Patent Application
20080112051
The present invention relates to a reflection mirror having a high reflectance in the visible region and having moisture resistance and sulfur resistance, and its production process.
Heretofore, a reflection mirror comprising a substrate of e.g. glass and a metal layer of e.g. aluminum or silver as a reflection film formed on the substrate, to be used for lighting equipment, cell-phones, liquid crystal displays, etc. has been known (e.g. Patent Document 1). In recent years, a reflection mirror comprising a silver film, which has a high reflectance over the entire visible region, has been mainly studied. However, silver is chemically unstable and is thereby likely to be degenerated into silver oxide, silver sulfide or the like by oxygen, moisture, sulfur dioxide, hydrogen sulfide, etc. in the air and to discolor.
To solve the above problem, a reflection mirror comprising, as a protective film, an oxide film of e.g. aluminum oxide formed on the silver film has been disclosed (Patent Document 2). However, for such a reflection mirror, an oxide film of e.g. aluminum oxide is formed on the silver film by a method such as sputtering. In such a case, since the film is formed in an oxidizing atmosphere, the surface of the silver film is likely to be oxidized, and a reflection mirror having a sufficient reflectance is hardly obtained. Further, degeneration of silver by e.g. oxygen, moisture, sulfur dioxide or hydrogen sulfide in the air can not sufficiently be suppressed by such a protective film, and moisture resistance and sulfur resistance of the reflection mirror are not sufficient yet.
Further, a reflection mirror comprising, as a protective film, a film of e.g. aluminum nitride or diamond-like carbon laminated on the silver film has been disclosed (Patent Document 3). Further, a reflection mirror comprising, as a protective film, a silicon nitride film formed on the silver film by a sputtering method has been disclosed (Patent Document 4). However, even with such a protective film, degeneration of silver by e.g. oxygen, moisture, sulfur dioxide or hydrogen sulfide in the air can not sufficiently be suppressed, and moisture resistance and sulfur resistance of the reflection mirror are not sufficient yet.
Patent Document 1: JP-U-5-73809
Patent Document 2: JP-A-2001-343510
Patent Document 3: JP-A-2001-13309
Patent Document 4: JP-A-2001-337210
The object of the present invention is to provide a reflection mirror having a high reflectance in the visible region and excellent in moisture resistance and sulfur resistance, and its production process.
The reflection mirror of the present invention is a reflection mirror comprising a substrate, a silicon nitride film and a silver film formed between the substrate and the silicon nitride film, wherein when 10 ppm of hydrogen sulfide is introduced and the reflection mirror is left to stand for 100 hours in an atmosphere at a temperature of 50° C. under a relative humidity of 80%, the rate of change of the luminous reflectance (chromaticity Y of the tristimulus value as defined in JIS Z8701 (1982)) after being left to stand is within 10% based on the luminous reflectance before being left to stand.
The reflection mirror of the present invention is preferably such that when the reflection mirror is left to stand for 100 hours in an atmosphere at a temperature of 60° C. under a relative humidity of 90%, the rate of change of the luminous reflectance (chromaticity Y of the tristimulus value as defined in JIS Z8701 (1982)) after being left to stand is within 5% based on the luminous reflectance before being left to stand.
The reflection mirror of the present invention preferably further has a protective film made of hard carbon formed on the silicon nitride film.
The reflection mirror of the present invention preferably further has an underlayer made of an oxide formed between the substrate and the silver film.
The oxide is preferably titanium oxide represented by TiOx (1.5≦x<2).
It is preferred that the silver film has a thickness of from 60 to 300 nm, and the silicon nitride film has a thickness of from 2 to 20 nm.
The protective film preferably has a thickness of from 2 to 20 nm.
The underlayer preferably has a thickness of from 1 to 50 nm.
The present invention further provides a process for producing a reflection mirror comprising a substrate, a silicon nitride film and a silver film formed between the substrate and the silicon nitride film, which comprises forming the silver film by a sputtering method and then forming the silicon nitride film by a chemical vapor deposition method.
