Method for manufacturing a timepiece or jewellery component

Abstract

The present invention relates to a method for manufacturing a timepiece or jewellery component made entirely or partly of a material comprising between 37.5% and 95% by weight of a precious metal relative to the total weight of the material, the material comprising a matrix configured to exhibit a predefined final hue, defined by its a*, b*, and L* coordinates in the CIE L*a*b* space, and at least particles based on the precious metal. The method comprises the following steps: a) providing a material intended to form the matrix; b) preparing initial particles based on the precious metal which also comprise at least one other metal, wherein the amount of the other metal is selected so that the hue of the particles based on the precious metal in the matrix is such that the colour difference ΔE* in the CIE L*a*b* colour space between the predefined final hue of the matrix and the hue of the particles based on the precious metal in the matrix is less than the colour difference ΔE* between the predefined final hue of the matrix and the hue of the pure native precious metal; c) optionally providing at least one additional component intended to constitute between 0% and 10% by weight of the material; d) combining the material intended to form the matrix with the initial particles based on the precious metal and optionally with the at least one additional component, in order to obtain a homogeneous mixture of particles based on the precious metal and optionally the at least one additional component in the matrix; e) producing, from the mixture obtained in step d), the timepiece or jewellery component, entirely or partly in the material, in which the maximum dimension of the particles based on the precious metal in the plane of the observed surface of the material is less than 100 μm, and the minimum dimension of the particles based on the precious metal in the plane of the observed surface of the material is preferably greater than 200 nm, preferentially greater than 0.5 μm, and more preferentially greater than 1 μm, wherein the particles based on the precious metal have no plasmonic effect, and the amount of particles based on the precious metal dispersed in the matrix is predetermined such that the material appears to have a hue identical or close to the predefined final hue of the matrix to one and the same observer positioned at least 30 cm from the surface of the material under the same conditions of illumination by an illuminant, and wherein the hue of the material is such that the colour difference ΔE* between the hue of the material and the predefined final hue of the matrix is less than 10.

Description

[0001] METHOD FOR MANUFACTURING A WATCHMAKING OR JEWELRY COMPONENT

[0002] technical field

[0003] The present invention relates to a method for manufacturing a watch or jewelry component made wholly or partly from a material comprising between 37.5% and 95% by weight of a precious metal, inclusive, relative to the total weight of the material, said material comprising a matrix and at least some particles based on the precious metal dispersed in the matrix.

[0004] State of the art

[0005] Precious metals, such as gold-based alloys, are commonly used in the manufacture of watch and jewelry components, either as a coating or in bulk form. These gold-based alloys are traditionally yellow, red, or gray. Watchmakers and jewelers are increasingly seeking to move beyond the natural color of gold and are particularly interested in developing gold alloys with different hues, such as dark or black. Such alloys can be achieved by depositing a black layer onto a gold material, for example, by electrodeposition with rhodium or ruthenium, or by chemical vapor deposition (CVD) with carbon black. Other processes utilize gold nanoparticles coated with at least one layer of a metal oxide, such as silicon dioxide, zirconium oxide, or titanium dioxide, based on the plasmonic effect of the gold nanoparticles.

[0006] For example, patent EP 2,369,022 describes a process for manufacturing a bulk material containing at least 12-karat or even 18-karat gold, composed of silica-coated gold nanoparticles. The color of the gold nanoparticles used is adjusted according to their size, geometry (spherical, cylindrical, and pyramidal), composition, and chemical environment. The bulk material is obtained by heating and microwave irradiation, a process that preserves the specific color of the gold nanoparticles. However, the patent describes the preparation of a bright red gold nanoparticle solution, a purple solution of silica-coated gold nanoparticles, and a black pellet obtained after heating and microwave irradiation. Therefore, the described process does not guarantee the preservation of the nanoparticle color and is thus not sufficiently robust.

[0007] EP 3 482 851 describes a process for manufacturing a material containing at least 18 carats of gold, formed from an assembly of gold nanoparticles in a titanium dioxide matrix. However, this process is complex because it requires the use of solvents and heating the mixture in the reactor. Furthermore, due to the significant absorption or less-than-ideal optical properties of titanium dioxide for light transmission, the depth of light penetration through the material is insufficient to achieve the maximum plasmonic effect of the gold nanoparticles, so the color of the resulting material is not a deep black. In addition, it is stated that the powder obtained is black before the compaction and sintering steps, while after these two steps, the material is anthracite in color. The initial color of the nanoparticles is therefore altered.Furthermore, the mechanical properties of titanium dioxide, such as hardness or toughness, are not always sufficient to meet the specifications imposed depending on the components.

[0008] The present invention aims to remedy these drawbacks by proposing a watch or jewelry component in a material comprising between 37.5% and 95% by weight of a precious metal relative to the total weight of the material and which has a uniform predefined final shade, in particular a dark or black shade.

[0009] Another objective of the present invention is to propose a method for manufacturing a watch or jewelry component in a material comprising between 37.5% and 95% by weight of a precious metal relative to the total weight of the material, allowing the attainment of a predefined final color.

[0010] Another object of the present invention is to propose a method for manufacturing a watch or jewelry component in a material comprising between 37.5% and 95% by weight of a precious metal relative to the total weight of the material, allowing for the simple production of a component comprising a precious metal, in particular gold, of a predefined color, such as a dark or black shade, and in particular deep black.

