ELECTROPLATED PRODUCT HAVING A PRECIOUS METAL FINISHING LAYER AND IMPROVED CORROSION RESISTANCE, METHOD FOR ITS PRODUCTION AND USES THEREOF

Abstract

 This invention provides an electroplated product with a precious metal finishing layer that has an improved corrosion and abrasion resistance. The electroplated product comprises two electroplated copper alloy layers having a different copper concentration (e.g. white bronze and yellow bronze). The electroplated product is especially suitable for use in jewelry, fashion, leather, watch, eyewear, trinkets and/or lock industry. Another advantage of the electroplated product is that the use of allergenic nickel or expensive palladium intermediate layers against copper migration can be dispensed with. This means that the electroplated product can be non-allergenic (nickel-free) and be provided in a more economical and environment-friendly manner. A method for the production of the inventive electroplated product is presented. Furthermore, the use of the inventive electroplated product in the jewelry, fashion, leather, watch, eyewear, trinkets and/or lock industry is suggested.

Description

[0001] This invention provides an electroplated product with a precious metal finishing layer that has an improved corrosion and abrasion resistance. The electroplated product comprises two electroplated copper alloy layers having a different copper concentration (e.g. white bronze and yellow bronze). The electroplated product is especially suitable for use in jewelry, fashion, leather, watch, eyewear, trinkets and/or lock industry. Another advantage of the electroplated product is that the use of allergenic nickel or expensive palladium intermediate layers against copper migration can be dispensed with. This means that the electroplated product can be non-allergenic (nickel-free) and be provided in a more economical and environment-friendly manner. A method for the production of the inventive electroplated product is presented. Furthermore, the use of the inventive electroplated product in the jewelry, fashion, leather, watch, eyewear, trinkets and/or lock industry is suggested. The underlayers presently used in the fashion market to provide a high corrosion and wear resistant support for a top gold finishing layer comprises nickel and/or nickel based alloys. The allergy associated with nickel and the classification of nickel salts as carcinogenic, mutagenic and reprotoxic substances makes the use of nickel and nickel based alloys more and more restricted in this market. Thus, its use has been strongly restricted, especially for fashion and jewelry applications. Several attempts have been made to develop a nickel-free electrolytic deposit for applying metal layers to substrates.

[0002] The most commonly used alternative to nickel is white bronze which is an alloy of copper, tin and zinc. However, this alloy alone can not meet the corrosion resistance requirements of the fashion industry. As an alternative to said alloy, layers of precious metals like palladium were used between the substrate and the final decorative finishing layer. However, palladium as an intermediate protective layer strongly increases the cost of the final item i.e. its use is uneconomical.

[0003] As an alternative to palladium, the use of different tin alloys as an intermediate barrier layer has been suggested. However, it was found that a tin content of more than 50 wt.-% in the alloy results in poor resistance to acidity and oxidants leading to corrosion and to a brightness level which are unsatisfactory for the fashion market. As a further alternative to palladium, intermediate layers consisting of chromium have been used. However, said chromium layers resulted in adhesion problems and corrosion resistance problems for the final precious metal layer such as gold. In addition, the use of toxic chromium VI is highly undesirable in the field of jewelry and fashion.

[0004] Moreover, WO 2013/164165 A1 discloses a multi-layered nickel-free surface coating for sanitary application having a copper layer, a coating of at least one metal layer consisting of an alloy of copper, tin and zinc or copper and tin, a coating of at least one metal layer consisting of chromium, copper, gold, palladium or iron and a final chromium layer. Importantly, the intermediate layer contains a precious metal (palladium or gold) that drastically increases the cost of the electroplated product or a metal such as chromium, copper and iron that drastically reduce adherence of the final decorative layer or lower the corrosion resistance of the electroplated product. Thus, the electroplated product is less suitable for the high requirements in the jewelry and/or fashion industry.

[0005] WO 2008/003216 A1 discloses an electroplated product including a copper layer on the surface of the base material, characterized in that the electroplated copper metal layer further includes a metal layer as a nickel substitute, and this nickel substitute metal is a Cu-Sn alloy, Ru, Rh, Pd, or an alloy composed of 2, 3, or 4 elements selected from Ru, Rh, Pd, and Co. However, the use of one single layer of Cu-Sn alloy is not sufficient to target the high corrosion resistance requirement for the jewelry or fashion market and the use of precious metal intermediate layers is very expensive.

[0006] Therefore, the prior art does not fulfill the requirements of the decorative, fashion and jewelry industry of providing in an economic and easy manner an electroplated product which is non-allergenic and has a high level of brightness and improved corrosion and abrasion resistance.

[0007] Starting therefrom, it was the object of the present invention to provide an electroplated product and method for its production which overcomes said disadvantages.

[0008] The object is solved by the electroplated product according to claim 1, the method for producing the inventive electroplated product according to claim 16 and the use of the inventive electroplated product according to claim 17. The dependent claims illustrate advantageous embodiments.

[0009] According to the invention, an electroplated product is provided, comprising

a) a base material;

b) a first layer comprising or consisting of copper, wherein the first layer is disposed on the base material;

c) a second layer comprising or consisting of a first copper alloy, wherein the first copper alloy comprises tin and zinc;

d) a third layer comprising or consisting of a second copper alloy, wherein the second copper alloy comprises tin and zinc; and

e) a fourth layer comprising or consisting of a precious metal, wherein the fourth layer is the finishing metal layer of the electroplated product;

characterized in that the second layer or third layer are disposed on the first layer and the copper concentration in the first copper alloy is different from the copper concentration in the second copper alloy and the first layer has a thickness in the range of >15 to 60 µm.

[0010] In the electroplated product, diffusion of copper from a copper containing layer into a layer containing less copper and/or a precious metal layer (like e.g. gold layer) is generally thermodynamically favoured. However, the presence of zinc in the copper containing layer was found to strongly decrease copper diffusion. Furthermore, it was discovered that if there is a first intermediate layer in the electroplated product which comprises or consists of a copper-zinc alloy having a lower copper concentration than a second intermediate layer which comprises or consists of a copper-zinc alloy, the first layer acts as a copper sink and prevents copper migration from copper containing layers of the electroplated product into the finishing precious metal layer of the electroplated product.

