JP7797274B2 - Radiative cooling film, how to use it, and how to make it - Google Patents

Description

The present invention is configured in a film body including an infrared emitting layer that emits infrared light from a radiation surface, a light reflecting layer made of silver or a silver alloy and located on the infrared emitting layer on the side opposite to the side on which the radiation surface is present, an adjacent-side protective layer located on the side of the light reflecting layer that is adjacent to the infrared emitting layer, and a remote-side protective layer located on the side of the light reflecting layer that is remote from the infrared emitting layer,
The present invention relates to a radiative cooling film in which the infrared radiation layer is a resin material layer whose thickness is adjusted to emit thermal radiation energy in the wavelength band of 8 μm to 14 μm that is greater than the absorbed solar light energy.

Radiation cooling is a phenomenon in which a substance's temperature drops when it radiates electromagnetic waves such as infrared rays into its surroundings. By utilizing this phenomenon, it is possible to create, for example, a radiative cooling film that cools an object without consuming energy such as electricity.

In radiative cooling films, the infrared emitting layer emits greater thermal radiation energy in the 8 μm to 14 μm wavelength band than the absorbed solar energy, and the light reflective layer sufficiently reflects sunlight, allowing the object to be cooled even in a daytime solar radiation environment.

In other words, the light reflecting layer reflects the light (ultraviolet light, visible light, infrared light) that has passed through the infrared radiation layer and radiates it from the radiation surface, thereby preventing the light (ultraviolet light, visible light, infrared light) that has passed through the infrared radiation layer from being projected onto the object to be cooled and heating the object, and thereby making it possible to cool the object to be cooled even in a daytime solar environment.
The light reflecting layer has the effect of reflecting, toward the infrared radiation layer, not only the light that has passed through the infrared radiation layer but also the light that is emitted from the infrared radiation layer toward the side where the light reflecting layer is present. However, in the following description, it will be explained that the purpose of providing the light reflecting layer is to reflect the light (ultraviolet light, visible light, and infrared light) that has passed through the infrared radiation layer.

In addition, by providing an adjacent-side protective layer located on the side of the light-reflecting layer adjacent to the infrared-emitting layer, and a distant-side protective layer located on the side of the light-reflecting layer away from the infrared-emitting layer, it is possible to prevent discoloration of silver and silver alloys due to moisture, and ensure that the light-reflecting layer properly reflects light.

Conventional examples of radiative cooling films include those in which the adjacent-side protective layer and the distant-side protective layer are made of materials such as acrylic resin, silicone resin, fluororesin, and oxide film (SiO ₂ , Al ₂ O ₃ ) (see, for example, Patent Document 1 (Fig. 15)).
Moreover, FIG. 17 of Patent Document 1 describes a radiative cooling film in which a film layer made of PET (polyethylene terephthalate) is provided as a separating-side protective layer, a light-reflecting layer and an adjacent-side protective layer are sequentially formed on the film layer, and the infrared radiation layer and the adjacent-side protective layer are bonded together with an adhesive layer (glue layer).

International Publication No. 2020/195743

One example of how radiative cooling films can be used is by applying an adhesive (glue) to the back of the film and then attaching it to an object (the cooling target), such as the exterior of a car. However, conventional films (radiative cooling films) have little extensibility (ease of stretching), so they can only be attached to flat or quadratic curved surfaces, and it is not possible to stretch the film during application to fine-tune the attachment state.

That is, since silver or silver alloy has ductility (ease of stretching), the light reflective layer has ductility (ease of stretching). However, in conventional radiative cooling films, the materials forming the adjacent-side protective layer and the separating-side protective layer are difficult to stretch, for example, acrylic resin is a material with high tensile strength that breaks when stretched slightly, and therefore conventional film bodies (radiative cooling films) have little ductility (ease of stretching).
Incidentally, silicone resin has extremely poor adhesion to silver (silver alloy), and is therefore unsuitable as a material for forming the adjacent-side protective layer and the spaced-side protective layer.

Furthermore, even when the separating-side protective layer is made of PET, PET is a material that is difficult to stretch, so the film body (radiative cooling film) will similarly have low extensibility (ease of stretching).

As described above, conventional radiative cooling films have poor conformability to the shape of the object to which they are attached (the object of application), which limits the objects to which they can be attached (the object of application). In other words, they cannot provide radiative cooling performance to the surfaces of various objects.
Incidentally, if the film body (radiative cooling film) has low extensibility (ease of stretching), it is likely to wrinkle (fold) when folded, making it difficult to use.

The present invention was made in consideration of these circumstances, and its purpose is to provide a radiative cooling film that has improved conformability to the shape of the object to which it is attached.

The radiative cooling film of the present invention is configured in a film body including an infrared emitting layer that emits infrared light from a emitting surface, a light reflecting layer made of silver or a silver alloy and located on the side of the infrared emitting layer opposite to the side where the emitting surface exists, an adjacent-side protective layer located on the side of the light reflecting layer adjacent to the infrared emitting layer, and a distant-side protective layer located on the side of the light reflecting layer away from the infrared emitting layer,
The infrared radiation layer is a resin material layer whose thickness is adjusted to emit thermal radiation energy in a wavelength band of 8 μm to 14 μm that is greater than the absorbed solar light energy, and its characteristic configuration is as follows:
the resin material forming the adjacent-side protective layer and the distant-side protective layer is any one of a urethane resin, an acrylic urethane resin, and a polyolefin resin;
The film body has a tensile strength of 140 N/2.5 cm or less at room temperature and an elongation at break of 30% or more,
The thickness of the light-reflecting layer is 70 nm or more and 300 nm or less .

First, the fact that the object to be cooled can be cooled even in a daytime solar radiation environment will be explained.
That is, sunlight incident from the emitting layer of the infrared emitting layer in the film body passes through the resin material layer, is reflected by the light reflecting layer located on the opposite side to the side where the emitting surface of the resin material layer is present, and is then released outside the system from the emitting surface.
In this specification, when simply referring to light, the concept of light includes ultraviolet light (ultraviolet light), visible light, and infrared light. When these are described in terms of the wavelength of light as electromagnetic waves, they include electromagnetic waves with wavelengths of 10 nm to 20,000 nm (electromagnetic waves of 0.01 μm to 20 μm).

Furthermore, heat transferred (heat input) to the film body is converted into infrared rays in the resin material layer serving as the infrared radiation layer, and is released to the outside of the system from the radiation surface.
In this way, the film body reflects sunlight irradiating onto it and can also radiate heat transferred to the film body (for example, heat transferred from the atmosphere or heat transferred from an object cooled by the film body) outside the system as infrared light.

The resin material layer is adjusted to a thickness that allows it to emit greater thermal radiation energy in the 8 μm to 14 μm wavelength band than the absorbed solar energy, allowing the light-reflecting layer to appropriately reflect sunlight while still providing cooling functionality even in daytime solar environments.

To explain further the ability of the light-reflecting layer to appropriately reflect sunlight, a light-reflecting layer made of silver or a silver alloy has reflectance characteristics of 90% or more at wavelengths of 0.4 μm to 0.5 μm and 96% or more at wavelengths longer than 0.5 μm, and can appropriately reflect sunlight.
That is, the solar spectrum exists in the wavelength range from 0.295 μm to 4 μm, and the intensity increases as the wavelength increases from 0.4 μm, and the intensity is particularly high in the wavelength range from 0.5 μm to 2.5 μm.
The light-reflecting layer made of silver or a silver alloy has reflective properties that show a reflectance of 90% or more in the wavelength range of 0.4 μm to 0.5 μm and a reflectance of 96% or more at wavelengths longer than 0.5 μm, so the light-reflecting layer absorbs only about 5% or less of the solar energy.

As a result, the solar energy absorbed by the light-reflecting layer at noon in summer can be reduced to approximately 50 W/m ² or less, and radiation cooling by the resin material layer can be performed well.
In this specification, unless otherwise specified, the spectrum of sunlight is assumed to be in accordance with the AM1.5G standard.
As described above, the object to be cooled can be cooled by radiative cooling even in a daytime solar radiation environment.

Furthermore, since the light-reflecting layer is provided with an adjacent-side protective layer and a distant-side protective layer, deterioration of the light-reflecting layer can be suppressed, such as by preventing moisture from reaching the silver or silver alloy that constitutes the light-reflecting layer, thereby preventing the silver or silver alloy from discoloring due to moisture, thereby allowing the light-reflecting layer to reflect light appropriately.
Incidentally, the adjacent-side protective layer also prevents radicals generated in the resin material layer from reaching the silver or silver alloy that forms the light-reflecting layer, and also prevents the silver or silver alloy of the light-reflecting layer from discoloring in a short period of time due to radicals generated in the resin material layer reaching the silver or silver alloy that forms the light-reflecting layer.

Furthermore, according to the characteristic configuration of the radiative cooling film of the present invention, the resin material forming the adjacent-side protective layer and the distant-side protective layer is either a urethane resin, an acrylic urethane resin, or a polyolefin resin, which allows the film body (radiative cooling film) to be provided with extensibility (ease of stretching).

