Thermochromic resin composition

Abstract

To provide a resin composition which exhibits such a thermochromic effect as to change transparency at a temperature of 60°C or lower, and exhibit excellent transparency on the high temperature side.SOLUTION: A thermochromic resin composition contains a polymer blend composed of 85 to 50 mass% of an acrylic polymer and 15 to 50 mass% of polyvinylidene fluoride, and 1 to 80 pts.mass of polyalkyl acrylate having an alkyl group having 12 to 22 carbon atoms with respect to 100 pts.mass of the polymer blend.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a thermochromic resin composition, and more particularly to a thermochromic resin composition that exhibits high transparency on the high-temperature side.

Background Art

[0002] In recent years, thermochromic materials that change color or transparency according 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. The thermochromic resin composition has a transparency change at a temperature of 60°C or higher near the melting point of polycaprolactone.

[0003] On the other hand, as thermochromic materials, those with a transparency change at a temperature near room temperature (25°C) or those with a transparency change at a temperature near human body temperature (36°C) are required, and those with different transparency-changing temperatures depending on the application are sought.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[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 resin composition that exhibits a thermochromic effect in which transparency changes at a temperature of 60°C or lower and excellent transparency is exhibited on the high-temperature side.

Means for Solving the Problems

[0006] The inventors of this invention have conducted extensive research to achieve the above objectives and have discovered that by blending an acrylic polymer, polyvinylidene fluoride, and a polyalkyl acrylate with an alkyl group having a specific number of carbon atoms within a particular range in specific proportions, a resin composition can be obtained that exhibits a thermochromic effect, where transparency changes at temperatures below 60°C and excellent transparency is observed at higher temperatures (temperatures higher than the melting point of the polyalkyl acrylate). Furthermore, the inventors have discovered that by changing the number of carbon atoms in the alkyl group of the polyalkyl acrylate, thermochromic resin compositions with different temperatures at which transparency changes can be obtained, thus completing the present invention.

[0007] In other words, the present invention provides the following embodiments. [1] A polymer blend consisting of 85-50% by mass of acrylic polymer and 15-50% by mass of polyvinylidene fluoride, Each 100 parts by mass of the polymer blend contains 1 to 80 parts by mass of a polyalkyl acrylate having an alkyl group with 12 to 22 carbon atoms, Contains death, The acrylic polymer is a polymer of at least one acrylic monomer selected from the group consisting of methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, methacrylic acid, and acrylic acid. , thermochromic resin composition. [2] A sea-island structure is formed comprising a sea phase made of the polymer blend and an island phase made of at least a portion of the polyalkyl acrylate. [1] The thermochromic resin composition described above. [3] The refractive index of the acrylic polymer at 50°C is 1.44 to 1.54, [1] or [2] The thermochromic resin composition described above. [4] The refractive index of the polyvinylidene fluoride at 50°C is 1.37 to 1.47, [1] to [ 3 A thermochromic resin composition according to any one of the items in the ]. [5] The refractive index of the polyalkyl acrylate at 50°C is 1.41 to 1.51, [1] to [ 4 A thermochromic resin composition according to any one of the items in the ]. [6] Furthermore, the polymer blend contains 1 to 100 parts by mass of a glass-based filler with a silicon dioxide purity of 90% or more per 100 parts by mass, [1] to [ 5 A thermochromic resin composition according to any one of the items in the ].

