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

Abstract

According to the present invention, a light control layer of a light control sheet includes: an acrylic resin layer which partitions a gap; and a liquid crystal composition which contains a liquid crystal compound, and with which the gap is filled. The acrylic resin layer is a polymer of a monofunctional alkyl acrylate that contains a saturated alkyl group having 2 to 8 carbon atoms and a polyfunctional acrylate, the glass transition temperature of the monofunctional alkyl acrylate is lower than the glass transition temperature of the polyfunctional acrylate and is 8°C or lower, and the mass of the monofunctional alkyl acrylate with respect to the mass of the polyfunctional acrylate is 11 mass% to 35 mass%.

Description

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

[0001] The present disclosure relates to a light control sheet in which a liquid crystal composition is filled into voids defined by an acrylic resin layer, a light control device including the light control sheet, and a method for manufacturing the light control sheet.

[0002] The light-controlling sheet comprises a light-controlling layer between two transparent electrode films. The light-controlling layer comprises an acrylic resin layer defining a plurality of voids and a liquid crystal composition filled in the voids. Changing the voltage between the transparent electrode films changes the alignment state of the liquid crystal compound. The change in alignment state of the liquid crystal compound changes the degree of scattering at the interface between the acrylic resin layer and the liquid crystal composition, thereby changing the transparency of the light-controlling sheet.

[0003] The time it takes for the transparency of a light-controlling sheet to respond to a change in voltage between the transparent electrode films depends on the environmental temperature in which the light-controlling sheet is installed. The lower the environmental temperature at which the transparency of the light-controlling sheet can respond to a change in voltage, the more suitable the light-controlling sheet is for use in low-temperature environments. A first example of lowering the application temperature of a light-controlling sheet is to add a viscosity reducer such as an adipic acid ester to the liquid crystal composition to reduce the viscosity of the liquid crystal composition in low-temperature environments (see, for example, Patent Documents 1 and 2). A second example of lowering the application temperature of a light-controlling sheet is to add an alkyl acrylate such as methyl acrylate or dodecyl acrylate to the acrylate used to form the acrylic resin layer in a normal-type light-controlling sheet (see, for example, Patent Document 3).

[0004] JP 2022-148343 A JP 2022-098845 A Japanese Patent No. 7099578 A

[0005] On the other hand, the addition of a viscosity-reducing agent reduces the blending ratio of the acrylic resin layer or the liquid crystal compound in the light-controlling layer. The reduction in the blending ratio reduces the interface between the acrylic resin layer and the liquid crystal composition, which reduces the degree of scattering of the light-controlling sheet, so there is a limit to the viscosity reduction that can be achieved by adding a viscosity-reducing agent.

[0006] In addition, the driving method for light-controlling sheets can be either a normal type, which increases transparency when a voltage signal is supplied, or a reverse type, which decreases transparency when a voltage signal is supplied. Reverse-type light-controlling sheets use the regulating force of the alignment layer as the driving force to increase transparency. Because the regulating force of the alignment layer acts more slowly on the liquid crystal compound than an electric field, reverse-type driving methods are prone to a response delay between the cessation of the voltage signal supply and achieving the desired transparency. This response delay is particularly noticeable when operating in a low-temperature environment.

[0007] One aspect of a light-controlling sheet is a light-controlling sheet comprising: a light-controlling layer sandwiched between a first transparent electrode layer and a second transparent electrode layer; a first alignment layer located between the first transparent electrode layer and the light-controlling layer; and a second alignment layer located between the second transparent electrode layer and the light-controlling layer; and the sheet changes the haze of the light-controlling layer by changing the voltage applied between the first transparent electrode layer and the second transparent electrode layer. The light-controlling layer comprises an acrylic resin layer defining voids; and a liquid crystal composition containing a liquid crystal compound and filling the voids. The acrylic resin layer is a polymer of a monofunctional alkyl acrylate containing a saturated alkyl group having 2 to 8 carbon atoms and a polyfunctional acrylate, the glass transition temperature of the monofunctional alkyl acrylate being lower than the glass transition temperature of the polyfunctional acrylate and being 8°C or lower, and the mass of the monofunctional alkyl acrylate relative to the mass of the polyfunctional acrylate is 11% by mass or higher and 35% by mass or lower.

[0008] One aspect of a light control device is a light control device comprising: a light control layer sandwiched between a first transparent electrode layer and a second transparent electrode layer; a first alignment layer located between the first transparent electrode layer and the light control layer; a second alignment layer located between the second transparent electrode layer and the light control layer; and a drive unit that changes the haze of the light control layer by changing the voltage applied between the first transparent electrode layer and the second transparent electrode layer. The light control layer comprises an acrylic resin layer that defines voids; and a liquid crystal composition that contains a liquid crystal compound and is filled into the voids. The acrylic resin layer is a polymer of a monofunctional alkyl acrylate containing a saturated alkyl group having from 2 to 8 carbon atoms and a polyfunctional acrylate. The glass transition temperature of the monofunctional alkyl acrylate is lower than the glass transition temperature of the polyfunctional acrylate and is 8°C or lower. The mass of the monofunctional alkyl acrylate relative to the mass of the polyfunctional acrylate is 11% by mass or higher and 35% by mass or lower.

[0009] One aspect of a method for manufacturing a light-controlling sheet includes forming a coating layer containing a polymerizable composition and a liquid crystal composition between a first alignment layer and a second alignment layer, and irradiating the coating layer with ultraviolet light to form a light-controlling layer between the first alignment layer and the second alignment layer, the light-controlling layer comprising an acrylic resin layer that defines voids and the liquid crystal composition that fills the voids. This method for manufacturing a light-controlling sheet changes the haze of the light-controlling layer by changing the voltage applied between the first alignment layer and the second alignment layer, and the polymerizable composition includes a monofunctional alkyl acrylate containing a saturated alkyl group having 2 to 8 carbon atoms, and a polyfunctional acrylate, the glass transition temperature of the monofunctional alkyl acrylate being lower than the glass transition temperature of the polyfunctional acrylate and being 8°C or lower, and the mass of the monofunctional alkyl acrylate relative to the mass of the polyfunctional acrylate is 11% by mass or higher and 35% by mass or lower.

