Radiation cooling cloth, radiation cooling fiber, and method for manufacturing radiation cooling cloth

Abstract

To provide a radiation cooling cloth, a radiation cooling fiber, and a method for manufacturing a radiation cooling cloth which have air permeability, flexibility and radio wave transmitting property, while satisfactorily exhibiting a radiation cooling function.SOLUTION: In a radiation cooling cloth using a radiation cooling film CP in which a first infrared radiation layer J1 as an infrared radiation layer which radiates infrared rays from a first radiation surface H1 and is composed of a resin material adjusted into such a thickness as to emit heat radiation energy larger than absorbed sunlight energy in a band region at a wavelength of 8 μm to 13 μm, and a light reflection layer B positioned opposite to the existence side of the first radiation surface H1 in the first infrared radiation layer J1 are laminated, a radiation cooling fiber S1 obtained by cutting the radiation cooling film CP in a cutting direction along the first radiation surface H1 is woven and formed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a radiative cooling fabric, a radiative cooling fiber, and a method for manufacturing a radiative cooling fabric. [Background technology]

[0002] Radiative cooling technology is known as a measure to adapt to global warming, and can passively lower temperatures outdoors without using external energy. Radiative cooling is a phenomenon in which a material's temperature drops when it emits electromagnetic waves such as infrared rays into its surroundings. By utilizing this phenomenon, it is possible to create radiative cooling materials that can cool objects without consuming energy such as electricity.

[0003] Patent Document 1 discloses a radiative cooling material that is configured by laminating an infrared emitting layer that emits infrared light from its emitting surface and a light reflecting layer that is positioned on the side of the infrared emitting layer opposite to the side where the emitting surface is present.

[0004] Furthermore, Patent Document 2 discloses a base fabric that has radiative cooling properties and is made by impregnating an inorganic filler into the base fabric and molding it.

[0005] Furthermore, Patent Document 3 proposes that, in order to address the energy crisis by raising the temperature settings of air conditioners in offices and the like, the fibers used in clothing should be replaced with fibers that have a relatively high infrared transmittance, instead of cotton or polyester, which do not transmit infrared rays emitted from the human body. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-25313 [Patent Document 2] Patent Publication No. 2021-075031 [Patent Document 3] Special Publication No. 2022-553811 Summary of the Invention [Problem to be solved by the invention]

[0007] The radiative cooling material disclosed in Patent Document 1 has high rigidity and low flexibility, so when applied to clothing as is, it can be uncomfortable to wear and reduce mobility. For this reason, when applied to clothing, it can only be applied to certain immovable parts of the clothing, such as the upper arms and back, which reduces the radiative cooling properties of the clothing as a whole.

[0008] Furthermore, the fabric disclosed in Patent Document 2 has the problem that it is not breathable, so when sweating occurs, the inside becomes stuffy, causing the perceived temperature to rise. Of course, ventilation holes can be provided on the surface of the fabric, but drilling countless ventilation holes with small opening diameters results in the problem of reduced tear strength of the fabric, and providing ventilation holes with large opening diameters impairs the radiative cooling properties of the ventilation hole areas, resulting in a problem of reduced overall radiative cooling properties. For the same reason, the fabric also does not have radio wave transparency.

[0009] Furthermore, the fiber disclosed in Patent Document 3 was developed for the purpose of increasing the transmittance of infrared rays emitted from the human body, and therefore does not have a sufficiently high reflectance of solar radiation, posing a problem that when used outdoors, the temperature rises due to solar radiation.

[0010] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a radiative cooling fabric, a radiative cooling fiber, and a method for manufacturing a radiative cooling fabric that exhibits good radiative cooling performance while also having breathability, flexibility, and radio wave transmittance. [Means for solving the problem]

[0011] The radiative cooling fabric to achieve the above purpose is: A radiative cooling fabric using a radiative cooling film in which a first infrared radiating layer as an infrared radiating layer made of a resin material adjusted to a thickness that radiates infrared light from a first radiating surface and also emits thermal radiation energy greater than absorbed solar light energy in a wavelength band of 8 μm to 13 μm, and a light reflecting layer located on the opposite side of the first radiating surface in the first infrared radiating layer, and its characteristic configuration is as follows: The radiative cooling film is formed by weaving together radiative cooling fibers cut along the cutting direction along the first radiating surface.

[0012] The radiative cooling fabric having the above-mentioned characteristic configuration comprises a first infrared radiating layer made of a resin material adjusted to a thickness that radiates infrared light from a first radiating surface and also emits thermal radiation energy in the wavelength band of 8 μm to 13 μm that is greater than the absorbed solar energy, and a light reflective layer located on the side of the first infrared radiating layer opposite to the first radiating surface. The radiative cooling fabric includes radiative cooling fibers cut along the cutting direction along the first radiating surface. Therefore, compared to fabrics made only of fibers that only have high infrared transmittance as shown in the prior art, the solar radiation reflection performance of the light reflective layer included in the radiative cooling fiber can be improved by appropriately weaving the radiative cooling fiber. As a result, for example, when wearing clothing made of the radiative cooling fabric, temperature rise can be effectively suppressed outdoors during the day when exposed to sunlight. Furthermore, the radiative cooling fabric having the above characteristic configuration is formed by weaving radiative cooling fibers cut to a predetermined fiber width, and therefore, the radiative cooling fabric has a woven fiber structure. This means that the fabric is expected to have improved breathability, radio wave transparency, and flexibility compared to when the radiative cooling film is used as a fabric in its original shape without being fiberized.

[0013] Further characteristic configurations of the radiative cooling fabric are: The radiative cooling film has a second infrared radiation layer on the side of the light reflecting layer opposite to the side where the first infrared radiation layer is present, the second infrared radiation layer being made of a resin material whose thickness is adjusted to emit infrared light from the second radiation surface opposite to the first radiation surface and thermal radiation energy greater than the absorbed solar energy in a wavelength band of 8 μm to 13 μm.

[0014] Now, when the radiative cooling fibers described so far are woven to form a radiative cooling fabric, the front and back of the radiative cooling fiber are reversed due to the twisting of the radiative cooling fiber, so it is preferable that infrared radiation and solar light reflection can be achieved from both the front and back sides. As described above, the radiative cooling film has a second infrared radiation layer on the side opposite to the first infrared radiation layer of the light-reflecting layer, the second infrared radiation layer being made of a resin material and having a thickness adjusted to emit infrared light from the second radiation surface opposite to the first radiation surface and thermal radiation energy greater than the absorbed solar energy in the wavelength band of 8 μm to 13 μm. Therefore, infrared radiation can be effectively radiated from both the first radiation surface, which is one side of the cooling fiber, and the second radiation surface, which is the other side. In addition, light can be reflected from both the surface of the light-reflecting layer facing the first infrared radiation layer and the surface facing the second infrared radiation layer. As a result, it is possible to realize a radiative cooling fabric made of radiative cooling fibers with even higher radiative cooling function.

[0015] Further characteristic configurations of the radiative cooling fabric are: The radiative cooling fiber contains 50% by mass or more, A form containing 1% by mass or more of resin fibers made of a resin that emits infrared light, The feature is that it is formed by weaving together both the radiative cooling fiber and the resin fiber.

[0016] As described above, the fiber contains 1% by mass or more of resin fibers made of a resin containing organic fibers. By appropriately selecting the resin fibers, it is possible to realize a radiative cooling fiber with added breathability, flexibility, and moisture absorption properties.

[0017] Further characteristic configurations of the radiative cooling fabric are: The radiative cooling fiber has a fiber width in a direction perpendicular to the cutting direction of 10 μm or more and 5000 μm or less.

[0018] As in the above characteristic configuration, the fiber width in the direction perpendicular to the cutting direction is preferably set to 10 μm or more and 5000 μm or less. If the fiber width in the direction perpendicular to the cutting direction is less than 10 μm, it is not preferable from the viewpoint of maintaining a certain level of strength of the radiative cooling fiber and because, based on the results of previous tests, the multilayer structure is prone to breakage due to the external force applied when slitting the film. On the other hand, if the fiber width exceeds 5000 μm, the rigidity of the radiative cooling fabric woven with the radiative cooling fiber becomes unnecessarily high, which is also not preferable.

[0019] The radiative cooling fabric that we have explained so far is: By ensuring that the arithmetic mean reflectance, which is the wavelength average of light reflectance in the wavelength range of 400 nm to 800 nm, is 70% or more, the arithmetic mean reflectance, which is the wavelength average of light reflectance in the wavelength range of 800 nm to 1200 nm, is 60% or more, and the wavelength average of emissivity in the wavelength range of 8 μm to 13 μm is 70% or more, a radiative cooling fabric that exhibits appropriate light reflection and radiation functions can be realized.

[0020] The radiative cooling fabric that we have explained so far is: It is preferable that the fiber width of the radiative cooling fiber in a direction perpendicular to the cutting direction is 10 μm or more and 5000 μm or less, and the mesh number of the radiative cooling fiber is 10 mesh or more and 230 mesh or less, It is further preferable that the fiber width of the radiative cooling fiber in a direction perpendicular to the cutting direction is 20 μm or more and 500 μm or less, and the mesh number of the radiative cooling fiber is 20 mesh or more and 150 mesh or less.

[0021] As described above, by setting the number of meshes of the radiative cooling fiber for each fiber width of the radiative cooling fiber, it is possible to realize a radiative cooling fabric that has appropriate flexibility, breathability, radio wave transmittance, and flexibility while properly exhibiting the radiative cooling function and allowing the appropriate number of stitches to be present between the radiative cooling fibers in the radiative cooling fabric.

[0022] Further characteristic configurations of the radiative cooling fabric are: the light-reflecting layer is made of a metal, The radiative cooling film has a protective layer that protects the metal on the side of the light reflecting layer opposite to the side on which the first infrared radiative layer is present, The protective layer is the second infrared emitting layer that emits infrared light from a second emitting surface opposite to the first emitting surface.

[0023] The inventors have confirmed that by constructing the light-reflecting layer from metal, as in the above characteristic configuration, a radiative cooling fabric with a lustrous luster can be achieved. Here, when a metal is used for the light-reflecting layer, it is conceivable that moisture or the like will adhere to the metal, causing oxidation and other deterioration. However, as in the above-described characteristic configuration, by providing a protective layer that protects the metal on the side of the light-reflecting layer opposite the side on which the first infrared radiation layer is present, deterioration of the light-reflecting layer made of metal can be suitably suppressed. Furthermore, as in the above-mentioned characteristic configuration, by using the second infrared radiation layer as the protective layer, which emits infrared light from the second radiation surface opposite to the first radiation surface, the radiative cooling fiber can emit infrared light from both the first radiation surface and the second radiation surface. As a result, the radiative cooling fabric made by knitting the radiative cooling fiber exhibits higher radiative cooling performance than a fabric without the second infrared radiation layer.

[0024] The radiative cooling fabric that we have explained so far is: It is preferable that the radiative cooling fibers and the resin fibers are woven as warp and weft.

[0025] The radiative cooling fabric can be realized by adopting various weaving methods. For example, the radiative cooling fiber and the resin fiber can be used as the warp and the weft to form the radiative cooling fabric. In addition, both the radiative cooling fiber and the resin fiber can be used in a predetermined ratio for the warp, and both the radiative cooling fiber and the resin fiber can be used in a predetermined ratio for the weft. Radiative cooling fabric can also be made by knitting radiative cooling fibers and resin fibers in the length direction of the fibers, connecting the fibers by heating.

