JP7527179B2 - Radiative cooling air-conditioned clothing - Google Patents

Description

The present invention relates to radiative cooling air-conditioned clothing with radiative cooling effect.

Conventional examples of air-conditioned clothing include clothing that is equipped with an air blower that blows cooling air between the clothing and the wearer, and has an outer surface that is exposed to the outside (see, for example, Patent Document 1 and Patent Document 2).

Incidentally, in Patent Document 1, the air blower is configured to send the sucked air into the space between the clothing body and the wearer, and the air flowing through the space between the clothing body and the wearer is exhausted through the gap between the collar of the clothing body and the wearer's neck, and the gap between the cuffs of the clothing body and the wearer's wrists.

In addition, in Patent Document 2, the air blowing section is configured to suck in and exhaust air in the space between the clothing body and the wearer to the outside, so that the space between the clothing body and the wearer becomes negative pressure, and outside air flows into the air flow passage through the gap between the collar of the clothing body and the wearer's neck, and the gap between the cuffs of the clothing body and the wearer's wrists.
Incidentally, in the case of this type of air-conditioned clothing, a member that forms a space through which air can flow between the clothing body and the wearer is often provided on the inner side of the clothing body.

Patent documents 1 and 2 omit detailed descriptions of the materials that make up the main body of the clothing, but generally, cotton or water-repellent polyester is often used as the material that makes up the main body of the clothing.

Patent No. 6158675 Patent No. 4399765

Conventional air-conditioned clothing is easy to feel cool when worn in a shady environment, but when worn in a daytime environment exposed to direct sunlight, it is difficult to feel cool and the wearer feels hot.

In other words, if the material that makes up the main body of the clothing is a light-blocking type, such as water-repellent polyester, when sunlight is irradiated onto the main body of the clothing, the sunlight is absorbed by the main body of the clothing, causing the main body of the clothing to become hotter than the person wearing it, and as a result, the inside of the main body of the clothing becomes hot, making the wearer feel hot.

Also, if the material that makes up the main body of the clothing is a non-light-blocking type such as cotton, the sunlight is absorbed by the main body of the clothing, preventing the main body of the clothing from becoming hotter than the person wearing it. However, sunlight that passes through the main body of the clothing shines on the person wearing it, making them feel hot.

In other words, when conventional air-conditioned clothing is used in a daytime environment with direct sunlight, there is a risk that the surface temperature of the wearer will rise above body temperature, causing the wearer to feel an increase in temperature, and improvements are needed.

The present invention was made in consideration of this situation, and its purpose is to provide a radiative cooling type air-conditioned garment that can lower the perceived temperature even when used in an environment with direct sunlight.

The radiative cooling type air-conditioned clothing of the present invention is provided with an air blower in the clothing body that blows cooling air through an air flow passage between the clothing body and the wearer,
A radiative cooling layer is attached to the outer surface of the clothing body,
The radiative cooling layer is configured to include an infrared radiative layer that radiates infrared light from a radiation surface, and a light reflecting layer that is located on the infrared radiative layer opposite to the side where the radiation surface is present,
the infrared radiation layer is a resin material layer whose thickness is adjusted to emit thermal radiation energy in a wavelength band of 8 μm to 14 μm that is greater than absorbed solar light energy,
The light-reflecting layer is characterized in that it comprises silver or a silver alloy.

In other words, radiative cooling is the phenomenon in which a material's temperature drops when it radiates electromagnetic waves such as infrared rays into its surroundings. By utilizing this phenomenon, it is possible to create a radiative cooling layer that cools an object without consuming energy such as electricity.

In other words, the radiative cooling layer has an infrared radiation layer that emits a large amount of thermal radiation energy in the wavelength range of 8 μm to 14 μm, and the light reflecting layer reflects the light (ultraviolet light, visible light, infrared light) that has passed through the infrared radiation layer and radiates it from the radiation surface, preventing the light (ultraviolet light, visible light, infrared light) that has passed through the infrared radiation layer from being projected onto the object to be cooled (the clothing itself) and heating the object to be cooled (the clothing itself), making it possible to cool the object to be cooled (the clothing itself) even in a daytime solar radiation environment.

In addition to the light that has passed through the infrared radiation layer, the light reflecting layer also reflects the light emitted from the infrared radiation layer toward the side where the light reflecting layer is present toward the infrared radiation layer. However, in the following explanation, the light reflecting layer is described as being provided for the purpose of reflecting the light (ultraviolet light, visible light, infrared light) that has passed through the infrared radiation layer.

To explain further, sunlight incident on the radiation surface of the resin material layer serving as the infrared radiation layer in the radiative cooling layer passes through the resin material layer, is reflected by the light reflecting layer on the opposite side to the side where the radiation surface of the resin material layer is present, and is allowed to escape from the system through the radiation surface.
In the present specification, when the term "light" is used, the concept of light includes ultraviolet light (ultraviolet light), visible light, and infrared light. When these are described in terms of the wavelength of light as electromagnetic waves, they include electromagnetic waves with wavelengths of 10 nm to 20,000 nm (0.01 μm to 20 μm).

In addition, heat transferred (heat input) to the radiative cooling layer is converted into infrared rays in the resin material layer and released to the outside of the system from the radiative surface.
In this way, the radiative cooling layer reflects the sunlight irradiated onto it, and also radiates heat transferred to the radiative cooling layer (for example, heat transferred from the atmosphere or from the clothing body cooled by the radiative cooling layer) outside the system as infrared light.

The thickness of the resin material layer is adjusted so that it emits greater thermal radiation energy in the 8 μm to 14 μm wavelength band than the absorbed solar energy, so that the light-reflecting layer, which is made of silver or a silver alloy, can adequately reflect sunlight while still providing a cooling function even in a daytime solar environment.

Therefore, even in a daytime solar radiation environment, the clothing body can be cooled by the radiative cooling layer attached to the outer surface of the clothing body, and as a result, the temperature rise of the clothing body can be suppressed even in a daytime solar radiation environment.
Of course, the presence of the radiative cooling layer prevents sunlight from reaching the clothing itself, so sunlight does not pass through the clothing and reach the wearer.
Therefore, even in a daytime solar radiation environment, the clothing itself can be cooled by radiative cooling, lowering the perceived temperature.

In other words, by allowing cooling air to flow between the clothing body and the wearer, evaporation from the wearer is encouraged and the wearer is cooled. In addition, by cooling the clothing body with a radiative cooling layer, the temperature of the cooling air flowing between the clothing body and the wearer is lowered, thereby appropriately lowering the temperature felt by the wearer.

Incidentally, since the resin material layer is formed from a highly flexible resin material, the resin material layer can be made flexible, and the light reflecting layer can be made flexible by being constructed as, for example, a thin silver film.
Therefore, the radiative cooling layer comprising the resin material layer and the light reflecting layer can be made flexible, and can be worn well while being aligned along the outer surface of the clothing body.

In short, the characteristic configuration of the radiative cooling air-conditioned clothing of the present invention makes it possible to lower the perceived temperature even when the environment in which it is used is a solar radiation environment with direct sunlight.

A further characteristic configuration of the radiative cooling type air-conditioned clothing of the present invention is configured to have a protective layer between the infrared emitting layer and the light reflecting layer,
The protective layer is made of a polyolefin resin having a thickness of 300 nm or more and 40 μm or less, or a polyethylene terephthalate resin having a thickness of 17 μm or more and 40 μm or less.

In other words, sunlight that enters through the radiation surface of the resin material layer acting as the infrared radiation layer passes through the resin material layer and protective layer, is reflected by the light reflecting layer on the opposite side to the side where the radiation surface of the resin material layer is located, and is then released outside the system through the radiation surface.

In addition, the protective layer is made of polyolefin resin with a thickness of 300 nm or more and 40 μm or less, or made of ethylene terephthalate resin with a thickness of 17 μm or more and 40 μm or less, so that discoloration of the silver or silver alloy in the light-reflecting layer can be suppressed even in a daytime solar radiation environment, and therefore the light-reflecting layer can appropriately reflect sunlight while providing an adequate cooling function even in a daytime solar radiation environment.

In other words, if the protective layer were not present, radicals generated in the resin material layer would reach the silver or silver alloy that forms the light reflecting layer, or moisture that penetrates the resin material layer would reach the silver or silver alloy that forms the light reflecting layer, causing the silver or silver alloy of the light reflecting layer to discolor in a short period of time and resulting in a state in which the light reflecting function is not properly performed. However, the presence of the protective layer can prevent the silver or silver alloy of the light reflecting layer from discoloring in a short period of time.

An additional explanation will be given below regarding the protective layer for preventing discoloration of silver or silver alloy in the light reflective layer.
When the protective layer is formed from a polyolefin-based resin to a thickness of 300 nm or more and 40 μm or less, the polyolefin-based resin is a synthetic resin whose ultraviolet light absorptance is 10% or less over the entire ultraviolet wavelength range of 0.3 μm to 0.4 μm, and therefore the protective layer is less susceptible to deterioration due to absorption of ultraviolet light.

The thickness of the polyolefin resin forming the protective layer is 300 nm or more, so it effectively blocks radicals generated in the resin material layer from reaching the silver or silver alloy forming the light reflecting layer, and also blocks moisture that penetrates the resin material layer from reaching the silver or silver alloy forming the light reflecting layer, thereby suppressing discoloration of the silver or silver alloy forming the light reflecting layer.

In other words, the protective layer made of polyolefin resin will deteriorate as it absorbs ultraviolet light, forming radicals on the surface side away from the reflective layer. However, because the thickness is 300 nm or more, the radicals formed will not reach the light reflective layer. Even if the protective layer deteriorates while forming radicals, the rate of deterioration is slow due to the low ultraviolet light absorption, so the above-mentioned blocking function will be maintained for a long period of time.

When the protective layer is formed from ethylene terephthalate resin with a thickness of 17 μm or more and 40 μm or less, ethylene terephthalate resin is a resin material that has a higher ultraviolet light absorption rate in the ultraviolet wavelength range of 0.3 μm to 0.4 μm than polyolefin resins, but since the thickness is 17 μm or more, it can effectively block radicals generated in the resin material layer from reaching the silver or silver alloy that forms the light reflecting layer, and can also block moisture that penetrates the resin material layer from reaching the silver or silver alloy that forms the light reflecting layer, for a long period of time, thereby suppressing discoloration of the silver or silver alloy that forms the protective layer.

