Patent Application
20140305164
The invention concerns a timepiece or piece of jewellery made of a gold alloy.
The invention also concerns a gold-based alloy, called 18 carat red gold and more particularly an alloy of this type having improved discolouration properties.
The invention concerns the field of the metallurgy of gold alloys for horology and jewellery.
Standard 5N red gold according to ISO standard 8654 (composition: Au750Cu205Ag45) is currently the most used alloy in the timepiece market, particularly for making external timepiece parts, typically watch cases, bracelets, etc. Unfortunately, this red gold alloy, which has an interesting attractive appearance, discolours over time and slowly changes from its initial red colour to yellow. This phenomenon frequently leads to claims from clients who are dissatisfied with this transformation. The cause of the discolouration is the selective dissolution of Cu close to the surface causing an increase in the concentration of Au at the surface which turns the alloy yellow. There is already known from EP Patent Application No. 1512766A1, a red gold alloy with added platinum, which increases resistance to discolouration compared to prior red gold alloys. However, although more slowly, this gold alloy also exhibits a colour change which can be improved in certain wear conditions, such as when it is subjected to perspiration or acid rain. Further, it is known that platinum is an element with a very high melting point (1768° C.) requiring preparations of mixtures with other specific elements (Au and/or Cu) to lower its melting temperature, which makes the implementation of the alloy more complicated and more expensive. Indeed, without the addition of these alloy elements, platinum does not dissolve homogeneously in gold and makes it mechanically more difficult to deform for certain horological applications.
Thus, platinum remains a very expensive material which increases the cost of the alloy.
It is therefore an object of the present invention to overcome the aforementioned drawbacks of the prior art by providing a timepiece or piece of jewellery made of an 18 carat red gold alloy exhibiting improved resistance to discolouration compared to the typically 5N prior art red gold alloys.
It is also an object of the invention to provide a timepiece or a piece of jewellery made of an 18 carat red gold alloy with alloy preparations having lower melting points in order to facilitate implementation of the alloy.
It is also an object of the invention to provide a timepiece or piece of jewellery made of an 18 carat red gold alloy having lower alloy costs.
The invention therefore concerns a timepiece or piece of jewellery made of a nickel free and cobalt free gold alloy, whose composition by weight comprises between 75% and 77.5% gold, between 1.2 and 1.6% palladium and between 20.1 and 23.8% copper.
The invention also concerns an 18 carat red gold based alloy, characterized in that it is formed of a mixture comprising by weight:
Advantageously, the gold-based alloy (including that of the timepiece of the invention) comprises between 1.35 and 1.45% and preferably 1.4% by weight palladium.
Preferably, the gold-based alloy (including that of the timepiece of the invention) further includes between 0.45 and 2% by weight of an element selected from among iron, zinc, silver and indium or a combination of said elements.
According to a preferred embodiment, the gold-based alloy (including that of the timepiece of the invention) includes 0.48% by weight platinum.
According to another preferred embodiment, the gold-based alloy (including that of the timepiece of the invention) further includes 1.81% by weight silver.
Advantageously, the gold-based alloy (including that of the timepiece of the invention) further includes at most 1% by weight of any one element or of a combination of elements selected from the group including gallium, magnesium, calcium, lithium, aluminium, sodium, titanium, molybdenum, tin, silicon, rhodium, zirconium, potassium and chromium.
Preferably, the gold-based alloy (including that of the timepiece of the invention) includes at most 0.05% by weight iridium, rhenium, or ruthenium and advantageously the alloy includes 0.01% by weight iridium.
It was observed that the timepieces or pieces of jewellery as defined by the annexed claims are very advantageous as regards their colour, brilliance and price.
Other features and advantages of the invention will appear upon reading the following detailed description, with reference to the annexed drawings, in which:
Table 1 shows example alloy compositions in weight % o according to the invention with the exception of alloys No 103 and No 113 which respectively represent prior art 18 carat red gold alloy compositions.
Each of these gold alloys was subjected to three discolouration tests, respectively in a saturated sodium chloride solution, in an artificial sweat solution and in an acid rain solution. The discolouration of each alloy was then measured. Table 2 sets out the composition of the test solutions and the thermal conditions in which they were used. The “artificial sweat” and “acid rain” test compositions represent the conditions that a timepiece may experience during wear in the climatic conditions of areas of Asia.
Citizen type
acid sweat
Hangzou
(pH = 4.5):
The three discolouration tests were performed on gold alloy washers having a diameter of 20 mm and a thickness of 2.5 mm. The washers were polished in succession with 320, 600, 1200, 2400 grit sandpaper up to felt containing diamond particles of 3 to 1 μm mean diameter.
Each washer was immersed in 200 ml of a solution corresponding to the tests set out in Table 2 for 42 days. Each washer was placed at the bottom of a closed vial (Ø65 mm, made of polypropylene). For statistical reasons, 3 washers of each alloy from Table 1 were tested for each of the three tests.
The washers were removed and rinsed to measure discolouration at different times during the test period and to observe the evolution of discolouration. It was then possible to draw the curves of
The change in colour or discolouration ΔEi after i days was calculated in accordance with the following formula:
ΔE
i=√{square root over ((Li*−L0*)2+(ai*−a0*)2+(bi*−b0*)2)}{square root over ((Li*−L0*)2+(ai*−a0*)2+(bi*−b0*)2)}{square root over ((Li*−L0*)2+(ai*−a0*)2+(bi*−b0*)2)}.
where L*, a*, b* are colorimetric values of samples measured with a “Varian Cary 1E” spectrophotometer with an integrating sphere of 70 mm.
The results of the discolouration test in saturated NaCl solution at 70° C. show that the red gold alloys according to the invention, alloys No 126, No 128, No 129 and No 139, discolour considerably more slowly than the prior art 18 carat red gold alloy No 103 in this saline atmosphere. These results are illustrated in
The results of the discolouration test in the artificial sweat solution at 40° C. show that the red gold alloys according to the invention, alloys No 126, No 128, No 129 and No 139, discolour considerably more slowly than the prior art 18 carat red gold alloy No 103 in this atmosphere of sweat. These results are illustrated in
The results of the discolouration test in the acid rain solution at 70° C. show that the red gold alloys according to the invention, alloys No 126, No 128, No 129 and No 139, discolour considerably more slowly than the prior art 18 carat red gold alloy No 103 in this acid atmosphere. These results are illustrated in
These tests therefore clearly show that the resistance to discolouration of the alloys according to the invention is considerably improved compared to the prior art 18 carat gold alloys in saline and acid atmospheres and slightly improved in the case of the artificial sweat test.
| Number | Date | Country | Kind |
|---|---|---|---|
| 11188305.4 | Nov 2011 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2012/071962 | 11/7/2012 | WO | 00 | 5/8/2014 |
