Radiation cooling device and radiation cooling method

Abstract

Provided is a radiation cooling device that has flexibility and is capable of cooling a cooling object in a sunny environment. An infrared radiation layer A that radiates infrared light IR from a radiation surface H, a light reflection layer B that is positioned on the opposite side of the infrared radiation layer A from the existing side of the radiation surface H, and a protective layer D between the infrared radiation layer A and the light reflection layer B are provided, the infrared radiation layer A is a resin material layer J of a thickness adjusted to emit greater thermal radiation energy than absorbed solar light energy in a band of wavelengths 8 μm to 14 μm, the light reflection layer B has silver or a silver alloy, and the protective layer D is formed in a form having a thickness of 300 nm or more and 40 μm or less using a polyolefin-based resin or in a form having a thickness of 17 μm or more and 40 μm or less using a terephthalate resin.

Description

Technical Field

[0001] This invention relates to a radiation cooling device comprising an infrared radiating layer that radiates infrared light from a radiating surface, a light reflecting layer located on the side of the infrared radiating layer opposite to the side where the radiating surface exists, and a protective layer between the infrared radiating layer and the light reflecting layer.

[0002] The aforementioned infrared radiating layer is a resin material layer, its thickness adjusted to emit thermal radiation energy greater than the absorbed solar energy in the wavelength band from 8μm to 14μm.

[0003] The aforementioned light-reflecting layer has silver or a silver alloy; and the radiation cooling method using the radiation cooling device. Background Technology

[0004] Radiation cooling refers to the phenomenon where a substance lowers its temperature by emitting electromagnetic waves such as infrared radiation into its surroundings. This phenomenon can be utilized to construct radiation cooling devices that cool objects without consuming energy such as electricity.

[0005] Furthermore, because the light-reflecting layer, made of silver or silver alloy, fully reflects sunlight, it can cool the object even under daytime sunlight.

[0006] That is, the light-reflecting layer reflects the light (ultraviolet, visible, and infrared) that passes through the infrared radiating layer and radiates it from the radiating surface, preventing the light (ultraviolet, visible, and infrared) that passes through the infrared radiating layer from being projected onto the object being cooled and heating it. Thus, the object can be cooled even in daylight.

[0007] It should be noted that, in addition to the light passing through the infrared radiation layer, the light reflector also reflects the light emitted from the infrared radiation layer towards the infrared radiation layer. However, in the following explanation, the light reflector is described as being designed to reflect light (ultraviolet light, visible light, and infrared light) that passes through the infrared radiation layer.

[0008] As existing examples of such radiation cooling devices, there are those that have a protective layer consisting of aluminum oxide and silicon dioxide, or that have a protective layer consisting of polymethyl methacrylate with a thickness of 50 nm (see, for example, Patent Document 1).

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Publication No. 2018-526599. Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] In the conventional radiation cooling device disclosed in Patent Document 1, if the protective layer is constructed in the form of aluminum oxide and silicon dioxide, the protective layer is an inorganic material and therefore lacks flexibility. That is, the infrared radiating layer is formed using a flexible resin material layer, and the light-reflecting layer is constructed as a thin film such as silver. Even though it has flexibility, the protective layer made of inorganic materials lacks flexibility, and therefore the radiation cooling device lacks flexibility. Furthermore, if the infrared radiating layer is made flexible, cracks and peeling occur in the protective layer, resulting in a loss of protective function. In other words, conventional radiation cooling devices using inorganic materials for the protective layer lack flexibility.

[0014] Therefore, conventional radiation cooling devices with protective layers made of inorganic materials are difficult to add to the outer walls of existing outdoor equipment of any shape to provide radiation cooling performance.

[0015] In the conventional radiation cooling device disclosed in Patent Document 1, if the protective layer is made of polymethyl methacrylate with a thickness of 50 nm, the drawback is that the protective layer deteriorates in a short time due to the absorption of ultraviolet light, causing the silver or silver alloy forming the reflective layer to discolor.

[0016] That is, the protective layer needs to play a shielding role, blocking free radicals generated by the resin material layer from reaching the silver or silver alloy that forms the reflective layer, and also blocking moisture that penetrates the resin material layer from reaching the silver or silver alloy that forms the protective layer, thereby inhibiting the discoloration of the silver or silver alloy that forms the reflective layer.

[0017] However, the protective layer made of polymethyl methacrylate with a thickness of 50 nm deteriorates in a short time due to the absorption of ultraviolet light, and cannot perform the above-mentioned shielding function. Therefore, there is a defect that the silver or silver alloy forming the reflective layer will change color in a short time.

[0018] Furthermore, if the silver or silver alloy forming the reflective layer discolors, the reflective layer will not be able to reflect sunlight properly, and the temperature will rise due to the absorption of sunlight. As a result, the radiation cooling device will not be able to cool the object under daytime sunlight.

[0019] The present invention was made in view of the aforementioned actual situation, and its object is to provide a radiation cooling device that is flexible and capable of cooling an object under sunlight, and a radiation cooling method using the radiation cooling device.

[0020] Methods for solving problems

[0021] The radiation cooling device of the present invention includes an infrared radiation layer that radiates infrared light from a radiation surface, a light reflection layer located on the side of the infrared radiation layer opposite to the side where the radiation surface exists, and a protective layer between the infrared radiation layer and the light reflection layer.

[0022] The aforementioned infrared radiating layer is a resin material layer, its thickness adjusted to emit thermal radiation energy greater than the absorbed solar energy in the wavelength band from 8μm to 14μm.

[0023] The aforementioned light-reflecting layer is made of silver or a silver alloy, characterized in that,

[0024] The aforementioned protective layer is formed with a polyolefin resin having a thickness of 300 nm or more and 40 μm or less, or with a polyethylene terephthalate resin having a thickness of 17 μm or more and 40 μm or less.

[0025] That is, sunlight incident from the radiating surface of the resin material layer, which serves as the infrared radiating layer, is reflected by the light-reflecting layer located on the opposite side of the radiating surface of the resin material layer after passing through the resin material layer and the protective layer, and escapes from the radiating surface out of the system.

[0026] It should be noted that, in this specification, when referred to simply as light, the concept of light includes ultraviolet light (ultraviolet radiation), visible light, and infrared light. If expressed in terms of the wavelength of light as electromagnetic waves, it includes electromagnetic waves with wavelengths from 10 nm to 20,000 nm (electromagnetic waves from 0.01 μm to 20 μm).

[0027] Furthermore, the heat (heat input) transmitted to the radiation cooling device is converted into infrared radiation in the resin material layer and escapes from the radiation surface out of the system.

[0028] In this way, according to the above configuration, it is possible to reflect sunlight irradiating the radiative cooling device, and furthermore, to radiate heat transmitted to the radiative cooling device (e.g., heat transferred from the atmosphere, heat transferred from the object being cooled by the radiative cooling device) as infrared light to the outside of the system.

[0029] Furthermore, the resin material layer is adjusted to have a thickness that emits thermal radiation energy greater than the absorbed solar energy in the wavelength band from 8μm to 14μm. In addition, the protective layer is formed with a polyolefin resin with a thickness of 300nm or more and 40μm or less, or with a polyethylene terephthalate resin with a thickness of 17μm or more and 40μm or less. Therefore, even under daytime sunlight, the discoloration of the silver or silver alloy in the light-reflecting layer can be suppressed. Thus, while the light-reflecting layer appropriately reflects sunlight, it can also perform a cooling function even under daytime sunlight.

[0030] Furthermore, the resin material layer is formed from a highly flexible resin material, thus enabling the resin material layer to be flexible, and the protective layer is also formed from a highly flexible resin material, thus enabling the protective layer to be flexible. Moreover, the light-reflecting layer, by being configured as, for example, a thin film of silver, is also capable of being flexible.

[0031] Therefore, a radiation cooling device having a resin material layer, a protective layer, and a light-reflecting layer can be flexible.

[0032] Additional explanation is provided regarding the use of a protective layer to suppress discoloration of silver or silver alloys in light-reflecting layers.

[0033] In other words, without a protective layer, free radicals generated by the resin material layer can reach the silver or silver alloy that forms the light-reflecting layer, and moisture can also reach the silver or silver alloy that forms the light-reflecting layer through the resin material layer. This raises concerns that the silver or silver alloy in the light-reflecting layer may discolor in a short period of time and become unable to properly perform its light-reflecting function. However, the presence of a protective layer can suppress the discoloration of the silver or silver alloy in the light-reflecting layer in a short period of time.

[0034] When the protective layer is formed of polyolefin resin with a thickness of 300 nm or more and 40 μm or less, the polyolefin resin is a synthetic resin with a light absorption rate of less than 10% in the entire wavelength region of ultraviolet light from 0.3 μm to 0.4 μm. Therefore, the protective layer is unlikely to deteriorate due to the absorption of ultraviolet light.

[0035] Furthermore, the thickness of the polyolefin resin forming the protective layer is more than 300 nm, thus effectively shielding the silver or silver alloy forming the light-reflecting layer from free radicals generated by the resin material layer. In addition, it also shields the silver or silver alloy forming the light-reflecting layer from moisture that penetrates the resin material layer, thereby suppressing the discoloration of the silver or silver alloy forming the light-reflecting layer.

[0036] Furthermore, the protective layer formed by polyolefin resin deteriorates as it absorbs ultraviolet light and forms free radicals on the surface away from the reflective layer. However, since the thickness is more than 300 nm, the free radicals formed cannot reach the light reflective layer. In addition, even if it deteriorates as it forms free radicals, the absorption of ultraviolet light is low, so the deterioration process is slow, thus maintaining the above-mentioned shielding function for a long time.

[0037] When the protective layer is formed from polyethylene terephthalate resin with a thickness of 17 μm or more and 40 μm or less, polyethylene terephthalate resin is a synthetic resin with a higher ultraviolet light absorption rate in the ultraviolet wavelength region of 0.3 μm to 0.4 μm compared to polyolefin resins. However, because the thickness is 17 μm or more, it can prevent free radicals formed on the surface of the protective layer away from the reflective layer from reaching the reflective layer. In addition, because the thickness is 17 μm or more, it can effectively block free radicals generated in the resin material layer from reaching the silver or silver alloy forming the light reflective layer for a long time. Furthermore, it can suppress discoloration of the silver or silver alloy forming the protective layer by blocking moisture that penetrates through the resin material layer from reaching the silver or silver alloy forming the light reflective layer.

[0038] That is, the protective layer formed by polyethylene terephthalate resin deteriorates while absorbing ultraviolet light and forming free radicals on the surface away from the reflective layer. However, since the thickness is more than 17 μm, the free radicals formed cannot reach the reflective layer. Furthermore, even if it deteriorates while forming free radicals, it can still perform the above-mentioned shielding function for a long time because the thickness is more than 17 μm.

[0039] It should be noted that the reason for specifying an upper limit on the thickness of the protective layer when it is formed by polyolefin resin and polyethylene terephthalate resin is to prevent the protective layer from performing its insulating properties that do not contribute to radiative cooling. That is, the thicker the protective layer, the less it performs its insulating properties that do not contribute to radiative cooling. Therefore, in order to perform the function of protecting the reflective layer while avoiding its insulating properties that do not contribute to radiative cooling, an upper limit on the thickness is specified.

[0040] In short, the characteristic configuration of the radiation cooling device according to the present invention enables the provision of a radiation cooling device that is flexible and capable of cooling the object during the day.

[0041] A further feature of the radiation cooling device of the present invention is that the reflectivity of the aforementioned light-reflecting layer for wavelengths of 0.4 μm to 0.5 μm is 90% or more, and the reflectivity for wavelengths longer than 0.5 μm is 96% or more.

[0042] That is, the solar spectrum exists from wavelength 0.3 μm to 4 μm, and the intensity increases as the wavelength increases from 0.4 μm, especially from wavelength 0.5 μm to wavelength 2.5 μm.

[0043] If the light-reflecting layer has a reflectivity of over 90% for wavelengths from 0.4μm to 0.5μm and over 96% for wavelengths longer than 0.5μm, then the light-reflecting layer absorbs only about 5% or less of the solar energy.

[0044] As a result, at midday in summer, the solar energy absorbed by the reflective layer can reach 50 W / m². 2 Below the left and right sides, it can effectively utilize the radiative cooling of the resin material layer.

[0045] It should be noted that, unless otherwise specified, the spectrum of sunlight in this instruction manual is set to the AM1.5G standard.

[0046] In short, according to a further feature of the radiation cooling device of the present invention, the absorption of solar energy caused by the light-reflecting layer can be suppressed, and radiation cooling using the resin material layer can be effectively performed.

[0047] A further feature of the radiation cooling device of the present invention is that the film thickness of the aforementioned resin material layer is adjusted to the following state:

[0048] It exhibits light absorption characteristics with an average wavelength absorption rate of less than 13% for wavelengths from 0.4 μm to 0.5 μm, less than 4% for wavelengths from 0.5 μm to 0.8 μm, less than 1% for wavelengths from 0.8 μm to 1.5 μm, and less than 40% for wavelengths from 1.5 μm to 2.5 μm.

[0049] It has thermal radiation characteristics with an average wavelength of over 40% emissivity ranging from 8 μm to 14 μm.

[0050] It should be noted that the wavelength average of light absorption rate from 0.4 μm to 0.5 μm refers to the average value of light absorption rate for each wavelength in the range of 0.4 μm to 0.5 μm, and the same applies to the wavelength averages of light absorption rate from 0.5 μm to 0.8 μm, 0.8 μm to 1.5 μm, and 1.5 μm to 2.5 μm. Furthermore, other similar descriptions, including emissivity, also refer to the same average values, as will be in this specification below.

[0051] That is, the light absorptivity and emissivity (light emissivity) of the resin material layer vary with its thickness. Therefore, it is necessary to adjust the thickness of the resin material layer in a way that emits large thermal radiation in the wavelength band (the region of light wavelength from 8 μm to 20 μm) of the so-called atmospheric window region, where sunlight is absorbed as little as possible.

[0052] Specifically, considering the light absorption rate (light absorption characteristics) of the resin material layer, the average wavelength absorption rate should be less than 13% for wavelengths from 0.4μm to 0.5μm, less than 4% for wavelengths from 0.5μm to 0.8μm, less than 1% for wavelengths from 0.8μm to 1.5μm, and less than 40% for wavelengths from 1.5μm to 2.5μm. It should be noted that for light absorption rates from 2.5μm to 4μm, an average wavelength absorption rate of less than 100% is sufficient.

[0053] Under such a light absorption rate distribution, the light absorption rate of sunlight reaches less than 10%, and in terms of energy, it reaches less than 100W.

[0054] That is, the light absorption rate of sunlight increases with increasing the thickness of the resin material layer. If the resin material layer is made into a thick film, the emissivity of the atmospheric window is almost 1, and the thermal radiation released into space is 125 W / m. 2 Up to 160W / m 2 .