[0026] The radiative cooling fabric that we have explained so far is: The light reflecting layer may preferably contain at least one of silver, a silver alloy, aluminum, an aluminum alloy, a copper alloy, and a resin containing a plurality of white fillers. In particular, the inventors have confirmed that a radiative cooling fabric with a lustrous luster can be achieved by constructing the light-reflecting layer from silver, a silver alloy, aluminum, an aluminum alloy, or a copper alloy.

[0027] The radiative cooling fabric that we have explained so far is: The infrared radiation layer can be preferably configured to contain at least one of polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, and polyvinylidene fluoride.

[0028] The radiative cooling fibers explained so far are: A radiative cooling fiber is a radiative cooling film in which a first infrared radiating layer as an infrared radiating layer made of a resin material adjusted to a thickness that radiates infrared light from a first radiating surface and also emits thermal radiation energy greater than absorbed solar energy in a wavelength band of 8 μm to 13 μm, and a light reflecting layer located on the opposite side of the first radiating surface of the first infrared radiating layer, is laminated, and the first infrared radiating layer is cut along a cutting direction along the first radiating surface, and its characteristic configuration is as follows: The fiber width along the first radiation surface is 10 μm or more and 5000 μm or less.

[0029] The radiative cooling fiber can be woven to produce a radiative cooling fabric or the like that exhibits excellent radiative cooling function. Such a radiative cooling fiber can be produced, for example, by cutting a radiative cooling film along the first radiating surface to a sufficiently narrow width using a processing method such as microslit processing.

[0030] The characteristic configuration of the manufacturing method of the radiative cooling cloth to achieve the above object is as follows: a cutting step of cutting a radiative cooling film, which is composed of a first infrared radiating layer made of a resin material adjusted to a thickness that radiates infrared light from a first radiating surface and also emits thermal radiation energy greater than absorbed solar light energy in a wavelength band of 8 μm to 13 μm, and a light reflecting layer located on the opposite side of the first radiating surface in the first infrared radiating layer, along a cutting direction along the first radiating surface, to cut out radiative cooling fibers; and a weaving step of weaving the radiative cooling fibers.

[0031] According to this manufacturing method for radiative cooling cloth, it is possible to successfully manufacture a radiative cooling cloth that exhibits the effects described above.

[0032] A further characteristic configuration of the above manufacturing method is: The radiative cooling fiber contains 50% by mass or more, The feature is that the method includes the step of weaving together the radiative cooling fibers and the resin fibers in a form containing 1 mass % or more of resin fibers made of a resin that radiates infrared light.

[0033] As described above, the fiber contains 1% by mass or more of resin fibers made of a resin containing organic fibers. By appropriately selecting the resin fibers, it is possible to realize a radiative cooling fiber with added breathability, flexibility, and radio wave transparency. [Brief explanation of the drawings]

[0034] [Figure 1] FIG. 1 is a diagram illustrating the manufacturing process of the radiative cooling cloth. [Figure 2] Figure 1 shows a radiative cooling fiber cut from a radiative cooling film and its cross section. [Figure 3] FIG. 1 is a diagram showing the schematic configuration of a radiative cooling cloth. [Figure 4] FIG. 10 is a diagram showing the connection structure of radiative cooling fibers and resin fibers. [Figure 5] 1 is an example of a cross section of a radiative cooling fiber. [Figure 6] 1 is an example of a cross section of a radiative cooling fiber. [Figure 7] FIG. 10 is a diagram showing the relationship between the light absorptance of a resin material and wavelength. [Figure 8] FIG. 1 is a diagram showing the emissivity spectrum of vinyl chloride resin. [Figure 9] FIG. 1 shows the light reflectance spectrum of a silver-based light-reflecting layer. [Figure 10] FIG. 1 is a diagram showing a specific configuration of a radiative cooling film. [Figure 11] FIG. 1 is a diagram showing a specific configuration of a radiative cooling film. [Figure 12] FIG. 1 is a diagram showing a specific configuration of a radiative cooling film. [Figure 13] FIG. 1 is a diagram showing a specific configuration of a radiative cooling film. [Figure 14] FIG. 1 is a diagram showing the relationship between light transmittance and wavelength of polyethylene. [Figure 15] FIG. 1 is a diagram illustrating a test configuration. [Figure 16] FIG. 10 is a diagram showing test results when the protective layer is made of polyethylene. [Figure 17] FIG. 10 is a diagram showing test results when the protective layer is made of ultraviolet absorbing acrylic. [Figure 18] FIG. 1 shows the emissivity spectrum of polyethylene. [Figure 19] FIG. 10 is a diagram showing test results in which a plasticizer is mixed into a vinyl chloride resin. [Figure 20] FIG. 1 is a diagram showing the relationship between wavelength and absorbance of a plasticizer. [Figure 21] FIG. 1 is a diagram showing the relationship between wavelength and absorbance of a plasticizer. [Figure 22] FIG. 1 is a diagram showing the relationship between wavelength and absorbance of a plasticizer. [Figure 23] FIG. 1 is a diagram showing the relationship between wavelength and absorbance of a plasticizer. [Figure 24] FIG. 10 illustrates another configuration of the radiative cooling film. [Figure 25] 10A and 10B are diagrams illustrating a configuration in which a filler is mixed into an infrared radiation layer. [Figure 26] 10A and 10B are diagrams illustrating a configuration in which the front and back surfaces of the infrared radiation layer are uneven. [Figure 27] 10 is a graph showing experimental results. [Figure 28] FIG. 1 is a diagram illustrating a method for evaluating flexibility. DETAILED DESCRIPTION OF THE INVENTION

[0035] The radiative cooling cloth, radiative cooling fiber, and manufacturing method of the radiative cooling cloth according to the embodiments of the present invention exhibit good radiative cooling performance while also having breathability, flexibility, and moisture absorption. Hereinafter, the radiative cooling cloth, radiative cooling fiber, and method for manufacturing the radiative cooling cloth according to the embodiment will be described based on the drawings.

[0036] The radiative cooling fiber S1 according to this embodiment is a radiative cooling fiber S1 using a radiative cooling film CP, which is made of a resin material whose thickness is adjusted to emit infrared light from a first radiation surface H1 and thermal radiation energy greater than the absorbed solar energy in a wavelength band of 8 μm to 13 μm, and a light reflecting layer B located on the opposite side of the first radiation surface H1 of the first infrared radiation layer J1, as shown in Fig. 1 or 2. The radiative cooling fiber S1 is cut along a cutting direction X along the first radiation surface H1. Incidentally, the radiative cooling fiber S1 shown in Fig. 2 has a first protective layer D1 provided between the light reflecting layer B and the first infrared radiation layer J1 as a protective layer D to protect the light reflecting layer B. The radiative cooling cloth HN according to this embodiment is formed by weaving the above-mentioned radiative cooling fiber S1. The detailed configuration of the radiative cooling film CP will be described later.

[0037] The radiative cooling cloth HN is manufactured by a manufacturing method including a cutting process in which the above-mentioned radiative cooling film CP is cut along the cutting direction X along the first radiation surface H1 by a cutting device K as shown in Fig. 1 to cut out the radiative cooling fibers S1, and a weaving process in which the radiative cooling fibers S1 are woven in as shown in Fig. 3.

[0038] To further explain the cutting process, as shown in Figure 1, the cutting device K is equipped with a first circular rotary blade K1 and a second circular rotary blade K2, and both the first rotary blade K1 and the second rotary blade K2 rotate at the same rotational speed to cut the radiative cooling film CP moving along the cutting direction X, thereby cutting the radiative cooling film CP into radiative cooling fibers S1. To explain further, the annular first rotary blade K1 has a plurality of annular blades each having the fiber width of the radiative cooling fiber S1, which are arranged at equal intervals across a first gap of the fiber width of the radiative cooling fiber S1 in a direction perpendicular to the cutting direction X. Furthermore, the annular second rotary blade K2 has a plurality of annular blades each having the fiber width of the radiative cooling fiber S1, which are arranged at equal intervals across a second gap of the fiber width of the radiative cooling fiber S1 in a direction perpendicular to the cutting direction X. The first rotary blade K1 and the second rotary blade K2 are arranged in a direction perpendicular to the cutting direction X, with the multiple annular blades of the first rotary blade K1 positioned in the second gaps of the second rotary blade K2 and the multiple annular blades of the second rotary blade K2 positioned in the first gaps of the first rotary blade K1. Furthermore, the first rotary blade K1 and the second rotary blade K2 are provided with overlapping portions that cut the radiative cooling film CP in a direction perpendicular to the cutting direction X.

[0039] As described above, the radiative cooling fiber S1 cut out from the radiative cooling film CP by the cutting device K preferably has a fiber width in the direction perpendicular to the cutting direction of 10 μm or more and 5000 μm or less, more preferably 300 μm or more and 1000 μm or less.

[0040] It is preferable that the radiative cooling fabric HN into which the radiative cooling fiber S1 is woven has an arithmetic mean reflectance, which is the wavelength average of the light reflectance in the wavelength range of 400 nm to 800 nm, of 70% or more, an arithmetic mean reflectance, which is the wavelength average of the light reflectance in the wavelength range of 800 nm to 1200 nm, of 60% or more, and a wavelength average of the emissivity in the wavelength range of 8 μm to 13 μm, of 70% or more.

[0041] When the fiber width L1 (shown in Figure 2) in the direction perpendicular to the cutting direction X of the radiative cooling fiber S1 is 10 μm or more and 5000 μm or less, the mesh number of the radiative cooling cloth HN is preferably 10 meshes or more and 230 meshes or less, and when the fiber width L1 (shown in Figure 2) in the direction perpendicular to the cutting direction X of the radiative cooling fiber S1 is 20 μm or more and 500 μm or less, the mesh number of the radiative cooling cloth HN is preferably 20 meshes or more and 150 meshes or less.

[0042] In the radiative cooling film CP that becomes the radiative cooling fiber S1, the light reflecting layer B preferably contains at least one of silver, silver alloy, aluminum, aluminum alloy, copper alloy, and resin containing multiple white fillers. In particular, when the light reflecting layer B is made of a metal such as silver, a silver alloy, aluminum, an aluminum alloy, or a copper alloy, it is preferable that the front and back surfaces thereof are protected by a protective layer D. To add further explanation, the radiative cooling film CP preferably comprises the first infrared emitting layer J1, the first protective layer D1, the light reflecting layer B, and the second protective layer D2 in the order listed from the first emitting surface H1 side, as shown in Fig. 5. That is, the radiative cooling film CP has the second protective layer D2 that protects the metal as the light reflecting layer B on the side opposite to the side where the first infrared emitting layer J1 exists of the light reflecting layer B. Here, the second protective layer D2 may function as an infrared emitting layer (an example of a second infrared emitting layer) that emits infrared light from a second emitting surface (not shown in FIG. 5) opposite to the first emitting surface H1. When the second protective layer D2 is made to function as an infrared emitting layer, materials such as acrylic, urethane, vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride can be used. The material and other details of the protective layer D will be described later.

[0043] When the light-reflecting layer B is made of a resin containing multiple white fillers, the white fillers can be made of silicon dioxide (SiO2), titanium oxide (TiO2), aluminum oxide (Al2O3), magnesium oxide (MgO), etc., and the maximum arithmetic mean particle size can be set to be approximately 0.1 μm or more and 10 μm or less. The fillers can be in various shapes, such as spherical, elliptical, or polygonal. The resin that makes up the light-reflecting layer B can be made of vinyl chloride, vinylidene chloride, vinyl fluoride, polyester, polyolefin, acrylic, urethane, silicone, etc.

