Light control sheet, light control device, and method for producing light control sheet

Abstract

In the present invention, a liquid crystal composition comprises a liquid crystal compound and one or more dichroic dyes. The percentage of the mass of the liquid crystal compound with respect to the sum of the mass of a transparent polymer layer and the mass of the liquid crystal composition is 45 mass% or more. A light control sheet in a second state has a total light transmittance T of 10% to 80%. The dichroic dye has an anisotropy value Rm of 0.25 to 0.94, and the anisotropy value Rm satisfies formula (1). In formula (1), ln is a natural logarithm.　Formula (1): Anisotropy value Rm ≥ 0.3434 ln (T) - 0.4297

Description

Light-modulating sheet, light-modulating device, and method for manufacturing light-modulating sheet

[0001] The present disclosure relates to a light control sheet, a light control device, and a method for manufacturing a light control sheet.

[0002] An example of a light-adjusting device constituting a window includes a pair of conductive layers and a switching layer positioned between the conductive layers. The switching layer includes a liquid crystal compound and a dichroic dye, but does not include a transparent polymer layer. The light-adjusting device is configured to be able to exhibit a bright state and a dark state depending on whether or not a voltage is applied to the switching layer included in the light-adjusting device. In order to increase the light transmittance when the light-adjusting device exhibits a bright state, the anisotropy value R and the transmittance τv in the bright state are defined as follows (see, for example, Patent Document 1):

[0003] Rmin<R<Rmax Rmin=0.8*(0.015*τv-0.45) Rmax=1.2*(0.015*τv-0.45)

[0004] Special table 2016-510907 publication

[0005] Another example of a light-adjusting device includes a light-adjusting layer including a transparent polymer layer having a plurality of voids, instead of the switching layer described above. In the light-adjusting layer, the liquid crystal compound and the dichroic dye are filled in the voids of the transparent polymer layer. The light-adjusting device is configured to be able to switch between a state in which refraction and scattering occur at the interface between the liquid crystal compound and the transparent polymer layer and a state in which refraction and scattering hardly occur, depending on whether or not a voltage is applied to the light-adjusting layer. Therefore, the light-adjusting device can exhibit a transparent state and an opaque state.

[0006] As a dichroic dye contained in such a light-adjusting device, for example, a black dye has been proposed. A light-adjusting device containing a black dichroic dye can exhibit a transparent state and a blackish opaque state. As a result, when the light-adjusting device exhibits a transparent state, it allows objects to be seen through the light-adjusting device, while when the light-adjusting device exhibits an opaque state, it makes it impossible to see objects through the light-adjusting device. Therefore, such light-adjusting devices are often used in two spaces separated by a light-adjusting device to protect the privacy of one space from people in the other space.

[0007] Light-adjusting devices used for such applications are required to maintain light transmission in a transparent state while suppressing light transmission when the device is colored and opaque, not just black, so as to enable privacy protection through the light-adjusting device. In other words, the light-adjusting sheet is required to be able to increase the contrast, which is the ratio of the transmittance when the device is transparent to the transmittance when the device is opaque.

[0008] One aspect of the light-controlling sheet comprises a first transparent electrode layer, a second transparent electrode layer, and a light-controlling layer located between the first and second transparent electrode layers, the light-controlling layer including a transparent polymer layer containing a plurality of voids and a liquid crystal composition filled in the voids. The light-controlling sheet exhibits a first state and a second state having a lower haze value than the first state, depending on the magnitude of the voltage applied to the light-controlling layer. The liquid crystal composition includes a liquid crystal compound and one or more dichroic dyes. The percentage of the mass of the liquid crystal compound relative to the sum of the mass of the transparent polymer layer and the mass of the liquid crystal composition is 45 mass% or more. The total light transmittance T of the light-controlling sheet exhibiting the second state is 10% or more and 80% or less. The anisotropy value Rm of the dichroic dye is 0.25 or more and 0.94 or less, and satisfies the following formula (1): Anisotropy value Rm≧0.3434ln(T)−0.4297 (1) In the formula (1), ln is the natural logarithm.

[0009] One aspect of the light-controlling sheet comprises a first transparent electrode layer, a second transparent electrode layer, and a light-controlling layer located between the first and second transparent electrode layers, the light-controlling layer including a transparent polymer layer containing a plurality of voids and a liquid crystal composition filled in the voids. The light-controlling sheet exhibits a first state and a second state having a lower haze value than the first state, depending on the magnitude of the voltage applied to the light-controlling layer. The liquid crystal composition includes a liquid crystal compound and one or more dichroic dyes. The percentage of the mass of the liquid crystal compound relative to the sum of the mass of the transparent polymer layer and the mass of the liquid crystal composition is 55% by mass or more. The total light transmittance T of the light-controlling sheet exhibiting the second state is 10% or more and 80% or less. The anisotropy value Rm of the dichroic dye is 0.25 or more and 0.94 or less, and satisfies the following formula (2): Anisotropy value Rm≧0.2989ln(T)−0.3472 (2) In the formula (2), ln is the natural logarithm.

[0010] One aspect of a light-adjusting device includes the above-described light-adjusting sheet and a driving unit configured to be able to apply a voltage to the light-adjusting layer provided in the light-adjusting sheet.

[0011] One aspect of a method for manufacturing a light-controlling sheet includes a first transparent electrode layer, a second transparent electrode layer, and a light-controlling layer located between the first and second transparent electrode layers, the light-controlling layer including a transparent polymer layer containing a plurality of voids and a liquid crystal composition filled in the voids, the light-controlling sheet exhibiting a first state and a second state having a lower haze value than the first state depending on the magnitude of a voltage applied to the light-controlling layer. The manufacturing method includes preparing a coating liquid containing a liquid crystal compound, a dichroic dye, and a polymerizable composition, forming a coating film between the first and second transparent electrode layers using the coating liquid, and polymerizing the polymerizable composition in the coating film. Adjusting the coating liquid includes adjusting the coating liquid so that the percentage of the mass of the liquid crystal compound relative to the total mass of the coating liquid is 45 mass % or more, and selecting the dichroic dye having an anisotropy value Rm of 0.25 to 0.94 and satisfying the following formula (1): The total light transmittance T of the light-controlling sheet exhibiting the second state is 10% to 80%: Anisotropy value Rm≧0.3434ln(T)−0.4297 … formula (1) In formula (1), ln is the natural logarithm.

[0012] One aspect of a method for manufacturing a light-controlling sheet includes a first transparent electrode layer, a second transparent electrode layer, and a light-controlling layer located between the first transparent electrode layer and the second transparent electrode layer, the light-controlling layer including a transparent polymer layer including a plurality of voids and a liquid crystal composition filled in the voids, the light-controlling sheet exhibiting a first state and a second state having a lower haze value than the first state depending on the magnitude of a voltage applied to the light-controlling layer. The manufacturing method includes preparing a coating liquid including a liquid crystal compound, a dichroic dye, and a polymerizable composition, forming a coating film between the first transparent electrode layer and the second transparent electrode layer using the coating liquid, and polymerizing the polymerizable composition in the coating film. Adjusting the coating liquid includes adjusting the coating liquid so that the percentage of the mass of the liquid crystal compound relative to the total mass of the coating liquid is 55 mass % or more, and selecting the dichroic dye having an anisotropy value Rm of 0.25 to 0.94 and satisfying the following formula (2): The total light transmittance T of the light-controlling sheet exhibiting the second state is 10% to 80%: Anisotropy value Rm≧0.2989ln(T)−0.3472 … formula (2) In formula (2), ln is the natural logarithm.

