WO2012057073A1

WO2012057073A1 - Solar thermal collector member and manufacturing method thereof

Info

Publication number: WO2012057073A1
Application number: PCT/JP2011/074424
Authority: WO
Inventors: 箕浦　潔; 彰信石動; 千明三成; 貴文端山
Original assignee: シャープ株式会社
Priority date: 2010-10-25
Filing date: 2011-10-24
Publication date: 2012-05-03

Abstract

Disclosed is a solar thermal collector member (10A, 10B) provided with a metal layer (M) having a surface. The surface of the metal layer (M) has a moth eye structure containing multiple convexities (10p) or an inverted moth eye structure containing multiple concavities (10q), and, seen from the normal direction, the two-dimensional size of the multiple convexities (10p) or the multiple concavities (10q) is 50nm or greater and less than 380nm. By this means, the disclosed solar thermal collector member is capable of efficient heat collection.

Description

Solar heat collecting member and manufacturing method thereof

The present invention relates to a solar heat collecting member and a manufacturing method thereof.

In recent years, interest in the use of solar energy has increased from the viewpoint of environmental harmony. Solar heat is available at a relatively low cost and can be used stably regardless of the season. An apparatus using solar heat includes, for example, a hot water supply system including a solar heat collecting member.

It is known that a periodic structure is formed on the surface of a solar heat collecting member in order to perform wavelength selective absorption of solar heat (for example, see Patent Document 1). Patent Document 1 describes that a rectangular cavity is provided on the surface of a solar heat collecting member (wavelength selective solar absorbing material).

FIG. 33 shows a schematic diagram of a solar heat collecting member 900A provided with a rectangular cavity of Patent Document 1. Patent Document 1 describes that the wavelength dependency of the absorptance is caused by absorption by surface plasmons induced by a periodic structure and absorption of a standing wave mode by a cavity structure. In solar heat collecting member 900A, the opening diameter and depth of the cavity provided on the surface of the tungsten substrate are substantially the same as the specific wavelengths in the visible light and near infrared wavelength regions of sunlight. Patent Document 1 describes that high-speed atomic beam etching is performed using an alumina mask from which a barrier layer has been removed in order to form a solar heat collecting member 900A.

Patent Document 1 describes another solar heat collecting member. FIG. 34 shows a schematic diagram of the solar heat collecting member 900B. In the solar heat collecting member 900B, a quadrangular pyramid (pyramid shape) microstructure is arranged in a matrix on the surface of a tungsten substrate. Note that Patent Document 1 does not mention a specific method for manufacturing the solar heat collecting member 900B.

JP 2003-332607 A

As a result of earnest research, the inventor of the present application has not been able to sufficiently collect heat with the solar

heat collecting members

900A and 900B, and particularly cannot absorb light with a relatively short wavelength, and the solar heat collecting member It was found that 900A and 900B cannot be easily produced.

The present invention has been made in view of the above problems, and an object thereof is to provide a solar heat collecting member capable of efficiently collecting heat. Another object of the present invention is to provide a simple method for producing a solar heat collecting member.

A solar heat collecting member according to the present invention is a solar heat collecting member comprising a metal layer having a surface, wherein the surface of the metal layer has a moth-eye structure including a plurality of convex portions or an inverted moth eye including a plurality of concave portions. The two-dimensional size of each of the plurality of convex portions or the plurality of concave portions when viewed from the normal direction is 50 nm or more and less than 380 nm.

In an embodiment, an average distance between the plurality of recesses or the plurality of recesses when viewed from the normal direction is not less than 50 nm and less than 380 nm.

In one embodiment, a flange is provided between two adjacent convex portions of the plurality of convex portions or two adjacent concave portions of the plurality of concave portions.

In an embodiment, an average distance between the plurality of convex portions or the plurality of concave portions is smaller than a two-dimensional size of each of the plurality of convex portions or the plurality of concave portions.

In one embodiment, the average height of the plurality of convex portions or the average depth of the plurality of concave portions is 50 nm or more and less than 500 nm.

In one embodiment, the surface of the metal layer has an inverted moth-eye structure including the plurality of recesses.

In one embodiment, the metal layer includes at least one selected from the group consisting of gold, silver, copper, aluminum, nickel, zinc, platinum, tungsten, and tantalum.

In one embodiment, the solar heat collecting member further includes an aluminum layer, and a porous alumina layer positioned between the aluminum layer and the metal layer.

In one embodiment, the plurality of convex portions or the plurality of concave portions do not have periodicity.

A method for producing a solar heat collecting member according to the present invention is a method for producing a solar heat collecting member having a surface of a moth-eye structure including a plurality of protrusions or an inverted moth-eye structure including a plurality of recesses, comprising: (a) aluminum A step of preparing a mold substrate or an aluminum substrate having a layer; and (b) a porous layer that defines a plurality of fine recesses by partially anodizing the aluminum layer or the aluminum substrate, and A step of forming a porous alumina layer having a barrier layer provided on the bottom of each of the plurality of fine recesses, and (c) after the step (b), by bringing the porous alumina layer into contact with an etching solution. Etching to enlarge the plurality of fine recesses of the porous alumina layer; and (d) the porous alumina layer. Comprising a step of forming a metal layer on the plurality of minute recesses.

In one embodiment, electroplating or vapor deposition is performed in the step (d).

In one embodiment, the method for producing the solar heat collecting member further includes (e) a step of peeling the metal layer from the porous alumina layer.

A method for producing a solar heat collecting member according to the present invention is a method for producing a solar heat collecting member having a surface of a moth-eye structure including a plurality of protrusions or an inverted moth-eye structure including a plurality of recesses, comprising: (a) aluminum A step of preparing a mold substrate or an aluminum substrate having a layer; and (b) a porous layer that defines a plurality of fine recesses by partially anodizing the aluminum layer or the aluminum substrate, and A step of forming a porous alumina layer having a barrier layer provided on the bottom of each of the plurality of fine recesses, and (c) after the step (b), by bringing the porous alumina layer into contact with an etching solution. Etching to enlarge the plurality of fine recesses of the porous alumina layer; and (d) the porous alumina layer. Comprising a step of preparing a mold having a plurality of fine convex portions corresponding to the plurality of minute recesses, and forming a metal layer on the (e) the mold.

In one embodiment, in the step (d), the photocurable resin is irradiated with ultraviolet rays in a state where the photocurable resin is applied to the plurality of fine recesses of the porous alumina layer. A step of curing the resin, and a step of peeling the photocurable resin from the porous alumina layer.

In one embodiment, the method for producing the solar heat collecting member further includes (f) a step of peeling the metal layer from the mold.

In one embodiment, the method for producing a solar heat collecting member further includes a step of repeating the step (b) and the step (c) until adjacent fine concave portions among the plurality of fine concave portions are continuous. To do.

The solar heat collecting member according to the present invention can efficiently collect heat. Moreover, according to this invention, a solar-heat collection member can be produced simply.