[0044] Moreover, the radiative cooling film CP that becomes the radiative cooling fiber S1 may be configured to include a second infrared radiative layer J2 in addition to the second protective layer D2, as shown in Fig. 6. To explain further, the radiative cooling film CP may be configured to include, from the first radiation surface H1 side, the first infrared radiation layer J1, the first protective layer D1, the light reflecting layer B, the second protective layer D2, and the second infrared radiation layer J2 as the infrared radiation layer J, in this order, as shown in Fig. 6. In other words, the radiative cooling film CP has, on the side opposite to the side where the first infrared radiation layer J1 exists of the light reflecting layer B, the second infrared radiation layer J2 as the infrared radiation layer J, made of a resin material whose thickness is adjusted to emit infrared light from the second radiation surface H2 opposite to the first radiation surface H1 and emit thermal radiation energy greater than the absorbed solar light energy in the wavelength band from 8 μm to 13 μm. In the cross-sectional view of Fig. 6, the radiative cooling film CP has a first radiation surface H1 on one side opposite to the side where the first protective layer D1 of the first infrared radiative layer J1 exists, and a second radiation surface H2 on the other side opposite to the side where the second protective layer D2 of the second infrared radiative layer J2 exists.

[0045] The first infrared-emitting layer J1 and the second infrared-emitting layer J2, which are the infrared-emitting layers J, are made of a resin material containing at least one of polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, and polyvinylidene fluoride. The details of the infrared-emitting layer J will be described later.

[0046] Now, when the radiative cooling cloth HN has only the first infrared radiation layer J1 as the infrared radiation layer J, for example, as shown in FIG. 2, in other words, when the infrared radiation layer J is present only on one side of the light reflecting layer B and no infrared radiation layer J is present on the other side, sufficient infrared emissivity may not be obtained. Therefore, as shown in Fig. 2, the radiative cooling cloth HN is preferably formed by weaving in, in addition to the radiative cooling fiber S1, resin fiber S2 containing a resin material made of a resin that emits infrared light. The resin material can be made of the same resin as that constituting the infrared radiation layer J. Note that, as shown in Fig. 4, the radiative cooling fiber S1 and the resin fiber S2 may be thermally welded in the longitudinal direction of the fibers and woven into the radiative cooling cloth HN. Specifically, the resin constituting the infrared radiation layer J and the resin fibers S2 preferably contains at least one of polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, and polyvinylidene fluoride.

[0047] Here, the radiative cooling cloth HN may be woven using either the radiative cooling fiber S1 or the resin fiber S2 as the warp and the other as the weft, or may contain both the radiative cooling fiber S1 and the resin fiber S2 in a predetermined ratio in the warp and both the radiative cooling fiber S1 and the resin fiber S2 in a predetermined ratio in the weft. Incidentally, the radiative cooling cloth HN can be woven in various ways, such as plain weave or twill weave. More specifically, the radiative cooling cloth HN is preferably formed by weaving together both the radiative cooling fiber S1 and the resin fiber S2 in a form containing 50% by mass or more, preferably 50% by mass or more and 100% by mass or less of the radiative cooling fiber S1, and 1% by mass or more, preferably 1% by mass or more and 50% by mass or less of the resin fiber S2.

[0048] The resin fibers S2 do not necessarily have to be made of a resin that radiates infrared rays. For example, in order to improve flexibility, materials such as urethane, polyester, and vinyl chloride can be suitably used.

[0049] [Basic structure of radiative cooling film] As shown in Fig. 2, the radiative cooling film CP is formed into a film shape and includes an infrared emitting layer J that emits infrared light IR from an emitting surface H, a light reflecting layer B that is located on the infrared emitting layer J on the side opposite to the side where the emitting surface H exists, and a protective layer D between the infrared emitting layer J and the light reflecting layer B, all stacked together. That is, the radiative cooling film CP is configured as a radiative cooling film.

[0050] The light-reflecting layer B reflects light L, such as sunlight, that has passed through the infrared radiation layer J and the protective layer D. Its reflection characteristics are such that the reflectance at wavelengths of 0.4 μm to 0.5 μm is 90% or more, and the reflectance at wavelengths longer than 0.5 μm is 96% or more. The solar spectrum spans wavelengths from 0.295 μm (295 nm) to 4 μm (4000 nm), with intensity increasing as wavelengths increase from 0.4 μm (400 nm), and is particularly intense from 0.5 μm (500 nm) to 1.8 μm (1800 nm).

[0051] In this embodiment, light L includes ultraviolet light (ultraviolet light), visible light, and infrared light, and when expressed in terms of the wavelength of light as electromagnetic waves, includes electromagnetic waves with wavelengths of 10 nm to 20,000 nm (electromagnetic waves of 0.01 μm to 20 μm). In this specification, the wavelength range of ultraviolet light (ultraviolet light) is defined as a range of 295 nm (0.295 μm) or more and 400 nm (0.4 μm) or less.

[0052] Light-reflecting layer B exhibits a reflectivity of 90% or more in the wavelength range of 0.4 μm to 0.5 μm, and a reflectivity of 96% or more for wavelengths longer than 0.5 μm. This enables the radiative cooling film CP (radiative cooling film) to reduce the solar energy absorbed by light-reflecting layer B to 5% or less. In other words, the solar energy absorbed at noon in summer can be reduced to about 50 W.

[0053] As an example, the light-reflecting layer B is made of silver or a silver alloy, or has a laminated structure of silver or a silver alloy located adjacent to the protective layer D and aluminum or an aluminum alloy located on the side away from the protective layer D (in other words, a laminated structure of silver or a silver alloy located on the side where the infrared radiation layer J is present and aluminum or an aluminum alloy located on the side away from the infrared radiation layer J), and is flexible, the details of which will be described later.

[0054] The infrared radiation layer J is made of a resin material whose thickness is adjusted to emit thermal radiation energy in the wavelength band of 8 μm to 13 μm that is greater than the absorbed solar energy. The infrared radiation layer J will be described in detail later, but in this embodiment, the resin material forming the infrared radiation layer J is vinyl chloride resin mixed with a plasticizer. Note that the resin material forming the infrared radiation layer J may also be vinylidene chloride resin mixed with a plasticizer.

[0055] Therefore, the radiative cooling film CP is configured so that a part of the light L incident on the radiative cooling film CP is reflected by the radiation surface H of the infrared radiation layer J, and the light (sunlight, etc.) that has passed through the resin material constituting the infrared radiation layer J and the protective layer D is reflected by the light reflecting layer B and escapes from the radiation surface H to the outside.

[0056] The radiative cooling film CP is configured to cool an object to be cooled (not shown) located on the opposite side of the light reflecting layer B from the object to be cooled (not shown) (for example, heat input by thermal conduction from the object to be cooled (not shown)), by converting the heat into infrared light IR by the infrared radiative layer J and radiating it.

[0057] That is, the radiative cooling film CP is configured to reflect light L irradiated onto the radiative cooling film CP and to radiate heat transferred to the radiative cooling film CP (e.g., heat transferred from the atmosphere or from the object to be cooled (not shown)) to the outside as infrared light IR. Furthermore, the infrared emitting layer J, the protective layer D, and the light reflecting layer B are flexible, so that the radiative cooling film CP (radiative cooling film) is configured to be flexible.

[0058] In addition, the radiative cooling film CP is used to implement a radiative cooling method in which infrared light IR is radiated from a radiation surface H on the opposite side of the surface of the infrared emitting layer J that is in contact with the light reflecting layer B. Specifically, the radiation surface H is directed toward the sky, and the radiative cooling method is implemented in which infrared light IR is radiated from the radiation surface H that faces the sky.

[0059] [Outline of infrared radiation layer] The light absorptivity and emissivity (light emissivity) of the resin material (vinyl chloride resin) that forms the infrared radiation layer J change depending on the thickness. Therefore, it is necessary to adjust the thickness of the resin material so that it absorbs as little sunlight as possible and emits large thermal radiation in the so-called atmospheric window wavelength band (wavelength band from 8 μm to 13 μm).

[0060] Specifically, from the perspective of the light absorptance of sunlight, the thickness of the infrared radiation layer J needs to be adjusted to a thickness such that the wavelength average light absorptance from 0.4 μm to 0.5 μm is 13% or less, the wavelength average light absorptance from 0.5 μm to 0.8 μm is 4% or less, the wavelength average light absorptance from 0.8 μm to 1.5 μm is within 1%, the wavelength average light absorptance from 1.5 μm to 2.5 μm is 40% or less, and the wavelength average light absorptance from 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 100W or less in terms of energy.

[0061] As will be explained later, the light absorption rate of resin material increases as the resin material film thickness increases. When the resin material is made thick, the emissivity of the atmospheric window becomes almost 1, and the thermal radiation emitted into space at that time is 125 W / m 2 to 160 W / m 2 The solar light absorption in the protective layer D and the light-reflecting layer B is 50 W / m 2The sum of the solar absorption of the infrared emitting layer J, the protective layer D, and the light reflecting layer B is 150 W / m 2 As described above, it is preferable to use a resin material for forming the infrared radiation layer J that has a small light absorption rate near the peak value of the solar spectrum.

[0062] Furthermore, from the viewpoint of infrared radiation (thermal radiation), the thickness of the infrared radiation layer J needs to be adjusted to a thickness such that the wavelength average of the emissivity in the wavelength range of 8 μm to 13 μm is 40% or more. 50W / m absorbed by protective layer D and light-reflecting layer B 2 In order to radiate the same amount of thermal energy from sunlight into space from infrared radiation layer J, infrared radiation layer J must emit more thermal radiation than that. For example, when the outside temperature is 30°C, the maximum thermal radiation of the atmospheric window between 8 μm and 13 μm is 200 W / m 2 (calculated with an emissivity of 1). This value can be obtained on clear days in dry environments with thin air, such as high mountains. In lowlands, the atmosphere is thicker than in high mountains, so the wavelength band of the atmospheric window narrows and the transmittance decreases. Incidentally, this is called "the atmospheric window narrowing."

[0063] In addition, the environment in which the radiative cooling film CP (radiative cooling film) is actually used may be humid, and in that case the atmospheric window will be narrow. When used in lowlands, the thermal radiation generated in the atmospheric window area is 160 W / m at 30°C under good conditions. 2 (calculated with an emissivity of 1). When there is haze or smog in the sky, which is common in Japan, the atmospheric window becomes even narrower, and radiation into space is estimated at 125 W / m 2 It will be about that amount. In consideration of this situation, the wavelength average of the emissivity of wavelengths from 8 μm to 13 μm is set to 40% or more (thermal radiation intensity in the atmospheric window band is 50 W / m 2 ) it cannot be used in low altitude areas of the mid-latitudes.

[0064] Therefore, if the thickness of the infrared radiation layer J is adjusted so that it falls within the optically specified range taking the above points into consideration, the heat output at the atmospheric window will be greater than the heat input due to the absorption of sunlight, and it will be possible to cool the temperature below the outside air by radiative cooling outdoors even in a solar radiation environment. In this embodiment, the thickness of the infrared radiation layer J made of vinyl chloride resin is 100 μm or less and 10 μm or more.

[0065] [Details of resin material] According to Kirchhoff's law, the emissivity (ε) and the light absorptance (A) are equal. The light absorptance can be calculated from the absorption coefficient (α) using the following formula (1) (hereinafter sometimes referred to as the light absorptance relational equation): A=1-exp(-αt) (1) where t is the film thickness. In other words, by adjusting the film thickness of the infrared radiation layer J, it is possible to obtain a large thermal radiation in a wavelength band with a large absorption coefficient. When performing radiative cooling outdoors, it is recommended to use a material with a large absorption coefficient in the wavelength band of 8 μm to 13 μm, which is the atmospheric window. In addition, to suppress the absorption of sunlight, it is advisable to use a material that has no or a small absorption coefficient in the wavelength range of 0.3 μm to 4 μm, especially in the range of 0.4 μm to 2.5 μm. As can be seen from the relationship between the absorption coefficient and absorptance, the light absorptance (emissivity) changes depending on the film thickness of the resin material.

