JP2000109990A - Surface decoloration resistant article and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the surface decoloration caused by corrosive gas by providing a part or the whole of the surface which of ten discolors in the case of being left in the air with a discoloration preventing layer formed of titania. SOLUTION: Preferably the titania to be used is amorphous titania or crystalline titania, and the discoloration preventing layer is the one applied to the surface of the surface discolorable article subjected to surface cleaning by the sputtering of inert gas and has 10 to 2000 Å and >=90% noncoloring degree. Moreover, preferably, the total area of the coating defective part in the discoloration preventing layer in the treated region is <=10% of the region, and the surface of the surface discolorable article is formed of a silver and/or copper- contg. material. Preferably, as to the surface to be applied with the discoloration preventing layer, the discoloration preventing layer formed of titania is applied on the surface by the abrasion of titania crystals using an ultraviolet laser in an atmosphere of 0.5 to 50 mTorr oxygen partial pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface discoloration-resistant article such as money and various metal crafts, and a method for producing the article.

[0002]

2. Description of the Related Art Metal articles made of silver, copper, and the like are discolored by corrosive gases that may be present in the atmosphere, for example, sulfur-containing gases such as hydrogen sulfide, mercaptan, and SOx. Discoloration also occurs due to gas or mist of acids such as acetic acid. Metal handicrafts lose their aesthetics due to their surface discoloration and have a reduced value. On the other hand, in the case of money, they pose a problem in distribution.

[0003] Rust prevention and prevention of surface discoloration of metal crafts have long been performed by applying a rust preventive paint or by using an organic inhibitor such as benzotriazole. Recently, many techniques for forming a thin layer of various ceramics on a metal surface by an ion process have been proposed for the purpose of rust prevention and decoration of a metal article. However, rust-preventive paints and organic inhibitors are effective in the short term but have a problem in the long-term effect.In addition, depending on the type of rust-preventive paint, the ground color of metal articles changes when applied. There are also problems that are difficult to apply to metal crafts. On the other hand, thin layers of various ceramics are conventionally used mainly to prevent oxidation by oxygen in the atmosphere or by oxygen in the presence of moisture, and are effective in preventing surface discoloration of metal articles. But generally poor.

In view of the above, the present inventors conducted rust prevention research on surface discolorable articles, such as silver and copper articles, which discolor when exposed to the air. New knowledge has been obtained that the surface discoloration can be prevented by applying titania to part or all of the surface of the article.

[0005]

SUMMARY OF THE INVENTION The present invention has been developed and completed on the basis of the above-mentioned new findings, and is intended for a surface discolorable article which may discolor when left in the air. It is an object of the present invention to provide a technique for preventing surface discoloration due to corrosive gas, and in particular, a technique for preventing surface discoloration while maintaining the background color of the surface discolorable article as much as possible.

[0006]

The above object can be attained by the following surface discoloration-resistant article and its manufacturing method. (1) A surface discoloration-resistant article characterized by having a discoloration prevention layer formed of titania on a part or the entire surface of the surface discoloration article which may be discolored when left in the air. (2) The above (1), wherein the titania is amorphous titania
The surface discoloration-resistant article according to the above. (3) The surface discoloration-resistant article according to (1), wherein the titania is crystalline titania. (4) The surface discoloration-resistant article according to any one of the above (1) to (3), wherein the discoloration prevention layer is applied to the surface of the surface discoloration article whose surface has been cleaned by sputtering of an inert gas ion. . (5) The anti-tarnish layer having a thickness of 10 to 2000 mm.
The surface discoloration-resistant article according to any one of (1) to (4). (6) The above (1) wherein the anti-tarnish layer has a degree of non-coloring of 90% or more.
The surface discoloration-resistant article according to any one of (1) to (5). (7) The surface discoloration resistant surface according to any of (1) to (6) above, wherein the total area of the covering defect portions of the discoloration preventing layer in the region provided with the discoloration preventing layer is 10% or less of the area of the region. Products. (8) The above (1) to (10), wherein the surface discolorable article has at least its surface formed of a silver and / or copper containing material.
The surface discoloration-resistant article according to any one of (7) and (8). (9) A titania crystal using an ultraviolet laser under an atmosphere having an oxygen partial pressure of 0.5 to 50 mTorr on at least a surface of a surface-discolorable article which may be discolored when left in the air, on which a discoloration preventing layer is to be applied. A method for producing a surface discoloration-resistant article, characterized by applying a discoloration preventing layer formed of titania on the surface by ablation of (1). (10) The above, wherein the ultraviolet laser is an excimer laser
(9) The method for producing a surface discoloration-resistant article according to (9). (11) Prior to the application of the anti-tarnish layer, at least the surface of the surface-discolorable article on which the anti-tarnish layer is to be applied is cleaned by inert gas ion sputtering (9) or (1).
0) The method for producing a surface discoloration-resistant article according to the above.

