Radiative cooling device and radiative cooling method

Abstract

Provided is a radiant cooling device that can be made flexible and can cool an object to be cooled, even in a solar radiation environment.　The radiant cooling device comprises: an infrared radiation layer A that radiates infrared light IR from a radiation surface H; a light reflection layer B that is located on the opposite side of the infrared radiation layer A from the side where the radiation surface H is present; and a protection layer D that is between the infrared radiation layer A and the light reflection layer B. The infrared radiation layer A is a resin material layer J that has been adjusted to a thickness such that thermal radiation energy that is greater than absorbed sunlight energy is released in an 8 μm to 14 μm wavelength band. The light reflection layer B comprises silver or a silver alloy. The protection layer D is configured from a polyolefin resin at a thickness of 300 nm to 40 μm, or is configured from an ethylene terephthalate resin at a thickness of 17 μm to 40 μm.

Description

[Technical field]

[0001] The present invention provides a light emitting device comprising: an infrared emitting layer that emits infrared light from a radiation surface; a light reflecting layer that is located on a side of the infrared emitting layer opposite to a side on which the radiation surface is present; and a protective layer between the infrared emitting layer and the light reflecting layer, the infrared radiation layer is a resin material layer whose thickness is adjusted to emit thermal radiation energy in a wavelength band of 8 μm to 14 μm that is greater than the absorbed solar light energy, The present invention relates to a radiative cooling device in which the light reflective layer comprises silver or a silver alloy, and a radiative cooling method using the radiative cooling device. [Background technology]

[0002] Radiative cooling is a phenomenon in which a substance's temperature drops when it radiates electromagnetic waves such as infrared rays to its surroundings. By utilizing this phenomenon, it is possible to create a radiative cooling device that cools an object without consuming energy such as electricity. Furthermore, since the light reflective layer containing silver or a silver alloy sufficiently reflects sunlight, the object to be cooled can be cooled even in a daytime solar radiation environment.

[0003] In other words, the light reflecting layer reflects the light (ultraviolet light, visible light, infrared light) that has passed through the infrared radiation layer and radiates it from the radiation surface, thereby preventing the light (ultraviolet light, visible light, infrared light) that has passed through the infrared radiation layer from being projected onto the object to be cooled and heating the object, and thereby making it possible to cool the object to be cooled even in a daytime solar environment. Incidentally, the light reflecting layer has the effect of reflecting, toward the infrared radiation layer, in addition to the light that has transmitted through the infrared radiation layer, the light that is emitted from the infrared radiation layer toward the side where the light reflecting layer is present. However, in the following description, the light reflecting layer will be described as being provided for the purpose of reflecting light (ultraviolet light, visible light, infrared light) that has transmitted through the infrared radiation layer.

[0004] Conventional examples of such radiative cooling devices include a protective layer that contains aluminum oxide and silicon dioxide, or a protective layer that is made of polymethyl methacrylate and has a thickness of 50 nm (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2018-526599 Summary of the Invention [Problem to be solved by the invention]

[0006] In the conventional radiative cooling device disclosed in Patent Document 1, if the protective layer is configured to include aluminum oxide and silicon dioxide, the protective layer is made of an inorganic material and has no flexibility. In other words, even if the infrared emitting layer is formed of a flexible resin material layer and the light reflecting layer is configured as, for example, a thin silver film and has flexibility, the protective layer made of an inorganic material does not have flexibility, so the radiative cooling device has no flexibility. In addition, if the flexibility of the infrared emitting layer is followed, the protective layer will crack or peel off, and the protective function will be lost. In other words, the conventional radiative cooling device using an inorganic material for the protective layer had poor flexibility. Therefore, it is difficult to provide radiative cooling performance to a conventional radiative cooling device whose protective layer is made of an inorganic material by retrofitting it to an exterior wall of any shape in an existing outdoor facility.

[0007] In the conventional radiative cooling device disclosed in Patent Document 1, when the protective layer is made of polymethyl methacrylate with a thickness of 50 nm, the protective layer deteriorates in a short period of time due to absorption of ultraviolet rays, and the silver or silver alloy forming the reflective layer is discolored, which is an inconvenience.

[0008] In other words, the protective layer needs to exhibit a blocking effect, such as blocking radicals generated in the resin material layer from reaching the silver or silver alloy that forms the reflective layer, and blocking moisture that permeates the resin material layer from reaching the silver or silver alloy that forms the protective layer, thereby suppressing discoloration of the silver or silver alloy that forms the reflective layer. However, a protective layer made of polymethyl methacrylate and having a thickness of 50 nm deteriorates in a short period of time due to absorption of ultraviolet rays and no longer exhibits the above-mentioned blocking effect, which has the disadvantage of discoloring the silver or silver alloy that forms the reflective layer after a short period of time.

[0009] If the silver or silver alloy that forms the reflective layer discolors, the reflective layer will no longer be able to properly reflect sunlight and will absorb the sunlight, causing the temperature to rise. As a result, the radiative cooling device will no longer be able to cool the object to be cooled in a daytime solar radiation environment.

[0010] The present invention has been made in consideration of the above circumstances, and its purpose is to provide a radiative cooling device that is flexible and capable of cooling an object to be cooled in a solar radiation environment, and a radiative cooling method using the radiative cooling device. [Means for solving the problem]

[0011] The radiative cooling device of the present invention includes an infrared radiative layer that radiates infrared light from a radiation surface, a light reflecting layer that is positioned on the opposite side of the infrared radiative layer from the side where the radiation surface is present, and a protective layer between the infrared radiative layer and the light reflecting layer. the infrared radiation layer is a resin material layer whose thickness is adjusted to emit thermal radiation energy in a wavelength band of 8 μm to 14 μm that is greater than the absorbed solar light energy, The light reflective layer comprises silver or a silver alloy, and its characteristic configuration is as follows: The protective layer is made of a polyolefin resin and has a thickness of 300 nm or more and 40 μm or less, or made of an ethylene terephthalate resin and has a thickness of 17 μm or more and 40 μm or less.

[0012] That is, sunlight incident on the radiation surface of the resin material layer serving as the infrared radiation layer passes through the resin material layer and the protective layer, and is then reflected by the light reflecting layer located on the opposite side to the side where the radiation surface of the resin material layer is present, and is then allowed to escape from the system through the radiation surface. In the description of this specification, when simply referring to light, the concept of light includes ultraviolet light (ultraviolet light), visible light, and infrared light. When these are described 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).

[0013] In addition, the heat transferred (heat input) to the radiative cooling device is converted into infrared rays in the resin material layer and released outside the system from the radiating surface. In this way, with the above configuration, sunlight irradiated onto the radiative cooling device can be reflected, and heat transferred to the radiative cooling device (for example, heat transferred from the atmosphere or from the object to be cooled by the radiative cooling device) can be radiated outside the system as infrared light.

[0014] In addition, the resin material layer is adjusted to a thickness that emits thermal radiation energy in the wavelength range of 8 μm to 14 μm that is greater than the absorbed solar energy, and the protective layer is formed of a polyolefin resin with a thickness of 300 nm or more and 40 μm or less, or of an ethylene terephthalate resin with a thickness of 17 μm or more and 40 μm or less. Therefore, even in a daytime solar radiation environment, discoloration of the silver or silver alloy in the light reflective layer can be suppressed, and the light reflective layer can appropriately reflect sunlight while providing a cooling function even in a daytime solar radiation environment.

[0015] Since the resin material layer is made of a highly flexible resin material, the resin material layer can be made flexible, and since the protective layer is made of a highly flexible resin material, the protective layer can be made flexible. Incidentally, the light reflective layer can be made flexible by being formed as a thin silver film, for example. Therefore, the radiative cooling device comprising the resin material layer, the protective layer, and the light reflecting layer can be made flexible.

[0016] An additional explanation will be given below regarding the protective layer for preventing discoloration of silver or silver alloy in the light reflective layer. In other words, if the protective layer were not present, radicals generated in the resin material layer would reach the silver or silver alloy that forms the light-reflecting layer, or moisture that penetrates the resin material layer would reach the silver or silver alloy that forms the light-reflecting layer, causing the silver or silver alloy of the light-reflecting layer to discolor within a short period of time and no longer be able to properly perform its light-reflecting function; however, the presence of the protective layer can prevent the silver or silver alloy of the light-reflecting layer from discoloring within a short period of time.

[0017] When the protective layer is made of polyolefin resin and has a thickness of 300 nm or more and 40 μm or less, the polyolefin resin is a synthetic resin that has an ultraviolet light absorptance of 10% or less over the entire ultraviolet wavelength range of 0.3 μm to 0.4 μm, so that the protective layer is less likely to deteriorate due to absorption of ultraviolet light.

[0018] Furthermore, since the thickness of the polyolefin resin forming the protective layer is 300 nm or more, it effectively performs blocking functions such as blocking radicals generated in the resin material layer from reaching the silver or silver alloy forming the light-reflecting layer, and blocking moisture penetrating the resin material layer from reaching the silver or silver alloy forming the light-reflecting layer, thereby suppressing discoloration of the silver or silver alloy forming the light-reflecting layer.

[0019] Incidentally, the protective layer made of polyolefin resin deteriorates as it absorbs ultraviolet light, forming radicals on the surface side away from the reflective layer. However, since the thickness is 300 nm or more, the formed radicals do not reach the light reflective layer. Even if the protective layer deteriorates as radicals are formed, the rate of deterioration is slow due to the low ultraviolet light absorption, so the above-mentioned blocking function can be maintained for a long period of time.

[0020] When the protective layer is made of ethylene terephthalate resin and has a thickness of 17 μm or more and 40 μm or less, ethylene terephthalate resin is a synthetic resin that has a higher ultraviolet light absorption rate in the ultraviolet wavelength range of 0.3 μm to 0.4 μm than polyolefin resin, but since the thickness is 17 μm or more, radicals formed on the surface side of the protective layer away from the reflective layer can be prevented from reaching the reflective layer. In addition, since the thickness is 17 μm or more, the blocking function of blocking radicals generated in the resin material layer from reaching the silver or silver alloy forming the light reflective layer and blocking moisture that permeates the resin material layer from reaching the silver or silver alloy forming the light reflective layer can be well exhibited for a long period of time, and discoloration of the silver or silver alloy forming the protective layer can be suppressed.

[0021] In other words, the protective layer made of ethylene terephthalate resin will deteriorate as it absorbs ultraviolet rays, forming radicals on the surface side away from the reflective layer. However, since the thickness is 17 μm or more, the formed radicals will not reach the reflective layer. Furthermore, even if the protective layer deteriorates while forming radicals, the thickness is 17 μm or more, so the above-mentioned blocking function will be maintained for a long period of time.

[0022] In addition, when the protective layer is formed of a polyolefin resin and an ethylene terephthalate resin, the reason for setting the upper limit of the thickness is to prevent the protective layer from exhibiting heat insulation that does not contribute to radiative cooling. In other words, the thicker the protective layer is, the more heat insulation it exhibits that does not contribute to radiative cooling. Therefore, the upper limit of the thickness is set in order to avoid the protective layer from exhibiting heat insulation that does not contribute to radiative cooling while still exerting the function of protecting the reflective layer.

[0023] In summary, the characteristic configuration of the radiative cooling device of the present invention makes it possible to provide a radiative cooling device that is flexible and can cool an object to be cooled during the daytime.

[0024] A further characteristic feature of the radiative cooling device of the present invention is that the light reflecting layer has a reflectance of 90% or more at wavelengths from 0.4 μm to 0.5 μm and a reflectance of 96% or more at wavelengths longer than 0.5 μm.

[0025] That is, the solar spectrum exists in the wavelength range from 0.3 μm to 4 μm, and the intensity increases as the wavelength increases from 0.4 μm, and the intensity is particularly high in the wavelength range from 0.5 μm to 2.5 μm. If the light-reflecting layer has reflective characteristics that show a reflectance of 90% or more from 0.4 μm to 0.5 μm wavelengths and a reflectance of 96% or more at wavelengths longer than 0.5 μm, the light-reflecting layer will only absorb about 5% or less of the solar energy.

[0026] As a result, the solar energy absorbed by the light-reflecting layer at noon in summer was reduced to 50 W / m 2 The thickness can be set to about 100 μm or less, and radiation cooling by the resin material layer can be performed satisfactorily. In this specification, unless otherwise specified, the spectrum of sunlight is in accordance with the AM1.5G standard.

[0027] In summary, according to a further characteristic configuration of the radiative cooling device of the present invention, the absorption of solar energy by the light reflecting layer can be suppressed, and radiative cooling by the resin material layer can be performed satisfactorily.

[0028] A further characteristic feature of the radiative cooling device of the present invention is that the film thickness of the resin material layer is The wavelength average of the light absorptance of the light having a wavelength of 0.4 μm to 0.5 μm is 13% or less, the wavelength average of the light absorptance of the light having a wavelength of 0.5 μm to 0.8 μm is 4% or less, the wavelength average of the light absorptance of the light having a wavelength of 0.8 μm to 1.5 μm is within 1%, and the wavelength average of the light absorptance of the light having a wavelength of 1.5 μm to 2.5 μm is 40% or less, and The thickness is adjusted to provide thermal radiation characteristics such that the wavelength average emissivity from 8 μm to 14 μm is 40% or more.

[0029] The wavelength average of the light absorptance at wavelengths of 0.4 μm to 0.5 μm means the average value of the light absorptance for each wavelength in the range of 0.4 μm to 0.5 μm, and the same applies to the wavelength average of the light absorptance at wavelengths of 0.5 μm to 0.8 μm, the wavelength average of the light absorptance at wavelengths of 0.8 μm to 1.5 μm, and the wavelength average of the light absorptance at wavelengths of 1.5 μm to 2.5 μm. Other similar descriptions including emissivity also mean similar average values, and the same applies hereinafter in this specification.