[0011] Disclosure of the invention

[0012] To this end, the present invention relates to a method for manufacturing a watch or jewelry component made wholly or partly from a material comprising between 37.5% and 95% by weight of a precious metal, inclusive, relative to the total weight of the material, said method comprising the following steps: a) providing a material for forming the matrix selected from the group comprising at least a thermoplastic resin, a thermosetting resin, an elastomer, ceramic particles having a density less than or equal to 10 g / cm³ 3 , preferably less than or equal to 8 g / cm² 3(b) said matrix being configured to exhibit a predefined final hue, defined by its coordinates a*, b*, and L* in the CIE L*a*b* color space; (b) prepare at least some initial precious metal-based particles, said initial precious metal-based particles also comprising at least one other metal, the amount of said other metal being chosen such that the hue of the precious metal-based particles in the matrix is ​​such that the color difference AE* in the CIE L*a*b* color space between the predefined final hue of the matrix and the hue of the precious metal-based particles in the matrix is ​​less than the color difference AE* in the CIE L*a*b* color space between the predefined final hue of the matrix and the hue of the pure native precious metal; (c) optionally provide at least one additional component intended to constitute between 0% and 10% by weight of the material,including limits; d) combine the material intended to form the matrix supplied in step a) with the initial precious metal-based particles prepared in step b) and optionally with said at least one additional component supplied in step c), in order to obtain a homogeneous mixture of precious metal-based particles and optionally said at least one additional component in the matrix of said predefined shade; e) produce from the mixture obtained in step d) the watch component, in whole or in part, in said material in which the precious metal-based particles have dimensions such that the maximum dimension of said precious metal-based particles in the plane of the observed surface of the material is less than 100 pm, preferably less than 60 pm, preferably less than 50 pm, preferably less than 30 pm,and the minimum dimension of said precious metal-based particles in the plane of the observed material surface is greater than 1 nm, preferably greater than 5 nm, preferably greater than 10 nm, preferably greater than 100 nm, preferably greater than 200 nm, preferably greater than 0.5 pm, and more preferably greater than 1 pm, said precious metal-based particles being plasmonic-free, and the quantity of precious metal-based particles dispersed in the matrix being predetermined so that said material appears to have the same or a similar hue to the predetermined final hue of the matrix to the same observer placed at least 30 cm, and preferably at least 10 cm, from the surface of said material under the same illumination conditions by an illuminant,said material tint being such that the AE* color difference in the CIE L*a*b* color space between the material tint and the predefined final tint of the matrix is ​​less than 10, preferably less than or equal to 5, preferably less than or equal to 4, and more preferably less than or equal to 3, more preferably less than or equal to 2, and more preferably less than or equal to 1.

[0013] Thus, by optical effect, the same observer placed at least 30 cm from the surface of the watch or jewelry component will perceive, under the same conditions of illumination by an illuminant, a watch or jewelry component comprising between 37.5% and 95% by weight of a precious metal relative to the total weight of the material and which has a uniform overall color identical or close to the final color of the matrix chosen at the start.

[0014] For example, in the case of a predefined black or dark hue matrix defined in the CIE L*a*b space by the parameters -10 <a*< 10, -10 <b*< 10 et 0 <L*< 50, de préférence -5 <a*< 5, -5 <b*< 5 et L*< 30, de préférence -5 <a*< 5, -5 <b*< 5 et L*< 15, un même observateur placé à au moins 30 cm de la surface du composant horloger ou de bijouterie percevra, par effet d’optique, dans les mêmes conditions d’illumination par un illuminant, un composant horloger ou de bijouterie comprenant entre 37.5% et 95% en poids d’un métal précieux par rapport au poids total du matériau et qui présente une couleur globale uniforme noire ou foncée telle que définie ci- dessus correspondant à la teinte finale prédéfinie de la matrice.

[0015] Such manufacturing processes are simple to implement.

[0016] Brief description of the drawings

[0017] Other features and advantages of the present invention will become apparent from the following detailed description of various embodiments of the invention, given by way of non-limiting examples, and made with reference to the attached drawing in which: Figure 1 schematically represents the steps of the process according to the invention.

[0018] Embodiments of the invention

[0019] The present invention relates to a method for manufacturing a watch or jewelry component made wholly or partly from a material comprising between 37.5% and 95% by weight of a precious metal relative to the total weight of the material, including the terminals. Such a watch or jewelry component consists, for example, of an oscillating weight, a watch casing element such as a dial, a cover, an appliqué, a crown, a hand, a case, a bracelet element, all or part of these components, as well as a decorative element, for example, or a piece of jewelry.

[0020] The said material of the watch or jewelry component comprises a matrix configured to exhibit a predefined final hue defined by its coordinates a*, b*, and L* in the CIE L*a*b* space, and at least particles based on said precious metal dispersed in the matrix.