[0007]

The discoloration preventing layer formed of titania has a function of decomposing various corrosive gases by a photocatalytic action, so that it protects the surface discolorable articles from corrosive gases and has an antibacterial action. Thus, the surface discoloration-resistant article of the present invention does not or hardly undergo surface discoloration even when left in the atmosphere containing corrosive gas for a long period of time. In the manufacturing method of the present invention, the ablation of the titania crystal and the deposition of the titania can be performed at a low temperature using an ultraviolet laser. Performing the above-mentioned action under an oxygen partial pressure of 0.5 mTorr or more contributes to the formation of titania having better colorless transparency with prevention of by-products such as dititanium trioxide or lightness. On the other hand, performing the treatment under an oxygen partial pressure of 50 mTorr or less can prevent or oxidize the surface of the surface-discoloring article and the discoloration-preventing layer, or improve the coloring of the discoloration-preventing layer and improve the adhesion between the surface-discoloring article and the discoloration-preventing layer. To

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As a surface discolorable article, various articles that discolor the surface when left in a normal atmosphere, for example, for one hour to one month can be used. Regarding the degree of surface discoloration at that time, at least normal discoloration can be perceived by the naked eye compared to the surface color of the undiscolored surface discolorable article stored under conditions that do not discolor the surface, such as in a vacuum. Should be fine. At this time, the comparison of the surface colors is performed under the condition that only natural light is received at an angle of 45 degrees in a room facing north. The surface discoloration may be discoloration that spreads substantially uniformly on at least a part of the surface of the surface discolorable article, discoloration that is scattered on at least a part of the surface of the surface discolorable article, or the like.

[0009] A typical example of a surface discolorable article is one in which at least its surface is formed of a material containing silver and / or copper. The silver at this time may be silver having a purity of 95% by weight or more containing various impurities, or an alloy containing silver as one component. Similarly, the copper in this case may be low-grade copper specified in JIS-H2101, pure copper having a purity of 99.4% by weight or more, and is frequently used in alloys containing copper as one component, for example, money. Ag-Cu alloy such as sterling silver, Cu-
Cd-based alloy, Cu-Cr-based alloy, Cu-Be-based alloy, C
u-Be-Co based alloy, Cu-Te based alloy, Cu-Zn based alloy such as brass, Cu-Sn based alloy such as bronze and gunmetal, Cu-Al based alloy such as aluminum bronze, cupronickel, nickel silver, nickel Cu-Ni alloy such as white, Cu
-Si based alloy, Cu-Pb based alloy or the like may be used.

As a specific example of the surface discolorable article, an article entirely formed of at least one selected from the group consisting of silver, silver alloy, copper, and copper alloy, such as a medal, a cup, a medal, etc. Goods, money, tie pins, earrings,
Decoration accessories such as brooches, necklaces, and pendants. As another specific example of the surface discolorable article, an article in which only the surface and its adjacent layer are formed of at least one selected from the group consisting of silver, silver alloy, copper, and copper alloy;
For example, ornaments, daily tools, various equipment cases, building materials, etc., in which the metal is directly plated on the surface of a material or molded product such as wood, pottery, plastic, or the like, or a sheet having a layer of the metal is attached. And so on.

In some surface discolorable articles, it is sufficient to prevent discoloration only on a specific surface, and in other surface discolorable articles, it is necessary to prevent discoloration on the entire surface. Therefore, the surface discoloration-resistant article of the present invention only needs to have a discoloration prevention layer on at least the surface where discoloration prevention is required.