[0055] As described above, the solar light absorption of the light-reflecting layer is preferably 50 W / m. 2 the following.

[0056] Therefore, the sum of the solar light absorption by the resin material layer and the light-reflecting layer is 150 W / m. 2 Cooling will proceed if atmospheric conditions are favorable. As described above, a resin material layer with low absorptivity near the peak of the solar spectrum can be used for the resin material layer.

[0057] Furthermore, from the perspective of the emissivity (thermal radiation characteristics) of the infrared light emitted by the resin material layer, an average wavelength emissivity of over 40% is required for wavelengths ranging from 8 μm to 14 μm.

[0058] That is, in order to make the light-reflecting layer absorb 50W / m 2 The thermal radiation from the sun on both sides is released from the resin material layer into the universe, and the resin material layer needs to release thermal radiation above that.

[0059] For example, when the external temperature is 30°C, the maximum thermal radiation in the atmospheric window with wavelengths from 8 μm to 14 μm is 200 W / m. 2 (Calculation with emissivity set to 1). This value is obtained under clear skies in environments such as high mountains where the air is thin and sufficiently dry. In low-lying areas, the atmosphere is thicker than in high mountains, thus narrowing the wavelength band of the atmospheric window and reducing transmittance. This is referred to as "atmospheric window narrowing".

[0060] Furthermore, the environments in which radiative cooling devices are actually used are sometimes humid, in which case the atmospheric window narrows. The thermal radiation generated in the atmospheric window area during lowland utilization is estimated at 160 W / m² under good conditions at 30°C. 2 (Calculate with emissivity set to 1).

[0061] Furthermore, in Japan, it is common for atmospheric windows to narrow further when haze or smog is present, resulting in radiation into space of 125 W / m². 2 about.

[0062] Given the aforementioned situation, the wavelength average emissivity of the 8μm to 14μm wavelength range is not greater than 40% (the thermal radiation intensity in the atmospheric window band is 50W / m). 2 (The above) cannot be used in the lowlands of the mid-latitude zone.

[0063] Therefore, by adjusting the thickness of the resin material layer to achieve the aforementioned optical specifications, the heat output of the atmospheric window is greater than the heat input caused by the absorption of sunlight, and it can also be radiatively cooled outdoors under daytime sunlight conditions.

[0064] In short, according to a further feature of the radiative cooling device of the present invention, the heat output of the atmospheric window is greater than the heat input caused by the absorption of sunlight, and radiative cooling can be achieved outdoors even in a sunlight environment.

[0065] A further feature of the radiation cooling device of the present invention is that the resin material forming the aforementioned resin material layer is selected from resins having one or more carbon-fluorine bonds, siloxane bonds, carbon-chlorine bonds, carbon-oxygen bonds, ether bonds, ester bonds, or benzene rings.

[0066] That is, the resin material used to form the resin material layer can be a colorless resin material having one or more of the following: carbon-fluorine bond (CF), siloxane bond (Si-O-Si), carbon-chlorine bond (C-Cl), carbon-oxygen bond (CO), ether bond (R-COO-R), ester bond (COC), or benzene ring.

[0067] According to Kirchhoff's laws, emissivity (ε) equals light absorptivity (A). Light absorptivity (A) can be obtained from the absorption coefficient (α) using Equation 1 below.

[0068] A = 1 - exp(-αt)···(Equation 1) It should be noted that t is the film thickness.

[0069] That is, if the thickness of the resin material layer is increased, greater thermal radiation is obtained in the wavelength band with a high absorption coefficient. In the case of outdoor radiative cooling, materials with a high absorption coefficient in the wavelength band of 8 μm to 14 μm, which serves as an atmospheric window, can be used. Furthermore, in order to suppress the absorption of sunlight, materials with no absorption coefficient or a small absorption coefficient in the wavelength range of 0.3 μm to 4 μm, particularly 0.4 μm to 2.5 μm, can be used. As can be seen from the relationship between the absorption coefficient and the light absorptivity in Equation 1 above, the light absorptivity (emissivity) varies with the film thickness of the resin material layer.

[0070] In order to reduce the temperature compared with the surrounding atmosphere through radiative cooling under sunlight, if the resin material used to form the resin material layer is selected, it is possible to create a state in which almost no sunlight is absorbed, but a large amount of thermal radiation from the atmospheric window is released by adjusting the film thickness of the resin material layer. That is, a state in which the output of radiative cooling is greater than the input of sunlight.

[0071] Additional explanation is provided regarding the absorption spectrum of the resin material forming the resin material layer.

[0072] Regarding carbon-fluorine bonds (CF), the absorption coefficients derived from CHF and CF2 broaden significantly in the wide wavelength range of 8 μm to 14 μm, which serves as an atmospheric window, with a particularly high absorption coefficient at 8.6 μm. Meanwhile, regarding the wavelength range of sunlight, there are no significant absorption coefficients in the high-energy wavelength range of 0.3 μm to 2.5 μm.

[0073] As a resin material with CF bonds, examples can be cited.

[0074] Polytetrafluoroethylene (PTFE) as a fully fluorinated resin

[0075] Polyvinyl chloride trifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF) are partially fluorinated resins.

[0076] Perfluoroalkoxy fluoropolymers (PFA) are fluoropolymer copolymers.

[0077] Tetrafluoroethylene-hexafluoropropylene copolymer (FEP)

[0078] Ethylene-tetrafluoroethylene copolymer (ETFE)

[0079] Ethylene-chlorotrifluoroethylene copolymer (ECTFE).

[0080] If we calculate the bond energies of the C, C, and C bonds in the basic structural unit represented by polyvinylidene fluoride (PVDF), they are 4.50 eV, 4.46 eV, and 5.05 eV, respectively. These correspond to wavelengths of 0.275 μm, 0.278 μm, and 0.246 μm, respectively, indicating the absorption of light at shorter wavelengths compared to these wavelengths.

[0081] The solar spectrum contains only wavelengths longer than 0.300 μm, so when using fluoropolymers, it absorbs almost no ultraviolet, visible, or near-infrared rays from sunlight.

[0082] It should be noted that ultraviolet light is defined as the range of wavelengths shorter than 0.400 μm, visible light is defined as the range of wavelengths from 0.400 μm to 0.800 μm, near-infrared light is defined as the range of wavelengths from 0.800 μm to 3 μm, mid-infrared light is defined as the range of wavelengths from 3 μm to 8 μm, and far-infrared light is defined as the range of wavelengths longer than 8 μm.

[0083] Examples of resin materials containing siloxane bonds (Si-O-Si) include silicone rubber and silicone resin. For this resin, the large absorption coefficient originating from the stretching of the C-Si bonds is broad around a wavelength of 13.3 μm, the absorption coefficient originating from the outward bending (longitudinal rocking) of CSiH2 is broad around a wavelength of 10 μm, and the absorption coefficient originating from the inward bending (shearing) of CSiH2 is small near a wavelength of 8 μm. This results in a large absorption coefficient within the atmospheric window. Regarding the ultraviolet region, the bond energy of the Si-O-Si in the main chain is 4.60 eV, corresponding to a wavelength of 0.269 μm, absorbing light at wavelengths shorter than this. The solar spectrum only contains wavelengths longer than 0.300 μm; therefore, when using siloxane bonds, it absorbs almost no ultraviolet, visible, or near-infrared light from sunlight.

[0084] Regarding the carbon-chlorine bond (C-Cl), the absorption coefficient based on the C-Cl stretching vibration appears in a broadband domain with a half-width of more than 1 μm, centered at a wavelength of 12 μm.

[0085] Furthermore, polyvinyl chloride (PVC) is an example of a resin material containing carbon-chlorine bonds (C-Cl). In the case of PVC, due to the electron-withdrawing effect of chlorine, the absorption coefficient of the bending vibration of the CH group of the olefin contained in the main chain appears around a wavelength of 10 μm. That is, it is possible to release large amounts of thermal radiation in the wavelength band of the atmospheric window. It should be noted that the bond energy between carbon and chlorine in the olefin is 3.28 eV, which corresponds to a wavelength of 0.378 μm, absorbing light at wavelengths shorter than that. That is, it absorbs ultraviolet light from sunlight, but has almost no absorption in the visible region.

[0086] Regarding ether bonds (R-COO-R) and ester bonds (COC), absorption coefficients are observed from wavelengths of 7.8 μm to 9.9 μm. Furthermore, regarding the carbon-oxygen bonds contained in ester and ether bonds, strong absorption coefficients are observed in the wavelength band from 8 μm to 10 μm.

[0087] If a benzene ring is introduced into the side chain of a hydrocarbon resin, it will exhibit absorption over a wide range of wavelengths from 8.1 μm to 18 μm through the vibration of the benzene ring itself and the vibration of surrounding elements caused by the influence of the benzene ring.

[0088] Resins containing these bonds include polymethyl methacrylate resin, polyethylene terephthalate resin, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate. For example, the C / C bond energy of methyl methacrylate is 3.93 eV, corresponding to a wavelength of 0.315 μm. It absorbs sunlight at wavelengths shorter than this, but has almost no absorption in the visible region.

[0089] As long as the resin material forming the resin material layer possesses the aforementioned emissivity and absorptivity characteristics, the resin material layer can be a single-layer film of one resin material, a multilayer film of multiple resin materials, a single-layer film of a blend of multiple resin materials, or a multilayer film of a blend of multiple resin materials. It should be noted that blends also include copolymers such as alternating copolymers, random copolymers, block copolymers, graft copolymers, and modified products with substituted side chains.

[0090] In short, according to a further feature of the radiative cooling device of the present invention, it is possible to create a state in which the output of radiative cooling is greater than the input of sunlight.

[0091] A further feature of the radiation cooling device of the present invention is that the main component of the resin material forming the aforementioned resin material layer is a siloxane.

[0092] The thickness of the aforementioned resin material layer is 1 μm or more.

[0093] That is, as can be seen from Equation 1 above, A = 1 - exp(-αt), the light absorptivity (emissivity) changes with the thickness t. The required thickness is one where the resin material has a large absorption coefficient in the atmospheric window.

[0094] In the case of resin materials with siloxane bonds (Si-O-Si) as the main constituent element, if the film thickness is greater than 1 μm, the radiation intensity in the atmospheric window increases, and it is possible to create a state in which the output of radiation cooling is greater than the input of sunlight.

[0095] In short, according to a further feature of the radiation 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 of radiation cooling is greater than the input of sunlight.

[0096] A further feature of the radiation cooling device of the present invention is that the thickness of the aforementioned resin material layer is 10 μm or more.

[0097] That is, in the case of resin materials with any of the following as the main constituent elements: carbon-fluorine bond (CF), carbon-chlorine bond (C-Cl), carbon-oxygen bond (CO), ester bond (R-COO-R), ether bond (COC), and benzene ring, if the film thickness is greater than 10 μm, the radiation intensity in the atmospheric window increases, and it is possible to create a state in which the output of radiation cooling is greater than the input of sunlight.

[0098] In short, according to a further feature of the radiation cooling device of the present invention, when the resin material forming the resin material layer is a resin material whose main constituent element is any one of carbon-fluorine bond (CF), carbon-chlorine bond (C-Cl), carbon-oxygen bond (CO), ester bond (R-COO-R), ether bond (COC), or benzene ring, it is possible to produce a state in which the output of radiation cooling is greater than the input of sunlight.

[0099] A further feature of the radiation cooling device of the present invention is that the thickness of the aforementioned resin material layer is 20 mm or less.

[0100] That is, the thermal radiation from the atmospheric window of the resin material forming the resin material layer is generated within a range of about 100 μm from the material surface.

[0101] That is, even if the thickness of the resin material increases, the thickness contributing to radioactive cooling remains unchanged, and the remaining thickness serves to insulate against heat and cold after radioactive cooling. Ideally, if a resin material layer that does not absorb sunlight at all can be made, then sunlight will only be absorbed in the light-reflecting layer of the radioactive cooling device.

[0102] The thermal conductivity of resin materials is generally around 0.2 W / m·K. Considering this thermal conductivity, if the thickness of the resin material layer is greater than 20 mm, the temperature of the cooling surface (the side opposite to the side containing the light-reflecting layer) will rise. Even if an ideal resin material exists that does not absorb sunlight at all, because the thermal conductivity of resin materials is generally around 0.2 W / m·K, if the thickness is set to be greater than 20 mm, the object to be cooled cannot be cooled by the thermal radiation (radiative cooling) of the resin material layer. The object to be cooled will be heated by sunlight, therefore a film thickness of more than 20 mm is not feasible.

[0103] In short, according to a further feature of the radiation cooling device of the present invention, the object to be cooled can be cooled appropriately.

[0104] A further feature of the radiation cooling device of the present invention is that the resin material forming the aforementioned resin material layer is a fluororesin or a silicone rubber.

[0105] In other words, fluoropolymers with carbon-fluorine bonds (CF) as the main component, namely polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluoropolymer (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer (FEPP), have almost no light absorption in the ultraviolet, visible, and near-infrared regions of the solar spectrum.

[0106] Furthermore, resins with siloxane bonds (Si-O-Si) as the main chain and small molecular weight of the side chains, namely silicone rubber and fluoropolymers, have almost no light absorption in the ultraviolet, visible, and near-infrared regions of the solar spectrum.

[0107] Fluoropolymers and silicone rubbers have a thermal conductivity of 0.2 W / m·K. If this point is taken into account, these resins can still provide radiative cooling even when the thickness reaches 20 mm.

[0108] In short, according to a further feature of the radiation cooling device of the present invention, when the resin material of the resin material layer is a fluoropolymer or silicone rubber, the radiation cooling function can be appropriately performed.

[0109] A further feature of the radiation cooling device of the present invention is that the resin material forming the aforementioned resin material layer is a resin with a hydrocarbon as the main chain having one or more carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, or benzene rings, or a silicone resin with two or more carbon atoms in the hydrocarbon side chains.

[0110] The thickness of the aforementioned resin material layer is less than 500 μm.

[0111] That is, when the resin material forming the resin material layer is a resin with a hydrocarbon as the main chain having one or more carbon-chlorine bonds (CF), carbon-oxygen bonds (CO), ester bonds (R-COO-R), ether bonds (COC), or benzene rings, or a silicone resin with two or more carbon atoms in the hydrocarbons of the side chains, in addition to ultraviolet absorption based on covalent bond electrons, absorption based on bond bending, stretching, etc. occurs in the near-infrared region.

[0112] Specifically, absorption of the fundamental frequencies (reference tones) based on transitions to the first excited states of CH3, CH2, and CH occurs at wavelengths of 1.6 μm to 1.7 μm, 1.65 μm to 1.75 μm, and 1.7 μm, respectively. Furthermore, absorption of the fundamental frequencies based on the recombination frequencies (binding tones) of CH3, CH2, and CH occurs at wavelengths of 1.35 μm, 1.38 μm, and 1.43 μm, respectively. Furthermore, overtones (harmonics) of transitions to the second excited states of CH2 and CH occur at a wavelength of 1.24 μm. The fundamental frequencies of CH bond bending and stretching are distributed in a wide bandwidth from 2 μm to 2.5 μm. Moreover, in the case of a structure like R1-CO2-R2, a large light absorption exists at a wavelength of 1.9 μm.