[0021] According to the invention, said process comprises the following steps: a) providing a material for forming the matrix selected from the group comprising at least a thermoplastic resin, a thermosetting resin, an elastomer, ceramic particles having a density less than or equal to 10 g / cm³ 3 , preferably less than or equal to 8 g / cm² 3said matrix being configured to exhibit a predefined final hue, defined by its coordinates a*, b*, and L* in the CIE L*a*b* color space; preferably the predefined final hue is such that the color difference AE* in the CIE L*a*b* color space between the predefined final hue of the matrix and the hue of the pure native precious metal is greater than 15, preferably greater than 20, preferably greater than 50, and more preferably greater than 100; b) prepare at least some initial precious metal-based particles, said initial precious metal-based particles also comprising at least one other metal,the quantity of said other metal being chosen so that the hue of the precious metal-based particles in the matrix is ​​such that the AE* color difference in the CIE L*a*b* color space between the predefined final hue of the matrix and the hue of the precious metal-based particles in the matrix is ​​less than the AE* color difference in the CIE L*a*b* color space between the predefined final hue of the matrix and the hue of the pure native precious metal; (c) optionally supply at least one additional component intended to constitute between 0% and 10% by weight of the material, inclusive; (d) combine the material intended to form the matrix supplied in step (a) with the initial precious metal-based particles prepared in step (b) and optionally with said at least one additional component supplied in step (c).in order to obtain a homogeneous mixture of particles based on the precious metal and optionally said at least one additional component in the matrix of said predefined shade; e) to produce from the mixture obtained in step d) the watch component, in whole or in part, in said material in which the particles based on the precious metal have dimensions such that the maximum dimension of said particles based on the precious metal in the plane of the observed surface of the material is less than 100 pm, preferably less than 60 pm, preferably less than 50 pm, preferably less than 30 pm, and the minimum dimension of said particles based on the precious metal in the plane of the observed surface of the material is greater than 1 nm, preferably greater than 5 nm, preferably greater than 10 nm, preferably greater than 100 nm, preferably greater than 200 nm, preferably greater than 0.5 pm, and more preferably greater than 1 pm,said precious metal-based particles being without plasmonic effect, and the quantity of precious metal-based particles dispersed in the matrix being predetermined so that said material appears to have the same or close hue to the predetermined final hue of the matrix to the same observer placed at least 30 cm, and preferably at least 10 cm, from the surface of said material under the same illumination conditions by an illuminant, said hue of the material being such that the AE* color difference in the CIE L*a*b* color space between the hue of the material and the predetermined final hue of the matrix is ​​less than 10, preferably less than or equal to 5, preferably less than or equal to 4, and more preferably less than or equal to 3, more preferably less than or equal to 2, and more preferably less than or equal to 1,and preferably such that the AE* color difference in the CIE L*a*b* color space between the hue of the material and the hue of the pure native precious metal is greater than 15, preferably greater than 20, preferably greater than 50, and most preferably greater than 100.

[0022] The material intended to form the matrix, supplied in step a), may advantageously be a thermosetting resin selected from the group comprising epoxy resins, polyurethane resins, and dimethacrylate urethane polymers (IIDMA). The thermosetting resin is crosslinked by a suitable crosslinking system, depending on its nature. In particular, the thermosetting resin is crosslinked by a suitable chemical crosslinking agent, such as a hardener, by the application of heat or by irradiation, notably by photopolymerization, for example by UV light. Different crosslinking systems may be combined. For example, a hardener may be combined with a temperature increase. The crosslinking reaction is advantageously carried out at temperatures below approximately 500°C and can be performed under a controlled atmosphere and / or controlled pressure.Depending on the crosslinking system chosen, the material intended to form the matrix supplied in step a) may also include a hardener, an initiator, a polymerization catalyst which is mixed with the resin during step a).

[0023] The thermoplastic resin can be, for example, polypropylene (PP), polyetheretherketone (PEEK), polysulfone (PSU), or polyamide (PA).

[0024] The elastomer can be a natural rubber, a silicone rubber, a fluoroelastomer (FKM), a thermoplastic elastomer (TPE), a styrene-butadiene rubber (SBR), a butyl rubber.

[0025] The material intended to form the matrix provided in step a) may also be formed of ceramic particles having a density less than or equal to 10 g / cm³ 3 , preferably less than or equal to 8 g / cm² 3 , preferably less than or equal to 6 g / cm² 3, and preferably greater than or equal to 1g / cm² 3 . Said ceramic is for example zirconia, alumina, silicon oxycarbide, silicon carbide, silicon nitride, silicon carbonitride, silicon oxynitride, titanium carbide, titanium nitride, titanium diboride, boron carbide, or mixtures thereof.

[0026] The matrix may include, if necessary, a coloring agent chosen to impart the desired final predefined color to the matrix. This coloring agent may be a pigment, for example, in the form of oxides or salts, including metallic oxides or salts such as chromium oxide, iron oxide, cobalt oxide, carbonates, sulfates, mica powder, or in the form of carbon, for example, nanotubes or carbon black, which are particularly suitable for producing a black or dark color. The coloring agent may also be an organic dye or pigment. If the matrix is ​​a ceramic, the desired final predefined color of the ceramic may be achieved by using a specific firing atmosphere during sintering, which can produce certain colors through the in-situ formation of oxides.

[0027] Preferably, the coloring agent is chosen to give the matrix a final dark or black tint, said coloring agent being, for example, carbon black, carbon nanotubes, and / or at least a suitable oxide.

[0028] The precious metal-based particles supplied in step (b) are preferably particles based on gold, silver, palladium, platinum, rhodium, and mixtures thereof. Preferably, the particles based on said precious metal are gold-based particles, and the material preferably comprises between 37.5% and 87.5% gold by weight relative to the total weight of the material, or preferably between 9 and 21 carats of gold. If the particles based on said precious metal are platinum-based particles, the material may preferably comprise between 50% and 95% platinum by weight relative to the total weight of the material.

