JP2013216920A - Discoloration prevention method of silver-based material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method which can efficiently perform discoloration prevention treatment of a silver-based material in a relatively simple method without using a harmful compound, such as hexavalent chromium, and by which the treated silver-based material has little deterioration in appearance and also little deterioration in various performance.SOLUTION: Discoloration prevention treatment can be performed in a simple method by performing electrolytic treatment at a liquid temperature of 55°C or less using an object to be treated including a silver-based material as a cathode in a composition for discoloration prevention treatment which comprises an aqueous solution containing a zinc ion and a nitrate ion, without decreasing reflectance and conductivity of the silver-based material.

Description

  The present invention is a method for preventing discoloration of silver-based materials such as silver and silver alloys, and in particular, with respect to a silver plating film used as a reflector for LED lighting or the like, good discoloration without almost reducing the reflectance. The present invention relates to a method for imparting prevention performance.

  In recent years, lighting using LED elements (LED lighting) has become widespread as an alternative to incandescent bulbs and fluorescent lamps. LED lighting requires a reflector to reflect the light generated by the LED element in a certain direction. In addition to white resin and ceramic, metals such as silver and silver alloys with high reflectivity in the visible light region are used. In general, electroplating or electroless plating is often employed as a method for forming a silver-based film.

  However, the silver-based film has a drawback that it easily changes color because it forms silver sulfide when it comes into contact with a sulfur compound. LED lighting has a lifespan of 40,000 hours or more, and discoloration of the silver-based film used for the reflector due to sulfide or the like is a big problem because it leads to a decrease in luminance.

  Conventionally, in order to prevent discoloration of the silver-based film, immersion chromate treatment or electrolytic chromate treatment using hexavalent chromium and discoloration prevention treatment by strongly adsorbing an organic protective film on the silver surface have been performed.

  Among these treatments, the chromate treatment is effective as a discoloration prevention treatment, but use of hexavalent chromium is limited due to environmental problems. Also, the anti-discoloration treatment for adsorbing organic matter cannot maintain high reflectivity over a long period of time in LED lighting because the organic matter layer is decomposed and deteriorated by light and heat generated from the element.

A method using a metal oxide has been reported as an anti-discoloration treatment without using organic substances. For example, the following Patent Document 1 describes that the reflectance is not lowered even in a severe corrosion resistance test by forming a metal oxide such as ITO, ZnO, IZO, SnO ₂ or the like about 3 to 50 nm as a discoloration preventing layer. Has been.

JP 2006-98856 JP

  However, in order to form such a very thin metal oxide uniformly, vacuum processes such as vacuum deposition, sputtering, and CVD are necessary. In the case of forming the film, it is necessary to form a plating film and dry it, and then place it in a vacuum processing chamber (chamber) to carry out the treatment, and the productivity is very low, and an increase in cost is inevitable. For this reason, the method for preventing discoloration using a vacuum process is not suitable as an industrial production method.

  The present invention has been made in view of the current state of the prior art as described above, and its main purpose is that it can be processed efficiently by a relatively simple method without using harmful compounds such as hexavalent chromium. This is a method for preventing discoloration of a silver-based material, and the silver-based material after processing is less likely to cause deterioration in appearance such as reflectivity and gloss, and has little deterioration in various performances such as wire bonding and solderability. Is to provide.

  The present inventor has intensively studied to achieve the above-described object. As a result, in the case where an aqueous solution containing zinc ions and nitrate ions is used as the treatment liquid and the electrolytic treatment is performed at a relatively low current density under a limited temperature condition of 55 ° C. or lower, the silver to be treated It has been found that a very thin film in an amorphous state can be uniformly formed on a system material and can impart good discoloration prevention performance. Moreover, since the silver-based material that has been subjected to the discoloration prevention treatment by this method is formed with a very thin uniform film, the reflectance is hardly lowered, and while maintaining good performance as a reflector, We have found that various performances such as wire bonding and solderability can be maintained well. The present invention has been made based on these findings.

