JP4351144B2 - Silver alloy - Google Patents

Description

  The present invention relates to a silver alloy. In particular, the present invention relates to a silver alloy suitable as a constituent material of a reflective film that can suppress a decrease in reflectance even in long-term use.

  An optical recording medium such as a CD-ROM or a DVD-ROM usually comprises a recording layer, a reflective film layer, and a protective layer (overcoat) on a substrate. In the past, aluminum alloys have been used for this reflective layer in consideration of cost and reflectance. However, the mainstream of optical recording media is a write-once / rewritable medium (CD-R / RW, DVD-R / RW / With the transition to (RAM), application of a material with higher reflectivity is demanded. This is because organic dye materials are widely used as the constituent material of the recording layer of write-once and rewritable media, and the organic dye material increases the attenuation of the light beam, thereby improving the reflectivity of the reflective layer. By trying to supplement this attenuation.

  From the viewpoint of reflectivity, silver is applied as a material for the reflective layer of the optical recording medium. Silver is a preferred material because it has high reflectivity and is less expensive than gold, which also has high reflectivity. However, silver is poor in oxidation resistance and sulfidation resistance, and there is a problem that it corrodes due to oxidation and sulfidation and turns black to reduce the reflectance. In particular, silver has a problem that the organic dye material applied in the recording layer of the write-once / rewritable optical recording medium has a poor corrosion resistance and a decrease in reflectance due to long-term use.

  In order to cope with the problem of a decrease in reflectivity associated with the use of an optical recording medium, conventionally, an optical recording medium has been developed in which a silver alloy that has improved corrosion resistance while ensuring reflectivity is applied as a reflective layer. Yes. Most of these contain silver as a main component, and various additive elements are added to the silver. For example, 0.5 to 10 atomic% ruthenium and 0.1 to 10 atomic% are added to silver. In which 0.5 to 4.9 atomic% of palladium is added to silver, etc. are disclosed. These silver alloys have good corrosion resistance and can maintain the reflectance even in the use environment, and are suitable for the reflective layer (see Patent Documents 1 and 2 for details of these prior arts). ).

Japanese Patent Laid-Open No. 11-134715 JP 2000-109943 A

  For the above silver alloys, there is a temporary improvement in corrosion resistance. However, even these silver alloys do not corrode at all under the use environment. Further, this does not completely guarantee the decrease in reflectivity, and a material that can maintain the reflectivity at a higher level is required.

  In the field of optical recording devices, a red semiconductor laser (wavelength 650 nm) is currently applied as a recording light source. Recently, there is a prospect of practical use of a blue laser (wavelength 405 nm). ing. When this blue laser is applied, a storage capacity of 5 to 6 times that of the current optical recording apparatus can be secured. Therefore, it is considered that the next-generation optical recording apparatus is mainly applied with a blue laser. Here, according to the present inventors, it has been confirmed that the change in the reflectance of the reflective layer varies depending on the wavelength of the laser to be irradiated, and in particular for short-wavelength laser irradiation, it is reflected regardless of the presence or absence of corrosion. It has been confirmed that the rate decreases and the decrease in reflectance due to corrosion is often more pronounced than in the case of long wavelength laser irradiation. Therefore, in order to produce a recording medium that can cope with the transition of the recording light source in the future, development of a material that has high reflectivity even for laser irradiation in the short wavelength region and can maintain the practical range. Is desired.

  The present invention has been made under the background as described above, and is a silver alloy that constitutes a reflective layer of an optical recording medium, and can function without lowering the reflectance even after long-term use. The object is to provide a material for the layer. In addition, the present invention provides a material having a high reflectance even with a short wavelength laser beam.

  In order to solve this problem, the present inventors have found a suitable reflective layer material from a direction different from that of the prior art while using silver as a main component, as in the prior art. The reason why silver is a main component is that the advantages (high reflectance and low cost) of silver as described above are taken into consideration. The approach different from the prior art adopted by the present inventors corresponds to the fact that the prior art has improved only the corrosion resistance by adding an additive element. That is, corrosion (oxidation) of the reflective layer during the use process cannot be avoided in practice. Therefore, the present inventors dared to allow oxidation during the use process, and thought that a silver alloy that does not cause a decrease in reflectance even when oxidized is suitable as a material for the reflective layer. As a silver alloy that does not cause a decrease in reflectivity even when oxidized, a silver alloy added with indium and / or tin that is oxidized preferentially over silver and does not affect the reflectivity even when oxidized is found. The present invention has been conceived.

