GB2218109A

GB2218109A - Semi-bright plating of ornamental articles

Info

Publication number: GB2218109A
Application number: GB8909435A
Authority: GB
Inventors: Yasuhiko Fujiyu
Original assignee: Citizen Watch Co Ltd
Current assignee: Citizen Watch Co Ltd
Priority date: 1988-04-28
Filing date: 1989-04-25
Publication date: 1989-11-08
Anticipated expiration: 2009-04-25
Also published as: GB2218109B; GB8909435D0; JPH01275796A; CN1020355C; JP2693480B2; KR890016208A; CN1037224A; SG1093G; KR930004560B1; HK27793A

Abstract

A metal-made ornamental article, e.g. a watchcase, of a copper alloy or zinc is provided with a semi-bright surface finish having a relative reflectivity of 4 to 7 [by plating] to give an old-fashioned or antique impression is produced by (a) providing a watchcase base body made of a copper alloy or zinc on the surface thereof with an underplating layer of nickel formed in a first electrolytic bath; and (b) forming a finishing plating layer of a noble metal selected from the group consisting of palladium, rhodium and gold or an alloy of gold on the surface of the underplating layer in a second electrolytic plating bath, either one or both of the first and second electrolytic plating baths containing a brightening agent in a concentration which is about a half of the concentration thereof conventionally used and the total thickness of the underplating layer and the finishing plating layer being in the range from 2 mu m to 5 mu m.

Description

Semi-Bright Watchcåse and t1d for the the-Preparation thereof.

The present invention relates to a metal-made ornamental article such as a watchcase of improved semi-bright surface finish and a method for the preparation thereof.

In the prior art, it is usual that the surface of a metal made ornamental article such as a watchcase or an accessory thereof, e.g. a watchstrap, is finished by providing one or more plating layers with the object of imparting increased decorativeness and resistance to atmospheric influences.When a bright silvery surface finish with brilliant lustre is desired of a watchcase, a watchcase body for example (referred to hereinafter as the substrate) made of brass or stainless steel is first provided with a plating layer of nickel and then with a plating layer of palladium. When a bright golden finish with brilliant lustre is desired, a watchcase body made of brass is first provided with a plating layer of nickel and then with a plating layer of an alloy mainly composed of gold.

In contrast to the aboveimentioned bright surface finishing with a noble metal, it is a trend of fashion in recent years that some people prefer watchcases end watchstraps with a dull-finished or semi-bright surface capable of giving an old-fashioned or antique impression or looking like a wo m vout surface of stainless steel or gold after many years of use.It is almost impossible to obtain such a seni-bright surface finish by a conventional plating method so that according to one usual method the surface of the base body of a watchcase is subjected to a honing treatment to impart a deliberately unevenly roughened surface, before the surface is provided with an underplating layer of nickel and a finishing plating layer of palladium or of an alloy of gold.

This method of uneven honing, however, is not wholly satisfactory from the aesthetic point of view due to the appearance of the honed marks on the surface and is unable to reproduce the somewhat dull surface of stainless steel or gold which may be obtained when innumerable scratches are formed at random on a Fm-out surface.

It has also been proposed to apply the uneven honing treatment to a surface with an underplating layer of nickel but this method is economically unacceptable because the thickness of the underplating layer must at least be doubled, since otherwise the underplating layer is readily destroyed by the honing treatment.

The inventors have continued extensive investigations to provide a watchcase and accessories thereof having a surface finished to give an old-fashioned or antique impression of a high aesthetic value to surpass conventional bright finishing and have arrived at a discovery on the basis of which the present invention has been completed.

Thus, the semi-bright metalnade ornamental article according to the invention comprises: (a) a base body of the article as a substrate made of a copper alloy or zinc, optionally having a corrosion-resistant plating layer; (b) an underplating layer of nickel formed on the surface of the substrate; and (c) a finishing plating layer of a noble metal selected from the group consisting of palladium, rhodium and gold or an alloy of gold formed on the surface of the underplating layer, the total thickness of the underplating layer and the finishing plating layer being in the range from 2 pm to 5 pm and the relative reflectivity of the surface of the finishing plating layer being in the range from 4 to 7.

Such a controlled surface condition of the plating layer can be obtained by a method in which the underplating layer and the finishing plating layer are formed each by a wet-process plating procedure in a plating bath and either one or both of the plating -baths in the wet-process plating procedure for the underplating and finishing platings contain a brightening agent in an amount which is about a half 6f the amount conventionally in use.

The base body of the watchcase or the like as the substrate is necessarily made of a copper alloy, such as brass, nickel silver or the like, or zinc. Optionally the substrate surface of zinc is provided with a corrosion-resistant plating layer of, for example, copper and/or nickel. The substrate surface, with or without the corrosion-resistant plating layer, is first provided with an under-plating layer of nickel and then with a finishing plating layer of a noble metal which may be palladium, rhodium, gold or an alloy of gold. Optionally t > n or trore plating layers of different noble metals are formed to provide together a finishing plating layer. These noble metals can be of a c3nuenticnal grade used in plating treatment.