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

When the protective layer is made of polyolefin resin and ethylene terephthalate resin, the reason for setting an upper limit on the thickness is to prevent the protective layer from having insulating properties that do not contribute to radiative cooling. In other words, the thicker the protective layer is, the more insulating the layer is that it does not contribute to radiative cooling. Therefore, the upper limit on the thickness is set to prevent the protective layer from having insulating properties that do not contribute to radiative cooling while still functioning to protect the reflective layer.

In short, this further characteristic configuration of the radiative cooling air-conditioned clothing of the present invention allows the clothing body to be cooled effectively while preventing the silver or silver alloy in the light-reflecting layer from discoloring in a short period of time.

A further characteristic feature of the radiative cooling air-conditioned clothing of the present invention is that the radiative cooling layer is attached to the outer surface of the clothing body with a connecting layer of adhesive or pressure-sensitive adhesive.

In other words, the radiative cooling layer can be precisely attached to the outer surface of the flexible clothing body in a state where it is in close contact with the outer surface via a connecting layer of adhesive or pressure sensitive adhesive.
Incidentally, the outer surface of the clothing body is generally not a mirror surface but is formed in a state with some unevenness. However, since the radiative cooling layer is connected to the outer surface of the clothing body with a connecting layer of adhesive or pressure-sensitive adhesive, the unevenness of the outer surface of the clothing body is prevented from being reflected in the light reflecting layer, and the light reflecting layer can be maintained in a flat state.

In other words, if the unevenness of the outer surface of the clothing body is reflected in the light-reflecting layer, the unevenness of the outer surface of the clothing body will cause light to be scattered, reducing the reflectance of the light-reflecting layer and resulting in the inconvenience of light being absorbed. However, by maintaining the light-reflecting layer in a flat state, the reduction in the reflectance of the light-reflecting layer can be suppressed.

In short, according to a further characteristic configuration of the radiative cooling air-conditioned clothing of the present invention, the radiative cooling layer can be accurately attached in a state where it is in close contact with the outer surface of the flexible clothing body.

A further characteristic feature of the radiative cooling air-conditioned clothing of the present invention is that the radiative surface of the radiative cooling layer is formed in an uneven shape.

In other words, by forming the radiation surface in an uneven shape, the surface area of the radiation surface can be increased, and as a result, the radiative cooling layer can be cooled by wind, improving the cooling function.

For example, if an electric fan is installed in a workplace where a person wearing the fan works, the cooling function can be improved by blowing the wind from the electric fan against the radiating surface.

In short, the additional characteristic configuration of the radiative cooling air-conditioned clothing of the present invention can improve the cooling function.

A further characteristic feature of the radiative cooling air-conditioned clothing of the present invention is that the light-reflecting layer has a reflectance of 90% or more for wavelengths between 0.4 μm and 0.5 μm, and a reflectance of 96% or more for wavelengths longer than 0.5 μm.

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

As a result, the solar energy absorbed by the light reflective layer at noon in summer can be reduced to about 50 W/m2 or ^less , and radiation cooling by the resin material layer can be performed satisfactorily.
In this specification, unless otherwise specified, the spectrum of sunlight is in accordance with the AM1.5G standard.

In short, this further characteristic configuration of the radiative cooling air-conditioned clothing of the present invention reduces the absorption of solar energy by the light-reflecting layer, and allows for good radiative cooling by the resin material layer.

A further characteristic feature of the radiative cooling type air-conditioned clothing of the present invention is that the film thickness of the resin material layer is
The wavelength average of the light absorptance at wavelengths of 0.4 μm to 0.5 μm is 13% or less, the wavelength average of the light absorptance at wavelengths of 0.5 μm to 0.8 μm is 4% or less, the wavelength average of the light absorptance at wavelengths of 0.8 μm to 1.5 μm is within 1%, and the wavelength average of the light absorptance at wavelengths of 1.5 μm to 2.5 μm is 40% or less, and
The thickness is adjusted to provide thermal radiation characteristics such that the wavelength average of the emissivity from 8 μm to 14 μm is 40% or more.

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

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

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

In other words, the light absorption rate of sunlight increases as the thickness of the resin material layer increases. When the resin material layer is made thick, the emissivity of the atmospheric window becomes almost 1, and the thermal radiation emitted into space at that time becomes 125 W/ ^m2 to 160 W/ ^m2 .
As described above, it is preferable that the solar light absorption in the light reflecting layer is 50 W/m ² or less.
Therefore, if the sum of the solar light absorption in the resin material layer and the light reflective layer is 150 W/ ^m2 or less and the atmospheric condition is good, cooling will proceed. As described above, it is preferable to use a resin material layer that has a small absorption rate near the peak value of the solar light spectrum.

From the viewpoint of the emissivity (thermal radiation characteristics) of the resin material layer for emitting infrared light, the wavelength average of the emissivity in the wavelength range of 8 μm to 14 μm must be 40% or more.
That is, in order to release the thermal radiation of sunlight of about 50 W/m ² that is absorbed by the light reflecting layer from the resin material layer into space, the resin material layer needs to emit thermal radiation of more than that.
For example, when the outside temperature is 30°C, the maximum thermal radiation of the atmospheric window for wavelengths from 8 μm to 14 μm is 200 W/ ^m2 (calculated with an emissivity of 1). This value can be obtained on a clear day in a dry environment with thin air, such as a high mountain. Since the atmosphere is thicker in lowlands than in high mountains, the wavelength band of the atmospheric window is narrower and the transmittance is lower. Incidentally, this is called the "narrowing of the atmospheric window."

In addition, the environment in which the radiative cooling air-conditioned clothing is actually used may be humid, in which case the atmospheric window is also narrow. The thermal radiation generated in the atmospheric window area when used in low altitudes is estimated to be 160 W/ ^m2 at 30°C under good conditions (calculated with an emissivity of 1).
In addition, when there is haze or smog in the sky, which is common in Japan, the atmospheric window becomes even narrower and radiation into space is around 125 W/ ^m2 .

In consideration of these circumstances, unless the wavelength average of the emissivity in the wavelength range from 8 μm to 14 μm is 40% or more (thermal radiation intensity in the atmospheric window zone is 50 W/ ^m2 or more), it cannot be used in low altitude areas in the mid-latitude zone.
Therefore, by adjusting the thickness of the resin material layer so that it falls within the above-mentioned optical specification range, the heat output from the atmospheric window becomes greater than the heat input due to the absorption of sunlight, making it possible to achieve radiative cooling outdoors even in a daytime solar radiation environment.

In short, according to a further characteristic configuration of the radiative cooling air-conditioned clothing of the present invention, the heat output from the atmospheric window is greater than the heat input due to the absorption of sunlight, making it possible to achieve radiative cooling even in a solar radiation environment.

A further characteristic feature of the radiative cooling air-conditioned clothing of the present invention is that the resin material forming the resin material layer is selected from resins having one or more of the following bonds: carbon-fluorine bond, siloxane bond, carbon-chlorine bond, carbon-oxygen bond, ether bond, ester bond, and benzene ring.

In other words, the resin material that forms the resin material layer can be a colorless resin material that has one or more of the following bonds: carbon-fluorine bond (C-F), siloxane bond (Si-O-Si), carbon-chlorine bond (C-Cl), carbon-oxygen bond (C-O), ether bond (R-COO-R), ester bond (C-O-C), or benzene ring.

According to Kirchhoff's law, the emissivity (ε) is equal to the light absorptance (A). The light absorptance (A) can be calculated from the absorption coefficient (α) using the following formula 1.
A=1−exp(−αt) (Formula 1) where t is the film thickness.
In other words, if the thickness of the resin material layer is increased, a large thermal radiation can be obtained in a wavelength band with a large absorption coefficient. When performing radiative cooling outdoors, it is recommended to use a material with a large absorption coefficient in the wavelength band of 8 μm to 14 μm, which is the atmospheric window. In addition, in order to suppress the absorption of sunlight, it is recommended to use a material that has no absorption coefficient or has a small absorption coefficient in the wavelength range of 0.3 μm to 4 μm, especially 0.4 μm to 2.5 μm. As can be seen from the relationship between the absorption coefficient and the light absorptance in Equation 1 above, the light absorptance (radiance) changes depending on the film thickness of the resin material layer.

In order to lower the temperature below the surrounding atmosphere by radiative cooling in a solar radiation environment, if a material that has a large absorption coefficient in the wavelength band of the atmospheric window and almost no absorption coefficient in the wavelength band of sunlight is selected as the resin material that forms the resin material layer, then by adjusting the film thickness of the resin material layer, it is possible to create a state in which almost no sunlight is absorbed but a lot of thermal radiation of the atmospheric window is emitted, in other words, a state in which the output from radiative cooling is greater than the input of sunlight.

The absorption spectrum of the resin material forming the resin material layer will now be described.
Regarding carbon-fluorine bonds (C-F), the absorption coefficients due to CHF and _CF2 are widely spread over a wide band from 8 μm to 14 μm, which is the atmospheric window, and the absorption coefficient is particularly large at 8.6 μm. In addition, regarding the wavelength band of sunlight, there is no noticeable absorption coefficient in the high-energy wavelength range of 0.3 μm to 2.5 μm.

Examples of resin materials having a C—F bond include:
Polytetrafluoroethylene (PTFE), a fully fluorinated resin;
partially fluorinated resins polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF);
Perfluoroalkoxy fluororesin (PFA), which is a fluorinated resin copolymer;
Tetrafluoroethylene-hexafluoropropylene copolymer (FEP),
Ethylene-tetrafluoroethylene copolymer (ETFE),
An example is ethylene-chlorotrifluoroethylene copolymer (ECTFE).

The bond energies of the C-C bond, C-H bond, and C-F bond in the basic structure of polyvinylidene fluoride (PVDF) are 4.50 eV, 4.46 eV, and 5.05 eV, which correspond to wavelengths of 0.275 μm, 0.278 μm, and 0.246 μm, respectively, and absorb light at shorter wavelengths than these wavelengths.
Since the solar spectrum only includes wavelengths longer than 0.300 μm, when a fluororesin is used, it hardly absorbs ultraviolet light, visible light, or near infrared light of sunlight.
In addition, ultraviolet rays are defined as rays having wavelengths shorter than 0.400 μm, visible light rays are defined as rays having wavelengths in the range of 0.400 μm to 0.800 μm, near-infrared rays are defined as rays having wavelengths in the range of 0.800 μm to 3 μm, mid-infrared rays are defined as rays having wavelengths in the range of 3 μm to 8 μm, and far-infrared rays are defined as rays having wavelengths longer than 8 μm.

