JP7626109B2 - Thermochromic resin composite material and laminate using same - Google Patents

Description

The present invention relates to a thermochromic resin composite material and a laminate using the same.

In recent years, attention has been focused on thermochromic materials, whose color or transparency changes in response to temperature changes. For example, Japanese Patent Application Laid-Open No. 2001-354952 (Patent Document 1) discloses a thermochromic material obtained by adding a solution or dispersion in which a dye, inorganic pigment, and/or organic pigment is dissolved or dispersed in water or an organic solvent to an aqueous polymer solution and/or an aqueous hydrogel solution, and then concentrating the solution. However, because this thermochromic material contains water as a medium, it has been difficult to use it in components in which the visible light absorption rate is low at high temperatures (e.g., 70°C or higher) and the visible light absorption rate is high at low temperatures (e.g., 40°C or lower).

JP 2001-354952 A

The present invention has been made in consideration of the problems associated with the above-mentioned conventional technologies, and aims to provide a resin composite material that exhibits low visible light absorptance at high temperatures (e.g., 70°C or higher) and high visible light absorptance at low temperatures (e.g., 40°C or lower), as well as a composite material that exhibits high visible light reflectance at high temperatures (e.g., 70°C or higher) and low visible light reflectance at low temperatures (e.g., 40°C or lower).

As a result of intensive research conducted by the inventors to achieve the above object, they discovered that a resin composition containing an acrylic polymer, polyvinylidene fluoride, and polycaprolactone in a specific ratio exhibits a thermochromic effect that improves transparency at high temperatures of 70°C or higher, and that a resin composite material in which a black colorant is blended with this resin composition exhibits low visible light absorption at high temperatures of 70°C or higher and high visible light absorption at low temperatures of 40°C or lower, and further discovered that a laminate in which a metal film is provided on one side of a member made of this resin composite material exhibits high visible light reflectance at high temperatures of 70°C or higher and low visible light reflectance at low temperatures of 40°C or lower, thereby completing the present invention.

That is, the present invention provides the following aspects:

[1] A thermochromic resin composite material comprising a thermochromic resin composition containing 15 to 84 mass% of polymethyl methacrylate, 15 to 84 mass% of polyvinylidene fluoride, and 1 to 40 mass% of polycaprolactone, and 0.0005 to 0.03 parts by mass of at least one black colorant selected from the group consisting of black pigments and black dyes, per 100 parts by mass of the thermochromic resin composition.

[2] The thermochromic resin composite material according to [1], further comprising 50 parts by mass or less of a glass-based filler per 100 parts by mass of the thermochromic resin composition.

[3] The thermochromic resin composite material according to [2], in which the glass-based filler has a silicon dioxide purity of 90% or more.

[4] A thermochromic resin composite material according to any one of [1] to [3], in which the black colorant is carbon particles having a graphite structure.

[5] A laminate comprising a member made of the thermochromic resin composite material described in any one of [1] to [4] and a metal film having a visible light reflectance of 70% or more and disposed on at least a portion of one side of the member.

The reason why the thermochromic resin composite material of the present invention has a low visible light absorptance at high temperatures of 70°C or higher and a high visible light absorptance at low temperatures of 40°C or lower, and why the laminate of the present invention has a high visible light reflectance at high temperatures of 70°C or higher and a low visible light reflectance at low temperatures of 40°C or lower, is not entirely clear, but the inventors speculate as follows.

That is, since polycaprolactone has a melting point of about 60°C, it forms a crystalline phase at a low temperature of 40°C or less. Therefore, when the thermochromic resin composite material of the present invention is exposed to a low temperature of 40°C or less, a sea-island structure is formed having a sea phase consisting of a polymer blend of an acrylic polymer and polyvinylidene fluoride and an island phase consisting of at least a part of polycaprolactone crystals. When visible light is irradiated to a thermochromic resin composite material having such a sea-island structure at a low temperature of 40°C or less, the incident visible light is scattered by the island phase, and the optical path length when propagating through the thermochromic resin composite material becomes longer, so that the light is easily absorbed by the black colorant contained in the thermochromic resin composite material. As a result, it is presumed that the absorptance of visible light is high at a low temperature of 40°C or less. In addition, it is presumed that when visible light is irradiated to the laminate of the present invention at a low temperature of 40°C or less, the visible light is absorbed in the member consisting of the thermochromic resin composite material of the present invention, and the reflection of visible light by the metal film is reduced, resulting in a lower reflectance of visible light.

