Heat storage material and method for manufacturing the same

Abstract

By using a metal layer with an uneven surface, a heat storage material is provided that possesses light absorption and heat storage properties that are normally incompatible. [Solution] A heat storage material comprising a metal layer containing an uneven surface, and a heat storage member bonded to the metal layer and temporarily storing the heat obtained by the metal layer, wherein the height of the uneven surface is 100 nm or more and 1000 nm or less.

Description

[Technical Field]

[0001] The present invention relates to a heat storage material and a method for producing the same. [Background technology]

[0002] In recent years, the use of light-absorbing and heat-storing materials has been expanding in solar thermal power generation and space equipment. Ideally, these materials should absorb visible electromagnetic waves (light) and emit little infrared electromagnetic waves (light). One example of a light-absorbing material is black electroless nickel plating (see, for example, Non-Patent Document 1). This process involves oxidizing the nickel plating on the surface of an object to create a micro-textured surface, thereby blackening the surface and using it as a light-absorbing material. Furthermore, a technique has been demonstrated in which a resin with a microstructure on its surface is manufactured by injection molding using a mold with a metal surface having a micro-textured shape (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2004-261910 [Non-patent literature]

[0004] [Non-Patent Document 1] "Black Electroless Nickel Plating," Surface Technology, Vol. 66, No. 11, 503-506, 2015. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, the black material shown in Non-Patent Document 1 has the problem of exhibiting high radiation even in the far-infrared region and not showing excellent heat storage properties. Furthermore, the invention described in Patent Document 1 is made by injection molding of resin using a mold, and it is not possible to mold a metal film in a highly versatile form, making it difficult to apply to various products and posing challenges to its practicality. [Means for solving the problem]

[0006] The present invention has been made in view of the above problems, and aims to provide a heat storage material having the characteristics of absorbing visible light and near-infrared rays (i.e., low reflectivity) and low far-infrared radiation (i.e., high reflectivity), which are normally incompatible, and a method for manufacturing the same.

[0007] The heat storage material according to the present invention is characterized in that it comprises a metal layer containing an uneven surface on the surface of the heat storage member, wherein the height of the uneven surface is 100 nm or more and 1000 nm or less.

[0008] The present invention relates to a method for manufacturing a heat storage material, characterized by comprising: a first step of forming an uneven shape of a metal oxide; a second step of forming a metal layer on the uneven shape of the metal oxide; and a third step of bonding a heat storage member to the side of the metal layer opposite to the uneven shape of the metal oxide. [Effects of the Invention]

[0009] According to the present invention, by using a metal layer having an uneven surface, it is possible to provide a heat storage material that has light absorption and heat storage properties that are normally incompatible. [Brief explanation of the drawing]

[0010] [Figure 1A] This is a schematic diagram showing an embodiment of the heat storage material of the present invention. [Figure 1B] This is a schematic diagram showing an embodiment of the heat storage material of the present invention. [Figure 1C] This is a schematic diagram showing an embodiment of the heat storage material of the present invention. [Figure 2A] This is a schematic diagram showing an embodiment of the heat storage material of the present invention. [Figure 2B] This is a schematic diagram showing an embodiment of the heat storage material of the present invention. [Figure 3A] This is a process diagram showing one embodiment of the method for manufacturing the heat storage material of the present invention. [Figure 3B] This is a process diagram showing one embodiment of the method for manufacturing the heat storage material of the present invention. [Figure 3C] It is a process diagram showing an embodiment of a method for manufacturing a heat storage material of the present invention. [Figure 3D] It is a process diagram showing an embodiment of a method for manufacturing a heat storage material of the present invention. [Figure 3E] It is a process diagram showing an embodiment of a method for manufacturing a heat storage material of the present invention. [Figure 3F] It is a process diagram showing an embodiment of a method for manufacturing a heat storage material of the present invention. [Figure 3G] It is a process diagram showing an embodiment of a method for manufacturing a heat storage material of the present invention. [Figure 3H] It is a process diagram showing an embodiment of a method for manufacturing a heat storage material of the present invention. [Figure 4] It is an electron microscope observation diagram of a partial cross section of the heat storage material obtained in Example 1. [Figure 5] It is a measurement result of the reflectance spectrum in the visible light region of the heat storage materials obtained in Example 1 and Example 3 and the heat storage material obtained in Comparative Example 1. [Figure 6] It is a measurement result of the reflectance spectrum in the infrared region of the heat storage materials obtained in Example 1 and Example 3 and the heat storage material obtained in Comparative Example 1. [Figure 7] It is an electron microscope observation diagram of the cross section of the heat storage material obtained in Example 3. [Figure 8] It is a schematic diagram showing an embodiment of an article of the present invention. [Figure 9A] It is a schematic diagram showing an embodiment of an article of the present invention. [Figure 9B] It is a schematic diagram showing an embodiment of an article of the present invention. [Figure 10] It is a schematic diagram showing an embodiment of an article of the present invention.

Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail.

[0012] One embodiment of the heat storage material of the present invention (for example, a heat storage device or clothing) is characterized in that, as shown in Figure 2A, the surface of the heat storage member 5 is provided with a metal layer 1 containing fine irregularities, and the height of the fine irregularities is 100 nm or more and 1000 nm or less. (The fine irregularities may be simply referred to as irregularities or fine irregularities.) The heat storage member 5 is an element that temporarily stores the heat obtained by the metal layer 1, and the heat storage material contained in the heat storage member 5 is not particularly limited as long as it has a large heat capacity, and may be a material containing any of water, paraffin, oil, fiber, sand, salt, metal, alloy, or metal oxide. Among the alloys of the heat storage material, Al-Si alloy is particularly desirable because it has excellent heat storage properties. Among the metal oxides of the heat storage material, magnesium oxide, calcium oxide, or lithium silicate are desirable because they have excellent heat storage properties. Among the metals of the heat storage material, aluminum is particularly desirable because it has excellent heat storage properties. As heat storage materials, sodium nitrate-potassium nitrate-sodium nitrite mixed molten salts, hydroxide-based mixed molten salts, alkali carbonates, or alkali halide molten salts are particularly desirable because they have excellent heat storage properties.

[0013] The heat storage member 5 may have a base material (not shown) provided between the metal layer 1 and the heat storage material. The shape of the base material (not shown) can be any shape that can be made according to the purpose of use, and examples include, but are not limited to, flat plates, films, and sheets. Examples of materials for the base material (not shown) include, but are not limited to, metals, glass, ceramics, wood, paper, and resins. Examples of resins include polyester, triacetylcellulose, cellulose acetate, polyethylene terephthalate, polypropylene, polystyrene, and polycarbonate. Examples of thermoplastic resins include films and molded products of polymethyl methacrylate, ABS resin, polyphenylene oxide, polyurethane, polyethylene, and polyvinyl chloride. Furthermore, examples of thermosetting resins include unsaturated polyester resin, phenolic resin, crosslinked polyurethane, crosslinked acrylic resin, and crosslinked saturated polyester resin.

[0014] As shown in Figure 2B, in another embodiment of the present invention, the metal layer 1 and the heat storage member 5 may be bonded together by an adhesive layer 6. The adhesive layer 6 can be any layer that can bond the metal layer 1 and the heat storage member 5, but examples include a layer made of a cured adhesive resin (e.g., epoxy resin), double-sided tape, etc.

[0015] Figures 2A and 2B show a member (shown in Figure 1C, described later) having a metal layer 1 with a fine, uneven surface 3 of transparent metal oxide and a metal oxide layer 4. However, instead of the film shown in Figure 1C, the member may have the film shown in Figure 1A or 1B, described later.