[0029] It is specified that, in this description, the expression "based on said precious metal" means that the particle "based on said precious metal" comprises, predominantly by weight, said precious metal and said other metal. According to the invention, said particles based on said initial precious metal also comprise at least one other metal, which is advantageously palladium, platinum, iridium, ruthenium, nickel, iron, chromium, silver, copper, zinc, rhodium, aluminum, tin, indium, magnesium, manganese, titanium, zirconium, or osmium, said other metal being chosen according to said precious metal. The precious metal / other metal combinations can be chosen according to the color of the resulting alloy. For example, gold can be alloyed with palladium, platinum, nickel, iron, chromium, manganese, zinc, or rhodium to change from the standard yellow color of pure native yellow gold to a whiter hue.

[0030] The use of such an alloyed precious metal advantageously allows precious metal-based particles to achieve a tint that closely matches the predetermined final color of the matrix. For example, with gold-based particles, without plasmonic effects, using gold alloyed with one of the metals mentioned above reduces the yellow or reddish color of the gold particles, resulting in gold-based particles with a more neutral color than the yellow gold of pure native gold.

[0031] According to one embodiment, step b) can be carried out by coating, for example by coating particles of the precious metal with at least one layer of said other metal or conversely by coating particles of said other metal with at least one layer of said precious metal. An additional metal oxide shell may be provided to form metal / ceramic core-shell particles.

[0032] According to another embodiment, step b) can be carried out by forming precious metal-based particles from a precious metal-metal precursor by precipitation.

[0033] According to another embodiment, step b) can be carried out by forming precious metal-based particles from a precious metal-metal alloy by atomizing an ingot of said alloy. Step b) therefore comprises the fabrication of an ingot of said alloy and the atomization of said ingot by water, laser, crushing, etc., in order to obtain the alloy particles necessary for carrying out the process of the invention. The composition of the metallic alloy prepared in step b) is determined so as to obtain the desired color effect while respecting the required purity levels.

[0034] Preferably, the precious metal-based particles, especially gold-based, initials provided in step b) have dimensions between 1 nm and 1 pm, for example between 10 nm and 1 pm.The dimensions of the initial precious metal-based particles are chosen so that the precious metal-based particles formed in the matrix have the desired dimensions, i.e. dimensions such that the maximum dimension of the precious metal-based particles in the plane of the observed material surface is less than 100 pm, preferably less than 60 pm, preferably less than 50 pm, preferably less than 30 pm, preferably less than 10 pm, preferably less than 5 pm, and the minimum dimension of the precious metal-based particles in the plane of the observed material surface is greater than 1 nm, preferably greater than 5 nm, preferably greater than 10 nm, preferably greater than 50 nm, preferably greater than 100 nm, preferably greater than 200 nm, preferably greater than 0.5 pm, and more preferably greater than 1 pm.Indeed, the apparent dimensions of the initial precious metal-based particles can increase due to the agglomeration of the precious metal-based particles during the manufacturing of the component.

[0035] In the present invention, the size or dimension of a particle is defined as its equivalent diameter, that is, the diameter of the sphere that would behave identically during particle size analysis of the particles (or of the powder formed from said particles, or agglomerates of these powders), the particle size distribution (the set of particle sizes) being measured in particular by laser granulometry according to ISO 13320:2009. For example, if the particles are spherical, the diameter in the plane of the observed surface of the material is the diameter of the spheres. If the particles have another shape, for example pyramidal, the largest surface area of ​​the particle in the plane of the observed surface of the material can be determined.The particle sizes indicated in this application correspond to the D95 percentile, meaning that 95% of the particles (or agglomerates of these particles) in the set of particles considered have a size less than D95.

[0036] Furthermore, the precious metal-based particles of the watch or jewelry component material are dispersed homogeneously in the matrix, i.e., in the mass.

[0037] Furthermore, the matrix and size of the precious metal-based particles, particularly gold-based particles, said precious metal-based particles being without plasmonic effect, are chosen within the limits indicated above, and the quantity of precious metal-based particles dispersed in the matrix is ​​predetermined during the manufacture of said component so that said material has the desired purity and such that, by optical effect, said material appears to have the same or close hue to the predefined final hue of the matrix to the same observer placed at least 30 cm, and preferably at least 10 cm, from the surface of said material under the same illumination conditions by an illuminant, said hue of the material being such that the AE* color difference in the CIE L*a*b* color space between the hue of the material and the predefined final hue of the matrix taken alone is less than 10, preferably less than or equal to 8,preferably less than or equal to 7, preferably less than or equal to 5, preferably less than or equal to 4, more preferably less than or equal to 3, more preferably less than or equal to 2, and more preferably less than or equal to 1, and preferably such that the AE* color difference in the CIE L*a*b* color space between the hue of the material and the hue of the pure native precious metal is greater than 15, preferably greater than 20, preferably greater than 50, more preferably greater than 100.

