Thermochromic resin composition

Abstract

To provide a thermochromic resin composition that is soluble in general-purpose solvents, exhibits a high haze value at low temperatures, and a low haze value at high temperatures. [Solution] 50-95% by mass of a copolymer of 10-70 mol% of fluoro(meth)acrylate having a refractive index of 1.32-1.37 at 23°C and 30-90 mol% of (meth)acrylate having a refractive index of 1.40-1.52 at 23°C, and 5-50% by mass of polyalkyl (meth)acrylate with side chain alkyl groups having 14-22 carbon atoms. A thermochromic resin composition characterized by containing the following:

Description

Technical Field

[0001] The present invention relates to a thermochromic resin composition, and more particularly to a thermochromic resin composition in which the haze value decreases on the low-temperature side and increases on the high-temperature side.

Background Art

[0002] In recent years, thermochromic materials that change color and transparency in response to temperature changes have attracted attention. For example, Japanese Patent Application Laid-Open No. 2023-38497 (Patent Document 1) discloses a polymer blend composed of 85 to 15% by mass of an acrylic polymer and 15 to 85% by mass of polyvinylidene fluoride, and 5 to 120 parts by mass of polycaprolactone with respect to 100 parts by mass of the polymer blend, a thermochromic resin composition having improved transparency at high temperatures.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, since the thermochromic resin composition described in Patent Document 1 contains a polymer blend composed of an acrylic polymer and polyvinylidene fluoride, there is a problem that the types of solvents that can be dissolved are few, and the types of solvents used in molding processing methods such as the solvent casting method are limited. Therefore, there is a demand for a thermochromic resin composition that can be dissolved in a general-purpose solvent.

[0005] The present invention has been made in view of the problems of the above prior art, and an object thereof is to provide a thermochromic resin composition that can be dissolved in a general-purpose solvent, has a high haze value at low temperatures, and a low haze value at high temperatures. [Means for solving the problem]

[0006] As a result of diligent research to achieve the above objective, the present inventors have discovered that by blending a copolymer of fluoro(meth)acrylate and (meth)acrylate with a copolymerization ratio within a predetermined range and polyalkyl(meth)acrylate in a predetermined proportion, a thermochromic resin composition can be obtained that is soluble in common solvents and exhibits a high haze value at low temperatures (temperatures below the melting point of polyalkyl(meth)acrylate) and a low haze value at high temperatures (temperatures above the melting point of polyalkyl(meth)acrylate), thus completing the present invention.

[0007] In other words, the present invention provides the following embodiments. [1] 50-95% by mass of a copolymer of 10-70 mol% of fluoro(meth)acrylate having a refractive index of 1.32-1.37 at 23°C and 30-90 mol% of (meth)acrylate having a refractive index of 1.40-1.52 at 23°C, and 5-50% by mass of polyalkyl (meth)acrylate with side chain alkyl groups having 14-22 carbon atoms. A thermochromic resin composition containing [the specified substance]. [2] The thermochromic resin composition according to [1], wherein the refractive index of the polyalkyl (meth)acrylate at 50°C is 1.40 to 1.46. [3] The thermochromic resin composition according to [1] or [2], wherein the (meth)acrylate is methyl (meth)acrylate. [4] The thermochromic resin composition according to any one of [1] to [3], wherein the fluoro(meth)acrylate is 2,2,2-trifluoroethyl(meth)acrylate.

[0008] Although the reason why the thermochromic effect occurs in the thermochromic resin composition of the present invention, where the haze value is higher at low temperatures and lower at high temperatures, is not entirely clear, the inventors speculate as follows.

