Composite cooling device and method for manufacturing same

Abstract

To exhibit a high radiation cooling function by improving plane thermal conductivity by effectively suppressing the occurrence of local deterioration due to heat while maintaining a configuration excellent in economic efficiency by suppressing the use of an expensive material.SOLUTION: A composite cooling device (CP) includes an infrared radiation layer (J) that radiates infrared light from a radiation surface (H), and a light reflection layer (B) that is located on a side of the infrared radiation layer (J) opposite to a side where the radiation surface (H) is present, wherein the infrared radiation layer (J) is made of an infrared radiation resin material that emits heat radiation energy larger than absorbed sunlight energy at a wavelength of 8 μm to 13 μm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a complex cooling device including an infrared emitting layer that emits infrared light from an emitting surface and a light reflecting layer that is located on the infrared emitting layer opposite to the side where the emitting surface is present, and a manufacturing method thereof. [Background technology]

[0002] BACKGROUND ART A hybrid cooling device is known as a device that can passively cool an object to be cooled, for example, outdoors under the blazing sun, without using an external energy source (see, for example, Patent Document 1). For this reason, as disclosed in Patent Document 2, for example, a technology has been proposed in which a box with a radiative cooling function is applied to boxes equipped with housings for storing various items, such as a power distribution case for storing electrical equipment for power distribution, a battery case for storing storage batteries, an electrical case for storing electrical equipment, and a container for storing various transport items, in which it is desired to suppress the rise in the internal temperature of the housing in a daytime solar radiation environment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-165611 [Patent Document 2] Patent No. 7454968 Summary of the Invention [Problem to be solved by the invention]

[0004] Now, among the devices (boxes) with radiative cooling functions known to date, many have a relatively thin metal layer as a light-reflecting layer from the viewpoints of economy and daylighting, as described in Patent Document 2. In such devices (boxes) with radiative cooling functions, when a heat source is locally present inside, the temperature rises only in a part of the device due to the low planar thermal conductivity of the device, which causes problems such as localized deterioration of the combined cooling device due to heat and obstruction of efficient radiation. Therefore, for example, as a conventional technique, it is conceivable to increase the thickness of the metal layer as the light reflecting layer, but this is not desirable because it makes the entire device expensive and also makes the device less flexible.

[0005] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a composite cooling device that can effectively suppress localized deterioration due to heat while maintaining an economical configuration by reducing the use of expensive materials, and can improve planar thermal conductivity to exhibit high radiative cooling performance, as well as a manufacturing method thereof. [Means for solving the problem]

[0006] The combined cooling device for achieving the above object is: an infrared emitting layer that emits infrared light from a radiation surface; and a light reflecting layer that is located on the infrared emitting layer on the opposite side to the radiation surface, The infrared radiation layer is made of an infrared radiation resin material that emits thermal radiation energy at a wavelength of 8 μm to 13 μm that is greater than the absorbed solar light energy, and the composite cooling device has the following characteristics: The present invention is characterized in that a substrate layer containing flaky carbon in which a plurality of graphenes are stacked in layers is provided on the side of the light reflecting layer opposite to the side on which the infrared emitting layer is present.

[0007] According to the above-mentioned characteristic configuration, in addition to the infrared emitting layer and the light reflecting layer, the substrate layer is provided which contains flaky carbon formed by stacking multiple layers of graphene with high thermal conductivity, so that, for example, even if the object to be cooled (heat source) is locally present at a predetermined position in the layer direction along the substrate layer, the heat of the object to be cooled (heat source) can be conducted along the layer direction of the substrate layer. As a result, the heat is diffused over a wide area of ​​the infrared emitting layer in the layer direction, thereby realizing efficient radiation. Furthermore, even if the object to be cooled (heat source) is located locally at a specific position in the layer direction along the base material layer, the heat of the object to be cooled (heat source) can be conducted along the layer direction of the base material layer, thereby preventing the composite cooling device from deteriorating due to localized heating. Furthermore, since the base layer is provided on the side of the light reflecting layer opposite to the side on which the infrared emitting layer is present, it is possible to effectively suppress absorption of sunlight incident from the emitting surface. As a result, it is possible to realize a composite cooling device that can effectively suppress localized deterioration due to heat, improve planar thermal conductivity, and exhibit high radiative cooling capabilities, while maintaining an economical configuration by reducing the use of expensive materials such as silver as a light-reflecting layer.

[0008] Further features of the combined cooling device include: The base layer is characterized in that the base resin material contains 0.5% by mass or more and 50% by mass or less of the flaky carbon.

[0009] As described above, by forming the substrate layer by incorporating 0.5% by mass or more of flake carbon into a predetermined substrate resin material, sufficient thermal conductivity can be obtained to adequately demonstrate radiative cooling function. On the other hand, by incorporating 50% by mass or less of flake carbon into a predetermined substrate resin material, the flake carbon can be well dispersed in the substrate resin material, resulting in appropriate strength and durability. Furthermore, by maintaining the viscosity of the dispersion obtained by dispersing the flake carbon in the substrate resin material at a certain level during film formation, a substrate layer of approximately uniform thickness can be efficiently formed. It is more preferable that the base layer contains 2% by mass or more and 25% by mass or less of flaky carbon in a predetermined base resin material.

[0010] Further features of the combined cooling device include: The thickness of the base layer is 1 μm or more.

[0011] By setting the thickness of the base material layer to 1 μm or more, it is possible to realize a composite cooling device that can exhibit sufficient thermal conductivity while the base material layer satisfactorily functions to protect the light reflecting layer. Although there is no particular upper limit to the thickness of the substrate layer, the thicker it is, the more expensive it becomes, so from an economical point of view it is desirable that it is thin.

[0012] Further features of the combined cooling device include: One feature of the flaky carbon is that it has a thickness of 1 nm or more and 100 nm or less in the stacking direction in which the graphenes are stacked.

[0013] As in the above characteristic configuration, when the thickness of the flaky carbon is 1 nm or more and 100 nm or less, the base layer can exhibit sufficient thermal conductivity and heat dissipation properties. The thickness of the flaky carbon is measured by observation with a transmission electron microscope (TEM). The thickness of the flaky carbon is more preferably 1 nm or more and 20 nm or less.

[0014] Further features of the combined cooling device include: One of the flaky carbons has a maximum length, which is the longest length between one end and the other end in a layer direction perpendicular to the stacking direction in which the graphenes are stacked, of 100 nm or more.

[0015] As in the above characteristic configuration, by using flake carbon having a maximum length of 100 nm or more, which is the longest length between one end and the other end in the layer direction perpendicular to the stacking direction in which multiple graphenes are stacked, the thermal conductivity can be further improved. The maximum length of the flaky carbon is preferably 500 nm or more, and more preferably 1000 nm or more. The maximum length of the flaky carbon is not particularly limited because the longer the length, the better the thermal conductivity and heat dissipation. The upper limit of the maximum length of the flaky carbon is usually about 100 μm.

[0016] The size of the flaky carbon is measured by observation with a transmission electron microscope (TEM).

[0017] Further characteristic configurations of the combined cooling device include: The base layer is preferably composed of a base resin material that is at least one of polyester-based resin, acrylic-based resin, urethane-based resin, silicone-based resin, melamine-based resin, rubber-based resin, and epoxy-based resin, and that contains the flake-like carbon.

[0018] Further features of the combined cooling device include: The flaky carbon is dispersed inside the base layer in a form in which a layer direction perpendicular to the stacking direction in which the graphene is stacked is along the surface of the base layer.

[0019] As shown in the test results described below, the inventors have confirmed that the base layer can be endowed with appropriate thermal conductivity by dispersing flaky carbon inside the base layer in a form in which the layer direction perpendicular to the stacking direction of multiple graphene layers is along the surface of the base layer.

[0020] Further features of the combined cooling device include: The light reflecting layer contains at least one of silver, a silver alloy, aluminum, an aluminum alloy, and a copper alloy, and has a thickness of 50 nm to 500 nm.

[0021] As explained above, the thermal conductivity in the layer direction of the composite cooling device can be achieved by the base material layer, so the light-reflecting layer only needs to ensure the function of reflecting incident light from the radiation surface. That is, in the composite cooling device of the present invention, the light-reflecting layer contains at least one of silver, a silver alloy, aluminum, an aluminum alloy, and a copper alloy, and has a thickness of 50 nm or more and 500 nm or less, thereby realizing a flexible composite cooling device that appropriately reflects incident light from the radiation surface. In the composite cooling device according to the present invention, from the viewpoints explained above, the metal constituting the light reflecting layer can be made sufficiently thin, and a highly economical composite cooling device can be realized.