[0030] That is, the light absorptivity and emissivity (light emissivity) of the resin material layer change depending on the thickness. Therefore, it is necessary to adjust the thickness of the resin material layer so that it absorbs as little sunlight as possible and emits large thermal radiation in the wavelength band of the so-called atmospheric window region (the region of light wavelengths from 8 μm to 20 μm).

[0031] Specifically, in terms of the light absorptance (light absorption characteristics) of sunlight in the resin material layer, the wavelength average light absorptance of 0.4 μm to 0.5 μm wavelengths must be 13% or less, the wavelength average light absorptance of 0.5 μm to 0.8 μm wavelengths must be 4% or less, the wavelength average light absorptance of 0.8 μm to 1.5 μm wavelengths must be within 1%, and the wavelength average light absorptance of 1.5 μm to 2.5 μm must be 40% or less. Note that for the light absorptance of 2.5 μm to 4 μm, the wavelength average must be 100% or less. When the light absorptance is distributed in this way, the light absorptance of sunlight is 10% or less, which corresponds to 100 W or less in terms of energy.

[0032] In other words, the light absorption rate of sunlight increases as the thickness of the resin material layer increases. When the resin material layer is made thick, the emissivity of the atmospheric window becomes almost 1, and the thermal radiation emitted into space is 125 W / m 2 from 160 W / m 2 It becomes. As mentioned above, the solar light absorption in the light reflecting layer is 50 W / m 2 It is preferable that: Therefore, the sum of the solar light absorption in the resin material layer and the light reflective layer is 150 W / m 2As described above, it is preferable to use a resin material layer having a small absorptance near the peak value of the solar spectrum.

[0033] Furthermore, in terms of the emissivity (thermal radiation characteristics) of the resin material layer that radiates infrared light, the wavelength average of the emissivity in the wavelength range from 8 μm to 14 μm must be 40% or more. That is, 50 W / m absorbed by the light reflecting layer 2 In order to emit the same amount of thermal radiation as sunlight from a resin material layer into space, the resin material layer needs to emit more thermal radiation than that. For example, when the outside temperature is 30°C, the maximum thermal radiation of the atmospheric window with wavelengths from 8 μm to 14 μm is 200 W / m 2 (Calculated with an emissivity of 1). This value can be obtained on a clear day in a dry environment with thin air, such as a high mountain. Since the atmosphere is thicker in lowlands than in high mountains, the wavelength band of the atmospheric window is narrower and the transmittance is lower. Incidentally, this is called the "atmospheric window becoming narrower."

[0034] In addition, the environment in which a radiative cooling device is actually used may be humid, in which case the atmospheric window is also narrow. When used in low-lying areas, the thermal radiation generated in the atmospheric window is 160 W / m at 30°C under good conditions. 2 (calculated assuming emissivity of 1). In addition, when there is haze or smog in the sky, as is common in Japan, the atmospheric window becomes even narrower and radiation into space is reduced to 125 W / m 2 It will be about that amount.

[0035] In consideration of this situation, the wavelength average of the emissivity from 8 μm to 14 μm is set to 40% or more (thermal radiation intensity in the atmospheric window band is 50 W / m 2 Unless the temperature is above 100°C, it cannot be used in low altitude areas of the mid-latitudes. Therefore, by adjusting the thickness of the resin material layer so that it falls within the above-mentioned optical specification range, the heat output at the atmospheric window becomes greater than the heat input due to the absorption of sunlight, making it possible to achieve radiative cooling outdoors even in a daytime solar radiation environment.

[0036] In short, according to a further characteristic configuration of the radiative cooling device of the present invention, the heat output at the atmospheric window is greater than the heat input due to the absorption of sunlight, making it possible to perform radiative cooling outdoors even in a solar radiation environment.

[0037] A further characteristic feature of the radiative cooling device of the present invention is that the resin material forming the resin material layer is selected from resins having one or more of a carbon-fluorine bond, a siloxane bond, a carbon-chlorine bond, a carbon-oxygen bond, an ether bond, an ester bond, and a benzene ring.

[0038] That is, the resin material that forms the resin material layer can be a colorless resin material having one or more of a carbon-fluorine bond (CF), a siloxane bond (Si-O-Si), a carbon-chlorine bond (C-Cl), a carbon-oxygen bond (CO), an ether bond (R-COO-R), an ester bond (COC), or a benzene ring.

[0039] According to Kirchhoff's law, the emissivity (ε) is equal to the light absorptivity (A). The light absorptivity (A) can be calculated from the absorption coefficient (α) using the following formula 1. A=1-exp(-αt) (Equation 1) where t is the film thickness. In other words, by increasing the thickness of the resin material layer, a large thermal radiation can be obtained in the 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 14 μm, which is the atmospheric window. In addition, to suppress the absorption of sunlight, it is recommended to use a material that has no absorption coefficient or has a small absorption coefficient in the wavelength range of 0.3 μm to 4 μm, especially 0.4 μm to 2.5 μm. As can be seen from the relationship between the absorption coefficient and light absorptance in Equation 1 above, the light absorptance (radiance) changes depending on the film thickness of the resin material layer.

[0040] In order to lower the temperature below the surrounding atmosphere by radiative cooling in a solar radiation environment, if a material 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 is selected as the resin material for forming the resin material layer, then by adjusting the film thickness of the resin material layer, it is possible to create a state in which almost no sunlight is absorbed but a lot of thermal radiation of the atmospheric window is emitted, in other words, a state in which the output by radiative cooling is greater than the input of sunlight can be created.

[0041] The absorption spectrum of the resin material forming the resin material layer will now be described. Regarding carbon-fluorine bonds (CF), the absorption coefficients due to CHF and CF2 are widely distributed over a wide band from 8 μm to 14 μm, which is the atmospheric window, with a particularly large absorption coefficient at 8.6 μm. In addition, regarding the solar wavelength band, there is no noticeable absorption coefficient in the high-energy wavelength range of 0.3 μm to 2.5 μm.

[0042] Resin materials having C—F bonds include: Polytetrafluoroethylene (PTFE), a fully fluorinated resin; Partially fluorinated resins polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), Perfluoroalkoxy fluororesin (PFA), a fluorinated resin copolymer; Tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Ethylene-tetrafluoroethylene copolymer (ETFE), Examples include ethylene-chlorotrifluoroethylene copolymer (ECTFE).

[0043] The bond energies of the C-C bond, C-H bond, and C-F bond 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 absorb light at wavelengths shorter than these. Since the solar spectrum only contains wavelengths longer than 0.300 μm, when fluororesin is used, it hardly absorbs ultraviolet light, visible light, or near-infrared light in sunlight. In addition, ultraviolet rays are defined as rays with wavelengths shorter than 0.400 μm, visible light rays are defined as rays with wavelengths ranging from 0.400 μm to 0.800 μm, near-infrared rays are defined as rays with wavelengths ranging from 0.800 μm to 3 μm, mid-infrared rays are defined as rays with wavelengths ranging from 3 μm to 8 μm, and far-infrared rays are defined as rays with wavelengths longer than 8 μm.

[0044] Resin materials with siloxane bonds (Si-O-Si) include silicone rubber and silicone resin. The resin has a large absorption coefficient caused by the stretching and contraction of the C-Si bond, which appears broadly around a wavelength of 13.3 μm, a broad absorption coefficient caused by the out-of-plane bending angle (pitch swing) of CSiH2, which appears broadly around a wavelength of 10 μm, and a small absorption coefficient caused by the in-plane bending angle (scissors) of CSiH2, which appears around a wavelength of 8 μm. Thus, it has a large absorption coefficient in the atmospheric window. In the ultraviolet region, the bond energy of the Si-O-Si main chain is 4.60 eV, which corresponds to a wavelength of 0.269 μm, and it absorbs light with wavelengths shorter than this wavelength. Since the solar spectrum only contains wavelengths longer than 0.300 μm, when siloxane bonds are used, it hardly absorbs ultraviolet, visible, or near-infrared light from sunlight.

[0045] 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. Polyvinyl chloride (PVC) is an example of a resin material that has a carbon-chlorine bond (C-Cl). In the case of polyvinyl chloride, due to the electron withdrawal of chlorine, an absorption coefficient originating from the bending vibration of CH of the alkene contained in the main chain appears at a wavelength of around 10 μm. In other words, it is possible to emit large thermal radiation in the wavelength range of the atmospheric window. The bond energy between carbon and chlorine in an alkene is 3.28 eV, which corresponds to a wavelength of 0.378 μm, and it absorbs light at wavelengths shorter than this wavelength. In other words, it absorbs ultraviolet rays from sunlight, but has almost no absorption in the visible range.

[0046] Ether bonds (R-COO-R) and ester bonds (COC) 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. Resins with these bonds include polymethyl methacrylate resin, ethylene terephthalate resin, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate. For example, the bond energy of the C-C bond in methyl methacrylate is 3.93 eV, which corresponds to a wavelength of 0.315 μm, and it absorbs sunlight with wavelengths shorter than this, but has almost no absorption in the visible range.

[0047] As long as the resin material forming the resin material layer has the above-mentioned emissivity and absorptivity characteristics, the resin material layer may be a single layer film of one type of resin material, a multilayer film of multiple types of resin materials, a single layer film of a resin material in which multiple types are blended, or a multilayer film of a resin material in which multiple types are blended. Note that blends also include copolymers such as alternating copolymers, random copolymers, block copolymers, and graft copolymers, as well as modified products with substituted side chains.

[0048] In short, according to a further characteristic configuration of the radiative cooling device of the present invention, it is possible to create a state in which the output from radiative cooling is greater than the input of sunlight.

[0049] A further characteristic feature of the radiative cooling device of the present invention is that the main component of the resin material forming the resin material layer is siloxane, The resin material layer has a thickness of 1 μm or more.

[0050] That is, as can be seen from A=1-exp(-αt) in the above formula 1, the light absorptance (emissivity) changes depending on the thickness t. The resin material needs to have a thickness that provides a large absorption coefficient in the atmospheric window. In the case of resin materials whose main component is siloxane bonds (Si-O-Si), if the film thickness is 1 μm or more, the radiation intensity at the atmospheric window becomes large, creating a state in which the output due to radiative cooling is greater than the input of sunlight.

[0051] In summary, according to a further characteristic configuration of the radiative cooling device of the present invention, when the main component of the resin material forming the resin material layer is siloxane, it is possible to create a state in which the output by radiative cooling is greater than the input of sunlight.

[0052] A further characteristic feature of the radiative cooling device of the present invention is that the thickness of the resin material layer is 10 μm or more.

[0053] In other words, in the case of a resin material whose main components are carbon-fluorine bonds (CF), carbon-chlorine bonds (C-Cl), carbon-oxygen bonds (CO), ester bonds (R-COO-R), ether bonds (COC), or benzene rings, if the film thickness is 10 μm or more, the radiation intensity at the atmospheric window becomes large, making it possible to create a state in which the output due to radiative cooling is greater than the input of sunlight.

[0054] In summary, according to a further characteristic configuration of the radiative cooling device of the present invention, when the resin material forming the resin material layer is a resin material whose main component is any one of 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), and a benzene ring, it is possible to create a state in which the output by radiative cooling is greater than the input of sunlight.

[0055] A further characteristic feature of the radiative cooling device of the present invention is that the thickness of the resin material layer is 20 mm or less.

[0056] That is, the thermal radiation from the atmospheric window of the resin material forming the resin material layer occurs within a range of about 100 μm from the material surface. In other words, even if the thickness of the resin material increases, the thickness that contributes to radiative cooling does not change, and the remaining thickness acts to insulate the cold heat after radiative cooling. Ideally, if a resin material layer that does not absorb any sunlight is created, the sunlight is absorbed only by the light reflective layer of the radiative cooling device.

[0057] The thermal conductivity of resin materials is generally around 0.2 W / m·K, and calculations taking this thermal conductivity into account show that if the thickness of the resin material layer exceeds 20 mm, the temperature of the cooling surface (the surface of the light reflective layer opposite the side where the resin material layer is present) will rise. Even if an ideal resin material exists that does not absorb any sunlight, the thermal conductivity of resin materials is generally around 0.2 W / m·K, so if the thickness is made greater than 20 mm, the thermal radiation (radiative cooling) of the resin material layer will not be able to cool the object to be cooled on the cooling surface, and the object will be exposed to solar radiation and heated, so the film thickness cannot be made greater than 20 mm.

[0058] In summary, according to a further characteristic configuration of the radiative cooling device of the present invention, the object to be cooled can be appropriately cooled.

[0059] A further characteristic feature of the radiative cooling device of the present invention is that the resin material forming the resin material layer is a fluororesin or silicone rubber.

[0060] In other words, fluororesins whose main component is carbon-fluorine bond (CF), i.e., polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesin (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer (FEPP), have almost no light absorption in the ultraviolet, visible, and near-infrared regions of the solar spectrum.

[0061] In addition, a resin that has a siloxane bond (Si-O-Si) in its main chain and a small molecular weight in its side chains, i.e., silicone rubber, like fluororesin, has almost no light absorption in the ultraviolet, visible, and near-infrared regions of the solar spectrum. The thermal conductivity of fluororesin and silicone rubber is 0.2 W / m K. Considering this, these resins can exhibit radiative cooling function even when made thicker than 20 mm.

[0062] In short, according to a further characteristic configuration of the radiative cooling device of the present invention, when the resin material of the resin material layer is a fluororesin or silicone rubber, the radiative cooling function can be properly exhibited.

[0063] A further characteristic feature of the radiative cooling device of the present invention is that the resin material forming the resin material layer is a resin having a main chain of a hydrocarbon having one or more of a carbon-chlorine bond, a carbon-oxygen bond, an ester bond, an ether bond, or a benzene ring, or a silicone resin having a hydrocarbon side chain with two or more carbon atoms; The thickness of the resin material layer is 500 μm or less.

