Light-shielding material

Abstract

To provide a light shielding member capable of controlling transmission and non-transmission of light by temperature and having high transmittance.SOLUTION: A light shielding member of the present invention includes a first polarizing plate, a second polarizing plate facing the first polarizing plate, and a temperature-sensitive sheet sandwiched between the first polarizing plate and the second polarizing plate. The first polarizing plate and the second polarizing plate are positioned such that their transmission axes are different from each other. The thermosensitive sheet contains a side chain crystalline polymer that crystallizes at a temperature below the melting point and is fluid at a temperature equal to or higher than the melting point. The side chain crystalline polymer is oriented in one direction.SELECTED DRAWING: Figure 2

Description

Technical Field

[0004] , , , , ,

[0005] , , , , , , ,

[0001] The present invention relates to a light-shielding member.

Background Art

[0002] A light-shielding member that electrically controls light transmission and non-transmission is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a light-shielding member that can control light transmission and non-transmission by temperature and has a high transmittance.

Means for Solving the Problems

[0005] As a result of intensive studies to solve the above problems, the present inventors have found a solution means having the following configuration and have completed the present invention. (1) A light-shielding member comprising a first polarizing plate, a second polarizing plate facing the first polarizing plate, and a temperature-sensitive sheet sandwiched between the first polarizing plate and the second polarizing plate, wherein the first polarizing plate and the second polarizing plate are positioned such that their transmission axes are different from each other, the temperature-sensitive sheet contains a side-chain crystalline polymer that crystallizes at a temperature below the melting point and exhibits fluidity at a temperature above the melting point, and the side-chain crystalline polymer is oriented in one direction. (2) The light-shielding member according to (1), wherein when light is allowed to travel from one of the first polarizing plate and the second polarizing plate to the other, the light is transmitted at a temperature below the melting point and is not transmitted at a temperature above the melting point. (3) The light-shielding member according to (1) or (2), wherein the temperature-sensitive sheet is positioned such that the orientation direction of the side-chain crystalline polymer is different with respect to the transmission axis of the first polarizer and the second polarizer, respectively. (4) The light-shielding member according to any one of (1) to (3), wherein the thickness of the temperature-sensitive sheet is 1 to 300 μm. (5) The light-shielding member according to any one of (1) to (4) above, wherein the temperature-sensitive sheet is a uniaxially oriented sheet. (6) The light-shielding member according to any one of (1) to (5), wherein the side-chain crystalline polymer contains a (meth)acrylate having a linear alkyl group with 16 or more carbon atoms as a monomer component. [Effects of the Invention]

[0006] According to the present invention, the transmission and non-transmission of light can be controlled by temperature, and it has the effect of having high transmittance. [Brief explanation of the drawing]

[0007] [Figure 1] This is a side view showing a light-shielding member according to one embodiment of the present invention. [Figure 2] Figure 1 is an exploded perspective view of the light-shielding member shown. [Modes for carrying out the invention]

[0008] A light-shielding member according to one embodiment of the present invention will be described in detail below with reference to Figures 1 and 2.

[0009] As shown in Figures 1 and 2, the light-shielding member 1 of this embodiment comprises a first polarizing plate 2, a second polarizing plate 3 facing the first polarizing plate 2, and a temperature-sensitive sheet 4 sandwiched between the first polarizing plate 2 and the second polarizing plate 3. The light-shielding member 1 of this embodiment is a laminate in which the first polarizing plate 2 is laminated on one side of the temperature-sensitive sheet 4, and the second polarizing plate 3 is laminated on the other side of the temperature-sensitive sheet 4.

[0010] The first polarizing plate 2 and the second polarizing plate 3 are positioned such that their respective transmission axes are different from each other. The temperature-sensitive sheet 4 contains a side-chain crystalline polymer that crystallizes at temperatures below its melting point and exhibits fluidity at temperatures above its melting point. The side-chain crystalline polymer (side-chain crystalline component) is oriented in one direction.

[0011] The above-described configuration allows for temperature control of light transmission and opacity, while also providing high transmittance. Specifically, the side-chain crystalline polymer described above is a polymer with a melting point. The melting point is the temperature at which a specific part of a polymer, initially aligned in an ordered arrangement, becomes disordered due to a certain equilibrium process. This value is obtained by measuring with a differential thermal scanning calorimeter (DSC) under measurement conditions of 10°C / min. The side-chain crystalline polymer crystallizes at temperatures below its melting point and undergoes a phase transition above its melting point, exhibiting fluidity. In other words, the side-chain crystalline polymer has thermosensitivity, reversibly switching between a crystalline state and a fluid state (amorphous state) in response to temperature changes. Since the thermosensitive sheet 4 contains such a side-chain crystalline polymer, it possesses thermosensitivity derived from the side-chain crystalline polymer.

