Method for manufacturing a timepiece or jewellery component, and said timepiece or jewellery component

Abstract

The present invention relates to a method for manufacturing a timepiece or jewellery component from a material comprising between 9 and 21 carat gold, comprising the following steps: a) preparing gold-based particles which have a melting temperature Tf higher than the melting temperature TfAu of gold; b) providing ceramic particles; c) combining the ceramic particles with the gold-based particles prepared according to step a) in order to obtain a mixture; d) producing a semi-finished product entirely or partly from a material comprising between 9 and 21 carat gold inclusive, by shaping the mixture obtained in step c) and sintering in order to form the timepiece or jewellery component; e) producing the timepiece or jewellery component entirely or partly from the material comprising between 9 and 21 carat gold inclusive, from the semi-finished product obtained in step d). The present invention also relates to a timepiece or jewellery component obtained by the manufacturing method as defined above, wherein the timepiece or jewellery component is obtained from a semi-finished product that has a colour defined in the CIE L*a*b* colour space by the parameters -5 <a*< 5, -5 <b*< 5 and L*< 30.

Description

[0001] METHOD FOR MANUFACTURED A WATCHMAKING OR JEWELRY COMPONENT AND SAID WATCHMAKING OR JEWELRY COMPONENT

[0002] technical field

[0003] The present invention relates to a method of manufacturing a watch or jewelry component made wholly or partly from a material comprising between 9 and 21 carats of gold, inclusive of limits, that is to say comprising between 37.5% and 87.5% gold by weight relative to the total weight of the material.

[0004] The present invention also relates to a semi-finished product for the manufacture of a watch or jewelry component and said watch or jewelry component capable of being obtained by means of said manufacturing process.

[0005] State of the art

[0006] Gold alloys are commonly used in the manufacture of watch and jewelry components, either as a coating or in solid form. These alloys are traditionally yellow, red, or gray. Watchmakers and jewelers often seek to move away from 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 obtained by depositing a black layer onto a gold piece, for example, by electrodeposition with rhodium or ruthenium, or chemical vapor deposition (CVD) with carbon black. This process of plating a black layer onto gold results in a superficial black color, not a color that permeates the entire gold. Furthermore, it has the disadvantage that the deposited black layer can be damaged, revealing the true color of the gold beneath.

[0007] Other watch and jewelry component manufacturing processes use gold nanoparticles mixed with a ceramic, leveraging the plasmonic effect of these gold nanoparticles to obtain a material with a predetermined color, such as a dark or black shade. This plasmonic effect gives the gold nanoparticles extremely interesting optical properties, including colorimetric properties. Due to the plasmonic effect, the color of the gold nanoparticles varies depending on their size and shape. These watch and jewelry component manufacturing processes are implemented in such a way as to preserve the size and shape of the initial gold nanoparticles, ensuring that the initial plasmonic effect of the gold nanoparticles is maintained in the final watch or jewelry component.Thus, the color of the initial gold nanoparticles used in the process is not altered by the various heat treatments required to obtain the watch or jewelry component, and said watch or jewelry component generally retains the color of the initial gold nanoparticles. Such a process is described in application WO 2023 / 194293 filed by the applicant.

[0008] Another method for manufacturing a watch or jewelry component made wholly or partly from a material comprising at least 9 carats of gold, using gold particles mixed with a ceramic matrix, has been proposed by the applicant in application PCT / EP2024 / 077818, incorporated by reference. This method is based on an optical effect. According to this invention, the gold particles have dimensions that must be less than 60 µm and preferably greater than 1 µm, the gold particles being dispersed homogeneously in the ceramic matrix.The quantity of gold particles dispersed in the matrix is ​​predetermined so that, by optical effect, the same observer placed at least 30 cm from the surface of the watch or jewelry component will perceive a watch or jewelry component of at least 9 carats of gold which has a uniform overall color identical or close to the color of the matrix chosen at the start, for example a dark or black tint when the ceramic matrix is ​​chosen in a dark or black tint.