It is typical sectional drawing of embodiment of the solar-heat collection member by this invention. (A) is a typical perspective view of the solar heat collecting member of this embodiment, (b) is a typical top view. (A) And (b) is a typical perspective view of the solar-heat collection member of this embodiment, respectively. It is a typical top view of the solar heat collecting member of this embodiment. It is typical sectional drawing of embodiment of the solar-heat collection member by this invention. (A) is a typical perspective view of the solar heat collecting member of this embodiment, (b) is a typical top view. (A) And (b) is a typical perspective view of the solar-heat collection member of this embodiment, respectively. (A)-(e) is a schematic diagram for demonstrating the manufacturing method of the solar-heat collection member of this embodiment, respectively. (A)-(g) is a schematic diagram for demonstrating the manufacturing method of the solar-heat collection member of this embodiment, respectively. It is a figure which shows the SEM image of the solar-heat collection member of this embodiment. (A) is a schematic diagram which shows the behavior of the light of a comparatively short wavelength, (b) is a schematic diagram which shows the behavior of the light of a comparatively long wavelength. It is a graph which shows a sunlight spectrum. It is a graph which shows the radiation spectrum of a black body. It is a graph which shows the wavelength dependence of the absorptivity of the solar heat collecting member of this embodiment. (A) is a diagram showing samples 1 to 3, and (b) is a diagram showing sample 4. FIG. (A) is an image obtained by measuring the sample 1 with an optical microscope, and (b) to (d) are images obtained by measuring the sample 1 with a scanning electron microscope. (A) And (b) is the SEM perspective image and SEM front image of sample 2, respectively. (A) And (b) is the SEM perspective image and SEM front image of the sample 4, respectively. 6 is a graph showing the wavelength dependence of the reflectance of samples 1 to 4. (A) is a graph which shows the wavelength dependence of the absorptance of

samples

1, 3, and 4, (b) and (c) are graphs which show the wavelength dependence of the absorptivity of the conventional solar heat collecting member. (A)-(c) is a figure for demonstrating the model used for calculation of a reflectance and an absorptance. (A) is a graph which shows the wavelength dependence of the absorption factor of the different angle of the solar heat collection member of this embodiment, (b) shows the wavelength dependency of the absorption factor of the different angle of the conventional solar heat collection member. It is a graph. (A) to (j) are schematic diagrams of samples 5 to 10c, respectively. 10 is a graph showing the wavelength dependence of the reflectance of samples 5 to 8. 10 is a graph showing the wavelength dependence of the reflectance of samples 9a to 10c. It is a graph which shows the wavelength dependence of the reflectance of the solar-heat collection member containing gold | metal | money. It is a graph which shows the wavelength dependence of the reflectance of the solar-heat collection member containing aluminum. It is a graph which shows the wavelength dependence of the reflectance of the solar-heat collection member containing copper. It is a graph which shows the wavelength dependence of the reflectance of the solar-heat collection member containing silver. It is a graph which shows the wavelength dependence of the reflectance of the solar-heat collection member containing nickel. It is a schematic diagram of a solar heat collector provided with the solar heat collecting member of this embodiment. It is a schematic diagram of a hot water supply system provided with the solar-heat collector shown in FIG. It is a schematic diagram which shows the conventional solar heat collecting member. It is a schematic diagram which shows another conventional solar heat collecting member.

Hereinafter, with reference to the drawings, embodiments of the solar heat collecting member and the manufacturing method thereof according to the present invention will be described. However, the present invention is not limited to the following embodiments.

FIG. 1 shows a schematic diagram of a solar heat collecting member 10A of the present embodiment. The solar heat collecting member 10 A includes a metal layer M. In FIG. 1, the surface of the metal layer M has a moth-eye structure including a plurality of convex portions 10p. The metal layer M includes at least one selected from the group consisting of gold, silver, copper, zinc, aluminum, nickel, platinum, tungsten, and tantalum. The thickness of the metal layer M is 100 nm or more.

In the solar heat collecting member 10A of the present embodiment, the (two-dimensional) size of the convex portion 10p is shorter than the wavelength of light in the visible region. Specifically, the two-dimensional size of each of the plurality of convex portions 10p when viewed from the normal direction is not less than 50 nm and less than 380 nm. Here, the convex portions 10p are arranged almost periodically. For example, the average height of the convex portion 10p is 50 nm or more and less than 500 nm. The average height of the convex portion 10p may be smaller than the wavelength of light in the visible region. For example, the average height of the convex portion 10p may be 50 nm or more and less than 380 nm.

Generally, light incident on a member is reflected at the interface, absorbed by the member, or transmitted through the member. The metal layer M is made of metal, or its main component is metal, and the metal layer M has a thickness greater than or equal to a predetermined thickness, so that light does not pass through the solar heat collecting member 10A.

The surface of the metal layer M has a moth-eye structure in which the two-dimensional size of each protrusion 10p is 50 nm or more and less than 380 nm, and reflection of light in the visible region at the interface is suppressed. As a result, solar heat collection Most of the light incident on the member 10A is absorbed. For this reason, the solar heat collecting member 10A can efficiently absorb solar heat.

In addition, although not shown in FIG. 1, the metal layer M may be affixed to a support body, and a support body may have heat insulation. In FIG. 1, the lower surface of the metal layer M is shown flat, but the lower surface of the metal layer M may not be flat and may have a surface corresponding to the moth-eye structure with a substantially constant thickness. . Moreover, the metal layer M may be supported by a support body, and a support body may have heat insulation.

FIG. 2 (a) shows a schematic perspective view of the solar heat collecting member 10A, and FIG. 2 (b) shows a schematic top view of the solar heat collecting member 10A. The convex portion 10p has a substantially conical shape. Here, each convex part 10p is comprised by the substantially constant size. The outer edge shape of the convex portion 10p when viewed from the direction perpendicular to the main surface is typically a regular hexagon. The protrusions 10p have an array that is two-dimensionally filled with the highest density when viewed from a direction perpendicular to the main surface, and the array of protrusions 10p has periodicity. Here, the fact that the arrangement of the convex portions 10p has periodicity is based on the geometric center of gravity of the certain convex portion 10p (hereinafter simply referred to as “center of gravity”) when viewed from the direction perpendicular to the main surface. It means that the sum of the vectors directed to the centroids of all the convex portions 10p adjacent to the convex portion 10p becomes zero. Here, the six vectors from the centroid of a certain convex portion 10p to the centroids of the six adjacent convex portions 10p have substantially the same length, and their directions are different from each other by 60 degrees. The sum is zero. Actually, if the sum of the vectors is less than 5% of the total length of the vector, it can be determined that the vector has periodicity. In FIG. 2, one convex portion 10p is surrounded by six adjacent convex portions 10p, but each convex portion 10p is connected to three to six convex portions 10p adjacent to the convex portion 10p. You may be surrounded.

In FIG. 2, the convex portion 10p has a substantially conical shape, and the full width at half maximum along the cross section of the convex portion 10p is almost half the size of the convex portion 10p, but the present invention is not limited to this.

As shown in FIG. 3 (a), the full width at half maximum along the cross section with the convex portion 10p may be larger than half of the size of the convex portion 10p. Or as shown in FIG.3 (b), the full width at half maximum along a cross section with the convex part 10p is smaller than the half of the magnitude | size of the convex part 10p, and the convex part 10p may have a pointed shape.

Moreover, a collar part may be provided on the ridge line connecting the vertices 10t of the adjacent convex parts 10p.

FIG. 4 shows a schematic top view of the solar heat collecting member 10A. As described above, a plurality of convex portions 10p having substantially the same length of vectors connecting the centroids are arranged around a certain convex portion 10p. Here, the average inter-adjacent distance indicating the distance between the apexes 10t of the adjacent convex portions 10p among the plurality of convex portions 10p is slightly smaller than the average diameter (two-dimensional size) of the plurality of convex portions 10p. A flange portion 10s is provided between the apexes 10t of the adjacent convex portions 10p. The collar portion 10s is located on a ridge line connecting the vertices 10t of the adjacent convex portions 10p. Further, the flange portion 10s is located on a ridge line connecting adjacent bottom points 10u. Also in FIG. 4, one convex portion 10p is surrounded by six adjacent convex portions 10p, but each convex portion 10p is surrounded by three to six convex portions 10p adjacent to the convex portion 10p. It may be.

In addition, although the moth-eye structure was formed in the surface of the metal layer M of the solar heat collecting member 10A mentioned above, this invention is not limited to this. An inverted moth-eye structure may be formed on the surface of the metal layer M.

FIG. 5 shows a schematic diagram of the solar heat collecting member 10B. The solar heat collection member 10B has the same configuration as the solar heat collection member 10A described above except for the surface structure of the metal layer M, and redundant description is omitted to avoid redundancy.

The solar heat collecting member 10B includes a metal layer M. In FIG. 5, the surface of the metal layer M has an inverted moth-eye structure including a plurality of recesses 10q. The two-dimensional size of each of the plurality of recesses 10q when viewed from the normal direction is not less than 50 nm and less than 380 nm. For example, the average depth of the recess 10q is 50 nm or more and less than 500 nm. The average depth of the recess 10q may be smaller than the wavelength of light in the visible region. For example, the average depth of the recess 10q may be 50 nm or more and less than 380 nm.

