Resin multilayer film

Abstract

To exhibit high cooling capability under direct sunlight and exhibit high radio wave transmission, as well as prevent a decrease in radiation cooling performance and a decrease in cooling performance due to fouling of a hole when a hole is opened in a resin material.SOLUTION: A light reflection layer B has a plurality of holes K and is formed from a second resin, an infrared radiation layer J is formed from a first resin that emits larger thermal radiation energy than absorbed solar energy in wavelengths from 8 μm to 13 μm, the holes included in the infrared layer J being fewer than the holes included in the light reflection layer B. A multilayer resin layer M including the light reflection layer B and the infrared radiation layer J is characterized in that an arithmetic average reflectance which is a wavelength average of light reflectance in wavelengths from 400 nm to 800 nm is 80% or greater, an arithmetic average reflectance which is a wavelength average of light reflectance in wavelengths from 800 nm to 1200 nm is 70% or greater, and the wavelength average of emissivity in wavelengths from 8 μm to 13 μm is 43% or greater.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminated resin film comprising an infrared emitting layer that emits infrared light from an emitting surface, and a light reflecting layer located on the infrared emitting layer opposite to the side where the emitting surface is present. [Background technology]

[0002] A conventional example of a composite cooling material that uses the radiative cooling phenomenon is one that is configured by stacking an infrared emitting layer that emits infrared light from its emitting surface and a light reflecting layer that is positioned on the opposite side of the infrared emitting layer from the side where the emitting surface is present (see, for example, Patent Document 1). In order to dissipate heat into space through the radiative cooling phenomenon and cool an object under direct sunlight, it is important to have both high solar reflectance and high infrared emissivity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2018-526599 [Patent Document 2] Special Publication No. 2022-528289 [Patent Document 3] International Publication No. 2018 / 062541 Summary of the Invention [Problem to be solved by the invention]

[0004] Previous radiative cooling materials have achieved high solar reflectivity by reflecting sunlight with a thin metal film, but the use of a thin metal film has the problem of increasing absorption, which causes the material temperature to rise under direct sunlight.In addition, the use of a thin metal film has low radio wave permeability, which has the problem of making it difficult for communication devices to function when enclosed in a space. Furthermore, when a thin metal film is used as a reflective layer, if the surface is scratched and the metal layer is exposed, corrosion will begin from the metal layer, and the metal layer will become discolored due to oxidation, which can lead to a decrease in reflectivity. Furthermore, when a metal thin film is used as a reflective layer, even a small amount of metal oxide is likely to cause coloration, and therefore there is a problem that the degree of decrease in reflectance when deteriorated is greater than in a reflective layer made of resin.

[0005] There are also radiative cooling materials that increase the reflectivity of sunlight by making the resin porous (see Patent Document 2). In the case of such radiative cooling materials, if the porous portion is exposed on the outermost surface, they are easily soiled by rainwater, etc. If the outermost surface of the radiative cooling material becomes soiled, even if the soiling absorbs sunlight, the radiative cooling material itself does not heat up because there is little thermal contact between the soiling and the radiative cooling material. However, if the inside of the porous portion becomes contaminated, the heat converted from sunlight by the soiling has nowhere to escape and heats up the material. As described above, radiative cooling materials with porous portions exposed on the surface are avoided from the standpoint of contamination.

[0006] There are also radiative cooling materials that utilize the porous structure itself as a radiation layer (see Patent Document 3). It is difficult to maximize the radiative cooling capacity of such radiative cooling materials in the atmospheric window region. Porous materials include various types, such as polyethylene terephthalate, polypropylene, polyethylene, and polyethylene naphthalate. However, since the amount of material contributing to radiation decreases when the material is made porous, it is necessary to increase the thickness to achieve a large radiative cooling capacity. Radiative cooling materials are designed to cool the object to which they are attached, and increasing the resin layer, especially the porous resin layer, impedes the radiative cooling capacity. From this perspective, designs that use the porous resin layer itself to radiate pose a challenge to cooling the object.

[0007] Furthermore, when improving radiation capacity by using a porous material, the poor thermal conductivity of the porosity prevents the temperature of the object to be cooled from reaching the resin located on the outermost surface, resulting in insufficient cooling of the object. Furthermore, in the case of porous resin layers in which air-containing layers are stacked in a mille-feuille-like pattern, the emissivity tends to decrease when the layers are multi-layered compared to when the layers are not multi-layered. This is because the optical multilayer film structure forms a photonic bandgap structure, improving reflectivity. For this reason, using a porous resin layer not only as a reflective layer but also as an emissive layer is not desirable in terms of improving the cooling structure of radiative cooling materials.

[0008] The object of the present invention is to provide a resin laminate film that can exhibit high cooling capacity and high radio wave transmittance under direct sunlight, and can prevent a decrease in radiative cooling performance when holes are provided in the resin material and a decrease in cooling performance due to contamination of the holes. [Means for solving the problem]

[0009] The resin laminate film for achieving the above object is A resin laminate film comprising an infrared emitting layer that emits infrared light from a radiation surface, and a light reflecting layer located on the infrared emitting layer on the opposite side to the side where the radiation surface is present, characterized in that: the light reflecting layer has a plurality of pores and is made of a second resin; the infrared radiation layer is made of a first resin that emits thermal radiation energy at a wavelength of 8 μm to 13 μm that is greater than the absorbed solar light energy; the number of pores contained in the infrared emitting layer is smaller than the number of pores contained in the light reflecting layer, The laminated resin layer including the light-reflecting layer and the infrared-emitting layer has an arithmetic mean reflectance, which is the wavelength average of light reflectance in the wavelength range of 400 nm to 800 nm, of 80% or more, an arithmetic mean reflectance, which is the wavelength average of light reflectance in the wavelength range of 800 nm to 1200 nm, of 70% or more, and a wavelength average of emissivity in the wavelength range of 8 μm to 13 μm of 43% or more.

[0010] According to the above-mentioned characteristic configuration, firstly, since a metal thin film is not used as the light reflective layer, the solar light absorption rate can be reduced and the temperature rise of the resin laminate film can be suppressed compared to a configuration using a metal thin film as the light reflective layer. Furthermore, since the radio wave transmittance can be made relatively high, good communication by the wireless communication device can be maintained even in a situation where the wireless communication device is surrounded by the resin material film having the above-mentioned characteristic configuration. Furthermore, the infrared radiation layer, which is usually installed with its radiation surface facing the atmosphere, is configured so that the number of pores contained in the infrared radiation layer is fewer than the number of pores contained in the light reflection layer, and more preferably so that the number of pores contained in the infrared radiation layer is substantially zero. This makes it difficult for the infrared radiation layer to become dirty with rainwater and the like, and effectively prevents the dirt from absorbing sunlight and heating the infrared radiation layer.

[0011] In addition, by configuring the infrared radiation layer to have substantially no pores, the volume fraction of the first resin material that contributes to radiation in the radiative cooling layer can be sufficiently secured, ensuring sufficient radiative cooling capacity. Furthermore, the thermal conductivity can be improved, making it easier for the heat of the object to be cooled to be transferred to the radiative surface, and improving the cooling effect can be expected. Furthermore, since a configuration can be realized in which a photonic band gap structure is not substantially formed inside the first resin layer that constitutes the infrared radiation layer, the emissivity of the infrared radiation layer can be improved.

[0012] In addition to the configurations described above, by configuring the light-reflecting layer from a second resin having a plurality of voids, the inventors have confirmed through tests described below that it is possible to realize a resin laminate film in which the laminate resin layer combining the light-reflecting layer and the infrared-emitting layer has an arithmetic mean reflectance, which is the wavelength average of the light reflectance at wavelengths of 400 nm to 800 nm, of 80% or more, an arithmetic mean reflectance, which is the wavelength average of the light reflectance at wavelengths of 800 nm to 1200 nm, of 70% or more, and an wavelength average of the emissivity at wavelengths of 8 μm to 13 μm, of 43% or more.

[0013] As described above, in a laminated resin layer having an arithmetic mean reflectance of 80% or more, which is the wavelength average of the light reflectance of wavelengths from 400 nm to 800 nm, and an arithmetic mean reflectance of 70% or more, which is the wavelength average of the light reflectance of wavelengths from 800 nm to 1200 nm, the light reflective layer absorbs only about 2% of the solar energy, due in part to the absence of metal. As a result, at noon in the summer, the solar energy absorbed by the light reflective layer is reduced to 20 W / m 2 The radiation cooling can be performed even better.