[0012] As described above, the first polarizing plate 2 and the second polarizing plate 3 are positioned so that their respective transmission axes are different from each other. Therefore, when light is passed through the first polarizing plate 2 and then the second polarizing plate 3 in the absence of the temperature-sensitive sheet 4, the light that passes through the first polarizing plate 2 does not pass through the second polarizing plate 3. This is also true when light is passed through the second polarizing plate 3 and then the first polarizing plate 2.

[0013] Here, when the side-chain crystalline polymer is in a crystalline state, light is scattered within the temperature-sensitive sheet 4. Therefore, when the light-shielding member 1 is heated to a temperature below its melting point, the light that passes through the first polarizing plate 2 is scattered when it passes through the temperature-sensitive sheet 4, and as a result, passes through the second polarizing plate 3. At this time, since the side-chain crystalline polymer is oriented in one direction, the transmittance can be improved by aligning the direction of refraction of light, and therefore the light-shielding member 1 has high transmittance. Also, when the side-chain crystalline polymer is in a fluid state, light is not scattered within the temperature-sensitive sheet 4. Therefore, when the light-shielding member 1 is heated to a temperature above its melting point, the light that passes through the first polarizing plate 2 is not scattered even when it passes through the temperature-sensitive sheet 4, and therefore does not pass through the second polarizing plate 3.

[0014] Thus, the light-shielding member 1 utilizes not only the temperature sensitivity of the side-chain crystalline polymer but also the change in the optical properties of the side-chain crystalline polymer, allowing the light-shielding function (change in brightness) to be controlled by temperature. Specifically, when light is transmitted from one of the first polarizer plates 2 and the second polarizer plate 3 to the other, the light-shielding member 1 transmits light at temperatures below its melting point and does not transmit light at temperatures above its melting point. For example, the light-shielding member 1 is transparent at temperatures below its melting point and black at temperatures above its melting point. Furthermore, the light-shielding member 1 can repeatedly transmit and block light because the side-chain crystalline polymer reversibly changes between a crystalline state and a fluid state in response to temperature changes.

[0015] The thickness of the first polarizing plate 2 is, for example, 200 to 1000 μm. The thickness of the second polarizing plate 3 is, for example, 200 to 1000 μm. The thicknesses of the first polarizing plate 2 and the second polarizing plate 3 may be the same or different. Commercially available polarizing plates 2 and 3 can be used.

[0016] The transmission axes of the first polarizer 2 and the second polarizer 3 should be at angles such that, when light is transmitted from one polarizer 2 to the other without the temperature-sensitive sheet 4, the light transmitted through one polarizer does not pass through the other. For example, such angles can be 80 to 100°. In Figure 2, the transmission axes of the first polarizer 2 and the second polarizer 3 are shown to be 90° apart. That is, the first polarizer 2 and the second polarizer 3 shown in Figure 2 are positioned so that their transmission axes are 90° apart.

[0017] The phrase "side-chain crystalline polymers are oriented in one direction" does not mean that all side-chain crystalline polymers contained in the temperature-sensitive sheet 4 are strictly oriented in one direction. It is sufficient that the side-chain crystalline polymers are substantially oriented in one direction in the temperature-sensitive sheet 4. Furthermore, confirmation that the side-chain crystalline polymers are oriented in one direction may be performed, for example, using an X-ray scattering device.

[0018] The temperature-sensitive sheet 4 may be positioned such that the orientation direction A of the side-chain crystalline polymer differs with respect to the respective transmission axes of the first polarizer 2 and the second polarizer 3. In this case, it is easier to improve the transmittance. The orientation direction A of the side-chain crystalline polymer may differ by, for example, 10 to 80° with respect to the respective transmission axes of the first polarizer 2 and the second polarizer 3. In Figure 2, the temperature-sensitive sheet 4 is shown positioned such that the orientation direction A of the side-chain crystalline polymer differs by 45° with respect to the respective transmission axes of the first polarizer 2 and the second polarizer 3.