[0009] In other words, a copolymer of fluoro(meth)acrylate and (meth)acrylate (hereinafter also referred to as "fluoro(meth)acrylate-based copolymer") can have its refractive index changed by changing the copolymerization ratio of fluoro(meth)acrylate and (meth)acrylate. By setting the copolymerization ratio of fluoro(meth)acrylate and (meth)acrylate within a predetermined range, a fluoro(meth)acrylate-based copolymer having a refractive index close to that of molten polyalkyl(meth)acrylate can be obtained. By spin-casting the thermochromic resin composition of the present invention containing such a fluoro(meth)acrylate-based copolymer and polyalkyl(meth)acrylate having a copolymerization ratio within a predetermined range using a common good solvent, or by melt-kneading using a known kneader, a sea-island structure having a sea phase made of the fluoro(meth)acrylate-based copolymer and an island phase made of molten polyalkyl(meth)acrylate can be formed. When a thermochromic resin composition having such a sea-island structure is irradiated with visible light at a temperature above the melting point of the polyalkyl (meth)acrylate contained therein, it is presumed that the refractive index of the fluoro(meth)acrylate copolymer and the refractive index of the molten polyalkyl (meth)acrylate are close, suppressing the scattering of incident visible light, and thus the haze value of the resin composition becomes low.

[0010] On the other hand, when the thermochromic resin composition of the present invention is exposed to a temperature below the melting point of the polyalkyl (meth)acrylate contained therein, at least a portion of the polyalkyl (meth)acrylate crystallizes, forming a sea-island structure having a sea phase made of the fluoro(meth)acrylate copolymer and an island phase made of the crystallized polyalkyl (meth)acrylate. When visible light is irradiated onto such a thermochromic resin composition having a sea-island structure at a temperature below the melting point of the polyalkyl (meth)acrylate contained therein, it is presumed that the haze value of the resin composition will increase because the incident visible light is scattered by the island phase. [Effects of the Invention]

[0011] According to the present invention, it is possible to obtain a thermochromic resin composition that is soluble in general-purpose solvents, and whose haze value increases at low temperatures and decreases at high temperatures. [Modes for carrying out the invention]

[0012] The present invention will be described in detail below with reference to its preferred embodiments.

[0013] The thermochromic resin composition of the present invention contains 50 to 95% by mass of a copolymer (fluoro(meth)acrylate-based copolymer) of 10 to 70 mol% of fluoro(meth)acrylate having a refractive index of 1.32 to 1.37 at 23°C and 30 to 90 mol% of (meth)acrylate having a refractive index of 1.40 to 1.52 at 23°C, and 5 to 50% by mass of polyalkyl(meth)acrylate having 14 to 22 carbon atoms in the side chain alkyl group.

[0014] (Fluoro(meth)acrylate copolymer) The fluoro(meth)acrylate copolymer used in the present invention is a copolymer of 10 to 70 mol% fluoro(meth)acrylate and 30 to 90 mol% (meth)acrylate. If the proportion of fluoro(meth)acrylate falls below the lower limit (i.e., the proportion of (meth)acrylate exceeds the upper limit), the haze value of the resin composition at high temperatures increases, and the thermochromic effect does not occur. On the other hand, if the proportion of fluoro(meth)acrylate exceeds the upper limit (i.e., the proportion of (meth)acrylate falls below the lower limit), the haze value of the resin composition at high temperatures increases, and its solubility in the solvent decreases. Furthermore, from the viewpoint of increasing the difference between the low-temperature and high-temperature sides of the haze value of the resin composition, it is preferable that the proportion of fluoro(meth)acrylate is 25 to 60 mol% and the proportion of (meth)acrylate is 40 to 75 mol%, more preferably that the proportion of fluoro(meth)acrylate is 35 to 55 mol% and the proportion of (meth)acrylate is 45 to 65 mol%, and even more preferably that the proportion of fluoro(meth)acrylate is 35 to 45 mol% and the proportion of (meth)acrylate is 55 to 65 mol%.

[0015] The fluoro(meth)acrylate used in this invention has a refractive index of 1.32 to 1.37 at 23°C. If the refractive index of the fluoro(meth)acrylate falls below the lower limit, its solubility and reactivity decrease, making it difficult to obtain a copolymer with (meth)acrylate. On the other hand, if the refractive index of the fluoro(meth)acrylate exceeds the upper limit, the refractive index of the copolymer with (meth)acrylate and the refractive index of the polyalkyl acrylate do not match sufficiently, resulting in a high haze value at high temperatures for the resin composition.