On the other hand, polycaprolactone melts at about 60°C, and therefore the crystals melt completely at high temperatures of 70°C or higher. Therefore, when the thermochromic resin composite material of the present invention is exposed to high temperatures of 70°C or higher, a sea-island structure is formed having a sea phase made of a polymer blend containing an acrylic polymer and polyvinylidene fluoride in a predetermined ratio and an island phase made of molten polycaprolactone. When visible light is irradiated to a thermochromic resin composite material having such a sea-island structure at high temperatures of 70°C or higher, the refractive index of the molten polycaprolactone matches the refractive index of the polymer blend containing an acrylic polymer and polyvinylidene fluoride in a predetermined ratio, suppressing scattering of the incident visible light, and shortening the optical path length when propagating through the thermochromic resin composite material, making it difficult for the black colorant contained in the thermochromic resin composite material to absorb visible light. As a result, it is presumed that the absorptance of visible light is reduced at high temperatures of 70°C or higher. In addition, when visible light is irradiated onto the laminate of the present invention at high temperatures of 70°C or higher, it is presumed that the visible light is less absorbed by the member made of the thermochromic resin composite material of the present invention, and more visible light is reflected by the metal film, resulting in a higher reflectance of visible light.

According to the present invention, it is possible to obtain a resin composite material that exhibits low visible light absorptance at high temperatures of 70°C or higher and high visible light absorptance at low temperatures of 40°C or lower. Furthermore, by providing a metal film on one side of a member made of such a resin composite material, it is possible to obtain a laminate that exhibits high visible light reflectance at high temperatures of 70°C or higher and low visible light reflectance at low temperatures of 40°C or lower. Furthermore, in such a laminate, it is possible to control the amount of heat generated by sunlight by changing the temperature.

The present invention will be described in detail below with reference to preferred embodiments.

[Thermochromic resin composite material]
First, the thermochromic resin composite material of the present invention will be described. The thermochromic resin composite material of the present invention contains a thermochromic resin composition containing 15 to 84 mass% of an acrylic polymer, 15 to 84 mass% of polyvinylidene fluoride, and 1 to 40 mass% of polycaprolactone, and 0.0005 to 0.03 mass parts of at least one black colorant selected from the group consisting of black pigments and black dyes, relative to 100 mass parts of the thermochromic resin composition. In addition, the thermochromic resin composite material of the present invention preferably further contains 50 mass parts or less of a glass-based filler, relative to 100 mass parts of the thermochromic resin composition.

(Acrylic polymer)
The acrylic polymer used in the present invention includes homopolymers and copolymers of acrylic monomers. The ratio of acrylic monomer units in the copolymer of acrylic monomers is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more. Among these acrylic polymers, homopolymers of acrylic monomers are preferred from the viewpoints that they have excellent heat resistance and transparency, and that the obtained resin composite material has a low visible light absorption rate at high temperatures of 70°C or more.

Examples of the acrylic monomer include alkyl methacrylate esters (e.g., methyl methacrylate, ethyl methacrylate, etc.), alkyl acrylate esters (e.g., methyl acrylate, ethyl acrylate, etc.), methacrylic acid, and acrylic acid. Among these acrylic monomers, alkyl methacrylate esters are preferred, and methyl methacrylate is more preferred, from the viewpoint of excellent heat resistance and moldability.

Other copolymerizable monomers in copolymers of acrylic monomers include, for example, olefins (e.g., ethylene, propylene, etc.) and aromatic vinyl monomers (e.g., styrene, α-methylstyrene, etc.).

Specific examples of the acrylic polymers used in the present invention include polymethacrylic acid alkyl esters (e.g., polymethyl methacrylate, polyethyl methacrylate, etc.), polyacrylic acid alkyl esters (e.g., polymethyl acrylate, polyethyl acrylate, etc.), acrylic acid/methacrylic acid alkyl ester copolymers (e.g., acrylic acid/methyl methacrylate copolymers, etc.), methacrylic acid alkyl ester/acrylic acid alkyl ester copolymers (e.g., methyl methacrylate/ethyl acrylate copolymers, etc.), ethylene/methacrylic acid alkyl esters (e.g., ethylene/methyl methacrylate copolymers, etc.), ethylene/acrylic acid alkyl esters (e.g., ethylene/ethyl acrylate copolymers, etc.), styrene/methacrylic acid alkyl esters (e.g., styrene/methyl methacrylate copolymers, etc.), and styrene/acrylic acid alkyl esters (e.g., styrene/ethyl acrylate copolymers, etc.). Among these acrylic polymers, polymethacrylic acid alkyl esters are preferred, and polymethyl methacrylate is more preferred, from the viewpoint of excellent heat resistance and compatibility with polyvinylidene fluoride.

