WO2015194455A1

WO2015194455A1 - High-durability silver mirror

Info

Publication number: WO2015194455A1
Application number: PCT/JP2015/066902
Authority: WO
Inventors: 健一近江; 廣川　智也
Original assignee: 岡本硝子株式会社
Priority date: 2014-06-17
Filing date: 2015-06-11
Publication date: 2015-12-23
Also published as: CN106062590B; JP6340608B2; TWI600535B; JPWO2015194455A1; CN106062590A; TW201605610A

Abstract

There exists a need for a high-reflectance, high-durability mirror that has higher reflectance than an enhanced-reflection aluminum mirror, and the durability required for use as an optical component in a projector or the like, as well as being serviceable as a collection mirror exposed to heat and light for extended periods, or as a reflecting optical component for an automobile. According to the present invention, a silver mirror of high reflectance and high durability is obtained by forming on a base material a first layer composed of an oxide film, a second layer composed of a film of metal selected from metals having a face-centered cubic crystalline structure, a third layer composed of a silver film, a fourth layer composed of an ITO film having thickness of 3-12 nm, and a fifth layer composed of a protective film, in that order. Glass, Si, or the like can be used as the base material. By forming a foundation layer that comprises SiO/SiO₂, a high-durability silver mirror employing a resin base material can be obtained. Through a prescribed heat treatment, there can be obtained a high-reflectance, high-durability silver mirror having excellent heat resistance.

Description

High durability silver mirror

The invention according to the present application is not only a reflection optical system for optical products such as cameras, copiers and projectors, but also a reflection optical system for vehicles such as a condensing mirror for concentrating solar cells and a head-up display (HUD) of an automobile. In particular, the present invention relates to a highly durable silver mirror that combines high reflectivity and excellent durability that can withstand harsh usage environments.

As a reflective mirror having a high reflectance, an aluminum (Al) mirror that exhibits a high reflectance in a wide visible light region is generally used. The Al mirror is a glass or resin substrate coated with an Al film and has an average reflectance of about 90% in the visible light region. When it is desired to further increase the reflectance, an interference film for increasing the reflectance, that is, an increased reflection film is formed on the Al film. The average reflectance of the Al mirror provided with the increased reflection film reaches about 95%. Here, the average reflectance is used as a simple average reflectance of reflectance at a wavelength of 420 to 680 nm of visible light. The same meaning is used hereinafter.

The Ag mirror is a mirror in which an Ag film is formed instead of the conventional Al film, and has a higher reflectance in a wide visible light region than the Al mirror, and the average reflectance is about 93%. Reach. And when an increased reflection film is formed on an Ag film, the average reflectance can be increased to 97% or more.

JP 2000-241612 A JP 2003-4919 A Japanese Patent No. 4307921 JP 2007-147667 A JP 2010-19875 A JP 2012-47856 A

In an apparatus having a reflection optical system such as a projector, a large number of reflection mirrors are used to change an optical path. In a reflective optical system that repeats reflection many times, the amount of light finally reaching the target optical element decreases exponentially according to the reflectance of the reflection mirror and the number of reflections. Therefore, when it is necessary to use a large number of reflecting mirrors in the reflecting optical system, maintaining the reflectance of the reflecting mirror at a high reflectance is a very important issue in increasing the amount of light and ensuring brightness. ing.

The increased reflection Al mirror that is most popular as a high-reflectance mirror has an average reflectivity of only about 95% at most, even when the reflectivity is increased by the increased reflection film that also functions as a protective film. In addition, there is a problem that it cannot be used for applications that require higher reflectance.

In addition to having high reflectivity, high durability is also important. This is because these reflecting mirrors constantly receive intense light and are exposed to high temperatures by light absorption. This is because even when receiving light or heat, it is required to maintain a high reflectance over a long period of time. Furthermore, a convex mirror used in an optical system for concentrating sunlight on a photoelectric conversion element in a concentrating solar cell that has become widespread in recent years, and a concave mirror used for in-vehicle use such as an automotive head-up display In that case, it will be exposed to the outdoors or the same environment as the outdoors for a long period of time, so it will be more durable and corrosive assuming urban areas compared to conventional projection projector applications. It is also required to have durability against gas and salt damage assuming use near the coast.

On the other hand, as described above, the Ag mirror has a higher reflectance than the Al mirror in a wide region of visible light, and when an increased reflection layer that also functions as a protective layer is provided, the average reflectance is 97% or more. Reach. However, since the Ag film has a lower durability than the Al film and is easily corroded, there is a problem that the Ag film is not suitable for applications requiring high durability.

The reason why the durability of the Ag film is low is that the film is peeled off or damaged when the adhesion with the substrate is insufficient. It is also known that when subjected to heat or ultraviolet rays, Ag atoms are easy to move and aggregate so as to form large grains, the film becomes non-uniform, and the reflectance decreases. The degree of deterioration becomes prominent when exposed to high temperatures and ultraviolet rays over a long period of time. The concentrating mirror for concentrating solar cells is exposed to such an environment.

It can be considered that salt damage and corrosion of metals in general are due to ionization and chemical reaction (oxidation, etc.) of metals by electrolytes and reactive gases. Therefore, it is important that the Ag mirror does not allow the electrolyte to reach the metal and is not exposed to a corrosive atmosphere. For this purpose, the presence of a strong protective film against the metal film is important, but it is considered that the protection function was not sufficient with the configuration of the conventional Ag mirror. When corrosive gases such as sulfurous acid gas, hydrogen sulfide gas, and chlorine gas are present in the environment, these corrosive gases permeate the protective film and combine with Ag atoms to blacken as AgS or AgCl. It is considered that reflection is impaired.

Because of these thermal and environmental factors, even if an average reflectivity as high as 97% is achieved immediately after the production of the Ag mirror, after various durability tests, that is, long-term use. Later, the reflectivity decreases and the initial performance is often not maintained. Such thermal and environmental factors are by no means unique, and concentrating solar cells installed in coastal areas and automobiles traveling in urban areas are constantly exposed.

In order to solve such a problem, a technique for making the Ag mirror highly durable has been proposed. For example, Non-Patent Document 1 discloses a means for improving durability by alloying Ag. However, at the same time, it is also described that the reflectance is likely to decrease due to alloying of Ag.

In Patent Document 1, in order to improve the adhesion of an Ag film formed on a resin substrate, first, a base layer made of a silicon monoxide film (SiO film) is formed, and an intermediate layer is further formed between the SiO film and the Ag film. A technique for obtaining an Ag mirror excellent in moisture resistance and durability by improving the adhesion with a resin substrate by interposing a metal film (for example, Cu film) is disclosed. However, Patent Document 1 improves the adhesion between the resin substrate and the Ag film. However, as the protective film on the surface side of the Ag film, the intensifying film only serves as the protective film. No mention is made of the durability against moisture, electrolyte and corrosive gas from the side, and there is no description as to whether or not strict requirement specifications for solar cells and automobiles are satisfied, for example.