[0113] For example, polymethyl methacrylate resin, polyethylene terephthalate resin, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and polyvinyl chloride exhibit the same light absorption characteristics originating from CH3, CH2, and CH in the near-infrared region. If these resin materials are thickened to a thickness of 20 mm, as specified from the perspective of thermal conductivity, they absorb near-infrared rays contained in sunlight and are heated. Therefore, when using these resin materials, a thickness of 500 μm or less is required.

[0114] In short, according to a further feature of the radiation cooling device of the present invention, when the resin material is a resin with a hydrocarbon as the main chain having one or more carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, or benzene rings, or a silicone resin with two or more carbon atoms in the side chain hydrocarbons, the absorption of near-infrared rays can be suppressed.

[0115] A further feature of the radiation cooling device of the present invention is that the resin material forming the aforementioned resin material layer is a blend of a resin containing carbon-fluorine bonds, siloxane bonds, and a resin with a hydrocarbon main chain, and the thickness of the aforementioned resin material layer is 500 μm or less.

[0116] That is, when the resin material forming the resin layer is a resin material obtained by blending a resin with a carbon-fluorine bond (CF) or siloxane bond (Si-O-Si) main chain with a hydrocarbon main chain, light absorption in the near-infrared region originating from CH, CH2, CH3, etc., occurs depending on the proportion of hydrocarbon main chain resins in the blend. When carbon-fluorine bonds or siloxane bonds are the main components, the light absorption in the near-infrared region originating from hydrocarbons is smaller, so the thickness can be increased to an upper limit of 20 mm from the perspective of thermal conductivity. However, when the blended hydrocarbon resin is the main component, the thickness needs to be 500 μm or less.

[0117] Blends of fluoropolymers or silicone rubbers with hydrocarbons also include substances in which the side chains of the fluoropolymers or silicone rubbers are replaced with hydrocarbons, alternating copolymers of fluorine monomers and silicone monomers with hydrocarbon monomers, random copolymers, block copolymers, and graft copolymers. It should be noted that examples of alternating copolymers of fluorine monomers and hydrocarbon monomers include fluoroethylene-vinyl ester (FEVE), fluoroolefin-acrylate copolymers, ethylene-tetrafluoroethylene copolymers (ETFE), and ethylene-chlorotrifluoroethylene copolymers (ECTFE).

[0118] Depending on the molecular weight and proportion of the substituted hydrocarbon side chains, light absorption in the near-infrared region originating from CH, CH2, CH3, etc., occurs.

[0119] When the monomer introduced as a side chain or copolymer is of low molecular weight, or when the density of the introduced monomer is low, the light absorption in the near-infrared region derived from the hydrocarbon decreases, thus allowing for a thickness increase to the limit of 20 mm from the perspective of thermal conductivity.

[0120] When a high molecular weight hydrocarbon is introduced as a side chain or copolymer monomer of a fluoropolymer or silicone rubber, the thickness of the resin needs to be less than 500 μm.

[0121] In short, according to a further feature of the radiation cooling device of the present invention, when the resin material is a blend of a resin containing carbon-fluorine bonds, siloxane bonds, and a resin with a hydrocarbon main chain, it is possible to suppress the absorption of near-infrared rays.

[0122] A further feature of the radiation cooling device of the present invention is that the resin material forming the aforementioned resin material layer is a fluororesin.

[0123] The thickness of the aforementioned resin material layer is less than 300 μm.

[0124] In other words, from a practical standpoint for radiation cooling devices, a thinner resin layer is preferable. Resin materials generally have lower thermal conductivity compared to metals and glass. For effective cooling of the object, the resin layer thickness should ideally be at the minimum required level. A thicker resin layer results in greater thermal radiation from the atmospheric window; however, if the thickness exceeds a certain threshold, the thermal radiation energy from the atmospheric window becomes saturated.

[0125] The thickness of a saturated resin layer varies depending on the resin material; in the case of fluororesins, it is approximately 300 μm for complete saturation. Therefore, from the perspective of thermal conductivity, it is desirable to suppress the film thickness of the resin layer to below 300 μm compared to 500 μm.

[0126] Furthermore, although the thermal radiation is not saturated, sufficient thermal radiation can be obtained in the atmospheric window region even with a thickness of around 100 μm. The heat transfer rate is improved when the thickness is thin, which more effectively reduces the temperature of the object being cooled. Therefore, for example, in the case of fluoropolymers, the thickness can be set to around 100 μm or less.

[0127] Furthermore, in the case of fluoropolymers, the absorption coefficients derived from carbon-silicon bonds, carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds are larger than those derived from CF bonds. Of course, from a thermal conductivity perspective, it is desirable to suppress the film thickness to below 300 μm compared to 500 μm, but if the film thickness is further reduced to improve thermal conductivity, a greater radioactive cooling effect can be expected.

[0128] Furthermore, as an example of fluoropolymers, polyvinylidene fluoride (PVF) and polyvinylidene fluoride (PVDF) can be used. PVF and PVDF are flame-retardant and difficult to biodegrade, making them suitable as resin materials for forming resin layers in outdoor radiation cooling devices.

[0129] In short, according to a further feature of the radiation cooling device of the present invention, the radiation cooling effect can be improved when the resin material is a fluororesin.

[0130] A further feature of the radiation cooling device of the present invention is that the resin material forming the aforementioned resin material layer is a resin material having one or more of the following: carbon-chlorine bond, carbon-oxygen bond, ester bond, ether bond, and benzene ring.

[0131] The thickness of the aforementioned resin material layer is less than 50 μm.

[0132] That is, in the case of resin materials containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, even with a thickness of 100 μm, the thermal radiation energy of the atmospheric window is saturated, and even with a thickness of 50 μm, sufficient thermal radiation is obtained in the atmospheric window region.

[0133] When the resin material is thin, the heat transfer rate is increased, and the temperature of the object being cooled is reduced more effectively. Therefore, in the case of resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, if the thickness is set to less than 50μm, the thermal insulation is reduced, but the object being cooled can be cooled more effectively.

[0134] The benefits of thinning are not limited to reducing insulation and facilitating the transfer of heat and cold. They also include suppressing near-infrared light absorption in the near-infrared region, originating from CH, CH2, and CH3, exhibited by resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds. Thinning reduces the absorption of sunlight caused by these bonds, thus improving the cooling capacity of the radiative cooling device.

[0135] Based on the above viewpoints, in the case of resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, if the thickness is set to less than 50 μm, it can more effectively exert a radiative cooling effect under sunlight.

[0136] In short, according to a further feature of the radiation cooling device of the present invention, a resin material having one or more of the following: a carbon-chlorine bond, a carbon-oxygen bond, an ester bond, an ether bond, or a benzene ring, can improve the radiation cooling effect.

[0137] A further feature of the radiation cooling device of the present invention is that the resin material forming the aforementioned resin material layer is a resin material having carbon-silicon bonds.

[0138] The thickness of the aforementioned resin material layer is less than 10 μm.

[0139] In other words, with resin materials containing carbon-silicon bonds, even at a thickness of 50 μm, thermal radiation is fully saturated in the atmospheric window region, and even at a thickness of 10 μm, sufficient thermal radiation is obtained in the atmospheric window region. Thinner resin materials result in higher heat transfer rates, more effectively reducing the temperature of the object being cooled. Therefore, with resin materials containing carbon-silicon bonds, if the thickness is set to less than 10 μm, the thermal insulation is reduced, but the object being cooled can still be cooled effectively. Further thinning reduces solar radiation absorption, thus improving the cooling capacity of the radiative cooling device.

[0140] Based on the above viewpoints, in the case of resin materials containing carbon-silicon bonds, if the thickness is set to less than 10 μm, it can more effectively exert a radiative cooling effect under sunlight.

[0141] In short, according to a further feature of the radiation cooling device of the present invention, the resin material having carbon-silicon bonds can improve the radiation cooling effect.

[0142] A further feature of the radiation cooling device of the present invention is that the resin material forming the aforementioned resin material layer is vinyl chloride resin or vinylidene chloride resin.

[0143] The thickness of the aforementioned resin material layer is less than 100 μm and more than 10 μm.

[0144] That is, vinyl chloride resin (polyvinyl chloride) or vinylidene chloride resin (polyvinylidene chloride) with a thickness of less than 100 μm and more than 10 μm receives sufficient thermal radiation in the atmospheric window region.

[0145] Vinyl chloride resin or vinylidene chloride resin is slightly inferior to fluoropolymers, which have high thermal radiation properties in the atmospheric window region, but is superior to other resin materials such as silicone rubber. It is significantly cheaper than fluoropolymers, and therefore effective for constructing radiative cooling devices that reduce the temperature to below the ambient temperature under direct sunlight at a low cost.

[0146] Furthermore, thin-film vinyl chloride resin or vinylidene chloride resin is flexible, making it difficult to damage even upon contact with other objects, thus maintaining its aesthetic appearance for a long time. In contrast, thin-film fluoropolymer resin is rigid, making it easily damaged upon contact with other objects and difficult to maintain its aesthetic appearance. 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 layer of outdoor radiation cooling devices.

[0147] In short, according to the further features of the radiation cooling device of the present invention, a radiation cooling device that reduces temperature compared to the ambient temperature under direct sunlight and is resistant to scratches can be obtained at low cost.

[0148] A further feature of the radiation cooling device of the present invention is that the aforementioned light-reflecting layer is made of silver or a silver alloy and has a thickness of 50 nm or more.

[0149] In other words, in order for the light reflective layer to have the above-mentioned reflectivity characteristics, namely, a reflectivity of 90% or more for wavelengths from 0.4 μm to 0.5 μm and a reflectivity of 96% or more for wavelengths longer than 0.5 μm, the reflective material on the radiating side of the light reflective layer needs to be silver or a silver alloy.

[0150] Furthermore, in the case of reflecting sunlight with the aforementioned reflectivity characteristics solely through silver or silver alloys, a thickness of 50 nm or more is required.

[0151] In short, according to a further feature of the radiation cooling device of the present invention, the absorption of solar energy by the light-reflecting layer can be effectively suppressed, and radiation cooling by the resin material layer can be effectively performed.

[0152] A further feature of the radiation cooling device of the present invention is that the aforementioned light-reflecting layer is a stacked structure of silver or silver alloy adjacent to the aforementioned protective layer and aluminum or aluminum alloy located on the side away from the aforementioned protective layer.

[0153] That is, in order to give the light-reflecting layer the aforementioned reflectivity characteristics, it can be configured as a structure obtained by laminating silver or a silver alloy with aluminum or an aluminum alloy. It should be noted that in this case, the reflective material on the radiating surface side also needs to be silver or a silver alloy. In this case, the thickness of the silver needs to be at least 10 nm, and the thickness of the aluminum needs to be at least 30 nm.

[0154] Furthermore, aluminum or aluminum alloys are cheaper than silver or silver alloys, thus enabling the cost-effectiveness of light-reflecting layers while maintaining appropriate reflectivity characteristics.

[0155] That is, while reducing the cost of expensive silver or silver alloys and making the light reflective layer cheaper, by setting the light reflective layer as a stacked structure of silver or silver alloy and aluminum or aluminum alloy, the light reflective layer can be made cheaper while having appropriate reflectivity characteristics.

[0156] In short, a further feature of the radiation cooling device according to the present invention enables the reduction of the cost of the light-reflecting layer while having appropriate reflectivity characteristics.

[0157] A further feature of the radiation cooling device of the present invention is that the aforementioned resin material layer, the aforementioned protective layer and the aforementioned light reflective layer are in a film-like state when stacked.

[0158] That is, the resin material layer, the protective layer, and the light-reflecting layer are stacked in a film-like state. In other words, a radiation cooling device in which the resin material layer, the protective layer, and the light-reflecting layer are stacked is fabricated as a radiation cooling film.

[0159] Furthermore, since the resin material layer and the protective layer are flexible, the light-reflecting layer is made into a thin film, making the light-reflecting layer flexible, thereby making the radiation cooling device (radiation cooling film) flexible.

[0160] Therefore, it is possible to effectively attach a flexible, membrane-like radiative cooling device (radiative cooling film) to the outer wall of existing outdoor equipment to achieve radiative cooling performance.

[0161] Furthermore, various forms have been considered for fabricating the radiation cooling device (radiation cooling film) into a film-like structure. For example, it is considered to fabricate it by coating a protective layer and a resin material layer onto a film-like light-reflecting layer. Alternatively, it is considered to fabricate it by attaching a protective layer and a resin material layer onto a film-like light-reflecting layer. Or, it is considered to form a protective layer on a film-like resin material layer by coating or laminating, and then fabricate a light-reflecting layer on the protective layer by means of vapor deposition, sputtering, ion plating, silver mirror reaction, etc.

[0162] In short, the further features of the radiation cooling device according to the present invention enable it to be well added to existing equipment to achieve radiation cooling performance.

[0163] A further feature of the radiation cooling device of the present invention is that the aforementioned resin material layer is bonded to the aforementioned protective layer using an adhesive or bonding agent.

[0164] That is, the resin material layer and the protective layer are bonded together with an adhesive or bonding agent. Therefore, by forming the light reflective layer and the protective layer into a stacked state, and then bonding the resin material layer and the protective layer together with the bonding layer, the resin material layer, the protective layer and the light reflective layer can be well formed into a stacked state.

[0165] If the adhesive or bonding agent's durability against shear tension weakens, layer misalignment occurs over time due to the difference in thermal expansion coefficients between the resin material layer and the protective layer. The misaligned portion lacks the resin material layer that forms the infrared radiating layer, thus losing its radiative cooling properties. Furthermore, the misaligned portion exposes the bonding layer, and various forms of degradation begin from this point. Deterioration due to shear tension is an undesirable degradation mode. If the bonding layer is thick, its resistance to shear tension weakens. That is, the creep characteristics of the resin material layer and the protective layer deteriorate; from this perspective, the bonding layer is desirable to be thinner than 150 μm. However, if it is too thin, its resistance to peel impact weakens, and the resin material layer and the protective layer easily peel off; therefore, a thickness of 1 μm or more is required. If the bonding layer becomes thick, its thermal conductivity deteriorates; therefore, unnecessary thickening is unnecessary. From this perspective, the bonding layer is desirable to be 100 μm or less.

[0166] As mentioned above, the desired thickness of the bonding layer is a range of 1 μm or more and 100 μm or less. To reduce the thickness of the bonding layer while improving its creep resistance and peel impact strength, it is necessary to increase the degree of polymerization of the resin in the bonding layer. However, increasing the degree of polymerization results in hardening and reduced flexibility. From the viewpoint of the workability of the radioactive cooling raw material (radioactive cooling device), flexibility and the elongation of the raw material are important; therefore, from this perspective, the desired thickness of the bonding layer is further a range of 1 μm or more and 50 μm or less.