The acrylic polymer used in the present invention preferably has a refractive index at 60°C of 1.44 to 1.56, more preferably 1.46 to 1.56, even more preferably 1.46 to 1.54, and particularly preferably 1.47 to 1.51. If the refractive index of the acrylic polymer is less than the lower limit or exceeds the upper limit, the difference in refractive index with polycaprolactone becomes large, the transparency of the resulting resin composition at high temperatures of 70°C or higher decreases, and the visible light absorptance of the resulting resin composite material at high temperatures of 70°C or higher tends to increase.

(Polyvinylidene fluoride)
The polyvinylidene fluoride used in the present invention includes homopolymers and copolymers of vinylidene fluoride. The ratio of vinylidene fluoride units in the copolymer of vinylidene fluoride is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more. Among such polyvinylidene fluorides, homopolymers of vinylidene fluoride are preferred from the viewpoint of excellent compatibility with the acrylic polymer (particularly polymethyl methacrylate).

Other copolymerizable monomers in vinylidene fluoride copolymers include, for example, fluoroolefins (e.g., trifluoroethylene, hexafluoropropylene, etc.) and aromatic vinyls (e.g., styrene, α-methylstyrene, p-fluorostyrene, α-fluorostyrene, etc.).

The polyvinylidene fluoride used in the present invention preferably has a refractive index at 60°C of 1.36 to 1.47, more preferably 1.36 to 1.46, even more preferably 1.37 to 1.46, and particularly preferably 1.40 to 1.44. If the refractive index of the polyvinylidene fluoride is less than the lower limit or exceeds the upper limit, the difference in refractive index with polycaprolactone becomes large, the transparency of the resulting resin composition at high temperatures of 70°C or higher decreases, and the visible light absorptance of the resulting resin composite material at high temperatures of 70°C or higher tends to increase.

(Polycaprolactone)
The polycaprolactone used in the present invention is a ring-opening polymer of ε-caprolactone. Such a ring-opening polymer of ε-caprolactone may be a homopolymer of ε-caprolactone or a copolymer of ε-caprolactone and another monomer. The proportion of ε-caprolactone units in the copolymer of ε-caprolactone is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more. Among such polycaprolactones, a homopolymer of ε-caprolactone is preferred from the viewpoints of excellent heat resistance, high opacity at low temperatures of 40° C. or less in the resulting resin composition, and high visible light absorptance at low temperatures of 40° C. or less in the resulting resin composite material.

Other copolymerizable monomers in ε-caprolactone copolymers include, for example, glycolic acid and lactic acid.

The polycaprolactone used in the present invention preferably has a refractive index at 60°C of 1.41 to 1.51, and more preferably 1.44 to 1.48. If the refractive index of the polycaprolactone is less than the lower limit or exceeds the upper limit, the difference in refractive index with a polymer blend containing an acrylic polymer and polyvinylidene fluoride in a specified ratio becomes large, the transparency of the resulting resin composition at high temperatures of 70°C or higher tends to decrease, and the visible light absorptance of the resulting resin composite material at high temperatures of 70°C or higher tends to increase.

(Thermochromic resin composition)
The thermochromic resin composition used in the present invention contains 15 to 84% by mass of the acrylic polymer, 15 to 84% by mass of the polyvinylidene fluoride, and 1 to 40% by mass of the polycaprolactone. Such a thermochromic resin composition exhibits improved transparency at high temperatures of 70° C. or higher, i.e., it exhibits a thermochromic effect, and the resulting resin composite material exhibits low visible light absorptance at high temperatures of 70° C. or higher.

In the thermochromic resin composition, the content of the acrylic polymer must be 15 to 84% by mass. If the content of the acrylic polymer is less than the lower limit or exceeds the upper limit, the thermochromic effect is not expressed, transparency is not improved even at high temperatures of 70°C or higher, and the resulting resin composite material has a high visible light absorptance at high temperatures of 70°C or higher. In addition, from the viewpoints that the thermochromic effect is sufficiently expressed, transparency is sufficiently improved at high temperatures of 70°C or higher, and the resulting resin composite material has a low visible light absorptance at high temperatures of 70°C or higher, the content of the acrylic polymer is preferably 25 to 77% by mass, more preferably 40 to 75% by mass.

In addition, the content of the polyvinylidene fluoride in the thermochromic resin composition must be 15 to 84% by mass. If the content of the polyvinylidene fluoride is less than the lower limit or exceeds the upper limit, the thermochromic effect is not expressed, transparency is not improved even at high temperatures of 70°C or higher, and the resulting resin composite material has a high visible light absorptance at high temperatures of 70°C or higher. In addition, from the viewpoints that the thermochromic effect is sufficiently expressed, transparency is sufficiently improved at high temperatures of 70°C or higher, and the resulting resin composite material has a low visible light absorptance at high temperatures of 70°C or higher, the content of the polyvinylidene fluoride is preferably 20 to 72% by mass, more preferably 20 to 55% by mass.

