Heat storage material and its manufacturing method

Abstract

According to the present invention, a light-absorbing and heat-storing film is characterized by comprising a metal layer including a protrusion-and-recess-shaped object, wherein the average height of the protrusion-and-recess-shaped object is 100 nm to 1,000 nm.

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 heat storage materials has expanded in solar thermal power generation and space equipment. It is desirable for light-absorbing heat storage materials to absorb electromagnetic waves (light) in the visible range and emit only small amounts of electromagnetic waves (light) in the infrared range. An example of a light-absorbing material is black electroless nickel plating (see, for example, Non-Patent Document 1). This is achieved by oxidizing the nickel plating on the surface of an object to form a finely textured surface, thereby blackening the surface and making it a light-absorbing material. A technique has also been shown in which a mold with a metal surface having a finely textured surface is used to injection mold a resin with a fine structure on its surface (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-261910 [Non-patent literature]

[0004] [Non-Patent Document 1] "Black Electroless Nickel Plating", Surface Technology, Vol. 66, No. 11, 503-506, 2015 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the black material shown in Non-Patent Document 1 has a problem in that it emits a large amount of radiation even in the far-infrared region and does not exhibit excellent heat storage properties. In addition, the invention described in Patent Document 1 is based on injection molding of resin using a mold, and it is not possible to form a metal film in a versatile form, making it difficult to apply to various products and also posing a problem in terms of 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 that has the properties of absorbing visible light and near-infrared rays (i.e., low reflectance), which are normally incompatible, and emitting little far-infrared rays (i.e., high reflectance), and a method for producing the same.

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

[0008] The method for producing a heat storage material according to the present invention is characterized by comprising a first step of forming a metal oxide uneven shape, a second step of forming a metal layer on the metal oxide uneven shape, and a third step of adhering a heat storage member to the side of the metal layer opposite to the metal oxide uneven shape. [Effects of the Invention]

[0009] According to the present invention, by using a metal layer having a concave-convex shape, it is possible to provide a heat storage material having light absorption and heat storage properties, which are normally incompatible. [Brief explanation of the drawings]

[0010] [Figure 1A] 1 is a schematic diagram showing an embodiment of the heat storage material of the present invention. [Figure 1B] 1 is a schematic diagram showing an embodiment of the heat storage material of the present invention. [Figure 1C] 1 is a schematic diagram showing an embodiment of the heat storage material of the present invention. [Figure 2A] 1 is a schematic diagram showing an embodiment of the heat storage material of the present invention. [Figure 2B] 1 is a schematic diagram showing an embodiment of the heat storage material of the present invention. [Figure 3A] 1 is a process diagram showing an embodiment of a method for producing a heat storage material of the present invention. FIG. [Figure 3B] 1 is a process diagram showing an embodiment of a method for producing a heat storage material of the present invention. FIG. [Figure 3C] 1 is a process diagram showing an embodiment of a method for producing a heat storage material of the present invention. FIG. [Figure 3D] 1 is a process diagram showing an embodiment of a method for producing a heat storage material of the present invention. FIG. [Figure 3E] 1 is a process diagram showing an embodiment of a method for producing a heat storage material of the present invention. FIG. [Figure 3F] 1 is a process diagram showing an embodiment of a method for producing a heat storage material of the present invention. FIG. [Figure 3G] 1 is a process diagram showing an embodiment of a method for producing a heat storage material of the present invention. FIG. [Figure 3H] 1 is a process diagram showing an embodiment of a method for producing a heat storage material of the present invention. FIG. [Figure 4] 1 is an electron microscope image of a partial cross section of the heat storage material obtained in Example 1. FIG. [Figure 5] 1 shows the results of measuring the reflectance spectra in the visible light region of the heat storage materials obtained in Examples 1 and 3 and the heat storage material obtained in Comparative Example 1. [Figure 6] 1 shows the results of measuring the reflectance spectra in the infrared region of the heat storage materials obtained in Examples 1 and 3 and the heat storage material obtained in Comparative Example 1. [Figure 7] FIG. 10 is an electron microscope image of a cross section of the heat storage material obtained in Example 3. [Figure 8] 1 is a schematic diagram illustrating an embodiment of an article of the present invention. [Figure 9A] 1 is a schematic diagram illustrating an embodiment of an article of the present invention. [Figure 9B] 1 is a schematic diagram illustrating an embodiment of an article of the present invention. [Figure 10] 1 is a schematic diagram illustrating an embodiment of an article of the present invention. DETAILED DESCRIPTION OF THE INVENTION

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

[0012] As shown in FIG. 2A, one embodiment of the heat storage material (e.g., a heat storage device or clothing) of the present invention is characterized by comprising a metal layer 1 having fine irregularities on the surface of the heat storage member 5, the height of which is 100 nm to 1000 nm. (The fine irregularities may be simply referred to as irregularities or fine irregularities.) The heat storage member 5 is an element that temporarily stores heat acquired by the metal layer 1. 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, and metal oxide. Al-Si alloys are particularly desirable as alloys for heat storage materials, as they have excellent heat storage properties. Magnesium oxide, calcium oxide, or lithium silicate are desirable as metal oxides for heat storage materials, as they have excellent heat storage properties. Aluminum is particularly desirable as a metal for heat storage materials, as it has excellent heat storage properties. As the salt of the heat storage material, a mixed molten salt of sodium nitrate-potassium nitrate-sodium nitrite, a mixed molten salt of hydroxides, an alkali carbonate, or an alkali halide molten salt is particularly preferable because of its excellent heat storage properties.

[0013] The heat storage member 5 may have a substrate (not shown) disposed between the metal layer 1 and the heat storage material. The substrate (not shown) may have any shape suitable for its intended use, including, but not limited to, a flat plate, a film, or a sheet. Materials for the substrate (not shown) include, but are not limited to, metal, glass, ceramics, wood, paper, and resin. Resins include, but are not limited to, polyester, triacetyl cellulose, cellulose acetate, polyethylene terephthalate, polypropylene, polystyrene, and polycarbonate. Other examples include films and molded articles made of thermoplastic resins such as polymethyl methacrylate, ABS resin, polyphenylene oxide, polyurethane, polyethylene, and polyvinyl chloride. Other examples include thermosetting resins such as unsaturated polyester resin, phenolic resin, crosslinked polyurethane, crosslinked acrylic resin, and crosslinked saturated polyester resin.

