 and 100, more preferably between 20 and 50. 6. Article according to one of the preceding claims, characterized in that each layer (4) can be a transparent, translucent or semi-transparent layer with a choice of materials from oxides, nitrides, fluorides, metals and semiconductors. 7. Article according to one of the preceding claims, characterized in that the stack (3) alternates a layer (4) with a refractive index greater than 2 with a layer (4) having a refractive index less than 1.7. 8. Article according to the preceding claim, characterized in that the stack (3) comprises alternating layers (4) of TiO2/SiO2 or Ta2O5/SiO2. 9. Article according to one of claims 1 to 6, characterized in that the stack (3) alternates a layer (4) with a refractive index greater than 2 with a layer (4) having a refractive index between 1.7 and 2 with a layer (4) having a refractive index less than 1.7. 10. Article according to the preceding claim, characterized in that the stack (3) comprises alternating layers (4) of TiO2/Al2O3/SiO2. 11. Article according to one of the preceding claims, characterized in that each layer (4) has an average thickness of between 1 nm and 900 nm, preferably between 100 nm and 500 nm. 12. Article according to one of the preceding claims, characterized in that the substrate (2) is opaque and comprises a metal layer between the substrate (2) and the stack (3). 13. Article according to one of the preceding claims, characterized in that it is a covering component or a watch movement. 14. Article according to the preceding claim, characterized in that it is a transparent bezel (1). 15. Process for manufacturing an iridescent colored article according to one of the preceding claims, comprising the following steps: – Provision of the substrate (2), – Deposition of said single layer (4) or layers (4) of the stack (3), said single layer (4) or the stack (3) having a variable thickness with the maximum thickness Y and in one or several places the thickness less than or equal to 0.98*Y to obtain said article of iridescent color. 16. Manufacturing method according to the preceding claim, characterized in that the variable thickness is obtained during deposition by using a cache or a mask (5) to hide one or more locations during the deposition of each layer (4) or certain layers (4) of the stack (3) or by placing the substrate (2) on an inclined support (6). 17. Process for manufacturing an iridescent colored article according to one of claims 1 to 14, comprising the following steps: – Provision of the substrate (2), – Deposition of said single layer (4) or layers (4) of the stack (3) having a substantially constant thickness, – Structuring of said single layer (4) or the stack (3) of layers (4) to obtain a stack having a variable thickness with the maximum thickness Y and in one or more places a thickness which is less than or equal to 0.98*Y. 18. Manufacturing method according to the preceding claim, characterized in that the structuring is carried out by laser engraving or photolithography. 19. Manufacturing method according to one of claims 15 to 17, characterized in that the deposition of each layer (4) of the stack (3) is carried out by PVD, CVD, sol-gel or ALD.