Furthermore, in the thermochromic resin composition, the content of the polycaprolactone must be 1 to 40% by mass. If the content of the polycaprolactone is less than the lower limit, the thermochromic properties are not expressed, transparency is not likely to decrease at low temperatures of 40°C or less, and the resulting resin composite material has a low visible light absorptance at low temperatures of 40°C or less. On the other hand, if the content of the polycaprolactone exceeds the upper limit, the mechanical properties of the resin composition at 60°C or more are reduced. In addition, from the viewpoint that the thermochromic effect is fully expressed, transparency is reduced at low temperatures of 40°C or less, and the resulting resin composite material has a high visible light absorptance at low temperatures of 40°C or less, the content of the polycaprolactone is preferably 3 to 40% by mass, more preferably 5 to 40% by mass.

In addition, in the thermochromic resin composition, it is preferable that a sea-island structure is formed, which includes a sea phase made of a polymer blend containing the acrylic polymer and the polyvinylidene fluoride in a predetermined ratio, and an island phase made of at least a part of the polycaprolactone. By forming such a sea-island structure, at low temperatures of 40°C or less, the polycaprolactone in the island phase crystallizes, making the resin composition opaque, and the visible light absorption rate of the resulting resin composite material is high, and at high temperatures of 70°C or more, the polycaprolactone melts, making the refractive index of the island phase similar to that of the polymer blend in the sea phase, improving transparency and expressing a thermochromic effect, and the visible light absorption rate of the resulting resin composite material is low.

In the sea-island structure, the size of the island phases is preferably such that the maximum length of the island phases (diameter when the island phases are circular) is 50 nm to 100 μm, more preferably 100 nm to 80 μm, and particularly preferably 150 nm to 50 μm. If the size of the island phases is less than the lower limit, the thermochromic effect is not fully expressed, transparency is unlikely to decrease at low temperatures of 40° C. or less, and the resulting resin composite material tends to have a low visible light absorptance at low temperatures of 40° C. or less. On the other hand, if the size of the island phases exceeds the upper limit, molding processability tends to decrease.

(Black coloring agent)
The black colorant used in the present invention is at least one selected from the group consisting of black pigments and black dyes. Examples of the black pigment include carbon black, carbon nanotubes, carbon fibers, titanium black, perylene black, and oxides, composite oxides, sulfides, sulfates, carbonates, etc. of metals such as copper, iron, manganese, cobalt, chromium, nickel, zinc, calcium, and silver. Examples of the black dye include organic dyes such as anthraquinones, perinones, perylenes, azos, methines, and quinolines. Among these black colorants, carbon particles having a graphite structure are preferred from the viewpoint of affinity with the thermochromic resin composition.

In the thermochromic resin composite material of the present invention, it is preferable that 30% by mass or more (preferably 50% by mass or more, more preferably 70% by mass or more) of the black colorant is present in the island phase of the sea-island structure (the phase consisting of the polycaprolactone). This increases the visible light absorption rate at low temperatures of 40°C or less. In other words, at low temperatures of 40°C or less, the polycaprolactone forms a crystalline phase, and visible light incident on the thermochromic resin composite material is scattered by the crystalline phase. At this time, the black colorant is present in the island phase, so that visible light is efficiently absorbed.

The size and shape of the black pigment are preferably spherical with a diameter of 5 nm to 30 μm (preferably 7 nm to 20 μm, more preferably 10 nm to 10 μm). If the size of the black pigment is less than the lower limit, the handling of the black pigment during the preparation of the thermochromic resin composite material tends to become complicated, while if the size of the black pigment exceeds the upper limit, the phase structure of the resin composition tends to become disordered, and the change in visible light absorptance due to temperature tends to become smaller.

(Glass-based filler)
The glass-based filler used in the present invention is not particularly limited, but is preferably one with a silicon dioxide purity of 90% or more. The glass-based filler with a silicon dioxide purity of 90% or more has a refractive index similar to that of the polymer blend containing an acrylic polymer and polyvinylidene fluoride at a predetermined ratio or the polycaprolactone at a high temperature of 70°C or more, so that in the resin composition containing the acrylic polymer, the polyvinylidene fluoride, the polycaprolactone, and the glass-based filler, the transparency is improved at a high temperature of 70°C or more, and the thermochromic effect is maintained, and in the resin composite material obtained, the scratch resistance can be improved while maintaining a low visible light absorptance at a high temperature of 70°C or more. In addition, in a resin composition containing the acrylic polymer, the polyvinylidene fluoride, the polycaprolactone, and the glass-based filler, the thermochromic effect is sufficiently maintained, transparency at a high temperature of 70° C. or higher is sufficiently improved, and the obtained resin composite material has a sufficiently low visible light absorptance at a high temperature of 70° C. or higher, so that the silicon dioxide purity of the glass-based filler is preferably 95% or higher, and more preferably 98% or higher. On the other hand, a glass-based filler having a silicon dioxide purity below the lower limit has a refractive index significantly different from that of the polymer blend and the polycaprolactone at a high temperature of 70° C. or higher, so that in a resin composition containing the acrylic polymer, the polyvinylidene fluoride, the polycaprolactone, and the glass-based filler, the thermochromic effect is not maintained, transparency at a high temperature of 70° C. or higher is reduced, and the obtained resin composite material tends to have a high visible light absorptance at a high temperature of 70° C. or higher.