[0014] 2B, in another embodiment of the present invention, the metal layer 1 and the heat storage member 5 may be bonded by an adhesive layer 6. The adhesive layer 6 may be any layer that can bond the metal layer 1 and the heat storage member 5, and examples thereof include a layer made of a cured product of an adhesive resin (such as an epoxy resin), and double-sided tape.

[0015] 2A and 2B show a member (the member shown in FIG. 1C described later) having a transparent metal oxide fine concave-convex structure 3 and a metal oxide layer 4 on the surface of a metal layer 1. However, instead of the film shown in FIG. 1C, a member having a film shown in FIG. 1A or 1B described later may be used.

[0016] Highly conductive metals, such as aluminum and nickel, emit little far-infrared light and have heat storage properties, but they do not absorb light. On the other hand, micro-textures with subwavelength structures smaller than the wavelength of visible light are known to have anti-reflection properties, and continuously varying the spatial occupancy of the structure is known to exhibit excellent wavelength band and incident angle characteristics. Therefore, micro-texturing a metal surface reduces reflection on the metal surface over a wide wavelength range of visible light, reducing reflectance across the entire visible light range, making the surface appear black and exhibiting light absorption properties. Furthermore, using highly conductive metals, such as aluminum and nickel, for such metals with micro-texture reduces far-infrared radiation. Therefore, metal components with micro-texture surfaces are believed to have both light absorption and heat storage properties. The visible range is, for example, a wavelength range from 360 nm to 1000 nm. Far-infrared rays are, for example, a wavelength range of 2 μm or longer. However, the light-absorbing material disclosed in Non-Patent Document 1 has a fine uneven surface obtained by oxidizing the nickel surface, but it has high radiation (low reflectance) even in the far-infrared region and does not exhibit heat storage properties. Based on this, the present inventors discovered that in addition to the heat storage properties of the metal itself, the specific shape of the fine uneven surface of the metal is important for exhibiting light absorption and heat storage properties, and have completed the present invention (the fine uneven surface may be referred to as a fine uneven shape or simply as an uneven shape).

[0017] The heat storage material of this embodiment has a specific fine concave-convex structure provided on the surface of the metal layer, and therefore can exhibit both light absorption and heat storage properties. The metal layer including the fine concave-convex structure of the heat storage material of this embodiment preferably 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 absorption of energy. On the other hand, when energy is absorbed and the temperature rises, far-infrared rays are emitted into the surrounding area, releasing the energy. Therefore, materials with low radiation in the far-infrared range can reduce energy radiation. In other words, materials that absorb visible light and have low radiation in the far-infrared range can efficiently absorb energy and store heat by suppressing energy release. Therefore, the film formed on the surface of the heat storage member of the heat storage material of 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 the metal layer with excellent heat storage properties.

[0019] <Metal layer> First, the metal layer of the heat storage material of this embodiment will be described with reference to FIG. 1. As shown in FIG. 1A, one embodiment of the metal layer 1 is a film including a metal layer 1 having a fine unevenness 2 on its surface. The material of the metal layer 1 is preferably a metal with high electrical conductivity. Examples of highly conductive metals 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 unevenness 2 provided on the surface of the metal layer 1 is also preferably made of the above-mentioned highly conductive metal, 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 irregularities 2 are minute irregularities formed on one surface of the metal layer 1, and the height of the fine irregularities 2 refers to the difference in elevation between the peaks of the convex portions and the bottoms of the concave portions formed on the surface of the metal layer. The average height of the fine irregularities 2 is 100 nm to 1000 nm, preferably 100 nm to 500 nm. Here, the height of the fine irregularities 2 refers to the difference in elevation between the peaks and the valleys as defined in JIS-B-061, "Definition and Display of Surface Roughness," and corresponds to the maximum roughness (Rmax). Furthermore, the film having the metal layer 1 of this embodiment preferably has an average surface roughness Ra', calculated by surface-extending the centerline average roughness Ra, of 1 nm to 50 nm on its surface. Here, the average surface roughness Ra' value (nm) is the centerline average roughness Ra defined in JIS B 0601, which is applied to the measurement surface and expanded three-dimensionally. It is expressed as "the average of the absolute values ​​of the deviations from the reference surface to the specified surface," and can be 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 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. X L ~X R is the range of the X coordinate of the measurement surface, and 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, the film having the metal layer 1 of this embodiment preferably has a specific surface area Sr of its surface of 1.0 or more and 3.0 or less. The specific surface area Sr can be calculated by the following formula (2). Sr=S / S0 formula (2)

[0024] In equation (2), S0 is the surface area when the measurement surface is assumed to be ideally flat, and S is the surface area of ​​the actual measurement surface.

[0025] The actual surface area of ​​the measurement surface is determined by dividing the surface into infinitesimal triangles ΔABC consisting of the three closest data points (A, B, C), and then calculating the area ΔS of each infinitesimal triangle using the vector product as shown in the following equation (3). The sum of these ΔS is the desired surface area S. [ΔS(ΔABC)] 2 =[s(s-AB)(s-BC)(s-CA)] Equation (3)

[0026] In equation (3), AB, BC, and CA are the lengths of each side, and 2s = AB + BC + CA.

[0027] The height of the fine irregularities 2 can be determined by observing the cross section of the metal layer 1 using a scanning electron microscope or the like. The average surface roughness Ra' and specific surface area of ​​the surface of the film having a metal layer of the heat storage material of the present invention can be determined by observing the surface of the film having a metal layer using a scanning probe microscope or the like. The film having a metal layer may have deposits on the surface of the fine irregularities 2 (for example, metal oxides, which will be described later), and the average surface roughness Ra' and specific surface area of ​​the surface of the heat storage material having a metal layer are values ​​including the deposits. In this specification, the film having a metal layer may also be referred to as a light absorption heat storage film.