[0009] The various known processes for manufacturing a watch or jewelry component from gold and ceramic generally include a sintering step to form said watch or jewelry component.

[0010] The problem is that the gold particles, whose melting point is approximately 1064°C, will melt under the heat and pressure applied during sintering, which typically takes place at temperatures of around 1200°C when the ceramic is zirconia, for example. As a result, the gold particles are transformed, particularly by the heat, and will attract each other, changing shape and size as they melt. The material may experience a reduction in the number of particles or particle clusters, and the distances between particles or clusters will be altered. One possible consequence is the modification, or even loss, of their plasmonic or optical properties.

[0011] These gold nanoparticles can be coated with at least one layer of metal oxide, such as silicon dioxide, zirconium oxide, or titanium dioxide, to protect the gold core. The drawback of this process is that the metal oxide layer can be fragile and unable to withstand the mechanical stresses required for manufacturing watch or jewelry components, for example, during a compaction step preceding sintering. Consequently, the gold nanoparticles are no longer protected during sintering.

[0012] The present invention aims to remedy these drawbacks by proposing a method for manufacturing a watch or jewelry component made entirely or partly from a material comprising between 9 and 21 carats of gold, including the limits, allowing the agglomeration of gold particles to be prevented in order to guarantee stability of the dimensions and shape of the initial gold particles, the size and shape of said initial gold particles being chosen according to the desired plasmonic or optical effect.

[0013] Another objective of the present invention is to propose a method for manufacturing a watch or jewelry component made wholly or partly from a material comprising between 9 and 21 carats of gold, allowing for the simple production of a component comprising gold of a predefined color, such as a dark or black tint, and in particular deep black.

[0014] Disclosure of the invention

[0015] To this end, the invention relates to a method for manufacturing a watch or jewelry component made wholly or partly from a material comprising between 9 and 21 carats of gold, said method comprising the following steps: a) preparing gold-based particles having a melting point Tf higher than the melting point TfAu of gold; b) supplying ceramic particles; c) combining said ceramic particles with the gold-based particles prepared according to step a) in order to obtain a mixture; d) producing a semi-finished product wholly or partly from a material comprising between 9 and 21 carats of gold, inclusive, by shaping the mixture obtained in step c) and sintering in order to form said watch or jewelry component; e) producing the watch or jewelry component wholly or partly from said material comprising between 9 and 21 carats of gold, inclusive, from the semi-finished product obtained in step d).

[0016] Preferably, the gold-based particles are prepared in step a) so that their melting temperature Tf is higher than the sintering temperature during the sintering carried out in step d).

[0017] Thus, the process according to the invention makes it possible to use gold-based particles whose melting point is increased relative to the melting point TfAu of gold, which is approximately 1064°C, thereby enabling them to better withstand the heat during sintering. More specifically, the process according to the invention makes it possible to use gold-based particles whose melting point is increased so that it becomes higher than the sintering temperature. Therefore, the process according to the invention makes it possible to use gold-based particles that withstand the heat of sintering so that they will not melt and, consequently, will not agglomerate, deteriorate, or migrate under the effect of heat.Thus, the size and shape of the gold particles prepared in step a), chosen according to the desired plasmonic or optical effect, are preserved so that this plasmonic or optical effect is maintained in the semi-finished product as well as in the resulting watch or jewelry component containing at least 9 carats of gold. In particular, the semi-finished product and the resulting watch or jewelry component have substantially the same color as the gold-based particles prepared in step a) or the ceramic supplied according to step b), depending on the desired plasmonic or optical effect, this color advantageously being black.

[0018] The present invention also relates to a semi-finished product in a material comprising between 9 and 21 carats of gold, obtainable during the implementation of the manufacturing process of a watch or jewelry component as defined above, said semi-finished product having a color defined in the CIE L*a*b space by the parameters -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.

[0019] The present invention also relates to a watch or jewelry component obtainable by the manufacturing process as defined above, said watch or jewelry component being obtained from a semi-finished product which has a color defined in the CIE L*a*b space by the parameters - 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.

