Light control sheet

Abstract

To provide a light control sheet which can increase the reliability to application of high voltages.SOLUTION: A light control sheet 10 includes: a light control layer 20 including a liquid crystal composition; and first and second transparent electrode layers 31 and 32 that are a pair of transparent electrode layers in which the light control layer 20 is to be inserted. At a frequency of 10 Hz, the parallel capacitance per unit area of the light control sheet 10 is not less than 0.20 nF / cm2 and not more than 0.37 nF / cm2. The thickness of the light control layer 20 is 20 μm to 35 μm, and the area of the light control layer 20 is 0.135 m2 to 1.5 m2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a light control sheet with variable light transmittance. [Background technology]

[0002] A light-controlling sheet comprises a light-controlling layer containing a liquid crystal composition and a pair of transparent electrode layers sandwiching the light-controlling layer. A driving voltage is applied between the pair of transparent electrode layers. The orientation state of the liquid crystal compound in the light-controlling layer changes depending on whether or not a driving voltage is applied, making it possible to switch between a transparent state in which light passes through the light-controlling layer and an opaque state in which light transmission through the light-controlling layer is suppressed by scattering or the like (see, for example, Patent Document 1). Light-controlling sheets are used as building materials such as windows and partitions in buildings, and in automotive applications such as vehicle windows. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-45135 Summary of the Invention [Problem to be solved by the invention]

[0004] Light-controlling films undergo various reliability tests. In particular, higher reliability standards are applied to automotive applications than to building materials. One of these reliability tests is the voltage resistance test. In this test, a high voltage is applied to the light-controlling film, calculated by multiplying the standard operating voltage for the film by a safety factor. If the application of high voltage partially destroys the insulation of the light-controlling layer, causing a short circuit between the transparent electrode layers, the short circuit will cause point-defect-like appearance defects due to heat generation at the site of the short circuit. The voltage resistance test evaluates whether or not such short circuit-related appearance defects occur. Therefore, light-controlling films are required to have a low rate of short circuit occurrence when high voltage is applied. [Means for solving the problem]

[0005] Various aspects of the light controlling sheet for solving the above problems will be described below. [Aspect 1] A light-controlling sheet comprising a light-controlling layer containing a liquid crystal composition and a pair of transparent electrode layers, a first transparent electrode layer and a second transparent electrode layer, sandwiching the light-controlling layer, wherein the parallel capacitance per unit area of ​​the light-controlling sheet at a frequency of 10 Hz is 0.20 nF / cm 2 More than 0.37nF / cm 2 Below is the photochromic sheet.

[0006] According to the above configuration, the occurrence of partial short circuits between the transparent electrode layers when a high voltage is applied is suppressed, while the deterioration of the function of switching between the transparent state and the opaque state is also suppressed, thereby ensuring the reliability of the light-controlling sheet.

[0007] [Aspect 2] The light-control sheet according to [Aspect 1], wherein the thickness of the light-control layer is 20 μm or more and 35 μm or less. According to the above-mentioned configuration, the light-controlling layer can be easily formed, good optical properties can be obtained, and the capacitance can be easily controlled within the above-mentioned range.

[0008] [Aspect 3] The area of ​​the light-controlling layer is 0.135 m 2 More than 1.5m 2 A light-controlling sheet according to [Aspect 1] or [Aspect 2] below. According to the above configuration, the light-controlling sheet can be easily applied to building materials and vehicle applications, and the capacitance can be easily controlled within the above range.

[0009] [Aspect 4] The light-controlling sheet according to any one of [Aspect 1] to [Aspect 3], wherein the light-controlling layer contains a dichroic dye and black spacers. According to the above configuration, in the light-controlling sheet that contains a dichroic dye and is colored in an opaque state, the occurrence of a short circuit when a high voltage is applied is suppressed.