[0064] That is, when the resin material forming the resin material layer is a resin having a main chain of a hydrocarbon having one or more of a carbon-chlorine bond (CF), a carbon-oxygen bond (CO), an ester bond (R-COO-R), an ether bond (COC), or a benzene ring, or when the resin material is a silicone resin having two or more carbon atoms in the hydrocarbon side chain, in addition to ultraviolet absorption due to covalent bond electrons, absorption due to vibrations such as bond bending and stretching appears in the near-infrared region.

[0065] Specifically, the absorption due to the reference tones of the transitions to the first excited state 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, the absorption due to the reference 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, the overtones of the transitions to the second excited state of CH2 and CH appear at wavelengths of around 1.24 μm. The reference tones of the bending and stretching of the CH bond are distributed over a wide band from 2 μm to 2.5 μm. In addition, when the structural formula is R1-CO2-R2, there is a large optical absorption at around 1.9 μm.

[0066] For example, polymethylmethacrylate resin, ethylene terephthalate resin, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and polyvinyl chloride show similar light absorption characteristics due to CH3, CH2, and CH in the near infrared region. If these resin materials are made thicker to a thickness of 20 mm, which is specified from the viewpoint of thermal conductivity, they will absorb the near infrared rays contained in sunlight and heat up. Therefore, when using these resin materials, the thickness must be 500 μm or less.

[0067] In summary, according to a further characteristic configuration of the radiative cooling device of the present invention, the absorption of near-infrared rays can be suppressed when the resin material is a resin having a main chain made of a hydrocarbon having one or more of a carbon-chlorine bond, a carbon-oxygen bond, an ester bond, an ether bond, or a benzene ring, or a silicone resin having a hydrocarbon side chain with two or more carbon atoms.

[0068] A further characteristic feature of the radiative cooling device of the present invention is that the resin material forming the resin material layer is a blend of a resin containing a carbon-fluorine bond and a siloxane bond, and a resin having a hydrocarbon main chain, and the thickness of the resin material layer is 500 μm or less.

[0069] That is, when the resin material forming the resin material layer is a blend of a resin whose main chain is a carbon-fluorine bond (CF) or a siloxane bond (Si-O-Si) and a resin whose main chain is a hydrocarbon, light absorption in the near infrared region due to CH, CH2, CH3, etc. appears depending on the ratio of the blended resin whose main chain is a hydrocarbon. When the main component is a carbon-fluorine bond or a siloxane bond, light absorption in the near infrared region due to a hydrocarbon becomes small, so the thickness can be increased up to 20 mm, which is the upper limit from the viewpoint of thermal conductivity. However, when the main component is a blended hydrocarbon resin, the thickness must be 500 μm or less.

[0070] Blends of fluororesin or silicone rubber with hydrocarbons include those in which the side chains of fluororesin or silicone rubber are replaced with hydrocarbons, and alternating copolymers, random copolymers, block copolymers, and graft copolymers of fluoromonomers, silicone monomers, and hydrocarbon monomers. Examples of alternating copolymers of fluoromonomers and hydrocarbon monomers include fluoroethylene-vinyl ester (FEVE), fluoroolefin-acrylate copolymer, ethylene-tetrafluoroethylene copolymer (ETFE), and ethylene-chlorotrifluoroethylene copolymer (ECTFE).

[0071] Depending on the molecular weight and proportion of the substituting hydrocarbon side chains, optical absorption in the near infrared region due to CH, CH2, CH3, etc. appears. When the monomer introduced as a side chain or copolymer is a low molecular weight monomer, or when the density of the monomer introduced is low, the optical absorption in the near infrared region caused by 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 a fluororesin or silicone rubber or as a copolymerizable monomer, the thickness of the resin must be 500 μm or less.

[0072] In summary, according to a further characteristic configuration of the radiative cooling device of the present invention, when the resin material is a blend of a resin containing a carbon-fluorine bond or a siloxane bond, and a resin having a hydrocarbon main chain, the absorption of near-infrared rays can be suppressed.

[0073] A further characteristic feature of the radiative cooling device of the present invention is that the resin material forming the resin material layer is a fluororesin, The thickness of the resin material layer is 300 μm or less.

[0074] That is, from the viewpoint of practical use of the radiative cooling device, it is better for the resin material layer to be thin. The thermal conductivity of resin materials is generally lower than that of metals, glass, etc. In order to effectively cool an object to be cooled, the thickness of the resin material layer should be the minimum necessary. The thicker the resin material layer is, the greater the thermal radiation of the atmospheric window becomes, and when a certain thickness is exceeded, the thermal radiation energy at the atmospheric window becomes saturated.

[0075] The thickness of the resin material layer that becomes saturated depends on the resin material, but in the case of fluororesin, saturation is generally sufficient with a thickness of about 300 μm. Therefore, from the viewpoint of thermal conductivity, it is preferable to keep the thickness of the resin material layer to 300 μm or less rather than 500 μm. Incidentally, although thermal radiation is not saturated, sufficient thermal radiation can be obtained in the window region to the atmosphere even with a thickness of about 100 μm. The thinner the thickness, the higher the thermal conductivity and the more effectively the temperature of the object to be cooled can be lowered, so for example, in the case of fluororesin, the thickness may be about 100 μm or less.

[0076] In the case of fluororesin, the absorption coefficients derived from carbon-silicon bonds, carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds are greater than the absorption coefficient derived from C-F bonds. Naturally, from the viewpoint 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 further reduced to increase thermal conductivity. As an example of fluororesin, polyvinyl fluoride (PVF) and polyvinylidene fluoride (PVDF) can be suitably used. Polyvinyl fluoride (PVF) and polyvinylidene fluoride (PVDF) are flame retardant and not easily biodegradable, so they are suitable as resin materials for forming the resin material layer of radiative cooling devices used outdoors.

[0077] In summary, according to a further characteristic configuration of the radiative cooling device of the present invention, the radiative cooling effect can be improved when the resin material is a fluororesin.

[0078] A further characteristic feature of the radiative cooling device of the present invention is that the resin material forming the resin material layer is a resin material having one or more of a carbon-chlorine bond, a carbon-oxygen bond, an ester bond, an ether bond, and a benzene ring, The thickness of the resin material layer is 50 μm or less.

[0079] In other words, in the case of a resin material containing a carbon-chlorine bond, a carbon-oxygen bond, an ester bond, an ether bond, or a benzene ring, even if the thickness is 100 μm, the thermal radiation energy in the atmospheric window is saturated, and even if the thickness is 50 μm, sufficient thermal radiation can be obtained in the atmospheric window region. The thinner the resin material, the higher the thermal conductivity and the more effectively it can lower the temperature of the object to be cooled. Therefore, in the case of resins that contain 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 more effectively.

[0080] The benefit of making the resin thinner 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 that contain carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds. Making the resin thinner reduces the amount of sunlight absorbed by these bonds, which increases the cooling capacity of radiative cooling devices. From the above perspective, in the case of resins that contain carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, a thickness of 50 μm or less can more effectively produce a radiative cooling effect under sunlight.

[0081] In summary, according to a further characteristic configuration of the radiative cooling device of the present invention, the radiative cooling effect can be improved in a resin material having one or more of a carbon-chlorine bond, a carbon-oxygen bond, an ester bond, an ether bond, and a benzene ring.

[0082] A further characteristic feature of the radiative cooling device of the present invention is that the resin material forming the resin material layer is a resin material having a carbon-silicon bond, The thickness of the resin material layer is 10 μm or less.

[0083] That is, in the case of resin materials with carbon-silicon bonds, even with a thickness of 50 μm, thermal radiation is saturated in the atmospheric window region, and even with a thickness of 10 μm, sufficient thermal radiation can be obtained in the atmospheric window region. The thinner the resin material, 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 resin materials containing carbon-silicon bonds, a thickness of 10 μm or less reduces the insulation and allows the object to be cooled more effectively. A thinner material reduces solar absorption, increasing the cooling capacity of the radiative cooling device.

[0084] From the above perspective, in the case of resin materials containing carbon-silicon bonds, a thickness of 10 μm or less can more effectively achieve radiative cooling effects under sunlight.

[0085] In summary, according to a further characteristic configuration of the radiative cooling device of the present invention, the radiative cooling effect can be improved in a resin material having carbon-silicon bonds.

[0086] A further characteristic configuration of the radiative cooling device of the present invention is that the resin material forming the resin material layer is a vinyl chloride resin or a vinylidene chloride resin, The thickness of the resin material layer is not more than 100 μm and not less than 10 μm.

[0087] That is, vinyl chloride resin (polyvinyl chloride) or vinylidene chloride resin (polyvinylidene chloride) having a thickness of 100 μm or less and 10 μm or more can provide sufficient thermal radiation in the window region of the atmosphere. Although the thermal radiation characteristics of polyvinyl chloride resin or vinylidene chloride resin are somewhat inferior to those of fluororesin, which can obtain large thermal radiation in the atmospheric window region, they are superior to other resin materials such as silicone rubber and are considerably cheaper than fluororesin, so they are effective in inexpensively constructing a radiative cooling device whose temperature drops below the ambient temperature when exposed to direct sunlight.

[0088] Furthermore, thin-film vinyl chloride resin or vinylidene chloride resin is soft and therefore difficult to be scratched by contact with other objects, and can therefore be maintained in a beautiful state for a long time. Thin-film fluororesin is hard and therefore easily scratched by contact with other objects, and therefore difficult to maintain in a beautiful state. In addition, vinyl chloride resin and vinylidene chloride resin are flame retardant and difficult to biodegrade, making them suitable as resin materials for forming the resin material layer of radiative cooling devices used outdoors.

[0089] In short, according to a further characteristic configuration of the radiative cooling device of the present invention, a radiative cooling device that is less likely to be scratched and whose temperature drops below the ambient temperature under direct sunlight can be obtained at low cost.

[0090] A further characteristic feature of the radiative cooling device of the present invention is that the light reflective layer is made of silver or a silver alloy and has a thickness of 50 nm or more.

[0091] In other words, in order for the light-reflecting layer to have the above-mentioned reflectance characteristics, i.e., a reflectance of 90% or more at wavelengths from 0.4 μm to 0.5 μm and a reflectance of 96% or more at wavelengths longer than 0.5 μm, the reflective material on the radiation surface side of the light-reflecting layer needs to be silver or a silver alloy. If the above-mentioned reflectance characteristics are to be imparted to silver or a silver alloy alone in order to reflect sunlight, a thickness of 50 nm or more is required.

[0092] In short, according to a further characteristic configuration of the radiative cooling device of the present invention, the absorption of solar energy by the light reflecting layer can be appropriately suppressed, and radiative cooling by the resin material layer can be performed satisfactorily.

[0093] A further characteristic feature of the radiative cooling device of the present invention is that the light reflecting layer has a laminated structure of silver or a silver alloy located adjacent to the protective layer and aluminum or an aluminum alloy located away from the protective layer.

[0094] That is, to give the light reflecting layer the above-mentioned reflectance characteristics, it may be a structure in which silver or silver alloy and aluminum or aluminum alloy are laminated. Note that in this case, the reflective material on the emitting surface side must be silver or silver alloy. In this case, the thickness of the silver must be 10 nm or more, and the thickness of the aluminum must be 30 nm or more.

[0095] Furthermore, since aluminum or an aluminum alloy is less expensive than silver or a silver alloy, it is possible to reduce the cost of the light reflective layer while still providing appropriate reflectance characteristics. In other words, by making the expensive silver or silver alloy thinner to reduce the cost of the light-reflecting layer, the light-reflecting layer can be made of a laminated structure of silver or silver alloy and aluminum or aluminum alloy, thereby making it possible to reduce the cost of the light-reflecting layer while maintaining appropriate reflectance characteristics.

[0096] In summary, according to a further characteristic configuration of the radiative cooling device of the present invention, it is possible to reduce the cost of the light reflective layer while maintaining appropriate reflectance characteristics.

[0097] A further characteristic feature of the radiative cooling device of the present invention is that the resin material layer, the protective layer, and the light reflecting layer are in the form of a film when stacked together.

[0098] That is, the resin material layer, the protective layer, and the light reflecting layer are laminated to form a film. That is, a radiative cooling device formed in a state in which the resin material layer, the protective layer, and the light reflecting layer are laminated is produced as a radiative cooling film. And because the resin material layer and the protective layer are flexible, by making the light reflecting layer thin and providing flexibility to the light reflecting layer, the radiative cooling device (radiative cooling film) will have flexibility.

[0099] Therefore, a film-like and flexible radiative cooling device (radiative cooling film) can be easily attached to the exterior walls of existing outdoor facilities to provide radiative cooling performance.

[0100] Incidentally, there are various ways to fabricate a radiative cooling device (radiative cooling film) in the form of a film. For example, it is possible to fabricate it by applying a protective layer and a resin material layer to a light-reflecting layer fabricated in the form of a film. Alternatively, it is possible to fabricate it by attaching a protective layer and a resin material layer to a light-reflecting layer fabricated in the form of a film. Alternatively, it is possible to form a protective layer by coating or pasting on a resin material layer fabricated in the form of a film, and then fabricate a light-reflecting layer on the protective layer by deposition, sputtering, ion plating, silver mirror reaction, etc.

[0101] In summary, a further characteristic feature of the radiative cooling device of the present invention makes it possible to retrofit existing equipment to provide radiative cooling performance.

[0102] A further characteristic feature of the radiative cooling device of the present invention is that the resin material layer and the protective layer are joined by a joining layer of an adhesive or pressure-sensitive adhesive.