[0016] Examples of such fluoro(meth)acrylates include 2,2,2-trifluoroethyl(meth)acrylate, 1,1,1,3,3,3-hexafluoroisopropyl(meth)acrylate, 2,2,3,3,3-pentafluoropropyl(meth)acrylate, 2,2,3,3,4,4,4-heptafluorobutyl(meth)acrylate, and methyl 2-fluoroacrylate. Among these fluoro(meth)acrylates, 2,2,2-trifluoroethyl(meth)acrylate, 1,1,1,3,3,3-hexafluoroisopropyl(meth)acrylate, and 2,2,3,3,3-pentafluoropropyl(meth)acrylate are preferred from the viewpoint of ease of handling and high reactivity with (meth)acrylate, and 2,2,2-trifluoroethyl(meth)acrylate and 2,2,3,3,3-pentafluoropropyl(meth)acrylate are more preferred.

[0017] The (meth)acrylate used in this invention has a refractive index of 1.40 to 1.52 at 23°C. If the refractive index of the (meth)acrylate falls below the lower limit, the refractive index of the copolymer with fluoro(meth)acrylate and the refractive index of the polyalkyl acrylate do not match sufficiently, and the haze value of the resin composition at high temperatures increases. On the other hand, if the refractive index of the fluoro(meth)acrylate exceeds the upper limit, the solubility of the copolymer with fluoro(meth)acrylate in the solvent decreases.

[0018] Examples of such (meth)acrylates include alkyl (meth)acrylates such as methyl (meth)acrylate and ethyl (meth)acrylate, hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, aromatic (meth)acrylates such as benzyl (meth)acrylate, and alkoxyalkyl (meth)acrylates such as 2-ethoxyethyl (meth)acrylate. Among these (meth)acrylates, from the viewpoint of high reactivity with fluoro (meth)acrylate, methyl (meth)acrylate, ethyl (meth)acrylate, and 2-ethoxyethyl (meth)acrylate are preferred, and methyl (meth)acrylate and ethyl (meth)acrylate are more preferred.

[0019] The number average molecular weight of the fluoro (meth)acrylate copolymer used in the present invention is not particularly limited, but from the viewpoints of solubility in a solvent and ease of handling, 40,000 to 150,000 is preferred, and 60,000 to 100,000 is more preferred.

[0020] (Polyalkyl (meth)acrylate) The polyalkyl (meth)acrylate used in the present invention has a side chain alkyl group having 14 to 22 carbon atoms, and specifically, it is a polymer (homopolymer and copolymer) of an alkyl (meth)acrylate monomer having a side chain alkyl group having 14 to 22 carbon atoms. The proportion of the alkyl (meth)acrylate monomer unit in the copolymer of the alkyl (meth)acrylate monomer is preferably 50 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, and particularly preferably 90 mol% or more. Among such polyalkyl (meth)acrylates, from the viewpoint of increasing the degree of temperature change of the haze value of the obtained resin composition, the homopolymer of the alkyl (meth)acrylate monomer is preferred.

[0021] In such polyalkyl (meth) acrylates, by changing the number of carbon atoms of the side-chain alkyl group within the above range, the melting point can be adjusted within the range of 10 to 60 °C, and a thermochromic resin composition in which the haze value changes at a temperature within the above range can be obtained. The number of carbon atoms of the side-chain alkyl group can be appropriately set according to the desired temperature for changing the haze value of the resin composition, but is preferably 14 to 20, and more preferably 15 to 18. By setting the number of carbon atoms of the side-chain alkyl group within the above range, the melting point of the polyalkyl (meth) acrylate can be adjusted preferably within the range of 10 to 55 °C (more preferably 15 to 50 °C), and a thermochromic resin composition in which the haze value changes at a temperature within the above range can be obtained.