Thus, on the surface of the metal layer M of the solar heat collecting member 10B, an inverted moth-eye structure in which the two-dimensional size of each recess 10q is 50 nm or more and less than 380 nm is formed. For this reason, reflection of the light of the visible region which injects into the solar-heat collection member 10B is suppressed, and, thereby, solar heat can be absorbed efficiently.

In addition, although not shown in FIG. 5, the metal layer M may be affixed to a support body, and a support body may have heat insulation. Further, in FIG. 5, the lower surface of the metal layer M is shown flat, but the lower surface of the metal layer M does not have to be flat, and has a surface corresponding to the moth-eye structure inverted at a substantially constant thickness. May be. Moreover, the metal layer M may be supported by a support body, and a support body may have heat insulation.

Fig. 6 (a) shows a schematic perspective view of the solar heat collecting member 10B, and Fig. 6 (b) shows a schematic top view of the solar heat collecting member 10B. Here, the concave portion 10q has a substantially conical shape, and each concave portion 10q has a substantially constant size. The outer edge shape of the recess 10q when viewed from the direction perpendicular to the main surface is typically a regular hexagon. The recesses 10q have an array that is two-dimensionally filled with the highest density when viewed from the direction perpendicular to the main surface, and the array of recesses 10q has periodicity. Here, the arrangement of the recesses 10q having periodicity means that the fine pores have a geometrical center of gravity (hereinafter simply referred to as “center of gravity”) when viewed from a direction perpendicular to the main surface. This means that the sum of the vectors toward the center of gravity of all the pores adjacent to the pore becomes zero. Here, the six vectors from the center of gravity of a certain recess 10q to the center of gravity of each of the six adjacent recesses 10q have substantially the same length, and their directions differ from each other by 60 degrees, so the sum of these vectors is Zero. Actually, if the sum of the vectors is less than 5% of the total length of the vector, it can be determined that the vector has periodicity.

As described above, around a certain recess 10q, a plurality of recesses 10q having substantially the same length of vectors connecting the centers of gravity are arranged. Here, the average inter-adjacent distance indicating the distance between the bottom points 10u of the adjacent recesses 10q among the plurality of recesses 10q is slightly smaller than the average diameter of the plurality of recesses 10q, and the bottom point 10u of the adjacent recesses 10q. A flange 10s is provided between the two. The flange portion 10s is located on a ridge line connecting the bottom points 10u of the adjacent concave portions 10q. Further, the collar portion 10s is located on a ridge line connecting adjacent vertices 10t. In FIG. 6, each concave portion 10q is surrounded by six concave portions 10q adjacent to the concave portion 10q, but each concave portion 10q is surrounded by three to six concave portions 10q adjacent to the concave portion 10q. Also good.

In FIG. 6, the recess 10q has a substantially conical shape, and the full width at half maximum along the cross section of the recess 10q is almost half of the size of the recess 10q. However, the present invention is not limited to this. As shown in FIG. 7A, the full width at half maximum along the cross section having the recess 10q may be larger than half the size of the recess 10q. Or as shown in FIG.7 (b), the full width at half maximum along a cross section with the recessed part 10q is smaller than the half of the magnitude | size of the recessed part 10q, and the recessed part 10q may have a pointed shape.

For example, the solar

heat collecting members

10A and 10B can be produced by forming the metal layer M on the porous alumina layer Sc formed by anodic oxidation.

Hereinafter, a method for producing the solar heat collecting member of the present embodiment will be described with reference to FIG.

First, as shown in FIG. 8A, a mold base S is prepared. The mold substrate S has a support and an aluminum layer supported by the support. FIG. 8A shows only the aluminum layer of the mold base S. The aluminum layer is formed by a known method (for example, electron beam evaporation method or sputtering method). For example, the aluminum layer is formed by sputtering an aluminum target having a purity of 99.99% by mass or more. The thickness of the aluminum layer is preferably 500 nm or more, and preferably 3000 nm or less from the viewpoint of productivity. For example, the thickness of the aluminum layer is 1000 nm (1 μm). Alternatively, the mold substrate S itself may be an aluminum substrate.

Next, as shown in FIG. 8B, a plurality of fine recesses (pores) Sp are defined by anodizing the aluminum layer or the aluminum substrate partially (surface portion) under predetermined conditions. The porous alumina layer Sc having the porous layer Sa and the barrier layer Sb provided at the bottom of each of the plurality of fine recesses Sp is formed. The average inter-adjacent distance D _int between the bottom points of the adjacent pores Sp is represented by the sum of the average thickness 2L of the pore walls and the average pore diameter D _p of the pores Sp. Since the thickness of the pore wall is equal to the thickness L of the barrier layer, the average thickness of the entire pore wall separating the two pores Sp is expressed as 2L.

The generation density, pore diameter, depth, and the like of the pores Sp can be controlled according to the conditions of anodization (for example, the formation voltage, the type and concentration of the electrolytic solution, and the anodization time). Further, the regularity of the arrangement of the pores Sp can be controlled by controlling the magnitude of the formation voltage. As the electrolytic solution, for example, an acidic aqueous solution containing an acid selected from the group consisting of oxalic acid, tartaric acid, phosphoric acid, chromic acid, citric acid, and malic acid is used.

An oxalic acid aqueous solution is preferably used as the electrolytic solution. By using an oxalic acid aqueous solution, a hard porous alumina layer can be suitably formed, and such a porous alumina layer exhibits high durability. For example, the temperature of the oxalic acid aqueous solution is 5 ° C. or more and 30 ° C. or less, and the concentration of the oxalic acid aqueous solution is 0.1 mass% or more and 2 mass% or less. When the concentration of the oxalic acid aqueous solution is lower than 0.1% by mass, the direction in which the pores extend is not perpendicular to the substrate surface. On the other hand, if the concentration of the oxalic acid aqueous solution is larger than 2% by mass, anodization starts before the formation voltage reaches a predetermined value, and a desired moth-eye structure may not be formed.

Since the porous alumina layer Sc that is initially generated may contain many defects due to the influence of impurities or the like, the porous alumina layer Sc that is formed first is removed as necessary, and then the porous alumina layer Sc Sc may be formed again. The thickness of the porous alumina layer Sc initially formed and removed is preferably 200 nm or more from the viewpoint of reproducibility, and preferably 2000 nm or less from the viewpoint of productivity. Of course, if necessary, the initially formed porous alumina layer Sc may be partially removed (for example, from the surface to a certain depth). The removal of the porous alumina layer Sc can be performed by a known method such as immersion in a phosphoric acid aqueous solution or a chromium phosphoric acid mixed solution for a predetermined time.

As shown in FIG. 8C, etching is performed by bringing the porous alumina layer Sc into contact with an etching solution to enlarge a plurality of minute recesses Sp of the porous alumina layer Sc. By performing wet etching, the pores Sp can be enlarged approximately isotropically. The amount of etching (that is, the size and depth of the pores Sp) can be controlled by adjusting the type / concentration of the etching solution and the etching time. As the etching solution, for example, an aqueous solution of 10% by mass of phosphoric acid, an organic acid such as formic acid, acetic acid or citric acid, or a mixed solution of chromium phosphoric acid can be used. Alternatively, for example, an acidic aqueous solution such as sulfuric acid, hydrochloric acid, or oxalic acid, or an alkaline aqueous solution such as sodium hydroxide may be used as the etching solution. For example, an aqueous phosphoric acid solution is preferably used as the etching solution. The phosphoric acid aqueous solution is not only inexpensive and low in danger, but also can control the etching rate relatively easily. For example, the temperature of the phosphoric acid aqueous solution is 10 ° C. or more and 50 ° C. or less, and the concentration of the phosphoric acid aqueous solution is 0.1 M or more and 10 M or less.