[0038] In a particularly preferred manner, the predefined final tint of the matrix is ​​a dark or black tint, such that the material comprising said matrix and the precious metal particles dispersed in the matrix appears dark or black. In the present invention, a dark or black tint means a color defined in the CIE L*a*b* color space by the parameters -10 <a*< 10, -10 <b*< 10 et 0 <L*< 50, de préférence -5 <a*< 5, -5 <b*< 5 et L*< 30, de préférence -5 <a*< 5, -5 <b*< 5 et L*< 15, plus préférentiellement -1 <a*< 1 , -1 <b*< 1 et 0 < L*< 10, et plus préférentiellement -1 <a*< 1 , -1 < b*< 1 et 0< L*< 6.

[0039] Therefore, the precious metal-based particles in the matrix have a hue such as -15 <a*< 10, -10 <b*< 10 et 50 <L*< 100, de préférence -10 <a*< 10, -10 <b*< 10 et 50 <L*< 100, et plus préférentiellement -5 <a*< 5, -5 <b*< 5 et 50 <L*< 100, l’ajout d’un autre métal aux particules de métal précieux permettant de modifier essentiellement les valeurs de a* et de b*.

[0040] The color difference or AE* color deviation in the CIE L*a*b* color space is defined as a measure of difference between two colors by equation (I): b are the coordinates in the CIE L*a*b* color space of the first color to be compared and L2, a2* , are the coordinates in the CIE L*a*b* color space of the second color to be compared.

[0041] These values b2 in the CIE L*a*b* color space are measured objectively using a colorimeter under the same illumination conditions by a standardized illuminant of type D65.

[0042] An AE* color difference between two colors of less than 10, preferably less than or equal to 8, preferably less than or equal to 7, preferably less than or equal to 5, preferably less than or equal to 4, more preferably less than or equal to 3, more preferably less than or equal to 2, and more preferably less than or equal to 1, measured objectively using a colorimeter, indicates that the two colors are almost or even identical to the same observer under the same illumination conditions by an illuminant.The colorimeter measures the hue (coordinates a*, b*, and L*) of a sample of a material made in a similar way to the material used in the invention but comprising only the matrix, without precious metal-based particles, and the hue (coordinates a*, b*, and L*) of a sample corresponding to the projection of a sample of the material used in the invention into a parallel plane placed at least 30 cm, and preferably at least 10 cm, from the surface of said material, and compares the two hues to calculate the color difference AE* between the two samples.

[0043] Thus, the said material of the watch or jewelry component will have the desired quality and will appear, in the mass, to be of the same or close shade to the predefined final shade of the matrix to the same observer placed at least 30 cm, and preferably at least 10 cm, from the surface of said material, under the same conditions of illumination by an illuminant, by an optical effect, the particles based on the precious metal, and in particular the particles of alloyed gold, visually blending with the matrix, an observer perceiving the surface of the material as being a uniform surface, for example of dark or black shade, corresponding to the predefined final shade of the matrix.

[0044] In the present invention, the illuminant is standardized to type D65, as defined in the CIE class of standard illuminants. It is also specified that the present invention relates only to optical effects in the visible range of the spectrum, defined between 400 nm and 790 nm.

[0045] The final predefined color of the matrix can be any size, as the size and quantity of precious metal-based particles, particularly gold-based particles, without plasmonic effect, as well as the density of the matrix material, are chosen and adjusted within the limits indicated above by a person skilled in the art to obtain, through an optical effect, a material with the desired fineness and the desired AE* value, as defined above. For example, in the case of gold-based particles, pure yellow gold particles are defined in the CIE L*a*b* space by the parameters L* = 86.9, a* = -1.9, b* = 87.1. This means that the AE* color difference in the CIE L*a*b* color space between the final predefined hue of the matrix taken alone and the hue of pure yellow gold particles can be greater than 15, preferably greater than 20, preferably greater than 50, or even greater than 80 or 100.If the final predefined hue of the matrix is ​​dark or black, the AE* color difference in the CIE L*a*b* color space between the final predefined hue of the matrix alone and the hue of pure yellow gold particles is greater than 100. When the gold particles are alloyed, for example, with platinum or palladium, the resulting gold-based particles are gray / white, so the AE* color difference in the CIE L*a*b* color space between the final predefined hue of the matrix alone and the hue of the alloyed gold particles can be less than 50, which reduces the color gap and allows the alloyed gold particles to blend more easily into the final predefined hue of the matrix.Thus, by an optical effect, the tint of the material perceived by the same observer placed at least 30 cm, and preferably at least 10 cm, from the surface of said material, under the same conditions of illumination by an illuminant, is such that the AE* color difference in the CIE L*a*b* color space between the tint of the material and the predefined final tint of the matrix taken alone is less than 10, preferably less than or equal to 8, preferably less than or equal to 7, preferably less than or equal to 5, preferably less than or equal to 4, more preferably less than or equal to 3, more preferably less than or equal to 2, and more preferably less than or equal to 1, whereas the AE* color difference in the CIE L*a*b* color space between the tint of the material and the tint of pure native gold is greater than 15, preferably greater than 20, preferably greater than 50, more preferably greater than 100.

