GB2163456A

GB2163456A - Method of forming a coloured hard coating

Info

Publication number: GB2163456A
Application number: GB08517461A
Authority: GB
Inventors: Katsuhiro Okubo
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-07-13
Filing date: 1985-07-10
Publication date: 1986-02-26
Also published as: GB2163456B; KR860001216A; JPS6126769A; GB8517461D0

Abstract

A coloured hard coating for an eye-glass frame, a wrist-watch or the like is formed by depositing a hard transparent coating on a layer of coloured coating by ion-plating. The hard coating may be TiN, TiC, oxides of Al, B, Si, In, Ti, Zr, Ta or other ceramics.

Description

SPECIFICATION Method of forming a coloured hard coating Description This invention relates to a method of forming a coloured hard coating, more particularly to a method of forming a wear-resistant, corrosion-resistant and coloured hard coating comprising a combination of a coloured coating selected from conventional electro-plated colour coatings, chemically coloured coatings and ion-plated colour coatings and a hard coating, which is transparent at least in a thin coating and selected from coatings of titanium nitride, carbide or a mixture thereof, coatings of oxides of aluminium, boron, silicon, indium, titanium, zirconium and tantalum and other ceramic coatings.

A number of products having electro-plated colour coatings or chemically coloured coatings are in increasing demand due to their beautiful and highgrade image. However, such coatings are inferior in their wear-resistance, so that their usage is limited to applications that cause little or no frictional wear. Consequently, a coating for a product, such as an eye-glass frame, a wrist watch or the like subjected to frequent frictional contact must be protected by an additional plastic coating thereon.

Even so the coating remains imperfect in its durability, so that a product of high grade still cannot be obtained.

A method of forming a coloured coating has been developed, in which a highly wear-resistant coloured coating of titanium compound may be formed by an ion-plating technique directly onto a material to be processed. However, such type of coating is poor in colour and brittle in practical use. Further, a practical method of forming a highly wear-resistant coloured coating by a flame spray technique has been developed but still has many problems in that a material to be processed must be resistant to a high temperature and that a surface-grinding treatment must be applied after the flame spraying process. Since the products having coloured coatings have recently been in increased demand, it is desired to develop a practical method of forming a highly wear-resistant coloured coating at a relatively low cost.

The object of the invention is to provide a method of forming a highly wear-resistant and corrosion resistant coloured beautiful coating at a relatively low cost.

According to the invention there is provided a method of forming a coloured hard coating on a substrate, in which a layer of coloured coating is provided thereon with a hard coating, which is transparent at least in a thin coating, in a thickness of 0.0005 to 3y by means of ion-plating.

It has now been found that a coating of oxides of aluminium, boron, silicon, indium, titanium zirconium, tantalum or other ceramic materials by the ion-plating procedure, or a coating of substantially titanium compound by the ion-plating procedure is hard and highly corrosion-resistant and may be used for forming a highly wear-resistant and corrosion-resistant coloured hard coating, when combined with a conventional electro-plated or chemically coloured coating.

Further, it has been found that a combination of the coloured coating selected from electro-plated coloured coatings, ion-plated colour coatings or chemically coloured coatings with a transparent hard coating in a thickness of 0.0005 to 3 > selected from coatings of substantially titanium nitride, titanium carbide or a mixture thereof, coatings of oxides of aluminium, boron, silicon, indium, titanium, zirconium, tantalum or other ceramic materials may provide an excellent wear-resistant and corrosion-resistant coloured coating by means of the ion-plating procedure.

In accordance with the invention the conventional coloured coating is provided on the substrate with the thin, transparent and hard coating in a thickness of 0.0005 to 31l preferably at a temperature of 200 to 500"C by the ion-plating procedure. Thus, the porous coloured coating, such as electro-plated or chemically coloured coating, may be integrated with the transparent hard coating, such as hard oxide compound, to enhance denseness and wear-resistance of the final coating. Furthermore, a thin coating of 0.0005 to 3,uW thickness results in a low cost.A thickness of less than 0.0005 cannot provide a satisfactory effect, while a thickness of more than 3 gives the colour of the hard coating itself to the final coating so that the colour of the prime-coating is masked. A coating of titanium compound alone without the prime coating is weak and poor in wear-resistance.

A thickness of more than 1 E is acceptable, provided that the colour of the prime coating is visible through the outer hard coating. Further, as the substrate, there may be used any metal, such as stainless steel, iron, copper, copper-zinc alloy, aluminium, cadmium, zinc, silver, nickel-chrome alloy and nickel-based alloy.

The invention will now be further described with reference to the following non-limiting Examples.

EXAMPLES Example 1 A wrist watch band of stainless steel (SUS304) was cleansed and then cathodically electrolysed in a solution of 3v/v% sulphuric acid and 15Wlv% citric acid for 2 minutes under a current density of SAl dm2. Then, it was activated, washed and electroplated in a commercially available black chromeplating liquor, CHEMICRON CR (supplied from MURATA Chemicals Co., Limited.) for 10 minutes under a current density of 30A/dm2 to form a coloured coating layer of black chrome plating of 1.2 > thickness.

Thereafter, 300ml/min. of an acetylene gas was passed thereon, while aluminium oxide (A120s) was ion-plated in an ion-plating apparatus (Shinko Seiki Model AIH-16110SB) for 30 minutes under a condition of a gas pressure of 5x103 Torr, an ionizing voltage of 40V and current of 10A, a base voltage of 1.5KV and a base current of 300A to form an aluminium oxide coating of 0.004pew thickness, which did not affect the black colour of the prime chrome-coating.