In other words, the light-reflecting layer has ductility (ease of stretching) because silver or a silver alloy has malleability, and by making the infrared radiation layer a resin material layer using a resin material that has ductility (ease of stretching), the infrared radiation layer can be made ductile (ease of stretching).
In addition, since urethane resin, acrylic urethane resin, and polyolefin resin have extensibility (ease of stretching), the adjacent-side protective layer and the separating-side protective layer can be made extensible (ease of stretching).
As a result, the film body (radiative cooling film) can be made extensible (easily stretchable), and its ability to conform to the shape of the object to which it is attached can be improved.

In short, the characteristic configuration of the radiative cooling film of the present invention allows for increased conformability to the shape of the object to which it is attached.

Furthermore, the radiative cooling film of the present invention has the following advantageous effects due to its characteristic configuration that the tensile strength at room temperature is 140 N/2.5 cm or less and the elongation at break is 30% or more.
In the present invention, room temperature is defined as 23°C (the temperature defined in JIS K 6732).
Furthermore, since the adjacent-side protective layer and the separating-side protective layer are formed of urethane resin, acrylic urethane resin, or polyolefin resin and have sufficiently large extensibility (ease of stretching), in the present invention, the tensile strength and elongation at break (elongation limit) of the film body at room temperature are determined by the extensibility (ease of stretching) of the resin material layer (infrared radiation layer) and the light-reflecting layer.

In other words, because the tensile strength of the film body at room temperature is 140 N/2.5 cm or less and the elongation at break (elongation limit) of the film body is 30% or more, it accurately increases the conformability to the shape of the object to which it is attached (the object to be applied) and suppresses the occurrence of creases.

To further explain, if the tensile strength per 2.5 cm of the film (JIS K 6732) is 70 N/2.5 cm or less, the film will be highly adaptable to curved surfaces. When applying the film to a curved surface, it is stretched while heated to 80°C or higher using a heat gun or similar device. When the film is heated to 80°C or higher, the tensile strength of the resin material layer (e.g., polyvinyl chloride resin mixed with plasticizer) generally drops to less than half of what it is at room temperature. Therefore, considering that the film will be heated to 80°C or higher during application, it is desirable for the tensile strength at 23°C to be 140 N/2.5 cm or less.

Furthermore, when attaching (sticking) a film body to an object to be attached (for example, a car hood or the end of a truck container), a minimum elongation of 30% is required, and an elongation of 30% is sufficient for the attachment.
Furthermore, if the film has an elongation of 30%, it is possible to prevent wrinkles (fold wrinkles) from occurring when the film body is folded.

In short, this additional characteristic feature of the radiative cooling film of the present invention accurately increases its ability to conform to the shape of the object to which it is attached, and also suppresses the occurrence of creases.

Furthermore, the radiative cooling film of the present invention has the following advantageous effects due to the characteristic configuration that the thickness of the light reflecting layer is 70 nm or more and 300 nm or less.

That is, when sunlight is to be reflected while the light-reflecting layer has the above-mentioned reflectance characteristics, i.e., a reflectance of 90% or more at wavelengths of 0.4 μm to 0.5 μm and a reflectance of 96% or more at wavelengths longer than 0.5 μm, it is desirable that the thickness of the light-reflecting layer be 50 nm or more.
Furthermore, since a silver or silver alloy light-reflecting layer will break if stretched beyond 40%, considering that the light-reflecting layer will be stretched by 40% when applied to the curved surface of the film body, by making the thickness of the light-reflecting layer 70 nm or more, which is 1.4 times 50 nm, the light-reflecting layer can be provided with appropriate reflective properties even when applied to the film body in a stretched state.

Furthermore, if the light-reflecting layer were to break, the tensile strength of the light-reflecting layer would become zero. However, if the tensile strength of the light-reflecting layer accounts for a large proportion of the overall tensile strength of the film body, when the light-reflecting layer breaks, the change in the tensile strength of the film body would be large, making it difficult to apply.
If the tensile strength of the light-reflecting layer is 1 N/2.5 cm or less, the proportion of the tensile strength of the film body as a whole (for example, if the tensile strength of the film body as a whole is 140 N/2.5 cm, this proportion will be 1% or less), and when the light-reflecting layer breaks, the change in the tensile strength of the film body will be small, which will reduce the difficulty of application.

In the case of silver or a silver alloy, there is no change in the tensile strength even when it is heated from room temperature to about 80°C.
Therefore, it is desirable that the thickness of the light-reflecting layer is 300 nm or less, and the tensile strength of the light-reflecting layer is 1 N/2.5 cm or less.

In other words, the silver or silver alloy that makes up the light-reflective layer will break if it is stretched by more than 40%. Therefore, while the light-reflective layer is unlikely to break when the film is stretched during application, even if it does break, the change in the tensile strength of the film can be minimized, allowing the film to remain in a state that makes it easy to apply.

In short, this further characteristic feature of the radiative cooling film of the present invention allows for good application of the film body to an object while stretching it, while still providing the light-reflecting layer with appropriate reflective properties even when the film body is stretched and attached to the object.

Further characteristic features of the radiative cooling film of the present invention are:
The thickness of the resin material layer is
The thickness is adjusted to have light absorption characteristics in which the wavelength average of the light absorptance in the wavelength range of 0.4 μm to 0.5 μm is 13% or less, the wavelength average of the light absorptance in the wavelength range of 0.5 μm to 0.8 μm is 4% or less, the wavelength average of the light absorptance in the wavelength range of 0.8 μm to 1.5 μm is within 1%, and the wavelength average of the light absorptance in the wavelength range of 1.5 μm to 2.5 μm is 40% or less, and thermal radiation characteristics in which the wavelength average of the emissivity in the wavelength range of 8 μm to 14 μm is 40% or more,
The resin material layer has a tensile strength of 139 N/2.5 cm or less, an elongation at break of 50% or more, and the tensile strength decreases with increasing temperature.

Note that the wavelength average of light absorptance in the wavelength range of 0.4 μm to 0.5 μm refers to the average value of light absorptance for each wavelength in the range of 0.4 μm to 0.5 μm. The same applies to the wavelength average of light absorptance in the wavelength range of 0.5 μm to 0.8 μm, the wavelength average of light absorptance in the wavelength range of 0.8 μm to 1.5 μm, and the wavelength average of light absorptance in the wavelength range of 1.5 μm to 2.5 μm. Other similar terms, including emissivity, also refer to similar average values, and this also applies hereinafter in this specification.

In other words, the light absorptivity and emissivity (light emissivity) of the resin material layer change depending on its thickness. Therefore, it is necessary to adjust the thickness of the resin material layer so that it absorbs as little sunlight as possible and emits a large amount of thermal radiation in the wavelength band of the so-called atmospheric window (the region with light wavelengths of 8 μm to 14 μm).

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

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

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

In addition, the actual environment in which the radiative cooling film is used may be humid, which also narrows the atmospheric window. When used in low-lying areas, the thermal radiation generated in the atmospheric window is estimated to be 160 W/ ^m2 at 30°C under good conditions (calculated with an emissivity of 1).
Furthermore, when there is haze or smog in the sky, which is common in Japan, the atmospheric window becomes even narrower, and radiation into space is around 125 W/ ^m2 .

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

The resin material layer has a tensile strength of 139 N/2.5 cm or less and an elongation at break of 50% or more, and the tensile strength decreases with increasing temperature. Therefore, even if the thickness of the resin material layer is increased to improve ease of application when attaching the film body to an object, when applying it to a curved surface, the film body can be successfully applied to the curved surface by stretching it while heating it to 80°C or more using a heat gun or the like.

In short, this further characteristic feature of the radiative cooling film of the present invention makes the heat output at the atmospheric window greater than the heat input due to sunlight absorption, enabling radiative cooling outdoors even in a solar radiation environment, and the film body can be easily attached to curved surfaces.

Further characteristic features of the radiative cooling film of the present invention are:
The resin material forming the resin material layer is a vinyl chloride resin mixed with a plasticizer, and the thickness of the resin material layer is 14 μm or more and 330 μm or less.
The vinyl chloride resin used in the present invention is a homopolymer of vinyl chloride or vinylidene chloride or a copolymer of vinyl chloride or vinylidene chloride, and can be produced by a conventionally known polymerization method.

In other words, vinyl chloride resins with a thickness of 10 μm or more can provide sufficient thermal radiation in the atmospheric window region, and as a result, can provide appropriate radiative cooling outdoors even in a solar radiation environment. In other words, vinyl chloride resins have thermal radiation properties equivalent to those of fluororesins and silicone rubber, which provide significant thermal radiation in the atmospheric window region, and are significantly cheaper than these resins, making them effective for inexpensively constructing films (radiative cooling films) whose temperature drops below the ambient temperature under direct sunlight.

Moreover, since a plasticizer is mixed into the vinyl chloride resin, the resin material layer has sufficient extensibility (ease of stretching), and as a result, the radiative cooling film has sufficient extensibility (ease of stretching).
Therefore, the film body can be smoothly attached to the object while being stretched.

By the way, vinyl chloride resins can be made soft by adding plasticizers, and when they come into contact with other objects, they can flexibly change shape to fit the object, avoiding damage and allowing them to maintain a beautiful appearance for a long period of time.By the way, thin film fluororesins are hard, so they cannot flexibly change shape when they come into contact with other objects, are easily damaged, and it is difficult to maintain a beautiful appearance.
Furthermore, by adding a plasticizer to vinyl chloride resin, even if it is scratched, it can be deformed by heating it to 80°C or above, eliminating the surface scratches and smoothing it out, meaning that it can self-repair. Fluorine resin and silicone rubber do not have this property. This property of soft vinyl chloride resin allows it to maintain a clean state for a long period of time. This leads to the maintenance of radiative cooling performance over a long period of time.
In this way, by adding a plasticizer, the durability of the film body (radiative cooling film) is improved.
Furthermore, vinyl chloride resins are flame retardant and difficult to biodegrade, making them suitable as resin materials for forming the resin material layer of radiative cooling films that are used outdoors for long periods of time.