[0008] The reason why the thermochromic effect occurs in the thermochromic resin composition of the present invention, where transparency changes at temperatures below 60°C and excellent transparency is exhibited at higher temperatures (temperatures higher than the melting point of the polyalkyl acrylate), is not entirely clear, but the inventors speculate as follows. That is, the thermochromic resin composition of the present invention contains a polymer blend containing an acrylic polymer and polyvinylidene fluoride in specific proportions, and a polyalkyl acrylate in specific proportions where the number of carbon atoms in the alkyl group is within a specific range. In such a thermochromic resin composition, preferably, a sea-island structure is formed comprising a sea phase consisting of the polymer blend and an island phase consisting of at least a portion of the polyalkyl acrylate. The polyalkyl acrylate has an alkyl group with 12 to 22 carbon atoms, and has a melting point of 15 to 60°C depending on the number of carbon atoms in the alkyl group. Therefore, in the temperature range below the melting point of the polyalkyl acrylate (low temperature side), the island phase consisting of the polyalkyl acrylate becomes a crystalline phase, and light scattering occurs due to the difference in refractive index between it and the sea phase (amorphous phase) consisting of the polymer blend, making the resin composition opaque. On the other hand, in the temperature range above the melting point of the polyalkyl acrylate (high temperature side), the crystals of the polyalkyl acrylate melt, and the refractive index of the melted polyalkyl acrylate and the polymer blend become approximately the same, so the resin composition exhibits excellent transparency. Therefore, it is presumed that in the thermochromic resin composition of the present invention, a thermochromic effect is exhibited in which the transparency changes at temperatures below 60°C (specifically, temperatures near the melting point of the polyalkyl acrylate), and excellent transparency is exhibited on the high temperature side (temperature range above the melting point of the polyalkyl acrylate).

[0009] Furthermore, although the reason why the thermochromic effect is maintained in the thermochromic resin composition of the present invention containing a glass-based filler with a silicon dioxide purity of 90% or more is not entirely clear, the inventors speculate as follows: That is, the glass-based filler with a silicon dioxide purity of 90% or more has a refractive index similar to that of the thermochromic resin composition containing the polymer blend and a specific amount of the polyalkyl acrylate relative to the polymer blend at high temperatures (for example, 80°C or higher, preferably 60°C or higher), and therefore the thermochromic effect is presumed to be maintained. [Effects of the Invention]

[0010] According to the present invention, it is possible to obtain a resin composition that exhibits a thermochromic effect in which transparency changes at temperatures below 60°C (particularly near the melting point of the polyalkyl acrylate) and excellent transparency at higher temperatures (temperatures higher than the melting point of the polyalkyl acrylate). [Brief explanation of the drawing]

[0011] [Figure 1] This is a scanning electron microscope image of the polished cross-section of the flat plate obtained in Example 1. [Figure 2] This is a scanning electron microscope image of the polished cross-section of the flat plate obtained in Example 2. [Figure 3] This is a scanning electron microscope image of the polished cross-section of the flat plate obtained in Example 4. [Figure 4] This graph shows the relationship between the temperature and haze value of the flat plates obtained in the examples and comparative examples. [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 comprises a polymer blend composed of 85 to 50% by mass of an acrylic polymer and 15 to 50% by mass of polyvinylidene fluoride, and 1 to 80 parts by mass of a polyalkyl acrylate having an alkyl group with 12 to 22 carbon atoms with respect to 100 parts by mass of the polymer blend.

[0014] (Acrylic polymer) Examples of the acrylic polymer used in the present invention include polymers (homopolymers and copolymers) of acrylic monomers. The proportion of acrylic monomer units in the copolymer of acrylic monomers 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 acrylic polymers, a homopolymer of an acrylic monomer is preferred from the viewpoint of excellent heat resistance and transparency of the resin composition.

[0015] Examples of the acrylic monomer include alkyl methacrylate esters having an alkyl group with 11 or less carbon atoms (e.g., methyl methacrylate, ethyl methacrylate, etc.), alkyl acrylate esters having an alkyl group with 11 or less carbon atoms (e.g., methyl acrylate, ethyl acrylate, etc.), methacrylic acid, and acrylic acid. These acrylic monomers may be used alone or in combination of two or more. Among these acrylic monomers, alkyl methacrylate esters having an alkyl group with 11 or less carbon atoms are preferred, and methyl methacrylate is more preferred, from the viewpoint of excellent heat resistance and molding processability.

[0016] Examples of other copolymerizable monomers in the copolymer of acrylic monomers include olefins (e.g., ethylene, propylene, etc.) and aromatic vinyl monomers (e.g., styrene, α-methylstyrene, etc.). These other copolymerizable monomers may be used alone or in combination of two or more.

