JP2005275029A - Back reflection mirror and pentaprism equipped with same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a back reflection mirror excellent in corrosion resistance, and to provide a pentaprism equipped with the back reflection mirror. <P>SOLUTION: The corrosion of a silver is prevented by laminating a protective film 12 made of chrome oxide on a reflection film 11 made of silver laminated on a glass substrate 10. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a back reflector and a pentaprism having the same.

  The back reflector is formed by forming a reflective layer on the back surface of a transparent substrate such as glass. Light incident from the surface of the transparent substrate is reflected by the reflective layer and emitted from the surface of the transparent substrate. The back surface reflecting mirror is used as a reflecting mirror of a pentaprism of a camera, for example.

  Silver is frequently used as the reflective layer. The silver thin film has a characteristic that the reflectance of visible light is higher than that of other metal thin films.

However, silver has poor corrosion resistance in the atmosphere, causes oxidation and sulfurization, and the silver thin film is discolored or peeled off after long-term use. For this reason, conventionally, a metal such as copper is vapor-deposited on a silver thin film, and spray coating is further performed on the metal thin film, or a protective layer composed of a cerium oxide and a metal layer is formed on the silver thin film. Corrosion of the silver thin film is prevented by using a method of forming (see JP-A-7-5308).
Japanese Patent Laid-Open No. 7-5308

  When copper is deposited on a silver thin film, copper particles having a large particle size collide with the copper thin film due to bumping (copper particles having a diameter larger than the film thickness evaporate violently). It may penetrate the thin film and reach the surface of the silver thin film and further the transparent substrate. At this time, moisture enters between the copper thin film and the silver thin film. As a result, the silver thin film is corroded by the battery action resulting from the ionization tendency.

  In addition, even if a protective layer composed of cerium oxide and a metal layer is formed on the silver thin film, moisture will enter between the protective layer and the silver thin film, and corrosion will occur in the silver thin film as well. It was inevitable.

  As described above, the corrosion of the silver thin film could not be sufficiently prevented by using any method.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a back reflector having excellent corrosion resistance and a pentaprism having the same.

  In order to solve the above problems, the invention described in claim 1 is characterized by comprising a reflective film made of silver and a protective film made of chromium oxide laminated on the reflective film.

  According to a second aspect of the present invention, in the back reflector according to the first aspect, the protective film has a thickness of 10 to 300 nm.

  According to a third aspect of the present invention, in the back reflector according to the first aspect, the protective film has a thickness of 50 to 200 nm.

  According to a fourth aspect of the present invention, in the back reflector according to any one of the first to third aspects, the reflective film is laminated on a transparent plastic substrate, and between the plastic substrate and the reflective film, A first intermediate layer made of silicon monoxide and a second intermediate layer made of aluminum oxide are formed, the first intermediate layer is located on the plastic substrate, and the first intermediate layer The second intermediate layer is located on the layer, and the reflective film is located on the second intermediate layer.

  The invention according to claim 5 is a pentaprism comprising the back reflector according to any one of claims 1 to 4.

  As described above, according to the present invention, a back reflector having excellent corrosion resistance and a pentaprism having the same can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a conceptual diagram showing a cross section of a back reflector according to the first embodiment of the present invention.

  This back reflector is composed of a reflective film 11, a protective film 12, and a protective film 13.

  The reflective film 11 is formed using silver as a material, and is laminated on the back surface (surface opposite to the incident side) of the glass substrate 10. The glass substrate 10 is made of BK7 (borosilicate crown glass (n = 1, 5163)).

The protective film 12 is formed using chromium oxide (Cr ₂ O ₃ ) as a material, and is laminated on the reflective film 11.

  The protective film 13 is formed using an epoxy resin paint (for example, Epola 2000H (trademark): Nippon Special Paint Co., Ltd.) and covers the glass substrate 10, the reflective film 11, and the protective film 12.

  Next, a method for forming a back reflector will be described.

A vacuum apparatus (not shown) is set to a predetermined degree of vacuum (2 × 10 ⁻⁵ Torr), a glass substrate 10 having a cleaned back surface is disposed, and a silver reflective film 11 having a film thickness of 100 to 300 nm is disposed on the back surface. Is formed by vacuum evaporation or sputtering.

  As a basic function required for the back reflector, light incident from the surface of the glass substrate 10 must be reflected by the reflective film 11, but when the thickness of the reflective film 11 becomes less than 100 nm, a part of the incident light is reflected. Is transmitted through the reflective film, the reflectivity decreases. In order to avoid the transmission of incident light, the thickness of the reflective film 11 may be set to 100 nm or more. However, when the thickness of the reflective film 11 exceeds 300 nm, the film is in close contact with the glass substrate 10 due to tensile stress generated in the reflective film 11. And the reflective film 11 peels from the glass substrate 10. Therefore, it is desirable that the thickness of the reflective film 11 be 100 to 300 nm.

  Next, a chromium oxide protective film 12 having a thickness of 10 to 300 nm is formed on the silver reflective film 11 by vacuum deposition or sputtering. At this time, it is preferable that the film thickness of the protective film 12 of chromium oxide be 50 to 200 nm in consideration of manufacturing errors.

  It is difficult to form the protective film 12 having a thickness of less than 10 nm. Further, when the thickness of the protective film 12 exceeds 300 nm, the adhesiveness with the reflective film 11 is lowered by the tensile stress generated in the protective film 12, and the protective film 12 is peeled off from the reflective film 11.

  Finally, as shown in FIG. 1, the protective film 13 is formed on the protective film 12 by coating with an epoxy resin paint to a film thickness of about 40 μm. Although not shown, a metal such as copper may be vapor-deposited instead of painting with an epoxy resin paint.