[0010] [Aspect 5] A light-controlling sheet according to any one of [Aspect 1] to [Aspect 4], wherein the light-controlling layer comprises a transparent polymer layer containing a plurality of voids, and the liquid crystal composition is held in the voids. According to the above configuration, an opaque state is achieved by scattering light, and in such a light-controlling sheet, the occurrence of a short circuit when a high voltage is applied is suppressed. [Effects of the Invention]

[0011] According to the present disclosure, the reliability of a light-controlling sheet against application of high voltage can be improved. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing the configuration of a light controlling sheet according to one embodiment. [Figure 2] FIG. 2 is a diagram showing the relationship between the short circuit occurrence rate and the capacitance per unit area in the examples and the comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of a light controlling sheet will be described with reference to the drawings. [Basic structure of light control sheet] 1, the light-controlling sheet 10 includes a light-controlling layer 20, a first transparent electrode layer 31, a second transparent electrode layer 32, a first transparent support layer 41, and a second transparent support layer 42. The light-controlling layer 20 is sandwiched between the first transparent electrode layer 31 and the second transparent electrode layer 32 and is in contact with these transparent electrode layers 31 and 32. The first transparent support layer 41 supports the first transparent electrode layer 31 on the side opposite the light-controlling layer 20 with respect to the first transparent electrode layer 31, and the second transparent support layer 42 supports the second transparent electrode layer 32 on the side opposite the light-controlling layer 20 with respect to the second transparent electrode layer 32.

[0014] The light-controlling layer 20 includes a transparent polymer layer and a liquid crystal composition. The transparent polymer layer has a plurality of voids, which are filled with the liquid crystal composition. The voids may have a spherical, ellipsoidal, or irregular shape.

[0015] The structure for retaining the liquid crystal composition in the light-controlling layer 20 is either a polymer network type, a polymer dispersion type, or an encapsulation type. The polymer network type light-controlling layer 20 has a polymer network with a three-dimensional mesh structure. The polymer network is an example of a transparent polymer layer, and the liquid crystal composition is retained in the interconnected voids of the polymer network. The polymer dispersion type light-controlling layer 20 has a transparent polymer layer that defines a large number of isolated voids, and the liquid crystal composition is retained in the voids dispersed in the transparent polymer layer. The encapsulation type light-controlling layer 20 retains the liquid crystal composition in the voids within capsules dispersed in the transparent polymer layer.

[0016] The transparent polymer layer is a polymer of a photopolymerizable compound. The photopolymerizable compound is, for example, an ultraviolet-polymerizable compound. The ultraviolet-polymerizable compound is, for example, an acrylate compound such as butyl ethyl acrylate or cyclohexyl acrylate, a methacrylate compound such as N,N-dimethylaminoethyl methacrylate or phenoxyethyl methacrylate, a stilbene compound, a diacrylate compound, a dimethacrylate compound, a triacrylate compound, a trimethacrylate compound, a tetraacrylate compound, a tetramethacrylate compound, or an oligomer of each of these compounds. The proportion of the transparent polymer layer to the total mass of the light-controlling layer 20 is preferably 20% by mass or more and 80% by mass or less.

[0017] The liquid crystal composition contains a liquid crystal compound having positive dielectric anisotropy, i.e., the dielectric constant of the liquid crystal compound in the long axis direction is greater than the dielectric constant of the liquid crystal compound in the short axis direction. The liquid crystal compound is, for example, a Schiff base-based, azo-based, azoxy-based, biphenyl-based, terphenyl-based, benzoate ester-based, tolan-based, pyrimidine-based, pyridazine-based, cyclohexanecarboxylic acid ester-based, phenylcyclohexane-based, biphenylcyclohexane-based, dicyanobenzene-based, naphthalene-based, or dioxane-based compound. In addition to the liquid crystal compound, the liquid crystal composition may contain a viscosity reducing agent, an antifoaming agent, an antioxidant, a weathering agent, etc. Examples of the weathering agent are an ultraviolet absorber and a light stabilizer.

[0018] The liquid crystal composition may further contain a dichroic dye. The dichroic dye is characterized by a higher absorbance in the visible region in the direction of the long axis of the molecule than in the direction of the short axis. The dichroic dye is oriented in a guest-host manner using the liquid crystal compound as a host, and exhibits a predetermined color when the long axis is approximately perpendicular to the direction of incident light. The color exhibited by the dichroic dye is, for example, black or a color close to black.

[0019] Examples of the dichroic dye include polyiodine, azo compounds, anthraquinone compounds, naphthoquinone compounds, azomethine compounds, tetrazine compounds, quinophthalone compounds, merocyanine compounds, perylene compounds, and dioxazine compounds. The ratio of the dichroic dye to the total mass of the switchable layer 20 is preferably 0.5% by mass to 10% by mass, and more preferably 1% by mass to 5% by mass.