The silver or silver alloy light-reflective layer will break if it is stretched by more than 40%. Taking into consideration that the film will be stretched by 40% when applied to the curved surface, the thickness of the resin material layer is set to 14 nm or more, which is 1.4 times 10 nm. Therefore, even when the film is applied in a stretched state, the resin material layer can be provided with appropriate thermal radiation properties.

Furthermore, because the thickness of the resin material layer formed from vinyl chloride resin is 330 μm or less, the tensile strength of the resin material layer can be reduced to 139 N/2.5 cm or less. As mentioned above, when applying to curved surfaces, the film can be heated to 80°C or higher using a heat gun or the like while being stretched, allowing the film to be applied well to curved surfaces.

In short, this additional characteristic of the radiative cooling film of the present invention allows for cost-effective film that can provide radiative cooling outdoors even in solar radiation environments, and also allows the film to be easily attached to curved surfaces, particularly three-dimensional curved surfaces.

A further characteristic feature of the radiative cooling film of the present invention is that the thickness of the resin material layer is 50 μm or more and 330 μm or less.

In other words, since the thickness of the resin material layer formed from vinyl chloride resin is 50 μm or more, even if the film body is applied in a state where it is stretched by 40%, the thickness of the resin material layer will be approximately 36 μm, and it will be able to have sufficiently large thermal radiation properties.
As a result, proper radiative cooling can be achieved outdoors even in a solar radiation environment.
Incidentally, since the thickness of the resin material layer formed from vinyl chloride resin is 330 μm or less, the film body can be applied to a curved surface satisfactorily as described above.

In short, this additional characteristic configuration of the radiative cooling film of the present invention enables appropriate radiative cooling outdoors, even in a solar radiation environment.

A further characteristic feature of the radiative cooling film of the present invention is that the plasticizer comprises one or more compounds selected from the group consisting of phthalate esters, aliphatic dibasic acid esters, and phosphate esters.

In other words, because the plasticizer mixed into the vinyl chloride resin is one or more compounds selected from the group consisting of phthalate esters, aliphatic dibasic acid esters, and phosphate esters, the plasticizer is less likely to absorb the ultraviolet light contained in sunlight (ultraviolet light with wavelengths of 295 nm to 400 nm), thereby appropriately improving the weather resistance of the vinyl chloride resin mixed with the plasticizer.

In other words, when plasticizers mixed into vinyl chloride resins absorb ultraviolet light, the hydrolysis of the plasticizer progresses, causing the vinyl chloride resin to undergo dechlorination, discoloring (brown), and possibly reducing its mechanical strength. However, because the plasticizers are less likely to absorb the ultraviolet light contained in sunlight, the weather resistance of vinyl chloride resins mixed with plasticizers can be improved.

In short, the characteristic configuration of the radiative cooling film of the present invention makes it possible to provide a radiative cooling film with improved weather resistance.

A further characteristic feature of the radiative cooling film of the present invention is that the plasticizer is mixed in an amount ranging from 7 parts by weight to 50 parts by weight per 100 parts by weight of the vinyl chloride resin.

In other words, the plasticizer mixed into the vinyl chloride resin is in the range of 7 parts by weight to 50 parts by weight per 100 parts by weight of vinyl chloride resin, which gives the resin material layer appropriate extensibility (ease of stretching) while preventing a decrease in the durability of the resin material layer.

In other words, since the plasticizer mixed into the vinyl chloride resin is 7 parts by weight or more per 100 parts by weight of the vinyl chloride resin, the resin material layer can be given appropriate extensibility (ease of stretching).
Furthermore, since the plasticizer mixed into the vinyl chloride resin is 50 parts by weight or less per 100 parts by weight of the vinyl chloride resin, deterioration in the durability of the resin material layer can be suppressed.

In short, this further characteristic feature of the radiative cooling film of the present invention provides the resin material layer with appropriate extensibility (ease of stretching) while preventing a decrease in the durability of the resin material layer.

A further characteristic feature of the radiative cooling film of the present invention is that the plasticizer is mixed in an amount ranging from 15 to 50 parts by weight per 100 parts by weight of the vinyl chloride resin.

In other words, the plasticizer mixed into the vinyl chloride resin is 15 parts by weight or more per 100 parts by weight of vinyl chloride resin, which sufficiently improves the extensibility (ease of stretching) of the resin material layer.

In short, this additional characteristic feature of the radiative cooling film of the present invention can sufficiently improve the extensibility (ease of stretching) of the resin material layer.

A further characteristic feature of the radiative cooling film of the present invention is that the thicknesses of the adjacent-side protective layer and the distant-side protective layer are 300 nm or more and 40 μm or less.

In other words, since the thickness of each of the adjacent-side protective layer and the separating-side protective layer is 300 nm or more, it is possible to appropriately prevent moisture that passes through the resin material layer from reaching the silver or silver alloy that forms the light-reflecting layer, and to appropriately prevent moisture from the object to be cooled (for example, the object to which the film body is attached) from reaching the silver or silver alloy that forms the light-reflecting layer, thereby appropriately suppressing deterioration of the light-reflecting layer.
Furthermore, since the thickness of the adjacent-side protective layer is 300 nm or more, radicals generated in the resin material layer are appropriately prevented from reaching the silver or silver alloy that forms the light-reflecting layer.

Furthermore, because the thickness of the adjacent-side protective layer and the distant-side protective layer is 40 μm or less, the adjacent-side protective layer and the distant-side protective layer increase the insulating properties of the film body, thereby preventing a decrease in the radiative cooling performance of the film body.

In short, this additional characteristic configuration of the radiative cooling film of the present invention appropriately suppresses deterioration of the light-reflecting layer and prevents a decrease in the radiative cooling performance of the film body.

A further characteristic configuration of the radiative cooling film of the present invention is that the resin material layer and the adjacent-side protective layer are bonded together by an adhesive layer,
The adhesive layer is formed from any one of a urethane resin adhesive, an acrylic urethane resin adhesive, and a polyolefin resin adhesive.

In other words, because the resin material layer and adjacent-side protective layer are bonded together by an adhesive layer, the resin material layer, adjacent-side protective layer, light-reflecting layer, and adjacent-side protective layer can be formed in a laminated state in a satisfactory manner by, for example, forming the separating-side protective layer, light-reflecting layer, and adjacent-side protective layer integrally in a laminated state, and then bonding a separately manufactured resin material layer to the adjacent-side protective layer with an adhesive layer.

The thickness of the adhesive layer is preferably 1 μm or more and 30 μm or less.
In addition, since the urethane resin adhesive, acrylic urethane resin adhesive, and polyolefin resin adhesive that form the adhesive layer have particularly excellent extensibility (ease of stretching), such as the elongation at break of urethane resin being in the range of 100% to 10,000%, in the present invention, even when an adhesive layer is present, the tensile strength and elongation at break (elongation limit) of the film body at room temperature are determined by the extensibility (ease of stretching) of the resin material layer (infrared radiation layer) and the light-reflecting layer.

Incidentally, if an adhesive layer is located between the resin material layer and the adjacent-side protective layer, radicals will also be generated from the adhesive layer, but the adjacent-side protective layer can prevent the radicals generated in the adhesive layer from reaching the light-reflecting layer.

In short, this further characteristic feature of the radiative cooling film of the present invention allows the resin material layer, adjacent-side protective layer, light-reflecting layer, and distant-side protective layer to be formed in a well-layered state.

The characteristic configuration of the method for using the radiative cooling film of the present invention is the method for using the radiative cooling film described above,
The film is used in a state where the elongation of the film is within 40%.

In other words, the silver and silver alloy in the light-reflective layer will break if it stretches beyond 40%, so by using the film with an elongation of 40% or less, you can successfully attach the film to the object to which it is to be attached while preventing the light-reflective layer from breaking.

In short, the characteristic features of the method for using the radiative cooling film of the present invention allow the film body to be successfully attached to the attachment target while preventing breakage of the light-reflecting layer.

The method for producing a radiative cooling film of the present invention is the method for producing the radiative cooling film described above,
a release layer, the spacing-side protective layer, the reflective layer, and the adjacent-side protective layer are sequentially laminated on an upper portion of a substrate to form a reflective layer-side laminate;
The resin material layer is separately formed,
the resin material layer and the reflective layer-side laminate are bonded together by the adhesive layer;
Thereafter, the release layer is separated from the separating-side protective layer.

That is, to create a film body in which a resin material layer, adjacent-side protective layer, light-reflecting layer, and spacing-side protective layer are laminated, first, a release layer, spacing-side protective layer, reflective layer, and adjacent-side protective layer are laminated in that order on top of the substrate to form a reflective layer-side laminate. A resin material layer is also formed separately.

Next, the resin material layer and the reflective layer side laminate are bonded together with an adhesive layer.
Thereafter, the release layer is removed from the separating-side protective layer, and the substrate is separated.
The release layer is preferably made of either a silicone resin or a fluororesin, and the substrate may be made of ethylene terephthalate resin (PET).

