JP7806599B2 - dimmer - Google Patents

Description

This disclosure relates to a light control device equipped with a light control sheet that reversibly changes from transparent to opaque.

Normal-type light-control sheets have a light-control layer containing liquid crystal compounds. The drive signal for the light-control sheet creates an electric field in the light-control layer so as to align the long axis direction of the liquid crystal compounds. This allows the normal-type light-control sheet to reversibly change from opaque when not driven to transparent when driven.

A reverse-type light-controlling sheet comprises a light-controlling layer containing a liquid crystal compound and an alignment layer that applies an alignment-controlling force to the liquid crystal compound. One example of the alignment-controlling force is to control the alignment of the liquid crystal compound so that the long axis direction of the liquid crystal compound is approximately perpendicular to the surface direction of the alignment layer when the light-controlling sheet is not driven. The drive signal for the light-controlling sheet forms an electric field that opposes the alignment-controlling force so that the long axis direction of the liquid crystal compound is approximately parallel to the surface direction of the alignment layer. This allows the reverse-type light-controlling sheet to reversibly change from transparent when not driven to opaque when driven (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2019-194654

A light-controlling sheet comprising a transparent polymer layer and particles of a liquid crystal composition dispersed within the transparent polymer layer achieves opacity through scattering by the particles. Adding a dichroic dye to the particles achieves colorless transparency when not driven, while adding color to the opaque surface when driven.

On the other hand, excessively increasing the blend ratio of dichroic dye increases the degree of color when opaque, but weakens dispersion by the particles and reduces the responsiveness of the liquid crystal compound. As a result, there is a new demand for light control devices that contain dichroic dye in the liquid crystal composition, whether normal or reverse type, to increase the contrast of the light control device, that is, to increase the difference in light transmittance between transparent and opaque.

The light control device that solves the above problem comprises a liquid crystal composition containing a liquid crystal compound and a dichroic dye, and a transparent polymer layer having voids filled with the liquid crystal composition. The light control device reversibly changes from transparent to opaque by changing the orientation of the liquid crystal compound, and the absorbance difference, which is the value obtained by subtracting the average absorbance of the liquid crystal composition from the absorbance of the light control device when opaque, is 0.8 or more.

As mentioned above, the contrast of a light control device is the ratio of the total light transmittance when transparent to the total light transmittance when opaque. The total transmitted light of a light control device includes direct light that passes through the device without being scattered by the transparent polymer layer, and scattered light that is scattered by the transparent polymer layer. The total light transmittance of a light control device depends on the sum of the amount of direct light and the amount of scattered light.

Increasing the dichroic dye ratio in a liquid crystal composition simply reduces the amount of scattered light. Increasing the dichroic dye ratio reduces the total light transmittance by the amount of the reduced scattered light, thereby improving contrast. However, the dichroic dye ratio is actually set to approximately the upper limit within the range that achieves the responsiveness of the liquid crystal compound. Ultimately, there is a limit to how much increasing the dichroic dye ratio can improve contrast.

On the other hand, the absorption characteristics of dichroic dyes are such that, based on the dichroic ratio, they exhibit high absorbance for scattered light and low absorbance for linear light. The absorbance of such dichroic dyes increases exponentially and steeply with the optical path length as a variable. Promoting scattering of linear light in the transparent polymer layer reduces the total light transmittance when opaque, thereby enabling improved contrast. However, steep absorption by dichroic dyes requires not only promoting the scattering of linear light, but also increasing scattering to the extent that light scattered at the interface between the transparent polymer layer and the liquid crystal composition reaches the dichroic dye.

Here, the absorbance of the light control device when it is opaque reflects the light scattered at the interface between the transparent polymer layer and the liquid crystal composition being absorbed by the dichroic dye. On the other hand, the absorbance of the liquid crystal composition does not reflect the extension of the optical path length due to scattering, i.e., the increase in absorption due to the extension of the optical path length. The absorbance difference, which is the value obtained by subtracting the average absorbance of the liquid crystal composition from the absorbance when it is opaque, indicates the increase in absorption due to the extension of the optical path length.

Through extensive research into the relationship between the contrast of a light control device and its optical parameters, the inventors discovered a range within the absorbance difference of the light control device that sharply increases contrast. With the above configuration, the absorbance difference of the light control device is 0.8 or greater, making it possible to significantly increase the contrast of the light control device.

The above-mentioned light control device comprises a first light control sheet that reversibly changes from transparent to opaque, and a second light control sheet that reversibly changes from transparent to opaque, wherein the first light control sheet is overlaid on the second light control sheet, the transparent polymer layer is a laminated structure, the first light control sheet comprises a first transparent polymer layer that constitutes the transparent polymer layer, and a first liquid crystal composition that fills the voids in the first transparent polymer layer and constitutes the liquid crystal composition, and the second light control sheet comprises a second transparent polymer layer that constitutes the transparent polymer layer, and a second liquid crystal composition that fills the voids in the second transparent polymer layer and constitutes the liquid crystal composition, and the first light control sheet and the second light control sheet may simultaneously change to opaque.

With the above configuration, one light control device is composed of a first light control sheet and a second light control sheet. Therefore, even if the absorbance difference of the first light control sheet is less than 0.8, a light control device with an absorbance difference of 0.8 or more can be constructed by overlapping the second light control sheet on the first light control sheet. Furthermore, the absorbance difference of the light control device can be increased by increasing the volume density of the voids while maintaining their size, or by increasing the size of the voids to a size that allows scattering while maintaining their volume density. With the above configuration, because the transparent polymer layer is composed of a first transparent polymer layer and a second transparent polymer layer, it is also possible to impart different configurations to the first transparent polymer layer and the second transparent polymer layer to achieve an absorbance difference of 0.8 or more.

In the above-mentioned light control device, the first light control sheet and the second light control sheet may be separate light control sheets, and the absorbance difference, which is the value obtained by subtracting the average absorbance of the liquid crystal composition from the absorbance of the light control sheet in the opaque state, may be 0.4 or more. The haze of the light control sheet in the opaque state may be 79% or more. The total light transmittance of the light control sheet in the opaque state may be 25% or less. The diffuse transmittance of the light control sheet in the opaque state may be 16% or less. The parallel ray transmittance of the light control sheet in the opaque state may be 5% or less. The clarity of the light control sheet in the opaque state may be 95% or less. Each of these configurations enhances the effectiveness of achieving the above-mentioned effects.

In the above-mentioned light control device, the first light control sheet and the second light control sheet are separate light control sheets, each comprising a first transparent electrode layer, a second transparent electrode layer, a first alignment layer positioned between the first transparent electrode layer and the transparent polymer layer, and a second alignment layer positioned between the second transparent electrode layer and the transparent polymer layer, and the thickness of the light control sheet may be 10 μm or less.

Reverse-type light-controlling sheets that use an alignment control force are thinner than normal-type light-controlling sheets because the alignment control force acts across the entire thickness. There is a stronger demand for reverse-type light-controlling sheets than for normal-type light-controlling sheets to enhance contrast. In this regard, the above configuration also makes it possible to enhance contrast in light-controlling devices that use reverse-type light-controlling sheets.

In the above-mentioned light control device, the transparent polymer layer may have a single-layer structure. With this configuration, the layer structure of the light control device for enhancing contrast can be simplified because the transparent polymer layer has a single-layer structure.

This disclosure makes it possible to increase the contrast of a dimming device.

FIG. 1 is a cross-sectional view showing the layer structure of a light control device. FIG. 2 is a cross-sectional view showing the layer structure of the light controlling sheet. FIG. 3 is a table showing the optical properties of the light-controlling sheet of the test example. FIG. 4 is a table showing the optical properties of the light-controlling sheet of the test example. FIG. 5 is a graph showing the relationship between haze and contrast. FIG. 6 is a graph showing the relationship between haze and contrast. FIG. 7 is a graph showing the relationship between the absorbance difference and the contrast. FIG. 8 is a graph showing the relationship between the absorbance difference and the contrast. FIG. 9 is a graph showing the relationship between transmittance and contrast.

An embodiment of a light control device will be described with reference to FIGS. 1 to 9. FIG.
The light control sheet that constitutes the light control device is attached to windows of moving objects such as vehicles and aircraft, etc. The light control sheet is also attached to windows of various buildings such as houses, train stations, and airports, partitions installed in offices, show windows installed in stores, and screens for projecting images, for example.

The shape of the light-adjusting sheet may be flat or curved. The light-adjusting sheet may be a normal type that changes from opaque to transparent when a drive signal is input, or a reverse type that changes from transparent to opaque when a drive signal is input. A light-adjusting device is equipped with one or more light-adjusting sheets. The light-adjusting sheet equipped in a light-adjusting device may be a single layer consisting of one light-adjusting sheet, or a laminate in which one light-adjusting sheet overlaps another light-adjusting sheet.

Hereinafter, an example will be shown in which the light-controlling sheet provided in the light-controlling device is a laminated body made up of two reverse-type light-controlling sheets.
[Light control device]
An example of a light control device will be described with reference to FIGS. 1 and 2. FIG.