In Patent Document 2, a base layer made of an aluminum oxide film (Al ₂ O ₃ film) is formed in order to improve the adhesion between the substrate and the Ag film. Furthermore, it is also disclosed that an Al ₂ O ₃ film and a titanium oxide film (TiO ₂ film) are formed on the Ag film to improve the corrosion resistance. However, Patent Document 2 is intended to improve adhesion and durability with a small number of layers, and it has been described that tape peelability has been improved, but also from the surface side of the Ag film. No mention is made of durability against moisture, electrolytes and corrosive gases, and there is no description as to whether or not strict required specifications for solar cells and automobiles are met.

In Patent Document 3, in a reflecting mirror in which a reflecting film is formed on a resin substrate, a base film made of Al ₂ O ₃ is formed between the resin substrate and the reflecting film, and a fluorine-containing silicon compound is further formed on the reflecting film. By forming a water-repellent film, preventing the penetration of moisture and electrolyte from the resin substrate side and film surface side, preventing corrosion of the reflective film, and ensuring a good balance of excellent reflective properties and durability Is described. However, although the technique disclosed in Patent Document 3 describes that the reflectance and durability of 97% or more are compatible, the protective film against the oxidation or corrosion of the Ag film is not formed on the Ag film. Therefore, it is unclear whether or not the high temperature test for solar cells and the durability against electrolytes and corrosive gases required for automobiles are satisfied.

Patent Document 4 uses an Al ₂ O ₃ underlayer described in Patent Document 2, and uses a nickel chromium alloy film (Ni—Cr alloy film) as an intermediate layer described in Patent Document 1, and an Ag film. An upper buffer layer made of an Al ₂ O ₃ film and a silicon oxide film (SiO ₂ film) is formed on the surface to prevent corrosion, and an increased reflection film made of a TiO ₂ film is formed to further increase the reflectance. It is. However, although the technique disclosed in Patent Document 4 is described as having a high reflectance of 99% or more even after the heat cycle test, the high temperature and high humidity test, the high temperature exposure test, and the salt spray test, Does the protective film (anti-oxidation film) against heat, oxidation and corrosion of the Ag film on the Ag film satisfy the durability against high temperature test for solar cells and corrosive gas required for automobiles? Whether it is unknown.

In Patent Document 5, a reflective film formed by sequentially laminating a base layer, an Ag layer, and a protective layer composed of a plurality of layers on a substrate, a layer in contact with the Ag layer among the plurality of layers constituting the protective layer is disclosed. By making the Si layer free of oxygen, the antioxidant effect and moisture resistance are improved. It is said that a stable high reflectance can be obtained by using the Si layer. However, Patent Document 5 discloses a technique for forming a Si protective film directly on the Ag film in order to improve the antioxidant effect and moisture resistance. However, only a high-temperature and high-temperature and high-humidity test are performed. However, it is unclear whether long-term durability required for use in automobiles, such as high-temperature tests for solar cells and durability against corrosive gases, is satisfied.

In Patent Document 6, when a reflective layer containing Ag is formed on a resin base material, in order to cut UV light that is transmitted through the reflective layer and deteriorates the resin base material, A reflector having an ITO layer formed thereon is disclosed. Among them, a configuration is disclosed in which an ITO layer having a thickness of about 7 to 15 nm is also formed on the reflective layer in order to achieve both long-term weather resistance, gas barrier properties and transparency. However, Patent Document 6 relates to a reflector for a lighting fixture, and is different in technical field and application from the present invention. Therefore, the film configuration is different from that of the reflection mirror of the optical device or optical apparatus, and it is different in that a melamine resin coating film is used as a base film or a protective film. In addition, by sandwiching an Ag film between ITO films, it can withstand long-term irradiation of a mercury lamp at a predetermined intensity, but it is unclear whether it can withstand other durability tests, especially those required for automobiles. is there.

A dielectric multilayer film mirror in which a large number of high-refractive index transparent films and low-refractive index transparent films are alternately laminated can also achieve a high reflectivity by the interference of light, but compared to Al mirrors and Ag mirrors. The wavelength range where high reflectivity can be obtained is narrow, and the number of film layers required to achieve high reflectivity is much higher, resulting in very high costs. Not popular.

The object of the invention according to the present application is to provide a highly durable silver mirror having both high reflectivity of a pure silver (Ag) mirror and excellent durability not inferior to an Al mirror or an Ag alloy mirror. Concentrated solar power generation that not only satisfies the durability required when used in optical products such as projectors, which was the main application of this type of mirror, but also is exposed to heat and light over a long period of time. It is to provide an Ag mirror that has improved durability to a level that can be used for a product including a reflective optical system for automobiles that is exposed to an environment close to the outdoors in an urban area for a long period of time. .

More specifically, it provides a highly durable silver mirror in which even when subjected to heat or ultraviolet rays over a long period of time, Ag atoms are not aggregated, the uniformity of the film is maintained, and the reflectance is not lowered. In addition, even when corrosive gases such as sulfurous acid gas, hydrogen sulfide gas, nitrogen oxide gas, and chlorine gas exist in the environment, these gases are combined with Ag atoms, and AgS, AgCl, etc. Thus, a highly durable silver mirror that is blackened and does not lose its reflection is realized.

In order to solve the above-mentioned conventional problems, the present invention provides a metal film selected from a metal having a face-centered cubic crystal structure as a second layer and an oxide film as a first layer on a substrate. A highly durable silver mirror comprising a silver film as a third layer, an ITO film having a thickness of 3 to 12 nm as a fourth layer, and a protective film as a fifth layer in this order.

The highly durable silver mirror of this invention has the basic film structure which consists of a film | membrane of said 1st layer to the 5th layer in which each exhibits the outstanding function. As a base material that can be used in the present invention, the inventors have continued intensive research. As well as a glass base material, a semiconductor base material such as a Si substrate, a cycloolefin polymer resin (COP resin), etc. It has been found that even if a resin base material or a metal base material such as brass is used, the silver mirror having the basic film structure composed of the first layer to the fifth layer has high reflectivity and excellent durability. .

In the present invention, particularly when durability (wear resistance) against abrasion is required, a silicon oxide (SiO _x ) film, magnesium fluoride as a wear-resistant film is formed on the protective layer as the fifth layer. It is desirable to form a (MgF ₂ ) film or a film of these two layers. Here, the term “SiO _x film” means a film having an oxidation degree between the SiO film and the SiO ₂ film. However, in order to prevent a decrease in reflectance due to light absorption, the SiO _x film may be an SiO ₂ film. desirable. When comparing the SiO _x film as the wear resistant film with the MgF ₂ film or the MgF ₂ / SiO _x 2 layer film, the MgF ₂ / SiO _x 2 layer film shows the most excellent wear resistance.

In the present invention, in order to achieve unprecedented high durability, after the first to fifth layers are formed on the glass substrate, or after the wear-resistant film is formed on the fifth layer. The heat treatment is preferably performed in the temperature range of 400 to 500 ° C. for 30 to 90 minutes. Examples of the substrate that can withstand the heat treatment in such a temperature range include a glass substrate, a semiconductor substrate, and a metal substrate. On the other hand, since the resin base material deteriorates when kept at such a temperature, the heat treatment cannot be performed. Note that when it is described as 400 to 500 ° C., it means 400 ° C. or more and 500 ° C. or less, and when it is described as 30 to 90 minutes, it also means 30 minutes or more and 90 minutes or less. The same meaning is used hereinafter.