That is, the present invention provides a method for preventing discoloration of the silver-based material described below and an article subjected to discoloration prevention treatment.
Item 1. In the composition for anti-discoloration treatment comprising an aqueous solution containing zinc ions and nitrate ions, an electrolytic treatment is carried out at a liquid temperature of 55 ° C. or less, using an object to be treated containing a silver-based material as a cathode. Material discoloration prevention method.
Item 2. Item ^{2. The} method for preventing discoloration of a silver-based material according to Item 1, wherein the cathode current density during electrolytic treatment is 0.01 to ² mA / cm ² .
Item 3. Item 3. The silver according to Item 1 or 2, wherein the composition for preventing discoloration is an aqueous solution containing 0.05 mol / L to 0.2 mol / L of zinc ions and 0.05 mol / L to 0.2 mol / L of nitrate ions. Method for preventing discoloration of materials.
Item 4. Item 4. The method for preventing discoloration of a silver-based material according to any one of Items 1 to 3, wherein the electrolytic treatment time is 10 seconds or less.
Item 5. Item including silver-based material, which has been subjected to discoloration prevention treatment by any one of items 1 to 4.
Item 6. Item 6. The article according to Item 5, which is a reflector for LED lighting.
Item 7. A silver-based material on which a discoloration-preventing film is formed,
The silver-based material, wherein the discoloration-preventing film is a film having a thickness of 20 nm or less containing zinc hydroxide that uniformly coats the surface to be treated of the silver-based material.

  Hereinafter, the method for preventing discoloration of the silver-based material of the present invention will be specifically described.

Composition for Discoloration Prevention Treatment In the present invention, an aqueous solution containing zinc ions and nitrate ions is used as the composition for discoloration prevention treatment used for the discoloration prevention treatment of the silver-based material. As such an aqueous solution, for example, an aqueous solution containing zinc nitrate as an ion source of both zinc ions and nitrate ions, a water-soluble zinc salt as a zinc ion source, and nitric acid or water-soluble as a nitrate ion source. An aqueous solution containing nitrate can be used.

  The water-soluble zinc salt that can be incorporated into the composition for preventing discoloration is not particularly limited, and examples thereof include zinc nitrate, zinc sulfate, zinc chloride, zinc acetate, zinc phosphate, zinc pyrophosphate, and zinc carbonate. be able to. The water-soluble nitrate is not particularly limited, and examples thereof include zinc nitrate, ammonium nitrate, sodium nitrate, potassium nitrate, lithium nitrate, and urea nitrate.

  As the compound used as the zinc ion source and the compound used as the nitrate ion source, one type of each may be used, or a plurality of types may be used in combination.

  In the composition for preventing discoloration, the concentration of zinc ions and nitrate ions can be adjusted in a wide range, but if the concentration is too low, a uniform discoloration preventing film having a thin film thickness can be formed even if the electrolysis conditions are adjusted. However, when the concentration is too high, zinc hydroxide and a non-uniform zinc oxide film tend to be formed. For this reason, it is usually appropriate that the respective concentrations of zinc ions and nitrate ions are in the range of about 0.05 to 0.2 mol / L, and in particular, the respective concentrations are 0.07 to 0.15 mol / L. It is preferable that it is about L.

  About pH of the composition for preventing discoloration treatment, if the pH of the electrolytic solution becomes too high, precipitation tends to occur in the electrolytic solution. It is preferable to do.

Discoloration prevention treatment method In the discoloration prevention treatment method of the present invention, the above-described discoloration prevention treatment composition is used, and the object to be treated is treated as a cathode at a liquid temperature of 55 ° C. or lower, preferably 40 to 55 ° C. with or without stirring. The electrolytic treatment may be performed as follows.