The discoloration preventing layer is formed of titania such as amorphous titania and crystalline titania. Note that titania is not limited to high-purity titania, but may contain titanium monoxide, dititanium trioxide, or other impurities in a small amount of up to 5% by weight. However, such impurities tend to degrade the anti-tarnish function of the anti-tarnish layer or to color the anti-tarnish layer itself. Therefore, the total content of the impurities is 1% by weight or less, particularly 0.1% by weight or less. Is preferred.

If the thickness of the anti-discoloration layer is too small, the effect of preventing discoloration is poor. On the other hand, if the thickness is too large, the effect of preventing discoloration is saturated. Therefore, the thickness of the anti-tarnish layer is 10 to 2000 °, especially 20 to 800 °.

Although titania is originally a colorless and transparent material, the anti-tarnish layer itself may be colored in some cases. This coloring appears to be due to various causes according to the study of the present inventors, but actually occurs mainly due to the thickness itself of the discoloration prevention layer and the inclusion of impurities. That is, when the thickness of the anti-discoloration layer is increased, it is caused by a light interference phenomenon. The types and contents of impurities vary depending on the method and conditions for forming the anti-tarnish layer.
The coloring of the discoloration preventing layer itself has a problem that, when the coloring is high, the background color of the surface discolorable article is discolored. Therefore, when coloring of the anti-tarnish layer itself is a problem, the degree of non-coloring evaluated by the method described below is preferably 90% or more, particularly preferably 95% or more. [Degree of non-coloring of the anti-tarnish layer] The surface discolorable article having the anti-tarnish layer was inspected using a normal spectrophotometer to determine the JI.
In accordance with the method specified in SZ-8722, the incident light intensity I ₀ and the reflected light intensity I transmitted through the anti-tarnish layer and reflected on the surface of the surface discolorable article are measured. The ratio I / I ₀ (%) is defined as the degree of non-coloring. The higher the value, the lower the degree of coloring.

The anti-tarnish layer having a degree of non-coloring of 90% or more is obtained, for example, when its thickness is 500 ° or less, particularly 20 to 400 °, and its total impurity content is 1% by weight or less.

As described above, titania has a function of decomposing various corrosive gases by photocatalysis. Therefore, the discoloration prevention layer made of titania decomposes corrosive gas that can reach the coating defect even if there are some coating defects such as pinholes and layer missing parts in the surrounding titania and corrodes that part. It acts to protect against volatile gases. However, in order to obtain a more favorable aspect of the anti-tarnishing performance in the present invention, the total area of the coating defect portions of the anti-tarnishing layer in the area where the anti-tarnishing layer is applied is 10% or less of the area of the area,
In particular, it is preferably at most 5%.

The anti-tarnish layer may be formed by various well-known methods capable of forming a titania layer, particularly a thin layer. Typical methods include, for example, a PVD method such as a vacuum evaporation method, an ion plating method, and a sputtering method, and a thermal C method.
Examples of the method include a CVD method such as a VD method, a plasma CVD method, an MOCVD method, and a photo CVD method, and other methods such as a sol-gel method and a thermal spraying method. Above all, an ion plating method, particularly a laser ablation method described later is preferable.

In forming the anti-tarnish layer, the surface of the surface-tarnishing article is usually cleaned with an organic solvent or the like to remove adhering fats and oils and dust, and then cleaned. However, in some cases, the treatment with such an organic solvent results in insufficient cleaning, resulting in poor adhesion between the anti-tarnish layer and the surface of the surface-discolorable article, and the anti-tarnish layer being easily peeled off. There is. Therefore, as the surface discoloration-resistant article of the present invention,
It is particularly preferable that the surface of the surface discolorable article is obtained by cleaning the surface by sputtering of inert gas ions described later, for example, sputtering of argon ions, and then forming a discoloration preventing layer thereon.

The surface discoloration-resistant article of the present invention can be produced by forming a discoloration preventing layer made of titania on at least the surface of the surface discoloring article on which the discoloration preventing layer is to be applied by the above-described method. The laser ablation method will be described below as an example.

In the laser ablation method, at least the surface of the surface-discolorable article on which the anti-discoloration layer is to be coated is subjected to ablation of titania crystals using an ultraviolet laser in an oxygen atmosphere to prevent discoloration formed on the surface by titania. Apply layers.