The refractive index of the glass-based filler at 60°C is preferably 1.40 to 1.50, and more preferably 1.44 to 1.48. If the refractive index of the glass-based filler is less than the lower limit or exceeds the upper limit, the transparency of the resin composition containing the acrylic polymer, the polyvinylidene fluoride, the polycaprolactone, and the glass-based filler at high temperatures of 70°C or higher decreases, and the resulting resin composite material tends to have a high visible light absorptance at high temperatures of 70°C or higher.

The size and shape of the glass-based filler are preferably spherical with a diameter of 100 nm to 2 mm (preferably 200 nm to 1.5 mm, more preferably 500 nm to 1 mm) or fibrous with a fiber diameter of 100 nm to 2 mm (preferably 200 nm to 1.5 mm, more preferably 500 nm to 1 mm) and a fiber length of 100 μm to 50 mm (preferably 200 μm to 30 mm, more preferably 300 μm to 10 mm). If the size of the glass-based filler is less than the lower limit, it tends to be difficult to handle, while if it exceeds the upper limit, the moldability of the resin composition tends to decrease.

(Thermochromic resin composite material)
The thermochromic resin composite material of the present invention contains 0.0005 to 0.03 parts by mass of the black colorant relative to 100 parts by mass of the thermochromic resin composition. This thermochromic resin composite material changes the visible light absorptance depending on the temperature, and the visible light absorptance is low at high temperatures of 70°C or higher, and high at low temperatures of 40°C or lower. For example, in the case of a plate-shaped thermochromic resin composite material having a thickness of 0.5 mm, the difference in visible light absorptance between low temperatures of 40°C or lower and high temperatures of 70°C or higher is 10% or more. On the other hand, if the content of the black colorant is less than the lower limit, the visible light absorptance does not improve (particularly at low temperatures of 40°C or lower), and on the other hand, if the content of the black colorant exceeds the upper limit, the visible light absorptance becomes too high, making it difficult for the visible light absorptance to change with temperature. From the viewpoint of increasing the difference in visible light absorptance between a low temperature of 40° C. or less and a high temperature of 70° C. or more, the content of the black colorant is preferably 0.001 to 0.025 parts by mass, more preferably 0.002 to 0.020 parts by mass, and particularly preferably 0.003 to 0.015 parts by mass, relative to 100 parts by mass of the thermochromic resin composition.

In addition, the thermochromic resin composite material of the present invention preferably further contains 50 parts by mass or less of a glass-based filler relative to 100 parts by mass of the thermochromic resin composition. By including the glass-based filler, the scratch resistance of the resulting resin composite material can be improved, and the radiation cooling ability of the thermochromic resin composite material can be improved. On the other hand, if the content of the glass-based filler exceeds the upper limit, the molding processability tends to decrease. In addition, from the viewpoint of the scratch resistance, radiation cooling ability, and molding processability of the resulting resin composite material, the content of the glass-based filler is more preferably 5 to 40 parts by mass, and particularly preferably 10 to 30 parts by mass, relative to 100 parts by mass of the thermochromic resin composition.

There is no particular restriction on the method for producing such a thermochromic resin composite material, and known kneading methods such as melt kneading can be adopted. However, from the viewpoint of making the black colorant exist in the island phase consisting of the polycaprolactone and dispersing this island phase uniformly, first, the black colorant and the polycaprolactone are dry blended, and the resulting mixture is kneaded (preferably melt kneaded) to prepare a master batch, and then the acrylic polymer, the polyvinylidene fluoride, the polycaprolactone, the master batch, and the glass-based filler, if necessary, are dry blended, and the resulting mixture is kneaded (preferably melt kneaded) to produce the thermochromic resin composite material of the present invention. Furthermore, this thermochromic resin composite material may be molded into a desired shape.

[Laminate]
Next, the laminate of the present invention will be described. The laminate of the present invention includes a member made of the thermochromic resin composite material of the present invention, and a metal film having a visible light reflectance of 70% or more that is disposed on at least a part of one surface of the member.