[0022] Specific examples of the alkyl (meth) acrylate monomer include (meth) acrylates having a side-chain alkyl group with 14 to 22 carbon atoms (preferably 14 to 20, more preferably 15 to 18), such as tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, nonadecyl (meth) acrylate, eicosyl (meth) acrylate, heneicosyl (meth) acrylate, docosyl (meth) acrylate, etc. These alkyl (meth) acrylate monomers may be used alone or in combination of two or more.

[0023] Examples of other copolymerization monomers in the copolymer of the alkyl (meth) acrylate monomer include olefins (such as ethylene, propylene, etc.) and aromatic vinyl monomers (such as styrene, α-methylstyrene, etc.). These other copolymerization monomers may be used alone or in combination of two or more.

[0024] Specifically, the polyalkyl (meth)acrylates used in the present invention include polyalkyl methacrylates having a side-chain alkyl group with 14 to 22 carbon atoms (preferably 14 to 20, more preferably 15 to 18) (e.g., polytetradecyl methacrylate, polyhexadecyl methacrylate, polyoctadecyl methacrylate, etc.) and copolymers thereof, and polyalkyl acrylates having a side-chain alkyl group with 14 to 22 carbon atoms (preferably 14 to 20, more preferably 15 to 18) (e.g., polytetradecyl acrylate, polyhexadecyl acrylate). Copolymers of methacrylic acid and alkyl acrylates having a side chain alkyl group with 14 to 22 carbon atoms (preferably 14 to 20, more preferably 15 to 18) (e.g., methacrylic acid-tetradecyl acrylate copolymer, methacrylic acid-hexadecyl acrylate copolymer, methacrylic acid-octadecyl acrylate copolymer, etc.), alkyl methacrylates having a side chain alkyl group with 14 to 22 carbon atoms (preferably 14 to 20, more preferably 15 to 18) and methacrylic acid (preferably Copolymers of ethylene with alkyl acrylates having side chain alkyl groups with 14 to 20 (preferably 15 to 18) carbon atoms (e.g., hexadecyl methacrylate-octadecyl acrylate copolymer, tetradecyl methacrylate-dodecyl acrylate copolymer, octadecyl methacrylate-hexadecyl acrylate copolymer, etc.), and copolymers of ethylene with alkyl acrylates having side chain alkyl groups with 14 to 22 (preferably 14 to 20, more preferably 15 to 18) carbon atoms (e.g., ethylene-tetradecyl acrylate copolymer, ethylene-hexadecyl acrylate copolymer) ethylene tetradecyl methacrylate copolymer, ethylene hexadecyl methacrylate copolymer, ethylene octadecyl methacrylate copolymer, etc., alkyl methacrylate copolymer having ethylene and a side chain alkyl group having 14 to 22 carbon atoms (preferably 14 to 20, more preferably 15 to 18) (for example, ethylene tetradecyl methacrylate copolymer, ethylene hexadecyl methacrylate copolymer, ethylene octadecyl methacrylate copolymer, etc.), alkyl acrylate copolymer having styrene and a side chain alkyl group having 14 to 22 carbon atoms (preferably 14 to 20, more preferably 15 to 18) (for example,Examples include styrene-tetradecyl acrylate copolymers, styrene-hexadecyl acrylate copolymers, styrene-octadecyl acrylate copolymers, etc., and alkyl methacrylate copolymers having styrene and a side-chain alkyl group having 14 to 22 carbon atoms (preferably 14 to 20, more preferably 15 to 18) (e.g., styrene-tetradecyl methacrylate copolymers, styrene-hexadecyl methacrylate copolymers, styrene-octadecyl methacrylate copolymers, etc.). These polyalkyl (meth)acrylates may be used individually or in combination of two or more. Among these polyalkyl (meth)acrylates, from the viewpoint of increasing the degree of temperature dependence of the haze value of the resulting resin composition, polyalkyl (meth)acrylates having a side-chain alkyl group having 14 to 22 carbon atoms are preferred, polytetradecyl methacrylate and polyhexadecyl methacrylate are more preferred, and polyhexadecyl methacrylate is particularly preferred.