[0022] The composite cooling system explained so far is the light-reflecting layer is made of a light-reflecting resin material containing a plurality of fillers, The arithmetic mean particle size of the filler is preferably 2 μm or less.

[0023] The inventors have confirmed through the tests described below that by constructing the light-reflecting layer from a light-reflecting resin material containing filler with an arithmetic mean particle diameter of 2 μm or less, as in the above-mentioned characteristic configuration, the difference in refractive index between the light-reflecting resin material and the filler can ensure that a certain level of light-reflecting performance can be exhibited. The arithmetic mean particle size of the filler is preferably 2 μm or less, and more preferably 0.2 μm or more and 1 μm or less. The arithmetic mean particle size of the filler means the mean value of the shortest diameter of the filler.

[0024] The composite cooling system explained so far is the light-reflecting layer is made of a light-reflecting resin material having a plurality of pores, the refractive index of the holes is smaller than the refractive index of the light reflecting resin material, The arithmetic mean diameter of the pores is preferably 0.01 μm or more and 2.0 μm or less.

[0025] The inventors have confirmed through the tests described below that, as described above, by constructing the light-reflecting layer from a light-reflecting resin material having a plurality of pores, the refractive index of the pores being smaller than the refractive index of the light-reflecting resin material, and the arithmetic mean pore diameter of the pores being 0.01 μm or more and 2.0 μm or less, it is possible to exhibit a certain level of light-reflecting performance. The arithmetic mean pore diameter of the pores means the mean value of the shortest inner diameter of the pores.

[0026] Further features of the combined cooling device include: the infrared radiation layer is made of the infrared radiation resin material containing a plurality of fillers, The arithmetic mean particle size of the filler is 2 μm or less.

[0027] As described above, by including a filler in the infrared-emitting resin material that constitutes the infrared-emitting layer, the infrared-emitting layer can also exhibit a certain level of light-reflecting performance due to the difference in refractive index between the infrared-emitting resin layer material and the filler. This allows the infrared-emitting layer to exhibit a solar-radiation reflecting function in addition to the solar-radiation reflecting function of the light-reflecting layer, thereby increasing the reflectance of the entire combined cooling device. The arithmetic mean particle size of the filler is preferably 2 μm or less, and more preferably 0.2 μm or more and 1 μm or less.

[0028] Further features of the combined cooling device include: The infrared radiation resin material contains at least one of polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polyethylene terephthalate, polyethylene naphthalate, and polymethyl methacrylate.

[0029] Details will be given later, but as shown in Figure 2, the absorption coefficient of resins containing carbon-fluorine bonds (CF) due to CHF and CF2 is widely spread over a wide band from 8 μm to 13 μm, which is the atmospheric window, with a particularly large absorption coefficient at 8.6 μm. In addition, with regard to the wavelength band of sunlight, there is no noticeable absorption coefficient in the wavelength range from 0.3 μm to 2.5 μm, where the energy intensity is high.

[0030] In addition, resins with carbon-chlorine bonds (C-Cl) have an absorption coefficient due to the C-Cl stretching vibration that appears in a broad band with a half-width of 1 μm or more, centered around a wavelength of 12 μm. In the case of vinyl chloride resin, an absorption coefficient due to the CH bending vibration of the alkene contained in the main chain appears at a wavelength of around 10 μm due to the influence of chlorine electron withdrawal. The inventors have selected an infrared radiation resin material taking into consideration these absorption characteristics.

[0031] In particular, regarding the wavelengths at which resin materials with carbon-fluorine bonds (CF) have absorption coefficients in the ultraviolet to visible range, the bond energies of the C-C, C-H, and C-F bonds in the basic structure of polyvinylidene fluoride (PVDF) are 4.50 eV, 4.46 eV, and 5.05 eV. These correspond to wavelengths of 0.275 μm, 0.278 μm, and 0.246 μm, respectively, and light of these wavelengths is absorbed. Therefore, from the viewpoint of absorbing ultraviolet rays in the infrared emitting layer and reducing the amount of ultraviolet rays that pass through the light reflecting layer, it is preferable to use polyvinyl fluoride or polyvinylidene fluoride as the infrared emitting resin material.

[0032] A method for manufacturing a composite cooling device to achieve the above object includes: an infrared emitting layer that emits infrared light from a radiation surface; and a light reflecting layer that is located on the infrared emitting layer on the opposite side to the radiation surface, The infrared radiation layer is made of an infrared radiation resin material that emits thermal radiation energy at a wavelength of 8 μm to 13 μm that is greater than the absorbed solar light energy, and the manufacturing method of the composite cooling device is characterized by the following configuration: The present invention is characterized in that a dispersion liquid obtained by mixing and stirring flaky carbon having a plurality of graphene layers with a base resin material is applied by a bar coating method to the side of the light reflecting layer opposite to the side where the infrared radiation layer is present, and cured to form a base layer.

[0033] The inventors have confirmed through tests that, when a composite cooling device having the above-described effects is manufactured using the above-described manufacturing method, the orientation of graphene can be improved and the angle between the layer direction perpendicular to the stacking direction of multiple layers of graphene and the direction along the surface of the substrate layer can be reduced, compared to methods such as a casting method in which a resin is dropped onto a substrate layer to form a film. This improves the thermal conductivity along the layer direction of the substrate layer. [Brief explanation of the drawings]

[0034] [Figure 1] 1 is a schematic configuration diagram of a combined cooling device according to a first embodiment. [Figure 2] FIG. 10 is a schematic configuration diagram of a combined cooling device according to a second embodiment. [Figure 3] FIG. 10 is a schematic configuration diagram of a combined cooling device according to a third embodiment. [Figure 4] 1 is an SEM image of the layer surface of a substrate layer containing flaky carbon. [Figure 5] 1 is an SEM image of a cross section along the stacking direction of a substrate layer containing flaky carbon. [Figure 6] FIG. 10 is a diagram showing the relationship between the absorption coefficient of a resin material and a wavelength band. [Figure 7] FIG. 10 is a diagram showing the relationship between the light absorptance of a resin material and wavelength. [Figure 8] FIG. 1 is a diagram showing the emissivity spectrum of vinyl chloride resin. [Figure 9] FIG. 1 is a diagram showing the emissivity spectrum of vinylidene chloride resin. [Figure 10] FIG. 1 is a diagram showing the emissivity spectrum of ethylene terephthalate resin. [Figure 11] FIG. 10 is a diagram showing the relationship between the temperature of the radiation surface and the temperature of the light reflecting layer. [Figure 12]FIG. 1 is a diagram showing the light absorptance spectrum of ethylene terephthalate resin. DETAILED DESCRIPTION OF THE INVENTION

[0035] The composite cooling device and its manufacturing method according to the embodiment of the present invention are capable of effectively suppressing localized deterioration due to heat, improving planar thermal conductivity, and exhibiting high radiative cooling performance, while maintaining an economical configuration by reducing the use of expensive materials. Hereinafter, a composite cooling device according to an embodiment will be described with reference to FIGS.

[0036] [First embodiment] As shown in Fig. 1, the complex cooling device CP is formed as a film, and includes an infrared emitting layer J that emits infrared light IR from an emitting surface H and a light reflecting layer B located on the side of the infrared emitting layer J opposite to the side where the emitting surface H exists. In other words, the complex cooling device CP is configured as a radiative cooling film. The light reflecting layer B and the infrared emitting layer J are connected by a connecting layer S. In this specification, the direction in which the infrared emitting layer J and the light reflecting layer B are stacked and which is perpendicular to the radiation surface H is referred to as the stacking direction (the direction along the arrow Z in FIGS. 1 to 3), and the direction along the surfaces of the infrared emitting layer J and the light reflecting layer B and which is along the radiation surface H is referred to as the layer direction (the direction along the plane including the arrows X and Y in FIGS. 1 to 3).