As a result, the reflective film 11 is not exposed to the atmosphere, and corrosion of the reflective film 11 due to hydrogen sulfide gas (H ₂ S) or the like can be reduced.

  There is a gas corrosion test as a method for evaluating the back reflector after the protective films 12 and 13 are formed in this manner. JIS stipulates that the gas corrosion test be performed under the following conditions (temperature, humidity, concentration, etc.).

The back reflector was left in a Cl ₂ (concentration 0.1 ppm) gas atmosphere in an environment of a temperature of 40 ° C. and a humidity of 80% (JISC0090). When the back reflector was inspected after 20 hours, no corrosion was observed.

The back reflector was left in a H ₂ S (concentration 15 ppm) gas atmosphere in an environment of temperature 50 ° C. and humidity 90% (JIS C0092). When the back reflector was inspected after 20 hours, no corrosion was observed.

  According to this embodiment, the protective films 12 and 13 can improve the corrosion resistance of the reflective film 11 made of silver.

  FIG. 2 is a conceptual diagram showing a cross section of a back reflector according to the second embodiment of the present invention.

  This back reflector is composed of a transparent plastic substrate 21, a first intermediate layer 22, a second intermediate layer 23, a reflective film 24, and a protective film 25.

  The material of the plastic substrate 21 is polycarbonate resin, acrylic resin, or the like.

  The reflection film 24 is formed using silver as a material, and is laminated on the back surface (surface opposite to the incident side) of the plastic substrate 21.

The protective film 25 is formed using chromium oxide (Cr ₂ O ₃ ) as a material, and is laminated on the reflective film 24.

  When the transparent plastic substrate 21 is used, the adhesion of the reflective film 24 is often insufficient, so that the adhesion needs to be improved.

  Therefore, a first intermediate layer 22 made of silicon monoxide and a second intermediate layer 23 made of aluminum oxide are arranged between the plastic substrate 21 and the reflective film 24.

  As shown in FIG. 2, the first intermediate layer 22 is located on the plastic substrate 21, the second intermediate layer 23 is located on the first intermediate layer 22, and the second intermediate layer 23 is located on the first intermediate layer 22. The reflective film 24 is located on the top. With this structure, the adhesion between the plastic substrate 21 and the reflective film 24 is improved.

  The protective film 25 can reduce corrosion of the reflective film 24 due to hydrogen sulfide gas or the like.

  Next, a method for forming a back reflector will be described.

A vacuum device (not shown) is set to a predetermined degree of vacuum (2 × 10 ⁻⁵ Torr), a plastic substrate 21 is disposed in the vacuum device, and a first intermediate layer 22 of silicon monoxide is provided on the back surface thereof. Is formed by vacuum evaporation or sputtering.

  Next, a second intermediate layer 23 made of aluminum oxide is formed on the first intermediate layer 22 by vacuum evaporation or sputtering.

  At this time, the film thickness of the first intermediate layer 22 and the film thickness of the second intermediate layer 23 are set to 5 to 30 nm and 20 to 50 nm, respectively, in consideration of the adhesion between the plastic substrate 21 and the reflective film 24 and the reflectance. To do.

  Thereafter, a silver reflective film 24 having a thickness of 100 to 300 nm is formed on the second intermediate layer 23 by vacuum deposition or sputtering.

  Finally, a protective film 25 of chromium oxide having a thickness of 10 to 300 nm is formed on the silver reflective film 24 by vacuum deposition or sputtering. At this time, it is preferable that the film thickness of the chromium oxide protective film 25 be 50 to 200 nm in consideration of manufacturing errors.

  As a result, the reflective film 24 is covered with the protective film 25 and the reflective film 24 is not exposed to the atmosphere.

  According to this embodiment, the same effect as that of the first embodiment is achieved, and the adhesion between the plastic substrate 21 and the reflective film 24 is improved.

  The plastic substrate 21, the first intermediate layer 22, the second intermediate layer 23, the reflective film 24, and the protective film 25 are covered with an epoxy resin paint, or a metal such as copper is evaporated. It may be done (not shown). This further improves the corrosion resistance of the back reflector.

  Moreover, since it is recognized that the characteristics of the silver reflecting film are not impaired in the back surface reflecting mirrors of the above-described embodiments and an extremely good reflectance can be obtained, the back surface reflecting mirrors are high over the entire visible range. Suitable for pentaprism reflectors that require reflectivity.

FIG. 1 is a conceptual diagram showing a cross section of a back reflector according to the first embodiment of the present invention. FIG. 2 is a conceptual diagram showing a cross section of a back reflector according to the second embodiment of the present invention.

Explanation of symbols

11,24 Reflective film 12,25 Protective film 21 Plastic substrate 22 First intermediate layer 23 Second intermediate layer

Claims (5)

A reflective film made of silver,
And a protective film made of chromium oxide laminated on the reflective film.   The back reflector according to claim 1, wherein the protective film has a thickness of 10 to 300 nm.   The back reflector according to claim 1, wherein the protective film has a thickness of 50 to 200 nm. The reflective film is laminated on a transparent plastic substrate,
A first intermediate layer made of silicon monoxide and a second intermediate layer made of aluminum oxide are formed between the plastic substrate and the reflective film,
The first intermediate layer is located on the plastic substrate, the second intermediate layer is located on the first intermediate layer, and the reflective film is located on the second intermediate layer. The back reflector according to any one of claims 1 to 3, wherein   A pentaprism comprising the back reflecting mirror according to claim 1.

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