JP2024014588A - Dimming sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dimming sheet that makes it possible for all of a haze value when a dimming sheet exhibits transparency, a drive voltage of the dimming sheet, and a response speed of the dimming sheet to be included within an appropriate range.

SOLUTION: A dimming sheet 11R comprises: a first orientation layer 21; a second orientation layer 22; and a dimming layer 23 positioned between the first orientation layer 21 and the second orientation layer 22, the dimming layer 23 including a transparent polymer layer with a plurality of domains dispersed therein and liquid crystal compositions each that contain liquid crystal molecules and are filled in the domain. A domain diameter D being an indicator in a size of the domain and a first polar angle anchoring coefficient W_a1 being a polar angle anchoring coefficient of the first orientation layer 21 relative to the liquid crystal molecules satisfy the numerical formula (1): 3.6≤|D*log₁₀(W_a1)|≤9.3.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a light control sheet.

The reverse type light control sheet includes a light control layer containing liquid crystal molecules, a pair of transparent electrode layers sandwiching the light control layer, and an alignment layer located between each transparent electrode layer and the light control layer. . Since each alignment layer is a vertical alignment layer, when no voltage is applied between the pair of transparent electrode layers, the liquid crystal molecules are aligned substantially perpendicular to the plane in which the alignment layer extends. Therefore, the light control sheet exhibits transparency in a state where no voltage is applied between the pair of transparent electrode layers. On the other hand, when a voltage is applied between the pair of transparent electrode layers, the liquid crystal molecules are aligned substantially horizontally to the plane in which the alignment layer extends. Therefore, in a state where a voltage is applied between the pair of transparent electrodes, the light control sheet becomes opaque (see, for example, Patent Document 1).

Japanese Patent Application Publication No. 2019-194654

By the way, the reverse type light control sheet is transparent when no voltage is applied to the light control layer. Therefore, even if the light control sheet cannot be energized due to a power outage or failure, the field of view will not be blocked by the light control sheet. In this way, the reverse type light control sheet has a high level of safety, so the objects to which the reverse type light control sheet is applied are not limited to transparent members of buildings, but also moving vehicles such as cars, trains, and airplanes. It is also spreading to the body. Due to this expansion of applications, light control sheets are required to have higher transparency from the viewpoint of safety and aesthetics. Further, from the viewpoint that the magnitude of the voltage that can be applied to the light control sheet is limited, it is required to lower the driving voltage for driving the liquid crystal molecules. Furthermore, it is required that the response speed, which is the speed at which the light control sheet changes from an opaque state to a transparent state, does not easily decrease even in a low-temperature environment in which a moving body can be used.

A light control sheet for solving the above problems includes a first alignment layer, a second alignment layer, and a light control layer located between the first alignment layer and the second alignment layer, The light control layer includes a transparent polymer layer in which domains are dispersed, and a liquid crystal composition containing liquid crystal molecules and filled in the domains. In the light control sheet, the domain diameter D, which is an index of the size of the domain, and the first polar angle anchoring coefficient W _a1 , which is the polar angle anchoring coefficient of the first alignment layer with respect to the liquid crystal molecules, are expressed by the formula ( 1) is satisfied.
3.6≦｜D*log ₁₀ (W _a1 )｜≦9.3 … Formula (1)

According to the light control sheet, in the vicinity of the first alignment layer, the first polar angle anchoring coefficient W _a1 of the first alignment layer is prevented from becoming excessively small, and the domain diameter D is prevented from becoming excessively large. It will be done. This prevents the force of the first alignment layer from orienting liquid crystal molecules from becoming excessively small, which increases the haze value when the light control sheet becomes transparent and slows down the response speed in low-temperature environments. It can be prevented from happening. Further, it is possible to prevent the first polar angle anchoring coefficient W _a1 from becoming excessively large and the domain diameter D from becoming excessively small. This prevents the force with which the first alignment layer orients the liquid crystal molecules from becoming excessively large, thereby suppressing the driving voltage of the light control sheet from increasing.

In the above light control sheet, the domain diameter D and the second polar angle anchoring coefficient Wa2, which is the polar angle anchoring coefficient of the second alignment layer with respect to the liquid crystal molecules, may satisfy formula (2).
3.6≦｜D*log ₁₀ (W _a2 )｜≦9.3 … Formula (2)

According to the light control sheet, the second polar anchoring coefficient W _a2 of the second alignment layer becomes excessively small in the vicinity of the second alignment layer, as in the vicinity of the first alignment layer, and the domain This prevents the diameter D from becoming excessively large. This prevents the force of the second alignment layer from orienting liquid crystal molecules from becoming excessively small, which increases the haze value when the light control sheet becomes transparent and slows down the response speed in low-temperature environments. It can be prevented from happening. Further, the second polar angle anchoring coefficient W _a2 is prevented from becoming excessively large, and the domain diameter D is prevented from becoming excessively small. This prevents the force with which the second alignment layer orients the liquid crystal molecules from becoming excessively large, thereby suppressing the driving voltage of the light control sheet from increasing.

In the light control sheet, the domain diameter may be 0.5 μm or more and 4.0 μm or less. According to this light control sheet, since the domain diameter is 0.5 μm or more and 4.0 μm or less, the haze value of the light control sheet is suppressed from increasing when no voltage is applied to the light control sheet.

In the light control sheet, the first polar angle anchoring coefficient W _a1 may be 1.0×10 ⁻⁴ or more and 1.0×10 ⁻² or less. According to this light control sheet, since the first polar angle anchoring coefficient W _a1 is within the range of 1.0 × 10 ^-4 or more and 1.0 × 10 ^-2 or less, the first polar angle anchoring coefficient Compared to the case where W _a1 is less than the lower limit value, the size of the domain diameter D that satisfies Equation (1) is suppressed from increasing. This suppresses an increase in haze value when exhibiting transparency and a decrease in response speed in a low-temperature environment. On the other hand, compared to the case where the first polar angle anchoring coefficient W _a1 exceeds the upper limit value, the size of the domain diameter D that satisfies Equation (1) is suppressed from becoming smaller. This prevents the driving voltage of the light control sheet from increasing.

