WO2018146623A1

WO2018146623A1 - Yellow/rose inox bronze and its use in galvanized products

Info

Publication number: WO2018146623A1
Application number: PCT/IB2018/050800
Authority: WO
Inventors: Lorenzo Cavaciocchi; Serena CINOTTI; Leandro Luconi; Gabriele Gori
Original assignee: Bluclad S.R.L.
Priority date: 2017-02-09
Filing date: 2018-02-09
Publication date: 2018-08-16
Also published as: EP3580364A1; IT201700014377A1

Abstract

Object of the present invention is a stainless copper/tin alloy having yellow/pink coloring and galvanized objects containing it.

Description

YELLOW/ROSE INOX BRONZE AND ITS USE IN GALVANIZED PRODUCTS

FIELD OF THE INVENTION

The present invention relates to the field of alloys, in particular to bronzes containing palladium in large quantities, to galvanized objects containing such alloys and to the method for their production and use.

BACKGROUND

Copper and tin alloys containing palladium are already known for their resistance as possible low-cost substitutes for pure palladium deposits and as nickel substitutes for objects that must respect the anallergicity characteristics. The patent JPH06293990, for example, treats a tin alloy 10-20%, copper 10- 80% and palladium 10-50% plus other elements in small quantities that has color and strength comparable to pure palladium.

The patent JPH0978286 treats of a galvanic bath for the deposition of copper, tin, zinc and palladium alloys with high concentrations of palladium in a non- cyanurate environment.

The patent JPH10204677 treats instead of generic tin-palladium alloys in which the tin is present in a variable concentration in alloy ranging between 21 -35% while palladium is present in a variable concentration in alloy between 35-60%. The patent application PCT/IB2016/054703 describes Cu/Sn alloys having white colors and characterized by copper concentrations less than 60% and of Palladium less than 10% white deposits are obtained. Said application describes white bronze having composition

Sn 25-45%

Zn 0-15%

Pd 0.25- 10%

Cu as needed to 100% but still less than 60%

and colorimetric coordinates: L=85-88 , a=-0.5-0.7, b= 3-5.

The above mentioned alloys try to replicate the final white appearance of pure palladium with a lower expenditure of precious metal anyway maintaining the characteristics of resistance to mechanical and chemical stresses unaltered. As can be easily deduced from the aforementioned patents that all the patented alloys do not take into consideration the possibility of obtaining a yellow and/or pink deposit, also it very resistant, capable of reducing the production costs of all metal accessories comprising gold finishes of various tonality. The absence of this type of analysis therefore shows that the work carried out has been approximate and the indicated ranges have not really been investigated.

Thus, in the state of the art, an important gap results in bronze alloys that embraces all the golden finishes (in tonality from yellow to pink).

Currently it is well known that to succeed pass the oxidation tests after turbula it is necessary to reinforce a galvanized object to avoid that the scratches reach the easily oxidizable non-noble deposits. In the nickel cycles are the thicknesses of electroplating of nickel and nickel-phosphorus under the finishing layer with noble metal (generally gold) that perform this function while, in nickel-free cycles this function is performed from the electroplated palladium layer which, positioned between bronze and external finish, is deposited with thicknesses of 0.5-1 micron. It is therefore evident, seen what has been said above, the need to develop new alloys and new electroplating cycles capable of responding efficiently to industrial requirements and to equate to electroplating cycles that use nickel both in terms of oxidation resistance and wear resistance (nickel thicknesses of about 10 micron with hardness around 450 Vickers).

SUMMARY OF THE INVENTION

The present invention allows to overcome the above mentioned problems thanks to bronze alloys, consisting of copper, tin, palladium and optionally zinc, polished and bright which have a high resistance to oxidation and a higher hardness (therefore greater resistance to wear) whose coloring can be varied in tonality from yellow to pink.

Subject of the invention is a copper/tin alloy according to claim 1 , containing palladium and optionally zinc wherein the palladium content is 10-45%, tin 25- 10% and zinc 0-1 0%, such that the overall concentration Pd+Sn+Zn is 20-65%; where the % are by weight calculated on the total weight of the alloy. A further subject of the invention are galvanized objects in which at least one deposit is composed of the alloy object of the invention. Surprisingly, these objects have an improved resistance to corrosion and abrasion.