The reflection mirror of the present invention has a high reflectance in the visible region and is excellent in moisture resistance and sulfur resistance.
According to the process for producing a reflection mirror of the present invention, a reflection mirror having a high reflectance in the visible region and excellent in moisture resistance and sulfur resistance, can be obtained.
(Reflection Mirror)
(Substrate)
A material of the substrate 11 may, for example, be glass; or a plastic such as a polyethylene terephthalate, an acrylic resin or a polycarbonate.
The shape of the substrate may be any of various shapes required for the substrate of a reflection mirror, such as a plane, a diffusion surface, a concave, a convex and a trapezoid.
The substrate 11 is particularly preferably a plastic film, with which weight saving is achieved.
The thickness of the substrate 11 is preferably from 30 to 500 μm in the case of a plane.
The substrate 11 may be subjected to e.g. plasma treatment so as to improve adhesion to e.g. the underlayer 12 or the silver layer 13, in the case of a film.
(Underlayer)
The underlayer 12 is a film made of an oxide. By forming the underlayer, the adhesion between the substrate 11 and the silver film 13 which are in contact therewith, can be increased. As a result, moisture resistance of the reflection mirror 10 will further improve.
The oxide may, for example, be titanium oxide, zinc oxide, tin oxide, indium oxide, aluminum oxide, chromium oxide or niobium oxide. Among them, preferred is titanium oxide in view of adhesion, and particularly preferred is titanium oxide having oxygen defects represented by TiOx (1.5≦x<2).
The underlayer 12 may be a single layer or may comprise a plurality of layers.
The thickness of the underlayer 12 is preferably from 1 to 50 nm, particularly preferably from 3 to 15 nm. If the thickness of the underlayer 12 is less than 1 nm, the effect of improving the adhesion between the substrate 11 and the silver film 13 is hardly obtained. If the thickness of the underlayer 12 exceeds 50 nm, irregularities on the surface of the underlayer 12 tend to be large, whereby the reflectance tends to deteriorate, or the internal stress tends to be high, whereby the adhesion tends to deteriorate.
In the present invention, the “thickness” means the physical film thickness, and the physical film thickness can be determined by an ellipsometer, a stylus profilometer or the like.
(Silver Film)
The silver film 13 is a film made of silver or a silver alloy, and functions as a reflection film which reflects light. By the reflection film being a silver film 13, the reflectance of the reflection mirror 10 in the visible region can be increased, and the dependence of the reflectance on the incident angle can be reduced. In the present invention, the “visible region” means a wavelength region of from 400 to 700 nm. Further, the “incident angle” means an angle to a line vertical to the film surface.
The silver alloy is preferably an alloy of silver with at least one other metal selected from the group consisting of gold, palladium, tin, gallium, indium, copper, titanium and bismuth, whereby durability of the silver film 13 will improve, and the reflectance will further improve. As other metal, particularly preferred is gold in view of the high temperature high humidity resistance and the reflectance.
In a case where the silver film 13 is a film made of a silver alloy, the amount of silver is preferably from 90 to 99.8 at % based on the total amount (100 at %) of silver and other metal in the silver film 13. Further, the amount of other metal is preferably from 0.2 to 10 at % in view of durability.
The thickness of the silver film 13 is preferably from 60 to 300 nm, particularly preferably from 80 to 200 nm. If the thickness of the silver film 13 is less than 60 nm, the reflectance in the visible region tends to deteriorate. If the thickness of the silver film 13 exceeds 300 nm, irregularities are likely to occur on the surface of the silver film 13, whereby light scattering will occur, and the reflectance in the visible region may deteriorate.
(Silicon Nitride Film)
The silicon nitride film 14 is a film made of silicon nitride, and is a film which suppresses degeneration of the silver film 13 to be in contact therewith and consequently improves moisture resistance and sulfur resistance of the reflection mirror 10.