The basic structure of the present invention is a film configuration in which the first to fifth layers are formed on various base materials. When a glass substrate, a semiconductor substrate represented by a silicon (Si) substrate, or a metal substrate is used as the substrate, these substrates hardly change even when subjected to the action of light or heat, and are resistant to corrosion. Further, durability is further improved in that gas is not generated and the film is not deteriorated.

In the present invention, the oxide film as the first layer serves as an underlayer for ensuring adhesion between the base material and the silver (Ag) film. Even if an Ag film, which is a highly reflective layer, is formed directly on the base material, it will be immediately peeled off from the base material due to wear or the like, but if an oxide film is formed, the adhesion is improved. The underlayer made of an oxide film also functions to trap oxygen gas diffusing from the base material side and prevent oxidation of the Ag film. Therefore, the oxide film does not have to be completely stoichiometric, and may be a composition in an oxygen-deficient state. Although an oxide film in an oxygen-deficient state often exhibits light absorption, in the present invention, since the first layer is formed on the lower side (base material side) of the Ag film, the reflectance of the Ag film is lowered. It doesn't matter.

The oxide film is formed as the first layer because the oxide film has good adhesion to a glass substrate that is also an oxide. In the present invention, the semiconductor substrate other than the glass substrate is used. Even in the case of a metal substrate, an oxide film is formed as the first layer. This is considered to be related to the fact that a thin oxide film is formed on the surface of these base materials even if they are semiconductor base materials or metal base materials.

As the type of the oxide film, various oxide films that can be formed by a vapor deposition method or a sputtering method can be used, but an aluminum oxide film (Al ₂ O ₃ film), a silicon oxide film (SiO ₂ film), or It is desirable that it is one of titanium oxide films (TiO ₂ films). This is because these oxide films are easy to form, have a small residual stress, and have excellent adhesion to a glass substrate. These oxide films do not necessarily have a stoichiometric composition. For example, the composition of the aluminum oxide film is stoichiometrically Al ₂ O ₃ , but in the present invention, it is not necessarily Al ₂ O ₃ , and the composition in a state in which oxygen is slightly depleted (Al ₂ O _3-X is often described).

When an Al ₂ O ₃ film, a SiO ₂ film, or a TiO ₂ film is used as the oxide film, various durability of the highly durable silver mirror of the present invention can be enhanced. Furthermore, the Al ₂ O ₃ film is most excellent for improving heat resistance.

A film formed between the base material and the Ag film to improve the adhesion of the Ag film has been conventionally formed with a film thickness of about 40 to 200 nm, but the first oxide film in the present invention is A thinner film thickness is sufficient, specifically, a film thickness of about 10 nm to 60 nm may be used. Of course, even if it is formed with a film thickness of 60 nm or more, there is no problem in performance, but it should be noted that film stress is likely to occur. On the other hand, when the thickness is 10 nm or less, the performance of trapping corrosive gas from the glass substrate side may be insufficient.

The metal film of the second layer of the present invention is an intermediate layer for enhancing the adhesion between the base material and the oxide film of the first layer and the Ag film. Since a metal film is generally rich in ductility, it is easily deformed, and the force for peeling off the Ag film such as tensile stress and shear stress can be weakened. Further, since it has an affinity for oxygen atoms, it has an effect of preventing oxidation of the Ag film due to diffusion of moisture and the like from the substrate side. In the present invention, it is important to use a metal film selected from metals having a face-centered cubic crystal structure. This is because the crystal structure of the Ag film formed on the upper layer of the metal film is a face-centered cubic type. By using a metal film having the same face-centered cubic crystal structure as that of the Ag film as the intermediate layer, the crystallinity of the Ag film can be increased, and thus the reflectance can be increased.

Examples of the metal having a face-centered cubic crystal structure include aluminum (Al), copper (Cu), nickel (Ni), platinum (Pt), gold (Au), and the like. The film is preferably an Al film, a Cu film, or a Ni film. This is because these metals are relatively inexpensive, easy to form, and the lattice constant is relatively close to the lattice constant of Ag, so that it is expected to promote crystallization of the Ag film. .

When an Al film, Cu film or Ni film is used as the second layer metal film of the present invention, crystallization of the Ag film can be promoted and durability can be improved. Furthermore, the Ni film is the most excellent for increasing heat resistance.

The thickness of the metal film is sufficient if it is about 10 to 60 nm. Patent Document 1 relates to a resin base material, and a Cu film having a thickness of 100 to 200 nm is used as an intermediate layer. However, a thinner metal film is sufficient in the present invention. In Patent Document 3, an Al ₂ O ₃ film is formed as a first layer with a thickness of 20 to 60 nm, and a Ni—Cr alloy layer is formed thereon with a thickness of 20 to 60 nm. In the present invention, A slightly thinner metal film can be used. Even if the metal film is made thicker, the antioxidant effect and the crystallization promoting effect are not enhanced, and it is not preferable because it is disadvantageous in terms of film stress and cost. On the other hand, if the thickness is reduced to 10 nm or less, the effect of relaxing the tensile stress and the shear breaking force is weakened, and the crystallinity is lowered.

The third layer is an Ag film as a highly reflective film. Although the reflectance of the Ag film decreases as it approaches the ultraviolet region, it has a higher reflectance than the Al film in a wide visible light region and is suitable as a reflective film. In the present invention, the Ag film is desirably formed with a thickness of about 100 to 200 nm. If it is thinner than 100 nm, the reflectance becomes insufficient. In particular, the reflectance on the short wavelength side tends to decrease. For example, at a wavelength of 380 nm, when the Ag film thickness is 50 nm, the reflectance decreases by about 1% compared to the case of 100 nm. On the other hand, even if it is thicker than 200 nm, the reflectance and durability hardly change. Since silver as a film forming material is expensive, it is desirable to make it as thin as possible within the range satisfying the reflectance and durability from the viewpoint of cost.

In the present invention, the third-layer Ag film is preferably made of pure silver substantially free of components other than silver (Ag). In the Ag film, impurities of a level that cannot be removed even by purification of Ag cannot be mixed, but in order to achieve high reflectivity, the Ag film must be made of pure silver that does not substantially contain components other than Ag. This is because it is desirable. According to the description of Non-Patent Document 1, an improvement in durability is expected by adding a metal such as palladium (Pd) or niobium (Nb) to silver. I can't escape. From this point, in the present invention, in order to obtain high reflectivity, it is desirable to use an Ag raw material of 3N grade (99.9% or more) or higher as the Ag material for film formation. The present invention is characterized in that, while maintaining the high reflectance of pure silver, the durability is not improved by alloying silver but is improved by the action of the entire film structure.

