CH715203A1 - Alloy based on gold with a color change and its use in the field of jewelry 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 group of platinoids, said alloy having color change properties as a function of viewing and / or lighting angle. It also relates to the use of said alloy in the manufacture of luxury items such as jewelry and watches.

Description

Description Technical Field [0001] The present invention relates to the field of watchmaking and jewelry, it relates more precisely to a gold alloy having particular optical properties and a significant tarnishing resistance and its use for Obtaining luxury objects with quality visuals that are easily recognizable without resorting to long and tedious methods of analysis.

State of the art Swiss watchmaking is one of the industrial jewels of the country. Its reputation over the centuries has exceeded the limit of the Alps or the Jura, the seriousness, the complexity, the quality of Swiss watches make it more than mere indicators of time, but exceptional and luxury pieces. With the complexity of the pieces sometimes qualified as works of art for some, an exceptional design also testifies to their beauty and the quality of these.

It is therefore natural that precious metals have taken an increasingly important place in the design of watches or luxury jewelry. The use of 18-carat gold has become common in the luxury realm. 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 These basic alloys have gradually been replaced by gray or pink gold, providing new renderings appreciated by consumers and always synonymous with luxury and beauty.

A nickel-free gray gold is for example described in application EP 1 227 166, the invention relates to a gray gold alloy claimed without nickel, cobalt, iron and silver comprising, by weight: (a) Au : 75 to 76%; (b) Cu> 17%; (c) Mn less than 7%; (d) Zn <2%.

This gold alloy may also contain, by weight: (a) Si <0.5%; (b) at least one of the elements Ti less than 0.3% or Ta less than 0.3%; (c) 0% Pd and at most 2% Pt. In application WO 2014122 233 the invention relates to a timepiece or a piece of jewelry comprising a rose gold alloy containing at least 750% o mass of however, said alloy also containing copper, palladium and indium, the sum of the concentrations of palladium and indium being less than or equal to 35% o, or less than or equal to 30% o, or even less than or equal at 25% o, and / or the sum of the concentrations of palladium and indium being between 15% o and 35% o, or between 20% o and 35% o, or even between 25% o and 33% o.

One of the major drawbacks of these alloys is the tarnishing which occurs over time and during the use of the watch or the timepiece. In fact, the wear and tear of time, exposure to temperature variations, humidity, cold, hot, friction, exposure to air and therefore oxygen, are all factors that affect the long-term quality and rendering of the precious material that makes up the watch or the jewel.

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

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

In a world where watchmaking and jewelry are subject to significant counterfeiting which impacts 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.

Thus there is a need always present to have new gold alloys resistant to tarnishing and to attacks of time, allowing the simplest manufacturing that is, being able to give materials having quality visual renderings impacting the design and the value of the object that contains it, while allowing this alloy to be distinguished from the others visually and at a lower cost without the need to resort to costly complex and / or invasive analysis techniques.

Disclosure of the invention One of the aims of the invention is therefore to remedy at least one of the aforementioned drawbacks by proposing a gold alloy of color of at least 18 carats comprising gold as well as copper and at least one metal Μ from the group of platinoids, said alloy having colors which are expressed in the chromatic space CEE LCh * by a chroma C <16 and a saturation h * <70.

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

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

CH 715 203 A1 [0014] Said alloy according to the invention can also include 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 of these.

The amount of copper in the alloy for 100% of its mass is 10 to 20% by mass and that of silver 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 can also include grain-refining metals.

The alloy according to the invention may also include hardeners.

The alloy according to the invention may also include deoxidizers.

The alloy according to the invention may also include bleachers.

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 being selected from boron, molybdenum, iridium, rhenium, ruthenium or a mixture of these.

Said deoxidizers being selected from aluminum or silicon or a mixture of these.

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

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

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) Mixture of the compounds included in the composition of the alloy according to any one of the preceding claims in the form of powder or of pure metal or in the form of pre-alloy ii) Progressive heating of the various compounds present at a temperature above 900 ° C. ili) Solidification by progressive cooling after melting of the various compounds at ambient temperature. The cooling leading to the solidification of the alloy according to the invention which can be obtained by the methods of convection, quenching, transfer to neutral substrate. or pouring into a neutral solid.

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

Said object obtained from the shaping techniques described above can be a piece of jewelry or timepiece comprising one or more parts constituting it made from an alloy according to the invention.

