Cladding part made of ceramic material with a protective layer and method for manufacturing such a cladding part

Abstract

The invention relates to a covering piece (10) comprising a substrate (11) made of ceramic material on a surface of which is extended a transparent inorganic protective coating (12), said protective coating (12) being configured so as to have a refractive index substantially equal to that of the substrate (11) in the visible range of the light spectrum so that the covering piece (10) has a color substantially identical to the intrinsic color of the substrate (11), said coating (12) extending over a thickness chosen between 300 nm and 5 µm.

Description

Technical field of the invention

[0001] The invention relates to decorative articles in the fields of watchmaking, jewelry or fashion articles, and more particularly relates to a decorative part made of ceramic material comprising a protective coating and a method for producing such a decorative part.

[0002] In this text, the terms "dressing part" designate, in a manner commonly accepted in the aforementioned fields, a part visible to a user, and having a particularly decorative function.

[0003] Furthermore, fashion items include clothing items or accessories, such as belts, shoes, clothes, etc., and also include writing instruments, eyewear, leather goods, telephones, or any decorative object. Technological background

[0004] In the field of watchmaking, several solutions have been developed to protect ceramic exterior parts, such as dials, flanges, bezels, casebands, crowns, pushers, links, etc., from chemical and / or mechanical attacks, which can modify the appearance or color.

[0005] For example, the trim parts may include a thin protective layer deposited by a vacuum deposition method, such as a PVD (Physical Vapor Deposition) deposition method, a CVD (Chemical Vapor Deposition) deposition method or an ALD (Atomic Layer Deposition) deposition method.

[0006] However, no state-of-the-art solution is entirely satisfactory. Indeed, no state-of-the-art protective layer has a low thickness, for example less than 5 µm, while being perfectly transparent, i.e. not absorbing, in the visible range of the light spectrum, part of the incident light radiation, not giving off interference colors and presenting appropriate resistance to chemical and mechanical attacks.

[0007] It should be noted that thin films deposited by ALD deposition methods have advantages over thin films deposited by PVD and CVD deposition methods. Indeed, these ALD thin films are very effective in protecting the substrate from chemical attack, and due to their low thickness, are invisible to the naked eye so that they do not impact the visual appearance of the substrate they cover.

[0008] However, being very thin, these layers are very sensitive to mechanical stresses, for example friction or shocks. They cannot therefore be used to cover parts of the exterior that may come into contact with external elements, such as the bezel or case of a watch.

[0009] Layers with a thickness greater than that of ALD thin films, typically in the order of microns, offer greater resistance to mechanical stress. However, these layers are visible on the substrate and therefore do not meet the requirements if the visual appearance of the substrate must be preserved, particularly for decorative reasons.

[0010] There is therefore a need for an effective protection solution against chemical and mechanical attacks, and adapted to preserve the visual appearance of the substrate thus protected. Summary of the invention

[0011] The invention solves the aforementioned drawbacks and relates, for this purpose, to a decorative part, preferably for a watch, comprising a substrate made of ceramic material on a surface of which extends a transparent inorganic protective coating. The coating is configured so as to have a refractive index, at least at the interface with the substrate, substantially equal to that of the substrate for the wavelengths in the visible range of the light spectrum so that it does not generate any interference phenomenon, or very little, that is to say substantially not visible to the naked eye, and so that the decorative part has a color substantially identical to the intrinsic color of the substrate.

[0012] Also, the coating has a relatively low thickness, which allows for savings in deposition time and production costs of the cladding part, while being high enough to give it good mechanical resistance to abrasion and good protection against chemical attack. In particular, the thickness of the coating is between 300 nm and 5 µm. The coating can advantageously have a high hardness, typically a Vickers hardness of around 25 GPa.

[0013] The invention thus makes it possible to protect the cladding part while allowing it to retain the intrinsic color of the substrate.

[0014] In particular embodiments, the invention may further comprise one or more of the following features, taken individually or in any technically possible combination.

[0015] In particular embodiments, the protective coating is configured such that it gives the trim part a color whose difference from the intrinsic color of the substrate is characterized by Delta E ≤ 10 in the L*a*b* color space.

[0016] In particular embodiments, the protective coating is configured such that it provides the trim piece with a color whose difference from the intrinsic color of the substrate is characterized by Delta E ≤ 5 in the L*a*b* color space.