[0017] Specifically, the acrylic polymers used in the present invention include polyalkyl methacrylate esters with 11 or fewer carbon atoms in the alkyl group (e.g., polymethyl methacrylate, polyethyl methacrylate, etc.), polyalkyl acrylate esters with 11 or fewer carbon atoms in the alkyl group (e.g., polymethyl acrylate, polyethyl acrylate, etc.), copolymers of acrylic acid and alkyl methacrylate esters with 11 or fewer carbon atoms in the alkyl group (e.g., acrylic acid-methyl methacrylate copolymer, etc.), and copolymers of alkyl methacrylate esters with 11 or fewer carbon atoms in the alkyl group and alkyl acrylate esters with 11 or fewer carbon atoms in the alkyl group (e.g., methacrylate copolymer, etc.). Examples of acrylic polymers include methyl methacrylate copolymers, copolymers of ethylene and alkyl methacrylate esters with 11 or fewer carbon atoms in the alkyl group (e.g., ethylene-methyl methacrylate copolymers), copolymers of ethylene and alkyl acrylate esters with 11 or fewer carbon atoms in the alkyl group (e.g., ethylene-ethyl acrylate copolymers), copolymers of styrene and alkyl methacrylate esters with 11 or fewer carbon atoms in the alkyl group (e.g., styrene-methyl methacrylate copolymers), and copolymers of styrene and alkyl acrylate esters with 11 or fewer carbon atoms in the alkyl group (e.g., styrene-ethyl acrylate copolymers). These acrylic polymers may be used individually or in combination of two or more. Among these acrylic polymers, polyalkyl methacrylate esters with 11 or fewer carbon atoms in the alkyl group are preferred, and polymethyl methacrylate is more preferred, from the viewpoint of excellent heat resistance and compatibility with polyvinylidene fluoride.

[0018] Furthermore, the acrylic polymer used in the present invention preferably has a refractive index of 1.44 to 1.54 at 50°C, and more preferably 1.47 to 1.51. If the refractive index of the acrylic polymer is below the lower limit or above the upper limit, the refractive index difference with the polyalkyl acrylate becomes large, and the transparency of the resin composition at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate) tends to decrease.

[0019] (Polyvinylidene fluoride) Polyvinylidene fluoride used in the present invention includes polymers (homopolymers and copolymers) of vinylidene fluoride. In the copolymer of vinylidene fluoride, the proportion of vinylidene fluoride units 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 (especially polymethyl methacrylate).

[0020] Other copolymer monomers in the vinylidene fluoride copolymer include, for example, fluoroolefins (e.g., trifluoroethylene, hexafluoropropylene, etc.) and aromatic vinyls (e.g., styrene, α-methylstyrene, p-fluorostyrene, α-fluorostyrene, etc.). These other copolymer monomers may be used individually or in combination of two or more.

[0021] Furthermore, the polyvinylidene fluoride used in the present invention preferably has a refractive index of 1.37 to 1.47 at 50°C, and more preferably 1.39 to 1.45. If the refractive index of the polyvinylidene fluoride is below the lower limit or above the upper limit, the refractive index difference with the polyalkyl acrylate becomes large, and the transparency of the resin composition at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate) tends to decrease.

[0022] (Polyalkyl acrylate) The polyalkyl acrylate used in the present invention has an alkyl group having 12 to 22 carbon atoms, and specifically, it is a polymer (homopolymer and copolymer) of alkyl acrylate monomers having an alkyl group having 12 to 22 carbon atoms. The proportion of alkyl acrylate monomer units in the copolymer of alkyl acrylate 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 such polyalkyl acrylates, homopolymers of the alkyl acrylate monomers are preferred from the viewpoint of increasing the degree of temperature dependence of the transparency of the resulting resin composition.