[0016] Highly conductive metals such as aluminum and nickel emit little far-infrared radiation and have heat storage properties, but do not exhibit light absorption. On the other hand, micro-rough surfaces with subwavelength structures smaller than the wavelength of visible light are known to have an anti-reflective effect, and by continuously changing the spatial occupancy rate of the structural parts, they are known to exhibit excellent wavelength band characteristics and incident angle characteristics. Therefore, when a metal surface is made micro-rough, reflection from the metal surface is suppressed over a wide wavelength range of visible light, the reflectivity across the entire visible light range decreases, it appears black, and light absorption is exhibited. Furthermore, by using highly conductive metals such as aluminum and nickel in metals with such micro-rough surfaces, far-infrared radiation is reduced. Thus, it is thought that metal components with a micro-rough surface structure can possess both light absorption and heat storage properties. The visible range is, for example, the wavelength range from 360 nm to 1000 nm. Far-infrared radiation is, for example, the wavelength range of 2 μm or more. However, the light-absorbing material described in Non-Patent Document 1 has a surface with fine irregularities obtained by oxidizing the nickel surface, but it emits a large amount of radiation (low reflectivity) even in the far-infrared region and does not exhibit heat storage properties. From this, the inventors have found that, in addition to the heat storage properties of the metal itself, the specific shape of the fine irregularities on the metal surface is important for exhibiting light absorption and heat storage properties, and have completed the present invention (the fine irregularities may be referred to as fine irregularities or simply irregularities).

[0017] The heat storage material of this embodiment has specific fine irregularities on its surface, which are provided on a metal layer, thereby enabling it to exhibit both light absorption and heat storage properties. Preferably, the metal layer containing the fine irregularities of the heat storage material of this embodiment has a reflectance of 10% or less in the visible light region (550 nm) and a reflectance of 70% or more in the far-infrared light region (10 μm).

[0018] Most of the energy in sunlight is visible light. Therefore, absorbing visible light allows for more efficient energy absorption. On the other hand, when energy is absorbed and the temperature rises, it emits far-infrared radiation into the surroundings, releasing energy. Therefore, materials that emit less radiation in the far-infrared region can reduce energy emission. In other words, materials that absorb visible light and emit less radiation in the far-infrared region can efficiently absorb energy and suppress energy release, thereby storing heat. Thus, the film formed on the surface of the heat storage member of the heat storage material in this embodiment has excellent heat storage properties, and can efficiently store heat in the heat storage material of the heat storage member that is in contact with a metal layer with excellent heat storage properties.

[0019] <Metal layer> First, the metal layer of the heat storage material in this embodiment will be described using Figure 1. As shown in Figure 1A, one embodiment of the metal layer 1 is a film comprising a metal layer 1 with fine irregularities 2 on its surface. As the material of the metal layer 1, a metal with high conductivity is preferred. Examples of metals with high conductivity include silver, copper, gold, aluminum, magnesium, tungsten, cobalt, zinc, nickel, and chromium, with nickel, zinc, and chromium being preferred, and nickel being particularly preferred. The fine irregularities 2 provided on the surface of the metal layer 1 are also preferably made of the above-mentioned metal with high conductivity, and more preferably made of the same metal as the metal layer 1. Furthermore, the metal layer 1 is preferably a plated layer formed by plating.

[0020] The fine uneven surface shape 2 is a fine uneven surface shape provided on one surface of the metal layer 1, and the height of the fine uneven surface shape 2 refers to the difference in height between the peaks of the protrusions and the bottoms of the recesses formed on the surface of the metal layer. The average height of the fine uneven surface shape 2 is 100 nm or more and 1000 nm or less, preferably 100 nm or more and 500 nm or less. Here, the height of the fine uneven surface shape 2 means the difference in height between the peaks and valleys as defined in "Definition and indication of surface roughness" of JIS-B-061, and corresponds to the maximum roughness (Rmax). Furthermore, in the film having the metal layer 1 of this embodiment, it is preferable that the average surface roughness Ra' obtained by expanding the centerline average roughness Ra on its surface is 1 nm or more and 50 nm or less. Here, the average surface roughness Ra' value (nm) is an extension of the centerline average roughness Ra defined in JIS B 0601 to the measurement surface in three dimensions, and is expressed as "the average of the absolute values ​​of the deviation from the reference surface to the specified surface," and is calculated using the following formula (1).

[0021]

number

[0022] In equation (1), Ra' is the average surface roughness (nm), and S0 is the area |X| when the measurement surface is assumed to be ideally flat. R -X L |×|Y T -Y B |, F(X,Y) is the height at the measurement point (X,Y) where the X coordinate is X and the Y coordinate is Y. L ~X R The range of the X coordinate of the measurement surface is Y B ~Y T is the range of the Y coordinate of the measurement surface, and Z0 is the average height within the measurement surface.

[0023] Furthermore, it is preferable that the film having the metal layer 1 of this embodiment has a specific surface area Sr of 1.0 or more and 3.0 or less. The specific surface area Sr can be calculated using the following formula (2). Sr=S / S0 formula (2)

[0024] In Equation (2), S0 is the surface area when the measurement surface is ideally flat, and S is the surface area of the actual measurement surface.

[0025] Note that the surface area of the actual measurement surface is divided into minute triangles ΔABC composed of the three data points (A, B, C) closest to the surface. Then, the area ΔS of each minute triangle is obtained using the vector product as described in the following Equation (3), and the sum of these ΔS values is the surface area S to be obtained. [ΔS(ΔABC)] 2 =[s(s - AB)(s - BC)(s - CA)] Equation (3)

[0026] In Equation (3), AB, BC, and CA are the lengths of the respective sides, and 2s = AB + BC + CA.

[0027] The height of the fine concavo-convex shaped object 2 can be determined by observing the cross-section of the metal layer 1 with a scanning electron microscope or the like. Also, the average surface roughness Ra' and the specific surface area of the surface of the film provided with the metal layer of the heat storage material of the present invention can be determined by observing the surface of the film provided with the metal layer using a scanning probe microscope or the like. The film provided with the metal layer may have an attachment on the surface of the fine concavo-convex shaped object 2 (for example, a metal oxide described later), and the average surface roughness Ra' and the specific surface area of the surface of the heat storage material provided with the metal layer are values including the attachment. In this specification, the film provided with the metal layer may be referred to as an absorptive heat storage film.

[0028] In another embodiment of the heat storage material film (film with a metal layer) of this embodiment, as shown in Figure 1B, it may have a transparent metal oxide micro-texture 3 that is in close contact with the micro-texture object 2. In yet another embodiment of the film of this embodiment, as shown in Figure 1C, it may further have a transparent metal oxide layer 4 that covers the surface of the metal oxide micro-texture 3 that is not in contact with the micro-texture object 2. Here, "in close contact" means that the metal oxide constituting the metal oxide micro-texture 3 fills the space surrounded by the micro-texture object 2 and reaches the metal layer 1. When the surface of the micro-texture object 2 is provided with the micro-texture 3 and the metal oxide layer 4, it is preferable that the average surface roughness Ra' and specific surface area of ​​the surface are such that the average surface roughness Ra', obtained by extending the centerline average roughness Ra, is 1 nm or more and 50 nm or less. It is also preferable that the specific surface area Sr of the surface of the micro-texture object 2 is 1.0 or more and 3.0 or less.

[0029] The material of the metal oxide with fine irregularities 3 is not particularly limited, but it is preferably mainly composed of alumina, and more preferably contains plate-like crystals mainly composed of alumina. The plate-like crystals mainly composed of alumina are formed from plate-like crystals mainly composed of aluminum oxide or hydroxide or hydrates thereof, and a particularly preferred crystal is boehmite. Here, the plate-like crystals mainly composed of alumina may be plate-like crystals consisting only of alumina, or they may be plate-like crystals containing trace amounts of zirconium, silicon, titanium, zinc, etc.