[0013] FIG. 1 is a cross-sectional view showing the structure of a first light-adjusting device equipped with a normal-type light-adjusting sheet. FIG. 2 is a partially enlarged cross-sectional view showing a portion of the structure of the light-adjusting sheet shown in FIG. 1 when no voltage is applied to the light-adjusting layer. FIG. 3 is a partially enlarged cross-sectional view showing a portion of the structure of the light-adjusting sheet shown in FIG. 1 when a voltage is applied to the light-adjusting layer. FIG. 4 is a cross-sectional view showing the structure of a second light-adjusting device equipped with a reverse-type light-adjusting sheet. FIG. 5 is a partially enlarged cross-sectional view showing a portion of the structure of the light-adjusting sheet shown in FIG. 4 when no voltage is applied to the light-adjusting layer. FIG. 6 is a partially enlarged cross-sectional view showing a portion of the structure of the light-adjusting sheet shown in FIG. 4 when a voltage is applied to the light-adjusting layer. FIG. 7 is a graph showing the relationship between contrast and thickness of the light-adjusting layer in the light-adjusting sheet. FIG. 8 is a graph showing the relationship between total light transmittance and thickness of the light-adjusting layer in the light-adjusting sheet. FIG. 9 is a graph showing the relationship between total light transmittance and contrast in the light-adjusting sheet. Fig. 10 is a graph showing the relationship between the anisotropy value Rm of the dichroic dye and the total light transmittance T of the light-controlling sheet when the concentration of the liquid crystal compound is 55% by mass. Fig. 11 is a graph showing the relationship between the anisotropy value Rm of the dichroic dye and the total light transmittance T of the light-controlling sheet when the concentration of the liquid crystal compound is 45% by mass.

[0014] An embodiment of a light controlling sheet will be described with reference to Figures 1 to 11. The light controlling sheet of the present disclosure may be of either a normal type or a reverse type. Below, a first light controlling device including a normal type light controlling sheet and a drive unit will be described with reference to Figures 1 to 3, and a second light controlling device including a reverse type light controlling sheet and a drive unit will be described with reference to Figures 4 to 6.

[0015] The light-controlling sheet is attached to a transparent member provided in windows of various buildings such as houses, train stations, and airports, partitions installed in offices, and show windows installed in stores. Alternatively, the light-controlling sheet is attached to a transparent member provided in windows of moving objects such as vehicles and aircraft. The shape of the light-controlling sheet may be flat or curved.

[0016] [First light control device] The first light control device will be described with reference to Figures 1 to 3. Figure 1 shows the structure of a light control device equipped with a normal-type light control sheet. Figure 2 shows a portion of the structure of the light control sheet when no voltage is applied to the light control layer. Figure 3 shows a portion of the structure of the light control sheet when a voltage is applied to the light control layer.

[0017] 1 , the first light control device 10N includes a normal-type light control sheet 11N and a drive unit 12. The light control sheet 11N includes a first transparent electrode layer 21, a second transparent electrode layer 22, and a light control layer 23. The light control sheet 11N also includes a first transparent substrate 24 that supports the first transparent electrode layer 21, and a second transparent substrate 25 that supports the second transparent electrode layer 22.

[0018] In the light-controlling sheet 11N, the light-controlling layer 23 is located between the first transparent electrode layer 21 and the second transparent electrode layer 22. The first transparent electrode layer 21 is located between the first transparent substrate 24 and the light-controlling layer 23. The second transparent electrode layer 22 is located between the second transparent substrate 25 and the light-controlling layer 23.

[0019] The light-controlling sheet 11N exhibits a first state and a second state having a lower haze value than the first state, depending on the magnitude of the voltage applied to the light-controlling layer 23. Because the light-controlling sheet 11N included in the first light-controlling device 10N is a normal type, the light-controlling sheet 11N exhibits the first state when no voltage is applied to the light-controlling layer 23. In contrast, the light-controlling sheet 11N exhibits the second state when a voltage is applied to the light-controlling layer 23. The light-controlling sheet 11N exhibiting the first state is opaque, and the light-controlling sheet 11N exhibiting the second state is transparent. For example, the haze value of the light-controlling sheet 11N exhibiting the first state may be 80% or more, and the haze value of the light-controlling sheet 11N exhibiting the second state may be 10% or more and 80% or less. The haze value of the light-controlling sheet 11N exhibiting the first state is preferably higher than 80%.

[0020] The light controlling sheet 11N includes a first electrode 21E attached to a portion of the first transparent electrode layer 21 and a second electrode 22E attached to a portion of the second transparent electrode layer 22. The light controlling sheet 11N further includes a wiring 26 connected to the first electrode 21E and a wiring 26 connected to the second electrode 22E. The first electrode 21E is connected to the drive unit 12 via the wiring 26. The second electrode 22E is connected to the drive unit 12 via the wiring 26.

[0021] The first transparent electrode layer 21 and the second transparent electrode layer 22 apply a voltage to the light control layer 23 to switch the light control layer 23 between a first state and a second state. Each transparent electrode layer 21, 22 has optical transparency that allows visible light to pass through. The optical transparency of the first transparent electrode layer 21 enables visual recognition of objects through the light control sheet 11N. The optical transparency of the second transparent electrode layer 22, like the optical transparency of the first transparent electrode layer 21, enables visual recognition of objects through the light control sheet 11N.

[0022] The material for forming each transparent electrode layer 21, 22 may be, for example, any one selected from the group consisting of indium tin oxide, fluorine-doped tin oxide, tin oxide, zinc oxide, carbon nanotubes, and poly(3,4-ethylenedioxythiophene).

[0023] The material forming each of the transparent substrates 24, 25 may be a synthetic resin or an inorganic compound. Examples of synthetic resins include polyester, polyacrylate, polycarbonate, and polyolefin. Examples of polyesters include polyethylene terephthalate and polyethylene naphthalate. Examples of polyacrylates include polymethyl methacrylate. Examples of inorganic compounds include silicon dioxide, silicon oxynitride, and silicon nitride.

[0024] Each of the electrodes 21E, 22E is, for example, a flexible printed circuit (FPC). The FPC includes a support layer, a conductor portion, and a protective layer. The conductor portion is sandwiched between the support layer and the protective layer. The support layer and the protective layer are formed of an insulating synthetic resin. The support layer and the protective layer are formed of, for example, polyimide. The conductor portion is formed of, for example, a thin metal film. The thin metal film may be formed of, for example, copper. Each of the electrodes 21E, 22E is not limited to an FPC, and may be, for example, a metal tape.

