JP2018095488A - Heat radiation element for space and design method thereof and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat radiation controlling element with higher emissivity than before while keeping sunlight absorptivity at the same level with before, and to provide a manufacturing method thereof.SOLUTION: A heat radiation controlling element comprises an inorganic material substrate 10 containing either of quartz and inorganic glass, and a reflection membrane 80 provided at one face side of the inorganic material substrate 10. The inorganic material substrate 10 has a structure S that independent multiple convex parts 10a are arranged in two dimensions on another face side of the reflection membrane 80.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a thermal radiation control element and a manufacturing method thereof, and more particularly to a thermal radiation control element used for a spacecraft such as an artificial satellite.

  Since the outer space is a vacuum, the heat radiation control from the onboard equipment installed in the spacecraft such as an artificial satellite is performed by thermal radiation (thermal radiation). Therefore, in order to maintain the temperature in the spacecraft within an appropriate range, a thermal radiation control element called OSR (Optical Solar Reflector) is attached to the surface of the spacecraft. Here, in addition to the heat radiation to outer space, the thermal radiation control element needs to block the heat absorption due to the incidence of sunlight.

  Here, the thermal radiation control element 500 used in the prior art will be described with reference to FIG. The thermal radiation control element 500 includes an inorganic material substrate 10 and a reflective film 80 provided on one surface side of the inorganic material substrate 10. In the prior art, the inorganic material substrate is usually made of quartz, and a reflective film 80 made of Ag or the like is coated on the back surface of the inorganic material substrate 10, and the thermal radiation control element 500 is used in the spacecraft 1 (artificial satellite). Etc.) on the surface 1A. The surface (exposed surface) of the inorganic material substrate 10 is a flat surface.

  As shown in FIG. 1, the sunlight L incident on the surface of the quartz substrate (inorganic material substrate) 10 is transmitted through the quartz substrate 10, the sunlight L is reflected by the reflective film 80, and again passes through the quartz substrate 10. Radiated to the outside. Further, heat radiation of the heat H inside the spacecraft 1 is performed via the quartz substrate 10 particularly in the infrared light region. In the heat radiation control element, the heat radiation of the heat H and the reflection of the sunlight L are performed in this way. Therefore, the heat radiation control element has a high heat radiation rate and a low sunlight absorption rate. Is desired.

  Patent Document 1 discloses, as such a thermal radiation control element, a radiation-resistant glass substrate, a silver film formed on the surface thereof, and a protective film formed on the surface of the silver film. However, there is disclosed a heat control mirror characterized by having a two-layer structure of a lower layer made of a cerium oxide film and an upper layer made of a silicon oxide film.

JP-A-5-77799

Here, in this specification, a value (ε) calculated by the following equation (1) for an ideal black body at a certain temperature T is referred to as “emissivity”.
Here, I (λ, T) is the spectral radiation intensity at temperature T and wavelength λ, and ε (λ, T) is the spectral radiation rate at temperature T and wavelength λ of the thermal radiation control element. Note that λ ₁ and λ ₂ are the shortest wavelength and the longest wavelength in the wavelength range governing the blackbody radiation at the temperature T. Further, a value calculated by the following formula (2) at a temperature of 300 K is referred to as “vertical emissivity”. The wavelength range for calculating the vertical emissivity is 5 μm to 30 μm.

Moreover, in this specification, the "sunlight absorption rate" means that the spectral radiation intensity at each wavelength in the spectral radiation spectrum of the sun (AM0) is 1, and the solar wavelength region (in this specification, 300 to 2500 nm) The value (α) calculated by the following formula (3).
Here, I _solar (λ) is the spectral radiant intensity of sunlight at the wavelength λ, and α _s (λ) is the spectral absorptance of sunlight at the wavelength λ of the thermal radiation control element.

  Now, the ideal value of the vertical emissivity of the thermal radiation control element is 1, and the ideal value of the solar absorptance is 0. In the case of the thermal radiation control element in the prior art, the vertical emissivity (ε) at 300 K is approximately 0.84, and the solar absorptance (α) according to the prior art is approximately 0.07 to 0.10. As shown in FIG. 2, the spectral spectrum of quartz emissivity (hereinafter referred to as the radiation spectrum) and the black body radiation spectrum at 300K, quartz has a relatively high spectral emissivity in the infrared region, but 300K black. Since the spectral emissivity is low in the vicinity of 9 μm, which is the peak wavelength region of the radiation spectrum of the body, it is difficult to set the vertical emissivity to an ideal value of 1. This reason is due to the characteristic of quartz, and is explained by the complex refractive index of quartz shown in FIG. The refractive index of quartz has an imaginary part k that increases due to molecular vibrations in the vicinity of wavelengths of 9 μm and 21 μm, and quartz itself reflects light in this wavelength region, so that the vertical emissivity is lowered.

  The radiation spectrum of quartz of the thermal radiation control element in the prior art will be further described. FIG. 4 shows an analysis of the emission spectrum of quartz having a planar structure by the RCWA (Rigorous Coupled-Wave Analysis) method. In this thermal radiation control element of the prior art, it is confirmed that the spectral emissivity is greatly reduced near the wavelength of 9 μm and near the wavelength of 21 μm.

  FIG. 5 shows a reflection spectrum and an absorption spectrum obtained by calculating the spectral reflectance and the spectral absorptance of the thermal radiation control element in the prior art by the optical simulation TFCalc. In addition, in FIG. 5, sunlight spectrum AM0 is shown collectively. Although the radiant intensity peak of the solar spectrum is in the ultraviolet to visible light range, the spectral reflectance (solid line) due to the reflective film decreases sharply at a wavelength of 500 nm or less, while the spectral absorption rate (dotted line) sharply decreases in the wavelength range. It is confirmed that it has increased.

  Although the vertical emissivity and solar absorptivity of the thermal radiation control element according to the prior art are as described above, it is considered that the vertical emissivity according to the prior art is sufficiently high and the solar absorptivity is sufficiently low. I came. In recent years, however, the amount of heat generated by the on-board machine has increased with the improvement in performance of the on-board equipment in the spacecraft. Therefore, an element capable of radiating heat with higher efficiency has been demanded. On the other hand, it has been considered that it is difficult to further improve the thermal emissivity of the thermal radiation control element due to the characteristics unique to quartz.

  However, if the thermal radiation rate of the thermal radiation control element can be improved, the area where the thermal radiation control element is installed on the heat radiation surface of the spacecraft (that is, the weight of the thermal radiation panel) can be reduced. Weight reduction and spacecraft payload ratio can be improved.

  Therefore, an object of the present invention is to provide a thermal radiation control element having a higher thermal emissivity than before and a method for manufacturing the same while maintaining the solar light absorption rate at the same level as before.

  The inventors of the present invention have intensively studied to achieve the above-mentioned objects, and pay attention to the surface structure of the inorganic material substrate, and by providing a structure composed of a plurality of convex portions on the surface of the inorganic material substrate, It was found that thermal radiation control with high thermal emissivity can be realized.

The present invention is based on the above findings by the present inventors, and means for solving the above problems are as follows. That is,
<1> an inorganic material substrate containing either quartz or inorganic glass;
A thermal radiation control element having a reflective film provided on one surface side of the inorganic material substrate,
The inorganic material substrate is a thermal radiation control element having a structure in which a plurality of independent protrusions are two-dimensionally arranged on the surface opposite to the reflective film.
According to the thermal radiation control element described in <1>, it is possible to provide a thermal radiation control element having a higher thermal emissivity than the conventional one while maintaining the solar light absorption rate at the same level as the conventional one.

  <2> The thermal radiation control element according to <1>, wherein the convex portion includes a tip portion.

  <3> The thermal radiation control element according to <1>, wherein the convex portion includes a vertex.

  <4> The thermal radiation control element according to <3>, wherein in the cross-sectional view including the central axis of the convex portion, a ridge line between the adjacent convex portions is curved.

  <5> In the cross-sectional view including the central axis of the convex portion, the ridge line of the convex portion is the thermal radiation control element according to <3>, wherein the ridge line has a bending point.

  <6> The thermal radiation control element according to <3>, wherein the convex portion is a cone.

  <7> In any one of the above items <1> to <6>, an area of a cross section cut along a horizontal plane perpendicular to the height direction of the convex portion decreases along a direction from the bottom surface of the convex portion toward the apex. It is a thermal radiation control element of description.

  <8> The thermal radiation control element according to any one of <1> to <7>, wherein a bottom shape of the convex portion includes a circle or a regular polygon.

  <9> The thermal radiation control element according to <8>, wherein a bottom shape of the convex portion includes a circle or a regular hexagon, and the two-dimensional array is a hexagonal close-packed array.

  <10> The thermal radiation control element according to any one of <1> to <8>, wherein the lattice arrangement is a square lattice arrangement.

  <11> The thermal radiation control element according to any one of <1> to <10>, wherein a ratio H / W of a height H of the convex portion to a width W of the bottom surface of the convex portion is 0.25 or more. It is.

  <12> The thermal radiation control element according to any one of <1> to <11>, wherein an interval P between the adjacent convex portions is 15 μm or more.

  <13> The thermal radiation control element according to <12>, wherein a ratio W / P of a width W of the bottom surface to the interval P is 0.7 or more.

  <14> The thermal radiation control element according to any one of <1> to <13>, further including a protective film on a surface of the reflective film opposite to the inorganic material substrate.

<15> An additional reflection film is further provided between the inorganic material substrate and the reflection film,
The thermal reflection control element according to any one of <1> to <14>, wherein the increased reflection film includes two or more dielectric layers.

  Any one of said <1>-<15> with which the <16> above-mentioned convex part and the exposed flat surface of the said inorganic material board | substrate are coat | covered with the dielectric multilayer mirror which reflects the light of the wavelength below near infrared light. It is a thermal radiation control element of description.