The ITO film as the fourth layer is a film that should be said to be a deterioration preventing layer for achieving high reflectivity and excellent durability by preventing the Ag film from deteriorating in the film structure of the present invention. It is very important. By forming the thin ITO film directly on the Ag film, it is possible to prevent the Ag film from being deteriorated due to oxidation or the like when the protective film is formed as the fifth layer. As a result of diligent research on what film material is optimal as a layer to be formed immediately above the Ag film in order to prevent the deterioration of the Ag film, the inventors have obtained a high reflectance and excellent properties other than the ITO film. We could not find one that could satisfy both durability. When a very thin metal film such as Ni, Nb, Ti or the like was used instead of the ITO film, it had a certain effect as an anti-oxidation of the Ag film, but in order to maintain a high reflectance, It was necessary to form the film with a very thin film thickness of 1 nm or less, it was difficult to control the film thickness, and durability and reflectance were not stable.

The thickness of the ITO film is desirably in the range of 3 to 12 nm, that is, 3 nm or more and 12 nm or less. When the film thickness of the ITO layer is out of this range, the effect of achieving both high reflectivity and excellent durability is significantly reduced. That is, when the thickness is less than 3 nm or exceeds 12 nm, the reflectance decreases immediately after film formation or by a durability test. Although the action of the ITO film exhibiting an excellent protective effect on the Ag film is not clear, it may be considered to prevent the oxidation or corrosion of the Ag film by absorbing, adsorbing or binding oxygen and corrosive gas. it can. ITO is an oxide in which tin oxide is doped in indium oxide, but the same effect was obtained when the ratio of tin oxide was in the range of 5 to 20 wt%.

The fifth layer is a protective film that reinforces the effect of preventing the deterioration of the Ag film by the ITO film. It functions as a layer for preventing moisture and corrosive gas from diffusing from the surface side of the film toward the Ag film. The protective film may be a single layer film, but is preferably formed as a multilayer film. This is because when a single-layer thick film is formed, the film has a columnar structure, a gap is formed between the columns, and moisture and corrosive gas are diffused toward the Ag film. Because it becomes. Since the multi-layer structure inhibits the development of the columnar structure, the function as a protective film is improved. Further, by appropriately selecting the refractive index and thickness of each layer of the multilayer film, the multilayer film can function as an increased reflection film that increases the reflectance. In order to further refine each layer of the multilayer film and improve the function of the protective film, it is effective to form the film by vacuum deposition using plasma assist or ion assist.

There are many combinations of film materials, film configurations and film thicknesses for protective films that can provide an enhanced reflection effect, but avoid the configuration where any layer is extremely thick and any layer is extremely thin. Is desirable. This is because an extremely thick film thickness easily develops crystal growth of a so-called columnar structure in the film thickness direction, resulting in a sparse structure between the columnar structure and the columnar structure, and the barrier performance against moisture and corrosive gas decreases. An extremely thin layer reduces the barrier performance.

As an example of the protective film, a three-layer film in which an aluminum oxide film having a thickness of 28 nm, a silicon oxide film having a thickness of 26 nm, and a titanium oxide film having a thickness of 44 nm are sequentially formed in a predetermined thickness can be exemplified. With this configuration, it is possible to prevent the attack of moisture and corrosive gas from the surface side on the Ag film as the third layer, assist the effect of the ITO layer, and increase the reflectance by optical interference action. . These films directly affect the reflectance, unlike the first layer and second layer films formed on the lower side (glass substrate side) of the Ag film. That is, when these films are not transparent but have light absorption, the reflectivity decreases accordingly. In order to eliminate light absorption, these films are preferably an Al ₂ O ₃ film, an SiO ₂ film, and a TiO ₂ film that are as close to the stoichiometric composition as possible. In order to enhance the reflection enhancing effect, it is conceivable to increase the interference effect by increasing the number of layers. However, even if the number of layers is further increased to two or more layers, a reflection enhancing film consisting of five or more layers can be increased. The effect is not improved so much, and on the contrary, there is a possibility that film stress becomes high and film peeling occurs.

In the present invention, a substrate having a conical or parabolic shape can also be used as the substrate. Since these base materials are not flat plates, a multilayer film constituting a highly durable silver mirror is formed on the inner surface of the cone formed by the concave portion, the inner surface of the paraboloid, the outer surface of the cone formed by the convex portion, and the outer surface of the paraboloid. . In this case, there is a high possibility that the thickness and the structure of each layer to be formed are not uniform depending on the position of the concave portion or the convex portion. In particular, as a protective film on the third-layer silver film and the fourth-layer ITO film, when a multilayer film that generates an optical interference action is formed, the reflectivity decreases due to the interference action, or an interference color is exhibited. It is not preferable. Therefore, when such a non-flat substrate is used, it is desirable to use a SiO ₂ single layer film as the protective film of the fifth layer. Even in such an embodiment, the present invention can achieve both high reflectivity and excellent durability.

In the present invention, after the fifth protective film is formed from the first oxide film on the substrate, heat treatment may be performed at a temperature range of 400 to 500 ° C. for 30 to 90 minutes. preferable. Here, the heat treatment means maintaining in the temperature range. This is because the film structure can be densified and the durability can be further improved by the heat treatment. After the heat treatment, it may be taken out to a room temperature atmosphere and naturally cooled as it is. When a multilayer film including an Ag film is heat-treated at such a high temperature, conventionally, Ag atoms move and aggregate due to thermal migration to form large crystal grains, resulting in a non-uniform film, and reflectivity and durability. Often caused a drop. In an extreme case, a phenomenon occurs in which the grain-grown Ag film grows through the upper and lower layers and is exposed. However, in the film configuration of the present invention, it has been found that even when such heat treatment is performed, aggregation of the Ag film is suppressed.

In the present invention, when using a substrate that can withstand the heat treatment, such as a glass substrate, a semiconductor substrate, or a metal substrate, the heat treatment is particularly required for applications that require excellent heat resistance. It is desirable to do.

Although the effect that the durability can be enhanced without aggregating the Ag film by performing the heat treatment under the above-mentioned conditions has not been elucidated based on which action of the film configuration of the present invention, Can be thought of as That is, first, it is considered that the crystallinity of both the metal film as the second layer and the Ag film as the third layer is improved by heat treatment, and the structural order (crystallinity) is increased. . It can be expected that migration of Ag atoms is suppressed by increasing the crystallinity. Second, due to the high adhesion between the second layer metal film and the fourth layer ITO film and the Ag film, thermal migration of Ag atoms is suppressed, and the Ag film does not form a granular structure. It can be thought that it is because it has become dense. Third, during the heat treatment, Sn atoms and Ag atoms contained in the ITO film on the surface of the Ag film form an extremely thin Ag-Sn alloy in the atomic layer order, which is durable without reducing the reflectance. The effect | action of improving a property is also considered.

Furthermore, the heat treatment not only has an effect on the densification of the film from the second layer to the fourth layer, but also has an effect on the densification of the film of the first layer and the fifth layer as the protective film. I can expect that. Note that it is not preferable that the heat treatment condition is out of the temperature range described above because the Ag film or the like is not sufficiently densified or conversely causes oxidation of the Ag film. In addition, when the heat treatment is performed outside the above-described time range, the same problem occurs.