If necessary, anodic oxidation and etching may be repeated. Thus, by alternately repeating the above-described anodizing step and etching step, a porous alumina layer Sc having pores (fine concave portions) Sp having a desired uneven shape can be obtained. By appropriately setting the conditions of each step of the anodizing step and the etching step, the step shape on the side surface of the pore Sp can be controlled along with the generation density, pore diameter and depth of the pore Sp. Further, the pore diameter of the pore Sp may be expanded until adjacent pores Sp are continuous. In this case, the average pore diameter D _p of the pores Sp is approximately equal to the average distance D _int between the pores Sp. In addition, in order to make the bottom part of the pore Sp small, it is preferable to finish by an anodic oxidation process (the subsequent etching process is not performed). In this case, since the tip of the recessed portion of the inverted moth-eye structure can be made small, light can be efficiently reflected. When viewed from the normal direction, the two-dimensional size of the plurality of minute recesses (pores) Sp is 50 nm or more and less than 380 nm, and the distance between the bottom points of the adjacent pores Sp is 50 nm or more and 380 nm. It is preferable that it is less than.

In addition, here, an example in which the anodizing process and the etching process are alternately performed has been described, but the cleaning process and the drying process are performed between the anodizing process and the etching process or between the etching process and the anodizing process. A process may be performed. Moreover, you may change conditions, such as a formation voltage, between each anodizing process.

As shown in FIG. 8 (d1) and FIG. 8 (d2), the metal layer M is formed on the porous alumina layer Sc. The metal layer M is formed by, for example, electroplating or vapor deposition. The metal layer M containing at least one of gold, silver, copper, nickel and platinum can be formed by electroplating. Thus, electroplating is suitable for forming the metal layer M containing a noble metal. Alternatively, for example, the metal layer M including at least one of gold, silver, copper, aluminum, nickel, zinc, tungsten, tantalum, and platinum can be formed by vapor deposition. The metal layer M is suitably used as a solar heat collecting member or a part thereof.

As shown in FIG. 8D1, when the thin metal layer M is formed on the porous alumina layer Sc, an inverted moth-eye structure is formed on the surface of the metal layer M. When viewed from the normal direction, when the two-dimensional size of the plurality of fine recesses (pores) is 50 nm or more and less than 380 nm, the metal layer M is used as the solar heat collecting member 10B described above. Note that the two-dimensional size of the plurality of fine recesses (pores) may correspond to the wavelength in the visible region. For example, when the two-dimensional size of the plurality of fine recesses (pores) is 380 nm or more and less than 500 nm, the metal layer M may be used as the solar heat collecting member 10b. In the solar

heat collecting members

10B and 10b, the aluminum layer, the porous alumina layer Sc, and the metal layer M are laminated in this order. The solar

heat collecting members

10B and 10b can be easily produced by anodic oxidation and etching.

Alternatively, when forming a thick (for example, 1 mm thick) metal layer M as shown in FIG. 8 (d2), the metal layer M is then peeled off from the porous alumina layer Sc as shown in FIG. 8 (e). May be. If peeling cannot be easily performed, the porous alumina layer Sc may be dissolved with an electrolytic solution. The surface of the peeled metal layer M has a moth-eye structure. In addition, after forming the metal layer M on the porous alumina layer Sc by electroplating, peeling the metal layer M from the porous alumina layer Sc is also called electroforming. When viewed from the normal direction, when the two-dimensional size of the plurality of fine protrusions is 50 nm or more and less than 380 nm, the metal layer M is used as the solar heat collecting member 10A described above. Note that the two-dimensional size of the plurality of fine protrusions may correspond to the wavelength in the visible region. For example, when the two-dimensional size of the plurality of fine recesses (pores) is 380 nm or more and less than 500 nm, the metal layer M may be used as the solar heat collecting member 10a. As described above, the solar

heat collecting members

10A and 10a can be easily manufactured by anodic oxidation and etching. Moreover, solar

heat collecting member

10A, 10a is affixed on a metal base material as needed.

In the above description with reference to FIG. 8, the metal layer M is formed directly on the porous alumina layer, but the present invention is not limited to this. You may form the metal layer M on the type | mold (for example, photocurable resin layer) which transferred the fine recessed part of the porous alumina layer.

Hereinafter, a method for producing the solar heat collecting member of this embodiment will be described with reference to FIG.

First, as shown in FIG. 9A, a mold base S having an aluminum layer is prepared. Alternatively, the mold substrate S itself may be an aluminum substrate.

As shown in FIG. 9 (b), by partially anodizing the surface of the aluminum layer or the aluminum substrate, each of the porous layer Sa defining the plurality of minute recesses Sp and the plurality of minute recesses A porous alumina layer Sc having a barrier layer Sb provided on the bottom of the substrate is formed.

As shown in FIG. 9 (c), etching is performed by bringing the porous alumina layer Sc into contact with an etching solution to enlarge a plurality of minute recesses Sp of the porous alumina layer Sc.

If necessary, anodic oxidation and etching may be repeated until adjacent concave portions Sp are continuous. The porous alumina layer Sc formed as described above is used as a mold. 9A to 9C are the same as those described above with reference to FIGS. 8A to 8C, and redundant description is omitted to avoid redundancy. .

As shown in FIG. 9 (d), the photocurable resin layer K is formed by irradiating the photocurable resin with ultraviolet rays in a state where the photocurable resin is applied to the plurality of fine recesses Sp of the porous alumina layer Sc. Form. Photocurability is obtained by irradiating the photocurable resin with ultraviolet rays (UV) through the mold substrate S in a state where the photocurable resin is applied between the surface of the workpiece L and the porous alumina layer Sc. Cure the resin. Thereby, the photocurable resin layer K in which the convex part was formed is formed in the surface which contact | connects a porous alumina layer. The photocurable resin may be applied to the surface of the workpiece L or may be applied to the porous alumina layer Sc. As the photocurable resin, for example, an acrylic resin can be used.

As shown in FIG. 9E, by separating the porous alumina layer Sc from the photocurable resin layer K, the photocurable resin layer K to which the concavo-convex structure of the porous alumina layer Sc is transferred becomes the workpiece L. Formed on the surface.

9 (f1) and FIG. 9 (f2), a metal layer M is formed on the surface of the photocurable resin layer K corresponding to the plurality of fine recesses. Specifically, the metal layer M is formed by electroplating or vapor deposition. This metal layer M is suitably used as a solar heat collecting member or a part thereof.

As shown in FIG. 9 (f 1), when the thin metal layer M is formed on the photocurable resin layer K, a moth-eye structure is formed on the surface of the metal layer M. When viewed from the normal direction, when the two-dimensional size of the plurality of fine protrusions is 50 nm or more and less than 380 nm, the metal layer M is used as the solar heat collecting member 10A described above. Note that the two-dimensional size of the plurality of fine protrusions may correspond to the wavelength in the visible region. For example, when the two-dimensional size of the plurality of fine protrusions is 380 nm or more and less than 500 nm, the metal layer M may be used as the solar heat collecting member 10a. In the solar

heat collecting members

10A and 10a, the workpiece L, the photocurable resin layer K, and the metal layer M are laminated in this order. The solar

heat collecting members

10A and 10a can be easily produced by anodic oxidation and etching.

Alternatively, when a thick (for example, 1 mm thick) metal layer M is formed as shown in FIG. 9 (f2), the metal layer M is then removed from the photocurable resin layer K as shown in FIG. 9 (g). It may be peeled off. In this way, the metal layer M having a surface provided with a plurality of recesses corresponding to the plurality of minute recesses of the porous alumina layer Sc is formed. When viewed from the normal direction, when the two-dimensional size of the plurality of fine recesses (pores) is 50 nm or more and less than 380 nm, the metal layer M is used as the solar heat collecting member 10B described above. Note that the two-dimensional size of the plurality of fine recesses (pores) may correspond to the wavelength in the visible region. For example, when the two-dimensional size of the plurality of fine recesses (pores) is not less than 380 nm and less than 500 nm, the metal layer M may be used as the solar heat collecting member 10b. As described above, the solar

heat collecting members

10B and 10b can be easily manufactured by anodic oxidation and etching. Moreover, the solar-

heat collection members

10B and 10b are affixed on a metal base material as needed.