[0046] Preferably, the initial precious metal-based particles prepared in step b) comprise particles without plasmonic effect. The maximum size of the precious metal-based particles, and in particular gold-based particles, in the plane of the observed material surface is less than 100 pm, preferably less than 60 pm, preferably less than 50 pm, preferably less than 30 pm, preferably less than 20 pm, preferably less than 10 pm, and more preferably less than 5 pm. The minimum size of the precious metal-based particles, and in particular gold-based particles, in the plane of the observed material surface may be greater than 200 nm, preferably greater than 0.5 pm, and more preferably greater than 1 pm.Thus, the precious metal-based particles, and in particular the gold-based particles formed in the material, are of micrometric size, preferably exhibiting dimensions in the plane of the observed material surface greater than 200 nm and less than 100 pm, and are without plasmonic effect, the color of the material being obtained by an optical effect.It is also possible that the minimum dimension of the precious metal-based particles, and in particular the gold-based particles, in the plane of the observed material surface is greater than 1 nm and less than 200 nm, but due to the distance between particles, their sizes or other reasons occurring during the manufacture of the material, the plasmonic effect does not occur for these precious metal-based particles, and in particular for these gold-based particles, so that, for these precious metal-based particles, and in particular for these gold-based particles, the color of the material is related solely to an optical effect.Thus, by an optical effect, and depending on the resolving power of his eye, an observer no longer perceives the particles based on the precious metal, and in particular the gold-based particles, which are more neutral in color than yellow, embedded in the matrix of predefined final tint, for example dark or black, and perceives the surface of the material as a uniform surface, for example dark or black, corresponding to the predefined final tint of the matrix.

[0047] The initial precious metal-based particles prepared in step b) may also include precious metal-based nanoparticles with dimensions and shapes that impart a plasmonic effect corresponding to the predefined final color of the matrix, at least in the visible range. Preferably, the precious metal-based particles are nanoparticles with dimensions less than 200 nm, preferably between 10 nm and 200 nm, or even less than 150 nm or 100 nm, thus conferring this plasmonic effect while remaining invisible to the naked eye.

[0048] These precious metal-based nanoparticles may include the precious metal itself as well as the other metal as defined above. The use of such an alloyed precious metal is also advantageous for the nanoparticles because it allows precious metal-based nanoparticles that might otherwise lose their plasmonic effect during manufacturing to have a more neutral hue than that of the pure native precious metal, by reducing the yellow or reddish color of gold nanoparticles that have lost their plasmonic effect. Nanoparticles can lose their plasmonic effect due to their size, for example, due to agglomeration, lighting, or other conditions. Gold-based nanoparticles may, for example, consist of a core made of one of the metals mentioned above and a gold shell.

[0049] The matrix configured to present the predefined final tint then comprises, dispersed in said matrix, first particles based on precious metal, in particular gold-based, of micrometric size, as defined above, allowing to obtain a tint essentially by optical effect in cooperation with the matrix, as well as second particles based on precious metal, in particular gold-based, of nanometric size, chosen to present a plasmonic effect of a tint identical or close to that of the matrix in order to promote the predefined final tint of the matrix and to reinforce the optical effect obtained with the first particles based on precious metal, in particular gold-based.The material obtained comprising the first and second particles based on the precious metal, in particular based on gold dispersed in the matrix, has the desired fineness due to the contribution of the first and second particles and a tint such that the color difference AE* is always as defined above.

[0050] The additional component, possibly supplied in step c), is, for example, reinforcing fillers such as carbon fibers, a coupling agent, a ceramic, or any other additive that allows for adjusting the chemical, physical, or rheological properties of the composition. Such additional components may be chosen to improve particle distribution, viscosity, or adhesion between material components, such as the matrix and precious metal-based particles.

[0051] Advantageously, this additional component is a ceramic in the form of nano- or microparticles. Preferably, the ceramic nano- or microparticles are made of alumina, zirconia, or silica, for example. They improve mechanical strength, particularly scratch resistance. Preferably, ceramic nanoparticles are used so that they are invisible to the naked eye while improving the overall properties of the material. For example, they produce smoother surfaces. These ceramic nanoparticles can also be pigmented or can acquire color under various conditions (e.g., oxidation, carbon addition during the process or by post-processing) and can also be used to adjust the matrix color, as a coloring agent as described above.

[0052] Preferably, the matrix is ​​made from a thermosetting resin or a ceramic of predetermined dark or black final color, and the precious metal-based particles are at least plasmonic-free gold-based particles, the gold being alloyed with palladium, or platinum for example, and having the dimensions defined above and in the predetermined quantity as defined above, the matrix also comprising various additives, including ceramic nano- or micro-particles, and preferably ceramic nanoparticles, and reinforcing fillers, such as carbon fibers.

[0053] Advantageously, the initial quantity of precious metal-based particles supplied in step b) is determined from the quantity of precious metal-based particles in the material which is predetermined by prior tests using a colorimeter in order to establish a correlation between the particle size of the precious metal-based particles formed in the material, the desired color of the material, the desired fineness, and the volume ratio between the precious metal-based particles and the matrix.

[0054] Step d) can preferably be carried out by progressively incorporating the precious metal-based particles supplied in step b) and optionally at least one additional component supplied in step c), such as ceramic micro- or nanoparticles, into the matrix material supplied in step a) using a mechanical mixer to ensure homogeneous mixing. The precious metal-based particles can be in dry powder form. If nanoparticles are used, they can be introduced via a solvent as a colloidal suspension. Between steps d) and e), a pretreatment can be performed, allowing, for example, at least one cycle of removal of inaccessible chemical substances before the component is manufactured.This pretreatment can be done by treatment under pressure, under vacuum, under a controlled atmosphere (for example oxidizing or reducing), with heat or by a mixture of these processes.