[0066] In order to lower the temperature below the surrounding atmosphere through radiative cooling in a solar radiation environment, if a material is selected that has a large absorption coefficient in the wavelength band of the atmospheric window and almost no absorption coefficient in the wavelength band of sunlight, then by adjusting the film thickness, it will absorb almost no sunlight but emit a lot of thermal radiation from the atmospheric window, meaning that it is possible to create a state in which the output from radiative cooling is greater than the input of sunlight.

[0067] The solar spectrum only contains wavelengths longer than 0.295 μm. Note that ultraviolet light is defined as the range of wavelengths shorter than 0.4 μm, visible light is defined as the range of wavelengths from 0.4 μm to 0.8 μm, near-infrared light is defined as the range of wavelengths from 0.8 μm to 3 μm, mid-infrared light is defined as the range of wavelengths from 3 μm to 8 μm, and far-infrared light is defined as the range of wavelengths longer than 8 μm.

[0068] Regarding the carbon-chlorine bond (C-Cl), the bond energy between carbon and chlorine in alkenes is 3.28 eV, and the wavelength is 0.378 μm, so they absorb a lot of ultraviolet light in sunlight, but have almost no absorption in the visible range. Figure 7 shows the absorption spectrum of a 100 μm thick vinyl chloride resin in the ultraviolet to visible region, and shows that light absorption increases at wavelengths shorter than 0.38 μm.

[0069] Figure 8 shows the emissivity of polyvinyl chloride (PVC), a resin with carbon-chlorine bonds, at the atmospheric window. Regarding the carbon-chlorine bond, the absorption coefficient due to the C-Cl stretching vibration appears in a broad band with a half-width of 1 μm or more centered at a wavelength of 12 μm. In addition, in the case of polyvinyl chloride resin, due to the electron-withdrawing effect of chlorine, an absorption coefficient originating from the bending vibration of CH of the alkene contained in the main chain appears at a wavelength of around 10 μm. Due to these effects, the wavelength average of the emissivity for a 10 μm thick film is 43% at wavelengths from 8 μm to 13 μm, which falls within the wavelength average of 40% or more. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

[0070] The thermal radiation of the atmospheric window of the infrared radiation layer J occurs near the surface of the resin material. As shown in Figure 8, in the case of vinyl chloride resin, even if the thickness exceeds 100 μm, there is almost no increase in thermal radiation in the atmospheric window region. In other words, in the case of vinyl chloride resin, thermal radiation in the atmospheric window occurs within a depth of approximately 100 μm from the surface, and radiation from deeper parts does not escape to the outside.

[0071] As described above, the thermal radiation from the surface of the resin material in the atmospheric window region occurs within a depth of approximately 100 μm from the surface. If the resin thickness increases beyond this, the cold generated by the radiative cooling film CP is insulated by the resin material, which does not contribute to thermal radiation. Consider fabricating an infrared emitting layer J, which ideally does not absorb any sunlight, on top of a light-reflecting layer B. In this case, sunlight is absorbed only by the light-reflecting layer B of the radiative cooling film CP. The thermal conductivity of resin materials is generally about 0.2 W / m / K. When this thermal conductivity is taken into account, calculations show that if the thickness of the infrared radiation layer J exceeds 20 mm, the temperature of the cooling surface (the surface of the light-reflecting layer B opposite to the side where the infrared radiation layer J is present) will rise.

[0072] Even if an ideal resin material that does not absorb sunlight at all exists, the thermal conductivity of resin materials is generally about 0.2 W / m / K, so if the thickness exceeds 20 mm, the light-reflecting layer B will be heated by solar radiation, and the object to be cooled (not shown) placed on the light-reflecting layer side will be heated. In other words, the thickness of the resin material of the radiative cooling film CP needs to be 20 mm or less.

[0073] [Thickness of the infrared radiation layer] From the viewpoint of practical use of the radiative cooling film CP, it is better for the infrared radiative layer J to be thin. The thermal conductivity of resin materials is generally lower than that of metals, glass, etc. To effectively cool the object to be cooled, it is better for the thickness of the infrared radiative layer J to be the minimum necessary. The thicker the infrared radiative layer J is, the greater the thermal radiation from the atmospheric window becomes, and once the thickness exceeds a certain value, the thermal radiation energy at the atmospheric window becomes saturated.

[0074] The saturation film thickness depends on the resin material, but in the case of resins containing carbon-chlorine bonds, saturation occurs even at a thickness of 100 μm, and sufficient heat radiation can be obtained in the atmospheric window region even at a thickness of 50 μm. The thinner the resin material, the higher the thermal conductivity and the more effectively the temperature of the object being cooled can be lowered, so in the case of resins containing carbon-chlorine bonds, a thickness of 50 μm or less reduces the insulating properties and allows the object to be cooled effectively. In the case of carbon-chlorine bonds, a thickness of 100 μm or less allows the object to be cooled effectively.

[0075] The benefit of making the film thinner is not just that it reduces heat insulation and makes it easier to transfer cold. It also reduces the absorption of near-infrared light from CH, CH2, and CH3, which are present in resins containing carbon-chlorine bonds. By making the film thinner, the amount of sunlight absorbed by these compounds can be reduced, which increases the cooling capacity of the radiative cooling film CP. From the above perspective, in the case of vinyl chloride resin, which is a resin containing carbon-chlorine bonds, a thickness of 50 μm or less can more effectively produce a radiative cooling effect under sunlight.

[0076] [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 infrared emitting layer J exists) must be silver or a silver alloy. As shown in FIG. 9, if the light-reflecting layer B is made of silver as a base, the reflectance required for the light-reflecting layer B can be obtained.

[0077] 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 copper, palladium, gold, zinc, tin, magnesium, nickel, or titanium is added to silver in an amount of, for example, about 0.4% to 4.5% by mass. A specific example is "APC-TR (made by Furuya Metal)," a silver alloy made by adding copper and palladium to silver.

[0078] In order to provide the light-reflecting layer B with the above-mentioned reflectance characteristics, it may have a structure 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 radiation surface H exists (the side where the infrared radiation layer J exists) must be silver or a silver alloy. When the film is made up of two layers of silver (silver alloy) and aluminum (aluminum alloy), the thickness of the silver must be 10 nm or more, and the thickness of the aluminum 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 will be difficult to bend.

[0079] Incidentally, as an "aluminum alloy," an alloy in which copper, manganese, silicon, magnesium, zinc, carbon steel for mechanical structures, yttrium, lanthanum, gadolinium, or terbium is added to aluminum can be used.

[0080] Silver and silver alloys are vulnerable to rain and humidity and need to be protected from these and to prevent discoloration. For this reason, a protective layer D is required to protect the silver, and is placed adjacent to the silver or silver alloy, as shown in Figures 5 to 8. The protective layer D will be described in detail later.

[0081] [Plasticizer details] The plasticizer mixed into the vinyl chloride resin that forms the infrared emitting layer J is one or more compounds selected from the group consisting of phthalate esters, aliphatic dibasic acid esters, and phosphate esters. The plasticizer is mixed in an amount of 1 part by weight or more and 200 parts by weight or less with respect to 100 parts by weight of the vinyl chloride resin. From the viewpoint of processing, the weight part of the plasticizer is preferably 100 parts by weight or less.

[0082] The aliphatic dibasic acid ester as a plasticizer may be composed of one or more compounds selected from the group consisting of adipic acid esters, adipic acid ester copolymers, azelaic acid esters, azelaic acid ester copolymers, sebacic acid esters, sebacic acid ester copolymers, succinic acid esters, and succinic acid ester copolymers.

[0083] The aliphatic dibasic acid ester as the plasticizer is preferably an aliphatic dibasic acid and two molecules of a saturated aliphatic alcohol bonded together via an ester bond. The phthalate ester of the plasticizer is preferably formed by ester bonding between phthalic acid and two molecules of a saturated aliphatic alcohol. The phosphate ester as the plasticizer may be a phosphate triester or an aromatic phosphate ester.

[0084] <Details of phthalate esters> The phthalate esters are listed below. Dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DPP), di-2-ethylhexyl phthalate (DOP), diisononyl phthalate (DINP), diisodecyl phthalate (DIDP), diundecyl phthalate (DUP), ditridecyl phthalate (DTDP), bis(2-ethylhexyl) terephthalate (DOTP), bis(2-ethylhexyl) isophthalate (DOIP), etc.

[0085] <Details of aliphatic dibasic acid esters> The aliphatic dibasic acid esters are listed below. Dibutyl adipate (DBA), diisobutyl adipate (DIBA), di-2-ethylhexyl adipate (DOA), diisononyl adipate (DINA), diisodecyl adipate (DIDA), bis-2-ethylhexyl azelaate (DOZ), dibutyl sebacate (DBS), di-2-ethylhexyl sebacate (DOS), diisononyl sebacate (DINS), diethyl succinate (DESU), and the like. Also, an aliphatic polyester having a molecular weight of 400 to 4000 synthesized by copolymerization (polyesterification) of a dibasic acid such as adipic acid with a diol (difunctional alcohol or glycol).

[0086] <Phosphate triester> The phosphoric acid triesters are listed below. Trimethyl phosphate (TMP), triethyl phosphate (TEP), tributyl phosphate (TBP), tris(2-ethylhexyl) phosphate (TOP).

[0087] <Aromatic phosphate ester> The aromatic phosphate esters are listed below. Triphenyl phosphate (TPP), tricresyl phosphate (TCP), trixylenyl phosphate (TXP), tresyl diphenyl phosphate (CDP), 2-ethylhexyl diphenyl phosphate.

[0088] <Evaluation of appropriate plasticizers> Plasticizers for vinyl chloride resin include phthalate esters, aliphatic dibasic acid esters, phosphate triesters, aromatic phosphate esters, trimellitic acid esters, and epoxidized fatty acid esters. The following compounds were selected from these plasticizers, and 43 parts by weight of each plasticizer was mixed with 100 parts by weight of vinyl chloride and evaluated using a xenon weather test. The vinyl chloride resin was mixed with 0.5 parts by weight of a triazine-based ultraviolet absorber and a hindered amine-based light stabilizer per 100 parts by weight of vinyl chloride.

[0089] Representative phthalate esters include di-2-ethylhexyl phthalate (DOP) and diisodecyl phthalate (DIDP). Representative aliphatic dibasic acid esters include di-2-ethylhexyl adipate (DOA), butanediol adipate copolymer (average molecular weight of about 1000), and diisononyl adipate (DINA). A representative phosphate triester is tributyl phosphate (TBP). Tricresyl phosphate (TCP) is a representative aromatic phosphate ester. A representative trimellitic acid ester is tri-2-ethylhexyl trimellitate (TOTM). Epoxidized soybean oil is a representative example of epoxidized fatty acid esters.

[0090] Durability tests were conducted using a xenon weather test for 1,920 hours (equivalent to four years of actual exposure), and the results were used to determine the superiority or inferiority of durability. Note that 487 hours is equivalent to one year of UV exposure. The conditions for the xenon weather test are as follows: UV intensity 180W / m 2 (wavelength 295-400nm). <Conditions without watering> BPT 89℃, humidity 50%, 1 hour 42 minutes. <Conditions with watering> Tank temperature 38°C, humidity 90%, 18 minutes.