[0020] 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.

[0021] Embodiments of the invention

[0022] The present invention relates to a method of manufacturing a watch or jewelry component made wholly or partly from a material comprising between 9 and 21 carats of gold, inclusive of limits, that is to say comprising between 37.5% and 87.5% gold by weight relative to the total weight of the material.

[0023] Such a watch or jewelry component may consist of an oscillating weight, a bridge, a disc, a wheel, a watch casing element, or a piece of jewelry. 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 the powder formed from said particles), the particle size distribution (the set of particle sizes) being measured in particular by laser granulometry according to ISO 13320:2009. The particle sizes indicated in this application correspond to the D95 percentile, meaning that 95% of the particles in the set of particles considered have a size smaller than D95.

[0024] According to the invention, said process comprises a first step a) of preparing gold-based particles which have a melting temperature Tf greater than the melting temperature TfAu of gold and a second step b) of providing ceramic particles, said ceramic being sintered according to a standard sintering at a sintering temperature Tfrit.

[0025] In a particularly preferred manner, the melting temperature Tf of gold-based particles prepared in step a) is higher than the sintering temperature Tfrit during sintering carried out in step d).

[0026] The process of the invention is particularly advantageous when the ceramic particles supplied in step b) are such that the sintering temperature Tfrit during the sintering carried out in step d) is higher than the melting temperature TfAu of gold. In other words, this means more generally that the process of the invention is particularly advantageous when the ceramic particles supplied in step b) are such that, if the particles supplied in step a) were gold particles with a melting temperature TfAu, the amount of heat required to sinter said ceramic particles supplied in step d) would be sufficient to cause the melting of said gold particles, with a melting temperature TfAu, which would result in a loss of integrity (in particular a loss of shape and / or dimensions) of said gold particles.Conversely, in the process of the invention, the melting temperature Tf of the gold-based particles prepared in step a) is higher than the sintering temperature Tfrit during the sintering carried out in step d). In other words, this means more generally that the amount of heat required for sintering the ceramic particles supplied in step d) is not sufficient to cause the gold-based particles, with their melting temperature Tf, to melt. Consequently, the integrity, in particular the shape and / or size, of said gold-based particles is preserved.

[0027] The choice of gold-based particles supplied in step a) depends on the plasmonic effect or optical effect applied in the watch or jewelry component to be manufactured.

[0028] Specifically, when a plasmonic effect is desired, gold-based particles are gold nanoparticles with dimensions and shapes that impart a plasmonic effect, at least in the visible spectrum. Preferably, these nanoparticles have dimensions smaller than 200 nm, preferably between 1 nm and 200 nm, and more preferably between 10 nm and 200 nm to achieve a plasmonic effect. Controlling the dimensions and shape of the gold-based nanoparticles allows for obtaining the desired color based on the plasmonic effect achieved. Colors ranging from red to violet can be obtained depending on size, generally with spherical nanoparticles, while colors such as green and blue can be obtained by manipulating the shape factor, for example, with more or less elongated nanoparticles, such as rod-shaped ones. We can also have shapes like cubes, stars, etc.

[0029] In a preferred embodiment, the gold-based nanoparticles are configured to exhibit a dark or black color defined in the CIE L*a*b space by the parameters -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.

[0030] Where the optical effect is desired, the gold-based particles are plasmonic-free and have dimensions less than 60 pm, preferably less than 30 pm, and preferably greater than 1 pm. They are homogeneously dispersed within the ceramic particles that constitute a matrix. Furthermore, the quantity of gold-based particles dispersed in said matrix is ​​predetermined so that the gold-based particles visually blend with the matrix, an observer perceiving the surface of the material as a uniform surface, for example, dark or black, corresponding to the chosen color of the matrix, as described in the applicant's PCT / EP2024 / 077818.

[0031] In the following description, gold-based particles and gold particles used to obtain said gold-based particles described refer to both nanoparticles as defined above to obtain the plasmonic effect and particles as defined above to obtain the optical effect depending on the desired effect, unless otherwise indicated.