[0028] Another embodiment of the film including a metal layer of the heat storage material of this embodiment (film having a metal layer) may include a transparent metal oxide micro-concave and convex structure 3 in close contact with the micro-concave and convex structure 2, as shown in FIG. 1B. Another embodiment of the film of this embodiment may further include a transparent metal oxide layer 4 covering the surface of the metal oxide micro-concave and convex structure 3 that is not in contact with the micro-concave and convex structure 2, as shown in FIG. 1C. Here, "closely contacted" means that the metal oxide constituting the metal oxide micro-concave and convex structure 3 fills the space surrounded by the micro-concave and convex structure 2 and reaches the metal layer 1. When the surface of the micro-concave and convex structure 2 includes the micro-concave and convex structure 3 and the metal oxide layer 4, the average surface roughness Ra' and specific surface area, calculated by expanding the centerline average roughness Ra, are preferably 1 nm or more and 50 nm or less. Furthermore, the specific surface area Sr of the surface of the micro-concave and convex structure 2 is preferably 1.0 or more and 3.0 nm or less.

[0029] The material of the metal oxide micro-irregularities 3 is not particularly limited, but is preferably alumina-based, and more preferably contains alumina-based plate crystals. The alumina-based plate crystals are formed from alumina-based plate crystals containing aluminum oxide, hydroxide, or hydrates thereof as the main component, with boehmite being a particularly preferred crystal. Here, the alumina-based plate crystals may be alumina-based plate crystals or alumina-based plate crystals containing trace amounts of zirconium, silicon, titanium, zinc, etc.

[0030] The provision of the metal oxide fine concave-convex structure 3 can protect the fine concave-convex object 2. When the metal oxide fine concave-convex structure 3 is a plate-like structure of plate crystals mainly composed of alumina, it is preferable that the plate crystals mainly composed of alumina are arranged in a direction perpendicular to the surface 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 preferably contains an amorphous gel of alumina. The metal oxide layer 4 increases the hardness of the surface of the film of the present invention while reducing the light absorption. Therefore, the thickness of the metal oxide layer 4 may be appropriately determined so as to satisfy the required hardness and light absorption.

[0032] The aluminum element, silicon element, and the like in the fine texture 2, the fine texture 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 a transmission electron microscope (TEM). They can also be detected by X-ray photoelectron spectroscopy (XPS) or other methods. The same can be said for metal elements such as silver, copper, gold, aluminum, magnesium, tungsten, cobalt, zinc, nickel, and chromium in the metal layer 1. That is, they can be detected by energy dispersive X-ray analysis (EDX) or X-ray photoelectron spectroscopy (XPS) during surface or cross-sectional observation using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). When the fine texture 2, the fine texture 3, or the metal oxide layer 4 is provided, the proportions change in the direction perpendicular to the surface direction of the metal layer 1. In other words, the proportion of metal oxides such as aluminum elements decreases relatively from the surface (metal oxide layer 4) to the interior (metal layer 1), and the proportion of metal elements that make up the metal layer 1 and the fine uneven structure 2 increases, until finally only metal elements are detected.

[0033] <Method of manufacturing heat storage material> Hereinafter, the method for producing the heat storage material of this embodiment will be described with reference to FIG.

[0034] The method for producing a heat storage material of this embodiment includes a first step of forming a fine concave-convex shape of metal oxide, and a second step of forming a metal layer 1 on the fine concave-convex shape of metal oxide. It also includes a step of bonding a heat storage member 5 to the surface of the metal layer 1 opposite to the surface in contact with the fine concave-convex shape of metal oxide 3.

[0035] (First step: Fabrication of fine irregularities in metal oxide) In the first step, a fine concave-convex shape of metal oxide is formed as a mold.

[0036] The material for the metal oxide micro-texture is not particularly limited, but alumina is preferred as the main component. The micro-texture can be formed by known gas phase methods such as chemical vapor deposition (CVD) and physical vapor deposition (PVD), and by a sol-gel liquid phase method. These methods can be used to form a metal oxide micro-texture containing alumina-based plate crystals. Among these, a method in which an aluminum-containing film is treated with warm water to grow alumina plate crystals is preferred.

[0037] Examples of the aluminum-containing film include an alumina gel film formed by applying a sol-gel coating liquid containing an aluminum compound, and a film containing metallic aluminum formed by dry film formation such as vacuum deposition or sputtering. Forming the metal oxide fine concave-convex shape using an alumina gel film is preferred in terms of reactivity and ease of adjusting the height of the metal oxide fine concave-convex shape.

[0038] As the raw material for the alumina gel film, aluminum compounds such as aluminum alkoxides, aluminum halides, aluminum salts, etc. From the viewpoint of film formation, 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, as well as their oligomers, aluminum halides such as aluminum chloride, aluminum salts such as aluminum nitrate, aluminum acetate, aluminum phosphate, and aluminum sulfate, aluminum acetylacetonate, and aluminum hydroxide.

[0040] The alumina gel film may also contain other compounds, such as alkoxides, halides, salts, and combinations thereof, of zirconium, silicon, titanium, and zinc. By including other compounds in the alumina gel film, the height of the fine irregularities formed by the metal oxide can be increased compared to when the alumina gel film does not include these compounds.

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

[0042] Examples of organic solvents that can be used include alcohols, carboxylic acids, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, esters, ketones, ethers, and mixtures thereof. Examples of alcohols include methanol, ethanol, 2-propanol, butanol, 2-methoxyethanol, 2-ethoxyethanol, 1-methoxy-2-propanol, and 1-ethoxy-2-propanol. Examples of other organic solvents 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, iso-valeric 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. Examples of aliphatic or alicyclic hydrocarbons include n-hexane, n-octane, cyclohexane, cyclopentane, and cyclooctane. Examples of aromatic hydrocarbons include toluene, xylene, and ethylbenzene. Examples of esters include ethyl formate, ethyl acetate, n-butyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, and ethylene glycol monobutyl ether acetate. Examples of ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Examples of ethers include dimethoxyethane, tetrahydrofuran, dioxane, and diisopropyl ether. Among these, alcohols are preferred in terms of the stability of the sol-gel coating solution.