(Components made of thermochromic resin composite materials)
The member made of the thermochromic resin composite material used in the present invention is obtained by molding the thermochromic resin composite material of the present invention into a desired shape. The shape of the member made of the thermochromic resin composite material is not particularly limited, and examples thereof include a plate shape such as a square plate or a disk, and a flexible film shape.

When the member made of the thermochromic resin composite material is a plate-shaped member, its thickness is preferably 0.01 to 3.0 mm, more preferably 0.05 to 2.5 mm, and particularly preferably 0.1 to 2.0 mm. If the thickness of the plate-shaped member is less than the lower limit, the change in visible light absorptance with temperature tends to be small, while if the thickness of the plate-shaped member exceeds the upper limit, the temperature responsiveness of the visible light absorptance tends to decrease.

(Metal Film)
The metal film used in the present invention has a visible light (particularly, a wavelength of 589 nm) reflectance of 70% or more. When the visible light reflectance of the metal film is less than the lower limit, the change in visible light absorptance due to temperature becomes small. The visible light reflectance of the metal film is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more.

Examples of such metal films include silver foil (visible light (wavelength 589 nm) reflectance: 94%) and aluminum foil (visible light (wavelength 589 nm) reflectance: 81%).

In the metal film, the content (purity) of the main component metal (for example, silver in the case of silver foil, aluminum in the case of aluminum foil) is preferably 70% by mass or more, more preferably 75% by mass or more, and particularly preferably 80% by mass or more. If the content (purity) of the main component metal is below the lower limit, the change in visible light absorptance due to temperature tends to be small.

The thickness of the metal film is preferably 50 nm to 100 μm, more preferably 75 nm to 50 μm, and particularly preferably 100 nm to 25 μm. If the thickness of the metal film is less than the lower limit, the change in visible light absorptance due to temperature tends to be small, while if the thickness of the plate-like member exceeds the upper limit, the flexibility of the member tends to decrease.

(Laminate)
The laminate of the present invention comprises a member made of the thermochromic resin composite material and the metal film disposed on at least a part of one side of the member. The reflectance of visible light in this laminate changes with temperature, and the reflectance of visible light is high at high temperatures of 70° C. or higher and is low at low temperatures of 40° C. or lower. For example, in the case of a laminate comprising a plate-shaped member made of the thermochromic resin composite material having a thickness of 0.5 mm, the difference in reflectance of visible light (wavelength 589 nm) between low temperatures of 40° C. or lower and high temperatures of 70° C. or higher is 10% or more.

There are no particular limitations on the method for producing such a laminate. For example, the member made of the thermochromic resin composite material and the metal film may be superimposed on each other, and then they may be thermocompressed by press molding or the like, or the metal film may be vapor-deposited onto the surface of the member made of the thermochromic resin composite material.

The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples. The raw materials used in the examples and comparative examples are listed below.

(Raw materials)
PMMA: polymethyl methacrylate ("Parapet G grade" manufactured by Kuraray Co., Ltd., refractive index: 1.492 (23°C), 1.489 (60°C)).
PVDF: polyvinylidene fluoride (manufactured by Aldrich, catalog number: 427144, refractive index: 1.42 (23° C.)).
PCL: polycaprolactone (Aldrich, catalog number: 440744, refractive index: 1.46 (50° C.)).
Black pigment: carbon black (manufactured by Aldrich, catalog number: 05-1530-5-500G-J, particle size: 24 nm).
Black dye: oil-soluble azine dye (a mixture of linear alkylbenzene sulfonic acid and oil-soluble anthraquinone dye, "NUBIAN BLACK PC-8550" manufactured by Orient Chemical Industry Co., Ltd.).
SiO ₂ : silicon dioxide ("SO-C6" manufactured by Admatechs Co., Ltd., silicon dioxide purity: 99% or more, particle size: 1.8 to 2.3 μm).
Silver foil: manufactured by Kenis Co., Ltd., catalog number: 68381066, thickness: 400 nm.

Example 1
First, PCL (100 parts by mass) and black pigment (0.44 parts by mass) were dry-blended, and the resulting mixture was then placed in a small tabletop kneader (Minilab, manufactured by Haake Corporation) and kneaded at 170° C. for 5 minutes to prepare a master batch (MB1).

Next, PMMA, PVDF, PCL, the master batch (MB1), and _SiO2 were dry-blended so that the PMMA was 52 parts by mass, the PVDF was 28 parts by mass, the PCL was 20 parts by mass, the black pigment was 0.01 parts by mass, and the _SiO2 was 25 parts by mass. The resulting mixture was then placed in a small benchtop kneader ("Minilab" manufactured by Haake Co., Ltd.) and kneaded at 220 ° C. for 5 minutes to prepare a resin composite material.