[0167] Furthermore, when the bonding layer is located between the resin material layer and the protective layer, free radicals are also 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 polyethylene terephthalate resin forming the protective layer is 17 μm or more, the free radicals generated by the bonding layer can be suppressed from reaching the light-reflecting layer for a long time.

[0168] A further feature of the radiation cooling device of the present invention is that an inorganic filler is incorporated into the resin material layer.

[0169] That is, by incorporating inorganic fillers into the resin material layer, the resin material layer can be made to have a light-scattering structure.

[0170] Furthermore, by incorporating light scattering, glare from the radiating surface can be suppressed when observing it.

[0171] Silica (SiO2) can be suitable as an inorganic material for forming fillers. 、 Titanium oxide (TiO2), aluminum oxide (Al2O3), magnesium oxide (MgO), etc. It should be noted that if fillers are mixed into the resin material layer, the resin material layer will have an uneven surface on both sides.

[0172] Furthermore, the bonding layer is located between the resin material layer and the protective layer, so even if the back side of the resin material layer is uneven, the resin material layer and the protective layer can be properly bonded by the bonding layer.

[0173] In short, the further features of the radiation cooling device according to the present invention can suppress glare from the radiation surface and can properly bond the resin material layer and the protective layer.

[0174] A further feature of the radiation cooling device of the present invention is that the two sides of the resin material layer are formed in an uneven shape.

[0175] That is, the front and back sides of the resin material layer are formed in an uneven shape, thereby enabling the resin material layer to have a light scattering structure.

[0176] Furthermore, by incorporating light scattering, glare from the radiating surface can be suppressed when observing it.

[0177] Furthermore, in order to make the front and back sides of the resin material layer uneven, it can be done by embossing, surface damage treatment, etc.

[0178] Furthermore, the bonding layer is located between the resin material layer and the protective layer, so even if the back side of the resin material layer is uneven, the resin material layer and the protective layer can be properly bonded by the bonding layer.

[0179] In short, the further features of the radiation cooling device according to the present invention can suppress glare from the radiation surface and can properly bond the resin material layer and the protective layer.

[0180] The radiation cooling method of the present invention is a radiation cooling method that uses a radiation cooling device having any of the above-described features to radiate the aforementioned infrared light from the radiation surface opposite to the side of the aforementioned resin material layer where the aforementioned light-reflecting layer exists. Its characteristic feature is that...

[0181] The aforementioned radiating surface faces the air, and the aforementioned infrared light is emitted from the radiating surface.

[0182] Based on the above configuration, infrared light escaping from the radiation source can be emitted into the air, i.e., into space. Furthermore, it can suppress the absorption of sunlight and improve cooling performance.

[0183] In short, the characteristic configuration of the radiation cooling method according to the present invention can suppress the absorption of sunlight while improving cooling performance. Attached Figure Description

[0184] Figure 1 This is a diagram illustrating the basic structure of a radiation cooling device.

[0185] Figure 2 This is a graph showing the relationship between the absorption coefficient of the resin material and the wavelength band.

[0186] Figure 3 This is a graph showing the relationship between the light absorption rate of the resin material and the wavelength.

[0187] Figure 4 This is a graph showing the emissivity spectrum of silicone rubber.

[0188] Figure 5 This is a graph showing the radiance spectrum of PFA.

[0189] Figure 6 This is a graph showing the emissivity spectrum of vinyl chloride resin.

[0190] Figure 7 This is a graph showing the emissivity spectrum of polyethylene terephthalate resin.

[0191] Figure 8 This is a graph showing the emissivity spectrum of olefin-modified materials.

[0192] Figure 9 It is a graph showing the relationship between the temperature of the radiating surface and the temperature of the light-reflecting layer.

[0193] Figure 10 This is a graph showing the light absorption spectra of silicone rubber and perfluoroalkoxy fluororesin.

[0194] Figure 11 This is a graph showing the light absorption spectrum of polyethylene terephthalate resin.

[0195] Figure 12 This is a graph showing the light reflectance spectrum of a silver-based light-reflecting layer.

[0196] Figure 13 This is a graph showing the emissivity spectrum of vinyl fluoride.

[0197] Figure 14 This is a graph showing the emissivity spectrum of vinylidene chloride resin.

[0198] Figure 15 This is a table showing the experimental results.

[0199] Figure 16 This is a diagram showing the specific structure of the radiation cooling device.

[0200] Figure 17 This is a diagram showing the specific structure of the radiation cooling device.

[0201] Figure 18 This is a diagram showing the specific structure of the radiation cooling device.

[0202] Figure 19This is a diagram showing the specific structure of the radiation cooling device.

[0203] Figure 20 This is a graph showing the relationship between the light absorption rate of the resin material and the wavelength.

[0204] Figure 21 This is a graph showing the relationship between the light transmittance of polyethylene and wavelength.

[0205] Figure 22 It is a diagram illustrating the structure used in the experiment.

[0206] Figure 23 This is a graph showing the test results when the protective layer is polyethylene.

[0207] Figure 24 This is a graph showing the test results when the protective layer is made of ultraviolet-absorbing acrylic resin.

[0208] Figure 25 This is a graph showing the emissivity spectrum of polyethylene.

[0209] Figure 26 This is a diagram illustrating another component of the radiation cooling device.

[0210] Figure 27 This diagram illustrates the composition of a resin material layer incorporating fillers.

[0211] Figure 28 This diagram illustrates the construction of a resin material layer with an uneven surface on both sides.

[0212] Figure 29 This is a graph showing the experimental results.

[0213] Figure 30 This is a diagram showing the appropriate specific configuration of a radiation cooling device.

[0214] Figure 31 This is a graph showing the light reflectance spectrum of a properly configured radioactive cooling device.

[0215] Figure 32 It is a graph showing the emissivity spectrum of a radiation cooling device with appropriate specific configuration. Detailed Implementation

[0216] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0217] [Basic Components of a Radiation Cooling Device]

[0218] like Figure 1As shown, the radiation cooling device CP has an infrared radiation layer A that radiates infrared light IR from the radiation surface H, a light reflection layer B located on the side of the infrared radiation layer A opposite to the side where the radiation surface H exists, and a protective layer D between the infrared radiation layer A and the light reflection layer B, and is formed in a film-like state.

[0219] That is, the radiation cooling device CP is configured as a radiation cooling film.

[0220] The light-reflecting layer B reflects sunlight and other light L that has passed through the infrared radiation layer A and the protective layer D. The reflectivity of this layer is over 90% for wavelengths from 400nm to 500nm, and over 96% for wavelengths longer than 500nm.

[0221] Solar spectrum Figure 10 As shown, it exists from wavelength 300nm to 4000nm, and the intensity increases as the wavelength increases from 400nm, especially from wavelength 500nm to wavelength 1800nm.

[0222] It should be noted that in this embodiment, light L includes ultraviolet light (ultraviolet radiation), visible light, and infrared light. If these are expressed in terms of the wavelength of light as electromagnetic waves, they include electromagnetic waves with wavelengths from 10 nm to 20000 nm (electromagnetic waves from 0.01 μm to 20 μm). Furthermore, in this specification, the wavelength range of ultraviolet light (ultraviolet radiation) is set to between 300 nm and 400 nm.

[0223] The light-reflecting layer B exhibits a reflectivity of over 90% from wavelengths of 400nm to 500nm, and a reflectivity of over 96% for wavelengths longer than 500nm. This allows the solar energy absorbed by the radiative cooling device CP (radiative cooling film) in the light-reflecting layer B to be suppressed to below 5%, meaning that the solar energy absorbed at noon in summer is around 50W.

[0224] The light-reflecting layer B is composed of silver or a silver alloy, or is a laminated structure of silver or a silver alloy adjacent to the protective layer D and aluminum or an aluminum alloy located on the side away from the protective layer D, and is flexible, as detailed below.

[0225] The infrared radiating layer A is composed of a resin material layer J, which is adjusted to have a thickness that emits thermal radiation energy greater than the absorbed solar energy in the wavelength band from 8 μm to 14 μm, as detailed below.

[0226] Therefore, the radiation cooling device CP is configured to reflect a portion of the light L incident on the radiation cooling device CP using the radiation surface H of the infrared radiation layer A, and to reflect the light (such as sunlight) that passes through the resin material layer J and the protective layer D in the light L incident on the radiation cooling device CP using the light reflection layer B, so that the light escapes to the outside from the radiation surface H.

[0227] Furthermore, the device is configured such that heat (e.g., heat entering the cooling object E via thermal conduction from the object E located on the opposite side of the resin material layer J, which is the side of the light-reflecting layer B) is converted into infrared light IR and emitted through the resin material layer J, thereby cooling the object E.

[0228] That is, the radiation cooling device CP is configured to reflect the light L that is irradiated toward the radiation cooling device CP, and to radiate the heat transferred to the radiation cooling device CP (e.g., heat transferred from the atmosphere, heat transferred from the object being cooled E) to the outside in the form of infrared light IR.

[0229] Furthermore, the resin material layer J, the protective layer D, and the light-reflecting layer B are configured to be flexible, thereby making the radiation cooling device CP (radiation cooling film) flexible.

[0230] In addition, the radiation cooling device CP is used to implement a radiation cooling method that radiates infrared light IR from the radiation surface H on the opposite side of the contact surface of the resin material layer J and the light reflective layer B. Specifically, it implements a radiation cooling method that radiates infrared light IR from the radiation surface H facing the air.

[0231] [Summary of the resin material layer]

[0232] The light absorptivity and emissivity (light emissivity) of the resin material forming the resin material layer J vary depending on its thickness. Therefore, it is necessary to adjust the thickness of the resin material layer J in a way that releases large amounts of thermal radiation in a wavelength band (wavelength band from 8 μm to 14 μm) that absorbs as little sunlight as possible, a so-called atmospheric window.

[0233] Specifically, from the perspective of sunlight absorption rate, the thickness of the resin material layer J needs to be adjusted to a thickness where the average wavelength absorption rate is less than 13% for wavelengths from 0.4μm to 0.5μm, less than 4% for wavelengths from 0.5μm to 0.8μm, less than 1% for wavelengths from 0.8μm to 1.5μm, less than 40% for wavelengths from 1.5μm to 2.5μm, and less than 100% for wavelengths from 2.5μm to 4μm.

[0234] With this absorptivity distribution, the light absorption rate of sunlight reaches below 10%, and in terms of energy, it reaches below 100W.

[0235] As will be discussed later, the light absorption rate of the resin material increases with increasing the film thickness. If the resin material is made into a thick film, the emissivity of the atmospheric window is almost 1, and the thermal radiation released into space is 125 W / m.2 Up to 160W / m 2 The solar radiation absorption in the protective layer D and the light-reflecting layer B is 50 W / m. 2 The sum of the solar radiation absorption of the resin material layer J, the protective layer D, and the light-reflecting layer B is 150 W / m. 2 Cooling will proceed if atmospheric conditions are favorable. The resin material used to form resin material layer J, as described above, can be a resin material with low absorptivity near the peak of the solar spectrum.

[0236] Furthermore, from the perspective of infrared radiation (thermal radiation), the thickness of the resin material layer J needs to be adjusted to a thickness where the average wavelength of emissivity for wavelengths from 8 μm to 14 μm is above 40%.

[0237] In order to absorb 50W / m in the protective layer D and the light-reflecting layer B 2 The thermal energy of the sun's rays is released into the universe through the thermal radiation of the resin material layer J. The resin material layer J needs to release more than that thermal radiation.

[0238] For example, when the external temperature is 30°C, the maximum thermal radiation in the atmospheric window of 8μm to 14μm is 200W / m². 2 (Calculation with emissivity set to 1). This value is obtained under clear conditions in environments such as high mountains where the air is thin and sufficiently dry. In low-lying areas, the atmosphere is thicker than in high mountains, thus narrowing the wavelength band of the atmospheric window and reducing transmittance. This is referred to as "atmospheric window narrowing".

[0239] Furthermore, the actual environments in which radiative cooling devices (CP) are used sometimes have high humidity, which narrows the atmospheric window. The thermal radiation generated in the atmospheric window region during lowland utilization is estimated at 160 W / m² under ideal conditions at 30°C. 2 (Calculations are performed with emissivity set to 1). Furthermore, in Japan, it is common for atmospheric windows to narrow further when there is haze or smog in the sky, resulting in 125 W / m² of radiation into space. 2 about.

[0240] Given the aforementioned situation, the wavelength average emissivity of the 8μm to 14μm wavelength range is not greater than 40% (the thermal radiation intensity in the atmospheric window band is 50W / m). 2 If it is not used in the lowlands of the mid-latitude zone, then it cannot be used.

[0241] Therefore, if the thickness of the resin material layer J is adjusted in a manner that reaches the range specified by the optical requirements mentioned above, the heat output in the atmospheric window is greater than the heat input caused by the absorption of sunlight, and even in a sunny environment, it is possible to achieve a lower temperature outdoors through radiative cooling compared to the outside air.

[0242] [Details of the resin material]

[0243] The resin material can be a colorless resin material containing carbon-fluorine bonds (CF), siloxane bonds (Si-O-Si), carbon-chlorine bonds (C-Cl), carbon-oxygen bonds (CO), ester bonds (R-COO-R), ether bonds (COC bonds), and benzene rings.

[0244] For each resin material (excluding carbon-oxygen bonds), the wavelength region of the absorption coefficient with an atmospheric window is shown in the figure. Figure 2 .

[0245] According to Kirchhoff's laws, emissivity (ε) equals light absorptivity (A). Light absorptivity can be obtained from the absorption coefficient (α) using the relationship A = 1 - exp(-αt) (hereinafter referred to as the light absorptivity relationship). It should be noted that t is the film thickness.

[0246] That is, by adjusting the film thickness of the resin material layer J, large thermal radiation can be obtained in the wavelength band with a high absorption coefficient. In the case of outdoor radiative cooling, materials with a high absorption coefficient in the wavelength band of 8 μm to 14 μm, which serves as an atmospheric window, can be used.

[0247] Furthermore, to suppress the absorption of sunlight, materials with no absorption coefficient or a small absorption coefficient in the wavelength range of 0.3 μm to 4 μm, particularly 0.4 μm to 2.5 μm, can be used. From the relationship between absorption coefficient and absorptivity, it can be seen that the light absorptivity (radiative power) varies with the film thickness of the resin material.

[0248] In order to reduce the temperature compared to the surrounding atmosphere through radiative cooling under sunlight, if a material with 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, it is possible to create a state that hardly absorbs sunlight but releases a large amount of thermal radiation from the atmospheric window by adjusting the film thickness. That is, a state in which the output of radiative cooling is greater than the input of sunlight.