In other words, by using a procedure in which the separating-side protective layer, the light-reflecting layer, and the adjacent-side protective layer are integrally formed in a laminated state, and a separately manufactured resin material layer and the adjacent-side protective layer are bonded together with an adhesive layer, the resin material layer, the adjacent-side protective layer, the light-reflecting layer, and the separating-side protective layer can be formed in a laminated state.
In this case, when forming the separating-side protective layer, the light-reflecting layer, and the adjacent-side protective layer integrally in a laminated state, by using a substrate with an appropriate thickness and appropriate shape retention, the release layer, the separating-side protective layer, the reflective layer, and the adjacent-side protective layer are sequentially laminated on top of the substrate to form a reflective layer-side laminate, which makes it possible to form the separating-side protective layer, the light-reflecting layer, and the adjacent-side protective layer in a well-laid state.

Then, after bonding the resin material layer and the reflective layer-side laminate with the adhesive layer, the release layer is removed from the separating-side protective layer to separate the substrate, resulting in a laminated state of the resin material layer, adjacent-side protective layer, light-reflecting layer, and separating-side protective layer, i.e., a satisfactory film body can be formed.

In short, the characteristic configuration of the radiative cooling film production method allows for the film body to be formed well.

Further characteristic features of the method for producing a radiative cooling film of the present invention are as follows:
The resin material layer and the reflective layer-side laminate are bonded together by the adhesive layer, and then the release layer is separated from the separation-side protective layer.

In other words, the resin material layer and the reflective layer-side laminate are bonded together with an adhesive layer, and then the release layer is removed from the separating-side protective layer to separate the substrate. This results in a film body in which the resin material layer, adjacent-side protective layer, light-reflecting layer, and separating-side protective layer are laminated.

In short, the characteristic configuration of the radiative cooling film production method allows for the film body to be formed well.

FIG. 1 illustrates the basic configuration of a radiative cooling film. FIG. 10 is a diagram showing the relationship between the light absorptance of a resin material and wavelength. FIG. 1 is a diagram showing the emissivity spectrum of vinyl chloride resin. FIG. 1 is a diagram showing the emissivity spectrum of vinylidene chloride resin. FIG. 1 is a diagram showing a specific configuration of a radiative cooling film. FIG. 1 illustrates the fabrication procedure for a radiative cooling film. 1 is a table showing the relationship between the amount of plasticizer added and tensile strength. 1 is a table showing the relationship between the amount of plasticizer added and the elongation limit. FIG. 10 is a diagram showing the transmittance of a resin material layer to which an ultraviolet absorber is added. FIG. 1 shows the light reflectance spectrum of a silver-based light-reflecting layer. FIG. 1 is a diagram showing the relationship between light transmittance and wavelength of polyethylene. FIG. 1 is a diagram illustrating a test configuration. FIG. 10 is a diagram showing test results when the adjacent-side protective layer is made of polyethylene. FIG. 10 is a diagram showing test results when the adjacent-side protective layer is made of ultraviolet-absorbing acrylic. FIG. 1 shows the emissivity spectrum of polyethylene. FIG. 10 is a diagram showing test results in which a plasticizer is mixed into a vinyl chloride resin. FIG. 1 is a diagram showing the relationship between wavelength and absorbance of a plasticizer. FIG. 1 is a diagram showing the relationship between wavelength and absorbance of a plasticizer. FIG. 1 is a diagram showing the relationship between wavelength and absorbance of a plasticizer. FIG. 1 is a diagram showing the relationship between wavelength and absorbance of a plasticizer. 10A and 10B are diagrams illustrating a configuration in which the front and back surfaces of a resin material layer are uneven. 10A and 10B are diagrams illustrating a configuration in which a filler is mixed into a resin material layer. 1 is a table showing the relationship between plasticizer, tensile strength, and elongation at break.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[Basic structure of radiative cooling film]
As shown in Fig. 1, the radiative cooling film CP is configured as a film body F including an infrared emitting layer A that radiates infrared light IR from a emitting surface H, a light reflecting layer B located on the side of the infrared emitting layer A opposite to the side where the emitting surface H exists, an adjacent-side protective layer Du on the surface of the light reflecting layer B adjacent to the infrared emitting layer A, and a distant-side protective layer Ds on the surface of the light reflecting layer B away from the infrared emitting layer A.

The film body F has a tensile strength of 140 N/2.5 cm or less at room temperature and an elongation at break of 30% or more.
In this embodiment, the infrared radiation layer A has a tensile strength of 139 N/2.5 cm or less at room temperature and an elongation at break of 50% or more, and the light-reflecting layer B has a tensile strength of 1 N/2.5 cm or less at room temperature and an elongation at break of 30% or more.
Incidentally, normal temperature is defined as 23°C (the temperature specified in JIS K 6732).

The light-reflecting layer B is made of silver or a silver alloy and reflects light L, such as sunlight, that has passed through the infrared radiation layer A and the adjacent-side protective layer Du. Its reflection characteristics are such that the reflectance is 90% or more for wavelengths of 0.4 μm to 0.5 μm and 96% or more for wavelengths longer than 0.5 μm.
The solar spectrum exists in the wavelength range from 0.295 μm (295 nm) to 4 μm (4000 nm), and the intensity increases as the wavelength increases from 0.4 μm (400 nm), and the intensity is particularly high in the wavelength range from 0.5 μm (500 nm) to 1.8 μm (1800 nm).

In this embodiment, light L includes ultraviolet light (ultraviolet rays), visible light, and infrared light, which, when expressed in terms of the wavelength of light as electromagnetic waves, include electromagnetic waves with wavelengths of 10 nm to 20,000 nm (electromagnetic waves of 0.01 μm to 20 μm). In this document, the wavelength range of ultraviolet light (ultraviolet rays) is defined as being greater than or equal to 295 nm (0.295 μm) and less than or equal to 400 nm (0.4 μm).

The light-reflecting layer B exhibits a reflectivity of 90% or more from wavelengths of 0.4 μm to 0.5 μm, and a reflectivity of 96% or more for wavelengths longer than 0.5 μm, which means that the solar energy absorbed by the light-reflecting layer B of the radiative cooling film CP (film body F) can be reduced to 5% or less. In other words, the solar energy absorbed at noon in summer can be reduced to around 50 W.

The infrared radiation layer A is configured as a resin material layer J made of vinyl chloride resin adjusted to a thickness that emits thermal radiation energy greater than the absorbed solar energy in the wavelength band of 8 μm to 14 μm.
The vinyl chloride resin used in the present invention is a homopolymer of vinyl chloride or vinylidene chloride or a copolymer of vinyl chloride or vinylidene chloride, and is produced by a conventionally known polymerization method.

Although details of the resin material layer J will be described later, in this embodiment, the resin material forming the resin material layer J is a vinyl chloride resin mixed with a plasticizer. In other words, the resin material forming the resin material layer J is a vinyl chloride resin mixed with a resin plasticizer, or a vinylidene chloride resin mixed with a plasticizer.
Vinyl chloride resins mixed with plasticizers have excellent ductility (ease of stretching) and exhibit a property in which the tensile strength decreases with increasing temperature.

The radiative cooling film CP (film body F) is therefore configured to reflect a portion of the light L incident on the radiative cooling film CP from the radiation surface H of the infrared radiation layer A, and to reflect the light L incident on the radiative cooling film CP that has passed through the resin material layer J and the adjacent-side protective layer Du (such as sunlight) from the light reflection layer B, allowing it to escape to the outside from the radiation surface H.

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

That is, the radiative cooling film CP (film body F) is configured to reflect the light L irradiated onto the radiative cooling film CP, and to radiate heat transferred to the radiative cooling film CP (film body F) (for example, heat transferred from the atmosphere or the object to be cooled E) to the outside as infrared light IR.
Furthermore, the resin material layer J, adjacent-side protective layer Du, light-reflecting layer B, and distant-side protective layer Ds are configured to have extensibility, so that the radiative cooling film CP (film body F) is configured to have extensibility.

In addition, the radiative cooling film CP (film body F) is used to implement a radiative cooling method in which infrared light IR is radiated from the radiation surface H on the side opposite to the surface of the resin material layer J that is in contact with the light-reflecting layer B. Specifically, the radiation surface H is directed toward the sky, and the radiation cooling method is implemented in which infrared light IR is radiated from the radiation surface H that faces the sky.

The target (cooling target E) to which the radiative cooling film CP (radiative cooling film) of the present invention can be attached can be any object that requires cooling, such as the outer surface of various tents (membrane materials), the outer surface of boxes that store electrical equipment, the outer surface of containers for transporting goods, the outer surface of milk tanks that store milk, the outer surface of the milk storage part of milk tanker trucks, etc.
Furthermore, the radiative cooling film CP (film body) of the present invention can be attached to existing objects to easily exert its radiative cooling capacity, such as by applying glue and wrapping it around the periphery of a car, the outer wall of a warehouse or building, or the periphery of a helmet.

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

Specifically, the thickness of the resin material layer J is adjusted to have light absorption characteristics such that the wavelength average light absorptance in the wavelength range of 0.4 μm to 0.5 μm is 13% or less, the wavelength average light absorptance in the wavelength range of 0.5 μm to 0.8 μm is 4% or less, the wavelength average light absorptance in the wavelength range of 0.8 μm to 1.5 μm is within 1%, and the wavelength average light absorptance in the wavelength range of 1.5 μm to 2.5 μm is 40% or less, and thermal radiation characteristics such that the wavelength average emissivity in the wavelength range of 8 μm to 14 μm is 40% or more.