The resulting resin composite material was press molded using a benchtop press at 220°C and 6 MPa for 30 seconds to produce a flat plate measuring 50 mm x 50 mm x 0.5 mm.

(Examples 2 to 6)
A resin composite material was prepared in the same manner as in Example 1 except that the contents of PMMA, PVDF, PCL, black pigment and _SiO2 were changed to the amounts shown in Table 1, and a flat plate measuring 50 mm x 50 mm x 0.5 mm was further prepared.

(Example 7)
Except for using a black dye (0.44 parts by mass) instead of the black pigment, a master batch (MB2) was prepared in the same manner as in Example 1. Except for using this master batch (MB2) instead of the master batch (MB1), a resin composite material was prepared in the same manner as in Example 3, and a flat plate of 50 mm × 50 mm × 0.5 mm was produced.

(Comparative Example 1)
PMMA (65 parts by mass), PVDF (35 parts by mass), black pigment (0.005 parts by mass), and SiO ₂ (25 parts by mass) were dry-blended, and the resulting mixture was placed in a small benchtop kneader (Minilab, manufactured by Haake Corporation) and kneaded for 5 minutes at 220° C. to prepare a resin composite material. A 50 mm × 50 mm × 0.5 mm flat plate was produced in the same manner as in Example 1, except that this resin composite material was used instead of the resin composite material prepared in Example 1.

(Comparative Example 2)
A resin composite material was prepared in the same manner as in Example 1 except that the contents of PMMA, PVDF, PCL, black pigment and _SiO2 were changed to the amounts shown in Table 1, and a flat plate measuring 50 mm x 50 mm x 0.5 mm was further prepared.

<Light Absorption Rate>
A temperature controller was installed in the sample chamber of a haze meter ("HGM-3DP" manufactured by Suga Test Instruments Co., Ltd.), and the total light transmittance [%] of the flat plate was measured at each temperature (25 to 100°C) using this haze meter. From the total light transmittance thus obtained, the following formula was calculated:
Light absorptance [%] = 100 - total light transmittance [%]
The light absorption rate [%] was calculated by the above method. The results are shown in Table 1.

As shown in Table 1, the resin composite materials (Examples 1 to 7) containing acrylic polymer, polyvinylidene fluoride, polycaprolactone, and black colorant in a specified ratio had a difference in visible light absorptance of 10% or more between room temperature (25°C) and high temperature (80°C), confirming that they are thermochromic resin composite materials whose visible light absorptance changes with temperature.

On the other hand, the resin composite material that does not contain polycaprolactone (Comparative Example 1) did not contain any light scattering source, and therefore no change in visible light absorptance due to temperature was observed.

In addition, the resin composite material (Comparative Example 2) containing more than the specified amount of black colorant had too high a visible light absorption rate, so no change in visible light absorption rate due to temperature was observed.

(Example 8)
The flat plate prepared in Example 1 was placed on the silver foil and then press molded for 30 seconds at a temperature of 220°C and a pressure of 6 MPa using a bench press to produce a laminate in which the silver foil was thermocompressed onto the entire back surface of the flat plate.

(Example 9)
A laminate was produced in the same manner as in Example 8, except that the flat plate produced in Example 3 was used instead of the flat plate produced in Example 1, and a silver foil was thermocompression-bonded to the entire back surface of the flat plate.

(Example 10)
A laminate was produced in the same manner as in Example 8, except that the flat plate produced in Example 5 was used instead of the flat plate produced in Example 1, and a silver foil was thermocompression-bonded to the entire back surface of the flat plate.

Example 11
A laminate was produced in the same manner as in Example 8, except that the flat plate produced in Example 7 was used instead of the flat plate produced in Example 1, and a silver foil was thermocompression-bonded to the entire back surface of the flat plate.

(Comparative Example 3)
PMMA (52 parts by mass), PVDF (28 parts by mass), PCL (20 parts by mass), and SiO ₂ (25 parts by mass) were dry-blended, and the resulting mixture was placed in a small tabletop kneader (Minilab, manufactured by Haake Co., Ltd.) and kneaded at 220° C. for 5 minutes to prepare a resin composite material. A 50 mm×50 mm×0.5 mm flat plate was prepared in the same manner as in Example 1, except that this resin composite material was used instead of the resin composite material prepared in Example 1. Furthermore, a laminate in which silver foil was thermocompression-bonded to the entire back surface of the flat plate was prepared in the same manner as in Example 8, except that this flat plate was used instead of the flat plate prepared in Example 1.

(Comparative Example 4)
A laminate was produced in the same manner as in Example 8, except that the flat plate produced in Comparative Example 1 was used instead of the flat plate produced in Example 1, and a silver foil was thermocompression-bonded to the entire back surface of the flat plate.