[0025] Furthermore, in the polyalkyl (meth)acrylate used in the present invention, it is preferable that the refractive index at 50°C is 1.40 to 1.46. If the refractive index of the polyalkyl (meth)acrylate is below the lower limit or above the upper limit, the difference between the refractive index of the fluoro(meth)acrylate copolymer and the refractive index of the molten polyalkyl (meth)acrylate becomes large, the haze value at high temperatures of the resin composition increases, and the thermochromic effect tends not to be fully expressed.

[0026] [Thermochromic resin composition] The thermochromic resin composition of the present invention contains 50 to 95% by mass of the fluoro(meth)acrylate copolymer and 5 to 50% by mass of the polyalkyl(meth)acrylate. Such a thermochromic resin composition exhibits a thermochromic effect in which the haze value increases at low temperatures and decreases at high temperatures.

[0027] In the thermochromic resin composition of the present invention, the content of polyalkyl (meth)acrylate must be 5 to 50% by mass relative to the total amount of the resin composition. If the content of polyalkyl (meth)acrylate falls below the lower limit, the haze value of the resin composition at low temperatures will not be high, and the thermochromic effect will not be exhibited. On the other hand, if the content of polyalkyl (meth)acrylate exceeds the upper limit, the mechanical strength of the resin composition will decrease at high temperatures. Furthermore, from the viewpoint of sufficiently exhibiting the thermochromic effect, the lower limit of the polyalkyl (meth)acrylate content is preferably 10% by mass or more, and more preferably 15% by mass or more. Also, from the viewpoint of obtaining a resin composition with good mechanical strength at high temperatures, the upper limit of the polyalkyl (meth)acrylate content is preferably 40% by mass or less, and more preferably 30% by mass or less.

[0028] Furthermore, in the thermochromic resin composition of the present invention, the content of the fluoro(meth)acrylate copolymer must be 50 to 95% by mass relative to the total amount of the resin composition. If the content of the fluoro(meth)acrylate copolymer falls below the lower limit, the mechanical strength of the resin composition decreases at high temperatures. On the other hand, if the content of the fluoro(meth)acrylate copolymer exceeds the upper limit, the haze value of the resin composition at low temperatures does not increase, and the thermochromic effect does not manifest. Furthermore, from the viewpoint of obtaining a resin composition with good mechanical strength at high temperatures, the lower limit of the content of the fluoro(meth)acrylate copolymer is preferably 60% by mass or more, and more preferably 70% by mass or more. Furthermore, from the viewpoint of sufficiently manifesting the thermochromic effect, the upper limit of the content of the fluoro(meth)acrylate copolymer is preferably 90% by mass or less, and more preferably 85% by mass or less.

[0029] Furthermore, in the thermochromic resin composition of the present invention, it is preferable that a sea-island structure is formed comprising a sea phase made of the fluoro(meth)acrylate copolymer and an island phase made of at least a portion of the polyalkyl(meth)acrylate. With such a sea-island structure formed, at low temperatures, the polyalkyl(meth)acrylate in the island phase crystallizes, increasing the haze value of the resin composition, and at high temperatures, the polyalkyl(meth)acrylate melts, causing the refractive index of the island phase to approach that of the fluoro(meth)acrylate copolymer in the sea phase, thus lowering the haze value of the resin composition and exhibiting a thermochromic effect.

[0030] In the aforementioned sea-island structure, the size of the island phase is preferably such that the maximum length of the island phase (or diameter if the island phase is circular) is 50 nm to 100 μm, more preferably 70 nm to 70 μm, and particularly preferably 100 nm to 50 μm. If the size of the island phase is less than the lower limit, the thermochromic effect does not manifest sufficiently, and the haze value of the resin composition at low temperatures tends not to increase. On the other hand, if the size of the island phase exceeds the upper limit, the moldability of the resin composition tends to decrease.