In terms of the light absorption rate of sunlight, the light absorption rate of the resin material increases as the film thickness of the resin material increases. When the resin material is made thick, the emissivity of the atmospheric window becomes nearly 1, and the thermal radiation emitted into space at that time becomes 125 W/ ^m² to 160 W/ ^m² . The sunlight absorption in the adjacent-side protective layer Du and the light-reflecting layer B is 50 W/ ^m² or less. If the sum of the sunlight absorption in the resin material layer J, the adjacent-side protective layer Du, and the light-reflecting layer B is 150 W/ ^m² or less and the atmospheric conditions are good, cooling will proceed. As described above, it is preferable to use a resin material that has a small light absorption rate near the peak value of the sunlight spectrum for the resin material layer J.

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

Furthermore, the environment in which the radiative cooling film CP is actually used may be humid, and even in that case, the atmospheric window will be narrow. The thermal radiation generated in the atmospheric window when used in low-lying areas is estimated to be 160 W/ ^m2 at 30°C under good conditions (calculated with an emissivity of 1). Furthermore, 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 about 125 W/ ^m2 .
In view of these circumstances, unless the wavelength average of the emissivity in the wavelength range of 8 μm to 14 μm is 40% or more (thermal radiation intensity in the atmospheric window zone is 50 W/m ² ), it cannot be used in lowlands in the mid-latitude zone.

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

In this embodiment, the thickness of the resin material layer J made of vinyl chloride resin is 14 μm or more and 330 μm or less. Preferably, the thickness of the resin material layer J made of vinyl chloride resin is 50 μm or more and 330 μm or less.
By doing so, the resin material layer J made of vinyl chloride resin has a tensile strength of 139 N/2.5 cm or less and an elongation at break (elongation limit) of 50% or more.
Furthermore, the tensile strength of the resin material layer J made of vinyl chloride resin decreases with increasing temperature. For example, when heated to 80°C, the tensile strength of the resin material layer J made of vinyl chloride resin generally decreases to half or less compared to that at room temperature.

[Details of resin material]
According to Kirchhoff's law, the emissivity (ε) is equal to the light absorptance (A). 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 formula):
A=1-exp(-αt) (1) where t is the film thickness.
In other words, by adjusting the film thickness of the resin material 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 14 μm, which is the atmospheric window wavelength band.
Furthermore, to suppress absorption of sunlight, it is advisable to use a material that has no or a small absorption coefficient in the wavelength range of 0.3 μm to 4 μm, particularly 0.4 μm to 2.5 μm. As can be seen from the relational expression between the absorption coefficient and the absorptance (light absorptance relational expression), the light absorptance (emissivity) changes depending on the film thickness of the resin material.

In order to lower the temperature below the surrounding atmosphere through radiative cooling in a solar radiation environment, a material with a large absorption coefficient in the wavelength band of the atmospheric window and almost no absorption coefficient in the wavelength band of sunlight can be selected. By adjusting the film thickness, it is possible to absorb almost no sunlight but emit a large amount of thermal radiation from the atmospheric window. In other words, it is possible to create a state in which the output from radiative cooling is greater than the input of sunlight.

The solar spectrum only contains wavelengths longer than 0.295 μm. Ultraviolet rays are 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 rays are defined as the range of wavelengths from 0.8 μm to 3 μm, mid-infrared rays are defined as the range of wavelengths from 3 μm to 8 μm, and far-infrared rays are defined as the range of wavelengths longer than 8 μm.

Regarding the carbon-chlorine bond (C—Cl), the bond energy between carbon and chlorine in an alkene is 3.28 eV, and the wavelength is 0.378 μm, so it absorbs a lot of ultraviolet light in sunlight, but has almost no absorption in the visible range.
FIG. 2 shows the absorption spectrum of a 100 μm thick vinyl chloride resin in the ultraviolet to visible region, and shows that the light absorption is large on the shorter wavelength side than 0.38 μm.
The absorption spectrum of a 100 μm thick vinylidene chloride resin in the ultraviolet to visible region is shown in FIG. 2, and a slight increase in the absorption spectrum is observed on the shorter wavelength side than 0.4 μm.

Figure 2 also shows the ultraviolet to visible absorbance spectrum of 40 μm-thick ethylene terephthalate resin (PET) and the ultraviolet to visible absorbance spectrum of polyethylene (olefin-based).

Figure 3 shows the emissivity of polyvinyl chloride resin (PVC) with carbon-chlorine bonds at the atmospheric window, and Figure 4 shows the emissivity of polyvinylidene chloride resin (PVDC) 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 wide band with a half-width of 1 μm or more centered at a wavelength of 12 μm.
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 C—H bond 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 of a 10 μm thick film is 43% in the wavelength range from 8 μm to 14 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.

As shown in Figure 3, 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 about 100 μm from the surface, and radiation from deeper parts does not escape to the outside.
As shown in FIG. 4, it can be seen that vinylidene chloride resin is similar to vinyl chloride resin.

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

Even if an ideal resin material existed that did not absorb any sunlight, the thermal conductivity of resin materials is generally around 0.2 W/m/K. Therefore, if the thickness exceeds 20 mm, the light-reflecting layer B would be heated by sunlight, and the object to be cooled E placed on the light-reflecting layer side would be heated. In other words, the thickness of the resin material of the radiative cooling film CP (film body F) needs to be 20 mm or less.

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

The film thickness at which saturation occurs 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 is 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 to be cooled can be lowered. Therefore, in the case of resins containing carbon-chlorine bonds, a thickness of 50 μm or less reduces the insulating properties and allows for effective cooling of object E. In the case of carbon-chlorine bonds, a thickness of 100 μm or less allows for effective cooling of object E.

The benefit of thinning the film is not only to reduce heat insulation and improve cold conduction, but also to suppress the absorption of near-infrared light from CH, _CH2 , and _CH3 , which are present in resins containing carbon-chlorine bonds. Thinning the film reduces the sunlight absorption caused by these, thereby increasing the cooling capacity of the radiative cooling film CP.
From the above viewpoint, 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 exert a radiative cooling effect under sunlight.

As mentioned above, if the thickness of the resin material layer J is 10 μm or more, it can produce a radiative cooling effect under sunlight, but if it is assumed that the radiative cooling film CP (film body F) will be stretched by nearly 40% when applied, the thickness of the resin material layer J needs to be 14 μm or more, as mentioned above. And if the thickness of the resin material layer J is 50 μm or more, the resin material layer J can produce a sufficiently large radiative cooling effect.
Furthermore, in order to make the tensile strength of the resin material layer J 139 N/2.5 cm or less, the thickness of the resin material layer J must be 300 μm or less.

(Regarding the tensile strength of the resin material layer J)
7 illustrates the relationship between the thickness (μm) and tensile strength (N/2.5 cm) of the resin material layer J. Specifically, in the case where DOP (di-2-ethylhexyl phthalate) is added as a plasticizer to the resin material layer J (vinyl chloride resin), the relationship between the thickness (μm) and tensile strength (N/2.5 cm) of the resin material layer J is illustrated while changing the amount (parts by weight) of DOP added.

7, the upper limit of the weight parts of DOP added to 100 parts by weight of the resin material layer J is 50 parts by weight. That is, the amount of plasticizer added is limited to 50 parts by weight from the viewpoint of durability.
As shown in Figure 7, when the amount of plasticizer added is 50 parts by weight per 100 parts by weight of the resin material layer J, in order to achieve a tensile strength of 139 N/2.5 cm or less, the upper limit of the thickness of the resin material layer J is approximately 330 μm, and it is even better to set the upper limit of the thickness of the resin material layer J to 320 μm.
Incidentally, if the type of plasticizer changes, the relationship between the thickness (μm) and tensile strength (N/2.5 cm) of the resin material layer J can be determined by multiplying the plasticizing efficiency of the plasticizer by the weight part.

[Details of the light-reflecting layer]
In order to provide the light reflecting layer B with the above-mentioned reflectance characteristics, the reflecting material on the side where the radiation surface H exists (the side where the resin material layer J exists) must be silver or a silver alloy.
As shown in FIG. 10, 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.

When sunlight is reflected using only silver or a silver alloy while maintaining the above-mentioned reflectance characteristics, a thickness of 50 nm or more is required.
Incidentally, silver and silver alloys will break if elongated beyond 40%, so the radiative cooling film CP (film body F) needs to be used with an elongation of 40% or less. In other words, the radiative cooling film CP of the present invention needs to be used in a state where the elongation of the film body F is 40% or less.

Even if the light reflecting layer B expands by 40%, in order to ensure that the thickness of the light reflecting layer B is 50 nm, the thickness of the light reflecting layer B needs to be 70 nm or more.
In order to make the tensile strength of the light reflecting layer B equal to or less than 1 N/2.5 cm, the upper limit of the thickness of the light reflecting layer B is 0.3 μm.
That is, in the radiative cooling film CP (film body F) of the present invention, the thickness of the light reflecting layer B is set to be 70 nm or more and 0.3 μm or less.