In the light control sheet, the density of the domains per thickness of the light control layer may be lowest in a central portion in the thickness direction of the light control layer. According to this light control sheet, since the density of domains is lowest at the central portion in the thickness direction of the light control layer, it is possible to reduce the number of liquid crystal molecules located at a portion far from each alignment layer. This makes it easier for the alignment regulating force of each alignment layer to act on the liquid crystal molecules, making it possible to increase the transparency of the light control sheet, or lower the haze value, even when no voltage is applied to the light control sheet. It is.

According to the present invention, the haze value when the light control sheet exhibits transparency, the driving voltage of the light control sheet, and the response speed of the light control sheet are all within an appropriate range.

It is a sectional view showing the structure of a light control sheet in one embodiment. FIG. 2 is a cross-sectional view schematically showing the structure of the light control layer shown in FIG. 1. FIG. 2 is a schematic diagram for explaining the polar angle anchoring coefficient of the first alignment layer in the light control layer shown in FIG. 1. FIG. It is a table showing evaluation results for light control sheets of Examples and Comparative Examples.

An embodiment of a light control sheet will be described with reference to FIGS. 1 to 4.
[Dimmer device]
The light control device will be explained with reference to FIG.

As shown in FIG. 1, the light control device 10R includes a reverse type light control sheet 11R and a drive section 12. The light control sheet 11R may be applied to, for example, a window provided in a moving object such as a vehicle or an aircraft. In addition, the light control sheet 11R can be applied to, for example, windows in various buildings such as houses, stations, and airports, partitions installed in offices, show windows installed in stores, and screens that project images. It may be. The light control sheet 11R is attached to these applications using, for example, an adhesive layer. The shape of the light control sheet 11R may be planar or curved. The light control sheet 11R may have enough flexibility to follow the shape of the object to which it is applied.

The light control sheet 11R includes a first alignment layer 21, a second alignment layer 22, and a light control layer 23. The light control layer 23 is located between the first alignment layer 21 and the second alignment layer 22. The light control layer 23 includes a transparent polymer layer in which a plurality of domains are dispersed, and a liquid crystal composition containing liquid crystal molecules and filled in the domains.

The light control sheet 11R further includes a first transparent electrode layer 24, a second transparent electrode layer 25, a first transparent base material 26, and a second transparent base material 27. In the thickness direction of the light control sheet 11R, the first transparent electrode layer 24 and the second transparent electrode layer 25 sandwich the pair of alignment layers 21 and 22. The first alignment layer 21 is located between the first transparent electrode layer 24 and the light control layer 23. A second alignment layer 22 is located between the second transparent electrode layer 25 and the light control layer 23. The first transparent base material 26 supports the first transparent electrode layer 24. The second transparent base material 27 supports the second transparent electrode layer 25.

The light control sheet 11R includes a first electrode 24A attached to a part of the first transparent electrode layer 24 and a second electrode 25A attached to a part of the second transparent electrode layer 25. The light control sheet 11R further includes a wiring 28 connected to the first electrode 24A and a wiring 28 connected to the second electrode 25A. The first electrode 24A and the second electrode 25A are each connected to the drive unit 12 by wiring 28.

The first transparent electrode layer 24 and the second transparent electrode layer 25 have a light transmittance that allows visible light to pass therethrough. The light transmittance of the first transparent electrode layer 24 enables visual recognition of objects through the light control sheet 11R. The light transmittance of the second transparent electrode layer 25, like the light transmittance of the first transparent electrode layer 24, enables visual recognition of objects through the light control sheet 11R. The thickness of each transparent electrode layer 24, 25 may be, for example, 0.005 μm or more and 0.1 μm or less. This ensures proper driving of the light control sheet 11R, and prevents cracks from occurring in the light control sheet 11R when the light control sheet 11R is bent.

The materials for forming each of the transparent electrode layers 24 and 25 include, for example, indium tin oxide, fluorine-doped tin oxide, tin oxide, zinc oxide, carbon nanotubes, and poly(3,4-ethylenedioxythiophene). It may be any one selected from the group.

The material forming each transparent base material 26, 27 may be a synthetic resin or an inorganic compound. The synthetic resin may be, for example, polyester, polyacrylate, polycarbonate, polyolefin, and the like. Polyesters may be, for example, polyethylene terephthalate and polyethylene naphthalate. The polyacrylate may be, for example, polymethyl methacrylate. The inorganic compound may be, for example, silicon dioxide, silicon oxynitride, silicon nitride, and the like. The thickness of each transparent base material 26, 27 may be, for example, 16 μm or more and 250 μm or less. Since the thickness of the transparent base materials 26 and 27 is 16 μm or more, the light control sheet 11R can be easily processed and constructed. By setting the thickness of the transparent base materials 26 and 27 to 250 μm or less, it is possible to manufacture the light control sheet 11R by roll-to-roll.

Each electrode 24A, 25A is, for example, a flexible printed circuit (FPC). The FPC includes a support layer, a conductor, and a protective layer. A conductor portion is sandwiched between a support layer and a protective layer. The support layer and the protective layer are made of insulating synthetic resin. The support layer and the protective layer are made of polyimide, for example. The conductor portion is formed of, for example, a metal thin film. The material forming the metal thin film may be copper, for example. The electrodes 24A and 25A are not limited to FPC, but may be made of metal tape, for example.

Note that each electrode 24A, 25A is attached to each transparent electrode layer 24, 25 by a conductive adhesive layer (not shown). The conductor portion of each electrode 24A, 25A is exposed from the protective layer or support layer at the portion connected to the conductive adhesive layer.