As shown in FIG. 1, the dimming device 10 includes a dimming unit 11 and a drive unit 12. The dimming unit 11 includes two reverse-type dimming sheets. One dimming sheet includes a dimming layer 21, a first alignment layer 22, a second alignment layer 23, a first transparent electrode layer 24, and a second transparent electrode layer 25. In the thickness direction of the dimming layer 21, the first alignment layer 22 and the second alignment layer 23 sandwich the dimming layer 21. The dimming layer 21 is located between the first alignment layer 22 and the second alignment layer 23. The dimming layer 21 is in contact with the first alignment layer 22 and the second alignment layer 23. In the thickness direction of the dimming layer 21, the first transparent electrode layer 24 and the second transparent electrode layer 25 sandwich the pair of alignment layers 22, 23. The dimming layer 21 is located between the transparent electrode layers 24, 25. The first transparent electrode layer 24 is in contact with the first alignment layer 22. The second transparent electrode layer 25 is in contact with the second alignment layer 23. The light-controlling sheet includes a first transparent substrate 26 that supports the first transparent electrode layer 24. The light-controlling sheet includes a second transparent substrate 27 that supports the second transparent electrode layer 25.

The dimming device 10 includes a first electrode 24A attached to a portion of the first transparent electrode layer 24 and a second electrode 25A attached to a portion of the second transparent electrode layer 25. The dimming device 10 includes a first wiring 24B connected to the first electrode 24A and a second wiring 25B connected to the second electrode 25A. The first electrode 24A is connected to the drive unit 12 by the first wiring 24B. The second electrode 25A is connected to the drive unit 12 by the second wiring 25B.

The dimming device 10 has two dimming units. The two dimming units are composed of a first dimming unit 11UN1 and a second dimming unit 11UN2. One dimming unit has one dimming sheet, a first electrode 24A, a first wiring 24B, a second electrode 25A, and a second wiring 25B. One dimming unit is a repeating unit in the thickness direction of the dimming sheet in the dimming device 10.

The first dimming unit 11UN1 has a similar structure to the second dimming unit 11UN2. The second transparent substrate 27 of the second dimming unit 11UN2 overlaps the first transparent substrate 26 of the first dimming unit 11UN1. The second transparent substrate 27 of the second dimming unit 11UN2 is adhered to the first transparent substrate 26 of the first dimming unit 11UN1 via an optically transparent adhesive. A dimming device 10 consisting of multiple dimming units has a longer optical path length for light entering the dimming device 10 than a dimming device 10 consisting of a single dimming unit.

The dimming device 10 may include two drive units 12. One drive unit 12 inputs a drive signal to the first dimming unit 11UN1 and another drive unit 12 inputs a drive signal to the second dimming unit 11UN2. The other drive unit 12 inputs a drive signal to the second dimming unit 11UN2. The two drive units 12 simultaneously make the first dimming unit 11UN1 and the second dimming unit 11UN2 opaque. The two drive units 12 simultaneously make the first dimming unit 11UN1 and the second dimming unit 11UN2 transparent. The two drive units 12 may also separately make the first dimming unit 11UN1 and the second dimming unit 11UN2 opaque. The dimming device 10 may include a single drive unit 12. One driver 12 inputs a drive signal to the first dimming unit 11UN1 and inputs a drive signal to the second dimming unit 11UN2. One driver 12 simultaneously makes the first dimming unit 11UN1 and the second dimming unit 11UN2 opaque. One driver 12 simultaneously makes the first dimming unit 11UN1 and the second dimming unit 11UN2 transparent. One driver 12 may also separately make the first dimming unit 11UN1 and the second dimming unit 11UN2 opaque.

[Light control sheet]
As shown in FIG. 2, the light-controlling layer 21 includes a transparent polymer layer 21P and a liquid crystal composition 21LC.

The transparent polymer layer 21P is optically transparent, allowing visible light to pass through. It has numerous voids 21D. The transparent polymer layer is a cured product of a polymerizable composition. The transparent polymer layer may be a cured product of a photocurable compound or a cured product of a thermosetting compound. The liquid crystal composition 21LC fills the voids 21D.

An example of the photo-compound that forms the transparent polymer layer 21P is at least one selected from the group consisting of acrylate compounds, methacrylate compounds, styrene compounds, thiol compounds, and oligomers of each of these compounds. Acrylate compounds include monoacrylate compounds, diacrylate compounds, triacrylate compounds, and tetraacrylate compounds. Examples of acrylate compounds are butyl ethyl acrylate, ethylhexyl acrylate, and cyclohexyl acrylate. Examples of methacrylate compounds are dimethacrylate compounds, trimethacrylate compounds, and tetramethacrylate compounds. Examples of methacrylate compounds are N,N-dimethylaminoethyl methacrylate, phenoxyethyl methacrylate, methoxyethyl methacrylate, and tetrahydrofurfuryl methacrylate. Examples of thiol compounds are 1,3-propanedithiol and 1,6-hexanedithiol. Examples of styrene compounds are styrene and methylstyrene.

Liquid crystal composition 21LC contains liquid crystal compound LCM and a dichroic dye. In addition to liquid crystal compound LCM and dichroic dye, liquid crystal composition 21LC may contain a polymerizable composition for forming transparent polymer layer 21P, a plasticizer for reducing the viscosity of liquid crystal composition 21LC, and the like. The mass ratio of liquid crystal composition 21LC to the total mass of light-controlling layer 21 may be 30% by mass or more and 60% by mass or less. Liquid crystal composition 21LC further contains a reactive mesogen compound. When liquid crystal compound LCM is vertically aligned, the reactive mesogen compound is also vertically aligned. The vertically aligned reactive mesogen compound is networked, thereby promoting the vertical alignment of liquid crystal compound LCM. In other words, the alignment control force of the networked reactive mesogen compound promotes the vertical alignment of liquid crystal compound LCM.

The photochromic layer 21 is of a polymer-dispersed type. A polymer-dispersed photochromic layer 21 includes a transparent polymer layer 21P that defines a large number of voids 21D. The liquid crystal composition 21LC is held in the voids 21D dispersed in the transparent polymer layer 21P. The polymer-dispersed photochromic layer 21 may be a polymer network-type photochromic layer 21 or an encapsulated-type photochromic layer 21. A polymer network-type photochromic layer 21 includes a transparent polymer layer 21P having a three-dimensional mesh structure, and holds the liquid crystal composition 21LC in the interconnected mesh voids 21D. A encapsulated-type photochromic layer 21 holds the liquid crystal composition 21LC in the encapsulated voids 21D dispersed in the transparent polymer layer 21P.

An example of the liquid crystal compound LCM is at least one selected from the group consisting of Schiff bases, azos, azoxys, biphenyls, terphenyls, benzoates, tolanes, pyrimidines, cyclohexanecarboxylic acid esters, phenylcyclohexanes, and dioxanes.

The NI point of the liquid crystal compound LCM is the temperature at which the liquid crystal compound LCM undergoes a phase transition from a nematic phase (N phase) to an isotropic liquid phase (I phase). The NI point of the liquid crystal compound LCM indicates the degree to which the anisotropy of the liquid crystal compound LCM disappears at ambient temperature. The NI point of the liquid crystal compound LCM reflects the degree of intermolecular interaction in the liquid crystal compound LCM to a certain extent. When the liquid crystal compound LCM is a combination of two or more compounds, the NI point of the liquid crystal compound LCM is a weighted average of the NI points of each compound, weighted by the blending ratio of each compound. The NI point of the liquid crystal compound LCM can be increased or decreased by combining two or more liquid crystal compounds with different NI points. When it is necessary to enhance the orientational order of the liquid crystal compound LCM at a high ambient temperature such as 100°C, the NI point is preferably 100°C or higher. When it is necessary to enhance the uniformity of the liquid crystal compound LCM and the polymerizable composition for forming the transparent polymer layer 21P, the NI point is preferably 145°C or lower.

The CN point of a liquid crystal compound LCM is the temperature at which the liquid crystal compound LCM undergoes a phase transition from a crystalline phase (C phase) to a nematic phase (N phase). The CN point of a liquid crystal compound LCM indicates the degree to which the liquid crystal compound LCM loses its fluidity at ambient temperature. When the liquid crystal compound LCM is a combination of two or more compounds, the CN point of the liquid crystal compound LCM is lower than the weighted average of the CN points of each compound, weighted by the blending ratio of each compound. The CN point of the liquid crystal compound LCM can be increased or decreased by the composition of two or more compounds with different NI points. When it is necessary to increase the fluidity of the liquid crystal compound LCM at low ambient temperatures such as -20°C, the CN point is preferably 25°C or lower, and more preferably 0°C or lower.

The refractive index difference Δn between the long and short axis directions of the liquid crystal compound LCM (Δn = extraordinary refractive index ne - ordinary refractive index no) indicates the degree of attraction and repulsion in the liquid crystal compound LCM. The refractive index difference Δn of the liquid crystal compound LCM is the difference in refractive index for visible light with a wavelength of 650 nm, and indicates the difference in the degree of scattering of visible light between when a drive signal is supplied and when it is not. When the liquid crystal compound LCM is a combination of two or more compounds, the upper limit of the refractive index difference Δn of the liquid crystal compound LCM is the upper limit obtained from the refractive index differences Δn of all the compounds. The lower limit of the refractive index difference Δn of the liquid crystal compound LCM is the lower limit obtained from the refractive index differences Δn of all the compounds.