Resin materials having siloxane bonds (Si-O-Si) include silicone rubber and silicone resin. In this resin, a large absorption coefficient caused by the expansion and contraction of the C-Si bond appears broadly around a wavelength of 13.3 μm, an absorption coefficient caused by the out-of-plane bending angle (pitch swing) of CSiH ₂ appears broadly around a wavelength of 10 μm, and an absorption coefficient caused by the in-plane bending angle (scissors) of CSiH ₂ appears small around a wavelength of 8 μm. Thus, it has a large absorption coefficient in the atmospheric window. In the ultraviolet region, the bond energy of the Si-O-Si main chain is 4.60 eV, which corresponds to a wavelength of 0.269 μm, and absorbs light on the shorter wavelength side than this wavelength. Since the solar spectrum only has wavelengths longer than 0.300 μm, when siloxane bonds are used, ultraviolet rays, visible light, and near-infrared rays of sunlight are hardly absorbed.

Regarding the carbon-chlorine bond (C--Cl), the absorption coefficient due to the C--Cl stretching vibration appears in a broad band having a half-width of 1 μm or more centered at a wavelength of 12 μm.
Furthermore, polyvinyl chloride (PVC) is an example of a resin material that has a carbon-chlorine bond (C-Cl). In the case of polyvinyl chloride, due to the electron withdrawal of chlorine, an absorption coefficient originating from the bending vibration of C-H of the alkene contained in the main chain appears at a wavelength of around 10 μm. In other words, it is possible to emit a large amount of thermal radiation in the wavelength band of the atmospheric window. The bond energy between carbon and chlorine in an alkene is 3.28 eV, which corresponds to a wavelength of 0.378 μm, and it absorbs light on the shorter wavelength side than this wavelength. In other words, it absorbs ultraviolet rays from sunlight, but has almost no absorption in the visible range.

Ether bonds (R-COO-R) and ester bonds (C-O-C) have absorption coefficients in the wavelength range of 7.8 μm to 9.9 μm. Furthermore, carbon-oxygen bonds contained in ester bonds and ether bonds have strong absorption coefficients in the wavelength range of 8 μm to 10 μm.
When a benzene ring is introduced into the side chain of a hydrocarbon resin, a wide absorption appears in the wavelength range from 8.1 μm to 18 μm due to the vibration of the benzene ring itself and the vibration of surrounding elements caused by the influence of the benzene ring.
Resins having these bonds include polymethyl methacrylate resin, ethylene terephthalate resin, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and polybutylene naphthalate. For example, the bond energy of the C-C bond in methyl methacrylate is 3.93 eV, which corresponds to a wavelength of 0.315 μm, and it absorbs sunlight with wavelengths shorter than this wavelength, but has almost no absorption in the visible range.

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

In short, according to a further characteristic configuration of the radiative cooling type air-conditioned clothing of the present invention, the radiative cooling layer can create a state in which the output from radiative cooling is greater than the input from sunlight.

A further characteristic feature of the radiative cooling type air-conditioned clothing of the present invention is that the main component of the resin material forming the resin material layer is siloxane,
The thickness of the resin material layer is 1 μm or more.

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

In short, according to a further characteristic configuration of the radiative cooling type air-conditioned clothing of the present invention, when the main component of the resin material forming the resin material layer is siloxane, the radiative cooling layer can create a state in which the output from radiative cooling is greater than the input of sunlight.

A further characteristic feature of the radiative cooling air-conditioned clothing of the present invention is that the thickness of the resin material layer is 10 μm or more.

In other words, in the case of a resin material whose main components are carbon-fluorine bonds (C-F), carbon-chlorine bonds (C-Cl), carbon-oxygen bonds (C-O), ester bonds (R-COO-R), ether bonds (C-O-C), or benzene rings, if the film thickness is 10 μm or more, the radiation intensity at the atmospheric window increases, creating a state in which the output from radiative cooling is greater than the input of sunlight.

In short, according to a further characteristic configuration of the radiative cooling type air-conditioned clothing of the present invention, when the resin material forming the resin material layer is a resin material whose main components are carbon-fluorine bonds (C-F), carbon-chlorine bonds (C-Cl), carbon-oxygen bonds (C-O), ester bonds (R-COO-R), ether bonds (C-O-C), or benzene rings, the radiative cooling layer can create a state in which the output from radiative cooling is greater than the input from sunlight.

A further characteristic feature of the radiative cooling air-conditioned clothing of the present invention is that the thickness of the resin material layer is 20 mm or less.

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

The thermal conductivity of resin materials is generally around 0.2 W/m·K, and when calculations are made taking this thermal conductivity into account, if the thickness of the resin material layer exceeds 20 mm, the temperature of the cooling surface (the surface of the light-reflecting layer opposite the side where the resin material layer is present) will rise. Even if an ideal resin material exists that does not absorb any sunlight, the thermal conductivity of resin materials is generally around 0.2 W/m·K, so if the thickness is made 20 mm or more, the thermal radiation (radiative cooling) of the resin material layer will not be able to cool the main body of the clothing that is cooled by the cooling surface, and the main body of the clothing will be exposed to solar radiation and heat up, so the film thickness cannot be made 20 mm or more.

In short, the further characteristic configuration of the radiative cooling air-conditioned clothing of the present invention allows the clothing body to be appropriately cooled.

A further characteristic feature of the radiative cooling air-conditioned clothing of the present invention is that the resin material forming the resin material layer is a fluororesin or silicone rubber.

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

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

In short, according to a further characteristic configuration of the radiative cooling type air-conditioned clothing of the present invention, when the resin material of the resin material layer is a fluororesin or silicone rubber, the radiative cooling layer can adequately exert the radiative cooling function.

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

In other words, if the resin material forming the resin material layer is a resin whose main chain is a hydrocarbon having one or more of the following bonds: carbon-chlorine bond (C-F), carbon-oxygen bond (C-O), ester bond (R-COO-R), ether bond (C-O-C), or benzene ring, or if it is a silicone resin whose side chain has two or more carbon atoms in the hydrocarbon, then in addition to the ultraviolet absorption due to covalent bond electrons, absorption due to vibrations such as bond bending and stretching appears in the near infrared region.

Specifically, the absorption due to the reference tone of the transition to the first excited state of CH ₃ , CH ₂ , and CH appears at wavelengths of 1.6 μm to 1.7 μm, 1.65 μm to 1.75 μm, and 1.7 μm, respectively. Furthermore, the absorption due to the reference tone of the combination tone of CH ₃ , CH ₂ , and CH appears at wavelengths of 1.35 μm, 1.38 μm, and 1.43 μm, respectively. Furthermore, the overtones of the transition to the second excited state of CH ₂ and CH appear at wavelengths of around 1.24 μm, respectively. The reference tone of the bending and stretching of the C-H bond is distributed in a wide band from wavelengths of 2 μm to 2.5 μm. In addition, in the case of a structural formula such as R ₁ -CO ₂ -R ₂ , there is a large light absorption at a wavelength of around 1.9 μm.

For example, polymethylmethacrylate resin, ethylene terephthalate resin, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and polyvinyl chloride exhibit similar light absorption characteristics in the near infrared region due to _CH3 , _CH2 , and CH. If these resin materials are made thicker to a thickness of 20 mm, which is specified from the viewpoint of thermal conductivity, they will absorb the near infrared rays contained in sunlight and heat up. Therefore, when using these resin materials, the thickness needs to be 500 μm or less.

In short, according to a further characteristic configuration of the radiative cooling air-conditioned clothing of the present invention, near-infrared absorption can be suppressed when the resin material is a resin whose main chain is a hydrocarbon 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, or a silicone resin whose side chain has two or more carbon atoms in the hydrocarbon.

A further characteristic feature of the radiative cooling air-conditioned clothing of the present invention is that the resin material forming the resin material layer is a blend of a resin containing a carbon-fluorine bond or a siloxane bond, and a resin with a hydrocarbon main chain, and the thickness of the resin material layer is 500 μm or less.

That is, when the resin material forming the resin material layer is a blend of a resin having a main chain of carbon-fluorine bonds (C-F) or siloxane bonds (Si-O-Si) and a resin having a main chain of hydrocarbon, light absorption in the near infrared region caused by CH, _CH2 , _CH3 , etc. appears according to the ratio of the blended resin having a main chain of hydrocarbon. When carbon-fluorine bonds or siloxane bonds are the main components, light absorption in the near infrared region caused by hydrocarbons becomes small, so the thickness can be increased up to 20 mm, which is the upper limit from the viewpoint of thermal conductivity. However, when the main component is a blended hydrocarbon resin, the thickness needs to be 500 μm or less.

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

Depending on the molecular weight and proportion of the substituting hydrocarbon side chains, optical absorption in the near infrared region due to CH, CH ₂ , CH ₃ and the like appears.
When the monomer introduced as a side chain or copolymer has a low molecular weight, or when the density of the monomer introduced is low, the optical absorption in the near infrared region caused by hydrocarbons is small, so the thickness can be increased up to 20 mm, which is the limit from the viewpoint of thermal conductivity.
When a high molecular weight hydrocarbon is introduced as a side chain of a fluororesin or silicone rubber or as a copolymerizable monomer, the thickness of the resin must be 500 μm or less.

In short, according to a further characteristic configuration of the radiative cooling air-conditioned clothing of the present invention, when the resin material is a blend of a resin containing a carbon-fluorine bond or a siloxane bond, and a resin with a hydrocarbon main chain, the absorption of near-infrared rays can be suppressed.

A further characteristic feature of the radiative cooling type air-conditioned clothing of the present invention is that the resin material forming the resin material layer is a fluororesin,
The thickness of the resin material layer is 300 μm or less.

In other words, from a practical standpoint, it is better for the radiative cooling layer to have a thin resin material layer. The thermal conductivity of resin materials is generally lower than that of metals, glass, etc. To effectively cool the object to be cooled (the clothing itself), the thickness of the resin material layer should be the bare minimum necessary. The thicker the resin material layer is, the greater the thermal radiation from the atmospheric window becomes, and once a certain thickness is exceeded, the thermal radiation energy at the atmospheric window becomes saturated.

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

In the case of fluororesin, the absorption coefficients derived from carbon-silicon bonds, carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds are greater than the absorption coefficient derived from C-F bonds. Naturally, from the viewpoint of thermal conductivity, it is more desirable to keep the film thickness at 300 μm or less than 500 μm, but an even greater radiative cooling effect can be expected by further reducing the film thickness to increase thermal conductivity.
Incidentally, examples of fluororesins that can be suitably used include polyvinyl fluoride (PVF) and polyvinylidene fluoride (PVDF).