[0091] The test results for 1920 hours are shown in Figure 19. Incidentally, although the experiment was conducted using vinyl chloride resin in this embodiment, the same results were obtained with vinylidene chloride resin. The results of the above experiment revealed that durability was significantly reduced when trimellitic acid ester (TOTM) and epoxidized fatty acid ester (epoxidized soybean oil) were used as plasticizers. Note that epoxidized fatty acid turned brown after 1,120 hours, making it impossible to continue the test, so it is not shown in the figure.

[0092] In contrast, it was found that when phthalate esters, aliphatic dibasic acid esters, phosphate triesters, or aromatic phosphate esters were used as plasticizers to be mixed into the vinyl chloride resin, the reflectance of the radiative cooling film CP did not decrease even after about four years, but when trimellitate esters or epoxidized fatty acid esters were used as plasticizers to be mixed into the vinyl chloride resin, the reflectance of the radiative cooling film CP decreased significantly even before about four years had passed.

[0093] The above test results show that phthalate esters, aliphatic dibasic acid esters, phosphate triesters, and aromatic phosphate esters are excellent in durability as plasticizers for vinyl chloride resins, while trimellitate esters and epoxidized fatty acid esters are not durable. The reason for this will be discussed later.

[0094] [Other additives] The vinyl chloride resin forming the infrared radiation layer J may contain a flame retardant, a stabilizer, a stabilizing aid, a filler, an antioxidant, an ultraviolet absorber, and a light stabilizer. <Flame retardant> Examples of flame retardants include inorganic compounds such as aluminum hydroxide, antimony trioxide, magnesium hydroxide, and zinc borate, phosphorus compounds such as cresyl diphenyl phosphate, trischloroethyl phosphate, trischloropropyl phosphate, and trisdichloropropyl phosphate, and halogen compounds such as chlorinated paraffin, etc. The amount of flame retardant to be blended per 100 parts by weight of vinyl chloride resin is about 0.1 to 20 parts by weight.

[0095] <Stabilizer> Examples of stabilizers include metal soap compounds such as lithium stearate, magnesium stearate, magnesium laurate, calcium ricinoleate, calcium stearate, barium laurate, barium ricinoleate, barium stearate, zinc octoate, zinc laurate, zinc ricinoleate, and zinc stearate, organotin compounds such as dimethyltin bis-2-ethylhexylthioglycolate, dibutyltin maleate, dibutyltin bisbutylmaleate, and dibutyltin dilaurate, and antimony mercaptide compounds. The amount of stabilizer blended per 100 parts by weight of vinyl chloride resin is about 0.1 to 20 parts by weight.

[0096] <Stabilizing agent> Examples of stabilizing aids include phosphite compounds such as triphenyl phosphite, monooctyldiphenyl phosphite, tridecyl phosphite, etc., beta-diketone compounds such as acetylacetone, benzoylacetone, etc., polyol compounds such as glycerin, sorbitol, pentaerythritol, polyethylene glycol, etc., perchlorate compounds such as barium perchlorate, sodium perchlorate, etc., hydrotalcite compounds, zeolites, etc. The amount of stabilizing aid to be blended per 100 parts by weight of vinyl chloride resin is about 0.1 to 20 parts by weight.

[0097] <Filler> Examples of fillers include calcium carbonate, silica, alumina, clay, talc, diatomaceous earth, ferrite and other metal oxides, glass, carbon, metal fibers and powders, glass spheres, graphite, aluminum hydroxide, barium sulfate, magnesium oxide, magnesium carbonate, magnesium silicate, calcium silicate, etc. The amount of filler to be blended per 100 parts by weight of vinyl chloride resin is about 1 to 100 parts by weight.

[0098] <Antioxidants> Examples of antioxidants include phenolic compounds such as 2,6-di-tert-butylphenol, tetrakis[methylene-3-(3,5-tert-butyl-4-hydroxyphenol)propionate]methane, and 2-hydroxy-4-methoxybenzophenone; sulfur compounds such as alkyl disulfides, thiodipropionic acid esters, and benzothiazole; phosphoric acid compounds such as trisnonylphenyl phosphite, diphenylisodecyl phosphite, triphenyl phosphite, and tris(2,4-di-tert-butylphenyl)phosphite; and organometallic compounds such as zinc dialkyldithiophosphate and zinc diaryldithiophosphate. The amount of antioxidant to be blended per 100 parts by weight of vinyl chloride resin is approximately 0.2 to 20 parts by weight.

[0099] <UV absorber> Examples of ultraviolet absorbers include salicylate compounds such as phenyl salicylate and p-tert-butylphenyl salicylate, benzophenone compounds such as 2-hydroxy-4-n-octoxybenzophenone and 2-hydroxy-4-n-methoxybenzophenone, benzotriazole compounds such as 5-methyl-1H-benzotriazole and 1-dioctylaminomethylbenzotriazole, as well as cyanoacrylate compounds, triazine compounds, etc. The amount of ultraviolet absorber to be blended per 100 parts by weight of vinyl chloride resin is about 0.1 to 10 parts by weight.

[0100] <Light stabilizer> Light stabilizers include bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate and methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate (mixture), bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate, decanedioic acid bis(2,2,6,6-tetramethyl-1(octyloxy)phenyl]methyl, methyl methyl methyl malonate, methyl ... (ii)-4-piperidyl) esters and reaction products of 1,1-dimethylethyl hydroperoxide with octane, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, ester mixtures of 2,2,6,6-tetramethyl-4-piperidinol and higher fatty acids, tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate Xylate, polycondensation polymer of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol, poly[{(6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl){(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}}, dibutylamine·1,3,5-triazine·N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)imino Examples of the light stabilizer include a polycondensate of N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine and a hindered amine such as N,N',N'',N'''-tetrakis-(4,6-bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidin-4-yl)amino)-triazin-2-yl)-4,7-diazadecane-1,10-diamine. The amount of the light stabilizer to be blended per 100 parts by weight of the vinyl chloride resin is about 0.1 to 10 parts by weight.

[0101] [Specific configuration of radiative cooling film] The radiative cooling film CP of the present invention can be made into a film structure as shown in Figures 10 to 13. Because the resin materials forming the infrared emitting layer J and the protective layer D are flexible, when the light reflecting layer B is made thin, the light reflecting layer B can also be made flexible, and as a result, the radiative cooling film CP can be made into a flexible film (radiative cooling film).

[0102] The film-type radiative cooling film CP (radiative cooling film) can be attached to existing objects with adhesive and wrapped around the outside of a car, the outer wall of a warehouse or building, or the outside of a helmet to provide radiative cooling, making it easy to demonstrate radiative cooling capabilities. The film-type radiative cooling film CP (radiative cooling film) can be attached to various objects that require cooling, such as the outer surfaces of various tents, the outer surfaces of boxes that store electrical equipment, the outer surfaces of containers for transporting goods, the outer surfaces of milk tanks that store milk, and the outer surfaces of the milk storage sections of milk tanker trucks.

[0103] There are various ways to fabricate the radiative cooling film CP. For example, it can be fabricated by coating a protective layer D and an infrared-emitting layer J on a light-reflecting layer B fabricated in film form. Alternatively, it can be fabricated by attaching a protective layer D and an infrared-emitting layer J to a light-reflecting layer B fabricated in film form. Alternatively, it can be fabricated by coating or attaching a protective layer D on an infrared-emitting layer J fabricated in film form, and then fabricating a light-reflecting layer B on the protective layer D by vapor deposition, sputtering, ion plating, silver mirror reaction, etc.

[0104] Specifically, the radiative cooling film CP in Fig. 10 has a light-reflecting layer B formed as a single layer of silver or silver alloy, or two layers of silver (silver alloy) and aluminum (aluminum alloy), and has a protective layer D formed on the upper side of the light-reflecting layer B, and an infrared radiative layer J formed on the protective layer D. In addition, a lower protective layer Ds is also formed below the light-reflecting layer B.

[0105] The radiative cooling film CP (radiative cooling film) in Fig. 10 can be fabricated by sequentially applying a protective layer D, a light-reflecting layer B, and a lower protective layer Ds onto a film-like infrared radiative layer J, and molding them into an integrated structure.

[0106] The radiative cooling film CP (radiative cooling film) in Fig. 11 has a light-reflecting layer B composed of an aluminum layer B1 made of aluminum foil that functions as aluminum (aluminum alloy) and a silver layer B2 made of silver or a silver alloy, a protective layer D formed on the upper side of the light-reflecting layer B, and an infrared-radiative layer J formed on top of the protective layer D.

[0107] The radiative cooling film CP (radiative cooling film) in Fig. 11 can be fabricated by sequentially applying a silver layer B2, a protective layer D, and an infrared radiative layer J on an aluminum layer B1 made of aluminum foil, and molding them into an integrated structure. Alternatively, an alternative manufacturing method may be employed in which the infrared emitting layer J is formed into a film, a protective layer D and a silver layer B2 are successively applied onto the film-like infrared emitting layer J, and an aluminum layer B1 is attached to the silver layer B2.

[0108] The radiative cooling film CP (radiative cooling film) in Fig. 12 is configured such that the light-reflecting layer B is formed as a single layer of silver or silver alloy, or as two layers of silver (silver alloy) and aluminum (aluminum alloy), a protective layer D is formed on the upper side of the light-reflecting layer B, an infrared-radiative layer J (transparent resin film) is formed on top of the protective layer D, and a film layer F such as PET is formed under the light-reflecting layer B.

[0109] The radiative cooling film CP (radiative cooling film) in Fig. 12 can be fabricated by sequentially coating a light-reflecting layer B and a protective layer D on a film layer F (corresponding to the substrate) formed into a film shape using PET (ethylene terephthalate resin) or the like, and integrally molding them. Then, a separately formed film-shaped infrared radiative layer J is bonded (adhered) to the protective layer D with an adhesive layer N (an example of a bonding layer). The adhesive (pressure-sensitive adhesive) used in the glue layer N may be, for example, a urethane-based adhesive (pressure-sensitive adhesive), an acrylic-based adhesive (pressure-sensitive adhesive), or an EVA (ethylene vinyl acetate)-based adhesive (pressure-sensitive adhesive), and it is desirable for it to be highly transparent to sunlight.

[0110] The radiative cooling film CP (radiative cooling film) in Fig. 13 has a light-reflecting layer B 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), and the aluminum layer B1 is formed on top of a film layer F (corresponding to the substrate) made of PET (ethylene terephthalate resin) or the like. A protective layer D is formed on the silver layer B2, and an infrared radiative layer J (transparent resin film) is formed on top of the protective layer D.

[0111] The radiative cooling film CP (radiative cooling film) in Fig. 13 can be fabricated by applying an aluminum layer B1 on a film layer F to integrally form the film layer F and the aluminum layer B1, separately applying a protective layer D and a silver layer B2 on a film-like infrared radiative layer J to integrally form the infrared radiative layer J, the protective layer D, and the silver layer B2, and then bonding the aluminum layer B1 and the silver layer B2 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), or an EVA (ethylene vinyl acetate)-based adhesive (pressure-sensitive adhesive), and it is desirable for it to be highly transparent to sunlight.

[0112] [Details of the 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.

[0113] Figure 7 shows the ultraviolet absorption rates of polyethylene, vinylidene chloride resin, ethylene terephthalate resin, and vinyl chloride resin. FIG. 14 shows the light transmittance of polyethylene, which is suitable as the synthetic resin for forming the protective layer D.