When it is required to improve the alignment controllability of the liquid crystal compound LCM at high ambient temperatures, it is preferable that the lower limit value of the refractive index difference Δn is high. When it is required to improve the difference in haze between transparent and opaque, it is preferable that the lower limit value of the refractive index difference Δn is high. When it is required to improve the alignment controllability of the liquid crystal compound LCM at high ambient temperatures such as 100°C, it is preferable that the lower limit value of the refractive index difference Δn of the liquid crystal compound LCM is 0.05, and more preferably 0.1. When it is required to improve the difference in haze, it is preferable that the lower limit value of the refractive index difference Δn of the liquid crystal compound LCM is 0.05, and more preferably 0.1.

The dichroic dye increases the absorbance of visible light in the direction of the long molecular axis compared to the absorbance of visible light in the direction of the short molecular axis. It is driven by a guest-host system, with the liquid crystal compound LCM as the host. The dichroic dye reversibly changes from transparent to colored in accordance with changes in the orientation of the liquid crystal compound LCM. Liquid crystal composition 21LC contains one type of dichroic dye or a combination of two or more types of dichroic dye. The combination of dichroic dyes is appropriately adjusted so that the color exhibited by the combination of dichroic dyes is the color exhibited when the light-controlling sheet is opaque.

The color exhibited by the light-controlling sheet when opaque may be black or a black tinged with chromatic colors. An example of a dichroic dye is one in which the chromaticity a* of the CIE 1976 (L*a*b*) color system in an opaque light-controlling sheet is between -15 and 15, and the chromaticity b* of the CIE 1976 (L*a*b*) color system is between -15 and 15. The chromaticity a* and chromaticity b* in the CIE 1976 (L*a*b*) color system are determined in accordance with the method for calculating color coordinates in the CIE 1976 (L*a*b*) color space specified in JIS-Z-8781-4 (ISO 11664-4). The ratio of the mass of the dichroic dye to the total mass of the light-controlling layer 21 is the dichroic dye blend ratio. An example of the dichroic dye blend ratio is between 1% and 5% by mass. Increasing the dichroic dye blend ratio increases the contrast of the light control device 10, but decreases the responsiveness of the liquid crystal compound LCM. From the perspective of increasing the contrast of the light control device 10, it is preferable that the dichroic dye blend ratio be at the upper limit of the range in which the responsiveness of the liquid crystal compound LCM can be obtained.

The dichroic dye is driven by a guest-host mechanism using a liquid crystal compound as a host, thereby exhibiting a specific color. The dichroic dye is 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 is a single compound or a combination of two or more compounds. When the total mass of the light-controlling layer 21 is set to 100% by mass, the mass of the dichroic dye may be 1% by mass or more and 5% by mass or less, and preferably 1% by mass or more and 3.5% by mass or less. When improved light resistance and an increased dichroic ratio are required, the dichroic dye is at least one selected from the group consisting of azo compounds and anthraquinone compounds, and more preferably an azo compound.

The light-adjusting layer 21 may contain spacers. The spacers are dispersed throughout the light-adjusting layer 21. The spacers determine the thickness of the light-adjusting layer 21 around the spacers and make the thickness of the light-adjusting layer 21 uniform. The spacers may be bead spacers or photospacers formed by exposing and developing a photoresist. The spacers may be colorless and transparent, or colored and transparent. If it is required to reduce the visibility of the spacers when the light-adjusting sheet is opaque, or to reduce the brightness of the color exhibited when the light-adjusting sheet is opaque, it is preferable that the color exhibited by the spacers be the same color as the color exhibited when the light-adjusting sheet is opaque.

An example thickness of the light-controlling layer 21 is 2 μm or more and 30 μm or less. When it is required to strengthen the alignment control force on the liquid crystal compound LCM, the thickness of the light-controlling layer 21 is preferably 5 μm or more and 25 μm or less. When the transparent polymer layer 21P is formed by phase separation, a thickness of the light-controlling layer 21 of 5 μm or more enables uneven distribution of voids 21D with a diameter of 1 μm or less. Furthermore, it is possible to generate regions in the light-controlling layer 21 with different densities of the liquid crystal composition 21LC in the thickness direction of the light-controlling layer 21. By setting the thickness of the light-controlling layer 21 to 25 μm or less, appropriate phase separation between the liquid crystal compound LCM and the transparent polymer layer 21P is possible when a coating liquid containing the liquid crystal compound LCM and a polymerizable composition is exposed to light during the production of the light-controlling layer 21.

The first alignment layer 22 exerts an alignment regulating force on the liquid crystal compound LCM from the surface of the light-controlling layer 21 that contacts the first alignment layer 22. The second alignment layer 23 exerts an alignment regulating force on the liquid crystal compound LCM from the surface of the light-controlling layer 21 that contacts the second alignment layer 23. The alignment layers 22, 23 are optically transparent, transmitting visible light. An example of the alignment layers 22, 23 is a vertical alignment layer. The alignment regulating force exerted by the vertical alignment layer aligns the long axis of the liquid crystal compound LCM so that it is perpendicular to the surface of the alignment layers 22, 23 that contacts the light-controlling layer 21. The alignment layers 22, 23 may also align the liquid crystal compound LCM so that the long axis is tilted by several degrees relative to the vertical, as long as the long axis of the liquid crystal compound LCM is determined to be substantially perpendicular to the transparent electrode layers 24, 25. An example thickness of the alignment layers 22, 23 is 0.02 μm or more and 0.5 μm or less.

The material constituting the alignment layers 22, 23 may be an organic compound, an inorganic compound, or an organic-inorganic composite material thereof. The material constituting the first alignment layer 22 and the material constituting the second alignment layer 23 may be the same or different. An example of an organic compound constituting the alignment layers 22, 23 is at least one selected from the group consisting of polyimide, polyamide, polyvinyl alcohol, and cyanide compounds. An example of an inorganic compound constituting the alignment layers 22, 23 is silicon oxide or zirconium oxide. The organic-inorganic composite material constituting the alignment layers 22, 23 is silicone, which has both an inorganic structure and an organic structure.

When a drive signal is input, the first transparent electrode layer 24 and the second transparent electrode layer 25 form an electric field in the thickness direction of the light-controlling layer 21. The transparent electrode layers 24 and 25 are optically transparent, allowing visible light to pass through. An example thickness of the transparent electrode layers 24 and 25 is 0.005 μm or more and 0.1 μm or less.

The material constituting the transparent electrode layers 24, 25 may be an inorganic compound, an organic compound, or an organic-inorganic composite material. An example of an inorganic compound constituting the transparent electrode layers 24, 25 is at least one selected from the group consisting of indium tin oxide, fluorine-doped tin oxide, tin oxide, and zinc oxide. An example of an organic compound constituting the transparent electrode layers 24, 25 is poly(3,4-ethylenedioxythiophene). The organic-inorganic composite material constituting the transparent electrode layers 24, 25 is an organic compound containing metal nanowires.

The first transparent substrate 26 supports the first transparent electrode layer 24. The second transparent substrate 27 supports the second transparent electrode layer 25. The transparent substrates 26, 27 may be flexible enough to conform to the curved surface to which the light-adjusting sheet is attached, or may be rigid enough not to deform under its own weight. At least one of the transparent substrates 26, 27 is attached to the object to which the light-adjusting device 10 is applied. An example of the thickness of the transparent substrates 26, 27 is 15 μm or more and 250 μm or less. Having a thickness of 15 μm or more for the transparent substrates 26, 27 improves the mechanical durability of the light-adjusting sheet and the chemical durability of the light-adjusting layer 21. Having a thickness of 250 μm or less for the transparent substrates 26, 27 enables the light-adjusting sheet to be manufactured using a roll-to-roll process.

The material constituting the transparent substrates 26, 27 may be an organic compound or an inorganic compound. An example of the organic compound constituting the transparent substrates 26, 27 is at least one selected from the group consisting of polyester, polyacrylate, polycarbonate, and polyolefin. An example of the inorganic compound constituting the transparent substrates 26, 27 is at least one selected from the group consisting of silicon dioxide, silicon oxynitride, and silicon nitride. The adhesive applied to the transparent substrates 26, 27 is a resin that has transparent adhesive properties and insulating properties. The adhesive for the transparent substrates 26, 27 is, for example, an optical clear adhesive (OCA: Optical Clear Adhesive).

The electrodes 24A, 25A may be flexible printed circuit boards or metal tape. The electrodes 24A, 25A may be attached to the transparent electrode layers 24, 25 with a conductive adhesive layer. The driver 12 inputs a drive signal to the dimming layer 21 through the transparent electrode layers 24, 25. The drive signal may be an AC voltage signal or a DC voltage signal.

The light-controlling layer 21 changes the orientation of the liquid crystal compound LCM due to changes in the electric field formed between the two transparent electrode layers 24 and 25. The change in orientation of the liquid crystal compound LCM changes the degree of scattering, absorption, and transmission of visible light that enters the light-controlling layer 21.