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

Each wiring 28 is formed of, for example, a metal wire and an insulating layer covering the metal wire. The wire is made of copper, for example.
The drive unit 12 applies an AC voltage between the first transparent electrode layer 24 and the second transparent electrode layer 25. It is preferable that the drive unit 12 applies an AC voltage having a rectangular waveform between the pair of transparent electrode layers 24 and 25. Note that the drive unit 12 may apply an AC voltage having a shape other than a rectangular waveform between the pair of transparent electrode layers 24 and 25. For example, the drive unit 12 may apply an AC voltage having a sine wave shape between the pair of transparent electrode layers 24 and 25.

In the light control layer 23, the orientation of liquid crystal molecules changes in response to changes in the voltage generated between the two transparent electrode layers 24 and 25. Changes in the orientation of liquid crystal molecules change the degree of scattering, absorption, and transmission of visible light entering the light control layer 23. The reverse type light control sheet 11R has a relatively high haze value when the light control sheet 11R is energized, that is, when a potential difference is generated between the first transparent electrode layer 24 and the second transparent electrode layer 25. has. The reverse type light control sheet 11R has a relatively low haze when the light control sheet 11R is not energized, that is, when there is no potential difference between the first transparent electrode layer 24 and the second transparent electrode layer 25. has value. For example, the reverse type light control sheet 11R is opaque when the light control sheet 11R is energized, and transparent when the light control sheet 11R is not energized.
The haze of the light control sheet 11R is calculated by a method based on JIS K 7136:2000 "How to determine the haze of plastics - transparent materials".

[Dimmer sheet]
With reference to FIG. 2, the structure of the light control sheet 11R, particularly the structure of the light control layer 23 included in the light control sheet 11R, will be described in more detail. FIG. 2 schematically shows the cross-sectional structure of the light control sheet 11R. In addition, in FIG. 2, illustration of the transparent base materials 26 and 27 is abbreviate|omitted for convenience of illustration. In addition, in FIG. 2, for convenience of explaining the structure of the light control layer 23, the thickness of each alignment layer 21, 22 and the ratio of the thickness of the light control layer 23 to the thickness of each transparent electrode layer 24, 25 are shown. , larger than the actual ratio. Moreover, FIG. 2 shows the state of the light control layer 23 in a state where no potential difference is generated between the pair of transparent electrode layers 24 and 25.

As described above, the light control sheet 11R includes the first alignment layer 21 and the second alignment layer 22. The materials for forming the first alignment layer 21 and the second alignment layer 22 are organic compounds, inorganic compounds, and mixtures thereof. Examples of the organic compound include polyimide, polyamide, polyvinyl alcohol, and cyanide compounds. Inorganic compounds include silicon oxide and zirconium oxide. Note that the material for forming the alignment layers 21 and 22 may be silicone. Silicones are compounds that have inorganic and organic parts. The thickness of each alignment layer 21, 22 may be, for example, 0.02 μm or more and 0.5 μm or less.

The first alignment layer 21 and the second alignment layer 22 are vertical alignment layers. The vertical alignment layer aligns liquid crystal molecules so that it is perpendicular to the surface opposite to the surface in contact with the first transparent electrode layer 24 and the surface opposite to the surface in contact with the second transparent electrode layer 25. Orient the long axis. Note that the alignment layers 21 and 22 are arranged so that the long axes of the liquid crystal molecules 23LM are tilted several degrees with respect to the vertical, within a range where the long axes of the liquid crystal molecules 23LM are determined to be substantially perpendicular to each surface. It may be oriented.

As described above, the light control layer 23 includes the transparent polymer layer 23P and the liquid crystal composition 23L. A plurality of domains 23D are dispersed within the transparent polymer layer 23P. The liquid crystal composition 23L includes liquid crystal molecules 23LM and is filled in the domains 23D.

The domain diameter, which is an index of the size of the domain 23D, may be 0.5 μm or more and 4.0 μm or less. The domain diameter is specified in the domain 23D included in a cross section perpendicular to the plane in which the light control layer 23 spreads. When the domain 23D has a circular shape, the diameter of the domain 23D is the domain diameter. When the domain 23D has an elliptical shape, the long axis of the domain 23D is the domain diameter. When the domain 23D has an irregular shape, the diameter of a circle circumscribing the domain 23D is the domain diameter.

The liquid crystal molecules 23LM included in the liquid crystal composition 23L are negative type liquid crystal molecules with negative dielectric anisotropy. Examples of the liquid crystal molecules 23LM include Schiff base-based, azo-based, azoxy-based, biphenyl-based, terphenyl-based, benzoic acid ester-based, tolan-based, pyrimidine-based, cyclohexanecarboxylic acid ester-based, cyclohexane-based, phenylcyclohexane-based, and dioxane. The liquid crystal composition 23L may include first liquid crystal molecules and second liquid crystal molecules of a different type from the first liquid crystal molecules.

The liquid crystal molecules 23LM are preferably cyclohexane-based, phenylcyclohexane-based, biphenyl-based, terphenyl-based, alkyne-based, or cyclohexanecarboxylic acid ester-based. Furthermore, it is more preferable that the liquid crystal molecules 23LM are any of the liquid crystal molecules represented by the following chemical formulas (1) to (11).

In addition, in chemical formulas (1) to chemical formulas (11), R1 and R2 each independently represent an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, It is an alkenyloxy group having 2 to 12 carbon atoms, or an alkyl group having 1 to 12 carbon atoms in which one or more hydrogens have been replaced with fluorine or chlorine.

The transparent polymer layer 23P is a cured product of a photopolymerizable compound. The photopolymerizable compound may be an ultraviolet curable compound or an electron beam curable compound. The photopolymerizable compound is compatible with the liquid crystal composition. In order to improve the dimensional controllability of the domain 23D, the photopolymerizable compound is preferably an ultraviolet curable compound. An example of an ultraviolet curable compound includes a polymerizable unsaturated bond at the end of its molecular structure. Alternatively, the ultraviolet curable compound contains a polymerizable unsaturated bond other than the terminal end of the molecular structure. The photopolymerizable compound is one type of polymerizable compound or a combination of two or more types of polymerizable compounds.