[0019] As shown in Fig. 2, when the first polarizing plate 2 and the second polarizing plate 3 are positioned such that their transmission axes are different from each other by 90°, and the thermosensitive sheet 4 is positioned such that the orientation direction A of the side-chain crystalline polymer is different from the transmission axes of the first polarizing plate 2 and the second polarizing plate 3 by 45°, the transmittance at a wavelength of 500 nm at a temperature below the melting point is preferably 5% or more, more preferably 15% or more. The upper limit value of the transmittance at a wavelength of 500 nm is not particularly limited, and may be, for example, 50% or less. The transmittance at a wavelength of 500 nm is a value obtained by measurement with a spectrocolorimeter.

[0020] The melting point of the side-chain crystalline polymer is preferably higher than 23°C, more preferably higher than 23°C and 70°C or lower, and still more preferably 35 to 70°C. When the melting point is higher than 23°C, the light shielding member 1 transmits light at room temperature (room temperature). Therefore, the transmittance at room temperature (transmission state) can be improved. The melting point can be adjusted, for example, by changing the composition of the monomer components constituting the side-chain crystalline polymer.

[0021] The side-chain crystalline polymer contains (meth)acrylate having a linear alkyl group with 16 or more carbon atoms as a monomer component. The (meth)acrylate having a linear alkyl group with 16 or more carbon atoms functions as a side-chain crystalline site in the side-chain crystalline polymer with its linear alkyl group having 16 or more carbon atoms. That is, the side-chain crystalline polymer is a comb-shaped polymer having a linear alkyl group with 16 or more carbon atoms in the side chain, and this side chain crystallizes by being aligned in an orderly arrangement by intermolecular forces or the like. The above-mentioned (meth)-acrylate refers to acrylate or methacrylate. <​​Examples of (meth)acrylates having a linear alkyl group with 16 or more carbon atoms include cetyl (meth)acrylate, stearyl (meth)acrylate, eicosyl (meth)acrylate, and behenyl (meth)acrylate, which have linear alkyl groups with 16 to 22 carbon atoms. The exemplified (meth)acrylates may be used individually or in combination of two or more. The (meth)acrylate having a linear alkyl group with 16 or more carbon atoms is preferably included in the monomer component constituting the side-chain crystalline polymer in a proportion of 10 to 99% by weight, more preferably 15 to 99% by weight.

[0023] The monomer components constituting the side-chain crystalline polymer may include other monomers that can copolymerize with (meth)acrylates having a linear alkyl group with 16 or more carbon atoms. Examples of other monomers include (meth)acrylates having alkyl groups with 1 to 6 carbon atoms, polar monomers, and so on.

[0024] Examples of (meth)acrylates having an alkyl group with 1 to 6 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and hexyl (meth)acrylate. The exemplified (meth)acrylates may be used individually or in combination of two or more. The (meth)acrylate having an alkyl group with 1 to 6 carbon atoms is preferably included in the monomer component constituting the side-chain crystalline polymer in a proportion of 80% by weight or less, more preferably 0 to 80% by weight.

[0025] Examples of polar monomers include ethylenically unsaturated monomers having a carboxyl group, such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid; and ethylenically unsaturated monomers having a hydroxyl group, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 2-hydroxyhexyl (meth)acrylate. The exemplified polar monomers may be used individually or in combination of two or more. The polar monomers are preferably present in the monomer components constituting the side-chain crystalline polymer in an amount of 10% by weight or less, more preferably 1 to 10% by weight.

[0026] A preferred composition of the side-chain crystalline polymer is 15-90% by weight of (meth)acrylate having a linear alkyl group with 16 or more carbon atoms, 5-75% by weight of (meth)acrylate having an alkyl group with 1-6 carbon atoms, and 5-10% by weight of a polar monomer. In the side-chain crystalline polymer, if the weight ratio of (meth)acrylate having a linear alkyl group with 16 or more carbon atoms is higher than that of (meth)acrylate having an alkyl group with 1-6 carbon atoms, the crystallinity is increased, making it easier to improve the transmittance at temperatures below the melting point.

[0027] Polymerization methods for monomer components include, for example, solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization. When using solution polymerization, the monomer components and solvent are mixed, polymerization initiators and chain transfer agents are added as needed, and the mixture is reacted at approximately 40-90°C for 2-10 hours while stirring.

[0028] The weight-average molecular weight of the side-chain crystalline polymer is preferably 100,000 or more, more preferably 200,000 to 900,000, and even more preferably 250,000 to 700,000. The weight-average molecular weight is measured by gel permeation chromatography (GPC), and the obtained measurement value is converted to polystyrene equivalent.