[0025] Each of the electrodes 21E and 22E is attached to the corresponding transparent electrode layer 21 or 22 by a conductive adhesive layer (not shown). In each of the electrodes 21E and 22E, the conductor portion is exposed from the protective layer or the support layer at the portion connected to the conductive adhesive layer.

[0026] The conductive adhesive layer may be formed of, for example, an anisotropic conductive film (ACF), an anisotropic conductive paste (ACP), an isotropic conductive film (ICF), an isotropic conductive paste (ICP), etc. From the viewpoint of ease of handling in the manufacturing process of the light control device 10, the conductive adhesive layer is preferably an anisotropic conductive film.

[0027] Each of the wirings 26 is formed of, for example, a metal wire and an insulating layer covering the metal wire. The wire is formed of, for example, copper.

[0028] The driver 12 is configured to be able to apply a voltage to the light-controlling layer 23 included in the light-controlling sheet 11N. The driver 12 applies an AC voltage between the first transparent electrode layer 21 and the second transparent electrode layer 22. The driver 12 preferably applies an AC voltage having a rectangular waveform between the pair of transparent electrode layers 21, 22. In other words, the driver 12 preferably outputs a rectangular wave voltage signal.

[0029] The light-controlling layer 23 will be described in more detail with reference to Figures 2 and 3. As shown in Figure 2, the light-controlling layer 23 includes a transparent polymer layer 23T and a liquid crystal composition 23L. The transparent polymer layer 23T includes a plurality of voids 23D. The liquid crystal composition 23L is filled into the voids 23D of the transparent polymer layer 23T, and includes a liquid crystal compound 23LM and a dichroic dye 23P.

[0030] The retention type of the liquid crystal composition 23L is any one selected from the group consisting of a polymer network type, a polymer dispersion type, and a capsule type. The polymer network type has a transparent polymer network with a three-dimensional mesh shape, and retains the liquid crystal composition 23L in interconnected mesh-like voids 23D. The polymer network is an example of a transparent polymer layer 23T. The polymer dispersion type has a large number of isolated voids 23D in the transparent polymer layer 23T, and retains the liquid crystal composition in the voids 23D dispersed in the transparent polymer layer 23T. The capsule type retains the liquid crystal composition 23L having a capsule shape in the transparent polymer layer 23T. As a result, voids 23D into which the liquid crystal composition 23L is filled are formed in the transparent polymer layer 23T.

[0031] In the photochromic layer 23, the void diameter of the voids 23D may be 0.1 μm or more and 30 μm or less. By having the void diameter fall within the range of 0.1 μm or more and 30 μm or less, it is possible to enhance the effectiveness of the anisotropy value Rm of the dichroic dye 23P satisfying formulas (1) and (2). The void diameter is measured in a cross section of the photochromic layer 23 along the thickness direction of the photochromic layer 23. In the cross section, if the voids 23D have a circular shape, the diameter of the voids 23D is the void diameter. In the case where the voids 23D have an elliptical shape, the major axis of the voids 23D is the void diameter. In the case where the voids 23D have an irregular shape, the major axis of the ellipse with the smallest major axis among the ellipses circumscribing the voids 23D is the void diameter of the voids 23D.

[0032] An example of the liquid crystal compound 23LM is any one selected from the group consisting of Schiff bases, azos, azoxys, biphenyls, terphenyls, benzoates, tolanes, pyrimidines, cyclohexanecarboxylic acid esters, phenylcyclohexanes, and dioxanes. The liquid crystal composition 23L contains, as the liquid crystal compound 23LM, a positive nematic liquid crystal having positive dielectric anisotropy.

[0033] The concentration of the liquid crystal compound 23LM in the light-controlling layer 23 is the percentage of the mass of the liquid crystal composition 23L with respect to the total mass of the light-controlling layer 23. In other words, the concentration of the liquid crystal compound 23LM is the percentage of the mass of the liquid crystal compound 23LM with respect to the sum of the mass of the transparent polymer layer 23T and the mass of the liquid crystal composition 23L. The concentration of the liquid crystal compound 23LM may be, for example, 45% by mass or more, or 55% by mass or more.

[0034] The dichroic dye 23P has an elongated shape. The absorbance in the visible region in the long axis direction of the dichroic dye 23P molecule is greater than the absorbance in the visible region in the short axis direction of the molecule. The dichroic dye 23P is nearly transparent when the long axis direction is parallel or approximately parallel to the incident direction of light. In contrast, the dichroic dye 23P exhibits a predetermined color when the long axis direction is perpendicular or approximately perpendicular to the incident direction of light.

[0035] Therefore, the dichroic dye 23P exhibits transparency when oriented such that its long axis direction is parallel or substantially parallel to the normal direction of the contact surface of the light-modulating layer 23 with the first transparent electrode layer 21 and the contact surface of the light-modulating layer 23 with the second transparent electrode layer 22. In contrast, the dichroic dye 23P exhibits a predetermined color when oriented such that its long axis direction is perpendicular or substantially perpendicular to the normal direction of the contact surface of the light-modulating layer 23 with the first transparent electrode layer 21 and the contact surface of the light-modulating layer 23 with the second transparent electrode layer 22. The color exhibited by the dichroic dye 23P is preferably black or a color close to black. The dichroic dye 23P is driven in a guest-host mode using the liquid crystal compound 23LM as a host, thereby causing the dichroic dye 23P to exhibit color.

[0036] The dichroic dye 23P may be at least one selected from the group consisting of polyiodine, azo compounds, anthraquinone compounds, naphthoquinone compounds, azomethine compounds, tetrazine compounds, quinophthalone compounds, merocyanine compounds, perylene compounds, and dioxazine compounds. The dichroic dye 23P may be one type of dye or a combination of two or more types of dyes. From the viewpoint of improving the light resistance of the dichroic dye 23P and increasing the dichroic ratio, the dichroic dye 23P is preferably at least one selected from the group consisting of azo compounds and anthraquinone compounds. The dichroic dye 23P is more preferably an azo compound.

[0037] The liquid crystal composition 23L may contain, in addition to the liquid crystal compound 23LM and the dichroic dye 23P described above, a monomer for forming the transparent polymer layer 23T, for example.

[0038] As shown in Figure 2, when no voltage is applied to the light-controlling layer 23, the liquid crystal compound 23LM is randomly oriented. As a result, the dichroic dye 23P is randomly oriented, just like the liquid crystal compound 23LM. Therefore, the light-controlling layer 23, and therefore the light-controlling sheet 11N, is opaque when no voltage is applied to the light-controlling layer 23. As a result, the light-controlling sheet 11N exhibits a first state having a relatively high haze value. Furthermore, the light-controlling sheet 11N exhibits a predetermined color due to the dichroic dye 23P.

[0039] The haze value of the light-controlling sheet 11N in the first state is 80% or more. The haze value is obtained by a measurement method conforming to ASTM D 1003-00. An example of an instrument for measuring the haze value is a BYK haze-gard i instrument (manufactured by BYK Gardner). When measuring the haze value, the light rays contained in the light beam incident on the light-controlling sheet 11N are straight rays. The maximum angle between the light rays contained in the light beam incident on the light-controlling sheet 11N and the optical axis of the light beam is less than 3°. The light-controlling sheet 11N is fixed so that the surface of the light-controlling sheet 11N and the light beam incident on the surface are approximately perpendicular, within ±2°.