The ultraviolet curable compound is at least one selected from the group consisting of acrylate compounds, methacrylate compounds, styrene compounds, thiol compounds, and oligomers of each compound.

Acrylate compounds include monoacrylate compounds, diacrylate compounds, triacrylate compounds, and tetraacrylate compounds. Examples of acrylate compounds are butylethyl 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, tetrahydrofurfuryl methacrylate. Examples of thiol compounds are 1,3-propanedithiol and 1,6-hexanedithiol. An example of a styrene compound is styrene and methylstyrene.

The lower limit of the content of the transparent polymer layer 23P relative to the total amount of the transparent polymer layer 23P and the liquid crystal composition 23L may be 30% by mass, and the more preferable lower limit of the content may be 40% by mass. The upper limit of the content of the transparent polymer layer 23P with respect to the total amount of the transparent polymer layer 23P and the liquid crystal composition 23L may be 70% by mass, and the more preferable upper limit of the content may be 60% by mass.

The lower limit and upper limit of the content of the transparent polymer layer 23P are within a range in which the liquid crystal particles made of the liquid crystal composition 23L phase separate from the cured product of the photopolymerizable compound during the curing process of the photopolymerizable compound. When it is necessary to increase the mechanical strength of the transparent polymer layer 23P, it is preferable that the lower limit of the content of the transparent polymer layer 23P is high. When it is necessary to lower the driving voltage of the liquid crystal molecules 23LM, it is preferable that the upper limit of the content of the transparent polymer layer 23P is low.

In this embodiment, the liquid crystal composition 23L may contain a dichroic dye. Dichroic dyes have an elongated shape. The absorbance in the visible region in the long axis direction of the dichroic dye molecule is greater than the absorbance in the visible region in the short axis direction of the molecule. A dichroic dye exhibits substantially transparency when its long axis direction is parallel or substantially parallel to the direction of incidence of light. On the other hand, a dichroic dye exhibits a predetermined color when its long axis direction is perpendicular or substantially perpendicular to the direction of incidence of light.

Therefore, the dichroic dye is oriented in the major axis direction with respect to the normal direction of the contact surface with the first alignment layer 21 in the light control layer 23 and the contact surface with the second alignment layer 22 in the light control layer 23. When they are oriented parallel or nearly parallel, they exhibit transparency. On the other hand, the dichroic dye has the following properties: When oriented so that the long axis direction is perpendicular or substantially perpendicular, it exhibits a predetermined color. The color exhibited by the dichroic dye is preferably black or a color close to black. The dichroic dye is driven by a guest-host type using the liquid crystal molecule 23LM as a host, and thereby the dichroic dye develops color.

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

In addition, the liquid crystal composition may contain, for example, a monomer for forming a transparent polymer layer, in addition to the above-mentioned liquid crystal molecules and dichroic dye.
The thickness of the light control layer 23 may be, for example, 2 μm or more and 10 μm or less. Further, the thickness of the light control layer 23 may be 3.0 μm or more and 8.0 μm or less.

The density of the domains 23D per unit thickness of the light control layer 23 may be lowest in the central portion of the light control layer 23 in the thickness direction. Note that the density of the domains 23D per unit thickness is the value obtained by dividing the number of domains 23D per cross section by the thickness of the light control layer 23 in a cross section perpendicular to the plane in which the light control layer 23 spreads. Further, the central portion in the thickness direction of the light control layer 23 bisects the distance from the surface in contact with the first alignment layer 21 to the surface in contact with the second alignment layer 22 in the thickness direction of the light control layer 23. It is a part.

As shown in FIG. 2, it is preferable that the domain 23D is not located at the center of the light control layer 23 in the thickness direction. Moreover, it is preferable that the light control layer 23 includes only a domain 23D in contact with the first alignment layer 21 and a domain 23D in contact with the second alignment layer 22.

Since the density of the domains 23D is lowest in the central part of the light control layer 23 in the thickness direction, it is possible to reduce the number of liquid crystal molecules 23LM located in a region far from each of the alignment layers 21 and 22. This makes it easier for the alignment regulating force of each alignment layer 21, 22 to act on the liquid crystal molecules 23LM, thereby increasing the transparency of the light control sheet 11R when no voltage is applied between the transparent electrode layers 24, 25. In other words, it is possible to lower the haze value.

[Polar anchoring coefficient]
The polar angle anchoring coefficient acting on the liquid crystal molecules 23LM will be explained with reference to FIG.
The liquid crystal molecules 23LM receive an alignment regulating force at the interface with the alignment layers 21 and 22, and are aligned in a predetermined state. In this embodiment, since the alignment layers 21 and 22 are vertical alignment layers, the liquid crystal molecules 23LM are vertically aligned under the alignment regulating force. The alignment regulating force is said to be caused by chemical interaction between the liquid crystal molecules 23LM and the alignment layers 21 and 22, or by physical interaction between the liquid crystal molecules 23LM and the alignment layers 21 and 22.

The orientation regulating force includes a polar anchoring coefficient and an azimuthal anchoring coefficient. The polar anchoring coefficient is an anchoring coefficient that acts on the rotation of the director in the normal direction of the alignment layers 21, 22. The azimuthal anchoring coefficient is an anchoring coefficient that acts on the rotation of the director in the in-plane direction of the alignment layers 21, 22. The director is a unit vector representing the average orientation of the long axis of the liquid crystal molecules 23LM in a region that is sufficiently large from the scale of the liquid crystal molecules 23LM and sufficiently small from the macroscopic scale.

The polar angle anchoring coefficient W _a is expressed by the following equation (3).