[0037] In the composite cooling device CP according to the first embodiment, the first light-reflecting layer B1 as the light-reflecting layer B has a plurality of pores K and is made of a light-reflecting resin material, and the infrared radiation layer J is made of an infrared radiation resin material that emits thermal radiation energy at a wavelength of 8 μm to 13 μm that is greater than the absorbed solar light energy. From the viewpoint of improving the reflectance in the ultraviolet to visible light ranges, the infrared radiation resin material may contain a plurality of first fillers F1 as filler F, as shown in Fig. 1, and although not shown, the light reflecting resin material of the first light reflecting layer B1 may contain a plurality of second fillers F2 as filler F. Also, the resin material may contain either the first filler F1 or the second filler F2, or neither of them. The filler F can be one or more of titanium oxide, glass microbeads, silicon dioxide, ground calcium carbonate powder, barium sulfate, zinc sulfate, aluminum silicate, ground calcium carbonate, aluminum oxide, zinc oxide, zirconium oxide, cerium oxide, lanthanum oxide, rhodium oxide, magnesium oxide, and barium titanate, and the first filler F1 contained in the infrared radiation resin material and the second filler F2 contained in the light reflection resin material may be different materials. The arithmetic mean particle size of the filler F is preferably 2 μm or less, and more preferably about 0.2 μm or more and 1 μm or less.

[0038] Incidentally, the reflectivity can be improved by selecting materials for the infrared radiation layer J, the connection layer S, and the light reflection layer B that have a large difference in refractive index from each other. As an example, polyvinylidene chloride containing TiO2 can be used for the infrared radiation layer J, an acrylic adhesive can be used for the connection layer S, and polyethylene terephthalate containing multiple pores K can be used for the light reflection layer B.

[0039] The composite cooling device CP explained so far reduces the amount of solar energy absorbed to less than 2%, and the amount of solar energy absorbed at noon in the Japanese summer is 20W / m 2 That's about it.

[0040] The composite cooling device CP is disposed so that light L such as sunlight is incident on the radiation surface H. Therefore, the composite cooling device CP is configured to reflect a portion of the light L incident on the composite cooling device CP at the radiation surface H of the infrared radiation layer J, and to reflect the light L incident on the composite cooling device CP that has passed through the infrared radiation layer J (such as sunlight) at the light reflecting layer B and allow it to escape to the outside from the radiation surface H.

[0041] Incidentally, in this embodiment, light L includes ultraviolet light, visible light, and infrared light, and when these are expressed in terms of the wavelength of light as electromagnetic waves, they include electromagnetic waves with wavelengths of 10 nm to 20,000 nm (electromagnetic waves of 0.01 μm to 20 μm). The solar spectrum exists in the wavelength range from 300 nm to 4000 nm, and the intensity increases as the wavelength increases from 400 nm, and the intensity is particularly high in the wavelength range from 500 nm to 1800 nm.

[0042] The heat input to the composite cooling device CP from an object to be cooled (not shown) located on the opposite side of the light reflecting layer B from the side where the infrared radiation layer J is present (for example, heat input due to thermal conduction from the object to be cooled) is converted into infrared light IR by the infrared radiation layer J and radiated, thereby cooling the object to be cooled.

[0043] In other words, the composite cooling device CP is configured to reflect light L irradiated onto the composite cooling device CP and to radiate heat transferred to the composite cooling device CP (for example, heat transferred from the atmosphere or from the object to be cooled) to the outside as infrared light IR.

[0044] The light-reflecting layer B and the infrared-emitting layer J are connected by a connecting layer S made of at least one of an adhesive, a pressure-sensitive adhesive, and a glue. Although not shown, the connecting layer S contains at least one of a filler and hollow particles, which can improve the reflectance of light in the ultraviolet to visible region and reduce the thickness of the composite cooling device CP (particularly the light-reflecting layer B) to obtain the desired reflectance. The filler preferably has an arithmetic mean particle diameter of approximately 0.2 μm to 1 μm. Examples of suitable fillers include granulated titanium oxide, glass microbeads, silicon dioxide, ground calcium carbonate powder, barium sulfate, zinc sulfate, aluminum silicate, ground calcium carbonate, aluminum oxide, zinc oxide, zirconium oxide, cerium oxide, lanthanum oxide, rhodium oxide, magnesium oxide, and barium titanate. The hollow particles preferably have an arithmetic mean particle diameter of about 0.2 μm or more and 1 μm or less. This improves the reflectance of light in the ultraviolet to visible region, and reduces the thickness of the complex cooling device CP (particularly the light reflecting layer B) to obtain a desired reflectance.

[0045] In addition, the composite cooling device CP is used to implement a radiative cooling method in which infrared light IR is radiated from a radiation surface H opposite to the surface of the infrared radiation layer J that is in contact with the light-reflecting layer B. Specifically, the radiation surface H is directed toward the sky, and the radiation cooling method is implemented in which infrared light IR is radiated from the radiation surface H that faces the sky.

[0046] Now, in the case of the composite cooling device CP described so far, particularly when the first light-reflecting layer B1 as the light-reflecting layer B is made of a light-reflecting resin material rather than metal, if a heat source is locally present on the side opposite to the side where the radiation surface H of the device is present, the low planar thermal conductivity (thermal conductivity in the layer direction) will cause the temperature to rise only in a part of the device, which will hinder efficient radiation or cause localized deterioration of the composite cooling device CP due to heat.

[0047] Therefore, the composite cooling device CP according to the first embodiment is provided with a substrate layer HT containing flake carbon G having multiple graphenes stacked in layers on the side opposite to the side on which the infrared radiation layer J is present of the first light reflecting layer B1. The base layer HT contains flaky carbon G, which has high thermal conductivity, and therefore exhibits high thermal conductivity in the layer direction, suppressing local temperature increases in the device and suppressing local deterioration of the composite cooling device CP due to heat, while promoting efficient radiation.

[0048] The above-mentioned composite cooling device CP is configured so that the infrared radiative layer J, the light reflective layer B, and the base layer HT are flexible, thereby making the composite cooling device CP (radiative cooling film) flexible. The infrared radiation layer, the light reflection layer, and the substrate layer will be described in detail below.

[0049] [Infrared radiation layer] The infrared-emitting resin material forming the infrared-emitting layer J preferably contains an ultraviolet absorber, and the infrared-emitting layer J preferably has an arithmetic mean reflectance, which is the wavelength average of the reflectance of ultraviolet rays in the wavelength range of 340 nm to 400 nm, of 50% or less. Suitable ultraviolet absorbers include benzotriazole-based ultraviolet absorbers, triazine-based ultraviolet absorbers, hindered amine-based stabilizers, benzophenone-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, and oxanilide-based ultraviolet absorbers. Benzotriazole-based ultraviolet absorbers, triazine-based ultraviolet absorbers, and hindered amine-based stabilizers are particularly preferred because they can absorb ultraviolet rays up to the longer wavelength side. The infrared radiation resin material preferably contains at least one of polyethylene terephthalate, polyethylene naphthalate, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, and polymethyl methacrylate, and more preferably contains at least one of polyvinyl chloride, polyvinylidene chloride, and polyvinylidene fluoride.

[0050] The infrared radiation resin material that forms the infrared radiation layer J can be a colorless resin material that contains a carbon-fluorine bond (CF), a carbon-chlorine bond (C-Cl), a carbon-oxygen bond (CO), an ester bond (R-COO-R), an ether bond (COC bond), or a benzene ring. For each resin material (excluding carbon-oxygen bonds), the wavelength ranges with absorption coefficients in the atmospheric window wavelength band are shown in Figure 6.

[0051] According to Kirchhoff's law, emissivity (ε) and light absorptance (A) are equal. Light absorptance can be calculated from the absorption coefficient (α) using the equation A=1-exp(-αt) (hereafter referred to as the light absorptance equation), where t is the film thickness. In other words, by adjusting the film thickness of the infrared radiation layer J, it is possible to obtain a large thermal radiation in a wavelength band with a large absorption coefficient. When performing radiative cooling outdoors, it is recommended to use a material with a large absorption coefficient in the wavelength band of 8 μm to 13 μm, which is the atmospheric window. In addition, to suppress the absorption of sunlight, it is advisable to use a material that has no or a small absorption coefficient in the wavelength range of 0.3 μm to 4 μm, especially in the range of 0.4 μm to 2.5 μm. As can be seen from the relationship between the absorption coefficient and absorptance, the light absorptance (emissivity) changes depending on the film thickness of the resin material.

[0052] In order to lower the temperature below the surrounding atmosphere through radiative cooling in a solar radiation environment, if a material is selected that has a large absorption coefficient in the wavelength band of the atmospheric window and almost no absorption coefficient in the wavelength band of sunlight, then by adjusting the film thickness, it will absorb almost no sunlight but emit a lot of thermal radiation from the atmospheric window, meaning that it is possible to create a state in which the output from radiative cooling is greater than the input of sunlight.