As described above, the surface of the metal layer M of the solar heat collecting member of the present embodiment may have a moth-eye structure or an inverted moth-eye structure. When the metal layer M is peeled off from the porous alumina layer Sc or the mold, the moth-eye structure is formed as described above with reference to FIG. 8, and the inverted moth-eye structure is as described above with reference to FIG. It is formed. In this case, the uneven structure of the porous alumina layer Sc is not directly transferred to the metal layer M, but the uneven structure of the porous alumina layer Sc is indirectly transferred to the metal layer M via the photocurable resin layer K. The metal layer M can be easily peeled off. For this reason, the inverted moth-eye structure can be formed efficiently.

In the above description, the convex portions 10p or the concave portions 10q are arranged almost periodically, but the present invention is not limited to this. In order to suppress the generation of diffracted light, it is preferable that the concave portion or the convex portion array in the concave-convex structure has no periodicity. Non-periodicity means that if the sum of vectors from the center of gravity of a pore toward the center of gravity of all pores adjacent to the pore is 5% or more of the total length of the vector, the period is substantially periodic. It can be said that it does not have sex. When the concavo-convex structure has periodicity, the period is preferably smaller than the wavelength of light.

FIG. 10 is a view showing an image obtained by photographing the surface of the solar heat collecting member 10B with a scanning electron microscope (SEM). Here, the solar heat collecting member 10B is manufactured according to the process described above with reference to FIG. 9, and the metal layer M is formed of nickel. Here, the recess 10q has no periodicity. Further, the vertex 10t is formed in a pointed shape, and a flange portion 10s is formed between the adjacent concave portions 10q. The average distance between adjacent recesses is about 200 nm.

In the above description, the reflection and absorption of light in the visible region by the moth-eye structure or the inverted moth-eye structure has been described. However, in order to collect heat efficiently, not only the heat absorption but also the heat absorption is effective. It is necessary to efficiently suppress radiation. Hereinafter, heat radiation will also be described.

FIG. 11A is a schematic diagram showing the behavior when light having a relatively short wavelength is incident on the solar

heat collecting members

10A and 10B, and FIG. 11B is a diagram showing light having a relatively long wavelength. It is a schematic diagram which shows the behavior at the time of entering into 10A, 10B. For example, light having a wavelength of 300 nm or more and less than 2000 nm shows the behavior shown in FIG. 11A, and light having a wavelength of 2000 nm or more and less than 10000 nm shows the behavior shown in FIG.

As shown in FIGS. 11 (a) and 11 (b), in the solar

heat collecting members

10A and 10B, reflection of short wavelength light is efficiently suppressed, whereas long wavelength light is efficient. Reflected in. A general metal exhibits a high reflectance on a flat surface, but the surface of the metal layer M of the solar

heat collecting members

10A and 10B has a moth-eye structure or an inversion in which the size of the convex portion 10p or the concave portion 10q is 50 nm or more and less than 380 nm. Since the moth-eye structure is provided, the reflectance of light having a wavelength substantially equal to the size of the structure is low, while the reflectance of light having a wavelength sufficiently longer than the size of the structure is high. Long-wavelength light behaves like a flat surface even if a moth-eye structure or an inverted moth-eye structure is provided. In addition, when the height of the convex part 10p and the depth of the recessed part 10q are substantially equal, even if any of the convex part 10p and the recessed part 10q is provided in the surface of a solar heat collecting member, there is almost no difference in those optical characteristics. However, as described above, when the relatively thick metal layer M is formed, the metal layer M having the concave portion 10q is more easily peeled off than the metal layer M having the convex portion 10p, and the peeling is performed on the concave portion 10q. The smaller the depth, the easier.

In addition, not only the magnitude | size of the convex part 10p or the recessed part 10q but the height of the convex part 10p or the depth of the recessed part 10q influences similarly. When the height of the convex portion 10p or the depth of the concave portion 10q is 50 nm or more and less than 380 nm, the reflectance of light having a wavelength substantially equal to the height or depth of the structure is low. On the other hand, when the wavelength of light is sufficiently longer than the height or depth of the structure, the reflectance is high even if it has a moth-eye structure or an inverted moth-eye structure, as in the case of incidence on a flat surface. Thus, the reflectance of the solar

heat collecting members

10A and 10B changes according to the wavelength of light. Further, as described above, since the reflectivity has an anti-correlation with the absorptance, the absorptance of the solar

heat collecting members

10A and 10B varies depending on the wavelength of light. Such solar

heat collecting members

10A and 10B are also called selective absorbing members.

The reflectance of the solar

heat collecting members

10A and 10B is relatively low in the visible region and relatively high in the infrared region (particularly the mid-infrared region). The relationship between light reflection and radiation will be described below.

As described above, light incident on a certain member is reflected, transmitted, or absorbed. For this reason, from the point of energy conservation law, the absorption rate is shown as follows.
Absorptivity = 100%-reflectance-transmittance

The above reflectance is strictly a reflectance including not only a regular reflection component but also a diffuse reflection component. Such reflectance is measured using, for example, an integrating sphere. Moreover, when this member is a metal, the transmittance | permeability is substantially zero. If the thickness of the metal is approximately 100 nm, the incident light behaves in substantially the same manner as when the metal layer M is bulk due to the influence of free electrons.

Also, as a relationship between heat absorption and radiation, it is known that the absorptance is proportional to the emissivity. Such a relationship is also called Kirchhoff's law. According to this law, the spectral absorptance is proportional to the spectral emissivity. For example, a black body is relatively easy to absorb heat, but is relatively easy to radiate heat. On the other hand, metal is relatively difficult to radiate heat, but relatively difficult to absorb heat. Spectral emissivity is expressed as the ratio of the radiant emittance of a thermal radiator with the same temperature to the radiant emittance of a perfect radiator (black body) at a certain temperature.

In the absence of fluorescence and phosphorescence, the above formula is shown as follows:
Spectral absorptivity = 100%-Spectral reflectance-Spectral transmittance

The solar spectrum and the radiation spectrum from the black body are described below.

Fig. 12 shows the wavelength dependence of the spectral radiation distribution of sunlight. FIG. 12 shows the spectrum outside the atmosphere (air mass 0) together with the spectrum on the ground (air mass 1.5). In any spectrum, the radiant intensity in the visible region is relatively high, and the radiant intensity in the infrared region (particularly at a wavelength of 2000 nm or more) is relatively low.

Fig. 13 shows the blackbody radiation spectrum. FIG. 13 also shows changes in the peak wavelength of the black body obtained by Wien's law. According to Wien's law, the peak wavelength of light in thermal radiation is short at high temperatures and long at low temperatures. For example, in the case of 6000 K on the solar surface, the peak wavelength of the emitted light is about 0.5 μm, and in the room temperature environment (300 K), the peak wavelength of the emitted light is about 10 μm.

During solar irradiation, the temperature of the solar

heat collecting members

10A and 10B is about 400K to 500K. While most wavelengths of sunlight are less than 2 μm, most wavelengths of emitted light from the solar heat collecting members 10 A and 10 B are 2 μm or more. For this reason, the solar

heat collecting members

10A and 10B have relatively high absorptance at a short wavelength (for example, less than 2 μm), and relatively low at a long wavelength (for example, 2 μm or more). When it is low (that is, the reflectance is relatively high), heat collection can be performed efficiently.

FIG. 14 shows the wavelength dependency of the absorption rate. Here, for comparison, changes in absorption rates of general metals and silicon carbide are also shown. In general, metals have a relatively high reflectivity, and metals exhibit a relatively low absorption for light of any wavelength. On the other hand, silicon carbide exhibits a relatively high absorption rate with respect to light of an arbitrary wavelength. On the other hand, the solar

heat collecting members

10A and 10B used for heat collection preferably have a relatively high absorption rate in the visible region and relatively low in the infrared region. In particular, it is preferable that the absorptance is high (that is, the reflectance is low) at a short wavelength of less than 2 μm and low at a long wavelength of 2 μm or more.

Below, the reflectance of samples 1 to 4 will be compared and described. Samples 1 to 4 are all produced by nickel electroforming. Hereinafter, samples 1 to 4 will be described with reference to FIGS.