[0043] When aluminum alkoxide is used as the aluminum compound, its high reactivity with water can rapidly hydrolyze the aluminum alkoxide when exposed to moisture in the air or the addition of water, resulting in cloudiness 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. Examples of stabilizers that can be used 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 isopropyl acetoacetate, 2-methoxyethyl acetoacetate, sec-butyl acetoacetate, tert-butyl acetoacetate, and isobutyl acetoacetate. Examples of alkanolamines include monoethanolamine, diethanolamine, triethanolamine, etc. The amount of the stabilizer relative to the aluminum alkoxide is preferably about 1:1 in molar ratio.

[0044] A catalyst may be used to promote the hydrolysis reaction of aluminum alkoxide, such as nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, or ammonia.

[0045] Furthermore, a water-soluble organic polymer compound can be added to the alumina gel film as needed. The water-soluble organic polymer compound is easily dissolved from the alumina gel film by immersion in warm water, thereby increasing the reaction surface area between the aluminum compound and the warm water, enabling the formation of a fine unevenness at low temperature and in a short time. Furthermore, by changing the type and molecular weight of the organic polymer added, it becomes possible to control the height of the formed fine unevenness. Polyether glycols such as polyethylene glycol and polypropylene glycol are preferred as organic polymers, as they are easily dissolved from the alumina gel film by immersion in warm water. The amount of polyether glycol relative to the weight of the aluminum compound in the alumina gel film is preferably in the range of 0.1 to 10 times by weight.

[0046] A method for producing a metal oxide micro-texture 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 the aluminum-containing film 7. Alternatively, a film containing metallic aluminum as the aluminum-containing film 7 is formed on the base substrate 8 by dry film formation 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 a stabilizer, it is preferable to apply the coating in an inert gas atmosphere such as dry air or dry nitrogen. The relative humidity of the dry atmosphere is preferably 30% or less. Known coating methods, such as dipping, spin coating, spraying, printing, flow coating, and combinations of these, can be used as appropriate for forming the alumina gel film. The film thickness can be controlled by changing the pulling speed in the dipping method, the substrate rotation speed in the spin coating method, and the concentration of the sol-gel coating solution. Drying can be performed at room temperature for about 30 minutes. If necessary, drying or heat treatment can be performed at a higher temperature. The higher the heat treatment temperature, the more stable the metal oxide micro-relief 3 can be formed by the immersion treatment described below. The aluminum-containing film 7 has a suitable film thickness of 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 warm water to form a fine alumina texture. Immersing the alumina gel film in warm water causes the surface of the alumina gel film to undergo peptization, resulting in the elution of some components. However, due to differences in the solubility of various hydroxides in warm water, plate-like crystals primarily composed of alumina precipitate and grow on the surface of the alumina gel film, forming the metal oxide fine texture 3. Furthermore, when a film containing metallic aluminum is used instead of an alumina gel film, the aluminum reacts with the warm water to be oxidized to alumina, and then the metal oxide fine texture 3 is formed, similar to when an alumina gel film is used. Therefore, when the material of the base substrate 8 primarily contains aluminum or alumina, the formation of the aluminum-containing film 7 on the base substrate 8 can be omitted. The temperature of the warm water is preferably 40°C or higher but lower than 100°C. The immersion time is preferably approximately 5 minutes to 24 hours. In the immersion treatment of an alumina gel film containing compounds other than the alumina component, the difference in solubility of each component in hot water is utilized to crystallize alumina plate crystals. Therefore, unlike the immersion treatment of an alumina gel film containing only alumina, the size of the plate crystals can be controlled over a wide range by changing the composition of the inorganic components. Furthermore, the height of the alumina fine irregularities 3 can be adjusted by adjusting the film thickness of the aluminum-containing film 7. The average height of the metal oxide fine irregularities 3 is preferably 100 nm or more and 1000 nm or less, more preferably 100 nm or more and 500 nm or less. As a result, the fine irregularities formed by the plate crystals can be controlled over a wide range.

[0048] (Second step: Metal layer formation step) In the second step, a metal layer is formed on the metal oxide micro-relief, forming a micro-relief structure on the metal layer, with the micro-relief transferred onto it. The process of forming the metal layer 1 on the metal oxide micro-relief 3 is described below with reference to FIG. 3C. The metal layer 1 is preferably formed by metal plating, and more preferably by electroless plating. 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, or a tin compound such as tin chloride to the metal oxide micro-relief 3. Activation may also be performed by immersing the metal oxide micro-relief 3 together with the base substrate 8 in an aqueous solution containing a palladium compound. Then, the metal layer 1 is deposited on the metal oxide micro-relief 3 using an electroless plating solution. The metal ions in the electroless plating solution correspond to the metal layer of the present invention. An electroless plating solution containing nickel ions, chromium ions, or zinc ions is preferred, with a nickel plating solution containing nickel ions being particularly preferred. The nickel plating solution may contain phosphorus or boron in addition to the nickel component. Examples of commercially available nickel plating solutions include the Top Nicoron series from Okuno Pharmaceutical Industries. The temperature of the plating solution during electroless plating is preferably 30°C or higher and 98°C or lower, more preferably 50°C or higher and 90°C or lower. The electroless plating time can be adjusted depending on the thickness of the metal layer to be formed, and is typically 30 seconds to 1 hour. In this way, a metal layer 1 is formed to fill the gaps in the fine unevenness, forming a metal layer 1 including a fine unevenness 2 to which the fine unevenness 3 of the metal oxide has been transferred. As a result, the metal layer 1 has an unevenness corresponding to the fine unevenness 3 of the metal oxide.

[0049] It is preferable to perform electroless plating so that the thickness of the metal layer 1 including the fine unevenness 2 is 200 nm or more and 15,000 nm or less. The average height of the fine unevenness 2 corresponds to the average height of the metal oxide fine unevenness 3, and is 100 nm or more and 1,000 nm or less. When the thickness of the metal layer 1 including the fine unevenness 2 is 200 nm or more, the light absorption and heat storage film of the present invention exhibits excellent light absorption and heat storage properties.