The right elements combination in the alloy according to the invention allows obtaining deposits of yellow and pink tonality to use in substitution to the gold deposits or as a sublayer to gold deposits, ensuring high color uniformity after intense wear also for very low gold thicknesses with a consequent reduction in production costs compared to the use of high thick gold (0.5-1 .0 micron). Furthermore, the convenience in using a yellow/pink bronze alloy containing palladium, according to the invention, is particularly marked as a sub-layer to gold deposits for nickel-free metal accessories which, for passing wear and oxidation tests that otherwise would require high thickness of palladium deposit. DETAILED DESCRIPTION OF THE INVENTION

The alloys according to the present invention have the following composition (the percentages are intended by weight with respect to the total weight of the alloy):

Sn 10-25%

Pd 10-45%

Zn 0-10%

Cu as needed to 100%;

wherein the overall concentration of Pd + Sn + Zn is 20-65%; said alloy having colorimetric coordinates: L = 78-86, a = 3-6, b = 8-1 9; wherein % are by weight calculated on the total weight of the alloy.

The alloys according to the invention may possibly contain traces of brightening or grain finishers metals, where by traces we mean quantities of less than 0.25% by weight on the alloy and for brightening or grain finishers metals we mean those normally used for this purpose in this field of activity.

The variation in tonality linked to the maintenance of the high resistance to oxidative tests of the deposit is a function of the metals relative concentrations that compose the alloy.

For low palladium and tin concentrations (10-35% and 10-20% respectively) and high copper (> 55%), wherein Pd + Sn + Zn is at most 45%, yellow deposits are obtained thanks to the greater presence of copper in alloy. While when the copper concentration is 25-55%, the palladium concentration is 25-45 with the concentration of tin 20-25% wherein Pd + Sn + Zn is at most 65%, then the deposit acquires a pink tonality. The increase of zinc concentration in alloys allows increasing the green color component for yellow and pink deposits. Preferably, the alloys according to the invention have a composition:

Pink bronze

Sn 1 5-25%; preferably 15-22%; more preferably 19-21 ;

Pd 25-45%; preferably 28-40%; %; more preferably 34-38;

Cu 35-55%; preferably 36-51 %; %; more preferably 39-49;

Zn 0-10% Zn; preferably 0-7%; more preferably 2-5;

wherein Sn + Pd + Zn is at most 65%; said alloy having colorimetric coordinates: L = 78-82, a = 3-5, b = 8-1 2.

Yellow Bronze

Sn 1 0-20%; preferably 10-1 7%; more preferably 10-15%;

Pd 1 0-35%; preferably 20-33%; more preferably 25-31 %;

Cu remainder to 100 but anyway greater than 55%;

Zn 0-10% preferably 0-7%; more preferably 0.5-5%;

wherein Sn + Pd + Zn is at most 45%; said alloy having colorimetric coordinates: L = -80-86, a = 3-6, b = 12.5-19.

Moreover, in the solutions and in the deposit can be included the brighteners and grain finishers commonly used for this purpose among which trace metals such as bismuth, tellurium, gallium, indium, silver, molybdenum, thallium, antimony.

For an aspect, the present invention relates also to solutions for electroplating of an alloy according to the invention and the related electroplating process. Preferably, the cyanide content in the solutions is 1 - 100 g/l.

The above indicated metals are preferably present in solution as soluble oxides, sulphates, cyanides, ammonia salts and other suitable soluble compounds and the cyanide is in the form of sodium cyanurate, of potassium or derives from the salts of the metals constituting the alloy in the form of cyanurates complexes such as copper cyanide, zinc cyanide and palladium cyanide. The copper content in solution is preferably included between 2 and 30 g/l, more preferably between 5 and 20 g/l, with a ratio between copper and cyanide in the electrolyte preferably included for the pink version between 1 : 3 and 1 :1 2 while for the yellow between 1 : 2 and 1 : 7 calculated based on potassium or sodium cyanide.

The tin concentration in the electrolyte can vary between 2 and 30 g/l with an amount of free hydroxide that can vary between 0 and 20 g/l calculated on the base of potassium or sodium hydroxide.