[0040] As shown in FIG. 3 , when a voltage is applied to the light-controlling layer 23, the liquid crystal compound 23LM is aligned parallel to the electric field. The light-controlling sheet 11N is configured so that when a voltage is applied to the light-controlling layer 23, the long axis direction of the liquid crystal compound 23LM is perpendicular to the contact surface. That is, the liquid crystal compound 23LM is aligned vertically. As a result, the dichroic dye 23P is aligned vertically, just like the liquid crystal compound 23LM. Therefore, the light-controlling layer 23, and therefore the light-controlling sheet 11N, is transparent when a voltage is applied to the light-controlling layer 23. As a result, the light-controlling sheet 11N exhibits a second state having a relatively low haze value. Furthermore, the light-controlling sheet 11N does not exhibit the predetermined color due to the dichroic dye 23P.

[0041] [Second light control device] The second light control device will be described with reference to Figures 4 to 6. The second light control device differs from the first light control device 10N described above in that it includes a reverse-type light control sheet. Therefore, the following will describe in detail the differences between the second light control device and the first light control device 10N, while the components of the second light control device that are common to the first light control device 10N will be denoted by the same reference numerals as the first light control device 10N, and detailed descriptions of those components will be omitted.

[0042] 4 , the second light control device 10R includes a reverse-type light control sheet 11R and a drive unit 12. The light control sheet 11R includes a first alignment layer 37 and a second alignment layer 38. The first alignment layer 37 is located between the light control layer 23 and the first transparent electrode layer 21. The second alignment layer 38 is located between the light control layer 23 and the second transparent electrode layer 22.

[0043] The first alignment layer 37 and the second alignment layer 38 are vertical alignment films that align the long axis direction of the liquid crystal compound so that it is perpendicular to the surface opposite to the surface in contact with the first transparent electrode layer 21 and the surface opposite to the surface in contact with the second transparent electrode layer 22. In this way, the alignment layers 37 and 38 regulate the orientation of the multiple liquid crystal compounds contained in the light control layer 23.

[0044] The materials for forming the first alignment layer 37 and the second alignment layer 38 are organic compounds, inorganic compounds, and mixtures thereof. Examples of organic compounds include polyimide, polyamide, polyvinyl alcohol, and cyanide compounds. Examples of inorganic compounds include silicon oxide and zirconium oxide. The material for forming the alignment layers 37 and 38 may be silicone. Silicone is a compound having both inorganic and organic portions.

[0045] The light-controlling layer 23 will be described in more detail with reference to Figures 5 and 6. As shown in Figure 5, the light-controlling layer 23, like the light-controlling layer 23 provided in the normal-type light-controlling sheet 11N, includes a transparent polymer layer 23T including voids 23D and a liquid crystal composition 23L filled in the voids 23D. The liquid crystal composition 23L includes a liquid crystal compound 23LM and a dichroic dye 23P. However, the liquid crystal composition 23L includes, as the liquid crystal compound 23LM, a negative-type nematic liquid crystal with negative dielectric anisotropy.

[0046] As shown in Figure 5, when no voltage is applied to the light-controlling layer 23, the liquid crystal compound 23LM is aligned perpendicular to the contact surface due to the alignment restricting force of the alignment layers 37 and 38. As a result, the dichroic dye 23P is aligned perpendicular to the liquid crystal compound 23LM. Therefore, the light-controlling layer 23, and therefore the light-controlling sheet 11R, is transparent when no voltage is applied to the light-controlling layer 23. As a result, the light-controlling sheet 11R exhibits a second state having a relatively low haze value. Furthermore, the light-controlling sheet 11R does not exhibit the color due to the dichroic dye 23P.

[0047] As shown in FIG. 6 , when a voltage is applied to the light-controlling layer 23, the liquid crystal compound 23LM is aligned perpendicular to the electric field. The light-controlling sheet 11R is configured so that when a voltage is applied to the light-controlling layer 23, the long axis direction of the liquid crystal compound 23LM is parallel to the contact surface. That is, the liquid crystal compound 23LM is aligned horizontally. However, the azimuth angle of the long axis direction is random within the plane in which the liquid crystal compound 23LM is located. As a result, the dichroic dye 23P is aligned horizontally, similar to the liquid crystal compound 23LM. However, the azimuth angle of the longitudinal direction of the dichroic dye 23P is random within the plane in which the dichroic dye 23P is located. Therefore, the light-controlling layer 23, and therefore the light-controlling sheet 11R, is opaque when a voltage is applied to the light-controlling layer 23. As a result, the light-controlling sheet 11R exhibits a first state having a relatively high haze value. The light controlling sheet 11R exhibits a predetermined color due to the dichroic dye 23P.

[0048] [Optical Properties of Light Control Sheet] The optical properties of the light control sheets 11N and 11R will be described with reference to Figures 7 to 11. The light control sheet 11R has a vertical alignment layer, while the light control layer 23 is common in that it contains a transparent polymer layer 23T and a liquid crystal composition 23L containing a dichroic dye 23P. Therefore, the following description of the optical properties of the light control sheet 11N will be used instead of the description of the optical properties of the light control sheet 11R.

[0049] The dimming sheet 11N of the present disclosure has a total light transmittance T of 10% or more and 80% or less when in the second state, and an anisotropy value Rm of the dichroic dye 23P of 0.25 or more and 0.94 or less, and in addition satisfies any of the following conditions:

[0050] (Condition 1) The concentration of the liquid crystal compound 23LM is 45% by mass or more, and the anisotropy value Rm of the dichroic dye 23P satisfies the following formula (1): Anisotropy value Rm≧0.3434ln(T)−0.4297 formula (1) In formula (1), ln is the natural logarithm.

[0051] (Condition 2) The concentration of the liquid crystal compound 23LM is 55% by mass or more, and the anisotropy value Rm of the dichroic dye 23P satisfies the following formula (2): Anisotropy value Rm≧0.2989ln(T)−0.3472 formula (2) In formula (2), ln is the natural logarithm.

[0052] The anisotropy value Rm, which is one of the parameters indicating the light absorption characteristics of the dichroic dye 23P contained in the light controlling sheet 11N, is defined by the following formula (4): Rm={E(p)-E(s)} / {E(p)+2×E(s)} (4)

[0053] In equation (4), absorbance E(p) is the measured value of the absorbance of light polarized parallel to the alignment direction of the liquid crystal compound. In other words, it is the measured value of the absorbance in a horizontally aligned cell containing only a liquid crystal compound and a dichroic dye, with the dichroic dye horizontally aligned. Absorbance E(s) is the measured value of the absorbance of light polarized perpendicular to the alignment direction of the liquid crystal compound. In other words, it is the measured value of the absorbance in a vertically aligned cell, with the dichroic dye vertically aligned. The light used to measure absorbances E(p) and E(s) has a wavelength of 550 nm.

