EP1512766A1 - Article of watch or jewelry having color resistance - Google Patents

Abstract

A watchmaking, jewellery or jewellers items is fabricated in an alloy containing by wt at least 75% of gold and between 15 and 18% of copper together with between 0.5 and 4% of platinum, with the exclusion of the value equal to 0.5% when the value of the copper is equal to 15%.

Description

The invention relates to a timepiece, jewelery or jewelery made of an alloy comprising by weight not less than 75% gold and not less than 6% copper. More particularly, the invention is relates to such a piece made of an alloy comprising by weight not less than 75% of gold and not less than 15% of copper.

The color of such gold alloys depends on their copper and silver grades. A copper content greater than 18% and a silver content of around 4% give them a red color. The color evolves towards the rose then to the yellow if the copper content decreases from 18% to 15% then from 15% to 6% and if the silver content increases from 4% to 15%. The color is defined so conventional by a point of CIELAB space formed of a green-red axis on the abscissa, a blue-yellow axis in ordered and an axis representative of the contrast (cf. ISO 7724 standard established by the International Commission Lighting). The colors of the gold alloys are defined in the tri-chromatic space according to the ISO standard 8654.

The plaintiff has found that enclosures or watch bracelets made in these gold alloys usually tended to change of their color under the action of the water of the faucet, sea water, water pools, water salty or soapy water. DE-A-19958800 discloses a timepiece or jewelery made from an alloy of between 40% and 80% gold, between 0% and 15% copper, between 1% and 40% of silver, between 1% and 15% iron and between 0% and 15% palladium. Iron is allied with these elements to replace nickel considered allergenic, to limit the palladium content considered to be expensive and for give the alloy a white gold color. The alloy may contain between 0% and 0.5% of any of the platinum, ruthenium, rhodium, iridium, tungsten or tantalum to refine the grain size.

The specialized literature reports an accelerated tarnishing study performed on an alloy intended for the manufacture of jewelery pieces and comprising 75% gold, 12% copper and 12% silver. The tests take place in the gas phase or in the liquid phase. Tarnishing is quantitatively determined by the color difference of the alloy before and after the test. The reactants in contact with which the alloy is exposed comprise essentially pure sulfur or sulfur compounds. The tarnishing observed is attributed to the formation of silver sulphide Ag ₂ S. (See "Tarnishing of AuAgCu alloys", 43, pp. 48-55, 1992, Werkstoffe und Korrosion) . Document CH-219 711 discloses an alloy intended for the manufacture of dental prostheses and comprising between 65% and 75% of a mixture of gold and platinum in which platinum is between 2% and 5%, between 1% and 6% silver, between 8% and 14% copper, between 8% and 14% cadmium and between 0.1% and 1% zinc. Platinum is alloyed with these elements to give this yellow gold alloy good resistance to tarnishing and corrosion in the mouth.

Another study focused on an alloy with no more than 71% gold, between 12% and 14% copper, between 7.5% and 25% silver, between 0.6% and 4% platinum, and between 0.9% and 3.7% palladium to determine its biocompatible character for use in the manufacture of dental prostheses. Corrosion tests are carried out at room temperature in an aqueous solution containing lactic acid and sodium chloride, at an acid pH of about 2.3. An increase in the concentration of metal ions shows that copper and silver go into solution. The depletion of the two constituents is corroborated by an analysis of the first atomic layers of the surface of the alloy carried out by Auger spectroscopy. Under the pH-metric conditions tested, the depletion of copper appears all the more important as the gold and platinum content decreases. In contrast, platinum content has no significant effect on silver dissolution (see "Biocompatibility of dental alloys", 3 (10), 2001, Advanced engineering materials) .

GB-A-2,279,662 discloses an alloy for watchmaking, jewelery or jewelery, between 33% and 90% of gold, between 0.1% and 2.5% of iron, between 0.01% and 62.5% silver, between 0.01% and 62.5% between 0.01% and 62.5% of zinc and hardness between 100 and 280 Hv. Iron is allied with other elements of the alloy to give it a more high hardness and prevent grain growth during welding operations. In addition, a better resistance to color changes is found during heat treatments. The alloy can contain between 0.01% and 25% of palladium, nickel or cadmium, between 0.01% and 10% of indium, tin, gallium, cobalt, platinum, rhodium, between 0.01% and 3% iridium, ruthenium, silicon or boron. The alloys provided as examples include all 37.53% gold, 8.70% or 9.20% silver, 42.40% copper, 10.87% or 10.67% or 10.57% or 10.37% of zinc and 0.5% or 0.7% or 0.8% or 1% iron.

