JP2014178401A - Reflective member, secondary mirror for solar heat power generation system, and manufacturing method of reflective member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective member in which heat resistance is significantly improved, and a manufacturing method of the same.SOLUTION: A reflective member includes a glass substrate 110, a silica film 130, and a metal reflection film 120 arranged between the glass substrate 110 and the silica film 130. The silica film 130 has an extinction coefficient of 1×10or less, a refractive index of 1.466 or more and a content of carbon of 3 atom% or less, in a wavelength of 632 nm. The metal refraction film 120 favorably includes silver or silver alloy. Further, between the glass substrate 110 and the metal reflection film 120, at least one selected from the group consisting of a metal nitride, a metal oxide and a metal acid nitride may be included.

Description

  The present invention relates to a reflective member, for example, a reflective member that can be used in a secondary mirror or the like for a solar thermal power generation system.

  2. Description of the Related Art In recent years, solar thermal power generation systems that generate power using thermal energy obtained by concentrating sunlight have attracted attention. There are various types of solar thermal power generation systems such as a linear Fresnel type and a tower type.

  Of these, in a solar thermal power generation system including a primary mirror and a secondary mirror (both linear Fresnel type and tower type systems are of this type), first, sunlight is applied to the primary mirror, where Reflected. Next, the reflected sunlight is applied to the secondary mirror, where it is reflected again and collected on the heat storage member. Thereby, solar energy is accumulate | stored as thermal energy in a thermal storage member. Therefore, electric power can be generated by using this thermal energy to generate high-temperature and high-pressure steam (for example, Non-Patent Document 1).

NEDO Renewable Energy Technology White Paper (written by New Energy and Industrial Technology Development Organization)

  In general, the secondary mirror used in the solar thermal power generation system is a mirror having a reflective layer made of a metal such as aluminum, and in order to improve reflection characteristics, a glass substrate, a metal reflective film, a low refractive index film, Some have a basic structure based on a high refractive index film. A silica film is usually used as the low refractive index film.

  Here, since a secondary mirror is arrange | positioned in the vicinity of the thermal storage member which accumulate | stores solar thermal energy, stability at high temperature, for example, 400 degreeC, ie, heat resistance, is requested | required with favorable reflectivity.

  However, it is known that the reflection characteristics of current secondary mirrors gradually deteriorate after long-term use. As one factor of the deterioration of the characteristics, it is considered that oxygen in the atmosphere gradually enters the secondary mirror, thereby oxidizing the metal reflection film.

  For this reason, in the secondary mirror for solar thermal power generation systems, further improvement in heat resistance is required.

  In addition, the problem that the characteristics deteriorate with time of use is not necessarily limited to the secondary mirror for the solar thermal power generation system. That is, even in other reflective members used at high temperatures, the same problem regarding characteristic deterioration may occur in a situation where oxidation of the metal reflective film may occur. Therefore, there is a great need for a measure that can further improve the heat resistance of all reflective members for high temperature applications.

  The present invention has been made in view of such a background, and in the present invention, heat resistance is significant in a reflective member including a glass substrate, a silica film, and a metal reflective film disposed therebetween. An object of the present invention is to provide an improved reflective member. Moreover, it aims at providing the manufacturing method of such a reflective member in this invention.

In the present invention,
Having a glass substrate, a silica film, and a metal reflective film disposed between the two,
The silica film has an extinction coefficient k at a wavelength of 632 nm of 1 × 10 ⁻⁴ or less, a refractive index n of 1.466 or more, and a carbon content of 3 atomic% or less. A sex member is provided.

  Here, in the reflective member according to the present invention, the metal reflective film may include at least one film selected from the group consisting of gold, silver, aluminum, palladium, chromium, nickel, and titanium.

  In the reflective member according to the present invention, the metal reflective film may contain silver or a silver alloy.

  The reflective member according to the present invention further includes at least one film selected from the group consisting of a metal nitride, a metal oxide, and a metal oxynitride between the glass substrate and the metal reflective film. You may do it.

  In the reflective member according to the present invention, the glass substrate may have a sodium oxide content of 4% by weight or less.

  The reflective member according to the present invention may further include a film having a refractive index higher than that of the silica film on the opposite side of the silica film from the metal reflective film.

  In the reflective member according to the present invention, the film having a refractive index higher than that of the silica film may be a silicon nitride film.

  Furthermore, in this invention, the secondary mirror for solar power generation systems which has a reflective member which has the above characteristics is provided.

Further, in the present invention, a method for producing a reflective member,
(A) forming a metal reflective film on the glass substrate;
(B) forming a silica film on the metal reflective film;
Have
The manufacturing method is characterized in that the step (b) is performed by a plasma CVD method under a pressure of 2 Pa or less.

Here, in the manufacturing method according to the present invention, the silica film formed by the step (b) has an extinction coefficient k of 1 × 10 ⁻⁴ or less at a wavelength of 632 nm and a refractive index n of 1.466 or more. The carbon content may be 3 atomic% or less.

