CH715203B1 - Gold-based alloy exhibiting a color change and its use in the field of jewelery and watchmaking. - Google Patents

Abstract

The subject of the present invention is a gold alloy of at least 18 carats comprising gold as well as copper and at least one metal M from the platinum group, said alloy having properties that change color as a function of angle of observation and/or illumination. It also relates to the use of said alloy in the manufacture of luxury items such as jewelry and watches.

Description

Technical area

The present invention relates to the field of watchmaking and jewelry, it relates more specifically to a gold alloy having particular optical properties and a high resistance to tarnishing and its use for obtaining luxury objects with quality visual renderings that are easily recognizable without having to resort to long and tedious analysis methods.

State of the art

[0002] Swiss watchmaking is one of the country's industrial flagships. Its reputation over the centuries has gone far beyond the limits of the Alps or the Jura, the seriousness, complexity and quality of Swiss watches make them more than simple indicators of time, but exceptional and luxury pieces. With the complexity of the pieces, sometimes qualified as a work of art for some, an exceptional design also testifies to their beauty and the quality of these.

[0003] It is therefore quite natural that precious metals have taken on an increasingly important place in the design of watches or luxury jewellery. The use of 18 carat gold has become common in the luxury sector. These alloys are most often compounds comprising gold, copper and silver. These basic alloys have gradually been replaced by gray or pink gold, providing new renderings that are appreciated by consumers and still synonymous with luxury and beauty.

[0004] A white gold free of nickel is for example described in application EP 1 227 166, the invention relates to a claimed white gold alloy free of nickel, cobalt, iron and silver comprising, by weight: (a) Au : 75 to 76%; (b) Cu ≥ 17%; (c) Mn less than 7%; (d) Zn ≤ 2%.

[0005] This gold alloy may also contain, by weight: (a) Si ≤ 0.5%; (b) at least one of Ti less than 0.3% or Ta less than 0.3%; (c) 0% Pd and at most 2% Pt. In application WO2014122233 the invention relates to a timepiece or a piece of jewelery comprising a pink gold alloy containing at least 750 ‰ by weight of gold, said alloy also containing copper, palladium and indium, the sum of the concentrations of palladium and indium being less than or equal to 35 ‰, or less than or equal to 30 ‰, or even less than or equal to 25 ‰, and / or the sum of the palladium and indium concentrations being between 15‰ and 35%o, or between 20‰ and 35‰, or even between 25‰ and 33‰.

[0006] One of the major drawbacks of these alloys is the tarnishing that occurs over time and with the use of the watch or the timepiece. Indeed, the wear and tear of time, exposure to temperature variations, humidity, cold, heat, friction, exposure to air and therefore to oxygen, are all factors that have an impact on the long term the quality and rendering of the precious material that makes up the watch or jewel.

[0007] This is all the more unfortunate for objects that are worth several tens of thousands of francs or even hundreds of thousands of francs, because the degradation or tarnishing of the gold alloy does not only have an impact on the visual rendering of the object, but also has an impact on its value which will necessarily decrease.

Another drawback also encountered when using these different gold alloys in the field of watchmaking and jewelry, is that it is difficult to distinguish one pink gold from another pink gold visually, or a white gold from another white gold. Nothing looks more like white gold than another white gold, unless the comparison is made through the use of physico-chemical analysis techniques that are often long and costly.

[0009] In a world where watchmaking and jewelry are subject to major counterfeits which impact the brand image of companies in the field of valuable watches, it is sometimes difficult to distinguish a gold alloy on an original watch. of its almost identical copy using a less expensive gold alloy or an equivalent material which is even less so.

[0010] Thus there is an ever-present need to have new gold alloys resistant to tarnishing and the attacks of time, allowing the simplest manufacture possible, which can give materials with quality visual renderings impacting the design. and the value of the object that contains it, while making it possible to distinguish this alloy from others visually and at a lower cost without the need to resort to complex and/or invasive costly analysis techniques.