[0014] As a result, a resin laminate film can be realized that can exhibit high cooling capacity under direct sunlight and high radio wave transmittance, and can prevent a decrease in radiative cooling performance when holes are provided in the resin material and a decrease in cooling performance due to contamination of the holes.

[0015] Further characteristic configurations of the resin laminate film are: The infrared radiation layer is characterized in that the first resin contains a filler.

[0016] As explained above, an infrared radiation layer, which is usually installed with its radiation surface facing the atmosphere, is composed of a first resin layer that does not have pores, and is intended to improve antifouling properties, radiation cooling capacity, and heat transfer in a direction intersecting the radiation surface. However, by including a filler in the first resin as in the above characteristic configuration, the infrared radiation layer can also exhibit a certain level of light reflection performance due to the difference in refractive index between the first resin layer and the filler. This allows the light-reflecting layer to reflect solar radiation, and the infrared radiation layer to reflect solar radiation as well, thereby maintaining a high reflectance for the entire material.

[0017] Further characteristic configurations of the resin laminate film are: The thickness of the second resin is 10 μm or more and 500 μm or less.

[0018] As described above, by setting the thickness of the second resin of the light-reflecting layer to 10 μm or more, the light-reflecting layer, which is made of a second resin with multiple voids, can ensure the reflectivity required for radiative cooling. Furthermore, by setting the thickness to 500 μm or less, the insulating effect of the second resin with voids containing air or other substances can be kept below a certain level, ensuring a certain level of cooling performance for the object to be cooled. Incidentally, thicknesses of 500 μm or more are undesirable because, from the perspective of rigidity, it becomes difficult to conform the material to curved parts when applied to curved parts, and forcing the material to conform can result in destruction of the material. Furthermore, excessive thickness during roll-to-roll processing is undesirable because it reduces the amount of material that can be produced at one time. That is, by selecting an appropriate material as the second resin having a plurality of pores and providing a light-reflecting layer with a thickness of the second resin set to 10 μm or more and 500 μm or less together with the infrared radiation layer, it is possible to achieve an arithmetic mean reflectance, which is the wavelength average of the light reflectance for wavelengths from 400 nm to 800 nm, of 80% or more, and an arithmetic mean reflectance, which is the wavelength average of the light reflectance for wavelengths from 800 nm to 1200 nm, of 70% or more. The thickness of the light reflecting layer is preferably 50 to 300 μm, and more preferably 75 to 200 μm.

[0019] Further characteristic configurations of the resin laminate film include: The thickness of the first resin is preferably 10 μm or more and 500 μm or less. In particular, in the resin laminate film according to the present invention, the first resin of the infrared-emitting layer does not contain multiple voids and can exhibit higher radiation performance than infrared-emitting layers that contain voids. Therefore, even a relatively thin film layer of 500 μm can satisfactorily ensure the required radiation performance. Incidentally, thicknesses of 500 μm or more are undesirable because, from the perspective of rigidity, it becomes difficult to conform the material to curved parts when applied to curved parts, and forcing the material to conform can result in destruction of the material. Furthermore, if the thickness is too thick during roll-to-roll processing, the amount of material that can be produced at one time is reduced, which is undesirable. Furthermore, by ensuring a thickness of 10 μm or more, sufficient emissivity can be ensured, and even if there are irregularities on the surface of the light-reflecting layer due to multiple voids contained in the second resin, the irregularities are unlikely to be reflected on the radiation surface of the infrared radiation layer, and adhesion of dirt to the radiation surface can be effectively suppressed.

[0020] Further characteristic configurations of the resin laminate film are: the pores in the second resin have a refractive index smaller than that of the second resin; The arithmetic mean diameter of the pores is 0.1 μm or more and 3.0 μm or less.

[0021] As in the above characteristic configuration, the pores in the second resin of the light reflecting layer preferably have a refractive index smaller than that of the second resin, and an arithmetic mean pore diameter of the pores of 0.1 μm or more and 3.0 μm or less. The inventors have confirmed that when the arithmetic mean pore diameter of the pores is set to a plurality of arithmetic mean pore diameters in the range of 0.1 μm or more and 3.0 μm or less, good light reflectance can be achieved in the wavelength range of 400 nm to 800 nm and in the wavelength range of 800 nm to 1200 nm. In the present invention, the arithmetic mean pore diameter of the pores is defined as the arithmetic mean of the shortest inner diameters of the pores. The shape of the pores is not limited to a spherical shape, and may be a flat structure having short and long sides, a polyhedral structure, or the like.

[0022] Further characteristic configurations of the resin laminate film are: The volume ratio of the pores in the light reflecting layer is 0.1% by volume or more and 60% by volume or less.

[0023] The inventors have confirmed that the reflectance of the light reflecting layer can be set to the above-mentioned arithmetic mean reflectance by setting the volume ratio of the voids in the light reflecting layer as described above. More preferably, the volume percentage of the pores in the light reflecting layer is 1% by volume or more and 50% by volume or less, and the volume percentage of the pores in the light reflecting layer is 10% by volume or more and 40% by volume or less. If the porosity is 60% or more by volume, the thermal conductivity will decrease, which is undesirable from the viewpoint of heat dissipation in a system with an internal heat source, as heat will accumulate. Also, if the porosity is 60% or more by volume, the strength will decrease. Furthermore, if the volume fraction of the pores is 0.1% by volume or less, it is difficult to sufficiently improve the reflectance even if the average particle size of the pores or their arrangement is devised.

[0024] Furthermore, the laminated resin layer preferably has an arithmetic mean reflectance, which is the wavelength average of the reflectance of light at wavelengths of 400 nm to 800 nm, of 84% or more, and an arithmetic mean reflectance, which is the wavelength average of the reflectance of light at wavelengths of 800 nm to 1200 nm, of 75% or more, and more preferably has an arithmetic mean reflectance of 88% or more at wavelengths of 400 nm to 800 nm, and 80% or more at wavelengths of 800 nm to 1200 nm.

[0025] Further characteristic configurations of the resin laminate film are: The laminated resin layer has an arithmetic mean transmittance, which is the wavelength average of the transmittance of light having a wavelength of 400 nm to 800 nm, of 1% to 12%.

[0026] According to the present invention, the arithmetic mean transmittance, which is the wavelength average of the light transmittance in the wavelength range of 400 nm to 800 nm, is set to 1% or more and 12% or less. Therefore, light in the wavelength range of 400 nm to 800 nm is transmitted well through both the first resin of the infrared radiation layer and the second resin of the light reflection layer, and light is reflected at the boundary between the second resin of the light reflection layer and the pores, thereby improving the reflectance of the laminated resin layer. In other words, the absorption rate in the laminated resin layer can be reduced. Also, by having a light transmittance of 1% or more, it is possible to ensure good lighting when used outdoors.

[0027] Furthermore, the laminated resin layer preferably has an average wavelength emissivity of 70% or more in the wavelength range of 8 μm to 13 μm, and more preferably has an average wavelength emissivity of 85% or more in the wavelength range of 8 μm to 13 μm.

[0028] Further characteristic configurations of the resin laminate film are: The second resin contains a filler.

[0029] As in the above characteristic configuration, the second resin forming the light-reflecting layer is configured to contain a filler in addition to the multiple voids described above, so that light can be reflected not only at the boundary between the second resin and the voids but also at the boundary between the second resin and the filler.Therefore, for example, in order to ensure a certain level of thermal conductivity, even if the volume ratio of voids to the second resin is made relatively low or the thickness is kept thin, a high arithmetic mean reflectance can be maintained.

[0030] Further characteristic configurations of the resin laminate film are: The filler is one or more of titanium oxide, glass microbeads, silicon dioxide, ground calcium carbonate powder, barium sulfate, zinc sulfate, aluminum silicate, ground calcium carbonate, aluminum oxide, zinc oxide, zirconium oxide, cerium oxide, lanthanum oxide, rhodium oxide, magnesium oxide, and barium titanate, and may be porous.