When an electric field is formed in the light-controlling layer 21, i.e., when a potential difference is generated between the two transparent electrode layers 24, 25, each unit 11UN1, 11UN2 drives the liquid crystal compound LCM against the alignment control forces of the alignment layers 22, 23, etc., resulting in a relatively high haze. When a voltage is applied to the light-controlling layer 21, each unit 11UN1, 11UN2 becomes cloudy, i.e., opaque, due to scattering caused by the refractive index difference between the transparent polymer layer 21P and the liquid crystal compound LCM. The dichroic dye follows the drive of the liquid crystal compound LCM and aligns to increase absorbance. As a result, when a voltage is applied to the light-controlling layer 21, each unit 11UN1, 11UN2 becomes black and opaque.

When no voltage is applied to the light-controlling layer 21, i.e., when no potential difference exists between the two transparent electrode layers 24, 25, each unit 11UN1, 11UN2 follows the alignment control forces of the alignment layers 22, 23 and has a lower haze than when a potential difference exists. When no voltage is applied to the light-controlling layer 21, each unit 11UN1, 11UN2 reduces the refractive index difference between the transparent polymer layer 21P and the liquid crystal compound LCM, thereby suppressing light scattering in the light-controlling layer 21. The dichroic dye follows the alignment of the liquid crystal compound LCM and aligns to reduce absorbance. As a result, when no voltage is applied to the light-controlling layer 21, each unit 11UN1, 11UN2 is colorless and transparent.

The dimming device 10 is in a dark state when each unit 11UN1, 11UN2 is black and opaque. The dimming device 10 is in a bright state when each unit 11UN1, 11UN2 is colorless and transparent. The total light transmittance of the dimming device 10 in the dark state is lower than the total light transmittance of the dimming device 10 in the bright state. The dimming device 10 may be semi-transparent, with the first dimming unit 11UN1 being black and opaque and the second dimming unit 11UN2 being colorless and transparent. The dimming device 10 may be semi-transparent, with the second dimming unit 11UN2 being black and opaque and the first dimming unit 11UN1 being colorless and transparent.

[Optical properties of light-controlling sheet]
The light control device 10 satisfies the following condition 1. Each light control sheet of the light control device 10 may satisfy at least one of the following conditions 2 and 3. Satisfying at least one of conditions 2 and 3 may mean satisfying condition 2, satisfying condition 3, or satisfying both conditions 2 and 3.

Furthermore, if it is required to increase the contrast of the light control device 10, it is preferable that each light control sheet of the light control device 10 satisfy at least one of the following conditions 4 to 7. Satisfying at least one of conditions 4 to 7 may mean one selected from conditions 4 to 7, or a combination of two or more selected from conditions 4 to 7. Note that if each light control sheet of the light control device 10 is a reverse type, each light control sheet of the light control device 10 may satisfy the following condition 8 instead of condition 3.

(Condition 1) The absorbance difference, which is the value obtained by subtracting the average absorbance of the liquid crystal composition 21LC from the absorbance of the light control device 10 when it is opaque, is 0.8 or more.
(Condition 2) The haze of each light-controlling sheet when opaque is 79% or more.

(Condition 3) The absorbance difference, which is the value obtained by subtracting the average absorbance of the liquid crystal composition 21LC from the absorbance of each light-controlling sheet when it is opaque, is 0.4 or more.
(Condition 4) The total light transmittance of each light-controlling sheet when opaque is 25% or less.
(Condition 5) The diffuse transmittance of each light-controlling sheet when opaque is 16% or less.

(Condition 6) The parallel ray transmittance of each light-controlling sheet when opaque is 5% or less.
(Condition 7) The clarity of each light-controlling sheet when opaque is 95% or less.
(Condition 8) The absorbance difference, which is the value obtained by subtracting the horizontal absorbance of the liquid crystal composition 21LC from the absorbance of each light-controlling sheet when it is opaque, is 0.1 or more.

Haze is measured using a method conforming to ASTM D 1003-00. A haze measuring instrument, for example, is the BYK haze-gard instrument (manufactured by BYK Gardner). When measuring haze, the light rays contained in the light beam incident on the light-controlling sheet are straight rays. The maximum angle between the light rays contained in the light beam incident on the light-controlling sheet and the optical axis of the light beam is less than 3°. The light-controlling sheet is fixed so that the surface of the light-controlling sheet and the light beam incident on that surface form an approximately right angle, within ±2°.

Of the transmitted light that passes through a light-adjusting sheet, light that deviates by more than ±2.5° from the light beam incident on the sheet is wide-angle scattered light. Haze is the percentage of transmitted light that passes through a light-adjusting sheet that is wide-angle scattered light due to forward scattering. Diffuse transmittance is the percentage of incident light that enters a light-adjusting sheet that is wide-angle scattered light due to forward scattering.

Of the transmitted light that passes through a light-adjusting sheet, light that deviates by less than ±2.5° from the light beam incident on the sheet is parallel transmitted light. Parallel transmittance is the percentage of parallel transmitted light due to forward scattering among the incident light that enters the light-adjusting sheet. Total light transmittance is the sum of diffuse transmittance and parallel transmittance.

Of the transmitted light that passes through a light-adjusting sheet, light that does not deviate from the light beam incident on the sheet is straight-transmitted light. Light that deviates from straight-transmitted light by less than ±2.5° is the parallel-transmitted light described above. Clarity is calculated using the light intensity LC of straight-transmitted light and the light intensity LR of parallel-transmitted light according to the following formula (1):

100×(LR-LC)/(LR+LC)...Equation (1)
The total light transmittance, diffuse transmittance, parallel light transmittance, and clarity are obtained by measurements in accordance with ASTM D 1003-00.

Absorbance is measured using an absorptiometer in accordance with JIS K 0115:2004. The light source of the absorptiometer is a white LED that emits visible light from 380 nm to 780 nm. The photometer's photometer's photometer detects light intensity across the entire visible light range from 380 nm to 780 nm.

The contrast of the light-adjusting device 10 is the ratio of the total light transmittance when transparent to the total light transmittance when opaque. In other words, the contrast of the light-adjusting device 10 is the ratio of the total light transmittance when bright to the total light transmittance when dark. The total transmitted light of each light-adjusting sheet that makes up the light-adjusting device 10 includes direct transmitted light that passes through the light-adjusting sheet without being scattered by it, and scattered light scattered by the light-adjusting sheet. The total light transmittance of the light-adjusting sheet depends on the sum of the amount of direct transmitted light and the amount of scattered light. The haze of the light-adjusting sheet is the ratio of the diffuse transmittance to the total light transmittance. In other words, the haze of the light-adjusting sheet depends on the amount of scattered light relative to the sum of the amount of direct transmitted light and the amount of scattered light. Total light transmittance and haze are optical properties that can change independently, just as the amount of scattered light relative to the sum of the amount of direct transmitted light and the amount of scattered light changes even when the sum of the amount of direct transmitted light and the amount of scattered light is constant.

Increasing the dichroic dye ratio in liquid crystal composition 21LC simply reduces the amount of scattered light. Increasing the dichroic dye ratio reduces the total light transmittance by the amount of the reduced scattered light, thereby improving contrast. However, the dichroic dye ratio is actually set to approximately the upper limit within the range that achieves the responsiveness of liquid crystal compound LCM. Ultimately, there is a limit to how much the dichroic dye ratio can be increased in terms of improving the contrast of light control device 10.

On the other hand, as mentioned above, the absorption characteristics of dichroic dyes are such that, based on the dichroic ratio, they exhibit high absorbance for scattered light and low absorbance for directly transmitted light. The absorbance of such dichroic dyes increases exponentially and steeply with the optical path length as a variable. Promoting scattering of directly transmitted light in a light-controlling sheet reduces the total light transmittance when opaque, thereby improving contrast. However, in order to sharply increase absorbance using a dichroic dye, it is necessary not only to promote scattering of directly transmitted light, but also to increase scattering to the extent that light scattered at the interface between the transparent polymer layer 21P and the liquid crystal composition 21LC reaches the dichroic dye.

Here, the absorbance of the light control device 10 in the dark state reflects the absorption of light scattered at the interface between the transparent polymer layer 21P and the liquid crystal composition 21LC by the dichroic dye. On the other hand, the absorbance of the liquid crystal composition 21LC itself, considered to be opaque, does not reflect the extension of the optical path length due to scattering, i.e., the increase in absorption due to the extension of the optical path length. The absorbance difference, which is the value obtained by subtracting the absorbance of the liquid crystal composition considered to be opaque from the absorbance of the liquid crystal composition considered to be opaque, indicates the increase in absorption due to the extension of the optical path length. The absorbance of the liquid crystal composition 21LC considered to be opaque may be any value that can simulate the absorbance of the liquid crystal composition 21LC in the opaque state. The absorbance of the liquid crystal composition 21LC considered to be opaque is, for example, the average value of the vertical and horizontal absorbance of the liquid crystal composition 21LC, which is considered to be the absorbance when the liquid crystal compound LCM is randomly aligned. Alternatively, since the liquid crystal compound LCM can be aligned between random alignment and horizontal alignment when opaque, the absorbance of liquid crystal composition 21LC considered to be opaque may be, for example, the horizontal absorbance of liquid crystal composition 21LC.