Disclosure of Invention

One of the aims of the invention is therefore to remedy at least one of the aforementioned drawbacks by proposing a colored gold alloy of at least 18 carats comprising gold as well as copper and at least a metal M from the platinum group, said alloy exhibiting colors which are expressed in the CIE LCh* chromatic space by a chroma C < 16 and a hue h* < 70.

[0012] Said alloy according to the invention also exhibits color change properties depending on the angle of observation and/or lighting.

According to the invention, the quantity of gold present in the alloy for 100% of its mass is between 75 and 80% by mass.

[0014] Said alloy according to the invention may also comprise silver.

The metal M in the alloy according to the invention is selected from the group of platinoids and consists of palladium, platinum or a mixture thereof.

[0016] The quantity of copper in the alloy for 100% of its mass is 10 to 20% by mass and that of silver is between 0 and 10% by mass.

In the alloy according to the invention, the copper-silver mixture does not exceed 20% by mass, preferably it does not exceed 18% by mass.

The amount of metal M in the alloy according to the invention is 5 to 10% by mass.

The alloy according to the invention may also comprise grain refiner metals.

The alloy according to the invention may also include hardeners.

The alloy according to the invention may also comprise deoxidizers.

The alloy according to the invention may also include whiteners.

In the case of the present invention, the concentration of refining metals or also the deoxidizers does not exceed 1% by mass.

Said refining metals are selected from boron, molybdenum, iridium, rhenium, ruthenium or a mixture thereof.

Said deoxidizers are selected from aluminum or silicon or a mixture thereof.

In the case of the present invention, the concentration of hardeners or whiteners does not exceed 3% by mass.

Said hardeners or whiteners are selected from zinc, indium, gallium, iron, tin, germanium, chromium, vanadium, zirconium or titanium or a mixture thereof.

Another object of the present invention relates to a process for obtaining the alloy according to the invention obtained by the implementation of the following steps: i) Mixing of the compounds included in the composition of the alloy according to invention in the form of pure metal or in the form of a pre-alloy ii) Gradual heating of the various compounds present at a temperature above 900°C iii) Solidification by gradual cooling after melting of the various compounds at room temperature

The cooling leading to the solidification of the alloy according to the invention can be obtained by the methods of convection, quenching, transfer onto a neutral substrate or casting in a neutral solid.

Another aspect of the present invention relates to an object obtained from the alloy according to the invention by shaping said alloy by techniques of deformation, welding, sintering, casting or additive manufacturing or the implementation sequence of any of these techniques.

[0031] Said object obtained from the shaping techniques described above can be an object of jewelry or watchmaking comprising one or more parts constituting it made from an alloy according to the invention.

Brief description of figures

[0032] FIG. 1 shows the reflectance spectra as a function of wavelength of different metals such as copper, silver, gold and platinum. Fig. 2 represents the reflectance spectra as a function of the wavelength, of an 18 carat gold alloy of the state of the art containing a mixture of copper and silver whose copper and silver ratio exceeds the ratio such than covered by the alloys according to the invention. The alloy is a standard rose gold alloy called 4N according to the ISO 8654 standard. FIG. 3 represents the reflectance spectra as a function of the wavelength, of an 18 carat gold alloy according to the invention comprising gold, copper and palladium.

detailed description

The present invention will be described in more detail and using one or more examples which in no way limit the invention.

[0034] 18-carat gold is the most common precious alloy in the field of jewelry and luxury watchmaking. These alloys are synonymous with value, durability and aesthetics with quality renderings.

These are most often made of an alloy for 100% of their mass comprising gold (Au) up to at least 75% by mass of the alloy, as well as silver (Ag ) and copper (Cu). When it comes to color, gold and copper are the only color metals. The colors are related to the spectral signature of reflectance as a function of wavelength as shown in Fig. 1.

The curves of reflectance as a function of wavelength show a pronounced inflection around a wavelength of 600 nm (Cu - red) respectively 550 nm (Aujaune). The Ag shows the same signature, but with an inflection in the ultraviolet (UV) right next to the visible range (VIS).