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

Silver and silver alloys are vulnerable to rain and humidity and need to be protected from these and to prevent discoloration. To this end, an adjacent-side protective layer Du and a distant-side protective layer Ds are required to protect the silver and silver alloy, as shown in FIG.
The adjacent-side protective layer Du and the distant-side protective layer Ds will be described in detail later.

[Plasticizer details]
The plasticizer mixed into the vinyl chloride resin forming the resin material layer J is one or more compounds selected from the group consisting of phthalate esters, aliphatic dibasic acid esters, and phosphate esters.
The amount of the plasticizer added is 7 parts by weight or more and 50 parts by weight or less, preferably 15 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the vinyl chloride resin.

The aliphatic dibasic acid ester used 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.

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.

<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), and the like.

<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, aliphatic polyesters having a molecular weight of 400 to 4,000 synthesized by copolymerization (polyesterification) of a dibasic acid such as adipic acid with a diol (difunctional alcohol or glycol).

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

<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.

<Relationship between plasticizers and elongation limits>
Figure 8 shows the relationship between the amount of plasticizer added (parts by weight) and the elongation limit (elongation at break) of the resin material layer J (vinyl chloride resin) for each of adipic acid polyester (aliphatic dibasic acid esters), di-2-ethylhexyl phthalate (DOP), and di-2-ethylhexyl adipate (DOA).
Referring to Figure 8, when di-2-ethylhexyl adipate (DOA) is added as a plasticizer in an amount of 7 parts by weight or more, the elongation limit (elongation at break) is 40% or more, and the radiative cooling film CP (film body F) satisfies the condition for use with an elongation of 40% or less.
Furthermore, when 15 parts by weight or more of plasticizer is added, the elongation limits (limit elongation) of each of adipate polyester, di-2-ethylhexyl phthalate (DOP), and di-2-ethylhexyl adipate (DOA) are reliably 40% or more, and the radiative cooling film CP (film body F) reliably meets the condition of being used with an elongation of 40% or less.

<Evaluation of appropriate plasticizers>
Plasticizers for vinyl chloride resin include phthalates, 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.

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).
A representative aromatic phosphate ester is tricresyl phosphate (TCP).
A representative example of trimellitic acid esters is tri-2-ethylhexyl trimellitate (TOTM).
Epoxidized soybean oil is a representative example of epoxidized fatty acid esters.

Durability was judged based on the results of a 1,920-hour xenon weather test (equivalent to four years of actual exposure). 487 hours is equivalent to one year of UV exposure.
The conditions for the xenon weather test are as follows:
Ultraviolet light intensity 180W/m ² (wavelength 295-400nm).
<Conditions without watering> BPT 89°C, humidity 50%, 1 hour 42 minutes.
<Conditions with watering> Temperature inside the tank: 38°C, humidity: 90%, 18 minutes.

The test results for 1920 hours are shown in Figure 16. 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.

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. However, 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.

The above test results show that phthalate esters, aliphatic dibasic acid esters, phosphate triesters, and aromatic phosphate esters are highly durable plasticizers for vinyl chloride resins, while trimellitate esters and epoxidized fatty acid esters are not durable.

[Other additives]
The vinyl chloride resin forming the resin material layer J may contain a flame retardant, a stabilizer, a stabilizing aid, a filler, an antioxidant, an ultraviolet absorber, and a light stabilizer.
<Flame retardants>
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.

<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.

<Stabilizing aid>
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.

<Filler>
Examples of fillers include calcium carbonate, silica, alumina, clay, talc, diatomaceous earth, metal oxides such as ferrite, fibers and powders of glass, carbon, metals, etc., 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.

<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 about 0.2 to 20 parts by weight.

<Ultraviolet 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 and triazine compounds. 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.

It is desirable to blend an ultraviolet absorber into the resin material layer J (infrared radiation layer A) to set the transmittance of light with a wavelength of 290 nm or more and 330 nm or less through the resin material layer J (infrared radiation layer A) to 0%. When light with a wavelength of 290 nm or more and 330 nm or less is transmitted to the light reflecting layer B, radicals are formed in the adjacent protective layer Du present around the silver, which react with the silver and cause coloration of the light reflecting layer B.
FIG. 9 shows the transmittance of vinyl chloride resin using diisononyl phthalate (DINP) as a plasticizer.

<Light stabilizer>
Examples of 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-piperidylsebacate (mixture), bis(1,2,2,6,6-pentamethyl-4-piperidyl)[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butylmalonate, bis(2,2,6,6-tetramethyl-1(octyloxy)decanediate), 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, 2,2,6,6-tetramethyl-4-piperidinol and higher fatty acid ester mixtures, tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, tetrakis(1,2,2,6,6-penta ... Xylate, polycondensate 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.

[Specific configuration of radiative cooling film]
The specific configuration of the radiative cooling film CP (film body) is as shown in Fig. 5, in which a resin material layer J and a laminated portion consisting of an adjacent-side protective layer Du, a light-reflecting layer B, and a distant-side protective layer Ds are bonded together with an adhesive layer N.
The adhesive layer N is, for example, a urethane resin adhesive (adhesive), an acrylic urethane resin adhesive (adhesive), or a polyolefin resin adhesive (adhesive), and it is desirable that the adhesive layer N has high transparency to sunlight.

An example of producing a radiative cooling film CP (film body F) is shown in Figure 6.
First, a release layer G is formed on top of a film-like substrate K such as PET, and then a separation-side protective layer Ds is applied or attached to the release layer G. A light-reflecting layer B is formed on the separation-side protective layer Ds by vapor deposition, sputtering, ion plating, silver mirror reaction, etc., and then an adjacent-side protective layer Du is applied or attached to the light-reflecting layer B.
That is, a release layer G, a spacing-side protective layer Ds, a light-reflecting layer B, and an adjacent-side protective layer Du are sequentially laminated on top of a substrate K to form a reflective layer-side laminate P.
In addition, a resin material layer J is separately formed in the form of a film.

Then, the resin material layer J fabricated in a film form and the reflective layer side laminate P are bonded together with an adhesive layer N.
Thereafter, the release layer G is removed from the separating-side protective layer Ds, and the substrate K is separated.
The release layer G is made of either a silicone resin or a fluorine resin.

<Considerations on adhesive layer>
Resin materials with good ductility include the following resin materials.
・Soft vinyl chloride resin ・Urethane resin ・Acrylic-urethane copolymer resin (acrylic urethane resin)
Polyolefin resins and silicone resins. Of these resins, urethane resins, acrylic urethane resins, and polyolefin resins are suitable for adhesives. All of them have high elongation but low tensile strength.
The thickness of the adhesive layer is preferably 1 μm or more and 30 μm or less.

Incidentally, acrylic resin has a tensile strength of approximately 48 MPa to 73 MPa and an elongation at break (elongation limit) of 2% to 7%, and since it is a material with a small elongation at break (elongation limit) and is difficult to stretch, acrylic resin alone cannot be used as the adhesive layer N.
In contrast, urethane resin has a tensile strength of approximately 1 MPa to 69 MPa and an elongation at break (elongation limit) of 100% to 10,000%, making it a highly stretchable material. When an acrylic urethane resin, which is a copolymer of acrylic and urethane, is used, the elongation of urethane is added to the acrylic, making it highly stretchable. Therefore, acrylic urethane resin is desirable.

[Details of the protective layer]
The adjacent-side protective layer Du and the distant-side protective layer Ds are made of any one of urethane resin, acrylic urethane resin, and polyolefin-based resin, and have a thickness of 300 nm or more and 40 μm or less.
Polyolefin resins include polyethylene and polypropylene.

Figure 2 shows the ultraviolet absorptance of polyethylene (olefin-based), vinylidene chloride resin, and vinyl chloride resin. Note that Figure 2 also shows the ultraviolet absorptance of ethylene terephthalate resin (PET) for reference, but since ethylene terephthalate resin (PET) is a material that is difficult to stretch, it cannot be used as a material for manufacturing the radiative cooling film CP (film body F), and cannot be used for the adjacent-side protective layer Du or the separating-side protective layer Ds.
FIG. 11 shows the light transmittance of polyethylene, which is suitable as a synthetic resin for forming the adjacent-side protective layer Du and the distant-side protective layer Ds.

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

When the adjacent-side protective layer Du is formed from a polyolefin-based resin with a thickness of 300 nm or more and 40 μm or less, the polyolefin-based resin is a synthetic resin with an ultraviolet light absorption rate of 10% or less over the entire ultraviolet wavelength range of 0.3 μm to 0.4 μm, making the adjacent-side protective layer Du less susceptible to degradation due to ultraviolet absorption.

Furthermore, because the thickness of the polyolefin resin forming the adjacent-side protective layer Du is 300 nm or more, it effectively exhibits a blocking function, blocking radicals generated in the resin material layer J from reaching the silver or silver alloy forming the light-reflecting layer B and blocking moisture that permeates the resin material 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.

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

When the adjacent-side protective layer Du and the separating-side protective layer Ds are formed from polyolefin resin, urethane resin, or acrylic urethane resin, the reason for setting an upper limit on their thickness is to prevent the adjacent-side protective layer Du and the separating-side protective layer Ds from exhibiting insulating properties that do not contribute to radiative cooling. In other words, the thicker the adjacent-side protective layer Du and the separating-side protective layer Ds, the less insulating properties they exhibit that do not contribute to radiative cooling. Therefore, an upper limit on the thickness is set to prevent the adjacent-side protective layer Du and the separating-side protective layer Ds from exhibiting insulating properties that do not contribute to radiative cooling while still functioning as a protective layer for the light-reflecting layer B.