[0030] The fine uneven surface 3 of the metal oxide can protect the fine uneven surface 2. Furthermore, when the fine uneven surface 3 of the metal oxide is a plate-like structure of plate-like crystals mainly composed of alumina, it is preferable that the plate-like crystals mainly composed of alumina are arranged perpendicular to the plane direction of the metal layer 1, and that their spatial occupancy rate changes continuously.

[0031] The material of the metal oxide layer 4 is not particularly limited, but it is preferable that it contains an amorphous gel of alumina. The metal oxide layer 4 increases the surface hardness of the film of the present invention while decreasing its absorbance. Therefore, the thickness of the metal oxide layer 4 should be appropriately determined to satisfy the required hardness and absorbance.

[0032] The aluminum, silicon, and other elements in the finely textured object 2, the finely textured object 3, and the metal oxide layer 4 can be detected by energy-dispersive X-ray analysis (EDX) during surface or cross-sectional observation using a scanning electron microscope (SEM) or transmission electron microscope (TEM). They can also be detected by X-ray electron spectroscopy (XPS). The same applies to the metal elements in the metal layer 1, such as silver, copper, gold, aluminum, magnesium, tungsten, cobalt, zinc, nickel, and chromium. In other words, they can be detected by energy-dispersive X-ray analysis (EDX) or X-ray electron spectroscopy (XPS) during surface or cross-sectional observation using a scanning electron microscope (SEM) or transmission electron microscope (TEM). When the finely textured object 2, the finely textured object 3, or the metal oxide layer 4 are present, the proportion changes in the direction perpendicular to the surface direction of the metal layer 1. In other words, the proportion of metal oxides such as aluminum decreases relatively from the surface (metal oxide layer 4) towards the interior (metal layer 1), while the proportion of metal elements constituting metal layer 1 and the finely textured object 2 increases, until finally only metal elements are detected.

[0033] <Method for manufacturing heat storage materials> The method for manufacturing the heat storage material of this embodiment will be described below with reference to Figure 3.

[0034] The method for manufacturing the heat storage material of this embodiment includes a first step of forming a fine uneven shape of a metal oxide, and a second step of forming a metal layer 1 on the fine uneven shape of the metal oxide. Furthermore, it includes a step of bonding a heat storage member 5 to the side of the metal layer 1 opposite to the side in contact with the fine uneven shape 3 of the metal oxide.

[0035] (Step 1: Process for creating a fine, uneven surface on a metal oxide) In the first step, a fine, uneven shape is formed in the metal oxide that will serve as the mold.

[0036] The material for the metal oxide with a finely textured surface is not particularly limited, but it is preferable that it be mainly composed of alumina. The finely textured surface can be formed by known vapor phase methods such as chemical vapor deposition (CVD) and physical vapor deposition (PVD), as well as by liquid phase methods of sol-gels. These methods can be used to create a metal oxide with a finely textured surface containing plate-like crystals mainly composed of alumina. Among these, a method of growing alumina plate-like crystals by treating an aluminum-containing film with hot water is preferred.

[0037] Examples of aluminum-containing films include alumina gel films formed by applying a sol-gel coating solution containing an aluminum compound, and films containing metallic aluminum formed by dry deposition methods such as vacuum deposition or sputtering. It is preferable to use an alumina gel film to form the fine surface texture of the metal oxide because it allows for easy adjustment of reactivity and the height of the fine surface texture of the metal oxide.

[0038] Aluminum compounds such as aluminum alkoxides, aluminum halides, and aluminum salts can be used as raw materials for alumina gel films. From the viewpoint of film-forming properties, it is preferable to use aluminum alkoxides.

[0039] Examples of aluminum compounds include aluminum alkoxides such as aluminum ethoxide, aluminum isopropoxide, aluminum-n-butoxide, aluminum-sec-butoxide, and aluminum-tert-butoxide. Other examples include their oligomers, aluminum halides such as aluminum chloride, aluminum salts such as aluminum nitrate, aluminum acetate, aluminum phosphate, and aluminum sulfate, as well as aluminum acetylacetonate and aluminum hydroxide.

[0040] Furthermore, the alumina gel film may contain other compounds. Examples of other compounds include zirconium, silicon, titanium, zinc alkoxides, halides, salts, and combinations thereof. By including other compounds in the alumina gel film, the height of the fine surface irregularities of the metal oxide formed can be increased compared to cases where these compounds are not included.

[0041] The alumina gel film is formed on a base substrate by applying a sol-gel coating solution containing an aluminum compound, as shown below. The sol-gel coating solution is prepared by dissolving the aluminum compound in an organic solvent. The amount of organic solvent to the aluminum compound is preferably about 20 times in molar ratio.

[0042] As organic solvents, alcohols, carboxylic acids, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, esters, ketones, ethers, or mixtures thereof can be used. Examples of alcohols include methanol, ethanol, 2-propanol, butanol, 2-methoxyethanol, 2-ethoxyethanol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol. Other examples include 1-propoxy-2-propanol, 4-methyl-2-pentanol, 2-ethylbutanol, 3-methoxy-3-methylbutanol, ethylene glycol, diethylene glycol, and glycerin. Examples of carboxylic acids include n-butyric acid, α-methylbutyric acid, isovaleric acid, 2-ethylbutyric acid, 2,2-dimethylbutyric acid, 3,3-dimethylbutyric acid, 2,3-dimethylbutyric acid, and 3-methylpentanoic acid. Other examples include 4-methylpentanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, 2,2-dimethylpentanoic acid, 3,3-dimethylpentanoic acid, 2,3-dimethylpentanoic acid, 2-ethylhexanoic acid, and 3-ethylhexanoic acid. Aliphatic or alicyclic hydrocarbons include, for example, n-hexane, n-octane, cyclohexane, cyclopentane, and cyclooctane. Aromatic hydrocarbons include, for example, toluene, xylene, and ethylbenzene. Esters include, for example, ethyl formate, ethyl acetate, n-butyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, and ethylene glycol monobutyl ether acetate. Ketones include, for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Ethers include, for example, dimethoxyethane, tetrahydrofuran, dioxane, and diisopropyl ether. Among these, it is preferable to use alcohol from the viewpoint of the stability of the sol-gel coating solution.

[0043] When using aluminum alkoxide as the aluminum compound, its high reactivity to water can cause rapid hydrolysis of the aluminum alkoxide due to moisture in the air or the addition of water, resulting in turbidity and precipitation of the sol-gel coating solution. To prevent this, it is preferable to add a stabilizer to the sol-gel coating solution to stabilize it. Suitable stabilizers include β-diketone compounds, β-ketoester compounds, and alkanolamines. Examples of β-diketone compounds include acetylacetone, trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, 3-methyl-2,4-pentanedione, and 3-ethyl-2,4-pentanedione. Examples of β-ketoester compounds include methyl acetoacetate, ethyl acetoacetate, butyl acetoacetate, hexyl acetoacetate, allyl acetoacetate, and benzyl acetoacetate. Other examples include iso-propyl acetoacetate, 2-methoxyethyl acetoacetate, sec-butyl acetoacetate, tert-butyl acetoacetate, and iso-butyl acetoacetate. Examples of alkanolamines include monoethanolamine, diethanolamine, and triethanolamine. The amount of stabilizer relative to the aluminum alkoxide is preferably about 1 in molar ratio.