If the noble elements Au, Ag and Cu are combined, their spectral signature, namely the inflection in the reflectance curve, persists, but its position shifts and thus generates a different color. In the case of 18k gold alloys, this shift as a function of the Ag/Cu ratio explains the standard colors varying from pale yellow (inflection towards blue) to red (inflection between those of gold and copper).

[0038] All other elements alloyed with 18k gold will flatten the curve and thus discolor the alloy until it appears grey.

[0039] In addition, 18ct alloys with a high Cu content show a phase transition in the solid state (“Au Cu” transition). Although this transition can be exploited to harden the alloy, it causes problems in the manufacturing process. The phase stable at high temperature (> 350°C, depending on the exact composition) is ductile and malleable while the phase stable at room temperature is hard and brittle, thus limiting its deformability.

Thus during production at each heat treatment cycle, the alloy must be quenched in order to retain the ductile structure subsequently allowing easy shaping by deformation. The 2 phases having a different structure and symmetry, each partial or complete transition generates non-uniform stresses which can cause distortion or even cracking of the part.

Any modification as mentioned above of the ratios between gold, copper and silver has an impact on the properties of the alloy obtained. Finding the right compromise between ductility, color and resistance to tarnishing is therefore far from being, given the number of material parameters to be modified, a routine exercise and requires significant research efforts.

[0042] If we add to these parameters, which are already important in the quality of the alloys used in watchmaking, the fact of being able to recognize them easily without resorting to costly or invasive physicochemical methods, this becomes really difficult and requires careful research.

[0043] It is thus that, surprisingly, it has been found that a gold alloy of at least 18 carats comprising gold as well as copper and at least one metal M from the group of platinoids has particular optical properties which are not encountered in the alloys of the state of the art mentioned above. Said optical properties being mainly that of a color change as a function of the angle of observation and/or illumination.

[0044] Said alloy makes it possible to achieve colors rarely achieved until then, i.e. outside those defined by the ISO 8654 standard and those of conventional white golds. The table below gives examples of alloys according to the invention (alloy A to E), and the colors obtained in La*b* coordinates, measured using a spectrophotometer with Minolta CM- 3610d CRBISS. For comparison, the colorimetric coordinates according to ISO 8654 of 4N to 6N color alloys and of a white gold. A 80.75 4.77 10.36b 80.77 4.04 8.89 C 81.17 3.49 8.23 D 82.88 5.66 9.96 E 81.97 88.9 6.13 21.24 5N 87.7 8.32 18.57 6N 86.3 10.13 15.57 Gray gold 80.16 1.18 5.63

The colors of the alloys according to the invention are outside the conventional ranges of 2N to 6N gold alloys: they are characterized by a color which is expressed in the CIE LCh* chromatic space by a chroma C < 16 and a shade h* < 70. In addition, it has a Yellowness Index (ASTMD 1925) strictly greater than 25, which also distinguishes it from white golds.

[0046] Indeed, FIG. 3 illustrates the spectral reflectance of an alloy of gold, copper and palladium according to the invention as a function of the viewing angle. The La*b* curve obtained from a CIELa*b* colorimetric measurement corresponds to an angle of 0°. The two other curves of specular reflectance of this alloy are measured under different angles of inclination (40° and 70°).

The La*b* curve as represented in FIG. 3, shows a significant spectral variation in the VIS, which results in the perception of a “pink” color. As the viewing angle increases, the curve rotates, reflecting more and more the blue part and less to less the yellow-red part of the spectrum, until it becomes almost flat (70°) . Consequently the color of the alloy is perceived gray under a high angle of observation.

[0048] By way of comparison are also shown in FIG. 2 the same curves for an Au-Ag-Cu alloy in 4N (“pink gold”) color. In this case the effect of the inclination is different from that of the alloy defined in the invention (FIG. 3). Fig. 2 shows that the inflection always remains present and located in the same place whatever the angle of observation: the color does not change. Only the intensity decreases when the viewing angle increases: the alloy is perceived as duller, less shiny.