In the present invention, a resin substrate represented by a cycloolefin polymer (COP) resin can also be used as the substrate. However, in the case of a resin base material, in order to increase the adhesion between the base material and the film, it is necessary to form a two-layer base layer composed of a SiO film / SiO ₂ film as a base layer on the surface of the base material. . An Al ₂ O ₃ film is preferably used as the oxide film of the first layer. When a SiO film / SiO ₂ film is formed as a base layer on the surface of the resin substrate, it is considered that there is an effect of making the surface of the resin substrate equivalent to the surface of the glass substrate. When a resin substrate is used as the substrate, the above heat treatment cannot be performed because the resin substrate cannot withstand a high temperature of 400 to 500 ° C.

In the highly durable silver mirror of the present invention, as described above, when a SiO _x film, a MgF ₂ film, or a MgF ₂ / SiO _x 2 layer film is further formed as a wear-resistant film on the protective film of the fifth layer. Abrasion resistance can be greatly improved. In this case, it is desirable to form the wear-resistant film with a thickness of about 10 to 20 nm. This is because these wear-resistant films are formed not for providing an increased reflection effect but for improving the wear resistance. The SiO _x film, the MgF ₂ film or the MgF ₂ / SiO _x 2 layer film is suitable as the wear-resistant film because these films are difficult to take a crystal structure and have a smooth surface, and are resistant to wear. It is because it is hard to be damaged. These films are also preferable in that they have a low refractive index and are not noticeable even if scratches are present. When these wear-resistant films are formed, the heat treatment for 30 to 90 minutes in the temperature range of 400 to 500 ° C. is preferably performed after these wear-resistant films are formed. This is because these wear-resistant films are also densified.

In the present invention, a water- and oil-repellent film made of a fluorine organic compound or the like is formed as an outermost layer on the fifth protective film or on the wear-resistant film formed on the protective film. You can also. The water / oil repellent film functions to repel moisture in addition to functioning as a surface antifouling film. Therefore, excellent barrier properties are exhibited by repelling salt water, particularly in an environment exposed to salt water. Since the water / oil repellent film itself is colorless and transparent and the film thickness may be about several nanometers, the optical characteristics are not affected without affecting the light interference.

In the present invention, when the heat treatment is performed, the water / oil repellent film must be formed after the heat treatment. This is because if formed before the heat treatment, the water / oil repellent film is decomposed by the heat treatment and disappears.

The highly durable silver mirror of the present invention can withstand a very severe heat resistance test when the heat treatment is performed. The condensing mirror used in the concentrating solar power generation module has an average reflectance of 97% or more in the visible light region even after a heat resistance test of holding at a high temperature of 300 ° C. for 2,000 hours. Although it is required, the highly durable silver mirror of the present invention subjected to the heat treatment can satisfy this requirement. By having durability that can pass such a heat resistance test, it can be used as a highly durable silver mirror that is exposed to direct sunlight over a long period of time. Such heat resistance can also be considered as a result of improving the durability by the action of the entire film structure and heat treatment.

The highly durable silver mirror of the present invention can withstand a high concentration salt water immersion test (30 ° C, immersed in 15% salt water for 24 hours) and a salt spray test, and has an average reflectance of 97% or more even after the test. Can be maintained. The salt water immersion test and salt water spray test are one of the test items required for solar power generation systems installed in coastal areas and parts used in automobiles traveling along the coastal areas. This is a test for evaluating possession. The high durability silver mirror of the present invention can withstand a high concentration salt water immersion test and a salt spray test, such as the effect of ITO film, the effect of a predetermined heat treatment, the effect of a base film and the effect of a protective film. It can be thought of as a composite.

In addition, the highly durable silver mirror of the present invention has an average reflectance of 97% or more in the visible light region even after the corrosion-resistant gas test specified in JIS H8502. This corrosion-resistant gas test is a severe test in which hydrogen sulfide (H ₂ S) gas having a concentration of 10 ppm is used and exposed to an environment of 40 ° C. and 90% RH for 24 hours. This can be cleared. By having such durability, it can be used as a highly durable silver mirror for vehicle use that is used over a long period of time in an environment equivalent to the outdoors in an urban area. Similarly, even after the mixed corrosive gas test described in Non-Patent Document 2 corresponding to five years of exposure in the hot and humid Southeast Asian region, an average reflectance of 97% or more can be maintained. it can. The durability against such a corrosive gas can also be considered as a result of improving the durability by the action of the entire film structure and the heat treatment.

As described above, by using the film configuration disclosed in the present invention, a highly durable silver mirror capable of achieving both high reflectance and excellent durability in a wide visible light region can be obtained. By making the Ag film of the third layer, which is a light reflection layer, pure silver substantially free of impurities, it contributes to the realization of high reflectivity.

A highly durable silver mirror capable of achieving both high reflectivity and excellent durability including heat resistance in a wide range of visible light by heat treatment for 30-90 minutes in a temperature range of 400 to 500 ° C. after film formation; can do. And by combining these actions, we assumed severe heat tests for concentrating solar power generation, high-concentration salt water immersion tests and salt spray tests for coastal areas, and long-term use in urban areas. Even in a corrosion-resistant gas test required for in-vehicle optical products, it can be used as a highly durable silver mirror that can maintain an average reflectance of 97% or more in the visible light region.

The highly durable silver mirror of the present invention is a sunshine carbon arc lamp type weather resistance tester (6.8 mW / cm in an environment of 83 ° C.), which is an accelerated weather resistance test (light resistance) of automobile parts specified in JIS D0205. It was confirmed that an average reflectance of 97% or more can be maintained even after the test of spraying water while irradiating the carbon arc lamp ² for 1,080 hours.

By this invention, the silver mirror with the outstanding durability which was not able to be achieved by the prior art is realizable. Even after various durability tests, an average reflectance of 97% or more in a wide visible light region can be realized. As well as clearing the durability required for reflectors used in liquid crystal projectors, heat resistance tests, salt water immersion tests, salt spray tests, and automotive parts required for concentrating solar power collectors Even after a corrosion-resistant gas test, a salt-water immersion test, and a salt spray test that are required for use, a highly durable silver mirror that maintains a reflectance of 97% or more can be obtained. As a result, it can be used as a concave mirror used in a concentrating solar power collector mirror or a head-up display for automobiles, and can be expected to have a wide range of uses as a silver mirror that can be used in even more severe environments.

It is a figure which shows an example of the film | membrane structure of the highly durable silver mirror of this invention. In an example of the film | membrane structure of the highly durable silver mirror of this invention, it is a figure which shows the relationship between the thickness of an ITO film | membrane, and an average reflectance. It is a figure which shows an example of the base material which has the inclined surface which can be used for this invention. It is a figure which shows arrangement | positioning to the board | substrate dome of a vapor deposition apparatus of the base material which is not planar shape.

Unless otherwise specified, the basic film configuration is composed of glass substrate / Al ₂ O ₃ / Ni / Ag / ITO / Al ₂ O ₃ / SiO ₂ / TiO ₂ (hereinafter referred to as the basic film configuration of the present invention) 7 It is a layer structure. These films were formed using a vacuum evaporation apparatus (Showa Vacuum product number SGC26WA). JEOL product number BS80020CPPS was used as the plasma assist device.