[0044] A catalyst may be used to accelerate the hydrolysis reaction of aluminum alkoxides. Examples of catalysts include nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, and ammonia.

[0045] Furthermore, water-soluble organic polymer compounds can be added to the alumina gel film as needed. The water-soluble organic polymer compounds readily dissolve from the alumina gel film upon immersion in hot water, thereby increasing the surface area for reaction between the aluminum compound and the hot water, enabling the formation of fine uneven surfaces at low temperatures and in a short time. In addition, by changing the type and molecular weight of the added organic polymer, it is possible to control the height of the formed fine uneven surfaces. Polyether glycols such as polyethylene glycol and polypropylene glycol are preferred as organic polymers because they readily dissolve from the alumina gel film upon immersion in hot water. The amount of polyether glycols in the alumina gel film is preferably in the range of 0.1 to 10 times the weight of the aluminum compound by weight.

[0046] A method for manufacturing the fine uneven surface of a metal oxide is described with reference to Figures 3A and 3B. An aluminum compound, and optionally other compounds, stabilizers, and water-soluble organic polymer compounds, are dissolved or suspended in an organic solvent to prepare a sol-gel coating solution. This sol-gel coating solution is applied to a base substrate 8 and dried to form an alumina gel film as an aluminum-containing film 7. Alternatively, a film containing metallic aluminum as an aluminum-containing film 7 is formed on the base substrate 8 by dry deposition such as vacuum deposition or sputtering. The material of the base substrate 8 is not particularly limited, and various materials such as glass, plastic, and metal can be used. When forming an alumina gel film using a sol-gel coating solution that does not contain stabilizers, it is preferable to use an inert gas atmosphere such as dry air or dry nitrogen for the coating. The relative humidity of the dry atmosphere is preferably 30% or less. As a solution coating method for forming the alumina gel film, known coating methods such as dipping, spin coating, spraying, printing, flow coating, and combinations thereof can be appropriately employed. The film thickness can be controlled by changing the pulling speed in the dipping method and the substrate rotation speed in the spin coating method, as well as by changing the concentration of the sol-gel coating solution. Drying can be done at room temperature for about 30 minutes. If necessary, drying or heat treatment can be performed at a higher temperature, and the higher the heat treatment temperature, the more stable the fine irregular shape 3 of the metal oxide can be formed in the immersion treatment described later. A suitable film thickness for the aluminum-containing film 7 is 100 nm to 600 nm, preferably 100 nm to 300 nm, and more preferably 100 nm to 200 nm.

[0047] Next, the aluminum-containing film 7 is immersed in hot water to form a fine, uneven surface of alumina. When the alumina gel film is immersed in hot water, the surface layer of the alumina gel film undergoes gelatinization, and some components dissolve. However, due to differences in the solubility of various hydroxides in hot water, plate-like crystals mainly composed of alumina precipitate and grow on the surface layer of the alumina gel film, forming a fine, uneven surface of metal oxide 3. Furthermore, if a film containing metallic aluminum is used instead of the alumina gel film, the aluminum reacts with hot water and is oxidized to alumina, after which the fine, uneven surface of metal oxide 3 is formed in the same way as when the alumina gel film is used. Therefore, if the base substrate 8 mainly contains aluminum or alumina, the process of forming the aluminum-containing film 7 on the base substrate 8 can be omitted. The temperature of the hot water is preferably 40°C or higher and less than 100°C. The immersion treatment time is preferably about 5 minutes to 24 hours. In the immersion treatment of alumina gel films with other compounds added besides alumina, the difference in solubility of each component in hot water is used to crystallize the plate-like crystals of alumina. Therefore, unlike the immersion treatment of alumina gel films containing only alumina, the size of the plate-like crystals can be controlled over a wide range by changing the composition of the inorganic components. Furthermore, the height of the fine irregularities 3 of the alumina can be adjusted by adjusting the film thickness of the aluminum-containing film 7. The average height of the fine irregularities 3 of the metal oxide is preferably 100 nm to 1000 nm, and more preferably 100 nm to 500 nm. As a result, it becomes possible to control the fine irregularities formed by the plate-like crystals over a wide range.

[0048] (Second step: Formation of the metal layer) In the second step, a metal layer is formed on the fine uneven surface of the metal oxide, and a fine uneven surface object with the transferred fine uneven surface is formed on the metal layer. Referring to Figure 3C, the step of forming the metal layer 1 on the fine uneven surface 3 of the metal oxide is described below. As a method for forming the metal layer 1, metal plating is preferred, and electroless plating is even more preferred. In electroless plating, activation is performed by applying an aqueous solution containing a palladium compound such as palladium chloride, a gold compound such as gold chloride, a silver compound such as silver chloride, a tin compound such as tin chloride, etc., to the fine uneven surface 3 of the metal oxide. Activation may also be performed by immersing the fine uneven surface 3 of the metal oxide together with the base substrate 8 in an aqueous solution containing a dissolved palladium compound. After that, the metal layer 1 is deposited on the fine uneven surface 3 of the metal oxide using an electroless plating solution. The metal ions in the electroless plating solution correspond to the metal layer of the present invention, and an electroless plating solution containing nickel ions, chromium ions, and zinc ions is preferred, and a nickel plating solution containing nickel ions is particularly preferred. Nickel plating solutions may contain phosphorus or boron components in addition to nickel. Examples of commercially available nickel plating solutions include the Top Nicolon series from Okuno Pharmaceutical Co., Ltd. The temperature of the plating solution in electroless plating is preferably 30°C to 98°C, and more preferably 50°C to 90°C. The time for electroless plating can be adjusted according to the thickness of the metal layer to be formed, and is usually from 30 seconds to 1 hour. In this way, a metal layer 1 is formed so as to fill the gaps in the fine uneven shape, and a metal layer 1 containing a fine uneven shape object 2 onto which the fine uneven shape 3 of the metal oxide has been transferred is formed. As a result, the metal layer 1 has an uneven shape corresponding to the fine uneven shape 3 of the metal oxide.

[0049] It is preferable to perform electroless plating so that the thickness of the metal layer 1 containing the fine uneven surface 2 is between 200 nm and 15,000 nm. Furthermore, the average height of the fine uneven surface 2 corresponds to the average height of the fine uneven surface 3 of the metal oxide, and is between 100 nm and 1,000 nm. When the thickness of the metal layer 1 containing the fine uneven surface 2 is 200 nm or more, the light-absorbing heat storage film of the present invention exhibits excellent light-absorbing heat storage characteristics.

[0050] After performing the electroless plating treatment described above, electroplating may be performed on the side of the metal layer 1 opposite to the side on which the fine uneven surface 2 is provided in order to increase the thickness of the metal layer 1. Known electroplating solutions can be used for the electroplating treatment, and for example, an electroplating solution containing nickel ions, iron ions, copper ions, etc. as metal ions can be used. If the same metal as the metal of metal layer 1 is used for the electroplating treatment, the thickness of the metal layer can be increased by the electroplating treatment. If a different metal than the metal of metal layer 1 is used for the electroplating treatment, the metal layer provided by the electroplating treatment becomes a heat storage member 5. In addition to inorganic salts that serve as raw materials for metal ions, conductive salts, salts for adjusting counterions, carboxylic acid-based additives to improve the homogeneity of the plating film, brighteners, etc. may be added to the electroplating solution as needed. Furthermore, the thickness of the metal layer 1 can be set to a desired thickness by adjusting the temperature of the electroplating solution, the current density, and the plating time during the electroplating process. If necessary, before the electroplating process, the side of the metal layer 1 opposite to the side with the fine irregularities 2 may be activated with an aqueous solution containing an acid or the like. Furthermore, in order to improve the quality of the film formed by the electroplating process, in addition to stirring the electroplating solution during the electroplating process, a step to remove foreign matter from the electroplating solution may also be included.