FIG. 15 (a) shows Samples 1 to 3, and FIG. 15 (b) shows Sample 4.

Samples

2 and 3 are different regions within the same nickel plate.

FIG. 16A shows an image of sample 1 measured with an optical microscope, and FIGS. 16B to 16D show images of sample 1 measured with SEM. The magnifications in FIGS. 16B to 16D are 1K, 10K, and 35K, respectively.

Sample 1 has an inverted moth-eye structure. In sample 1, the pitch (average distance between adjacent neighbors) is 200 nm, and the height is 400 nm. Thus, the sample 1 has convex portions formed with an average distance between adjacent neighbors smaller than the wavelength in the visible region, and the surface of the sample 1 looks black.

Sample 1 is created as follows. An aluminum layer having a thickness of 1 μm is formed on a glass substrate, and an inverted moth-eye structure is formed by repeating anodization and etching. Anodization is performed for 55 seconds at 0.3 wt% oxalic acid, 80 V, and a liquid temperature of 5 degrees. Etching is performed at a liquid temperature of 30 ° C. for 25 minutes using 1 mol / l of phosphoric acid. Anodization and etching are alternately performed. Anodization is performed 5 times in total, and etching is performed 4 times in total. As described above, a porous alumina layer having a reversed moth-eye structure is formed. Thereafter, electroplating is performed on such a porous alumina layer using a nickel electrolytic solution to form a metal layer M having a thickness of 1 mm on the porous alumina layer. Since it is difficult to easily peel off the metal layer M from the glass substrate, the glass layer is beaten and immersed in phosphoric acid for one day, and then etching is performed to release the metal layer M. Sample 1 is formed by such electroforming.

In FIGS. 16 (a), 16 (b), and 16 (c), a portion of the sample 1 that is scratched is circled. This area has a metallic luster.

FIGS. 17A and 17B show a SEM perspective image and a SEM front image of Sample 2, respectively. A micro corner cube array is provided on the surface of the sample 2. The pitch of the sample 2 shown in FIGS. 17A and 17B is 12 μm.

Sample 2 and sample 3 are produced as follows. First, a semiconductor wafer is prepared, and anisotropic etching is performed on a part of the surface of the semiconductor wafer. Thereafter, the shape of this portion of the semiconductor wafer is mechanically adjusted to form a micro corner cube array. Note that another region of the semiconductor wafer remains substantially flat. Such a semiconductor wafer is electroplated using a nickel electrolytic solution to form a metal layer M having a thickness of 1 mm on the semiconductor wafer. This metal layer M can be easily peeled from the semiconductor wafer.

Samples

2 and 3 are formed by such electroforming.

18A and 18B show a SEM perspective image and a SEM front image of Sample 4, respectively. Sample 4 has an inverted moth-eye structure. The average distance between adjacent recesses is 200 nm, and the height is 200 nm. Thus, the sample 4 has recesses formed with an average distance between adjacent neighbors smaller than the wavelength in the visible region, and the surface of the sample 4 looks black.

Sample 4 is formed as follows. First, a porous alumina layer is formed in the same manner as the formation of Sample 1. Thereafter, this formed product is used as a mold and transferred to an acrylic photocurable resin. Electroplating is performed on the acrylic photocurable resin using a nickel electrolytic solution to form a metal layer M having a thickness of 1 mm on the semiconductor wafer. This metal layer M can be easily peeled off. Sample 4 is formed by such electroforming.

Sample 1 was prepared by forming metal layer M directly on the porous alumina layer formed on the glass substrate, whereas sample 4 was light obtained by transferring the porous alumina layer formed on the glass substrate. A metal layer M is formed on the curable resin. The porous alumina layer when forming the sample 4 is formed in the same manner as the porous alumina layer of the sample 1, but the average height of the convex portions of the metal layer M formed in the sample 1 is about 400 nm. The average depth of the recesses of the metal layer M formed in is about 200 nm.

Fig. 19 shows the wavelength dependence of the reflectance of samples 1 to 4. Here, as the sample 2, nickel provided with a micro corner cube array having a pitch of 24 μm is used. Further, here, the reflectance at a wavelength of 350 nm to 2000 nm is measured using a spectrophotometer U-4100 manufactured by Hitachi, Ltd., and the reflectance at a wavelength of 2500 nm to 15000 nm is measured using an infrared reflectance meter. . For example, a main body Nicolet Avatar 370 manufactured by Thermo Fisher Scientific Co., Ltd. and a microscope Continuum are used as an infrared reflectance measuring device. Note that the reflectance is measured using three light sources having different wavelengths of emitted light. Here, since there are portions where the wavelengths of the three light sources do not overlap, the straight lines shown in the graph are not continuous.

Sample 3 has a relatively flat surface of nickel, and it is considered that a general metal reflection spectrum was obtained from the visible region to the infrared region. Since Sample 2 has a μm level structure, the reflectance is considered to remain low even in the infrared region. On the other hand, Sample 1 and Sample 4 have a structure at the nm level, and the reflectance of light having a shorter wavelength than that of the structure is low, but the reflectance of light having a relatively longer wavelength than that of the structure is comparative. It is thought that it becomes high. Such a sample 1 is used as the solar heat collecting member 10A described with reference to FIG. 1, and the sample 4 is used as the solar heat collecting member 10B described with reference to FIG.

Note that, as described above, the average height of the convex portion 10p of the sample 1 is 400 nm, whereas the average depth of the concave portion 10q of the sample 4 is 200 nm. Thus, since the degree of unevenness of sample 1 is larger than that of sample 4, the rising wavelength of reflectance of sample 1 is considered to be larger than the rising wavelength of reflectance of sample 4.

The wavelength dependency of the absorption rate will be described with reference to FIG. FIG. 20A shows the wavelength dependence of the absorption rate of

Samples

1, 3, and 4. In FIG. 19, the vertical axis represents the reflectance, but in FIG. 20A, the vertical axis represents the absorption rate.

As described above, sample 3 has a substantially flat surface, and the absorptance is relatively low over the entire wavelength. On the other hand,

Samples

1 and 4 have a moth-eye structure or an inverted moth-eye structure, and have a relatively high absorption rate at a low wavelength and a relatively low absorption rate at a high wavelength.

FIG. 20B shows the wavelength dependency of the absorption rate of the solar heat collecting member 900A shown in FIG. 33, and FIG. 20C shows the wavelength dependency of the absorption rate of the solar heat collecting member 900B shown in FIG. Showing gender. As can be understood from the comparison between FIG. 20 (a) to FIG. 20 (c), the absorption rate in the visible region of

samples

1 and 4 is relatively high. For this reason, solar heat can be absorbed efficiently.

The reflectance and absorptance of the solar heat collecting member can be calculated. In general, interfacial reflection is explained by Fresnel's law regardless of the material of the substance (metal or insulator). Here, the interface refers to a bonded surface of dissimilar materials in which a change in refractive index occurs at a thickness (for example, 1/10) or less sufficiently smaller than the wavelength of the target light. However, if the refractive index varies over a region that is equal to or longer than the wavelength, the reflection does not follow normal Fresnel law. In this case, for example, as in the effective refractive index medium theory (Effect medium theory), the virtual refractive index is set by virtually dividing into layers sufficiently thinner than the wavelength, and Fresnel reflection at all virtual interfaces is performed. Handling such as integration is required. Hereinafter, the structure of the metal layer and the model used for calculation will be described with reference to FIG.

FIG. 21 (a) is a schematic cross-sectional view of a solar heat collecting member having a moth-eye structure, which is provided with fine convex portions arranged densely. Here, as shown in FIG. 21A, a moth-eye structure including a fine convex portion in which a cross section including a vertex is substantially represented by an isosceles triangle is considered. In the calculation exemplified below, it is assumed that the refractive index (effective refractive index) of the moth-eye structure changes linearly with respect to the height of the convex portion.