  In the manufacturing method according to the present invention, the step (a) may be performed by a sputtering method.

  In the manufacturing method according to the present invention, the steps (a) and (b) may be performed by an inline method.

  In the manufacturing method according to the present invention, the metal reflective film may contain silver or a silver alloy.

The manufacturing method according to the present invention further includes:
(C) forming a film having a refractive index higher than that of the silica film on the silica film;
You may have.

  In this case, the film having a higher refractive index than the silica film may be silicon nitride.

  In the present invention, in a reflective member comprising a glass substrate, a silica film, and a metal reflective film disposed between the two, a reflective member having significantly improved heat resistance can be provided. Moreover, in this invention, the manufacturing method of such a reflective member can be provided.

1 is a schematic cross-sectional view of a reflective member according to an embodiment of the present invention. It is the figure which showed typically the flow of the manufacturing method of the reflective member by one Example of this invention. 1 is a schematic cross-sectional view of a mirror device according to an embodiment of the present invention. It is the figure which showed change amount (DELTA) Tv (%) of the visible light transmittance | permeability after heat processing of each sample in a preliminary test.

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

  FIG. 1 is a schematic cross-sectional view of a reflective member according to an embodiment of the present invention.

  As shown in FIG. 1, the reflective member 100 according to an embodiment of the present invention is configured by arranging a metal reflective film 120 and a silica film 130 on a glass substrate 110 in this order.

  Here, it is known that the reflection characteristics of a conventional general reflective member are gradually deteriorated by long-term use in a high-temperature environment (for example, 400 ° C.). As a cause of the deterioration of the characteristics, it is conceivable that oxygen in the atmosphere gradually enters the inside of the reflective member from the silica film side, thereby oxidizing the metal reflective film.

  Meanwhile, the reflective member 100 according to an embodiment of the present invention has a feature that the silica film 130 is formed as a dense film so as to suppress oxygen in the atmosphere from entering the reflective member 100. .

  When such a silica film 130 is used, due to the good oxygen barrier property of the silica film 130, oxygen in the environment enters the inside of the reflective member 100 (the metal reflective film 120 side) through the silica film 130. Is significantly suppressed. Therefore, in the reflective member 100 according to one embodiment of the present invention, even if the reflective member 100 is used at a high temperature for a long period of time, the oxidation of the metal reflective film 120 can be significantly suppressed, and thus the reflective member It is possible to significantly suppress the decrease in the reflection characteristic of 100.

  In general, it is difficult to quantitatively express the denseness of the silica film. For this reason, in the present application, the refractive index n is used as a quantitative index representing the denseness of the silica film 130.

  As will be described in detail in the following examples, according to the inventors of the present application, when the light absorption characteristics of the silica film are the same, the silica film having a higher refractive index n can obtain better oxygen barrier properties. Has been issued. Therefore, the oxygen barrier property and further the denseness of the silica film can be expressed by the refractive index n of the silica film. Here, it can be said that the higher the refractive index n of the silica film, the better the density of the silica film.

  On the other hand, in the reflective member, the light absorption characteristic of the silica film is also an important parameter. This is because when the absorption of light in the silica film increases, it becomes difficult to increase the amount of light reflected by the metal reflection film and emitted from the reflective member.

  Therefore, in the present application, the light absorption characteristic of the silica film is defined using the extinction coefficient k. The extinction coefficient k is a parameter representing light absorption, and it can be said that the smaller the extinction coefficient k in the silica film, the lower the light absorption of the silica film.

  Furthermore, impurities present in the silica film can be cited as factors affecting the denseness and light absorption characteristics of the silica film. For example, in the case of a silica film formed by a CVD process, an organic metal compound gas such as tetramethyldisiloxane is usually used as a raw material gas. Carbon derived from the metal compound gas is taken in and the denseness is deteriorated. Furthermore, since the refractive index of carbon is larger than the refractive index of the silica film, the inclusion of carbon in the film is a factor that increases the value of the refractive index n despite the deterioration of the denseness of the silica film. Can be. Therefore, it can be said that a dense silica film needs to have a small amount of carbon present in the film and a high refractive index n.

To express the above configuration more specifically, in the reflective member 100 according to one embodiment of the present invention, the silica film 130 has an extinction coefficient k of 1 × 10 ⁻⁴ or less at a wavelength of 632 nm and a refractive index n of It is 1.466 or more, and the carbon content is 3 atom% or less.

  By using the silica film 130 having such characteristics, the oxidation of the metal reflective film 120 in a high temperature environment is significantly suppressed, and the light absorption in the silica film 130 is significantly suppressed. Accordingly, the heat resistance of the reflective member 100 at a high temperature is thereby significantly improved, and good reflective characteristics can be maintained over a long period.