[0051] (Step 3: Bonding process for heat storage components) In the heat storage material manufacturing method of this embodiment, as shown in Figure 3D, the heat storage member 5 is bonded to the surface of the metal layer 1 obtained above that is opposite to the surface on which the fine uneven shape 2 is provided. The shape and material of the heat storage member 5 can be those described above. If the base material of the heat storage member 5 is metal, the metal that will be the base material of the heat storage member 5 may be further laminated on the surface of the metal layer 1 that is opposite to the surface on which the fine uneven shape 2 is provided. As for the method of laminating the metal, it may be laminated by the electroplating treatment described above, or it may be laminated by physical vapor deposition such as sputtering. Also, if the base material of the heat storage member 5 is resin, the heat storage member may be provided by depositing the resin that will become the heat storage member 5 on the surface of the metal layer 1 that is opposite to the fine uneven shape 3 of the metal oxide, and then curing it. The heat storage member 5 may be bonded to the metal layer 1 by an adhesive layer 6. The adhesive used for the adhesive layer 6 is not particularly limited, and any material that firmly bonds the heat storage member 5 and the metal layer 1 is acceptable.

[0052] (Step 4: Etching process) The etching process will be explained in detail using a heat storage material comprising a heat storage member 5 and an adhesive layer 6 as an example, as shown in Figures 3E to 3H. However, the heat storage member 5 may be etched with only the substrate bonded to it, and then the heat storage material may be attached to the substrate to form the heat storage member. Alternatively, the heat storage member 5 may be etched with only the substrate attached, without the adhesive layer 6, and then the heat storage material may be attached to the substrate to form the heat storage member. Note that Figure 3E is an inverted version of the heat storage material shown in Figure 3D.

[0053] First, to obtain the heat storage material of this embodiment, the base substrate 8 is removed as shown in Figure 3F. After the removal of the base substrate 8, the heat storage material has a film 7 containing aluminum on its surface. If the film 7 containing aluminum is a film containing metallic aluminum, visible light is reflected by the metallic aluminum, so as shown in Figure 3G, it is necessary to further remove the film containing metallic aluminum by etching. Also, if the film 7 containing aluminum is an alumina gel film, the alumina gel film is the metal oxide layer 4 of the heat storage member. Therefore, the alumina gel film may be removed by etching to satisfy the required surface hardness and light absorption. As an etching method, wet etching, which dissolves the film 7 containing aluminum using an acid or alkaline solution, is preferred. Examples of acids include hydrochloric acid, nitric acid, and sulfuric acid. Examples of alkalis include sodium hydroxide and potassium hydroxide. From the viewpoint of work efficiency, an etching method using an alkaline solution is more preferred. The etching concentration is preferably in the range of several percent to several tens of percent, and the etching time is preferably in the range of several hours to several days. Also, as shown in Figure 3H, the fine uneven shape 3 of the metal oxide may also be removed by etching. A heat storage member in which a metal layer 1 containing finely textured material 2 on its outermost surface is bonded to a heat storage member 5 via an adhesive layer 6 achieves particularly excellent light absorption.

[0054] The remaining metal oxides such as alumina after etching (metal oxides adhering to the metal layer) can be detected by EDX or XPS measurements during surface or cross-sectional observation using SEM or TEM.

[0055] As described above, the degree of etching should be adjusted according to the balance between the light absorption and heat storage performance and surface hardness of the desired heat storage member or metal layer. Alternatively, the etching process in this step may be performed before the bonding process of the heat storage member 5, which is the third step, and then the heat storage member 5 may be bonded.

[0056] The heat storage material of this embodiment, obtained in this way, comprises a metal layer 1 containing a finely uneven surface 2. Therefore, it absorbs visible light, resulting in a low reflectivity in the visible light region, and emits little far-infrared radiation, resulting in a high reflectivity in the far-infrared region, thus achieving excellent light absorption and heat storage characteristics.

[0057] A film containing the metal layer 1 of this embodiment (light-absorbing heat-storing film) can be provided on the surface of various components. By forming the light-absorbing heat-storing film of this embodiment on the surface of a cloth, it can be used to create clothing with heat-storing properties. Furthermore, the light-absorbing heat-storing film of this embodiment may be used as a heat-storing decorative film. For example, the light-absorbing heat-storing film of the present invention can be applied as a heat-storing decorative film to the surfaces of vehicle interiors, mobile devices, electronic devices such as home appliances, parasols, and tent equipment. Various adhesives can be used when providing the light-absorbing heat-storing film of the present invention on the surface of a component or heat-storing material. Therefore, the light-absorbing heat-storing film of the present invention can be provided on the surface of components and heat-storing materials depending on the purpose of use, and the surfaces of components and heat-storing materials are not limited to smooth surfaces, but may also have two-dimensional or three-dimensional curved surfaces.

[0058] Providing an insulating material on or around the heat-absorbing heat-storage film of this embodiment is desirable because it further enhances heat storage capacity. It is even more desirable if the insulating material is light-transmitting, as this increases the efficiency of light absorption.

[0059] The heat storage material of this embodiment has excellent light absorption and heat storage properties, so it can be used in a variety of items. For example, because it can efficiently utilize solar energy, it can be used in solar water heating systems. When used in a solar water heating system, a steam generation pipe (not shown) is passed through the heat storage member 5. At night or other times when sunlight cannot be used, an unheated heat transfer medium is flowed through this steam generation pipe, and the heat storage material contained in the heat storage member 5, whose temperature has risen, can heat the heat transfer medium.

[0060] The heat storage material of this embodiment has excellent heat storage properties, allowing for efficient use of solar energy, and can therefore be used in solar thermal power generation systems. When used in a solar thermal power generation system, steam generation piping (not shown) is passed through the heat storage member 5. At night or during times when sunlight cannot be used, an unheated heat transfer medium is flowed through this steam generation piping, and the heat storage material contained in the heat storage member 5, whose temperature has risen, heats the heat transfer medium. The heated heat transfer medium generates steam in a steam generator (not shown), and electricity can be generated by operating a steam turbine (not shown).

[0061] The heat storage material of this embodiment has excellent heat storage properties, allowing for efficient utilization of solar energy, and can therefore be used in artificial satellites. Since artificial satellites experience large temperature differences between the sun-exposed and undexposed sides, it is desirable to reduce this temperature difference by storing heat when exposed to sunlight and releasing heat when not exposed. For example, using a device having both the heat storage material and the heat release material of this embodiment, the temperature difference can be reduced as follows: When the artificial satellite is at a low temperature, the heat storage material of this embodiment is exposed to the outside by means of exposing it to store heat, thereby suppressing a decrease in temperature. When the satellite is at a high temperature, the heat release material is exposed to the outside by means of exposing it to release heat, thereby suppressing a rise in temperature. The means for exposing the heat storage material and the heat release material may be the same or different. Using this method significantly reduces the power consumption of the heating element.

[0062] The heat storage material of this embodiment has excellent heat storage properties, allowing for efficient utilization of solar energy, and can therefore be used in solar collectors and solar pots. Figure 8 shows a solar collector, which is an example of an article 20 containing the heat storage material. In article 20 as a solar collector, water can be used as the heat storage member 5, for example. The heat storage member 5 (water) is contained in a container 9. A metal layer 1 is provided on the outside of the container 9. The container 5 is positioned between the heat storage member 5 and the metal layer 1. An insulating material 10 is provided on the outside of the metal layer 1. The metal layer 1 is positioned between the insulating material 10 and the heat storage member 5. Xerogel can be used as the insulating material 10, for example. This allows solar heat to be stored in the water (heat storage member 5) contained in the container 9.