Through extensive research into the relationship between the contrast of the light control device 10 and its optical parameters, the inventors of the present application discovered a range of absorbance differences in the light control device 10 that sharply increases the contrast. Furthermore, if the absorbance difference of the light control device 10 is 0.8 or greater, it is possible to significantly increase the contrast of the light control device 10.

Furthermore, through extensive research into the relationship between the contrast of the light control device 10 and the optical properties of the light control sheet, the inventors of the present application discovered a range in the haze of each light control sheet stacked on top of another that sharply increases contrast. Furthermore, if the light control device 10 satisfies the above-mentioned condition 2, the haze of each light control sheet when opaque is 79% or greater, thereby enhancing the effectiveness of the significant increase in contrast in the light control device 10.

Furthermore, through extensive research into the relationship between the contrast of the light control device 10 and the optical characteristics of the light control sheet, the inventors of the present application discovered a range within the absorbance difference between each of the light control sheets stacked on top of each other that sharply increases the contrast. Furthermore, if the light control device 10 satisfies the above-mentioned condition 3, the average absorbance difference between each of the light control sheets is 0.4 or more, thereby significantly increasing the contrast of the light control device 10. Furthermore, if the light control device 10 satisfies the above-mentioned condition 8, the horizontal absorbance difference between each of the light control sheets is 0.1 or more, thereby significantly increasing the contrast of the light control device 10.

[Distribution of voids 21D]
The light-switching layer 21 may include a first high-density portion 21H1, a second high-density portion 21H2, and a low-density portion 21L.

The density of liquid crystal composition 21LC per unit thickness in the first high-density portion 21H1 is higher than the density of liquid crystal composition 21LC per unit thickness in the low-density portion 21L. The quantity density of voids 21D per unit thickness in the first high-density portion 21H1 is higher than the quantity density of voids 21D per unit thickness in the low-density portion 21L. The first high-density portion 21H1 is in contact with the first alignment layer 22.

The density of liquid crystal composition 21LC per unit thickness in the second high-density portion 21H2 is higher than the density of liquid crystal composition 21LC per unit thickness in the low-density portion 21L. The quantity density of voids 21D per unit thickness in the second high-density portion 21H2 is higher than the quantity density of voids 21D per unit thickness in the low-density portion 21L. The second high-density portion 21H2 is in contact with the second alignment layer 23.

The density of liquid crystal composition 21LC in the light-controlling layer 21 is lowest in the middle of the light-controlling layer 21 in the thickness direction. The middle of the light-controlling layer 21 in the thickness direction is a portion closer to the center of the light-controlling layer 21 than the pair of opposing surfaces in the thickness direction of the light-controlling layer 21. The density of liquid crystal composition 21LC per unit thickness in each portion of the light-controlling layer 21 is calculated by dividing the volume of liquid crystal composition 21LC contained in each portion by the thickness of each portion. The density of liquid crystal composition 21LC in the light-controlling layer 21 may be lowest in a portion including the center of the light-controlling layer 21 in the thickness direction.

The quantity density of voids 21D in the transparent polymer layer 21P is lowest in the middle of the thickness direction of the photochromic layer 21. The quantity density of voids 21D per unit thickness in each portion of the transparent polymer layer 21P is calculated by dividing the number of voids 21D contained in each portion by the thickness of each portion. The quantity density of voids 21D in the transparent polymer layer 21P may be lowest in a portion including the center of the thickness direction of the photochromic layer 21.

The uneven distribution of the liquid crystal compound LCM in the transparent polymer layer 21P near the alignment layers 22 and 23 enhances the effect of the alignment control force of the alignment layers 22 and 23. This uneven distribution of the liquid crystal compound LCM increases the light transmittance of the light control device 10 when it is transparent.

In the light-controlling layer 21, for example, the thickness TH1 of the first high-density portion 21H1, the thickness TH2 of the second high-density portion 21H2, and the thickness TL of the low-density portion 21L are approximately equal to one another. That is, for example, the thickness TH1 of the first high-density portion 21H1, the thickness TH2 of the second high-density portion 21H2, and the thickness TL of the low-density portion 21L are 1/3 of the thickness T21 of the light-controlling layer 21. Note that the thickness TL of the low-density portion 21L may be thicker or thinner than the thicknesses TH1 and TH2 of the high-density portions 21H1 and 21H2. Furthermore, the thickness TH1 of the first high-density portion 21H1 may be equal to or different from the thickness of the second high-density portion 21H2.

In a cross section of the light-controlling layer 21 taken along the thickness direction, the percentage of the total area of the voids 21D contained in the low-density portions 21L relative to the area of the low-density portions 21L may be 10% or less. This reduces the proportion of liquid crystal composition 21LC held by the voids 21D in the low-density portions 21L, thereby preventing the liquid crystal compound LCM contained in the low-density portions 21L from increasing the opacity of the light-controlling sheet when no potential difference is present between the transparent electrode layers 24, 25.

Furthermore, the low-density portion 21L does not have to have voids 21D. In other words, the low-density portion 21L does not have to contain the liquid crystal composition 21LC. This makes it easier for all of the liquid crystal compound LCM contained in the light-controlling layer 21 to be aligned in accordance with the alignment regulating forces of the alignment layers 22, 23 and the reactive mesogen compound, thereby further reducing the haze of the light-controlling sheet when no voltage difference is generated between the transparent electrode layers 24, 25.

In this way, in the low-density portion 21L, the sum SD of the areas of the voids 21D relative to the area SL of the low-density portion 21L may be 10% or less, 5% or less, or 0%. Furthermore, the voids 21D may be located within a range of 3.0 μm or less from the first alignment layer 22 and within a range of 3.0 μm or less from the second alignment layer 23 in a cross section along the thickness direction of the switchable layer 21.

When it is required to increase the alignment control force acting on the liquid crystal compound LCM, it is preferable that each void 21D included in the first high-density portion 21H1 be in contact with the first alignment layer 22. Furthermore, it is preferable that each void 21D included in the second high-density portion 21H2 be in contact with the second alignment layer 23.

In the light-controlling sheet, the thickness T21 of the light-controlling layer 21 may be 2 μm or more and 30 μm or less, and the diameter of the void 21D may be 0.1 μm or more and 2 μm or less. The diameter of the void 21D is the diameter of a circle circumscribing the void 21D in a cross section including the thickness direction of the light-controlling layer 21. When the thickness of the light-controlling layer 21 is 2 μm or more and 30 μm or less, and the diameter of the void 21D is 0.1 μm or more and 2 μm or less, the formation of the void 21D at a position away from the alignment layers 22, 23 is suppressed. When the size of the void 21D is 0.1 μm or more and 2 μm or less, the liquid crystal composition 21LC is retained near the alignment layers 22, 23. This makes it possible to improve the transparency of the light-controlling sheet when no voltage difference is generated between the transparent electrode layers 24, 25. If it is required to increase the degree of scattering by the voids 21D, the size of the voids 21D is preferably 2 μm or less. If it is required to suppress the degree of narrow-angle scattering by the voids 21D, it is preferable that the size of the voids 21D be 0.1 μm or more.

[Method of manufacturing light controlling sheet]
To manufacture a light-controlling sheet, first, transparent substrates 26 and 27 on which transparent electrode layers 24 and 25 are formed are prepared. Next, alignment layers 22 and 23 are formed on the transparent electrode layers 24 and 25. Next, a coating liquid is applied to the alignment layers 22 and 23. The coating liquid contains a polymerizable composition for forming a transparent polymer layer 21P, a liquid crystal compound LCM, and a dichroic dye. The polymerizable composition is a monomer or oligomer that can be polymerized by irradiation with ultraviolet light. Next, ultraviolet light is irradiated onto the coating liquid through the transparent electrode layers 24 and 25. As a result, a transparent polymer layer 21P having voids 21D is formed, and the liquid crystal compound LCM and the dichroic dye are retained in the voids 21D.

When the coating liquid is cured by ultraviolet irradiation, the liquid crystal compound LCM and the liquid crystal composition 21LC containing the dichroic dye are distributed almost uniformly throughout the polymerizable composition. Next, the polymerizable composition begins to harden near the alignment layers 22, 23, and the liquid crystal composition 21LC separates from the polymer of the polymerizable composition. Some of the liquid crystal composition 21LC present in the coating film is more stable when combined with the separated liquid crystal composition 21LC, and therefore moves toward the alignment layers 22, 23. Then, as almost the entire polymerizable composition hardens, a transparent polymer layer 21P is formed, with voids 21D surrounding the liquid crystal composition 21LC.