[0031] (Glass-based filler) The thermochromic resin composition of the present invention preferably contains a glass-based filler with a silicon dioxide purity of 90% or more. A glass-based filler with a silicon dioxide purity of 90% or more has a refractive index close to that of the fluoro(meth)acrylate copolymer or the polyalkyl(meth)acrylate at high temperatures. Therefore, in a thermochromic resin composition containing such a glass-based filler, the haze value at high temperatures is reduced, and scratch resistance can be improved while maintaining the thermochromic effect. Furthermore, from the viewpoint of sufficiently maintaining the thermochromic effect and sufficiently reducing the haze value of the resin composition at high temperatures, the silicon dioxide purity of the glass-based filler is preferably 95% or more, and more preferably 98% or more. On the other hand, a glass-based filler with a silicon dioxide purity below the lower limit has a refractive index that is significantly different from that of the fluoro(meth)acrylate copolymer or the polyalkyl(meth)acrylate at high temperatures. Therefore, the thermochromic effect in the thermochromic resin composition is not maintained, and the haze value of the resin composition at high temperatures is not easily reduced.

[0032] In the glass-based filler used in the present invention, the refractive index at 23°C is preferably 1.40 to 1.52, and more preferably 1.43 to 1.49. If the refractive index of the glass-based filler is below the lower limit or above the upper limit, the haze value of the resin composition at high temperatures tends to increase.

[0033] Furthermore, the size and shape of the glass-based filler used in the present invention 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 200 μm (preferably 200 nm to 100 μm, more preferably 500 nm to 50 μm) 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 below the lower limit, it tends to become difficult to handle, while if it exceeds the upper limit, the moldability of the resin composition tends to decrease.

[0034] In the thermochromic resin composition of the present invention, the content of such glass-based filler is preferably 1 to 100 parts by mass, and more preferably 5 to 50 parts by mass, per 100 parts by mass of the fluoro(meth)acrylate copolymer. If the content of glass-based filler is below the lower limit, the effect of improving scratch resistance due to the addition of glass-based filler tends not to be sufficiently obtained, on the other hand, if it exceeds the upper limit, the moldability of the resin composition tends to decrease.

[0035] There are no particular limitations on the method for producing the thermochromic resin composition of the present invention, and known kneading methods such as melt kneading can be employed. For example, it can be produced by dry blending the fluoro(meth)acrylate copolymer, the polyalkyl(meth)acrylate, and the glass-based filler as needed, and then melt kneading the resulting mixture. Alternatively, it can be produced by dissolving the fluoro(meth)acrylate copolymer and the polyalkyl(meth)acrylate in a common good solvent, further mixing in the glass-based filler as needed, and then performing solvent casting. [Examples]

[0036] 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 polyhexadecyl acrylate (PHDA) used in the examples and comparative examples was synthesized by the following method.

[0037] (Synthesis Example 1) 3.5 mg of 2,2'-azobisisobutyronitrile (AIBN, manufactured by Tokyo Chemical Industry Co., Ltd., product code: A0566) and 4.26 g of hexadecyl acrylate (HDA, manufactured by Tokyo Chemical Industry Co., Ltd., product code: H1168) were dissolved in 0.74 ml of toluene. The mixture was then stirred at 80°C for 24 hours under a nitrogen atmosphere to polymerize the HDA. The resulting toluene solution of polyhexadecyl acrylate (PHDA) was diluted with 15 ml of chloroform, and this solution was added dropwise to 300 ml of methanol to reprecipitate the PHDA. The resulting precipitate was separated and recovered by suction filtration. Subsequently, reprecipitation was performed again using chloroform and methanol, and the resulting precipitate was separated and recovered by suction filtration. After vacuum drying to remove the remaining solvent, PHDA with a number average molecular weight of 135100, a refractive index of 1.46 (50°C), and a melting point of 35°C was obtained. The number-average molecular weight was measured using gel permeation chromatography (GPC-101, manufactured by Shoko Science Co., Ltd.), the refractive index was measured using an Abbe refractometer (DR-M2, manufactured by Atago Co., Ltd.), and the melting point was measured using a differential scanning calorimeter (X3, manufactured by TA Instruments).