[0050] After the electroless plating process described above, electroplating may be performed on the opposite side of the metal layer 1 from the side on which the micro-convex structure 2 is formed to increase the thickness of the metal layer 1. A known electroplating solution can be used for the electroplating, such as an electroplating solution containing nickel ions, iron ions, or copper ions as metal ions. When electroplating is performed using the same metal as the metal layer 1, the thickness of the metal layer can be increased by the electroplating process. When electroplating is performed using a metal different from the metal layer 1, the metal layer formed by the electroplating process becomes the heat storage member 5. In addition to inorganic salts serving as raw materials for the metal ions, the electroplating solution may also contain, as necessary, conductive salts, salts for adjusting counterions, carboxylic acid additives for improving the uniformity of the plating film, brighteners, and the like. Furthermore, the desired thickness of the metal layer 1 can be achieved by adjusting the temperature, current density, and plating time of the electroplating solution during the electroplating process. If necessary, prior to the electroplating step, the surface of the metal layer 1 opposite to the surface on which the fine concave-convex structure 2 is formed 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 step, a step of removing foreign matter from the electroplating solution may be provided in addition to stirring the electroplating solution during the electroplating step.

[0051] (Third step: Heat storage member bonding step) In the method for producing a heat storage material of this embodiment, as shown in FIG. 3D , a heat storage member 5 is bonded to the surface of the metal layer 1 obtained above opposite to the surface on which the fine concave-convex structure 2 is provided. The shape and material of the heat storage member 5 may be those described above. When the base material of the heat storage member 5 is metal, a metal that serves as the base material of the heat storage member 5 may be further laminated on the surface on which the metal layer 1 has the fine concave-convex structure 2 provided opposite to the surface on which the metal layer 1 has the fine concave-convex structure 2 provided. The metal may be laminated by the electroplating process described above or by physical vapor deposition such as sputtering. When the base material of the heat storage member 5 is resin, the resin that serves as the heat storage member 5 may be deposited on the surface of the metal layer 1 opposite to the metal oxide fine concave-convex structure 3, and then cured to provide the heat storage member. 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, as long as it is a material that firmly bonds the heat storage member 5 and the metal layer 1.

[0052] (Fourth step: Etching step) The etching step will be described in detail using a heat storage material having a heat storage member 5 and an adhesive layer 6 as an example, as shown in Figures 3E to 3H, but it is also possible to etch the heat storage member 5 with only the base material adhered, and then attach the heat storage material to the base material to form a heat storage member. Alternatively, it is also possible to etch the heat storage member 5 with only the base material without the adhesive layer 6, and then attach the heat storage material to the base material to form a heat storage member. Note that Figure 3E shows the heat storage material shown in Figure 3D upside down.

[0053] First, to obtain the heat storage material of this embodiment, the base substrate 8 is removed as shown in FIG. 3F. The heat storage material after removing the base substrate 8 has an aluminum-containing film 7 on its surface. If the aluminum-containing film 7 is a film containing metallic aluminum, visible light is reflected by the metallic aluminum. Therefore, as shown in FIG. 3G, the aluminum-containing film must be further removed by etching. Furthermore, if the aluminum-containing film 7 is an alumina gel film, the alumina gel film is the metal oxide layer 4 of the heat storage material. Therefore, the alumina gel film may be removed by etching to satisfy the required surface hardness and light absorption properties. A preferred etching method is wet etching, in which the aluminum-containing film 7 is dissolved using an acid or alkaline solution. 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. Furthermore, as shown in FIG. 3H, the metal oxide fine unevenness 3 may also be removed by etching. A heat storage member in which the metal layer 1 having the fine unevenness 2 on its outermost surface is bonded to the heat storage member 5 via the adhesive layer 6 achieves particularly excellent light absorption properties.

[0054] Residual metal oxides such as alumina after etching (metal oxides attached to the metal layer) can be detected by EDX or XPS measurements when observing the surface or cross section using SEM or TEM.

[0055] As described above, the degree of etching may be adjusted depending on the desired balance between the light absorption and heat storage performance of the heat storage member or metal layer and the surface hardness. Furthermore, the etching step may be performed before the third step, which is the step of adhering the heat storage member 5, and then the heat storage member 5 may be adhered.

[0056] The heat storage material of this embodiment obtained in this manner has a metal layer 1 containing fine uneven shapes 2, and therefore absorbs visible light, resulting in a low reflectance in the visible light region, and emits little far-infrared light, resulting in a high reflectance in the far-infrared region, thereby achieving excellent light absorption and heat storage properties.

[0057] A film (light-absorbing heat storage film) including the metal layer 1 of this embodiment can be provided on the surface of various components. The light-absorbing heat storage film of this embodiment can also be formed on the surface of fabric to produce heat-storing clothing. The light-absorbing heat storage film of this embodiment can also be used as a heat-storing decorative film. For example, the light-absorbing heat storage film of the present invention can be attached as a heat-storing decorative film to the surfaces of vehicle interiors, mobile devices, electronic devices such as home appliances, parasols, and tents. Various adhesives can be used when providing the light-absorbing heat storage film of the present invention on the surface of a component or heat storage material. Therefore, the light-absorbing heat storage film of the present invention can be provided on the surface of a component or heat storage material depending on the intended use. The surfaces of the component and heat storage material are not limited to being smooth, but may also have two-dimensional or three-dimensional curves.

[0058] It is desirable to provide a heat insulating material on the light absorbing and heat storing film or around the heat storing member of this embodiment, as this will further enhance the heat storing ability. It is even more desirable for the heat insulating material to be light transmissive, as this will increase the light absorption efficiency.

[0059] The heat storage material of this embodiment has excellent light absorption and heat storage properties, and therefore can be used in a variety of products. For example, since it can efficiently utilize solar energy, it can be used in a solar hot water supply system. When used in a solar hot water supply system, a steam generation pipe (not shown) is passed through the heat storage member 5. During times when sunlight cannot be utilized, such as at night, an unheated heat medium is passed through this steam generation pipe, and the heat medium can be heated by the heat storage material contained in the heat storage member 5, whose temperature has risen.