The Zn content in solution, if present, can be included between 0.1 and 10 g/l based on the relative concentration of the other metals for obtaining the alloy of the invention.

The content of the fourth alloy component, palladium, can range from 0.05 g/l to 8 g/l, preferably for obtaining the desired alloys it can vary between 0.1 and 5 g/l.

The solution can also contain one or more complexing agents capable of regulating the metal components deposition and guaranteeing the stability in solution as is known for compositions of this type.

Some examples of complexing agents are, for example, complexing agents suitable for the purpose may be nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), alkali metal phosphonate salts such as ethylenediaminotetramethyl phosphonic acid (EDTMPA), 1 -hydroxyethylidene diphosphonic acid (HEDP), derivatives or salts of polyhydroxylated organic substances such as gluconates and more or less complex sugars.

In the solutions also surfactants may be present and surfactants mixtures well known to the skilled in the art such as wetting agents of the family of phosphonate alkylethers, sulfonated alkylethers, alkylarylpolyethoxylates and the relative sulphonated derivatives, quaternary ammonium salts of alkanes or aromatic compounds.

Moreover, in the solutions can be included the brighteners and grain finishers commonly used for this purpose among which trace metals such as bismuth, tellurium, gallium, indium, silver, molybdenum, thallium, antimony and organic compounds of the aromatic heterocycles family.

Subject of the present invention are also electroplated objects that show high resistance characteristics to oxidative and mechanical tests recognized by the major fashion houses worldwide.

For galvanized objects means objects included in the following merchandise classes in which at least one step of the production process involves the electroplating of a metal or metal alloys: jewelery, costume jewelery, leather goods, watches, eyewear, bric-a-brac, closures.

For an aspect, the present invention has as subject also a galvanized object comprising at least one layer consisting of an alloy as described above.

Preferably, the galvanized object according to the invention is comprising or consisting of:

a) a base material;

b) a preparatory layer which depends on the base material used, said preparatory layer deposited onto the base material;

c) a first coating layer consisting of white bronze containing palladium deposited on the preparatory layer so that it protects the base material and the easily oxidizable underlying layers; said white bronze layer present in nickel-free cycles;

d) a second coating layer consisting of bronze containing palladium according to the invention, as described above, whose color is as close as possible to the final deposit of the object that determines the appearance; said second bronze layer deposited on the white bronze layer in nickel-free cycles or directly on preparatory layer;

e) a final layer, usually consisting of precious metals which determines the final appearance of the object.

Among the various layers, other deposits of low thickness (less than 0.1 micron) usually called Flash can be interposed, in order to optimize the adhesion between the various galvanic layers avoiding delamination of the upper layers from the lower layers. For processes containing nickel, the first white bronze layer containing palladium is not recommended since there is an increase in production costs without appreciable improvement in oxidation resistance tests.

The base material may consist of or comprise bronze, brass, zamak, german silver, steel and other copper and tin alloys.

The preparatory layer is chosen by the skilled in the art according to the base material used and to the type of structural finishing (not colorimetric) that one wants to obtain. For example, for shiny looking finishes, both copper from glossy leveling copper baths and nickel from galvanic glossy leveling copper baths can be deposited, while for finishes with an opaque and aged look, the base material can be pre-treated with a tumbling process and subsequently deposit non- leveling nickel or bronze to preserve the roughness obtained on the base material.

Preferably in the nickel-free or hypoallergenic cycles in which the base material is brass or zamak, the preparatory layer is copper; when the base material is steel, preferably the preparatory layer is a flash of gold to optimize adhesion ; for cycles which include nickel if the base material is brass then the preparatory layer is nickel directly, whereas if the base material is the zamak, it must in any case be pretreated with copper before making the deposit of the nickel preparatory layer. In the cycles in which the outer layer (gold) is 0.5-1 micron, introduce the stainless yellow bronze of the present invention over the nickel (of white color) and thus reduce the gold thicknesses to 0.1 -0.2 micron is economically advantageous .

The preparatory layer preferably has a thickness of 7-15 micron.

The precious metal constituting the final layer comprises gold, silver, platinum, ruthenium, rhodium, palladium, osmium, iridium, and alloys thereof , more preferably gold, silver rhodium and palladium and even more preferably gold and palladium.