Until the transparent polymer layer 21P is formed, the separated liquid crystal composition 21LC gathers together to stabilize energy. If the polymerizable composition cures quickly or if the liquid crystal composition 21LC moves quickly, the liquid crystal composition 21LC gathers over a wide area, resulting in large voids 21D. The cure rate of the polymerizable composition can be increased by raising the temperature of the coating liquid when irradiated. On the other hand, if the polymerizable composition cures over a wide area, the voids 21D are separated from each other before the liquid crystal composition 21LC gathers. The area where the polymerizable composition cures simultaneously can be expanded by increasing the irradiance of the ultraviolet light irradiated onto the coating liquid. Because there is a limit to the size that the voids 21D can grow, further increasing the cure rate of the polymerizable composition can easily extend the area where the voids 21D are formed into the low-density portion 21L.

[Test Example]
A specific test example of the light-control sheet is shown below.
The light-controlling sheets of Test Examples 1 to 10 are reverse type. The light-controlling sheets of Test Examples 1 to 10 include alignment layers 22 and 23, transparent electrode layers 24 and 25, and transparent substrates 26 and 27. The light-controlling sheets of Test Examples 1 to 10 were obtained by forming a coating film containing a liquid crystal compound LCM, a dichroic dye, a reactive mesogen compound, an ultraviolet-curable compound, a spacer 21S, and a polymerization initiator between the alignment layers 22 and 23, and polymerizing the ultraviolet-curable compound in the coating film.

The light-controlling sheets of Test Examples 21 to 24 are of the normal type. Test Examples 21 to 24 include alignment layers 22, 23, transparent electrode layers 24, 25, and transparent substrates 26, 27. The light-controlling sheets of Test Examples 21 to 24 were obtained by forming a coating film containing a liquid crystal compound LCM, a dichroic dye, a reactive mesogenic compound, a UV-curable compound, spacer 21S, and a polymerization initiator between the alignment layers 22, 23, and then polymerizing the UV-curable compound within the coating film. The normal-type alignment layers 22, 23 exert an alignment control force on the dichroic dye, enhancing light absorption due to the horizontal alignment of the dichroic dye.

The light-controlling sheets of Test Examples 25 to 37 were configured without the alignment layers 22 and 23, and instead included transparent electrode layers 24 and 25 and transparent substrates 26 and 27. The light-controlling sheets of Test Examples 25 to 37 were obtained by forming a coating film containing a liquid crystal compound LCM, a dichroic dye, a reactive mesogen compound, a UV-curable compound, spacer 21S, and a polymerization initiator between the transparent electrode layers 24 and 25, and then polymerizing the UV-curable compound within the coating film.

The materials (a) to (h) common to the light-adjusting sheets of Test Examples 1 to 10 are shown below. Note that materials (c) to (h) are common to the light-adjusting sheets of Test Examples 21 to 37.
(a) Alignment layers 22, 23: vertical alignment films (b) Transparent electrode layers 24, 25: indium tin oxide (c) Transparent substrates 26, 27: polyethylene terephthalate films (d) Spacer 21S: spherical silica particles (e) Liquid crystal compound LCM: fluorine-based liquid crystal compound (f) Polymerization initiator: photopolymerization initiator (Irgacure Oxe04: manufactured by BASF)
(g) Polymerizable composition: a mixture of isobornyl acrylate, pentaerythritol triacrylate, and urethane acrylate. (h) Dichroic dye: an azo compound mixed dye (product name Irgaphor Black X12 DC, manufactured by BASF).
[Test Example 1]
The compounding ratios of materials (e) to (h) in the coating liquid for producing the light-modulating sheet of Test Example 1 are shown below.
(e) Liquid crystal compound LCM: 46% by mass
(f) Polymerization initiator: 1% by mass
(g) Polymerizable composition: 49% by mass
(h) Dichroic dye: 2% by mass
The coating liquid of Test Example 1 was applied to the first alignment layer 22 so that black spacers 21S with a particle size of 7 μm were arranged on the first alignment layer 22, forming a coating film of Test Example 1. Next, with the coating film of Test Example 1 sandwiched between the first alignment layer 22 and the second alignment layer 23, 365 nm ultraviolet light was irradiated toward the first transparent substrate 26, forming a light-control sheet of Test Example 1 with a light-control layer thickness of 7 μm. At this time, the integrated light intensity of the ultraviolet light was set to 1380 mJ/ ^cm2 .

[Test Example 2]
A light-modulating sheet of Test Example 2 was obtained by the same manufacturing method as in Test Example 1.
[Test Example 3]
A light-controlling sheet of Test Example 3 having a light-controlling layer thickness of 8 μm was obtained in the same manufacturing method as Test Example 1, except that the particle size of the spacer 21S was changed to 8 μm, the coating liquid of Test Example 1 was used, and the cumulative light amount of ultraviolet light was changed to 780 mJ/ ^cm2 .

[Test Example 4]
A light-controlling sheet of Test Example 4 was obtained by the same manufacturing method as in Test Example 3.
[Test Example 5]
The compounding ratios of materials (e) to (h) in the coating liquid for producing the light-modulating sheet of Test Example 5 are shown below.
(e) Liquid crystal compound LCM: 50% by mass
(f) Polymerization initiator: 1% by mass
(g) Polymerizable composition: 45% by mass
(h) Dichroic dye: 2% by mass
The coating liquid of Test Example 5 was applied to the first alignment layer 22 so that black spacers 21S with a particle size of 8 μm were arranged on the first alignment layer 22, forming a coating film of Test Example 5. Next, with the coating film of Test Example 5 sandwiched between the first alignment layer 22 and the second alignment layer 23, 365 nm ultraviolet light was irradiated toward the first transparent substrate 26, forming a light-control sheet of Test Example 5 with a light-control layer thickness of 8 μm. At this time, the integrated light intensity of the ultraviolet light was set to 810 mJ/ ^cm2 .

[Test Example 6]
A light-controlling sheet of Test Example 6 was obtained by the same manufacturing method as in Test Example 5.
[Test Example 7]
A light-controlling sheet of Test Example 7 having a light-controlling layer thickness of 8 μm was obtained in the same manufacturing method as Test Example 1, except that the particle size of the spacer 21S was changed to 8 μm, the coating liquid of Test Example 1 was used, and the cumulative light amount of ultraviolet light was changed to 920 mJ/ ^cm2 .

[Test Example 8]
A light-controlling sheet of Test Example 8 having a light-controlling layer thickness of 8 μm was obtained in the same manufacturing method as Test Example 1, except that the particle size of the spacer 21S was changed to 8 μm, the coating liquid of Test Example 1 was used, and the cumulative light amount of ultraviolet light was changed to 1380 mJ/ ^cm2 .

[Test Example 9]
A light-control sheet of Test Example 9 having a light-control layer thickness of 8 μm was obtained using the same manufacturing method as Test Example ⁵ , except that the coating liquid of Test Example 5 was used and the cumulative amount of ultraviolet light was changed to 840 mJ/cm2.

[Test Example 10]
A light-control sheet of Test Example 10 having a light-control layer thickness of 8 μm was obtained using the same manufacturing method as Test Example ⁵ , except that the coating liquid of Test Example 5 was used and the cumulative amount of ultraviolet light was changed to 800 mJ/cm2.

[Test Example 11]
The light-adjusting sheet of Test Example 2 was stacked and joined to the light-adjusting sheet of Test Example 1, thereby obtaining the light-adjusting device 10 of Test Example 11. In this case, the light-adjusting sheet of Test Example 2 was attached to the light-adjusting sheet of Test Example 1 using an optical transparent adhesive.

[Test Example 12]
The light-adjusting sheet of Test Example 4 was stacked and joined to the light-adjusting sheet of Test Example 3, thereby obtaining the light-adjusting device 10 of Test Example 12. In this case, the light-adjusting sheet of Test Example 4 was attached to the light-adjusting sheet of Test Example 3 using an optical transparent adhesive.

[Test Example 13]
The light-adjusting sheet of Test Example 6 was stacked and joined to the light-adjusting sheet of Test Example 5, thereby obtaining the light-adjusting device 10 of Test Example 13. In this case, the light-adjusting sheet of Test Example 6 was attached to the light-adjusting sheet of Test Example 5 using an optical transparent adhesive.

[Test Example 14]
The light-adjusting sheet of Test Example 7 was stacked and joined with the light-adjusting sheet of Test Example 8, thereby obtaining the light-adjusting device 10 of Test Example 14. In this case, the light-adjusting sheet of Test Example 8 was attached to the light-adjusting sheet of Test Example 7 using an optical transparent adhesive.

[Test Example 15]
The light-adjusting sheet of Test Example 9 was stacked and joined with the light-adjusting sheet of Test Example 10, thereby obtaining the light-adjusting device 10 of Test Example 15. In this case, the light-adjusting sheet of Test Example 10 was attached to the light-adjusting sheet of Test Example 9 using an optical transparent adhesive.

[Test Example 21]
The compounding ratios of materials (e) to (h) in the coating liquid for producing the light-modulating sheet of Test Example 21 are shown below.
(e) Liquid crystal compound LCM: 55% by mass
(f) Polymerization initiator: 1% by mass
(g) Polymerizable composition: 40% by mass
(h) Dichroic dye: 2.2% by mass
The coating liquid of Test Example 21 was applied onto the first alignment layer 22 so that black spacers 21S with a particle size of 15 μm were arranged on the first alignment layer 22, thereby forming a coating film of Test Example 21. Next, with the coating film of Test Example 21 sandwiched between the first alignment layer 22 and the second alignment layer 23, 365 nm ultraviolet light was irradiated toward the first transparent substrate 26, thereby forming a light-control sheet of Test Example 21 having a light-control layer thickness of 15 μm. At this time, the integrated light intensity of the ultraviolet light was set to 1200 mJ/ ^cm2 .