Here, the refractive index n of the silica film 130 at a wavelength of 632 nm may be, for example, 1.469 or more, and is preferably 1.47 or more. Further, the extinction coefficient k of the silica film 130 may be, for example, 1 × 10 ⁻⁵ or less, and is preferably 1 × 10 ⁻⁶ or less. Further, the carbon content of the silica film 130 may be 2 atomic% or less, and is preferably 1 atomic% or less.

  In the above, the characteristic structure of the reflective member 100 by one Example of this invention was demonstrated. However, the configuration of the reflective member of the present invention is not limited to such an embodiment.

  For example, in the reflective member 100 shown in FIG. 1, another layer is disposed between the glass substrate 110 and the metal reflective film 120, between the metal reflective film 120 and the silica film 130, and above the silica film 130. May be. In this sense, it should be noted that the configuration of the reflective member 100 shown in FIG. 1 is a configuration that should be referred to as a “basic structure of the reflective member according to the present invention”, which shows only the minimum necessary layer structure. There is a need.

  Moreover, the metal reflective film 120 does not necessarily need to be composed of a single layer, and the metal reflective film 120 may be composed of a plurality of layers having different materials and / or compositions.

(About manufacturing method)
Next, an example of a method for manufacturing the reflective member 100 according to an embodiment of the present invention as shown in FIG. 1 will be described. The following manufacturing method is merely an example, and the reflective member 100 according to an embodiment of the present invention may be manufactured by another method.

  FIG. 2 shows a schematic flowchart of a method for manufacturing the reflective member 100 according to an embodiment of the present invention.

As shown in FIG.
(A) forming a metal reflective film on the glass substrate (step S110);
(B) forming a silica film on the upper part of the metal reflective film by a plasma CVD method under a pressure of 2 Pa or less (step S120);
Have Hereinafter, each step will be described in detail.

(Step S110)
First, a glass substrate is prepared. The composition of the glass substrate is not particularly limited.

  Next, a metal reflective film is formed on the glass substrate. The method for forming the metal reflective film is not particularly limited. The material of the metal reflective film is not particularly limited as long as appropriate reflectivity is exhibited in the finally produced reflective member.

  For example, the metal reflective film may be formed by sputtering. The thickness of the metal reflective film is, for example, 200 mm or more. The upper limit of the thickness of the metal reflection film is not particularly limited. The metal reflection film may be a single layer or a plurality of layers.

(Step S120)
Next, a silica film is formed on the metal reflective film obtained in step S110.

  Here, the silica film is formed by a plasma CVD method. The film forming pressure during film formation is 2 Pa or less. The film forming pressure is preferably 1 Pa or less, and more preferably 0.5 Pa or less.

  Steps S110 and S120 may be performed in an inline manner. Implementation in an in-line method simplifies the production process and enables film formation over a large area, which can contribute to improvement in productivity.

By forming a silica film under such conditions, the extinction coefficient k at a wavelength of 632 nm as described above is 1 × 10 ⁻⁴ or less, the refractive index n is 1.466 or more, A silica film having a content of 3 atomic% or less can be formed. Moreover, by forming such a silica film on the upper part of the metal reflective film, the silica film exhibits an oxygen barrier property, and oxidation of the metal reflective film is performed when the finally manufactured reflective member is used. It becomes possible to suppress.

  The other conditions for the CVD process are not particularly limited.

  For example, the source gas is not particularly limited, and the source gas may be, for example, a mixed gas of oxygen and tetramethyldisiloxane (TMDSO). In this case, the volume ratio of oxygen to TMDSO may be in the range of 100: 3 to 100: 15.

  The plasma power may be in the range of 15 to 100 kW / m.

  Through the above steps, the reflective member 100 according to the embodiment of the present invention as shown in FIG. 1 can be manufactured.

(About one application example of the reflective member of the present invention)
Next, an application example of the reflective member of the present invention having the above-described features will be described with reference to the drawings.

  In FIG. 3, the structure of the mirror apparatus which can be used for the secondary mirror etc. of a solar thermal power generation system is shown roughly.

  As shown in FIG. 3, the mirror device 200 includes a glass substrate 210, a first layer 220, a second layer 230, a third layer 240, a fourth layer 250, and a fifth layer 260 in this order. It is configured by stacking.

  The first layer 220 is installed in order to improve the adhesion between the glass substrate 210 and the second layer 230. The first layer 220 may include, for example, metal nitride, metal oxide, and / or metal oxynitride. Note that the first layer 220 is not an essential member and is often omitted.

  The second layer 230 has a role of effectively reflecting light in the wavelength region of sunlight, and includes a metal reflective film.

  The third layer 240 has a role of suppressing diffusion of oxygen in the environment toward the second layer 230 when the fourth layer 250 is formed. However, the third layer 240 is not an essential member and is often omitted.

  The fourth layer 250 is formed as a low refractive index film having a lower refractive index than the fifth layer 260. The fourth layer 250 includes a silica film.

  The fifth layer 260 is formed as a high refractive index film having a higher refractive index than the fourth layer 250. By laminating the fifth layer 260 having a high refractive index on the fourth layer 250 having a low refractive index, the reflectivity of the mirror device 200 as a whole can be significantly increased.