[0023] In such polyalkyl acrylates, the melting point can be adjusted to a range of 10 to 60°C by changing the number of carbon atoms in the alkyl group within the aforementioned range, thereby obtaining a thermochromic resin composition whose transparency changes within that temperature range. The number of carbon atoms in the alkyl group can be appropriately set according to the desired temperature at which the transparency of the resin composition changes, but 12 to 20 is preferred, 13 to 18 is more preferred, and 14 to 16 is even more preferred. By setting the number of carbon atoms in the alkyl group within the aforementioned range, the melting point of the polyalkyl acrylate can be adjusted to a range of preferably 10 to 55°C (more preferably 15 to 50°C, and even more preferably 20 to 40°C), making it possible to obtain a thermochromic resin composition whose transparency changes within that temperature range.

[0024] Specific examples of the alkyl acrylate monomers include acrylates having an alkyl group with 12 to 22 carbon atoms, such as dodecyl acrylate, tridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, heptadecyl acrylate, octadecyl acrylate, nonadecyl acrylate, eicosyl acrylate, hene-eicosyl acrylate, and docosyl acrylate; and methacrylates having an alkyl group with 12 to 22 carbon atoms, such as dodecyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptadecyl methacrylate, octadecyl methacrylate, nonadecyl methacrylate, eicosyl methacrylate, hene-eicosyl methacrylate, and docosyl methacrylate. These alkyl acrylate monomers may be used individually or in combination of two or more.

[0025] Other copolymer monomers used in copolymers of alkyl acrylate monomers include, for example, olefins (e.g., ethylene, propylene, etc.) and aromatic vinyl monomers (e.g., styrene, α-methylstyrene, etc.). These other copolymer monomers may be used individually or in combination of two or more.

[0026] Specifically, the polyalkyl acrylates used in the present invention include polyalkyl acrylates having an alkyl group with 12 to 22 carbon atoms (e.g., polydodecyl acrylate, polytetradecyl acrylate, polyhexadecyl acrylate, polyoctadecyl acrylate, etc.) and copolymers thereof, and polyalkyl methacrylates having an alkyl group with 12 to 22 carbon atoms (e.g., polydodecyl methacrylate, polytetradecyl methacrylate, polyhexadecyl methacrylate, polyoctadecyl methacrylate, etc.) and copolymers thereof. , copolymers of methacrylic acid and alkyl acrylates having an alkyl group with 12 to 22 carbon atoms (e.g., methacrylic acid-dodecyl acrylate copolymer, methacrylic acid-tetradecyl acrylate copolymer, methacrylic acid-hexadecyl acrylate copolymer, methacrylic acid-octadecyl acrylate copolymer, etc.), copolymers of alkyl methacrylates having an alkyl group with 12 to 22 carbon atoms and alkyl acrylates having an alkyl group with 12 to 22 carbon atoms (e.g., dodecyl methacrylate-tetradecyl acrylate copolymer, hexa Copolymers of ethylene and alkyl acrylates having an alkyl group having 12 to 22 carbon atoms (e.g., ethylene-dodecyl acrylate copolymer, ethylene-tetradecyl acrylate copolymer, ethylene-hexadecyl acrylate copolymer, ethylene-octadecyl acrylate copolymer, etc.), and copolymers of ethylene and alkyl groups having 12 to 22 carbon atoms Copolymers with alkyl methacrylates (e.g., ethylene-dodecyl methacrylate copolymer, ethylene-tetradecyl methacrylate copolymer, ethylene-hexadecyl methacrylate copolymer, ethylene-octadecyl methacrylate copolymer, etc.), copolymers of styrene and alkyl acrylates having an alkyl group with 12 to 22 carbon atoms (e.g., styrene-dodecyl acrylate copolymer, styrene-tetradecyl acrylate copolymer, styrene-hexadecyl acrylate copolymer, styrene-octadecyl acrylate copolymer, etc.),Examples include copolymers of styrene and alkyl methacrylates having an alkyl group with 12 to 22 carbon atoms (e.g., styrene-dodecyl methacrylate copolymer, styrene-tetradecyl methacrylate copolymer, styrene-hexadecyl methacrylate copolymer, styrene-octadecyl methacrylate copolymer, etc.). These polyalkyl acrylates may be used individually or in combination of two or more. Among these polyalkyl acrylates, from the viewpoint of increasing the degree of temperature dependence of the transparency of the resulting resin composition, polyalkyl acrylates having an alkyl group with 12 to 22 carbon atoms are preferred, polytetradecyl methacrylate and polyhexadecyl methacrylate are more preferred, and polyhexadecyl methacrylate is particularly preferred.

