JP2024151249A - Light control device - Google Patents

Abstract

[Problem] To provide a light control device that enhances contrast. [Solution] The light control device includes a transparent polymer layer 21P having voids 21D, and a liquid crystal composition 21LC that contains a liquid crystal compound LCM and a dichroic dye DP and fills the voids 21D, and reversibly changes from a transparent state to an opaque state, and an absorbance difference, which is the value obtained by subtracting the absorbance of the light control device in the transparent state from the absorbance of the light control device in the opaque state, is 0.6 or more. The absorbance difference may be 1.3 or less. [Selected Figure] Figure 3

Description

This disclosure relates to a light control device that can be reversibly changed from transparent to opaque.

Normal-type light-adjusting sheets have a light-adjusting layer that contains liquid crystal compounds. A drive signal input to the light-adjusting sheet creates an electric field in the light-adjusting layer so as to align the long axis direction of the liquid crystal compounds. This allows the normal-type light-adjusting sheet to reversibly change from transparent when driven to opaque when not 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 regulating force to the liquid crystal compound. One example of the alignment regulating force is to regulate 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. A drive signal input to the light-controlling sheet forms an electric field that opposes the alignment regulating force so that the long axis direction of the liquid crystal compound is approximately parallel to the surface direction of the alignment layer. This causes the reverse-type light-controlling sheet to reversibly change from transparent when not driven to opaque when driven (see, for example, Patent Document 1).

JP 2019-194654 A

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 caused by the difference in refractive index between the transparent polymer layer and the particles. Adding a dichroic dye to the particles gives color to the opaqueness when driven while achieving colorless transparency when not driven.

On the other hand, excessively increasing the blend ratio of dichroic dyes increases the degree of color when opaque, but weakens the dispersion due to refractive index differences and reduces the responsiveness of the liquid crystal compound. As a result, there is a new demand for light-control sheets that contain dichroic dyes in the liquid crystal composition, whether normal type 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 for solving the above problem comprises a transparent polymer layer having voids, and a liquid crystal composition that contains a liquid crystal compound and a dichroic dye and fills the voids, and is a light control device that reversibly changes from a transparent state to an opaque state, and the absorbance difference, which is the value obtained by subtracting the absorbance of the light control device when it is transparent from the absorbance of the light control device when it is opaque, is 0.6 or more.

The dimming device disclosed herein can improve contrast.

FIG. 1 is a cross-sectional view showing the layer structure of a light control device according to a first example. FIG. 2 is a cross-sectional view showing the layer structure of the light control device of the second example. FIG. 3 is a cross-sectional view showing the layer structure of the light controlling sheet. FIG. 4 is a cross-sectional view showing the layer structure of the light controlling sheet. FIG. 5 is a graph showing the relationship between the transmittance difference and the contrast in Test Example 1. FIG. 6 is a graph showing the relationship between the absorbance difference and the contrast in Test Example 1. FIG. 7 is a graph showing the relationship between the absorbance ratio and the contrast in Test Example 1. FIG. 8 is a graph showing the relationship between the absorbance ratio and the contrast in Test Example 2. FIG. 9 is a graph showing the relationship between the thickness of the light-controlling layer in Test Example 1 and the absorbance in the transparent state. FIG. 10 is a graph showing the relationship between absorbance and contrast in the light-modulating layer of Test Example 1.

An embodiment of a light control device will be described with reference to FIGS.
The light control sheet constituting the light control device 10 may be attached to a window of a moving object such as a vehicle or an aircraft. The light control sheet may be attached to a window of various buildings such as a house, a station, an airport, a partition installed in an office, a show window installed in a store, a screen for projecting images, etc. The shape of the light control sheet may be flat or curved.

The light-adjusting sheet reversibly changes from transparent to opaque. The type of 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. The light-adjusting device 10 is equipped with one or more light-adjusting sheets. The light-adjusting sheet equipped in the light-adjusting device 10 may be a single layer composed of one light-adjusting sheet, or may be a laminate in which one light-adjusting sheet overlaps another light-adjusting sheet.

In the following, an example will be shown in which the light controlling sheet provided in the light controlling device 10 is a reverse type light controlling sheet.
[First Example of Light Adjustment Device 10]
As shown in FIG. 1, the light control device 10 of the first example includes one light control unit 11 and one driving unit 12. The light control unit 11 includes one reverse-type light control sheet. The light control sheet includes a light control 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 light control layer 21, the first alignment layer 22 and the second alignment layer 23 sandwich the light control layer 21. The light control layer 21 is located between the first alignment layer 22 and the second alignment layer 23. The light control layer 21 contacts the first alignment layer 22 and the second alignment layer 23. In the thickness direction of the light control layer 21, the first transparent electrode layer 24 and the second transparent electrode layer 25 sandwich a pair of alignment layers 22, 23. The light-controlling layer 21 is located between a first transparent electrode layer 24 and a second transparent electrode layer 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 supporting the first transparent electrode layer 24, and a second transparent substrate 27 supporting 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 includes one dimming unit 11UN. The dimming unit 11UN is a repeating unit in the thickness direction of the dimming sheet. The dimming device 10 of the example shown in FIG. 1 includes one dimming unit 11UN. The dimming unit 11UN 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. The dimming unit 11UN includes one dimming sheet, a first electrode 24A, a first wiring 24B, a second electrode 25A, and a second wiring 25B. The dimming unit 11UN may include other functional layers such as a hard coat layer, an ultraviolet absorbing layer, and an infrared absorbing layer.

[Second Example of Light Control Device 10]
As shown in FIG. 2, the light control device 10 of the second example includes one light control unit 11 and two driving units 12. The light control unit 11 includes two reverse-type light control sheets. One light control sheet includes a light control 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 light control layer 21, the first alignment layer 22 and the second alignment layer 23 sandwich the light control layer 21. The light control layer 21 is located between the first alignment layer 22 and the second alignment layer 23. The light control layer 21 contacts the first alignment layer 22 and the second alignment layer 23. In the thickness direction of the light control layer 21, the first transparent electrode layer 24 and the second transparent electrode layer 25 sandwich a pair of alignment layers 22 and 23. The light control layer 21 is located between the transparent electrode layers 24 and 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 light control device 10 includes two light control units 11UN. The two light control units 11UN include a first light control unit 11UN1 and a second light control unit 11UN2.
The first dimming unit 11UN1 has a similar structure to the second dimming unit 11UN2. The second transparent base material 27 of the second dimming unit 11UN2 overlaps with the first transparent base material 26 of the first dimming unit 11UN1. The second transparent base material 27 of the second dimming unit 11UN2 is bonded to the first transparent base material 26 of the first dimming unit 11UN1 via an optical transparent adhesive. The dimming device 10 composed of a plurality of dimming units 11UN makes the optical path length of the light entering the dimming device 10 longer in the dimming device 10 compared to the dimming device 10 composed of one dimming unit 11UN.

One driver 12 inputs a drive signal to the first dimming unit 11UN1. The other driver 12 inputs a drive signal to the second dimming unit 11UN2. The two drivers 12 simultaneously make the first dimming unit 11UN1 and the second dimming unit 11UN2 opaque. The two drivers 12 simultaneously make the first dimming unit 11UN1 and the second dimming unit 11UN2 transparent. The two drivers 12 may separately make the first dimming unit 11UN1 and the second dimming unit 11UN2 opaque. The two drivers 12 may separately make the first dimming unit 11UN1 and the second dimming unit 11UN2 transparent.