[0020] The light-switching layer 20 may also include spacers dispersed throughout the transparent polymer layer. The spacers determine the thickness of the light-switching layer 20 around the spacers, thereby making the thickness of the light-switching layer 20 uniform. The spacers may be bead spacers or photospacers formed by exposing and developing a photoresist, as long as they are light-transmitting. The spacers may be colorless and transparent, or colored and transparent. When the liquid crystal composition contains a dichroic dye, the color exhibited by the colored and transparent spacers is preferably the same color as the color exhibited by the dichroic dye.

[0021] Each of the first transparent electrode layer 31 and the second transparent electrode layer 32 is conductive and transparent to light in the visible region. The transparent electrode layers 31 and 32 may be made of a material such as indium tin oxide, fluorine-doped tin oxide, tin oxide, zinc oxide, carbon nanotubes, poly(3,4-ethylenedioxythiophene), silver, or a silver alloy.

[0022] Each of the first transparent support layer 41 and the second transparent support layer 42 is a base material that is transparent to light in the visible region. The material of the transparent support layers 41, 42 is, for example, a synthetic resin or an inorganic compound. Examples of synthetic resins include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyacrylates such as polymethyl methacrylate, polycarbonates, and polyolefins. Examples of inorganic compounds include silicon dioxide, silicon oxynitride, and silicon nitride.

[0023] At the end of the first transparent electrode layer 31, the first transparent electrode layer 31 is exposed from the light-controlling layer 20, the second transparent electrode layer 32, and the second transparent support layer 42, and a first wiring section 51 is connected to this exposed portion. The first wiring section 51 has the function of electrically connecting the first transparent electrode layer 31 to a control section 50 that generates a voltage for driving the light-controlling sheet 10.

[0024] At the end of the second transparent electrode layer 32, the second transparent electrode layer 32 is exposed from the light control layer 20, the first transparent electrode layer 31, and the first transparent support layer 41, and the second wiring section 52 is connected to this exposed portion. The second wiring section 52 has the function of electrically connecting the second transparent electrode layer 32 to the control section 50.

[0025] Each of the first wiring portion 51 and the second wiring portion 52 includes, for example, a conductive adhesive layer and a wiring substrate. The conductive adhesive layer is formed of, for example, an anisotropic conductive film (ACF), an anisotropic conductive paste (ACP), an isotropic conductive film (ICF), an isotropic conductive paste (ICP), or the like. The wiring substrate is, for example, a flexible printed circuit (FPC). Alternatively, each of the first wiring portion 51 and the second wiring portion 52 may have a structure in which a conductive material such as a conductive tape and a conductor are joined by soldering.

[0026] The transparent electrode layers 31 and 32 are electrically connected to the control unit 50 via wiring units 51 and 52. The control unit 50 applies a driving voltage, which is an AC voltage for changing the alignment state of the liquid crystal compound, to the transparent electrode layers 31 and 32 via the wiring units 51 and 52. The control unit 50 controls the potential difference between the transparent electrode layers 31 and 32 by controlling whether or not a voltage is applied and the magnitude of the voltage to be applied. The light controlling sheet 10, the control unit 50, and the wiring units 51 and 52 constitute a light controlling device.

[0027] The light controlling sheet 10 switches between a transparent state and an opaque state based on a change in the alignment state of the liquid crystal compound. The transparent state is a state in which the light transmittance, i.e., the parallel ray transmittance, is relatively high, and the opaque state is a state in which the light transmittance is relatively low. The transparent state is a state in which the haze is relatively low, and the opaque state is a state in which the haze is relatively high.

[0028] When no driving voltage is applied, the orientation of the long axes of the liquid crystal compounds is random. As a result, light incident on the light-controlling sheet 10 is scattered in various directions by the light-controlling layer 20 due to the birefringence of the liquid crystal compounds and the difference in refractive index between the liquid crystal compounds and the transparent polymer layer. When the liquid crystal composition contains a dichroic dye, the orientation of the long axes of the dichroic dye is also random, and at least a portion of the dichroic dye exhibits a color. Therefore, the light-controlling sheet 10 is in an opaque state when no driving voltage is applied. In the opaque state, if the liquid crystal composition does not contain a dichroic dye, the light-controlling sheet 10 appears cloudy white. If the liquid crystal composition contains a dichroic dye, the light-controlling sheet 10 appears in a color corresponding to the color of the dichroic dye.