[0027] Furthermore, the polyalkyl acrylate used in the present invention preferably has a refractive index of 1.41 to 1.51 at 50°C, and more preferably 1.43 to 1.49. If the refractive index of the polyalkyl acrylate is below the lower limit or above the upper limit, the refractive index difference with the polymer blend containing acrylic polymer and polyvinylidene fluoride in a predetermined ratio becomes large, and the transparency of the resin composition at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate) tends to decrease.

[0028] [Thermochromic resin composition] The thermochromic resin composition of the present invention contains a polymer blend comprising 85 to 50% by mass of the acrylic polymer and 15 to 50% by mass of the polyvinylidene fluoride, and 1 to 80 parts by mass of the polyalkyl acrylate per 100 parts by mass of the polymer blend. Such a thermochromic resin composition exhibits a thermochromic effect in which transparency changes at temperatures below 60°C and excellent transparency is shown at higher temperatures (temperatures higher than the melting point of the polyalkyl acrylate).

[0029] In the polymer blend, the content of the acrylic polymer must be 85 to 50% by mass. If the content of the acrylic polymer is below the lower limit or above the upper limit, the thermochromic effect will not be sufficiently expressed, and the transparency of the resin composition will not improve at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate). Furthermore, from the viewpoint of sufficiently expressing the thermochromic effect and sufficiently improving the transparency of the resin composition at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate), the content of the acrylic polymer is preferably 80 to 55% by mass, and more preferably 75 to 60% by mass.

[0030] Furthermore, the polymer blend must contain 15 to 50% by mass of polyvinylidene fluoride. If the polyvinylidene fluoride content is below the lower limit or above the upper limit, the thermochromic effect will not be sufficiently expressed, and the transparency of the resin composition will not improve at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate). From the viewpoint of ensuring that the thermochromic effect is sufficiently expressed and that the transparency of the resin composition is sufficiently improved at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate), the polyvinylidene fluoride content is preferably 20 to 45% by mass, and more preferably 25 to 40% by mass.

[0031] In the thermochromic resin composition of the present invention, the content of the polyalkyl acrylate must be 1 to 80 parts by mass per 100 parts by mass of the polymer blend. If the content of the polyalkyl acrylate is below the lower limit, the thermochromic effect will not be exhibited, and the transparency of the resin composition will not decrease on the low temperature side (temperature range lower than the melting point of the polyalkyl acrylate). On the other hand, if the content of the polyalkyl acrylate exceeds the upper limit, the mechanical properties of the resin composition will decrease on the high temperature side (temperature range higher than the melting point of the polyalkyl acrylate). Furthermore, from the viewpoint of sufficiently exhibiting the thermochromic effect and sufficiently improving the transparency of the resin composition on the high temperature side (temperature range higher than the melting point of the polyalkyl acrylate), the lower limit of the content of the polyalkyl acrylate is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 7 parts by mass or more, per 100 parts by mass of the polymer blend. Furthermore, from the viewpoint of obtaining a resin composition with good mechanical properties at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate), the upper limit of the polyalkyl acrylate content is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, and particularly preferably 30 parts by mass or less, per 100 parts by mass of the polymer blend.

[0032] Furthermore, in the thermochromic resin composition of the present invention, it is preferable that a sea-island structure is formed comprising a sea phase consisting of the polymer blend and an island phase consisting of at least a portion of the polyalkyl acrylate. With such a sea-island structure formed, at low temperatures (temperatures lower than the melting point of the polyalkyl acrylate), the polyalkyl acrylate in the island phase crystallizes, making the resin composition opaque, and at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate), the polyalkyl acrylate melts, and the refractive index of the island phase becomes about the same as that of the polymer blend in the sea phase, thereby improving the transparency of the resin composition and exhibiting a thermochromic effect.