[0029] The temperature-sensitive sheet 4 may contain a proportion of side-chain crystalline polymer such that it exhibits temperature sensitivity derived from the side-chain crystalline polymer. For example, the temperature-sensitive sheet 4 may contain side-chain crystalline polymer as its main component. The main component is the component that is present in the temperature-sensitive sheet 4 in the highest weight ratio. The content of side-chain crystalline polymer may be 80% by weight or more. Furthermore, the upper limit of the content of side-chain crystalline polymer may be 100% by weight or less.

[0030] The temperature-sensitive sheet 4 may contain additives in addition to the side-chain crystalline polymer. Examples of additives include crosslinking agents. Examples of crosslinking agents include metal chelate compounds, aziridine compounds, isocyanate compounds, and epoxy compounds. The crosslinking agent content is preferably 0.1 to 10 parts by weight per 100 parts by weight of the side-chain crystalline polymer. The crosslinking conditions are a heating temperature of about 90 to 120°C and a heating time of about 1 to 20 minutes.

[0031] The thickness of the temperature-sensitive sheet 4 is preferably 1 to 300 μm, more preferably 20 to 150 μm. This prevents a decrease in the scattering force of the temperature-sensitive sheet 4 and also prevents a decrease in transmittance. When the thickness of the temperature-sensitive sheet 4 is 20 to 150 μm, it is easier to improve the transmittance. Note that the temperature-sensitive sheet 4 is not limited to a sheet, but is a concept that also includes film or plate forms, as long as it does not impair the effects of this embodiment.

[0032] The temperature-sensitive sheet 4 may be a uniaxially oriented sheet. A uniaxially oriented sheet means a sheet that has been stretched in one axial direction. When the temperature-sensitive sheet 4 is a uniaxially oriented sheet, it is possible to orient the contained side-chain crystalline polymer in one direction. The uniaxial stretching treatment may be performed at a temperature above the melting point of the temperature-sensitive sheet 4. The stretching ratio may be, for example, 1.03 to 5 times.

[0033] Furthermore, the temperature-sensitive sheet 4 is not limited to a uniaxially stretched sheet, as long as the side-chain crystalline polymer is oriented in one direction. For example, the temperature-sensitive sheet 4 may be an oriented film or a sheet that has undergone a rubbing treatment.

[0034] The temperature-sensitive sheet 4 may be in direct contact with the first polarizing plate 2 and the second polarizing plate 3. In this case, light transmitted through the first polarizing plate 2 or the second polarizing plate 3 is incident on the temperature-sensitive sheet 4 without loss, so the light-shielding member 1 exhibits excellent light-shielding function.

[0035] Furthermore, since the temperature-sensitive sheet 4 can fix the first polarizing plate 2 and the second polarizing plate 3 without the need for an adhesive layer or the like, it can directly contact the first polarizing plate 2 and the second polarizing plate 3. Specifically, when the temperature of the temperature-sensitive sheet 4 is raised to a temperature above its melting point, the side-chain crystalline polymer becomes fluid, allowing the temperature-sensitive sheet 4 to be attached to the first polarizing plate 2 and the second polarizing plate 3. When the side-chain crystalline polymer becomes fluid, the temperature-sensitive sheet 4 follows the fine irregularities present on the surfaces of the first polarizing plate 2 and the second polarizing plate 3. When the temperature-sensitive sheet 4 in this state is cooled to a temperature below its melting point, the side-chain crystalline polymer crystallizes, resulting in a so-called anchoring effect, and as a result, the first polarizing plate 2 and the second polarizing plate 3 can be fixed with the temperature-sensitive sheet 4. If necessary, other materials may be interposed between the temperature-sensitive sheet 4 and the first polarizing plate 2. Similarly, other materials may be interposed between the temperature-sensitive sheet 4 and the second polarizing plate 3.

[0036] The form of the light-shielding member 1 is not particularly limited. The light-shielding member 1 may be, for example, a film, a sheet, a plate, or the like.

[0037] The light-shielding member 1 is suitable for use in locations where light-shielding is required and temperature changes are likely to occur. The light-shielding member 1 may be used for window glass, partitions, automobile glass, etc. However, the applications of the light-shielding member 1 are not limited to those exemplified.

[0038] The present invention will be described in detail below with reference to synthesis examples and embodiments, but the present invention is not limited to the following synthesis examples and embodiments.