[0011] The electroplated product fulfills the main requirements of the fashion industry in terms of corrosion resistance, wear resistance and copper diffusion barrier properties. Compared to known alternatives in the prior art of palladium-less and nickel-less electroplated products, the inventive electroplated product shows a better corrosion performance, a better abrasion performance, an increased shelflife and a decreased production cost.

[0012] The copper concentration of the first copper alloy (in wt.-%) may differ from the copper concentration of the second copper alloy (in wt.-%) by an absolute value of 1 to 99 wt.-%, preferably 5 to 80 wt.-%, more preferably 10 to 60 wt.-%, even more preferably 15 to 40 wt.-%, most prefer ably 20 to 30 wt.-%.

[0013] The inventive electroplated product may be characterized in that

i) the second layer is disposed on the first layer, the third layer is disposed on the second layer and the fourth layer is disposed on the third layer; or

ii) the third layer is disposed on the first layer, the second layer is disposed on the third layer and the fourth layer is disposed on the second layer.

[0014] The copper concentration in the second alloy can be higher than the copper concentration in the first alloy. Thus, the second alloy (e.g. yellow bronze) gives better brightness than the first alloy and may be deposited at faster deposition rates (higher productivity). On the other hand, the first alloy having a lower copper concentration (e.g. white bronze) gives a harder layer and better corrosion and abrasion resistance properties compared to the second alloy. Thus, if increased hardness is desired, it is beneficial if the second layer is disposed on the third layer in the electroplated product whereas if increased brightness is desired, it is beneficial if the third layer is deposited on the second layer. In terms of corrosion resistance, it has turned out that the best sequence is if the second layer (e.g. white bronze layer) is deposited on the first layer (e.g. copper layer), the third layer (e.g. yellow bronze layer) is deposited on the second layer (e.g. white bronze layer) and the fourth layer (e.g. gold layer) is deposited on the third layer (e.g. yellow bronze layer).

[0015] The copper concentration in the

i) first copper alloy may be≤ 65 wt.-%, preferably 30 to 64 wt.-%, more preferably 40 to 60 wt.-%, most preferably 45 to 55 wt.-%, in relation to the whole weight of the copper alloy; and/or

ii) the second copper alloy may be ≥ 66 wt.-%, preferably 66 to 90 wt.-%, more preferably 70 to 87 wt.-%, most preferably 75 to 85 wt.-%, in relation to the whole weight of the copper alloy.

[0016] The zinc concentration in the

i) first copper alloy may be ≥ 10 wt.-%, preferably 11 to 35 wt.-%, more preferably 12 to 25 wt.-%, most preferably 15 to 20 wt.-%, in relation to the whole weight of the copper alloy; and/or

ii) the second copper alloy may be≤ 15 wt.-%, preferably 2 to 10 wt.-%, more preferably 3 to 8 wt.-%, most preferably 4 to 7 wt.-% (optionally 5 to 7 wt.-%), in relation to the whole weight of the copper alloy.

[0017] The tin concentration in the

i) first copper alloy may be ≥ 26 wt.-%, preferably 26 to 35 wt.-%, in relation to the whole weight of the copper alloy; and/or

ii) the second copper alloy may be≤ 25 wt.-%, preferably 1 to 25 wt.-%, more preferably 10 to 25 wt.-%, most preferably 15 to 25 wt.-%, in relation to the whole weight of the copper alloy.

[0018] In a preferred embodiment of the invention, the first copper alloy and/or the second copper alloy comprises Bi, Pb and/or Sb, preferably Bi. Having Bi in the alloy has the advantage that the alloy becomes both brighter and has an improved blocking ability of copper migration. The first copper alloy and/or the second copper alloy may also comprise phosphorus and/or silicon.

[0019] In a preferred embodiment of the invention, the first copper alloy is white bronze and/or the second copper alloy is yellow bronze.

[0020] The fourth layer may be disposed on the second or third layer.

[0021] In a preferred embodiment of the invention, there is no layer comprising or consisting of palladium between the first layer and fourth layer. Preferably, the electroplated product does not comprise palladium.

[0022] In a further preferred embodiment of the invention, there is no layer comprising or consisting of nickel, cobalt and/or chromium between the first layer and fourth, wherein the electroplated product preferably does not comprise nickel, cobalt and/or chromium, most preferably no nickel.

[0023] An organic protection layer can be disposed on the fourth layer. The layer may comprise or consist of a hydrophobic substance and is preferably a monolayer of a hydrophobic substance, more preferably a monolayer of a hydrophobic substance being a corrosion inhibitor, most preferably a monolayer of a corrosion inhibitor comprising thiol groups, especially a monolayer of alkanethiol monomers or alkanethiol polymers like e.g. octadecanethiol monomers. This has the advantage that the surface of the finishing precious metal layer is made more hydrophobic and thus less prone to corrosion. Especially acid corrosion and corrosion due to sweat or interaction with leather is decreased. If the layer is only monomolecular in thickness, it is not visible and does not affect the appearance of the electroplated products.

[0024] The precious metal may be selected from the group consisting of gold, silver, platinum, ruthenium, rhodium, palladium, osmium, iridium and alloys thereof, preferably gold, silver, palladium and alloys thereof, more preferably gold, palladium and alloys thereof, most preferably gold.

[0025] The base material may comprise or consist of bronze, brass, zamak, alpaca, copper alloy, tin alloy and/or steel. It is especially preferred that the base material comprises or consists of zamak. The base material may be an article selected from the group consisting of jewelry, fashion, leather industry, watches, eyewear, trinkets and locks.

The thickness of

[0026] 

i) the first layer may be 16 to 60 µm, preferably 20 to 55 µm, more preferably 25 to 50 µm, most preferably 30 to 45 µm;

ii) the second layer may be 1 to 10 µm, preferably 2 to 8 µm;

iii) the third layer may be 1 to 10 µm, preferably 2 to 4 µm; and/or

iv) the fourth layer may be 0.1 to 5 µm, preferably 0.2 to 1 µm.

[0027] Moreover, a method of producing the inventive electroplated product is presented, the method comprising the steps:

a) electroplating a layer comprising or consisting of a first copper alloy on a copper layer disposed on a substrate;

b) electroplating a layer comprising or consisting of a second copper alloy on the layer of step a);

c) electroplating a layer comprising or consisting of a precious metal on the layer of step b),

characterized in that the first copper alloy layer is plated with a copper concentration different from that of the second copper alloy layer.