Brief description of the figures

Fig. 1 shows the reflectance spectra as a function of the 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 prior art containing a mixture of copper and silver whose copper and silver ratio exceeds the ratio as than covered by the alloys according to the invention. The alloy is a standard rose gold alloy known as 4N according to ISO 8654.

Fig. 3 shows the reflectance spectra as a function of the wavelength of an 18 carat gold alloy according to the invention comprising copper gold 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.

CH 715 203 A1 18-carat gold is the most widespread precious alloy in the field of jewelry and luxury watchmaking. These alloys are synonymous with value, durability and aesthetics with quality results.

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). As far as color is concerned, gold and copper are the only colored metals. The colors are related to the spectral signature of the reflectance as a function of the wavelength as illustrated in fig. 1.

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

If we combine the noble elements Au, Ag and Cu, their spectral signature, namely the inflection in the reflectance curve, persists, but its position moves and thus generates a different color. In the case of 18ct gold alloys, this displacement 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).

All the other elements alloyed with 18ct gold will flatten the curve and thus discolor the alloy until it appears gray.

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

Thus during production at each heat treatment cycle, the alloy must be quenched in order to retain the ductile structure allowing subsequent 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 relationships between gold, copper and silver has an impact on the properties of the alloy obtained. Finding the right compromise between ductility, color, tarnish resistance is far from being, given the number of material parameters to be modified, a routine exercise and requires significant research efforts.

If we add to these parameters already important in the quality of the alloys used in watchmaking, the fact of being able to recognize them easily without resorting to expensive or invasive physicochemical methods from one another it becomes really difficult and require careful research.

Thus, 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 métal from the group of platinoids said alloy has particular optical properties which are not encountered in the alloys of the prior art previously cited. Said optical properties being mainly that of a change in color as a function of the angle of observation and / or lighting.

Said alloy achieves colors rarely achieved until then, Le. apart from those defined by ISO 8654 and those of conventional gray gold. The table below gives examples of alloys according to the invention (alloy A to E), and the colors obtained in coordinates La * b *, measured using a spectrophotometer with sphere of integration Minolta CM- 3610d CRBISS. For comparison, the color coordinates according to ISO 8654 of alloys of colors 4N to 6N and of white gold.

The at* b * AT 80.75 4.77 10.36 B 80.77 4.04 8.89 VS 81.17 3.49 8.23 D 82.88 5.66 9.96 E 81.97 3.89 8.45 4N 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 gold alloys 2N to 6N: they are characterized by a color which is expressed in the chromatic space CLE LCh * by a chroma C <16 and a saturation h * <70. In addition, it has a Yellowness Index (ASTMD 1925) strictly greater than 25, which also distinguishes it from gray golds.

CH 715 203 A1 In fact, FIG. 3 illustrates the spectral reflectance of an alloy of gold, copper and palladium according to the invention as a function of the angle of observation. The curve La * b * obtained from a CIELa * b * color measurement corresponds to an angle of 0 °. The other two specular reflectance curves of this alloy are measured at different angles of inclination (40 ° and 70 °).

The curve La * b * as shown in fig. 3, shows a significant spectral variation in the VIS, which results in the perception of a "pink" color. When the observation angle increases, the curve rotates, reflecting more and more the blue part and less and 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.

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

This characteristic related to the variation in optical property depending on the angle of observation or lighting also called "color-shift", provides an advantage to the alloy according to the invention compared to those of the state of art and is a valuable element of differentiation compared to conventional alloys.

In the context of the present invention, the alloy which has color change properties as a function of the angle of observation and / or lighting, can be used not only for manufacturing parts with quality renderings and colors never obtained until then, but this can also offer a most aesthetic effect by changing color according to the inclination of the watch or jewelry. 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 depending on the shape.

In the alloy according to the invention, the metal Μ is selected from Palladium (Pd) or Platinum (Pt) or a mixture of these.

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

In addition, the presence of the metal Μ 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 admixture with Silver, this does not exceed 20% by mass, preferably the mixture does not exceed 18% mass. Thus the mixture may preferably contain more copper than silver or even a small or zero amount of silver and predominantly copper. It is important that the mixture of two metals does not exceed 20% by mass, in order to obtain the good ductility or malleability properties as well as the tarnish resistance properties 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 conventional ranges of 2N gold alloys at 6N, it is characterized by a color which is expressed in the chromatic space CEE LCh * by a chroma C <16 and a saturation h * <70.