  The present invention is a silver alloy for a reflective film that contains indium and tin as additive elements, and the balance is made of silver, and is a silver alloy having a total concentration of additive elements of 0.1 to 2.0% by weight.

  The oxides of indium and tin added as additive elements in the present invention are transparent as can be seen from the wide application as transparent electrode materials. The silver-indium / tin alloy according to the present invention oxidizes indium and / or tin in the course of use, but the oxide is transparent and does not impair the reflectivity of the alloy. In the alloy according to the present invention, indium oxide and tin oxide are dispersed inside the alloy, and an oxide film made of indium oxide and tin oxide is formed on the alloy surface. This oxide film functions as a protective layer for further oxidation of the alloy and suppresses the oxidation of silver as a base material. The reflective layer formed of the alloy according to the present invention can maintain the reflectivity by the action as described above.

  Here, the content of indium and tin as additive elements in the present invention is preferably set to a concentration of 0.1 to 25% by weight of both indium and tin, considering only the maintenance of reflectance. If the addition amount is less than 0.1, there is no effect of maintaining the reflectivity. If the additive element concentration exceeds 25%, the reflectivity is greatly reduced depending on the use environment and the wavelength of the incident laser beam, which impedes practical use. This is because it may occur. A particularly preferred concentration is 0.1 to 2.0% by weight. This is because within this range, the reflectance can be maintained at a higher level regardless of the use environment and the wavelength of the laser beam. These concentration ranges indicate the concentration ranges of all the additive elements. When both indium and tin are contained, the total concentration of each element is within these ranges.

  The silver alloy according to the present invention is suitable as a material for a reflective layer of an optical recording medium, but a more preferable characteristic when the silver alloy is provided as a material for a reflective layer is high thermal conductivity. This is because the sensitivity of the recording medium may be lowered if the thermal conductivity of the reflective layer is low. Therefore, it is more preferable that the silver alloy according to the present invention, which has preferable characteristics in both maintenance of reflectance and high thermal conductivity, has an additive element concentration of indium and tin of 0.1 to 0.5% by weight. According to the present inventors, an alloy exceeding 0.5% by weight has a low thermal conductivity, which is a fraction of the thermal conductivity of silver, which is the main component of the alloy.

  The silver alloy as the reflective layer material according to the present invention described above can be manufactured by a melt casting method. There is no particular difficulty in the production by this melt casting method, and it can be produced by a general method in which each raw material is weighed, melted and mixed and cast.

  By the way, the actual production of the reflective layer is often performed by forming a thin film by sputtering using a target made of a material for the reflective layer. As described above, in the silver alloy according to the present invention, indium and tin contained are preferentially oxidized, and the oxide generated at this time is used as a protective film, so that subsequent oxidation and sulfidation can be suppressed. Therefore, when the silver alloy according to the present invention is used as a reflective film, in the sputtering method, oxygen is mixed with argon gas introduced into the sputtering apparatus, and reactive sputtering is performed to form the reflective layer while oxidizing it. A protective film can be formed from the initial stage of forming the reflective layer.

  On the other hand, this reactive sputtering requires a delicate control for oxygen gas introduction in order to control the degree of oxidation of the reflective layer, which may impair the production efficiency of the reflective layer. Therefore, the inventors of the present invention have made the reflective layer in a normal sputtering process without introducing oxygen gas that requires delicate control by oxidizing indium and tin as additive elements in advance for the alloy according to the present invention. It was thought that a protective film could be formed. That is, the present inventors internally oxidize a part or all of indium and / or tin as additive elements in the silver alloy according to the present invention containing silver as a main component and containing indium and / or tin as additive elements. It was decided. It has been found that when a thin film is produced using the internally oxidized alloy as a target, a thin film in which indium and tin oxides are uniformly dispersed can be formed from the time of production of the thin film.