The dimming device 10 of the second example may include one driving unit 12. The driving unit 12 inputs a driving signal to the first dimming unit 11UN1 and inputs a driving signal to the second dimming unit 11UN2. The driving unit 12 simultaneously makes the first dimming unit 11UN1 and the second dimming unit 11UN2 opaque. The driving unit 12 simultaneously makes the first dimming unit 11UN1 and the second dimming unit 11UN2 transparent. The driving unit 12 may separately make the first dimming unit 11UN1 and the second dimming unit 11UN2 opaque. The driving unit 12 may separately make the first dimming unit 11UN1 and the second dimming unit 11UN2 transparent.

[Light control sheet]
The light controlling sheets provided in the light controlling devices 10 of the first and second examples will be described below.
As shown in Fig. 3, the light control layer 21 includes a transparent polymer layer 21P and a liquid crystal composition 21LC. The transparent polymer layer 21P has optical transparency that transmits visible light. The transparent polymer layer 21P includes a large number of voids 21D. The transparent polymer layer 21P is a cured product of a polymerizable composition. The transparent polymer layer 21P may be a cured product of a photocurable compound or a cured product of a thermosetting compound. The liquid crystal composition 21LC fills the inside of the voids 21D.

The photocurable compound forming the transparent polymer layer 21P may be at least one selected from the group consisting of acrylate compounds, methacrylate compounds, styrene compounds, thiol compounds, and oligomers of each of these compounds. The acrylate compound may be at least one selected from the group consisting of monoacrylate compounds, diacrylate compounds, triacrylate compounds, and tetraacrylate compounds. The acrylate compound may be at least one selected from the group consisting of butyl ethyl acrylate, ethylhexyl acrylate, and cyclohexyl acrylate. The methacrylate compound may be at least one selected from the group consisting of dimethacrylate compounds, trimethacrylate compounds, and tetramethacrylate compounds. The methacrylate compound may be at least one selected from the group consisting of N,N-dimethylaminoethyl methacrylate, phenoxyethyl methacrylate, methoxyethyl methacrylate, and tetrahydrofurfuryl methacrylate. The thiol compound may be 1,3-propanedithiol or 1,6-hexanedithiol. The styrene compound may be styrene or methylstyrene.

The liquid crystal composition 21LC includes a liquid crystal compound LCM and a dichroic dye DP. In addition to the liquid crystal compound LCM and the dichroic dye DP, the liquid crystal composition 21LC may contain a polymerizable composition for forming the transparent polymer layer 21P, a plasticizer for reducing the viscosity of the liquid crystal composition 21LC, and the like. The ratio of the mass of the liquid crystal composition 21LC to the total mass of the light control layer 21 may be 30% by mass or more and 70% by mass or less, or 40% by mass or more and 60% by mass or less. The liquid crystal composition 21LC may further contain a reactive mesogen compound. When the liquid crystal compound LCM is vertically aligned, the reactive mesogen compound is also vertically aligned. The vertically aligned reactive mesogen compound is networked to promote the vertical alignment of the liquid crystal compound LCM. In other words, the alignment control force of the networked reactive mesogen compound promotes the vertical alignment of the liquid crystal compound LCM.

The type of the light control layer 21 is a polymer dispersion type. The polymer dispersion type light control layer 21 has 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 dispersion type light control layer 21 may be a polymer network type light control layer 21 or a capsule type light control layer 21. The polymer network type light control layer 21 has a transparent polymer layer 21P having a three-dimensional mesh shape, and holds the liquid crystal composition 21LC in the interconnected mesh voids 21D. The capsule type light control layer 21 holds the liquid crystal composition 21LC in the capsule-shaped voids 21D dispersed in the transparent polymer layer 21P.

The liquid crystal compound LCM may be at least one selected from the group consisting of Schiff base type, azo type, azoxy type, biphenyl type, terphenyl type, benzoic acid ester type, tolane type, pyrimidine type, cyclohexane carboxylate type, phenylcyclohexane type, and dioxane type.

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 the 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 the weighted average value 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 depending on the composition of two or more liquid crystal compounds LCM with different NI points. When it is required to increase the orientation order of the liquid crystal compound LCM at a high ambient temperature such as 100°C, it is preferable that the NI point is 100°C or higher. When it is required to increase the uniformity of the polymerizable composition for forming the transparent polymer layer 21P and the liquid crystal compound LCM, it is preferable that the NI point is 145°C or lower.

The CN point of the 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 the 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 value 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 depending on the composition of two or more compounds with mutually different NI points. When it is required to increase the fluidity of the liquid crystal compound LCM at a low ambient temperature 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 (Δn = extraordinary light refractive index ne - ordinary light refractive index no) between the long axis direction and the short axis direction of the liquid crystal compound LCM 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 stopped. When the liquid crystal compound LCM is a combination of two or more types of compounds, the upper limit value of the refractive index difference Δn of the liquid crystal compound LCM is the upper limit value obtained from the refractive index differences Δn of all the compounds. The lower limit value of the refractive index difference Δn of the liquid crystal compound LCM is the lower limit value obtained from the refractive index differences Δn of all the compounds.

When it is required to increase the alignment controllability of the liquid crystal compound LCM at high environmental temperatures, it is preferable that the lower limit value of the refractive index difference Δn is high. When it is required to increase 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 increase the alignment controllability of the liquid crystal compound LCM at high environmental 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 increase 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 DP increases the absorbance of visible light in the long axis direction of the molecule more than the absorbance of visible light in the short axis direction of the molecule. The dichroic dye DP is driven by a guest-host system with the liquid crystal compound LCM as the host. The dichroic dye DP reversibly changes from transparent to colored in accordance with the change in orientation of the liquid crystal compound LCM. The liquid crystal composition 21LC contains one type of dichroic dye DP or a combination of two or more types of dichroic dye DP. The combination of dichroic dyes DP is appropriately adjusted so that the color exhibited by the combination of dichroic dyes DP is the color exhibited when the light-adjusting sheet is opaque.

The color of the light-adjusting sheet when opaque may be black or may be black with a chromatic color. One example of the dichroic dye DP is a dichroic dye that has a chromaticity a* of -15 to 15 and a chromaticity b* of -15 to 15 in the CIE1976 (L*a*b*) color system in an opaque light-adjusting sheet. The chromaticity a* and chromaticity b* in the CIE1976 (L*a*b*) color system are specified in accordance with the method of calculating the color coordinates of the CIE1976 (L*a*b*) color space specified in JIS-Z-8781-4 (ISO 11664-4). The ratio of the mass of the dichroic dye DP to the total mass of the light-adjusting layer 21 is the compounding ratio of the dichroic dye DP. The compounding ratio of the dichroic dye DP may be 0.2% by mass or more and 5% by mass or less, 1% by mass or more and 4% by mass or less, or 2% by mass or more and 4% by mass or less. Increasing the compounding ratio of the dichroic dye DP increases the contrast of the light control device 10 while decreasing the responsiveness of the liquid crystal compound LCM. From the viewpoint of increasing the contrast of the light control device 10, it is preferable that the compounding ratio of the dichroic dye DP is the upper limit value within the range in which the responsiveness of the liquid crystal compound LCM can be obtained.