[0103] In other words, since the resin material layer and the protective layer are joined with a bonding layer of adhesive or pressure-sensitive adhesive, for example, the light-reflecting layer and the protective layer can be formed in a laminated state, and a separately manufactured resin material layer and protective layer can be joined with the bonding layer, thereby making it possible to satisfactorily form the resin material layer, the protective layer, and the light-reflecting layer in a laminated state. When the adhesive or pressure-sensitive adhesive becomes weak against shear tension, the difference in thermal expansion coefficient between the resin material layer and the protective layer causes the layers to shift over time. Since the shifted portion does not have the resin material layer that serves as the infrared radiation layer, the radiation cooling performance is lost. In addition, the bonding layer is exposed in the shifted portion, and various types of deterioration begin from there. In this way, deterioration due to shear tension is a deterioration mode that should not occur. If the bonding layer is thick, it becomes weak against shear tension. In other words, the creep characteristics between the resin material layer and the protective layer become poor. From this perspective, it is desirable for the bonding layer to be thin, at 150 μm or less. However, if it is too thin, it becomes weak against peeling impact and the resin material layer and the protective layer easily peel off, so a thickness of 1 μm or more is necessary. If the bonding layer becomes thick, its thermal conductivity deteriorates, so it should not be made unnecessarily thick. For this reason, it is desirable for the bonding layer to be 100 μm or less. As described above, it is desirable for the thickness of the bonding layer to be in the range of 1 μm or more and 100 μm or less. In order to reduce the thickness of the bonding layer while improving the creep resistance and peel impact strength of the bonding layer, it is necessary to increase the degree of polymerization of the resin in the bonding layer. Increasing the degree of polymerization makes the layer harder and reduces its flexibility. From the perspective of the workability of radiative cooling materials (radiative cooling devices), flexibility and material elongation are important, and from this perspective it is even more desirable for the thickness of the bonding layer to be in the range of 1 μm or more and 50 μm or less.

[0104] Incidentally, when a bonding layer is located between the resin material layer and the protective layer, radicals will also be generated from the bonding layer. However, if the thickness of the polyolefin resin forming the protective layer is 300 nm or more and the thickness of the ethylene terephthalate resin forming the protective layer is 17 μm or more, the radicals generated in the bonding layer can be prevented from reaching the light reflective layer for a long period of time.

[0105] A further characteristic feature of the radiative cooling device of the present invention is that inorganic filler is mixed into the resin material layer.

[0106] That is, by mixing inorganic filler into the resin material layer, the resin material layer can be provided with a light scattering structure. Furthermore, by providing a light scattering structure, glare on the emitting surface when viewed can be suppressed.

[0107] The inorganic material that forms the filler is silicon dioxide (SiO2). 、 Suitable examples of the material that can be used include titanium oxide (TiO2), aluminum oxide (Al2O3), magnesium oxide (MgO), etc. When a filler is mixed into the resin material layer, both the front and back surfaces of the resin material layer become uneven.

[0108] Furthermore, since the bonding layer is located between the resin material layer and the protective layer, even if the back surface of the resin material layer is uneven, the resin material layer and the protective layer can be appropriately bonded by the bonding layer.

[0109] In summary, according to a further characteristic configuration of the radiative cooling device of the present invention, glare on the radiative surface can be suppressed and the resin material layer and the protective layer can be appropriately bonded.

[0110] A further characteristic feature of the radiative cooling device of the present invention is that both the front and back surfaces of the resin material layer are formed in an uneven shape.

[0111] That is, by forming both the front and back surfaces of the resin material layer to have projections and recesses, the resin material layer can be provided with a light scattering structure. Furthermore, by providing a light scattering structure, glare on the emitting surface when viewed can be suppressed. Incidentally, both the front and back surfaces of the resin material layer can be made uneven by embossing or scratching the surface.

[0112] Furthermore, since the bonding layer is located between the resin material layer and the protective layer, even if the back surface of the resin material layer is uneven, the resin material layer and the protective layer can be appropriately bonded by the bonding layer.

[0113] In summary, according to a further characteristic configuration of the radiative cooling device of the present invention, glare on the radiative surface can be suppressed and the resin material layer and the protective layer can be appropriately bonded.

[0114] The radiative cooling method of the present invention is a radiative cooling method in which the infrared light is radiated from the radiation surface opposite to the surface on which the light reflecting layer of the resin material layer is present, using a radiative cooling device having any of the above-mentioned characteristic configurations, and the characteristic configuration is as follows: The radiation surface is directed toward the sky, and the infrared light is emitted from the radiation surface.

[0115] According to the above configuration, the infrared light that is released from the radiation surface to the outside of the system can be radiated toward the sky, i.e., into space. Furthermore, the absorption of sunlight can be suppressed, and the cooling performance can be improved.

[0116] In short, according to the characteristic configuration of the radiative cooling method of the present invention, it is possible to improve cooling performance while suppressing absorption of sunlight. [Brief description of the drawings]

[0117] [Figure 1] FIG. 1 is a diagram illustrating the basic configuration of a radiative cooling device. [Diagram 2] FIG. 4 is a diagram showing the relationship between the absorption coefficient of a resin material and a wavelength band. [Diagram 3] FIG. 4 is a diagram showing the relationship between the light absorptance of a resin material and the wavelength. [Figure 4] FIG. 1 is a diagram showing the emissivity spectrum of silicone rubber. [Diagram 5] FIG. 1 shows the emissivity spectrum of PFA. [Figure 6] FIG. 1 is a diagram showing the emissivity spectrum of polyvinyl chloride resin. [Figure 7] FIG. 2 is a diagram showing the emissivity spectrum of ethylene terephthalate resin. [Figure 8] FIG. 1 is a diagram showing the emissivity spectrum of an olefin modified material. [Figure 9] FIG. 4 is a diagram showing the relationship between the temperature of the radiation surface and the temperature of the light reflecting layer. [Figure 10] FIG. 2 is a diagram showing the light absorptance spectra of silicone rubber and perfluoroalkoxy fluororesin. [Figure 11] FIG. 2 is a diagram showing the light absorptance spectrum of ethylene terephthalate resin. [Figure 12] FIG. 2 shows the light reflectance spectrum of a silver-based light reflective layer. [Figure 13] FIG. 2 shows the emissivity spectrum of fluoroethylene vinyl ether. [Figure 14] FIG. 2 is a diagram showing the emissivity spectrum of vinylidene chloride resin. [Figure 15] 13 is a table showing experimental results. [Figure 16] FIG. 1 is a diagram showing a specific configuration of a radiative cooling device. [Figure 17] FIG. 1 is a diagram showing a specific configuration of a radiative cooling device. [Figure 18] FIG. 1 is a diagram showing a specific configuration of a radiative cooling device. [Figure 19] FIG. 1 is a diagram showing a specific configuration of a radiative cooling device. [Figure 20] FIG. 4 is a diagram showing the relationship between the light absorptance of a resin material and the wavelength. [Figure 21] FIG. 1 is a graph showing the relationship between light transmittance and wavelength of polyethylene. [Figure 22] FIG. 1 is a diagram illustrating a test configuration. [Figure 23] FIG. 13 is a diagram showing test results when the protective layer is made of polyethylene. [Figure 24] FIG. 13 is a diagram showing test results when the protective layer is made of ultraviolet absorbing acrylic. [Diagram 25] FIG. 2 is a diagram showing the emissivity spectrum of polyethylene. [Figure 26] FIG. 1 is a diagram illustrating another configuration of a radiative cooling device. [Figure 27] 13A and 13B are diagrams illustrating a configuration in which a filler is mixed into a resin material layer. [Figure 28] 13A and 13B are diagrams illustrating a configuration in which the front and back surfaces of a resin material layer are uneven. [Figure 29] 13 is a graph showing experimental results. [Diagram 30] FIG. 1 shows a proper specific configuration of a radiative cooling device. [Diagram 31]FIG. 13 shows the light reflectance spectrum of a radiative cooling device of a suitable embodiment. [Diagram 32] FIG. 13 shows the emissivity spectrum of a radiative cooling device with a proper specific configuration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0118] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [Basic configuration of radiative cooling device] As shown in FIG. 1, the radiative cooling device CP includes an infrared emitting layer A that emits infrared light IR from a radiation surface H, a light reflecting layer B that is located on the side of the infrared emitting layer A opposite to the side where the radiation surface H exists, and a protective layer D between the infrared emitting layer A and the light reflecting layer B, which are laminated together and formed into a film. In other words, the radiative cooling device CP is configured as a radiative cooling film.

[0119] The light-reflecting layer B reflects light L, such as sunlight, that has passed through the infrared-emitting layer A and the protective layer D, and its reflection characteristics are a reflectance of 90% or more at wavelengths of 400 nm to 500 nm and a reflectance of 96% or more at wavelengths longer than 500 nm. As shown in FIG. 10, the solar spectrum exists between wavelengths of 300 nm and 4000 nm, and the intensity increases as the wavelength increases from 400 nm, and is particularly high between wavelengths of 500 nm and 1800 nm.

[0120] In this embodiment, the light L includes ultraviolet light (ultraviolet light), visible light, and infrared light, and when these are described 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). Incidentally, in this document, the wavelength range of ultraviolet light (ultraviolet light) is between 300 nm and 400 nm.

[0121] Since light-reflecting layer B exhibits a reflectance of 90% or more from 400 nm to 500 nm and a reflectance of 96% or more for wavelengths longer than 500 nm, the solar energy absorbed by the light-reflecting layer B of the radiative cooling device CP (radiative cooling film) can be reduced to 5% or less. In other words, the solar energy absorbed at noon in summer can be reduced to about 50 W.

[0122] The light-reflecting layer B is composed of silver or a silver alloy, or is composed of a laminated structure of silver or a silver alloy located adjacent to the protective layer D and aluminum or an aluminum alloy located away from the protective layer D, and is flexible, as will be described in more detail below.

[0123] The infrared radiation layer A is configured as a resin material layer J whose thickness is adjusted so that it emits thermal radiation energy in the wavelength band from 8 μm to 14 μm that is greater than the absorbed solar light energy, and its details will be described later.

[0124] Therefore, the radiative cooling device CP is configured to reflect a portion of the light L incident on the radiative cooling device CP at the radiation surface H of the infrared radiation layer A, and to reflect the light (sunlight, etc.) that is transmitted through the resin material layer J and the protective layer D from the light L incident on the radiative cooling device CP at the light reflecting layer B and to allow it to escape to the outside from the radiation surface H.

[0125] The radiative cooling device CP is configured to cool the object to be cooled E by converting the heat input from the object to be cooled E, which is located on the opposite side of the light reflecting layer B to the side where the resin material layer J is present (for example, heat input by thermal conduction from the object to be cooled E, into infrared light IR by the resin material layer J and radiating it.

[0126] In other words, the radiative cooling device CP is configured to reflect light L irradiated to the radiative cooling device CP and to radiate heat transferred to the radiative cooling device CP (e.g., heat transferred from the atmosphere or from the object to be cooled E) to the outside as infrared light IR. Furthermore, the resin material layer J, the protective layer D, and the light reflecting layer B are flexible, so that the radiative cooling device CP (radiative cooling film) is configured to be flexible.

[0127] In addition, the radiative cooling device CP is used to implement a radiative cooling method in which infrared light IR is radiated from a radiation surface H on the opposite side to the surface of the resin material layer J that is in contact with the light reflecting layer B. Specifically, the radiation surface H is directed toward the sky, and the radiative cooling method is implemented in which infrared light IR is radiated from the radiation surface H directed toward the sky.

[0128] [Outline of resin material layer] The light absorptivity and emissivity (light emissivity) of the resin material forming the resin material layer J change depending on the thickness. Therefore, it is necessary to adjust the thickness of the resin material layer J so that it absorbs as little sunlight as possible and emits large thermal radiation in the so-called atmospheric window wavelength band (wavelength band from 8 μm to 14 μm).

[0129] Specifically, in terms of the light absorptance of sunlight, the thickness of the resin material layer J needs to be adjusted to a thickness such that the wavelength average of the light absorptance from wavelengths of 0.4 μm to 0.5 μm is 13% or less, the wavelength average of the light absorptance from wavelengths of 0.5 μm to 0.8 μm is 4% or less, the wavelength average of the light absorptance from wavelengths of 0.8 μm to 1.5 μm is within 1%, the wavelength average of the light absorptance from wavelengths of 1.5 μm to 2.5 μm is 40% or less, and the wavelength average of the light absorptance from wavelengths of 2.5 μm to 4 μm is 100% or less. In the case of such an absorptance distribution, the light absorptance of sunlight is 10% or less, which corresponds to 100 W or less in terms of energy.

[0130] As described later, the light absorption rate of the resin material increases as the thickness of the resin material increases. When the resin material is made thick, the emissivity of the atmospheric window becomes almost 1, and the thermal radiation emitted into space is 125 W / m 2 from 160 W / m 2 The solar light absorption in the protective layer D and the light reflecting layer B is 50 W / m 2 The sum of the solar light absorption in the resin material layer J, the protective layer D and the light reflecting layer B is 150 W / m2 The temperature is below 100° C., and cooling proceeds if the atmospheric conditions are good. As described above, it is preferable to use a resin material that has a small light absorptance near the peak value of the solar spectrum for the resin material layer J.

[0131] Moreover, from the viewpoint of infrared radiation (thermal radiation), the thickness of the resin material layer J needs to be adjusted to a thickness such that the wavelength average of the emissivity in the wavelength range from 8 μm to 14 μm is 40% or more. 50W / m absorbed by protective layer D and light-reflecting layer B 2 In order to release about that amount of thermal energy of sunlight from the resin material layer J into space through thermal radiation from the resin material layer J, the resin material layer J needs to emit more thermal radiation than that amount. For example, when the outside temperature is 30°C, the maximum thermal radiation of the 8μm to 14μm atmospheric window is 200W / m 2 (Calculated with an emissivity of 1). This value can be obtained on a clear day in a dry environment with thin air, such as a high mountain. Since the atmosphere is thicker in lowlands than in high mountains, the wavelength band of the atmospheric window is narrower and the transmittance is lower. Incidentally, this is called the "atmospheric window becoming narrower."