The first layer of white bronze can be any white bronze containing Pd. Preferably, and advantageously, the first bronze layer consists of a white bronze alloy with variable composition between Sn 25-45%, Zn 0-1 5%, Pd 0.25-10%, Cu as needed to 1 00% but anyway less than 60%, in accordance with what is described in the patent application PCT/IB2016/054703. The thickness of the first bronze layer is preferably ranging from 0.5 micron to 1 0 micron, more preferably from 1 micron to 5 micron, even more preferably from 1 .1 micron to 4 micron.

The second bronze layer consists of an alloy according to the present invention, as described above, and preferably has a thickness ranging from 0.1 micron to 3 micron, more preferably from 0.25 micron to 2 micron, even more preferably from 0.35 micron to 1 .5 micron.

The second bronze layer is convenient to have the color as close as possible to the final deposit of the object that determines its appearance. Thanks to the color coordinates of the alloys as described above and to the possibility of modulating them by varying the percentages of Pd, Sn and Zn, it is possible to adapt the coloring of the second bronze layer by virtue of the color of the outer layer.

The thickness of the final precious metal layer depends on the thickness of the underlying bronze deposit object of the invention and on the type of finishing we want to obtain. For high bronze thicknesses and/or for shiny finishing, low thicknesses of precious metal are sufficient, while for low bronze thicknesses and/or finishing that require tumbling on the finished object, greater thicknesses of precious metal are required. The thickness may also depend on the hardness of the final deposit; in general, soft gold deposits (about 100HV) require greater thickness, while harder deposits such as palladium (about 600HV) require smaller thicknesses.

In general, the thicknesses of precious can vary from Flash (lower than 0.05 micron) to 2 micron, more preferably from 0.1 micron to 1 .5 micron even more preferably from 0.1 5 micron to 1 .0 micron.

The present invention will be better understood in the light of the following embodiment examples.

Example 1 (Formulation)

The following electrolyte solution has been prepared:

10 g/l of copper as copper cyanide 5 g/l of zinc as zinc cyanide or zinc oxide

2.0 g/l of palladium as palladium dichloro tetrammine complex

5 ppm of bismuth as bismuth citrate

30 g/l of EDTA

20 g/l of sodium or potassium carbonate

60 g/l of potassium cyanide

5 g/l of potassium hydroxide

100 ppm of sodium laurylphosphate

A 5 x 3.5 cm brass sheet, on which a copper layer had previously been deposited, has been plated with the solution described above at 60°C for 7 minutes at a current of 1 .5 A/dmq.

The deposit thickness is 0.75 micron.

By placing a drop of concentrated nitric acid on the deposit, a slight brown ring is formed after 1 minute under the drop. The acid takes about 10 minutes to reach the attackable layer of copper.

Under SEM scanning electron microscope, the deposit shows a concentration by weight of palladium in the alloy of 35.4%.

The deposited alloy has the following composition:

Cu 39.9%

Sn 19.6%

Zn 5.1 %

Pd 35.4%

The Lab colorimetric coordinates measured with a KONICA MINOLTA

SENSING CM-700d spectrophotometer are: L = 79.7, a = 3.5, b = 1 1 .6

Example 2 (Formulation)

The following electrolyte solution has been prepared:

18 g/l of copper as copper cyanide

10 g/l of tin such as potassium or sodium stannate

3 g/l of palladium as palladium dichloro tetrammine complex

15ppm of bismuth as bismuth citrate

20 g/l of EDTA 45 g/l of potassium cyanide

15 g/l of potassium hydroxide

150 ppm of sodium laurylphosphate

A 5 x 3.5 cm brass sheet, on which a copper layer had previously been deposited, has been plated with the solution described above at 50°C for 15 minutes at a current of 1 A/dmq.

The deposit thickness is 1 .8 micron.

By placing a drop of concentrated nitric acid on the sheet metal, a brown area is immediately formed where the acid is in contact with the deposit. However, the acid takes about 15 minutes to reach the attackable layer of copper. Under

SEM scanning electron microscope the deposit shows concentration by weight of palladium in the alloy of 26.1 %.