In formula (3), θ is the angle in the polar direction. θe is the angle of the easy orientation axis e in the polar angle direction. Note that the easy orientation axis e is a direction in which the directors on the surfaces of the orientation layers 21 and 22 are easily stabilized. The easy axis e of orientation is provided by the orientation layers 21 and 22. However, in reality, since the directors on the surfaces of the alignment layers 21 and 22 are influenced by the bulk director, the easy axis e of alignment becomes stable at a position that is changed by a certain angle from the surfaces of the alignment layers 21 and 22.

FIG. 3 shows the coordinates of the easy alignment axis e and the liquid crystal molecules 23LM on the surface of the first alignment layer 21. As shown in FIG. 3, the angle of the easy orientation axis e in the polar angle direction is θe. Note that the angle θe of the easy orientation axis e in the polar angle direction is an angle formed by the XY plane and the easy orientation axis e in a plane that includes the easy orientation axis e and is orthogonal to the XY plane. Further, the angle in the polar angle direction of the liquid crystal molecules 23LM is θ. The angle θ in the polar direction of the liquid crystal molecule 23LM is an angle formed by the XY plane and the director in a plane that includes the director of the liquid crystal molecule 23LM and is perpendicular to the XY plane.

Note that the angle of the easy orientation axis e in the azimuth direction is Φe. The angle Φe of the easy orientation axis e in the azimuth direction is the angle formed by the projection axis of the easy orientation axis e onto the XY plane and the X axis. Further, the angle in the azimuth direction of the liquid crystal molecules 23LM is Φ. The angle Φ in the azimuthal direction of the liquid crystal molecules 23LM is the angle formed by the projection axis of the director of the liquid crystal molecules 23LM onto the XY plane and the X axis.

Although FIG. 3 shows the easy alignment axis e and the coordinates of the liquid crystal molecules 23LM on the surface of the first alignment layer 21, the coordinates of the easy alignment axis e and the liquid crystal molecules 23LM on the surface of the second alignment layer 22 are similar to those on the surface of the first alignment layer 21. Then, the easy alignment axis e and the coordinates of the liquid crystal molecules 23LM are determined.

Further, the dielectric anisotropy Δε of the liquid crystal molecules 23LM is expressed by the following formula (4).

In Equation (4), ε ₀ is the dielectric constant of vacuum, which is 8.85×10 ⁻¹² F/m. ε _⊥ is the dielectric constant in the direction perpendicular to the director. V is the voltage perpendicular to the director and z is the thickness perpendicular to the director. Note that the dielectric anisotropy Δε is expressed as follows using a dielectric constant ε _⊥ in a direction perpendicular to the director and a dielectric constant ε _∥ in a direction parallel to the director.

Δε = ε _∥ − ε _⊥
Further, the elastic constant of the liquid crystal molecule 23LM is expressed by the following equation (5).

In Equation (5), K ₁₁ is an elastic constant for splay deformation, and K ₃₃ is an elastic constant for bend deformation.

The energy _{U a} given to the liquid crystal molecules 23LM existing in the light control layer 23 is expressed by the following equation (6).

Further, the energy U _b given to the liquid crystal molecules 23LM existing in the vicinity of the alignment layers 21 and 22, that is, in the minute thickness Δd, is expressed by the following equation (7). Note that F in formula (7) is (Fa+Fk).

From the above, U, which is (Ua+Ub), is expressed by the following formula (8).

According to the Euler-Lagrange equation, when Equation (8) is satisfied, Equation (9) below holds true.

It is possible to calculate the polar angle anchoring coefficient W _a in the alignment layers 21 and 22 using these equations (3) to (9).

In the present disclosure, the light control layer 23 satisfies Condition 1 below.
(Condition 1) The domain diameter D, which is an index of the size of the domain 23D, and the first polar angle anchoring coefficient Wa1, which is the polar angle anchoring coefficient of the first alignment layer 21 with respect to the liquid crystal molecules 23LM, are expressed by formula (1). satisfy.
3.6≦|D*log ₁₀ (W _a1 )≦9.3| … Formula (1)

Further, the first polar angle anchoring coefficient W _a1 is greater than or equal to 1.0×10 ⁻⁴ and less than or equal to 1.0×10 ⁻² .

Further, in this bulletin, the light control layer 23 satisfies the following condition 2.
(Condition 2) The second polar angle anchoring coefficient W _a2 , which is the polar angle anchoring coefficient of the second alignment layer 22 with respect to the liquid crystal molecules 23LM, satisfies formula (2).
3.6≦｜D*log ₁₀ (W _a2 )｜≦9.3 … Formula (2)

[Effect]
When the light control sheet 11R satisfies the above-mentioned condition 1, the first polar angle anchoring coefficient W _a1 of the first alignment layer 21 becomes excessively small in the vicinity of the first alignment layer 21, and the domain diameter D can be prevented from becoming excessively large. This prevents the force of the first alignment layer 21 from orienting the liquid crystal molecules 23LM from becoming excessively small, which increases the haze value when the light control sheet 11R exhibits transparency and improves response in low-temperature environments. This prevents the speed from slowing down. Further, it is possible to prevent the first polar angle anchoring coefficient W _a1 from becoming excessively large and the domain diameter D from becoming excessively small. This prevents the force of the first alignment layer 21 from orienting the liquid crystal molecules 23LM from becoming excessively large, thereby suppressing the driving voltage of the light control sheet 11R from increasing.

Furthermore, since the light control sheet 11R satisfies the above-mentioned condition 2, the second polar anchoring coefficient W of the second alignment layer 22 can be set in the vicinity of the second alignment layer 22 in the same way as in the vicinity of the first alignment layer 21. This prevents _a2 from becoming excessively small and the domain diameter D from becoming excessively large. This prevents the force with which the second alignment layer 22 aligns the liquid crystal molecules 23LM from becoming excessively small, so that the haze value when the light control sheet 11R becomes transparent increases, and the response in a low-temperature environment increases. This prevents the speed from slowing down. Further, the second polar angle anchoring coefficient W _a2 is prevented from becoming excessively large, and the domain diameter D is prevented from becoming excessively small. This prevents the force of the second alignment layer 22 from orienting the liquid crystal molecules 23LM from becoming excessively large, thereby suppressing the driving voltage of the light control sheet 11R from increasing.