[0028] Finally, the use of the electroplated product in jewelry industry, fashion industry, leather industry, watch industry, eyewear industry, trinkets industry and/or lock industry, is proposed.

[0029] With reference to the following figures and examples, the subject-matter according to the invention is intended to be explained in more detail without wishing to restrict said subject-matter to the special embodiments shown here.

Figure 1 shows the GDOES depth profile of a nickel-less electroplated product according to Example 4 (2 µm white bronze layer (wt.-% of Cu:Sn:Zn = 40:40:20), no palladium intermediate layer) before (A) and after a heat-treatment at 180 °C for 24 hours (B). Extensive mutual diffusion of the metal atoms at the gold-white bronze interface is obvious. Due to the absence of calibration, the thicknesses and metallic concentrations illustrated in the GDOES depth profile do not mirror the true layer thicknesses and metallic concentrations. This applies also to Figg. 2-6.

Figure 2 shows the GDOES depth profile of a nickel-containing electroplated product according to Example 5 (2 µm white bronze layer, palladium-nickel intermediate layer) before (A) and after a heat-treatment at 180 °C for 24 hours (B). The nickel/palladium layer inhibits any major metal migration at the interfaces.

Figure 3 shows the GDOES depth profile of a nickel-free electroplated product according to Example 6 (2 µm white bronze layer with wt.-% of Cu:Sn:Zn = 40:40:20, 3 µm yellow bronze layer with wt.-% of Cu:Sn:Zn = 70:20:10, no palladium intermediate layer) before (A) and after a heat-treatment at 180 °C for 24 hours (B). The migration of gold and copper at the interface concerned is strongly reduced. Copper migrates predominantly from yellow to white bronze.

Figure 4 shows the GDOES depth profile of a nickel-less electroplated product according to Example 7 (2-3 µm yellow bronze layer with wt.-% of Cu:Sn:Zn = 80:15:05 next to bright copper layer, 2-3 µm white bronze layer with wt.-% of Cu:Sn:Zn = 50:35:15 next to gold finishing layer) before (A) and after a heat-treatment at 180 °C for 24 hours (B). The GDOES analysis reveals a higher diffusion of the gold in the white bronze layer compared to the one observed in Figure 3.

Figure 5 shows the GDOES depth profile of a nickel-less electroplated product according to the first assay of Example 8 (2-3 µm white bronze layer with wt.-% of Cu:Sn:Zn = 50:35:15 next to the gold finishing layer and another, identical 2-3 µm white bronze layer next to the bright copper layer) before (A) and after a heat-treatment at 180 °C for 24 hours (B). The effect of a double layer of white bronze is not very different from that of a single layer (see Fig. 1). The GDOES analysis reveals an alteration of the surface and thickness of the gold finishing layer due to gold diffusion into the white bronze layers.

Figure 6 shows the GDOES depth profile of a nickel-less electroplated product according to the second assay of Example 8 (2-3 µm yellow bronze layer with wt.-% of Cu:Sn:Zn = 80:15:05 next to the gold finishing layer and another, identical 2-3 µm yellow bronze layer next to the bright copper layer) before (A) and after a heat-treatment at 180 °C for 24 hours (B). A double layer of yellow bronze does not show the reduced diffusion as compared to Figg. 3 for a white bronze-yellow bronze sequence and 4 for a yellow-bronze-white bronze sequence. The GDOES analysis reveals that the gold finishing layer surface is intact, but also reveals an internal alteration of the substrate which is likely responsible for the observed lower corrosion protection.

Figure 7 shows a model to explain the observed prevention of any major copper migration into the gold finishing layer 4. Migration of copper in the electroplated product is observed owing to the high mobility of copper atoms during the heat treatment of the electroplated product. Since the first copper alloy layer 2 (white bronze) has a reduced copper content compared to the second copper alloy layer 3 (yellow bronze) it acts as a copper sink which draws copper atoms from the second copper alloy layer 3 and also from the first copper layer 1. This creates a strong flow of copper from the second copper alloy layer 3 towards the first copper alloy layer 2. This strong flow of copper appears to prevent copper from migrating from the second copper alloy layer 3 into the gold finishing layer 4 and thus ensures a low copper concentration in the gold finishing layer 4 which leads to an improved corrosion resistance of the electroplated product and preservation of its gold color tone. The thickness of the arrows in the illustrated model are supposed to indicate the intensity of copper migration i.e. the thicker the arrow the stronger the copper migration in the indicated direction. A small gold migration from the gold finishing layer 4 to the second copper alloy layer 3 (not shown) compensates the copper migration from the second copper alloy layer 3 to the gold finishing layer 4 at this interface. Figures 1-3 show that there is also a thermodynamically driven, concomitant migration of tin and zinc.

Example 1 - Composition and properties of employed white and yellow bronze

[0030] 

White bronze
	Examples 4, 5 and 6	Examples 7 and 8
copper:	50-54 wt.-%**	40-54 wt.-%
tin:	28-32 wt.-%	28-40 wt.-%
zinc:	15-20 wt.-%	10-20 wt.-%

	Examples 4 to 8
layer density:	8.3 g/cm3
hardness:	550 HV
Colorimetric parameters*:	L 87-90; a 0,5-2,5; b 2-4

* measured with Minolta CM-503i spectrophotometer. Illuminant used was Daylight D65 (6500K) with reflective component included (sci). Observer was set at standard (10°) and the measurements were done in the Color space CIE L*a*b*.

Yellow bronze
	Examples 4, 5 and 6	Examples 7 and 8
copper:	72-77 wt.-%	70-80 wt.-%
tin:	17-23 wt.-%	15-23 wt.-%
zinc:	3-7 wt.-%	3-10 wt.-%

	Examples 4 to 8
layer density:	8.2 g/cm3
hardness:	400 HV
Colorimetric parameters*:	L 87-90; a 4-6; b 18-20

* measured with Minolta CM-503i spectrophotometer. Illuminant used was Daylight D65 (6500K) with reflective component included (sci). Observer was set at standard (10°) and the measurements were done in the Color space CIE L*a*b*. ** measured by EDS microanalysis BRUCKER SVE 6, microprobe X Flash 610 mini

Example 2 - GDOES principle and GDOES analysis of the layer structure of inventive electroplated products and electroplated products of the prior art

Principle of GDOES (glow discharge optical emission spectrometry)

[0031] The sample forms the cathode and a thin (4 mm diameter) copper tube forms the anode. A small O-ring separates the anode from the cathode. High-purity argon is pumped into the anode chamber. A high voltage (DC or RF) between sample and anode ionizes the argon to produce a glow discharge. The excited argon ions bombard the electroplated product sample and cause uniform sputtering of the sample surface. Atoms ejected are then excited by an Argon plasma, and finally come back to their fundamental energy level, emitting a characteristic X-ray photon.