In short, according to a further characteristic configuration of the radiative cooling type air-conditioned clothing of the present invention, the radiative cooling effect can be improved when the resin material is a fluororesin.

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

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

The benefit of making the resin thinner is not only to reduce heat insulation and make it easier to transfer cold heat, but also to suppress the absorption of near-infrared light originating from CH, _CH2 , and _CH3 in the near-infrared region, which is exhibited by resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds. By making the resin thinner, the solar absorption caused by these bonds can be reduced, thereby increasing the cooling capacity of the radiative cooling device.
From the above perspective, in the case of resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, a thickness of 50 μm or less can more effectively produce a radiative cooling effect under sunlight.

In short, according to a further characteristic configuration of the radiative cooling air-conditioned clothing of the present invention, the radiative cooling effect can be improved in a resin material having one or more of the following bonds: carbon-chlorine bond, carbon-oxygen bond, ester bond, ether bond, or benzene ring.

A further characteristic feature of the radiative cooling type air-conditioned clothing of the present invention is that the resin material forming the resin material layer is a resin material having a carbon-silicon bond,
The thickness of the resin material layer is 10 μm or less.

In other words, in the case of resin materials with carbon-silicon bonds, even with a thickness of 50 μm, thermal radiation is saturated in the atmospheric window region, and even with a thickness of 10 μm, sufficient thermal radiation can be obtained in the atmospheric window region. The thinner the resin material, the higher the thermal transmittance and the more effectively the temperature of the object to be cooled can be lowered, so in the case of resin materials containing carbon-silicon bonds, a thickness of 10 μm or less reduces the insulating properties and allows the object to be cooled to be cooled effectively. A thinner material reduces solar absorption, increasing the cooling capacity of the radiative cooling air-conditioned clothing.

From the above perspective, in the case of resin materials containing carbon-silicon bonds, a thickness of 10 μm or less can more effectively produce a radiative cooling effect in a solar radiation environment.

In short, according to a further characteristic configuration of the radiative cooling type air-conditioned clothing of the present invention, the radiative cooling effect can be improved in resin materials having carbon-silicon bonds.

A further characteristic configuration of the radiative cooling type air-conditioned clothing of the present invention is that the resin material forming the resin material layer is a vinyl chloride resin or a vinylidene chloride resin,
The thickness of the resin material layer is in the range of 100 μm or less and 10 μm or more.

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

Furthermore, thin-film polyvinyl chloride resin or vinylidene chloride resin is soft and therefore not easily scratched by contact with other objects, and can therefore be maintained in a beautiful condition for a long period of time. By the way, thin-film fluororesin is hard and therefore easily scratched by contact with other objects, and is difficult to maintain in a beautiful condition.

In short, according to the further characteristic configuration of the radiative cooling type air-conditioned clothing of the present invention, it is possible to obtain a radiative cooling layer at low cost that is less likely to be damaged and whose temperature drops below the ambient temperature even in a solar radiation environment.

A further characteristic feature of the radiative cooling air-conditioned clothing of the present invention is that the light-reflecting layer is made of silver or a silver alloy and has a thickness of 50 nm or more.

That is, in order to give the light-reflecting layer the above-mentioned reflectance characteristics, i.e., a reflectance of 90% or more at wavelengths from 0.4 μm to 0.5 μm and a reflectance of 96% or more at wavelengths longer than 0.5 μm, the reflective material on the radiation surface side of the light-reflecting layer needs to be silver or a silver alloy.
When reflecting sunlight while providing the above-mentioned reflectance characteristics using only silver or a silver alloy, a thickness of 50 nm or more is required.

In short, this further characteristic configuration of the radiative cooling air-conditioned clothing of the present invention accurately suppresses the absorption of solar energy by the light reflecting layer, allowing for good radiative cooling by the resin material layer.

A further characteristic feature of the radiative cooling type air-conditioned clothing of the present invention is that it is configured in a form having a protective layer between the infrared radiation layer and the light reflecting layer, the protective layer being a polyolefin resin having a thickness of 300 nm or more and 40 μm or less, or a polyethylene terephthalate resin having a thickness of 17 μm or more and 40 μm or less, and the light reflecting layer being a laminated structure of silver or a silver alloy located adjacent to the protective layer and aluminum or an aluminum alloy located away from the protective layer.

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

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

In short, this further characteristic configuration of the radiative cooling air-conditioned clothing of the present invention makes it possible to reduce the cost of the light-reflecting layer while still providing appropriate reflectance characteristics.

This is a diagram explaining the basic configuration of a radiative cooling type air-conditioned suit. FIG. 4 is a diagram showing the relationship between the absorption coefficient of a resin material and a wavelength band. FIG. 4 is a diagram showing the relationship between the light absorptance of a resin material and the wavelength. FIG. 1 is a diagram showing the emissivity spectrum of silicone rubber. FIG. 1 is a diagram showing the emissivity spectrum of PFA. FIG. 1 is a diagram showing the emissivity spectrum of polyvinyl chloride resin. FIG. 2 is a diagram showing the emissivity spectrum of ethylene terephthalate resin. FIG. 1 shows the emissivity spectrum of an olefin modified material. FIG. 4 is a diagram showing the relationship between the temperature of the radiation surface and the temperature of the light reflecting layer. FIG. 2 is a diagram showing the light absorptance spectra of silicone rubber and perfluoroalkoxy fluororesin. FIG. 2 is a diagram showing the light absorptance spectrum of ethylene terephthalate resin. FIG. 2 shows the light reflectance spectrum of a silver-based light reflective layer. FIG. 2 shows the emissivity spectrum of fluoroethylene vinyl ether. FIG. 2 is a diagram showing the emissivity spectrum of vinylidene chloride resin. 1 is a table showing the experimental results of the radiative cooling layer. FIG. 1 is a diagram showing the specific configuration of a radiative cooling type air-conditioned suit. FIG. 1 is a diagram showing the specific configuration of a radiative cooling type air-conditioned suit. FIG. 1 is a diagram showing the specific configuration of a radiative cooling type air-conditioned suit. FIG. 1 is a diagram showing the specific configuration of a radiative cooling type air-conditioned suit. FIG. 4 is a diagram showing the relationship between the light absorptance of a resin material and the wavelength. FIG. 1 is a graph showing the relationship between light transmittance and wavelength of polyethylene. FIG. 1 is a diagram illustrating a test configuration. FIG. 13 is a diagram showing test results when the protective layer is made of polyethylene. FIG. 13 is a diagram showing test results when the protective layer is made of ultraviolet absorbing acrylic. FIG. 2 is a diagram showing the emissivity spectrum of polyethylene. Graph showing experimental results of radiative cooling cloth. FIG. 13 is a diagram illustrating another configuration of the radiative cooling layer. FIG. 13 is a diagram showing a configuration in which a radiative cooling layer is formed in an uneven shape. FIG. 13 is a diagram showing a specific example of an uneven radiative cooling layer. FIG. 13 is a diagram showing a specific example of an uneven radiative cooling layer.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[Basic configuration of radiative cooling air-conditioned clothing]
As shown in Figure 1, the radiative cooling type air-conditioned clothing W is provided with a clothing body E worn by a wearer M, a blower fan 1 (an example of a blower section) that circulates cooling air between the clothing body E and the wearer M, and a radiative cooling layer CP is attached to the outer surface of the clothing body E.
In other words, the radiative cooling type air-conditioned clothing W is configured so that the clothing body E is cooled by the radiative cooling action of the radiative cooling layer CP.

The radiative cooling type air-conditioned clothing W shown in the example is configured so that a pair of left and right blower fans 1 installed on the waist side of the back of the clothing body E send out sucked-in air into the space between the clothing body E and the wearer M. The air flowing through the space between the clothing body E and the wearer M is then discharged through the gap between the collar of the clothing body E and the neck of the wearer M, and the gap between the cuffs of the clothing body E and the wrists of the wearer M.

Generally, a person wearing the suit will wear underwear, a shirt, and other clothing, and then put on the radiative cooling type air-conditioned suit W. In other words, the air sucked in by the blower fan 1 flows between the clothing worn by the person M and the suit body E.
Although not shown in the drawings, a fastener for opening and closing the front part is attached to the front part of the clothing body E. The radiative cooling cloth described later may be used on the entire clothing body E or on a part of the clothing body E.

In this embodiment, the clothing body E is made of cloth impregnated with polyvinyl chloride resin. Note that various materials such as polyester can be used for the clothing body E.

The radiative cooling layer CP is formed in a film shape and includes an infrared radiative layer A that radiates infrared light IR from a radiation surface H, a light reflecting layer B that is located on the side of the infrared radiative layer A opposite to the side where the radiation surface H exists, and a protective layer D between the infrared radiative layer A and the light reflecting layer B.
That is, the radiative cooling layer CP is configured as a radiative cooling film.

The light-reflecting layer B reflects light L, such as sunlight, that has passed through the infrared radiation layer A and the protective layer D, and has reflection characteristics such that the reflectance at wavelengths of 400 nm (0.4 μm) to 500 nm (0.5 μm) is 90% or more, and the reflectance at wavelengths longer than 500 nm is 96% or more.
As shown in FIG. 10, the solar spectrum exists between wavelengths of 300 nm and 4000 nm, and the intensity increases as the wavelength increases from 400 nm, and is particularly high between wavelengths of 500 nm and 1800 nm.

In this embodiment, light L includes ultraviolet light (ultraviolet rays), visible light, and infrared light, and when these are described in terms of the wavelength of light as electromagnetic waves, they include electromagnetic waves with wavelengths of 10 nm to 20,000 nm (electromagnetic waves of 0.01 μm to 20 μm). Incidentally, in this document, the wavelength range of ultraviolet light (ultraviolet rays) is between 300 nm and 400 nm.

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

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

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

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

The heat input to the radiation cooling layer CP from the clothing body E, which is located on the opposite side of the light reflecting layer B from the side where the resin material layer J is present (for example, heat input by thermal conduction from the clothing body E), is converted into infrared light IR by the resin material layer J and radiated, thereby cooling the clothing body E.

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

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

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

As described below, the light absorptivity of the resin material increases as the film thickness of the resin material increases. When the resin material is made thick, the emissivity of the window to the atmosphere becomes nearly 1, and the thermal radiation emitted to space at that time becomes 125 W/ ^m2 to 160 W/ ^m2 . The solar light absorption in the protective layer D and the light reflecting layer B is 50 W/ ^m2 or less. If the sum of the solar light absorption in the resin material layer J, the protective layer D, and the light reflecting layer B is 150 W/ ^m2 or less and the atmospheric condition is good, cooling proceeds. As described above, it is preferable to use a resin material that has a small light absorptivity near the peak value of the solar spectrum as the resin material for forming the resin material layer J.