  <17> The thermal radiation control element according to any one of <1> to <16>, wherein an outermost surface on a side where the convex portion is provided is covered with a transparent conductive film.

<18> a structure forming step of forming a structure in which a plurality of independent protrusions are two-dimensionally arranged on the surface of an inorganic material substrate containing either quartz or inorganic glass;
A method of manufacturing a thermal radiation control element, comprising: a reflective film forming step of forming a reflective film on a surface of the inorganic material substrate opposite to a surface on which the structure is formed.
According to the method for producing a thermal radiation control element described in <18>, a method for producing a thermal radiation control element having a higher thermal emissivity than the conventional one is provided while maintaining the solar absorption rate at the same level as the conventional one. can do.

  <19> The method for manufacturing a thermal radiation control element according to <18>, wherein the structure forming step includes an etching step.

  <20> The method for manufacturing a thermal radiation control element according to <18>, wherein in the structure formation step, the structure is formed by machining or laser processing the inorganic material substrate.

  <21> The <18>, wherein the structure forming step includes a step of forming a mold by machining or laser processing, and a forming step of forming the structure by forming a sol-gel using the mold. It is a manufacturing method of the thermal radiation control element of description.

  <22> The structure forming step includes a step of forming a mold by machining or laser processing, and a transfer step of forming the structure on the surface of the inorganic material substrate by shape transfer of the mold. 18>. The manufacturing method of the thermal radiation control element according to 18>.

  <23> The method according to any one of <18> to <22>, further including a heat treatment step of performing a heat treatment below the glass softening point of the inorganic material substrate under vacuum or atmospheric pressure after the structure forming step. It is a manufacturing method of a thermal radiation control element.

  <24> The method for producing a thermal radiation control element according to any one of <18> to <23>, further including a dielectric multilayer mirror forming step of forming a dielectric multilayer mirror on the surface of the structure. .

  <25> The method for producing a thermal radiation control element according to any one of <18> to <24>, further including a transparent conductive film forming step of forming a transparent conductive film on the surface of the structure.

  <26> The thermal radiation control element according to any one of <18> to <25>, further including a protective film forming step of forming a protective film on a surface of the reflective film opposite to the inorganic material substrate. It is a manufacturing method.

  According to the present invention, the conventional problems can be solved, the object can be achieved, and the thermal radiation control having a higher thermal emissivity than the conventional one while maintaining the solar absorptance at the same level as the conventional one. An element and a manufacturing method thereof can be provided.

It is a schematic diagram explaining the thermal radiation control element according to a prior art. It is a graph which shows the conventionally known radiation spectrum of quartz and black body radiation spectrum of 300K. It is a graph which shows the conventionally known complex refractive index of quartz. It is a graph which shows the radiation spectrum of the thermal radiation control element according to a prior art. It is a graph which shows the reflection spectrum and absorption spectrum of a thermal radiation control element according to a prior art, and a sunlight spectrum. (A) is a schematic diagram which shows the thermal radiation control element according to one Embodiment of this invention, (B) is a schematic diagram which shows another embodiment of this invention. (A)-(D) are the schematic diagrams explaining the convex part in the thermal radiation control element according to one Embodiment of this invention. It is a schematic diagram explaining the convex part according to the 1st suitable aspect of this invention, and its arrangement | sequence, (A) is a top view, (B) is II sectional drawing in (A), (C) is ( It is II-II sectional drawing in A). It is a schematic diagram explaining the convex part according to the 2nd suitable aspect of this invention, and its arrangement | sequence, (A) is a top view, (B) is III-III sectional drawing in (A). (A) is a schematic diagram explaining the arrangement | sequence of the convex part according to the 3rd suitable aspect of this invention, (B) is a schematic diagram explaining the arrangement | sequence of the convex part according to the 4th suitable aspect of this invention. (A) is a schematic diagram explaining the 1st deformation | transformation aspect of the convex part according to this invention, (B) is a schematic diagram explaining the 2nd deformation | transformation aspect of the convex part according to this invention. It is a schematic diagram explaining the thermal radiation control element according to suitable embodiment of this invention. It is a schematic diagram explaining the thermal radiation control element according to the reference form of this invention. It is a schematic cross section explaining one embodiment of a manufacturing method according to the present invention. It is a schematic cross section explaining suitable embodiment of the manufacturing method according to this invention. It is a graph which shows the radiation spectrum in Example 1, (A) is P of 3 micrometers, (B) is P of 9 micrometers, (C) is P of 21 micrometers, (D) is P of 84 micrometers. is there. 4 is a graph showing the vertical emissivity with respect to P in Example 1. It is a graph which shows the emission spectrum in Example 1, (A) is W / P 1.0, (B) is W / P 0.9, (C) is W / P is 0.00. 8 and (D) has a W / P of 0.7. It is a figure which shows the reflection intensity distribution in Example 1, (A) is W / P 1.0 and (B) is W / P 0.7. 4 is a graph showing the vertical emissivity with respect to W / P in Example 1. 6 is a graph showing a vertical emissivity with respect to an aspect ratio H / W in Example 1. It is a graph which shows the sunlight absorption factor with respect to P in Example 2. FIG. It is a graph which shows the sunlight absorptance with respect to aspect ratio H / W in Example 2. FIG. It is a graph which shows the radiation spectrum in Example 3, (A) is a case where a convex part is a hexagonal close-packed arrangement | sequence, (B) is a case where a convex part is a tetragonal lattice arrangement | sequence. It is a graph which shows the radiation spectrum in Example 3, (A) is a case where a convex part is a cone, (B) is a case where a convex part is a quadrangular pyramid. It is a graph which shows the radiation spectrum in Example 3, (A) is a case where the ridgeline between convex parts is a semicircle shape, (B) is a case where the ridgeline between convex parts is a semicircle shape which has a bending point. . It is a graph which shows the reflection spectrum and absorption spectrum in Example 4, (A) is the reflection spectrum of the dielectric multilayer film mirror in Reference Example 1, (B) is the reflection spectrum of Reference Example 1, (C ) Is an absorption spectrum of Reference Example 1-1. It is a graph which shows the reflection spectrum and absorption spectrum in Example 4, (A) is a reflection spectrum of the dielectric multilayer film mirror in Reference Example 2, (B) is the reflection spectrum of Reference Example 2, (C ) Is an absorption spectrum of Reference Example 1-2. It is a graph which shows the reflection spectrum and absorption spectrum in Example 4, (A) is a reflection spectrum of the dielectric multilayer mirror single in Reference Example 3, (B) is the reflection spectrum of Reference Example 3, (C ) Is an absorption spectrum of Reference Example 1-3. It is a graph which shows the reflection spectrum and absorption spectrum in Example 4, (A) is a reflection spectrum of the dielectric multilayer film mirror in Reference Example 4, (B) is the reflection spectrum of Reference Example 4, (C ) Is an absorption spectrum of Reference Example 1-4. It is a SEM image of the board | substrate surface of invention example 1-1 in Example 5, (A) is a cross-sectional image, (B) is a perspective image. It is an emission spectrum of Invention Example 1-1 and Conventional Example 1 in Example 5. It is a SEM image of the board | substrate surface of invention example 1-2 in Example 5, (A) is a cross-sectional image, (B) is a perspective image. It is an emission spectrum of Invention Example 1-2 and Conventional Example 1 in Example 5. It is a SEM image of the board | substrate surface of invention example 1-3 in Example 5, (A) is a cross-sectional image, (B) is a perspective image. It is an emission spectrum of Invention Example 1-3 and Conventional Example 1 in Example 5. It is a radiation spectrum of invention example 2-1 in Example 6, and the prior art example 1. FIG. It is a SEM image of the substrate surface before heat processing in Example 7, (A) is a cross-sectional image, (B) is a perspective image. It is a SEM image of the substrate surface after heat processing in Example 7, (A) is a cross-sectional image, (B) is a perspective image. It is a graph which shows the absorption rate change amount before and behind the heat processing in Example 7. It is a SEM image of the substrate surface in Example 8, (A) before heat treatment, (B) after heat treatment at 1200 ° C, (C) after heat treatment at 1225 ° C, and (D) after heat treatment at 1250 ° C. (E) is a cross-sectional image after heat treatment at 1275 ° C.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In principle, the same components are denoted by the same reference numerals, and description thereof is omitted. In each figure, for convenience of explanation, the vertical and horizontal ratios of the substrate and each layer are exaggerated from the actual ratios.

(Thermal radiation control element)
As shown in FIGS. 6A and 6B, the thermal radiation control element according to the embodiment of the present invention includes an inorganic material substrate 10, a reflective film 80 provided on one surface side of the inorganic material substrate 10, Have The inorganic material substrate 10 contains either quartz or inorganic glass.

  6A, the inorganic material substrate 10 has a structure S in which a plurality of independent protrusions 10a are two-dimensionally arranged on the surface opposite to the reflective film 80. As shown in FIG. Here, the two-dimensional arrangement means that the convex portions 10a are regularly or irregularly arranged in a two-dimensional plane when the thermal radiation control element 100 is viewed from above. In the embodiment shown in FIG. 6A, since the convex portion 10a has the structure S formed by processing the surface of the inorganic material substrate 10, the convex portion 10a and the material of the inorganic material substrate 10 are the same. is there. Further, as in another embodiment shown in FIG. 6B, the convex portion 20 a may be formed of a material different from that of the inorganic material substrate 10. Even in this case, the convex portion 20a includes either quartz or inorganic glass. Hereinafter, the present invention will be specifically described with reference to the embodiment of FIG. 6A, but it is experimentally shown that the effect of the present invention can be obtained even in another embodiment shown in FIG. 6B. Confirmed (see Example 6). Moreover, the manufacturing method of convex part 10a, 20a is mentioned later in embodiment of a manufacturing method.