As shown in Figure 5, when an adhesive layer N is located between the resin material layer J and the adjacent-side protective layer Du, radicals will also be generated from the adhesive layer N. However, because the thickness of the polyolefin resin forming the adjacent-side protective layer Du is 300 nm or more, the radicals generated in the adhesive layer N can be prevented from reaching the light-reflecting layer B for a long period of time.

As mentioned above, if the adjacent-side protective layer Du is thick, there is no disadvantage in terms of preventing coloration of the silver (silver alloy) of the light-reflecting layer B, but it causes problems in terms of radiative cooling. In other words, if the thickness is increased, 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 adjacent-side protective layer Du, has a low emissivity at the atmospheric window, as shown in Figure 15, so even if it is formed thick, it does not contribute to radiative cooling. On the contrary, increasing the thickness of the resin actually increases the thermal insulation 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, and the effect of increasing solar absorption increases.
Due to these factors, a thick adjacent-side protective layer Du is disadvantageous for radiative cooling. From this viewpoint, the thickness of the adjacent-side protective layer Du made of a polyolefin resin is preferably 5 μm or less, and more preferably 1 μm or less.

[Considerations on the protective layer]
In order to examine the difference in the way silver is colored by the adjacent-side protective layer Du, a sample was prepared in which the adjacent-side protective layer Du was exposed and did not have the resin material layer J as the infrared radiation layer A, as shown in Figure 12, and the coloring of silver after irradiation with simulated sunlight was examined.
Specifically, samples were prepared by applying two types of adjacent-side protective layer Du, namely, a general acrylic resin that absorbs ultraviolet light (for example, methyl methacrylate resin mixed with a benzotriazole-based ultraviolet absorber) and polyethylene, using a bar coater, onto a film layer U (corresponding to the substrate) that includes silver as the light-reflecting layer B, and the function of the adjacent-side protective layer Du was examined. The thicknesses of the applied adjacent-side protective layers Du were 10 μm and 1 μm, respectively.
The film layer U (corresponding to the substrate) is formed into a film shape using PET (ethylene terephthalate resin) or the like.

As shown in Figure 14, if the adjacent-side protective layer Du is made of an acrylic resin that absorbs UV rays well, the adjacent-side protective layer Du is decomposed by UV rays to form radicals, and the silver immediately turns yellow and no longer functions as a radiative cooling film CP (it absorbs sunlight and, like general materials, its temperature rises when exposed to solar radiation).
The 600h line in the figure is the reflectance spectrum after 600 hours of xenon weather testing (ultraviolet light energy 60 W/ ^m2 ) under the conditions of JIS standard 5600-7-7, and the 0h line is the reflectance spectrum before the xenon weather testing.

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

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

Furthermore, from the viewpoint of ultraviolet absorption, fluororesin-based materials can also be used to form the adjacent-side protective layer Du, but when actually formed as the adjacent-side protective layer Du, they become discolored and deteriorate during the formation stage, and therefore cannot be used as materials to form the adjacent-side protective layer Du.
Furthermore, silicone resin can also be used as a material for forming the adjacent-side protective layer Du from the viewpoint of ultraviolet absorption, but it has extremely poor adhesion to silver (silver alloy) and cannot be used as a material for forming the adjacent-side protective layer Du.

[Considerations on plasticizers]
The plasticizers mixed into vinyl chloride resins will be considered below.
(Deterioration of vinyl chloride resin)
The deterioration of vinyl chloride resin (film) due to sunlight is largely due to the deterioration of plasticizers caused 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 the absorption of sunlight in order to achieve radiative cooling performance. Therefore, it is not possible to add enough additives, dyes, or pigments to protect the plasticizer.

As shown in Figure 5, the radiative cooling film CP (film body F) has an adhesive layer N and an adjacent-side protective layer Du underneath a resin material layer J made of vinyl chloride resin, and underneath that is a light-reflecting layer B containing silver. The light-reflecting layer B makes the resin material layer J even more susceptible to the effects of sunlight. In other words, sunlight that has entered the radiative cooling film CP (film body F) once is reflected by the light-reflecting layer B and passes through the resin material layer J twice. This means that the degradation effect of sunlight is approximately twice as great as usual.

Furthermore, when comparing the resin material layer J formed on the light reflecting layer B containing silver with the resin material layer J formed on aluminum, iron or ceramics, which have low reflectivity, the radiative cooling film CP having the resin material layer J formed on the light reflecting layer B containing silver is more affected by sunlight.
These facts suggest that the vinyl chloride resin of the radiative cooling film CP (film body F), which comprises the resin material layer J on the light-reflecting layer B containing silver, is more sensitive to ultraviolet rays contained in sunlight than vinyl chloride resins for general use.

Degradation of ester-based plasticizers due to ultraviolet light occurs mainly due to the plasticizer absorbing ultraviolet energy.
UV absorption occurs mainly due to electron transitions that exceed the bond energy of the ester bond in the plasticizer. The activation energy provided by UV light and water molecules accelerates the 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 dechlorination and discoloration, which also reduces the mechanical strength.
If the vinyl chloride resin becomes colored, the radiative cooling film CP (film body F) will absorb sunlight and will no longer be able to cool during the day.

Therefore, as shown in the experimental results in Figure 16, plasticizers (trimellitic acid esters, epoxidized fatty acid esters) used in outdoor applications where the film is exposed to direct sunlight cannot be used in the radiative cooling film CP. Instead, phthalate esters, aliphatic dibasic acid esters, phosphate triesters, and aromatic phosphate esters can be used as plasticizers for the radiative cooling film CP (film body F).

(Protective properties of the resin material layer with ultraviolet absorbers)
The vinyl chloride resin forming the resin material layer J of the radiative cooling film CP (film body F) used in the experiment was mixed with an ultraviolet absorber, and the reflectance of the radiative cooling film CP (film body F) at the time of production was adjusted to be 10% or less in the wavelength range of 295 nm or more and 350 nm or less (see Fig. 16).
This ultraviolet absorber is present to protect the adhesive layer N, adjacent side protective layer Du, and light-reflecting layer B containing silver that are located below the resin material layer J, and its effect in protecting the resin material layer J from ultraviolet rays is limited.

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 light travels through the resin material layer J (vinyl chloride resin), it is gradually absorbed by the resin material layer J. In other words, the ultraviolet protection effect of the ultraviolet absorber cannot be expected, particularly on the sunlight incident side of the resin material layer J (vinyl chloride resin).
That is, 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).

(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.

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.
That is, if the hydrocarbon group is an unsaturated hydrocarbon group, 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 resin material layer J of the radiative cooling film CP.
In short, the suitability of a plasticizer depends on how easily the plasticizer absorbs ultraviolet light.

(About phthalates)
First, we will compare phthalates, which are aromatic carboxylic acid esters, with trimellitic acid esters. An example of a phthalate ester is DOP (di-2-ethylhexyl phthalate), and an example of a trimellitic acid 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.

The following formula (3) represents the relationship between the absorption wavelength (λ _A) and the binding energy (E):
λ _A =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. An example is shown in Figure 17.
In Figure 17, DEHP and DINCH are phthalate esters, and TOTM is trimellitate ester. Note that DEHP is the same as DOP.

Terrestrial sunlight exists in the wavelength range longer than 295 nm, but TOTM effectively absorbs ultraviolet light in the wavelength range longer than 295 nm. This absorption comes from the ester bond, and becomes 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 exposed to direct sunlight, but it cannot be used for the vinyl chloride that forms the resin material layer J of the radiative cooling film CP, even though it is also for outdoor use. In general outdoor use, the vinyl chloride layer is often sufficiently colored, such as black, to be less susceptible to the effects of UV rays, and is therefore less susceptible to deterioration due to UV rays.

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 sufficiently. Therefore, plasticizers that are used for outdoor applications exposed to direct sunlight cannot be used in this application.
Trimellitic acid esters include tri-2-ethylhexyl trimellitate (TOTM), triisononyl trimellitate (TINTM), triisodecyl trimellitate (TIDTM), etc., but all of them are unsuitable.

Figure 18 shows the absorbance of other phthalate esters, DOP (di-2-ethylhexyl phthalate) and DBP (dibutyl phthalate), and shows that they have almost no absorption at wavelengths longer than 295 nm.

When the hydrocarbon group is an alkyl group, the strength of the ester bond is highly dependent on the type of carboxylic acid, and ultraviolet absorption shows similar trends when the type of carboxylic acid is the same. When the hydrocarbon group is an alkyl group, light absorption at the longest wavelength side of the ultraviolet region of 400 nm or less is due to the bond energy of the ester bond.
Phthalic acid esters, whose hydrocarbon group is an alkyl group, do not absorb light in the ultraviolet region longer than 295 nm that exists in the spectrum of terrestrial sunlight, and are not hydrolyzed by the ultraviolet energy of sunlight.

On the other hand, in trimellitic acid esters whose hydrocarbon group is an alkyl group, the ester bond absorbs the ultraviolet energy of sunlight, and the energy promotes hydrolysis. The acid and alcohol generated by the hydrolysis absorb ultraviolet light and promote reactions with the surrounding oligomers and vinyl chloride, which causes embrittlement and coloration of the resin material 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.

(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.