[0039] (Synthesis Examples 1-2: Side-chain crystalline polymers) First, the monomers shown in Table 1 were added to the reaction vessel in the proportions shown in Table 1. The monomers shown in Table 1 are as follows: C22A: Behenyl acrylate C1A: Methyl acrylate AA: Acrylic acid

[0040] Next, "Perbutyl ND" manufactured by NOF Corporation was added to the reaction vessel as a polymerization initiator at a ratio of 0.5 parts by weight per 100 parts by weight of the monomer mixture. Then, a mixed solvent of ethyl acetate:heptane = 70:30 (by weight) was added to the reaction vessel to obtain a mixture, with a solid content concentration of 30% by weight. The obtained mixture was stirred at 55°C for 4 hours, and then stirred at 80°C for 2 hours to copolymerize each monomer and obtain a side-chain crystalline polymer.

[0041] Table 1 shows the weight-average molecular weight and melting point of the obtained side-chain crystalline polymers. The weight-average molecular weight is the value obtained by GPC and converted to polystyrene equivalent. The melting point is the value measured using DSC under measurement conditions of 10°C / min.

[0042] [Table 1]

[0043] [Examples 1-6 and Comparative Examples 1-3] <Fabrication of light-shielding material> First, 100 parts by weight of the side-chain crystalline polymer obtained in Synthesis Example 1 was mixed with 0.5 parts by weight of a crosslinking agent to obtain a mixture. The crosslinking agents used are as follows: Crosslinking agent: Chemitite PZ-33, an aziridine compound manufactured by Nippon Shokubai Co., Ltd.

[0044] Next, the obtained mixture was adjusted with ethyl acetate to a solid content concentration of 23% by weight to obtain a coating solution. The obtained coating solution was then applied to a release film placed on a hot plate heated to 70°C, and a crosslinking reaction was carried out under the conditions of 110°C for 3 minutes to obtain a temperature-sensitive sheet with a thickness of 40 μm as shown in Table 2. The release film used was a polyethylene terephthalate film with a thickness of 50 μm and a silicone coating on its surface.

[0045] The temperature-sensitive sheets with thicknesses of 80 μm, 160 μm, and 320 μm shown in Table 2 were prepared using the 40 μm thick temperature-sensitive sheet obtained above. Specifically, the 80 μm thick temperature-sensitive sheet was obtained by bonding two of the 40 μm thick temperature-sensitive sheets obtained above on a hot plate heated to 60°C. The 160 μm thick temperature-sensitive sheet was obtained by bonding two of the 80 μm thick temperature-sensitive sheets obtained above on a hot plate heated to 60°C. The 320 μm thick temperature-sensitive sheet was obtained by bonding two of the 160 μm thick temperature-sensitive sheets obtained above on a hot plate heated to 60°C.

[0046] In Examples 1-6, a temperature-sensitive sheet was stretched uniaxially to form a uniaxially oriented sheet, and the side-chain crystalline polymer was oriented in one direction. The temperature during the stretching process was set to 70°C, which is above the melting point of the side-chain crystalline polymer. The thickness and stretching ratio after stretching are shown in Table 2.

[0047] In Comparative Examples 1-3, the temperature-sensitive sheets were not stretched in a uniaxial direction.

[0048] Next, a temperature-sensitive sheet was sandwiched between the first and second polarizing plates to obtain a laminate. At this time, the first and second polarizing plates were positioned so that their respective transmission axes were 90° apart from each other.

[0049] Furthermore, the same polarizer was used for both the first and second polarizers. The polarizers used are as follows: Polarizing plate: A polarizing plate manufactured by Artec Co., Ltd. with a thickness of 250 μm.

[0050] In Examples 1 to 6, the temperature-sensitive sheets were positioned such that their stretching direction (orientation direction of the side-chain crystalline polymer) differed by 45° from the transmission axis of the first polarizing plate and the second polarizing plate, respectively.

[0051] Next, the resulting laminate was heated to a temperature above its melting point (70°C) using a dryer, and temperature-sensitive sheets were attached to the first and second polarizing plates. Then, the laminate was cooled to room temperature (23°C) to fix the first and second polarizing plates with the temperature-sensitive sheets, thereby obtaining a light-shielding member.

[0052] <Rating> The transmittance at a wavelength of 500 nm at temperatures below the melting point of the obtained light-shielding material was measured. The measurement was performed using a spectrophotometer. The measurement temperature was set to 23°C, which is below the melting point and corresponds to room temperature. The transmittance at a wavelength of 500 nm at temperatures below the melting point (23°C) was also measured for the temperature-sensitive sheet alone in the same manner as the light-shielding material. The transmittance at a wavelength of 500 nm at 70°C was also measured. The results are shown in Table 2.