[0063] Figure 9A shows an example of an artificial satellite, which includes a heat storage material. The satellite comprises a heat control unit 11, a control unit 12, a power generation unit 13, and a communication unit 14. Figure 9B shows a cross-sectional view of the heat control unit 11 along line A-A' in Figure 9A. A metal layer 1 is provided on the heat storage member 5. The metal layer 1 is bonded to a container 5 that houses the heat storage member 5 via an adhesive layer 6 located between the metal layer 1 and the heat storage member 5. For example, paraffin can be used as the heat storage member 5. The heat control unit 11 can store heat from sunlight.

[0064] An article 20, such as an artificial satellite, can be equipped with a heat dissipation material. When a predetermined part of the article 20 (e.g., the control unit 12) is below a predetermined temperature (low temperature), heat can be stored in the heat storage material of the thermal control unit 11. When the predetermined part (e.g., the control unit 12) is above a predetermined temperature (high temperature), heat can be released from the heat dissipation material. The article 20, as an artificial satellite, can be deformed and displaced to switch between such heat storage and heat dissipation. For example, a shape in which the heat storage material faces the outside of the artificial satellite (e.g., the side opposite to the control unit 12) and the heat dissipation material faces the inside of the artificial satellite (e.g., the side of the control unit 12) is a heat storage shape. And a shape in which the heat dissipation material faces the outside of the artificial satellite (e.g., the side opposite to the control unit 12) and the heat storage material faces the inside of the artificial satellite (e.g., the side of the control unit 12) is a heat dissipation shape. The artificial satellite can be deformed to switch between the heat storage shape and the heat dissipation shape. Alternatively, the satellite can be displaced so that the heat storage material faces the heat source surrounding the satellite (e.g., the sun), and the heat dissipation material faces the opposite side of the heat source (e.g., the Earth).

[0065] The heat storage material of this embodiment can be used in combination with solar cells to create a hybrid type of photovoltaic power generation system. Solar cells can be made of silicon, organic semiconductors, organic-inorganic perovskite semiconductors, etc. By placing solar cells on the heat storage material to create a hybrid type of photovoltaic power generation unit, the heat storage material absorbs the transmitted light from the solar cells, suppressing radiation and allowing for efficient heat storage and utilization of solar heat. It is desirable to encapsulate the hybrid type of photovoltaic power generation unit in a vacuum. Encapsulation in a vacuum is desirable because it suppresses heat conduction, allowing for more efficient heat storage. It is also desirable to provide a light-transmitting insulating material in the hybrid type of photovoltaic power generation system. Examples of light-transmitting insulating materials include aerogel and xerogel.

[0066] Figure 10 shows a solar panel, which is an example of an article 20 including a heat storage material. In article 20 as a solar panel, oil can be used as the heat storage member 5. The heat storage member 5 (oil) is housed in a container 9. A metal layer 1 is provided on the outside of the container 9. The container 5 is located between the heat storage member 5 and the metal layer 1. The metal layer 1 is bonded to the heat storage member 5 via an adhesive layer 6, and the adhesive layer 6 is located between the container 5 and the metal layer 1. A photovoltaic cell 15 is provided on the outside of the metal layer 1. Silicon can be used for the photovoltaic cell 15. The metal layer 1 is located between the photovoltaic cell 15 and the heat storage member 5. An insulating material 10 is provided on the outside of the photovoltaic cell 15. The photovoltaic cell 15 is located between the insulating material 10 and the metal layer 1. The photovoltaic cell 15 is provided between the heat storage material, which includes the heat storage member 5 and the metal layer 1 provided on the heat storage member 5, and the insulating material 10. Vacuum-sealed glass can be used as the insulating material 10. This allows for the creation of a hybrid solar power generation system that can generate electricity and store heat using sunlight.

[0067] A system that utilizes the thermal energy of the sun can be called a solar thermal system. Solar thermal systems include the solar hot water supply system and solar thermal power generation system described above. A solar thermal system is equipped with the heat storage material of this embodiment, and the solar thermal system includes an article equipped with the heat storage material. The article equipped with the heat storage material may also be equipped with insulating material and heat dissipating material in addition to the heat storage material. The insulating material and heat dissipating material in the article equipped with the heat storage material may be fixed to the heat storage material. Furthermore, a solar thermal system may include other articles in addition to the article equipped with the heat storage material, such as piping, heat transfer fluid, and steam turbines. Other articles in a solar thermal system do not need to be fixed to the article equipped with the heat storage material.

[0068] A system that utilizes the light energy of the sun can be called a solar energy utilization system. Solar energy utilization systems include the solar power generation system and solar lighting system described above. A solar energy utilization system is equipped with the heat storage material of this embodiment, and the solar energy utilization system includes an article equipped with the heat storage material. The article equipped with the heat storage material may also be equipped with insulating material and heat dissipating material in addition to the heat storage material. The insulating material and heat dissipating material in the article equipped with the heat storage material may be fixed to the heat storage material. Furthermore, a solar energy utilization system may include other articles in addition to the article equipped with the heat storage material, such as wiring, batteries, and power conditioners. Other articles in a solar thermal utilization system do not need to be fixed to the article equipped with the heat storage material.

[0069] Solar thermal systems and photovoltaic systems can also be called solar systems. A solar system may include solar collectors, solar pods, and solar panels. [Examples]

[0070] The present invention will be described in more detail below using examples.

[0071] However, the present invention is not limited to the following embodiments.

[0072] The reflectance spectrum in the visible light region of the examples was measured using a lens reflectance analyzer (product name: USPM-RU III, manufactured by Olympus Corporation).

[0073] The infrared reflectance spectrum measurements in the examples were performed using a Fourier transform infrared spectrophotometer (FT / IR-6600, manufactured by JASCO Corporation).

[0074] (Example 1) An alumina sol solution was prepared by dissolving aluminum-sec-butoxide (hereinafter also referred to as "Al(O-sec-Bu)3") and ethyl acetoethyl (hereinafter also referred to as "siRNA") in 2-propanol (hereinafter also referred to as "IPA") and stirring at room temperature for approximately 3 hours. The molar ratio of each component in the alumina sol solution was Al(O-sec-Bu)3:siRNA:IPA = 1:1:20. A 0.01 M dilute hydrochloric acid aqueous solution was added to the alumina sol solution so that the amount of hydrochloric acid added was twice the molar ratio of Al(O-sec-Bu)3, and the mixture was refluxed for approximately 6 hours to prepare a sol-gel coating solution. The sol-gel coating solution was applied to a quartz glass substrate, which was the base substrate, by spin coating to form a coating film. Subsequently, the coating film was heat-treated at 100°C for 1 hour to obtain a transparent alumina gel film. Next, the alumina gel film was immersed in 80°C hot water for 30 minutes, and then dried at 100°C for 10 minutes to form an alumina layer with a finely textured surface.

[0075] An aqueous palladium chloride solution was applied to an alumina layer with a finely textured surface using a spin-coating method, and then dried at 100°C. Subsequently, the material was immersed for 1 minute in a nickel-phosphorus plating solution (phosphorus content approximately 10 wt%) set at 80°C to form a material with a finely textured surface and a nickel layer as a metallic layer.

[0076] An epoxy resin adhesive layer was applied to the side of the metal layer opposite to the alumina layer, which had a finely textured surface, and cured. A PET film was then bonded to the metal layer as a base material for the heat storage component. Subsequently, it was peeled off the quartz glass substrate. The base material was then attached to a quartz cell filled with water as a heat storage material.