The refractive index (effective refractive index) of such a moth-eye structure is equivalent to the refractive index of a laminate having a plurality of layers whose refractive index increases from the air side toward the substrate side, as shown in FIG. You can think of it. As shown in FIG. 21 (c), the refractive index of the moth-eye structure increases stepwise from the air (refractive index n = 1.00) side to the substrate side. In the illustrated calculation, the number of layers is 30 and the thickness of each layer is equal. The calculation of the reflectance is based on the effective refractive index medium theory (for example, Tatsuta Tatsuo, Applied Optics (Baifukan) Chapter 4).

Here, the angle dependency of the absorption rate will be described with reference to FIG. FIG. 22A shows the wavelength dependency of the absorption rate of the solar heat collecting member 10A. In FIG. 22, the horizontal axis represents the wavelength, and the vertical axis represents the absorption rate. Here, the solar heat collecting member 10A is a nickel layer having a height h of the convex portion of 900 nm. In addition, the calculation is performed assuming that the number of layers is 30 and the thicknesses of the respective layers are equal. Further, reflectances of 0 °, 20 °, 40 °, 60 ° and 80 ° in the front are obtained. In addition, the refractive index for each wavelength of nickel refers to the JK Consulting website (Internet http://www.krushwitz.com/ni.htm).

FIG. 22B shows the angle dependency of the absorption rate of the solar heat collecting member 900A shown in FIG. As understood from the comparison between FIG. 22A and FIG. 22B, the absorption rate of the solar heat collecting member 10A is relatively high in the visible region over an angle of 0 ° to 60 °, and the solar heat absorption is efficiently performed. It can be carried out.

Although the reflection and absorption of samples 1 to 4 produced by electroforming nickel were compared and described below, the reflection and absorption of other samples 5 to 10c will be compared and described below. Samples 5 to 10c are produced as follows.

Sample 5 has an acrylic photocurable resin layer formed in the same manner as sample 4, and this acrylic photocurable resin layer itself is used as a sample. Moreover, the film is affixed on the black acrylic board.

Sample 6 is formed as follows. First, an acrylic photocurable resin layer is formed in the same manner as the formation of the sample 5. Thereafter, the metal layer M is formed by coating the acrylic photocurable resin layer with gold. This coating is performed by sputtering, for example. For example, a quick coater (VPS-020 type manufactured by Vacuum Kiko Co., Ltd.) that is also preferably used for preventing charging during SEM observation can be used. Here, the processing time is about 3 minutes.

Sample 7 forms a porous alumina layer on a glass substrate in the same manner as the formation of sample 1, and uses this porous alumina layer itself as a sample.

Sample 8 is formed as follows. First, a porous alumina layer is formed on a glass substrate in the same manner as the formation of the sample 7, and the metal layer M is formed by coating the porous alumina layer with gold. This coating is performed by sputtering, for example. For example, a quick coater (VPS-020 type manufactured by Vacuum Kiko Co., Ltd.) that is also preferably used for preventing charging during SEM observation can be used. Here, the processing time is about 3 minutes.

Samples 9a, 9b, and 9c form a porous alumina layer on a glass substrate in the same manner as the formation of sample 1, and the porous alumina layer itself is used as a sample. However, in sample 1, the anodic oxidation time is 25 seconds and the depth of the concave portion is 400 nm, whereas in sample 9a, the anodic oxidation time is 15 seconds and the depth of the concave portion is 240 nm. In sample 9b, the anodization time is 23 seconds and the depth of the recess is 370 nm. In sample 9c, the anodization time is 31 seconds, and the depth of the recess is 500 nm.

Samples

10a, 10b, and 10c are formed as follows. First, a porous alumina layer is formed on a glass substrate similarly to the formation of samples 9a, 9b, and 9c. Thereafter, a metal layer M is formed by coating the porous alumina layer with gold. This coating is performed by sputtering, for example. For example, a quick coater (VPS-020 type manufactured by Vacuum Kiko Co., Ltd.) that is also preferably used for preventing charging during SEM observation can be used. Here, the processing time is about 3 minutes.

FIGS. 23 (a) to 23 (j) show schematic diagrams of Samples 5 to 10c, respectively.

FIG. 24 shows the wavelength dependence of the reflectance of samples 5 to 8, and FIG. 25 shows the wavelength dependence of the reflectance of samples 9a to 10c. 24 and 25 show the results of measuring the reflectance of samples 5 to 10c over a wavelength range of 350 nm to 2000 nm using a spectrophotometer U-4100 manufactured by Hitachi, Ltd. FIG.

As shown in FIG. 24, in the sample 5 provided with the photocurable resin layer having the moth-eye structure, the reflectance remains low from the wavelength of 350 nm to 2000 nm, whereas the moth-eye structure is formed on the photocurable resin layer. It can be seen that in the sample 6 provided with the metal layer M, the reflectance increases from the region exceeding the wavelength of 800 nm. However, the photocurable resin layer does not reflect light, but transmits light, so that the sample 5 cannot efficiently absorb solar heat. The sample 6 is used as the solar heat collecting member 10A described with reference to FIG.

Each of Sample 7 and Sample 8 has an inverted moth-eye structure, but Sample 7 laminated with glass / aluminum / alumite has a relatively high reflectance even in the visible region (wavelength 350 nm to 800 nm). When the wavelength is longer than 800 nm, it further increases. On the other hand, in the sample 8, the metal layer M is provided on the surface and absorbs light in the visible region, so that the reflectance in the visible region is particularly low. Note that the difference in reflectance between the sample 7 and the sample 8 in the visible region can also be confirmed visually. The sample 8 is used as the solar heat collecting member 10B described with reference to FIG.

As shown in FIG. 25, the reflectivities of the glass / aluminum / alumite laminated samples 9a, 9b, 9c are relatively high in the visible region (350 nm to 800 nm), respectively, and further increase when the wavelength is longer than 800 nm.

The reflectance of the

samples

10a, 10b, and 10c in which the metal layer M is further laminated on the glass / aluminum / alumite differs in the wavelength at which the reflectance starts to increase depending on the height of the recess. Specifically, when the depth of the recess is 250 nm, the reflectance starts increasing from a wavelength of about 500 nm, and when the depth of the recess is 370 nm, the reflectance starts increasing from a wavelength of about 600 nm. When the depth of the recess is 500 nm, the reflectance starts increasing from a wavelength of about 800 nm. This is considered to be because when the concave portion is deep, the refractive index gradually changes under the influence of the shape of the metal layer M even with long-wavelength light, and reflection is easily suppressed.

Such samples

10a, 10b, and 10c are used as the solar heat collecting member 10B described with reference to FIG.

As can be understood from the comparison of the samples 9a, 9b, and 9c, in the absence of the metal layer M, the reflectance does not change so much regardless of the height of the concave portion of the porous alumina layer. On the other hand, as understood from the comparison of the

samples

10a, 10b, and 10c, when the metal layer M is provided, the wavelength at which the reflectance rises according to the height of the convex portion of the metal layer M increases. Further, as understood from the comparison of the

samples

10a, 10b, and 10c, when the metal layer M is provided, the change in the reflectance with respect to the wavelength increases as the height of the convex portion increases. This is presumably because the influence of interference increases depending on the height of the convex portion.

In the above description, the case where the solar

heat collecting members

10A and 10B are made of nickel or gold has been described, but the present invention is not limited to this.

Here, referring again to FIG. 21, the wavelength dependence of the reflectance of the solar heat collecting member 10A will be described. In the illustrated calculation, the number of layers is 30 and the thickness of each layer is equal. Here, as the metal layer M, five types of gold, aluminum, copper, silver, and nickel, and the height h of the convex portion are required to have reflectances of three types of 300 nm, 900 nm, and 3000 nm. In addition, the refractive index for each wavelength of gold, aluminum, copper, and silver is based on Keiji Keiei, Basic Physical Properties Chart, Kyoritsu Publishing Co., Ltd. As mentioned above, the refractive index for each wavelength of nickel is JK. Consulting website (Internet http://www.krushwitz.com/ni.htm).

FIG. 26 to FIG. 30 show the calculation results of the reflectance of the solar heat collecting member 10A having a moth-eye structure including convex portions having a height of 300 nm, 900 nm, and 3000 nm for gold, aluminum, copper, silver, and nickel, respectively. It is a graph, and a horizontal axis is a wavelength (nm). Here, the pitch of the convex portions is 200 nm.