<Inorganic material substrate>
First, as described above, the inorganic material substrate 10 contains either quartz or inorganic glass. Quartz may be either fused quartz or synthetic quartz made of SiO ₂ and has high transmittance in a wide wavelength range. The inorganic glass is, for example, silica glass, non-alkali glass, borosilicate glass, and the like, and has high transmittance in a wide wavelength range, like quartz.

<Reflective film>
The reflective film 80 is not particularly limited as long as it is a material that can reflect light in the visible range with high sunlight spectrum intensity, and any material can be used, but at least one of Ag or Al is used. Can be included. Either Ag or Al having a high reflectance may be used, and an alloy containing these is preferably used. By using a reflective film of these materials, the solar absorptance can be reduced.

<Shape of convex part>
The shape of the convex portion 10a is not particularly limited as long as the plurality of convex portions 10a are independent from each other and adjacent convex portions 10a are not connected to each other. A rectangular parallelepiped shape shown in FIG. 7A is one specific example. Moreover, all the some convex parts 10a may be the same shape, and different shapes may be contained. In the present specification, geometrical expressions such as “circle”, “square”, “cuboid”, “cone”, “polygonal pyramid”, “regular polygonal pyramid”, “conical” have mathematical meanings. It is not intended to specify the exact shape at this point, and inevitable deformations in industrial production are allowed. For example, the convex portions shown in FIGS. 35A and 35B, which will be described in detail later, have roundness in the vicinity of the apex, and thus differ from a cone in a strict mathematical sense, but this is regarded as a cone. Shall.

  The convex portion 10a may include a tip portion A. Here, the tip portion means a flat surface having a constant height in the height direction of the convex portion. For example, a truncated cone shape can be used as shown in FIG. 7A, or a quadrangular frustum shape can be used as shown in FIG. 7B. Although FIG. 7B is a quadrangular frustum, it is naturally understood that this is an example of a polygonal frustum. Further, in the case of FIGS. 7A and 7B, although the center of the tip portion A of the convex portion 10a and the center of the bottom surface coincide with the two-dimensional projection, in the example shown in FIG. When the center of the tip A of the convex portion 10a and the center of the bottom are two-dimensionally projected, they do not coincide. Such a case is also included in the convex portion 10a. However, higher symmetry is preferred. When the convex portion 10a includes the tip portion A, the tip portion that tends to be structurally brittle can be planarized in advance, it can be easily pressed when affixed to a satellite, and a dielectric multilayer mirror described later can be easily formed. It is valid.

  Moreover, as shown to FIG 7 (D), it is also preferable that the convex part 10a is provided with the vertex A. FIG. The vertex A here means a point where the height of the convex portion 10a is maximized. It is preferable to use a cone as the convex portion 10a having the apex. Such a cone is preferably a cone, a regular polygonal pyramid, or a polygonal pyramid.

  Moreover, although the bottom face shape of the convex part 10a is arbitrary, when industrial productivity is considered, it is preferable that a bottom face shape is circular or a regular polygon.

  By providing the structure S in which the plurality of independent protrusions 10a are two-dimensionally arranged, the emissivity of the thermal radiation control element 100 can be improved as compared with the case where the surface of the inorganic material substrate 10 is a flat surface. It was confirmed by numerical analysis and experiments by the present inventors (details will be described later using vertical emissivity). Although the theoretical background for obtaining such an effect is under investigation, it is considered that the effect of increasing the surface area of the heat radiation surface of the inorganic material substrate 10 is one of the reasons for improving the emissivity.

  Moreover, in any case of the convex portion 10a described above, it is preferable that the area of the cross section cut along the horizontal plane orthogonal to the height direction of the convex portion 10a decreases along the direction from the bottom surface of the convex portion 10a to the apex. . In this case, it is more preferable that the adjacent convex part 10a contacts in a bottom face. This is because the emissivity by the structure S can be improved by reducing the area of the exposed flat surface of the inorganic material substrate 10 as much as possible (that is, by increasing the filling rate).

<Arrangement of convex portions>
The specific arrangement form of the two-dimensional array of the protrusions 10a is arbitrary, and the plurality of protrusions 10a can be arranged in a regular lattice, and as shown in FIG. Is preferred. In addition, an arbitrary arrangement such as an orthorhombic lattice arrangement, a hexagonal lattice arrangement, a rectangular lattice arrangement, and a parallel body lattice arrangement may be used. FIGS. 8A to 8C are schematic diagrams for explaining the convex portions 10a and the arrangement thereof according to the first preferred embodiment of the present invention. The convex portions 10a are cones (the bottom surface is circular), and the convex portions 10a. Is a hexagonal close-packed array. The “hexagonal close-packed arrangement” referred to here means an arrangement in which six circles of the same size are in contact with a predetermined circle. When six circles of the same size are surrounded and arranged with respect to a predetermined circle, it is called a hexagonal arrangement. FIGS. 9A and 9B are schematic diagrams for explaining the convex portions and their arrangements according to the second preferred embodiment of the present invention. Is FIG. 8 a hexagonal close-packed arrangement or a square lattice arrangement? Is different.

  When the bottom surface shape of the convex portion 10a is circular, the first preferred embodiment (see FIG. 8) is more preferable in terms of emissivity improvement than the second preferred embodiment (FIG. 9). This is because the area of the exposed flat surface E of the inorganic material substrate 10 can be reduced. Moreover, although the arrangement | sequence of the convex part 10a is as above-mentioned, the arrangement | sequence which can reduce the area of the exposed flat surface E of the inorganic material board | substrate 10 is more preferable. That is, when the bottom surface shape of the convex portion 10a is circular, a hexagonal arrangement is preferable, and a hexagonal close-packed arrangement is most preferable. Also, as shown in FIG. 10A, a square lattice arrangement is preferred when the convex shape of the convex portion 10a is square, and as shown in FIG. 10B, the convex shape of the convex portion 10a is a regular hexagon. Is most preferably a hexagonal close-packed arrangement. In FIG. 10A, the convex portion 10a is a regular quadrangular pyramid, and in FIG. 10B, the convex portion 10a is a regular hexagonal pyramid.

<Deformation aspect of convex part>
Here, in the present embodiment, the shape of the convex portion 10a is not limited to the above-described cone or frustum shape, and as shown in FIG. 11A, in the cross-sectional view including the central axis, adjacent convex portions 10a. In the cross-sectional view including the central axis, as shown in FIG. 11B, the ridge line between adjacent convex portions 10a is curved, and the ridge line is It is also preferable to have a bending point. In the case where the width and height of the convex portions are approximately 15 μm or less, it is preferable to form the convex portions by etching described with reference to FIG. 14 described later in consideration of productivity. In this case, the ridge lines between the cones are cut off. This is because the shape between the apexes becomes a semicircular shape as schematically shown in FIG. Further, for example, if a process described later in FIG. 14 (that is, cleaning, film formation, patterning, and etching) is repeated twice, bent points can be formed on the ridgeline as shown in FIG. If this process is repeated multiple times, it is also possible to form the folds of the ridgeline in multiple stages. In either case, the same emissivity improving effect as that when the convex portion 10a is a cone is obtained.

<Relationship between convex size and adjacent convex portion>
Hereinafter, a preferable size and distance relationship between adjacent convex portions 10a will be described using a case where the convex portion 10a is a cone. Here, as shown in FIG. 8, the interval between adjacent convex portions 10a, in particular, the interval between the vertices is expressed as P, the width of the convex portion 10a is expressed as W, and the height of the convex portion 10a is expressed as H. write. In addition, what is necessary is just to define the distance between the centers of an upper surface as P, when the convex part 10a has the front-end | tip part A. FIG. In addition, regarding the width W of the convex portion 10a, the diameter is W when the bottom surface shape of the convex portion 10a is circular, and the bottom surface shape of the convex portion 10a is not circular, such as a polygon. Let W be the diameter of the largest diameter. 11A and 11B, the interval P, the width W, and the height H can be defined in the same manner in the above-described modification of the convex portion 10a. Details of the technical significance of each parameter will be described later in the first embodiment.

  Here, the ratio of the height H of the convex portion 10a to the width W of the convex portion 10a (hereinafter referred to as “aspect ratio”) H / W is preferably 0.25 or more, more preferably 0.5 or more. preferable. By doing so, the emissivity can be improved more reliably. In addition, the aspect ratio of the convex part 10a produced by embodiment of the manufacturing method using wet etching mentioned later is generally about 0.5. In addition, there is almost no influence on the sunlight absorption rate by the aspect ratio.

  The interval P is arbitrary and can be set to, for example, 1 μm or more and 500 μm or less, and the emissivity can be improved. The interval P is preferably 9 μm or more, and more preferably 15 μm or more. By setting the interval P to 15 μm or more, in addition to the emissivity improvement effect, it is also possible to obtain a solar absorption rate reduction effect.

  Further, the ratio W / P of the bottom surface width W to the interval P is preferably 0.7 or more, more preferably 0.8 or more, and particularly preferably W / P is 0.9. The ratio W / P corresponds to the filling ratio of the convex portions, and by setting W / P to 0.7 or more, the emissivity can be reliably improved. The larger the ratio W / P value, the more the inorganic material The area of the exposed flat surface E of the substrate 10 can be reduced, and as a result, the emissivity can be further improved.

  Note that the width W and the height H are arbitrary, and can be, for example, 1 μm or more and 500 μm or less. However, in this range, the above-described H / W is preferably set to 0.25 or more. / P is preferably 0.7 or more. A more preferable range is as described above.

<Other configurations>
In addition, as shown in FIG. 12, the thermal radiation element 100 according to the embodiment of the present invention may further include a protective film 90, an increased reflection film 70, a dielectric multilayer mirror 30, and a transparent conductive film 50. Good. Hereinafter, each configuration will be described in order.