[0132] In addition, the environment in which the radiative cooling device CP (radiative cooling film) is actually used may be humid, and in that case the atmospheric window will be narrow. When used in low altitudes, the thermal radiation generated in the atmospheric window area is 160 W / m at 30°C under good conditions. 2 (calculated with emissivity of 1). When there is haze or smog in the sky, which is common in Japan, the atmospheric window becomes even narrower, and radiation into space is estimated at 125 W / m 2 It will be about that amount. In consideration of this situation, the wavelength average of the emissivity from 8 μm to 14 μm is set to 40% or more (thermal radiation intensity in the atmospheric window band is 50 W / m 2 ) it cannot be used in low altitude areas of the mid-latitudes.

[0133] Therefore, if the thickness of the resin material layer J is adjusted so as to fall within the optically specified range taking into consideration the above factors, the heat output at the atmospheric window will be greater than the heat input due to absorption of sunlight, and it will be possible to cool the temperature below the outside air temperature by radiative cooling even outdoors in a solar radiation environment.

[0134] [Details of resin material] The resin material can be a colorless resin material that contains a carbon-fluorine bond (CF), a siloxane bond (Si-O-Si), 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 in which they have an absorption coefficient in the atmospheric window wavelength band are shown in Figure 2.

[0135] 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 relation A=1-exp(-αt) (hereafter referred to as the light absorptance relation). Here, t is the film thickness. In other words, by adjusting the film thickness of the resin material layer J, a large thermal radiation can be obtained 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 the atmospheric window, that is, from 8 μm to 14 μm. In addition, to suppress the absorption of sunlight, it is advisable to use a material that has no or has 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 relational equation between the absorption coefficient and the absorptance, the light absorptance (emissivity) changes depending on the film thickness of the resin material.

[0136] In order to lower the temperature below the surrounding atmosphere by 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 it is possible to create a state in which the output from radiative cooling is greater than the input of sunlight.

[0137] Regarding carbon-fluorine bonds (CF), the absorption coefficients due to CHF and CF2 are widely distributed over a wide band from 8 μm to 14 μm, which is the atmospheric window, with the absorption coefficient being particularly large at 8.6 μm. In addition, regarding the solar wavelength band, there is no noticeable absorption coefficient in the wavelength range from 0.3 μm to 2.5 μm, where the energy intensity is high.

[0138] Resin materials having carbon-fluorine bonds (CF) include: Polytetrafluoroethylene (PTFE), a fully fluorinated resin; Partially fluorinated resins polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), Perfluoroalkoxy fluororesin (PFA), a fluorinated resin copolymer; Tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Ethylene-tetrafluoroethylene copolymer (ETFE), Examples include ethylene-chlorotrifluoroethylene copolymer (ECTFE).

[0139] Resin materials having a siloxane bond (Si-O-Si) include silicone rubber and silicone resin. In this resin, a large absorption coefficient caused by the expansion and contraction of C-Si bonds appears broadly around a wavelength of 13.3 μm, an absorption coefficient caused by the out-of-plane bending angle (vertical rocking) of CSiH2 appears broadly around a wavelength of 10 μm, and a small absorption coefficient caused by the in-plane bending angle (scissors) of CSiH2 appears around a wavelength of 8 μm.

[0140] 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 resin (PVC) and polyvinylidene chloride resin (PVDC). In the case of polyvinyl chloride resin, due to the electron-withdrawing effect of chlorine, an absorption coefficient originating from the bending vibration of CH of the alkene contained in the main chain appears at a wavelength of around 10 μm.

[0141] 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.

[0142] Resins having these bonds include methyl methacrylate resin, ethylene terephthalate resin, trimethylene terephthalate resin, butylene terephthalate resin, ethylene naphthalate resin, and butylene naphthalate resin.

[0143] [Optical absorption considerations] Let us consider the light absorption in the ultraviolet-visible region of resin materials with the bonds and functional groups described above, that is, sunlight absorption. The origin of the absorption of ultraviolet to visible light is the transition of electrons that contribute to the bonds. Absorption in this wavelength range can be understood by calculating the bond energy. First, let us 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 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 absorb light of these wavelengths.

[0144] Since the solar spectrum only contains wavelengths longer than 0.300μm, 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 0.400μm, visible light as wavelengths from 0.400μm to 0.800μm, near-infrared rays as wavelengths from 0.800μm to 3μm, mid-infrared rays as wavelengths from 3μm to 8μm, and far-infrared rays as wavelengths longer than 8μm.

[0145] The absorptance spectrum of 50μm thick PFA (perfluoroalkoxy fluororesin) from the ultraviolet to visible range is shown in Figure 3, which shows that it has almost no absorptance. Although a slight increase in the absorptance spectrum is observed on the shorter wavelength side than 0.4μm, this increase is merely due to the effect of scattering in the sample used for measurement, and there is no actual increase in absorptance.

[0146] In the ultraviolet region of siloxane bonds (Si-O-Si), the bond energy of the Si-O-Si in the main chain is 4.60 eV, which corresponds to a wavelength of 269 nm. Since the solar spectrum only contains wavelengths longer than 0.300 μm, in the majority of cases, siloxane bonds hardly absorb any ultraviolet, visible, or near-infrared light in sunlight.

[0147] The absorptance spectrum of 100μm thick silicone rubber in the ultraviolet to visible range is shown in Figure 3, which shows that it has almost no absorptance. Although a slight increase in the absorptance spectrum can be seen on the shorter wavelength side than 0.4μm, this increase is merely due to the effect of scattering in the sample used for measurement, and there is no actual increase in absorptance.

[0148] Regarding the carbon-chlorine bond (C-Cl), the bond energy between the carbon and chlorine in an alkene is 3.28 eV, and the wavelength is 0.378 μm, so it absorbs a lot of ultraviolet light in sunlight, but has almost no absorption in the visible range. Figure 3 shows the absorption spectrum of a 100 μm thick polyvinyl chloride resin in the ultraviolet to visible range, and shows that optical absorption is high at wavelengths shorter than 0.38 μm. FIG. 3 shows the absorptance spectrum of a 100 μm thick vinylidene chloride resin in the ultraviolet to visible range, and a slight increase in the absorptance spectrum is observed on the shorter wavelength side than 0.4 μm.

[0149] Resins with ester bonds (R-COO-R), ether bonds (COC bonds), and benzene rings include methyl methacrylate resin, ethylene terephthalate resin, trimethylene terephthalate resin, butylene terephthalate resin, ethylene naphthalate resin, and butylene 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.

[0150] As an example of a resin material having these bonds and functional groups, the absorption spectrum from ultraviolet to visible light of a 5 mm-thick methyl methacrylate resin is shown in Figure 3. The methyl methacrylate resin shown 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 on the shorter wavelength side than 0.38 μm, which is longer than the wavelength of 0.315.

[0151] 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 the absorptance increases sharply at a wavelength of 0.315 μm. Note that with ethylene terephthalate resin, as the thickness is increased, the absorptance due to the absorption edge derived from the C-C bond increases slightly longer than the wavelength of 0.315 μm, and the absorptance in ultraviolet light increases in the same way as with commercially available methyl methacrylate resin.

[0152] As long as the resin material layer J uses a resin material having the aforementioned emissivity (light emissivity) and light absorptivity characteristics, it may be a single layer film of one type of resin material, a multilayer film of multiple types of resin materials, a single layer film of a resin material in which multiple types of resin materials are blended, or a multilayer film of a resin material in which multiple types of resin materials are blended. The blends include copolymers such as alternating copolymers, random copolymers, block copolymers and graft copolymers, as well as modified products with substituted side chains.

[0153] [Emissivity of silicone rubber] Figure 4 shows the emissivity spectrum of the air window of silicone rubber with siloxane bonds. Silicone rubber exhibits a large broad absorption coefficient due to the stretching of C-Si bonds, centered around a wavelength of 13.3 μm. CSiH2 exhibits a broad absorption coefficient due to the out-of-plane bending angle (vertical rocking) of the target object, centered around a wavelength of 10 μm. CSiH2 exhibits a small absorption coefficient due to the in-plane bending angle (scissors) of the target object, centered around a wavelength of 8 μm. Due to this effect, the wavelength average of the emissivity of a 1 μm thick film is 80% at wavelengths from 8 μm to 14 μm, which falls within the regulation of a wavelength average of 40% or more. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

[0154] Incidentally, the emission spectrum when quartz, an inorganic material, with a thickness of 1 μm is present on silver is also shown in Figure 4. When quartz is 1 μm thick, it has only a narrow-band emission peak between wavelengths of 8 μm and 14 μm. When this thermal radiation is averaged over the wavelength range from 8 μm to 14 μm, the emissivity in the wavelength range from 8 μm to 14 μm is 32%, making it difficult to demonstrate radiative cooling performance.

[0155] The radiative cooling device CP (radiative cooling film) of the present invention using the resin material layer J can obtain radiative cooling performance even with a thinner infrared radiative layer A than the conventional technology using an inorganic material as the light reflecting layer B. In other words, when the infrared radiation layer A is formed from inorganic materials such as quartz or tempax glass, the infrared radiation layer A does not provide radiative cooling performance with a film thickness of 1 μm. However, in the radiative cooling device CP of the present invention using the resin material layer J, the resin material layer J exhibits radiative cooling performance even with a film thickness of 1 μm.

[0156] [Emissivity of PFA] Figure 5 shows the emissivity in the atmospheric window of perfluoroalkoxy fluororesin (PFA), a representative example of a resin with carbon-fluorine bonds. The absorption coefficients due to CHF and CF2 are widely distributed over a wide band from 8 μm to 14 μm, which is the atmospheric window, and the absorption coefficient is particularly large at 8.6 μm. Due to this effect, the wavelength average of the emissivity of a 10 μm thick film is 45% at wavelengths from 8 μm to 14 μm, which falls within the regulation of a wavelength average of 40% or more. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

[0157] [Emissivity of polyvinyl chloride resin and vinylidene chloride resin] Figure 6 shows the emissivity of polyvinyl chloride resin (PVC) at the atmospheric window as a representative example of resin with carbon-chlorine bonds, and Figure 14 shows the emissivity of polyvinylidene chloride resin (PVDC) at the atmospheric window. For carbon-chlorine bonds, 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 the case of polyvinyl chloride resin, the absorption coefficient due to the bending vibration of CH of the alkene contained in the main chain appears at a wavelength of around 10 μm due to the electron-withdrawing effect of chlorine. The same is true for vinylidene chloride resin. Due to these effects, the wavelength average of the emissivity of a 10 μm thick film is 43% at wavelengths from 8 μm to 14 μm, which falls within the regulation of a wavelength average of 40% or more. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

[0158] [Ethylene terephthalate resin] Figure 7 shows the emissivity of ethylene terephthalate resin in the atmospheric window as a representative example of a resin having an ester bond or a benzene ring. Ester bonds have an absorption coefficient in the wavelength range from 7.8 μm to 9.9 μm. Furthermore, the carbon-oxygen bonds contained in ester bonds have a strong absorption coefficient in the wavelength range from 8 μm to 10 μm. When a benzene ring is introduced into the side chain of a hydrocarbon resin, absorption appears in a wide 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. Due to these effects, the wavelength average of the emissivity of a 10 μm thick film is 71% at wavelengths from 8 μm to 14 μm, which falls within the regulation of a wavelength average of 40% or more. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

[0159] [Emissivity of olefin modified materials] Figure 8 shows the emissivity spectrum of an olefin-modified material that does not contain carbon-fluorine bonds (CF), carbon-chlorine bonds (C-Cl), ester bonds (R-COO-R), ether bonds (COC bonds), or benzene rings, and whose main component is olefin. The sample was prepared by applying olefin resin onto evaporated silver with a bar coater and drying it. As shown in the figure, the emissivity in the atmospheric window region is small, and as a result, the wavelength average of the emissivity for a thickness of 10 μm is 27% at wavelengths from 8 μm to 14 μm, which does not fall within the regulation that the wavelength average is 40% or more.

[0160] The emissivity shown is that of an olefin resin modified for application with a bar coater, and in the case of a pure olefin resin, the emissivity in the atmospheric window region is even smaller. Thus, radiative cooling is not possible unless the molecule contains a carbon-fluorine bond (CF), a carbon-chlorine bond (C-Cl), an ester bond (R-COO-R), an ether bond (COC bond), or a benzene ring.

[0161] [Surface Temperature of Light Reflecting Layer and Resin Material Layer] Thermal radiation from the atmospheric window of the resin material layer J occurs near the surface of the resin material. As shown in Figure 4, in the case of silicone rubber, if the thickness is greater than 10 μm, the thermal radiation in the air window region does not increase. In other words, in the case of silicone rubber, most of the thermal radiation in the air window occurs within a depth of about 10 μm from the surface, and radiation from deeper areas does not escape.

[0162] As can be seen from Figure 5, in the case of fluororesin, 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 fluororesin, thermal radiation in the atmospheric window occurs within a depth of about 100 μm from the surface, and radiation from deeper parts does not escape to the outside. As can be seen from Figure 6, in the case of polyvinyl 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 polyvinyl chloride resin, thermal radiation in the atmospheric window occurs within a depth of about 100 μm from the surface, and radiation from deeper parts does not escape to the outside. From FIG. 14, it can be seen that vinylidene chloride resin is similar to vinyl chloride resin.

[0163] As shown in Fig. 7, in the case of ethylene terephthalate resin, even if the thickness exceeds 125 μm, there is almost no increase in thermal radiation in the air window region. In other words, in the case of ethylene terephthalate resin, thermal radiation in the air window occurs at a depth of about 100 μm from the surface, and radiation from deeper parts does not escape to the outside.