[0054] On the other hand, the absorbances E(p) and E(s) can also be expressed by the following equations: E(p)=εp×d×c (5) E(s)=εs×d×c (6)

[0055] In equations (5) and (6), the absorption coefficient εp is the absorption coefficient of the dichroic dye 23P when the dichroic dye is horizontally aligned in a horizontally aligned cell. The absorption coefficient εs is the absorption coefficient of the dichroic dye 23P when the dichroic dye 23P is vertically aligned in a vertically aligned cell. d is the thickness of the horizontally aligned cell. c is the concentration of the dichroic dye.

[0056] On the other hand, the dichroic ratio DR of the dichroic dye 23P is expressed by the following formula (7): DR=E(p) / E(s) Formula (7) The dichroic ratio DR can be expressed as follows from formulas (5) to (7): DR=(εp×d×c) / (εs×d×c)=εp / εs Formula (8) Therefore, it can be said that the dichroic ratio DR is a value specific to the liquid crystal composition 23L.

[0057] Similarly, from equations (4) to (6), the calculated anisotropy value Rc can be expressed as follows: Rc=(DR-1) / (DR+2) ... equation (9) Therefore, like the dichroic ratio DR, the anisotropy value Rc can be said to be a value specific to the liquid crystal composition 23L.

[0058] In contrast, in the light-modulating sheet 11N of the present disclosure, the light-modulating layer 23 includes the transparent polymer layer 23T, and therefore the absorbances E(p) and E(s) are expressed by the following equations: E(p) = εp × d × n × c Equation (10) E(s) = εs × d × c Equation (6)

[0059] In formula (10), the absorption coefficient εp, thickness d, and concentration c are the same as the absorption coefficient εp, thickness d, and concentration c included in formula (5). Meanwhile, n is an extension coefficient of the effective optical path length as a result of refraction and scattering of light at the interface between the liquid crystal composition 23L and the transparent polymer layer 23T. The extension coefficient n varies depending on the thickness of the light-controlling layer 23, the difference in refractive index between the liquid crystal compound 23LM and the transparent polymer layer 23T, and other factors.

[0060] As a result, the dichroic ratio DR is expressed by the following formula: DR = (εp × d × n × c) / (εs × d × c) = (εp × n) / εs ... Formula (11) Therefore, in the light-controlling sheet 11N having the light-controlling layer 23 including the transparent polymer layer 23T, the dichroic ratio DR is not a value specific to the liquid crystal composition 23L.

[0061] As described above, the extension coefficient n varies depending on the thickness of the light-adjusting layer 23 and the refractive index of the liquid crystal compound 23LM, specifically, the difference between the refractive index ne of extraordinary light and the refractive index np of the transparent polymer layer 23T. Additionally, the light-adjusting layer 23 includes a liquid crystal composition 23L and a transparent polymer layer 23T, and the dichroic dye 23P is included in both the liquid crystal composition 23L and the transparent polymer layer 23T. The orientation of the dichroic dye 23P included in the liquid crystal composition 23L changes depending on whether or not a voltage is applied to the light-adjusting layer 23, which changes the absorbance of the dichroic dye 23P. In contrast, the orientation of the dichroic dye 23P included in the transparent polymer layer 23T is fixed, so the absorbance of the dichroic dye 23P does not change. The amount of dichroic dye 23P contained in the transparent polymer layer 23T varies depending on the concentration of the liquid crystal compound 23LM in the light-adjusting layer 23, so the absorbance of the light-adjusting sheet 11N varies depending on the concentration of the liquid crystal compound 23LM in the light-adjusting layer 23.

[0062] The following describes the relationship between the contrast in the light controlling sheet 11N of the present disclosure and the thickness of the light controlling layer 23. The light controlling sheet 11N for measuring the contrast was produced using the following materials.

[0063] (a) Transparent electrode layers 21, 22: indium tin oxide (b) Transparent substrates 24, 25: polyethylene terephthalate (c) Spacers: spherical particles made of silicon dioxide (d) Liquid crystal compound 23LM: fluorine-based liquid crystal compound (e) Polymerization initiator: photopolymerization initiator (Irgacure Oxe04, manufactured by BASF) (f) Polymerizable composition: one or more members selected from the group consisting of monofunctional acrylate, polyfunctional acrylate, monofunctional methacrylate, urethane acrylate, and polyester acrylate (g) Dichroic dye 23P: azo-based compound mixed dye (yellow, blue, red)

[0064] (g) For the dichroic dye 23P, the dichroic ratio DR calculated by the above-mentioned formula (8) was 16, and the anisotropy value Rm calculated by formula (4) was 0.83. Furthermore, the refractive index ne of the extraordinary light of the liquid crystal compound 23LM (d) was 1.68, and the refractive index np of the transparent polymer layer 23T formed by polymerization (f) was 1.51. Therefore, the value obtained by subtracting the refractive index np of the transparent polymer layer 23T from the refractive index ne of the extraordinary light of the liquid crystal compound 23LM was 0.17.

[0065] The dichroic ratio DR was calculated using the measurement results of the extinction coefficients εp and εs, the thickness d of the horizontally aligned cell, the thickness d of the vertically aligned cell, and the concentration c. The spectra for obtaining the extinction coefficients εp and εs and the absorbances E(p) and E(s) were measured using a UV-Vis-NIR spectrophotometer (Lambda 1050, manufactured by Perkin Elmer).

[0066] A first transparent substrate 24 having a first transparent electrode layer 21 and a second transparent substrate 25 having a second transparent electrode layer 22 were prepared. Next, a coating liquid containing liquid crystal compound 23LM, a polymerization initiator, a polymerizable compound, and a spacer was prepared. At this time, the percentage of the mass of liquid crystal compound 23LM relative to the total mass of the coating liquid, i.e., the concentration of liquid crystal compound 23LM, was set to 55 mass%. Furthermore, the percentage of the mass of dichroic dye 23P relative to the total mass of the coating liquid, i.e., the concentration of dichroic dye 23P, was set to 2.5 mass%.

[0067] A coating film was formed between the first transparent electrode layer 21 and the second transparent electrode layer 22 using a coating liquid, and then the polymerizable composition was polymerized in the coating film to obtain a light-controlling sheet 11N. A plurality of light-controlling sheets 11N with different thicknesses were manufactured to evaluate the dichroic ratio DR. The thickness of each light-controlling sheet 11N was set to a value within the range of 6 μm to 25 μm.

[0068] The contrast of each light-adjusting sheet 11N was measured by the following method: The contrast was calculated by dividing the total light transmittance when the light-adjusting sheet 11N was in the second state by the total light transmittance when the light-adjusting sheet 11N was in the first state.

[0069] The total light transmittance of each light-controlling sheet 11N was calculated using the following method. For each of the above-mentioned light-controlling sheets 11N, the total light transmittance in the first state and the total light transmittance in the second state were calculated using a method in accordance with ASTM D 1003-00. For each light-controlling sheet 11N, the second state was set to a state in which an AC voltage having a rectangular waveform of 50 Hz and 40 V was applied between a pair of transparent electrode layers. On the other hand, the first state was set to a state in which no voltage was applied between the pair of transparent electrodes for each light-controlling sheet 11N. A haze / transparency measuring instrument (BYK haze-gard i instrument, manufactured by BYK Gardner) was used to calculate the total light transmittance.