[0010] Fig. 1 is a diagram illustrating the configuration of a light-adjusting device. Fig. 2 is an enlarged cross-sectional view of a light-adjusting sheet. Fig. 3 shows the blending ratio of polymerizable compositions in test examples. Fig. 4 shows a method for evaluating responsiveness in test examples. Fig. 5 shows the evaluation results of test examples.

[0011] [Light control device 10] As shown in Fig. 1, the light control device 10 includes a light control sheet 11 and a drive unit 12. The light control device 10 may be used as a partition device that divides a space. The light control sheet 11 itself may be the partition member that divides the space, or a light control adhesive body having the light control sheet 11 mounted on a transparent member may be the partition member that divides the space. The partition member may be window glass or a partition. The window glass may be mounted on a moving body such as a vehicle or an airplane, or may be installed in a building such as an office building or a public facility. The partition may be placed in a vehicle interior space or an indoor space.

[0012] The light control device 10 may be used as a screen for displaying an image. The light control sheet 11 itself may be the screen, or a light control adhesive body in which the light control sheet 11 is mounted on a transparent member may be the screen. The screen may be a front screen that uses reflected light for the image, or a rear screen that uses transmitted light for the image.

[0013] The light-adjusting adhesive may have one light-adjusting sheet 11 mounted on one transparent member, or may have multiple light-adjusting sheets 11 mounted on one transparent member. The light-adjusting adhesive may have the light-adjusting sheet 11 sandwiched between two transparent substrates. The light-adjusting sheet 11 is flexible. The light-adjusting adhesive may or may not be flexible. The light-adjusting adhesive may have a flat shape or a curved shape.

[0014] The driving format of the light controlling sheet 11 is reverse type. The driving unit 12 supplies a voltage signal to the reverse type light controlling sheet 11. The reverse type light controlling sheet 11 changes from transparent to opaque when a voltage signal is supplied. The reverse type light controlling sheet 11 remains opaque while the voltage signal is supplied. The reverse type light controlling sheet 11 returns from opaque to transparent when the supply of the voltage signal is stopped.

[0015] The light-adjusting sheet 11 achieves opacity by scattering transmitted light through the light-adjusting sheet 11. The opaque light-adjusting sheet 11 has a lower parallel light transmittance than the transparent light-adjusting sheet 11. The opaque light-adjusting sheet 11 has a higher haze than the transparent light-adjusting sheet 11. The color of the opaque light-adjusting sheet 11 may be either achromatic or chromatic. The color of the transparent light-adjusting sheet 11 may be either achromatic or chromatic.

[0016] [Light Control Sheet 11] The light control sheet 11 includes a light control layer 31, a first alignment layer 32, a second alignment layer 33, a first transparent electrode layer 34, a second transparent electrode layer 35, a first transparent support layer 36, and a second transparent support layer 37.

[0017] The light-controlling layer 31 is located between a first alignment layer 32 and a second alignment layer 33. A first surface 31F of the light-controlling layer 31 contacts the first alignment layer 32. A second surface 31S of the light-controlling layer 31 contacts the second alignment layer 33. The first alignment layer 32 is located between the light-controlling layer 31 and the first transparent electrode layer 34 and contacts both the light-controlling layer 31 and the first transparent electrode layer 34. The second alignment layer 33 is located between the light-controlling layer 31 and the second transparent electrode layer 35 and contacts both the light-controlling layer 31 and the second transparent electrode layer 35.

[0018] The first transparent electrode layer 34 is connected to the driving unit 12 through the first connection terminal 22A and the first wiring 23A. The first transparent electrode layer 34 is located between the first alignment layer 32 and the first transparent support layer 36, and is in contact with the first alignment layer 32 and the first transparent support layer 36.

[0019] The second transparent electrode layer 35 is connected to the driving unit 12 through the second connection terminal 22B and the second wiring 23B. The second transparent electrode layer 35 is located between the second alignment layer 33 and the second transparent support layer 37, and is in contact with the second alignment layer 33 and the second transparent support layer 37.

[0020] The first transparent electrode layer 34 and the second transparent electrode layer 35 are visually recognized as colorless and transparent or colored and transparent, respectively. The materials constituting the first transparent electrode layer 34 and the second transparent electrode layer 35 are each a conductive inorganic oxide, a metal, or a conductive organic polymer compound. An example of the conductive inorganic oxide is any one selected from the group consisting of indium tin oxide, fluorine-doped tin oxide, tin oxide, and zinc oxide. The metal is gold or silver nanowires. An example of the conductive organic polymer compound is any one selected from the group consisting of carbon nanotubes and poly(3,4-ethylenedioxythiophene). An example of the thickness of the first transparent electrode layer 34 and the second transparent electrode layer 35 is 5 nm or more and 200 nm or less.

[0021] The first transparent support layer 36 and the second transparent support layer 37 are visually recognized as colorless and transparent or colored and transparent, respectively. The materials constituting the first transparent support layer 36 and the second transparent support layer 37 are organic polymer compounds or inorganic polymer compounds. An example of the organic polymer compound is any one selected from the group consisting of polyester, polyacrylate, polycarbonate, and polyolefin. An example of the inorganic polymer compound is any one selected from the group consisting of silicon oxide, silicon oxynitride, and silicon nitride. An example of the thickness of the first transparent support layer 36 and the second transparent support layer 37 is 20 μm or more and 400 μm or less, respectively.