[0053] Regarding carbon-fluorine bonds (CF), the absorption coefficients due to CHF and CF2 are widely distributed over a wide wavelength band from 8 μm to 13 μm, which is the atmospheric window, with a particularly large absorption coefficient at 8.6 μm. In addition, in the solar wavelength band, there is no significant absorption coefficient in the wavelength range from 0.3 μm to 2.5 μm, where the energy intensity is high.

[0054] Resin materials with carbon-fluorine bonds (CF) include: One example is polyvinylidene fluoride (PVDF), a partially fluorinated resin. In the following, polyvinylidene fluoride may be referred to as vinylidene fluoride resin, but the two terms are used to refer to the same material. The same applies to other resins.

[0055] For carbon-chlorine bonds (C-Cl), the absorption coefficient due to the C-Cl stretching vibration appears in a broad band with a half-width of 1 μm or more centered at a wavelength of 12 μm. Resin materials include polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC). In the case of polyvinyl chloride, the electron-withdrawing effect of chlorine causes an absorption coefficient at a wavelength of around 10 μm that is derived from the bending vibration of the CH of the alkene contained in the main chain.

[0056] Ester bonds (R-COO-R) and ether bonds (COC bonds) have absorption coefficients in the wavelength range of 7.8 μm to 9.9 μm. In addition, the carbon-oxygen bonds contained in ester bonds and ether bonds have strong absorption coefficients in the wavelength range of 8 μm to 10 μm. When a benzene ring is introduced into the side chain of a hydrocarbon resin, absorption appears over a wide wavelength range from 8.1 μm to 18 μm due to the vibration of the benzene ring itself and the vibration of surrounding elements caused by the influence of the benzene ring.

[0057] Resins having these bonds include ethylene terephthalate resin, ethylene naphthalate resin, and polymethyl methacrylate resin.

[0058] [Considerations of light absorption] Let us consider the light absorption in the ultraviolet-visible region of resin materials with the bonds and functional groups described above, i.e., sunlight absorption. The origin of the absorption of ultraviolet to visible light is the transition of electrons that contribute to the bond. Absorption in this wavelength range can be understood by calculating the bond energy. First, let's consider the wavelengths at which resin materials with carbon-fluorine bonds (CF) have absorption coefficients in the ultraviolet to visible range. The bond energies of the CC, CH, and CF bonds in the basic structural parts of polyvinylidene fluoride (PVDF) are 4.50 eV, 4.46 eV, and 5.05 eV. These correspond to wavelengths of 0.275 μm, 0.278 μm, and 0.246 μm, respectively, and light of these wavelengths is absorbed.

[0059] Since the solar spectrum only contains wavelengths longer than 0.300 μm, when fluororesin is used, it hardly absorbs the ultraviolet, visible, or near-infrared rays of sunlight. Note that ultraviolet rays are defined as wavelengths shorter than 0.400 μm, visible light is defined as wavelengths from 0.400 μm to 0.800 μm, near-infrared rays are defined as wavelengths from 0.800 μm to 3 μm, mid-infrared rays are defined as wavelengths from 3 μm to 8 μm, and far-infrared rays are wavelengths longer than 8 μm.

[0060] Regarding the carbon-chlorine bond (C-Cl), the bond energy between carbon and chlorine in alkenes is 3.28 eV, and the wavelength is 0.378 μm, so they absorb a lot of ultraviolet light in sunlight, but have almost no absorption in the visible range. Figure 7 shows the absorption spectrum of a 100 μm thick vinyl chloride resin in the ultraviolet to visible region, and shows that light absorption increases at wavelengths shorter than 0.38 μm. FIG. 7 shows the absorption spectrum of a 100 μm thick vinylidene chloride resin in the ultraviolet to visible region, and shows a slight increase in the absorption spectrum on the shorter wavelength side than 0.4 μm.

[0061] Resins with ester bonds (R-COO-R), ether bonds (C-O-C bonds), and benzene rings include methyl methacrylate resin, ethylene terephthalate resin, and ethylene naphthalate resin. For example, the bond energy of the C-C bond in acrylic is 3.93 eV, and it absorbs sunlight with wavelengths shorter than 0.315 μm, but has almost no absorption in the visible range.

[0062] As an example of a resin material having these bonds and functional groups, the absorbance spectrum from ultraviolet to visible light of a 5 mm thick methyl methacrylate resin is shown in Figure 7. The methyl methacrylate resin shown here is a commonly available product on the market, and contains a benzotriazole-based ultraviolet absorber. Because the plate is 5 mm thick, the wavelengths with small absorption coefficients are also large, and light absorption is greater at wavelengths longer than 0.315 μm and shorter than 0.38 μm.

[0063] As an example of a resin material having these bonds and functional groups, the absorption spectrum from ultraviolet to visible light of a 40 μm thick ethylene terephthalate resin is shown in FIG. As shown in the figure, the absorptance increases as the wavelength approaches 0.315 μm, and absorbance increases sharply at a wavelength of 0.315 μm. Note that with ethylene terephthalate resin, as the thickness increases, the absorptance due to the absorption edge derived from C-C bonds increases at wavelengths slightly longer than 0.315 μm, and similar to methyl methacrylate resin, the absorptance in ultraviolet light increases.

[0064] The infrared radiation layer J may be a single layer film made of one type of resin material, a multilayer film made of multiple types of resin materials, a single layer film made of a resin material in which multiple types of resin materials are blended, or a multilayer film made of a resin material in which multiple types of resin materials are blended, as long as it is made of a resin material having the above-mentioned emissivity (light emissivity) and light absorptivity properties. The blends also include copolymers such as alternating copolymers, random copolymers, block copolymers and graft copolymers, as well as modified products with substituted side chains.

[0065] [Emissivity of vinyl chloride resin and vinylidene chloride resin] Figure 8 shows the emissivity of polyvinyl chloride resin (PVC) at the atmospheric window, as a representative example of resins with carbon-chlorine bonds. Figure 9 also shows the emissivity of polyvinylidene chloride resin (PVDC) at the atmospheric window. Regarding the carbon-chlorine bond, the absorption coefficient due to the C-Cl stretching vibration appears in a broad band with a half-width of 1 μm or more centered at a wavelength of 12 μm. In addition, in the case of vinyl chloride resin, the electron-withdrawing effect of chlorine causes an absorption coefficient at a wavelength of around 10 μm, which is due to the bending vibration of the CH of the alkene contained in the main chain. The same is true for vinylidene chloride resin. Due to these effects, the wavelength average of the emissivity for a 10 μm thick film is 43% at wavelengths from 8 μm to 13 μm, which falls within the wavelength average of 43% or more as specified. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

[0066] [Emissivity of ethylene terephthalate resin] Figure 10 shows the emissivity of ethylene terephthalate resin in the atmospheric window as a typical example of a resin having an ester bond or a benzene ring. Ester bonds have an absorption coefficient in the wavelength range of 7.8 μm to 9.9 μm. Furthermore, the carbon-oxygen bond contained in the ester bond exhibits a strong absorption coefficient in the wavelength range of 8 μm to 10 μm. When a benzene ring is introduced into the side chain of a hydrocarbon resin, a wide range of absorption appears in the wavelength range of 8.1 μm to 18 μm due to the vibration of the benzene ring itself and the vibration of surrounding elements caused by the influence of the benzene ring. Due to these effects, the wavelength average of the emissivity for a 10 μm thick film is 71% at wavelengths from 8 μm to 13 μm, which falls within the wavelength average of 40% or more. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

[0067] [Surface temperature of light reflecting layer and infrared emitting layer] The thermal radiation of the atmospheric window of the infrared radiation layer J occurs near the surface of the resin material. Figure 8 shows that in the case of vinyl chloride resin, even if the thickness exceeds 100 μm, there is almost no increase in thermal radiation in the atmospheric window region. In other words, in the case of vinyl chloride resin, thermal radiation in the atmospheric window occurs within a depth of approximately 100 μm from the surface, and radiation from deeper parts does not escape to the outside. From FIG. 9, it can be seen that vinylidene chloride resin is similar to vinyl chloride resin.

[0068] 10, in the case of ethylene terephthalate resin, even if the thickness exceeds 125 μm, there is almost no increase in thermal radiation in the atmospheric window region. In other words, in the case of ethylene terephthalate resin, thermal radiation in the atmospheric window occurs at a depth of about 100 μm from the surface, and radiation from deeper parts does not escape to the outside.