[0029] When a driving voltage is applied, the liquid crystal compounds are oriented so that their long axes are aligned with the electric field direction. That is, the orientation of the liquid crystal compounds changes so that their long axes are aligned with the thickness direction of the light-controlling layer 20. When the liquid crystal composition contains a dichroic dye, the dichroic dye is also oriented so that its long axes are aligned with the electric field direction. As a result, scattering and absorption of light in the light-controlling layer 20 is suppressed, and light is more easily transmitted through the light-controlling sheet 10. Therefore, the light-controlling sheet 10 is in a transparent state when a driving voltage is applied.

[0030] At least one of the front and back surfaces of the light controlling sheet 10 is attached to a transparent plate made of glass, resin, or the like. Examples of the transparent plate include window glass in various buildings, partitions installed indoors, and window glass or windshields in moving objects such as vehicles and aircraft. The surface of the transparent plate may be flat or curved.

[0031] [Capacitance] In this embodiment, the capacitance Cp, which is the parallel capacitance per unit area of ​​the light controlling sheet 10 when an AC voltage of 10 Hz is applied, is 0.20 nF / cm 2 More than 0.37nF / cm 2 The parallel capacitance is the capacitance when the equivalent circuit of the light-controlling sheet 10 is regarded as a parallel circuit of a capacitor and a resistor. The area of ​​the light-controlling sheet 10 used to calculate the capacitance Cp is the area of ​​the portion of the light-controlling sheet 10 where the light-controlling layer 20 is located in a planar view.

[0032] The smaller the capacitance Cp, the less charge is stored in each of the transparent electrode layers 31 and 32 when a voltage is applied, making it less likely that a short circuit will occur between the transparent electrode layers 31 and 32. On the other hand, the smaller the capacitance Cp, the greater the minimum voltage required to switch between the transparent state and the opaque state, and therefore the lower the switching function between the transparent state and the opaque state, i.e., the dimming function. Conversely, the larger the capacitance Cp, the better the light control function, but the more likely it is that a short circuit between the transparent electrode layers 31 and 32 will occur.

[0033] In contrast, the inventors have found that the capacitance Cp is 0.20 nF / cm 2 More than 0.37nF / cm 2 It has been found that, if the capacitance Cp is within the above range, it is possible to achieve both suppression of short circuits and good dimming function. In particular, when the dimming layer 20 contains a dichroic dye, short circuits are likely to occur between the transparent electrode layers 31 and 32 due to the action of the dichroic dye or the interaction between the dichroic dye and the liquid crystal compound. Even in this case, by controlling the capacitance Cp within the above range, it is possible to appropriately suppress short circuits in a configuration containing a dichroic dye.

[0034] The capacitance Cp is calculated based on measurements using an LCR meter. Because the effect of capacitance on impedance is dominant in the low-frequency range, the capacitance Cp obtained at a measurement frequency of 10 Hz can be used to accurately evaluate the susceptibility to short-circuiting, which is affected by the amount of charge stored in the transparent electrode layers 31 and 32, and the dimming function.

[0035] The capacitance Cp can be adjusted by the composition, thickness, and area of ​​the switchable layer 20. For example, the capacitance Cp can be increased by increasing the ratio of the liquid crystal composition to the transparent polymer layer in the switchable layer 20.

[0036] The thickness of the switchable layer 20 is preferably 20 μm or more and 35 μm or less. If the thickness of the switchable layer 20 is within the above range, the switchable layer 20 is easily formed, and good optical properties are obtained. Furthermore, it is easy to control the capacitance Cp within the above range.

[0037] The area of ​​the light-control layer 20 is 0.135 m 2 More than 1.5m 2 If the area of ​​the light control layer 20 is within the above range, the light control sheet 10 can be easily applied to building materials and vehicle applications. In addition, the capacitance Cp can be easily controlled within the above range.