[0070] The contrast of the light-adjusting sheet 11N was as shown in Figure 7. As shown in Figure 7, it was found that the contrast of the light-adjusting sheet 11N tends to increase as the thickness of the light-adjusting layer 23 increases. In other words, it was found that when the dichroic dye 23P is applied to the light-adjusting layer 23 including the transparent polymer layer 23T, the contrast is not uniquely determined. Furthermore, when the thickness of the light-adjusting layer 23 is less than 21 μm, the contrast of the light-adjusting sheet 11N is less than the dichroic ratio DR of 16 calculated by equation (8). In contrast, when the thickness of the light-adjusting layer 23 is 21 μm or more, the contrast of the light-adjusting sheet 11N is greater than or equal to the dichroic ratio DR calculated by equation (8).

[0071] When the thickness of the light-controlling layer 23 is less than 21 μm, the contrast in the light-controlling sheet 11N is thought to fall below 16 for the following reason: The inclusion of the transparent polymer layer 23T in the light-controlling layer 23 increases the optical path length within the light-controlling layer 23, thereby increasing the dichroic ratio DR. However, this increase is thought to be outweighed by the decrease in the dichroic ratio DR due to the fixed orientation of the dichroic dye 23P contained in the transparent polymer layer 23T.

[0072] In contrast, when the thickness of the light-adjusting layer 23 is 21 μm or more, the contrast in the light-adjusting sheet 11N is considered to be 16 or more for the following reason: The inclusion of the transparent polymer layer 23T in the light-adjusting layer 23 increases the optical path length within the light-adjusting layer 23, and this increase in contrast is considered to outweigh the decrease in contrast caused by the fixed orientation of the dichroic dye 23P contained in the transparent polymer layer 23T.

[0073] The total light transmittance T was measured for each of the light-controlling sheets 11N for which the contrast was calculated. Furthermore, a plurality of light-controlling sheets 11N were produced in the same manner as when the concentration of liquid crystal compound 23LM was 55% by mass, except that the concentration of liquid crystal compound 23LM was changed to 45% by mass. In the coating liquid for forming a light-controlling layer having a concentration of liquid crystal compound 23LM of 45% by mass, the amount of the polymerizable composition was increased by the amount of the liquid crystal compound 23LM reduced in the coating liquid having a concentration of liquid crystal compound 23LM of 55% by mass.

[0074] The total light transmittance T of each light controlling sheet 11N was measured using the same method as when the contrast of the light controlling sheet 11N was measured.

[0075] The measurement results of the total light transmittance T were as shown in Figure 8. In Figure 8, the relationship between the total light transmittance T and the thickness of the light-controlling layer 23 when the concentration of the liquid crystal compound 23LM was 55% by mass is shown by a solid line, and the relationship between the total light transmittance T and the thickness of the light-controlling layer 23 when the concentration of the liquid crystal compound 23LM was 45% by mass is shown by a dashed line.

[0076] 8, when the thickness of the light-controlling layer 23 is in the range of 6 μm or more and 25 μm or less, the total light transmittance T when the concentration of the liquid crystal compound 23LM is 55 mass % is higher than the total light transmittance T when the concentration of the liquid crystal compound 23LM is 45 mass %. Furthermore, regardless of the concentration of the liquid crystal compound 23LM, it is found that the light-controlling sheet 11N has a tendency for the total light transmittance T to decrease as the thickness of the light-controlling layer 23 increases.

[0077] In each light controlling sheet 11N, the refractive index no of ordinary light in the liquid crystal compound 23LM is equal to the refractive index np of the transparent polymer layer 23T. Therefore, in each light controlling sheet 11N exhibiting the second state, it can be considered that no refraction or scattering of light incident on the light controlling sheet 11N occurs within the light controlling sheet 11N.

[0078] Furthermore, in the light controlling sheet 11N exhibiting the second state, the absorption coefficient of the liquid crystal composition 23L differs from the absorption coefficient of the transparent polymer layer 23T. As described above, the absorption coefficient of the liquid crystal composition 23L is εs. In contrast, when the major axis directions of the dichroic dye 23P contained in the transparent polymer layer 23T are random, the absorption coefficient of the transparent polymer layer 23T is considered to be expressed by the following formula: (εp+2εs) / 3 ... Formula (12)

[0079] Because the absorption coefficient εp is greater than the absorption coefficient εs, the absorption coefficient in the transparent polymer layer 23T is also greater than the absorption coefficient εs. Therefore, when the volume of the transparent polymer layer 23T in the light-controlling layer 23 increases, i.e., when the volume of the liquid crystal composition 23L decreases, the proportion of the dichroic dye 23P located in the transparent polymer layer 23T increases, which is thought to result in a decrease in the total light transmittance of the light-controlling sheet 11N. The measurement results shown in Figure 8 also show that the transmittance when the concentration of the liquid crystal compound 23LM is 45% by mass is lower than the transmittance when the concentration of the liquid crystal compound 23LM is 55% by mass.

[0080] The contrast of each light controlling sheet 11N in which the concentration of the liquid crystal compound 23LM was 45% by mass was calculated in the same manner as that of each light controlling sheet 11N in which the concentration of the liquid crystal compound 23LM was 55% by mass.

[0081] Furthermore, for each light-controlling sheet 11N containing 55% by mass of liquid crystal compound 23LM, the haze value was calculated when the light-controlling sheet 11N was in the first state. The haze value was calculated using a method conforming to ASTM D 1003-00, similar to the calculation of the total light transmittance T, and a haze / transparency measuring instrument (BYK haze-gard instrument, manufactured by BYK Gardner) was used. The haze value of the light-controlling sheet 11N was 80% or more and 99% or less, i.e., 80% or more, and it was observed that the haze value of the light-controlling sheet 11N monotonically increased as the thickness of the light-controlling sheet 11N increased from 6 μm to 25 μm. When the light-controlling sheet 11N was in the first state, the effectiveness of the above-mentioned formulas (1) to (3) could be enhanced by having the light-controlling sheet 11N be 80% or more.

[0082] 9 shows the relationship between contrast and total light transmittance T in the light-adjusting sheet 11N. The total light transmittance T is the total light transmittance when the light-adjusting sheet 11N is in the second state. In FIG. 9, the relationship between the total light transmittance T and contrast when the concentration of the liquid crystal compound 23LM is 55% by mass is shown by a solid line, and the relationship between the total light transmittance T and contrast when the concentration of the liquid crystal compound 23LM is 45% by mass is shown by a dashed line.