The silicon nitride film 14 is preferably a silicon nitride film formed by a chemical vapor deposition method (hereinafter referred to as CVD method). The silicon nitride film formed by a CVD method has advantages such as low film stress, good coverage on a complicated shape, and high gas barrier properties, as compared with a is silicon nitride film formed by a sputtering method. As a result, sulfur resistance of the reflection mirror 10 will improve.
The thickness of the silicon nitride film 14 is preferably from 2 to 20 nm, particularly preferably from 3 to 15 nm. If the thickness of the silicon nitride film 14 is less than 2 nm, moisture resistance and sulfur resistance of the reflection mirror 10 may be insufficient. If the thickness of the silicon nitride film 14 exceeds 20 nm, the reflectance may decrease due to coloring (absorption) by the silicon nitride film 14.
(Protective Film)
The protective film 15 is a film made of hard carbon, formed as the outermost layer of the reflection mirror 10. By forming the protective film 15, moisture resistance and sulfur resistance of the reflection mirror 10 will further improve.
The reason why the sulfur resistance improves has not been understood in detail yet but is considered to be as follows. Namely, since the bonding energy between carbon atoms in the hard carbon and sulfur atoms in sulfur-containing molecules such as hydrogen sulfide is high, a large quantity of energy will be required when the sulfur-containing molecules are attached to the surface of the protective film 15. Consequently, the sulfur-containing molecules are less likely to be attached to the surface of the protective film 15, thus improving sulfur resistance.
The hard carbon is also called diamond-like carbon (hereinafter referred to as DLC), i-carbon, amorphous carbon or hydrogenated carbon, and known one may properly be used. A film made of hard carbon has excellent properties as a protective film, such as excellent surface smoothness, a low coefficient of friction on the surface, chemical inactivity, and low wettability, which makes it be less likely to be stained.
A typical hard carbon may be DLC. DLC is amorphous hard carbon in which a graphite structure (SP2 orbital) and a diamond structure (SP3 orbital) coexist, having a peak within a range of from 1,400 to 1,600 cm−1 in Raman spectrometry.
The hard carbon preferably contains hydrogen atoms, whereby the hardness will increase, and the abrasion resistance and weatherability of the reflection mirror will improve. The reason why the weatherability improves by the hard carbon containing hydrogen atoms has not been understood yet, but is considered to be because uncombined defects present in a large amount in the hard carbon are stabilized by addition of hydrogen atoms. However, in a case where the substrate 11 is a film, the protective film is required to be soft to such an extent that it conforms with the film. Accordingly, the amount of hydrogen atoms is preferably at most 20 at % in the hard carbon (100 at %).
The amount of carbon atoms is preferably at least 50 mass %, more preferably at least 80 mass %, particularly preferably at least 90 mass % in the hard carbon (100 at %).
The total amount of carbon atoms and hydrogen atoms in the hard carbon is preferably at least 95 at % in the hard carbon (100 at %). The hard carbon may contain fluorine atoms in addition to carbon atoms and hydrogen atoms.
The protective film 15 is required to be a transparent film in view of the reflectance of the reflection mirror 10. Specifically, the extinction coefficient in the visible region is preferably at most 0.1, particularly preferably at most 0.08, most preferably at most 0.05. The “extinction coefficient” in the present invention means an imaginary part in a complex refractive index in the visible region and can be measured by a spectroscopic ellipsometer.
The thickness of the protective film 15 is preferably from 2 to 20 nm, particularly preferably from 4 to 10 nm. If the thickness of the protective film 15 is less than 2 nm, the effect to improve adhesion to the silicon nitride film 14 is hardly obtained. If the thickness of the protective film 15 exceeds 20 nm, the reflectance may be low.
(Process for Producing Reflection Mirror)
The reflection mirror 10 is obtained by sequentially forming the respective films on the substrate 11 by a sputtering method, a CVD method, an ion plating method or the like.
As compared with the CVD method or the ion plating method, the sputtering method is preferred in that a film having a large area can be formed, and a transparent film can easily be formed. Further, it is preferred in that the surface roughness can be made small, whereby the reflectance can be maintained at a high level.