[0077] (Observation of cross-sectional shape) In Example 1 described above, a nickel layer was formed on an alumina layer having a fine uneven shape. After cutting with a dicing saw, the cross-sectional thinning was performed using the focused ion beam (FIB) method, and the cross-section was observed using a scanning electron microscope (SEM). The cross-sectional observation was performed using a scanning transmission electron microscope (product name: HD-2300, manufactured by Hitachi High-Technologies Corporation). From the observation image shown in Figure 4, it can be seen that a nickel fine uneven shape object 2 is formed to fill the interior of the alumina plate-like crystal, which is the metal oxide fine uneven shape 3 formed from the alumina gel film on the base substrate 8, and the nickel layer, which is the metal layer 1, is present on top of the fine uneven shape object 2.

[0078] The average height of the finely textured object 2 obtained in Example 1 was 323 nm, the average height of the finely textured object 3 was 255 nm, and the thickness of the aluminum-containing film 7 was 68 nm. The average surface roughness Ra' was 1.0 nm, and the specific surface area was 1.0.

[0079] (evaluation) The reflectance spectra in the visible light region and the infrared region were measured for Example 1. The reflectance spectra were measured using a lens reflectance meter (product name: USPM-RU III, manufactured by Olympus Corporation), and the reflectance spectra in the infrared region were measured using a Fourier transform infrared spectrophotometer (product name: FT / IR-6600, manufactured by JASCO Corporation). The results of the visible light region reflectance spectrum measurement are shown in Figure 5, and the results of the infrared region reflectance spectrum measurement are shown in Figure 6. Table 1 shows the reflectance in the visible light and infrared regions obtained from the reflectance spectrum measurements of Example 1. From Figure 5, it can be said that Example 1 has excellent absorbance because of its low reflectance in the visible light region.

[0080] As shown in Figure 6, Example 1 exhibits superior heat storage capabilities because its reflectivity increases towards longer wavelengths in the mid-infrared and far-infrared regions.

[0081] (Comparative Example 1) For samples prepared using the same method as described in Non-Patent Document 1, the reflectance spectra in the visible light region and the infrared region were measured under the same conditions as the sample in Example 1. The results are shown in Figures 5 and 6, and Table 1.

[0082] As shown in Figure 5, Comparative Example 1, although inferior to the sample in Example 1, had a low reflectivity in the visible light to near-infrared region.

[0083] On the other hand, as shown in Figure 6, the reflectance of the sample in Comparative Example 1 was inferior to that of Example 1 in the mid-infrared and far-infrared regions.

[0084] (Example 2) Similar to Example 1, an alumina sol solution was prepared and applied to a quartz glass substrate, which was the base substrate, by spin coating to form a coated film. The coated film was then heat-treated at 100°C for 1 hour to obtain a transparent alumina gel film. Next, the alumina gel film was immersed in 80°C hot water for 30 minutes, and then dried at 100°C for 10 minutes to form an alumina layer with a fine uneven surface.

[0085] An aqueous palladium chloride solution was applied to an alumina layer with a finely textured surface using a spin-coating method, and then dried at room temperature. Subsequently, the material was immersed for 20 minutes in a nickel-phosphorus plating solution (phosphorus content approximately 10 wt%) set at 80°C to form a material with a finely textured surface and a nickel layer as a metallic layer.

[0086] Subsequently, the film was peeled off the quartz glass substrate. The total film thickness obtained was approximately 10 μm. The average height of the fine surface texture of the obtained film was 303 nm, the average height of the fine surface texture was 233 nm, and the film thickness of the aluminum-containing film was 70 nm. Furthermore, the average surface roughness Ra' of the film was 1.0 nm, and the specific surface area was 1.0.

[0087] In Examples 3 through 11, the number of gel film layers and etching conditions were varied to produce the films.

[0088] (Example 3) A film was manufactured in the same manner as in Example 2. The film, peeled from a quartz glass substrate, was etched using a 3M sodium hydroxide aqueous solution at room temperature for 50 hours as an etching step. The average height of the fine surface irregularities of the obtained film was 251 nm, the average height of the fine surface irregularities was 213 nm, the average surface roughness Ra' was 5.0 nm, and the specific surface area was 1.1. The results of the reflectance spectrum measurement in the visible light region are shown in Figure 5, and the results of the reflectance spectrum measurement in the infrared region are shown in Figure 6. Cross-sections were prepared using the FIB method, and the cross-sections were observed using a scanning electron microscope (product name: ULTRA55, manufactured by Carl Zeiss). From the observation image shown in Figure 7, it was found that fine surface irregularities 2 of nickel were formed on the nickel layer, which is the metal layer 1, and a small amount of alumina remained on top of the fine surface irregularities 2. SEM-EDX analysis and XPS measurements revealed that the alumina layer showed a relative decrease in the proportion of Al elements from the surface towards the interior in the cross-sectional thickness direction, while the proportion of Ni elements increased.

[0089] (Example 4) The film was manufactured in the same manner as in Example 3, except that the etching process involved etching with a 7.5 M sodium hydroxide aqueous solution at room temperature for 47 hours. The average height of the fine surface irregularities of the obtained film was 235 nm, the average surface roughness Ra' was 18 nm, and the specific surface area was 1.4.

[0090] (Example 5) The film was manufactured in the same manner as in Example 3, except that a nickel-phosphorus plating solution (phosphorus content approximately 1-2 wt%) was used as the plating solution. The average height of the fine surface irregularities of the obtained film was 272 nm, the average surface roughness Ra' was 3.8 nm, and the specific surface area was 1.1.

[0091] (Example 6) An alumina sol solution, as shown in Example 2, was prepared and applied to a quartz glass substrate, which was the base substrate, by spin coating to form a coated film. The coated film was then heat-treated at 100°C for 1 hour, and the same coating and drying process was repeated to obtain a transparent alumina gel film with two layers of alumina gel. The film was then manufactured in the same manner as in Example 2. The average height of the fine surface irregularities of the obtained film was 371 nm, the average height of the fine surface irregularities was 306 nm, the average surface roughness Ra' was 1.1 nm, and the specific surface area was 1.0.

[0092] (Example 7) A metal film containing an alumina layer was peeled from a quartz glass substrate, and then an etching process was performed using a 3M sodium hydroxide aqueous solution at room temperature for 50 hours. The film was manufactured in the same manner as in Example 6, except that the etching process was carried out in the same manner as in Example 6. The average height of the fine surface texture of the obtained film was 315 nm, the average surface roughness Ra' was 10 nm, and the specific surface area was 1.2.

[0093] (Example 8) The film was manufactured in the same manner as in Example 7, except that the etching process involved etching with a 7.5 M sodium hydroxide aqueous solution at room temperature for 50 hours. The average height of the fine surface irregularities of the obtained film was 303 nm, the average surface roughness Ra' was 27 nm, and the specific surface area was 1.7.

[0094] (Example 9) The film was manufactured in the same manner as in Example 2, except that the number of alumina gel layers was increased to three. The average height of the fine surface texture of the obtained film was 419 nm, the average height of the fine surface texture was 374 nm, the average surface roughness Ra' was 1.2 nm, and the specific surface area was 1.0.

[0095] (Example 10) A metal film comprising an alumina layer was peeled from a quartz glass substrate, and then the film was manufactured in the same manner as in Example 9, except that the etching process involved etching with a 3M sodium hydroxide aqueous solution at room temperature for 50 hours. The average height of the fine surface irregularities of the obtained film was 354 nm, the average surface roughness Ra' was 16 nm, and the specific surface area was 1.3.