The titania crystal as a target has a purity of at least 99% by weight, particularly a purity of at least 9% by weight.
9.9% by weight of single or polycrystalline is preferred. By using such high-purity titania crystals, high-purity titania
Thus, it is possible to form a discoloration preventing layer made of titania having a degree of non-coloring of 90% or more.

Ultraviolet lasers generally have higher lattice energies than other lasers, and therefore have a greater intermolecular dissociation force, so that they can ablate titania crystals at lower temperatures. A high quality anti-tarnish layer can be formed thereon without substantially oxidizing the surface of the surface discolorable article. As ultraviolet laser, gas laser,
Various ultraviolet lasers, such as solid state lasers or other pulsed or non-pulsed lasers, can be used. Ar-F, Ar-C for gas laser
Excimer lasers using an excited dimer such as 1, Kr-F, Kr-Cl, Xe-F, and Xe-Cl; and solid-state lasers such as a YAG laser (using a fourth harmonic). In particular, excimer lasers with both high top energy value and average energy value,
Above all, an Ar-F excimer laser is preferred.

When an ultraviolet laser is used, the deposition of titania can be performed at room temperature or a relatively wide temperature range. However, if the temperature is high, the adhesion of the anti-discoloration layer formed by crystallization or oxidation of the surface layer of the surface-discolorable article may decrease. Therefore, the surface temperature of the surface-discoloring article when depositing titania is preferably kept at 0 to 100 ° C, particularly 10 to 50 ° C.

If the oxygen partial pressure of the atmosphere in which the ablation of the titania crystal and the deposition of the titania are performed (hereinafter, the atmosphere is referred to as “reaction atmosphere”) is too low,
Due to oxygen deficiency, the amount of by-products of non-titania components such as titanium monoxide and dititanium trioxide increases, causing the discoloration prevention layer itself to be colored. There is a problem that λ becomes small, the efficiency of deposition on the surface of the surface discolorable article decreases, or the surface layer of the surface discolorable article is oxidized. Therefore, in the present invention, the oxygen partial pressure of the reaction atmosphere is set to 0.5
-50 mTorr, preferably 5-30 mTorr, more preferably 10-25 mTorr.

With respect to the reaction atmosphere, the presence of inert gases such as nitrogen, hydrogen, carbon dioxide and rare gases can be tolerated if their total pressure is 1/100 or less, especially 1/500 or less of the oxygen partial pressure. . However, the total pressure of the reaction atmosphere is
It is particularly preferable that the reaction atmosphere is substantially equal to the oxygen partial pressure, in other words, the reaction atmosphere consists essentially of only oxygen from the viewpoint of producing high-quality titania. Since the ablation of the titania crystal and the deposition of the titania are performed in a film forming chamber described later, the gas in the film forming chamber corresponds to the reaction atmosphere.

In forming the anti-tarnish layer, necessary members are placed in a film forming chamber, and the inside of the chamber is vacuum-pumped to a suitable degree, for example, 10 ^-4 to 10 ^-5 Torr.
r, and then high-purity oxygen gas is introduced into the chamber until a predetermined partial pressure is reached. Thereafter, the operation of the vacuum pump and the introduction of high-purity oxygen gas are simultaneously and continuously performed to keep the inside of the film forming chamber. Is maintained at the above-mentioned value.

Hereinafter, the method of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of an example of an apparatus used in the method of the present invention. 1 is a cylindrical film forming chamber, 2 is an ultraviolet laser (details of the cross section are omitted), 3 is a target made of titania crystal, Is a surface discolorable article, 5 is a degassing tube, 6 is an oxygen introduction tube, and 7 is a pressure sensitive part of a vacuum gauge. The film forming chamber 1 is provided with three holes H1, H2, and H3, and an ultraviolet-transparent plate (not shown) is hermetically fitted into the hole H1 via a hermetic plug H11. I have. As the ultraviolet transmitting plate, a plate made of pure quartz, sapphire or the like, which is provided with an anti-reflection coating on both surfaces, is used. The laser light oscillated from the ultraviolet laser 2 passes through the condenser lens 21 and is condensed as shown by a dotted line,
Then, the light reaches the target 3 through an ultraviolet-transparent plate. In the hole H2, a fixing base H22 inserted through the airtight plug H21 in an airtight manner is hermetically installed via the airtight plug H21, and the surface discoloring article 4 is provided on the upper surface of the fixing base H22. Is placed. In the hole H3, a deaeration tube 5, an oxygen introduction tube 6, and a pressure-sensitive portion 7 of a vacuum gauge inserted and hermetically penetrated through the hermetic plug H31 are hermetically installed via the hermetic plug H31.