[0032] In order to obtain said gold-based particles which have a melting temperature Tf higher than the melting temperature TfAu of gold, said gold-based particles prepared in step a) comprise gold and at least one metal which has a melting temperature higher than the melting temperature TfAu of gold, the amount of metal being chosen so that said gold-based particles have said melting temperature Tf.

[0033] Preferably, said metal is chosen from the group comprising platinum, tungsten, cobalt, rhodium, ruthenium, iridium, palladium, titanium, chromium, vanadium, zirconium, niobium, hafnium, tantalum, molybdenum, rhenium, and their alloys. More generally, any non-toxic material suitable for the manufacture of a watch or jewelry component according to the invention, and whose melting point is higher than the melting point TfAu of gold alone, could be used.

[0034] A person skilled in the art can determine the quantity of metal required to obtain gold-metal particles with the melting temperature Tf from the Au-metal phase diagrams corresponding to the metal used in combination with gold. In general, very small quantities of said metal are sufficient to obtain gold-metal particles with a melting temperature Tf higher than the melting temperature TfAu of gold alone, and more particularly a melting temperature Tf higher than the sintering temperature Tfrit of the sintering carried out in step d).

[0035] For example, a quantity of metal less than 10%, or even 5%, as an atomic percentage of the total material composition can be used. The quantity of gold-based particles to be used is then chosen to obtain a material containing the amount of gold corresponding to the desired carat weight.

[0036] The said gold-based particles comprising gold and at least one other metal can be prepared in step a) according to various manufacturing techniques.

[0037] According to one technique, step a) can be carried out by coating gold particles with at least one layer of said metal. This coating can be achieved through various processes, notably physical deposition (PVD, for example) of said metal onto the surface of the gold particles, followed by diffusion of the metal into the gold via Joule heating. Another coating process involves forming a shell or outer coating of said metal around the gold particles using a solution of a corresponding metallic precursor. Electrodeposition is another coating process. The resulting shell consists solely of metal and is distinct from metal oxide shells used in known ways to produce, for example, Au@metal oxide core-shell nanoparticles.

[0038] According to another manufacturing technique, step a) can be carried out by forming gold-based and metal particles from a gold-metal bimetallic precursor by coprecipitation, allowing these gold-based particles to be manufactured directly without going through a metal shell.

[0039] According to another manufacturing technique, step a) can be carried out by forming gold-based and metal particles from a gold-metal alloy by atomizing an ingot of said alloy. Step a) 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 gold-metal alloy particles necessary for carrying out the process of the invention.

[0040] Regardless of the manufacturing technique used in step a), the gold-based particles are prepared in step a) so that they have, in particular, the dimensions required to achieve the optical effect or the dimensions and shape required to achieve the desired plasmonic effect in the watch or jewelry component to be manufactured. This means that, for manufacturing techniques using initial gold particles to form said gold-based particles, the dimensions and, where applicable, the shape of the initial gold particles are also chosen so that the resulting gold-based particles achieve the desired optical or plasmonic effect.

[0041] Advantageously, the ceramic supplied in step b) is 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. Preferably, the ceramic is zirconia, which exhibits fracture toughness particularly well-suited to watchmaking and jewelry applications. For example, this toughness is superior to that of other ceramics, such as titanium carbide. Furthermore, zirconia is particularly well-suited to the process of the invention since it has a sintering temperature of approximately 1200°C, which is higher than the melting point of gold.This means that the amount of heat that would need to be supplied during the sintering of a composite material comprising zirconia and unmodified gold particles could lead to the melting of said gold particles.

[0042] Preferably, the dimensions of the ceramic particles supplied in step b) are between 1 nm and 200 pm.

[0043] In particular, when the optical effect is desired, the dimensions of the ceramic particles provided in step b) can preferably be between 1 nm and 30 pm, more preferably between 20 nm and 30 pm.