The dichroic dye DP is driven by a guest-host system with the liquid crystal compound LCM as a host, thereby exhibiting a specific color. The dichroic dye DP 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 DP is a single compound or a combination of two or more compounds. When it is required to increase the light resistance and the dichroic ratio, the dichroic dye DP 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 a spacer. The spacer is dispersed throughout the light-adjusting layer 21. The spacer determines the thickness of the spacer to the thickness of the light-adjusting layer 21 around the spacer, and makes the thickness of the light-adjusting layer 21 uniform. The spacer may be a bead spacer, or a photospacer formed by exposing and developing a photoresist. The spacer may be colorless and transparent, or colored and transparent. When it is required to reduce the visibility of the spacer when the light-adjusting sheet is opaque, or to reduce the brightness of the color exhibited when the light-adjusting sheet is opaque, the color exhibited by the spacer may be the same color as the color exhibited when the light-adjusting sheet is opaque, or may be the same color as the color exhibited by the dichroic dye DP.

The thickness of the light-adjusting layer 21 may be 2 μm or more and 30 μm or less, or 5 μm or more and 25 μm or less. When it is required to strengthen the effect of the alignment control force on the liquid crystal compound LCM, the thickness of the light-adjusting layer 21 is preferably 5 μm or more and 25 μm or less. When the transparent polymer layer 21P is formed by phase separation, the thickness of the light-adjusting layer 21 being 5 μm or more enables uneven distribution of voids 21D having a diameter of 1 μm or less. In addition, it is possible to generate a region in the light-adjusting layer 21 in which the density of the liquid crystal composition 21LC differs in the thickness direction of the light-adjusting layer 21. When the thickness of the light-adjusting layer 21 is 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 during the manufacture of the light-adjusting layer 21.

The first alignment layer 22 exerts an alignment regulating force on the liquid crystal compound LCM from the surface of the light control 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 control layer 21 that contacts the second alignment layer 23. The alignment layers 22 and 23 have optical transparency that transmits visible light. The alignment layers 22 and 23 may be vertical alignment layers. The alignment regulating force exerted by the vertical alignment layer aligns the long axis direction of the liquid crystal compound LCM so that it is perpendicular to the surface of the alignment layers 22 and 23 that contacts the light control layer 21. The alignment layers 22 and 23 may orient the liquid crystal compound LCM so that the long axis is inclined by several degrees from the vertical within a range in which the long axis of the liquid crystal compound LCM is judged to be substantially perpendicular to the transparent electrode layers 24 and 25. The thickness of the alignment layers 22 and 23 may be 0.02 μm or more and 0.5 μm or less, or 0.05 μm or more and 0.3 μm or less.

The material constituting the alignment layers 22 and 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 as each other or different from each other. The organic compound constituting the alignment layers 22 and 23 may be at least one selected from the group consisting of polyimide, polyamide, polyvinyl alcohol, and cyanide compounds. The inorganic compound constituting the alignment layers 22 and 23 may be silicon oxide or zirconium oxide. The organic-inorganic composite material constituting the alignment layers 22 and 23 may be silicone having an inorganic structure and an organic structure.

The first transparent electrode layer 24 and the second transparent electrode layer 25 form an electric field in the thickness direction of the dimming layer 21 when a drive signal is input. The transparent electrode layers 24 and 25 are optically transparent and transmit visible light. The thickness of the transparent electrode layers 24 and 25 may be 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. The inorganic compound constituting the transparent electrode layers 24, 25 may be at least one selected from the group consisting of indium tin oxide, fluorine-doped tin oxide, tin oxide, and zinc oxide. The organic compound constituting the transparent electrode layers 24, 25 may be poly(3,4-ethylenedioxythiophene). The organic-inorganic composite material constituting the transparent electrode layers 24, 25 may be 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 so as to conform to the curved surface to which the light-adjusting sheet is attached, or may be rigid so as 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. The thickness of the transparent substrates 26, 27 may be 15 μm or more and 250 μm or less. Having the transparent substrates 26, 27 be 15 μm or more increases the mechanical durability of the light-adjusting sheet and the chemical durability of the light-adjusting layer 21. Having the transparent substrates 26, 27 be 250 μm or less in thickness enables the light-adjusting sheet to be manufactured by roll-to-roll.

The material constituting the transparent substrates 26, 27 may be an organic compound or an inorganic compound. The organic compound constituting the transparent substrates 26, 27 may be at least one selected from the group consisting of polyester, polyacrylate, polycarbonate, and polyolefin. The inorganic compound constituting the transparent substrates 26, 27 may be 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 having transparent adhesiveness 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 a flexible printed circuit board or a metal tape. The electrodes 24A, 25A may be attached to the transparent electrode layers 24, 25 by 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-adjusting layer 21 changes the orientation of the liquid crystal compound LCM by changing the electric field formed between the two transparent electrode layers 24, 25. The change in orientation in the liquid crystal compound LCM changes the degree of scattering, absorption, and transmission of visible light that enters the light-adjusting layer 21.

When an electric field is formed in the light-adjusting 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 regulating force of the alignment layers 22, 23, etc., and has a relatively high haze. When a voltage is applied to the light-adjusting 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 DP 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-adjusting layer 21, each unit 11UN1, 11UN2 becomes colored and opaque.

When no voltage is applied to the light-adjusting layer 21, i.e., when no potential difference occurs between the two transparent electrode layers 24, 25, each unit 11UN1, 11UN2 has a lower haze than when a potential difference occurs, according to the orientation regulation force of the orientation layers 22, 23, etc. When no voltage is applied to the light-adjusting layer 21, each unit 11UN1, 11UN2 reduces the refractive index difference between the transparent polymer layer 21P and the liquid crystal compound LCM to suppress light scattering in the light-adjusting layer 21. The dichroic dye DP follows the orientation of the liquid crystal compound LCM and is oriented to reduce absorbance. As a result, when no voltage is applied to the light-adjusting layer 21, each unit 11UN1, 11UN2 becomes transparent.

The state in which one light control sheet is colored and opaque is the dark state of the light control device 10 of the first example. The state in which each unit 11UN1, 11UN2 is colored and opaque is the dark state of the light control device 10 of the second example. The colored opaque may be black opaque or a colored opaque other than black.

When one light control sheet is transparent, the light control device 10 of the first example is in a bright state. When each unit 11UN1, 11UN2 is transparent, the light control device 10 is in a bright state. The transparency may be colorless transparency or colored transparency. The colored transparency may be black transparency or a colored transparency other than black.

The light-adjusting sheet may have a translucency that is intermediate between transparency and opacity. The translucency may be colorless translucency or colored translucency. The colored translucency may be black translucency or a colored translucency other than black. The driver 12 that achieves translucency sets the voltage applied to the light-adjusting layer 21 to an intermediate value between transparency and opacity.

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. In the second example of the dimming device 10, the first dimming unit 11UN1 may be colored and opaque, and the second dimming unit 11UN2 may be colored and opaque. In the second example of the dimming device 10, the first dimming unit 11UN1 may be opaque, and the second dimming unit 11UN2 may be translucent. In the second example of the dimming device 10, the first dimming unit 11UN1 may be opaque, and the second dimming unit 11UN2 may be transparent.