[0017] In particular embodiments, the thickness of the protective coating is between 300 nm and 1 µm.

[0018] In particular embodiments, the protective coating is formed from at least two compounds having, respectively, for wavelengths in the visible range of the light spectrum, a refractive index greater than that of the substrate and a refractive index lower than that of the substrate. Controlling the proportion of each compound in the composition of the protective coating then makes it possible to finely control the refractive index of the protective coating so that it is substantially equal to the refractive index of the substrate and thus eliminates any interference phenomenon.

[0019] In particular embodiments, the protective coating comprises at least one layer made of Ti x Al y O z .

[0020] In particular embodiments, the protective coating comprises at least one layer made of Si x O y N z .

[0021] In particular embodiments, the substrate may be made of oxide, nitride, carbide, carbonitride, boride, in particular alumina Al 2 O 3 , zirconia ZrO 2 or alumina-zirconia composite.

[0022] According to another aspect, the present invention further relates to a method of manufacturing a trim part, for example as described above, comprising the steps of preparing a surface of a substrate, and of depositing a transparent inorganic protective coating on said surface by a vacuum deposition method, in a reactive or non-reactive atmosphere.

[0023] The deposition step is carried out from at least one source of at least one material chosen so that the protective coating has a refractive index substantially equal to that of the substrate in the visible range of the light spectrum, said step being further carried out so that the protective coating has a thickness of between 300 nm and 5 µm, so that it resists mechanical and chemical attacks.

[0024] In particular embodiments, the step of depositing a protective coating is carried out by the cathodic sputtering method.

[0025] In particular embodiments, the protective coating is deposited from at least two sources of different materials, said materials being chosen so that during the deposition step, they each form a compound having, in the visible range of the light spectrum, respectively a refractive index greater than that of the substrate and a refractive index lower than that of the substrate. The sputtering power of each of the sources is controlled so that the proportions of each compound in the protective coating are such that said coating has a refractive index substantially identical to that of the substrate.

[0026] In particular embodiments, the protective coating is deposited from at least one source of a mixture of at least two materials, said materials being chosen so that during the deposition step, they each form a compound having, in the visible range of the light spectrum, respectively a refractive index greater than that of the substrate and a refractive index lower than that of the substrate. The source is prepared so as to comprise predefined proportions of said materials so that the protective coating has, at the end of the deposition step, a refractive index substantially identical to that of the substrate.

[0027] In particular embodiments, the materials chosen are Al and Ti, the deposition step being carried out using O 2 as a reactive gas so that at the end of the deposition step, the protective coating comprises a mixture of TiO 2 and Al 2 O 3 so as to form a compound of the type Ti x Al y O z .

[0028] In particular embodiments, the protective coating is deposited from at least one source of a single material chosen so that, during the deposition step, it forms several compounds by reacting with several reactive gases present. The compounds have, in the visible range of the light spectrum, respectively a refractive index greater than that of the substrate and a refractive index lower than that of the substrate, the reactive gases being present in predefined proportions so that the protective coating has, at the end of the deposition step, a refractive index substantially identical to that of the substrate.

[0029] In particular embodiments, the deposition step is carried out from a source made of Si and using O 2 and N 2 as reactive gases so that at the end of the deposition step, the protective coating comprises a mixture of SiO 2 and Si 3 N 4 so as to form a compound of the type Si x O y N z . Brief description of the figures

[0030] Other characteristics and advantages of the invention will appear on reading the following detailed description given by way of non-limiting example, with reference to the figure 1 schematically representing a cross-sectional view of a cladding part according to a preferred embodiment of the invention.

[0031] Note that the figure is not necessarily drawn to scale for clarity. Detailed description of the invention

[0032] The invention relates to a covering part 10, as shown schematically in the figure 1The covering part 10 according to the invention is suitable for the fields of watchmaking, jewelry, jewelry, fashion items, etc. Preferably, the covering part 10 is intended to form a watch dial, a case middle, a bezel, a bracelet or any other watch component visible to a user.

[0033] The covering part 10 comprises a dielectric substrate 11, for example made of ceramic material, such as alumina Al 2 O 3 , or zirconia ZrO 2 or alumina-zirconia composite, with or without pigments coloring said substrate. The covering part 10 further comprises a transparent inorganic protective coating 12 extending over a surface of the substrate 11 intended to be visible to a user.