The deposited alloy has the following composition:

Cu 60.2%

Sn 13.7%

Pd 26.1 %

Lab colorimetric coordinates measured with a KONICA MINOLTA SENSING CM-700d spectrophotometer, are: L = 84, a = 4.7, b = 1 6.6

Example 3 (Comparative)

Eleven belt buckles in brass have been galvanized according to a standard galvanic cycle containing nickel with the following galvanic layers:

The objects were then subjected to the following tests after having carried out as pre-treatment the wear test TURBULA ISO 23160: 201 1 both at 3 and at 30 minutes: Table 1

The objects pass all the tests to which they have been submitted.

In addition, the TURBULA wear test used as pretreatment showed no significant color change due to wear of the objects at neither 3 minutes nor at 30 minutes. On the eleventh buckle the wear test has been pushed up to 120 minutes obtaining a marked rediscovery of the deposit especially on the edges of the piece with evident color difference between the yellow of the gold and the white of the nickel.

Example 4 (Comparative)

Eleven belt buckles made of brass like those used in example 1 , have been galvanized with the following galvanic layers:

The objects have been then subjected to the tests reported in Tablella 1 after having carried out as pre-treatment the wear test TURBULA ISO 23160: 201 1 both at 3 and at 30 minutes. The objects only pass the Thioacetamide test with Turbula pretreatment 3 minutes and none of the other tests to which they have been subjected.

The TURBULA wear test used as pretreatment showed no significant color change due to wear of objects at neither 3 minutes nor at 30 minutes. On the eleventh buckle the wear test has been pushed up to 1 20 minutes obtaining a marked rediscovery of the deposit especially on the edges of the piece with evident color difference between the yellow of the gold and the white of the white bronze.

Example 5 (Comparative)

Eleven belt buckles made of brass like those used in example 1 have been galvanized with the following galvanic layers:

The objects have been then subjected to the tests of Table 1 after having carried out as pre-treatment the wear test TURBULA ISO 23160: 201 1 both at 3 and at 30 minutes.

The objects do not pass any of the tests they have been subjected to.

The TURBULA wear test used as pretreatment showed no significant color change due to wear of objects at neither 3 minutes nor at 30 minutes. On the eleventh buckle the wear test has been pushed up to 1 20 minutes anyway maintaining the color unaltered thanks to the presence of the yellow bronze under the deposit of gold.

Example 6 (Comparative)

Eleven belt buckles made of brass like those used in example 1 have been galvanized with the following galvanic layers: Composition Thicknes s (micron)

Base material Brass

Preparatory layer Polished Copper 8

First coating Yellow Bronze 1 .0

ternary alloy copper 75%, tin 20%, zinc

5% not containing palladium

Second coating White bronze 2.0

alloy containing palladium copper 53%,

tin 35%, zinc 10%, palladium 2%

External coating Gold L=87, a=4.5, b=25.5 0.5

(Louis Vuitton icon color)

The objects have been then subjected to the tests of Table 1 after having carried out as pre-treatment the wear test TURBULA ISO 23160:201 1 both at 3 and at 30 minutes:

The objects pass tests of Oxidation Sulfur Dioxide, Thioacetamide, Wet Heat with wear pre-treatment with Turbula 3 minutes while they do not pass SO2/NOX OXIDATION and wet heat with leather under UNI ISO 461 1 : 201 1 with wear pretreatment with Turbula 3 minutes neither all tests after a wear pretreatment of 30 minutes.

The TURBULA wear test used as pretreatment showed no significant color change due to wear of objects at neither 3 minutes nor at 30 minutes. On the eleventh buckle the wear test has been pushed up to 1 20 minutes obtaining a marked rediscovery of the deposit especially on the edges of the piece with evident color difference between the yellow of the gold and the white of the white bronze below.

Example 7 (Comparative)

Eleven belt buckles made of brass like those used in example 1 , have been galvanized with the following galvanic layers: Composition Thicknes s (micron)

Base material Brass

Preparatory layer Polished copper 1 1

First coating Yellow bronze 1 .2

ternary alloy copper 75%, tin 25%, zinc

5% not containing palladium

Second coating White bronze 2.0

alloy containing palladium copper 53%,

tin 35%, zinc 10%, palladium 2%

Third coating Palladium 1 .0

External coating Gold L=87, a=4.5, b=25.5 0.5

(Louis Vuitton icon color)

The objects pass all the tests after the pretreatment of wear at 3 minutes while for those with pretreatment of wear with Turbula at 30 minutes pass only oxidation sulfur dioxide, thioacetamide, wet heat.