<< Protective film >>
The thermal radiation control element 100 preferably further includes a protective film 90 on the surface of the reflective film 80 opposite to the inorganic material substrate 10. When Ag and Al are exposed to the atmosphere, they gradually change in quality due to oxidation, moisture absorption, etc., and the reflectance decreases. Therefore, by providing the protective film 90, it is possible to improve oxidation prevention and moisture resistance, and to suppress a decrease in the reflectance of the thermal radiation control element 100. Any material can be used for the protective film 90 as long as the alteration of the reflective film 80 can be prevented, and any of Cr, Ni, Cr alloy, Ni alloy, SiO ₂ and Al ₂ O ₃ is preferable. For example, Cr, Ni, an alloy containing these, materials such as SiO ₂ , Al ₂ O ₃ can be used as the protective film, and the thickness is preferably 10 nm or more.

  The protective film 90 can be formed using a known method such as a sputtering method, a vapor deposition method, a CVD method, or a sol-gel method. Moreover, since Ag and Al are mechanically soft and easily scratched and cause scattering, it is preferable to form the protective film 90 from this viewpoint.

<< Increased reflection film >>
The thermal radiation control element 100 preferably further includes an increased reflection film 70 between the inorganic material substrate 10 and the reflection film 80, and the increased reflection film 70 preferably includes two or more dielectric layers. This is to supplement the reflection by the reflection film 80 and further improve the reflectance of the thermal radiation control element 100. Such an increased reflection film can be formed by laminating two or more layers of a high refractive index dielectric and a low refractive index dielectric, and the reflectance can be improved as compared with the case of the reflective film 80 alone. it can. As the material of the dielectric is not particularly limited, typical ones can be _{used, SiO 2, Ta 2 O 5} , TiO 2, Al 2 O 3, Nb 2 O 5, LaO, MgF 2, HfO ₂ or the like can be used in combination.

<< Dielectric multilayer mirror >>
In the thermal radiation control element 100, it is more preferable that the convex portion 10a and the exposed flat surface E of the inorganic material substrate 10 are covered with a dielectric multilayer mirror 30 that reflects light having a wavelength of near infrared light or less. As shown in FIG. 5 described above, it is difficult to completely reflect the ultraviolet to visible light having a high sunlight spectrum intensity only on the surface with the inorganic material substrate 10 and the reflective film 80 alone. Therefore, the dielectric multilayer mirror 30 is covered with the convex portion 10a and the exposed flat surface E of the inorganic material substrate 10 to reflect the light in the wavelength region before entering the inorganic material substrate 10 to absorb sunlight. The rate can be further reduced.

Such a dielectric multilayer mirror 30 has a high refractive index dielectric (H film) and a low refractive index dielectric (L film) alternately with a thickness of λ / 4 with respect to a desired central wavelength λ. What is necessary is just to laminate. Since the intensity of the sunlight spectrum is the strongest in the wavelength range of about 400 to 600 nm, it is sufficient to form a multilayer film in which about 5 layers of H films and L films are alternately stacked with respect to the center wavelength of 500 nm. Effects can be obtained. Preferably, it is desirable to reflect not only the visible range but also the light of “ultraviolet to visible to near-infrared range”, in which case the dielectric corresponding to each band (ultraviolet / blue / green / red / near infrared) A wider reflection band can be obtained by designing and superposing body mirrors. In this case, as a film configuration, the thickness of each layer is set so that the inorganic material substrate 10 side where the convex portion 10a is provided reflects the long wavelength region and reflects the shorter wavelength region toward the outermost surface. Is preferably designed. However, the order is not limited at all. The dielectric multilayer mirror 30 can have a multilayer structure of about 10 to 200 layers. Moreover, as a dielectric material of each layer, SiO ₂ , Ta ₂ O ₅ , TiO ₂ , Al ₂ O ₃ , Nb ₂ O ₅ , LaO, MgF ₂ , HfO ₂ or the like can be used, and these are appropriately combined. Just do it.

  The dielectric multilayer mirror 30 and the increased reflection film 70 can be formed using a known method such as sputtering, vapor deposition, CVD, or sol-gel method. In consideration of the connection to the convex portion 10a, it is more preferable to apply the oblique vapor deposition method or the oblique sputtering method in forming the dielectric multilayer mirror 30. As shown in FIG. 12, since the dielectric multilayer mirror 30 is affected by the shape of the convex portion 10a, each layer of the dielectric multilayer mirror 30 also has an uneven shape.

<< Transparent conductive film >>
Furthermore, in the thermal radiation control element 100, it is preferable that the outermost surface on the side where the convex portion 10a is provided is covered with the transparent conductive film 50. That is, when the dielectric multilayer mirror 30 is not provided in the heat-control radiating element 100, it is preferable that the transparent conductive film 50 directly covers the convex portions 10a and the exposed flat surface E of the inorganic material substrate 10. Further, when the dielectric multilayer mirror 30 is provided in the thermal control radiation element 100, it is preferable that the transparent conductive film 50 covers the dielectric multilayer mirror 30.

By forming the transparent conductive film 50, damage to equipment due to charging in outer space can be reduced. The transparent conductive film 50 is not particularly limited as long as this antistatic effect can be obtained. For example, ITO, ZnO, metal nanowire, metal mesh, CNT, or the like can be used. Examples of the resistance value of the transparent conductive film 50 that can prevent charging include 10 ¹² Ω / □ or less. As a forming method, a film can be formed using a known method such as a sputtering method, a vapor deposition method, a CVD method, or a sol-gel method.

(Reference form)
Here, as shown in FIG. 13, the thermal radiation control element 300 according to the reference embodiment of the present invention includes an inorganic material substrate 10, a reflective film 80 provided on one surface side of the inorganic material substrate 10, and an inorganic material. And a dielectric multilayer mirror 30 provided on the other surface side of the substrate 10. In the thermal radiation control element 300, the inorganic material substrate 10 and the dielectric multilayer mirror 30 are both flat surfaces. In the reference embodiment, similarly to the embodiment of the present invention, the protective film 90, the reflective reflection film 70, and the transparent conductive film 50 may be arbitrarily provided, and redundant description is omitted.

(Method for manufacturing thermal radiation control element)
Next, the method for manufacturing a thermal radiation control element according to the present invention has a structure in which a plurality of independent protrusions 10a (20a) are two-dimensionally arranged on the surface of an inorganic material substrate 10 containing either quartz or inorganic glass. It includes at least a structure forming step for forming S and a reflecting film forming step for forming a reflecting film 80 on the surface of the inorganic material substrate 10 opposite to the surface on which the structure S is formed.

  The reflective film forming step may be performed prior to the structure forming step, but it is preferable to perform the reflective film forming step after the structure forming step because mask formation on the reflective film can be omitted in an etching process described later.

<Protrusion formation including etching>
The structure forming step preferably includes an etching step. This embodiment will be described in more detail with reference to FIG.

First, the inorganic material substrate 10 is cleaned, and a metal mask M is formed by sputtering or vapor deposition (FIG. 14A). The metal mask M may have a two-layer structure such as Cr, CrN, Cr ₂ O ₃ and Cr / Au obtained by laminating these materials and Au, or a Si-based material such as SiN or amorphous Si.

  Next, a desired resist mask pattern R is formed on the metal mask M by a photolithography process (FIG. 14B). Next, using the resist mask pattern R as a mask, the metal mask M is etched by a wet etching process using a Cr etching solution to form a pattern of the metal mask M (FIG. 14C). Etching of the metal mask M may be performed by dry etching. Further, the resist mask pattern R may be either removed or not (removed in the drawing).

  Then, using the pattern of the metal mask M as a mask, a structure S composed of desired convex portions 10a is formed on the surface of the inorganic material substrate 10 by wet etching using HF, BHF liquid, or the like (FIG. 14D). . After the convex portion 10a is formed on the surface of the inorganic material substrate 10, the metal mask (Cr) is removed with an etching solution or the like, and the inorganic material substrate 10 is washed (FIG. 14E). Finally, a reflective film 80 made of Ag or the like is formed on the back surface of the inorganic material substrate 10 by sputtering or vapor deposition (FIG. 14F).

  In addition to the above-described method of forming a pattern on the metal mask M by etching, the convex portion 10a can be formed by various methods. For example, a method of forming a mask for forming the convex portion 10a by a printing method such as a photolithography process and screen printing, a transfer method, an ink jet method, or the like can be used. Also, the etching to the metal mask M may be either wet etching or dry etching.

<Projection formation including machining>
Furthermore, in the structure forming step, the structure S may be formed by machining or laser processing the inorganic material substrate 10. Further, the structure forming step may include a step of forming a mold by machining or laser processing, and a forming step of forming a structure S by molding a sol-gel using the mold. Furthermore, the structure forming step may include a step of forming a mold by machining or laser processing, and a transfer step of forming the structure S on the surface of the inorganic material substrate 10 by transferring the shape of the mold.

  When the structure S according to the present invention is used, the reflectance of the inorganic material substrate 10 is not limited even if it is a concavo-convex structure with a period larger than 9 μm and 21 μm, which are wavelengths for reducing the reflectance (that is, a wavelength for improving the emissivity) Therefore, it is also possible to apply machining, grinding, molding using a mold, transfer such as a heat press, or a technique using a laser. However, when applying these mechanical processes, it is preferable to set the interval P to 15 μm or more with respect to the size of the convex part 10a (the convex part 20a) in consideration of the processing accuracy. When the structure S is formed by sol-gel molding, even if the same material is used for the inorganic material substrate 10 and the convex portion 20a, some differences in purity can occur. However, even in this case, the same effect as that obtained when the convex portion 10a is formed by the above-described etching can be obtained.

<Heat treatment process>
Here, in the embodiment of the manufacturing method of the present invention, it is preferable to further include a heat treatment step of performing a heat treatment below the glass softening point under vacuum or atmospheric pressure after the structure forming step. By performing the heat treatment step, the convex portion 10a can be smoothed. This embodiment will be described in more detail with reference to FIG.