[0022] The driver 12 is separately connected to the first transparent electrode layer 34 and the second transparent electrode layer 35. The driver 12 applies a voltage between the first transparent electrode layer 34 and the second transparent electrode layer 35 by supplying a voltage signal. The driver 12 changes the voltage between the first transparent electrode layer 34 and the second transparent electrode layer 35 by stopping the supply of the voltage signal. Supplying and stopping the supply of the voltage signal changes the alignment state of the liquid crystal compound LCM. The driver 12 reversibly switches the light control sheet 11 from transparent to opaque by changing the alignment state of the liquid crystal compound LCM.

[0023] When the driving unit 12 stops supplying a voltage signal, the orientation state of the liquid crystal compound LCM follows the orientation restriction force of the first orientation layer 32 and the second orientation layer 33. The orientation state of the liquid crystal compound LCM following the orientation restriction force allows visible light to pass through the light control layer 31. This makes the light control sheet 11 transparent. When the driving unit 12 is supplying a voltage signal, the liquid crystal compound LCM is subjected to the action force of an electric field that resists the orientation restriction force. The orientation state of the liquid crystal compound LCM following the action force of the electric field causes visible light to be scattered in the light control layer 31. This makes the light control sheet 11 opaque.

[0024] The light-controlling sheet 11 may include another functional layer between the first transparent electrode layer 34 and the first transparent support layer 36. The light-controlling sheet 11 may include another functional layer between the second transparent electrode layer 35 and the second transparent support layer 37. The other functional layer may be a gas barrier layer that suppresses the transmission of oxygen and moisture toward the light-controlling layer 31, or an ultraviolet barrier layer that suppresses the transmission of ultraviolet rays other than those of a specific wavelength toward the light-controlling layer 31. The other functional layer may be a hard coat layer that mechanically protects the light-controlling sheet 11, or an adhesive layer that improves adhesion between layers in the light-controlling sheet 11.

[0025] [Light Control Layer 31] As shown in FIG. 2, the light control layer 31 includes a liquid crystal composition 31LC, spacers SP, and an acrylic resin layer 31P.

[0026] The liquid crystal composition 31LC includes a liquid crystal compound LCM. The liquid crystal composition 31LC may contain additives such as a dichroic dye DP, an antifoaming agent, an antioxidant, a weathering agent, and a solvent. Examples of weathering agents include an ultraviolet absorber and a light stabilizer. The liquid crystal composition 31LC may also contain a viscosity reducing agent that reduces the viscosity of the liquid crystal composition 31LC below that of the liquid crystal compound LCM. The viscosity reducing agent is an adipate ester such as dibutyl adipate, bis(2-ethylhexyl) adipate, diisononyl adipate, diisodecyl adipate, or bis(2-butoxyethyl) adipate. The viscosity reducing agent is at least one selected from the group consisting of an adipate ester, diethyl malonate, di-n-butyl phthalate, bis(2-ethylhexyl) phthalate, tris(2-ethylhexyl) trimellitate, tributyl o-acetylcitrate, and methyl benzoate. The viscosity reducing agent is at least one selected from the group consisting of tripropyl phosphate, tributyl phosphate, and tripentyl phosphate.

[0027] The liquid crystal compound LCM may have a positive dielectric anisotropy, i.e., the dielectric constant in the long axis direction is larger than the dielectric constant in the short axis direction of the liquid crystal compound LCM. The liquid crystal compound LCM may have a negative dielectric anisotropy, i.e., the dielectric constant in the long axis direction is smaller than the dielectric constant in the short axis direction of the liquid crystal compound LCM. The dielectric anisotropy of the liquid crystal compound LCM is appropriately selected based on the driving format of the light controlling sheet 11.

[0028] The liquid crystal compound LCM is at least one selected from the group consisting of Schiff base-based, azo-based, azoxy-based, biphenyl-based, terphenyl-based, benzoate ester-based, tolan-based, pyrimidine-based, pyridazine-based, cyclohexanecarboxylic acid ester-based, phenylcyclohexane-based, biphenylcyclohexane-based, dicyanobenzene-based, naphthalene-based, and dioxane-based liquid crystal compounds. The liquid crystal compound LCM is one type of liquid crystal compound LCM or a combination of two or more types of liquid crystal compounds LCM.

[0029] An example of the structure of the liquid crystal compound LCM is represented by the following formula 1: １１ -A １１ -Z １１ -A １２ -Z １２ -A １３-Z １３ -A １４ -R １２ ...Formula 1 R shown in Formula 1 １１ is a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. １１ One or two or more non-adjacent methylene bonds contained in the alkyl group of formula (I) can be substituted with any bond selected from the group consisting of an oxygen atom, an ethylene bond, an ester bond, and a diether bond. １２ is a hydrogen atom, a fluorine atom, a chlorine atom, a cyano group, a trifluoromethyl group, a trifluoromethoxy group, a difluoromethoxy group, or an alkyl group having 1 to 15 carbon atoms. １２ One or two or more non-adjacent methylene bonds contained in the alkyl group can be substituted with any bond selected from the group consisting of an oxygen atom, an ethylene bond, an ester bond, and a diether bond.

[0030] A shown in Formula 1 １１ , A １２ , A １３ , A １４ each independently represents a 1,4-phenylene group or a 2,6-naphthylene group. One or more hydrogen atoms of the 1,4-phenylene group or the 2,6-naphthylene group can be substituted with a fluorine atom, a chlorine atom, a trifluoromethyl group, or a trifluoromethoxy group. １１ , A １２ , A １３ , A １４ may each independently represent a 1,4-cyclohexylene group, a 3,6-cyclohexenylene group, a 1,3-dioxane-2,5-diyl group, or a pyridine-2,5-diyl group. １３ , A １４ may each independently be a single bond. １１ , Z １２ , Z １３ each independently represents any one bond selected from the group consisting of a single bond, an ester bond, a diether bond, an ethylene bond, a fluoroethylene bond, and a carbonyl bond.