[0033] 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 falls below the lower limit, the thermochromic effect does not manifest sufficiently, and the transparency of the resin composition tends not to decrease at low temperatures (temperatures lower than the melting point of the polyalkyl acrylate). On the other hand, if it exceeds the upper limit, the moldability of the resin composition tends to decrease.

[0034] (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. Since the glass-based filler with a silicon dioxide purity of 90% or more has a refractive index similar to that of the polymer blend and the polyalkyl acrylate at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate), the thermochromic resin composition containing such a glass-based filler has improved transparency at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate), and can improve scratch resistance while maintaining the thermochromic effect. Furthermore, from the viewpoint of sufficiently maintaining the thermochromic effect and sufficiently improving the transparency of the resin composition at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate), the silicon dioxide purity of the glass-based filler is preferably 95% or more, and more preferably 98% or more. On the other hand, glass-based fillers with silicon dioxide purity below the lower limit have a refractive index that is significantly different from that of the polymer blend and the polyalkyl acrylate at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate). As a result, the thermochromic effect in the thermochromic resin composition is not maintained, and the transparency of the resin composition does not improve easily at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate).

[0035] In the glass-based filler used in the present invention, the refractive index at 50°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 below the lower limit or above the upper limit, the transparency of the resin composition tends to decrease at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate).

[0036] 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.

[0037] 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 polymer blend. 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.

[0038] 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, the composition can be produced by dry blending the acrylic polymer, the polyvinylidene fluoride, the polyalkyl acrylate, and optionally the glass-based filler, and then melt kneading the resulting mixture. [Examples]

[0039] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples. The polyhexadecyl acrylate and polytetradecyl acrylate used in the examples and comparative examples were synthesized by the following method.

[0040] (Synthesis Example 1) 3 g of hexadecyl acrylate (HDA, manufactured by Tokyo Chemical Industry Co., Ltd., product code: H1168) and 20 mg of 2,2'-azobisisobutyronitrile (AIBN, manufactured by Kishida Chemical Co., Ltd., product code: 010-05992) were dissolved in 10 ml of toluene. The mixture was then stirred at 70°C for 8 hours under a nitrogen atmosphere to polymerize the HDA. The resulting toluene solution of polyhexadecyl acrylate (PHDA) was added dropwise to a sufficient amount of methanol to reprecipitate the PHDA, and the resulting precipitate (PHDA) was separated and recovered by filtration. Subsequently, the obtained PHDA was dried in an oven at room temperature under reduced pressure to remove methanol, yielding PHDA with a number-average molecular weight of approximately 20,000, a refractive index of 1.46 (at 50°C), and a melting point of 34°C. 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).

[0041] (Synthesis Example 2) Polytetradecyl acrylate (PTDA) with a number-average molecular weight of approximately 15,000, a refractive index of 1.46 (at 50°C), and a melting point of 20°C was obtained in the same manner as in Synthesis Example 1, except that 3 g of tetradecyl acrylate (TDA, manufactured by Tokyo Chemical Industry Co., Ltd., product code: T2265) was used instead of hexadecyl acrylate. The number-average molecular weight, refractive index, and melting point were measured in the same manner as in Synthesis Example 1.

[0042] (Example 1) 65 parts by mass of polymethyl methacrylate (PMMA, Kuraray Co., Ltd. "Parapet G grade", refractive index: 1.492 (23℃), 1.489 (60℃)), 35 parts by mass of polyvinylidene fluoride (PVDF, Aldrich Corporation, catalog number: 427144, refractive index: 1.420 (23℃), 1.417 (60℃)), and 10 parts by mass of PHDA (refractive index: 1.46 (50℃)) obtained in Synthesis Example 1 were dry-blended. The resulting mixture was then placed in a tabletop miniature kneader (Thermo Fisher Scientific Microcompounder "Haake Minilab") and melt-kneaded at 220℃ for 5 minutes to prepare a resin composition.