[0032] Emitted photons, whose energy is characteristic of the energy level of a chemical element, are then collected by photomultipliers. The intensity of each emission depends on the concentration of the element in the sample. The recorded signals are processed to obtain the distribution of the elements according to the erosion time. GDOES provides depth profiling analysis of solids like metals, powders, polymers, glasses and ceramics (in the present case: depth profiling of electroplated substrates).

[0033] The advantages of GDOES are its rapid, multi-elemental acquisition, a simple implementation (no ultra-high vacuum) and the high sensitivity of detection for light elements, (like e.g. C, N and O).

Present GDOES analysis

[0034] In the present analysis, the following GDOES parameters were used:

■ GD Profiler, HORIBA, Jobin Yvon

■ detection of elements: Au, Cu, Zn, Sn , Ni

■ diameter of the anode: 4 mm

■ analyses of the samples without and with heat treatment:

• Sample 1: acidic copper+ gold 0.5 µm
• Sample 2: acidic copper+ flash bronze (1 µm) + gold 0.5 µm
• Sample 3: acidic copper+ white bronze (2 µm) + gold 0.5 µm
• Sample 4: acidic copper+ white bronze (2 µm) +palladium/nickel flash 0,1 µm + gold 0.5 µm
• Sample 5 : acidic copper + white bronze (2-3 µm) + yellow bronze (2-3 µm) + gold 0.5 µm
• Sample 6: acidic copper + yellow bronze (2-3 µm) + white bronze (2-3 µm) + gold 0.5 µm;
• Sample 7: acidic copper + white bronze (2-3 µm) + white bronze (2-3 µm) + gold 0.5 µm;
• Sample 8: acidic copper + yellow bronze (2-3 µm) + yellow bronze (2-3 µm) + gold 0.5 µm.

■ analyze before and after heat treatment for 24 hours at 180°C

■ power: 25 W

■ pressure: 620 Pa

■ wavelengths of the spectral lines used (in nm): Au 242,8 ; Cu 224, 7; Zn 481; Sn 317,5; Ni 341,5.

[0035] A low power was retained to decrease the speed of abrasion of the deposits with low thickness and to obtain maximum information at the interface. Quantified compositional results were evaluated automatically utilizing the standard Jobin Yvon quantum Intelligent Quantification software. The instrument was calibrated with standards of known composition. Depths were calculated using relative sputter rates, obtained from the sputter yields of each major element with corrections for composition and discharge conditions.

[0036] The Figures 1 to 6 give the GDOES depth profile for the different electroplated products of Examples 4 and 8 before and after the heat treatment at 180°C for 24 hours. The concentration of each chemical element Au, Cu, Zn, Sn and eventually Ni (when this element is present to determine the Pd-Ni coating) is shown (y-axis in wt.-%) as a function of the distance from the surface of the finishing layer towards the base material of the electroplated product (x-axis in µm). The thicknesses of the layers given for the process of the argon ablation (abscissa) and the metal concentrations (ordinate) are not normalized, but reflect the progress of the metal migration from the as-plated to the annealed state (annealing at 180 °C for 24 h).

Example 3 - Performance in corrosion and abrasion tests of a nickel-containing electroplated product of the prior art

[0037] An electroplated nickel-containing product of the prior art comprises the following layers electrolytically deposited on a brass substrate:

bright nickel layer:	10 µm
nickel phosphorus layer:	2 µm
gold layer as finishing layer:	0.5 µm

[0038] Said electroplated nickel-containing product has the following properties:

NFS 80772:	24 HOURS;
ABRASION WITH TURBULA:	5 MINUTES
LEATHER INTERACTION UNDER ISO 4611:	96 HOURS;
ISO 4538:	48 HOURS;
ISO 4524/2:	8 HOURS;
ISO 4611:	96 HOURS;
ABRASION TEST BY TURBULA UNDER ISO 23160:	no color change after 30 min.

[0039] Aim of the Turbula test is to simulate general wear that results from wearing the parts. The test was performed using an industrial rotating machine (Turbula, model T2F, Willy A. Bachofen AG Maschinenfabrik, Switzerland). Abrasive load was composed of abrasion ceramic elements mixed with fresh water containing a surface tension agent. Detailed information on the size of the ceramic elements is described in the ISO 23160 reference (see Table 1 - page 3). Test duration was 30 minutes. Evaluation of wear was done by visual inspection and comparison with reference samples. In particular, a color change after abrasion was used to evaluate wear resistance of the tested parts. The Turbula test is considered positive if no colour change is visible in the tested parts, especially on the edges or regions that are more exposed.

[0040] The result of this test gave that the nickel sequence gives a very good performance, especially regarding abrasion due to the thick layer of nickel that does not give discoloration.

Example 4 - Performance in corrosion and abrasion tests of a nickel-less electroplated product of the prior art

[0041] An electroplated nickel-less product of the prior art comprises the following layers electrolytically deposited on a brass substrate:

bright copper layer:	10 µm
white bronze layer:	2 µm
gold layer as finishing layer:	0.5 µm

[0042] Said electroplated nickel-free product has the following properties:

NFS 80772:	12 HOURS;
ABRASION WITH TURBULA:	5 MINUTES
LEATHER INTERACTION UNDER ISO 4611:	48-72 HOURS;
ISO 4538:	48 HOURS;
ISO 4524/2:	8 HOURS;
ISO 4611:	96 HOURS;
ABRASION TEST BY TURBULA UNDER ISO 23160:	no color change after 30 min.

[0043] Thus, the performance in some of the tests is reduced compared to the nickel-containing electroplated product.