[Distribution of voids 21D]
In Figures 3 and 4, for convenience of illustration, the transparent substrates 26 and 27 are omitted. In Figures 3 and 4, for convenience of explaining the structure of the light-adjusting layer 21, the ratio of the thickness of the light-adjusting layer 21 to the thicknesses of the alignment layers 22 and 23 and the transparent electrode layers 24 and 25 is larger than the actual ratio. Figures 3 and 4 show a schematic state of the light-adjusting layer 21 when no potential difference is generated between the transparent electrode layers 24 and 25.

As shown in FIG. 3, an example of the light-controlling 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 the liquid crystal composition 21LC per unit thickness in the first high density portion 21H1 is higher than the density of the liquid crystal composition 21LC per unit thickness in the low density portion 21L. The quantity density of the voids 21D per unit thickness in the first high density portion 21H1 is higher than the quantity density of the 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 the liquid crystal composition 21LC in the light-adjusting layer 21 is lowest at the middle of the light-adjusting layer 21 in the thickness direction. The middle of the light-adjusting layer 21 in the thickness direction is closer to the center of the light-adjusting layer 21 than the pair of opposing surfaces in the thickness direction of the light-adjusting layer 21. The density of the liquid crystal composition 21LC per unit thickness in each part of the light-adjusting layer 21 is calculated by dividing the volume of the liquid crystal composition 21LC contained in each part by the thickness of each part. The density of the liquid crystal composition 21LC in the light-adjusting layer 21 may be lowest at a part including the center in the thickness direction of the light-adjusting layer 21. Since the light-adjusting layer 21 is very thin, instead of calculating the volume of the liquid crystal composition 21LC contained in the light-adjusting layer 21, each density may be calculated as an approximate value using the area of the liquid crystal composition 21LC calculated from an SEM image of a cross section of the light-adjusting layer 21 and the area of the light-adjusting layer 21.

The quantity density of voids 21D in the transparent polymer layer 21P is lowest in the middle of the thickness direction of the light-adjusting layer 21. The quantity density of voids 21D per unit thickness in each part of the transparent polymer layer 21P is calculated by dividing the number of voids 21D contained in each part by the thickness of each part. The quantity density of voids 21D in the transparent polymer layer 21P may be lowest in a part including the center in the thickness direction of the light-adjusting 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. Such uneven distribution of the liquid crystal compound LCM enhances the light transmittance when the light control device 10 is transparent.

In the light control 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 each other. That is, an example of 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 is 1/3 of the thickness T21 of the light control 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. Also, 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 along the thickness direction of the light-adjusting layer 21, the percentage of the total area of each gap 21D contained in the low-density portion 21L relative to the area of the low-density portion 21L may be 10% or less. This makes it possible to reduce the proportion of the liquid crystal composition 21LC held by the gaps 21D of the low-density portion 21L, and therefore prevents the liquid crystal compound LCM contained in the low-density portion 21L from increasing the opacity of the light-adjusting sheet when no potential difference is generated between the transparent electrode layers 24, 25.

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

In this way, in the low-density portion 21L, the sum of the areas of the voids 21D relative to the area 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 light-adjusting 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 contacts the first alignment layer 22. It is also preferable that each void 21D included in the second high density portion 21H2 contacts the second alignment layer 23.

In the light-adjusting sheet, the thickness T21 of the light-adjusting 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-adjusting layer 21. When the thickness of the light-adjusting 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 held in the vicinity of the alignment layers 22, 23. Therefore, it is possible to increase the transparency of the light-adjusting sheet when no voltage difference occurs between the transparent electrode layers 24, 25. If it is required to increase the degree of scattering by the voids 21D, it is preferable that the size of the voids 21D is 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 is 0.1 μm or more.

As shown in FIG. 4, another example of the photochromic layer 21 includes a single void layer formed by multiple voids 21D in contact with the first alignment layer 22 and a single void layer formed by multiple voids 21D in contact with the second alignment layer 23. In each void layer, a single void 21D is aligned along the interface between each alignment layer 22, 23 and the photochromic layer 21.

The void layer in contact with the first alignment layer 22 includes at least one void 21D that is in contact with any of the voids 21D in the void layer in contact with the second alignment layer 23. All of the voids 21D included in the void layer in contact with the first alignment layer 22 may be in contact with any of the voids 21D included in the void layer in contact with the second alignment layer 23.

In the void layer in contact with the first alignment layer 22, the surface in contact with the first alignment layer 22 is the first surface, and the surface opposite to the first surface is the second surface. The second surface is a plane including the portion of the void 21D contained in the void layer that is the furthest from the first alignment layer 22. In the void layer in contact with the second alignment layer 23, the surface in contact with the second alignment layer 23 is the first surface, and the surface opposite to the first surface is the second surface. The second surface is a plane including the portion of the void 21D contained in the void layer that is the furthest from the second alignment layer 23. The second surface of the void layer in contact with the first alignment layer 22 and the second surface of the void layer in contact with the second alignment layer 23 may be the same surface.

Another example of the light control layer 21 includes a first high density portion 21H1, a second high density portion 21H2, and a low density portion 21L. In the thickness direction of the light control layer 21, the low density portion 21L is sandwiched between the first high density portion 21H1 and the second high density portion 21H2. The low density portion 21L includes a portion in the gap layer in contact with the first alignment layer 22 where the gap 21D is not located, and includes a portion in the gap layer in contact with the second alignment layer 23 where the gap 21D is not located. The density of the liquid crystal composition 21LC in the low density portion 21L is smaller than the density of the liquid crystal composition 21LC in the first high density portion 21H1 and the density of the liquid crystal composition 21LC in the second high density portion 21H2. The density of the liquid crystal composition 21LC in the middle portion of the thickness direction of the light control layer 21 is the lowest in the light control layer 21.

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

When the coating liquid is cured by irradiation with ultraviolet light, the liquid crystal composition 21LC containing the liquid crystal compound LCM and the dichroic dye DP is distributed almost uniformly in the polymerizable composition. Next, the polymerizable composition begins to cure near the alignment layers 22, 23, and the liquid crystal composition 21LC separates from the polymer of the polymerizable composition. A portion of the liquid crystal composition 21LC present in the coating film is likely to become stable by being integrated with the separated liquid crystal composition 21LC, and therefore moves toward the alignment layers 22, 23. Then, almost the entire polymerizable composition is cured, forming a transparent polymer layer 21P having voids 21D surrounding the liquid crystal composition 21LC.

Until the transparent polymer layer 21P is formed, the liquid crystal composition 21LC separated from each other gathers to stabilize the energy. When the polymerizable composition is cured at a high speed, or when the liquid crystal composition 21LC moves at a high speed, the liquid crystal composition 21LC is encouraged to gather over a wide range, and the size of the voids 21D is large. The speed at which the polymerizable composition is cured can be increased by increasing the temperature of the coating liquid when irradiating the coating liquid. On the other hand, when the range of the polymerizable composition that is cured at the same time is wide, the voids 21D are separated from other voids 21D before the liquid crystal composition 21LC gathers. The range of the polymerizable composition that is cured at the same time can be expanded by increasing the illuminance of the ultraviolet light irradiated to the coating liquid. Since the size of the voids 21D that can grow is limited, the range in which the voids 21D are formed is likely to reach the low-density portion 21L by further increasing the curing speed of the polymerizable composition.

[contrast]
The contrast of the light control device 10 is the ratio of the total light transmittance when transparent to the total light transmittance when opaque, i.e., the contrast of the light control device 10 is the ratio of the total light transmittance when bright to the total light transmittance when dark.