[0038] [Example] The above-mentioned light controlling sheet will be explained using specific examples and comparative examples. Example 1 A liquid crystal compound, a photopolymerizable compound, a photopolymerization initiator, and a spacer were mixed in the following ratio to prepare a coating liquid for forming a light-control layer. Details of the materials are as follows: Liquid crystal compound: cyanobiphenyl compound 50.0% by mass Photopolymerizable compound (ultraviolet curable compound): 47.5% by mass of a mixture of isobornyl acrylate, pentaerythritol triacrylate, and urethane acrylate Photopolymerization initiator: 1.0% by mass of 1-hydroxycyclohexyl phenyl ketone (Irgacure 184, manufactured by BASF Japan Ltd.) Spacer: 1.5% by mass of white spherical particles (particle size 20 μm) made of polymethyl methacrylate

[0039] A first sheet was fabricated as a laminate of the first transparent support layer and the first transparent electrode layer by sputtering a first transparent electrode layer on the first transparent support layer. Similarly, a second sheet was fabricated as a laminate of the second transparent support layer and the second transparent electrode layer by sputtering a second transparent electrode layer on the second transparent support layer. Each of the first and second transparent support layers was made of polyethylene terephthalate and had a thickness of 125 μm. Each of the first and second transparent electrode layers was made of indium tin oxide and had a thickness of 30 nm.

[0040] A coating film made from the above coating liquid was formed between the first transparent electrode layer and the second transparent electrode layer to produce a laminate of the first sheet, the coating film, and the second sheet. Subsequently, the first transparent support layer of the laminate was irradiated with 365 nm ultraviolet light to polymerize the photopolymerizable compound, thereby forming a light-controlling layer. The intensity of the ultraviolet light was 12 mW / cm. 2 The irradiation time of the ultraviolet light is 120 seconds. The thickness of the photochromic layer is 20 μm. The area of ​​the region where the photochromic layer is located is 0.135 m. 2 The laminate was molded so as to obtain the light-controlling sheet of Example 1.

[0041] Example 2 The area of ​​the photochromic layer is 0.380m 2 A light-controlling sheet of Example 2 was obtained using the same materials and manufacturing method as in Example 1, except that the shape of the sheet was changed so that:

[0042] Example 3 The area of ​​the photochromic layer is 1,500m 2 A light-controlling sheet of Example 3 was obtained using the same materials and manufacturing method as in Example 1, except that the shape of the sheet was changed so that:

[0043] Example 4 A light-controlling sheet of Example 4 was obtained using the same materials and manufacturing method as in Example 1, except that the thickness of the light-controlling layer was changed to 35 μm by changing the particle size of the spacers.

[0044] Example 5 A light-controlling sheet of Example 5 was obtained using the same materials and manufacturing method as in Example 1, except that the composition of the coating liquid for forming the light-controlling layer was changed as follows: The thickness of the light-controlling layer of Example 5 was 25 μm and the area was 0.135 m 2 is. Liquid crystal compound: cyanobiphenyl compound 45.0% by mass Dichroic dye: black dichroic dye (YH-428, manufactured by Mitsui Fine Chemicals Co., Ltd.) 5.0% by mass Photopolymerizable compound (ultraviolet curable compound): 47.5% by mass of a mixture of isobornyl acrylate, pentaerythritol triacrylate, and urethane acrylate Photopolymerization initiator: 1.0% by mass of 1-hydroxycyclohexyl phenyl ketone (Irgacure 184, manufactured by BASF Japan Ltd.) Spacer: 1.5% by mass of black, transparent, spherical particles (particle size 25 μm) made of polymethyl methacrylate

[0045] Example 6 The area of ​​the photochromic layer is 0.380m 2 A light-controlling sheet of Example 6 was obtained using the same materials and manufacturing method as in Example 5, except that the shape of the sheet was changed so that:

[0046] Example 7 The area of ​​the photochromic layer is 1,500m 2 A light-controlling sheet of Example 7 was obtained using the same materials and manufacturing method as in Example 5, except that the shape of the sheet was changed so that:

[0047] Example 8 A light-controlling sheet of Example 8 was obtained using the same materials and manufacturing method as in Example 5, except that the thickness of the light-controlling layer was changed to 35 μm by changing the particle size of the spacers.