[0055] When the matrix is ​​made from a thermosetting resin, step e) involves molding the mixture obtained in step d) using a suitable mold, and curing the thermosetting resin with a hardener, by the application of heat, or by photopolymerization. Molding is carried out by pouring the mixture prepared in step d) into the mold, and then applying the chosen curing system. For example, the mixture can be left to harden in the mold at room temperature.

[0056] When the matrix is ​​made from a thermoplastic resin, step e) can be carried out by injection molding.

[0057] When the matrix is ​​a ceramic, step e) includes shaping the mixture obtained in step d) and sintering to form the watch or jewelry component. More specifically, step e) includes shaping the mixture obtained in step d) by pressing, extrusion, injection molding, slip casting, 3D printing, or filter pressing, for example, to form a compact, raw semi-finished product traditionally called a "green body" or near-net-shape, meaning very close to the final shape of the component to be manufactured. This may involve debinding, depending on the composition of the material intended to form the matrix of the predefined final color, followed by sintering. This sintering may be high-temperature sintering, for example, 900°C–1500°C for zirconia, irradiation, flash sintering, or UHS sintering.

[0058] Advantageously, ultrafast high-temperature (UHS) sintering is achieved by heating at a rate between 500 and 10 6 °C / min, preferably between 500 and 10 5 °C / min, more preferably between 500 and 10,000 °C / min, and more preferably between 1,500 and 8,000 °C / min, and for a duration greater than 30 seconds, preferably greater than 60 seconds and preferably between 30 seconds and 500 seconds, preferably between 30 seconds and 300 seconds, more preferably between 60 seconds and 180 seconds.

[0059] The ultrafast high temperature (U HS) sintering process advantageously takes place in an inert / protective sintering atmosphere in a vacuum chamber, the atmosphere of which is controlled by the injection of inert gases (argon, N2, N2 / H2) and allows high temperatures to be reached quickly without requiring pressure to be exerted on the material to maintain electrical contact with the material, unlike known sintering processes, notably Flash sintering also called SPS (Spark Plasma Sintering) which requires pressures of 5 to 100 MPa, or even 600 to 800 MPa.

[0060] Furthermore, unlike known sintering processes, the ultrafast high-temperature (UHS) sintering process applied to the composite material according to the invention improves the diffusion kinetics, i.e., the sintering rate, of the densification mechanisms responsible for closing the ceramic pores, while limiting surface diffusion, which is responsible for the loss of sintering reactivity of the ceramic and the coalescence of the precious metal-based particles. Advantageously, the ultrafast high-temperature (UHS) sintering process applied to the composite material according to the invention eliminates non-densifying diffusion mechanisms (surface diffusion, for example), limits grain growth kinetics, and maintains high sintering reactivity, while preserving the ceramic pore geometry.

[0061] In the process according to the invention, the diffusion mechanism of sintering is accelerated with lower temperatures, increased speed and without the need for pressure.

[0062] The invention makes it possible to completely densify the matrix formed by the ceramic at low temperature while preserving the size of the particles based on the precious metal.

[0063] Regardless of the embodiments implemented, step e) may include post-processing, for example mechanical machining and / or finishing treatment, such as sanding and / or polishing the surface of the component, to obtain said watch or jewelry component.

[0064] In the embodiment where the matrix has a predefined final shade of black or dark, the present invention advantageously makes it possible to obtain a watch or jewelry component made wholly or partly from a material comprising between 37.5% and 95% by weight of a precious metal, inclusive, relative to the total weight of the material, said material appearing by optical effect to an observer placed at least 30 cm, and preferably at least 10 cm, from the surface of said material, as having a uniform overall color defined in CIE L*a*b* space by its coordinates a*, b*, and L* in CIE L*a*b* space such as, for example, -10

Claims

Demands 1. A method for manufacturing a watch or jewelry component made wholly or partly from a material comprising between 37.5% and 95% by weight of a precious metal, inclusive, relative to the total weight of the material, said material comprising a matrix and at least some particles based on said precious metal, characterized in that said method comprises the following steps: a) providing a material for forming the matrix selected from the group comprising at least a thermoplastic resin, a thermosetting resin, an elastomer, or ceramic particles having a density less than or equal to 10 g / cm³ 3 , preferably less than or equal to 8 g / cm² 3(b) to prepare at least some initial precious metal-based particles, said initial precious metal-based particles also comprising at least one other metal, the amount of said other metal being chosen so that the hue of the precious metal-based particles in the matrix is ​​such that the color difference AE* in the CIE L*a*b* color space between the predefined final hue of the matrix and the hue of the precious metal-based particles in the matrix is ​​less than the color difference AE* in the CIE L*a*b* color space between the predefined final hue of the matrix and the hue of the pure native precious metal; (c) optionally to provide at least one additional component intended to constitute between 0% and 10% by weight of the material, inclusive;d) combine the material intended to form the matrix supplied in step a) with the initial precious metal-based particles prepared in step b) and optionally with at least one additional component supplied in step c), in order to obtain a homogeneous mixture of base particles; of the precious metal and optionally of said at least one additional component in the matrix; e) produce from the mixture obtained in step d) the watch or jewellery component all or part of said material in which the precious metal-based particles have dimensions such that the maximum dimension of said precious metal-based particles in the plane of the observed material surface is less than 100 pm, preferably less than 60 pm, preferably less than 50 pm, preferably less than 30 pm, and the minimum dimension of said precious metal-based particles in the plane of the observed material surface is greater than 1 nm, preferably greater than 5 nm, preferably greater than 10 nm, preferably greater than 100 nm, preferably greater than 200 nm, preferably greater than 0.5 pm, and more preferably greater than 1 pm, said precious metal-based particles being plasmonic-free, and the quantity of precious metal-based particles dispersed in the matrix being predetermined so that said material appears to be of the same or near the predetermined final color of the matrix to the same observer placed at least 30 cm, and preferably at least 10 cm, from the surface of said material under the same illumination conditions by an illuminant, said color of the material being such that the AE* color difference in the CIE L*a*b* color space between the color of the material and the predetermined final color of the matrix is ​​less than 10, preferably less than or equal to 5, preferably less than or equal to 4, more preferably less than or equal to 3, more preferably less than or equal to 2, and more preferably less than or equal to 1.