The dimming layer 21 of the dimming device 10 changes the orientation of the liquid crystal compound LCM by changing the voltage between the two transparent electrode layers 24, 25. The change in the orientation of the liquid crystal compound LCM changes the degree of scattering, absorption, and transmission of visible light entering the dimming layer 21. Scattering of visible light gives the dimming layer 21 a cloudy state, i.e., opaqueness or translucency. Scattering and absorption of visible light gives the dimming layer 21 a dark opaqueness or dark translucency. The total transmitted light of the dimming device 10 includes straight transmitted light that passes through the dimming device 10 without being scattered by the dimming device 10, and scattered light that is scattered by the dimming device 10. The total light transmittance of the dimming device 10 depends on the sum of the amount of straight transmitted light and the amount of scattered light. Even if the sum of the amount of straight transmitted light and the amount of scattered light is constant, the amount of scattered light by the dimming device 10 changes.

As described above, the dichroic dye DP increases the absorbance of visible light in the long axis direction of the molecule more than the absorbance of visible light in the short axis direction of the molecule. Increasing the blend ratio of the dichroic dye DP in the liquid crystal composition 21LC simply reduces the amount of scattered light passing through the dimming device 10. Increasing the blend ratio of the dichroic dye DP reduces the total light transmittance by the amount of the reduction in the amount of scattered light, thereby enabling improvement of contrast. However, increasing the blend ratio of the dichroic dye DP reduces the responsiveness of the liquid crystal compound LCM. For this reason, the blend ratio of the dichroic dye DP is actually set to approximately the upper limit within the range in which the responsiveness of the liquid crystal compound LCM is obtained. Ultimately, there is a limit to increasing the blend ratio of the dichroic dye DP in terms of improving the contrast of the dimming device 10.

On the other hand, the absorption characteristics of the dichroic dye DP show high absorbance for scattered light and low absorbance for straight transmitted light based on the dichroic ratio. The absorbance of the dichroic dye DP increases exponentially with the light path length in the dimming device 10 as a variable. Promoting the scattering of straight transmitted light in the dimming device 10 reduces the total light transmittance when opaque by improving the degree of absorbance of the dichroic dye DP, thereby enabling improvement of contrast. However, in order to sharply increase the absorbance by the dichroic dye DP, it is necessary not only to simply promote the scattering of straight transmitted light, but also to increase the scattering to the extent that the light scattered at the interface between the transparent polymer layer 21P and the liquid crystal composition 21LC reaches the dichroic dye DP.

The light-controlling layer 21 of the light-controlling sheet is formed by curing the coating film. The coating film contains a polymerizable composition for forming a transparent polymer layer 21P, a liquid crystal compound LCM, and a dichroic dye DP. When the coating film is irradiated with ultraviolet light that polymerizes the polymerizable composition, the polymerizable composition begins to cure from the area irradiated with the ultraviolet light, and the liquid crystal composition 21LC phase-separates from the polymer of the polymerizable composition.

On the other hand, phase separation of the liquid crystal composition 21LC causes variation in the concentration of the dichroic dye DP among the voids 21D. For example, when the speed of phase separation of the liquid crystal composition 21LC is fast, many voids 21D are formed instantly. Therefore, before the concentration diffusion of the dichroic dye DP reaches equilibrium among the voids 21D, the concentration gradient of the dichroic dye DP among the voids 21D is fixed together with the formation of the voids 21D. As a result, the concentration of the dichroic dye DP varies in many parts scattered in the light-adjusting layer 21 due to insufficient concentration diffusion. For example, when the speed of phase separation of the liquid crystal composition 21LC is slow, the voids 21D are formed sequentially from the ultraviolet ray irradiation site. Therefore, the phase separation of the liquid crystal composition 21LC proceeds in the direction in which the formation of the voids 21D proceeds spatially. As a result, a gradient is formed in the density of the voids 21D in the direction in which the formation of the voids 21D progresses, and the variation in the density of the voids 21D causes variation in the concentration of the dichroic dye DP.

As described above, the compounding ratio of the dichroic dye DP is set to approximately the upper limit within the range in which the responsiveness of the liquid crystal compound LCM is obtained. Increasing the concentration of the dichroic dye DP to such an upper limit increases the variation in the concentration of the dichroic dye DP due to phase separation of the liquid crystal composition 21LC.

The thickness of the light control layer 21 in a reverse-type light control sheet that uses an orientation control force is required to be thinner than that of the light control layer 21 in a normal-type light control sheet, because the orientation control force acts over the entire thickness direction. A reverse-type light control sheet, in which the thickness of the light control layer 21 is limited, is less likely to increase contrast than a normal-type light control sheet. Also, a reverse-type light control sheet, in which the orientation control force continues to act, is less likely to obtain random orientation of the liquid crystal compound LCM than a normal-type light control sheet. A light control sheet that is less likely to obtain random orientation is even more difficult to increase contrast. For this reason, whether it is a normal type or a reverse type, improved contrast is required of light control sheets, but in particular, there is a stronger demand for increased contrast for reverse-type light control sheets than for normal-type light control sheets.

[Absorbance of light control device 10]
The inventors of the present application have found ranges in which the contrast is sharply increased in (i) the absorbance difference of the light control device 10, (ii) the absorbance ratio of the light control device 10, and (iii) the absorbance when the light control device 10 is transparent, while diligently studying the relationship between the contrast of the light control device 10 and the optical characteristics of the light control device 10. The inventors of the present application have found ranges in which the contrast is sharply increased in (iii) the absorbance when the light control device 10 is transparent, while diligently studying the relationship between the contrast of the light control device 10 and the optical characteristics of the light control device 10.

When it is required to increase the contrast, the dimmer 10 of the first and second examples may satisfy at least one selected from the group consisting of (Condition 1A), (Condition 2A), and (Condition 3A) below. Note that satisfying at least one selected from the group consisting of (Condition 1A), (Condition 2A), and (Condition 3A) may mean satisfying (Condition 1A), (Condition 2A), or (Condition 3A). Satisfying at least one selected from the group consisting of (Condition 1A), (Condition 2A), and (Condition 3A) may mean satisfying a combination of two or more selected from the group consisting of (Condition 1A), (Condition 2A), and (Condition 3A).

When the dimmer 10 satisfies (Condition 1A), the dimmer 10 may further satisfy at least one selected from the group consisting of (Condition 1B) to (Condition 1D). When the dimmer 10 satisfies (Condition 1A), the dimmer 10 may further satisfy (Condition 2B) or (Condition 2C). When the dimmer 10 satisfies (Condition 1A), the dimmer 10 may further satisfy (Condition 3B).

When the dimmer 10 satisfies (Condition 2A), the dimmer 10 may further satisfy (Condition 2B) or (Condition 2C). When the dimmer 10 satisfies (Condition 2A), the dimmer 10 may further satisfy (Condition 3B).

The dimmer 10 of the first and second examples may satisfy (Condition 3A) when it is required to suppress the variation in contrast. If the dimmer 10 satisfies (Condition 3A), the dimmer 10 may further satisfy (Condition 3B).

(Condition 1A) (i) the absorbance difference of the light control device 10 is 0.6 or more.
(Condition 1B) (i) the absorbance difference of the light control device 10 is 1.3 or less.
(Condition 1C) (i) the absorbance difference of the light control device 10 is 0.8 or more and 1.2 or less.
(Condition 1D) The total light transmittance of the light control device 10 in a dark, opaque state is 7% or less.