[0044] Advantageously, all or part of said ceramic particles supplied in step b) have dimensions between 1 nm and 50 nm, preferably between 4 nm and 40 nm, preferably between 4 nm and 30 nm, and more preferably between 4 nm and 19 nm, or dimensions between 1 nm and 19 nm, preferably between 4 nm and 19 nm. A synthesis for the fabrication of such nanoparticles is described, for example, in the publication "Large-scale synthesis of organophilic zirconia nanoparticles and their application in organic-inorganic nanocomposites for efficient volume holography", G. Garnweitner et al., Small 2007, 3, No. 9, 1626-1632.Step b) may then also include the supply of ceramic particles with dimensions greater than 50 nm, preferably between 50 nm and 200 nm, more preferably between 50 nm and 100 nm, in a ratio of "small ceramic particles" to "larger ceramic particles" of between 5 / 95 and 95 / 5, where the small ceramic particles have dimensions less than 50 nm and the larger ceramic particles have dimensions greater than 50 nm. Preferably, the ratio of "small ceramic particles" to "larger ceramic particles" is 1 / 4, 1 / 3, 1 / 2, 1 / 1, 2 / 1, 3 / 1, or 4 / 1. Thus, the ceramic supplied in step b) is a mixture of ceramic particles comprising small and larger particles.Furthermore, the particle size distribution of the mixture is advantageously chosen to obtain the most compact material possible. Numerical models of bidisperse distribution can, for example, be used to optimize this distribution. The use of small ceramic particles advantageously reduces the amount of heat required for sintering these ceramic particles. Consequently, this allows either a reduction in the sintering temperature or a reduction in the exposure time to the sintering temperature, and these two possibilities can be combined. As a result, the gold-based particles will receive less heat during sintering and will be more resistant to the effects of heat.

[0045] Advantageously, when the plasmonic effect is desired, the ceramic is chosen to be more transparent than the gold after sintering in step d) so that light interacts more with the gold than with the sintered ceramic. Furthermore, when the gold-based nanoparticles are black, the ceramic is chosen to be black after sintering when used alone, without gold-based nanoparticles.

[0046] When an optical effect is desired, the ceramic particles are chosen to form a matrix with a shade corresponding to that required for the watch or jewelry component. Preferably, in the case of a dark or black shade, defined in the CIE L*a*b color space by the parameters -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, la céramique peut être choisie parmi une zircone pigmentée par un pigment de teinte noire, tel que le carbone, une alumine pigmentée par un pigment de teinte noire, tel que le carbone, le carbure de silicium, le nitrure de silicium, ou leurs mélanges.

[0047] Then, according to step c) of the process of the invention, the ceramic particles provided in step b) are combined with the gold-based particles prepared according to step a) to obtain a mixture. The quantities of ceramic particles and gold-based particles are chosen so as to obtain a material comprising between 9 and 21 carats of gold.

[0048] Preferably, the gold-based particles are dispersed homogeneously within the ceramic particles.

[0049] Step c) can be carried out by mixing gold powder and ceramic powder in solid form to form a dry powder.

[0050] Advantageously, step c) can be carried out by mixing said ceramic particles with said gold-based particles in a solvent to form a colloidal liquid solution in which the gold-based and ceramic particles are optimally and stably dispersed. Such a solvent can be water or any other suitable solvent. For example, the two powders, gold-based and ceramic, can be mixed in the solvent, or a solution of ceramic particles can be prepared in advance and dispersed with the gold-based particles, or a solution of gold-based particles can be prepared in advance and dispersed with the ceramic powder, or a solution of ceramic particles and a solution of gold-based particles can be prepared and the two solutions mixed.

[0051] Then, according to step (d) of the process of the invention, a semi-finished product, in whole or in part, is produced in a material comprising between 9 and 21 carats of gold, inclusive, by shaping the mixture obtained in step (c) and sintering it at the standard sintering temperature (Tfrit) in order to form said watch or jewelry component, the integrity (in particular, the shape and dimensions) of the gold-based particles supplied in step (a) being preserved, as detailed above. The shaping in step (d) can be carried out by traditional ceramic shaping processes. It consists of forming a compact, raw semi-finished product traditionally called a "green body" or near-net-shape, that is to say, very close to the final shape of the component to be manufactured.