[0031] The dichroic dye DP is driven by a guest-host system using the liquid crystal compound LCM as a host, and exhibits color. The dichroic dye DP is at least one selected from the group consisting of polyiodine, azo compounds, anthraquinone compounds, naphthoquinone compounds, azomethine compounds, tetrazine compounds, quinophthalone compounds, merocyanine compounds, perylene compounds, and dioxazine compounds. The dichroic dye DP is a single compound or a combination of two or more compounds. When improved lightfastness and an increased dichroic ratio are required, 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.

[0032] The spacers SP are dispersed throughout the acrylic resin layer 31P. The particle size of the spacers SP determines the thickness of the light-controlling layer 31. An example of the thickness of the light-controlling layer 31 is 5 μm or more and 100 μm or less. The spacers SP make the thickness of the light-controlling layer 31 uniform. The spacers SP may be bead spacers or photospacers formed by exposing and developing a photoresist. The spacers SP may be colorless and transparent, or colored and transparent. When the liquid crystal composition 31LC contains a dichroic dye DP, the color of the spacers SP is preferably the same color as the color exhibited by the dichroic dye DP.

[0033] The first alignment layer 32 and the second alignment layer 33 each regulate the alignment direction of the liquid crystal compound LCM. The first alignment layer 32 and the second alignment layer 33 each appear colorless and transparent or colored and transparent. The first alignment layer 32 and the second alignment layer 33 may be vertical alignment films or horizontal alignment films.

[0034] The material constituting the first alignment layer 32 and the second alignment layer 33 is an organic polymer compound or an inorganic oxide. An example of the organic polymer compound is any one selected from the group consisting of polyimide, polyamide, and polyvinyl alcohol. An example of the inorganic oxide is any one selected from the group consisting of silicon oxide, zirconium oxide, and silicone. An example of the thickness of the first alignment layer 32 and the second alignment layer 33 is 20 nm or more and 500 nm or less, respectively.

[0035] When the first alignment layer 32 and the second alignment layer 33 are each vertical alignment films, the first alignment layer 32 and the second alignment layer 33 each apply an alignment restriction force to the liquid crystal compound LCM so as to align the long axis direction of the liquid crystal compound LCM with the thickness direction of the light control layer 31. As a result, the first alignment layer 32 and the second alignment layer 33 allow visible light to pass through the light control layer 31 during a period when the supply of a voltage signal is stopped.

[0036] When the first alignment layer 32 and the second alignment layer 33 are each horizontal alignment films, the light control sheet 11 includes a polarizing layer. The first alignment layer 32 and the second alignment layer 33 apply an alignment restriction force to the liquid crystal compound LCM so that the long axis direction of the liquid crystal compound LCM is parallel to the extension direction of the transmission axis of the polarizing layer. As a result, the first alignment layer 32 and the second alignment layer 33 transmit visible light through the polarizing layer to the light control layer 31 during a period when the supply of a voltage signal is stopped.

[0037] When the first alignment layer 32 and the second alignment layer 33 are each horizontal alignment films, the light control sheet 11 includes polarizing layers arranged in crossed Nicols. The first alignment layer 32 applies an alignment force to the liquid crystal compound LCM so that the long axis of the liquid crystal compound LCM is parallel to the extension direction of the transmission axis of one polarizing layer. The second alignment layer 33 applies an alignment force to the liquid crystal compound LCM so that the long axis of the liquid crystal compound LCM is parallel to the extension direction of the transmission axis of the other polarizing layer. In other words, the first alignment layer 32 and the second alignment layer 33 apply a twist alignment force to the liquid crystal compound LCM. As a result, the first alignment layer 32 and the second alignment layer 33 transmit visible light through the polarizing layers to the light control layer 31 during periods when the supply of a voltage signal is stopped.

[0038] [Acrylic Resin Layer 31P] The acrylic resin layer 31P is a polymer of a monofunctional alkyl acrylate and a polyfunctional acrylate. The lower limit of the blending ratio of the acrylic resin layer 31P relative to the total amount of the acrylic resin layer 31P and the liquid crystal composition 31LC is 20% by mass, and more preferably 30% by mass. If the blending ratio of the acrylic resin layer 31P is 20% by mass or more, high transmittance is likely to be obtained when the liquid crystal layer 31 is transparent. The upper limit of the blending ratio of the acrylic resin layer 31P relative to the total amount of the acrylic resin layer 31P and the liquid crystal composition 31LC is 70% by mass, and more preferably 60% by mass. If the blending ratio of the acrylic resin layer 31P is 70% by mass or less, high haze is likely to be obtained when the liquid crystal layer 31 is opaque.

[0039] The upper and lower limits of the blending ratio of the acrylic resin layer 31P are within a range in which liquid crystal particles of the liquid crystal composition 31LC phase-separate from the acrylate polymer during the acrylate polymerization process. When it is necessary to increase the mechanical strength of the acrylic resin layer 31P, a higher lower limit of the blending ratio of the acrylic resin layer 31P is preferable. When it is necessary to reduce the driving voltage of the liquid crystal compound LCM, a lower upper limit of the blending ratio of the acrylic resin layer 31P is preferable. The lower limit of the blending ratio of the acrylic resin layer 31P relative to the total amount of the acrylic resin layer 31P and the liquid crystal composition 31LC may be 20% by mass or more and 70% by mass or less, or 30% by mass or more and 70% by mass or less. The lower limit of the blending ratio of the acrylic resin layer 31P relative to the total amount of the acrylic resin layer 31P and the liquid crystal composition 31LC may be 20% by mass or more and 60% by mass or less, or 30% by mass or more and 60% by mass or less.

[0040] The acrylic resin layer 31P defines a void 31D in the light-controlling layer 31. The liquid crystal composition 31LC is filled in the void 31D. The void 31D may be isolated from another void 31D adjacent to the void 31D, or may be connected to another adjacent void 31D. The void 31D may have two or more sizes. The shape of the void 31D is spherical, ellipsoidal, or irregular. The diameter of the sphere circumscribing the void 31D may be 0.4 μm or more, or 1 μm or more. The diameter of the sphere circumscribing the void 31D may be 20 μm or less, or 10 μm or less. The diameter of the sphere circumscribing the void 31D is, for example, 1 μm or more and 10 μm or less.