  Here, the mirror device 200 has a “basic structure of a reflective member according to the present invention” as shown in FIG. That is, in the mirror device 200, the glass substrate 210, the second layer 230, and the fourth layer are respectively formed on the glass substrate 110, the metal reflective film 120, and the silica film 130 of the reflective member 100 shown in FIG. Correspond.

  In a conventional general mirror device, when used in a high temperature environment for a long time, oxygen enters the inside of the device from the environment side, and this oxygen causes a film containing a metal, for example, the second layer 230 and / or the second layer. It can occur that the third layer 240 is oxidized. In particular, when such metal oxidation occurs in the second layer 230 that is directly related to the reflection characteristics of the mirror device, the reflection characteristics of the mirror device are significantly degraded.

  On the other hand, the mirror device 200 shown in FIG. 3 has the “basic structure of the reflective member according to the present invention”. In this case, due to the effect of the silica film as described above, that is, the good oxygen barrier property of the second layer 230, oxygen in the environment passes through the second layer 230 during the use of the mirror device 200, and the second layer 230 Reaching the second layer 230 is significantly suppressed.

  Therefore, in the mirror device 200, even when the mirror device 200 is used at a high temperature for a long period of time, the oxidation of the second layer 230 can be significantly suppressed, thereby significantly reducing the reflection characteristics of the mirror device 200. It becomes possible to suppress.

  In manufacturing such a mirror device 200, for example, the method described with reference to FIG. 2 described above can be applied.

  For example, in the mirror device 200, the first layer 220 is formed by a sputtering method, the second layer 230 is formed by a sputtering method, the third layer 240 is formed by a sputtering method, and the first layer 220 is formed by a plasma CVD method. The fourth layer 250 may be formed, and the fifth layer 260 may be formed by sputtering. The film formation pressure when forming the fourth layer 250 by the plasma CVD method is 2 Pa or less, and the film formation pressure may be 1 Pa or less, for example.

  Alternatively, the mirror device 200 may be manufactured by other methods. For example, the first layer 220 to the third layer 240 and the fifth layer 260 are not necessarily formed by a sputtering method, and may be formed by another film formation method.

(About each member constituting the mirror device)
Next, each member constituting the mirror device 200 will be described in detail. Note that a part of the following description can be equally applied to each member (that is, the glass substrate 110, the metal reflective film 120, and the silica film 130) constituting the reflective member 100 shown in FIG. It will be apparent to those skilled in the art that this can be done.

(Glass substrate 210)
The type of the glass substrate 210 is not particularly limited as long as the Na ₂ O content is 4% by weight or less. The glass substrate 210 may be, for example, non-alkali metal glass, AN100, or the like.

  The thickness of the glass substrate 210 is not particularly limited, but may be in a range of, for example, 0.5 mm to 8.0 mm from the viewpoint of strength and ease of use.

  The shape of the glass substrate 210 is not particularly limited. The glass substrate 210 may be planar or curved.

(First layer 220)
As described above, the first layer 220 has a role of improving the adhesion between the glass substrate 210 and the second layer 230.

  The first layer 220 is composed of at least one selected from the group consisting of metal nitride, metal oxide, and metal oxynitride. For example, the first layer 220 may be composed of zinc oxide. In this case, the zinc oxide may be doped with at least one element selected from the group consisting of aluminum, titanium, gallium, and tin.

  The first layer 220 has a thickness of 200 mm or more. The upper limit of the thickness of the first layer 220 is not particularly limited. The first layer 220 may be a single layer or a plurality of layers.

(Second layer 230)
As described above, the second layer 230 is a layer including a metal reflection film, and the light reaching the second layer 230 is reflected here.

  The metal reflective film constituting the second layer 230 may include, for example, silver or a silver alloy. The silver alloy may be an alloy containing at least one element selected from the group consisting of silver and gold, palladium, copper, nickel, and chromium, for example. In this case, the content of metals other than silver in the silver alloy may be in the range of 0.5% to 5% by mass.

  When silver or a silver alloy is contained in the second layer 130, the reflectance of light in the wavelength region of sunlight (300 nm to 2500 nm) in the second layer 130 is improved, and the dependency of the reflectance on the incident angle is improved. Can be reduced.

  The second layer 230 may have a thickness in the range of, for example, 800 to 3000 inches.

(Third layer 240)
As described above, the third layer 240 has a role of suppressing diffusion of oxygen in the environment toward the second layer 230 when the fourth layer 250 is formed.

  The third layer 240 may include an oxide layer. In this case, the oxide film may be made of zinc oxide. In this case, the zinc oxide may be doped with at least one element selected from the group consisting of aluminum, titanium, gallium, and tin.

  Further, the third layer 240 may include a metal layer. For example, it may be made of at least one metal selected from the group consisting of zinc, titanium, nickel, chromium, tin, and aluminum.