[0034] It should be noted that the term "transparent" in this text refers to the capacity of a material not to absorb light in a way that is visible to the human eye.

[0035] The protective coating 12 may be formed by a single thin layer or by several thin layers.

[0036] Advantageously, the protective coating 12 makes it possible to protect the substrate 11 against chemical attacks, in particular generated by humidity, sulfur gases, oxygen and acidic environments. In addition, the protective coating 12 is dimensioned so as to resist mechanical stresses, in particular generated by friction or impacts.

[0037] For this purpose, the protective coating 12 extends over a chosen thickness, for example, between 300 nm and 5 µm, more particularly between 300 nm and 1 µm. Preferably, the thickness of the protective coating 12 is equal to 1 µm.

[0038] The protective coating 12 is configured so as to have a refractive index substantially equal to that of the substrate 11 in the visible range of the light spectrum, at least at the interface with said substrate 11. In the present text, the refractive index of the protective coating 12 is substantially equal to that of the substrate 11 insofar as it is within an interval of plus or minus five percent relative to the value of the latter.

[0039] These characteristics advantageously allow the protective coating 12 not to produce or to produce very little optical interference, and therefore allow the covering part 10 protected by the layer 12 to have the intrinsic color of the substrate 11. It should be noted that any interference produced is so low that it is not visible to a user and is therefore negligible.

[0040] The concept of “intrinsic color” refers, in the present text, to the color of the substrate 11 without coating as it is perceived by a user when it is illuminated by white light, due to the material(s) that compose it. Thus, the protective coating 12 is not visible to the naked eye in the sense that the covering part 10 has substantially the same color with or without the protective coating 12 deposited on the substrate 11.

[0041] More precisely, the protective coating 12 is configured so that it gives the covering part 10 a color whose difference with the intrinsic color of the substrate 11 is characterized by Delta E ≤ 10 in the colorimetric space L*a*b*, and more particularly Delta E ≤ 5.

[0042] In summary, thanks to the characteristics of the invention, the covering part 10 includes chemical protection of the substrate 11 while retaining the aesthetic appearance and mechanical strength of the latter.

[0043] Preferably, the protective coating is formed from at least two compounds having respectively, for wavelengths in the visible range of the light spectrum, a refractive index greater than that of the substrate 11 and a refractive index lower than that of the substrate 11.

[0044] For example, the protective coating 12 may comprise a mixture of TiO 2 , which has a high refractive index, and Al 2 O 3 , which has a low refractive index. It should be noted that this example of protective coating 12 is not compatible with a substrate 11 which would be made of a material whose refractive index is lower than that of a coating of Al 2 O 3 alone or higher than that of a coating of TiO 2 alone.

[0045] Alternatively, the protective coating 12 may comprise a mixture of Si 3 Ni 4 , which has a high refractive index, and SiO 2 , which has a low refractive index.

[0046] More generally, to summarize, the protective coating 12 may comprise at least one thin layer made of Ti x Al y O z or Si x O y N z .

[0047] The present invention also relates to a method for manufacturing a trim part 10, for example the trim part 10 as previously described. The method comprises the steps of preparing the surface of the substrate 11 intended to be visible to a user, and of depositing the protective coating 12 on said surface by a vacuum deposition method.

[0048] The preparation step may consist of polishing the substrate 11, sanding it, brushing it, satin finishing it, or performing any other surface preparation operation.

[0049] The deposition step is carried out by using one or more sources of materials whose composition is chosen so as to form a protective coating 12 having a refractive index substantially equal to that of the substrate 11 in the visible range of the light spectrum.

[0050] This deposition step is further carried out so as to deposit the protective coating 12 so that it has a thickness such that it resists mechanical attacks, in particular abrasion, and chemical attacks, as described previously.

[0051] Furthermore, the method may comprise a preliminary step of preparing at least one source of material used during the deposition step. The step of preparing the sources makes it possible, for example, to adapt the appropriate type of source according to the vacuum deposition method used during the deposition step and to adapt the proportion of materials in the source when it comprises several in order to obtain the desired protective coating 12. The type of source of material varies according to the vacuum deposition method used, insofar as the source is a target in solid form if the deposition method used is a physical vapor deposition (PVD) method, and the source is a precursor in the gas phase if the deposition method used is a chemical vapor deposition (CVD) method or an atomic layer deposition (ALD) method.