[0164] 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 radiative cooling device CP is insulated by the resin material that does not contribute to thermal radiation. Consider creating a resin material layer J that ideally does not absorb any sunlight on the light reflecting layer B. In this case, sunlight is absorbed only by the light reflecting layer B of the radiative cooling device CP. The thermal conductivity of resin materials is generally about 0.2 W / m / K. When calculations are made taking this thermal conductivity into account, if the thickness of the resin material layer J exceeds 20 mm, the temperature of the cooling surface (the surface of the light-reflecting layer B opposite the side where the resin material layer J is present) will rise.

[0165] Even if an ideal resin material that does not absorb any sunlight exists, the thermal conductivity of resin materials is generally about 0.2 W / m / K, so if the thickness exceeds 20 mm as shown in Figure 9, the light-reflecting layer B will be heated by solar radiation, and the object to be cooled E placed on the light-reflecting layer side will be heated. In other words, the thickness of the resin material of the radiative cooling device CP needs to be 20 mm or less.

[0166] Figure 9 is a plot of the surface temperature of the radiative surface H of the radiative cooling device (radiative cooling film) CP and the temperature of the light-reflecting layer B, calculated assuming a clear day in the south in midsummer in western Japan. The sunlight is AM1.5 and 1000W / m 2 The outside temperature is 30°C, and the radiant energy varies depending on the temperature, but is 100W at 30°C. This calculation assumes that the resin material layer does not absorb sunlight. It is assumed that there is no wind, and the convection heat transfer coefficient is 5W / m 2 / K.

[0167] [Light absorptivity of silicone rubber, etc.] Figure 10 shows the light absorptance of silicone rubber with CH3 side chains at a thickness of 100 μm against the sunlight spectrum, and the light absorptance spectrum of perfluoroalkoxy fluororesin at a thickness of 100 μm against the sunlight spectrum. As mentioned above, it can be seen that both resins have almost no light absorptance in the ultraviolet region.

[0168] For silicone rubber, in the near infrared region, the light absorptance increases in the region longer than 2.35 μm. However, because the intensity of the solar spectrum in this wavelength region is weak, even if the light absorptance on the longer wavelength side than 2.35 μm is 100%, the solar energy absorbed is only 20 W / m 2 It is.

[0169] Perfluoroalkoxy fluororesin has almost no light absorption in the wavelength range of 0.3 μm to 2.5 μm, but has light absorption on the longer wavelength side than 2.5 μm. However, even if the film thickness of the resin is increased and the light absorption on the longer wavelength side than 2.5 μm becomes 100%, the solar energy absorbed is about 7 W.

[0170] In addition, when the thickness (film thickness) of the resin material layer J is increased, the emissivity of the atmospheric window region becomes approximately 1. In other words, in the case of a thick film, the thermal radiation radiated into space in the atmospheric window region when used at low altitudes is 160 W / m at 30°C. 2 from 125 W / m 2 The light absorption in the light reflecting layer B is about 50 W / m 2 Even if the light absorption of the light reflective layer B and the sunlight absorption when the silicone rubber or perfluoroalkoxy fluororesin is made into a thick film are added together, the total amount is smaller than the thermal radiation radiated into space. From the above, the maximum film thickness of silicone rubber and perfluoroalkoxy fluororesin is 20 mm from the viewpoint of thermal conductivity.

[0171] [Light absorption of hydrocarbon resins] When the resin material forming the resin material layer J is a resin having a main chain made of a hydrocarbon having one or more carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, or benzene rings, or when the resin material is a silicone resin having two or more carbon atoms in the hydrocarbon side chain, in addition to the ultraviolet absorption due to the covalent bond electrons described above, absorption due to vibrations such as bond bending and stretching is observed in the near-infrared region.

[0172] Specifically, the absorption due to the reference tones of the transitions to the first excited state 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, the absorption due to the reference 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, the overtones of the transitions to the second excited state of CH2 and CH appear at wavelengths of around 1.24 μm. The reference tones of the bending and stretching of the CH bond are distributed over a wide band from 2 μm to 2.5 μm.

[0173] Furthermore, when an ester bond (R-COO-R) or an ether bond (COC) is present, a large optical absorption occurs at a wavelength of around 1.9 μm. According to the above-mentioned relational expression of light absorptance, the light absorptance caused by these factors becomes small and inconspicuous when the film thickness of the resin material is thin, but becomes large when the film thickness is thick.

[0174] FIG. 11 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 from 25 μm to 125 μm to 500 μm, the optical absorption in the wavelength range longer than 1.5 μm caused by the respective vibrations increases. In addition, the light absorption increases not only on the long wavelength side but also from the ultraviolet region to the visible region. This is due to the broadening of the light absorption edge caused by chemical bonds.

[0175] When the film thickness is thin, the light absorption rate is high at the wavelength with the largest absorption coefficient, but when the film thickness is thick, the weak absorption coefficient at the absorption edge with a broader spread appears as the absorption rate according to the above-mentioned light absorption rate relational expression. As a result, the light absorption increases from the ultraviolet region to the visible region as the film thickness increases. When the thickness is 25 μm, the absorption of the solar spectrum is 15 W / m 2 When the thickness is 125 μm, the absorption of the solar spectrum is 41 W / m 2 , the solar spectrum absorption at a thickness of 500 μm is 88 W / m 2 It is.

[0176] The light absorption of the light reflecting layer B is 50 W / m 2 Therefore, when the film thickness is 500 μm, the sum of the solar light absorption of the ethylene terephthalate resin and the solar light absorption of the light reflective layer B is 138 W / m 2 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 160 W at 30°C on a day with good atmospheric conditions, and usually about 125 W. From the above, it is found that if the thickness of the ethylene terephthalate resin film is 500 μm or more, the radiative cooling performance is not exhibited.

[0177] The origin of the absorption spectrum in the wavelength band from 1.5 μm to 4 μm is the vibration of the hydrocarbon main chain, not the functional group, and if it is a hydrocarbon-based resin, it will show the same behavior as ethylene terephthalate resin. In addition, hydrocarbon-based resins have light absorption due to chemical bonds in the ultraviolet range, and they show the same behavior as ethylene terephthalate resin from ultraviolet to visible light. In other words, hydrocarbon resins behave similarly to ethylene terephthalate resins from wavelengths of 0.3 μm to 4 μm. For this reason, the film thickness of hydrocarbon resins must be thinner than 500 μm.

[0178] [Light absorption of blended resins] When the resin material is a blend of a resin having a main chain of a carbon-fluorine bond or a siloxane bond and a resin having a main chain of a hydrocarbon, light absorption in the near-infrared region caused by CH, CH2, CH3, etc. appears according to the ratio of the blended resin having a main chain of a hydrocarbon. When the main component is carbon-fluorine bond or siloxane bond, the light absorption in the near infrared region caused by hydrocarbon is small, so the thickness can be increased up to the upper limit of 20 mm from the viewpoint of thermal conductivity. However, when the main component is a blended hydrocarbon resin, the thickness must be 500 μm or less.

[0179] Blends of fluororesin or silicone rubber with hydrocarbons include those in which the side chains of fluororesin or silicone rubber are replaced with hydrocarbons, and alternating copolymers, random copolymers, block copolymers, and graft copolymers of fluoromonomers, silicone monomers, and hydrocarbon monomers. Examples of alternating copolymers of fluoromonomers and hydrocarbon monomers include fluoroethylene-vinyl ester (FEVE), fluoroolefin-acrylic acid ester copolymer, ethylene-tetrafluoroethylene copolymer (ETFE), and ethylene-chlorotrifluoroethylene copolymer (ECTFE).

[0180] Depending on the molecular weight and ratio of the substituted hydrocarbon side chains, optical absorption in the near infrared region caused by CH, CH2, CH3, etc. appears. When the monomers introduced as side chains or copolymers are low molecular weight, or when the density of the monomers introduced is low, optical absorption in the near infrared region caused by 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 a fluororesin or silicone rubber or as a copolymerizable monomer, the thickness of the resin must be 500 μm or less.

[0181] [Thickness of resin material layer] From the viewpoint of practical use of the radiative cooling device CP, it is preferable that the thickness of the resin material 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 E, it is preferable that the thickness of the resin material layer J is the minimum necessary. The thicker the resin material layer J is, the greater the thermal radiation of the atmospheric window becomes, and above a certain thickness, the thermal radiation energy at the atmospheric window becomes saturated.

[0182] The thickness at which the film saturates depends on the resin material, but in the case of fluororesin, 300 μm is generally sufficient for saturation. Therefore, from the perspective of thermal conductivity, it is preferable to keep the film thickness at 300 μm or less rather than 500 μm. Furthermore, although thermal radiation is not saturated, 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 at around 100 μm or less.

[0183] The absorption coefficients due to carbon-silicon bonds, carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds are greater than the absorption coefficient due to C-F bonds. Naturally, from the viewpoint 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 to increase thermal conductivity. In the case of resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, even a thickness of 100 μm is saturated, and even a thickness of 50 μm provides sufficient thermal radiation in the atmospheric window region. The thinner the resin material, 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-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, a thickness of 50 μm or less reduces the insulation and allows the object to be cooled E to be cooled effectively. In the case of carbon-chlorine bonds, a thickness of 100 μm or less allows the object to be cooled E to be cooled effectively.

[0184] The benefit of making the resin thinner 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 that contain carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds. Making the resin thinner reduces the amount of sunlight absorbed by these bonds, which increases the cooling capacity of the radiative cooling device CP. From the above perspective, 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 can more effectively produce a radiative cooling effect under sunlight.

[0185] In the case of carbon-silicon bonds, even with a thickness of 50 μm, thermal radiation is saturated in the atmospheric window region, and even with a thickness of 10 μm, sufficient thermal radiation can be obtained in the atmospheric window region. The thinner the resin material layer J, the higher the thermal transmittance and the more effectively the temperature of the object to be cooled E can be lowered, so in the case of resins containing carbon-silicon bonds, a thickness of 10 μm or less reduces the insulation and allows the object to be cooled E to be cooled effectively. By making the layer thinner, the solar light absorption can be reduced, and the cooling capacity of the radiative cooling device CP is increased. 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.

[0186] [Details of the light reflecting layer] In order to provide the light reflecting layer B with the above-mentioned reflectance characteristics, the reflective material on the side where the emitting surface H exists (the side where the resin material layer J exists) needs to be silver or a silver alloy. As shown in FIG. 12, if the light-reflecting layer B is formed based on silver, the reflectance required for the light-reflecting layer B can be obtained.

[0187] When reflecting sunlight using only silver or a silver alloy while maintaining the above-mentioned reflectance characteristics, a thickness of 50 nm or more is required. However, in order to provide flexibility to the light reflecting layer B, the thickness must be 100 μm or less. If it is thicker than this, it becomes difficult to bend. Incidentally, the "silver alloy" may be an alloy in which, for example, 0.4% to 4.5% by mass of any of copper, palladium, gold, zinc, tin, magnesium, nickel, and titanium is added to silver. A specific example is "APC-TR (made by Furuya Metal)," a silver alloy made by adding copper and palladium to silver.

[0188] In order to provide the light reflecting layer B with the above-mentioned reflectance characteristics, a structure may be used in which silver or a silver alloy is located adjacent to the protective layer D and aluminum or an aluminum alloy is located away from the protective layer D. Even in this case, the reflective material on the side where the emitting surface H exists (the side where the resin material layer J exists) needs to be silver or a silver alloy. When it is composed of two layers of silver (silver alloy) and aluminum (aluminum alloy), the thickness of the silver needs to be 10 nm or more, and the thickness of the aluminum needs to be 30 nm or more. However, in order to provide flexibility to the light reflective layer B, the total thickness of the silver and aluminum must be 100 μm or less. If it is thicker than this, it becomes difficult to bend.

[0189] Incidentally, examples of "aluminum alloys" that can be used include alloys in which aluminum has been doped with copper, manganese, silicon, magnesium, zinc, carbon steel for mechanical structures, yttrium, lanthanum, gadolinium, and terbium.

[0190] Silver and silver alloys are vulnerable to rain and humidity and need to be protected from them, and also need to be prevented from tarnishing. For this reason, a protective layer D is required to protect the silver, in a form adjacent to the silver or silver alloy, as shown in Figures 16 to 19. The protective layer D will be described in detail later.

[0191] [About the experimental results] Silver was formed to a thickness of 300 nm on a glass substrate, and silicone rubber with siloxane bonds, fluoroethylene vinyl ether with carbon-fluorine bonds, olefin modified material (olefin modified material), and polyvinyl chloride resin were applied on top of it while controlling the film thickness with a bar coater, and the radiative cooling performance was measured. The evaluation of radiative cooling performance was carried out three hours after sundown outdoors in late June when the outside temperature was 35°C, and the temperature (°C) of the backside of the board was measured while the board was kept highly insulated. However, for polyvinyl chloride resin, the evaluation was carried out when the outside temperature was 29°C. The presence or absence of a radiative cooling effect was evaluated based on whether the temperature five minutes after placement on the jig was lower or higher than the outside temperature. The results of the radiative cooling test are shown in Figure 15.

[0192] Incidentally, the emissivity of the atmospheric window region of fluoroethylene vinyl ether is as shown in Figure 13. The emissivity of silicone rubber is as shown in Figure 4, the emissivity of an olefin modified body (olefin modified material) is as shown in Figure 8, and the emissivity of polyvinyl chloride resin is as shown in Figure 6.

[0193] In the case of silicone rubber containing siloxane bonds, it was found that a thickness of 1 μm or more exhibits radiative cooling capabilities, as predicted by theory. It was found that fluoroethylene vinyl ether, which has a carbon-fluorine bond, exhibits radiative cooling ability at a film thickness of 5 μm, which is thinner than the theoretically predicted thickness of 10 μm. This is because the optical absorption rate of the atmospheric window is increased by not only the optical absorption of the carbon-fluorine bond but also the optical absorption of the ether bond of the vinyl ether, compared to when each is used alone. Olefin modified materials (olefin modified materials) have no radiative cooling ability because they hardly radiate heat in the atmospheric window region.