First, the inorganic material substrate 10 is cleaned, and a metal mask M is formed by sputtering or vapor deposition (FIG. 15A). The metal mask M may have a two-layer structure such as Cr, CrN, Cr ₂ O ₃ and Cr / Au obtained by laminating these materials and Au, or a Si-based material such as SiN or amorphous Si.

  Next, a desired resist mask pattern R is formed on the metal mask M by a photolithography process (FIG. 15B). Next, using the resist mask pattern R as a mask, the metal mask M is etched by a wet etching process using a Cr etching solution to form a pattern of the metal mask M (FIG. 15C). Etching of the metal mask M may be performed by dry etching. Further, the resist mask pattern R may be either removed or not (removed in the drawing).

  Then, using the pattern of the metal mask M as a mask, a structure S composed of desired convex portions 10a is formed on the surface of the inorganic material substrate 10 by wet etching using HF, BHF liquid, or the like (FIG. 15D). . After the convex portion 10a is formed on the surface of the inorganic material substrate 10, the metal mask (Cr) is removed with an etching solution or the like, and the inorganic material substrate 10 is washed (FIG. 15E).

  In order to remove impurities that may adhere to the surface of the inorganic material substrate 10 on which the convex portions 10a are formed by the wet etching process, heat treatment (annealing treatment) is performed after acid cleaning. The heat treatment temperature is preferably a heat treatment below the glass softening point of the inorganic material substrate 10 and is preferably 1200 ° C. to 1275 ° C. or less. The heat treatment time is preferably 5 hours or less. It should be noted that this process is advantageous in that the heat treatment is performed so that the tip of the convex portion has a gentle R shape, so that the surroundings of the dielectric multilayer mirror 30 are improved.

  Finally, a reflective film 80 made of Ag or the like is formed on the back surface of the inorganic material substrate 10 by sputtering or vapor deposition (FIG. 15F).

<Other processes>
Moreover, in the embodiment of the manufacturing method of the present invention, it is preferable to further include a dielectric multilayer mirror forming step of forming the dielectric multilayer mirror 30 on the surface of the structure S. The dielectric multilayer mirror 30 is as described above in the embodiment of the thermal radiation control element, and redundant description is omitted. The same applies to the following dielectric multilayer mirror 30 and protective film 90.

  In the embodiment of the manufacturing method of the present invention, it is preferable to further include a transparent conductive film forming step of forming the transparent conductive film 50 on the surface of the structure S. Furthermore, in the embodiment of the manufacturing method of the present invention, it is preferable to further include a protective film forming step of forming a protective film 90 on the surface of the reflective film 80 opposite to the inorganic material substrate 10. In the embodiment of the manufacturing method of the present invention, it is also preferable to form the enhanced reflection film 70 between the inorganic material substrate 10 and the reflection film 80.

Further, in the embodiment of the manufacturing method of the present invention, after the structure forming step, the dielectric multilayer film mirror forming step and the transparent conductive film forming step are sequentially included, and the enhanced reflective film forming step, the reflective film forming step, The protective film forming step is preferably included sequentially.

  As described above, the thermal radiation control element according to the present invention can provide a thermal radiation control element having thermal radiation characteristics superior to those of the conventional thermal radiation control element and a method for manufacturing the thermal radiation control element.

  Further, although the embodiments of the present invention have been described so far, the present invention is not limited thereto, and various modifications can be made based on the technical idea of the present invention. For example, the specific numerical values given in the embodiment and the following examples are merely examples, and it is needless to say that numerical values different from these may be used as necessary.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to a following example at all.

Example 1
<Interval P>
First, as shown in FIG. 8, in order to confirm the emissivity improvement effect by the structure S when a quartz substrate is used as the inorganic material substrate 10 and the convex portion 10a is a cone and the hexagonal close-packed arrangement is used, the RCWA method is used. Spectral emissivity was analyzed and the emission spectrum was shown in FIG. In both cases, the interval P and the width W were matched, and the aspect ratio H / W was fixed to 0.5.
In FIG. 16A, P is 3 μm, W is 3 μm, and H is 1.5 μm.
In FIG. 16B, P is 9 μm, W is 9 μm, and H is 4.5 μm.
In FIG. 16C, P is 21 μm, W is 21 μm, and H is 10.5 μm.
In FIG. 16D, P is 84 μm, W is 84 μm, and H is 42 μm.
When the convex portion 10a is not formed (that is, a quartz substrate having a flat surface), the radiation spectrum already described in FIG. 4 is obtained, and the spectral emissivity is greatly reduced in the vicinity of wavelengths of 9 μm and 21 μm.

When a conical structure is formed on the surface of the quartz substrate, it can be confirmed that the spectral emissivity is improved from the plane at wavelengths of 9 μm and 21 μm in any structural dimension. When P is 1 μm, 3 μm, 5 μm, 6 μm, 7 μm, 9 μm, 21 μm, 27 μm, 36 μm, 42 μm, 84 μm, 168 μm, 336 μm, the radiation spectrum is obtained from the result of calculating the radiation spectrum of each structure by the RCWA method. It was. From each radiation spectrum, the vertical emissivity (ε) at 300 K was calculated by the following equation (2). A graph of vertical emissivity versus P is shown in FIG. In either case, the relationship of P = W and H / W = 0.5 is fixed.
Here, I (λ) is the spectral radiation intensity at the wavelength λ, and ε (λ) is the spectral radiation intensity at the wavelength λ of the thermal radiation control element.

  As shown in FIG. 17, the vertical emissivity (ε) is obtained by setting the interval P of the conical structure and the diameter W of the bottom surface of the conical structure (where P = W; W / P = 1.0) to 1 μm or more. This is confirmed to be improved as compared with the conventional planar structure. It was also confirmed that when P is 5 μm or more, the vertical emissivity (ε) is 0.90 or more, and when P is 7 μm or more, the vertical emissivity (ε) is improved to 0.94 or more. When P is 36 μm or more, the structure period is larger than the wavelengths near 9 μm and 21 μm where the spectral emissivity, which is a characteristic unique to quartz material, is observed. At this time, the vertical emissivity (ε) is remarkable. The improvement can be confirmed.

<Filling rate W / P>
Next, the spectral emissivity accompanying the packing density (arrangement density) of the conical convex structure was analyzed by the RCWA method to obtain a radiation spectrum. Furthermore, the vertical emissivity (ε) was calculated using equation (1). In both cases, P is fixed to 84 μm and the aspect ratio H / W is fixed to 0.5. The results are shown in FIG. In either case, the convex portions have a conical shape and are arranged in a hexagonal close-packed arrangement or a hexagonal arrangement.
In FIG. 18A, P is 84 μm, W / P = 1.0, and H / W = 0.5.
In FIG. 18B, P is 84 μm, W / P = 0.9, and H / W = 0.5.
In FIG. 18C, P is 84 μm, W / P = 0.8, and H / W = 0.5.
In FIG. 18D, P is 84 μm, W / P = 0.7, and H / W = 0.5.

  From FIG. 18, the area of the exposed flat surface E increases as W / P decreases, so it can be confirmed that the spectral emissivity tends to decrease at wavelengths near 9 μm and 21 μm. FIG. 19 shows the reflection intensity distribution for a wavelength of 9 μm.

FIG. 19A shows a reflection intensity distribution corresponding to FIG. 18A. The reflectivity for a wavelength of 9 μm is 0.09 and the absorptance is 0.91.
On the other hand, FIG. 19B shows a reflection intensity distribution corresponding to FIG. 18D (that is, P = 84, W = 59, H = 29.5, W / P = 0.7), and has a wavelength of 9 μm. The reflectance is 0.41 and the absorptance is 0.59. Even if FIG. 19A is compared with FIG. 19B, the reflectance increases due to the increase in the number of flat portions (exposed flat surfaces) between the convex portions, and thus the absorptance tends to decrease. In FIGS. 19A and 19B, the circles in the drawing indicate the vicinity of the conical convex portion. Further, when the tip of the convex portion is flat, the reflectance increases for the same reason, and thus the absorption rate tends to decrease.

  Further, from the radiation spectra shown in FIGS. 18A to 18D, the vertical emissivity (ε) at 300 K was calculated by the equation (1) and shown in the graph of FIG. The vertical emissivity of the planar structure of the prior art is also shown by a broken line. It was confirmed that when a conical convex portion is formed on the quartz surface, the vertical emissivity can be improved compared to the planar structure regardless of W / P.

<Aspect ratio H / W>
Next, the spectral emissivity when the aspect ratio H / W was changed was analyzed. In either case, the convex portions have a conical shape and are arranged in a hexagonal close-packed manner. When the interval P between the apexes of the conical convex portion 10a and the diameter W of the conical bottom surface are the same (P = W), and the height of the convex portion 10a (cone) is H, the aspect ratio is H / W. When the aspect ratio was 0.25, 0.5, 1.0, and 1.5, the interval P between the conical structures was analyzed as 3 μm, 9 μm, 21 μm, and 84 μm, respectively. FIG. 21 shows the vertical emissivity (ε) when the aspect ratio of the cone is changed. The vertical emissivity (ε) of the planar structure according to the prior art is also shown.

  The vertical emissivity (ε) of the planar structure is 0.84, whereas when the conical convex structure is formed, the vertical emissivity (ε) is improved over the planar structure. I understand. In particular, when the interval P between the conical structures is 9 μm or more, it was confirmed that the vertical emissivity (ε) can be improved to 0.95 or more by setting the aspect ratio to 0.5 or more. Further, from the result of FIG. 21, it was confirmed that the larger the aspect ratio, the more preferable, regardless of the size of the interval P.

  From the results of Example 1 above, it was confirmed that the vertical emissivity can be improved by forming the convex portion 10a according to the present invention as compared with the conventional planar structure.