[0041] The voids 31D may be unevenly distributed in the acrylic resin layer 31P or may be uniformly dispersed in the acrylic resin layer 31P. The voids 31D may be unevenly distributed in a range 31H1 closer to the first alignment layer 32 than the center in the thickness direction of the acrylic resin layer 31P, so that the voids 31D become more numerous in a region closer to the first alignment layer 32. The voids 31D may be unevenly distributed in a range 31H2 closer to the second alignment layer 33 than the center in the thickness direction of the acrylic resin layer 31P, so that the voids 31D become more numerous in a region closer to the second alignment layer 33. The acrylic resin layer 31P may have a portion in the thickness direction center of the acrylic resin layer 31P where no voids 31D exist, and may have a void 31D between this portion and the first alignment layer 32. The acrylic resin layer 31P may have a portion in the thickness direction center of the acrylic resin layer 31P where no voids 31D exist, and may have a void 31D between this portion and the second alignment layer 33.

[0042] The voids 31D are formed by phase separation between the cured product of the polymerizable composition and the liquid crystal composition 31LC. A region 31H1 of the acrylic resin layer 31P that is closer to the first alignment layer 32 than the center in the thickness direction is a region where irradiation with ultraviolet light begins, and where the voids 31D begin to form. A region 31H2 of the acrylic resin layer 31P that is closer to the second alignment layer 33 than the center in the thickness direction is also a region where irradiation with ultraviolet light begins, and where the voids 31D begin to form.

[0043] Phase separation between the cured polymerizable composition and the liquid crystal composition 31LC causes unreacted low-molecular-weight compounds, such as monofunctional monomers and oligomers, to remain in the liquid crystal composition 31LC. Low-molecular-weight compounds, such as monofunctional monomers and oligomers, tend to increase the viscosity of the liquid crystal composition 31LC as the temperature decreases. The glass transition temperature of the monofunctional monomer is 8°C or lower, which prevents the monofunctional monomers and oligomers remaining in the liquid crystal composition 31LC from increasing the viscosity of the liquid crystal composition 31LC.

[0044] The acrylic resin layer 31P is formed by applying a photochromic coating solution containing a polymerizable composition and a liquid crystal compound LCM, and irradiating the coating layer with ultraviolet light. The photochromic coating solution contains a polymerization initiator for initiating polymerization. The acrylic resin layer 31P contains a polymerization initiator that initiates polymerization. The polymerization initiator may be at least one selected from the group consisting of a diketone compound, an acetophenone compound, a benzoin compound, a benzophenone compound, and a thioxanthone compound. The polymerization initiator may be a single compound or a combination of two or more compounds. An example of the polymerization initiator is any one selected from the group consisting of benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and cyclohexyl phenyl ketone.

[0045] [Polymerizable Composition] The polymerizable composition is a mixture of a monofunctional alkyl acrylate and a polyfunctional acrylate.

[0046] The monofunctional alkyl acrylate contains a saturated alkyl group having 2 to 8 carbon atoms. The saturated alkyl group may be a linear alkyl group or a branched alkyl group. The glass transition temperature of the monofunctional alkyl acrylate is lower than that of the polyfunctional acrylate. The glass transition temperature of the monofunctional alkyl acrylate is 8°C or lower. The glass transition temperature of the monofunctional alkyl acrylate may be -20°C or lower, or -50°C or lower. The monofunctional alkyl acrylate may be methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, hexyl acrylate, 2-ethylbutyl acrylate, or 2-ethylhexyl acrylate. The monofunctional alkyl acrylate may be at least one selected from the group consisting of ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate.

[0047] Examples of polyfunctional acrylates include urethane acrylates such as pentaerythritol compounds, trimethylolpropane compounds, glycol compounds, and urethane prepolymers. Pentaerythritol compounds include pentaerythritol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxytetraacrylate, dipentaerythritol triacrylate, dipentaerythritol tetraacrylate, dipentaerythritol ethoxytetraacrylate, dipentaerythritol hexaacrylate, and trispentaerythritol octaacrylate. Trimethylolpropane compounds include trimethylolpropane triacrylate, trimethylolpropane ethoxytriacrylate, and ditrimethylolpropane tetraacrylate. The glycol compounds are glycerin diacrylate, glycerin triacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, 3-methyl-1,5-pentadiol diacrylate, and 1,6-hexanediol diacrylate.

[0048] The mass of the monofunctional alkyl acrylate relative to the mass of the polyfunctional acrylate is 11% by mass or more and 35% by mass or less. The mass of the monofunctional alkyl acrylate relative to the mass of the polyfunctional acrylate may be 20% by mass or more and 35% by mass or less, or 20% by mass or more and 30% by mass or less. The mass of the monofunctional alkyl acrylate relative to the mass of the liquid crystal compound LCM may be 10% by mass or more and 30% by mass or less, or 20% by mass or more and 30% by mass or less.

[0049] [Method for manufacturing light-controlling sheet 11] The method for manufacturing light-controlling sheet 11 includes forming a first alignment layer 32 on a first transparent electrode layer 34, and forming a second alignment layer 33 on a second transparent electrode layer 35. The first alignment layer 32 is formed by applying an alignment coating liquid to the first transparent electrode layer 34 laminated on a first transparent support layer 36, and heating the alignment coating layer. The second alignment layer 33 is formed by applying an alignment coating liquid to the second transparent electrode layer 35 laminated on a second transparent support layer 37, and heating the alignment coating layer.