[0083] As shown in Figure 9, regardless of the concentration of liquid crystal compound 23LM, the light controlling sheet 11N tended to have a lower total light transmittance T as the contrast increased. Furthermore, when the concentration of liquid crystal compound 23LM was 55% by mass, the contrast was found to be 2 or greater when the total light transmittance T was 47.6% or less. In contrast, when the concentration of liquid crystal compound 23LM was 45% by mass, the contrast was found to be 2 or greater when the total light transmittance T was 34.0% or less. When the contrast of the light controlling sheet 11N is 2 or greater, it is possible to achieve a difference of more than two times in the amount of light transmitted through the light controlling sheet 11N between when the sheet is in the first state and when it is in the second state. Therefore, the light controlling sheet 11N can satisfy the light quantity changing function required of the light controlling sheet 11N. Regardless of the concentration of the liquid crystal compound 23LM, the total light transmittance T when the contrast is 2 or more corresponds to the total light transmittance T when the thickness of the light-controlling layer 23 is 9 μm or more.

[0084] Additionally, multiple dichroic pigments 23P were prepared, each with a different anisotropy value Rm, calculated by Equation (4), within the range of 0.25 to 0.94. The dichroic pigments 23P with a specific anisotropy value Rm may be a single dichroic pigment or a mixed pigment containing two or more dichroic pigments. For the light-controlling sheet 11N containing each dichroic pigment 23P, the total light transmittance T was measured and the contrast calculated using the same method as for the dichroic pigment 23P with an anisotropy value Rm of 0.83 described above. Thus, the total light transmittance T at a contrast of 2 was calculated for each light-controlling sheet 11N containing each dichroic pigment 23P.

[0085] The calculated anisotropy value Rm of the dichroic dye 23P contained in the light-controlling sheet 11N and the measured total light transmittance T were as shown in Table 1 below.

[0086]

[0087] The calculation results of the anisotropy value Rm of the dichroic dye 23P in the light-modulating sheet 11N, whose contrast was less than 2, and the measurement results of the total light transmittance T were as shown in Table 2 below.

[0088]

[0089] 10 and 11 show the relationship between the anisotropy value Rm and the total light transmittance T when the contrast is 2. Note that Fig. 10 shows the relationship between the anisotropy value Rm and the total light transmittance T when the concentration of liquid crystal compound 23LM is 55% by mass. In contrast, Fig. 11 shows the relationship between the anisotropy value Rm and the total light transmittance T when the concentration of liquid crystal compound 23LM is 45% by mass.

[0090] The approximate curve shown in Fig. 10 can be expressed by the following formula (13): Rm = 0.2989 ln(T) - 0.3472 (formula (13)) The approximate curve shown in Fig. 11 can be expressed by the following formula (14): Rm = 0.3434 ln(T) - 0.4297 (formula (14))

[0091] 10 and 11 , it was found that, in order to obtain the same total light transmittance T, when the concentration of liquid crystal compound 23LM is 45% by mass, the light-controlling layer 23 needs to contain a dichroic dye 23P with a higher anisotropy value Rm than when the concentration of liquid crystal compound 23LM is 55% by mass. Furthermore, as described above with reference to FIG. 9 , the contrast tends to increase as the total light transmittance T decreases. Therefore, when the concentration of liquid crystal compound 23LM is 45% by mass or more, it is sufficient that the anisotropy value Rm calculated by formula (4) is equal to or greater than formula (14). Furthermore, when the concentration of liquid crystal compound 23LM is 55% by mass or more, it is sufficient that the anisotropy value Rm calculated by formula (4) is equal to or greater than formula (13).

[0092] Thus, the light-controlling sheet 11N of the present disclosure satisfies either condition 1 or condition 2 described above. According to the light-controlling sheet 11N of the present disclosure, the anisotropy value Rm, which can be calculated from the absorbances E(p) and E(s) specific to the dichroic dye 23P, satisfies either formula (1) or formula (2), thereby making it possible to obtain a light-controlling sheet 11N having a contrast of 2 or more. In other words, in the light-controlling sheet 11N capable of exhibiting black in the first state, it is possible to increase the contrast, which is the ratio of the luminance in the second state to the luminance in the first state. Note that, in the present disclosure, the luminance in the first state and the luminance in the second state are the total light transmittance T in each state.

[0093] Furthermore, the value obtained by subtracting the refractive index np of the transparent polymer layer 23T from the refractive index ne of the extraordinary light in the liquid crystal compound 23LM may be 0.17 or more, which can enhance the effectiveness of extending the optical path length by refraction and scattering at the interface between the liquid crystal composition 23L and the transparent polymer layer 23T.

[0094] [Method for Manufacturing Light Control Sheet] The method for manufacturing a light control sheet of the present disclosure includes preparing a coating liquid containing a liquid crystal compound, a dichroic dye, and a polymerizable composition, forming a coating film between the first transparent electrode layer 21 and the second transparent electrode layer 22 using the coating liquid, and polymerizing the polymerizable composition in the coating film. Preparing the coating liquid includes adjusting the coating liquid so that the percentage of the mass of the liquid crystal compound 23LM relative to the total mass of the coating liquid is 45 mass% or more, and selecting a dichroic dye 23P having an anisotropy value Rm of 0.25 to 0.94 and satisfying the following formula (1): The total light transmittance T of the light control sheets 11N and 11R exhibiting the second state is 10% to 80%. Anisotropy value Rm≧0.3434ln(T)−0.4297 … formula (1)

[0095] When the coating liquid is prepared so that the mass percentage of the liquid crystal compound 23LM is 55 mass % or more, the dichroic dye 23P having an anisotropy value Rm that satisfies the following formula (2) may be selected: Anisotropy value Rm≧0.2989ln(T)−0.3472 (Formula (2))

[0096] Below, the process of forming the light-controlling layer 23 in the manufacturing method of the light-controlling sheets 11N and 11R will be explained in more detail. Note that the reverse-type light-controlling sheet 11R differs from the normal-type light-controlling sheet 11N in that it has a pair of alignment layers 37 and 38, which are vertical alignment films. However, the process of forming the light-controlling layer 23 provided in the reverse-type light-controlling sheet 11R is common to the process of forming the light-controlling layer 23 provided in the normal-type light-controlling sheet 11N. Therefore, below, we will explain the method of manufacturing the normal-type light-controlling sheet 11N, while omitting an explanation of the method of manufacturing the reverse-type light-controlling sheet 11R.

[0097] When manufacturing the light controlling sheet 11N, first, a first transparent substrate 24 on which a first transparent electrode layer 21 is formed and a second transparent substrate 25 on which a second transparent electrode layer 22 is formed are prepared.

[0098] Next, a coating liquid containing liquid crystal compound 23LM, dichroic dye 23P, and a polymerizable composition is prepared. As described above, the coating liquid may contain a polymerization initiator and may also contain a spacer. The polymerization initiator may be, for example, a photopolymerization initiator. The spacer may have, for example, a spherical shape, and in this case, the diameter of the spacer is appropriately set depending on the thickness required for the light-controlling layer 23. At this time, the coating liquid is prepared so that the percentage of the mass of liquid crystal compound 23LM relative to the mass of the coating liquid, i.e., the blending ratio of liquid crystal compound 23LM, is 45 mass% or more or 55 mass% or more.

[0099] Next, a coating film is formed between the first transparent electrode layer 21 and the second transparent electrode layer 22 using a coating liquid. For example, after forming a coating film on the first alignment layer 37 using the coating liquid, the second alignment layer 38 is superimposed on the coating film, thereby sandwiching the coating film between the first transparent electrode layer 21 and the second transparent electrode layer 22.