[0249] Regarding carbon-fluorine (CF) bonds, the absorption coefficients derived from CHF and CF2 broaden significantly in the wide wavelength range of 8 μm to 14 μm, which serves as an atmospheric window, with a particularly high absorption coefficient at 8.6 μm. Meanwhile, regarding the wavelength range of sunlight, there are no significant absorption coefficients in the high-energy wavelength range of 0.3 μm to 2.5 μm.

[0250] Examples of resin materials containing carbon-fluorine bonds (CF) include

[0251] Polytetrafluoroethylene (PTFE) as a fully fluorinated resin

[0252] Polyvinyl chloride trifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF) are partially fluorinated resins.

[0253] Perfluoroalkoxy fluoropolymers (PFA) are fluoropolymer copolymers.

[0254] Tetrafluoroethylene-hexafluoropropylene copolymer (FEP)

[0255] Ethylene-tetrafluoroethylene copolymer (ETFE)

[0256] Ethylene-chlorotrifluoroethylene copolymer (ECTFE).

[0257] Examples of resin materials with siloxane bonds (Si-O-Si) include silicone rubber and silicone resin.

[0258] In this resin, the large absorption coefficient originating from the stretching of C-Si bonds is broad around a wavelength of 13.3 μm, the absorption coefficient originating from the outward bending (longitudinal rocking) of CSiH2 is broad around a wavelength of 10 μm, and the absorption coefficient originating from the inward bending (shearing) of CSiH2 is small around a wavelength of 8 μm.

[0259] Regarding the carbon-chlorine bond (C-Cl), the absorption coefficient based on the C-Cl stretching vibration appears in a broadband domain with a half-width of more than 1 μm, centered at a wavelength of 12 μm.

[0260] In addition, examples of resin materials include vinyl chloride resin (PVC) and vinylidene chloride resin (PVDC). In the case of vinyl chloride resin, due to the electron-withdrawing effect of chlorine, the absorption coefficient of the bending vibration of CH in the olefin contained in the main chain appears at a wavelength of around 10 μm.

[0261] Regarding ester bonds (R-COO-R) and ether bonds (COC bonds), absorption coefficients are observed from wavelengths of 7.8 μm to 9.9 μm. Furthermore, regarding the carbon-oxygen bonds contained within ester and ether bonds, strong absorption coefficients are exhibited in the wavelength band from 8 μm to 10 μm.

[0262] If a benzene ring is introduced into the side chain of a hydrocarbon resin, it will exhibit absorption over a wide range of wavelengths from 8.1 μm to 18 μm through the vibration of the benzene ring itself and the vibration of surrounding elements caused by the influence of the benzene ring.

[0263] Resins containing these bonds include methyl methacrylate resin, polyethylene terephthalate resin, trimethyl terephthalate resin, butylene terephthalate resin, polyethylene naphthalate resin, and butylene naphthalate resin.

[0264] [Examination of light absorption]

[0265] The absorption of light in the ultraviolet-visible region, i.e., solar light absorption, of resin materials possessing the aforementioned bonds and functional groups was investigated. The origin of absorption from ultraviolet to visible light is the transition of electrons contributing to the bonds. The bond energy can be calculated from the absorption in this wavelength region.

[0266] First, we consider the wavelengths in the ultraviolet to visible region where the absorption coefficient occurs in resin materials with carbon-fluorine bonds (CF). If we calculate the bond energies of the CC, CH, and CF bonds in the basic structural unit represented by polyvinylidene fluoride (PVDF), they are 4.50 eV, 4.46 eV, and 5.05 eV, respectively. These correspond to wavelengths of 0.275 μm, 0.278 μm, and 0.246 μm, respectively, indicating the absorption of light at these wavelengths.

[0267] The solar spectrum contains only wavelengths longer than 0.300 μm. Therefore, when using fluoropolymers, there is almost no absorption of ultraviolet, visible, or near-infrared radiation from sunlight. It should be noted that ultraviolet radiation is defined as wavelengths shorter than 0.400 μm; visible light is defined as wavelengths from 0.400 μm to 0.800 μm; near-infrared radiation is defined as the range from 0.800 μm to 3 μm; mid-infrared radiation is defined as the range from 3 μm to 8 μm; and far-infrared radiation is defined as wavelengths longer than 8 μm.

[0268] The absorbance spectrum of a 50 μm thick PFA (perfluoroalkoxy fluoropolymer) in the UV to visible region is shown in the figure. Figure 3 It can be seen that there is almost no absorbance. It should be noted that some increase in absorbance spectrum was observed at shorter wavelengths compared to 0.4 μm, but this increase only indicates the effect of scattering by the sample used in the measurement, and the actual absorbance did not increase.

[0269] Regarding the ultraviolet region of siloxane bonds (Si-O-Si), the bond energy of the Si-O-Si main chain is 4.60 eV, corresponding to a wavelength of 269 nm. The solar spectrum only contains wavelengths longer than 0.300 μm; therefore, when siloxane bonds are predominant, there is almost no absorption of ultraviolet, visible, or near-infrared radiation from sunlight.

[0270] The absorbance spectrum of a 100 μm thick silicone rubber in the ultraviolet to visible region is shown in the figure. Figure 3 It can be seen that there is almost no absorption. It should be noted that some increase in the absorbance spectrum was observed at shorter wavelengths compared to 0.4 μm, but this increase only indicates the effect of scattering by the sample used in the measurement, and the actual absorbance did not increase.

[0271] Regarding the carbon-chlorine bond (C-Cl), the bond energy between carbon and chlorine in alkenes is 3.28 eV, with a wavelength of 0.378 μm. Therefore, it absorbs a large amount of ultraviolet light from sunlight, but has almost no absorption in the visible region.

[0272] The absorbance spectrum of a 100 μm thick vinyl chloride resin in the ultraviolet to visible region is shown in the figure. Figure 3 At shorter wavelengths compared to 0.38 μm, light absorption increases.

[0273] The absorbance spectrum of vinylidene chloride resin with a thickness of 100 μm in the ultraviolet to visible region is shown in the figure. Figure 3 An increase in the absorption spectrum was observed at shorter wavelengths compared to 0.4 μm.

[0274] Resins containing ester bonds (R-COO-R), ether bonds (COC bonds), and benzene rings include methyl methacrylate resin, polyethylene terephthalate resin, trimethyl terephthalate resin, butylene terephthalate resin, polyethylene naphthalate resin, and butylene naphthalate resin. For example, the C / C bond of the acryloyl group has a bond energy of 3.93 eV, absorbing sunlight with wavelengths shorter than 0.315 μm, but exhibiting almost no absorption in the visible region.

[0275] As an example of a resin material possessing these bonds and functional groups, the absorbance spectrum of a 5 mm thick methyl methacrylate resin in the ultraviolet to visible region is shown in the figure. Figure 3 It should be noted that the methyl methacrylate resin exemplified is a commercially available resin mixed with a benzotriazole-based ultraviolet absorber.

[0276] Because the plate is 5mm thick, the wavelength with the smallest absorption coefficient becomes larger, and the light absorption increases at the shorter wavelength side of 0.38μm, which is longer than the wavelength of 0.315.

[0277] As an example of a resin material possessing these bonds and functional groups, the absorbance spectrum of a 40 μm thick polyethylene terephthalate resin in the ultraviolet to visible region is shown in the figure. Figure 3 .

[0278] As shown in the figure, the closer to the wavelength of 0.315 μm, the greater the absorption rate, with a sharp increase at 0.315 μm. It should be noted that the ethylene terephthalate resin also exhibits increased absorption at slightly longer wavelengths compared to 0.315 μm, primarily due to absorption at the C / C bond end, similar to commercially available methyl methacrylate resin, where the absorption rate for ultraviolet light increases.

[0279] If the resin material layer J uses a resin material with the aforementioned characteristics of emissivity (light emissivity) and light absorptivity, it can be a single-layer film of one resin material, a multilayer film of multiple resin materials, a single-layer film of a resin material blended with multiple resin materials, or a multilayer film of a resin material blended with multiple resin materials.

[0280] It should be noted that blends also include copolymers such as alternating copolymers, random copolymers, block copolymers, graft copolymers, and modified products with side chain substitutions.

[0281] [Emissivity of silicone rubber]

[0282] Figure 4 The image shows the radiance spectrum of an atmospheric window of a silicone rubber with siloxane bonds.

[0283] In silicone rubber, the large absorption coefficients derived from the stretching of C-Si bonds are broad around a wavelength of 13.3 μm, the absorption coefficients derived from the outward bending (longitudinal rocking) of CSiH2 are broad around a wavelength of 10 μm, and the absorption coefficients derived from the inward bending (shearing) of CSiH2 are small around a wavelength of 8 μm.

[0284] This effect results in the emissivity of a 1 μm thick film having an average wavelength of 80% in the wavelength range of 8 μm to 14 μm, falling within the specified range of over 40% for average wavelength. As shown in the figure, if the film thickness increases, the emissivity in the atmospheric window region increases.

[0285] and, Figure 4 The radiation spectrum of quartz, which is an inorganic material, with a thickness of 1 μm on silver is also shown. When the quartz is 1 μm thick, it has only a narrow band of radiation peaks in the wavelength range of 8 μm to 14 μm.

[0286] If the thermal radiation is averaged over a wavelength range of 8 μm to 14 μm, the emissivity of the wavelength range of 8 μm to 14 μm is 32%, which is insufficient to demonstrate the radiation cooling performance.

[0287] The radiation cooling device CP (radiation cooling film) of the present invention, which uses resin material layer J, achieves radiation cooling performance even with a thinner infrared radiation layer A, compared to conventional technology that uses inorganic materials as light reflective layer B.

[0288] That is, when the infrared radiation layer A is formed by quartz or Tempax glass, which are inorganic materials, radiation cooling performance cannot be obtained when the infrared radiation layer A has a film thickness of 1 μm. However, in the radiation cooling device CP of the present invention, which uses a resin material layer J, radiation cooling performance is shown even when the resin material layer J has a film thickness of 1 μm.

[0289] [Emissivity of PFA]

[0290] Figure 5 In this study, the emissivity of perfluoroalkoxy fluoropolymer (PFA) within the atmospheric window is shown as a representative example of resins with carbon-fluorine bonds. The absorption coefficients derived from CHF and CF2 broaden significantly in the wide wavelength range of 8 μm to 14 μm, which serves as the atmospheric window, with a particularly high absorption coefficient at 8.6 μm.

[0291] This effect results in the emissivity of a 10 μm thick film having an average wavelength of 45% in the wavelength range of 8 μm to 14 μm, falling within the specified range of over 40%. As shown in the figure, if the film thickness increases, the emissivity in the atmospheric window region increases.

[0292] [Emissivity of vinyl chloride resin and vinylidene chloride resin]

[0293] Figure 6 In the example, the emissivity of vinyl chloride resin (PVC) in the atmospheric window is shown as a representative example of resins with carbon-chlorine bonds. Furthermore, Figure 14 The figure shows the emissivity of vinylidene chloride (PVDC) resin in the atmospheric window.

[0294] Regarding the carbon-chlorine bond, the absorption coefficient based on the C-Cl stretching vibration appears in a broadband domain with a half-width of more than 1 μm, centered at a wavelength of 12 μm.

[0295] Furthermore, in the case of vinyl chloride resin, due to the electron-withdrawing effect of chlorine, the absorption coefficient of the bending vibration of CH in the olefins originating from the main chain appears near a wavelength of 10 μm. The same applies to vinylidene chloride resin.

[0296] These effects result in an emissivity of 43% on average wavelength in the 8-14 μm wavelength range for a 10 μm thickness, falling within the specified range of over 40% on average wavelength. As shown in the figure, if the film thickness increases, the emissivity in the atmospheric window region increases.

[0297] [Ethylene terephthalate resin]

[0298] Figure 7 In the example, the emissivity of polyethylene terephthalate resin in the atmospheric window is shown as a representative example of resins with ester bonds and benzene rings.

[0299] Regarding ester bonds, an absorption coefficient is observed from wavelengths of 7.8 μm to 9.9 μm. Furthermore, regarding the carbon-oxygen bonds contained within the ester bonds, a strong absorption coefficient is observed in the wavelength band from 8 μm to 10 μm. If a benzene ring is introduced into the side chain of a hydrocarbon resin, absorption is widely observed from wavelengths of 8.1 μm to 18 μm through the vibrations of the benzene ring itself and the vibrations of surrounding elements caused by the influence of the benzene ring.

[0300] These effects result in an emissivity of 71% on average wavelength in the 8-14 μm wavelength range for a 10 μm thickness, falling within the specified range of over 40% on average wavelength. As shown in the figure, if the film thickness increases, the emissivity in the atmospheric window region increases.

[0301] [Emissivity of olefin-modified materials]

[0302] Figure 8 The image shows the emissivity spectrum of an olefin-modified material whose main component is an olefin and which does not contain carbon-fluorine (CF), carbon-chlorine (C-Cl), ester (R-COO-R), ether (COC) bonds, or benzene rings. The sample was prepared by coating olefin resin onto evaporated silver using a rod coater and then drying.

[0303] As shown in the figure, the emissivity is low in the atmospheric window region. As a result, the wavelength average emissivity of a 10 μm thickness is 27% in the wavelength range of 8 μm to 14 μm, which does not fall within the requirement of an average wavelength of over 40%.

[0304] The emissivity shown in the figure is for olefin resins modified for bar coating. In the case of pure olefin resins, the emissivity in the atmospheric window region is further reduced.

[0305] In this way, if there are no carbon-fluorine bonds (CF), carbon-chlorine bonds (C-Cl), ester bonds (R-COO-R), ether bonds (COC bonds), or benzene rings, then radiation cooling cannot be performed.

[0306] [Surface temperature of the light-reflecting layer and resin material layer]

[0307] Thermal radiation from the atmospheric window of resin material layer J is generated near the surface of the resin material.

[0308] Depend on Figure 4 It can be seen that if the thickness of the silicone rubber exceeds 10 μm, the thermal radiation in the atmospheric window region does not increase. That is, in the case of silicone rubber, most of the thermal radiation in the atmospheric window is generated in the portion from the surface to a depth of about 10 μm, and the radiation in the deeper portion does not radiate outward.

[0309] Depend on Figure 5 It is known that, in the case of fluoropolymers, even when the thickness exceeds 100 μm, the thermal radiation in the atmospheric window region does not increase significantly. That is, in the case of fluoropolymers, the thermal radiation in the atmospheric window is generated in the portion from the surface to a depth of approximately 100 μm, and the radiation in the deeper portion does not radiate outward.

[0310] Depend on Figure 6It can be seen that, in the case of vinyl chloride resin, even if the thickness is greater than 100 μm, the thermal radiation in the atmospheric window region does not increase much. That is, in the case of vinyl chloride resin, the thermal radiation in the atmospheric window is generated in the part from the surface to a depth of about 100 μm, and the radiation in the deeper part is not emitted outward.