[0069] As described above, the thermal radiation from the atmospheric window region generated from the surface of the resin material occurs within a depth of approximately 100 μm from the surface. If the resin thickness increases beyond this, the cold generated by the radiation cooling of the composite cooling device CP is insulated by the resin material, which does not contribute to thermal radiation. Ideally, the infrared emitting layer J is made of an infrared emitting resin material that does not absorb any sunlight, and the infrared emitting layer J is fabricated on the light reflecting layer B. In this case, sunlight is absorbed only by the light reflecting layer B of the composite cooling device CP. The thermal conductivity of resin materials is generally about 0.2 W / m / K. When this thermal conductivity is taken into account, calculations show that if the thickness of the infrared radiation layer J exceeds 20 mm, the temperature of the cooling surface (the surface of the light-reflecting layer B opposite to the side where the infrared radiation layer J is present) will rise.

[0070] Even if an ideal resin material that does not absorb sunlight at all exists, the thermal conductivity of the infrared emitting resin material of infrared emitting layer J is generally around 0.2 W / m / K, so if the thickness exceeds 20 mm as shown in Figure 11, light reflecting layer B will be heated by sunlight, and the object to be cooled placed on the side of light reflecting layer B will be heated. In other words, the thickness of the infrared emitting resin material of infrared emitting layer J needs to be 20 mm or less.

[0071] Figure 11 shows the surface temperature of the radiative surface H of the composite cooling device CP (radiative cooling film) and the temperature of the light-reflecting layer B, calculated assuming a sunny day in summer in western Japan at noon. The sunlight is assumed to be AM1.5, and the average value of the solar radiation intensity during the day in summer is 350 W / m 2The outside temperature is 30°C, and the radiant energy varies depending on the temperature, but is 100W at 30°C. This calculation assumes that no sunlight is absorbed by the infrared radiation layer J. Assuming no wind, the convective heat transfer coefficient is 5W / m 2 / K.

[0072] [Light absorption of hydrocarbon resins] If the resin material (infrared radiation resin material, light reflection resin material) is a resin whose main chain is a hydrocarbon having one or more carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, or benzene rings, absorption due to vibrations such as bond bending and stretching is observed in the near-infrared region in addition to the ultraviolet absorption due to the covalently bonded electrons mentioned above.

[0073] Specifically, absorption due to the fundamental tones of the transitions to the first excited states of CH3, CH2, and CH appears at wavelengths of 1.6 μm to 1.7 μm, 1.65 μm to 1.75 μm, and 1.7 μm, respectively. Furthermore, absorption due to the fundamental tones of the combination tones of CH3, CH2, and CH appears at wavelengths of 1.35 μm, 1.38 μm, and 1.43 μm, respectively. Furthermore, overtones of the transitions to the second excited states of CH2 and CH appear at wavelengths around 1.24 μm. The fundamental tones of the bending and stretching of the C-H bond are distributed over a wide band from 2 μm to 2.5 μm.

[0074] Furthermore, when an ester bond (R-COO-R) or an ether bond (COC) is present, there is a large optical absorption at a wavelength of around 1.9 μm. According to the above-mentioned optical absorptance relational expression, the optical absorptance caused by these factors becomes smaller and less noticeable when the resin material film is thin, but becomes larger when the film is thick.

[0075] FIG. 12 shows the relationship between the light absorptance and the spectrum of sunlight when the film thickness of ethylene terephthalate resin having an ester bond and a benzene ring is changed. As shown in the figure, as the film thickness increases to 25 μm, 125 μm, and 500 μm, the light absorption in the wavelength range longer than 1.5 μm, which is caused by the respective vibrations, increases. Furthermore, the optical absorption increases not only on the long wavelength side but also from the ultraviolet region to the visible region, due to the broadening of the optical absorption edge caused by chemical bonding.

[0076] When the film thickness is thin, the light absorption rate is high at the wavelength with the largest absorption coefficient, but as the film thickness increases, a weak absorption coefficient at the broadened absorption edge appears as the absorptance according to the light absorption rate relational expression mentioned above. As a result, as the film thickness increases, light absorption increases from the ultraviolet region to the visible region. Regarding reflectance, if the arithmetic mean reflectance, which is the wavelength average of light reflectance at wavelengths from 400nm to 800nm, is 80% or more, and the arithmetic mean reflectance, which is the wavelength average of light reflectance at wavelengths from 800nm ​​to 1200nm, is 43% or more, then if the absorption energy of sunlight and the wavelength average of the emissivity at wavelengths from 8μm to 13μm are 43% or more, then the solar energy is 350W / m 2 Absorption is 85W / m 2 Furthermore, if the emissivity is 43% or more, the radiation can be reduced to 200 W / m on a day with good atmospheric conditions. 2 85W / m for radiation of about 2 In other words, the resin layer including the light-reflecting layer B and the infrared-emitting layer J preferably has an arithmetic mean reflectance, which is the wavelength average of the light reflectance at wavelengths of 400 nm to 800 nm, of 80% or more, an arithmetic mean reflectance, which is the wavelength average of the light reflectance at wavelengths of 800 nm to 1200 nm, of 70% or more, and a wavelength average of the emissivity at wavelengths of 8 μm to 13 μm of 43% or more.

[0077] By having the light-reflecting layer B exhibit a reflection characteristic of 80% or more arithmetic mean reflectance in the wavelength range from 400nm to 800nm, and 70% or more arithmetic mean reflectance in the wavelength range from 800nm ​​to 1200nm, the solar energy absorbed by the light-reflecting layer B in the composite cooling device (radiative cooling film) can be reduced to 25% or less, i.e., the solar energy absorbed at noon in summer can be reduced to about 85W. In addition, when humidity is high, the atmospheric window narrows, but it can be reduced to, for example, 125W / m 2Even if the radiation level drops to about 70%, an emissivity of 70% or more is desirable because it can emit more energy than solar energy.

[0078] As mentioned above, the maximum value of infrared radiation in the wavelength band of the atmospheric window in the summer in lowlands of Japan is about 160W at 30°C on a day with good atmospheric conditions, and is usually about 125W. If both the infrared emitting resin material forming the infrared emitting layer J and the light reflecting resin material forming the light reflecting layer B are ethylene terephthalate resin, a hydrocarbon resin, and the film thickness of each is 500 μm, the sum of the solar light absorption in both the infrared emitting layer J and the light reflecting layer B is 176 W / m 2 This becomes: From the above, when the infrared emitting resin material forming the infrared emitting layer J and the light reflecting resin material forming the light reflecting layer B are both ethylene terephthalate resin, a hydrocarbon-based resin, if the film thickness of each of the infrared emitting layer J and the light reflecting layer B is 500 μm or more, the radiative cooling performance will not be exhibited. In other words, the thickness of the infrared emitting resin material of the infrared emitting layer J and the thickness of the light reflecting resin material of the light reflecting layer B are each preferably 500 μm or less. The thickness of the infrared emitting resin material of the infrared emitting layer J and the thickness of the light reflecting resin material of the light reflecting layer B are each preferably 10 μm or more, and the lower limit of the film thickness is determined from the viewpoint of ensuring infrared emissivity and light reflectivity.

[0079] [Light absorption of blended resins] When a resin material (infrared radiation resin material, light reflecting resin material) is a blend of a resin with a carbon-fluorine bond main chain and a resin with a hydrocarbon main chain, light absorption in the near-infrared region due to CH, CH2, CH3, etc. appears depending on the proportion of the blended resin with a hydrocarbon main chain. When carbon-fluorine bonds are the main component, the light absorption in the near-infrared region caused by hydrocarbons is small, so the thickness can be increased up to 20 mm, which is the upper limit from the viewpoint of thermal conductivity. However, when a blended hydrocarbon resin is the main component, the thickness of each of the infrared radiation resin material and the light reflection resin material must be 500 μm or less.

[0080] The blend of fluororesin and hydrocarbon also includes those in which the fluororesin is substituted with hydrocarbon, and alternating copolymers, random copolymers, block copolymers and graft copolymers of fluoromonomers and hydrocarbon monomers.

