EP0229665B1

EP0229665B1 - Specular product of golden tone and method for manufacturing same

Info

Publication number: EP0229665B1
Application number: EP19870100414
Authority: EP
Inventors: Ken Matsuda; Teruo Takada
Original assignee: Mitsubishi Kasei Corp
Current assignee: Mitsubishi Kasei Corp
Priority date: 1986-01-14
Filing date: 1987-01-14
Publication date: 1990-11-22
Anticipated expiration: 2007-01-14
Also published as: EP0229665A1; JPH0762274B2; JPS62164893A; DE3766258D1

Description

This invention relates to a specular product of golden tone, and more particularly to a specular product presenting a color of golden tone which is obtained by electroplating and a method for manufacturing the same.
It is widely known in the art that copper-zinc alloy electrodeposits present a color of golden tone. However, the copper-zinc alloy deposit which is generally called brass electrodeposits presents relatively high value of yellowish tone and is easy to discolor.
The present invention has been made in view of the foregoing disadvantage while taking notice of the fact that when copper-zinc-nickel is electrodeposited under the conditions of keeping a metal deposition ratio within a predetermined range, the resultant deposit presents a color of moderate yellowish elegant golden tone and possesses good resistance to discoloration.
Accordingly, it is an object of the present invention to provide a specular product which presents a color of golden tone and possesses good resistance to discoloration.
It is another object of the present invention to provide a method for manufacturing a specular product which presents a color of golden tone and possesses good resistance to discoloration by electroplating. In accordance with the present invention, there is provided a specular product of golden tone having a specular deposit of copper-zinc-nickel alloys electrodeposited on a surface of a metal base, characterized in that the copper-zinc-nickel deposition ratio in said deposit is 70-85:15-25:1-10 by atomic percent and said deposit has a color described by the parameters of L^*=8095, a^*=-5-0 and b*=15-25 as defined by the CIE-1976 (L^*, a^*, b^*) color space indication.
In the terms of Recommendation 2 of the "Supplement No. 2 to CIE Publication No. 15 (E-1.3.1) 1971/(TC-1.3.) 1978", the quantities L^*, a^* and b^* are defined by

L*=116(Y/Y_n)^1/3-16
a*=500((X/X_n)^1/3-(Y/Y_n)^1/3)
b*=200((Y/Y_n)^1/3-(Z/Z_n)^1/3)
XlX_n, YIY_n, Z/Z_n>0.01

In the present invention, the tristimulus values X_n, Y_n and Z_" define the color of the white reflective acryl mirror with Y_n equal to 100.
The method according to the invention is characterized by the specular deposit of copper-zinc-nickel alloys as defined in Claim 1 being prepared from an electroplating bath essentially consisting of (a) water-soluble salts of copper, zinc and nickel, whereby the weight ratio of copper to nickel in the bath is within the range of 100/1-20 based on the metal, (b) hydroxycarboxylic acid or its salt, (c) sodium cyanide or potassium cyanide, and (d) hydroxide of alkaline metal.
A material used for a metal base in the present invention is not limited to any specific metal. The metal base may be formed of any of various metals such as aluminium, aluminium alloy, iron, copper, brass, nickel and the like, as long as electroplating can be carried out thereon. Aluminium or aluminium alloy is particularly suitable for the metal base material. In addition to the elemental metals, a composite material, such as, for example, a laminated board comprising a synthetic resin sheet and a metal sheet bonded onto either one or both surfaces of the synthetic resin sheet can be conveniently used for this purpose.
The specular product of the present invention is obtained by electroplating copper-zinc-nickel alloy deposits on the metal base. The deposits have a Cu:Zn:Ni deposition ratio within the range of 70-85:15-25:1-10 by atomic percent and a color described by the parameters of L^*=80-95, a^*=-5-0 and b*=15-25 as defined by the CIE-1976 (L^*, a^*, b^*) color space indication.
A deposition ratio of the copper-zinc-nickel alloys and its tone correspond to each other when the surface conditions of the metal base to be electroplated such as smoothness and the like are constant. If the deposition ratio is out of the above range, the deposit does present the desired tone. More particularly, if the ratio of zinc is below the above range, the quantity a^* increases and the deposit becomes reddish. To the contrary, if the ratio of zinc is beyond the above range quantity, the b^* decreases and the deposit loses a yellowish tone. If the ratio of nickel is below the above range, the quantity b^* increases and the deposit presents relatively high degree of yellowish tone whereas if the ratio of zinc is over the above range, the deposit of uniform tone is not obtainable due to the occurrence of iregular color, streak or the like.
A bath for electroplating the copper-zinc-nickel alloys on the metal base for use in the production of the specular product of the present invention is not limited to any specific type so long as it provides the desired deposition ratio and tone in the copper-zinc-nickel alloy electrodeposits. As an example of the bath formulation for use in the electrodeposition of copper-zinc-nickel alloys on the metal surface so as to obtain the specular product of golden tone according to the present invention, the following has been found to be highly suitable for use in this invention.