From the viewpoint of infrared radiation (thermal radiation), the thickness of the resin material layer J needs to be adjusted to a thickness such that the wavelength average of the emissivity in the wavelength range from 8 μm to 14 μm is 40% or more.
In order to release the thermal energy of sunlight of about 50 W/m2, which is absorbed by the protective layer D and the light-reflecting layer B, from the resin material layer J into space through thermal radiation from the resin material layer J, the resin material layer J needs to emit greater thermal radiation than this.
For example, when the outside temperature is 30°C, the maximum thermal radiation of the atmospheric window from 8 μm to 14 μm is 200 W/ ^m2 (calculated with an emissivity of 1). This value can be obtained on a clear day in a dry environment with thin air, such as a high mountain. Since the atmosphere is thicker in lowlands than in high mountains, the wavelength band of the atmospheric window is narrower and the transmittance is lower. Incidentally, this is called the "narrowing of the atmospheric window."

In addition, the environment in which the radiative cooling layer CP (radiative cooling film) is actually used may be humid, and even in that case, the atmospheric window is narrow. The thermal radiation generated in the atmospheric window area when used in low altitudes is estimated to be 160 W/ ^m2 at 30°C under good conditions (calculated with emissivity of 1). In addition, when there is haze in the sky or smog, which is common in Japan, the atmospheric window becomes even narrower, and radiation into space is about 125 W/ ^m2 .
In consideration of these circumstances, unless the wavelength average of the emissivity in the wavelength range from 8 μm to 14 μm is 40% or more (thermal radiation intensity in the atmospheric window zone is 50 W/m ² ), it cannot be used in low altitudes in the mid-latitude zone.

Therefore, if the thickness of the resin material layer J is adjusted to fall within the optically specified range taking the above into consideration, the heat output from the atmospheric window will be greater than the heat input due to the absorption of sunlight, making it possible to achieve radiative cooling outdoors even in a solar radiation environment.

[Details of resin material]
The resin material can be a colorless resin material containing a carbon-fluorine bond (C-F), a siloxane bond (Si-O-Si), a carbon-chlorine bond (C-Cl), a carbon-oxygen bond (C-O), an ester bond (R-COO-R), an ether bond (C-O-C bond), or a benzene ring.
FIG. 2 shows the wavelength ranges in which each resin material (excluding carbon-oxygen bonds) has an absorption coefficient in the atmospheric window wavelength band.

According to Kirchhoff's law, emissivity (ε) and light absorptance (A) are equal. Light absorptance can be calculated from the absorption coefficient (α) using the relational expression A=1-exp(-αt) (hereafter referred to as the light absorptance relational expression), where t is the film thickness.
In other words, large thermal radiation can be obtained in a wavelength band with a large absorption coefficient by adjusting the film thickness of the resin material layer J. When performing radiative cooling outdoors, it is advisable to use a material with a large absorption coefficient in the wavelength band of the atmospheric window, that is, from 8 μm to 14 μm.
In order to suppress the absorption of sunlight, it is advisable to use a material that has no or a small absorption coefficient in the wavelength range of 0.3 μm to 4 μm, particularly in the range of 0.4 μm to 2.5 μm. As can be seen from the relation between the absorption coefficient and the absorptance, the light absorptance (radiance) changes depending on the film thickness of the resin material.

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

Regarding carbon-fluorine bonds (C-F), the absorption coefficients due to CHF and _CF2 are widely spread over a wide band from 8 μm to 14 μm, which is the atmospheric window, and the absorption coefficient is particularly large at 8.6 μm. In addition, regarding the wavelength band of sunlight, there is no noticeable absorption coefficient in the wavelength range from 0.3 μm to 2.5 μm, where the energy intensity is high.

Examples of resin materials having a carbon-fluorine bond (C-F) include:
Polytetrafluoroethylene (PTFE), a fully fluorinated resin;
partially fluorinated resins polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF);
Perfluoroalkoxy fluororesin (PFA), which is a fluorinated resin copolymer;
Tetrafluoroethylene-hexafluoropropylene copolymer (FEP),
Ethylene-tetrafluoroethylene copolymer (ETFE),
An example is ethylene-chlorotrifluoroethylene copolymer (ECTFE).

Resin materials having a siloxane bond (Si--O--Si) include silicone rubber and silicone resin.
In this resin, a large absorption coefficient caused by the expansion and contraction of C-Si bonds appears broadly around a wavelength of 13.3 μm, an absorption coefficient caused by the out-of-plane bending angle (vertical shaking) of CSiH ₂ appears broadly around a wavelength of 10 μm, and a small absorption coefficient caused by the in-plane bending angle (scissors) of CSiH ₂ appears around a wavelength of 8 μm.

Regarding the carbon-chlorine bond (C--Cl), the absorption coefficient due to the C--Cl stretching vibration appears in a broad band having a half-width of 1 μm or more centered at a wavelength of 12 μm.
Furthermore, examples of resin materials include polyvinyl chloride resin (PVC) and polyvinylidene chloride resin (PVDC). In the case of polyvinyl chloride resin, an absorption coefficient derived from the deformation vibration of C-H of the alkene contained in the main chain appears at a wavelength of around 10 μm due to the influence of electron attraction of chlorine.

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

Resins that have these bonds include methyl methacrylate resin, ethylene terephthalate resin, trimethylene terephthalate resin, butylene terephthalate resin, ethylene naphthalate resin, and butylene naphthalate resin.

[Optical absorption considerations]
Let us consider the light absorption in the ultraviolet-visible region of resin materials with the bonds and functional groups described above, that is, sunlight absorption. The origin of the absorption of ultraviolet to visible light is the transition of electrons that contribute to the bonds. Absorption in this wavelength range can be understood by calculating the bond energy.
First, let us consider the wavelengths at which resin materials with carbon-fluorine bonds (C-F) have absorption coefficients in the ultraviolet to visible range. The bond energies of the C-C bonds, C-H bonds, and C-F bonds in the basic structure of polyvinylidene fluoride (PVDF) are 4.50 eV, 4.46 eV, and 5.05 eV. These correspond to wavelengths of 0.275 μm, 0.278 μm, and 0.246 μm, respectively, and absorb light of these wavelengths.

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

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

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

Figure 3 shows the absorptance spectrum of 100 μm thick silicone rubber in the ultraviolet to visible range, and shows that it has almost no absorptance. There is a slight increase in the absorptance spectrum at wavelengths shorter than 0.4 μm, but this increase is merely the effect of scattering from the sample used in the measurement, and there is no actual increase in absorptance.

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

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

As an example of a resin material having these bonds and functional groups, the absorption spectrum from ultraviolet to visible light of a 5 mm-thick methyl methacrylate resin is shown in Figure 3. The methyl methacrylate resin shown is a commonly available product on the market, and contains a benzotriazole-based ultraviolet absorber.
Since the plate is 5 mm thick, the wavelength with a small absorption coefficient also becomes large, and light absorption becomes large on the shorter wavelength side than 0.38 μm, which is longer than the wavelength of 0.315.

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

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

[Emissivity of silicone rubber]
FIG. 4 shows the emissivity spectrum of the air window of silicone rubber having siloxane bonds.
Silicone rubber exhibits a large broad absorption coefficient caused by the expansion and contraction of C-Si bonds around a wavelength of 13.3 μm, a broad absorption coefficient caused by the out-of-plane bending angle (vertical rocking) of CSiH ₂ around a wavelength of 10 μm, and a small absorption coefficient caused by the in-plane bending angle (scissors) of CSiH ₂ around a wavelength of 8 μm.
Due to this effect, the wavelength average of the emissivity for a thickness of 1 μm is 80% at wavelengths from 8 μm to 14 μm, which falls within the regulation of a wavelength average of 40% or more. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

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

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

[Emissivity of PFA]
Figure 5 shows the emissivity of perfluoroalkoxy fluororesin (PFA) in the atmospheric window as a representative example of a resin with carbon-fluorine bonds. The absorption coefficient due to CHF and _CF2 is widely spread over a wide band from 8 μm to 14 μm, which is the atmospheric window, and the absorption coefficient is particularly large at 8.6 μm.
Due to this effect, the wavelength average of the emissivity of a 10 μm thick film is 45% at wavelengths from 8 μm to 14 μm, which falls within the regulation of a wavelength average of 40% or more. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

[Emissivity of polyvinyl chloride resin and vinylidene chloride resin]
Fig. 6 shows the emissivity of polyvinyl chloride resin (PVC) at the atmospheric window as a representative example of resin having carbon-chlorine bonds, and Fig. 14 shows the emissivity of polyvinylidene chloride resin (PVDC) at the atmospheric window.
Regarding the carbon-chlorine bond, the absorption coefficient due to the C-Cl stretching vibration appears in a broad band having a half-width of 1 μm or more centered at a wavelength of 12 μm.
In the case of polyvinyl chloride resin, the absorption coefficient due to the bending vibration of C-H of the alkene contained in the main chain appears at a wavelength of about 10 μm due to the influence of electron withdrawal of chlorine. The same is true for vinylidene chloride resin.
Due to these effects, the wavelength average of the emissivity of a 10 μm thick film is 43% at wavelengths from 8 μm to 14 μm, which falls within the regulation of a wavelength average of 40% or more. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

[Ethylene terephthalate resin]
FIG. 7 shows the emissivity of ethylene terephthalate resin in the atmospheric window as a representative example of a resin having an ester bond or a benzene ring.
Ester bonds have an absorption coefficient in the wavelength range of 7.8 μm to 9.9 μm. Furthermore, the carbon-oxygen bonds contained in ester bonds have a strong absorption coefficient in the wavelength range of 8 μm to 10 μm. When a benzene ring is introduced into the side chain of a hydrocarbon resin, a wide absorption occurs in the wavelength range of 8.1 μm to 18 μm due to the vibration of the benzene ring itself and the vibration of surrounding elements caused by the influence of the benzene ring.
Due to these effects, the wavelength average of the emissivity of a 10 μm thick film is 71% at wavelengths from 8 μm to 14 μm, which falls within the regulation of a wavelength average of 40% or more. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

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

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

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

5, in the case of fluororesin, even if the thickness exceeds 100 μm, there is almost no increase in thermal radiation in the air window region. In other words, in the case of fluororesin, thermal radiation in the air window occurs within a depth of about 100 μm from the surface, and radiation from deeper parts does not reach the outside.
6, in the case of polyvinyl chloride resin, even if the thickness exceeds 100 μm, there is almost no increase in thermal radiation in the air window region. In other words, in the case of polyvinyl chloride resin, thermal radiation in the air window occurs within a depth of about 100 μm from the surface, and radiation from deeper parts does not escape to the outside.
From FIG. 14, it can be seen that vinylidene chloride resin is similar to vinyl chloride resin.