[0031] By including the above-mentioned filler in the first resin forming the infrared emitting layer or the second resin forming the light reflecting layer, it is possible to achieve good light reflectance for the entire laminated resin layer. The inventors have confirmed that, in particular, when one or more of titanium oxide, glass microbeads, silicon dioxide, heavy calcium carbonate powder, barium sulfate, zinc sulfate, aluminum silicate, heavy calcium carbonate, aluminum oxide, zinc oxide, zirconium oxide, cerium oxide, lanthanum oxide, rhodium oxide, magnesium oxide, and barium titanate are used as the filler, the laminated resin layer can exhibit high arithmetic mean reflectance, which is the wavelength average of the reflectance of light in the wavelength range of 400 nm to 800 nm, and arithmetic mean reflectance, which is the wavelength average of the reflectance of light in the wavelength range of 800 nm to 1200 nm, to a degree that allows the radiative cooling function to be appropriately exhibited.

[0032] Furthermore, the second resin of the light-reflecting layer preferably contains at least one of polyethylene terephthalate, polypropylene, polyethylene, polyethylene naphthalate, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polymethyl methacrylate, and polycarbonate, and more preferably, the first resin forming the infrared radiation layer contains at least one of polyethylene terephthalate, polyethylene naphthalate, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, and polymethyl methacrylate.

[0033] As shown in Figure 2, the absorption coefficient of resins containing carbon-fluorine bonds (CF) due to CHF and CF2 is spread widely across a wide wavelength band from 8 μm to 13 μm, which is the atmospheric window, with a particularly large absorption coefficient at 8.6 μm. Furthermore, with regard to the wavelength band of sunlight, there is no noticeable absorption coefficient in the wavelength range from 0.3 μm to 2.5 μm, where the energy intensity is high.

[0034] In addition, resins with carbon-chlorine bonds (C-Cl) have an absorption coefficient due to the C-Cl stretching vibration that appears in a broad band with a half-width of 1 μm or more, centered around a wavelength of 12 μm. In the case of vinyl chloride resin, an absorption coefficient due to the CH bending vibration of the alkene contained in the main chain appears at a wavelength of around 10 μm due to the influence of chlorine electron withdrawal. The inventors have taken these absorption-related characteristics into consideration when selecting the material for the first resin.

[0035] The first resin preferably includes at least one of polyvinyl chloride, polyvinylidene chloride, and polyvinylidene fluoride.

[0036] In particular, regarding the wavelengths at which resin materials with carbon-fluorine bonds (CF) have absorption coefficients in the ultraviolet to visible range, the bond energies of the C-C, C-H, and C-F bonds in the basic structure of polyvinylidene fluoride (PVDF) are 4.50 eV, 4.46 eV, and 5.05 eV. These correspond to wavelengths of 0.275 μm, 0.278 μm, and 0.246 μm, respectively, and light of these wavelengths is absorbed. Therefore, from the viewpoint of absorbing ultraviolet rays in the first resin of the infrared radiation layer and reducing the amount of ultraviolet rays that pass through the light reflecting layer, it is preferable to use polyvinyl fluoride or polyvinylidene fluoride as the first resin.

[0037] Further characteristic configurations of the resin laminate film are: the first resin contains an ultraviolet absorber, The infrared radiation layer has an arithmetic mean reflectance, which is the wavelength average of the reflectance of ultraviolet rays having a wavelength of 340 nm to 400 nm, of 50% or less.

[0038] According to the above-described characteristic configuration, the first resin forming the infrared radiation layer contains an ultraviolet absorber, and the arithmetic mean reflectance, which is the wavelength average of the ultraviolet reflectance of the infrared radiation layer in the wavelength range of 340 nm to 400 nm, is 50% or less. Therefore, ultraviolet rays can be suitably absorbed by the ultraviolet absorber, and ultraviolet rays are not easily reflected. This reduces the amount of ultraviolet rays that transmit through the first resin forming the infrared radiation layer and the second resin forming the light reflecting layer, and effectively suppresses deterioration of the first resin layer and the second resin layer due to ultraviolet rays.

[0039] Further characteristic configurations of the resin laminate film are: the light reflecting layer and the infrared emitting layer are connected by a connecting layer made of at least one of an adhesive, a pressure-sensitive adhesive, and a glue, the connecting layer being included in the laminated resin layer; The connecting layer includes at least one of a filler and hollow particles.

[0040] In particular, as described above, by incorporating fillers or hollow particles having an arithmetic mean particle size of, for example, about 0.1 μm or more and 5 μm or less into the connecting layer, the reflectance of light in the ultraviolet to visible region can be improved, and the thickness of the laminated resin layer (particularly the light-reflecting layer) can be reduced to obtain the desired reflectance.

[0041] Further characteristic configurations of the resin laminate film are: The pores of the second resin have a flat shape.

[0042] According to the above characteristic configuration, it is possible to provide multiple layers with different refractive indices, which makes it easier for light to be reflected compared to when the holes have a non-flat structure at the same thickness, and has the advantage of making it easier to increase the reflectivity even at the same thickness. [Brief explanation of the drawings]

[0043] [Figure 1] 1A and 1B are diagrams illustrating an embodiment of a resin laminate film. [Figure 2] FIG. 10 is a diagram illustrating another embodiment of the resin laminate film. [Figure 3] FIG. 10 is a diagram showing the relationship between the absorption coefficient of a resin material and a wavelength band. [Figure 4] FIG. 10 is a diagram showing the relationship between the light absorptance of a resin material and wavelength. [Figure 5] FIG. 1 is a diagram showing the emissivity spectrum of vinyl chloride resin. [Figure 6] FIG. 1 is a diagram showing the emissivity spectrum of vinylidene chloride resin. [Figure 7] FIG. 1 is a diagram showing the emissivity spectrum of ethylene terephthalate resin. [Figure 8] FIG. 10 is a diagram showing the relationship between the temperature of the radiation surface and the temperature of the light reflecting layer. [Figure 9] FIG. 1 is a diagram showing the light absorptance spectrum of ethylene terephthalate resin. DETAILED DESCRIPTION OF THE INVENTION

[0044] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [Basic structure of resin laminate film] As shown in FIG. 1, the resin laminate film CP includes an infrared emitting layer J that emits infrared light IR from an emitting surface H, and 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 is present, in a laminated state, and is formed into a film shape. That is, the laminated resin film CP is configured as a radiative cooling film.

[0045] The light-reflecting layer B has a plurality of pores K and is made of a second resin, and the infrared-emitting layer J is made of a first resin that emits thermal radiation energy at a wavelength of 8 μm to 13 μm that is greater than the absorbed solar light energy. The infrared-emitting layer J contains fewer pores K than the light-reflecting layer B, and the infrared-emitting layer J is a layer that does not substantially contain pores K.

[0046] Furthermore, the laminated resin layer M, which is a combination of the light-reflecting layer B and the infrared-emitting layer J, is configured so that the arithmetic mean reflectance, which is the wavelength average of the light reflectance at wavelengths of 400 nm to 800 nm, is 80% or more, the arithmetic mean reflectance, which is the wavelength average of the light reflectance at wavelengths of 800 nm to 1200 nm, is 70% or more, and the wavelength average of the emissivity at wavelengths of 8 μm to 13 μm is 43% or more. In this specification, the laminated resin layer M is a concept that also includes the connection layer S that connects the light reflecting layer B and the infrared emitting layer J.

[0047] More preferably, the laminated resin layer M has an arithmetic mean reflectance, which is the wavelength average of the reflectance of light over wavelengths of 400 nm to 800 nm, of 84% or more, and an arithmetic mean reflectance, which is the wavelength average of the reflectance of light over wavelengths of 800 nm to 1200 nm, of 75% or more, and the laminated resin layer M has an arithmetic mean reflectance, which is the wavelength average of the reflectance of light over wavelengths of 400 nm to 800 nm, of 88% or more, and an arithmetic mean reflectance, which is the wavelength average of the reflectance of light over wavelengths of 800 nm to 1200 nm, of 80% or more. Furthermore, the laminated resin layer M more preferably has an average wavelength emissivity of 70% or more in the wavelength range of 8 μm to 13 μm, and even more preferably has an average wavelength emissivity of 85% or more. Incidentally, the reflectivity can be improved by selecting materials for the infrared radiation layer J, the connection layer S, and the light-reflecting layer B that have a large difference in refractive index from each other. As an example, polyvinylidene chloride containing TiO2 can be used for the infrared radiation layer, an acrylic adhesive can be used for the connection layer S, and PET containing multiple pores can be used for the light-reflecting layer B.