[Test Example 22]
A light-controlling sheet of Test Example 22 having a light-controlling layer thickness of 15 μm was obtained in the same manner as in Test Example 21, except that the alignment layers 22 and 23 were subjected to rubbing treatment.

[Test Example 23]
In the same manner as in the manufacturing method of Test Example 21, a light-controlling sheet of Test Example 23 having a light-controlling layer thickness of 15 μm was obtained.

[Test Example 24]
In the same manner as in the manufacturing method of Test Example 22, a light-controlling sheet of Test Example 24 having a light-controlling layer thickness of 15 μm was obtained.

[Test Example 25]
The compounding ratios of materials (e) to (h) in the coating liquid for producing the light-modulating sheet of Test Example 25 are shown below.
(e) Liquid crystal compound LCM: 55% by mass
(f) Polymerization initiator: 1% by mass
(g) Polymerizable composition: 39% by mass
(h) Dichroic dye: 3.0% by mass
The coating liquid of Test Example 25 was applied to the first transparent electrode layer 24 so that black spacers 21S with a particle size of 15 μm were arranged on the first transparent electrode layer 24, thereby forming a coating film of Test Example 25. Next, with the coating film of Test Example 25 sandwiched between the first transparent electrode layer 24 and the second transparent electrode layer 25, 365 nm ultraviolet light was irradiated toward the first transparent substrate 26, thereby forming a light-control sheet of Test Example 21 with a light-control layer thickness of 15 μm. At this time, the cumulative light intensity of the ultraviolet light was set to 1500 mJ/ ^cm2 .

[Test Example 26] to [Test Example 29]
In the same manner as in the manufacturing method of Test Example 25, light-control sheets of Test Examples 26 to 29, each having a light-control layer thickness of 15 μm, were obtained.

[Test Example 30] to [Test Example 31]
Except for changing the compounding ratio of the dichroic dye to 4.0% by mass and changing the polymerizable composition to 38% by mass, the manufacturing method was the same as that of Test Example 25 to obtain light-control sheets of Test Examples 30 to 31, each having a light-control layer thickness of 15 μm.

[Test Example 32] to [Test Example 37]
The light-controlling sheets of Test Examples 32 to 37, each having a thickness of 15 μm, were obtained using the same manufacturing method as Test Example 25, except that the compounding ratio of the dichroic dye was changed to 5.0 mass% and the polymerizable composition was changed to 37 mass%.

[Evaluation method]
For each of the light-controlling sheets of Test Examples 1 to 10 and Test Examples 21 to 37, the total light transmittance, diffuse transmittance, parallel ray transmittance, haze, and clarity were measured using a measurement method conforming to ASTM D 1003-00. For each of the light-controlling devices 10 of Test Examples 11 to 15, the total light transmittance, diffuse transmittance, parallel ray transmittance, haze, and clarity were measured using a measurement method conforming to ASTM D 1003-00. A 40 V square wave AC voltage with a frequency of 50 Hz was used as the drive signal for the light-controlling sheet during the measurement of optical properties. A haze meter (BYK haze-gard indtrument, manufactured by BYK Gardner) was used as the optical property measuring instrument.

For each of the light-controlling sheets in Test Examples 1 to 10 and Test Examples 21 to 37, the absorbance of visible light from 380 nm to 780 nm was measured using a measurement method in accordance with JIS K 0115:2004. For each of the light-controlling devices 10 in Test Examples 11 to 15, the absorbance of visible light from 380 nm to 780 nm was measured using a measurement method in accordance with JIS K 0115:2004.

For liquid crystal composition 21LC included in the light-modulating sheets of test examples 1 to 37, the horizontal absorbance, which is the absorbance for visible light of 380 nm to 780 nm in horizontal alignment, and the average absorbance were measured using a measurement method in accordance with JIS K 0115:2004. The average absorbance is the average value of the absorbance for liquid crystal composition 21LC in horizontal alignment and the absorbance for liquid crystal composition 21LC in vertical alignment. The absorbance of liquid crystal composition 21LC containing a dichroic dye was obtained by placing liquid crystal composition 21LC in a 6 μm-thick cell for horizontal alignment and a 6 μm-thick cell for vertical alignment.

For each of Test Examples 1 to 10 and Test Examples 21 to 37, the average absorbance difference was calculated as the value obtained by subtracting the average absorbance of liquid crystal composition 21LC from the absorbance of the light control device 10 when opaque. For each of Test Examples 11 to 15, the average absorbance difference was calculated as the value obtained by subtracting the average absorbance of liquid crystal composition 21LC from the absorbance of the light control device 10 when opaque.

For each of Test Examples 1 to 10 and Test Examples 21 to 37, the horizontal absorbance difference was calculated as the value obtained by subtracting the horizontal absorbance of liquid crystal composition 21LC from the absorbance when opaque. For each of Test Examples 11 to 15, the horizontal absorbance difference was calculated as the value obtained by subtracting the horizontal absorbance of liquid crystal composition 21LC from the absorbance of light control device 10 when opaque.

For each of Test Examples 1 to 37, the ratio of the total light transmittance in the light state to the total light transmittance in the dark state of the light control device 10 was calculated as the contrast. For each of Test Examples 11 to 15, the ratio of the contrast of the light control device 10 to the sum of the contrasts of the two light control sheets that make up the light control device 10 was calculated as the increase rate.

[Evaluation results]
The evaluation results of Test Examples 1 to 37 are shown in FIGS. 3 and 4 together with the configuration of each test example.
Fig. 5 is a graph showing the relationship between haze and contrast, and the relationship between clarity and contrast, for Test Examples 1 to 15. Fig. 6 is a graph showing the relationship between haze and contrast, for Test Examples 1 to 37. Fig. 7 is a graph showing the relationship between horizontal absorbance difference and contrast, and the relationship between average absorbance difference and contrast, for Test Examples 1 to 15.

Figure 8 is a graph showing the relationship between the average absorbance difference and contrast for Test Examples 1 to 15 and Test Examples 21 to 37. Figure 9 is a graph showing the relationship between the parallel transmittance and contrast, and the relationship between the diffuse transmittance and contrast for Test Examples 1 to 15.

As shown in Figures 3 and 5, the evaluation results for Test Examples 1 to 10 showed that when the haze of one light-adjusting sheet was between 56% and 87%, the contrast of the light-adjusting sheet remained at 2.3 or less. Furthermore, the evaluation results for Test Example 11 showed that when the haze of one light-adjusting sheet was between 50% and 79%, the contrast remained at 2.3 or less, even in a light-adjusting device 10 with two light-adjusting sheets stacked on top of each other.

In contrast, the evaluation results of Test Examples 12 to 15 showed that when the haze of one light-adjusting sheet was 79% or higher, the contrast increased sharply in the light-adjusting device 10 in which two light-adjusting sheets were stacked. Furthermore, the evaluation results of Test Examples 11 to 15 also showed that when the haze of both light-adjusting sheets was 79% or higher, the contrast increase rate was 1 or higher in the light-adjusting device 10 in which two light-adjusting sheets were stacked.

The evaluation results for Test Examples 1 to 10 showed that when the clarity of a single light-adjusting sheet was in the range of 86% to 99%, the contrast of the light-adjusting sheet remained at 2.3 or less. Furthermore, the evaluation results for Test Examples 11 to 15 showed that when the clarity of a single light-adjusting sheet was 95% ± 3%, the contrast of the light-adjusting device 10, which was made by stacking two light-adjusting sheets, varied significantly. In other words, no relationship was found between the clarity of a single light-adjusting sheet and a light-adjusting device 10 with high contrast.

As shown in Figures 3, 4, and 6, the evaluation results for Test Examples 21 to 37 showed that when the haze of the light-adjusting sheet was less than 79%, the contrast was approximately 3, the same as that of a single reverse-type light-adjusting sheet. In contrast, the evaluation results for Test Examples 21 to 37 showed that when the haze of the light-adjusting sheet was 79% or more, the contrast increased sharply, achieving a high contrast of approximately 4 or more, as if two reverse-type light-adjusting sheets were stacked on top of each other.

As shown in Figures 3 and 7, the evaluation results for Test Examples 1 to 10 showed that when the average absorbance difference of a single light-adjusting sheet was 0.28 or more and 0.54 or less, the contrast of the light-adjusting sheet remained at 2.3 or less. The evaluation results for Test Examples 1 to 10 showed that when the horizontal absorbance difference of a single light-adjusting sheet was 0.04 or more and 0.25 or less, the contrast of the light-adjusting sheet remained at 2.3 or less.