In any of the five types of gold, silver, copper, aluminum, and nickel, light is easily absorbed in the visible region and easily reflected in the infrared region due to the moth-eye structure in which the refractive index changes slowly. Further, the lower the convex portion, the smaller the wavelength at which the reflectance starts to increase, and the change in reflectance with respect to the change in wavelength becomes severe. On the other hand, the higher the convex portion, the larger the wavelength at which the reflectance starts to increase, and the change in reflectance with respect to the change in wavelength becomes slower.

Although the wavelength dependence of the reflectance of the solar heat collecting member 10A having a moth-eye structure including a convex portion has been described with reference to FIGS. The member 10B also shows the same tendency. That is, the shallower the recess, the smaller the wavelength at which the reflectance starts to increase, and the change in reflectance with respect to the change in wavelength becomes more severe. On the other hand, the deeper the recess, the larger the wavelength at which the reflectance starts to increase, and the change in reflectance with respect to the change in wavelength becomes slower. As described above, when the height of the convex portion (or the depth of the concave portion) is large (for example, about 3 μm), the reflectance on the long wavelength side is lowered, and accordingly, the emissivity is increased. It is understood.

FIG. 31 shows a schematic diagram of the solar heat collector 100 of the present embodiment. The solar heat collector 100 includes solar

heat collecting members

10A, 10B, 10a, or 10b and a path 120 through which the heat medium can move. The solar heat collecting member 10 A, 10 B, 10 a, or 10 b is disposed on the surface of the solar heat collector 100. The solar heat collector 100 is preferably arranged at a place where sunlight is directly applied to the solar

heat collecting members

10A, 10B, 10a, or 10b at least at a certain time in fine weather. The outer wall of the path 120 may be in direct contact with the solar

heat collecting members

10A, 10B, 10a, or 10b.

In FIG. 31, the entire solar

heat collecting members

10A and 10B are shown in contact with the outer wall of the path, but a part of the solar

heat collecting members

10A, 10B, 10a or 10b is in contact with the outer wall of the path. The other parts of the solar

heat collecting members

10A, 10B, 10a or 10b may not be in contact with the outer wall of the path. Alternatively, a vacuum may be maintained between the path 120 and the solar

heat collecting members

10A, 10B, 10a, or 10b.

The solar heat collector 100 may be a flat plate heat collector. Further, the heat medium may be circulated naturally or may be forcibly retained. Alternatively, the solar heat collector 100 may be a vacuum tube type heat collector. In this case, for example, the solar

heat collecting member

10A or 10B may be used as the outer wall itself of the path through which the heat medium in the vacuum tube passes or a member that contacts the outer wall. Alternatively, the solar heat collector 100 may be a concentrating heat collector.

Further, the heat medium may be a liquid such as water or an antifreeze, or may be a gas such as air.

The solar heat collector 100 may be used for thermoelectric power generation. Or you may use the solar-heat collector 100 for a hot-water supply system.

FIG. 32 shows a schematic diagram of the hot water supply system 200 of the present embodiment. The hot water supply system 200 includes a solar heat collector 100 and a heat storage tank 210. The heat storage tank 210 can store heat collected in the solar heat collector 100. Here, the heat medium is antifreeze.

For example, the heat storage tank 210 has a heat exchanger 212 that exchanges heat from a heat medium that conveys the heat collected in the solar heat collector 100. In the heat exchanger 212, heat from the heat medium is transferred to water. The hot water supply system 200 may further include a heat source 300. The heat source 300 is, for example, a boiler. The heat source 300 can supply heat even when the heat storage in the heat storage tank 210 is insufficient.

According to the present invention, heat can be collected efficiently. Moreover, according to this invention, a solar-heat collection member can be produced simply.

M metal layer

10A, 10B Solar heat collecting member 100 Solar heat collector

Claims

A solar heat collecting member comprising a metal layer having a surface,
The surface of the metal layer has a moth-eye structure including a plurality of convex portions or an inverted moth-eye structure including a plurality of concave portions,
The solar heat collecting member, wherein a two-dimensional size of each of the plurality of convex portions or the plurality of concave portions when viewed from the normal direction is 50 nm or more and less than 380 nm.
2. The solar heat collecting member according to claim 1, wherein an average distance between the plurality of recesses or the plurality of recesses when viewed from the normal direction is 50 nm or more and less than 380 nm.
The solar heat collecting member according to claim 1 or 2, wherein a flange portion is provided between two adjacent convex portions of the plurality of convex portions or two adjacent concave portions of the plurality of concave portions.
4. The average distance between adjacent ones of the plurality of convex portions or the plurality of concave portions is smaller than the two-dimensional size of each of the plurality of convex portions or the plurality of concave portions. 5. Solar heat collecting member.
The solar heat collecting member according to any one of claims 1 to 4, wherein an average height of the plurality of convex portions or an average depth of the plurality of concave portions is 50 nm or more and less than 500 nm.
The solar heat collecting member according to any one of claims 1 to 5, wherein the surface of the metal layer has an inverted moth-eye structure including the plurality of recesses.
The solar heat collecting member according to any one of claims 1 to 6, wherein the metal layer includes at least one selected from the group consisting of gold, silver, copper, aluminum, nickel, zinc, platinum, tungsten, and tantalum. .
An aluminum layer;
The solar heat collecting member according to any one of claims 1 to 7, further comprising a porous alumina layer positioned between the aluminum layer and the metal layer.
The solar heat collecting member according to any one of claims 1 to 8, wherein the plurality of convex portions or the plurality of concave portions have no periodicity.
A method for producing a solar heat collecting member having a surface of a moth-eye structure including a plurality of convex portions or an inverted moth-eye structure including a plurality of concave portions,
(A) preparing a mold substrate having an aluminum layer or an aluminum substrate;
(B) A porous layer that defines a plurality of fine recesses by partially anodizing the aluminum layer or the aluminum substrate, and a barrier layer provided at the bottom of each of the plurality of fine recesses Forming a porous alumina layer having:
(C) after the step (b), performing the etching by bringing the porous alumina layer into contact with an etching solution, and enlarging the plurality of fine recesses of the porous alumina layer;
(D) forming a metal layer on the plurality of fine concave portions of the porous alumina layer.
The method for producing a solar heat collecting member according to claim 10, wherein electroplating or vapor deposition is performed in the step (d).
(E) The method for producing a solar heat collecting member according to claim 10 or 11, further comprising a step of peeling the metal layer from the porous alumina layer.
A method for producing a solar heat collecting member having a surface of a moth-eye structure including a plurality of convex portions or an inverted moth-eye structure including a plurality of concave portions,
(A) preparing a mold substrate having an aluminum layer or an aluminum substrate;
(B) A porous layer that defines a plurality of fine recesses by partially anodizing the aluminum layer or the aluminum substrate, and a barrier layer provided at the bottom of each of the plurality of fine recesses Forming a porous alumina layer having:
(C) after the step (b), performing the etching by bringing the porous alumina layer into contact with an etching solution, and enlarging the plurality of fine recesses of the porous alumina layer;
(D) producing a mold having a plurality of fine convex portions corresponding to the plurality of fine concave portions of the porous alumina layer;
(E) A method for producing a solar heat collecting member, comprising a step of forming a metal layer on the mold.
The step (d)
A step of curing the photocurable resin by irradiating the photocurable resin with ultraviolet rays in a state in which the photocurable resin is applied to the plurality of fine recesses of the porous alumina layer;
The method for producing a solar heat collecting member according to claim 13, further comprising a step of peeling the photocurable resin from the porous alumina layer.
The method for producing a solar heat collecting member according to claim 13 or 14, wherein electroplating or vapor deposition is performed in the step (d).
(F) The method for producing a solar heat collecting member according to any one of claims 13 to 15, further comprising a step of peeling the metal layer from the mold.
The solar heat collection according to any one of claims 10 to 16, further comprising a step of repeating the step (b) and the step (c) until adjacent fine concave portions among the plurality of fine concave portions are continuous. A method for producing a thermal member.