Moreover, by setting the domain diameter to 0.5 μm or more and 4.0 μm or less, it is possible to suppress the haze value of the light control sheet 11R from increasing when no voltage is applied to the light control sheet 11R.

[Example]
Examples and comparative examples will be described with reference to FIG. 4.
[Comparative example 1]
A liquid mixture was prepared in which Loctite 3736 (registered trademark, manufactured by Henkel) and 1,6-hexanediol diacrylate were mixed at a mass ratio of 1:1 as monomers for forming a transparent polymer layer. In addition, a liquid crystal composition containing MLC-6608 (manufactured by Merck & Co., Ltd.) was prepared as a liquid crystal composition. The liquid crystal molecules were negative-type nematic liquid crystals, and the refractive index anisotropy Δn of the liquid crystal molecules was 0.20. Then, a coating liquid containing 65 parts by mass of the liquid crystal composition and 55 parts by mass of monomer was prepared.

Two transparent films including an ITO layer with a thickness of 20 nm and a polyethylene terephthalate film with a thickness of 125 μm were prepared. A polyimide alignment layer having a thickness of 200 nm was formed on each ITO layer.

Then, a coating film is formed by applying a coating liquid onto the alignment layer of one transparent film so that the thickness after curing is 200 nm, and then the alignment layer of the other transparent film is coated. was brought into contact with the membrane. Thereby, the coating film was sandwiched between a pair of transparent films.

Then, a pair of ultraviolet lamps were arranged to sandwich the pair of transparent films, and then the coating film was irradiated with ultraviolet rays using the pair of lamps. At this time, the illuminance of the ultraviolet rays was set to 18 mW/cm ² and the irradiation time of the ultraviolet rays was set to 150 seconds. Phase separation was caused in the coating film by irradiation with ultraviolet rays, thereby forming a light control layer having an average domain diameter D of 0.6 μm. Thereby, a light control sheet of Comparative Example 1 was obtained.

[Example 1]
A light control sheet of Example 1 was obtained in the same manner as in Comparative Example 1, except that the illuminance of the ultraviolet rays was changed to 16 mW/cm ² .

[Example 2]
A light control sheet of Example 2 was obtained in the same manner as in Comparative Example 1, except that the illuminance of the ultraviolet rays was changed to 10 mW/cm ² .

[Comparative example 2]
A light control sheet of Comparative Example 2 was obtained in the same manner as in Comparative Example 1 except that the illuminance of the ultraviolet rays was changed to 6 mW/cm ² .

[Comparative example 3]
A light control sheet of Comparative Example 3 was obtained in the same manner as in Comparative Example 1 except that the illuminance of ultraviolet rays was changed to 2 mW/cm ² .

[Comparative example 4]
Comparative Example 1 was the same as Comparative Example 1, except that the mixed liquid was changed to a mixed liquid of Loctite 3736 (registered trademark, manufactured by Henkel) and 1,6-hexanediol diacrylate at a mass ratio of 3:4. A light control sheet of Comparative Example 4 was obtained by the method described above.

[Example 3]
A light control sheet of Example 3 was obtained in the same manner as in Comparative Example 4, except that the illuminance of the ultraviolet rays was changed to 10 mW/cm ² .

[Example 4]
A light control sheet of Example 4 was obtained in the same manner as in Comparative Example 4, except that the illuminance of the ultraviolet rays was changed to 8 mW/cm ² .

[Example 5]
A light control sheet of Example 5 was obtained in the same manner as in Comparative Example 4, except that the illuminance of the ultraviolet rays was changed to 5 mW/cm ² .

[Comparative example 5]
A light control sheet of Comparative Example 5 was obtained in the same manner as in Comparative Example 4, except that the illuminance of the ultraviolet rays was changed to 2 mW/cm ² .

[Comparative example 6]
Same as Comparative Example 1 except that the mixed liquid was changed to a mixed liquid of Loctite 3736 (registered trademark, manufactured by Henkel) and 1,6-hexanediol diacrylate at a mass ratio of 2:3. A light control sheet of Comparative Example 6 was obtained by the method.

[Comparative Example 7]
A light control sheet of Comparative Example 7 was obtained in the same manner as in Comparative Example 6, except that the illuminance of the ultraviolet rays was changed to 10 mW/cm ² .

[Example 6]
A light control sheet of Comparative Example 8 was obtained in the same manner as in Comparative Example 6 except that the illuminance of the ultraviolet rays was changed to 8 mW/cm ² .

[Example 7]
A light control sheet of Example 6 was obtained in the same manner as in Comparative Example 6, except that the illuminance of the ultraviolet rays was changed to 6 mW/cm ² .

[Example 8]
A light control sheet of Example 7 was obtained in the same manner as in Comparative Example 6, except that the illuminance of the ultraviolet rays was changed to 2 mW/cm ² .

[Evaluation method]
[Domain diameter]
After the light control sheets of each Example and each Comparative Example were embedded in paraffin, the side surfaces of the light control sheets were scraped with a microtome along a plane perpendicular to the plane in which the light control sheets spread. Then, a platinum film was laminated by sputtering on the surface of the light control sheet that had been scraped with a microtome, thereby creating an observation surface. Next, the observation surface was observed using a scanning electron microscope (Regulus 8220, Hitachi High-Tech Corporation). At this time, the domain diameters of five domains included in the observation surface were measured, and then the average value of the domain diameters of the five domains was calculated. The average value of the domain diameters was set as the domain diameter in each light control sheet.

