GB2173218A - A metal-made article for personal ornament having coloured surface - Google Patents

Abstract

A coloured, strongly corrosion-resistant personal ornamental article of a copper alloy-made substrate body is prepared by providing the substrate surface with a triple coating composed of a first plating layer of nickel, then an intermediate plating layer of an alloy of palladium and nickel in a specific weight proportion and finally a coloured finish layer of a nitride, carbide or oxide selected from titanium, tantalum, zirconium, hafnium, chromium, molybdenum, niobium and vanadium.

Description

SPECIFICATION A Metal-made Article for Personal Ornament Having Coloured Surface The present invention relates to a metal-made article for personal ornament having an aesthetically acceptable and durably coloured surface. More particularly, the invention relates to a metal-made article of a copper alloy for personal ornament having a coloured surface by providing a multi-layered plating formed by utilizing the techniques of ion plating or sputtering.

As is known, various kinds of metal-made articles of copper alloys for personal ornament use are provided with a coloured surface with an object to increase the aesthetic value thereof. For example, an article of a copper alloy is first provided with an underlying plating layer of nickel followed by a treatment of ion plating to form an overcoating layer of titanium nitride. An improvement for the above mentioned nickel- and titanium nitride-plated article of a copper alloy is proposed in Japanese Patent Kokai 60-70171, according to which an ornamental article of a copper alloy is first plated with nickel as an undercoating layer on which an intermediate plating layer is formed of palladium or rhodium and finally an overcoating finish layer of titanium nitride is formed bythe method of ion plating or sputtering.

When comparison is made between an ornamental article of a copper-based alloy by the above described coating method of ion plating or sputtering to form a coloured layer of titanium nitride on the undercoating layer of nickel and a gold-plated article by the traditional plating method, the former is inferior to the latter in the following respects. Namely, the former article provided with the bilayer plating of nickel and titanium nitride cannot have sufficient corrosion resistance and durability of colour since the coloured layer of titanium nitride is usually so thin that no sufficient protection is provided to the underlying nickel layer which is not free from pin holes susceptible to corrosion therethrough unless the nickel layer has a thickness of 10 um or larger.Such a large thickness of the nickel plating to achieve corrosion resistance is necessarily accompanied by a problem in the appearance of finished articles since the aesthetic value of decorative delicate patterns formed on the base article is greatly reduced with obscureness and dullness by the thick plating layer of nickel so that the method of increased thickness of the nickel layer cannot be applied to articles of high precision works.

The above mentioned improvement by forming an intermediate layer of palladium or rhodium to provide a triply plated coating is indeed advantageous in respect of the corrosion resistance when the intermediate layer has a considerably large thickness in comparison with the doubly plated coating of nickel and titanium nitride. Ornamental articles triply plated with nickel, palladium or rhodium and titanium nitride, however, are not without problems and disadvantages to be improved. For example, the corrosion resistance of the article is still not quite satisfactory, in particular, when the thickness of the intermediate layer is small. In addition, palladium metal, in particular, has a relatively low hardness of, for example, 300 to 400 HV so that the article is not free from a problem in the abrasion resistance required for articles of exterior ornament.The plating layer of palladium or rhodium is not sufficiently resistant against galvanic corrosion due to the large potential difference thereof from nickel. Moreover, the rate of electrolytic deposition of the plating layer of palladium or rhodium is relatively low and deposition of a palladium layer of 1 pm thickness usually takes 7 to 10 minutes so that the intermediate layer of palladium or rhodium is disadvantageous in respect of productivity even by setting aside the expensiveness of palladium or, in particular, rhodium.

We have now found it possible to provide a copper alloy-made personal ornamental article provided with a coloured coating having high corrosion resistance equatable with that of gold plating without the above described problems and disadvantages in the prior art articles finished by ion plating or sputtering to form a layer of titanium nitride or other coloured finishing layer.