The thickness of the plating layers is an important factor for achieving the object of the invention. Namely, the total thickness of the underplating layer and the finishing plating layer must be in the range from 2 pm to 5 pm. This limitation must be observed even when the finishing plating layer is formed of tWD or irore plating layers of different noble metals. When the total thickness of the plating layers is outside this range, the appearance of the plated surface may not satisfy the require brent for the semi-bright surface condition as desired.

Various mDdifications are possible in the actual procedures for forming the plating layers. When semi-bright silvery finishing is desired, for example, a brassinade substrate may be first provided with a semi-bright plating layer of nickel and then with a bright plating layer or palladium. When semi-bright golden finishing is desired, on the other hand, a brass-made substrate may be first provided with a dull-surface plating layer of nickel and then with a bright plating layer of a gold alloy as the finishing plating layer. Alternatively, the finishing plating layer in this case may be composed of a bright palladium plating layer and a bright gold plating layer thereon. In short, it is not always necessary that all of the plating layers have a semi-bright surface. The semi-bright surface plating layer of nickel here inplied is a plating layer obtained by a wet-process plating process in which the plating bath contains a brightening agent in an amount which is about a half of the amount conven- tionally used for forming a bright plating layer.

The brightening agents usable in the process according to the invention include primary brightening agents such as a compound having a -C-S02- linkage, e.g. saccharin, sodium 1,5-naphthalene disulphonate, 1,3,6 -naphthal ene trisulphonate and the like, and secondary brightening agents such as coumarine, 2-butyne, 2-butyn-1,4-diol, ethylene cyanhydrin., thiourea, guinoline, pyridine and the like.

When the finishing plating layer of a noble metal is desired to have a semi-bright surface, the amount of the brightening agents added to this plating bath also should be about a half of that added to a plating bath for forming a bright plating layer of the same noble metal.

According to the invention the total thickness of the underplating layer and the finishing plating layer is controlled in a range from 2 um to 5 pm and the wet-process plating procedure is conducted in a plating bath containing a controlled arrpunt of a brightening agent so as to limit the relative reflectivity of the finished surface to a value in the range from 4 to 7.The relative reflectivity here implied is a value obtained from a goniophoto- metric curve for the light incident at the plated surface with an angle of 60 and regularly reflected by the measurement with an automatic goniopDbometer such as that manufactured by Murakami Shikisai Gijutsu Kenkyusho. ab. Semi-bright plated surfaces of watchcases after a honing treatment usually have a relative reflectivity of 9 or larger as measured with the same instrument.

In this regard, the relative reflectivity of 4 to 7 according to the invention is unique.

The accompanying Figures la, ib and ic each illustrate a goniophotometric curve obtained with a goniophotoitter model GP 1HR for the surfaces obtained in the following Examples 1, 2 and 3, raspectively, of the invention while Figure id, the peak head of which reaches the measurement ceiling, is for a conventional bright-plated surface described for comparative purposes in Example 1. These figures clearly show the matt or semi-bright condition of the surfaces according to the invention, which give an Impression of high-class goods with reduced brightness.When the relative reflectivity of the plated surface is controlled within a range of 4 to 7 and the total thickness of the plating layers is controlled within a relatively narrow range, the light passing through one layer is subject to interference with the light passing through another layer to give a high aesthetic value of an old-fashioned or antique impression of the watchcase which could not be obtained by the prior art products and processes.

The invention is further described in greater detail by means of the following non-limiting Examples.

Example 1.

A brass-made base body of a watchcase was first provided with a dull-surface plating layer of nickel having a thickness of 3 by an electrolytic plating method in a plating bath at a temperature of 40 to 550C with a current density of 2 to 10 A/dm2 on the cathode.The fonrulation of the plating bath, which had a pH of 3.5 to 4.5, was as follows: Nickel sulphate 250 g/litre Nickel chloride 45 g/litre Boric acid 40 g/litre Sodium 1,5-naphthalene disulphonate 5 g/litre 1,4 -Butyndiol 0.1 g/litre Formalin 1.2 g/litre The thus-formed underplating layer of nickel was further provided thereon with a bright finishing plating layer of palladium having a thickness of 2 pin by an electrolytic plating method in a plating bath at a temperature of 25 to 350C with a current density of 0.2 to 1.5 A/dm2 on the cathode.The formulation of the plating bath, which has a pH of 8.5 to 9.5, was as follows: Palladium chloride 5 g/litre Nickel chloride 30 g/litre Ammonium chloride 50 g/litre Brightening agent 3-5 g/litre The brightening agent was a corrrrerical product sold under the trade name of Eugilite No. 61 manufactured by Ebara Eugilite Co. of which the principal ingredient was O-hydrDxy coumaric anhydride.