[0052] When the mixture obtained in step c) is in the form of a dry powder, the shaping of the mixture obtained in step c) may consist of a pressing process, such as uniaxial pressing or cold isostatic pressing, an extrusion process, injection molding, slip casting, using for this purpose a mold suitable for the component to be manufactured, for example a PTFE mold, to obtain, after shaping, a "green body".

[0053] When the mixture obtained in step c) is in the form of a liquid solution, the shaping of the mixture obtained in step c) may consist of an extrusion process, injection molding, slip casting, to obtain, after shaping, a "green body".

[0054] The shaping process could also consist of depositing thin layers of the ceramic / gold-based particle mixture by coating onto another material.

[0055] The sintering carried out in step d) is possibly preceded by debinding depending on the composition of the "green body" obtained after shaping.

[0056] Sintering can be done by exposure to radiation, such as UV or microwaves, by traditional heat treatment, by Flash sintering also called SPS (Spark Plasma Sintering), or by ultrafast high temperature sintering (UHS).

[0057] 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.

[0058] 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.

[0059] 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 gold-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.

[0060] 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.

[0061] The invention makes it possible to completely densify the matrix formed by the ceramic at low temperature while preserving the size of the gold-based particles.

[0062] Then, according to step e), the watch or jewelry component is produced, in whole or in part, from said material comprising between 9 and 21 carats of gold, including limits, from the semi-finished product obtained in step d). Regardless of the embodiments of steps c) and d), step e) may include a mechanical machining and / or finishing treatment of the semi-finished product obtained in step d) to obtain said watch or jewelry component.

[0063] The semi-product obtained in step d) and the watch or jewelry component obtained in step e) have a color identical or very close to that of the gold-based nanoparticles of step a) in the case of the plasmonic effect or of the ceramic matrix of step b) in the case of the optical effect, the size and shape of the gold-based particles used initially having been preserved.

[0064] Indeed, since the gold-based particles have a melting point (Tf) higher than the sintering temperature during the sintering process carried out in step (d) according to the invention, said gold-based particles do not melt and therefore do not agglomerate. Consequently, said gold-based particles do not change in size or shape. Therefore, the plasmonic or optical effect associated with the choice of these gold-based particles is preserved in the semi-finished product and in the resulting watch or jewelry component.The color of the gold-based nanoparticles in the case of the plasmonic effect or the color of the matrix in the case of the optical effect is not altered by the various heat treatments required to obtain the watch or jewelry component, so the AE difference in the CIE Lab color space between the colors of the gold-based nanoparticles or the matrix and the color of the watch or jewelry component obtained is preferably less than 10, preferably less than or equal to 8, and more preferably less than or equal to 7.

[0065] Preferably, in plasmonic-effect-based embodiments, where the gold-based nanoparticles are configured to exhibit a dark or black color defined in the CIE L*a*b space by the parameters -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, ou dans les modes de réalisation basés sur l’effet optique, où la matrice de céramique est de teinte prédéfinie noire ou foncée, la présente invention permet avantageusement d’obtenir un semi-produit dans un matériau comprenant entre 9 et 21 carats d’or présentant une couleur définie dans l'espace CIE L*a*b par les paramètres -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, en particulier pour le cas de l’effet optique,when viewed by an observer placed at least 30 cm, and preferably at least 10 cm, from the surface of said material.