[0060] The heat storage material of this embodiment has excellent heat storage properties, and can efficiently utilize solar energy, so it can be used in a solar thermal power generation system. When used in a solar thermal power generation system, a steam generation pipe (not shown) is passed through the heat storage member 5. At times when sunlight cannot be utilized, such as at night, an unheated heat medium is passed through this steam generation pipe, and the heat medium is heated by the heat storage material contained in the heat storage member 5, whose temperature has risen. The heated heat medium generates steam in a steam generator (not shown), which can operate a steam turbine (not shown) to generate electricity.

[0061] The heat storage material of this embodiment has excellent heat storage properties, allowing it to efficiently utilize solar energy and therefore can be used in artificial satellites. Since the temperature difference between the surface of an artificial satellite exposed to sunlight and the surface not exposed to sunlight is large, it is desirable to store heat when exposed to sunlight and release heat when not exposed to sunlight, thereby reducing the temperature difference. For example, a device having two heat storage materials and a heat release material of this embodiment can be used to reduce the temperature difference as follows. When the temperature of the artificial satellite is low, the heat storage material of this embodiment is exposed to the outside by a means for exposing the heat storage material to the outside, thereby storing heat and suppressing a decrease in temperature. When the temperature is high, the heat release material is exposed to the outside by a means for exposing the heat release material to the outside, thereby suppressing an increase in temperature. The means for exposing the heat storage material to the outside and the means for exposing the heat release material to the outside may be the same or different. Using this device in this manner can significantly reduce the power consumed by a heater for keeping the satellite warm.

[0062] The heat storage material of this embodiment has excellent heat storage properties, and can efficiently utilize solar energy, so it can be used in solar collectors and solar pots. FIG. 8 shows a solar collector, which is an example of an article 20 including a heat storage material. In the article 20 as a solar collector, water, for example, can be used as the heat storage member 5. 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 located between the heat storage member 5 and the metal layer 1. A heat insulating material 10 is provided on the outside of the metal layer 1. The metal layer 1 is located between the heat insulating material 10 and the heat storage member 5. Xerogel, for example, can be used as the heat insulating material 10. This makes it possible to store solar heat in the water (heat storage member 5) contained in the container 9.

[0063] FIG. 9A shows an artificial satellite, which is an example of the article 20 including a heat storage material. The artificial satellite 20 includes a heat control unit 11, a control unit 12, a power generation unit 13, and a communication unit 14. FIG. 9B shows a cross-sectional view of the heat control unit 11 in FIG. 9A taken along line A-A'. 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. Paraffin, for example, can be used as the heat storage member 5. The heat control unit 11 can store heat using sunlight.

[0064] A heat dissipation material can be provided on the article 20, such as an artificial satellite. When a predetermined portion 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 heat control unit 11. Furthermore, when the predetermined portion (e.g., the control unit 12) is above a predetermined temperature (high temperature), heat can be dissipated from the heat dissipation material. The article 20, such as an artificial satellite, can undergo at least one of deformation and displacement so as to switch between 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 opposite side from 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. A shape in which the heat dissipation material faces the outside of the artificial satellite (e.g., the opposite side from 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 a heat source (e.g., the sun) around the satellite and the heat dissipation material faces the opposite side of the heat source (e.g., the earth) around the satellite.

[0065] The heat storage material of this embodiment can be combined with a solar cell and used for hybrid solar power generation. The solar cell can be made of silicon, an organic semiconductor, an organic-inorganic perovskite semiconductor, or the like. By providing a solar cell on the heat storage material to create a hybrid solar power generation unit, the light transmitted through the solar cell can be absorbed by the heat storage material and radiation can be suppressed, allowing for efficient heat storage and solar heat utilization. It is desirable to encapsulate the hybrid solar power generation unit in a vacuum. Encapsulating the hybrid solar power generation unit in a vacuum is desirable because it can suppress thermal conduction and therefore enable more efficient heat storage. It is also desirable to provide a translucent heat insulating material in the hybrid solar power generation unit. Examples of the translucent heat insulating material that can be used include aerogel and xerogel.

[0066] FIG. 10 shows a solar panel, which is an example of an article 20 including a heat storage material, as shown in FIG. 8. In the article 20 as a solar panel, oil can be used, for example, 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. Photovoltaic cells 15 are provided on the outside of the metal layer 1. Silicon can be used for the photovoltaic cells 15. The metal layer 1 is located between the photovoltaic cells 15 and the heat storage member 5. A heat insulating material 10 is provided on the outside of the photovoltaic cells 15. The photovoltaic cells 15 are located between the heat insulating material 10 and the metal layer 1. The photovoltaic cells 15 are provided between the heat storage material 10 and the heat storage member 5, which includes the heat storage member 5 and the metal layer 1 provided on the heat storage member 5. Vacuum sealed glass, for example, can be used as the heat insulating material 10. This creates a hybrid solar power generation system that can generate electricity and store heat using sunlight.

[0067] A system that utilizes solar thermal energy can be called a solar thermal utilization system. The solar thermal utilization system is the solar thermal hot water supply system or solar thermal power generation system described above. The solar thermal utilization system includes the heat storage material of this embodiment, and the solar thermal utilization system includes an article that includes the heat storage material. The article that includes the heat storage material may include a heat insulating material or a heat dissipation material in addition to the heat storage material. The heat insulating material or the heat dissipation material in the article that includes the heat storage material may be fixed to the heat storage material. Furthermore, the solar thermal utilization system may include other articles such as piping, a heat medium, and a steam turbine in addition to the article that includes the heat storage material. The other articles in the solar thermal utilization system do not need to be fixed to the article that includes the heat storage material.

[0068] A system that utilizes solar light energy can be called a solar power utilization system. The solar power utilization system is the solar power generation system or solar lighting system described above. The solar power utilization system includes the heat storage material of this embodiment, and the solar power utilization system includes an article that includes the heat storage material. The article that includes the heat storage material may include a heat insulating material or a heat dissipation material in addition to the heat storage material. The heat insulating material or the heat dissipation material in the article that includes the heat storage material may be fixed to the heat storage material. Furthermore, the solar power utilization system may include other articles such as wiring, a battery, and a power conditioner in addition to the article that includes the heat storage material. The other articles in the solar thermal utilization system do not need to be fixed to the article that includes the heat storage material.