Finally, a timepiece, jewelery or of jewelery made of an alloy comprising minus 75% gold and between 15% and 23% copper is known of Japanese Patent Application JP 10245646 published in 1998. The alloy also comprises between 0.3% and 5% of palladium to present greater resistance to the cracking during molding of the part.

One of the aims of the invention is to improve the resistance to a color change of a room of timepieces, jewelery or manufactured jewelery in a gold alloy and subjected, in use, to weakly aggressive aqueous media.

For this purpose, the subject of the invention is a part of timepieces, jewelery or manufactured jewelery in an alloy comprising by weight at least 75% of gold and between 15% and 18% copper or at least 18% copper, characterized in that the alloy also comprises between 0.5% and 4% platinum, excluding the value equal to 0.5% when the copper value is equal to 15%.

The platinum content makes it possible to increase resistance to a change in the color of the room subjected to the action of tap water, sea water, swimming pool water, salt water or water soap.

The timepiece, jewelery or jewelery can be made of an alloy comprising additionally 4% at most of palladium to enhance the effect resistance to a color change. It is by example the case for a yellow-colored alloy comprising between 6% and 15% copper.

Other advantages will appear in the light of the description of a particular embodiment of the invention illustrated by the drawings.

Figure 1 shows two experimental curves of discoloration obtained respectively on a red alloy according to the invention, curve (b), and on a 5N red alloy according to the prior art, curve (a).

Figures 2a and 2b show two profiles of concentration obtained respectively on both alloys having undergone the fading test illustrated by Figure 1.

Table I reports test results from discoloration obtained on different alloys according to the invention.

A reference alloy 5N of red color consisting of 75% gold, 20.5% copper and 4.5% silver is subjected to a fading test. The alloy is immersed in a neutral solution saturated with sodium chloride to a temperature of 40 degrees C for several dozens of days. The color is measured according to the standard ISO 7724. The kinetics of discoloration is illustrated by the curve (a) of Figure 1. In the abscissa, the immersion time in days and ordinates, the standard of ΔElab vector connecting the representative points of the color of the alloy in CIELAB space, between the initial moment and the different immersion times. Compared to the time range explored, discoloration appears continuous and monotonous with immersion time.

A red colored alloy comprising according to the invention 76% gold, 21% copper and 3% platinum is tested under the same conditions as those of the alloy reference. The kinetics of discoloration is illustrated by the curve (b). The latter shows that the standard of vector connecting points representative of color of the alloy according to the invention between the initial moment and the different immersion times is less than he is for the reference alloy without platinum. In other words, the presence of platinum increased the resistance to discoloration of the alloy according to the invention. Quantitatively, we define a factor improvement by the ratio between the modifications of color of the reference alloy and alloy according to the invention, considered after the same duration immersion. In this case, the factor improvement is about 3 after a time 60 days immersion.

Analyzes were performed by Rutherford Backscattered Spectroscopy to explore a depth significant matter compared to the wave path in the two alloys tested previously, the of reflected light waves determining the color of the alloy.

Figures 2a and 2b show the profiles of concentration obtained respectively on the 5N alloy of reference and on the alloy according to the invention, after 60 days of immersion in the test solution. For the reference 5N alloy, FIG. in relation to copper concentration and concentration of silver in the volume of the alloy, a decrease in copper concentration in proportion of that of gold over a depth of matter between the first 10 and the first 20 nanometers as well as maintaining concentration in money on that same depth. In contrast, Figure 2b, the concentration of copper in proportion to that of gold decreases less strongly and less deeply for the alloy according to the invention.

These analyzes show that the discolouration of the reference 5N alloy is due to a dissolution of the copper in a deep layer of a few dozen nanometers. Platinum content limits the dissolution of the copper in the alloy according to the invention and thus to increase the resistance of the latter to the discoloration in the test solution.