This characteristic linked to the variation in optical property according to the angle of observation or lighting, also called "color-shift", gives an advantage to the alloy according to the invention compared to those of the state of the art and is a valuable differentiator from conventional alloys.

[0050] In the context of the present invention, the alloy which has properties of color change depending on the angle of observation and/or lighting, can be used not only to manufacture parts with quality renderings and colors never before obtained, but this one can also offer a most aesthetic effect by changing color according to the inclination of the watch or the jewel. Indeed, the advantage of such an alloy is its ability to change its color depending on the lighting and observation conditions, which is particularly attractive for worn objects. This accentuates and thus highlights the contours of an object of complex shape because the angle of observation varies locally according to the shape.

In the alloy according to the invention, the metal M is selected from palladium (Pd) or platinum (Pt) or a mixture thereof.

The metal M from the group of platinoids is selected from platinum and palladium or a mixture thereof and will be present within the alloy in the amount of 5 to 10% by mass. Its presence within the alloy will make it possible to reduce the copper and/or silver content within the alloy. The presence of the metal M in these proportions contributes to obtaining the desired properties of the alloy (color and malleability among others) and has a positive impact on the reduction of the effects of tarnishing, due to the reduced content of copper and /or silver compared to what is observed in the alloys of the state of the art.

In addition, the presence of the metal M makes it possible to reduce the copper/gold ratio and to move away from the critical shaping zone linked to the “Au-Cu” transformation, as described above. The development and formatting are greatly facilitated.

In order to meet the 18 carat gold criterion, the gold will be present in the alloy for 100% of its mass according to the invention in an amount of 75 to 80% by mass.

As for the copper within the alloy for 100% of its mass according to the invention in a mixture with the silver, this does not exceed 20% by weight, preferably the mixture does not exceed 18% mass. Thus the mixture may preferably contain more copper than silver or even a small or zero quantity of silver and a majority of copper. It is important that the mixture of two metals does not exceed 20% by mass, in order to obtain the good properties of ductility or malleability as well as the properties of resistance to tarnishing and the desired optical properties.

The alloy according to the invention has excellent rendering characteristics suitable for use in the field of watchmaking and jewelry. The color of the alloy is outside the classic ranges of 2N to 6N gold alloys, it is characterized by a color which is expressed in the CIE LCh* chromatic space by a chroma C < 16 and a hue h* < 70.

The CIE LCh* values, like the CIELa*b* values, allowing the color of a surface, an alloy or a sample to be characterized, can be easily obtained using a spectrophotometer working in reflectance.

In order to ensure during the preparation of the alloy to have a fine casting microstructure, grain refiner metals or deoxidizers are added within the alloy during its preparation.

[0059] Mention will be made, among these by way of non-limiting example, for the metal refiners boron, molybdenum, iridium, rhenium, ruthenium or a mixture thereof and for the deoxidizers aluminum or again silicon or a mixture thereof. Their presence within the alloy according to the invention does not exceed 1% by weight.

[0060] In addition to the grain-refining metals, hardening or whitening compounds can be found within the alloy. Their presence within the alloy is greater than that of grain refiners while not exceeding 3% by mass. By way of non-limiting example of hardeners or whiteners, mention will be made of zinc, indium, gallium, iron, tin, germanium, chromium, vanadium, zirconium or titanium or a mixture thereof. this.

The alloy according to the invention is obtained by mixing different metals which constitute it without a specific order being required. The method of implementation comprises in a first step or first step of the method, the mixture of the compounds entering into the composition of the alloy in the form of pure metal or in the form of pre-alloy. By pre-alloy, one can very well design a pre-alloy without being limiting to Au/Cu or a pre-alloy Au/Ag or even Cu/Ag, as long as the proportions as covered by the claims are respected.

The different metals or compounds entering into the composition of the alloy according to the invention are placed in a crucible or any suitable receptacle which can be heated to a high temperature. In a second phase or second stage of the process, said crucible or receptacle containing the various metals and compounds or pre-alloy is heated to a temperature above 900° C. in order to ensure that the mixture is in a state of merger. Adequate mechanical agitation of the molten mixture can be implemented.