[0048] By having this characteristic, the laminated resin layer M can suppress the solar energy absorption to 2% or less, and the solar energy absorbed at the meridian in the summer in Japan can be reduced to 20 W / m 2 It can be about.

[0049] In this embodiment, light L includes ultraviolet light, visible light, and infrared light, and when these are described in terms of the wavelength of light as electromagnetic waves, they include electromagnetic waves with wavelengths of 10 nm to 20,000 nm (electromagnetic waves of 0.01 μm to 20 μm). The solar spectrum exists in the wavelength range from 300 nm to 4000 nm, and the intensity increases as the wavelength increases from 400 nm, and the intensity is particularly high in the wavelength range from 500 nm to 1800 nm.

[0050] In this embodiment, the laminated resin layer M is configured so that the arithmetic mean transmittance, which is the wavelength average of the light transmittance in the wavelength range of 400 nm to 800 nm, is 1% or more and 12% or less.

[0051] Therefore, the resin laminate film CP is configured to reflect a portion of the light L incident on the resin laminate film CP at the radiation surface H of the infrared radiation layer J, and to reflect the light (sunlight, etc.) that is transmitted through the infrared radiation layer J out of the light L incident on the resin laminate film CP at the light reflecting layer B and allow it to escape to the outside from the radiation surface H.

[0052] The resin laminate 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 side where the infrared radiation layer J is present (for example, heat input due to thermal conduction from the object to be cooled), by converting the heat into infrared light IR by the infrared radiation layer J and radiating it, thereby cooling the object to be cooled.

[0053] In other words, the resin laminate film CP is configured to reflect light L irradiated onto the resin laminate film CP and to radiate heat transferred to the resin laminate film CP (for example, heat transferred from the atmosphere or from the object to be cooled) to the outside as infrared light IR. Furthermore, the infrared radiation layer J and the light reflection layer B are flexible, so that the laminated resin film CP (radiative cooling film) is configured to be flexible.

[0054] The light-reflecting layer B and the infrared-emitting layer J are connected by a connecting layer S made of at least one of an adhesive, a pressure-sensitive adhesive, and a glue. Although not shown, the connecting layer S may contain at least one of a filler and hollow particles, thereby improving the reflectance of light in the ultraviolet to visible light range and enabling the thickness of the laminated resin layer M (particularly the light-reflecting layer) to be reduced to obtain the desired reflectance. The filler and hollow particles preferably have an arithmetic mean particle diameter of approximately 0.1 μm to 5 μm. Examples of suitable fillers include granulated titanium oxide, glass microbeads, silicon dioxide, ground calcium carbonate powder, barium sulfate, zinc sulfate, aluminum silicate, ground calcium carbonate, aluminum oxide, zinc oxide, zirconium oxide, cerium oxide, lanthanum oxide, rhodium oxide, magnesium oxide, and barium titanate. This improves the reflectance of light in the ultraviolet to visible region, and reduces the thickness of the laminated resin layer M (particularly the light reflecting layer B) to obtain a desired reflectance.

[0055] In addition, the resin laminate 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 infrared radiation layer J from the surface that contacts the light reflecting layer B. Specifically, the radiation surface H is directed toward the sky, and the radiation cooling method is implemented in which infrared light IR is radiated from the radiation surface H that faces the sky.

[0056] [Infrared radiation layer] The first resin forming the infrared-emitting layer J preferably contains an ultraviolet absorber, and the infrared-emitting layer J preferably has an arithmetic mean reflectance of 50% or less, which is the wavelength average of the reflectance of ultraviolet rays in the wavelength range of 340 nm to 400 nm. Suitable ultraviolet absorbers include benzotriazole-based ultraviolet absorbers, triazine-based ultraviolet absorbers, hindered amine-based stabilizers, benzophenone-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, and oxanilide-based ultraviolet absorbers. Benzotriazole-based ultraviolet absorbers, triazine-based ultraviolet absorbers, and hindered amine-based stabilizers are particularly preferred because they can absorb ultraviolet rays up to the longer wavelength side. The first resin preferably contains at least one of polyethylene terephthalate, polyethylene naphthalate, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, and polymethyl methacrylate, and more preferably contains at least one of polyvinyl chloride, polyvinylidene chloride, and polyvinylidene fluoride.

[0057] The first resin forming the infrared radiation layer J can be a colorless resin material containing a carbon-fluorine bond (CF), a carbon-chlorine bond (C-Cl), a carbon-oxygen bond (CO), an ester bond (R-COO-R), an ether bond (COC bond), or a benzene ring. For each resin material (excluding carbon-oxygen bonds), the wavelength ranges with absorption coefficients in the atmospheric window wavelength band are shown in Figure 3.

[0058] According to Kirchhoff's law, emissivity (ε) and light absorptance (A) are equal. Light absorptance can be calculated from the absorption coefficient (α) using the equation A=1-exp(-αt) (hereafter referred to as the light absorptance equation), where t is the film thickness. In other words, by adjusting the film thickness of the infrared radiation layer J, it is possible to obtain a large thermal radiation in a wavelength band with a large absorption coefficient. When performing radiative cooling outdoors, it is recommended to use a material with a large absorption coefficient in the wavelength band of 8 μm to 13 μm, which is the atmospheric window. In addition, to suppress the absorption of sunlight, it is advisable to use a material that has no or a small absorption coefficient in the wavelength range of 0.3 μm to 4 μm, especially in the range of 0.4 μm to 2.5 μm. As can be seen from the relationship between the absorption coefficient and absorptance, the light absorptance (emissivity) changes depending on the film thickness of the resin material.

[0059] 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.

[0060] Regarding carbon-fluorine bonds (CF), the absorption coefficients due to CHF and CF2 are widely distributed over a wide wavelength band from 8 μm to 13 μm, which is the atmospheric window, with a particularly large absorption coefficient at 8.6 μm. In addition, in the solar wavelength band, there is no significant absorption coefficient in the wavelength range from 0.3 μm to 2.5 μm, where the energy intensity is high.

[0061] Resin materials with carbon-fluorine bonds (CF) include: One example is polyvinylidene fluoride (PVDF), a partially fluorinated resin. In the following, polyvinylidene fluoride may be referred to as vinylidene fluoride resin, but the two terms are used to refer to the same material. The same applies to other resins.

[0062] For carbon-chlorine bonds (C-Cl), the absorption coefficient due to the C-Cl stretching vibration appears in a broad band with a half-width of 1 μm or more centered at a wavelength of 12 μm. Resin materials include polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC). In the case of polyvinyl chloride, the electron-withdrawing effect of chlorine causes an absorption coefficient at a wavelength of around 10 μm that is derived from the bending vibration of the CH of the alkene contained in the main chain.

[0063] Ester bonds (R-COO-R) and ether bonds (COC bonds) have absorption coefficients in the wavelength range of 7.8 μm to 9.9 μm. In addition, the carbon-oxygen bonds contained in ester bonds and ether bonds have strong absorption coefficients in the wavelength range of 8 μm to 10 μm. When a benzene ring is introduced into the side chain of a hydrocarbon resin, absorption appears over a wide wavelength range from 8.1 μm to 18 μm due to the vibration of the benzene ring itself and the vibration of surrounding elements caused by the influence of the benzene ring.

[0064] Resins having these bonds include ethylene terephthalate resin, ethylene naphthalate resin, and polymethyl methacrylate resin.

[0065] [Considerations of light absorption] Let us consider the light absorption in the ultraviolet-visible region of resin materials with the bonds and functional groups described above, i.e., sunlight absorption. The origin of the absorption of ultraviolet to visible light is the transition of electrons that contribute to the bond. Absorption in this wavelength range can be understood by calculating the bond energy. First, let's consider the wavelengths at which resin materials with carbon-fluorine bonds (CF) have absorption coefficients in the ultraviolet to visible range. The bond energies of the CC, CH, and CF bonds in the basic structural parts of polyvinylidene fluoride (PVDF) are 4.50 eV, 4.46 eV, and 5.05 eV. These correspond to wavelengths of 0.275 μm, 0.278 μm, and 0.246 μm, respectively, and light of these wavelengths is absorbed.

