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

Abstract

The present invention relates to a method for manufacturing a timepiece or jewellery component in a material comprising between 9 and 21 carat gold, comprising the following steps: a) providing gold-based particles; b) providing ceramic particles, all or some of the ceramic particles having 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; c) combining the ceramic particles with the gold-based particles to obtain a mixture; d) producing a semi-finished product entirely or partly in a material comprising between 9 and 21 carat gold inclusive by shaping the mixture obtained in step c) and sintering to form the timepiece or jewellery component, wherein the sintering temperature and / or the sintering time is lower than the sintering temperature and / or the sintering time, respectively, of ceramic particles of the same type as the particles provided in step b) but of larger size; e) producing the timepiece or jewellery component entirely or partly in 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, the timepiece or jewellery component being obtained from a semi-finished product that exhibits 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) supplying gold-based particles; b) supplying ceramic particles, all or part of said ceramic particles having 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; c) combining said ceramic particles with the gold-based particles to obtain a mixture;d) produce a semi-finished product, in whole or in part, in 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, the sintering temperature and / or the duration of sintering being lower than the sintering temperature, respectively the duration of sintering, of ceramic particles of the same nature as the particles supplied in step b) but of larger dimensions; e) produce the watch or jewelry component, in whole or in part, in said material comprising between 9 and 21 carats of gold, inclusive, from the semi-finished product obtained in step d).;

[0016] Thus, using ceramic particles with dimensions smaller, or even much smaller, than the standard ceramic particles according to the invention makes it possible to reduce the amount of heat required to sinter these ceramic particles. This reduction in heat allows for a lower sintering temperature for small ceramic particles compared to the sintering temperature of larger ceramic particles of the same type as those supplied in step b), and / or a shorter sintering time for small ceramic particles compared to the sintering time for larger ceramic particles of the same type as those supplied in step b).Thus, in step d), the gold-based particles are sintered with ceramic particles at a lower sintering temperature than those used in standard sintering, or with a shorter exposure time to the sintering temperature, which allows them to better withstand the heat during sintering. More specifically, the process according to the invention makes it possible to use gold-based particles that are resistant to the heat of sintering, so that they will not melt and, consequently, will not agglomerate, deteriorate, or migrate under the effect of heat. Advantageously, the size and, where applicable, the 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 watch or jewelry component obtained 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 being advantageously black.

[0017] 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.

[0018] 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. D’autres caractéristiques et avantages de la présente invention apparaîtront à la lecture de la description détaillée suivante de différents modes de réalisation de l’invention, donnés à titre d’exemples non limitatifs.

[0019] Embodiments of the invention

[0020] 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.

[0021] 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.

[0022] In the present invention, the size or dimension of a particle is defined as its equivalent diameter, that is to say, the diameter of the sphere that would behave identically during the particle size analysis of the particles (or of the powder formed from said particles), the particle size distribution (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 less than D95.

[0023] According to the invention, said process includes a first step a) consisting of providing gold-based particles.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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 said 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.

[0028] In the following description, gold-based particles refer to both nanoparticles as defined above to achieve the plasmonic effect and particles as defined above to achieve the optical effect, depending on the desired effect, unless otherwise indicated.

[0029] Gold-based particles can be 24-karat pure gold particles, whose melting point (TfAu) is approximately 1064°C. Gold-based particles can also be Au@metal oxide particles comprising a gold core coated with a metal oxide shell, obtained by reacting a metal oxide precursor with gold particles. Advantageously, the metal oxide is selected from the group including silicon dioxide, zirconium oxide, and titanium dioxide. Advantageously, nanoparticles comprising a gold core with a silica oxide shell are synthesized, and more preferably, nanoparticles comprising a gold core with a zirconium oxide shell.

[0030] Gold-based particles may be gold / metal particles with a melting point (Tf) higher than the melting point (TfAu) of gold. Such gold / metal particles comprise gold and at least one other metal with a melting point higher than that of gold, the amount of metal being chosen so that the gold-based particles have said melting point (Tf). These gold / metal particles may be in the form of gold particles coated with at least one layer of said metal or be obtained from an ingot of an alloy of gold and said metal. Said metal may be platinum, tungsten, cobalt, rhodium, ruthenium, iridium, palladium, titanium, chromium, vanadium, zirconium, niobium, hafnium, tantalum, molybdenum, rhenium, and their alloys.