(Examples 1 to 8)
After the glass substrate was washed with warm water, it was set in a vacuum deposition apparatus and evacuated to a vacuum degree of 0.9 mPa. And the surface of the glass substrate was plasma-cleaned using oxygen as a reaction gas, and then the degree of vacuum (back pressure) was adjusted to 3 mPa. In the formation of the first oxide film (for example, Al ₂ O ₃ film), oxygen gas was introduced and the film was formed under the conditions described in Table 1. Similarly, the second and subsequent layers are formed under the conditions described in Table 1, so that No. 2 is formed on the glass substrate. 1-No. Up to 8 films were formed in order. In Table 1, “VD” in the column of the film formation method means normal vacuum evaporation, and the film was formed by evaporating the evaporation material using an electron gun. “PAD” means vapor deposition using a plasma assist device, and a plasma gun that promotes ionization of the vapor deposition material is supplementarily used. The plasma assist current at that time was described as PA current. The fourth ITO film is formed in an argon gas atmosphere, Ni and Ag are not introduced with any gas, and other materials are formed in an oxygen gas atmosphere. It was. The O ₂ gas flow rate is described when the film is formed in an oxygen gas atmosphere, the Ar gas flow rate is described when the film is formed in an argon gas atmosphere, and the pressure is described when the pressure during film formation is controlled. After the film formation was completed, the film was taken out from the vacuum deposition apparatus, placed in a furnace controlled at a temperature of 450 ° C., and heat-treated for 60 minutes.

Table 2 shows the film configurations of seven samples (Examples 1 to 7) prepared as examples using the film formation conditions shown in Table 1. In Examples 1 to 4, the thickness of the ITO film was changed in 4 steps from 3 to 10 nm, and the thicknesses of the other layers were all the same. In Examples 5 and 6, instead of the Al ₂ O ₃ film used in Examples 1 to 4, a SiO ₂ film or a TiO ₂ film was used as the first layer film, respectively. In that case, the film formation conditions of the SiO ₂ film and the TiO ₂ film were in accordance with the film formation conditions of the first Al ₂ O ₃ film in Table 1. In Example 7, a Cu film was used instead of the Ni film as the second layer.

(Comparative Examples 1 to 8)
Table 3 shows a film configuration of a comparative example prepared for evaluation in comparison with the examples. Comparative Example 1 has a film configuration in which an Ni film is directly formed on a glass substrate without using an oxide film as the first layer. Comparative Example 2 and Comparative Example 3 are film configurations that do not use the fourth-layer ITO film in the present invention. Comparative Example 4 and Comparative Example 5 are examples in which a Ni film or a Cu film is formed instead of the fourth layer ITO film in the present invention, and the film thickness is about 1 nm. Comparative Example 6 has a film configuration using a Cr film as the second-layer metal film in the present invention. Comparative Example 7 is the film configuration disclosed in Patent Document 2, and Comparative Example 8 is the film structure disclosed in Patent Document 4. In preparation of Comparative Example 8, as described in Patent Document 4, a Ni—Cr alloy containing 15 wt% of Cr was used as a vapor deposition material as the second metal film, and a Ni film was formed. A Ni—Cr film was formed under conditions according to the film conditions.

FIG. 2 shows the result of examining the relationship between the ITO film thickness, which plays an important role in the present invention, and the average reflectance. Here, the same film structure as in Examples 1 to 4 was used as the basic film structure, the ITO film thickness was changed from 3 nm to 15 nm, and then the reflectivity after heat treatment at 450 ° C. for 60 minutes was measured. Is. In the figure, two line graphs are the results of two sets of experiments, both of which have the same tendency. From this result, it was found that the thickness of the ITO film must be 12 nm or less in order to achieve an average reflectance of 97% or more.

Various durability tests shown in Table 4 were carried out on the film configurations of Examples and Comparative Examples. Adhesion test by tape peeling specified in JISH8504, heat resistance test required by solar cell manufacturer, constant temperature and humidity test and salt water immersion test required by solar cell manufacturer and auto parts manufacturer, required by auto parts manufacturer Such as corrosion tests. As a salt water immersion test, a salt water test A under more severe conditions required by some parts was also conducted in addition to a salt water test A under general conditions. In addition to the corrosion test A according to JIS H8502, the corrosion test B was also performed as a corrosion test B corresponding to actual exposure described in Non-Patent Document 2.

The test results are summarized in Table 5 for the examples and Table 6 for the comparative examples. The circles in the result column of Test A in Table 5 and Table 6 indicate that film peeling did not occur in the adhesion test. A cross indicates that the film has been peeled off. Other annotations are shown outside Table 6.

From the above, it was found that Example 1 of the present invention showed an average reflectance of 97% or more after all the tests conducted, and had excellent durability and high reflectance. Examples 2, 3 and 4 differ from Example 1 only in the thickness of the ITO film of the fourth layer, and since the ITO film thickness is thicker than Example 1, All tests are considered to be cleared. In the adhesion test conducted just in case, the film was not peeled off, and it was confirmed that the high reflectance of 97% or more was maintained after the salt water test A and the salt water test B. In Examples 5 and 6, the SiO ₂ film or the TiO ₂ film is used in place of the Al ₂ O ₃ film that is the base layer in Examples 1 to 4, and these oxide films are used as the first layer. Even when it was used, as a result of Test A, Test D, and Test E, it was found to have durability equivalent to that of Examples 1 to 4. In Example 7, the second-layer metal film in Examples 1 to 4 was constituted by using a Cu film instead of the Ni film, and it was confirmed that excellent durability was similarly exhibited. However, in Examples 5, 6 and 7, a decrease in reflectance of about 3 to 6% was observed only after test B (heat resistance test). From this, it was found that from the viewpoint of heat resistance, the Al ₂ O ₃ film is excellent as the first layer oxide film, and the Ni film is excellent as the second layer metal film.

The following became clear from the test results of the comparative examples. Comparative Example 1 is an example in which the Al ₂ O ₃ film is not formed on the glass substrate, but the adhesion is poor and peeling occurred in the adhesion test. Comparative Example 2 and Comparative Example 3 are examples in which the ITO film in the present invention was not formed, but it was observed that the film surface was deteriorated by the heat resistance test, and a large number of white and black particles were generated. Discoloration of the film has also been observed. Comparative Example 4 and Comparative Example 5 are examples in which a Ni film or a Cu film having a thickness of 1 nm is formed instead of the ITO film in the present invention. %, The durability test was not performed. In Comparative Example 6, a Cr film was used instead of the Ni film as the metal film of the second layer in Examples 1 to 4, but the reflectivity was reduced to 93.3% by the heat treatment. The test was not conducted. As described above, Examples 1 to 8 using Ni and Cu having a face-centered cubic crystal structure as the second-layer metal film showed excellent durability. When Cr having a crystal structure is used as the metal film of the second layer, it has been clarified that the reflectance is lowered by the heat treatment. Comparative Example 7 is a silver mirror having a film configuration disclosed in Patent Document 2, and uses a thick Al ₂ O ₃ film as a base film. However, the heat resistance test revealed that the film deteriorated in a short time and part of the film peeled off. Comparative Example 8 is a silver mirror having a film configuration disclosed in Patent Document 4, in which an ITO film is not formed as compared with the film configuration of the present invention, and the second metal film is Ni—Cr. An alloy film is formed, and the other films are slightly thicker than the present invention. As a result of various tests, although high reflectivity can be maintained for the salt water test A and the corrosion test B, the reflectivity drop after the salt water test B is large and 97% reflectivity cannot be maintained. Later it was found that the reflectivity drop was somewhat large, below 97%.