The sputtering method may, for example, be an alternate current (AC), direct current (DC) or radio frequency (RF) sputtering method. The DC sputtering method includes a pulse DC sputtering method. The AC sputtering method and the pulse DC sputtering method are effective with a view to preventing abnormal electrical discharge. Further, from a viewpoint that a dense film can be formed, the AC or DC reactive sputtering method is preferred.
The underlayer 12 is preferably formed by the sputtering method. The atmosphere is preferably an atmosphere of a rare gas such as argon containing substantially no oxidative gas. The amount of the oxidative gas such as oxygen is preferably at most 18 vol %.
The target for the underlayer 12 is preferably an oxide target, whereby an oxide film can be formed in an atmosphere containing substantially no oxidative gas. The oxide target may be at least one member selected from the group consisting of titanium oxide, zinc oxide, tin oxide, indium oxide, aluminum oxide, chromium oxide and niobium oxide.
In a case of forming the underlayer 12 by the DC sputtering method, preferred is an oxygen deficient target, whereby it is possible to form a film at a high rate. The oxygen deficient target may, for example, be one represented by TiOx (1.5≦x<2.0).
The silver film 13 is preferably formed by the sputtering method in an argon gas atmosphere using a target made of silver or a silver alloy.
The silver target is preferably a target containing at least 95 mass % of silver. The silver alloy target is preferably a target containing from 95 to 99.7 mass % of silver and containing from 0.3 to 5.0 mass % of other metal.
The silicon nitride film 14 is preferably formed by the CVD method. Sulfur resistance of the reflection mirror 10 will improve by forming the silicon nitride film 14 by the CVD method.
The CVD method is a method of imparting energy to a gas containing a starting material by heat or light or bringing it in a plasma state by radio frequency to react the starting material thereby to deposit a film of the reaction product.
The starting material may, for example, be a gas mixture of silane gas with ammonia gas.
The protective film 15 can be formed by the sputtering method, the CVD method, the ion plating method or the like using a target containing carbon (graphite) as the main component. Preferred is the sputtering method, whereby a film made of hard carbon can be made amorphous and a denser film made of hard carbon will be obtained. The atmosphere is preferably an atmosphere of a rare gas such as argon containing substantially no oxidative gas. The amount of the oxidative gas is preferably at most 1 vol %.
The reflection mirror 10 preferably has a luminous reflectance as defined in JIS Z8701 of at least 90%, more preferably at least 95%, most preferably at least 97%, whereby the reflectance of the reflection mirror 10 will be high, and when it is used for an imaging device for e.g. a projection TV or a liquid crystal display, an image can be projected without deterioration of the brightness.
When a high temperature high humidity test is carried out in which the reflection mirror 10 is left to stand for 100 hours in an atmosphere at a temperature of 60° C. under a relative humidity of 90%, the rate of change of the luminous reflectance (chromaticity Y of the tristimulus value as defined in JIS Z8701 (1982)) after the high temperature high humidity test is preferably within 5% based on the luminous reflectance before the high temperature high humidity test, whereby the moisture resistance of the reflection mirror 10 will be sufficiently high. The rate of change of the luminous reflectance after the high temperature high humidity test can be determined from the following formula:
Rate of change (%)={1−(luminous reflectance (%) after high temperature high humidity test/luminous reflectance (%) before high temperature high humidity test)}×100
When hydrogen sulfide resistance test is carried out in which 10 ppm of hydrogen sulfide is introduced, and the reflection mirror is left to stand for 100 hours in an atmosphere at a temperature of 50° C. under a relative humidity of 80%, the rate of change of the luminous reflectance (chromaticity Y of the tristimulus value as defined in JIS Z8701 (1982)) after the hydrogen sulfide resistance test is preferably within 10% based on the luminous reflectance before the hydrogen sulfide resistance test, whereby sulfur resistance of the reflection mirror 10 will be sufficiently high. The rate of change of the luminous reflectance after the hydrogen sulfide resistance test can be determined from the following formula:
Rate of change (%)={1−(luminous reflectance (%) after hydrogen sulfide resistance test/luminous reflectance (%) before hydrogen sulfide resistance test)}×100
Now, the present invention will be described in further detail with reference to Examples. However, the present invention is by no means restricted to the following Examples.