[0081] Depending on the molecular weight and proportion of the hydrocarbon side chains substituted, optical absorption in the near-infrared region due to CH, CH2, CH3, etc. appears. When the monomers introduced as side chains or copolymers are low molecular weight, or when the density of the introduced monomers is low, optical absorption in the near-infrared region due to hydrocarbons becomes small, so the thickness can be increased up to 20 mm, which is the limit from the viewpoint of thermal conductivity. When a high molecular weight hydrocarbon is introduced as a side chain of the fluororesin or as a copolymerizable monomer, the thickness of each of the infrared radiation resin material and the light reflection resin material must be 500 μm or less.

[0082] [Thickness of the infrared radiation layer] From the viewpoint of practical use of the composite cooling device CP, it is preferable that the thickness of the infrared radiation layer J is thin. The thermal conductivity of resin materials is generally lower than that of metals, glass, etc. In order to effectively cool the object to be cooled, it is preferable that the thickness of the infrared radiation layer J is kept to the minimum necessary. The thicker the thickness of the infrared radiation layer J, the greater the thermal radiation from the atmospheric window, and once a certain thickness is exceeded, the thermal radiation energy from the atmospheric window becomes saturated.

[0083] The thickness at which the film saturates depends on the resin material, but in the case of fluororesin, saturation is generally sufficient at around 300 μm. Therefore, from the perspective of thermal conductivity, it is preferable to keep the film thickness below 300 μm rather than 500 μm. Furthermore, although thermal radiation does not saturate, even a thickness of around 100 μm can provide sufficient thermal radiation in the atmospheric window region. The thinner the thickness, the higher the thermal conductivity and the more effectively the temperature of the object being cooled can be lowered, so in the case of fluororesin, it is best to keep the thickness below around 100 μm.

[0084] The absorption coefficients resulting from carbon-silicon bonds, carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds are greater than the absorption coefficient resulting from C—F bonds. Naturally, from the perspective of thermal conductivity, it is preferable to keep the film thickness to 300 μm or less rather than 500 μm, but an even greater radiative cooling effect can be expected if the film thickness is made even thinner and thermal conductivity is increased. In the case of resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, saturation occurs even at a thickness of 100 μm, and sufficient thermal radiation is obtained in the atmospheric window region at a thickness of 50 μm. The thinner the resin material, the higher the thermal transmittance and the more effectively the temperature of the object being cooled can be lowered, so in the case of resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, a thickness of 50 μm or less reduces the insulating properties and allows the object to be cooled effectively. In the case of carbon-chlorine bonds, a thickness of 100 μm or less allows the object to be cooled effectively.

[0085] The benefit of thinning the resin is not just that it reduces heat insulation and makes it easier to transfer cold. It also reduces the absorption of near-infrared light from CH, CH2, and CH3 in the near-infrared range, which is exhibited by resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds. Thinning the resin reduces the amount of sunlight absorbed by these bonds, which increases the cooling capacity of the composite cooling device CP. From the above perspective, in the case of resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, or benzene rings, a thickness of 50 μm or less can more effectively produce a radiative cooling effect under sunlight.

[0086] In the case of carbon-silicon bonds, thermal radiation is saturated in the atmospheric window region even at a thickness of 50 μm, and sufficient thermal radiation can be obtained in the atmospheric window region even at a thickness of 10 μm. The thinner the infrared radiation layer J, the higher the thermal transmittance and the more effectively the temperature of the object to be cooled can be lowered, so in the case of resins containing carbon-silicon bonds, a thickness of 10 μm or less reduces the insulating properties and allows the object to be cooled effectively. Thinner layers can reduce solar absorption, thereby increasing the cooling capacity of the composite cooling device CP. From the above perspective, in the case of resins containing carbon-silicon bonds, a thickness of 10 μm or less can more effectively produce a radiative cooling effect under sunlight.

[0087] As described above, in the combined cooling device CP according to the first embodiment, a resin is also used for the light reflecting layer B. Although the light reflecting layer B contains pores K at a certain volume ratio, a certain amount of heat radiation can be expected. In consideration of this point, it is preferable to further reduce the thickness of the infrared radiation layer J described above.

[0088] [Details of the light-reflecting layer] The light-reflecting layer B has the above-mentioned reflection characteristics (reflecting characteristics as the composite cooling device CP) by making the refractive index of the light-reflecting resin material forming the light-reflecting layer different from the refractive index of the material inside the multiple voids K contained in the light-reflecting resin material. Specifically, the light-reflecting resin material of the light-reflecting layer B preferably contains at least one of polyethylene terephthalate, polypropylene, polyethylene, polyethylene naphthalate, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polymethyl methacrylate, and polycarbonate. Conversely, polyimide and bakelite are not desirable as the light-reflecting resin material of the light-reflecting layer B because the resin itself is easily colored and the reflectance is easily reduced.

[0089] Furthermore, various gases or fluids can be contained inside the pores K of the light-reflecting resin material of the light-reflecting layer B, but air is preferably contained therein. The refractive index of the pores K (more specifically, the gas or fluid contained in the pores K) is smaller than that of the light-reflecting resin material. The arithmetic mean diameter of the pores K is preferably 0.1 μm or more and 2.0 μm or less. The shape of the holes K can be various shapes such as spherical or elliptical, but from the viewpoint of improving light reflectance, it is preferable that they be flat, and more preferably, the long axis of the holes K is aligned in a direction along the film surface (radiation surface H) of the composite cooling device CP. Furthermore, the volume fraction of the pores K in the light reflecting layer B is preferably 0.1% by volume or more and 60% by volume or less, more preferably 1% by volume or more and 50% by volume or less, and even more preferably 10% by volume or more and 40% by volume or less.

[0090] Furthermore, as a result of extensive research by the inventors, the thickness of the light-reflecting resin material of the light-reflecting layer B is preferably 10 μm or more and 500 μm or less. By setting the thickness of the light-reflecting resin material of the light-reflecting layer B to 10 μm or more, the light-reflecting layer B made of a light-reflecting resin material having a plurality of pores K can satisfactorily ensure the reflectivity required for radiative cooling. In addition, by setting the thickness to 500 μm or less, the heat-insulating effect of the light-reflecting resin material having pores K containing air or the like can be kept below a certain level, thereby ensuring a certain level of cooling performance for the object to be cooled. The thickness of the light-reflecting resin material of the light-reflecting layer B is preferably 50 to 300 μm, and more preferably 75 to 200 μm. A thickness of 500 μm or more reduces the thermal conductivity in the thickness direction and increases the heat insulation. Therefore, when applied to a housing with an internal heat source, the heat accumulation within the housing increases, which is undesirable from the perspective of heat radiation.

[0091] [Details of base layer] As described above, the base layer HT is composed of a base resin material, which is a predetermined resin material, and contains flake carbon G in which multiple graphenes are stacked in layers on the side opposite to the side of the light-reflecting layer B where the infrared radiation layer J is present. The base layer HT preferably contains 0.5% by mass or more and 50% by mass or less of flaky carbon G in the base resin material, and more preferably 2% by mass or more and 25% by mass or less. By configuring the substrate layer HT by including 0.5% by mass or more of flaky carbon G in a predetermined substrate resin material, sufficient thermal conductivity can be obtained to properly demonstrate the radiative cooling function. On the other hand, by configuring the substrate layer HT by including 50% by mass or less of flaky carbon G in a predetermined substrate resin material, the flaky carbon G can be well dispersed in the substrate resin material, resulting in appropriate strength and durability. Furthermore, by maintaining the viscosity of the dispersion obtained by dispersing the flaky carbon G in the substrate resin material at a certain level or less during film formation, a substrate layer HT with a substantially uniform thickness can be efficiently formed. If the flaky carbon G is less than 0.5% by mass, there is a risk that sufficient thermal conductivity may not be exhibited, whereas if the flaky carbon G is more than 50% by mass, there is a risk that appropriate strength and durability may not be obtained.

[0092] The thickness of the substrate layer HT is preferably 1 μm or more, and more preferably 5 μm or more. By making the thickness of the substrate layer HT 1 μm or more, it is possible to realize a composite cooling device CP that can exhibit sufficient thermal conductivity while the substrate layer HT satisfactorily functions to protect the light-reflecting layer B. Although there is no particular upper limit on the thickness of the substrate layer HT, the thicker it is, the more expensive it becomes, so from an economical standpoint, it is desirable for it to be thin. Furthermore, the base resin material for the base layer HT is at least one of polyester-based resin, acrylic-based resin, urethane-based resin, silicone-based resin, melamine-based resin, rubber-based resin, and epoxy-based resin, which makes it easier for the flake carbon G to be held in a dispersed state within the resin material.