(Condition 2A) (ii) the absorbance ratio of the light-adjusting device 10 is 2.1 or more.
(Condition 2B) (ii) the absorbance ratio of the light-adjusting device 10 is 3.3 or more.
(Condition 2C) The contrast of the light control device 10 is 4 or more.

(Condition 3A) (iii) the absorbance when the light control device 10 is in a bright state, ie, transparent, is 0.33 or more and 1.1 or less.
(Condition 3B) (iii) the absorbance when the light control device 10 is in a bright state, ie, transparent, is 0.8 or less.

The absorbance difference of the dimmer 10 is a value obtained by subtracting the absorbance when the dimmer 10 is in a transparent, bright state from the absorbance when the dimmer 10 is in an opaque, dark state.
The absorbance ratio of the dimmer 10 is the ratio of the absorbance when the dimmer 10 is in a dark state, that is, opaque, to the absorbance when the dimmer 10 is in a bright state, that is, transparent.

The absorbance of the light control device 10 is generally measured using an absorptiometer conforming to JIS K 0115:2004. This measurement method uses linear transmittance to distinguish between the absorbance of the sample and the attenuation of light due to scattering of the sample. In other words, this measurement method is premised on the fact that the object does not scatter. However, since the light control sheet switches between transparent (bright state) and opaque (dark state) due to scattering and transmission, the measurement method using linear transmittance conforming to JIS K 0115:2004 cannot measure the absorbance in the opaque state for the above-mentioned reasons. Therefore, the inventors decided to use total light transmittance. That is, the total light transmittance of the sample was measured using a haze meter, and the absorbance was calculated using a method conforming to JIS K 0115:2004. The light source unit of the absorptiometer is a white LED that irradiates visible light of 380 nm to 780 nm. The photometric section of the spectrophotometer detects light intensity across the entire visible light range from 380 nm to 780 nm.

The longer the optical path length of light incident on the dimming layer 21, the more the dimming device 10 weakens the straight light that passes through the dimming device 10 when it is opaque. When it is required to increase the absorbance of the dimming device 10 when it is opaque by weakening the straight light, the absorbance may be adjusted by increasing the thickness of the dimming layer 21. Alternatively, when it is required to increase the absorbance of the dimming device 10 when it is opaque by weakening the straight light, the absorbance may be adjusted by increasing the number of dimming layers 21 that the dimming device 10 has.

(i) Absorbance Difference of the Light Control Device 10 The absorbance of the light control device 10 when it is opaque 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 DP. On the other hand, the absorbance of the light control device 10 when it is transparent reflects the weak absorption of the straight light by the dichroic dye DP, but does not reflect the extension of the optical path length due to scattering, i.e., the absorption due to the extension of the optical path length. (i) The absorbance difference of the light control device 10 functions as an index value of the degree of the optical path length substantially extended by scattering due to the internal structure of the light control layer 21, the degree of absorption of the scattered light by the dichroic dye DP, and the degree of increase in absorption due to these. That is, (i) the absorbance difference of the light control device 10 functions as an index value for increasing the contrast of the light control device 10.

(ii) Absorbance ratio of the light control device 10 As described above, the absorbance of the light control device 10 when transparent reflects the weak absorption of the straight light by the dichroic dye DP to a certain extent. Therefore, the thicker the light control layer 21, the greater the absorbance of the light control device 10 when transparent. And, even if the scattering per unit thickness due to the internal structure of the light control layer 21 is the same between the light control devices 10, the higher the absorbance of the light control device 10 when transparent, the easier it is to further increase the absorbance when opaque. (ii) The absorbance ratio of the light control device 10 is normalized by dividing the absorbance when opaque by the absorbance when transparent. Therefore, (ii) the absorbance ratio of the light control device 10, like (i) the absorbance difference, functions as an index value of the degree of increase in absorption caused by scattering due to the internal structure of the light control layer 21, and further reduces the influence of the difference in thickness of the light control layer 21. That is, (ii) the absorbance ratio of the light-adjusting device 10 is an index value that enhances the contrast of the light-adjusting device 10 and functions as an index value that largely reflects the internal structure of the light-adjusting layer 21 .

(iii) Absorbance of the Light-Adjusting Device 10 in a Transparent State The variation in the concentration of the dichroic dye DP in the light-adjusting layer 21 depends on the concentration of the dichroic dye DP and the thickness of the light-adjusting layer 21 .

For example, when the thickness of the photochromic layer 21 is thick, the energy irradiated per unit mass of the polymerizable composition during exposure is reduced compared to when the thickness of the photochromic layer 21 is thin. This slows down the polymerization rate of the polymerizable compound. The dichroic dye DP present in the liquid crystal composition 21LC and the polymerizable composition takes a long time to diffuse during phase separation of the liquid crystal composition 21LC, which makes it difficult for a concentration gradient of the dichroic dye DP to occur due to insufficient concentration diffusion. On the other hand, when the polymerization rate of the polymerizable composition slows down, sequential phase separation of the liquid crystal composition 21LC occurs, resulting in non-uniform polymer density and density of the voids 21D. As a result, a concentration gradient of the dichroic dye DP occurs due to the variation in density of the voids 21D.

For example, when the thickness of the light-adjusting layer 21 is thin, the energy irradiated per unit mass of the polymerizable composition increases during exposure compared to when the thickness of the light-adjusting layer 21 is thick. This increases the rate at which the polymerizable compound polymerizes. Furthermore, the dichroic dye DP that was present in the liquid crystal composition 21LC and the polymerizable composition has a short time to diffuse during phase separation of the liquid crystal composition 21LC, which results in a concentration gradient of the dichroic dye DP due to insufficient concentration diffusion.

Insufficient concentration diffusion of the dichroic dye DP or fixed spatial bias of the dichroic dye DP makes it easier for the dichroic dye DP to be incorporated into the transparent polymer layer 21P. The dichroic dye DP incorporated into the transparent polymer layer 21P does not drive like the dichroic dye DP contained in the liquid crystal composition 21LC. The dichroic dye DP incorporated into the transparent polymer layer 21P reduces the light absorption by the dichroic dye DP incorporated into the transparent polymer layer 21P when it is opaque, preventing improvement of the contrast.

As described above, the manner in which the liquid crystal composition 21LC is phase-separated is largely determined by the thickness of the light-adjusting layer 21 and the rate at which the polymerizable composition is polymerized. The degree to which the dichroic dye DP is incorporated into the transparent polymer layer 21P is also largely determined by the thickness of the light-adjusting layer 21 and the rate at which the polymerizable composition is polymerized. Phase separation that does not cause variation in the concentration of the dichroic dye DP incorporates only a constant amount of the dichroic dye DP per unit thickness of the transparent polymer layer 21P.

When a constant amount of dichroic dye DP is incorporated per unit thickness of the transparent polymer layer 21P, the absorbance of the light control device 10 in the transparent state has a positive proportional relationship such that the absorbance is greater as the thickness of the light control layer 21 increases. On the other hand, when the amount of dichroic dye DP incorporated in the transparent polymer layer 21P is less than a constant amount, the absorbance of the light control device 10 in the transparent state is smaller than the value obtained from the proportional relationship described above. In this case, the incorporation of the dichroic dye DP by the liquid crystal composition 21LC, which causes variation in the concentration of the dichroic dye DP, is presumed to be phase separation of the liquid crystal composition 21LC.