In a vacuum chamber, a flat polyethylene terephthalate film (thickness: 50 μm) having an acrylic hard coat applied was set as a substrate.
As targets, a TiOx oxygen deficient target (tradename: TXO, manufactured by Asahi Glass Ceramics Co., Ltd.) and a gold-doped silver alloy target (gold content: 1 mass %, silver content: 99 mass %) were respectively set so that they were opposed to the substrate on the cathode. The interior of the vacuum chamber was evacuated to 2×10−5 Pa.
200 sccm of argon gas was introduced to the vacuum chamber, and the substrate was irradiated with ionized argon ions from an ion beam source (LIS-150, tradename, manufactured by ADVANCED ENERGY INDUSTRIES, INC.) by applying an electric power of 100 W to carry out dry cleaning of the substrate.
Then, as a sputtering gas, argon gas was introduced to the vacuum chamber. By a DC sputtering method, pulse sputtering with a reverse pulse duration of 1 μsec was carried out under a pressure of 0.15 Pa at a frequency of is 100 kHz at a power density of 0.79 W/cm2 by means of a TiOx oxygen deficient target to form a titanium oxide film (underlayer) in a thickness of 5 nm on the substrate. The composition of the titanium oxide film was equal to the target.
Then, the residual gas was discharged, and then, as a sputtering gas, argon gas was introduced to the vacuum chamber. By a DC sputtering method, pulse sputtering with a reverse pulse duration of 5 μsec was carried out under a pressure of 0.15 Pa at a frequency of 100 kHz at a power density of 2.46 W/cm2 by means of a gold-doped silver alloy target to form a gold-doped silver alloy film in a thickness of 150 nm on the titanium oxide film. The composition of the silver alloy film was equal to the target.
Then, using a plasma enhanced CVD apparatus (manufactured by ULVAC, Inc., model: CIH-130), a silicon nitride film was formed on the silver alloy film. As raw materials (source gas), silane gas (SiH4) and ammonia gas (NH3) were used. The raw materials were supplied at a flow rate ratio of NH3/SiH4 of 20 vol %, and radio frequency at 27.12 MHz were applied to the raw materials at 400 W under a pressure of 100 Pa to bring the raw materials into a plasma state, to form a silicon nitride film in a thickness of 10 nm. The substrate temperature at the film formation was 80° C.
The obtained reflection mirror was subjected to the following evaluation. The results are shown in Tables 1 to 3.
(1) High Temperature High Humidity Test
The reflection mirror was cut into 50 mm×100 mm to obtain a sample. The sample was left to stand for 100 hours in an atmosphere at a temperature of 60° C. under a relative humidity of 90%, whereupon the delamination and the presence or absence of corrosion were ascertained.
◯: No delamination or corrosion was observed.
X: Delamination and/or corrosion was observed.
(2) High Temperature Test
The reflection mirror was cut into 50 mm×100 mm to obtain a sample. The sample was left to stand for 100 hours in an atmosphere at a temperature of 85° C. under a relative humidity of at most 30%, whereupon delamination and the presence or absence of corrosion were ascertained.
◯: No delamination or corrosion was observed.
X: Delamination and/or corrosion was observed.
(3) Tape-Peeling Test
The film surface of the reflection mirror was cut by a cutter to form 100 cross-cut sections. An adhesive tape (manufactured by Nichiban Co., Ltd.) was strongly bonded to the film surface manually and rapidly peeled, whereupon the presence or absence of peeling of the cross-cut sections of the film surface was ascertained. A case where no peeling was observed was rated to be 100/100, and a case where all sections were peeled was rated to be 0/100. Such a peeling test was carried out immediately after the film deposition, after the high temperature high humidity test and after the high temperature test.