[0053] [Examples 7-9] <Fabrication of light-shielding material> Examples 7 and 8 involved obtaining coating solutions in the same manner as in Examples 1 to 6, and then using the obtained coating solutions to obtain temperature-sensitive sheets of the thickness shown in Table 2. Example 9 involved obtaining a coating solution in the same manner as in Examples 1 to 6, except that the side-chain crystalline polymer obtained in Synthesis Example 2 was used, and then using the obtained coating solution to obtain temperature-sensitive sheets of the thickness shown in Table 2.

[0054] Next, the obtained temperature-sensitive sheet was stretched uniaxially in the same manner as in Examples 1 to 6 to form a uniaxially stretched sheet, and the side-chain crystalline polymer was oriented in one direction. Then, a light-shielding member was obtained in the same manner as in Examples 1 to 6, except that this temperature-sensitive sheet was used.

[0055] <Rating> The transmittance of the obtained light-shielding material at a wavelength of 500 nm at temperatures below the melting point (23°C) and at 70°C was measured in the same manner as in Examples 1 to 6. The transmittance of the temperature-sensitive sheet alone at a wavelength of 500 nm at temperatures below the melting point (23°C) was also measured in the same manner as in Examples 1 to 6. The results are shown in Table 2.

[0056] [Table 2]

[0057] As is clear from Table 2, Examples 1-6 have higher transmittance than Comparative Examples 1-3. Examples 1, 2, 4, and 5, which had a temperature-sensitive sheet thickness of 20-150 μm, had even higher transmittance. Examples 7-9 also had higher transmittance than Comparative Examples 1-3.

[0058] Next, the light-shielding function of the light-shielding members of Examples 1 to 9 was evaluated. Specifically, when the light-shielding members of Examples 1 to 9 were visually observed at room temperature (23°C), they were transparent. Next, when the light-shielding members were heated to a temperature above their melting point (70°C) using a hairdryer and visually observed, the light-shielding members changed to black. When the light-shielding members were cooled back to room temperature and visually observed again, the light-shielding members changed to transparent. As is clear from these results, Examples 1 to 9 transmit light at temperatures below their melting point and do not transmit light at temperatures above their melting point. Furthermore, Examples 1 to 9 can be seen to repeatedly transmit and block light.

[0059] The light-shielding functions of the light-shielding members of Comparative Examples 1 to 3 were evaluated in the same manner as in Examples 1 to 9. As a result, the light-shielding members of Comparative Examples 1 to 3 also showed that they transmitted light at temperatures below their melting point, did not transmit light at temperatures above their melting point, and repeatedly transmitted and blocked light. [Explanation of symbols]

[0060] 1. Light-shielding material 2. First polarizing plate 3. Second polarizing plate 4. Temperature-sensitive sheet

Claims

1. The first polarizing plate and A second polarizing plate facing the first polarizing plate, A temperature-sensitive sheet sandwiched between the first polarizing plate and the second polarizing plate, The first polarizer and the second polarizer are positioned such that their respective transmission axes are different from each other. The temperature-sensitive sheet contains a side-chain crystalline polymer that crystallizes at a temperature below its melting point and exhibits fluidity at a temperature above its melting point. The aforementioned side-chain crystalline polymer is oriented in one direction, forming a light-shielding member.

2. The light-shielding member according to claim 1, wherein when light is propagated from one of the first polarizing plate and the second polarizing plate toward the other, it transmits light at a temperature below the melting point and does not transmit light at a temperature above the melting point.

3. The light-shielding member according to claim 1 or 2, wherein the temperature-sensitive sheet is positioned such that the orientation direction of the side-chain crystalline polymer is different with respect to the transmission axis of the first polarizing plate and the second polarizing plate, respectively.

4. The light-shielding member according to any one of claims 1 to 3, wherein the thickness of the temperature-sensitive sheet is 1 to 300 μm.

5. The light-shielding member according to any one of claims 1 to 4, wherein the temperature-sensitive sheet is a uniaxially stretched sheet.

6. The light-shielding member according to any one of claims 1 to 5, wherein the side-chain crystalline polymer contains a (meth)acrylate having a linear alkyl group with 16 or more carbon atoms as a monomer component.

Images