The TURBULA wear test used as pretreatment showed no significant color change due to wear of objects at neither 3 minutes nor at 30 minutes. On the eleventh buckle the wear test has been pushed up to 1 20 minutes obtaining a marked rediscovery of the deposit especially on the edges of the piece with evident color difference between the yellow of the gold and the white of the palladium.

Example 8

Base material Brass

Preparatory layer Polished copper 10

First coating White bronze 2.0

alloy containing palladium copper 53%,

tin 35%, zinc 10%, palladium 2%

Second coating Yellow bronze subject of the invention 0.5

of coordinates L=84, a=4.5, b= 16.5

copper 55%, tin 15%, palladium 27%,

zinc 4%

External coating Gold L=87, a=4.5, b=25.5 0.2

(Louis Vuitton icon color)

The objects pass all the tests after the wear pretreatment at 3 minutes while for those with wear pretreatment with Turbula at 30 minutes pass only oxidation sulfur dioxide, thioacetamide, wet heat.

The TURBULA wear test used as pretreatment showed no significant color change due to wear of objects at neither 3 minutes nor at 30 minutes. On the eleventh buckle the wear test has been pushed up to 1 20 minutes anyway maintaining the color unaltered thanks to the presence of the yellow bronze subject of this invention under the gold deposit.

Example 9

Composition Thicknes s (micron)

Base material Brass

Preparatory layer Polished copper 12

First coating White bronze 2.0

alloy containing palladium copper 53%,

tin 35%, zinc 10%, palladium 2%

Second coating Yellow bronze subject of the invention 1 .0

of coordinates L=84, a=3.3, b= 14.8

copper 60%, tin 10%, palladium 30%

External coating Gold L=87, a=4.5, b=25.5 0.2

(Louis Vuitton icon color) The objects have been then subjected to the tests of Table 1 after having carried out as pre-treatment the wear test TURBULA ISO 23160:201 1 both at 3 and at 30 minutes:

The objects pass all tests after the wear pretreatment both at 3 minutes and those at 30 minutes.

The TURBULA wear test used as pretreatment showed no significant color change due to wear of objects at neither 3 minutes nor at 30 minutes. On the eleventh buckle the wear test has been pushed up to 120 minutes anyway maintaining the color unaltered thanks to the presence of the yellow bronze subject of the present invention under the gold deposit.

Example 10

The objects pass all tests after both the wear pretreatment both at 3 minutes and those at 30 minutes.

The TURBULA wear test used as pretreatment showed no significant color change due to wear of objects at neither 3 minutes nor at 30 minutes. On the eleventh buckle the wear test has been pushed up to 1 20 minutes anyway maintaining the color unaltered thanks to the presence of the pale pink deposit of the pink bronze alloy subject of the present invention under the light gold deposit. Example 1 1

The objects pass all tests after both the pretreatment of wear both at 3 minutes and those at 30 minutes. The most oxidative tests such as wet heat with skin and oxidation SO2/NOX slightly alter the color of the gold by reddening it.

The TURBULA wear test used as pretreatment showed no significant color change due to wear of objects at neither 3 minutes nor at 30 minutes. On the eleventh buckle the wear test has been pushed up to 1 20 minutes anyway maintaining the color unaltered thanks to the presence of the pale pink deposit of the bronze rose alloy subject of the present invention under the light gold deposit.

Example 12

Base material Brass

Preparatory layer Polished copper 10

First coating White bronze 2.0

alloy containing palladium copper 53%,

tin 35%, zinc 10%, palladium 2%

Second coating Pink bronze subject of the invention of 1 .0

coordinates L=80, a=3.0, b= 1 1 .5

copper 39%, tin 20%, palladium 38%,

zinc 3%

External coating Gold L=87, a=4.5, b=25.5 0.2

(Louis Vuitton icon color)

The objects pass all tests after the wear pretreatment both at 3 and at 30 minutes.