  Here, for the production of the internally oxidized silver alloy, a silver alloy containing indium and / or tin with a predetermined composition is produced, and this is pressurized and heated in a high-pressure oxygen atmosphere, and a part of the alloy is produced. Alternatively, it can be produced by oxidizing all indium and tin. As specific oxidation conditions, it is preferable to perform pressurization and heat treatment at 700 to 800 ° C. for 60 to 80 hours in an atmosphere having an oxygen pressure of 0.1 to 1 MPa.

  The silver alloy which concerns on this invention demonstrated above has a characteristic preferable as a reflection layer, and the fall of a reflectance is suppressed in the use process. Further, as described later, even under irradiation with a laser beam with a short wavelength, the reflectance and the maintenance thereof are better than those of the conventional reflective layer material. As described above, the sputtering method is generally applied in the production of the reflective layer of the optical recording medium. Therefore, the sputtering target made of the silver alloy according to the present invention can produce an optical recording medium provided with a reflective layer having desirable characteristics.

  As described above, the silver alloy according to the present invention differs from the conventional idea in that the reflectance in the process of use is improved by adding an element that generates an oxide that does not adversely affect the reflectance even when oxidized. The decrease is suppressed. According to the present invention, it is possible to manufacture a reflective layer with little decrease in reflectivity even after long-term use, thereby prolonging the life of the optical recording medium. Moreover, the silver alloy which concerns on this invention shows a favorable reflectance and its maintenance rather than the conventional reflective layer material also under the laser beam irradiation of a short wavelength. Accordingly, the present invention can also be applied to a recording medium for an optical recording apparatus using a short wavelength laser as a light source, which will become the mainstream in the future.

  Hereinafter, preferred embodiments of the present invention will be described together with comparative examples.

Example 1 Here, a target having an Ag-1.2 wt% In-0.8 wt% Sn composition was produced as a silver alloy, and a thin film was formed by sputtering based on this target. The thin film was subjected to a corrosion test (acceleration test) under various environments, and the change in reflectance after the corrosion test was examined.

  In the production of a silver alloy, each metal is weighed to a predetermined concentration, melted in a high frequency melting furnace, and mixed to obtain an alloy. This was cast into a mold and solidified to form an ingot, which was forged, rolled, and heat treated, and then molded into a sputtering target.

For the production of the thin film, the substrate (borosilicate glass) and the target are placed in a sputtering apparatus, the inside of the apparatus is evacuated to 5.0 × 10 ⁻³ Pa, and then the argon gas is reduced to 5.0 × 10 ⁻¹ Pa. Introduced. As sputtering conditions, a film was formed for 1 minute at a direct current of 1 kW, and the film thickness was 1000 mm. The film thickness distribution was within ± 10%.

  The thin film corrosion test is performed by exposing the thin film to the following environments and measuring the reflectance of the thin film after the test while changing the wavelength with a spectrophotometer. The change was examined as a standard.

(1) Heating in air | atmosphere at 250 degreeC for 2 hours The thin film was mounted on the hotplate, and it heated at the said temperature and time. This test environment is for examining the oxidation resistance of the thin film.
(2) Immersion in warm water for 30 minutes The thin film was immersed in pure water at 60 ° C. This test environment is for examining the moisture resistance of the thin film.
(3) Immersion in alkaline solution The thin film was immersed in a 3% sodium hydroxide solution (temperature 30 ° C.) for 10 minutes. This test environment is for examining the alkali resistance of the thin film.

Comparative Example : As a comparison with the silver alloy according to the present embodiment, Ag-1.0 wt% Au-1.0 wt% Cu, Ag-1.0 wt% Pd, developed for the same purpose as the present invention. A thin film was produced from a target composed of three types of silver alloy gold of −1.0 wt% Cu and Ag—1.0 wt% Nd—1.0 wt% Cu, and the same corrosion test was performed. The change of was measured.

  The results of the corrosion test of this example are shown in Tables 1 to 3. The reflectances shown in these tables are relative values with the reflectance of silver immediately after film formation being 100. Each measured value is a reflectance at wavelengths of 650 nm, 560 nm, and 400 nm (corresponding to wavelengths of red, yellow, and blue lasers, respectively).