  Of these metals, zinc is preferred. In this case, the metal layer may contain zinc and may be doped with at least one element selected from the group consisting of titanium, aluminum, tin, and gallium. The third layer 240 may be a single layer or a plurality of layers.

  The third layer 240 may have a thickness in the range of 10 to 100 inches, for example.

  Note that the third layer 240 is not an essential member and may be omitted. In particular, in the case of the mirror device 200 according to an embodiment of the present invention, the fourth layer 250 formed thereafter includes a silica film having the above-described characteristics. For this reason, even when the third layer 240 is omitted, the oxidation of the second layer 230 can be significantly suppressed by the oxygen barrier property of the fourth layer 250.

(Fourth layer 250)
The fourth layer 250 is made of a material having a lower refractive index than that of the fifth layer 260. The fourth layer 250 includes a silica film.

As described above, the silica film has an extinction coefficient k of 1 × 10 ⁻⁴ or less at a wavelength of 632 nm, a refractive index n of 1.466 or more, and a carbon content of 3 atomic% or less. As a result, the fourth layer 250 exhibits a denseness, that is, an oxygen barrier property, and can improve the heat resistance of the mirror device 200 at a high temperature.

  The fourth layer 250 may have a film thickness in the range of 300 to 1500 mm, for example.

(Fifth layer 260)
The fifth layer 260 is made of a material having a higher refractive index than the fourth layer 250. For example, the fifth layer 260 may have an optical constant having a refractive index n of 1.7 or more and an extinction coefficient k of 0.01 or less at a wavelength of 550 nm.

  The material included in the fifth layer 260 is not particularly limited as long as the above condition is satisfied. The fifth layer 260 is made of, for example, silicon nitride, aluminum nitride, silicon oxynitride, aluminum oxynitride, niobium oxide, zirconium oxide, tantalum oxide, hafnium oxide, titanium oxide, zinc oxide, and / or tin oxide. Also good. The fifth layer 260 may be a composite oxynitride.

  Of these materials, silicon nitride is preferred. When the fifth layer 260 includes silicon nitride, the fifth layer 260 exhibits an effect of suppressing entry of oxygen in the environment into the interior. Therefore, in this case, the oxidation of the second layer can be further suppressed by the oxygen barrier effect of both the fourth layer 250 and the fifth layer 260.

  The fifth layer 260 may have a thickness in the range of 300 to 1500 inches. Further, the fifth layer 260 may be a single layer or a plurality of layers.

  Next, examples of the present invention will be described.

(Preliminary test)
(Sample 1)
A preliminary test sample was prepared by sequentially forming a first silica film, a metal titanium film, and a second silica film on the surface of the glass substrate by the following method.

  First, a glass substrate was prepared. The glass substrate is soda lime glass having dimensions of 100 mm length × 100 mm width × 2 mm thickness.

  A first silica film having a thickness of 50 nm (target value) was formed on one surface of the glass substrate by plasma CVD.

  As a raw material, a mixed gas of oxygen and tetramethyldisiloxane (TMDSO) was used, the flow rate of oxygen was 400 sccm, and the flow rate of TMDSO was 50 sccm. In addition, the film formation pressure during the plasma CVD process was 0.47 Pa, and the plasma power was 20 kW / m.

  Next, a metal titanium film was formed on the first silica film by an ordinary sputtering method. The thickness of the metal titanium film was 10 nm (target value).

  A metal titanium target was used as the target, and argon gas was used as the film forming gas. The sputtering pressure was 0.35 Pa, a DC power source was used, and the input power was 0.5 kW.

  Further, a second silica film was formed on the metal titanium film by plasma CVD. The deposition conditions for the second silica film are substantially the same as the deposition conditions for the first silica film.

  Through the above processing, a preliminary test sample (hereinafter referred to as “sample 1”) was produced.

  For the second silica film of Sample 1, the refractive index n and the extinction coefficient k at a wavelength of 632 nm were measured by spectroscopic ellipsometry (manufactured by JA Woollam, trade name: M-2000DI). As a result of the measurement, the refractive index n of the second silica film was 1.4772, and the extinction coefficient k was 0.

  Further, the chemical composition was analyzed by XPS depth profile analysis using an XPS analyzer (trade name: PHI5000, manufactured by ULVAC-PHI). As a result of the measurement, the carbon content in the second silica film was below the detection limit (detection limit value was 0.1%).

(Sample 2)
Sample 2 having a first silica film, a metal titanium film, and a second silica film on the surface of the glass substrate was produced in the same manner as in Sample 1 described above.

  However, when the sample 2 was produced, the film formation pressure when forming the first and second silica films was 0.56 Pa. Other manufacturing conditions are the same as those in the case of Sample 1.

  With respect to the obtained second silica film of Sample 2, the refractive index n and the extinction coefficient k were measured by the method described above. As a result of the measurement, the refractive index n at a wavelength of 632 nm was 1.4773, and the extinction coefficient k was 0. Further, the carbon content in the second silica film was below the detection limit (detection limit value was 0.1%).