Zinc oxide is an n-type oxide semiconductor, and its use as a transparent conductive film and a structural material for solar cells is attracting attention. However, high purity and crystallinity are required for these uses. In the case of forming a zinc oxide film from an aqueous solution of zinc nitrate by an electrolytic method, it has been reported that good crystallinity can be obtained at a relatively high temperature, and many reports use a film forming temperature of 60 ° C. or higher. Yes. (Appl. Phys. Lett. 68 (17), April 1996 M. Izaki T. Omi; Appl. Phys. Lett. 83 (24), December 2003 M. Izaki S. Watase H. Takahashi, etc.)
However, at the film formation temperature of 60 ° C. or higher as reported in these reports, in order to form a uniform film by growing crystals and partially depositing zinc oxide having a large particle size, a comparison of about 50 to 100 nm is required. It is necessary to form a thick zinc oxide film. For this reason, even if a uniform zinc oxide film is formed on the silver-based film, the reflectance, the conductivity, the wire bonding property and the like are reduced.

  On the other hand, when the electrolytic treatment is performed at a liquid temperature of 55 ° C. or lower using the above-described composition for preventing discoloration, a uniform film is formed by short-time electrolytic treatment while suppressing crystal growth. can do. For this reason, only by forming a very thin film of about 20 nm or less, which was impossible when performing electrolytic treatment at a temperature exceeding 55 ° C., the silver-based material as the object to be treated is uniformly coated, Sufficient discoloration prevention performance can be imparted. The silver-based material after the discoloration prevention treatment by this method has little deterioration in appearance such as reflectance and gloss, and various performances such as conductivity, wire bonding property and solderability are almost the same as the state before treatment. Maintained. The film formed by this treatment method is an amorphous film having low crystallinity and a film containing zinc hydroxide.

In the present invention, the electrolysis conditions are not particularly limited, but in order to provide a good discoloration prevention function with a very thin film thickness, it is preferably about ² mA / cm ² or less, and 0.01 to ² mA. / M ² is more preferable. If the current density is too high, coarse crystals grow and partial precipitation occurs, and a uniform film cannot be obtained.

Accordingly, in the present invention, in the composition for preventing discoloration at a liquid temperature of 55 ° C. or less, a uniform film having a very thin film thickness can be obtained by performing the treatment at a cathode current density of about ² mA / cm ² or less. Sufficient discoloration prevention performance can be imparted only by forming a thin film having a thickness of about 20 nm or less, preferably about 10 nm or less.

  The treatment time for preventing discoloration varies depending on the current density and the like, but is usually about 15 seconds or less, preferably about 10 seconds or less, particularly about 5 to 10 seconds. According to the method of the present invention, sufficient discoloration prevention performance can be imparted in such a short processing time. For this reason, the discoloration prevention treatment can be efficiently performed by a series of treatment steps that are continuous with the silver plating treatment.

  As the anode used for the electrolytic treatment, for example, any anode used for ordinary galvanizing treatment can be used. For example, in addition to zinc, which is a soluble anode, insoluble anode materials such as carbon, platinum, and platinum-plated titanium can be used. Among these, when zinc is used as the anode, the dissolution is uniform and the composition of the electrolytic solution is kept almost stable. When an insoluble anode such as platinum or platinum-plated titanium is used, continuous operation is possible by supplying zinc salt and nitrate and adjusting the pH of the electrolyte.

  In the present invention, the article to be subjected to the discoloration prevention treatment is an article containing a silver-based material made of silver or a silver alloy. For example, an article formed from a silver-based material made of silver or a silver alloy; an article partially containing the silver material; an article formed with a film made of silver or a silver alloy can be treated. In particular, when an LED illumination reflector having a silver or silver alloy plating film formed thereon is used as a processing target, it is satisfactory with almost no decrease in reflectance with respect to the plating film made of silver or silver alloy. Discoloration preventing property can be imparted, and good conductivity, wire bonding property, solderability, etc. can be maintained.

  The type of the silver alloy is not particularly limited as long as it is an alloy mainly composed of silver. For example, silver such as an Ag—Pd alloy and an Ag—Au alloy is about 80% by weight or more, preferably 90% by weight. Alloys containing more than about can be treated.

  According to the silver material discoloration prevention method of the present invention, the silver material can be efficiently discolored by a relatively simple method without using harmful compounds such as hexavalent chromium. The silver-based material that has been subjected to the discoloration prevention treatment by the method of the present invention has little deterioration in appearance, can maintain a high reflectance, and there is little deterioration in various performances such as conductivity and wire bonding properties.