[0114] The radiative cooling film CP (radiative cooling film) exerts its radiative cooling effect not only at night but also under sunlight. 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 under sunlight.

[0115] When the protective layer D is formed from a polyolefin resin with a thickness of 300 nm or more and 40 μm or less, the 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 to 0.4 μm, and therefore the protective layer D is less likely to deteriorate due to absorption of ultraviolet rays.

[0116] Furthermore, since the thickness of the polyolefin resin forming the protective layer D is 300 nm or more, it effectively exhibits a blocking function, such as blocking radicals generated in the infrared emitting layer J from reaching the silver or silver alloy forming the light reflecting layer, and blocking moisture that penetrates the infrared emitting layer J from reaching the silver or silver alloy forming the light reflecting layer B, thereby suppressing discoloration of the silver or silver alloy forming the light reflecting layer B.

[0117] Incidentally, the protective layer D made of polyolefin resin deteriorates by absorbing ultraviolet rays, forming radicals on the surface side away from the light-reflecting layer B. However, since the thickness is 300 nm or more, the formed radicals do not reach the light-reflecting layer. Furthermore, even if the protective layer D deteriorates by forming radicals, the rate of deterioration is slow due to the low absorption of ultraviolet rays, so the above-mentioned blocking function can be maintained for a long period of time.

[0118] When the protective layer D is formed from ethylene terephthalate resin to a thickness of 17 μm or more and 40 μm or less, ethylene terephthalate resin is a synthetic resin that has a higher ultraviolet light absorption rate than polyolefin resin in the ultraviolet wavelength range of 0.3 to 0.4 μm. However, since the thickness is 17 μm or more, the protective layer D effectively exhibits blocking functions for a long period of time, such as blocking radicals generated in the infrared emitting layer J from reaching the silver or silver alloy that forms the light reflective layer B and blocking moisture that penetrates the infrared emitting layer J from reaching the silver or silver alloy that forms the light reflective layer, and thus suppressing discoloration of the silver or silver alloy that forms the light reflective layer B.

[0119] In other words, the protective layer made of ethylene terephthalate resin deteriorates as it absorbs ultraviolet rays, forming radicals on the surface side away from the light-reflecting layer B. However, since the thickness is 17 μm or more, the formed radicals do not reach the reflective layer. Furthermore, even if the protective layer deteriorates while forming radicals, the thickness is 17 μm or more, so the above-mentioned blocking function can be maintained for a long period of time.

[0120] To explain further, the deterioration of ethylene terephthalate resin (PET) is caused by ultraviolet light cleaving the ester bond between ethylene glycol and terephthalic acid, forming radicals. This deterioration progresses from the surface of the PET that is exposed to ultraviolet light.

[0121] For example, when ethylene terephthalate resin (PET) is irradiated with ultraviolet rays of the intensity found in Osaka, the ester bonds of the PET are cleaved by approximately 9 nm per day, starting from the irradiated surface. Because the ethylene terephthalate resin (PET) is sufficiently polymerized, the cleaved ethylene terephthalate resin (PET) on the surface does not attack the silver (silver alloy) of light-reflecting layer B. However, if the cleaved end of the ethylene terephthalate resin (PET) reaches the silver (silver alloy) of light-reflecting layer B, the silver (silver alloy) will discolor.

[0122] Therefore, for outdoor use, in order for protective layer D to last for one year or more, a thickness of approximately 3 μm is required, calculated by multiplying 9 nm / day by 365 days. In order for the ethylene terephthalate resin (PET) of protective layer D to last for three years or more, a thickness of 10 μm or more is required. In order for it to last for five years or more, a thickness of 17 μm or more is required.

[0123] When the protective layer D is formed of a polyolefin resin and an ethylene terephthalate resin, the reason for setting an upper limit on the thickness is to prevent the protective layer D from exhibiting heat insulating properties that do not contribute to radiative cooling. In other words, the thicker the protective layer D, the more heat insulating properties it exhibits that do not contribute to radiative cooling. Therefore, an upper limit on the thickness is set to prevent the protective layer D from exhibiting heat insulating properties that do not contribute to radiative cooling while still functioning as a protector for the light reflecting layer B.

[0124] As shown in Figure 12, when a glue layer N is located between the infrared radiation 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.

[0125] As mentioned above, if the protective layer D is made thicker, there is no disadvantage in terms of preventing coloration of the silver (silver alloy) in the light-reflecting layer B, but it does cause problems in terms of radiative cooling. In other words, if the protective layer D is made thicker, the heat insulating properties of the radiative cooling material will increase. 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 18, so even if it is formed thickly, it does not contribute to radiative cooling. On the contrary, making it thicker actually increases the insulating properties of the radiative cooling material. Next, as the thickness increases, absorption in the near-infrared region due to the vibration of the main chain increases, increasing the effect of increasing solar absorption. Due to these factors, a thick protective layer D is disadvantageous for radiative cooling. From this perspective, the thickness of the protective layer D made of a polyolefin resin is preferably 5 μm or less, and more preferably 1 μm or less.

[0126] [Considerations on the protective layer] In order to examine the difference in how the protective layer D colored silver, a sample was prepared in which the protective layer D was exposed but did not include the infrared-emitting layer J, as shown in FIG. 15 , and the coloring of the silver after being irradiated with simulated sunlight was examined. That is, two types of protective layer D were prepared by applying, with a bar coater, two types of materials: a general acrylic resin that absorbs ultraviolet light (for example, a methyl methacrylate resin mixed with a benzotriazole-based ultraviolet absorber) and polyethylene onto a film layer F (corresponding to the substrate) containing silver as a light-reflecting layer B, to form samples, and their function as 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.

[0127] As shown in Figure 17, if the protective layer D is made of acrylic resin, which has good UV absorption, the protective layer D is decomposed by UV to form radicals, and the silver quickly turns yellow, causing it to no longer function as a radiative cooling film CP (it absorbs sunlight and, like general materials, its temperature rises when exposed to sunlight). The 600h line in the figure indicates the results of a xenon weather test (ultraviolet light energy 60W / m) under the conditions of JIS standard 5600-7-7. 2 The reflectance spectrum after 600 hours of xenon weathering is shown in Fig. 1. The 0h line is the reflectance spectrum before the xenon weathering test.

[0128] As shown in Figure 21, when protective layer D is made of polyethylene, which has low ultraviolet light absorption, no decrease in reflectance is observed from the near-infrared region to the visible region. In other words, resins whose main component is polyethylene (polyolefin resins) hardly absorb the ultraviolet light contained in sunlight that reaches the ground, and therefore do not easily form radicals even when exposed to sunlight, so coloring of the silver serving as light-reflecting layer B does not occur even when exposed to sunlight. The 600h line in the figure indicates the results of a xenon weather test (ultraviolet light energy 60W / m) under the conditions of JIS standard 5600-7-7. 2 The reflectance spectrum after 600 hours of xenon weathering is shown in Fig. 1. The 0h line is the reflectance spectrum before the xenon weathering test.

[0129] The reason for the undulations in the reflectance spectrum in this wavelength range is 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 changes slightly between the 0h line and the 600h line. However, no significant decrease in reflectance in the ultraviolet-visible range due to the yellowing of the silver is observed.

[0130] Furthermore, 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.

[0131] [Considerations on plasticizers] Below, we will consider the plasticizers that are mixed into vinyl chloride resins. (Deterioration of vinyl chloride resin) The deterioration of vinyl chloride resin (film) due to sunlight is largely due to the deterioration of plasticizers by ultraviolet rays. PVC resins (mixed with plasticizers) that are normally used outdoors for long periods are protected from the ultraviolet rays contained in sunlight by coloring and additives. For example, they are often colored black or other colors to make them less susceptible to the effects of ultraviolet rays. On the other hand, in the case of radiative cooling film CP, it is necessary to minimize sunlight absorption in order to achieve radiative cooling performance. For this reason, it is not possible to add enough additives, dyes, or pigments to protect the plasticizer.

[0132] As shown in Fig. 12, the radiative cooling film CP has an infrared emitting layer J made of vinyl chloride resin, an adhesive layer N (bonding layer), and a protective layer D under it, and a light-reflecting layer B containing silver under that. The light-reflecting layer B makes the infrared emitting layer J more susceptible to the influence of sunlight. In other words, sunlight that has once entered the radiative cooling film CP is reflected by the light-reflecting layer B and then passes through the infrared emitting layer J twice. This means that the influence of sunlight on degradation is about twice as strong as usual.

[0133] Furthermore, when comparing the infrared radiation layer J formed on the light-reflecting layer B containing silver with the infrared radiation layer J formed on aluminum, iron, or ceramics, which have lower reflectivity than silver, the radiative cooling film CP with the infrared radiation layer J formed on the light-reflecting layer B containing silver is more affected by sunlight. These findings suggest that the vinyl chloride resin of the radiative cooling film CP, which has an infrared emitting layer J on a light-reflecting layer B with silver, is more sensitive to ultraviolet rays contained in sunlight than general-purpose vinyl chloride.

[0134] Degradation of ester-based plasticizers due to ultraviolet light occurs mainly due to the plasticizer absorbing ultraviolet energy. Ultraviolet light absorption occurs mainly due to electron transitions that exceed the bond energy of the ester bond in the plasticizer. The activation energy provided by ultraviolet light and water molecules promotes hydrolysis of the plasticizer mixed into the vinyl chloride resin. When the plasticizer bonds break, the broken bonds attack the surrounding vinyl chloride resin, causing dehydrochlorination and discoloration, which also reduces the mechanical strength. When the vinyl chloride resin becomes discolored, the radiative cooling film CP absorbs sunlight and is no longer able to cool during the day.

[0135] Therefore, as shown in the experimental results in Fig. 19, plasticizers (trimellitic acid esters, epoxidized fatty acid esters) used in outdoor applications exposed to direct sunlight cannot be used in radiative cooling film CP, and phthalate esters, aliphatic dibasic acid esters, phosphate triesters, and aromatic phosphate esters can be used as plasticizers for radiative cooling film CP.

[0136] (Protection of infrared radiation layer by ultraviolet absorber) The vinyl chloride resin forming the infrared radiation layer J of the radiative cooling film CP used in the experiment is mixed with an ultraviolet absorber, and the reflectance of the radiative cooling film CP at the time of its manufacture is adjusted to be 10% or less in the wavelength range of 295 nm or more and 350 nm or less (see Figure 19). This ultraviolet absorber is present to protect the adhesive layer N (bonding layer), protective layer D, and light-reflecting layer B containing silver that are located below the infrared-emitting layer J, and its effect in protecting the infrared-emitting layer J from ultraviolet rays is limited.

[0137] The absorbance (A) of the ultraviolet absorber can be expressed by the following formula (2). A=1-exp(-αt) (2) where α is the absorption coefficient and t is the film thickness. From this equation, it can be seen that as the light travels through the infrared-emitting layer J (vinyl chloride layer), it is gradually absorbed by the infrared-emitting layer J. In other words, the ultraviolet protection effect of the ultraviolet absorber cannot be expected, particularly on the sunlight incident side of the infrared-emitting layer J (vinyl chloride layer). In other words, the experimental results showed that when trimellitic acid was used as the plasticizer, the radiative cooling film CP deteriorated as it was gouged out from the sunlight-irradiated surface (radiation surface H).