[0050] The method for producing the light-controlling sheet 11 includes forming a light-controlling coating layer containing a polymerizable composition and a liquid crystal composition 31LC between a first alignment layer 32 and a second alignment layer 33. The method for producing the light-controlling sheet 11 includes forming a light-controlling layer 31 between the first alignment layer 32 and the second alignment layer 33 by irradiating the light-controlling coating layer with ultraviolet light.

[0051] The polymerizable composition irradiated with ultraviolet light initiates polymerization and phase-separates the liquid crystal particles of liquid crystal composition 31LC from the polymer. Phase separation of the liquid crystal particles of liquid crystal composition 31LC proceeds through polymerization of the polymerizable composition and diffusion of the liquid crystal composition 31LC. The polymerization rate of the polymerizable composition varies depending on the intensity of the ultraviolet light irradiated onto the polymerizable composition. The diffusion rate of the liquid crystal composition 31LC varies depending on the processing temperature during polymerization of the polymerizable composition. In phase separation of liquid crystal composition 31LC, the intensity of the ultraviolet light is set so that the liquid crystal particles have the desired size, i.e., so that the size of voids 31D has the desired size. In addition, heating may be performed to promote diffusion of the liquid crystal composition 31LC in phase separation of liquid crystal composition 31LC.

[0052] When it is required to reduce the size of the voids 31D, it is preferable to increase the intensity of the ultraviolet light and carry out the polymerization at a low temperature to suppress the diffusion of the liquid crystal composition 31LC, whereas when it is required to increase the size of the voids 31D, it is preferable to decrease the intensity of the ultraviolet light and carry out the polymerization at a high temperature to promote the diffusion of the liquid crystal composition 31LC.

[0053] [Test Examples] The light-controlling sheets 11 of the test examples are shown below. The light-controlling sheets 11 of the test examples have vertical alignment films as the first alignment layer 32 and the second alignment layer 33. The drive system of the test examples is reverse type. The light-controlling sheets 11 of test examples 1 to 10 were obtained using polymerizable monomers with different alkyl groups or polymerizable compositions with different blending ratios, but in the same manner as above.

[0054] The constituent materials of the first alignment layer 32, second alignment layer 33, first transparent electrode layer 34, second transparent electrode layer 35, first transparent support layer 36, and second transparent support layer 37 are shown below. Alignment layers 32, 33: 100 nm thick polyimide layer Transparent electrode layers 34, 35: 30 nm thick indium tin oxide Transparent support layers 36, 37: 125 μm thick polyethylene terephthalate film [Light Control Layer 31] The constituent materials and blending ratios of the light control layer 31 are shown below. The constituent materials of the acrylates in Test Examples 1 to 10 are shown in Figure 3. The evaluation method and evaluation results of the light control sheet 11 are shown in Figures 4 and 5.

[0055] First, a light-controlling coating solution was produced using the following liquid crystal compound LCM, spacer SP, polymerization initiator, and polymerizable composition. The polymerizable composition was a mixture of the following compounds 1 to 8. Next, the light-controlling coating solution was applied to the first alignment layer 32 using a bar coater, and a second alignment layer 33 was placed on the light-controlling coating layer to form a light-controlling coating layer sandwiched between the first alignment layer 32 and the second alignment layer 33. Then, ultraviolet light was irradiated from the first transparent support layer 36 toward the light-controlling coating layer, and ultraviolet light was irradiated from the second transparent support layer 37 toward the light-controlling coating layer. This resulted in a light-controlling layer 31 with a thickness of 10 μm.

[0056] [Light-modulating coating liquid raw materials] Liquid crystal compound LCM: fluorine-based nematic mixed liquid crystal (product name: MLC-6608, refractive index anisotropy Δn=0.20 (manufactured by Merck Ltd.)) Spacer SP: PMMA spherical with a diameter of 10 μm (manufactured by Sekisui Plastics Co., Ltd.) Polymerization initiator: 1-hydroxycyclohexyl phenyl ketone (manufactured by IGM Resins B.V.) [Polymerizable composition] As monofunctional compound 1, 2-ethylhexyl acrylate having a homopolymer glass transition temperature of −70° C. was used. As monofunctional compound 2, butyl acrylate having a homopolymer glass transition temperature of −55° C. was used. As monofunctional compound 3, ethyl acrylate having a homopolymer glass transition temperature of −24° C. was used. As monofunctional compound 4, methyl acrylate having a homopolymer glass transition temperature of 8° C. was used. Furthermore, as monofunctional compound 5, methyl methacrylate having a homopolymer glass transition temperature of 105° C. was used. The alkyl acrylates of the monofunctional compounds 1 to 4 all have a glass transition temperature of 8° C. or less in the form of homopolymers.

[0057] As the polyfunctional compound 6, pentaerythritol triacrylate (product name: A-TMM-3L (manufactured by Shin-Nakamura Chemical Co., Ltd.)) having a glass transition temperature of 103°C as a homopolymer was used. As the polyfunctional compound 7, 3-methyl-1,5-pentadiol diacrylate (product name: Light Acrylate MPD-A (manufactured by Kyoeisha Chemical Co., Ltd.)) having a glass transition temperature of 105°C as a homopolymer was used. As the polyfunctional compound 8, urethane acrylate (product name: CN929 (manufactured by Sartomer Corporation)) having a glass transition temperature of 43°C as a homopolymer was used. All of the polyfunctional acrylates of polyfunctional compounds 6 to 8 have higher glass transition temperatures than the monofunctional alkyl acrylates.

[0058] In Test Examples 1 to 6, the mass of the monofunctional alkyl acrylate relative to the mass of the liquid crystal compound LCM is 10% by mass or more and 30% by mass or less. In Test Examples 1 to 6, the mass of the monofunctional alkyl acrylate relative to the mass of the polyfunctional acrylate is 11% by mass or more and 35% by mass or less.

[0059] In Test Example 7, the mass of the monofunctional alkyl acrylate relative to the mass of the liquid crystal compound LCM is 36.1 mass %. In Test Example 7, the mass of the monofunctional alkyl acrylate relative to the mass of the polyfunctional acrylate is 40.1 mass % or less.