(Example 2)
<Interval P>
Based on the absorption spectrum of the band in the ultraviolet region (wavelength 0.3 μm) to the near infrared region (wavelength 2.5 μm) calculated by the RCWA method in FIG. ) Was calculated and plotted. In either case, the convex portions have a conical shape and are arranged in a hexagonal close-packed manner. Further, regarding the convex portion, P was analyzed under nine conditions of 3 μm, 6 μm, 9 μm, 12 μm, 15 μm, 18 μm, 21 μm, 36 μm, and 84 μm under the conditions of P = W and H / W = 0.5. Yes.
Here, I _solar (λ) is the spectral radiant intensity of sunlight at the wavelength λ, and α _s (λ) is the spectral absorptance of sunlight at the wavelength λ of the thermal radiation control element.

  As shown in FIG. 22, it was found that when the interval P between the convex portions is increased (15 μm or more), the solar absorption rate (α) equivalent to that of the planar structure can be obtained. In addition, when the space | interval P is small (3-12 micrometers), although it was confirmed that sunlight absorption rate ((alpha)) will become a little higher than a planar structure, in this case, it is also less than 0.10, and comparison It can be said that the solar absorption rate (α) is small.

<Aspect ratio H / W>
FIG. 23 shows the sunlight absorption rate (α) when the aspect ratio H / W is changed. In either case, the convex portions have a conical shape and are arranged in a hexagonal close-packed manner. Further, regarding the convex portion, P = W. In the analysis, in each of cases where the aspect ratio H / W was 0.25, 0.5, 1.0, and 1.5, the intervals P between the vertices of the convex portions were set to 3 μm, 9 μm, 21 μm, and 84 μm. It was found that when the distance P was 3 μm and 9 μm, the solar light absorption rate (α) was slightly higher than the planar structure regardless of the aspect ratio. However, it has been found that by increasing the interval P between the cone structures to 21 μm and 84 μm, the same characteristics as the planar structure can be obtained regardless of the aspect ratio.

  From these results, in the thermal radiation control element 100 according to the present invention, when the convex portion has a conical shape, in particular, when the interval P and the diameter W of the bottom surface of the convex portion are the same (P = W) on the quartz substrate surface. , P is 15 μm or more, and the height ratio H / W of the convex structure is 0.25 or more, so that the solar absorptance (α) is kept equal to the conventional planar structure, It was confirmed that the vertical emissivity (ε) can be improved as compared with the conventional planar structure. That is, it was confirmed that the thermal radiation control element having both the emissivity and the reflectance superior to the thermal radiation control element having the conventional planar structure can be reliably provided.

(Example 3)
<Arrangement of convex portions>
In order to confirm the influence of the emissivity due to the difference between the above described hexagonal close-packed arrangement and the square lattice arrangement using FIGS. 8A and 9A, the spectral emissivity is analyzed by the RCWA method, A spectrum was obtained. FIG. 24A shows a radiation spectrum by the hexagonal close-packed arrangement shown in FIG. 8, and FIG. 24B shows a radiation spectrum by the square lattice arrangement shown in FIG. In all cases, the convex portion was conical, P was 84 μm, W was 84 μm, and H was 42 μm. Further, from the radiation spectrum, the vertical emissivity (ε) at 300 K in each thermal radiation control element is calculated by the above equation (1) and shown in the graph.

  From FIG. 24, it was confirmed that in both the hexagonal close-packed array and the tetragonal lattice array, the spectral emissivity in the vicinity of wavelengths of 9 μm and 21 μm was improved as compared with the planar structure. Furthermore, it was found that the vertical emissivity (ε) was also improved. Therefore, the arrangement structure of the convex portions may be either a hexagonal close-packed arrangement or a tetragonal lattice arrangement, and it can be said that the hexagonal close-packed arrangement is more preferable. It was also confirmed that any arrangement can be applied from the viewpoint of improving the vertical emissivity (ε) as compared with the prior art.

<Shape of convex part>
Furthermore, the spectral emissivity between the case where the cones shown in FIG. 9A are arranged in a square lattice and the case where the square pyramids shown in FIG. The emission spectrum was obtained. The results are shown in FIGS. 25 (A) and 25 (B), respectively. From the radiation spectrum, the vertical emissivity (ε) at 300 K in each thermal radiation control element is calculated from the above equation (1) and shown in the graph. In both the cone and the regular pyramid, P was 84 μm, W (the diameter of the inscribed circle was used as described above for the regular pyramid) was 84 μm, and H was 42 μm.

  From FIG. 25, it was confirmed that the spectral emissivity in the vicinity of wavelengths of 9 μm and 21 μm was improved as compared with the case of the planar structure in both the conical square lattice arrangement and the tetragonal pyramid square lattice arrangement. . Furthermore, it was found that the vertical emissivity (ε) was also improved.

Next, the spectral emissivity in the case of the convex shape shown in FIGS. 11A and 11B was calculated by the RCWA method to obtain a radiation spectrum. This radiation spectrum is shown in FIG. From the radiation spectrum, the vertical emissivity (ε) at 300 K was calculated from the above equation (1). Here, in FIG. 26A, as shown in FIG. 11A, the ridge line between the adjacent convex portions is semicircular in the cross-sectional view (therefore, the concave portion between the adjacent convex portions is hemispherical. ), P is 84 μm, W is 84 μm, and H is 42 μm. FIG. 26B shows an analysis of a convex portion in which a semicircular shape is formed in two steps in the cross-sectional view as shown in FIG. 11B and the ridgeline between the convex portions includes a bending point. P is 80 μm, W ₁ is 76 μm, W ₂ is 60 μm, H is 38 μm, and h is 30 μm. In any case, the convex portions are arranged in a hexagonal close-packed manner.

  In any case, it was confirmed that the spectral emissivity at wavelengths near 9 μm and 21 μm was improved as compared with the planar structure as compared with the planar structure. Furthermore, it was found that the vertical emissivity (ε) was improved to 0.93 or more. From these results, it was confirmed that the convex portion does not have to be a cone shape, and the cross-sectional area in the height direction of the convex portion only needs to be reduced along the direction from the bottom surface to the apex. Therefore, the cone structure of the convex portion may be either a cone or a quadrangular pyramid, and even if a polygonal pyramid such as a hexagonal pyramid is used, the emissivity improvement effect can be obtained, and the shape of the convex portion is limited to the cone. It was also confirmed that it was not done.

Example 4
<Reference Example 1>
The configuration of the HL dielectric multilayer mirror using Nb ₂ O ₅ as the high refractive index dielectric (H film) and SiO ₂ as the low refractive index dielectric (L film) is as shown in Table 1 below. The influence on the solar light absorption rate (α) by the multilayer mirror was analyzed using an optical simulation TFCalc. In this HL dielectric multilayer mirror, λ / 4 alternating multilayer films are formed by repeating five sets of H films and L films with respect to the center wavelength of each band, and they are superposed to form a total of 62 layers and a total thickness of 5098. Reflects light in the wavelength range of 350 to 900 nm with a 7 nm configuration. Then, the characteristics (reflectance and absorptance) at 0 degree incidence are analyzed using a configuration in which the HL dielectric multilayer mirror is disposed on the flat surface of the quartz substrate and an Ag reflection film is provided on the back surface of the quartz substrate. did. Here, the thickness of the Ag reflection film is 150 nm, and the thickness of the quartz substrate is 200 μm. In the table, the number of layers means the number of layers counted from the substrate.

  FIG. 27A shows the reflection spectrum when only the dielectric multilayer mirror of Reference Example 1 is formed on the surface of the quartz substrate (that is, there is no Ag reflection film on the back surface). FIG. 27B shows a reflection spectrum when an Ag reflection film is provided on the back surface of the quartz substrate in addition to the dielectric multilayer mirror. Further, FIG. 27C shows an absorption spectrum when a dielectric multilayer mirror and a reflective film Ag are provided on a quartz substrate. Further, the solar light absorption rate (α) according to Reference Example 1 is 0.04, and the solar light absorption rate (α) by the configuration in which the Ag reflection film is formed on the back surface of the quartz substrate having a planar structure according to the conventional technique is 0. 07.

  As shown in FIG. 27A, light with a wavelength region of 350 to 900 nm can be efficiently reflected on the surface of the dielectric multilayer film mirror formed on the surface of the quartz substrate. In addition, as shown in FIG. 27B, by forming a reflective film Ag on the back surface of the quartz substrate on which the dielectric multilayer mirror is formed, light in the near infrared region as well as the wavelength region of 350 to 900 nm can be obtained. The reflective film Ag on the back surface can be efficiently reflected. In the configuration of the prior art, since the reflectance characteristics depend on the Ag reflection film, the absorptance increases rapidly at a wavelength of 500 nm or less, but the sunlight spectrum has high intensity even at short wavelengths of 500 nm or less and in the ultraviolet region. It becomes a factor that the light absorption rate becomes high. On the other hand, since the reference example 1 can efficiently reflect light in the wavelength region of 350 to 900 nm where the intensity of the sunlight spectrum is high, the absorptance can be reduced. As a result, since the solar absorptance (α) can be reduced as compared with the configuration of the prior art, an absorption characteristic superior to the conventional thermal radiation control element can be obtained.

<Reference Example 2>
The thicknesses of the H film and the L film in Reference Example 1 were optimized using simulation software (TFCalc), and Reference Example 2 was obtained. The total of 64 layers and the total thickness was 5069.5 nm.

  FIG. 28A shows a reflection spectrum when only the dielectric multilayer film mirror of Reference Example 2 is formed on the surface of the quartz substrate (that is, there is no Ag reflection film on the back surface). FIG. 28B shows a reflection spectrum when an Ag reflection film is provided on the back surface of the quartz substrate in addition to the dielectric multilayer mirror. Further, FIG. 28C shows an absorption spectrum when a dielectric multilayer mirror and a reflective film Ag are provided on a quartz substrate. Further, the solar absorptance (α) according to Reference Example 2 is 0.03, and the solar absorptance (α) according to the configuration in which an Ag reflection film is formed on the back surface of a quartz substrate having a planar structure according to the prior art is 0. A significant improvement was seen compared to 07. In Reference Example 2, since the absorption characteristics were improved and ripples were reduced by optimization, the solar absorption rate was further reduced from the solar absorption rate (α) 0.04 of Reference Example 1. I was able to.