[0069] Solar thermal systems and photovoltaic systems can also be called solar systems. Solar systems can include solar collectors, solar pots, and solar panels. [Example]

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

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

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

[0073] In the examples, the reflectance spectrum in the infrared region was measured using a Fourier transform infrared spectrophotometer (manufactured by JASCO Corporation, FT / IR-6600).

[0074] Example 1 An alumina sol solution was prepared by dissolving aluminum sec-butoxide (Al(O-sec-Bu)3) and ethyl acetoacetate (EtOAcAc) in 2-propanol (IPA) and stirring for approximately 3 hours at room temperature. The molar ratio of each component in the alumina sol solution was Al(O-sec-Bu)3: EtOAcAc: IPA = 1:1:20. A 0.01 M dilute hydrochloric acid solution was added to the alumina sol solution so that the molar ratio of hydrochloric acid added was twice that 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 as a base substrate by spin coating to form a coating film. The coating 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 warm water at 80°C for 30 minutes, and then dried at 100°C for 10 minutes to form an alumina layer having a fine concave-convex shape.

[0075] A palladium chloride aqueous solution was applied by spin coating onto the alumina layer with the fine irregularities, and then dried at 100°C.Then, the substrate was immersed for 1 minute in a nickel-phosphorus plating solution (phosphorus content: approximately 10 wt%) set at 80°C to form the fine irregularities and a nickel layer as a metal layer.

[0076] An epoxy resin adhesive layer was applied to the surface of the metal layer opposite the alumina layer with the fine irregularities, and then cured. A PET film was attached to the adhesive layer as the base material for the heat storage material. The PET film was then peeled off from the quartz glass substrate. The base material was then attached to a quartz cell filled with water as the heat storage material.

[0077] (Observation of cross-sectional shape) In Example 1, the alumina layer having a finely textured structure and a nickel layer formed thereon was cut using a dicing saw, then sliced ​​in the cross-sectional direction using a focused ion beam (FIB) method, and the cross-section was observed using an SEM. The cross-sectional observation was performed using a scanning transmission electron microscope (product name: HD-2300, manufactured by Hitachi High-Technologies Corporation). The observation image shown in Figure 4 shows that nickel finely textured structures 2 are formed so as to fill the interiors of alumina plate crystals, which are metal oxide finely textured structures 3 formed from an alumina gel film on a base substrate 8, and a nickel layer, which is a metal layer 1, is present on the finely textured structures 2.

[0078] The average height of the obtained fine unevenness 2 of Example 1 was 323 nm, the average height of the fine unevenness 3 was 255 nm, and the film 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 spectrum in the visible light region and the reflectance spectrum in the infrared region of Example 1 were measured. The reflectance spectrum was measured using a lens reflectance measuring instrument (trade name: USPM-RU III, manufactured by Olympus Corporation), and the reflectance spectrum in the infrared region was measured using a Fourier transform infrared spectrophotometer (trade name: FT / IR-6600, manufactured by JASCO Corporation). The results of the reflectance spectrum measurement in the visible light region are shown in FIG. 5, and the results of the reflectance spectrum measurement in the infrared region are shown in FIG. 6. Table 1 also shows the reflectance in the visible light and infrared regions obtained by measuring the reflectance spectrum in the visible light and infrared regions of Example 1. From FIG. 5, it can be said that Example 1 has excellent light absorption, since it has low reflectance in the visible light region.

[0080] From FIG. 6, it can be said that Example 1 has excellent heat storage properties because the reflectance increases toward the longer wavelength side in the mid-infrared and far-infrared regions.

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

[0082] As shown in FIG. 5, Comparative Example 1, although inferior to the sample of Example 1, had low reflectance in the visible to near-infrared region.

[0083] On the other hand, as shown in FIG. 6, the sample of Comparative Example 1 had poorer reflectance in the mid-infrared region and the far-infrared region than Example 1.

[0084] Example 2 An alumina sol solution was prepared in the same manner as in Example 1, and this was applied to a quartz glass substrate, which was the base material, by spin coating to form a coating film. The coating 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 warm water at 80°C for 30 minutes and then dried at 100°C for 10 minutes to form an alumina layer with a fine concave-convex shape.

[0085] A palladium chloride solution was spin-coated onto the alumina layer with the fine irregularities, then dried at room temperature.Then, the substrate was immersed in a nickel-phosphorus plating solution (phosphorus content: approximately 10 wt%) at 80°C for 20 minutes to form the fine irregularities and a nickel layer as a metal layer.

[0086] The film was then peeled off from the quartz glass substrate. The resulting total film thickness was approximately 10 μm. The average height of the fine irregularities in the resulting film was 303 nm, the average height of the fine irregularities 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 the following Examples 3 to 11, films were produced by changing the number of gel film layers and etching conditions.

[0088] Example 3 A film was produced in the same manner as in Example 2. The film peeled from the quartz glass substrate was then etched using a 3M aqueous sodium hydroxide solution at room temperature for 50 hours to produce a film. The average height of the fine irregularities in the resulting film was 251 nm, the average height of the fine irregularities was 213 nm, the average surface roughness Ra' was 5.0 nm, and the specific surface area was 1.1. The results of reflectance spectroscopy in the visible light region are shown in Figure 5, and the results of reflectance spectroscopy in the infrared region are shown in Figure 6. A cross-section was also extracted using the FIB method, and the cross-section was observed using an SEM. The cross-section was observed using a scanning electron microscope (product name: ULTRA55, manufactured by Carl Zeiss). The image shown in Figure 7 reveals that nickel fine irregularities 2 were formed on the nickel layer, which was the metal layer 1, and a trace amount of alumina remained on the fine irregularities 2. In the alumina layer detected by SEM-EDX analysis and XPS measurement, the proportion of Al element relatively decreased from the surface toward the inside in the film thickness direction of the cross section, while the proportion of Ni element increased.