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

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

Even if an ideal resin material that does not absorb any sunlight exists, the thermal conductivity of resin materials is generally around 0.2 W/m/K. Therefore, if the thickness exceeds 20 mm as shown in Figure 9, the light reflecting layer B will be heated by sunlight, and the clothing body E placed on the light reflecting layer side will be heated. In other words, the thickness of the resin material of the radiative cooling layer CP needs to be 20 mm or less.

In addition, Fig. 9 is a plot of the surface temperature of the radiative surface H of the radiative cooling layer (radiative cooling film) CP and the temperature of the light reflecting layer B, calculated assuming a meridian on a clear day in Western Japan in midsummer. The sunlight is AM1.5 and has an energy density of 1000 W/ ^m2 . The outside temperature is 30°C, and the radiant energy varies depending on the temperature, but is 100 W at 30°C. The calculation assumes that the resin material layer does not absorb sunlight. It is assumed that there is no wind, and the convective heat transfer coefficient is 5 W/ ^m2 /K.

[Light absorptivity of silicone rubber, etc.]
10 shows the light absorptance of silicone rubber having a _CH3 side chain with respect to the sunlight spectrum when the thickness is 100 μm, and the light absorptance spectrum of perfluoroalkoxy fluororesin with a thickness of 100 μm with respect to the sunlight spectrum. As mentioned above, it can be seen that both resins have almost no light absorptance in the ultraviolet region.

For silicone rubber, in the near infrared region, the light absorptance increases in the region longer than 2.35 μm. However, because the intensity of the solar spectrum in this wavelength region is weak, even if the light absorptance on the longer side of the wavelength than 2.35 μm becomes 100%, the solar energy absorbed is only 20 W/ ^m2 .

Perfluoroalkoxy fluororesin has almost no light absorption in the wavelength range of 0.3 μm to 2.5 μm, but does absorb light at wavelengths longer than 2.5 μm. However, even if the film thickness of the resin is increased and the light absorption rate at wavelengths longer than 2.5 μm becomes 100%, the solar energy absorbed is only about 7 W.

In addition, as the thickness (film thickness) of the resin material layer J is increased, the emissivity of the atmospheric window region becomes approximately 1. That is, in the case of a thick film, the thermal radiation radiated into space in the atmospheric window region when used at low altitudes is approximately 160 W/ ^m2 to 125 W/ ^m2 at 30°C. The light absorption in the light reflecting layer B is approximately 50 W/ ^m2 as specified above, and even if the light absorption of the light reflecting layer B and the solar light absorption when silicone rubber or perfluoroalkoxy fluororesin is made into a thick film are added together, this is smaller than the thermal radiation radiated into space.
From the above, the maximum film thickness of silicone rubber and perfluoroalkoxy fluororesin is 20 mm from the viewpoint of thermal conductivity.

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

Specifically, the absorption due to the reference tones of the transitions to the first excited state of _CH3 , _CH2 , and CH appears at wavelengths of 1.6 μm to 1.7 μm, 1.65 μm to 1.75 μm, and 1.7 μm, respectively. Furthermore, the absorption due to the reference tones of the combination tones of _CH3 , _CH2 , and CH appears at wavelengths of 1.35 μm, 1.38 μm, and 1.43 μm, respectively. Furthermore, the overtones of the transitions to the second excited state of _CH2 and CH appear at wavelengths of around 1.24 μm. The reference tones of the bending and stretching of C-H bonds are distributed over a wide band from 2 μm to 2.5 μm.

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

FIG. 11 shows the relationship between the light absorptance and the spectrum of sunlight when the film thickness of an ethylene terephthalate resin having an ester bond and a benzene ring is changed.
As shown in the figure, as the film thickness increases from 25 μm to 125 μm to 500 μm, the light absorption in the wavelength range longer than 1.5 μm caused by the respective vibrations increases.
In addition, the light absorption increases not only on the long wavelength side but also from the ultraviolet region to the visible region. This is due to the broadening of the light absorption edge caused by chemical bonds.

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

Since the light absorption of the light reflecting layer B is 50 W/ ^m2 according to the above-mentioned regulation, when the film thickness is 500 μm, the sum of the solar light absorption of the ethylene terephthalate resin and the solar light absorption of the light reflecting layer B is 138 W/ ^m2 . In the summer in the lowlands of Japan, the maximum value of infrared radiation in the wavelength band of the atmospheric window is about 160 W at 30° C. on a day with good atmospheric conditions, and is usually about 125 W, as described above.
From the above, when the film thickness of the ethylene terephthalate resin is 500 μm or more, the radiative cooling performance is not exhibited.

The origin of the absorption spectrum in the wavelength band from 1.5 μm to 4 μm is vibration of the hydrocarbon of the main chain, not functional group, and the hydrocarbon resin shows the same behavior as ethylene terephthalate resin. Moreover, the hydrocarbon resin has light absorption due to chemical bonds in the ultraviolet region, and shows the same behavior as ethylene terephthalate resin from ultraviolet to visible.
In other words, the hydrocarbon resin behaves in the same manner as the ethylene terephthalate resin from wavelengths of 0.3 μm to 4 μm. For this reason, the film thickness of the hydrocarbon resin needs to be thinner than 500 μm.

[Light absorption of blended resins]
When the resin material is a blend of a resin having a carbon-fluorine bond or a siloxane bond as its main chain and a resin having a hydrocarbon as its main chain, light absorption in the near-infrared region caused by CH, _CH2 , _CH3 , etc. appears depending on the ratio of the blended resin having a hydrocarbon as its main chain.
When the main component is a carbon-fluorine bond or a siloxane bond, the light absorption in the near infrared region caused by hydrocarbons is small, so the thickness can be increased up to the upper limit of 20 mm from the viewpoint of thermal conductivity. However, when the main component is a blended hydrocarbon resin, the thickness must be 500 μm or less.

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

Depending on the molecular weight and ratio of the substituting hydrocarbon side chain, optical absorption in the near infrared region due to CH, _CH2 , _CH3 , etc. appears. When the monomer introduced as the side chain or copolymer has a low molecular weight, or when the density of the introduced monomer is low, optical absorption in the near infrared region due to the hydrocarbon becomes small, so the thickness can be increased up to 20 mm, which is the limit from the viewpoint of thermal conductivity.
When a high molecular weight hydrocarbon is introduced as a side chain of a fluororesin or silicone rubber or as a copolymerizable monomer, the thickness of the resin must be 500 μm or less.

[Thickness of resin material layer]
From the viewpoint of practical use of the radiative cooling layer CP, it is preferable that the thickness of the resin material layer J is thin. The thermal conductivity of resin materials is generally lower than that of metals, glass, etc. In order to effectively cool the clothing body E, it is preferable that the thickness of the resin material layer J is the minimum necessary. The thicker the resin material layer J is, the greater the thermal radiation of the atmospheric window becomes, and when a certain thickness is exceeded, the thermal radiation energy at the atmospheric window becomes saturated.

The film thickness at which saturation occurs depends on the resin material, but in the case of fluororesin, 300 μm is generally sufficient for saturation. Therefore, from the perspective of thermal conductivity, it is preferable to keep the film thickness below 300 μm rather than 500 μm. Furthermore, although thermal radiation is not saturated, sufficient thermal radiation can be obtained in the atmospheric window region even with a thickness of about 100 μm. The thinner the thickness, the higher the thermal conductivity and the more effectively the temperature of the clothing body E can be lowered, so in the case of fluororesin, it is best to keep the thickness below about 100 μm.

The absorption coefficients derived from carbon-silicon bonds, carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds are greater than the absorption coefficient derived from C-F bonds. Naturally, from the viewpoint of thermal conductivity, it is more desirable to keep the film thickness to 300 μm or less than 500 μm, but an even greater radiative cooling effect can be expected by further reducing the film thickness and increasing the thermal conductivity.
In the case of resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, even a thickness of 100 μm is saturated, and even a thickness of 50 μm provides sufficient heat radiation in the atmospheric window region. The thinner the resin material, the higher the thermal transmittance and the more effectively the temperature of the clothing body E can be lowered, so in the case of resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, a thickness of 50 μm or less reduces the heat insulation and allows the clothing body E to be effectively cooled. In the case of carbon-chlorine bonds, a thickness of 100 μm or less allows the clothing body E to be effectively cooled.

The benefit of making the layer thinner is not only to reduce the thermal insulation and make it easier to transfer cold heat, but also to suppress the absorption of near-infrared light originating from CH, _CH2 , and _CH3 in the near-infrared region, which is exhibited by resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds. By making the layer thinner, the solar light absorption caused by these bonds can be reduced, which increases the cooling capacity of the radiative cooling layer CP.
From the above viewpoints, in the case of a resin containing a carbon-chlorine bond, a carbon-oxygen bond, an ester bond, an ether bond, or a benzene ring, a thickness of 50 μm or less can more effectively exert a radiative cooling effect under sunlight.

In the case of carbon-silicon bonds, even with a thickness of 50 μm, thermal radiation is saturated in the window region of the atmosphere, and even with a thickness of 10 μm, sufficient thermal radiation can be obtained in the window region of the atmosphere. The thinner the resin material layer J, the higher the thermal transmittance and the more effectively the temperature of the clothing body E can be lowered. Therefore, in the case of resins containing carbon-silicon bonds, a thickness of 10 μm or less reduces the heat insulation and effectively cools the clothing body E. By making the layer thinner, the solar light absorption can be reduced, and the cooling capacity of the radiative cooling layer CP is increased.
From the above viewpoints, in the case of a resin containing carbon-silicon bonds, a thickness of 10 μm or less can more effectively exert a radiative cooling effect under sunlight.

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

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

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

Incidentally, examples of "aluminum alloys" that can be used include alloys in which copper, manganese, silicon, magnesium, zinc, carbon steel for mechanical construction, yttrium, lanthanum, gadolinium, and terbium have been added to aluminum.