<Reference Example 3>
In place of the high refractive index dielectric (H film) made of Nb ₂ O ₅ in Reference Example 1, TiO ₂ was used as the H film, a total of 86 layers, and the total thickness was 3158.0 nm, and the dielectric in Reference Example 3 A multilayer mirror was obtained. This dielectric multilayer mirror reflects light having a wavelength range of 350 to 1800 nm.

  FIG. 29A shows the reflection spectrum when only the dielectric multilayer mirror of Reference Example 3 is formed on the surface of the quartz substrate (that is, there is no Ag reflection film on the back surface). FIG. 29B shows a reflection spectrum when an Ag reflection film is provided on the back surface of the quartz substrate in addition to the dielectric multilayer mirror. Further, FIG. 29C shows an absorption spectrum when a dielectric multilayer mirror and a reflective film Ag are provided on a quartz substrate. The solar absorptance (α) according to Reference Example 3 is 0.02, and the solar absorptivity (α) according to the configuration in which the Ag reflection film is formed on the back surface of the quartz substrate having a planar structure according to the conventional technique is 0.07. A significant improvement was seen.

<Reference Example 4>
As in Reference Example 1, the first to 60th layers use Nb ₂ O ₅ as the high refractive index dielectric (H film) and SiO ₂ as the low refractive index dielectric (L film). From the first layer to the 80th layer, HfO ₂ is used as the high refractive index dielectric (H film), and SiO ₂ is used as the low refractive index dielectric (L film), for a total of 80 layers and a total thickness of 5496.0 nm. 4 was used. This dielectric multilayer mirror reflects light having a wavelength range of 300 to 900 nm.

  FIG. 30A shows the reflection spectrum when only the dielectric multilayer film mirror of Reference Example 4 is formed on the surface of the quartz substrate (that is, there is no Ag reflection film on the back surface). FIG. 30B shows a reflection spectrum when an Ag reflection film is provided on the back surface of the quartz substrate in addition to the dielectric multilayer mirror. Further, FIG. 30C shows an absorption spectrum when a dielectric multilayer mirror and a reflective film Ag are provided on a quartz substrate. The solar absorptance (α) according to Reference Example 4 is 0.01, and the solar absorptance due to the configuration in which an Ag reflection film is formed on the back surface of a quartz substrate having a planar structure according to the prior art is 0.07. There was a significant improvement compared to.

<Evaluation of incident angle>
Table 2 below shows the solar absorptance (α) characteristics in the wavelength range of 300 to 2500 nm with respect to the incident angle in the conventional configuration, Reference Example 3, and Reference Example 4. The incident angles were analyzed at 0 °, 15 °, 30 °, 45 °, 60 °, 75 °, and 89 °. Moreover, the average value of the sunlight absorptivity ((alpha)) with respect to these incident angles was also shown collectively.

  In the conventional configuration, the sunlight absorption rate (α) for each incident angle is 0.03 to 0.07, and the average value is 0.07. On the other hand, in the reference example 3, the sunlight absorption rate ((alpha)) with respect to each incident angle is 0.01-0.02, and an average value is 0.02. In Reference Example 4, the solar light absorption rate (α) with respect to each incident angle is 0.01 to 0.03, and the average value is 0.02.

  As a result, the solar absorptance (α) can be reduced by forming the dielectric multilayer mirror regardless of the incident angle of sunlight. And it can be said that the average value of sunlight absorption rate ((alpha)) and the sunlight absorption rate ((alpha)) in each angle are fundamentally comparable. Therefore, even when the dielectric multilayer film mirror is formed on the surface of the inorganic material substrate on which the convex portions are two-dimensionally arranged, it is recognized that there is a sufficient effect of reducing the solar absorptance (α). Note that even if a dielectric multilayer mirror is formed on the surface of an inorganic material substrate provided with protrusions, it does not affect the reflectivity in the infrared region, so it does not affect the vertical emissivity (ε). Was also confirmed.

(Example 5)
<Invention Example 1-1>
According to the flowchart of FIG. 14, a thermal radiation control element in which the convex portions 10a shown in FIG. First, the surface of a synthetic quartz substrate (thickness 0.6 mm) was cleaned. The cleaning conditions were acid cleaning, and low concentration HF cleaning with a concentration of 0.5 wt% was performed for 60 seconds. Next, a metal mask M made of Cr was formed by sputtering. Next, a resist mask pattern R is formed on the metal mask M by a photolithography process, and the metal mask M is etched by a wet etching process using a Cr etching solution using the resist mask pattern R as a mask. M pattern formation was performed. Then, using the pattern of the metal mask M as a mask, a structure S composed of desired convex portions 10a was formed on the surface of the synthetic quartz substrate by wet etching using HF liquid (concentration: 50 wt%). After the protrusion 10a was formed, the metal mask M was removed, the synthetic quartz substrate was washed, and finally an Ag reflection film was formed on the back surface of the synthetic quartz substrate by sputtering. Thus, the thermal radiation control element according to Invention Example 1 was produced.

  FIG. 31 shows an SEM image of the substrate surface of Invention Example 1-1. FIG. 31A is a cross-sectional image, and FIG. 31B is a perspective image. The size of the produced protrusions was 80 μm for P, 55 μm for W, 30 μm for H, 0.55 for aspect ratio H / W, and 0.7 for W / P.

<Conventional example 1>
A thermal radiation control element according to Conventional Example 1 was produced in the same manner as Invention Example 1-1 except that the convex portions were not formed. That is, the substrate surface of Conventional Example 1 has a planar structure, and an Ag reflection film is formed on the back surface.

  About the thermal radiation control element of invention example 1-1 and the prior art example 1, the infrared reflectance measuring device (made by PerkinElmer; Spectrum-GX) is used, and the spectral reflectance in the infrared region of a wavelength range of 5-14 micrometers is measured. did. Using this spectral reflectance, the spectral emissivity was calculated by subtracting the spectral reflectance from the total incident light. The results are shown in FIG. In FIG. 32, the spectral emissivity of Conventional Example 1 is also shown for comparison. From FIG. 32, it was confirmed that the spectral emissivity was improved in a band of wavelength 8 μm or more. In addition, in the wavelength range of 5 to 14 μm, the vertical spectral emissivity of the conventional example (only the wavelength range was changed from Equation (1)) was 0.84, whereas in the same wavelength range of Invention Example 1-1 Since the vertical emissivity was 0.87, it was confirmed that the emissivity was improved in the infrared region.

<Invention Example 1-2>
In the same manner as in Invention Example 1-1, a thermal radiation control element in which the convex portions 10a are arranged in hexagons as schematically shown in FIG. Note that the etching conditions were as follows in the production of the convex portions. First, a first-stage etching process similar to that shown in FIGS. 14A to 14E was performed. Next, alignment is performed on the convex surface formed by this etching process, and the second stage etching process, that is, mask formation, resist pattern formation, mask pattern formation by wet etching, and formation of structure S by wet etching are performed. went. In the first-stage etching process and the second-stage etching process, the conditions used for the photolithographic pattern and the etching are the same except for the resist coating method on the convex portions. In the first stage, the resist is applied to the flat portion of the substrate by a spin coating method, whereas in the second stage, the resist is applied to the convex portion by a spray coating method.

FIG. 33 shows an SEM image of the substrate surface of Invention Example 1-2. Note that FIG. 33A is a cross-sectional image, and FIG. 33B is a perspective image. In addition, the size of the produced convex part is as follows: P is 80 μm, W ₁ is 65 μm, W ₂ is 42.4 μm, H is 40 μm, h is 26.7 μm, aspect ratio H / W is 0.6, W / P Was 0.8. In addition, in the perspective view of FIG. 33 (B), there is a convex portion that appears to be attached, but this is a metal deposit at the time of SEM image acquisition.

  In the same manner as in Invention Example 1-1, the spectral reflectance in the infrared region of Invention Example 1-2 was measured to obtain the spectral emissivity. The results are shown in FIG. FIG. 34 also shows the spectral emissivity of Conventional Example 1 for comparison. In Invention Example 1-2, it was confirmed that the spectral emissivity was improved in the band of wavelength 8 μm or more as in Invention Example 1-1. The vertical emissivity of the conventional example in the wavelength range of 5 to 14 μm (only the wavelength range was changed from the formula (1)) was 0.84, whereas the vertical emissivity in the same wavelength range of the invention example 1-2. The emissivity was 0.89, and further improvement of the emissivity in the infrared region was confirmed.

<Invention Example 1-3>
Unlike Invention Examples 1-1 and 1-2, in Invention Example 1-3, a thermal radiation control element was fabricated using a molding method. First, a mold was produced by machining (machining center), and silica glass was poured into the mold by a sol-gel method to mold the convex portion 20a. The shape of the convex portion was a cone, and the cones were arranged in a hexagonal close-packed manner. After molding, an Ag reflective film was formed on the back surface in the same manner as in Invention Example 1-1.

  FIG. 35 shows an SEM image of the substrate surface of Invention Example 1-3. 35A is a cross-sectional image, and FIG. 35B is a perspective image. In addition, the size of the produced convex part was P of 370 μm, W of 310 μm, H of 335 μm, an aspect ratio H / W of 1.1, and W / P of 0.85.

  In the same manner as in Invention Example 1-1, the spectral reflectance in the infrared region of Invention Example 1-3 was measured, and the spectral emissivity was obtained. The results are shown in FIG. FIG. 36 also shows the spectral emissivity of Conventional Example 1 for comparison. In Invention Example 1-3, as in Invention Example 1-1, it was confirmed that the spectral emissivity was improved in a band having a wavelength of 8 μm or more. Further, the vertical emissivity of the conventional example in the wavelength range of 5 to 14 μm (only the wavelength range was changed from Equation (1)) was 0.84, whereas the vertical emissivity in the same wavelength range of Invention Example 1-3. The emissivity was 0.92, confirming further improvement in the emissivity in the infrared region.