[0066] Since the solar spectrum only contains wavelengths longer than 0.300 μm, when fluororesin is used, it hardly absorbs the ultraviolet, visible, or near-infrared rays of sunlight. Note that ultraviolet rays are defined as wavelengths shorter than 0.400 μm, visible light is defined as wavelengths from 0.400 μm to 0.800 μm, near-infrared rays are defined as wavelengths from 0.800 μm to 3 μm, mid-infrared rays are defined as wavelengths from 3 μm to 8 μm, and far-infrared rays are wavelengths longer than 8 μm.

[0067] 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 4 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. Figure 4 shows the absorption spectrum of a 100 μm thick vinylidene chloride resin in the ultraviolet to visible region, and shows a slight increase in the absorption spectrum on the shorter wavelength side than 0.4 μm.

[0068] Resins with ester bonds (R-COO-R), ether bonds (C-O-C bonds), and benzene rings include methyl methacrylate resin, ethylene terephthalate resin, and ethylene naphthalate resin. For example, the bond energy of the C-C bond in acrylic is 3.93 eV, and it absorbs sunlight with wavelengths shorter than 0.315 μm, but has almost no absorption in the visible range.

[0069] As an example of a resin material having these bonds and functional groups, the absorbance spectrum from ultraviolet to visible light of a 5 mm thick methyl methacrylate resin is shown in Figure 4. The methyl methacrylate resin shown here is a commonly available product on the market, and contains a benzotriazole-based ultraviolet absorber. Because the plate is 5 mm thick, the wavelengths with small absorption coefficients are also large, and light absorption is greater on the shorter wavelength side than 0.38 μm, which is longer than the wavelength of 0.315 μm.

[0070] As an example of a resin material having these bonds and functional groups, the absorption spectrum from ultraviolet to visible light of a 40 μm thick ethylene terephthalate resin is shown in FIG. As shown in the figure, the absorptance increases as the wavelength approaches 0.315 μm, and absorbance increases sharply at a wavelength of 0.315 μm. Note that with ethylene terephthalate resin, as the thickness increases, the absorptance due to the absorption edge derived from C-C bonds increases at wavelengths slightly longer than 0.315 μm, and similar to methyl methacrylate resin, the absorptance in ultraviolet light increases.

[0071] The infrared radiation layer J may be a single layer film made of one type of resin material, a multilayer film made of multiple types of resin materials, a single layer film made of a resin material in which multiple types of resin materials are blended, or a multilayer film made of a resin material in which multiple types of resin materials are blended, as long as it is made of a resin material having the above-mentioned emissivity (light emissivity) and light absorptivity properties. The blends also include copolymers such as alternating copolymers, random copolymers, block copolymers and graft copolymers, as well as modified products with substituted side chains.

[0072] [Emissivity of vinyl chloride resin and vinylidene chloride resin] Figure 5 shows the emissivity of polyvinyl chloride resin (PVC) at the atmospheric window, as a representative example of resins with carbon-chlorine bonds. Figure 6 shows the emissivity of polyvinylidene chloride resin (PVDC) at the atmospheric window. Regarding the carbon-chlorine bond, the absorption coefficient due to the C-Cl stretching vibration appears in a broad band with a half-width of 1 μm or more centered at a wavelength of 12 μm. In addition, in the case of vinyl chloride resin, the electron-withdrawing effect of chlorine causes an absorption coefficient at a wavelength of around 10 μm, which is due to the bending vibration of the CH of the alkene contained in the main chain. The same is true for vinylidene chloride resin. Due to these effects, the wavelength average of the emissivity for a 10 μm thick film is 43% at wavelengths from 8 μm to 13 μm, which falls within the wavelength average of 43% or more as specified. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

[0073] [Emissivity of ethylene terephthalate resin] Figure 7 shows the emissivity of ethylene terephthalate resin in the atmospheric window as a typical example of a resin having an ester bond or a benzene ring. Ester bonds have an absorption coefficient in the wavelength range of 7.8 μm to 9.9 μm. Furthermore, the carbon-oxygen bond contained in the ester bond exhibits a strong absorption coefficient in the wavelength range of 8 μm to 10 μm. When a benzene ring is introduced into the side chain of a hydrocarbon resin, a wide range of absorption appears in the wavelength range of 8.1 μm to 18 μm due to the vibration of the benzene ring itself and the vibration of surrounding elements caused by the influence of the benzene ring. Due to these effects, the wavelength average of the emissivity for a 10 μm thick film is 71% at wavelengths from 8 μm to 13 μm, which falls within the wavelength average of 40% or more. As shown in the figure, the emissivity in the atmospheric window region increases as the film thickness increases.

[0074] [Surface temperature of light reflecting layer and infrared emitting layer] The thermal radiation of the atmospheric window of the infrared radiation layer J occurs near the surface of the resin material. Figure 5 shows that in the case of vinyl chloride resin, even if the thickness exceeds 100 μm, there is almost no increase in thermal radiation in the atmospheric window region. In other words, in the case of vinyl chloride resin, thermal radiation in the atmospheric window occurs within a depth of approximately 100 μm from the surface, and radiation from deeper parts does not escape to the outside. From FIG. 6, it can be seen that vinylidene chloride resin is similar to vinyl chloride resin.

[0075] As can be seen from Figure 7, in the case of ethylene terephthalate resin, even if the thickness exceeds 125 μm, there is almost no increase in thermal radiation in the atmospheric window region. In other words, in the case of ethylene terephthalate resin, thermal radiation in the atmospheric window occurs in a region about 100 μm deep from the surface, and radiation from deeper regions does not escape to the outside.

[0076] As described above, the thermal radiation from the atmospheric window region generated from the surface of the resin material occurs within a depth of approximately 100 μm from the surface. If the resin thickness increases beyond this, the cold generated by the radiation cooling of the resin laminate film is insulated by the resin material that does not contribute to thermal radiation. Ideally, the infrared emitting layer J is made of a first resin that does not absorb sunlight at all, and the infrared emitting layer J is fabricated on the light reflecting layer B. In this case, sunlight is absorbed only by the light reflecting layer B of the resin laminate 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.

[0077] Even if an ideal resin material that does not absorb sunlight at all exists, the thermal conductivity of the first resin of the infrared radiation layer J is generally around 0.2 W / m / K, so if the thickness exceeds 20 mm as shown in Figure 8, the light-reflecting layer B will be heated by sunlight, and the object to be cooled placed on the side of the light-reflecting layer B will be heated. In other words, the thickness of the first resin of the infrared radiation layer J needs to be 20 mm or less.

[0078] Figure 8 is a plot of the surface temperature of the radiative surface H of the resin laminated film (radiative cooling film) and the temperature of the light-reflecting layer B, calculated assuming a sunny day in western Japan in the summer at noon. The sunlight is assumed to be AM1.5, and the average value of the solar radiation intensity during the day in summer is 350 W / m 2 The outside temperature is 30°C, and the radiant energy varies depending on the temperature, but is 100W at 30°C. This calculation assumes that no sunlight is absorbed by the infrared radiation layer J. Assuming no wind, the convective heat transfer coefficient is 5W / m 2 / K.

[0079] [Light absorption of hydrocarbon resins] If the resin materials (first resin, second resin) are resins whose main chain is a hydrocarbon having one or more carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, or benzene rings, then in addition to the ultraviolet absorption due to the covalently bonded electrons mentioned above, absorption due to vibrations such as bond bending and stretching is observed in the near-infrared region.

[0080] Specifically, absorption due to the fundamental tones of the transitions to the first excited states of CH3, CH2, and CH appears at wavelengths of 1.6 μm to 1.7 μm, 1.65 μm to 1.75 μm, and 1.7 μm, respectively. Furthermore, absorption due to the fundamental tones of the combination tones of CH3, CH2, and CH appears at wavelengths of 1.35 μm, 1.38 μm, and 1.43 μm, respectively. Furthermore, overtones of the transitions to the second excited states of CH2 and CH appear at wavelengths around 1.24 μm. The fundamental tones of the bending and stretching of the C-H bond are distributed over a wide band from 2 μm to 2.5 μm.