[0043] The obtained resin composition was press-molded using a tabletop press at a temperature of 220°C and a pressure of 6 MPa for 30 seconds to produce a flat plate measuring 50 mm × 50 mm × 0.5 mm.

[0044] (Example 2) A resin composition was prepared in the same manner as in Example 1, except that the amount of PHDA was changed to 20 parts by mass. A flat plate measuring 50 mm × 50 mm × 0.5 mm was then produced.

[0045] (Example 3) A resin composition was prepared in the same manner as in Example 1, except that 65 parts by mass of PMMA, 35 parts by mass of PVDF, 10 parts by mass of PHDA, and 25 parts by mass of spherical silica (SO-C6 manufactured by Admatex Co., Ltd., silicon dioxide purity: 99% or higher, particle size: 1.8~2.3 μm, refractive index: 1.46 (23℃)) were dry-blended, and a 50 mm × 50 mm × 0.5 mm flat plate was then prepared.

[0046] (Example 4) A resin composition was prepared in the same manner as in Example 1, except that 10 parts by mass of PTDA (refractive index: 1.46 (50℃)) obtained in Synthesis Example 2 was used instead of PHDA, and a 50mm × 50mm × 0.5mm flat plate was then fabricated.

[0047] (Comparative Example 1) A resin composition was prepared in the same manner as in Example 1, except that the amount of PMMA was changed to 90 parts by mass and the amount of PVDF to 10 parts by mass. A flat plate measuring 50 mm × 50 mm × 0.5 mm was then produced.

[0048] (Comparative Example 2) A resin composition was prepared in the same manner as in Example 1, except that the amount of PMMA was changed to 40 parts by mass and the amount of PVDF to 60 parts by mass. A flat plate measuring 50 mm × 50 mm × 0.5 mm was then produced.

[0049] <Scanning Electron Microscope (SEM) Observation> Observation samples were cut from the edges of each plate obtained in the examples, and observation surfaces were prepared by resin embedding and polishing the surfaces. After applying a platinum coating to these observation surfaces, secondary electron images were observed using a scanning electron microscope (SU3500, Hitachi High-Technologies Corporation) at an acceleration voltage of 15kV. Figures 1 to 3 are SEM images of the polished cross-sections of each plate obtained in Examples 1, 2, and 4, respectively.

[0050] As shown in Figures 1 to 3, it was confirmed that each plate obtained in Examples 1, 2, and 4 had a sea-island structure consisting of a sea phase (light gray area) made of a polymer blend of PMMA and PVDF and an island phase (dark gray area) made of PHDA (Examples 1 and 2) or PTDA (Example 4). Furthermore, based on the scanning electron microscope image shown in Figure 1, the size (maximum length) of the island phase in the plate obtained in Example 1 was measured using image analysis software (ImageJ) and was found to be 0.9 to 6.1 μm.

[0051] <Transparency> 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 flat plate (50 mm × 50 mm × 0.5 mm) obtained in the examples and comparative examples were measured at temperatures from 10 to 45°C. The results are shown in Table 1 and Figure 4. For the measurement at 10°C, the flat plate was left to stand in the freezer and the measurement was performed before the temperature of the flat plate reached 25°C.

[0052] [Table 1]

[0053] As shown in Table 1 and Figure 4, in resin compositions containing PMMA, PVDF, and PHDA in predetermined proportions (Examples 1-2), the haze value decreased significantly between 34°C and 40°C (a temperature range including the melting point of PHDA (34°C)). In the temperature range below the melting point of PHDA (below 34°C), the composition was opaque (haze value of 70% or more), while in the temperature range above the melting point of PHDA (above 40°C), it became transparent (haze value of 20% or less). This confirmed the appearance of a so-called thermochromic effect, where transparency changes with temperature changes across the melting point of PHDA.