[0031] The gold particles, gold / metal particles and Au@metal oxide particles supplied in step a) are prepared to have, in particular, the dimensions to obtain the optical effect or the dimensions and shape to obtain the desired plasmonic effect in the watch or jewelry component to be manufactured.

[0032] Preferably, the gold-based particles supplied in step a) are gold nanoparticles or Au@metal oxide nanoparticles, the desired effect in the watch or jewelry component being the plasmonic effect.

[0033] The process according to the invention comprises a second step b) which consists of providing ceramic particles, all or part of said ceramic particles having 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.

[0034] 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 suited to watchmaking or jewelry applications.

[0035] Advantageously, step b) may 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.

[0036] Thus, the ceramic supplied in step b) is a mixture of ceramic particles comprising small particles and larger particles.

[0037] Furthermore, advantageously, the particle size distribution of the mixture is chosen to obtain the most compact material possible. Bidisperse numerical models can, for example, be used to optimize this distribution. 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. Moreover, when the gold-based nanoparticles are black, the ceramic is chosen to be black after sintering when used alone, without gold-based nanoparticles.

[0038] 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.

[0039] Then, according to step c) of the process of the invention, the ceramic particles supplied in step b) are combined with the gold-based particles supplied in 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.

[0040] Advantageously, the gold-based particles supplied in step a) are gold nanoparticles or Au@oxide nanoparticles, preferably zirconium Au@oxide, or Au / Pt particles as defined above, and the ceramic particles are zirconia (ZrC^) particles.

[0041] Preferably, the gold-based particles are dispersed homogeneously within the ceramic particles.

[0042] Step c) can be carried out by mixing gold powder and ceramic powder in solid form to form a dry powder. 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.

[0043] Advantageously, step c) can be carried out for example by mixing ZrU2 powder and gold-based nanoparticles with a solvent to form a colloidal liquid solution in which the gold-based and ceramic particles are optimally and stably dispersed, without sedimentation of the ZrU2 particles.

[0044] 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 in order to form said watch or jewelry component, wherein the sintering temperature Tfrit is lower than the standard sintering temperature Tfritstand of ceramic particles of the same nature as the particles supplied in step b) but of larger dimensions, and / or, the sintering temperature being the standard sintering temperature Tfritstand, the duration of the sintering, that is to say the time of exposure to said standard sintering temperature Tfritstand, is less than the duration of the sintering of ceramic particles of the same nature as the particles supplied in step b) but of larger dimensions, so as to reduce the amount of heat to be supplied for the sintering of the ceramic particles.

[0045] Indeed, because ceramic particles are smaller than those traditionally used, they have a larger specific surface area. Therefore, for sintering, these ceramic particles require a lower energy input, meaning a smaller quantity of heat, defined by Q = m x C x AT, where Q represents the amount of energy transferred in joules (J), m represents the mass of the substance in grams (g), C represents the specific heat capacity of the substance in J / (g °C), and AT represents the temperature change in °C. Since the amount of heat required for sintering is less, this allows either a lower sintering temperature or a shorter exposure time to the sintering temperature, which can be combined.

[0046] Therefore, when the sintering temperature Tfrit during the sintering step d) is lowered, advantageously by several tens of degrees, said sintering temperature Tfrit approaches the melting point of gold, which allows the gold-based particles to better withstand the heat during sintering. Preferably, the sintering temperature Tfrit during the sintering step d) is lower than the standard sintering temperature Tfritstand so that the sintering temperature Tfrit is below the melting point of gold. For example, for a traditionally used zirconia with a sintering temperature Tfritstand of 1200°C, the zirconia particles used in the invention have a sintering temperature Tfrit of 1000°C.

[0047] When the sintering temperature Tfrit in step d) is equal to, or even lower than, the standard sintering temperature Tfritstand, the sintering time—that is, the exposure time to said sintering temperature Tfrit—is shorter than the sintering time at Tfritstand for ceramic particles of the same type as those supplied in step b) but with larger dimensions. This allows the gold-based particles to receive less heat during sintering and thus to better withstand the effects of heat.