[0096] (Example 11) The film was manufactured in the same manner as in Example 10, except that the etching process involved etching with a 6M sodium hydroxide aqueous solution at room temperature for 45 hours. The average height of the fine surface texture of the obtained film was 346 nm, the average surface roughness Ra' was 35 nm, and the specific surface area was 2.1.

[0097] Table 1 shows the reflectance in the visible light and infrared regions obtained by measuring the reflectance spectra in the visible light and infrared regions of the samples prepared in Examples 1 to 11 and Comparative Example 1.

[0098] [Table 1]

[0099] (Evaluation of heat storage capacity) (Example 12) Similar to Example 1, a sample was prepared by placing 40 ml of water in a 10 mm × 10 mm × 45 mm quartz cell. The sample, which had been left at room temperature (25°C), was irradiated with a 150 W halogen lamp from a distance of 10 mm. After irradiation, the halogen lamp was stopped and the water was left for 10 minutes, at which point the water temperature was measured using a thermocouple. The results are shown in Table 2.

[0100] (Comparative Example 2) The light-absorbing material of Comparative Example 1 was evaluated in the same manner as the sample prepared in Example 12. The results are shown in Table 2.

[0101] [Table 2]

[0102] Since the temperature raised by irradiating with the same energy was higher in Example 12 than in Comparative Example 2, it was found that heat storage was more efficient.

[0103] From the above, it was found that the heat storage material of the present invention has excellent light absorption and heat storage properties.

[0104] The present invention provides a light-absorbing heat storage film and a heat storage member that absorb visible light and near-infrared rays (low reflectivity) and emit little far-infrared radiation (high reflectivity), which are normally incompatible. The light-absorbing heat storage film and heat storage member of the present invention can be used as a heat storage member in space-related equipment such as artificial satellites and in solar thermal power generation, and can also be used as an exterior film, solar collector, etc.

[0105] The present invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are attached to make the scope of the invention public.

[0106] This application claims priority based on Japanese Patent Application No. 2020-162586, filed on September 28, 2020, and all of its contents are incorporated herein by reference.

Claims

1. A metal layer containing an uneven surface, The system comprises a heat storage member bonded to the metal layer and which temporarily stores the heat obtained by the metal layer, A heat storage material characterized in that the height of the uneven surface is 100 nm or more and 1000 nm or less.

2. The heat storage material according to claim 1, characterized in that the heat storage material included in the heat storage member is a material containing one of the following: water, paraffin, oil, fiber, sand, salt, metal, alloy, or metal oxide.

3. The heat storage material according to claim 2, characterized in that the alloy is an Al-Si alloy.

4. The heat storage material according to claim 2, characterized in that the metal oxide is magnesium oxide, calcium oxide, or lithium silicate.

5. The heat storage material according to claim 2, characterized in that the aforementioned metal is aluminum.

6. The heat storage material according to claim 2, characterized in that the salt is a sodium nitrate-potassium nitrate-sodium nitrite mixed dissolved salt, a hydroxide-based mixed dissolved salt, an alkali carbonate, or an alkali halide dissolved salt.

7. The heat storage member is characterized by comprising the heat storage material and a base material provided between the metal layer and the heat storage material, as described in any one of claims 2 to 6.

8. The heat storage material according to claim 7, characterized in that the base material is one of metal, glass, ceramics, wood, paper, or resin.

9. The heat storage material according to claim 7, wherein the base material is a metal, and is laminated on the surface of the metal layer opposite to the surface on which the uneven shape is provided.

10. The heat storage material according to any one of claims 7 to 9, characterized in that the substrate is in a planar shape, a film shape, or a sheet shape.

11. The heat storage material according to any one of claims 2 to 10, characterized in that the heat storage member includes a container for housing the heat storage material.

12. The heat storage material according to claim 11, characterized in that the metal layer and the container are bonded together by an adhesive layer.

13. The heat storage material according to any one of claims 1 to 11, characterized in that the metal layer and the heat storage member are bonded together by an adhesive layer.

14. The heat storage material according to claims 1 to 13, further comprising a metal oxide that is in contact with the aforementioned uneven-shaped object and includes an uneven shape that conforms to the unevenness of the aforementioned uneven-shaped object.

15. The heat storage material according to claim 14, characterized in that the metal oxide includes plate-like crystals mainly composed of alumina.

16. The heat storage material according to claim 14 or 15, further comprising a transparent metal oxide layer covering the surface of the metal oxide that is not in contact with the uneven surface.

17. The heat storage material according to claim 16, characterized in that the transparent metal oxide layer contains an amorphous gel of alumina.

18. The heat storage material according to any one of claims 1 to 17, characterized in that the average surface roughness Ra' is 1 nm or more and 50 nm or less.

19. A heat storage material according to any one of claims 1 to 18, characterized in that the specific surface area Sr of the surface is 1.0 or more and 3.0 or less.

20. The heat storage material according to any one of claims 1 to 19, characterized in that the material of the metal layer includes one selected from nickel, chromium, and zinc.

21. The heat storage material according to any one of claims 1 to 20, characterized in that the metal layer has a reflectance of 10% or less for light with a wavelength of 550 nm and a reflectance of 70% or more for light with a wavelength of 10 μm.

22. An article comprising a heat storage material according to any one of claims 1 to 21 and an insulating material.

23. An article comprising a heat storage material and a heat dissipation material according to any one of claims 1 to 22.

24. An article comprising a heat storage material according to any one of claims 1 to 21, a heat insulating material, and a heat dissipating material, An article characterized by undergoing at least one of deformation and displacement such that when a predetermined part of the article is below a predetermined temperature, heat is stored in the heat storage material, and when the predetermined part is above the predetermined temperature, heat is released from the heat dissipation material.

25. An article comprising a heat storage material according to any one of claims 1 to 21, and a medium heated by the heat storage material.

26. An artificial satellite having a heat storage material that stores solar energy, The aforementioned heat storage material is A metal layer containing an uneven surface with a height of 100 nm or more and 1000 nm or less, A heat storage member that temporarily stores the heat obtained by the metal layer, An artificial satellite characterized by having an adhesive layer that bonds the metal layer and the heat storage member.

27. The artificial satellite according to claim 26, wherein the heat storage member comprises paraffin as a heat storage material and a container for housing the heat storage material, and the container and the metal layer are bonded together.

28. It further includes a heat dissipation material, The artificial satellite according to claim 26 or 27, characterized in that heat is stored in the heat storage material when a predetermined portion is below a predetermined temperature, and heat is released from the heat dissipation material when the predetermined portion is above the predetermined temperature.

29. The artificial satellite according to claim 28, characterized in that it can be switched between a heat storage shape in which the heat storage material faces the outside of the artificial satellite and the heat dissipation material faces the inside of the artificial satellite, and a heat dissipation shape in which the heat storage material faces the inside of the artificial satellite and the heat dissipation material faces the outside of the artificial satellite.

30. The artificial satellite according to claim 28, characterized in that the heat storage material faces a heat source surrounding the artificial satellite, and the heat dissipation material faces the opposite side from the heat source.

31. Insulation material, Solar power generation cells and A metal layer containing an uneven surface with a height of 100 nm or more and 1000 nm or less, A heat storage member that temporarily stores the heat obtained by the metal layer, A solar panel characterized by comprising an adhesive layer for bonding the metal layer and the heat storage member.

32. The solar panel according to claim 31, wherein the heat storage member includes an oil which is a heat storage material and a container which contains the heat storage material, and the container and the metal layer are bonded together.

33. The solar panel according to claim 31 or 32, characterized in that the aforementioned insulating material is vacuum-sealed glass.

34. A solar thermal energy utilization system characterized by comprising a heat storage material according to any one of claims 1 to 21.

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