[0054] Furthermore, in a resin composition (Example 3) further containing spherical silica with a silicon dioxide purity of 99% or higher in a predetermined proportion, the haze value decreased significantly in the same temperature range as in Examples 1 and 2. While it was opaque (haze value of 75% or higher) in the temperature range below the melting point of PHDA (34°C or lower), it became transparent (haze value of 40% or lower) in the temperature range above the melting point of PHDA (40°C or higher). This confirmed that a so-called thermochromic effect occurred, where transparency changed with temperature changes across the melting point of PHDA.

[0055] Furthermore, in a resin composition containing PMMA, PVDF, and PTDA in predetermined proportions (Example 4), the haze value decreased significantly between 10°C and 25°C (a temperature range including the melting point of PTDA (20°C)). At temperatures below the melting point of PTDA (10°C), it was opaque (haze value of 89%), while at temperatures above the melting point of PTDA (25°C and above), it became transparent (haze value of 35% or less). This confirmed that a so-called thermochromic effect occurred, where transparency changed with temperature changes across the melting point of PTDA.

[0056] On the other hand, in resin compositions containing a predetermined amount of PHDA in a polymer blend of PMMA and PVDF, but with a higher amount of PMMA and a lower amount of PVDF (Comparative Example 1), and in resin compositions with a lower amount of PMMA and a higher amount of PVDF (Comparative Example 2), the haze value decreased in the same temperature range as in Examples 1-3, but the decrease was smaller than that of the resin compositions obtained in Examples 1-3, and the transparency was insufficient (haze value of 50-70%) in the temperature range above the melting point of PHDA (40°C or higher).

[0057] From the above results, it was confirmed that a resin composition exhibiting a so-called thermochromic effect, where transparency changes with temperature, can be obtained by blending acrylic polymer, polyvinylidene fluoride, and polyalkyl acrylate in specific proportions. In particular, it was found that the blending ratio of acrylic polymer to polyvinylidene fluoride is important for obtaining high transparency at high temperatures. Furthermore, it was found that the temperature at which transparency changes can be controlled by changing the number of carbon atoms in the alkyl group of the polyalkyl acrylate. In addition, it was confirmed that the thermochromic effect is maintained even when a glass-based filler with a silicon dioxide purity of 90% or higher is blended in a specific proportion to improve properties such as mechanical strength and thermal conductivity in the thermochromic resin composition. [Industrial applicability]

[0058] As described above, the present invention makes it possible to obtain a resin composition that exhibits a thermochromic effect, in which transparency changes at temperatures below 60°C (particularly near the melting point of the polyalkyl acrylate) and excellent transparency at high temperatures (temperatures higher than the melting point of the polyalkyl acrylate). Therefore, the thermochromic resin composition of the present invention is useful in applications such as a surface material that allows for visual recognition of temperature, and a surface material that can adjust the surface temperature of structures exposed to sunlight.

Claims

1. A polymer blend consisting of 85-50% by mass of acrylic polymer and 15-50% by mass of polyvinylidene fluoride, Amount to 100 parts by mass of the polymer blend, 1 to 80 parts by mass of polyalkyl acrylate having an alkyl group with 12 to 22 carbon atoms, It contains, The acrylic polymer is a polymer of at least one acrylic monomer selected from the group consisting of methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, methacrylic acid, and acrylic acid. A thermochromic resin composition characterized by the following features.

2. The thermochromic resin composition according to claim 1, characterized in that a sea-island structure is formed comprising a sea phase made of the polymer blend and an island phase made of at least a portion of the polyalkyl acrylate.

3. The thermochromic resin composition according to claim 1, characterized in that the refractive index of the acrylic polymer at 50°C is 1.44 to 1.

54.

4. The thermochromic resin composition according to claim 1, characterized in that the refractive index of the polyvinylidene fluoride at 50°C is 1.37 to 1.

47.

5. The thermochromic resin composition according to claim 1, characterized in that the refractive index of the polyalkyl acrylate at 50°C is 1.41 to 1.

51.

6. Furthermore, the thermochromic resin composition according to claim 1 is characterized by containing 1 to 100 parts by mass of a glass-based filler with a silicon dioxide purity of 90% or more per 100 parts by mass of the polymer blend.

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