It was observed that the light control sheets of each Example and each Comparative Example had only domains in contact with the first alignment layer and domains in contact with the second alignment layer as domains dispersed in the transparent polymer layer.

[Polar anchoring coefficient]
The liquid crystal molecules used in the light control sheets of the Examples and Comparative Examples were each encapsulated in a liquid crystal cell for evaluation (KSRP-05/B111P1NSS05X, manufactured by EHC Co., Ltd.), thereby creating a liquid crystal cell for measurement. An ITO layer and a vertical alignment layer made of polyimide were formed on the corresponding surfaces of the liquid crystal cell for evaluation, and a rubbing treatment was performed on the surface of the vertical alignment layer so that the layers were antiparallel.

For each liquid crystal cell for measurement, the dielectric constant ε _⊥ in the vertical direction and the dielectric constant ε _∥ in the horizontal direction were measured using an LCR meter (E4980A, manufactured by Keysight Technologies). From these values, the dielectric anisotropy Δε was calculated for each liquid crystal cell for measurement. Next, the dielectric constants ε _⊥ , ε _∥ , the dielectric anisotropy Δε, the elastic constant K ₁₁ for splay deformation of each liquid crystal molecule, and the elastic constant K ₃₃ for bend deformation are calculated from the above-mentioned formula (3). The polar angle anchoring coefficient W _a was calculated using Equation (9). Note that both the first polar angle anchoring coefficient W _a1 in the first alignment layer 21 and the second polar angle anchoring coefficient W _a2 in the second alignment layer 22 are equal to the polar angle anchoring coefficient W _a . .

[Haze value when transparent]
For the light control sheets of each Example and each Comparative Example, the haze value was calculated in a state where no voltage was applied between the transparent electrode layers. The haze value was calculated using a method based on JIS K 7136:2000 "Plastic - How to determine haze of transparent materials". Note that a haze meter (NDH-7000, manufactured by Nippon Denshoku Kogyo Co., Ltd.) was used for measurement when calculating the haze value.

[Drive voltage]
The driving voltage was measured for the light control sheets of each Example and each Comparative Example. Note that the driving voltage was set as follows. An alternating current voltage of 0 V or more to 150 V was applied to the light control sheet, thereby creating a voltage-haze curve. Then, the minimum value of the AC voltage that gave a haze value of 90% of the maximum value of the haze value in the voltage-haze curve was specified, and the minimum value was set as the drive voltage. Note that the voltage-haze curve was created using a haze meter that was used to measure the haze value when transparent.

[response speed]
The response speed in a -10°C environment was measured as follows. First, an AC dynamic voltage of 60 V was applied to the light control sheets of each Example and each Comparative Example, and then the haze value of the light control sheets was maintained in an increased state. Next, the time from when the AC voltage was switched to 0 V until the haze value on the light control sheet reached the following haze value A was measured.
Haze value A = (Haze value when transparent) + (Haze when transparent) x 0.1

[Evaluation results]
The evaluation results for each light control sheet were as shown in FIG.

As shown in FIG. 4, in the light control sheets of Examples 1 and 2 and Comparative Examples 1 to 3, the polar angle anchoring coefficient W _a was 10×10 ⁻⁴ . Further, the domain diameter D of the light control sheet was 0.6 μm in Comparative Example 1, 0.9 μm in Example 1, 2.1 in Example 2, and 3.0 μm in Comparative Example 2. , in Comparative Example 3, it was found to be 4.2 μm. Therefore, |D*log ₁₀ (W _a )| is 2.4 in Comparative Example 1, 3.6 in Example 1, 8.4 in Example 2, and 12.0 in Comparative Example 2. In Comparative Example 3, it was found to be 16.8.

Further, in the light control sheets of Examples 3 to 5 and Comparative Examples 4 and 5, the polar angle anchoring coefficient W _a was 10×10 ⁻³ . Further, the domain diameter D of the light control sheet was 0.6 μm in Comparative Example 4, 1.2 μm in Example 3, 2.2 in Example 4, and 3.1 μm in Example 5. , in Comparative Example 5, it was found to be 4.1. Therefore, |D*log ₁₀ (W _a )| is 1.8 in Comparative Example 4, 3.6 in Example 3, 6.6 in Example 4, and 9. 3, and in Comparative Example 5 it was found to be 12.3.

Further, in the light control sheets of Examples 6 to 8 and Comparative Examples 6 and 7, the polar angle anchoring coefficient W _a was 10×10 ⁻² . In addition, the domain diameter D of the light control sheet was 0.5 in Comparative Example 6, 1.1 in Comparative Example 7, 2.2 in Example 6, and 2.9 in Example 7. , was found to be 3.8 in Example 8. Therefore, |D*log ₁₀ (W _a )| is 1.0 in Comparative Example 6, 2.2 in Comparative Example 7, 4.4 in Example 6, and 5.0 in Example 7. 8, and in Example 8 it was found to be 7.6.

According to the light control sheets of Examples 1 to 8, it was observed that the haze value when the light control sheets were transparent was less than 6%. On the other hand, according to the light control sheets of Comparative Examples 1, 4, 6, and 7, the haze value when the light control sheets exhibit transparency is less than 6%, while the light control sheets of Comparative Examples 2, 3, and 5 have a haze value of less than 6%. The light control sheet was found to have a haze of 6% or more when the light control sheet was transparent.

According to the light control sheets of Examples 1 to 8, it was observed that the driving voltage was less than 80V. Furthermore, it was observed that the driving voltage of the light control sheets of Comparative Examples 2, 3, and 5 was less than 80V, while the driving voltage of the light control sheets of Comparative Examples 1, 4, 6, and 7 was 80V or more. .

According to the light control sheets of Examples 1 to 8, it was observed that the response speed was less than 20 seconds. On the other hand, it was observed that the response speed of the light control sheets of Comparative Examples 1, 4 to 7 was less than 20 seconds, while the response speed of the light control sheets of Comparative Examples 2 and 3 was 20 seconds or more. It was done.