In a third step of the process, the alloy according to the invention being molten in its crucible or its receptacle, it is gradually cooled to room temperature in order to allow the solidification of the molten mixture.

The gradual cooling of said alloy can be obtained by cooling the crucible using a liquid (water) or a gas, by injecting the molten mixture into a gas or liquid (atomization), by casting in a heat-resistant container (metal or graphite mold or ingot mold, for example), or by transfer onto a neutral substrate. Injection having the advantage of producing powder or shot, casting in a mold or container or ingot mold to produce preforms such as wires or plates, transfer onto a neutral substrate to deposit on a large surface a fairly thin layer of the alloy in order to use it directly for the preparation of parts such as watch movement components.

The alloy thus obtained can then be used in the manufacture of luxury objects such as watches or jewellery.

The object which is obtained from the alloy according to the invention, is obtained by shaping said alloy by standard techniques in the field of luxury objects such as deformation, welding, sintering , casting or additive manufacturing or the sequential implementation of any of these techniques.

The object which is obtained from the alloy according to the invention can be an object of jewelery or watchmaking and comprise at least one part made from the alloy according to the invention.

As mentioned previously, in addition to the new colors and varying according to the angle of observation, the alloy according to the invention has significant resistance to tarnishing.

Corrosion and tarnishing tests were carried out on washers with the composition of a sample of the alloy according to the invention. To do this, washers were prepared with one half of the surface satin-finished and the other half polished. Half of these surfaces were then masked with a lacquer in order to serve as a reference surface after the tests. These pucks were then subjected to thioacetamide, damp heat and salt spray testing in accordance with NIHS 96-50.

[0070] After the tests, the protective lacquer was removed, making it possible to directly compare the surfaces exposed to the test agents with the reference surfaces. No visual difference could be observed between these surfaces due to corrosion and/or tarnishing. This is in stark contrast to conventional pink/red color alloys (4N to 6N color alloy) which show clearly visible degradation after this type of testing.

The invention cannot be limited to the application in which the alloy according to the invention is used. Other modifications can be envisaged without departing from the scope of the present invention defined by the appended claims.

Claims (6)

1. Gold alloy of at least 18 carats characterized in that it comprises gold as well as copper and at least one metal M from the group of platinoids and optionally silver, said alloy being constituted for 100 % of its mass of: 75 to 80 wt% gold 10 to 20% copper by mass 0 to 10% by mass of silver, such that the sum of the percentages of copper and silver does not exceed 20% by mass, preferably does not exceed 18% by mass. 5 to 10% by weight of a metal M selected from palladium, platinum or a mixture thereof 0 to 1% by weight of grain-refining metals 0 to 1% by mass of deoxidizers 0 to 3% by mass of hardeners 0 to 3% by mass of whiteners and also characterized in that the color of said alloy is expressed in the CIE LCh* chromatic space by a chroma C < 16 and a hue h* < 70. 2. Alloy according to claim 1, in which the refining metals are selected from boron, molybdenum, iridium, rhenium, ruthenium or a mixture thereof. 3. Alloy according to claim 1 in which the hardeners are selected from zinc, indium, gallium, iron, tin, germanium, chromium, vanadium, zirconium or titanium or a mixture of those -this. 4. Process for obtaining an alloy according to any one of the preceding claims comprising the following steps: i) Mixture of compounds entering into the composition of the alloy according to any one of the preceding claims in the form of pure metal or in the form of pre-alloy ii) Gradual heating of the various compounds present at a temperature above 900°C iii) Solidification by cooling of the molten mixture. 5. Object obtained from the alloy according to any one of claims 1 to 3 obtained by shaping said alloy by techniques of deformation, welding, sintering, casting or additive manufacturing or the sequential implementation of the any of these techniques. 6. Jewelery or watchmaking object comprising one or more parts constituting it made from an alloy according to any one of claims 1 to 3.