Let us consider DOA (di-2-ethylhexyl adipate), a typical example of an aliphatic dibasic acid ester. Figure 19 shows the absorbance of DOA in the ultraviolet region, and it can be seen that DOA has an even lower solar absorptivity than the aforementioned DOP (di-2-ethylhexyl phthalate), which has almost no absorption in wavelengths longer than 295 nm.
In FIG. 16, both the phthalate ester and the aliphatic dibasic acid ester endured 2000 hours in the xenon weather test, but optically, DOA had higher durability.

(Regarding phosphate esters)
Phosphate ester plasticizers include phosphate triesters and aromatic phosphate triesters. Phosphate esters have 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 (CPs). Phosphate esters also have flame retardancy.

As mentioned above, the phosphate triester includes trimethyl phosphate (TMP), triethyl phosphate (TEP), tributyl phosphate (TBP), and tris(2-ethylhexyl) phosphate (TOP).
FIG. 20 shows the absorbance of tributyl phosphate (TBP), which shows that it hardly absorbs ultraviolet light with wavelengths longer than 295 nm.

As mentioned above, 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 ester hardly absorbs ultraviolet light with wavelengths longer than 295 nm.

(Regarding 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.
As epoxidized fatty acid esters, there are epoxidized esters such as epoxidized soybean oil and epoxidized linseed oil, but none of them can be used as a plasticizer to be mixed into the vinyl chloride resin of the radiative cooling film CP.

[Another configuration of the infrared radiation layer]
As shown in Fig. 22, a light scattering structure may be provided by mixing an inorganic filler V into the resin material layer J (vinyl chloride resin mixed with a plasticizer) constituting the infrared radiation layer A. Also, as shown in Fig. 21, both the front and back surfaces of the resin material layer J constituting the infrared radiation layer A 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.

In other words, the above-mentioned resin material layer J is flat on both the front and back sides and is configured so that no filler V is mixed in. In such a configuration, the radiation surface H is mirror-like, so that glare is perceived when looking at the radiation surface H, but this glare can be suppressed by providing a light-scattering configuration.
Furthermore, when filler V is mixed into the resin material layer J, if an adjacent side protective layer Du and a light-reflecting layer B are present, the light reflectivity is improved compared to when only the resin material layer J mixed with filler V is present or when only the light-reflecting layer B is present.

Silicon dioxide ( _SiO2 ) _, titanium oxide ( _TiO2 ), aluminum oxide ( _Al2O3 ), magnesium oxide (MgO), _etc. can be suitably used as the inorganic material forming the filler V. When the filler V is mixed into the resin material layer J, both the front and back surfaces of the resin material layer J become uneven.
In addition, the front and back surfaces of the resin material layer J can be made uneven by embossing or scratching the surface.

When the rear surface of the resin material layer J is uneven, it is desirable to position an adhesive layer N between the resin material layer J and the adjacent-side protective layer Du, similar to the configuration described in FIG.
In other words, even if the back surface of the resin material layer J is uneven, the adhesive layer N (bonding layer) is located between the resin material layer J and the adjacent side protective layer Du, so the resin material layer J and the adjacent side protective layer Du can be properly bonded together.

In cases where the back surface of the resin material layer J is uneven, the resin material layer J and the adjacent protective layer Du may be directly bonded, for example, by plasma bonding. Plasma bonding is a method of forming radicals by emitting plasma on the bonding surfaces of the resin material layer J and the adjacent protective layer Du, and then bonding is performed using these radicals.

Incidentally, if filler V is mixed into the adjacent-side protective layer Du, the back surface of the adjacent-side protective layer Du that contacts the light-reflecting layer B will become uneven, causing the surface of the light-reflecting layer B to deform unevenly. Therefore, it is necessary to avoid mixing filler V into the adjacent-side protective layer Du. In other words, if the surface of the light-reflecting layer B deforms unevenly, it will not be able to reflect light properly, and as a result, radiative cooling will not be able to be performed properly.

23 shows an example of the tensile strength (N/2.5 cm) and elongation at break (%) of a resin material layer J (vinyl chloride resin) mixed with filler V (titanium oxide: TiO ₂ ) and a plasticizer (PE-based). The PE-based plasticizer is a polyester-based (adipic acid polyester).
In addition, Figure 23 illustrates the tensile strength (N/2.5 cm) and elongation at break (%) of a resin material layer J (vinyl chloride resin) mixed with a plasticizer (PE-based) but not with filler V, as well as the tensile strength (N/2.5 cm) and elongation at break (%) of a resin material layer J (vinyl chloride resin) mixed with a plasticizer (DOP: di-2-ethylhexyl phthalate) but not with filler V.

[Another embodiment]
Other embodiments will be listed below.
(1) In the above embodiment, an object (e.g., a membrane material) that is in close contact with the back surface of the radiative cooling film CP (film body F) is exemplified as the object to be cooled E. However, various types of objects to be cooled, such as a space to be cooled, can be used as the object to be cooled E.

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

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

(3) As a method for producing the film body F, instead of the method described in the above embodiment, other formation methods may be used, such as forming an adhesive layer N on the resin material layer J, forming an adjacent protective layer Du on the adhesive layer N, directly depositing a light-reflecting layer B on the adjacent protective layer Du, and forming a separating protective layer Ds on the light-reflecting layer B.

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

A Infrared radiation layer B Light reflection layer Ds Separating side protective layer Du Adjacent side protective layer F Film body G Release layer H Radiation surface J Resin material layer N Adhesive layer P Reflection side laminate

Claims (12)

the film body includes an infrared radiation layer that emits infrared light from a radiation surface, a light reflection layer made of silver or a silver alloy and located on the side of the infrared radiation layer opposite to the side on which the radiation surface is present, an adjacent-side protective layer that is located on the side of the light reflection layer that is adjacent to the infrared radiation layer, and a remote-side protective layer that is located on the side of the light reflection layer that is remote from the infrared radiation layer,
The radiative cooling film is a resin material layer whose thickness is adjusted to emit thermal radiation energy greater than absorbed solar light energy in a wavelength band of 8 μm to 14 μm,
the resin material forming the adjacent-side protective layer and the distant-side protective layer is any one of a urethane resin, an acrylic urethane resin, and a polyolefin resin;
The film body has a tensile strength of 140 N/2.5 cm or less at room temperature and an elongation at break of 30% or more,
The radiative cooling film , wherein the thickness of the light reflecting layer is 70 nm or more and 300 nm or less . The thickness of the resin material layer is
The thickness is adjusted to have light absorption characteristics in which the wavelength average of the light absorptance in the wavelength range of 0.4 μm to 0.5 μm is 13% or less, the wavelength average of the light absorptance in the wavelength range of 0.5 μm to 0.8 μm is 4% or less, the wavelength average of the light absorptance in the wavelength range of 0.8 μm to 1.5 μm is within 1%, and the wavelength average of the light absorptance in the wavelength range of 1.5 μm to 2.5 μm is 40% or less, and thermal radiation characteristics in which the wavelength average of the emissivity in the wavelength range of 8 μm to 14 μm is 40% or more,
2. The radiative cooling film according to claim 1, wherein the resin material layer has a tensile strength of 139 N/2.5 cm or less, an elongation at break of 50% or more, and the tensile strength decreases with increasing temperature. 3. The radiative cooling film according to claim 1, wherein the resin material forming the resin material layer is a vinyl chloride resin mixed with a plasticizer, and the thickness of the resin material layer is 14 μm or more and 330 μm or less . 4. The radiative cooling film according to claim 3, wherein the resin material layer has a thickness of 50 μm or more and 330 μm or less . 5. The radiative cooling film according to claim 3, wherein the plasticizer comprises one or more compounds selected from the group consisting of phthalate esters, aliphatic dibasic acid esters, and phosphate esters . The radiative cooling film according to any one of claims 3 to 5, wherein the plasticizer is mixed in a range of 7 parts by weight or more and 50 parts by weight or less with respect to 100 parts by weight of the vinyl chloride resin . 7. The radiative cooling film according to claim 6, wherein the plasticizer is mixed in an amount ranging from 15 parts by weight to 50 parts by weight with respect to 100 parts by weight of the vinyl chloride resin . The radiative cooling film according to any one of claims 1 to 7, wherein the thickness of the adjacent-side protective layer and the distant-side protective layer is 300 nm or more and 40 μm or less . the resin material layer and the adjacent-side protective layer are bonded together by an adhesive layer,
The radiative cooling film according to any one of claims 1 to 8, wherein the adhesive layer is formed of any one of a urethane resin-based adhesive, an acrylic urethane resin-based adhesive, and a polyolefin resin-based adhesive . A method of using the radiative cooling film according to any one of claims 1 to 9,
A method for using a radiative cooling film, wherein the film body is used in a state where its elongation is 40% or less. 10. A method of making a radiative cooling film according to claim 9, comprising:
a release layer, the spacing-side protective layer, the light-reflecting layer, and the adjacent-side protective layer are sequentially laminated on an upper portion of a substrate to form a reflective layer-side laminate;
The resin material layer is separately formed,
a method for producing a radiative cooling film, wherein the resin material layer and the reflection layer side laminate are bonded together by the adhesive layer. 12. The method for making a radiative cooling film according to claim 11, wherein the resin material layer and the reflection-layer-side laminate are bonded together by the adhesive layer, and then the release layer is separated from the separation-side protective layer.