[0066] The present invention relates to a watch or jewelry component made wholly or partly from a material comprising between 9 and 21 carats of gold, inclusive of the limits, obtainable by the manufacturing process as described above, and obtained from a semi-finished product as described above, said material having a uniform overall color defined in the Cl EL*a*b space by the parameters -5

Claims

Demands 1. A process for manufacturing a watch or jewelry component made wholly or partly from a material comprising between 9 and 21 carats of gold, inclusive, said process comprising the following steps: a) preparing gold-based particles having a melting point Tf higher than the melting point TfAu of gold; b) supplying ceramic particles; c) combining said ceramic particles with the gold-based particles prepared according to step a) in order to obtain a mixture; d) producing a semi-finished product wholly or partly from a material comprising between 9 and 21 carats of gold, inclusive, by shaping the mixture obtained in step c) and sintering in order to form said watch or jewelry component; e) producing the watch or jewelry component wholly or partly from said material comprising between 9 and 21 carats of gold, inclusive, from the semi-finished product obtained in step d).

2. A process according to claim 1, characterized in that the melting temperature Tf of gold-based particles prepared in step a) is greater than the sintering temperature during sintering carried out in step d).

3. A process according to any one of the preceding claims, characterized in that the gold-based particles prepared in step a) comprise gold and at least one metal which has a melting point higher than that of gold, the amount of metal being chosen so that said gold-based particles have said melting point Tf.

4. A method according to claim 3, characterized in that the metal is selected from the group comprising platinum, tungsten, cobalt, rhodium, ruthenium, iridium, palladium, titanium, chromium, vanadium, zirconium, niobium, hafnium, tantalum, molybdenum, rhenium and their alloys.

5. A method according to any one of claims 3 and 4, characterized in that step a) is carried out by coating gold particles with at least one layer of said metal.

6. A process according to any one of claims 3 and 4, characterized in that step a) is carried out by forming gold-based particles from a gold-metal precursor by precipitation.

7. A process according to any one of claims 3 and 4, characterized in that step a) is carried out by forming gold-based particles from a gold-metal alloy by atomizing an ingot of said alloy.

8. A method according to any one of the preceding claims, characterized in that step c) is carried out by mixing said ceramic particles with said gold-based particles to form a dry powder or with a solvent to form a colloidal liquid solution.

9. A manufacturing process according to any one of the preceding claims, characterized in that the shaping in step d) is carried out by pressing, extrusion, injection molding, casting.

10. A manufacturing process according to any one of the preceding claims, characterized in that the sintering in step d) is radiation sintering, heat treatment sintering, flash sintering, or high-temperature ultrafast sintering.

11. A manufacturing process according to any one of the preceding claims, characterized in that the gold-based particles are nanoparticles which have dimensions and shapes which give them a plasmonic effect at least in the visible range.

12. Manufacturing process according to claim 11, characterized in that said nanoparticles have dimensions less than 200 nm, preferably between 10 nm and 200 nm.

13. A manufacturing process according to any one of the preceding claims, characterized in that the gold-based particles have dimensions less than 60 pm, preferably less than 30 pm, and are dispersed in homogeneously in the ceramic particles that constitute a matrix, and in that the quantity of gold-based particles dispersed in said matrix is ​​predetermined so that said gold-based particles visually blend with the matrix.

14. A manufacturing process according to any one of the preceding claims, characterized in that the ceramic is 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.

15. Manufacturing process according to any one of the preceding claims, characterized in that step e) comprises a mechanical machining and / or finishing treatment of the semi-product obtained in step d) to obtain said watch or jewelry component.

16. A manufacturing process according to any one of the preceding claims, characterized in that said semi-finished product obtained in step d) has a color defined in the CIE L*a*b space by the parameters -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.

17. Semi-finished product in a material comprising between 9 and 21 carats of gold, inclusive of the terminals, capable of being obtained during the implementation of the manufacturing process of a watch or jewelry component according to any one of the preceding claims, characterized in that said semi-finished product has a color defined in the CIE L*a*b space by the parameters -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 O< L*< 6.

18. Watchmaking or jewelry component that can be obtained by the manufacturing process according to any one of claims 1 to 16.

19. Watchmaking or jewelry component according to claim 18, characterized in that it consists of an oscillating weight, a bridge, a disc, a wheel, a watch casing element, a piece of jewelry.