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

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

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

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

[Specific configuration of radiative cooling air-conditioned clothing]
Since the resin material forming the resin material layer J and the protective layer D of the radiative cooling layer CP is flexible, when the light reflecting layer B is made thin, the light reflecting layer B can also be made flexible. As a result, the radiative cooling layer CP can be made into a flexible film (radiative cooling film).

As shown in Figures 16 to 19, the clothing body E can be cooled by attaching a film-like radiative cooling layer CP (radiative cooling film) to the outer surface of the clothing body E with a connecting layer S of adhesive or pressure-sensitive adhesive.
The adhesive or pressure-sensitive adhesive used for the connection layer S includes a urethane-based adhesive (pressure-sensitive adhesive), an acrylic-based adhesive (pressure-sensitive adhesive), an EVA (ethylene vinyl acetate)-based adhesive (pressure-sensitive adhesive), and the like.

There are various possible ways to fabricate the radiative cooling layer CP in the form of a film. For example, it can be fabricated by applying a protective layer D and a resin material layer J to a light reflecting layer B fabricated in the form of a film. Alternatively, it can be fabricated by attaching a protective layer D and a resin material layer J to a light reflecting layer B fabricated in the form of a film. Alternatively, it can be fabricated by applying or attaching a protective layer D to a resin material layer J fabricated in the form of a film, and fabricating a light reflecting layer B on the protective layer D by deposition, sputtering, ion plating, silver mirror reaction, or the like.

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

The radiative cooling layer CP (radiative cooling film) in Figure 16 can be produced by sequentially applying a protective layer D, a light-reflecting layer B, and a lower protective layer Ds onto a film-like resin material layer J, and molding them together as a single unit.

The radiative cooling layer CP (radiative cooling film) in Figure 17 is configured such that the light reflecting layer B is composed of an aluminum layer B1 formed of aluminum foil that functions as aluminum (aluminum alloy) and a silver layer B2 made of silver or a silver alloy, a protective layer D 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.

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

The radiative cooling layer CP (radiative cooling film) in Figure 18 is formed by forming a protective layer D on the upper side of the light reflecting layer B, forming a resin material layer J on the top of the protective layer D, and forming a film layer F of PET or the like on the lower side of the light reflecting layer B when the light reflecting layer B is formed as a single layer of silver or silver alloy, or is composed of two layers of silver (silver alloy) and aluminum (aluminum alloy).

The method of producing the radiative cooling layer CP (radiative cooling film) in Fig. 18 can be a method of sequentially coating a light reflecting layer B and a protective layer D on a film layer F (corresponding to a substrate) formed in a film shape using PET (ethylene terephthalate resin) or the like, forming them integrally, and then adhering a film-shaped resin material layer J formed separately to the protective layer D with a glue layer N.
The adhesive (pressure-sensitive adhesive) used in the glue layer N may be, for example, a urethane-based adhesive (pressure-sensitive adhesive), an acrylic-based adhesive (pressure-sensitive adhesive), an EVA (ethylene vinyl acetate)-based adhesive (pressure-sensitive adhesive), etc., and it is preferable for it to be one that has high transparency to sunlight.

The radiative cooling layer CP (radiative cooling film) in Figure 19 is configured such that the light reflecting layer B is composed of an aluminum layer B1 that functions as aluminum (aluminum alloy) and a silver layer B2 that is made of silver or a silver alloy (silver substitute), the aluminum layer B1 is formed on top of a film layer F (corresponding to the substrate) that is formed in a film shape from PET (ethylene terephthalate resin) or the like, a protective layer D is formed on the top of the silver layer B2, and a resin material layer J is formed on the top of the protective layer D.

The method of producing the radiative cooling layer CP (radiative cooling film) in Fig. 19 can be as follows: an aluminum layer B1 is applied onto a film layer F, and the film layer F and the aluminum layer B1 are integrally formed; a protective layer D and a silver layer B2 are applied onto a film-like resin material layer J, and the resin material layer J, the protective layer D, and the silver layer B2 are integrally formed; and the aluminum layer B1 and the silver layer B2 are bonded together with a glue layer N.
The adhesive (pressure-sensitive adhesive) used in the glue layer N may be, for example, a urethane-based adhesive (pressure-sensitive adhesive), an acrylic-based adhesive (pressure-sensitive adhesive), an EVA (ethylene vinyl acetate)-based adhesive (pressure-sensitive adhesive), etc., and it is preferable for it to be one that has high transparency to sunlight.

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

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

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

When protective layer D is formed from polyolefin resin with a thickness of 300 nm or more and 40 μm or less, polyolefin resin is a synthetic resin with an ultraviolet light absorption rate of 10% or less over the entire ultraviolet wavelength range of 0.3 μm to 0.4 μm, so protective layer D is less likely to deteriorate due to ultraviolet absorption.

The thickness of the polyolefin resin forming protective layer D is 300 nm or more, so it effectively blocks radicals generated in resin material layer J from reaching the silver or silver alloy forming the light reflecting layer, and also blocks moisture that passes through resin material layer J from reaching the silver or silver alloy forming light reflecting layer B, thereby suppressing discoloration of the silver or silver alloy forming light reflecting layer B.

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

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

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

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

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

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

When the protective layer D is formed from polyolefin resin and ethylene terephthalate resin, the reason for setting an upper limit on the thickness is to prevent the protective layer D from having insulating properties that do not contribute to radiative cooling. In other words, the thicker the protective layer D is, the more insulating the layer D is that it does not contribute to radiative cooling. Therefore, an upper limit on the thickness is set to prevent the protective layer D from having insulating properties that do not contribute to radiative cooling while still functioning to protect the light reflecting layer B.

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

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

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

As shown in Figure 24, if the protective layer D is made of an acrylic resin that absorbs ultraviolet rays well, the protective layer D is decomposed by ultraviolet rays to form radicals, and the silver immediately turns yellow and no longer functions as a radiative cooling layer CP (it absorbs sunlight and rises in temperature when exposed to solar radiation like general materials).
The 600h line in the figure is the reflectance spectrum after 600h (hours) of a xenon weather test (ultraviolet light energy of 60 W/ ^m2 ) under the conditions of JIS standard 5600-7-7, and the 0h line is the reflectance spectrum before the xenon weather test.

23, when the protective layer D is made of polyethylene with low ultraviolet light absorption, no decrease in reflectance is observed from the near infrared region to the visible region. In other words, a resin whose main component is polyethylene (polyolefin resin) hardly absorbs the ultraviolet light contained in sunlight that reaches the ground, and therefore is unlikely to form radicals even when exposed to sunlight, so that coloring of silver as the light reflecting layer B does not occur even when exposed to sunlight.
The 600h line in the figure is the reflectance spectrum after 600h (hours) of a xenon weather test (ultraviolet light energy of 60 W/ ^m2 ) under the conditions of JIS standard 5600-7-7, and the 0h line is the reflectance spectrum before the xenon weather test.

The reason the reflectance spectrum in this wavelength band ripples is due to the Fabry-Perot resonance of the polyethylene layer. This is due to changes in the thickness of the polyethylene layer caused by heat during the xenon weather test, and it can be seen that the resonance position differs slightly between the 0h line and the 600h line, but no significant decrease in reflectance in the ultraviolet-visible range due to the yellowing of silver is observed.

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

[Radiative cooling fabric experiment results]
The experimental results on the difference in sensible temperature between a general cloth and a radiative cooling cloth with a radiative cooling layer CP are shown in Figure 26. The sensible temperature is the temperature measured by a blackbody thermometer. The experiment was conducted on August 19th.
The white cloth was a vinyl chloride-impregnated cloth (E65TS manufactured by Kanbou Plus Co., Ltd.) that had no moisture permeability. The aluminum vapor deposition light-shielding film was Techmirror manufactured by Nippon Wavelock Co., Ltd. The radiative cooling cloth was a laminate of a vinyl chloride-impregnated cloth and a radiative cooling layer CP (radiative cooling film).

A closed space was created using a vinyl chloride-impregnated cloth, an aluminum-deposited light-shielding film, and a radiative cooling cloth, and the temperature of the side of the closed space facing the sky was measured. For example, in the case of the radiative cooling cloth, the sensible temperature was measured for a person's shoulder when standing upright, and for the back when bending over.
As shown in Figure 26, the sensible temperature at 12 o'clock was 46.3°C for the vinyl chloride-impregnated cloth, 44.1°C for the aluminum vapor-deposited heat shielding film, and 36.1°C for the radiative cooling cloth.

The heat stroke index WBGT in a closed space can be calculated using the following formula.
In other words, it can be calculated as WBGT = 0.7 x wet-bulb temperature + 0.3 x blackbody temperature.
According to this formula, the heatstroke index of the radiative cooling cloth is 3°C lower than that of a cloth impregnated with polyvinyl chloride and 2.4°C lower than that of an aluminum vapor deposition heat shielding film at the same humidity.
If outside air is forcibly drawn into the air-conditioned clothing made of radiative cooling fabric by a blower fan 1 (in the case of radiative cooling type air-conditioned clothing), and the humidity inside the air-conditioned clothing is assumed to be approximately the same as the relative humidity of the outside air, then at the same time, the outside temperature is 35°C, the relative humidity is 50%, and the wet-bulb temperature is 26.2°C. Therefore, the heat stroke index of the white fabric impregnated with polyvinyl chloride is 32.2°C, the heat stroke index of the aluminum vapor deposition heat-shielding film is 31.6°C, and the heat stroke index of the radiative cooling type air-conditioned clothing W is 29.2°C.

According to the guidelines on heatstroke index provided by the Ministry of the Environment, if the heatstroke index is 31.0°C or higher, exercise should be suspended as a general rule, and if the heatstroke index is between 28°C and 31°C, extreme caution should be exercised (all strenuous exercise should be suspended).
Therefore, by wearing the radiative cooling air-conditioned suit W with a heatstroke index of 29.2°C, various types of work can be performed.

[Another configuration of the radiative cooling layer]
As shown in FIG. 27 , the radiative cooling layer CP may be configured to include an anchor layer G on top of a film layer F (corresponding to a substrate), and a light reflecting layer B, a protective layer D, and an infrared radiative layer A on top of the anchor layer G.
The film layer F (corresponding to the substrate) is formed into a film shape using, for example, PET (ethylene terephthalate resin) or the like.