Next, a method of using the apparatus shown in FIG. 1 will be described. First, the inside of the film forming chamber 1 is continuously degassed from a degassing pipe 5 connected to a vacuum pump (not shown).
To continuously maintain the inside of the film forming chamber 1 at a predetermined pressure. Next, a laser beam is oscillated from the ultraviolet laser 2 to irradiate the surface of the target 3 and is ablated. Thus, on the surface of the surface discolorable article 4, a discoloration preventing layer of titania is formed. In addition, 8 in FIG. 1 conceptually shows evaporated smoke generated from the target 3 by ablation by the ultraviolet laser 2.

The irradiation angle θ of the laser beam from the ultraviolet laser 2 to the surface of the target 3 is 30 to 80 degrees,
Particularly, 45 to 65 degrees is appropriate, and the irradiation fluence is 5 to 65 degrees.
00 to 5000 mJ / cm ² , especially 1000 to 3000
mJ / cm ² is appropriate. The distance between the surface of the target 3 and the surface of the surface discolorable article 4 varies depending on the volume of the film forming chamber 1, the surface area of the surface discolorable article 4, the irradiation fluence, and the like. When using a film forming chamber, 15 to 100 mm
About 30 mm is suitable.

In the formation of the anti-tarnish layer, as described above, it is preferable to clean the surface of the surface-discolorable article by sputtering inert gas ions. At that time, ions of a rare gas such as He, Ne, or Ar, particularly Ar ions, are used as the inert gas, and a condition that the surface of the surface discolorable article is not shaved, for example, 100 to 1000 is used.
It is preferable to perform sputtering for about 1 to 2 minutes under application of V, particularly 200 to 600 V.

[0031]

EXPERIMENTAL EXAMPLES Hereinafter, the present invention will be described in more detail with reference to experimental examples.

EXPERIMENTAL EXAMPLE 1 A 1 mm-thick, 10 mm square silver piece sampled from a rolled silver sheet having a purity of 99.9% by weight was used as a surface discolorable article, and a commercially available titania baked product having a purity of 99.9% by weight was used as a target. A high-purity oxygen having a purity of 99.99% by volume or more is used as the oxygen.
An ArF excimer laser having a pulse width of 3 nm and a pulse width of 17 nm (using LPX200 manufactured by Lambda Physics Co., Ltd.) was used. The surface of the above silver piece was polished to a mirror surface with a 200 mm particle size abrasive containing iron oxide, chromium oxide, and aluminum oxide, and then subjected to ultrasonic cleaning in the order of a petroleum degreasing agent, acetone, and ethanol. It was installed at a predetermined position in a film forming chamber made of stainless steel (with a quartz glass window) as shown in FIG. At that time, the distance between the opposing surfaces of the target and the silver piece in the film forming chamber was set to 25 mm. Next, the inside of the film formation chamber is reached with a turbo molecular pump to reach a degree of vacuum of 4 ×.
The chamber is evacuated to 10 ⁻⁵ Torr, oxygen gas is introduced, and the partial pressure of oxygen in the chamber (total pressure in the chamber) is reduced to 20%.
After that, the pump was continuously operated and high-purity oxygen gas was constantly supplied to maintain the oxygen partial pressure in the film forming chamber at the above-mentioned value. A in that state
Activate the rF excimer laser and repeat 3H
z, irradiation angle (θ) with respect to the target surface 50 to 60
The target was ablated by irradiating laser light for 2 minutes under the conditions of irradiation fluence of 600 to 1200 mJ / cm ² . During this time, the surface temperature of the silver pieces was at room temperature (about 25 ° C.). Thus, a discoloration preventing layer of amorphous titania having an average thickness of about 30 ° was formed on one surface of the silver piece to obtain a surface discoloration-resistant article. The thickness of the anti-tarnish layer was measured with a quartz crystal film thickness monitor (manufactured by Nidec Anelva). The same applies to the following experimental examples and comparative examples.