[0038] (Example 1) 6.58 ml of dioxane was dissolved with 7 mg of 2,2'-azobisisobutyronitrile (AIBN, manufactured by Tokyo Chemical Industry Co., Ltd., product code: A0566), 2.56 ml of methyl methacrylate (MMA, manufactured by Tokyo Chemical Industry Co., Ltd., product code: M0087, refractive index at 23°C: 1.41), and 0.85 ml of 2,2,2-trifluoroethyl methacrylate (3FEMA, manufactured by Tokyo Chemical Industry Co., Ltd., product code: M0738, refractive index at 23°C: 1.36). The mixture was then stirred at 80°C for 6 hours under a nitrogen atmosphere to copolymerize 3FEMA with MMA. The resulting dioxane solution of the 3FEMA-MMA copolymer was diluted with 40 ml of chloroform, and this solution was added dropwise to 400 ml of methanol to reprecipitate the copolymer. The resulting precipitate was separated and recovered by suction filtration. Subsequently, reprecipitation was performed again using chloroform and methanol. The resulting precipitate was separated and recovered by suction filtration, and then vacuum-dried to remove the remaining solvent, yielding a copolymer with a number-average molecular weight of 97,900 and a copolymerization ratio of 3FEMA to MMA of 20 mol%:80 mol%. The number-average molecular weight was measured using gel permeation chromatography (GPC-101, manufactured by Shoko Science Co., Ltd.), and the copolymerization ratio of 3FEMA to MMA was measured for the obtained copolymer. 1 These values ​​were obtained from the H-NMR spectrum.

[0039] 160 mg of the obtained copolymer and 40 mg of PHDA synthesized in Synthesis Example 1 were dissolved in 1 ml of methyl isobutyl ketone (MIBK) and thoroughly stirred. The resulting solution was dropped onto a glass slide, and the MIBK was removed by air drying to prepare a resin composition film with a thickness of approximately 200 μm.

[0040] (Example 2) Except for changing the amount of dioxane to 6.50 ml, the amount of MMA to 2.24 ml, and the amount of 3FEMA to 1.28 ml, a copolymer with a number average molecular weight of 134100 and a copolymerization ratio of 3FEMA:MMA = 29 mol%:71 mol% was prepared in the same manner as in Example 1, and a resin composition film with a thickness of approximately 200 μm was then fabricated.

[0041] (Example 3) Except for changing the amount of dioxane to 6.36 ml, the amount of MMA to 1.92 ml, and the amount of 3FEMA to 1.70 ml, a copolymer with a number-average molecular weight of 108,100 and a copolymerization ratio of 3FEMA:MMA = 41 mol%:59 mol% was prepared in the same manner as in Example 1, and a resin composition film with a thickness of approximately 200 μm was then fabricated.

[0042] (Example 4) Except for changing the amount of dioxane to 6.26 ml, the amount of MMA to 1.60 ml, and the amount of 3FEMA to 2.14 ml, a copolymer with a number-average molecular weight of 93,900 and a copolymerization ratio of 3FEMA:MMA = 50 mol%:50 mol% was prepared in the same manner as in Example 1, and a resin composition film with a thickness of approximately 200 μm was then fabricated.

[0043] (Comparative Example 1) Polymethyl methacrylate (PMMA) was prepared in the same manner as in Example 1, except that the amount of dioxane was changed to 13.6 ml, the amount of AIBN to 14 mg, and the amount of MMA to 6.4 ml, and 3FEMA was not used. A resin composition film with a thickness of approximately 200 μm was then fabricated. The number-average molecular weight of the obtained PMMA was determined to be 61600 in the same manner as in Example 1.