The graph which shows the relationship between the liquid temperature of the composition for discoloration prevention processing calculated | required in Example 1, the reflectance of the silver plating film after a discoloration prevention process, and the reflectance after a sulfuration resistance test. The SEM photograph which shows the surface state of the sample which performed the discoloration prevention process at the liquid temperature of 50 degreeC, and the sample which performed the discoloration prevention process at the liquid temperature of 60 degreeC. The graph which shows the relationship between the etching time and the abundance ratio of each element calculated | required from the photoelectron spectrum about the sample which processed for 10 second with the cathode temperature density of 50 degreeC of liquid temperature, and current density of 0.5 mA / cm < ² >. Liquid temperature 50 ° C., a current density of 0.5 mA / Ag3d photoelectron spectrum for the cathode current density for 10 seconds processing was performed samples cm ² and Zn2p3 / 2 illustrates the photoelectron spectrum. Liquid temperature 50 ° C., a current density of 0.5 mA / Ag3d photoelectron spectrum for the cathode current density for 10 seconds processing was performed samples cm ² and Zn2p3 / 2 illustrates the photoelectron spectrum.

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

Example 1
As an object to be processed, a 1 μm Ni plating film was formed on a rolled copper plate, and then a 1 μm silver plating film was used, and immersed in a composition for preventing discoloration consisting of a 0.1 mol / L zinc nitrate aqueous solution. Using a product as a cathode and a zinc plate as an anode, a direct current was applied to prevent discoloration. Table 1 shows the liquid temperature of the aqueous zinc nitrate solution, the cathode current density, and the treatment time during the treatment. About the silver plating film after a process, the external appearance and discoloration resistance were evaluated by the following method. The results are shown in Table 1 below.

* Appearance evaluation The appearance after the discoloration prevention treatment was visually observed. The results are indicated by the following symbols.

○: Appearance good Δ: Slightly yellow ×: Yellow

* Discoloration resistance (sulfuration resistance) test After measuring the reflectance (wavelength: 450 nm) of the sample after anti-discoloration treatment, immerse it in a 2 ml / L aqueous solution of ammonium sulfide at 25 ° C for 5 minutes, and then reflect the reflectance again. Measurement (wavelength: 450 nm) was performed, and the resistance to discoloration was evaluated by the change in reflectance. The results are indicated by the following symbols.

○: Decrease in reflectance is 5% or less △: Decrease in reflectance is 5-10%
×: Decrease in reflectance is 10% or more

FIG. 1 shows a sample treated with a cathode current density of 0.5 mA / cm ² for 10 seconds, the liquid temperature of the composition for preventing discoloration, and the reflectance of the silver plating film after the discoloration preventing treatment (wavelength: 450 nm). ) As a graph. Further, the graph of FIG. 1 shows the temperature of the anti-discoloration treatment solution and the silver plating film after the discoloration resistance (sulfuration resistance) test for the sample after the discoloration resistance test was performed by the above-described method. The relationship with the reflectance (wavelength: 450 nm) is also shown.

  As can be seen from FIG. 1, when the anti-discoloration treatment is performed at a liquid temperature of 55 ° C. or less, the coating after the anti-discoloration treatment maintains a high reflectance and is immersed in an aqueous ammonium sulfide solution for resistance. Even after the discoloration (sulfuration resistance) test, it was confirmed that there was little decrease in reflectivity and good discoloration prevention property.

Further, FIG. 2 shows a sample subjected to the discoloration prevention treatment at a liquid temperature of 50 ° C. and a discoloration prevention treatment at a liquid temperature of 60 ° C. among the samples subjected to the treatment at a cathode current density of 0.5 mA / cm ² for 10 seconds. It is a SEM photograph which shows the surface state of the performed sample. As is clear from FIG. 2, for the sample treated at a liquid temperature of 60 ° C., particulate precipitates are formed, and it can be seen that most of the surface of the silver plating film is exposed. For this reason, it is considered that discoloration occurred in the discoloration resistance (sulfuration resistance) test, resulting in a significant decrease in reflectance. On the other hand, in the sample subjected to the discoloration prevention treatment at a liquid temperature of 50 ° C., no particulate precipitate is observed, and it can be confirmed that a uniform thin film is formed on the entire surface of the silver plating. For this reason, it is considered that the results showed no decrease in reflectance even in the discoloration resistance (sulfuration resistance) test.