In this way, in the light control sheet, when the value of |D*log ₁₀ (W _a )| is within the range of 3.6 or more and 9.3 or less, the haze value, driving voltage, and It was observed that all of the response speeds were within suitable ranges. On the other hand, if the value of |D*log ₁₀ (W _a )| is not within the above range, at least one of the haze value, drive voltage, and response speed when exhibiting transparency is suitable. It was recognized that this was not within the specified range. Specifically, it was found that the driving voltage was increased when the value of |D*log ₁₀ (W _a )| was less than 3.6. On the other hand, it was observed that when the value of |D*log ₁₀ (W _a )| exceeds 9.3, the haze value when exhibiting transparency increases and the response speed at -10°C becomes slower. It was done.

As explained above, according to one embodiment of the light control sheet, the effects described below can be obtained.
(1) In the vicinity of the first alignment layer 21, the first polar angle anchoring coefficient W _a1 of the first alignment layer 21 is prevented from becoming excessively small, and the domain diameter D is prevented from becoming excessively large. This prevents the force of the first alignment layer 21 from orienting the liquid crystal molecules 23LM from becoming excessively small, so that the haze value when the light control sheet 11R becomes transparent increases, and the response in a low-temperature environment increases. This prevents the speed from slowing down. Moreover, the first polar angle anchoring coefficient W _a1 is prevented from becoming excessively large, and the domain diameter D is prevented from becoming excessively small. This prevents the force of the first alignment layer 21 from orienting the liquid crystal molecules 23LM from becoming excessively large, thereby suppressing the driving voltage of the light control sheet 11R from increasing.

(2) In the vicinity of the second alignment layer 22, the second polar angle anchoring coefficient W _a2 of the second alignment layer 22 is prevented from becoming excessively small, and the domain diameter D is prevented from becoming excessively large. This prevents the force with which the second alignment layer 22 aligns the liquid crystal molecules 23LM from becoming excessively small, so that the haze value when the light control sheet 11R becomes transparent increases, and the response in a low-temperature environment increases. This prevents the speed from slowing down. Further, the second polar angle anchoring coefficient W _a2 is prevented from becoming excessively large, and the domain diameter D is prevented from becoming excessively small. This prevents the force of the second alignment layer 22 from orienting the liquid crystal molecules 23LM from becoming excessively large, thereby suppressing the driving voltage of the light control sheet 11R from increasing.

(3) By setting the domain diameter D to 0.5 μm or more and 4.0 μm or less, it is possible to suppress the haze value of the light control sheet 11R from increasing when no voltage is applied to the light control sheet 11R.

(4) The first polar angle anchoring coefficient W _a1 is within the range of 1.0×10 ⁻⁴ or more and 1.0×10 ^{−2 or} less, so that the first polar angle anchoring coefficient W _a1 reaches the lower limit value. Compared to the case where the domain diameter D satisfies the formula (1), it is suppressed from increasing. This suppresses an increase in haze value when exhibiting transparency and a decrease in response speed in a low-temperature environment. On the other hand, compared to the case where the first polar angle anchoring coefficient W _a1 exceeds the upper limit value, the size of the domain diameter D that satisfies Equation (1) is suppressed from becoming smaller. This prevents the driving voltage of the light control sheet from increasing.

(5) Since the density of the domains 23D is the lowest in the central part of the light control layer 23 in the thickness direction, it is possible to reduce the number of liquid crystal molecules 23LM located in a region far from each alignment layer 21, 22. . This makes it easier for the alignment regulating force of each alignment layer 21, 22 to act on the liquid crystal molecules 23LM, thereby increasing the transparency of the light control sheet 11R when no voltage is applied between the transparent electrode layers 24, 25. In other words, it is possible to reduce haze.

Note that the embodiment described above can be modified and implemented as follows.
[Dimmer layer]
- The light control layer 23 may have a domain 23D at the center of the cross section along the thickness direction of the light control layer 23. Even in this case, an effect similar to (1) described above can be obtained by satisfying Condition 1 described above.

[Dimmer sheet]
- The light control sheet 11R does not need to satisfy condition 2. Even in this case, if the light control sheet 11R satisfies Condition 1, it is possible to obtain an effect similar to (1) described above.

11R... Light control sheet 21... First alignment layer 22... Second alignment layer 23... Light control layer 23D... Domain 23L... Liquid crystal composition 23LM... Liquid crystal molecule 24... First transparent electrode layer 25... Second transparent electrode layer

Claims (5)

a first alignment layer;
a second orientation layer;
A light control layer located between the first alignment layer and the second alignment layer, comprising a transparent polymer layer in which a plurality of domains are dispersed, and a liquid crystal composition containing liquid crystal molecules and filled in the domains. and the light control layer containing a substance,
a domain diameter D, which is an index of the size of the domain;
The first polar angle anchoring coefficient W _a1 , which is the polar angle anchoring coefficient of the first alignment layer with respect to the liquid crystal molecules, satisfies formula (1): 3.6≦|D*log ₁₀ (W _a1 )|≦ 9.3... Formula (1)
Light control sheet. the domain diameter;
The second polar angle anchoring coefficient W _a2 , which is the polar angle anchoring coefficient of the second alignment layer with respect to the liquid crystal molecules, satisfies formula (2) 3.6≦|D*log ₁₀ (W _a1 )|≦ 9.3... Formula (2)
The light control sheet according to claim 1. The light control sheet according to claim 1 or 2, wherein the domain diameter is 0.5 μm or more and 4.0 μm or less. The light control sheet according to claim 1 or 2, wherein the first polar angle anchoring coefficient W _a1 is 1.0×10 ⁻⁴ or more and 1.0×10 ⁻² or less. The light control sheet according to claim 1 or 2, wherein the density of the domains per thickness of the light control layer is lowest at a central portion in the thickness direction of the light control layer.

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