(Sample 3)
A sample 3 having a first silica film, a metal titanium film, and a second silica film on the surface of the glass substrate was produced in the same manner as in the above-described sample 1.

  However, when producing Sample 3, the flow rate of oxygen when forming the first and second silica films was 236 sccm, and the flow rate of TMDSO was 15 sccm. In addition, the film formation pressure during the plasma CVD process was 0.35 Pa, and the plasma power was 80 kW / m.

  With respect to the obtained second silica film of Sample 3, the refractive index and the extinction coefficient k were measured by the method described above. As a result of the measurement, the refractive index n at a wavelength of 632 nm was 1.469, and the extinction coefficient k was 0. Further, the carbon content in the second silica film was below the detection limit (detection limit value was 0.1%).

(Sample 4)
A sample 4 having a first silica film, a metal titanium film, and a second silica film on the surface of the glass substrate was produced in the same manner as in the above-described sample 1.

  However, when the sample 4 was produced, the film formation pressure when forming the first and second silica films was 3.89 Pa. Other manufacturing conditions are the same as those in the case of Sample 1.

  The refractive index n and extinction coefficient k of the second silica film of Sample 4 obtained were measured by the method described above. As a result of the measurement, the refractive index n at a wavelength of 632 nm was 1.4611, and the extinction coefficient k was 0. Further, the carbon content in the second silica film was below the detection limit (detection limit value was 0.1%).

(Sample 5)
A first silica film was formed on the surface of the glass substrate used in Sample 1 described above by a conventional sputtering method. The film formation pressure during film formation is 0.27 Pa. The thickness of the first silica film was 50 nm (target value).

  A metal silicon target (boron-doped polycrystalline target, silicon content 99.999 mass%) was used as the target, and a silicon oxide film was formed by a pulsed DC reactive sputtering method. As the sputtering gas, oxygen gas (flow rate 30 sccm) and argon gas (flow rate 20 sccm) were used. The input power was 1.5 kW and the frequency was 20 kHz.

  Next, a metal titanium film was formed on the first silica film by an ordinary sputtering method. The thickness of the metal titanium film was 10 nm (target value). The conditions for forming the metal titanium film are the same as in Sample 1.

  Further, a second silica film was formed on the metal titanium film by a sputtering method. The conditions for forming the second silica film are substantially the same as the conditions for forming the first silica film.

  Sample 5 was produced by the above processing.

  About the obtained 2nd silica film | membrane of the sample 5, the refractive index n and the extinction coefficient k were measured with the above-mentioned method. As a result of the measurement, the refractive index n at a wavelength of 632 nm was 1.4602, and the extinction coefficient k was 0. Further, the carbon content in the second silica film was below the detection limit (detection limit value was 0.1%).

  Table 1 summarizes the production conditions of Samples 1 to 5, and the measurement results of the refractive index n, the extinction coefficient k, and the carbon content.

（耐熱性の評価）
前述の方法で作製したサンプル１〜５を用いて、耐熱性評価試験を実施した。

(Evaluation of heat resistance)
A heat resistance evaluation test was performed using Samples 1 to 5 produced by the method described above.

  The heat resistance evaluation test was performed as follows.

First, for each sample, the visible light transmittance Tv is measured with a spectrophotometer (U4100 manufactured by HITACHI). The visible light transmittance Tv is obtained by multiplying the value of the spectral transmittance by the multiplication coefficient obtained from the spectrum of the CIE daylight D65 and the wavelength distribution of the visibility, and averaging the results. The obtained visible light transmittance Tv is defined as initial visible light transmittance Tv ₀ .

Next, each sample is heat-treated at 400 ° C. for 35 minutes in the atmosphere. Similarly to measure the visible light transmittance Tv of the sample after heat treatment, which is referred to as heat treatment after the visible light transmittance Tv _a. After the resulting heat-treated from the difference between the visible light transmittance Tv _a initial visible light transmittance Tv _0, obtains the variation .DELTA.TV of visible light transmittance Tv before and after heat treatment _{(ΔTv = Tv 0 -Tv a)} .

Here, in the initial sample, a metal titanium film is interposed between the silica films. For this reason, in any sample, the initial visible light transmittance Tv ₀ is a relatively low value.

On the other hand, the sample after the heat treatment, in particular, by difference the oxygen barrier property of the second silica film, the value of the heat treatment after the visible light transmittance Tv _a largely changes. For example, when the oxygen barrier property of the second silica film is not very good, oxygen in the atmosphere passes through the second silica film and reaches the titanium film during the heat treatment. This also oxidizes the titanium film and increases the transparency of the titanium film. As a result, the visible light transmittance Tv _a increases after heat treatment. However, when the oxygen barrier property of the second silica film is relatively good, oxygen in the atmosphere reaches the titanium film significantly. As a result, oxidation of the titanium film can be suppressed, increase in the heat treatment after the visible light transmittance Tv _a is significantly suppressed.