[0311] Depend on Figure 14 It can be seen that vinylidene chloride resin is the same as vinyl chloride resin.

[0312] Depend on Figure 7 It is known that, in the case of polyethylene terephthalate resin, even with a thickness greater than 125 μm, the thermal radiation in the atmospheric window region does not increase significantly. That is, in the case of polyethylene terephthalate resin, the thermal radiation in the atmospheric window is generated in the portion from the surface to a depth of approximately 100 μm, and the radiation in the deeper portion does not radiate outward.

[0313] As described above, thermal radiation from the atmospheric window region generated from the surface of the resin material is generated in the portion within a depth of approximately 100 μm from the surface. If the thickness of the resin increases beyond that, it does not contribute to thermal radiation. Through such a resin material, the thermal insulation of the radiation cooling device CP is achieved.

[0314] Ideally, a resin material layer J that does not absorb sunlight at all could be fabricated on the light-reflecting layer B. In this case, sunlight would only be absorbed in the light-reflecting layer B of the radiative cooling device CP.

[0315] The thermal conductivity of resin materials is generally around 0.2 W / m / K. If this thermal conductivity is taken into account, and the thickness of the resin material layer J is greater than 20 mm, the temperature of the cooling surface (the side of the light-reflecting layer B opposite to the side where the resin material layer J exists) will rise.

[0316] Even if an ideal resin material exists that does not absorb sunlight at all, the thermal conductivity of resin materials is generally around 0.2 W / m / K. Therefore, if... Figure 9 If the thickness is greater than 20mm, the light-reflecting layer B will be heated by sunlight, and the object to be cooled, E, located on the side of the light-reflecting layer, will also be heated. Therefore, the thickness of the resin material in the radiation cooling device CP needs to be less than 20mm.

[0317] It should be explained that Figure 9 This is a plot of the surface temperature of the radiating surface H of the radiative cooling device (radiative cooling film) CP and the temperature of the light-reflecting layer B, calculated based on a typical midday day in western Japan during a pleasant summer. Sunlight intensity is set to AM 1.5 and 1000 W / m². 2The energy density is calculated. The external temperature is 30°C, and the radiant energy varies with temperature, reaching 100W at 30°C. No solar radiation absorption is considered in the resin material layer. A windless condition is assumed, and the convective thermal conductivity is set at 5W / m. 2 / K.

[0318] [Regarding the light absorption rate of silicone rubber, etc.]

[0319] Figure 10 The image shows the light absorption spectrum of a 100 μm thick silicone rubber with CH3 side chains, and the light absorption spectrum of a 100 μm thick perfluoroalkoxy fluororesin. As mentioned earlier, both resins exhibit almost no light absorption in the ultraviolet region.

[0320] Regarding silicone rubber, in the near-infrared region, the light absorption rate increases in the longer wavelength side compared to 2.35 μm. However, the intensity of the solar spectrum in this wavelength region is weak, so even if the light absorption rate in the longer wavelength side compared to 2.35 μm reaches 100%, the absorbed solar energy is only 20 W / m². 2 .

[0321] Regarding perfluoroalkoxy fluoropolymers, they exhibit almost no light absorption in the wavelength range of 0.3 μm to 2.5 μm, but do absorb light at wavelengths longer than 2.5 μm. However, even with increased film thickness, while the light absorption at wavelengths longer than 2.5 μm reaches 100%, the absorbed solar energy is only about 7 W.

[0322] It should be noted that if the thickness of the resin material layer J (film thickness) is increased, the emissivity of the atmospheric window region almost reaches 1. That is, in the case of a thick film, the thermal radiation radiated into space from the atmospheric window region during low-altitude utilization is 160 W / m² at 30°C. 2 Up to 125W / m 2 The light absorption in the light-reflecting layer B is 50 W / m, as specified above. 2 The sum of the light absorption of the light-reflecting layer B and the sunlight absorption when the silicone rubber or perfluoroalkoxy fluoropolymer is made into a thick film is less than the thermal radiation radiated into the universe.

[0323] Based on the above, the maximum film thickness of silicone rubber and perfluoroalkoxy fluoropolymers is 20 mm from the viewpoint of thermal conductivity.

[0324] [Regarding the light absorption of hydrocarbon-based resins]

[0325] When the resin material forming the resin material layer J is a resin with a hydrocarbon main chain having one or more carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, or benzene rings, or a silicone resin with two or more carbon atoms in the side chain hydrocarbons, in addition to the ultraviolet absorption using covalent bond electrons mentioned above, absorption based on bond bending, stretching, and other vibrations is also observed in the near-infrared region.

[0326] Specifically, absorptions based on the fundamental frequencies of transitions to the first excited states of CH3, CH2, and CH occur at wavelengths of 1.6 μm to 1.7 μm, 1.65 μm to 1.75 μm, and 1.7 μm, respectively. Furthermore, absorptions based on the fundamental frequencies of recombination frequencies of CH3, CH2, and CH occur at wavelengths of 1.35 μm, 1.38 μm, and 1.43 μm, respectively. Furthermore, overtones of transitions to the second excited states of CH2 and CH occur at a wavelength of 1.24 μm. The fundamental frequencies of CH bond bending and stretching are distributed in a wide bandwidth from 2 μm to 2.5 μm.

[0327] Furthermore, in the presence of ester bonds (R-COO-R) and ether bonds (COC), there is significant light absorption near the wavelength of 1.9 μm.

[0328] As can be seen from the above light absorption rate relationship, if the resin film is thin, the light absorption rate will be small and inconspicuous, while if the film is thick, the light absorption rate will be large.

[0329] Figure 11 The paper describes the relationship between the light absorption rate and the spectrum of sunlight when the film thickness of a polyethylene terephthalate resin with ester bonds and benzene rings is changed.

[0330] As shown in the figure, for every increase in film thickness of 25 μm, 125 μm, and 500 μm, the light absorption in the longer wavelength region, which originates from each vibration, increases compared to the wavelength of 1.5 μm.

[0331] Furthermore, light absorption increases not only at longer wavelengths but also from the ultraviolet region to the visible region. This is because the absorption end of light originating from chemical bonds is broadened.

[0332] When the film thickness is thin, the light absorption rate increases at the wavelength with the maximum absorption coefficient. However, if the film thickness increases, as shown in the above-mentioned light absorption rate relationship, a weak absorption coefficient with a broadened absorption end appears, resulting in increased absorption. Therefore, if the film thickness increases, light absorption increases from the ultraviolet region to the visible region.

[0333] The absorption of the solar spectrum at a thickness of 25 μm is 15 W / m. 2 The absorption of the solar spectrum is 41 W / m when the thickness is 125 μm. 2The absorption of the solar spectrum at a thickness of 500 μm is 88 W / m. 2 .

[0334] The light absorption of the light-reflecting layer B is 50 W / m, as specified above. 2 Therefore, with a film thickness of 500 μm, the sum of the solar absorption of the polyethylene terephthalate resin and the solar absorption of the light-reflecting layer B reaches 138 W / m. 2 As mentioned earlier, the maximum value of infrared radiation in the wavelength band of the atmospheric window in the lowlands of Japan during summer is around 160W under good atmospheric conditions at 30°C, and is usually around 125W.

[0335] Based on the above, when the film thickness of polyethylene terephthalate resin is 500 μm or more, it does not exhibit radioactive cooling properties.

[0336] The absorption spectrum in the wavelength band from 1.5 μm to 4 μm originates not from functional groups, but from the vibrations of the hydrocarbon backbone. If it is a hydrocarbon-based resin, it exhibits the same behavior as polyethylene terephthalate resin. Furthermore, hydrocarbon-based resins exhibit light absorption in the ultraviolet region originating from chemical bonds, and also show the same behavior as polyethylene terephthalate resin for the ultraviolet to visible region.

[0337] That is, if it is a hydrocarbon resin, it behaves the same as polyethylene terephthalate resin at wavelengths from 0.3 μm to 4 μm. Based on the above, the film thickness of hydrocarbon-based resins needs to be less than 500 μm.

[0338] [Regarding the light absorption of blended resins]

[0339] When a resin material is obtained by blending a resin with a carbon-fluorine bond or siloxane bond as the main chain and a resin with a hydrocarbon main chain, light absorption in the near-infrared region originating from CH, CH2, CH3, etc. occurs depending on the proportion of the hydrocarbon main chain resins blended.

[0340] When the main component is a carbon-fluorine bond or a siloxane bond, the light absorption in the near-infrared region derived from hydrocarbons is reduced, thus allowing for a thickness increase to the upper limit of 20 mm from a thermal conductivity perspective. However, when the blended hydrocarbon resin is the main component, the thickness needs to be set to 500 μm or less.

[0341] Blends of fluoropolymers or silicone rubbers with hydrocarbons also include substances in which the side chains of the fluoropolymers or silicone rubbers are replaced with hydrocarbons, alternating copolymers of fluorinated monomers and silicone monomers with hydrocarbon monomers, random copolymers, block copolymers, and graft copolymers. It should be noted that examples of alternating copolymers of fluorinated monomers and hydrocarbon monomers include fluoroethylene-vinyl ester (FEVE), fluoroolefin-acrylate copolymers, ethylene-tetrafluoroethylene copolymers (ETFE), and ethylene-chlorotrifluoroethylene copolymers (ECTFE).

[0342] Depending on the molecular weight and proportion of the substituted hydrocarbon side chains, light absorption in the near-infrared region originating from CH, CH2, CH3, etc., occurs. When the monomer introduced as a side chain or through copolymerization is of low molecular weight, or when the density of the introduced monomer is low, the light absorption in the near-infrared region originating from the hydrocarbon decreases, thus allowing for thickness increases up to 20 mm, which is considered a limit in terms of thermal conductivity.

[0343] When high molecular weight hydrocarbons are introduced as side chains or copolymer monomers of fluoropolymers or silicone rubbers, the resin thickness needs to be set to less than 500 μm.

[0344] [Regarding the thickness of the resin material layer]

[0345] From a practical standpoint for the radiation cooling device CP, a thinner resin material layer J is preferable. The thermal conductivity of resin materials is generally lower than that of metals and glass. To effectively cool the object E, the thickness of the resin material layer J should be at the minimum required level. A thicker resin material layer J results in greater thermal radiation through the atmospheric window; however, if the thickness exceeds a certain threshold, the thermal radiation energy through the atmospheric window becomes saturated.

[0346] The saturation film thickness varies depending on the resin material; in the case of fluoropolymers, it is approximately 300 μm for complete saturation. Therefore, from a thermal conductivity perspective, it is desirable to suppress the film thickness to below 300 μm compared to 500 μm. Furthermore, while thermal radiation is not saturated, sufficient thermal radiation can be obtained in the atmospheric window region even at a thickness of around 100 μm. A thinner thickness increases heat transfer efficiency, more effectively reducing the temperature of the object being cooled; therefore, in the case of fluoropolymers, a thickness of around 100 μm or less can be achieved.

[0347] Compared to absorption coefficients derived from CF bonds, absorption coefficients derived from carbon-silicon bonds, carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds are larger. Of course, from a thermal conductivity perspective, it is desirable to suppress the film thickness to below 300 μm compared to 500 μm, but if the film thickness is further reduced to improve thermal conductivity, a further significant radioactive cooling effect can be expected.

[0348] 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 results in saturation, and even a thickness of 50 μm provides sufficient thermal radiation within the atmospheric window region. Thinner resin materials increase heat transfer efficiency, more effectively reducing the temperature of the object being cooled. Therefore, 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 results in reduced thermal insulation, but still allows for effective cooling of the object E. In the case of carbon-chlorine bonds, a thickness of 100 μm or less effectively cools the object E.

[0349] The benefits of thinning are not limited to reducing insulation and facilitating the transfer of heat and cold. They also include suppressing light absorption in the near-infrared region originating from CH, CH2, and CH3 in resins containing carbon-chlorine, carbon-oxygen, ester, and ether bonds. Thinning reduces the absorption of sunlight caused by these bonds, thus improving the cooling capacity of the CP (conductive radiative cooling device).

[0350] Based on the above viewpoints, in the case of resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, if the thickness is set to less than 50 μm, it can more effectively exert a radiative cooling effect under sunlight.

[0351] In the case of carbon-silicon bonds, even with a thickness of 50 μm, thermal radiation is fully saturated in the atmospheric window region, and even with a thickness of 10 μm, sufficient thermal radiation is obtained in the atmospheric window region. A thinner resin layer J increases heat transfer efficiency, more effectively reducing the temperature of the object being cooled, E. Therefore, in the case of resins containing carbon-silicon bonds, if the thickness is set to less than 10 μm, the thermal insulation is reduced, but the object being cooled, E, can be cooled effectively. Further thinning reduces solar absorption, thus increasing the cooling capacity of the radiation cooling device CP.

[0352] Based on the above viewpoints, in the case of resins containing carbon-silicon bonds, if the thickness is set to less than 10 μm, it can more effectively exert a radiative cooling effect under sunlight.

[0353] [Details of the light-reflecting layer]

[0354] In order for the light-reflecting layer B to have the above-mentioned reflectivity characteristics, the reflective material on the side where the radiating surface H exists (the side where the resin material layer J exists) needs to be silver or a silver alloy.

[0355] like Figure 12 As shown, if the light-reflecting layer B is constructed based on silver, the required reflectivity of the light-reflecting layer B can be obtained.

[0356] In the case of reflecting sunlight with the aforementioned reflectivity characteristics achieved solely through silver or silver alloys, a thickness of 50 nm or more is required.

[0357] However, in order to make the light-reflecting layer B flexible, its thickness needs to be set below 100 μm. If it is thicker than that, it becomes difficult to bend.

[0358] Furthermore, as a "silver alloy", an alloy can be used in which copper, palladium, gold, zinc, tin, magnesium, nickel, or titanium are added to silver, for example, at a mass percentage of about 0.4% to 4.5% by mass. As a specific example, a silver alloy made by adding copper and palladium to silver, namely "APC-TR (Fullya Metal)," can be used.

[0359] To achieve the aforementioned reflectivity characteristics, the light-reflecting layer B can be configured as a stack of silver or a silver alloy adjacent to the protective layer D and aluminum or an aluminum alloy on the side furthest from the protective layer D. It should be noted that even in this case, the reflective material on the side where the radiating surface H exists (the side where the resin material layer J exists) must also be silver or a silver alloy.

[0360] In the case of a two-layer structure consisting of silver (silver alloy) and aluminum (aluminum alloy), the thickness of the silver layer needs to be at least 10 nm, and the thickness of the aluminum layer needs to be at least 30 nm.

[0361] However, in order for the light-reflecting layer B to be flexible, the total thickness of the silver and aluminum needs to be less than 100 μm. If it is thicker than that, it will be difficult to bend.