[0093] Because the flaky carbon G has excellent thermal conductivity, its thickness (the stacking direction in which multiple graphenes are stacked, Lz in the cross-sectional SEM image of FIG. 5) is 1 nm to 100 nm, preferably 1 nm to 20 nm. When the thickness of the flaky carbon G is 100 nm or less, a substrate layer HT having sufficient thermal conductivity can be obtained.

[0094] In the base layer HT, the content of flaky carbon G having a thickness of 1 nm to 20 nm relative to all flaky carbon G is 80 mass % or more, more preferably 90 mass % or more. The base layer HT may contain flaky carbon G having a thickness exceeding 20 nm. Preferably, the thickness of most of the flaky carbon G in the base layer HT is adjusted to 20 nm or less.

[0095] The thickness of the flaky carbon G is measured by observation with a transmission electron microscope (TEM).

[0096] The flaky carbon G preferably has a layered structure in which 300 or less layers of graphene (i.e., 1 to 300 layers) are stacked, more preferably has a layered structure in which 1 to 60 layers of graphene are stacked, and even more preferably has a layered structure in which 1 to 30 layers of graphene are stacked.

[0097] In the base layer HT, the content of flaky carbon G having 1 to 30 layers relative to the total flaky carbon G is preferably 80% by mass or more, more preferably 90% by mass or more. The base layer HT may contain flaky carbon G having more than 30 layers. Preferably, in the base layer HT, most of the flaky carbon G has 30 layers or less.

[0098] The number of layers of the flaky carbon G was calculated based on the thickness measured by observation with a transmission electron microscope (TEM).

[0099] Since the flaky carbon G usually has a planar shape (shape along the layer direction) with many convex and concave angles, it is difficult to define its size other than its thickness. In this specification, the size of one flaky carbon G in the layer direction is defined by the maximum length (e.g., Lx in the surface SEM image of Figure 4), which is the longest length between one end and the other end of one flaky carbon G in the layer direction perpendicular to the stacking direction in which multiple graphenes are stacked. The maximum length of the flaky carbon G is preferably 100 nm or more, more preferably 500 nm or more, and even more preferably 1000 nm or more. By including flaky carbon G having a size within this range in the base layer HT, the thermal conductivity can be further improved.

[0100] Since larger flaky carbon G is preferable because it has better thermal conductivity, there is no particular upper limit to the maximum length of the flaky carbon G. The upper limit of the maximum length of the flaky carbon G is usually about 100 μm.

[0101] The maximum length of the flaky carbon G is measured by observation with a transmission electron microscope (TEM).

[0102] [Method for manufacturing a composite cooling device] In the manufacturing method of the complex cooling device CP according to the first embodiment, first, a dispersion liquid is prepared by mixing and stirring flaky carbon G having a plurality of graphene layers stacked thereon with a base resin material. Next, the above dispersion liquid is applied by a bar coating method to the infrared radiation layer J and the first light reflecting layer B1 connected by the connecting layer S on the side of the first light reflecting layer B1 opposite to the side on which the infrared radiation layer J is present, and then cured to form the base material layer HT. The viscosity of the dispersion applied by the bar coating method is about 0.1 mPa·s or more and 3000 mPa·s or less, and the moving speed of the bar coater in the bar coating method is 0.3 m / min or more and 20 m / min or less.

[0103] In the substrate layer HT of the composite cooling device CP manufactured by the above-mentioned manufacturing method, when viewed from above on the surface of the substrate layer HT, it can be seen that multiple flake carbon G are present in a form that is approximately uniformly dispersed in the layer direction, as shown in the surface SEM image of Figure 4.

[0104] Furthermore, in the substrate layer HT manufactured by the above-mentioned manufacturing method, when viewed in a cross-section along the stacking direction of the composite cooling device CP, as shown in the cross-sectional SEM image in Figure 5, it can be seen that the flake carbon G is dispersed inside the substrate layer HT in a form in which the layer direction (Y1 in Figure 5) perpendicular to the stacking direction in which multiple graphenes are stacked is along the surface of the substrate layer HT (the interface between the substrate layer HT and the light-reflecting layer B, the surface along the arrow Y in Figure 5). The inventors have confirmed through the test described below that the base layer HT manufactured by the above-mentioned manufacturing method exhibits high thermal conductivity in the layer direction.

[0105] Second Embodiment A composite cooling device CP according to a second embodiment will be described with reference to FIG. The complex cooling device CP according to the second embodiment differs from the complex cooling device CP according to the first embodiment in the configuration of the light reflecting layer B. The following description will focus on the configuration related to the light reflecting layer B, and the same configuration as that of the combined cooling device CP according to the first embodiment will be given the same reference numerals as in FIG. 1 and the description thereof may be omitted. The light-reflecting layer B of the composite cooling device CP of the second embodiment is composed of a first light-reflecting layer B1 made of a light-reflecting resin material containing a plurality of second fillers F2, and a second light-reflecting layer B2 made of metal. The first light reflecting layer B1 and the second light reflecting layer B2 are connected by a connecting layer S, and the first light reflecting layer B1 and the second light reflecting layer B2 are provided in the stated order from the side closer to the infrared radiation layer J. A base layer HT is provided on the side of the second light reflecting layer B2 opposite to the side where the first light reflecting layer B1 is present. In the second embodiment, the light reflecting layer B may have only the second light reflecting layer B2 without providing the first light reflecting layer B1.

[0106] The second light reflecting layer B2 is made of a metal containing at least one of silver, a silver alloy, aluminum, an aluminum alloy, and a copper alloy. The thickness of the second light reflecting layer B2 is preferably 50 nm or more and 500 nm or less.

[0107] In addition, in the composite cooling device CP according to the second embodiment, the first light reflecting layer B1 does not include pores K, and the infrared radiation resin material of the infrared radiation layer J does not include the first filler F1.

[0108] Third Embodiment A composite cooling device CP according to a third embodiment will be described with reference to FIG. The complex cooling device CP according to the third embodiment differs from the complex cooling device CP according to the first embodiment in the configuration of the light reflecting layer B. The following description will focus on the configuration related to the light reflecting layer B, and the same configuration as that of the combined cooling device CP according to the first embodiment will be given the same reference numerals as in FIG. 1 and the description thereof may be omitted. The light reflecting layer B of the complex cooling device CP according to the second embodiment is composed of a second light reflecting layer B2 made of metal. A protective layer PT is provided on the infrared radiation layer J side of the second light reflecting layer B2 to protect the second light reflecting layer B2 made of metal. That is, in the composite cooling device CP according to the second embodiment, an infrared radiation layer J, a protective layer PT, a second light-reflecting layer B2, and a base material layer HT are arranged in the stated order from the radiation surface H side, and the infrared radiation layer J and the protective layer PT are connected by a connection layer S, and the protective layer PT and the second light-reflecting layer B2 are connected by a connection layer S. The protective layer PT is preferably made of a material such as an acrylic resin, a urethane resin, a silicone resin, a polyvinyl chloride resin, a polyvinylidene chloride resin, a polyvinyl fluoride resin, a polyvinylidene fluoride resin, or a polyester resin, and its thickness is preferably about 1 μm or more and 500 μm or less.

[0109] The second light reflecting layer B2 is made of a metal containing at least one of silver, a silver alloy, aluminum, an aluminum alloy, and a copper alloy. The thickness of the second light reflecting layer B2 is preferably 50 nm or more and 500 nm or less.

[0110] [Test results] The results of various tests on the examples and comparative examples of the composite cooling device CP described so far, including visible light reflectance (reflectance at wavelengths from 400 nm to 800 nm), infrared reflectance (reflectance at wavelengths from 800 nm to 1200 nm), infrared emissivity, planar thermal conductivity, and antifouling properties, are shown in Tables 1 and 2 below. Incidentally, Tables 1 and 2 also show various characteristics of the composite cooling devices CP constituting the examples and comparative examples, with the top row of the tables representing the radiation surface H and the layers listed in stacking order. Note that the tables do not show connection layers. Here, Example 1 includes an infrared radiation layer, a connection layer, a protective layer, a connection layer, a light reflection layer (metallic reflection layer), and a base layer in this order from the radiation surface side. Example 2 includes, from the radiation surface side, an infrared radiation layer, a connection layer, a light reflection layer (resin reflection layer), a connection layer, a light reflection layer (metal reflection layer), and a base layer, in this order. In Examples 3 and 4, an infrared radiation layer, a connection layer, a light reflection layer (resin reflection layer), and a base layer are provided in this order from the radiation surface side. Comparative Examples 1 and 2 have an infrared emitting layer, a connecting layer, a protective layer, a connecting layer, a light reflecting layer (metallic reflecting layer), and a base layer in this order from the emitting surface side. Comparative Example 3 has a configuration in which no infrared radiation layer is provided, and includes a protective layer, a connection layer, a light reflecting layer (metallic reflecting layer), and a base layer in the order listed. Comparative Example 4 has a configuration in which no infrared radiation layer is provided, and includes a light reflection layer (resin reflection layer) and a substrate layer in the order shown.