[0138] (Regarding suitable and unsuitable plasticizers) Suitable plasticizers to be mixed into the vinyl chloride resin are, as mentioned above, phthalates, aliphatic dibasic acid esters, phosphate triesters, and aromatic phosphate esters. The aliphatic dibasic acid ester is preferably an ester bond between an aliphatic dibasic acid and two molecules of a saturated aliphatic alcohol, and the phthalic acid ester is preferably an ester bond between phthalic acid and two molecules of a saturated aliphatic alcohol. In addition, for each of the phthalic acid ester, aliphatic dibasic acid ester, and phosphate triester, it is desirable that the hydrocarbon group of the ester is an alkyl group.

[0139] As mentioned above, unsuitable plasticizers are trimellitic esters and epoxidized fatty acid esters. Furthermore, plasticizers in which the hydrocarbon group of the phthalate ester, aliphatic dibasic acid ester, or phosphate triester is an unsaturated hydrocarbon group are also unsuitable. In other words, it is desirable that the hydrocarbon group of the phthalate ester, aliphatic dibasic acid ester, or phosphate triester is a saturated hydrocarbon group. In other words, if the hydrocarbon group is unsaturated, the unsaturated bond causes coloration, absorbs sunlight well, and reduces the radiative cooling performance. In addition, the unsaturated bond absorbs sunlight and cleaves, promoting reactions with the surrounding oligomers and vinyl chloride, which causes embrittlement and coloration of the infrared emitting layer J of the radiative cooling film CP. In short, the suitability of plasticizers depends on how easily they absorb ultraviolet light.

[0140] (About phthalates) First, we will compare phthalates, which are aromatic carboxylic acid esters, with trimellitates. An example of a phthalate ester is DOP (di-2-ethylhexyl phthalate), and an example of a trimellitate ester is TOTM (tri-2-ethylhexyl trimellitate). Decomposition outdoors under ultraviolet light occurs through hydrolysis of the ester bond. UV light provides the activation energy for this reaction. The bond energy of the ester bond in trimellitic esters is weaker than that of phthalic acid. This difference is reflected in the difference in UV absorption.

[0141] The following equation (3) represents the relationship between the absorption wavelength (λA) and the binding energy (E). λA=1240 / E---(3) This equation shows that as the bond energy (E) decreases, the ultraviolet absorption wavelength that activates the bond electron transfer shifts to longer wavelengths. Figure 20 shows an example. In Figure 20, DEHP and DINCH are phthalate esters, and TOTM is trimellitate ester. Note that DEHP is the same as DOP.

[0142] While terrestrial sunlight exists in wavelengths longer than 295 nm, TOTM effectively absorbs ultraviolet light in wavelengths longer than 295 nm. This absorption comes from the ester bond, and provides the activation energy for hydrolysis, in which ultraviolet light reacts with surrounding water. Incidentally, trimellitic acid ester is a plasticizer that is also used in soft PVC electric wires that are exposed to direct sunlight, but it cannot be used in the PVC that forms the infrared radiative layer J of the radiative cooling film CP, even though they are also for outdoor use. In general outdoor applications, the PVC layer is often sufficiently colored black or other colors to be less susceptible to the effects of UV rays, and degradation due to UV rays is unlikely to occur.

[0143] On the other hand, in the case of radiative cooling film CP, it is necessary to minimize the absorption of sunlight in order to achieve radiative cooling performance, and therefore additives, dyes, and pigments to protect the plasticizer cannot be added in sufficient quantities. Therefore, plasticizers that are used in other outdoor applications where the film is exposed to direct sunlight cannot be used in this application. Trimellitic acid esters include tri-2-ethylhexyl trimellitate (TO™), triisononyl trimellitate (TINT™), triisodecyl trimellitate (TID™), and the like, but all of them are unsuitable.

[0144] FIG. 21 shows the absorbance of other phthalate esters, DOP (di-2-ethylhexyl phthalate) and DBP (dibutyl phthalate), and shows that they have almost no absorption in wavelengths longer than 295 nm.

[0145] When the hydrocarbon group is an alkyl group, the strength of the ester bond is highly dependent on the type of carboxylic acid, and UV absorption shows similar trends for the same type of carboxylic acid. When the hydrocarbon group is an alkyl group, the light absorption at the longest wavelengths in the UV range below 400 nm is due to the bond energy of the ester bond. Phthalate esters, whose hydrocarbon group is an alkyl group, do not absorb light in the ultraviolet region longer than 295 nm, which is present in the terrestrial sunlight spectrum, and are not hydrolyzed by the ultraviolet energy of sunlight.

[0146] On the other hand, in trimellitic esters, whose hydrocarbon group is an alkyl group, the ester bond absorbs the ultraviolet energy of sunlight, and this energy accelerates hydrolysis. The acids and alcohols produced by hydrolysis absorb ultraviolet light and react with the surrounding oligomers and vinyl chloride, causing embrittlement and coloration of the infrared radiative layer J of the radiative cooling film CP. In other words, aromatic carboxylic acid esters used as plasticizers include phthalates and trimellitates, and while phthalates can be used as radiative cooling materials, trimellitates cannot.

[0147] (Aliphatic dibasic acid esters) When the hydrocarbon group is an alkyl group, the strength of the ester bond is highly dependent on the type of carboxylic acid, and as explained in the sections on phthalic acid and trimellitic acid, if the type of carboxylic acid is the same, the ultraviolet absorption will show similar trends. Consider the case where the aliphatic dibasic acid of the aliphatic dibasic acid ester is a saturated dicarboxylic acid such as adipic acid, azelaic acid, sebacic acid, or succinic acid, and the ester is an ester bond between such an acid and saturated glucose. This also includes copolymers of saturated dicarboxylic acids and saturated glucose. In this case, the only functional group that has optical characteristics in the ultraviolet region is the ester bond, and theoretically, the absorption spectrum in the ultraviolet region (200 nm or more and 400 nm or less) is the same for all aliphatic dibasic acid esters.

[0148] Let us consider DOA (di-2-ethylhexyl adipate), a typical example of an aliphatic dibasic acid ester. Figure 22 shows the absorbance of DOA in the ultraviolet region, and it can be seen that its solar light absorption rate is even lower than that of the aforementioned DOP (di-2-ethylhexyl phthalate), which has almost no absorption in wavelengths longer than 295 nm. In Figure 19, both the phthalate ester and the aliphatic dibasic acid ester endured 2000 hours in a xenon weather test, but optically, DOA had higher durability.

[0149] (About phosphate esters) Phosphate ester plasticizers include phosphate triesters and aromatic phosphate triesters. Phosphate esters have a large bond energy and do not hydrolyze under ultraviolet light with wavelengths longer than 295 nm. Therefore, they are excellent plasticizers for radiative cooling films (CP). Furthermore, when made into phosphate esters, they are flame retardant.

[0150] As mentioned above, the phosphate triester includes trimethyl phosphate (TMP), triethyl phosphate (TEP), tributyl phosphate (TBP), and tris(2-ethylhexyl) phosphate (TOP). FIG. 23 shows the absorbance of tributyl phosphate (TBP), which shows that it hardly absorbs ultraviolet light with wavelengths longer than 295 nm.

[0151] As mentioned above, the aromatic phosphate esters include triphenyl phosphate (TPP), tricresyl phosphate (TCP), trixylenyl phosphate (TXP), tresyl diphenyl phosphate (CDP), and 2-ethylhexyl diphenyl phosphate. Although not shown in the figure, aromatic phosphate esters hardly absorb ultraviolet light with wavelengths longer than 295 nm.

[0152] (Epoxidized fatty acid esters) Epoxidized fatty acid esters, like the above-mentioned TOTM (trimellitic acid ester), effectively absorb ultraviolet light with wavelengths longer than 295 nm. In other words, the epoxy groups in epoxidized fatty acid esters absorb and decompose ultraviolet light with wavelengths longer than 295 nm. They are also decomposed by microorganisms. Therefore, they cannot be used outdoors. Epoxidized fatty acid esters include epoxidized soybean oil and epoxidized linseed oil, but none of them can be used as plasticizers to be mixed into the vinyl chloride resin of the radiative cooling film CP.

[0153] [Another configuration of radiative cooling film] As shown in FIG. 24, the structure may be such that an anchor layer G is provided on top of a film layer F (corresponding to the substrate), and a light-reflecting layer B, a protective layer D, and an infrared-emitting layer J (an infrared-emitting layer J made of vinyl chloride resin mixed with a plasticizer) are provided on top of the anchor layer G. The film layer F (corresponding to the substrate) is formed into a film shape using, for example, PET (ethylene terephthalate resin) or the like.

[0154] The anchor layer is introduced to strengthen the adhesion between the film layer F and the light-reflecting layer B. In other words, if an attempt was made to deposit silver (Ag) directly on the film layer F, it would easily peel off. The anchor layer G is preferably made primarily of acrylic, polyolefin, or urethane, with a mixture of compounds containing isocyanate groups or melamine resin. As this is a coating for areas that are not directly exposed to sunlight, it is acceptable for the material to absorb ultraviolet light. Note that 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 it with plasma.

[0155] [Another configuration of the infrared radiation layer] As shown in Fig. 25, a light-scattering structure may be provided by mixing inorganic filler V into the infrared-emitting layer J (vinyl chloride resin mixed with a plasticizer) constituting the infrared-emitting layer J. Also, as shown in Fig. 26, both the front and back surfaces of the infrared-emitting layer J constituting the infrared-emitting layer J may be formed unevenly to provide a light-scattering structure. With this configuration, glare from the radiation surface H can be suppressed when the radiation surface H is viewed.

[0156] In other words, the above-mentioned infrared radiation layer J is flat on both the front and back surfaces and is configured so that no filler V is mixed in. In such a configuration, the radiation surface H is mirror-like, and glare is perceived when looking at the radiation surface H, but this glare can be suppressed by providing a light-scattering configuration. Furthermore, when the filler V is mixed into the infrared emitting layer J, the presence of the protective layer D and the light reflecting layer B improves the light reflectance compared to the case where only the infrared emitting layer J mixed with the filler V is present or the case where only the light reflecting layer B is present.

[0157] Silicon dioxide (SiO), titanium oxide (TiO), aluminum oxide (AlO), magnesium oxide (MgO), etc. can be suitably used as the inorganic material forming the filler V. When the filler V is mixed into the infrared emitting layer J, both the front and back surfaces of the infrared emitting layer J become uneven. In addition, the front and back surfaces of the infrared emitting layer J can be made uneven by embossing or scratching the surface.

[0158] When the rear surface of the infrared emitting layer J is uneven, it is desirable to position an adhesive layer N (bonding layer) between the infrared emitting layer J and the protective layer D, similar to the configuration described in FIG. In other words, even if the back surface of the infrared emitting layer J is uneven, the adhesive layer N (bonding layer) is located between the infrared emitting layer J and the protective layer D, so the infrared emitting layer J and the protective layer D can be bonded appropriately.

[0159] In addition, when the back surface of the infrared emitting layer J is uneven, the infrared emitting layer J and the protective layer D may be directly bonded by, for example, plasma bonding. Note that plasma bonding is a form in which radicals are formed on the bonding surfaces of the infrared emitting layer J and the protective layer D by emitting plasma, and bonding is performed by the radicals.

[0160] Incidentally, if filler V is mixed into protective layer D, the back surface of protective layer D that contacts light-reflecting layer B will become uneven, causing the surface of light-reflecting layer B to deform into an uneven shape, so it is necessary to avoid mixing filler V into protective layer D. In other words, if the surface of light-reflecting layer B deforms into an uneven shape, it will not be able to reflect light properly, and as a result, radiative cooling will not be able to be performed properly.