For this reason, (ii) the absorbance when the dimming device 10 is transparent functions as an index value of the degree to which the dichroic dye DP is incorporated into the transparent polymer layer 21P. In addition, (ii) the absorbance when the dimming device 10 is transparent also functions as an index value of the degree of variation in the dichroic dye DP. In other words, (iii) the absorbance when the dimming device 10 is transparent functions as an index value that provides an appropriately enhanced contrast so as to suppress variation.

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

The materials used to form the light-adjusting sheet of Test Example 1 are shown below. Note that materials (a) to (g) are common to the light-adjusting sheets of each test example. Material (h) is different for each test example.

(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: mixture of a cyano-based liquid crystal compound and a 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 DP: 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 controlling sheet in the light controlling device 10 of Test Example 1 are shown below.
(e) Liquid crystal compound LCM: 52% by mass
(f) Polymerization initiator: 1% by mass
(g) Polymerizable composition: 44.5% by mass
(h) Dichroic dye DP: 2.5% by mass
The coating liquid of Test Example 1 was applied onto the first alignment layer 22 so that black spacers 21S with a particle size of 25 μm were arranged on the first alignment layer 22, forming a coating film of Test Example 1. Next, while the coating film of Test Example 1 was sandwiched between the first alignment layer 22 and the second alignment layer 23, 360 nm ultraviolet light was irradiated toward the first transparent substrate 26, forming a light-control sheet of Test Example 1 in which the light-control layer 21 had a thickness of 25 μm. At this time, the amount of ultraviolet light was set to 10 mW/ ^cm2 .

In addition, except that the particle size of the spacer 21S was changed to within a range of 6 μm or more and 24 μm or less, multiple light-control sheets of Test Example 1 were obtained in which the thickness of the light-control layer 21 was different from each other within a range of 6 μm to 24 μm or less, using the same manufacturing method as described above.

[Test Example 2]
The compounding ratios of materials (e) to (h) in the coating liquid for producing the light-adjusting sheet of Test Example 2 are shown below. The light-adjusting sheet of Test Example 2 has a dichroic ratio (absorption coefficient ratio) different from that of the dichroic dye DP used in the formation of the light-adjusting sheet of Test Example 1.

(e) Liquid crystal compound LCM: 52% by mass
(f) Polymerization initiator: 1% by mass
(g) Polymerizable composition: 43% by mass
(h) Dichroic dye DP: 4% by mass
The coating liquid of Test Example 2 was applied onto the first alignment layer 22 so that black spacers 21S having a particle size of 25 μm were arranged on the first alignment layer 22, thereby forming a coating film of Test Example 2. Next, in a state in which the coating film of Test Example 2 was sandwiched between the first alignment layer 22 and the second alignment layer 23, ultraviolet light of 360 nm was irradiated toward the first transparent substrate 26, and a light-controlling layer was formed. A light-controlling sheet having a thickness of 25 μm was formed as in Test Example 2. At this time, the amount of ultraviolet light was set to 10 mW/cm ² .

In addition, except that the particle size of the spacer 21S was changed to within the range of 6 μm or more and 24 μm or less, multiple light-control sheets of Test Example 2 were obtained in which the thickness of the light-control layer 21 was different from each other within the range of 6 μm to 24 μm or less, using the same manufacturing method as described above.

[Evaluation method]
For each of the light control devices 10 of the test examples, the total light transmittance was measured by a measurement method conforming to ASTM D 1003-00. For each of the light control devices 10 of the test examples, the absorbance for visible light of 380 nm or more and 780 nm or less was measured by a measurement method conforming to JIS K 0115:2004.

A total of nine points were set as the measurement points for absorbance in the light control device 10 of each test example, including the center, four corners, and a point between the center and the corners on the surface of the light control sheet. In addition, an AC voltage of 40 V square wave with a frequency of 50 Hz was used as the drive signal for the light control sheet when measuring the optical properties. A haze meter (BYK haze-gard i indtrument: manufactured by BYK Gardner) was used to measure the total light transmittance.

For each of the dimmers 10 in each test example, a difference value was calculated for each measurement point by subtracting the absorbance in the light state (transparent) from the absorbance in the dark state (opaque) of the dimmer 10. In addition, for each test example, the average value of the difference values for all measurement points was calculated, and this average value was calculated as the (i) absorbance difference for that test example.

For each of the dimmers 10 in each test example, the ratio of the absorbance in the dark state (opaque state) to the absorbance in the light state (transparent state) in the dimmer 10 was calculated for each measurement point. In addition, for each test example, the average value of the ratios for all measurement points was calculated, and this average value was calculated as the (ii) absorbance ratio for that test example.

For each of the light control devices 10 in each test example, the ratio of the total light transmittance in the light state (transparent) to the total light transmittance in the dark state (opaque) of the light control device 10 was calculated for each measurement point. In addition, for each test example, the average value of the ratios of the total light transmittances at all measurement points was calculated, and this average value was calculated as the contrast of that test example. In addition, a difference value was calculated by subtracting the minimum value from the maximum value of the ratios of the total light transmittances at all measurement points, and this difference value was calculated as the variation in contrast for that test example.

For each of the light control devices 10 in each test example, a difference value was calculated for each measurement point by subtracting the total light transmittance in the dark state (opaque) from the total light transmittance in the light state (transparent) of the light control device 10. In addition, for each test example, the average value of the difference values of the total light transmittance at all measurement points was calculated, and this average value was calculated as the transmittance difference for that test example.

[Evaluation Results]
The evaluation results of each test example are shown in FIG. 5 to FIG.
Fig. 5 shows the relationship between the (i) transmittance difference and the contrast in Test Example 1. As shown in Fig. 5, even when the transmittance difference is about the same, such as in the range of the transmittance difference of 0.1 or more, it was found that the contrasts are significantly different from each other. In particular, in the range where a clear transmittance difference is obtained, such as the range of the transmittance difference of 0.15 or more, there is a large variation in the contrast for each transmittance difference, so no clear correlation was found between the transmittance difference and the contrast.

Figure 6 shows the relationship between the absorbance difference and the contrast for each test example. As shown in Figure 6, (i) it was observed that the greater the absorbance difference, the higher the contrast. In particular, when the absorbance difference was 0.6 or more, it was observed that the contrast increased sharply compared to when the absorbance difference was less than 0.6. Furthermore, it was observed that when the absorbance difference was 0.8 or more, an even higher contrast could be obtained.

On the other hand, the larger the absorbance difference, the larger the change in contrast in response to a change in the absorbance difference. On the other hand, the smaller the absorbance difference, the smaller the change in contrast in response to a change in the absorbance difference. (i) It was found that when the absorbance difference is 1.3 or less, the change in contrast in response to a change in the absorbance difference in the light control device 10 is suppressed, and abrupt changes in contrast variation can be suppressed.

It has been found that when the absorbance difference is 0.8 or more and 1.2 or less, an even higher contrast can be obtained, and the effectiveness of suppressing the change in contrast in response to the change in absorbance difference within the dimmer 10 is improved.