[0048] The shaping in step d) can be carried out by traditional ceramic shaping processes. It consists of forming a compact raw semi-product traditionally called a "green body" near-net-shape, i.e. very close to the final shape of the component to be manufactured.

[0049] 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".

[0050] 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".

[0051] The shaping process could also consist of depositing thin layers of the ceramic / gold-based particle mixture by coating onto another material.

[0052] The sintering carried out in step d) is possibly preceded by debinding depending on the composition of the "green body" obtained after shaping.

[0053] 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).

[0054] 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.

[0055] The ultrafast high-temperature (UHS) 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] The use of a colloidal liquid solution of ceramic and gold-based particles prevents agglomeration and results in a more homogeneous mixture. Consequently, the green body mixture will be more homogeneous, and therefore, the resulting material will be more homogeneous.

[0060] The use of a mixture of small and large ceramic particles, as described above, allows for a high level of compaction of the green body and a faster sintering speed, as the sintering of the smaller particles is quicker. Furthermore, the smaller particles are sintered first and form a binder for the gold-based particles and the larger ceramic particles, enabling their agglomeration without the need for higher temperatures or longer sintering times. Then, according to step e), the watch or jewelry component is produced, in whole or in part, from the semi-finished product obtained in step d), using the said material containing between 9 and 21 carats of gold, including the terminals.

[0061] Regardless of the methods of implementation of steps c) and d), step e) may include mechanical machining and / or finishing of the semi-product obtained in step d) to obtain said watch or jewelry component.

[0062] 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.

[0063] Indeed, since the sintering temperature Tfrit during the sintering carried out in step d) is lowered to be close to the melting temperature Tf of the gold-based particles, and preferably lower than the melting temperature Tf of the gold-based particles, according to the invention, and / or the sintering time is shorter, said gold-based particles will resist the heat of the sintering so that they will not melt and consequently will not agglomerate, deteriorate, or migrate under the effect of heat. Thus, advantageously, the size and, where applicable, the shape of the gold particles supplied in step a), chosen according to the desired plasmonic or optical effect, are preserved. Consequently, the plasmonic or optical effect related to 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.

[0064] 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.

[0065] 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, including 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 CIE L*a*b color space by the parameters -5

Claims

Demands 1. A method for manufacturing a watch or jewelry component made wholly or partly from a material comprising between 9 and 21 carats of gold, inclusive, said method comprising the following steps: a) supplying gold-based particles; b) supplying ceramic particles, all or part of said ceramic particles having 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; c) combining said ceramic particles with said gold-based particles to obtain a mixture;d) produce a semi-finished product, in whole or in part, in 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, the sintering temperature and / or the duration of sintering being lower than the sintering temperature, respectively the duration of sintering, of ceramic particles of the same nature as the particles supplied in step b) but of larger dimensions; e) produce the watch or jewelry component, in whole or in part, in said material comprising between 9 and 21 carats of gold, inclusive, from the semi-finished product obtained in step d).; 2. A method according to claim 1, 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.

3. 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.

4. 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 ultrafast high-temperature (UHS) sintering.

5. 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.

6. A manufacturing process according to claim 5, characterized in that the gold-based particles are nanoparticles having dimensions less than 200 nm, preferably between 10 nm and 200 nm.

7. 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, in that they are dispersed homogeneously in the ceramic particles which 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.

8. A manufacturing process according to any one of the preceding claims, characterized in that the gold-based particles are gold particles.

9. A manufacturing process according to any one of claims 1 to 7, characterized in that the gold-based particles are Au@metal oxide particles comprising a gold core covered with a metal oxide shell.

10. Manufacturing process according to claim 9, characterized in that the metal oxide is selected from the group comprising silicon oxide, zirconium oxide and titanium oxide.

11. A manufacturing process according to any one of the preceding claims, characterized in that step b) also includes the supply of ceramic particles with dimensions greater than 50 nm, preferably between 50 nm and 200 nm, and more preferably between 50 nm and 100 nm.

12. 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.

13. 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.

14. 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 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.

15. 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.

16. Watchmaking or jewelry component that can be obtained by the manufacturing process according to any one of claims 1 to 14.

17. Watchmaking or jewelry component according to claim 16, characterized in that it consists of an oscillating weight, a bridge, a disc, a wheel, a watch casing element, a piece of jewelry.