[0044] The reason for which the bronze layer is very thin is related with the level of quality of bronze plating processes known in the prior art that do not allow exceeding 2 µm of the deposit while maintaining the desired bright aspect. In other words, this is the reason why thicker deposits of white bronze are undesirable for the jewelry and/or fashion industry because of a lack of brightness. Due to the fact that the precious metal layers are regularly a very thin deposit (approx. 0.5 µm), it is easy for corrosive media or mechanical action to reach the underlying bronze layer. Said bronze layer is softer than nickel and has a slightly lower thickness. Thus, it is less resistant to mechanical stress and can be damaged easily. Upon damage of the white bronze layer, the underlying copper layer will appear and be exposed to the atmosphere and oxidation. For these reasons, the nickel-free plated parts are more easily damaged by aggressive media, like leather and the acid sweat of human skin.

Example 5 - Performance in corrosion and abrasion tests of a nickel-containing electroplated product of the prior art having a palladium-nickel intermediate layer

[0045] An electroplated nickel-containing product of the prior art comprises the following layers electrolytically deposited on a brass substrate:

bright copper layer:	10 µm
white bronze layer:	2 µm
palladium-nickel layer:	0.3 µm
gold layer as finishing layer:	0.5 µm

[0046] Said electroplated nickel-free product has the following properties:

NFS 80772:	24 HOURS;
ABRASION WITH TURBULA:	5 MINUTES
LEATHER INTERACTION UNDER ISO 4611:	48-72 HOURS;
ISO 4538:	48 HOURS;
ISO 4524/2:	8 HOURS;
ISO 4611:	96 HOURS;
ABRASION TEST BY TURBULA
UNDER ISO 23160:	change of color in article edges more exposed to abrasion (copper color)

[0047] In fact, even a palladium intermediate layer with only 0.3 µm thickness increases the performance in the NFS 80772 test from 12 hours to almost 24 hours. However, the disadvantage of having said palladium intermediate layer is that the electroplating of the substrates is cost-intensive.

Example 6 - Performance in corrosion and abrasion tests of a nickel-less electroplated product

[0048] A first example of an electroplated nickel-less product comprises the following layers electrolytically deposited on a brass substrate:

bright copper layer:	10 µm
white bronze layer (Cu:Sn:Zn = 40:40:20):	2-4 µm
yellow bronze layer (Cu:Sn:Zn = 70:20:10):	3-4 µm
gold layer as finishing layer:	0.5 µm

[0049] A second example of an electroplated nickel-less product comprises the following layers electrolytically deposited on a brass substrate:

bright copper layer:	10 µm
yellow bronze layer (Cu:Sn:Zn = 70:20:10):	3-4 µm
white bronze layer (Cu:Sn:Zn = 40:40:20):	2-3 µm
palladium layer as finishing layer:	0.5 µm

[0050] The electroplated nickel-free products of the first and second example have the following properties:

NFS 80772:	24 HOURS;
ABRASION WITH TURBULA:	5 MINUTES
LEATHER INTERACTION UNDER ISO 4611:	96 HOURS;
ISO 4538:	48 HOURS;
ISO 4524/2:	8 HOURS;
ISO 4611:	96 HOURS;
ABRASION TEST BY TURBULA
UNDER ISO 23160:	no color change after 30 min.

[0051] Thus, the improvement of performance is essentially related to the protection of the copper underlayer on the one hand and to the conservation of the quality of the top gold layer on the other hand by the presence of both the white and yellow bronze layer.

Example 7 - Performance in corrosion and abrasion tests of a nickel-less electroplated product - assessing the influence of the sequence of the bronze layers

[0052] A white bronze layer is deposited next to the gold layer and a yellow bronze layer is deposited next to the bright copper layer i.e. the electroplated nickel-less product comprises the following layers electrolytically deposited on a brass (indicated relations of the elements in the bronze layer are in weight-%):

bright copper layer:	>10 µm
yellow bronze layer (Cu:Sn:Zn = 80:15:05):	2-3 µm
white bronze layer (Cu:Sn:Zn = 50:35:15):	2-3 µm
gold layer as finishing layer:	0.5 µm

[0053] The electroplated nickel-free product has the following properties:

NFS 80772:	12 HOURS;
ABRASION WITH TURBULA:	3 MINUTES
LEATHER INTERACTION UNDER ISO 4611:	56 HOURS;
ABRASION TEST BY TURBULA
UNDER ISO 23160:	no color change after 60 min.

[0054] The properties of the electroplated nickel-free product obtained for the plating sequence of example 4 are better than the properties obtained for the plating sequence of this example, showing that the sequence bright copper/yellow bronze/white bronze is less adapted as underlayer of gold than the sequence copper/white bronze/yellow bronze. The present sequence is more adapted as an underlayer of Palladium as final finish.

Example 8 - Performance in corrosion and abrasion tests of two non-inventive nickel-less electroplated product - assessing the significance of the difference in copper concentration of the bronze layers

[0055] In a first assay, next to the gold layer and next to the bright copper layer a white bronze layer with identical composition is deposited i.e. the electroplated nickel-less product comprises the following layers electrolytically deposited on a brass (indicated relations of the elements in the bronze layer are in weight-%):

bright copper layer:	>10 µm
white bronze layer (Cu:Sn:Zn = 50:35:15):	2-3 µm
white bronze layer (Cu:Sn:Zn = 50:35:15):	2-3 µm
gold layer as finishing layer:	0.5 µm

[0056] The electroplated nickel-free product has the following properties:

NFS 80772:	12 HOURS;
ABRASION WITH TURBULA:	3 MINUTES
LEATHER INTERACTION UNDER ISO 4611:	48 HOURS;
ABRASION TEST BY TURBULA UNDER ISO 23160:	no color change after 60 min.

[0057] In a second assay, next to the gold layer and next to the bright copper layer a yellow bronze layer with identical composition is deposited i.e. the electroplated nickel-less product comprises the following layers electrolytically deposited on a brass substrate (indicated relations of the elements in the bronze layer are in weight-%):

bright copper layer:	>10 µm
yellow bronze layer (Cu:Sn:Zn = 80:15:05):	2-3 µm
yellow bronze layer (Cu:Sn:Zn = 80:15:05):	2-3 µm
gold layer as finishing layer:	0.5 µm

[0058] The electroplated nickel-free product has the following properties:

NFS 80772:	6 HOURS;
ABRASION WITH TURBULA:	3 MINUTES
LEATHER INTERACTION UNDER ISO 4611:	48 HOURS;
ABRASION TEST BY TURBULA UNDER ISO 23160:	no color change after 120 min.