(4) Film Surface Reflectance
By means of a color analyzer (TOPSCAN, tradename, manufactured by Tokyo Denshoku Co., Ltd.), the reflectance of the film surface side was measured, and chromaticity Y of the tristimulus value as defined in JIS Z8701 (1982) was obtained by calculation to determine the luminous reflectance. The measurement was carried out by a SCI system by measuring both the regular reflected light and the diffusion light. The luminous reflectance was measured immediately after the film deposition, after the high temperature high humidity test and after the high temperature test.
(5) Hydrogen Sulfide Resistance Test
The reflection mirror was cut into 50×100 mm to obtain a sample. 10 ppm of hydrogen sulfide was introduced, and the sample was left to stand for 100 hours in an atmosphere at a temperature of 50° C. under a relative humidity of 80%, whereupon the luminous reflectance, and the delamination and the presence or absence of corrosion were ascertained. The luminous reflectance was measured by the same method as in (4).
With respect to the presence or absence of corrosion, evaluation was made under the following evaluation standards.
◯: No delamination or corrosion was observed.
Δ: Delamination or corrosion was slightly observed, but was not a practically problematic level.
X: Delamination and/or corrosion was observed.
On the silicon nitride film in Example 1, a DLC film (protective film) was formed.
As a sputtering gas, hydrogen and argon gas were respectively introduced to the vacuum chamber and adjusted so that the amount of hydrogen was 50 vol % in the sputtering gas. Oxygen was not intentionally introduced. By a DC sputtering method, pulse sputtering with a reverse pulse duration of 4.5 μsec was carried out under a pressure of 0.25 Pa at a frequency of 100 kHz at a power density of 1.48 W/cm2 by means of a graphite target (IG-15, tradename, manufactured by TOYO TANSO CO., LTD., carbon content: at least 99.6 mass %) to form a DLC film in a thickness of 5 nm to obtain a reflection mirror in Example 2. The obtained reflection mirror was subjected to evaluation in the same manner as in Example 1. The results are shown in Tables 1 to 3.
A reflection mirror was obtained in the same manner as in Example 1 except that the silicon nitride film was formed by a sputtering method.
As a sputtering gas, a gas mixture having 30 mass % of nitrogen gas mixed with argon gas was introduced to the vacuum chamber. By a DC sputtering method, pulse sputtering with a reverse pulse duration of 1 μsec was carried out under a pressure of 0.25 Pa at a frequency of 100 kHz at a power density of 1.48 W/cm2 by means of a boron-doped polycrystalline silicon target having a resistivity of 0.004 Ω·cm to form a silicon nitride film in a thickness of 15 nm. The obtained reflection mirror was subjected to evaluation in the same manner as in Example 1. The results are shown in Tables 1 to 3.
A reflection mirror was obtained in the same manner as in Example 1 except that an aluminum nitride film was formed instead of the silicon nitride film.
As a sputtering gas, a gas mixture having 30 mass % of nitrogen gas mixed with argon gas was introduced to the vacuum chamber. By a DC sputtering method, pulse sputtering with a reverse pulse duration of 1 μsec was carried out under a pressure of 0.25 Pa at a frequency of 100 kHz at a power density of 1.72 W/cm2 by means of an aluminum target having a purity of 99.9 mass % to form an aluminum nitride film in a thickness of 15 nm. The obtained reflection mirror was subjected to evaluation in the same manner as in Example 1. The results are shown in Tables 1 to 3.
The reflection mirror of the present invention is useful as a reflection member for a light source for a display to be used for flat panel displays, projection TV, cell-phones, etc., particularly as a reflection member for a light source for displays of electronic equipment such as mobile personal computers, cell-phones, PDAs and portable game equipment.
The entire disclosure of Japanese Patent Application No. 2005-201541 filed on Jul. 11, 2005 including specification, claims, drawings and summary is incorporated herein by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-201541 | Jul 2005 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2006/313125 | Jun 2006 | US |
| Child | 11972761 | Jan 2008 | US |