The anchor layer G is introduced to strengthen the adhesion between the film layer F and the light reflecting layer B. In other words, if silver (Ag) is directly formed on the film layer F, there is a risk that peeling may occur easily. The anchor layer G is preferably made of acrylic, polyolefin, or urethane as the main component, and is mixed with a compound having an isocyanate group or melamine resin. It is a coating for the part that is not directly exposed to sunlight, so it is acceptable for the material to absorb ultraviolet rays.
There are other methods for strengthening the adhesion between the film layer F and the light reflecting layer B than inserting the anchor layer G. For example, the adhesion can be increased by roughening the surface of the film layer F by irradiating the surface with plasma.

[Considerations on connection layers]
When attaching a radiative cooling layer CP to the outer surface of the clothing body E, it is preferable that the thickness of the connection layer S be 5 μm or more and 100 μm or less.
That is, the outer surface (surface) of the clothing body E is often not a mirror surface. The outer surface (material surface) of the clothing body E, which is not a mirror surface, often has numerous scratches and irregularities on the order of several μm.
If the μm-level irregularities present on the outer surface (material surface) of the clothing body E are transferred to the light reflecting layer B (silver layer) of the radiative cooling layer CP, the reflectance will decrease.
Therefore, it is necessary to introduce a structure that prevents the unevenness present on the outer surface (material surface) from being reflected in the radiative cooling layer CP. For this purpose, it is advisable to join the radiative cooling layer CP to the outer surface of the clothing body E with a connecting layer S having a thickness of about 5 μm to 100 μm.

When a connection layer S of 5 μm or more and made of adhesive or pressure sensitive adhesive is present, the connection layer S absorbs the unevenness of the outer surface of the clothing body E, and the light reflecting layer B (silver layer) of the radiative cooling layer CP becomes flat.
When the light reflecting layer B (silver layer) is made flat, a decrease in the solar light reflectance (in other words, an increase in the solar light absorptance) can be prevented.
However, as the thickness of the connection layer S increases, the thermal insulation improves. This is not good because the thermal insulation of the radiative cooling layer CP is insulated. From this viewpoint, an unnecessarily thick connection layer S is not necessary, and a thickness of 100 μm is sufficient.

[Another example of radiative cooling air-conditioned clothing]
As shown in FIG. 28, it is preferable to form the radiation surface H of the radiative cooling layer CP in an uneven shape.
That is, for example, the radiation surface H may be formed in such a manner that the protrusion U exists.
Examples of the uneven shape include a line-and-space structure in which rectangular parallelepiped protrusions U are lined up (see Figure 29), a structure in which conical prism-shaped protrusions U are lined up vertically and horizontally (see Figure 30), a structure in which triangular prism or pyramid-shaped protrusions U are lined up in a line-and-space pattern (not shown), a structure in which rectangular shaped protrusions U are lined up vertically and horizontally, and a structure in which protrusions U are formed randomly.
Incidentally, when the radiation surface H is formed in an uneven shape, the height difference is about 100 μm.

The advantage of forming the radiation surface H in an uneven shape is that the surface area of the radiation surface H is increased, so that, for example, when an electric fan is installed in the workplace where the wearer of the radiative cooling type air-conditioned suit W works, the wind blown by the fan is blown against the radiation surface H, improving the cooling function.

Forming the radiation surface H in an uneven shape also has an advantage in terms of appearance. When the radiation surface H (upper surface) of the radiative cooling layer CP is formed in an uneven shape, sunlight is scattered more than when the radiation surface H (upper surface) of the radiative cooling layer CP is a mirror surface, so the glare of the radiative cooling layer CP is reduced.
Furthermore, even if the radiation surface H is endowed with the function of "scattering," the light absorption in the silver (silver alloy) of the light reflecting layer B does not increase, so radiation cooling can be performed satisfactorily.

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

(2) In the above embodiment, a case where protective layer D is provided is exemplified, but protective layer D may be omitted.

(3) In the above embodiment, the radiation surface H of the resin material layer J is exposed. However, a hard coat may be provided to cover the radiation surface H.
The hard coat may be any of UV-curable acrylic, heat-curable acrylic, UV-curable silicone, heat-curable silicone, organic-inorganic hybrid, and vinyl chloride. An organic antistatic agent may be used as an additive.
Among the UV-curable acrylics, urethane acrylate is particularly good.

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

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

(4) The radiative cooling type air-conditioned clothing W exemplified in the above embodiment is configured such that the blower fan 1 provided on the waist side of the back of the clothing body E draws in air from the outside and sends it into the space between the clothing body E and the wearer M. Alternatively, the blower fan 1 may suck in and exhaust air in the space between the clothing body E and the wearer M to the outside. In this case, the space between the clothing body E and the wearer M becomes negative pressure, and outside air flows into the space between the clothing body E and the wearer M through the gap between the collar of the clothing body E and the neck of the wearer M, or the gap between the cuffs of the clothing body E and the wrists of the wearer M. Incidentally, in the case of this form of radiative cooling type air-conditioned clothing W, it is preferable to provide a member on the inner side of the clothing body E that forms a space through which air flows between the clothing body E and the wearer M.

The configurations disclosed in the above embodiment (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, so long as no contradiction arises. Furthermore, the embodiments disclosed in this specification are merely examples, and the present invention is not limited to these embodiments. They can be modified as appropriate within the scope of the purpose of the present invention.

1 Ventilation part A Infrared emitting layer B Light reflecting layer D Protective layer E Clothes body H Emitting surface J Resin material layer U Uneven part

Claims (19)

The clothing body is provided with an air blowing section for blowing cooling air between the clothing body and the wearer,
A radiative cooling layer is attached to the outer surface of the clothing body,
The radiative cooling layer is configured to include an infrared radiative layer that radiates infrared light from a radiation surface, and a light reflecting layer that is located on the infrared radiative layer opposite to the side where the radiation surface is present,
the infrared radiation layer is a resin material layer whose thickness is adjusted to emit thermal radiation energy in a wavelength band of 8 μm to 14 μm that is greater than absorbed solar light energy,
The light reflective layer is made of silver or a silver alloy. A protective layer is provided between the infrared emitting layer and the light reflecting layer,
The radiative cooling type air-conditioned clothing according to claim 1, wherein the protective layer is made of a polyolefin resin having a thickness of 300 nm or more and 40 μm or less, or a polyethylene terephthalate resin having a thickness of 17 μm or more and 40 μm or less. The radiative cooling type air-conditioned suit according to claim 1 or 2, in which the radiative cooling layer is attached to the outer surface of the suit body with a connecting layer of adhesive or pressure-sensitive adhesive. The radiative cooling type air-conditioned clothing according to any one of claims 1 to 3, wherein the radiation surface of the radiative cooling layer is formed with unevenness. The radiative cooling type air-conditioned clothing according to any one of claims 1 to 4, wherein the light reflective layer has a reflectance of 90% or more for wavelengths between 0.4 μm and 0.5 μm, and a reflectance of 96% or more for wavelengths longer than 0.5 μm. The thickness of the resin material layer is
The wavelength average of the light absorptance at wavelengths of 0.4 μm to 0.5 μm is 13% or less, the wavelength average of the light absorptance at wavelengths of 0.5 μm to 0.8 μm is 4% or less, the wavelength average of the light absorptance at wavelengths of 0.8 μm to 1.5 μm is within 1%, and the wavelength average of the light absorptance at wavelengths of 1.5 μm to 2.5 μm is 40% or less, and
The radiative cooling type air-conditioned clothing according to any one of claims 1 to 5, wherein the thickness is adjusted to a state in which the clothing has thermal radiation characteristics such that the wavelength average of the emissivity from 8 μm to 14 μm is 40% or more. The radiative cooling air-conditioned clothing according to any one of claims 1 to 6, wherein the resin material forming the resin material layer is selected from resin materials having one or more of the following bonds: carbon-fluorine bond, siloxane bond, carbon-chlorine bond, carbon-oxygen bond, ether bond, ester bond, and benzene ring. a main component of a resin material forming the resin material layer is siloxane;
The radiative cooling type air-conditioned clothing according to any one of claims 1 to 6, wherein the resin material layer has a thickness of 1 μm or more. The radiative cooling air-conditioned clothing according to claim 7, wherein the thickness of the resin material layer is 10 μm or more. The radiative cooling type air-conditioned clothing according to any one of claims 1 to 9, wherein the thickness of the resin material layer is 20 mm or less. The radiative cooling type air-conditioned clothing according to claim 10, wherein the resin material forming the resin material layer is a fluororesin or silicone rubber. the resin material forming the resin material layer is a resin material having a main chain made of a hydrocarbon having at least one of a carbon-chlorine bond, a carbon-oxygen bond, an ester bond, an ether bond, and a benzene ring, or a silicone resin having a hydrocarbon side chain with two or more carbon atoms;
The radiative cooling type air-conditioned clothing according to any one of claims 1 to 9, wherein the resin material layer has a thickness of 500 μm or less. The radiative cooling type air-conditioned clothing according to any one of claims 1 to 9, wherein the resin material forming the resin material layer is a blend of a resin containing a carbon-fluorine bond or a siloxane bond, and a resin having a hydrocarbon main chain, and the thickness of the resin material layer is 500 μm or less. the resin material forming the resin material layer is a fluororesin,
The radiative cooling type air-conditioned clothing according to any one of claims 1 to 9, wherein the resin material layer has a thickness of 300 μm or less. the resin material forming the resin material layer is a resin material having at least one of a carbon-chlorine bond, a carbon-oxygen bond, an ester bond, an ether bond, and a benzene ring;
The radiative cooling type air-conditioned clothing according to any one of claims 1 to 9, wherein the resin material layer has a thickness of 50 μm or less. the resin material forming the resin material layer is a resin material having a carbon-silicon bond,
The radiative cooling type air-conditioned clothing according to any one of claims 1 to 9, wherein the resin material layer has a thickness of 10 µm or less. the resin material forming the resin material layer is a vinyl chloride resin or a vinylidene chloride resin,
The radiative cooling type air-conditioned clothing according to any one of claims 1 to 6, wherein the thickness of the resin material layer is 100 μm or less and 10 μm or more. The radiative cooling air-conditioned clothing according to any one of claims 1 to 17, wherein the light-reflecting layer is made of silver or a silver alloy and has a thickness of 50 nm or more. A protective layer is provided between the infrared emitting layer and the light reflecting layer,
the protective layer is made of a polyolefin resin having a thickness of 300 nm or more and 40 μm or less, or a polyethylene terephthalate resin having a thickness of 17 μm or more and 40 μm or less,
The radiative cooling type air-conditioned clothing according to any one of claims 3 to 17, wherein the light reflective layer has a laminated structure of silver or a silver alloy located adjacent to the protective layer and aluminum or an aluminum alloy located away from the protective layer.

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