[0048] (Comparative Example 1) A light-control sheet of Comparative Example 1 was obtained using the same materials and manufacturing method as in Example 1, except that the composition of the coating liquid for forming the light-control layer was changed as follows: The thickness of the light-control layer of Comparative Example 1 was 16 μm, and the area was 0.135 m 2 is. Liquid crystal compound: cyanobiphenyl compound 52.0% by mass Photopolymerizable compound (ultraviolet curable compound): 45.5% by mass of a mixture of isobornyl acrylate, pentaerythritol triacrylate, and urethane acrylate Photopolymerization initiator: 1.0% by mass of 1-hydroxycyclohexyl phenyl ketone (Irgacure 184, manufactured by BASF Japan Ltd.) Spacer: 1.5% by mass of white spherical particles (particle size 16 μm) made of polymethyl methacrylate

[0049] (Comparative Example 2) The area of ​​the photochromic layer is 0.380m 2 A light-controlling sheet of Comparative Example 2 was obtained using the same materials and manufacturing method as in Comparative Example 1, except that the shape of the sheet was changed so that:

[0050] (Comparative Example 3) A light-control sheet of Comparative Example 3 was obtained using the same materials and manufacturing method as in Comparative Example 1, except that the thickness of the light-control layer was changed to 20 μm by changing the particle size of the spacers.

[0051] Comparative Example 4 By changing the particle size of the spacers, the thickness of the photochromic layer was changed to 20 μm, and the area of ​​the photochromic layer was changed to 0.380 m 2 A light-control sheet of Comparative Example 4 was obtained using the same materials and manufacturing method as in Comparative Example 1, except that the shape of the sheet was changed so that:

[0052] (Comparative Example 5) A light-control sheet of Comparative Example 5 was obtained using the same materials and manufacturing method as in Example 1, except that the composition of the coating liquid for forming the light-control layer was changed as follows: The thickness of the light-control layer of Comparative Example 5 was 20 μm and the area was 0.135 m 2 is. Liquid crystal compound: cyanobiphenyl compound 46.0% by mass Dichroic dye: black dichroic dye (YH-428, manufactured by Mitsui Fine Chemicals Co., Ltd.) 3.0% by mass Photopolymerizable compound (ultraviolet curable compound): 48.5% by mass of a mixture of isobornyl acrylate, pentaerythritol triacrylate, and urethane acrylate Photopolymerization initiator: 1.0% by mass of 1-hydroxycyclohexyl phenyl ketone (Irgacure 184, manufactured by BASF Japan Ltd.) Spacer: 1.5% by mass of black, transparent, spherical particles (particle size 20 μm) made of polymethyl methacrylate

[0053] (Comparative Example 6) A light-control sheet of Comparative Example 6 was obtained using the same materials and manufacturing method as in Comparative Example 5, except that the thickness of the light-control layer was changed to 25 μm by changing the particle size of the spacers.

[0054] (Comparative Example 7) The area of ​​the photochromic layer is 0.380m 2 A light-control sheet of Comparative Example 7 was obtained using the same materials and manufacturing method as in Comparative Example 5, except that the shape of the sheet was changed so that:

[0055] (Comparative Example 8) By changing the particle size of the spacers, the thickness of the photochromic layer was changed to 25 μm, and the area of ​​the photochromic layer was changed to 0.380 m 2A light-control sheet of Comparative Example 8 was obtained using the same materials and manufacturing method as in Comparative Example 5, except that the shape of the sheet was changed so that:

[0056] (Evaluation method) <Capacitance Cp> For each example and comparative example of light-controlling sheets, the parallel capacitance was measured using an LCR meter (ZM2372, manufactured by NF Corporation), and the capacitance per unit area Cp was calculated. The parallel capacitance was measured by connecting the lead wires attached to the LCR meter to the connection area of ​​the wiring part of the light-controlling sheet, and was performed under the conditions of voltage: 1.0 V, frequency: 10 Hz.

[0057] <Short circuit occurrence rate> A voltage resistance test was conducted on the light-control sheets of each example and comparative example. In the voltage resistance test, a sine wave voltage of 150 V, 60 Hz was applied to the light-control sheet for 30 consecutive seconds, and then a square wave voltage of 150 V, 60 Hz was applied to the light-control sheet for 30 consecutive seconds. After the voltage resistance test, the light-control sheet was visually inspected for the occurrence of a short circuit. If there was a circular area with a diameter of 0.5 mm or more where the light transmittance did not change when current was applied, it was judged that a short circuit had occurred. For each example and comparative example, 100 samples were checked for the above short circuit after the withstand voltage test, and the proportion of samples in which a short circuit was found to have occurred was taken as the short circuit occurrence rate. <Dimming function>

[0058] For each example and comparative example, the light-controlling sheet was connected to a power source, and it was confirmed whether the light-controlling sheet could be switched between a transparent state and an opaque state by turning the applied voltage on and off. The power source voltage was an AC voltage of 80 V, 60 Hz. In evaluating the light-controlling function, if the sheet switched between a transparent state and an opaque state, it was evaluated as good (○), and if it did not switch between a transparent state and an opaque state, it was evaluated as bad (×).