[0060] In Test Example 8, the mass of the monofunctional alkyl acrylate relative to the mass of the liquid crystal compound LCM was 0.2 mass %. In Test Example 8, the mass of the monofunctional alkyl acrylate relative to the mass of the polyfunctional acrylate was 0.2 mass %.

[0061] In Test Example 9, the mass of the monofunctional alkyl acrylate relative to the mass of the liquid crystal compound LCM was 0.0 mass %. In Test Example 8, the mass of the monofunctional alkyl acrylate relative to the mass of the polyfunctional acrylate was 0.0 mass %.

[0062] In Test Example 10, the mass of the monofunctional alkyl methacrylate relative to the mass of the liquid crystal compound LCM was 29.9 mass %. In Test Example 8, the mass of the monofunctional alkyl methacrylate relative to the mass of the polyfunctional acrylate was 33.2 mass %.

[0063] [Evaluation Method] Using the light-controlling sheets 11 of Test Examples 1 to 10, the parallel ray transmittance of the light-controlling sheets 11 in an environment at 23°C was measured. At this time, an AC voltage of 30 V was used as the voltage signal, and the parallel ray transmittance when the voltage signal was supplied and when the voltage signal was not supplied were measured. Furthermore, low-temperature environments of 0°C, 5°C, and 10°C were prepared, and the light-controlling sheets 11 of Test Examples 1 to 10 were used to measure the response time, which was the time from the cessation of the supply of the voltage signal until the parallel ray transmittance of the light-controlling sheets 11 in the low-temperature environment to saturation. A cell forming a low-temperature environment was used to measure the parallel ray transmittance. The parallel ray transmittance was measured using a method in accordance with ASTM D 1003-00, using a BYK haze-gard instrument (manufactured by BYK Gardner) as the measuring instrument.

[0064] As shown in Figure 4, the temperature control cell 80 that forms a low-temperature environment has two transparent side walls that face each other. The two side walls expand in the same direction as the light-controlling sheet 11. Each of the two side walls is configured to allow a refrigerant to flow inside the side wall. The two side walls are housed in a parallel-beam transmittance measuring device while facing each other, and are disposed between a light source 81 and a light-receiving unit 82. The temperature control cell 80 places the light-controlling sheet 11 in a low-temperature environment by sandwiching the light-controlling sheet 11 between the two side walls.

[0065] In measuring parallel ray transmittance, the light rays contained in the light beam incident on the light-adjusting sheet 11 are straight rays. The maximum angle between the light rays contained in the light beam incident on the light-adjusting sheet 11 and the optical axis of the light beam is less than 3°. The light-adjusting sheet 11 is fixed so that the surface of the light-adjusting sheet 11 and the light beam incident on the surface are approximately perpendicular, within ±2°. Of the transmitted light that passes through the light-adjusting sheet 11, light that deviates by ±2.5° or more from the light beam incident on the light-adjusting sheet 11 is wide-angle scattered light. Of the transmitted light that passes through the light-adjusting sheet 11, light that deviates by less than ±2.5° from the light beam incident on the light-adjusting sheet 11 is parallel transmitted light. Parallel transmittance is the percentage of parallel transmitted light due to forward scattering among the incident light incident on the light-adjusting sheet 11.

[0066] [Evaluation Results] As shown in Figure 5, the parallel ray transmittance of Test Examples 1 to 9 was 80% or more when no voltage was applied, and 20% or less when a voltage was applied. On the other hand, no difference was observed in the parallel ray transmittance of Test Example 10 between when a voltage was applied and when no voltage was applied. In other words, it was confirmed that the light-controlling sheet 11 could be driven as a reverse type because the monofunctional compound contained in the polymerizable composition was a monofunctional acrylate with a glass transition temperature of 8°C or less.

[0067] Furthermore, it was observed that the parallel ray transmittance when a voltage was applied was 5% or less in Test Examples 1 to 6 and 9, while the parallel ray transmittance when a voltage was applied was only 18% in Test Example 7. That is, it was observed that the parallel ray transmittance when a voltage was applied was significantly reduced by setting the mass of the monofunctional alkyl acrylate to 35% by mass or less relative to the mass of the polyfunctional acrylate. It was also observed that the parallel ray transmittance when a voltage was applied was significantly reduced by setting the mass of the monofunctional alkyl acrylate to 30% by mass or less relative to the mass of the liquid crystal compound LCM.

[0068] It was also found that while the parallel ray transmittance when a voltage was applied was 5% or less in Test Examples 1 to 6 and 9, the parallel ray transmittance when a voltage was applied was only 15% in Test Example 8. That is, it was also found that the parallel ray transmittance when a voltage was applied was significantly reduced when the mass of the monofunctional alkyl acrylate relative to the mass of the polyfunctional acrylate was 11% by mass or more. It was also found that the parallel ray transmittance when a voltage was applied was significantly reduced when the mass of the monofunctional alkyl acrylate relative to the mass of the liquid crystal compound LCM was 10% by mass or more.

[0069] Furthermore, it was observed that the response times at 10°C of Test Examples 1 to 8 were 8 seconds or less, while the response time at 10°C of Test Example 9 was as long as 54 seconds. It was also observed that the response times at 5°C of Test Examples 1 to 8 were 45 seconds or less, while the response time at 5°C of Test Example 9 was as long as 143 seconds. It was also observed that the response times at 0°C of Test Examples 1 to 8 were 85 seconds or less, while the response time at 0°C of Test Example 9 was as long as 134 seconds. In other words, it was observed that the response time was shortened by including a monofunctional alkyl acrylate in the polymerizable composition.