[0059] From this experiment, it is evident that if two bronze layers with identical copper concentration (either two white bronze layers or two yellow bronze layers) are deposited, the corrosion resistance of the resulting substrate is worse than if the two bronze layers with different copper concentration are deposited. In addition, it can be observed that plating two white bronze layers provides better corrosion protection than plating two yellow bronze layers. This indicates that the worse corrosion protection observed may be caused by a higher copper content in the gold finishing layer of the final substrate due to copper migration into said layer.

Example 9 - Corrosion and abrasion resistance of an electroplated article which comprises a palladium alloy as intermediate layer

[0060] Zamac is massively used in the luxury industry due to its low cost: compared to brass, the proportion between copper and zinc are opposed and the massive object contains mainly zinc. The zinc potential of corrosion is lower than copper and reduces the "nobility" of the final article.

[0061] On the other hand, the final object to be electroplated is stamped starting from ingots with low compactness. The stamping step will compress the material, but porosity remains and is uncontrollable during the stamping process.

[0062] The galvanic sequence will have to protect the material either from the attacks coming from outside (such as oxidizing medias), but also from the inside considering holes residues for the original ingot and the stamping process. The stamping process will concentrate the pores in the thickness of the final article but as it happens frequently, the base material external composition presents low porosity density close to the galvanic treatment. The use of a poorly resistant substrate as a base material is then problematic, even more in the case that the substrate has a porous composition like zamak. In fact, cavity corrosion can occur in the pores which alters the visual aspect of the electroplated article.

[0063] This is a reference example as the electroplated article contains a palladium layer as intermediate layer.

[0064] The ageing useful to evaluate abrasion and corrosion resistance is in line with the following parameters:

• TURBULA^® set at 62 rounds/min (three-dimensional movement) and a container with a capacity of 2L;
• Ceramic abrasive: 2.5 kg, supplier* ROSLER RS06/06S (angle cutting)

[0065] This example describes the known use of a precious metal such as palladium as intermediate layer to save production costs compared to the expensive gold finishing. This example of an electroplated nickel-less product comprises the following layers electrolytically deposited on a zamak substrate:

copper layer:	> 15 µm (30 - 50 µm)
bronze layer (Cu-Sn-Zn alloy layer):	3 µm
palladium alloy layer (nickel-free):	0.5 µm
gold layer:	0.5 microns

[0066] This use of a palladium alloy layer is expensive in terms of final thickness of precious metal. On the other side, the hydrogen embrittlement that occurs during palladium plating will raise the risk of under-layer cracking during ageing due to the close distance between pores of the substrate and holes left by hydrogen release.

[0067] The electroplated article was submitted to the synthetic sweat resistance test (performed following NFS 80772 standard with ageing).

[0068] Globally, it turned out that the gold surface seems to be covered by copper after 24 hours of sweat interaction.

[0069] After an analysis with an optical microscope, it has turned out that before the synthetic sweat resistance test, there were holes visible on the surface. After said test, the holes were enlarged compared to before the test an oxidation was visible. In addition, copper covers the tested article (red stains are formed on top of gold in contact with the synthetic sweat). Due to the difference of potential of corrosion between the first copper layer and zinc as the main component of the substrate, the "battery effect" occurs and copper is dissolved.

[0070] Synthetic sweat is a conductive liquid. It will transport copper ions until the precious metal finishing where the opposite phenomenon happens and copper ions are reduced. This phenomenon is enhanced by the difference of corrosion potential between the substrate and the first copper layer and the presence of palladium below the gold layer due to high nobility of the final galvanic treatments. In fact, the presence of a Palladium layer between the copper layer and the gold layer enhances the copper dissolution rate.

[0071] An electron microscope allows the identification of the chemical composition of the surface of an article.

[0072] When viewing the electroplated article under an electron microscope before the synthetic sweat resistance test, it was observed that the surface of the article is mechanically altered, some open pores are visible with the mechanical alteration and the gold is the main element detected with mapping analysis.

[0073] When the same article was viewed after said test, it was observed that gold was missing at a distance of 100 µm around the hole which indicates that the base material is directly exposed to the oxidizing media. It was also observed that the strong synthetic sweat testing conditions create a stressed area between the porous substrate and the hydrogen present in the palladium. Due to the noble finishing and the substrate sensitive to corrosion, the copper is electrochemically dissolved. Through conductive synthetic sweat, dissolved copper ions are reduced on top of gold by potentiometric difference.

[0074] Table 1 below is a summary of the chemical composition obtained by EDS measurement located at the surface of the electroplated article before synthetic sweat interaction, on copper reduced areas and on oxidized areas.

Table 1

	before sweat interaction	after sweat interaction
		unaltered areas (copper reduced areas)	altered areas (oxidized areas)
Au	82 wt.%	75 wt.%	0 wt.%
Pd	10 wt.%	10 wt.%	0 wt. %
Cu	5 wt.%	5 wt.%	5 wt.%
Sn	-	-	2 wt.%
Zn	3 wt.%	2 wt.%	55 wt.%
O	-	8 wt.%	38 wt.%

Example 10 - Corrosion and abrasion resistance of an electroplated article having a substrate with high zinc content and low thickness of first copper layer

[0075] This is a reference example as the thickness of the first copper layer is maximally 15 µm.

[0076] The ageing useful to evaluate abrasion and corrosion resistance is in line with the following parameters:

• TURBULA^® set at 62 rounds/min (three-dimensional movement) and a container with a capacity of 2L;
• Ceramic abrasive: 2.5 kg, supplier* ROSLER RS06/06S (angle cutting)

[0077] This example describes a sequence on zamak with a copper thickness lower than 15 µm. The zamak alloy is mainly composed of zinc (around 70 - 80%). Zinc being soluble in most acids, an interaction with the synthetic sweat would directly destroy the base material. This example of an electroplated nickel-less product comprises the following layers electrolytically deposited on a zinc alloy (zamak) substrate:

copper layer:	≤15 µm (8-15µm)
white bronze layer (Cu-Sn-Zn alloy layer):	3 µm
yellow bronze layer (Cu-Sn-Zn alloy layer):	3 µm
gold layer:	0.5 microns

[0078] The properties of the deposited white bronze layer and yellow bronze layer are summarized in Table 2.