[0111] Visible light reflectance (reflectance at wavelengths from 400 nm to 800 nm) was evaluated using the arithmetic mean of reflectance at wavelengths from 400 nm to 800 nm measured using a UV-Visible Spectrometer UV-2600 (Shimadzu Corporation). A reflectance of 80% or higher was defined as meeting the criteria (high reflectance at wavelengths from 400 nm to 800 nm).

[0112] Infrared reflectance (reflectance at wavelengths from 800 nm to 1200 nm) was evaluated using the arithmetic mean of reflectance at wavelengths from 800 nm to 1200 nm measured using an ultraviolet-visible spectrometer UV-2600 (Shimadzu Corporation). A reflectance of 80% or higher was defined as satisfying the condition (high reflectance at wavelengths from 800 nm to 1200 nm).

[0113] Infrared emissivity was evaluated using the arithmetic mean of the emissivity in the wavelength range of 8 μm to 13 μm measured using an FT-IR Tracer-100 (Shimadzu Corporation). Products with an emissivity of 90% or higher were defined as meeting the criteria (high emissivity in the wavelength range of 8 μm to 13 μm).

[0114] For the planar thermal conductivity test, each sample was attached to an A4-sized, 0.3 mm thick SUS316 plate, a heat source (60°C) was attached to the top right corner, and the temperature at the bottom left corner was measured with a thermocouple to evaluate the thermal conductivity. The closer the temperature was to 60°C, the higher the planar thermal conductivity. A temperature of 37°C or higher was defined as high (good) planar thermal conductivity.

[0115] For stain resistance, the color difference (ΔE) before and after exposure was measured after three months of outdoor exposure in Osaka Prefecture, and stain resistance was evaluated as good if ΔE<2.0. Note that color difference ΔE refers to the "CIEDE2000 color difference" based on JIS Z8781.

[0116] In the table, PET stands for polyethylene terephthalate, and PVC stands for polyvinyl chloride.

[0117] [Table 1]

[0118] [Table 2]

[0119] As shown in the above test results, good results were obtained in all tests in Examples 1 to 4, and it can be seen that, in particular, with regard to planar thermal conductivity, those having both a metal reflective layer and a substrate layer exhibited the best thermal conductivity characteristics, as shown in Examples 1 and 2. Here, as shown in Example 3, even a combined cooling device not having a metal reflective layer exhibited thermal conductivity comparable to that of the combined cooling devices shown in Examples 1 and 2 having a metal reflective layer. Incidentally, compared to Examples 1 to 3 in which the content of flaky carbon in the base layer is as high as 20 mass %, Example 4 in which the content of flaky carbon in the base layer is as low as 5 mass % shows lower thermal conductivity.

[0120] Furthermore, as shown in Comparative Examples 1 and 2, in the case where the content of flaky carbon in the substrate layer is 0 to 0.1 mass%, which is outside the scope of the present invention, the thermal conductivity is significantly reduced compared to that shown in the Examples.

[0121] Incidentally, in Comparative Examples 3 and 4, since no infrared radiation layer is provided, the test conditions for infrared emissivity are not met, and in Comparative Example 4, the resin reflective layer, which is the outermost layer, has a porous structure with voids, so the anti-fouling conditions are not met.

[0122] [Another embodiment] (1) The radiation surface H of the infrared radiation layer J may be protected by a protective layer (not shown). The protective layer may be made of a material such as fluorine or acrylic fluorine, and its thickness is preferably about 0.1 μm or more and 100 μm or less. Polyethylene or polypropylene, which has a low emissivity at the atmospheric window, may be used as the material. The protective layer has a stain-proof function, a scratch-proof function, and also serves as a sacrificial layer.

[0123] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradictions arise. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be modified as appropriate within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0124] The composite cooling device and its manufacturing method of the present invention can be effectively used as a composite cooling device and its manufacturing method that can effectively suppress localized deterioration due to heat, improve planar thermal conductivity, and exhibit high radiative cooling function while maintaining an economical configuration by reducing the use of expensive materials. [Explanation of symbols]

[0125] B1: 1st light reflective layer B2: Second light reflective layer CP: Composite cooling device F: Filler F1: First filler F2: Second filler G: Flake carbon H: Radiation surface HT: Base material layer J: Infrared radiation layer K: Vacancy

Claims

1. an infrared emitting layer that emits infrared light from a emitting surface; and a light reflecting layer that is located on the infrared emitting layer on the opposite side to the side where the emitting surface is present; The infrared radiation layer is made of an infrared radiation resin material that emits thermal radiation energy at a wavelength of 8 μm to 13 μm that is greater than the absorbed solar light energy, A composite cooling device comprising a substrate layer containing flaky carbon on which a plurality of graphenes are stacked in layers, on the side of the light reflecting layer opposite to the side on which the infrared radiation layer is present.

2. The composite cooling device according to claim 1 , wherein the base layer contains the flaky carbon in a base resin material in an amount of 0.5 mass % to 50 mass %.

3. The complex cooling device according to claim 1 or 2, wherein the thickness of the base material layer is 1 μm or more.

4. The composite cooling device according to claim 1 or 2, wherein one of the flaky carbons has a thickness of 1 nm or more and 100 nm or less in a stacking direction in which the graphene is stacked.

5. 3. The composite cooling device according to claim 1, wherein one of the flake carbons has a maximum length, which is the maximum length between one end and the other end in a layer direction perpendicular to the stacking direction in which the graphene is stacked, of 100 nm or more.

6. The composite cooling device of claim 1 or 2, wherein the base material layer is composed of a base material resin material that is at least one of polyester-based resin, acrylic-based resin, urethane-based resin, silicone-based resin, melamine-based resin, rubber-based resin, and epoxy-based resin, and that contains the flake carbon.

7. 3. The composite cooling device according to claim 1, wherein the flaky carbon is dispersed within the substrate layer in a manner such that a layer direction perpendicular to a stacking direction in which the graphene is stacked is along the surface of the substrate layer.

8. 3. The complex cooling device according to claim 1, wherein the light reflecting layer contains at least one of silver, a silver alloy, aluminum, an aluminum alloy, and a copper alloy, and has a thickness of 50 nm to 500 nm.

9. the light-reflecting layer is made of a light-reflecting resin material containing a plurality of fillers, 3. The complex cooling device according to claim 1, wherein the filler has an arithmetic mean particle size of 2 μm or less.

10. the light-reflecting layer is made of a light-reflecting resin material having a plurality of pores, the refractive index of the holes is smaller than the refractive index of the light reflecting resin material, 3. The complex cooling device according to claim 1, wherein the arithmetic mean diameter of the pores is 0.01 μm or more and 2.0 μm or less.

11. the infrared radiation layer is made of the infrared radiation resin material containing a plurality of fillers, 3. The complex cooling device according to claim 1, wherein the filler has an arithmetic mean particle size of 2 μm or less.

12. 3. The composite cooling device according to claim 1, wherein the infrared radiation resin material includes at least one of polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polyethylene terephthalate, polyethylene naphthalate, and polymethyl methacrylate.

13. an infrared emitting layer that emits infrared light from a emitting surface; and a light reflecting layer that is located on the infrared emitting layer on the opposite side to the side where the emitting surface is present; A method for manufacturing a composite cooling device, wherein the infrared radiation layer is made of an infrared radiation resin material that emits thermal radiation energy at a wavelength of 8 μm to 13 μm that is greater than absorbed solar light energy, A method for manufacturing a composite cooling device, comprising: mixing and stirring flaky carbon having a plurality of graphene layers with a base resin material; applying the obtained dispersion liquid by a bar coating method to the side of the light reflecting layer opposite to the side where the infrared radiation layer is present; and curing the dispersion liquid to form a base layer.

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