The TURBULA wear test used as pretreatment, showed no significant color change due to wear of objects at 3 minutes, while at 30 minutes and even more markedly on the eleventh buckle on which the wear test has been continued up to 120 minutes, it is highlighted a rediscovery of the deposit located mainly on the edges of the piece with a difference in color between the yellow of the gold and the pale pink of the pink bronze alloy subject of the present invention. Example 13

Composition Thicknes s (micron)

Base material Brass

Preparatory layer Polished copper 10

First coating White bronze 2.0

alloy containing palladium copper 53%,

tin 35%, zinc 10%, palladium 2%

Second coating Pink bronze subject of the invention of 1 .0

coordinates L=80, a=3.0, b= 13.0

copper 42%, tin 19%, palladium 35%,

zinc 4%

External coating Gold L=87, a=4.5, b=25.5 0.5

(Louis Vuitton icon color)

The objects have been then subjected to the following tests after having carried out as pre-treatment the TURBULA ISO 23160:201 1 wear test at both 3 and 30 minutes:

The TURBULA wear test used as pretreatment showed no significant color change due to wear of objects at neither 3 minutes nor at 30 minutes. On the eleventh buckle the wear test has been pushed up to 120 minutes obtaining a marked rediscovery of the deposit especially on the edges of the piece with evident color difference between the yellow of the gold and the pale pink of the pink bronze alloy subject of the present invention.

Below is the table 2 recapitulatory of the results of the examples 3-13 described above:

EXAMPLE 14 (Scale-up)

A galvanic bath, formulated as in Example 1 , having a volume of 200 liters has been used to perform a scale-up from the laboratory volumes (0.5-1 liter) to the classic production volumes for the type of application for which the bath was studied.

24 belt buckles, with a unit surface area of 0.7dm², they have been assembled on two rod frames with pliers discs and locked on the bridge by the frame pliers contacts. The two frames have been galvanized simultaneously according to the following galvanic cycle:

For the electroplating of the first white bronze coating a galvanic bath it has been used, as described in PCT/IB2016/054703, having the following composition: 8 g/l of copper as copper cyanide

16 g/l of tin such as potassium or sodium stannate

2 g/l of zinc as zinc cyanide or zinc oxide

0.025 g/l of palladium as palladium dichloro tetrammine complex

20 g/l of EDTA

10 g/l of sodium or potassium carbonate

50 g/l of potassium cyanide

10 g/l of potassium hydroxide

100 ppm of sodium laurylphosphate

The galvanic bath object of the invention (that for the electroplating of the pink bronze alloy according to the present invention) has been heated to 60°C and the two frames have been galvanized simultaneously by applying a current of 18A corresponding to about 1 A/dm² ( 2.3V average) for a time equal to 16 minutes.

At the end of the galvanic cycle the buckles have been dried and have been divided according to their position on the frame. Since the two frames are the same and loaded with the same number of buckles, we have that each disc of the four that make up each frame contains 4 positions of pliers, so starting from the top we have 4 buckles per frame then 8 buckles that have been subjected to very similar conditions. In particular, taking into account the potential drop on the frame and the tip effect of the electric charge we can divide the 24 buckles into 3 groups of 8 divided as follows:

• 8 buckles in areas of low current density

• 8 buckles in areas of medium current density

• 8 buckles in areas of high current density

A buckle in each group has been subjected to metallographic cut for thickness analysis and quantitative and qualitative elemental analysis by SEM Carl Zeiss' EVO MA10 scanning electron microscope with a lanthanum hexaboride filament.

The results are shown in the tables below:

Low current density

Composition Thicknes s (micron)

Base material Brass

Preparatory layer Polished copper 7.5

First coating White bronze 1 .8

alloy containing palladium copper

50.3%, tin 34.6%, zinc 13.48%,

palladium 1 .62%

Second coating Pink bronze subject of the invention 0.9

copper 46.9%, tin 17.1 %, palladium

30.9%, zinc 5.1 %

of coordinates L=80, a=3.1 , b= 1 0.9

External coating Gold L=87, a=2.1 , b=13.7 0.17

(Gucci icon color) Medium current density

High current density

For each group of buckles, 5 have been chosen and have been subjected to the test in Table 1 after having carried out the TURBULA ISO 231 60: 201 1 wear test at 30 minutes as a pre-treatment:

The objects pass all the tests to which they have been submitted.