Table 2

	white bronze layer	yellow bronze layer
colour of the layer	white	yellow
%Cu	46 - 49 wt.%	75 - 85 wt.%
%Sn	40 - 45 wt.%	15 - 20 wt.%
%Zn	10 -15 wt.%	2 - 7 wt.%
density of the alloy	8.3 g/cm3	8.1 g/cm3

[0079] Ageing of the electroplated articles was performed applying 3 minutes of TURBULA^®. The electroplated article was submitted to the synthetic sweat resistance test (performed following NFS 80772 standard with ageing).

[0080] An improvement compared to the plating sequence in Example 9 was observed: Compared to example 9, the reduction of copper did not occur on the whole surface but rather only locally.

[0081] The analysis with the optical microscope showed that copper seems to be locally dissolved and reduced on the gold finishing, but this phenomenon remains localized.

[0082] An analysis with the electron microscope allows the identification of the chemical composition of the surface before and after synthetic sweat resistance test on article submitted to ageing before the interaction with sweat. This analysis was performed with the electroplated articles. It was observed that the opening of holes in the substrate occurs like observed in Example 9, but a different behavior is observed. In fact, corrosion is only located around the holes and does not spread on the entire gold finishing surface. Moreover, copper dissolution is limited which is most likely due to the substitution of the palladium intermediate layer. As a consequence, the final galvanic treatment is globally less noble. Copper dissolution can happen between substrate and the first copper layer, but copper reduction was observed to slow down on the external surface of the article.

[0083] Table 3 below is a summary of the chemical composition located at the surface of the electroplated article before synthetic sweat interaction, on copper reduced areas and on oxidized areas.

Table 3

	before sweat interaction	after sweat interaction
		unaltered areas (copper reduced areas)	altered areas (oxidized areas)
Au	95 wt.%	88 wt.%	0 wt. %
Cu	3 wt.%	5 wt.%	5 wt.%
Sn	-	-	2 wt.%
Zn	2 wt.%	2 wt.%	55 wt.%
O	-	5 wt.%	38 wt.%

Example 11 - Corrosion and abrasion resistance of an electroplated article having a substrate with high zinc content and high thickness of first copper layer

[0084] This is an example according to the invention as the thickness of the first copper layer is more than 15 µm.

[0085] The ageing useful to evaluate abrasion and corrosion resistance is in line with the following parameters:

• TURBULA^® set at 62 rounds/min (three-dimensional movement) and a container with a capacity of 2L;
• Ceramic abrasive: 2.5 kg, supplier* ROSLER RS06/06S (angle cutting)

[0086] This example describes a sequence on zamak with a copper thickness of more than 15 µm. The zamak alloy is mainly composed of zinc (around 70 - 80%). Zinc being soluble in most acids, an interaction with the synthetic sweat would directly destroy the base material. This example of an electroplated nickel-less product comprises the following layers electrolytically deposited on a zinc alloy (zamak) substrate:

copper layer:	> 15 µm (30 - 50 µm)
white bronze layer (Cu-Sn-Zn alloy layer):	3 µm
yellow bronze layer (Cu-Sn-Zn alloy layer):	3 µm
gold layer:	0.5 microns

[0087] The properties of the deposited white bronze layer and yellow bronze layer are summarized in Table 4.

Table 4

	white bronze layer	yellow bronze layer
colour of the layer	white	yellow
%Cu	46 - 49 wt.%	75 - 85 wt.%
%Sn	40 - 45 wt.%	15 - 20 wt.%
%Zn	10 -15 wt.%	2 - 7 wt.%
density of the alloy	8.3 g/cm3	8.1 g/cm3

[0088] The electroplated article was submitted to the synthetic sweat resistance test (performed following NFS 80772 standard with ageing).

[0089] Indeed, it was discovered that by combining a copper layer thickness of more than 15 µm with the sequence consisting of the double bronze combination followed by the precious metal final layer led to a raise in the resistance performance. Specifically, it was observed that the synthetic sweat test opens the holes created by the TURBULA^® treatment, but no detrimental consequences occur. In fact, it turned out that the copper of the copper layer is not dissolved by synthetic sweat and the electroplated article remains unchanged after 24 hours in contact with synthetic sweat. Despite the articles presenting mechanical alteration, no chemical oxidation is visible.

[0090] Moreover, the chemical analysis of the surface of the electroplated article confirms that there are no sign of corrosion. Firstly, only the metals are detected i.e. no oxygen from corrosion is seen and the composition is unchanged. Secondly, the electron microscope (SEM) pictures before and after the corrosion test are identical and show no sign of corrosion on the surface after the synthetic sweat interaction for 24 hours.

[0091] Table 5 below is a summary of the chemical composition located at the surface of the electroplated article before synthetic sweat interaction and after the synthetic sweat interaction.

Table 5 n/o: no altered areas observed

	before sweat interaction	after sweat interaction
		unaltered areas (copper reduced areas)	altered areas (oxidized areas)
Au	96 wt.%	95.6 wt.%	n/o
Cu	2 wt.%	2.6 wt.%
Sn	-	-
Zn	2 wt.%	1.2 wt.%
O	-	-

[0092] In Table 6 below the galvanic sequences applied on the zinc alloy as base material are reported

Table 6

	Example 9	Example 10	Example 11
Substrate	zamak	zamak	zamak
First Copper layer	copper: 30-50 microns	copper: 8 -15 microns	copper: 30 - 50 microns
	white bronze alloy	white bronze alloy	white bronze alloy
	46 - 49 wt.-% Cu	46 - 49 wt.-% Cu	46 - 49 wt.-% Cu
Second layer	40 - 45 wt.-% Sn	40 - 45 wt.-% Sn	40 - 45 wt.-% Sn
	10 - 15 wt.-% Zn	10 - 15 wt.-% Zn	10 -15 wt.-% Zn
	2.5 microns	2.5 microns	2.5 microns
		yellow bronze alloy	yellow bronze alloy
	palladium alloy 0.5 micron	75 - 85 wt.-% Cu	75 - 85 wt.-% Cu
Third layer		15 - 20 wt.-% Sn	15 - 20 wt.-% Sn
		2 - 7 wt.-% Zn	2 - 7wt.-% Zn
		2.5 microns	2.5 microns
Finishing	Gold 0.5 micron	Gold 0.5 micron	Gold 0.5 micron

[0093] Table 7 below summarizes the obtained data regarding the electroplated articles of Examples 9 to 11.