(Example 6)
A thermal radiation control element according to Reference Example 2-1 was produced in the same manner as in Invention Example 1-3, except that the planar structure was produced with sol-gel silica glass by a molding method. In the same manner as in Invention Example 1-1, the spectral reflectance in the infrared region of Reference Example 2-1 was measured to obtain the spectral emissivity, and compared with Conventional Example 1, as shown in FIG. . In both Reference Example 2-1 and Conventional Example 1, since the structure S was not formed, the spectral emissivity was equivalent, and it was confirmed that the spectral emissivity was reduced at a wavelength of 9 μm. Moreover, the vertical emissivity of Reference Example 2-1 in the wavelength range of 5 to 14 μm (only the wavelength range was changed from Equation (1)) was 0.84, and the vertical emissivity in the same wavelength range as that of Conventional Example 1 was equivalent. It was confirmed that. Therefore, it was confirmed that the vertical emissivity characteristics differ depending on the presence or absence of the convex shape, regardless of the formation of the convex shape by etching and the formation of the convex shape by the silica glass formation of the sol-gel. From this, it was confirmed that the vertical emissivity ([epsilon]) can be improved even when the sol-gel is formed in a convex shape by silica glass, as in Example 1-1.

(Example 7)
A thermal radiation control element according to Invention Example 2-1 was produced in the same manner as Invention Example 1-1 except that the substrate was not cleaned by acid cleaning before the metal mask M was formed. FIG. 38 shows an SEM image of the substrate surface of Invention Example 2-1. FIG. 38A is a cross-sectional image, and FIG. 38B is a perspective image. As shown in FIG. 38, the surface of the convex portion was rough. The size of the produced protrusions was 80 μm for P, 55 μm for W, 30 μm for H, 0.55 for aspect ratio H / W, and 0.7 for W / P.

  Light scattering and diffraction occurs due to the roughness of the convex surface, and light larger than the critical angle is confined inside the thermal radiation control element (inside the substrate) due to the light confinement effect, and then absorbed by the Ag reflection film. Thus, the solar light absorption rate (α) is worse than that of the conventional example 1. Therefore, the manufactured thermal radiation control element was further subjected to heat treatment. The annealing heat treatment conditions were 1250 ° C., which is below the softening point of synthetic quartz, pressure: 0.1 MPa, temperature: 1250 ° C., and 2 hours. An SEM image after annealing is shown in FIG. FIG. 39A is a cross-sectional image, and FIG. 39B is a perspective image. By performing the annealing at a temperature higher than the temperature at which the thermal deformation of synthetic quartz proceeds, the quartz surface is softened, and the streak-like marks (surface roughened portion) generated on the convex surface shown in FIG. It was confirmed that the surface roughness of the convex portion can be improved. It was also confirmed that the tip, which had an acute angle before annealing, could be made into a gentle R shape. The size of the protrusions after annealing was as follows: P was 80 μm, W was 60 μm, H was 24 μm, aspect ratio H / W was 0.4, and W / P was 0.75.

  Using a spectrophotometer (manufactured by PerkinElmer; Lambda900), the reflectance in the wavelength range of 300 to 2200 nm was measured, and the change in the absorbance before and after annealing was measured. The results are shown in FIG. Compared with before annealing, it was confirmed that the absorptivity characteristics were lowered after annealing in the entire band of wavelengths from 350 to 2200 nm. Further, when the amount of change in solar absorptance (α) and vertical emissivity (ε) before and after annealing was determined, the difference in solar absorptance (α) ([after annealing] − [before annealing]) was −0 The difference in vertical emissivity (ε) ([after annealing] − [before annealing]) was 0. Therefore, it was confirmed that the solar absorptance (α) can be reduced while maintaining the vertical emissivity (ε) by annealing.

(Example 8)
Finally, the annealing treatment temperature and the change in shape of the convex portion were confirmed. First, a thermal radiation control element was produced under the same conditions as in Invention Example 1-1. The same thermal radiation control element was annealed at 1200 ° C., 1225 ° C., 1250 ° C., 1275 ° C. and 1300 ° C., respectively. Other annealing conditions are the same as in Example 7.

  FIG. 41 shows an SEM cross-sectional image. FIG. 41A shows a state before heat treatment, FIG. 41B shows a state after heat treatment at 1200 ° C., FIG. 41C shows a state after heat treatment at 1225 ° C., FIG. ) Is a cross-sectional image after heat treatment at 1275 ° C. The softening of the shape of the convex portion starts at 1200 ° C., and the tip that was an acute angle becomes a gentle R shape, and the shape change becomes remarkable as the temperature rises. However, when the temperature exceeded 1300 ° C., thermal deformation increased and cracking of the substrate occurred. From this result, it was confirmed that the solar absorption rate (α) can be reduced by annealing in the range of 1200 ° C. to 1275 ° C.

  According to the present invention, it is possible to provide a thermal radiation control element having a higher thermal emissivity than the conventional one and a method for manufacturing the same while maintaining the solar absorptance at the same level as the conventional one.

10 ... Inorganic material substrate 10a ... convex part 20a ... convex part (different materials)
DESCRIPTION OF SYMBOLS 30 ... Dielectric multilayer mirror 50 ... Transparent conductive film 70 ... Increasing reflection film 80 ... Reflective film 90 ... Protective film 100 ... Thermal radiation control element

Claims (26)

An inorganic material substrate containing either quartz or inorganic glass;
A thermal radiation control element having a reflective film provided on one surface side of the inorganic material substrate,
The inorganic material substrate is a thermal radiation control element having a structure in which a plurality of independent protrusions are two-dimensionally arranged on a surface opposite to the reflective film.   The thermal radiation control element according to claim 1, wherein the convex portion includes a tip portion.   The thermal radiation control element according to claim 1, wherein the convex portion has a vertex.   4. The thermal radiation control element according to claim 3, wherein in a cross-sectional view including a central axis of the convex portion, a ridge line between the adjacent convex portions is curved.   4. The thermal radiation control element according to claim 3, wherein in the cross-sectional view including the central axis of the convex portion, the ridge line of the convex portion has a bending point. 5.   The thermal radiation control element according to claim 3, wherein the convex portion is a cone.   The heat radiation according to any one of claims 1 to 6, wherein an area of a cross section cut along a horizontal plane perpendicular to the height direction of the convex portion decreases along a direction from the bottom surface of the convex portion toward the apex. Control element.   The thermal radiation control element of any one of Claims 1-7 in which the bottom face shape of the said convex part contains circular or a regular polygon.   The thermal radiation control element according to claim 8, wherein the bottom surface shape of the convex portion includes a circle or a regular hexagon, and the two-dimensional array is a hexagonal close-packed array.   The thermal radiation control element according to any one of claims 1 to 8, wherein the lattice arrangement is a square lattice arrangement.   The thermal radiation control element of any one of Claims 1-10 whose ratio H / W of the height H of the said convex part with respect to the width W of the bottom face of the said convex part is 0.25 or more.   The thermal radiation control element of any one of Claims 1-11 whose space | interval P between the said adjacent convex parts is 15 micrometers or more.   The thermal radiation control element according to claim 12, wherein a ratio W / P of a width W of the bottom surface to the interval P is 0.7 or more.   The thermal radiation control element of any one of Claims 1-13 which further has a protective film in the surface on the opposite side to the said inorganic material board | substrate of the said reflecting film. Further comprising a reflection enhancing film between the inorganic material substrate and the reflective film,
The thermal radiation control element according to claim 1, wherein the increased reflection film includes two or more dielectric layers.   The heat according to any one of claims 1 to 15, wherein the protrusion and the exposed flat surface of the inorganic material substrate are covered with a dielectric multilayer mirror that reflects light having a wavelength of near-infrared light or less. Radiation control element.   The thermal radiation control element of any one of Claims 1-16 by which the outermost surface of the side in which the said convex part was provided is coat | covered with a transparent conductive film. A structure forming step of forming a structure in which a plurality of independent protrusions are two-dimensionally arranged on the surface of an inorganic material substrate containing either quartz or inorganic glass;
A method of manufacturing a thermal radiation control element, comprising: a reflection film forming step of forming a reflection film on a surface of the inorganic material substrate opposite to a surface on which the structure is formed.   The method of manufacturing a thermal radiation control element according to claim 18, wherein the structure forming step includes an etching step.   The method for manufacturing a thermal radiation control element according to claim 18, wherein the structure is formed by machining or laser processing the inorganic material substrate in the structure forming step.   The thermal radiation according to claim 18, wherein the structure forming step includes a step of forming a mold by machining or laser processing, and a forming step of forming the structure by forming a sol-gel using the mold. A method for manufacturing a control element.   The structure forming step includes a step of forming a mold by machining or laser processing, and a transfer step of forming the structure on the surface of the inorganic material substrate by shape transfer of the mold. Of manufacturing a thermal radiation control element.   The thermal radiation control element according to any one of claims 18 to 22, further comprising a heat treatment step of performing a heat treatment below the glass softening point of the inorganic material substrate under vacuum or atmospheric pressure after the structure forming step. Manufacturing method.   The manufacturing method of the thermal radiation control element of any one of Claims 18-23 which further includes the dielectric multilayer mirror forming process which forms a dielectric multilayer mirror on the surface of the said structure.   The manufacturing method of the thermal radiation control element of any one of Claims 18-24 which further includes the transparent conductive film formation process which forms a transparent conductive film in the surface of the said structure.   The manufacturing method of the thermal radiation control element of any one of Claims 18-25 which further has a protective film formation process which forms a protective film in the surface on the opposite side to the said inorganic material board | substrate of the said reflecting film.