(Comparative Example 5)
A laminate was produced in the same manner as in Example 8, except that the flat plate produced in Comparative Example 2 was used instead of the flat plate produced in Example 1, and a silver foil was thermocompression-bonded to the entire back surface of the flat plate.

<Light reflectance>
A rubber heater was placed on the back surface of the obtained laminate (the surface of the silver foil), and the light reflectance [%] of the laminate was measured by irradiating the surface of the laminate (the surface without the silver foil) with light having a wavelength of 589 nm using an ultraviolet-visible spectrophotometer equipped with an integrating sphere (Shimadzu Corporation, "UV-3600") at 25° C. and 70° C. The results are shown in Table 2.

As shown in Table 2, it was confirmed that the laminates (Examples 8 to 11) in which silver foil was thermocompressed onto the entire back surface of a flat plate made of a resin composite material containing acrylic polymer, polyvinylidene fluoride, polycaprolactone, and a black colorant in a specified ratio had improved light reflectance at high temperatures (70°C) compared to room temperature (25°C).

On the other hand, the change in light reflectance due to temperature was very small in all of the laminates in which silver foil was thermocompression-bonded to the entire back surface of a flat plate made of a resin composite material that did not contain a black colorant (Comparative Example 3), the laminates in which silver foil was thermocompression-bonded to the entire back surface of a flat plate made of a resin composite material that did not contain polycaprolactone (Comparative Example 4), and the laminates in which silver foil was thermocompression-bonded to the entire back surface of a flat plate made of a resin composite material that contained more than a specified amount of black colorant (Comparative Example 5).

<Heat generated by sunlight>
An outdoor test apparatus was prepared using a rubber heater and a data logger. The laminated plate prepared in Example 9 was placed in this outdoor test apparatus. The amount of heat input to the heater was measured at 45° C. and 70° C. when the surface of the laminated plate (the surface without the silver foil) was not irradiated with sunlight and when it was irradiated with sunlight, and the amount of heat input was calculated using the following formula:
The amount of heat generated by sunlight was calculated by the formula: amount of heat generated by sunlight = amount of heat input to heater when irradiated with sunlight - amount of heat input to heater when not irradiated with sunlight. The results are shown in Table 3.

As shown in Table 3, the amount of heat generated by sunlight in the laminate produced in Example 9 changed between 45°C and 70°C, indicating that the laminate is a composite material whose amount of heat generated by sunlight changes autonomously with temperature changes.

As described above, according to the present invention, it is possible to obtain a resin composite material that exhibits low visible light absorptance at high temperatures of 70°C or higher and high visible light absorptance at low temperatures of 40°C or lower. Furthermore, by providing a metal film on one side of a member made of such a resin composite material, it is possible to obtain a laminate that exhibits high light reflectance at high temperatures of 70°C or higher and low light reflectance at low temperatures of 40°C or lower.

When such a laminate of the present invention is irradiated with sunlight, if the temperature is low, the absorption rate of sunlight is high (the reflectance of visible light is low), so the amount of heat generated by sunlight is large, and on the other hand, if the temperature is high, the absorption rate of sunlight is low (the reflectance of visible light is high), so the amount of heat generated by sunlight is small.

Therefore, the laminate of the present invention can be used as an autonomous temperature control material in which the amount of heat generated by sunlight changes with changes in the outside air temperature, and is useful as a laminate for use in, for example, buildings such as houses, factories, and warehouses, and transportation vehicles such as automobiles and trains. In addition, by attaching such a laminate to the surface of an adherend (e.g., a roof or wall surface) so that the adherend is placed on the metal film side of the laminate, when the temperature is low, the laminate generates heat due to sunlight, making it possible to heat the adherend by this heat generation, and when the temperature is high, sunlight is reflected by the laminate, making it possible to suppress heating of the adherend by sunlight.

Claims (5)

A thermochromic resin composition comprising 15 to 84 mass% of polymethyl methacrylate , 15 to 84 mass% of polyvinylidene fluoride, and 1 to 40 mass% of polycaprolactone; and a thermochromic resin composite material comprising, per 100 mass parts of the thermochromic resin composition, 0.0005 to 0.03 mass parts of at least one black colorant selected from the group consisting of black pigments and black dyes. The thermochromic resin composite material according to claim 1, further comprising 50 parts by mass or less of a glass-based filler per 100 parts by mass of the thermochromic resin composition. The thermochromic resin composite material according to claim 2, characterized in that the glass-based filler has a silicon dioxide purity of 90% or more. The thermochromic resin composite material according to claim 1, characterized in that the black colorant is carbon particles having a graphite structure. A laminate comprising a member made of the thermochromic resin composite material according to claim 1 and a metal film having a visible light reflectance of 70% or more arranged on at least a portion of one side of the member.