[0052] In an alternative embodiment of the method, the protective coating 12 is deposited from at least two sources of different materials, for example different metallic materials. Said materials are chosen so that, during the deposition step, they each form a compound, for example an oxide, a nitride or a carbide, said compounds having, in the visible range of the light spectrum, respectively a refractive index greater than that of the substrate 11 and a refractive index lower than that of the substrate 11. During the deposition step, by controlling the sputtering power of each of the sources, the proportion of each compound deposited to constitute the protective coating 12 is controlled so that the latter has the desired refractive index. This desired refractive index of the protective coating 12 is substantially identical to that of the substrate 11, as described above.

[0053] For example, one of the materials may be Al and the other may be Ti. The preliminary preparation step is then carried out so as to obtain two sources, one of which is made of Ti and the other of Al, and the deposition step is carried out using O 2 as the reactive gas. In this example, at the end of the deposition step, the protective coating 12 is then formed from a mixture of TiO 2 and Al 2 O 3 . These two metal oxides having respectively a refractive index higher and lower than that of the substrate 11, controlling their proportion in the protective coating 12 makes it possible to control the refractive index of the coating 12.

[0054] In another alternative embodiment of the method, the protective coating 12 is deposited from at least one source of a mixture of at least two materials. Said materials are also chosen so that, during the deposition step, they each form a compound, for example an oxide, a nitride, a boride or a carbide, said compounds having, in the visible range of the light spectrum, respectively a refractive index greater than that of the substrate 11 and a refractive index lower than that of the substrate 11. During the preliminary step, the source is prepared so as to comprise predefined proportions of said materials so as to control the composition of the deposited protective coating 12 so that the latter has, at the end of the deposition step, the desired refractive index.

[0055] For example, it is conceivable that the preliminary preparation step is implemented so as to obtain a source of a mixture of Ti and Al, and that the deposition step is implemented using O 2 as a reactive gas. In this example, at the end of the deposition step, the protective coating 12 is then composed of a mixture of TiO 2 and Al 2 O 3 . In the same way as in the previous implementation variant, these two metal oxides having respectively a refractive index higher and lower than that of the substrate 11, the control of their proportion in the protective coating 12 makes it possible to control the refractive index of the coating 12 so that it is substantially equal to that of the substrate 11. The source being prepared upstream with the predefined proportions of each material, this variant is more suitable for implementing the method industrially, in a simple, rapid and stable manner.

[0056] In yet another alternative embodiment of the method, the protective coating 12 may be deposited from at least one source of a single material chosen so that, during the deposition step, depending on the reactive gases used, such as O 2 or N 2 , it forms different compounds. The compounds have, in the visible range of the light spectrum, respectively a refractive index lower than that of the substrate 11 and a refractive index higher than that of the substrate 11. Thus, by controlling the quantity of each gas present during the deposition step, the stoichiometry of the compounds constituting the protective coating 12 is controlled so as to obtain the desired refractive index of the protective coating 12.

[0057] For example, the preliminary preparation step can be implemented so as to obtain a Si source, and the deposition step can be implemented using N 2 and O 2 as reactive gases. In this example, at the end of the deposition step, the protective coating 12 is composed of a mixture of SiO 2 and Si 3 N 4 The mixture between a metal oxide and a nitride of the same metal in controlled proportions therefore makes it possible to control the refractive index of the coating 12 so that it is substantially identical to that of the substrate 11.

[0058] These different implementation variants advantageously make it possible to obtain a protective coating 12 with an effective refractive index corresponding as precisely as possible to that of the substrate 11, with a high capacity for adaptation and in a relatively simple manner, by adjusting the ratios between the different compounds constituting the protective coating 12.

[0059] The step of depositing a protective coating 12 is preferably carried out by a physical vapor deposition (PVD) method, for example by arc evaporation, laser ablation, ion beam sputtering or electron beam evaporation or Joule effect, preferably by cathode sputtering, in a reactive or non-reactive atmosphere. Alternatively, the deposition step can be carried out by any chemical vapor deposition (CVD) or atomic layer deposition (ALD) method.

[0060] More generally, it should be noted that the methods of implementation and embodiment considered above have been described as non-limiting examples, and that other variants are consequently conceivable.

[0061] In particular, materials different from those mentioned in the variants of implementation of the method described above may be used. In particular, the use of sources of metallic materials has been described but it is conceivable to use sources of non-metallic materials.