  Therefore, the heat resistance of the sample can be evaluated by evaluating the change ΔTv in the visible light transmittance Tv of the sample before and after the heat treatment. More specifically, it can be said that the smaller the amount of change ΔTv, the better the heat resistance.

  The results obtained by the heat resistance evaluation test are collectively shown in FIG. Further, Table 1 shows the value of the change amount ΔTv of the visible light transmittance Tv obtained in each sample.

  From these results, it can be seen that the change amount ΔTv of the visible light transmittance Tv is significantly suppressed in the samples 1 to 3 compared to the samples 4 and 5.

  Samples 1 to 3 have silica films having refractive indexes n of 1.4772, 1.4773, and 1.469, respectively. On the other hand, Sample 4 and Sample 5 have silica films with refractive indexes n of 1.4611 and 1.4602, respectively. Therefore, the difference in the change ΔTv in the visible light transmittance Tv is due to the refractive index n of the silica film. When the refractive index n exceeds 1.4611, the oxygen barrier property of the silica film is improved and the heat resistance of the sample is increased. It can be said that the sex is improved. In particular, if the refractive index n of the silica film is 1.467 or more, the sample is estimated to have good heat resistance.

  It can be seen that in any sample, the amount of carbon in the silica film is below the detection limit, and the relationship between the refractive index n and the denseness is certain.

(Heat resistance test of mirror sample)
From the result of the preliminary test described above, it was confirmed that when the refractive index n of the silica film exceeds 1.467, the silica film exhibits good oxygen barrier properties. Then, the mirror sample provided with the structure of an actual mirror apparatus was produced next, and this heat resistance was evaluated.

(Mirror sample 1)
The mirror sample (mirror sample 1) was produced as follows.

First, a glass substrate is prepared. The glass substrate is a non-alkali glass having dimensions of 100 mm in length, 100 mm in width, and 3 mm in thickness, and the Na ₂ O content is 0% by weight. On one surface of this glass substrate, a first layer (target thickness 20 nm), a second layer (target thickness 120 nm), a third layer (target thickness 2.2 nm), a fourth layer (target thickness) A thickness of 50 nm) and a fifth layer (target thickness of 50 nm) were sequentially formed, and the mirror sample 1 having the layer configuration as shown in FIG. 3 was prepared.

  The first layer is composed of zinc oxide doped with aluminum, the second layer is composed of a silver alloy containing 1 wt% of gold, and the third layer is zinc doped with aluminum. The fourth layer is made of silica, and the fifth layer is made of silicon nitride.

  Among these, the 1st layer-the 3rd layer, and the 5th layer were formed into a film by the usual sputtering method.

  First, an aluminum-doped zinc oxide film was formed on a glass substrate by a DC sputtering method using a zinc target doped with 5 at% aluminum. Argon gas (flow rate 60 sccm) and oxygen gas (flow rate 140 sccm) were used as the sputtering gas. The input power was 0.5 kW.

  Next, after exhausting the remaining gas, a silver alloy film was formed on a glass substrate having an aluminum-doped zinc oxide film by a DC sputtering method using a silver alloy target containing 1 wt% of gold. Argon gas (flow rate 200 sccm) was used as the sputtering gas. The input power was 0.9 kW.

  On the other hand, the fourth layer made of silica was formed by a plasma CVD method. As the conditions for the plasma CVD process, the same conditions as those for forming the second silica film in Sample 2 of the preliminary test described above were adopted. Therefore, the refractive index n of the fourth layer at a wavelength of 632 nm is 1.4773, the extinction coefficient k is 0, and the carbon content is below the detection limit.

  Next, after exhausting the residual gas, a silicon nitride film was formed by a pulse DC reactive sputtering method using a metal silicon target (boron-doped polycrystalline target, silicon content 99.999 mass%). Nitrogen gas (flow rate 60 sccm) and argon gas (flow rate 140 sccm) were used as the sputtering gas. The input power was 1 kW, and the frequency was 20 kHz.

(Mirror sample 2)
A mirror sample (mirror sample 2) having the same layer configuration as the mirror sample 1 was produced. However, in this mirror sample, the fourth layer was formed by a plasma CVD method. As the conditions for the plasma CVD process, the same conditions as those for forming the second silica film in the sample 3 of the preliminary test described above were adopted. Therefore, the refractive index n of the fourth layer at a wavelength of 632 nm is 1.469, the extinction coefficient k is 0, and the carbon content is below the detection limit.

  Other film forming conditions are the same as those of the mirror sample 1.

(Mirror sample 3)
A mirror sample (mirror sample 3) having the same layer configuration as the mirror sample 1 was produced. However, in this mirror sample 3, the fourth layer, that is, the silica film, was formed by a normal sputtering method. As the film formation conditions, the same conditions as those for forming the second silica film in Sample 5 of the preliminary test described above were adopted. Therefore, the refractive index n of the fourth layer at a wavelength of 632 nm is 1.4602, and the extinction coefficient k is 0.