[0081] Furthermore, when an ester bond (R-COO-R) or an ether bond (COC) is present, there is a large optical absorption at a wavelength of around 1.9 μm. According to the above-mentioned optical absorptance relational expression, the optical absorptance caused by these factors becomes smaller and less noticeable when the resin material film is thin, but becomes larger when the film is thick.

[0082] FIG. 9 shows the relationship between the light absorptance and the spectrum of sunlight when the film thickness of ethylene terephthalate resin having an ester bond and a benzene ring is changed. As shown in the figure, as the film thickness increases to 25 μm, 125 μm, and 500 μm, the light absorption in the wavelength range longer than 1.5 μm, which is caused by the respective vibrations, increases. Furthermore, the optical absorption increases not only on the long wavelength side but also from the ultraviolet region to the visible region, due to the broadening of the optical absorption edge caused by chemical bonding.

[0083] When the film thickness is thin, the light absorption rate is high at the wavelength with the largest absorption coefficient, but as the film thickness increases, a weak absorption coefficient at the broadened absorption edge appears as the absorptance according to the light absorption rate relational expression mentioned above. As a result, as the film thickness increases, light absorption increases from the ultraviolet region to the visible region. Regarding reflectance, if the arithmetic mean reflectance, which is the wavelength average of light reflectance at wavelengths from 400nm to 800nm, is 80% or more, and the arithmetic mean reflectance, which is the wavelength average of light reflectance at wavelengths from 800nm ​​to 1200nm, is 43% or more, then if the absorption energy of sunlight and the wavelength average of the emissivity at wavelengths from 8μm to 13μm are 43% or more, then the solar energy is 350W / m 2 Absorption is 85W / m 2 Furthermore, if the emissivity is 43% or more, the radiation can be reduced to 200W / m on a day with good atmospheric conditions. 2 85W / m for radiation of about 2 In other words, it is preferable that the laminated resin layer including the light-reflecting layer and the infrared-emitting layer has an arithmetic mean reflectance, which is the wavelength average of the light reflectance at wavelengths of 400 nm to 800 nm, of 80% or more, an arithmetic mean reflectance, which is the wavelength average of the light reflectance at wavelengths of 800 nm to 1200 nm, of 70% or more, and a wavelength average of the emissivity at wavelengths of 8 μm to 13 μm of 43% or more.

[0084] If light-reflecting layer B exhibits a reflectance of 80% or more from 400nm to 800nm ​​and a reflectance of 70% or more from 800nm ​​to 1200nm, the solar energy absorbed by the light-reflecting layer B of the radiative cooling device (radiative cooling film) can be reduced to 25% or less, meaning that the solar energy absorbed at noon in summer can be reduced to about 85W. Furthermore, although the atmospheric window narrows when humidity is high, even if radiation drops to about 125W / m2, for example, an emissivity of 70% or more is desirable because it can emit more energy than solar energy.

[0085] As mentioned above, the maximum value of infrared radiation in the wavelength band of the atmospheric window in the summer in lowlands of Japan is about 160W at 30°C on a day with good atmospheric conditions, and is usually about 125W. If both the first resin forming the infrared emitting layer J and the second resin forming the light reflecting layer B are ethylene terephthalate resin, a hydrocarbon-based resin, and the thickness of each is 500 μm, the sum of the solar light absorption of the laminated resin layer M (both the infrared emitting layer J and the light reflecting layer B) is 176 W / m 2 This becomes: From the above, when both the first resin forming the infrared emitting layer J and the second resin forming the light reflecting layer B are made of ethylene terephthalate resin, a hydrocarbon-based resin, if the film thickness of each of the infrared emitting layer J and the light reflecting layer B is 500 μm or more, that is, if the film thickness of the laminated resin layer M is 1000 μm or more, the radiative cooling performance will not be exhibited. In other words, the thickness of the first resin of the infrared emitting layer J and the thickness of the second resin of the light reflecting layer B are each preferably 500 μm or less. The thickness of the first resin of the infrared emitting layer J and the thickness of the second resin of the light reflecting layer B are preferably 10 μm or more, and the lower limit of the film thickness is determined from the viewpoint of ensuring infrared emissivity and light reflectivity.

[0086] [Light absorption of blended resins] When the resin material (first resin, second resin) is a blend of a resin with a carbon-fluorine bond as its main chain and a resin with a hydrocarbon as its main chain, light absorption in the near-infrared region due to CH, CH2, CH3, etc. appears depending on the proportion of the blended resin with a hydrocarbon as its main chain. When carbon-fluorine bonds are the main component, the light absorption in the near-infrared region caused by hydrocarbons is small, so the thickness can be increased up to 20 mm, which is the upper limit from the viewpoint of thermal conductivity. However, when a blended hydrocarbon resin is the main component, the thickness of each of the first resin and second resin must be 500 μm or less.

[0087] The blend of fluororesin and hydrocarbon also includes those in which the fluororesin is substituted with hydrocarbon, and alternating copolymers, random copolymers, block copolymers and graft copolymers of fluoromonomers and hydrocarbon monomers.

[0088] Depending on the molecular weight and proportion of the hydrocarbon side chains substituted, optical absorption in the near-infrared region due to CH, CH2, CH3, etc. appears. When the monomers introduced as side chains or copolymers are low molecular weight, or when the density of the introduced monomers is low, optical absorption in the near-infrared region due to hydrocarbons becomes small, so the thickness can be increased up to 20 mm, which is the limit from the viewpoint of thermal conductivity. When a high molecular weight hydrocarbon is introduced as a side chain of the fluororesin or as a copolymerizable monomer, the thickness of each of the first resin and the second resin must be 500 μm or less.

[0089] [Thickness of the infrared radiation layer] From the viewpoint of practical use of the resin laminate film CP, it is preferable that the thickness of the infrared radiation layer J is thin. The thermal conductivity of resin materials is generally lower than that of metals, glass, etc. In order to effectively cool the object to be cooled, it is preferable that the thickness of the infrared radiation layer J is kept to the minimum necessary. The thicker the thickness of the infrared radiation layer J, the greater the thermal radiation from the atmospheric window, and once a certain thickness is exceeded, the thermal radiation energy from the atmospheric window becomes saturated.

[0090] The thickness at which the film saturates depends on the resin material, but in the case of fluororesin, saturation is generally sufficient at around 300 μm. Therefore, from the perspective of thermal conductivity, it is preferable to keep the film thickness below 300 μm rather than 500 μm. Furthermore, although thermal radiation does not saturate, even a thickness of around 100 μm can provide sufficient thermal radiation in the atmospheric window region. The thinner the thickness, the higher the thermal conductivity and the more effectively the temperature of the object being cooled can be lowered, so in the case of fluororesin, it is best to keep the thickness below around 100 μm.

[0091] The absorption coefficients resulting from carbon-silicon bonds, carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds are greater than the absorption coefficient resulting from C—F bonds. Naturally, from the perspective of thermal conductivity, it is preferable to keep the film thickness to 300 μm or less rather than 500 μm, but an even greater radiative cooling effect can be expected if the film thickness is made even thinner and thermal conductivity is increased. In the case of resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, saturation occurs even at a thickness of 100 μm, and sufficient thermal radiation is obtained in the atmospheric window region at a thickness of 50 μm. The thinner the resin material, the higher the thermal transmittance and the more effectively the temperature of the object being cooled can be lowered, so in the case of resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, and benzene rings, a thickness of 50 μm or less reduces the insulating properties and allows the object to be cooled effectively. In the case of carbon-chlorine bonds, a thickness of 100 μm or less allows the object to be cooled effectively.

[0092] Thinner film has another benefit besides lowering heat insulation and making it easier to transfer heat. It also reduces the absorption of near-infrared light from CH, CH2, and CH3 in the near-infrared region, which is exhibited by resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, and ether bonds. Thinner film reduces the amount of sunlight absorbed by these bonds, which increases the cooling capacity of the resin laminate film CP. From the above perspective, in the case of resins containing carbon-chlorine bonds, carbon-oxygen bonds, ester bonds, ether bonds, or benzene rings, a thickness of 50 μm or less can more effectively produce a radiative cooling effect under sunlight.