[0362] Moreover, as an "aluminum alloy", alloys can be obtained by adding copper, manganese, silicon, magnesium, zinc, carbon steel for mechanical structures, yttrium, lanthanum, gadolinium, and terbium to aluminum.

[0363] Silver and silver alloys are susceptible to damage from rain and humidity, requiring protection to prevent their discoloration. Therefore, measures such as... Figures 16 to 19 As shown, a protective layer D is needed to protect silver in a form adjacent to silver and silver alloys.

[0364] Details of protective layer D are described below.

[0365] [Regarding the experimental results]

[0366] Silver was formed on a glass substrate to a thickness of 300 nm. Then, using a rod coater, silicone rubber with siloxane bonds, vinyl fluorinated ether with carbon-fluorine bonds, an olefin modifier (olefin-modified material), and vinyl chloride resin were coated onto the substrate while controlling the film thickness. The radioactive cooling performance was then measured. Evaluation of the radioactive cooling performance was conducted outdoors in late June at noon for 3 hours with an external temperature of 35°C, while maintaining high thermal insulation on the substrate, and the temperature (°C) of the back side of the substrate was measured. However, for vinyl chloride resin, the evaluation was conducted at an external temperature of 29°C. The radioactive cooling effect was evaluated by whether the temperature after 5 minutes on the fixture was lower or higher than the external temperature.

[0367] The results of the radiation cooling test are shown in Figure 15 .

[0368] Moreover, the emissivity of the atmospheric window region of vinyl fluoride is as follows: Figure 13 As shown. It should be noted that the emissivity of silicone rubber is as follows: Figure 4 As shown, the emissivity of the olefin-modified body (olefin-modified material) is as follows: Figure 8 As shown, the emissivity of vinyl chloride resin is as follows: Figure 6 As shown.

[0369] In the case of silicone rubber with siloxane bonds, it is known that, as theoretically expected, it can exert its radiation cooling capability at a thickness of 1 μm or more.

[0370] It is known that fluoroethylene vinyl ethers with carbon-fluorine bonds exhibit radiocooling capabilities at a film thickness of 5 μm, which is thinner than the theoretically predicted 10 μm. This is because not only is there light absorption through the atmospheric window of the carbon-fluorine bonds, but also light absorption through the ether bonds of the vinyl ether, resulting in an increased light absorption rate through the atmospheric window compared to either of these alone.

[0371] Olefin-modified products (olefin-modified materials) have almost no thermal radiation in the atmospheric window region, and therefore do not have radiation cooling capabilities.

[0372] [Specific composition of the radiation cooling device]

[0373] The radiation cooling device CP of the present invention is as follows Figures 16-19 As shown, a membrane structure can be fabricated. The resin material forming the resin material layer J and the protective layer D is flexible, so if the light-reflecting layer B is made into a thin film, the light-reflecting layer B can also be made flexible. As a result, the radiation cooling device CP can be made into a flexible film (radiation cooling film).

[0374] A film-like radiation cooling device, CP (radiation cooling film), is coated with a paste and wrapped around the outer perimeter of vehicles, warehouses, building walls, and helmets, thereby exerting radiation cooling. When applied to existing objects, it can easily exert radiation cooling capabilities.

[0375] As the object to which the CP (radiative cooling film) membrane is assembled, it can be any kind of object that needs to be cooled, such as the outer surface of various tents, the outer surface of boxes that store electrical machinery, the outer surface of containers for transporting goods, the outer surface of milk tanks for storing milk, the outer surface of the milk storage section of milk tankers.

[0376] Various configurations have been considered for fabricating the radiation cooling device CP as a film. For example, it is considered to fabricate it by coating a protective layer D and a resin material layer J onto a film-shaped light-reflecting layer B. Alternatively, it is considered to fabricate it by attaching a protective layer D and a resin material layer J onto a film-shaped light-reflecting layer B. Alternatively, it is considered to fabricate it by coating or attaching a protective layer D onto a film-shaped resin material layer J, and fabricating the light-reflecting layer B on the protective layer D through methods such as vapor deposition, sputtering, ion plating, or silver mirror reaction.

[0377] If explained in detail, then Figure 16 In the case where the light reflective layer B is formed as a single layer of silver or a silver alloy, or as two layers of silver (silver alloy) and aluminum (aluminum alloy), a protective layer D is formed on the upper side of the light reflective layer B, a resin material layer J is formed on the upper part of the protective layer D, and a lower protective layer Ds is also formed on the lower side of the light reflective layer B.

[0378] As Figure 16 The method for manufacturing the radiation cooling device CP (radiation cooling film) can be to sequentially coat a protective layer D, a light reflective layer B, and a lower protective layer Ds onto a film-like resin material layer J, and then integrally mold it.

[0379] Figure 17 The light-reflecting layer B of the radiation cooling device CP (radiation cooling film) is composed of an aluminum layer B1 formed from aluminum foil that functions as aluminum (aluminum alloy) and a silver layer B2 containing silver or a silver alloy. A protective layer D is formed on the upper side of the light-reflecting layer B, and a resin material layer J is formed on the upper part of the protective layer D.

[0380] As Figure 17 The method for manufacturing the radiation cooling device CP (radiation cooling film) can be to sequentially coat a silver layer B2, a protective layer D, and a resin material layer J onto an aluminum layer B1 made of aluminum foil, and then integrally mold them.

[0381] It should be noted that, as an alternative manufacturing method, a method can be adopted in which a resin material layer J is formed into a film, a protective layer D and a silver layer B2 are sequentially coated on the film-shaped resin material layer J, and an aluminum layer B1 is bonded to the silver layer B2.

[0382] Figure 18In the case where the light-reflecting layer B is formed as a single layer of silver or a silver alloy, or as two layers of silver (silver alloy) and aluminum (aluminum alloy), a protective layer D is formed on the upper side of the light-reflecting layer B, a resin material layer J is formed on the upper part of the protective layer D, and a film layer F such as PET is formed on the lower side of the light-reflecting layer B.

[0383] As Figure 18 The method for manufacturing the radiation cooling device CP (radiation cooling film) can be as follows: a light reflective layer B and a protective layer D are sequentially coated on a film layer F (equivalent to a substrate) formed from PET (ethylene terephthalate resin) or the like, and integrally molded. The protective layer D is then bonded (adheded) with a separately formed film-like resin material layer J using a paste layer N (an example of a bonding layer).

[0384] The adhesives used in the paste layer N include, for example, urethane-based adhesives, acrylic-based adhesives, and EVA (ethylene vinyl acetate)-based adhesives, which are expected to have high transparency to sunlight. The thickness of the paste layer N is preferably in the range of 1 μm or more and 100 μm or less, and further preferably in the range of 1 μm or more and 50 μm or less.

[0385] Figure 19 The light-reflecting layer B of the radiation cooling device CP (radiation cooling film) is composed of an aluminum layer B1 that functions as aluminum (aluminum alloy) and a silver layer B2 containing silver or a silver alloy (instead of silver). The aluminum layer B1 is formed on top of a film layer F (equivalent to a substrate) formed from PET (ethylene terephthalate resin) or the like. A protective layer D is formed on top of the silver layer B2, and a resin material layer J is formed on top of the protective layer D.

[0386] As Figure 19 The method for manufacturing the radiation cooling device CP (radiation cooling film) can be as follows: an aluminum layer B1 is coated on the film layer F, and the film layer F and the aluminum layer B1 are integrally formed. In addition, a protective layer D and a silver layer B2 are coated on the film-like resin material layer J, and the resin material layer J, the protective layer D, and the silver layer B2 are integrally formed. The aluminum layer B1 and the silver layer B2 are bonded together with a paste layer N.

[0387] The adhesives used in the paste layer N include, for example, urethane-based adhesives, acrylic-based adhesives, and EVA (ethylene vinyl acetate)-based adhesives, which are expected to have high transparency to sunlight. The thickness of the paste layer N is preferably in the range of 1 μm or more and 100 μm or less, and further preferably in the range of 1 μm or more and 50 μm or less.

[0388] Figure 30The diagram shows a suitable specific configuration of a radiation cooling device CP (radiation cooling film), and the light reflectance spectrum of this suitable specific configuration of the radiation cooling device CP (radiation cooling film) is shown in the figure. Figure 31 The emissivity spectrum is shown in Figure 32 .

[0389] Figure 30 The light-reflecting layer B of the radiation cooling device CP (radiation cooling film) is composed of silver (Ag) with a thickness of 80 nm. On the upper side of the light-reflecting layer B, a protective layer D is formed by polyethylene terephthalate (PET) with a thickness of 25 nm. On the upper part of the protective layer D, a resin material layer J formed by vinyl chloride (PVC) with a thickness of 40 μm is bonded (adheded) with a paste layer N containing a urethane adhesive (referred to as PU (polyurethane)) with a thickness of 10 μm. A lower protective layer Ds is also formed on the lower side of the light-reflecting layer B.

[0390] [Details of the protective layer]

[0391] The protective layer D is a polyolefin resin with a thickness of 300 nm or more and 40 μm or less, or polyethylene terephthalate with a thickness of 17 μm or more and 40 μm or less.

[0392] Polyolefin resins include polyethylene and polypropylene.

[0393] Figure 20 The ultraviolet absorption rates of polyethylene, vinylidene chloride resin, polyethylene terephthalate resin, and vinyl chloride resin are shown in the figure.

[0394] also, Figure 21 The light transmittance of polyethylene, a suitable synthetic resin for forming the protective layer D, is shown in the figure.

[0395] The radiative cooling device CP (radiative cooling film) plays a radiative cooling role not only at night but also in sunlight. Therefore, in order to maintain the light reflection function of the light reflection layer B, it is necessary to protect the light reflection layer B with a protective layer D so that the silver of the light reflection layer B does not discolor in sunlight.

[0396] When the protective layer D is formed of polyolefin resin with a thickness of 300 nm or more and 40 μm or less, the polyolefin resin is a synthetic resin with a light absorption rate of less than 10% of ultraviolet light in the entire wavelength region of ultraviolet light with a wavelength of 0.3 to 0.4 μm. Therefore, the protective layer D is unlikely to deteriorate due to the absorption of ultraviolet light.

[0397] Furthermore, the thickness of the polyolefin resin forming the protective layer D is 300 nm or more, thus effectively shielding the silver or silver alloy formed by the free radicals generated by the resin material layer J from reaching the silver or silver alloy forming the light reflective layer B. In addition, it also shields the silver or silver alloy formed by the moisture that passes through the resin material layer from reaching the silver or silver alloy forming the light reflective layer B, thereby suppressing the discoloration of the silver or silver alloy forming the light reflective layer B.

[0398] Furthermore, the protective layer D, formed from polyolefin resin, deteriorates as it absorbs ultraviolet light and forms free radicals on the surface away from the reflective layer B. However, since the thickness is over 300 nm, the free radicals formed cannot reach the light reflective layer. In addition, even if it deteriorates as it forms free radicals, the absorption of ultraviolet light is low, so the deterioration process is slow, thus maintaining the aforementioned shielding function for a long time.

[0399] When the protective layer D is formed with polyethylene terephthalate resin in a form with a thickness of 17 μm or more and 40 μm or less, polyethylene terephthalate resin is a synthetic resin with a higher light absorption rate in the ultraviolet wavelength region of 0.3 to 0.4 μm compared with polyolefin resins. However, since the thickness is 17 μm or more, it can effectively block free radicals generated by the resin material layer J from reaching the silver or silver alloy that forms the light reflective layer B for a long time. In addition, it can also block moisture that passes through the resin material layer J from reaching the silver or silver alloy that forms the light reflective layer, and suppress the discoloration of the silver or silver alloy that forms the light reflective layer B.

[0400] That is, the protective layer formed by polyethylene terephthalate resin deteriorates at the same time as it absorbs ultraviolet light and forms free radicals on the surface side away from the light reflective layer B. However, since the thickness is more than 17 μm, the free radicals formed cannot reach the reflective layer. Furthermore, even if it deteriorates at the same time as the formation of free radicals, it can still perform the above-mentioned shielding function for a long time because the thickness is more than 17 μm.

[0401] To explain, the degradation of polyethylene terephthalate (PET) resin is caused by the breaking of the ester bonds between ethylene glycol and terephthalic acid due to ultraviolet radiation, forming free radicals. This degradation proceeds sequentially from the surface of the PET resin exposed to ultraviolet radiation.

[0402] For example, if polyethylene terephthalate (PET) is irradiated with ultraviolet light of Osaka intensity, the ester bonds of the PET will crack sequentially by approximately 9 nm from the irradiated surface every day. Since the PET is fully polymerized, the cracked PET surface will not attack the silver (silver alloy) of the light-reflecting layer B. However, if the cracked end of the PET reaches the silver (silver alloy) of the light-reflecting layer B, the silver (silver alloy) will discolor.

[0403] Therefore, for outdoor use, to ensure the protective layer D has a durability of more than one year, multiplying 9 nm / day by 365 days, a thickness of approximately 3 μm is required. To ensure the polyethylene terephthalate (PET) resin of the protective layer D has a durability of more than three years, a thickness of more than 10 μm is required. To ensure a durability of more than five years, a thickness of more than 17 μm is required.

[0404] It should be noted that the reason for specifying an upper limit on the thickness of the protective layer D, which is formed by polyolefin resin and polyethylene terephthalate resin, is to prevent the protective layer D from exhibiting insulation properties that do not contribute to radiative cooling. That is, the thicker the protective layer D, the more it exhibits insulation properties that do not contribute to radiative cooling. Therefore, in order to perform the function of protecting the light-reflecting layer B while avoiding the performance of insulation properties that do not contribute to radiative cooling, an upper limit on the thickness is specified.

[0405] However, as Figure 18 As shown, when the paste layer N is located between the resin material layer J and the protective layer D, free radicals are also generated from the paste 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 polyethylene terephthalate resin forming the protective layer D is 17 μm or more, the free radicals generated by the paste layer N can be suppressed from reaching the light-reflecting layer B for a long time.

[0406] Furthermore, as mentioned above, if the protective layer D is thickened, it does not cause a disadvantage in preventing the silver (silver alloy) of the light-reflecting layer B from becoming colored, but it does cause a problem in terms of radiation cooling. That is, if it is thickened, the thermal insulation of the radiation cooling material is improved.

[0407] For example, a good example of a synthetic resin that forms the protective layer D is a polyethylene resin, such as... Figure 25 As shown, the emissivity in atmospheric windows is low, so even with a thicker layer, it does not contribute to radiative cooling. Furthermore, increasing the thickness improves the thermal insulation of the radiative cooling material. Subsequently, further thickness increases absorption in the near-infrared region originating from chain vibrations, thus enhancing the effect of increased solar radiation absorption.

[0408] For these reasons, a thicker protective layer D is detrimental to radiation cooling. From this perspective, the thickness of the protective layer D formed from a polyolefin resin is preferably 5 μm or less, and more preferably 1 μm or less.