Thus, the personal ornamental article of the present invention provided with a coloured coating thereon comprises: (a) a substrate made of a copper alloy; (b) a first plating layer of nickel formed on the substrate and having a thickness in the range, preferably, from 1 to 10 pm; (c) an intermediate plating layer of an alloy of nickel and palladium in a weight proportion of palladium to nickel in the range from 50:50 to 90:10 or, preferably, from 55:45 to 65::35 formed on the first layer of nickel and having a thickness in the range, preferably, from 0.5 to 5 pm; and (d) a finish layer of a nitride, carbide or oxide of a metal or a mixture thereof having a thickness in the range, preferably, from 0.1 to 2.0 lim formed on the intermediate layer of nickel-palladium alloy by the method of ion plating or sputtering, the metal being selected from the group consisting of titanium, tantalum, zirconium, chromium, hafnium, molybdenum, niobium and vanadium.

As is understood from the above given summarizing description, the personal ornamental article of the invention has a triple-layered coating on the surface composed of a first layer of nickel, an intermediate layer of a nickel-palladium alloy and a finish layer of the above mentioned nitride, carbide and/or oxide of a metal such us titanium nitride. The most characteristic feature of the invention is in the intermediate layer which is, different from the conver,;ional intermediate plating layer of palladium or rhodium alone, made of an alloy of nickel and palladium in a specific alloying proportion.

By virtue of this unique feature in the coating, the ornamental article of the invention has several advantages over conventional ones including the high abrasion resistance suitable as an exterior ornament with only a tenth or less of wearing in comparison with the articles provided with an intermediate layer of palladium alone as a result of the high hardness of the nickel-palladium alloy in the range from 500 to 600 HV, high resistance against galvanic corrosion as a result of the proximity in the potential difference, outstandingly high rate of electrolytic deposition of the alloy taking, usually, only 4 minutes for the deposition of a 1 pm thick layer.

The figure in the accompanying drawing schematically illustrates a partial cross section of the inventive article as cut perpendicularly to the surface, in which the substrate body 1 of the ornamental article made of a copper alloy is coated with a first plating layer 2 of nickel, then an intermediate layer 3 of an alloy of palladium and nickel and finally a finish layer 4 of a nitride, carbide and/or oxide of the above specified metal or a mixture thereof, each layer preferably having a specified thickness.

The substrate body of the inventive ornamental article should be made of a copper alloy although any body made of other materials can be used provided that a substrate base coating or plating layer of a copper alloy is formed beforehand on the surface. The copper alloy here implied is not particularly limitative and includes brass, bronze, German silver and the like provided that the major constituent thereof is copper.

The substrate body of copper alloy is pretreated in a conventional manner by washing with an organic solvent, e.g. trichloroethylene, degreasing with an alkali and neutralization with an acid followed by thorough rinse with water prior to nickel plating. The nickel plating is performed, preferably, eiectrolytically according to a known procedure. The formulation of the electrolytic plating bath and the electrolytic conditions are well known in the art. Following are the typical bath formulation and electrolytic conditions used in an example.

Electrolytic Plating Bath: Nickel sulphate 250 g/litre Nickel chloride 50 g/litre Boric acid 40 g/litre Non-leveling agent (Hi-nickel i200, a trade name by Shimizu Shoji Co.) 15 ml/litre Electrolytic Conditions: Current density 5Aldm2 Bath temperature 45"C Length oftime 3 minutes When the electrolytic nickel plating is performed in the plating bath and under the conditions specified above, a nickel plating layer having a thickness of about 3 pm is obtained although the thickness thereof can be in the range from 1 to 10 pm. When the thickness of the nickel plating is smaller than 1 pm, no satisfactory corrosion resistance can be obtained while a nickel plating layer having a thickness larger than 10 lim is undesirable in respect of the decreased productivity and loss of decorativeness in fine and delicately designed patterns.

When the first electrolytic plating procedure is completed in the above described manner, the nickel-plated substrate body is thoroughly rinsed with water and transferred into a second electrolytic plating bath for the intermediate layer of a palladium-nickel alloy. Typical formulation of the electrolytic bath and the electrolytic conditions are as follows.