[0093] In the case of carbon-silicon bonds, thermal radiation is saturated in the atmospheric window region even at a thickness of 50 μm, and sufficient thermal radiation can be obtained in the atmospheric window region even at a thickness of 10 μm. The thinner the infrared radiation layer J, the higher the thermal transmittance and the more effectively the temperature of the object to be cooled can be lowered. Therefore, in the case of resins containing carbon-silicon bonds, a thickness of 10 μm or less reduces the insulating properties and allows the object to be cooled more effectively. Thinner films can reduce solar absorption, thereby increasing the cooling capacity of the resin laminate film CP. From the above perspective, in the case of resins containing carbon-silicon bonds, a thickness of 10 μm or less can more effectively produce a radiative cooling effect under sunlight.

[0094] As will be described later, in the resin laminate film CP according to this embodiment, a resin is also used for the light-reflecting layer B. Although the light-reflecting layer B contains pores K at a certain volumetric ratio, a certain amount of heat radiation can be expected. In consideration of this point, it is preferable to further reduce the thickness of the infrared-emitting layer J described above.

[0095] [Details of the light-reflecting layer] The light-reflecting layer B has the above-mentioned reflection characteristics (reflecting characteristics as the laminated resin layer M) by making the refractive index of the second resin forming the light-reflecting layer different from the refractive index of the material inside the multiple voids K contained in the second resin. Specifically, the second resin of the light-reflecting layer B preferably contains at least one of polyethylene terephthalate, polypropylene, polyethylene, polyethylene naphthalate, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polymethyl methacrylate, and polycarbonate. Conversely, polyimide and bakelite are not desirable as the second resin of the light-reflecting layer B because the resin itself is easily discolored and tends to have low reflectance.

[0096] Furthermore, various gases or fluids can be contained inside the pores K of the second resin of the light reflecting layer B, but air is preferably contained therein. The refractive index of the pores K (more specifically, the gas or fluid contained in the pores K) is smaller than that of the second resin. Furthermore, it is preferable that the arithmetic mean pore diameter of the pores K is 0.1 μm or more and 3.0 μm or less. In this embodiment, the arithmetic mean pore diameter means the arithmetic mean of the smallest inner diameters of the pores K. The shape of the voids K can be various shapes such as spherical or elliptical, but from the viewpoint of improving light reflectance, it is preferable that they be flat, and more preferably, the long axis of the voids K is aligned in the direction along the film surface (radiating surface H) of the resin laminated film CP. Furthermore, the volume fraction of the pores K in the light reflecting layer B is preferably 0.1% by volume or more and 60% by volume or less, more preferably 1% by volume or more and 50% by volume or less, and even more preferably 10% by volume or more and 40% by volume or less.

[0097] Furthermore, as a result of extensive research by the inventors, the thickness of the second resin of the light-reflecting layer B is preferably 10 μm or more and 500 μm or less. By making the thickness of the second resin of the light-reflecting layer B 10 μm or more, the light-reflecting layer B made of the second resin having a plurality of pores K can satisfactorily ensure the reflectivity required for radiative cooling. In addition, by making the thickness 500 μm or less, the insulating effect of the second resin having pores K containing air or the like can be kept below a certain level, thereby ensuring a certain level of cooling performance for the object to be cooled. The thickness of the second resin of the light-reflecting layer B is preferably 50 to 300 μm, and more preferably 75 to 200 μm. A thickness of 500 μm or more reduces the thermal conductivity in the thickness direction and increases the insulating properties. Therefore, when applied to a housing with an internal heat source, the tendency for heat accumulation within the housing increases, which is undesirable from the perspective of thermal radiation.

[0098] 2, the resin laminate film CP may contain filler F (F1, F2) in the first resin forming the infrared emitting layer J and the second resin forming the light reflecting layer B. The filler F (F1, F2) may be contained in at least one of the first resin forming the infrared emitting layer J and the second resin forming the light reflecting layer B. The filler F (F1, F2) can be one or more of titanium oxide, glass microbeads, silicon dioxide, ground calcium carbonate powder, barium sulfate, zinc sulfate, aluminum silicate, ground calcium carbonate, aluminum oxide, zinc oxide, zirconium oxide, cerium oxide, lanthanum oxide, rhodium oxide, magnesium oxide, and barium titanate, and the filler F1 contained in the first resin and the filler F2 contained in the second resin may be different materials.

[0099] [Experimental results] For the examples and comparative examples of the laminated resin films described above, various tests were conducted on antifouling properties, ultraviolet reflectance, reflectance at wavelengths of 400 nm to 800 nm, reflectance at wavelengths of 800 nm to 1200 nm, transmittance at wavelengths of 400 nm to 800 nm, infrared emissivity, thermal conductivity, xenon weather resistance, and electromagnetic wave transmittance, and the results are shown in the following Tables 1 to 4. In the test results shown in the tables, underlined portions indicate that the conditions of the various tests were not met. Incidentally, Tables 1 to 4 also show various conditions for the films constituting the Examples and Comparative Examples.

[0100] Stain resistance was evaluated using the color difference ΔE before and after a one-month outdoor exposure test in Osaka City, with a ΔE<2.0 defined as high (good) stain resistance. Note that color difference ΔE refers to the "CIEDE2000 color difference" based on JIS Z8781.

[0101] UV reflectance was evaluated using the arithmetic mean of reflectance in the wavelength range of 340 nm to 400 nm measured using a UV-Visible Spectrometer UV-2600 (Shimadzu Corporation). A reflectance of 50% or less was defined as meeting the criteria (low UV reflectance).

[0102] The reflectance in the wavelength range of 400 to 800 nm was evaluated using the arithmetic mean of the reflectance in the wavelength range of 400 to 800 nm measured using a UV-Visible spectrometer UV-2600 (Shimadzu Corporation). A reflectance of 80% or higher was defined as satisfying the condition (high reflectance in the wavelength range of 400 to 800 nm).

[0103] The reflectance in the wavelength range of 800 to 1200 nm was evaluated using the arithmetic mean of the reflectance in the wavelength range of 800 to 1200 nm measured using a UV-Visible spectrometer UV-2600 (Shimadzu Corporation). A reflectance of 70% or higher was defined as satisfying the condition (high reflectance in the wavelength range of 800 to 1200 nm).

[0104] The transmittance in the wavelength range of 400 to 800 nm was evaluated using the arithmetic mean of the transmittance in the wavelength range of 400 to 800 nm measured using a UV-Visible spectrometer UV-2600 (Shimadzu Corporation). A transmittance of 1% or more was defined as satisfying the condition (high transmittance in the wavelength range of 400 to 800 nm).

[0105] Infrared emissivity was evaluated using the arithmetic mean of the emissivity at wavelengths from 8 μm to 13 μm measured using an FT-IR Tracer-100 (Shimadzu Corporation). Materials with an emissivity of 70% or higher were defined as meeting the criteria (high reflectivity at wavelengths from 400 nm to 800 nm).

[0106] Thermal conductivity was measured using the laser flash method defined in JIS R1611, and a thermal conductivity of 0.3 W / m·K or higher was defined as high (good) thermal conductivity.

[0107] Xenon weather resistance is measured in the xenon weather resistance test defined in JIS K5600, where the black panel temperature (BPT) is 63°C and the ultraviolet intensity is 180W / m 2 The sample was exposed to ultraviolet light for 3000 hours, and the color difference ΔE between before and after the test was measured. Samples with a ΔE of <2.0 were defined as having high (good) weather resistance.

[0108] 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.

[0109] In the table, PET stands for polyethylene terephthalate, PEN stands for polyethylene naphthalate, PVC stands for polyvinyl chloride, PVDC stands for polyvinylidene chloride, PVDF stands for polyvinylidene fluoride (polyvinylidene fluoride), and PP stands for polypropylene.

[0110] The sample of Example 1 was prepared by forming a thin film of vinyl chloride resin containing TiO2 by a calendaring method, and bonding it to a PET film containing TiO2 by a dry lamination method.