The CIE LCh * values, like the CIELa * b * values used to characterize the color of a surface, an alloy or a sample, 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 refiners or deoxidizers are added to the alloy during its preparation.

Mention will be made, among these, by way of nonlimiting example for the refining metals, of boron, molybdenum, iridium, rhenium, ruthenium or a mixture of these and for deoxidizers aluminum or still silicon or a mixture of these. Their presence within the alloy according to the invention does not exceed 1% by mass.

In addition to the grain refining metals, hardening or bleaching compounds can be found within the alloy. Their presence within the alloy is greater than that of the grain refiners while not exceeding

CH 715 203 A1 not 3% by mass. By way of nonlimiting example of hardeners or whiteners, mention will be made of zinc, indium, gallium, iron, tin, germanium, chromium, vanadium, zirconium or titanium or a mixture of these. this.

The alloy according to the invention is obtained by mixing different metals which constitutes it without a precise order being required. The implementation process comprises, firstly or first step of the process, the mixture of the compounds included in the composition of the alloy in the form of powder, of pure metal or in the form of pre-alloy. By pre alloy we can very well design a pre alloy without limiting Au / Cu or a pre alloy Au / Ag or Cu / Ag, as long as the proportions as covered by the claims are respected.

The various metals or compounds used in the composition of the alloy according to the invention are placed in a crucible or any suitable receptacle which can be subjected to heating at high temperature. In a second stage or second stage of the process, the 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 fusion. 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 progressive 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 into a heat-resistant container (mold or ingot mold made of metal or graphite for example), or by transfer to a neutral substrate. Injection having the advantage of producing powder or shot, pouring it into a mold or container or ingot mold to produce preforms such as wires or plates, transfer to a neutral substrate to deposit on a large surface a fairly thin layer of the alloy for direct use in the preparation of parts such as watch movement components.

The alloy thus obtained can then be used in the manufacture of luxury items such as watches or jewelry. The object which is obtained from the alloy according to the invention, is by shaping said alloy by standard techniques in the field of luxury items such as deformation, welding, sintering , casting or additive manufacturing or sequential implementation of any of these techniques.

The object which is obtained from the alloy according to the invention can be a piece of jewelry or watchmaking and comprise at least one piece made from the alloy according to the invention.

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

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 half of the satin surface 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 washers were then subjected to thioacetamide, moist heat and salt spray tests in accordance with NIHS 96-50.

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 a phenomenon of corrosion and / or tarnishing. This is in stark contrast to conventional pink / red alloys (4N to 6N color alloys) 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 claims appended hereto.

Claims (8)

claims 1. A gold alloy of at least 18 carats characterized in that it comprises gold as well as copper and at least one metal Μ from the group of platinoids and optionally silver, said alloy comprising for 100% of its mass: 75 to 80% by mass of gold, 10 to 20% by mass of copper, 0 to 10% by mass of silver, so that the sum of the percentages of copper and of silver does not exceed 20% by mass, preferably does not exceed 18% by mass. 5 to 10% by mass of a metal Μ selected from palladium, platinum or a mixture of these and also characterized in that the color of said alloy is expressed in the chromatic space CJE LCh * by a chroma C < 16 and a saturation h * <70. 2. Alloy according to claim 1 characterized in that said alloy has color change properties depending on the angle of observation and / or lighting. 3. An alloy according to any one of the preceding claims, which may also include grain-refining metals and / or hardeners. CH 715 203 A1 4. An alloy according to claim 3 in which the concentration of refining metals does not exceed 1% by mass selected from boron, molybdenum, iridium, rhenium, ruthenium or a mixture of these 5. An alloy according to claim 3 in which the concentration of hardeners does not exceed 3% by mass selected from zinc, indium, gallium, iron, tin, germanium, chromium, vanadium, zirconium or titanium or a mixture thereof. 6. Method for obtaining an alloy according to any one of the preceding claims according to: I) Mixture of the compounds included in the composition of the alloy according to any one of the preceding claims in the form of powder or of pure metal or in the form of pre-alloy ii) Gradual heating of the various compounds present at a temperature above 900 ° C ili) Solidification by cooling the molten mixture. 7. An object obtained from the alloy according to any one of the preceding claims obtained by the shaping of said alloy by deformation techniques, welding, sintering, casting or additive manufacturing or the sequential implementation of l any of these techniques. 8. A piece of jewelry or timepiece comprising one or more parts constituting it made from an alloy according to any one of claims 1 to 6. CH 715 203 A1 reflectance