Electrolytic Plating Bath: Palladium ammine complex (as Pd) 8 g/litre Nickel chloride (as Ni) 8 g/litre Ammonium chloride 100 g/litre Brightening agents (Udylites 610, 62 and 63, trade names) each 1-20 ml/litre pH 7.8 Electrolytic Conditions: Current density 1.0 A/dm2 Bath temperature room temperature Length of time 12 minutes When the electrolytic plating is performed in the bath and under the conditions specified above, a coating layer of a palladium-nickel alloy composed of about 80% by weight of palladium and about 20% by weight of nickel having a thickness of about 3 pn ì is formed on the surface of the underlying nickel plating although the alloy composition and the thickness of the plating layer are not particularly limited to the above.For example, the thickness of the palladium-nickel alloy should be in the range from 0.5 to 5 pm.

When the thickness is smaller than 0.5 pom, no satisfactory corrosion resistance can be obtained while a thickness largerthan 5pm is undesirable mainlyforan economical reason.

The final step to prepare the inventive ornamental article is the ion plating or sputtering to form a coloured finish layer of a nitride, carbide or oxide of a metal or a mixture thereof on the intermediate layer of the palladium-nickel alloy, which can be performed according to a known procedure. In the case of ion plating, for example, the ornamental article after completion of the second electrolytic plating to form the intermediate layer of a palladium-nickel alloy is placed in a bell jar of an apparatus for ion plating and cleaned by ion bombardment in low-pressure argon.Thereafter, a gaseous mixture of argon as an inert carrier gas and, assuming that the desired finish layer is of a metal nitride, nitrogen as a reactive gas is introduced into the bell jar under continuous evacuation to control and maintain the pressure inside at about 2.0x10-3 Torr and an electric power of 3.0 kV is impressed between the electrodes to generate plasma inside the bell jar so that the metal, e.g. titanium, tantalum, niobium and the like, in a boat below is vapourized so as to deposit the metal vapor on the surface of the palladium-nickel alloy layer on the substrate body in the form of the metal nitride. In this manner, a beautiful golden-brig ht yellow finish is obtained on the substrate body when the finish layer is of titanium nitride.The techniques of sputtering are also well known in the art so that no detailed description is given here. The colour can be modified by suitably selecting the kinds of the metal and the reactive gas as is mentioned below.

When the nitrogen as the reactive gas is replaced with a carbon-containing gas such as acetylene, ethylene, methane and the like or an oxygen or oxygen-containing gas, the layer of the finish coating formed by the ion plating can be of a carbide or oxide of the metal having an aesthetically acceptable colour other than golden-bright yellow. It is of course that use of a gaseous mixture of two types of reactive gases may result in the formation of a finish coating made of a mixture of nitride, carbide and oxide by the ion plating or sputtering.

EXAMPLE 1 With an object to make a comparison of the corrosion resistance between the articles according to the invention and those according to conventional methods, brass-made substrate bodies were provided first with a layer of nickel plating having a varied thickness of 1 to 10 pm and then with an intermediate layer of a palladium-nickel alloy having a thickness of 0.5 or 3 um according to the typical bath formulations and electrolytic conditions shown before followed by finishing in an ion plating procedure to form a finish layer of titanium nitride having a thickness of 0.5 pm. Comparative test specimens finished by ion plating to form a titanium nitride layer were prepared by omitting the intermediate layer or by providing an intermediate layer of palladium alone instead of the palladium-nickel alloy. In addition, further comparative specimens were prepared by gold plating according to the GP3 p specification of a 1 pm layer of 18K Au/Ag plus 2 pm layer of 22K Au/Ni on an underlying nickel plating of 3 pm thickness. The number of the test specimens prepared for each combination of the types of the layers and the values of thickness thereof was 100.

The test specimens prepared in the above described manner were subjected to the test of corrosion resistance by dipping in a simulated perspiration according to the specification of ISO 3160/2 7-4 for 24 hours to give the results shown in Table 1 below, in which the corrosion resistance was given by 4 ratings of A, B, C and D according to the number of etched spots on the surface, the grades A and D corresponding to absolute absence of any changes and unacceptably poor corrosion resistance, respectively.