a. water-soluble salts of copper, zinc and nickel, b. hydroxycarboxylic acid or its salt,
c. sodium cyanide or potassium cyanide, and
d. hydroxide of alkaline metal; wherein a weight ratio of copper to nickel in the bath is within a range of 100/1-20 based on the metal. The bath contains water-soluble salts of copper, zinc and nickel as a metal to be electrodeposited. The concentrations of copper, zinc and nickel in the bath are normally 1-8 gil, 0.3-2 g/I and 0.03-3 g/I, respectively. A weight ratio of copper to nickel is within a range of 100/ 1-20, and preferably 100/2-9. The amount of nickel out of this range makes it difficult to give the intended deposition ratio. A weight ratio of copper to zinc is within a range of 100/10-45, and preferably 100/18-36. The weight ratio out of this range makes it difficult to give the intended deposition ratio.

Hydroxycarboxylic acid suitable for use in the present invention includes dihydroxysuccinic acid, monohydroxycarboxylic acid such as malic acid, citric acid or the like, and polyhydroxycar- boxylic acid as well as sodium and potassium salts thereof. Dihydroxysuccinic acid or its salt is highly suitable for use in this invention. The concentration of such an acid in the bath is preferably within a range of 5-80 g/I based on free acid. The concentration below the above range is apt to deteriorate the stability of the bath, whereas the concentration thereabove makes it difficult to obtain the uniform deposit.
The concentration of sodium cyanide or potassium cyanide is preferably within a range of 2-25 g/I based on CN. A weight ratio of copper to cyanogen is preferably within a range of 100/ 60-190. The ratio out of the above range makes it impossible to give the intended deposition ratio.
Hydroxide of alkaline metal is required to keep a pH of the bath at a high level and to provide the bath with conductivity. The hydroxide includes sodium hydroxide, potassium hydroxide and the like. The concentration of the hydroxide in the bath is preferably 10 g/I or more. The concentration of the hydroxide below this level decreases pH and conductivity of the bath and causes various problems.
The operating temperature of the bath should be approximately 20-30°C and the cathode current density range used in the bath should be preferably 0.5-3 A/dm2. When the bath is operated at the lower temperature the deposition velocity copper-zinc-nickel alloys is significantly reduced. When the bath is operated at the higher temperature, the electrodeposits of uniform tone is difficult to obtain. The cathode current density should be maintained in the range of 0.5-3 A/ dm². If it is smaller than 0.5 A/dm², irregular color is apt to occur on the deposit. While, if it is higher than 3 Aldm², a failure in deposition, such as, for example, streak, is generated on the deposit.
In the electroplating, an insoluble electrode such as iron, stainless steel, ferrite or the like is generally used as an anode. Alternatively, copper, zinc, and its alloy may be used as the anode or a part thereof to automatically replenish metal components consumed due to the electrodeposition.
Electroplating for manufacturing of the specular product of the present invention may be carried out in any electrolytic coating process for which the copper-zinc-nickel alloys having the deposition ratio and tone described above can be electrodeposited. A pretreatment for electroplating the copper-zinc-nickel alloys in the present invention may be carried out utilizing any of various conventional coating technique widely used in the art as long as it is suitable for the copper-zinc-nickel electrodeposition. For example, the surface of the metal base is abraded, degreased and rinsed, and then it is subjected to the pretreatment depending upon the metal base, and a single or multiple nickel layers are electrodeposited thereon. In the preferred embodiment of the present invention, a single or multiple bright nickel layers are electroplated on the base metal which is subjected to a suitable pretreatment and then the copper-zinc-nickel alloys are electroplated on the nickel layers. In order to have the electrodeposits provided with better resistance to corrosion and resistance to discoloration, a rust preventive treatment such as a conventional chromate treatment, a painting treatment using a transparent paint, or the like may be applied onto the copper-zinc-nickel alloy electrodeposits.
The following example is given to further illustrate the present invention. It is to be understood, however, that the scope of the invention is not to be limited to the specific example.