Then, the coating thus formed was compared with the coating of black chrome-plating alone for their wear-resistance by rubbing them ten times with a force of 10Kg using a commercially available grinding cloth (Silbo Blue from SILBO & CO.) to find out that the chrome coating alone was worn out to expose the stainless steel material, while the coating with additional aluminium oxide coating was not affected by the rubbing test.

Example 2 An eye-glass frame of Cu-Zn-Ni alloy was cleansed, nickel-plated and then subjected to the black chrome plating for 15 minutes under the same condition as in Example 1.

Thus, a black chrome plated layer of 1.5 to 1.7so was obtained. Then, 250ml/min. of an acetylene gas and 40mllmin. of a nitrogen gas were passed thereon, while silicon oxide (SiO2) was ion-plated in the same ion-plating apparatus as in Example 1 for 40 minutes under a condition of a gas pressure of 4x10-3 Torr, an ionizing voltage and current of 35V and 1oA, respectively, as well as a base voltage and current of 1.7KV and 500A, respectively, to form a silicon oxide coating of 0.005 thickness, which did not affect the black colour of the prime chrome-coating.

Then, the coating thus formed was compared with the prime coating alone for their wear-resistance by the same procedure as in Example 1 to find out that the prime coating alone was worn out to expose the nickel plating layer, while the coating with the ion-plated silicon coating was not affected by the rubbing test. Further, the coating thus formed was subjected to a corrosion-resistance test for 168 hours using an artifical sweat, but was not affected thereby.

Example 3 Usual chrome-plating were applied on a stainless steel directly and on Cu-Zn-Ni alloy after nickelplated under the same condition for ion-plating as in Examples 1 and 2. Then, silicon oxide was ionplated thereon to form a silicon oxide coating of the same thickness as in Examples 1 and 2.

The resulting coatings were subjected to the corrosion test to find no deterioration therefrom.

However, the colour was grayish and dull, so that a high grade image could not be observed. In order to provide the high grade image, more amounts of acetylene gas was passed for ion-plating to increase the black colour. In this way, the colour itself was improved similarly to those in Examples 1 and 2, but the wear-resistance and the corrosion-resistance became inferior to those in Examples 1 and 2, as well as the previous grayish coating.

Example 4 A gold-palladium alloy was plated on the same material as in Example 1, and then ion-plated with boron oxide (B2O3) under the same condition as in Example 1 to obtain a coating of beautiful brown colour. The coating of boron oxide had a thickness of 0.00411 and showed very good results in the wear-and corrosion-resistance tests.

Example 5 A cobalt plating was chemically applied on the same material as in Example 2, and then ion-plated with boron oxide under the same condition as in Example 2 to obtain a coating keeping colour of the chemical cobalt plating. The coating of the boron oxide had a thickness of 0.0051l and showed very good results in the wear- and corrosion-resistance tests.

Example 6 Aluminium oxide was ion-plated on the ionplated coloured coating layer under the same condition as in Example 1 to obtain very good results as in Example 1.

As the hard coating of oxide compound, there were used oxides of indium, titanium, zirconium, tantalum and other ceramic materials to form respective coatings, which showed very good results as in Example 1.

Example 7 The same coloured coating layer was formed on the same material as in Example 1, and thereon 300ml/min of acetylene gas was passed, while titanium was ion-plated in the same apparatus as in Example 1 for 30 minutes under a condition of a gas pressure of 5x10-3 Torr, ionizing voltage and current of 40V and 10A, as well as base voltage and current of 0.8KV and 300A to form a coating of substantially titanium compound having a thickness of 0.4u and keeping the colour of black chrome.

Thus, very good results could be obtained as in Example 1.

Example 8 Instead of silicon oxide, titanium was ion-plated for 40 minutes, using the same materials under the same conditions as in Examples 2 and 3 to obtain a coating, which showed the same good results as in Examples 2 and 3.

Example 9 Instead of boron oxide, titanium was ion-plated on the same materials under the same conditions as in Examples 4 and 5 to obtain a coating, which showed the same good results as in Examples 4 and 5.

As described hereinabove, in accordance with the invention the layer of coloured coating is provided thereon with the hard coating, which is transparent at least in a thin coating, in a thickness of 0.0005 to 3FL by means of the ion-plating technique, so that the colour of the prime coating may be maintained and the beautiful final coating of high wear- and corrosion-resistance may be readily obtained in a low cost.

Claims

1. A method of forming a coloured hard coating on a substrate characterised in that a layer of coloured coating is provided thereon with a hard coating which is transparent at least in a thin coating, in a thickness of 0.0005 to 311 by means of ionplating.

2. A method according to claim 1, wherein the coloured coating is selected from electro-plated colour coatings, ion-plated colour coatings, and chemically coloured coatings.

3. A method according to claim 1 or 2, wherein the hard coating is selected from coatings of substantially titanium nitride, carbide or a mixture thereof, and coatings of oxides of aluminium, boron, silicon, indium, titanium zirconium or tantalum and other ceramic coatings.

4. A method as claimed in claim 1, 2 or 3 wherein the ion-plating is carried out at 200 to 500"C.

5. A method as claimed in any one of claims 1 to 4 wherein the hard coating has a thickness of 1 to 3It.

6. A method as claimed in any one of claims 1 to 5 wherein the substrate is a metal.

7. A method as claimed in claim 6 wherein the metal is selected from stainless steel, iron, copper, copper-zinc alloy, aluminium, cadmium, zinc, silver, nickel-chrome alloy and nickel-based alloy.

8. A method of forming a coloured hard coating on a substrate substantially as hereinbefore described with reference to any one of the Examples.

9. A coloured hard coating produced by a method as claimed -in any one of claims 1 to 8.