EXAMPLE 2 To make a further comparison, the same experimental procedure as above was repeated except that the finish layeroftitanium nitride was replaced with a layeroftitanium carbide formed by the techniques of ion plating in which the reactive gas was ethylene in place of nitrogen and the gaseous pressure was kept at 3.5x 10-3 Torr and the voltage of the electric power was 7.0 kV. The finished test specimens were each coloured in beautiful grey.The test specimens including those of the present invention and of the prior art as well as the gold-plated ones were subjected to the test of corrosion resistance in the same manner as above to give substantially the same conclusion that the coated ornamental articles according to the invention are much superior to those of the prior art and comparable to those of the gold-plated ones in respect of the corrosion resistance.

TABLE 1 Thickness of Corrosion Resistance, Layers, pm Number of Test Pieces Overall Nickel Plating Intermediate Layer A B C D Evaluation 0.5 (Pd/Ni) 99 1 0 0 Good 1 3(Pd/Ni) 100 0 0 0 Good 3 0.5 (Pd/Ni) 97 3 0 o Good Present invention 3 3 (Pd/Ni) 100 0 0 0 Good 5 0.5 (Pd/Ni) 99 1 0 0 Good 5 3 (Pd/Ni) 100 0 0 0 Good 10 0.5 (Pd/Ni) 99 1 0 0 Good 1 - 77 9 9 5 Poor 3 - 84 8 5 3 Poor 5 - 90 6 3 1 Poor Prior art 10 - 95 4 1 0 Poor 3 0.3 (Pd) 93 .5 5 2 0 Fair 6 0.3 (Pd) 96 3 1 0 Fair Gold 3 3 (GP3,u) 100 0 0 0 Good plating EXAMPLE 3 The nickel plating for the underlying layer and plating of a palladium-nickel alloy as the intermediate layer was performed in substantially the same manner as in Example 1 and a finish layer of a hafnium nitride was provided thereon by placing the substrate article in the bell jar of the ion-plating apparatus and cleaned by ion bombardment in an atmosphere of argon followed by introducing nitrogen gas at a rate of 20 ml/minute to maintain the pressure inside at lx 10-3 Torr and impression of a direct current voltage of 500 V between the substrate and the hafnium metal in a boat placed below while the hafnium metal was evaporated with electron beams.The hafnium nitride layer thus formed had a thickness of about 1.0 m pm and the article was coloured in beautiful blue. The corrosion resistance of the thus treated articles was as good as the articles prepared in Example 1 according to the invention.

EXAMPLE 4 The experimental procedure was substantially the same as in Example 1 except that the finish layer of titanium nitride was formed by the method of sputtering. Thus, the substrate article of a copper alloy provided with the first plating layer of nickel and the intermediate plating layer of the palladium-nickel alloy was placed in a bell jar into which, after ion bombardment of the article in an argon atmosphere, nitrogen gas was introduced at a rate of 20 ml/minute to keep the pressure inside at 5x 10-3 Torr, and a direct current voltage of 500 V was impressed between the article and the titanium metal in a boat below by the direct-current magnetron method. The thus prepared article provided with a finish layer of titanium nitride was golden yellow in colour and the corrosion resistance thereof was as good as those prepared in Example 1 according to the invention.

Claims (4)

1. A coloured personal ornamental article which comprises: (a) a substrate made of a copper alloy; (b) a first plating layer of nickel formed on the surface of the substrate and having a thickness in the range from 1 to 10pom; (c) an intermediate plating layer of an alloy of nickel and palladium in a weight proportion of palladium to nickel in the range from 50:50 to 90:10 formed on the first plating layer of nickel and having a thickness in the range from 0.5 to 5 pm; and (d) a finish layer of a coloured nitride, carbide or oxide of a metal or a mixture thereof having a thickness in the range from 0.1 to 2.0 pm formed on the intermediate plating layer of the palladium-nickel alloy by the method of ion plating or sputtering, the metal being selected from the group consisting of titanium, tantalum, zirconium, chromium, hafnium, molybdenum, niobium and vanadium.

2. The coloured personal ornamental article according to claim 1 wherein the intermediate plating layer is formed of an alloy of palladium and nickel in a weight ratio in the range from 55:45 to 65:35.

3. An article according to claim 1 substantially as herein described.

4. Each and every novel product, process, method, apparatus, feature and combination substantially as herein disclosed.