[0100] The polymerizable composition in the coating film is polymerized by irradiating the laminate including the pair of transparent electrode layers 21, 22 and the coating film with light. During this process, for example, ultraviolet light is irradiated onto the laminate. By irradiating the coating film with ultraviolet light, the polymerizable composition is polymerized so as to phase-separate the liquid crystal compound 23LM and the transparent polymer layer 23T. As a result, the transparent polymer layer 23T having voids 23D is formed from the polymerizable composition, and the liquid crystal composition 23L containing the liquid crystal compound 23LM and the dichroic dye 23P is positioned in the voids 23D.

[0101] As described above, one embodiment of the light controlling sheet can provide the following effects: (1) When the concentration of the liquid crystal compound is 45% by mass or more, the anisotropy value Rm is equal to or greater than the formula (1), thereby enabling the contrast to be increased in the light controlling sheets 11N and 11R that can exhibit color in the first state.

[0102] (2) When the concentration of the liquid crystal compound is 55% by mass or more, the anisotropy value Rm is equal to or greater than formula (2), thereby enabling the contrast to be increased in the dimming sheets 11N and 11R, which can exhibit color in the first state.

[0103] (3) When the light-adjusting sheets 11N and 11R are in the first state, the effectiveness of satisfying the above-mentioned formula (1) or formula (2) can be enhanced by having the haze value of the light-adjusting sheets 11N and 11R be 80% or more.

[0104] (4) By having the void diameter fall within the range of 0.1 μm or more and 30 μm or less, it is possible to enhance the effectiveness of the anisotropy value Rm of the dichroic dye 23P satisfying the above-mentioned formula (1) or formula (2).

[0105] (5) When the value obtained by subtracting the refractive index np from the refractive index ne is 0.17 or more, it is possible to increase the effectiveness of extending the optical path length by refraction and scattering at the interface between the liquid crystal composition 23L and the transparent polymer layer 23T.

Claims

1. A light-controlling sheet comprising: a first transparent electrode layer; a second transparent electrode layer; and a light-controlling layer located between the first transparent electrode layer and the second transparent electrode layer, the light-controlling layer including a transparent polymer layer including a plurality of voids and a liquid crystal composition filled in the voids, the light-controlling sheet exhibiting a first state and a second state having a lower haze value than the first state depending on the magnitude of a voltage applied to the light-controlling layer, the liquid crystal composition including a liquid crystal compound and one or more dichroic dyes, the percentage of the mass of the liquid crystal compound relative to the sum of the mass of the transparent polymer layer and the mass of the liquid crystal composition being 45 mass% or more, the total light transmittance T of the light-controlling sheet exhibiting the second state being 10% or more and 80% or less, the anisotropy value Rm of the dichroic dye being 0.25 or more and 0.94 or less, and satisfying the following formula (1): anisotropy value Rm≧0.3434ln(T)-0.4297 ... formula (1) In formula (1), ln is the natural logarithm of the light-control sheet.

2. A light-controlling sheet comprising: a first transparent electrode layer; a second transparent electrode layer; and a light-controlling layer located between the first transparent electrode layer and the second transparent electrode layer, the light-controlling layer including a transparent polymer layer including a plurality of voids and a liquid crystal composition filled in the voids, the light-controlling sheet exhibiting a first state and a second state having a lower haze value than the first state depending on the magnitude of a voltage applied to the light-controlling layer, the liquid crystal composition including a liquid crystal compound and one or more dichroic dyes, the percentage of the mass of the liquid crystal compound relative to the sum of the mass of the transparent polymer layer and the mass of the liquid crystal composition being 55 mass % or more, the total light transmittance T of the light-controlling sheet exhibiting the second state being 10% or more and 80% or less, the anisotropy value Rm of the dichroic dye being 0.25 or more and 0.94 or less, and satisfying the following formula (2): anisotropy value Rm≧0.2989ln(T)-0.3472 ... formula (2) In equation (2), ln is the natural logarithm of the light-control sheet.

3. A light-adjusting sheet as described in claim 1 or 2, wherein the haze value of the light-adjusting sheet exhibiting the first state is 80% or more.

4. The light-adjusting sheet according to claim 1 or 2, wherein the void diameter is from 0.1 μm to 30 μm.

5. The light-controlling sheet according to claim 1 or 2, wherein the value obtained by subtracting the refractive index of said transparent polymer layer from the refractive index of extraordinary light in said liquid crystal compound is 0.17 or more.

6. A light control device comprising: a light control sheet according to claim 1 or 2; and a drive unit configured to be able to apply a voltage to the light control layer of the light control sheet.

7. A method for producing a light-controlling sheet comprising: a first transparent electrode layer; a second transparent electrode layer; and a light-controlling layer located between the first transparent electrode layer and the second transparent electrode layer, the light-controlling layer comprising a transparent polymer layer including a plurality of voids and a liquid crystal composition filled in the voids, the light-controlling sheet exhibiting a first state and a second state having a lower haze value than the first state depending on the magnitude of a voltage applied to the light-controlling layer, the method comprising: preparing a coating liquid including a liquid crystal compound, a dichroic dye, and a polymerizable composition; forming a coating film between the first transparent electrode layer and the second transparent electrode layer using the coating liquid; and polymerizing the polymerizable composition in the coating film, the method comprising: adjusting the coating liquid such that a percentage of the mass of the liquid crystal compound relative to the total mass of the coating liquid is 45 mass% or more; and selecting the dichroic dye having an anisotropy value Rm of 0.25 to 0.94 and satisfying the following formula (1): A method for producing a light-controlling sheet, wherein the total light transmittance T of the light-controlling sheet exhibiting the second state is 10% or more and 80% or less; and anisotropy value Rm≧0.3434ln(T)−0.4297 (1), where ln is a natural logarithm.

8. A method for producing a light-controlling sheet comprising: a first transparent electrode layer; a second transparent electrode layer; and a light-controlling layer located between the first transparent electrode layer and the second transparent electrode layer, the light-controlling layer comprising a transparent polymer layer including a plurality of voids and a liquid crystal composition filled in the voids, the light-controlling sheet exhibiting a first state and a second state having a lower haze value than the first state depending on the magnitude of a voltage applied to the light-controlling layer, the method comprising: preparing a coating liquid including a liquid crystal compound, a dichroic dye, and a polymerizable composition; forming a coating film between the first transparent electrode layer and the second transparent electrode layer using the coating liquid; and polymerizing the polymerizable composition in the coating film, the method comprising: adjusting the coating liquid such that a percentage of the mass of the liquid crystal compound relative to the total mass of the coating liquid is 55 mass% or more; and selecting the dichroic dye having an anisotropy value Rm of 0.25 to 0.94 and satisfying the following formula (2): A method for manufacturing a light-controlling sheet, wherein the total light transmittance T of the light-controlling sheet exhibiting the second state is 10% or more and 80% or less; and anisotropy value Rm≧0.2989ln(T)−0.3472 (2), where ln is a natural logarithm.

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