[0111] [Table 1]

[0112] [Table 2]

[0113] [Table 3]

[0114] [Table 4]

[0115] As shown by the above experimental results, the resin laminate films CP according to Examples 1 to 16 of the present invention satisfy the specified conditions in terms of antifouling properties, ultraviolet reflectance, reflectance at wavelengths of 400 nm to 800 nm, reflectance at wavelengths of 800 nm to 1200 nm, transmittance at wavelengths of 400 nm to 800 nm, infrared emissivity, thermal conductivity, xenon weather resistance, and electromagnetic wave transmittance.

[0116] On the other hand, in Comparative Examples 1 to 4, a relatively large number of pores K are formed in the infrared radiation layer J as a surface layer, so the antifouling condition is not satisfied and the layer is susceptible to adhesion of dirt. In Comparative Examples 1 and 5, since the second resin as the light-reflecting layer B is not provided, the conditions for reflectance at wavelengths of 400 nm to 800 nm and reflectance at wavelengths of 800 nm to 1200 nm are not satisfied, resulting in low reflectance. In Comparative Example 6, PET vapor-deposited with metallic silver was used as the light-reflecting layer B, which did not meet the transmittance requirements for wavelengths of 400 nm to 800 nm, resulting in poor light transmission and not meeting the requirements for radio wave transmittance. In addition, in Comparative Examples 1 and 5, the infrared emissivity does not satisfy the conditions because the second resin as the light-reflecting layer B is not provided, and it is presumed that the second resin as the light-reflecting layer B contributes to the infrared emissivity to a certain extent. In Comparative Examples 2 and 4, it is presumed that the infrared emissivity conditions are not satisfied because a plurality of pores K are provided in the relatively thin 100 μm infrared-emitting layer J. In Comparative Examples 3 and 4, the resin layer having voids K was thick, resulting in a low thermal conductivity for the entire material, and therefore the thermal conductivity conditions were not met. In Comparative Examples 1 to 5, the weather resistance of the PET against ultraviolet rays was insufficient, and yellowing occurred when xenon weather resistance was evaluated, so the xenon weather resistance conditions were not met.

[0117] [Another embodiment] (1) The radiation surface H of the infrared radiation layer J may be protected by a protective layer (not shown). The protective layer may be made of a material such as fluorine or acrylic fluorine, and its thickness is preferably about 0.1 μm or more and 100 μm or less. Polyethylene or polypropylene, which has a low emissivity at the atmospheric window, may be used as the material. The protective layer has a stain-proof function, a scratch-proof function, and also serves as a sacrificial layer.

[0118] (2) A connecting resin layer may be provided on the side of the reflective layer B opposite to the infrared radiation layer J. As an example, the connecting resin layer may be a connecting layer made of polyvinyl chloride, which allows for suitable connection to a film material made of vinyl chloride, a tarpaulin, or a steel plate.

[0119] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradictions arise. Furthermore, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited to these, and can be modified as appropriate within the scope that does not deviate from the purpose of the present invention. [Industrial Applicability]

[0120] The resin laminate film of the present invention can be effectively used as a resin laminate film that can exhibit high cooling capacity under direct sunlight and high radio wave transmittance, and can prevent a decrease in radiative cooling performance when holes are provided in the resin material and a decrease in cooling performance due to contamination of the holes. [Explanation of symbols]

[0121] B: Light reflective layer CP: Resin laminated film F: Filler H: Radiation surface IR: Infrared light J: Infrared radiation layer K: Vacancy M: Laminated resin layer S: Connection layer

Claims

1. A resin laminate film comprising: an infrared emitting layer that emits infrared light from a radiation surface; and a light reflecting layer that is located on the infrared emitting layer on the opposite side to the side where the radiation surface is present, the light reflecting layer has a plurality of pores and is made of a second resin; the infrared radiation layer is made of a first resin that emits thermal radiation energy at a wavelength of 8 μm to 13 μm that is greater than the absorbed solar light energy; the number of pores contained in the infrared emitting layer is smaller than the number of pores contained in the light reflecting layer, The laminated resin layer including the light-reflecting layer and the infrared-emitting layer has an arithmetic mean reflectance, which is the wavelength average of light reflectance at wavelengths of 400 nm to 800 nm, of 80% or more, an arithmetic mean reflectance, which is the wavelength average of light reflectance at wavelengths of 800 nm to 1200 nm, of 70% or more, and a wavelength average of emissivity at wavelengths of 8 μm to 13 μm, of 43% or more.

2. The resin laminate film according to claim 1 , wherein the infrared radiation layer contains a filler in the first resin.

3. The resin laminate film according to claim 1 or 2, wherein the second resin has a thickness of 10 μm or more and 500 μm or less.

4. The resin laminate film according to claim 1 or 2, wherein the first resin has a thickness of 10 μm or more and 500 μm or less.

5. the pores in the second resin have a refractive index smaller than that of the second resin; 3. The resin laminate film according to claim 1, wherein the pores have an arithmetic mean pore size of 0.1 μm or more and 3.0 μm or less.

6. 3. The resin laminate film according to claim 1, wherein the volume ratio of the voids in the light reflecting layer is 0.1% by volume or more and 60% by volume or less.

7. 3. The resin laminate film according to claim 1, wherein the volume ratio of the voids in the resin laminate layer is 1% by volume or more and 50% by volume or less.

8. 3. The resin laminate film according to claim 1, wherein the volume ratio of the voids in the laminate resin layer is 10% by volume or more and 40% by volume or less.

9. The laminated resin layer has an arithmetic mean reflectance of 88% or more, which is the wavelength average of the reflectance of light having a wavelength of 400 nm to 800 nm, and an arithmetic mean reflectance of 800 nm to 1200 nm, which is the wavelength average of the reflectance of light having a wavelength of 800 nm to 1200 nm. The resin laminated film according to claim 1 or 2.

10. 3. The resin laminate film according to claim 1, wherein the laminate resin layer has an arithmetic mean transmittance, which is a wavelength average of light transmittance in the wavelength range of 400 nm to 800 nm, of 1% to 12%.

11. 3. The resin laminate film according to claim 1, wherein the laminate resin layer has an average wavelength emissivity of 70% or more in the wavelength range of 8 μm to 13 μm.

12. The resin laminate film according to claim 1 , wherein the second resin contains a filler.

13. 3. The resin laminate film according to claim 2, wherein the filler is one or more of titanium oxide, glass microbeads, silicon dioxide, ground calcium carbonate powder, barium sulfate, zinc sulfate, aluminum silicate, ground calcium carbonate, aluminum oxide, zinc oxide, zirconium oxide, cerium oxide, lanthanum oxide, rhodium oxide, magnesium oxide, and barium titanate.

14. 13. The resin laminate film according to claim 12, wherein the filler is at least one of titanium oxide, glass microbeads, silicon dioxide, ground calcium carbonate powder, barium sulfate, zinc sulfate, aluminum silicate, ground calcium carbonate, aluminum oxide, zinc oxide, zirconium oxide, cerium oxide, lanthanum oxide, rhodium oxide, magnesium oxide, and barium titanate.

15. 3. The resin laminate film according to claim 1, wherein the second resin comprises at least one of polyethylene terephthalate, polypropylene, polyethylene, polyethylene naphthalate, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, polymethyl methacrylate, and polycarbonate.

16. The resin laminate film according to claim 1 or 2, wherein the first resin comprises at least one of polyethylene terephthalate, polyethylene naphthalate, polyvinyl chloride, polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride, and polymethyl methacrylate.

17. The resin laminate film according to claim 1 or 2, wherein the first resin contains at least one of polyvinyl chloride, polyvinylidene chloride, and polyvinylidene fluoride.

18. the first resin contains an ultraviolet absorber, 3. The resin laminate film according to claim 1, wherein the infrared radiation layer has an arithmetic mean reflectance, which is a wavelength average of reflectance of ultraviolet rays having a wavelength of 340 nm to 400 nm, of 50% or less.

19. the light reflecting layer and the infrared emitting layer are connected by a connecting layer made of at least one of an adhesive, a pressure sensitive adhesive, and a glue; The resin laminate film according to claim 1 or 2, wherein the connection layer is included in the laminate resin layer.

20. The resin laminate film according to claim 19 , wherein the connection layer contains at least one of a filler and a hollow particle.

21. The resin laminate film according to claim 1 or 2, wherein the pores of the second resin have a flat shape.

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