[0089] Example 4 A film was produced in the same manner as in Example 3, except that the etching step involved etching using a 7.5 M aqueous sodium hydroxide solution at room temperature for 47 hours. The average height of the fine irregularities in 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 A film was produced in the same manner as in Example 3, except that a nickel-phosphorus plating solution (phosphorus content: approximately 1 to 2 wt%) was used as the plating solution. The average height of the fine irregularities in 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 The alumina sol solution shown in Example 2 was prepared and applied to a quartz glass substrate (base substrate) by spin coating to form a coating film. The coating film was then heat-treated at 100°C for 1 hour, and the same film application and film drying process was repeated again to obtain a transparent alumina gel film containing aluminum, with two layers of alumina gel film. The film was then manufactured in the same manner as in Example 2. The average height of the fine irregularities in the obtained film was 371 nm, the average height of the fine 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 film was produced in the same manner as in Example 6, except that after peeling the metal film with the alumina layer from the quartz glass substrate, an etching process was performed using a 3M aqueous sodium hydroxide solution at room temperature for 50 hours. The average height of the fine irregularities in 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 A film was produced in the same manner as in Example 7, except that the etching step involved etching using a 7.5 M aqueous sodium hydroxide solution at room temperature for 50 hours. The average height of the fine irregularities in 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 A film was produced in the same manner as in Example 2, except that the number of laminated alumina gel films was changed to three. The average height of the fine irregularities in the obtained film was 419 nm, the average height of the fine irregularities was 374 nm, the average surface roughness Ra' was 1.2 nm, and the specific surface area was 1.0.

[0095] Example 10 A film was produced in the same manner as in Example 9, except that after peeling the metal film with the alumina layer from the quartz glass substrate, etching was performed at room temperature for 50 hours using a 3M aqueous sodium hydroxide solution in the etching step. The average height of the fine irregularities in 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 A film was produced in the same manner as in Example 10, except that the etching step involved etching using a 6 M aqueous sodium hydroxide solution at room temperature for 45 hours. The average height of the fine irregularities in 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 reflectances in the visible light region and the infrared light region obtained by measuring the reflection spectra in the visible light region and the infrared light region of the samples produced in Examples 1 to 11 and Comparative Example 1.

[0098] [Table 1]

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

[0101] [Table 2]

[0102] The temperature rise achieved by irradiation with the same energy was higher in Example 12 than in Comparative Example 2, demonstrating that heat was stored more efficiently.

[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 can provide a light-absorbing and heat-storing film and a heat-storing member that absorb visible light and near-infrared rays (low reflectance) and emit little far-infrared rays (high reflectance), which are normally incompatible. The light-absorbing and heat-storing film and a heat-storing member of the present invention can be used as heat-storing members in space-related equipment such as artificial satellites and solar thermal power generation, and can also be used as exterior films, solar collectors, etc.

[0105] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention.

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

Claims

1. a heat storage member; and a metal layer including a concave-convex shape provided on the heat storage member, The height of the uneven shape is 100 nm or more and 1000 nm or less, The heat storage material is 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.

2. The heat storage material according to claim 1, wherein the heat storage member contains one of water, paraffin, oil, fiber, sand, and salt.

3. 3. The heat storage material according to claim 1, further comprising a metal oxide in contact with the uneven object and having an uneven shape that follows the unevenness of the uneven object.

4. 4. The heat storage material according to claim 3, wherein the metal oxide contains plate-like crystals containing alumina as a main component.

5. A heat storage material described in any one of claims 1 to 4, characterized in that it further has a transparent metal oxide layer covering the surface of the metal oxide that is not in contact with the uneven surface.

6. The heat storage material described in Claim 5, characterized in that the transparent metal oxide layer contains an amorphous gel of alumina.

7. 7. The heat storage material according to claim 1, wherein the average surface roughness Ra' is 1 nm or more and 50 nm or less, and the specific surface area Sr is 1.0 or more and 3.0 or less.

8. 8. The heat storage material according to claim 1, wherein the material of the metal layer contains any one selected from the group consisting of nickel, chromium, and zinc.

9. A heat storage material described in any one of claims 1 to 7, characterized in that the material of the metal layer is nickel.

10. 10. The heat storage material according to claim 1, wherein the metal layer and the heat storage member are bonded together by an adhesive layer.

11. 11. The heat storage material according to claim 1, wherein the heat storage member comprises a heat storage material and a substrate provided between the metal layer and the heat storage material.

12. 12. The heat storage material according to claim 11, wherein the substrate is one of metal, glass, ceramics, wood, paper, and resin.

13. a heat storage member; and a metal layer including a concave-convex shape provided on the heat storage member, The heat storage material is 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.

14. An article comprising the heat storage material according to any one of claims 1 to 13 and a heat insulating material.

15. An article comprising the heat storage material according to any one of claims 1 to 13 and a heat dissipation material.

16. The article according to claim 15, characterized in that it undergoes at least one of deformation and displacement so as to store heat in the heat storage material when a predetermined portion of the article is below a predetermined temperature, and to radiate heat from the heat dissipation material when the predetermined portion is at or above the predetermined temperature.

17. An article comprising the heat storage material according to any one of claims 1 to 13 and a medium heated by the heat storage material.

18. An artificial satellite comprising the heat storage material according to any one of claims 1 to 13.

19. A solar heat utilization system comprising the heat storage material according to any one of claims 1 to 13.

20. A photovoltaic power generation system comprising the heat storage material according to any one of claims 1 to 13.

21. 21. The photovoltaic power generation system according to claim 20, further comprising a heat insulating material, and a photovoltaic power generation cell is provided between the heat storage material and the heat insulating material.

22. A first step of immersing an aluminum-containing film in warm water to form a metal oxide texture; a second step of forming a metal layer having a concave-convex shape corresponding to the concave-convex shape of the metal oxide on the concave-convex shape of the metal oxide; a third step of adhering a heat storage member to the surface of the metal layer opposite to the surface having the concave-convex shape.

23. 23. The method for producing a heat storage material according to claim 22, further comprising the step of removing at least a portion of the metal oxide after the second step.

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