[0409] [Examination of the protective layer]

[0410] To investigate the different ways silver is colored due to the protective layer D, a sample was fabricated as follows: Figure 22 The coloration of silver after irradiation with simulated sunlight was studied in a sample that did not have a resin material layer J as an infrared radiating layer A and exposed the protective layer D.

[0411] Specifically, as protective layer D, two types of resins were coated using a rod coater: a general acrylic resin that absorbs ultraviolet light (e.g., methyl methacrylate resin mixed with a benzotriazole-based ultraviolet absorber) and polyethylene, both of which are silver-coated layers (equivalent to a substrate) to form a sample. The function of the coated protective layer D was then investigated. The thicknesses of the coated protective layers D were 10 μm and 1 μm, respectively.

[0412] It should be noted that the film layer F (equivalent to the substrate) is formed into a film using PET (ethylene terephthalate resin) or the like.

[0413] like Figure 24 As shown, when the protective layer D is an acrylic resin that absorbs ultraviolet light well, the protective layer D is decomposed by ultraviolet light to form free radicals, and the silver immediately turns yellow and fails to function as a radiation cooling device CP (absorbing sunlight, and like ordinary materials, the temperature rises when exposed to sunlight).

[0414] It should be noted that the 600h line in the figure represents the xenon weathering test conducted under JIS standard 5600-7-7 conditions (UV energy of 60W / m²). 2 The reflectance spectrum after 600 hours. Additionally, the 0-hour line represents the reflectance spectrum before the xenon weathering test.

[0415] like Figure 23 As shown, when the protective layer D is made of polyethylene with low ultraviolet light absorption, it can be observed that there is no decrease in reflectivity from the near-infrared region to the visible region. That is, the resin whose main component is polyethylene (polyolefin resin) hardly absorbs the ultraviolet rays of sunlight reaching the ground, so it is difficult to form free radicals even when exposed to sunlight. Therefore, even when exposed to sunlight, the silver that serves as the light-reflecting layer B does not produce coloration.

[0416] It should be noted that the 600h line in the figure represents the xenon weathering test conducted under JIS standard 5600-7-7 conditions (UV energy of 60W / m²). 2 The reflectance spectrum after 600 hours. Additionally, the 0-hour line represents the reflectance spectrum before the xenon weathering test.

[0417] It should be noted that the reason for the spectral fluctuations in this wavelength band is the Fabry-Pérot resonance of the polyethylene layer. Due to the heat and other factors caused by the xenon weathering test, the thickness of the polyethylene layer changes. Based on the above reasons, it can be known that the resonance position changes somewhat between the 0h and 600h lines, but no large decrease in reflectance in the ultraviolet-visible region caused by the yellowing of silver was observed.

[0418] It should be noted that fluoropolymers can also be used as materials for forming the protective layer D from the perspective of ultraviolet absorption. However, if the protective layer D is actually formed, it will be colored and deteriorated during the formation stage, so it cannot be used as a material for forming the protective layer D.

[0419] In addition, silicone can also be used as a material to form protective layer D from the perspective of ultraviolet absorption, but its adhesion to silver (silver alloy) is extremely poor, so it cannot be used as a material to form protective layer D.

[0420] [Another component of the radiation cooling device]

[0421] like Figure 26 As shown, it can be configured such that an anchoring layer G is on the upper part of the film layer F (equivalent to the substrate), and a light-reflecting layer B, a protective layer D, and an infrared radiating layer A are on the upper part of the anchoring layer G.

[0422] It should be noted that the film layer F (equivalent to the substrate) is formed into a film, for example, using PET (ethylene terephthalate resin).

[0423] An anchoring layer is introduced to enhance the adhesion between film layer F and light-reflecting layer B. That is, if a silver (Ag) film is to be directly applied to film layer F, peeling will easily occur. Anchoring layer G is ideally composed primarily of acrylic resin, polyolefin, and urethane, mixed with compounds containing isocyanate groups and melamine resin. It is a coating for the portion not directly exposed to sunlight, and even raw materials that absorb ultraviolet light are not a problem.

[0424] It should be noted that there are other methods besides adding an anchoring layer G to enhance the adhesion between the film layer F and the light-reflecting layer B. For example, if the surface of the film layer F is roughened by plasma irradiation, the adhesion will be improved.

[0425] [Another component of the infrared radiation layer]

[0426] like Figure 27 As shown, an inorganic filler V can be mixed into the resin material layer J constituting the infrared radiating layer A, resulting in a light-scattering structure. Furthermore, as... Figure 28 As shown, the resin material layer J constituting the infrared radiating layer A can be formed into an uneven shape on both sides, which has a light scattering structure.

[0427] If configured in this way, glare from the radiating surface H can be suppressed when observing the radiating surface H.

[0428] That is, the resin material layer J is flat on both sides and does not contain filler V. However, in this case, the radiating surface H is mirror-like, so when observing the radiating surface H, glare is felt. If it has a light scattering structure, the glare can be suppressed.

[0429] Furthermore, when filler V is mixed into resin material layer J, if protective layer D and light-reflecting layer B are present, the light reflectivity is improved compared to the case where resin material layer J contains only filler V or only light-reflecting layer B.

[0430] Silica (SiO2) can be suitable as an inorganic material for forming filler V. 、 Titanium oxide (TiO2), aluminum oxide (Al2O3), magnesium oxide (MgO), etc. It should be noted that if filler V is mixed into the resin material layer J, the two sides of the resin material layer J will form an uneven surface.

[0431] In addition, in order to make the front and back sides of the resin material layer J into an uneven shape, it can be done by embossing, surface damage processing, etc.

[0432] When the back surface of resin material layer J is irregularly shaped, it is in harmony with... Figure 18 Similarly, as described in the text, it is desirable that the paste layer N (bonding layer) is located between the resin material layer J and the protective layer D.

[0433] That is, even if the back side of the resin material layer J is uneven, the paste 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 properly bonded.

[0434] It should be noted that when the back surface of the resin material layer J is uneven, the resin material layer J and the protective layer D can be directly bonded, for example, by plasma bonding. It should be noted that plasma bonding refers to the formation of free radicals through plasma radiation on the bonding surfaces of the resin material layer J and the protective layer D; this is a bonding method achieved through the free radicals.

[0435] Furthermore, if filler V is mixed into the protective layer D, the back side of the protective layer D that contacts the light-reflecting layer B will become uneven, causing the surface of the light-reflecting layer B to deform into an uneven shape. Therefore, it is necessary to avoid mixing filler V into the protective layer D. That is, if the surface of the light-reflecting layer B is deformed into an uneven shape, light reflection cannot be performed properly, and as a result, proper radioactive cooling cannot be performed.

[0436] The experimental results at this point are based on Figure 29 Please provide an explanation.

[0437] Figure 29 The phrase "directly forming an Ag layer on a light diffusion layer" refers to forming a light reflection layer B by depositing a silver (Ag) film on the surface of an infrared radiating layer A (resin material layer J) with embossed texture on the Ag layer side, which is mixed with filler V or serves as a light reflection layer B.

[0438] In addition, "mirror-like Ag light diffusion layer" refers to a mirror-like layer formed on top of the Ag layer, which serves as the light reflection layer B, and the upper part of the Ag layer, the protective layer D, and the infrared radiation layer A (resin material layer J) with uneven texture mixed with filler V or embossed.

[0439] like Figure 29 As shown, in the case of "forming an Ag layer directly on the light diffusion layer", the surface of the light reflection layer B becomes uneven, thus significantly reducing the light reflectivity. However, in the case of "forming a light diffusion layer on a mirror Ag", the surface of the light reflection layer B remains mirror-like, resulting in an appropriate light reflectivity.

[0440] [Alternative implementation methods]

[0441] The following are alternative implementation methods.

[0442] (1) In the above embodiments, various materials are exemplified as resin materials for forming resin material layer J. As suitable resin materials, vinyl chloride resin (PVC), vinylidene chloride resin (PVDC), vinyl fluoride resin (PVF), and vinylidene fluoride resin (PVDF) can be cited.

[0443] (2) In the above embodiments, the object to be cooled, E, is an example of an object that is tightly sealed on the back side of the radiation cooling device CP (radiation cooling film). Various cooling objects, such as cooling object space, can be used as the object to be cooled, E.

[0444] (3) In the above embodiments, the form in which the radiating surface H of the resin material layer J is directly exposed is shown. It can also be implemented in the form of providing a hard coating covering the radiating surface H.

[0445] As a hard coating, UV-curable acrylic, thermosetting acrylic, UV-curable silicone, thermosetting silicone, organic-inorganic hybrid, and vinyl chloride coatings can all be used. Organic antistatic agents can be used as additives.

[0446] Among UV-curable acrylic resins, urethane acrylates are particularly good.

[0447] As a film-forming method for hard coatings, gravure coating, bar coating, knife coating, roller coating, doctor blade coating, and mold coating can be used.

[0448] The thickness of the hard coating (film) is 1~50μm, with a particularly desirable thickness of 2~20μm.

[0449] When using vinyl chloride resin as the resin material for resin layer J, the amount of plasticizer in the vinyl chloride resin can be reduced, resulting in a rigid vinyl chloride resin or a semi-rigid vinyl chloride resin. In this case, the vinyl chloride itself of the infrared radiating layer A becomes a hard coating layer.

[0450] It should be noted that the configurations disclosed in the above embodiments (including other embodiments, the same below) can be combined with the configurations disclosed in other embodiments without causing contradictions. 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 without departing from the purpose of the present invention.

[0451] Explanation of reference numerals in the attached figures

[0452] A Infrared Emission Layer

[0453] B. Light reflective layer

[0454] D Protective layer

[0455] H Radiation surface

[0456] J Resin Material Layer

[0457] N bonding layer

Claims

1. A radiation cooling device comprising an infrared radiating layer that radiates infrared light from a radiating surface, a light reflecting layer located on the side of the infrared radiating layer opposite to the side where the radiating surface exists, and a protective layer between the infrared radiating layer and the light reflecting layer. The aforementioned infrared radiating layer is a resin material layer, its thickness adjusted to emit thermal radiation energy greater than the absorbed solar energy in the wavelength band from 8μm to 14μm. The aforementioned light-reflecting layer contains silver or a silver alloy. The aforementioned protective layer is formed with a polyolefin resin having a thickness of 300 nm or more and 40 μm or less, or with a polyethylene terephthalate resin having a thickness of 17 μm or more and 40 μm or less.

2. The radiation cooling device according to claim 1, wherein, The aforementioned light-reflecting layer has a reflectivity of over 90% for wavelengths from 0.4 μm to 0.5 μm, and a reflectivity of over 96% for wavelengths longer than 0.5 μm.

3. The radiation cooling device according to claim 1 or 2, wherein, The film thickness of the aforementioned resin material layer is adjusted to the following state: It has light absorption characteristics with an average wavelength absorption rate of less than 13% for wavelengths from 0.4 μm to 0.5 μm, an average wavelength absorption rate of less than 4% for wavelengths from 0.5 μm to 0.8 μm, an average wavelength absorption rate of less than 1% for wavelengths from 0.8 μm to 1.5 μm, and an average wavelength absorption rate of less than 40% for wavelengths from 1.5 μm to 2.5 μm, and thermal radiation characteristics with an average wavelength emissivity of more than 40% for wavelengths from 8 μm to 14 μm.

4. The radiation cooling device according to claim 1 or 2, wherein, The resin material forming the aforementioned resin material layer is selected from resin materials having one or more of the following: carbon-fluorine bond, siloxane bond, carbon-chlorine bond, carbon-oxygen bond, ether bond, ester bond, and benzene ring.

5. The radiation cooling device according to claim 1 or 2, wherein, The main component of the resin material forming the aforementioned resin material layer is siloxane. The thickness of the aforementioned resin material layer is 1 μm or more.

6. The radiation cooling device according to claim 4, wherein, The thickness of the aforementioned resin material layer is 10 μm or more.

7. The radiation cooling device according to claim 1 or 2, wherein, The thickness of the aforementioned resin material layer is less than 20 mm.

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

9. The radiation cooling device according to claim 1 or 2, wherein, The resin material forming the aforementioned resin material layer is a resin material with a hydrocarbon having one or more carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, or benzene rings as the main chain, or a silicone resin with two or more carbon atoms in the hydrocarbons of the side chains. The thickness of the aforementioned resin material layer is less than 500 μm.

10. The radiation cooling device according to claim 1 or 2, wherein, The resin material forming the aforementioned resin material layer is a blend of a resin containing carbon-fluorine bonds and siloxane bonds and a resin with a hydrocarbon main chain, and the thickness of the aforementioned resin material layer is less than 500 μm.

11. The radiation cooling device according to claim 1 or 2, wherein, The resin material forming the aforementioned resin material layer is a fluoropolymer. The thickness of the aforementioned resin material layer is less than 300 μm.

12. The radiation cooling device according to claim 1 or 2, wherein, The resin material forming the aforementioned resin material layer is a resin material having one or more of the following: carbon-chlorine bond, carbon-oxygen bond, ester bond, ether bond, or benzene ring. The thickness of the aforementioned resin material layer is less than 50 μm.

13. The radiation cooling device according to claim 1 or 2, wherein, The resin material forming the aforementioned resin material layer is a resin material with carbon-silicon bonds. The thickness of the aforementioned resin material layer is less than 10 μm.

14. The radiation cooling device according to claim 1 or 2, wherein, The resin material forming the aforementioned resin material layer is vinyl chloride resin or vinylidene chloride resin. The thickness of the aforementioned resin material layer is less than 100 μm and more than 10 μm.

15. The radiation cooling device according to claim 1 or 2, wherein, The aforementioned light-reflecting layer is made of silver or a silver alloy and has a thickness of 50 nm or more.

16. The radiation cooling device according to claim 1 or 2, wherein, The aforementioned light-reflecting layer is a stacked structure of silver or silver alloy adjacent to the aforementioned protective layer and aluminum or aluminum alloy located on the side away from the aforementioned protective layer.

17. The radiation cooling device according to claim 1 or 2, wherein, The aforementioned resin material layer, the aforementioned protective layer, and the aforementioned light-reflecting layer are in a film-like state when stacked.

18. The radiation cooling device according to claim 1 or 2, wherein, The aforementioned resin material layer is bonded to the aforementioned protective layer using an adhesive bonding layer.

19. The radiation cooling device according to claim 18, wherein, Inorganic fillers are mixed into the aforementioned resin material layer.

20. The radiation cooling device according to claim 18, wherein, The aforementioned resin material layer has an uneven surface on both sides.

21. A radiation cooling method, using the radiation cooling apparatus according to any one of claims 1 to 20, radiating the aforementioned infrared light from the radiation surface opposite to the surface of the aforementioned resin material layer that contacts the aforementioned light-reflecting layer. The aforementioned radiating surface faces the air, and the aforementioned infrared light is emitted from the radiating surface.

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