[0194] [Specific configuration of radiative cooling device] The radiative cooling device CP of the present invention can be made into a film structure as shown in Figures 16 to 19. Since the resin material forming the resin material layer J and the protective layer D is flexible, when the light reflecting layer B is made into a thin film, the light reflecting layer B can also be made flexible, and as a result, the radiative cooling device CP can be made into a flexible film (radiative cooling film).

[0195] The film-type radiative cooling device CP (radiative cooling film) can be attached to existing objects with glue and wrapped around the outside of a car, the exterior wall of a warehouse or building, or the outside of a helmet to provide radiative cooling, and can easily provide radiative cooling capabilities. The film-type radiative cooling device CP (radiative cooling film) can be attached to various objects that require cooling, such as the outer surfaces of various tents, the outer surfaces of boxes that store electrical equipment, the outer surfaces of containers for transporting goods, the outer surfaces of milk tanks that store milk, and the outer surfaces of the milk storage sections of milk tanker trucks.

[0196] There are various ways to make the radiative cooling device CP in the form of a film. For example, it is possible to make it by applying a protective layer D and a resin material layer J to a light-reflecting layer B made in the form of a film. Alternatively, it is possible to make it by attaching a protective layer D and a resin material layer J to a light-reflecting layer B made in the form of a film. Alternatively, it is possible to create it by applying or attaching a protective layer D on a resin material layer J made in the form of a film, and then create a light-reflecting layer B on the protective layer D by deposition, sputtering, ion plating, silver mirror reaction, etc.

[0197] Specifically, the radiative cooling device CP (radiative cooling film) in Fig. 16 has a light reflecting layer B formed as a single layer of silver or silver alloy, or two layers of silver (silver alloy) and aluminum (aluminum alloy), with a protective layer D formed on the upper side of the light reflecting layer B and a resin material layer J formed on the upper part of the protective layer D, and also has a lower protective layer Ds formed on the lower side of the light reflecting layer B.

[0198] The radiative cooling device CP (radiative cooling film) in Fig. 16 can be produced by sequentially applying a protective layer D, a light-reflecting layer B, and a lower protective layer Ds onto a film-like resin material layer J, and molding them integrally.

[0199] The radiative cooling device CP (radiative cooling film) in Figure 17 has a light-reflecting layer B composed of an aluminum layer B1 formed of aluminum foil that functions as aluminum (aluminum alloy) and a silver layer B2 made of silver or a silver alloy, a protective layer D formed on the upper side of the light-reflecting layer B, and a resin material layer J formed on the upper part of the protective layer D.

[0200] The radiative cooling device CP (radiative cooling film) in Fig. 17 can be fabricated by sequentially applying a silver layer B2, a protective layer D, and a resin material layer J onto an aluminum layer B1 made of aluminum foil, and molding them together. As another manufacturing method, a method can be adopted in which the resin material layer J is formed into a film, a protective layer D and a silver layer B2 are successively applied onto the film-like resin material layer J, and an aluminum layer B1 is attached to the silver layer B2.

[0201] The radiative cooling device CP (radiative cooling film) in Fig. 18 has a light-reflecting layer B formed as a single layer of silver or silver alloy, or two layers of silver (silver alloy) and aluminum (aluminum alloy), a protective layer D formed on the upper side of the light-reflecting layer B, a resin material layer J formed on the upper part of the protective layer D, and a film layer F such as PET formed on the lower side of the light-reflecting layer B.

[0202] The radiative cooling device CP (radiative cooling film) in Fig. 18 can be fabricated by sequentially applying a light reflecting layer B and a protective layer D onto a film layer F (corresponding to a substrate) formed into a film shape using PET (ethylene terephthalate resin) or the like, forming them into an integrated body, and then bonding (adhering) a separately formed film-shaped resin material layer J to the protective layer D with a glue layer N (an example of a bonding layer). The adhesive (pressure-sensitive adhesive) used in the glue layer N may be, for example, a urethane adhesive (pressure-sensitive adhesive), an acrylic adhesive (pressure-sensitive adhesive), an EVA (ethylene vinyl acetate) adhesive (pressure-sensitive adhesive), etc., and is preferably one having high transparency to sunlight. The thickness of the glue layer N is preferably in the range of 1 μm or more and 100 μm or less, and more preferably, the thickness of the glue layer N is in the range of 1 μm or more and 50 μm or less.

[0203] The radiative cooling device CP (radiative cooling film) in Fig. 19 has a light reflecting layer B composed of an aluminum layer B1 functioning as aluminum (aluminum alloy) and a silver layer B2 made of silver or a silver alloy (silver substitute). The aluminum layer B1 is formed on the top of a film layer F (corresponding to a substrate) formed in a film shape from PET (ethylene terephthalate resin) or the like. A protective layer D is formed on the top of the silver layer B2, and a resin material layer J is formed on the top of the protective layer D.

[0204] The method of producing the radiative cooling device CP (radiative cooling film) in Fig. 19 can be as follows: an aluminum layer B1 is applied onto a film layer F, and the film layer F and the aluminum layer B1 are integrally formed; a protective layer D and a silver layer B2 are applied onto a film-like resin material layer J, and the resin material layer J, the protective layer D, and the silver layer B2 are integrally formed; and the aluminum layer B1 and the silver layer B2 are bonded together with a glue layer N. The adhesive (pressure-sensitive adhesive) used in the glue layer N may be, for example, a urethane adhesive (pressure-sensitive adhesive), an acrylic adhesive (pressure-sensitive adhesive), an EVA (ethylene vinyl acetate) adhesive (pressure-sensitive adhesive), etc., and is preferably one having high transparency to sunlight. The thickness of the glue layer N is preferably in the range of 1 μm or more and 100 μm or less, and more preferably, the thickness of the glue layer N is in the range of 1 μm or more and 50 μm or less.

[0205] Figure 30 shows a proper specific configuration of a radiative cooling device CP (radiative cooling film), and Figure 31 shows the light reflectance spectrum of the proper specific configuration of the radiative cooling device CP (radiative cooling film), and Figure 32 shows the emissivity spectrum. The radiative cooling device CP (radiative cooling film) in Figure 30 has a light reflecting layer B made of silver (Ag) with a thickness of 80 nm, a protective layer D made of polyethylene terephthalate (PET) with a thickness of 25 nm formed on the upper side of the light reflecting layer B, a resin material layer J made of polyvinyl chloride (PVC) with a thickness of 40 μm on the upper side of the protective layer D, and bonded (adhered) with a glue layer N made of a urethane-based adhesive (written as PU (polyurethane) in the figure) with a thickness of 10 μm, and a lower protective layer Ds is also formed on the lower side of the light reflecting layer B.

[0206] [Details of protective layer] The protective layer D is made of a polyolefin resin having a thickness of 300 nm or more and 40 μm or less, or a polyethylene terephthalate having a thickness of 17 μm or more and 40 μm or less. Polyolefin resins include polyethylene and polypropylene.

[0207] FIG. 20 shows the ultraviolet light absorptance of polyethylene, vinylidene chloride resin, ethylene terephthalate resin, and vinyl chloride resin. FIG. 21 shows the light transmittance of polyethylene, which is suitable as the synthetic resin for forming the protective layer D.

[0208] The radiative cooling device CP (radiative cooling film) exerts a radiative cooling effect not only at night but also in a solar radiation environment. Therefore, in order to maintain the state in which the light-reflecting layer B exerts its light-reflecting function, it is necessary to protect the light-reflecting layer B with a protective layer D so that the silver of the light-reflecting layer B does not discolor in a solar radiation environment.

[0209] When protective layer D is formed from a polyolefin resin to have a thickness of 300 nm or more and 40 μm or less, polyolefin resin is a synthetic resin whose ultraviolet light absorptance is 10% or less over the entire ultraviolet wavelength range of 0.3 to 0.4 μm, and therefore protective layer D is less susceptible to deterioration due to absorption of ultraviolet light.

[0210] Furthermore, since the thickness of the polyolefin resin forming protective layer D is 300 nm or more, it effectively performs the blocking function of blocking radicals generated in resin material layer J from reaching the silver or silver alloy forming the light-reflecting layer, and also blocks moisture penetrating resin material layer J from reaching the silver or silver alloy forming light-reflecting layer B, thereby suppressing discoloration of the silver or silver alloy forming light-reflecting layer B.

[0211] Incidentally, the protective layer D made of a polyolefin resin will deteriorate as it absorbs ultraviolet rays, forming radicals on the surface side away from the light-reflecting layer B. However, since the thickness is 300 nm or more, the formed radicals will not reach the light-reflecting layer. Even if the protective layer D deteriorates as radicals are formed, the rate of deterioration is slow due to the low absorption of ultraviolet rays, so the protective layer D will exhibit the above-mentioned blocking function for a long period of time.

[0212] When protective layer D is formed from ethylene terephthalate resin to a thickness of 17 μm or more and 40 μm or less, ethylene terephthalate resin is a synthetic resin that has a higher ultraviolet light absorption rate in the ultraviolet wavelength range of 0.3 to 0.4 μm than polyolefin resins. However, since the thickness is 17 μm or more, it can effectively perform blocking functions for a long period of time, such as blocking radicals generated in resin material layer J from reaching the silver or silver alloy that forms light reflecting layer B and blocking moisture that penetrates resin material layer J from reaching the silver or silver alloy that forms light reflecting layer B, thereby suppressing discoloration of the silver or silver alloy that forms light reflecting layer B.

[0213] In other words, the protective layer made of ethylene terephthalate resin will deteriorate as it absorbs ultraviolet rays, forming radicals on the surface side away from the light-reflecting layer B. However, since the thickness is 17 μm or more, the formed radicals will not reach the reflective layer. Furthermore, even if the protective layer deteriorates while forming radicals, the thickness is 17 μm or more, so the above-mentioned blocking function will be maintained for a long period of time.

[0214] To explain further, the deterioration of ethylene terephthalate resin (PET) is caused by ultraviolet light cleaving the ester bonds between ethylene glycol and terephthalic acid to form radicals. This deterioration progresses from the surface of the ethylene terephthalate resin (PET) that is irradiated with ultraviolet light.

[0215] For example, when ethylene terephthalate resin (PET) is irradiated with ultraviolet rays with the strength in Osaka, the ester bonds of the ethylene terephthalate resin (PET) are cleaved by about 9 nm per day, starting from the irradiated surface. Because the ethylene terephthalate resin (PET) is sufficiently polymerized, the cleaved ethylene terephthalate resin (PET) on the surface does not attack the silver (silver alloy) of the light-reflecting layer B. However, when the cleaved end of the ethylene terephthalate resin (PET) reaches the silver (silver alloy) of the light-reflecting layer B, the silver (silver alloy) will discolor.

[0216] Therefore, in order for protective layer D to last for one year or more when used outdoors, a thickness of about 3 μm is required, calculated by multiplying 9 nm / day by 365 days. In order for the ethylene terephthalate resin (PET) of protective layer D to last for three years or more, a thickness of 10 μm or more is required. In order for it to last for five years or more, a thickness of 17 μm or more is required.

[0217] In addition, when the protective layer D is formed of a polyolefin resin and an ethylene terephthalate resin, the reason for determining the upper limit of the thickness is to prevent the protective layer D from exhibiting heat insulating properties that do not contribute to radiative cooling. In other words, the protective layer D exhibits heat insulating properties that do not contribute to radiative cooling as the thickness increases, so the upper limit of the thickness is determined to prevent the protective layer D from exhibiting heat insulating properties that do not contribute to radiative cooling while still exerting the function of protecting the light reflecting layer B.

[0218] Incidentally, as shown in FIG. 18, when a glue layer N is located between the resin material layer J and the protective layer D, radicals will also be generated from the glue layer N. However, if the thickness of the polyolefin resin forming the protective layer D is 300 nm or more and the thickness of the ethylene terephthalate resin forming the protective layer D is 17 μm or more, the radicals generated in the glue layer N can be prevented from reaching the light reflecting layer B for a long period of time.

[0219] Incidentally, as mentioned above, if the protective layer D becomes thick, there is no disadvantage in terms of preventing coloring of the silver (silver alloy) of the light reflecting layer B, but a problem occurs in terms of radiative cooling. In other words, making the protective layer D thicker increases the thermal insulation of the radiative cooling material. For example, a resin whose main component is polyethylene, which is an excellent synthetic resin for forming the protective layer D, has a low emissivity at the atmospheric window, as shown in Figure 25, so even if it is formed thickly, it does not contribute to radiative cooling. On the contrary, making it thicker increases the thermal insulation of the radiative cooling material. Next, as the thickness increases, absorption of near-infrared light originating from the vibration of the main chain increases, increasing the effect of increasing solar absorption. Due to these factors, it is disadvantageous for radiative cooling to have a thick protective layer D. From this viewpoint, the thickness of the protective layer D made of a polyolefin resin is preferably 5 μm or less, and more preferably 1 μm or less.

[0220] [Considerations on protective layer] In order to examine the difference in the way the protective layer D colored the silver, a sample was prepared in which the protective layer D was exposed and did not have the resin material layer J as the infrared radiation layer A, as shown in Figure 22, and the coloring of the silver after being irradiated with simulated sunlight was examined. That is, as the protective layer D, samples were formed by applying two types of materials, a general acrylic resin that absorbs ultraviolet rays (for example, methyl methacrylate resin mixed with a benzotriazole-based ultraviolet absorber) and polyethylene, to a film layer F (corresponding to the substrate) containing silver as a light reflecting layer B using a bar coater, and the function of the protective layer D was examined. The thicknesses of the applied protective layers D were 10 μm and 1 μm, respectively. The film layer F (corresponding to the substrate) is formed into a film shape using PET (ethylene terephthalate resin) or the like.