Experimental Example 2 Discoloration of amorphous titania having an average thickness of about 60 ° on one side of a silver piece was performed under the same method and conditions as in Experimental Example 1 except that the irradiation time of the laser beam was 4 minutes. The prevention layer was formed to obtain a surface discoloration-resistant article.

Experimental Example 3 Discoloration of amorphous titania having an average thickness of about 400 ° on one side of a silver piece was performed under the same method and conditions as in Experimental example 1, except that the laser light irradiation time was set to 20 minutes. The prevention layer was formed to obtain a surface discoloration-resistant article.

Experimental Examples 4 to 6 Silver pieces (mirror polishing + ultrasonic cleaning) used in Experimental Example 1 were X
PS device (using JEOL's JPS-9000MC)
As a result of the surface analysis, O1s and C1s, which are considered to be based on a trace amount of organic matter contained in the abrasive, were observed. Therefore, the silver pieces were exposed to Ar ions for about 100 seconds at 400 V and 0.4 mA. A cleaning treatment was performed by sputtering.
In the silver flakes thus treated, neither O nor C was observed by surface analysis using an XPS apparatus. Therefore, the silver pieces were used in place of the silver pieces used in Experimental Examples 1 to 3, and
The average thickness is about 30 mm on one side using the same method and conditions as above.
(Experimental Example 4), about 60 ° (Experimental Example 5), and about 400 °
(4) An anti-tarnishing layer of amorphous titania of (Experimental Example 6) was formed to obtain each surface discoloration-resistant article.

Experimental Example 7 A titania layer having an average thickness of about 400 ° was formed on one side of the film by the same method and under the same conditions as in Experimental Example 1 except that the oxygen partial pressure in the film forming chamber was set to 0.01 mTorr.

Experimental Example 8 A titania layer having an average thickness of about 400 ° was formed on one side of the film by the same method and under the same conditions as in Experimental Example 1 except that the oxygen partial pressure in the film forming chamber was set to 70 mTorr.

Experimental Example 9 The silver piece (mirror polishing + ultrasonic cleaning) used in Experimental Example 1 was used, and the surface thereof was coated with a mercaptobenzothiazole layer having a thickness of about 10 mm by an ordinary method.

Surface discoloration of each silver piece with a titania layer obtained from Experimental Examples 1 to 8 and the silver piece with a mercaptobenzothiazole layer (MBT layer) obtained from Experimental Example 9 by a corrosive gas by the following method. Of the prevention of
For each silver piece with a titania layer obtained from No. 8, the degree of non-coloring and the adhesion of the titania layer were measured by the following methods. Table 1 shows the results. Experimental example 1
Each of the titania layers Nos. To 8 was confirmed to be amorphous from their X-ray diffraction.

[0040]

[Table 1]

[0041] Using a spectrophotometer [unpigmented of the titania layer] (using Kurabo of COLOR7e ^2), were measured by the method described above.

[Method of Measuring the Prevention of Surface Discoloration by Corrosive Gas] Temperature 20 containing about 50 ppm of hydrogen sulfide gas
It was left for 8 hours in the air at about 100 ° C. and a relative humidity of about 100%. For the sample before and after standing, the incident light intensity I ₀ and the reflected light intensity I were measured using the same spectrophotometer as that used for the measurement of the degree of non-coloring of the titania layer, and the optical density K from the measured values was measured. [Log (I ₀ / I)] is calculated. Next, assuming that the optical density of the sample before standing is Kb and that after standing is Ks, the inhibition rate D of surface discoloration was calculated by the following equation.
The greater the value of the suppression rate D, the higher the ability to prevent surface discoloration. D (%) = (Kb−Ks) / Kb × 100

[Adhesion of Titania Layer] Using a rubbing tester (manufactured by Taihei Rika Kogyo Co., Ltd.), rubbing was carried out with a felt under a load of 500 g, and the number of rubs required for peeling off the titania layer was measured and evaluated as follows. did. Excellent: No peeling after rubbing 100 times. Good: Peeled off at 50 or more and less than 100. Impossible. Peeled off after less than 50 rubs.