The kinetics of discoloration of the alloy according to the invention tends, with reference to the curve (b) of the FIG. 1, towards a limit value starting from the fifteenth about day. The existence of this limit value of stable thermodynamic equilibrium that the composition alloy confers matter. Obtaining such a color stabilization of the alloy remains a completely unexpected result in the conditions of the discoloration test used. This test can be useful for industrial plan to finish a part of timepieces, jewelery or manufactured jewelery in an alloy comprising by weight at least 75% of gold, between 15% and 18% copper or at least 18% copper and between 0.5% and 4% platinum, excluding the value equal to 0.5% when the copper value is equal to 15%, by which the piece is immersed in a saline solution saturated at neutral pH for a period of time and at a determined temperature to reach the value of balance of the color of the room. In a way general, any solution allowing the dissolution superficial copper to achieve color balance could be used. It is right to note that the limit value of discoloration illustrated curve (b) remains below the limit of perception by the eye of a color change of the room.

Table I reports the results of the test of discoloration performed on different alloys compositions numbered from 1 to 20. A row of the table indicates the content of the alloy in gold, copper, platinum and palladium and the limit value of discoloration ΔELab and the fading enhancement factor after a 60-day immersion test. Conditions experimental are identical to those experienced previously: immersion in a saturated solution of sodium chloride at neutral pH and at a temperature of 40 degrees Celsius.

Alloys whose compositions are referenced from 20 to 9 in Table I attest to a factor for improving the resistance to fading typically between 1.5 and 4. Designated alloys by 5N and 4N serve as a reference for calculating the factor of improvement respectively of alloys 1 to 18 and 19 to 20.

An alloy comprising 91.7% of gold and 8.3% of copper has a lower improvement factor than the unit, as indicated by reference 8. This result shows that the simple search for an increase in the gold content has an opposite effect to that of the increase resistance to discoloration of the alloy.

Similarly, the addition of elements such as aluminum, niobium, tantalum, titanium or silicon for the purpose of form an oxide layer to limit the dissolution copper in saturated saline solution at neutral pH does not leads no more to an improvement in resistance to discoloration of alloys. On the contrary, alloys whose compositions are referenced from 7 to 3 in the Table I show an improvement factor at most equal to 1.

The results shown in Table I, reference 2, finally show that the addition of zinc in the purpose of forming a sacrificial anode on the surface of the alloy does not lead to an improvement of resistance to fading.

The improvement factor depends on the content weight of copper in the alloys according to the invention.

Preferably, this content is between 20% and 22% for a platinum content of between 1.5% and 3%.

In addition, the platinum content between 0.5% and 4% confers on timepieces, jewelery or jewelery according to the invention color that it was impossible to get up to present. While copper has a blushing effect and money a greening effect, platinum has an effect whitening. The addition of platinum or palladium to the grayish effect allows to gradually move warm, discreet and velvety colors for lowest grades to more technical colors and colder for the higher grades.

More particularly, a timepiece, jewelery or jewelery made of an alloy comprising by weight at least 75% gold, between 20% and 22% of copper, between 1.5% and 3% of platinum and not more than 0,5% of any of the elements selected from silver, cadmium, chromium, cobalt, iron, indium, manganese, nickel or zinc has a color nominal having in space CIELAB, an equal abscissa at 7,41 along the green-red axis, an ordinate equal to 15.67 along the blue-yellow axis and a value of contrast equal to 86.75. Depending on the composition exact of the alloy, these coordinates may vary between 5.71 and 8.51 along the green-red axis and between 13.67 and 16.67 according to the blue-yellow axis for a value of contrast L varying between 76.75 and 96, 75.

The invention applies to any room timepieces, jewelery or jewelery manufactured in from an alloy according to the usual methods like machining, stamping or wax casting lost.

Claims (3)

Timepieces, jewelery or jewelery, made of an alloy comprising by weight at least 75% of gold and between 15% and 18% of copper or at least 18% of copper, characterized in that it also includes between 0.5% and 4% platinum, excluding the value equal to 0.5% when the value of copper is equal to 15%. Timepiece, jewelery or jewelery according to claim 1, characterized in that the alloy comprises between 20% and 22% copper and between 1.5% and 3% platinum. Timepiece, jewelery or jewelery according to claim 2, characterized in that the alloy comprises by weight at most 0.5% of any of the elements selected from silver, cadmium, chromium, cobalt, iron, indium, manganese, nickel or zinc.

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