[0059] (Evaluation results) For each example and comparative example, the presence or absence of a dichroic dye in the photochromic layer, the thickness of the photochromic layer, the area of ​​the photochromic layer, the measured parallel capacitance, the capacitance per unit area Cp, the incidence of short circuits, and the evaluation results of the photochromic function are shown in Table 1. Figure 2 also shows the relationship between the capacitance per unit area Cp and the incidence of short circuits based on Table 1.

[0060] [Table 1]

[0061] As shown in Table 1, regardless of whether the dichroic dye is contained in the light-control layer, the capacitance Cp is 0.20 nF / cm 2 More than 0.37nF / cm 2 In the following Examples 1 to 8, the incidence of short circuits was low and the dimming function was good. 2 In Comparative Examples 1, 2, and 5 to 8, the short circuit occurrence rate was significantly increased, and the capacitance Cp was 0.20 nF / cm 2 In Comparative Examples 3 and 4, where the value was less than 100%, the light control function was poor.

[0062] As shown in Figure 2, the short circuit occurrence rate is 2 If it is less than this, it is close to 0%, but if the capacitance Cp is 0.37nF / cm 2 Therefore, when the capacitance Cp exceeds 0.37nF / cm 2 When the capacitance Cp is 0.20 nF / cm or less, the occurrence of a short circuit in the light-controlling sheet can be suitably suppressed. 2 If this is the case, the deterioration of the dimming function can be suppressed.

[0063] According to the above-described embodiments and examples, the following effects can be obtained. (1) The capacitance Cp of the light-control sheet is 0.37 nF / cm 2 By keeping the capacitance Cp at 0.20 nF / cm or less, the occurrence of partial short circuits between the transparent electrode layers when a high voltage is applied can be suppressed. 2As a result, the function of switching between the transparent state and the opaque state is prevented from being deteriorated, thereby ensuring the reliability of the light controlling sheet.

[0064] (2) When the thickness of the photochromic layer is 20 μm or more and 35 μm or less, the photochromic layer is easily formed, good optical properties are obtained, and the capacitance Cp can be easily controlled within the above range.

[0065] (3) The area of ​​the photochromic layer is 0.135 m 2 More than 1.5m 2 If the capacitance Cp is less than 100%, the light-controlling sheet can be easily applied to building materials and automotive applications, and the capacitance Cp can be easily controlled within the above range.

[0066] (4) If the light-controlling layer contains a dichroic dye and a black spacer, the color of the opaque light-controlling sheet will be a color corresponding to the color of the dichroic dye. Furthermore, by keeping the capacitance Cp within the above range in such a light-controlling sheet, it is possible to effectively prevent the occurrence of short circuits and the deterioration of the light-controlling function.

[0067] (5) If the light-controlling layer has a structure in which the liquid crystal composition is held in the voids of the transparent polymer layer, an opaque state is realized by light scattering. Furthermore, by having the capacitance Cp of such a light-controlling sheet within the above range, it is possible to effectively prevent the occurrence of short circuits and the deterioration of the light-controlling function. [Explanation of symbols]

[0068] 10...Light-adjusting sheet 20...Photochromic layer 31,32...Transparent electrode layer 41,42...Transparent support layer 50...Control unit 51,52...Wiring section

Claims

1. a light-controlling layer containing a liquid crystal composition; A light-controlling sheet comprising a pair of transparent electrode layers, a first transparent electrode layer and a second transparent electrode layer, sandwiching the light-controlling layer, The parallel capacitance per unit area of ​​the light-control sheet at a frequency of 10 Hz is 0.20 nF / cm ２ 0.37nF / cm or more ２ is Dimming sheet.

2. The thickness of the light-controlling layer is 20 μm or more and 35 μm or less. The light-controlling sheet according to claim 1 .

3. The area of ​​the light-controlling layer is 0.135 m ２ 1.5m or more ２ is The light-controlling sheet according to claim 1 .

4. The light-modulating layer includes a dichroic dye and a black spacer. The light-controlling sheet according to claim 1 .

5. The light-controlling layer comprises a transparent polymer layer containing a plurality of voids, and the liquid crystal composition is held in the voids. The light-controlling sheet according to claim 1 .

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