Claims

1. Dressing piece (10) characterized in that it comprises a substrate (11) made of ceramic material on a surface of which extends a transparent inorganic protective coating (12), said protective coating (12) being configured so as to have a refractive index substantially equal to that of the substrate (11) in the visible range of the light spectrum so that the covering part (10) has a color substantially identical to the intrinsic color of the substrate (11), said coating (12) extending over a thickness chosen between 300 nm and 5 µm.

2. A trim piece (10) according to claim 1, wherein the protective coating (12) is configured such that it gives the trim piece (10) a color whose difference from the intrinsic color of the substrate (11) is characterized by Delta E ≤ 10 in L*a*b* color space.

3. A trim piece (10) according to claim 2, wherein the protective coating (12) is configured such that it gives the trim piece (10) a color whose difference from the intrinsic color of the substrate (11) is characterized by Delta E ≤ 5 in L*a*b* color space.

4. Covering part (10) according to one of claims 1 to 3, in which the thickness of the protective coating (12) is between 300 nm and 1 µm.

5. Covering part (10) according to one of claims 1 to 4, in which the protective coating (12) is formed from at least two compounds having respectively, for wavelengths in the visible range of the light spectrum, a refractive index greater than that of the substrate and a refractive index lower than that of the substrate.

6. Covering part (10) according to one of claims 1 to 5, in which the protective coating (12) comprises at least one layer made of Ti x Al y O z .

7. Covering part (10) according to one of claims 1 to 5, in which the protective coating (12) comprises at least one layer made of Si x O y N z .

8. Covering part (10) according to one of claims 1 to 6, in which the substrate (11) is made of alumina Al2O3, zirconia ZrO2 or alumina-zirconia composite.

9. Method for manufacturing a trim part (10) comprising the steps of: - preparing a surface of a substrate (11), and - depositing a transparent inorganic protective coating (12) on said surface by a vacuum deposition method; the method being characterized in thatsaid deposition step is carried out from at least one source of at least one material chosen so that the protective coating (12) has a refractive index substantially equal to that of the substrate (11) in the visible range of the light spectrum, said step being further carried out so that the protective coating (12) has a thickness of between 300 nm and 5 µm.

10. Manufacturing method according to claim 9, in which the step of depositing a protective coating (12) is carried out by cathode sputtering method.

11. Manufacturing method according to claim 9 or 10, wherein the protective coating (12) is deposited from at least two sources of different materials, said materials being chosen so that during the deposition step, they each form a compound having, in the visible range of the light spectrum, respectively a refractive index greater than that of the substrate (11) and a refractive index lower than that of the substrate (11), the sputtering power of each of the sources being controlled so that the proportions of each compound in the protective coating (12) are such that said coating has a refractive index substantially identical to that of the substrate (11).

12. Manufacturing method according to claim 9 or 10, wherein the protective coating (12) is deposited from at least one source of a mixture of materials, said materials being chosen so that during the deposition step, they each form a compound having, in the visible range of the light spectrum, respectively a refractive index greater than that of the substrate (11) and a refractive index lower than that of the substrate (11), said source being prepared so as to comprise predefined proportions of said materials so that the protective coating 12 has, at the end of the deposition step, a refractive index substantially identical to that of the substrate (11).

13. Manufacturing method according to claim 11 or 12, in which the materials chosen are Al and Ti, the deposition step being carried out using O2 as a reactive gas so that at the end of the deposition step, the protective coating (12) comprises a mixture of TiO2 and Al2O3 so as to form a compound of the Ti type x Al y O z .

14. Manufacturing method according to claim 9 or 10, wherein the protective coating (12) is deposited from at least one source of a single material chosen so that, during the deposition step, it forms several compounds by reacting with several reactive gases present, said compounds having, in the visible range of the light spectrum, respectively a refractive index greater than that of the substrate (11) and a refractive index lower than that of the substrate (11), the reactive gases being present in predefined proportions so that the protective coating (12) has, at the end of the deposition step, a refractive index substantially identical to that of the substrate (11).

15. Manufacturing method according to claim 14, in which the deposition step is carried out from a source made of Si and using O2 and N2 as reactive gases so that at the end of the deposition step, the protective coating (12) comprises a mixture of SiO2 and Si3N4 so as to form a compound of the Si type x O y N z .