Table 7

	Example 9	Example 10	Example 11
sweat resistance	negative	negative	positive
global aspect after sweat interaction	surface covered by copper reduction from the first layer	local opening of holes from the substrate which lead to their oxidation	local opening of holes without oxidation
EDS analysis of the global surface	oxygen content is raised	oxygen content is raised	element concentration does not change
EDS analysis on localized defect	mainly zinc and oxygen	mainly zinc and oxygen	no defect

Claims

1. Electroplated product, comprising

a) a base material;

b) a first layer comprising or consisting of copper, wherein the first layer is disposed on the base material;

c) a second layer comprising or consisting of a first copper alloy, wherein the first copper alloy comprises tin and zinc;

d) a third layer comprising or consisting of a second copper alloy, wherein the second copper alloy comprises tin and zinc; and

e) a fourth layer comprising or consisting of a precious metal,
wherein the fourth layer is the finishing metal layer of the electroplated product;

characterized in that the second layer or third layer are disposed on the first layer and the copper concentration in the first copper alloy is different from the copper concentration in the second copper alloy and the first layer has a thickness in the range of >15 to 60 µm.

2. Electroplated product according to claim 1, characterized in that

i) the second layer is disposed on the first layer, the third layer is disposed on the second layer and the fourth layer is disposed on the third layer; or

ii) the third layer is disposed on the first layer, the second layer is disposed on the third layer and the fourth layer is disposed on the second layer;

wherein optionally, the copper concentration in the second alloy is higher than the copper concentration in the first alloy.

3. Electroplated product according to one of the preceding claims, characterized in that the copper concentration of the first copper alloy differs from the copper concentration of the second copper alloy by an absolute value of 1 to 99 wt.-%, preferably 5 to 80 wt.-%, more preferably 10 to 60 wt.-%, even more preferably 15 to 40 wt.-%, most prefer ably 20 to 30 wt.-%.

4. Electroplated product according to one of the preceding claims, characterized in that the copper concentration in the

i) first copper alloy is ≤ 65 wt.-%, preferably 30 to 64 wt.-%, more preferably 40 to 60 wt.-%, most preferably 45 to 55 wt.-%, in relation to the whole weight of the copper alloy; and/or

ii) the second copper alloy is ≥ 66 wt.-%, preferably 66 to 90 wt.-%, more preferably 70 to 87 wt.-%, most preferably 75 to 85 wt.-%, in relation to the whole weight of the copper alloy.

5. Electroplated product according to one of the preceding claims, characterized in that the zinc concentration in the

i) first copper alloy is ≥ 10 wt.-%, preferably 11 to 35 wt.-%, more preferably 12 to 25 wt.-%, most preferably 15 to 20 wt.-%, in relation to the whole weight of the copper alloy; and/or

ii) the second copper alloy may be ≤ 15 wt.-%, preferably 2 to 10 wt.-%, more preferably 3 to 8 wt.-%, most preferably 4 to 7 wt.-%, in relation to the whole weight of the copper alloy.

6. Electroplated product according to one of the preceding claims, characterized in that the tin concentration in the

i) first copper alloy may be ≥ 26 wt.-%, preferably 26 to 35 wt.-%, in relation to the whole weight of the copper alloy; and/or

ii) the second copper alloy may be ≤ 25 wt.-%, preferably 1 to 25 wt.-%, more preferably 10 to 25 wt.-%, most preferably 15 to 25 wt.-%, in relation to the whole weight of the copper alloy.

7. Electroplated product according to one of the preceding claims, characterized in that the first copper alloy and/or the second copper alloy comprises Bi, Pb and/or Sb, preferably Bi.

8. Electroplated product according to one of the preceding claims, characterized in that the first copper alloy is white bronze and/or the second copper alloy is yellow bronze.

9. Electroplated product according to one of the preceding claims, characterized in that the fourth layer is disposed on the second or third layer.

10. Electroplated product according to one of the preceding claims, characterized in that there is no layer comprising or consisting of palladium between the first layer and fourth layer, wherein the electroplated product preferably does not comprise palladium.

11. Electroplated product according to one of the preceding claims, characterized in that there is no layer comprising or consisting of nickel, cobalt and/or chromium between the first layer and fourth, wherein the electroplated product preferably does not comprise nickel, cobalt and/or chromium, most preferably no nickel.

12. Electroplated product according to one of the preceding claims, characterized in that an organic protection layer is disposed on the fourth layer, preferably a layer comprising or consisting of a hydrophobic substance, more preferably a monolayer of a hydrophobic substance, even more preferably a monolayer of a hydrophobic substance being a corrosion inhibitor, most preferably a monolayer of a hydrophobic substance comprising thiol groups, especially a monolayer of alkanethiol monomers or alkanethiol polymers.

13. Electroplated product according to one of the preceding claims, characterized in that the precious metal is selected from the group consisting of gold, silver, platinum, ruthenium, rhodium, palladium, osmium, iridium and alloy thereof, preferably gold, silver, palladium and alloys thereof, more preferably gold, palladium and alloys thereof, most preferably gold.

14. Electroplated product according to one of the preceding claims, characterized in that the base material comprises or consists of bronze, brass, zamak, alpaca, copper alloy, tin alloy and/or steel, preferably comprises or consists of zamak.

15. Electroplated product according to one of the preceding claims, characterized in that the thickness of

i) the first layer is 16 to 60 µm, preferably 20 to 55 µm, more preferably 25 to 50 µm, most preferably 30 to 45 µm;

ii) the second layer is 1 to 10 µm, preferably 2 to 8 µm;

iii) the third layer is 1 to 10 µm, preferably 2 to 4 µm; and/or

iv) the fourth layer is 0.1 to 5 µm, preferably 0.2 to 1 µm.

16. Method of producing an electroplated product according to one of the preceding claims, comprising the steps:

a) electroplating a layer comprising or consisting of a first copper alloy on a copper layer disposed on a substrate;

b) electroplating a layer comprising or consisting of a second copper alloy on the layer of step a);

c) electroplating a layer comprising or consisting of a precious metal on the layer of step b),

characterized in that the first copper alloy layer is plated with a copper concentration different from that of the second copper alloy layer.

17. Use of the electroplated product according to one of claims 1 to 15 in the jewelry industry, fashion industry, leather industry, watch industry, eyewear industry, trinkets industry and/or lock industry.

Drawing