[0070] Furthermore, it was observed that the response times at 5°C of Test Examples 1, 2, and 4 to 6 were 39 seconds or less, while the response time at 5°C of Test Example 3 was 45 seconds. It was also observed that the response times at 0°C of Test Examples 1, 2, and 4 to 6 were 78 seconds or less, while the response time at 0°C of Test Example 3 was 85. In other words, it was observed that by lowering the glass transition temperature of the monofunctional alkyl acrylate contained in the polymerizable composition to -24°C or less, the response time was further shortened in a low-temperature environment of 5°C or less.

[0071] According to the above embodiment, the following effects can be obtained. (1) Even if a monofunctional alkyl acrylate having a glass transition temperature of 8° C. or less remains in the liquid crystal composition 31LC as a monomer or oligomer, it is unlikely to cause the liquid crystal composition 31LC to thicken in a low-temperature environment. Therefore, by including a monofunctional alkyl acrylate having a glass transition temperature of 8° C. or less in the polymerizable composition, the reverse-type light-controlling sheet 11 can easily switch from opaque to transparent in a low-temperature environment.

[0072] (2) When the mass of the monofunctional alkyl acrylate relative to the mass of the multifunctional acrylate is 35% by mass or less, a dense network derived from the multifunctional acrylate is likely to be formed in the acrylic resin layer 31P. Also, voids 31D for achieving high opacity are likely to be formed in the acrylic resin layer 31P. Therefore, when the mass of the monofunctional alkyl acrylate relative to the mass of the multifunctional acrylate is 35% by mass or less, the opacity of the light-controlling sheet 11 is enhanced when no voltage is applied.

[0073] (3) When the mass of the monofunctional alkyl acrylate relative to the mass of the multifunctional acrylate is 11% by mass or more, the formation of an overcrowded network due to the multifunctional acrylate is moderately suppressed. Furthermore, voids 31D of a size suitable for driving the liquid crystal compound LCM are easily formed in the acrylic resin layer 31P. Therefore, when the mass of the monofunctional alkyl acrylate relative to the mass of the multifunctional acrylate is 11% by mass or more, the opacity of the light-controlling sheet 11 is enhanced when no voltage is applied.

[0074] (4) When the monofunctional alkyl acrylate is at least one selected from the group consisting of ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate, the response time for switching from opaque to transparent in a low-temperature environment is further shortened.

[0075] (5) When the mass of the monofunctional alkyl acrylate is 10% by mass or more and 30% by mass or less relative to the mass of the liquid crystal compound LCM, the effectiveness of obtaining the effects equivalent to the above (1) to (4) is increased.

Claims

1. A light-controlling sheet comprising: a light-controlling layer sandwiched between a first transparent electrode layer and a second transparent electrode layer; a first alignment layer located between the first transparent electrode layer and the light-controlling layer; and a second alignment layer located between the second transparent electrode layer and the light-controlling layer, wherein the haze of the light-controlling layer is changed by changing the voltage applied between the first transparent electrode layer and the second transparent electrode layer, wherein the light-controlling layer comprises: an acrylic resin layer defining voids; and a liquid crystal composition containing a liquid crystal compound and filling the voids, wherein the acrylic resin layer is a polymer of a monofunctional alkyl acrylate containing a saturated alkyl group having from 2 to 8 carbon atoms and a polyfunctional acrylate, wherein the glass transition temperature of the monofunctional alkyl acrylate is lower than the glass transition temperature of the polyfunctional acrylate and is 8°C or lower, and wherein the mass of the monofunctional alkyl acrylate relative to the mass of the polyfunctional acrylate is 11% by mass or higher and 35% by mass or lower.

2. The light-controlling sheet according to claim 1, wherein the monofunctional alkyl acrylate is at least one selected from the group consisting of ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate.

3. The light-controlling sheet according to claim 2, wherein the polyfunctional acrylate is pentaerythritol triacrylate, 3-methyl-1,5-pentanediol diacrylate, and urethane acrylate.

4. A light-controlling sheet according to any one of claims 1 to 3, wherein the mass of the monofunctional alkyl acrylate relative to the mass of the liquid crystal compound is 10 mass % or more and 30 mass % or less.

5. A light control device comprising: a light control layer sandwiched between a first transparent electrode layer and a second transparent electrode layer; a first alignment layer located between the first transparent electrode layer and the light control layer; a second alignment layer located between the second transparent electrode layer and the light control layer; and a drive unit that changes the haze of the light control layer by changing the voltage applied between the first transparent electrode layer and the second transparent electrode layer, wherein the light control layer comprises: an acrylic resin layer that defines a gap; and a liquid crystal composition that contains a liquid crystal compound and is filled in the gap, the acrylic resin layer is a polymer of a monofunctional alkyl acrylate containing a saturated alkyl group having from 2 to 8 carbon atoms and a polyfunctional acrylate, the glass transition temperature of the monofunctional alkyl acrylate being lower than the glass transition temperature of the polyfunctional acrylate and being 8°C or lower, and the mass of the monofunctional alkyl acrylate relative to the mass of the polyfunctional acrylate is 11% by mass or higher and 35% by mass or lower.

6. A method for manufacturing a light-controlling sheet, which includes: forming a coating layer containing a polymerizable composition and a liquid crystal composition between a first alignment layer and a second alignment layer; and irradiating the coating layer with ultraviolet light to form a light-controlling layer between the first alignment layer and the second alignment layer, the light-controlling layer comprising an acrylic resin layer that defines voids and the liquid crystal composition that fills the voids; and which changes the haze of the light-controlling layer by changing the voltage applied between the first alignment layer and the second alignment layer, wherein the polymerizable composition includes a monofunctional alkyl acrylate containing a saturated alkyl group having 2 to 8 carbon atoms and a polyfunctional acrylate, the glass transition temperature of the monofunctional alkyl acrylate being lower than the glass transition temperature of the polyfunctional acrylate and being 8°C or lower, and the mass of the monofunctional alkyl acrylate relative to the mass of the polyfunctional acrylate being 11% by mass or higher and 35% by mass or lower.

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