  From this result, as an overall trend, the reflectance decreases as the incident light wavelength becomes shorter (the same applies to the thin film without the corrosion test immediately after film formation). And the thin film manufactured with the silver alloy which concerns on a present Example shows a higher value than any comparative example when the value of a reflectance is seen. In particular, in this example, the reflectance immediately after film formation is maintained in any environment subjected to the corrosion test, but in the case of the comparative example, the reflectance varies depending on the environment of the corrosion test. Therefore, it can be seen that the thin film according to this example is more preferable as the reflective layer than the prior art.

Example 2 In this example, the relationship between the additive element concentration of the silver alloy and the reflectance after the corrosion test was investigated, and the upper limit value was examined. Here, the silver alloy produced and used was an Ag—Sn alloy, and a silver alloy in which the tin concentration was changed to 2 to 50% by weight was examined. The method for producing the silver alloy in this example is the same as that in Example 1. However, the corrosion test environment is not limited to the test environment in Example 1, and is 0. The test was conducted by immersing in a 01% aqueous sodium sulfide solution (temperature 25 ° C.) for 1 hour. The reflectance measurement after the corrosion test was performed in the same manner as in Example 1. The results are shown in Tables 4-6.

  From the above results, when the acceptance criterion as a reflective layer is set to 60 (the reflectance of silver is set to 100), depending on the incident light wavelength, when an additive element of 25% by weight or more is added from the tendency of this example. The reflectivity in the initial state (immediately after film formation) is low, and when the corrosion slightly occurs, it often falls below the acceptance standard. Therefore, the content of the additive element is estimated to be 25% by weight. It can also be seen that the additive element concentration is more preferably 5.0% by weight or less in order to maintain the reflectivity at a higher dimension (in order to show a value of 80 or more).

Example 3 Here, in order to examine the lower limit value of the additive element, an Ag—In—Sn alloy containing 0.05 to 0.5% by weight of indium and tin is manufactured, a thin film is manufactured therefrom, and a corrosion test is performed. The change in reflectivity was measured. The manufacturing method of the alloy, the corrosion test environment, and the like are the same as in Example 2. The results are shown in Tables 7-9.

  From this result, the silver alloy examined in Example 3 has good reflectivity immediately after film formation, but the change in reflectivity due to atmospheric heating is large, and there is a correlation between the additive element concentration and reflectivity. As shown, the reflectivity after heating tends to decrease as the additive element concentration decreases. As in Example 2, when the acceptance criterion is 60, the thin film having an additive element concentration of less than 0.1% by weight (0.05%) cannot maintain the reflectance after atmospheric oxidation. I understand. Therefore, it is considered appropriate that the lower limit value of the additive element concentration is 0.1% by weight.

Example 4 : Here, in order to examine the relationship between the concentration of the additive element and the thermal conductivity, an Ag-In-Sn alloy containing 0.05 to 2.0% by weight of indium and tin was manufactured. It was manufactured and its thermal conductivity was determined. The formation of the thin film is the same as in Examples 1 and 2. Moreover, since it is difficult to directly measure the thermal conductivity of the thin film, first, the specific resistance was measured, and the thermal conductivity was calculated from the value by the Wiedemann-Franz law. The results are shown in Table 10. Table 10 shows Ag-1.0 wt% Au-1.0 wt% Cu, Ag-1.0 wt% Pd-1.0 wt% Cu, Ag-1. The thermal conductivity of three silver alloys of 0 wt% Nd-1.0 wt% Cu and a pure silver thin film are shown together.

From Table 10, it can be seen that the thermal conductivity of the Ag—In—Sn alloy thin film of this example decreases as the additive element concentration increases. And considering that the thermal conductivity is 50% or more of silver as an acceptable line, considering the thermal conductivity, it is considered appropriate to suppress the addition amount of the additive element to 0.5% by weight or less. . Then, considering the results of Example 3 together, it was confirmed that the preferable additive element concentration was 0.1 to 0.5% by weight with respect to the two conditions of maintaining the reflectance and high thermal conductivity. The silver alloy thin films of the comparative examples all had a thermal conductivity of less than 50% of silver.

Claims (2)

A silver alloy for a reflective film of an optical recording medium containing indium and tin as additive elements, the balance being silver,
The concentration of the additive element is 0.1 to 0.5% by weight (except for the case where indium is 0.1 atomic% and tin is 0.1 atomic%) . A sputtering target comprising the silver alloy according to claim 1 .