2. A method for manufacturing a watch or jewelry component according to claim 1, characterized in that the precious metal-based particles are particles based on gold, silver, palladium, platinum, rhodium, and mixtures thereof 3. A method for manufacturing a watch or jewelry component according to any one of the preceding claims, characterized in that said other metal is palladium, platinum, iridium, ruthenium, nickel, iron, chromium, silver, copper, zinc, rhodium, manganese, titanium, zirconium, osmium, aluminum, tin, indium, magnesium, said other metal being chosen according to said precious metal.

4. A method according to any one of the preceding claims, characterized in that step b) is carried out by coating.

5. A process according to any one of claims 1 to 3, characterized in that step b) is carried out by forming precious metal-based particles from a precious metal-metal precursor by precipitation.

6. A process according to any one of claims 1 to 3, characterized in that step b) is carried out by forming precious metal-based particles from a precious metal-metal alloy by atomizing an ingot of said alloy.

7. A process according to any one of the preceding claims, characterized in that the initial precious metal-based particles prepared in step b) comprise particles without plasmonic effect and preferably having dimensions in the plane of the observed material surface greater than 200 nm and less than 100 pm.

8. A method for manufacturing a watch or jewelry component according to any one of the preceding claims, characterized in that the initial precious metal-based particles prepared in step b) comprise precious metal-based nanoparticles which have dimensions and shapes giving them a plasmonic effect corresponding to the predefined tint at least in the visible range.

9. A method for manufacturing a watch or jewelry component according to any one of the preceding claims, characterized in that the predefined final color matrix is ​​dark or black and is defined by its coordinates a*, b*, and L* in CIE L*a*b* space such that -10 <a*< 10, -10 <b*< 10 et 0 <l*<50, preferably -5 <a*< 5, -5 <b*< 5 et 0 <l*< 30, plus préférentiellement <a*< l*< 15.

10. A method for manufacturing a watch or jewelry component according to claim 9, characterized in that the precious metal-based particles in the matrix have a tint such that -15 <a*< 10, -10 <b*< 10 et 50 <l*< 100, de préférence <a*< plus préférentiellement -5 5, 5 100.

11. A method for manufacturing a watch or jewelry component according to one of the preceding claims, characterized in that the quantity of precious metal-based particles is predetermined by preliminary tests using a colorimeter in order to establish a correlation between the particle size of the precious metal-based particles, the desired color of the material and the volume ratio between the precious metal-based particles and the predefined final color matrix.

12. A method for manufacturing a watch or jewelry component according to any one of the preceding claims, characterized in that the matrix comprises a coloring agent chosen to give the matrix said predefined final color.

13. Method of manufacturing a watch or jewelry component according to claim 12, characterized in that the coloring agent is chosen to give the matrix the final predefined dark or black tint, said coloring agent being carbon black, carbon nanotubes, and / or at least one oxide.

14. A method for manufacturing a watch or jewelry component according to any one of the preceding claims, characterized in that the material intended to form the matrix supplied in step a) is a thermosetting resin selected from the group comprising epoxy resins, polyurethane resins, dimethacrylate urethane polymers (IIDMA), step e) comprising molding the mixture obtained in step d) and crosslinking the thermosetting resin with a hardener, by the application of heat or by photopolymerization.

15. Method for manufacturing a watch or jewelry component according to claim 14, characterized in that the additional component is a ceramic in the form of nano- or microparticles, preferably in the form of nanoparticles.

16. Method of manufacturing a watch or jewelry component according to any one of claims 1 to 13, characterized in that the predefined final color matrix is ​​a ceramic, step e) comprising shaping the mixture obtained in step d) and sintering in order to form said watch or jewelry component.

17. Method of manufacturing a watch or jewelry component according to claim 16, characterized in that the predefined final color matrix is ​​a ceramic selected from the group comprising zirconia, alumina, silicon oxycarbide, silicon carbide, silicon nitride, silicon carbonitride, silicon oxynitride, titanium carbide, titanium nitride, titanium diboride, boron carbide, or mixtures thereof.

18. A method for manufacturing a watch or jewelry component according to any one of the preceding claims, characterized in that step e) comprises a mechanical machining and / or finishing treatment to obtain said watch or jewelry component.

19. Method of manufacturing a watch or jewelry component according to one of the preceding claims, characterized in that said watch or jewelry component consists of an oscillating weight, a bridge, a disc, a wheel, a watch casing element, a piece of jewelry.

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