It was also found that the greater the absorbance difference of the dimmer 10, the smaller the total light transmittance of the dimmer 10 when it is opaque. And, when the absorbance difference is 0.6 or more and the total light transmittance of the dimmer 10 when it is opaque, which is its dark state, is 7% or less, it was found that a higher contrast can be obtained within the range of absorbance difference of 0.6 or more.

7 shows the relationship between the absorbance ratio and the contrast (ii) in Test Example 1. FIG. 8 shows the relationship between the absorbance ratio and the contrast (ii) in Test Example 2.
As shown in FIG. 7, in Test Example 1, (ii) it was confirmed that the larger the absorbance ratio, the higher the contrast. In particular, when the absorbance ratio is 2.1 or more, it was confirmed that the contrast increases sharply compared to when the absorbance ratio is less than 2.1. The rate of change in contrast when the absorbance ratio is 2.1 or more is greater than the rate of change in contrast when the absorbance ratio is less than 2.1. That is, it was confirmed that the contrast increases sharply when the value of the absorbance ratio normalized by 2.5 mass % which is the concentration of the dichroic dye DP is 0.8 or more (2.1/2.5=0.84). It was also confirmed that when the absorbance ratio is 2.1 or more, a high contrast of 4 or more can be obtained.

As shown in FIG. 8, in Test Example 2, (ii) the greater the absorbance ratio, the higher the contrast. In particular, when the absorbance ratio is 3.3 or more, the contrast increases sharply compared to when the absorbance ratio is less than 3.3. The rate of change in contrast when the absorbance ratio is 3.3 or more is greater than the rate of change in contrast when the absorbance ratio is less than 3.3. In other words, when the absorbance ratio is normalized by the concentration of the dichroic dye DP, which is 4% by mass, it is 0.8 or more (3.3/4=0.83), the contrast increases sharply. It is noted that when the absorbance ratio is 3.3 or more, a high contrast of 3 or more can be obtained.

Figure 9 shows the relationship between the thickness of the photochromic layer 21 in Test Example 1 and the (iii) absorbance when the photochromic device 10 in Test Example 1 is transparent. As shown in Figure 9, in Test Example 1, it was confirmed that the thicker the photochromic layer 21, the greater the (iii) absorbance. In particular, when the thickness of the photochromic layer 21 is 10 μm or more and 20 μm or less, it was confirmed that there is a positive proportional relationship such that the (iii) absorbance is in the range of 0.33 to 1.1, and the thicker the photochromic layer 21, the higher the absorbance. In other words, it was confirmed that when the (iii) absorbance is 0.33 to 1.1, the dichroic dye DP per unit thickness is approximately constant and stable.

On the other hand, when the thickness of the photochromic layer 21 is in the range exceeding 20 μm, i.e. (iii) when the absorbance exceeds 1.1, the absorbance was lower than the extrapolated value of the proportional relationship in the range of 0.33 to 1.1. Also, when the thickness of the photochromic layer 21 is in the range below 10 μm, i.e. (iii) when the absorbance is below 0.33, the absorbance was also lower than the extrapolated value of the proportional relationship in the range of 0.33 to 1.1.

Figure 10 shows the relationship between absorbance and contrast (iii). As shown in Figure 10, in Test Example 1, (iii) it was observed that the higher the absorbance, the greater the contrast. In particular, (iii) it was observed that when the absorbance was 0.33 or more and 1.1 or less, the contrast was increased in the range of 2.5 or more and 5.5 or less. It was also observed that (iii) when the absorbance was 0.33 or more and 1.1 or less, the variation in contrast was suppressed compared to when the absorbance exceeded 1.1.

In addition, (iii) when the absorbance exceeds 1.1, a steep increase in contrast is observed, but it has been found that the contrast variation also increases in accordance with the contrast itself. In cases where it is required to further suppress the contrast variation, it has also been found that (iii) an absorbance of 0.8 or less is preferable.

As described above, according to the above embodiment, the following effects can be obtained.
(1-1) When the absorbance difference of the light control device 10 is 0.6 or more, the contrast of the light control device 10 is increased.

(1-2) When the absorbance difference of the dimmer 10 is 0.6 or more and 1.3 or less, the contrast of the dimmer 10 is increased and the contrast variation in the dimmer 10 is suppressed.

(1-3) When the absorbance difference of the light-adjusting device 10 is 0.8 or more and 1.2 or less, the effectiveness of obtaining the effect equivalent to (1-2) is increased.
(1-4) When the total light transmittance of the light control device 10 in its dark, opaque state is 7% or less, the brightness of the light control device 10 in its dark state is suppressed, thereby enhancing the effectiveness of increasing the contrast.

(2-1) When the absorbance ratio of the light control device 10 is 2.1 or more, the contrast of the light control device 10 is increased.
(2-2) When the absorbance ratio of the light control device 10 is 3.3 or more, the effectiveness of increasing the contrast of the light control device 10 increases.

(2-3) When the contrast of the light control device 10 is 4 or more, the contrast of the light control device 10 is increased and the variation in contrast in the light control device 10 is suppressed.
(3-1) When the absorbance of the light control device 10 in the transparent state is 0.33 or more and 1.1 or less, the contrast of the light control device 10 is increased and the variation in contrast is suppressed.

(3-2) When the light-adjusting device 10 has an absorbance of 0.8 or less when transparent, the effectiveness of the effect equivalent to (3-1) is further increased.
(3-3) The dichroic dye DP-containing light control device 10 is colored even when transparent due to the light absorption of the dichroic dye DP. If the transparency of the light control device 10 is evaluated by the transmittance, it is unclear whether the good transparency indicated by a certain range of transmittance is due to insufficient light absorption of the dichroic dye DP or is good transparency under normal light absorption of the dichroic dye DP. In other words, when the transmittance is used for evaluation, there are various types of transmittance (linear, scattering, solid angle) indices, and the transmittance also differs depending on the observation angle. Therefore, the transmittance has not been a unified index indicating the transparency (blackness when transparent). In other words, the method of evaluating the dichroic dye DP-containing light control device 10 by the total light transmittance cannot be said to allow the user of the light control device 10 to accurately grasp the state of the dichroic dye DP in the light control layer 21. In this regard, evaluating whether the absorbance due to the light absorption characteristics of the dichroic dye DP when the dimming device 10 is transparent is within a specified range allows the user of the dimming device 10 to accurately grasp the state of the dichroic dye DP in the dimming layer 21.

DP...dichroic dye 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 21P...transparent polymer layer 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 (6)

A transparent polymer layer having voids;
a liquid crystal composition that contains a liquid crystal compound and a dichroic dye and fills the gaps;
A light control device that reversibly changes from a transparent state to an opaque state,
A light control device, characterized in that an absorbance difference, which is a value obtained by subtracting the absorbance of said light control device in said transparent state from the absorbance of said light control device in said opaque state, is 0.6 or more. The light control device according to claim 1 , wherein the absorbance difference is 1.3 or less. The light control device according to claim 1 , wherein the absorbance difference is equal to or greater than 0.8 and equal to or less than 1.2. The light control device according to claim 1 , wherein the light control device has a total light transmittance of 7% or less in the opaque state. The light control device includes one light control sheet,
The light control device according to claim 1 , wherein the light control sheet comprises the transparent polymer layer and the liquid crystal composition. The light control device includes a plurality of light control sheets,
The light control device according to claim 1 , wherein each of the light control sheets comprises the transparent polymer layer and the liquid crystal composition.

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