  In the mirror sample 3, the fifth layer was not silicon nitride but titanium dioxide (target thickness: 50 nm).

  Other film forming conditions are the same as those of the mirror sample 1.

(Mirror sample 4)
A mirror sample (mirror sample 4) having the same layer configuration as that of the mirror sample 3 was produced. However, in this mirror sample 4, the fifth layer was not titanium dioxide but silicon nitride (target thickness 50 nm).

  Other film forming conditions are the same as those of the mirror sample 3.

  Table 2 collectively shows the manufacturing conditions of the fourth layer of the mirror samples 1 to 4, the values of the refractive index n and extinction coefficient k of the fourth layer, and the material of the fifth layer.

（耐熱試験）
ミラーサンプル１〜４を用いて、耐熱試験を実施した。耐熱試験は、各ミラーサンプルを、大気下５００℃で３時間熱処理することにより実施した。

(Heat resistance test)
The heat resistance test was implemented using the mirror samples 1-4. The heat resistance test was performed by heat-treating each mirror sample at 500 ° C. for 3 hours in the atmosphere.

  The solar energy reflectance Re was measured for each mirror sample after the heat treatment. This solar energy reflectance: Re is a value calculated according to ISO 9050-2003. Specifically, the measured value of the spectral absolute reflectance (300 nm to 2500 nm) is overlapped indicating the standard spectral distribution of solar radiation. It means a weighted average value multiplied by a coefficient. Moreover, the external appearance of the mirror sample after heat processing was observed visually.

  The results of the heat resistance test for each mirror sample are summarized in Table 2 above.

  From the results shown in Table 2, it can be seen that the mirror samples 1 and 2 after the heat treatment have significantly higher energy reflectance Re than the mirror samples 3 and 4. Further, turbidity was observed in the mirror samples 3 and 4 after the heat treatment. On the other hand, the mirror samples 1 and 2 after the heat treatment were not particularly abnormal in appearance.

From the above, the fourth layer has a refractive index n of 1.467 or more at a wavelength of 632 nm, an extinction coefficient k of 1 × 10 ⁻⁴ or less, and a carbon content of 3 atomic% or less. In the mirror samples 1 and 2 made of a silica film, the fourth layer shows better heat resistance than the mirror samples 3 and 4 made of a silica film having a refractive index n of about 1.46. It was confirmed.

  The present invention can be used for a secondary mirror or the like in a solar thermal power generation system such as a linear Fresnel type or a tower type.

DESCRIPTION OF SYMBOLS 100 Reflective member 110 Glass substrate 120 Metal reflective film 130 Silica film 200 Mirror apparatus 210 Glass substrate 220 1st layer 230 2nd layer 240 3rd layer 250 4th layer 260 5th layer

Claims (14)

A reflective member,
Having a glass substrate, a silica film, and a metal reflective film disposed between the two,
The silica film has an extinction coefficient k at a wavelength of 632 nm of 1 × 10 ⁻⁴ or less, a refractive index n of 1.466 or more, and a carbon content of 3 atomic% or less. .   The reflective member according to claim 1, wherein the metal reflective film includes silver or a silver alloy.   The reflection according to claim 1, further comprising at least one film selected from the group consisting of a metal nitride, a metal oxide, and a metal oxynitride between the glass substrate and the metal reflection film. Sexual member.   The reflective member according to any one of claims 1 to 3, wherein the glass substrate is a glass having a sodium oxide content of 4% by weight or less.   Furthermore, the reflective member as described in any one of Claims 1 thru | or 4 which has a film | membrane with a refractive index higher than a silica film on the opposite side to the said metal reflective film of the said silica film.   The reflective member according to claim 5, wherein the film having a higher refractive index than the silica film is a silicon nitride film.   A secondary mirror for a solar thermal power generation system, comprising the reflective member according to any one of claims 1 to 6. A method of manufacturing a reflective member,
(A) forming a metal reflective film on the glass substrate;
(B) forming a silica film on the metal reflective film;
Have
The step (b) is performed by a plasma CVD method under a pressure of 2 Pa or less. The silica film formed by the step (b) has an extinction coefficient k of 1 × 10 ⁻⁴ or less at a wavelength of 632 nm, a refractive index n of 1.466 or more, and a carbon content of 3 atomic% or less. The manufacturing method according to claim 8, wherein   The manufacturing method according to claim 8 or 9, wherein the step (a) is performed by a sputtering method.   The manufacturing method according to claim 8, wherein the steps (a) and (b) are performed by an inline method.   The manufacturing method according to claim 8, wherein the metal reflective film includes silver or a silver alloy. further,
(C) forming a film having a refractive index higher than that of the silica film on the silica film;
The manufacturing method according to claim 8, comprising:   The manufacturing method according to claim 13, wherein the film having a refractive index higher than that of the silica film is silicon nitride.

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