Furthermore, the evaluation results of Test Example 11 showed that when the average absorbance difference between one light-adjusting sheet is less than 0.4, the contrast remained at 2.3 or less even in a light-adjusting device 10 in which two light-adjusting sheets were stacked. Furthermore, the evaluation results of Test Example 11 showed that when the average absorbance difference between one light-adjusting sheet is less than 0.1, the contrast remained at 2.3 or less even in a light-adjusting device 10 in which two light-adjusting sheets were stacked.

In contrast, the evaluation results of Test Examples 12 to 15 showed that when the average absorbance difference between one light-adjusting sheet is 0.4 or more, the contrast increased sharply in the light-adjusting device 10 in which two light-adjusting sheets were stacked. In the evaluation results of Test Examples 12 to 15, the evaluation results of Test Examples 12 to 15 showed that when the horizontal absorbance difference between one light-adjusting sheet is 0.1 or more, the contrast increased sharply in the light-adjusting device 10 in which two light-adjusting sheets were stacked.

Furthermore, the evaluation results of Test Examples 11 to 15 also confirmed that when the average absorbance of the two light-adjusting sheets was 0.4 or higher, the contrast increase rate was 1 or higher in the light-adjusting device 10 in which two light-adjusting sheets were stacked. Furthermore, the evaluation results of Test Examples 11 to 15 also confirmed that when the horizontal absorbance of the two light-adjusting sheets was 0.1 or higher, the contrast increase rate was 1 or higher in the light-adjusting device 10 in which two light-adjusting sheets were stacked.

Furthermore, as shown in Figures 3, 4, and 8, the evaluation results for Test Examples 1 to 37 showed that when the average absorbance difference in the light control device 10 was less than 0.8, the contrast remained at around 3. On the other hand, when the average absorbance difference in the light control device 10 was 0.8 or more, the contrast increased even more sharply.

As shown in Figures 3, 4, and 9, the evaluation results for Test Examples 1 to 15 demonstrated that the dependence of contrast on diffuse transmittance was significantly greater than the dependence of contrast on parallel transmittance. In other words, promoting the scattering of linearly transmitted light in the light-controlling sheet was shown to increase the light absorption by the dichroic dye, accelerating the improvement in contrast.

As shown in Figure 3, when the haze of one light-adjusting sheet is 79% or more and the total light transmittance is 25% or less, it was also confirmed that the contrast in a light-adjusting device 10 in which two light-adjusting sheets are stacked can be increased to 4 or more. When the average absorbance difference in one light-adjusting sheet is 0.4 or more and the total light transmittance is 25% or less, it was also confirmed that the contrast in a light-adjusting device 10 in which two light-adjusting sheets are stacked can be increased to 4 or more.

It was also found that when the haze of one light-adjusting sheet is 79% or more and the diffuse transmittance is 16% or less, the probability of the contrast being increased to 4 or more in a light-adjusting device 10 in which two light-adjusting sheets are stacked is increased. It was also found that when the average absorbance difference of one light-adjusting sheet is 0.4 or more and the diffuse transmittance is 16% or less, the probability of the contrast being increased to 4 or more in a light-adjusting device 10 in which two light-adjusting sheets are stacked is increased.

It was also found that when the haze of one light-adjusting sheet is 79% or more and the parallel ray transmittance is 5% or less, the probability of the contrast being increased to 4 or more in a light-adjusting device 10 in which two light-adjusting sheets are stacked is increased. It was also found that when the average absorbance difference of one light-adjusting sheet is 0.4 or more and the parallel ray transmittance is 5% or less, the probability of the contrast being increased to 4 or more in a light-adjusting device 10 in which two light-adjusting sheets are stacked is increased.

It was also found that when the haze of one light-adjusting sheet is 79% or more and the clarity is 95% or less, the probability of the contrast being increased to 4 or more in a light-adjusting device 10 in which two light-adjusting sheets are stacked is increased. It was also found that when the average absorbance difference of one light-adjusting sheet is 0.4 or more and the clarity is 95% or less, the probability of the contrast being increased to 4 or more in a light-adjusting device 10 in which two light-adjusting sheets are stacked is increased.

As described above, according to the above embodiment, the following effects can be obtained.
(1) Since the average absorbance difference of the light control device 10 is 0.8 or more, the contrast of the light control device 10 can be significantly improved.

(2) Since the opaque haze of each light-controlling sheet constituting the light-controlling device 10 is 79% or more, the effectiveness of significantly increasing the contrast in the light-controlling device 10 is enhanced.
(3) Since the difference in average absorbance between the light-adjusting sheets constituting the light-adjusting device 10 is 0.4 or more, the effectiveness of significantly increasing the contrast in the light-adjusting device 10 is enhanced.

(4) If the configuration satisfies not only condition 1 but also at least one of conditions 4 to 7, the feasibility of obtaining effects equivalent to (1) and (2) above is increased.
(5) If the dimming device 10 is equipped with a reverse-type dimming sheet that satisfies condition 1, it is possible to obtain high contrast even in a dimming device 10 that forms a dark state solely through the alignment control force of the alignment layers 22, 23 or the reactive mesogenic compound.

The above-described embodiment can be modified as follows.
In the light-controlling layer 21, the voids 21D of the transparent polymer layer 21P may be dispersed throughout the entire transparent polymer layer 21P in the thickness direction, or may be dispersed uniformly throughout the entire transparent polymer layer 21P in the thickness direction.

LCM...liquid crystal compound 10...light control device 11...light control sheet 11UN1...first light control unit 11UN2...second light control unit 21...light control layer 21D...gap 21L...transparent polymer layer 21LC...liquid crystal composition 22...first alignment layer 23...second alignment layer 24...first transparent electrode layer 25...second transparent electrode layer 26...first transparent substrate 27...second transparent substrate

Claims (10)

a liquid crystal composition containing a liquid crystal compound and a dichroic dye;
a transparent polymer layer having voids, the voids being filled with the liquid crystal composition;
A light control device that can be reversibly changed from transparent to opaque by changing the orientation of the liquid crystal compound,
an absorbance difference, which is a value obtained by subtracting an average absorbance of the liquid crystal composition from the absorbance of the light control device in the opaque state , is 0.8 or more;
the average absorbance is an average value of the absorbance in the horizontal alignment and the absorbance in the vertical alignment of the liquid crystal composition,
the absorbance in the horizontal alignment state is an absorbance obtained by placing the liquid crystal composition containing the liquid crystal compound and the dichroic dye in a cell for horizontal alignment having a thickness of 6 μm,
The absorbance in the case of vertical alignment is the absorbance obtained by placing the liquid crystal composition containing the liquid crystal compound and the dichroic dye in a cell for vertical alignment having a thickness of 6 μm.
A light control device characterized by: a first light-controlling sheet that reversibly changes from transparent to opaque;
a second light-controlling sheet that reversibly changes from transparent to opaque;
The first light controlling sheet is overlaid on the second light controlling sheet,
the transparent polymer layer is a laminated structure,
The first light controlling sheet is
a first transparent polymer layer constituting the transparent polymer layer;
a first liquid crystal composition that fills the voids in the first transparent polymer layer and constitutes the liquid crystal composition;
The second light controlling sheet is
a second transparent polymer layer constituting the transparent polymer layer;
a second liquid crystal composition that fills the voids in the second transparent polymer layer and constitutes the liquid crystal composition;
The first light-controlling sheet and the second light-controlling sheet simultaneously become opaque.
The light control device according to claim 1 . The first light controlling sheet and the second light controlling sheet are separate light controlling sheets,
The light control device according to claim 2 , wherein an absorbance difference, which is a value obtained by subtracting an average absorbance of the liquid crystal composition from the absorbance of the light control sheet in the opaque state, is 0.4 or more. The first light controlling sheet and the second light controlling sheet are separate light controlling sheets,
The light-adjusting device according to claim 2 or 3, wherein the haze of the light-adjusting sheet in the opaque state is 79% or more. The first light controlling sheet and the second light controlling sheet are separate light controlling sheets,
The light-adjusting device according to claim 2 or 3, wherein the light-adjusting sheet has a total light transmittance of 25% or less when opaque. The first light controlling sheet and the second light controlling sheet are separate light controlling sheets,
The light-adjusting device according to claim 2 or 3, wherein the diffuse transmittance of the light-adjusting sheet in the opaque state is 16% or less. The first light controlling sheet and the second light controlling sheet are separate light controlling sheets,
The light-adjusting device according to claim 2 or 3, wherein the parallel ray transmittance of the light-adjusting sheet in the opaque state is 5% or less. The first light controlling sheet and the second light controlling sheet are separate light controlling sheets,
The light-adjusting device according to claim 2 or 3, wherein the clarity of the light-adjusting sheet in the opaque state is 95% or less. The first light controlling sheet and the second light controlling sheet are separate light controlling sheets,
The light-controlling sheet is
a first transparent electrode layer;
A second transparent electrode layer;
a first alignment layer located between the first transparent electrode layer and the transparent polymer layer;
a second alignment layer located between the second transparent electrode layer and the transparent polymer layer;
The thickness of the light-controlling sheet is 10 μm or less.
The light control device according to claim 2 or 3. The light control device according to claim 1 , wherein the transparent polymer layer has a single layer structure.