In order to evaluate the environmental durability, weather resistance, wear resistance, etc. of the highly durable silver mirror of the present invention when a semiconductor or a resin is used as a base material, in addition to the various tests described in Table 4, it is described in Table 7. Various durability tests were conducted. Test L and Test M are tests based on JIS B7080: 2015 newly established in accordance with ISO9211 series established as a test method for optical coating. The designated sand eraser used in Test M is a uniform mixture of rubber and abrasive as described in the standard.

(Examples 8, 9, and 10 and Comparative Examples 9 and 10)
In addition to corrosion resistance, a highly durable silver mirror having a film configuration suitable for applications requiring particularly excellent wear resistance was prepared and evaluated by performing tests A, K, L and M. did. Table 8 shows the film configurations evaluated as examples and comparative examples. Up to the seventh layer on the glass substrate is the basic film configuration of the present invention, and the same applies to Examples 8, 9, and 10 and Comparative Examples 9 and 10. In Example 8, an MgF ₂ film having a thickness of 120 nm was formed as a wear-resistant film on the seventh layer of TiO ₂ film. In Example 9, a 20 nm thick SiO ₂ film was formed on the MgF ₂ film. In Example 10, a water / oil repellent film having a thickness of 3 nm was formed on the SiO ₂ film. On the other hand, in Comparative Example 9, an MgF ₂ film having a thickness of 25 nm is formed on the seventh TiO ₂ film. In Comparative Example 10, an SiO ₂ film having a thickness of 20 nm was formed as an abrasion resistant film, and a water / oil repellent film having a thickness of 3 nm was formed thereon.

The film forming conditions for each layer are as described in Table 1. Conditions for forming the MgF ₂ film not listed in Table 1, using MgF ₂ as the evaporation source, was evacuated to a pressure within the deposition chamber (back pressure) is below 0.9 mPa, the electron beam Vapor deposition was performed. As the water / oil repellent film, a commercially available pellet for vapor deposition impregnated with a fluorine-containing organosilicon compound (eg, Surf Clear manufactured by Canon Optron) was used as a vapor deposition source, and was also vapor deposited by the same electron beam method.

For the examples and comparative examples shown in Table 8, a salt spray test (Test K), a tape peeling test after the salt water test (Test A), an environmental durability test (Test L), and an abrasion resistance test (Test M) did. The results are shown in Table 9. In the salt spray test, none of the reflectances decreased by 1.0% or more after the test, and both the examples and comparative examples had excellent corrosion resistance. Moreover, as a result of performing the tape peeling test after the salt spray test, no peeling of the film was observed for any of the samples, and excellent adhesion was obtained. Next, also in the environmental durability test, the change in reflectance before and after the test was less than 1% and had excellent corrosion resistance. As for the abrasion resistance test, in Examples 8, 9 and 10, even though light was observed after the abrasion test and observed, light transmission due to abrasion scratches was not observed, whereas Comparative Example 9 And 10, thin light streaks were observed. That is, in Comparative Examples 9 and 10, it is considered that the silver film is worn by the wear test and light is transmitted. From the above, it was found that by using the MgF ₂ film as the wear resistant film, excellent wear resistance at a level that passes the sand eraser test can be imparted. However, it was found that when the MgF ₂ single layer film is an abrasion resistant film, the sand eraser test cannot be passed if the film thickness is thin (Comparative Example 9).

(Examples 11 and 12)
The highly durable silver mirror of this invention was created on Si base material which is a semiconductor, and durability was evaluated. Table 10 shows the evaluated film configuration. Up to the seventh layer is the basic film configuration of the present invention. In Example 11, an SiO ₂ film having a thickness of 20 nm is formed on the seventh layer as an abrasion resistant film. In Example 12, a 3 nm thick water / oil repellent film is formed on the SiO ₂ film. Table 11 shows the results of the salt spray test (Test K) for these two examples. The decrease in reflectance after the salt spray test was less than 1%, and it was found that the highly durable silver mirror of the present invention has excellent durability even on a Si substrate.

(Examples 13 to 16 and Comparative Examples 11 to 16)
The highly durable silver mirror of this invention was created using the resin base material, and various durability was evaluated. As the resin substrate, a cycloolefin polymer having a thickness of 2 mm (ZEONOR (registered trademark) manufactured by Zenon Japan Ltd., hereinafter abbreviated as COP) was used. The film configurations and evaluation results of the evaluated examples and comparative examples are shown in Table 12 and Table 13, respectively.

The following matters were clarified from the results of various durability evaluations regarding the highly durable silver mirror on the COP substrate. In Examples 13 to 16, Al ₂ O ₃ / Ni / Ag / ITO / Al ₂ O ₃ / SiO ₂ / TiO _2, which is the basic film configuration of the present invention, is formed in this order. Before the ₂ O ₃ film is formed, the SiO / SiO ₂ base film is formed in this order on the COP substrate. That is, unlike the film configuration on the glass substrate or the Si substrate, the Al ₂ O ₃ film is not formed first as the first layer for the COP substrate, but the thickness as the first base film. A silicon monoxide (SiO) film having a thickness of about 5 nm is formed, a silicon dioxide (SiO ₂ ) film having a thickness of about 150 to 300 nm is formed thereon as a second base film, and then an Al ₂ O ₃ film is formed. It is essential. By forming a base film composed of two layers of SiO film / SiO ₂ film in this way, a highly durable silver mirror having high reflectivity and excellent durability can be obtained even if a resin base material is used. It can be done. In the table, ◯ indicates that there was no corrosion or peeling of the film, and X indicates that film corrosion or peeling was observed after the test.

It was found that the Al ₂ O ₃ film formed on the base film may have a thickness of about 5 nm by forming the base film composed of the two layers. It was also found that the thickness of the Ni film formed under the Ag film can be reduced. In Examples 13, 15 and 16, a 20 nm thick SiO ₂ film was formed as an abrasion resistant film, and in Example 14, a water / oil repellent film was further formed on the SiO ₂ film. is there.

When the base film having a two-layer structure is not formed, the durability of the Ag mirror on the COP substrate is insufficient. In Comparative Example 11, a SiO ₂ single layer film having a thickness of 100 nm was formed as a base film, and in Comparative Example 12, a SiO single layer film having a thickness of 100 nm was formed as a base film. In Example 14, an Al ₂ O ₃ film was formed directly on the COP base material without forming a base film, but in each example, an abnormality occurred on the surface of the COP base material by the moisture resistance test (Test P). It turned out that the film | membrane formed on it peels or a reflectance falls significantly. Comparative Example 13 is a case where an underlayer film having a two-layer structure is formed, but an Al ₂ O ₃ film is not formed thereon, and an abnormality occurs on the surface of the COP substrate in the moisture resistance test, and the tape drawing is performed. Also in the peeling test (Test A), peeling of the film was observed. In Comparative Examples 15 and 16, a base film having a two-layer structure is formed, and an Al ₂ O ₃ film is formed thereon. The thickness of the SiO ₂ film as the second base film is 50 nm. Since the film was thin as follows, the film peeling was also observed because the corrosion of the Ag film from the substrate side could not be sufficiently prevented and the film stress could not be sufficiently relaxed.