Test example 1
In Example 1, the surface of a sample treated for 10 seconds at a cathode current density of 50 ° C. and a current density of 0.5 mA / cm ² was subjected to photoelectron spectroscopy (XPS), and each 0.1 min sputtering with an Ar ion gun. The depth direction analysis was performed by measuring and repeating this 30 times. The measurement conditions are as follows.

Measuring equipment: ESCA-5800 made by ULVAC-PHI Excitation X-ray: AlKα ray Output: 400W
As for the etching rate by sputtering, a sample in which a ZnO film is formed to a thickness of 90 nm on the surface of the Ag plating is preliminarily tested under the same sputtering conditions as described above, and the sputtering rate for the ZnO film is 6 nm / min. It was confirmed beforehand.

  FIG. 3 is a graph showing the relationship between the etching time and the photoelectron spectrum. As is apparent from FIG. 3, the Zn ion and Ag ion concentrations are about the same in an etching time of about 0.3 minutes, and the thickness of the film formed on the silver plating film is about 2 nm. I was able to confirm.

  FIG. 4 shows the Ag3d photoelectron spectrum and Zn2p3 / 2 photoelectron spectrum of this sample. In FIG. 4, the curves indicated by 1 and 2 are spectra showing the surface state before sputtering, and the curves indicated by 3, 4, 5 and 6 are respectively 0.1 minutes, 0.2 minutes, It is a spectrum after performing sputtering for 0.3 minute and 0.4 minute. As apparent from the Ag3d photoelectron spectrum, almost no Ag was detected on the surface before sputtering, and it was confirmed that a uniform film was formed on the silver plating film. Further, as apparent from the Zn2p3 / 2 photoelectron spectrum, it was confirmed that the film formed on the silver plating film contained zinc hydroxide.

Figure 5, liquid temperature of 60 ° C., a current density of 0.5 mA / cm for the surface of the sample subjected to 10 seconds treated with ² of cathode current density, Ag3d photoelectron spectra and Zn2p3 / 2 was measured in the same manner as described above The photoelectron spectrum is shown. As is clear from the Ag3d photoelectron spectrum in FIG. 5, a clear Ag peak was observed on the sample surface before sputtering. When electrolytic treatment was performed at a liquid temperature of 60 ° C., the surface of the silver plating film was observed. It was confirmed that a uniform film was not formed and at least a part of the film was exposed.

Claims (7)

In the composition for anti-discoloration treatment comprising an aqueous solution containing zinc ions and nitrate ions, an electrolytic treatment is carried out at a liquid temperature of 55 ° C. or less, using an object to be treated containing a silver-based material as a cathode. Material discoloration prevention method. The method for preventing discoloration of a silver-based material according to claim 1, wherein the cathode current density during the electrolytic treatment is 0.01 to ² mA / cm2. The composition for discoloration prevention treatment is an aqueous solution containing zinc ions 0.05 mol / l to 0.2 mol / l and nitrate ions 0.05 mol / l to 0.2 mol / l. A method for preventing discoloration of silver-based materials. The method for preventing discoloration of a silver-based material according to any one of claims 1 to 3, wherein the electrolytic treatment time is 10 seconds or less. An article containing a silver-based material, which has been subjected to a discoloration prevention treatment by the method according to claim 1. The article according to claim 5, which is a reflector for LED lighting. A silver-based material on which a discoloration-preventing film is formed,
The silver-based material, wherein the discoloration-preventing film is a film having a thickness of 20 nm or less containing zinc hydroxide that uniformly coats the surface to be treated of the silver-based material.

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