As is clear from Table 1, each of the surface discoloration-resistant articles obtained from Experimental Examples 1 to 8 having a titania layer was compared with the silver flake of Experimental Example 9 coated with a mercaptobenzothiazole layer. Each of them has remarkably excellent surface discoloration prevention performance, and the surface discoloration-resistant articles of Experimental Examples 3 and 6 to 8 in which the thickness of the titania layer is as large as about 400 mm have more excellent surface discoloration prevention performance. ing. On the other hand, the surface discoloration-resistant articles obtained from Experimental Examples 1 to 8, particularly, the thickness of the titania layer was about 30 °.
Alternatively, the surface discoloration-resistant articles of Experimental Examples 1-2 and 4-5, which are as thin as about 60 °, are excellent in the degree of non-coloring of each titania layer itself. Furthermore, the surface discoloration-resistant articles of Experimental Examples 4 to 6 cleaned by Ar ion sputtering are:
It can also be seen that the adhesion of the titania layer is superior to those of Experimental Examples 1 to 3 in which only the normal cleaning treatment is performed.

[0045]

The surface discoloration-resistant article of the present invention is suitable as various silver and copper products which dislike the surface discoloration since its surface does not discolor even if left in the atmosphere containing corrosive gas for a long period of time. . In particular, those in which the discoloration preventing layer has a degree of non-coloring of 90% or more are suitable as money and various crafts since the discoloration preventing layer itself is nearly colorless and transparent. On the other hand, according to the production method of the present invention, the surface discoloration-resistant article described above can be easily produced using a simple apparatus.

[Brief description of the drawings]

FIG. 1 is a sectional view of an example of an apparatus used in a method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Film-forming chamber 2 Ultraviolet laser 3 Target made of titania crystal 4 Surface-discoloring article 5 Degassing tube 6 Oxygen introducing tube 7 Pressure-sensitive part of vacuum gauge

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G047 CA05 CB04 CC03 CD02 4K044 AA06 AB06 BA12 BC02 CA07 CA13 4K053 PA01 PA06 PA17 QA04 RA31 4K062 AA10 BA14 CA02 EA08 FA16 GA10

Claims (11)

[Claims] 1. A surface discoloration-resistant article characterized by having a discoloration prevention layer formed of titania on a part or all of the surface of a surface discolorable article which may be discolored when left in the air. Goods. 2. The surface discoloration-resistant article according to claim 1, wherein the titania is amorphous titania. 3. The surface discoloration-resistant article according to claim 1, wherein the titania is crystalline titania. 4. The surface discoloration-resistant article according to claim 1, wherein the discoloration prevention layer is applied to the surface of the surface discoloration-resistant article whose surface has been cleaned by sputtering of an inert gas ion. 5. The surface discoloration-resistant article according to claim 1, wherein the discoloration preventing layer has a thickness of 10 to 2000 °. 6. The surface discoloration-resistant article according to claim 1, wherein the discoloration preventing layer has a degree of non-coloring of 90% or more. 7. The surface discoloration resistance according to claim 1, wherein the total area of the covering defect portions of the discoloration prevention layer in the region provided with the discoloration prevention layer is 10% or less of the area of the region. Goods. 8. The surface discoloration-resistant article according to claim 1, wherein at least the surface of the surface discoloration article is formed of a silver and / or copper-containing material. 9. An ultraviolet laser is used under an atmosphere of an oxygen partial pressure of 0.5 to 50 mTorr on at least a surface of a surface-discolorable article which may be discolored when left in the air, on which a discoloration preventing layer is to be applied. A method for producing a surface discoloration-resistant article, characterized by applying a discoloration preventing layer formed of titania on the surface by ablation of titania crystals. 10. The method according to claim 9, wherein the ultraviolet laser is an excimer laser. 11. The surface discoloration resistant article according to claim 9, wherein prior to the application of the discoloration preventing layer, at least the surface of the surface discolorable article to which the discoloration preventing layer is to be applied is cleaned by sputtering with an inert gas ion. Method for producing a conductive article.