Furthermore, the TURBULA wear test used as pre-treatment showed no significant color change due to wear on objects.

Claims

1 . An electroplated copper/tin alloy comprising

Sn 10-25%

Pd 10-45%

Zn 0-10%

Cu as needed to 100%

wherein the overall concentration of Pd+Sn+Zn is 20-65%; said alloy having colorimetric coordinates: L=78-86, a=3-6, b=8-19; wherein % are by weight calculated on the total weight of the alloy; said alloy optionally comprising brighteners and grain finishers commonly used for this including trace metals selected from bismuth, tellurium, gallium, indium, silver, molybdenum, thallium and antimony.

2. The alloy according to claim 1 , wherein

Sn 15-25%;

Pd 25-45%;

Cu 35-55%;

Zn 0-10%;

wherein Sn+Pd+Zn is at most 65%; said alloy having colorimetric coordinates: L=78-82, a=3-5, b=8-12.

3. The alloy according to claim 2, wherein

Sn 15-22%;

Pd 28-40%;

Cu 36-51 %;

Zn 0-7%.

4. The alloy according to claim 1 , wherein

Sn 10-20%;

Pd 10-35%;

Cu as needed to 100 but still greater than 55%;

Zn 0-10%, preferably 0.5-5%;

wherein Sn+ Pd+Zn is at most 45%; said alloy having colorimetric coordinates: L=-80-86, a=3-6, b=12.5-1 9.

5. The alloy according to claim 4, wherein Sn 10-1 7%;

Pd 20-33%;

Cu as needed to 100 but still greater than 55%;

Zn 0-7%.

6. Solutions for electroplating of an alloy according to any one of the claims 1 - 5; said solutions in which the cyanide content is equal to 1 - 100 g/l; the copper content is between 2 and 30 g/l with a copper/cyanide ratio comprised for the pink version between 1 :3 and 1 :12 while for the yellow between 1 : 2 and 1 :7; the tin content is comprised between 2 and 30 g/l; the free hydroxide content is comprised between 0 and 20 g/l; the palladium content is comprised between 0.05 g/l and 8 g/l; the Zn content, if present, is comprised between 0.1 and 10 g/l; the metals indicated above are present in solution as soluble oxides, sulphates, cyanides, ammonium salts and other suitable soluble compounds and the cyanide is in the form of sodium cyanurate, of potassium or derives from the salts of the metals constituting the alloy in the form of cyanurate complexes; said solutions may further comprise one or more complexing agents, surfactants and mixtures of surfactants, brighteners and grain finishers commonly used for this purpose including trace metals such as bismuth, tellurium, gallium, indium, silver, molybdenum, thallium, antimony and organic compounds from the family of the aromatic heterocycles.

7. Galvanized objects wherein at least one deposition consists of an alloy according to any one of claims 1 -5.

8. A galvanized object according to claim 7, comprising or consisting of:

a) a base material;

b) a preparatory layer depending on the base material used, said preparatory layer deposited on the base material;

c) a first coating layer consisting of white bronze containing palladium deposited on the preparatory layer so as to protect the base material and the easily oxidizable underlying layers; said white bronze layer present in nickel-free cycles; d) a second coating layer consisting of bronze containing palladium according to any one of claims 1 -6, whose color is as close as possible to the final deposition of the object that determines the appearance thereof; said second bronze layer deposited on the white bronze layer in nickel-free cycles, or directly on preparatory layer;

e) a final layer, usually consisting of precious metals, which determines the final appearance of the object;

wherein other depositions of a thickness of less than 0.1 micron may be interposed between the various layers.

9. A galvanized object according to any one of claims 7-8, wherein the second bronze layer has a thickness ranging from 0.1 micron to 3 micron.

10. A galvanized object according to any one of claims, 7-9, wherein the first bronze layer consists of a white bronze alloy with variable composition between Sn 25-45%, Zn 0-15%, Pd 0.25-1 0%, Cu as needed to 100% but still less than 60%.

1 1 . A galvanized object according to any one of claims 7-10, wherein the final layer has a thickness ranging from 0.05 micron to 2 micron.