[0221] As shown in Figure 24, if protective layer D is made of acrylic resin, which absorbs ultraviolet rays well, the protective layer D is decomposed by ultraviolet rays to form radicals, and the silver immediately turns yellow and no longer functions as a radiative cooling device CP (it absorbs sunlight and rises in temperature when exposed to solar radiation, like general materials). The 600h line in the figure indicates the time when the product was subjected to a xenon weather test under the conditions of JIS standard 5600-7-7 (ultraviolet light energy is 60W / m 2 The reflectance spectrum after 600h (hours) of exposure to xenon weathering is shown in Fig. 1. The 0h line is the reflectance spectrum before the xenon weathering test.

[0222] As shown in Figure 23, when protective layer D is made of polyethylene with low ultraviolet light absorption, no decrease in reflectance is observed from the near infrared region to the visible region. In other words, resins whose main component is polyethylene (polyolefin resins) hardly absorb the ultraviolet light contained in sunlight that reaches the ground, and therefore radicals are unlikely to form even when exposed to sunlight, so coloring of the silver serving as light-reflecting layer B does not occur even when exposed to sunlight. The 600h line in the figure indicates the time when the product was subjected to a xenon weather test under the conditions of JIS standard 5600-7-7 (ultraviolet light energy is 60W / m 2 The reflectance spectrum after 600h (hours) of exposure to xenon weathering is shown in Fig. 1. The 0h line is the reflectance spectrum before the xenon weathering test.

[0223] The reason why the reflectance spectrum in this wavelength band is wavy is due to the Fabry-Perot resonance of the polyethylene layer. It can be seen that the resonance position is slightly different between the 0h line and the 600h line due to the change in the thickness of the polyethylene layer caused by the heat of the xenon weather test, but no significant decrease in reflectance in the ultraviolet-visible range due to the yellowing of silver is observed.

[0224] In addition, from the viewpoint of ultraviolet absorption, fluororesin-based materials can also be used as materials for forming the protective layer D. However, when actually formed as the protective layer D, they become discolored and deteriorate during the formation stage, and therefore cannot be used as materials for forming the protective layer D. Silicone can also be used as a material for forming the protective layer D from the viewpoint of UV absorption, but it has extremely poor adhesion to silver (silver alloys) and cannot be used as a material for forming the protective layer D.

[0225] [Another configuration of the radiative cooling device] As shown in Figure 26, an anchor layer G may be provided on top of a film layer F (corresponding to the substrate), and a light reflecting layer B, a protective layer D, and an infrared emitting layer A may be provided on top of the anchor layer G. The film layer F (corresponding to the substrate) is formed into a film shape using, for example, PET (ethylene terephthalate resin) or the like.

[0226] The anchor layer is introduced to strengthen the adhesion between the film layer F and the light-reflecting layer B. In other words, if an attempt was made to form a film of silver (Ag) directly on the film layer F, peeling would easily occur. The anchor layer G is preferably made primarily of acrylic, polyolefin, or urethane, with a mixture of a compound with an isocyanate group or melamine resin. As it is a coating for parts that are not directly exposed to sunlight, it is acceptable for it to be made of a material that absorbs ultraviolet rays. There are other methods for strengthening the adhesion between the film layer F and the light reflecting layer B than inserting the anchor layer G. For example, the adhesion can be increased by roughening the surface of the film layer F by irradiating the surface with plasma.

[0227] [Another configuration of the infrared radiation layer] As shown in Fig. 27, a light scattering structure may be provided by mixing an inorganic filler V into the resin material layer J constituting the infrared radiation layer A. Also, as shown in Fig. 28, both the front and back surfaces of the resin material layer J constituting the infrared radiation layer A may be formed in an uneven shape to provide a light scattering structure. With this configuration, glare from the emitting surface H when the emitting surface H is viewed can be suppressed.

[0228] In other words, the above-mentioned resin material layer J is flat on both sides and does not contain any filler V. In the case of such a configuration, the radiation surface H becomes mirror-like, so that glare is perceived when looking at the radiation surface H. However, this glare can be suppressed by providing a light scattering configuration. Furthermore, when a filler V is mixed into the resin material layer J, if a protective layer D and a light-reflecting layer B are present, the light reflectance is improved compared to the case where only the resin material layer J containing the filler V is present or the case where only the light-reflecting layer B is present.

[0229] The inorganic material forming the filler V is silicon dioxide (SiO2). 、 Titanium oxide (TiO2), aluminum oxide (Al2O3), magnesium oxide (MgO), etc. When the filler V is mixed into the resin material layer J, both the front and back surfaces of the resin material layer J become uneven. Moreover, both the front and back surfaces of the resin material layer J can be made uneven by embossing or scratching the surface.

[0230] When the rear surface of the resin material layer J is uneven, it is desirable to position a glue layer N (bonding layer) between the resin material layer J and the protective layer D, similar to the configuration described in FIG. In other words, even if the back surface of the resin material layer J is uneven, the adhesive layer N (bonding layer) is located between the resin material layer J and the protective layer D, so that the resin material layer J and the protective layer D can be bonded appropriately.

[0231] In addition, when the back surface of the resin material layer J is uneven, the resin material layer J and the protective layer D may be directly bonded by, for example, plasma bonding. Note that the plasma bonding is a form in which radicals are formed on the bonding surface of the resin material layer J and the bonding surface of the protective layer D by emitting plasma, and bonding is performed by the radicals.

[0232] Incidentally, if filler V is mixed into protective layer D, the back surface of protective layer D that contacts light reflecting layer B will become uneven, which will cause the surface of light reflecting layer B to deform into an uneven shape, and therefore it is necessary to avoid mixing filler V into protective layer D. In other words, if the surface of light reflecting layer B deforms into an uneven shape, light reflection will not be performed properly, and as a result, radiative cooling will not be performed properly.

[0233] The experimental results regarding this point will be explained with reference to FIG. In Figure 29, "forming an Ag layer directly on the light diffusion layer" means forming a light reflecting layer B by mixing filler V or depositing a silver (Ag) film by vapor deposition or the like on the surface of the infrared radiation layer A (resin material layer J) which has embossed irregularities on the Ag layer side which is the light reflecting layer B. In addition, "a light diffusion layer on a mirror-like Ag surface" means that the upper surface of the Ag layer, which is the light-reflecting layer B, is formed in a mirror-like shape, and on top of the Ag layer, a protective layer D, and an infrared radiation layer A (resin material layer J) containing filler V or having an embossed uneven surface are laminated.

[0234] As shown in Figure 29, in the case of "forming an Ag layer directly on the light diffusion layer," the surface of light-reflecting layer B becomes uneven, resulting in a significant drop in light reflectance. However, in the case of "light-diffusing layer on mirror-like Ag," the surface of light-reflecting layer B is maintained in a mirror-like state, and appropriate light reflectance is obtained.

[0235] [Another embodiment] Other embodiments are listed below. (1) In the above embodiment, various resin materials are exemplified as the resin material for forming the resin material layer J, but examples of resin materials that can be suitably used include polyvinyl chloride resin (PVC), polyvinylidene chloride resin (PVDC), polyvinyl fluoride resin (PVF), and polyvinylidene fluoride resin (PVDF).

[0236] (2) In the above embodiment, an object to be cooled E is illustrated as being in close contact with the rear surface of the radiative cooling device CP (radiative cooling film). However, various types of cooling objects, such as a space to be cooled, can be used as the cooling object E.

[0237] (3) In the above embodiment, the radiation surface H of the resin material layer J is exposed as is. However, the radiation surface H may be covered with a hard coat. The hard coat may be any of the following: UV-curable acrylic, heat-curable acrylic, UV-curable silicone, heat-curable silicone, organic-inorganic hybrid, and vinyl chloride. An organic antistatic agent may be used as an additive. Among the UV-curable acrylics, urethane acrylates are particularly good.

[0238] The hard coat can be formed by a method such as gravure coating, bar coating, knife coating, roll coating, blade coating, or die coating. The thickness of the hard coat (coating film) is 1 to 50 μm, and preferably 2 to 20 μm.

[0239] When vinyl chloride resin is used as the resin material of the resin material layer J, the amount of plasticizer in the vinyl chloride resin may be reduced to make it a rigid vinyl chloride resin or a semi-rigid vinyl chloride resin. In this case, the vinyl chloride itself of the infrared emitting layer A becomes a hard coat layer.

[0240] In addition, 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, provided no contradiction arises. Furthermore, the embodiments disclosed in this specification are illustrative, and the embodiments of the present invention are not limited thereto, and can be appropriately modified within the scope that does not deviate from the purpose of the present invention. [Explanation of symbols]

[0241] A Infrared radiation layer B Light reflective layer D Protective layer H radiation surface J Resin material layer N bonding layer

Claims

1. an infrared emitting layer that emits infrared light from a emitting surface; a light reflecting layer that is located on a side of the infrared emitting layer opposite to a side on which the emitting surface is present; and a protective layer between the infrared emitting layer and the light reflecting layer; the infrared radiation layer is a resin material layer whose thickness is adjusted to emit thermal radiation energy in a wavelength band of 8 μm to 14 μm that is greater than absorbed solar light energy, A radiative cooling device, wherein the light reflective layer comprises silver or a silver alloy, The protective layer is made of a polyolefin resin and has a thickness of 300 nm or more and 40 μm or less, or made of an ethylene terephthalate resin and has a thickness of 17 μm or more and 40 μm or less. A radiative cooling device.

2. 2. The radiative cooling device according to claim 1, wherein the light reflective layer has a reflectance of 90% or more at wavelengths from 0.4 μm to 0.5 μm and a reflectance of 96% or more at wavelengths longer than 0.5 μm.

3. The thickness of the resin material layer is The wavelength average of the light absorptance at wavelengths of 0.4 μm to 0.5 μm is 13% or less, the wavelength average of the light absorptance at wavelengths of 0.5 μm to 0.8 μm is 4% or less, the wavelength average of the light absorptance at wavelengths of 0.8 μm to 1.5 μm is within 1%, and the wavelength average of the light absorptance at wavelengths of 1.5 μm to 2.5 μm is 40% or less, and The radiative cooling device according to claim 1 or 2, wherein the thickness is adjusted to a state in which the device has thermal radiation characteristics such that the wavelength average of the emissivity from 8 μm to 14 μm is 40% or more.

4. The resin material forming the resin material layer is selected from resin materials having one or more of a carbon-fluorine bond, a siloxane bond, a carbon-chlorine bond, a carbon-oxygen bond, an ether bond, an ester bond, and a benzene ring. The radiative cooling device according to any one of claims 1 to 3.

5. a main component of a resin material forming the resin material layer is siloxane, The radiative cooling device according to any one of claims 1 to 3, wherein the resin material layer has a thickness of 1 μm or more.

6. 5. The radiative cooling device of claim 4, wherein the resin material layer has a thickness of 10 μm or more.

7. The radiative cooling device according to any one of claims 1 to 6, wherein the resin material layer has a thickness of 20 mm or less.

8. The radiative cooling device according to claim 7, wherein the resin material forming the resin material layer is a fluororesin or a silicone rubber.

9. the resin material forming the resin material layer is a resin material having a main chain made of a hydrocarbon having at least one of a carbon-chlorine bond, a carbon-oxygen bond, an ester bond, an ether bond, and a benzene ring, or a silicone resin having a hydrocarbon side chain with two or more carbon atoms; The radiative cooling device according to any one of claims 1 to 6, wherein the resin material layer has a thickness of 500 μm or less.

10. The radiative cooling device according to any one of claims 1 to 6, wherein the resin material forming the resin material layer is a blend of a resin containing a carbon-fluorine bond or a siloxane bond and a resin having a hydrocarbon main chain, and the thickness of the resin material layer is 500 μm or less.

11. the resin material forming the resin material layer is a fluororesin, The radiative cooling device according to any one of claims 1 to 6, wherein the resin material layer has a thickness of 300 μm or less.

12. the resin material forming the resin material layer is a resin material having at least one of a carbon-chlorine bond, a carbon-oxygen bond, an ester bond, an ether bond, and a benzene ring; The radiative cooling device according to any one of claims 1 to 6, wherein the resin material layer has a thickness of 50 μm or less.

13. the resin material forming the resin material layer is a resin material having a carbon-silicon bond, The radiative cooling device according to any one of claims 1 to 6, wherein the resin material layer has a thickness of 10 μm or less.

14. the resin material forming the resin material layer is a vinyl chloride resin or a vinylidene chloride resin, The radiative cooling device according to any one of claims 1 to 3, wherein the thickness of the resin material layer is 100 μm or less and 10 μm or more.

15. The radiative cooling device according to any one of claims 1 to 14, wherein the light reflective layer is made of silver or a silver alloy and has a thickness of 50 nm or more.

16. The radiative cooling device according to any one of claims 1 to 14, wherein the light reflective layer has a laminated structure of silver or a silver alloy located adjacent to the protective layer and aluminum or an aluminum alloy located away from the protective layer.

17. The radiative cooling device according to any one of claims 1 to 16, wherein the resin material layer, the protective layer, and the light reflecting layer are in a film-like state when stacked together.

18. The radiative cooling device according to any one of claims 1 to 17, wherein the resin material layer and the protective layer are joined by a joining layer of an adhesive or a pressure-sensitive adhesive.

19. 19. The radiative cooling device of claim 18, wherein the resin material layer is mixed with an inorganic filler.

20. The radiative cooling device according to claim 18, wherein both the front and back surfaces of the resin material layer are formed in an uneven shape.

21. A radiative cooling method in which the infrared light is radiated from the radiation surface opposite to the surface of the resin material layer in contact with the light reflecting layer using the radiative cooling device according to any one of claims 1 to 20, A radiative cooling method comprising: directing the radiation surface toward the sky and radiating the infrared light from the radiation surface.

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