For comparison, the same plating procedures as above were Undertaken except that the underplating of nickel was performed using a conventional plating bath for a bright nickel plating.

The relative reflectivity of the surface of the thus-finished watchcase was at least 9 and no semi-bright surface could be obtained.

Example 2.

A brass-made base body of a watchcase was first provided with a bright plating layer of nickel having a thickness of I jin by an electrolytic plating method in a plating bath at a temperature of 50 to 700C with a current density of 0.5 to 6 A/dm2 on the cathode. The e formulation of the plating bath, which had a pH of 4 to 4.5, was as follows: Nickel sulphate 280 g/litre Nickel chloride 40 g/litre Boric acid 40 g/litre Brightening agent 3 g/litre Pit inhibitor 5 g/litre The brightening agent used above was the same as in the plating bath for palladium plating in Example 1.

Thereafter, the nickel-plated substrate was provided with a dull-surface plating layer of palladium having a thickness of 2 pm by an electrolytic plating method in a plating bath at a temperature of 25 to 350C with a current density of 0.2 to 1.5 A/dm2 on the cathode. The formulation of the plating bath, which had a pH of 8.5 to 9.5, was as follows. The brightening agent was the same one as used in the nickel plating.

Palladium chloride 8 g/litre Nickel chloride 40 g/litre Ammonium chloride 8.8 g/litre Brightening agent 1.2 g/litre Further, the thus palladium-plated surface was provided with a bright plating layer of a gold alloy having a thickness of 1 pm by an electrolytic plating method in a plating bath at a temperature of 45 to 500C with a current density of 0.2 to 1.0 A/dm2 on the cathode. The formulation of the plating bath, which had a pH of 9 to 9.5, was as follows: Sodium gold sulphide 0.5 litre Palladium (as metal) 3.0 g/litre EDr-zn 1.0 g/litre Arsenious acid 1.0 g/litre EDTA-2Na 100 g/litre EXample 3.

A zinc made watchcase was first provided with a corrosionresistant plating composed of a layer of copper of a bright surface having a thickness of 15 to 20 pm and a layer of nickel of bright surface having a thickness of 10 to 15 jin. The copper plating was performed in a plating bath of the formulation shown below at a -temperature of 500C with a current density of 0.5 to 5 A/dm2 on the cathode while the nickel plating was performed using the same plating bath and under the same conditions as in the bright nickel plating in Example 2.

Copper sulphate 200 g/litre Sulphuric acid 50 g/litre Phenol 1 g/litre Thiourea 0.01 g/litre Dextran 0.01 litre In the next place, a dull-surface plating layer of nickel having a thickness of 2 m was provided on the abovedescribed corrosion-resistant plating layer using the same plating bath and under the same conditions as in Example 1. Finally, a bright-surface palladium plating layer having a thickness of 2 was formed on the underplating layer of nickel using the same plating bath and under the same conditions as in Example 1. The thus-finished palladiumplated silvery surface had a relative reflectivity of 6.4.

When the aboveementioned bright-surface palladium plating was omitted and, instead, a bright-surface gold-alloy finishing plating was performed using the same plating bath and under the same conditions as in Example 2, a watchcase having a semi-bright golden surface could be obtained.

Claims

AI

1. A semi-bright mefalxmade ornamental article which comprises: ~(a) a base body of the article as a substrate made of a copper alloy or zinc; (b) an underplating layer of nickel formed on the surface of the substrate; and (c) a finishing plating layer of a noble metal selected from the group consisting of palladium, rhodium and gold or an alloy of gold formed on the surface of the underplating layer, the total thickness of the underplating layer and the finishing plating layer being in the range from 2 pm to 5 trim and the relative reflectivity of the surface of the finishing plating layer being in the range from 4 to 7.

2. A method for the preparation of a semi-bright metal-made ornamental article of which the relative reflectivity of the surface is in the range from 4 to 7, which method comprises the steps of: (a) providing a base body of the article made of a copper alloy or zinc on the surface thereof with an underplating layer of nickel formed in a first electrolytic bath; and (b) forming a finishing plating layer of a noble metal selected from the group consisting of palladium, rhodium and gold or an alloy of gold on the surface cf the underplating laier in a second electrolytic plating bath, either one or both of the first and second electrolytic plating baths containing a brightening agent in a concentration which is about a half of the concentration thereof conventionally in use and the total thickness of the underplating layer and the finishing plating layer being in the range from 2 ym to 5 pm.

3. A method for the preparation of a semi-bright metalemade ornamental article, said method being as claimed in claim 2 and substantially as hereinbefore described in any of the foregoing Examples.

4. A semi-bright netalinade ornamental article when made by a method as claimed in claim 2 or claim 3.