[0044] (Comparative Example 2) A resin film with a thickness of approximately 200 μm was prepared in the same manner as in Example 2, except that PHDA was not used.

[0045] (Comparative Example 3) Poly(2,2,2-trifluoroethyl methacrylate) (P3FEMA) was prepared in the same manner as in Example 1, except that the amount of dioxane was changed to 6.72 ml and the amount of 3FEMA to 4.27 ml, and MMA was not used. A resin film with a thickness of approximately 200 μm was then fabricated. The number-average molecular weight of the obtained P3FEMA was determined to be 64300 in the same manner as in Example 1.

[0046] <Haze value> A homemade temperature control unit was installed inside a haze meter (HGM-3DP, manufactured by Suga Test Instruments Co., Ltd.), and the haze values ​​of each film (thickness: approximately 200 μm) obtained in the examples and comparative examples were measured at room temperature and at a temperature of 50°C. The results are shown in Table 1.

[0047] [Table 1]

[0048] As shown in Table 1, in resin composition films (Examples 1-4) containing a copolymer of 3FEMA and MMA within a predetermined copolymerization ratio and PHDA in predetermined proportions, it was found that the haze value decreased by 8% or more when the temperature was raised from room temperature to 50°C, exhibiting a so-called thermochromic effect in which the haze value changes with temperature.

[0049] On the other hand, in the resin composition film containing PMMA and PHDA (Comparative Example 1), the haze value did not change between room temperature and 50°C, and no thermochromic effect was observed. Furthermore, in the resin film containing only a copolymer of 3FEMA and MMA within a predetermined copolymerization ratio (Comparative Example 2), the transparency was extremely high at both room temperature and 50°C, and no thermochromic effect was observed.

[0050] Furthermore, in the resin composition film containing P3FEMA and PHDA (Comparative Example 3), a homogeneous film could not be produced. This is thought to be because the compatibility between P3FEMA and PHDA is extremely low, leading to the formation of a coarse phase separation structure in the resin composition, and the PHDA melted and desorbed due to the increase in temperature during film drying.

[0051] From the above results, it was confirmed that by blending a copolymer of fluoro(meth)acrylate and (meth)acrylate with a copolymerization ratio within a predetermined range and a polyalkyl acrylate in a predetermined proportion, a resin composition exhibiting a so-called thermochromic effect, in which the haze value changes with temperature changes, can be obtained. [Industrial applicability]

[0052] As described above, according to the present invention, it is possible to obtain a resin composition that is soluble in general-purpose solvents and exhibits a thermochromic effect in which the haze value increases at low temperatures (especially below the melting point of the polyalkyl (meth)acrylate) and decreases at high temperatures (especially above the melting point of the polyalkyl (meth)acrylate).

[0053] Therefore, the thermochromic resin composition of the present invention is useful in that it is opaque at low temperatures and relatively permeable to visible light at high temperatures, making it possible to easily manufacture surface materials that allow temperature to be visually recognized, or surface materials that can adjust the surface temperature of structures exposed to sunlight.

Claims

1. A copolymer of 10-70 mol% of fluoro(meth)acrylate having a refractive index of 1.32-1.37 at 23°C and 30-90 mol% of (meth)acrylate having a refractive index of 1.40-1.52 at 23°C, and 50-95% by mass, and 5-50% by mass of polyalkyl (meth)acrylate with side chain alkyl groups having 14-22 carbon atoms. A thermochromic resin composition characterized by containing the following:

2. The thermochromic resin composition according to claim 1, characterized in that the refractive index of the polyalkyl (meth)acrylate at 50°C is 1.40 to 1.

46.

3. The thermochromic resin composition according to claim 1, characterized in that the (meth)acrylate is methyl (meth)acrylate.

4. The thermochromic resin composition according to claim 1, characterized in that the fluoro(meth)acrylate is 2,2,2-trifluoroethyl(meth)acrylate.

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