Example

A luster-finished aluminium sheet having dimensions of 7 cmx10 cm and a thickness of 1 mm was used as a metal base. On one surface of the aluminum sheet, a non-conductive coating material was applied, and plating treatments were carried out on the other surface according to the following manner.
The surface of the aluminium sheet was first subjected to degreasing, pickling, zinc substitution utilizing the conventional process, and then bright nickel plating. Then, the aluminium sheet was electrolyzed in a bath for use in the electrodeposition of copper-zinc-nickel alloys which has such a formulation described below and subjected to electroplating for 1 minute using a stainless steel anode under the conditions that the bath temperature and cathode current density were set at 25°C and 1.5 A/dm², respectively.
The resulting product had a specular surface of elegant golden tone. As a result of Auger electron analysis, it was found that the copper-zinc-nickel alloy electrodeposit at the central portion of the product had a Cu:Zn:Ni deposition ratio of 75:18:7 by atomic percent. The deposit had a color described by the parameters of L^*=₈₆.0, a^*=-1.5, and b^*=18 as defined by the CIE-1976 (L^*, a^*, b^*) color space indication. These figures were measured by a chromameter CR-100 (Minoruta Camera Co., Ltd.) using a white reflective acryl mirror (L^*=100, a^*=0.0, b^*=0.0) as standard.
The advantages of this invention should be fairly apparent from the disclosure set forth above. However, it should also be clearly apparent that the specular product discovered and disclosed herein is highly advantageous and believed to be commercially significant for the reason that the specular product described herein presents a color of moderate yellowish elegant golden tone and possesses good discoloration properties as compared with the conventional copper-zinc-alloy electrodeposits. Accordingly, it is highly useful in various decorative application. Also, the specular product discovered and disclosed is very easy to produce by the method of the present invention.

Claims

1. A specular product of golden tone having a specular deposit of copper-zinc-nickel alloys electrodeposited on a surface of a metal base, characterized in that the copper-zinc-nickel deposition ratio in said deposit is 70-85:15-25:1-10 by atomic percent and said deposit has a color described by the parameters of L^*=₈₀―₉₅, a^*=-5-0 and b^*=15-25 as defined by the CIE-1976 (L^*, a^*, b^*) color space indication.

2. The specular product as claimed in Claim 1, wherein said metal base is formed from aluminium or aluminium alloy.

3. The specular product as claimed in Claim 1, wherein said metal base is formed of a composite sheet comprising a synthetic resin sheet and a metal sheet bonded to either one or both surfaces of said synthetic resin sheet.

4. The specular product as claimed in Claim 3, wherein said composite sheet comprises a synthetic resin sheet and metal sheets bonded to both surfaces thereof, one of said metal sheets of said composite sheet is provided with said specular deposit of copper-zinc-nickel alloys on the surface thereof, and the other remaining metal sheet is provided with a non-conductive coating layer formed on the surface thereof.

5. The specular product as claimed in Claim 2 or 3, wherein a single or multiple bright nickel layers are electroplated on said metal base and said specular deposit of copper-zinc-nickel alloys are electrodeposited on said nickel deposit.

6. A method of manufacturing the specular product of any of Claims 1 to 5, whereby a specular deposit of copper-zinc-nickel alloys as defined in Claim 1 is prepared from an electroplating bath essentially consisting of (a) water-soluble salts of copper, zinc and nickel, whereby the weight ratio of copper to nickel in said bath is within the range of 100/1-20 based on the metal, (b) hydroxycarboxylic acid or its salt, (c) sodium cyanide or potassium cyanide, and (d) hydroxide of alkaline metal; and the weight ratio of copper to cyanogen being within the range of 100/ 60-190.

7. The method as claimed in Claim 6, wherein the weight ratio of copper to zinc in said bath is within the range of 100/10-45.

8. The method as claimed in Claim 6 or 7, wherein said hydroxycarboxylic acid in said bath is selected from the group consisting of dihydroxysuccinic acid and its salts.