[0161] The experimental results regarding this point will be explained with reference to FIG. In Figure 27, "directly forming an Ag layer on the light diffusion layer" means that a filler V is mixed in or a silver (Ag) film is formed by vapor deposition or the like on the surface of the infrared radiation layer J (infrared radiation layer J) that has embossed irregularities on the Ag layer side, which is the light reflection layer B, to form the light reflection layer B. Furthermore, "a light diffusion layer on a mirror-like Ag" means that the upper surface of the Ag layer, which is the light-reflecting layer B, is formed in a mirror-like shape, and on top of the Ag layer, a protective layer D, and an infrared radiation layer J (infrared radiation layer J) containing filler V or having embossed irregularities are laminated.

[0162] As shown in Figure 27, when "an Ag layer is formed directly on the light diffusion layer," the surface of the light-reflecting layer B becomes uneven, resulting in a significant drop in light reflectance. However, when "a light-diffusing layer is formed on mirror-like Ag," the surface of the light-reflecting layer B remains mirror-like, resulting in an appropriate light reflectance.

[0163] [Test results] Now, regarding the radiative cooling fabric HN explained so far, the test results for visible light reflectance, infrared reflectance, infrared emissivity, breathability, flexibility, and radio wave transmittance are shown below. In Examples 1 to 13, both the warp and weft were made of radiative cooling fiber S1, and in Examples 14 to 26 and Comparative Examples 3 to 6, the warp was made of radiative cooling fiber S1 and the weft was made of resin fiber S2. Specific materials etc. for the radiative cooling fibers S1 and resin fibers S2 constituting the Examples and Comparative Examples are as shown in the following Tables 1 to 7. Note that the radiative cooling fibers S1 constituting the Examples and Comparative Examples are either provided with the second infrared radiation layer J2 or not, but those with the second infrared radiation layer J2 have the layered state shown in Fig. 11, and those with the second infrared radiation layer J2 have the layered state shown in Fig. 10.

[0164] The fabric of Comparative Example 1 is a laminate of a UV-reflecting multilayer optical film, a connecting layer, a reflective microporous layer, a connecting layer, and a fabric layer, and is not a fabric with woven fibers. That is, the fabric of Comparative Example 1 is a fabric with a radiative cooling film attached to it. Specifically, a 50-μm-thick silver alloy vapor-deposited polyester film is bonded to a 75-μm-thick polyvinyl chloride film via a resin adhesive layer, and a urethane fabric is bonded to the back of the film via a different resin connecting layer. The fabric of Comparative Example 2 is a laminate of a functional filler layer, in which multiple fillers are mixed into a resin material, and a base layer, and is not a fabric with woven fibers. Specifically, it is a 500 μm-thick urethane fabric coated with a 100 μm-thick acrylic resin layer (containing 20% ​​by mass of titanium oxide with an average particle size of 250 nm).

[0165] The visible light reflectance (400 to 800 nm) was measured using an ultraviolet-visible spectrometer UV-2600 (Shimadzu Corporation). When the arithmetic mean of the reflectance in the wavelength range of 400 to 800 nm was less than 70%, it was marked as "×", when it was 70% or more and 80% or less it was marked as "◯", and when it was more than 80%, it was marked as "◎". Infrared reflectance (800 to 1200 nm) was measured using an ultraviolet-visible spectrometer UV-2600 (Shimadzu Corporation). If the arithmetic mean of the reflectance at wavelengths of 800 to 1200 nm was less than 70%, it was marked as "X", and if it was 70% or more, it was marked as "O". The infrared emissivity was measured using an FT-IR IRTracer-100 (Shimadzu Corporation). When the arithmetic mean of the emissivity in the wavelength range of 8 to 13 μm was less than 70%, it was marked as "x", and when it was 70% or more, it was marked as "o". The breathability is measured using the breathability evaluation defined in JIS L1096, and is measured at 30cm 3 / cm 2 ·s or more was defined as having high (good) breathability. Flexibility was evaluated using the following method. As shown in Figure 29, fabrics measuring 30.5 cm in length and 5 cm in width were prepared and glued together with a 0.5 cm overlap to create a ring-shaped structure WA with a circumference of 30 cm. Next, the ring-shaped structure WA was placed on a flat surface HA, and one end of the long axis, WA1, was fixed, while the other end, WA2, was pulled with a force of 5 gw. Flexibility was expressed as the ratio of the long axis lengths of the ring-shaped structure WA before and after the test (= β - α / α: see Figure 29). A ratio of less than 30% was marked "x," and a ratio of 30% or greater was marked "o." Radio wave permeability was measured at 800MHz using the KEC method at the Kansai Electronics Industry Development Center, a general incorporated association. An attenuation of 10dB or less was defined as high (good) radio wave permeability.

[0166] [Table 1]

[0167] [Table 2]

[0168] [Table 3]

[0169] [Table 4]

[0170] [Table 5]

[0171] [Table 6]

[0172] [Table 7]

[0173] As shown in Tables 1 to 6 above, the radiative cooling fabric HN according to the examples met the requirements for visible light reflectance, infrared reflectance, infrared emissivity, breathability, flexibility, and radio wave transmittance. On the other hand, Comparative Example 1 has a structure in which a conventional radiative cooling film is attached to fabric, and therefore it is seen that the breathability, flexibility, and radio wave transmittance are insufficient. Comparative Example 2 also does not have a structure in which fibers are woven, and is therefore presumed to lack breathability and flexibility.

[0174] Reference Examples 1 and 2 are examples for explaining the effect of fiber density (= fiber width × density / 1 inch). If the fiber density is too high, the breathability and radio wave transmittance decrease, as in Reference Example 1, and if the fiber density is too low, the infrared emissivity, visible light reflectance, and infrared reflectance decrease, as in Reference Example 2. Furthermore, in Reference Example 1, the high fiber density results in high rigidity and low flexibility when woven. Incidentally, Reference Example 3 is an example in which polyimide is used for the weft. Polyimide, as a resin alone, turns brown, resulting in low visible light reflectance and infrared reflectance.

[0175] [Another embodiment] Other embodiments will be listed below.

[0176] (1) In the above embodiment, the radiation surface H of the infrared radiation layer J is exposed as is. However, the radiation surface H may be covered with a hard coat. The hard coat may be any of UV-curable acrylic, thermosetting acrylic, UV-curable silicone, thermosetting silicone, organic-inorganic hybrid, or vinyl chloride. An organic antistatic agent may also be used as an additive. Among UV-curable acrylics, urethane acrylate is particularly good.

[0177] 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.

[0178] The configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradiction arises. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be modified as appropriate within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0179] The radiative cooling cloth, radiative cooling fiber, and method for manufacturing a radiative cooling cloth of the present invention can be effectively used as a radiative cooling cloth, radiative cooling fiber, and method for manufacturing a radiative cooling cloth that exhibits good radiative cooling performance while also having breathability, flexibility, and radio wave transmittance. [Explanation of symbols]

[0180] B: Light reflective layer CP: Radiative cooling film D: Protective layer H: Radiation surface H1: 1st radiation surface H2: Second radiation surface HN: Radiant cooling cloth IR: Infrared light J1: First infrared radiation layer J2: Second infrared radiation layer L1: Fiber width S1: Radiative cooling fiber S2: Resin fiber X: Cutting direction

Claims

1. A radiative cooling fabric using a radiative cooling film in which a first infrared radiating layer as an infrared radiating layer made of a resin material adjusted to a thickness that radiates infrared light from a first radiating surface and also emits thermal radiation energy greater than absorbed solar light energy in a wavelength band of 8 μm to 13 μm, and a light reflecting layer located on the first infrared radiating layer on the opposite side to the side where the first radiating surface is present, is laminated, A radiative cooling fabric formed by weaving radiative cooling fibers cut in the radiative cooling film along the cutting direction along the first radiating surface.

2. The radiative cooling fabric according to claim 1, wherein the radiative cooling film has a second infrared radiation layer on the side of the light reflecting layer opposite to the side where the first infrared radiation layer is present, the second infrared radiation layer being made of a resin material whose thickness is adjusted to emit infrared light from a second radiation surface opposite to the first radiation surface and thermal radiation energy greater than absorbed solar energy in a wavelength band of 8 μm to 13 μm.

3. The radiative cooling fiber contains 50% by mass or more, A form containing 1% by mass or more of resin fibers made of a resin that emits infrared light, The radiative cooling fabric according to claim 1 or 2, wherein both the radiative cooling fiber and the resin fiber are woven together.

4. The radiative cooling fabric according to claim 1 or 2, wherein the radiative cooling fiber has a fiber width in a direction perpendicular to the cutting direction of 10 μm or more and 5000 μm or less.

5. The radiative cooling fabric according to claim 1, wherein the arithmetic mean reflectance, which is the wavelength average of light reflectance at wavelengths of 400 nm to 800 nm, is 70% or more, the arithmetic mean reflectance, which is the wavelength average of light reflectance at wavelengths of 800 nm to 1200 nm, is 60% or more, and the wavelength average of emissivity in the wavelength band of 8 μm to 13 μm is 70% or more.

6. The radiative cooling fabric according to claim 1 or 2, wherein the radiative cooling fiber has a fiber width in a direction perpendicular to the cutting direction of 10 μm or more and 5000 μm or less, and a mesh number of 10 mesh or more and 230 mesh or less.

7. The radiative cooling fabric according to claim 1 or 2, wherein the radiative cooling fiber has a fiber width in a direction perpendicular to the cutting direction of 20 μm or more and 500 μm or less, and a mesh number of 20 meshes or more and 150 meshes or less.

8. the light-reflecting layer is made of a metal, The radiative cooling film has a protective layer that protects the metal on the side of the light reflecting layer opposite to the side on which the first infrared radiative layer is present, The radiative cooling fabric according to claim 2, wherein the protective layer is the second infrared radiation layer that emits infrared light from the second radiation surface opposite to the first radiation surface.

9. The radiative cooling fabric according to claim 3, wherein the radiative cooling fibers and the resin fibers are woven as warp and weft.

10. The radiative cooling fabric according to claim 1 or 2, wherein the light reflecting layer contains at least one of silver, a silver alloy, aluminum, an aluminum alloy, a copper alloy, and a resin containing a plurality of white fillers.

11. The radiative cooling fabric according to claim 1 or 2, wherein the infrared radiative layer comprises at least one of polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, and polyvinylidene fluoride.

12. a radiative cooling fiber cut along a cutting direction along the first radiation surface, the radiative cooling film being a laminate of a first infrared radiation layer as an infrared radiation layer made of a resin material adjusted to a thickness that radiates infrared light from a first radiation surface and also emits thermal radiation energy greater than absorbed solar light energy in a wavelength band of 8 μm to 13 μm, and a light reflecting layer located on the opposite side of the first infrared radiation layer to the side where the first radiation surface is present; The radiative cooling fiber having a fiber width along the first radiation surface of 10 μm or more and 5000 μm or less.

13. a cutting step of cutting a radiative cooling film, which includes a first infrared radiation layer made of a resin material adjusted to a thickness that radiates infrared light from a first radiation surface and also emits thermal radiation energy in a wavelength band of 8 μm to 13 μm that is greater than absorbed solar light energy, and a light reflecting layer located on the opposite side of the first infrared radiation layer to the side where the first radiation surface is present, along a cutting direction along the first radiation surface, to cut out radiative cooling fibers; A method for manufacturing a radiative cooling fabric, comprising: a weaving step of weaving the radiative cooling fiber.

14. The radiative cooling fiber contains 50% by mass or more, The method for manufacturing a radiative cooling fabric according to claim 13, comprising the weaving step of weaving both the radiative cooling fiber and the resin fiber in a form containing 1 mass% or more of resin fiber made of a resin that radiates infrared light.

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