For Example 13, a severe thermal shock test was conducted in which a cycle of holding at a temperature of −40 ° C. for 1 hour, and then rapidly heating to 85 ° C. and holding for 1 hour was repeated 456 times. The initial value was 95.8%. It was also found that the highly durable silver mirror of the present invention on the COP substrate had excellent thermal shock resistance since the reflectivity decreased only to 94.5%.

A highly durable silver mirror was created on a substrate that was not flat and the durability was evaluated. The base material 20 processed from brass (Cu—Zn alloy) has a cone cut away from the bottom surface of the rectangular parallelepiped toward the apex B. FIG. 3 is a cross-sectional view, and an angle ABC formed by A and C and B on the bottom surface is θ. In this example, a brass substrate with θ = 50 ° was prepared, and a highly durable silver mirror film was formed on the slope ABC. That is, in this brass base material 20, a film is formed on the inclined conical slope made of ABC.

A substrate holder (often called a substrate dome) for setting a substrate to be coated in a vapor deposition apparatus is a spherical surface, and a large number of substrates are arranged in a circumferential direction or a diameter direction of the spherical surface. A membrane is performed. And when this base material is a plane, the thickness of the film | membrane formed on a base-material plane becomes substantially the same, regardless of the position on the spherical surface of a base-material holder, a base material is set. However, when the substrate is not flat, the thickness of the coating on the substrate differs depending on which position of the substrate holder is set in which direction. In the case of forming a multilayer film, it is difficult to obtain optical characteristics (for example, reflectance) as designed by stacking the thickness differences of the layers.

As shown in FIG. 4, the glass substrate is disposed at four positions on the substrate holder at an angle of 25 ° from the vertical plane, and the high durability of Example 17 shown in Table 14 and Example 1 shown in Table 2 A silver mirror was formed. In contrast to Example 17 and Example 1, in Example 17, the protective film is a 20 nm thick SiO ₂ single layer film, whereas in Example 1, Al ₂ O ₃ / SiO ₂ / TiO _{2 is used.} A three-layer protective film made of the above and an SiO ₂ film as an abrasion resistant film are formed. In Example 17, the Ag film is formed as thick as 500 nm.

Table 15 shows the results of measuring the average reflectance of the highly durable silver mirrors of Example 17 and Example 1 arranged at the four positions shown in FIG. In Example 1, the reflectivity varies greatly depending on the position and direction on the substrate holder, whereas in Example 17 where the protective film of the SiO2 single layer is formed by increasing the thickness of the silver film, the position on the substrate holder is It was found that high reflectivity was realized regardless of the direction.

Next, Table 16 shows three types of film configurations formed on the conical slope using the brass base material shown in FIG. 3, and Table 17 shows the results of the constant temperature and humidity test performed on these film configurations. Comparative Example 17 has a film configuration in which no ITO film is formed as compared with Example 18, and Comparative Example 18 has a film configuration in which neither an ITO film nor a protective film is formed on the silver film.

In Example 18, an SiO ₂ film having a thickness of 20 nm was formed as a protective layer on the ITO film, and the effect of increasing reflection by the protective film was not obtained, and the average reflection due to light absorption by the ITO film. Although the rate remained at about 95%, it was found that the reflectance did not decrease even when the constant temperature and humidity test (Test C) was conducted for more than 1,000 hours. On the other hand, in Comparative Example 17 in which the SiO2 film is formed on the Ag film without forming the ITO film and in Comparative Example 18 in which the protective film is not formed on the Ag film, the initial reflectance is high, but the constant temperature. It turned out that the reflectance fall by a constant humidity test was large.

About the highly durable silver mirror of Example 1, the sunshine carbon weather meter test (Test I: accelerated weathering test) was implemented using the test apparatus (made by Suga Test Instruments Co., Ltd.) prescribed | regulated to JISB7753. The test conditions were such that the black panel temperature was 83 ° C., the carbon arc was irradiated for 60 minutes, water was sprayed for 12 minutes, and this was repeated for 1,080 hours. The test results are shown in Table 18.

As a result, it was found that the highly durable silver mirror of Example 1 did not cause a decrease in reflectance even in the accelerated weather resistance test and had excellent weather resistance.

1 ... Robust silver mirror 10 ... glass substrate 11 ... first layer _(Al 2 _{O 3} film)
12 ... Second layer (Ni film)
13 ... Third layer (Ag film)
14 ... Fourth layer (ITO film)
15 ... Fifth layer (protective film)
16 ... Wear-resistant layer (SiO ₂ film)
20 ... Brass base material 151..Al ₂ O ₃ film (first layer of protective film)
152 .. SiO ₂ film (second layer of protective film)
153 .. TiO2 film (third layer of protective film)

Claims

On the substrate, an oxide film as the first layer, a metal film selected from a metal having a face-centered cubic crystal structure as the second layer, a silver film as the third layer, and a thickness as the fourth layer A highly durable silver mirror comprising an ITO film having a thickness of 3 to 12 nm and a protective film as a fifth layer formed in this order.
2. The high durability silver mirror according to claim 1, wherein a silicon oxide film, a magnesium fluoride film, or a film of these two layers is formed as an abrasion resistant film on the protective film of the fifth layer. .
After the fifth protective film is formed or after the wear resistant film is formed on the protective film, it is heat-treated at a temperature range of 400 to 500 ° C. for 30 to 90 minutes. The highly durable silver mirror of Claim 1 or Claim 2.
The high durability silver mirror according to claim 1, wherein the base material is a glass base material.
The highly durable silver mirror according to claim 1, wherein the base material is a semiconductor base material.
The base material is a resin base material, and a base layer composed of two layers of SiO / SiO 2 is formed before the oxide film of the first layer is formed. Or the highly durable silver mirror of Claim 2.
The base material is a base material having a conical or parabolic shape, and the protective layer formed as the fifth layer on the conical or parabolic surface is a SiO 2 single layer film. The high durability silver mirror according to claim 1 characterized by these.
The highly durable silver mirror according to any one of claims 1 to 7, wherein the silver film of the third layer is made of pure silver substantially free of components other than silver (Ag).
9. The high durability silver mirror according to claim 1, wherein the oxide film of the first layer is any one selected from an aluminum oxide film, a silicon oxide film, and a titanium oxide film.
9. The highly durable silver mirror according to claim 1, wherein the oxide film of the first layer is aluminum oxide.
11. The metal film selected from metals having a crystal structure of face centered cubic in the second layer is any one of a Ni film, a Cu film, and an Al film. Highly durable silver mirror as described in
11. The high durability silver mirror according to claim 1, wherein the metal film selected from a metal whose crystal structure of the second layer is a face-centered cubic type is a Ni film.
13. The highly durable silver mirror according to claim 1, wherein a water / oil repellent film is formed as an outermost surface layer.